High-Temperature Isothermal Capacitance Transient Spectroscopy Study on Inductively Coupled Plasma Etching Damage for p-GaN Surfaces

NASA Astrophysics Data System (ADS)

Aoki, Toshichika; Wakayama, Hisashi; Kaneda, Naoki; Mishima, Tomoyoshi; Nomoto, Kazuki; Shiojima, Kenji

2013-11-01

The effects of the inductively coupled plasma (ICP) etching damage on the electrical characteristics of low-Mg-doped p-GaN Schottky contacts were evaluated by high-temperature isothermal capacitance transient spectroscopy. A large single peak for an acceptor-type surface state was dominantly detected for as-grown samples. The energy level and state density were obtained to be 1.18 eV above the valence band, which is close to a Ga vacancy (VGa), and 1.5×1013 cm-2, respectively. It was speculated that a small portion of Ga atoms were missing from the surface, and a high VGa density was observed in a few surface layers. The peak intensity decreased by 60% upon annealing at 800 °C, and further decrease was found by ICP etching. This decrease is consistent with the suppression of the memory effect in current-voltage characteristics. Upon annealing and ICP etching, since the VGa structure might be disordered, the peak intensity decreased.

Characterization of the high density plasma etching process of CCTO thin films for the fabrication of very high density capacitors

NASA Astrophysics Data System (ADS)

Altamore, C.; Tringali, C.; Sparta', N.; Di Marco, S.; Grasso, A.; Ravesi, S.

2010-02-01

In this work the feasibility of CCTO (Calcium Copper Titanate) patterning by etching process is demonstrated and fully characterized in a hard to etch materials etcher. CCTO sintered in powder shows a giant relative dielectric constant (105) measured at 1 MHz at room temperature. This feature is furthermore coupled with stability from 101 Hz to 106 Hz in a wide temperature range (100K - 600K). In principle, this property can allow to fabricate very high capacitance density condenser. Due to its perovskite multi-component structure, CCTO can be considered a hard to etch material. For high density capacitor fabrication, CCTO anisotropic etching is requested by using high density plasma. The behavior of etched CCTO was studied in a HRe- (High Density Reflected electron) plasma etcher using Cl2/Ar chemistry. The relationship between the etch rate and the Cl2/Ar ratio was also studied. The effects of RF MHz, KHz Power and pressure variation, the impact of HBr addiction to the Cl2/Ar chemistry on the CCTO etch rate and on its selectivity to Pt and photo resist was investigated.

A junction-level optoelectronic characterization of etching-induced damage for third-generation HgCdTe infrared focal-plane array photodetectors

NASA Astrophysics Data System (ADS)

Wang, Peng; Wang, Yueming; Wu, Mingzai; Ye, Zhenhua

2018-06-01

Third-generation HgCdTe-based infrared focal plane arrays require high aspect ratio trenches with admissible etch induced damage at the surface and sidewalls for effectively isolating the pixels. In this paper, the high-density inductively coupled plasma enhanced reaction ion etching technique has been used for micro-mesa delineation of HgCdTe for third-generation infrared focal-plane array detectors. A nondestructive junction-level optoelectronic characterization method called laser beam induced current (LBIC) is used to evaluate the lateral junction extent of HgCdTe etch-induced damage scanning electron microscopy. It is found that the LBIC profiles exhibit evident double peaks and valleys phenomena. The lateral extent of etch induced mesa damage of ∼2.4 μm is obtained by comparing the LBIC profile and the scanning electron microscopy image of etched sample. This finding will guide us to nondestructively identify the distributions of the etching damages in large scale HgCdTe micro-mesa.

A method to accelerate creation of plasma etch recipes using physics and Bayesian statistics

NASA Astrophysics Data System (ADS)

Chopra, Meghali J.; Verma, Rahul; Lane, Austin; Willson, C. G.; Bonnecaze, Roger T.

2017-03-01

Next generation semiconductor technologies like high density memory storage require precise 2D and 3D nanopatterns. Plasma etching processes are essential to achieving the nanoscale precision required for these structures. Current plasma process development methods rely primarily on iterative trial and error or factorial design of experiment (DOE) to define the plasma process space. Here we evaluate the efficacy of the software tool Recipe Optimization for Deposition and Etching (RODEo) against standard industry methods at determining the process parameters of a high density O2 plasma system with three case studies. In the first case study, we demonstrate that RODEo is able to predict etch rates more accurately than a regression model based on a full factorial design while using 40% fewer experiments. In the second case study, we demonstrate that RODEo performs significantly better than a full factorial DOE at identifying optimal process conditions to maximize anisotropy. In the third case study we experimentally show how RODEo maximizes etch rates while using half the experiments of a full factorial DOE method. With enhanced process predictions and more accurate maps of the process space, RODEo reduces the number of experiments required to develop and optimize plasma processes.

Application of porous silicon in solar cell

NASA Astrophysics Data System (ADS)

Maniya, Nalin H.; Ashokan, Jibinlal; Srivastava, Divesh N.

2018-05-01

Silicon is widely used in solar cell applications with over 95% of all solar cells produced worldwide composed of silicon. Nanostructured thin porous silicon (PSi) layer acting as anti-reflecting coating is used in photovoltaic solar cells due to its advantages including simple and low cost fabrication, highly textured surfaces enabling lowering of reflectance, controllability of thickness and porosity of layer, and high surface area. PSi layers have previously been reported to reduce the reflection of light and replaced the conventional anti-reflective coating layers on solar cells. This can essentially improve the efficiency and decrease the cost of silicon solar cells. Here, we investigate the reflectance of different PSi layers formed by varying current density and etching time. PSi layers were formed by a combination of current density including 60 and 80 mA/cm2 and time for fabrication as 2, 4, 6, and 8 seconds. The fabricated PSi layers were characterized using reflectance spectroscopy and field emission scanning electron microscopy. Thickness and pore size of PSi layer were increased with increase in etching time and current density, respectively. The reflectance of PSi layers was decreased with increase in etching time until 6 seconds and increased again after 6 seconds, which was observed across both the current density. Reduction in reflectance indicates the increase of absorption of light by silicon due to the thin PSi layer. In comparison with the reflectance of silicon wafer, PSi layer fabricated at 80 mA/cm2 for 6 seconds gave the best result with reduction in reflectance up to 57%. Thus, the application of PSi layer as an effective anti-reflecting coating for the fabrication of solar cell has been demonstrated.

A review on plasma-etch-process induced damage of HgCdTe

NASA Astrophysics Data System (ADS)

Liu, Lingfeng; Chen, Yiyu; Ye, Zhenhua; Ding, Ruijun

2018-05-01

Dry etching techniques with minimal etch induced damage are required to develop highly anisotropic etch for pixel delineation of HgCdTe infrared focal plane arrays (IRFPAs). High density plasma process has become the main etching technique for HgCdTe in the past twenty years, In this paper, high density plasma electron cyclotron resonance (ECR) and inductively coupled plasma (ICP) etching of HgCdTe are summarized. Common plasma-etch-process induced type conversion and related mechanisms are reviewed particularly.

Investigation on the structural characterization of pulsed p-type porous silicon

NASA Astrophysics Data System (ADS)

Wahab, N. H. Abd; Rahim, A. F. Abd; Mahmood, A.; Yusof, Y.

2017-08-01

P-type Porous silicon (PS) was sucessfully formed by using an electrochemical pulse etching (PC) and conventional direct current (DC) etching techniques. The PS was etched in the Hydrofluoric (HF) based solution at a current density of J = 10 mA/cm2 for 30 minutes from a crystalline silicon wafer with (100) orientation. For the PC process, the current was supplied through a pulse generator with 14 ms cycle time (T) with 10 ms on time (Ton) and pause time (Toff) of 4 ms respectively. FESEM, EDX, AFM, and XRD have been used to characterize the morphological properties of the PS. FESEM images showed that pulse PS (PPC) sample produces more uniform circular structures with estimated average pore sizes of 42.14 nm compared to DC porous (PDC) sample with estimated average size of 16.37nm respectively. The EDX spectrum for both samples showed higher Si content with minimal presence of oxide.

III-Nitride Blue Laser Diode with Photoelectrochemically Etched Current Aperture

NASA Astrophysics Data System (ADS)

Megalini, Ludovico

Group III-nitride is a remarkable material system to make highly efficient and high-power optoelectronics and electronic devices because of the unique electrical, physical, chemical and structural properties it offers. In particular, InGaN-based blue Laser Diodes (LDs) have been successfully employed in a variety of applications ranging from biomedical and military devices to scientific instrumentation and consumer electronics. Recently their use in highly efficient Solid State Lighting (SSL) has been proposed because of their superior beam quality and higher efficiency at high input power density. Tremendous advances in research of GaN semi-polar and non-polar crystallographic planes have led both LEDs and LDs grown on these non-basal planes to rival with, and with the promise to outperform, their equivalent c-plane counterparts. However, still many issues need to be addressed, both related to material growth and device fabrication, including a lack of conventional wet etching techniques. GaN and its alloys with InN and AlN have proven resistant essentially to all known standard wet etching techniques, and the predominant etching methods rely on chlorine-based dry etching (RIE). These introduce sub-surface damage which can degrade the electrical properties of the epitaxial structure and reduce the reliability and lifetime of the final device. Such reasons and the limited effectiveness of passivation techniques have so far suggested to etch the LD ridges before the active region, although it is well-known that this can badly affect the device performance, especially in narrow stripe width LDs, because the gain guiding obtained in the planar configuration is weak and the low index step and high lateral current leakage result in devices with threshold current density higher than devices whose ridge is etched beyond the active region. Moreover, undercut etching of III-nitride layers has proven even more challenging, with limitations in control of the lateral etch distance. In this dissertation it is presented the first nitride blue edge emitting LD with a photoelectrochemical etched current aperture (CA-LD) into the device active region. Photoelectrochemical etching (PECE) has emerged as a powerful wet etching technique for III-nitride compounds. Beyond the advantages of wet etching technique, PECE offers bandgap selectivity, which is particularly desirable because it allows more freedom in designing new and advanced devices with higher performances. In the first part of this thesis a review of PECE is presented, and it is shown how it can be used to achieve a selective and controllable deep undercut of the active region of LEDs and LDs, in particular the selective PECE of MQW active region of (10-10) m-plane and (20-2-1) plane structures is reported. In the second part of this thesis, the fabrication flow process of the CA-LD is described. The performance of these devices is compared with that of shallow etched ridge LDs with a nominally identical epitaxial structure and active region width and it is experimentally shown that the CA-LD design has superior performance. CW operation of a (20-2-1) CA-LD with a 1.5 microm wide active region is demonstrated. Finally, in the third and last part of this thesis, the CA-LD performance is discussed in more details, in particular, an analysis of optical scattering losses caused by the rough edges of the remnant PEC etched active region is presented.

Fabrication of through-silicon via arrays by photo-assisted electrochemical etching and supercritical electroplating

NASA Astrophysics Data System (ADS)

Chuang, Ho-Chiao; Yang, Hsi-Min; Wu, Cheng-Xiang; Sanchez, Jorge; Shyu, Jenq-Huey

2017-01-01

This paper aims to fabricate high aspect ratio through silicon via (TSV) by photo-assisted electrochemical etching (PAECE) and supercritical CO2 copper electroplating. A blind-holed silicon array was first fabricated by PAECE. By studying the etching parameters, including hydrofluoric acid concentration, etchant temperature, stirring speed, tetrabutylammonium perchlorate (TBAP) content, and Ohmic contact thickness, an array of pores with a 1∶45 aspect ratio (height=250 μm and diameter=5.5 μm) was obtained successfully. Moreover, TBAP and Kodak Photo-Flo (PF) solution were added into the etchant to acquire smooth sidewalls for the first time. TBAP was added for the first time to serve as an antistatic agent in deionized water-based etchant to prevent side-branch etching, and PF was used to degasify hydrogen bubbles in the etchant. The effect of gold thickness over Ohmic contact was investigated. Randomized etching was observed with an Au thickness of 200 Å, but it can be improved by increasing the etching voltage. The silicon mold of through-holes was filled with metal using supercritical CO2 copper electroplating, which features high diffusivity, permeability, and density. The TSV structure (aspect ratio=1∶35) was obtained at a supercritical pressure of 2000 psi, temperature of 50°C, and current density of 30 mA/cm2 in 2.5 h.

Crystal defects observed by the etch-pit method and their effects on Schottky-barrier-diode characteristics on (\\bar{2}01) β-Ga2O3

NASA Astrophysics Data System (ADS)

Kasu, Makoto; Oshima, Takayoshi; Hanada, Kenji; Moribayashi, Tomoya; Hashiguchi, Akihiro; Oishi, Toshiyuki; Koshi, Kimiyoshi; Sasaki, Kohei; Kuramata, Akito; Ueda, Osamu

2017-09-01

A pixel array of vertical Schottky-barrier diodes (SBDs) was fabricated and measured on the surface of a (\\bar{2}01) β-Ga2O3 single crystal. Subsequently, etch pits and patterns were observed on the same surface. Three types of etch pits were discovered: (1) a line-shaped etch pattern originating from a void and extending toward the [010] direction, (2) an arrow-shaped etch pit whose arrow’s head faces toward the [102] direction and, (3) a gourd-shaped etch pit whose point head faces toward the [102] direction. Their average densities were estimated to be 5 × 102, 7 × 104, and 9 × 104 cm-2, respectively. We confirmed no clear relationship between the leakage current in SBDs and these crystalline defects. Such results are obtained because threading dislocations run mainly in the [010] growth direction and do not go through the (\\bar{2}01) sample plate.

Burnout current density of bismuth nanowires

NASA Astrophysics Data System (ADS)

Cornelius, T. W.; Picht, O.; Müller, S.; Neumann, R.; Völklein, F.; Karim, S.; Duan, J. L.

2008-05-01

Single bismuth nanowires with diameters ranging from 100nmto1μm were electrochemically deposited in ion track-etched single-pore polycarbonate membranes. The maximum current density the wires are able to carry was investigated by ramping up the current until failure occurred. It increases by three to four orders of magnitude for nanowires embedded in the template compared to bulk bismuth and rises with diminishing diameter. Simulations show that the wires are heated up electrically to the melting temperature. Since the surface-to-volume ratio rises with diminishing diameter, thinner wires dissipate the heat more efficiently to the surrounding polymer matrix and, thus, can tolerate larger current densities.

Preparation of etched tantalum semimicro capacitor stimulation electrodes.

PubMed

Robblee, L S; Kelliher, E M; Langmuir, M E; Vartanian, H; McHardy, J

1983-03-01

The ideal electrode for stimulation of the nervous system is one that will inject charge by purely capacitive processes. One approach is to exploit the type of metal-oxide combination used in electrolytic capacitors, e.g., Ta/Ta2O5. For this purpose, fine tantalum wire (0.25 mm diam) was etched electrolytically at constant current in a methanol solution of NH4Br containing 1.5 wt % H2O. Electrolytic etching produced a conical tip with a length of ca. 0.5 mm and shaft diameters ranging from 0.10 to 0.16 mm. The etched electrodes were anodized to 10 V (vs. SCE) in 0.1 vol % H3PO4. The capacitance values normalized to geometric area of etched electrodes ranged from 0.13 to 0.33 micro F mm-2. Comparison of these values to the capacitance of "smooth" tantalum anodized to 10 V (0.011 micro F mm-2) indicated that the degree of surface enhancement, or etch ratio, was 12-30. The surface roughness was confirmed by scanning electron microscopy studies which revealed an intricate array of irregularly shaped surface projections about 1-2 micrometers wide. The etched electrodes were capable of delivering 0.06-0.1 micro C of charge with 0.1 ms pulses at a pulse repetition rate of 400 Hz when operated at 50% of the anodization voltage. This quantity of charge corresponded to volumetric charge densities of 20-30 micro C mm-3 and area charge densities of 0.55-0.88 micro C mm-2. Charge storage was proportionately higher at higher fractional values of the formation voltage. Leakage currents at 5 V were ca. 2 nA. Neither long-term passive storage (1500 h) nor extended pulsing time (18 h) had a deleterious effect on electrode performance. The trend in electrical stimulation work is toward smaller electrodes. The procedures developed in this study should be particularly well-suited to the fabrication of even smaller electrodes because of the favorable electrical and geometric characteristics of the etched surface.

Improving the Fabrication of Semiconductor Bragg Lasers

NASA Astrophysics Data System (ADS)

Chen, Eric Ping Chun

Fabrication process developments for Bragg reflection lasers have been optimized in this thesis using resources available to the group. New e-beam lithography and oxide etch recipes have been developed to minimize sidewall roughness and residues. E-beam evaporated metal contacts for semiconductor diode laser utilizing oblique angle deposition have also been developed in-house for the first time. Furthermore, improvement in micro-loading effect of DFB laser etching has been demonstrated where the ratio of tapered portion of the sidewall to total etch depth is reduced by half, from 33% to 15%. Electrical, optical and thermal performance of the fabricated lasers are characterized. Comparing the results to previous generation lasers, average dynamic resistance is decreased drastically from 14 Ohms to 7 Ohms and threshold current density also reduced from 1705A/cm2 to 1383A/ cm2. Improvement in laser performance is result of reduced loss from optimized fabrication processes. BRL bow-tie tapered lasers is then fabricated for the first time and output power of 18mW at 200mA input is measured. Benefiting from the increased effective area and better carrier utilization, reduction in threshold current density from 1383A/cm 2 to 712A/cm2 is observed.

Electrical Current Leakage and Open-Core Threading Dislocations in AlGaN-Based Deep Ultraviolet Light-Emitting Diodes.

DOE PAGES

Moseley, Michael William; Allerman, Andrew A.; Crawford, Mary H.; ...

2014-08-04

Electrical current transport through leakage paths in AlGaN-based deep ultraviolet (DUV) lightemitting diodes (LEDs) and their effect on LED performance are investigated. Open-core threading dislocations, or nanopipes, are found to conduct current through nominally insulating Al0.7Ga0.3N layers and limit the performance of DUV-LEDs. A defect-sensitive phosphoric acid etch reveals these opencore threading dislocations in the form of large, micron-scale hexagonal etch pits visible with optical microscopy, while closed-core screw-, edge-, and mixed-type threading dislocations are represented by smaller and more numerous nanometer-scale pits visible by atomic-force microscopy. The electrical and optical performances of DUV-LEDs fabricated on similar Si-doped Al0.7Ga0.3N templatesmore » are found to have a strong correlation to the density of these nanopipes, despite their small fraction (<0.1% in this study) of the total density of threading dislocations.« less

Influence of etching current density on microstructural, optical and electrical properties of porous silicon (PS):n-Si heterostructure

NASA Astrophysics Data System (ADS)

Das, M.; Nath, P.; Sarkar, D.

2016-02-01

In this article effect of etching current density (J) on the microstructural, optical and electrical properties of photoelectrochemically prepared heterostructure is reported. Prepared samples are characterized by FESEM, XRD, UV-Visible, Raman and photoluminescence (PL) spectra and current-voltage (I-V) characteristics. FESEM shows presence of mixture of randomly distributed meso- and micro-pores. Porous layer thickness determined by cross section view of SEM is proportional to J. XRD shows crystalline nature but gradually extent of crystallinity decreases with increasing J. Raman spectra show large red-shift and asymmetric broadening with respect to crystalline silicon (c-Si). UV-visible reflectance and PL show blue shift in peaks with increasing J. The I-V characteristics are analyzed by the conventional thermionic emission (TE) model and Cheung's model to estimate the barrier height (φb), ideality factor (n) and series resistance (Rs) for comparison between the two models. The latter model is found to fit better.

Effect of fabrication parameters on morphological and optical properties of highly doped p-porous silicon

NASA Astrophysics Data System (ADS)

Zare, Maryam; Shokrollahi, Abbas; Seraji, Faramarz E.

2011-09-01

Porous silicon (PS) layers were fabricated by anodization of low resistive (highly doped) p-type silicon in HF/ethanol solution, by varying current density, etching time and HF concentration. Atomic force microscopy (AFM) and field emission scanning electron microscope (FESEM) analyses were used to investigate the physical properties and reflection spectrum was used to investigate the optical behavior of PS layers in different fabrication conditions. Vertically aligned mesoporous morphology is observed in fabricated films and with HF concentration higher than 20%. The dependence of porosity, layer thickness and rms roughness of the PS layer on current density, etching time and composition of electrolyte is also observed in obtained results. Correlation between reflectivity and fabrication parameters was also explored. Thermal oxidation was performed on some mesoporous layers that resulted in changes of surface roughness, mean height and reflectivity of the layers.

Computer controlled performance mapping of thermionic converters: effect of collector, guard-ring potential imbalances on the observed collector current-density, voltage characteristics and limited range performance map of an etched-rhenium, niobium planar converter

NASA Technical Reports Server (NTRS)

Manista, E. J.

1972-01-01

The effect of collector, guard-ring potential imbalance on the observed collector-current-density J, collector-to-emitter voltage V characteristic was evaluated in a planar, fixed-space, guard-ringed thermionic converter. The J,V characteristic was swept in a period of 15 msec by a variable load. A computerized data acquisition system recorded test parameters. The results indicate minimal distortion of the J,V curve in the power output quadrant for the nominal guard-ring circuit configuration. Considerable distortion, along with a lowering of the ignited-mode striking voltage, was observed for the configuration with the emitter shorted to the guard ring. A limited-range performance map of an etched-rhenium, niobium, planar converter was obtained by using an improved computer program for the data acquisition system.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Banerjee, D.; Sankaranarayanan, S.; Khachariya, D.

We demonstrate a method for nanowire formation by natural selection during wet anisotropic chemical etching in boiling phosphoric acid. Nanowires of sub-10 nm lateral dimensions and lengths of 700 nm or more are naturally formed during the wet etching due to the convergence of the nearby crystallographic hexagonal etch pits. These nanowires are site controlled when formed in augmentation with dry etching. Temperature and power dependent photoluminescence characterizations confirm excitonic transitions up to room temperature. The exciton confinement is enhanced by using two-dimensional confinement whereby enforcing greater overlap of the electron-hole wave-functions. The surviving nanowires have less defects and a small temperaturemore » variation of the output electroluminescent light. We have observed superluminescent behaviour of the light emitting diodes formed on these nanowires. There is no observable efficiency roll off for current densities up to 400 A/cm{sup 2}.« less

Electrical properties of Schottky barrier diodes fabricated on (001) β-Ga2O3 substrates with crystal defects

NASA Astrophysics Data System (ADS)

Oshima, Takayoshi; Hashiguchi, Akihiro; Moribayashi, Tomoya; Koshi, Kimiyoshi; Sasaki, Kohei; Kuramata, Akito; Ueda, Osamu; Oishi, Toshiyuki; Kasu, Makoto

2017-08-01

The electrical properties of Schottky barrier diodes (SBDs) on a (001) β-Ga2O3 substrate were characterized and correlated with wet etching-revealed crystal defects below the corresponding Schottky contacts. The etching process revealed etched grooves and etched pits, indicating the presence of line-shaped voids and small defects near the surface, respectively. The electrical properties (i.e., leakage currents, ideality factor, and barrier height) exhibited almost no correlation with the density of the line-shaped voids. This very weak correlation was reasonable considering the parallel positional relation between the line-shaped voids extending along the [010] direction and the (001) basal plane in which the voids are rarely exposed on the initial surface in contact with the Schottky metals. The distribution of small defects and SBDs with unusually large leakage currents showed similar patterns on the substrate, suggesting that these defects were responsible for the onset of fatal leak paths. These results will encourage studies on crystal defect management of (001) β-Ga2O3 substrates for the fabrication of devices with enhanced performance using these substrates.

ICP etching for InAs-based InAs/GaAsSb superlattice long wavelength infrared detectors

NASA Astrophysics Data System (ADS)

Huang, Min; Chen, Jianxin; Xu, Jiajia; Wang, Fangfang; Xu, Zhicheng; He, Li

2018-05-01

In this work, we study and report the dry etching processes for InAs-based InAs/GaAsSb strain-free superlattice long wavelength infrared (LWIR) detectors. The proper etching parameters were first obtained through the parametric studies of Inductively Coupled Plasma (ICP) etching of both InAs and GaSb bulk materials in Cl2/N2 plasmas. Then an InAs-based InAs/GaAsSb superlattice LWIR detector with PπN structure was fabricated by using the optimized etching parameters. At 80 K, the detector exhibits a 100% cut-off wavelength of 12 μm and a responsivity of 1.5 A/W. Moreover, the dark current density of the device under a bias of -200 mV reaches 5.5 × 10-4 A/cm2, and the R0A is 15 Ω cm2. Our results pave the way towards InAs-based superlattice LWIR detectors with better performances.

Barium-strontium-titanate etching characteristics in chlorinated discharges

NASA Astrophysics Data System (ADS)

Stafford, Luc; Margot, Joëlle; Langlois, Olivier; Chaker, Mohamed

2003-07-01

The etching characteristics of barium-strontium-titanate (BST) were investigated using a high-density plasma sustained by surface waves at 190 MHz in Ar/Cl2 gas mixtures. The etch rate was examined as a function of both the total gas pressure and the Cl2 fraction in Ar/Cl2 using a wafer temperature of 10 °C. The results were correlated to positive ion density and plasma composition obtained from Langmuir probes and mass spectrometry. The BST etch rate was found to increase linearly with the positive ion density and to decrease with increasing chlorine atom concentration. This result indicates that for the temperature conditions used, the interaction between chlorine and BST yields compounds having a volatility that is lower than the original material. As a consequence, the contribution of neutral atomic Cl atoms to the etch mechanism is detrimental, thereby reducing the etch rate. As the wafer temperature increases, the role of chemistry in the etching process is enhanced.

A comparative study of capacitively coupled HBr/He, HBr/Ar plasmas for etching applications: Numerical investigation by fluid model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gul, Banat, E-mail: banatgul@gmail.com; Research Group PLASMANT, Department of Chemistry, University of Antwerp, Universiteitsplein 1, B-2610 Antwerp; Aman-ur-Rehman, E-mail: amansadiq@gmail.com

Fluid model has been applied to perform a comparative study of hydrogen bromide (HBr)/He and HBr/Ar capacitively coupled plasma discharges that are being used for anisotropic etching process. This model has been used to identify the most dominant species in HBr based plasmas. Our simulation results show that the neutral species like H and Br, which are the key player in chemical etching, have bell shape distribution, while ions like HBr{sup +}, Br{sup +}, which play a dominant rule in the physical etching, have double humped distribution and show peaks near electrodes. It was found that the dilution of HBrmore » by Ar and/or He results in an increase in electron density and electron temperature, which results in more ionization and dissociation and hence higher densities of neutral and charged species can be achieved. The ratio of positive ion flux to the neutral flux increases with an increase in additive gas fraction. Compare to HBr/He plasma, the HBr/Ar plasma shows a maximum change in the ion density and flux and hence the etching rate can be considered in the ion-assisted and in the ion-flux etch regime in HBr/Ar discharge. The densities of electron and other dominant species in HBr/Ar plasma are higher than those of HBr/He plasma. The densities and fluxes of the active neutrals and positive ions for etching and subsequently chemical etching versus physical sputtering in HBr/Ar and HBr/He plasmas discharge can be controlled by tuning gas mixture ratio and the desire etching can be achieved.« less

Low-damage direct patterning of silicon oxide mask by mechanical processing

PubMed Central

2014-01-01

To realize the nanofabrication of silicon surfaces using atomic force microscopy (AFM), we investigated the etching of mechanically processed oxide masks using potassium hydroxide (KOH) solution. The dependence of the KOH solution etching rate on the load and scanning density of the mechanical pre-processing was evaluated. Particular load ranges were found to increase the etching rate, and the silicon etching rate also increased with removal of the natural oxide layer by diamond tip sliding. In contrast, the local oxide pattern formed (due to mechanochemical reaction of the silicon) by tip sliding at higher load was found to have higher etching resistance than that of unprocessed areas. The profile changes caused by the etching of the mechanically pre-processed areas with the KOH solution were also investigated. First, protuberances were processed by diamond tip sliding at lower and higher stresses than that of the shearing strength. Mechanical processing at low load and scanning density to remove the natural oxide layer was then performed. The KOH solution selectively etched the low load and scanning density processed area first and then etched the unprocessed silicon area. In contrast, the protuberances pre-processed at higher load were hardly etched. The etching resistance of plastic deformed layers was decreased, and their etching rate was increased because of surface damage induced by the pre-processing. These results show that etching depth can be controlled by controlling the etching time through natural oxide layer removal and mechanochemical oxide layer formation. These oxide layer removal and formation processes can be exploited to realize low-damage mask patterns. PMID:24948891

Recovery of GaN surface after reactive ion etching

NASA Astrophysics Data System (ADS)

Fan, Qian; Chevtchenko, S.; Ni, Xianfeng; Cho, Sang-Jun; Morko, Hadis

2006-02-01

Surface properties of GaN subjected to reactive ion etching and the impact on device performance have been investigated by surface potential, optical and electrical measurements. Different etching conditions were studied and essentially high power levels and low chamber pressures resulted in higher etch rates accompanying with the roughening of the surface morphology. Surface potential for the as-grown c-plane GaN was found to be in the range of 0.5~0.7 V using Scanning Kevin Probe Microscopy. However, after reactive ion etching at a power level of 300 W, it decreased to 0.1~0.2 V. A nearly linear reduction was observed on c-plane GaN with increasing power. The nonpolar a-plane GaN samples also showed large surface band bending before and after etching. Additionally, the intensity of the near band-edge photoluminescence decreased and the free carrier density increased after etching. These results suggest that the changes in the surface potential may originate from the formation of possible nitrogen vacancies and other surface oriented defects and adsorbates. To recover the etched surface, N II plasma, rapid thermal annealing, and etching in wet KOH were performed. For each of these methods, the surface potential was found to increase by 0.1~0.3 V, also the reverse leakage current in Schottky diodes fabricated on treated samples was reduced considerably compared with as-etched samples, which implies a partial-to-complete recovery from the plasma-induced damage.

Measurement of the Electron Density and the Attachment Rate Coefficient in Silane/Helium Discharges.

DTIC Science & Technology

1986-09-01

materials -- in this case hydrogenated amorphous silicon . One of the biggest problems in such a task is the fact that the discharge creates complex radicals...electron density is enhanced -- even on a time-averaged basis, and the silicon deposition rate is also increased. The physical process for the density...etching and deposition of semiconductor materials. Plasma etching (also known as dry etching) Of silicon using flourine bearing gases has made it possible

Two-Dimensional Si-Nanodisk Array Fabricated Using Bio-Nano-Process and Neutral Beam Etching for Realistic Quantum Effect Devices

NASA Astrophysics Data System (ADS)

Huang, Chi-Hsien; Igarashi, Makoto; Woné, Michel; Uraoka, Yukiharu; Fuyuki, Takashi; Takeguchi, Masaki; Yamashita, Ichiro; Samukawa, Seiji

2009-04-01

A high-density, large-area, and uniform two-dimensional (2D) Si-nanodisk array was successfully fabricated using the bio-nano-process, advanced etching techniques, including a treatment using nitrogen trifluoride and hydrogen radical (NF3 treatment) and a damage-free chlorine neutral beam (NB). By using the surface oxide formed by neutral beam oxidation (NBO) for the preparation of a 2D nanometer-sized iron core array as an etching mask, a well-ordered 2D Si-nanodisk array was obtained owing to the dangling bonds of the surface oxide. By changing the NF3 treatment time without changing the quantum effect of each nanodisk, we could control the gap between adjacent nanodisks. A device with two electrodes was fabricated to investigate the electron transport in a 2D Si-nanodisk array. Current fluctuation and time-dependent currents were clearly observed owing to the charging-discharging of the nanodisks adjacent to the current percolation path. The new structure may have great potential for future novel quantum effect devices.

Phase Analysis of Laser Direct Etching and Water Assisted Laser Combined Etching of SiC Ceramics

NASA Astrophysics Data System (ADS)

Yuan, Genfu; Cong, Qidong; Zhang, Chen; Xie, Bingbing

2017-12-01

In this study, to discover the etching mechanism of SiC ceramics under laser direct etching and water-jet assisted laser combined etching, the phenomena of substance change on the etched surface were investigated. Also, the rules of substance transfer in etching are discussed. The elemental content change and the phase change of the etching products on the etched surface were analyzed by energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD), respectively. These studies showed a high amount of carbon black on the etched surface, because of the decomposition of SiC ceramics under the high-power-density laser irradiation. SiC decomposed to Si under the laser irradiation, and the subsequent chemical reaction of Si and O2 easily produced SiO2. The SiO2 on the etched surface melted and vaporized, whereas most of SiO2 was removed through splashing, changing the chemical composition of the etched surface. Following the water jet introduction, an increased amount of O existed on the combined etching surface, because the chemical reaction of SiC and H2O easily produced SiO2 under the high-power-density laser irradiation.

Stability of amorphous silicon thin film transistors and circuits

NASA Astrophysics Data System (ADS)

Liu, Ting

Hydrogenated amorphous silicon thin-film transistors (a-Si:H TFTs) have been widely used for the active-matrix addressing of flat panel displays, optical scanners and sensors. Extending the application of the a-Si TFTs from switches to current sources, which requires continuous operation such as for active-matrix organic light-emitting-diode (AMOLED) pixels, makes stability a critical issue. This thesis first presents a two-stage model for the stability characterization and reliable lifetime prediction for highly stable a-Si TFTs under low gate-field stress. Two stages of the threshold voltage shift are identified from the decrease of the drain saturation current under low-gate field. The first initial stage dominates up to hours or days near room temperature. It can be characterized with a stretched-exponential model, with the underlying physical mechanism of charge trapping in the gate dielectric. The second stage dominates in the long term and then saturates. It corresponds to the breaking of weak bonds in the amorphous silicon. It can be modeled with a "unified stretched exponential fit," in which a thermalization energy is used to unify experimental measurements of drain current decay at different temperatures into a single curve. Two groups of experiments were conducted to reduce the drain current instability of a-Si TFTs under prolonged gate bias. Deposition conditions for the silicon nitride (SiNx) gate insulator and the a-Si channel layer were varied, and TFTs were fabricated with all reactive ion etching steps, or with all wet etching steps, the latter in a new process. The two-stage model that unites charge trapping in the SiNx gate dielectric and defect generation in the a-Si channel was used to interpret the experimental results. We identified the optimal substrate temperature, gas flow ratios, and RF deposition power densities. The stability of the a-Si channel depends also on the deposition conditions for the underlying SiNx gate insulator. TFTs made with wet etching are more stable than TFTs made with reactive ion etching. Combining the various improvements raised the extrapolated 50% decay time of the drain current of back channel passivated dry-etched TFTs under continuous operation at 20°C from 3.3 x 104 sec (9.2 hours) to 4.4 x 107 sec (1.4 years). The 50% lifetime can be further improved by ˜2 times through wet etching process. Two assumptions in the two-stage model were revisited. First, the distribution of the gap state density in a-Si was obtained with the field-effect technique. The redistribution of the gap state density after low-gate field stress supports the idea that defect creation in a-Si dominates in the long term. Second, the drain-bias dependence of drain current degradation was measured and modeled. The unified stretched exponential was validated for a-Si TFTs operating in saturation. Finally, a new 3-TFT voltage-programmed pixel circuit with an in-pixel current source is presented. This circuit is largely insensitive to the TFT threshold voltage shift. The fabricated pixel circuit provides organic light-emitting diode (OLED) currents ranging from 25 nA to 2.9 microA, an on/off ratio of 116 at typical quarter graphics display resolution (QVGA) display timing. The overall conclusion of this thesis research is that the operating life of a-Si TFTs can be quite long, and that these transistors can expect to find yet more applications in large area electronics.

3D-fabrication of tunable and high-density arrays of crystalline silicon nanostructures

NASA Astrophysics Data System (ADS)

Wilbers, J. G. E.; Berenschot, J. W.; Tiggelaar, R. M.; Dogan, T.; Sugimura, K.; van der Wiel, W. G.; Gardeniers, J. G. E.; Tas, N. R.

2018-04-01

In this report, a procedure for the 3D-nanofabrication of ordered, high-density arrays of crystalline silicon nanostructures is described. Two nanolithography methods were utilized for the fabrication of the nanostructure array, viz. displacement Talbot lithography (DTL) and edge lithography (EL). DTL is employed to perform two (orthogonal) resist-patterning steps to pattern a thin Si3N4 layer. The resulting patterned double layer serves as an etch mask for all further etching steps for the fabrication of ordered arrays of silicon nanostructures. The arrays are made by means of anisotropic wet etching of silicon in combination with an isotropic retraction etch step of the etch mask, i.e. EL. The procedure enables fabrication of nanostructures with dimensions below 15 nm and a potential density of 1010 crystals cm-2.

Simulations of Control Schemes for Inductively Coupled Plasma Sources

NASA Astrophysics Data System (ADS)

Ventzek, P. L. G.; Oda, A.; Shon, J. W.; Vitello, P.

1997-10-01

Process control issues are becoming increasingly important in plasma etching. Numerical experiments are an excellent test-bench for evaluating a proposed control system. Models are generally reliable enough to provide information about controller robustness, fitness of diagnostics. We will present results from a two dimensional plasma transport code with a multi-species plasma chemstry obtained from a global model. [1-2] We will show a correlation of external etch parameters (e.g. input power) with internal plasma parameters (e.g. species fluxes) which in turn are correlated with etch results (etch rate, uniformity, and selectivity) either by comparison to experiment or by using a phenomenological etch model. After process characterization, a control scheme can be evaluated since the relationship between the variable to be controlled (e.g. uniformity) is related to the measurable variable (e.g. a density) and external parameter (e.g. coil current). We will present an evaluation using the HBr-Cl2 system as an example. [1] E. Meeks and J. W. Shon, IEEE Trans. on Plasma Sci., 23, 539, 1995. [2] P. Vitello, et al., IEEE Trans. on Plasma Sci., 24, 123, 1996.

Versatile control of metal-assisted chemical etching for vertical silicon microwire arrays and their photovoltaic applications

PubMed Central

Um, Han-Don; Kim, Namwoo; Lee, Kangmin; Hwang, Inchan; Hoon Seo, Ji; Yu, Young J.; Duane, Peter; Wober, Munib; Seo, Kwanyong

2015-01-01

A systematic study was conducted into the use of metal-assisted chemical etching (MacEtch) to fabricate vertical Si microwire arrays, with several models being studied for the efficient redox reaction of reactants with silicon through a metal catalyst by varying such parameters as the thickness and morphology of the metal film. By optimizing the MacEtch conditions, high-quality vertical Si microwires were successfully fabricated with lengths of up to 23.2 μm, which, when applied in a solar cell, achieved a conversion efficiency of up to 13.0%. These solar cells also exhibited an open-circuit voltage of 547.7 mV, a short-circuit current density of 33.2 mA/cm2, and a fill factor of 71.3% by virtue of the enhanced light absorption and effective carrier collection provided by the Si microwires. The use of MacEtch to fabricate high-quality Si microwires therefore presents a unique opportunity to develop cost-effective and highly efficient solar cells. PMID:26060095

Dry etching, surface passivation and capping processes for antimonide based photodetectors

NASA Astrophysics Data System (ADS)

Dutta, Partha; Langer, Jeffery; Bhagwat, Vinay; Juneja, Jasbir

2005-05-01

III-V antimonide based devices suffer from leakage currents. Surface passivation and subsequent capping of the surfaces are absolutely essential for any practical applicability of antimonide based devices. The quest for a suitable surface passivation technology is still on. In this paper, we will present some of the promising recent developments in this area based on dry etching of GaSb based homojunction photodiodes structures followed by various passivation and capping schemes. We have developed a damage-free, universal dry etching recipe based on unique ratios of Cl2/BCl3/CH4/Ar/H2 in ECR plasma. This novel dry plasma process etches all III-V compounds at different rates with minimal damage to the side walls. In GaSb based photodiodes, an order of magnitude lower leakage current, improved ideality factor and higher responsivity has been demonstrated using this recipe compared to widely used Cl2/Ar and wet chemical etch recipes. The dynamic zero bias resistance-area product of the Cl2/BCl3/CH4/Ar/H2 etched diodes (830 Ω cm2) is higher than the Cl2/Ar (300 Ω cm2) and wet etched (330 Ω cm2) diodes. Ammonium sulfide has been known to passivate surfaces of III-V compounds. In GaSb photodiodes, the leakage current density reduces by a factor of 3 upon sulfur passivation using ammonium sulfide. However, device performance degrades over a period of time in the absence of any capping or protective layer. Silicon Nitride has been used as a cap layer by various researchers. We have found that by using silicon nitride caps, the devices exhibit higher leakage than unpassivated devices probably due to plasma damage during SiNx deposition. We have experimented with various polymers for capping material. It has been observed that ammonium sulfide passivation when combined with parylene capping layer (150 Å), devices retain their improved performance for over 4 months.

Formation of bimetallic metal-organic framework nanosheets and their derived porous nickel-cobalt sulfides for supercapacitors.

PubMed

Chen, Chen; Wu, Meng-Ke; Tao, Kai; Zhou, Jiao-Jiao; Li, Yan-Li; Han, Xue; Han, Lei

2018-04-24

Metal-organic frameworks (MOFs) show great advantages as new kinds of active materials for energy storage. In this study, bimetallic metal-organic frameworks (Ni/Co-MOFs) with nanosheet-assembled flower-like structures were synthesized by etching Ni-MOF microspheres in a cobalt nitrate solution. It can be clearly observed that the amount of Co(NO3)2 and etching time play crucial roles in the formation of Ni/Co-MOF nanosheets. The Ni/Co-MOFs were used as electrode materials for supercapacitors and the optimized Ni/Co-MOF-5 exhibited the highest capacitances of 1220.2 F g-1 and 986.7 F g-1 at current densities of 1 A g-1 and 10 A g-1, respectively. Ni/Co-MOF-5 was further sulfurized, and the derived Ni-Co-S electrode showed a higher specific capacitance of 1377.5 F g-1 at a current density of 1 A g-1 and a retention of 89.4% when the current density was increased to 10 A g-1, indicating superior rate capability. Furthermore, Ni/Co-MOF-5 and Ni-Co-S showed excellent cycling stability, i.e. about 87.8% and 93.7% of initial capacitance can be still maintained after 3000 cycles of charge-discharge. More interestingly, the Ni/Co-MOF-5//AC ASC shows an energy density of 30.9 W h kg-1 at a power density of 1132.8 W kg-1, and the Ni-Co-S//AC ASC displays a high energy density of 36.9 W h kg-1 at a power density of 1066.42 W kg-1. These results demonstrate that the as-synthesized bimetallic Ni/Co-MOF nanosheets and their derived nickel-cobalt sulfides have promising applications in electrochemical supercapacitors.

Effect of a Cooling Step Treatment on a High-Voltage GaN LED During ICP Dry Etching

NASA Astrophysics Data System (ADS)

Lin, Yen-Sheng; Hsiao, Sheng-Yu; Tseng, Chun-Lung; Shen, Ching-Hsing; Chiang, Jung-Sheng

2017-02-01

In this study, a lower dislocation density for a GaN surface and a reduced current path are observed at the interface of a SiO2 isolation sidewall, using high-resolution transmission electron microscopy. This is grown using a 3-min cooling step treatment during inductivity coupled plasma dry etching. The lower forward voltage is measured, the leakage current decreases from 53nA to 32nA, and the maximum output power increases from 354.8 W to 357.2 W for an input current of 30 mA. The microstructure and the optoelectronic properties of high-voltage light-emitting-diodes is proven to be affected by the cooling step treatment, which allows enough time to release the thermal energy of the SiO2 isolation well.

Trends in Dielectric Etch for Microelectronics Processing

NASA Astrophysics Data System (ADS)

Hudson, Eric A.

2003-10-01

Dielectric etch technology faces many challenges to meet the requirements for leading-edge microelectronics processing. The move to sub 100-nm device design rules increases the aspect ratios of certain features, imposes tighter restrictions on etched features' critical dimensions, and increases the density of closely packed arrays of features. Changes in photolithography are driving transitions to new photoresist materials and novel multilayer resist methods. The increasing use of copper metallization and low-k interlayer dielectric materials has introduced dual-damascene integration methods, with specialized dielectric etch applications. A common need is the selective removal of multiple layers which have very different compositions, while maintaining close control of the etched features' profiles. To increase productivity, there is a growing trend toward in-situ processing, which allows several films to be successively etched during a single pass through the process module. Dielectric etch systems mainly utilize capacitively coupled etch reactors, operating with medium-density plasmas and low gas residence time. Commercial technology development increasingly relies upon plasma diagnostics and modeling to reduce development cycle time and maximize performance.

Homogeneous alignment of nematic liquid crystals by ion beam etched surfaces

NASA Technical Reports Server (NTRS)

Wintucky, E. G.; Mahmood, R.; Johnson, D. L.

1979-01-01

A wide range of ion beam etch parameters capable of producing uniform homogeneous alignment of nematic liquid crystals on SiO2 films are discussed. The alignment surfaces were generated by obliquely incident (angles of 5 to 25 deg) argon ions with energies in the range of 0.5 to 2.0 KeV, ion current densities of 0.1 to 0.6 mA sq cm and etch times of 1 to 9 min. A smaller range of ion beam parameters (2.0 KeV, 0.2 mA sq cm, 5 to 10 deg and 1 to 5 min.) were also investigated with ZrO2 films and found suitable for homogeneous alignment. Extinction ratios were very high (1000), twist angles were small ( or = 3 deg) and tilt-bias angles very small ( or = 1 deg). Preliminary scanning electron microscopy results indicate a parallel oriented surface structure on the ion beam etched surfaces which may determine alignment.

Ion track etching revisited: II. Electronic properties of aged tracks in polymers

NASA Astrophysics Data System (ADS)

Fink, D.; Muñoz Hernández, G.; Cruz, S. A.; Garcia-Arellano, H.; Vacik, J.; Hnatowicz, V.; Kiv, A.; Alfonta, L.

2018-02-01

We compile here electronic ion track etching effects, such as capacitive-type currents, current spike emission, phase shift, rectification and background currents that eventually emerge upon application of sinusoidal alternating voltages across thin, aged swift heavy ion-irradiated polymer foils during etching. Both capacitive-type currents and current spike emission occur as long as obstacles still prevent a smooth continuous charge carrier passage across the foils. In the case of sufficiently high applied electric fields, these obstacles are overcome by spike emission. These effects vanish upon etchant breakthrough. Subsequent transmitted currents are usually of Ohmic type, but shortly after breakthrough (during the track' core etching) often still exhibit deviations such as strong positive phase shifts. They stem from very slow charge carrier mobility across the etched ion tracks due to retarding trapping/detrapping processes. Upon etching the track's penumbra, one occasionally observes a split-up into two transmitted current components, one with positive and another one with negative phase shifts. Usually, these phase shifts vanish when bulk etching starts. Current rectification upon track etching is a very frequent phenomenon. Rectification uses to inverse when core etching ends and penumbra etching begins. When the latter ends, rectification largely vanishes. Occasionally, some residual rectification remains which we attribute to the aged polymeric bulk itself. Last not least, we still consider background currents which often emerge transiently during track etching. We could assign them clearly to differences in the electrochemical potential of the liquids on both sides of the etched polymer foils. Transient relaxation effects during the track etching cause their eventually chaotic behaviour.

Performance of InGaAs short wave infrared avalanche photodetector for low flux imaging

NASA Astrophysics Data System (ADS)

Singh, Anand; Pal, Ravinder

2017-11-01

Opto-electronic performance of the InGaAs/i-InGaAs/InP short wavelength infrared focal plane array suitable for high resolution imaging under low flux conditions and ranging is presented. More than 85% quantum efficiency is achieved in the optimized detector structure. Isotropic nature of the wet etching process poses a challenge in maintaining the required control in the small pitch high density detector array. Etching process is developed to achieve low dark current density of 1 nA/cm2 in the detector array with 25 µm pitch at 298 K. Noise equivalent photon performance less than one is achievable showing single photon detection capability. The reported photodiode with low photon flux is suitable for active cum passive imaging, optical information processing and quantum computing applications.

Lithography for enabling advances in integrated circuits and devices.

PubMed

Garner, C Michael

2012-08-28

Because the transistor was fabricated in volume, lithography has enabled the increase in density of devices and integrated circuits. With the invention of the integrated circuit, lithography enabled the integration of higher densities of field-effect transistors through evolutionary applications of optical lithography. In 1994, the semiconductor industry determined that continuing the increase in density transistors was increasingly difficult and required coordinated development of lithography and process capabilities. It established the US National Technology Roadmap for Semiconductors and this was expanded in 1999 to the International Technology Roadmap for Semiconductors to align multiple industries to provide the complex capabilities to continue increasing the density of integrated circuits to nanometre scales. Since the 1960s, lithography has become increasingly complex with the evolution from contact printers, to steppers, pattern reduction technology at i-line, 248 nm and 193 nm wavelengths, which required dramatic improvements of mask-making technology, photolithography printing and alignment capabilities and photoresist capabilities. At the same time, pattern transfer has evolved from wet etching of features, to plasma etch and more complex etching capabilities to fabricate features that are currently 32 nm in high-volume production. To continue increasing the density of devices and interconnects, new pattern transfer technologies will be needed with options for the future including extreme ultraviolet lithography, imprint technology and directed self-assembly. While complementary metal oxide semiconductors will continue to be extended for many years, these advanced pattern transfer technologies may enable development of novel memory and logic technologies based on different physical phenomena in the future to enhance and extend information processing.

Self-Positioned Nanosized Mask for Transparent and Flexible Ferroelectric Polymer Nanodiodes Array.

PubMed

Hyun, Seung; Kwon, Owoong; Choi, Chungryong; Vincent Joseph, Kanniyambatti L; Kim, Yunseok; Kim, Jin Kon

2016-10-12

High density arrays of ferroelectric polymer nanodiodes have gained strong attention for next-generation transparent and flexible nonvolatile resistive memory. Here, we introduce a facile and innovative method to fabricate ferroelectric polymer nanodiode array on an ITO-coated poly(ethylene terephthalate) (PET) substrate by using block copolymer self-assembly and oxygen plasma etching. First, polystyrene-block-poly(2-vinylpyridine) copolymer (PS-b-P2VP) micelles were spin-coated on poly(vinylidene fluoride-ran-trifluoroethylene) copolymer (P(VDF-TrFE)) film/ITO-coated PET substrate. After the sample was immersed in a gold precursor (HAuCl 4 ) containing solution, which strongly coordinates with nitrogen group in P2VP, oxygen plasma etching was performed. During the plasma etching, coordinated gold precursors became gold nanoparticles (GNPs), which successfully acted as self-positioned etching mask to fabricate a high density array of P(VDF-TrFE)) nanoislands with GNP at the top. Each nanoisland shows clearly individual diode property, as confirmed by current-voltage (I-V) curve. Furthermore, due to the transparent and flexible nature of P(VDF-TrFE)) nanoisland as well as the substrate, the P(VDF-TrFE) nanodiode array was highly tranparent, and the diode property was maintained even after a large number of bendings (for instance, 1000 times). The array could be used as the next-generation tranparent and flexible nonvolatile memory device.

Suppression of Lateral Diffusion and Surface Leakage Currents in nBn Photodetectors Using an Inverted Design

NASA Astrophysics Data System (ADS)

Du, X.; Savich, G. R.; Marozas, B. T.; Wicks, G. W.

2018-02-01

Surface leakage and lateral diffusion currents in InAs-based nBn photodetectors have been investigated. Devices fabricated using a shallow etch processing scheme that etches through the top contact and stops at the barrier exhibited large lateral diffusion current but undetectably low surface leakage. Such large lateral diffusion current significantly increased the dark current, especially in small devices, and causes pixel-to-pixel crosstalk in detector arrays. To eliminate the lateral diffusion current, two different approaches were examined. The conventional solution utilized a deep etch process, which etches through the top contact, barrier, and absorber. This deep etch processing scheme eliminated lateral diffusion, but introduced high surface current along the device mesa sidewalls, increasing the dark current. High device failure rate was also observed in deep-etched nBn structures. An alternative approach to limit lateral diffusion used an inverted nBn structure that has its absorber grown above the barrier. Like the shallow etch process on conventional nBn structures, the inverted nBn devices were fabricated with a processing scheme that only etches the top layer (the absorber, in this case) but avoids etching through the barrier. The results show that inverted nBn devices have the advantage of eliminating the lateral diffusion current without introducing elevated surface current.

Is actinometry reliable for monitoring Si and silicone halides produced in silicon etching plasmas? A comparison with their absolute densities measured by UV broad band absorption

NASA Astrophysics Data System (ADS)

Kogelschatz, M.; Cunge, G.; Sadeghi, N.

2006-03-01

SiCl{x} radicals, the silicon etching by-products, are playing a major role in silicon gate etching processes because their redeposition on the wafer leads to the formation of a SiOCl{x} passivation layer on the feature sidewalls, which controls the final shape of the etching profile. These radicals are also the precursors to the formation of a similar layer on the reactor walls, leading to process drifts. As a result, the understanding and modelling of these processes rely on the knowledge of their densities in the plasma. Actinometry technique, based on optical emission, is often used to measure relative variations of the density of the above mentioned radicals, even if it is well known that the results obtained with this technique might not always be reliable. To determine the validity domain of actinometry in industrial silicon-etching high density plasmas, we measure the RF source power and pressure dependences of the absolute densities of SiCl{x} (x=0{-}2), SiF and SiBr radicals, deduced from UV broad band absorption spectroscopy. These results are compared to the evolution of the corresponding actinometry signals from these radicals. It is shown that actinometry predicts the global trends of the species density variations when the RF power is changed at constant pressure (that is to say when only the electron density changes) but it completely fails if the gas pressure, hence the electron temperature, changes.

An optimized one-step wet etching process of Pb(Zr0.52Ti0.48)O3 thin films for microelectromechanical system applications

NASA Astrophysics Data System (ADS)

Che, L.; Halvorsen, E.; Chen, X.

2011-10-01

The existence of insoluble residues as intermediate products produced during the wet etching process is the main quality-reducing and structure-patterning issue for lead zirconate titanate (PZT) thin films. A one-step wet etching process using the solutions of buffered HF (BHF) and HNO3 acid was developed for patterning PZT thin films for microelectomechanical system (MEMS) applications. PZT thin films with 1 µm thickness were prepared on the Pt/Ti/SiO2/Si substrate by the sol-gel process for compatibility with Si micromachining. Various compositions of the etchant were investigated and the patterns were examined to optimize the etching process. The optimal result is demonstrated by a high etch rate (3.3 µm min-1) and low undercutting (1.1: 1). The patterned PZT thin film exhibits a remnant polarization of 24 µC cm-2, a coercive field of 53 kV cm-1, a leakage current density of 4.7 × 10-8 A cm-2 at 320 kV cm-1 and a dielectric constant of 1100 at 1 KHz.

Correlation between optical properties surface morphology of porous silicon electrodeposited by Fe3+ ion

NASA Astrophysics Data System (ADS)

Mabrouk, Asma; Lorrain, N.; Haji, M. L.; Oueslati, Meherzi

2015-01-01

In this paper, we analyze the photoluminescence spectra (PL) of porous silicon (PS) layer which is elaborated by electrochemical etching and passivated by Fe3+ ions (PSF) via current density, electro-deposition and temperature measurements. We observe unusual surface morphology of PSF surface and anomalous emission behavior. The PSF surface shows regular distribution of cracks, leaving isolated regions or ;platelets; of nearly uniform thickness. These cracks become more pronounced for high current densities. The temperature dependence of the PL peak energy (EPL) presents anomalous behaviors, i.e., the PL peak energy shows a successive red/blue/redshift (S-shaped behavior) with increasing temperature that we attribute to the existence of strong potential fluctuations induced by the electrochemical etching of PS layers. A competition process between localized and delocalized excitons is used to discuss these PL properties. In this case, the potential confinement plays a key role on the enhancement of PL intensity in PSF. To explain the temperature dependence of the PL intensity, we have proposed a recombination model based on the tunneling and dissociation of excitons.

Effect of threading defects on InGaN /GaN multiple quantum well light emitting diodes

NASA Astrophysics Data System (ADS)

Ferdous, M. S.; Wang, X.; Fairchild, M. N.; Hersee, S. D.

2007-12-01

Photoelectrochemical etching was used to measure the threading defect (TD) density in InGaN multiple quantum well light-emitting diodes (LEDs) fabricated from commercial quality epitaxial wafers. The TD density was measured in the LED active region and then correlated with the previously measured characteristics of these LEDs. It was found that the reverse leakage current increased exponentially with TD density. The temperature dependence of this dislocation-related leakage current was consistent with a hopping mechanism at low reverse-bias voltage and Poole-Frenkel emission at higher reverse-bias voltage. The peak intensity and spectral width of the LED electroluminescence were found to be only weakly dependent on TD density for the measured TD range of 1×107-2×108cm-2.

Response of murine bone marrow-derived mesenchymal stromal cells to dry-etched porous silicon scaffolds.

PubMed

Hajj-Hassan, Mohamad; Khayyat-Kholghi, Maedeh; Wang, Huifen; Chodavarapu, Vamsy; Henderson, Janet E

2011-11-01

Porous silicon shows great promise as a bio-interface material due to its large surface to volume ratio, its stability in aqueous solutions and to the ability to precisely regulate its pore characteristics. In the current study, porous silicon scaffolds were fabricated from single crystalline silicon wafers by a novel xenon difluoride dry etching technique. This simplified dry etch fabrication process allows selective formation of porous silicon using a standard photoresist as mask material and eliminates the post-formation drying step typically required for the wet etching techniques, thereby reducing the risk of damaging the newly formed porous silicon. The porous silicon scaffolds supported the growth of primary cultures of bone marrow derived mesenchymal stromal cells (MSC) plated at high density for up to 21 days in culture with no significant loss of viability, assessed using Alamar Blue. Scanning electron micrographs confirmed a dense lawn of cells at 9 days of culture and the presence of MSC within the pores of the porous silicon scaffolds. Copyright © 2011 Wiley Periodicals, Inc.

Synthesis and characterization of porous silicon gas sensors

NASA Astrophysics Data System (ADS)

abbas, Roaa A.; Alwan, Alwan M.; Abdulhamied, Zainab T.

2018-05-01

In this work, photo-electrochemical etching process of n-type Silicon of resistivity(10 Ω.cm) and (100) orientation, using two illumination sources IR and violet wavelength in HF acid have been used to produce PSi gas detection device. The fabrication process was carried out at a fixed etching current density of 25mA/cm2 and at different etching time (5, 10, 15 and 20) min and (8, 16, 24, and 30) min. Two configurations of gas sensor configuration planer and sandwich have been made and investigated. The morphological properties have been studied using SEM,the FTIR measurement show that the (Si-Hx) and (Si-O-Si) absorption peak were increases with increasing etching time,and Photoluminescence properties of PSi layer show decrease in the peak of PL peak toward the violet shift. The gas detection process is made on the CO2 gas at different operating temperature and fixed gas concentration. In the planner structure, the gas sensing was measured through, the change in the resistance readout as a function to the exposure time, while for sandwich structure J-V characteristic have been made to determine the sensitivity.

METHOD FOR ELECTRO-NICKEL PLATING WOLFRAM CARBIDE

DOEpatents

Slatin, H.L.

1959-05-01

A WC body can be electroplated with Ni after anodic etching in Na/sub 4/ P/sub 2/O/sub 7/ solution (200 g/l) with a Pb cathode. A current density of 2 amp/in./sup 2/ for 10 min is sufficient. This allows Ni to be electrodeposited in an adherent coating which is weldable. (T.R.H.)

Real-time plasma control in a dual-frequency, confined plasma etcher

NASA Astrophysics Data System (ADS)

Milosavljević, V.; Ellingboe, A. R.; Gaman, C.; Ringwood, J. V.

2008-04-01

The physics issues of developing model-based control of plasma etching are presented. A novel methodology for incorporating real-time model-based control of plasma processing systems is developed. The methodology is developed for control of two dependent variables (ion flux and chemical densities) by two independent controls (27 MHz power and O2 flow). A phenomenological physics model of the nonlinear coupling between the independent controls and the dependent variables of the plasma is presented. By using a design of experiment, the functional dependencies of the response surface are determined. In conjunction with the physical model, the dependencies are used to deconvolve the sensor signals onto the control inputs, allowing compensation of the interaction between control paths. The compensated sensor signals and compensated set-points are then used as inputs to proportional-integral-derivative controllers to adjust radio frequency power and oxygen flow to yield the desired ion flux and chemical density. To illustrate the methodology, model-based real-time control is realized in a commercial semiconductor dielectric etch chamber. The two radio frequency symmetric diode operates with typical commercial fluorocarbon feed-gas mixtures (Ar/O2/C4F8). Key parameters for dielectric etching are known to include ion flux to the surface and surface flux of oxygen containing species. Control is demonstrated using diagnostics of electrode-surface ion current, and chemical densities of O, O2, and CO measured by optical emission spectrometry and/or mass spectrometry. Using our model-based real-time control, the set-point tracking accuracy to changes in chemical species density and ion flux is enhanced.

Use of Nanostructures in Fabrication of Large Scale Electrochemical Film

NASA Astrophysics Data System (ADS)

Chen, Chien Chon; Chen, Shih Hsun; Shyu, Sheang Wen; Hsieh, Sheng Jen

Control of electrochemical parameters when preparing small-scale samples for academic research is not difficult. In mass production environments, however, maintenance of constant current density and temperature become a critical issue. This article describes the design of several molds for large work pieces. These molds were designed to maintain constant current density and to facilitate the occurrence of electrochemical reactions in designated areas. Large-area thin films with fine nanostructure were successfully prepared using the designed electrochemical molds and containers. In addition, current density and temperature could be controlled well. This electrochemical system has been verified in many experimental operations, including etching of Al surfaces; electro-polishing of Al, Ti and stainless steel; and fabrication of anodic alumina oxide (AAO), Ti-TiO2 interference membrane, TiO2 nanotubes, AAO-TiO2 nanotubes, Ni nanowires and porous tungsten

Plasma etching of polymers like SU8 and BCB

NASA Astrophysics Data System (ADS)

Mischke, Helge; Gruetzner, Gabi; Shaw, Mark

2003-01-01

Polymers with high viscosity, like SU8 and BCB, play a dominant role in MEMS application. Their behavior in a well defined etching plasma environment in a RIE mode was investigated. The 40.68 MHz driven bottom electrode generates higher etch rates combined with much lower bias voltages by a factor of ten or a higher efficiency of the plasma with lower damaging of the probe material. The goal was to obtain a well-defined process for the removal and structuring of SU8 and BCB using fluorine/oxygen chemistry, defined using variables like electron density and collision rate. The plasma parameters are measured and varied using a production proven technology called SEERS (Self Excited Electron Resonance Spectroscopy). Depending on application and on Polymer several metals are possible (e.g., gold, aluminum). The characteristic of SU8 and BCB was examined in the case of patterning by dry etching in a CF4/O2 chemistry. Etch profile and etch rate correlate surprisingly well with plasma parameters like electron density and electron collision rate, thus allowing to define to adjust etch structure in situ with the help of plasma parameters.

Spectroscopic ellipsometry of columnar porous Si thin films and Si nanowires

NASA Astrophysics Data System (ADS)

Fodor, Bálint; Defforge, Thomas; Agócs, Emil; Fried, Miklós; Gautier, Gaël; Petrik, Péter

2017-11-01

Columnar mesoporous Si thin films and dense nanowire (SiNW) carpets were investigated by spectroscopic ellipsometry in the visible-near-infrared wavelength range. Porous Si layers were formed by electrochemical etching while structural anisotropy was controlled by the applied current. Layers of highly oriented SiNWs, with length up to 4.1 μm were synthesized by metal-assisted chemical etching. Ellipsometric spectra were fitted with different multi-layered, effective medium approximation-based (EMA) models. Isotropic, in-depth graded, anisotropic and hybrid EMA models were investigated with the help of the root mean square errors obtained from the fits. Ellipsometric-fitted layer thicknesses were also cross-checked by scanning electron microscopy showing an excellent agreement. Furthermore, in the case of mesoporous silicon, characterization also revealed that, at low current densities (<100 mA/cm2), in-depth inhomogeneity shows a more important feature in the ellipsometric spectra than anisotropy. On the other hand, at high current densities (>100 mA/cm2) this behavior turns around, and anisotropy becomes the dominant feature describing the spectra. Characterization of SiNW layers showed a very high geometrical anisotropy. However, the highest fitted geometrical anisotropy was obtained for the layer composed of ∼1 μm long SiNWs indicating that for thicker layers, collapse of the nanowires occurs.

Large scale, highly dense nanoholes on metal surfaces by underwater laser assisted hydrogen etching near nanocrystalline boundary

NASA Astrophysics Data System (ADS)

Lin, Dong; Zhang, Martin Yi; Ye, Chang; Liu, Zhikun; Liu, C. Richard; Cheng, Gary J.

2012-03-01

A new method to generate large scale and highly dense nanoholes is presented in this paper. By the pulsed laser irradiation under water, the hydrogen etching is introduced to form high density nanoholes on the surfaces of AISI 4140 steel and Ti. In order to achieve higher nanohole density, laser shock peening (LSP) followed by recrystallization is used for grain refinement. It is found that the nanohole density does not increase until recrystallization of the substructures after laser shock peening. The mechanism of nanohole generation is studied in detail. This method can be also applied to generate nanoholes on other materials with hydrogen etching effect.

High density plasma etching of magnetic devices

NASA Astrophysics Data System (ADS)

Jung, Kee Bum

Magnetic materials such as NiFe (permalloy) or NiFeCo are widely used in the data storage industry. Techniques for submicron patterning are required to develop next generation magnetic devices. The relative chemical inertness of most magnetic materials means they are hard to etch using conventional RIE (Reactive Ion Etching). Therefore ion milling has generally been used across the industry, but this has limitations for magnetic structures with submicron dimensions. In this dissertation, we suggest high density plasmas such as ECR (Electron Cyclotron Resonance) and ICP (Inductively Coupled Plasma) for the etching of magnetic materials (NiFe, NiFeCo, CoFeB, CoSm, CoZr) and other related materials (TaN, CrSi, FeMn), which are employed for magnetic devices like magnetoresistive random access memories (MRAM), magnetic read/write heads, magnetic sensors and microactuators. This research examined the fundamental etch mechanisms occurring in high density plasma processing of magnetic materials by measuring etch rate, surface morphology and surface stoichiometry. However, one concern with using Cl2-based plasma chemistry is the effect of residual chlorine or chlorinated etch residues remaining on the sidewalls of etched features, leading to a degradation of the magnetic properties. To avoid this problem, we employed two different processing methods. The first one is applying several different cleaning procedures, including de-ionized water rinsing or in-situ exposure to H2, O2 or SF6 plasmas. Very stable magnetic properties were achieved over a period of ˜6 months except O2 plasma treated structures, with no evidence of corrosion, provided chlorinated etch residues were removed by post-etch cleaning. The second method is using non-corrosive gas chemistries such as CO/NH3 or CO2/NH3. There is a small chemical contribution to the etch mechanism (i.e. formation of metal carbonyls) as determined by a comparison with Ar and N2 physical sputtering. The discharge should be NH3-rich to achieve the highest etch rates. Several different mask materials were investigated, including photoresist, thermal oxide and deposited oxide. Photoresist etches very rapidly in CO/NH 3 and use of a hard mask is necessary to achieve pattern transfer. Due to its physically dominated nature, the CO/NH3 chemistry appears suited to shallow etch depth (≤0.5mum) applications, but mask erosion leads to sloped feature sidewalls for deeper features.

High quality InP-on-Si for solar cell applications

NASA Technical Reports Server (NTRS)

Shellenbarger, Zane A.; Goodwin, Thomas A.; Collins, Sandra R.; Dinetta, Louis C.

1994-01-01

InP on Si solar cells combine the low-cost and high-strength of Si with the high efficiency and radiation tolerance of InP. The main obstacle in the growth of single crystal InP-on-Si is the high residual strain and high dislocation density of the heteroepitaxial InP films. The dislocations result from the large differences in lattice constant and thermal expansion mismatch of InP and Si. Adjusting the size and geometry of the growth area is one possible method of addressing this problem. In this work, we conducted a material quality study of liquid phase epitaxy overgrowth layers on selective area InP grown by a proprietary vapor phase epitaxy technique on Si. The relationship between growth area and dislocation density was quantified using etch pit density measurements. Material quality of the InP on Si improved both with reduced growth area and increased aspect ratio (length/width) of the selective area. Areas with etch pit density as low as 1.6 x 10(exp 4) sq cm were obtained. Assuming dislocation density is an order of magnitude greater than etch pit density, solar cells made with this material could achieve the maximum theoretical efficiency of 23% at AMO. Etch pit density dependence on the orientation of the selective areas on the substrate was also studied.

Infrared gas phase study on plasma-polymer interactions in high-current diffuse dielectric barrier discharge

NASA Astrophysics Data System (ADS)

Liu, Y.; Welzel, S.; Starostin, S. A.; van de Sanden, M. C. M.; Engeln, R.; de Vries, H. W.

2017-06-01

A roll-to-roll high-current diffuse dielectric barrier discharge at atmospheric pressure was operated in air and Ar/N2/O2 gas mixtures. The exhaust gas from the discharge was studied using a high-resolution Fourier-transform infrared spectrometer in the range from 3000 to 750 cm-1 to unravel the plasma-polymer interactions. The absorption features of HxNyOz, COx, and HCOOH (formic acid) were identified, and the relative densities were deduced by fitting the absorption bands of the detected molecules. Strong interactions between plasma and polymer (Polyethylene-2,6-naphthalate, or PEN) in precursor-free oxygen-containing gas mixtures were observed as evidenced by a high COx production. The presence of HCOOH in the gas effluent, formed through plasma-chemical synthesis of COx, turns out to be a sensitive indicator for etching. By adding tetraethylorthosilicate precursor in the plasma, dramatic changes in the COx production were measured, and two distinct deposition regimes were identified. At high precursor flows, a good agreement with the precursor combustion and the COx production was observed, whereas at low precursor flows an etching-deposition regime transpires, and the COx production is dominated by polymer etching.

Development program on a cold cathode electron gun

NASA Technical Reports Server (NTRS)

Spindt, C. A.; Holland, C. E.

1985-01-01

During this phase of the cathode development program, SRI improved the multiple electron beam exposure system used to print hole patterns for the cathode arrays, studied anisotropic etch processes, conducted cathode investigations using an emission microscope, reviewed possible alternate materials for cathode fabrication, studied cathode storage techniques, conducted high power operation experiments, and demonstrated high-current-density operation with small arrays of tips.

Development of Functional Surfaces on High-Density Polyethylene (HDPE) via Gas-Assisted Etching (GAE) Using Focused Ion Beams.

PubMed

Sezen, Meltem; Bakan, Feray

2015-12-01

Irradiation damage, caused by the use of beams in electron and ion microscopes, leads to undesired physical/chemical material property changes or uncontrollable modification of structures. Particularly, soft matter such as polymers or biological materials is highly susceptible and very much prone to react on electron/ion beam irradiation. Nevertheless, it is possible to turn degradation-dependent physical/chemical changes from negative to positive use when materials are intentionally exposed to beams. Especially, controllable surface modification allows tuning of surface properties for targeted purposes and thus provides the use of ultimate materials and their systems at the micro/nanoscale for creating functional surfaces. In this work, XeF2 and I2 gases were used in the focused ion beam scanning electron microscope instrument in combination with gallium ion etching of high-density polyethylene surfaces with different beam currents and accordingly different gas exposure times resulting at the same ion dose to optimize and develop new polymer surface properties and to create functional polymer surfaces. Alterations in the surface morphologies and surface chemistry due to gas-assisted etching-based nanostructuring with various processing parameters were tracked using high-resolution SEM imaging, complementary energy-dispersive spectroscopic analyses, and atomic force microscopic investigations.

Etching in Chlorine Discharges Using an Integrated Feature Evolution-Plasma Model

NASA Technical Reports Server (NTRS)

Hwang, Helen H.; Bose, Deepak; Govindan, T. R.; Meyyappan, M.; Biegel, Bryan (Technical Monitor)

2001-01-01

Etching of semiconductor materials is reliant on plasma properties. Quantities such as ion and neutral fluxes, both in magnitude and in direction, are often determined by reactor geometry (height, radius, position of the coils, etc.) In order to obtain accurate etching profiles, one must also model the plasma as a whole to obtain local fluxes and distributions. We have developed a set of three models that simulates C12 plasmas for etching of silicon, ion and neutral trajectories in the plasma, and feature profile evolution. We have found that the location of the peak in the ion densities in the reactor plays a major role in determining etching uniformity across the wafer. For a stove top coil inductively coupled plasma (ICP), the ion density is peaked at the top of the reactor. This leads to nearly uniform neutral and ion fluxes across the wafer. A side coil configuration causes the ion density to peak near the sidewalls. Ion fluxes are thus greater toward the wall's and decrease toward the center. In addition, the ions bombard the wafer at a slight angle. This angle is sufficient to cause slanted profiles, which is highly undesirable.

Dry-plasma-free chemical etch technique for variability reduction in multi-patterning (Conference Presentation)

NASA Astrophysics Data System (ADS)

Kal, Subhadeep; Mohanty, Nihar; Farrell, Richard A.; Franke, Elliott; Raley, Angelique; Thibaut, Sophie; Pereira, Cheryl; Pillai, Karthik; Ko, Akiteru; Mosden, Aelan; Biolsi, Peter

2017-04-01

Scaling beyond the 7nm technology node demands significant control over the variability down to a few angstroms, in order to achieve reasonable yield. For example, to meet the current scaling targets it is highly desirable to achieve sub 30nm pitch line/space features at back-end of the line (BEOL) or front end of line (FEOL); uniform and precise contact/hole patterning at middle of line (MOL). One of the quintessential requirements for such precise and possibly self-aligned patterning strategies is superior etch selectivity between the target films while other masks/films are exposed. The need to achieve high etch selectivity becomes more evident for unit process development at MOL and BEOL, as a result of low density films choices (compared to FEOL film choices) due to lower temperature budget. Low etch selectivity with conventional plasma and wet chemical etch techniques, causes significant gouging (un-intended etching of etch stop layer, as shown in Fig 1), high line edge roughness (LER)/line width roughness (LWR), non-uniformity, etc. In certain circumstances this may lead to added downstream process stochastics. Furthermore, conventional plasma etches may also have the added disadvantage of plasma VUV damage and corner rounding (Fig. 1). Finally, the above mentioned factors can potentially compromise edge placement error (EPE) and/or yield. Therefore a process flow enabled with extremely high selective etches inherent to film properties and/or etch chemistries is a significant advantage. To improve this etch selectivity for certain etch steps during a process flow, we have to implement alternate highly selective, plasma free techniques in conjunction with conventional plasma etches (Fig 2.). In this article, we will present our plasma free, chemical gas phase etch technique using chemistries that have high selectivity towards a spectrum of films owing to the reaction mechanism ( as shown Fig 1). Gas phase etches also help eliminate plasma damage to the features during the etch process. Herein we will also demonstrate a test case on how a combination or plasma assisted and plasma free etch techniques has the potential to improve process performance of a 193nm immersion based self aligned quandruple patterning (SAQP) for BEOL compliant films (an example shown in Fig 2). In addition, we will also present on the application of gas etches for (1) profile improvement, (2) selective mandrel pull (3) critical dimension trim of mandrels, with an analysis of advantages over conventional techniques in terms of LER and EPE.

Photoelectrochemical etching measurement of defect density in GaN grown by nanoheteroepitaxy

NASA Astrophysics Data System (ADS)

Ferdous, M. S.; Sun, X. Y.; Wang, X.; Fairchild, M. N.; Hersee, S. D.

2006-05-01

The density of dislocations in n-type GaN was measured by photoelectrochemical etching. A 10× reduction in dislocation density was observed compared to planar GaN grown at the same time. Cross-sectional transmission electron microscopy studies indicate that defect reduction is due to the mutual cancellation of dislocations with equal and opposite Burger's vectors. The nanoheteroepitaxy sample exhibited significantly higher photoluminescence intensity and higher electron mobility than the planar reference sample.

Light-trapping optimization in wet-etched silicon photonic crystal solar cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eyderman, Sergey, E-mail: sergey.eyderman@utoronto.ca; John, Sajeev; Department of Physics, King Abdul-Aziz University, Jeddah

2015-07-14

We demonstrate, by numerical solution of Maxwell's equations, near-perfect solar light-trapping and absorption over the 300–1100 nm wavelength band in silicon photonic crystal (PhC) architectures, amenable to fabrication by wet-etching and requiring less than 10 μm (equivalent bulk thickness) of crystalline silicon. These PhC's consist of square lattices of inverted pyramids with sides comprised of various (111) silicon facets and pyramid center-to-center spacing in the range of 1.3–2.5 μm. For a wet-etched slab with overall height H = 10 μm and lattice constant a = 2.5 μm, we find a maximum achievable photo-current density (MAPD) of 42.5 mA/cm{sup 2}, falling not far from 43.5 mA/cm{sup 2}, correspondingmore » to 100% solar absorption in the range of 300–1100 nm. We also demonstrate a MAPD of 37.8 mA/cm{sup 2} for a thinner silicon PhC slab of overall height H = 5 μm and lattice constant a = 1.9 μm. When H is further reduced to 3 μm, the optimal lattice constant for inverted pyramids reduces to a = 1.3 μm and provides the MAPD of 35.5 mA/cm{sup 2}. These wet-etched structures require more than double the volume of silicon, in comparison to the overall mathematically optimum PhC structure (consisting of slanted conical pores), to achieve the same degree of solar absorption. It is suggested these 3–10 μm thick structures are valuable alternatives to currently utilized 300 μm-thick textured solar cells and are suitable for large-scale fabrication by wet-etching.« less

Enhancing elastic stress relaxation in SiGe/Si heterostructures by Si pillar necking

NASA Astrophysics Data System (ADS)

Isa, F.; Salvalaglio, M.; Arroyo Rojas Dasilva, Y.; Jung, A.; Isella, G.; Erni, R.; Timotijevic, B.; Niedermann, P.; Gröning, P.; Montalenti, F.; von Känel, H.

2016-10-01

We demonstrate that the elastic stress relaxation mechanism in micrometre-sized, highly mismatched heterostructures may be enhanced by employing patterned substrates in the form of necked pillars, resulting in a significant reduction of the dislocation density. Compositionally graded Si1-xGex crystals were grown by low energy plasma enhanced chemical vapour deposition, resulting in tens of micrometres tall, three-dimensional heterostructures. The patterned Si(001) substrates consist of micrometre-sized Si pillars either with the vertical {110} or isotropically under-etched sidewalls resulting in narrow necks. The structural properties of these heterostructures were investigated by defect etching and transmission electron microscopy. We show that the dislocation density, and hence the competition between elastic and plastic stress relaxation, is highly influenced by the shape of the substrate necks and their proximity to the mismatched epitaxial material. The SiGe dislocation density increases monotonically with the crystal width but is significantly reduced by the substrate under-etching. The drop in dislocation density is interpreted as a direct effect of the enhanced compliance of the under-etched Si pillars, as confirmed by the three-dimensional finite element method simulations of the elastic energy distribution.

A facile synthesis of reduced holey graphene oxide for supercapacitors.

PubMed

Hu, Xinjun; Bai, Dongchen; Wu, Yiqi; Chen, Songbo; Ma, Yu; Lu, Yue; Chao, Yuanzhi; Bai, Yongxiao

2017-12-12

Hydroxyl radicals (˙OH) generated from a UV/O 3 solution reaction is used to efficiently etch graphene oxide nanosheets under moderate conditions. Reduced holey graphene oxide is directly used as a supercapacitor electrode material and exhibits high specific capacitance (224 F g -1 at a current density of 1 A g -1 ) and high volumetric capacitance (up to 206 F cm -3 ).

Room-Temperature Wet Chemical Synthesis of Au NPs/TiH2/Nanocarved Ti Self-Supported Electrocatalysts for Highly Efficient H2 Generation.

PubMed

Amin, Mohammed A; Fadlallah, Sahar A; Alosaimi, Ghaida S; Ahmed, Emad M; Mostafa, Nasser Y; Roussel, Pascal; Szunerits, Sabine; Boukherroub, Rabah

2017-09-06

Self-supported electrocatalysts are a new class of materials exhibiting high catalytic performance for various electrochemical processes and can be directly equipped in energy conversion devices. We present here, for the first time, sparse Au NPs self-supported on etched Ti (nanocarved Ti substrate self-supported with TiH 2 ) as promising catalysts for the electrochemical generation of hydrogen (H 2 ) in KOH solutions. Cleaned, as-polished Ti substrates were etched in highly concentrated sulfuric acid solutions without and with 0.1 M NH 4 F at room temperature for 15 min. These two etching processes yielded a thin layer of TiH 2 (the corrosion product of the etching process) self-supported on nanocarved Ti substrates with different morphologies. While F - -free etching process led to formation of parallel channels (average width: 200 nm), where each channel consists of an array of rounded cavities (average width: 150 nm), etching in the presence of F - yielded Ti surface carved with nanogrooves (average width: 100 nm) in parallel orientation. Au NPs were then grown in situ (self-supported) on such etched surfaces via immersion in a standard gold solution at room temperature without using stabilizers or reducing agents, producing Au NPs/TiH 2 /nanostructured Ti catalysts. These materials were characterized by scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS), grazing incidence X-ray diffraction (GIXRD), and X-ray photoelectron spectroscopy (XPS). GIXRD confirmed the formation of Au 2 Ti phase, thus referring to strong chemical interaction between the supported Au NPs and the substrate surface (also evidenced from XPS) as well as a titanium hydride phase of chemical composition TiH 2 . Electrochemical measurements in 0.1 M KOH solution revealed outstanding hydrogen evolution reaction (HER) electrocatalytic activity for our synthesized catalysts, with Au NPs/TiH 2 /nanogrooved Ti catalyst being the best one among them. It exhibited fast kinetics for the HER with onset potentials as low as -22 mV vs. RHE, high exchange current density of 0.7 mA cm -2 , and a Tafel slope of 113 mV dec -1 . These HER electrochemical kinetic parameters are very close to those measured here for a commercial Pt/C catalyst (onset potential: -20 mV, Tafel slope: 110 mV dec -1 , and exchange current density: 0.75 mA cm -2 ). The high catalytic activity of these materials was attributed to the catalytic impacts of both TiH 2 phase and self-supported Au NPs (active sites for the catalytic reduction of water to H 2 ), in addition to their nanostructured features which provide a large-surface area for the HER.

Defect sensitive etching of hexagonal boron nitride single crystals

NASA Astrophysics Data System (ADS)

Edgar, J. H.; Liu, S.; Hoffman, T.; Zhang, Yichao; Twigg, M. E.; Bassim, Nabil D.; Liang, Shenglong; Khan, Neelam

2017-12-01

Defect sensitive etching (DSE) was developed to estimate the density of non-basal plane dislocations in hexagonal boron nitride (hBN) single crystals. The crystals employed in this study were precipitated by slowly cooling (2-4 °C/h) a nickel-chromium flux saturated with hBN from 1500 °C under 1 bar of flowing nitrogen. On the (0001) planes, hexagonal-shaped etch pits were formed by etching the crystals in a eutectic mixture of NaOH and KOH between 450 °C and 525 °C for 1-2 min. There were three types of pits: pointed bottom, flat bottom, and mixed shape pits. Cross-sectional transmission electron microscopy revealed that the pointed bottom etch pits examined were associated with threading dislocations. All of these dislocations had an a-type burgers vector (i.e., they were edge dislocations, since the line direction is perpendicular to the [ 2 11 ¯ 0 ]-type direction). The pit widths were much wider than the pit depths as measured by atomic force microscopy, indicating the lateral etch rate was much faster than the vertical etch rate. From an Arrhenius plot of the log of the etch rate versus the inverse temperature, the activation energy was approximately 60 kJ/mol. This work demonstrates that DSE is an effective method for locating threading dislocations in hBN and estimating their densities.

Silicon etching of difluoromethane atmospheric pressure plasma jet combined with its spectroscopic analysis

NASA Astrophysics Data System (ADS)

Sung, Yu-Ching; Wei, Ta-Chin; Liu, You-Chia; Huang, Chun

2018-06-01

A capacitivly coupled radio-frequency double-pipe atmospheric-pressure plasma jet is used for etching. An argon carrier gas is supplied to the plasma discharge jet; and CH2F2 etch gas is inserted into the plasma discharge jet, near the silicon substrate. Silicon etchings rate can be efficiently-controlled by adjusting the feeding etching gas composition and plasma jet operating parameters. The features of silicon etched by the plasma discharge jet are discussed in order to spatially spreading plasma species. Electronic excitation temperature and electron density are detected by increasing plasma power. The etched silicon profile exhibited an anisotropic shape and the etching rate was maximum at the total gas flow rate of 4500 sccm and CH2F2 concentration of 11.1%. An etching rate of 17 µm/min was obtained at a plasma power of 100 W.

Effects of silicon nanowire morphology on optical properties and hybrid solar cell performance

NASA Astrophysics Data System (ADS)

Syu, Hong-Jhang; Shiu, Shu-Chia; Hung, Yung-Jr; Lee, San-Liang; Lin, Ching-Fuh

2012-10-01

Silicon nanowire (SiNW) arrays are widespread applied on hybrid photovoltaic devices because SiNW arrays can substitute the pyramid texture and anti-reflection coating due to its strong light trapping. Also, SiNWs can be prepared through a cost-efficient process of metal-assisted chemical etching. However, though longer SiNW arrays have lower reflectance, the top of long SiNWs aggregate together to make junction synthesis difficult for SiNW/organic hybrid solar cell. To control and analyze the effect of SiNW array morphology on hybrid solar cells, here we change the metal deposition condition for metal-assisted chemical etching to obtain different SiNW array morphologies. The experiment was separated to two groups, by depositing metal, say, Ag, before etching (BE) or during etching (DE). For group BE, Ag was deposited on n-type Si (n-Si) wafers by thermal evaporation; then etched by H2O2 and HF. For group DE, n-Si was etched by Ag+ and HF directly. Ag was deposited on n-Si during etching process. Afterwards, residual Ag and SiO2 were removed by HNO3 and buffered HF, successively; then Ti and Ag were evaporated on the bottom of Si to be a cathode. Finally, SiNWs were stuck on the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) that was spincoated on the ITO coated glass to form SiNW/organic heterojunction. The results show that group BE has reflectance lower than that in group DE in solar spectrum. However, group BE has smaller power conversion efficiency (PCE) of 8.65% and short-circuit current density (Jsc) of 24.94 mA/cm2 than group DE of PCE of 9.47% and Jsc of 26.81 mA/cm2.

Understanding and controlling the step bunching instability in aqueous silicon etching

NASA Astrophysics Data System (ADS)

Bao, Hailing

Chemical etching of silicon has been widely used for more than half a century in the semiconductor industry. It not only forms the basis for current wafer cleaning processes, it also serves as a powerful tool to create a variety of surface morphologies for different applications. Its potential for controlling surface morphology at the atomic scale over micron-size regions is especially appealing. In spite of its wide usage, the chemistry of silicon etching is poorly understood. Many seemingly simple but fundamental questions have not been answered. As a result, the development of new etchants and new etching protocols are based on expensive and tedious trial-and-error experiments. A better understanding of the etching mechanism would direct the rational formulation of new etchants that produce controlled etch morphologies. Particularly, micron-scale step bunches spontaneously develop on the vicinal Si(111) surface etched in KOH or other anisotropic aqueous etchants. The ability to control the size, orientation, density and regularity of these surface features would greatly improve the performance of microelectromechanical devices. This study is directed towards understanding the chemistry and step bunching instability in aqueous anisotropic etching of silicon through a combination of experimental techniques and theoretical simulations. To reveal the cause of step-bunching instability, kinetic Monte Carlo simulations were constructed based on an atomistic model of the silicon lattice and a modified kinematic wave theory. The simulations showed that inhomogeneity was the origin of step-bunching, which was confirmed through STM studies of etch morphologies created under controlled flow conditions. To quantify the size of the inhomogeneities in different etchants and to clarify their effects, a five-parallel-trench pattern was fabricated. This pattern used a nitride mask to protect most regions of the wafer; five evenly spaced etch windows were opened to the Si(110) substrate. Combining data from these etched patterns and surface IR spectra, a modified mechanism, which explained most experimental observations, was proposed. Control of the step-bunching instability was accomplished with a second micromachined etch barrier pattern which consisted of a circular array of seventy-two long, narrow trenches in an etch mask. Using this pattern, well aligned, regularly shaped, evenly-distributed, near-atomically flat terraces in micron size were produced controllably.

Effects of dextrose and lipopolysaccharide on the corrosion behavior of a Ti-6Al-4V alloy with a smooth surface or treated with double-acid-etching.

PubMed

Faverani, Leonardo P; Assunção, Wirley G; de Carvalho, Paulo Sérgio P; Yuan, Judy Chia-Chun; Sukotjo, Cortino; Mathew, Mathew T; Barao, Valentim A

2014-01-01

Diabetes and infections are associated with a high risk of implant failure. However, the effects of such conditions on the electrochemical stability of titanium materials remain unclear. This study evaluated the corrosion behavior of a Ti-6Al-4V alloy, with a smooth surface or conditioned by double-acid-etching, in simulated body fluid with different concentrations of dextrose and lipopolysaccharide. For the electrochemical assay, the open-circuit-potential, electrochemical impedance spectroscopy, and potentiodynamic test were used. The disc surfaces were characterized by scanning electron microscopy and atomic force microscopy. Their surface roughness and Vickers microhardness were also tested. The quantitative data were analyzed by Pearson's correlation and independent t-tests (α = 0.05). In the corrosion parameters, there was a strong lipopolysaccharide correlation with the Ipass (passivation current density), Cdl (double-layer capacitance), and Rp (polarization resistance) values (p<0.05) for the Ti-6Al-4V alloy with surface treatment by double-acid-etching. The combination of dextrose and lipopolysaccharide was correlated with the Icorr (corrosion current density) and Ipass (p<0.05). The acid-treated groups showed a significant increase in Cdl values and reduced Rp values (p<0.05, t-test). According to the topography, there was an increase in surface roughness (R2 = 0.726, p<0.0001 for the smooth surface; R2 = 0.405, p = 0.036 for the double-acid-etching-treated surface). The microhardness of the smooth Ti-6Al-4V alloy decreased (p<0.05) and that of the treated Ti-6Al-4V alloy increased (p<0.0001). Atomic force microscopy showed changes in the microstructure of the Ti-6Al-4V alloy by increasing the surface thickness mainly in the group associated with dextrose and lipopolysaccharide. The combination of dextrose and lipopolysaccharide affected the corrosion behavior of the Ti-6Al-4V alloy surface treated with double-acid-etching. However, no dose-response corrosion behavior could be observed. These results suggest a greater susceptibility to corrosion of titanium implants in diabetic patients with associated infections.

Effects of Dextrose and Lipopolysaccharide on the Corrosion Behavior of a Ti-6Al-4V Alloy with a Smooth Surface or Treated with Double-Acid-Etching

PubMed Central

Faverani, Leonardo P.; Assunção, Wirley G.; de Carvalho, Paulo Sérgio P.; Yuan, Judy Chia-Chun; Sukotjo, Cortino; Mathew, Mathew T.; Barao, Valentim A.

2014-01-01

Diabetes and infections are associated with a high risk of implant failure. However, the effects of such conditions on the electrochemical stability of titanium materials remain unclear. This study evaluated the corrosion behavior of a Ti-6Al-4V alloy, with a smooth surface or conditioned by double-acid-etching, in simulated body fluid with different concentrations of dextrose and lipopolysaccharide. For the electrochemical assay, the open-circuit-potential, electrochemical impedance spectroscopy, and potentiodynamic test were used. The disc surfaces were characterized by scanning electron microscopy and atomic force microscopy. Their surface roughness and Vickers microhardness were also tested. The quantitative data were analyzed by Pearson's correlation and independent t-tests (α = 0.05). In the corrosion parameters, there was a strong lipopolysaccharide correlation with the Ipass (passivation current density), Cdl (double-layer capacitance), and Rp (polarization resistance) values (p<0.05) for the Ti-6Al-4V alloy with surface treatment by double-acid-etching. The combination of dextrose and lipopolysaccharide was correlated with the Icorr (corrosion current density) and Ipass (p<0.05). The acid-treated groups showed a significant increase in Cdl values and reduced Rp values (p<0.05, t-test). According to the topography, there was an increase in surface roughness (R2 = 0.726, p<0.0001 for the smooth surface; R2 = 0.405, p = 0.036 for the double-acid-etching-treated surface). The microhardness of the smooth Ti-6Al-4V alloy decreased (p<0.05) and that of the treated Ti-6Al-4V alloy increased (p<0.0001). Atomic force microscopy showed changes in the microstructure of the Ti-6Al-4V alloy by increasing the surface thickness mainly in the group associated with dextrose and lipopolysaccharide. The combination of dextrose and lipopolysaccharide affected the corrosion behavior of the Ti-6Al-4V alloy surface treated with double-acid-etching. However, no dose-response corrosion behavior could be observed. These results suggest a greater susceptibility to corrosion of titanium implants in diabetic patients with associated infections. PMID:24671257

System for characterizing semiconductor materials and photovoltaic device

DOEpatents

Sopori, B.L.

1996-12-03

Apparatus for detecting and mapping defects in the surfaces of polycrystalline material in a manner that distinguishes dislocation pits from grain boundaries includes a first laser of a first wavelength for illuminating a wide spot on the surface of the material, a second laser of a second relatively shorter wavelength for illuminating a relatively narrower spot on the surface of the material, a light integrating sphere with apertures for capturing light scattered by etched dislocation pits in an intermediate range away from specular reflection while allowing light scattered by etched grain boundaries in a near range from specular reflection to pass through, and optical detection devices for detecting and measuring intensities of the respective intermediate scattered light and near specular scattered light. A center blocking aperture or filter can be used to screen out specular reflected light, which would be reflected by nondefect portions of the polycrystalline material surface. An X-Y translation stage for mounting the polycrystalline material and signal processing and computer equipment accommodate raster mapping, recording, and displaying of respective dislocation and grain boundary defect densities. A special etch procedure is included, which prepares the polycrystalline material surface to produce distinguishable intermediate and near specular light scattering in patterns that have statistical relevance to the dislocation and grain boundary defect densities. A reflectance measurement of the piece of material is obtained by adding together the signals from the optical detection devices. In the case where the piece of material includes a photovoltaic device, the current induced in the device by the illuminating light can be measured with a current sensing amplifier after the light integrating sphere is moved away from the device. 22 figs.

System for characterizing semiconductor materials and photovoltaic device

DOEpatents

Sopori, Bhushan L.

1996-01-01

Apparatus for detecting and mapping defects in the surfaces of polycrystalline material in a manner that distinguishes dislocation pits from grain boundaries includes a first laser of a first wavelength for illuminating a wide spot on the surface of the material, a second laser of a second relatively shorter wavelength for illuminating a relatively narrower spot on the surface of the material, a light integrating sphere with apertures for capturing light scattered by etched dislocation pits in an intermediate range away from specular reflection while allowing light scattered by etched grain boundaries in a near range from specular reflection to pass through, and optical detection devices for detecting and measuring intensities of the respective intermediate scattered light and near specular scattered light. A center blocking aperture or filter can be used to screen out specular reflected light, which would be reflected by nondefect portions of the polycrystalline material surface. An X-Y translation stage for mounting the polycrystalline material and signal processing and computer equipment accommodate raster mapping, recording, and displaying of respective dislocation and grain boundary defect densities. A special etch procedure is included, which prepares the polycrystalline material surface to produce distinguishable intermediate and near specular light scattering in patterns that have statistical relevance to the dislocation and grain boundary defect densities. A reflectance measurement of the piece of material is obtained by adding together the signals from the optical detection devices. In the case where the piece of material includes a photovoltaic device, the current induced in the device by the illuminating light can be measured with a current sensing amplifier after the light integrating sphere is moved away from the device.

High-density plasma etching of III-nitrides: Process development, device applications and damage remediation

NASA Astrophysics Data System (ADS)

Singh, Rajwinder

Plasma-assisted etching is a key technology for III-nitride device fabrication. The inevitable etch damage resulting from energetic pattern transfer is a challenge that needs to be addressed in order to optimize device performance and reliability. This dissertation focuses on the development of a high-density inductively-coupled plasma (ICP) etch process for III-nitrides, the demonstration of its applicability to practical device fabrication using a custom built ICP reactor, and development of techniques for remediation of etch damage. A chlorine-based standard dry etch process has been developed and utilized in fabrication of a number of electronic and optoelectronic III-nitride devices. Annealing studies carried out at 700°C have yielded the important insight that the annealing time necessary for making good-quality metal contacts to etch processed n-GaN is very short (<30 sec), comparable with the annealing times necessary for dopant activation of p-GaN films and provides an opportunity for streamlining process flow. Plasma etching degrades contact quality on n-GaN films and this degradation has been found to increase with the rf bias levels (ion energies) used, most notably in films with higher doping levels. Immersion in 1:1 mixture of hydrochloric acid and de-ionized water, prior to metallization, removes some of the etch damage and is helpful in recovering contact quality. In-situ treatment consisting of a slow ramp-down of rf bias at the end of the etch is found to achieve the same effect as the ex-situ treatment. This insitu technique is significantly advantageous in a large-scale production environment because it eliminates a process step, particularly one involving treatment in hydrochloric acid. ICP equipment customization for scaling up the process to full 2-inch wafer size is described. Results on etching of state of the art 256 x 256 AlGaN focal plane arrays of ultraviolet photodetectors are reported, with excellent etch uniformity over the wafer area.

Etude fondamentale des mecanismes de gravure par plasma de materiaux de pointe: Application a la fabrication de dispositifs photoniques

NASA Astrophysics Data System (ADS)

Stafford, Luc

Advances in electronics and photonics critically depend upon plasma-based materials processing either for transferring small lithographic patterns into underlying materials (plasma etching) or for the growth of high-quality films. This thesis deals with the etching mechanisms of materials using high-density plasmas. The general objective of this work is to provide an original framework for the plasma-material interaction involved in the etching of advanced materials by putting the emphasis on complex oxides such as SrTiO3, (Ba,Sr)TiO 3 and SrBi2Ta2O9 films. Based on a synthesis of the descriptions proposed by different authors to explain the etching characteristics of simple materials in noble and halogenated plasma mixtures, we propose comprehensive rate models for physical and chemical plasma etching processes. These models have been successfully validated using experimental data published in literature for Si, Pt, W, SiO2 and ZnO. As an example, we have been able to adequately describe the simultaneous dependence of the etch rate on ion and reactive neutral fluxes and on the ion energy. From an exhaustive experimental investigation of the plasma and etching properties, we have also demonstrated that the validity of the proposed models can be extended to complex oxides such as SrTiO3, (Ba,Sr)TiO 3 and SrBi2Ta2O9 films. We also reported for the first time physical aspects involved in plasma etching such as the influence of the film microstructural properties on the sputter-etch rate and the influence of the positive ion composition on the ion-assisted desorption dynamics. Finally, we have used our deep investigation of the etching mechanisms of STO films and the resulting excellent control of the etch rate to fabricate a ridge waveguide for photonic device applications. Keywords: plasma etching, sputtering, adsorption and desorption dynamics, high-density plasmas, plasma diagnostics, advanced materials, photonic applications.

Preparation, patterning, and properties of thin YBa2Cu3O(7-delta) films

NASA Astrophysics Data System (ADS)

de Vries, J. W. C.; Dam, B.; Heijman, M. G. J.; Stollman, G. M.; Gijs, M. A. M.

1988-05-01

High T(c) superconducting thin films were prepared on (100) SrTiO3 substrates by dc triode sputtering and subsequent annealing. In these films Hall-bar structures having a width down to 5 microns were patterned using a reactive ion-etching technique. Superconductivity above 77 K was observed. When compared with the original film there is only a small reduction in T(c). The critical current density determined by electrical measurements is substantially reduced. On the other hand, the critical current density in the bulk of the grains as measured by the torque on a film is not reduced by the patterning process. It is suggested that superconductor-normal metal-superconductor junctions between the grains account for this difference.

Study on the performance of 2.6 μm In0.83Ga0.17As detector with different etch gases

NASA Astrophysics Data System (ADS)

Li, Ping; Tang, Hengjing; Li, Tao; Li, Xue; Shao, Xiumei; Ma, Yingjie; Gong, Haimei

2017-09-01

In order to obtain a low-damage recipe in the ICP processing, ICP-induced damage using Cl2/CH4 etch gases in extended wavelength In0.83Ga0.17As detector materials was studied in this paper. The effect of ICP etching on In0.83Ga0.17As samples was characterized qualitatively by the photoluminescence (PL) technology. The etch damage of In0.83Ga0.17As samples was characterized quantitatively by the Transmission Line Model (TLM), current voltage (IV) measurement, signal and noise testing and the Fourier Transform Infrared Spectroscopy (FTIR) technologies. The results showed that the Cl2/CH4 etching processing could lead better detector performance than that Cl2/N2, such as a larger square resistance, a lower dark current, a lower noise voltage and a higher peak detectivity. The lower PL signal intensity and lower dark current could be attributed to the hydrogen decomposed by the CH4 etch gases in the plasma etching process. These hydrogen particles generated non-radiative recombination centers in inner materials to weaken the PL intensity and passivated dangling bond at the surface to reduce the dark current. The larger square resistance resulted from the lower etch damage. The lower dark current meant that the detectors have less dangling bonds and leakage channels.

Kerfless epitaxial silicon wafers with 7 ms carrier lifetimes and a wide lift-off process window

NASA Astrophysics Data System (ADS)

Gemmel, Catherin; Hensen, Jan; David, Lasse; Kajari-Schröder, Sarah; Brendel, Rolf

2018-04-01

Silicon wafers contribute significantly to the photovoltaic module cost. Kerfless silicon wafers that grow epitaxially on porous silicon (PSI) and are subsequently detached from the growth substrate are a promising lower cost drop-in replacement for standard Czochralski (Cz) wafers. However, a wide technological processing window appears to be a challenge for this process. This holds in particularly for the etching current density of the separation layer that leads to lift-off failures if it is too large or too low. Here we present kerfless PSI wafers of high electronic quality that we fabricate on weakly reorganized porous Si with etch current densities varying in a wide process window from 110 to 150 mA/cm2. We are able to detach all 17 out of 17 epitaxial wafers. All wafers exhibit charge carrier lifetimes in the range of 1.9 to 4.3 ms at an injection level of 1015 cm-3 without additional high-temperature treatment. We find even higher lifetimes in the range of 4.6 to 7.0 ms after applying phosphorous gettering. These results indicate that a weak reorganization of the porous layer can be beneficial for a large lift-off process window while still allowing for high carrier lifetimes.

Pattern transfer from nanoparticle arrays

NASA Astrophysics Data System (ADS)

Hogg, Charles R., III

This project contributes to the long-term extensibility of bit-patterned media (BPM), by removing obstacles to using a new and smaller class of self-assembling materials: surfactant-coated nanoparticles. Self-assembly rapidly produces regular patterns of small features over large areas. If these patterns can be used as templates for magnetic bits, the resulting media would have both high capacity and high bit density. The data storage industry has identified block copolymers (BCP) as the self-assembling technology for the first generation of BPM. Arrays of surfactant-coated nanoparticles have long shown higher feature densities than BCP, but their patterns could not previously be transferred into underlying substrates. I identify one key obstacle that has prevented this pattern transfer: the particles undergo a disordering transition during etching which I have called "cracking". I compare several approaches to measuring the degree of cracking, and I develop two novel techniques for preventing it and allowing pattern transfer. I demonstrate two different kinds of pattern transfer: positive (dots) and negative (antidots). To make dots, I etch the substrate between the particles with a directional CF4-based reactive ion etch (RIE). I find the ultrasmall gaps (just 2 nm) cause a tremendous slowdown in the etch rate, by a factor of 10 or more---an observation of fundamental significance for any pattern transfer at ultrahigh bit densities. Antidots are made by depositing material in the interstices, then removing the particles to leave behind a contiguous inorganic lattice. This lattice can itself be used as an etch mask for CF4-based RIE, in order to increase the height contrast. The antidot process promises great generality in choice of materials, both for the antidot lattice and the particles themselves; here, I present lattices of Al and Cr, ternplated from arrays of 13.7 nm-diameter Fe3O4 or 30 nm-diameter MnO nanoparticles. The fidelity of transfer is also noticeably better for antidots than for dots, making antidots the more promising technique for industrial applications. The smallest period for which I have shown pattern transfer (15.7 nm) is comparable to (but slightly smaller than) the smallest period currently shown for pattern transfer from block copolymers (17 nm); hence, my results compare favorably with the state of the art. Ultimately, by demonstrating that surfactant-coated nanoparticles can be used as pattern masks, this work increases their viability as an option to continue the exponential growth of bit density in magnetic storage media.

Detection and modeling of leakage current in AlGaN-based deep ultraviolet light-emitting diodes

DOE PAGES

Moseley, Michael William; Allerman, Andrew A.; Crawford, Mary H.; ...

2015-03-01

Current-voltage (IV) characteristics of two AlGaN-based deep ultraviolet (DUV) light-emitting diodes (LEDs) with differing densities of open-core threading dislocations (nanopipes) are analyzed. A three-diode circuit is simulated to emulate the IV characteristics of the DUV-LEDs, but is only able to accurately model the lower leakage current, lower nanopipe density DUV-LED. It was found that current leakage through the nanopipes in these structures is rectifying, despite nanopipes being previously established as inherently n-type. Using defect-sensitive etching, the nanopipes are revealed to terminate within the p-type GaN capping layer of the DUV-LEDs. The circuit model is modified to account for another p-nmore » junction between the n-type nanopipes and the p-type GaN, and an excellent fit to the IV characteristics of the leaky DUV-LED is achieved.« less

Modeling of electron cyclotron resonance discharges

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meyyappan, M.; Govindan, T.R.

The current trend in plasma processing is the development of high density plasma sources to achieve high deposition and etch rates, uniformity over large ares, and low wafer damage. Here, is a simple model to predict the spatially-averaged plasma characteristics of electron cyclotron resonance (ECR) reactors is presented. The model consists of global conservation equations for species concentration, electron density and energy. A gas energy balance is used to predict the neutral temperature self-consistently. The model is demonstrated for an ECR argon discharge. The predicted behavior of the discharge as a function of system variables agrees well with experimental observations.

Radial tunnel diodes based on InP/InGaAs core-shell nanowires

NASA Astrophysics Data System (ADS)

Tizno, Ofogh; Ganjipour, Bahram; Heurlin, Magnus; Thelander, Claes; Borgström, Magnus T.; Samuelson, Lars

2017-03-01

We report on the fabrication and characterization of radial tunnel diodes based on InP(n+)/InGaAs(p+) core-shell nanowires, where the effect of Zn-dopant precursor flow on the electrical properties of the devices is evaluated. Selective and local etching of the InGaAs shell is employed to access the nanowire core in the contact process. Devices with an n+-p doping profile show normal diode rectification, whereas n+-p+ junctions exhibit typical tunnel diode characteristics with peak-to-valley current ratios up to 14 at room temperature and 100 at 4.2 K. A maximum peak current density of 28 A/cm2 and a reverse current density of 7.3 kA/cm2 at VSD = -0.5 V are extracted at room temperature after normalization with the effective junction area.

Impact of recess etching and surface treatments on ohmic contacts regrown by molecular-beam epitaxy for AlGaN/GaN high electron mobility transistors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Joglekar, S.; Azize, M.; Palacios, T.

Ohmic contacts fabricated by regrowth of n{sup +} GaN are favorable alternatives to metal-stack-based alloyed contacts in GaN-based high electron mobility transistors. In this paper, the influence of reactive ion dry etching prior to regrowth on the contact resistance in AlGaN/GaN devices is discussed. We demonstrate that the dry etch conditions modify the surface band bending, dangling bond density, and the sidewall depletion width, which influences the contact resistance of regrown contacts. The impact of chemical surface treatments performed prior to regrowth is also investigated. The sensitivity of the contact resistance to the surface treatments is found to depend uponmore » the dangling bond density of the sidewall facets exposed after dry etching. A theoretical model has been developed in order to explain the observed trends.« less

Self-etch and etch-and-rinse adhesive systems in clinical dentistry.

PubMed

Ozer, Fusun; Blatz, Markus B

2013-01-01

Current adhesive systems follow either an "etch-and-rinse" or "self-etch" approach, which differ in how they interact with natural tooth structures. Etch-and-rinse systems comprise phosphoric acid to pretreat the dental hard tissues before rinsing and subsequent application of an adhesive. Self-etch adhesives contain acidic monomers, which etch and prime the tooth simultaneously. Etch-and-rinse adhesives are offered as two- or three-step systems, depending on whether primer and bonding are separate or combined in a single bottle. Similarly, self-etch adhesives are available as one- or two-step systems. Both etch-and-rinse and self-etch systems form a hybrid layer as a result of resins impregnating the porous enamel or dentin. Despite current trends toward fewer and simpler clinical application steps, one-step dentin bonding systems exhibit bonding agent lower bond strengths and seem less predictable than multi-step etch-and-rinse and self-etch systems. The varying evidence available today suggests that the choice between etch-and-rinse and self-etch systems is often a matter of personal preference. In general, however, phosphoric acid creates a more pronounced and retentive etching pattern in enamel. Therefore, etch-and-rinse bonding systems are often preferred for indirect restorations and when large areas of enamel are still present. Conversely, self-etch adhesives provide superior and more predictable bond strength to dentin and are, consequently, recommended for direct composite resin restorations, especially when predominantly supported by dentin.

Correlation of III/V semiconductor etch results with physical parameters of high-density reactive plasmas excited by electron cyclotron resonance

NASA Astrophysics Data System (ADS)

Gerhard, FRANZ; Ralf, MEYER; Markus-Christian, AMANN

2017-12-01

Reactive ion etching is the interaction of reactive plasmas with surfaces. To obtain a detailed understanding of this process, significant properties of reactive composite low-pressure plasmas driven by electron cyclotron resonance (ECR) were investigated and compared with the radial uniformity of the etch rate. The determination of the electronic properties of chlorine- and hydrogen-containing plasmas enabled the understanding of the pressure-dependent behavior of the plasma density and provided better insights into the electronic parameters of reactive etch gases. From the electrical evaluation of I(V) characteristics obtained using a Langmuir probe, plasmas of different compositions were investigated. The standard method of Druyvesteyn to derive the electron energy distribution functions by the second derivative of the I(V) characteristics was replaced by a mathematical model which has been evolved to be more robust against noise, mainly, because the first derivative of the I(V) characteristics is used. Special attention was given to the power of the energy dependence in the exponent. In particular, for plasmas that are generated by ECR with EM modes, the existence of Maxwellian distribution functions is not to be taken as a self-evident fact, but the bi-Maxwellian distribution was proven for Ar- and Kr-stabilized plasmas. In addition to the electron temperature, the global uniform discharge model has been shown to be useful for calculating the neutral gas temperature. To what extent the invasive method of using a Langmuir probe could be replaced with the non-invasive optical method of emission spectroscopy, particularly actinometry, was investigated, and the resulting data exhibited the same relative behavior as the Langmuir data. The correlation with etchrate data reveals the large chemical part of the removal process—most striking when the data is compared with etching in pure argon. Although the relative amount of the radial variation of plasma density and etch rate is approximately +/- 5 % , the etch rate shows a slightly concave shape in contrast to the plasma density.

Surface microroughness of ion-beam etched optical surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Savvides, N.

2005-03-01

Ion-beam etching (IBE) and ion-beam figuring techniques using low-energy ion-beam sources have been applied for more than ten years in the fabrication and finishing of extremely smooth high-performance optics. We used optical interferometric techniques and atomic force microscopy to study the evolution of the surface root-mean-square (rms) microroughness, Rq, as a function of depth of a material removed (0-3000 nm) by a broad ion-beam source (Ar{sup +} ions of energy 600 eV and ion current density of 1 mA cm{sup -2}). Highly polished samples of fused silica and Zerodur (Rq{approx}3.5 A) showed a small decrease in microroughness (to 2.5 A)more » after 3000-nm IBE removal while an ultrapolished single-crystal sapphire sample (Rq{approx}1 A rms) retained its very low microroughness during IBE. Power spectral density functions over the spatial frequency interval of measurement (f=5x10{sup -3}-25 {mu}m{sup -1}) indicate that the IBE surfaces have minimal subsurface damage and low optical scatter.« less

Modeling and measurement of hydrogen radical densities of in situ plasma-based Sn cleaning source

NASA Astrophysics Data System (ADS)

Elg, Daniel T.; Panici, Gianluca A.; Peck, Jason A.; Srivastava, Shailendra N.; Ruzic, David N.

2017-04-01

Extreme ultraviolet (EUV) lithography sources expel Sn debris. This debris deposits on the collector optic used to focus the EUV light, lowering its reflectivity and EUV throughput to the wafer. Consequently, the collector must be cleaned, causing source downtime. To solve this, a hydrogen plasma source was developed to clean the collector in situ by using the collector as an antenna to create a hydrogen plasma and create H radicals, which etch Sn as SnH4. This technique has been shown to remove Sn from a 300-mm-diameter stainless steel dummy collector. The H radical density is of key importance in Sn etching. The effects of power, pressure, and flow on radical density are explored. A catalytic probe has been used to measure radical density, and a zero-dimensional model is used to provide the fundamental science behind radical creation and predict radical densities. Model predictions and experimental measurements are in good agreement. The trends observed in radical density, contrasted with measured Sn removal rates, show that radical density is not the limiting factor in this etching system; other factors, such as SnH4 redeposition and energetic ion bombardment, must be more fully understood in order to predict removal rates.

Carbon Nanotube Spaceframes for Low-Density Aerospace Materials

DTIC Science & Technology

2012-01-26

different types of oxidative etching chemistries have been reported in the literature, with acidic conditions such as nitric acid etching and piranha...and reduce the production of adhered fulvic acid species.1 A range of RCA type different etching conditions were investigated involving different...carboxylic and hydroxyl type sites together by first using a dicarboxylic acid (preferably in a highly reactive form such as oxalic chloride or succinic

Laser-etch patterning of metal oxide coated carbon nanotube 3D architectures.

PubMed

Aksu, Cemile; Ingram, Wade; Bradford, Philip D; Jur, Jesse S

2018-08-17

This paper describes a way to fabricate novel hybrid low density nanostructures containing both carbon nanotubes (CNTs) and ceramic nanotubes. Using atomic layer deposition, a thin film of aluminum oxide was conformally deposited on aligned multiwall CNT foams in which the CNTs make porous, three-dimensional interconnected networks. A CO 2 laser was used to etch pure alumina nanotube structures by burning out the underlying CNT substrate in discrete locations via the printed laser pattern. Structural and morphological transitions during the calcination process of aluminum oxide coated CNTs were investigated through in situ transmission electron microscopy and high-resolution scanning electron microscopy. Laser parameters were optimized to etch the CNT away (i.e. etching speed, power and focal length) while minimizing damage to the alumina nanotubes due to overheating. This study opens a new route for fabricating very low density three dimensionally patterned materials with areas of dissimilar materials and properties. To demonstrate the attributes of these structures, the etched areas were used toward anisotropic microfluidic liquid flow. The demonstration used the full thickness of the material to make complex pathways for the liquid flow in the structure. Through tuning of processing conditions, the alumina nanotube (etched) regions became hydrophilic while the bulk material remained hydrophobic and electrically conductive.

The endpoint detection technique for deep submicrometer plasma etching

NASA Astrophysics Data System (ADS)

Wang, Wei; Du, Zhi-yun; Zeng, Yong; Lan, Zhong-went

2009-07-01

The availability of reliable optical sensor technology provides opportunities to better characterize and control plasma etching processes in real time, they could play a important role in endpoint detection, fault diagnostics and processes feedback control and so on. The optical emission spectroscopy (OES) method becomes deficient in the case of deep submicrometer gate etching. In the newly developed high density inductively coupled plasma (HD-ICP) etching system, Interferometry endpoint (IEP) is introduced to get the EPD. The IEP fringe count algorithm is investigated to predict the end point, and then its signal is used to control etching rate and to call end point with OES signal in over etching (OE) processes step. The experiment results show that IEP together with OES provide extra process control margin for advanced device with thinner gate oxide.

Image analysis used to count and measure etched tracks from ionizing radiation

NASA Technical Reports Server (NTRS)

Blanford, George E.; Schulz, Cindy K.

1995-01-01

We have developed techniques to use digitized scanning electron micrographs and computer image analysis programs to measure track densities in lunar soil grains and plastic dosimeters. Tracks in lunar samples are formed by highly ionizing solar energetic particles and cosmic rays during near surface exposure on the Moon. The track densities are related to the exposure conditions (depth and time). Distributions of the number of grains as a function of their track densities can reveal the modality of soil maturation. We worked on two samples identified for a consortium study of lunar weathering effects, 61221 and 67701. They were prepared by the lunar curator's staff as polished grain mounts that were etched in boiling 1 N NaOH for 6 h to reveal tracks. We determined that backscattered electron images taken at 10 percent contrast and approximately 50 percent brightness produced suitable high contrast images for analysis. We used the NIH Image program to cut out areas that were unsuitable for measurement such as edges, cracks, etc. We ascertained a gray-scale threshold of 25 to separate tracks from background. We used the computer to count everything that was two pixels or greater in size and to measure the area to obtain track densities. We found an excellent correlation with manual measurements for track densities below 1 x 10(exp 8) cm(exp -2). For track densities between 1 x 10(exp 8) cm(exp -2) to 1 x 10(exp 9) cm(exp -2) we found that a regression formula using the percentage area covered by tracks gave good agreement with manual measurements. We determined the track density distributions for 61221 and 67701. Sample 61221 is an immature sample, but not pristine. Sample 67701 is a submature sample that is very close to being fully mature. Because only 10 percent of the grains have track densities less than 10(exp 9) cm(exp -2), it is difficulty to determine whether the sample matured in situ or is a mixture of a mature and a submature soil. Although our analysis of plastic dosimeters is at an early stage of development, results are encouraging. The dosimeter was etched in 6.25 N NaOH at 70 deg C for 16 h. We took 200x secondary electron images of the sample and used the NIH Image software to count and measure major and minor diameters of the etched tracks. We calculated the relative track etch rate from a formula that relates it to the major and minor diameters. We made a histogram of the number of tracks versus their relative etch rate. The relative track etching rate is proportional to the linear energy transfer of the particle. With appropriate calibration experiments, the histogram could be used to calculate the radiation dose.

Image analysis used to count and measure etched tracks from ionizing radiation

NASA Astrophysics Data System (ADS)

Blanford, George E.; Schulz, Cindy K.

1995-07-01

We have developed techniques to use digitized scanning electron micrographs and computer image analysis programs to measure track densities in lunar soil grains and plastic dosimeters. Tracks in lunar samples are formed by highly ionizing solar energetic particles and cosmic rays during near surface exposure on the Moon. The track densities are related to the exposure conditions (depth and time). Distributions of the number of grains as a function of their track densities can reveal the modality of soil maturation. We worked on two samples identified for a consortium study of lunar weathering effects, 61221 and 67701. They were prepared by the lunar curator's staff as polished grain mounts that were etched in boiling 1 N NaOH for 6 h to reveal tracks. We determined that backscattered electron images taken at 10 percent contrast and approximately 50 percent brightness produced suitable high contrast images for analysis. We used the NIH Image program to cut out areas that were unsuitable for measurement such as edges, cracks, etc. We ascertained a gray-scale threshold of 25 to separate tracks from background. We used the computer to count everything that was two pixels or greater in size and to measure the area to obtain track densities. We found an excellent correlation with manual measurements for track densities below 1 x 10(exp 8) cm(exp -2). For track densities between 1 x 10(exp 8) cm(exp -2) to 1 x 10(exp 9) cm(exp -2) we found that a regression formula using the percentage area covered by tracks gave good agreement with manual measurements. We determined the track density distributions for 61221 and 67701. Sample 61221 is an immature sample, but not pristine. Sample 67701 is a submature sample that is very close to being fully mature. Because only 10 percent of the grains have track densities less than 10(exp 9) cm(exp -2), it is difficulty to determine whether the sample matured in situ or is a mixture of a mature and a submature soil. Although our analysis of plastic dosimeters is at an early stage of development, results are encouraging. The dosimeter was etched in 6.25 N NaOH at 70 deg C for 16 h.

Characterization of Etch Pit Formation via the Everson-Etching Method on CdZnTe Crystal Surfaces from the Bulk to the Nano-Scale

DOE Office of Scientific and Technical Information (OSTI.GOV)

Teague, L.; Duff, M.; Cadieux, J.

2010-09-24

A combination of atomic force microscopy, optical microscopy, and mass spectrometry was employed to study CdZnTe crystal surface and used etchant solution following exposure of the CdZnTe crystal to the Everson etch solution. We discuss the results of these studies in relationship to the initial surface preparation methods, the performance of the crystals as radiation spectrometers, the observed etch pit densities, and the chemical mechanism of surface etching. Our results show that the surface features that are exposed to etchants result from interactions with the chemical components of the etchants as well as pre-existing mechanical polishing.

Cryogenic Etching of Silicon: An Alternative Method For Fabrication of Vertical Microcantilever Master Molds

PubMed Central

Addae-Mensah, Kweku A.; Retterer, Scott; Opalenik, Susan R.; Thomas, Darrell; Lavrik, Nickolay V.; Wikswo, John P.

2013-01-01

This paper examines the use of deep reactive ion etching (DRIE) of silicon with fluorine high-density plasmas at cryogenic temperatures to produce silicon master molds for vertical microcantilever arrays used for controlling substrate stiffness for culturing living cells. The resultant profiles achieved depend on the rate of deposition and etching of a SiOxFy polymer, which serves as a passivation layer on the sidewalls of the etched structures in relation to areas that have not been passivated with the polymer. We look at how optimal tuning of two parameters, the O2 flow rate and the capacitively coupled plasma (CCP) power, determine the etch profile. All other pertinent parameters are kept constant. We examine the etch profiles produced using e-beam resist as the main etch mask, with holes having diameters of 750 nm, 1 µm, and 2 µm. PMID:24223478

Performance improvement of GaN-based metal-semiconductor-metal photodiodes grown on Si(111) substrate by thermal cycle annealing process

NASA Astrophysics Data System (ADS)

Lin, Jyun-Hao; Huang, Shyh-Jer; Su, Yan-Kuin

2014-01-01

A simple thermal cycle annealing (TCA) process was used to improve the quality of GaN grown on a Si substrate. The X-ray diffraction (XRD) and etch pit density (EPD) results revealed that using more process cycles, the defect density cannot be further reduced. However, the performance of GaN-based metal-semiconductor-metal (MSM) photodiodes (PDs) prepared on Si substrates showed significant improvement. With a two-cycle TCA process, it is found that the dark current of the device was only 1.46 × 10-11 A, and the photo-to-dark-current contrast ratio was about 1.33 × 105 at 5 V. Also, the UV/visible rejection ratios can reach as high as 1077.

The effects of intragrain defects on the local photoresponse of polycrystalline silicon solar cells

NASA Astrophysics Data System (ADS)

Inoue, N.; Wilmsen, C. W.; Jones, K. A.

1981-02-01

Intragrain defects in Wacker cast and Monsanto zone-refined polycrystalline silicon materials were investigated using the electron-beam-induced current (EBIC) technique. The EBIC response maps were compared with etch pit, local diffusion length and local photoresponse measurements. It was determined that the Wacker polycrystalline silicon has a much lower density of defects than does the Monsanto polycrystalline silicon and that most of the defects in the Wacker material are not active recombination sites. A correlation was found between the recombination site density, as determined by EBIC, and the local diffusion length. It is shown that a large density of intragrain recombination sites greatly reduces the minority carrier diffusion length and thus can significantly reduce the photoresponse of solar cells.

The correlation of blue shift of photoluminescence and morphology of silicon nanoporous

DOE Office of Scientific and Technical Information (OSTI.GOV)

Al-Jumaili, Batool E. B., E-mail: batooleneaze@gmail.com; Department of Physics, Anbar University; Talib, Zainal A.

Porous silicon with diameters ranging from 6.41 to 7.12 nm were synthesized via electrochemical etching by varied anodization current density in ethanoic solutions containing aqueous hydrofluoric acid up to 65 mA/cm{sup 2}.The luminescence properties of the nanoporous at room temperature were analyzed via photoluminescence spectroscopy. Photoluminescence PL spectra exhibit a broad emission band in the range of 360-700 nm photon energy. The PL spectrum has a blue shift in varied anodization current density; the blue shift incremented as the existing of anodization although the intensity decreased. The current blue shift is owning to alteration of silicon nanocrystal structure at themore » superficies. The superficial morphology of the PS layers consists of unified and orderly distribution of nanocrystalline Si structures, have high porosity around (93.75%) and high thickness 39.52 µm.« less

A comparison of etched-geometry and overgrown silicon permeable base transistors by two-dimensional numerical simulations

NASA Astrophysics Data System (ADS)

Vojak, B. A.; Alley, G. D.

1983-08-01

Two-dimensional numerical simulations are used to compare etched geometry and overgrown Si permeable base transistors (PTBs), considering both the etched collector and etched emitter biasing conditions made possible by the asymmetry of the etched structure. In PTB devices, the two-dimensional nature of the depletion region near the Schottky contact base grating results in a smaller electron barrier and, therefore, a larger collector current in the etched than in the overgrown structure. The parasitic feedback effects which result at high base-to-emitter bias levels lead to a deviation from the square-law behavior found in the collector characteristics of the overgrown PBT. These structures also have lower device capacitances and smaller transconductances at high base-to-emitter voltages. As a result, overgrown and etched structures have comparable predicted maximum values of the small signal unity short-circuit current gain frequency and maximum oscillation frequency.

Alternative process for thin layer etching: Application to nitride spacer etching stopping on silicon germanium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Posseme, N., E-mail: nicolas.posseme@cea.fr; Pollet, O.; Barnola, S.

2014-08-04

Silicon nitride spacer etching realization is considered today as one of the most challenging of the etch process for the new devices realization. For this step, the atomic etch precision to stop on silicon or silicon germanium with a perfect anisotropy (no foot formation) is required. The situation is that none of the current plasma technologies can meet all these requirements. To overcome these issues and meet the highly complex requirements imposed by device fabrication processes, we recently proposed an alternative etching process to the current plasma etch chemistries. This process is based on thin film modification by light ionsmore » implantation followed by a selective removal of the modified layer with respect to the non-modified material. In this Letter, we demonstrate the benefit of this alternative etch method in term of film damage control (silicon germanium recess obtained is less than 6 A), anisotropy (no foot formation), and its compatibility with other integration steps like epitaxial. The etch mechanisms of this approach are also addressed.« less

Fabrication of high-quality superconductor-insulator-superconductor junctions on thin SiN membranes

NASA Technical Reports Server (NTRS)

Garcia, Edouard; Jacobson, Brian R.; Hu, Qing

1993-01-01

We have successfully fabricated high-quality and high-current density superconductor-insulator-superconductor (SIS) junctions on freestanding thin silicon nitride (SIN) membranes. These devices can be used in a novel millimeter-wave and THz receiver system which is made using micromachining. The SIS junctions with planar antennas were fabricated first on a silicon wafer covered with a SiN membrane, the Si wafer underneath was then etched away using an anisotropic KOH etchant. The current-voltage characteristics of the SIS junctions remained unchanged after the whole process, and the junctions and the membrane survived thermal cycling.

Method to fabricate functionalized conical nanopores

DOEpatents

Small, Leo J.; Spoerke, Erik David; Wheeler, David R.

2016-07-12

A pressure-based chemical etch method is used to shape polymer nanopores into cones. By varying the pressure, the pore tip diameter can be controlled, while the pore base diameter is largely unaffected. The method provides an easy, low-cost approach for conically etching high density nanopores.

Large-Diameter InGaAs/AlGaAs Vertical-Cavity Surface-Emitting Lasers with Low Threshold Current Density Fabricated Using a Simple Chemical Etch Process

DTIC Science & Technology

1994-03-01

Epitaxial structure of vertical cavity surface - emitting laser ( VCSEL ...diameter (75 tum < d< 150 prm) vertical - cavity surface - emitting lasers fabricated from an epitaxial structure containing a single In0 .2Ga 8.,As quantum...development of vertical - cavity surface - emitting lasers ( VCSELs ) [1] has enabled III-V semiconductor technology to be applied to cer- tain optical

Classification review of dental adhesive systems: from the IV generation to the universal type

PubMed Central

Sofan, Eshrak; Sofan, Afrah; Palaia, Gaspare; Tenore, Gianluca; Romeo, Umberto; Migliau, Guido

2017-01-01

Summary Adhesive dentistry has undergone great progress in the last decades. In light of minimal-invasive dentistry, this new approach promotes a more conservative cavity design, which relies on the effectiveness of current enamel-dentine adhesives. Adhesive dentistry began in 1955 by Buonocore on the benefits of acid etching. With changing technologies, dental adhesives have evolved from no-etch to total-etch (4th and 5th generation) to self-etch (6th, 7th and 8th generation) systems. Currently, bonding to dental substrates is based on three different strategies: 1) etch-and-rinse, 2) self-etch and 3) resin-modified glass-ionomer approach as possessing the unique properties of self-adherence to the tooth tissue. More recently, a new family of dentin adhesives has been introduced (universal or multi-mode adhesives), which may be used either as etch-and-rinse or as self-etch adhesives. The purpose of this article is to review the literature on the current knowledge for each adhesive system according to their classification that have been advocated by many authorities in most operative/restorative procedures. As noted by several valuable studies that have contributed to understanding of bonding to various substrates helps clinicians to choose the appropriate dentin bonding agents for optimal clinical outcomes. PMID:28736601

Reticulated shallow etch mesa isolation for controlling surface leakage in GaSb-based infrared detectors

NASA Astrophysics Data System (ADS)

Nolde, J. A.; Jackson, E. M.; Bennett, M. F.; Affouda, C. A.; Cleveland, E. R.; Canedy, C. L.; Vurgaftman, I.; Jernigan, G. G.; Meyer, J. R.; Aifer, E. H.

2017-07-01

Longwave infrared detectors using p-type absorbers composed of InAs-rich type-II superlattices (T2SLs) nearly always suffer from high surface currents due to carrier inversion on the etched sidewalls. Here, we demonstrate reticulated shallow etch mesa isolation (RSEMI): a structural method of reducing surface currents in longwave single-band and midwave/longwave dual-band detectors with p-type T2SL absorbers. By introducing a lateral shoulder to increase the separation between the n+ cathode and the inverted absorber surface, a substantial barrier to surface electron flow is formed. We demonstrate experimentally that the RSEMI process results in lower surface current, lower net dark current, much weaker dependence of the current on bias, and higher uniformity compared to mesas processed with a single deep etch. For the structure used, a shoulder width of 2 μm is sufficient to block surface currents.

New type of dummy layout pattern to control ILD etch rate

NASA Astrophysics Data System (ADS)

Pohland, Oliver; Spieker, Julie; Huang, Chih-Ta; Govindaswamy, Srikanth; Balasinski, Artur

2007-12-01

Adding dummy features (waffles) to drawn geometries of the circuit layout is a common practice to improve its manufacturability. As an example, local dummy pattern improves MOSFET line and space CD control by adjusting short range optical proximity and reducing the aggressiveness of its correction features (OPC) to widen the lithography process window. Another application of dummy pattern (waffles) is to globally equalize layout pattern density, to reduce long-range inter-layer dielectric (ILD) thickness variations after the CMP process and improve contact resistance uniformity over the die area. In this work, we discuss a novel type of dummy pattern with a mid-range interaction distance, to control the ILD composition driven by its deposition and etch process. This composition is reflected on sidewall spacers and depends on the topography of the underlying poly pattern. During contact etch, it impacts the etch rate of the ILD. As a result, the deposited W filling the damascene etched self-aligned trench contacts in the ILD may electrically short to the underlying gates in the areas of isolated poly. To mitigate the dependence of the ILD composition on poly pattern distribution, we proposed a special dummy feature generation with the interaction range defined by the ILD deposition and etch process. This helped equalize mid-range poly pattern density without disabling the routing capability with damascene trench contacts in the periphery which would have increased the layout footprint.

Large-Area Permanent-Magnet ECR Plasma Source

NASA Technical Reports Server (NTRS)

Foster, John E.

2007-01-01

A 40-cm-diameter plasma device has been developed as a source of ions for material-processing and ion-thruster applications. Like the device described in the immediately preceding article, this device utilizes electron cyclotron resonance (ECR) excited by microwave power in a magnetic field to generate a plasma in an electrodeless (noncontact) manner and without need for an electrically insulating, microwave-transmissive window at the source. Hence, this device offers the same advantages of electrodeless, windowless design - low contamination and long operational life. The device generates a uniform, high-density plasma capable of sustaining uniform ion-current densities at its exit plane while operating at low pressure [<10(exp -4) torr (less than about 1.3 10(exp -2) Pa)] and input power <200 W at a frequency of 2.45 GHz. Though the prototype model operates at 2.45 GHz, operation at higher frequencies can be achieved by straightforward modification to the input microwave waveguide. Higher frequency operation may be desirable in those applications that require even higher background plasma densities. In the design of this ECR plasma source, there are no cumbersome, power-hungry electromagnets. The magnetic field in this device is generated by a permanent-magnet circuit that is optimized to generate resonance surfaces. The microwave power is injected on the centerline of the device. The resulting discharge plasma jumps into a "high mode" when the input power rises above 150 W. This mode is associated with elevated plasma density and high uniformity. The large area and uniformity of the plasma and the low operating pressure are well suited for such material-processing applications as etching and deposition on large silicon wafers. The high exit-plane ion-current density makes it possible to attain a high rate of etching or deposition. The plasma potential is <3 V low enough that there is little likelihood of sputtering, which, in plasma processing, is undesired because it is associated with erosion and contamination. The electron temperature is low and does not vary appreciably with power.

Fabrication and characterization of active nanostructures

NASA Astrophysics Data System (ADS)

Opondo, Noah F.

Three different nanostructure active devices have been designed, fabricated and characterized. Junctionless transistors based on highly-doped silicon nanowires fabricated using a bottom-up fabrication approach are first discussed. The fabrication avoids the ion implantation step since silicon nanowires are doped in-situ during growth. Germanium junctionless transistors fabricated with a top down approach starting from a germanium on insulator substrate and using a gate stack of high-k dielectrics and GeO2 are also presented. The levels and origin of low-frequency noise in junctionless transistor devices fabricated from silicon nanowires and also from GeOI devices are reported. Low-frequency noise is an indicator of the quality of the material, hence its characterization can reveal the quality and perhaps reliability of fabricated transistors. A novel method based on low-frequency noise measurement to envisage trap density in the semiconductor bandgap near the semiconductor/oxide interface of nanoscale silicon junctionless transistors (JLTs) is presented. Low-frequency noise characterization of JLTs biased in saturation is conducted at different gate biases. The noise spectrum indicates either a Lorentzian or 1/f. A simple analysis of the low-frequency noise data leads to the density of traps and their energy within the semiconductor bandgap. The level of noise in silicon JLT devices is lower than reported values on transistors fabricated using a top-down approach. This noise level can be significantly improved by improving the quality of dielectric and the channel interface. A micro-vacuum electron device based on silicon field emitters for cold cathode emission is also presented. The presented work utilizes vertical Si nanowires fabricated by means of self-assembly, standard lithography and etching techniques as field emitters in this dissertation. To obtain a high nanowire density, hence a high current density, a simple and inexpensive Langmuir Blodgett technique to deposit silica nanoparticles as a mask to etch Si is adopted. Fabrication and characterization of a metal-gated microtriode with a high current density and low operating voltage are presented.

Toward a durable superhydrophobic aluminum surface by etching and ZnO nanoparticle deposition.

PubMed

Rezayi, Toktam; Entezari, Mohammad H

2016-02-01

Fabrication of suitable roughness is a fundamental step for acquiring superhydrophobic surfaces. For this purpose, a deposition of ZnO nanoparticles on Al surface was carried out by simple immersion and ultrasound approaches. Then, surface energy reduction was performed using stearic acid (STA) ethanol solution for both methods. The results demonstrated that ultrasound would lead to more stable superhydrophobic Al surfaces (STA-ZnO-Al-U) in comparison with simple immersion method (STA-ZnO-Al-I). Besides, etching in HCl solution in another sample was carried out before ZnO deposition for acquiring more mechanically stable superhydrophobic surface. The potentiodynamic measurements demonstrate that etching in HCl solution under ultrasound leads to superhydrophobic surface (STA-ZnO-Al(E)-U). This sample shows remarkable decrease in corrosion current density (icorr) and long-term stability improvement versus immersion in NaCl solution (3.5%) in comparison with the sample prepared without etching (STA-ZnO-Al-U). Scanning electron micrograph (SEM) and energy-dispersive X-ray spectroscopy (EDX) confirmed a more condense and further particle deposition on Al substrate when ultrasound was applied in the system. The crystallite evaluation of deposited ZnO nanoparticles was carried out using X-ray diffractometer (XRD). Finally, for STA grafting verification on Al surface, Fourier transform infrared in conjunction with attenuated total reflection (FTIR-ATR) was used as a proper technique. Copyright © 2015 Elsevier Inc. All rights reserved.

Photolithography-free laser-patterned HF acid-resistant chromium-polyimide mask for rapid fabrication of microfluidic systems in glass

NASA Astrophysics Data System (ADS)

Zamuruyev, Konstantin O.; Zrodnikov, Yuriy; Davis, Cristina E.

2017-01-01

Excellent chemical and physical properties of glass, over a range of operating conditions, make it a preferred material for chemical detection systems in analytical chemistry, biology, and the environmental sciences. However, it is often compromised with SU8, PDMS, or Parylene materials due to the sophisticated mask preparation requirements for wet etching of glass. Here, we report our efforts toward developing a photolithography-free laser-patterned hydrofluoric acid-resistant chromium-polyimide tape mask for rapid prototyping of microfluidic systems in glass. The patterns are defined in masking layer with a diode-pumped solid-state laser. Minimum feature size is limited to the diameter of the laser beam, 30 µm minimum spacing between features is limited by the thermal shrinkage and adhesive contact of the polyimide tape to 40 µm. The patterned glass substrates are etched in 49% hydrofluoric acid at ambient temperature with soft agitation (in time increments, up to 60 min duration). In spite of the simplicity, our method demonstrates comparable results to the other current more sophisticated masking methods in terms of the etched depth (up to 300 µm in borosilicate glass), feature under etch ratio in isotropic etch (~1.36), and low mask hole density. The method demonstrates high yield and reliability. To our knowledge, this method is the first proposed technique for rapid prototyping of microfluidic systems in glass with such high performance parameters. The proposed method of fabrication can potentially be implemented in research institutions without access to a standard clean-room facility.

Note: Circuit design for direct current and alternating current electrochemical etching of scanning probe microscopy tips.

PubMed

Jobbins, Matthew M; Raigoza, Annette F; Kandel, S Alex

2012-03-01

We present control circuits designed for electrochemically etching, reproducibly sharp STM probes. The design uses an Arduino UNO microcontroller to allow for both ac and dc operation, as well as a comparator driven shut-off that allows for etching to be stopped in 0.5-1 μs. The Arduino allows the instrument to be customized to suit a wide variety of potential applications without significant changes to hardware. Data is presented for coarse chemical etching of 80:20 platinum-iridium, tungsten, and nickel tips.

Etching Characteristics of VO2 Thin Films Using Inductively Coupled Cl2/Ar Plasma

NASA Astrophysics Data System (ADS)

Ham, Yong-Hyun; Efremov, Alexander; Min, Nam-Ki; Lee, Hyun Woo; Yun, Sun Jin; Kwon, Kwang-Ho

2009-08-01

A study on both etching characteristics and mechanism of VO2 thin films in the Cl2/Ar inductively coupled plasma was carried. The variable parameters were gas pressure (4-10 mTorr) and input power (400-700 W) at fixed bias power of 150 W and initial mixture composition of 25% Cl2 + 75% Ar. It was found that an increase in both gas pressure and input power results in increasing VO2 etch rate while the etch selectivity over photoresist keeps a near to constant values. Plasma diagnostics by Langmuir probes and zero-dimensional plasma model provided the data on plasma parameters, steady-state densities and fluxes of active species on the etched surface. The model-based analysis of the etch mechanism showed that, for the given ranges of operating conditions, the VO2 etch kinetics corresponds to the transitional regime of ion-assisted chemical reaction and is influenced by both neutral and ion fluxes with a higher sensitivity to the neutral flux.

Reparable, high-density microelectronic module provides effective heat sink

NASA Technical Reports Server (NTRS)

Carlson, K. J.; Maytone, F. F.

1967-01-01

Reparable modular system is used for packaging microelectronic flat packs and miniature discrete components. This three-dimensional compartmented structure incorporates etched phosphor bronze sheets and frames with etched wire conductors. It provides an effective heat sink for electric power dissipation in the absence of convective cooling means.

Simulation of SiO2 etching in an inductively coupled CF4 plasma

NASA Astrophysics Data System (ADS)

Xu, Qing; Li, Yu-Xing; Li, Xiao-Ning; Wang, Jia-Bin; Yang, Fan; Yang, Yi; Ren, Tian-Ling

2017-02-01

Plasma etching technology is an indispensable processing method in the manufacturing process of semiconductor devices. Because of the high fluorine/carbon ratio of CF4, the CF4 gas is often used for etching SiO2. A commercial software ESI-CFD is used to simulate the process of plasma etching with an inductively coupled plasma model. For the simulation part, CFD-ACE is used to simulate the chamber, and CFD-TOPO is used to simulate the surface of the sample. The effects of chamber pressure, bias voltage and ICP power on the reactant particles were investigated, and the etching profiles of SiO2 were obtained. Simulation can be used to predict the effects of reaction conditions on the density, energy and angular distributions of reactant particles, which can play a good role in guiding the etching process.

Effects of epitaxial structure and processing on electrical characteristics of InAs-based nBn infrared detectors

NASA Astrophysics Data System (ADS)

Du, X.; Savich, G. R.; Marozas, B. T.; Wicks, G. W.

2017-02-01

The conventional processing of the III-V nBn photodetectors defines mesa devices by etching the contact n-layer and stopping immediately above the barrier, i.e., a shallow etch. This processing enables great suppression of surface leakage currents without having to explore surface passivation techniques. However, devices that are made with this processing scheme are subject to lateral diffusion currents. To address the lateral diffusion current, we compare the effects of different processing approaches and epitaxial structures of nBn detectors. The conventional solution for eliminating lateral diffusion current, a deep etch through the barrier and the absorber, creates increased dark currents and an increased device failure rate. To avoid deep etch processing, a new device structure is proposed, the inverted-nBn structure. By comparing with the conventional nBn structure, the results show that the lateral diffusion current is effectively eliminated in the inverted-nBn structure without elevating the dark currents.

One-Dimensional Porous Silicon Nanowires with Large Surface Area for Fast Charge⁻Discharge Lithium-Ion Batteries.

PubMed

Chen, Xu; Bi, Qinsong; Sajjad, Muhammad; Wang, Xu; Ren, Yang; Zhou, Xiaowei; Xu, Wen; Liu, Zhu

2018-04-27

In this study, one-dimensional porous silicon nanowire (1D⁻PSiNW) arrays were fabricated by one-step metal-assisted chemical etching (MACE) to etch phosphorus-doped silicon wafers. The as-prepared mesoporous 1D⁻PSiNW arrays here had especially high specific surface areas of 323.47 m²·g -1 and were applied as anodes to achieve fast charge⁻discharge performance for lithium ion batteries (LIBs). The 1D⁻PSiNWs anodes with feature size of ~7 nm exhibited reversible specific capacity of 2061.1 mAh·g -1 after 1000 cycles at a high current density of 1.5 A·g -1 . Moreover, under the ultrafast charge⁻discharge current rate of 16.0 A·g -1 , the 1D⁻PSiNWs anodes still maintained 586.7 mAh·g -1 capacity even after 5000 cycles. This nanoporous 1D⁻PSiNW with high surface area is a potential anode candidate for the ultrafast charge⁻discharge in LIBs with high specific capacity and superior cycling performance.

Normally-off p-GaN/AlGaN/GaN high electron mobility transistors using hydrogen plasma treatment

NASA Astrophysics Data System (ADS)

Hao, Ronghui; Fu, Kai; Yu, Guohao; Li, Weiyi; Yuan, Jie; Song, Liang; Zhang, Zhili; Sun, Shichuang; Li, Xiajun; Cai, Yong; Zhang, Xinping; Zhang, Baoshun

2016-10-01

In this letter, we report a method by introducing hydrogen plasma treatment to realize normally-off p-GaN/AlGaN/GaN HEMT devices. Instead of using etching technology, hydrogen plasma was adopted to compensate holes in the p-GaN above the two dimensional electron gas (2DEG) channel to release electrons in the 2DEG channel and form high-resistivity area to reduce leakage current and increase gate control capability. The fabricated p-GaN/AlGaN/GaN HEMT exhibits normally-off operation with a threshold voltage of 1.75 V, a subthreshold swing of 90 mV/dec, a maximum transconductance of 73.1 mS/mm, an ON/OFF ratio of 1 × 107, a breakdown voltage of 393 V, and a maximum drain current density of 188 mA/mm at a gate bias of 6 V. The comparison of the two processes of hydrogen plasma treatment and p-GaN etching has also been made in this work.

Design and fabrication of low power GaAs/AlAs resonant tunneling diodes

NASA Astrophysics Data System (ADS)

Md Zawawi, Mohamad Adzhar; Missous, Mohamed

2017-12-01

A very low peak voltage GaAs/AlAs resonant tunneling diode (RTD) grown by molecular beam epitaxy (MBE) has been studied in detail. Excellent growth control with atomic-layer precision resulted in a peak voltage of merely 0.28 V (0.53 V) in forward (reverse) direction. The peak current density in forward bias is around 15.4 kA/cm2 with variation of within 7%. As for reverse bias, the peak current density is around 22.8 kA/cm2 with 4% variation which implies excellent scalability. In this work, we have successfully demonstrated the fabrication of a GaAs/AlAs RTD by using a conventional optical lithography and chemical wet-etching with very low peak voltage suitable for application in low dc input power RTD-based sub-millimetre wave oscillators.

Photo-electrochemically synthesized light emtting nanoporous silicon based UV photodetector: influence of current density

NASA Astrophysics Data System (ADS)

Thahe, Asad A.; Bidin, Noriah; Hassan, Z.; Bakhtiar, Hazri; Qaeed, M. A.; Bououdina, Mohamed; Ahmed, Naser M.; Talib, Zainal A.; Al-Azawi, Mohammed A.; Alqaraghuli, Hasan; Uday, M. B.; Hamad Ahmed, Omar

2017-11-01

Nanoporous silicon (n-PSi) with diverse morphologies was prepared on silicon (Si) substrate via photo-electrochemical etching technique. The role of changing current density (15, 30 and 45 mA cm-2) on the structure, morphology and optical properties was determined. As-prepared samples were systematically characterized using XRD, FESEM, AFM and photoluminescence measurements. Furthermore, the achieved n-PSi sample was used to make metal-semiconductor-metal (MSM) UV photodetector. The performance of these photodetectors was evaluated upon exposing to visible light of wavelength 530 nm (power density 1.55 mW cm-2), which exhibited very high sensitivity of 150.26 with a low dark current. The achieved internal photoconductive gain was 2.50, the photoresponse peak was 1.23 A W-1 and the response time was 0.49 s and the recovery time was 0.47 s. Excellent attributes of the fabricated photodetectors suggest that the present approach may provide a cost effective and simple way to obtain n-PSi suitable for sundry applications.

Growth and field emission properties of tubular carbon cones.

PubMed

Li, J J; Wang, Q; Gu, C Z

2007-09-01

New forms of tubular carbon cone (TCC) were grown on gold wires by hot-filament chemical vapor deposition (HFCVD). They have a long-cone-shaped appearance with a herringbone hollow interior, surrounded by helical sheets of graphite that are coiled around it. It is considered that TCC formation results because the size of the catalyst particle located in the top of the TCC decreases continuously during growth, due to etching effects in the CVD plasma, reflecting competition between the growth and etching processes in the plasma. In addition, field emission measurements show that TCCs have a very low-threshold field of 0.27 V/microm, and that a stable macroscopic emitting current density of 1 mA/cm2 can be obtained at only 0.5 V/microm. TCCs have good field emission properties, compared to other forms of carbon field emitter, and may be good candidates for use in field emission display devices.

Study on Silicon Microstructure Processing Technology Based on Porous Silicon

NASA Astrophysics Data System (ADS)

Shang, Yingqi; Zhang, Linchao; Qi, Hong; Wu, Yalin; Zhang, Yan; Chen, Jing

2018-03-01

Aiming at the heterogeneity of micro - sealed cavity in silicon microstructure processing technology, the technique of preparing micro - sealed cavity of porous silicon is proposed. The effects of different solutions, different substrate doping concentrations, different current densities, and different etching times on the rate, porosity, thickness and morphology of the prepared porous silicon were studied. The porous silicon was prepared by different process parameters and the prepared porous silicon was tested and analyzed. For the test results, optimize the process parameters and experiments. The experimental results show that the porous silicon can be controlled by optimizing the parameters of the etching solution and the doping concentration of the substrate, and the preparation of porous silicon with different porosity can be realized by different doping concentration, so as to realize the preparation of silicon micro-sealed cavity, to solve the sensor sensitive micro-sealed cavity structure heterogeneous problem, greatly increasing the application of the sensor.

Evaluation of Pentafluoroethane and 1,1-Difluoroethane for a Dielectric Etch Application in an Inductively Coupled Plasma Etch Tool

NASA Astrophysics Data System (ADS)

Karecki, Simon; Chatterjee, Ritwik; Pruette, Laura; Reif, Rafael; Sparks, Terry; Beu, Laurie; Vartanian, Victor

2000-07-01

In this work, a combination of two hydrofluorocarbon compounds, pentafluoroethane (FC-125, C2HF5) and 1,1-difluoroethane (FC-152a, CF2H-CH3), was evaluated as a potential replacement for perfluorocompounds in dielectric etch applications. A high aspect ratio oxide via etch was used as the test vehicle for this study, which was conducted in a commercial inductively coupled high density plasma etch tool. Both process and emissions data were collected and compared to those provided by a process utilizing a standard perfluorinated etch chemistry (C2F6). Global warming (CF4, C2F6, CHF3) and hygroscopic gas (HF, SiF4) emissions were characterized using Fourier transform infrared (FTIR) spectroscopy. FC-125/FC-152a was found to produce significant reductions in global warming emissions, on the order of 68 to 76% relative to the reference process. Although etch stopping, caused by a high degree of polymer deposition inside the etched features, was observed, process data otherwise appeared promising for an initial study, with good resist selectivity and etch rates being achieved.

Mechanical and chemical effects of ion-texturing biomedical polymers

NASA Technical Reports Server (NTRS)

Weigand, A. J.; Cenkus, M. A.

1979-01-01

To determine whether sputter etching may provide substantial polymer surface texturing with insignificant changes in chemical and mechanical properties, an 8 cm beam diameter, electron bombardment, argon ion source was used to sputter etch (ion-texture process) nine biomedical polymers. The materials included silicone rubber, 32% carbon impregnated polyolefin, polyoxymethylene, polytetrafluoroethylene, ultrahigh molecular weight (UHMW) polyethylene, UHMW polyethylene with carbon fibers (10%), and several polyurethanes (bioelectric, segmented, and cross linked). Ion textured microtensile specimens of each material except UHMW polyethylene and UHMW polyethylene with 10% carbon fibers were used to determine the effect of ion texturing on tensile properties. Scanning electron microscopy was used to determine surface morphology changes, and electron spectroscopy for chemical analysis was used to analyze the near surface chemical changes that result from ion texturing. Ion energies of 500 eV with beam current densities ranging from 0.08 to 0.19 mA/sq cm were used to ion texture the various materials. Standard microtensile specimens of seven polymers were exposed to a saline environment for 24 hours prior to and during the tensile testing. The surface chemical changes resulting from sputter etching are minimal in spite of the often significant changes in the surface morphology.

Low resistivity of graphene nanoribbons with zigzag-dominated edge fabricated by hydrogen plasma etching combined with Zn/HCl pretreatment

NASA Astrophysics Data System (ADS)

Liu, Fengkui; Li, Qi; Wang, Rubing; Xu, Jianbao; Hu, Junxiong; Li, Weiwei; Guo, Yufen; Qian, Yuting; Deng, Wei; Ullah, Zaka; Zeng, Zhongming; Sun, Mengtao; Liu, Liwei

2017-11-01

Graphene nanoribbons (GNRs) have attracted intensive research interest owing to their potential applications in high performance graphene-based electronics. However, the deterioration of electrical performance caused by edge disorder is still an important obstacle to the applications. Here, we report the fabrication of low resistivity GNRs with a zigzag-dominated edge through hydrogen plasma etching combined with the Zn/HCl pretreatment method. This method is based on the anisotropic etching properties of hydrogen plasma in the vicinity of defects created by sputtering zinc (Zn) onto planar graphene. The polarized Raman spectra measurement of GNRs exhibits highly polarization dependence, which reveals the appearance of the zigzag-dominated edge. The as-prepared GNRs exhibit high carrier mobility (˜1332.4 cm2 v-1 s-1) and low resistivity (˜0.7 kΩ) at room temperature. Particularly, the GNRs can carry large current density (5.02 × 108 A cm-2) at high voltage (20.0 V) in the air atmosphere. Our study develops a controllable method to fabricate zigzag edge dominated GNRs for promising applications in transistors, sensors, nanoelectronics, and interconnects.

Characterization of Plasma-Induced Damage of Selectively Recessed GaN/InAlN/AlN/GaN Heterostructures Using SiCl4 and SF6

NASA Astrophysics Data System (ADS)

Ostermaier, Clemens; Pozzovivo, Gianmauro; Basnar, Bernhard; Schrenk, Werner; Carlin, Jean-François; Gonschorek, Marcus; Grandjean, Nicolas; Vincze, Andrej; Tóth, Lajos; Pécz, Bela; Strasser, Gottfried; Pogany, Dionyz; Kuzmik, Jan

2010-11-01

We have investigated an inductively coupled plasma etching recipe using SiCl4 and SF6 with a resulting selectivity >10 for GaN in respect to InAlN. The formation of an etch-resistant layer of AlF3 on InAlN required about 1 min and was noticed by a 4-times-higher initial etch rate on bare InAlN barrier high electron mobility transistors (HEMTs). Comparing devices with and without plasma-treatment below the gate showed no degradation in drain current and gate leakage current for plasma exposure durations shorter than 30 s, indicating no plasma-induced damage of the InAlN barrier. Devices etched longer than the required time for the formation of the etch-resistant barrier exhibited a slight decrease in drain current and an increase in gate leakage current which saturated for longer etching-time durations. Finally, we could prove the quality of the recipe by recessing the highly doped 6 nm GaN cap layer of a GaN/InAlN/AlN/GaN heterostructure down to the 2 nm thin InAlN/AlN barrier layer.

Single Etch-Pit Shape on Off-Angled 4H-SiC(0001) Si-Face Formed by Chlorine Trifluoride

NASA Astrophysics Data System (ADS)

Hatayama, Tomoaki; Tamura, Tetsuya; Yano, Hiroshi; Fuyuki, Takashi

2012-07-01

The etch pit shape of an off-angled 4H-SiC Si-face formed by chlorine trifluoride (ClF3) in nitrogen (N2) ambient has been studied. One type of etch pit with a crooked hexagonal shape was formed at an etching temperature below 500 °C. The angle of the etch pit measured from a cross-sectional atomic force microscopy image was about 10° from the [11bar 20] view. The dislocation type of the etch pit was discussed in relation to the etch pit shape and an electron-beam-induced current image.

Stability of field emission current from porous n-GaAs(110)

NASA Astrophysics Data System (ADS)

Tondare, V. N.; Naddaf, M.; Bhise, A. B.; Bhoraskar, S. V.; Joag, D. S.; Mandale, A. B.; Sainkar, S. R.

2002-02-01

Field electron emission from porous GaAs has been investigated. The emitter was prepared by anodic etching of n-GaAs (110) in 0.1 M HCl solution. The as-etched porous GaAs shows nonlinear Fowler-Nordheim (FN) characteristics, with a low onset voltage. The emitter, after operating for 6 h at the residual gas pressure of 1×10-8 mbar, shows a linear FN characteristics with a relatively high onset voltage and poor field emission current stability as compared to the as-etched emitter. The change in the behavior was attributed to the residual gas ion bombardment during field electron emission. X-ray photoelectron spectroscopic investigations were carried out on as-etched sample and the one which was studied for field emission. The studies indicate that the as-etched surface contains As2O3 and the surface after field electron emission for about 6 h becomes gallium rich. The presence of As2O3 seems to be a desirable feature for the stable field emission current.

Qualitative modeling of silica plasma etching using neural network

NASA Astrophysics Data System (ADS)

Kim, Byungwhan; Kwon, Kwang Ho

2003-01-01

An etching of silica thin film is qualitatively modeled by using a neural network. The process was characterized by a 23 full factorial experiment plus one center point, in which the experimental factors and ranges include 100-800 W radio-frequency source power, 100-400 W bias power and gas flow rate ratio CHF3/CF4. The gas flow rate ratio varied from 0.2 to 5.0. The backpropagation neural network (BPNN) was trained on nine experiments and tested on six experiments, not pertaining to the original training data. The prediction ability of the BPNN was optimized as a function of the training parameters. Prediction errors are 180 Å/min and 1.33, for the etch rate and anisotropy models, respectively. Physical etch mechanisms were estimated from the three-dimensional plots generated from the optimized models. Predicted response surfaces were consistent with experimentally measured etch data. The dc bias was correlated to the etch responses to evaluate its contribution. Both the source power (plasma density) and bias power (ion directionality) strongly affected the etch rate. The source power was the most influential factor for the etch rate. A conflicting effect between the source and bias powers was noticed with respect to the anisotropy. The dc bias played an important role in understanding or separating physical etch mechanisms.

Quantum cascade laser based monitoring of CF{sub 2} radical concentration as a diagnostic tool of dielectric etching plasma processes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hübner, M.; Lang, N.; Röpcke, J.

2015-01-19

Dielectric etching plasma processes for modern interlevel dielectrics become more and more complex by the introduction of new ultra low-k dielectrics. One challenge is the minimization of sidewall damage, while etching ultra low-k porous SiCOH by fluorocarbon plasmas. The optimization of this process requires a deeper understanding of the concentration of the CF{sub 2} radical, which acts as precursor in the polymerization of the etch sample surfaces. In an industrial dielectric etching plasma reactor, the CF{sub 2} radical was measured in situ using a continuous wave quantum cascade laser (cw-QCL) around 1106.2 cm{sup −1}. We measured Doppler-resolved ro-vibrational absorption lines andmore » determined absolute densities using transitions in the ν{sub 3} fundamental band of CF{sub 2} with the aid of an improved simulation of the line strengths. We found that the CF{sub 2} radical concentration during the etching plasma process directly correlates to the layer structure of the etched wafer. Hence, this correlation can serve as a diagnostic tool of dielectric etching plasma processes. Applying QCL based absorption spectroscopy opens up the way for advanced process monitoring and etching controlling in semiconductor manufacturing.« less

Transport of a helicon plasma by a convergent magnetic field for high speed and compact plasma etching

NASA Astrophysics Data System (ADS)

Takahashi, Kazunori; Motomura, Taisei; Ando, Akira; Kasashima, Yuji; Kikunaga, Kazuya; Uesugi, Fumihiko; Hara, Shiro

2014-10-01

A high density argon plasma produced in a compact helicon source is transported by a convergent magnetic field to the central region of a substrate located downstream of the source. The magnetic field converging near the source exit is applied by a solenoid and further converged by installing a permanent magnet (PM) behind the substrate, which is located downstream of the source exit. Then a higher plasma density above 5 × 1012 cm-3 can be obtained in 0.2 Pa argon near the substrate, compared with the case without the PM. As no noticeable changes in the radially integrated density near the substrate and the power transfer efficiency are detected when testing the source with and without the PM, it can be deduced that the convergent field provided by the PM plays a role in constricting the plasma rather than in improving the plasma production. Furthermore it is applied to physical ion etching of silicon and aluminum substrates; then high etching rates of 6.5 µm min-1 and 8 µm min-1 are obtained, respectively.

Controllable Fabrication of Non-Close-Packed Colloidal Nanoparticle Arrays by Ion Beam Etching

NASA Astrophysics Data System (ADS)

Yang, Jie; Zhang, Mingling; Lan, Xu; Weng, Xiaokang; Shu, Qijiang; Wang, Rongfei; Qiu, Feng; Wang, Chong; Yang, Yu

2018-06-01

Polystyrene (PS) nanoparticle films with non-close-packed arrays were prepared by using ion beam etching technology. The effects of etching time, beam current, and voltage on the size reduction of PS particles were well investigated. A slow etching rate, about 9.2 nm/min, is obtained for the nanospheres with the diameter of 100 nm. The rate does not maintain constant with increasing the etching time. This may result from the thermal energy accumulated gradually in a long-time bombardment of ion beam. The etching rate increases nonlinearly with the increase of beam current, while it increases firstly then reach its saturation with the increase of beam voltage. The diameter of PS nanoparticles can be controlled in the range from 34 to 88 nm. Based on the non-close-packed arrays of PS nanoparticles, the ordered silicon (Si) nanopillars with their average diameter of 54 nm are fabricated by employing metal-assisted chemical etching technique. Our results pave an effective way to fabricate the ordered nanostructures with the size less than 100 nm.

On-site SiH4 generator using hydrogen plasma generated in slit-type narrow gap

NASA Astrophysics Data System (ADS)

Takei, Norihisa; Shinoda, Fumiya; Kakiuchi, Hiroaki; Yasutake, Kiyoshi; Ohmi, Hiromasa

2018-06-01

We have been developing an on-site silane (SiH4) generator based on use of the chemical etching reaction between solid silicon (Si) and the high-density H atoms that are generated in high-pressure H2 plasma. In this study, we have developed a slit-type plasma source for high-efficiency SiH4 generation. High-density H2 plasma was generated in a narrow slit-type discharge gap using a 2.45 GHz microwave power supply. The plasma’s optical emission intensity distribution along the slit was measured and the resulting distribution was reflected by both the electric power distribution and the hydrogen gas flow. Because the Si etching rate strongly affects the SiH4 generation rate, the Si etching behavior was investigated with respect to variations in the experimental parameters. The weight etch rate increased monotonically with increasing input microwave power. However, the weight etch rate decreased with increasing H2 pressure and an increasing plasma gap. This reduction in the etch rate appears to be related to shrinkage of the plasma generation area because increased input power is required to maintain a constant plasma area with increasing H2 pressure and the increasing plasma gap. Additionally, the weight etch rate also increases with increasing H2 flow rate. The SiH4 generation rate of the slit-type plasma source was also evaluated using gas-phase Fourier transform infrared absorption spectroscopy and the material utilization efficiencies of both Si and the H2 gas for SiH4 gas formation were discussed. The main etch product was determined to be SiH4 and the developed plasma source achieved a SiH4 generation rate of 10 sccm (standard cubic centimeters per minute) at an input power of 900 W. In addition, the Si utilization efficiency exceeded 60%.

Reactive ion etching of indium-tin oxide films by CCl4-based Inductivity Coupled Plasma

NASA Astrophysics Data System (ADS)

Juneja, Sucheta; Poletayev, Sergey D.; Fomchenkov, Sergey; Khonina, Svetlana N.; Skidanov, Roman V.; Kazanskiy, Nikolay L.

2016-08-01

Indium tin oxide (ITO) films have been a subject of extensive studies in fabrication of micro-electronic devices for opto-electronic applications ranging from anti-reflection coatings to transparent contacts in photovoltaic devices. In this paper, a new and effective way of reactive ion etching of a conducting indium-tin oxide (ITO) film with Carbon tetrachloride (CCl4) has been investigated. CCl4 plasma containing an addition of gases mixture of dissociated argon and oxygen were used. Oxygen is added to increase the etchant percentage whereas argon was used for stabilization of plasma. The etching characteristics obtained with these gaseous mixtures were explained based on plasma etch chemistry and etching regime of ITO films. An etch rate as high as ∼20 nm/min can be achieved with a controlled process parameter such as power density, total flow rate, composition of reactive gases gas and pressure. Our Investigation represents some of the extensive work in this area.

Damage-Free Smooth-Sidewall InGaAs Nanopillar Array by Metal-Assisted Chemical Etching.

PubMed

Kong, Lingyu; Song, Yi; Kim, Jeong Dong; Yu, Lan; Wasserman, Daniel; Chim, Wai Kin; Chiam, Sing Yang; Li, Xiuling

2017-10-24

Producing densely packed high aspect ratio In 0.53 Ga 0.47 As nanostructures without surface damage is critical for beyond Si-CMOS nanoelectronic and optoelectronic devices. However, conventional dry etching methods are known to produce irreversible damage to III-V compound semiconductors because of the inherent high-energy ion-driven process. In this work, we demonstrate the realization of ordered, uniform, array-based In 0.53 Ga 0.47 As pillars with diameters as small as 200 nm using the damage-free metal-assisted chemical etching (MacEtch) technology combined with the post-MacEtch digital etching smoothing. The etching mechanism of In x Ga 1-x As is explored through the characterization of pillar morphology and porosity as a function of etching condition and indium composition. The etching behavior of In 0.53 Ga 0.47 As, in contrast to higher bandgap semiconductors (e.g., Si or GaAs), can be interpreted by a Schottky barrier height model that dictates the etching mechanism constantly in the mass transport limited regime because of the low barrier height. A broader impact of this work relates to the complete elimination of surface roughness or porosity related defects, which can be prevalent byproducts of MacEtch, by post-MacEtch digital etching. Side-by-side comparison of the midgap interface state density and flat-band capacitance hysteresis of both the unprocessed planar and MacEtched pillar In 0.53 Ga 0.47 As metal-oxide-semiconductor capacitors further confirms that the surface of the resultant pillars is as smooth and defect-free as before etching. MacEtch combined with digital etching offers a simple, room-temperature, and low-cost method for the formation of high-quality In 0.53 Ga 0.47 As nanostructures that will potentially enable large-volume production of In 0.53 Ga 0.47 As-based devices including three-dimensional transistors and high-efficiency infrared photodetectors.

Platinum-catalyzed hydrolysis etching of SiC in water: A density functional theory study

NASA Astrophysics Data System (ADS)

Van Bui, Pho; Toh, Daisetsu; Isohashi, Ai; Matsuyama, Satoshi; Inagaki, Kouji; Sano, Yasuhisa; Yamauchi, Kazuto; Morikawa, Yoshitada

2018-05-01

A comprehensive study of the physicochemical interactions and the reaction mechanism of SiC etching with water by Pt catalysts can reveal key details about the surface treatment and catalytic phenomena at interfaces. Therefore, density functional theory simulations were performed to study the kinetics of Pt-assisted water dissociation and breaking of a Si–C bond compared to the HF-assisted mechanism. These calculations carefully considered the elastic and chemical interaction energies at the Pt–SiC interface, activation barriers of Si–C bond dissociation, and the catalytic role of Pt. It was found that the Pt-catalyzed etching of SiC in water is initiated via hydrolysis reactions that break the topmost Si–C bonds. The activation barrier strongly depends on the elastic and chemical interactions. However, chemical interactions are a dominant factor and mainly contribute to the lowering of the activation barrier, resulting in an increased rate of reaction.

High electronegativity multi-dipolar electron cyclotron resonance plasma source for etching by negative ions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stamate, E.; Draghici, M.

2012-04-15

A large area plasma source based on 12 multi-dipolar ECR plasma cells arranged in a 3 x 4 matrix configuration was built and optimized for silicon etching by negative ions. The density ratio of negative ions to electrons has exceeded 300 in Ar/SF{sub 6} gas mixture when a magnetic filter was used to reduce the electron temperature to about 1.2 eV. Mass spectrometry and electrostatic probe were used for plasma diagnostics. The new source is free of density jumps and instabilities and shows a very good stability for plasma potential, and the dominant negative ion species is F{sup -}. Themore » magnetic field in plasma volume is negligible and there is no contamination by filaments. The etching rate by negative ions measured in Ar/SF{sub 6}/O{sub 2} mixtures was almost similar with that by positive ions reaching 700 nm/min.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pak, S.; Sites, J.R.

A Kaufman-type broad beam ion source, used for sputtering and etching purposes, has been operated with Ar, Kr,O/sub 2/ and N/sub 2/ gas inputs over a wide range of beam energies (200-1200 eV) and gas flow rates (1-10 sccm). The maximum ion beam current density for each gas saturates at about 2.5 mA/sq. cm. as gas flow is increased. The discharge threshold voltage necessary to produce a beam and the beam efficiency (beam current/molecular current), however, varied considerably. Kr had the lowest threshold and highest efficiency, Ar next, then N/sub 2/ and O/sub 2/. The ion beam current varied onlymore » weakly with beam energy for low gas flow rates, but showed a factor of two increase when the gas flow was higher.« less

Progress in Electron Beam Mastering of 100 Gbit/inch2 Density Disc

NASA Astrophysics Data System (ADS)

Takeda, Minoru; Furuki, Motohiro; Yamamoto, Masanobu; Shinoda, Masataka; Saito, Kimihiro; Aki, Yuichi; Kawase, Hiroshi; Koizumi, Mitsuru; Miyokawa, Toshiaki; Mutou, Masao; Handa, Nobuo

2004-07-01

We developed an electron beam recorder (EBR) capable of recording master discs under atmospheric conditions using a novel differential pumping head. Using the EBR and optimized fabrication process for Si-etched discs with reactive ion etching (RIE), a bottom signal jitter of 9.6% was obtained from a 36 Gbit/inch2 density disc, readout using a near-field optical pickup with an effective numerical aperture (NA) of 1.85 and a wavelength of 405 nm. We also obtained the eye patterns from a 70 Gbit/inch2 density disc readout using an optical pickup with a 2.05 NA and the same wavelength, and showed almost the same modulation ratio as the simulation value. Moreover, the capability of producing pit patterns corresponding to a 104 Gbit/inch2 density is demonstrated.

Anisotropic diamond etching through thermochemical reaction between Ni and diamond in high-temperature water vapour.

PubMed

Nagai, Masatsugu; Nakanishi, Kazuhiro; Takahashi, Hiraku; Kato, Hiromitsu; Makino, Toshiharu; Yamasaki, Satoshi; Matsumoto, Tsubasa; Inokuma, Takao; Tokuda, Norio

2018-04-27

Diamond possesses excellent physical and electronic properties, and thus various applications that use diamond are under development. Additionally, the control of diamond geometry by etching technique is essential for such applications. However, conventional wet processes used for etching other materials are ineffective for diamond. Moreover, plasma processes currently employed for diamond etching are not selective, and plasma-induced damage to diamond deteriorates the device-performances. Here, we report a non-plasma etching process for single crystal diamond using thermochemical reaction between Ni and diamond in high-temperature water vapour. Diamond under Ni films was selectively etched, with no etching at other locations. A diamond-etching rate of approximately 8.7 μm/min (1000 °C) was successfully achieved. To the best of our knowledge, this rate is considerably greater than those reported so far for other diamond-etching processes, including plasma processes. The anisotropy observed for this diamond etching was considerably similar to that observed for Si etching using KOH.

Quantitative Analysis of Etching Rate Profiles for 11B+-Implanted Si3N4 Film

NASA Astrophysics Data System (ADS)

Nakata, Jyoji; Kajiyama, Kenji

1983-01-01

Etching rate enhancement for 11B+-implanted Si3N4 film was investigated both experimentally and theoretically. The etching solution was concentrated H3PO4 at ˜165°C Film thicknesses were precisely measured by ellipsometry. Enhancement resulted from Si-N bond breaking. This was confirmed by a decrease of infrared absorption at a 12.0 μm wavelength for Si-N bond vibration. Main and additional peaks were observed in the etching rate profile. The former was due to nuclear damage and was well represented by the calculated etching rate profile deduced from the nuclear deposited energy density distribution. The latter existed in the surface region only when the ion projected range was shorter than the film thickness. This peak was possibly caused by charge accumulation in the insulating Si3N4 film during 11B+ implantation.

Tridimensional morphology and kinetics of etch pit on the {l_brace}0 0 0 1{r_brace} plane of sapphire crystal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang Lunyong; Sun Jianfei, E-mail: jfsun_hit@263.net; Zuo Hongbo

2012-08-15

The tridimensional morphology and etching kinetics of the etch pit on the C-{l_brace}0 0 0 1{r_brace} plane of sapphire crystal ({alpha}-Al{sub 2}O{sub 3}) in molten KOH were studied experimentally. It was shown that the etch pit takes on tridimensional morphologies with triangular symmetry same as the symmetric property of the sapphire crystal. Pits like centric and eccentric triangular pyramid as well as hexagonal pyramid were observed, but the latter is less in density. In-depth analyses show the side walls of the etch pits belong to the {l_brace}1 1{sup Macron} 0 2{sup Macron }{r_brace} family, and the triangular pit contains edgesmore » full composed by Al{sup 3+} ions on the etching surface so it is more stable than the hexagonal pit since its edges on the etching surface contains Al{sup 2+} ions. The etch pits developed in a manner of kinematic wave by the step moving with constant speed, which is controlled by the chemical reaction with activation energy of 96.6 kJ/mol between Al{sub 2}O{sub 3} and KOH. - Graphical abstract: Schematic showing the atomic configuration of the predicted side walls of regular triangular pyramid shaped etch pit on the C-{l_brace}0 0 0 1{r_brace} plane of sapphire crystal. Highlights: Black-Right-Pointing-Pointer Observed the tridimensional morphology of etch pits. Black-Right-Pointing-Pointer Figured out the atomic configuration origin of the etch pits. Black-Right-Pointing-Pointer Quantitatively determined the etch rates of the etch pits.« less

Fabrication of Microstripline Wiring for Large Format Transition Edge Sensor Arrays

NASA Technical Reports Server (NTRS)

Chervenak, James A.; Adams, J. M.; Bailey, C. N.; Bandler, S.; Brekosky, R. P.; Eckart, M. E.; Erwin, A. E.; Finkbeiner, F. M.; Kelley, R. L.; Kilbourne, C. A.;

Reduction in Susceptibility of MOS Devices to Radiation- and Electrically-Induced Defects

DTIC Science & Technology

2012-05-01

current density of 150 nA/cm2 for a time varying between 5 and 60 sec. Following implantation , the PMMA was etched off, and circular Al dots (2.67 x 10...calculations showing location of He ions implanted at 5.2 keV through 70 nm of PMMA on 35.6 nm SiO2. We have done TRIM calculations for energies...Instability (NBTI) and to radiation damage could be reduced. To that end, two techniques were attempted. In the first attempt, helium ions were implanted

The fabrication of nitrogen detector porous silicon nanostructures

NASA Astrophysics Data System (ADS)

Husairi, F. S.; Othman, N.; Eswar, K. A.; Guliling, Muliyadi; Khusaimi, Z.; Rusop, M.; Abdullah, S.

2018-05-01

In this study the porous silicon nanostructure used as a the nitrogen detector was fabricated by using anodization method because of simple and easy to handle. This method using 20 mA/ cm2 of current density and the etching time is from 10 - 40 minutes. The properties of the porous silicon nanostructure analyzed using I-V testing (electrical properties) and photoluminescence spectroscopy. From the I-V testing, sample PsiE40 where the sensitivity is 25.4% is a sensitivity of PSiE40 at 10 seconds exposure time.

Controlled ion track etching

NASA Astrophysics Data System (ADS)

George, J.; Irkens, M.; Neumann, S.; Scherer, U. W.; Srivastava, A.; Sinha, D.; Fink, D.

2006-03-01

It is a common practice since long to follow the ion track-etching process in thin foils via conductometry, i.e . by measurement of the electrical current which passes through the etched track, once the track breakthrough condition has been achieved. The major disadvantage of this approach, namely the absence of any major detectable signal before breakthrough, can be avoided by examining the track-etching process capacitively. This method allows one to define precisely not only the breakthrough point before it is reached, but also the length of any non-transient track. Combining both capacitive and conductive etching allows one to control the etching process perfectly. Examples and possible applications are given.

Nanolaminated Permalloy Core for High-Flux, High-Frequency Ultracompact Power Conversion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, J; Kim, M; Galle, P

2013-09-01

Metallic magnetic materials have desirable magnetic properties, including high permeability, and high saturation flux density, when compared with their ferrite counterparts. However, eddy-current losses preclude their use in many switching converter applications, due to the challenge of simultaneously achieving sufficiently thin laminations such that eddy currents are suppressed (e.g., 500 nm-1 mu m for megahertz frequencies), while simultaneously achieving overall core thicknesses such that substantial power can be handled. A CMOS-compatible fabrication process based on robot-assisted sequential electrodeposition followed by selective chemical etching has been developed for the realization of a core of substantial overall thickness (tens to hundreds ofmore » micrometers) comprised of multiple, stacked permalloy (Ni80Fe20) nanolaminations. Tests of toroidal inductors with nanolaminated cores showed negligible eddy-current loss relative to total core loss even at a peak flux density of 0.5 T in the megahertz frequency range. To illustrate the use of these cores, a buck power converter topology is implemented with switching frequencies of 1-2 MHz. Power conversion efficiency greater than 85% with peak operating flux density of 0.3-0.5 T in the core and converter output power level exceeding 5 W was achieved.« less

Simultaneous Perforation and Doping of Si Nanoparticles for Lithium-Ion Battery Anode.

PubMed

Lv, Guangxin; Zhu, Bin; Li, Xiuqiang; Chen, Chuanlu; Li, Jinlei; Jin, Yan; Hu, Xiaozhen; Zhu, Jia

2017-12-27

Silicon nanostructures have served as promising building blocks for various applications, such as lithium-ion batteries, thermoelectrics, and solar energy conversions. Particularly, control of porosity and doping is critical for fine-tuning the mechanical, optical, and electrical properties of these silicon nanostructures. However, perforation and doping are usually separated processes, both of which are complicated and expensive. Here, we demonstrate that the porous nano-Si particles with controllable dopant can be massively produced through a facile and scalable method, combining ball-milling and acid-etching. Nano-Si with porosity as high as 45.8% can be achieved with 9 orders of magnitude of conductivity changes compared to intrinsic silicon. As an example for demonstration, the obtained nano-Si particles with 45.8% porosity and 3.7 atom % doping can serve as a promising anode for lithium-ion batteries with 2000 mA h/g retained over 100 cycles at the current density of 0.5 C, excellent rate performance with 1600 mA h/g at the current density of 5 C, and a stable cycling performance of above 1500 mA h/g retained over 940 cycles at the current density of 1 C with carbon coating.

Defect structure of web silicon ribbon

NASA Technical Reports Server (NTRS)

Cunningham, B.; Strunk, H.; Ast, D.

1980-01-01

The results of a preliminary study of two dendritic web samples are presented. The structure and electrical activity of the defects in the silicon webs were studied. Optical microscopy of chemically etched specimens was used to determine dislocation densities. Samples were mechanically polished, then Secco etched for approximately 5 minutes. High voltage transmission electron microscopy was used to characterize the crystallographic nature of the defects.

Preparation of scanning tunneling microscopy tips using pulsed alternating current etching

DOE Office of Scientific and Technical Information (OSTI.GOV)

Valencia, Victor A.; Thaker, Avesh A.; Derouin, Jonathan

An electrochemical method using pulsed alternating current etching (PACE) to produce atomically sharp scanning tunneling microscopy (STM) tips is presented. An Arduino Uno microcontroller was used to control the number and duration of the alternating current (AC) pulses, allowing for ready optimization of the procedures for both Pt:Ir and W tips using a single apparatus. W tips prepared using constant and pulsed AC power were compared. Tips fashioned using PACE were sharper than those etched with continuous AC power alone. Pt:Ir tips were prepared with an initial coarse etching stage using continuous AC power followed by fine etching using PACE.more » The number and potential of the finishing AC pulses was varied and scanning electron microscope imaging was used to compare the results. Finally, tip quality using the optimized procedures was verified by UHV-STM imaging. With PACE, at least 70% of the W tips and 80% of the Pt:Ir tips were of sufficiently high quality to obtain atomically resolved images of HOPG or Ni(111)« less

Model polymer etching and surface modification by a time modulated RF plasma jet: role of atomic oxygen and water vapor

NASA Astrophysics Data System (ADS)

Luan, P.; Knoll, A. J.; Wang, H.; Kondeti, V. S. S. K.; Bruggeman, P. J.; Oehrlein, G. S.

2017-01-01

The surface interaction of a well-characterized time modulated radio frequency (RF) plasma jet with polystyrene, poly(methyl methacrylate) and poly(vinyl alcohol) as model polymers is investigated. The RF plasma jet shows fast polymer etching but mild chemical modification with a characteristic carbonate ester and NO formation on the etched surface. By varying the plasma treatment conditions including feed gas composition, environment gaseous composition, and treatment distance, we find that short lived species, especially atomic O for Ar/1% O2 and 1% air plasma and OH for Ar/1% H2O plasma, play an essential role for polymer etching. For O2 containing plasma, we find that atomic O initiates polymer etching and the etching depth mirrors the measured decay of O atoms in the gas phase as the nozzle-surface distance increases. The etching reaction probability of an O atom ranging from 10-4 to 10-3 is consistent with low pressure plasma research. We also find that adding O2 and H2O simultaneously into Ar feed gas quenches polymer etching compared to adding them separately which suggests the reduction of O and OH density in Ar/O2/H2O plasma.

Wafer-scale development and experimental verification of 0.36 mm2 228 mV open-circuit-voltage solid-state CMOS-compatible glucose fuel cell

NASA Astrophysics Data System (ADS)

Arata, Shigeki; Hayashi, Kenya; Nishio, Yuya; Kobayashi, Atsuki; Nakazato, Kazuo; Niitsu, Kiichi

2018-04-01

The world’s smallest (0.36 mm2) solid-state CMOS-compatible glucose fuel cell, which exhibits an open-circuit voltage (OCV) of 228 mV and a power generation density of 1.32 µW/cm2 with a 30 mM glucose solution, is reported in this paper. Compared with conventional wet etching, dry etching (reactive ion etching) for patterning minimizes damage to the anode and cathode, resulting in a cell with a small size and a high OCV, sufficient for CMOS circuit operation.

LWIR HgCdTe Detectors Grown on Ge Substrates

NASA Astrophysics Data System (ADS)

Vilela, M. F.; Lofgreen, D. D.; Smith, E. P. G.; Newton, M. D.; Venzor, G. M.; Peterson, J. M.; Franklin, J. J.; Reddy, M.; Thai, Y.; Patten, E. A.; Johnson, S. M.; Tidrow, M. Z.

2008-09-01

Long-wavelength infrared (LWIR) HgCdTe p-on- n double-layer heterojunctions (DLHJs) for infrared detector applications have been grown on 100 mm Ge (112) substrates by molecular beam epitaxy (MBE). The objective of this current work was to grow our baseline p-on- n DLHJ detector structure (used earlier on Si substrates) on 100 mm Ge substrates in the 10 μm to 11 μm LWIR spectral region, evaluate the material properties, and obtain some preliminary detector performance data. Material characterization techniques included are X-ray rocking curves, etch pit density (EPD) measurements, compositional uniformity determined from Fourier-transform infrared (FTIR) transmission, and doping concentrations determined from secondary-ion mass spectroscopy (SIMS). Detector properties include resistance-area product (RoA), spectral response, and quantum efficiency. Results of LWIR HgCdTe detectors and test structure arrays (TSA) fabricated on both Ge and silicon (Si) substrates are presented and compared. Material properties demonstrated include X-ray full-width of half-maximum (FWHM) as low as 77 arcsec, typical etch pit densities in mid 106 cm-2 and wavelength cutoff maximum/minimum variation <2% across the full wafer. Detector characteristics were found to be nearly identical for HgCdTe grown on either Ge or Si substrates.

Synthesis of hollow carbon nanoshells and their application for supercapacitors

NASA Astrophysics Data System (ADS)

Rudakov, G. A.; Sosunov, A. V.; Ponomarev, R. S.; Khenner, V. K.; Reza, Md. Shamim; Sumanasekera, Gamini

2018-01-01

This work is devoted to the study of the synthesis, the description of the structure, and the use of hollow carbon nanoshells 3-5 nm in size. Hollow carbon nanoshells were synthesized by thermolysis of a mixture of nickel acetate and citric acid in the temperature range of 500-700°C. During the chemical reaction, nickel nuclei 3-5 nm in size are formed, separated from each other by carbon layers. At an annealing temperature of 600°C, the most ordered, close-packed structure is formed, evenly distributed throughout the sample. The etching of nickel with nitric acid resulted in hollow carbon nanoshells with a high specific surface area ( 1200 m2/g) and a homogeneous structure. Raman spectroscopy shows that the graphene-like structure of carbon nanoshells is preserved before and after the etching of nickel, and their defect density does not increase, which enables them to be subjected to new processing (functionalization) in order to obtain additional physical properties. The resulting carbon nanoshells were used as active material of the supercapacitor electrodes. The conducted electrochemical measurements showed that the specific capacitance of the supercapacitor did not fall below 120 F/g at a current density of 0.3 to 3 A after 800 charge/discharge cycles.

Defect detection and control in an analog CMOS process

NASA Astrophysics Data System (ADS)

Taucher, Franz; Evans, Ivor R.

1996-09-01

Over the last 12 months, Austria Mikro Systeme has installed an even more rigorous system of defect density measurement, monitoring and control in its facility at Unterpremstatten. To accomplish this, 2 test devices (Medusa 1 and 2) were designed which allow possible defects in all layers of the process to be located. These devices are 8 by 9 mm2 in area and contain various structures to quantify the density of defects causing continuity, bridging and inter-layer isolation failure. The devices move through the waferfab receiving all process steps with the usual handling and operator procedures, from which it is clear, that the density of defects measured is representative of that of normal production material. The wafers are tested electrically using a Keithley S450, and data analysis is done with RS1 and EXCEL. By using yield models available from the literature, the correspondence in yield estimates made in this way and actual production yields were generally within 3%. Applying this technique allows the yield loss mechanisms to be isolated and then prioritized. The chipset identified several areas within the process which required special attention. These included implant optimization to reduce gate oxide damage, defect reduction in the metal-etch process, increased leakage currents caused by implant channeling and second poly etch-control to avoid 'bridging' around poly 1 periphery. Successful actions at these points have led to a significant improvement in wafer probe yields at Austria Mikro Systeme.

Humidity sensing properties of morphology-controlled ordered silicon nanopillar

NASA Astrophysics Data System (ADS)

Li, Wei; Hu, Mingyue; Ge, Pengpeng; Wang, Jing; Guo, YanYan

2014-10-01

Ordered silicon nanopillar array (Si-NPA) was fabricated by nanosphere lithography. The size of silicon nanopillars can be easily controlled by an etching process. The period and density of nanopillar arrays are determined by the initial diameter of polystyrene (PS) spheres. It was studied as a sensing material to detect humidity. Room temperature current sensitivity of Si-NPA sensor was investigated at a relative humidity (RH) ranging from 50 to 70%. As a result, the measured current showed there was a significant increase at 70% RH. The response and recovery time was about 10 s and 15 s. These excellent sensing characteristics indicate that Si-NPA might be a practical sensing material.

Method and apparatus for spatially uniform electropolishing and electrolytic etching

DOEpatents

Mayer, Steven T.; Contolini, Robert J.; Bernhardt, Anthony F.

1992-01-01

In an electropolishing or electrolytic etching apparatus the anode is separated from the cathode to prevent bubble transport to the anode and to produce a uniform current distribution at the anode by means of a solid nonconducting anode-cathode barrier. The anode extends into the top of the barrier and the cathode is outside the barrier. A virtual cathode hole formed in the bottom of the barrier below the level of the cathode permits current flow while preventing bubble transport. The anode is rotatable and oriented horizontally facing down. An extended anode is formed by mounting the workpiece in a holder which extends the electropolishing or etching area beyond the edge of the workpiece to reduce edge effects at the workpiece. A reference electrode controls cell voltage. Endpoint detection and current shut-off stop polishing. Spatially uniform polishing or etching can be rapidly performed.

Method and apparatus for spatially uniform electropolishing and electrolytic etching

DOEpatents

Mayer, S.T.; Contolini, R.J.; Bernhardt, A.F.

1992-03-17

In an electropolishing or electrolytic etching apparatus the anode is separated from the cathode to prevent bubble transport to the anode and to produce a uniform current distribution at the anode by means of a solid nonconducting anode-cathode barrier. The anode extends into the top of the barrier and the cathode is outside the barrier. A virtual cathode hole formed in the bottom of the barrier below the level of the cathode permits current flow while preventing bubble transport. The anode is rotatable and oriented horizontally facing down. An extended anode is formed by mounting the workpiece in a holder which extends the electropolishing or etching area beyond the edge of the workpiece to reduce edge effects at the workpiece. A reference electrode controls cell voltage. Endpoint detection and current shut-off stop polishing. Spatially uniform polishing or etching can be rapidly performed. 6 figs.

Rational construction of three dimensional hybrid Co3O4@NiMoO4 nanosheets array for energy storage application

NASA Astrophysics Data System (ADS)

Hong, Wei; Wang, Jinqing; Gong, Peiwei; Sun, Jinfeng; Niu, Lengyuan; Yang, Zhigang; Wang, Zhaofeng; Yang, Shengrong

2014-12-01

Electrodes with rationally designed hybrid nanostructures can offer many opportunities for the enhanced performance in electrochemical energy storage. In this work, the uniform 2D Co3O4-based building blocks have been prepared through a facile chemical etching assistant approach and a following treatment of thermal annealing. The obtained nanosheets array has been directly employed as 2D backbone for the subsequent construction of hybrid nanostructure of Co3O4@NiMoO4 by a simple hydrothermal synthesis. As a binder-free electrode, the constructed 3D hybrid nanostructures exhibit a high specific capacitance of 1526 F g-1 at a current density of 3 mA cm-2 and a capacitance retention of 72% with the increase of current density from 3 mA cm-2 to 30 mA cm-2. Moreover, an asymmetric supercapacitor based on this hybrid Co3O4@NiMoO4 and activated carbon can deliver a maximum energy density of 37.8 Wh kg-1 at a power density of 482 W kg-1. The outstanding electrochemical behaviors presented here suggest that this hybrid nanostructured material has potential applications in energy storage.

MEMS cantilever based magnetic field gradient sensor

NASA Astrophysics Data System (ADS)

Dabsch, Alexander; Rosenberg, Christoph; Stifter, Michael; Keplinger, Franz

2017-05-01

This paper describes major contributions to a MEMS magnetic field gradient sensor. An H-shaped structure supported by four arms with two circuit paths on the surface is designed for measuring two components of the magnetic flux density and one component of the gradient. The structure is produced from silicon wafers by a dry etching process. The gold leads on the surface carry the alternating current which interacts with the magnetic field component perpendicular to the direction of the current. If the excitation frequency is near to a mechanical resonance, vibrations with an amplitude within the range of 1-103 nm are expected. Both theoretical (simulations and analytic calculations) and experimental analysis have been carried out to optimize the structures for different strength of the magnetic gradient. In the same way the impact of the coupling structure on the resonance frequency and of different operating modes to simultaneously measure two components of the flux density were tested. For measuring the local gradient of the flux density the structure was operated at the first symmetrical and the first anti-symmetrical mode. Depending on the design, flux densities of approximately 2.5 µT and gradients starting from 1 µT mm-1 can be measured.

Effect of source frequency and pulsing on the SiO2 etching characteristics of dual-frequency capacitive coupled plasma

NASA Astrophysics Data System (ADS)

Kim, Hoe Jun; Jeon, Min Hwan; Mishra, Anurag Kumar; Kim, In Jun; Sin, Tae Ho; Yeom, Geun Young

2015-01-01

A SiO2 layer masked with an amorphous carbon layer (ACL) has been etched in an Ar/C4F8 gas mixture with dual frequency capacitively coupled plasmas under variable frequency (13.56-60 MHz)/pulsed rf source power and 2 MHz continuous wave (CW) rf bias power, the effects of the frequency and pulsing of the source rf power on the SiO2 etch characteristics were investigated. By pulsing the rf power, an increased SiO2 etch selectivity was observed with decreasing SiO2 etch rate. However, when the rf power frequency was increased, not only a higher SiO2 etch rate but also higher SiO2 etch selectivity was observed for both CW and pulse modes. A higher CF2/F ratio and lower electron temperature were observed for both a higher source frequency mode and a pulsed plasma mode. Therefore, when the C 1s binding states of the etched SiO2 surfaces were investigated using X-ray photoelectron spectroscopy (XPS), the increase of C-Fx bonding on the SiO2 surface was observed for a higher source frequency operation similar to a pulsed plasma condition indicating the increase of SiO2 etch selectivity over the ACL. The increase of the SiO2 etch rate with increasing etch selectivity for the higher source frequency operation appears to be related to the increase of the total plasma density with increasing CF2/F ratio in the plasma. The SiO2 etch profile was also improved not only by using the pulsed plasma but also by increasing the source frequency.

Optical and electrical properties of ion beam textured Kapton and Teflon

NASA Technical Reports Server (NTRS)

Mirtich, M. J.; Sovey, J. S.

1977-01-01

An electron bombardment argon ion source was used to ion etch polyimide (Kapton) and fluorinated ethylene, FEP (Teflon). Samples of polyimide and FEP were exposed to (0.5-1.0) keV Ar ions at ion current densities of (1.0-1/8) mA/sq cm for various exposure times. Changes in the optical and electrical properties of the samples were used to characterize the exposure. Spectral reflectance and transmittance measurements were made between 0.33 and 2.16 micron m using an integrating sphere after each exposure. From these measurements, values of solar absorptance were obtained. Total emittance measurements were also recorded for some samples. Surface resistivity was used to determine changes in the electrical conductivity of the etched samples. A scanning electron microscope recorded surface structure after exposure. Spectral optical data, resistivity measurements, calculated absorptance and emittance measurements are presented along with photomicrographs of the surface structure for the various exposures to Ar ions.

EUV process improvement with novel litho track hardware

NASA Astrophysics Data System (ADS)

Stokes, Harold; Harumoto, Masahiko; Tanaka, Yuji; Kaneyama, Koji; Pieczulewski, Charles; Asai, Masaya

2017-03-01

Currently, there are many developments in the field of EUV lithography that are helping to move it towards increased HVM feasibility. Targeted improvements in hardware design for advanced lithography are of interest to our group specifically for metrics such as CD uniformity, LWR, and defect density. Of course, our work is focused on EUV process steps that are specifically affected by litho track performance, and consequently, can be improved by litho track design improvement and optimization. In this study we are building on our experience to provide continual improvement for LWR, CDU, and Defects as applied to a standard EUV process by employing novel hardware solutions on our SOKUDO DUO coat develop track system. Although it is preferable to achieve such improvements post-etch process we feel, as many do, that improvements after patterning are a precursor to improvements after etching. We hereby present our work utilizing the SOKUDO DUO coat develop track system with an ASML NXE:3300 in the IMEC (Leuven, Belgium) cleanroom environment to improve aggressive dense L/S patterns.

Etching Enhancement Followed by Nitridation on Low-k SiOCH Film in Ar/C5F10O Plasma

NASA Astrophysics Data System (ADS)

Miyawaki, Yudai; Shibata, Emi; Kondo, Yusuke; Takeda, Keigo; Kondo, Hiroki; Ishikawa, Kenji; Okamoto, Hidekazu; Sekine, Makoto; Hori, Masaru

2013-02-01

The etching rates of low-dielectric-constant (low-k), porous SiOCH (p-SiOCH) films were increased by nitrogen-added Ar/C5F10O plasma etching in dual-frequency (60 MHz/2 MHz)-excited parallel plate capacitively coupled plasma. Previously, perfluoropropyl vinyl ether [C5F10O] provided a very high density of CF3+ ions [Nagai et al.: Jpn. J. Appl. Phys. 45 (2006) 7100]. Surface nitridation on the p-SiOCH surface exposed to Ar/N2 plasma led to the etching of larger amounts of p-SiOCH in Ar/C5F10O plasma, which depended on the formation of bonds such as =C(sp2)=N(sp2)- and -C(sp)≡N(sp).

Inductive plasmas for plasma processing

NASA Astrophysics Data System (ADS)

Keller, John H.

1996-05-01

With the need for high plasma density and low pressure in single wafer etching tools, a number of inductive etching systems have been and are being developed for commercial sale. This paper reviews some of the history of low-pressure inductive plasmas, gives features of inductive plasmas, limitations, corrections and presents uses for plasma processing. The theory for the skin depth, rf coil impedance and efficiency is also discussed.

High gain photoconductive semiconductor switch having tailored doping profile zones

DOEpatents

Baca, Albert G.; Loubriel, Guillermo M.; Mar, Alan; Zutavern, Fred J; Hjalmarson, Harold P.; Allerman, Andrew A.; Zipperian, Thomas E.; O'Malley, Martin W.; Helgeson, Wesley D.; Denison, Gary J.; Brown, Darwin J.; Sullivan, Charles T.; Hou, Hong Q.

2001-01-01

A photoconductive semiconductor switch with tailored doping profile zones beneath and extending laterally from the electrical contacts to the device. The zones are of sufficient depth and lateral extent to isolate the contacts from damage caused by the high current filaments that are created in the device when it is turned on. The zones may be formed by etching depressions into the substrate, then conducting epitaxial regrowth in the depressions with material of the desired doping profile. They may be formed by surface epitaxy. They may also be formed by deep diffusion processes. The zones act to reduce the energy density at the contacts by suppressing collective impact ionization and formation of filaments near the contact and by reducing current intensity at the contact through enhanced current spreading within the zones.

Dislocation substructure of mantle-derived olivine as revealed by selective chemical etching and transmission electron microscopy

USGS Publications Warehouse

Kirby, S.H.; Wegner, M.W.

1978-01-01

Cleaved and mechanically polished surfaces of olivine from peridotite xenoliths from San Carlos, Arizona, were chemically etched using the techniques of Wegner and Christie (1974). Dislocation etch pits are produced on all surface orientations and they tend to be preferentially aligned along the traces of subgrain boundaries, which are approximately parallel to (100), (010), and (001). Shallow channels were also produced on (010) surfaces and represent dislocations near the surface that are etched out along their lengths. The dislocation etch channel loops are often concentric, and emanate from (100) subgrain boundaries, which suggests that dislocation sources are in the boundaries. Data on subgrain misorientation and dislocation line orientation and arguments based on subgrain boundary energy minimization are used to characterize the dislocation structures of the subgrain boundaries. (010) subgrain boundaries are of the twist type, composed of networks of [100] and [001] screw dislocations. Both (100) and (001) subgrain boundaries are tilt walls composed of arrays of edge dislocation with Burgers vectors b=[100] and [001], respectively. The inferred slip systems are {001} ???100???, {100} ???001???, and {010} ???100??? in order of diminishing importance. Exploratory transmission electron microscopy is in accord with these identifications. The flow stresses associated with the development of the subgrain structure are estimated from the densities of free dislocations and from the subgrain dimensions. Inferred stresses range from 35 to 75 bars using the free dislocation densities and 20 to 100 bars using the subgrain sizes. ?? 1978 Springer-Verlag.

Effect of substrate dislocations on the Hg in-diffusion in CdZnTe substrates used for HgCdTe epilayer growth

NASA Astrophysics Data System (ADS)

Kumar, Shiv; Kapoor, A. K.; Nagpal, A.; Sharma, S.; Verma, D.; Kumar, A.; Raman, R.; Basu, P. K.

2006-12-01

Chemical-etched HgCdTe epilayers grown onto CdZnTe substrates have been studied using defect etching and EDS on cleaved (1 1 0) face. Formation of etch pits and mercury (Hg) in-diffusion into CZT substrate has been correlated with the substrate quality i.e. the presence of dislocations around second phase inclusions. That the Hg in-diffusion takes place through these dislocations is authenticated by the presence of Te-inclusions in substrates where large density of etch pits are revealed after chemical etching. X-ray rocking curve measurements were carried out to reveal crystalline quality of the substrates. FTIR spectroscopy indicates low transmission values and absence of interference fringes in MCT epilayers with large Hg diffusion. Hg diffusion into CZT substrate upto 25 μm in samples with low FWHM values and upto 250 μm in samples with multiple peaks and high FWHM values was observed.

Focused ion beam micromachining of TiNi film on Si( 1 1 1 )

NASA Astrophysics Data System (ADS)

Xie, D. Z.; Ngoi, B. K. A.; Ong, A. S.; Fu, Y. Q.; Lim, B. H.

2003-11-01

Having an excellent shape memory effect, titanium-nickel (TiNi) thin films are often used for fabrication of microactuators in microelectromechanical systems. In this work, the Ga + focused ion beam (FIB) etching characteristics of TiNi thin films has been investigated. The thin films were deposited on Si(1 1 1) wafers by co-sputtering NiTi and Ti targets using a magnetron-sputtering system. Some patterns have been etched on the surface of the films by FIB. Atomic force microscopy has been used to analyze the surface morphology of the etched areas. It is found that the etched depth depends linearly on the ion dose per area with a slope of 0.259 μm/(nC/μm 2). However, the etching depth decreases with increasing the ion beam current. The root-mean-square (RMS) surface roughness changes nonlinearly with ion dose and reaches a minimum of about 5.00 nm at a dose of about 0.45 nC/μm 2. The RMS decreases with increasing ion beam current and reaches about 4.00 nm as the ion beam current is increased to 2 nA.

Modification of Patterned Nanoporous Gold Thin Film Electrodes via Electro-annealing and Electrochemical Etching

NASA Astrophysics Data System (ADS)

Dorofeeva, Tatiana

Nanostructured materials have had a major impact on various fields, including medicine, catalysis, and energy storage, for the major part due to unique phenomena that arise at nanoscale. For this reason, there is a sustained need for new nanostructured materials, techniques to pattern them, and methods to precisely control their nanostructure. To that end, the primary focus of this dissertation is to demonstrate novel techniques to fabricate and tailor the morphology of a class of nanoporous metals, obtained by a process known as dealloying. In this process, while the less noble constituent of an alloy is chemically dissolved, surface-diffusion of the more noble constituent leads to self-assembly of a bicontinuous ligament network with characteristic porosity of ˜70% and ligament diameter of 10s of nanometers. As a model material produced by dealloying, this work employ nanoporous gold (np-Au), which has attracted significant attention of desirable features, such as high effective surface area, electrical conductivity, well-defined thiol-based surface modification strategies, microfabrication-compatibility, and biocompatibility. The most commonly method used to modify the morphology of np-Au is thermal treatment, where the enhanced diffusivity of the surface atoms leads to ligament (and consequently pore) coarsening. This method, however, is not conducive to modifying the morphology of thin films at specific locations on the film, which is necessary for creating devices that may need to contain different morphologies on a single device. In addition, coarsening attained by thermal treatment also leads to an undesirable reduction in effective surface area. In response to these challenges, this work demonstrates two different techniques that enables in situ modification of np-Au thin film electrodes obtained by sputter-deposition of a precursors silver-rich gold-silver alloy. The first method, referred to as electro-annealing, is achieved by injecting electrical current to np-Au electrodes, which leads coarsening due to a combination of Joule heating and other mechanisms. This method offers the capability to anneal different electrodes to varying degrees of coarsening in one step, by employing electrodes patterns with different cross-sectional areas - easily attained since np-Au can be patterned into arbitrary shapes via photolithography - to control electrode resistivity, thus current density and the amount of electro-annealing of an electrode. A surprising finding was that electro-annealing lead to electrode coarsening at much lower temperatures than conventional thermal treatment, which was attributed to augmented electron-surface atom interactions at high current densities that may in turn enhance surface atom diffusivity. A major advantage of electro-annealing is the ability to monitor the resistance change of the electrode (surrogate for electrode morphology) in real-time and vary the electro-annealing current accordingly to establish a closed-loop electro-annealing configuration. In nanostructured materials, the electrical resistance is often a function of nanostructure, thus changes in resistance can be directly linked to morphological changes of the electrode. Examination of the underlying mechanisms of nanostructure-dependent resistance change revealed that both ligament diameter and grain size play a role in dictating the observed electrode resistance change. The second method relies on electrochemical etching of ligaments to modify electrode morphology in order to maintain both a high effective surface area and large pores for unhindered transport of molecules to/from the ligament surfaces - an important consideration for many physico-chemical processes, such fuel cells, electrochemical sensors, and drug delivery platforms. The advantage of this method over purely chemical approach is that while an entire sample in exposed to the chemical reagent, the etching process does not occur until the necessary electrochemical potential is applied. Similar to the electro-annealing methods, electrical addressability allows for differentially modifying the morphology individual electrodes on a single substrate. The results of this study also revealed that electrochemical etching is a combination of coarsening and etching processes, where the optimization of etching parameters makes it possible precisely control the etching by favoring one process over the other. In summary, the two techniques, taken together in combination with np-Au's compatibility with microfabrication processes, can be extended to create multiple electrode arrays that display different morphologies for studying structure?property relationships and tuning catalysts/sensors for optimal performance.

Arrays of quasi-hexagonally ordered silica nanopillars with independently controlled areal density, diameter and height gradients

NASA Astrophysics Data System (ADS)

Özdemir, Burcin; Huang, Wenting; Plettl, Alfred; Ziemann, Paul

2015-03-01

A consecutive fabrication approach of independently tailored gradients of the topographical parameters distance, diameter and height in arrays of well-ordered nanopillars on smooth SiO2-Si-wafers is presented. For this purpose, previously reported preparation techniques are further developed and combined. First, self-assembly of Au-salt loaded micelles by dip-coating with computer-controlled pulling-out velocities and subsequent hydrogen plasma treatment produce quasi-hexagonally ordered, 2-dimensional arrays of Au nanoparticles (NPs) with unidirectional variations of the interparticle distances along the pulling direction between 50-120 nm. Second, the distance (or areal density) gradient profile received in this way is superimposed with a diameter-controlled gradient profile of the NPs applying a selective photochemical growth technique. For demonstration, a 1D shutter is used for locally defined UV exposure times to prepare Au NP size gradients varying between 12 and 30 nm. Third, these double-gradient NP arrangements serve as etching masks in a following reactive ion etching step delivering arrays of nanopillars. For height gradient generation, the etching time is locally controlled by applying a shutter made from Si wafer piece. Due to the high flexibility of the etching process, the preparation route works on various materials such as cover slips, silicon, silicon oxide, silicon nitride and silicon carbide.

The magnetic properties and microstructure of Co-Pt thin films using wet etching process.

PubMed

Lee, Chang-Hyoung; Cho, Young-Lae; Lee, Won-Pyo; Suh, Su-Jeong

2014-11-01

Perpendicular magnetic recording (PMR) is a promising candidate for high density magnetic recording and has already been applied to hard disk drive (HDD) systems. However, media noise still limits the recording density. To reduce the media noise and achieve a high signal-to-noise ratio (SNR) in hard disk media, the grains of the magnetic layer must be magnetically isolated from each other. This study examined whether sputter-deposited Co-Pt thin films can have adjacent grains that are physically isolated. To accomplish this, the effects of the sputtering conditions and wet etching process on magnetic properties and the microstructure of the films were investigated. The film structure was Co-Pt (30 nm)/Ru (30 nm)/NiFe (10 nm)/Ta (5 nm). The composition of the Co-Pt thin films was Co-30.7 at.% Pt. The Co-Pt thin films were deposited in Ar gas at 5, 10, 12.5, and 15 mTorr. Wet etching process was performed using 7% nitric acid solution at room temperature. These films had high out-of-plane coercivity of up to 7032 Oe, which is twice that of the as-deposited film. These results suggest that wet etched Co-Pt thin films have weaker exchange coupling and enhanced out-of-plane coercivity, which would reduce the medium noise.

BeZnCdSe quantum-well ridge-waveguide laser diodes under low threshold room-temperature continuous-wave operation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feng, Jijun; Electronics and Photonics Research Institute, National Institute of Advanced Industrial Science and Technology; Akimoto, Ryoichi, E-mail: r-akimoto@aist.go.jp

2015-10-19

Low threshold current ridge-waveguide BeZnCdSe quantum-well laser diodes (LDs) have been developed by completely etching away the top p-type BeMgZnSe/ZnSe:N short-period superlattice cladding layer, which can suppress the leakage current that flows laterally outside of the electrode. The waveguide LDs are covered with a thick SiO{sub 2} layer and planarized with chemical-mechanical polishing and a reactive ion etching process. Room-temperature lasing under continuous-wave condition is achieved with the laser cavity formed by the cleaved waveguide facets coated with high-reflectivity dielectric films. For a 4 μm-wide green LD lasing around a wavelength of 535 nm, threshold current and voltage of 7.07 mA and 7.89 Vmore » are achieved for a cavity length of 300 μm, and the internal differential quantum efficiency, internal absorption loss, gain constant, and nominal transparency current density are estimated to be 27%, 4.09 cm{sup −1}, 29.92 (cm × μm)/kA and 6.35 kA/(cm{sup 2 }× μm), respectively. This compact device can realize a significantly improved performance with much lower threshold power consumption, which would benefit the potential application for ZnSe-based green LDs as light sources in full-color display and projector devices installed in consumer products such as pocket projectors.« less

Investigation of porous silicon obtained under different conditions by the contact angle method

NASA Astrophysics Data System (ADS)

Belorus, A. O.; Bukina, Y. V.; Pastukhov, A. I.; Stebko, D. S.; Spivak, Yu M.; Moshnikov, V. A.

2017-11-01

This paper investigates a hydrophobicity/hydrophilicity of porous silicon by the contact angle method. Porous silicon series were obtained by electrochemical anodic etching of n-Si (100) and (111) under the current anodization density range of 5-120 mA/cm2. For this purpose the original laboratory installation and the software «Measurement of contact angle» were developed. It is shown that, the contact angle can vary significantly (up to 80 degrees for (100)) depending on the current anodization Discussion of the results is carried out taking in account the composition of the functional groups and of surface morphology of the porous silicon. These results are important for developing porous silicon particles as nanocontainers in the targeted drug delivery.

Pulsed Laser-Assisted Focused Electron-Beam-Induced Etching of Titanium with XeF 2 : Enhanced Reaction Rate and Precursor Transport

DOE PAGES

Noh, J. H.; Fowlkes, J. D.; Timilsina, R.; ...

2015-01-28

We introduce a laser-assisted focused electron-beam-induced etching (LA-FEBIE) process which is a versatile, direct write nanofabrication method that allows nanoscale patterning and editing; we do this in order to enhance the etch rate of electron-beam-induced etching. The results demonstrate that the titanium electron stimulated etch rate via the XeF2 precursor can be enhanced up to a factor of 6 times with an intermittent pulsed laser assist. Moreover, the evolution of the etching process is correlated to in situ stage current measurements and scanning electron micrographs as a function of time. Finally, the increased etch rate is attributed to photothermally enhancedmore » Ti–F reaction and TiF4 desorption and in some regimes enhanced XeF2 surface diffusion to the reaction zone.« less

Evaluation of microtensile bond strength of self-etching adhesives on normal and caries-affected dentin.

PubMed

Shibata, Shizuma; Vieira, Luiz Clovis Cardoso; Baratieri, Luiz Narciso; Fu, Jiale; Hoshika, Shuhei; Matsuda, Yasuhiro; Sano, Hidehiko

2016-01-01

The purpose of this study was to evaluate the µTBS (microtensile bond strength) of currently available self-etching adhesives with an experimental self-etch adhesive in normal and caries-affected dentin, using a portable hardness measuring device, in order to standardize dentin Knoop hardness. Normal (ND) and caries-affected dentin (CAD) were obtained from twenty human molars with class II natural caries. The following adhesive systems were tested: Mega Bond (MB), a 2-step self-etching adhesive; MTB-200 (MTB), an experimental 1-step self-etching adhesive (1-SEA), and two commercially available one-step self-etching systems, G-Bond Plus (GB) and Adper Easy Bond (EB). MB-ND achieved the highest µTBS (p<0.05). The mean µTBS was statistically lower in CAD than in ND for all adhesives tested (p<0.05), and the 2-step self-etch adhesive achieved better overall performance than the 1-step self-etch adhesives.

Industrial ion source technology

NASA Technical Reports Server (NTRS)

Kaufman, H. R.; Robinson, R. S.

1979-01-01

In reactive ion etching of Si, varying amounts of O2 were added to the CF4 background. The experimental results indicated an etch rate less than that for Ar up to an O2 partial pressure of about .00006 Torr. Above this O2 pressure, the etch rate with CF4 exceeded that with Ar alone. For comparison the random arrival rate of O2 was approximately equal to the ion arrival rate at a partial pressure of about .00002 Torr. There were also ion source and ion pressure gauge maintenance problems as a result of the use of CF4. Large scale (4 sq cm) texturing of Si was accomplished using both Cu and stainless steel seed. The most effective seeding method for this texturing was to surround the sample with large inclined planes. Designing, fabricating, and testing a 200 sq cm rectangular beam ion source was emphasized. The design current density was 6 mA/sq cm with 500 eV argon ions, although power supply limitations permitted operation to only 2 mA/sq cm. The use of multiple rectangular beam ion sources for continuous processing of wider areas than would be possible with a single source was also studied. In all cases investigated, the most uniform coverage was obtained with 0 to 2 cm beam overlay. The maximum departure from uniform processing at optimum beam overlap was found to be +15%.

Normally-off AlGaN/GaN-based MOS-HEMT with self-terminating TMAH wet recess etching

NASA Astrophysics Data System (ADS)

Son, Dong-Hyeok; Jo, Young-Woo; Won, Chul-Ho; Lee, Jun-Hyeok; Seo, Jae Hwa; Lee, Sang-Heung; Lim, Jong-Won; Kim, Ji Heon; Kang, In Man; Cristoloveanu, Sorin; Lee, Jung-Hee

2018-03-01

Normally-off AlGaN/GaN-based MOS-HEMT has been fabricated by utilizing damage-free self-terminating tetramethyl ammonium hydroxide (TMAH) recess etching. The device exhibited a threshold voltage of +2.0 V with good uniformity, extremely small hysteresis of ∼20 mV, and maximum drain current of 210 mA/mm. The device also exhibited excellent off-state performances, such as breakdown voltage of ∼800 V with off-state leakage current as low as ∼10-12 A and high on/off current ratio (Ion/Ioff) of 1010. These excellent device performances are believed to be due to the high quality recessed surface, provided by the simple self-terminating TMAH etching.

Surface Passivation of CdZnTe Detector by Hydrogen Peroxide Solution Etching

NASA Technical Reports Server (NTRS)

Hayes, M.; Chen, H.; Chattopadhyay, K.; Burger, A.; James, R. B.

1998-01-01

The spectral resolution of room temperature nuclear radiation detectors such as CdZnTe is usually limited by the presence of conducting surface species that increase the surface leakage current. Studies have shown that the leakage current can be reduced by proper surface preparation. In this study, we try to optimize the performance of CdZnTe detector by etching the detector with hydrogen peroxide solution as function of concentration and etching time. The passivation effect that hydrogen peroxide introduces have been investigated by current-voltage (I-V) measurement on both parallel strips and metal-semiconductor-metal configurations. The improvements on the spectral response of Fe-55 and 241Am due to hydrogen peroxide treatment are presented and discussed.

320 x 256 Complementary Barrier Infrared Detector Focal Plane Array for Long-Wave Infrared Imaging

NASA Technical Reports Server (NTRS)

Nguyen, Jean; Rafol, Sir B.; Soibel, Alexander; Khoskhlagh, Arezou; Ting, David Z.-Y.; Liu, John K.; Mumolo, Jason M.; Gunapala, Sarath D.

2012-01-01

A 320 x 256 Complementary Barrier Infrared (CBIRD) focal plane array for long-wavelength infrared (LWIR) imaging is reported. The arrays were grown by molecular beam expitaxy (MBE) with a 300 period 1.9 um thick absorber. The mean dark current density of 2.2 x 10-4 A/cm2 was measured at an operating bias of 128 mV with a long wavelength cutoff of 8.8 ?m observed at 50% of the peak. The maximum quantum efficiency was 54% measured at 5.6 ?m. Operating at T = 80K, the array yielded an 81% fill factor with 97% operability. Good imagery with a mean noise equivalent different temperature (NE?T) of 18.6 mK and a mean detectivity of D* = 1.3 x 1011 cm-Hz1/2/W was achieved. The substrate was thinned using mechanical lapping and neither an AR coating nor a passivation layer was applied. This article provides the details of the fabrication process for achieving low-dark current LWIR CBIRD arrays. Discussion for an effective hard mask for excellent pattern transfer is given and appropriate mounting techniques for good thermal contact during the dry etching process is described. The challenges and differences between etching large 200 ?m test diodes and small 28 ?m FPA pixels are given.

Correlation between dislocations and leakage current of p-n diodes on a free-standing GaN substrate

NASA Astrophysics Data System (ADS)

Usami, Shigeyoshi; Ando, Yuto; Tanaka, Atsushi; Nagamatsu, Kentaro; Deki, Manato; Kushimoto, Maki; Nitta, Shugo; Honda, Yoshio; Amano, Hiroshi; Sugawara, Yoshihiro; Yao, Yong-Zhao; Ishikawa, Yukari

2018-04-01

Dislocations that cause a reverse leakage current in vertical p-n diodes on a GaN free-standing substrate were investigated. Under a high reverse bias, dot-like leakage spots were observed using an emission microscope. Subsequent cathodoluminescence (CL) observations revealed that the leakage spots coincided with part of the CL dark spots, indicating that some types of dislocation cause reverse leakage. When etch pits were formed on the dislocations by KOH etching, three sizes of etch pits were obtained (large, medium, and small). Among these etch pits, only the medium pits coincided with leakage spots. Additionally, transmission electron microscopy observations revealed that pure screw dislocations are present under the leakage spots. The results revealed that 1c pure screw dislocations are related to the reverse leakage in vertical p-n diodes.

Wafer-scale high-throughput ordered arrays of Si and coaxial Si/Si(1-x)Ge(x) wires: fabrication, characterization, and photovoltaic application.

PubMed

Pan, Caofeng; Luo, Zhixiang; Xu, Chen; Luo, Jun; Liang, Renrong; Zhu, Guang; Wu, Wenzhuo; Guo, Wenxi; Yan, Xingxu; Xu, Jun; Wang, Zhong Lin; Zhu, Jing

2011-08-23

We have developed a method combining lithography and catalytic etching to fabricate large-area (uniform coverage over an entire 5-in. wafer) arrays of vertically aligned single-crystal Si nanowires with high throughput. Coaxial n-Si/p-SiGe wire arrays are also fabricated by further coating single-crystal epitaxial SiGe layers on the Si wires using ultrahigh vacuum chemical vapor deposition (UHVCVD). This method allows precise control over the diameter, length, density, spacing, orientation, shape, pattern and location of the Si and Si/SiGe nanowire arrays, making it possible to fabricate an array of devices based on rationally designed nanowire arrays. A proposed fabrication mechanism of the etching process is presented. Inspired by the excellent antireflection properties of the Si/SiGe wire arrays, we built solar cells based on the arrays of these wires containing radial junctions, an example of which exhibits an open circuit voltage (V(oc)) of 650 mV, a short-circuit current density (J(sc)) of 8.38 mA/cm(2), a fill factor of 0.60, and an energy conversion efficiency (η) of 3.26%. Such a p-n radial structure will have a great potential application for cost-efficient photovoltaic (PV) solar energy conversion. © 2011 American Chemical Society

Evaluation of Surlyn 8920 as PHE Visor Material and Evaluations of New Adhesives for Improving Bonding Between Teflon and Stainless Steel at Cryogenic Temperature

NASA Technical Reports Server (NTRS)

Ray, Asit K.

1991-01-01

Two studies are presented, and in the first study, Surlyn 8920 (an ionic and amorphous low density polyethylene made by Dupont) was evaluated as a possible replacement of Plexyglass G as PHE visor material. Four formulations of the polymer were made by adding different amounts of UV stabilizer, energy quencher, and antioxident in a Brabender Plasticorder. The formulated polymers were molded in the form of sheets in a compression molder. Cut samples from the molded sheets were exposed in a weatherometer and tested on Instron Tensile Tester for strength and elongation. Specially molded samples of the formulated polymers were subjected to Charpy Impact Tests. In the second study, preliminary evaluations of adhesives for improvement of bonding between Teflon and stainless steel (SS) were performed. Kapton, a high temperature polyimide made by Dupont, and a rubber based adhesive made by Potter Paint Co., were evaluated against industrial quality epoxy, the current material used to bond Teflon and SS. The degreased surfaces of the SS discs were etched mechanically, with a few of these etched chemically. The surfaces of the SS discs were etched mechanically, with a few of these etched chemically. Bonding strengths were evaluated using lap shear tests on the Instron Tensile Tester for the samples bonded by Kapton and industrial quality epoxy. Bond strengths were also evaluated using a pull test on the Instron for the samples bonded by Potter adhesive (CWL-152) and industrial quality epoxy. Based on limited lap shear data, Kapton gave bond strength favorable compared to that of industrial epoxy. Based on limited pull test data, Kapton bonded and CWL-152 bonded samples showed poor strength compared to epoxy bonded sample.

Femtosecond laser etching of dental enamel for bracket bonding.

PubMed

Kabas, Ayse Sena; Ersoy, Tansu; Gülsoy, Murat; Akturk, Selcuk

2013-09-01

The aim is to investigate femtosecond laser ablation as an alternative method for enamel etching used before bonding orthodontic brackets. A focused laser beam is scanned over enamel within the area of bonding in a saw tooth pattern with a varying number of lines. After patterning, ceramic brackets are bonded and bonding quality of the proposed technique is measured by a universal testing machine. The results are compared to the conventional acid etching method. Results show that bonding strength is a function of laser average power and the density of the ablated lines. Intrapulpal temperature changes are also recorded and observed minimal effects are observed. Enamel surface of the samples is investigated microscopically and no signs of damage or cracking are observed. In conclusion, femtosecond laser exposure on enamel surface yields controllable patterns that provide efficient bonding strength with less removal of dental tissue than conventional acid-etching technique.

Evolution and characteristics of GaN nanowires produced via maskless reactive ion etching.

PubMed

Haab, Anna; Mikulics, Martin; Sutter, Eli; Jin, Jiehong; Stoica, Toma; Kardynal, Beata; Rieger, Torsten; Grützmacher, Detlev; Hardtdegen, Hilde

2014-06-27

The formation of nanowires (NWs) by reactive ion etching (RIE) of maskless GaN layers was investigated. The morphological, structural and optical characteristics of the NWs were studied and compared to those of the layer they evolve from. It is shown that the NWs are the result of a defect selective etching process. The evolution of density and length with etching time is discussed. Densely packed NWs with a length of more than 1 μm and a diameter of ∼60 nm were obtained by RIE of a ∼2.5 μm thick GaN layer. The NWs are predominantly free of threading dislocations and show an improvement of optical properties compared to their layer counterpart. The production of NWs via a top down process on non-masked group III-nitride layers is assessed to be very promising for photovoltaic applications.

Enhanced ultraviolet photoconductivity in porous GaN prepared by metal-assisted electroless etching

NASA Astrophysics Data System (ADS)

Guo, X. Y.; Williamson, T. L.; Bohn, P. W.

2006-10-01

The ultraviolet photoconductivity of porous GaN (PGaN) produced by Pt-assisted electroless etching has been investigated. The photoresponse of PGaN prepared from highly doped GaN ( n>1018 cm) shows enhanced ( 15×) magnitude and faster decay of persistent photoconductivity relative to bulk crystalline (CGaN), suggesting advantages for PGaN in photodetector applications. A space charge model for changes in photoconductivity is used to explain these observations. Heightened defect density in the etched material plays an important role in the enhanced photoconductivity in PGaN. Flux-dependent optical quenching (OQ) behavior, linked to the presence of metastable states, is also observed in PGaN as in CGaN.

Inorganic Bi/In thermal resist as a high-etch-ratio patterning layer for CF4/CHF3/O2 plasma etch

NASA Astrophysics Data System (ADS)

Tu, Yuqiang; Chapman, Glenn H.; Peng, Jun

2004-05-01

Bimetallic thin films containing indium and with low eutectic points, such as Bi/In, have been found to form highly sensitive thermal resists. They can be exposed by lasers with a wide range of wavelengths and be developed by diluted RCA2 solutions. The exposed bimetallic resist Bi/In can work as an etch masking layer for alkaline-based (KOH, TMAH and EDP) "wet" Si anisotropic etching. Current research shows that it can also act as a patterning and masking layer for Si and SiO2 plasma "dry" etch using CF4/CHF3. The profile of etched structures can be tuned by adding CHF3 and other gases such as Ar, and by changing the CF4/CHF3 ratio. Depending on the fluorocarbon plasma etching recipe the etch rate of laser exposed Bi/In can be as low as 0.1nm/min, 500 times lower than organic photoresists. O2 plasma ashing has little etching effect on exposed Bi/In, indicating that laser exposure is an oxidation process. Experiment result shows that single metal Indium film and bilayer Sn/In exhibit thermal resist characteristics but at higher exposure levels. They can be developed in diluted RCA2 solution and used as etch mask layers for Si anisotropic etch and plasma etch.

Bi/In thermal resist for both Si anisotropic wet etching and Si/SiO2 plasma etching

NASA Astrophysics Data System (ADS)

Chapman, Glenn H.; Tu, Yuqiang; Peng, Jun

2004-01-01

Bi/In thermal resist is a bilayer structure of Bi over In films which can be exposed by laser with a wide range of wavelengths and can be developed by diluted RCA2 solutions. Current research shows bimetallic resist can work as etch masking layer for both dry plasma etching and wet anisotropic etching. It can act as both patterning and masking layers for Si and SiO2 with plasma "dry" etch using CF4/CHF3. The etching condition is CF4 flow rate 50 sccm, pressure 150 mTorr, and RF power 100 - 600W. The profile of etched structures can be tuned by adding CHF3 and other gases such as Ar, and by changing the CF4/CHF3 ratio. Depending on the fluorocarbon plasma etching recipe the etch rate of laser exposed Bi/In can be as low as 0.1 nm/min, 500 times lower than organic photoresists. O2 plasma ashing has little etching effect on exposed Bi/In. Bi/In also creates etch masking layers for alkaline-based (KOH, TMAH and EDP) "wet" anisotropic bulk Si etch without the need of SiO2 masking steps. The laser exposed Bi/In etches two times more slowly than SiO2. Experiment result shows that single metal Indium film exhibits thermal resist characteristics but at twice the exposure levels. It can be developed in diluted RCA2 solution and used as an etch mask layer for Si anisotropic etch. X-ray diffraction analysis shows that laser exposure causes both Bi and In single film to oxidize. In film may become amorphous when exposed to high laser power.

Acid Etching and Plasma Sterilization Fail to Improve Osseointegration of Grit Blasted Titanium Implants

PubMed Central

Saksø, Mikkel; Jakobsen, Stig S; Saksø, Henrik; Baas, Jørgen; Jakobsen, Thomas; Søballe, Kjeld

2012-01-01

Interaction between implant surface and surrounding bone influences implant fixation. We attempted to improve the bone-implant interaction by 1) adding surface micro scale topography by acid etching, and 2) removing surface-adherent pro-inflammatory agents by plasma cleaning. Implant fixation was evaluated by implant osseointegration and biomechanical fixation. The study consisted of two paired animal sub-studies where 10 skeletally mature Labrador dogs were used. Grit blasted titanium alloy implants were inserted press fit in each proximal tibia. In the first study grit blasted implants were compared with acid etched grit blasted implants. In the second study grit blasted implants were compared with acid etched grit blasted implants that were further treated with plasma sterilization. Implant performance was evaluated by histomorphometrical investigation (tissue-to-implant contact, peri-implant tissue density) and mechanical push-out testing after four weeks observation time. Neither acid etching nor plasma sterilization of the grit blasted implants enhanced osseointegration or mechanical fixation in this press-fit canine implant model in a statistically significant manner. PMID:22962567

Defect mapping system

DOEpatents

Sopori, Bhushan L.

1995-01-01

Apparatus for detecting and mapping defects in the surfaces of polycrystalline materials in a manner that distinguishes dislocation pits from grain boundaries includes a laser for illuminating a wide spot on the surface of the material, a light integrating sphere with apertures for capturing light scattered by etched dislocation pits in an intermediate range away from specular reflection while allowing light scattered by etched grain boundaries in a near range from specular reflection to pass through, and optical detection devices for detecting and measuring intensities of the respective intermediate scattered light and near specular scattered light. A center blocking aperture or filter can be used to screen out specular reflected light, which would be reflected by nondefect portions of the polycrystalline material surface. An X-Y translation stage for mounting the polycrystalline material and signal processing and computer equipment accommodate rastor mapping, recording, and displaying of respective dislocation and grain boundary defect densities. A special etch procedure is included, which prepares the polycrystalline material surface to produce distinguishable intermediate and near specular light scattering in patterns that have statistical relevance to the dislocation and grain boundary defect densities.

Defect mapping system

DOEpatents

Sopori, B.L.

1995-04-11

Apparatus for detecting and mapping defects in the surfaces of polycrystalline materials in a manner that distinguishes dislocation pits from grain boundaries includes a laser for illuminating a wide spot on the surface of the material, a light integrating sphere with apertures for capturing light scattered by etched dislocation pits in an intermediate range away from specular reflection while allowing light scattered by etched grain boundaries in a near range from specular reflection to pass through, and optical detection devices for detecting and measuring intensities of the respective intermediate scattered light and near specular scattered light. A center blocking aperture or filter can be used to screen out specular reflected light, which would be reflected by nondefect portions of the polycrystalline material surface. An X-Y translation stage for mounting the polycrystalline material and signal processing and computer equipment accommodate rastor mapping, recording, and displaying of respective dislocation and grain boundary defect densities. A special etch procedure is included, which prepares the polycrystalline material surface to produce distinguishable intermediate and near specular light scattering in patterns that have statistical relevance to the dislocation and grain boundary defect densities. 20 figures.

Fabrication of self-aligned, nanoscale, complex oxide varactors

NASA Astrophysics Data System (ADS)

Fu, Richard X.; Toonen, Ryan C.; Hirsch, Samuel G.; Ivill, Mathew P.; Cole, Melanie W.; Strawhecker, Kenneth E.

2015-01-01

Applications in ferroelectric random access memory and superparaelectric devices require the fabrication of ferroelectric capacitors at the nanoscale that exhibit extremely small leakage currents. To systematically study the material-size dependence of ferroelectric varactor performance, arrays of parallel-plate structures have been fabricated with nanoscale dielectric diameters. Electron beam lithography and inductively coupled plasma dry etching have been used to fabricate arrays of ferroelectric varactors using top electrodes as a self-aligned etch mask. Parallel-plate test structures using RF-sputtered Ba0.6Sr0.4TiO3 thin-films were used to optimize the fabrication process. Varactors with diameters down to 20 nm were successfully fabricated. Current-voltage (I-V) characteristics were measured to evaluate the significance of etch-damage and fabrication quality by ensuring low leakage currents through the structures.

Near-infrared emission from mesoporous crystalline germanium

NASA Astrophysics Data System (ADS)

Boucherif, Abderraouf; Korinek, Andreas; Aimez, Vincent; Arès, Richard

2014-10-01

Mesoporous crystalline germanium was fabricated by bipolar electrochemical etching of Ge wafer in HF-based electrolyte. It yields uniform mesoporous germanium layers composed of high density of crystallites with an average size 5-7 nm. Subsequent extended chemical etching allows tuning of crystallites size while preserving the same chemical composition. This highly controllable nanostructure exhibits photoluminescence emission above the bulk Ge bandgap, in the near-infrared range (1095-1360nm) with strong evidence of quantum confinement within the crystallites.

Spectroscopic and microscopic investigation of MBE-grown CdTe (211)B epitaxial thin films on GaAs (211)B substrates

NASA Astrophysics Data System (ADS)

Özden, Selin; Koc, Mumin Mehmet

2018-03-01

CdTe epitaxial thin films, for use as a buffer layer for HgCdTe defectors, were grown on GaAs (211)B using the molecular beam epitaxy method. Wet chemical etching (Everson method) was applied to the epitaxial films using various concentrations and application times to quantify the crystal quality and dislocation density. Surface characterization of the epitaxial films was achieved using Atomic force microscopy and Scanning electron microscopy (SEM) before and after each treatment. The Energy Dispersive X-Ray apparatus of SEM was used to characterize the chemical composition. Untreated CdTe films show smooth surface characteristics with root mean square (RMS) roughnesses of 1.18-3.89 nm. The thicknesses of the CdTe layers formed were calculated via FTIR spectrometry and obtained by ex situ spectroscopic ellipsometry. Raman spectra were obtained for various temperatures. Etch pit densities (EPD) were measured, from which it could be seen that EPD changes between 1.7 × 108 and 9.2 × 108 cm-2 depending on the concentration of the Everson etch solution and treatment time. Structure, shape and depth of pits resulting from each etch pit implementation were also evaluated. Pit widths varying between 0.15 and 0.71 µm with heights varying between 2 and 80 nm were observed. RMS roughness was found to vary by anything from 1.56 to 26 nm.

Modeling Cl2/O2/Ar inductively coupled plasmas used for silicon etching: effects of SiO2 chamber wall coating

NASA Astrophysics Data System (ADS)

Tinck, S.; Boullart, W.; Bogaerts, A.

2011-08-01

In this paper, simulations are performed to gain a better insight into the properties of a Cl2/Ar plasma, with and without O2, during plasma etching of Si. Both plasma and surface properties are calculated in a self-consistent manner. Special attention is paid to the behavior of etch products coming from the wafer or the walls, and how the chamber walls can affect the plasma and the resulting etch process. Two modeling cases are considered. In the first case, the reactor walls are defined as clean (Al2O3), whereas in the second case a SiO2 coating is introduced on the reactor walls before the etching process, so that oxygen will be sputtered from the walls and introduced into the plasma. For this reason, a detailed reaction set is presented for a Cl2/O2/Ar plasma containing etched species, as well as an extensive reaction set for surface processes, including physical and chemical sputtering, chemical etching and deposition processes. Density and flux profiles of various species are presented for a better understanding of the bulk plasma during the etching process. Detailed information is also given on the composition of the surfaces at various locations of the reactor, on the etch products in the plasma and on the surface loss probabilities of the plasma species at the walls, with different compositions. It is found that in the clean chamber, walls are mostly chlorinated (Al2Cl3), with a thin layer of etch products residing on the wall. In the coated chamber, an oxy-chloride layer is grown on the walls for a few nanometers during the etching process. The Cl atom wall loss probability is found to decrease significantly in the coated chamber, hence increasing the etch rate. SiCl2, SiCl4 and SiCl3 are found to be the main etch products in the plasma, with the fraction of SiCl2 being always slightly higher. The simulation results compare well with experimental data available from the literature.

Inductively Coupled Plasma-Induced Electrical Damage on HgCdTe Etched Surface at Cryogenic Temperatures

NASA Astrophysics Data System (ADS)

Liu, L. F.; Chen, Y. Y.; Ye, Z. H.; Hu, X. N.; Ding, R. J.; He, L.

2018-03-01

Plasma etching is a powerful technique for transferring high-resolution lithographic patterns into HgCdTe material with low etch-induced damage, and it is important for fabricating small-pixel-size HgCdTe infrared focal plane array (IRFPA) detectors. P- to n-type conversion is known to occur during plasma etching of vacancy-doped HgCdTe; however, it is usually unwanted and its removal requires extra steps. Etching at cryogenic temperatures can reduce the etch-induced type conversion depth in HgCdTe via the electrical damage mechanism. Laser beam-induced current (LBIC) is a nondestructive photoelectric characterization technique which can provide information regarding the vertical and lateral electrical field distribution, such as defects and p-n junctions. In this work, inductively coupled plasma (ICP) etching of HgCdTe was implemented at cryogenic temperatures. For an Ar/CH4 (30:1 in SCCM) plasma with ICP input power of 1000 W and RF-coupled DC bias of ˜ 25 V, a HgCdTe sample was dry-etched at 123 K for 5 min using ICP. The sample was then processed to remove a thin layer of the plasma-etched region while maintaining a ladder-like damaged layer by continuously controlling the wet chemical etching time. Combining the ladder etching method and LBIC measurement, the ICP etching-induced electrical damage depth was measured and estimated to be about 20 nm. The results indicate that ICP etching at cryogenic temperatures can significantly suppress plasma etching-induced electrical damage, which is beneficial for defining HgCdTe mesa arrays.

Fabrication of optical filters using multilayered porous silicon

NASA Astrophysics Data System (ADS)

Gaber, Noha; Khalil, Diaa; Shaarawi, Amr

2011-02-01

In this work we describe a method for fabricating optical filters using multilayered porous silicon 1D photonic structure. An electrochemical cell is constructed to control the porosity of variable layers in p-type Si wafers. Porous silicon multilayered structures are formed of λ/4 (or multiples) thin films that construct optical interference filters. By changing the anodizing current density of the cell during fabrication, different porosities can be obtained as the optical refractive index is a direct function of the layer porosity. To determine the morphology, the wavelength dependent refractive index n and absorption coefficient α, first, porous silicon free standing mono-layers have been fabricated at different conditions and characterized in the near infrared region (from 1000 to 2500nm). Large difference in refractive index (between 1.6 and 2.6) is obtained. Subsequently, multilayer structures have been fabricated and tested. Their spectral response has been measured and it shows good agreement with numerical simulations. A technique based on inserting etching breaks is adopted to ensure the depth homogeneity. The effect of differing etching/break times on the reproducibility of the filters is studied.

Bottom-up and top-down fabrication of nanowire-based electronic devices: In situ doping of vapor liquid solid grown silicon nanowires and etch-dependent leakage current in InGaAs tunnel junctions

NASA Astrophysics Data System (ADS)

Kuo, Meng-Wei

Semiconductor nanowires are important components in future nanoelectronic and optoelectronic device applications. These nanowires can be fabricated using either bottom-up or top-down methods. While bottom-up techniques can achieve higher aspect ratio at reduced dimension without having surface and sub-surface damage, uniform doping distributions with abrupt junction profiles are less challenging for top-down methods. In this dissertation, nanowires fabricated by both methods were systematically investigated to understand: (1) the in situ incorporation of boron (B) dopants in Si nanowires grown by the bottom-up vapor-liquid-solid (VLS) technique, and (2) the impact of plasma-induced etch damage on InGaAs p +-i-n+ nanowire junctions for tunnel field-effect transistors (TFETs) applications. In Chapter 2 and 3, the in situ incorporation of B in Si nanowires grown using silane (SiH4) or silicon tetrachloride (SiCl4) as the Si precursor and trimethylboron (TMB) as the p-type dopant source is investigated by I-V measurements of individual nanowires. The results from measurements using a global-back-gated test structure reveal nonuniform B doping profiles on nanowires grown from SiH4, which is due to simultaneous incorporation of B from nanowire surface and the catalyst during VLS growth. In contrast, a uniform B doping profile in both the axial and radial directions is achieved for TMBdoped Si nanowires grown using SiCl4 at high substrate temperatures. In Chapter 4, the I-V characteristics of wet- and dry-etched InGaAs p+-i-n+ junctions with different mesa geometries, orientations, and perimeter-to-area ratios are compared to evaluate the impact of the dry etch process on the junction leakage current properties. Different post-dry etch treatments, including wet etching and thermal annealing, are performed and the effectiveness of each is assessed by temperaturedependent I-V measurements. As compared to wet-etched control devices, dry-etched junctions have a significantly higher leakage current and a current kink in the reverse bias regime, which is likely due to additional trap states created by plasma-induced damage during the Cl2/Ar/H2 mesa isolation step. These states extend more than 60 nm from the mesa surface and can only be partially passivated after a thermal anneal at 350°C for 20 minutes. The evolution of the electrical properties with post-dry etch treatments indicates that the shallow and deep-level trap states resulting from ion-induced point defects, arsenic vacancies and hydrogen-dopant complexes are the primary cause of degradation in the electrical properties of the dry-etched junctions.

Low-k SiOCH Film Etching Process and Its Diagnostics Employing Ar/C5F10O/N2 Plasma

NASA Astrophysics Data System (ADS)

Nagai, Mikio; Hayashi, Takayuki; Hori, Masaru; Okamoto, Hidekazu

2006-09-01

We proposed an environmental harmonic etching gas of C5F10O (CF3CF2CF2OCFCF2), and demonstrated the etching of low-k SiOCH films employing a dual-frequency capacitively coupled etching system. Dissociative ionization cross sections for the electron impact ionizations of C5F10O and c-C4F8 gases have been measured by quadrupole mass spectroscopy (QMS). The dissociative ionization cross section of CF3+ from C5F10O gas was much higher than those of other ionic species, and 10 times higher than that of CF3+ from C4F8 gas. CF3+ is effective for increasing the etching rate of SiO2. As a result, the etching rate of SiOCH films using Ar/C5F10O/N2 plasma was about 1000 nm/min, which is much higher than that using Ar/C4F8/N2 plasma. The behaviours of fluorocarbon radicals in Ar/C5F10O/N2 plasma, which were measured by infrared diode laser absorption spectroscopy, were similar to those in Ar/C4F8/N2 plasma. The densities of CF and CF3 radicals were markedly decreased with increasing N2 flow rate. Etching rate was controlled by N2 flow rate. A vertical profile of SiOCH with a high etching rate and less microloading was realized using Ar/C5F10O/N2 plasma chemistry.

Effects of dry etching processes on exciton and polariton characteristics in ZnTe

NASA Astrophysics Data System (ADS)

Sun, J. H.; Xie, W. B.; Shen, W. Z.; Ogawa, H.; Guo, Q. X.

2003-12-01

We have employed temperature-dependent reflection spectra to study the effects of reactive ion etching (RIE) on the exciton and polariton characteristics in ZnTe crystals exposed to CH4/H2 gases under different rf plasma powers. Classic exciton-polariton theory has been used to calculate the reflection spectra. By comparing with an as-grown ZnTe crystal and the temperature-dependent behavior, we are able to identify the excitons and RIE-induced polariton structures in these dry etched ZnTe crystals. An increase of the rf plasma power will lead to an increase of defect density in the surface damage layers, resulting in a decrease of the photon energies of the observed exciton and polariton structures.

Natural substrate lift-off technique for vertical light-emitting diodes

NASA Astrophysics Data System (ADS)

Lee, Chia-Yu; Lan, Yu-Pin; Tu, Po-Min; Hsu, Shih-Chieh; Lin, Chien-Chung; Kuo, Hao-Chung; Chi, Gou-Chung; Chang, Chun-Yen

2014-04-01

Hexagonal inverted pyramid (HIP) structures and the natural substrate lift-off (NSLO) technique were demonstrated on a GaN-based vertical light-emitting diode (VLED). The HIP structures were formed at the interface between GaN and the sapphire substrate by molten KOH wet etching. The threading dislocation density (TDD) estimated by transmission electron microscopy (TEM) was reduced to 1 × 108 cm-2. Raman spectroscopy indicated that the compressive strain from the bottom GaN/sapphire was effectively released through the HIP structure. With the adoption of the HIP structure and NSLO, the light output power and yield performance of leakage current could be further improved.

Microplasma illumination enhancement of vertically aligned conducting ultrananocrystalline diamond nanorods

PubMed Central

2012-01-01

Vertically aligned conducting ultrananocrystalline diamond (UNCD) nanorods are fabricated using the reactive ion etching method incorporated with nanodiamond particles as mask. High electrical conductivity of 275 Ω·cm−1 is obtained for UNCD nanorods. The microplasma cavities using UNCD nanorods as cathode show enhanced plasma illumination characteristics of low threshold field of 0.21 V/μm with plasma current density of 7.06 mA/cm2 at an applied field of 0.35 V/μm. Such superior electrical properties of UNCD nanorods with high aspect ratio potentially make a significant impact on the diamond-based microplasma display technology. PMID:23009733

High density circuit technology, part 3

NASA Technical Reports Server (NTRS)

Wade, T. E.

1982-01-01

Dry processing - both etching and deposition - and present/future trends in semiconductor technology are discussed. In addition to a description of the basic apparatus, terminology, advantages, glow discharge phenomena, gas-surface chemistries, and key operational parameters for both dry etching and plasma deposition processes, a comprehensive survey of dry processing equipment (via vendor listing) is also included. The following topics are also discussed: fine-line photolithography, low-temperature processing, packaging for dense VLSI die, the role of integrated optics, and VLSI and technology innovations.

The Influence of Pores in Track Etched Membranes and Prepared on their Base Polymer/Metal Composites on their Fracture Strength

NASA Astrophysics Data System (ADS)

Gumirova, V. N.; Bedin, S. A.; Abdurashidova, G. S.; Razumovskaya, I. V.

The strength of track etched membranes and prepared on their base polymer/metal composites is analysed in point of view of the pores form evolution during the extension and the interaction of elastic mechanical fields on closely positioned pores. The stress-strain curves for track membranes and composites PET/Cu are demonstrated for pore density 1.2×107сm-2 and diameters from 0.06 μm to 2.9 μm

Cr-Si Schottky nano-diodes utilizing anodic aluminum oxide templates.

PubMed

Kwon, Namyong; Kim, Kyohyeok; Heo, Jinhee; Chung, Ilsub

2014-04-01

We have fabricated Cr nanodot Schottky diodes utilizing AAO templates formed on n-Si substrates. The diameters of the diodes were 75.0, 57.6, and 35.8 nm. Cr nanodot Schottky diodes with smaller diameters yield higher current densities than those with larger diameters due to an enhanced tunnel current contribution, which is attributed to a reduction in the barrier thickness. The diameters of Cr nanodots smaller than the Debye length (156 nm) play an important role in the reduction of barrier thickness. Also, we have fabricated Cr-Si nanorod Schottky diodes with three different lengths (130, 220, and 330 nm) by dry etching of n-Si substrate. Cr-Si nanorod Schottky diodes with longer nanorods yield higher reverse current than those with shorter nanorods due to the enhanced electric field, which is attributed to a high aspect ratio of Si nanorod.

Interface Trap Density Reduction for Al2O3/GaN (0001) Interfaces by Oxidizing Surface Preparation prior to Atomic Layer Deposition.

PubMed

Zhernokletov, Dmitry M; Negara, Muhammad A; Long, Rathnait D; Aloni, Shaul; Nordlund, Dennis; McIntyre, Paul C

2015-06-17

We correlate interfacial defect state densities with the chemical composition of the Al2O3/GaN interface in metal-oxide-semiconductor (MOS) structures using synchrotron photoelectron emission spectroscopy (PES), cathodoluminescence and high-temperature capacitance-voltage measurements. The influence of the wet chemical pretreatments involving (1) HCl+HF etching or (2) NH4OH(aq) exposure prior to atomic layer deposition (ALD) of Al2O3 were investigated on n-type GaN (0001) substrates. Prior to ALD, PES analysis of the NH4OH(aq) treated surface shows a greater Ga2O3 component compared to either HCl+HF treated or as-received surfaces. The lowest surface concentration of oxygen species is detected on the acid etched surface, whereas the NH4OH treated sample reveals the lowest carbon surface concentration. Both surface pretreatments improve electrical characteristics of MOS capacitors compared to untreated samples by reducing the Al2O3/GaN interface state density. The lowest interfacial trap density at energies in the upper band gap is detected for samples pretreated with NH4OH. These results are consistent with cathodoluminescence data indicating that the NH4OH treated samples show the strongest band edge emission compared to as-received and acid etched samples. PES results indicate that the combination of reduced carbon contamination while maintaining a Ga2O3 interfacial layer by NH4OH(aq) exposure prior to ALD results in fewer interface traps after Al2O3 deposition on the GaN substrate.

Fabrication of Schottky Junction Between Au and SrTiO3

NASA Astrophysics Data System (ADS)

Inoue, Akira; Izumisawa, Kei; Uwe, Hiromoto

2001-05-01

A Schottky junction with a high rectification ratio between Au and La-doped SrTiO3 has been fabricated using a simple surface treatment. Highly La-doped (5%) SrTiO3 single crystals are annealed in O2 atmosphere at about 1000°C for 1 h and etched in HNO3 for more than five min. The HNO3 etching is performed in a globe box containing N2 to prevent pollution from the air. After the treatment, Au is deposited on the SrTiO3 surface in a vacuum (˜ 10-7 Torr) with an e-gun evaporator. The current voltage characteristics of the junction have shown excellent rectification properties, although junctions using neither annealed nor etched SrTiO3 exhibit high leak current in reverse voltage. The rectification ratio of the junction at 1 V is more than six orders of magnitude and there is no hysteresis in the current voltage spectra. The logarithm of the current is linear with the forward bias voltage. The ideal factor of the junction is estimated to be about 1.68. These results suggest that, if prevented from being pollution by the air, a good Schottky junction can be obtained by easy processes such as annealing in oxygen atmosphere and surface etching with acid.

Effect of thermionic cathode heating current self-magnetic field on gaseous plasma generator characteristics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lopatin, I. V., E-mail: lopatin@opee.hcei.tsc.ru; Akhmadeev, Yu. H.; Koval, N. N.

2015-10-15

The performance capabilities of the PINK, a plasma generator with a thermionic cathode mounted in the cavity of a hollow cathode, depending for its operation on a non-self-sustained low-pressure gas discharge have been investigated. It has been shown that when a single-filament tungsten cathode 2 mm in diameter is used and the peak filament current is equal to or higher than 100 A, the self-magnetic field of the filament current significantly affects the discharge current and voltage waveforms. This effect is due to changes in the time and space distributions of the emission current density from the hot cathode. Whenmore » the electron mean free path is close to the characteristic dimensions of the thermionic cathode, the synthesized plasma density distribution is nonuniform and the cathode is etched nonuniformly. The cathode lifetime in this case is 8–12 h. Using a cathode consisting of several parallel-connected tungsten filaments ∼0.8 mm in diameter moderates the effect of the self-magnetic field of the filament current and nearly doubles the cathode lifetime. The use of this type of cathode together with a discharge igniting electrode reduces the minimum operating pressure in the plasma generator to about one third of that required for the generator operation with a single-filament cathode (to 0.04 Pa)« less

Stacking sequence and interlayer coupling in few-layer graphene revealed by in situ imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Zhu-Jun; Dong, Jichen; Cui, Yi

In the transition from graphene to graphite, the addition of each individual graphene layer modifies the electronic structure and produces a different material with unique properties. Controlled growth of few-layer graphene is therefore of fundamental interest and will provide access to materials with engineered electronic structure. Here we combine isothermal growth and etching experiments with in situ scanning electron microscopy to reveal the stacking sequence and interlayer coupling strength in few-layer graphene. The observed layer-dependent etching rates reveal the relative strength of the graphene graphene and graphene substrate interaction and the resulting mode of adlayer growth. Scanning tunnelling microscopy andmore » density functional theory calculations confirm a strong coupling between graphene edge atoms and platinum. Simulated etching confirms that etching can be viewed as reversed growth. This work demonstrates that real-time imaging under controlled atmosphere is a powerful method for designing synthesis protocols for sp2 carbon nanostructures in between graphene and graphite.« less

Lithography-free glass surface modification by self-masking during dry etching

NASA Astrophysics Data System (ADS)

Hein, Eric; Fox, Dennis; Fouckhardt, Henning

2011-01-01

Glass surface morphologies with defined shapes and roughness are realized by a two-step lithography-free process: deposition of an ~10-nm-thin lithographically unstructured metallic layer onto the surface and reactive ion etching in an Ar/CF4 high-density plasma. Because of nucleation or coalescence, the metallic layer is laterally structured during its deposition. Its morphology exhibits islands with dimensions of several tens of nanometers. These metal spots cause a locally varying etch velocity of the glass substrate, which results in surface structuring. The glass surface gets increasingly rougher with further etching. The mechanism of self-masking results in the formation of surface structures with typical heights and lateral dimensions of several hundred nanometers. Several metals, such as Ag, Al, Au, Cu, In, and Ni, can be employed as the sacrificial layer in this technology. Choice of the process parameters allows for a multitude of different glass roughness morphologies with individual defined and dosed optical scattering.

Stacking sequence and interlayer coupling in few-layer graphene revealed by in situ imaging

DOE PAGES

Wang, Zhu-Jun; Dong, Jichen; Cui, Yi; ...

2016-10-19

In the transition from graphene to graphite, the addition of each individual graphene layer modifies the electronic structure and produces a different material with unique properties. Controlled growth of few-layer graphene is therefore of fundamental interest and will provide access to materials with engineered electronic structure. Here we combine isothermal growth and etching experiments with in situ scanning electron microscopy to reveal the stacking sequence and interlayer coupling strength in few-layer graphene. The observed layer-dependent etching rates reveal the relative strength of the graphene graphene and graphene substrate interaction and the resulting mode of adlayer growth. Scanning tunnelling microscopy andmore » density functional theory calculations confirm a strong coupling between graphene edge atoms and platinum. Simulated etching confirms that etching can be viewed as reversed growth. This work demonstrates that real-time imaging under controlled atmosphere is a powerful method for designing synthesis protocols for sp2 carbon nanostructures in between graphene and graphite.« less

Stacking sequence and interlayer coupling in few-layer graphene revealed by in situ imaging

PubMed Central

Wang, Zhu-Jun; Dong, Jichen; Cui, Yi; Eres, Gyula; Timpe, Olaf; Fu, Qiang; Ding, Feng; Schloegl, R.; Willinger, Marc-Georg

2016-01-01

In the transition from graphene to graphite, the addition of each individual graphene layer modifies the electronic structure and produces a different material with unique properties. Controlled growth of few-layer graphene is therefore of fundamental interest and will provide access to materials with engineered electronic structure. Here we combine isothermal growth and etching experiments with in situ scanning electron microscopy to reveal the stacking sequence and interlayer coupling strength in few-layer graphene. The observed layer-dependent etching rates reveal the relative strength of the graphene–graphene and graphene–substrate interaction and the resulting mode of adlayer growth. Scanning tunnelling microscopy and density functional theory calculations confirm a strong coupling between graphene edge atoms and platinum. Simulated etching confirms that etching can be viewed as reversed growth. This work demonstrates that real-time imaging under controlled atmosphere is a powerful method for designing synthesis protocols for sp2 carbon nanostructures in between graphene and graphite. PMID:27759024

A Dry-Etch Process for Low Temperature Superconducting Transition Edge Sensors for Far Infrared Bolometer Arrays

NASA Technical Reports Server (NTRS)

Allen, Christine A.; Chervenak, James A.; Hsieh, Wen-Ting; McClanahan, Richard A.; Miller, Timothy M.; Mitchell, Robert; Moseley, S. Harvey; Staguhn, Johannes; Stevenson, Thomas R.

2003-01-01

The next generation of ultra-low power bolometer arrays, with applications in far infrared imaging, spectroscopy and polarimetry, utilizes a superconducting bilayer as the sensing element to enable SQUID multiplexed readout. Superconducting transition edge sensors (TES s) are being produced with dual metal systems of superconductinghormal bilayers. The transition temperature (Tc) is tuned by altering the relative thickness of the superconductor with respect to the normal layer. We are currently investigating MoAu and MoCu bilayers. We have developed a dry-etching process for MoAu TES s with integrated molybdenum leads, and are working on adapting the process to MoCu. Dry etching has the advantage over wet etching in the MoAu system in that one can achieve a high degree of selectivity, greater than 10, using argon ME, or argon ion milling, for patterning gold on molybdenum. Molybdenum leads are subsequently patterned using fluorine plasma.. The dry-etch technique results in a smooth, featureless TES with sharp sidewalls, no undercutting of the Mo beneath the normal metal, and Mo leads with high critical current. The effects of individual processing parameters on the characteristics of the transition will be reported.

InGaAsP/InP buried-heterostructure lasers /lambda = 1.5 microns/ with chemically etched mirrors

NASA Astrophysics Data System (ADS)

Adachi, S.; Kawaguchi, H.; Takahei, K.; Noguchi, Y.

1981-09-01

The monolithic fabrication of buried heterostructure InGaAsP/InP lasers operating at a wavelength of 1.5 microns with chemically etched mirrors is reported. The buried heterostructure lasers were prepared from InGaAsP/InP DH wafers reverse-mesa etched with a Br2:CH3OH solution, with the reverse-mesa walls buried by subsequent LPE growth. To fabricate the etched mirror laser, Au-Zn metal was evaporated onto the epitaxial-layer side of the wafer and an Au-Zn contact was defined by photolithography; photolithographic techniques were used to define a SiO2 mask directly over the Au-Zn contact for etched mirror definition using either 0.3 vol % Br2:CH3OH or HCl:CH3COOH:H2O2 1:2:1 solutions. A threshold current of 50 mA is obtained from lasers thus produced, which is nearly the same as that of conventionally fabricated cleaved-mirror lasers. The procedure presented thus allows low threshold-current devices to be obtained with a much greater flexibility in design and fabrication than previously attained.

Metal-assisted electroless fabrication of nanoporous p-GaN for increasing the light extraction efficiency of light emitting diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang Ruijun; Liu Duo; Zuo Zhiyuan

2012-03-15

We report metal-assisted electroless fabrication of nanoporous p-GaN to improve the light extraction efficiency of GaN-based light emitting diodes (LEDs). Although it has long been believed that p-GaN cannot be etched at room temperature, in this study we find that Ag nanocrystals (NCs) on the p-GaN surface enable effective etching of p-GaN in a mixture of HF and K{sub 2}S{sub 2}O{sub 8} under ultraviolet (UV) irradiation. It is further shown that the roughened GaN/air interface enables strong scattering of photons emitted from the multiple quantum wells (MQWs). The light output power measurements indicate that the nanoporous LEDs obtained after 10more » min etching show a 32.7% enhancement in light-output relative to the conventional LEDs at an injection current of 20 mA without significant increase of the operating voltage. In contrast, the samples etched for 20 min show performance degradation when compared with those etched for 10 min, this is attributed to the current crowding effect and increased surface recombination rate.« less

O2 Plasma Etching and Antistatic Gun Surface Modifications for CNT Yarn Microelectrode Improve Sensitivity and Antifouling Properties.

PubMed

Yang, Cheng; Wang, Ying; Jacobs, Christopher B; Ivanov, Ilia N; Venton, B Jill

2017-05-16

Carbon nanotube (CNT) based microelectrodes exhibit rapid and selective detection of neurotransmitters. While different fabrication strategies and geometries of CNT microelectrodes have been characterized, relatively little research has investigated ways to selectively enhance their electrochemical properties. In this work, we introduce two simple, reproducible, low-cost, and efficient surface modification methods for carbon nanotube yarn microelectrodes (CNTYMEs): O 2 plasma etching and antistatic gun treatment. O 2 plasma etching was performed by a microwave plasma system with oxygen gas flow and the optimized time for treatment was 1 min. The antistatic gun treatment flows ions by the electrode surface; two triggers of the antistatic gun was the optimized number on the CNTYME surface. Current for dopamine at CNTYMEs increased 3-fold after O 2 plasma etching and 4-fold after antistatic gun treatment. When the two treatments were combined, the current increased 12-fold, showing the two effects are due to independent mechanisms that tune the surface properties. O 2 plasma etching increased the sensitivity due to increased surface oxygen content but did not affect surface roughness while the antistatic gun treatment increased surface roughness but not oxygen content. The effect of tissue fouling on CNT yarns was studied for the first time, and the relatively hydrophilic surface after O 2 plasma etching provided better resistance to fouling than unmodified or antistatic gun treated CNTYMEs. Overall, O 2 plasma etching and antistatic gun treatment improve the sensitivity of CNTYMEs by different mechanisms, providing the possibility to tune the CNTYME surface and enhance sensitivity.

Non-chapped, vertically well aligned titanium dioxide nanotubes fabricated by electrochemical etching

NASA Astrophysics Data System (ADS)

Loan Nguyen, Thu; Dieu Thuy Ung, Thi; Liem Nguyen, Quang

2014-06-01

This paper reports on the fabrication of non-chapped, vertically well aligned titanium dioxide nanotubes (TONTs) by using electrochemical etching method and further heat treatment. Very highly ordered metallic titanium nanotubes (TNTs) were formed by directly anodizing titanium foil at room temperature in an electrolyte composed of ammonium fluoride (NH4F), ethylene glycol (EG), and water. The morphology of as-formed TNTs is greatly dependent on the applied voltage, NH4F content and etching time. Particularly, we have found two interesting points related to the formation of TNTs: (i) the smooth surface without chaps of the largely etched area was dependent on the crystalline orientation of the titanium foil; and (ii) by increasing the anodizing potential from 15 V to 20 V, the internal diameter of TNT was increased from about 50 nm to 60 nm and the tube density decreased from 403 tubes μm-2 down to 339 tubes μm-2, respectively. For the anodizing duration from 1 h to 5 h, the internal diameter of each TNT was increased from ˜30 nm to 60 nm and the tube density decreased from 496 tubes μm-2 down to 403 tubes μm-2. After annealing at 400 °C in open air for 1 h, the TNTs were transformed into TONTs in anatase structure; further annealing at 600 °C showed the structural transformation from anatase to rutile as determined by Raman scattering spectroscopy.

High-power LEDs based on InGaAsP/InP heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rakovics, V.; Imenkov, A. N.; Sherstnev, V. V.

2014-12-15

High-power light-emitting diodes (LEDs) with mesa diameters of 100, 200, and 300 μm are developed on the basis of InGaAsP/InP heterostructures. The mesas are close in shape to a truncated cone with a generatrix inclination angle of ∼45° in the vicinity of the active region of the LED, with a ring etched around the mesa serving as a reflector. The emission spectra and directivity patterns of these LEDs are studied in a wide range of current densities and it is shown that radiative recombination is dominant to a current density of ∼5000 A/cm{sup 2}, which makes these structures promising formore » the development of high-power LEDs. An emission power of ∼14 mW is obtained in the continuous-wave mode (I = 0.2 A, λ = 1.1 μm), and that of 77 mW, in the pulsed mode (I = 2 A, λ = 1.1 μm), which corresponds to external quantum efficiencies of 6.2 and 3.4%, respectively.« less

Electrochemical Corrosion Properties of Commercial Ultra-Thin Copper Foils

NASA Astrophysics Data System (ADS)

Yen, Ming-Hsuan; Liu, Jen-Hsiang; Song, Jenn-Ming; Lin, Shih-Ching

2017-08-01

Ultra-thin electrodeposited Cu foils have been developed for substrate thinning for mobile devices. Considering the corrosion by residual etchants from the lithography process for high-density circuit wiring, this study investigates the microstructural features of ultra-thin electrodeposited Cu foils with a thickness of 3 μm and their electrochemical corrosion performance in CuCl2-based etching solution. X-ray diffraction and electron backscatter diffraction analyses verify that ultra-thin Cu foils exhibit a random texture and equi-axed grains. Polarization curves show that ultra-thin foils exhibit a higher corrosion potential and a lower corrosion current density compared with conventional (220)-oriented foils with fan-like distributed fine-elongated columnar grains. Chronoamperometric results also suggest that ultra-thin foils possess superior corrosion resistance. The passive layer, mainly composed of CuCl and Cu2O, forms and dissolves in sequence during polarization.

GPU based 3D feature profile simulation of high-aspect ratio contact hole etch process under fluorocarbon plasmas

NASA Astrophysics Data System (ADS)

Chun, Poo-Reum; Lee, Se-Ah; Yook, Yeong-Geun; Choi, Kwang-Sung; Cho, Deog-Geun; Yu, Dong-Hun; Chang, Won-Seok; Kwon, Deuk-Chul; Im, Yeon-Ho

2013-09-01

Although plasma etch profile simulation has been attracted much interest for developing reliable plasma etching, there still exist big gaps between current research status and predictable modeling due to the inherent complexity of plasma process. As an effort to address this issue, we present 3D feature profile simulation coupled with well-defined plasma-surface kinetic model for silicon dioxide etching process under fluorocarbon plasmas. To capture the realistic plasma surface reaction behaviors, a polymer layer based surface kinetic model was proposed to consider the simultaneous polymer deposition and oxide etching. Finally, the realistic plasma surface model was used for calculation of speed function for 3D topology simulation, which consists of multiple level set based moving algorithm, and ballistic transport module. In addition, the time consumable computations in the ballistic transport calculation were improved drastically by GPU based numerical computation, leading to the real time computation. Finally, we demonstrated that the surface kinetic model could be coupled successfully for 3D etch profile simulations in high-aspect ratio contact hole plasma etching.

Morphologies and optical and electrical properties of InGaN/GaN micro-square array light-emitting diode chips.

PubMed

Han, Dan; Ma, Shufang; Jia, Zhigang; Liu, Peizhi; Jia, Wei; Shang, Lin; Zhai, Guangmei; Xu, Bingshe

2018-04-10

InGaN/GaN micro-square array light-emitting diode (LED) chips (micro-chips) have been prepared via the focused ion beam (FIB) etching technique, which can not only reduce ohmic contact degradation but also control the aspect ratio precisely in three-dimensional (3D) structure LED (3D-LED) device fabrication. The effects of FIB beam current and micro-square array depth on morphologies and optical and electrical properties of the micro-chips have been studied. Our results show that sidewall surface morphology and optical and electrical properties of the micro-chips degrade with increased beam current. After potassium hydroxide etching with different times, an optimal current-voltage and luminescence performance can be obtained. Combining the results of cathodoluminescence mappings and light output-current characteristics, the light extraction efficiency of the micro-chips is reduced as FIB etch depth increases. The mechanisms of micro-square depth on light extraction have been revealed by 3D finite difference time domain.

Influence of Different Etching Modes on Bond Strength to Enamel using Universal Adhesive Systems.

PubMed

Diniz, Ana Cs; Bandeca, Matheus C; Pinheiro, Larissa M; Dos Santosh Almeida, Lauber J; Torres, Carlos Rg; Borges, Alvaro H; Pinto, Shelon Cs; Tonetto, Mateus R; De Jesus Tavarez, Rudys R; Firoozmand, Leily M

2016-10-01

The adhesive systems and the techniques currently used are designed to provide a more effective adhesion with reduction of the protocol application. The objective of this study was to evaluate the bond strength of universal adhesive systems on enamel in different etching modes (self-etch and total etch). The mesial and distal halves of 52 bovine incisors, healthy, freshly extracted, were used and divided into seven experimental groups (n = 13). The enamel was treated in accordance with the following experimental conditions: FUE-Universal System - Futurabond U (VOCO) with etching; FUWE - Futurabond U (VOCO) without etching; SB-Total Etch System - Single Bond 2 (3M); SBUE-Universal System - Single Bond Universal (3M ESPE) with etching; SBUWE - Single Bond Universal (3M ESPE) without etching; CLE-Self-etch System - Clearfil SE Bond (Kuraray) was applied with etching; CLWE - Clearfil SE Bond (Kuraray) without etching. The specimens were made using the composite spectrum TPH (Dentsply) and stored in distilled water (37 ± 1°C) for 1 month. The microshear test was performed using the universal testing machine EMIC DL 2000 with the crosshead speed of 0.5 mm/minute. The bond strength values were analyzed using statistical tests (Kruskal-Wallis test and Mann-Whitney test) with Bonferroni correction. There was no statistically significant difference between groups (p < 0.05), where FUE (36.83 ± 4.9 MPa) showed the highest bond strength values and SBUWE (18.40 ± 2.2 MPa) showed the lowest bond strength values. The analysis of adhesive interface revealed that most failures occurred between the interface composite resin and adhesive. The universal adhesive system used in dental enamel varies according to the trademark, and the previous enamel etching for universal systems and the self-etch both induced greater bond strength values. Selective enamel etching prior to the application of a universal adhesive system is a relevant strategy for better performance bonding.

Evaluation of four inch diameter VGF-Ge substrates used for manufacturing multi-junction solar cell

NASA Astrophysics Data System (ADS)

Kewei, Cao; Tong, Liu; Jingming, Liu; Hui, Xie; Dongyan, Tao; Youwen, Zhao; Zhiyuan, Dong; Feng, Hui

2016-06-01

Low dislocation density Ge wafers grown by a vertical gradient freeze (VGF) method used for the fabrication of multi-junction photovoltaic cells (MJC) have been studied by a whole wafer scale measurement of the lattice parameter, X-ray rocking curves, etch pit density (EPD), impurities concentration, minority carrier lifetime and residual stress. Impurity content in the VGF-Ge wafers, including that of B, is quite low although B2O3 encapsulation is used in the growth process. An obvious difference exists across the whole wafer regarding the distribution of etch pit density, lattice parameter, full width at half maximum (FWHM) of the X-ray rocking curve and residual stress measured by Raman spectra. These are in contrast to a reference Ge substrate wafer grown by the Cz method. The influence of the VGF-Ge substrate on the performance of the MJC is analyzed and evaluated by a comparison of the statistical results of cell parameters. Project supported by the National Natural Science Foundation of China (No. 61474104).

Dislocation reduction in heteroepitaxial Ge on Si using SiO{sub 2} lined etch pits and epitaxial lateral overgrowth

DOE Office of Scientific and Technical Information (OSTI.GOV)

Leonhardt, Darin; Han, Sang M.

2011-09-12

We report a technique that significantly reduces threading dislocations in Ge on Si heteroepitaxy. Germanium is first grown on Si and etched to produce pits in the surface where threading dislocations terminate. Further processing leaves a layer of SiO{sub 2} only within etch pits. Subsequent selective epitaxial Ge growth results in coalescence above the SiO{sub 2}. The SiO{sub 2} blocks the threading dislocations from propagating into the upper Ge epilayer. With annealed Ge films grown on Si, the said method reduces the defect density from 2.6 x 10{sup 8} to 1.7 x 10{sup 6} cm{sup -2}, potentially making the layermore » suitable for electronic and photovoltaic devices.« less

Light scattering apparatus and method for determining radiation exposure to plastic detectors

DOEpatents

Hermes, Robert E.

2002-01-01

An improved system and method of analyzing cumulative radiation exposure registered as pits on track etch foils of radiation dosimeters. The light scattering apparatus and method of the present invention increases the speed of analysis while it also provides the ability to analyze exposure levels beyond that which may be properly measured with conventional techniques. Dosimeters often contain small plastic sheets that register accumulated damage when exposed to a radiation source. When the plastic sheet from the dosimeter is chemically etched, a track etch foil is produced wherein pits or holes are created in the plastic. The number of these pits, or holes, per unit of area (pit density) correspond to the amount of cumulative radiation exposure which is being optically measured by the apparatus. To measure the cumulative radiation exposure of a track etch foil a high intensity collimated beam is passed through foil such that the pits and holes within the track etch foil cause a portion of the impinging light beam to become scattered upon exit. The scattered light is focused with a lens, while the primary collimated light beam (unscattered light) is blocked. The scattered light is focused by the lens onto an optical detector capable of registering the optical power of the scattered light which corresponds to the cumulative radiation to which the track etch foil has been exposed.

Computational nanometrology of line-edge roughness: noise effects, cross-line correlations and the role of etch transfer

NASA Astrophysics Data System (ADS)

Constantoudis, Vassilios; Papavieros, George; Lorusso, Gian; Rutigliani, Vito; Van Roey, Frieda; Gogolides, Evangelos

2018-03-01

The aim of this paper is to investigate the role of etch transfer in two challenges of LER metrology raised by recent evolutions in lithography: the effects of SEM noise and the cross-line and edge correlations. The first comes from the ongoing scaling down of linewidths, which dictates SEM imaging with less scanning frames to reduce specimen damage and hence with more noise. During the last decade, it has been shown that image noise can be an important budget of the measured LER while systematically affects and alter the PSD curve of LER at high frequencies. A recent method for unbiased LER measurement is based on the systematic Fourier or correlation analysis to decompose the effects of noise from true LER (Fourier-Correlation filtering method). The success of the method depends on the PSD and HHCF curve. Previous experimental and model works have revealed that etch transfer affects the PSD of LER reducing its high frequency values. In this work, we estimate the noise contribution to the biased LER through PSD flat floor at high frequencies and relate it with the differences between the PSDs of lithography and etched LER. Based on this comparison, we propose an improvement of the PSD/HHCF-based method for noise-free LER measurement to include the missed high frequency real LER. The second issue is related with the increased density of lithographic patterns and the special characteristics of DSA and MP lithography patterns exhibits. In a previous work, we presented an enlarged LER characterization methodology for such patterns, which includes updated versions of the old metrics along with new metrics defined and developed to capture cross-edge and cross-line correlations. The fundamental concept has been the Line Center Roughness (LCR), the edge c-factor and the line c-factor correlation function and length quantifying the line fluctuations and the extent of cross-edge and cross-line correlations. In this work, we focus on the role of etch steps on cross-edge and line correlation metrics in SAQP data. We find that the spacer etch steps reduce edge correlations while etch steps with pattern transfer increase these. Furthermore, the density doubling and quadrupling increase edge correlations as well as cross-line correlations.

Electrical transport characterization of PEDOT:PSS/n-Si Schottky diodes and their applications in solar cells.

PubMed

Khurelbaatar, Zagarzusem; Hyung, Jung-Hwan; Kim, Gil-Sung; Park, No-Won; Shim, Kyu-Hwan; Lee, Sang-Kwon

2014-06-01

We demonstrate locally contacted PEDOT:PSS Schottky diodes with excellent rectifying behavior, fabricated on n-type Si substrates using a spin-coating process and a reactive-ion etching process. Electrical transport characterizations of these Schottky diodes were investigated by both current-voltage (I-V) and capacitance-voltage (C-V) measurements. We found that these devices exhibit excellent modulation in the current with an on/off ratio of - 10(6). Schottky junction solar cells composed of PEDOT:PSS and n-Si structures were also examined. From the current density-voltage (J-V) measurement of a solar cell under illumination, the short circuit current (I(sc)), open circuit voltage (V(oc)), and conversion efficiency (eta) were - 19.7 mA/cm2, - 578.5 mV, and - 6.5%, respectively. The simple and low-cost fabrication process of the PEDOT:PSS/n-Si Schottky junctions makes them a promising candidate for further high performance solar cell applications.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Donnelly, Vincent M.; Kornblit, Avinoam

The field of plasma etching is reviewed. Plasma etching, a revolutionary extension of the technique of physical sputtering, was introduced to integrated circuit manufacturing as early as the mid 1960s and more widely in the early 1970s, in an effort to reduce liquid waste disposal in manufacturing and achieve selectivities that were difficult to obtain with wet chemistry. Quickly, the ability to anisotropically etch silicon, aluminum, and silicon dioxide in plasmas became the breakthrough that allowed the features in integrated circuits to continue to shrink over the next 40 years. Some of this early history is reviewed, and a discussionmore » of the evolution in plasma reactor design is included. Some basic principles related to plasma etching such as evaporation rates and Langmuir–Hinshelwood adsorption are introduced. Etching mechanisms of selected materials, silicon, silicon dioxide, and low dielectric-constant materials are discussed in detail. A detailed treatment is presented of applications in current silicon integrated circuit fabrication. Finally, some predictions are offered for future needs and advances in plasma etching for silicon and nonsilicon-based devices.« less

Development of a Contactless Technique for Electrodeposition and Porous Silicon Formation

NASA Astrophysics Data System (ADS)

Zhao, Mingrui

One of the key active manufacturing technologies for 3D integration is through silicon vias (TSVs), which involves etching of deep vias in a silicon substrate that are filled with an electrodeposited metal, and subsequent removal of excess metal by chemical mechanical planarization (CMP). Electrodeposition often results in undesired voids in the TSV metal fill as well as a thick overburden layer. These via plating defects can severely degrade interconnect properties and lead to variation in via resistance, electrically open vias, and trapped plating chemicals that present a reliability hazard. Thick overburden layers result in lengthy and expensive CMP processing. We are proposing a technique that pursues a viable method of depositing a high quality metal inside vias with true bottom-up filling, using an additive-free deposition solution. The mechanism is based on a novel concept of electrochemical oxidation of backside silicon that releases electrons, and subsequent chemical etching of silicon dioxide for regeneration of the surface. Electrons are transported through the bulk silicon to the interface of the via bottom and the deposition solution, where the metal ions accept these electrons and electrodeposit resulting in the bottom-up filling of the large aspect ratio vias. With regions outside the vias covered bydielectric, no metal electrodeposition should occur in these regions. Our new bottom-up technique was initially examined and successfully demonstrated on blanket silicon wafers and shown to supply electrons to provide bottom-up filling advantage of through-hole plating and the depth tailorability of blind vias. We have also conducted a fundamental study that investigated the effect of various process parameters on the characteristics of deposited Cu and Ni and established correlations between metal filling properties and various electrochemical and solution variables. A copper sulfate solution with temperature of about 65°C was shown to be suitable for achieving stable and high values of current density that translated to copper deposition rates of 2.4 mum/min with good deposition uniformity. The importance of backside silicon oxidation and subsequent oxide etching on the kinetics of metal deposition on front side silicon has also been highlighted. Further, a process model was also developed to simulate the through silicon via copper filling process using conventional and contactless electrodeposition methods with no additives being used in the electrolyte solution. A series of electrochemical measurements were employed and integrated in the development of the comprehensive process simulator. The experimental data not only provided the necessary parameters for the model but also validated the simulation accuracy. From the simulation results, the "pinch-off" effect was observed for the additive-free conventional deposition process, which further causes partial filling and void formation. By contrast, a void-free filling with higher deposition rates was achieved by the use of the contactless technique. Moreover, experimental results of contactless electrodeposition on patterned wafers showed fast rate bottom-up filling ( 3.3 mum/min) in vias of 4 mum diameter and 50 mum depth (aspect ratio = 12.5) without void formation and no copper overburden in the regions outside the vias. Efforts were also made to extend the use of the contactless technique to other applications such as synthesis of porous silicon. We were able to fabricate porous silicon with a morphological gradient using a novel design of the experimental cell. The resulted porous silicon layers show a large distribution in porosity, pore size and depth along the radius of the samples. Symmetrical arrangements were attributed to decreasing current density radially inward on the silicon surface exposed to surfactant containing HF based etchant solution. The formation mechanism as well as morphological properties and their dependence on different process parameters has been investigated in detail. In the presence of surfactants, an increase in the distribution range of porosity, pore diameter and depth was observed by increasing HF concentration or lowering pH of the etchant solution, as the formation of pores was considered to be limited by the etch rates of silicon dioxide. Gradient porous silicon was also found to be successfully formulated both at high and low current densities. Interestingly, the morphological gradient was not developed when dimethyl sulfoxide (instead of surfactants) was used in etchant solution potentially due to limitations in the availability of oxidizing species at the silicon-etchant solution interface. In the last part of the dissertation, we have discussed the gradient bottom up filling of Cu in porous silicon substrates using the contactless electrochemical method. The radially symmetric current that gradually varied across the radius of the sample area was achieved by utilizing the modified cell design, which resulted in gradient filling in the vias. Effect of different deposition parameters such as applied current density, copper sulfate concentration and etching to deposition area ratio has been examined and discussed. (Abstract shortened by ProQuest.).

Overview of several applications of chemical downstream etching (CDE) for IC manufacturing: advantages and drawbacks versus WET processes

NASA Astrophysics Data System (ADS)

de Buttet, Côme; Prevost, Emilie; Campo, Alain; Garnier, Philippe; Zoll, Stephane; Vallier, Laurent; Cunge, Gilles; Maury, Patrick; Massin, Thomas; Chhun, Sonarith

2017-03-01

Today the IC manufacturing faces lots of problematics linked to the continuous down scaling of printed structures. Some of those issues are related to wet processing, which are often used in the IC manufacturing flow for wafer cleaning, material etching and surface preparation. In the current work we summarize the limitations for the next nodes of wet processing such as metallic contaminations, wafer charging, corrosion and pattern collapse. As a replacement, we promoted the isotropic chemical dry etching (CDE) which is supposed to fix all the above drawbacks. Etching steps of SI3N4 layers were evaluated in order to prove the interest of such technique.

Edge-Controlled Growth and Etching of Two-Dimensional GaSe Monolayers

DOE PAGES

Li, Xufan; Dong, Jichen; Idrobo, Juan C.; ...

2016-12-07

Understanding the atomistic mechanisms governing the growth of two-dimensional (2D) materials is of great importance in guiding the synthesis of wafer-sized, single-crystalline, high-quality 2D crystals and heterostructures. Etching, in many cases regarded as the reverse process of material growth, has been used to study the growth kinetics of graphene. In this paper, we explore a growth–etching–regrowth process of monolayer GaSe crystals, including single-crystalline triangles and irregularly shaped domains formed by merged triangles. We show that the etching begins at a slow rate, creating triangular, truncated triangular, or hexagonally shaped holes that eventually evolve to exclusively triangles that are rotated 60°more » with respect to the crystalline orientation of the monolayer triangular crystals. The regrowth occurs much faster than etching, reversibly filling the etched holes and then enlarging the size of the monolayer crystals. A theoretical model developed based on kinetic Wulff construction (KWC) theory and density functional theory (DFT) calculations accurately describe the observed morphology evolution of the monolayer GaSe crystals and etched holes during the growth and etching processes, showing that they are governed by the probability of atom attachment/detachment to/from different types of edges with different formation energies of nucleus/dents mediated by chemical potential difference Δμ between Ga and Se. Finally, our growth–etching–regrowth study provides not only guidance to understand the growth mechanisms of 2D binary crystals but also a potential method for the synthesis of large, shape-controllable, high-quality single-crystalline 2D crystals and their lateral heterostructures.« less

The Effect of Hydrofluoric Acid Etching Duration on the Surface Micromorphology, Roughness, and Wettability of Dental Ceramics

PubMed Central

Ramakrishnaiah, Ravikumar; Alkheraif, Abdulaziz A.; Divakar, Darshan Devang; Matinlinna, Jukka P.; Vallittu, Pekka K.

2016-01-01

The current laboratory study is evaluating the effect of hydrofluoric acid etching duration on the surface characteristics of five silica-based glass ceramics. Changes in the pore pattern, crystal structure, roughness, and wettability were compared and evaluated. Seventy-five rectangularly shaped specimens were cut from each material (IPS e-max™, Dentsply Celtra™, Vita Suprinity™, Vita mark II™, and Vita Suprinity FC™); the sectioned samples were finished, polished, and ultrasonically cleaned. Specimens were randomly assigned into study groups: control (no etching) and four experimental groups (20, 40, 80 and 160 s of etching). The etched surfaces’ microstructure including crystal structure, pore pattern, pore depth, and pore width was studied under a scanning electron microscope, and the surface roughness and wettability were analyzed using a non-contact surface profilometer and a contact angle measuring device, respectively. The results were statistically analyzed using one-way analysis of variance (ANOVA) and the post hoc Tukey’s test. The results showed a significant change in the pore number, pore pattern, crystal structure, surface roughness, and wettability with increased etching duration. Etching for a short time resulted in small pores, and etching for longer times resulted in wider, irregular grooves. A significant increase in the surface roughness and wettability was observed with an increase in the etching duration. The findings also suggested a strong association between the surface roughness and wettability. PMID:27240353

Effect of lattice defects on Hele-Shaw flow over an etched lattice

DOE Office of Scientific and Technical Information (OSTI.GOV)

Decker, E.L.; Ignes-Mullol, J.; Baratt, A.

We examine the patterns formed by injecting nitrogen gas into the center of a horizontal, radial Hele-Shaw cell filled with paraffin oil. We use smooth plates and etched plates with lattices having different amounts of defects (0{endash}10&hthinsp;{percent}). In all cases, a quantitative measure of the pattern ramification shows a regular trend with injection rate and cell gap, such that the dimensionless perimeter scales with the dimensionless time. By adding defects to the lattice, we observe increased branching in the pattern morphologies. However, even in this case, the scaling behavior persists. Only the prefactor of the scaling function shows a dependencemore » on the defect density. For different lattice defect densities, we examine the nature of the different morphology phases. {copyright} {ital 1999} {ital The American Physical Society}« less

Sidewall GaAs tunnel junctions fabricated using molecular layer epitaxy

PubMed Central

Ohno, Takeo; Oyama, Yutaka

2012-01-01

In this article we review the fundamental properties and applications of sidewall GaAs tunnel junctions. Heavily impurity-doped GaAs epitaxial layers were prepared using molecular layer epitaxy (MLE), in which intermittent injections of precursors in ultrahigh vacuum were applied, and sidewall tunnel junctions were fabricated using a combination of device mesa wet etching of the GaAs MLE layer and low-temperature area-selective regrowth. The fabricated tunnel junctions on the GaAs sidewall with normal mesa orientation showed a record peak current density of 35 000 A cm-2. They can potentially be used as terahertz devices such as a tunnel injection transit time effect diode or an ideal static induction transistor. PMID:27877466

Nano-cone resistive memory for ultralow power operation.

PubMed

Kim, Sungjun; Jung, Sunghun; Kim, Min-Hwi; Kim, Tae-Hyeon; Bang, Suhyun; Cho, Seongjae; Park, Byung-Gook

2017-03-24

SiN x -based nano-structure resistive memory is fabricated by fully silicon CMOS compatible process integration including particularly designed anisotropic etching for the construction of a nano-cone silicon bottom electrode (BE). Bipolar resistive switching characteristics have significantly reduced switching current and voltage and are demonstrated in a nano-cone BE structure, as compared with those in a flat BE one. We have verified by systematic device simulations that the main cause of reduction in the performance parameters is the high electric field being more effectively concentrated at the tip of the cone-shaped BE. The greatly improved nonlinearity of the nano-cone resistive memory cell will be beneficial in the ultra-high-density crossbar array.

Enhanced photo-response of porous silicon photo-detectors by embeddingTitanium-dioxide nano-particles

NASA Astrophysics Data System (ADS)

Ali, Hiba M.; Makki, Sameer A.; Abd, Ahmed N.

2018-05-01

Porous silicon (n-PS) films can be prepared by photoelectochemical etching (PECE) Silicon chips n - types with 15 (mA / cm2), in 15 minutes etching time on the fabrication nano-sized pore arrangement. By using X-ray diffraction measurement and atomic power microscopy characteristics (AFM), PS was investigated. It was also evaluated the crystallites size from (XRD) for the PS nanoscale. The atomic force microscopy confirmed the nano-metric size chemical fictionalization through the electrochemical etching that was shown on the PS surface chemical composition. The atomic power microscopy checks showed the roughness of the silicon surface. It is also notified (TiO2) preparation nano-particles that were prepared by pulse laser eradication in ethanol (PLAL) technique through irradiation with a Nd:YAG laser pulses TiO2 target that is sunk in methanol using 400 mJ of laser energy. It has been studied the structural, optical and morphological of TiO2NPs. It has been detected that through XRD measurement, (TiO2) NPs have been Tetragonal crystal structure. While with AFM measurements, it has been realized that the synthesized TiO2 particles are spherical with an average particle size in the (82 nm) range. It has been determined that the energy band gap of TiO2 NPs from optical properties and set to be in (5eV) range.The transmittance and reflectance spectra have determined the TiO2 NPs optical constants. It was reported the effectiveness of TiO2 NPs expansion on the PS Photodetector properties which exposes the benefits in (Al/PS/Si/Al). The built-in tension values depend on the etching time current density and laser flounce. Al/TiO2/PS/Si/Al photo-detector heterojunction have two response peaks that are situated at 350 nm and (700 -800nm) with max sensitivity ≈ 0.7 A/W. The maximum given detectivity is 9.38at ≈ 780 nm wavelength.

Antireflection and SiO2 Surface Passivation by Liquid-Phase Chemistry for Efficient Black Silicon Solar Cells: Preprint

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yuan, H. C.; Oh, J.; Zhang, Y.

2012-06-01

We report solar cells with both black Si antireflection and SiO2 surface passivation provided by inexpensive liquid-phase chemistry, rather than by conventional vacuum-based techniques. Preliminary cell efficiency has reached 16.4%. Nanoporous black Si antireflection on crystalline Si by aqueous etching promises low surface reflection for high photon utilization, together with lower manufacturing cost compared to vacuum-based antireflection coating. Ag-nanoparticle-assisted black Si etching and post-etching chemical treatment recently developed at NREL enables excellent control over the pore diameter and pore separation. Performance of black Si solar cells, including open-circuit voltage, short-circuit current density, and blue response, has benefited from these improvements.more » Prior to this study, our black Si solar cells were all passivated by thermal SiO2 produced in tube furnaces. Although this passivation is effective, it is not yet ideal for ultra-low-cost manufacturing. In this study, we report, for the first time, the integration of black Si with a proprietary liquid-phase deposition (LPD) passivation from Natcore Technology. The Natcore LPD forms a layer of <10-nm SiO2 on top of the black Si surface in a relatively mild chemical bath at room temperature. We demonstrate black Si solar cells with LPD SiO2 with a spectrum-weighted average reflection lower than 5%, similar to the more costly thermally grown SiO2 approach. However, LPD SiO2 provides somewhat better surface-passivation quality according to the lifetime analysis by the photo-conductivity decay measurement. Moreover, black Si solar cells with LPD SiO2 passivation exhibit higher spectral response at short wavelength compared to those passivated by thermally grown SiO2. With further optimization, the combination of aqueous black Si etching and LPD could provide a pathway for low-cost, high-efficiency crystalline Si solar cells.« less

SEM based overlay measurement between resist and buried patterns

NASA Astrophysics Data System (ADS)

Inoue, Osamu; Okagawa, Yutaka; Hasumi, Kazuhisa; Shao, Chuanyu; Leray, Philippe; Lorusso, Gian; Baudemprez, Bart

2016-03-01

With the continuous shrink in pattern size and increased density, overlay control has become one of the most critical issues in semiconductor manufacturing. Recently, SEM based overlay of AEI (After Etch Inspection) wafer has been used for reference and optimization of optical overlay (both Image Based Overlay (IBO) and Diffraction Based Overlay (DBO)). Overlay measurement at AEI stage contributes monitor and forecast the yield after formation by etch and calibrate optical measurement tools. however those overlay value seems difficult directly for feedback to a scanner. Therefore, there is a clear need to have SEM based overlay measurements of ADI (After Develop Inspection) wafers in order to serve as reference for optical overlay and make necessary corrections before wafers go to etch. Furthermore, to make the corrections as accurate as possible, actual device like feature dimensions need to be measured post ADI. This device size measurement is very unique feature of CDSEM , which can be measured with smaller area. This is currently possible only with the CD-SEM. This device size measurement is very unique feature of CD-SEM , which can be measured with smaller area. In this study, we assess SEM based overlay measurement of ADI and AEI wafer by using a sample from an N10 process flow. First, we demonstrate SEM based overlay performance at AEI by using dual damascene process for Via 0 (V0) and metal 1 (M1) layer. We also discuss the overlay measurements between litho-etch-litho stages of a triple patterned M1 layer and double pattern V0. Second, to illustrate the complexities in image acquisition and measurement we will measure overlay between M1B resist and buried M1A-Hard mask trench. Finally, we will show how high accelerating voltage can detect buried pattern information by BSE (Back Scattering Electron). In this paper we discuss the merits of this method versus standard optical metrology based corrections.

Plasma-Etching of Spray-Coated Single-Walled Carbon Nanotube Films for Biointerfaces

NASA Astrophysics Data System (ADS)

Kim, Joon Hyub; Lee, Jun-Yong; Min, Nam Ki

2012-08-01

We present an effective method for the batch fabrication of miniaturized single-walled carbon nanotube (SWCNT) film electrodes using oxygen plasma etching. We adopted the approach of spray-coating for good adhesion of the SWCNT film onto a pre-patterned Pt support and used O2 plasma patterning of the coated films to realize efficient biointerfaces between SWCNT surfaces and biomolecules. By these approaches, the SWCNT film can be easily integrated into miniaturized electrode systems. To demonstrate the effectiveness of plasma-etched SWCNT film electrodes as biointerfaces, Legionella antibody was selected as analysis model owing to its considerable importance to electrochemical biosensors and was detected using plasma-etched SWCNT film electrodes and a 3,3',5,5'-tetramethyl-benzidine dihydrochloride/horseradish peroxidase (TMB/HRP) catalytic system. The response currents increased with increasing concentration of Legionella antibody. This result indicates that antibodies were effectively immobilized on plasma-etched and activated SWCNT surfaces.

Surface Participation Effects in Titanium Nitride and Niobium Resonators

NASA Astrophysics Data System (ADS)

Dove, Allison; Kreikebaum, John Mark; Livingston, William; Delva, Remy; Qiu, Yanjie; Lolowang, Reinhard; Ramasesh, Vinay; O'Brien, Kevin; Siddiqi, Irfan

Improving the coherence time of superconducting qubits requires a precise understanding of the location and density of surface defects. Superconducting microwave resonators are commonly used for quantum state readout and are a versatile testbed to systematically characterize materials properties as a function of device geometry and fabrication method. We report on sputter deposited titanium nitride and niobium on silicon coplanar waveguide resonators patterned using reactive ion etches to define the device geometry. We discuss the impact of different growth conditions (temperature and electrical bias) and processing techniques on the internal quality factor (Q) of these devices. In particular, to investigate the effect of surface participation, we use a Bosch process to etch many-micron-deep trenches in the silicon substrate and quantify the impact of etch depth and profile on the internal Q. This research was supported by the ARO.

Deterministic Nanopatterning of Diamond Using Electron Beams.

PubMed

Bishop, James; Fronzi, Marco; Elbadawi, Christopher; Nikam, Vikram; Pritchard, Joshua; Fröch, Johannes E; Duong, Ngoc My Hanh; Ford, Michael J; Aharonovich, Igor; Lobo, Charlene J; Toth, Milos

2018-03-27

Diamond is an ideal material for a broad range of current and emerging applications in tribology, quantum photonics, high-power electronics, and sensing. However, top-down processing is very challenging due to its extreme chemical and physical properties. Gas-mediated electron beam-induced etching (EBIE) has recently emerged as a minimally invasive, facile means to dry etch and pattern diamond at the nanoscale using oxidizing precursor gases such as O 2 and H 2 O. Here we explain the roles of oxygen and hydrogen in the etch process and show that oxygen gives rise to rapid, isotropic etching, while the addition of hydrogen gives rise to anisotropic etching and the formation of topographic surface patterns. We identify the etch reaction pathways and show that the anisotropy is caused by preferential passivation of specific crystal planes. The anisotropy can be controlled by the partial pressure of hydrogen and by using a remote RF plasma source to radicalize the precursor gas. It can be used to manipulate the geometries of topographic surface patterns as well as nano- and microstructures fabricated by EBIE. Our findings constitute a comprehensive explanation of the anisotropic etch process and advance present understanding of electron-surface interactions.

Growth Method-Dependent and Defect Density-Oriented Structural, Optical, Conductive, and Physical Properties of Solution-Grown ZnO Nanostructures.

PubMed

Rana, Abu Ul Hassan Sarwar; Lee, Ji Young; Shahid, Areej; Kim, Hyun-Seok

2017-09-10

It is time for industry to pay a serious heed to the application and quality-dependent research on the most important solution growth methods for ZnO, namely, aqueous chemical growth (ACG) and microwave-assisted growth (MAG) methods. This study proffers a critical analysis on how the defect density and formation behavior of ZnO nanostructures (ZNSs) are growth method-dependent. Both antithetical and facile methods are exploited to control the ZnO defect density and the growth mechanism. In this context, the growth of ZnO nanorods (ZNRs), nanoflowers, and nanotubes (ZNTs) are considered. The aforementioned growth methods directly stimulate the nanostructure crystal growth and, depending upon the defect density, ZNSs show different trends in structural, optical, etching, and conductive properties. The defect density of MAG ZNRs is the least because of an ample amount of thermal energy catered by high-power microwaves to the atoms to grow on appropriate crystallographic planes, which is not the case in faulty convective ACG ZNSs. Defect-centric etching of ZNRs into ZNTs is also probed and methodological constraints are proposed. ZNS optical properties are different in the visible region, which are quite peculiar, but outstanding for ZNRs. Hall effect measurements illustrate incongruent conductive trends in both samples.

Selective dry etching of III-V nitrides in Cl{sub 2}/Ar, CH{sub 4}/H{sub 2}/Ar, ICi/Ar, and IBr/Ar

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vartuli, C.B.; Pearton, S.J.; MacKenzie, J.D.

1996-10-01

The selectivity for etching the binary (GaN, AlN, and InN) and ternary nitrides (InGaN and InAlN) relative to each other in Cl{sub 2}/Ar, CH{sub 4}/H{sub 2}/Ar, ICl/Ar, or IBr/Ar electron cyclotron resonance (ECR) plasmas, and Cl{sub 2}/Ar or CH{sub 4}/H{sub 2}/Ar reactive ion (RIE) plasmas was investigated. Cl-based etches appear to be the best choice for maximizing the selectivity of GaN over the other nitrides. GaN/AlN and GaN/InGaN etch rate ratios of {approximately} 10 were achieved at low RF power in Cl{sub 2}/Ar under ECR and RIE conditions, respectively. GaN/InN selectivity of 10 was found in ICl under ECR conditions.more » A relatively high selectivity (> 6) of InN/GaN was achieved in CH{sub 4}/H{sub 2}/Ar under ECR conditions at low RF powers (50 W). Since the high bond strengths of the nitrides require either high ion energies or densities to achieve practical etch rates it is difficult to achieve high selectivities.« less

Very High Quality Crystals of Wide-Gap II-VI Semiconductors: What for?

DTIC Science & Technology

2001-01-01

the reciprocal space mapping , by the etch pit density (EPD) measurements (to determine the density of dislocations) and by the measurement of the width...crystals. The EPD was in the range 5 x 1 + 104 cmn2 for Cdl.,ZnxTe crystals and about 104 cmz for ZnTe. The reciprocal space mapping of the crystals

Low-density polyethylene films treated by an atmospheric Ar-O2 post-discharge: functionalization, etching, degradation and partial recovery of the native wettability state

NASA Astrophysics Data System (ADS)

Abou Rich, S.; Dufour, T.; Leroy, P.; Nittler, L.; Pireaux, J. J.; Reniers, F.

2014-02-01

To optimize the adhesion of layers presenting strong barrier properties on low-density polyethylene (LDPE) surfaces, we investigated the influence of argon and argon-oxygen atmospheric pressure post-discharges. This study was performed using x-ray photoelectron spectroscopy, atomic force microscopy, optical emission spectroscopy (OES) and dynamic water contact angle (WCA) measurements. After the plasma treatment, a slight increase in the roughness was emphasized, more particularly for the samples treated in a post-discharge supplied in oxygen. Measurements of the surface roughness and of the oxygen surface concentration suggested the competition of two processes playing a role on the surface hydrophilicity and occurring during the post-discharge treatment: the etching and the activation of the surface. The etching rate was estimated to about 2.7 nm s-1 and 5.8 nm s-1 for Ar and Ar-O2 post-discharges, respectively. The mechanisms underlying this etching were investigated through experiments, in which we discuss the influence of the O2 flow rate and the distance (gap) separating the plasma torch from the LDPE surface located downstream. O atoms and NO molecules (emitting in the UV range) detected by OES seem to be good candidates to explain the etching process. An ageing study is also presented to evidence the stability of the treated surfaces over 60 days. After 60 days of storage, we showed that whatever the O2 flow rate, the treated films registered a loss of their hydrophilic state since their WCA increased towards a common threshold of 80°. This ‘hydrophobic recovery’ effect was mostly attributed to the reorientation of induced polar chemical groups into the bulk of the material. Indeed, the relative concentrations of the carbonyl and carboxyl groups at the surface decreased with the storage time and seemed to reach a plateau after 30 days.

HF/H2O2 treated graphite felt as the positive electrode for vanadium redox flow battery

NASA Astrophysics Data System (ADS)

He, Zhangxing; Jiang, Yingqiao; Meng, Wei; Jiang, Fengyun; Zhou, Huizhu; Li, Yuehua; Zhu, Jing; Wang, Ling; Dai, Lei

2017-11-01

In order to improve the electrochemical performance of the positive graphite felt electrode in vanadium flow redox battery, a novel method is developed to effectively modify the graphite felt by combination of etching of HF and oxidation of H2O2. After the etching of HF for the graphite felt at ambient temperature, abundant oxygen-containing functional groups were further introduced on the surface of graphite felt by hydrothermal treatment using H2O2 as oxidant. Benefiting from the surface etching and introduction of functional groups, mass transfer and electrode process can be improved significantly on the surface of graphite felt. VO2+/VO2+ redox reaction on the graphite felt modified by HF and H2O2 jointly (denote: GF-HF/H2O2) exhibits superior electrochemical kinetics in comparison with the graphite felt modified by single HF or H2O2 treatment. The cell using GF-HF/H2O2 as the positive electrode was assembled and its electrochemical properties were evaluated. The increase of energy efficiency of 4.1% for GF-HF/H2O2 at a current density of 50 mA cm-2 was obtained compared with the pristine graphite felt. The cell using GF-HF/H2O2 also demonstrated higher discharge capacity. Our study revealed that HF/H2O2 treatment is an efficient method to enhance the electrochemical performance of graphite felt, further improving the comprehensive energy storage performance of the vanadium flow redox battery.

Structural and dielectric properties of thin ZrO2 films on silicon grown by atomic layer deposition from cyclopentadienyl precursor

NASA Astrophysics Data System (ADS)

Niinistö, J.; Putkonen, M.; Niinistö, L.; Kukli, K.; Ritala, M.; Leskelä, M.

2004-01-01

ZrO2 thin films with thicknesses below 20 nm were deposited by the atomic layer deposition process on Si(100) substrates at 350 °C. An organometallic precursor, Cp2Zr(CH3)2 (Cp=cyclopentadienyl, C5H5) was used as the zirconium source and water or ozone as oxygen source. The influence of oxygen source and substrate pretreatment on the dielectric properties of ZrO2 films was investigated. Structural characterization with high-resolution transmission electron microscopy was performed to films grown onto HF-etched or native oxide covered silicon. Strong inhibition of ZrO2 film growth was observed with the water process on HF-etched Si. Ozone process on HF-etched Si resulted in interfacial SiO2 formation between the dense and uniform film and the substrate while water process produced interfacial layer with intermixing of SiO2 and ZrO2. The effective permittivity of ZrO2 in Al/ZrO2/Si/Al capacitor structures was dependent on the ZrO2 layer thickness and oxygen source used. The interfacial layer formation increased the capacitance equivalent oxide thickness (CET). CET of 2.0 nm was achieved with 5.9 nm ZrO2 film deposited with the H2O process on HF-stripped Si. The ozone-processed films showed good dielectric properties such as low hysteresis and nearly ideal flatband voltage. The leakage current density was lower and breakdown field higher for the ozone-processed ZrO2 films.

Surface treatment influences electrochemical stability of cpTi exposed to mouthwashes.

PubMed

Beline, Thamara; Garcia, Camila S; Ogawa, Erika S; Marques, Isabella S V; Matos, Adaias O; Sukotjo, Cortino; Mathew, Mathew T; Mesquita, Marcelo F; Consani, Rafael X; Barão, Valentim A R

2016-02-01

The role of surface treatment on the electrochemical behavior of commercially pure titanium (cpTi) exposed to mouthwashes was tested. Seventy-five disks were divided into 15 groups according to surface treatment (machined, sand blasted with Al2O3, and acid etched) and electrolyte solution (artificial saliva — control, 0.12% chlorhexidine digluconate, 0.05% cetylpyridinium chloride, 0.2% sodium fluoride, and 1.5% hydrogen peroxide) (n = 5). Open-circuit-potential and electrochemical impedance spectroscopy were conducted at baseline and after 7 and 14 days of immersion in each solution. Potentiodynamic test and total weight loss of disks were performed after 14 days of immersion. Scanning electron microscopy, energy dispersive spectroscopy, white light interferometry and profilometry were conducted for surface characterization before and after the electrochemical tests. Sandblasting promoted the lowest polarization resistance (Rp) (P b .0001) and the highest capacitance (CPE) (P b .006), corrosion current density (Icorr) and corrosion rate (P b .0001). In contrast, acid etching increased Rp and reduced CPE, independent to the mouthwash; while hydrogen peroxide reduced Rp (P b .008) and increased Icorr and corrosion rate (P b .0001). The highest CPE values were found for hydrogen peroxide and 0.2% sodium fluoride. Immersion for longer period improved the electrochemical stability of cpTi (P b .05). In conclusion, acid etching enhanced the electrochemical stability of cpTi. Hydrogen peroxide and sodium fluoride reduced the resistance to corrosion of cpTi, independent to the surface treatment. Chlorhexidine gluconate and cetylpyridinium chloride did not alter the corrosive behavior of cpTi.

Facile method for modulating the profiles and periods of self-ordered three-dimensional alumina taper-nanopores.

PubMed

Li, Juan; Li, Congshan; Chen, Cheng; Hao, Qingli; Wang, Zhijia; Zhu, Jie; Gao, Xuefeng

2012-10-24

We report a facile nanofabrication method, one-step hard anodizing and etching peeling (OS-HA-EP) of aluminum foils followed by multistep mild anodizing and etching pore-widening (MS-MA-EW), for the controllable tailoring of hexagonally packed three-dimensional alumina taper-nanopores. Their profiles can be precisely tailored by the synergistic control of anodizing time, etching time and cyclic times at the MS-MA-EW stage, exemplified by linear cones, whorl-embedded cones, funnels, pencils, parabolas, and trumpets. Meantime, their periods can also be modulated in the range of 70-370 nm by choosing matched anodizing electrolytes (e.g., H(2)C(2)O(4), H(2)SO(4), H(2)C(2)O(4)-H(2)SO(4), and H(2)C(2)O(4)-C(2)H(5)OH mixture) and anodizing voltages at the OS-HA-EP stage. We also demonstrated that the long-range ordering of nanopits and the peak voltage of stable self-ordered HA, which are unachievable in a single H(2)C(2)O(4) electrolyte system, can be effectively tuned by simply adding tiny quantity of H(2)SO(4) and C(2)H(5)OH to keep an appropriate HA current density, respectively. This method of using the combination of simple pure chemical nanofabrication technologies is very facile and efficient in realizing the controllable tailoring of large-area alumina membranes containing self-ordered taper-nanopores. Our work opens a door for exploring the novel physical and chemical properties of different materials of nanotaper arrays.

Dependence of performance of Si nanowire solar cells on geometry of the nanowires.

PubMed

Khan, Firoz; Baek, Seong-Ho; Kim, Jae Hyun

2014-01-01

The dependence of performance of silicon nanowires (SiNWs) solar cells on the growth condition of the SiNWs has been described. Metal-assisted electroless etching (MAE) technique has been used to grow SiNWs array. Different concentration of aqueous solution containing AgNO3 and HF for Ag deposition is used. The diameter and density of SiNWs are found to be dependent on concentration of solution used for Ag deposition. The diameter and density of SiNWs have been used to calculate the filling ratio of the SINWs arrays. The filling ratio is increased with increase in AgNO3 concentration, whereas it is decreased with increase in HF concentration. The minimum reflectance value achieved is ~1% for SiNWs of length of ~1.2 μ m in the wavelength range of 300-1000 nm. The performance and diode parameters strongly depend on the geometry of SiNWs. The maximum short circuit current density achieved is 35.6 mA/cm(2). The conversion efficiency of solar cell is 9.73% for SiNWs with length, diameter, and wire density of ~1.2 μ m, ~75 nm, and 90 μ m(-2), respectively.

Fluorinion transfer in silver-assisted chemical etching for silicon nanowires arrays

NASA Astrophysics Data System (ADS)

Feng, Tianyu; Xu, Youlong; Zhang, Zhengwei; Mao, Shengchun

2015-08-01

Uniform silicon nanowires arrays (SiNWAs) were fabricated on unpolished rough silicon wafers through KOH pretreatment followed by silver-assisted chemical etching (SACE). Density functional theory (DFT) calculations were used to investigate the function of silver (Ag) at atomic scale in the etching process. Among three adsorption sites of Ag atom on Si(1 0 0) surface, Ag(T4) above the fourth-layer surface Si atoms could transfer fluorinion (F-) to adjacent Si successfully due to its stronger electrostatic attraction force between Ag(T4) and F-, smaller azimuth angle of Fsbnd Ag(T4)sbnd Si, shorter bond length of Fsbnd Si compared with Fsbnd Ag. As F- was transferred to adjacent Si by Ag(T4) one by one, the Si got away from the wafer in the form of SiF4 when it bonded with enough F- while Ag(T4) was still attached onto the Si wafer ready for next transfer. Cyclic voltammetry tests confirmed that Ag can improve the etching rate by transferring F- to Si.

Study of Etching Pits in a Large-grain Single Cell Bulk Niobium Cavity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Xin; Ciovati, Gianluigi; Reece, Charles E.

2009-11-01

Performance of SRF cavities are limited by non-linear localized effects. The variation of local material characters between "hot" and "cold" spots is thus of intense interest. Such locations were identified in a BCP-etched large-grain single-cell cavity and removed for examination by high resolution electron microscopy (SEM), electron-back scattering diffraction microscopy (EBSD), optical microscopy, and 3D profilometry. Pits with clearly discernable crystal facets were observed in both "hotspot" and "coldspot" specimens. The pits were found in-grain, at bi-crystal boundaries, and on tri-crystal junctions. They are interpreted as etch pits induced by surface crystal defects (e.g. dislocations). All "coldspots" examined had qualitativelymore » low density of etching pits or very shallow tri-crystal boundary junction. EBSD revealed crystal structure surrounding the pits via crystal phase orientation mapping, while 3D profilometry gave information on the depth and size of the pits. In addition, a survey of the samples by energy dispersive X-ray analysis (EDX) did not show any significant contamination of the samples surface.« less

Enhanced performance of photonic crystal GaN light-emitting diodes with graphene transparent electrodes

NASA Astrophysics Data System (ADS)

Ge, Hai-Liang; Xu, Chen; Xu, Kun; Xun, Meng; Wang, Jun; Liu, Jie

2015-03-01

The two-dimensional (2D) triangle lattice air hole photonic crystal (PC) GaN-based light-emitting diodes (LED) with double-layer graphene transparent electrodes (DGTE) have been produced. The current spreading effect of the double-layer graphene (GR) on the surface of the PC structure of the LED has been researched. Specially, we found that the part of the graphene suspending over the air hole of the PC structure was of much higher conductivity, which reduced the average sheet resistance of the graphene transparent conducting electrode and improved the current spreading of the PC LED. Therefore, the work voltage of the DGTE-PC LED was obviously decreased, and the output power was greatly enhanced. The COMSOL software was used to simulate the current density distribution of the samples. The results show that the etching of PC structure results in the degradation of the current spreading and that the graphene transparent conducting electrode can offer an uniform current spreading in the DGTE-PC LED. PACS: 85.60.Jb; 68.65.Pq; 42.70.Qs

Self-etching adhesives: review of adhesion to tooth structure part II.

PubMed

Strydom, C

2005-02-01

Self-etching adhesives are steadily increasing in popularity among dental practitioners with their easy handling technique and their promise of no post-op sensitivity. As with any new bonding material, in vitro and in vivo investigations are required to assess the clinical efficacy of these systems. The current literature was reviewed to provide information on these systems, including the influence of their acidity and permeability on the quality of the bond, the role of water in long-term degradation of the bond in in vivo and in vitro studies, and the clinical efficacy of the self-etching adhesives in clinical research studies. Published abstracts, reviews, laboratory reports and clinical research papers in the dental literature. Very little information is available on self-etching systems pertaining to the long-term in vitro and in vivo durability of their bond and their medium- to long-term clinical outcome. Although post-op sensitivity seems to be something of the past, short-term clinical studies show that some self-etching adhesives do not perform as well as total-etch systems.

Novel passivation dielectrics-The boron- or phosphorus-doped hydrogenated amorphous silicon carbide films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, C.Y.; Fang, Y.K.; Huang, C.F.

1985-02-01

Hydrogenated amorphous silicon carbide (a-SiC:H) thin films were prepared and studied in a radiofrequency glowdischarge system, using a gas mixture of SiH/sub 4/ and one of the following carbon sources: methane (CH/sub 4/), benzene (C/sub 6/H/sub 6/), toluene (C/sub 7/H/sub 8/), sigma-xylene (C/sub 8/H/sub 10/), trichloroethane (C/sub 2/H/sub 3/Cl/sub 3/), trichloroethylene (C/sub 2/HCl/sub 3/), or carbon tetrachloride (CCl/sub 4/). The effect of doping phosphorus and boron into those a-SiC:H films on chemical etching rate, electrica dc resistivity, breakdown strength, and optical refractive index have been systematically investigated. Their chemical etching properties were examined by immersing in 49% HF, buffered HF,more » 180/sup 0/C H/sub 3/PO/sub 4/ solutions, or in CF/sub 4/ + O/sub 2/ plasma. It was found that the boron-doped a-SiC:H film possesses five times slower etching rate than the undoped one, while phosphorus-doped a-SiC:H film shows about three times slower. Among those a-SiC:H films, the one obtained from a mixture of SiH/sub 4/ and benzene shows the best etch-resistant property, while the ones obtained from a mixture of SiH/sub 4/ and chlorine containing carbon sources (e.g., trichloroethylene, trichloroethane, or carbon tetrachloride) shows that they are poor in etching resistance (i.e., the etching rate is higher). By measuring dc resistivity, dielectric breakdown strength, and effective refractive index, it was found that boron- or phosphorus-doped a-SiC:H films exhibit much higher dielectric strength and resistivity, but lower etching rate, presumably because of higher density.« less

Optical Diagnostics in the Gaseous Electronics Conference Reference Cell

PubMed Central

Hebner, G. A.; Greenberg, K. E.

1995-01-01

A number of laser-induced fluorescence and absorption spectroscopy studies have been conducted using Gaseous Electronics Conference Reference Cells. Laser-induced fluorescence has been used to measure hydrogen atom densities, to measure argon metastable spatial profiles, to determine the sheath electric field, and to infer the electron density and temperature. Absorption spectroscopy, using lamp sources and diode lasers, has been used to measure metastable atom densities in helium and argon discharges and fluorocarbon densities in silicon etching discharges. The experimental techniques and sample results of these investigations are reviewed. PMID:29151748

Effect of pH on ion current through conical nanopores

NASA Astrophysics Data System (ADS)

Chander, M.; Kumar, R.; Kumar, S.; Kumar, N.

2018-05-01

Here, we examined ionic current behavior of conical nanopores at different pH and a fixed ion concentration of potassium halide (KCl). Conical shaped nanopores have been developed by chemical etching technique in polyethylene terephthalate (PET) membrane/foil of thickness 12 micron. For this we employed a self-assembled electrochemical cell having two chambers and the foil was fitted in the centre of cell. The nanopores were produced in the foil using etching and stopping solutions. The experimental results show that ionic current rectification (ICR) occurs through synthesized conical nanopores. Further, ion current increases significantly with increase of voltage from the base side of nanopores to the tip side at fixed pH of electrolyte.

Porous CrN thin films by selectively etching CrCuN for symmetric supercapacitors

NASA Astrophysics Data System (ADS)

Wei, Binbin; Mei, Gui; Liang, Hanfeng; Qi, Zhengbing; Zhang, Dongfang; Shen, Hao; Wang, Zhoucheng

2018-05-01

Transition metal nitrides are regarded as a new class of excellent electrode materials for high-performance supercapacitors due to their superior chemical stability and excellent electrical conductivity. We synthesize successfully the porous CrN thin films for binder-free supercapacitor electrodes by reactive magnetron co-sputtering and selective chemical etching. The porous CrN thin film electrodes exhibit high-capacitance performance (31.3 mF cm-2 at 1.0 mA cm-2) and reasonable cycling stability (94% retention after 20000 cycles). Moreover, the specific capacitance is more than two-fold higher than that of the CrN thin film electrodes in previous work. In addition, a symmetric supercapacitor device with a maximum energy density of 14.4 mWh cm-3 and a maximum power density of 6.6 W cm-3 is achieved. These findings demonstrate that the porous CrN thin films will have potential applications in supercapacitors.

Fabrication and optical characterization of imaging fiber-based nanoarrays.

PubMed

Tam, Jenny M; Song, Linan; Walt, David R

2005-09-15

In this paper, we present a technique for fabricating arrays containing a density at least 90 times higher than previously published. Specifically, we discuss the fabrication of two imaging fiber-based nanoarrays, one with 700nm features, another with 300nm features. With arrays containing up to 4.5x10(6) array elements/mm(2), these nanoarrays have an ultra-high packing density. A straightforward etching protocol is used to create nanowells into which beads can be deposited. These beads comprise the sensing elements of the nanoarray. Deposition of the nanobeads into the nanowells using two techniques is described. The surface characteristics of the etched arrays are examined with atomic force microscopy and scanning electron microscopy. Fluorescence microscopy was used to observe the arrays. The 300nm array features and the 500nm center-to-center distance approach the minimum feature sizes viewable using conventional light microscopy.

Dose equivalent neutron dosimeter

DOEpatents

Griffith, Richard V.; Hankins, Dale E.; Tomasino, Luigi; Gomaa, Mohamed A. M.

1983-01-01

A neutron dosimeter is disclosed which provides a single measurements indicating the amount of potential biological damage resulting from the neutron exposure of the wearer, for a wide range of neutron energies. The dosimeter includes a detecting sheet of track etch detecting material such as a carbonate plastic, for detecting higher energy neutrons, and a radiator layer containing conversion material such as .sup.6 Li and .sup.10 B lying adjacent to the detecting sheet for converting moderate energy neutrons to alpha particles that produce tracks in the adjacent detecting sheet. The density of conversion material in the radiator layer is of an amount which is chosen so that the density of tracks produced in the detecting sheet is proportional to the biological damage done by neutrons, regardless of whether the tracks are produced as the result of moderate energy neutrons striking the radiator layer or as the result of higher energy neutrons striking the sheet of track etch material.

Design of Hybrid Nanostructural Arrays to Manipulate SERS-Active Substrates by Nanosphere Lithography.

PubMed

Zhao, Xiaoyu; Wen, Jiahong; Zhang, Mengning; Wang, Dunhui; Wang, Yaxin; Chen, Lei; Zhang, Yongjun; Yang, Jinghai; Du, Youwei

2017-03-01

An easy-handling and low-cost method is utilized to controllably fabricate nanopattern arrays as the surface-enhanced Raman scattering (SERS) active substrates with high density of SERS-active areas (hot spots). A hybrid silver array of nanocaps and nanotriangles are prepared by combining magnetron sputtering and plasma etching. By adjusting the etching time of polystyrene (PS) colloid spheres array in silver nanobowls, the morphology of the arrays can be easily manipulated to control the formation and distribution of hot spots. The experimental results show that the hybrid nanostructural arrays have large enhancement factor, which is estimated to be seven times larger than that in the array of nanocaps and three times larger than that in the array of nanorings and nanoparticles. According to the results of finite-difference time-domain simulation, the excellent SERS performance of this array is ascribed to the high density of hot spots and enhanced electromagnetic field.

Quadrilateral Micro-Hole Array Machining on Invar Thin Film: Wet Etching and Electrochemical Fusion Machining

PubMed Central

Choi, Woong-Kirl; Kim, Seong-Hyun; Choi, Seung-Geon; Lee, Eun-Sang

2018-01-01

Ultra-precision products which contain a micro-hole array have recently shown remarkable demand growth in many fields, especially in the semiconductor and display industries. Photoresist etching and electrochemical machining are widely known as precision methods for machining micro-holes with no residual stress and lower surface roughness on the fabricated products. The Invar shadow masks used for organic light-emitting diodes (OLEDs) contain numerous micro-holes and are currently machined by a photoresist etching method. However, this method has several problems, such as uncontrollable hole machining accuracy, non-etched areas, and overcutting. To solve these problems, a machining method that combines photoresist etching and electrochemical machining can be applied. In this study, negative photoresist with a quadrilateral hole array pattern was dry coated onto 30-µm-thick Invar thin film, and then exposure and development were carried out. After that, photoresist single-side wet etching and a fusion method of wet etching-electrochemical machining were used to machine micro-holes on the Invar. The hole machining geometry, surface quality, and overcutting characteristics of the methods were studied. Wet etching and electrochemical fusion machining can improve the accuracy and surface quality. The overcutting phenomenon can also be controlled by the fusion machining. Experimental results show that the proposed method is promising for the fabrication of Invar film shadow masks. PMID:29351235

Nonlinear THz Plamonic Disk Resonators

NASA Astrophysics Data System (ADS)

Seren, Huseyin; Zhang, Jingdi; Keiser, George; Maddox, Scott; Fan, Kebin; Cao, Lingyue; Bank, Seth; Zhang, Xin; Averitt, Richard

2013-03-01

Particle surface plasmons (PPSs) at visible wavelengths continue to be actively investigated with the goal of nanoscale control of light. In contrast, terahertz (THz) surface plasmon experiments are at a nascent stage of investigation. Doped semiconductors with proper carrier density and mobility support THz PSPs. One approach is to utilize thick doped films etched into subwavelength disks. Given the ease of tuning the semiconductor carrier density, THz PSPs are tunable and exhibit interesting nonlinear THz plasmonic effects. We created THz PSP structures using MBE grown 2um thick InAs films with a doping concentration of 1e17cm-3 on 500um thick semi-insulating GaAs substrate. We patterned 40um diameter disks with a 60um period by reactive ion etching. Our THz time-domain measurements reveal a resonance at 1.1THz which agrees well with simulation results using a Drude model. A nonlinear response occurs at high THz electric field strengths (>50kV/cm). In particular, we observed a redshift and quenching of the resonance due to impact ionization which resulted in changes in the carrier density and effective mass due to inter-valley scattering.

Temperature induced degradation mechanisms of AlInAs/InGaAs/InP quantum cascade lasers

NASA Astrophysics Data System (ADS)

Pierścińska, D.; Pierściński, K.; Płuska, M.; Sobczak, G.; Kuźmicz, A.; Gutowski, P.; Bugajski, M.

2018-01-01

In this paper, we report on the investigation of temperature induced degradation mode of quantum cascade lasers (QCLs) with an emphasis on the influence of different processing technology. We investigate and compare lattice matched AlInAs/InGaAs/InP QCLs of various constructions, i.e., double trench, buried heterostructure and ridge waveguide regarding thermal management, reliability and sources of degradation. The analysis was performed by CCD thermoreflectance spectroscopy, scanning electron microscope inspection and destructive analysis by focused ion beam etching, enabling determination of the source and mode of degradation for investigated lasers. Experimental temperature data relate temperature rise, arising from supply current, with device geometry. Results clearly indicate, that the buried heterostructure geometry, allows reaching the highest maximal operating current densities, before the degradation occurs. Microscopic images of degradation confirm that degradation includes the damage of the contact layer as well as damage of the active region layers.

Array Technology for Terahertz Imaging

NASA Technical Reports Server (NTRS)

Reck, Theodore; Siles, Jose; Jung, Cecile; Gill, John; Lee, Choonsup; Chattopadhyay, Goutam; Mehdi, Imran; Cooper, Ken

2012-01-01

Heterodyne terahertz (0.3 - 3THz) imaging systems are currently limited to single or a low number of pixels. Drastic improvements in imaging sensitivity and speed can be achieved by replacing single pixel systems with an array of detectors. This paper presents an array topology that is being developed at the Jet Propulsion Laboratory based on the micromachining of silicon. This technique fabricates the array's package and waveguide components by plasma etching of silicon, resulting in devices with precision surpassing that of current metal machining techniques. Using silicon increases the versatility of the packaging, enabling a variety of orientations of circuitry within the device which increases circuit density and design options. The design of a two-pixel transceiver utilizing a stacked architecture is presented that achieves a pixel spacing of 10mm. By only allowing coupling from the top and bottom of the package the design can readily be arrayed in two dimensions with a spacing of 10mm x 18mm.

Effects of UV light intensity on electrochemical wet etching of SiC for the fabrication of suspended graphene

NASA Astrophysics Data System (ADS)

O, Ryong-Sok; Takamura, Makoto; Furukawa, Kazuaki; Nagase, Masao; Hibino, Hiroki

2015-03-01

We report on the effects of UV light intensity on the photo assisted electrochemical wet etching of SiC(0001) underneath an epitaxially grown graphene for the fabrication of suspended structures. The maximum etching rate of SiC(0001) was 2.5 µm/h under UV light irradiation in 1 wt % KOH at a constant current of 0.5 mA/cm2. The successful formation of suspended structures depended on the etching rate of SiC. In the Raman spectra of the suspended structures, we did not observe a significant increase in the intensity of the D peak, which originates from defects in graphene sheets. This is most likely explained by the high quality of the single-crystalline graphene epitaxially grown on SiC.

Twin-Slot Antenna-Coupled Superconducting Ti Transition-Edge Sensor at 350 GHz

NASA Astrophysics Data System (ADS)

Zhang, W.; Miao, W.; Wang, Z.; Guo, X. H.; Liu, D.; Zhong, J. Q.; Yao, Q. J.; Shi, S. C.

2018-05-01

We have developed four-leg-supported superconducting Ti transition-edge sensors (TES) formed by KOH wet etching. Energy relaxation mechanism is changed from electron-phonon coupling to diffusive phonon after wet etching. The current-voltage curves of the same TES device were measured before and after wet etching. After wet etching, its thermal conductance (G) is reduced to 500 pW/K from 8950 pW/K. The measured effective response time (τ eff) is 143 μs, about 30 times larger. In addition, we have studied the optical noise equivalent power (NEP) with a cryogenic blackbody in combination with metal-mesh filters to define the radiation bandwidth. The obtained optical NEP is 5 × 10-16 W/√Hz, which is suitable for ground-based astronomical applications.

TOPICAL REVIEW: Black silicon method X: a review on high speed and selective plasma etching of silicon with profile control: an in-depth comparison between Bosch and cryostat DRIE processes as a roadmap to next generation equipment

NASA Astrophysics Data System (ADS)

Jansen, H V; de Boer, M J; Unnikrishnan, S; Louwerse, M C; Elwenspoek, M C

2009-03-01

An intensive study has been performed to understand and tune deep reactive ion etch (DRIE) processes for optimum results with respect to the silicon etch rate, etch profile and mask etch selectivity (in order of priority) using state-of-the-art dual power source DRIE equipment. The research compares pulsed-mode DRIE processes (e.g. Bosch technique) and mixed-mode DRIE processes (e.g. cryostat technique). In both techniques, an inhibitor is added to fluorine-based plasma to achieve directional etching, which is formed out of an oxide-forming (O2) or a fluorocarbon (FC) gas (C4F8 or CHF3). The inhibitor can be introduced together with the etch gas, which is named a mixed-mode DRIE process, or the inhibitor can be added in a time-multiplexed manner, which will be termed a pulsed-mode DRIE process. Next, the most convenient mode of operation found in this study is highlighted including some remarks to ensure proper etching (i.e. step synchronization in pulsed-mode operation and heat control of the wafer). First of all, for the fabrication of directional profiles, pulsed-mode DRIE is far easier to handle, is more robust with respect to the pattern layout and has the potential of achieving much higher mask etch selectivity, whereas in a mixed-mode the etch rate is higher and sidewall scalloping is prohibited. It is found that both pulsed-mode CHF3 and C4F8 are perfectly suited to perform high speed directional etching, although they have the drawback of leaving the FC residue at the sidewalls of etched structures. They show an identical result when the flow of CHF3 is roughly 30 times the flow of C4F8, and the amount of gas needed for a comparable result decreases rapidly while lowering the temperature from room down to cryogenic (and increasing the etch rate). Moreover, lowering the temperature lowers the mask erosion rate substantially (and so the mask selectivity improves). The pulsed-mode O2 is FC-free but shows only tolerable anisotropic results at -120 °C. The downside of needing liquid nitrogen to perform cryogenic etching can be improved by using a new approach in which both the pulsed and mixed modes are combined into the so-called puffed mode. Alternatively, the use of tetra-ethyl-ortho-silicate (TEOS) as a silicon oxide precursor is proposed to enable sufficient inhibiting strength and improved profile control up to room temperature. Pulsed-mode processing, the second important aspect, is commonly performed in a cycle using two separate steps: etch and deposition. Sometimes, a three-step cycle is adopted using a separate step to clean the bottom of etching features. This study highlights an issue, known by the authors but not discussed before in the literature: the need for proper synchronization between gas and bias pulses to explore the benefit of three steps. The transport of gas from the mass flow controller towards the wafer takes time, whereas the application of bias to the wafer is relatively instantaneous. This delay causes a problem with respect to synchronization when decreasing the step time towards a value close to the gas residence time. It is proposed to upgrade the software with a delay time module for the bias pulses to be in pace with the gas pulses. If properly designed, the delay module makes it possible to switch on the bias exactly during the arrival of the gas for the bottom removal step and so it will minimize the ionic impact because now etch and deposition steps can be performed virtually without bias. This will increase the mask etch selectivity and lower the heat impact significantly. Moreover, the extra bottom removal step can be performed at (also synchronized!) low pressure and therefore opens a window for improved aspect ratios. The temperature control of the wafer, a third aspect of this study, at a higher etch rate and longer etch time, needs critical attention, because it drastically limits the DRIE performance. It is stressed that the exothermic reaction (high silicon loading) and ionic impact (due to metallic masks and/or exposed silicon) are the main sources of heat that might raise the wafer temperature uncontrollably, and they show the weakness of the helium backside technique using mechanical clamping. Electrostatic clamping, an alternative technique, should minimize this problem because it is less susceptible to heat transfer when its thermal resistance and the gap of the helium backside cavity are minimized; however, it is not a subject of the current study. Because oxygen-growth-based etch processes (due to their ultra thin inhibiting layer) rely more heavily on a constant wafer temperature than fluorocarbon-based processes, oxygen etches are more affected by temperature fluctuations and drifts during the etching. The fourth outcome of this review is a phenomenological model, which explains and predicts many features with respect to loading, flow and pressure behaviour in DRIE equipment including a diffusion zone. The model is a reshape of the flow model constructed by Mogab, who studied the loading effect in plasma etching. Despite the downside of needing a cryostat, it is shown that—when selecting proper conditions—a cryogenic two-step pulsed mode can be used as a successful technique to achieve high speed and selective plasma etching with an etch rate around 25 µm min-1 (<1% silicon load) with nearly vertical walls and resist etch selectivity beyond 1000. With the model in hand, it can be predicted that the etch rate can be doubled (50 µm min-1 at an efficiency of 33% for the fluorine generation from the SF6 feed gas) by minimizing the time the free radicals need to pass the diffusion zone. It is anticipated that this residence time can be reduced sufficiently by a proper inductive coupled plasma (ICP) source design (e.g. plasma shower head and concentrator). In order to preserve the correct profile at such high etch rates, the pressure during the bottom removal step should be minimized and, therefore, the synchronized three-step pulsed mode is believed to be essential to reach such high etch rates with sufficient profile control. In order to improve the etch rate even further, the ICP power should be enhanced; the upgrading of the turbopump seems not yet to be relevant because the throttle valve in the current study had to be used to restrict the turbo efficiency. In order to have a versatile list of state-of-the-art references, it has been decided to arrange it in subjects. The categories concerning plasma physics and applications are, for example, books, reviews, general topics, fluorine-based plasmas, plasma mixtures with oxygen at room temperature, wafer heat transfer and high aspect ratio trench (HART) etching. For readers 'new' to this field, it is advisable to study at least one (but rather more than one) of the reviews concerning plasma as found in the first 30 references. In many cases, a paper can be classified into more than one category. In such cases, the paper is directed to the subject most suited for the discussion of the current review. For example, many papers on heat transfer also treat cryogenic conditions and all the references dealing with highly anisotropic behaviour have been directed to the category HARTs. Additional pointers could get around this problem but have the disadvantage of creating a kind of written spaghetti. I hope that the adapted organization structure will help to have a quick look at and understanding of current developments in high aspect ratio plasma etching. Enjoy reading... Henri Jansen 18 June 2008

Characteristics of n-GaN After Cl2/Ar and Cl2/N2 Inductively Coupled Plasma Etching

NASA Astrophysics Data System (ADS)

Han, Yan-Jun; Xue, Song; Guo, Wen-Ping; Sun, Chang-Zheng; Hao, Zhi-Biao; Luo, Yi

2003-10-01

A systematic study on the effect of inductively coupled plasma (ICP) etching on n-type GaN is presented. The optical and electrical properties and surface stoichiometry of n-type GaN are evaluated using room-temperature photoluminescence (PL) and current-voltage (I-V) characteristic measurements, and X-ray photoelectron spectroscopy (XPS), respectively. Investigation of the effect of additive gas (N2 and Ar) and RF power on these characteristics has also been carried out. It is shown that the decrease in the O/Ga ratio after ICP etching can suppress the deterioration of the near-band-edge emission intensity. Furthermore, N vacancy (VN) with a shallow donor nature and Ga vacancy (VGa) with a deep acceptor nature are generated after ICP etching upon the addition of Ar and N2 to Cl2 plasma, respectively. Lower ohmic contact resistance could be obtained when VN or ion-bombardment-induced defect is dominant at the surface. Improved etching conditions have been obtained based on these results.

Characterization of plasma processing induced charging damage to MOS devices

NASA Astrophysics Data System (ADS)

Ma, Shawming

1997-12-01

Plasma processing has become an integral part of the fabrication of integrated circuits and takes at least 30% of whole process steps since it offers advantages in terms of directionality, low temperature and process convenience. However, wafer charging during plasma processes is a significant concern for both thin oxide damage and profile distortion. In this work, the factors affecting this damage will be explained by plasma issues, device structure and oxide quality. The SPORT (Stanford Plasma On-wafer Real Time) charging probe was developed to investigate the charging mechanism of different plasma processes including poly-Si etching, resist ashing and PECVD. The basic idea of this probe is that it simulates a real device structure in the plasma environment and allows measurement of plasma induced charging voltages and currents directly in real time. This measurement is fully compatible with other charging voltage measurement but it is the only one to do in real-time. Effect of magnetic field induced plasma nonuniformity on spatial dependent charging is well understood by this measurement. In addition, the plasma parameters including ion current density and electron temperature can also be extracted from the probe's plasma I-V characteristics using a dc Langmuir probe like theory. It will be shown that the MOS device tunneling current from charging, the dependence on antenna ratio and the etch uniformity can all be predicted by using this measurement. Moreover, the real-time measurement reveals transient and electrode edge effect during processing. Furthermore, high aspect ratio pattern induced electron shading effects can also be characterized by the probe. On the oxide quality issue, wafer temperature during plasma processing has been experimentally shown to be critical to charging damage. Finally, different MOS capacitor testing methods including breakdown voltage, charge-to-breakdown, gate leakage current and voltage-time at constant current bias were compared to find the optimum method for charging device reliability testing.

Polyaniline nanowire arrays aligned on nitrogen-doped carbon fabric for high-performance flexible supercapacitors.

PubMed

Yu, Pingping; Li, Yingzhi; Yu, Xinyi; Zhao, Xin; Wu, Lihao; Zhang, Qinghua

2013-09-24

A combination of vertical polyaniline (PANI) nanowire arrays and nitrogen plasma etched carbon fiber cloths (eCFC) was fabricated to create 3D nanostructured PANI/eCFC composites. The small size of the highly ordered PANI nanowires can greatly reduce the scale of the diffusion length, allowing for the improved utilization of electrode materials. A two-electrode flexible supercapacitor based on PANI/eCFC demonstrates a high specific capacitance (1035 F g(-1) at a current density of 1 A g(-1)), good rate capability (88% capacity retention at 8 A g(-1)), and long-term cycle life (10% capacity loss after 5000 cycles). The lightweight, low-cost, flexible composites are promising candidates for use in energy storage device applications.

10 K gate I(2)L and 1 K component analog compatible bipolar VLSI technology - HIT-2

NASA Astrophysics Data System (ADS)

Washio, K.; Watanabe, T.; Okabe, T.; Horie, N.

1985-02-01

An advanced analog/digital bipolar VLSI technology that combines on the same chip 2-ns 10 K I(2)L gates with 1 K analog devices is proposed. The new technology, called high-density integration technology-2, is based on a new structure concept that consists of three major techniques: shallow grooved-isolation, I(2)L active layer etching, and I(2)L current gain increase. I(2)L circuits with 80-MHz maximum toggle frequency have developed compatibly with n-p-n transistors having a BV(CE0) of more than 10 V and an f(T) of 5 GHz, and lateral p-n-p transistors having an f(T) of 150 MHz.

Plasma generating apparatus for large area plasma processing

DOEpatents

Tsai, C.C.; Gorbatkin, S.M.; Berry, L.A.

1991-07-16

A plasma generating apparatus for plasma processing applications is based on a permanent magnet line-cusp plasma confinement chamber coupled to a compact single-coil microwave waveguide launcher. The device creates an electron cyclotron resonance (ECR) plasma in the launcher and a second ECR plasma is created in the line cusps due to a 0.0875 tesla magnetic field in that region. Additional special magnetic field configuring reduces the magnetic field at the substrate to below 0.001 tesla. The resulting plasma source is capable of producing large-area (20-cm diam), highly uniform (.+-.5%) ion beams with current densities above 5 mA/cm[sup 2]. The source has been used to etch photoresist on 5-inch diam silicon wafers with good uniformity. 3 figures.

Plasma generating apparatus for large area plasma processing

DOEpatents

Tsai, Chin-Chi; Gorbatkin, Steven M.; Berry, Lee A.

1991-01-01

A plasma generating apparatus for plasma processing applications is based on a permanent magnet line-cusp plasma confinement chamber coupled to a compact single-coil microwave waveguide launcher. The device creates an electron cyclotron resonance (ECR) plasma in the launcher and a second ECR plasma is created in the line cusps due to a 0.0875 tesla magnetic field in that region. Additional special magnetic field configuring reduces the magnetic field at the substrate to below 0.001 tesla. The resulting plasma source is capable of producing large-area (20-cm diam), highly uniform (.+-.5%) ion beams with current densities above 5 mA/cm.sup.2. The source has been used to etch photoresist on 5-inch diam silicon wafers with good uniformity.

Cryo-Etched Black Silicon for Use as Optical Black

NASA Technical Reports Server (NTRS)

Yee, Karl Y.; White, Victor E.; Mouroulis, Pantazis; Eastwood, Michael L.

2011-01-01

Stray light reflected from the surface of imaging spectrometer components in particular, the spectrometer slit degrade the image quality. A technique has been developed for rapid, uniform, and cost-effective black silicon formation based on inductively coupled plasma (ICP) etching at cryogenic temperatures. Recent measurements show less than 1-percent total reflectance from 350 2,500 nm of doped black silicon formed in this way, making it an excellent option for texturing of component surfaces for reduction of stray light. Oxygen combines with SF6 + Si etch byproducts to form a passivation layer atop the Si when the etch is performed at cryogenic temperatures. Excess flow of oxygen results in micromasking and the formation of black silicon. The process is repeatable and reliable, and provides control over etch depth and sidewall profile. Density of the needles can be controlled to some extent. Regions to be textured can be patterned lithographically. Adhesion is not an issue as the nanotips are part of the underlying substrate. This is in contrast to surface growth/deposition techniques such as carbon nanotubes (CNTs). The black Si surface is compatible with wet processing, including processing with solvents, the textured surface is completely inorganic, and it does not outgas. In radiometry applications, optical absorbers are often constructed using gold black or CNTs. This black silicon technology is an improvement for these types of applications.

Development of scanning graphene Hall probes for magnetic microscopy

NASA Astrophysics Data System (ADS)

Schaefer, Brian T.; Wang, Lei; McEuen, Paul L.; Nowack, Katja C.

We discuss our progress on developing scanning Hall probes fabricated from hexagonal boron nitride (hBN)-encapsulated graphene, with the goal to image magnetic fields with submicron resolution. In contrast to scanning superconducting quantum interference device (SQUID) microscopy, this technique is compatible with a large applied magnetic field and not limited to cryogenic temperatures. The field sensitivity of a Hall probe depends inversely on carrier density, while the primary source of noise in the measurement is Johnson noise originating from the device resistance. hBN-encapsulated graphene demonstrates high carrier mobility at low carrier densities, therefore making it an ideal material for sensitive Hall probes. Furthermore, engineering the dielectric environment of graphene by encapsulating in hBN reduces low-frequency charge noise and disorder from the substrate. We outline our plans for adapting these devices for scanning, including characterization of the point spread function with a scanned current loop and fabrication of a deep-etched structure that enables positioning the sensitive area within 100 nanometers of the sample surface.

Computer image analysis of etched tracks from ionizing radiation

NASA Technical Reports Server (NTRS)

Blanford, George E.

1994-01-01

I proposed to continue a cooperative research project with Dr. David S. McKay concerning image analysis of tracks. Last summer we showed that we could measure track densities using the Oxford Instruments eXL computer and software that is attached to an ISI scanning electron microscope (SEM) located in building 31 at JSC. To reduce the dependence on JSC equipment, we proposed to transfer the SEM images to UHCL for analysis. Last summer we developed techniques to use digitized scanning electron micrographs and computer image analysis programs to measure track densities in lunar soil grains. Tracks were formed by highly ionizing solar energetic particles and cosmic rays during near surface exposure on the Moon. The track densities are related to the exposure conditions (depth and time). Distributions of the number of grains as a function of their track densities can reveal the modality of soil maturation. As part of a consortium effort to better understand the maturation of lunar soil and its relation to its infrared reflectance properties, we worked on lunar samples 67701,205 and 61221,134. These samples were etched for a shorter time (6 hours) than last summer's sample and this difference has presented problems for establishing the correct analysis conditions. We used computer counting and measurement of area to obtain preliminary track densities and a track density distribution that we could interpret for sample 67701,205. This sample is a submature soil consisting of approximately 85 percent mature soil mixed with approximately 15 percent immature, but not pristine, soil.

Toward Edge-Defined Holey Boron Nitride Nanosheets

NASA Technical Reports Server (NTRS)

Lin, Yi; Liao, Yunlong; Chen, Zhongfan; Connell, John W.

2015-01-01

"Holey" two-dimensional (2D) nanosheets with well-defined holy morphology and edge chemistry are highly desirable for applications such as energy storage, catalysis, sensing, transistors, and molecular transport/separation. For example, holey grapheme is currently under extensive investigation for energy storage applications because of the improvement in ion transport due to through the thickness pathways provided by the holes. Without the holes, the 2D materials have significant limitations for such applications in which efficient ion transport is important. As part of an effort to apply this approach to other 2D nanomaterials, a method to etch geometrically defined pits or holes on the basal plane surface of hexagonal boron nitride (h-BN) nanosheets has been developed. The etching, conducted via heating in ambient air using metal nanoparticles as catalysts, was facile, controllable, and scalable. Starting h-BN layered crystals were etched and subsequently exfoliated into boron nitride nanosheets (BNNSs). The as-etched and exfoliated h-BN nanosheets possessed defined pit and hole shapes that were comprised of regulated nanostructures at the edges. The current finding are the first step toward the bulk preparation of holey BNNSs with defined holes and edges.

Frequency-tuning radiofrequency plasma source operated in inductively-coupled mode under a low magnetic field

NASA Astrophysics Data System (ADS)

Takahashi, Kazunori; Nakano, Yudai; Ando, Akira

2017-07-01

A radiofrequency (rf) inductively-coupled plasma source is operated with a frequency-tuning impedance matching system, where the rf frequency is variable in the range of 20-50 MHz and the maximum power is 100 W. The source consists of a 45 mm-diameter pyrex glass tube wound by an rf antenna and a solenoid providing a magnetic field strength in the range of 0-200 Gauss. A reflected rf power for no plasma case is minimized at the frequency of ˜25 MHz, whereas the frequency giving the minimum reflection with the high density plasma is about 28 MHz, where the density jump is observed when minimizing the reflection. A high density argon plasma above 1× {{10}12} cm-3 is successfully obtained in the source for the rf power of 50-100 W, where it is observed that an external magnetic field of a few tens of Gauss yields the highest plasma density in the present configuration. The frequency-tuning plasma source is applied to a compact and high-speed silicon etcher in an Ar-SF6 plasma; then the etching rate of 8~μ m min-1 is obtained for no bias voltage to the silicon wafer, i.e. for the case that a physical ion etching process is eliminated.

Microleakage of Self-Etch Adhesive System in Class V Cavities Prepared by Using Er:YAG Laser with Different Pulse Modes.

PubMed

Phanombualert, Jutipond; Chimtim, Pijitta; Heebthamai, Thitirat; Weera-Archakul, Wilawan

2015-09-01

In vitro studies evaluated cementum surface morphology and microleakage of three different energy density parameters of Erbium: Yttrium Aluminum Garnet (Er:YAG) laser compared with diamond bur preparation on class V cavities with self-etch adhesive system and composite resin restoration. Standard class V cavities were prepared at cervical area below the cementoenamel junction (CEJ) in 80 extracted premolars, by using a diamond bur on the buccal surface. All teeth were randomly allocated into four groups: Group 1, diamond bur; Group 2, Er:YAG 50 mJ/15 Hz, 3.77 J/cm(2); Group 3, Er:YAG 75 mJ/15 Hz, 5.65 J/cm(2); and Group 4, Er:YAG 100 mJ/15 Hz, 7.53 J/cm(2). Five cavities from each group were evaluated by scanning electron microscopy (SEM). The 15 remaining cavities from each group were restored with self-etch adhesive and nano-hybrid composite. After thermocycling, all sample teeth were immersed in 0.2% methylene blue dye and sectioned buccolingually. Statistics were analyzed using the one way ANOVA and Mann-Whitney U tests with Bonferroni correction. The morphology showed micro-irregularities in the cementum surface of the laser group with the absence of a smear layer. The microstructure characteristics were increased surface roughness followed by increasing laser energy transmission. The Er:YAG laser groups were statistically significant, with less microleakage than the diamond bur group (p<0.05). There was statistically significant difference between the occlusal and gingival microleakage in all the groups (p<0.05). When the laser groups were compared, the lowest microleakage was achieved with energy density at 3.77 J/cm(2) on the occlusal and gingival cementum margin, which showed less microleakage than at energy densities of 5.65 and 7.53 J/cm(2) with Er:YAG laser. These observations indicate that the micro-irregularities of the cementum surface could facilitate the formation of a hybridization zone with a self-etch adhesive system. Therefore, the microleakage of Er:YAG laser irradiation was significantly decreased compared with diamond bur cavities.

Diagnostic for Plasma Enhanced Chemical Vapor Deposition and Etch Systems

NASA Technical Reports Server (NTRS)

Cappelli, Mark A.

1999-01-01

In order to meet NASA's requirements for the rapid development and validation of future generation electronic devices as well as associated materials and processes, enabling technologies ion the processing of semiconductor materials arising from understanding etch chemistries are being developed through a research collaboration between Stanford University and NASA-Ames Research Center, Although a great deal of laboratory-scale research has been performed on many of materials processing plasmas, little is known about the gas-phase and surface chemical reactions that are critical in many etch and deposition processes, and how these reactions are influenced by the variation in operating conditions. In addition, many plasma-based processes suffer from stability and reliability problems leading to a compromise in performance and a potentially increased cost for the semiconductor manufacturing industry. Such a lack of understanding has hindered the development of process models that can aid in the scaling and improvement of plasma etch and deposition systems. The research described involves the study of plasmas used in semiconductor processes. An inductively coupled plasma (ICP) source in place of the standard upper electrode assembly of the Gaseous Electronics Conference (GEC) radio-frequency (RF) Reference Cell is used to investigate the discharge characteristics and chemistries. This ICP source generates plasmas with higher electron densities (approximately 10(exp 12)/cu cm) and lower operating pressures (approximately 7 mTorr) than obtainable with the original parallel-plate version of the GEC Cell. This expanded operating regime is more relevant to new generations of industrial plasma systems being used by the microelectronics industry. The motivation for this study is to develop an understanding of the physical phenomena involved in plasma processing and to measure much needed fundamental parameters, such as gas-phase and surface reaction rates. species concentration, temperature, ion energy distribution, and electron number density. A wide variety of diagnostic techniques are under development through this consortium grant to measure these parameters. including molecular beam mass spectrometry (MBMS). Fourier transform infrared (FTIR) spectroscopy, broadband ultraviolet (UV) absorption spectroscopy, a compensated Langmuir probe. Additional diagnostics. Such as microwave interferometry and microwave absorption for measurements of plasma density and radical concentrations are also planned.

Fabrication of WS2/GaN p-n Junction by Wafer-Scale WS2 Thin Film Transfer

PubMed Central

Yu, Yang; Fong, Patrick W. K.; Wang, Shifeng; Surya, Charles

2016-01-01

High quality wafer-scale free-standing WS2 grown by van der Waals rheotaxy (vdWR) using Ni as a texture promoting layer is reported. The microstructure of vdWR grown WS2 was significantly modified from mixture of crystallites with their c-axes both parallel to (type I) and perpendicular to (type II) the substrate to large type II crystallites. Wafer-scale transfer of vdWR grown WS2 onto different substrates by an etching-free technique was demonstrated for the first time that utilized the hydrophobic property of WS2 and hydrophilic property of sapphire. Our results show that vdWR is a reliable technique to obtain type-II textured crystallites in WS2, which is the key factor for the wafer-scale etching-free transfer. The transferred films were found to be free of observable wrinkles, cracks, or polymer residues. High quality p-n junctions fabricated by room-temperature transfer of the p-type WS2 onto an n-type GaN was demonstrated with a small leakage current density of 29.6 μA/cm2 at −1 V which shows superior performances compared to the directly grown WS2/GaN heterojunctions. PMID:27897210

Nanometer scale fabrication and optical response of InGaN/GaN quantum disks

NASA Astrophysics Data System (ADS)

Lai, Yi-Chun; Higo, Akio; Kiba, Takayuki; Thomas, Cedric; Chen, Shula; Lee, Chang Yong; Tanikawa, Tomoyuki; Kuboya, Shigeyuki; Katayama, Ryuji; Shojiki, Kanako; Takayama, Junichi; Yamashita, Ichiro; Murayama, Akihiro; Chi, Gou-Chung; Yu, Peichen; Samukawa, Seiji

2016-10-01

In this work, we demonstrate homogeneously distributed In0.3Ga0.7N/GaN quantum disks (QDs), with an average diameter below 10 nm and a high density of 2.1 × 1011 cm-2, embedded in 20 nm tall nanopillars. The scalable top-down fabrication process involves the use of self-assembled ferritin bio-templates as the etch mask, spin coated on top of a strained In0.3Ga0.7N/GaN single quantum well (SQW) structure, followed by a neutral beam etch (NBE) method. The small dimensions of the iron cores inside ferritin and nearly damage-free process enabled by the NBE jointly contribute to the observation of photoluminescence (PL) from strain-relaxed In0.3Ga0.7N/GaN QDs at 6 K. The large blueshift of the peak wavelength by over 70 nm manifests a strong reduction of the quantum-confined Stark effect (QCSE) within the QD structure, which also agrees well with the theoretical prediction using a 3D Schrödinger equation solver. The current results hence pave the way towards the realization of large-scale III-N quantum structures using the combination of bio-templates and NBE, which is vital for the development of next-generation lighting and communication devices.

Optimization of hybrid organic/inorganic poly(3-hexylthiophene-2,5-diyl)/silicon solar cells

NASA Astrophysics Data System (ADS)

Weingarten, Martin; Sanders, Simon; Stümmler, Dominik; Pfeiffer, Pascal; Vescan, Andrei; Kalisch, Holger

2016-04-01

In the last years, hybrid organic/silicon solar cells have attracted great interest in photovoltaic research due to their potential to become a low-cost alternative for the conventionally used silicon pn-junction solar cells. This work is focused on hybrid solar cells based on the polymer poly(3-hexylthiophene-2,5-diyl), which was deposited on n-doped crystalline silicon via spin-coating under ambient conditions. By employing an anisotropic etching step with potassium hydroxide (KOH), the reflection losses at the silicon surface were reduced. Hereby, the short-circuit current density of the hybrid devices was increased by 31%, leading to a maximum power conversion efficiency (PCE) of 13.1% compared to a PCE of 10.7% for the devices without KOH etching. In addition, the contacts were improved by replacing gold with the more conductive silver as top grid material to reduce the contact resistance and by introducing a thin (˜0.5 nm) lithium fluoride layer between the silicon and the aluminum backside contact to improve electron collection and hole blocking. Hereby, the open-circuit voltage and the fill factor of the hybrid solar cells were further improved and devices with very high PCE up to 14.2% have been realized.

Fabrication of WS2/GaN p-n Junction by Wafer-Scale WS2 Thin Film Transfer.

PubMed

Yu, Yang; Fong, Patrick W K; Wang, Shifeng; Surya, Charles

2016-11-29

High quality wafer-scale free-standing WS 2 grown by van der Waals rheotaxy (vdWR) using Ni as a texture promoting layer is reported. The microstructure of vdWR grown WS 2 was significantly modified from mixture of crystallites with their c-axes both parallel to (type I) and perpendicular to (type II) the substrate to large type II crystallites. Wafer-scale transfer of vdWR grown WS 2 onto different substrates by an etching-free technique was demonstrated for the first time that utilized the hydrophobic property of WS 2 and hydrophilic property of sapphire. Our results show that vdWR is a reliable technique to obtain type-II textured crystallites in WS 2 , which is the key factor for the wafer-scale etching-free transfer. The transferred films were found to be free of observable wrinkles, cracks, or polymer residues. High quality p-n junctions fabricated by room-temperature transfer of the p-type WS 2 onto an n-type GaN was demonstrated with a small leakage current density of 29.6 μA/cm 2 at -1 V which shows superior performances compared to the directly grown WS 2 /GaN heterojunctions.

The Effect of the Wall Contact and Post-Growth C001-Down on Defects in CdTe Crystals Grown by Contactless PVT

NASA Technical Reports Server (NTRS)

Palosz, W.; Grasza, K.; Dudley, M.; Raghothamachar, B.; Cai, L.; Durose, K.; Halliday, D.; Boyall, N. M.; Rose, M. Franklin (Technical Monitor)

2001-01-01

In crystal growth, the quality of the final material may depend, among other factors, on its interaction with the walls of the ampoule during and after the growth, and on the rate of the crystal cool-down at the end of ate the process. To investigate the above phenomena, a series of CdTe crystal growth processes was carried out, The crystals were grown by physical vapor transport without contact with the side walls of the silica glass ampoules, applying the Low Supersaturation Nucleation technique. The source temperature was 930 C, the undercooling was a few degrees. The crystals, having the diameter of 25 mm, grew at the rate of a few mm per day. The post-growth cool-down to the room temperature was conducted at different rates, and lasted from a few minutes to four days. The crystals were characterized using chemical etching low temperature luminescence, and Synchrotron White Beam X-ray Topography techniques. The dislocation (etch pit) density was measured and its distribution was analyzed by comparison with Poisson curves and with the Normalized Radial Distribution Correlation Function. It was found that the contact of the crystal with silica leads to a strain field and high (in the 105 sq cm range) dislocation (etch pit) density. Similar defect concentrations were found in crystals subjected to fast post-growth cool-down. Typical EPD values for lower cool-down rates and in regions not affected by wall interactions are in the lower 10(exp 4) sq cm range. In some areas the actual dislocation density was about 10(exp 3) sq cm or even less. No apparent effect of the cool-down rate on polygonization was observed. A fine structure could be discerned in low-temperature PL spectra of crystals with low dislocation density.

Minimum reaction network necessary to describe Ar/CF4 plasma etch

NASA Astrophysics Data System (ADS)

Helpert, Sofia; Chopra, Meghali; Bonnecaze, Roger T.

2018-03-01

Predicting the etch and deposition profiles created using plasma processes is challenging due to the complexity of plasma discharges and plasma-surface interactions. Volume-averaged global models allow for efficient prediction of important processing parameters and provide a means to quickly determine the effect of a variety of process inputs on the plasma discharge. However, global models are limited based on simplifying assumptions to describe the chemical reaction network. Here a database of 128 reactions is compiled and their corresponding rate constants collected from 24 sources for an Ar/CF4 plasma using the platform RODEo (Recipe Optimization for Deposition and Etching). Six different reaction sets were tested which employed anywhere from 12 to all 128 reactions to evaluate the impact of the reaction database on particle species densities and electron temperature. Because many the reactions used in our database had conflicting rate constants as reported in literature, we also present a method to deal with those uncertainties when constructing the model which includes weighting each reaction rate and filtering outliers. By analyzing the link between a reaction's rate constant and its impact on the predicted plasma densities and electron temperatures, we determine the conditions at which a reaction is deemed necessary to the plasma model. The results of this study provide a foundation for determining which minimal set of reactions must be included in the reaction set of the plasma model.

Metalorganic vapor phase epitaxy of AlN on sapphire with low etch pit density

NASA Astrophysics Data System (ADS)

Koleske, D. D.; Figiel, J. J.; Alliman, D. L.; Gunning, B. P.; Kempisty, J. M.; Creighton, J. R.; Mishima, A.; Ikenaga, K.

2017-06-01

Using metalorganic vapor phase epitaxy, methods were developed to achieve AlN films on sapphire with low etch pit density (EPD). Key to this achievement was using the same AlN growth recipe and only varying the pre-growth conditioning of the quartz-ware. After AlN growth, the quartz-ware was removed from the growth chamber and either exposed to room air or moved into the N2 purged glove box and exposed to H2O vapor. After the quartz-ware was exposed to room air or H2O, the AlN film growth was found to be more reproducible, resulting in films with (0002) and (10-12) x-ray diffraction (XRD) rocking curve linewidths of 200 and 500 arc sec, respectively, and EPDs < 100 cm-2. The EPD was found to correlate with (0002) linewidths, suggesting that the etch pits are associated with open core screw dislocations similar to GaN films. Once reproducible AlN conditions were established using the H2O pre-treatment, it was found that even small doses of trimethylaluminum (TMAl)/NH3 on the quartz-ware surfaces generated AlN films with higher EPDs. The presence of these residual TMAl/NH3-derived coatings in metalorganic vapor phase epitaxy (MOVPE) systems and their impact on the sapphire surface during heating might explain why reproducible growth of AlN on sapphire is difficult.

Effect of back reflectors on photon absorption in thin-film amorphous silicon solar cells

NASA Astrophysics Data System (ADS)

Hossain, Mohammad I.; Qarony, Wayesh; Hossain, M. Khalid; Debnath, M. K.; Uddin, M. Jalal; Tsang, Yuen Hong

2017-10-01

In thin-film solar cells, the photocurrent conversion productivity can be distinctly boosted-up utilizing a proper back reflector. Herein, the impact of different smooth and textured back reflectors was explored and effectuated to study the optical phenomena with interface engineering strategies and characteristics of transparent contacts. A unique type of wet-chemically textured glass-substrate 3D etching mask used in superstrate (p-i-n) amorphous silicon-based solar cell along with legitimated back reflector permits joining the standard light-trapping methodologies, which are utilized to upgrade the energy conversion efficiency (ECE). To investigate the optical and electrical properties of solar cell structure, the optical simulations in three-dimensional measurements (3D) were performed utilizing finite-difference time-domain (FDTD) technique. This design methodology allows to determine the power losses, quantum efficiencies, and short-circuit current densities of various layers in such solar cell. The short-circuit current densities for different reflectors were varied from 11.50 to 13.27 and 13.81 to 16.36 mA/cm2 for the smooth and pyramidal textured solar cells, individually. Contrasted with the comparable flat reference cell, the short-circuit current density of textured solar cell was increased by around 24%, and most extreme outer quantum efficiencies rose from 79 to 86.5%. The photon absorption was fundamentally improved in the spectral region from 600 to 800 nm with no decrease of photocurrent shorter than 600-nm wavelength. Therefore, these optimized designs will help to build the effective plans next-generation amorphous silicon-based solar cells.

Morphology and electronic properties of silicon carbide surfaces

NASA Astrophysics Data System (ADS)

Nie, Shu

2007-12-01

Several issues related to SiC surfaces are studied in the thesis using scanning tunneling microscopy/spectroscopy (STM/S) and atomic force microscopy (AFM). Specific surfaces examined include electropolished SiC, epitaxial graphene on SiC, and vicinal (i.e. slightly miscut from a low-index direction) SiC that have been subjected to high temperature hydrogen-etching. The electropolished surfaces are meant to mimic electrochemically etched SiC, which forms a porous network. The chemical treatment of the surface is similar between electropolishing and electrochemical etching, but the etching conditions are slightly different such that the former produces a flat surface (that is amenable to STM study) whereas the latter produces a complex 3-dimensional porous network. We have used these porous SiC layers as semi-permeable membranes in a biosensor, and we find that the material is quite biocompatible. The purpose of the STM/STS study is to investigate the surface properties of the SiC on the atomic scale in an effort to explain this biocompatibility. The observed tunneling spectra are found to be very asymmetric, with a usual amount of current at positive voltages but no observable current at negative voltages. We propose that this behavior is due to surface charge accumulating on an incompletely passivated surface. Measurements on SiC surfaces prepared by various amounts of hydrogen-etching are used to support this interpretation. Comparison with tunneling computations reveals a density of about 10 13 cm-2 fixed charges on both the electro-polished and the H-etched surfaces. The relatively insulating nature observed on the electro-polished SiC surface may provide an explanation for the biocompatibility of the surface. Graphene, a monolayer of carbon, is a new material for electronic devices. Epitaxial graphene on SiC is fabricated by the Si sublimation method in which a substrate is heated up to about 1350°C in ultra-high vacuum (UHV). The formation of the graphene is monitored using low-energy electron diffraction (LEED) and Auger electron spectroscopy, and the morphology of the graphitized surface is studied using AFM and STM. Use of H-etched SiC substrates enables a relatively flat surface morphology, although residual steps remain due to unintentional miscut of the wafers. Additionally, some surface roughness in the form of small pits is observed, possibly due to the fact that the surface treatments (H-etching and UHV annealing) having been performed in separate vacuum chambers with an intervening transfer through air. Field-effect transistors have been fabricated with our graphene layers; they show a relatively strong held effect at room temperature, with an electron mobility of 535 cm 2/Vs. This value is somewhat lower than that believed to be theoretically possible for this material, and one possible reason may be the nonideal morphology of the surface (i.e. because of the observed steps and pits). Tunneling spectra of the graphene reveal semi-metallic behavior, consistent with that theoretically expected for an isolated layer of graphene. However, additional discrete states are observed in the spectra, possibly arising from bonding at the graphene/SiC interface. The observation of these states provides important input towards an eventual determination of the complete interface structure, and additionally, such states may be relevant in determining the electron mobility of the graphene. Stepped vicinal SIC{0001} substrates are useful templates for epitaxial growth of various types of layers: thick layers of compound semiconductor (in which the steps help preserving the stacking arrangement in the overlayer), monolayers of graphene, or submonolayer semiconductor layers that form quantum wires along the step edges. Step array produced by H-etching of vicinal SiC (0001) and (0001¯) with various miscut angles have been studied by AFM. H-etching is found to produce full unit-cell-high steps on the (0001) Si-face surfaces, but half unit-cell-high steps on the (0001¯) C-face surfaces. These observations are consistent with an asymmetry in the surface energy (i.e. etch rate) of the two types of step terminations occurring on the different surfaces. For high miscut angles, facet formation is observed on the vicinal Si-face, but less so on the C-face. This difference is interpreted in terms of a lower surface energy of the C-face. In terms of applying the stepped surfaces as a template, a much better uniformity in the step-step separation is found for the C-face surfaces.

Comparison of Langmuir probe and multipole resonance probe measurements in argon, hydrogen, nitrogen, and oxygen mixtures in a double ICP discharge

NASA Astrophysics Data System (ADS)

Fiebrandt, Marcel; Oberberg, Moritz; Awakowicz, Peter

2017-07-01

The results of a Multipole Resonance Probe (MRP) are compared to a Langmuir probe in measuring the electron density in Ar, H2, N2, and O2 mixtures. The MRP was designed for measurements in industry processes, i.e., coating or etching. To evaluate a possible influence on the MRP measurement due to molecular gases, different plasmas with increasing molecular gas content in a double inductively coupled plasma at 5 Pa and 10 Pa at 500 W are used. The determined electron densities from the MRP and the Langmuir probe slightly differ in H2 and N2 diluted argon plasmas, but diverge significantly with oxygen. In pure molecular gas plasmas, electron densities measured with the MRP are always higher than those measured with the Langmuir Probe, in particular, in oxygen containing mixtures. The differences can be attributed to etching of the tungsten wire in the Ar:O2 mixtures and rf distortion in the pure molecular discharges. The influence of a non-Maxwellian electron energy distribution function, negative ions or secondary electron emission seems to be of no or only minor importance.

Biomechanical properties of jaw periosteum-derived mineralized culture on different titanium topography.

PubMed

Att, Wael; Kubo, Katsutoshi; Yamada, Masahiro; Maeda, Hatsuhiko; Ogawa, Takahiro

2009-01-01

This study evaluated the biomechanical properties of periosteum-derived mineralized culture on different surface topographies of titanium. Titanium surfaces modified by machining or by acid etching were analyzed using scanning electron microscopy (SEM). Rat mandibular periosteum-derived cells were cultured on either of the titanium surfaces. Cell proliferation was evaluated by cell counts, and gene expression was analyzed using a reverse-transcriptase polymerase chain reaction. Alkaline phosphatase (ALP) stain assay was employed to evaluate osteoblastic activity. Matrix mineralization was examined via von Kossa stain assay, total calcium deposition, and SEM. The hardness and elastic modulus of mineralized cultures were measured using a nano-indenter. The machined surface demonstrated a flat topographic configuration, while the acid-etched surface revealed a uniform micron-scale roughness. Both cell density and ALP activity were significantly higher on the machined surface than on the acid-etched surface. The expression of bone-related genes was up-regulated or enhanced on the acid-etched surface compared to the machined surface. Von Kossa stain showed significantly greater positive areas for the machined surface compared to the acid-etched surface, while total calcium deposition was statistically similar. Mineralized culture on the acid-etched surface was characterized by denser calcium deposition, more mature collagen deposition on the superficial layer, and larger and denser globular matrices inside the matrix than the culture on the machined surface. The mineralized matrix on the acid-etched surface was two times harder than on the machined surface, whereas the elastic modulus was comparable between the two surfaces. The design of this study can be used as a model to evaluate the effect of implant surface topography on the biomechanical properties of periosteum-derived mineralized culture. The results suggest that mandibular periosteal cells respond to different titanium surface topographies differently enough to produce mineralized matrices with different biomechanical qualities.

Gap Fill Materials Using Cyclodextrin Derivatives in ArF Lithography

NASA Astrophysics Data System (ADS)

Takei, Satoshi; Shinjo, Tetsuya; Sakaida, Yasushi; Hashimoto, Keisuke

2007-11-01

High planarizing gap fill materials based on β-cyclodextrin in ArF photoresist under-layer materials have been developed for fast etching in CF4 gas. Gap fill materials used in the via-first dual damascene process need to have high etch rates to prevent crowning or fencing on top of the trench after etching and a small thickness bias between the dense and blanket areas to minimize issues observed during trench lithography by narrowing the process latitude. Cyclodextrin is a circular oligomer with a nanoscale porous structure that has a high number of oxygen atoms, as calculated using the Ohnishi parameter, providing high etch rates. Additionally, since gap fill materials using cyclodextrin derivatives have low viscosities and molecular weights, they are expected to exhibit excellent flow properties and minimal thermal shrinkage during baking. In this paper, we describe the composition and basic film properties of gap fill materials; planarization in the via-first dual damascene process and etch rates in CF4 gas compared with dextrin with α-glycoside bonds in polysaccharide, poly(2-hydroxypropyl methacrylate) and poly(4-hydroxystyrene). The β-cyclodextrin used in this study was obtained by esterifying the hydroxyl groups of dextrin resulting in improved wettability on via substrates and solubility in photoresist solvents such as propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate and ethyl lactate. Gap fill materials using cyclodextrin derivatives showed good planarization and via filling performance without observing voids in via holes. In addition to superior via filling performance, the etch rate of gap fill materials using β-cyclodextrin derivatives was 2.8-2.9 times higher than that of an ArF photoresist, evaluated under CF4 gas conditions by reactive ion etching. These results were attributed to the combination of both nanoscale porous structures and a high density of oxygen atoms in our gap fill materials using cyclodextrin derivatives. The cyclodextrin derivatives may be applicable as a new type of sacrificial material under the photoresist in ArF lithography.

Growth of KOH etched AZO nanorods and investigation of its back scattering effect in thin film a-Si solar cell

NASA Astrophysics Data System (ADS)

Sharma, Jayasree Roy; Mitra, Suchismita; Ghosh, Hemanta; Das, Gourab; Bose, Sukanta; Mandal, Sourav; Mukhopadhyay, Sumita; Saha, Hiranmay; Barua, A. K.

2018-02-01

In order to increase the stabilized efficiencies of thin film silicon (TFS) solar cells it is necessary to use better light management techniques. Texturization by etching of sputtered aluminum doped zinc oxide (Al:ZnO or AZO) films has opened up a variety of promises to optimize light trapping schemes. RF sputtered AZO film has been etched by potassium hydroxide (KOH). A systematic study of etching conditions such as etchant concentration, etching time, temperature management etc. have been performed in search of improved electrical and optical performances of the films. The change in etching conditions has exhibited a noticeable effect on the structure of AZO films for which the light trapping effect differs. After optimizing the etching conditions, nanorods have been found on the substrate. Hence, nanorods have been developed only by chemical etching, rather than the conventional development method (hydrothermal method, sol-gel method, electrolysis method etc.). The optimized etched substrate has 82% transmittance, moderate haze in the visible range and sheet resistance ∼13 (Ω/□). The developed nanorods (optimized etched substrate) provide better light trapping within the cell as the optical path length has been increased by using the nanorods. This provides an effect on carrier collection as well as the efficiency in a-Si solar cells. Finite difference time domain (FDTD) simulations have been performed to observe the light trapping by AZO nanorods formed on sputtered AZO films. For a p-i-n solar cell developed on AZO nanorods coated with sputtered AZO films, it has been found through simulations that, the incident light is back scattered into the absorbing layer, leading to an increase in photogenerated current and hence higher efficiency. It has been found that, the light that passes through the nanorods is not getting absorbed and maximum amount of light is back scattered towards the solar cell.

Correlation between oxidant concentrations, morphological aspects and etching kinetics of silicon nanowires during silver-assist electroless etching

NASA Astrophysics Data System (ADS)

Moumni, Besma; Jaballah, Abdelkader Ben

2017-12-01

Silicon porosification by silver assisted chemical etching (Ag-ACE) for a short range of H2O2 concentration is reported. We experimentally show that porous silicon (PSi) is obtained for 1% H2O2, whereas silicon nanowires (SiNWs) appeared by simply tuning the concentration of H2O2 to relatively high concentrations up to 8%. The morphological aspects are claimed by scanning electron microscopy proving that the kinetics of SiNWs formation display nonlinear relationships versus H2O2 concentration and etching time. A semi-qualitative electrochemical etching model based on local anodic, Ic, and cathodic, Ia, currents is proposed to explain the different morphological changes, and to unveil the formation pathways of both PS and SiNWs. More importantly, an efficient antireflective character for silicon solar cell (reflectance close to 2%) is realized at 8% H2O2. In addition, the luminescence of the prepared Si-nanostructures is claimed by photoluminescence which exhibit a large enhancement of the intensity and a blue shift for narrow and deep SiNWs.

Efficiency calibration of the first multilayer-coated holographic ion-etched flight grating for a sounding rocket high-resolution spectrometer.

PubMed

Kowalski, M P; Barbee, T W; Heidemann, K F; Gursky, H; Rife, J C; Hunter, W R; Fritz, G G; Cruddace, R G

1999-11-01

We have fabricated the four flight gratings for a sounding rocket high-resolution spectrometer using a holographic ion-etching technique. The gratings are spherical (4000-mm radius of curvature), large (160 mm x 90 mm), and have a laminar groove profile of high density (3600 grooves/mm). They have been coated with a high-reflectance multilayer of Mo/Si. Using an atomic force microscope, we examined the surface characteristics of the first grating before and after multilayer coating. The average roughness is approximately 3 A rms after coating. Using synchrotron radiation, we completed an efficiency calibration map over the wavelength range 225-245 A. At an angle of incidence of 5 degrees and a wavelength of 234 A, the average efficiency in the first inside order is 10.4 +/- 0.5%, and the derived groove efficiency is 34.8 +/- 1.6%. These values exceed all previously published results for a high-density grating.

High T(sub c) Superconducting Bolometer on Chemically Etched 7 Micrometer Thick Sapphire

NASA Technical Reports Server (NTRS)

Lakew, B.; Brasunas, J. C.; Pique, A.; Fettig, R.; Mott, B.; Babu, S.; Cushman, G. M.

1997-01-01

A transition-edge IR detector, using a YBa2Cu3O(7-x) (YBCO) thin film deposited on a chemically etched, 7 micrometer thick sapphire substrate has been built. To our knowledge it is the first such high T(sub c) superconducting (HTS) bolometer on chemically thinned sapphire. The peak optical detectivity obtained is l.2 x 10(exp 10) cmHz(sup 1/2)/W near 4Hz. Result shows that it is possible to obtain high detectivity with thin films on etched sapphire with no processing after the deposition of the YBCO film. We discuss the etching process and its potential for micro-machining sapphire and fabricating 2-dimensional detector arrays with suspended sapphire membranes. A 30 micrometer thick layer of gold black provided IR absorption. Comparison is made with the current state of the art on silicon substrates.

Investigation of phase distribution using Phame® in-die phase measurements

NASA Astrophysics Data System (ADS)

Buttgereit, Ute; Perlitz, Sascha

2009-03-01

As lithography mask processes move toward 45nm and 32nm node, mask complexity increases steadily, mask specifications tighten and process control becomes extremely important. Driven by this fact the requirements for metrology tools increase as well. Efforts in metrology have been focused on accurately measuring CD linearity and uniformity across the mask, and accurately measuring phase variation on Alternating/Attenuated PSM and transmission for Attenuated PSM. CD control on photo masks is usually done through the following processes: exposure dose/focus change, resist develop and dry etch. The key requirement is to maintain correct CD linearity and uniformity across the mask. For PSM specifically, the effect of CD uniformity for both Alternating PSM and Attenuated PSM and etch depth for Alternating PSM becomes also important. So far phase measurement has been limited to either measuring large-feature phase using interferometer-based metrology tools or measuring etch depth using AFM and converting etch depth into phase under the assumption that trench profile and optical properties of the layers remain constant. However recent investigations show that the trench profile and optical property of layers impact the phase. This effect is getting larger for smaller CD's. The currently used phase measurement methods run into limitations because they are not able to capture 3D mask effects, diffraction limitations or polarization effects. The new phase metrology system - Phame(R) developed by Carl Zeiss SMS overcomes those limitations and enables laterally resolved phase measurement in any kind of production feature on the mask. The resolution of the system goes down to 120nm half pitch at mask level. We will report on tool performance data with respect to static and dynamic phase repeatability focusing on Alternating PSM. Furthermore the phase metrology system was used to investigate mask process signatures on Alternating PSM in order to further improve the overall PSM process performance. Especially global loading effects caused by the pattern density and micro loading effects caused by the feature size itself have been evaluated using the capability of measuring phase in the small production features. The results of this study will be reported in this paper.

Measurement and Modeling of Blocking Contacts for Cadmium Telluride Gamma Ray Detectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beck, Patrick R.

2010-01-07

Gamma ray detectors are important in national security applications, medicine, and astronomy. Semiconductor materials with high density and atomic number, such as Cadmium Telluride (CdTe), offer a small device footprint, but their performance is limited by noise at room temperature; however, improved device design can decrease detector noise by reducing leakage current. This thesis characterizes and models two unique Schottky devices: one with an argon ion sputter etch before Schottky contact deposition and one without. Analysis of current versus voltage characteristics shows that thermionic emission alone does not describe these devices. This analysis points to reverse bias generation current ormore » leakage through an inhomogeneous barrier. Modeling the devices in reverse bias with thermionic field emission and a leaky Schottky barrier yields good agreement with measurements. Also numerical modeling with a finite-element physics-based simulator suggests that reverse bias current is a combination of thermionic emission and generation. This thesis proposes further experiments to determine the correct model for reverse bias conduction. Understanding conduction mechanisms in these devices will help develop more reproducible contacts, reduce leakage current, and ultimately improve detector performance.« less

FIB Secondary Etching Method for Fabrication of Fine CNT Forest Metamaterials

NASA Astrophysics Data System (ADS)

Pander, Adam; Hatta, Akimitsu; Furuta, Hiroshi

2017-10-01

Anisotropic materials, like carbon nanotubes (CNTs), are the perfect substitutes to overcome the limitations of conventional metamaterials; however, the successful fabrication of CNT forest metamaterial structures is still very challenging. In this study, a new method utilizing a focused ion beam (FIB) with additional secondary etching is presented, which can obtain uniform and fine patterning of CNT forest nanostructures for metamaterials and ranging in sizes from hundreds of nanometers to several micrometers. The influence of the FIB processing parameters on the morphology of the catalyst surface and the growth of the CNT forest was investigated, including the removal of redeposited material, decreasing the average surface roughness (from 0.45 to 0.15 nm), and a decrease in the thickness of the Fe catalyst. The results showed that the combination of FIB patterning and secondary etching enabled the growth of highly aligned, high-density CNT forest metamaterials. The improvement in the quality of single-walled CNTs (SWNTs), defined by the very high G/D peak ratio intensity of 10.47, demonstrated successful fine patterning of CNT forest for the first time. With a FIB patterning depth of 10 nm and a secondary etching of 0.5 nm, a minimum size of 150 nm of CNT forest metamaterials was achieved. The development of the FIB secondary etching method enabled for the first time, the fabrication of SWNT forest metamaterials for the optical and infrared regime, for future applications, e.g., in superlenses, antennas, or thermal metamaterials.

Superior characteristics of microscale light emitting diodes through tightly lateral oxide-confined scheme

NASA Astrophysics Data System (ADS)

Huang, Shen-Che; Li, Heng; Zhang, Zhe-Han; Chen, Hsiang; Wang, Shing-Chung; Lu, Tien-Chang

2017-01-01

We report on the design of the geometry and chip size-controlled structures of microscale light-emitting diodes (micro-LEDs) with a shallow-etched oxide-refilled current aperture and their performance. The proposed structure, which combines an indium-tin-oxide layer and an oxide-confined aperture, exhibited not only uniform current distribution but also remarkably tight current confinement. An extremely high injection level of more than 90 kA/cm2 was achieved in the micro-LED with a 5-μm aperture. Current spreading and the droop mechanism in the investigated devices were characterized through electroluminescence measurements, optical microscopy, and beam-view imaging. Furthermore, we utilized the β-model and S-model to elucidate current crowding and the efficiency droop phenomenon in the investigated micro-LEDs. The luminescence results evidenced the highly favorable performance of the fabricated micro-LEDs, which is a result of their more uniform current spreading and lower junction temperature relative to conventional LEDs. Moreover, the maximum endured current density could be further increased by reducing the aperture size of the micro-LEDs. The proposed design, which is expected to be beneficial for the development of high-performance array-based micro-LEDs, is practicable through current state-of-the-art processing techniques.

An investigation of supercritical-CO2 copper electroplating parameters for application in TSV chips

NASA Astrophysics Data System (ADS)

Chuang, Ho-Chiao; Lai, Wei-Hong; Sanchez, Jorge

2015-01-01

This study uses supercritical electroplating for the filling of through silicon vias (TSVs) in chips. The present study utilizes the inductively coupled plasma reactive ion etching (ICP RIE) process technique to etch the TSVs and discusses different supercritical-CO2 electroplating parameters, such as the supercritical pressure, the electroplating current density’s effect on the TSV Cu pillar filling time, the I-V curve, the electrical resistance and the hermeticity. In addition, the results for all the tests mentioned above have been compared to results from traditional electroplating techniques. For the testing, we will first discuss the hermeticity of the TSV Cu pillars, using a helium leaking test apparatus to assess the vacuum sealing of the fabricated TSV Cu pillars. In addition, this study also conducts tests for the electrical properties, which include the measurement of the electrical resistance of the TSV at both ends in the horizontal direction, followed by the passing of a high current (10 A, due to probe limitations) to check if the TSV can withstand it without burnout. Finally, the TSV is cut in half in cross-section to observe the filling of Cu pillars by the supercritical electroplating and check for voids. The important characteristic of this study is the use of the supercritical electroplating process without the addition of any surfactants to aid the filling of the TSVs, but by taking advantage of the high permeability and low surface tension of supercritical fluids to achieve our goal. The results of this investigation point to a supercritical pressure of 2000 psi and a current density of 3 A dm-2 giving off the best electroplating filling and hermeticity, while also being able to withstand a high current of 10 A, with a relatively short electroplating time of 3 h (when compared to our own traditional dc electroplating).

Comparison of tensile bond strengths of four one-bottle self-etching adhesive systems with Er:YAG laser-irradiated dentin.

PubMed

Jiang, Qianzhou; Chen, Minle; Ding, Jiangfeng

2013-12-01

This study aimed to investigate the interaction of current one-bottle self-etching adhesives and Er:YAG laser with dentin using a tensile bond strength (TBS) test and scanning electron microscopy (SEM) in vitro. Two hundred and thirteen dentin discs were randomly distributed to the Control Group using bur cutting and to the Laser Group using an Er:YAG laser (200 mJ, VSP, 20 Hz). The following adhesives were investigated: one two-step total-etch adhesive [Prime & Bond NT (Dentsply)] and four one-step self-etch adhesives [G-Bond plus (GC), XENO V (Dentsply), iBond Self Etch (Heraeus) and Adper Easy One (3 M ESPE)]. Samples were restored with composite resin, and after 24-hour storage in distilled water, subjected to the TBS test. For morphological analysis, 12 dentin specimens were prepared for SEM. No significant differences were found between the control group and laser group (p = 0.899); dentin subjected to Prime & Bond NT, XENOV and Adper Easy One produced higher TBS. In conclusion, this study indicates that Er:YAG laser-prepared dentin can perform as well as bur on TBS, and some of the one-step one-bottle adhesives are comparable to the total-etch adhesives in TBS on dentin.

Atomic-scale etching of hexagonal boron nitride for device integration based on two-dimensional materials.

PubMed

Park, Hamin; Shin, Gwang Hyuk; Lee, Khang June; Choi, Sung-Yool

2018-05-29

Hexagonal boron nitride (h-BN) is considered an ideal template for electronics based on two-dimensional (2D) materials, owing to its unique properties as a dielectric film. Most studies involving h-BN and its application to electronics have focused on its synthesis using techniques such as chemical vapor deposition, the electrical analysis of its surface state, and the evaluation of its performance. Meanwhile, processing techniques including etching methods have not been widely studied despite their necessity for device fabrication processes. In this study, we propose the atomic-scale etching of h-BN for integration into devices based on 2D materials, using Ar plasma at room temperature. A controllable etching rate, less than 1 nm min-1, was achieved and the low reactivity of the Ar plasma enabled the atomic-scale etching of h-BN down to a monolayer in this top-down approach. Based on the h-BN etching technique for achieving electrical contact with the underlying molybdenum disulfide (MoS2) layer of an h-BN/MoS2 heterostructure, a top-gate MoS2 field-effect transistor (FET) with h-BN gate dielectric was fabricated and characterized by high electrical performance based on the on/off current ratio and carrier mobility.

Electrodeposited manganese dioxide nanostructures on electro-etched carbon fibers: High performance materials for supercapacitor applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kazemi, Sayed Habib, E-mail: habibkazemi@iasbs.ac.ir; Center for Research in Climate Change and Global Warming; Maghami, Mostafa Ghaem

Highlights: • We report a facile method for fabrication of MnO{sub 2} nanostructures on electro-etched carbon fiber. • MnO{sub 2}-ECF electrode shows outstanding supercapacitive behavior even at high discharge rates. • Exceptional cycle stability was achieved for MnO{sub 2}-ECF electrode. • The coulombic efficiency of MnO{sub 2}-ECF electrode is nearly 100%. - Abstract: In this article we introduce a facile, low cost and additive/template free method to fabricate high-rate electrochemical capacitors. Manganese oxide nanostructures were electrodeposited on electro-etched carbon fiber substrate by applying a constant anodic current. Nanostructured MnO{sub 2} on electro-etched carbon fiber was characterized by scanning electron microscopy,more » X-ray diffraction and energy dispersive X-ray analysis. The electrochemical behavior of MnO{sub 2} electro-etched carbon fiber electrode was investigated by electrochemical techniques including cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. A maximum specific capacitance of 728.5 F g{sup −1} was achieved at a scan rate of 5 mV s{sup −1} for MnO{sub 2} electro-etched carbon fiber electrode. Also, this electrode showed exceptional cycle stability, suggesting that it can be considered as a good candidate for supercapacitor electrodes.« less

Applications of MICP source for next-generation photomask process

NASA Astrophysics Data System (ADS)

Kwon, Hyuk-Joo; Chang, Byung-Soo; Choi, Boo-Yeon; Park, Kyung H.; Jeong, Soo-Hong

2000-07-01

As critical dimensions of photomask extends into submicron range, critical dimension uniformity, edge roughness, macro loading effect, and pattern slope become tighter than before. Fabrication of photomask relies on the ability to pattern features with anisotropic profile. To improve critical dimension uniformity, dry etcher is one of the solution and inductively coupled plasma (ICP) sources have become one of promising high density plasma sources for dry etcher. In this paper, we have utilized dry etcher system with multi-pole ICP source for Cr etch and MoSi etch and have investigated critical dimension uniformity, slope, and defects. We will present dry etch process data by process optimization of newly designed dry etcher system. The designed pattern area is 132 by 132 mm2 with 23 by 23 matrix test patterns. 3 (sigma) of critical dimension uniformity is below 12 nm at 0.8 - 3.0 micrometers . In most cases, we can obtain zero defect masks which is operated by face- down loading.

High quality of InAsSb epilayer with cutoff wavelength longer than 10 μm grown on GaAs by the modified LPE technique

NASA Astrophysics Data System (ADS)

Hu, S. H.; Sun, C. H.; Sun, Y.; Ge, J.; Wang, R.; Wu, J.; Wang, Q. W.; Dai, N.

2009-04-01

The InAsSb epilayers with a cutoff wavelength of 11.5 μm were successfully grown on highly lattice-mismatched semi-insulating (1 0 0) GaAs substrate by the modified liquid phase epitaxy (LPE) technique. Fourier transform infrared (FTIR) transmission spectrum revealed a strong band gap narrowing for this alloy. The electrical properties were investigated by the Van der Pauw measurements at 300 and 77 K. InAsSb epilayers showed high Hall mobilities being 11,800 cm 2/V s at room temperature (RT). After an annealing treament for 10 h, the electron mobility at 77 K were improved from 1730 cm 2/V s (prior to annealing) to 13,470 cm 2/V s. Wet etching was used to display the surface etch pits prior to and after annealing treatment, showing that the mobility improvement was due to the reduction of the etch pits density.

In vitro remineralization of acid-etched human enamel with Ca 3SiO 5

NASA Astrophysics Data System (ADS)

Dong, Zhihong; Chang, Jiang; Deng, Yan; Joiner, Andrew

2010-02-01

Bioactive and inductive silicate-based bioceramics play an important role in hard tissue prosthetics such as bone and teeth. In the present study, a model was established to study the acid-etched enamel remineralization with tricalcium silicate (Ca 3SiO 5, C 3S) paste in vitro. After soaking in simulated oral fluid (SOF), Ca-P precipitation layer was formed on the enamel surface, with the prolonged soaking time, apatite layer turned into density and uniformity and thickness increasingly from 250 to 350 nm for 1 day to 1.7-1.9 μm for 7 days. Structure of apatite crystals was similar to that of hydroxyapatite (HAp). At the same time, surface smoothness of the remineralized layer is favorable for the oral hygiene. These results suggested that C 3S treated the acid-etched enamel can induce apatite formation, indicating the biomimic mineralization ability, and C 3S could be used as an agent of inductive biomineralization for the enamel prosthesis and protection.

Morphology modulating the wettability of a diamond film.

PubMed

Tian, Shibing; Sun, Weijie; Hu, Zhaosheng; Quan, Baogang; Xia, Xiaoxiang; Li, Yunlong; Han, Dong; Li, Junjie; Gu, Changzhi

2014-10-28

Control of the wetting property of diamond surface has been a challenge because of its maximal hardness and good chemical inertness. In this work, the micro/nanoarray structures etched into diamond film surfaces by a maskless plasma method are shown to fix a surface's wettability characteristics, and this means that the change in morphology is able to modulate the wettability of a diamond film from weakly hydrophilic to either superhydrophilic or superhydrophobic. It can be seen that the etched diamond surface with a mushroom-shaped array is superhydrophobic following the Cassie mode, whereas the etched surface with nanocone arrays is superhydrophilic in accordance with the hemiwicking mechnism. In addition, the difference in cone densities of superhydrophilic nanocone surfaces has a significant effect on water spreading, which is mainly derived from different driving forces. This low-cost and convenient means of altering the wetting properties of diamond surfaces can be further applied to underlying wetting phenomena and expand the applications of diamond in various fields.

Low-temperature oxidizing plasma surface modification and composite polymer thin-film fabrication techniques for tailoring the composition and behavior of polymer surfaces

NASA Astrophysics Data System (ADS)

Tompkins, Brendan D.

This dissertation examines methods for modifying the composition and behavior of polymer material surfaces. This is accomplished using (1) low-temperature low-density oxidizing plasmas to etch and implant new functionality on polymers, and (2) plasma enhanced chemical vapor deposition (PECVD) techniques to fabricate composite polymer materials. Emphases are placed on the structure of modified polymer surfaces, the evolution of polymer surfaces after treatment, and the species responsible for modifying polymers during plasma processing. H2O vapor plasma modification of high-density polyethylene (HDPE), low-density polyethylene (LDPE), polypropylene (PP), polystyrene (PS), polycarbonate (PC), and 75A polyurethane (PU) was examined to further our understanding of polymer surface reorganization leading to hydrophobic recovery. Water contact angles (wCA) measurements showed that PP and PS were the most susceptible to hydrophobic recovery, while PC and HDPE were the most stable. X-ray photoelectron spectroscopy (XPS) revealed a significant quantity of polar functional groups on the surface of all treated polymer samples. Shifts in the C1s binding energies (BE) with sample age were measured on PP and PS, revealing that surface reorganization was responsible for hydrophobic recovery on these materials. Differential scanning calorimetry (DSC) was used to rule out the intrinsic thermal properties as the cause of reorganization and hydrophobic recovery on HDPE, LDPE, and PP. The different contributions that polymer cross-linking and chain scission mechanisms make to polymer aging effects are considered. The H2O plasma treatment technique was extended to the modification of 0.2 microm and 3.0 microm track-etched polycarbonate (PC-TE) and track-etched polyethylene terephthalate (PET-TE) membranes with the goal of permanently increasing the hydrophilicity of the membrane surfaces. Contact angle measurements on freshly treated and aged samples confirmed the wettability of the membrane surfaces was significantly improved by plasma treatment. XPS and SEM analyses revealed increased oxygen incorporation onto the surface of the membranes, without any damage to the surface or pore structure. Contact angle measurements on a membrane treated in a stacked assembly suggest the plasma effectively modified the entire pore cross section. Plasma treatment also increased water flux through the membranes, with results from plasma modified membranes matching those from commercially available hydrophilic membranes (treated with wetting agent). Mechanisms for the observed modification are discussed in terms of OH and O radicals implanting oxygen functionality into the polymers. Oxidizing plasma systems (O2, CO2, H2O vapor, and formic acid vapor) were used to modify track-etched polycarbonate membranes and explore the mechanisms and species responsible for etching polycarbonate during plasma processing. Etch rates were measured using scanning electron microscopy; modified polycarbonate surfaces were further characterized using x-ray photoelectron spectroscopy and water contact angles. Etch rates and surface characterization results were combined with optical emission spectroscopy data used to identify gas-phase species and their relative densities. Although the oxide functionalities implanted by each plasma system were similar, the H2O vapor and formic acid vapor plasmas yielded the lowest contact angles after treatment. The CO2, H2O vapor, and formic acid vapor plasma-modified surfaces were, however, found to be similarly stable one month after treatment. Overall, etch rate correlated directly to the relative gas-phase density of atomic oxygen and, to a lesser extent, hydroxyl radicals. PECVD of acetic acid vapor (CH3COOH) was used to deposit films on PC-TE and silicon wafer substrates. The CH3COOH films were characterized using XPS, wCA, and SEM. This modification technique resulted in continuous deposition and self-limiting deposition of a-CxO yHz films on Si wafers and PC-TE, respectively. The self-limiting deposition on PC-TE revealed that resulting films have minimal impact on 3D PC structures. This technique would allow for more precise fabrication of patterned or nano-textured PC. PECVD is used to synthesize hydrocarbon/fluorocarbon thin films with compositional gradients by continuously changing the ratio of gases in a C 3F8/H2 plasma. The films are characterized using variable angle spectroscopic ellipsometry (VASE), Fourier transform infrared spectroscopy (FTIR), XPS, wCA, and SEM. These methods revealed that shifting spectroscopic signals can be used to characterize organization in the deposited film. Using these methods, along with gas-phase diagnostics, film chemistry and the underlying deposition mechanisms are elucidated, leading to a model that accurately predicts film thickness.

Focal-Plane Arrays of Quantum-Dot Infrared Photodetectors

NASA Technical Reports Server (NTRS)

Gunapala, Sarath; Wilson, Daniel; Hill, Cory; Liu, John; Bandara, Sumith; Ting, David

2007-01-01

Focal-plane arrays of semiconductor quantum-dot infrared photodetectors (QDIPs) are being developed as superior alternatives to prior infrared imagers, including imagers based on HgCdTe devices and, especially, those based on quantum-well infrared photodetectors (QWIPs). HgCdTe devices and arrays thereof are difficult to fabricate and operate, and they exhibit large nonunformities and high 1/f (where f signifies frequency) noise. QWIPs are easier to fabricate and operate, can be made nearly uniform, and exhibit lower 1/f noise, but they exhibit larger dark currents, and their quantization only along the growth direction prevents them from absorbing photons at normal incidence, thereby limiting their quantum efficiencies. Like QWIPs, QDIPs offer the advantages of greater ease of operation, greater uniformity, and lower 1/f noise, but without the disadvantages: QDIPs exhibit lower dark currents, and quantum efficiencies of QDIPs are greater because the three-dimensional quantization of QDIPs is favorable to the absorption of photons at normal or oblique incidence. Moreover, QDIPs can be operated at higher temperatures (around 200 K) than are required for operation of QWIPs. The main problem in the development of QDIP imagers is to fabricate quantum dots with the requisite uniformity of size and spacing. A promising approach to be tested soon involves the use of electron-beam lithography to define the locations and sizes of quantum dots. A photoresist-covered GaAs substrate would be exposed to the beam generated by an advanced, high-precision electron beam apparatus. The exposure pattern would consist of spots typically having a diameter of 4 nm and typically spaced 20 nm apart. The exposed photoresist would be developed by either a high-contrast or a low-contrast method. In the high-contrast method, the spots would be etched in such a way as to form steep-wall holes all the way down to the substrate. The holes would be wider than the electron beam spots perhaps as wide as 15 to 20 nm, but may be sufficient to control the growth of the quantum dots. In the low-contrast method, the resist would be etched in such a way as to form dimples, the shapes of which would mimic the electron-beam density profile. Then by use of a transfer etching process that etches the substrate faster than it etches the resist, either the pattern of holes or a pattern comprising the narrow, lowest portions of the dimples would be imparted to the substrate. Having been thus patterned, the substrate would be cleaned. The resulting holes or dimples in the substrate would serve as nucleation sites for the growth of quantum dots of controlled size in the following steps. The substrate would be cleaned, then placed in a molecular-beam-epitaxy (MBE) chamber, where native oxide would be thermally desorbed and the quantum dots would be grown.

Double sided grating fabrication for high energy X-ray phase contrast imaging

DOE PAGES

Hollowell, Andrew E.; Arrington, Christian L.; Finnegan, Patrick; ...

2018-04-19

State of the art grating fabrication currently limits the maximum source energy that can be used in lab based x-ray phase contrast imaging (XPCI) systems. In order to move to higher source energies, and image high density materials or image through encapsulating barriers, new grating fabrication methods are needed. In this work we have analyzed a new modality for grating fabrication that involves precision alignment of etched gratings on both sides of a substrate, effectively doubling the thickness of the grating. Furthermore, we have achieved a front-to-backside feature alignment accuracy of 0.5 µm demonstrating a methodology that can be appliedmore » to any grating fabrication approach extending the attainable aspect ratios allowing higher energy lab based XPCI systems.« less

Apparatus and Process for Controlled Nanomanufacturing Using Catalyst Retaining Structures

NASA Technical Reports Server (NTRS)

Nguyen, Cattien (Inventor)

2013-01-01

An apparatus and method for the controlled fabrication of nanostructures using catalyst retaining structures is disclosed. The apparatus includes one or more modified force microscopes having a nanotube attached to the tip portion of the microscopes. An electric current is passed from the nanotube to a catalyst layer of a substrate, thereby causing a localized chemical reaction to occur in a resist layer adjacent the catalyst layer. The region of the resist layer where the chemical reaction occurred is etched, thereby exposing a catalyst particle or particles in the catalyst layer surrounded by a wall of unetched resist material. Subsequent chemical vapor deposition causes growth of a nanostructure to occur upward through the wall of unetched resist material having controlled characteristics of height and diameter and, for parallel systems, number density.

Core-coat conductor of lipid bilayer and micromachined silicon.

PubMed

Fromherz, P; Klingler, J

1991-02-11

We have etched a groove into a (110) plane of silicon and have covered it with a bilayer of glycerol monooleate. We have varied the depth of the groove, the concentration of salt in the electrolyte and the density of gramicidin in the membrane. We have clamped one end of the groove at a constant voltage with respect to the bath keeping the other end sealed or electrically open with respect to the bath. We have measured (i) the voltage at the center of the groove and at the sealed distal end and (ii) the current through the system in sealed and open configuration. We have found that the spread of voltage is in quantitative agreement with the stationary solutions of Kelvin's equation for a homogeneous cable.

Preparation and Thermal Characterization of Annealed Gold Coated Porous Silicon.

PubMed

Behzad, Kasra; Mat Yunus, Wan Mahmood; Talib, Zainal Abidin; Zakaria, Azmi; Bahrami, Afarin

2012-01-16

Porous silicon (PSi) layers were formed on a p-type Si wafer. Six samples were anodised electrically with a 30 mA/cm² fixed current density for different etching times. The samples were coated with a 50-60 nm gold layer and annealed at different temperatures under Ar flow. The morphology of the layers, before and after annealing, formed by this method was investigated by scanning electron microscopy (SEM). Photoacoustic spectroscopy (PAS) measurements were carried out to measure the thermal diffusivity (TD) of the PSi and Au/PSi samples. For the Au/PSi samples, the thermal diffusivity was measured before and after annealing to study the effect of annealing. Also to study the aging effect, a comparison was made between freshly annealed samples and samples 30 days after annealing.

Plasma Properties of an Exploding Semiconductor Igniter

NASA Astrophysics Data System (ADS)

McGuirk, J. S.; Thomas, K. A.; Shaffer, E.; Malone, A. L.; Baginski, T.; Baginski, M. E.

1997-11-01

Requirements by the automotive industry for low-cost, pyrotechnic igniters for automotive airbags have led to the development of several semiconductor devices. The properties of the plasma produced by the vaporization of an exploding semiconductor are necessary in order to minimize the electrical energy requirements. This work considers two silicon-based semiconductor devices: the semiconductor bridge (SCB) and the semiconductor junction igniter both consisting of etched silicon with vapor deposited aluminum structures. Electrical current passing through the device heats a narrow junction region to the point of vaporization creating an aluminum and silicon low-temperature plasma. This work will investigate the electrical characteristics of both devices and infer the plasma properties. Furthermore optical spectral measurements will be taken of the exploding devices to estimate the temperature and density of the plasma.

Characteristics of indium-gallium-nitride multiple-quantum-well blue laser diodes grown by MOCVD

NASA Astrophysics Data System (ADS)

Mack, M. P.; Abare, A. C.; Hansen, M.; Kozodoy, P.; Keller, S.; Mishra, U.; Coldren, L. A.; DenBaars, S. P.

1998-06-01

Room temperature (RT) pulsed operation of blue (420 nm) nitride-based multi-quantum well (MQW) laser diodes grown on c-plane sapphire substrates has been demonstrated. Atmospheric pressure MOCVD was used to grow the active region of the device which consisted of a 10 pair In 0.21Ga 0.79N (2.5 nm)/In 0.07Ga 0.93N (5 nm) InGaN MQW. Threshold current densities as low as 12.6 kA/cm 2 were observed for 10×1200 μm lasers with uncoated reactive ion etched (RIE) facets. The emission is strongly TE polarized and has a sharp transition in the far-field pattern above threshold. Laser diodes were tested under pulsed conditions lasted up to 6 h at room temperature.

The surface chemical properties of multi-walled carbon nanotubes modified by thermal fluorination for electric double-layer capacitor

NASA Astrophysics Data System (ADS)

Jung, Min-Jung; Jeong, Euigyung; Lee, Young-Seak

2015-08-01

The surfaces of multi-walled carbon nanotubes (MWCNTs) were thermally fluorinated at various temperatures to enhance the electrochemical properties of the MWCNTs for use as electric double-layer capacitor (EDLC) electrodes. The fluorine functional groups were added to the surfaces of the MWCNTs via thermal fluorination. The thermal fluorination exposed the Fe catalyst on MWCNTs, and the specific surface area increased due to etching during the fluorination. The specific capacitances of the thermally fluorinated at 100 °C, MWCNT based electrode increased from 57 to 94 F/g at current densities of 0.2 A/g, respectively. This enhancement in capacitance can be attributed to increased polarization of the thermally fluorinated MWCNT surface, which increased the affinity between the electrode surface and the electrolyte ions.

Double sided grating fabrication for high energy X-ray phase contrast imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hollowell, Andrew E.; Arrington, Christian L.; Finnegan, Patrick

State of the art grating fabrication currently limits the maximum source energy that can be used in lab based x-ray phase contrast imaging (XPCI) systems. In order to move to higher source energies, and image high density materials or image through encapsulating barriers, new grating fabrication methods are needed. In this work we have analyzed a new modality for grating fabrication that involves precision alignment of etched gratings on both sides of a substrate, effectively doubling the thickness of the grating. Furthermore, we have achieved a front-to-backside feature alignment accuracy of 0.5 µm demonstrating a methodology that can be appliedmore » to any grating fabrication approach extending the attainable aspect ratios allowing higher energy lab based XPCI systems.« less

Periodically Aligned Si Nanopillar Arrays as Efficient Antireflection Layers for Solar Cell Applications

PubMed Central

2010-01-01

Periodically aligned Si nanopillar (PASiNP) arrays were fabricated on Si substrate via a silver-catalyzed chemical etching process using the diameter-reduced polystyrene spheres as mask. The typical sub-wavelength structure of PASiNP arrays had excellent antireflection property with a low reflection loss of 2.84% for incident light within the wavelength range of 200–1,000 nm. The solar cell incorporated with the PASiNP arrays exhibited a power conversion efficiency (PCE) of ~9.24% with a short circuit current density (JSC) of ~29.5 mA/cm2 without using any extra surface passivation technique. The high PCE of PASiNP array-based solar cell was attributed to the excellent antireflection property of the special periodical Si nanostructure. PMID:21124636

Highly scaled equivalent oxide thickness of 0.66 nm for TiN/HfO2/GaSb MOS capacitors by using plasma-enhanced atomic layer deposition

NASA Astrophysics Data System (ADS)

Tsai, Ming-Li; Wang, Shin-Yuan; Chien, Chao-Hsin

2017-08-01

Through in situ hydrogen plasma treatment (HPT) and plasma-enhanced atomic-layer-deposited TiN (PEALD-TiN) layer capping, we successfully fabricated TiN/HfO2/GaSb metal-oxide-semiconductor capacitors with an ultrathin equivalent oxide thickness of 0.66 nm and a low density of states of approximately 2 × 1012 cm-2 eV-1 near the valence band edge. After in situ HPT, a native oxide-free surface was obtained through efficient etching. Moreover, the use of the in situ PEALD-TiN layer precluded high-κ dielectric damage that would have been caused by conventional sputtering, thereby yielding a superior high-κ dielectric and low gate leakage current.

Advanced Baffle Materials Technology Development

DTIC Science & Technology

1991-10-01

few baffle materials, data from Misty North and Diesel Train provide guidance on damage mechanisms and give points with which theory can be compared...adequate to permit correlation of theory with experiment for thin film baffle structures which can be approximated as a series of planes. No means of...etching to produce surface microtexture on samples of 3 aluminum (see Figure 3-5). Current theory predicts that sputter texture etching works because

Imaging optical sensor arrays.

PubMed

Walt, David R

2002-10-01

Imaging optical fibres have been etched to prepare microwell arrays. These microwells have been loaded with sensing materials such as bead-based sensors and living cells to create high-density sensor arrays. The extremely small sizes and volumes of the wells enable high sensitivity and high information content sensing capabilities.

Etching-free patterning method for electrical characterization of atomically thin MoSe2 films grown by chemical vapor deposition

NASA Astrophysics Data System (ADS)

Utama, M. Iqbal Bakti; Lu, Xin; Zhan, Da; Ha, Son Tung; Yuan, Yanwen; Shen, Zexiang; Xiong, Qihua

2014-10-01

Patterning two-dimensional materials into specific spatial arrangements and geometries is essential for both fundamental studies of materials and practical applications in electronics. However, the currently available patterning methods generally require etching steps that rely on complicated and expensive procedures. We report here a facile patterning method for atomically thin MoSe2 films using stripping with an SU-8 negative resist layer exposed to electron beam lithography. Additional steps of chemical and physical etching were not necessary in this SU-8 patterning method. The SU-8 patterning was used to define a ribbon channel from a field effect transistor of MoSe2 film, which was grown by chemical vapor deposition. The narrowing of the conduction channel area with SU-8 patterning was crucial in suppressing the leakage current within the device, thereby allowing a more accurate interpretation of the electrical characterization results from the sample. An electrical transport study, enabled by the SU-8 patterning, showed a variable range hopping behavior at high temperatures.Patterning two-dimensional materials into specific spatial arrangements and geometries is essential for both fundamental studies of materials and practical applications in electronics. However, the currently available patterning methods generally require etching steps that rely on complicated and expensive procedures. We report here a facile patterning method for atomically thin MoSe2 films using stripping with an SU-8 negative resist layer exposed to electron beam lithography. Additional steps of chemical and physical etching were not necessary in this SU-8 patterning method. The SU-8 patterning was used to define a ribbon channel from a field effect transistor of MoSe2 film, which was grown by chemical vapor deposition. The narrowing of the conduction channel area with SU-8 patterning was crucial in suppressing the leakage current within the device, thereby allowing a more accurate interpretation of the electrical characterization results from the sample. An electrical transport study, enabled by the SU-8 patterning, showed a variable range hopping behavior at high temperatures. Electronic supplementary information (ESI) available: Further experiments on patterning and additional electrical characterizations data. See DOI: 10.1039/c4nr03817g

Deep silicon etching: current capabilities and future directions

NASA Astrophysics Data System (ADS)

Westerman, Russ; Martinez, Linnell; Pays-Volard, David; Mackenzie, Ken; Lazerand, Thierry

2014-03-01

Deep Reactive Ion Etching (DRIE) has revolutionized a wide variety of MEMS applications since its inception nearly two decades ago. The DRIE technology has been largely responsible for allowing lab scale technology demonstrations to become manufacturable and profitable consumer products. As applications which utilize DRIE technologies continue to expand and evolve, they continue to spawn a range of new requirements and open up exciting opportunities for advancement of DRIE. This paper will examine a number of current and emerging DRIE applications including nanotechnology, and DRIE related packaging technologies such as Through Silicon Via (TSV) and plasma dicing. The paper will discuss a number of technical challenges and solutions associated with these applications including: feature profile control at high aspect ratios, causes and elimination of feature tilt/skew, process options for fragile device structures, and problems associated with through substrate etching. The paper will close with a short discussion around the challenges of implementing DRIE in production environments as well as looking at potentially disruptive enhancements / substitutions for DRIE.

Investigation on electrical tree propagation in polyethylene based on etching method

NASA Astrophysics Data System (ADS)

Shi, Zexiang; Zhang, Xiaohong; Wang, Kun; Gao, Junguo; Guo, Ning

2017-11-01

To investigate the characteristic of electrical tree propagation in semi-crystalline polymers, the low-density polyethylene (LDPE) samples containing electrical trees are cut into slices by using ultramicrotome. Then the slice samples are etched by potassium permanganate etchant. Finally, the crystalline structure and the electrical tree propagation path in samples are observed by polarized light microscopy (PLM). According to the observation, the LDPE spherocrystal structure model is established on the basis of crystallization kinetics and morphology of polymers. And the electrical tree growth process in LDPE is discussed based on the free volume breakdown theory, the molecular chain relaxation theory, the electromechanical force theory, the thermal expansion effect and the space charge shielding effect.

Nanowires from dirty multi-crystalline Si for hydrogen generation

NASA Astrophysics Data System (ADS)

Li, Xiaopeng; Schweizer, Stefan L.; Sprafke, Alexander; Wehrspohn, Ralf B.

2013-09-01

Silicon nanowires are considered as a promising architecture for solar energy conversion systems. By metal assisted chemical etching of multi-crystalline upgraded metallurgical silicon (UMG-Si), large areas of silicon nanowires (SiNWs) with high quality can be produced on the mother substrates. These areas show a low reflectance comparable to black silicon. More interestingly, we find that various metal impurities inside UMG-Si are removed due to the etching through element analysis. A prototype cell was built to test the photoelectrochemical (PEC) properties of UMG-SiNWs for water splitting. The on-set potential for hydrogen evolution was much reduced, and the photocurrent density showed an increment of 35% in comparison with a `dirty' UMG-Si wafer.

Comparison of photoemission characteristics between square and circular wire array GaAs photocathodes.

PubMed

Deng, Wenjuan; Peng, Xincun; Zou, Jijun; Wang, Weilu; Liu, Yun; Zhang, Tao; Zhang, Yijun; Zhang, Daoli

2017-11-10

Two types of negative electron affinity gallium arsenide (GaAs) wire array photocathodes were fabricated by reactive ion etching and inductively coupled plasma etching of bulk GaAs material. High density GaAs wire arrays with high periodicity and good morphology were verified using scanning electron microscopy, and photoluminescence spectra confirmed the wire arrays had good crystalline quality. Reflection spectra showed that circular GaAs wire arrays had superior light trapping compared with square ones. However, after Cs/O activation, the square GaAs wire array photocathodes showed enhanced spectral response. The integral sensitivity of the square wire array photocathodes was approximately 2.8 times that of the circular arrays.

Phosphorus oxide gate dielectric for black phosphorus field effect transistors

NASA Astrophysics Data System (ADS)

Dickerson, W.; Tayari, V.; Fakih, I.; Korinek, A.; Caporali, M.; Serrano-Ruiz, M.; Peruzzini, M.; Heun, S.; Botton, G. A.; Szkopek, T.

2018-04-01

The environmental stability of the layered semiconductor black phosphorus (bP) remains a challenge. Passivation of the bP surface with phosphorus oxide, POx, grown by a reactive ion etch with oxygen plasma is known to improve photoluminescence efficiency of exfoliated bP flakes. We apply phosphorus oxide passivation in the fabrication of bP field effect transistors using a gate stack consisting of a POx layer grown by reactive ion etching followed by atomic layer deposition of Al2O3. We observe room temperature top-gate mobilities of 115 cm2 V-1 s-1 in ambient conditions, which we attribute to the low defect density of the bP/POx interface.

Increased Multilayer Fabrication and RF Characterization of a High-Density Stacked MIM Capacitor Based on Selective Etching

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tseng, VFG; Xie, HK

2014-07-01

This paper presents the fabrication and characterization of a high-density multilayer stacked metal-insulator-metal (MIM) capacitor based on a novel process of depositing the MIM multilayer on pillars followed by polishing and selective etching steps to form a stacked capacitor with merely three photolithography steps. In this paper, the pillars were made of glass to prevent substrate loss, whereas an oxide-nitride-oxide dielectric was employed for lower leakage, better voltage/frequency linearity, and better stress compensation. MIM capacitors with six dielectric layers were successfully fabricated, yielding capacitance density of 3.8 fF/mu m(2), maximum capacitance of 2.47 nF, and linear and quadratic voltage coefficientsmore » of capacitance below 21.2 ppm/V and 2.31 ppm/V-2. The impedance was measured from 40 Hz to 3 GHz, and characterized by an analytically derived equivalent circuit model to verify the radio frequency applicability. The multilayer stacking-induced plate resistance mismatch and its effect on the equivalent series resistance (ESR) and effective capacitance was also investigated, which can be counteracted by a corrected metal thickness design. A low ESR of 800 m Omega was achieved, whereas the self-resonance frequency was >760 MHz, successfully demonstrating the feasibility of this method to scale up capacitance densities for high-quality-factor, high-frequency, and large-value MIM capacitors.« less

Effects of prolonged light exposure times on water sorption, solubility and cross-linking density of simplified etch-and-rinse adhesives.

PubMed

Wambier, Letícia; Malaquias, Tamirez; Wambier, Denise Stadler; Patzlaff, Rafael T; Bauer, José; Loguercio, Alessandro D; Reis, Alessandra

2014-06-01

This study evaluated the effects of light exposure times on water sorption, solubility, and polymer cross-linking density of simplified etch-and-rinse adhesives. Four commercial adhesives (XP Bond, Adper Single Bond 2, Tetric N-Bond, and Ambar) were selected, and resin disks 5 mm in diameter and 1.0 mm thick were prepared and light cured for 20, 40, or 80 s using an LED light-curing unit at 1200 mW/cm2. Water sorption and solubility were evaluated over a 28-day period. For polymer cross-linking density, additional specimens were prepared and their Knoop hardness measured before and after immersion in 100% ethanol. The data from each test were evaluated using a two-way ANOVA and Tukey's test (α = 0.05). The XP Bond adhesive showed higher water sorption (similar to Adper Single Bond 2) and solubility (p < 0.05) than did the other materials. Prolonged exposure times did not reduce the water sorption but did reduce the solubility of all tested materials (p < 0.05). For Ambar, the increase in the exposure time resulted in a significantly lower percent reduction in hardness. Water sorption, solubility, and cross-linking density of the materials selected in this study seem to be mainly influenced by the adhesive composition. Prolonged light exposure times reduced the solubility of the materials.

Limitations of threshold voltage engineering of AlGaN/GaN heterostructures by dielectric interface charge density and manipulation by oxygen plasma surface treatments

NASA Astrophysics Data System (ADS)

Lükens, G.; Yacoub, H.; Kalisch, H.; Vescan, A.

2016-05-01

The interface charge density between the gate dielectric and an AlGaN/GaN heterostructure has a significant impact on the absolute value and stability of the threshold voltage Vth of metal-insulator-semiconductor (MIS) heterostructure field effect transistor. It is shown that a dry-etching step (as typically necessary for normally off devices engineered by gate-recessing) before the Al2O3 gate dielectric deposition introduces a high positive interface charge density. Its origin is most likely donor-type trap states shifting Vth to large negative values, which is detrimental for normally off devices. We investigate the influence of oxygen plasma annealing techniques of the dry-etched AlGaN/GaN surface by capacitance-voltage measurements and demonstrate that the positive interface charge density can be effectively compensated. Furthermore, only a low Vth hysteresis is observable making this approach suitable for threshold voltage engineering. Analysis of the electrostatics in the investigated MIS structures reveals that the maximum Vth shift to positive voltages achievable is fundamentally limited by the onset of accumulation of holes at the dielectric/barrier interface. In the case of the Al2O3/Al0.26Ga0.74N/GaN material system, this maximum threshold voltage shift is limited to 2.3 V.

Track-Etched Magnetic Micropores for Immunomagnetic Isolation of Pathogens

PubMed Central

Muluneh, Melaku; Shang, Wu

2014-01-01

A microfluidic chip is developed to selectively isolate magnetically tagged cells from heterogeneous suspensions, the track-etched magnetic micropore (TEMPO) filter. The TEMPO consists of an ion track-etched polycarbonate membrane coated with soft magnetic film (Ni20Fe80). In the presence of an applied field, provided by a small external magnet, the filter becomes magnetized and strong magnetic traps are created along the edges of the micropores. In contrast to conventional microfluidics, fluid flows vertically through the porous membrane allowing large flow rates while keeping the capture rate high and the chip compact. By utilizing track-etching instead of conventional semiconductor fabrication, TEMPOs can be fabricated with microscale pores over large areas A > 1 cm2 at little cost (< 5 ¢ cm−2). To demonstrate the utility of this platform, a TEMPO with 5 μm pore size is used to selectively and rapidly isolate immunomagnetically targeted Escherichia coli from heterogeneous suspensions, demonstrating enrichment of ζ > 500 at a flow rate of Φ = 5 mL h−1. Furthermore, the large density of micropores (ρ = 106 cm−2) allows the TEMPO to sort E. coli from unprocessed environmental and clinical samples, as the blockage of a few pores does not significantly change the behavior of the device. PMID:24535921

Laser etching of polymer masked leadframes

NASA Astrophysics Data System (ADS)

Ho, C. K.; Man, H. C.; Yue, T. M.; Yuen, C. W.

1997-02-01

A typical electroplating production line for the deposition of silver pattern on copper leadframes in the semiconductor industry involves twenty to twenty five steps of cleaning, pickling, plating, stripping etc. This complex production process occupies large floor space and has also a number of problems such as difficulty in the production of rubber masks and alignment, generation of toxic fumes, high cost of water consumption and sometimes uncertainty on the cleanliness of the surfaces to be plated. A novel laser patterning process is proposed in this paper which can replace many steps in the existing electroplating line. The proposed process involves the application of high speed laser etching techniques on leadframes which were protected with polymer coating. The desired pattern for silver electroplating is produced by laser ablation of the polymer coating. Excimer laser was found to be most effective for this process as it can expose a pattern of clean copper substrate which can be silver plated successfully. Previous working of Nd:YAG laser ablation showed that 1.06 μm radiation was not suitable for this etching process because a thin organic and transparent film remained on the laser etched region. The effect of excimer pulse frequency and energy density upon the removal rate of the polymer coating was studied.

Reflectance analysis of porosity gradient in nanostructured silicon layers

NASA Astrophysics Data System (ADS)

Jurečka, Stanislav; Imamura, Kentaro; Matsumoto, Taketoshi; Kobayashi, Hikaru

2017-12-01

In this work we study optical properties of nanostructured layers formed on silicon surface. Nanostructured layers on Si are formed in order to reach high suppression of the light reflectance. Low spectral reflectance is important for improvement of the conversion efficiency of solar cells and for other optoelectronic applications. Effective method of forming nanostructured layers with ultralow reflectance in a broad interval of wavelengths is in our approach based on metal assisted etching of Si. Si surface immersed in HF and H2O2 solution is etched in contact with the Pt mesh roller and the structure of the mesh is transferred on the etched surface. During this etching procedure the layer density evolves gradually and the spectral reflectance decreases exponentially with the depth in porous layer. We analyzed properties of the layer porosity by incorporating the porosity gradient into construction of the layer spectral reflectance theoretical model. Analyzed layer is splitted into 20 sublayers in our approach. Complex dielectric function in each sublayer is computed by using Bruggeman effective media theory and the theoretical spectral reflectance of modelled multilayer system is computed by using Abeles matrix formalism. Porosity gradient is extracted from the theoretical reflectance model optimized in comparison to the experimental values. Resulting values of the structure porosity development provide important information for optimization of the technological treatment operations.

Synthesis and characterization of porous silicon as hydroxyapatite host matrix of biomedical applications.

PubMed

Dussan, A; Bertel, S D; Melo, S F; Mesa, F

2017-01-01

In this work, porous-silicon samples were prepared by electrochemical etching on p-type (B-doped) Silicon (Si) wafers. Hydrofluoric acid (HF)-ethanol (C2H5OH) [HF:Et] and Hydrofluoric acid (HF)-dimethylformamide (DMF-C3H7NO) [HF:DMF] solution concentrations were varied between [1:2]-[1:3] and [1:7]-[1:9], respectively. Effects of synthesis parameters, like current density, solution concentrations, reaction time, on morphological properties were studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM) measurements. Pore sizes varying from 20 nm to micrometers were obtained for long reaction times and [HF:Et] [1:2] concentrations; while pore sizes in the same order were observed for [HF:DMF] [1:7], but for shorter reaction time. Greater surface uniformity and pore distribution was obtained for a current density of around 8 mA/cm2 using solutions with DMF. A correlation between reflectance measurements and pore size is presented. The porous-silicon samples were used as substrate for hydroxyapatite growth by sol-gel method. X-ray diffraction (XRD) and SEM were used to characterize the layers grown. It was found that the layer topography obtained on PS samples was characterized by the evidence of Hydroxyapatite in the inter-pore regions and over the surface.

Synthesis and characterization of porous silicon as hydroxyapatite host matrix of biomedical applications

PubMed Central

Dussan, A.; Bertel, S. D.; Melo, S. F.

2017-01-01

In this work, porous-silicon samples were prepared by electrochemical etching on p-type (B-doped) Silicon (Si) wafers. Hydrofluoric acid (HF)-ethanol (C2H5OH) [HF:Et] and Hydrofluoric acid (HF)-dimethylformamide (DMF-C3H7NO) [HF:DMF] solution concentrations were varied between [1:2]—[1:3] and [1:7]—[1:9], respectively. Effects of synthesis parameters, like current density, solution concentrations, reaction time, on morphological properties were studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM) measurements. Pore sizes varying from 20 nm to micrometers were obtained for long reaction times and [HF:Et] [1:2] concentrations; while pore sizes in the same order were observed for [HF:DMF] [1:7], but for shorter reaction time. Greater surface uniformity and pore distribution was obtained for a current density of around 8 mA/cm2 using solutions with DMF. A correlation between reflectance measurements and pore size is presented. The porous-silicon samples were used as substrate for hydroxyapatite growth by sol-gel method. X-ray diffraction (XRD) and SEM were used to characterize the layers grown. It was found that the layer topography obtained on PS samples was characterized by the evidence of Hydroxyapatite in the inter-pore regions and over the surface. PMID:28291792

InGaN/GaN light-emitting diode having direct hole injection plugs and its high-current operation.

PubMed

Kim, Sungjoon; Cho, Seongjae; Jeong, Jaedeok; Kim, Sungjun; Hwang, Sungmin; Kim, Garam; Yoon, Sukho; Park, Byung-Gook

2017-03-20

The light-emitting diode (LED) with an improved hole injection and straightforward process integration is proposed. p-type GaN direct hole injection plugs (DHIPs) are formed on locally etched multiple-quantum wells (MQWs) by epitaxial lateral overgrowth (ELO) method. We confirm that the optical output power is increased up to 23.2% at an operating current density of 100 A/cm². Furthermore, in order to identify the origin of improvement in optical performance, the transient light decay time and light intensity distribution characteristics were analyzed on the DHIP LED devices. Through the calculation of the electroluminescence (EL) decay time, internal quantum efficiency (IQE) is extracted along with the recombination parameters, which reveals that the DHIPs have a significant effect on enhancement of radiative recombination and reduction of efficiency droop. Furthermore, the mapping PL reveals that the DHIP LED also has a potential to improve the light extraction efficiency by hexagonal pyramid shaped DHIPs.

Diminiode thermionic conversion with 111-iridium electrodes

NASA Technical Reports Server (NTRS)

Koeger, E. W.; Bair, V. L.; Morris, J. F.

1976-01-01

Preliminary data indicating thermionic-conversion potentialities for a 111-iridium emitter and collector spaced 0.2 mm apart are presented. These results comprise output densities of current and of power as functions of voltage for three sets of emitter, collector, and reservoir temperatures: 1553, 944, 561 K; 1605, 898, 533 K; and 1656, 1028, 586 K. For the 1605 K evaluation, estimates produced work-function values of 2.22 eV for the emitter and 1.63 eV for the collector with a 2.0-eV barrier index (collector work function plus interelectrode voltage drop) corresponding to the maximum output of 5.5 W/sq cm at 0.24 volt. The current, voltage curve for the 1656 K 111-iridium diminiode yields a 6.2 W/sq cm maximum at 0.25 volt and is comparable with the 1700 K envelope for a diode with an etched-rhenium emitter and a 0.025-mm electrode gap made by TECO and evaluated by NASA.

Electrical characteristics of TMAH-surface treated Ni/Au/Al2O3/GaN MIS Schottky structures

NASA Astrophysics Data System (ADS)

Reddy, M. Siva Pratap; Lee, Jung-Hee; Jang, Ja-Soon

2014-03-01

The electrical characteristics and reverse leakage mechanisms of tetramethylammonium hydroxide (TMAH) surface-treated Ni/Au/Al2O3/GaN metal-insulator-semiconductor (MIS) diodes were investigated by using the current-voltage ( I-V) and capacitance-voltage ( C-V) characteristics. The MIS diode was formed on n-GaN after etching the AlGaN in the AlGaN/GaN heterostructures. The TMAH-treated MIS diode showed better Schottky characteristics with a lower ideality factor, higher barrier height and lower reverse leakage current compared to the TMAH-free MIS diode. In addition, the TMAH-free MIS diodes exhibited a transition from Poole-Frenkel emission at low voltages to Schottky emission at high voltages, whereas the TMAH-treated MIS diodes showed Schottky emission over the entire voltage range. Reasonable mechanisms for the improved device-performance characteristics in the TMAH-treated MIS diode are discussed in terms of the decreased interface state density or traps associated with an oxide material and the reduced tunneling probability.

Characterization of microwave discharge plasmas for surface processing

NASA Astrophysics Data System (ADS)

Nikolic, Milka

We have developed several diagnostic techniques to characterize two types of microwave (MW) discharge plasmas: a supersonic flowing argon MW discharge maintained in a cylindrical quartz cavity at frequency ƒ = 2.45 GHz and a pulse repetitive MW discharge in air at ƒ = 9.5 GHz. Low temperature MW discharges have been proven to posses attractive properties for plasma cleaning and etching of niobium surfaces of superconductive radio frequency (SRF) cavities. Plasma based surface modification technologies offer a promising alternative for etching and cleaning of SRF cavities. These technologies are low cost, environmentally friendly and easily controllable, and present a possible alternative to currently used acid based wet technologies, such as buffered chemical polishing (BCP), or electrochemical polishing (EP). In fact, weakly ionized. non-equilibrium, and low temperature gas discharges represent a powerful tool for surface processing due to the strong chemical reactivity of plasma radicals. Therefore, characterizing these discharges by applying non-perturbing, in situ measurement techniques is of vital importance. Optical emission spectroscopy has been employed to analyze the molecular structure and evaluate rotational and vibrational temperatures in these discharges. The internal plasma structure was studied by applying a tomographic numerical method based on the two-dimensional Radon formula. An automated optical measurement system has been developed for reconstruction of local plasma parameters. It was found that excited argon states are concentrated near the tube walls, thus confirming the assumption that the post discharge plasma is dominantly sustained by a travelling surface wave. Employing a laser induced fluorescence technique in combination with the time synchronization device allowed us to obtain time-resolved population densities of some excited atomic levels in argon. We have developed a technique for absolute measurements of electron density based on the time-resolved absolute intensity of a Nitrogen spectral band belonging to the Second Positive System, the kinetic model and the detailed particle balance of the N2 (C 3piu) state. Measured electron density waveforms are in fair agreement with electron densities obtained using the Stark broadening technique. In addition, time dependent population densities of Ar I metastable and resonant levels were obtained by employing a kinetic model developed based on analysis of population density rates of excited Ar I p levels. Both the experimental results and numerical models for both types of gas discharges indicate that multispecies chemistry of gases plays an important role in understanding the dynamics and characterizing the properties of these discharges.

In situ chemical functionalization of gallium nitride with phosphonic acid derivatives during etching.

PubMed

Wilkins, Stewart J; Greenough, Michelle; Arellano, Consuelo; Paskova, Tania; Ivanisevic, Albena

2014-03-04

In situ functionalization of polar (c plane) and nonpolar (a plane) gallium nitride (GaN) was performed by adding (3-bromopropyl) phosphonic acid or propyl phosphonic acid to a phosphoric acid etch. The target was to modulate the emission properties and oxide formation of GaN, which was explored through surface characterization with atomic force microscopy, X-ray photoelectron spectroscopy, photoluminescence (PL), inductively coupled plasma-mass spectrometry, and water contact angle. The use of (3-bromopropyl) phosphonic acid and propyl phosphonic acid in phosphoric acid demonstrated lower amounts of gallium oxide formation and greater hydrophobicity for both sample sets, while also improving PL emission of polar GaN samples. In addition to crystal orientation, growth-related factors such as defect density in bulk GaN versus thin GaN films residing on sapphire substrates were investigated as well as their responses to in situ functionalization. Thin nonpolar GaN layers were the most sensitive to etching treatments due in part to higher defect densities (stacking faults and threading dislocations), which accounts for large surface depressions. High-quality GaN (both free-standing bulk polar and bulk nonpolar) demonstrated increased sensitivity to oxide formation. Room-temperature PL stands out as an excellent technique to identify nonradiative recombination as observed in the spectra of heteroepitaxially grown GaN samples. The chemical methods applied to tune optical and physical properties of GaN provide a quantitative framework for future novel chemical and biochemical sensor development.

Characterization of etch pits found on a large-grain bulk niobium superconducting radio-frequency resonant cavity

DOE PAGES

Zhao, Xin; Ciovati, G.; Bieler, T. R.

2010-12-15

The performance of superconducting radio-frequency (SRF) resonant cavities made of bulk niobium is limited by nonlinear localized effects. Surface analysis of regions of higher power dissipation is thus of intense interest. Such areas (referred to as “hotspots”) were identified in a large-grain single-cell cavity that had been buffered-chemical polished and dissected for examination by high resolution electron microscopy, electron backscattered diffraction microscopy (EBSD), and optical microscopy. Pits with clearly discernible crystal facets were observed in both “hotspot” and “coldspot” specimens. The pits were found in-grain, at bicrystal boundaries, and on tricrystal junctions. They are interpreted as etch pits induced bymore » crystal defects (e.g. dislocations). All coldspots examined had a qualitatively lower density of etch pits or relatively smooth tricrystal boundary junctions. EBSD mapping revealed the crystal orientation surrounding the pits. Locations with high pit density are correlated with higher mean values of the local average misorientation angle distributions, indicating a higher geometrically necessary dislocation content. In addition, a survey of the samples by energy dispersive x-ray analysis did not show any significant contamination of the samples’ surface. In conclusion, the local magnetic field enhancement produced by the sharp-edge features observed on the samples is not sufficient to explain the observed degradation of the cavity quality factor, which starts at peak surface magnetic field as low as 20 mT.« less

Predictions of ion energy distributions and radical fluxes in radio frequency biased inductively coupled plasma etching reactors

NASA Astrophysics Data System (ADS)

Hoekstra, Robert J.; Kushner, Mark J.

1996-03-01

Inductively coupled plasma (ICP) reactors are being developed for low gas pressure (<10s mTorr) and high plasma density ([e]≳1011 cm-3) microelectronics fabrication. In these reactors, the plasma is generated by the inductively coupled electric field while an additional radio frequency (rf) bias is applied to the substrate. One of the goals of these systems is to independently control the magnitude of the ion flux by the inductively coupled power deposition, and the acceleration of ions into the substrate by the rf bias. In high plasma density reactors the width of the sheath above the wafer may be sufficiently thin that ions are able to traverse it in approximately 1 rf cycle, even at 13.56 MHz. As a consequence, the ion energy distribution (IED) may have a shape typically associated with lower frequency operation in conventional reactive ion etching tools. In this paper, we present results from a computer model for the IED incident on the wafer in ICP etching reactors. We find that in the parameter space of interest, the shape of the IED depends both on the amplitude of the rf bias and on the ICP power. The former quantity determines the average energy of the IED. The latter quantity controls the width of the sheath, the transit time of ions across the sheath and hence the width of the IED. In general, high ICP powers (thinner sheaths) produce wider IEDs.

Defect-Enabled Electrical Current Leakage in Ultraviolet Light-Emitting Diodes

DOE PAGES

Moseley, Michael William; Allerman, Andrew A.; Crawford, Mary H.; ...

2015-04-13

The AlGaN materials system offers a tunable, ultra-wide bandgap that is exceptionally useful for high-power electronics and deep ultraviolet optoelectronics. Moseley et al. (pp. 723–726) investigate a structural defect known as an open-core threading dislocation or ''nanopipe'' that is particularly detrimental to devices that employ these materials. Furthermore, an AlGaN thin film was synthesized using metal-organic chemical-vapor deposition. Electrical current leakage is detected at a discrete point using a conductive atomic-force microscope (CAFM). However, no physical feature or abnormality at this location was visible by an optical microscope. The AlGaN thin film was then etched in hot phosphoric acid, andmore » the same location that was previously analyzed was revisited with the CAFM. The point that previously exhibited electrical current leakage had been decorated with a 1.1 μm wide hexagonal pit, which identified the site of electrical current leakage as a nanopipe and allows these defects to be easily observed by optical microscopy. Moreover, with this nanopipe identification and quantification strategy, the authors were able to correlate decreasing ultraviolet light-emitting diode optical output power with increasing nanopipe density.« less

GaN nanowire arrays with nonpolar sidewalls for vertically integrated field-effect transistors

NASA Astrophysics Data System (ADS)

Yu, Feng; Yao, Shengbo; Römer, Friedhard; Witzigmann, Bernd; Schimpke, Tilman; Strassburg, Martin; Bakin, Andrey; Schumacher, Hans Werner; Peiner, Erwin; Suryo Wasisto, Hutomo; Waag, Andreas

2017-03-01

Vertically aligned gallium nitride (GaN) nanowire (NW) arrays have attracted a lot of attention because of their potential for novel devices in the fields of optoelectronics and nanoelectronics. In this work, GaN NW arrays have been designed and fabricated by combining suitable nanomachining processes including dry and wet etching. After inductively coupled plasma dry reactive ion etching, the GaN NWs are subsequently treated in wet chemical etching using AZ400K developer (i.e., with an activation energy of 0.69 ± 0.02 eV and a Cr mask) to form hexagonal and smooth a-plane sidewalls. Etching experiments using potassium hydroxide (KOH) water solution reveal that the sidewall orientation preference depends on etchant concentration. A model concerning surface bonding configuration on crystallography facets has been proposed to understand the anisotropic wet etching mechanism. Finally, NW array-based vertical field-effect transistors with wrap-gated structure have been fabricated. A device composed of 99 NWs exhibits enhancement mode operation with a threshold voltage of 1.5 V, a superior electrostatic control, and a high current output of >10 mA, which prevail potential applications in next-generation power switches and high-temperature digital circuits.

GaN nanowire arrays with nonpolar sidewalls for vertically integrated field-effect transistors.

PubMed

Yu, Feng; Yao, Shengbo; Römer, Friedhard; Witzigmann, Bernd; Schimpke, Tilman; Strassburg, Martin; Bakin, Andrey; Schumacher, Hans Werner; Peiner, Erwin; Wasisto, Hutomo Suryo; Waag, Andreas

2017-03-03

Vertically aligned gallium nitride (GaN) nanowire (NW) arrays have attracted a lot of attention because of their potential for novel devices in the fields of optoelectronics and nanoelectronics. In this work, GaN NW arrays have been designed and fabricated by combining suitable nanomachining processes including dry and wet etching. After inductively coupled plasma dry reactive ion etching, the GaN NWs are subsequently treated in wet chemical etching using AZ400K developer (i.e., with an activation energy of 0.69 ± 0.02 eV and a Cr mask) to form hexagonal and smooth a-plane sidewalls. Etching experiments using potassium hydroxide (KOH) water solution reveal that the sidewall orientation preference depends on etchant concentration. A model concerning surface bonding configuration on crystallography facets has been proposed to understand the anisotropic wet etching mechanism. Finally, NW array-based vertical field-effect transistors with wrap-gated structure have been fabricated. A device composed of 99 NWs exhibits enhancement mode operation with a threshold voltage of 1.5 V, a superior electrostatic control, and a high current output of >10 mA, which prevail potential applications in next-generation power switches and high-temperature digital circuits.

Shear bond strengths of self-etching adhesives to caries-affected dentin on the gingival wall.

PubMed

Koyuturk, Alp Erdin; Sengun, Abdulkadir; Ozer, Fusun; Sener, Yagmur; Gokalp, Alparslan

2006-03-01

The purpose of this study was to evaluate the bonding ability of five current self-etching adhesives to caries-affected dentin on the gingival wall. Seventy extracted human molars with approximal dentin caries were employed in this study. In order to obtain caries-affected dentin on the gingival wall, grinding was performed under running water. Following which, specimens mounted in acrylic blocks and composite resins of the bonding systems were bonded to dentin with plastic rings and then debonded by shear bond strength. With Clearfil SE Bond, bonding to caries-affected dentin showed the highest bond strength. With Optibond Solo Plus Self-Etch, bonding to caries-affected dentin showed higher shear bond strength than AQ Bond, Tyrian SPE & One-Step Plus, and Prompt-L-Pop (p<0.05). Further, the bond strengths of Clearfil SE Bond and Optibond Solo Plus Self-Etch to sound dentin were higher than those of Prompt-L-Pop, AQ Bond, and Tyrian SPE & One-Step Plus (p<0.05). In conclusion, besides micromechanical interlocking through hybrid layer formation, bond strength of self-etch adhesives to dentin may be increased from additional chemical interaction between the functional monomer and residual hydroxyapatite. The results of this study confirmed that differences in bond strength among self-etching adhesives to both caries-affected and sound dentin were due to chemical composition rather than acidity.

Comparison of separation performance of laser-ablated and wet-etched microfluidic devices

PubMed Central

Baker, Christopher A.; Bulloch, Rayford; Roper, Michael G.

2010-01-01

Laser ablation of glass allows for production of microfluidic devices without the need of hydrofluoric acid and photolithography. The goal of this study was to compare the separation performance of microfluidic devices produced using a low-cost laser ablation system and conventional wet etching. During laser ablation, cracking of the glass substrate was prevented by heating the glass to 300°C. A range of laser energy densities was found to produce channel depths ranging from 4 – 35 μm and channel widths from 118 – 162 μm. The electroosmotic flow velocity was lower in laser-ablated devices, 0.110 ± 0.005 cm s−1, as compared to wet-etched microfluidic chips, 0.126 ± 0.003 cm s−1. Separations of both small and large molecules performed on both wet- and laser-ablated devices were compared by examining limits of detection, theoretical plate count, and peak asymmetry. Laser-induced fluorescence detection limits were 10 pM fluorescein for both types of devices. Laser-ablated and wet-etched microfluidic chips had reproducible migration times with ≤ 2.8% RSD and peak asymmetries ranging from 1.0 – 1.8. Numbers of theoretical plates were between 2.8- and 6.2-fold higher on the wet-etched devices compared to laser-ablated devices. Nevertheless, resolution between small and large analytes was accomplished, which indicates that laser ablation may find an application in pedagogical studies of electrophoresis or microfluidic devices, or in settings where hydrofluoric acid cannot be used. PMID:20827468

Electrochemical fabrication of nanoporous copper films in choline chloride-urea deep eutectic solvent.

PubMed

Zhang, Q B; Abbott, Andrew P; Yang, C

2015-06-14

Nanoporous copper films were fabricated by a facile electrochemical alloying/dealloying process without the need of a template. A deep eutectic solvent made from choline chloride (ChCl) and urea was used with zinc oxide as the metal salt. Cyclic voltammetry was used to characterise the electrochemical reduction of zinc and follow Cu-Zn alloy formation on the copper substrate at elevated temperatures from 353 to 393 K. The alloy formation was confirmed by X-ray diffraction spectra. 3D, open and bicontinuous nanoporous copper films were obtained by in situ electrochemically etching (dealloying) of the zinc component in the Cu-Zn surface alloys at an appropriate potential (-0.4 V vs. Ag). This dealloying process was found to be highly temperature dependent and surface diffusion controlled, which involved the self-assembly of copper atoms at the alloy/electrolyte interface. Additionally, the effects of the deposition parameters, including deposition temperature, current density as well as total charge density on resulting the microstructure were investigated by scanning electron microscopy, and atomic force microscope.

Coralloid-like Nanostructured c-nSi/SiOx@Cy Anodes for High Performance Lithium Ion Battery.

PubMed

Zhuang, Xianhuan; Song, Pingan; Chen, Guorong; Shi, Liyi; Wu, Yuan; Tao, Xinyong; Liu, Hongjiang; Zhang, Dengsong

2017-08-30

Balancing the size of the primary Si unit and void space is considered to be an effective approach for developing high performance silicon-based anode materials and is vital to create a lithium ion battery with high energy density. We herein have demonstrated the facile fabrication of coralloid-like nanostructured silicon composites (c-nSi/SiO x @Cy) via sulfuric acid etching the Al 60 Si 40 alloy, followed by a surface growth carbon layer approach. The HRTEM images of pristine and cycled c-nSi/SiO x @Cy show that abundant nanoscale internal pores and the continuous conductive carbon layer effectively avoid the pulverization and agglomeration of Si units during multiple cycles. It is interesting that the c-nSi/SiO x @C 4.0 anode exhibits a high initial Coulombic efficiency of 85.53%, and typical specific capacity of over 850 mAh g -1 after deep 500 cycles at a current density of 1 A g -1 . This work offers a facile strategy to create silicon-based anodes consisting of highly dispersed primary nano-Si units.

Feature Profile Evolution of SiO2 Trenches In Fluorocarbon Plasmas

NASA Technical Reports Server (NTRS)

Hwang, Helen; Govindan, T. R.; Meyyappan, M.; Arunachalam, Valli; Rauf, Shahid; Coronell, Dan; Carroll, Carol W. (Technical Monitor)

1999-01-01

Etching of silicon microstructures for semiconductor manufacturing in chlorine plasmas has been well characterized. The etching proceeds in a two-part process, where the chlorine neutrals passivate the Si surface and then the ions etch away SiClx. However, etching in more complicated gas mixtures and materials, such as etching of SiO2 in Ar/C4F8, requires knowledge of the ion and neutral distribution functions as a function of angle and velocity, in addition to modeling the gas surface reactions. In order to address these needs, we have developed and integrated a suite of models to simulate the etching process from the plasma reactor level to the feature profile evolution level. This arrangement allows for a better understanding, control, and prediction of the influence of equipment level process parameters on feature profile evolution. We are currently using the HPEM (Hybrid Plasma Equipment Model) and PCMCM (Plasma Chemistry Monte Carlo Model) to generate plasma properties and ion and neutral distribution functions for argon/fluorocarbon discharges in a GEC Reference Cell. These quantities are then input to the feature scale model, Simulation of Profile Evolution by Level Sets (SPELS). A surface chemistry model is used to determine the interaction of the incoming species with the substrate material and simulate the evolution of the trench profile. The impact of change of gas pressure and inductive power on the relative flux of CFx and F to the wafer, the etch and polymerization rates, and feature profiles will be examined. Comparisons to experimental profiles will also be presented.

Micro/nanofabrication of poly({sub L}-lactic acid) using focused ion beam direct etching

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oyama, Tomoko Gowa; Nagasawa, Naotsugu; Taguchi, Mitsumasa

2013-10-14

Micro/nanofabrication of biocompatible and biodegradable poly({sub L}-lactic acid) (PLLA) using focused Ga ion beam direct etching was evaluated for future bio-device applications. The fabrication performance was determined with different ion fluences and fluxes (beam currents), and it was found that the etching speed and fabrication accuracy were affected by irradiation-induced heat. Focused ion beam (FIB)-irradiated surfaces were analyzed using micro-area X-ray photoelectron spectroscopy. Owing to reactions such as the physical sputtering of atoms and radiation-induced decomposition, PLLA was gradually carbonized with increasing C=C bonds. Controlled micro/nanostructures of PLLA were fabricated with C=C bond-rich surfaces expected to have good cell attachmentmore » properties.« less

A FED Prototype Using Patterned DLC Thin Films as the Cathode

NASA Astrophysics Data System (ADS)

Li, W.; Feng, T.; Mao, D. S.; Wang, X.; Liu, X. H.; Zou, S. C.; Zhu, Y. K.; Li, Q.; Xu, J. F.; Jin, S.; Zheng, J. S.

In our study, diamond-like-carbon (DLC) thin films were prepared by filtered arc deposition (FAD), which provided a way to deposit DLC thin films on large areas at room temperature. Glass slides coated 100nm chromium or titanium thin films were used as cathode substrates. Millions of rectangular holes with sizes of 5 × 5μm were made on the DLC films using a routine patterning process. Here a special reactive ion beam etching method was applied to etch the DLC films. The anodes of the devices were made by electrophoretic deposition. ZnO:Zn phosphor (P15) was employed, which has a broad band bluish green (centered at 490nm). Before electrophoretic deposition, the anode substrates (ITO glass slides) had been patterned into 50 anode electrodes. In order to improve the adherence of phosphor layers, the as-deposited screens were treated in Na2SiO3 solution for 24h to add additional binder. A kind of matrix-addressed diode FED prototype was designed and packaged. 50-100μm-thick glass slides were used as spacers and getters were applied to maintain the vacuum after the exhaustion. The applied DC voltage was ranged in 0-3000V and much higher current density was measured in the cathode-patterned prototypes than the unpatterned ones during the test. As a result, characters could be well displayed.

Web Growth Used to Confine Screw Dislocations to Predetermined Lateral Positions in 4H-SiC Epilayers

NASA Technical Reports Server (NTRS)

Powell, J. Anthony; Neudeck, Philip G.; Spry, David J.; Trunek, Andrew J.; Beheim, Glenn M.

2004-01-01

Silicon-carbide- (SiC-) based power devices could enable substantial aerospace electronics benefits over today's silicon-based electronics. However, present-day SiC wafers contain electrically harmful dislocations (including micropipes) that are unpredictably distributed in high densities across all commercial 4H- and 6H-SiC wafers. The NASA Glenn Research Center recently demonstrated a crystal growth process that moves SiC wafer dislocations to predetermined lateral positions in epitaxial layers so that they can be reproducibly avoided during subsequent SiC electronic device fabrication. The process starts by reactive ion etching mesa patterns with enclosed trench regions into commercial on-axis (0001) 4H- or 6H-SiC substrates. An example of a pregrowth mesa geometry with six enclosed triangular-shaped trench regions is shown. After the etch mask is stripped, homoepitaxial growth is carried out in pure stepflow conditions that enable thin cantilevers to grow laterally from the tops of mesas whose pregrowth top surfaces are not threaded by substrate screw dislocations. The image in the bottom figure shows the postgrowth structure that forms after the lateral cantilevers expand to coalesce and completely roof over each of the six triangular trench regions. Atomic force microscope (AFM) measurements of the roof revealed that three elementary screw dislocation growth spirals, each shown in the AFM insets of the bottom image on the previous page, formed in the film roof at three respective points of cantilever film coalescence. The image above shows the structure following an etch in molten potassium hydroxide (KOH) that produced surface etch pits at the dislocation defects. The larger KOH etch pits--S1, S2, and S3--shown in this image correspond to screw dislocations relocated to the final points of cantilever coalescence. The smaller KOH etch pits are consistent with epilayer threading edge dislocations from the pregrowth substrate mesa (P1, P3, and P4) and a final cantilever coalescence point (P2). No defects (i.e., no etch pits) are observed in other cantilevered portions of the film surface. On the basis of the principle of dislocation Burgers vector conservation, we hypothesize that all vertically propagating substrate dislocations in an enclosed trench region become combined into a single dislocation in the webbed film roof at the point of final roof coalescence. The point of final roof coalescence, and therefore the lateral location of a webbed roof dislocation, can be designed into the pregrowth mesa pattern. Screw dislocations with predetermined lateral positions can then be used to provide the new growth steps necessary for growing a 4H/6H-SiC epilayer with a lower dislocation density than the substrate. Devices fabricated on top of such films can be positioned to avoid the preplaced dislocations.

Method for surface treatment of a cadmium zinc telluride crystal

DOEpatents

James, Ralph; Burger, Arnold; Chen, Kuo-Tong; Chang, Henry

1999-01-01

A method for treatment of the surface of a CdZnTe (CZT) crystal that reduces surface roughness (increases surface planarity) and provides an oxide coating to reduce surface leakage currents and thereby, improve resolution. A two step process is disclosed, etching the surface of a CZT crystal with a solution of lactic acid and bromine in ethylene glycol, following the conventional bromine/methanol etch treatment, and after attachment of electrical contacts, oxidizing the CZT crystal surface.

Combining wet etching and real-time damage event imaging to reveal the most dangerous laser damage initiator in fused silica.

PubMed

Hu, Guohang; Zhao, Yuanan; Liu, Xiaofeng; Li, Dawei; Xiao, Qiling; Yi, Kui; Shao, Jianda

2013-08-01

A reliable method, combining a wet etch process and real-time damage event imaging during a raster scan laser damage test, has been developed to directly determine the most dangerous precursor inducing low-density laser damage at 355 nm in fused silica. It is revealed that ~16% of laser damage sites were initiated at the place of the scratches, ~49% initiated at the digs, and ~35% initiated at invisible defects. The morphologies of dangerous scratches and digs were compared with those of moderate ones. It is found that local sharp variation at the edge, twist, or inside of a subsurface defect is the most dangerous laser damage precursor.

TiO2 film properties as a function of processing temperature, volume 3

NASA Technical Reports Server (NTRS)

Fitzgibbons, E. T.; Sladek, K. J.; Hartwig, W. H.

1972-01-01

Thin film TiO2 was produced at 150 C by chemical vapor deposition using hydrolysis of tetraisopropyl titanate. Films were amorphous as grown, but annealing in air caused crystallization, with anatase formed beginning at 350 C and rutile at 700 C. Density and index of refraction increased substantially with increasing anneal temperature, while etch susceptibility in HF and H2SO4 decreased. Comparison with literature data showed two groups of processes. One group yields films having properties that gradually approach those of rutile with increasing process temperature. The other group gives rutile directly at moderate temperatures. Deposition of amorphous film followed by etching and annealing is suggested as a means for pattern definition.

Interdigitated back contact solar cells with polycrystalline silicon on oxide passivating contacts for both polarities

NASA Astrophysics Data System (ADS)

Haase, Felix; Kiefer, Fabian; Schäfer, Sören; Kruse, Christian; Krügener, Jan; Brendel, Rolf; Peibst, Robby

2017-08-01

We demonstrate an independently confirmed 25.0%-efficient interdigitated back contact silicon solar cell with passivating polycrystalline silicon (poly-Si) on oxide (POLO) contacts that enable a high open circuit voltage of 723 mV. We use n-type POLO contacts with a measured saturation current density of J 0n = 4 fA cm-2 and p-type POLO contacts with J 0p = 10 fA cm-2. The textured front side and the gaps between the POLO contacts on the rear are passivated by aluminum oxide (AlO x ) with J 0AlO x = 6 fA cm-2 as measured after deposition. We analyze the recombination characteristics of our solar cells at different process steps using spatially resolved injection-dependent carrier lifetimes measured by infrared lifetime mapping. The implied pseudo-efficiency of the unmasked cell, i.e., cell and perimeter region are illuminated during measurement, is 26.2% before contact opening, 26.0% after contact opening and 25.7% for the finished cell. This reduction is due to an increase in the saturation current density of the AlO x passivation during chemical etching of the contact openings and of the rear side metallization. The difference between the implied pseudo-efficiency and the actual efficiency of 25.0% as determined by designated-area light current-voltage (I-V) measurements is due to series resistance and diffusion of excess carriers into the non-illuminated perimeter region.

Preparation and Thermal Characterization of Annealed Gold Coated Porous Silicon

PubMed Central

Behzad, Kasra; Mat Yunus, Wan Mahmood; Talib, Zainal Abidin; Zakaria, Azmi; Bahrami, Afarin

2012-01-01

Porous silicon (PSi) layers were formed on a p-type Si wafer. Six samples were anodised electrically with a 30 mA/cm2 fixed current density for different etching times. The samples were coated with a 50–60 nm gold layer and annealed at different temperatures under Ar flow. The morphology of the layers, before and after annealing, formed by this method was investigated by scanning electron microscopy (SEM). Photoacoustic spectroscopy (PAS) measurements were carried out to measure the thermal diffusivity (TD) of the PSi and Au/PSi samples. For the Au/PSi samples, the thermal diffusivity was measured before and after annealing to study the effect of annealing. Also to study the aging effect, a comparison was made between freshly annealed samples and samples 30 days after annealing. PMID:28817037

Electrochemical performances of graphene nanoribbons interlacing hollow NiCo oxide nanocages

NASA Astrophysics Data System (ADS)

Zhao, Xiyu; Li, Xinlu; Huang, Yanchun; Su, Zelong; Long, Junjun; Zhang, Shilei; Sha, Junwei; Wu, Tianli; Wang, Ronghua

2017-12-01

A hybrid of graphene nanoribbons (GNRs) interlacing hollow NiCoO2 (G-HNCO) nanocages in a size range of 300 500 nm with rough surface is synthesized by a chemical etching Cu2O templates and followed by GNR interlacing process. The G-HNCO showed high electrochemical performance of oxygen evolution reaction (OER), which exhibited small onset potential of 1.50 V and achieved current densities of 10 mA cm-2 at potentials of 1.62 V. Also, the hybrid delivered high capacitance of 937.8 F g-1 at 1 A g-1 in supercapacitor (SC) tests as well as stable cycling performance in both OER and SC measurements. The approach to synthesize the hybrid is simple and scalable for other graphene nanoribbon-based electrocatalysts. [Figure not available: see fulltext.

Field emission from isolated individual vertically aligned carbon nanocones

NASA Astrophysics Data System (ADS)

Baylor, L. R.; Merkulov, V. I.; Ellis, E. D.; Guillorn, M. A.; Lowndes, D. H.; Melechko, A. V.; Simpson, M. L.; Whealton, J. H.

2002-04-01

Field emission from isolated individual vertically aligned carbon nanocones (VACNCs) has been measured using a small-diameter moveable probe. The probe was scanned parallel to the sample plane to locate the VACNCs, and perpendicular to the sample plane to measure the emission turn-on electric field of each VACNC. Individual VACNCs can be good field emitters. The emission threshold field depends on the geometric aspect ratio (height/tip radius) of the VACNC and is lowest when a sharp tip is present. VACNCs exposed to a reactive ion etch process demonstrate a lowered emission threshold field while maintaining a similar aspect ratio. Individual VACNCs can have low emission thresholds, carry high current densities, and have long emission lifetime. This makes them very promising for various field emission applications for which deterministic placement of the emitter with submicron accuracy is needed.

The Development of High-Density Vertical Silicon Nanowires and Their Application in a Heterojunction Diode.

PubMed

Chang, Wen-Chung; Su, Sheng-Chien; Wu, Chia-Ching

2016-06-30

Vertically aligned p-type silicon nanowire (SiNW) arrays were fabricated through metal-assisted chemical etching (MACE) of Si wafers. An indium tin oxide/indium zinc oxide/silicon nanowire (ITO/IZO/SiNW) heterojunction diode was formed by depositing ITO and IZO thin films on the vertically aligned SiNW arrays. The structural and electrical properties of the resulting ITO/IZO/SiNW heterojunction diode were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and current-voltage (I-V) measurements. Nonlinear and rectifying I-V properties confirmed that a heterojunction diode was successfully formed in the ITO/IZO/SiNW structure. The diode had a well-defined rectifying behavior, with a rectification ratio of 550.7 at 3 V and a turn-on voltage of 2.53 V under dark conditions.

Overview of diffraction gratings technologies for spaceflight satellites and ground-based telescopes

NASA Astrophysics Data System (ADS)

Cotel, A.; Liard, A.; Desserouer, F.; Pichon, P.

2017-11-01

The diffraction gratings are widely used in Space-flight satellites for spectrograph instruments or in ground-based telescopes in astronomy. The diffraction gratings are one of the key optical components of such systems and have to exhibit very high optical performances. HORIBA Jobin Yvon S.A.S. (part of HORIBA Group) is in the forefront of such gratings development for more than 40 years. During the past decades, HORIBA Jobin Yvon (HJY) has developed a unique expertise in diffraction grating design and manufacturing processes for holographic, ruled or etched gratings. We will present in this paper an overview of diffraction grating technologies especially designed for space and astronomy applications. We will firstly review the heritage of the company in this field with the space qualification of different grating types. Then, we will describe several key grating technologies developed for specific space or astronomy projects: ruled blazed low groove density plane reflection grating, high-groove density holographic toroidal and spherical grating, and finally transmission Fused Silica Etched (FSE) grism-assembled grating. We will not present the Volume Phase Holographic (VPHG) grating type which is used in Astronomy.

Overview of diffraction gratings technologies for space-flight satellites and astronomy

NASA Astrophysics Data System (ADS)

Cotel, Arnaud; Liard, Audrey; Desserouer, Frédéric; Bonnemason, Francis; Pichon, Pierre

2014-09-01

The diffraction gratings are widely used in Space-flight satellites for spectrograph instruments or in ground-based telescopes in astronomy. The diffraction gratings are one of the key optical components of such systems and have to exhibit very high optical performances. HORIBA Jobin Yvon S.A.S. (part of HORIBA Group) is in the forefront of such gratings development for more than 40 years. During the past decades, HORIBA Jobin Yvon (HJY) has developed a unique expertise in diffraction grating design and manufacturing processes for holographic, ruled or etched gratings. We will present in this paper an overview of diffraction grating technologies especially designed for space and astronomy applications. We will firstly review the heritage of the company in this field with the space qualification of different grating types. Then, we will describe several key grating technologies developed for specific space or astronomy projects: ruled blazed low groove density plane reflection grating, holographic blazed replica plane grating, high-groove density holographic toroidal and spherical grating and transmission Fused Silica Etched (FSE) grismassembled grating.

Pyramidal pits created by single highly charged ions in BaF{sub 2} single crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

El-Said, A. S.; Physics Department, Faculty of Science, Mansoura University, 35516 Mansoura; Heller, R.

2010-07-15

In various insulators, the impact of individual slow highly charged ions (eV-keV) creates surface nanostructures, whose size depends on the deposited potential energy. Here we report on the damage created on a cleaved BaF{sub 2} (111) surface by irradiation with 4.5xq keV highly charged xenon ions from a room-temperature electron-beam ion trap. Up to charge states q=36, no surface topographic changes on the BaF{sub 2} surface are observed by scanning force microscopy. The hidden stored damage, however, can be made visible using the technique of selective chemical etching. Each individual ion impact develops into a pyramidal etch pits, as canmore » be concluded from a comparison of the areal density of observed etch pits with the applied ion fluence (typically 10{sup 8} ions/cm{sup 2}). The dimensional analysis of the measured pits reveals the significance of the deposited potential energy in the creation of lattice distortions/defects in BaF{sub 2}.« less

Surface Morphology Evolution Mechanisms of InGaN/GaN Multiple Quantum Wells with Mixture N2/H2-Grown GaN Barrier.

PubMed

Zhou, Xiaorun; Lu, Taiping; Zhu, Yadan; Zhao, Guangzhou; Dong, Hailiang; Jia, Zhigang; Yang, Yongzhen; Chen, Yongkang; Xu, Bingshe

2017-12-01

Surface morphology evolution mechanisms of InGaN/GaN multiple quantum wells (MQWs) during GaN barrier growth with different hydrogen (H 2 ) percentages have been systematically studied. Ga surface-diffusion rate, stress relaxation, and H 2 etching effect are found to be the main affecting factors of the surface evolution. As the percentage of H 2 increases from 0 to 6.25%, Ga surface-diffusion rate and the etch effect are gradually enhanced, which is beneficial to obtaining a smooth surface with low pits density. As the H 2 proportion further increases, stress relaxation and H 2 over- etching effect begin to be the dominant factors, which degrade surface quality. Furthermore, the effects of surface evolution on the interface and optical properties of InGaN/GaN MQWs are also profoundly discussed. The comprehensive study on the surface evolution mechanisms herein provides both technical and theoretical support for the fabrication of high-quality InGaN/GaN heterostructures.

Influence of subsurface defects on damage performance of fused silica in ultraviolet laser

NASA Astrophysics Data System (ADS)

Huang, Jin; Zhou, Xinda; Liu, Hongjie; Wang, Fengrui; Jiang, Xiaodong; Wu, Weidong; Tang, Yongjian; Zheng, Wanguo

2013-02-01

In ultraviolet pulse laser, damage performance of fused silica optics is directly dependent on the absorptive impurities and scratches in subsurface, which are induced by mechanical polishing. In the research about influence of subsurface defects on damage performance, a series of fused silica surfaces with various impurity concentrations and scratch structures were created by hydrofluoric (HF) acid solution etching. Time of Flight secondary ion mass spectrometry and scanning probe microprobe revealed that with increasing etching depth, impurity concentrations in subsurface layers are decreased, the scratch structures become smoother and the diameter:depth ratio is increased. Damage performance test with 355-nm pulse laser showed that when 600 nm subsurface thickness is removed by HF acid etching, laser-induced damage threshold of fused silica is raised by 40 percent and damage density is decreased by over one order of magnitude. Laser weak absorption was tested to explain the cause of impurity elements impacting damage performance, field enhancement caused by change of scratch structures was calculated by finite difference time domain simulation, and the calculated results are in accord with the damage test results.

Reactive Intermediates or Inert Graphene? Temperature- and Pressure-Determined Evolution of Carbon in the CH 4–Ni(111) System

DOE PAGES

Yuan, Kaidi; Zhong, Jian-Qiang; Sun, Shuo; ...

2017-08-15

Atomic-level identification of carbon intermediates under reaction conditions is essential for carbon-related heterogeneous catalysis. Using the in operando technique of near-ambient-pressure X-ray photoelectron spectroscopy, we have identified in this paper various carbon intermediates during the thermal decomposition of CH 4 on Ni(111), including *CH, *C 1/Ni 3C, *C n (n ≥ 2), and clock-reconstructed Ni 2C at different temperature regions (300–900 K). These “reactive” carbon precursors can either react with probing molecules such as O 2 at room temperature or be etched away by CH 4. They can also develop into graphene flakes under controlled conditions: a temperature between 800more » and 900 K and a suitable CH 4 pressure (10 –3–10 –1 mbar, depending on temperature). The growth rate of graphene is significantly restrained at higher CH 4 pressures, due to the accelerated etching of its carbon precursors. The identification of in operando carbon intermediates and the control of their evolution have great potential in designing heterogeneous catalysts for the direct conversion of methane. Finally, the observed carbon aggregation/etching equilibrium reveals an underlying mechanism in coking prevention and in the fabrication of large-area single-crystal graphene, where the suppression of seeding density and etching up of small grains are required.« less

Reactive Intermediates or Inert Graphene? Temperature- and Pressure-Determined Evolution of Carbon in the CH 4–Ni(111) System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yuan, Kaidi; Zhong, Jian-Qiang; Sun, Shuo

Atomic-level identification of carbon intermediates under reaction conditions is essential for carbon-related heterogeneous catalysis. Using the in operando technique of near-ambient-pressure X-ray photoelectron spectroscopy, we have identified in this paper various carbon intermediates during the thermal decomposition of CH 4 on Ni(111), including *CH, *C 1/Ni 3C, *C n (n ≥ 2), and clock-reconstructed Ni 2C at different temperature regions (300–900 K). These “reactive” carbon precursors can either react with probing molecules such as O 2 at room temperature or be etched away by CH 4. They can also develop into graphene flakes under controlled conditions: a temperature between 800more » and 900 K and a suitable CH 4 pressure (10 –3–10 –1 mbar, depending on temperature). The growth rate of graphene is significantly restrained at higher CH 4 pressures, due to the accelerated etching of its carbon precursors. The identification of in operando carbon intermediates and the control of their evolution have great potential in designing heterogeneous catalysts for the direct conversion of methane. Finally, the observed carbon aggregation/etching equilibrium reveals an underlying mechanism in coking prevention and in the fabrication of large-area single-crystal graphene, where the suppression of seeding density and etching up of small grains are required.« less

Interface microstructure engineering by high power impulse magnetron sputtering for the enhancement of adhesion

NASA Astrophysics Data System (ADS)

Ehiasarian, A. P.; Wen, J. G.; Petrov, I.

2007-03-01

An excellent adhesion of hard coatings to steel substrates is paramount in practically all application areas. Conventional methods utilize Ar glow etching or cathodic arc discharge pretreatments that have the disadvantage of producing weak interfaces or adding droplets, respectively. One tool for interface engineering is high power impulse magnetron sputtering (HIPIMS). HIPIMS is based on conventional sputtering with extremely high peak power densities reaching 3kWcm-2 at current densities of >2Acm-2. HIPIMS of Cr and Nb was used to prepare interfaces on 304 stainless steel and M2 high speed steel (HSS). During the pretreatment, the substrates were biased to Ubias=-600V and Ubias=-1000V in the environment of a HIPIMS of Cr and Nb plasma. The bombarding flux density reached peak values of 300mAcm-2 and consisted of highly ionized metal plasma containing a high proportion of Cr1+ and Nb1+. Pretreatments were also carried out with Ar glow discharge and filtered cathodic arc as comparison. The adhesion was evaluated for coatings consisting of a 0.3μm thick CrN base layer and a 4μm thick nanolayer stack of CrN /NbN with a period of 3.4nm, hardness of HK0.025=3100, and residual stress of -1.8GPa. For HIPIMS of Cr pretreatment, the adhesion values on M2 HSS reached scratch test critical load values of LC=70N, thus comparing well to LC=51N for interfaces pretreated by arc discharge plasmas and to LC=25N for Ar etching. Cross sectional transmission electron microscopy studies revealed a clean interface and large areas of epitaxial growth in the case of HIPIMS pretreatment. The HIPIMS pretreatment promoted strong registry between the orientation of the coating and polycrystalline substrate grains due to the incorporation of metal ions and the preservation of crystallinity of the substrate. Evidence and conditions for the formation of cube-on-cube epitaxy and axiotaxy on steel and γ-TiAl substrates are presented.

Etching-free patterning method for electrical characterization of atomically thin MoSe2 films grown by chemical vapor deposition.

PubMed

Utama, M Iqbal Bakti; Lu, Xin; Zhan, Da; Ha, Son Tung; Yuan, Yanwen; Shen, Zexiang; Xiong, Qihua

2014-11-07

Patterning two-dimensional materials into specific spatial arrangements and geometries is essential for both fundamental studies of materials and practical applications in electronics. However, the currently available patterning methods generally require etching steps that rely on complicated and expensive procedures. We report here a facile patterning method for atomically thin MoSe2 films using stripping with an SU-8 negative resist layer exposed to electron beam lithography. Additional steps of chemical and physical etching were not necessary in this SU-8 patterning method. The SU-8 patterning was used to define a ribbon channel from a field effect transistor of MoSe2 film, which was grown by chemical vapor deposition. The narrowing of the conduction channel area with SU-8 patterning was crucial in suppressing the leakage current within the device, thereby allowing a more accurate interpretation of the electrical characterization results from the sample. An electrical transport study, enabled by the SU-8 patterning, showed a variable range hopping behavior at high temperatures.

Effect of Annealing on the Density of Defects in Epitaxial CdTe (211)/GaAs

NASA Astrophysics Data System (ADS)

Bakali, Emine; Selamet, Yusuf; Tarhan, Enver

2018-05-01

CdTe thin films were grown on GaAs (211) wafers by molecular beam epitaxy as the buffer layer for HgCdTe infrared detector applications. We studied the effect of annealing on the density of dislocation of these CdTe thin films under varying annealing parameters such as annealing temperature, annealing duration, and number of cycles. Annealings were carried out using a homemade annealing reactor possessing a special heater element made of a Si wafer for rapid heating. The density of dislocations, which were made observable with a scanning electron microscope after etching with an Everson solution, were calculated by counting the number of dislocations per unit surface area, hence the term etch pit density (EPD). We were able to decrease EPD values by one order of magnitude after annealing. For example, the best EPD value after a 20-min annealing at 400°C was ˜ 2 × 107 cm-2 for a 1.63-μm CdTe thin film which was about 9.5 × 107 cm-2 before annealing. We also employed Raman scattering measurements to see the changes in the structural quality of the samples. From the Raman measurements, we were able to see improvements in the quality of our samples from the annealing by studying the ratio of 2LO/LO phonon mode Raman intensities. We also observed a clear decrease in the intensity of Te precipitations-related modes, indicating a decrease in the size and number of these precipitations.

Modelling Of Chlorine Inductive Discharges

NASA Astrophysics Data System (ADS)

Chabert P.; Despiau-Pujo, E.

2010-07-01

III-V compounds such as GaAs, InP or GaN-based materials are increasingly important for their use in optoelectronic applications, especially in the telecommunications and light detection industries. Photonic devices including lasers, photodetectors or LEDs, require reliable etching processes characterized by high etch rate, profile control and low damage. Although many problems remain to be understood, inductively coupled discharges seem to be promising to etch such materials, using Cl2/Ar, Cl2/N2 and Cl2/H2 gas chemistries. Inductively coupled plasma (ICP) sources meet most of the requirements for efficient plasma processing such as high etch rates, high ion densities and low controllable ion energies. However, the presence of a negative ion population in the plasma alters the positive ion flux, reduces the electron density, changes the electron temperature, modifies the spatial structure of the discharge and can cause unstable operation. Several experimental studies and numerical simulation results have been published on inductively coupled Cl2/Ar plasmas but relatively few systematic comparisons of model predictions and experimental data have been reported in given reactor geometries under a wide range of op- erating conditions. Validation of numerical predictions is essential for chemically complex plasma processing and there is a need to benchmark the models with as many measurements as possible. In this paper, comparisons of 2D fluid simulations with experimental measurements of Ar/Cl2 plasmas in a low pressure ICP reactor are reported (Corr et al. 2008). The electron density, negative ion fraction and Cl atom density are investigated for various conditions of Ar/Cl2 ratio, gas pressure and applied RF power in H mode. Simulations show that the wall recombination coefficient of Cl atom (?) is a key parameter of the model and that neutral densities are very sensitive to its variations. The best agreement between model and experiment is obtained for ? = 0.02, which is much lower than the value predicted for stainless steel walls (? = 0.6). This is consistent with reactor wall contaminations classi- cally observed in such discharges. The plasma electronegativity decreases with RF power and increases with Cl2 content. At high pressure, the power absorption and distribution of charged particles become more localized below the quartz window. Although the experi- mental trends are well reproduced by the model, the calculated charged particle densities are systematically overestimated by a factor of 3-5. The reasons for this discrepancy are discussed in the paper. Experimental studies have also shown that low-pressure inductive discharges operating with electronegative gases are subject to instabilities near the transition between capacitive (E) and inductive (H) modes. A global model, consisting of two particle balance equations and one energy balance equation, has been previously proposed to describe the instability mechanism in SF6/ArSF6 (Lieberman et al. 1999). This model, which agrees qualitatively well with experimental observations, leaves significant quantitative differences. In this work, this global model is revisited with Cl2 as the feedstock gas (Despiau-Pujo and Chabert 2009). An alternative treatment of the inductive power deposition is evaluated and chlorine chemistry is included. Old and new models are systematically compared. The alternative inductive coupling description slightly modifies the results. The effect of gas chemistry is even more pronounced. The instability window is smaller in pressure and larger in absorbed power, the frequency is higher and the amplitudes of oscillations are reduced. The feedstock gas is weakly dissociated (~16%) and Cl2+ is the dominant positive ion, which is consistent with the moderate electron density during the instability cycle.

Intrinsic Josephson junctions in mesas and ultrathin BSCCO single crystals: Ultimate control of shape and dimensions

NASA Astrophysics Data System (ADS)

Yurgens, A.; You, L. X.; Torstensson, M.; Winkler, D.

2007-09-01

We describe experiments which are only possible through an ultimate control of sample shape and dimensions down to nanometer scale whereby transport measurements can be done in various restricted geometries. We use photolithography patterning together with a flip-chip technique to isolate very thin (d ∼ 100 nm) pieces of Bi2Sr2CaCu2O8+δ (BSCCO) single crystals. Ar-ion milling allows us to further thin these crystals down to a few nanometers in a controlled way. With decreasing thickness below two to three unit cells, the superconducting transition temperature gradually decreases to zero and the in-plane resistivity increases to large values indicating the existence of a superconductor-insulator transition in these ultrathin single crystals. In a refined technique, a precise control of the etching depth from both sides of the crystal makes it possible to form stacks of intrinsic Josephson junctions (IJJs) inside the ultrathin single crystals. The stacks can be tailor-made to any microscopic height (0-9 nm < d), i.e. enclosing a specific number of IJJs (0-6). In certain geometries, by feeding current into the topmost Cu2O4-layer of a mesa on the surface of a BSCCO single crystal, we measured the critical value of this current by detecting a sharp upturn or break in the current-voltage characteristics. From this, we estimate the sheet critical current density of a single Cu2O4 plane to be ∼0.3-0.7 A/cm at 4.5 K, corresponding to a bulk current density of ∼2-5 MA/cm2. These values are among the largest ever reported for BSCCO single crystals, thin-films and tapes.

Chemical etching of stainless steel 301 for improving performance of electrochemical capacitors in aqueous electrolyte

NASA Astrophysics Data System (ADS)

Jeżowski, P.; Nowicki, M.; Grzeszkowiak, M.; Czajka, R.; Béguin, F.

2015-04-01

The main purpose of the study was to increase the surface roughness of stainless steel 301 current collectors by etching, in order to improve the electrochemical performance of electrical double-layer capacitors (EDLC) in 1 mol L-1 lithium sulphate electrolyte. Etching was realized in 1:3:30 (HNO3:HCl:H2O) solution with times varying up to 10 min. For the considered 15 μm thick foil and a mass loss around 0.4 wt.%, pitting was uniform, with diameter of pits ranging from 100 to 300 nm. Atomic force microscopy (AFM) showed an increase of average surface roughness (Ra) from 5 nm for the as-received stainless steel foil to 24 nm for the pitted material. Electrochemical impedance spectroscopy realized on EDLCs with coated electrodes either on as-received or pitted foil in 1 mol L-1 Li2SO4 gave equivalent distributed resistance (EDR) of 8 Ω and 2 Ω, respectively, demonstrating a substantial improvement of collector/electrode interface after pitting. Correlatively, the EDLCs with pitted collector displayed a better charge propagation and low ohmic losses even at relatively high current of 20 A g-1. Hence, chemical pitting of stainless steel current collectors is an appropriate method for optimising the performance of EDLCs in neutral aqueous electrolyte.

Method for surface treatment of a cadmium zinc telluride crystal

DOEpatents

James, R.; Burger, A.; Chen, K.T.; Chang, H.

1999-08-03

A method for treatment of the surface of a CdZnTe (CZT) crystal is disclosed that reduces surface roughness (increases surface planarity) and provides an oxide coating to reduce surface leakage currents and thereby, improve resolution. A two step process is disclosed, etching the surface of a CZT crystal with a solution of lactic acid and bromine in ethylene glycol, following the conventional bromine/methanol etch treatment, and after attachment of electrical contacts, oxidizing the CZT crystal surface. 3 figs.

Fabrication and Characterization of the US Army Research Laboratory Surface Enhanced Raman Scattering (SERS) Substrates

DTIC Science & Technology

2017-12-04

gap spacing.92,93 By running current through an EBL-fabricated gap array, it has been shown to be possible to impact atomic positions within a...Spectra were collected and the instrument was run using Wire 2.0 software operating on a dedicated computer. 2.5 Data Analysis Data analysis...accomplished using the Unaxis VLR 700 Etch PM3-Dieclectric etch. For this step it is important to first run the process on a dummy wafer to

Sensors and Micromachined Devices for the Automotive and New Markets: The Delphi Delco Electronics MEMS Story.

NASA Astrophysics Data System (ADS)

Logsdon, James

2002-03-01

This presentation will provide a brief history of the development of MEMS products and technology, beginning with the manifold absolute pressure sensor in the late seventies through the current variety of Delphi Delco Electronics sensors available today. The technology development of micromachining from uncompensated P plus etch stops to deep reactive ion etching and the technology development of wafer level packaging from electrostatic bonding to glass frit sealing and silicon to silicon direct bonding will be reviewed.

Decontamination of metals using chemical etching

DOEpatents

Lerch, Ronald E.; Partridge, Jerry A.

1980-01-01

The invention relates to chemical etching process for reclaiming contaminated equipment wherein a reduction-oxidation system is included in a solution of nitric acid to contact the metal to be decontaminated and effect reduction of the reduction-oxidation system, and includes disposing a pair of electrodes in the reduced solution to permit passage of an electrical current between said electrodes and effect oxidation of the reduction-oxidation system to thereby regenerate the solution and provide decontaminated equipment that is essentially radioactive contamination-free.

Effect of thermal aging on the tensile bond strength at reduced areas of seven current adhesives.

PubMed

Baracco, Bruno; Fuentes, M Victoria; Garrido, Miguel A; González-López, Santiago; Ceballos, Laura

2013-07-01

The purpose of this study was to determine the micro-tensile bond strength (MTBS) to dentin of seven adhesive systems (total and self-etch adhesives) after 24 h and 5,000 thermocycles. Dentin surfaces of human third molars were exposed and bonded with two total-etch adhesives (Adper Scotchbond 1 XT and XP Bond), two two-step self-etch adhesives (Adper Scotchbond SE and Filtek Silorane Adhesive System) and three one-step self-etch adhesives (G-Bond, Xeno V and Bond Force). All adhesive systems were applied following manufacturers' instructions. Composite buildups were constructed and the bonded teeth were then stored in water (24 h, 37 °C) or thermocycled (5,000 cycles) before being sectioned and submitted to MTBS test. Two-way ANOVA and subsequent comparison tests were applied at α = 0.05. Characteristic de-bonded specimens were analyzed using scanning electron microscopy (SEM). After 24 h water storage, MTBS values were highest with XP Bond, Adper Scotchbond 1 XT, Filtek Silorane Adhesive System and Adper Scotchbond SE and lowest with the one-step self-etch adhesives Bond Force, Xeno V and G-Bond. After thermocycling, MTBS values were highest with XP Bond, followed by Filtek Silorane Adhesive System, Adper Scotchbond SE and Adper Scotchbond 1 XT and lowest with the one-step self-etch adhesives Bond Force, Xeno V and G-Bond. Thermal aging induced a significant decrease in MTBS values with all adhesives tested. The resistance of resin-dentin bonds to thermal-aging degradation was material dependent. One-step self-etch adhesives obtained the lowest MTBS results after both aging treatments, and their adhesive capacity was significantly reduced after thermocycling.

Gratings for synchrotron and FEL beamlines: a project for the manufacture of ultra-precise gratings at Helmholtz Zentrum Berlin.

PubMed

Siewert, F; Löchel, B; Buchheim, J; Eggenstein, F; Firsov, A; Gwalt, G; Kutz, O; Lemke, St; Nelles, B; Rudolph, I; Schäfers, F; Seliger, T; Senf, F; Sokolov, A; Waberski, Ch; Wolf, J; Zeschke, T; Zizak, I; Follath, R; Arnold, T; Frost, F; Pietag, F; Erko, A

2018-01-01

Blazed gratings are of dedicated interest for the monochromatization of synchrotron radiation when a high photon flux is required, such as, for example, in resonant inelastic X-ray scattering experiments or when the use of laminar gratings is excluded due to too high flux densities and expected damage, for example at free-electron laser beamlines. Their availability became a bottleneck since the decommissioning of the grating manufacture facility at Carl Zeiss in Oberkochen. To resolve this situation a new technological laboratory was established at the Helmholtz Zentrum Berlin, including instrumentation from Carl Zeiss. Besides the upgraded ZEISS equipment, an advanced grating production line has been developed, including a new ultra-precise ruling machine, ion etching technology as well as laser interference lithography. While the old ZEISS ruling machine GTM-6 allows ruling for a grating length up to 170 mm, the new GTM-24 will have the capacity for 600 mm (24 inch) gratings with groove densities between 50 lines mm -1 and 1200 lines mm -1 . A new ion etching machine with a scanning radiofrequency excited ion beam (HF) source allows gratings to be etched into substrates of up to 500 mm length. For a final at-wavelength characterization, a new reflectometer at a new Optics beamline at the BESSY-II storage ring is under operation. This paper reports on the status of the grating fabrication, the measured quality of fabricated items by ex situ and in situ metrology, and future development goals.

Measurements and modeling of the impact of weak magnetic fields on the plasma properties of a planar slot antenna driven plasma source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yoshikawa, Jun, E-mail: jun.yoshikawa@tel.com; Susa, Yoshio; Ventzek, Peter L. G.

The radial line slot antenna plasma source is a type of surface wave plasma source driven by a planar slot antenna. Microwave power is transmitted through a slot antenna structure and dielectric window to a plasma characterized by a generation zone adjacent to the window and a diffusion zone that contacts a substrate. The diffusion zone is characterized by a very low electron temperature. This renders the source useful for soft etch applications and thin film deposition processes requiring low ion energy. Another property of the diffusion zone is that the plasma density tends to decrease from the axis tomore » the walls under the action of ambipolar diffusion at distances far from where the plasma is generated. A previous simulation study [Yoshikawa and. Ventzek, J. Vac. Sci. Technol. A 31, 031306 (2013)] predicted that the anisotropy in transport parameters due to weak static magnetic fields less than 50 G could be leveraged to manipulate the plasma profile in the radial direction. These simulations motivated experimental tests in which weak magnetic fields were applied to a radial line slot antenna source. Plasma absorption probe measurements of electron density and etch rate showed that the magnetic fields remote from the wafer were able to manipulate both parameters. A summary of these results is presented in this paper. Argon plasma simulation trends are compared with experimental plasma and etch rate measurements. A test of the impact of magnetic fields on charge up damage showed no perceptible negative effect.« less

High-density, microsphere-based fiber optic DNA microarrays.

PubMed

Epstein, Jason R; Leung, Amy P K; Lee, Kyong Hoon; Walt, David R

2003-05-01

A high-density fiber optic DNA microarray has been developed consisting of oligonucleotide-functionalized, 3.1-microm-diameter microspheres randomly distributed on the etched face of an imaging fiber bundle. The fiber bundles are comprised of 6000-50000 fused optical fibers and each fiber terminates with an etched well. The microwell array is capable of housing complementary-sized microspheres, each containing thousands of copies of a unique oligonucleotide probe sequence. The array fabrication process results in random microsphere placement. Determining the position of microspheres in the random array requires an optical encoding scheme. This array platform provides many advantages over other array formats. The microsphere-stock suspension concentration added to the etched fiber can be controlled to provide inherent sensor redundancy. Examining identical microspheres has a beneficial effect on the signal-to-noise ratio. As other sequences of interest are discovered, new microsphere sensing elements can be added to existing microsphere pools and new arrays can be fabricated incorporating the new sequences without altering the existing detection capabilities. These microarrays contain the smallest feature sizes (3 microm) of any DNA array, allowing interrogation of extremely small sample volumes. Reducing the feature size results in higher local target molecule concentrations, creating rapid and highly sensitive assays. The microsphere array platform is also flexible in its applications; research has included DNA-protein interaction profiles, microbial strain differentiation, and non-labeled target interrogation with molecular beacons. Fiber optic microsphere-based DNA microarrays have a simple fabrication protocol enabling their expansion into other applications, such as single cell-based assays.

Effect of enamel etching time on roughness and bond strength.

PubMed

Barkmeier, Wayne W; Erickson, Robert L; Kimmes, Nicole S; Latta, Mark A; Wilwerding, Terry M

2009-01-01

The current study examined the effect of different enamel conditioning times on surface roughness and bond strength using an etch-and-rinse system and four self-etch adhesives. Surface roughness (Ra) and composite to enamel shear bond strengths (SBS) were determined following the treatment of flat ground human enamel (4000 grit) with five adhesive systems: (1) Adper Single Bond Plus (SBP), (2) Adper Prompt L-Pop (PLP), (3) Clearfil SE Bond (CSE), (4) Clearfil S3 Bond (CS3) and (5) Xeno IV (X4), using recommended treatment times and an extended treatment time of 60 seconds (n = 10/group). Control groups were also included for Ra (4000 grit surface) and SBS (no enamel treatment and Adper Scotchbond Multi-Purpose Adhesive). For surface roughness measurements, the phosphoric acid conditioner of the SBP etch-and-rinse system was rinsed from the surface with an air-water spray, and the other four self-etch adhesive agents were removed with alternating rinses of water and acetone. A Proscan 2000 non-contact profilometer was used to determine Ra values. Composite (Z100) to enamel bond strengths (24 hours) were determined using Ultradent fixtures and they were debonded with a crosshead speed of 1 mm/minute. The data were analyzed with ANOVA and Fisher's LSD post-hoc test. The etch-and- rinse system (SBP) produced the highest Ra (microm) and SBS (MPa) using both the recommended treatment time (0.352 +/- 0.028 microm and 40.5 +/- 6.1 MPa) and the extended treatment time (0.733 +/- 0.122 microm and 44.2 +/- 8.2 MPa). The Ra and SBS of the etch-and-rinse system were significantly greater (p < 0.05) than all the self-etch systems and controls. Increasing the treatment time with phosphoric acid (SBP) and PLP produced greater surface roughness (p < 0.05) but did not result in significantly higher bond strengths (p > 0.05).

Infrared Photodiodes Made by Low Energy Ion Etching of Molecular Beam Epitaxy Grown Mercury-Cadmium Alloy

NASA Astrophysics Data System (ADS)

Yoo, Sung-Shik

Ion etching was used to form junctions on the p-type (111)B Hg_{1-x}Cd_ {x}Te grown by Molecular Beam Epitaxy(MBE). When Hg_{1-x}Cd_{x}Te layers are etched by Ar ions at energies ranging between 300 and 450eV, the top Hg_{1 -x}Cd_{x}Te layer is converted to n-type. The converted region is electrically characterized as a defective n^+-region near the surface, and a low doped n^--region exist below the damaged region. The total thickness of the converted n-type layer was found to be considerable. These results suggest that the creation of the n-type layer is due to the filling of mercury vacancies by mercury atoms displaced by the Ar ion irradiation on the surface. For the performance of the resulting photodiodes on MBE grown (111)B Hg_{1-x}Cd _{x}Te using this technique, the dynamic resistances at 80K are one order of magnitude less than those of junctions made on Liquid Phase Epitaxially and Bulk grown Hg_{1 -x}Cd_{x}Te. The ion etching technique was compared with ion implantation technique by fabricating diodes on the same MBE grown (111)B Hg _{1-x}Cd_{x}Te layers. The result of the comparison illustrates that ion etching technique is as good as ion implantation technique for the fabrication of Hg_{1-x}Cd _{x}Te photodiodes. Also it is believed that the performance of the diodes is limited by a relatively large density of twin defects usually found in MBE grown (111)B Hg_{1-x}Cd _{x}Te.

Towards graphane field emitters

PubMed Central

Ding, Shuyi; Li, Chi; Zhou, Yanhuai; Collins, Clare M.; Kang, Moon H.; Parmee, Richard J.; Zhang, Xiaobing; Milne, William I.; Wang, Baoping

2015-01-01

We report on the improved field emission performance of graphene foam (GF) following transient exposure to hydrogen plasma. The enhanced field emission mechanism associated with hydrogenation has been investigated using Fourier transform infrared spectroscopy, plasma spectrophotometry, Raman spectroscopy, and scanning electron microscopy. The observed enhanced electron emissionhas been attributed to an increase in the areal density of lattice defects and the formation of a partially hydrogenated, graphane-like material. The treated GF emitter demonstrated a much reduced macroscopic turn-on field (2.5 V μm–1), with an increased maximum current density from 0.21 mA cm–2 (pristine) to 8.27 mA cm–2 (treated). The treated GFs vertically orientated protrusions, after plasma etching, effectively increased the local electric field resulting in a 2.2-fold reduction in the turn-on electric field. The observed enhancement is further attributed to hydrogenation and the subsequent formation of a partially hydrogenated structured 2D material, which advantageously shifts the emitter work function. Alongside augmentation of the nominal crystallite size of the graphitic superstructure, surface bound species are believed to play a key role in the enhanced emission. The hydrogen plasma treatment was also noted to increase the emission spatial uniformity, with an approximate four times reduction in the per unit area variation in emission current density. Our findings suggest that plasma treatments, and particularly hydrogen and hydrogen-containing precursors, may provide an efficient, simple, and low cost means of realizing enhanced nanocarbon-based field emission devices via the engineered degradation of the nascent lattice, and adjustment of the surface work function. PMID:28066543

Vertical nanowire heterojunction devices based on a clean Si/Ge interface.

PubMed

Chen, Lin; Fung, Wayne Y; Lu, Wei

2013-01-01

Different vertical nanowire heterojunction devices were fabricated and tested based on vertical Ge nanowires grown epitaxially at low temperatures on (111) Si substrates with a sharp and clean Si/Ge interface. The nearly ideal Si/Ge heterojuctions with controlled and abrupt doping profiles were verified through material analysis and electrical characterizations. In the nSi/pGe heterojunction diode, an ideality factor of 1.16, subpicoampere reverse saturation current, and rectifying ratio of 10(6) were obtained, while the n+Si/p+Ge structure leads to Esaki tunnel diodes with a high peak tunneling current of 4.57 kA/cm(2) and negative differential resistance at room temperature. The large valence band discontinuity between the Ge and Si in the nanowire heterojunctions was further verified in the p+Si/pGe structure, which shows a rectifying behavior instead of an Ohmic contact and raises an important issue in making Ohmic contacts to heterogeneously integrated materials. A raised Si/Ge structure was further developed using a self-aligned etch process, allowing greater freedom in device design for applications such as the tunneling field-effect transistor (TFET). All measurement data can be well-explained and fitted with theoretical models with known bulk properties, suggesting that the Si/Ge nanowire system offers a very clean heterojunction interface with low defect density, and holds great potential as a platform for future high-density and high-performance electronics.

High-density fiber-optic DNA random microsphere array.

PubMed

Ferguson, J A; Steemers, F J; Walt, D R

2000-11-15

A high-density fiber-optic DNA microarray sensor was developed to monitor multiple DNA sequences in parallel. Microarrays were prepared by randomly distributing DNA probe-functionalized 3.1-microm-diameter microspheres in an array of wells etched in a 500-microm-diameter optical imaging fiber. Registration of the microspheres was performed using an optical encoding scheme and a custom-built imaging system. Hybridization was visualized using fluorescent-labeled DNA targets with a detection limit of 10 fM. Hybridization times of seconds are required for nanomolar target concentrations, and analysis is performed in minutes.

Two new methods to increase the contrast of track-etch neutron radiographs

NASA Technical Reports Server (NTRS)

Morley, J.

1971-01-01

Methods for increasing the (optical density span) of radiographs were evaluated. In one method, fluorescent dye was deposited in the tracks of the radiograph. The radiograph was then examined under ultraviolet light. The second method was a crossed Polaroid filter technique. The radiograph was placed between the filters and then illuminated with a diffuse white-light source. An increase in the optical density span from .10 to .37 was obtained with the dye method. With the Polaroid method, the increase obtained was from .10 to 2.4.

Interface Lattice Engineering of Si Composite Wafers for Large-Format HgCdTe Infrared Focal Plane Arrays

DTIC Science & Technology

2012-08-07

sealed quartz ampoule under a mercury overpressure in a conventional clam-shell furnace . The reduction in the dislocation density has been studied as...46 2.6.4 Etch Pit Characterization . . . . . . . . . . . . . . . . . . . . . . . . 46 5 3 Furnace Setup and Calibration...Setup . . . . . . . . . . . . . . . . . . . . . . . 54 3.1.2 Furnace Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 4 In Situ

Unique method for controlling device level overlay with high-NA optical overlay technique using YieldStar in a DRAM HVM environment

NASA Astrophysics Data System (ADS)

Park, Dong-Kiu; Kim, Hyun-Sok; Seo, Moo-Young; Ju, Jae-Wuk; Kim, Young-Sik; Shahrjerdy, Mir; van Leest, Arno; Soco, Aileen; Miceli, Giacomo; Massier, Jennifer; McNamara, Elliott; Hinnen, Paul; Böcker, Paul; Oh, Nang-Lyeom; Jung, Sang-Hoon; Chai, Yvon; Lee, Jun-Hyung

2018-03-01

This paper demonstrates the improvement using the YieldStar S-1250D small spot, high-NA, after-etch overlay in-device measurements in a DRAM HVM environment. It will be demonstrated that In-device metrology (IDM) captures after-etch device fingerprints more accurately compared to the industry-standard CDSEM. Also, IDM measurements (acquiring both CD and overlay) can be executed significantly faster increasing the wafer sampling density that is possible within a realistic metrology budget. The improvements to both speed and accuracy open the possibility of extended modeling and correction capabilities for control. The proof-book data of this paper shows a 36% improvement of device overlay after switching to control in a DRAM HVM environment using indevice metrology.

Platinum-Based Nanocages with Subnanometer-Thick Walls and Well-Defined Facets

DOE PAGES

Zhang, Lei; Wang, Xue; Chi, Miaofang; ...

2015-07-24

A cost-effective catalyst should have a high dispersion of the active atoms, together with a controllable surface structure for the optimization of activity, selectivity, or both. We fabricated nanocages by depositing a few atomic layers of platinum (Pt) as conformal shells on palladium (Pd) nanocrystals with well-defined facets and then etching away the Pd templates. Density functional theory calculations suggest that the etching is initiated via a mechanism that involves the formation of vacancies through the removal of Pd atoms incorporated into the outermost layer during the deposition of Pt. With the use of Pd nanoscale cubes and octahedra asmore » templates, we obtained Pt cubic and octahedral nanocages enclosed by {100} and {111} facets, respectively, which exhibited distinctive catalytic activities toward oxygen reduction.« less

Optical waveguiding properties into porous gallium nitride structures investigated by prism coupling technique

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alshehri, Bandar; Dogheche, Elhadj, E-mail: elhadj.dogheche@univ-valenciennes.fr; Lee, Seung-Min

2014-08-04

In order to modulate the refractive index and the birefringence of Gallium Nitride (GaN), we have developed a chemical etching method to perform porous structures. The aim of this research is to demonstrate that optical properties of GaN can be tuned by controlling the pores density. GaN films are prepared on sapphire by metal organic chemical vapor deposition and the microstructure is characterized by transmission electron microscopy, and scanning electron microscope analysis. Optical waveguide experiment is demonstrated here to determine the key properties as the ordinary (n{sub 0}) and extraordinary (n{sub e}) refractive indices of etched structures. We report heremore » the dispersion of refractive index for porous GaN and compare it to the bulk material. We observe that the refractive index decreases when the porous density p is increased: results obtained at 0.975 μm have shown that the ordinary index n{sub 0} is 2.293 for a bulk layer and n{sub 0} is 2.285 for a pores density of 20%. This value corresponds to GaN layer with a pore size of 30 nm and inter-distance of 100 nm. The control of the refractive index into GaN is therefore fundamental for the design of active and passive optical devices.« less

Correlation of film density and wet etch rate in hydrofluoric acid of plasma enhanced atomic layer deposited silicon nitride

DOE Office of Scientific and Technical Information (OSTI.GOV)

Provine, J., E-mail: jprovine@stanford.edu; Schindler, Peter; Kim, Yongmin

2016-06-15

The continued scaling in transistors and memory elements has necessitated the development of atomic layer deposition (ALD) of silicon nitride (SiN{sub x}), particularly for use a low k dielectric spacer. One of the key material properties needed for SiN{sub x} films is a low wet etch rate (WER) in hydrofluoric (HF) acid. In this work, we report on the evaluation of multiple precursors for plasma enhanced atomic layer deposition (PEALD) of SiN{sub x} and evaluate the film’s WER in 100:1 dilutions of HF in H{sub 2}O. The remote plasma capability available in PEALD, enabled controlling the density of the SiN{submore » x} film. Namely, prolonged plasma exposure made films denser which corresponded to lower WER in a systematic fashion. We determined that there is a strong correlation between WER and the density of the film that extends across multiple precursors, PEALD reactors, and a variety of process conditions. Limiting all steps in the deposition to a maximum temperature of 350 °C, it was shown to be possible to achieve a WER in PEALD SiN{sub x} of 6.1 Å/min, which is similar to WER of SiN{sub x} from LPCVD reactions at 850 °C.« less

Design of a micro-Wankel rotary engine for MEMS fabrication

NASA Astrophysics Data System (ADS)

Jiang, Kyle C.; Prewett, Philip D.; Ward, M. C. L.; Tian, Y.; Yang, H.

2001-04-01

This paper presents the design of a micro Wankel engine for deep etching micro fabrication. The micro engine design is part of a research program in progress to develop a micro actuator to supply torque for driving micro machines. To begin with, the research work concentrates on the micro Wankel engine powered by liquid CO2. Then, a Wankel internal combustion engines will be investigated. The Wankel engine is a planetary rotation engine. It is selected because of its largely 2D structure which is suitable for lithographic processes. The engine has been simplified and redesigned to suit the fabrication processes. In particular, the fuel inlet has been moved to the top cover of the housing from the side, and the outlet is made as a groove on the housing, so that the both parts can be etched. A synchronization valve is mounted on the engine to control the supply of CO2. One of advantages of the micro engines is their high energy density compared with batteries. A research study has been conducted in comparing energy densities of commonly used fuels. It shows that the energy densities of fuels for combustion engines are 10 - 30 times higher than that of batteries. The deigns of the micro Wankel engines have been tested for verification by finite element analysis, CAD assembly, and construction of a prototype, which proves the design is valid.

Prediction of plasma-induced damage distribution during silicon nitride etching using advanced three-dimensional voxel model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuboi, Nobuyuki, E-mail: Nobuyuki.Kuboi@jp.sony.com; Tatsumi, Tetsuya; Kinoshita, Takashi

2015-11-15

The authors modeled SiN film etching with hydrofluorocarbon (CH{sub x}F{sub y}/Ar/O{sub 2}) plasma considering physical (ion bombardment) and chemical reactions in detail, including the reactivity of radicals (C, F, O, N, and H), the area ratio of Si dangling bonds, the outflux of N and H, the dependence of the H/N ratio on the polymer layer, and generation of by-products (HCN, C{sub 2}N{sub 2}, NH, HF, OH, and CH, in addition to CO, CF{sub 2}, SiF{sub 2}, and SiF{sub 4}) as ion assistance process parameters for the first time. The model was consistent with the measured C-F polymer layer thickness,more » etch rate, and selectivity dependence on process variation for SiN, SiO{sub 2}, and Si film etching. To analyze the three-dimensional (3D) damage distribution affected by the etched profile, the authors developed an advanced 3D voxel model that can predict the time-evolution of the etched profile and damage distribution. The model includes some new concepts for gas transportation in the pattern using a fluid model and the property of voxels called “smart voxels,” which contain details of the history of the etching situation. Using this 3D model, the authors demonstrated metal–oxide–semiconductor field-effect transistor SiN side-wall etching that consisted of the main-etch step with CF{sub 4}/Ar/O{sub 2} plasma and an over-etch step with CH{sub 3}F/Ar/O{sub 2} plasma under the assumption of a realistic process and pattern size. A large amount of Si damage induced by irradiated hydrogen occurred in the source/drain region, a Si recess depth of 5 nm was generated, and the dislocated Si was distributed in a 10 nm deeper region than the Si recess, which was consistent with experimental data for a capacitively coupled plasma. An especially large amount of Si damage was also found at the bottom edge region of the metal–oxide–semiconductor field-effect transistors. Furthermore, our simulation results for bulk fin-type field-effect transistor side-wall etching showed that the Si fin (source/drain region) was directly damaged by high energy hydrogen and had local variations in the damage distribution, which may lead to a shift in the threshold voltage and the off-state leakage current. Therefore, side-wall etching and ion implantation processes must be carefully designed by considering the Si damage distribution to achieve low damage and high transistor performance for complementary metal–oxide–semiconductor devices.« less

Nanopore arrays in a silicon membrane for parallel single-molecule detection: fabrication

NASA Astrophysics Data System (ADS)

Schmidt, Torsten; Zhang, Miao; Sychugov, Ilya; Roxhed, Niclas; Linnros, Jan

2015-08-01

Solid state nanopores enable translocation and detection of single bio-molecules such as DNA in buffer solutions. Here, sub-10 nm nanopore arrays in silicon membranes were fabricated by using electron-beam lithography to define etch pits and by using a subsequent electrochemical etching step. This approach effectively decouples positioning of the pores and the control of their size, where the pore size essentially results from the anodizing current and time in the etching cell. Nanopores with diameters as small as 7 nm, fully penetrating 300 nm thick membranes, were obtained. The presented fabrication scheme to form large arrays of nanopores is attractive for parallel bio-molecule sensing and DNA sequencing using optical techniques. In particular the signal-to-noise ratio is improved compared to other alternatives such as nitride membranes suffering from a high-luminescence background.

Nanopore arrays in a silicon membrane for parallel single-molecule detection: fabrication.

PubMed

Schmidt, Torsten; Zhang, Miao; Sychugov, Ilya; Roxhed, Niclas; Linnros, Jan

2015-08-07

Solid state nanopores enable translocation and detection of single bio-molecules such as DNA in buffer solutions. Here, sub-10 nm nanopore arrays in silicon membranes were fabricated by using electron-beam lithography to define etch pits and by using a subsequent electrochemical etching step. This approach effectively decouples positioning of the pores and the control of their size, where the pore size essentially results from the anodizing current and time in the etching cell. Nanopores with diameters as small as 7 nm, fully penetrating 300 nm thick membranes, were obtained. The presented fabrication scheme to form large arrays of nanopores is attractive for parallel bio-molecule sensing and DNA sequencing using optical techniques. In particular the signal-to-noise ratio is improved compared to other alternatives such as nitride membranes suffering from a high-luminescence background.

Corrosion of 2205 Duplex Stainless Steel Weldment in Chloride Medium Containing Sulfate-Reducing Bacteria

NASA Astrophysics Data System (ADS)

Antony, P. J.; Singh Raman, R. K.; Kumar, Pradeep; Raman, R.

2008-11-01

Influence of changes in microstructure caused due to welding on microbiologically influenced corrosion of a duplex stainless steel was studied by exposing the weldment and parent metal to chloride medium containing sulfate-reducing bacteria (SRB). Identically prepared coupons (same area and surface finish) exposed to sterile medium were used as the control. Etching-type attack was observed in the presence of SRB, which was predominant in the heat-affected zone (HAZ) of the weldment. The anodic polarization studies indicated an increase in current density for coupon exposed to SRB-containing medium as compared to that obtained for coupon exposed to sterile medium. The scanning electron microscopy (SEM) observations after anodic polarization revealed that the attack was preferentially in the ferrite phase of HAZ of the weldment, whereas it was restricted to the austenite phase of the parent metal.

Ge nanopillar solar cells epitaxially grown by metalorganic chemical vapor deposition

PubMed Central

Kim, Youngjo; Lam, Nguyen Dinh; Kim, Kangho; Park, Won-Kyu; Lee, Jaejin

2017-01-01

Radial junction solar cells with vertically aligned wire arrays have been widely studied to improve the power conversion efficiency. In this work, we report the first Ge nanopillar solar cell. Nanopillar arrays are selectively patterned on p-type Ge (100) substrates using nanosphere lithography and deep reactive ion etching processes. Nanoscale radial and planar junctions are realized by an n-type Ge emitter layer which is epitaxially grown by MOCVD using isobutylgermane. In situ epitaxial surface passivation is employed using an InGaP layer to avoid high surface recombination rates and Fermi level pinning. High quality n-ohmic contact is realized by protecting the top contact area during the nanopillar patterning. The short circuit current density and the power conversion efficiency of the Ge nanopillar solar cell are demonstrated to be improved up to 18 and 30%, respectively, compared to those of the Ge solar cell with a planar surface. PMID:28209964

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rahmani, N.; Dariani, R. S., E-mail: dariani@alzahra.ac.ir

Porous silicon films with porosity ranging from 42% to 77% were fabricated by electrochemical anodization under different current density. We used atomic force microscopy and dynamic scaling theory for deriving the surface roughness profile and processing the topography of the porous silicon layers, respectively. We first compared the topography of bare silicon surface with porous silicon and then studied the effect of the porosity of porous silicon films on their scaling behavior by using their self-affinity nature. Our work demonstrated that silicon compared to the porous silicon films has the highest Hurst parameter, indicating that the formation of porous layermore » due to the anodization etching of silicon surface leads to an increase of its roughness. Fractal analysis revealed that the evolution of the nanocrystallites’ fractal dimension along with porosity. Also, we found that both interface width and Hurst parameter are affected by the increase of porosity.« less

Light-Trapping Characteristics of Ag Nanoparticles for Enhancing the Energy Conversion Efficiency of Hybrid Solar Cells.

PubMed

Fan, Zhiqiang; Zhang, Weijia; Ma, Qiang; Yan, Lanqin; Xu, Lihua; Fu, Yaolong

2017-10-18

In this paper, we investigated the optical and electrical characteristics of hybrid solar cells using silicon pyramid/Ag nanoparticle and nanowire/Ag nanoparticle nanocomposite structures, which are obtained by the Ag-assisted electroless etching method. We introduced the application of the physical and chemical properties of Ag nanoparticles on four kinds of solar cells: silicon pyramid, silicon pyramid/PEDOT:PSS, silicon nanowire, and silicon nanowire/PEDOT:PSS. We simulated the absorption of these structures for different parameters. Furthermore, we also show the result of the current density-voltage (J-V) characterization of the sample with Ag nanoparticles, which exhibits an improvement of the power conversion efficiency (PCE) in contrast to the samples without Ag nanoparticles. It was found that the properties of light-trapping of Ag nanoparticles have a prominent impact on improving the PCE of hybrid solar cells.

WSi2/Si multilayer sectioning by reactive ion etching for multilayer Laue lens fabrication

NASA Astrophysics Data System (ADS)

Bouet, N.; Conley, R.; Biancarosa, J.; Divan, R.; Macrander, A. T.

2010-09-01

Reactive ion etching (RIE) has been employed in a wide range of fields such as semiconductor fabrication, MEMS (microelectromechanical systems), and refractive x-ray optics with a large investment put towards the development of deep RIE. Due to the intrinsic differing chemistries related to reactivity, ion bombardment, and passivation of materials, the development of recipes for new materials or material systems can require intense effort and resources. For silicon in particular, methods have been developed to provide reliable anisotropic profiles with good dimensional control and high aspect ratios1,2,3, high etch rates, and excellent material to mask etch selectivity. A multilayer Laue lens4 is an x-ray focusing optic, which is produced by depositing many layers of two materials with differing electron density in a particular stacking sequence where the each layer in the stack satisfies the Fresnel zone plate law. When this stack is sectioned to allow side-illumination with radiation, the diffracted exiting radiation will constructively interfere at the focal point. Since the first MLLs were developed at Argonne in the USA in 20064, there have been published reports of MLL development efforts in Japan5, and, very recently, also in Germany6. The traditional technique for sectioning multilayer Laue lens (MLL) involves mechanical sectioning and polishing7, which is labor intensive and can induce delamination or structure damage and thereby reduce yield. If a non-mechanical technique can be used to section MLL, it may be possible to greatly shorten the fabrication cycle, create more usable optics from the same amount of deposition substrate, and perhaps develop more advanced structures to provide greater stability or flexibility. Plasma etching of high aspect-ratio multilayer structures will also expand the scope for other types of optics fabrication (such as gratings, zone plates, and so-on). However, well-performing reactive ion etching recipes have been developed for only a small number of materials, and even less recipes exist for concurrent etching of more than one element so a fully material specific process needs to be developed. In this paper, sectioning of WSi2/Si multilayers for MLL fabrication using fluorinated gases is investigated. The main goals were to demonstrate the feasibility of this technique, achievement of high anisotropy, adequate sidewall roughness control and high etching rates. We note that this development for MLL sidewalls should be distinguished from work on improving aspect ratios in traditional Fresnel zone plates. Aspect ratios for MLL sidewalls are not similarly constrained.

Examination of the laser-induced variations in the chemical etch rate of a photosensitive glass ceramic

NASA Astrophysics Data System (ADS)

Voges, Melanie; Beversdorff, Manfred; Willert, Chris; Krain, Hartmut

2007-10-01

Previous studies in our laboratory have reported that the chemical etch rate of a commercial photosensitive glass ceramic (FoturanTM, Schott Corp., Germany) in dilute hydrofluoric acid is strongly dependent on the incident laser irradiance during patterning at λ=266 nm and λ=355 nm. To help elucidate the underlying chemical and physical processes associated with the laser-induced variations in the chemical etch rate, several complimentary techniques were employed at various stages of the UV laser exposure and thermal treatment. X-ray diffraction (XRD) was used to identify the crystalline phases that are formed in Foturan following laser irradiation and annealing, and monitor the crystalline content as a function of laser irradiance at λ=266 nm and λ=355 nm. The XRD results indicate the nucleation of lithium metasilicate (Li2SiO3) crystals as the exclusive phase following laser irradiation and thermal treatment at temperatures not exceeding 605 °C. The XRD studies also show that the Li2SiO3 density increases with increasing laser irradiance and saturates at high laser irradiance. For our thermal treatment protocol, the average Li2SiO3 crystal diameters are 117.0±10.0 nm and 91.2±5.8 nm for λ=266 nm and λ=355 nm, respectively. Transmission electron microscopy (TEM) was utilized to examine the microscopic structural features of the lithium metasilicate crystals. The TEM results reveal that the growth of lithium metasilicate crystals proceeds dendritically, and produces Li2SiO3 crystals that are ˜700 1000 nm in length for saturation exposures. Optical transmission spectroscopy (OTS) was used to study the growth of metallic silver clusters that act as nucleation sites for the Li2SiO3 crystalline phase. The OTS results show that the (Ag0)x cluster concentration has a dependence on incident laser irradiance that is similar to the etch rate ratios and Li2SiO3 concentration. A comparison between the XRD and optical transmission results and our prior etch rate results show that the etch rate contrast and absolute etch rates are dictated by the Li2SiO3 concentration, which is in turn governed by the (Ag0)x cluster concentration. These results characterize the relationship between the laser exposure and chemical etch rate for Foturan, and permit a more detailed understanding of the photophysical processes that occur in the general class of photostructurable glass ceramic materials. Consequently, these results may also influence the laser processing of other photoactive materials.

Pinch-off mechanism in double-lateral-gate junctionless transistors fabricated by scanning probe microscope based lithography

PubMed Central

Dehzangi, Arash; Abedini, Alam; Abdullah, Ahmad Makarimi; Saion, Elias; Hutagalung, Sabar D; Hamidon, Mohd N; Hassan, Jumiah

2012-01-01

Summary A double-lateral-gate p-type junctionless transistor is fabricated on a low-doped (1015) silicon-on-insulator wafer by a lithography technique based on scanning probe microscopy and two steps of wet chemical etching. The experimental transfer characteristics are obtained and compared with the numerical characteristics of the device. The simulation results are used to investigate the pinch-off mechanism, from the flat band to the off state. The study is based on the variation of the carrier density and the electric-field components. The device is a pinch-off transistor, which is normally in the on state and is driven into the off state by the application of a positive gate voltage. We demonstrate that the depletion starts from the bottom corner of the channel facing the gates and expands toward the center and top of the channel. Redistribution of the carriers due to the electric field emanating from the gates creates an electric field perpendicular to the current, toward the bottom of the channel, which provides the electrostatic squeezing of the current. PMID:23365794

Pulsed operation of (Al,Ga,In)N blue laser diodes

NASA Astrophysics Data System (ADS)

Abare, Amber C.; Mack, Michael P.; Hansen, Mark W.; Sink, R. K.; Kozodoy, Peter; Keller, Sarah L.; Hu, Evelyn L.; Speck, James S.; Bowers, John E.; Mishra, Umesh K.; Coldren, Larry A.; DenBaars, Steven P.

1998-04-01

Room temperature (RT) pulsed operation of blue (420 nm) nitride based multi-quantum well (MQW) laser diodes grown on a-plane and c-plane sapphire substrates has been demonstrated. A combination of atmospheric and low pressure metal organic chemical vapor deposition (MOCVD) using a modified two-flow horizontal reactor was employed. The emission is strongly TE polarized and has a sharp transition in the far field pattern above threshold. Threshold current densities as low as 12.6 kA/cm2 were observed for 10 X 1200 micrometer lasers with uncoated reactive ion etched (RIE) facets on c-plane sapphire. Cleaved facet lasers were also demonstrated with similar performance on a-plane sapphire. Differential efficiencies as high as 7% and output powers up to 77 mW were observed. Laser diodes tested under pulsed conditions operated up to 6 hours at room temperature. Performance was limited by resistive heating during the electrical pulses. Lasing was achieved up to 95 degrees Celsius and up to a 150 ns pulse length (RT). Threshold current increased with temperature with a characteristic temperature, T0, of 125 K.

Ion-Exchange-Induced Selective Etching for the Synthesis of Amino-Functionalized Hollow Mesoporous Silica for Elevated-High-Temperature Fuel Cells.

PubMed

Zhang, Jin; Liu, Jian; Lu, Shanfu; Zhu, Haijin; Aili, David; De Marco, Roland; Xiang, Yan; Forsyth, Maria; Li, Qingfeng; Jiang, San Ping

2017-09-20

As differentiated from conventional synthetic processes, amino-functionalized hollow mesoporous silica (NH 2 -HMS) has been synthesized using a new and facile strategy of ion-exchange-induced selective etching of amino-functionalized mesoporous silica (NH 2 -meso-silica) by an alkaline solution. Nuclear magnetic resonance (NMR) spectroscopy and in situ time-resolved small-angle X-ray scattering (SAXS) reveal that ion-exchange-induced selective etching arises from the gradient distribution of OH - in the NH 2 -meso-silica nanospheres. Moreover, the ion-exchange-induced selective etching mechanism is verified through a successful synthesis of hollow mesoporous silica. After infiltration with phosphotungstic acid (PWA), PWA-NH 2 -HMS nanoparticles are dispersed in the poly(ether sulfone)-polyvinylpyrrolidone (PES-PVP) matrix, forming a hybrid PWA-NH 2 -HMS/PES-PVP nanocomposite membrane. The resultant nanocomposite membrane with an optimum loading of 10 wt % of PWA-NH 2 -HMS showed an enhanced proton conductivity of 0.175 S cm -1 and peak power density of 420 mW cm -2 at 180 °C under anhydrous conditions. Excellent durability of the hybrid composite membrane fuel cell has been demonstrated at 200 °C. The results of this study demonstrated the potential of the facile synthetic strategy in the fabrication of NH 2 -HMS with controlled mesoporous structure for application in nanocomposite membranes as a technology platform for elevated-temperature proton exchange membrane fuel cells.

Microleakage in Class V cavities with self-etching adhesive system and conventional rotatory or laser Er,Cr:YSGG

PubMed Central

Arnabat, J; España-Tost, T

2012-01-01

Objective: To analyse microleakage in Class V cavity preparation with Er;Cr:YSGG at different parameters using a self-etching adhesive system. Background: Several studies reported microleakage around composite restorations when cavity preparation is done or treated by Er;Cr:YSGG laser. We want to compare different energy densities in order to obtain the best parameters, when using a self-etching adhesive system. Methods: A class V preparations was performed in 120 samples of human teeth were divided in 3 groups: (1) Preparation using the burr. (2) Er;Cr:YSGG laser preparation with high energy 4W, 30 Hz, 50% Water 50% Air and (3) Er;Cr:YSGG laser preparation lower energy 1.5 W, 30 Hz, 30% Water 30% Air. All the samples were restored with self-etching adhesive system and hybrid composite. Thermocycling (5000 cycles) and immersed in 0.5% fuchsin. The restorations were sectioned and evaluated the microleakage with a stereomicroscope. Results: Lower energy laser used for preparation showed significant differences in enamel and dentin. To group 3, the microleakage in the enamel was less, whilst the group 1, treated with the turbine, showed less microleakage at dentin level. Group 2 showed the highest microleakage at dentin/cement level. Conclusion: Burr preparation gives the lowest microleakage at cement/dentin level, whilst Er;Cr:YSGG laser at lower power has the low energy obtains lowest microleakage at enamel. On the contrary high-energy settings produce inferior results in terms of microleakage. PMID:24511195

Crystal growth and dislocation etch pits observation of chalcopyrite CdSiP2

NASA Astrophysics Data System (ADS)

He, Zhiyu; Zhao, Beijun; Zhu, Shifu; Chen, Baojun; Huang, Wei; Lin, Li; Feng, Bo

2018-01-01

CdSiP2 is the only crystal that can offer Non-critical Phase Matching (NCPM) for a 1064 nm pumped optical parametric oscillation (OPO) with idler output in the 6 μm range. In this paper, a large, crack-free CdSiP2 single crystal measuring 18 mm in diameter and 65 mm in length was successfully grown by the Vertical Bridgman method (MVB) with an explosion-proof quartz ampoule. The results of lattice parameters, element composition and IR transmittance of the as-grown crystal characterized by X-ray diffraction (XRD), energy dispersive X-ray spectrometer (EDS) and Fourier transformation infrared spectrometer (FTIR) showed the as grown crystal crystallized well and the absorption coefficients at 4878 cm-1 and 2500 cm-1 were 0.14 cm-1 and 0.06 cm-1. Moreover, a new etchant composed of Br2, HCl, HNO3, CH3OH and H2O (1:800:800:400:400 in volume ratio) was prepared and the dislocation etch pits on oriented faces of as-grown CdSiP2 crystal were observed for the first time. It is found the etch pits are in rectangular structure on the (1 0 1) face, but in trigonal pyramid structure on (3 1 2) face. According to the quantities of the etch pits, the average densities of dislocation were evaluated to be 2.28 × 105/cm2 and 1.4 × 105/cm2, respectively.

Ionizing Radiation Detector

DOEpatents

Wright, Gomez W.; James, Ralph B.; Burger, Arnold; Chinn, Douglas A.

2003-11-18

A CdZnTe (CZT) crystal provided with a native CdO dielectric coating to reduce surface leakage currents and thereby, improve the resolution of instruments incorporating detectors using CZT crystals is disclosed. A two step process is provided for forming the dielectric coating which includes etching the surface of a CZT crystal with a solution of the conventional bromine/methanol etch treatment, and passivating the CZT crystal surface with a solution of 10 w/o NH.sub.4 F and 10 w/o H.sub.2 O.sub.2 in water after attaching electrical contacts to the crystal surface.

Surface Treatment And Protection Method For Cadium Zinc Telluride Crystals

DOEpatents

Wright, Gomez W.; James, Ralph B.; Burger, Arnold; Chinn, Douglas A.

2006-02-21

A method for treatment of the surface of a CdZnTe (CZT) crystal that provides a native dielectric coating to reduce surface leakage currents and thereby, improve the resolution of instruments incorporating detectors using CZT crystals. A two step process is disclosed, etching the surface of a CZT crystal with a solution of the conventional bromine/methanol etch treatment, and after attachment of electrical contacts, passivating the CZT crystal surface with a solution of 10 w/o NH4F and 10 w/o H2O2 in water.

Vertically p-n-junctioned GaN nano-wire array diode fabricated on Si(111) using MOCVD.

PubMed

Park, Ji-Hyeon; Kim, Min-Hee; Kissinger, Suthan; Lee, Cheul-Ro

2013-04-07

We demonstrate the fabrication of n-GaN:Si/p-GaN:Mg nanowire arrays on (111) silicon substrate by metal organic chemical vapor deposition (MOCVD) method .The nanowires were grown by a newly developed two-step growth process. The diameter of as-grown nanowires ranges from 300-400 nm with a density of 6-7 × 10(7) cm(-2). The p- and n-type doping of the nanowires is achieved with Mg and Si dopant species. Structural characterization by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) indicates that the nanowires are relatively defect-free. The room-temperature photoluminescence emission with a strong peak at 370 nm indicates that the n-GaN:Si/p-GaN:Mg nanowire arrays have potential application in light-emitting nanodevices. The cathodoluminscence (CL) spectrum clearly shows a distinct optical transition of GaN nanodiodes. The nano-n-GaN:Si/p-GaN:Mg diodes were further completed using a sputter coating approach to deposit Au/Ni metal contacts. The polysilazane filler has been etched by a wet chemical etching process. The n-GaN:Si/p-GaN:Mg nanowire diode was fabricated for different Mg source flow rates. The current-voltage (I-V) measurements reveal excellent rectifying properties with an obvious turn-on voltage at 1.6 V for a Mg flow rate of 5 sccm (standard cubic centimeters per minute).

Vertically p-n-junctioned GaN nano-wire array diode fabricated on Si(111) using MOCVD

NASA Astrophysics Data System (ADS)

Park, Ji-Hyeon; Kim, Min-Hee; Kissinger, Suthan; Lee, Cheul-Ro

2013-03-01

We demonstrate the fabrication of n-GaN:Si/p-GaN:Mg nanowire arrays on (111) silicon substrate by metal organic chemical vapor deposition (MOCVD) method .The nanowires were grown by a newly developed two-step growth process. The diameter of as-grown nanowires ranges from 300-400 nm with a density of 6-7 × 107 cm-2. The p- and n-type doping of the nanowires is achieved with Mg and Si dopant species. Structural characterization by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) indicates that the nanowires are relatively defect-free. The room-temperature photoluminescence emission with a strong peak at 370 nm indicates that the n-GaN:Si/p-GaN:Mg nanowire arrays have potential application in light-emitting nanodevices. The cathodoluminscence (CL) spectrum clearly shows a distinct optical transition of GaN nanodiodes. The nano-n-GaN:Si/p-GaN:Mg diodes were further completed using a sputter coating approach to deposit Au/Ni metal contacts. The polysilazane filler has been etched by a wet chemical etching process. The n-GaN:Si/p-GaN:Mg nanowire diode was fabricated for different Mg source flow rates. The current-voltage (I-V) measurements reveal excellent rectifying properties with an obvious turn-on voltage at 1.6 V for a Mg flow rate of 5 sccm (standard cubic centimeters per minute).

Aqueous synthesis of zinc oxide films for GaN optoelectronic devices

NASA Astrophysics Data System (ADS)

Reading, Arthur H.

GaN-based LEDs have generally made use of ITO transparent contacts as current-spreading layers for uniform current injection. However, the high raw material and processing costs of ITO layers have generated interest in potentially cheaper alternatives. In this work, zinc oxide transparent layers were fabricated by a low-cost, low-temperature aqueous epitaxial growth method at 90°C for use as transparent contacts to GaN LEDs on c-plane sapphire, and on semipolar bulk GaN substrates. Low-voltage operation was achieved for c-plane devices, with voltages below 3.8V for 1mm2 broad-area LEDs at a current density of 30A/cm 2. Blue-green LEDs on 202¯1¯-plane GaN also showed low voltage operation below 3.5V at 30A/cm2. Ohmic contact resistivity of 1:8 x 10-2Ocm2 was measured for films on (202¯1) p-GaN templates. Ga-doped films had electrical conductivities as high as 660S/cm after annealing at 300°C. Optical characterization revealed optical absorption coefficients in the 50--200cm -1 range for visible light, allowing thick films with sheet resistances below 10O/□ to be grown while minimizing absorption of the emitted light. Accurate and reproducible etch-free patterning of the ZnO films was achieved using templated growths with SiOx hard masks. A roughening method is described which was found to increase peak LED efficiencies by 13% on c-plane patterned sapphire (PSS) substrates. In addition, ZnO films were successfully employed as laser-cladding layers for blue (202¯1) lasers, with a threshold current density of 8.8kA/cm 2.

Synthesis of two-dimensional titanium nitride Ti4N3 (MXene)

NASA Astrophysics Data System (ADS)

Urbankowski, Patrick; Anasori, Babak; Makaryan, Taron; Er, Dequan; Kota, Sankalp; Walsh, Patrick L.; Zhao, Mengqiang; Shenoy, Vivek B.; Barsoum, Michel W.; Gogotsi, Yury

2016-06-01

We report on the synthesis of the first two-dimensional transition metal nitride, Ti4N3-based MXene. In contrast to the previously reported MXene synthesis methods - in which selective etching of a MAX phase precursor occurred in aqueous acidic solutions - here a molten fluoride salt is used to etch Al from a Ti4AlN3 powder precursor at 550 °C under an argon atmosphere. We further delaminated the resulting MXene to produce few-layered nanosheets and monolayers of Ti4N3Tx, where T is a surface termination (F, O, or OH). Density functional theory calculations of bare, non-terminated Ti4N3 and terminated Ti4N3Tx were performed to determine the most energetically stable form of this MXene. Bare and functionalized Ti4N3 are predicted to be metallic. Bare Ti4N3 is expected to show magnetism, which is significantly reduced in the presence of functional groups.We report on the synthesis of the first two-dimensional transition metal nitride, Ti4N3-based MXene. In contrast to the previously reported MXene synthesis methods - in which selective etching of a MAX phase precursor occurred in aqueous acidic solutions - here a molten fluoride salt is used to etch Al from a Ti4AlN3 powder precursor at 550 °C under an argon atmosphere. We further delaminated the resulting MXene to produce few-layered nanosheets and monolayers of Ti4N3Tx, where T is a surface termination (F, O, or OH). Density functional theory calculations of bare, non-terminated Ti4N3 and terminated Ti4N3Tx were performed to determine the most energetically stable form of this MXene. Bare and functionalized Ti4N3 are predicted to be metallic. Bare Ti4N3 is expected to show magnetism, which is significantly reduced in the presence of functional groups. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr02253g

INTERNATIONAL CONFERENCE ON SEMICONDUCTOR INJECTION LASERS SELCO-87: Surface effects in laser diodes

NASA Astrophysics Data System (ADS)

Beister, G.; Maege, J.; Richter, G.

1988-11-01

Changes in the current-voltage characteristics below the threshold current were observed in gain-guided stripe laser diodes after preliminary lasing. This effect was not fully understood. Similar changes in the laser characteristics appeared as a result of etching in a gaseous medium. The observed changes were attributed tentatively to surface currents.

Tailored Height Gradients in Vertical Nanowire Arrays via Mechanical and Electronic Modulation of Metal-Assisted Chemical Etching.

PubMed

Otte, M A; Solis-Tinoco, V; Prieto, P; Borrisé, X; Lechuga, L M; González, M U; Sepulveda, B

2015-09-02

In current top-down nanofabrication methodologies the design freedom is generally constrained to the two lateral dimensions, and is only limited by the resolution of the employed nanolithographic technique. However, nanostructure height, which relies on certain mask-dependent material deposition or etching techniques, is usually uniform, and on-chip variation of this parameter is difficult and generally limited to very simple patterns. Herein, a novel nanofabrication methodology is presented, which enables the generation of high aspect-ratio nanostructure arrays with height gradients in arbitrary directions by a single and fast etching process. Based on metal-assisted chemical etching using a catalytic gold layer perforated with nanoholes, it is demonstrated how nanostructure arrays with directional height gradients can be accurately tailored by: (i) the control of the mass transport through the nanohole array, (ii) the mechanical properties of the perforated metal layer, and (iii) the conductive coupling to the surrounding gold film to accelerate the local electrochemical etching process. The proposed technique, enabling 20-fold on-chip variation of nanostructure height in a spatial range of a few micrometers, offers a new tool for the creation of novel types of nano-assemblies and metamaterials with interesting technological applications in fields such as nanophotonics, nanophononics, microfluidics or biomechanics. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Atomically Traceable Nanostructure Fabrication

PubMed Central

Ballard, Josh B.; Dick, Don D.; McDonnell, Stephen J.; Bischof, Maia; Fu, Joseph; Owen, James H. G.; Owen, William R.; Alexander, Justin D.; Jaeger, David L.; Namboodiri, Pradeep; Fuchs, Ehud; Chabal, Yves J.; Wallace, Robert M.; Reidy, Richard; Silver, Richard M.; Randall, John N.; Von Ehr, James

2015-01-01

Reducing the scale of etched nanostructures below the 10 nm range eventually will require an atomic scale understanding of the entire fabrication process being used in order to maintain exquisite control over both feature size and feature density. Here, we demonstrate a method for tracking atomically resolved and controlled structures from initial template definition through final nanostructure metrology, opening up a pathway for top-down atomic control over nanofabrication. Hydrogen depassivation lithography is the first step of the nanoscale fabrication process followed by selective atomic layer deposition of up to 2.8 nm of titania to make a nanoscale etch mask. Contrast with the background is shown, indicating different mechanisms for growth on the desired patterns and on the H passivated background. The patterns are then transferred into the bulk using reactive ion etching to form 20 nm tall nanostructures with linewidths down to ~6 nm. To illustrate the limitations of this process, arrays of holes and lines are fabricated. The various nanofabrication process steps are performed at disparate locations, so process integration is discussed. Related issues are discussed including using fiducial marks for finding nanostructures on a macroscopic sample and protecting the chemically reactive patterned Si(100)-H surface against degradation due to atmospheric exposure. PMID:26274555

Atomically Traceable Nanostructure Fabrication.

PubMed

Ballard, Josh B; Dick, Don D; McDonnell, Stephen J; Bischof, Maia; Fu, Joseph; Owen, James H G; Owen, William R; Alexander, Justin D; Jaeger, David L; Namboodiri, Pradeep; Fuchs, Ehud; Chabal, Yves J; Wallace, Robert M; Reidy, Richard; Silver, Richard M; Randall, John N; Von Ehr, James

2015-07-17

Reducing the scale of etched nanostructures below the 10 nm range eventually will require an atomic scale understanding of the entire fabrication process being used in order to maintain exquisite control over both feature size and feature density. Here, we demonstrate a method for tracking atomically resolved and controlled structures from initial template definition through final nanostructure metrology, opening up a pathway for top-down atomic control over nanofabrication. Hydrogen depassivation lithography is the first step of the nanoscale fabrication process followed by selective atomic layer deposition of up to 2.8 nm of titania to make a nanoscale etch mask. Contrast with the background is shown, indicating different mechanisms for growth on the desired patterns and on the H passivated background. The patterns are then transferred into the bulk using reactive ion etching to form 20 nm tall nanostructures with linewidths down to ~6 nm. To illustrate the limitations of this process, arrays of holes and lines are fabricated. The various nanofabrication process steps are performed at disparate locations, so process integration is discussed. Related issues are discussed including using fiducial marks for finding nanostructures on a macroscopic sample and protecting the chemically reactive patterned Si(100)-H surface against degradation due to atmospheric exposure.

Reduction of structural defects in thick 4H-SiC epitaxial layers grown on 4° off-axis substrates

NASA Astrophysics Data System (ADS)

Yazdanfar, M.; Ivanov, I. G.; Pedersen, H.; Kordina, O.; Janzén, E.

2013-06-01

By carefully controlling the surface chemistry of the chemical vapor deposition process for silicon carbide (SiC), 100 μm thick epitaxial layers with excellent morphology were grown on 4° off-axis SiC substrates at growth rates exceeding 100 μm/h. In order to reduce the formation of step bunching and structural defects, mainly triangular defects, the effect of varying parameters such as growth temperature, C/Si ratio, Cl/Si ratio, Si/H2 ratio, and in situ pre-growth surface etching time are studied. It was found that an in-situ pre growth etch at growth temperature and pressure using 0.6% HCl in hydrogen for 12 min reduced the structural defects by etching preferentially on surface damages of the substrate surface. By then applying a slightly lower growth temperature of 1575 °C, a C/Si ratio of 0.8, and a Cl/Si ratio of 5, 100 μm thick, step-bunch free epitaxial layer with a minimum triangular defect density and excellent morphology could be grown, thus enabling SiC power device structures to be grown on 4° off axis SiC substrates.

Optimization and characterization of bulk hexagonal boron nitride single crystals grown by the nickel-chromium flux method

NASA Astrophysics Data System (ADS)

Hoffman, Tim

Hexagonal boron nitride (hBN) is a wide bandgap III-V semiconductor that has seen new interest due to the development of other III-V LED devices and the advent of graphene and other 2-D materials. For device applications, high quality, low defect density materials are needed. Several applications for hBN crystals are being investigated, including as a neutron detector and interference-less infrared-absorbing material. Isotopically enriched crystals were utilized for enhanced propagation of phonon modes. These applications exploit the unique physical, electronic and nanophotonics applications for bulk hBN crystals. In this study, bulk hBN crystals were grown by the flux method using a molten Ni-Cr solvent at high temperatures (1500°C) and atmospheric pressures. The effects of growth parameters, source materials, and gas environment on the crystals size, morphology and purity were established and controlled, and the reliability of the process was greatly improved. Single-crystal domains exceeding 1mm in width and 200microm in thickness were produced and transferred to handle substrates for analysis. Grain size dependence with respect to dwell temperature, cooling rate and cooling temperature were analyzed and modeled using response surface morphology. Most significantly, crystal grain width was predicted to increase linearly with dwell temperature, with single-crystal domains exceeding 2mm in at 1700°C. Isotopically enriched 10B and 11B hBN crystal were produced using a Ni-Cr-B flux method, and their properties investigated. 10B concentration was evaluated using SIMS and correlated to the shift in the Raman peak of the E2g mode. Crystals with enrichment of 99% 10B and >99% 11B were achieved, with corresponding Raman shift peaks at 1392.0 cm-1 and 1356.6 cm-1, respectively. Peak FWHM also decreased as isotopic enrichment approached 100%, with widths as low as 3.5 cm-1 achieved, compared to 8.0 cm-1 for natural abundance samples. Defect selective etching was performed using a molten NaOH-KOH etchant at 425°C-525°C, to quantify the quality of the crystals. Three etch pit shapes were identified and etch pit width was investigated as a function of temperature. Etch pit density and etch pit activation energy was estimated at 5x107 cm-2 and 60 kJ/mol, respectively. Screw and mixed-type dislocations were identified using diffraction-contrast TEM imaging.

Method for improving the stability of amorphous silicon

DOEpatents

Branz, Howard M.

2004-03-30

A method of producing a metastable degradation resistant amorphous hydrogenated silicon film is provided, which comprises the steps of growing a hydrogenated amorphous silicon film, the film having an exposed surface, illuminating the surface using an essentially blue or ultraviolet light to form high densities of a light induced defect near the surface, and etching the surface to remove the defect.

Molecular transport through nanoporous silicon nitride membranes produced from self-assembling block copolymers.

PubMed

Montagne, Franck; Blondiaux, Nicolas; Bojko, Alexandre; Pugin, Raphaël

2012-09-28

To achieve fast and selective molecular filtration, membrane materials must ideally exhibit a thin porous skin and a high density of pores with a narrow size distribution. Here, we report the fabrication of nanoporous silicon nitride membranes (NSiMs) at the full wafer scale using a versatile process combining block copolymer (BCP) self-assembly and conventional photolithography/etching techniques. In our method, self-assembled BCP micelles are used as templates for creating sub-100 nm nanopores in a thin low-stress silicon nitride layer, which is then released from the underlying silicon wafer by etching. The process yields 100 nm thick free-standing NSiMs of various lateral dimensions (up to a few mm(2)). We show that the membranes exhibit a high pore density, while still retaining excellent mechanical strength. Permeation experiments reveal that the molecular transport rate across NSiMs is up to 16-fold faster than that of commercial polymeric membranes. Moreover, using dextran molecules of various molecular weights, we also demonstrate that size-based separation can be achieved with a very good selectivity. These new silicon nanosieves offer a relevant technological alternative to commercially available ultra- and microfiltration membranes for conducting high resolution biomolecular separations at small scales.

Effect of Interface Shape and Magnetic Field on the Microstructure of Bulk Ge:Ga

NASA Technical Reports Server (NTRS)

Cobb, S. D.; Szofran, F. R.; Volz, M. P.

1999-01-01

Thermal and compositional gradients induced during the growth process contribute significantly to the development of defects in the solidified boule. Thermal gradients and the solid-liquid interface shape can be greatly effected by ampoule material. Compositional gradients are strongly influenced by interface curvature and convective flow in the liquid. Results of this investigation illustrate the combined influences of interface shape and convective fluid flow. An applied magnetic field was used to reduce the effects of convective fluid flow in the electrically conductive melt during directional solidification. Several 8 mm diameter boules of Ga-doped Ge were grown at different field strengths, up to 5 Tesla, in four different ampoule materials. Compositional profiles indicate mass transfer conditions ranged from completely mixed to diffusion controlled. The influence of convection in the melt on the developing crystal microstructure and defect density was investigated as a function of field strength and ampoule material. Chemical etching and electron backscattered electron diffraction were used to map the crystal structure of each boule along the center plane. Dislocation etch pit densities were measured for each boule. Results show the influence of magnetic field strength and ampoule material on overall crystal quality.

Treated carbon fibers with improved performance for electrochemical and chemical applications

DOEpatents

Chu, X.; Kinoshita, Kimio

1999-02-23

A treated mesophase carbon fiber is disclosed having a high density of exposed edges on the fiber surface, and a method is described for making such a treated fiber. A carbon electrode is also described which is constructed from such treated mesophase carbon fibers. The resulting electrode, formed from such treated flexible carbon fibers, is characterized by a high density of active sites formed from such exposed edges, low corrosion, and good mechanical strength, and may be fabricated into various shapes. The treated mesophase carbon fibers of the invention are formed by first loading the surface of the mesophase carbon fiber with catalytic metal particles to form catalytic etch sites on a hard carbon shell of the fiber. The carbon fiber is then subject to an etch step wherein portions of the hard carbon shell or skin are selectively removed adjacent the catalytic metal particles adhering to the carbon shell. This exposes the underlying radial edges of the graphite-like layers within the carbon shell of the mesophase carbon fiber, which exposed radial edges then act as active sites of a carbon electrode subsequently formed from the treated mesophase carbon fibers. 14 figs.

Treated carbon fibers with improved performance for electrochemical and chemical applications

DOEpatents

Chu, Xi; Kinoshita, Kimio

1999-01-01

A treated mesophase carbon fiber is disclosed having a high density of exposed edges on the fiber surface, and a method of making such a treated fiber. A carbon electrode is also described which is constructed from such treated mesophase carbon fibers. The resulting electrode, formed from such treated flexible carbon fibers, is characterized by a high density of active sites formed from such exposed edges, low corrosion, and good mechanical strength, and may be fabricated into various shapes. The treated mesophase carbon fibers of the invention are formed by first loading the surface of the mesophase carbon fiber with catalytic metal particles to form catalytic etch sites on a hard carbon shell of the fiber. The carbon fiber is then subject to an etch step wherein portions of the hard carbon shell or skin are selectively removed adjacent the catalytic metal particles adhering to the carbon shell. This exposes the underlying radial edges of the graphite-like layers within the carbon shell of the mesophase carbon fiber, which exposed radial edges then act as active sites of a carbon electrode subsequently formed from the treated mesophase carbon fibers.

Compensation of long-range process effects on photomasks by design data correction

NASA Astrophysics Data System (ADS)

Schneider, Jens; Bloecker, Martin; Ballhorn, Gerd; Belic, Nikola; Eisenmann, Hans; Keogan, Danny

2002-12-01

CD requirements for advanced photomasks are getting very demanding for the 100 nm-node and below; the ITRS roadmap requires CD uniformities below 10 nm for the most critical layers. To reach this goal, statistical as well as systematic CD contributions must be minimized. Here, we focus on the reduction of systematic CD variations across the masks that may be caused by process effects, e.g. dry etch loading. We address this topic by compensating such effects via design data correction analogous to proximity correction. Dry etch loading is modeled by gaussian convolution of pattern densities. Data correction is done geometrically by edge shifting. As the effect amplitude has an order of magnitude of 10 nm this can only be done on e-beam writers with small address grids to reduce big CD steps in the design data. We present modeling and correction results for special mask patterns with very strong pattern density variations showing that the compensation method is able to reduce CD uniformity by 50-70% depending on pattern details. The data correction itself is done with a new module developed especially to compensate long-range effects and fits nicely into the common data flow environment.

Symmetric redox supercapacitor based on micro-fabrication with three-dimensional polypyrrole electrodes

NASA Astrophysics Data System (ADS)

Sun, Wei; Zheng, Ruilin; Chen, Xuyuan

To achieve higher energy density and power density, we have designed and fabricated a symmetric redox supercapacitor based on microelectromechanical system (MEMS) technologies. The supercapacitor consists of a three-dimensional (3D) microstructure on silicon substrate micromachined by high-aspect-ratio deep reactive ion etching (DRIE) method, two sputtered Ti current collectors and two electrochemical polymerized polypyrrole (PPy) films as electrodes. Electrochemical tests, including cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatical charge/discharge methods have been carried out on the single PPy electrodes and the symmetric supercapacitor in different electrolytes. The specific capacitance (capacitance per unit footprint area) and specific power (power per unit footprint area) of the PPy electrodes and symmetric supercapacitor can be calculated from the electrochemical test data. It is found that NaCl solution is a good electrolyte for the polymerized PPy electrodes. In NaCl electrolyte, single PPy electrodes exhibit 0.128 F cm -2 specific capacitance and 1.28 mW cm -2 specific power at 20 mV s -1 scan rate. The symmetric supercapacitor presents 0.056 F cm -2 specific capacitance and 0.56 mW cm -2 specific power at 20 mV s -1 scan rate.

Influences of ultrathin amorphous buffer layers on GaAs/Si grown by metal-organic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Hu, Haiyang; Wang, Jun; Cheng, Zhuo; Yang, Zeyuan; Yin, Haiying; Fan, Yibing; Ma, Xing; Huang, Yongqing; Ren, Xiaomin

2018-04-01

In this work, a technique for the growth of GaAs epilayers on Si, combining an ultrathin amorphous Si buffer layer and a three-step growth method, has been developed to achieve high crystalline quality for monolithic integration. The influences of the combined technique for the crystalline quality of GaAs on Si are researched in this article. The crystalline quality of GaAs epilayer on Si with the combined technique is investigated by scanning electron microscopy, double crystal X-ray diffraction (DCXRD), photoluminescence, and transmission electron microscopy measurements. By means of this technique, a 1.8-µm-thick high-quality GaAs/Si epilayer was grown by metal-organic chemical vapor deposition. The full-width at half-maximum of the DCXRD rocking curve in the (400) reflection obtained from the GaAs/Si epilayers is about 163 arcsec. Compared with only using three-step growth method, the current technique reduces etch pit density from 3 × 106 cm-2 to 1.5 × 105 cm-2. The results demonstrate that the combined technique is an effective approach for reducing dislocation density in GaAs epilayers on Si.

Infrared spectroscopic ellipsometry in semiconductor manufacturing

NASA Astrophysics Data System (ADS)

Guittet, Pierre-Yves; Mantz, Ulrich; Weidner, Peter; Stehle, Jean-Louis; Bucchia, Marc; Bourtault, Sophie; Zahorski, Dorian

2004-05-01

Infrared spectroscopic ellipsometry (IRSE) metrology is an emerging technology in semiconductor production environment. Infineon Technologies SC300 implemented the first worldwide automated IRSE in a class 1 clean room in 2002. Combining properties of IR light -- large wavelength, low absorption in silicon -- with a short focus optics -- no backside reflection -- which allow model-based analysis, a large number of production applications were developed. Part of Infineon IRSE development roadmap is now focused on depth monitoring for arrays of 3D dry-etched structures. In trench DRAM manufacturing, the areal density is high, and critical dimensions are much lower than mid-IR wavelength. Therefore, extensive use of effective medium theory is made to model 3D structures. IR-SE metrology is not limited by shrinking critical dimensions, as long as the areal density is above a specific cut-off value determined by trenches dimensions, trench-filling and surrounding materials. Two applications for depth monitoring are presented. 1D models were developed and successfully applied to the DRAM trench capacitor structures. Modeling and correlation to reference methods are shown as well as dynamic repeatability and gauge capability results. Limitations of the current tool configuration are reviewed for shallow structures.

Ion-rejection, electrokinetic and electrochemical properties of a nanoporous track-etched membrane and their interpretation by means of space charge model.

PubMed

Yaroshchuk, Andriy; Boiko, Yuriy; Makovetskiy, Alexandre

2009-08-18

Due to their straight cylindrical pores, nanoporous track-etched membranes are suitable materials for studies of the fundamentals of nanofluidics. In contrast to single nanochannels, the nano/micro interface, in this case, can be quantitatively considered within the scope of macroscopically 1D models. The pressure-induced changes in the concentration of dilute KCl solutions (salt rejection phenomenon) have been studied experimentally with a commercially available nanoporous track-etched membrane of poly (ethylene terephthalate) (pore diameter ca. 21 nm). Besides that, we have also studied the concomitant stationary transmembrane electrical phenomenon (filtration potential) and carried out time-resolved measurements of the electrical response to a rapid pressure switch-off (within 5-10 ms). The latter has enabled us to split the filtration potential into the streaming potential and membrane potential components. In this way, we could also confirm that the observed nonlinearity of filtration potential, as a function of the transmembrane volume flow, was primarily caused by the salt rejection. The results of experimental measurements have been interpreted by means of a space charge model with the surface charge density being a single fitting parameter (the pore size was estimated from the membrane hydraulic permeability). By using the surface charge density fitted to the salt rejection data, the results of electrical measurements could be reproduced theoretically with a typical accuracy of 10% or better. Taking into account the simplifications made in the modeling, this accuracy appears to be good and confirms the quantitative applicability of the basic concept of space charge model to the description of transport properties of dilute electrolyte solutions in nanochannels of ca. 20 nm.

InGaP/InGaAs field-effect transistor typed hydrogen sensor

NASA Astrophysics Data System (ADS)

Tsai, Jung-Hui; Liou, Syuan-Hao; Lin, Pao-Sheng; Chen, Yu-Chi

2018-02-01

In this article, the Pd-based mixture comprising silicon dioxide (SiO2) is applied as sensing material for the InGaP/InGaAs field-effect transistor typed hydrogen sensor. After wet selectively etching the SiO2, the mixture is turned into Pd nanoparticles on an interlayer. Experimental results depict that hydrogen atoms trapped inside the mixture could effectively decrease the gate barrier height and increase the drain current due to the improved sensing properties when Pd nanoparticles were formed by wet etching method. The sensitivity of the gate forward current from air (the reference) to 9800 ppm hydrogen/air environment approaches the high value of 1674. Thus, the studied device shows a good potential for hydrogen sensor and integrated circuit applications.

Study of copper-free back contacts to thin film cadmium telluride solar cells

NASA Astrophysics Data System (ADS)

Viswanathan, Vijay

The goals of this project are to study Cu free back contact alternatives for CdS/CdTe thin film solar cells, and to research dry etching for CdTe surface preparation before contact application. In addition, an attempt has been made to evaluate the stability of some of the contacts researched. The contacts studied in this work include ZnTe/Cu2Te, Sb2Te 3, and Ni-P alloys. The ZnTe/Cu2Te contact system is studied as basically an extension of the earlier work done on Cu2Te at USF. RF sputtering from a compound target of ZnTe and Cu2Te respectively deposits these layers on etched CdTe surface. The effect of Cu2Te thickness and deposition temperature on contact and cell performance will be studied with the ZnTe depositions conditions kept constant. C-V measurements to study the effect of contact deposition conditions on CdTe doping will also be performed. These contacts will then be stressed to high temperatures (70--100°C) and their stability with stress time is analyzed. Sb2Te3 will be deposited on glass using RF sputtering, to study film properties with deposition temperature. The Sb2Te 3 contact performance will also be studied as a function of the Sb 2Te3 deposition temperature and thickness. The suitability of Ni-P alloys for back contacts to CdTe solar cells was studied by forming a colloidal mixture of Ni2P in graphite paste. The Ni-P contacts, painted on Br-methanol etched CdTe surface, will be studied as a function of Ni-P concentration (in the graphite paste), annealing temperature and time. Some of these cells will undergo temperature stress testing to determine contact behavior with time. Dry etching of CdTe will be studied as an alternative for wet etching processes currently used for CdTe solar cells. The CdTe surface is isotropically etched in a barrel reactor in N2, Ar or Ar:O 2 ambient. The effect of etching ambient, pressure, plasma power and etch time on contact performance will be studied.

Bond strength of different adhesives to normal and caries-affected dentins.

PubMed

Xuan, Wei; Hou, Ben-xiang; Lü, Ya-lin

2010-02-05

Currently, several systems of dentin substrate-reacting adhesives are available for use in the restorative treatment against caries. However, the bond effectiveness and property of different adhesive systems to caries-affected dentin are not fully understood. The objective of this study was to evaluate the bond strength of different adhesives to both normal dentin (ND) and caries-affected dentin (CAD) and to analyze the dentin/adhesive interfacial characteristics. Twenty eight extracted human molars with coronal medium carious lesions were randomly assigned to four groups according to adhesives used. ND and CAD were bonded with etch-and-rinse adhesive Adper Single Bond 2 (SB2) or self-etching adhesives Clearfil SE Bond (CSE), Clearfil S(3) Bond (CS3), iBond GI (IB). Rectangular sticks of resin-dentin bonded interfaces 0.9 mm(2) were obtained. The specimens were subjected to microtensile bond strength (microTBS) testing at a crosshead speed of 1 mm/min. Mean microTBS was statistically analyzed with analysis of variance (ANOVA) and Student-Newman-Keuls tests. Interfacial morphologies were analyzed by Scanning Electron Microscopy (SEM). Etch-and-rinse adhesive Adper(TM) Single Bond 2 yielded high bond strength when applied to both normal and caries-affected dentin. The two-step self-etching adhesive Clearfil SE Bond generated the highest bond strength to ND among all adhesives tested but a significantly reduced strength when applied to CAD. For the one-step self-etching adhesives, Clearfil S(3) Bond and iBond GI, the bond strength was relatively low regardless of the dentin type. SEM interfacial analysis revealed that hybrid layers were thicker with poorer resin tag formation and less resin-filled lateral branches in the CAD than in the ND for all the adhesives tested. The etch-and-rinse adhesive performed more effectively to caries-affected dentin than the self-etching adhesives.

Pyrolyzed thin film carbon

NASA Technical Reports Server (NTRS)

Harder, Theodore (Inventor); Konishi, Satoshi (Inventor); Miserendino, Scott (Inventor); Tai, Yu-Chong (Inventor); Liger, Matthieu (Inventor)

2010-01-01

A method of making carbon thin films comprises depositing a catalyst on a substrate, depositing a hydrocarbon in contact with the catalyst and pyrolyzing the hydrocarbon. A method of controlling a carbon thin film density comprises etching a cavity into a substrate, depositing a hydrocarbon into the cavity, and pyrolyzing the hydrocarbon while in the cavity to form a carbon thin film. Controlling a carbon thin film density is achieved by changing the volume of the cavity. Methods of making carbon containing patterned structures are also provided. Carbon thin films and carbon containing patterned structures can be used in NEMS, MEMS, liquid chromatography, and sensor devices.

Consideration of correlativity between litho and etching shape

NASA Astrophysics Data System (ADS)

Matsuoka, Ryoichi; Mito, Hiroaki; Shinoda, Shinichi; Toyoda, Yasutaka

2012-03-01

We developed an effective method for evaluating the correlation of shape of Litho and Etching pattern. The purpose of this method, makes the relations of the shape after that is the etching pattern an index in wafer same as a pattern shape on wafer made by a lithography process. Therefore, this method measures the characteristic of the shape of the wafer pattern by the lithography process and can predict the hotspot pattern shape by the etching process. The method adopts a metrology management system based on DBM (Design Based Metrology). This is the high accurate contouring created by an edge detection algorithm used wafer CD-SEM. Currently, as semiconductor manufacture moves towards even smaller feature size, this necessitates more aggressive optical proximity correction (OPC) to drive the super-resolution technology (RET). In other words, there is a trade-off between highly precise RET and lithography management, and this has a big impact on the semiconductor market that centers on the semiconductor business. 2-dimensional shape of wafer quantification is important as optimal solution over these problems. Although 1-dimensional shape measurement has been performed by the conventional technique, 2-dimensional shape management is needed in the mass production line under the influence of RET. We developed the technique of analyzing distribution of shape edge performance as the shape management technique. In this study, we conducted experiments for correlation method of the pattern (Measurement Based Contouring) as two-dimensional litho and etch evaluation technique. That is, observation of the identical position of a litho and etch was considered. It is possible to analyze variability of the edge of the same position with high precision.

Faster and exact implementation of the continuous cellular automaton for anisotropic etching simulations

NASA Astrophysics Data System (ADS)

Ferrando, N.; Gosálvez, M. A.; Cerdá, J.; Gadea, R.; Sato, K.

2011-02-01

The current success of the continuous cellular automata for the simulation of anisotropic wet chemical etching of silicon in microengineering applications is based on a relatively fast, approximate, constant time stepping implementation (CTS), whose accuracy against the exact algorithm—a computationally slow, variable time stepping implementation (VTS)—has not been previously analyzed in detail. In this study we show that the CTS implementation can generate moderately wrong etch rates and overall etching fronts, thus justifying the presentation of a novel, exact reformulation of the VTS implementation based on a new state variable, referred to as the predicted removal time (PRT), and the use of a self-balanced binary search tree that enables storage and efficient access to the PRT values in each time step in order to quickly remove the corresponding surface atom/s. The proposed PRT method reduces the simulation cost of the exact implementation from {O}(N^{5/3}) to {O}(N^{3/2} log N) without introducing any model simplifications. This enables more precise simulations (only limited by numerical precision errors) with affordable computational times that are similar to the less precise CTS implementation and even faster for low reactivity systems.

Investigation of direct current electrical properties of electrochemically etched mesoporous silicon carbide

NASA Astrophysics Data System (ADS)

Gautier, G.; Biscarrat, J.; Defforge, T.; Fèvre, A.; Valente, D.; Gary, A.; Menard, S.

2014-12-01

In this study, we show I-V characterizations of various metal/porous silicon carbide (pSiC)/silicon carbide (SiC) structures. SiC wafers were electrochemically etched from the Si and C faces in the dark or under UV lighting leading to different pSiC morphologies. In the case of low porosity pSiC etched in the dark, the I-V characteristics were found to be almost linear and the extracted resistivities of pSiC were around 1.5 × 104 Ω cm at 30 °C for the Si face. This is around 6 orders of magnitude higher than the resistivity of doped SiC wafers. In the range of 20-200 °C, the activation energy was around 50 meV. pSiC obtained from the C face was less porous and the measured average resistivity was 10 Ω cm. In the case high porosity pSiC etched under UV illumination, the resistivity was found to be much higher, around 1014 Ω cm at room temperature. In this case, the extracted activation energy was estimated to be 290 meV.

Hybrid silicon honeycomb/organic solar cells with enhanced efficiency using surface etching.

PubMed

Liu, Ruiyuan; Sun, Teng; Liu, Jiawei; Wu, Shan; Sun, Baoquan

2016-06-24

Silicon (Si) nanostructure-based photovoltaic devices are attractive for their excellent optical and electrical performance, but show lower efficiency than their planar counterparts due to the increased surface recombination associated with the high surface area and roughness. Here, we demonstrate an efficiency enhancement for hybrid nanostructured Si/polymer solar cells based on a novel Si honeycomb (SiHC) structure using a simple etching method. SiHC structures are fabricated using a combination of nanosphere lithography and plasma treatment followed by a wet chemical post-etching. SiHC has shown superior light-trapping ability in comparison with the other Si nanostructures, along with a robust structure. Anisotropic tetramethylammonium hydroxide etching not only tunes the final surface morphologies of the nanostructures, but also reduces the surface roughness leading to a lower recombination rate in the hybrid solar cells. The suppressed recombination loss, benefiting from the reduced surface-to-volume ratio and roughness, has resulted in a high open-circuit voltage of 600 mV, a short-circuit current of 31.46 mA cm(-2) due to the light-trapping ability of the SiHCs, and yields a power conversion efficiency of 12.79% without any other device structure optimization.

Introducing etch kernels for efficient pattern sampling and etch bias prediction

NASA Astrophysics Data System (ADS)

Weisbuch, François; Lutich, Andrey; Schatz, Jirka

2018-01-01

Successful patterning requires good control of the photolithography and etch processes. While compact litho models, mainly based on rigorous physics, can predict very well the contours printed in photoresist, pure empirical etch models are less accurate and more unstable. Compact etch models are based on geometrical kernels to compute the litho-etch biases that measure the distance between litho and etch contours. The definition of the kernels, as well as the choice of calibration patterns, is critical to get a robust etch model. This work proposes to define a set of independent and anisotropic etch kernels-"internal, external, curvature, Gaussian, z_profile"-designed to represent the finest details of the resist geometry to characterize precisely the etch bias at any point along a resist contour. By evaluating the etch kernels on various structures, it is possible to map their etch signatures in a multidimensional space and analyze them to find an optimal sampling of structures. The etch kernels evaluated on these structures were combined with experimental etch bias derived from scanning electron microscope contours to train artificial neural networks to predict etch bias. The method applied to contact and line/space layers shows an improvement in etch model prediction accuracy over standard etch model. This work emphasizes the importance of the etch kernel definition to characterize and predict complex etch effects.

INTERNATIONAL CONFERENCE ON SEMICONDUCTOR INJECTION LASERS SELCO-87: Calculation of the yield of fault-free laser diodes from the characteristics of the (100)InP substrate material used in epitaxial double heterostructures

NASA Astrophysics Data System (ADS)

Baerwolff, A.; Enders, P.; Knauer, A.; Linke, D.; Zeimer, U.

1988-11-01

It is shown that the yield of fault-free laser diodes is related to the density and distribution of dislocations in the substrate. A method is described for visualization of etch pits and of their relationship to defects in the substrate.

Formation of a pn junction on an anisotropically etched GaAs surface using metalorganic chemical vapor deposition

NASA Technical Reports Server (NTRS)

Leon, R. P.; Bailey, S. G.; Mazaris, G. A.; Williams, W. D.

1986-01-01

A continuous p-type GaAs epilayer has been deposited on an n-type sawtooth GaAs surface using MOCVD. A wet chemical etching process was used to expose the intersecting (111)Ga and (-1 -1 1)Ga planes with 6-micron periodicity. Charge-collection microscopy was used to verify the presence of the pn junction thus formed and to measure its depth. The ultimate goal of this work is to fabricate a V-groove GaAs cell with improved absorptivity, high short-circuit current, and tolerance to particle radiation.

Surface treatment and protection method for cadmium zinc telluride crystals

DOEpatents

Wright, Gomez W.; James, Ralph B.; Burger, Arnold; Chinn, Douglas A.

2003-01-01

A method for treatment of the surface of a CdZnTe (CZT) crystal that provides a native dielectric coating to reduce surface leakage currents and thereby, improve the resolution of instruments incorporating detectors using CZT crystals. A two step process is disclosed, etching the surface of a CZT crystal with a solution of the conventional bromine/methanol etch treatment, and after attachment of electrical contacts, passivating the CZT crystal surface with a solution of 10 w/o NH.sub.4 F and 10 w/o H.sub.2 O.sub.2 in water.

Quantitative analysis of defects in silicon. Silicon sheet growth development for the large are silicon sheet task of the low-cost solar array project

NASA Technical Reports Server (NTRS)

Natesh, R.; Smith, J. M.; Bruce, T.; Oidwai, H. A.

1980-01-01

One hundred and seventy four silicon sheet samples were analyzed for twin boundary density, dislocation pit density, and grain boundary length. Procedures were developed for the quantitative analysis of the twin boundary and dislocation pit densities using a QTM-720 Quantitative Image Analyzing system. The QTM-720 system was upgraded with the addition of a PDP 11/03 mini-computer with dual floppy disc drive, a digital equipment writer high speed printer, and a field-image feature interface module. Three versions of a computer program that controls the data acquisition and analysis on the QTM-720 were written. Procedures for the chemical polishing and etching were also developed.

Evaluation of Mineral Content and Photon Interaction Parameters of Dental Enamel After Phosphoric Acid and Er:YAG Laser Treatment.

PubMed

Simsek, Huseyin; Gurbuz, Taskın; Buyuk, Suleyman Kutalmış; Ozdemir, Yuksel

2017-05-01

The purpose of this study was to evaluate the effects of laser and acid etching on the mineral content and photon interaction parameters of dental enamel in human teeth. The composition of dental enamel may vary, especially at the surface, depending on the reactions that occur during dental treatment. Forty maxillary premolars were divided randomly into 2 groups of 20 teeth. In the first group, half of teeth crowns were etched by using 37% phosphoric acid; in the second group, half of teeth crowns were etched by using an erbium:yttrium-aluminum-garnet (Er:YAG) laser. The remaining half crowns in each group were used as untreated controls. We characterized the calcium (Ca), phosphorus (P), magnesium (Mg), sodium (Na), and potassium (K) contents in each specimen by using wavelength dispersive X-ray fluorescence spectrometry. The total atomic cross-section ([Formula: see text]), effective atomic number ([Formula: see text]), and electron density (N e ) of the tooth samples were determined at photon energies of 22.1, 25, 59.5, and 88 keV by using a narrow beam transmission method. Data were analyzed statistically by using the Mann-Whitney U test. The mineral contents after Er:YAG laser and phosphoric acid etching did not differ significantly (p > 0.05), and no significant variation in [Formula: see text], [Formula: see text], or N e was observed. Therefore, we conclude that the Er:YAG laser and phosphoric acid systems used in this study did not affect mineral composition or photon interaction parameters of dental enamel.

Influence of Ar/O2/H2O Feed Gas and N2/O2/H2O Environment on the Interaction of Time Modulated MHz Atmospheric Pressure Plasma Jet (APPJ) with Model Polymers

NASA Astrophysics Data System (ADS)

Oehrlein, Gottlieb; Luan, Pingshan; Knoll, Andrew; Kondeti, Santosh; Bruggeman, Peter

2016-09-01

An Ar/O2/H2O fed time modulated MHz atmospheric pressure plasma jet (APPJ) in a sealed chamber was used to study plasma interaction with model polymers (polystyrene, poly-methyl methacrylate, etc.). The amount of H2O in the feed gas and/or present in the N2, O2, or N2/O2 environment was controlled. Short lived species such as O atoms and OH radicals play a crucial role in polymer etching and surface modifications (obtained from X-ray photoelectron spectroscopy of treated polymers without additional atmospheric exposure). Polymer etching depth for Ar/air fed APPJ mirrors the decay of gas phase O atoms with distance from the APPJ nozzle in air and is consistent with the estimated O atom flux at the polymer surface. Furthermore, whereas separate O2 or H2O admixture to Ar enhances polymer etching, simultaneous addition of O2 and H2O to Ar quenches polymer etching. This can be explained by the mutual quenching of O with OH, H and HO2 in the gas phase. Results where O2 and/or H2O in the environment were varied are consistent with these mechanisms. All results will be compared with measured and simulated species densities reported in the literature. We gratefully acknowledge funding from US Department of Energy (DE-SC0001939) and National Science Foundation (PHY-1415353).

Effect of defects on the electrical/optical performance of gallium nitride based junction devices

NASA Astrophysics Data System (ADS)

Ferdous, Mohammad Shahriar

Commercial GaN based electronic and optoelectronic devices possess a high density (107-109 cm-2) of threading dislocations (TDs) because of the large mismatch in the lattice constant and the thermal expansion coefficient between the epitaxial layer structure and the substrate. In spite of these dislocations, high brightness light emitting diodes (LEDs) utilizing InGaN or AlGaN multiple quantum wells (MQWs) and with an external quantum efficiency of more than 40%, have already been achieved. This high external quantum efficiency in the presence of a high density of dislocations has been explained by carrier localization induced by indium fluctuations in the quantum well. TDs have been found to increase the reverse leakage current in InGaN based LEDs and to shorten the operating lifetime of InGaN MQW/GaN/AlGaN laser diodes. Thus it is important that the TD density is further reduced. It remains unclear how the TDs interact with the device to cause the effects mentioned above, hence the careful and precise characterization of threading defects and their effects on the electrical and optical performances of InGaN/GaN MQW LEDs is needed. This investigation will be useful not only from the point of view of device optimization but also to develop a clear understanding of the physical processes associated with TDs and especially with their effect on leakage current. We have employed photoelectrochemical (PEC) etching to accurately measure the dislocation density initially in home-grown GaN-based epitaxial structures and recently in InGaN/GaN MQW LEDs fabricated from commercial grade epitaxial structures that were supplied by our industrial collaborators. Measuring the electrical and electroluminescence (EL) characteristics of these devices has revealed correlations between some aspects of the LED behavior and the TD density, and promises to allow a deeper understanding of the role of threading dislocations to be elucidated. We observed that the LED reverse leakage current increased exponentially, and electroluminescence intensity decreased by 22%, as the TD density in the LEDs increased from 1.7 x 107 cm-2 to 2 x 108 cm-2. Forward voltage remained almost constant with the increase of TD density. A model of carrier conduction via hopping through defect related states, was found to provide an excellent fit to the experimental I-V data and provides a useful basis for understanding carrier conduction in the presence of TDs.

Computer acquired performance data from an etched-rhenium, molybdenum planar diode

NASA Technical Reports Server (NTRS)

Manista, E. J.

1972-01-01

Performance data from an etched-rhenium, molybdenum thermionic converter are presented. The planar converter has a guard-ringed collector and a fixed spacing of 0.254 mm (10 mils). The data were acquired by using a computer and are available on microfiche as individual or composite parametric current, voltage curves. The parameters are the temperatures of the emitter T sub E, collector T sub C and cesium reservoir T sub R. The composite plots have constant T sub E, and varying T sub C or T sub R, or both. The envelope and composite plots having constant I sub E are presented. The diode was tested at increments between 1500 and 2000 K for the emitter, 750 and 1100 K for the collector, and 540 and 640 K for the reservoir. In all, 774 individual current, voltage curves were obtained.

Using Graphene Liquid Cell Transmission Electron Microscopy to Study in Situ Nanocrystal Etching.

PubMed

Hauwiller, Matthew R; Ondry, Justin C; Alivisatos, A Paul

2018-05-17

Graphene liquid cell electron microscopy provides the ability to observe nanoscale chemical transformations and dynamics as the reactions are occurring in liquid environments. This manuscript describes the process for making graphene liquid cells through the example of graphene liquid cell transmission electron microscopy (TEM) experiments of gold nanocrystal etching. The protocol for making graphene liquid cells involves coating gold, holey-carbon TEM grids with chemical vapor deposition graphene and then using those graphene-coated grids to encapsulate liquid between two graphene surfaces. These pockets of liquid, with the nanomaterial of interest, are imaged in the electron microscope to see the dynamics of the nanoscale process, in this case the oxidative etching of gold nanorods. By controlling the electron beam dose rate, which modulates the etching species in the liquid cell, the underlying mechanisms of how atoms are removed from nanocrystals to form different facets and shapes can be better understood. Graphene liquid cell TEM has the advantages of high spatial resolution, compatibility with traditional TEM holders, and low start-up costs for research groups. Current limitations include delicate sample preparation, lack of flow capability, and reliance on electron beam-generated radiolysis products to induce reactions. With further development and control, graphene liquid cell may become a ubiquitous technique in nanomaterials and biology, and is already being used to study mechanisms governing growth, etching, and self-assembly processes of nanomaterials in liquid on the single particle level.

Comparison of enamel bond fatigue durability between universal adhesives and two-step self-etch adhesives: Effect of phosphoric acid pre-etching.

PubMed

Suda, Shunichi; Tsujimoto, Akimasa; Barkmeier, Wayne W; Nojiri, Kie; Nagura, Yuko; Takamizawa, Toshiki; Latta, Mark A; Miyazaki, Masashi

2018-03-30

The effect of phosphoric acid pre-etching on enamel bond fatigue durability of universal adhesives and two-step self-etch adhesives was investigated. Four universal adhesives and three two-step self-etch adhesives were used. The initial shear bond strengths and shear fatigue strengths to enamel with and without phosphoric acid pre-etching using the adhesives were determined. SEM observations were also conducted. Phosphoric acid pre-etching of enamel was found to increase the bond fatigue durability of universal adhesives, but its effect on two-step self-etch adhesives was material-dependent. In addition, some universal adhesives with phosphoric acid pre-etching showed similar bond fatigue durability to the two-step self-etch adhesives, although the bond fatigue durability of universal adhesives in self-etch mode was lower than that of the two-step self-etch adhesives. Phosphoric acid pre-etching enhances enamel bond fatigue durability of universal adhesives, but the effect of phosphoric acid pre-etching on the bond fatigue durability of two-step self-etch adhesives was material-dependent.

Dry etching of metallization

NASA Technical Reports Server (NTRS)

Bollinger, D.

1983-01-01

The production dry etch processes are reviewed from the perspective of microelectronic fabrication applications. The major dry etch processes used in the fabrication of microelectronic devices can be divided into two categories - plasma processes in which samples are directly exposed to an electrical discharge, and ion beam processes in which samples are etched by a beam of ions extracted from a discharge. The plasma etch processes can be distinguished by the degree to which ion bombardment contributes to the etch process. This, in turn is related to capability for anisotropic etching. Reactive Ion Etching (RIE) and Ion Beam Etching are of most interest for etching of thin film metals. RIE is generally considered the best process for large volume, anisotropic aluminum etching.

Vanishing Act: Experiments on Fission Track Annealing in Monazite

NASA Astrophysics Data System (ADS)

Shipley, N. K.; Fayon, A. K.

2006-12-01

To determine the viability of monazite as a low temperature thermochronometer, we conducted fission track annealing experiments under isothermal conditions. These experiments evaluated the effects of uranium concentration and zoning on annealing rates. Fission track annealing rates in monazite were also compared to those in Durango apatite. Preliminary results indicate that monazite grains with higher initial track densities anneal at faster rates than those with low initial densities and that fission tracks in monazite anneal at a faster rate than those in apatite. Monazite sand grains were selected from a placer sand deposit, mounted in teflon, and polished. Grains were imaged with electron backscattering to characterize zoning patterns and variations in uranium concentration. Monazite grain mounts were etched in boiling 37% HCl for 50 minutes and fission track densities were determined using standard fission track counting techniques. Durango apatite was etched in 5N HNO3 at room temperature for 20 seconds. After the initial track densities were determined, mounts in one group were annealed at 150 ° C for 1to 6 h. The mounts in a second group were annealed at 200 ° C for 2 hour periods along with mounts of Durango apatite grains. All grains were re-polished prior to each anneal. Upon completion of the experiment, backscatter images were taken of grains from which fission track counts were obtained to verify continuance of concentric zoning. Results of these experiments indicate that annealing rates of fission tracks in monazite vary as a function of uranium concentration. Uranium concentration was constrained on the basis of zoning patterns obtained from electron backscatter images. Fission track densities in grains with initial track densities of approximately 2.4 × 106 tracks/cm2 were reduced at average rate of 16% every two hours. In contrast, track densities in grains with initial track densities of approximately 1.6 × 106 tracks/cm2 average 4.6% density reduction every two hours. In both cases, track density reduction in monazite was faster than the rate of 0.1 % every two hours obtained for apatite. This would indicate that fission track annealing occurs at a lower temperature in monazite than in apatite. Thus monazite would be useful as a low temperature chronometer for determining cooling histories in recently exhumed rocks.

Nano-porous electrode systems by colloidal lithography for sensitive electrochemical detection: fabrication technology and properties

NASA Astrophysics Data System (ADS)

Lohmüller, Theobald; Müller, Ulrich; Breisch, Stefanie; Nisch, Wilfried; Rudorf, Ralf; Schuhmann, Wolfgang; Neugebauer, Sebastian; Kaczor, Markus; Linke, Stephan; Lechner, Sebastian; Spatz, Joachim; Stelzle, Martin

2008-11-01

A porous metal-insulator-metal sensor system was developed with the ultimate goal of enhancing the sensitivity of electrochemical sensors by taking advantage of redox cycling of electro active molecules between closely spaced electrodes. The novel fabrication technology is based on thin film deposition in combination with colloidal self-assembly and reactive ion etching to create micro- or nanopores. This cost effective approach is advantageous compared to common interdigitated electrode arrays (IDA) since it does not require high definition lithography technology. Spin-coating and random particle deposition, combined with a new sublimation process are discussed as competing strategies to generate monolayers of colloidal spheres. Metal-insulator-metal layer systems with low leakage currents < 10 pA and an insulator thickness as low as 100 nm were obtained at high yield (typically > 90%). We also discuss possible causes of sensor failure with respect to critical fabrication processes. Short circuits which could occur during or as a result of the pore etching process were investigated in detail. Infrared microscopy in combination with focused ion beam etching/SEM were used to reveal a defect mechanism creating interconnects and increased leakage current between the top and bottom electrodes. Redox cycling provides for amplification factors of >100. A general applicability for electrochemical diagnostic assays is therefore anticipated.

Kinked silicon nanowires-enabled interweaving electrode configuration for lithium-ion batteries.

PubMed

Sandu, Georgiana; Coulombier, Michael; Kumar, Vishank; Kassa, Hailu G; Avram, Ionel; Ye, Ran; Stopin, Antoine; Bonifazi, Davide; Gohy, Jean-François; Leclère, Philippe; Gonze, Xavier; Pardoen, Thomas; Vlad, Alexandru; Melinte, Sorin

2018-06-28

A tri-dimensional interweaving kinked silicon nanowires (k-SiNWs) assembly, with a Ni current collector co-integrated, is evaluated as electrode configuration for lithium ion batteries. The large-scale fabrication of k-SiNWs is based on a procedure for continuous metal assisted chemical etching of Si, supported by a chemical peeling step that enables the reuse of the Si substrate. The kinks are triggered by a simple, repetitive etch-quench sequence in a HF and H 2 O 2 -based etchant. We find that the inter-locking frameworks of k-SiNWs and multi-walled carbon nanotubes exhibit beneficial mechanical properties with a foam-like behavior amplified by the kinks and a suitable porosity for a minimal electrode deformation upon Li insertion. In addition, ionic liquid electrolyte systems associated with the integrated Ni current collector repress the detrimental effects related to the Si-Li alloying reaction, enabling high cycling stability with 80% capacity retention (1695 mAh/g Si ) after 100 cycles. Areal capacities of 2.42 mAh/cm 2 (1276 mAh/g electrode ) can be achieved at the maximum evaluated thickness (corresponding to 1.3 mg Si /cm 2 ). This work emphasizes the versatility of the metal assisted chemical etching for the synthesis of advanced Si nanostructures for high performance lithium ion battery electrodes.

Demonstration of hetero-gate-dielectric tunneling field-effect transistors (HG TFETs).

PubMed

Choi, Woo Young; Lee, Hyun Kook

2016-01-01

The steady scaling-down of semiconductor device for improving performance has been the most important issue among researchers. Recently, as low-power consumption becomes one of the most important requirements, there have been many researches about novel devices for low-power consumption. Though scaling supply voltage is the most effective way for low-power consumption, performance degradation is occurred for metal-oxide-semiconductor field-effect transistors (MOSFETs) when supply voltage is reduced because subthreshold swing (SS) of MOSFETs cannot be lower than 60 mV/dec. Thus, in this thesis, hetero-gate-dielectric tunneling field-effect transistors (HG TFETs) are investigated as one of the most promising alternatives to MOSFETs. By replacing source-side gate insulator with a high- k material, HG TFETs show higher on-current, suppressed ambipolar current and lower SS than conventional TFETs. Device design optimization through simulation was performed and fabrication based on simulation demonstrated that performance of HG TFETs were better than that of conventional TFETs. Especially, enlargement of gate insulator thickness while etching gate insulator at the source side was improved by introducing HF vapor etch process. In addition, the proposed HG TFETs showed higher performance than our previous results by changing structure of sidewall spacer by high- k etching process.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gould, Benjamin; Greco, Aaron

White etching cracks (WECs) have been identified as a dominant mode of premature failure within wind turbine gearbox bearings. Though WECs have been reported in the field for over a decade, the conditions leading to WECs, and the process by which this failure culminates, are both highly debated. In previously published work, the generation of WECs on a benchtop scale was linked to sliding at the surface of the test sample, it was also postulated that the generation of WECs was dependent on the cumulative energy that had been applied to the sample over the entirety of the test. Inmore » this paper, a three ring on roller bench top test rig is used to systematically alter the cumulative energy that a sample experiences through changes in normal load, sliding, and run time, in an attempt to correlate cumulative energy with the formation of WECs. It was determined that, in the current test setup, the presence of WECs can be predicted by this energy criterion. The authors then used this information to study the process by which WECs initiate. Lastly, it was found that, under the current testing conditions, the formation of a dark etching microstructure precedes the formation of a crack, and a crack precedes the formation of white etching microstructure.« less

The Development of III-V Semiconductor MOSFETs for Future CMOS Applications

NASA Astrophysics Data System (ADS)

Greene, Andrew M.

Alternative channel materials with superior transport properties over conventional strained silicon are required for supply voltage scaling in low power complementary metal-oxide-semiconductor (CMOS) integrated circuits. Group III-V compound semiconductor systems offer a potential solution due to their high carrier mobility, low carrier effective mass and large injection velocity. The enhancement in transistor drive current at a lower overdrive voltage allows for the scaling of supply voltage while maintaining high switching performance. This thesis focuses on overcoming several material and processing challenges associated with III-V semiconductor development including a low thermal processing budget, high interface trap state density (Dit), low resistance source/drain contacts and growth on lattice mismatched substrates. Non-planar In0.53Ga0.47As FinFETs were developed using both "gate-first" and "gate-last" fabrication methods for n-channel MOSFETs. Electron beam lithography and anisotropic plasma etching processes were optimized to create highly scaled fins with near vertical sidewalls. Plasma damage was removed using a wet etch process and improvements in gate efficiency were characterized on MOS capacitor structures. A two-step, selective removal of the pre-grown n+ contact layer was developed for "gate-last" recess etching. The final In0.53Ga 0.47As FinFET devices demonstrated an ION = 70 mA/mm, I ON/IOFF ratio = 15,700 and sub-threshold swing = 210 mV/dec. Bulk GaSb and strained In0.36Ga0.64Sb quantum well (QW) heterostructures were developed for p-channel MOSFETs. Dit was reduced to 2 - 3 x 1012 cm-2eV-1 using an InAs surface layer, (NH4)2S passivation and atomic layer deposition (ALD) of Al2O3. A self-aligned "gate-first" In0.36Ga0.64Sb MOSFET fabrication process was invented using a "T-shaped" electron beam resist patterning stack and intermetallic source/drain contacts. Ni contacts annealed at 300°C demonstrated an ION = 166 mA/mm, ION/IOFF ratio = 1,500 and sub-threshold swing = 340 mV/dec. Split C-V measurements were used to extract an effective channel mobility of muh* = 300 cm2/Vs at Ns = 2 x 1012 cm -2. "Gate-last" MOSFETs grown with an epitaxial p + contact layer were fabricated using selective gate-recess etching techniques. A parasitic "n-channel" limited ION/I OFF ratio and sub-threshold swing, most likely due to effects from the InAs surface layer.

Controlled morphology and optical properties of n-type porous silicon: effect of magnetic field and electrode-assisted LEF.

PubMed

Antunez, Edgar E; Campos, Jose; Basurto, Miguel A; Agarwal, Vivechana

2014-01-01

Fabrication of photoluminescent n-type porous silicon (nPS), using electrode-assisted lateral electric field accompanied with a perpendicular magnetic field, is reported. The results have been compared with the porous structures fabricated by means of conventional anodization and electrode-assisted lateral electric field without magnetic field. The lateral electric field (LEF) applied across the silicon substrate leads to the formation of structural gradient in terms of density, dimension, and depth of the etched pores. Apart from the pore shape tunability, the simultaneous application of LEF and magnetic field (MF) contributes to a reduction of the dimension of the pores and promotes relatively more defined pore tips as well as a decreased side-branching in the pore walls of the macroporous structure. Additionally, when using magnetic field-assisted etching, within a certain range of LEF, an enhancement of the photoluminescence (PL) response was obtained.

Controlled morphology and optical properties of n-type porous silicon: effect of magnetic field and electrode-assisted LEF

PubMed Central

2014-01-01

Fabrication of photoluminescent n-type porous silicon (nPS), using electrode-assisted lateral electric field accompanied with a perpendicular magnetic field, is reported. The results have been compared with the porous structures fabricated by means of conventional anodization and electrode-assisted lateral electric field without magnetic field. The lateral electric field (LEF) applied across the silicon substrate leads to the formation of structural gradient in terms of density, dimension, and depth of the etched pores. Apart from the pore shape tunability, the simultaneous application of LEF and magnetic field (MF) contributes to a reduction of the dimension of the pores and promotes relatively more defined pore tips as well as a decreased side-branching in the pore walls of the macroporous structure. Additionally, when using magnetic field-assisted etching, within a certain range of LEF, an enhancement of the photoluminescence (PL) response was obtained. PMID:25313298

Reduction of the 355-nm laser-induced damage initiators by removing the subsurface cracks in fused silica

NASA Astrophysics Data System (ADS)

Yang, Minghong; Qi, Hongji; Zhao, Yuanan; Yi, Kui

2012-01-01

The 355 nm laser-induced damage thresholds (LIDTs) of polished fused silica with and without the residual subsurface cracks were explored. HF based wet etching and magnetorheological finishing was used to remove the subsurface cracks. To isolate the effect of subsurface cracks, chemical leaching was used to eliminate the photoactive impurities in the polishing layer. Results show that the crack number density decreased from~103 to <1cm-2, and the LIDT was improved as high as 2.8-fold with both the subsurface cracks and the polishing layer being removed. Subsurface cracks play a significant role in laser damage at fluencies between 15~31 J/cm2 (355nm, 8ns). HF Etching of the cracks was shown to increase the damage performance as nearly high as that of the samples in which subsurface cracks are well controlled.

Formation mechanism of graphite hexagonal pyramids by argon plasma etching of graphite substrates

NASA Astrophysics Data System (ADS)

Glad, X.; de Poucques, L.; Bougdira, J.

2015-12-01

A new graphite crystal morphology has been recently reported, namely the graphite hexagonal pyramids (GHPs). They are hexagonally-shaped crystals with diameters ranging from 50 to 800 nm and a constant apex angle of 40°. These nanostructures are formed from graphite substrates (flexible graphite and highly ordered pyrolytic graphite) in low pressure helicon coupling radiofrequency argon plasma at 25 eV ion energy and, purportedly, due to a physical etching process. In this paper, the occurrence of peculiar crystals is shown, presenting two hexagonal orientations obtained on both types of samples, which confirms such a formation mechanism. Moreover, by applying a pretreatment step with different time durations of inductive coupling radiofrequency argon plasma, for which the incident ion energy decreases at 12 eV, uniform coverage of the surface can be achieved with an influence on the density and size of the GHPs.

Synchrotron radiation x-ray topography and defect selective etching analysis of threading dislocations in GaN

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sintonen, Sakari, E-mail: sakari.sintonen@aalto.fi; Suihkonen, Sami; Jussila, Henri

2014-08-28

The crystal quality of bulk GaN crystals is continuously improving due to advances in GaN growth techniques. Defect characterization of the GaN substrates by conventional methods is impeded by the very low dislocation density and a large scale defect analysis method is needed. White beam synchrotron radiation x-ray topography (SR-XRT) is a rapid and non-destructive technique for dislocation analysis on a large scale. In this study, the defect structure of an ammonothermal c-plane GaN substrate was recorded using SR-XRT and the image contrast caused by the dislocation induced microstrain was simulated. The simulations and experimental observations agree excellently and themore » SR-XRT image contrasts of mixed and screw dislocations were determined. Apart from a few exceptions, defect selective etching measurements were shown to correspond one to one with the SR-XRT results.« less

A study of GaN-based LED structure etching using inductively coupled plasma

NASA Astrophysics Data System (ADS)

Wang, Pei; Cao, Bin; Gan, Zhiyin; Liu, Sheng

2011-02-01

GaN as a wide band gap semiconductor has been employed to fabricate optoelectronic devices such as light-emitting diodes (LEDs) and laser diodes (LDs). Recently several different dry etching techniques for GaN-based materials have been developed. ICP etching is attractive because of its superior plasma uniformity and strong controllability. Most previous reports emphasized on the ICP etching characteristics of single GaN film. In this study dry etching of GaN-based LED structure was performed by inductively coupled plasmas (ICP) etching with Cl2 as the base gas and BCl3 as the additive gas. The effects of the key process parameters such as etching gases flow rate, ICP power, RF power and chamber pressure on the etching properties of GaN-based LED structure including etching rate, selectivity, etched surface morphology and sidewall was investigated. Etch depths were measured using a depth profilometer and used to calculate the etch rates. The etch profiles were observed with a scanning electron microscope (SEM).

Degradation of Staphylococcus aureus bacteria by neutral oxygen atoms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cvelbar, U.; Mozetic, M.; Hauptman, N.

2009-11-15

The degradation of Staphylococcus aureus bacteria during treatment with neutral oxygen atoms was monitored by scanning electron microscopy. Experiments were performed in an afterglow chamber made from borosilicate glass. The source of oxygen atoms was remote inductively coupled radiofrequency oxygen plasma. The density of atoms at the samples was 8x10{sup 20} m{sup -3}. The treatment was performed at room temperature. The first effect was the removal of dried capsule. Capsule on exposed parts of bacteria was removed after receiving the dose of 6x10{sup 23} at./m{sup 2}, while the parts of capsule filling the gaps between bacteria were removed after receivingmore » the dose of 2.4x10{sup 24} m{sup -2}. After removing the capsule, degradation continued as etching of bacterial cell wall. The etching was rather nonuniform as holes with diameter of several 10 nm were observed. The cell wall was removed after receiving the dose of about 7x10{sup 24} m{sup -2}. The etching probabilities were about 2x10{sup -5} for the capsule and 2x10{sup -6} for the cell wall. The results were explained by different compositions of capsule and the cell wall.« less

Surface and structure modification induced by high energy and highly charged uranium ion irradiation in monocrystal spinel

NASA Astrophysics Data System (ADS)

Yang, Yitao; Zhang, Chonghong; Song, Yin; Gou, Jie; Zhang, Liqing; Meng, Yancheng; Zhang, Hengqing; Ma, Yizhun

2014-05-01

Due to its high temperature properties and relatively good behavior under irradiation, magnesium aluminate spinel (MgAl2O4) is considered as a possible material to be used as inert matrix for the minor actinides burning. In this case, irradiation damage is an unavoidable problem. In this study, high energy and highly charged uranium ions (290 MeV U32+) were used to irradiate monocrystal spinel to the fluence of 1.0 × 1013 ions/cm2 to study the modification of surface and structure. Highly charged ions carry large potential energy, when they interact with a surface, the release of potential energy results in the modification of surface. Atomic force microscopy (AFM) results showed the occurrence of etching on surface after uranium ion irradiation. The etching depth reached 540 nm. The surprising efficiency of etching is considered to be induced by the deposition of potential energy with high density. The X-ray diffraction results showed that the (4 4 0) diffraction peak obviously broadened after irradiation, which indicated that the distortion of lattice has occurred. After multi-peak Gaussian fitting, four Gaussian peaks were separated, which implied that a structure with different damage layers could be formed after irradiation.

Control of spectral transmission enhancement properties of random anti-reflecting surface structures fabricated using gold masking

NASA Astrophysics Data System (ADS)

Peltier, Abigail; Sapkota, Gopal; Potter, Matthew; Busse, Lynda E.; Frantz, Jesse A.; Shaw, L. Brandon; Sanghera, Jasbinder S.; Aggarwal, Ishwar D.; Poutous, Menelaos K.

2017-02-01

Random anti-reflecting subwavelength surface structures (rARSS) have been shown to suppress Fresnel reflection and scatter from optical surfaces. The structures effectively function as a gradient-refractive-index at the substrate boundary, and the spectral transmission properties of the boundary have been shown to depend on the structure's statistical properties (diameter, height, and density.) We fabricated rARSS on fused silica substrates using gold masking. A thin layer of gold was deposited on the surface of the substrate and then subjected to a rapid thermal annealing (RTA) process at various temperatures. This RTA process resulted in the formation of gold "islands" on the surface of the substrate, which then acted as a mask while the substrate was dry etched in a reactive ion etching (RIE) process. The plasma etch yielded a fused silica surface covered with randomly arranged "rods" that act as the anti-reflective layer. We present data relating the physical characteristics of the gold "island" statistical populations, and the resulting rARSS "rod" population, as well as, optical scattering losses and spectral transmission properties of the final surfaces. We focus on comparing results between samples processed at different RTA temperatures, as well as samples fabricated without undergoing RTA, to relate fabrication process statistics to transmission enhancement values.

Enhanced photoelectrochemical properties of copper-assisted catalyzed etching black silicon by electrodepositing cobalt

NASA Astrophysics Data System (ADS)

Cai, Weidong; Xiong, Haiying; Su, Xiaodong; Zhou, Hao; Shen, Mingrong; Fang, Liang

2017-11-01

Black silicon (Si) photoelectrodes are promising for improving the performance of photoelectrochemical (PEC) water splitting. Here, we report the fabrication of p-black Si and n+p-black Si photocathodes via a controllable copper-assisted catalyzed etching method. The etching process affects only the topmost less than 200 nm of Si and is independent of the surface doping. The synergistic effects of the excellent light harvesting of the black Si and the improved charge transfer properties of the p-n junction boost the production and utilization of photogenerated carriers. The mean reflectance of the pristine Si samples is about 10% from 400 to 950 nm, while that of the black Si samples is reduced as low as 5%. In addition, the PEC properties of the n+p-black Si photocathode can be further enhanced by depositing a cobalt (Co) layer. Compared with the p-Si sample, the onset potential of the Co/n+p-black Si photocathode is positively shifted by 560 mV to 0.33 V vs. reversible hydrogen electrode and the saturation photocurrent density is increased from 22.7 to 32.6 mA/cm2. The design of the Co/n+p-black Si photocathode offers an efficient strategy for preparing PEC solar energy conversion devices.

Tip-Based Nanofabrication of Arbitrary Shapes of Graphene Nanoribbons for Device Applications

PubMed Central

Estrada, David; Bashir, Rashid; King, William P.

2015-01-01

Graphene nanoribbons (GNRs) have promising applications in future nanoelectronics, chemical sensing and electrical interconnects. Although there are quite a few GNR nanofabrication methods reported, a rapid and low-cost fabrication method that is capable of fabricating arbitrary shapes of GNRs with good-quality is still in demand for using GNRs for device applications. In this paper, we present a tip-based nanofabrication method capable of fabricating arbitrary shapes of GNRs. A heated atomic force microscope (AFM) tip deposits polymer nanowires atop a CVD-grown graphene surface. The polymer nanowires serve as an etch mask to define GNRs through one step of oxygen plasma etching similar to a photoresist in conventional photolithography. Various shapes of GNRs with either linear or curvilinear features are demonstrated. The width of the GNR is around 270 nm and is determined by the width of the depositing polymer nanowire, which we estimate can be scaled down 15 nms. We characterize our TBN-fabricated GNRs using Raman spectroscopy and I-V measurements. The measured sheet resistances of our GNRs fall within the range of 1.65 kΩ/□−1 – 2.64 kΩ/□−1, in agreement with previously reported values. Furthermore, we determined the high-field breakdown current density of GNRs to be approximately 2.94×108 A/cm2. This TBN process is seamlessly compatible with existing nanofabrication processes, and is particularly suitable for fabricating GNR based electronic devices including next generation DNA sequencing technologies and beyond silicon field effect transistors. PMID:26257891

Study of Thermal Electrical Modified Etching for Glass and Its Application in Structure Etching

PubMed Central

Zhan, Zhan; Li, Wei; Yu, Lingke; Wang, Lingyun; Sun, Daoheng

2017-01-01

In this work, an accelerating etching method for glass named thermal electrical modified etching (TEM etching) is investigated. Based on the identification of the effect in anodic bonding, a novel method for glass structure micromachining is proposed using TEM etching. To validate the method, TEM-etched glasses are prepared and their morphology is tested, revealing the feasibility of the new method for micro/nano structure micromachining. Furthermore, two kinds of edge effect in the TEM and etching processes are analyzed. Additionally, a parameter study of TEM etching involving transferred charge, applied pressure, and etching roughness is conducted to evaluate this method. The study shows that TEM etching is a promising manufacture method for glass with low process temperature, three-dimensional self-control ability, and low equipment requirement. PMID:28772521

Two-year Randomized Clinical Trial of Self-etching Adhesives and Selective Enamel Etching.

PubMed

Pena, C E; Rodrigues, J A; Ely, C; Giannini, M; Reis, A F

2016-01-01

The aim of this randomized, controlled prospective clinical trial was to evaluate the clinical effectiveness of restoring noncarious cervical lesions with two self-etching adhesive systems applied with or without selective enamel etching. A one-step self-etching adhesive (Xeno V(+)) and a two-step self-etching system (Clearfil SE Bond) were used. The effectiveness of phosphoric acid selective etching of enamel margins was also evaluated. Fifty-six cavities were restored with each adhesive system and divided into two subgroups (n=28; etch and non-etch). All 112 cavities were restored with the nanohybrid composite Esthet.X HD. The clinical effectiveness of restorations was recorded in terms of retention, marginal integrity, marginal staining, caries recurrence, and postoperative sensitivity after 3, 6, 12, 18, and 24 months (modified United States Public Health Service). The Friedman test detected significant differences only after 18 months for marginal staining in the groups Clearfil SE non-etch (p=0.009) and Xeno V(+) etch (p=0.004). One restoration was lost during the trial (Xeno V(+) etch; p>0.05). Although an increase in marginal staining was recorded for groups Clearfil SE non-etch and Xeno V(+) etch, the clinical effectiveness of restorations was considered acceptable for the single-step and two-step self-etching systems with or without selective enamel etching in this 24-month clinical trial.

Influence of Pre-etching Times on Fatigue Strength of Self-etch Adhesives to Enamel.

PubMed

Takamizawa, Toshiki; Barkmeier, Wayne W; Tsujimoto, Akimasa; Endo, Hajime; Tsuchiya, Kenji; Erickson, Robert L; Latta, Mark A; Miyazaki, Masashi

To use shear bond strength (SBS) and shear fatigue strength (SFS) testing to determine the influence of phosphoric acid pre-etching times prior to application of self-etch adhesives on enamel bonding. Two single-step self-etch universal adhesives (Prime&Bond Elect and Scotchbond Universal), a conventional single-step self-etch adhesive (G-ӕnial Bond), and a conventional two-step self-etch adhesive (OptiBond XTR) were used. The SBS and SFS were obtained with phosphoric acid pre-etching for 3, 10, or 15 s prior to application of the adhesives, and without pre-etching (0 s) as a control. A staircase method was used to determine the SFS with 10 Hz frequency for 50,000 cycles or until failure occurred. The mean demineralization depth for each treated enamel surface was also measured using a profilometer. For all the adhesives, the groups with pre-etching showed significantly higher SBS and SFS than groups without pre-etching. However, there was no significant difference in SBS and SFS among groups with > 3 s of preetching. In addition, although the groups with pre-etching showed significantly deeper demineralization depths than groups without pre-etching, there was no significant difference in depth among groups with > 3 s of pre-etching. Three seconds of phosphoric acid pre-etching prior to application of self-etch adhesive can enhance enamel bonding effectiveness.

Vertically Free-Standing Ordered Pb(Zr0.52Ti0.48)O3 Nanocup Arrays by Template-Assisted Ion Beam Etching

NASA Astrophysics Data System (ADS)

Zhang, Xiaoyan; Tang, Dan; Huang, Kangrong; Hu, Die; Zhang, Fengyuan; Gao, Xingsen; Lu, Xubing; Zhou, Guofu; Zhang, Zhang; Liu, Junming

2016-04-01

In this report, vertically free-standing lead zirconate titanate Pb(Zr0.52Ti0.48)O3 (PZT) nanocup arrays with good ordering and high density (1.3 × 1010 cm-2) were demonstrated. By a template-assisted ion beam etching (IBE) strategy, the PZT formed in the pore-through anodic aluminum oxide (AAO) membrane on the Pt/Si substrate was with a cup-like nanostructure. The mean diameter and height of the PZT nanocups (NCs) was about 80 and 100 nm, respectively, and the wall thickness of NCs was about 20 nm with a hole depth of about 80 nm. Uppermost, the nanocup structure with low aspect ratio realized vertically free-standing arrays when losing the mechanical support from templates, avoiding the collapse or bundling when compared to the typical nanotube arrays. X-ray diffraction (XRD) and Raman spectrum revealed that the as-prepared PZT NCs were in a perovskite phase. By the vertical piezoresponse force microscopy (VPFM) measurements, the vertically free-standing ordered ferroelectric PZT NCs showed well-defined ring-like piezoresponse phase and hysteresis loops, which indicated that the high-density PZT nanocup arrays could have potential applications in ultra-high non-volatile ferroelectric memories (NV-FRAM) or other nanoelectronic devices.

Influence of different pre-etching times on fatigue strength of self-etch adhesives to dentin.

PubMed

Takamizawa, Toshiki; Barkmeier, Wayne W; Tsujimoto, Akimasa; Suzuki, Takayuki; Scheidel, Donal D; Erickson, Robert L; Latta, Mark A; Miyazaki, Masashi

2016-04-01

The purpose of this study was to use shear bond strength (SBS) and shear fatigue strength (SFS) testing to determine the influence on dentin bonding of phosphoric acid pre-etching times before the application of self-etch adhesives. Two single-step self-etch universal adhesives [Prime & Bond Elect (EL) and Scotchbond Universal (SU)], a conventional single-step self-etch adhesive [G-aenial Bond (GB)], and a two-step self-etch adhesive [OptiBond XTR (OX)] were used. The SBS and SFS values were obtained with phosphoric acid pre-etching times of 3, 10, or 15 s before application of the adhesives, and for a control without pre-etching. For groups with 3 s of pre-etching, SU and EL showed higher SBS values than control groups. No significant difference was observed for GB among the 3 s, 10 s, and control groups, but the 15 s pre-etching group showed significantly lower SBS and SFS values than the control group. No significant difference was found for OX among the pre-etching groups. Reducing phosphoric acid pre-etching time can minimize the adverse effect on dentin bonding durability for the conventional self-etch adhesives. Furthermore, a short phosphoric acid pre-etching time enhances the dentin bonding performance of universal adhesives. © 2016 Eur J Oral Sci.

Defect-engineered graphene chemical sensors with ultrahigh sensitivity.

PubMed

Lee, Geonyeop; Yang, Gwangseok; Cho, Ara; Han, Jeong Woo; Kim, Jihyun

2016-05-25

We report defect-engineered graphene chemical sensors with ultrahigh sensitivity (e.g., 33% improvement in NO2 sensing and 614% improvement in NH3 sensing). A conventional reactive ion etching system was used to introduce the defects in a controlled manner. The sensitivity of graphene-based chemical sensors increased with increasing defect density until the vacancy-dominant region was reached. In addition, the mechanism of gas sensing was systematically investigated via experiments and density functional theory calculations, which indicated that the vacancy defect is a major contributing factor to the enhanced sensitivity. This study revealed that defect engineering in graphene has significant potential for fabricating ultra-sensitive graphene chemical sensors.

Direct comparison of the performance of commonly used e-beam resists during nano-scale plasma etching of Si, SiO2, and Cr

NASA Astrophysics Data System (ADS)

Goodyear, Andy; Boettcher, Monika; Stolberg, Ines; Cooke, Mike

2015-03-01

Electron beam writing remains one of the reference pattern generation techniques, and plasma etching continues to underpin pattern transfer. We report a systematic study of the plasma etch resistance of several e-beam resists, both negative and positive as well as classical and Chemically Amplified Resists: HSQ[1,2] (Dow Corning), PMMA[3] (Allresist GmbH), AR-P6200 (Allresist GmbH), ZEP520 (Zeon Corporation), CAN028 (TOK), CAP164 (TOK), and an additional pCAR (non-disclosed provider). Their behaviour under plasma exposure to various nano-scale plasma etch chemistries was examined (SF6/C4F8 ICP silicon etch, CHF3/Ar RIE SiO2 etch, Cl2/O2 RIE and ICP chrome etch, and HBr ICP silicon etch). Samples of each resist type were etched simultaneously to provide a direct comparison of their etch resistance. Resist thicknesses (and hence resist erosion rates) were measured by spectroscopic ellipsometer in order to provide the highest accuracy for the resist comparison. Etch selectivities (substrate:mask etch rate ratio) are given, with recommendations for the optimum resist choice for each type of etch chemistry. Silicon etch profiles are also presented, along with the exposure and etch conditions to obtain the most vertical nano-scale pattern transfer. We identify one resist that gave an unusually high selectivity for chlorinated and brominated etches which could enable pattern transfer below 10nm without an additional hard mask. In this case the resist itself acts as a hard mask. We also highlight the differing effects of fluorine and bromine-based Silicon etch chemistries on resist profile evolution and hence etch fidelity.

Aggressiveness of contemporary self-etching adhesives. Part II: etching effects on unground enamel.

PubMed

Pashley, D H; Tay, F R

2001-09-01

The aggressiveness of three self-etching adhesives on unground enamel was investigated. Ultrastructural features and microtensile bond strength were examined, first using these adhesives as both the etching and resin-infiltration components, and then examining their etching efficacy alone through substitution of the proprietary resins with the same control resins. For SEM examination, buccal, mid-coronal, unground enamel from human extracted bicuspids were etched with either Clearfil Mega Bond (Kuraray), Non-Rinse Conditioner (NRC; Dentsply DeTrey) or Prompt L-Pop (ESPE). Those in the control group were etched with 32% phosphoric acid (Bisco) for 15s. They were all rinsed off prior to examination of the etching efficacy. For TEM examination, the self-etching adhesives were used as recommended. Unground enamel treated with NRC were further bonded using Prime&Bond NT (Dentsply), while those in the etched, control group were bonded using All-Bond 2 (Bisco). Completely demineralized, resin replicas were embedded in epoxy resin for examination of the extent of resin infiltration. For microtensile bond strength evaluation, specimens were first etched and bonded using the self-etching adhesives. A second group of specimens were etched with the self-etching adhesives, rinsed but bonded using a control adhesive. Following restoration with Z100 (3M Dental Products), they were sectioned into beams of uniform cross-sectional areas and stressed to failure. Etching patterns of aprismatic enamel, as revealed by SEM, and the subsurface hybrid layer morphology, as revealed by TEM, varied according to the aggressiveness of the self-etching adhesives. Clearfil Mega Bond exhibited the mildest etching patterns, while Prompt L-Pop produced an etching effect that approached that of the total-etch control group. Microtensile bond strength of the three experimental groups were all significantly lower than the control group, but not different from one another. When the self-etching adhesives were replaced with the control adhesive after etching, bond strengths of NRC/Prime&Bond NT and Prompt L-Pop were not significantly different from that of the control group, but were significantly higher than that of Clearfil Mega Bond. Both etching efficacy and strength of the resins are important contributing factors in bonding of self-etching adhesives to unground enamel.

Fabrication and Characterization of Gecko-inspired Fibrillar Adhesive

NASA Astrophysics Data System (ADS)

Kim, Yongkwan

Over the last decade, geckos' remarkable ability to stick to and climb surfaces found in nature has motivated a wide range of scientific interest in engineering gecko-mimetic surface for various adhesive and high friction applications. The high adhesion and friction of its pads have been attributed to a complex array of hairy structures, which maximize surface area for van der Waals interaction between the toes and the counter-surface. While advances in micro- and nanolithography technique have allowed fabrication of increasingly sophisticated gecko mimetic surfaces, it remains a challenge to produce an adhesive as robust as that of the natural gecko pads. In order to rationally design gecko adhesives, understanding the contact behavior of fibrillar interface is critical. The first chapter of the dissertation introduces gecko adhesion and its potential applications, followed by a brief survey of gecko-inspired adhesives. Challenges that limit the performance of the current adhesives are presented. In particular, it is pointed out that almost all testing of gecko adhesives have been on clean, smooth glass, which is ideal for adhesion due to high surface energy and low roughness. Surfaces in application are more difficult to stick to, so the understanding of failure modes in low energy and rough surfaces is important. The second chapter presents a fabrication method for thermoplastic gecko adhesive to be used for a detailed study of fibrillar interfaces. Low-density polyethylene nanofibers are replicated from a silicon nanowire array fabricated by colloidal lithography and metal-catalyzed chemical etching. This process yields a highly ordered array of nanofibers over a large area with control over fiber diameter, length, and number density. The high yield and consistency of the process make it ideal for a systematic study on factors that affect adhesion and friction of gecko adhesives. The following three chapters examine parameters that affect macroscale friction of fibrillar adhesives. Basic geometric factors, namely fiber length and diameter, are optimized on smooth glass for high friction. The test surfaces are then processed to intentionally introduce roughness or lower the surface energy in a systematic and quantifiable manner, so that the failure mechanisms of the adhesive can be investigated in detail. In these studies, observed macroscale friction is related to the nano-scale contact behavior with simple mechanical models to establish criteria to ensure high performance of fibrillar adhesives. Chapter 6 presents various methods to produce more complex fiber structures. The metal-assisted chemical etching of silicon nanowires is studied in detail, where the chemical composition of the etching bath can be varied to produce clumped, tapered, tilted, and curved nanowires, which provide interesting templates for molding and are potentially useful for applications in various silicon nanowire devices. Hierarchical fiber structures are fabricated by a few different methods, as well as composite structures where the fibers are embedded in another material. A way to precisely control tapering of microfibers is demonstrated, and the effect of tapering on macroscale friction is studied in detail. The final chapter summarizes the dissertation and suggests possible future works for both further investigating fibrillar interfaces and improving the current gecko adhesive.

Biomimetic artificial Si compound eye surface structures with broadband and wide-angle antireflection properties for Si-based optoelectronic applications

NASA Astrophysics Data System (ADS)

Leem, Jung Woo; Song, Young Min; Yu, Jae Su

2013-10-01

We report the biomimetic artificial silicon (Si) compound eye structures for broadband and wide-angle antireflection by integrating nanostructures (NSs) into periodically patterned microstructures (p-MSs) via thermal dewetting of gold and subsequent dry etching. The truncated cone microstructures with a two-dimensional hexagonal symmetry pattern were fabricated by photolithography and dry etching processes. The desirable shape and density of the nanostructures were obtained by controlled dewetting. The incorporation of p-MSs into the NS/Si surface further reduced the surface total reflectance over a wide wavelength range of 300-1030 nm at near normal incidence, indicating the average reflectance (Ravg) and solar weighted reflectance (RSWR) values of ~2.5% and 2%, respectively, compared to the only NSs on the flat Si surface (i.e., Ravg ~ 4.9% and RSWR ~ 4.5%). Additionally, the resulting structure improved the angle-dependent antireflection property due to its relatively omnidirectional shape, which exhibited the Ravg < 4.3% and RSWR < 3.7% in the wavelength region of 300-1100 nm even at a high incident light angle of 70° in the specular reflectance.We report the biomimetic artificial silicon (Si) compound eye structures for broadband and wide-angle antireflection by integrating nanostructures (NSs) into periodically patterned microstructures (p-MSs) via thermal dewetting of gold and subsequent dry etching. The truncated cone microstructures with a two-dimensional hexagonal symmetry pattern were fabricated by photolithography and dry etching processes. The desirable shape and density of the nanostructures were obtained by controlled dewetting. The incorporation of p-MSs into the NS/Si surface further reduced the surface total reflectance over a wide wavelength range of 300-1030 nm at near normal incidence, indicating the average reflectance (Ravg) and solar weighted reflectance (RSWR) values of ~2.5% and 2%, respectively, compared to the only NSs on the flat Si surface (i.e., Ravg ~ 4.9% and RSWR ~ 4.5%). Additionally, the resulting structure improved the angle-dependent antireflection property due to its relatively omnidirectional shape, which exhibited the Ravg < 4.3% and RSWR < 3.7% in the wavelength region of 300-1100 nm even at a high incident light angle of 70° in the specular reflectance. Electronic supplementary information (ESI) available: See DOI: 10.1039/c3nr02806b

Progress in design and fabrication of resonator quantum well infrared photodetectors (R-QWIP) (Conference Presentation)

NASA Astrophysics Data System (ADS)

Sun, Jason N.; Choi, Kwong-Kit; Olver, Kimberley A.; Fu, Richard X.

2017-05-01

Resonator-Quantum Well Infrared Photo detectors (R-QWIPs) are the next generation of QWIP detectors that use resonances to increase the quantum efficiency (QE). Recently, we are exploring R-QWIPs for broadband long wavelength applications. To achieve the expected performance, two optimized inductively coupled plasma (ICP) etching processes (selective and non-selective) are developed. Our selective ICP etching process has a nearly infinite selectivity of etching GaAs over Ga1-xAlxAs. By using the etching processes, two format (1Kx1K and 40x40) detectors with 25 μm pixel pitch were fabricated successfully. In despite of a moderate doping of 0.5 × 1018 cm-3 and a thin active layer thickness of 0.6 or 1.3 μm, we achieved a quantum efficiency 35% and 37% for 8 quantum wells and 19 quantum wells respectively. The temperature at which photocurrent equals dark current is about 66 K under F/2 optics for a cutoff wavelength up to 11 μm. The NEΔT of the FPAs is estimated to be 22 mK at 2 ms integration time and 60 K operating temperature. This good result thus exemplifies the advantages of R-QWIP.

Deep inductively coupled plasma etching of ELO-GaN grown with high fill factor

NASA Astrophysics Data System (ADS)

Gao, Haiyong; Lee, Jaesoong; Ni, Xianfeng; Leach, Jacob; Özgür, Ümit; Morkoç, Hadis

2011-02-01

The epitaxial lateral overgrowth (ELO) gallium nitride (GaN) was grown with high fill factor using metal organic chemical vapor deposition (MOCVD). The inductively coupled plasma (ICP) etching of ELO-GaN based on Cl2/Ar/SiCl4 gas mixture was performed. Surface properties of ELO-GaN subjected to ICP etching have been investigated and optimized etching condition in ELO-GaN with ICP etching is presented. Radiofrequency (RF) power and the flow rate of Cl2 gas were modified during the experiments. The window region, wing region and the edge region of ELO-GaN pattern present different etching characteristics. Different etching conditions were studied to get the minimized plasma-induced damage, relatively high etching rates, and excellent surface profiles. Etch depths of the etched ELO-GaN with smooth surface up to about 19 μm were achieved. The most suitable three-step etching condition is discussed with the assessment based on the morphology observation of the etched surface of ELO-GaN patterns.

Temperature-Dependent Nanofabrication on Silicon by Friction-Induced Selective Etching.

PubMed

Jin, Chenning; Yu, Bingjun; Xiao, Chen; Chen, Lei; Qian, Linmao

2016-12-01

Friction-induced selective etching provides a convenient and practical way for fabricating protrusive nanostructures. A further understanding of this method is very important for establishing a controllable nanofabrication process. In this study, the effect of etching temperature on the formation of protrusive hillocks and surface properties of the etched silicon surface was investigated. It is found that the height of the hillock produced by selective etching increases with the etching temperature before the collapse of the hillock. The temperature-dependent selective etching rate can be fitted well by the Arrhenius equation. The etching at higher temperature can cause rougher silicon surface with a little lower elastic modulus and hardness. The contact angle of the etched silicon surface decreases with the etching temperature. It is also noted that no obvious contamination can be detected on silicon surface after etching at different temperatures. As a result, the optimized condition for the selective etching was addressed. The present study provides a new insight into the control and application of friction-induced selective nanofabrication.