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Sample records for hydrogen-terminated silicon surfaces

  1. Reactions of Persistent Carbenes with Hydrogen-Terminated Silicon Surfaces.

    PubMed

    Zhukhovitskiy, Aleksandr V; Mavros, Michael G; Queeney, K T; Wu, Tony; Voorhis, Troy Van; Johnson, Jeremiah A

    2016-07-13

    Surface passivation has enabled the development of silicon-based solar cells and microelectronics. However, a number of emerging applications require a paradigm shift from passivation to functionalization, wherein surface functionality is installed proximal to the silicon surface. To address this need, we report here the use of persistent aminocarbenes to functionalize hydrogen-terminated silicon surfaces via Si-H insertion reactions. Through the use of model compounds (H-Si(TMS)3 and H-Si(OTMS)3), nanoparticles (H-SiNPs), and planar Si(111) wafers (H-Si(111)), we demonstrate that among different classes of persistent carbenes, the more electrophilic and nucleophilic ones, in particular, a cyclic (alkyl)(amino)carbene (CAAC) and an acyclic diaminocarbene (ADAC), are able to undergo insertion into Si-H bonds at the silicon surface, forming persistent C-Si linkages and simultaneously installing amine or aminal functionality in proximity to the surface. The CAAC (6) is particularly notable for its clean insertion reactivity under mild conditions that produces monolayers with 21 ± 3% coverage of Si(111) atop sites, commensurate with the expected maximum of ∼20%. Atomic force and transmission electron microscopy, nuclear magnetic resonance, X-ray photoelectron, and infrared spectroscopy, and time-of-flight secondary ion mass spectrometry provided evidence for the surface Si-H insertion process. Furthermore, computational studies shed light on the reaction energetics and indicated that CAAC 6 should be particularly effective at binding to silicon dihydride, trihydride, and coupled monohyride motifs, as well as oxidized surface sites. Our results pave the way for the further development of persistent carbenes as universal ligands for silicon and potentially other nonmetallic substrates. PMID:27366818

  2. Scanning tunneling microscopy characterization of the geometric and electronic structure of hydrogen-terminated silicon surfaces

    NASA Technical Reports Server (NTRS)

    Kaiser, W. J.; Bell, L. D.; Hecht, M. H.; Grunthaner, F. J.

    1988-01-01

    Scanning tunneling microscopy (STM) methods are used to characterize hydrogen-terminated Si surfaces prepared by a novel method. The surface preparation method is used to expose the Si-SiO2 interface. STM images directly reveal the topographic structure of the Si-SiO2 interface. The dependence of interface topography on oxide preparation conditions observed by STM is compared to the results of conventional surface characterization methods. Also, the electronic structure of the hydrogen-terminated surface is studied by STM spectroscopy. The near-ideal electronic structure of this surface enables direct tunnel spectroscopy measurements of Schottky barrier phenomena. In addition, this method enables probing of semiconductor subsurface properties by STM.

  3. Hydrogen-terminated silicon substrates for low-temperature molecular beam epitaxy

    NASA Technical Reports Server (NTRS)

    Grunthaner, P. J.; Grunthaner, F. J.; Fathauer, R. W.; Lin, T. L.; Hecht, M. H.; Bell, L. D.; Kaiser, W. J.

    1989-01-01

    The preparation of hydrogen-terminated silicon surfaces for use as starting substrates for low-temperature MBE growth is examined in detail. The procedure involves the ex situ removal under nitrogen of residual oxide from a silicon substrate using a spin-clean with HF in ethanol, followed by the in situ low-temperature desorption (150 C) of physisorbed etch residues. The critical steps and the chemical basis for these steps are examined using X-ray photoelectron spectroscopy. Impurity residues at the epilayer-substrate interface following subsequent homoepitaxial growth are studied using AES, SIMS and TEM. Finally, scanning tunneling microscopy is used to examine the effect of cleaning methods on substrate morphology.

  4. 1-octadecene monolayers on Si(111) hydrogen-terminated surfaces: Effect of substrate doping

    NASA Astrophysics Data System (ADS)

    Miramond, Corinne; Vuillaume, Dominique

    2004-08-01

    We have studied the electronic properties, in relation to structural properties, of monolayers of 1-octadecene attached on a hydrogen-terminated (111) silicon surface. The molecules are attached using the free-radical reaction between C C and Si H activated by an ultraviolet illumination. We have compared the structural and electrical properties of monolayers formed on silicon substrates of different types (n type and p type) and different doping concentrations, from low-doped (˜1014cm-3) to highly doped (˜1019cm-3). We show that the monolayers on n-, p-, and p+-silicon are densely packed and that they act as very good insulating films at a nanometer thickness with leakage currents as low as ˜10-7Acm-2 and high-quality capacitance-voltage characteristics. The monolayers formed on n+-type silicon are more disordered and therefore exhibit larger leakage current densities (>10-4Acm-2) when embedded in a silicon/monolayer/metal junction. The inferior structural and electronic properties obtained with n+-type silicon pinpoint the important role of surface potential and of the position of the surface Fermi level during the chemisorption of the organic monolayers.

  5. Hydrogen-terminated silicon nanowire photocatalysis: Benzene oxidation and methyl red decomposition

    SciTech Connect

    Lian, Suoyuan; Tsang, Chi Him A.; Kang, Zhenhui; Liu, Yang; Wong, Ningbew; Lee, Shuit-Tong

    2011-12-15

    Graphical abstract: H-SiNWs can catalyze hydroxylation of benzene and degradation of methyl red under visible light irradiation. Highlights: Black-Right-Pointing-Pointer Hydrogen-terminated silicon nanowires were active photocatalyst in the hydroxylation of benzene under light. Black-Right-Pointing-Pointer Hydrogen-terminated silicon nanowires were also effective in the decomposition of methyl red dye. Black-Right-Pointing-Pointer The Si/SiO{sub x} core-shell structure is the main reason of the obtained high selectivity during the hydroxylation. -- Abstract: Hydrogen-terminated silicon nanowires (H-SiNWs) were used as heterogeneous photocatalysts for the hydroxylation of benzene and for the decomposition of methyl red under visible light irradiation. The above reactions were monitored by GC-MS and UV-Vis spectrophotometry, respectively, which shows 100% selectivity for the transformation of benzene to phenol. A complete decomposition of a 2 Multiplication-Sign 10{sup -4} M methyl red solution was achieved within 30 min. The high selectivity for the hydroxylation of benzene and the photodecomposition demonstrate the catalytic activity of ultrafine H-SiNWs during nanocatalysis.

  6. Optical characterization of ultrasmall, hydrogen-terminated and carboxyl-functionalized silicon nanoparticles in aqueous environments

    NASA Astrophysics Data System (ADS)

    Eckhoff, Dean Alan

    The primary theme of this dissertation is to characterize the optical and chemical properties of ultrasmall (˜1 nm) silicon nanoparticles (Si-np) in aqueous environments, focusing on their potential for use as luminescent markers in biophysical and biological applications. Two systems are presented in detail: hydrogen-terminated Si-np prepared through electrochemical dispersion of a crystalline Si wafer and carboxyl-functionalized Si-np prepared via thermal hydrosilylation of surface Si-H bonds with an o-ester 1-alkene. Chemical and physical characterizations are done using nuclear magnetic resonance, size exclusion chromatography, and infrared spectroscopy. Optical characterization is done via absorption and steady-state photoluminescence (PL) and using capillary electrophoresis coupled with laser-induced fluorescence detection. The behavior of the hydrogen-terminated Si-np is studied over time as-prepared in isopropanol and during treatments with water, NaOH, HCl, and H2O 2. The PL spectra show three distinct, near-Gaussian states with a FWHM ˜0.45 eV and their respective emissions in the UV-B (˜305 nm), UV-A (˜340 nm), and 'hard-blue' (˜400 nm) regions of the spectrum. The 'hard-blue' emission is shown to have a simple pH dependence with a pKa ˜3, demonstrating the possibility of using Si-np as environmental probes. These results offer some promise for tailoring the PL properties of ultrasmall Si-np through control of their surface chemistry. In the second part, three central elements establish that the carboxyl-functionalized Si-np have excellent potential for use as a luminescent marker in aqueous systems. First, they are shown to be ultrasmall, with a diameter of ˜1 nm, comparable to that of common organic fluorophores. Second, they are shown to have narrow PL in the near-UV with a nearly-symmetric lineshape and a FWHM as small as 30 nm. Third, it is shown that standard chemical means can be used to functionalize the Si-np with carboxyl groups, giving

  7. A kinetic model of the formation of organic monolayers on hydrogen-terminated silicon by hydrosilation of alkenes.

    PubMed

    Woods, M; Carlsson, S; Hong, Q; Patole, S N; Lie, L H; Houlton, A; Horrocks, B R

    2005-12-22

    We have analyzed a kinetic model for the formation of organic monolayers based on a previously suggested free radical chain mechanism for the reaction of unsaturated molecules with hydrogen-terminated silicon surfaces (Linford, M. R.; Fenter, P. M.; Chidsey, C. E. D. J. Am. Chem. Soc 1995, 117, 3145). A direct consequence of this mechanism is the nonexponential growth of the monolayer, and this has been observed spectroscopically. In the model, the initiation of silyl radicals on the surface is pseudo first order with rate constant, ki, and the rate of propagation is determined by the concentration of radicals and unreacted Si-H nearest neighbor sites with a rate constant, kp. This propagation step determines the rate at which the monolayer forms by addition of alkene molecules to form a track of molecules that constitute a self-avoiding random walk on the surface. The initiation step describes how frequently new random walks commence. A termination step by which the radicals are destroyed is also included. The solution of the kinetic equations yields the fraction of alkylated surface sites and the mean length of the random walks as a function of time. In mean-field approximation we show that (1) the average length of the random walk is proportional to (kp/ki)1/2, (2) the monolayer surface coverage grows exponentially only after an induction period, (3) the effective first-order rate constant describing the growth of the monolayer and the induction period (kt) is k = (2ki kp)1/2, (4) at long times the effective first-order rate constant drops to ki, and (5) the overall activation energy for the growth kinetics is the mean of the activation energies for the initiation and propagation steps. Monte Carlo simulations of the mechanism produce qualitatively similar kinetic plots, but the mean random walk length (and effective rate constant) is overestimated by the mean field approximation and when kp > ki, we find k approximately ki0.7kp0.3 and Ea = (0.7Ei+ 0.3Ep

  8. Island growth in the atomic layer deposition of zirconium oxide and aluminum oxide on hydrogen-terminated silicon: Growth mode modeling and transmission electron microscopy

    SciTech Connect

    Puurunen, Riikka L.; Vandervorst, Wilfried; Besling, Wim F. A.; Richard, Olivier; Bender, Hugo; Conard, Thierry; Zhao Chao; Delabie, Annelies; Caymax, Matty; Gendt, Stefan de; Heyns, Marc; Viitanen, Minna M.; Ridder, Marco de; Brongersma, Hidde H.; Tamminga, Yde; Dao, Thuy; Win, Toon de; Verheijen, Marcel; Kaiser, Monja; Tuominen, Marko

    2004-11-01

    Atomic layer deposition (ALD) is used in applications where inorganic material layers with uniform thickness down to the nanometer range are required. For such thicknesses, the growth mode, defining how the material is arranged on the surface during the growth, is of critical importance. In this work, the growth mode of the zirconium tetrachloride/water and the trimethyl aluminum/water ALD process on hydrogen-terminated silicon was investigated by combining information on the total amount of material deposited with information on the surface fraction of the material. The total amount of material deposited was measured by Rutherford backscattering, x-ray fluorescence, and inductively coupled plasma-optical emission spectroscopy, and the surface fractions by low-energy ion scattering. Growth mode modeling was made assuming two-dimensional growth or random deposition (RD), with a 'shower model' of RD recently developed for ALD. Experimental surface fractions of the ALD-grown zirconium oxide and aluminum oxide films were lower than the surface fractions calculated assuming RD, suggesting the occurrence of island growth. Island growth was confirmed with transmission electron microscopy (TEM) measurements, from which the island size and number of islands per unit surface area could also be estimated. The conclusion of island growth for the aluminum oxide deposition on hydrogen-terminated silicon contradicts earlier observations. In this work, physical aluminum oxide islands were observed in TEM after 15 ALD reaction cycles. Earlier, thicker aluminum oxide layers have been analyzed, where islands have not been observed because they have already coalesced to form a continuous film. The unreactivity of hydrogen-terminated silicon surface towards the ALD reactants, except for reactive defect areas, is proposed as the origin of island growth. Consequently, island growth can be regarded as 'undesired surface-selective ALD'.

  9. Bonding Structure of Phenylacetylene on Hydrogen-Terminated Si(111) and Si(100): Surface Photoelectron Spectroscopy Analysis and Ab Initio Calculations

    SciTech Connect

    M Kondo; T Mates; D Fischer; F Wudl; E Kramer

    2011-12-31

    Interfaces between phenylacetylene (PA) monolayers and two silicon surfaces, Si(111) and Si(100), are probed by X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and the results are analyzed using ab initio molecular orbital calculations. The monolayer systems are prepared via the surface hydrosilylation reaction between PA and hydrogen-terminated silicon surfaces. The following spectral features are obtained for both of the PA-Si(111) and PA-Si(100) systems: a broad {pi}-{pi}* shakeup peak at 292 eV (XPS), a broad first ionization peak at 3.8 eV (UPS), and a low-energy C 1s {yields} {pi}* resonance peak at 284.3 eV (NEXAFS). These findings are ascribed to a styrene-like {pi}-conjugated molecular structure at the PA-Si interface by comparing the experimental data with theoretical analysis results. A conclusion is drawn that the vinyl group can keep its {pi}-conjugation character on the hydrogen-terminated Si(100) [H:Si(100)] surface composed of the dihydride (SiH{sub 2}) groups as well as on hydrogen-terminated Si(111) having the monohydride (SiH) group. The formation mechanism of the PA-Si(100) interface is investigated within cluster ab initio calculations, and the possible structure of the H:Si(100) surface is discussed based on available data.

  10. Reactive coupling of 4-vinylaniline with hydrogen-terminated Si(100) surfaces for electroless metal and "synthetic metal" deposition.

    PubMed

    Xu, D; Kang, E T; Neoh, K G; Tay, A A O

    2004-04-13

    Pristine and resist-patterned Si(100) substrates were etched by aqueous HF to produce hydrogen-terminated silicon (H-Si(100)) surfaces. The H-Si(100) surface was then subjected to UV-induced reactive coupling of 4-vinylaniline (VAn) to produce the VAn monolayer-modified silicon (VAn-Si) surface. The VAn-Si surface was first functionalized with a "synthetic metal" by oxidative graft polymerization of aniline with the aniline moieties of the coupled VAn molecules. The composition and topography of the VAn-Si and polyaniline (PAn)-grafted VAn-Si (PAn-VAn-Si) surfaces were characterized by X-ray photoelectron spectroscopy and atomic force microscopy, respectively. The doping-undoping (protonation-deprotonation) and redox-coupling (metal reduction) behavior, as well as the electrical conductivity, of the surface-grafted PAn were found to be similar to those of the aniline homopolymer. The VAn-Si surface was also funtionalized by the electroless plating of copper. Not only did the VAn layer provide chemisorption sites for the palladium catalyst, in the absence of prior sensitization by SnCl2, during the electroless plating process, it also served as an adhesion promotion layer and a low-temperature diffusion barrier for the electrolessly deposited copper. Finally, micropatterning of the grafted PAn and of the electrolessly deposited copper were demonstrated on the resist-patterned VAn-Si surfaces. PMID:15875865

  11. Quantum Point Contacts and Valley Filters on a 6-fold Degenerate Hydrogen-terminated Si(111) Surface

    NASA Astrophysics Data System (ADS)

    Robertson, Luke D.; Hu, Binhui; Kane, B. E.

    Hydrogen-terminated Si(111) surfaces preserve the 6-fold valley degeneracy and anisotropic electron mass predicted in bulk Si, providing a unique environment for 2-D electron systems (2DESs). Our group has demonstrated high mobility as well as the fractional quantum Hall effect for electrons confined on the Si(111) surfaces, establishing evidence that they are ideal platforms for 2DESs and lower dimensional systems. Recently, we have succeeded in fabricating high mobility ambipolar devices and have found that heavily p-doped regions can be used as lateral depletion gates for confinement of 2DESs induced by a top gate. Here, we describe our efforts to extend this technology to the nanoscale and in particular towards the fabrication of quantum point contacts (QPCs). QPCs realized in materials with anisotropic electron mass may exhibit valley filter phenomena leading to extreme sensitivity to single donor occupancy, and thus are of interest to measurement schemes for donor-based quantum information processing. Preliminary measurements and fabrication techniques will be discussed

  12. High-reliability passivation of hydrogen-terminated diamond surface by atomic layer deposition of Al2O3

    NASA Astrophysics Data System (ADS)

    Daicho, Akira; Saito, Tatsuya; Kurihara, Shinichiro; Hiraiwa, Atsushi; Kawarada, Hiroshi

    2014-06-01

    Although the two-dimensional hole gas (2DHG) of a hydrogen-terminated diamond surface provides a unique p-type conducting layer for high-performance transistors, the conductivity is highly sensitive to its environment. Therefore, the surface must be passivated to preserve the 2DHG, especially at high temperature. We passivated the surface at high temperature (450 °C) without the loss of C-H surface bonds by atomic layer deposition (ALD) and investigated the thermal reliability of the Al2O3 film. As a result, C-H bonds were preserved, and the hole accumulation effect appeared after the Al2O3 deposition by ALD with H2O as an oxidant. The sheet resistivity and hole density were almost constant between room temperature and 500 °C by the passivation with thick Al2O3 film thicker than 38 nm deposited by ALD at 450 °C. After the annealing at 550 °C in air The sheet resistivity and hole density were preserved. These results indicate the possibility of high-temperature application of the C-H surface diamond device in air. In the case of lower deposition temperatures, the sheet resistivity increased after air annealing, suggesting an insufficient protection capability of these films. Given the result of sheet resistivity after annealing, the increase in the sheet resistivity of these samples was not greatly significant. However, bubble like patterns were observed in the Al2O3 films formed from 200 to 400 °C by air annealing at 550 °C for 1 h. On the other hand, the patterns were no longer observed at 450 °C deposition. Thus, this 450 °C deposition is the sole solution to enabling power device application, which requires high reliability at high temperatures.

  13. Comparative investigation of surface transfer doping of hydrogen terminated diamond by high electron affinity insulators

    NASA Astrophysics Data System (ADS)

    Verona, C.; Ciccognani, W.; Colangeli, S.; Limiti, E.; Marinelli, Marco; Verona-Rinati, G.

    2016-07-01

    We report on a comparative study of transfer doping of hydrogenated single crystal diamond surface by insulators featured by high electron affinity, such as Nb2O5, WO3, V2O5, and MoO3. The low electron affinity Al2O3 was also investigated for comparison. Hole transport properties were evaluated in the passivated hydrogenated diamond films by Hall effect measurements, and were compared to un-passivated diamond films (air-induced doping). A drastic improvement was observed in passivated samples in terms of conductivity, stability with time, and resistance to high temperatures. The efficiency of the investigated insulators, as electron accepting materials in hydrogenated diamond surface, is consistent with their electronic structure. These surface acceptor materials generate a higher hole sheet concentration, up to 6.5 × 1013 cm-2, and a lower sheet resistance, down to 2.6 kΩ/sq, in comparison to the atmosphere-induced values of about 1 × 1013 cm-2 and 10 kΩ/sq, respectively. On the other hand, hole mobilities were reduced by using high electron affinity insulator dopants. Hole mobility as a function of hole concentration in a hydrogenated diamond layer was also investigated, showing a well-defined monotonically decreasing trend.

  14. Polycrystalline domain structure of pentacene thin films epitaxially grown on a hydrogen-terminated Si(111) surface

    SciTech Connect

    Nishikata, S.; Sadowski, J. T.; Al-Mahboob, A.; Nishihara, T.; Fujikawa, Y.; Sakurai, T.; Nakajima, K.; Sazaki, G.; Suto, S.

    2007-10-15

    Single-monolayer high pentacene (Pn) dendrites grown on a hydrogen-terminated Si(111) surface [H-Si(111)] under ultrahigh vacuum were observed by low-energy electron microscopy and microbeam low-energy electron diffraction analyses. We determined the epitaxial structure (type I) inside a unique polycrystalline domain structure of such dendrites, each of which has six equivalent epitaxial orientations of Pn two-dimensional (2D) unit cells. There are three sets of these cells, which are rotated {+-}120 deg. relative to each other. Domain boundaries inside each dendrite were successfully observed by scanning tunneling microscopy. In addition, we found another epitaxial relation (type II): the polycrystalline domain structure and lattice parameters are similar to those of the type-I dendrite; however, the 2D unit cells of the type-II dendrite are rotated approximately 90 deg. relative to those of the type-I dendrite. These results suggest that the crystal structure of the dendrites on H-Si(111) is determined mainly by the interaction between Pn molecules. Each dendrite is composed of domains that are exclusively of type I or II. The so-called point-on-line coincidences are found between the Pn 2D lattices of types I and II, and H-Si(111). The higher commensurability of the type-I dendrites than the type-II dendrites results in a higher probability of type-I dendrite formation. Moreover, for both the type-I and type-II dendrites, we found supercell structures. We estimated the minimum interface energy between the dendrite and H-Si(111) from an island's free energy, which is necessary to reproduce the growth of a single-monolayer high dendrite.

  15. Anisotropic surface phonon dispersion of the hydrogen-terminated Si(110)-(1×1) surface: One-dimensional phonons propagating along the glide planes

    SciTech Connect

    Matsushita, Stephane Yu; Matsui, Kazuki; Kato, Hiroki; Suto, Shozo; Yamada, Taro

    2014-03-14

    We have measured the surface phonon dispersion curves on the hydrogen-terminated Si(110)-(1×1) surface with the two-dimensional space group of p2mg along the two highly symmetric and rectangular directions of ΓX{sup ¯} and ΓX{sup ′¯} using high-resolution electron-energy-loss spectroscopy. All the essential energy-loss peaks on H:Si(110) were assigned to the vibrational phonon modes by using the selection rules of inelastic electron scattering including the glide-plane symmetry. Actually, the surface phonon modes of even-symmetry to the glide plane (along ΓX{sup ¯}) were observed in the first Brillouin zone, and those of odd-symmetry to the glide plane were in the second Brillouin zone. The detailed assignment was made by referring to theoretical phonon dispersion curves of Gräschus et al. [Phys. Rev. B 56, 6482 (1997)]. We found that the H–Si stretching and bending modes, which exhibit highly anisotropic dispersion, propagate along ΓX{sup ¯} direction as a one-dimensional phonon. Judging from the surface structure as well as our classical and quantum mechanical estimations, the H–Si stretching phonon propagates by a direct repulsive interaction between the nearest neighbor H atoms facing each other along ΓX{sup ¯}, whereas the H–Si bending phonon propagates by indirect interaction through the substrate Si atomic linkage.

  16. Morphology, structure, and magnetism of FeCo thin films electrodeposited on hydrogen-terminated Si(111) surfaces.

    PubMed

    Zarpellon, J; Jurca, H F; Mattoso, N; Klein, J J; Schreiner, W H; Ardisson, J D; Macedo, W A A; Mosca, D H

    2007-12-15

    In this work we describe the fabrication of FeCo alloy (less than 10 at% Co) thin films from aqueous ammonium sulfate solutions onto n-type Si(111) substrates using potentiostatic electrodeposition at room temperature. The incorporation of Co into the deposits tends to inhibit Fe silicide formation and to protect deposits against oxidation under air exposure. As the incorporation of Co was progressively increased, the sizes of nuclei consisting of FeCo alloy increased, leading to films with a highly oriented body-centered cubic structure with crystalline texture, where (110) planes remain preferentially oriented parallel to the film surface. PMID:17900605

  17. High-reliability passivation of hydrogen-terminated diamond surface by atomic layer deposition of Al{sub 2}O{sub 3}

    SciTech Connect

    Daicho, Akira Saito, Tatsuya; Kurihara, Shinichiro; Kawarada, Hiroshi; Hiraiwa, Atsushi

    2014-06-14

    Although the two-dimensional hole gas (2DHG) of a hydrogen-terminated diamond surface provides a unique p-type conducting layer for high-performance transistors, the conductivity is highly sensitive to its environment. Therefore, the surface must be passivated to preserve the 2DHG, especially at high temperature. We passivated the surface at high temperature (450 °C) without the loss of C-H surface bonds by atomic layer deposition (ALD) and investigated the thermal reliability of the Al{sub 2}O{sub 3} film. As a result, C-H bonds were preserved, and the hole accumulation effect appeared after the Al{sub 2}O{sub 3} deposition by ALD with H{sub 2}O as an oxidant. The sheet resistivity and hole density were almost constant between room temperature and 500 °C by the passivation with thick Al{sub 2}O{sub 3} film thicker than 38 nm deposited by ALD at 450 °C. After the annealing at 550 °C in air The sheet resistivity and hole density were preserved. These results indicate the possibility of high-temperature application of the C-H surface diamond device in air. In the case of lower deposition temperatures, the sheet resistivity increased after air annealing, suggesting an insufficient protection capability of these films. Given the result of sheet resistivity after annealing, the increase in the sheet resistivity of these samples was not greatly significant. However, bubble like patterns were observed in the Al{sub 2}O{sub 3} films formed from 200 to 400 °C by air annealing at 550 °C for 1 h. On the other hand, the patterns were no longer observed at 450 °C deposition. Thus, this 450 °C deposition is the sole solution to enabling power device application, which requires high reliability at high temperatures.

  18. Silicon surface passivation by silicon nitride deposition

    NASA Technical Reports Server (NTRS)

    Olsen, L. C.

    1984-01-01

    Silicon nitride deposition was studied as a method of passivation for silicon solar cell surfaces. The following three objectives were the thrust of the research: (1) the use of pecvd silicon nitride for passivation of silicon surfaces; (2) measurement techniques for surface recombination velocity; and (3) the importance of surface passivation to high efficiency solar cells.

  19. Hydrogen passivation and ozone oxidation of silicon surface

    SciTech Connect

    Kurokawa, Akira; Nakamura, Ken; Ichimura, Shingo

    1998-12-31

    The oxidation of H/Si(100) and H/Si(111) with high concentration ozone gas was investigated with X-ray photoelectron spectroscopy (XPS). The ozone oxidation of partially hydride-covered surface was observed. The hydrogen termination reduced the rate of oxygen insertion into silicon backbond. The reduction of oxygen insertion rate by the H-termination for H/Si(100) was larger than that for H/Si(111). The dissociation rate of ozone molecule on H/Si was estimated to be {approx_equal}0.2 with a directional mass analyzer.

  20. High performance hydrogen-terminated diamond field effect transistors

    NASA Astrophysics Data System (ADS)

    Russell, Stephen A. O.

    Diamond provides extreme properties which make it suitable as a new substrate material for high performance electronics. It has the potential to provide both high frequency and high power performance while operating in extreme environments such as elevated temperature or exposed to corrosive chemicals or radiation. Research to date has shown the potential of diamond for this purpose with hydrogen-terminated diamond surface channel transistors already showing promise in terms of high frequency operation. The inherent instability of using atmospheric molecules to induce a p-type doping at this hydrogen-terminated diamond surface has so far limited power performance and robustness of operation. This work reports upon the scaling of surface channel hydrogen-terminated transistors with FET gate lengths of 250 nm and 120 nm showing performance comparable to other devices published to date. The gate length was then scaled for the first time to sub-100 nm dimensions with a 50 nm gate length FET fabricated giving record high-frequency performance with a fT of 53 GHz. An adapted fabrication procedure was developed for this project with special attention paid to the volatility of the particles upon the diamond surface. Equivalent RF circuit models were extracted for each gate length and analysed in detail. Work was then undertaken to investigate a more stable alternative to the atmospheric induced doping effect with alternative electron accepting materials being deposited upon the hydrogen-terminated diamond surface. The as yet untested organic material F16CuPc was deposited on to hydrogen-terminated diamond and demonstrated its ability to encapsulate and preserve the atmospheric induced sub-surface conductivity at room temperature. For the first time an inorganic material was also investigated as a potential encapsulation for the hydrogen-terminated diamond surface, MoO3 was chosen due to its high electron affinity and like F16CuPc also showed the ability to preserve and

  1. Silicon sheet surface studies

    NASA Astrophysics Data System (ADS)

    Danyluk, S.

    1985-06-01

    Results of the program are presented on developing an understanding of the basic mechanisms of abrasion and wear of silicon and on the nondestructive measurement of residual stresses in sheet silicon. Experiments were conducted at various temperatures and in the presence of various fluids. In abrasive wear, it was shown that dislocations, microtwins, and cracks are generated beneath the contact surface. Residual stresses in ribbon by the edge defined film growth process were measured by use of a shadow moire interferometry technique.

  2. In situ infrared spectroscopy of hafnium oxide growth on hydrogen-terminated silicon surfaces by atomic layer deposition

    SciTech Connect

    Ho, M.-T.; Wang, Y.; Brewer, R.T.; Wielunski, L.S.; Chabal, Y.J.; Moumen, N.; Boleslawski, M.

    2005-09-26

    The interface formation between HfO{sub 2} and H-terminated Si(111) and Si(100) is studied by in situ infrared absorption spectroscopy during atomic layer deposition using alternating tetrakis-ethylmethylamino hafnium (TEMAH) and deuterium oxide (D{sub 2}O) pulses. The HfO{sub 2} growth is initiated by the reaction of TEMAH with Si-H rather than D{sub 2}O, and there is no evidence for SiO{sub 2} formation at moderate growth temperatures ({approx}100 deg. C). Although Rutherford backscattering shows a linear increase of Hf coverage, direct observations of Si-H, Si-O-Hf, and HfO{sub 2} phonons indicate that five cycles are needed to reach the steady state interface composition of {approx}50% reacted sites. The formation of interfacial SiO{sub 2} ({approx}0.7 nm) is observed after postdeposition annealing at 700 deg. C in ultrapure nitrogen.

  3. Luminescent, water-soluble silicon quantum dots via micro-plasma surface treatment

    NASA Astrophysics Data System (ADS)

    Wu, Jeslin J.; Kondeti, Vighneswara Siva Santosh Kumar; Bruggeman, Peter J.; Kortshagen, Uwe R.

    2016-03-01

    Silicon quantum dots (SiQDs), with their broad absorption, narrow and size-tunable emission, and potential biocompatibility are highly attractive materials in biological imaging applications. The inherent hydrophobicity and instability of hydrogen-terminated SiQDs are obstacles to their widespread implementation. In this work, we successfully produced highly luminescent, hydrophilic SiQDs with long-term stability in water using non-thermal plasma techniques. Hydrogen-terminated SiQDs were produced in a low-pressure plasma and subsequently treated in water using an atmospheric-pressure plasma jet for surface modification. Preliminary assessments of the chemical mechanism(s) involved in the creation of water-soluble SiQDs were performed using Fenton’s reaction and various plasma chemistries, suggesting both OH and O species play a key role in the oxidation of the SiQDs.

  4. Direct observation of silicon surface etching by water with scanning tunneling microscopy

    NASA Astrophysics Data System (ADS)

    Pietsch, G. J.; Köhler, U.; Henzler, M.

    1992-09-01

    One of the key processes in wet chemical preparation of silicon surfaces for device fabrication is a final rinsing step with water after oxide removal and hydrogen-termination with hydrofluoric acid. On rinsing at elevated temperature (boiling water) the slow statistical oxidation of the surface known from conventional treatment with water at room temperature is replaced by a rapid anisotropic etching attack. On Si(111) scanning tunneling microscopy shows characteristic triangular etch defects and flat (111) terraces separated by monatomic steps along <0 overline11>. The resulting surface is chemically homogeneous without any oxide. Structure and removal mechanism are compared to NH 4F-etched samples.

  5. High resolution core level spectroscopy of hydrogen-terminated (1 0 0) diamond.

    PubMed

    Schenk, A K; Rietwyk, K J; Tadich, A; Stacey, A; Ley, L; Pakes, C I

    2016-08-01

    Synchrotron-based photoelectron spectroscopy experiments are presented that address a long standing inconsistency in the treatment of the C1s core level of hydrogen terminated (1 0 0) diamond. Through a comparison of surface and bulk sensitive measurements we show that there is a surface related core level component to lower binding energy of the bulk diamond component; this component has a chemical shift of [Formula: see text] eV which has been attributed to carbon atoms which are part of the hydrogen termination. Additionally, our results indicate that the asymmetry of the hydrogen terminated (1 0 0) diamond C1s core level is an intrinsic aspect of the bulk diamond peak which we have attributed to sub-surface carbon layers. PMID:27299369

  6. High resolution core level spectroscopy of hydrogen-terminated (1 0 0) diamond

    NASA Astrophysics Data System (ADS)

    Schenk, A. K.; Rietwyk, K. J.; Tadich, A.; Stacey, A.; Ley, L.; Pakes, C. I.

    2016-08-01

    Synchrotron-based photoelectron spectroscopy experiments are presented that address a long standing inconsistency in the treatment of the C1s core level of hydrogen terminated (1 0 0) diamond. Through a comparison of surface and bulk sensitive measurements we show that there is a surface related core level component to lower binding energy of the bulk diamond component; this component has a chemical shift of -0.16+/- 0.05 eV which has been attributed to carbon atoms which are part of the hydrogen termination. Additionally, our results indicate that the asymmetry of the hydrogen terminated (1 0 0) diamond C1s core level is an intrinsic aspect of the bulk diamond peak which we have attributed to sub-surface carbon layers.

  7. Electrochemical hydrogen termination of boron-doped diamond

    SciTech Connect

    Hoffmann, Rene; Kriele, Armin; Obloh, Harald; Hees, Jakob; Wolfer, Marco; Smirnov, Waldemar; Yang Nianjun; Nebel, Christoph E.

    2010-08-02

    Boron-doped diamond is a promising transducer material for numerous devices which are designed for contact with electrolytes. For optimized electron transfer the surface of diamond needs to be hydrogen terminated. Up to now H-termination of diamond is done by plasma chemical vapor deposition techniques. In this paper, we show that boron-doped diamond can be H-terminated electrochemically by applying negative voltages in acidic solutions. Electrochemical H-termination generates a clean surface with virtually no carbon-oxygen bonds (x-ray photoelectron spectroscopy), a reduced electron affinity (scanning electron microscopy), a highly hydrophobic surface (water contact angle), and a fast electron exchange with Fe(CN){sub 6}{sup -3/-4} (cyclic voltammetry).

  8. Bulk-like pentacene epitaxial films on hydrogen-terminated Si(111)

    SciTech Connect

    Shimada, Toshihiro; Nogawa, Hiroyuki; Hasegawa, Tetsuya; Okada, Ryusuke; Ichikawa, Hisashi; Ueno, Keiji; Saiki, Koichiro

    2005-08-08

    The epitaxial growth of pentacene on hydrogen-terminated Si(111) is reported. Reflection high energy electron diffraction (RHEED) revealed that the crystal packing resembles that in the bulk crystal even at a monolayer thickness, which was maintained in multilayers. A ripening effect was clearly observed by atomic force microscopy (AFM). These results are important to obtain oriented crystalline films of pentacene combined with silicon microdevices with reduced defect densities.

  9. Delta-Doping at Wafer Level for High Throughput, High Yield Fabrication of Silicon Imaging Arrays

    NASA Technical Reports Server (NTRS)

    Hoenk, Michael E. (Inventor); Nikzad, Shoulch (Inventor); Jones, Todd J. (Inventor); Greer, Frank (Inventor); Carver, Alexander G. (Inventor)

    2014-01-01

    Systems and methods for producing high quantum efficiency silicon devices. A silicon MBE has a preparation chamber that provides for cleaning silicon surfaces using an oxygen plasma to remove impurities and a gaseous (dry) NH3 + NF3 room temperature oxide removal process that leaves the silicon surface hydrogen terminated. Silicon wafers up to 8 inches in diameter have devices that can be fabricated using the cleaning procedures and MBE processing, including delta doping.

  10. Properties of Hydrogen Terminated Diamond as a Photocathode

    SciTech Connect

    J Rameau; J Smedley; E Muller; T Kidd; P Johnson

    2011-12-31

    Electron emission from the negative electron affinity (NEA) surface of hydrogen terminated, boron doped diamond in the [100] orientation is investigated using angle resolved photoemission spectroscopy (ARPES). ARPES measurements using 16 eV synchrotron and 6 eV laser light are compared and found to show a catastrophic failure of the sudden approximation. While the high energy photoemission is found to yield little information regarding the NEA, low energy laser ARPES reveals for the first time that the NEA results from a novel Franck-Condon mechanism coupling electrons in the conduction band to the vacuum. The result opens the door to the development of a new class of NEA electron emitter based on this effect.

  11. Functionalization of Oxide-Free Silicon Surfaces with Redox-Active Assemblies.

    PubMed

    Fabre, Bruno

    2016-04-27

    This review provides a comprehensive survey of the derivatization of hydrogen-terminated, oxide-free silicon surfaces with electroactive assemblies (from molecules to polymers) attached through strong interactions (covalent, electrostatic, and chimisorption). Provided that surface modification procedures are thoroughly optimized, such an approach has appeared as a promising strategy toward high-quality functional interfaces exhibiting excellent chemical and electrochemical stabilities. The attachment of electroactive molecules exhibiting either two stable redox states (e.g., ferrocene and quinones) or more than two stable redox states (e.g., metalloporphyrins, polyoxometalates, and C60) is more particularly discussed. Attention is also paid to the immobilization of electrochemically polymerizable centers. Globally, these functional interfaces have been demonstrated to show great promise for the molecular charge storage and information processing or the elaboration of the electrochemically switchable devices. Besides, there are also some relevant examples dealing with their activity for other fields of interest, such as sensing and electrochemical catalysis. PMID:27064580

  12. Surface property modification of silicon

    NASA Technical Reports Server (NTRS)

    Danyluk, S.

    1984-01-01

    The main emphasis of this work has been to determine the wear rate of silicon in fluid environments and the parameters that influence wear. Three tests were carried out on single crystal Czochralski silicon wafers: circular and linear multiple-scratch tests in fluids by a pyramidal diamond simulated fixed-particle abrasion; microhardness and three-point bend tests were used to determine the hardness and fracture toughness of abraded silicon and the extent of damage induced by abrasion. The wear rate of (100) and (111) n and p-type single crystal Cz silicon abraded by a pyramidal diamond in ethanol, methanol, acetone and de-ionized water was determined by measuring the cross-sectional areas of grooves of the circular and linear multiple-scratch tests. The wear rate depends on the loads on the diamond and is highest for ethanol and lowest for de-ionized water. The surface morphology of the grooves showed lateral and median cracks as well as a plastically deformed region. The hardness and fracture toughness are critical parameters that influence the wear rate. Microhardness tests were conducted to determine the hardness as influenced by fluids. Median cracks and the damage zone surrounding the indentations were also related to the fluid properties.

  13. Surface alloying of silicon into aluminum substrate.

    SciTech Connect

    Xu, Z.

    1998-10-28

    Aluminum alloys that are easily castable tend to have lower silicon content and hence lower wear resistance. The use of laser surface alloying to improve the surface wear resistance of 319 and 320 aluminum alloys was examined. A silicon layer was painted onto the surface to be treated. A high power pulsed Nd:YAG laser with fiberoptic beam delivery was used to carry out the laser surface treatment to enhance the silicon content. Process parameters were varied to minimize the surface roughness from overlap of the laser beam treatment. The surface-alloyed layer was characterized and the silicon content was determined.

  14. Modification of crystalline silicon and diamond surfaces for the attachment of DNA

    NASA Astrophysics Data System (ADS)

    Strother, Todd Cory

    2001-07-01

    Hydrogen-terminated Si(111) surfaces are first modified by attachment of oligodeoxynucleotides, and characterized with respect to DNA surface density, chemical stability, and DNA hybridization binding specificity. Surface functionalization employs the reaction of o-unsaturated alkyl esters with the Si(111) surface using UV irradiation. Cleavage of the ester using potassium tert-butoxide yields a carboxyl-modified surface, which serves as a substrate for the attachment of DNA by means of an electrostatically adsorbed layer of polylysine and attachment of thiol modified DNA using a heterobifunctional cross-linker. The resultant DNA-modified surfaces are shown to exhibit excellent specificity and chemical stability under the conditions of DNA hybridization. The second approach is a more direct method of attaching oligonucleotides to silicon. UV light mediates the reaction of t-butyloxycarbonyl (t-BOC) protected o-unsaturated aminoalkane (10-aminodec-1-ene) with hydrogenterminated silicon (001). Removal of the t-BOC protecting group yields an aminodecane-modified silicon surface. The resultant amino groups can be coupled to thiol-modified oligodeoxyribonucleotides using a heterobifunctional crosslinker, permitting the preparation of DNA arrays. Two methods for controlling the surface density of oligodeoxyribonucleotides were explored: in the first, binary mixtures of 10-aminodec-1 ene and dodecene were utilized in the initial UV-mediated coupling reaction; a linear relationship was found between the mole fraction of aminodecene and the density of DNA hybridization sites. In the second, only a portion of the t-BOC protecting groups was removed from the surface by limiting the time allowed for the deprotection reaction. The final surface explored uses a UV-mediated reaction of alkenes to hydrogenterminated diamond. Polycrystalline diamond thin films are hydrogen terminated using a hydrogen plasma and are subjected to UV light in the presence of 1-alkenes. A

  15. Mechanisms and energetics of hydride dissociation reactions on surfaces of plasma-deposited silicon thin films

    NASA Astrophysics Data System (ADS)

    Singh, Tejinder; Valipa, Mayur S.; Mountziaris, T. J.; Maroudas, Dimitrios

    2007-11-01

    We report results from a detailed analysis of the fundamental silicon hydride dissociation processes on silicon surfaces and discuss their implications for the surface chemical composition of plasma-deposited hydrogenated amorphous silicon (a-Si:H) thin films. The analysis is based on a synergistic combination of first-principles density functional theory (DFT) calculations of hydride dissociation on the hydrogen-terminated Si(001)-(2×1) surface and molecular-dynamics (MD) simulations of adsorbed SiH3 radical precursor dissociation on surfaces of MD-grown a-Si :H films. Our DFT calculations reveal that, in the presence of fivefold coordinated surface Si atoms, surface trihydride species dissociate sequentially to form surface dihydrides and surface monohydrides via thermally activated pathways with reaction barriers of 0.40-0.55eV. The presence of dangling bonds (DBs) results in lowering the activation barrier for hydride dissociation to 0.15-0.20eV, but such DB-mediated reactions are infrequent. Our MD simulations on a-Si :H film growth surfaces indicate that surface hydride dissociation reactions are predominantly mediated by fivefold coordinated surface Si atoms, with resulting activation barriers of 0.35-0.50eV. The results are consistent with experimental measurements of a-Si :H film surface composition using in situ attenuated total reflection Fourier transform infrared spectroscopy, which indicate that the a-Si :H surface is predominantly covered with the higher hydrides at low temperatures, while the surface monohydride, SiH(s ), becomes increasingly more dominant as the temperature is increased.

  16. Hydrogen-terminated detonation nanodiamond: Impedance spectroscopy and thermal stability studies

    NASA Astrophysics Data System (ADS)

    Su, Shi; Li, Jiangling; Kundrát, Vojtěch; Abbot, Andrew M.; Ye, Haitao

    2013-01-01

    In this paper, we investigated the effect of hydrogen termination on the electrical properties and impedance spectra of detonation nanodiamond. The impedance spectra revealed that the hydrogen-termination process increases the electrical conductivity by four orders of magnitude at room temperature. An equivalent circuit has been proposed to correlate with the conduction mechanism. Arrhenius plot showed that there were two different activation energy levels located at 0.089 eV and 0.63 eV between 50 °C and 400 °C. The possible physical mechanism corresponding to these activation energy levels has been discussed. Hydrogen-terminated detonation nanodiamond has been further annealed at different temperatures prior to FTIR and XPS measurements in order to understand their thermal stability. The results demonstrated that the surface oxidization occurred between 100 °C and 150 °C. However, the C-H bonds could partially survive when the temperature reaches 400 °C in air.

  17. In situ transmission infrared spectroscopy of high-kappa oxide atomic layer deposition onto silicon surfaces

    NASA Astrophysics Data System (ADS)

    Ho, Ming-Tsung

    Ultra-thin aluminum oxide (Al2O3) and hafnium oxide (HfO2) layers have been grown by atomic layer deposition (ALD) using tri-methyl-aluminum (TMA) and tetrakis-ethyl-methyl-amino-hafnium (TEMAH) respectively with heavy water (D2O) as the oxidizing agent. Several different silicon surfaces were used as substrates such as hydrogen terminated silicon (H/Si), SC2 (or RCA 2) cleaned native silicon oxide (SiO 2/Si), and silicon (oxy)nitride. In-situ transmission Fourier transform infrared spectroscopy (FTIR) has been adopted for the study of the growth mechanisms during ALD of these films. The vibrational spectra of gas phase TEMAH and its reaction byproducts with oxidants have also been investigated. Density functional theory (DFT) normal mode calculations show a good agreement with the experimental data when it is combined with linear wave-number scaling method and Fermi resonance mechanism. Ether (-C-O-C-) and tertiary alkylamine (N(R1R 2R3)) compounds are the two most dominant products of TEMAH reacting with oxygen gas and water. When ozone is used as the oxidant, gas phase CH2O, CH3NO2, CH3-N=C=O and other compounds containing -(C=O)- and --C-O-C- (or --O-C-) segments are observed. With substrate temperatures less than 400°C and 300°C for TMA and TEMAH respectively, Al oxide and Hf oxide ALD can be appropriately performed on silicon surfaces. Thin silicon (oxy)nitride thermally grown in ammonia on silicon substrate can significantly reduce silicon oxide interlayer formation during ALD and post-deposition annealing. The crystallization temperature of amorphous ALD grown HfO2 on nitridized silicon is 600°C, which is 100°C higher than on the other silicon surfaces. When HfO2 is grown on H/Si(111) at 100°C deposition temperature, minimum 5--10 ALD cycles are required for the full surface coverage. The steric effect can be seen by the evolution of the H-Si stretching mode at 2083 cm-1. The observed red shift of H-Si stretching to ˜ 2060 cm-1 can be caused by Si

  18. Interactions between radical growth precursors on plasma-deposited silicon thin-film surfaces

    SciTech Connect

    Bakos, Tamas; Valipa, Mayur S.; Maroudas, Dimitrios

    2007-03-21

    We present a detailed analysis of the interactions between growth precursors, SiH{sub 3} radicals, on surfaces of silicon thin films. The analysis is based on a synergistic combination of density functional theory calculations on the hydrogen-terminated Si(001)-(2x1) surface and molecular-dynamics (MD) simulations of film growth on surfaces of MD-generated hydrogenated amorphous silicon (a-Si:H) thin films. In particular, the authors find that two interacting growth precursors may either form disilane (Si{sub 2}H{sub 6}) and desorb from the surface, or disproportionate, resulting in the formation of a surface dihydride (adsorbed SiH{sub 2} species) and gas-phase silane (SiH{sub 4}). The reaction barrier for disilane formation is found to be strongly dependent on the local chemical environment on the silicon surface and reduces (or vanishes) if one/both of the interacting precursors is/are in a ''fast diffusing state,'' i.e., attached to fivefold coordinated surface Si atoms. Finally, activation energy barriers in excess of 1 eV are obtained for two chemisorbed (i.e., bonded to a fourfold coordinated surface Si atom) SiH{sub 3} radicals. Activation energy barriers for disproportionation follow the same tendency, though, in most cases, higher barriers are obtained compared to disilane formation reactions starting from the same initial configuration. MD simulations confirm that disilane formation and disproportionation reactions also occur on a-Si:H growth surfaces, preferentially in configurations where at least one of the SiH{sub 3} radicals is in a ''diffusive state.'' Our results are in agreement with experimental observations and results of plasma process simulators showing that the primary source for disilane in low-power plasmas may be the substrate surface.

  19. Interactions between radical growth precursors on plasma-deposited silicon thin-film surfaces

    NASA Astrophysics Data System (ADS)

    Bakos, Tamas; Valipa, Mayur S.; Maroudas, Dimitrios

    2007-03-01

    We present a detailed analysis of the interactions between growth precursors, SiH3 radicals, on surfaces of silicon thin films. The analysis is based on a synergistic combination of density functional theory calculations on the hydrogen-terminated Si(001)-(2×1) surface and molecular-dynamics (MD) simulations of film growth on surfaces of MD-generated hydrogenated amorphous silicon (a-Si :H) thin films. In particular, the authors find that two interacting growth precursors may either form disilane (Si2H6) and desorb from the surface, or disproportionate, resulting in the formation of a surface dihydride (adsorbed SiH2 species) and gas-phase silane (SiH4). The reaction barrier for disilane formation is found to be strongly dependent on the local chemical environment on the silicon surface and reduces (or vanishes) if one/both of the interacting precursors is/are in a "fast diffusing state," i.e., attached to fivefold coordinated surface Si atoms. Finally, activation energy barriers in excess of 1eV are obtained for two chemisorbed (i.e., bonded to a fourfold coordinated surface Si atom) SiH3 radicals. Activation energy barriers for disproportionation follow the same tendency, though, in most cases, higher barriers are obtained compared to disilane formation reactions starting from the same initial configuration. MD simulations confirm that disilane formation and disproportionation reactions also occur on a-Si :H growth surfaces, preferentially in configurations where at least one of the SiH3 radicals is in a "diffusive state." Our results are in agreement with experimental observations and results of plasma process simulators showing that the primary source for disilane in low-power plasmas may be the substrate surface.

  20. Interactions between radical growth precursors on plasma-deposited silicon thin-film surfaces.

    PubMed

    Bakos, Tamas; Valipa, Mayur S; Maroudas, Dimitrios

    2007-03-21

    We present a detailed analysis of the interactions between growth precursors, SiH3 radicals, on surfaces of silicon thin films. The analysis is based on a synergistic combination of density functional theory calculations on the hydrogen-terminated Si(001)-(2x1) surface and molecular-dynamics (MD) simulations of film growth on surfaces of MD-generated hydrogenated amorphous silicon (a-Si:H) thin films. In particular, the authors find that two interacting growth precursors may either form disilane (Si2H6) and desorb from the surface, or disproportionate, resulting in the formation of a surface dihydride (adsorbed SiH2 species) and gas-phase silane (SiH4). The reaction barrier for disilane formation is found to be strongly dependent on the local chemical environment on the silicon surface and reduces (or vanishes) if one/both of the interacting precursors is/are in a "fast diffusing state," i.e., attached to fivefold coordinated surface Si atoms. Finally, activation energy barriers in excess of 1 eV are obtained for two chemisorbed (i.e., bonded to a fourfold coordinated surface Si atom) SiH3 radicals. Activation energy barriers for disproportionation follow the same tendency, though, in most cases, higher barriers are obtained compared to disilane formation reactions starting from the same initial configuration. MD simulations confirm that disilane formation and disproportionation reactions also occur on a-Si:H growth surfaces, preferentially in configurations where at least one of the SiH3 radicals is in a "diffusive state." Our results are in agreement with experimental observations and results of plasma process simulators showing that the primary source for disilane in low-power plasmas may be the substrate surface. PMID:17381225

  1. Hydrogen termination of CVD diamond films by high-temperature annealing at atmospheric pressure.

    PubMed

    Seshan, V; Ullien, D; Castellanos-Gomez, A; Sachdeva, S; Murthy, D H K; Savenije, T J; Ahmad, H A; Nunney, T S; Janssens, S D; Haenen, K; Nesládek, M; van der Zant, H S J; Sudhölter, E J R; de Smet, L C P M

    2013-06-21

    A high-temperature procedure to hydrogenate diamond films using molecular hydrogen at atmospheric pressure was explored. Undoped and doped chemical vapour deposited (CVD) polycrystalline diamond films were treated according to our annealing method using a H2 gas flow down to ~50 ml∕min (STP) at ~850 °C. The films were extensively evaluated by surface wettability, electron affinity, elemental composition, photoconductivity, and redox studies. In addition, electrografting experiments were performed. The surface characteristics as well as the optoelectronic and redox properties of the annealed films were found to be very similar to hydrogen plasma-treated films. Moreover, the presented method is compatible with atmospheric pressure and provides a low-cost solution to hydrogenate CVD diamond, which makes it interesting for industrial applications. The plausible mechanism for the hydrogen termination of CVD diamond films is based on the formation of surface carbon dangling bonds and carbon-carbon unsaturated bonds at the applied tempera-ture, which react with molecular hydrogen to produce a hydrogen-terminated surface. PMID:23802976

  2. Hydrogen termination of CVD diamond films by high-temperature annealing at atmospheric pressure

    NASA Astrophysics Data System (ADS)

    Seshan, V.; Ullien, D.; Castellanos-Gomez, A.; Sachdeva, S.; Murthy, D. H. K.; Savenije, T. J.; Ahmad, H. A.; Nunney, T. S.; Janssens, S. D.; Haenen, K.; Nesládek, M.; van der Zant, H. S. J.; Sudhölter, E. J. R.; de Smet, L. C. P. M.

    2013-06-01

    A high-temperature procedure to hydrogenate diamond films using molecular hydrogen at atmospheric pressure was explored. Undoped and doped chemical vapour deposited (CVD) polycrystalline diamond films were treated according to our annealing method using a H2 gas flow down to ˜50 ml/min (STP) at ˜850 °C. The films were extensively evaluated by surface wettability, electron affinity, elemental composition, photoconductivity, and redox studies. In addition, electrografting experiments were performed. The surface characteristics as well as the optoelectronic and redox properties of the annealed films were found to be very similar to hydrogen plasma-treated films. Moreover, the presented method is compatible with atmospheric pressure and provides a low-cost solution to hydrogenate CVD diamond, which makes it interesting for industrial applications. The plausible mechanism for the hydrogen termination of CVD diamond films is based on the formation of surface carbon dangling bonds and carbon-carbon unsaturated bonds at the applied tempera-ture, which react with molecular hydrogen to produce a hydrogen-terminated surface.

  3. Investigation of silicon surface passivation by silicon nitride film deposition

    NASA Technical Reports Server (NTRS)

    Olsen, L. C.

    1984-01-01

    The use of Sin sub x grown by plasma enhanced chemical vapor deposition (PECVO) for passivating silicon surfaces was studied. The application of PECVO SiN sub x films for passivations of silicon N+/P or P+/N solar cells is of particular interest. This program has involved the following areas of investigation: (1) Establishment of PECVO system and development of procedures for growth of SiN sub x; (2) Optical characterization of SiN sub x films; (3) Characterization of the SiN sub x/Si interface; (4) Surface recombination velocity deduced from photoresponse; (5) Current-Voltage analyses of silicon N+/P cells; and (6) Gated diode device studies.

  4. Tuned NV emission by in-plane Al-Schottky junctions on hydrogen terminated diamond

    PubMed Central

    Schreyvogel, Christoph; Wolfer, Marco; Kato, Hiromitsu; Schreck, Matthias; Nebel, Christoph E.

    2014-01-01

    The negatively charged nitrogen-vacancy (NV) centre exhibits outstanding optical and spin properties and thus is very attractive for applications in quantum optics. Up to now an active control of the charge state of near-surface NV centres is difficult and the centres switch in an uncontrolled way between different charge states. In this work, we demonstrate an active control of the charge state of NV centres (implanted 7 nm below the surface) by using an in-plane Schottky diode geometry from aluminium on hydrogen terminated diamond in combination with confocal micro-photoluminescence measurements. The partial quenching of NV-photoluminescence caused by the hole accumulation layer of the hydrogen terminated surface can be recovered by applying reverse bias potentials on this diode, i.e. the NV0 charge state is depleted while the NV− charge state is populated. This charge state conversion is caused by the bias voltage affected modulation of the band bending in the depletion region which shifts the Fermi level across the NV charge transition levels. PMID:24407227

  5. Systematic spatial and stoichiometric screening towards understanding the surface of ultrasmall oxygenated silicon nanocrystal

    NASA Astrophysics Data System (ADS)

    Niaz, Shanawer; Zdetsis, Aristides D.; Koukaras, Emmanuel N.; Gülseren, Oǧuz; Sadiq, Imran

    2016-11-01

    In most of the realistic ab initio and model calculations which have appeared on the emission of light from silicon nanocrystals, the role of surface oxygen has been usually ignored, underestimated or completely ruled out. We investigate theoretically, by density functional theory (DFT/B3LYP) possible modes of oxygen bonding in hydrogen terminated silicon quantum dots using as a representative case of the Si29 nanocrystal. We have considered Bridge-bonded oxygen (BBO), Doubly-bonded oxygen (DBO), hydroxyl (OH) and Mix of these oxidizing agents. Due to stoichiometry, all comparisons performed are unbiased with respect to composition whereas spatial distribution of oxygen species pointed out drastic change in electronic and cohesive characteristics of nanocrytals. From an overall perspective of this study, it is shown that bridge bonded oxygenated Si nanocrystals accompanied by Mix have higher binding energies and large electronic gap compared to nanocrystals with doubly bonded oxygen atoms. In addition, it is observed that the presence of OH along with BBO, DBO and mixed configurations further lowers electronic gaps and binding energies but trends in same fashion. It is also demonstrated that within same composition, oxidizing constituent, along with their spatial distribution substantially alters binding energy, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) gap (up to 1.48 eV) and localization of frontier orbitals.

  6. Microtextured Silicon Surfaces for Detectors, Sensors & Photovoltaics

    SciTech Connect

    Carey, JE; Mazur, E

    2005-05-19

    With support from this award we studied a novel silicon microtexturing process and its application in silicon-based infrared photodetectors. By irradiating the surface of a silicon wafer with intense femtosecond laser pulses in the presence of certain gases or liquids, the originally shiny, flat surface is transformed into a dark array of microstructures. The resulting microtextured surface has near-unity absorption from near-ultraviolet to infrared wavelengths well below the band gap. The high, broad absorption of microtextured silicon could enable the production of silicon-based photodiodes for use as inexpensive, room-temperature multi-spectral photodetectors. Such detectors would find use in numerous applications including environmental sensors, solar energy, and infrared imaging. The goals of this study were to learn about microtextured surfaces and then develop and test prototype silicon detectors for the visible and infrared. We were extremely successful in achieving our goals. During the first two years of this award, we learned a great deal about how microtextured surfaces form and what leads to their remarkable optical properties. We used this knowledge to build prototype detectors with high sensitivity in both the visible and in the near-infrared. We obtained room-temperature responsivities as high as 100 A/W at 1064 nm, two orders of magnitude higher than standard silicon photodiodes. For wavelengths below the band gap, we obtained responsivities as high as 50 mA/W at 1330 nm and 35 mA/W at 1550 nm, close to the responsivity of InGaAs photodiodes and five orders of magnitude higher than silicon devices in this wavelength region.

  7. Silicon nanopillars for field enhanced surface spectroscopy

    SciTech Connect

    Wells, Sabrina M; Merkulov, Igor A; Kravchenko, Ivan I; Lavrik, Nickolay V; Sepaniak, Michael J

    2012-01-01

    Silicon nanowire and nanopillar structures have continued to draw increased attention in recent years due in part to their unique optical properties. Herein, electron beam lithography combined with reactive-ion etching is used to reproducibly create individual silicon nanopillars of various sizes, shapes, and heights. Finite difference time domain numerical analysis predicts enhancements in localized fields in the vicinity of appropriately-sized and coaxially-illuminated silicon nanopillars of approximately two orders of magnitude. By analyzing experimentally measured strength of the silicon Raman phonon line (500 cm-1), it was determined that nanopillars produced field enhancement that are consistent with these predictions. Additionally, we demonstrate that a thin layer of Zn phthalocyanine deposited on the nanopillar surface produced prominent Raman spectra yielding enhancement factors (EFs) better than 300. Finally, silicon nanopillars of cylindrical and elliptical shapes were labeled with different fluorophors and evaluated for their surface enhanced fluorescence (SEF) capability. The EF derived from analysis of the acquired fluorescence microscopy images indicate that silicon nanopillar structures can provide enhancement comparable or even stronger than those typically achieved using plasmonic SEF structures without the drawbacks of the metal-based substrates. It is anticipated that scaled up arrays of silicon nanopillars will enable SEF assays with extremely high sensitivity, while a broader impact of the reported phenomena are anticipated in photovoltaics, subwavelength light focusing, and fundamental nanophotonics.

  8. Controlled Adhesion of Silicone Elastomer Surfaces

    NASA Astrophysics Data System (ADS)

    Owen, Michael

    2000-03-01

    Opportunities exist for controllably enhancing the adhesion of silicone surfaces, ranging from modest enhancement of release force levels of pressure-sensitive adhesive (PSA) release liners by incorporation of adhesion promoters known as high release additives (HRA), to permanent bonding of silicone elastomers using surface modification techniques such as plasma or corona treatment. Although only a part of the complex interaction of factors contributing to adhesion, surface properties such as wettability are a critical component in the understanding and control of release and adhesion phenomena. Surface characterization studies of low-surface-energy silicones before and after various adhesion modification strategies are reviewed. The silicones include polydimethylsiloxane (PDMS) and fluorosiloxane elastomers and coatings. Techniques used include contact angle, the Johnson, Kendall and Roberts (JKR) contact mechanics approach, scanning electron microscopy (SEM), atomic force microscopy (AFM), and x-ray photoelectron spectroscopy (XPS). Topics addressed are: use of HRA in PDMS release liners, the interaction of PDMS PSAs with polytetrafluoroethylene (PTFE), and the effect of plasma treatment on PDMS and fluorosiloxane surfaces.

  9. Nanoparticle-based etching of silicon surfaces

    SciTech Connect

    Branz, Howard; Duda, Anna; Ginley, David S.; Yost, Vernon; Meier, Daniel; Ward, James S.

    2011-12-13

    A method (300) of texturing silicon surfaces (116) such to reduce reflectivity of a silicon wafer (110) for use in solar cells. The method (300) includes filling (330, 340) a vessel (122) with a volume of an etching solution (124) so as to cover the silicon surface 116) of a wafer or substrate (112). The etching solution (124) is made up of a catalytic nanomaterial (140) and an oxidant-etchant solution (146). The catalytic nanomaterial (140) may include gold or silver nanoparticles or noble metal nanoparticles, each of which may be a colloidal solution. The oxidant-etchant solution (146) includes an etching agent (142), such as hydrofluoric acid, and an oxidizing agent (144), such as hydrogen peroxide. Etching (350) is performed for a period of time including agitating or stirring the etching solution (124). The etch time may be selected such that the etched silicon surface (116) has a reflectivity of less than about 15 percent such as 1 to 10 percent in a 350 to 1000 nanometer wavelength range.

  10. Oxide driven strength evolution of silicon surfaces

    SciTech Connect

    Grutzik, Scott J.; Zehnder, Alan T.; Milosevic, Erik; Boyce, Brad L.

    2015-11-21

    Previous experiments have shown a link between oxidation and strength changes in single crystal silicon nanostructures but provided no clues as to the mechanisms leading to this relationship. Using atomic force microscope-based fracture strength experiments, molecular dynamics modeling, and measurement of oxide development with angle resolved x-ray spectroscopy we study the evolution of strength of silicon (111) surfaces as they oxidize and with fully developed oxide layers. We find that strength drops with partial oxidation but recovers when a fully developed oxide is formed and that surfaces intentionally oxidized from the start maintain their high initial strengths. MD simulations show that strength decreases with the height of atomic layer steps on the surface. These results are corroborated by a completely separate line of testing using micro-scale, polysilicon devices, and the slack chain method in which strength recovers over a long period of exposure to the atmosphere. Combining our results with insights from prior experiments we conclude that previously described strength decrease is a result of oxidation induced roughening of an initially flat silicon (1 1 1) surface and that this effect is transient, a result consistent with the observation that surfaces flatten upon full oxidation.

  11. Oxide driven strength evolution of silicon surfaces

    NASA Astrophysics Data System (ADS)

    Grutzik, Scott J.; Milosevic, Erik; Boyce, Brad L.; Zehnder, Alan T.

    2015-11-01

    Previous experiments have shown a link between oxidation and strength changes in single crystal silicon nanostructures but provided no clues as to the mechanisms leading to this relationship. Using atomic force microscope-based fracture strength experiments, molecular dynamics modeling, and measurement of oxide development with angle resolved x-ray spectroscopy we study the evolution of strength of silicon (111) surfaces as they oxidize and with fully developed oxide layers. We find that strength drops with partial oxidation but recovers when a fully developed oxide is formed and that surfaces intentionally oxidized from the start maintain their high initial strengths. MD simulations show that strength decreases with the height of atomic layer steps on the surface. These results are corroborated by a completely separate line of testing using micro-scale, polysilicon devices, and the slack chain method in which strength recovers over a long period of exposure to the atmosphere. Combining our results with insights from prior experiments we conclude that previously described strength decrease is a result of oxidation induced roughening of an initially flat silicon (1 1 1) surface and that this effect is transient, a result consistent with the observation that surfaces flatten upon full oxidation.

  12. Nickel deposition on silicon surfaces

    NASA Astrophysics Data System (ADS)

    Beleznai, Cs.; Nanai, Laszlo; Leppaevuori, Seppo; Remes, Janne; Moilanen, Hannu; George, Thomas F.

    1998-08-01

    Experimental results of laser assisted chemical vapor deposition of nickel from Ni(CO)4 and theoretical treatment of deposition process are presented. The nickel deposition has ben realized by scanning of Ar+ laser beam (100 - 400 mW, (lambda) equals 515 nm and 488 nm) on Si surfaces in atmosphere of Ni(CO)4 with 0.2 - 2.0 mbars with scanning speeds of 20 - 700 micrometers /s. As a result homogeneous Ni lines on Si have been deposited with a typical volumetric growth rate of 250 micrometers 3/s and widths of 10 - 20 micrometers and thickness of 0.2 - 0.5 micrometers . The electrical resistivity of lines deposited was cca 7 (mu) (Omega) cm. The theoretical treatment includes computations of the temperature distribution in both gas- phase and solid substrate. The reaction rate is computed on base of local concentration and local temperatures, within the frame of finite element methods using triangles as a base of computing.

  13. A surface code quantum computer in silicon.

    PubMed

    Hill, Charles D; Peretz, Eldad; Hile, Samuel J; House, Matthew G; Fuechsle, Martin; Rogge, Sven; Simmons, Michelle Y; Hollenberg, Lloyd C L

    2015-10-01

    The exceptionally long quantum coherence times of phosphorus donor nuclear spin qubits in silicon, coupled with the proven scalability of silicon-based nano-electronics, make them attractive candidates for large-scale quantum computing. However, the high threshold of topological quantum error correction can only be captured in a two-dimensional array of qubits operating synchronously and in parallel-posing formidable fabrication and control challenges. We present an architecture that addresses these problems through a novel shared-control paradigm that is particularly suited to the natural uniformity of the phosphorus donor nuclear spin qubit states and electronic confinement. The architecture comprises a two-dimensional lattice of donor qubits sandwiched between two vertically separated control layers forming a mutually perpendicular crisscross gate array. Shared-control lines facilitate loading/unloading of single electrons to specific donors, thereby activating multiple qubits in parallel across the array on which the required operations for surface code quantum error correction are carried out by global spin control. The complexities of independent qubit control, wave function engineering, and ad hoc quantum interconnects are explicitly avoided. With many of the basic elements of fabrication and control based on demonstrated techniques and with simulated quantum operation below the surface code error threshold, the architecture represents a new pathway for large-scale quantum information processing in silicon and potentially in other qubit systems where uniformity can be exploited. PMID:26601310

  14. A surface code quantum computer in silicon

    PubMed Central

    Hill, Charles D.; Peretz, Eldad; Hile, Samuel J.; House, Matthew G.; Fuechsle, Martin; Rogge, Sven; Simmons, Michelle Y.; Hollenberg, Lloyd C. L.

    2015-01-01

    The exceptionally long quantum coherence times of phosphorus donor nuclear spin qubits in silicon, coupled with the proven scalability of silicon-based nano-electronics, make them attractive candidates for large-scale quantum computing. However, the high threshold of topological quantum error correction can only be captured in a two-dimensional array of qubits operating synchronously and in parallel—posing formidable fabrication and control challenges. We present an architecture that addresses these problems through a novel shared-control paradigm that is particularly suited to the natural uniformity of the phosphorus donor nuclear spin qubit states and electronic confinement. The architecture comprises a two-dimensional lattice of donor qubits sandwiched between two vertically separated control layers forming a mutually perpendicular crisscross gate array. Shared-control lines facilitate loading/unloading of single electrons to specific donors, thereby activating multiple qubits in parallel across the array on which the required operations for surface code quantum error correction are carried out by global spin control. The complexities of independent qubit control, wave function engineering, and ad hoc quantum interconnects are explicitly avoided. With many of the basic elements of fabrication and control based on demonstrated techniques and with simulated quantum operation below the surface code error threshold, the architecture represents a new pathway for large-scale quantum information processing in silicon and potentially in other qubit systems where uniformity can be exploited. PMID:26601310

  15. Porosity-dependent fractal nature of the porous silicon surface

    SciTech Connect

    Rahmani, N.; Dariani, R. S.

    2015-07-15

    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 layer 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.

  16. Copper-assisted, anti-reflection etching of silicon surfaces

    DOEpatents

    Toor, Fatima; Branz, Howard

    2014-08-26

    A method (300) for etching a silicon surface (116) to reduce reflectivity. The method (300) includes electroless deposition of copper nanoparticles about 20 nanometers in size on the silicon surface (116), with a particle-to-particle spacing of 3 to 8 nanometers. The method (300) includes positioning (310) the substrate (112) with a silicon surface (116) into a vessel (122). The vessel (122) is filled (340) with a volume of an etching solution (124) so as to cover the silicon surface (116). The etching solution (124) includes an oxidant-etchant solution (146), e.g., an aqueous solution of hydrofluoric acid and hydrogen peroxide. The silicon surface (116) is etched (350) by agitating the etching solution (124) with, for example, ultrasonic agitation, and the etching may include heating (360) the etching solution (124) and directing light (365) onto the silicon surface (116). During the etching, copper nanoparticles enhance or drive the etching process.

  17. Excimer laser induced nanostructuring of silicon surfaces.

    PubMed

    Kumar, Prashant; Krishna, Mamidipudi Ghanashyam; Bhattacharya, Ashok

    2009-05-01

    The effect of KrF excimer laser energy density (below and above the ablation threshold), number of shots and angle of laser incidence on the morphological reconstruction, structure and specular reflectance of Si[311] surfaces is reported. At low energy densities (0.1 to 0.3 J/cm2) laser irradiation results in a variety of nanostructures, depending on laser energy density and number of shots, such as nanopores (40-60 nm dia) and nanoparticles (40-80 nm dia). At energies greater than the laser ablation threshold (2 to 5 J/cm2) the formation of nanowires (200 nm dia, 6-8 microm length), and closely spaced silicon nanograins (100-150 nm dia) is observed. Experiments to study the effect of laser irradiation in the proximity of a fixed shape such as a linear step edge in the form of a stainless steel blade and a cylindrical cross-section Cu wire were also carried out. In both cases, linearly organized nanoparticles (150-200 nm diameter) and nanowires (60-80 nm diameter) formed close to the edge. There is a systematic degradation of long-range order with the number of shots and laser energy density as evidenced from X-ray diffraction studies. At an energy density of 2 J/cm2, and 100 shots the [311] oriented silicon surface made a transition to a randomly oriented nanocrystalline state. PMID:19452995

  18. Atomic Scale Flatness of Chemically Cleaned Silicon Surfaces Studied by Infrared Attenuated-Total-Reflection Spectroscopy

    NASA Astrophysics Data System (ADS)

    Sawara, Kenichi; Yasaka, Tatsuhiro; Miyazaki, Seiichi; Hirose, Masataka

    1992-07-01

    Hydrogen-terminated Si(111) and Si(100) surfaces obtained by aqueous HF or pH-modified (pH{=}5.3) buffered-HF (BHF) treatments have been characterized by a Fourier transform infrared (FT-IR) attenuated-total-reflection (ATR) technique. The BHF treatment provides better surface flatness than the HF treatment. Pure water rinse is effective for improving the Si(111) surface flatness, while this is not the case for Si(100) because the pure water acts as an alkaline etchant and promotes the formation of (111) microfacets or microdefects on the (100) surface.

  19. Comparison of the surface charge behavior of commercial silicon nitride and silicon carbide powders

    NASA Technical Reports Server (NTRS)

    Whitman, Pamela K.; Feke, Donald L.

    1988-01-01

    The adsorption and desorption of protons from aqueous solution onto the surfaces of a variety of commercial silicon carbide and silicon nitride powders has been examined using a surface titration methodology. This method provides information on some colloidal characteristics, such as the point of zero charge (pzc) and the variation of proton adsorption with dispersion pH, useful for the prediction of optimal ceramic-processing conditions. Qualitatively, the magnitude of the proton adsorption from solution reveals small differences among all of the materials studied. However, the results show that the pzc for the various silicon nitride powders is affected by the powder synthesis route. Complementary investigations have shown that milling can also act to shift the pzc exhibited by silicon nitride powder. Also, studies of the role of the electrolyte in the development of surface charge have indicated no evidence of specific adsorption of ammonium ion on either silicon nitride or silicon carbide powders.

  20. Strong explosive interaction of hydrogenated porous silicon with oxygen at cryogenic temperatures.

    PubMed

    Kovalev, D; Timoshenko, V Y; Künzner, N; Gross, E; Koch, F

    2001-08-01

    We report new types of heterogeneous hydrogen-oxygen and silicon-oxygen branched chain reactions which have been found to proceed explosively after the filling of pores of hydrogen-terminated porous silicon (Si) by condensed or liquid oxygen in the temperature range of 4.2-90 K. Infrared vibrational absorption spectroscopy shows that, while initially Si nanocrystals assembling the layers have hydrogen-terminated surfaces, the final products of the reaction are SiO2 and H2O. Time-resolved optical experiments show that the explosive reaction develops in a time scale of 10(-6) s. We emphasize the remarkable structural properties of porous Si layers which are crucial for the strong explosive interaction. PMID:11497868

  1. Surface passivation of heavily boron or phosphorus doped crystalline silicon utilizing amorphous silicon

    NASA Astrophysics Data System (ADS)

    Carstens, K.; Dahlinger, M.

    2016-05-01

    Excellent surface passivation of heavily boron or phosphorus doped crystalline silicon is presented utilizing undoped hydrogenated amorphous silicon (a-Si:H). For passivating boron doped crystalline silicon surfaces, amorphous silicon needs to be deposited at low temperatures 150°C ≤Tdep≤200°C , leading to a high bandgap. In contrast, low bandgap amorphous silicon causes an inferior surface passivation of highly boron doped crystalline silicon. Boron doping in crystalline silicon leads to a shift of the Fermi energy towards the valence band maximum in the undoped a-Si:H. A simulation, implementing dangling bond defects according to the defect pool model, shows this shift in the undoped a-Si:H passivation to be more pronounced if the a-Si:H has a lower bandgap. Hence, the inferior passivation of boron doped surfaces with low bandgap amorphous silicon stems from a lower silicon-hydrogen bond energy due to this shift of the Fermi energy. Hydrogen effusion and ellipsometry measurements support our interpretation.

  2. Review of literature surface tension data for molten silicon

    NASA Technical Reports Server (NTRS)

    Hardy, S.

    1981-01-01

    Measurements of the surface tension of molten silicon are reported. For marangoni flow, the important parameter is the variation of surface tension with temperature, not the absolute value of the surface tension. It is not possible to calculate temperature coefficients using surface tension measurements from different experiments because the systematic errors are usually larger than the changes in surface tension because of temperature variations. The lack of good surface tension data for liquid silicon is probably due to its extreme chemical reactivity. A material which resists attack by molten silicon is not found. It is suggested that all of the sessile drip surface tension measurements are probably for silicon which is contaminated by the substrate materials.

  3. Casimir forces from conductive silicon carbide surfaces

    NASA Astrophysics Data System (ADS)

    Sedighi, M.; Svetovoy, V. B.; Broer, W. H.; Palasantzas, G.

    2014-05-01

    Samples of conductive silicon carbide (SiC), which is a promising material due to its excellent properties for devices operating in severe environments, were characterized with the atomic force microscope for roughness, and the optical properties were measured with ellipsometry in a wide range of frequencies. The samples show significant far-infrared absorption due to concentration of charge carriers and a sharp surface phonon-polariton peak. The Casimir interaction of SiC with different materials is calculated and discussed. As a result of the infrared structure and beyond to low frequencies, the Casimir force for SiC-SiC and SiC-Au approaches very slowly the limit of ideal metals, while it saturates significantly below this limit if interaction with insulators takes place (SiC-SiO2). At short separations (<10 nm) analysis of the van der Waals force yielded Hamaker constants for SiC-SiC interactions lower but comparable to those of metals, which is of significance to adhesion and surface assembly processes. Finally, bifurcation analysis of microelectromechanical system actuation indicated that SiC can enhance the regime of stable equilibria against stiction.

  4. Broadband Infrared Antireflection Structured Silicon Surfaces

    NASA Technical Reports Server (NTRS)

    Stewart, Kenneth; Fettig, Rainer; Allen, Christine; Larocque, Jennifer

    1999-01-01

    Silicon and germanium are materials often used for infrared (IR) windows and optical elements. However they have a very high index of refraction, in the order of three to four, which causes large reflection losses on each surface. These losses are especially high under large angles of incidence which are often desirable if signals are faint and fast optics are to be used. Solid antireflection coatings are either not available because materials with appropriate index of refraction do not exist, or their use is limited to a small wavelength range and small angles of incidence. We will present the status of our work to calculate, create, and test the performance of graded structures in Si to reduce its surface reflection. The structures are expected to work over the very broad wavelength range of 10 micron to 1000 micron and a wide range of angle of incidence. We.have identified several high aspect ratio MEMS process techniques to create the structures and have done 3D electromagnetic modeling, which predicts significant effects. Measurements on different samples have validated our modeling.

  5. Broadband Infrared Antireflection Structured Silicon Surfaces

    NASA Technical Reports Server (NTRS)

    Stewart, Kenneth; Fettig, Rainer; Allen, Christine; Larocque, Jennifer

    1999-01-01

    Silicon and germanium are materials often used for IR windows and optical elements. However they have a very high index of refraction, in the order of three to four, which causes large reflection losses on each surface. These losses are especially high under large angles of incidence which are often desirable if signals are faint and fast optics are to be used. Solid antireflection coatings are either not available because materials with appropriate index of refraction do not exist, or their use is limited to a small wavelength range and small angles of incidence. We will present the status of our work to calculate, create, and test the performance of graded structures in Si to reduce its surface reflection. The structures are expected to work over the very broad wavelength range of 10 to 1000 micrometers and a wide range of angle of incidence. We have identified several high aspect ratio MEMS process techniques to Create the structures and have done 3D electromagnetic modeling, which predicts significant effects. Measurements on different samples have validated our modeling.

  6. Broadband Infrared Antireflection Structured Silicon Surfaces

    NASA Technical Reports Server (NTRS)

    Stewart, Kenneth; Fettig, Rainer; Allen, Christine; Fettig, Rainer; Larocque, Jennifer

    1998-01-01

    Silicon and germanium are materials often used for IR windows and optical elements. However they have a very high index of refraction, in the order of three to four, which causes large reflection losses on each surface. These losses are especially high under large angles of incidence which are often desirable if signals are faint and fast optics are to be used. Solid antireflection coatings are either not available because materials with appropriate index of refraction do not exist, or their use is limited to a small wavelength range and small angles of incidence. We will present the status of our work to calculate, create, and test the performance of graded structures in Si to reduce its surface reflection. The structures are expected to work over the very broad wavelength range of 10 microns to 1000 microns and a wide range of angle of incidence. We have identified several high aspect ratio MEMS process techniques to create the structures and have done 3D electromagnetic modeling, which predicts significant effects. Measurements on different samples have validated our modeling.

  7. Casimir force measurements from silicon carbide surfaces

    NASA Astrophysics Data System (ADS)

    Sedighi, M.; Svetovoy, V. B.; Palasantzas, G.

    2016-02-01

    Using an atomic force microscope we performed measurements of the Casimir force between a gold- coated (Au) microsphere and doped silicon carbide (SiC) samples. The last of these is a promising material for devices operating under severe environments. The roughness of the interacting surfaces was measured to obtain information for the minimum separation distance upon contact. Ellipsometry data for both systems were used to extract optical properties needed for the calculation of the Casimir force via the Lifshitz theory and for comparison to the experiment. Special attention is devoted to the separation of the electrostatic contribution to the measured total force. Our measurements demonstrate large contact potential V0(≈0.67 V ) , and a relatively small density of charges trapped in SiC. Knowledge of both Casimir and electrostatic forces between interacting materials is not only important from the fundamental point of view, but also for device applications involving actuating components at separations of less than 200 nm where surface forces play dominant role.

  8. Design of highly oleophobic cellulose surfaces from structured silicon templates.

    PubMed

    Aulin, Christian; Yun, Sang Ho; Wågberg, Lars; Lindström, Tom

    2009-11-01

    Structured silicon surfaces, possessing hierarchical porous characteristics consisting of micrometer-sized cavities superimposed upon a network of nanometer-sized pillars or wires, have been fabricated by a plasma-etching process. These surfaces have superoleophobic properties, after being coated with fluorinated organic trichlorosilanes, on intrinsically oleophilic surfaces. By comparison with flat silicon surfaces, which are oleophilic, it has been demonstrated that a combination of low surface energy and the structured features of the plasma-etched surface is essential to prevent oil from penetrating the surface cavities and thus induce the observed macroscopic superoleophobic phenomena with very low contact-angle hysteresis and low roll-off angles. The structured silicon surfaces were coated with cellulose nanocrystals using the polyelectrolyte multilayer technique. The cellulose surfaces prepared in this way were then coated with a monolayer of fluorinated trichlorosilanes. These porous cellulose films displayed highly nonwetting properties against a number of liquids with low surface tension, including alkanes such as hexadecane and decane. The wettability and chemical composition of the cellulose/silicon surfaces were characterized with contact-angle goniometry and X-ray photoelectron spectroscopy, respectively. The nano/microtexture features of the cellulose/silicon surfaces were also studied with field-emission scanning electron microscopy. The highly oleophobic structured cellulose surfaces are very interesting model surfaces for the development of biomimetic self-cleaning surfaces in a vast array of products, including green constructions, packaging materials, protection against environmental fouling, sports, and outdoor clothing, and microfluidic systems. PMID:20356113

  9. Consequences of Atomic Oxygen Interaction With Silicone and Silicone Contamination on Surfaces in Low Earth Orbit

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; deGroh, Kim K.; Rutledge, Sharon K.; Haytas, Christy A.

    1999-01-01

    The exposure of silicones to atomic oxygen in low Earth orbit causes oxidation of the surface, resulting in conversion of silicone to silica. This chemical conversion increases the elastic modulus of the surface and initiates the development of a tensile strain. Ultimately, with sufficient exposure, tensile strain leads to cracking of the surface enabling the underlying unexposed silicone to be converted to silica resulting in additional depth and extent of cracking. The use of silicone coatings for the protection of materials from atomic oxygen attack is limited because of the eventual exposure of underlying unprotected polymeric material due to deep tensile stress cracking of the oxidized silicone. The use of moderate to high volatility silicones in low Earth orbit has resulted in a silicone contamination arrival at surfaces which are simultaneously being bombarded with atomic oxygen, thus leading to conversion of the silicone contaminant to silica. As a result of these processes, a gradual accumulation of contamination occurs leading to deposits which at times have been up to several microns thick (as in the case of a Mir solar array after 10 years in space). The contamination species typically consist of silicon, oxygen and carbon. which in the synergistic environment of atomic oxygen and UV radiation leads to increased solar absorptance and reduced solar transmittance. A comparison of the results of atomic oxygen interaction with silicones and silicone contamination will be presented based on the LDEF, EOIM-111, Offeq-3 spacecraft and Mir solar array in-space results. The design of a contamination pin-hole camera space experiment which uses atomic oxygen to produce an image of the sources of silicone contamination will also be presented.

  10. Hydrogen-terminated diamond vertical-type metal oxide semiconductor field-effect transistors with a trench gate

    NASA Astrophysics Data System (ADS)

    Inaba, Masafumi; Muta, Tsubasa; Kobayashi, Mikinori; Saito, Toshiki; Shibata, Masanobu; Matsumura, Daisuke; Kudo, Takuya; Hiraiwa, Atsushi; Kawarada, Hiroshi

    2016-07-01

    The hydrogen-terminated diamond surface (C-H diamond) has a two-dimensional hole gas (2DHG) layer independent of the crystal orientation. A 2DHG layer is ubiquitously formed on the C-H diamond surface covered by atomic-layer-deposited-Al2O3. Using Al2O3 as a gate oxide, C-H diamond metal oxide semiconductor field-effect transistors (MOSFETs) operate in a trench gate structure where the diamond side-wall acts as a channel. MOSFETs with a side-wall channel exhibit equivalent performance to the lateral C-H diamond MOSFET without a side-wall channel. Here, a vertical-type MOSFET with a drain on the bottom is demonstrated in diamond with channel current modulation by the gate and pinch off.

  11. Critically coupled surface phonon-polariton excitation in silicon carbide.

    PubMed

    Neuner, Burton; Korobkin, Dmitriy; Fietz, Chris; Carole, Davy; Ferro, Gabriel; Shvets, Gennady

    2009-09-01

    We observe critical coupling to surface phonon-polaritons in silicon carbide by attenuated total reflection of mid-IR radiation. Reflectance measurements demonstrate critical coupling by a double scan of wavelength and incidence angle. Critical coupling occurs when prism coupling loss is equal to losses in silicon carbide and the substrate, resulting in maximal electric field enhancement. PMID:19724526

  12. Surface Behavior of Boronic Acid-Terminated Silicones.

    PubMed

    Mansuri, Erum; Zepeda-Velazquez, Laura; Schmidt, Rolf; Brook, Michael A; DeWolf, Christine E

    2015-09-01

    Silicone polymers, with their high flexibility, lie in a monolayer at the air-water interface as they are compressed until a critical pressure is reached, at which point multilayers are formed. Surface pressure measurements demonstrate that, in contrast, silicones that are end-modified with polar groups take up lower surface areas under compression because the polar groups submerge into the water phase. Boronic acids have the ability to undergo coordination with Lewis bases. As part of a program to examine the surface properties of boronic acids, we have prepared boronic acid-modified silicones (SiBAs) and examined them at the air-water interface to better understand if they behave like other end-functional silicones. Monolayers of silicones, aminopropylsilicones, and SiBAs were characterized at the air-water interface as a function of end functionalization and silicone chain length. Brewster angle and atomic force microscopies confirm domain formation and similar film morphologies for both functionalized and non-functionalized silicone chains. There is a critical surface pressure (10 mN m(-1)) independent of chain length that corresponds to a first-order phase transition. Below this transition, the film appears to be a homogeneous monolayer, whose thickness is independent of the chain length. Ellipsometry at the air-water interface indicates that the boronic acid functionality leads to a significant increase of film thickness at low molecular areas that is not seen for non-functionalized silicone chains. What differentiates the boronic acids from simple silicones or other end-functionalized silicones, in particular, is the larger area occupied by the headgroup when under compression compared to other or non-end-functionalized silicones, which suggests an in-plane rather than submerged orientation that may be driven by boronic acid self-complexation. PMID:26263385

  13. Nanoscale Etching and Indentation of Silicon Surfaces with Carbon Nanotubes

    NASA Technical Reports Server (NTRS)

    Dzegilenko, Fedor N.; Srivastava, Deepak; Saini, Subhash

    1998-01-01

    The possibility of nanolithography of silicon and germanium surfaces with bare carbon nanotube tips of scanning probe microscopy devices is considered with large scale classical molecular dynamics (MD) simulations employing Tersoff's reactive many-body potential for heteroatomic C/Si/Ge system. Lithography plays a key role in semiconductor manufacturing, and it is expected that future molecular and quantum electronic devices will be fabricated with nanolithographic and nanodeposition techniques. Carbon nanotubes, rolled up sheets of graphene made of carbon, are excellent candidates for use in nanolithography because they are extremely strong along axial direction and yet extremely elastic along radial direction. In the simulations, the interaction of a carbon nanotube tip with silicon surfaces is explored in two regimes. In the first scenario, the nanotubes barely touch the surface, while in the second they are pushed into the surface to make "nano holes". The first - gentle scenario mimics the nanotube-surface chemical reaction induced by the vertical mechanical manipulation of the nanotube. The second -digging - scenario intends to study the indentation profiles. The following results are reported in the two cases. In the first regime, depending on the surface impact site, two major outcomes outcomes are the selective removal of either a single surface atom or a surface dimer off the silicon surface. In the second regime, the indentation of a silicon substrate by the nanotube is observed. Upon the nanotube withdrawal, several surface silicon atoms are adsorbed at the tip of the nanotube causing significant rearrangements of atoms comprising the surface layer of the silicon substrate. The results are explained in terms of relative strength of C-C, C-Si, and Si-Si bonds. The proposed method is very robust and does not require applied voltage between the nanotube tips and the surface. The implications of the reported controllable etching and hole-creating for

  14. Diffusion of silver over atomically clean silicon surfaces

    SciTech Connect

    Dolbak, A. E. Ol'shanetskii, B. Z.

    2013-06-15

    The diffusion of silver the (111), (100), and (110) silicon surfaces is studied by Auger electron spectroscopy and low-energy electron diffraction. The mechanisms of diffusion over the (111) and (110) surfaces are revealed, and the temperature dependences of diffusion coefficients are measured. An anisotropy of silver diffusion over the (110) surface is detected.

  15. Dielectric properties of hydrogen-terminated Si(111) ultrathin films

    NASA Astrophysics Data System (ADS)

    Nakamura, Jun; Ishihara, Shunsuke; Natori, Akiko; Shimizu, Tomo; Natori, Kenji

    2006-03-01

    Dielectric properties of Si(111) ultrathin films have been investigated using first-principles ground-states calculations in external electrostatic fields. With increasing thickness of Si(111) ultrathin films, the optical dielectric constant evaluated at the center of the slab converges to the experimental bulk dielectric constant at a thickness of only eight bilayers, while the energy gap of the slab is still larger than that of bulk Si. The converged theoretical dielectric constant for bulk Si is only 6.2% higher than the experimental one. Furthermore, spatial variations of the dielectric constant have also been evaluated using the position-dependent macroscopic field given by a clear-cut definition. The results show that the dielectric constant is reduced distinctly at the first few bilayers from the surface, which stems from the penetration of depolarized charges induced at the surface. Such an effective reduction of the depolarization field near the surface is one of the reasons for the decrease in optical dielectric constant for the ultrathin films.

  16. The surface electronic structure of silicon terminated (100) diamond

    NASA Astrophysics Data System (ADS)

    Schenk, A. K.; Tadich, A.; Sear, M. J.; Qi, D.; Wee, A. T. S.; Stacey, A.; Pakes, C. I.

    2016-07-01

    A combination of synchrotron-based x-ray spectroscopy and contact potential difference measurements have been used to examine the electronic structure of the (3 × 1) silicon terminated (100) diamond surface under ultra high vacuum conditions. An occupied surface state which sits 1.75 eV below the valence band maximum has been identified, and indications of mid-gap unoccupied surface states have been found. Additionally, the pristine silicon terminated surface is shown to possess a negative electron affinity of ‑0.86 ± 0.1 eV.

  17. The surface electronic structure of silicon terminated (100) diamond.

    PubMed

    Schenk, A K; Tadich, A; Sear, M J; Qi, D; Wee, A T S; Stacey, A; Pakes, C I

    2016-07-01

    A combination of synchrotron-based x-ray spectroscopy and contact potential difference measurements have been used to examine the electronic structure of the (3 × 1) silicon terminated (100) diamond surface under ultra high vacuum conditions. An occupied surface state which sits 1.75 eV below the valence band maximum has been identified, and indications of mid-gap unoccupied surface states have been found. Additionally, the pristine silicon terminated surface is shown to possess a negative electron affinity of -0.86 ± 0.1 eV. PMID:27211214

  18. Atomic scale memory at a silicon surface

    NASA Astrophysics Data System (ADS)

    Bennewitz, R.; Crain, J. N.; Kirakosian, A.; Lin, J.-L.; McChesney, J. L.; Petrovykh, D. Y.; Himpsel, F. J.

    2002-08-01

    The limits of pushing storage density to the atomic scale are explored with a memory that stores a bit by the presence or absence of one silicon atom. These atoms are positioned at lattice sites along self-assembled tracks with a pitch of five atom rows. The memory can be initialized and reformatted by controlled deposition of silicon. The writing process involves the transfer of Si atoms to the tip of a scanning tunnelling microscope. The constraints on speed and reliability are compared with data storage in magnetic hard disks and DNA.

  19. Porous silicon nanocrystals in a silica aerogel matrix.

    PubMed

    Amonkosolpan, Jamaree; Wolverson, Daniel; Goller, Bernhard; Polisski, Sergej; Kovalev, Dmitry; Rollings, Matthew; Grogan, Michael D W; Birks, Timothy A

    2012-01-01

    Silicon nanoparticles of three types (oxide-terminated silicon nanospheres, micron-sized hydrogen-terminated porous silicon grains and micron-size oxide-terminated porous silicon grains) were incorporated into silica aerogels at the gel preparation stage. Samples with a wide range of concentrations were prepared, resulting in aerogels that were translucent (but weakly coloured) through to completely opaque for visible light over sample thicknesses of several millimetres. The photoluminescence of these composite materials and of silica aerogel without silicon inclusions was studied in vacuum and in the presence of molecular oxygen in order to determine whether there is any evidence for non-radiative energy transfer from the silicon triplet exciton state to molecular oxygen adsorbed at the silicon surface. No sensitivity to oxygen was observed from the nanoparticles which had partially H-terminated surfaces before incorporation, and so we conclude that the silicon surface has become substantially oxidised. Finally, the FTIR and Raman scattering spectra of the composites were studied in order to establish the presence of crystalline silicon; by taking the ratio of intensities of the silicon and aerogel Raman bands, we were able to obtain a quantitative measure of the silicon nanoparticle concentration independent of the degree of optical attenuation. PMID:22805684

  20. Porous silicon nanocrystals in a silica aerogel matrix

    PubMed Central

    2012-01-01

    Silicon nanoparticles of three types (oxide-terminated silicon nanospheres, micron-sized hydrogen-terminated porous silicon grains and micron-size oxide-terminated porous silicon grains) were incorporated into silica aerogels at the gel preparation stage. Samples with a wide range of concentrations were prepared, resulting in aerogels that were translucent (but weakly coloured) through to completely opaque for visible light over sample thicknesses of several millimetres. The photoluminescence of these composite materials and of silica aerogel without silicon inclusions was studied in vacuum and in the presence of molecular oxygen in order to determine whether there is any evidence for non-radiative energy transfer from the silicon triplet exciton state to molecular oxygen adsorbed at the silicon surface. No sensitivity to oxygen was observed from the nanoparticles which had partially H-terminated surfaces before incorporation, and so we conclude that the silicon surface has become substantially oxidised. Finally, the FTIR and Raman scattering spectra of the composites were studied in order to establish the presence of crystalline silicon; by taking the ratio of intensities of the silicon and aerogel Raman bands, we were able to obtain a quantitative measure of the silicon nanoparticle concentration independent of the degree of optical attenuation. PMID:22805684

  1. Secondary-electron emission from hydrogen-terminated diamond

    SciTech Connect

    Wang E.; Ben-Zvi, I.; Rao, T.; Wu, Q.; Dimitrov, D.A.; T. Xin, T.

    2012-05-20

    Diamond amplifiers demonstrably are an electron source with the potential to support high-brightness, high-average-current emission into a vacuum. We recently developed a reliable hydrogenation procedure for the diamond amplifier. The systematic study of hydrogenation resulted in the reproducible fabrication of high gain diamond amplifier. Furthermore, we measured the emission probability of diamond amplifier as a function of the external field and modelled the process with resulting changes in the vacuum level due to the Schottky effect. We demonstrated that the decrease in the secondary electrons average emission gain was a function of the pulse width and related this to the trapping of electrons by the effective NEA surface. The findings from the model agree well with our experimental measurements. As an application of the model, the energy spread of secondary electrons inside the diamond was estimated from the measured emission.

  2. Improving efficiency of silicon heterojunction solar cells by surface texturing of silicon wafers using tetramethylammonium hydroxide

    NASA Astrophysics Data System (ADS)

    Wang, Liguo; Wang, Fengyou; Zhang, Xiaodan; Wang, Ning; Jiang, Yuanjian; Hao, Qiuyan; Zhao, Ying

    2014-12-01

    Texturing of silicon surfaces is an effective method for improving the efficiency of silicon solar cells. Etching by using tetramethylammonium hydroxide (TMAH) is more attractive than other texturing processes because TMAH is non-toxic, and high-quality anisotropic features can be realized without any metal ion contaminants. In this study, TMAH texturing conditions are varied to optimize the surface morphology of silicon wafers. Excellent optical properties are obtained. This is because of the formation of pyramidal structures with different random sizes but uniform shapes; in fact, when the optimal etching conditions (2% TMAH, 10% isopropyl alcohol (IPA) at 80 °C) are used, the reflectance is only 10.7%. In comparison with NaOH texturing, the TMAH process described here yields smaller pyramids with smoother (111) facets, leading to improved performance in silicon heterojunction solar cells, with a conversion efficiency of 17.8%.

  3. Surface Figure Measurement of Silicon Carbide Mirrors at Cryogenic Temperatures

    NASA Technical Reports Server (NTRS)

    Blake, Peter; Mink, Ronald G.; Chambers, John; Robinson, F. David; Content, David; Davila, Pamela

    2005-01-01

    The surface figure of a developmental silicon carbide mirror, cooled to 87 K and then 20 K within a cryostat, was measured with unusually high precision at the Goddard Space Flight Center (GSFC). The concave spherical mirror, with a radius of 600 mm and a clear aperture of 150 mm, was fabricated of sintered silicon carbide. The mirror was mounted to an interface plate representative of an optical bench, made of the material Cesic@, a composite of silicon, carbon, and silicon carbide. The change in optical surface figure as the mirror and interface plate cooled from room temperature to 20 K was 3.7 nm rms, with a standard uncertainty of 0.23 nm in the rms statistic. Both the cryo-change figure and the uncertainty are among the lowest such figures yet published. This report describes the facilities, experimental methods, and uncertainty analysis of the measurements.

  4. Solution-processed amorphous silicon surface passivation layers

    SciTech Connect

    Mews, Mathias Sontheimer, Tobias; Korte, Lars; Rech, Bernd; Mader, Christoph; Traut, Stephan; Wunnicke, Odo

    2014-09-22

    Amorphous silicon thin films, fabricated by thermal conversion of neopentasilane, were used to passivate crystalline silicon surfaces. The conversion is investigated using X-ray and constant-final-state-yield photoelectron spectroscopy, and minority charge carrier lifetime spectroscopy. Liquid processed amorphous silicon exhibits high Urbach energies from 90 to 120 meV and 200 meV lower optical band gaps than material prepared by plasma enhanced chemical vapor deposition. Applying a hydrogen plasma treatment, a minority charge carrier lifetime of 1.37 ms at an injection level of 10{sup 15}/cm{sup 3} enabling an implied open circuit voltage of 724 mV was achieved, demonstrating excellent silicon surface passivation.

  5. Determination of surface recombination velocity in heavily doped silicon

    NASA Technical Reports Server (NTRS)

    Watanabe, M.; Gatos, H. C.; Actor, G.

    1976-01-01

    A method was developed and successfully tested for the determination of the effective surface recombination velocity of silicon layers doped by diffusion of phosphorus to a level of 10 to the 19th to 10 to the 21st per cu cm. The effective recombination velocity was obtained from the dependence of the electron-beam-induced current on the penetration of the electron beam of a scanning electron microscope. A special silicon diode was constructed which permitted the collection at the p-n junction of the carriers excited by the electron beam. This diode also permitted the study of the effects of surface preparation on the effective surface recombination velocity.

  6. Non-contact monitoring of electrical characteristics of silicon surface and near-surface region

    NASA Astrophysics Data System (ADS)

    Roman, P.; Brubaker, M.; Staffa, J.; Kamieniecki, E.; Ruzyllo, J.

    1998-11-01

    The SPV-based method of Surface Charge Profiling (SCP) is discussed, and its applications in silicon surface monitoring in IC manufacturing are reviewed. The SCP method shows high sensitivity to changes in the condition of the Si surface (e.g. surface cleaning operations) and a very thin near-surface region (e.g. variations of active dopant concentration near the surface).

  7. Optical second-harmonic spectroscopy of chemically-modified silicon and silicon-dioxide surfaces

    NASA Astrophysics Data System (ADS)

    Downer, M. C.; Jiang, Y. Y.; Lim, D.

    2002-03-01

    The optical second-harmonic generation (SHG) response of solid interfaces depends sensitively on chemical termination. We present a spectroscopic SHG study of chemically-modified Si and SiO2 surfaces that elucidates at the atomic level how adsorbates alter the electronic structure, and thereby the SHG response, of the surface. SHG spectra were measured on reconstructed Si(001) surfaces in UHV that were exposed to atomic H or to gas-phase precursors of Ge and B, and on the surfaces of 30 angstrom-thick silicon dioxide films on silicon substrates that were chemically functionalized to nucleate silicon nanocrystal formation. Microscopic models show that adsorbate-induced alterations of the surface SHG spectra are correlated with changes in near-surface charge polarization caused by surface dimer buckling, transfer of electrons to boron acceptors in second layer substitutional sites, or transfer of electrons from the silicon substrate, through the tunneling oxide, to the surface nanocrystals [1]. 1. M. C. Downer, B. S. Mendoza and V. I. Gavrilenko, Surf. Interface Anal. 31, 966 (2001).

  8. Formation of a silicon terminated (100) diamond surface

    SciTech Connect

    Schenk, Alex Sear, Michael; Pakes, Chris; Tadich, Anton; O'Donnell, Kane M.; Ley, Lothar; Stacey, Alastair

    2015-05-11

    We report the preparation of an ordered silicon terminated diamond (100) surface with a two domain 3 × 1 reconstruction as determined by low energy electron diffraction. Based on the dimensions of the surface unit cell and on chemical information provided by core level photoemission spectra, a model for the structure is proposed. The termination should provide a homogeneous, nuclear, and electron spin-free surface for the development of future near-surface diamond quantum device architectures.

  9. Etching of silicon surfaces using atmospheric plasma jets

    NASA Astrophysics Data System (ADS)

    Paetzelt, H.; Böhm, G.; Arnold, Th

    2015-04-01

    Local plasma-assisted etching of crystalline silicon by fine focused plasma jets provides a method for high accuracy computer controlled surface waviness and figure error correction as well as free form processing and manufacturing. We investigate a radio-frequency powered atmospheric pressure He/N2/CF4 plasma jet for the local chemical etching of silicon using fluorine as reactive plasma gas component. This plasma jet tool has a typical tool function width of about 0.5 to 1.8 mm and a material removal rate up to 0.068 mm3 min-1. The relationship between etching rate and plasma jet parameters is discussed in detail regarding gas composition, working distance, scan velocity and RF power. Surface roughness after etching was characterized using atomic force microscopy and white light interferometry. A strong smoothing effect was observed for etching rough silicon surfaces like wet chemically-etched silicon wafer backsides. Using the dwell-time algorithm for a deterministic surface machining by superposition of the local removal function of the plasma tool we show a fast and efficient way for manufacturing complex silicon structures. In this article we present two examples of surface processing using small local plasma jets.

  10. Chemical method for producing smooth surfaces on silicon wafers

    SciTech Connect

    Yu, Conrad

    2003-01-01

    An improved method for producing optically smooth surfaces in silicon wafers during wet chemical etching involves a pre-treatment rinse of the wafers before etching and a post-etching rinse. The pre-treatment with an organic solvent provides a well-wetted surface that ensures uniform mass transfer during etching, which results in optically smooth surfaces. The post-etching treatment with an acetic acid solution stops the etching instantly, preventing any uneven etching that leads to surface roughness. This method can be used to etch silicon surfaces to a depth of 200 .mu.m or more, while the finished surfaces have a surface roughness of only 15-50 .ANG. (RMS).

  11. Silicon nanohybrid-based surface-enhanced Raman scattering sensors.

    PubMed

    Wang, Houyu; Jiang, Xiangxu; Lee, Shuit-Tong; He, Yao

    2014-11-01

    Nanomaterial-based surface-enhanced Raman scattering (SERS) sensors are highly promising analytical tools, capable of ultrasensitive, multiplex, and nondestructive detection of chemical and biological species. Extensive efforts have been made to design various silicon nanohybrid-based SERS substrates such as gold/silver nanoparticle (NP)-decorated silicon nanowires, Au/Ag NP-decorated silicon wafers (AuNP@Si), and so forth. In comparison to free AuNP- and AgNP-based SERS sensors, the silicon nanohybrid-based SERS sensors feature higher enhancement factors (EFs) and excellent reproducibility, since SERS hot spots are efficiently coupled and stabilized through interconnection to the semiconducting silicon substrates. Consequently, in the past decade, giant advancements in the development of silicon nanohybrid-based SERS sensors have been witnessed for myriad sensing applications. In this review, the representative achievements related to the design of high-performance silicon nanohybrid-based SERS sensors and their use for chemical and biological analysis are reviewed in a detailed way. Furthermore, the major opportunities and challenges in this field are discussed from a broad perspective and possible future directions. PMID:25243935

  12. Epitaxy of silicon carbide on silicon: Micromorphological analysis of growth surface evolution

    NASA Astrophysics Data System (ADS)

    Shikhgasan, Ramazanov; Ştefan, Ţălu; Dinara, Sobola; Sebastian, Stach; Guseyn, Ramazanov

    2015-10-01

    The main purpose of our research was the study of evolution of silicon carbide films on silicon by micromorphological analysis. Surface micromorphologies of Silicon Carbide epilayers with two different thicknesses were compared by means of fractal geometry. Silicon Carbide films were prepared on Si substrates by magnetron sputtering of polycrystalline target SiC in Ar atmosphere (99.999% purity). Synthesis of qualitative SiC/Si templates solves the questions of large diameter SiC single-crystal wafers formation. This technology decreases financial expenditure and provides integration of SiC into silicon technology. These hybrid substrates with buffer layer of high oriented SiC are useful for growth of both wide band gap materials (SiC, AlN, GaN) and graphene. The main problem of SiC heteroepitaxy on Si (1 1 1) is the large difference (∼20%) of the lattice parameters. Fractal analysis of surface morphology of heteroepitaxial films could help to understand the films growth mechanisms. The 3D (three-dimensional) surfaces revealed a fractal structure at the nanometer scale. The fractal dimension (D) provided global quantitative values that characterize the scale properties of surface geometry.

  13. On the wettability transparency of graphene-coated silicon surfaces

    NASA Astrophysics Data System (ADS)

    Ramos-Alvarado, Bladimir; Kumar, Satish; Peterson, G. P.

    2016-01-01

    In order to better understand the behavior and governing characteristics of the wetting transparency phenomenon observed in graphene-coated surfaces, molecular dynamics simulations were coupled with a theoretical model. Graphene-coated silicon was selected for this analysis, due to potential applications of hybrid silicon-graphene materials as detectors in aqueous environments. The results indicate good agreement between the theory and simulations at the macroscopic conditions required to observe wetting transparency. A microscopic analysis was also conducted in order to identify the parameters, such as the interaction potential energy landscape and the interfacial liquid structure that govern the wetting behavior of graphene-coated surfaces. The interfacial liquid structure was found to be different between uncoated Si(100) and the graphene-coated version and very similar between uncoated Si(111) and the graphene-coated version. However, the concentration of liquid particles for both silicon surfaces was found to be very similar under transparent wetting conditions.

  14. Tribological interaction between polytetrafluoroethylene and silicon oxide surfaces

    SciTech Connect

    Uçar, A.; Çopuroğlu, M.; Suzer, S.; Baykara, M. Z.; Arıkan, O.

    2014-10-28

    We investigated the tribological interaction between polytetrafluoroethylene (PTFE) and silicon oxide surfaces. A simple rig was designed to bring about a friction between the surfaces via sliding a piece of PTFE on a thermally oxidized silicon wafer specimen. A very mild inclination (∼0.5°) along the sliding motion was also employed in order to monitor the tribological interaction in a gradual manner as a function of increasing contact force. Additionally, some patterns were sketched on the silicon oxide surface using the PTFE tip to investigate changes produced in the hydrophobicity of the surface, where the approximate water contact angle was 45° before the transfer. The nature of the transferred materials was characterized by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). XPS results revealed that PTFE was faithfully transferred onto the silicon oxide surface upon even at the slightest contact and SEM images demonstrated that stable morphological changes could be imparted onto the surface. The minimum apparent contact pressure to realize the PTFE transfer is estimated as 5 kPa, much lower than reported previously. Stability of the patterns imparted towards many chemical washing processes lead us to postulate that the interaction is most likely to be chemical. Contact angle measurements, which were carried out to characterize and monitor the hydrophobicity of the silicon oxide surface, showed that upon PTFE transfer the hydrophobicity of the SiO{sub 2} surface could be significantly enhanced, which might also depend upon the pattern sketched onto the surface. Contact angle values above 100° were obtained.

  15. Formation of nanostructured silicon surfaces by stain etching

    PubMed Central

    2014-01-01

    In this work, we report the fabrication of ordered silicon structures by chemical etching of silicon in vanadium oxide (V2O5)/hydrofluoric acid (HF) solution. The effects of the different etching parameters including the solution concentration, temperature, and the presence of metal catalyst film deposition (Pd) on the morphologies and reflective properties of the etched Si surfaces were studied. Scanning electron microscopy (SEM) was carried out to explore the morphologies of the etched surfaces with and without the presence of catalyst. In this case, the attack on the surfaces with a palladium deposit begins by creating uniform circular pores on silicon in which we distinguish the formation of pyramidal structures of silicon. Fourier transform infrared spectroscopy (FTIR) demonstrates that the surfaces are H-terminated. A UV-Vis-NIR spectrophotometer was used to study the reflectance of the structures obtained. A reflectance of 2.21% from the etched Si surfaces in the wavelength range of 400 to 1,000 nm was obtained after 120 min of etching while it is of 4.33% from the Pd/Si surfaces etched for 15 min. PMID:25435830

  16. Formation of nanostructured silicon surfaces by stain etching.

    PubMed

    Ayat, Maha; Belhousse, Samia; Boarino, Luca; Gabouze, Noureddine; Boukherroub, Rabah; Kechouane, Mohamed

    2014-01-01

    In this work, we report the fabrication of ordered silicon structures by chemical etching of silicon in vanadium oxide (V2O5)/hydrofluoric acid (HF) solution. The effects of the different etching parameters including the solution concentration, temperature, and the presence of metal catalyst film deposition (Pd) on the morphologies and reflective properties of the etched Si surfaces were studied. Scanning electron microscopy (SEM) was carried out to explore the morphologies of the etched surfaces with and without the presence of catalyst. In this case, the attack on the surfaces with a palladium deposit begins by creating uniform circular pores on silicon in which we distinguish the formation of pyramidal structures of silicon. Fourier transform infrared spectroscopy (FTIR) demonstrates that the surfaces are H-terminated. A UV-Vis-NIR spectrophotometer was used to study the reflectance of the structures obtained. A reflectance of 2.21% from the etched Si surfaces in the wavelength range of 400 to 1,000 nm was obtained after 120 min of etching while it is of 4.33% from the Pd/Si surfaces etched for 15 min. PMID:25435830

  17. Temperature-dependent photoluminescence of surface-engineered silicon nanocrystals.

    PubMed

    Mitra, Somak; Švrček, Vladimir; Macias-Montero, Manual; Velusamy, Tamilselvan; Mariotti, Davide

    2016-01-01

    In this work we report on temperature-dependent photoluminescence measurements (15-300 K), which have allowed probing radiative transitions and understanding of the appearance of various transitions. We further demonstrate that transitions associated with oxide in SiNCs show characteristic vibronic peaks that vary with surface characteristics. In particular we study differences and similarities between silicon nanocrystals (SiNCs) derived from porous silicon and SiNCs that were surface-treated using a radio-frequency (RF) microplasma system. PMID:27296771

  18. Surface acoustic wave/silicon monolithic sensor/processor

    NASA Technical Reports Server (NTRS)

    Kowel, S. T.; Kornreich, P. G.; Nouhi, A.; Kilmer, R.; Fathimulla, M. A.; Mehter, E.

    1983-01-01

    A new technique for sputter deposition of piezoelectric zinc oxide (ZnO) is described. An argon-ion milling system was converted to sputter zinc oxide films in an oxygen atmosphere using a pure zinc oxide target. Piezoelectric films were grown on silicon dioxide and silicon dioxide overlayed with gold. The sputtered films were evaluated using surface acoustic wave measurements, X-ray diffraction, scanning electron microscopy, Auger electron spectroscopy, and resistivity measurements. The effect of the sputtering conditions on the film quality and the result of post-deposition annealing are discussed. The application of these films to the generation of surface acoustic waves is also discussed.

  19. Temperature-dependent photoluminescence of surface-engineered silicon nanocrystals

    NASA Astrophysics Data System (ADS)

    Mitra, Somak; Švrček, Vladimir; Macias-Montero, Manual; Velusamy, Tamilselvan; Mariotti, Davide

    2016-06-01

    In this work we report on temperature-dependent photoluminescence measurements (15–300 K), which have allowed probing radiative transitions and understanding of the appearance of various transitions. We further demonstrate that transitions associated with oxide in SiNCs show characteristic vibronic peaks that vary with surface characteristics. In particular we study differences and similarities between silicon nanocrystals (SiNCs) derived from porous silicon and SiNCs that were surface-treated using a radio-frequency (RF) microplasma system.

  20. Temperature-dependent photoluminescence of surface-engineered silicon nanocrystals

    PubMed Central

    Mitra, Somak; Švrček, Vladimir; Macias-Montero, Manual; Velusamy, Tamilselvan; Mariotti, Davide

    2016-01-01

    In this work we report on temperature-dependent photoluminescence measurements (15–300 K), which have allowed probing radiative transitions and understanding of the appearance of various transitions. We further demonstrate that transitions associated with oxide in SiNCs show characteristic vibronic peaks that vary with surface characteristics. In particular we study differences and similarities between silicon nanocrystals (SiNCs) derived from porous silicon and SiNCs that were surface-treated using a radio-frequency (RF) microplasma system. PMID:27296771

  1. Surface modification of silicon dioxide, silicon nitride and titanium oxynitride for lactate dehydrogenase immobilization.

    PubMed

    Saengdee, Pawasuth; Chaisriratanakul, Woraphan; Bunjongpru, Win; Sripumkhai, Witsaroot; Srisuwan, Awirut; Jeamsaksiri, Wutthinan; Hruanun, Charndet; Poyai, Amporn; Promptmas, Chamras

    2015-05-15

    Three different types of surface, silicon dioxide (SiO2), silicon nitride (Si3N4), and titanium oxynitride (TiON) were modified for lactate dehydrogenase (LDH) immobilization using (3-aminopropyl)triethoxysilane (APTES) to obtain an amino layer on each surface. The APTES modified surfaces can directly react with LDH via physical attachment. LDH can be chemically immobilized on those surfaces after incorporation with glutaraldehyde (GA) to obtain aldehyde layers of APTES-GA modified surfaces. The wetting properties, chemical bonding composition, and morphology of the modified surface were determined by contact angle (CA) measurement, Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM), respectively. In this experiment, the immobilized protein content and LDH activity on each modified surface was used as an indicator of surface modification achievement. The results revealed that both the APTES and APTES-GA treatments successfully link the LDH molecule to those surfaces while retaining its activity. All types of tested surfaces modified with APTES-GA gave better LDH immobilizing efficiency than APTES, especially the SiO2 surface. In addition, the SiO2 surface offered the highest LDH immobilization among tested surfaces, with both APTES and APTES-GA modification. However, TiON and Si3N4 surfaces could be used as alternative candidate materials in the preparation of ion-sensitive field-effect transistor (ISFET) based biosensors, including lactate sensors using immobilized LDH on the ISFET surface. PMID:25108848

  2. Rapid Formation of Soft Hydrophilic Silicone Elastomer Surfaces

    SciTech Connect

    Efimenko,K.; Crowe, J.; Manias, E.; Schwark, D.; Fischer, D.; Genzer, J.

    2005-01-01

    We report on the rapid formation of hydrophilic silicone elastomer surfaces by ultraviolet/ozone (UVO) irradiation of poly(vinylmethylsiloxane) (PVMS) network films. Our results reveal that the PVMS network surfaces render hydrophilic upon only a short UVO exposure time (seconds to a few minutes). We also provide evidence that the brief UVO irradiation treatment does not cause dramatic changes in the surface modulus of the PVMS network. We compare the rate of formation of hydrophilic silicone elastomer surfaces made of PVMS to those of model poly(dimethyl siloxane) (PDMS) and commercial-grade PDMS (Sylgard-184). We find that relative to PVMS, 20 times longer UVO treatment times are needed to oxidize the PDMS network surfaces in order to achieve a comparable density of surface-bound hydrophilic moieties. The longer UVO treatment times for PDMS are in turn responsible for the dramatic increase in surface modulus of UVO treated PDMS, relative to PVMS. We also study the formation of self-assembled monolayers (SAMs) made of semifluorinated organosilane precursors on the PVMSUVO and PDMS-UVO network surfaces. By tuning the UVO treatment times and by utilizing mono- and tri-functional organosilanes we find that while mono-functionalized organosilanes attach directly to the substrate, SAMs of tri-functionalized organosilanes form in-plane networks on the underlying UVO-modified silicone elastomer surface, even with only short UVO exposure times.

  3. Passivation of c-Si surfaces by sub-nm amorphous silicon capped with silicon nitride

    NASA Astrophysics Data System (ADS)

    Wan, Yimao; Yan, Di; Bullock, James; Zhang, Xinyu; Cuevas, Andres

    2015-12-01

    A sub-nm hydrogenated amorphous silicon (a-Si:H) film capped with silicon nitride (SiNx) is shown to provide a high level passivation to crystalline silicon (c-Si) surfaces. When passivated by a 0.8 nm a-Si:H/75 nm SiNx stack, recombination current density J0 values of 9, 11, 47, and 87 fA/cm2 are obtained on 10 Ω.cm n-type, 0.8 Ω.cm p-type, 160 Ω/sq phosphorus-diffused, and 120 Ω/sq boron-diffused silicon surfaces, respectively. The J0 on n-type 10 Ω.cm wafers is further reduced to 2.5 ± 0.5 fA/cm2 when the a-Si:H film thickness exceeds 2.5 nm. The passivation by the sub-nm a-Si:H/SiNx stack is thermally stable at 400 °C in N2 for 60 min on all four c-Si surfaces. Capacitance-voltage measurements reveal a reduction in interface defect density and film charge density with an increase in a-Si:H thickness. The nearly transparent sub-nm a-Si:H/SiNx stack is thus demonstrated to be a promising surface passivation and antireflection coating suitable for all types of surfaces encountered in high efficiency c-Si solar cells.

  4. Spin chains and electron transfer at stepped silicon surfaces

    NASA Astrophysics Data System (ADS)

    Erwin, Steven; Aulbach, Julian; Claessen, Ralph; Schaefer, Joerg

    Stepped silicon surfaces oriented between Si(111) and Si(001) show unusual behavior when submonolayer amounts of gold are adsorbed: they self-assemble to form arrays of steps with virtually perfect structural order. Known examples include Si(553), Si(557), and Si(775). For the first two of these there is, in addition, strong theoretical and experimental evidence that the silicon step edges are spin polarized, raising the possibility of a magnetically ordered ground state at a silicon surface. The situation is different, however, for Si(775): theory and experiment both show that spin polarization does not occur. Here we use density-functional theory and scanning tunneling microscopy to develop a physically transparent picture explaining the formation of these 'spin chains' on the family of Si(hhk)-Au surfaces. Specifically, we explain why spin chains form on particular silicon (hhk) orientations but not on others. Finally, we use this understanding to propose strategies for using surface chemistry to control the formation or suppression of spin chains on Si(hhk)-Au surfaces.

  5. Surface quality of silicon wafer improved by hydrodynamic effect polishing

    NASA Astrophysics Data System (ADS)

    Peng, Wenqiang; Guan, Chaoliang; Li, Shengyi

    2014-08-01

    Differing from the traditional pad polishing, hydrodynamic effect polishing (HEP) is non-contact polishing with the wheel floated on the workpiece. A hydrodynamic lubricated film is established between the wheel and the workpiece when the wheel rotates at a certain speed in HEP. Nanoparticles mixed with deionized water are employed as the polishing slurry, and with action of the dynamic pressure, nanoparticles with high chemisorption due to the high specific surface area can easily reacted with the surface atoms forming a linkage with workpiece surface. The surface atoms are dragged away when nanoparticles are transported to separate by the flow shear stress. The development of grand scale integration put extremely high requirements on the surface quality on the silicon wafer with surface roughness at subnanometer and extremely low surface damage. In our experiment a silicon sample was processed by HEP, and the surface topography before and after polishing was observed by the atomic force microscopy. Experiment results show that plastic pits and bumpy structures on the initial surface have been removed away clearly with the removal depth of 140nm by HEP process. The processed surface roughness has been improved from 0.737nm RMS to 0.175nm RMS(10μm×10μm) and the section profile shows peaks of the process surface are almost at the same height. However, the machining ripples on the wheel surface will duplicate on the silicon surface under the action of the hydrodynamic effect. Fluid dynamic simulation demonstrated that the coarse surface on the wheel has greatly influence on the distribution of shear stress and dynamic pressure on the workpiece surface.

  6. Self assembly of magnetic nanoparticles at silicon surfaces.

    PubMed

    Theis-Bröhl, Katharina; Gutfreund, Philipp; Vorobiev, Alexei; Wolff, Max; Toperverg, Boris P; Dura, Joseph A; Borchers, Julie A

    2015-06-21

    Neutron reflectometry was used to study the assembly of magnetite nanoparticles in a water-based ferrofluid close to a silicon surface. Under three conditions, static, under shear and with a magnetic field, the depth profile is extracted. The particles have an average diameter of 11 nm and a volume density of 5% in a D2O-H2O mixture. They are surrounded by a 4 nm thick bilayer of carboxylic acid for steric repulsion. The reflectivity data were fitted to a model using a least square routine based on the Parratt formalism. From the scattering length density depth profiles the following behavior is concluded: the fits indicate that excess carboxylic acid covers the silicon surface and almost eliminates the water in the densely packed wetting layer that forms close to the silicon surface. Under constant shear the wetting layer persists but a depletion layer forms between the wetting layer and the moving ferrofluid. Once the flow is stopped, the wetting layer becomes more pronounced with dense packing and is accompanied by a looser packed second layer. In the case of an applied magnetic field the prolate particles experience a torque and align with their long axes along the silicon surface which leads to a higher particle density. PMID:25971712

  7. Silicon surface barrier detectors used for liquid hydrogen density measurement

    NASA Technical Reports Server (NTRS)

    James, D. T.; Milam, J. K.; Winslett, H. B.

    1968-01-01

    Multichannel system employing a radioisotope radiation source, strontium-90, radiation detector, and a silicon surface barrier detector, measures the local density of liquid hydrogen at various levels in a storage tank. The instrument contains electronic equipment for collecting the density information, and a data handling system for processing this information.

  8. Surface charge transport in Silicon (111) nanomembranes

    NASA Astrophysics Data System (ADS)

    Hu, Weiwei; Scott, Shelley; Jacobson, Rb; Savage, Donald; Lagally, Max; The Lagally Group Team

    Using thin sheets (``nanomembranes'') of atomically flat crystalline semiconductors, we are able to investigate surface electronic properties, using back-gated van der Pauw measurement in UHV. The thinness of the sheet diminishes the bulk contribution, and the back gate tunes the conductivity until the surface dominates, enabling experimental determination of surface conductance. We have previously shown that Si(001) surface states interact with the body of the membrane altering the conductivity of the system. Here, we extended our prior measurements to Si(111) in order to probe the electronic transport properties of the Si(111) 7 ×7 reconstruction. Sharp (7 ×7) LEED images attest to the cleanliness of the Si(111) surface. Preliminary results reveal a highly conductive Si(111) 7 ×7 surface with a sheet conductance Rs of order of μS/ □, for 110nm thick membrane, and Rs is a very slowly varying function of the back gate voltage. This is in strong contrast to Si(001) nanomembranes which have a minimum conductance several orders of magnitude lower, and hints to the metallic nature of the Si(111) surface. Research supported by DOE.

  9. The Nucleation and Growth of Cu Nanoclusters on Silicon Surfaces

    SciTech Connect

    Singh, Andy; Luening, Katharina; Brennan, Sean; Pianetta, Piero; Homma, Takayuki; Kubo, Nobuhiro

    2004-05-12

    Due to the recent adoption of copper interconnect technology by the semiconductor industry, there has been great interest in understanding the kinetics and mechanisms of copper metal deposition on silicon wafer surfaces in ultra pure water (UPW) solutions. To study the kinetics of the copper deposition mechanism on silicon surfaces, silicon [100] samples were immersed in non-deoxygenated and deoxygenated UPW solutions contaminated with a copper concentration of 100 ppb with dipping times ranging from 5 to 300 seconds and then measured using total reflection x-ray fluorescence (TXRF) at the Stanford Synchrotron Radiation Laboratory (SSRL). By measuring the Cu fluorescence signal as function of angle of incidence of the incoming x-rays, it was possible to ascertain whether the deposited copper was atomically dispersed or particle-like in nature. It was established that in non-deoxygenated UPW, the copper is incorporated atomically into the silicon surface oxide as a copper oxide, while in deoxygenated UPW, copper is deposited on the silicon surface in the form of nanoparticles. The heights of these particles were determined by performing quantitative fits to the angle scans using a spherical cap model to describe the Cu clusters. The results were consistent with measurements conducted with atomic force microscopy (AFM). Finally, the surface density of the metallic copper nanoparticles deposited in deoxygenated UPW was determined for the whole range of dipping times from the AFM measurements, indicating that Ostwald Ripening mechanisms, where large particles grow at the expense of smaller, less thermodynamically stable particles, describe the growth of Cu nanoclusters in deoxygenated UPW solutions.

  10. Surface effects in high voltage silicon solar cells

    NASA Technical Reports Server (NTRS)

    Meulenberg, A.; Arndt, R. A.

    1982-01-01

    The surface of low-resistivity silicon solar cells appears to be a major source of dark diffusion current. This region, consisting of the interface and the adjacent heavily doped layer, therefore, prevents attainment of the high open-circuit voltages expected from these cells. This paper describes the experimental effort carried out to reduce the various contributions of dark current from the surface. Analysis of results from this effort points to means of improving cell voltages by changing processing and structures.

  11. Silver diffusion over silicon surfaces with adsorbed tin atoms

    SciTech Connect

    Dolbak, A. E. Olshanetskii, B. Z.

    2015-02-15

    Silver diffusion over the (111), (100), and (110) surfaces of silicon with preliminarily adsorbed tin atoms is studied by Auger electron spectroscopy and low-energy electron diffraction. Diffusion is observed only on the surface of Si(111)-2√3 × 2√3-Sn. The diffusion mechanism is established. It is found that the diffusion coefficient depends on the concentration of diffusing atoms. The diffusion coefficient decreases with increasing silver concentration, while the activation energy and the preexponential factor increase.

  12. Defect distribution near the surface of electron-irradiated silicon

    NASA Technical Reports Server (NTRS)

    Wang, K. L.; Lee, Y. H.; Corbett, J. W.

    1978-01-01

    The surface-defect distributions of electron-irradiated n-type silicon have been investigated using a transient capacitance technique. Schottky, p-n junction, and MOS structures were used in profiling the defect distributions. Surface depletions of defects observed were attributed to the vacancy distribution, but not that of oxygen, and other capture centers' distributions. The vacancy diffusion length at 300 K was estimated to be about 3-6 microns.

  13. Surface self-diffusion of silicon during high temperature annealing

    SciTech Connect

    Acosta-Alba, Pablo E.; Kononchuk, Oleg; Gourdel, Christophe; Claverie, Alain

    2014-04-07

    The atomic-scale mechanisms driving thermally activated self-diffusion on silicon surfaces are investigated by atomic force microscopy. The evolution of surface topography is quantified over a large spatial bandwidth by means of the Power Spectral Density functions. We propose a parametric model, based on the Mullins-Herring (M-H) diffusion equation, to describe the evolution of the surface topography of silicon during thermal annealing. Usually, a stochastic term is introduced into the M-H model in order to describe intrinsic random fluctuations of the system. In this work, we add two stochastic terms describing the surface thermal fluctuations and the oxidation-evaporation phenomenon. Using this extended model, surface evolution during thermal annealing in reducing atmosphere can be predicted for temperatures above the roughening transition. A very good agreement between experimental and theoretical data describing roughness evolution and self-diffusion phenomenon is obtained. The physical origin and time-evolution of these stochastic terms are discussed. Finally, using this model, we explore the limitations of the smoothening of the silicon surfaces by rapid thermal annealing.

  14. Atmospheric oxygen plasma activation of silicon (100) surfaces

    SciTech Connect

    Habib, Sara B.; Gonzalez, Eleazar II; Hicks, Robert F.

    2010-05-15

    Silicon (100) surfaces were converted to a hydrophilic state with a water contact angle of <5 deg. by treatment with a radio frequency, atmospheric pressure helium, and oxygen plasma. A 2 in. wide plasma beam, operating at 250 W, 1.0 l/min O{sub 2}, 30 l/min He, and a source-to-sample distance of 3{+-}0.1 mm, was scanned over the sample at 100{+-}2 mm/s. Plasma oxidation of HF-etched silicon caused the dispersive component of the surface energy to decrease from 55.1 to 25.8 dyn/cm, whereas the polar component of the surface energy increased from 0.3 to 42.1 dyn/cm. X-ray photoelectron spectroscopy revealed that the treatment generated a monolayer of covalently bonded oxygen on the Si(100) surface 0.15{+-}0.10 nm thick. The surface oxidation kinetics have been measured by monitoring the change in water contact angle with treatment time, and are consistent with a process that is limited by the mass transfer of ground-state oxygen atoms to the silicon surface.

  15. Surface self-diffusion of silicon during high temperature annealing

    NASA Astrophysics Data System (ADS)

    Acosta-Alba, Pablo E.; Kononchuk, Oleg; Gourdel, Christophe; Claverie, Alain

    2014-04-01

    The atomic-scale mechanisms driving thermally activated self-diffusion on silicon surfaces are investigated by atomic force microscopy. The evolution of surface topography is quantified over a large spatial bandwidth by means of the Power Spectral Density functions. We propose a parametric model, based on the Mullins-Herring (M-H) diffusion equation, to describe the evolution of the surface topography of silicon during thermal annealing. Usually, a stochastic term is introduced into the M-H model in order to describe intrinsic random fluctuations of the system. In this work, we add two stochastic terms describing the surface thermal fluctuations and the oxidation-evaporation phenomenon. Using this extended model, surface evolution during thermal annealing in reducing atmosphere can be predicted for temperatures above the roughening transition. A very good agreement between experimental and theoretical data describing roughness evolution and self-diffusion phenomenon is obtained. The physical origin and time-evolution of these stochastic terms are discussed. Finally, using this model, we explore the limitations of the smoothening of the silicon surfaces by rapid thermal annealing.

  16. Spin Chains and Electron Transfer at Stepped Silicon Surfaces.

    PubMed

    Aulbach, J; Erwin, S C; Claessen, R; Schäfer, J

    2016-04-13

    High-index surfaces of silicon with adsorbed gold can reconstruct to form highly ordered linear step arrays. These steps take the form of a narrow strip of graphitic silicon. In some cases--specifically, for Si(553)-Au and Si(557)-Au--a large fraction of the silicon atoms at the exposed edge of this strip are known to be spin-polarized and charge-ordered along the edge. The periodicity of this charge ordering is always commensurate with the structural periodicity along the step edge and hence leads to highly ordered arrays of local magnetic moments that can be regarded as "spin chains." Here, we demonstrate theoretically as well as experimentally that the closely related Si(775)-Au surface has--despite its very similar overall structure--zero spin polarization at its step edge. Using a combination of density-functional theory and scanning tunneling microscopy, we propose an electron-counting model that accounts for these differences. The model also predicts that unintentional defects and intentional dopants can create local spin moments at Si(hhk)-Au step edges. We analyze in detail one of these predictions and verify it experimentally. This finding opens the door to using techniques of surface chemistry and atom manipulation to create and control silicon spin chains. PMID:26974012

  17. Surface engineered porous silicon for stable, high performance electrochemical supercapacitors

    NASA Astrophysics Data System (ADS)

    Oakes, Landon; Westover, Andrew; Mares, Jeremy W.; Chatterjee, Shahana; Erwin, William R.; Bardhan, Rizia; Weiss, Sharon M.; Pint, Cary L.

    2013-10-01

    Silicon materials remain unused for supercapacitors due to extreme reactivity of silicon with electrolytes. However, doped silicon materials boast a low mass density, excellent conductivity, a controllably etched nanoporous structure, and combined earth abundance and technological presence appealing to diverse energy storage frameworks. Here, we demonstrate a universal route to transform porous silicon (P-Si) into stable electrodes for electrochemical devices through growth of an ultra-thin, conformal graphene coating on the P-Si surface. This graphene coating simultaneously passivates surface charge traps and provides an ideal electrode-electrolyte electrochemical interface. This leads to 10-40X improvement in energy density, and a 2X wider electrochemical window compared to identically-structured unpassivated P-Si. This work demonstrates a technique generalizable to mesoporous and nanoporous materials that decouples the engineering of electrode structure and electrochemical surface stability to engineer performance in electrochemical environments. Specifically, we demonstrate P-Si as a promising new platform for grid-scale and integrated electrochemical energy storage.

  18. Surface engineered porous silicon for stable, high performance electrochemical supercapacitors.

    PubMed

    Oakes, Landon; Westover, Andrew; Mares, Jeremy W; Chatterjee, Shahana; Erwin, William R; Bardhan, Rizia; Weiss, Sharon M; Pint, Cary L

    2013-01-01

    Silicon materials remain unused for supercapacitors due to extreme reactivity of silicon with electrolytes. However, doped silicon materials boast a low mass density, excellent conductivity, a controllably etched nanoporous structure, and combined earth abundance and technological presence appealing to diverse energy storage frameworks. Here, we demonstrate a universal route to transform porous silicon (P-Si) into stable electrodes for electrochemical devices through growth of an ultra-thin, conformal graphene coating on the P-Si surface. This graphene coating simultaneously passivates surface charge traps and provides an ideal electrode-electrolyte electrochemical interface. This leads to 10-40X improvement in energy density, and a 2X wider electrochemical window compared to identically-structured unpassivated P-Si. This work demonstrates a technique generalizable to mesoporous and nanoporous materials that decouples the engineering of electrode structure and electrochemical surface stability to engineer performance in electrochemical environments. Specifically, we demonstrate P-Si as a promising new platform for grid-scale and integrated electrochemical energy storage. PMID:24145684

  19. Surface engineered porous silicon for stable, high performance electrochemical supercapacitors

    PubMed Central

    Oakes, Landon; Westover, Andrew; Mares, Jeremy W.; Chatterjee, Shahana; Erwin, William R.; Bardhan, Rizia; Weiss, Sharon M.; Pint, Cary L.

    2013-01-01

    Silicon materials remain unused for supercapacitors due to extreme reactivity of silicon with electrolytes. However, doped silicon materials boast a low mass density, excellent conductivity, a controllably etched nanoporous structure, and combined earth abundance and technological presence appealing to diverse energy storage frameworks. Here, we demonstrate a universal route to transform porous silicon (P-Si) into stable electrodes for electrochemical devices through growth of an ultra-thin, conformal graphene coating on the P-Si surface. This graphene coating simultaneously passivates surface charge traps and provides an ideal electrode-electrolyte electrochemical interface. This leads to 10–40X improvement in energy density, and a 2X wider electrochemical window compared to identically-structured unpassivated P-Si. This work demonstrates a technique generalizable to mesoporous and nanoporous materials that decouples the engineering of electrode structure and electrochemical surface stability to engineer performance in electrochemical environments. Specifically, we demonstrate P-Si as a promising new platform for grid-scale and integrated electrochemical energy storage. PMID:24145684

  20. Initial stages of silicon growth on the (100) surface of silicon by localized laser CVD

    NASA Astrophysics Data System (ADS)

    Kotecki, D. E.; Herman, I. P.

    1987-12-01

    This paper reports initial results of an experimental study of the early stages of silicon thin film growth on well prepared (100) c-Si surfaces by pyrolytic deposition from silane (SiH4) during localized laser chemical vapor deposition (LLCVD). The rate of silicon thin film growth during low pressure (less than 10 Torr) deposition using tightly focussed laser beams (514.5 nm, approximately 2.5 micron FWHM) is characterized and is shown to be much slower than expected based on the previously measured silane decomposition rate. Hybrid-heating experiments, in which laser heating induces a slight temperature increase on a uniformly heated substrate in the presence of silane gas, shows that growth is inhibited within the laser irradiation region. This result suggests that a nonpyrolytic mechanism contributes to silicon growth in laser CVD. Possible explanations for this nonpyrolytic growth mechanism are discussed.

  1. 22. 7% efficient silicon photovoltaic modules with textured front surface

    SciTech Connect

    Zhao, J.; Wang, A.; Campbell, P.; Green, M.A. . Photovoltaics Special Research Centre)

    1999-07-01

    This paper reports the highest ever independently confirmed efficiency for a photovoltaic module as demonstrated by two 778-cm[sup 2] silicon solar cell modules of 22.7% efficiency. A key feature of these modules was the use of a pyramidally textured top module surface to reduce reflection from this surface as well as from the underlying cell surface, by trapping light within the top cover sheet. Higher current density and higher energy conversion efficiency for such a textured module are theoretically predicted and experimentally measured compared to a standard module with a planar front surface. This advantage becomes more significant for obliquely incident light.

  2. The Surface Photovoltage Mechanism of a Silicon Nanoporous Pillar Array

    NASA Astrophysics Data System (ADS)

    Hu, Zhen-Gang; Tian, Yong-Tao; Li, Xin-Jian

    2013-08-01

    The surface photovoltage (SPV) mechanism of a silicon nanoporous pillar array (Si-NPA) is investigated by using SPV spectroscopy in different external electric fields. Through comparisons with the SPV spectrum of single crystal silicon (sc-Si), the silicon nano-crystallite (nc-Si)/SiOx nanostructure of Si-NPA is proved to be capable of producing obvious SPV in the wavelength range 300-580 nm. The SPV for the sc-Si layer and the nc-Si/SiOx nanostructure has shown certain contrary characters in different external electric fields. Through analysis, the localized states in the amorphous SiOx matrix are believed to dominate the SPV for the nc-Si/SiOx nanostructure.

  3. Electron stimulated oxidation of silicon surfaces

    SciTech Connect

    Munoz, M.C.; Sacedon, J.L.

    1981-04-15

    Experimental evidence of electron stimulated oxidation (ESO) has been given for Si(111) 7 x 7 surface. In a first stage, the oxide thickness as a function of time shows a linear relationship; in a second stage, the growth rate quickly decreases and a pressure dependent saturation oxide thickness is reached. During the oxidation process an electrical potential does exist across the oxide, as is required in the Cabrera--Mott theory. The linear kinetics and the electrical potential are shown to be explicable in terms of a modified coupled-current approach based on the Cabrera--Mott theory, provided a semiphenomenological pressure dependent parameter is included. This represents a contribution of the surface reaction to the transport equation. The saturation has been explained as due to the decrease of the negative surface charge (donor levels) which produces a decrease of the electron current.

  4. Dynamics of photosensitized formation of singlet oxygen by porous silicon in aqueous solution

    SciTech Connect

    Fujii, Minoru; Nishimura, Naoki; Fumon, Hirokazu; Hayashi, Shinji; Kovalev, Dmitry; Goller, Bernhard; Diener, Joachim

    2006-12-15

    Generation of singlet oxygen due to energy transfer from photoexcited silicon nanocrystals in D{sub 2}O is demonstrated. It is shown that the singlet oxygen generation efficiency, i.e., the intensity of near-infrared emission from singlet oxygen gradually decreases when Si nanocrystals are continuously irradiated in O{sub 2}-saturated D{sub 2}O. The mechanism of the photodegradation of the photosensitizing efficiency is studied using photoluminescence and infrared absorption techniques. Experimental results suggest that the interaction of photogenerated singlet oxygen with the hydrogen-terminated surface of silicon nanocrystals results in photo-oxidation of silicon nanocrystals, and the surface oxides reduce the photosensitizing efficiency. It is also demonstrated that photo-oxidation of porous silicon in O{sub 2}-saturated water results in a strong enhancement of the photoluminescence quantum yield of porous Si.

  5. Changes in surface chemistry of silicon carbide (0001) surface with temperature and their effect on friction

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Buckley, D. H.

    1980-01-01

    Friction studies were conducted with a silicon carbide (0001) surface contacting polycrystalline iron. The surface of silicon carbide was pretreated: (1) by bombarding it with argon ions for 30 minutes at a pressure of 1.3 pascals; (2) by heating it at 800 C for 3 hours in vacuum at a pressure of 10 to the minus eighth power pascal; or (3) by heating it at 1500 C for 3 hours in a vacuum of 10 to the minus eighth power pascal. Auger emission spectroscopy was used to determine the presence of silicon and carbon and the form of the carbon. The surfaces of silicon carbide bombarded with argon ions or preheated to 800 C revealed the main Si peak and a carbide type of C peak in the Auger spectra. The surfaces preheated to 1500 C revealed only a graphite type of C peak in the Auger spectra, and the Si peak had diminished to a barely perceptible amount. The surfaces of silicon carbide preheated to 800 C gave a 1.5 to 3 times higher coefficient of friction than did the surfaces of silicon carbide preheated to 1500 C. The coefficient of friction was lower in the 11(-2)0 direction than in the 10(-1)0 direction; that is, it was lower in the preferred crystallographic slip direction.

  6. Method For Silicon Surface Texturing Using Ion Implantation

    SciTech Connect

    Kadakia, Nirag; Naczas, Sebastian; Bakhru, Hassaram; Huang Mengbing

    2011-06-01

    As the semiconductor industry continues to show more interest in the photovoltaic market, cheaper and readily integrable methods of silicon solar cell production are desired. One of these methods - ion implantation - is well-developed and optimized in all commercial semiconductor fabrication facilities. Here we have developed a silicon surface texturing technique predicated upon the phenomenon of surface blistering of H-implanted silicon, using only ion implantation and thermal annealing. We find that following the H implant with a second, heavier implant markedly enhances the surface blistering, causing large trenches that act as a surface texturing of c-Si. We have found that this method reduces total broadband Si reflectance from 35% to below 5percent;. In addition, we have used Rutherford backscattering/channeling measurements investigate the effect of ion implantation on the crystallinity of the sample. The data suggests that implantation-induced lattice damage is recovered upon annealing, reproducing the original monocrystalline structure in the previously amorphized region, while at the same time retaining the textured surface.

  7. Mixed role of surface on intrinsic losses in silicon nanostructures

    NASA Astrophysics Data System (ADS)

    De, Subhadeep; Kunal, K.; Aluru, N. R.

    2016-03-01

    We utilize molecular dynamics simulations and show opposing roles of surface on dissipation in nanostructures. While the surface defects always aid in the entropy generation process, the scattering of phonons from rough surfaces can suppress Akhiezer damping. For the case of a silicon (2 × 1) reconstructed surface, the former dominates and Q-1 (Q is the quality factor) is found to increase with the decrease in size. However, different scaling trends are observed in the case of a hydrogen (H) terminated silicon surface with no defects and dimers. Particularly, in the case of a H-terminated silicon, if the resonator is operated with a frequency Ω such that Ωτph<1 , where τph is the phonon relaxation time and Q-1 is found to decrease with the decrease in size. The opposite scaling is observed for Ωτph>1 . A simplified model, based on two phonon groups (with positive and negative Grüneisen parameters), is considered to explain the observed trend. We show that the equilibration time between the two mode groups decreases with the decrease in size for the H-terminated structure. We also study the scaling of Q-1 factor with frequency for these cases.

  8. Method For Silicon Surface Texturing Using Ion Implantation

    NASA Astrophysics Data System (ADS)

    Kadakia, Nirag; Naczas, Sebastian; Bakhru, Hassaram; Huang, Mengbing

    2011-06-01

    As the semiconductor industry continues to show more interest in the photovoltaic market, cheaper and readily integrable methods of silicon solar cell production are desired. One of these methods—ion implantation—is well-developed and optimized in all commercial semiconductor fabrication facilities. Here we have developed a silicon surface texturing technique predicated upon the phenomenon of surface blistering of H-implanted silicon, using only ion implantation and thermal annealing. We find that following the H implant with a second, heavier implant markedly enhances the surface blistering, causing large trenches that act as a surface texturing of c-Si. We have found that this method reduces total broadband Si reflectance from 35% to below 5percent;. In addition, we have used Rutherford backscattering/channeling measurements investigate the effect of ion implantation on the crystallinity of the sample. The data suggests that implantation-induced lattice damage is recovered upon annealing, reproducing the original monocrystalline structure in the previously amorphized region, while at the same time retaining the textured surface.

  9. Effect of Surface Treated Silicon Dioxide Nanoparticles on Some Mechanical Properties of Maxillofacial Silicone Elastomer

    PubMed Central

    Zayed, Sara M.; Alshimy, Ahmad M.; Fahmy, Amal E.

    2014-01-01

    Current materials used for maxillofacial prostheses are far from ideal and there is a need for novel improved materials which mimic as close as possible the natural behavior of facial soft tissues. This study aimed to evaluate the effect of adding different concentrations of surface treated silicon dioxide nanoparticles (SiO2) on clinically important mechanical properties of a maxillofacial silicone elastomer. 147 specimens of the silicone elastomer were prepared and divided into seven groups (n = 21). One control group was prepared without nanoparticles and six study groups with different concentrations of nanoparticles, from 0.5% to 3% by weight. Specimens were tested for tear strength (ASTM D624), tensile strength (ASTM D412), percent elongation, and shore A hardness. SEM was used to assess the dispersion of nano-SiO2 within the elastomer matrix. Data were analyzed by one-way ANOVA and Scheffe test (α = 0.05). Results revealed significant improvement in all mechanical properties tested, as the concentration of the nanoparticles increased. This was supported by the results of the SEM. Hence, it can be concluded that the incorporation of surface treated SiO2 nanoparticles at concentration of 3% enhanced the overall mechanical properties of A-2186 silicone elastomer. PMID:25574170

  10. Forming high efficiency silicon solar cells using density-graded anti-reflection surfaces

    DOEpatents

    Yuan, Hao-Chih; Branz, Howard M.; Page, Matthew R.

    2014-09-09

    A method (50) is provided for processing a graded-density AR silicon surface (14) to provide effective surface passivation. The method (50) includes positioning a substrate or wafer (12) with a silicon surface (14) in a reaction or processing chamber (42). The silicon surface (14) has been processed (52) to be an AR surface with a density gradient or region of black silicon. The method (50) continues with heating (54) the chamber (42) to a high temperature for both doping and surface passivation. The method (50) includes forming (58), with a dopant-containing precursor in contact with the silicon surface (14) of the substrate (12), an emitter junction (16) proximate to the silicon surface (14) by doping the substrate (12). The method (50) further includes, while the chamber is maintained at the high or raised temperature, forming (62) a passivation layer (19) on the graded-density silicon anti-reflection surface (14).

  11. Forming high-efficiency silicon solar cells using density-graded anti-reflection surfaces

    DOEpatents

    Yuan, Hao-Chih; Branz, Howard M.; Page, Matthew R.

    2015-07-07

    A method (50) is provided for processing a graded-density AR silicon surface (14) to provide effective surface passivation. The method (50) includes positioning a substrate or wafer (12) with a silicon surface (14) in a reaction or processing chamber (42). The silicon surface (14) has been processed (52) to be an AR surface with a density gradient or region of black silicon. The method (50) continues with heating (54) the chamber (42) to a high temperature for both doping and surface passivation. The method (50) includes forming (58), with a dopant-containing precursor in contact with the silicon surface (14) of the substrate (12), an emitter junction (16) proximate to the silicon surface (14) by doping the substrate (12). The method (50) further includes, while the chamber is maintained at the high or raised temperature, forming (62) a passivation layer (19) on the graded-density silicon anti-reflection surface (14).

  12. A reclaiming process for solar cell silicon wafer surfaces.

    PubMed

    Pa, P S

    2011-01-01

    The low yield of epoxy film and Si3N4 thin-film deposition is an important factor in semiconductor production. A new design system using a set of three lamination-shaped electrodes as a machining tool and micro electro-removal as a precision reclaiming process of the Si3N4 layer and epoxy film removal from silicon wafers of solar cells surface is presented. In the current experiment, the combination of the small thickness of the anode and cathodes corresponds to a higher removal rate for the thin films. The combination of the short length of the anode and cathodes combined with enough electric power produces fast electroremoval. A combination of the small edge radius of the anode and cathodes corresponds to a higher removal rate. A higher feed rate of silicon wafers of solar cells combined with enough electric power produces fast removal. A precise engineering technology constructed a clean production approach for the removal of surface microstructure layers from silicon wafers is to develop a mass production system for recycling defective or discarded silicon wafers from solar cells that can reduce pollution and lower cost. PMID:21446525

  13. Passivation of c-Si surfaces by sub-nm amorphous silicon capped with silicon nitride

    SciTech Connect

    Wan, Yimao Yan, Di; Bullock, James; Zhang, Xinyu; Cuevas, Andres

    2015-12-07

    A sub-nm hydrogenated amorphous silicon (a-Si:H) film capped with silicon nitride (SiN{sub x}) is shown to provide a high level passivation to crystalline silicon (c-Si) surfaces. When passivated by a 0.8 nm a-Si:H/75 nm SiN{sub x} stack, recombination current density J{sub 0} values of 9, 11, 47, and 87 fA/cm{sup 2} are obtained on 10 Ω·cm n-type, 0.8 Ω·cm p-type, 160 Ω/sq phosphorus-diffused, and 120 Ω/sq boron-diffused silicon surfaces, respectively. The J{sub 0} on n-type 10 Ω·cm wafers is further reduced to 2.5 ± 0.5 fA/cm{sup 2} when the a-Si:H film thickness exceeds 2.5 nm. The passivation by the sub-nm a-Si:H/SiN{sub x} stack is thermally stable at 400 °C in N{sub 2} for 60 min on all four c-Si surfaces. Capacitance–voltage measurements reveal a reduction in interface defect density and film charge density with an increase in a-Si:H thickness. The nearly transparent sub-nm a-Si:H/SiN{sub x} stack is thus demonstrated to be a promising surface passivation and antireflection coating suitable for all types of surfaces encountered in high efficiency c-Si solar cells.

  14. Direct modification of silicon surface by nanosecond laser interference lithography

    NASA Astrophysics Data System (ADS)

    Wang, Dapeng; Wang, Zuobin; Zhang, Ziang; Yue, Yong; Li, Dayou; Maple, Carsten

    2013-10-01

    Periodic and quasi-periodic structures on silicon surface have numerous significant applications in photoelectronics and surface engineering. A number of technologies have been developed to fabricate the structures in various research fields. In this work, we take the strategy of direct nanosecond laser interference lithography technology, and focus on the silicon material to create different well-defined surface structures based on theoretical analysis of the formation of laser interference patterns. Two, three and four-beam laser interference systems were set up to fabricate the grating, regular triangle and square structures on silicon surfaces, respectively. From the AFM micrographs, the critical features of structures have a dependence on laser fluences. For a relative low laser fluence, grating and dot structures formed with bumps due to the Marangoni Effect. With the increase of laser fluences, melt and evaporation behaviors can be responsible for the laser modification. By properly selecting the process parameters, well-defined grating and dot structures can been achieved. It can be demonstrated that direct laser interference lithography is a facile and efficient technology with the advantage of a single process procedure over macroscale areas for the fabrication of micro and nano structures.

  15. Sputtering of dimers off a silicon surface

    NASA Astrophysics Data System (ADS)

    Nietiadi, Maureen L.; Rosandi, Yudi; Kopnarski, Michael; Urbassek, Herbert M.

    2012-10-01

    We present experimental and molecular-dynamics simulation results of the sputtering of a Si surface by 2 keV Ar ions. Results on both the monomer and dimer distributions are presented. In simulation, these distributions follow a generalized Thompson law with power exponent n=2 and n=3, respectively. The experimental data, obtained via plasma post-ionization in an SNMS (secondary neutral mass spectrometry) apparatus, show good agreement with respect to the dimer fraction, and the relative energy distributions of dimers and monomers. The consequences for the dimer sputtering mechanism are discussed.

  16. Ion Beam Analysis Of Silicon-Based Surfaces And Correlation With Surface Energy Measurements

    NASA Astrophysics Data System (ADS)

    Xing, Qian; Herbots, N.; Hart, M.; Bradley, J. D.; Wilkens, B. J.; Sell, D. A.; Sell, Clive H.; Kwong, Henry Mark; Culbertson, R. J.; Whaley, S. D.

    2011-06-01

    The water affinity of Si-based surfaces is quantified by contact angle measurement and surface free energy to explain hydrophobic or hydrophilic behavior of silicone, silicates, and silicon surfaces. Surface defects such as dangling bonds, surface free energy including Lewis acid-base and Lifshitz-van der Waals components are discussed. Water nucleation and condensation is further explained by surface topography. Tapping mode atomic force microscopy (TMAFM) provides statistical analysis of the topography of these Si-based surfaces. The correlation of the above two characteristics describes the behavior of water condensation at Si-based surfaces. Surface root mean square roughness increasing from several Å to several nm is found to provide nucleation sites that expedite water condensation visibly for silica and silicone. Hydrophilic surfaces have a condensation pattern that forms puddles of water while hydrophobic surfaces form water beads. Polymer adsorption on these surfaces alters the water affinity as well as the surface topography, and therefore controls condensation on Si-based surfaces including silicone intraocular lens (IOL). The polymer film is characterized by Rutherford backscattering spectrometry (RBS) in conjunction with 4.265 MeV 12C(α, α)12C, 3.045 MeV 16O(α,α)16O nuclear resonance scattering (NRS), and 2.8 MeV elastic recoil detection (ERD) of hydrogen for high resolution composition and areal density measurements. The areal density of hydroxypropyl methylcellulose (HPMC) film ranges from 1018 atom/cm2 to 1019 atom/cm2 gives the silica or silicone surface a roughness of several Å and a wavelength of 0.16±0.02 μm, and prevents fogging by forming a complete wetting layer during water condensation.

  17. Ion Beam Analysis Of Silicon-Based Surfaces And Correlation With Surface Energy Measurements

    SciTech Connect

    Xing Qian; Herbots, N.; Hart, M.; Bradley, J. D.; Wilkens, B. J.; Sell, D. A.; Culbertson, R. J.; Whaley, S. D.; Sell, Clive H.; Kwong, Henry Mark Jr.

    2011-06-01

    The water affinity of Si-based surfaces is quantified by contact angle measurement and surface free energy to explain hydrophobic or hydrophilic behavior of silicone, silicates, and silicon surfaces. Surface defects such as dangling bonds, surface free energy including Lewis acid-base and Lifshitz-van der Waals components are discussed. Water nucleation and condensation is further explained by surface topography. Tapping mode atomic force microscopy (TMAFM) provides statistical analysis of the topography of these Si-based surfaces. The correlation of the above two characteristics describes the behavior of water condensation at Si-based surfaces. Surface root mean square roughness increasing from several A ring to several nm is found to provide nucleation sites that expedite water condensation visibly for silica and silicone. Hydrophilic surfaces have a condensation pattern that forms puddles of water while hydrophobic surfaces form water beads. Polymer adsorption on these surfaces alters the water affinity as well as the surface topography, and therefore controls condensation on Si-based surfaces including silicone intraocular lens (IOL). The polymer film is characterized by Rutherford backscattering spectrometry (RBS) in conjunction with 4.265 MeV {sup 12}C({alpha}, {alpha}){sup 12}C, 3.045 MeV {sup 16}O({alpha},{alpha}){sup 16}O nuclear resonance scattering (NRS), and 2.8 MeV elastic recoil detection (ERD) of hydrogen for high resolution composition and areal density measurements. The areal density of hydroxypropyl methylcellulose (HPMC) film ranges from 10{sup 18} atom/cm{sup 2} to 10{sup 19} atom/cm{sup 2} gives the silica or silicone surface a roughness of several A ring and a wavelength of 0.16{+-}0.02 {mu}m, and prevents fogging by forming a complete wetting layer during water condensation.

  18. Quantum engineering at the silicon surface using dangling bonds

    PubMed Central

    Schofield, S. R.; Studer, P.; Hirjibehedin, C. F.; Curson, N. J.; Aeppli, G.; Bowler, D. R.

    2013-01-01

    Individual atoms and ions are now routinely manipulated using scanning tunnelling microscopes or electromagnetic traps for the creation and control of artificial quantum states. For applications such as quantum information processing, the ability to introduce multiple atomic-scale defects deterministically in a semiconductor is highly desirable. Here we use a scanning tunnelling microscope to fabricate interacting chains of dangling bond defects on the hydrogen-passivated silicon (001) surface. We image both the ground-state and the excited-state probability distributions of the resulting artificial molecular orbitals, using the scanning tunnelling microscope tip bias and tip-sample separation as gates to control which states contribute to the image. Our results demonstrate that atomically precise quantum states can be fabricated on silicon, and suggest a general model of quantum-state fabrication using other chemically passivated semiconductor surfaces where single-atom depassivation can be achieved using scanning tunnelling microscopy. PMID:23552064

  19. Silicon Nanotips Antireflection Surface for Micro Sun Sensor

    NASA Technical Reports Server (NTRS)

    Bae, Sam Y.; Lee, Choonsup; Mobasser, Sohrab; Manohara, Harish

    2006-01-01

    We have developed a new technique to fabricate antireflection surface using silicon nano-tips for use on a micro sun sensor for Mars rovers. We have achieved randomly distributed nano-tips of radius spanning from 20 nm to 100 nm and aspect ratio of 200 using a two-step dry etching process. The 30(deg) specular reflectance at the target wavelength of 1 (mu)m is only about 0.09 %, nearly three orders of magnitude lower than that of bare silicon, and the hemispherical reflectance is 8%. By changing the density and aspect ratio of these nanotips, the change in reflectance is demonstrated. Using surfaces covered with these nano-tips, the critical problem of ghost images that are caused by multiple internal reflections in a micro sun sensor was solved.

  20. Surface Breakdown Characteristics of Silicone Oil for Electric Power Apparatus

    NASA Astrophysics Data System (ADS)

    Wada, Junichi; Nakajima, Akitoshi; Miyahara, Hideyuki; Takuma, Tadasu; Okabe, Shigemitu; Kohtoh, Masanori; Yanabu, Satoru

    This paper describes the surface breakdown characteristics of the silicone oil which has the possibility of the application to innovative switchgear as an insulating medium. At the first step, we have experimentally studied on the impulse breakdown characteristics of the configuration with a triple-junction where a solid insulator is in contact with the electrode. The test configurations consist of solid material (Nomex and pressboard) and liquid insulation oil (silicone and mineral oil). We have discussed the experimental results based on the maximal electric field at a triple-junction. As the second step, we have studied the configuration which may improve the surface breakdown characteristics by lowering the electric field near the triple-junction.

  1. Methods of Attaching or Grafting Carbon Nanotubes to Silicon Surfaces and Composite Structures Derived Therefrom

    NASA Technical Reports Server (NTRS)

    Tour, James M. (Inventor); Chen, Bo (Inventor); Flatt, Austen K. (Inventor); Stewart, Michael P. (Inventor); Dyke, Christopher A. (Inventor); Maya, Francisco (Inventor)

    2012-01-01

    The present invention is directed toward methods of attaching or grafting carbon nanotubes (CNTs) to silicon surfaces. In some embodiments, such attaching or grafting occurs via functional groups on either or both of the CNTs and silicon surface. In some embodiments, the methods of the present invention include: (1) reacting a silicon surface with a functionalizing agent (such as oligo(phenylene ethynylene)) to form a functionalized silicon surface; (2) dispersing a quantity of CNTs in a solvent to form dispersed CNTs; and (3) reacting the functionalized silicon surface with the dispersed CNTs. The present invention is also directed to the novel compositions produced by such methods.

  2. Integrated silicon photonic interconnect with surface-normal optical interface

    NASA Astrophysics Data System (ADS)

    Zhang, Zanyun; Huang, Beiju; Zhang, Zan; Cheng, Chuantong; Liu, Hongwei; Li, Hongqiang; Chen, Hongda

    2016-05-01

    An integrated silicon photonic interconnect with surface-normal optical interface is demonstrated by connecting a bidirectional grating based E-O modulator and a germanium waveguide photodetector. To investigate this photonic interconnect, both static and dynamic performance of the discrete devices are characterized respectively. Based on the characterization work, data transmission experiment is carried out for the photonic interconnect. Eye diagram results indicate the photonic interconnect can operate up to 7 Gb/s.

  3. Peptide immobilisation on porous silicon surface for metal ions detection

    NASA Astrophysics Data System (ADS)

    Sam, Sabrina S.; Chazalviel, Jean-Noël Jn; Gouget-Laemmel, Anne Chantal Ac; Ozanam, François F.; Etcheberry, Arnaud A.; Gabouze, Nour-Eddine N.

    2011-06-01

    In this work, a Glycyl-Histidyl-Glycyl-Histidine (GlyHisGlyHis) peptide is covalently anchored to the porous silicon PSi surface using a multi-step reaction scheme compatible with the mild conditions required for preserving the probe activity. In a first step, alkene precursors are grafted onto the hydrogenated PSi surface using the hydrosilylation route, allowing for the formation of a carboxyl-terminated monolayer which is activated by reaction with N-hydroxysuccinimide in the presence of a peptide-coupling carbodiimide N-ethyl- N'-(3-dimethylaminopropyl)-carbodiimide and subsequently reacted with the amino linker of the peptide to form a covalent amide bond. Infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy are used to investigate the different steps of functionalization. The property of peptides to form stable complexes with metal ions is exploited to achieve metal-ion recognition by the peptide-modified PSi-based biosensor. An electrochemical study of the GlyHisGlyHis-modified PSi electrode is achieved in the presence of copper ions. The recorded cyclic voltammograms show a quasi-irreversible process corresponding to the Cu(II)/Cu(I) couple. The kinetic factors (the heterogeneous rate constant and the transfer coefficient) and the stability constant of the complex formed on the porous silicon surface are determined. These results demonstrate the potential role of peptides grafted on porous silicon in developing strategies for simple and fast detection of metal ions in solution.

  4. Controlled thinning and surface smoothening of silicon nanopillars.

    PubMed

    Kalem, S; Werner, P; Nilsson, B; Talalaev, V G; Hagberg, M; Arthursson, O; Södervall, U

    2009-11-01

    A convenient method has been developed to thin electron beam fabricated silicon nanopillars under controlled surface manipulation by transforming the surface of the pillars to an oxide shell layer followed by the growth of sacrificial ammonium silicon fluoride coating. The results show the formation of an oxide shell and a silicon core without significantly changing the original length and shape of the pillars. The oxide shell layer thickness can be controlled from a few nanometers up to a few hundred nanometers. While downsizing in diameter, smooth Si pillar surfaces of less than 10 nm roughness within 2 microm were produced after exposure to vapors of HF and HNO3 mixture as evidenced by transmission electron microscopy (TEM) analysis. The attempt to expose for long durations leads to the growth of a thick oxide whose strain effect on pillars can be assessed by coupled LO-TO vibrational modes of Si-O bonds. Photoluminescence (PL) of the pillar structures which have been downsized exhibits visible and infrared emissions, which are attributable to microscopic pillars and to the confinement of excited carriers in the Si core, respectively. The formation of smooth core-shell structures while reducing the diameter of the Si pillars has a potential in fabricating nanoscale electronic devices and functional components. PMID:19801781

  5. Influence of black silicon surfaces on the performance of back-contacted back silicon heterojunction solar cells.

    PubMed

    Ziegler, Johannes; Haschke, Jan; Käsebier, Thomas; Korte, Lars; Sprafke, Alexander N; Wehrspohn, Ralf B

    2014-10-20

    The influence of different black silicon (b-Si) front side textures prepared by inductively coupled reactive ion etching (ICP-RIE) on the performance of back-contacted back silicon heterojunction (BCB-SHJ) solar cells is investigated in detail regarding their optical performance, black silicon surface passivation and internal quantum efficiency. Under optimized conditions the effective minority carrier lifetime measured on black silicon surfaces passivated with Al(2)O(3) can be higher than lifetimes measured for the SiO(2)/SiN(x) passivation stack used in the reference cells with standard KOH textures. However, to outperform the electrical current of silicon back-contact cells, the black silicon back-contact cell process needs to be optimized with aspect to chemical and thermal stability of the used dielectric layer combination on the cell. PMID:25607304

  6. Controlling the dopant dose in silicon by mixed-monolayer doping.

    PubMed

    Ye, Liang; Pujari, Sidharam P; Zuilhof, Han; Kudernac, Tibor; de Jong, Michel P; van der Wiel, Wilfred G; Huskens, Jurriaan

    2015-02-11

    Molecular monolayer doping (MLD) presents an alternative to achieve doping of silicon in a nondestructive way and holds potential for realizing ultrashallow junctions and doping of nonplanar surfaces. Here, we report the mixing of dopant-containing alkenes with alkenes that lack this functionality at various ratios to control the dopant concentration in the resulting monolayer and concomitantly the dopant dose in the silicon substrate. The mixed monolayers were grafted onto hydrogen-terminated silicon using well-established hydrosilylation chemistry. Contact angle measurements, X-ray photon spectroscopy (XPS) on the boron-containing monolayers, and Auger electron spectroscopy on the phosphorus-containing monolayers show clear trends as a function of the dopant-containing alkene concentration. Dynamic secondary-ion mass spectroscopy (D-SIMS) and Van der Pauw resistance measurements on the in-diffused samples show an effective tuning of the doping concentration in silicon. PMID:25607722

  7. Surface plasmon polariton scattering by subwavelength silicon wires.

    PubMed

    Aporvari, Mehdi Shafiei; Aporvari, Ahmad Shafiei; Kheirandish, Fardin

    2016-03-20

    Surface plasmon polariton scattering from 2D subwavelength silicon wires is investigated using the finite-difference time-domain method. It is shown that coupling an incident surface plasmon polariton to intercavity modes of the particle can dramatically change transmitted fields and plasmon-induced forces. In particular, both transmission and optical forces are highly sensitive to the particle size that is related to the excitation of whispering gallery modes or standing wave modes depending on the particle shape and size. These features might have potential sensing applications. PMID:27140576

  8. LiBr treated porous silicon used for efficient surface passivation of crystalline silicon solar cells

    NASA Astrophysics Data System (ADS)

    Zarroug, Ahmed; Haddadi, Ikbel; Derbali, Lotfi; Ezzaouia, Hatem

    2015-04-01

    A simple but effective passivation method of both front and rear surfaces using porous silicon (PS) has been developed. This paper investigates the effect of LiBr on the passivation of PS. The immersion of as-etched PS in dilute LiBr solution followed by an annealing in an infrared furnace, under a controlled atmosphere at different temperatures, led to the passivation of the PS layer and the improvement of the electronic properties of the crystalline silicon substrates. The influence of substrate temperature was investigated, since the processed wafers were found to be sensitive to heat, which in turn was optimized to have a gettering effect. The bromide of lithium can effectively saturate dangling bonds and hence contributed to the formation of a stable passivation film, at both front and back surfaces. Such a reaction was found to have a beneficial effect on the passivation process of the PS layer grown on both sides. The obtained results exhibited a significant improvement of the minority carrier lifetime, which is an important parameter that defines the quality of crystalline silicon substrates, and an apparent enhancement of its photoluminescence (PL). The internal quantum efficiency was investigated and found to be significantly improved. The qualitative effect of the above-mentioned procedure proved a significant enhancement of the electronic quality of the treated substrates.

  9. Beam Simulation Studies of Plasma-Surface Interactions in Fluorocarbon Etching of Silicon and Silicon Dioxide

    NASA Astrophysics Data System (ADS)

    Gray, David C.

    1992-01-01

    A molecular beam apparatus has been constructed which allows the synthesis of dominant species fluxes to a wafer surface during fluorocarbon plasma etching. These species include atomic F as the primary etchant, CF _2 as a potential polymer forming precursor, and Ar^{+} or CF _{rm x}^{+} type ions. Ionic and neutral fluxes employed are within an order of magnitude of those typical of fluorocarbon plasmas and are well characterized through the use of in -situ probes. Etching yields and product distributions have been measured through the use of in-situ laser interferometry and line-of-sight mass spectrometry. XPS studies of etched surfaces were performed to assess surface chemical bonding states and average surface stoichiometry. A useful design guide was developed which allows optimal design of straight -tube molecular beam dosers in the collisionally-opaque regime. Ion-enhanced surface reaction kinetics have been studied as a function of the independently variable fluxes of free radicals and ions, as well as ion energy and substrate temperature. We have investigated the role of Ar ^{+} ions in enhancing the chemistries of F and CF_2 separately, and in combination on undoped silicon and silicon dioxide surfaces. We have employed both reactive and inert ions in the energy range most relevant to plasma etching processes, 20-500 eV, through the use of Kaufman and ECR type ion sources. The effect of increasing ion energy on the etching of fluorine saturated silicon and silicon dioxide surfaces was quantified through extensions of available low energy physical sputtering theory. Simple "site"-occupation models were developed for the quantification of the ion-enhanced fluorine etching kinetics in these systems. These models are suitable for use in topography evolution simulators (e.g. SAMPLE) for the predictive modeling of profile evolution in non-depositing fluorine-based plasmas such as NF_3 and SF_6. (Copies available exclusively from MIT Libraries, Rm. 14

  10. Photovoltage and work function measurement of silicon surfaces

    NASA Astrophysics Data System (ADS)

    Novikov, Alexander

    2005-12-01

    Photovoltage measurements on prepared silicon surfaces yielding information on surface state morphology and dynamics are reported. Surface photovoltage changes resulting from excitation using both tunable and fixed wavelength sources were monitored using a Kelvin Probe apparatus. Both sub-bandgap and super-bandgap excitation wavelengths were used on an array of doped and undoped Si surfaces. The majority of the measurements were conducted with the samples at atmospheric pressure. A simple theoretical model of finite crystal solid surfaces helped elaborate the essential difference between work function and the local work function determinations. Formulae for surface potential, surface state population and charge carrier relaxation resulting from selective excitation were derived using Shockley and Reed theory. The presence of atmospheric constituents chemisorbed on the surfaces was also investigated. Large photovoltage signals induced by laser excitation revealed optical saturation effects that could be related to surface potential information and work function evaluation. Narrow surface photovoltage and photoconductance spectral signatures of cleaved Si(111) samples observed at reduced temperature and pressure provided additional insight into the contribution of sub-bandgap excitation processes involving surface states.

  11. Silicon nanocrystal inks, films, and methods

    DOEpatents

    Wheeler, Lance Michael; Kortshagen, Uwe Richard

    2015-09-01

    Silicon nanocrystal inks and films, and methods of making and using silicon nanocrystal inks and films, are disclosed herein. In certain embodiments the nanocrystal inks and films include halide-terminated (e.g., chloride-terminated) and/or halide and hydrogen-terminated nanocrystals of silicon or alloys thereof. Silicon nanocrystal inks and films can be used, for example, to prepare semiconductor devices.

  12. Ionic Liquids Can Permanently Modify Porous Silicon Surface Chemistry.

    PubMed

    Trivedi, Shruti; Coombs, Sidney G; Wagle, Durgesh V; Bhawawet, Nakara; Baker, Gary A; Bright, Frank V

    2016-08-01

    To develop ionic liquid/porous silicon (IL/pSi) microarrays we have contact pin-printed 20 hydrophobic and hydrophilic ionic liquids onto as-prepared, hydrogen-passivated porous silicon (ap-pSi) and then determined the individual IL spot size, shape and associated pSi surface chemistry. The results reveal that the hydrophobic ionic liquids oxidize the ap-pSi slightly. In contrast, the hydrophilic ionic liquids lead to heavily oxidized pSi (i.e., ox-pSi). The strong oxidation arises from residual water within the hydrophilic ILs that is delivered from these ILs into the ap-pSi matrix causing oxidation. This phenomenon is less of an issue in the hydrophobic ILs because their water solubility is substantially lower. PMID:27405109

  13. Surface and allied studies in silicon solar cells

    NASA Technical Reports Server (NTRS)

    Lindholm, F. A.

    1984-01-01

    Significant improvements were made in the short-circuit current-decay method of measuring the recombination lifetime tau and the back surface recombination velocity S of the quasineutral base of silicon solar cells. The improvements include a circuit implementation that increases the speed of switching from the forward-voltage to the short-circuit conditions. They also include a supplementation of this method by some newly developed techniques employing small-signal admittance as a function of frequency omega. This supplementation is highly effective for determining tau for cases in which the diffusion length L greatly exceeds the base thickness W. Representative results on different solar cells are reported. Some advances made in the understanding of passivation provided by the polysilicon/silicon heterojunction are outlined. Recent measurements demonstrate that S 10,000 cm/s derive from this method of passivation.

  14. Silicon-wafer-surface damage revealed by surface photovoltage measurements

    NASA Astrophysics Data System (ADS)

    Goodman, Alvin M.

    1982-11-01

    Anomalous results of surface photovoltage (SPV) measurements on Si wafers are shown to be associated with a damaged region beneath the illuminated surface of the wafer being measured. The anomaly is a concave-upward curvature of the I0(α-1) plot with an r2 value, derived from linear regression analysis, less than the normally observed minimum value (˜0.98). Removal of the damaged region by an appropriate etching procedure allows subsequent SPV measurements whose results are substantially free of the previously observed anomaly. The qualitative character of the anomaly can be reproduced by a simple theoretical model in which only one effect of the damage is considered; this effect is a diminished quantum efficiency for hole-electron pair generation by photon absorption in the damaged region. The results suggest the use of SPV measurements as a test procedure for revealing the presence of surface damage in Si wafers.

  15. Instrumental studies on silicone oil adsorption to the surface of intraocular lenses

    NASA Astrophysics Data System (ADS)

    Kim, Chun Ho; Joo, Choun-Ki; Chun, Heung Jae; Yoo, Bok Ryul; Noh, Dong Il; Shim, Young Bock

    2012-12-01

    The purpose of this study was to examine the degree of adherence of silicone oil to various intraocular lenses (IOLs) through comparison of the physico-chemical properties of the oil and IOLs. Four kinds of IOLs comprising various biomaterials were examined: PMMA (720A™), PHEMA (IOGEL 1103™), Acrysof (MA60BM™), and silicone (SI30NB™). Each lens was immersed in silicone oil or carboxylated silicone (CS-PDMS) oil for 72 h. For determination of the changes in chemical and elemental compositions on the surfaces of IOLs caused by the contact with silicone oil, IOLs were washed and rinsed with n-pentane to remove as much of the adsorbed silicone oil as possible, then subjected to Fourier transform infrared spectroscopic (FTIR) and X-ray photoelectron spectroscopic (XPS) analyses. The results of FTIR studies strongly indicate that washing with n-pentane completely removed the adhered silicone oil on the surfaces of PHEMA and Acrysof IOLs, whereas the residual silicone oil was detected on the surfaces of PMMA and silicone IOLs. XPS studies showed that silicone oil coverage of PMMA lenses was 12%, even after washing with n-pentane. In the case of silicone IOLs, the relative O1s peak area of carboxyl group in the residual CS-PDMS oil was found to be ˜2.7%. Considering that 2.8% carboxyl group-substituted silicone oil was used in the present study, CS-PDMS oil covered the entire surface of the silicone IOLs.

  16. Tantalum oxide/silicon nitride: A negatively charged surface passivation stack for silicon solar cells

    SciTech Connect

    Wan, Yimao Bullock, James; Cuevas, Andres

    2015-05-18

    This letter reports effective passivation of crystalline silicon (c-Si) surfaces by thermal atomic layer deposited tantalum oxide (Ta{sub 2}O{sub 5}) underneath plasma enhanced chemical vapour deposited silicon nitride (SiN{sub x}). Cross-sectional transmission electron microscopy imaging shows an approximately 2 nm thick interfacial layer between Ta{sub 2}O{sub 5} and c-Si. Surface recombination velocities as low as 5.0 cm/s and 3.2 cm/s are attained on p-type 0.8 Ω·cm and n-type 1.0 Ω·cm c-Si wafers, respectively. Recombination current densities of 25 fA/cm{sup 2} and 68 fA/cm{sup 2} are measured on 150 Ω/sq boron-diffused p{sup +} and 120 Ω/sq phosphorus-diffused n{sup +} c-Si, respectively. Capacitance–voltage measurements reveal a negative fixed insulator charge density of −1.8 × 10{sup 12 }cm{sup −2} for the Ta{sub 2}O{sub 5} film and −1.0 × 10{sup 12 }cm{sup −2} for the Ta{sub 2}O{sub 5}/SiN{sub x} stack. The Ta{sub 2}O{sub 5}/SiN{sub x} stack is demonstrated to be an excellent candidate for surface passivation of high efficiency silicon solar cells.

  17. Surface Micromachined Silicon Carbide Accelerometers for Gas Turbine Applications

    NASA Technical Reports Server (NTRS)

    DeAnna, Russell G.

    1998-01-01

    A finite-element analysis of possible silicon carbide (SIC) folded-beam, lateral-resonating accelerometers is presented. Results include stiffness coefficients, acceleration sensitivities, resonant frequency versus temperature, and proof-mass displacements due to centripetal acceleration of a blade-mounted sensor. The surface micromachined devices, which are similar to the Analog Devices Inc., (Norwood, MA) air-bag crash detector, are etched from 2-pm thick, 3C-SiC films grown at 1600 K using atmospheric pressure chemical vapor deposition (APCVD). The substrate is a 500 gm-thick, (100) silicon wafer. Polysilicon or silicon dioxide is used as a sacrificial layer. The finite element analysis includes temperature-dependent properties, shape change due to volume expansion, and thermal stress caused by differential thermal expansion of the materials. The finite-element results are compared to experimental results for a SiC device of similar, but not identical, geometry. Along with changes in mechanical design, blade-mounted sensors would require on-chip circuitry to cancel displacements due to centripetal acceleration and improve sensitivity and bandwidth. These findings may result in better accelerometer designs for this application.

  18. Surface treatment and surface coating of silicon field emitter array

    NASA Astrophysics Data System (ADS)

    Hajra, Mahua Sudhakrishna

    The objectives of this research were to fabricate ungated Si field emitter arrays (FEA's), and then to identify ways to improve the performance of the emitters. In the first and second chapters, the basis of the research, including background, theory, and the goals of the research is presented. The third chapter discusses the fabrication methods used to form the ungated Si FEA's. The fourth chapter gives the details about surface treatment procedures used to improve initial operation. The fifth and the sixth chapter discuss the different surface coating materials used to study the emission properties of the Si field emitters. The seventh chapter summarizes the work and suggests possible follow up research. The four surface treatments discussed in chapter four employ, respectively, residual gas ions, low-energy electron-stimulated desorption, a hydrogen-enhanced residual gas atmosphere, and a plasma of a Ar (96%) and H2 (4%) gas mixture. The method, using the hydrogen-enriched residual gas atmosphere is very unique in that it uses getters to produce the hydrogen rich atmosphere. The method, using a plasma of Ar (96%) and H2 (4%) gas mixture, is an effective in-situ cleaning procedure, which can be performed prior to packaging the devices. In chapters five and six is a comparison of the field-emission properties of the Si FEA coated with various materials, including (1) nanoparticle clusters of diamond and gallium nitride (GaN), (2) a thin film of ultrananocrystalline diamond (UNCD), (3) a lead zirconate titanate (PZT) coating, and (4) carbon nanotubes. Among the above coatings, the conformal coating of UNCD produced electron emission at an extremely low threshold field of between 2 to 5 V/mum. A further study of the behavior of electron emission from UNCD-coated Si FEA during in-situ exposure to H2, N2, and Ar respectively showed that when the emitting surface is exposed to H 2, at 10-5 Torr and 10-4 Torr, the initial emission current (2 muA) increases by a factor

  19. Containment of a silicone fluid free surface in reduced gravity

    NASA Technical Reports Server (NTRS)

    Pline, A.; Jacobson, T.

    1988-01-01

    In support of the surface tension driven convection experiment planned for flight aboard the Space Shuttle, tests were conducted under reduced gravity in the 2.2-sec drop tower and the 5.0-sec Zero-G facility at the Lewis Research Center. The dynamics of controlling the test fluid, a 10-centistoke viscosity silicone fluid, in a low-gravity environment were investigated using different container designs and barrier coatings. Three container edge designs were tested without a barrier coating: a square edge, a sharp edge with a 45-deg slope, and a saw-tooth edge. All three edge designs were successful in containing the fluid below the edge.

  20. Front surface passivation of silicon solar cells with antireflection coating

    NASA Technical Reports Server (NTRS)

    Crotty, G.; Daud, T.; Kachare, R.

    1987-01-01

    It is demonstrated that the deposition and postdeposition sintering of an antireflection (AR) coating in hydrogen acts to passivate silicon solar cells. Cells with and without an SiO2 passivating layer, coated with a TiO(x)/Al2O3 AR coating, showed comparable enhancements in short-wavelength spectral response and in open-circuit voltage Voc after sintering at 400 C for 5 min in a hydrogen ambient. The improvement in Voc of cells without SiO2 is attributed to front-surface passivation by the AR coating during processing.

  1. Surface photovoltage method extended to silicon solar cell junction

    NASA Technical Reports Server (NTRS)

    Wang, E. Y.; Baraona, C. R.; Brandhorst, H. W., Jr.

    1974-01-01

    The conventional surface photovoltage (SPV) method is extended to the measurement of the minority carrier diffusion length in diffused semiconductor junctions of the type used in a silicon solar cell. The minority carrier diffusion values obtained by the SPV method agree well with those obtained by the X-ray method. Agreement within experimental error is also obtained between the minority carrier diffusion lengths in solar cell diffusion junctions and in the same materials with n-regions removed by etching, when the SPV method was used in the measurements.

  2. Improved Silicon Carbide Crystals Grown From Atomically Flat Surfaces

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.

    2003-01-01

    The NASA Glenn Research Center is demonstrating that atomically flat (i.e., step-free) silicon carbide (SiC) surfaces are ideal for realizing greatly improved wide bandgap semiconductor films with lower crystal defect densities. Further development of these improved films could eventually enable harsh-environment electronics beneficial to jet engine and other aerospace and automotive applications, as well as much more efficient and compact power distribution and control. The technique demonstrated could also improve blue-light lasers and light-emitting-diode displays.

  3. A new texturing technique of monocrystalline silicon surface with sodium hypochlorite

    NASA Astrophysics Data System (ADS)

    Sun, Linfeng; Tang, Jiuyao

    2009-08-01

    This work proposes a new texturing technique of monocrystalline silicon surface for solar cells with sodium hypochlorite. A mixed solution consisting of 5 wt% sodium hypochlorite and 10 vl% ethanol has been found that results in a homogeneous pyramidal structure, and an optimal size of pyramids on the silicon surface. The textured silicon surface exhibits a lower average reflectivity (about 10.8%) in the main range of solar spectrum (400-1000 nm).

  4. Elliptic cylindrical silicon nanowire hybrid surface plasmon polariton waveguide.

    PubMed

    Zhang, Li; Xiong, Qiulin; Li, Xiaopeng; Ma, Junxian

    2015-08-10

    We researched an elliptic cylindrical silicon nanowire hybrid surface plasmon polariton waveguide and evaluated its mode characteristics using the finite element method software COMSOL. The waveguide consists of three parts: an elliptic cylindrical silicon nanowire, a silver film layer, and a silica covering layer between them. All of the components are surrounded by air. After optimizing the geometrical parameters of the waveguide, we can achieve the waveguide's strong field confinement (ranging from λ2/270 to λ2/27) and long propagation distances (119-485 μm). In order to further understand the impact of the waveguide's architecture on its performance, we also studied the ridge hybrid waveguide. The results show that the ridge waveguide has moderate local field confinement ranging from λ2/190 to λ2/20 and its maximum propagation distance is about 340 μm. We compared the elliptic cylindrical and ridge nanowire hybrid waveguides with the cylindrical hybrid waveguide that we studied before. The elliptic cylindrical waveguide achieves a better trade-off between reasonable mode confinement and maximum propagation length in the three waveguides. The researched hybrid surface plasmon polaritons waveguides are useful to construct devices such as a directional coupler and may find potential applications in photonic integrated circuits or other novel SPP devices. PMID:26368373

  5. Silicon surface periodic structures produced by plasma flow induced capillary waves

    SciTech Connect

    Dojcinovic, I. P.; Kuraica, M. M.; Obradovic, B. M.; Puric, J.

    2006-08-14

    Silicon single crystal surface modification by the action of nitrogen quasistationary compression plasma flow generated by a magnetoplasma compressor is studied. It has been found that highly oriented silicon periodic cylindrical shape structures are produced during a single pulse surface treatment. The periodical structure formation can be related to the driven capillary waves quenched during fast cooling and resolidification phase of the plasma flow interaction with silicon surface. These waves are induced on the liquid silicon surface due to the compression plasma flow intrinsic oscillations.

  6. Impact of Surface Chemistry on Copper Deposition in Mesoporous Silicon.

    PubMed

    Darwich, Walid; Garron, Anthony; Bockowski, Piotr; Santini, Catherine; Gaillard, Frédéric; Haumesser, Paul-Henri

    2016-08-01

    An easy, efficient, and safe process is developed to metallize mesoporous silicon (PSi) with Cu from the decomposition of a solution of mesitylcopper (CuMes) in an imidazolium-based ionic liquid (IL), [C1C4Im][NTf2]. The impregnation of a solution of CuMes in IL affords the deposition of metallic islands not only on the surface but also deep within the pores of a mesoporous Si layer with small pores below 10 nm. Therefore, this process is well suited to efficiently and completely metallize PSi layers. An in-depth mechanistic study shows that metal deposition is due to the reduction of CuMes by surface silane groups rather than by Si oxidation as observed in aqueous or water-containing media. This could open a new route to the chemical metallization of PSi by less-noble metals difficult to attain by a conventional displacement reaction. PMID:27368422

  7. Surface and allied studies in silicon solar cells

    NASA Technical Reports Server (NTRS)

    Lindholm, F. A.

    1984-01-01

    Measuring small-signal admittance versus frequency and forward bias voltage together with a new transient measurement apparently provides the most reliable and flexible method available for determining back surface recombination velocity and low-injection lifetime of the quasineutral base region of silicon solar cells. The new transient measurement reported here is called short-circuit-current decay (SCCD). In this method, forward voltage equal to about the open-circuit or the maximum power voltage establishes excess holes and electrons in the junction transition region and in the quasineutral regions. The sudden application of a short circuit causes an exiting of the excess holes and electrons in the transition region within about ten picoseconds. From observing the slope and intercept of the subsequent current decay, the base lifetime and surface recombination velocity can be determined. The admittance measurement previously mentioned then enters to increase accuracy particularly for devices for which the diffusion length exceeds the base thickness.

  8. Electron-stimulated desorption of hydrogen from the Si(111) surface by scanning tunneling microscopy

    SciTech Connect

    Schwartzkopff, M.; Radojkovic, P.; Enachescu, M.; Hartmann, E.; Koch, F.

    1996-03-01

    Preparation of suitable silicon (111) wafers in weakly alkaline HF solutions results in the formation of atomically flat, hydrogen-terminated surfaces. Under high-vacuum conditions, the scanning tunneling microscope has been employed to selectively desorb the passivating hydrogen from nanometer-sized surface regions. The hydrogen depassivation process is studied as a function of current and applied bias voltage, voltage polarity, and exposure time to incident electrons either on individual surface locations or by varying the speed of tip motion to control the electron dose. The experimental findings are interpreted in terms of two distinct desorption mechanisms and the respective desorption yields are specified. {copyright} {ital 1996 American Vacuum Society}

  9. Reconstruction of silicon surfaces: A stochastic optimization problem

    NASA Astrophysics Data System (ADS)

    Ciobanu, Cristian V.; Predescu, Cristian

    2004-08-01

    Over the last two decades, scanning tunneling microscopy (STM) has become one of the most important ways to investigate the structure of crystal surfaces. STM has helped achieve remarkable successes in surface science such as finding the atomic structure of Si(111) and Si(001). For high-index Si surfaces the information about the local density of states obtained by scanning does not translate directly into knowledge about the positions of atoms at the surface. A commonly accepted strategy for identifying the atomic structure is to propose several possible models and analyze their corresponding simulated STM images for a match with the experimental ones. However, the number of good candidates for the lowest-energy structure is very large for high-index surfaces, and heuristic approaches are not likely to cover all the relevant structural models. In this paper, we take the view that finding the atomic structure of a surface is a problem of stochastic optimization, and we address it as such. We design a general technique for predicting the reconstruction of silicon surfaces with arbitrary orientation, which is based on parallel-tempering Monte Carlo simulations combined with an exponential cooling. The advantages of the method are illustrated using the Si(105) surface as an example, with two main results: (a) the correct single-step rebonded structure [e.g., Fujikawa, Akiyama, Nagao, Sakurai, Lagally, Hashimoto, Morikawa, and Terakura, Phys. Rev. Lett. 88, 176101 (2002)] is obtained even when starting from the paired-dimer model [Mo, Savage, Swartzentruber, and Lagally, Phys. Rev. Lett. 65, 1020 (1990)] that was assumed to be correct for many years, and (b) we have found several double-step reconstructions that have lower surface energies than any previously proposed double-step models.

  10. Surface chemistry and friction behavior of the silicon carbide (0001) surface at temperatures to 1500 deg C

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Buckley, D. H.

    1981-01-01

    X-ray photoelectron and Auger electron spectroscopy analyses and friction studies were conducted with a silicon carbide (0001) surface in contact with iron at various temperatures to 1200 or 1500 C in a vacuum of 10 to the minus 8th power Pa. The results indicate that there is a significant temperature influence on both the surface chemistry and friction properties of silicon carbide. The principal contaminant of adsorbed amorphous carbon on the silicon carbide surface in the as received state is removed by simply heating to 400 C. Above 400 C, graphite and carbide type carbine are the primary species on the silicon carbide surface, in addition to silicon. The coefficients of friction of polycrystalline iron sliding against a single crystal silicon carbide (0001) surface were high at temperatures to 800 C. Similar coefficients of friction were obtained at room temperature after the silicon carbide was preheated at various temperatures up 800 C. When the friction experiments were conducted above 800 C or when the specimens were preheated to above 800 C, the coefficients of friction were dramatically lower. At 800 C the silicon and carbide type carbon are at a maximum intensity in the XPS spectra. With increasing temperature above 800 C, the concentration of the graphite increases rapidly on the surface, whereas those of the carbide type carbon and silicon decrease rapidly.

  11. Photocurrent spectroscopy of Ge nanoclusters grown on oxidized silicon surface

    NASA Astrophysics Data System (ADS)

    Mykytiuk, A. A.; Kondratenko, S. V.; Lysenko, V. S.; Kozyrev, Yu. N.

    2014-05-01

    Germanium (Ge) nanoclusters are grown by a molecular-beam epitaxy technique on chemically oxidized Si(100) surface at 700ºC. Evidence for long-term photoinduced changes of surface conductivity in structures with Ge nanoclusters (NCs) grown on silicon oxide is presented. Photoexcitation NCs or Si by quanta with different energy allows observing two non-equilibrium steady-states with excess and shortage of conductivity values as compare to equilibrium one. The persistent photoconductivity (PPC) behaviour was observed after interband excitation of electron-hole pairs in Si(001) substrate. This effect may be attributed to spatial carrier separation of photoexcited electron-hole pairs by macroscopic fields in the depletion layer of near-surface Si. Photoquenching of surface conductivity, driven by optical recharging of Ge NC's and Si/SiO2 interface states, is observed. Conductivity decay is discussed in the terms of hole`s accumulation by Ge-NC states enhancing the local-potential variations and, therefore, decreasing the surface conductivity of p-Si.

  12. A silicon-based electrical source of surface plasmon polaritons

    NASA Astrophysics Data System (ADS)

    Walters, R. J.; van Loon, R. V. A.; Brunets, I.; Schmitz, J.; Polman, A.

    2010-01-01

    After decades of process scaling driven by Moore's law, the silicon microelectronics world is now defined by length scales that are many times smaller than the dimensions of typical micro-optical components. This size mismatch poses an important challenge for those working to integrate photonics with complementary metal oxide semiconductor (CMOS) electronics technology. One promising solution is to fabricate optical systems at metal/dielectric interfaces, where electromagnetic modes called surface plasmon polaritons (SPPs) offer unique opportunities to confine and control light at length scales below 100nm (refs 1, 2). Research groups working in the rapidly developing field of plasmonics have now demonstrated many passive components that suggest the potential of SPPs for applications in sensing and optical communication. Recently, active plasmonic devices based on III-V materials and organic materials have been reported. An electrical source of SPPs was recently demonstrated using organic semiconductors by Koller and colleagues. Here we show that a silicon-based electrical source for SPPs can be fabricated using established low-temperature microtechnology processes that are compatible with back-end CMOS technology.

  13. Novel antifouling surface with improved hemocompatibility by immobilization of polyzwitterions onto silicon via click chemistry

    NASA Astrophysics Data System (ADS)

    Zheng, Sunxiang; Yang, Qian; Mi, Baoxia

    2016-02-01

    A novel procedure is presented to develop an antifouling silicon surface with improved hemocompatibility by using a zwitterionic polymer, poly(sulfobetaine methacrylate) (polySBMA). Functionalization of the silicon surface with polySBMA involved the following three steps: (1) an alkyne terminated polySBMA was synthesized by RAFT polymerization; (2) a self-assembled monolayer with bromine end groups was constructed on the silicon surface, and then the bromine end groups were replaced by azide groups; and (3) the polySBMA was attached to the silicon surface by azide-alkyne cycloaddition click reaction. Membrane characterization confirmed a successful silicon surface modification with almost 100% coverage by polySBMA and an extremely hydrophilic surface after such modification. The polySBMA-modified silicon surface was found to have excellent anti-nonspecific adsorption properties for both bovine serum albumin (BSA) protein and model bacterial cells. Whole blood adsorption experiments showed that the polySBMA-modified silicon surface exhibited excellent hemocompatibility and effective anti-adhesion to blood cells. Silicon membranes with such antifouling and hemocompatible surfaces can be advantageously used to drastically extend the service life of implantable medical devices such as artificial kidney devices.

  14. Highly sensitive and reproducible silicon-based surface-enhanced Raman scattering sensors for real applications.

    PubMed

    Wang, Houyu; Jiang, Xiangxu; He, Yao

    2016-08-15

    During the past few decades, thanks to silicon nanomaterials' outstanding electronic/optical/mechanical properties, large surface-to-volume ratio, abundant surface chemistry, facile tailorability and good compatibility with modern semiconductor industry, different dimensional silicon nanostructures have been widely employed for rationally designing and fabricating high-performance surface-enhanced Raman scattering (SERS) sensors for the detection of various chemical and biological species. Among these, two-dimensional silicon nanostructures made of metal nanoparticle-modified silicon wafers and three-dimensional silicon nanostructures made of metal nanoparticle-decorated SiNW arrays are of particular interest, and have been extensively exploited as promising silicon-based SERS-active substrates for the construction of high-performance SERS sensors. With an aim to retrospect these important and exciting achievements, we herein focus on reviewing recent representative studies on silicon-based SERS sensors for sensing applications from a broad perspective and possible future direction, promoting readers' awareness of these novel powerful silicon-based SERS sensing technologies. Firstly, we summarize the two unique merits of silicon-based SERS sensors, and those are high sensitivity and good reproducibility. Next, we present recent advances of two- and three-dimensional silicon-based SERS sensors, especially for real applications. Finally, we discuss the major challenges and prospects for the development of silicon-based SERS sensors. PMID:27414500

  15. X-ray assisted chemical modification of silicon surfaces

    NASA Astrophysics Data System (ADS)

    Pinhero, Patrick Joseph

    Interest in surface photochemistry induced by x-irradiation has received a renaissance with the construction of new synchrotron radiation facilities worldwide. There are three general pathways that a x-ray excited gas-surface system can follow that will lead to reaction. These are: (1) direct excitation, (2) excitation by emitted secondary electrons, and (3) reactions induced by hot electrons at the surface. Two chemical systems are studied in a modified x-ray photoelectron spectrometer (XPS) that allows for reactions to be studied in situ. The systems studied were (1) Nsb2/Si(100) and (2) the SFsb6/Si system. The motivation for studying these two compounds is: they are both relatively inert, i.e. no spontaneous reactions; they both are technologically interesting, possible silicon nitride formation in the case of Nsb2, and SFsb6 is a popular etchant gas in the semiconductor industry; and these two compounds have the potential to exhibit contrasting behavior. Besides its etching qualities, SFsb6 possesses a large x-ray absorption cross section and it has a large electron capture cross section. Both systems are primarily studied by XPS. XPS has the quality of providing quantifiable information about the composition of the surface and details about the chemical environment of each constituent element present. Atomic force microscopy (AFM) is used with the SFsb6 system to observe any structural changes that may occur after reaction. In the Nsb2/Si(100) system, a silicon nitride is formed at very long exposures. This is first observed after 24 hours of simultaneous exposure to Nsb2 and x-irradiation. In the SFsb6 experiments, several subsystems are examined: (1) simultaneous exposure of a Si(100) surface to SFsb6 and x-irradiation at 298K; (2) x-irradiation of a SFsb6 film adsorbed on Si(100) at 100K; (3) simultaneous exposure of a natively oxidized Si surface to SFsb6 and x-rays at 298K; and (4) x-irradiation of a SFsb6 film adsorbed on natively oxidized Si at 100K

  16. Oscillations of light absorption in 2D macroporous silicon structures with surface nanocoatings

    NASA Astrophysics Data System (ADS)

    Karachevtseva, L.; Kuchmii, S.; Lytvynenko, O.; Sizov, F.; Stronska, O.; Stroyuk, A.

    2011-02-01

    We investigated the near-IR light absorption oscillations in 2D macroporous silicon structures with microporous silicon layers and CdTe, ZnO surface nanocrystals. The electro-optical effect was taken into account within the strong electric field approximation. Well-separated oscillations were observed in the spectral ranges of the surface bonds of macroporous silicon structures with surface nanocrystals. The model of the resonant electron scattering on impurity states in electric field of heterojunction “silicon-nanocoating” on macropore surface as well as realization of Wannier-Stark effect on the randomly distributed surface bonds were considered. The Wannier-Stark ladders are not broken by impurities because of the longer scattering lifetime as compared with the period of electron oscillations in an external electric field, in all spectral regions considered for macroporous silicon structures with CdTe and ZnO surface nanocrystals.

  17. Fabrication and application of porous silicon multilayered microparticles in sustained drug delivery

    NASA Astrophysics Data System (ADS)

    Maniya, Nalin H.; Patel, Sanjaykumar R.; Murthy, Z. V. P.

    2015-09-01

    In the present study, the ability of porous silicon (PSi) based distributed Bragg reflector (DBR) microparticles for sustained and observable delivery of the antiviral agent acyclovir (ACV) is demonstrated. DBR was fabricated by electrochemical etching of single crystal silicon wafers and ultrasonic fractured to prepare microparticles. The hydrogen-terminated native surface of DBR microparticles was modified by thermal oxidation and thermal hydrosilylation. Particles were loaded with ACV and drug release experiments were conducted in phosphate buffered saline. Drug loading and surface chemistry of particles were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. Drug release profiles from PSi DBR particles show sustained release behavior from all three studied surface chemistries. Drug release from particles was also monitored from change in color of particles.

  18. Electronic interface properties of silicon substrates after ozone based wet-chemical oxidation studied by SPV measurements

    NASA Astrophysics Data System (ADS)

    Angermann, Heike; Wolke, Klaus; Gottschalk, Christiane; Moldovan, Ana; Roczen, Maurizio; Fittkau, Jens; Zimmer, Martin; Rentsch, Jochen

    2012-08-01

    The preparation of ultra-thin oxide layers on mono-crystalline silicon substrate surfaces with ozone dissolved in ultra pure water at ambient temperature was investigated as a low cost alternative to current wet-chemical cleaning and passivation processes in solar cell manufacturing. Surface photovoltage technique was applied as fast, nondestructive, and surface sensitive method, to provide detailed information about the influence of oxidation rate and substrate surface morphology on electronic properties of the oxidised silicon interfaces and subsequently prepared hydrogen terminated surfaces. Sequences of wet-chemical oxidation in ozone containing ultra pure water and subsequent oxide removal in diluted hydrofluoric acid solution could be utilised to prepare hydrophobic substrates, which are predominantly required as starting point for layer deposition and contact formation. On so prepared hydrogen-terminated substrates values of interface state densities Dit,min ≈ 5 × 1011 eV-1 cm-2 could be achieved, comparable to values obtained on the same substrates by the standard RCA process followed by HF dip.

  19. Fabricating micro-instruments in surface-micromachined polycrystalline silicon

    SciTech Connect

    Comtois, J.H.; Michalicek, M.A.; Barron, C.C.

    1997-04-01

    Smaller, lighter instruments can be fabricated as Micro-Electro-Mechanical Systems (MEMS), having micron scale moving parts packaged together with associated control and measurement electronics. Batch fabrication of these devices will make economical applications such as condition-based machine maintenance and remote sensing. The choice of instrumentation is limited only by the designer`s imagination. This paper presents one genre of MEMS fabrication, surface-micromachined polycrystalline silicon (polysilicon). Two currently available but slightly different polysilicon processes are presented. One is the ARPA-sponsored ``Multi-User MEMS ProcesS`` (MUMPS), available commercially through MCNC; the other is the Sandia National Laboratories ``Sandia Ultra-planar Multilevel MEMS Technology`` (SUMMiT). Example components created in both processes will be presented, with an emphasis on actuators, actuator force testing instruments, and incorporating actuators into larger instruments.

  20. Barrier-Type AC Surface Photovoltage in Silicon with a Copper-Contaminated Surface

    NASA Astrophysics Data System (ADS)

    Shimizu, Hirofumi

    2002-10-01

    An AC surface photovoltage (SPV) was induced in n-type silicon (Si) wafers after the deposition of undesirable copper (Cu) atoms on the surface. Chemical analysis reveals that Cu ions (Cu2+) are deposited on Si surfaces, through electron capture because the oxidation reduction potential of Cu2+ is higher than that of Si and, as a result, a Cu-Si contact is formed. This Cu-Si contact may create a Schottky barrier between the Cu and n-type Si, resulting in the appearance of an AC SPV in n-type Si. In this note, a barrier-type SPV is proposed.

  1. The Relationship between the Hydrophilicity and Surface Chemical Composition Microphase Separation Structure of Multicomponent Silicone Hydrogels.

    PubMed

    Zhao, Zheng-Bai; An, Shuang-Shuang; Xie, Hai-Jiao; Han, Xue-Lian; Wang, Fu-He; Jiang, Yong

    2015-07-30

    Three series of multicomponent silicone hydrogels were prepared by the copolymerization of two hydrophobic silicon monomers bis(trimethylsilyloxy) methylsilylpropyl glycerol methacrylate (SiMA) and tris(trimethylsiloxy) 3-methacryloxypropylsilane (TRIS) with three hydrophilic monomers. The surface hydrophilicity of the silicone hydrogels was characterized by contact angle measurements, and an interesting phenomenon was found that the silicone hydrogels made from less hydrophobic monomer SiMA possess more hydrophobic surfaces than those made from TRIS. The surface properties such as morphology and elemental composition of the silicone hydrogels were explored by scanning electron microscopy (SEM) imaging and energy dispersive spectrometry (EDS) analysis, and their relationships with the surface hydrophilicity were investigated in details. The results show neither the surface morphology nor the elemental composition has obvious impact on the surface hydrophilicity. Atomic force microscopy (AFM) imaging revealed that SiMA hydrogel had a more significant phase separation structure, which also made its surface uneven: a lot of tiny holes were observed on the surface. This surface phase separation structure made SiMA hydrogel more difficult to be wetted by water or PBS buffer, i.e., more hydrophobic than TRIS hydrogel. On the basis of these results, we propose that the phase separation structure as well as the nature of silicon monomers might be the fundamental reasons of surface hydrophilicity. These results could help to design a silicone hydrogel with better surface properties and wider application. PMID:26125331

  2. New perspectives on thermal and hyperthermal oxidation of silicon surfaces

    NASA Astrophysics Data System (ADS)

    Khalilov, Umedjon

    The growth of (ultra)thin silica (SiO2) layers on crystalline silicon (c-Si) and controlling the thickness of SiO2 is an important issue in the fabrication of microelectronics and photovoltaic devices (e.g., MOSFETs, solar cells, optical fibers etc.). Such ultrathin oxide can be grown and tuned even at low temperature (including room temperature), by hyperthermal oxidation or when performed on non-planar Si surfaces (e.g., Si nanowires or spheres). However, hyperthermal silica growth as well as small Si-NW oxidation in general and the initial stages in particular have not yet been investigated in full detail. This work is therefore devoted to controlling ultrathin silica thickness on planar and non-planar Si surfaces, which can open new perspectives in nanodevice fabrication. The simulation of hyperthermal (1-100 eV) Si oxidation demonstrate that at low impact energy (<10 eV), oxygen does not damage the Si surface and this energy region could thus beneficially be used for Si oxidation. In contrast to thermal oxidation, 10 eV species can directly oxidize Si subsurface layers. A transition temperature of about 700 K was found: below this temperature, the oxide thickness only depends on the impact energy of the impinging species. Above this temperature, the oxide thickness depends on the impact energy, type of oxidant and the surface temperature. The results show that control over the ultrathin oxide (a-SiO2) thickness is possible by hyperthermal oxidation of silicon surfaces at temperatures below the transition temperature. In small Si-NWs, oxidation is a self-limiting process that occurs at low temperature, resulting in small Si core - SiO2 shell (semiconductor + dielectric) or c-Si|SiOx| a-SiO2 nanowire, which has also being envisaged to be used as nanowire field-effect transistors and photovoltaic devices in near-future nanotechnology. Above the transition temperature such core-shell nanowires are completely converted to a-SiO2 nanowires. It can be concluded that

  3. Modification of the surface morphology of silicon(111) with growth temperature

    NASA Astrophysics Data System (ADS)

    Charles, M.; Hartmann, J. M.

    2013-02-01

    Silicon epitaxy has been performed on nominally on-axis silicon(111) substrates by reduced pressure chemical vapour deposition at a variety of temperatures, keeping a constant deposited thickness. Atomic force microscopy of the resulting growth surfaces shows well defined step edges, and a clear modification of the surface morphology from smooth terraces to triangular island structures as the growth temperature is reduced. The radius of curvature of these growth forms links the diffusion distance to an Arrhenius plot, with a value of EA > 400 kJ/mol, which is nearly double the energy of a silicon-silicon bond (226 kJ/mol). This implies that the silicon atoms are held on the two dimensional surface by more than just a single Sisbnd Si bond. In addition, small residual islands on the smooth terraces have a similar density to that seen in similar growth studies on silicon(100).

  4. Bovine serum albumin adsorption on functionalized porous silicon surfaces

    NASA Astrophysics Data System (ADS)

    Tay, Li-Lin; Rowell, Nelson L.; Lockwood, David J.; Boukherroub, Rabah

    2004-10-01

    The large surface area within porous Si (pSi) and its strong room temperature photoluminescence (PL) make it an ideal host for biological sensors. In particular, the development of pSi-based optical sensors for DNA, enzyme and other biochemical molecules have become of great interest. Here, we demonstrate that the in-situ monitoring of the pSi PL behaviour can be used as a positive identification of bovine serum albumin (BSA) protein adsorption inside the porous matrix. Electrochemically prepared pSi films were first functionalized with undecylenic acid to produce an organic monolayer covalently attached to the porous silicon surfaces. The acid terminal group also provided favourable BSA binding sites on the pSi matrix sidewalls. In-situ PL spectra showed a gradual red shift (up to 12 meV) in the PL peak energy due to the protein incorporation into the porous matrix. The PL then exhibited a continuous blue shift after saturation of the protein molecules in the pores. This blue shift of the PL peak frequency and a steady increase in the PL intensity is evidence of surface oxidation. Comparing the specular reflectance obtained by Fourier transform infrared spectroscopy (FTIR) before and after BSA incubation confirmed the adsorption of protein in the pSi matrix.

  5. Porous silicon: electrochemical microstructuring, photoluminescence, and covalent modificaiton

    NASA Astrophysics Data System (ADS)

    Prigozhin, Maxim B.; Shiwsankar, Pauline; Algar, W. Russ; Krull, Ulrich J.

    2008-06-01

    Interest in porous silicon (PS) has increased dramatically over the past two decades due to aspects such as photoluminescence due to quantum confinement, large surface area, and micro/nanoscale architecture. In this work, <111> p-type silicon wafers have been electrochemically etched with ethanolic solutions of hydrofluoric acid. Discrete surface domains showing luminescence were observed. The domains were typically many tens of micrometers in size and had a height of about 6-8 μm. Interestingly, central round wells of 10-30 μm diameter were observed to form within domains. Investigation of luminescence in depth profile of the wells was done using confocal fluorescence microscopy, and the results indicated that the domains were fully porous and luminescent throughout the entire depth. Spectrally, the peak fluorescence emission was in the range of 550-750 nm and the spectra had an average FWHM equal to about 150 nm. Covalent attachment of organic monolayers to the porous silicon surfaces was done to try and passivate against oxidation, and also to explore the possibilities of bioconjugation and tuning of the photoluminescence wavelength. A reaction of hydrogen terminated silicon with ω-undecylenyl alcohol was done using irradiation by a UV source, and successful derivatization was confirmed with IR spectroscopy. Bulk electrochemical etching of silicon provided a method to generate distributed luminescent structures suitable for compartmentalization of reactions within wells of micrometer dimensions without the use of spatially resolved fabrication methodologies such as epitaxial deposition, lithography, or ion beam technologies.

  6. Modeling the surface photovoltage of silicon slabs with varying thickness.

    PubMed

    Vazhappilly, Tijo; Kilin, Dmitri S; Micha, David A

    2015-04-10

    The variation with thickness of the energy band gap and photovoltage at the surface of a thin semiconductor film are of great interest in connection with their surface electronic structure and optical properties. In this work, the change of a surface photovoltage (SPV) with the number of layers of a crystalline silicon slab is extracted from models based on their atomic structure. Electronic properties of photoexcited slabs are investigated using generalized gradient and hybrid density functionals, and plane wave basis sets. Si(1 1 1) surfaces have been terminated by hydrogen atoms to compensate for dangling bonds and have been described by large supercells with periodic boundary conditions. Calculations of the SPV of the Si slabs have been done in terms of the reduced density matrix of the photoactive electrons including dissipative effects due to their interaction with medium phonons and excitons. Surface photovoltages have been calculated for model Si slabs with 4-12, and 16 layers, to determine convergence trends versus slab thickness. Band gaps and the inverse of the SPVs have been found to scale nearly linearly with the inverse thickness of the slab, while the electronic density of states increases quadratically with thickness. Our calculations show the same trends as experimental values indicating band gap reduction and absorption enhancement for Si films of increasing thickness. Simple arguments on confined electronic structures have been used to explain the main effects of changes with slab thickness. A procedure involving shifted electron excitation energies is described to improve results from generalized gradient functionals so they can be in better agreement with the more accurate but also more computer intensive values from screened exchange hybrid functionals. PMID:25767101

  7. Modeling the surface photovoltage of silicon slabs with varying thickness

    NASA Astrophysics Data System (ADS)

    Vazhappilly, Tijo; Kilin, Dmitri S.; Micha, David A.

    2015-04-01

    The variation with thickness of the energy band gap and photovoltage at the surface of a thin semiconductor film are of great interest in connection with their surface electronic structure and optical properties. In this work, the change of a surface photovoltage (SPV) with the number of layers of a crystalline silicon slab is extracted from models based on their atomic structure. Electronic properties of photoexcited slabs are investigated using generalized gradient and hybrid density functionals, and plane wave basis sets. Si(1 1 1) surfaces have been terminated by hydrogen atoms to compensate for dangling bonds and have been described by large supercells with periodic boundary conditions. Calculations of the SPV of the Si slabs have been done in terms of the reduced density matrix of the photoactive electrons including dissipative effects due to their interaction with medium phonons and excitons. Surface photovoltages have been calculated for model Si slabs with 4-12, and 16 layers, to determine convergence trends versus slab thickness. Band gaps and the inverse of the SPVs have been found to scale nearly linearly with the inverse thickness of the slab, while the electronic density of states increases quadratically with thickness. Our calculations show the same trends as experimental values indicating band gap reduction and absorption enhancement for Si films of increasing thickness. Simple arguments on confined electronic structures have been used to explain the main effects of changes with slab thickness. A procedure involving shifted electron excitation energies is described to improve results from generalized gradient functionals so they can be in better agreement with the more accurate but also more computer intensive values from screened exchange hybrid functionals.

  8. Surface Structure and Surface Electronic States Related to Plasma Cleaning of Silicon and Germanium

    NASA Astrophysics Data System (ADS)

    Cho, Jaewon

    This thesis discusses the surface structure and the surface electronic states of Si and Ge(100) surfaces as well as the effects of oxidation process on the silicon oxide/Si(100) interface structure. The H-plasma exposure was performed in situ at low temperatures. The active species, produced in the H-plasma by the rf-excitation of H_2 gas, not only remove microcontaminants such as oxygen and carbon from the surface, but also passivate the surface with atomic hydrogen by satisfying the dangling bonds of the surface atoms. The surfaces were characterized by Angle Resolved UV-Photoemission Spectroscopy (ARUPS) and Low Energy Electron Diffraction (LEED). In the case of Si(100), H-plasma exposure produced ordered H-terminated crystallographic structures with either a 2 x 1 or 1 x 1 LEED pattern. The hydride phases, found on the surfaces of the cleaned Si(100), were shown to depend on the temperature of the surface during H-plasma cleaning. The electronic states for the monohydride and dihydride phases were identified by ARUPS. When the plasma cleaned surface was annealed, the phase transition from the dihydride to monohydride was observed. The monohydride Si-H surface bond was stable up to 460^circC, and the dangling bond surface states were identified after annealing at 500^circC which was accompanied by the spectral shift. The H-terminated surface were characterized to have a flat band structure. For the Ge(100) surface, an ordered 2 x 1 monohydride phase was obtained from the surface cleaned at 180 ^circC. After plasma exposure at <=170^circC a 1 x 1 surface was observed, but the ARUPS indicated that the surface was predominantly composed of disordered monohydride structures. After annealing above the H-dissociation temperatures, the shift in the spectrum was shown to occur with the dangling bond surface states. The H-terminated surfaces were identified to be unpinned. The interface structure of silicon oxide/Si(100) was studied using ARUPS. Spectral shifts were

  9. Role of silicon hydride bonding environment in alpha-silicon:hydrogen films for c-silicon surface passivation

    NASA Astrophysics Data System (ADS)

    Burrows, Michael Z.

    High efficiency silicon solar cells achieve greater than 700 mV open circuit voltage through excellent surface passivation of the monocyrstalline absorber. This work studies the bifacial plasma enhanced chemical vapor deposited (PECVD) intrinsic amorphous silicon ((i) alpha-Si:H) passivation structure. To enable the correct interpretation of FTIR detected vibrational modes a model of the layered substructure of ultra-thin (i) alpha-Si:H is constructed. A high fraction of di-hydride bonding is associated with defective, low density amorphous film, and control of this parameter is established by varying hydrogen dilution ratio. The hypothesis that a high fraction of di-hydride bonding over mono-hydride within the film would lead to a poor passivation layer is tested and shown to be false. This is due to the bulk layer within the model defining the di-hydride fraction and indicates that the interface layer plays the more dominant role. A comparison between rf plasma PECVD deposited films and dc plasma shows that upon 30 min, 285°C annealing, large improvements in passivation occur when dc plasma was used with gains in minority carrier effective lifetimes over 1 msec possible. The passivation quality of rf generated films is less effected by annealing. rf plasma films show detectable mono-, di-, and tri-hydride high-potential modes in the as-deposited condition that are removed upon annealing. The finite loss of bulk mono-hydride and these interfacial hydrides do not have a strong impact on film passivation quality. It is concluded that the film has reached an equilibrium level of interfacial defect density which is unaffected by the limited loss of hydride bonding observed. dc plasma films undergo large improvements in passivation quality upon annealing. An increase in mono-hydride bonding at the internal surfaces of nanometer sized voids is detected. It is proposed that this mono-hydride bonding is reducing the density of unsaturated bonds, lowering the interfacial

  10. Wave optical simulation of the light trapping properties of black silicon surface textures.

    PubMed

    Bett, Alexander Jürgen; Eisenlohr, Johannes; Höhn, Oliver; Repo, Päivikki; Savin, Hele; Bläsi, Benedikt; Goldschmidt, Jan Christoph

    2016-03-21

    Due to their low reflectivity and effective light trapping properties black silicon nanostructured surfaces are promising front side structures for thin crystalline silicon solar cells. For further optimization of the light trapping effect, particularly in combination with rear side structures, it is necessary to simulate the optical properties of black silicon. Especially, the angular distribution of light in the silicon bulk after passage through the front side structure is relevant. In this paper, a rigorous coupled wave analysis of black silicon is presented, where the black silicon needle shaped structure is approximated by a randomized cone structure. The simulated absorptance agrees well with measurement data. Furthermore, the simulated angular light distribution within the silicon bulk shows that about 70% of the light can be subjected to internal reflection, highlighting the good light trapping properties. PMID:27136865

  11. Origin of complex impact craters on native oxide coated silicon surfaces

    SciTech Connect

    Samela, Juha; Nordlund, Kai; Popok, Vladimir N.; Campbell, Eleanor E. B.

    2008-02-15

    Crater structures induced by impact of keV-energy Ar{sub n}{sup +} cluster ions on silicon surfaces are measured with atomic force microscopy. Complex crater structures consisting of a central hillock and outer rim are observed more often on targets covered with a native silicon oxide layer than on targets without the oxide layer. To explain the formation of these complex crater structures, classical molecular dynamics simulations of Ar cluster impacts on oxide coated silicon surfaces, as well as on bulk amorphous silica, amorphous Si, and crystalline Si substrates, are carried out. The diameter of the simulated hillock structures in the silicon oxide layer is in agreement with the experimental results, but the simulations cannot directly explain the height of hillocks and the outer rim structures when the oxide coated silicon substrate is free of defects. However, in simulations of 5 keV/atom Ar{sub 12} cluster impacts, transient displacements of the amorphous silicon or silicon oxide substrate surfaces are induced in an approximately 50 nm wide area surrounding the impact point. In silicon oxide, the transient displacements induce small topographical changes on the surface in the vicinity of the central hillock. The comparison of cluster stopping mechanisms in the various silicon oxide and silicon structures shows that the largest lateral momentum is induced in the silicon oxide layer during the impact; thus, the transient displacements on the surface are stronger than in the other substrates. This can be a reason for the higher frequency of occurrence of the complex craters on oxide coated silicon.

  12. Surface and Internal Structure of Pristine Presolar Silicon Carbide

    NASA Technical Reports Server (NTRS)

    Stroud, Rhonda, M.; Bernatowicz, Thomas J.

    2005-01-01

    Silicon carbide is the most well-studied type of presolar grain. Isotope measurements of thousands [1,2] and structural data from over 500 individual grains have been reported [3]. The isotope data indicate that approximately 98% originated in asymptotic giant branch stars and 2% in supernovae. Although tens of different polytypes of SiC are known to form synthetically, only two polytypes have been reported for presolar grains. Daulton et al. [3] found that for SiC grains isolated from Murchison by acid treatments, 79.4% are 3C cubic beta-SiC, 2.7% are 2H hexagonal alpha-SiC, 17.1% are intergrowths of and , and 0.9% are heavily disordered. They report that the occurrence of only the and polytypes is consistent with the observed range of condensation temperatures of circumstellar dust for carbon stars. Further constraint on the formation and subsequent alteration of the grains can be obtained from studies of the surfaces and interior structure of grains in pristine form, i.e., prepared without acid treatments [4,5]. The acid treatments remove surface coatings, produce etch pits around defect sites and could remove some subgrains. Surface oxides have been predicted by theoretical modeling as a survival mechanism for SiC grains exposed to the hot oxidizing solar nebula [6]. Scanning electron microscopy studies of pristine SiC shows some evidence for the existence of oxide and organic coatings [4]. We report herein on transmission electron microscopy studies of the surface and internal structure of two pristine SiC grains, including definitive evidence of an oxide rim on one grain, and the presence of internal TiC and AlN grains.

  13. Patterned biofunctional poly(acrylic acid) brushes on silicon surfaces.

    PubMed

    Dong, Rong; Krishnan, Sitaraman; Baird, Barbara A; Lindau, Manfred; Ober, Christopher K

    2007-10-01

    Protein patterning was carried out using a simple procedure based on photolithography wherein the protein was not subjected to UV irradiation and high temperatures or contacted with denaturing solvents or strongly acidic or basic solutions. Self-assembled monolayers of poly(ethylene glycol) (PEG) on silicon surfaces were exposed to oxygen plasma through a patterned photoresist. The etched regions were back-filled with an initiator for surface-initiated atom transfer radical polymerization (ATRP). ATRP of sodium acrylate was readily achieved at room temperature in an aqueous medium. Protonation of the polymer resulted in patterned poly(acrylic acid) (PAA) brushes. A variety of biomolecules containing amino groups could be covalently tethered to the dense carboxyl groups of the brush, under relatively mild conditions. The PEG regions surrounding the PAA brush greatly reduced nonspecific adsorption. Avidin was covalently attached to PAA brushes, and biotin-tagged proteins could be immobilized through avidin-biotin interaction. Such an immobilization method, which is based on specific interactions, is expected to better retain protein functionality than direct covalent binding. Using biotin-tagged bovine serum albumin (BSA) as a model, a simple strategy was developed for immobilization of small biological molecules using BSA as linkages, while BSA can simultaneously block nonspecific interactions. PMID:17880179

  14. Surface Micromachined Flexural Plate Wave Device Integrable on Silicon

    SciTech Connect

    Clem, P.G.; Dimos, D.; Garino, T.J.; Martin, S.J.; Mitchell, M.A.; Olson, W.R.; Ruffner, J.A.; Schubert, W.K.; Tuttle, B.A.

    1999-01-01

    Small, reliable chemical sensors are needed for a wide range of applications, such as weapon state-of-health monitoring, nonproliferation activities, and manufacturing emission monitoring. Significant improvements in present surface acoustic wave sensors could be achieved by developing a flexural plate-wave (FPW) architecture, in which acoustic waves are excited in a thin sensor membrane. Further enhancement of device performance could be realized by integrating a piezoelectric thin film on top of the membrane. These new FPW-piezoelectric thin film devices would improve sensitivity, reduce size, enhance ruggedness and reduce the operating frequency so that the FPW devices would be compatible with standard digital microelectronics. Development of these piezoelectric thin film // FPW devices requires integration of (1) acoustic sensor technology, (2) silicon rnicromachining techniques to fabricate thin membranes, and (3) piezoelectric thin films. Two piezoelectric thin film technologies were emphasized in this study: Pb(Zr,Ti)O{sub 3} (PZT) and AlN. PZT thin films were of sufficient quality such that the first high frequency SAW measurements on PZT thin films were measured during the course of this study. Further, reasonable ferroelectric properties were obtained from PZT films deposited on Si surface micromachined FPW device membranes. Fundamental understanding of the effect of nanodimension interfacial layers on AlN thin film domain configurations and piezoelectric response was developed. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the US Department of Energy under contract DE-AC04-94AL85000.

  15. Enhanced surface hardness in nitrogen-implanted silicon carbide

    SciTech Connect

    Uslu, C.; Lee, D.H.; Berta, Y.

    1995-06-01

    Preliminary studies have been performed on the feasibility of carbon-silicon nitride formation ({beta}-Si{sub 1.5}C{sub 1.5}N{sub 4}, the homologue of equilibrium {beta}-Si{sub 3}N{sub 4} or hypothetical {beta}-C{sub 3}N{sub 4}) by high dose N{sup +}-implantation into polycrystalline {beta}-SiC (cubic). Thin films were formed using 100 keV implantations with varying ion doses in the range from 1.1 x 10{sup 17} to 27.1 x 10{sup 17} N/cm{sup 2}, and target temperatures between -196{degrees}C and 980{degrees}C. X-ray diffraction with a position-sensitive detector and cross-sectional transmission electron microscopy revealed that the as-implanted surfaces (up to 860{degrees}C) contained {approximately}0.1 {mu}m thick buried amorphous layers. Rutherford backscattering spectroscopy showed that the peak concentration of nitrogen saturated up to approximately 54 at. % with increasing doses, suggesting formation of a new phase. Implantation to doses of 1.1 x 10{sup 17} and 2.3 x 10{sup 17} N/cm{sup 2} at 980{degrees}C caused enhanced surface hardness compared to SiC.

  16. Preparation and Surface Layer Modification of Silicon Nanoparticles Dispersed in 2-Propanol

    NASA Astrophysics Data System (ADS)

    Zhu, Yong; S, Iwasaki; K, Kimura; Zhang, Li-de

    1998-12-01

    Silicon nanoparticles dispersed in 2-propanol were prepared by using an arc plasma with gas flow method in a new designed home-made apparatus. The particles are composed of silicon crystal core covered by oxidized amorphous silicon shell. The composition of the particle surface layer can be modified by preparing the sample in different atmosphere. The particles can be also obtained with different core composition and different size which we need.

  17. Radical surface interactions in industrial silicon plasma etch reactors

    NASA Astrophysics Data System (ADS)

    Cunge, G.; Vempaire, D.; Ramos, R.; Touzeau, M.; Joubert, O.; Bodard, P.; Sadeghi, N.

    2010-06-01

    Silicon etching in Cl2-based plasmas is an important step for the fabrication of IC circuits but the plasma surface interactions involved in this process remain poorly understood. Based on the developments in plasma and reactor wall diagnostics, this paper reviews the recent progress in the understanding of radicals' interactions with surfaces during silicon etching processes. X-ray photoelectron spectroscopy analysis of the reactor walls shows that during Si etching in Cl2/O2 plasmas, the initial Al2O3 chamber walls are coated with a thin SiOCl layer. Broadband absorption spectroscopy with UV light emitting diodes is used to measure the densities of SiClX radicals (X = 0-2) and Cl2 molecules in steady state plasmas running with the chamber walls coated with different materials. To estimate the surface sticking/recombination probability of these radicals on different surfaces, we have performed time-resolved absorption measurements in the afterglow of pulsed discharges. Our work, in agreement with previous results, shows that the Cl2/Cl density ratio in the discharge is driven mainly by the chemical nature of the chamber walls explaining why process drifts are often observed in Cl2/O2 plasmas. The recombination coefficient of Cl atoms on SiOCl surfaces is about 0.007, while it is about 0.1 on clean walls (AlF3). Based on these results, we discuss the best strategy leading to reproducible process control, the present strategy being a systematic reactor cleaning/conditioning between wafers. The SiOCl layer deposition mechanism is then discussed in detail. The sticking coefficient of SiCl on this surface is near unity, while SiCl2 appears to be weakly reactive toward it. Therefore, SiCl (and SiCl+ ions) are the main vectors of Si deposition on the reactor walls, where their subsequent oxidization by O atoms leads to the formation of a SiOCl deposit. Furthermore, we show that SiCl reaction in the plasma volume with Cl2, through the exchange reaction SiCl + Cl2 → Si

  18. Cellular interactions of surface modified nanoporous silicon particles

    NASA Astrophysics Data System (ADS)

    Bimbo, Luis M.; Sarparanta, Mirkka; Mäkilä, Ermei; Laaksonen, Timo; Laaksonen, Päivi; Salonen, Jarno; Linder, Markus B.; Hirvonen, Jouni; Airaksinen, Anu J.; Santos, Hélder A.

    2012-05-01

    In this study, the self-assembly of hydrophobin class II (HFBII) on the surface of thermally hydrocarbonized porous silicon (THCPSi) nanoparticles was investigated. The HFBII-coating converted the hydrophobic particles into more hydrophilic ones, improved the particles' cell viability in both HT-29 and Caco-2 cell lines compared to uncoated particles, and enhanced the particles' cellular association. The amount of HFBII adsorbed onto the particles was also successfully quantified by both the BCA assay and a HPLC method. Importantly, the permeation of a poorly water-soluble drug, indomethacin, loaded into THCPSi particles across Caco-2 monolayers was not affected by the protein coating. In addition, 125I-radiolabelled HFBII did not extensively permeate the Caco-2 monolayer and was found to be stably adsorbed onto the THCPSi nanoparticles incubated in pH 7.4, which renders the particles the possibility for further track-imaging applications. The results highlight the potential of HFBII coating for improving wettability, increasing biocompatibility and possible intestinal association of PSi nanoparticulates for drug delivery applications.In this study, the self-assembly of hydrophobin class II (HFBII) on the surface of thermally hydrocarbonized porous silicon (THCPSi) nanoparticles was investigated. The HFBII-coating converted the hydrophobic particles into more hydrophilic ones, improved the particles' cell viability in both HT-29 and Caco-2 cell lines compared to uncoated particles, and enhanced the particles' cellular association. The amount of HFBII adsorbed onto the particles was also successfully quantified by both the BCA assay and a HPLC method. Importantly, the permeation of a poorly water-soluble drug, indomethacin, loaded into THCPSi particles across Caco-2 monolayers was not affected by the protein coating. In addition, 125I-radiolabelled HFBII did not extensively permeate the Caco-2 monolayer and was found to be stably adsorbed onto the THCPSi

  19. Surface chemistry dependent immunostimulative potential of porous silicon nanoplatforms.

    PubMed

    Shahbazi, Mohammad-Ali; Fernández, Tahia D; Mäkilä, Ermei M; Le Guével, Xavier; Mayorga, Cristobalina; Kaasalainen, Martti H; Salonen, Jarno J; Hirvonen, Jouni T; Santos, Hélder A

    2014-11-01

    Nanoparticles (NPs) have been suggested for immunotherapy applications in order to optimize the delivery of immuno-stimulative or -suppressive molecules. However, low attention towards the impact of the NPs' physicochemical properties has presented a major hurdle for developing efficient immunotherapeutic agents. Here, the effects of porous silicon (PSi) NPs with different surface chemistries were evaluated on human monocyte-derived dendritic cells (MDDCs) and lymphocytes in order to highlight the importance of the NPs selection in immuno-stimulative or -suppressive treatment. Although all the PSi NPs showed high biocompatibility, only thermally oxidized PSi (TOPSi) and thermally hydrocarbonized PSi (THCPSi) NPs were able to induce very high rate of immunoactivation by enhancing the expression of surface co-stimulatory markers of the MDDCs (CD80, CD83, CD86, and HLA-DR), inducing T-cell proliferation, and also the secretion of interleukins (IL-1β, IL-4, IL-6, IL-10, IL-12, IFN-γ, and TNF-α). These results indicated a balanced increase in the secretion of Th1, Th2, and Treg cytokines. Moreover, undecylenic acid functionalized THCPSi, as well as poly(methyl vinyl ether-alt-maleic acid) conjugated to (3-aminopropyl)triethoxysilane functionalized thermally carbonized PSi and polyethyleneimine conjugated undecylenic acid functionalized THCPSi NPs showed moderate immunoactivation due to the mild increase in the above-mentioned markers. By contrast, thermally carbonized PSi (TCPSi) and (3-aminopropyl)triethoxysilane functionalized TCPSi NPs did not induce any immunological responses, suggesting that their application could be in the delivery of immunosuppressive molecules. Overall, our findings suggest all the NPs containing more nitrogen or oxygen on the outermost backbone layer have lower immunostimulatory effect than NPs with higher C-H structures on the surface. PMID:25123922

  20. Influence of acetylcholinesterase immobilization on the photoluminescence properties of mesoporous silicon surface

    NASA Astrophysics Data System (ADS)

    Saleem, Muhammad; Rafiq, Muhammad; Seo, Sung-Yum; Lee, Ki Hwan

    2014-07-01

    Acetylcholinesterase immobilized p-type porous silicon surface was prepared by covalent attachment. The immobilization procedure was based on support surface chemical oxidation, silanization, surface activation with cyanuric chloride and finally covalent attachment of free enzyme on the cyanuric chloride activated porous silicon surface. Different pore diameter of porous silicon samples were prepared by electrochemical etching in HF based electrolyte solution and appropriate sample was selected suitable for enzyme immobilization with maximum trapping ability. The surface modification was studied through field emission scanning electron microscope, EDS, FT-IR analysis, and photoluminescence measurement by utilizing the fluctuation in the photoluminescence of virgin and enzyme immobilized porous silicon surface. Porous silicon showed strong photoluminescence with maximum emission at 643 nm and immobilization of acetylcholinesterase on porous silicon surface cause considerable increment on the photoluminescence of porous silicon material while acetylcholinesterase free counterpart did not exhibit any fluorescence in the range of 635-670 nm. The activities of the free and immobilized enzymes were evaluated by spectrophotometric method by using neostigmine methylsulfate as standard enzyme inhibitor. The immobilized enzyme exhibited considerable response toward neostigmine methylsulfate in a dose dependent manner comparable with that of its free counterpart alongside enhanced stability, easy separation from the reaction media and significant saving of enzyme. It was believed that immobilized enzyme can be exploited in organic and biomolecule synthesis possessing technical and economical prestige over free enzyme and prominence of easy separation from the reaction mixture.

  1. Effect of surface roughness on EPES and AREPES measurements: Flat and crenels silicon surfaces

    NASA Astrophysics Data System (ADS)

    Chelda, S.; Robert-Goumet, C.; Gruzza, B.; Bideux, L.; Monier, G.

    2008-06-01

    EPES (elastic peak electron spectroscopy) and AREPES (angle resolved elastic peak electron spectroscopy) are non destructive methods and very sensitive to the surface region. These techniques allow to measure the percentage ηe of elastically backscattered electrons from the surface excited by an electron beam. Both methods are combined with Monte-Carlo (MC) simulations to interpret experimental results. In this work, we underline the importance of a micrometric scale roughness at the surface. The use of an original Monte-Carlo method was fruitful for the simulation, moreover 3D representations have been developed for visualization and qualitative interpretation of the results. For a more precise quantitative study, a 2D representation was necessary. The calculated results have been compared with published experimental ones got for different incidence angles and primary energies, on a silicon surface having triangular saw-tooth aspect (crenels) obtained by photolithography. We have observed that the effect due to the roughness increases with the incidence angle.

  2. Surface and allied studies in silicon solar cells

    NASA Technical Reports Server (NTRS)

    Lindholm, F. A.

    1983-01-01

    Two main results are presented. The first deals with a simple method that determines the minority-carrier lifetime and the effective surface recombination velocity of the quasi-neutral base of silicon solar cells. The method requires the observation of only a single transient, and is amenable to automation for in-process monitoring in manufacturing. This method, which is called short-circuit current decay, avoids distortion in the observed transient and consequent inacccuracies that arise from the presence of mobile holes and electrons stored in the p/n junction spacecharge region at the initial instant of the transient. The second main result consists in a formulation of the relevant boundary-value problems that resembles that used in linear two-port network theory. This formulation enables comparisons to be made among various contending methods for measuring material parameters of p/n junction devices, and enables the option of putting the description in the time domain of the transient studies in the form of an infinite series, although closed-form solutions are also possible.

  3. Residual Silicone Detection. [external tank and solid rocket booster surfaces

    NASA Technical Reports Server (NTRS)

    Smith, T.

    1980-01-01

    Both photoelectron emission and ellipsometry proved successful in detecting silicone contamination on unpainted and epoxy painted metal surfaces such as those of the external tank and the solid rocket booster. Great success was achieved using photoelectron emission (PEE). Panels were deliberately contaminated to controlled levels and then mapped with PEE to reveal the areas and levels that were contaminated. The panels were then tested with regard to adhesive properties. Tapes were bonded over the contaminated and uncontaminated regions and the peel force was measured, or the contaminated panels were bonded (with CPR 483 foam) to uncontaminated panels and made into lap shear specimens. Other panels were bonded and made into wedge specimens for hydrothermal stress endurance tests. Strong adhesion resulted if the PEE signal fell within an acceptance window, but was poor outside the acceptance window. A prototype instrument is being prepared which can automatically be scanned over the external liquid hydrogen tank and identify those regions that are contaminated and will cause bond degradation.

  4. Porous silicon structures with high surface area/specific pore size

    DOEpatents

    Northrup, M. Allen; Yu, Conrad M.; Raley, Norman F.

    1999-01-01

    Fabrication and use of porous silicon structures to increase surface area of heated reaction chambers, electrophoresis devices, and thermopneumatic sensor-actuators, chemical preconcentrates, and filtering or control flow devices. In particular, such high surface area or specific pore size porous silicon structures will be useful in significantly augmenting the adsorption, vaporization, desorption, condensation and flow of liquids and gasses in applications that use such processes on a miniature scale. Examples that will benefit from a high surface area, porous silicon structure include sample preconcentrators that are designed to adsorb and subsequently desorb specific chemical species from a sample background; chemical reaction chambers with enhanced surface reaction rates; and sensor-actuator chamber devices with increased pressure for thermopneumatic actuation of integrated membranes. Examples that benefit from specific pore sized porous silicon are chemical/biological filters and thermally-activated flow devices with active or adjacent surfaces such as electrodes or heaters.

  5. Porous silicon structures with high surface area/specific pore size

    DOEpatents

    Northrup, M.A.; Yu, C.M.; Raley, N.F.

    1999-03-16

    Fabrication and use of porous silicon structures to increase surface area of heated reaction chambers, electrophoresis devices, and thermopneumatic sensor-actuators, chemical preconcentrates, and filtering or control flow devices. In particular, such high surface area or specific pore size porous silicon structures will be useful in significantly augmenting the adsorption, vaporization, desorption, condensation and flow of liquids and gases in applications that use such processes on a miniature scale. Examples that will benefit from a high surface area, porous silicon structure include sample preconcentrators that are designed to adsorb and subsequently desorb specific chemical species from a sample background; chemical reaction chambers with enhanced surface reaction rates; and sensor-actuator chamber devices with increased pressure for thermopneumatic actuation of integrated membranes. Examples that benefit from specific pore sized porous silicon are chemical/biological filters and thermally-activated flow devices with active or adjacent surfaces such as electrodes or heaters. 9 figs.

  6. Investigation of the surface of implanted silicon crystal by the contact angle

    SciTech Connect

    Lebedeva, N.N.; Bakovets, V.V.; Sedymova, E.A.; Pridachin, N.B.

    1987-03-01

    The authors study the dependence of the critical contact angle of silicon upon the dose of its irradiation by argon and boron ions. It is established that the system of immiscible liquids ether-water can be successfully used to study the influence of ion implantation of silicon on its wettability by water. The change in the wettability of implanted silicon is related to the increase in the level of the defect state of the layer surface. Wetting of implanted silicon by melts at high temperatures can be used for studying the kinetics and the annealing mechanism of defects.

  7. Surface trap mediated electronic transport in biofunctionalized silicon nanowires

    NASA Astrophysics Data System (ADS)

    Puppo, F.; Traversa, F. L.; Di Ventra, M.; De Micheli, G.; Carrara, S.

    2016-08-01

    Silicon nanowires (SiNWs), fabricated via a top-down approach and then functionalized with biological probes, are used for electrically-based sensing of breast tumor markers. The SiNWs, featuring memristive-like behavior in bare conditions, show, in the presence of biomarkers, modified hysteresis and, more importantly, a voltage memory component, namely a voltage gap. The voltage gap is demonstrated to be a novel and powerful parameter of detection thanks to its high-resolution dependence on charges in proximity of the wire. This unique approach of sensing has never been studied and adopted before. Here, we propose a physical model of the surface electronic transport in Schottky barrier SiNW biosensors, aiming at reproducing and understanding the voltage gap based behavior. The implemented model describes well the experimental I–V characteristics of the device. It also links the modification of the voltage gap to the changing concentration of antigens by showing the decrease of this parameter in response to increasing concentrations of the molecules that are detected with femtomolar resolution in real human samples. Both experiments and simulations highlight the predominant role of the dynamic recombination of the nanowire surface states, with the incoming external charges from bio-species, in the appearance and modification of the voltage gap. Finally, thanks to its compactness, and strict correlation with the physics of the nanodevice, this model can be used to describe and predict the I–V characteristics in other nanostructured devices, for different than antibody-based sensing as well as electronic applications.

  8. Microscopic Image of Martian Surface Material on a Silicone Substrate

    NASA Technical Reports Server (NTRS)

    2008-01-01

    [figure removed for brevity, see original site] Click on image for larger version of Figure 1

    This image taken by the Optical Microscope on NASA's Phoenix Mars Lander shows soil sprinkled from the lander's Robot Arm scoop onto a silicone substrate. The substrate was then rotated in front of the microscope. This is the first sample collected and delivered for instrumental analysis onboard a planetary lander since NASA's Viking Mars missions of the 1970s. It is also the highest resolution image yet seen of Martian soil.

    The image is dominated by fine particles close to the resolution of the microscope. These particles have formed clumps, which may be a smaller scale version of what has been observed by Phoenix during digging of the surface material.

    The microscope took this image during Phoenix's Sol 17 (June 11), or the 17th Martian day after landing. The scale bar is 1 millimeter (0.04 inch).

    Zooming in on the Martian Soil

    In figure 1, three zoomed-in portions are shown with an image of Martian soil particles taken by the Optical Microscope on NASA's Phoenix Mars Lander.

    The left zoom box shows a composite particle. The top of the particle has a green tinge, possibly indicating olivine. The bottom of the particle has been reimaged at a different focus position in black and white (middle zoom box), showing that this is a clump of finer particles.

    The right zoom box shows a rounded, glassy particle, similar to those which have also been seen in an earlier sample of airfall dust collected on a surface exposed during landing.

    The shadows at the bottom of image are of the beams of the Atomic Force Microscope.

    The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.

  9. Surface trap mediated electronic transport in biofunctionalized silicon nanowires.

    PubMed

    Puppo, F; Traversa, F L; Ventra, M Di; Micheli, G De; Carrara, S

    2016-08-26

    Silicon nanowires (SiNWs), fabricated via a top-down approach and then functionalized with biological probes, are used for electrically-based sensing of breast tumor markers. The SiNWs, featuring memristive-like behavior in bare conditions, show, in the presence of biomarkers, modified hysteresis and, more importantly, a voltage memory component, namely a voltage gap. The voltage gap is demonstrated to be a novel and powerful parameter of detection thanks to its high-resolution dependence on charges in proximity of the wire. This unique approach of sensing has never been studied and adopted before. Here, we propose a physical model of the surface electronic transport in Schottky barrier SiNW biosensors, aiming at reproducing and understanding the voltage gap based behavior. The implemented model describes well the experimental I-V characteristics of the device. It also links the modification of the voltage gap to the changing concentration of antigens by showing the decrease of this parameter in response to increasing concentrations of the molecules that are detected with femtomolar resolution in real human samples. Both experiments and simulations highlight the predominant role of the dynamic recombination of the nanowire surface states, with the incoming external charges from bio-species, in the appearance and modification of the voltage gap. Finally, thanks to its compactness, and strict correlation with the physics of the nanodevice, this model can be used to describe and predict the I-V characteristics in other nanostructured devices, for different than antibody-based sensing as well as electronic applications. PMID:27418560

  10. Surface Area, and Oxidation Effects on Nitridation Kinetics of Silicon Powder Compacts

    NASA Technical Reports Server (NTRS)

    Bhatt, R. T.; Palczer, A. R.

    1998-01-01

    Commercially available silicon powders were wet-attrition-milled from 2 to 48 hr to achieve surface areas (SA's) ranging from 1.3 to 70 sq m/g. The surface area effects on the nitridation kinetics of silicon powder compacts were determined at 1250 or 1350 C for 4 hr. In addition, the influence of nitridation environment, and preoxidation on nitridation kinetics of a silicon powder of high surface area (approximately equals 63 sq m/g) was investigated. As the surface area increased, so did the percentage nitridation after 4 hr in N2 at 1250 or 1350 C. Silicon powders of high surface area (greater than 40 sq m/g) can be nitrided to greater than 70% at 1250 C in 4 hr. The nitridation kinetics of the high-surface-area powder compacts were significantly delayed by preoxidation treatment. Conversely, the nitridation environment had no significant influence on the nitridation kinetics of the same powder. Impurities present in the starting powder, and those accumulated during attrition milling, appeared to react with the silica layer on the surface of silicon particles to form a molten silicate layer, which provided a path for rapid diffusion of nitrogen and enhanced the nitridation kinetics of high surface area silicon powder.

  11. Highly efficient industrial large-area black silicon solar cells achieved by surface nanostructured modification

    NASA Astrophysics Data System (ADS)

    Li, Ping; Wei, Yi; Zhao, Zengchao; Tan, Xin; Bian, Jiming; Wang, Yuxuan; Lu, Chunxi; Liu, Aimin

    2015-12-01

    Traditional black silicon solar cells show relatively low efficiencies due to the high surface recombination occurring at the front surfaces. In this paper, we present a surface modification process to suppress surface recombination and fabricate highly efficient industrial black silicon solar cells. The Ag-nanoparticle-assisted etching is applied to realize front surface nanostructures on silicon wafers in order to reduce the surface reflectance. Through a further tetramethylammonium hydroxide (TMAH) treatment, the carrier recombination at and near the surface is greatly suppressed, due to a lower surface dopant concentration after the surface modification. This modified surface presents a low reflectivity in a range of 350-1100 nm. Large-area solar cells with an average conversion efficiency of 19.03% are achieved by using the TMAH treatment of 30 s. This efficiency is 0.18% higher than that of standard silicon solar cells with pyramidal surfaces, and also a remarkable improvement compared with black silicon solar cells without TMAH modifications.

  12. Method of fabricating silicon carbide coatings on graphite surfaces

    DOEpatents

    Varacalle, Jr., Dominic J.; Herman, Herbert; Burchell, Timothy D.

    1994-01-01

    The vacuum plasma spray process produces well-bonded, dense, stress-free coatings for a variety of materials on a wide range of substrates. The process is used in many industries to provide for the excellent wear, corrosion resistance, and high temperature behavior of the fabricated coatings. In this application, silicon metal is deposited on graphite. This invention discloses the optimum processing parameters for as-sprayed coating qualities. The method also discloses the effect of thermal cycling on silicon samples in an inert helium atmosphere at about 1600.degree.C. which transforms the coating to silicon carbide.

  13. Method of fabricating silicon carbide coatings on graphite surfaces

    DOEpatents

    Varacalle, D.J. Jr.; Herman, H.; Burchell, T.D.

    1994-07-26

    The vacuum plasma spray process produces well-bonded, dense, stress-free coatings for a variety of materials on a wide range of substrates. The process is used in many industries to provide for the excellent wear, corrosion resistance, and high temperature behavior of the fabricated coatings. In this application, silicon metal is deposited on graphite. This invention discloses the optimum processing parameters for as-sprayed coating qualities. The method also discloses the effect of thermal cycling on silicon samples in an inert helium atmosphere at about 1,600 C which transforms the coating to silicon carbide. 3 figs.

  14. Dynamics of laser-induced surface phase explosion in silicon

    NASA Astrophysics Data System (ADS)

    Kudryashov, Sergey I.; Paul, Stanley; Lyon, Kevin; Allen, Susan D.

    2011-06-01

    Time-resolved ultrasonic studies revealed a second, delayed ablative pressure pulse after the first primary plasma pressure pulse in a silicon wafer irradiated by a UV nanosecond laser. The intensity-dependent delay time for the second pulse indicates the existence of a corresponding intensity-dependent homogeneous vapor bubble nucleation time in the superheated molten silicon prior to its phase explosion and ablative removal, since the integral pressure correlates with the ablation rate. A transient hot ablative plasma with calculated peak temperature ˜30-90 eV and pressure ˜20-110 GPa is suggested to superheat the bulk silicon via short-wavelength recombination and Bremsstrahlung emission.

  15. Surface morphological instability of silicon (100) crystals under microwave ion physical etching

    NASA Astrophysics Data System (ADS)

    Yafarov, R. K.; Shanygin, V. Ya.

    2016-02-01

    This paper presents the results of studies of the dynamics of relaxation modification of the morphological characteristics of atomically clean surfaces of silicon (100) crystals with different types of conductivity after microwave ion physical etching in an argon atmosphere. For the first time, the effect of the electronic properties on the morphological characteristics and the surface free energy of silicon crystals is experimentally shown and proven by physicochemical methods.

  16. Automated Array Assembly Task In-depth Study of Silicon Wafer Surface Texturizing

    NASA Technical Reports Server (NTRS)

    Jones, G. T.; Chitre, S.; Rhee, S. S.; Allison, K. L.

    1979-01-01

    A low cost wafer surface texturizing process was studied. An investigation of low cost cleaning operations to clean residual wax and organics from the surface of silicon wafers was made. The feasibility of replacing dry nitrogen with clean dry air for drying silicon wafers was examined. The two stage texturizing process was studied for the purpose of characterizing relevant parameters in large volume applications. The effect of gettering solar cells on photovoltaic energy conversion efficiency is described.

  17. An investigation of RF sputter etched silicon surfaces using helium ion backscatter

    NASA Technical Reports Server (NTRS)

    Sachse, G. W.; Miller, W. E.; Gross, C.

    1975-01-01

    The effect of RF sputter etching on the (111) surface of silicon was studied by observing backscatter spectra from a 2 MeV, He-4(+) beam oriented along the silicon 111 orientation channel. Silicon samples were RF sputter etched in an argon discharge at electrode bias potentials ranging from 0.5 to 2.5 kV. The samples were sputter etched for a time sufficient for the lattice damage to reach saturation. Analysis of these samples revealed that the thickness of this damage layer and the concentration of trapped argon increased with electrode bias potential. An annealing study of these damaged surfaces was carried out to 900 C.

  18. Enhanced cell adhesion to silicone implant material through plasma surface modification.

    PubMed

    Hauser, J; Zietlow, J; Köller, M; Esenwein, S A; Halfmann, H; Awakowicz, P; Steinau, H U

    2009-12-01

    Silicone implant material is widely used in the field of plastic surgery. Despite its benefits the lack of biocompatibility this material still represents a major problem. Due to the surface characteristics of silicone, protein adsorption and cell adhesion on this polymeric material is rather low. The aim of this study was to create a stable collagen I surface coating on silicone implants via glow-discharge plasma treatment in order to enhance cell affinity and biocompatibility of the material. Non-plasma treated, collagen coated and conventional silicone samples (non-plasma treated, non-coated) served as controls. After plasma treatment the change of surface free energy was evaluated by drop-shape analysis. The quality of the collagen coating was analysed by electron microscopy and Time-Of-Flight Secondary Ion Mass Spectrometry. For biocompatibility tests mouse fibroblasts 3T3 were cultivated on the different silicone surfaces and stained with calcein-AM and propidium iodine to evaluate cell viability and adherence. Analysis of the different surfaces revealed a significant increase in surface free energy after plasma pre-treatment. As a consequence, collagen coating could only be achieved on the plasma activated silicone samples. The in vitro tests showed that the collagen coating led to a significant increase in cell adhesion and cell viability. PMID:19641852

  19. Effective surface passivation of p-type crystalline silicon with silicon oxides formed by light-induced anodisation

    NASA Astrophysics Data System (ADS)

    Cui, Jie; Grant, Nicholas; Lennon, Alison

    2014-12-01

    Electronic surface passivation of p-type crystalline silicon by anodic silicon dioxide (SiO2) was investigated. The anodic SiO2 was grown by light-induced anodisation (LIA) in diluted sulphuric acid at room temperature, a process that is significantly less-expensive than thermal oxidation which is widely-used in silicon solar cell fabrication. After annealing in oxygen and then forming gas at 400 °C for 30 min, the effective minority carrier lifetime of 3-5 Ω cm, boron-doped Czochralski silicon wafers with a phosphorus-doped 80 Ω/□ emitter and a LIA anodic SiO2 formed on the p-type surface was increased by two orders of magnitude to 150 μs. Capacitance-voltage measurements demonstrated a very low positive charge density of 3.4 × 1011 cm-2 and a moderate density of interface states of 6 × 1011 eV-1 cm-2. This corresponded to a silicon surface recombination velocity of 62 cm s-1, which is comparable with values reported for other anodic SiO2 films, which required higher temperatures and longer growth times, and significantly lower than oxides grown by chemical vapour deposition techniques. Additionally, a very low leakage current density of 3.5 × 10-10 and 1.6 × 10-9 A cm-2 at 1 and -1 V, respectively, was measured for LIA SiO2 suggesting its potential application as insulation layer in IBC solar cells and a barrier for potential induced degradation.

  20. Surface States and Effective Surface Area on Photoluminescent P-Type Porous Silicon

    NASA Technical Reports Server (NTRS)

    Weisz, S. Z.; Porras, A. Ramirez; Resto, O.; Goldstein, Y.; Many, A.; Savir, E.

    1997-01-01

    The present study is motivated by the possibility of utilizing porous silicon for spectral sensors. Pulse measurements on the porous-Si/electrolyte system are employed to determine the surface effective area and the surface-state density at various stages of the anodization process used to produce the porous material. Such measurements were combined with studies of the photoluminescence spectra. These spectra were found to shift progressively to the blue as a function of anodization time. The luminescence intensity increases initially with anodization time, reaches a maximum and then decreases with further anodization. The surface state density, on the other hand, increases with anodization time from an initial value of about 2 x 10(exp 12)/sq cm surface to about 1013 sq cm for the anodized surface. This value is attained already after -2 min anodization and upon further anodization remains fairly constant. In parallel, the effective surface area increases by a factor of 10-30. This behavior is markedly different from the one observed previously for n-type porous Si.

  1. Biomimetic surface-conducting silicone rubber obtained by physical deposition of MWCNT

    NASA Astrophysics Data System (ADS)

    Zylka, Pawel

    2015-06-01

    The paper presents a minimal approach to produce superhydrophobic, surface-conducting silicone rubber with a strongly developed surface modified with multiwall carbon nanotubes partially embedded in the silicone elastic matrix. The modification was achieved by physical deposition of carbon nanotube powder on a semi-liquid silicone rubber surface prior to its cross-linking. The resulting biomimetic material displayed superhydrophobic properties (static wetting angle >160°, sliding angle ∼10°), as well as elevated electric surface resistance (surface resistivity approx 18 kΩ). A piezoresistive hysteretic response with nonmonotonic change of the surface resistance accompanying substantial linear stretching was also demonstrated in the developed specimens displaying negative resistance change in a broad range of extension ratios, making them applicable as highly compliant, large-specific-area electrodes.

  2. Nanoetching process on silicon solar cell wafers during mass production for surface texture improvement.

    PubMed

    Ahn, Chisung; Kulkarni, Atul; Ha, Soohyun; Cho, Yujin; Kim, Jeongin; Park, Heejin; Kim, Taesung

    2014-12-01

    Major challenge in nanotechnology is to improve the solar cells efficiency. This can be achieved by controlling the silicon solar cell wafer surface structure. Herein, we report a KOH wet etching process along with an ultrasonic cleaning process to improve the surface texture of silicon solar cell wafers. We evaluated the KOH temperature, concentration, and ultra-sonication time. It was observed that the surface texture of the silicon solar wafer changed from a pyramid shape to a rectangular shape under edge cutting as the concentration of the KOH solution was increased. We controlled the etching time to avoid pattern damage and any further increase of the reflectance. The present study will be helpful for the mass processing of silicon solar cell wafers with improved reflectance. PMID:25971104

  3. In situ observation of reaction between metal and Si surface by low energy RBS/channeling

    NASA Astrophysics Data System (ADS)

    Hasegawa, Masataka; Kobayashi, Naoto

    1997-02-01

    We have developed a low energy Rutherford backscattering spectrometry (RBS)/ion channeling measurement system for the analysis of thin films and solid surfaces with the use of several tens keV hydrogen ions, and of a time-of-flight spectrometer which was originally developed by Mendenhall and Weller. The depth resolution of our system is better than that of conventional RBS system with MeV helium ions and silicon surface barrier detectors. This RBS/ion channeling system is small in size compared to the conventional RBS/ion channeling measurement system with the use of MeV He ions, because of the small ion accelerator for several tens keV ions. The analysis of crystalline thin films which utilizes ion channeling effect can be performed with this low energy RBS/ion channeling measurement system. The in situ observation of the thermal reaction between iron and silicon substrate with the use of this measurement system is demonstrated. The deposited Fe (3.3 ML) on Si(001) clean surface diffused into the substrate by 380 °C annealing, while on the hydrogen-terminated (dihydride) Si(001) the 480 °C annealing did not lead to the diffusion. Present results indicates that the hydrogen termination of Si(001) surface prevents the deposited Fe from diffusing into the substrate up to relatively high temperature compared to the clean surface.

  4. Pyramidal texturing of silicon surface via inorganic-organic hybrid alkaline liquor for heterojunction solar cells

    NASA Astrophysics Data System (ADS)

    Wang, Fengyou; Zhang, Xiaodan; Wang, Liguo; Jiang, Yuanjian; Wei, Changchun; Zhao, Ying

    2015-10-01

    We demonstrate a new class of silicon texturing approach based on inorganic (sodium hydroxide, NaOH) and organic (tetramethylammonium hydroxide, TMAH) alkaline liquor etching processes for photovoltaic applications. The first stage of inorganic alkaline etching textures the silicon surface rapidly with large pyramids and reduces the cost. The subsequent organic alkaline second-etching improves the coverage of small pyramids on the silicon surface and strip off the metallic contaminants produced by the first etching step. In addition, it could smoothen the surface of the pyramids to yield good morphology. In this study, the texturing duration of both etching steps was controlled to optimize the optical and electrical properties as well as the surface morphology and passivation characteristics of the silicon substrates. Compared with traditional inorganic NaOH texturing, this hybrid process yields smoother (111) facets of the pyramids, fewer residual Na+ ions on the silicon surface, and a shorter processing period. It also offers the advantage of lower cost compared with the organic texturing method based on the use of only TMAH. We applied this hybrid texturing process to fabricate silicon heterojunction solar cells, which showed a remarkable improvement compared with the cells based on traditional alkaline texturing processes.

  5. A high volume cost efficient production macrostructuring process. [for silicon solar cell surface treatment

    NASA Technical Reports Server (NTRS)

    Chitre, S. R.

    1978-01-01

    The paper presents an experimentally developed surface macro-structuring process suitable for high volume production of silicon solar cells. The process lends itself easily to automation for high throughput to meet low-cost solar array goals. The tetrahedron structure observed is 0.5 - 12 micron high. The surface has minimal pitting with virtually no or very few undeveloped areas across the surface. This process has been developed for (100) oriented as cut silicon. Chemi-etched, hydrophobic and lapped surfaces were successfully texturized. A cost analysis as per Samics is presented.

  6. Application of PECVD for bulk and surface passivation of high efficiency silicon solar cells

    SciTech Connect

    Krygowski, T.; Doshi, P.; Cai, L.; Doolittle, A.; Rohatgi, A.

    1995-08-01

    Plasma enhanced chemical vapor deposition (PECVD) passivation of bulk and surface defects has been shown to be an important technique to improve the performance of multicrystalline silicon (mc-Si) and single crystalline silicon solar cells. In this paper, we report the status of our on-going investigation into the bulk and surface passivation properties of PECVD insulators for photovoltaic applications. The objective of this paper is to demonstrate the ability of PECVD films to passivate the front (emitter) surface, bulk, and back surface by proper tailoring of deposition and post-PECVD annealing conditions.

  7. Dwell Time and Surface Parameter Effects on Removal of Silicone Oil From D6ac Steel Using TCA

    NASA Technical Reports Server (NTRS)

    Boothe, R. E.

    2003-01-01

    This study was conducted to evaluate the impact of dwell time, surface roughness, and the surface activation state on 1,1,1-trichloroethane's (TCA's) effectiveness for removing silicone oil from D6ac steel. Silicone-contaminated test articles were washed with TCA solvent, and then the surfaces were analyzed for residue, using Fourier transform infrared spectroscopy. The predominant factor affecting the ability to remove the silicone oil was surface roughness.

  8. Initiation time of near-infrared laser-induced slip on the surface of silicon wafers

    SciTech Connect

    Choi, Sungho; Jhang, Kyung-Young

    2014-06-23

    We have determined the initiation time of laser-induced slip on a silicon wafer surface subjected to a near-infrared continuous-wave laser by numerical simulations and experiments. First, numerical analysis was performed based on the heat transfer and thermoelasticity model to calculate the resolved shear stress and the temperature-dependent yield stress. Slip initiation time was predicted by finding the time at which the resolved shear stress reached the yield stress. Experimentally, the slip initiation time was measured by using a laser scattering technique that collects scattered light from the silicon wafer surface and detects strong scattering when the surface slip is initiated. The surface morphology of the silicon wafer surface after laser irradiation was also observed using an optical microscope to confirm the occurrence of slip. The measured slip initiation times agreed well with the numerical predictions.

  9. Initiation time of near-infrared laser-induced slip on the surface of silicon wafers

    NASA Astrophysics Data System (ADS)

    Choi, Sungho; Jhang, Kyung-Young

    2014-06-01

    We have determined the initiation time of laser-induced slip on a silicon wafer surface subjected to a near-infrared continuous-wave laser by numerical simulations and experiments. First, numerical analysis was performed based on the heat transfer and thermoelasticity model to calculate the resolved shear stress and the temperature-dependent yield stress. Slip initiation time was predicted by finding the time at which the resolved shear stress reached the yield stress. Experimentally, the slip initiation time was measured by using a laser scattering technique that collects scattered light from the silicon wafer surface and detects strong scattering when the surface slip is initiated. The surface morphology of the silicon wafer surface after laser irradiation was also observed using an optical microscope to confirm the occurrence of slip. The measured slip initiation times agreed well with the numerical predictions.

  10. Porous silicon reorganization: Influence on the structure, surface roughness and strain

    NASA Astrophysics Data System (ADS)

    Milenkovic, N.; Drießen, M.; Weiss, C.; Janz, S.

    2015-12-01

    Porous silicon and epitaxial thickening is a lift-off approach for silicon foil fabrication to avoid kerf losses and produce foils with thicknesses less than 50 μm. The crystal quality of the epitaxial silicon film strongly depends on the porous silicon template, which can be adapted through a reorganization process prior to epitaxy. In this work, we investigated the influence of reorganization on the structure of etched porous silicon layers. The reorganization processes were carried out in a quasi-inline Atmospheric Pressure Chemical Vapor Deposition reactor. Variations on the temperatures and process durations for the reorganization step were examined. The cross-sections showed that porous silicon requires temperatures of approximately 1150 °C to produce an excellent template for epitaxy. Atomic Force Microscopy measurements on the samples annealed at different temperatures showed the evolution of the pores from as-etched to a closed surface. These measurements confirm that the surface is not yet closed after 30 min of reorganization at 1000 °C. Different durations of the reorganization step at a fixed temperature of 1150 °C all lead to a closed surface with a comparable roughness of less than 0.5 nm. X-ray diffraction measurements show a change in the strain in the porous layer from tensile to compressive when the reorganization temperature is increased from 800 °C to 1150 °C. A longer reorganization at a fixed temperature of 1150 °C leads to a reduction in the strain without reducing the quality of the surface roughness. Defect density measurements on silicon layers deposited on those templates confirm an improvement of the template for longer reorganization times. This study shows that our porous silicon templates achieve lower surface roughness and strain values than those reported in other publications.

  11. FTIR studies of H 2O and D 2O decomposition on porous silicon surfaces

    NASA Astrophysics Data System (ADS)

    Gupta, P.; Dillon, A. C.; Bracker, A. S.; George, S. M.

    1991-04-01

    The decomposition of H 2O and D 2O on silicon surfaces was studied using transmission Fourier-transform infrared (FTIR) spectroscopy. These FTIR studies were performed in situ in an ultrahigh vacuum chamber using high surface area porous silicon samples. The FTIR spectra revealed that H 2O (D 2O) initially dissociates upon adsorption at 300 K to form SiH (SiD) and SiOH (SiOD) surface species, i.e., H 2O → SiH + SiOH. The decomposition of these surface species was then monitored using the SiH (SiD) stretch at 2090 cm -1 (1513 cm -1), SiOH (SiOD) stretch at 3680 cm -1 (2707 cm -1) and the SiOSi stretch at 900-1100 cm -1. As the silicon surface was annealed to 650 K, the FTIR spectra revealed that the SiOH surface species progressively decomposed to SiOSi species and additional SiH species, i.e., SiOH → SiH + SiOSi. Above 650 K, the SiH surface species decreased concurrently with the desorption of H -1 from the porous silicon surface. New blue-shifted infrared features in the SiH stretching region were observed at 2119, 2176 and 2268 cm -1 after annealing above 600 K. Additional infrared studies of partially hydrogen-covered porous silicon surfaces exposed to O 2 suggested that these blue-shifted SiH stretching vibrations were associated with silicon surface atoms backbonded to one, two or three oxygen atoms, respectively.

  12. Pyramidal surface textures for light trapping and antireflection in perovskite-on-silicon tandem solar cells.

    PubMed

    Schneider, Bennett W; Lal, Niraj N; Baker-Finch, Simeon; White, Thomas P

    2014-10-20

    Perovskite-on-silicon tandem solar cells show potential to reach > 30% conversion efficiency, but require careful optical control. We introduce here an effective light-management scheme based on the established pyramidal texturing of crystalline silicon cells. Calculations show that conformal deposition of a thin film perovskite solar cell directly onto the textured front surface of a high efficiency silicon cell can yield front surface reflection losses as low as 0.52mA/cm(2). Combining this with a wavelength-selective intermediate reflector between the cells additionally provides effective light-trapping in the high-bandgap top cell, resulting in calculated absolute efficiency gains of 2 - 4%. This approach provides a practical and effective method to adapt existing high efficiency silicon cell designs for use in tandem cells, with conversion efficiencies approaching 35%. PMID:25607299

  13. Surface-Assisted Laser Desorption Ionization of Low Molecular Organic Substances on Oxidized Porous Silicon

    NASA Astrophysics Data System (ADS)

    Shmigol, I. V.; Alekseev, S. A.; Lavrynenko, O. Yu.; Zaitsev, V. N.; Barbier, D.; Pokrovskiy, V. A.

    Desorption/ionization on silicon (DIOS) mass spectra of methylene blue (MB+Cl-) were studied using p+-type oxidized monofunctional porous silicon (PS-OX mono ) free layers. Reduction/protonation processes of methylene blue (MB) dye were investigated. It was shown that SiH x terminal sites on oxidized surface of porous silicon (PS-OX) are not the rate-determining factor for the reduction/protonation in DIOS. Tunneling of electron through the dielectric layer of nanostructures on silicon surface under effect of local electrostatic and electromagnetic fields is considered to be the most significant factor of adsorbate-adsorbent electron exchange and further laser-induced ion formation.

  14. Flux stabilization of silicon nitride microsieves by backpulsing and surface modification with PEG moieties.

    PubMed

    Gironès, M; Bolhuis-Versteeg, L A M; Lammertink, R G H; Wessling, M

    2006-07-15

    The influence of the surface properties of chemically modified silicon nitride microsieves on the filtration of protein solutions and defatted milk is described in this research. Prior to membrane filtrations, an antifouling polymer based on poly(ethylene glycol), poly(TMSMA-r-PEGMA) was synthesized and applied on silicon-based surfaces like silicon, silicon nitride, and glass. The ability of such coating to repel proteins like bovine serum albumin (BSA) was confirmed by ellipsometry and confocal fluorescence microscopy. In BSA and skimmed milk filtrations no differences could be seen between unmodified and PEG-coated membranes (decreasing permeability in time). On the other hand, reduced fouling was observed with PEG-modified microsieves in combination with backpulsing and air sparging. PMID:16603173

  15. Sol-gel preparation of low oxygen content, high surface area silicon nitride and imidonitride materials.

    PubMed

    Sardar, Kripasindhu; Bounds, Richard; Carravetta, Marina; Cutts, Geoffrey; Hargreaves, Justin S J; Hector, Andrew L; Hriljac, Joseph A; Levason, William; Wilson, Felix

    2016-04-01

    Reactions of Si(NHMe)4 with ammonia are effectively catalysed by small ammonium triflate concentrations, and can be used to produce free-standing silicon imide gels. Firing at various temperatures produces amorphous or partially crystallised silicon imidonitride/nitride samples with high surface areas and low oxygen contents. The crystalline phase is entirely α-Si3N4 and structural similarities are observed between the amorphous and crystallised materials. PMID:26931152

  16. Computational Studies of the Interaction of H/H2 with Diamond and Silicon Surfaces

    NASA Technical Reports Server (NTRS)

    Walch, Stephen P.; Goddard, William A., III; Cagin, Tahir; Arnold, James (Technical Monitor)

    1998-01-01

    The interaction of hydrogen atoms and molecules with diamond and silicon surfaces is important in several important applications. Two areas that we are interested are: 1) tribology (molecular level friction) and 2) the role of H atoms in silicon chemical vapor deposition (CVD). In the tribology area, H atoms can be used to tie off dangling bonds, which otherwise form bonds between adjacent surfaces, and lead to resistance to sliding the surfaces by each other. Processes which are important in understanding molecular level friction include barriers to addition of H/H2 to the surface and barriers to migration of H atoms on the surface. In the silicon CVD area, we have studied the process of H2 elimination from the 100 surface of silicon. Cluster models for the dime surfaces of diamond are presented. The unrelaxed 100 surface has carbene like surface carbon atoms; however, for the relaxed surface these dimerize to give rows of surface dimers and there is a significant amount of p bonding between the radical orbitals of the dimer. The 110 surface has zig-zag rows of carbon atoms with a dangling bond on each carbon atom. These dangling bonds are hybridized away from each other and thus interact less strongly than for the 100 surface. Finally, the 111 surface has surface C atoms arranged in a triangular pattern and the surface dangling bonds are well separated from each other (second nearest neighbor distance) leading to almost no interaction between adjacent dangling bonds. These qualitative features may be quantified by computing the overlap of adjacent dangling bonds in a GVB(pp) calculation. The overlaps are 0.462, 0.292, and 0.016 for the diamond 100, 110, and 111 surfaces, respectively.

  17. Atmospheric vapor phase deposition of nanometer-thick anti-stiction fluoropolymer coatings for silicon surfaces

    NASA Astrophysics Data System (ADS)

    Itoh, Shintaro; Takahashi, Kazuhiro; Morita, Hiroyuki; Fukuzawa, Kenji; Zhang, Hedong

    2016-06-01

    Anti-stiction coatings for silicon surfaces are a key technology to prevent the failure of nanoelectromechanical systems (NEMS) during operation and improve the forming accuracy in nanoimprint technology. In this study, we propose an atmospheric vapor phase deposition method to coat a silicon surface with fluoropolymers such as the perfluoropolyethers Fomblin Zdol 2000 and Zdol 4000. Thickness distributions, surface energies, coverages, and stiction forces for the deposited films were evaluated experimentally. The proposed method resulted in over 90% coverage with a film thickness of about 1 nm. The film thickness uniformity was around 0.1 nm over an area of 5 × 5 mm2. This coating effectively reduced the stiction forces by half compared with a bare silicon surface.

  18. Surface roughening of silicon, thermal silicon dioxide, and low-k dielectric coral films in argon plasma

    SciTech Connect

    Yin Yunpeng; Sawin, Herbert H.

    2008-01-15

    The surface roughness evolutions of single crystal silicon, thermal silicon dioxide (SiO{sub 2}), and low dielectric constant film coral in argon plasma have been measured by atomic force microscopy as a function of ion bombardment energy, ion impingement angle, and etching time in an inductively coupled plasma beam chamber, in which the plasma chemistry, ion energy, ion flux, and ion incident angle can be adjusted independently. The sputtering yield (or etching rate) scales linearly with the square root of ion energy at normal impingement angle; additionally, the angular dependence of the etching yield of all films in argon plasma followed the typical sputtering yield curve, with a maximum around 60 deg. -70 deg. off-normal angle. All films stayed smooth after etching at normal angle but typically became rougher at grazing angles. In particular, at grazing angles the rms roughness level of all films increased if more material was removed; additionally, the striation structure formed at grazing angles can be either parallel or transverse to the beam impingement direction, which depends on the off-normal angle. More interestingly, the sputtering caused roughness evolution at different off-normal angles can be qualitatively explained by the corresponding angular dependent etching yield curve. In addition, the roughening at grazing angles is a strong function of the type of surface; specifically, coral suffers greater roughening compared to thermal silicon dioxide.

  19. Role of hydrogen plasma pretreatment in improving passivation of the silicon surface for solar cells applications.

    PubMed

    Wang, Fengyou; Zhang, Xiaodan; Wang, Liguo; Jiang, Yanjian; Wei, Changchun; Sun, Jian; Zhao, Ying

    2014-09-10

    We have investigated the role of hydrogen plasma pretreatment in promoting silicon surface passivation, in particular examining its effects on modifying the microstructure of the subsequently deposited thin hydrogenated amorphous silicon (a-Si:H) passivation film. We demonstrate that pretreating the silicon surface with hydrogen plasma for 40 s improves the homogeneity and compactness of the a-Si:H film by enhancing precursor diffusion and thus increasing the minority carrier lifetime (τ(eff)). However, excessive pretreatment also increases the density of dangling bond defects on the surface due to etching effects of the hydrogen plasma. By varying the duration of hydrogen plasma pretreatment in fabricating silicon heterojunction solar cells based on textured substrates, we also demonstrate that, although the performance of the solar cells shows a similar tendency to that of the τ(eff) on polished wafers, the optimal duration is prolonged owing to the differences in the surface morphology of the substrates. These results suggest that the hydrogen plasma condition must be carefully regulated to achieve the optimal level of surface atomic hydrogen coverage and avoid the generation of defects on the silicon wafer. PMID:25141300

  20. Rapid Covalent Modification of Silicon Oxide Surfaces through Microwave-Assisted Reactions with Alcohols.

    PubMed

    Lee, Austin W H; Gates, Byron D

    2016-07-26

    We demonstrate the method of a rapid covalent modification of silicon oxide surfaces with alcohol-containing compounds with assistance by microwave reactions. Alcohol-containing compounds are prevalent reagents in the laboratory, which are also relatively easy to handle because of their stability against exposure to atmospheric moisture. The condensation of these alcohols with the surfaces of silicon oxides is often hindered by slow reaction kinetics. Microwave radiation effectively accelerates this condensation reaction by heating the substrates and/or solvents. A variety of substrates were modified in this demonstration, such as silicon oxide films of various thicknesses, glass substrates such as microscope slides (soda lime), and quartz. The monolayers prepared through this strategy demonstrated the successful formation of covalent surface modifications of silicon oxides with water contact angles of up to 110° and typical hysteresis values of 2° or less. An evaluation of the hydrolytic stability of these monolayers demonstrated their excellent stability under acidic conditions. The techniques introduced in this article were successfully applied to tune the surface chemistry of silicon oxides to achieve hydrophobic, oleophobic, and/or charged surfaces. PMID:27396288

  1. Hydrogen passivation of silicon surfaces: A classical molecular-dynamics study

    NASA Astrophysics Data System (ADS)

    Hansen, U.; Vogl, P.

    1998-05-01

    We present a computationally efficient classical many-body potential that is capable of predicting the energetics of bulk silicon, silicon surfaces, and the interaction of hydrogen with silicon. The potential includes well established models for one-component Si and H systems and incorporates a newly developed Si-H interaction. It is shown that the present model yields hydrogen diffusion barriers, hydrogen abstraction, and H2 desorption reactions on silicon surfaces in excellent agreement with experiment and/or previous ab initio results. Detailed molecular-dynamics simulations are performed that elucidate the complex balance between adsorption and abstraction reactions during hydrogen passivation on Si(100) surfaces. We find a very high sticking coefficient of 0.6 for atomic hydrogen on clean Si(100)2×1 surfaces and provide a detailed qualitative and quantitative explanation for this prediction. Furthermore, we find that there are two efficient competing surface reactions of atomic hydrogen with monohydride Si surfaces. One is the Eley-Rideal abstraction of H2 molecules, and the other one is adsorption. Additionally, adsorbed hydrogen on hydrogenated Si surfaces acts as a reservoir that can lead to complete passivation of Si surfaces despite the efficient creation of voids in the hydrogen layer by the abstraction.

  2. Surface wave accelerator based on silicon carbide: theoretical study

    SciTech Connect

    Kalmykov, S.; Korobkin, D.; Neuner, B.; Shvets, G.

    2009-01-22

    Compact near-field solid-state accelerating structure powered by a carbon dioxide (CO{sub 2}) laser is considered. The accelerating luminous transverse magnetic mode is excited in a few-micron wide evacuated planar channel between two silicon carbide (SiC) films grown on silicon (Si) wafers. Laser coupling to this mode is accomplished through the properly designed Si gratings. Operating wavelength is dictated by the frequency-dependent dielectric permittivity of SiC and the channel width. The geometric loss factor {kappa} of the accelerating mode is computed. It is found that the unwanted excitation of the guided modes in Si wafers reduces the laser coupling efficiency and increases the fields inside the Si wafer.

  3. Porous silicon photonic crystals for detection of infections

    NASA Astrophysics Data System (ADS)

    Gupta, B.; Guan, B.; Reece, P. J.; Gooding, J. J.

    2012-10-01

    In this paper we demonstrate the possibility of modifying porous silicon (PSi) particles with surface chemistry and immobilizing a biopolymer, gelatin for the detection of protease enzymes in solution. A rugate filter, a one-dimensional photonic crystal, is fabricated that exhibits a high-reflectivity optical resonance that is sensitive to small changes in the refractive index. To immobilize gelatin in the pores of the particles, the hydrogen-terminated silicon surface was first modified with an alkyne, 1,8-nonadiyne via hydrosilylation to protect the silicon surfaces from oxidation. This modification allows for further functionality to be added such as the coupling of gelatin. Exposure of the gelatin modified particles to the protease subtilisin in solution causes a change in the refractive index, resulting in a shift of the resonance to shorter wavelengths, indicating cleavage of organic material within the pores. The ability to monitor the spectroscopic properties of microparticles, and shifts in the optical signature due to changes in the refractive index of the material within the pore space, is demonstrated.

  4. Surface acoustic waves/silicon monolithic sensor processor

    NASA Technical Reports Server (NTRS)

    Kowel, S. T.; Kornreich, P. G.; Fathimulla, M. A.; Mehter, E. A.

    1981-01-01

    Progress is reported in the creation of a two dimensional Fourier transformer for optical images based on the zinc oxide on silicon technology. The sputtering of zinc oxide films using a micro etch system and the possibility of a spray-on technique based on zinc chloride dissolved in alcohol solution are discussed. Refinements to techniques for making platinum silicide Schottky barrier junctions essential for constructing the ultimate convolver structure are described.

  5. Towards the characterization of silicon surfaces: Solid state nuclear magnetic resonance studies

    NASA Astrophysics Data System (ADS)

    Caylor, Rebecca Anne

    One of the developing areas in silicon chemistry is in small silicon particles, primarily the nanoparticles regime. When on the 'nano' scale, silicon possesses very different properties and characteristics from bulk silicon. These properties include novel optical and electronic properties that are size dependent. Semiconductor nanoparticles possess a unique bright photoluminescence when in the nanoparticle regime. The photoluminescence in the nanoparticle regime answers the problem of inefficient emissions, which have previously been a problem in bulk silicon, for use in solar cells. Nanoparticle silicon (np-Si) is also biocompatible, allowing for the use in various biological applications including biological tracers, biosensors, delivery of medicine, as well as many others. Although np-Si is widely used, its surface structure still remains largely debated. The surface structure of np-Si is of critical importance as it affects the reactivity of the sample as well as the properties the samples possess. Relative to other silicon samples, np-Si lends itself to be studied by solid state NMR due to its higher surface area, although other types of silicon samples have been studied to some degree in this dissertation project. The surface structure and adjacent interior of np-Si, obtained as commercially available silicon nanopowder, were studied in this project using multinuclear, solid-state NMR spectroscopy. The results are consistent with an overall picture in which the bulk of the np-Si interior consists of highly ordered ('crystalline') silicon atoms, each bound tetrahedrally to four other silicon atoms. From a combination of 1H and 29Si magic-angle-spinning (MAS) NMR results and quantum mechanical 29Si chemical shift calculations, silicon atoms on the surface of 'as-received' np-Si were found to exist in a variety of chemical structures, including primarily structures of the types (Si-O-)n(Si-) 3-nSi-H (with n = 1--3) and (Si-O-)2Si(H)OH, where Si stands for a

  6. Interfacial chemical bonding state and band alignment of CaF{sub 2}/hydrogen-terminated diamond heterojunction

    SciTech Connect

    Liu, J. W.; Liao, M. Y.; Cheng, S. H.; Imura, M.; Koide, Y.

    2013-03-28

    CaF{sub 2} films are deposited on hydrogen-terminated diamond (H-diamond) by a radio-frequency sputter-deposition technique at room temperature. Interfacial chemical bonding state and band alignment of CaF{sub 2}/H-diamond heterojunction are investigated by X-ray photoelectron spectroscopy. It is confirmed that there are only C-Ca bonds at the CaF{sub 2}/H-diamond heterointerface. Valence and conductance band offsets of the CaF{sub 2}/H-diamond heterojunciton are determined to be 3.7 {+-} 0.2 and 0.3 {+-} 0.2 eV, respectively. It shows a type I straddling band configuration. The large valence band offset suggests advantage of the CaF{sub 2}/H-diamond heterojunciton for the development of high power and high frequency field effect transistors.

  7. Surface/subsurface observation and removal mechanisms of ground reaction bonded silicon carbide

    NASA Astrophysics Data System (ADS)

    Yao, Wang; Zhang, Yu-Min; Han, Jie-cai; Zhang, Yun-long; Zhang, Jian-han; Zhou, Yu-feng; Han, Yuan-yuan

    2006-01-01

    Reaction Bonded Silicon Carbide (RBSiC) has long been recognized as a promising material for optical applications because of its unique combination of favorable properties and low-cost fabrication. Grinding of silicon carbide is difficult because of its high hardness and brittleness. Grinding often induces surface and subsurface damage, residual stress and other types of damage, which have great influence on the ceramic components for optical application. In this paper, surface integrity, subsurface damage and material removal mechanisms of RBSiC ground using diamond grinding wheel on creep-feed surface grinding machine are investigated. The surface and subsurface are studied with scanning electron microscopy (SEM) and optical microscopy. The effects of grinding conditions on surface and subsurface damage are discussed. This research links the surface roughness, surface and subsurface cracks to grinding parameters and provides valuable insights into the material removal mechanism and the dependence of grind induced damage on grinding conditions.

  8. Light-induced metal-like surface of silicon photonic waveguides

    PubMed Central

    Grillanda, Stefano; Morichetti, Francesco

    2015-01-01

    The surface of a material may exhibit physical phenomena that do not occur in the bulk of the material itself. For this reason, the behaviour of nanoscale devices is expected to be conditioned, or even dominated, by the nature of their surface. Here, we show that in silicon photonic nanowaveguides, massive surface carrier generation is induced by light travelling in the waveguide, because of natural surface-state absorption at the core/cladding interface. At the typical light intensity used in linear applications, this effect makes the surface of the waveguide behave as a metal-like frame. A twofold impact is observed on the waveguide performance: the surface electric conductivity dominates over that of bulk silicon and an additional optical absorption mechanism arises, that we named surface free-carrier absorption. These results, applying to generic semiconductor photonic technologies, unveil the real picture of optical nanowaveguides that needs to be considered in the design of any integrated optoelectronic device. PMID:26359202

  9. Protein-repellent silicon nitride surfaces: UV-induced formation of oligoethylene oxide monolayers.

    PubMed

    Rosso, Michel; Nguyen, Ai T; de Jong, Ed; Baggerman, Jacob; Paulusse, Jos M J; Giesbers, Marcel; Fokkink, Remko G; Norde, Willem; Schroën, Karin; van Rijn, Cees J M; Zuilhof, Han

    2011-03-01

    The grafting of polymers and oligomers of ethylene oxide onto surfaces is widely used to prevent nonspecific adsorption of biological material on sensors and membrane surfaces. In this report, we show for the first time the robust covalent attachment of short oligoethylene oxide-terminated alkenes (CH(3)O(CH(2)CH(2)O)(3)(CH(2))(11)-(CH═CH(2)) [EO(3)] and CH(3)O(CH(2)CH(2)O)(6)(CH(2))(11)-(CH═CH(2)) [EO(6)]) from the reaction of alkenes onto silicon-rich silicon nitride surfaces at room temperature using UV light. Reflectometry is used to monitor in situ the nonspecific adsorption of bovine serum albumin (BSA) and fibrinogen (FIB) onto oligoethylene oxide coated silicon-rich silicon nitride surfaces (EO(n)-Si(x)N(4), x > 3) in comparison with plasma-oxidized silicon-rich silicon nitride surfaces (SiO(y)-Si(x)N(4)) and hexadecane-coated Si(x)N(4) surfaces (C(16)-Si(x)N(4)). A significant reduction in protein adsorption on EO(n)-Si(x)N(4) surfaces was achieved, adsorption onto EO(3)-Si(x)N(4) and EO(6)-Si(x)N(4) were 0.22 mg m(-2) and 0.08 mg m(-2), respectively. The performance of the obtained EO(3) and EO(6) layers is comparable to those of similar, highly protein-repellent monolayers formed on gold and silver surfaces. EO(6)-Si(x)N(4) surfaces prevented significantly the adsorption of BSA (0.08 mg m(-2)). Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), X-ray reflectivity and static water contact angle measurements were employed to characterize the modified surfaces. In addition, the stability of EO(6)-Si(x)N(4) surfaces in phosphate-buffered saline solution (PBS) and alkaline condition (pH 10) was studied. Prolonged exposure of the surfaces to PBS solution for 1 week or alkaline condition for 2 h resulted in only minor degradation of the ethylene oxide moieties and no oxidation of the Si(x)N(4) substrates was observed. Highly stable antifouling coatings on Si(x)N(4) surfaces significantly broaden the application potential of silicon

  10. Surface transport kinetics in low-temperature silicon deposition determined from topography evolution

    NASA Astrophysics Data System (ADS)

    Bray, K. R.; Parsons, G. N.

    2002-01-01

    In this article, surface transport kinetics during low-temperature silicon thin film deposition are characterized using time dependent surface topography and dynamic scaling models. Analysis of surface morphology indicates that diffusion of adsorbed species dominates surface transport, with a characteristic diffusion length that increases with surface temperature. A diffusion activation barrier of ~0.2 eV is obtained, consistent with hydrogen-mediated adspecies diffusion on the growth silicon surface. Samples are compared over a range of deposition temperatures (25 to 350 °C) and film thickness (20 to 5000 Å) deposited using silane with helium or argon dilution, on glass and silicon substrates. Self-similar surface structure is found to depend on detailed film growth conditions, but is independent of film thickness after nuclei coalescence. For films deposited using helium dilution, static and dynamic scaling parameters are consistent with self-similar fractal geometry scaling, and the lateral correlation length increases from 45 to 150 nm as temperature increases from 25 to 150 °C. These results are discussed in relation to current silicon deposition models and with topography evolution observed during low temperature growth of other amorphous material systems.