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1

Direct tunneling stress-induced leakage current in ultrathin HfO2/SiO2 gate dielectric stacks  

NASA Astrophysics Data System (ADS)

The conduction mechanism(s) and behavior of direct tunneling stress-induced leakage current (SILC) through ultrathin hafnium oxide (HfO2)/silicon dioxide (SiO2) dual layer gate stack in metal-oxide-semiconductor (MOS) devices have been experimentally investigated in-depth. Both transient and steady-state SILCs have been studied after constant voltage stress (CVS) and constant current stress (CCS) in n-MOS capacitors with negative bias on the tantalum nitride (TaN) gate. The present report clearly indicates that the observed steady-state SILC is due to assisted tunneling via both monoenergetic trapped positive charges and neutral electron traps generated in the HfO2 layer during either CVS or CCS. SILC measured immediately after stress decays slowly due to tunnel detrapping of stress-induced trapped holes in the HfO2 layer. Furthermore, the mechanisms for stress-induced charge carrier generation/trapping and trap creation in the dielectric have been discussed. Our analysis also shows that CVS degrades the dielectric integrity more severely than CCS in the 4.2nm physically thick HfO2/SiO2 stack.

Samanta, Piyas; Man, Tsz Yin; Zhang, Qingchun; Zhu, Chunxiang; Chan, Mansun

2006-11-01

2

TDDB characteristic and breakdown mechanism of ultra-thin SiO2/HfO2 bilayer gate dielectrics  

NASA Astrophysics Data System (ADS)

The characteristics of TDDB (time-dependent dielectric breakdown) and SILC (stress-induced leakage current) for an ultra-thin SiO2/HfO2 gate dielectric stack are studied. The EOT (equivalent-oxide-thickness) of the gate stack (Si/SiO2/HfO2/TiN/TiAl/TiN/W) is 0.91 nm. The field acceleration factor extracted in TDDB experiments is 1.59 scm/MV, and the maximum voltage is 1.06 V when the devices operate at 125 C for ten years. A detailed study on the defect generation mechanism induced by SILC is presented to deeply understand the breakdown behavior. The trap energy levels can be calculated by the SILC peaks: one SILC peak is most likely to be caused by the neutral oxygen vacancy in the HfO2 bulk layer at 0.51 eV below the Si conduction band minimum; another SILC peak is induced by the interface traps, which are aligned with the silicon conduction band edge. Furthermore, the great difference between the two SILC peaks demonstrates that the degeneration of the high-k layer dominates the breakdown behavior of the extremely thin gate dielectric.

Fenfen, Tao; Hong, Yang; Bo, Tang; Zhaoyun, Tang; Yefeng, Xu; Jing, Xu; Qingpu, Wang; Jiang, Yan

2014-06-01

3

Scaling of HfO2 dielectric on CVD graphene  

NASA Astrophysics Data System (ADS)

The deposition of ultra-thin metal oxides on graphene is challenging due to the inert nature of the sp2 bonded graphene lattice. The feasibility of e-beam deposition of hafnium and hafnium oxide layers as seeds for further growth by atomic layer deposition on graphene CVD graphene is presented here. It is shown that metallic hafnium deposited in an ultra high vacuum environment readily reacts with graphene, forming a metal-carbide, rendering it unsuitable as a seed layer for the deposition of gate oxide materials. The deposition of HfO2 by reactive e-beam under an O2 partial pressure on the other hand eliminates the reaction with the underlying graphene. The uniformity of the e-beam HfO2 seed layers is found to control the uniformity of the subsequent films deposited by atomic layer deposition. Contrary to previous studies on graphite and exfoliated graphene substrates it is found that the uniformity and thickness scalability of atomic layer deposited thin films is limited on CVD graphene, most likely due to transfer induced residues on the graphene surface.

McDonnell, S.; Azcatl, A.; Mordi, G.; Floresca, C.; Pirkle, A.; Colombo, L.; Kim, J.; Kim, M.; Wallace, R. M.

2014-03-01

4

Improvement in electrical characteristics of HfO2 gate dielectrics treated by remote NH3 plasma  

NASA Astrophysics Data System (ADS)

We report the structural and electrical characteristics of hafnium oxide (HfO2) gate dielectrics treated by remote NH3 plasma under various radio-frequency (RF) powers at a low temperature. Significant increase of effective dielectric constant (keff), decrease of capacitance equivalent thickness (CET), reduction in leakage current density, and suppression of the interfacial layer thickness were observed with the increase of the RF power in the remote NH3 plasma treatment. The effects of hydrogen passivation and depassivation on the HfO2/Si interface due to the remote NH3 plasma treatment were also observed by the variation of photoluminescence (PL) intensity, indicating that the PL measurement is applicable to probe the interfacial properties. An ultrathin interfacial layer (0.3 nm), a high keff, (20.9), a low leakage current density (9 10-6 A/cm2), and a low CET (1.9 nm) in the nitrided HfO2 film were achieved, demonstrating that the nitridation process using remote NH3 plasma under a high RF power at a low temperature is a promising way to improve in electrical properties of high-K gate dielectrics.

Huang, Li-Tien; Chang, Ming-Lun; Huang, Jhih-Jie; Lin, Hsin-Chih; Kuo, Chin-Lung; Lee, Min-Hung; Liu, Chee Wee; Chen, Miin-Jang

2013-02-01

5

Electrical Characteristics of Ozone-Oxidized HfO2 Gate Dielectrics  

NASA Astrophysics Data System (ADS)

Electrical and reliability characteristics of HfO2 gate dielectrics prepared by low-temperature ozone (O3) oxidation of ultra thin Hf metal were investigated. Compared with control HfO2 annealed in O2 ambient, HfO2 annealed in O3 ambient exhibited excellent characteristics such as lower leakage current density, lower hysteresis, lower frequency dispersion, lower degree of charge trapping (? Vg), and larger charge to breakdown (Qbd) under electrical stress. The improved electrical and reliability characteristics can be attributed to the lower density of charge trap sites which are related to nonstoichiometry and oxygen vacancy. HfO2 prepared by O3 oxidation is a promising alternative gate dielectric for future metal-oxide-semiconductor (MOS) device applications.

Sim, Hyunjun; Chang, Hyosik; Hwang, Hyunsang

2003-04-01

6

High performance organic field-effect transistors with ultra-thin HfO2 gate insulator deposited directly onto the organic semiconductor  

NASA Astrophysics Data System (ADS)

We have produced stable organic field-effect transistors (OFETs) with an ultra-thin HfO2 gate insulator deposited directly on top of rubrene single crystals by atomic layer deposition (ALD). We find that ALD is a gentle deposition process to grow thin films without damaging rubrene single crystals, as results these devices have a negligibly small threshold voltage and are very stable against gate-bias-stress, and the mobility exceeds 1 cm2/V s. Moreover, the devices show very little degradation even when kept in air for more than 2 months. These results demonstrate thin HfO2 layers deposited by ALD to be well suited as high capacitance gate dielectrics in OFETs operating at small gate voltage. In addition, the dielectric layer acts as an effective passivation layer to protect the organic semiconductor.

Ono, S.; Husermann, R.; Chiba, D.; Shimamura, K.; Ono, T.; Batlogg, B.

2014-01-01

7

Characteristics of Fluorine Implantation for HfO2 Gate Dielectrics with High-Temperature Postdeposition Annealing  

NASA Astrophysics Data System (ADS)

In this work, we describe the characteristics of silicon surface fluorine implantation (SSFI) for HfO2 films with high-temperature postdeposition annealing. The thermal stability of HfO2 gate dielectrics is much improved owing to the incorporation of fluorine into HfO2 thin films. The gate leakage current of the SSFI HfO2 films is about three orders less than that of samples without any fluorine implantation. In addition, improvements in stress-induced leakage current (SILC) and charge trapping characteristics are realized in the HfO2 films with the SSFI. The incorporation of fluorine atoms into the HfO2 films reduces not only interface dangling bonds but also bulk traps, which is responsible for the improvements in properties.

Lai, Chao Sung; Wu, Woei Cherng; Wang, Jer Chyi; Chao, Tien Sheng

2006-04-01

8

Cubic HfO2 Doped with Y2O3 for Advanced Gate Dielectrics by MBE.  

NASA Astrophysics Data System (ADS)

High ? HfO2 (? =20) is currently employed as an alternative gate dielectric replacing SiO2 in CMOS scaling. There are three known crystal structures of HfO2, monoclinic, cubic, and tetragonal with varying dielectric constants [1]. Recently we showed HfO2 films epitaxially grown on GaAs(100) formed the stable monoclinic phase (?=? = 90 and ? 99) with the a and b axes aligned with the in-plane GaAs100axes resulting in four equivalent domains. This work demonstrates the successful alteration of the crystal structure of HfO2 from the lower ? monoclinic phase to the higher ? (? =30) cubic phase stabilized through epitaxy on GaAs(100) and Si(100) with the aid of Y2O3 doping ( 20% based on XPS). X-ray diffraction scans on these films clearly indicated the cubic symmetry. Doping Y2O3 is also to enhance the thermal stability of amorphous HfO2. Y2O3 doping was shown to help raise the re-crystallization temperature of HfO2 to becompatible with high temperature processing. [1] X. Zhao et al, PRB 65, 233106, (2002).

Yang, Zhikai; Lee, W. C.; Chang, Pen; Huang, Molin; Huang, Yi Lin; Hong, Minghwei; Huang, C. M.; Hsu, C. H.; Kwo, Raynien

2006-03-01

9

Grain boundary-driven leakage path formation in HfO 2 dielectrics  

NASA Astrophysics Data System (ADS)

The evolution over time of the leakage current in HfO 2-based MIM capacitors under continuous or periodic constant voltage stress (CVS) was studied for a range of stress voltages and temperatures. The data were analyzed based on the results of conductive atomic force microscopy (AFM) measurements demonstrating preferential current flow along grain boundaries (GBs) in the HfO 2 dielectric and ab initio calculations, which show the formation of a conductive sub-band due to the precipitation of oxygen vacancies at the GBs. The simulations using the statistical multi-phonon trap-assisted tunneling (TAT) current description successfully reproduced the experimental leakage current stress time dependency by using the calculated energy characteristics of the O-vacancies. The proposed model suggests that the observed reversible increase in the stress current is caused by segregation of the oxygen vacancies at the GBs and their conversion to the TAT-active charge state caused by reversible electron trapping during CVS.

Bersuker, G.; Yum, J.; Vandelli, L.; Padovani, A.; Larcher, L.; Iglesias, V.; Porti, M.; Nafra, M.; McKenna, K.; Shluger, A.; Kirsch, P.; Jammy, R.

2011-11-01

10

Constant voltage stress induced degradation in HfO2/SiO2 gate dielectric stacks  

NASA Astrophysics Data System (ADS)

Defect generation in HfO2/SiO2 gate dielectric stacks under constant voltage stress is investigated. It is found that the stress induced electrical degradation in HfO2/SiO2 stacks is different than in the SiO2 layer. The variation of the gate leakage current with different polarities shows different degradation characteristics after stress. Positive charge generation is also observed under both negative and positive gate voltage polarities. These degradation phenomena are explained by the composite effect of three components: neutral trap generation, electron trapping, and positive charge generation in the gate stacks.

Xu, Zhen; Houssa, Michel; Carter, Richard; Naili, Mohamed; De Gendt, Stefan; Heyns, Marc

2002-06-01

11

Impact of titanium addition on film characteristics of HfO2 gate dielectrics deposited by atomic layer deposition  

NASA Astrophysics Data System (ADS)

The impact of 8-to 45-at. % Ti on physical and electrical characteristics of atomic-layer-deposited and annealed hafnium dioxide was studied using vacuum-ultraviolet spectroscopic ellipsometry, secondary ion mass spectroscopy, transmission electron microscopy, atomic force microscopy, x-ray diffraction, Rutherford backscattering spectroscopy, x-ray photoelectron spectroscopy, and x-ray reflectometry. The role of Ti addition on the electrical performance is investigated using molybdenum (Mo)-gated capacitors. The film density decreases with increasing Ti addition. Ti addition stabilizes the amorphous phase of HfO2, resulting in amorphous films as deposited. After a high-temperature annealing, the films transition from an amorphous to a polycrystalline phase. Orthorhombic Hf-Ti-O peaks are detected in polycrystalline films containing 33-at. % or higher Ti content. As Ti content is decreased, monoclinic HfO2 becomes the predominant microstructure. No TiSi is formed at the dielectric/Si interface, indicating films with good thermal stability. The band gap of Hf-Ti-O was found to be lower than that of HfO2. Well-behaved capacitance-voltage and leakage current density-voltage characteristics were obtained for Hf-Ti-O. However, an increased leakage current density was observed with Ti addition. The data from capacitance-voltage stressing indicate a smaller flatband voltage (Vfb) shift in the HfO2 films with low Ti content when compared with the HfO2 films. This indicates less charge trapping with a small amount of Ti addition.

Triyoso, D. H.; Hegde, R. I.; Zollner, S.; Ramon, M. E.; Kalpat, S.; Gregory, R.; Wang, X.-D.; Jiang, J.; Raymond, M.; Rai, R.; Werho, D.; Roan, D.; White, B. E.; Tobin, P. J.

2005-09-01

12

Solid-state dewetting of ultra-thin Au films on SiO2 and HfO2.  

PubMed

Ultra-thin Au films with thickness (h) ranging from 0.5 to 6.0 nm were deposited at room temperature (RT) by means of e-beam evaporation on SiO2 and HfO2. Due to the natural solid-state dewetting (SSD) of the as-deposited films, Au nanoparticles (NPs) were formed on the substrates. By properly adjusting the h value, the size and the density of the Au NPs can be finely tuned. For h=0.5 nm, spherical-like Au NPs with diameter below 5 nm and density in the order of 10(12) Au NPs cm(-2) were obtained without any additional thermal treatment independently from the substrate. The dependence of the Au NPs characteristics on the substrate starts to be effective for h?1.0 nm where the Au NPs diameter is in the 5-10 nm range and the density is around 10(11) Au NPs cm(-2). The effect of a subsequent high temperature (400-800 C) annealing in N2 atmosphere on the Au NPs was investigated as well. For h?1.0 nm, the Au NPs characteristics evidenced an excellent thermal stability. Whereas the thermal treatment affects the cristallinity of the Au NPs. For the thicker films (2.0?h?6.0 nm), the thermal treatment becomes effective to induce the SSD. The proposed methodology can be exploited for the synthesis of Au NPs with diameter below 10 nm on different substrates at RT. PMID:25410136

Seguini, G; Llamoja Curi, J; Spiga, S; Tallarida, G; Wiemer, C; Perego, M

2014-12-12

13

Grazing incidence-X-ray fluorescence spectrometry for the compositional analysis of nanometer-thin high-kappa dielectric HfO2 layers.  

PubMed

In future microelectronic devices, SiO2 as a gate dielectric material will be replaced by materials with a higher dielectric constant. One such candidate material is HfO2. Thin layers are typically deposited from ligand-containing precursors in chemical vapor deposition (CVD) processes. In the atomic layer deposition (ALD) of HfO2, these precursors are often HfCl4 and H2O. Obviously, the material properties of the deposited films will be affected by residual ligands from the precursors. In this paper, we evaluate the use of grazing incidence--and total reflection-X-ray fluorescence spectrometry (GI-XRF and TXRF) for Cl trace analysis in nanometer-thin HfO2 films deposited using ALD. First, the results from different X-ray analysis approaches for the determination of Hf coverage are compared with the results from Rutherford backscattering spectrometry (RBS). Next, we discuss the selection of an appropriate X-ray excitation source for the analysis of traces within the high-kappa: layers. Finally, we combine both in a study on the accuracy of Cl determinations in HfO2 layers. PMID:16038507

Hellin, David; Delabie, Annelies; Puurunen, Riikka L; Beaven, Peter; Conard, Thierry; Brijs, Bert; De Gendt, Stefan; Vinckier, Chris

2005-07-01

14

Internal dielectric interface: SiO2- HfO2  

Microsoft Academic Search

Hafnia is the leading candidate to replace silica as the gate dielectric in CMOS technology. Typically, hafnia films are deposited by atomic layer deposition (ALD) on the oxidized surface of a silicon wafer. The oxide could be native or thermally grown. Therefore, the high-k dielectric film is not in direct contact with Si, but rather with silicon dioxide. We investigate

Onise Sharia; Alex Demkov; Genadi Bersuker; Byoung Hun Lee

2006-01-01

15

Atomic layer deposited TaCy metal gates: Impact on microstructure, electrical properties, and work function on HfO2 high-k dielectrics  

NASA Astrophysics Data System (ADS)

TaCy has been reported to have the appropriate work function for negative metal-oxide semiconductor metal in high-k metal-oxide field-effect transistors. As device size continues to shrink, a conformal deposition for metal gate electrodes is needed. In this work, we report on the development and characterization of a novel TaCy process by atomic layer deposition (ALD). Detailed physical properties of TaCy films are studied using ellipsometry, a four-point probe, Rutherford backscattering spectrometry (RBS), x-ray photoelectron spectroscopy (XPS), and x-ray diffraction (XRD). RBS and XPS analysis indicate that TaCy films are near-stoichiometric, nitrogen free, and have low oxygen impurities. Powder XRD spectra showed that ALD films have a cubic microstructure. XPS carbon bonding studies revealed that little or no glassy carbon is present in the bulk of the film. Excellent electrical properties are obtained using ALD TaCy as a metal gate electrode. Well-behaved capacitance-voltage characteristics with ALD HfO2 gate dielectrics are demonstrated for TaCy thicknesses of 50, 100, and 250 . A low fixed charge (2-410-11 cm-2) is observed for all ALD HfO2/ALD TaCy devices. Increasing the thickness of ALD TaCy results in a decrease in work function (4.77 to 4.54 eV) and lower threshold voltages.

Triyoso, D. H.; Gregory, R.; Schaeffer, J. K.; Werho, D.; Li, D.; Marcus, S.; Wilk, G. D.

2007-11-01

16

Atomic layer deposition of Y2O3 and yttrium-doped HfO2 using a newly synthesized Y(iPrCp)2(N-iPr-amd) precursor for a high permittivity gate dielectric  

NASA Astrophysics Data System (ADS)

We systematically investigated the effects of Y doping in HfO2 dielectric layer, focusing on structural phase transformation and the dielectric properties of the resultant films. Y doping was carried out using atomic layer deposition (ALD) with a novel Y(iPrCp)2(N-iPr-amd) precursor, which exhibits good thermal stability without any decomposition and clean evaporation. As a result, the ALD process of the Y2O3 films showed well-saturated and linear growth characteristics of 0.45 /cycle without significant incubation delays and produced pure Y2O3 films. Then, yttrium-doped HfO2 films with various Y/(Y + Hf) compositions (yttrium content: 0.6- 4.8 mol%) were prepared by alternating Y2O3 and HfO2 growth cycles. Structural and electrical characterization revealed that the addition of yttrium to HfO2 induced phase transformations from the monoclinic to the cubic or tetragonal phases, even at low post-annealing temperatures of 600 C, and improved leakage current densities by inducing oxygen vacancy-related complex defects. A maximum relative dielectric constant of 33.4 was obtained for films with a yttrium content of 1.2 mol%. Excellent EOT scalability was observed down to 1 nm without dielectric constant degradation.

Lee, Jae-Seung; Kim, Woo-Hee; Oh, Il-Kwon; Kim, Min-Kyu; Lee, Gyeongho; Lee, Chang-Wan; Park, Jusang; Lansalot-Matras, Clement; Noh, Wontae; Kim, Hyungjun

2014-04-01

17

Influence of Rapid Thermal Annealing on the Structure and Electrical Properties of Ce-Doped HfO2 Gate Dielectric  

NASA Astrophysics Data System (ADS)

Ce-doped HfO2 (HfCeO) films are prepared by radio-frequency magnetron sputtering. The influences of rapid thermal annealing on the structure and electrical properties of HfCeO films are investigated. The results show that the incorporation of Ce into HfO2 increases the crystallization temperature of HfO2, and the cubic phase of HfO2 can be stabilized by incorporating Ce into HfO2. After high temperature annealing, Hf 4f core level spectra shift to a higher energy, whereas O 1s core level spectra shift to a lower energy. With increasing annealing temperatures, the effective permittivity increases, whereas the flat-band voltage shift and effective oxide charge density decrease. Moreover, the leakage current density of the HfCeO films decreases initially, and then increases as the annealing temperature increases.

Meng, Yong-Qiang; Liu, Zheng-Tang; Feng, Li-Ping; Chen, Shuai

2014-07-01

18

Effect of pre-deposition annealing on the performance of MIS capacitor formed using atomic layer deposition of ultrathin HfO2  

NASA Astrophysics Data System (ADS)

In this work, we report the effect of pre-deposition annealing on electrical characteristics of metal-insulator-semiconductor (MIS) capacitors, with HfO2 as high-k insulator. HfO2 has been deposited via atomic layer deposition (ALD) using Tetrakis [Ethyl Methyl Amino] Hafnium, Hf[N(CH3)(C2H5(]4 (TEMAHf) as metal oxide precursor and water (H2O) as oxidizing precursor. The results obtained have shown that the pre-and post deposition annealing have profound effect on electrical characteristic of MIS Capacitors. This led us to hypothesize that the preparation of Silicon substrate with pre-deposition temperature treatment forms an interfacial layer between hafnium dioxide & substrate and that will have influence on the ALD deposition and consequentially on the electrical characteristic of the device formed through ALD. By controlling the post deposition conditions, the electrical characteristic behavior is ascribed to the predeposition treatment. The promising hypothesis of such a behavior, supported with some preliminary experimental data has been presented in this short communication.

Maurya, Savita; Singh, B. R.; Radhakrishna, M.

2013-06-01

19

Freestanding HfO2 grating fabricated by fast atom beam etching  

NASA Astrophysics Data System (ADS)

We report here the fabrication of freestanding HfO2 grating by combining fast atom beam etching (FAB) of HfO2 film with dry etching of silicon substrate. HfO2 film is deposited onto silicon substrate by electron beam evaporator. The grating patterns are then defined by electron beam lithography and transferred to HfO2 film by FAB etching. The silicon substrate beneath the HfO2 grating region is removed to make the HfO2 grating suspend in space. Period- and polarization-dependent optical responses of fabricated HfO2 gratings are experimentally characterized in the reflectance measurements. The simple process is feasible for fabricating freestanding HfO2 grating that is a potential candidate for single layer dielectric reflector. PACS: 73.40.Ty; 42.70.Qs; 81.65.Cf.

Wang, Yongjin; Wu, Tong; Kanamori, Yoshiaki; Hane, Kazuhiro

2011-04-01

20

2 MeV electron irradiation effects on the electrical characteristics of metal-oxide-silicon capacitors with atomic layer deposited Al2O3, HfO2 and nanolaminated dielectrics  

NASA Astrophysics Data System (ADS)

The effects of 2 MeV electron irradiation on the electrical characteristics of atomic layer deposited (ALD) high permittivity (high-k) layers of Al2O3, HfO2 and a nanolaminate of them are evaluated. Metal-oxide-semiconductor capacitors with a nominal dielectric physical thickness of 10 nm were fabricated on different p-type and n-type silicon substrates. The capacitance-voltage (C-V) and current-voltage (I-V) characteristics of the different structures are analyzed as a function of electron irradiation. A progressive negative shift of the C-V characteristics is observed with increasing electron irradiation, indicating the generation of effective positive charges. Similar generation rates for effective trapped charges and interface states are obtained for all the different high-k dielectric layers studied. The hysteresis of the C-V curves after irradiation increases in the case of Al2O3 samples, for HfO2 decreases while the irradiation has little impact on the hysteresis of the nanolaminate stack. A progressive increase of the leakage current with electron irradiation dose is observed for all the studied dielectrics. The analysis of the current-voltage characteristics measured at different temperatures point to Poole-Frenkel as the dominant conduction mechanism. Under the studied conditions, no impact of electron irradiation fluence on dielectric breakdown voltage has been appreciated.

Raf, J. M.; Campabadal, F.; Ohyama, H.; Takakura, K.; Tsunoda, I.; Zabala, M.; Beldarrain, O.; Gonzlez, M. B.; Garca, H.; Castn, H.; Gmez, A.; Dueas, S.

2013-01-01

21

Extremely Scaled (?0.2 nm) Equivalent Oxide Thickness of Higher-k (k = 40) HfO2 Gate Stacks Prepared by Atomic Layer Deposition and Oxygen-Controlled Cap Post-Deposition Annealing  

NASA Astrophysics Data System (ADS)

We fabricate ultrathin HfO2 gate stacks of very high permittivity by atomic layer deposition (ALD) and oxygen-controlled cap post-deposition annealing. The HfO2 layer is directly deposited on a wettability-controlled Si surface by ALD. To enhance permittivity, a cubic crystallographic phase is generated in ALD-HfO2 by short-time annealing with a Ti capping layer. The Ti layer absorbs residual oxygen in the HfO2 layer, which suppresses the growth of the interfacial SiO2 layer. The dielectric constant of ALD-HfO2 is increased to ?40, and a gate stack of extremely scaled equivalent oxide thickness (?0.2 nm) is obtained.

Morita, Yukinori; Migita, Shinji; Mizubayashi, Wataru; Ota, Hiroyuki

2012-02-01

22

Fabrication of HfO2 patterns by laser interference nanolithography and selective dry etching for III-V CMOS application  

PubMed Central

Nanostructuring of ultrathin HfO2 films deposited on GaAs (001) substrates by high-resolution Lloyd's mirror laser interference nanolithography is described. Pattern transfer to the HfO2 film was carried out by reactive ion beam etching using CF4 and O2 plasmas. A combination of atomic force microscopy, high-resolution scanning electron microscopy, high-resolution transmission electron microscopy, and energy-dispersive X-ray spectroscopy microanalysis was used to characterise the various etching steps of the process and the resulting HfO2/GaAs pattern morphology, structure, and chemical composition. We show that the patterning process can be applied to fabricate uniform arrays of HfO2 mesa stripes with tapered sidewalls and linewidths of 100 nm. The exposed GaAs trenches were found to be residue-free and atomically smooth with a root-mean-square line roughness of 0.18 nm after plasma etching. PACS: Dielectric oxides 77.84.Bw, Nanoscale pattern formation 81.16.Rf, Plasma etching 52.77.Bn, Fabrication of III-V semiconductors 81.05.Ea PMID:21711946

2011-01-01

23

Metal nanocrystal memory with solgel derived HfO 2 high-? tunnel oxide  

Microsoft Academic Search

An all-solution processed metaloxidesemiconductor (MOS) capacitor structure containing gold (Au) nanoparticles (NPs) within HfO2 high-? oxide was fabricated. The ultra-thin (~10nm) HfO2 high-? tunnel oxide layer was prepared by solgel process and showed good electrical properties, which were critical to superior memory property of the MOS structure. Au NPs with particle size of about 3.3nm were synthesized by chemical reduction

Ching-Chich Leu; Shih-Tang Chen; Fu-Ken Liu

2011-01-01

24

Impact of electrical stress on the electrical characteristics of 2 MeV electron irradiated metal-oxide-silicon capacitors with atomic layer deposited Al2O3, HfO2 and nanolaminated dielectrics  

NASA Astrophysics Data System (ADS)

In this work, the impact of electrical stress on the electrical characteristics of 2 MeV electron irradiated metal-oxide-silicon capacitors with atomic layer deposited (ALD) high permittivity (high-k) dielectric layers of Al2O3, HfO2 and a nanolaminate of them is evaluated. The aim is to investigate the susceptibility to electrical stress of the radiation effects created in irradiated MOS structures, paying especial attention to any possible interaction between the radiation-induced damage and the subsequent electrical stress degradation. For this study, MOS capacitors with a nominal dielectric physical thickness of 10 nm (equivalent oxide thickness (EOT) between 3 nm and 7 nm) on different p-type and n-type silicon substrates were investigated. An exponentially increasing stress current was forced to flow in accumulation through the different dielectric layers, registering the evolution of gate voltage versus stress time until dielectric breakdown occurred. Capacitance-voltage characteristics of the different irradiated and non-irradiated structures are analyzed as a function of electrical stress. Different charge trapping behaviors and significant polarity dependence in interface state generation are observed for the dielectric layers subjected to substrate and gate injections. No clear interaction between radiation and electrical stress damages is noticed under substrate injection (n-type samples). However, higher negative charge trapping near the metal/dielectric interface is registered for the irradiated Al2O3 and nanolaminate layers subjected to gate injection and, in the case of the most irradiated samples, the radiation-induced interface states damage is found to dominate against the damage generated in early stages of the electrical stress.

Raf, J. M.; Gonzlez, M. B.; Takakura, K.; Tsunoda, I.; Yoneoka, M.; Beldarrain, O.; Zabala, M.; Campabadal, F.

2013-11-01

25

Two-step annealing effects on ultrathin EOT higher-k (k = 40) ALD-HfO2 gate stacks  

NASA Astrophysics Data System (ADS)

Ultrathin HfO2 gate stacks with very high permittivity were fabricated by atomic layer deposition (ALD) and a novel two-step post-deposition annealing (PDA) technique. First, a no-cap pre-crystallization anneal degasses residual contaminations in the ALD layer, and second, a Ti-cap anneal enhances the permittivity of HfO2 by generating a cubic crystal phase. The Ti-cap layer simultaneously suppresses growth of interfacial SiO2 during annealing by absorbing residual oxygen released from HfO2. Using these techniques, the dielectric constant of the ALD-HfO2 could be enhanced to 40 for 2.4-4.0 nm HfO2 thickness.

Morita, Yukinori; Migita, Shinji; Mizubayashi, Wataru; Masahara, Meishoku; Ota, Hiroyuki

2013-06-01

26

Characterization of ultrathin gate dielectrics and multilayer charge injection barriers  

NASA Astrophysics Data System (ADS)

Since the invention of the first integrated circuit, the semiconductor industry has distinguished itself by a phenomenally rapid pace of improvements in device performance. This trend of ever smaller and faster devices is a result of the ability to exponentially reduce feature sizes of integrated circuits, a trend commonly known as "scaling". A reduction of overall feature sizes requires a simultaneous reduction in the thickness of the gate dielectric, SiO2, of a MOSFET. Gate oxides in the ultrathin regime (<35 A) feature a large direct tunneling leakage current. The presence of this leakage current requires a reevaluation of standard characterization techniques as well as a reevaluation of the continued usefulness of SiO 2 as the gate dielectric of choice for future applications. On the other hand, a thorough understanding of the dynamics of ultrathin oxides opens up a range of future device applications that were not possible with thicker oxides. Capacitance-voltage characterization has been the standard technique to study the electrical properties and interface quality of MOS devices. However, the presence of a large leakage current in ultrathin oxides distorts standard C-V measurements, rendering this technique no longer useful. In this work, a leakage compensated charge measurement is developed to overcome this difficulty. This technique produces static C-V curves, even for oxides as thin as 24 A, thereby permitting C-V characterization well into the direct tunneling regime. As an extension of this leakage problem, the usefulness of SiO2 as the gate dielectric of choice for future CMOS devices has been called into question. One solution---but not the only---calls for a new dielectric to replace SiO2 for future gate applications. This research presents some of the earliest results ever on the electrical properties of MOCVD and ALCVD hafnium oxides as a potential candidate. Electrical characterization revealed that the devices have characteristics such as large leakage currents, dielectric charging under stress, hysteresis and a large flatband voltage shift that is commonly found in materials such as the one that was investigated in this work. As one example of future device applications that become possible due to the scaling of ultrathin oxides, silicon-based multilayer charge injection barriers have been investigated. These barriers consist of alternating layers of ultrathin SiO2 and Si. The electrical properties of these structures were studied in detail and revealed that they can be used as an active tunnel dielectric in nonvolatile memory devices.

Dons, Edwin M.

27

Dielectric and pyroelectric properties of ultrathin, monocrystalline lithium tantalate  

NASA Astrophysics Data System (ADS)

Ultrathin, self-supporting lithium tantalate (LiTaO3) wafers have been fabricated out of a single crystal with a minimum thickness of about 0.4 ?m using ion-beam milling. The most decisive parameters (pyroelectric coefficient, relative permittivity, and dielectric loss factor) for their use in pyroelectric radiation detectors were studied in dependence on film thickness and temperature. The potential performance of pyroelectric materials was evaluated using appropriate figures of merit. In addition, the dielectric and pyroelectric properties of stoichiometric LiTaO3 were investigated and compared to congruent LiTaO3 bulk material conventionally used for pyroelectric detectors.

Schossig, Marco; Norkus, Volkmar; Gerlach, Gerald

2014-03-01

28

Effect of ion implantation energy for the synthesis of Ge nanocrystals in SiN films with HfO2/SiO2 stack tunnel dielectrics for memory application  

PubMed Central

Ge nanocrystals (Ge-NCs) embedded in SiN dielectrics with HfO2/SiO2 stack tunnel dielectrics were synthesized by utilizing low-energy (?5 keV) ion implantation method followed by conventional thermal annealing at 800C, the key variable being Ge+ ion implantation energy. Two different energies (3 and 5 keV) have been chosen for the evolution of Ge-NCs, which have been found to possess significant changes in structural and chemical properties of the Ge+-implanted dielectric films, and well reflected in the charge storage properties of the Al/SiN/Ge-NC + SiN/HfO2/SiO2/Si metal-insulator-semiconductor (MIS) memory structures. No Ge-NC was detected with a lower implantation energy of 3 keV at a dose of 1.5 1016 cm-2, whereas a well-defined 2D-array of nearly spherical and well-separated Ge-NCs within the SiN matrix was observed for the higher-energy-implanted (5 keV) sample for the same implanted dose. The MIS memory structures implanted with 5 keV exhibits better charge storage and retention characteristics compared to the low-energy-implanted sample, indicating that the charge storage is predominantly in Ge-NCs in the memory capacitor. A significant memory window of 3.95 V has been observed under the low operating voltage of 6 V with good retention properties, indicating the feasibility of these stack structures for low operating voltage, non-volatile memory devices. PMID:21711708

2011-01-01

29

Effect of ion implantation energy for the synthesis of Ge nanocrystals in SiN films with HfO2/SiO2 stack tunnel dielectrics for memory application  

NASA Astrophysics Data System (ADS)

Ge nanocrystals (Ge-NCs) embedded in SiN dielectrics with HfO2/SiO2 stack tunnel dielectrics were synthesized by utilizing low-energy (?5 keV) ion implantation method followed by conventional thermal annealing at 800C, the key variable being Ge+ ion implantation energy. Two different energies (3 and 5 keV) have been chosen for the evolution of Ge-NCs, which have been found to possess significant changes in structural and chemical properties of the Ge+-implanted dielectric films, and well reflected in the charge storage properties of the Al/SiN/Ge-NC + SiN/HfO2/SiO2/Si metal-insulator-semiconductor (MIS) memory structures. No Ge-NC was detected with a lower implantation energy of 3 keV at a dose of 1.5 1016 cm-2, whereas a well-defined 2D-array of nearly spherical and well-separated Ge-NCs within the SiN matrix was observed for the higher-energy-implanted (5 keV) sample for the same implanted dose. The MIS memory structures implanted with 5 keV exhibits better charge storage and retention characteristics compared to the low-energy-implanted sample, indicating that the charge storage is predominantly in Ge-NCs in the memory capacitor. A significant memory window of 3.95 V has been observed under the low operating voltage of 6 V with good retention properties, indicating the feasibility of these stack structures for low operating voltage, non-volatile memory devices.

Sahu, Bhabani Shankar; Gloux, Florence; Slaoui, Abdelilah; Carrada, Marzia; Muller, Dominique; Groenen, Jesse; Bonafos, Caroline; Lhostis, Sandrine

2011-12-01

30

Charge trapping properties of the HfO2 layer with various thicknesses for charge trap flash memory applications  

NASA Astrophysics Data System (ADS)

MHOS (metal-HfO2-SiO2-Si) structure capacitors were fabricated to investigate the charge trapping properties of HfO2 layer with various thicknesses for the applications of charge trap flash (CTF) memory devices. Also, the centroid of charge trap in HfO2 layer was extracted by constant current stress method and compared with that of conventional Si3N4 layer. The gate leakage current of MHOS capacitor due to tunneling was significantly reduced by stacking the HfO2 trap layer on thin SiO2 tunnel layer. The MHOS capacitors showed a larger memory window than the MNOS (metal-Si3N4-SiO2-Si) capacitors at the same trap layer thickness, because the HfO2 layer has better charge trapping efficiency than the Si3N4 layer. It is found that ultrathin HfO2 trap layer with a thickness of 2 nm stored almost the same charges with Si3N4 layer with a thickness of 7 nm. Consequently, the application of ultrathin HfO2 to charge storage layer can considerably improve the performance and enhance the high density of CTF memory.

You, Hee-Wook; Cho, Won-Ju

2010-03-01

31

Breakdown-induced thermochemical reactions in HfO2 high-?/polycrystalline silicon gate stacks  

NASA Astrophysics Data System (ADS)

The chemistry of dielectric-breakdown-induced microstructural changes in HfO2 high-?/polycrystalline silicon gate nMOSFETs under constant voltage stress has been studied. Based on an electron energy loss spectrometry analysis, the hafnium and oxygen chemical bonding in the breakdown induced Hf-based compounds of a "ball-shaped" defect is found to be different compared to the stoichiometric HfO2 and SiO2. The formation of possibly HfSixOy and HfSix compounds in the "ball-shaped" defect is attributed to a thermochemical reaction triggered by the gate dielectric breakdown.

Ranjan, R.; Pey, K. L.; Tung, C. H.; Tang, L. J.; Ang, D. S.; Groeseneken, G.; De Gendt, S.; Bera, L. K.

2005-12-01

32

Properties of thin HfO2 films  

NASA Astrophysics Data System (ADS)

To insure continuous downscaling of CMOS technology the semiconductor industry must make a transition from the Si-SiO_2-poly-Si triad to a much more complex Si-dielectric-metal system. The higher than silicon dioxide dielectric constant of the new gate dielectric will allow maintaining the gate capacitance and therefore the drain-source saturation current without the thickness reduction of the oxide. HfO2 is one of the leading candidates for a new gate material. We have investigated theoretically bulk and surface energies of three phases of hafnia and use this data to explain observed morphology and electric properties of ALD-grown hafnia films on Si. The surface electronic properties have been investigated and related to the band discontinuity with Si and several metals.

Demkov, A. A.; Triyoso, D.; Gregory, R.; Fejes, Peter

2004-03-01

33

Effects of aluminum incorporation on band alignment at the SiO2\\/HfO2 interface  

Microsoft Academic Search

A high- k HfO2\\/SiO2 gate stack is taking the place of SiO2 as a gate dielectric in a modern field effect transistor. The use of HfO2 requires employing a metal gate electrode that limits available options for controlling transistor threshold voltage by modulating the electrode work function. An alternative approach is to modify the overall band alignment in the gate

Onise Sharia; Alexander A. Demkov; Gennadi Bersuker; B. H. Lee

2008-01-01

34

Role of oxygen vacancies in HfO2-based gate stack breakdown  

NASA Astrophysics Data System (ADS)

We study the influence of multiple oxygen vacancy traps in the percolated dielectric on the postbreakdown random telegraph noise (RTN) digital fluctuations in HfO2-based metal-oxide-semiconductor transistors. Our electrical characterization results indicate that these digital fluctuations are triggered only beyond a certain gate stress voltage. First-principles calculations suggest the oxygen vacancies to be responsible for the formation of a subband in the forbidden band gap region, which affects the triggering voltage (VTRIG) for the RTN fluctuations and leads to a shrinkage of the HfO2 band gap.

Wu, X.; Migas, D. B.; Li, X.; Bosman, M.; Raghavan, N.; Borisenko, V. E.; Pey, K. L.

2010-04-01

35

ALD HfO2 using heavy water (D2O) for improved MOSFET stability  

Microsoft Academic Search

Device instability is one of the most challenging issues to implement high-k gate dielectrics. Incorporation of deuterium during the ALD (atomic layer deposition) process effectively improves the interface quality that enhances high-k device stability and reliability. Compared to H2O processed HfO2 devices, devices with D2O processing result in a significantly smaller Vt shift after constant voltage stressing at room temperature

H.-H. Tseng; M. E. Ramon; L. Hebert; P. J. Tobin; D. Triyoso; J. M. Grant; Z. X. Jiang; D. Roan; S. B. Samavedam; D. C. Gilmer; S. Kalpat; C. Hobbs; W. J. Taylor; O. Adetutu; B. E. White

2003-01-01

36

Modulation of the structural and optical properties of sputtering-derived HfO2 films by deposition power  

NASA Astrophysics Data System (ADS)

High-k gate dielectric HfO2 thin films have been deposited on Si and quartz substrate by radio frequency magnetron sputtering. The structural and optical properties of HfO2 thin films related to deposition power are investigated by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), ultraviolet-visible spectroscopy (UV-Vis), and spectroscopic ellipsometry (SE). Results confirmed by XRD have shown that the as-deposited HfO2 thin films are not amorphous state but in monoclinic phase, regardless of deposition power. Analysis from FTIR indicates that an interfacial layer has been formed between the Si substrate and the HfO2 thin film during deposition. AFM measurements illustrate that the root mean square (RMS) of the as-deposited HfO2 thin films' surface demonstrates an apparent reduction with the increase of deposition. Combined with UV-Vis and SE measurements, it can be noted reduction in band gap with an increase in power has been observed. Additionally, increase in refractive index (n) has been confirmed by SE.

Deng, B.; He, G.; Lv, J. G.; Chen, X. F.; Zhang, J. W.; Zhang, M.; Sun, Z. Q.

2014-11-01

37

Terahertz surface plasmons excitation by nonlinear mixing of lasers in over ultrathin metal film coated dielectric  

NASA Astrophysics Data System (ADS)

An ultrathin metal film deposited on dielectric plate supports low loss THz surface plasma wave (SPW). The SPW field falls off away from the metal film both inside the dielectric as well as in free space. Two lasers normally incident, from free space on the planar structure, exert a difference frequency ponderomotive force on the free electrons of the film and resonantly excite THz SPW. The ratio of SPW amplitude to lasers is 10-3 at laser intensity of 3 1012 W/cm2 at 1 ? m wavelength. The growth rate falls monotonically because at higher frequency the coupling of SPW is weak.

Kumar, Pawan; Tripathi, V. K.

2013-08-01

38

Modeling the breakdown statistics of Al2O3/HfO2 nanolaminates grown by atomic-layer-deposition  

NASA Astrophysics Data System (ADS)

The breakdown voltage statistics of Al2O3/HfO2 nanolaminate multilayer dielectrics fabricated by atomic layer deposition (ALD) are modeled within the percolation theory. Moreover, the nanolaminate breakdown properties are predicted from the breakdown statistics of the separate materials, thus providing a reliable breakdown design framework for nanolaminates. Comparison with experimental data suggests that the electric field in each of the dielectric layers, rather than the total gate voltage, is the variable that controls the breakdown statistics.

Conde, A.; Martnez, C.; Jimnez, D.; Miranda, E.; Raf, J. M.; Campabadal, F.; Su, J.

2012-05-01

39

Nonvolatile memories using deep traps formed in HfO2 by Nb ion implantation  

NASA Astrophysics Data System (ADS)

We report nonvolatile memories (NVMs) based on deep-energy trap levels formed in HfO2 by metal ion implantation. A comparison of Nb- and Ta-implanted samples shows that suitable charge-trapping centers are formed in Nb-implanted samples, but not in Ta-implanted samples. This is consistent with density-functional theory calculations which predict that only Nb will form deep-energy levels in the bandgap of HfO2. Photocurrent spectroscopy exhibits characteristics consistent with one of the trap levels predicted in these calculations. Nb-implanted samples showing memory windows in capacitance-voltage (V) curves always exhibit current (I) peaks in I-V curves, indicating that NVM effects result from deep traps in HfO2. In contrast, Ta-implanted samples show dielectric breakdowns during the I-V sweeps between 5 and 11 V, consistent with the fact that no trap levels are present. For a sample implanted with a fluence of 1013 Nb cm-2, the charge losses after 104 s are 9.8 and 25.5% at room temperature (RT) and 85C, respectively, and the expected charge loss after 10 years is 34% at RT, very promising for commercial NVMs.

Choul Kim, Min; Oh Kim, Chang; Taek Oh, Houng; Choi, Suk-Ho; Belay, K.; Elliman, R. G.; Russo, S. P.

2011-03-01

40

Ion implantation impurity profiles in HfO2  

Microsoft Academic Search

We implanted B, As, and P ions in a 110-nm-thick layer of HfO2 and extracted the parameters of a Pearson IV function. The projected range of the ion implantation was about half of that in SiO2. Thus, when impurities were ion implanted in an Si substrate through a thin layer of HfO2 or SiO2, a smaller dose was retained in

Kunihiro Suzuki; Yusuke Morisaki

2002-01-01

41

Development of Nitrous Oxide-Based Ultrathin Gate and Tunnel Dielectrics for MOS Devices.  

NASA Astrophysics Data System (ADS)

The use of ultrathin dielectric in the ULSI (Ultra -Large Scale Itegration) era is curcial for device functionality and reliability. However, it is well known that conventional thermally grown pure oxides in the ultra-thin regime (40 -60A) do not provide adequate electrical and reliability characteristics. The use of N_2O gas in oxidation produces oxides (oxynitrides) with better dielectric integrity, lower defect density, less boron penetration and better process control, etc.. The N _2O oxide is thus a better candidate for ultrathin oxide application. Pre-oxidation surface preparation by conventional RCA clean increases surface microroughness and provides no passivation to the wafer surface. A new cleaning method based on methanol/HF has been developed and show improvement in the dielectric integrity of both oxides and oxynitrides. A microscopic model is also proposed. The thickness dependent of stress-induced leakage current (SILC) was studied for pure oxides and N _2O oxides. A "turn around" effect was observed such that for thickness going down from ~ 50A, SILC actually decreases. This effect is modeled by the two-step trap-assisted tunneling model where trap generation rate and tunneling time constants are the determining factors for the SILC. Effects of oxide exposure, photoresist and gate dopant activation on the plasma damage immunity of ultrathin oxides were studied. It was found that not only charging damage and radiation damage are present during plasma exposure, photo-annealing by low energy UV light is competing with the damaging processes. The actual extent of damage depends on the plasma operating condition. It implies that using fully-covered MOSCAP structures is not an accurate indicator of the actual damage in integrated circuits. It was also found that photoresist quality affect plasma damage and patterning gate before ion implantation can reduce charging problem. Damage recovery effect of various RTA annealing processes is also studied. The effects of different gate dopant species, concentration and microstructure on the electrical and reliability characteristics of ultrathin oxides and N _2O oxynitrides are studied. Optimization of the gate doping level is based on poly depletion, charge -to-breakdown, and stress-induced leakage current. The optimization conditions for N+ and P+ gate are found to be very different.

Lai, Ka-Fai

42

SEMICONDUCTOR PHYSICS: Effect of annealing on characteristics of a HfOxNy-HfO2-HfOxNy sandwich stack compared with HfO2 film  

NASA Astrophysics Data System (ADS)

HfOxNy-HfO2-HfOxNy sandwich-stack (SS) film was investigated in comparison with HfO2 film of the same thickness. Higher thermal stability and better surface morphology can be observed for the SS film. This structure also shows stronger immunity to interfacial oxidation compared with HfO2 film. Meanwhile, unlike the HfOxNy dielectric, the capacitance performance of SS film was not worse (but was even better) than a pure HfO2 film of the same thickness. The SS structure appears to be a promising high-k gate dielectric compared with both pure HfOxNy and HfO2 dielectrics for future ULSI devices. Additionally, PDA treatment plays an important role in improving the characteristics of SS film, which is confirmed by effective channel electron mobility and stress induced leakage current (SILC) investigations.

Yan, Zhang; Ran, Jiang

2009-08-01

43

SILC during NBTI Stress in PMOSFETs with Ultra-Thin SiON Gate Dielectrics  

NASA Astrophysics Data System (ADS)

Negative bias temperature instability (NBTI) and stress-induced leakage current (SILC) both are more serious due to the aggressive scaling lowering of devices. We investigate the SILC during NBTI stress in PMOSFETs with ultra-thin gate dielectrics. The SILC sensed range from -1 V to 1 V is divided into four parts: the on-state SILC, the near-zero SILC, the off-state SILC sensed at lower positive voltages and the one sensed at higher positive voltages. We develop a model of tunnelling assisted by interface states and oxide bulk traps to explain the four different parts of SILC during NBTI stress.

Cao, Yan-Rong; Hao, Yue; Ma, Xiao-Hua; Yu, Lei; Hu, Shi-Gang

2008-04-01

44

Hafnium oxide films for application as gate dielectrics  

NASA Astrophysics Data System (ADS)

The deposition and characterization of HfO2 films for potential application as a high-kappa gate dielectric in MOS devices has been investigated. DC magnetron reactive sputtering was utilized to prepare the HfO2 films. Structural, chemical, and electrical analyses were performed to characterize the various physical, chemical and electrical properties of the sputtered HfO2 films. The sputtered HfO2 films were annealed to simulate the dopant activation process used in semiconductor processing, and to study the thermal stability of the high-kappa, films. The changes in the film properties due to the annealing are also discussed in this work. Glancing angle XRD was used to analyse the atomic scale structure of the films. The as deposited films exhibit an amorphous, regardless of the film thickness. During post-deposition annealing, the thicker films crystallized at lower temperature (< 600C), and ultra-thin (5.8 nm) film crystallized at higher temperature (600--720C). The crystalline phase which formed depended on the thickness of the films. The low temperature phase (monoclinic) formed in the 10--20 nm annealed films, and high temperature phase (tetragonal) formed in the ultra-thin annealed HfO2 film. TEM cross-section studies of as deposited samples show that an interfacial layer (< 1nm) exists between HfO2/Si for all film thicknesses. The interfacial layer grows thicker during heat treatment, and grows more rapidly when grain boundaries are present. XPS surface analysis shows the as deposited films are fully oxidized with an excess of oxygen. Interfacial chemistry analysis indicated that the interfacial layer is a silicon-rich silicate layer, which tends to transform to silica-like layer during heat treatment. I-V measurements show the leakage current density of the Al/as deposited-HfO 2/Si MOS diode is of the order of 10-3 A/cm 2, two orders of magnitude lower than that of a ZrO2 film with similar physical thickness. Carrier transport is dominated by Schottky emission at lower electric fields, and by Frenkel-Poole emission in the higher electric field region. After annealing, the leakage current density decreases significantly as the structure remains amorphous structure. It is suggested that this decrease is assorted with the densification and defect healing which accures when the porous as-deposited amorphous structure is annealed. The leakage current density increases of the HfO2 layer crystallizes on annealing, which is attributed to the presence of grain boundaries. C-V measurements of the as deposited film shows typical C-V characteristics, with negligible hystersis, a small flat band voltage shift, but great frequency dispersion. The relative permittivity of HfO2/interfacial layer stack obtained from the capacitance at accumulation is 15, which corresponds to an EOT (equivalent oxide thickness) = 1.66 nm. After annealing, the frequency dispersion is greatly enhanced, and the C-V curve is shifted toward the negative voltage. Reliability tests show that the HfO2 films which remain amorphous after annealing possess superior resistance to constant voltage stress and ambient aging. This study concluded that the sputtered HfO 2 films exhibit an amorphous as deposited. Postdeposition annealing alters the crystallinity, interfacial properties, and electrical characteristics. The HfO2 films which remain amorphous structure after annealing possess the best electrical properties.

Hsu, Shuo-Lin

45

Electronic stopping power of hydrogen in HfO2 at the stopping maximum and below  

NASA Astrophysics Data System (ADS)

Electronic energy loss of hydrogen ions in HfO2 was investigated in a wide energy range in the medium and low energy ion scattering regime. Experiments by Time-Of-Flight Medium-Energy Ion Scattering (TOF-MEIS) with proton and deuteron projectiles were performed in backscattering geometry for nm-films of HfO2 on Si with an ultrathin SiO2 interface layer prepared by ALD. At energies around the stopping maximum excellent agreement is found with earlier results from Behar et al. (2009) [45] and theoretical predictions. Towards lower energies discrepancies between experiment and calculations increase slightly. The low energy data exhibits excellent velocity proportionality and indicates the absence of clear effects due to distinct electronic states. Thus, no apparent velocity threshold can be extrapolated from the experiments within the uncertainty of present data. The magnitude of the energy loss is discussed in terms of a free-electron model and compared with the expected electron densities from plasmon frequencies.

Primetzhofer, D.

2014-02-01

46

Experimental evidence of the quantum point contact theory in the conduction mechanism of bipolar HfO2-based resistive random access memories  

NASA Astrophysics Data System (ADS)

The quantum point contact (QPC) model for dielectric breakdown is used to explain the electron transport mechanism in HfO2-based resistive random access memories (ReRAM) with TiN(30 nm)HfO2(5 nm)Hf(10 nm)TiN(30 nm) stacks. Based on experimental I-V characteristics of bipolar HfO2-based ReRAM, we extracted QPC model parameters related to the conduction mechanism in several devices in order to make a statistical study. In addition, we investigated the temperature effect on the conduction mechanism and compared it with the QPC model. Based on these experimental results, we show that the QPC model agrees well with the conduction behavior of HfO2-based ReRAM memory cells.

Prcel, L. M.; Trojman, L.; Moreno, J.; Crupi, F.; Maccaronio, V.; Degraeve, R.; Goux, L.; Simoen, E.

2013-08-01

47

A quantum mechanical treatment of low frequency noise in high-K NMOS transistors with ultra-thin gate dielectrics  

NASA Astrophysics Data System (ADS)

Our paper presents a quantum mechanical treatment of low-frequency noise in scaled NMOS transistors to extend the "unified" noise model and includes remote Coulomb scattering and surface roughness - the latter is a new consideration in the theory. Our experimental work focuses on scaled NMOS devices with a composite dielectric consisting of a 0.5 nm SiO2 covered with a high-K, 1.6 nm HfO2 with a metal gate. In the past, Coulomb scattering was assumed to arise from trapping centers located at the Si-SiO2 interface; however, this cannot give rise to a 1/f noise spectrum. We model remote Coulomb scattering into the dielectric film as traps in these films easily lie within a tunneling distance from the interface. This approach explains the decrease in the Coulomb scattering parameter (?) as a function of gate voltage. In addition, we introduce surface roughness scattering through fluctuations in the normal electric field due to fluctuations in the free carrier density with a surface scattering parameter (?) proportional to the SPICE surface roughness parameter, ?S. Good agreement is obtained between our model and experimental results for both IDS-VGS and the power spectral density, SId, characteristics in very strong inversion region where surface quantization of the 2D subbands is strong.

Zhang, Xiaochen; White, Marvin H.

2012-12-01

48

Subwavelength focusing of azimuthally polarized beams with vortical phase in dielectrics by using an ultra-thin lens  

E-print Network

We demonstrate that a planar and ultrathin binary lens can focus an azimuthally polarized beam with vortical phase (APV) to a subwavelength spot of transverse polarization. The results elaborates that, in the multi-layer medium, this focused spot, which is beyond the Rayleigh diffraction limitation, can be well maintained for several wavelengths after travelling through the dielectric interfaces, which is not attainable by using other vector beams (i.e., radially, linearly and circularly polarized beams) as the illuminating light. This compact optical system can be valuable in data writing and defect identification of wafer or silicon chips, owing to the enhanced polarized focusing through interfaces. It also enables to be highly integrated with traditional microscopy for the far-field super-resolution imaging, surface scanning and detection, and subwavelength focusing, owing to the enhanced focusing performance (reduced width and extended length) as well as the planarized configuration of the ultrathin lens.

Huang, Kun; Liu, Hong; Teng, Jinghua; Yeo, Swee Ping; Qiu, Cheng-Wei

2014-01-01

49

X-ray spectroscopic examination of thin HfO2 films ALD- and MOCVD-grown on the Si(100) surface  

NASA Astrophysics Data System (ADS)

HfO2 films 5 nm thick grown on Si(100) substrates by the methods of MOCVD hydride epitaxy and atomic layer deposition (ALD) are studied using X-ray photoelectron spectroscopy combined with Ar+ ion etching and X-ray reflectometry. It is found that (i) the ALD-grown HfO2 films are amorphous, while the MOCVD-grown films show signs of a crystal structure; (ii) the surface of the ALD-grown films is more prone to contamination and/or is more reactive; and (iii) the amount of interfacial silicon dioxide in the case of the MOCVD-grown film is greater than in the case of the films synthesized by ALD. It is also shown that the argon ion etching of the HfO2 film results in the formation of a metallic hafnium layer at the interface. This indicates that HfO2 can be used not only as a gate dielectric but also as a material suitable for fabricating nanodimensional conductors by direct decomposition.

Sokolov, A. A.; Ovchinnikov, A. A.; Lysenkov, K. M.; Marchenko, D. E.; Filatova, E. O.

2010-07-01

50

Fermi level pinning by defects in HfO2-metal gate stacks  

Microsoft Academic Search

Various mechanisms for the Fermi level pinning of p-gate metals on HfO2 are analyzed in detail. It is found that for Fermi energies below the Si valence band, HfO2 can oxidize Si by creating positively charged O vacancies. The band bending due to this vacancy concentration can account for the observed Fermi level pinning of p metals on HfO2.

J. Robertson; O. Sharia; A. A. Demkov

2007-01-01

51

Metal nanocrystal memory with sol-gel derived HfO2 high-? tunneling oxide  

Microsoft Academic Search

A metal-oxide-semiconductor (MOS) capacitor structure containing gold (Au) nanoparticles (NPs) within sol-gel derived HfO2 high-? oxide is fabricated. Firstly, the Au NPs with particle size of about 3.3 nm were synthesized by chemical reduction method. Then the 10 nm-thick HfO2 tunneling oxide, the Au NPs and the 15 nm-thick HfO2 control oxide were prepared by spin coating method to construct

Shih-Tang Chen; Kun-Cheng Huang; Hua-Chiang Chen; Fu-Ken Liu; Ching-Chich Leu

2010-01-01

52

Electrical properties of HfO2 deposited via atomic layer deposition using Hf(NO3)4 and H2O  

NASA Astrophysics Data System (ADS)

We report on the electrical properties of HfO2 deposited via atomic layer deposition using Hf(NO3)4 precursor for metal/oxide/semiconductor gate dielectric applications. Thin films, with less than 1% variation in accumulation capacitance over a 150 mm wafer, have been deposited directly on hydrogen-terminated Si wafers. The effective dielectric constant of thin (<10 nm) films was in the range of ?eff=10-12, the breakdown voltage was about 6-9 MV/cm, and the leakage current was between 3-6 orders of magnitude lower than that of SiO2. The relative benefit of lower leakage current of HfO2 over SiO2 decreased with decreasing effective thickness. Electron trapping was observed under constant voltage stressing.

Conley, J. F.; Ono, Y.; Solanki, R.; Stecker, G.; Zhuang, W.

2003-05-01

53

Electron beam induced local crystallization of HfO2 nanopores for biosensing applications  

PubMed Central

We report the development of single, locally crystallized nanopores in HfO2 membranes for biosensing applications. HfO2 is chosen for its isoelectric point of 7.0, mechanical and chemical stability in solution, and for its potential as a high-k material for nanopore ionic field effect transistor applications. The HfO2 membrane is deposited on a graphene layer suspended over a 300 nm FIB hole, where graphene is used as the mechanical support. Exposure of the membrane to a focused electron beam causes crystallization in the vicinity of the nanopore during pore formation. We investigate the effects of crystallization on the electrical and surface properties of HfO2 films. Our surface analysis of HfO2 reveals improved hydrophilicity of crystallized HfO2, a notable advantage over the hydrophobicity of as-deposited HfO2. We also demonstrate detection of dsDNA translocation through HfO2 nanopores under various applied bias levels. In addition, our device architecture also presents a promising first step toward the realization of high-k HfO2 nanopore transistors. PMID:23945603

Shim, Jiwook; Rivera, Jose; Bashir, Rashid

2013-01-01

54

Intrinsic versus extrinsic ferromagnetism in HfO2 -x and Ni: HfO 2 -x thin films  

NASA Astrophysics Data System (ADS)

We have investigated the possible evolution of an intrinsic stable ferromagnetic moment in oxygen deficient undoped and magnetically doped HfO2 -x thin films grown by reactive molecular beam epitaxy. Neither oxygen vacancies nor substituted Ni in combination with such vacancies results in an observable magnetic moment for a broad range of oxygen vacancy concentrations. By combining integral and element specific magnetization measurements, we show that a fluctuating deposition rate of the magnetic dopant induces extrinsic ferromagnetism by promoting the formation of metallic clusters. We suggest the element specific measurement of an induced magnetic moment at the nonmagnetic site as a proof of intrinsic ferromagnetism in diluted magnetic semiconductors.

Hildebrandt, Erwin; Yazdi, Mehrdad Baghaie; Kurian, Jose; Sharath, S. U.; Wilhelm, Fabrice; Rogalev, Andrei; Alff, Lambert

2014-10-01

55

Solid-state densification of spun-cast self-assembled monolayers for use in ultra-thin hybrid dielectrics  

NASA Astrophysics Data System (ADS)

Ultra-thin self-assembled monolayer (SAM)-oxide hybrid dielectrics have gained significant interest for their application in low-voltage organic thin film transistors (OTFTs). A [8-(11-phenoxy-undecyloxy)-octyl]phosphonic acid (PhO-19-PA) SAM on ultrathin AlOx (2.5 nm) has been developed to significantly enhance the dielectric performance of inorganic oxides through reduction of leakage current while maintaining similar capacitance to the underlying oxide structure. Rapid processing of this SAM in ambient conditions is achieved by spin coating, however, as-cast monolayer density is not sufficient for dielectric applications. Thermal annealing of a bulk spun-cast PhO-19-PA molecular film is explored as a mechanism for SAM densification. SAM density, or surface coverage, and order are examined as a function of annealing temperature. These SAM characteristics are probed through atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and near edge X-ray absorption fine structure spectroscopy (NEXAFS). It is found that at temperatures sufficient to melt the as-cast bulk molecular film, SAM densification is achieved; leading to a rapid processing technique for high performance SAM-oxide hybrid dielectric systems utilizing a single wet processing step. To demonstrate low-voltage devices based on this hybrid dielectric (with leakage current density of 7.7 10-8 A cm-2 and capacitance density of 0.62 ?F cm-2 at 3 V), pentacene thin-film transistors (OTFTs) are fabricated and yield sub 2 V operation and charge carrier mobilites of up to 1.1 cm2 V-1 s-1.

Hutchins, Daniel O.; Acton, Orb; Weidner, Tobias; Cernetic, Nathan; Baio, Joe E.; Castner, David G.; Ma, Hong; Jen, Alex K.-Y.

2012-11-01

56

Quantitatively enhanced reliability and uniformity of high-? dielectrics on graphene enabled by self-assembled seeding layers.  

PubMed

The full potential of graphene in integrated circuits can only be realized with a reliable ultrathin high-? top-gate dielectric. Here, we report the first statistical analysis of the breakdown characteristics of dielectrics on graphene, which allows the simultaneous optimization of gate capacitance and the key parameters that describe large-area uniformity and dielectric strength. In particular, vertically heterogeneous and laterally homogeneous Al2O3 and HfO2 stacks grown via atomic-layer deposition and seeded by a molecularly thin perylene-3,4,9,10-tetracarboxylic dianhydride organic monolayer exhibit high uniformities (Weibull shape parameter ? > 25) and large breakdown strengths (Weibull scale parameter, E(BD) > 7 MV/cm) that are comparable to control dielectrics grown on Si substrates. PMID:23387502

Sangwan, Vinod K; Jariwala, Deep; Filippone, Stephen A; Karmel, Hunter J; Johns, James E; Alaboson, Justice M P; Marks, Tobin J; Lauhon, Lincoln J; Hersam, Mark C

2013-03-13

57

Structural and electrical properties of high-k HfO2 films modified by CHF3 and C4F8/O2 plasmas  

NASA Astrophysics Data System (ADS)

As-deposited HfO2 films were modified by CHF3, C4F8, and mixed C4F8/O2 plasmas in a dual-frequency capacitively coupled plasma chamber driven by radio frequency generators of 60 MHz as the high frequency (HF) source and 2 MHz as the low frequency source (60/2 MHz). The influences of various surface plasma treatments under CHF3, C4F8, and C4F8/O2 were investigated in order to understand the chemical and structural changes in thin-film systems, as well as their influence on the electrical properties. Fluorine atoms were incorporated into the HfO2 films by either CHF3 or C4F8 plasma treatment; meanwhile, the C/F films were formed on the surface of the HfO2 films. The formation of C/F layers decreased the k value of the gate stacks because of its low dielectric constant. However, the addition of O2 gas in the discharge gases suppressed the formation of C/F layers. After thermal annealing, tetragonal HfO2 phase was investigated in both samples treated with CHF3 and C4F8 plasmas. However, the samples treated with O-rich plasmas showed monoclinic phase, which indicated that the addition of O plasmas could influence the Hf/O ratio of the HfO2 films. The mechanism of the t-HfO2 formation was attributed to oxygen insufficiency generated by the incorporation of F atoms. The capacitors treated with C4F8/O2 plasmas displayed the highest k value, which ascribed that the C/F layers were suppressed and the tetragonal phase of HfO2 was formed. Good electrical properties, especially on the hysteresis voltage and frequency dispersion, were obtained because the bulk traps were passivated by the incorporation of F atoms. However, the H-related traps were generated during the CHF3 plasma treatments, which caused the performance degradation. All the treated samples showed lower leakage current density than the as-deposited HfO2 films at negative bias due to the reduced trap-assisted tunneling by the incorporation of F to block the electrons transferring from metal electrode to the trap level.

Zhang, H. Y.; Jin, C. G.; Yang, Y.; Ye, C.; Zhuge, L. J.; Wu, X. M.

2014-08-01

58

Vacuum ultraviolet thin films. I - Optical constants of BaF2, CaF2, LaF3, MgF2, Al2O3, HfO2, and SiO2 thin films. II - Vacuum ultraviolet all-dielectric narrowband filters  

NASA Astrophysics Data System (ADS)

An iteration process matching calculated and measured reflectance and transmittance values in the 120-230 nm VUV region is presently used to ascertain the optical constants of bulk MgF2, as well as films of BaF2, CaF2, LaF3, MgF2, Al2O3, HfO2, and SiO2 deposited on MgF2 substrates. In the second part of this work, a design concept is demonstrated for two filters, employing rapidly changing extinction coefficients, centered at 135 nm for BaF2 and 141 nm for SiO2. These filters are shown to yield excellent narrowband spectral performance in combination with narrowband reflection filters.

Zukic, Muamer; Torr, Douglas G.; Spann, James F.; Torr, Marsha R.

1990-10-01

59

Vacuum ultraviolet thin films. I - Optical constants of BaF2, CaF2, LaF3, MgF2, Al2O3, HfO2, and SiO2 thin films. II - Vacuum ultraviolet all-dielectric narrowband filters  

NASA Technical Reports Server (NTRS)

An iteration process matching calculated and measured reflectance and transmittance values in the 120-230 nm VUV region is presently used to ascertain the optical constants of bulk MgF2, as well as films of BaF2, CaF2, LaF3, MgF2, Al2O3, HfO2, and SiO2 deposited on MgF2 substrates. In the second part of this work, a design concept is demonstrated for two filters, employing rapidly changing extinction coefficients, centered at 135 nm for BaF2 and 141 nm for SiO2. These filters are shown to yield excellent narrowband spectral performance in combination with narrowband reflection filters.

Zukic, Muamer; Torr, Douglas G.; Spann, James F.; Torr, Marsha R.

1990-01-01

60

Seeding atomic layer deposition of high-k dielectric on graphene with ultrathin poly(4-vinylphenol) layer for enhanced device performance and reliability  

NASA Astrophysics Data System (ADS)

We demonstrate that ultrathin poly(4-vinylphenol) (PVP) acts as an effective organic seeding layer for atomic layer deposition (ALD) of high-k dielectric on large-scale graphene fabricated by chemical vapor deposition (CVD). While identical ALD conditions result in incomplete and rough dielectric deposition on CVD graphene, the reactive groups provided by the PVP seeding layer yield conformal and pinhole-free dielectric films throughout the large-scale graphene. Top-gate graphene field effect transistors fabricated with the high quality, PVP-seeded Al2O3 gate dielectric show superior carrier mobility and enhanced reliability performance, which are desirable for graphene nanoelectronics.

Cheol Shin, Woo; Yong Kim, Taek; Sul, Onejae; Jin Cho, Byung

2012-07-01

61

Ultrathin nitride\\/oxide (N\\/O) gate dielectrics for p+-polysilicon gated PMOSFETs prepared by a combined remote plasma enhanced CVD\\/thermal oxidation process  

Microsoft Academic Search

Ultrathin nitride-oxide (N\\/O~1.5\\/2.6 nm) dual layer gate dielectrics have been incorporated into PMOSFETs with boron-implanted polysilicon gates. Boron penetration is effectively suppressed by the top plasma-deposited nitride layer leading to improved short channel performance as compared to PMOSFETs with oxide dielectrics. In addition, improved interface characteristics and hot carrier degradation immunity are also demonstrated for the devices with the N\\/O

Yider Wu; Gerald Lucovsky

1998-01-01

62

Investigation of E2g^1 and A1g Raman Modes of Few-Layer MoS2 on HfO2 Substrate  

NASA Astrophysics Data System (ADS)

The recent research work by Radisavljevic et al.[1] shows that the mobilities of monolayer MoS2 transistors can be improved by employing a thin layer of hafnium oxide as top-gate dielectric. Dielectric screening has been successfully demonstrated to suppress the Coulomb interactions of charged impurities on the substrate. Therefore, we develop an alternative method of building monolayer MoS2 transistors on HfO2 substrate. Owing to the low contrast of few-layer MoS2 flakes on thin HfO2 layer, which makes the realization of such device configuration difficult. By utilizing the thickness dependence of in-plane and out-of-plane Raman peaks of MoS2 flakes, E2g^1 andA1g, respectively, we establish an efficient approach to improve the identification of MoS2 layers by Raman spectrum instead of AFM. Our investigation of Raman spectrum of few-layer MoS2 on HfO2 shows the significant difference from those on SiO2. The substrate dependence of Raman spectrum as well as its further application will be discussed in this talk.[4pt] [1] Radisavljevic, et al., Nat. Nanotech. 6, 147 (2011)

Chien, Hui-Chun; Kumar, Jatinder; Chiu, Hsin-Ying

2013-03-01

63

Temperature dependent structural, optical and hydrophobic properties of sputtered deposited HfO2 films  

NASA Astrophysics Data System (ADS)

Hafnium oxide being high-k dielectric has been successfully utilized in electronic and optical applications. Being thermodynamically stable and having good mechanical strength, it can be used as a protective coating for outdoor HV insulators which are suffering from surface flashover problem due to contamination. In this paper, we are investigating the effect of substrate temperature on structural, optical and hydrophobic properties of hafnium oxide coating deposited over glass insulators by DC magnetron sputtering. X-ray diffraction is applied to determine the crystalline phase and crystallite size of the film. The morphology of the samples is examined using atomic force microscopy. The optical properties are studied using UV-vis-NIR spectrophotometer. The wettability of the film is investigated using contact angle meter. The thickness is measured using surface profilometer and verified through optical data. The relationship between substrate temperature with grain size, roughness, refractive index, and hydrophobicity is manifested. The maximum contact angle for HfO2 film was found to be 106 at 400C.

Dave, V.; Dubey, P.; Gupta, H. O.; Chandra, R.

2014-01-01

64

III-Nitride grating grown on freestanding HfO2 gratings  

PubMed Central

We report here the epitaxial growth of III-nitride material on freestanding HfO2 gratings by molecular beam epitaxy. Freestanding HfO2 gratings are fabricated by combining film evaporation, electron beam lithography, and fast atom beam etching of an HfO2 film by a front-side silicon process. The 60-?m long HfO2 grating beam can sustain the stress change during the epitaxial growth of a III-nitride material. Grating structures locally change the growth condition and vary indium composition in the InGaN/GaN quantum wells and thus, the photoluminescence spectra of epitaxial III-nitride grating are tuned. Guided mode resonances are experimentally demonstrated in fabricated III-nitride gratings, opening the possibility to achieve the interaction between the excited light and the grating structure through guided mode resonance. PACS: 78.55.Cr; 81.65.Cf; 81.15.Hi. PMID:21849084

2011-01-01

65

Chemical structures and electrical properties of atomic layer deposited HfO2 thin films grown at an extremely low temperature (?100 C) using O3 as an oxygen source  

NASA Astrophysics Data System (ADS)

The properties of atomic layer deposited (ALD) HfO2 films grown at low temperatures (?100 C) were examined for potential applications in flexible display and bioelectronics. A saturated ALD growth behavior was observed even at an extremely low temperature (30 C) due to the strong oxidizing potential of O3. However, HfO2 films grown at low temperatures showed a low film density and high impurity concentration, because the thermal energy during film growth was insufficient to remove ligands completely from Hf ions in precursor molecule. This resulted in low dielectric constant and high leakage current density of the films. Nevertheless, HfO2 film grown at 100 C using O3 gas with a high concentration (390 g/Nm3) showed a tolerable impurity concentration with the dielectric constant of 16 and breakdown field of 4 MV/cm, which are approximately two-thirds of those of HfO2 film grown at 250 C.

Kim, Jeong Hwan; Park, Tae Joo; Kim, Seong Keun; Cho, Deok-Yong; Jung, Hyung-Suk; Lee, Sang Young; Hwang, Cheol Seong

2014-02-01

66

Formation of the dopant-oxygen vacancy complexes and its influence on the photoluminescence emissions in Gd-doped HfO2  

NASA Astrophysics Data System (ADS)

Rare earth doping is widely used to improve the desired properties of high-k dielectric oxides. However, whether rare earth doping can suppress the formation of oxygen vacancies is still debated. By using the first-principles calculations with the generalized gradient approximation and more advanced hybrid functional, we have investigated the structural and electronic properties of the dopant-oxygen vacancy complexes in Gd-doped HfO2. Our calculations indicate that the Gd dopants interacting with oxygen vacancies can substantially shift up the VO energy states towards the conduction band edge. This together with other effects, such as capturing the localized electrons at the oxygen vacancy by Gd dopants and suppressing the randomicity of oxygen vacancy formation, improves the reliability of the devices made from Gd-doped HfO2. Based on our calculated results, we have presented an explanation for the experimentally observed decrease of the VO-related photoluminescence intensities upon Gd doping in HfO2.

Wang, L. G.; Tu, H. L.; Xiong, Y. H.; Xiao, W.; Du, J.; Wang, J. W.; Huang, G. J.

2014-09-01

67

Nonvolatile memories using deep traps formed in HfO2 by Nb ion implantation  

Microsoft Academic Search

We report nonvolatile memories (NVMs) based on deep-energy trap levels formed in HfO2 by metal ion implantation. A comparison of Nb- and Ta-implanted samples shows that suitable charge-trapping centers are formed in Nb-implanted samples, but not in Ta-implanted samples. This is consistent with density-functional theory calculations which predict that only Nb will form deep-energy levels in the bandgap of HfO2.

Min Choul Kim; Chang Oh Kim; Houng Taek Oh; Suk-Ho Choi; K. Belay; R. G. Elliman; S. P. Russo

2011-01-01

68

Schottky barrier height reduction for metal/n-InP by inserting ultra-thin atomic layer deposited high-k dielectrics  

NASA Astrophysics Data System (ADS)

Fermi level pinning at metal/n-InP interface and effective Schottky barrier height (?B,eff) were optimized by inserting ultrathin dielectrics in this work. Comparing the inserted monolayer and bilayer high-k dielectrics, we demonstrated that the introduction of bilayer dielectrics can further reduce ?B,eff (from 0.49 eV to 0.22 eV) than the monolayer dielectric (from 0.49 eV to 0.32 eV) even though the overall dielectric thickness was thicker. The additional dipole formed at high-k/high-k interfaces could be used to expound the mechanism. This work proposed an effective solution to reduce resistance contacts for InP based transistors and Schottky barrier transistors.

Zheng, Shan; Yang, Wen; Sun, Qing-Qing; Chen, Lin; Zhou, Peng; Wang, Peng-Fei; Wei Zhang, David; Xiao, Fei

2013-12-01

69

Schottky barrier height reduction for metal/n-InP by inserting ultra-thin atomic layer deposited high-k dielectrics  

SciTech Connect

Fermi level pinning at metal/n-InP interface and effective Schottky barrier height (?{sub B,eff}) were optimized by inserting ultrathin dielectrics in this work. Comparing the inserted monolayer and bilayer high-k dielectrics, we demonstrated that the introduction of bilayer dielectrics can further reduce ?{sub B,eff} (from 0.49?eV to 0.22?eV) than the monolayer dielectric (from 0.49?eV to 0.32?eV) even though the overall dielectric thickness was thicker. The additional dipole formed at high-k/high-k interfaces could be used to expound the mechanism. This work proposed an effective solution to reduce resistance contacts for InP based transistors and Schottky barrier transistors.

Zheng, Shan; Yang, Wen; Sun, Qing-Qing, E-mail: qqsun@fudan.edu.cn, E-mail: linchen@fudan.edu.cn; Zhou, Peng; Wang, Peng-Fei; Wei Zhang, David [State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai 200433 (China)] [State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai 200433 (China); Chen, Lin; Xiao, Fei [Department of Materials Science, Fudan University, Shanghai 200433 (China)] [Department of Materials Science, Fudan University, Shanghai 200433 (China)

2013-12-23

70

A new low thermal budget approach to interface nitridation for ultra-thin silicon dioxide gate dielectrics by combined plasma-assisted and rapid thermal processing  

Microsoft Academic Search

This paper reports a new low thermal budget approach to interface nitridation for ultra-thin gate dielectrics. Monolayer level nitrogen incorporation at Si-SiO2 interfaces is accomplished by combining a 300 C remote plasma-assisted oxidation step that forms ~0.5 to 0.6 nm of SiO2 with a post-oxidation remote plasma assisted nitridation. Incorporation of nitrogen is studied by a combination of secondary ion

H. Niimi; H. Y. Yang; G. Lucovsky

1998-01-01

71

Residual stress and interface effect on dielectric mechanisms in poled ultrathin relaxor ferroelectric single crystals  

NASA Astrophysics Data System (ADS)

We have investigated the dielectric performances and mechanism of super-thin Mn-doped Pb(Mg1/3Nb2/3)O3-PbTiO3 crystals, exhibiting significantly different dielectric behaviors compared with thick wafer. Dramatic decrease by 5 times and large frequency dispersion of permittivity, changed diffuse degree of phase transition, dielectric loss anomaly with frequency and dielectric performances with direct-current electric field for thin wafers are observed, proving the existence of large surface residual stress and interface effects. Additionally, a theoretical model of low-permittivity and low-ferroelectric surface damage layers is concurrently proposed. These observations have important implications for actual performances of thin wafers applied in practical devices.

Li, Long; Zhao, Xiangyong; Li, Xiaobing; Xu, Qing; Yang, Linrong; Wang, Sheng; Luo, Haosu

2014-05-01

72

In-Line Compositional and Thickness Metrology Using XPS for Ultra-Thin Dielectric Films  

SciTech Connect

65 nm and 45 nm silicon devices will utilize compositionally critical processes for gate dielectrics, capacitor dielectrics, gate and capacitor electrodes, and ultra shallow junction layers. For example, small changes in nitrogen composition have been correlated with unacceptable shifts in electrical properties of devices with SiOxNy gate dielectrics. Present optically-based metrology technologies for such applications are reaching limits for precise thickness measurements and do not provide direct and adequately precise compositional information. As a result, mature analytical techniques, such as x-ray photoelectron spectroscopy (XPS), are now being transitioned to in-line production metrology usage.We discuss the application of XPS optimized for 200/300 mm production to compositional and thickness metrology of SiOxNy and high k gate dielectrics, high k capacitor dielectrics, and new electrode materials. The development of optimized hardware, robust data analysis algorithms and high throughput, fully automated operation has led to production implementation of XPS in advanced logic applications. The precise correlation of plasma nitridation metrology data with electrical device parameters has proven valuable in detecting process drifts early in the process flow, without the need to prepare devices through the first metal layer for testing. High density maps of film thickness and composition have enabled optimization of oxidation, nitridation and post-nitridation anneal processes for SiOxNy film production for 90 nm, 65 nm and below. High precision compositional and thickness metrology data for high-k gate and capacitor dielectrics is also presented.

Truman, J. Kelly; Gurer, Emir; Larson, C. Thomas; Reed, David [ReVera, Inc., 810 Kifer Road, Sunnyvale, CA 94086 (United States)

2005-09-09

73

Effect of thermal annealing and oxygen partial pressure on the swelling of HfO2/SiO2/Si metal-oxide-semiconductor structure grown by rf sputtering: A synchrotron x-ray reflectivity study  

NASA Astrophysics Data System (ADS)

As-grown and rapid thermal annealed thin HfO2 films, deposited on Si(100) substrate by reactive rf sputtering at various partial pressures of O2 and Ar, are studied by synchrotron x-ray reflectivity. The growth of interfacial layer (IL) of SiO2 is more or less linear with the decrease in oxygen partial pressure (pO2) in the O2/Ar mixture. The thickest oxide is found to be grown at the minimum oxygen partial pressure (pO2). It is observed that the IL swells upon annealing at higher temperature, and swelling is maximum for the sample grown in minimum pO2. The surface roughness and thickness of the HfO2 films decrease upon annealing indicating a denser film. The HfO2/Si interface roughness is also decreased upon annealing. Therefore, lower annealing temperature and higher pO2 is to be set to reduce the IL thickness and for higher dielectric constant and larger oxide capacitance. High frequency capacitance-voltage (C-V) measurement on the devices, annealed at higher temperature, further shows the necessity for optimization of pO2 during the deposition of HfO2 film to minimize the fixed oxide charge density of metal-oxide-semiconductor devices.

Biswas, Debaleen; Md Faruque, Sk Abdul Kader; Sinha, Anil Kumar; Upadhyay, Anuj; Chakraborty, Supratic

2014-09-01

74

Study of the Reliability Impact of Chlorine Precursor Residues in Thin Atomic-Layer-Deposited HfO2 Layers  

Microsoft Academic Search

Atomic layer deposition (ALD) with HfCl4 as a precursor is widely used for HfO2 fabrication. Due to the nature of the precursor under study, i.e., HfCl4 and H2O, the presence of chlorine residues in the film due to insufficient hydrolysis is eminent. Obviously, the chlorine residue in the HfO2 film is suspected to affect the quality of the HfO2 film.

Moonju Cho; Robin Degraeve; Geoffrey Pourtois; Annelies Delabie; Lars-Ke Ragnarsson; Thomas Kauerauf; Guido Groeseneken; Stefan De Gendt; Marc Heyns; Cheol Seong Hwang

2007-01-01

75

Ultrathin ALD-Al2O3 layers for Ge(001) gate stacks: Local composition evolution and dielectric properties  

NASA Astrophysics Data System (ADS)

Correlations among physical and electrical properties of atomic layer deposited (ALD)-Al2O3 on H2O-prepulsed Ge(100) have been investigated to evaluate Al2O3 as an ultrathin interface passivation layer for higher-k/Al2O3/Ge gate stacks. In situ XPS in the ALD environment provides insights into the local composition evolution during the initial stages of ALD, evidencing (a) an incubation regime that may limit the minimum achievable capacitance equivalent thickness (CET) of these gate stacks, and (b) residual hydroxyl incorporation in the film consistent with the observed dielectric constant 7.2. Thickness scaling of the CET is consistent with a nearly abrupt interface as measured by synchrotron radiation photoemission spectroscopy (SRPES). SRPES studies also reveal that forming gas anneal provides passivation through monolayer-level formation of stoichiometric GeO2, suggesting a complex chemical interaction involving residual -OH groups in the as-grown ALD-Al2O3. Valence and conduction band offsets of prepulsed ALD-Al2O3 with respect to Ge are calculated to be 3.3 0.1 and 2.6 0.3 eV, indicating that these layers offer an effective barrier to hole and electron injection.

Swaminathan, Shankar; Sun, Yun; Pianetta, Piero; McIntyre, Paul C.

2011-11-01

76

Quantum size effect on dielectric function of ultrathin metal film: a first-principles study of Al(1?1?1).  

PubMed

Using first-principles calculations, we show manifestations of the quantum size effect in the dielectric function ?2 of free-standing Al(1?1?1) ultrathin films of 1monolayer to 20monolayers, taking into account size dependent contributions from both interband and intraband electronic transitions. Overall the in-plane components (interband transition) of ?2 increase with film thickness at all frequencies, converging towards a constant value. However, the out-of-plane components of ?2 show a more complex behavior, and, only at frequencies less than 0.75eV, increase with film thickness without convergence. This suggests that ultrathin films can possibly be used for low-loss plasmonics devices in the visible and ultraviolet range. Our findings may shed light on searching for low-loss plasmonic materials via quantum size effect. PMID:25419653

Ming, Wenmei; Blair, Steve; Liu, Feng

2014-12-17

77

Crystallization of HfO2 in InAs/HfO2 core-shell nanowires  

NASA Astrophysics Data System (ADS)

We report the impact of deposition parameters on the structure of HfO2 covering InAs nanowires (NWs) being potential candidates for future field-effect transistors (FETs). Molecular beam epitaxial-grown Au-free InAs NWs were covered with HfO2 deposited by atomic-layer deposition. The impact of the film thickness as well as the deposition temperature on the occurrence and amount of crystalline HfO2 regions was investigated by high-resolution transmission electron microscopy (TEM) and x-ray diffraction. Compared to the deposition on planar Si substrates, the formation probability of crystalline HfO2 on InAs NWs is significantly enhanced. Here, even 3 nm thick films deposited at 250 C are partly crystalline. Similarly, a low deposition temperature of 125 C does not result in completely amorphous 10 nm thick HfO2 films, they contain monoclinic as well as orthorhombic HfO2 nanocrystals. Combining HfO2 and Al2O3 into a laminate structure is capable of suppressing the formation of crystalline HfO2 grains.

Rieger, T.; Jrres, T.; Vogel, J.; Biermanns, A.; Pietsch, U.; Grtzmacher, D.; Lepsa, M. I.

2014-10-01

78

Monolayer-level controlled incorporation of nitrogen in ultra-thin gate dielectrics using remote plasma processing  

NASA Astrophysics Data System (ADS)

A low thermal budget approach to monolayer-level controlled incorporation of nitrogen in ultra-thin gate dielectrics using remote plasma processing is discussed. Incorporation of nitrogen at the Si-SiO2 interface, 'N-O' structure, is achieved by 300C O2/He remote plasma assisted oxidation of the Si surface followed by N2/He remote plasma nitridation at 0.3 Torr. Secondary ion mass spectroscopy (SIMS) showed that the interfacial nitrogen concentration was linearly proportional to the N2/He plasma exposure time. One monolayer of nitrogen, 7 x 1014 cm-2, at the Si-SiO 2 interface was achieved by the 90-second N2/He plasma nitridation. This monolayer of nitrogen at the interface reduced leakage currents in Fowler-Nordheim (F-N) and direct tunneling regimes. Core-level photoemission spectroscopy (PES) revealed that the post-oxidation nitridation reduced sub-oxide densities at the interface. This interfacial 'modification' contributed to the reduction of tunneling currents. Incorporation of nitrogen on the top surface of oxide, 'O-N' structure, is achieved by 300C N2/He remote plasma nitridation of the bulk oxide at 0.1 Torr. SIMS data showed the nitrogen was confined only at the top surface of oxide. This top surface 'nitrided' layer suppressed boron diffusion from boron doped p+ poly-Si gate-electrodes. Thus, combining interfacial and top surface nitridation processes, ' N-O-N' structure, reduced leakage currents and prevented boron diffusion, so that this combination is applicable for advanced symmetric complementary metal-oxide-semiconductor (CMOS) technology.

Niimi, Hiroaki

79

Experimental and theoretical studies of the energy-loss straggling of H and He ion beams in HfO2 films  

NASA Astrophysics Data System (ADS)

We report an experimental-theoretical study of the energy-loss straggling of protons and alpha particles in HfO{2} films. In the case of H ions the experiments were performed in the energy range 40-1750 keV. For the lower energy interval (40-250 keV) we have used the medium energy ion scattering (MEIS) technique with a resolution of ? E/E 410-3, while for the higher energies the Rutherford backscattering technique (RBS) was employed with an overall resolution of 7 keV. Concerning the He ions the straggling study has covered an energy range between 250 and 3000 keV by using RBS measurements, which in this case had a resolution better than 10 keV. The theoretical calculations were done in the framework of the dielectric formalism using the MELF-GOS model to obtain a proper description of the energy loss function (ELF) of the HfO{2} target. It is shown that for both projectiles the experimental data and the theoretical predictions for the energy-loss straggling display a very good agreement.

Abril, I.; Behar, M.; Garcia-Molina, R.; Fadanelli, R. C.; Nagamine, L. C. C. M.; Grande, P. L.; Schnemann, L.; Denton, C. D.; Arista, N. R.; Saitovitch, E. B.

2009-07-01

80

Gd-doping effect on performance of HfO2 based resistive switching memory devices using implantation approach  

NASA Astrophysics Data System (ADS)

An implantation doping approach is implemented to fabricate Gd-doped HfO2 resistive random access memory (RRAM) devices. The significantly enhanced performances are achieved in the Gd-doped HfO2 RRAM devices including improved uniformity of switching parameters, enlarged ON/OFF ratio, and increased switching speed without obvious reliability degradation. This performance improvement in the Gd-doped HfO2 RRAM devices is clarified to the suppressed randomicity of oxygen vacancy filaments' formation and the reduced oxygen ion migration barrier induced by trivalent Gd-doping effect. The achieved results also demonstrate the validity of implantation doping approach for the fabrication of RRAM devices.

Zhang, Haowei; Liu, Lifeng; Gao, Bin; Qiu, Yuanjun; Liu, Xiaoyan; Lu, Jing; Han, Ruqi; Kang, Jinfeng; Yu, Bin

2011-01-01

81

Femtosecond laser-induced damage of HfO2/SiO2 mirror with different stack structure.  

PubMed

Laser-induced damage of the "standard" (?/4 stack structure) and "modified" (reduced standing-wave field) HfO(2)/SiO(2) mirrors were investigated by a commercial 800 nm Ti:sapphire laser system. Three kinds of pulse duration of 50 fs, 105 fs, and 135 fs were chosen. The results show that the single-shot damage threshold of the "modified" mirror was about 14%-23% higher compared to that of the "standard" mirror. A model based on the rate equation for free electron generation was adopted to explain the threshold results. It took in account the transient changes in the dielectric function of material during the laser pulse. The simulated threshold agreed with the experimental very well. Besides, for two kinds of mirror, typical breakdown craters for both the single-shots and multi-shots damage tests reveal striking distinct characteristics. Interestingly, the multi-shots damage crater with zigzag-like edge was observed only on the "standard" mirror. These phenomena were illustrated reasonably by the distribution features of the electric field intensity within the mirrors. PMID:22945167

Chen, Shunli; Zhao, Yuan'an; Yu, Zhenkun; Fang, Zhou; Li, Dawei; He, Hongbo; Shao, Jianda

2012-09-01

82

Morphology and Photoluminescence of HfO2 Obtained by Microwave-Hydrothermal  

NASA Astrophysics Data System (ADS)

In this letter, we report on the obtention of hafnium oxide (HfO2) nanostructures by the microwave-hydrothermal method. These nanostructures were analyzed by X-ray diffraction (XRD), field-emission gum scanning electron microscopy (FEG-SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectrometry (EDXS), ultraviolet-visible (UV-vis) spectroscopy, and photoluminescence (PL) measurements. XRD patterns confirmed that this material crystallizes in a monoclinic structure. FEG-SEM and TEM micrographs indicated that the rice-like morphologies were formed due to an increase in the effective collisions between the nanoparticles during the MH processing. The EDXS spectrum was used to verify the chemical compositional of this oxide. UV-vis spectrum revealed that this material have an indirect optical band gap. When excited with 488 nm wavelength at room temperature, the HfO2 nanostructures exhibited only one broad PL band with a maximum at around 548 nm (green emission).

Elizirio, S. A.; Cavalcante, L. S.; Sczancoski, J. C.; Pizani, P. S.; Varela, J. A.; Espinosa, J. W. M.; Longo, E.

2009-11-01

83

Grain boundary mediated leakage current in polycrystalline HfO2 films  

SciTech Connect

In this work, we combine conductive atomic force microscopy (CAFM) and first principles calculations to investigate leakage current in thin polycrystalline HfO2 films. A clear correlation between the presence of grain boundaries and increased leakage current through the film is demonstrated. The effect is a result of a number of related factors, including local reduction in the oxide film thickness near grain boundaries, the intrinsic electronic properties of grain boundaries which enhance direct tunnelling relative to the bulk, and segregation of oxygen vacancy defects which increase trap assisted tunnelling currents. These results highlight the important role of grain boundaries in determining the electrical properties of polycrystalline HfO2 films with relevance to applications in advanced logic and memory devices.

Mckenna, Keith P.; Shluger, AL; Iglesias, V.; Porti, M.; Nafria, M.; Lanza, M.; Bersuker, G.

2011-07-01

84

J. A. Rogers and co-workers present an ultrathin, skin-like device for the wireless measurement of the dielectric properties and deformations of the skin. The construction exploits LC  

E-print Network

of the dielectric properties and deformations of the skin. The construction exploits LC resonators with capacitive/tissue contact. Dry elec- trodes based on ultrathin flexible polymer films (e.g., parylene)[1,2] and elastomer to London-dispersion effects between molecules of the skin and the elastomer substrate (e.g., PDMS), thereby

Rogers, John A.

85

Resistive switching properties of HfO2-based ReRAM with implanted Si/Al ions  

NASA Astrophysics Data System (ADS)

The effects of Si and Al ion implantation on the resistive switching properties of a HfO2-based resistive random access memory (RRAM) device are investigated. Testing results demonstrate that Si or Al implantation into HfO2 films results in reduced electroforming voltages and improves reproducibility of resistive switching over 1,000 cycles as measured by a DC voltage sweeping method. Furthermore, the Si or Al implantation into HfO2 resistive switching memory devices was found to improve device yields, reduce operating voltages and their variability, expand on/off resistance ratio (>103 for Al-doped, > 500 for Si-doped), and increase retention times (>3 105 s at room temperature). Doping by Si or Al ion is suggested to improve the formation of conducting filaments in HfO2 matrix and thus improve the performances of the Pt/Ti/HfO2/Pt device.

Xie, Hongwei; Wang, Ming; Kurunczi, Peter; Erokhin, Yuri; Liu, Qi; Lv, Hangbing; Li, Yingtao; Long, Shibing; Liu, Su; Liu, Ming

2012-11-01

86

Enhanced performance of supported HfO2 counter electrodes for redox couples used in dye-sensitized solar cells.  

PubMed

Mesoporous-graphitic-carbon-supported HfO2 (HfO2 -MGC) nanohybrids were synthesized by using a soft-template route. Characterization and a systematic investigation of the catalytic properties, stability, and catalytic mechanism were performed for HfO2 -MGC counter electrodes (CEs) in dye-sensitized solar cells (DSSCs). The new HfO2 -MGC as a CE in DSSCs showed a surprisingly high efficiency of 7.75 % for the triiodide/iodide redox couple and 3.69 % for the disulfide/thiolate redox couple, greater than the Pt electrode in the corresponding electrolyte system, which opens up a possibility for its practical application. PMID:24399514

Yun, Sining; Pu, Haihui; Chen, Junhong; Hagfeldt, Anders; Ma, Tingli

2014-02-01

87

Thickness independent reduced forming voltage in oxygen engineered HfO2 based resistive switching memories  

NASA Astrophysics Data System (ADS)

The conducting filament forming voltage of stoichiometric hafnium oxide based resistive switching layers increases linearly with layer thickness. Using strongly reduced oxygen deficient hafnium oxide thin films grown on polycrystalline TiN/Si(001) substrates, the thickness dependence of the forming voltage is strongly suppressed. Instead, an almost constant forming voltage of about 3 V is observed up to 200 nm layer thickness. This effect suggests that filament formation and switching occurs for all samples in an oxidized HfO2 surface layer of a few nanometer thickness while the highly oxygen deficient thin film itself merely serves as a oxygen vacancy reservoir.

Sharath, S. U.; Kurian, J.; Komissinskiy, P.; Hildebrandt, E.; Bertaud, T.; Walczyk, C.; Calka, P.; Schroeder, T.; Alff, L.

2014-08-01

88

HfO2/SiO2 chirped mirrors manufactured by electron beam evaporation.  

PubMed

A HfO2/SiO2 chirped mirror was manufactured by electron beam evaporation to increase the laser resistance. The hybrid monitoring strategy utilizing both monochromatic monitoring and quartz crystal monitoring was applied to the deposition compared to the single optical monitoring method. The coatings were characterized by transmission spectrophotometer and white light interferometry, and the experimental results showed that the chirped mirror monitored with the hybrid strategy possessed high reflectivity (>99.7%) and tolerable group delay dispersion oscillation (-5020?fs2) in the spectra range of 740-860?nm. PMID:21460969

Jinlong, Zhang; Xinbin, Cheng; Zhanshan, Wang; Hongfei, Jiao; Tao, Ding

2011-03-20

89

Effects of different dopants on switching behavior of HfO2-based resistive random access memory  

NASA Astrophysics Data System (ADS)

In this study the effects of doping atoms (Al, Cu, and N) with different electro-negativities and ionic radii on resistive switching of HfO2-based resistive random access memory (RRAM) are systematically investigated. The results show that forming voltages and set voltages of Al/Cu-doped devices are reduced. Among all devices, Cu-doped device shows the narrowest device-to-device distributions of set voltage and low resistance. The effects of different dopants on switching behavior are explained with deferent types of CFs formed in HfO2 depending on dopants: oxygen vacancy (Vo) filaments for Al-doped HfO2 devices, hybrid filaments composed of oxygen vacancies and Cu atoms for Cu-doped HfO2 devices, and nitrogen/oxygen vacancy filaments for N-doped HfO2 devices. The results suggest that a metal dopant with a larger electro-negativity than host metal atom offers the best comprehensive performance.

Deng, Ning; Pang, Hua; Wu, Wei

2014-10-01

90

Fully Solution-Processed Low-Voltage Aqueous In2O3 Thin-Film Transistors Using an Ultrathin ZrOx Dielectric.  

PubMed

We reported here "aqueous-route" fabrication of In2O3 thin-film transistors (TFTs) using an ultrathin solution-processed ZrOx dielectric thin film. The formation and properties of In2O3 thin films under various annealing temperatures were intensively examined by thermogravimetric analysis, Fourier transform infrared spectroscopy, and atomic force microscopy. The solution-processed ZrOx thin film followed by sequential UV/ozone treatment and low-temperature thermal-annealing processes showed an amorphous structure, a low leakage-current density (?1 10(-9) A/cm(2) at 2 MV/cm), and a high breakdown electric field (?7.2 MV/cm). On the basis of its implementation as the gate insulator, the In2O3 TFTs based on ZrOx annealed at 250 C exhibit an on/off current ratio larger than 10(7), a field-effect mobility of 23.6 cm(2)/Vs, a subthreshold swing of 90 mV/decade, a threshold voltage of 0.13 V, and high stability. These promising properties were obtained at a low operating voltage of 1.5 V. These results suggest that "aqueous-route" In2O3 TFTs based on a solution-processed ZrOx dielectric could potentially be used for low-cost, low-temperature-processing, high-performance, and flexible devices. PMID:25285983

Liu, Ao; Liu, Guo Xia; Zhu, Hui Hui; Xu, Feng; Fortunato, Elvira; Martins, Rodrigo; Shan, Fu Kai

2014-10-22

91

Low temperature atomic layer deposited HfO2 film for high performance charge trapping flash memory application  

NASA Astrophysics Data System (ADS)

The impact of key process parameters on the electrical characteristics of atomic layer deposited HfO2 films has been systematically studied with MHOS devices via capacitance-voltage (C-V) measurement. C-V hysteresis curves revealed that charge storage capacity is significantly enhanced with decreasing substrate temperature from 350 down to 150 C and/or increasing purge time of the inert gas. The developed HfO2 trapping layer was also demonstrated by a MAHOS memory device. Improved memory window, fast program speed and good retention characteristics have been obtained. The study provides a reference for memory performance improvement of HfO2-based charge trap flash memory.

Chen, Guoxing; Huo, Zongliang; Jin, Lei; Zhang, Dong; Zhao, Shengjie; Han, Yulong; Liu, Su; Liu, Ming

2014-04-01

92

Electronic properties of InP (001)/HfO2 (001) interface: Band offsets and oxygen dependence  

NASA Astrophysics Data System (ADS)

Using ab-initio methods, atomic structures and electronic properties of InP (001)/HfO2 (001) interface are studied within the framework of density functional theory. We examine the InP/HfO2 model interface electronic structures under varying oxidation conditions. The effects of indium and phosphorous concentrations on interfacial bonding, defect states, band offsets, and the thermodynamic stability at the interface are also investigated. The origin of interfacial gap states in InP (001)/HfO2 (001) interface are proposed, mainly from the P-rich oxides, which is validated by our experimental work. This highlights the importance of surface passivation prior to high-? deposition based on the in situ spectroscopic results of atomic layer deposition of HfO2 on InP.

KC, Santosh; Dong, Hong; Longo, Roberto C.; Wang, Weichao; Xiong, Ka; Wallace, Robert M.; Cho, Kyeongjae

2014-01-01

93

Chemical vapor deposition of anisotropic ultrathin gold films on optical fibers: real-time sensing by tilted fiber Bragg gratings and use of a dielectric pre-coating  

NASA Astrophysics Data System (ADS)

Tilted fiber Bragg gratings (TFBGs) are refractometry-based sensor platforms that have been employed herein as devices for the real-time monitoring of chemical vapour deposition (CVD) in the near-infrared range (NIR). The coreguided light launched within the TFBG core is back-reflected off a gold mirror sputtered onto the fiber-end and is scattered out into the cladding where it can interact with a nucleating thin film. Evanescent fields of the growing gold nanostructures behave differently depending on the polarization state of the core-guided light interrogating the growing film, therefore the resulting spectral profile is typically decomposed into two separate peak families for the orthogonal S- and P-polarizations. Wavelength shifts and attenuation profiles generated from gold films in the thickness regime of 5-100 nm are typically degenerate for deposition directly onto the TFBG. However, a polarization-dependence can be imposed by adding a thin dielectric pre-coating onto the TFBG prior to using the device for CVD monitoring of the ultrathin gold films. It is found that addition of the pre-coating enhances the sensitivity of the P-polarized peak family to the deposition of ultrathin gold films and renders the films optically anisotropic. It is shown herein that addition of the metal oxide coating can increase the peak-to-peak wavelength separation between orthogonal polarization modes as well as allow for easy resonance tracking during deposition. This is also the first reporting of anisotropic gold films generated from this particular gold precursor and CVD process. Using an ensemble of x-ray techniques, the local fine structure of the gold films deposited directly on the TFBG is compared to gold films of similar thicknesses deposited on the Al2O3 pre-coated TFBG and witness slides.

Mandia, David J.; Zhou, Wenjun; Ward, Matthew J.; Joress, Howie; Giorgi, Javier B.; Gordon, Peter; Albert, Jacques; Barry, Sen. T.

2014-09-01

94

RF Micro-Electro-Mechanical Systems Capacitive Switches Using Ultra Thin Hafnium Oxide Dielectric  

NASA Astrophysics Data System (ADS)

A ?-type RF capacitive switch using about 45-nm-thick HfO2 dielectric layer was fabricated. High isolation performance was obtained in wide-band range when the switch was down-state. The isolation was better than -40 dB at the frequency range of 4-35 GHz. Particularly, the isolation was better than -50 dB in the frequency range of 8-12 GHz, i.e., X band. HfO2 showed excellent process compatibility with conventional microfabrication procedure. The 45-nm-thick HfO2 film was prepared using sputtering at room temperature so that it was feasible to be integrated into RF switch and other microwave circuits. The results of constant bias stressing showed that the ultra thin HfO2 had excellent reliability. The electric breakdown of HfO2 was observed, which had no apparent negative effects on the reliability of the dielectric. HfO2 dielectrics were attractive in the application of RF micro-electro-mechanical systems (MEMS) switch for new generation of low-loss high-linearity microwave circuits.

Zhang, Yi; Onodera, Kazumasa; Maeda, Ryutaro

2006-01-01

95

Experimental evidence of two conduction mechanisms for direct tunnelling stress-induced leakage current through ultrathin silicon dioxide gate dielectrics  

NASA Astrophysics Data System (ADS)

A comprehensive analysis of the stress-induced leakage current (SILC) through thermally grown ultrathin silicon dioxide (SiO2) films has been presented based on experimental observations. Stressing and sensing measurements are done in tantalum nitride (TaN) gate metal-oxide-silicon (MOS) capacitors at negative gate bias in the direct tunnelling (DT) regime. Both transient and steady-state DT SILCs have been studied in oxides with thicknesses between 1.7 and 2.3 nm. On the premise of charge carrier generation/trapping characteristics, our experimental results give a better physical insight into the conduction mechanism of SILC through ultrathin SiO2 films stressed in the DT regime. We propose a physical model of SILC conduction on the basis of experimental evidence of two distinctly different conduction paths for DT SILC. Monitoring SILC behaviour, the monoenergetic nature of stress-induced neutral traps and hydrogen-induced defects in the oxide is established. Furthermore, our analysis shows that constant voltage stress degrades the device performance more severely than constant current stress.

Samanta, Piyas; Man, Tsz Yin; Keung Chan, Alain Chun; Zhang, Qingchun; Zhu, Chunxiang; Chan, Mansun

2006-10-01

96

Nucleation Studies of HfO2 Thin Films Produced by Atomic Layer Deposition Justin C. Hackley1  

E-print Network

Weapons & Materials Research Directorate, Army Research Laboratory, Aberdeen Proving Ground, Aberdeen, MD Microbalance (QCM) has been used for the deposition of HfO2 thin films with tetrakis (dimethylamino) hafnium starting surfaces. Spectroscopic ellipsometry (SE) and QCM measurements confirm linear growth of the films

Gougousi, Theodosia

97

Energetics and electronic structure of aluminum point defects in HfO2: A first-principles study  

E-print Network

with respect to the valence electron configuration 5d3 6s1 for hafnium atom, 2s2 2p4 for oxygen atom, and 3s2 3Energetics and electronic structure of aluminum point defects in HfO2: A first-principles study Z approximation, we studied the atomic structure, energetics, and electronic structure of the interstitial

Gong, Xingao

98

hal-00197196,version1-14Dec2007 Magnetic properties of HfO2 thin films.  

E-print Network

temperature reported recently in several oxides of d elements such as ZnO [1, 2], TiO2 [3, 4, 5, 6], HfO2 [7 pointed out the role of point defects in the stabilization of high- temperature ferromagnetism], point defects [17], intrinsic doping effect [18], anion or cation vacancies [19, 20], nor exchange

Boyer, Edmond

99

High-performance fully amorphous bilayer metal-oxide thin film transistors using ultra-thin solution-processed ZrOx dielectric  

NASA Astrophysics Data System (ADS)

In this study, we report high-performance amorphous In2O3/InZnO bilayer metal-oxide (BMO) thin-film transistor (TFT) using an ultra-thin solution-processed amorphous ZrOx dielectric. A thin layer of In2O3 offers a higher carrier concentration, thereby maximizing the charge accumulation and yielding high carrier mobility. A thick amorphous layer of InZnO controls the charge conductance resulting in low off-state current and suitable threshold voltage. As a consequence, the BMO TFT showed higher filed-effect mobility (37.9 cm2/V s) than single-layer InZnO TFT (7.6 cm2/V s). Apart from that we obtain an on/off current ratio of 109, a subthreshold swing voltage of 120 mV/decade, and a voltage shift ? 0.4 V under positive bias stress for 2.5 h, for a gate voltage of 3 V and drain voltage of 1 V. These data demonstrate that the BMO TFT has great potential for a broad range of applications as switching low-power transistors.

Liu, G. X.; Liu, A.; Shan, F. K.; Meng, Y.; Shin, B. C.; Fortunato, E.; Martins, R.

2014-09-01

100

Process development, material analysis, and electrical characterization of ultra thin hafnium silicate films for alternative gate dielectric application  

NASA Astrophysics Data System (ADS)

As aggressive scaling of the Metal-Oxide-Semiconductor (MOS) integrated circuit continues, the required equivalent oxide thickness (EOT) for 100nm technology and beyond is expected to be less than 12A. In this ultra-thin film regime, SiO2 or oxynitrides face serious limitations due to direct tunneling currents, dopant penetration, and reliability concerns. HfO 2, ZrO2 and their silicates are being considered as potential candidates for replacing conventional oxides or oxynitrides owing to their thermodynamic stability in contact with silicon, high dielectric constants, chemical stability at high temperatures, etc. Although HfO 2 has shown promising electrical characteristics such as low EOT and leakage, low crystallization temperature, poor interface quality, uncontrolled interfacial layer growth, and reliability issues are some of the concerns with it. HfSixOy has been sought as a solution to alleviate some of these problems. Hafnium silicate films were deposited by co-sputtering of hafnium and silicon in argon ambient followed by annealing. Hafnium silicates with more than 13% Si remains amorphous even after 1000C anneals. They also show better thermal stability characteristics than HfO2 at all compositions studied. They have been shown to be compatible with poly and TaN gate electrodes. Through process optimization, Hf-silicate films have been scaled down to 10.3A, with leakage in the order of 1mA/cm2 at -1.5V. Low dispersion, low stress-induced leakage currents, high effective breakdown fields, and large lifetimes were obtained. Good thermal stability with polysilicon and TaN electrodes were also obtained. MOS transistors have been demonstrated with poly and TaN electrodes, showing excellent subthreshold and drive current characteristics. The effects of NH3 pre-treatment on the electrical and reliability characteristics were also investigated. While thermal stability, EOT, leakage and breakdown were improved significantly, threshold voltage shifts, high hysteresis, poor MOSFET and poor reliability characteristics were obtained for the NH 3 pre-treated samples. In conclusion, promising electrical and material characteristics were obtained for Hf-silicates indicating that they are attractive candidates for alternative gate dielectric applications.

Gopalan, Sundararaman

101

The effect of aluminum doping on crystallinity, non-lattice oxygen, and resistance switching of Al-doped HfO2 films deposited by reactive sputtering  

NASA Astrophysics Data System (ADS)

In this work, the resistance switching characteristics of Al-doped HfO2 thin films were investigated with by systematically varying the Al concentration and analyzing of the microstructure and the chemical bonding states. TiN/Al-doped HfO2/Pt metal-insulator-metal stacks were fabricated with various Al concentrations of up to 16.8% by using reactive DC magnetron co-sputtering. X-ray diffraction and transmission electron microscopy measurement showed that HfO2 doped with more than 10.4% Al had an amorphous structure, while HfO2 doped with Al of less than 5.6% had a crystalline structure. X-ray photoelectron spectroscopy (XPS) showed that the concentration of non-lattice oxygen in Aldoped HfO2 films increased with increasing Al up to 5.6% and was saturated for Al concentrations above 5.6%. TiN/Al-doped HfO2/Pt stacks showed typical bipolar resistance switching characteristics. HfO2 doped with Al = 5.6% showed the smallest grains and the smallest uniformity in the forming electric field and the SET/RESET resistance distribution. We conclude that the grain boundaries play a more important role than point defects such as non-lattice oxygen in the resistance switching.

Lee, Kyumin; Na, Heedo; Sohn, Hyunchul; Kim, Jonggi

2014-09-01

102

Growth and Properties of Hafnicone and HfO2/Hafnicone Nanolaminate and Alloy Films Using Molecular Layer Deposition Techniques.  

PubMed

Molecular layer deposition (MLD) of the hafnium alkoxide polymer known as "hafnicone" was grown using sequential exposures of tetrakis(dimethylamido) hafnium (TDMAH) and ethylene glycol (EG) as the reactants. In situ quartz crystal microbalance (QCM) experiments demonstrated self-limiting reactions and linear growth versus the number of TDMAH/EG reaction cycles. Ex situ X-ray reflectivity (XRR) analysis confirmed linear growth and measured the density of the hafnicone films. The hafnicone growth rates were temperature-dependent and decreased from 1.2 per cycle at 105 C to 0.4 per cycle at 205 C. The measured density was ?3.0 g/cm(3) for the hafnicone films at all temperatures. Transmission electron microscopy images revealed very uniform and conformal hafnicone films. The XRR studies also showed that the hafnicone films were very stable with time. Nanoindentation measurements determined that the elastic modulus and hardness of the hafnicone films were 47 2 and 2.6 0.2 GPa, respectively. HfO2/hafnicone nanolaminate films also were fabricated using HfO2 atomic layer deposition (ALD) and hafnicone MLD at 145 C. The in situ QCM measurements revealed that HfO2 ALD nucleation on the hafnicone MLD surface required at least 18 TDMAH/H2O cycles. Hafnicone alloys were also fabricated by combining HfO2 ALD and hafnicone MLD at 145 C. The composition of the hafnicone alloy was varied by adjusting the relative number of TDMAH/H2O ALD cycles and TDMAH/EG MLD cycles in the reaction sequence. The electron density changed continuously from 8.2 10(23) e(-)/cm(3) for pure hafnicone MLD films to 2.4 10(24) e(-)/cm(3) for pure HfO2 ALD films. These hafnicone films and the HfO2/hafnicone nanolaminates and alloys may be useful for flexible thin-film devices. PMID:25203487

Lee, Byoung H; Anderson, Virginia R; George, Steven M

2014-10-01

103

Effects of nitrogen incorporation in HfO(2) grown on InP by atomic layer deposition: an evolution in structural, chemical, and electrical characteristics.  

PubMed

We investigated the effects of postnitridation on the structural characteristics and interfacial reactions of HfO2 thin films grown on InP by atomic layer deposition (ALD) as a function of film thickness. By postdeposition annealing under NH3 vapor (PDN) at 600 C, an InN layer formed at the HfO2/InP interface, and ionized NHx was incorporated in the HfO2 film. We demonstrate that structural changes resulting from nitridation of HfO2/InP depend on the film thickness (i.e., a single-crystal interfacial layer of h-InN formed at thin (2 nm) HfO2/InP interfaces, whereas an amorphous InN layer formed at thick (>6 nm) HfO2/InP interfaces). Consequently, the tetragonal structure of HfO2 transformed into a mixture structure of tetragonal and monoclinic because the interfacial InN layer relieved interfacial strain between HfO2 and InP. During postdeposition annealing (PDA) in HfO2/InP at 600 C, large numbers of oxidation states were generated as a result of interfacial reactions between interdiffused oxygen impurities and out-diffused InP substrate elements. However, in the case of the PDN of HfO2/InP structures at 600 C, nitrogen incorporation in the HfO2 film effectively blocked the out-diffusion of atomic In and P, thus suppressing the formation of oxidation states. Accordingly, the number of interfacial defect states (Dit) within the band gap of InP was significantly reduced, which was also supported by DFT calculations. Interfacial InN in HfO2/InP increased the electron-barrier height to ?0.6 eV, which led to low-leakage-current density in the gate voltage region over 2 V. PMID:24467437

Kang, Yu-Seon; Kim, Dae-Kyoung; Kang, Hang-Kyu; Jeong, Kwang-Sik; Cho, Mann-Ho; Ko, Dae-Hong; Kim, Hyoungsub; Seo, Jung-Hye; Kim, Dong-Chan

2014-03-26

104

Stress-induced leakage current and trap generation in HfO2 thin films  

NASA Astrophysics Data System (ADS)

Stress-induced leakage current (SILC) is studied in 10 nm HfO2 metal-insulator-metal capacitors. Three regimes are observed in the current-time characteristics, namely, (1) an absorption current, (2) a quasi linear increase of current with time (SILC), and (3) thermal breakdown. Magnitude of SILC is strongly correlated to the nature of the cathode (being large for TiN and weak for Pt and Au), showing that SILC is governed by electron injection. Recovery is observed when short-circuiting the samples, pointing out that SILC is a reversible phenomenon. Desorption current and SILC are not correlated, which indicates that different defects control the absorption current and SILC. SILC is ascribed to the generation of oxygen vacancies upon hot electron injection, while recovery is ascribed to the recombination of oxygen ions with vacancies. In the SILC regime, the current varies as Ktn (n = 1.15 at room temperature). Bias and temperature dependence of K and n are studied. The dependence of K on bias can be described either by a Fowler-Nordheim law or by an exponential law, while the exponent n is almost independent of bias. When temperature is increased, K increases according to an Arrhenius law and n decreases. SILC is modeled by considering the generation of oxygen vacancies by hot electron impact and subsequent electron trapping at vacancies (hopping conduction). An analytical expression for SILC growth is obtained from first order kinetics.

Mannequin, C.; Gonon, P.; Valle, C.; Latu-Romain, L.; Bsiesy, A.; Grampeix, H.; Salan, A.; Jousseaume, V.

2012-10-01

105

Optical constants of crystalline HfO2 for energy range 140-930 eV  

SciTech Connect

We calculated the optical constants of the monoclinic phase of a HfO2 film from reflection spectra measured using synchrotron radiation in the spectral region from 143 eV to 927 eV, which includes the HfN4,5{sup -}, HfN2,3{sup -}, and OK absorption edges. The calculations were carried out using the Kramers-Kronig relations. It could be shown that the relation R(E){approx}E{sup -4} can be used for extrapolation of the experimental reflection spectrum of HfO2 (and probably of other heavy elements) for energies such that {theta}/{theta}c>3.7.

Filatova, Elena; Sokolov, Andrey; Andre, Jean-Michel; Schaefers, Franz; Braun, Walter

2010-05-10

106

Dielectric Breakdown and Charge Trapping of Ultrathin ZrHfO/SiON High-k Gate Stacks  

NASA Astrophysics Data System (ADS)

One- and two-step breakdown phenomena were observed on the zirconium-doped hafnium oxide (ZrHfO) high-k dielectric films with equivalent oxide thicknesses 1.8 and 2.5 nm, respectively. The difference in the breakdown sequence was attributed to the bulk high-k layer thickness and interface layer structure. The trap generation and charge trapping in the high-k stack was investigated using a new stress-relax method through analyzing the relaxation current change. The results showed that new traps were only created under the high bias condition and the density could be comparable to or even larger than that of the preexisted traps.

Wan, Rui; Yan, Jiong; Kuo, Yue; Lu, Jiang

2008-03-01

107

Thermal stability of high-k Si-rich HfO(2) layers grown by RF magnetron sputtering.  

PubMed

The microstructure and optical properties of HfSiO films fabricated by RF magnetron sputtering were studied by means of x-ray diffraction, transmission electron microscopy, spectroscopic ellipsometry and attenuated total reflection infrared spectroscopy versus annealing treatment. It was shown that silicon incorporation in the HfO(2) matrix plays an important role in the structure stability of the layers. Thus, the increase of the annealing temperature up to 1000 degrees C did not lead to the crystallization of the films. The evolution of the chemical composition as well as a decrease of the density of the films was attributed to the phase separation of HfSiO on HfO(2) and SiO(2) phases in the film. An annealing at 1000-1100 degrees C results in the formation of the multilayer Si-rich/Hf-rich structure and was explained by a surface-directed spinodal decomposition. The formation of the stable tetragonal structure of HfO(2) phase was shown upon annealing treatment at 1100 degrees C. PMID:20585152

Khomenkova, L; Portier, X; Cardin, J; Gourbilleau, F

2010-07-16

108

Pairing of cation vacancies and gap-state creation in TiO2 and HfO2  

NASA Astrophysics Data System (ADS)

Based on the first-principles calculations, the authors study defect-defect interactions between cation vacancies in rutile TiO2 and monoclinic HfO2. It is found that vacancies are greatly stabilized at small separations because of a large reconstruction of nearby oxygen atoms that have two broken bonds. As a result, O-O bonds resembling O2 or O3 molecules are formed near the divacancy site. The defect levels originated from antibonding states of O p orbitals are identified within the energy gap, which can affect leakage currents and the density of trapped charges of oxides substantially.

Ahn, Hyo-Shin; Han, Seungwu; Hwang, Cheol Seong

2007-06-01

109

Temperature and bias-voltage dependence of atomic-layer-deposited HfO2-based magnetic tunnel junctions  

NASA Astrophysics Data System (ADS)

Magnetic tunnel junctions with HfO2 tunnel barriers were prepared through a combination of magnetron sputtering and atomic layer deposition. We investigated the tunneling transport behavior, including the tunnel magnetoresistance ratio and the current-voltage characteristics between room temperature and 2 K. Here, we achieved a tunneling magneto resistance ratio of 10.3% at room temperature and 19.3% at 2 K. Furthermore, we studied the bias-voltage and temperature dependencies and compared the results with those of commonly used alumina- and magnesia-based magnetic tunnel junctions. We observed a polycrystalline/amorphous electrode-barrier system via high-resolution transmission electron microscopy.

Fabretti, Savio; Zierold, Robert; Nielsch, Kornelius; Voigt, Carmen; Ronning, Carsten; Peretzki, Patrick; Seibt, Michael; Thomas, Andy

2014-09-01

110

dielectrics  

NASA Astrophysics Data System (ADS)

The (NH4)2S treatment can reduce native oxides and passivate GaAs. Atomic layer-deposited Al2O3 can further remove the residue native oxides by self-cleaning. Stacked with high dielectric constant TiO2 prepared by atomic layer deposition on Al2O3/(NH4)2S-treated GaAs MOS capacitor, the leakage current densities can reach 4.5 10-8 and 3.4 10-6 A/cm2 at 2 MV/cm. The net effective dielectric constant of the entire stack is 18 and the interface state density is about 4.2 1011/cm2/eV. The fabricated enhancement-mode n-channel GaAs MOSFET exhibited good electrical characteristics with a maximum g m of 122 mS/mm and electron mobility of 226 cm2/V s.

Lee, Ming-Kwei; Yen, Chih-Feng

2014-09-01

111

Mechanism for atmosphere dependence of laser damage morphology in HfO2/SiO2 high reflective films  

NASA Astrophysics Data System (ADS)

We show in this paper single-shot and multi-shot laser-induced damage thresholds (LIDTs) of HfO2/SiO2 high reflective films (the reflectance = 99.9%) are affected by the presence of a water layer absorbed on the surface of the porous films. When the water layer was removed with the process of pumping, the single-shot LIDT measured in vacuum dropped to 48% of that measured in air, while the multi-shot LIDT in vacuum dropped to 47% of its atmospheric value for the high reflective films. Typical damage micrographs of the films in air and in vacuum were obtained, showing distinct damage morphologies. Such atmosphere dependence of the laser damage morphology was found to originate from that formation of a water layer on the surface of porous films could cause an increase of horizontal thermal conductivity and a reduction of vertical thermal conductivity. Moreover, laser-induced periodic ripple damages in air were found in the SiO2 layer from the micrographs. A model of deformation kinematics was used to illustrate the occurrence of the periodic ripple damage, showing that it could be attributed to a contraction of the HfO2 layer under irradiation by the 5-ns laser pulses in air.

Pu, Yunti; Ma, Ping; Chen, Songlin; Zhu, Jiliang; Wang, Gang; Pan, Feng; Sun, Ping; Zhu, Xiaohong; Zhu, Jianguo; Xiao, Dingquan

2012-07-01

112

Electrical characteristics and thermal stability of HfO2 metal-oxide-semiconductor capacitors fabricated on clean reconstructed GaSb surfaces  

NASA Astrophysics Data System (ADS)

HfO2/GaSb interfaces fabricated by high-vacuum HfO2 deposition on clean reconstructed GaSb surfaces were examined to explore a thermally stable GaSb metal-oxide-semiconductor structure with low interface-state density (Dit). Interface Sb-O bonds were electrically and thermally unstable, and post-metallization annealing at temperatures higher than 200 C was required to stabilize the HfO2/GaSb interfaces. However, the annealing led to large Dit in the upper-half band gap. We propose that the decomposition products that are associated with elemental Sb atoms act as interface states, since a clear correlation between the Dit and the Sb coverage on the initial GaSb surfaces was observed.

Miyata, Noriyuki; Ohtake, Akihiro; Ichikawa, Masakazu; Mori, Takahiro; Yasuda, Tetsuji

2014-06-01

113

Enhancement of longitudinal magneto-optical Kerr effect in HfO2/Co/HfO2/Al/silicon thin films  

NASA Astrophysics Data System (ADS)

In this paper, the longitudinal magneto-optical Kerr effect (MOKE) properties of the quadrilayer structure HfO2/Co/HfO2/Al/silicon are investigated experimentally and theoretically. The cavity enhancement of HfO2 on the magneto-optical (MO) Kerr response of the quadrilayer has been confirmed. The giant longitudinal Kerr rotation of -1.04 at wavelength of 570 nm is tested when the cap and intermediate HfO2 layer thicknesses are 15 nm and 30 nm, respectively. The longitudinal Kerr rotation reversal in the wavelength range (440-720 nm) is also observed. It is strongly suggested that the enhanced MOKE stems from the optical reflection and interference of the quadrilayer structure.

Zhang, Shaoyin; Gao, Jinlong; Xia, Wenbin; Chen, Leyi; Tang, Yanmei; Li, Daoyong; Tang, Shaolong; Du, Youwei

2014-06-01

114

Comparative study of Laser induce damage of HfO2/SiO2 and TiO2/SiO2 mirrors at 1064 nm.  

PubMed

A comparative study of laser induced damage of HfO2/SiO2 and TiO2/SiO2 mirrors at 1064 nm has been carried out. One TiO2/SiO2 mirror with absorption of 300 ppm and two HfO2/SiO2 mirrors with absorption of 40 and 4.5 ppm were fabricated using electron beam evaporation method. For r-on-1 test, all HfO2/SiO2 mirrors with low average absorption are above 150 J/cm2 at 10 ns. However, the TiO2/SiO2 mirrors with high average absorption are just 9.5 J/cm2, which are probably due to the rather high absorption and rather low band gap energy. Meanwhile, all the samples were irradiated from front and back side respectively using the raster scan test mode. In case of front side irradiation, it is found that: for TiO2/SiO2 high reflectors, the representative damage morphologies are shallow pits that were probably caused by absorbing centers. However, for HfO2/SiO2 high reflectors, the dominant damage morphologies are micrometer-sized nodules ejected pits and the delamination initiating from the pits. The absorption of HfO2/SiO2 coatings is low enough to have minor influence on the laser damage resistance. In case of backside irradiation, the morphology of TiO2/SiO2 mirrors is mainly center melted pits that are thermal melting induced damage. Meanwhile, HfO2/SiO2 mirrors with isometrical fracture rings damage morphology are thermal induced stress damage. PMID:21369234

Jiao, Hongfei; Ding, Tao; Zhang, Qian

2011-02-28

115

O-vacancies in (i) nano-crystalline HfO2 and (i) non-crystalline SiO2 and Si3N4 studied by X-ray absorption spectroscopy.  

PubMed

Performance and reliability in semiconductor devices are limited by electronically active defects, primarily O-atom and N-atom vacancies. Synchrotron X-ray spectroscopy results, interpreted in the context of two-electron multiplet theories, have been used to analyze conduction band edge, and O-vacancy defect states in nano-crystalline transition metal oxides, e.g., HfO2, and the noncrystalline dielectrics, SiO2, Si3N4 and Si-oxynitride alloys. Two-electron multiplet theory been used to develop a high-spin state equivalent d2 model for O-vacancy allowed transitions and negative ion states as detected by X-ray absorption spectroscopy in the O K pre-edge regime. Comparisons between theory and experiment have used Tanabe-Sugano energy level diagrams for determining the symmetries and relative energies of intra-d-state transitions for an equivalent d2 ground state occupancy. Trap-assisted-tunneling, Poole-Frenkel hopping transport, and the negative bias temperature instability have been explained in terms of injection and/or trapping into O-atom and N-atom vacancy sites, and applied to gate dielectric, and metal-insulator-metal structures. PMID:22905534

Lucovsky, Gerald; Miotti, Leonardo; Bastos, Karen Paz

2012-06-01

116

Novel fabrication process to realize ultra-thin (EOT = 0.7 nm) and ultra-low-leakage SiON gate dielectrics  

Microsoft Academic Search

We have investigated the reaction mechanism of the nitridation process based on first principles calculations and experimental results. We found that oxidation-resistant Si3N4 film can be formed by uniformly arranging 3-fold coordinated N atoms into Si sub-surface layer, and we successfully incorporated O atoms into the SiN\\/Si interface with minimum disruption of SiN structures. We have realized a high-quality ultra-thin

D. Matsushita; K. Muraoka; K. Kato; Y. Nakasaki; S. Inumiya; K. Eguchi; M. Takayanagi

2005-01-01

117

Nitrogen incorporation in ultrathin gate dielectrics: A comparison of He\\/N2O and He\\/N2 remote plasma processes  

Microsoft Academic Search

Ultrathin Si oxynitride films grown by low-temperature remote plasma processing were examined by on-line Auger electron spectroscopy and angle-resolved x-ray photoelectron spectroscopy to determine the concentration, spatial distribution, and chemical bonding of nitrogen. The films were grown at 300 C on Si(100) substrates using two radio-frequency remote plasma processes: (i) He\\/N2O remote plasma-assisted oxidation (RPAO) and (ii) two-step remote plasma

Amit Khandelwal; Bradley C. Smith; H. Henry Lamb

2001-01-01

118

Charge storage characteristics of Au nanocrystal memory improved by the oxygen vacancy-reduced HfO2 blocking layer  

PubMed Central

This study characterizes the charge storage characteristics of metal/HfO2/Au nanocrystals (NCs)/SiO2/Si and significantly improves memory performance and retention time by annealing the HfO2 blocking layer in O2 ambient at 400C. Experimental evidence shows that the underlying mechanism can be effectively applied to reduce oxygen vacancy and suppress unwanted electron trap-assisted tunneling. A memory window of 1 V at an applied sweeping voltage of 2 V is also shown. The low program/erase voltage (2 V) and the promising retention performances indicate the potential application of NCs in low-voltage, non-volatile memory devices. PMID:23984794

2013-01-01

119

Effects of water vapor in high vacuum chamber on the properties of HfO2 films  

NASA Astrophysics Data System (ADS)

The influence of water vapor content in high vacuum chamber during the coating process on physical properties of HfO2 films was investigated. Coatings were deposited on BK7 substrates by electron beam evaporation and photoelectric maximum control method. An in situ residual gas analyzer (RGA) was used to monitor the residual gas composition in the vacuum chamber. The optical properties, microstructure, absorption and laser-induced damage threshold (LIDT) of the samples were characterized by Lambda 900 spectrophotometer, X-ray diffraction (XRD), surface thermal lensing (STL) technique and 1064-nm Q-switched pulsed laser at a pulse duration of 12 ns respectively. It was found that a cold trap is an effective equipment to suppress water vapor in the vacuum chamber during the pumping process, and the coatings deposited in the vacuum atmosphere with relatively low water vapor composition show higher refractive index and smaller grain size. Meanwhile, the higher LIDT value is corresponding to lower absorbance.

Ling, Bo; He, Hongbo; Shao, Jianda

2007-08-01

120

Pulsed laser deposition of HfO 2 and Pr xO y high-k films on Si(100)  

NASA Astrophysics Data System (ADS)

Pulsed laser deposition was used to grow thin films of the high-k materials praseodymium oxide (Pr xO y) and hafnium oxide (HfO 2) on Si(100) due to its experimental simplicity and flexibility. Most important factors for technical application, such as film morphology and interface quality, were investigated by optical microscopy, atomic force microscopy and Raman spectroscopy. During the growth process typical splashes, originating from the laser-target interaction, are embedded into the growing layer. The size of these splashes appears to depend strongly on the laser wavelength (355, 532, 1064 nm). The microscopic morphology of layers of both materials shows a dependence on substrate temperature, which is much more pronounced in case of HfO 2. Raman spectra of the films show relatively sharp phonon peaks, a single one for Pr xO y and a rich spectrum for HfO 2, clearly evidencing crystalline areas. This is corroborated by substrate Raman spectra which indicate a stressed interface, pointing to epitaxial Pr xO y and HfO 2 film growth, respectively, during the initial stages of growth.

Ratzke, M.; Wolfframm, D.; Kappa, M.; Kouteva-Arguirova, S.; Reif, J.

2005-07-01

121

Reliability of Strained SiGe Channel p-Channel Metal-Oxide-Semiconductor Field-Effect Transistors with Ultra-Thin (EOT=3.1 nm) N2O-Annealed SiN Gate Dielectric  

NASA Astrophysics Data System (ADS)

The p-channel metal-oxide-semiconductor field-effect transistor (pMOSFET) with 50-nm-thick Si0.85Ge0.15 channel and ultra-thin (EOT=3.1 nm) N2O-annealed SiN gate dielectric has been shown to have well-performing on/off and output characteristics. Several methodologies for the device reliability characterization, such as stress-induced-leakage-current (SILC), drain-avalanche-hot-carrier (DAHC) injection, channel hot-carrier (CHC) injection and negative-bias-temperature-instability (NBTI), have been used and the results were compared. In terms of the long-term degradation, the excellent quality of the N2O-annealed SiN gate dielectric can be firmly obtained because only negligible degradations have been found after stressing no matter which technique was employed. Even so, the experimental results have been compared and we found that the HC degradation is worse than the NBTI degradation and the channel-hot-carrier (CHC) stressing is the worst case for all kinds of reliability testing. Meanwhile, we have also verified that the interface state generation is the dominant mechanism responsible for the HC-induced degradation while the electron trapping dominates the device degradation for the NBTI stressing.

Chen, Ching-Wei; Chien, Chao-Hsin; Chen, Yi-Cheng; Hsu, Shih-Lu; Chang, Chun-Yen

2005-06-01

122

Ion beam studies of Hafnium based alternate high-k dielectric films deposited on silicon  

NASA Astrophysics Data System (ADS)

Hafnium based high dielectric constant materials are critical for the state-of-the-art integrated circuit technology. As the size of the transistor decreases, the thickness of the gate dielectric (SiO2) should be reduced to maintain device capacitance at a desired level. This thickness reduction results in high OFF-state leakage current due to quantum tunneling. Recently alternate high-k materials, like HfO2, have been introduced as gate dielectrics. However deposition of these high-k materials on Si wafers results in high concentration of interface defects due to their thermodynamic instability on Si. Introduction of thin inter layer of Silicon oxide/nitrides between Si and HfO2 is expected to improve interface quality. Hence it is important to study the composition, thickness and intermixing effects to optimize the fabrication of Hafnium based Metal-Oxide-Semiconductor (MOS) devices. Here, we have performed High Resolution Rutherford Backscattering Spectrometry (HRBS) and X-ray Reflectivity (XRR) measurements to characterize HfO2/SiO2/Si samples. These samples were further irradiated by 80 MeV Ni ions to study ion induced inter-diffusion of Hf and Si across HfO2/Si interface as a function of ion fluence.

Manikanthababu, N.; Chan, T. K.; Pathak, A. P.; Devaraju, G.; Srinivasa Rao, N.; Yang, P.; Breese, M. B. H.; Osipowicz, T.; Nageswara Rao, S. V. S.

2014-08-01

123

Tailoring the interface quality between HfO2 and GaAs via in situ ZnO passivation using atomic layer deposition.  

PubMed

We investigated ZnO surface passivation of a GaAs (100) substrate using an atomic layer deposition (ALD) process to prepare an ultrathin ZnO layer prior to ALD-HfO2 gate dielectric deposition. Significant suppression of both Ga-O bond formation near the interface and As segregation at the interface was achieved. In addition, this method effectively suppressed the trapping of carriers in oxide defects with energies near the valence band edge of GaAs. According to electrical analyses of the interface state response on p- and n-type GaAs substrates, the interface states in the bottom half of the GaAs band gap were largely removed. However, the interface trap response in the top half of the band gap increased somewhat for the ZnO-passivated surface. PMID:24911531

Byun, Young-Chul; Choi, Sungho; An, Youngseo; McIntyre, Paul C; Kim, Hyoungsub

2014-07-01

124

Fabrication of BaTiO3-Based Dielectrics for Ultrathin-Layer Multilayer Ceramic Capacitor Application by a Modified Coating Approach  

NASA Astrophysics Data System (ADS)

The development of multilayer ceramic capacitor (MLCC) with base metal electrode (BME) requires precise controlling of the microstructure in a very thin dielectric layer (<1 m). In this paper, a modified coating approach for high coverage of BaTiO3 powder for further MLCC application has been developed. The well dispersed and coated BaTiO3 powders are prepared and the relative mechanism has been discussed. Furthermore, the ultrafine grained X7R dielectric ceramics were produced by both conventional mixing and modified coating methods. Compared with the conventional mixing method, the ceramics prepared by the coating approach exhibited better TCC (the temperature coefficient of capacitance) performance, with dielectric constant over 2000 and grain size below 150 nm. In addition, it is found through the coating method the content of additives can be reduced to a relatively smaller amount than that required in conventional mixing method.

Tian, Zhibin; Wang, Xiaohui; Zhang, Yichi; Song, Tae-Ho; Hur, Kang Heon; Li, Longtu

2011-02-01

125

High-performance polycrystalline silicon thin-film transistors integrating sputtered aluminum-oxide gate dielectric with bridged-grain active channel  

E-print Network

(TFTs) integrating sputtered Al2O3 gate dielectric with bridged-grain active channel are demonstrated­7], such as Al2O3 [4], HfO2 [5], Pr2O3 [6] and Y2O3 [7], are applied into the poly-Si TFTs to improve device dielectrics [4­12]. In this work, poly-Si TFTs integrating a high-k Al2O3 gate dielectric with bridged

126

Addition of HfO2 interface layer for improved synaptic performance of phase change memory (PCM) devices  

NASA Astrophysics Data System (ADS)

In this work, we will focus on the use of phase change memory (PCM) to emulate synaptic behavior in emerging neuromorphic system-architectures. In particular, we will show that the performance and energy-efficiency of large scale neuromorphic systems can be improved by engineering individual PCM devices used as synapses. This is obtained by adding a thin HfO2 interface layer to standard GST PCM devices, allowing for the lowering of the Set/Reset currents and the increase of the number of intermediate resistance states (or synaptic weights) in the synaptic potentiation characteristics. The experimentally obtained potentiation characteristics of such PCM devices are used to simulate a 2-layer ultra-dense spiking neural network (SNN) and to perform a complex visual pattern extraction from a test case based on real world data (i.e. cars passing on a 6-lane freeway). The total power dissipated in the learning mode, for the pattern extraction experiment is estimated to be as low as 60 ?W. Average detection rate of cars is found to be greater than 90%.

Suri, M.; Bichler, O.; Hubert, Q.; Perniola, L.; Sousa, V.; Jahan, C.; Vuillaume, D.; Gamrat, C.; DeSalvo, B.

2013-01-01

127

In situ infrared spectroscopy study of the interface self-cleaning during the atomic layer deposition of HfO2 on GaAs(100) surfaces  

NASA Astrophysics Data System (ADS)

In situ attenuated total reflectance Fourier transform infrared spectroscopy was utilized to study the interface evolution during the atomic layer deposition (ALD) of HfO2 on GaAs surfaces using of tetrakis (dimethylamino) hafnium and H2O. The experiments were performed on chemical oxide and hydrogen fluoride etched GaAs(100) starting surfaces. For the deposition of HfO2 on chemical oxide GaAs surfaces at 275 C, which corresponds to the optimal ALD process temperature, continuous arsenic oxide removal was observed for the first 20 ALD cycles. The oxide removal was more pronounced at the initial 1-2 cycles but nonetheless persisted, at a reduced rate, up to the 20th cycle. The substrate temperature was confirmed to affect the arsenic oxide removal; the rate was significant at temperatures above 250 C while negligible below 200 C.

Ye, Liwang; Gougousi, Theodosia

2014-09-01

128

Theoretical study of the insulator\\/insulator interface: Band alignment at the SiO2\\/HfO2 junction  

Microsoft Academic Search

While the physics of the Schottky barrier is relatively well understood, much less is known about the band alignment at the insulator\\/insulator interface. As a model problem we study theoretically the band alignment at the technologically important SiO2\\/HfO2 interface using density functional theory. We report several different atomic level models of this interface along with their energies and electronic properties.

Onise Sharia; Alexander A. Demkov; Gennadi Bersuker; Byoung Hun Lee

2007-01-01

129

Low-frequency (1\\/f) noise behavior of locally stressed HfO2\\/TiN gate-stack pMOSFETs  

Microsoft Academic Search

The low-frequency noise behavior of locally strained pMOSFETs with a 7HfO2\\/TiN gate stack is reported. Different ways of compressive-strain engineering have been compared: a Si3N4 cap layer, SiGe source\\/drain (S\\/D) regions, or the combination of both. It is shown that the use of a cap layer does not degrade the 1\\/f noise magnitude, while an increase of this parameter is

G. Giusi; E. Simoen; G. Eneman; P. Verheyen; F. Crupi; K. De Meyer; C. Claeys; C. Ciofi

2006-01-01

130

Charging phenomena in dielectric/semiconductor heterostructures during x-ray photoelectron spectroscopy measurements  

NASA Astrophysics Data System (ADS)

The determination of the valence band offset (VBO) by x-ray photoelectron spectroscopy (XPS) is commonly performed using the so-called Kraut's method that was developed for VBO determination in semiconductor/semiconductor heterojunctions. Although the physical model, which is the basis of the method, can be safely extended to dielectric/semiconductor (D/S) heterojunctions, in these systems a careful evaluation of the experimental results is necessary due to the differential charging phenomena originating at D/S interface during x-ray bombardment. As a consequence, precise determination of the VBO requires an accurate calibration of the energy scale in order to remove artifacts induced by the progressive charging of the oxide during the XPS measurement. In this work a detailed analysis of the band alignment between e-beam evaporated amorphous HfO2 films and Si substrates is reported. The HfO2/Si heterojunction was selected as a prototype for this study since HfO2 based dielectrics have already been implemented as gate dielectrics in real devices and have been the subject of a wide number of publications providing controversial results in terms of VBO values. A clear dependence of the binding energy of the Hf 4f and O 1s core lines on the thickness of the HfO2 film is identified. The time evolution of these signals indicates that different steady states are reached after prolonged x-ray bombardment depending on the thickness of the HfO2 films. On the basis of the original work of Iwata et al. [J. App. Phys. 79, 6653 (1996)], a rigorous method to remove these artifacts and empirically determine the real band offsets in D/S heterojunctions is proposed and validated by comparison with internal photoemission and photoconductivity data obtained on the same set of samples.

Perego, M.; Seguini, G.

2011-09-01

131

Band alignment of HfO2/In0.18Al0.82N determined by angle-resolved x-ray photoelectron spectroscopy  

NASA Astrophysics Data System (ADS)

The band-alignment of atomic layer deposited (ALD)-HfO2/In0.18Al0.82N was studied by high resolution angle-resolved X-ray photoelectron spectroscopy measurements. The band bending near the HfO2/In0.18Al0.82N interface was investigated, and the potential variation across the interface was taken into account in the band alignment calculation. It is observed that the binding energies for N 1s and Al 2p in In0.18Al0.82N decreases and the corresponding extracted valence band offsets increases with increasing ? (i.e., closer to the HfO2/In0.18Al0.82N interface), as a result of an upward energy band bending towards the HfO2/In0.18Al0.82N interface. The resultant valence band offset and the conduction band offset for the ALD-HfO2/In0.18Al0.82N interface calculated was found to be 0.69 eV and 1.01 eV, respectively.

Owen, Man Hon Samuel; Bhuiyan, Maruf Amin; Zhang, Zheng; Pan, Ji Sheng; Tok, Eng Soon; Yeo, Yee-Chia

2014-07-01

132

Physics of trap generation and electrical breakdown in ultra-thin SiO2 and SiON gate dielectric materials  

Microsoft Academic Search

This work spans nearly a decade of industrial research in the reliability physics of deeply scaled SiO2 and SiON gate dielectrics. In this work, we will present our following original contributions to the field: \\u000a Below 5V stress, the dominant mechanism for stressed induced leakage current in the off-state is tunneling via interface traps in films less than 35 thick.

Paul Edward Nicollian

2007-01-01

133

Optical and Structural Properties of Ultra-thin Gold Films  

E-print Network

Realizing laterally continuous ultra-thin gold films on transparent substrates is a challenge of significant technological importance. In the present work, formation of ultra-thin gold films on fused silica is studied, demonstrating how suppression of island formation and reduction of plasmonic absorption can be achieved by treating substrates with (3-mercaptopropyl) trimethoxysilane prior to deposition. Void-free fi lms with deposition thickness as low as 5.4 nm are realized and remain structurally stable at room temperature. Based on detailed structural analysis of the fi lms by specular and diffuse X-ray reflectivity measurements, it is shown that optical transmission properties of continuous ultra-thin films can be accounted for using the bulk dielectric function of gold. However, it is important to take into account the non-abrupt transition zone between the metal and the surrounding dielectrics, which extends through several lattice constants for the laterally continuous ultra-thin films (film thickness...

Kossoy, Anna; Simakov, Denis; Leosson, Kristjan; Kna-Cohen, Stphane; Maier, Stefan A

2014-01-01

134

Nitrogen incorporation in ultrathin gate dielectrics: A comparison of He/N2O and He/N2 remote plasma processes  

NASA Astrophysics Data System (ADS)

Ultrathin Si oxynitride films grown by low-temperature remote plasma processing were examined by on-line Auger electron spectroscopy and angle-resolved x-ray photoelectron spectroscopy to determine the concentration, spatial distribution, and chemical bonding of nitrogen. The films were grown at 300 C on Si(100) substrates using two radio-frequency remote plasma processes: (i) He/N2O remote plasma-assisted oxidation (RPAO) and (ii) two-step remote plasma oxidation/nitridation. A 5 min He/N2O RPAO process produces a 2.5 nm oxynitride film incorporating approximately 1 monolayer of nitrogen at the Si-SiO2 interface. The interfacial nitrogen is bonded in a N-Si3 configuration, as in silicon nitride (Si3N4). By comparison, a 90 s He/N2 remote plasma exposure of a 1 nm oxide (grown by 10 s He/O2 RPAO) consumes substrate Si atoms creating a 1 nm subcutaneous Si3N4 layer. The nitrogen areal density obtained via the two-step process depends on the initial oxide thickness and the He/N2 remote plasma exposure time. Moreover, as the oxide thickness is increased (by increasing the He/O2 remote plasma exposure), the nitrogen distribution shifts away from the Si-SiO2 interface and into the oxide. More nitrogen with a tighter distribution is incorporated using He versus Ar dilution. Insight into the remote plasma chemistry was provided by optical emission spectroscopy. Strong N2 first positive and second positive emission bands were observed for He/N2O and He/N2 remote plasmas indicating the presence of N2 metastables and ground-state N atoms.

Khandelwal, Amit; Smith, Bradley C.; Lamb, H. Henry

2001-09-01

135

LaAlO3 gate dielectric with ultrathin equivalent oxide thickness and ultralow leakage current directly deposited on Si substrate  

NASA Astrophysics Data System (ADS)

By a careful choice of film deposition conditions, LaAlO3 (LAO) gate dielectric film with equivalent oxide thickness (EOT) of 0.31nm and gate leakage current density (Jg) of 0.1A /cm2 (at Vfb+1V) has been successfully demonstrated. Elimination of interfacial low-k layer at LAO/Si and reduction of defect density in LAO has been realized through both LAO film deposition at high-temperature (700C) and subsequent low-temperature (200C) annealing. By using thermal desorption spectroscopy technique, we find that our process reduces remnant H2O or OH- species in the LAO film, which are responsible for the degradation of EOT and Jg.

Suzuki, Masamichi; Yamaguchi, Takeshi; Fukushima, Noburu; Koyama, Masato

2008-02-01

136

Effects of vacuum ultraviolet and ultraviolet irradiation on ultrathin hafnium-oxide dielectric layers on (100)Si as measured with electron-spin resonance  

SciTech Connect

The effects of vacuum ultraviolet (VUV) (7.2 eV) and UV (4.9 eV) irradiation on hafnium-oxide dielectric layers were studied with electron-spin resonance to detect defect states. Silicon dangling-bond defects (P{sub b} centers) and positively charged oxygen vacancies (E{sup '} centers) were detected with g-factor fitting. VUV irradiation increases the level of P{sub b} states, while UV decreases the level of P{sub b} states but increases the level of E{sup '} states significantly. Rapid thermal annealing appears to mitigate these effects. Absolute values of the defect-state concentrations are presented.

Ren, H.; Shohet, J. L. [Department of Electrical and Computer Engineering, Plasma Processing and Technology Laboratory, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States); Cheng, S. L.; Nishi, Y. [Stanford University, Stanford, California 94305 (United States)

2010-05-10

137

Plasma Etching for Sub45-nm TaN Metal Gates on High-k Dielectrics  

Microsoft Academic Search

Etching of TaN gates on high-k dielectrics (HfO2 or HfAlO) is investigated using HBr\\/Cl2 chemistry in a decoupled plasma source (DPS). The patterning sequence includes 248-nm lithography, plasma photoresist trimming, etching of a SiN-SiO2 hard mask, and photoresist stripping, followed by TaN etching. TaN etching is studied by design of experiment (DOE) with four variables using a linear model with

Vladimir N. Bliznetsov; Lakshmi Kanta Bera; Haw Yun Soo; N. Balasubramanian; Rakesh Kumar; Guo-Qiang Lo; Won Jong Yoo; Chih Hung Tung; Linn Linn

2007-01-01

138

Nonvolatile memory capacitors based on Al2O3 tunneling and HfO2 blocking layers with charge storage in atomic-layer-deposited Pt nanocrystals  

NASA Astrophysics Data System (ADS)

The growth of Pt nanocrystals (NCs) on Al2O3 surface via atomic layer deposition (ALD) was investigated deeply. A charge trapping memory using Pt NC as charge trapping layer and amorphous ALD Al2O3/HfO2 as the tunneling/blocking layers was fabricated. Pure metallic Pt NC can be formed at the initial growth stage, following the nucleation incubation model. Electrical measurements of p-Si\\Al2O3\\Pt NCs\\HfO2 show a larger memory window of 6.6 V at the sweeping gate voltage of 12 V and 73% retention property after 105 s. Fowler-Nordheim tunneling serves as the dominant tunneling mechanism at the applied gate voltage of 10 V. Compared to that of 4.0 V with HfO2 blocking layer, control sample with Al2O3 blocking layer shows negligible memory window of 0.3 V at 10 V, which is attributed to the smaller electric field intensity in the Al2O3 tunneling layer of stacking structures of p-Si\\Al2O3\\Pt NCs\\Al2O3. ALD Pt NCs with a high density of 1.0 1012/cm2 provides a potential approach to fabricate large area nanocrystals for future ultrahigh density nonvolatile memory applications.

Liu, Xiao-Jie; Zhu, Lin; Gao, Mo-Yun; Li, Xue-Fei; Cao, Zheng-Yi; Zhai, Hai-Fa; Li, Ai-Dong; Wu, Di

2014-01-01

139

On the bipolar resistive-switching characteristics of Al2O3- and HfO2-based memory cells operated in the soft-breakdown regime  

NASA Astrophysics Data System (ADS)

In this article, we investigate extensively the bipolar-switching properties of Al2O3- and HfO2-based resistive-switching memory cells operated at low current down to <1 ?A. We show that the switching characteristics differ considerably from those typically reported for larger current range (>15 ?A), which we relate as intrinsic to soft-breakdown (SBD) regime. We evidence a larger impact of the used switching-oxide in this current range, due to lower density of oxygen-vacancy (Vo) defects in the SBD regime. In this respect, deep resetting and large memory window may be achieved using the stoichiometric Al2O3 material due to efficient Vo annihilation, although no complete erasure of the conductive-filament (CF) is obtained. We finally emphasize that the conduction may be described by a quantum point-contact (QPC) model down to very low current level where only a few Vo defects compose the QPC constriction. The large switching variability inherent to this latter aspect is mitigated by CF shape tuning through adequate engineering of an Al2O3HfO2 bilayer.

Goux, L.; Raghavan, N.; Fantini, A.; Nigon, R.; Strangio, S.; Degraeve, R.; Kar, G.; Chen, Y. Y.; De Stefano, F.; Afanas'ev, V. V.; Jurczak, M.

2014-10-01

140

Enhanced ultraviolet electroluminescence and spectral narrowing from ZnO quantum dots/GaN heterojunction diodes by using high-k HfO2 electron blocking layer  

NASA Astrophysics Data System (ADS)

We demonstrated the capability of realizing enhanced ZnO-related UV emissions by using the low-cost and solution-processable ZnO quantum dots (QDs) with the help of a high-k HfO2 electron blocking layer (EBL) for the ZnO QDs/p-GaN light-emitting diodes (LEDs). Full-width at half maximum of the LED devices was greatly decreased from 110 to 54 nm, and recombinations related to nonradiative centers were significantly suppressed with inserting HfO2 EBL. The electroluminescence of the ZnO QDs/HfO2/p-GaN LEDs demonstrated an interesting spectral narrowing effect with increasing HfO2 thickness. The Gaussian fitting revealed that the great enhancement of the Zni-related emission at 414 nm whereas the deep suppression of the interfacial recombination at 477 nm should be the main reason for the spectral narrowing effect.

Mo, Xiaoming; Long, Hao; Wang, Haoning; Li, Songzhan; Chen, Zhao; Wan, Jiawei; Feng, Yamin; Liu, Yuping; Ouyang, Yifang; Fang, Guojia

2014-08-01

141

Comparative studies of AlGaN/GaN MOS-HEMTs with stacked gate dielectrics by the mixed thin film growth method  

NASA Astrophysics Data System (ADS)

This paper reports Al0.27Ga0.73N/GaN metal-oxide-semiconductor high electron mobility transistors (MOS-HEMTs) with stacked Al2O3/HfO2 gate dielectrics by using hydrogen peroxideoxidation/sputtering techniques. The Al2O3 employed as a gate dielectric and surface passivation layer effectively suppresses the gate leakage current, improves RF drain current collapse and exhibits good thermal stability. Moreover, by stacking the good insulating high-k HfO2 dielectric further suppresses the gate leakage, enhances the dielectric breakdown field and power-added efficiency, and decreases the equivalent oxide thickness. The present MOS-HEMT design has demonstrated superior improvements of 10.1% (16.4%) in the maximum drain-source current (IDS, max), 11.4% (22.5%) in the gate voltage swing and 12.5%/14.4% (21.9%/22.3%) in the two-terminal gate-drain breakdown/turn-on voltages (BVGD/VON), and the present design also demonstrates the lowest gate leakage current and best thermal stability characteristics as compared to two reference MOS-HEMTs with a single Al2O3/(HfO2) dielectric layer of the same physical thickness.

Chou, Bo-Yi; Hsu, Wei-Chou; Lee, Ching-Sung; Liu, Han-Yin; Ho, Chiu-Sheng

2013-07-01

142

Ultrathin multiband gigahertz metamaterial absorbers  

NASA Astrophysics Data System (ADS)

We propose ultrathin multiband metamaterial absorbers in the microwave frequencies in which the design, analysis, fabrication, and measurement of the absorbers working in multiple bands are presented. The metamaterial absorbers consist of a periodic arrangement of different scales of electric-field-coupled-LC (ELC) resonators and a metallic background plane, separated by only 1 mm dielectric spacer. By tuning the scale factor of the ELC unit cells, we achieve independently multiple absorptions at different customized frequencies. Experiments demonstrate excellent absorption rates in the designed frequency bands over wide angles of incident waves for both transverse electric and magnetic polarizations. The explanation to the physical mechanism of the multiband metamaterial absorber is presented and verified.

Li, Hui; Yuan, Li Hua; Zhou, Bin; Shen, Xiao Peng; Cheng, Qiang; Cui, Tie Jun

2011-07-01

143

Investigation of nonuniformity phenomenon in nanoscale SiO2 and high-k gate dielectrics  

NASA Astrophysics Data System (ADS)

We proposed the concept of effective uniform area ratio (Keff) to evaluate the nonuniformity phenomena of SiO2 and HfO2 gate dielectrics below 3 nm. Keff can be considered as an indication of gate oxide uniformity. It is found that Keff increases with the thickness of SiO2, whereas decreases with increasing effective oxide thickness for HfO2. The reason for the observed phenomena is given in this work. The electrical and reliability characteristics were examined to check the feasibility of our concept. The tendency of Keff values was reconfirmed by the uniformity of leakage current and constant field stress test. It is believed that this methodology is useful for the future oxide quality test.

Lin, Chien-Chih; Hwu, Jenn-Gwo

2012-09-01

144

The Impact of Dielectric Material and Temperature on Dielectric Charging in RF MEMS Capacitive Switches  

NASA Astrophysics Data System (ADS)

The present work attempts to provide a better insight on the dielectric charging in RF-MEMS capacitive switches that constitutes a key issue limiting parameter of their commercialization. The dependence of the charging process on the nature of dielectric materials widely used in these devices, such as SiO2, Si3N4, AlN, Al2O3, Ta2O5, HfO2, which consist of covalent or ionic bonds and may exhibit piezoelectric properties is discussed taking into account the effect of deposition conditions and resulting material stoichiometry. Another key issue parameter that accelerates the charging and discharging processes by providing enough energy to trapped charges to be released and to dipoles to overcome potential barriers and randomize their orientation is the temperature will be investigated too. Finally, the effect of device structure will be also taken into account.

Papaioannou, George

145

Dielectric and carrier transport properties of vanadium dioxide thin films across the phase transition utilizing gated capacitor devices  

NASA Astrophysics Data System (ADS)

Vanadium dioxide (VO2) is a strongly correlated oxide that undergoes a sharp metal-insulator transition (MIT) in the vicinity of room temperature. Fundamental knowledge of the semiconducting properties of thin film VO2 is needed to advance our understanding of the microscopic transition mechanisms that are presently being actively explored and also for novel electron devices that could utilize the phase transition. In this report, the temperature dependence of the dielectric constant and carrier conduction in VO2 thin films are investigated, from quantitative capacitance-voltage analyses of a multilayer capacitor with HfO2/VO2/HfO2/n-Si -substrate stack structure. The finite conductance of the VO2 in the capacitor structure is taken into account in the impedance transformations to obtain material properties as a function of temperature. The dielectric constant of VO2 increases from a value of 36 at room temperature to a value exceeding 6104 at 100C . The carrier type of VO2 thin film is electronic, determined by the polarity of the capacitance-voltage spectra. The electron carrier concentration of the VO2 thin films shows about four orders of magnitude increase from room temperature to the temperature near phase transition. The approach of deriving insights into carrier conduction from capacitance measurement analyses can be applied to other materials beyond VO2 , wherein sensitive temperature-dependence or low carrier mobility makes Hall measurements challenging. Furthermore, the stack structure consisting of HfO2/VO2/HfO2/n-Si shows a strong temperature dependence of capacitance due to the MIT in the sandwiched VO2 layer. This suggests the potential for strongly correlated oxides that undergo a hysteretic MIT in thermally tunable capacitors that could be of interest for solid-state devices.

Yang, Zheng; Ko, Changhyun; Balakrishnan, Viswanath; Gopalakrishnan, Gokul; Ramanathan, Shriram

2010-11-01

146

Thermal Conductivity and Stability of HfO2-Y2O3 and La2Zr2O7 Evaluated for 1650 Deg C Thermal/Environmental Barrier Coating Applications  

NASA Technical Reports Server (NTRS)

HfO2-Y2O3 and La2Zr2O7 are candidate thermal and environmental barrier coating (T/EBC) materials for gas turbine ceramic matrix composite (CMC) combustor applications because of their relatively low thermal conductivity and high temperature capability. In this paper, thermal conductivity and high temperature stability of hot-pressed and plasma sprayed specimens with representative partially-stabilized and fully-cubic HfO2-Y2O3 compositions and La2Zr2O7 were evaluated at temperatures up to 1700 C using a steady-state laser heat-flux technique. Sintering behavior of the plasmasprayed coatings was determined by monitoring the thermal conductivity increases during a 20-hour test period at various temperatures. Durability and failure mechanisms of the HfO2-Y2O3 and La2Zr2O7 coatings on mullite/SiC hexoloy or SiC/SiC CMC substrates were investigated at 1650 C under thermal gradient cyclic conditions. Coating design and testing issues for the 1650 C thermal/environmental barrier coating applications are also discussed.

Zhu, Dong-Ming; Bansal, Narottam P.; Miller, Robert A.

2003-01-01

147

Ultra-thin multilayer capacitors.  

SciTech Connect

The fabrication of ultra-thin lanthanum-doped lead zirconium titanate (PLZT) multilayer ceramic capacitors (MLCCs) using a high-power pulsed ion beam was studied. The deposition experiments were conducted on the RHEPP-1 facility at Sandia National Laboratories. The goal of this work was to increase the energy density of ceramic capacitors through the formation of a multilayer device with excellent materials properties, dielectric constant, and standoff voltage. For successful device construction, there are a number of challenging requirements including achieving correct stoichiometric and crystallographic composition of the deposited PLZT, as well as the creation of a defect free homogenous film. This report details some success in satisfying these requirements, although 900 C temperatures were necessary for PLZT perovskite phase formation. These temperatures were applied to a previously deposited multi-layer film which was then post-annealed to this temperature. The film exhibited mechanical distress attributable to differences in the coefficient of thermal expansion (CTE) of the various layers. This caused significant defects in the deposited films that led to shorts across devices. A follow-on single layer deposition without post-anneal produced smooth layers with good interface behavior, but without the perovskite phase formation. These issues will need to be addressed in order for ion beam deposited MLCCs to become a viable technology. It is possible that future in-situ heating during deposition may address both the CTE issue, and result in lowered processing temperatures, which in turn could raise the probability of successful MLCC formation.

Renk, Timothy Jerome; Monson, Todd C.

2009-06-01

148

Local Dielectric Spectroscopy of Nanocomposite Materials Interfaces  

E-print Network

Local dielectric spectroscopy is performed to study how relaxation dynamics of a poly-vinyl-acetate ultra-thin film is influenced by inorganic nano-inclusions of a layered silicate (montmorillonite). Dielectric loss spectra are measured by electrostatic force microscopy in the frequency-modulation mode in ambient air. Spectral changes in both shape and relaxation time are evidenced across the boundary between pure polymer and montmorillonite sheets. Dielectric loss imaging is also performed, evidencing spatial variations of dielectric properties near to nanostructures with nanometer scale resolution.

Massimiliano Labardi; Daniele Prevosto; Kim Hung Nguyen; Simone Capaccioli; Mauro Lucchesi; Pierangelo Rolla

2009-11-09

149

Evolutionary search for new high-k dielectric materials: methodology and applications to hafnia-based oxides.  

PubMed

High-k dielectric materials are important as gate oxides in microelectronics and as potential dielectrics for capacitors. In order to enable computational discovery of novel high-k dielectric materials, we propose a fitness model (energy storage density) that includes the dielectric constant, bandgap, and intrinsic breakdown field. This model, used as a fitness function in conjunction with first-principles calculations and the global optimization evolutionary algorithm USPEX, efficiently leads to practically important results. We found a number of high-fitness structures of SiO2 and HfO2, some of which correspond to known phases and some of which are new. The results allow us to propose characteristics (genes) common to high-fitness structures--these are the coordination polyhedra and their degree of distortion. Our variable-composition searches in the HfO2-SiO2 system uncovered several high-fitness states. This hybrid algorithm opens up a new avenue for discovering novel high-k dielectrics with both fixed and variable compositions, and will speed up the process of materials discovery. PMID:24508952

Zeng, Qingfeng; Oganov, Artem R; Lyakhov, Andriy O; Xie, Congwei; Zhang, Xiaodong; Zhang, Jin; Zhu, Qiang; Wei, Bingqing; Grigorenko, Ilya; Zhang, Litong; Cheng, Laifei

2014-02-01

150

Multifunctional role of rare earth doping in optical materials: nonaqueous sol-gel synthesis of stabilized cubic HfO2 luminescent nanoparticles.  

PubMed

In this work a strategy for the control of structure and optical properties of inorganic luminescent oxide-based nanoparticles is presented. The nonaqueous sol-gel route is found to be suitable for the synthesis of hafnia nanoparticles and their doping with rare earths (RE) ions, which gives rise to their luminescence either under UV and X-ray irradiation. Moreover, we have revealed the capability of the technique to achieve the low-temperature stabilization of the cubic phase through the effective incorporation of trivalent RE ions into the crystal lattice. Particular attention has been paid to doping with europium, causing a red luminescence, and with lutetium. Structure and morphology characterization by XRD, TEM/SEM, elemental analysis, and Raman/IR vibrational spectroscopies have confirmed the occurrence of the HfO2 cubic polymorph for dopant concentrations exceeding a threshold value of nominal 5 mol %, for either Lu(3+) or Eu(3+). The optical properties of the nanopowders were investigated by room temperature radio- and photoluminescence experiments. Specific features of Eu(3+) luminescence sensitive to the local crystal field were employed for probing the lattice modifications at the atomic scale. Moreover, we detected an intrinsic blue emission, allowing for a luminescence color switch depending on excitation wavelength in the UV region. We also demonstrate the possibility of changing the emission spectrum by multiple RE doping in minor concentration, while deputing the cubic phase stabilization to a larger concentration of optically inactive Lu(3+) ions. The peculiar properties arising from the solvothermal nonaqueous synthesis here used are described through the comparison with thermally treated powders. PMID:23898781

Lauria, Alessandro; Villa, Irene; Fasoli, Mauro; Niederberger, Markus; Vedda, Anna

2013-08-27

151

Improved performance and reliability for metal-oxide-semiconductor field-effect-transistor with fluorinated silicate glass passivation layer  

NASA Astrophysics Data System (ADS)

The superior characteristics of the fluorinated HfO2/SiON gate dielectric are investigated comprehensively. Fluorine is incorporated into the gate dielectric through fluorinated silicate glass (FSG) passivation layer to form fluorinated HfO2/SiON dielectric. Fluorine incorporation has been proved to eliminate both bulk and interface trap densities due to Hf-F and Si-F bonds formation, which can strongly reduce trap generation as well as trap-assisted tunneling during subsequently constant voltage stress, and results in improved electrical characteristics and dielectric reliabilities. The results clearly indicate that the fluorinated HfO2/SiON gate dielectric using FSG passivation layer becomes a feasible technology for future ultrathin gate dielectric applications.

Hsieh, Chih-Ren; Chen, Yung-Yu; Lou, Jen-Chung

2010-01-01

152

Physicochemical and electrical characterizations of atomic layer deposition grown HfO2 on TiN and Pt for metal-insulator-metal application  

E-print Network

insulating materials with a higher dielectric constant.1 These materials shall lead to a high capacitance for the physicochemical characterization in order to study the junction interface and determine the oxide thickness. The actual downscaling of electronic devices implies to substitute the traditional SiO2 dielectric for new

Boyer, Edmond

153

In situ auger electron spectroscopy study of atomic layer deposition: growth initiation and interface formation reactions during ruthenium ALD on Si-H, SiO2, and HfO2 surfaces.  

PubMed

Growth initiation and film nucleation in atomic layer deposition (ALD) is important for controlling interface composition and achieving atomic-scale films with well-defined composition. Ruthenium ALD is studied here using ruthenocene and oxygen as reactants, and growth initiation and nucleation are characterized on several different growth surfaces, including SiO2, HfO2, and hydrogen terminated silicon, using on-line Auger electron spectroscopy and ex-situ X-ray photoelectron spectroscopy. The time needed to reach the full growth rate (typically approximately 1 A per deposition cycle) is found to increase as the surface energy of the starting surface (determined from contact angle measurements) decreased. Growth starts more readily on HfO2 than on SiO2 or Si-H surfaces, and Auger analysis indicates distinct differences in surface reactions on the various surfaces during film nucleation. Specifically, surface oxygen is consumed during ruthenocene exposure, so the nucleation rate will depend on the availability of oxygen and the energetics of surface oxygen bonding on the starting substrate surface. PMID:17461600

Park, Kie Jin; Terry, David B; Stewart, S Michael; Parsons, Gregory N

2007-05-22

154

Advanced passivation techniques for Si solar cells with high-? dielectric materials  

NASA Astrophysics Data System (ADS)

Electronic recombination losses at the wafer surface significantly reduce the efficiency of Si solar cells. Surface passivation using a suitable thin dielectric layer can minimize the recombination losses. Herein, advanced passivation using simple materials (Al2O3, HfO2) and their compounds H(Hf)A(Al)O deposited by atomic layer deposition (ALD) was investigated. The chemical composition of Hf and Al oxide films were determined by X-ray photoelectron spectroscopy (XPS). The XPS depth profiles exhibit continuous uniform dense layers. The ALD-Al2O3 film has been found to provide negative fixed charge (-6.4 1011 cm-2), whereas HfO2 film provides positive fixed charge (3.2 1012 cm-2). The effective lifetimes can be improved after oxygen gas annealing for 1 min. I-V characteristics of Si solar cells with high-? dielectric materials as passivation layers indicate that the performance is significantly improved, and ALD-HfO2 film would provide better passivation properties than that of the ALD-Al2O3 film in this research work.

Geng, Huijuan; Lin, Tingjui; Letha, Ayra Jagadhamma; Hwang, Huey-Liang; Kyznetsov, Fedor A.; Smirnova, Tamara P.; Saraev, Andrey A.; Kaichev, Vasily V.

2014-09-01

155

Enhancement of absorption and color contrast in ultra-thin highly absorbing optical coatings  

NASA Astrophysics Data System (ADS)

Recently a new class of optical interference coatings was introduced which comprises ultra-thin, highly absorbing dielectric layers on metal substrates. We show that these lossy coatings can be augmented by an additional transparent subwavelength layer. We fabricated a sample comprising a gold substrate, an ultra-thin film of germanium with a thickness gradient, and several alumina films. The experimental reflectivity spectra showed that the additional alumina layer increases the color range that can be obtained, in agreement with calculations. More generally, this transparent layer can be used to enhance optical absorption, protect against erosion, or as a transparent electrode for optoelectronic devices.

Kats, Mikhail A.; Byrnes, Steven J.; Blanchard, Romain; Kolle, Mathias; Genevet, Patrice; Aizenberg, Joanna; Capasso, Federico

2013-09-01

156

Ultra-thin quadri-band metamaterial absorber based on spiral structure  

NASA Astrophysics Data System (ADS)

We introduce a design of the metamaterial absorber (MA) consisting of spiral artificial inclusions printed on an ultra-thin dielectric layer backed by a metal plate. Both simulations and experiments show that the MA can achieve absorptions up to 96.49, 94.25, 98.94 and 92.04 % at 6.69, 8.70, 11.90 and 15.14 GHz, respectively. The surface current and power loss density of each absorption frequency were discussed to reveal the physical mechanism. Moreover, the proposed quadri-band MA possesses the advantages of being ultra-thin and polarization-insensitive and thus may find potential applications.

Wang, Wenjie; Yan, Mingbao; Pang, Yongqiang; Wang, Jiafu; Ma, Hua; Qua, Shaobo; Chen, Hongya; Xu, Cuilian; Feng, Mingde

2014-09-01

157

Development and Performance Evaluations of HfO2-Si and Rare Earth-Si Based Environmental Barrier Bond Coat Systems for SiC/SiC Ceramic Matrix Composites  

NASA Technical Reports Server (NTRS)

Ceramic environmental barrier coatings (EBC) and SiCSiC ceramic matrix composites (CMCs) will play a crucial role in future aircraft propulsion systems because of their ability to significantly increase engine operating temperatures, improve component durability, reduce engine weight and cooling requirements. Advanced EBC systems for SiCSiC CMC turbine and combustor hot section components are currently being developed to meet future turbine engine emission and performance goals. One of the significant material development challenges for the high temperature CMC components is to develop prime-reliant, high strength and high temperature capable environmental barrier coating bond coat systems, since the current silicon bond coat cannot meet the advanced EBC-CMC temperature and stability requirements. In this paper, advanced NASA HfO2-Si based EBC bond coat systems for SiCSiC CMC combustor and turbine airfoil applications are investigated. The coating design approach and stability requirements are specifically emphasized, with the development and implementation focusing on Plasma Sprayed (PS) and Electron Beam-Physic Vapor Deposited (EB-PVD) coating systems and the composition optimizations. High temperature properties of the HfO2-Si based bond coat systems, including the strength, fracture toughness, creep resistance, and oxidation resistance were evaluated in the temperature range of 1200 to 1500 C. Thermal gradient heat flux low cycle fatigue and furnace cyclic oxidation durability tests were also performed at temperatures up to 1500 C. The coating strength improvements, degradation and failure modes of the environmental barrier coating bond coat systems on SiCSiC CMCs tested in simulated stress-environment interactions are briefly discussed and supported by modeling. The performance enhancements of the HfO2-Si bond coat systems with rare earth element dopants and rare earth-silicon based bond coats are also highlighted. The advanced bond coat systems, when integrated with advanced EBC top coats, showed promise to achieve 1500 C temperature capability, helping enable next generation turbine engines with significantly improved engine component temperature capability and long-term durability.

Zhu, Dongming

2014-01-01

158

Interface Electronic State Characterization of Plasma Enhanced Atomic Layer Deposited Dielectrics on GaN  

NASA Astrophysics Data System (ADS)

In this dissertation, the interface chemistry and electronic structure of plasma-enhanced atomic layer deposited (PEALD) dielectrics on GaN are investigated with x-ray and ultraviolet photoemission spectroscopy (XPS and UPS). Three interrelated issues are discussed in this study: (1) PEALD dielectric growth process optimization, (2) interface electronic structure of comparative PEALD dielectrics on GaN, and (3) interface electronic structure of PEALD dielectrics on Ga- and N-face GaN. The first study involved an in-depth case study of PEALD Al2O3 growth using dimethylaluminum isopropoxide, with a special focus on oxygen plasma effects. Saturated and self-limiting growth of Al2O3 films were obtained with an enhanced growth rate within the PEALD temperature window (25--220 C). The properties of Al2O3 deposited at various temperatures were characterized to better understand the relation between the growth parameters and film properties. In the second study, the interface electronic structures of PEALD dielectrics on Ga-face GaN films were measured. Five promising dielectrics (Al2O3, HfO2, SiO2, La2O 3, and ZnO) with a range of band gap energies were chosen. Prior to dielectric growth, a combined wet chemical and in-situ H 2/N2 plasma clean process was employed to remove the carbon contamination and prepare the surface for dielectric deposition. The surface band bending and band offsets were measured by XPS and UPS for dielectrics on GaN. The trends of the experimental band offsets on GaN were related to the dielectric band gap energies. In addition, the experimental band offsets were near the calculated values based on the charge neutrality level model. The third study focused on the effect of the polarization bound charge of the Ga- and N-face GaN on interface electronic structures. A surface pretreatment process consisting of a NH4OH wet chemical and an in-situ NH3 plasma treatment was applied to remove carbon contamination, retain monolayer oxygen coverage, and potentially passivate N-vacancy related defects. The surface band bending and polarization charge compensation of Ga- and N-face GaN were investigated. The surface band bending and band offsets were determined for Al2O3, HfO2, and SiO 2 on Ga- and N-face GaN. Different dielectric thicknesses and post deposition processing were investigated to understand process related defect formation and/or reduction.

Yang, Jialing

159

High dielectric constant materials: a band line-up problem  

NASA Astrophysics Data System (ADS)

To insure continuous downscaling of CMOS technology the semiconductor industry must make a transition from the Si-SiO_2-poly-Si triad to a much more complex Si-dielectric-metal system. The dielectric constant of the new gate dielectric is expected to be higher than that of silicon dioxide (4). This will allow maintaining the gate capacitance and therefore the drain-source saturation current without the thickness reduction of the oxide, and thus will cut down the tunneling component of the parasitic gate leakage. The integration of this new stack into the current CMOS flow is one of the most urgent tasks of today's electronics. The oxide's gate action, among other factors, depends on the barrier height (same as band discontinuity) at the oxide-semiconductor and oxide-metal interfaces. The band alignment is often estimated within the so-called metal-induced gap states (MIGS) model. The MIGS model describes both Bardeen and Schottky limits and interpolates between the two in a linear fashion, provided that electron affinities, charge neutralities and the pinning factor are known. We use the complex band structure of several prospective gate dielectrics (SiO_2, SrTiO_3, HfO_2, and Al_2O_3) to calculate their charge neutrality level, and estimate the band offset to Si, Pt, and several other metals. Results of these model calculations are then compared to those obtained with direct electronic structure methods.

Fonseca, L.; Tomfohr, J.; Chagarov, E.; Sankey, O. F.; Demkov, A. A.

2003-03-01

160

Structural, electronic, vibrational and dielectric properties of selected high-shape K semiconductor oxides  

NASA Astrophysics Data System (ADS)

The semiconductor oxides SnO2, HfO2, ZrO2, TiO2 and SrTiO3 are interesting materials for applications as high-K dielectric gate materials in silicon-based devices and spintronics, among others. Here we review our theoretical work about the structural, electronic and vibrational properties of these oxides in their most stable structural phases, including dielectric properties as derived from the electronic structure taking into account the lattice contribution. Finally, we address the recent role played by the presence of transition metal atoms in semiconductor oxides, considering in particular SnO2 as an example in forming diluted magnetic alloys.

Scolfaro, L. M. R.; Leite Alves, H. W.; Borges, P. D.; Garcia, J. C.; da Silva, E. F., Jr.

2014-10-01

161

Ultrathin and broadband high impedance surface absorbers based on metamaterial substrates.  

PubMed

An ultrathin and simultaneously broadband high impedance surface absorber based on a metamaterial (MM) substrate is presented at microwave frequencies. The MM substrate is designed using metallic split ring resonators (SRRs) vertically embedded into a dielectric slab. Both the simulated and experimental results display two absorption peaks and an expanded absorption bandwidth of less than -10 dB compared to conventional ultrathin absorbers. By analyzing the field distributions and the substrate impedance characteristics, it is found that this feature is mainly related to the LC resonance of the substrate caused by the embedded SRRs. Our results demonstrate the great feasibility of broadening the absorption bandwidth of the ultrathin high impedance surface absorbers by the MMs incorporation. PMID:22714239

Pang, Yongqiang; Cheng, Haifeng; Zhou, Yongjiang; Li, Zenggnag; Wang, Jun

2012-05-21

162

Conformal surface plasmons propagating on ultrathin and flexible films.  

PubMed

Surface plasmon polaritons (SPPs) are localized surface electromagnetic waves that propagate along the interface between a metal and a dielectric. Owing to their inherent subwavelength confinement, SPPs have a strong potential to become building blocks of a type of photonic circuitry built up on 2D metal surfaces; however, SPPs are difficult to control on curved surfaces conformably and flexibly to produce advanced functional devices. Here we propose the concept of conformal surface plasmons (CSPs), surface plasmon waves that can propagate on ultrathin and flexible films to long distances in a wide broadband range from microwave to mid-infrared frequencies. We present the experimental realization of these CSPs in the microwave regime on paper-like dielectric films with a thickness 600-fold smaller than the operating wavelength. The flexible paper-like films can be bent, folded, and even twisted to mold the flow of CSPs. PMID:23248311

Shen, Xiaopeng; Cui, Tie Jun; Martin-Cano, Diego; Garcia-Vidal, Francisco J

2013-01-01

163

Conformal surface plasmons propagating on ultrathin and flexible films  

PubMed Central

Surface plasmon polaritons (SPPs) are localized surface electromagnetic waves that propagate along the interface between a metal and a dielectric. Owing to their inherent subwavelength confinement, SPPs have a strong potential to become building blocks of a type of photonic circuitry built up on 2D metal surfaces; however, SPPs are difficult to control on curved surfaces conformably and flexibly to produce advanced functional devices. Here we propose the concept of conformal surface plasmons (CSPs), surface plasmon waves that can propagate on ultrathin and flexible films to long distances in a wide broadband range from microwave to mid-infrared frequencies. We present the experimental realization of these CSPs in the microwave regime on paper-like dielectric films with a thickness 600-fold smaller than the operating wavelength. The flexible paper-like films can be bent, folded, and even twisted to mold the flow of CSPs. PMID:23248311

Shen, Xiaopeng; Cui, Tie Jun; Martin-Cano, Diego; Garcia-Vidal, Francisco J.

2013-01-01

164

Investigation of metal oxide dielectrics for non-volatile floating gate and resistance switching memory applications  

NASA Astrophysics Data System (ADS)

Floating gate transistor based flash memories have seen more than a decade of continuous growth as the prominent non-volatile memory technology. However, the recent trends indicate that the scaling of flash memory is expected to saturate in the near future. Several alternative technologies are being considered for the replacement of flash in the near future. The basic motivation for this work is to investigate the material properties of metal oxide based high-k dielectrics for potential applications in floating gate and resistance switching memory applications. This dissertation can be divided into two main sections. In the first section, the tunneling characteristics of the SiO2/HfO 2 stacks were investigated. Previous theoretical studies for thin SiO 2/ thick high-k stacks predict an increase in tunneling current in the high-bias regime (better programming) and a decrease in the low-bias regime (better retention) in comparison to pure SiO2 of same equivalent oxide thickness (EOT). However, our studies indicated that the performance improvement in SiO2/HfO2 stacks with thick HfO2 layer is difficult due to significant amount of charge traps in thick HfO2 layers. Oxygen anneal on the stacks did not improve the programming current and retention. X-ray photoelectron spectroscopy (XPS) studies indicated that this was due to formation of an interfacial oxide layer. The second part of the dissertation deals with the investigation of resistive switching in metal oxides. Although promising, practical applications of resistive random access memories (RRAM) require addressing several issues including high forming voltage, large operating currents and reliability. We first investigated resistive switching in HfTiOx nanolaminate with conventional TiN electrodes. The forming-free switching observed in the structures could be described by the quantum point contact model. The modelling results indicated that the forming-free characteristics can be due to a higher number of filaments in comparison to a device that requires forming. Forming-free resistive switching with low current operation in graphene-insulator-graphene structures was also investigated. Electrical as well as Raman and XPS analysis indicated that low current operation is due to the migration and subsequent physisorption of oxygen ions on the graphene surface during the set operation. A statistical model was also developed for quantitative prediction of the effect of noise on RRAM characteristics.

Chakrabarti, Bhaswar

165

Ultra-thin Multilayer Capacitors.  

National Technical Information Service (NTIS)

The fabrication of ultra-thin lanthanum-doped lead zirconium titanate (PLZT) multilayer ceramic capacitors (MLCCs) using a high-power pulsed ion beam was studied. The deposition experiments were conducted on the RHEPP-1 facility at Sandia National Laborat...

T. C. Monson, T. J. Renk

2009-01-01

166

Graphene field effect transistors with mica as gate dielectric layers.  

PubMed

Chemical vapor deposited monolayer graphene is transferred onto atomically flat and ultra-thin muscovite mica to study the transport characteristics of graphene with a test structure of mica-based graphene field effect transistor (GFET). The transfer curve of the 24 nm mica-based GFET shows an effective carrier mobility of 2748 cm(2) /Vs and a transconductance of 3.36 ?S, a factor of 2 and 7 larger than those values obtained from 40 nm SiO2 based GFET, respectively. The results demonstrate that mica is an excellent gate dielectric material due to its high dielectric constant, high dielectric strength, and atomically flat surface. PMID:25044452

Low, Chong Guan; Zhang, Qing; Hao, Yufeng; Ruoff, Rodney S

2014-10-01

167

Magnetism in ultrathin film structures  

NASA Astrophysics Data System (ADS)

In this paper, we review some of the key concepts in ultrathin film magnetism which underpin nanomagnetism. We survey the results of recent experimental and theoretical studies of well characterized epitaxial structures based on Fe, Co and Ni to illustrate how intrinsic fundamental properties such as the magnetic exchange interactions, magnetic moment and magnetic anisotropies change markedly in ultrathin films as compared with their bulk counterparts, and to emphasize the role of atomic scale structure, strain and crystallinity in determining the magnetic properties. After introducing the key length scales in magnetism, we describe the 2D magnetic phase transition and survey studies of the thickness dependent Curie temperature and the critical exponents which characterize the paramagnetic-ferromagnetic phase transition. We next discuss recent experimental and theoretical results on the determination of the exchange constant, followed by an overview of measurements of the magnetic moment in the elemental 3d transition metal thin films in the various crystal phases that have been successfully stabilized, thereby illustrating the sensitivity of the magnetic moment to the local symmetry and to the atomic environment. Finally, we discuss briefly the magnetic anisotropies of Fe, Co and Ni in the fcc crystalline phase, to emphasize the role of structure and the details of the interface in influencing the magnetic properties. The dramatic effect that adsorbates can have on the magnetic anisotropies of thin magnetic films is also discussed. Our survey demonstrates that the fundamental properties, namely, the magnetic moment and magnetic anisotropies of ultrathin films have dramatically different behaviour compared with those of the bulk while the comparable size of the structural and magnetic contributions to the total energy of ultrathin structures results in an exquisitely sensitive dependence of the magnetic properties on the film structure.

Vaz, C. A. F.; Bland, J. A. C.; Lauhoff, G.

2008-05-01

168

Wave manipulation with designer dielectric metasurfaces.  

PubMed

The concept of an ultra-thin metasurface made of single layer of only-dielectric disks for successful phase control over a full range is demonstrated. Conduction loss is avoided compared to its plasmonic counterpart. The interaction of the Mie resonances of the first two modes of the dielectric particles, magnetic and electric dipoles, is tailored by the dimensions of the disks, providing required phase shift for the transmitted beam from 0 to 360, together with high transmission efficiency. The successful performance of a beam-tilting array and a large-scale lens functioning at 195THz demonstrates the ability of the dielectric metasurface that is thin and has also high efficiency of more than 80%. Such configurations can serve as outstanding alternatives for plasmonic metasurfaces especially that it can be a scalable design. PMID:25361335

Cheng, Jierong; Ansari-Oghol-Beig, Davood; Mosallaei, Hossein

2014-11-01

169

Advanced PBTI reliability with 0.69 nm EOT GdHfO gate dielectric  

NASA Astrophysics Data System (ADS)

The reliability of 0.69 nm EOT GdHfO dielectric with metal gate is investigated. The threshold voltage shift at identical PBTI stress conditions is only 20% of the shift of a 0.78 nm EOT HfO 2 + La 2O 3 (or HfLaO) device. The resulting reliable gate over-drive at 10 years of this GdHfO device is 0.85 V. Analysis of the stress induced leakage current (SILC) shows that the improved PBTI in the GdHfO device is related to the reduced trap generation under low bias stress, which already exists in the HfLaO device.

Cho, Moonju; Aoulaiche, Marc; Degraeve, Robin; Kaczer, Ben; Kauerauf, Thomas; Ragnarsson, Lars-ke; Adelmann, Christoph; Elshocht, Sven Van; Hoffmann, Thomas Y.; Groeseneken, Guido

2011-09-01

170

Magnetoelectric Control of Magnetic Anisotropy in Ultrathin Fe Films  

NASA Astrophysics Data System (ADS)

Magnetoelectric switching of the magnetization vector could enable new low-power logic devices and non-volatile memory cells. Magnetoelectric switching typically requires complex multiferroic oxides or strain coupled magnetostrictive/piezoelectric composites. However, recently it has been demonstrated that surface magnetic anisotropy in ultrathin ferromagnetic metal films can be directly controlled by application of a strong electric field [1]. In this work we apply an electric field across a high-k oxide stack of MgO and ZrO2 to induce charge at the surface of an ultrathin Fe film. By using high-k dielectric materials more charge can be induced at the surface of the ferromagnetic film and the efficiency of the magnetoelectric effect can be enhanced. Under application of just a few volts across the oxide stack we observe a strong magnetoelectric effect which results in a shift of the spin reorientation thickness by 0.5 atomic layers and a change in perpendicular surface anisotropy of 120?J/m^2. Moreover, by engineering the high-k oxide stack we realize a novel charge pumping mechanism that permits optical imprinting of the magnetic state in the continuous Fe film. [1] T. Maruyama et al. Nature Nanotechnology 4, 158 - 161 (2009)

Bauer, Uwe; Przybylski, Marek; Kirschner, Jurgen; Beach, Geoffrey S. D.

2012-02-01

171

Electron tunneling through ultrathin boron nitride crystalline barriers.  

PubMed

We investigate the electronic properties of ultrathin hexagonal boron nitride (h-BN) crystalline layers with different conducting materials (graphite, graphene, and gold) on either side of the barrier layer. The tunnel current depends exponentially on the number of h-BN atomic layers, down to a monolayer thickness. Conductive atomic force microscopy scans across h-BN terraces of different thickness reveal a high level of uniformity in the tunnel current. Our results demonstrate that atomically thin h-BN acts as a defect-free dielectric with a high breakdown field. It offers great potential for applications in tunnel devices and in field-effect transistors with a high carrier density in the conducting channel. PMID:22380756

Britnell, Liam; Gorbachev, Roman V; Jalil, Rashid; Belle, Branson D; Schedin, Fred; Katsnelson, Mikhail I; Eaves, Laurence; Morozov, Sergey V; Mayorov, Alexander S; Peres, Nuno M R; Neto, Antonio H Castro; Leist, Jon; Geim, Andre K; Ponomarenko, Leonid A; Novoselov, Kostya S

2012-03-14

172

Dielectric resonators  

Microsoft Academic Search

Microwave passive and active devices containing dielectric resonators and the design procedures used to characterize these components are reviewed. The emphasis has been on low noise, small size, low cost and high temperature stability. Both filter and oscillator applications are described. The applications of dielectric resonators in the millimeter-wave frequency band are also discussed

P. Guillon

1988-01-01

173

Surface cleaning effects on reliability for devices with ultrathin oxides or oxynitrides  

NASA Astrophysics Data System (ADS)

A new wafer cleaning procedure has been developed for ultra-thin thermal oxidation process (Ultrathin thermal oxides (48 angstrom) and oxynitrides grown in N2O (42 angstrom) were prepared using this new cleaning and other commonly used cleaning methods to investigate the effects of surface preparation on dielectric integrity. It has been found that this two-dip method produces dielectrics with reduced leakage current and stress-induced leakage current, which are believed to be the critical parameters for ultrathin oxides. Furthermore, this new cleaning procedure improves both intrinsic and defect-related breakdown as well as the uniformity of the current- voltage characteristics across a 4-inch wafer. The methanol/HF dip time has also been optimized. The improvement is believed to be due to enhanced silicon surface passivation by hydrogen, the reduced surface micro-roughness and the absence of native oxide.

Lai, Kafai; Hao, Ming-Yin; Chen, Wei-Ming; Lee, Jack C.

1994-09-01

174

Design and model of wideband absorber made of ultrathin metamaterial structures  

NASA Astrophysics Data System (ADS)

A planar microwave ultrathin broadband absorber is proposed. It is composed of metallic patterns arranged on a dielectric material which is backed by a copper plate. The patterns of different dimensions allow to judiciously design absorption peaks at specific frequencies of interest. These peaks are due to the mode resonances of the cavities formed by the metallic patches, the dielectric substrate and the copper plate. In order to widen the absorption bandwidth, patterns of different dimensions are used, together with the different modes of these cavities. Numerical and experimental results are presented to validate the proposed method at microwave frequencies. It is also shown that the use of a composite air dielectric substrate supporting the metallic patterns helps to increase the absorption level.

Sellier, Alexandre; Teperik, Tatiana V.; Burokur, Shah Nawaz; Sabanowski, Guy; Piau, Grard-Pascal; de Lustrac, Andr

2014-08-01

175

Partitioning behavior and stabilization of hydrophobically coated HfO2, ZrO2 and Hfx Zr 1-x O2 nanoparticles with natural organic matter reveal differences dependent on crystal structure.  

PubMed

The interactions of engineered nanomaterials with natural organic matter (NOM) exert a profound influence on the mobilities of the former in the environment. However, the influence of specific nanomaterial structural characteristics on the partitioning and colloidal stabilization of engineered nanomaterials in various ecological compartments remains underexplored. Herein, we present a systematic study of the interactions of humic acid (HA, as a model for NOM) with monodisperse, well-characterized, ligand-passivated HfO(2), ZrO(2), and solid-solution Hf(x)Zr(1-x)O(2) nanoparticles (NPs). We note that mixing with HA induces the almost complete phase transfer of hydrophobically coated monoclinic metal oxide (MO) NPs from hexane to water. Furthermore, HA is seen to impart appreciable colloidal stabilization to the NPs in the aqueous phase. In contrast, phase transfer and aqueous-phase colloidal stabilization has not been observed for tetragonal MO-NPs. A mechanistic model for the phase transfer and aqueous dispersal of MO-NPs is proposed on the basis of evidence from transmission electron microscopy, ?-potential measurements, dynamic light scattering, Raman and infrared spectroscopies, elemental analysis, and systematic experiments on a closely related set of MO-NPs with varying composition and crystal structure. The data indicate the synergistic role of over-coating (micellar), ligand substitution (coordinative), and electrostatic processes wherein HA acts both as an amphiphilic molecule and a charged chelating ligand. The strong observed preference for the phase transfer of monoclinic instead of tetragonal NPs indicates the importance of the preferential binding of HA to specific crystallographic facets and suggests the possibility of being able to design NPs to minimize their mobilities in the aquatic environment. PMID:21963173

Navarro, Divina A; Depner, Sean W; Watson, David F; Aga, Diana S; Banerjee, Sarbajit

2011-11-30

176

Low Frequency Ultra-Thin Compact Metamaterial Absorber Comprising Split-Ring Resonators  

NASA Astrophysics Data System (ADS)

We present a design of a low frequency ultra-thin compact and polarization-insensitive metamaterial absorber (MA). The designed MA is a two-layer structure, a periodic array of novel split-ring resonators (SRRs), which are constructed in an FR4 dielectric layer, and another ultra-thin grounded sheet is attached to the bottom. Numerical simulated results show that the proposed MA can realize effective absorption at the frequency 281.9 MHz, and its overall thickness is just only 0.29% of the resonant wavelength, the unit space is only 2.57%, and the absorbance is kept well for a wide range of incident angles for different polarizations. In addition, the proposed MA is changed into a more compact one when the inter-digital structures are introduced in the SRRs. One convenient experiment is carried out in a rectangular waveguide simulator.

Lin, Bao-Qin; Da, Xin-Yu; Zhao, Shang-Hong; Meng, Wen; Li, Fan; Zheng, Qiu-Rong; Wang, Bu-Hong

2014-06-01

177

Broadband polarization-independent resonant light absorption using ultrathin plasmonic super absorbers.  

PubMed

Resonant plasmonic and metamaterial structures allow for control of fundamental optical processes such as absorption, emission and refraction at the nanoscale. Considerable recent research has focused on energy absorption processes, and plasmonic nanostructures have been shown to enhance the performance of photovoltaic and thermophotovoltaic cells. Although reducing metallic losses is a widely sought goal in nanophotonics, the design of nanostructured 'black' super absorbers from materials comprising only lossless dielectric materials and highly reflective noble metals represents a new research direction. Here we demonstrate an ultrathin (260 nm) plasmonic super absorber consisting of a metal-insulator-metal stack with a nanostructured top silver film composed of crossed trapezoidal arrays. Our super absorber yields broadband and polarization-independent resonant light absorption over the entire visible spectrum (400-700 nm) with an average measured absorption of 0.71 and simulated absorption of 0.85. Proposed nanostructured absorbers open a path to realize ultrathin black metamaterials based on resonant absorption. PMID:22044996

Aydin, Koray; Ferry, Vivian E; Briggs, Ryan M; Atwater, Harry A

2011-01-01

178

Dielectric properties and electronic transitions of porous and nanostructured cerium oxide films  

Microsoft Academic Search

Cerium dioxide (CeO2) exhibits exceptional electronic properties such as optical transparency and high refractive index (n) and high dc dielectric constant (k). Therefore, it is an attractive material for ultra-thin gate oxide in CMOS technology, where high-k dielectrics are required. We study the electronic properties of nanostructured and porous cerium oxide (CeOx) films, 110500nm thick, grown on Si by electron

S Logothetidis; P Patsalas; E. K Evangelou; N Konofaos; I Tsiaoussis; N Frangis

2004-01-01

179

Ultrathin, flexible organic-inorganic hybrid solar cells based on silicon nanowires and PEDOT:PSS.  

PubMed

Recently, free-standing, ultrathin, single-crystal silicon (c-Si) membranes have attracted considerable attention as a suitable material for low-cost, mechanically flexible electronics. In this paper, we report a promising ultrathin, flexible, hybrid solar cell based on silicon nanowire (SiNW) arrays and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The free-standing, ultrathin c-Si membranes of different thicknesses were produced by KOH etching of double-side-polished silicon wafers for various etching times. The processed free-standing silicon membranes were observed to be mechanically flexible, and in spite of their relatively small thickness, the samples tolerated the different steps of solar cell fabrication, including surface nanotexturization, spin-casting, dielectric film deposition, and metallization. However, in terms of the optical performance, ultrathin c-Si membranes suffer from noticeable transmission losses, especially in the long-wavelength region. We describe the experimental performance of a promising light-trapping scheme in the aforementioned ultrathin c-Si membranes of thicknesses as small as 5.7 ?m employing front-surface random SiNW texturization in combination with a back-surface distribution of silver (Ag) nanoparticles (NPs). We report the enhancement of both the short-circuit current density (JSC) and the open-circuit voltage (VOC) that has been achieved in the described devices. Such enhancement is attributable to the plasmonic backscattering effect of the back-surface Ag NPs, which led to an overall 10% increase in the power conversion efficiency (PCE) of the devices compared to similar structures without Ag NPs. A PCE in excess of 6.62% has been achieved in the described devices having a c-Si membrane of thickness 8.6 ?m. The described device technology could prove crucial in achieving an efficient, low-cost, mechanically flexible photovoltaic device in the near future. PMID:24568116

Sharma, Manisha; Pudasaini, Pushpa Raj; Ruiz-Zepeda, Francisco; Elam, David; Ayon, Arturo A

2014-03-26

180

Zirconium-doped tantalum oxide high-k gate dielectric films  

E-print Network

the gate dielectric layer for the next generation metal-oxide-semiconductor field effect transistor (MOSFET). Due to the aggressive device scaling in ultra-large-scale integrated circuitry (ULSI), the ultra-thin conventional gate oxide (SiO2...

Tewg, Jun-Yen

2005-02-17

181

Physicochemically functional ultrathin films by interfacial polymerization  

DOEpatents

Interfacially-polymerized ultrathin films containing physicochemically functional groups are disclosed, both with and without supports. Various applications are disclsoed, including membrane electrodes, selective membranes and sorbents, biocompatible materials, targeted drug delivery, and narrow band optical absorbers.

Lonsdale, Harold K. (Bend, OR); Babcock, Walter C. (Bend, OR); Friensen, Dwayne T. (Bend, OR); Smith, Kelly L. (Bend, OR); Johnson, Bruce M. (Bend, OR); Wamser, Carl C. (West Linn, OR)

1990-01-01

182

Ultrathin BaTiO3 templates for multiferroic nanostructures  

NASA Astrophysics Data System (ADS)

The structural, electronic and dielectric properties of high-quality ultrathin BaTiO3 films were investigated. The films, which were grown by ozone-assisted molecular beam epitaxy on Nb-doped SrTiO3(001) substrates and have thicknesses as low as 8 unit cells (u.c.) (3.2 nm), are unreconstructed and atomically smooth with large crystalline terraces. A strain-driven transition to three-dimensional (3D) island formation is observed for films of 13 u.c. thickness (5.2 nm). The high structural quality of the surfaces, together with dielectric properties similar to bulk BaTiO3 and dominantly TiO2 surface termination, makes these films suitable templates for the synthesis of high-quality metal-oxide multiferroic heterostructures for the fundamental study and exploitation of magneto-electric effects, such as a recently proposed interface effect in Fe/BaTiO3 heterostructures based on Fe-Ti interface bonds.

Chen, Xumin; Yang, Seolun; Kim, Ji-Hyun; Kim, Hyung-Do; Kim, Jae-Sung; Rojas, Geoffrey; Skomski, Ralph; Lu, Haidong; Bhattacharya, Anand; Santos, Tiffany; Guisinger, Nathan; Bode, Matthias; Gruverman, Alexei; Enders, Axel

2011-08-01

183

Electrostatic Gating of Ultrathin Films  

NASA Astrophysics Data System (ADS)

Electrostatic gating of ultrathin films can be used to modify electronic and magnetic properties of materials by effecting controlled alterations of carrier concentration while, in principle, not changing the level of disorder. As such, electrostatic gating can facilitate the development of novel devices and can serve as a means of exploring the fundamental properties of materials in a manner far simpler than is possible with the conventional approach of chemical doping. The entire phase diagram of a compound can be traversed by changing the gate voltage. In this review, we survey results involving conventional field effect devices as well as more recent progress, which has involved structures that rely on electrochemical configurations such as electric double-layer transistors. We emphasize progress involving thin films of oxide materials such as high-temperature superconductors, magnetic oxides, and oxides that undergo metal-insulator transitions.

Goldman, A. M.

2014-07-01

184

Anisotropic permittivity of ultra-thin crystalline Au films: Impacts on the plasmonic response of metasurfaces  

NASA Astrophysics Data System (ADS)

It has been determined by density functional theory (DFT) simulations that the extracted permittivities of ultra-thin crystalline gold (Au) films exhibit large anisotropies which are not predicted by classical models or previous experimental determinations of the dielectric function. The optical scattering characteristics of a periodic array of Au discs are simulated with the DFT extracted permittivity and contrasted against those obtained with several commonly used Au permittivity models. It is demonstrated that the DFT-based transmittance spectra for these plasmonic metasurfaces lead to significantly redshifted results when compared to those predicted by standard Drude and Johnson-Christy permittivity models.

Campbell, Sawyer D.; Ziolkowski, Richard W.; Cao, Jiangrong; Laref, Slimane; Muralidharan, Krishna; Deymier, Pierre

2013-08-01

185

UV protection filters by dielectric multilayer thin films on Glass BK-7 and Infrasil 301  

NASA Astrophysics Data System (ADS)

The increasing use of Ultraviolet (UV) light in medicine, industrial environments, for cosmetic use, and even in consumer products necessitates that greater attention be paid to the potential hazards of this type of electromagnetic radiation. To avoid any adverse effects of exposure to this type of radiation, four suitable protection filters were produced to block three UV bands (UVA, UVB, and UVC). The design structure of the required dielectric multilayer filters was done by optical thin film technology using the absorbing property of UV radiation for the substrates and dielectric materials. The computer analyses of the multilayer filter formulas were prepared using Macleod Software for the production processes. The deposition technique was achieved on optical substrates (Glass BK-7 and Infrasil 301) by dielectric material combinations including Titanium dioxide (Ti 2O 3), Hafnium dioxide (HfO 2), and Lima (mixture of oxides SiO 2/Al 2O 3); deposition being achieved using an electron beam gun. The output results of the theoretical and experimental transmittance values for spectral band from 200 nm to 800 nm were discussed in four processes. To analyze the suitability for use in 'real world' applications, the test pieces were subjected to the durability tests (adhesion, abrasion resistance, and humidity) according to Military Standard MIL-C-675C and MIL-C-48497A.

Abdel-Aziz, M. M.; Azim, Osama A.; Abdel-Wahab, L. A.; Seddik, Mohamed M.

2006-10-01

186

Memory functions of nanocrystalline cadmium selenide embedded ZrHfO high-k dielectric stack  

NASA Astrophysics Data System (ADS)

Metal-oxide-semiconductor capacitors made of the nanocrystalline cadmium selenide nc-CdSe embedded Zr-doped HfO2 high-k stack on the p-type silicon wafer have been fabricated and studied for their charge trapping, detrapping, and retention characteristics. Both holes and electrons can be trapped to the nanocrystal-embedded dielectric stack depending on the polarity of the applied gate voltage. With the same magnitude of applied gate voltage, the sample can trap more holes than electrons. A small amount of holes are loosely trapped at the nc-CdSe/high-k interface and the remaining holes are strongly trapped to the bulk nanocrystalline CdSe site. Charges trapped to the nanocrystals caused the Coulomb blockade effect in the leakage current vs. voltage curve, which is not observed in the control sample. The addition of the nanocrystals to the dielectric film changed the defect density and the physical thickness, which are reflected on the leakage current and the breakdown voltage. More than half of the originally trapped holes can be retained in the embedded nanocrystals for more than 10 yr. The nanocrystalline CdSe embedded high-k stack is a useful gate dielectric for this nonvolatile memory device.

Lin, Chi-Chou; Kuo, Yue

2014-02-01

187

Silicon nanowires with high-k hafnium oxide dielectrics for sensitive detection of small nucleic acid oligomers.  

PubMed

Nanobiosensors based on silicon nanowire field effect transistors offer advantages of low cost, label-free detection, and potential for massive parallelization. As a result, these sensors have often been suggested as an attractive option for applications in point-of-care (POC) medical diagnostics. Unfortunately, a number of performance issues, such as gate leakage and current instability due to fluid contact, have prevented widespread adoption of the technology for routine use. High-k dielectrics, such as hafnium oxide (HfO(2)), have the known ability to address these challenges by passivating the exposed surfaces against destabilizing concerns of ion transport. With these fundamental stability issues addressed, a promising target for POC diagnostics and SiNWFETs has been small oligonucleotides, more specifically, microRNA (miRNA). MicroRNAs are small RNA oligonucleotides which bind to mRNAs, causing translational repression of proteins, gene silencing, and expressions are typically altered in several forms of cancer. In this paper, we describe a process for fabricating stable HfO(2) dielectric-based silicon nanowires for biosensing applications. Here we demonstrate sensing of single-stranded DNA analogues to their microRNA cousins using miR-10b and miR-21 as templates, both known to be upregulated in breast cancer. We characterize the effect of surface functionalization on device performance using the miR-10b DNA analogue as the target sequence and different molecular weight poly-l-lysine as the functionalization layer. By optimizing the surface functionalization and fabrication protocol, we were able to achieve <100 fM detection levels of the miR-10b DNA analogue, with a theoretical limit of detection of 1 fM. Moreover, the noncomplementary DNA target strand, based on miR-21, showed very little response, indicating a highly sensitive and highly selective biosensing platform. PMID:22695179

Dorvel, Brian R; Reddy, Bobby; Go, Jonghyun; Duarte Guevara, Carlos; Salm, Eric; Alam, Muhammad Ashraful; Bashir, Rashid

2012-07-24

188

Silicon Nanowires with High-k Hafnium Oxide Dielectrics for Sensitive Detection of Small Nucleic Acid Oligomers  

PubMed Central

Nanobiosensors based on silicon nanowire field effect transistors offer advantages of low cost, label-free detection, and potential for massive parallelization. As a result, these sensors have often been suggested as an attractive option for applications in Point-of-care (POC) medical diagnostics. Unfortunately, a number of performance issues such as gate leakage and current instability due to fluid contact, have prevented widespread adoption of the technology for routine use. High-k dielectrics, such as hafnium oxide (HfO2), have the known ability to address these challenges by passivating the exposed surfaces against destabilizing concerns of ion transport. With these fundamental stability issues addressed, a promising target for POC diagnostics and SiNWFETs has been small oligonucleotides, more specifically microRNA (miRNA). MicroRNAs are small RNA oligonucleotides which bind to messenger RNAs, causing translational repression of proteins, gene silencing, and expressions are typically altered in several forms of cancer. In this paper, we describe a process for fabricating stable HfO2 dielectric based silicon nanowires for biosensing applications. Here we demonstrate sensing of single stranded DNA analogues to their microRNA cousins using miR-10b and miR-21 as templates, both known to be upregulated in breast cancer. We characterize the effect of surface functionalization on device performance using the miR-10b DNA analogue as the target sequence and different molecular weight poly-l-lysine as the functionalization layer. By optimizing the surface functionalization and fabrication protocol, we were able to achieve <100fM detection levels of miR-10b DNA analogue, with a theoretical limit of detection of 1fM. Moreover, the non-complementary DNA target strand, based on miR-21, showed very little response, indicating a highly sensitive and highly selective biosensing platform. PMID:22695179

Dorvel, Brian R.; Reddy, Bobby; Go, Jonghyun; Guevara, Carlos Duarte; Salm, Eric; Alam, Muhammad Ashraful; Bashir, Rashid

2012-01-01

189

Hybrid gate dielectric materials for unconventional electronic circuitry.  

PubMed

Recent advances in semiconductor performance made possible by organic ?-electron molecules, carbon-based nanomaterials, and metal oxides have been a central scientific and technological research focus over the past decade in the quest for flexible and transparent electronic products. However, advances in semiconductor materials require corresponding advances in compatible gate dielectric materials, which must exhibit excellent electrical properties such as large capacitance, high breakdown strength, low leakage current density, and mechanical flexibility on arbitrary substrates. Historically, conventional silicon dioxide (SiO2) has dominated electronics as the preferred gate dielectric material in complementary metal oxide semiconductor (CMOS) integrated transistor circuitry. However, it does not satisfy many of the performance requirements for the aforementioned semiconductors due to its relatively low dielectric constant and intransigent processability. High-k inorganics such as hafnium dioxide (HfO2) or zirconium dioxide (ZrO2) offer some increases in performance, but scientists have great difficulty depositing these materials as smooth films at temperatures compatible with flexible plastic substrates. While various organic polymers are accessible via chemical synthesis and readily form films from solution, they typically exhibit low capacitances, and the corresponding transistors operate at unacceptably high voltages. More recently, researchers have combined the favorable properties of high-k metal oxides and ?-electron organics to form processable, structurally well-defined, and robust self-assembled multilayer nanodielectrics, which enable high-performance transistors with a wide variety of unconventional semiconductors. In this Account, we review recent advances in organic-inorganic hybrid gate dielectrics, fabricated by multilayer self-assembly, and their remarkable synergy with unconventional semiconductors. We first discuss the principals and functional importance of gate dielectric materials in thin-film transistor (TFT) operation. Next, we describe the design, fabrication, properties, and applications of solution-deposited multilayer organic-inorganic hybrid gate dielectrics, using self-assembly techniques, which provide bonding between the organic and inorganic layers. Finally, we discuss approaches for preparing analogous hybrid multilayers by vapor-phase growth and discuss the properties of these materials. PMID:24428627

Ha, Young-Geun; Everaerts, Ken; Hersam, Mark C; Marks, Tobin J

2014-04-15

190

Hafnium oxide and hafnium aluminum oxide for CMOS applications  

NASA Astrophysics Data System (ADS)

The continued scaling of the CMOS gate dielectric to its fundamental limit governed by the large gate leakage current requires the introduction of high-k material for sub-100-nm technology nodes. This dissertation research deals with the physical and electrical properties of a promising high-k candidate, hafnium oxide, as a gate dielectric for CMOS applications. Hafnium oxide made by the Jet-Vapor-Deposition process shows very promising properties in terms of surface roughness, dielectric constant, and energy bandgap, but there are also severe challenges, such as low crystallization temperature, high charge trapping probability, and low channel mobility, which have been studied in detail in this thesis. We have found that the crystallization of HfO2 could result in a significant increase of the leakage current. This problem has been solved by adding Al in the HfO2 film. The impacts of Al inclusion in HfO 2 film on crystallization temperature, bandgap energy, and dielectric constant have been investigated. Considering the trade-off among the crystallization temperature, bandgap energy, and dielectric constant, we have concluded that the optimum concentration is about 30% Al for conventional self-aligned CMOS gate processing technology. The charge trapping properties of ultra-thin HfO2 in metal-oxide-silicon capacitors during constant voltage stress have also been investigated. The effects of stress voltage, substrate type, annealing temperature, and gate electrode have been studied in detail, and reported in this dissertation. Accurate measurements and degradation mechanisms of the channel mobility for MOSFETs with HfO2 as the gate dielectric have been systemetically studied. The error in mobility extraction caused by a high density of interface traps for a MOSFET with high-k gate dielectric has been analyzed, and a new method to correct this error has been proposed. Other sources of error in mobility extraction, including gate leakage current, channel resistance, and contact resistance for a MOSFET with ultra-thin high-k dielectric have also been investigated and reported in this thesis. Based on the accurately measured channel mobility, we have analyzed the degradation mechanisms of channel mobility for a MOSFET with HfO2 as the gate dielectric. The mobility degradation due to Coulomb scatting arising from interface trapped charges, and that due to remote soft optical phonon scattering are discussed.

Zhu, Wenjuan

191

Ultrathin, highly flexible and stretchable PLEDs  

NASA Astrophysics Data System (ADS)

We demonstrate ultrathin (2 m thick) red and orange polymer light-emitting diodes with unprecedented mechanical properties in terms of their flexibility and ability to be stretched. The devices have a luminance greater than 100 cd m-2, sufficient for a variety of optoelectronic applications including indoor displays. They can be operated as free-standing ultrathin films, allowing for crumpling during device operation. Furthermore, they may be applied to almost any surface whether rigid or elastomeric, and can withstand the associated mechanical deformation. They are shown to be extremely flexible, with radii of curvature under 10 m, and stretch-compatible to 100% tensile strain. Such ultrathin light-emitting foils constitute an important step towards integration with malleable materials like textiles and artificial skin.

White, Matthew S.; Kaltenbrunner, Martin; G?owacki, Eric D.; Gutnichenko, Kateryna; Kettlgruber, Gerald; Graz, Ingrid; Aazou, Safae; Ulbricht, Christoph; Egbe, Daniel A. M.; Miron, Matei C.; Major, Zoltan; Scharber, Markus C.; Sekitani, Tsuyoshi; Someya, Takao; Bauer, Siegfried; Sariciftci, Niyazi Serdar

2013-10-01

192

Advancing quasi-freestanding epitaxial graphene electronics through integration of wafer scale hexagonal boron nitride dielectrics  

NASA Astrophysics Data System (ADS)

A key limitation to graphene based electronics is graphene's interaction with dielectric interfaces. SiO2 and various high-k gate dielectrics can introduce scattering from charged surface states, impurities, and surface optical phonons; degrading the transport properties of graphene. Hexagonal boron nitride (h-BN) exhibits an atomically smooth surface that is expected to be free of dangling bonds, leading to an interface that is relatively free of surface charge traps and adsorbed impurities. Additionally, the decreased surface optical phonon interaction from h-BN is expected to further reduce scattering. While h-BN gated graphene FETs have been demonstrated on a small scale utilizing CVD grown or exfoliated graphene, integrating quasi-freestanding epitaxial graphene (QFEG) with h-BN gate dielectrics on a wafer scale has not been explored. We present results from the first large scale CVD growth of h-BN and its subsequent transfer to a 75mm QFEG wafer. The effects of growth conditions on the thickness and quality of the h-BN film and its potential and limitations as a gate dielectric to QFEG are discussed. The introduction of charged impurities during the transfer process resulted in an average degradation in mobility of only 9%. Despite the slight degradation, we show that h-BN is highly beneficial compared to high-k dielectrics when the charged impurity concentration of QFEG is below 5x1012cm-2. Here we show improvements in mobility of >3x and intrinsic cutoff frequency of >2x compared to HfO2.

Bresnehan, Michael S.; Hollander, Matthew J.; Marucci, Rebecca L.; LaBella, Michael; Trumbull, Kathleen A.; Cavalero, Randal; Snyder, David W.; Robinson, Joshua A.

2012-09-01

193

Ultrathin core-sheath fibers for liposome stabilization.  

PubMed

Ultrathin core-sheath fibers with small unilamellar vesicles (SUVs) in the core were prepared by coaxial electrospinning. SUVs/sodium hyaluranate (HA-Na)/water and polyvinylpyrrolidone (PVP)/ethanol solutions were used as core and sheath fluid in electrospinning, respectively. The ultrathin fibers were characterized by scanning and transmission electron microscopy (SEM and TEM) and laser scanning confocal microscopy (LSCM). The SUVs were successfully encapsulated in the core HA-Na matrix of the ultrathin fibers and are in the elliptic shape. The SUVs encapsulated in the core matrix of the ultrathin fibers have an excellent stability. The SUVs embedded in the ultrathin fibers are stable. When the ultrathin fibers were re-dissolved in water after one-month storage at room temperature, the rehydrated SUVs have the similar size and size distribution as the as-prepared SUVs. The liposome-loaded ultrathin fiber mats have the promising applications in wound healing materials. PMID:25130418

Li, Zhuang; Kang, Hongliang; Li, Qinmei; Che, Ning; Liu, Zhijing; Li, Pingping; Zhang, Chao; Liu, Ruigang; Huang, Yong

2014-10-01

194

Glass Transition Measurements of Ultrathin Polystyrene Films  

E-print Network

1 Glass Transition Measurements of Ultrathin Polystyrene Films Cynthia Buenviaje, Franco Dinelli. Measurements taken on polystyrene surfaces of various film thickness provide insight into how the glass results obtained with the techniques, listed in table 1, on similar systems (such as polystyrene

195

Brilliant Whiteness in Ultrathin Beetle Scales  

E-print Network

Brilliant Whiteness in Ultrathin Beetle Scales Pete Vukusic,1 * Benny Hallam,2 Joe Noyes1 T he. Archetypal brilliant whiteness that is not augmented by fluores- cence, such as whiteness from snow or milk or kaolin crystal inclusions and optical brightening agents (blue fluorescing dyes) are added to paper

Exeter, University of

196

Characterization of ALD Beryllium Oxide as a Potential High- k Gate Dielectric for Low-Leakage AlGaN/GaN MOSHEMTs  

NASA Astrophysics Data System (ADS)

The chemical and electrical characteristics of atomic layer deposited (ALD) beryllium oxide (BeO) on GaN were studied via x-ray photoelectron spectroscopy, current-voltage, and capacitance-voltage measurements and compared with those of ALD Al2O3 and HfO2 on GaN. Radiofrequency (RF) and power electronics based on AlGaN/GaN high-electron-mobility transistors are maturing rapidly, but leakage current reduction and interface defect ( D it) minimization remain heavily researched. BeO has received recent attention as a high- k gate dielectric due to its large band gap (10.6 eV) and thermal stability on InGaAs and Si, but little is known about its performance on GaN. Unintentionally doped GaN was cleaned in dilute aqueous HCl immediately prior to BeO deposition (using diethylberyllium and H2O precursors). Formation of an interfacial layer was observed in as-deposited samples, similar to the layer formed during ALD HfO2 deposition on GaN. Postdeposition anneal (PDA) at 700C and 900C had little effect on the observed BeO binding state, confirming the strength of the bond, but led to increased Ga oxide formation, indicating the presence of unincorporated oxygen in the dielectric. Despite the interfacial layer, gate leakage current of 1.1 10-7 A/cm2 was realized, confirming the potential of ALD BeO for use in low-leakage AlGaN/GaN metal-oxide-semiconductor high-electron-mobility transistors.

Johnson, Derek W.; Yum, Jung Hwan; Hudnall, Todd W.; Mushinski, Ryan M.; Bielawski, Christopher W.; Roberts, John C.; Wang, Wei-E.; Banerjee, Sanjay K.; Harris, H. Rusty

2014-01-01

197

Surface band bending and band alignment of plasma enhanced atomic layer deposited dielectrics on Ga- and N-face gallium nitride  

NASA Astrophysics Data System (ADS)

The effects of surface pretreatment, dielectric growth, and post deposition annealing on interface electronic structure and polarization charge compensation of Ga- and N-face bulk GaN were investigated. The cleaning process consisted of an ex-situ wet chemical NH4OH treatment and an in-situ elevated temperature NH3 plasma process to remove carbon contamination, reduce oxygen coverage, and potentially passivate N-vacancy related defects. After the cleaning process, carbon contamination decreased below the x-ray photoemission spectroscopy detection limit, and the oxygen coverage stabilized at 1 monolayer on both Ga- and N-face GaN. In addition, Ga- and N-face GaN had an upward band bending of 0.8 0.1 eV and 0.6 0.1 eV, respectively, which suggested the net charge of the surface states and polarization bound charge was similar on Ga- and N-face GaN. Furthermore, three dielectrics (HfO2, Al2O3, and SiO2) were prepared by plasma-enhanced atomic layer deposition on Ga- or N-face GaN and annealed in N2 ambient to investigate the effect of the polarization charge on the interface electronic structure and band offsets. The respective valence band offsets of HfO2, Al2O3, and SiO2 with respect to Ga- and N-face GaN were 1.4 0.1, 2.0 0.1, and 3.2 0.1 eV, regardless of dielectric thickness. The corresponding conduction band offsets were 1.0 0.1, 1.3 0.1, and 2.3 0.1 eV, respectively. Experimental band offset results were consistent with theoretical calculations based on the charge neutrality level model. The trend of band offsets for dielectric/GaN interfaces was related to the band gap and/or the electronic part of the dielectric constant. The effect of polarization charge on band offset was apparently screened by the dielectric-GaN interface states.

Yang, Jialing; Eller, Brianna S.; Nemanich, Robert J.

2014-09-01

198

Real time spectroscopic ellipsometry on ultrathin (<50 A?) hydrogenated amorphous silicon films on Si(100) and GaAs(100)  

NASA Astrophysics Data System (ADS)

Real time spectroscopic ellipsometry was used to determine the time evolution of the dielectric function, bulk thickness, and surface roughness during hot-wire chemical vapor deposition of hydrogenated amorphous silicon (a-Si:H). The amorphous silicon films were deposited on native-oxide-covered c-Si(100) and GaAs(100) substrates at temperatures in the range from 70to350C. Data analysis by a three layer optical model, consisting of substrate, bulk, and surface roughness layer, revealed that the dielectric function of the a-Si :H film changes in the initial growth regime (d<50), which can be attributed to a higher optical band gap for films with a smaller thickness. It is argued that the origin of this higher band gap lies most likely in quantum confinement effects of the electron wave function in the ultrathin film, with possibly a small contribution of a higher hydrogen content in the ultrathin film. In addition, we show that the trends in surface roughness and bulk thickness are only marginally affected, regardless of whether the change in dielectric function with film thickness is incorporated in the data analysis.

van den Oever, P. J.; van de Sanden, M. C. M.; Kessels, W. M. M.

2007-06-01

199

Effects of gate-first and gate-last process on interface quality of In0.53Ga0.47As metal-oxide-semiconductor capacitors using atomic-layer-deposited Al2O3 and HfO2 oxides  

NASA Astrophysics Data System (ADS)

We have investigated the effects of gate-first and gate-last process on oxide/InGaAs interface quality using In0.53Ga0.47As metal-oxide-semiconductor capacitors (MOSCAPs) with atomic-layer-deposited (ALD) oxides. Sequence of source/drain activation anneal in the process results in remarkable electrical and physical difference. Applying gate-last process provides significant frequency dispersion reduction and interface trap density reduction for InGaAs MOSCAPs compared to gate-first process. A large amount of In-O, Ga-O, and As-As bonds was observed on InGaAs surface after gate-first process while no detectable interface reaction after gate-last process. Electrical and physical results also show that ALD Al2O3 exhibits better interface quality on InGaAs than HfO2.

Zhao, Han; Huang, Jeff; Chen, Yen-Ting; Yum, Jung Hwan; Wang, Yanzhen; Zhou, Fei; Xue, Fei; Lee, Jack C.

2009-12-01

200

Monte Carlo Simulations of Ultrathin Magnetic Dots  

E-print Network

In this work we study the thermodynamic properties of ultrathin ferromagnetic dots using Monte Carlo simulations. We investigate the vortex density as a function of the temperature and the vortex structure in monolayer dots with perpendicular anisotropy and long-range dipole interaction. The interplay between these two terms in the hamiltonian leads to an interesting behavior of the thermodynamic quantities as well as the vortex density.

M. Rapini; R. A. Dias; D. P. Landau; B. V. Costa

2006-04-10

201

Growth, strain relaxation properties and high-? dielectric integration of mixed-anion GaAs1-ySby metamorphic materials  

NASA Astrophysics Data System (ADS)

Mixed-anion, GaAs1-ySby metamorphic materials with a wide range of antimony (Sb) compositions extending from 15% to 62%, were grown by solid source molecular beam epitaxy (MBE) on GaAs substrates. The impact of different growth parameters on the Sb composition in GaAs1-ySby materials was systemically investigated. The Sb composition was well-controlled by carefully optimizing the As/Ga ratio, the Sb/Ga ratio, and the substrate temperature during the MBE growth process. High-resolution x-ray diffraction demonstrated a quasi-complete strain relaxation within each composition of GaAs1-ySby. Atomic force microscopy exhibited smooth surface morphologies across the wide range of Sb compositions in the GaAs1-ySby structures. Selected high-? dielectric materials, Al2O3, HfO2, and Ta2O5 were deposited using atomic layer deposition on the GaAs0.38Sb0.62 material, and their respective band alignment properties were investigated by x-ray photoelectron spectroscopy (XPS). Detailed XPS analysis revealed a valence band offset of >2 eV for all three dielectric materials on GaAs0.38Sb0.62, indicating the potential of utilizing these dielectrics on GaAs0.38Sb0.62 for p-type metal-oxide-semiconductor (MOS) applications. Moreover, both Al2O3 and HfO2 showed a conduction band offset of >2 eV on GaAs0.38Sb0.62, suggesting these two dielectrics can also be used for n-type MOS applications. The well-controlled Sb composition in several GaAs1-ySby material systems and the detailed band alignment analysis of multiple high-? dielectric materials on a fixed Sb composition, GaAs0.38Sb0.62, provides a pathway to utilize GaAs1-ySby materials in future microelectronic and optoelectronic applications.

Zhu, Y.; Clavel, M.; Goley, P.; Hudait, M. K.

2014-10-01

202

Microwave absorptions of ultrathin conductive films and designs of frequency-independent ultrathin absorbers  

NASA Astrophysics Data System (ADS)

We study the absorption properties of ultrathin conductive films in the microwave regime, and find a moderate absorption effect which gives rise to maximal absorbance 50% if the sheet (square) resistance of the film meets an impedance matching condition. The maximal absorption exhibits a frequency-independent feature and takes place on an extremely subwavelength scale, the film thickness. As a realistic instance, 5 nm thick Au film is predicted to achieve the optimal absorption. In addition, a methodology based on metallic mesh structure is proposed to design the frequency-independent ultrathin absorbers. We perform a design of such absorbers with 50% absorption, which is verified by numerical simulations.

Li, Sucheng; Anwar, Shahzad; Lu, Weixin; Hang, Zhi Hong; Hou, Bo; Shen, Mingrong; Wang, Chin-Hua

2014-01-01

203

Extreme scaling with ultra-thin Si channel MOSFETs  

Microsoft Academic Search

We examine the scaling limits for planar single gate technology using the ultra-thin Si channel MOSFET. Characteristics for extreme scaled devices with physical gate lengths down to 6 nm and SOI channels as thin as 4 nm are presented. For the first time, we report ring oscillators with 26 nm gate lengths and ultra-thin Si channels.

B. Doris; Meikei Ieong; T. Kanarsky; Ying Zhang; R. A. Roy; O. Dokumaci; Zhibin Ren; Fen-Fen Jamin; Leathen Shi; W. Natzle; Hsiang-Jen Huang; J. Mezzapelle; A. Mocuta; S. Womack; M. Gribelyuk; E. C. Jones; R. J. Miller; H.-S. P. Wong; W. Haensch

2002-01-01

204

Abnormal sub-threshold swing degradation under dynamic hot carrier stress in HfO2/TiN n-channel metal-oxide-semiconductor field-effect-transistors  

NASA Astrophysics Data System (ADS)

This work finds abnormal sub-threshold swing (S.S.) degradation under dynamic hot carrier stress (HCS) in n-channel metal-oxide-semiconductor field-effect-transistors with high-k gate dielectric. Results indicate that there is no change in S.S. after dynamic HCS due to band-to-band hot hole injection at the drain side which acts to diminish the stress field. Moreover, the impaired stress field causes the interface states to mainly distribute in shallow states. This results in ON state current and transconductance decreases, whereas S.S. degradation is insignificant after dynamic HCS. The proposed model is confirmed by one-side charge pumping measurement and gate-to-drain capacitance at varying frequencies.

Tsai, Jyun-Yu; Chang, Ting-Chang; Lo, Wen-Hung; Chen, Ching-En; Ho, Szu-Han; Chen, Hua-Mao; Tai, Ya-Hsiang; Cheng, Osbert; Huang, Cheng-Tung

2013-07-01

205

Semitransparent ultrathin CdTe solar cells Semitransparent ultrathin CdTe solar cells and durabilityand durability  

E-print Network

sizes but poor efficiency, striped appearance) · Thinfilm CdTe, laser or chemically etched to removeSemitransparent ultrathin CdTe solar cells Semitransparent ultrathin CdTe solar cells PV coatings based on CdTe. ...for transparent window PV:...for transparent window PV: , p g · The X26

Rollins, Andrew M.

206

Measurement of effective carrier lifetime at the semiconductor-dielectric interface by Photoconductive Decay (PCD) Method  

NASA Astrophysics Data System (ADS)

The semiconductor-dielectric interface is of key importance to the performance of Metal-Oxide-Semiconductor transistors (MOSFETs). The near-surface Photoconductance Decay (ns-PCD) method using probe contacts is shown in this study to be very useful in measuring effective carrier lifetime at the semiconductor-dielectric interface. By doing so, it provides direct information on the condition of the charge transport environment in the MOSFET channel without a need to fabricate a transistor. The way measurement is implemented depends on the thickness of dielectric. For dielectric layers thicker than about 5 nm, etched windows in the dielectric layer are necessary to achieve an ohmic contact with the semiconductor layer. For dielectric layers thinner than about 5 nm, however, the ohmic contact to the semiconductor substrate, essential to the performance of this measurement, is established using probes and electrical contact formation process. The measurements were performed on thermally oxidized Si-SiO2 structures as well as Si-Al2O3 (3 nm) and Si-Ta2O5 (3 nm) structures formed by means of Atomic Layer Deposition (ALD). The results obtained demonstrate that the PCD method adapted as discussed in this work can be very useful in monitoring condition of semiconductor - ultra-thin (<5 nm) dielectric interface by measuring carrier lifetime in the as-processed samples, i.e. without subjecting it to any processing step beyond dielectric deposition.

Drummond, P. J.; Bhatia, D.; Ruzyllo, J.

2013-03-01

207

Gate stack dielectric degradation of rare-earth oxides grown on high mobility Ge substrates  

NASA Astrophysics Data System (ADS)

We report on the reliability characteristics and their analysis, of rare-earth oxides (REOs) dielectric degradation, when used as interfacial buffer layers together with HfO2 high-k films (REOs/HfO2) on high mobility Ge substrates. Metal-oxide-semiconductor (MOS) devices with these stacks, show dissimilar charge trapping phenomena under varying levels of constant-voltage-stress (CVS) conditions, influencing the measured densities of the interface (Nit) and border (NBT) traps. In the present study, we report on C-Vg hysteresis curves related to both Nit and NBT. We propose a new model based on the Maxwell-Wagner mechanism, and this model explains the current decay transient observed under CVS bias from low to higher fields of MOS gate stack devices grown on Ge substrates. The proposed model is unlike to those used for other MOS devices. Finally, CVS measurements for very long times at moderate fields reveal an initial current decay due to relaxation, followed by charge trapping and generation of stress-induced leakage which eventually lead to hard breakdown.

Shahinur Rahman, Md.; Evangelou, E. K.; Konofaos, N.; Dimoulas, A.

2012-11-01

208

Structural Relaxation of Stacked Ultrathin Polystyrene Films  

NASA Astrophysics Data System (ADS)

The kinetic behavior of stacked polystyrene ultrathin films is investigated by differential scanning calorimetry (DSC) and compared to the behavior of bulk polystyrene. The fictive temperature (Tf) was measured as a function of cooling rate and as a function of aging time for aging temperatures below the nominal glass transition temperature (Tg). The stacked thin films show enthalpy overshoots in DSC heating scans which are reduced in height but occur over a broader temperature range relative to the bulk response for a given change in fictive temperature. The cooling rate dependence of the limiting fictive temperature, Tf' is also found to be higher for the stacked thin film samples; the result is that the magnitude of the Tg depression between the thin film sample and the bulk is inversely proportional to the cooling rate consistent with other results in the literature. We also find that the rate of physical aging of the stacked thin films is comparable to the bulk when aging is performed at the same distance from Tg; however, when conducted at the same aging temperature, the thin film samples show accelerated physical aging due to their depressed Tg values. This result is in contrast to recent work in the literature on PMMA ultrathin films and on o-TP confined in nanopores.

Koh, Yung P.; Simon, Sindee L.

2008-03-01

209

An ultrathin but nearly perfect direct current electric cloak  

NASA Astrophysics Data System (ADS)

We propose and experimentally demonstrate an ultrathin but nearly perfect dc electric invisibility cloak. In the dc limit, transformation optics reduces to transformation electrostatics. Based on a special coordinate transformation, we derive a nearly perfect dc electric cloak which is composed of homogeneous and anisotropic conducting material. Due to the homogeneity feature, the dc cloak is realized using an ultrathin dc metamaterial with only one-unit-cell thickness, which is the ultra limit for practical artificial materials. Although ultrathin, our experimental results show that the dc cloak has excellent performance with nearly perfect cloaking behaviour.

Xiang Jiang, Wei; Yang Luo, Chen; Lei Mei, Zhong; Jun Cui, Tie

2013-01-01

210

Ultrathin optical panel and a method of making an ultrathin optical panel  

DOEpatents

An ultrathin optical panel, and a method of producing an ultrathin optical panel, are disclosed, including stacking a plurality of glass sheets, which sheets may be coated With a transparent cladding substance or may be uncoated, fastening together the plurality of stacked coated glass sheets using an epoxy or ultraviolet adhesive, applying uniform pressure to the stack, curing the stack, sawing the stack to form an inlet face on a side of the stack and an outlet face on an opposed side of the stack, bonding a coupler to the inlet face of the stack, and fastening the stack, having the coupler bonded thereto, within a rectangular housing having an open front which is aligned with the outlet face, the rectangular housing having therein a light generator which is optically aligned with the coupler. The light generator is preferably placed parallel to and proximate with the inlet face, thereby allowing for a reduction in the depth of the housing.

Biscardi, Cyrus (Bellport, NY); Brewster, Calvin (North Patchogue, NY); DeSanto, Leonard (Patchogue, NY); Veligdan, James T. (Manorville, NY)

2002-01-01

211

Ultrathin optical panel and a method of making an ultrathin optical panel  

DOEpatents

An ultrathin optical panel, and a method of producing an ultrathin optical panel, are disclosed, including stacking a plurality of glass sheets, which sheets may be coated with a transparent cladding substance or may be uncoated, fastening together the plurality of stacked coated glass sheets using an epoxy or ultraviolet adhesive, applying uniform pressure to the stack, curing the stack, sawing the stack to form an inlet face on a side of the stack and an outlet face on an opposed side of the stack, bonding a coupler to the inlet face of the stack, and fastening the stack, having the coupler bonded thereto, within a rectangular housing having an open front which is aligned with the outlet face, the rectangular housing having therein a light generator which is optically aligned with the coupler. The light generator is preferably placed parallel to and proximate with the inlet face, thereby allowing for a reduction in the depth of the housing.

Biscardi, Cyrus (Bellport, NY); Brewster, Calvin (North Patchogue, NY); DeSanto, Leonard (Patchogue, NY); Veligdan, James T. (Manorville, NY)

2003-02-11

212

Ultrathin Optical Panel And A Method Of Making An Ultrathin Optical Panel.  

DOEpatents

An ultrathin optical panel, and a method of producing an ultrathin optical panel, are disclosed, including stacking a plurality of glass sheets, which sheets may be coated with a transparent cladding substance or may be uncoated, fastening together the plurality of stacked coated glass sheets using an epoxy or ultraviolet adhesive, applying uniform pressure to the stack, curing the stack, sawing the stack to form an inlet face on a side of the stack and an outlet face on an opposed side of the stack, bonding a coupler to the inlet face of the stack, and fastening the stack, having the coupler bonded thereto, within a rectangular housing having an open front which is aligned with the outlet face, the rectangular housing having therein a light generator which is optically aligned with the coupler. The light generator is preferably placed parallel to and proximate with the inlet face, thereby allowing for a reduction in the depth of the housing.

Biscardi, Cyrus (Bellport, NY); Brewster, Calvin (North Patchogue, NY); DeSanto, Leonard (Patchogue, NY); Veligdan, James T. (Manorville, NY)

2005-05-17

213

Ultrathin Optical Panel And A Method Of Making An Ultrathin Optical Panel.  

DOEpatents

An ultrathin optical panel, and a method of producing an ultrathin optical panel, are disclosed, including stacking a plurality of glass sheets, which sheets may be coated with a transparent cladding substance or may be uncoated, fastening together the plurality of stacked coated glass sheets using an epoxy or ultraviolet adhesive, applying uniform pressure to the stack, curing the stack, sawing the stack to form an inlet face on a side of the stack and an outlet face on an opposed side of the stack, bonding a coupler to the inlet face of the stack, and fastening the stack, having the coupler bonded thereto, within a rectangular housing having an open front which is aligned with the outlet face, the rectangular housing having therein a light generator which is optically aligned with the coupler. The light generator is preferably placed parallel to and proximate with the inlet face, thereby allowing for a reduction in the depth of the housing.

Biscardi, Cyrus (Bellport, NY); Brewster, Calvin (North Patchoque, NY); DeSanto, Leonard (Patchoque, NY); Veligdan, James T. (Manorville, NY)

2005-02-15

214

Ultrathin optical panel and a method of making an ultrathin optical panel  

DOEpatents

An ultrathin optical panel, and a method of producing an ultrathin optical panel, are disclosed, including stacking a plurality of glass sheets, which sheets may be coated with a transparent cladding substance or may be uncoated, fastening together the plurality of stacked coated glass sheets using an epoxy or ultraviolet adhesive, applying uniform pressure to the stack, curing the stack, sawing the stack to form an inlet face on a side of the stack and an outlet face on an opposed side of the stack, bonding a coupler to the inlet face of the stack, and fastening the stack, having the coupler bonded thereto, within a rectangular housing having an open front which is aligned with the outlet face, the rectangular housing having therein a light generator which is optically aligned with the coupler. The light generator is preferably placed parallel to and proximate with the inlet face, thereby allowing for a reduction in the depth of the housing.

Biscardi, Cyrus (Bellport, NY); Brewster, Calvin (North Patchogue, NY); DeSanto, Leonard (Patchogue, NY); Veligdan, James T. (Manorville, NY)

2001-10-09

215

Surface and interface characterization of high-k dielectric materials on III-antimony semiconductor substrates  

NASA Astrophysics Data System (ADS)

Interface formation between high-k dielectric oxide materials and semiconductor surfaces is of critical importance to the development of the next generation of metal-oxide-semiconductor field effect transistors (MOSFETs) and tunnel field effect transistors (TFETs). This work investigates the deposition and characterization of a range of candidate high-k materials on III-Sb (InSb and GaSb) semiconductor substrates, with the focus on interface formation. The characterization techniques used to study the interface were X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED), ion scattering spectroscopy, while atomic force microscopy (AFM) was used in some experiments for surface roughness measurements. The first part of this study evaluates the in-situ evolution of aluminum oxide (Al2O3) on indium antimonide (InSb) and gallium antimonide (GaSb) surfaces discussing preparation methods prior to dielectric deposition aimed at removing the native oxides and passivating the surfaces while keeping surface roughness to a minimum. For InSb surface the optimization of the ammonium sulphide (NH4) 2S passivation treatment was investigated in terms of the effectiveness at native oxide removal and minimizing defect generation. The interactions between hafnium oxide (HfO2) on HCl acid etched and (NH4) 2S treated GaSb surfaces as well as Al2O3 evolution on oxide free GaSb substrate were examined in the second part. A crystalline oxide/InAs(100) interface, as a potential path to avoid interface defect formation, was also investigated in term of stability upon Al2O3 deposition and air exposure.

Zhernokletov, Dmitry M.

216

Electric field effect in ultrathin black phosphorus  

NASA Astrophysics Data System (ADS)

Black phosphorus exhibits a layered structure similar to graphene, allowing mechanical exfoliation of ultrathin single crystals. Here, we demonstrate few-layer black phosphorus field effect devices on Si/SiO2 and measure charge carrier mobility in a four-probe configuration as well as drain current modulation in a two-point configuration. We find room-temperature mobilities of up to 300 cm2/Vs and drain current modulation of over 103. At low temperatures, the on-off ratio exceeds 105, and the device exhibits both electron and hole conduction. Using atomic force microscopy, we observe significant surface roughening of thin black phosphorus crystals over the course of 1 h after exfoliation.

Koenig, Steven P.; Doganov, Rostislav A.; Schmidt, Hennrik; Castro Neto, A. H.; zyilmaz, Barbaros

2014-03-01

217

Ultra-thin microporous/hybrid materials  

DOEpatents

Ultra-thin hybrid and/or microporous materials and methods for their fabrication are provided. In one embodiment, the exemplary hybrid membranes can be formed including successive surface activation and reaction steps on a porous support that is patterned or non-patterned. The surface activation can be performed using remote plasma exposure to locally activate the exterior surfaces of porous support. Organic/inorganic hybrid precursors such as organometallic silane precursors can be condensed on the locally activated exterior surfaces, whereby ALD reactions can then take place between the condensed hybrid precursors and a reactant. Various embodiments can also include an intermittent replacement of ALD precursors during the membrane formation so as to enhance the hybrid molecular network of the membranes.

Jiang, Ying-Bing (Albuquerque, NM); Cecchi, Joseph L. (Albuquerque, NM); Brinker, C. Jeffrey (Albuquerque, NM)

2012-05-29

218

Langmuir-Blodgett Fabrication of Nanosheet-Based Dielectric Films without an Interfacial Dead Layer  

NASA Astrophysics Data System (ADS)

Langmuir-Blodgett (LB) deposition was employed to fabricate high-? dielectric nanofilms of titania nanosheets. The LB-based layer-by-layer approach using an atomically flat SrRuO3 substrate is effective for the fabrication of atomically uniform and highly dense nanofilms. These films exhibited both high dielectric constant (?123) and low leakage current density (J< 10-7 A cm-2) for thicknesses down to 5 nm, while eliminating the size-effect problems encountered in current high-? films. From analyses of interfacial structures by transmission electron microscopy and hard X-ray photoelectron spectroscopy, we have clarified that the films are composed of a well-ordered lamellar structure without an interfacial dead layer. According to first-principles calculations, a highly polarizable nature of titania nanosheets can bring improved dielectric properties, yielding high-? values even in an ultrathin geometry (<10 nm).

Osada, Minoru; Akatsuka, Kosho; Ebina, Yasuo; Kotani, Yoshinori; Ono, Kanta; Funakubo, Hiroshi; Ueda, Shigenori; Kobayashi, Keisuke; Takada, Kazunori; Sasaki, Takayoshi

2008-09-01

219

Enhanced Breakdown Reliability and Spatial Uniformity of Atomic Layer Deposited High-k Gate Dielectrics on Graphene via Organic Seeding Layers  

NASA Astrophysics Data System (ADS)

Ultra-thin high-? top-gate dielectrics are essential for high-speed graphene-based nanoelectronic circuits. Motivated by the need for high reliability and spatial uniformity, we report here the first statistical analysis of the breakdown characteristics of dielectrics grown on graphene. Based on these measurements, a rational approach is devised that simultaneously optimizes the gate capacitance and the key parameters of large-area uniformity and dielectric strength. In particular, vertically heterogeneous oxide stacks grown via atomic-layer deposition (ALD) seeded by a molecularly thin perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) organic monolayer result in improved reliability (Weibull shape parameter ? 25) compared to the control dielectric directly grown on graphene without PTCDA (? 1). The optimized sample also showed a large breakdown strength (Weibull scale parameter, EBD 7 MV/cm) that is comparable to that of the control dielectric grown on Si substrates.

Sangwan, Vinod; Jariwala, Deep; Filippone, Stephen; Karmel, Hunter; Johns, James; Alaboson, Justice; Marks, Tobin; Lauhon, Lincoln; Hersam, Mark

2013-03-01

220

Dielectric Constant of Powders  

Microsoft Academic Search

MEASUREMENTS have been made at 9,200 Mc\\/s to determine the dependence of dielectric constant of powder samples' packing densities. The net polarization P produced in a substance in an electric field consists of the contributions of electronic, atomic and dipolar polarizations. It is related to the dielectric constant by Clausius-Masotti relation: where K = (? - l)\\/(? + 2), M

Prem Swarup; R. P. Arora

1964-01-01

221

All-dielectric nanolaser  

E-print Network

We demonstrate theoretically that a subwavelength spherical dielectric nanoparticle coated with an amplifying shell forms a nanolaser with lasing modes associated with the Mie resonances of the nanoparticle. We establish a general condition for the lasing threshold and show that the use of dielectric media allows for lasing with a threshold significantly lower than that for nanolasers based on plasmonic nanoparticles.

Baranov, D G; Lisyansky, A A

2014-01-01

222

Theory of dielectric elastomers  

Microsoft Academic Search

In response to a stimulus, a soft material deforms, and the deformation provides a function. We call such a material a soft active material (SAM). This review focuses on one class of soft active materials: dielectric elastomers. When a membrane of a dielectric elastomer is subject to a voltage through its thickness, the membrane reduces thickness and expands area, possibly

Zhigang Suo

2010-01-01

223

Dielectric spectroscopy of blood  

Microsoft Academic Search

An experimental investigation of complex dielectric spectra of human blood in the frequency range 30 Hz30 MHz has been carried out for various blood cell concentrations, temperature and environment. Electrode impedances and other distorting effects have been excluded. The average values of the dielectric constant (DC) ? and conductivity ? of normal heparinized blood for the lowest (?0,?0) and the

T. Chelidze

2002-01-01

224

Thermal analysis of ultrathin, compliant sensors for characterization of the human skin  

E-print Network

screening, skin hydration sensing, and local skin heating and thermal therapy. A theoretical frameworkThermal analysis of ultrathin, compliant sensors for characterization of the human skin Zuguang work establishes that ultrathin, stretchable sensors can enable high precision thermal characterization

Rogers, John A.

225

Development of Ulsi MOS Dielectrics and Their Scalability.  

NASA Astrophysics Data System (ADS)

In this dissertation, two novel oxynitride processing techniques for advanced ULSI gate/tunneling oxide applications have been developed. The electrical and reliability characteristics of MOS devices with N_2O-reoxidized NH_3-nitrided N_2 O oxide (N_2O-ROXNOX) and NO-nitrided SiO_2 (NO-oxynitride), has been examined. Results indicate that a high level of nitrogen concentration while maintaining excellent oxide integrity and reliability can be achieved in these dielectrics. Reliability and scalability issues of ultrathin MOS dielectrics (SiO_2 and N _2O/NO-based oxynitrides) have been investigated in detail. A physical model, based on two competing defect generation mechanisms--degradation of injection interface and degradation of structural transition layer (STL), has been proposed to explain the polarity and thickness dependence of dielectric breakdown. It is believed that since STL only exists near the SiO_2/Si interface, degradation of STL plays an important role only under -V_{g} stressing, hence causing the polarity dependence of dielectric breakdown and the increased asymmetry with decreasing oxide thickness. In addition, under -V_{g} stressing, due to the improved STL of oxide grown in N_2O ambient, N_2 O-oxynitrides show unique improvement in Q _{BD} characteristics as compared to NO-oxynitrides and SiO_2. Under +V_{g} stressing, due to the improved interface hardness and suppressed H depassivation by virtue of nitrogen incorporation, both NO- and N_2O-oxynitride show better Q_{BD} characteristics as compared to SiO_2. A framework for understanding the SILC behavior in ultrathin SiO _2 and NO-oxynitride has also been illustrated. It is found that the current conduction mechanism of SILC is thermally-assisted tunneling locally at the traps and the trap creation mechanisms for SILC is hydrogen-related. Reduced SILC can be achieved in scaled SiO_2 if stress electric field is kept below a threshold value which increases with decreasing oxide thickness or replacing SiO_2 by using NO-oxynitrides. A promising technology to extend the limitation of gate dielectric scaling in dual-gate CMOS structure has been suggested. It is demonstrated that amorphous -Si gate process is able to extend the limitation of gate oxide thickness scaling down to ultrathin regime without showing the boron penetration induced device instability problem. However, the use of amorphous-Si gates requires higher than normal budget than poly-Si gates to suppress gate depletion, which manifests itself as an reduction of effective capacitance thus reducing MOSFET drive current. It is also demonstrated that the use of NO-oxynitrides effectively suppresses the boron penetration down to ultrathin gate oxide thickness regime even though poly-Si gates were used, thereby significantly improving the process window. This finding, together with the fact that NO-oxynitride exhibits excellent performance and reliability in both n- and p -MOSFETs, make NO-oxynitride with poly-Si gate process highly attractive for dual-gate CMOS technology.

Han, Liang-Kai

226

All-nanosheet ultrathin capacitors assembled layer-by-layer via solution-based processes.  

PubMed

All-nanosheet ultrathin capacitors of Ru0.95O20.2-/Ca2Nb3O10-/Ru0.95O20.2- were successfully assembled through facile room-temperature solution-based processes. As a bottom electrode, conductive Ru0.95O20.2- nanosheets were first assembled on a quartz glass substrate through a sequential adsorption process with polycations. On top of the Ru0.95O20.2- nanosheet film, Ca2Nb3O10- nanosheets were deposited by the Langmuir-Blodgett technique to serve as a dielectric layer. Deposition parameters were optimized for each process to construct a densely packed multilayer structure. The multilayer buildup process was monitored by various characterizations such as atomic force microscopy (AFM), ultraviolet-visible absorption spectra, and X-ray diffraction data, which provided compelling evidence for regular growth of Ru0.95O20.2- and Ca2Nb3O10- nanosheet films with the designed multilayer structures. Finally, an array of circular films (50 ?m ?) of Ru0.95O20.2- nanosheets was fabricated as top electrodes on the as-deposited nanosheet films by combining the standard photolithography and sequential adsorption processes. Microscopic observations by AFM and cross-sectional transmission electron microscopy, as well as nanoscopic elemental analysis, visualized the sandwich metal-insulator-metal structure of Ru0.95O20.2-/Ca2Nb3O10-/Ru0.95O20.2- with a total thickness less than 30 nm. Electrical measurements indicate that the system really works as an ultrathin capacitor, achieving a capacitance density of ?27.5 ?F cm(-2), which is far superior to currently available commercial capacitor devices. This work demonstrates the great potential of functional oxide nanosheets as components for nanoelectronics, thus contributing to the development of next-generation high-performance electronic devices. PMID:24548057

Wang, Chengxiang; Osada, Minoru; Ebina, Yasuo; Li, Bao-Wen; Akatsuka, Kosho; Fukuda, Katsutoshi; Sugimoto, Wataru; Ma, Renzhi; Sasaki, Takayoshi

2014-03-25

227

A New NIST Database for the Simulation of Electron Spectra for Surface Analysis (SESSA): Application to Angle-Resolved X-ray Photoelectron Spectroscopy of HfO2, ZrO2, HfSiO4, and ZrSiO4 Films on Silicon  

NASA Astrophysics Data System (ADS)

We describe a new NIST database for the Simulation of Electron Spectra for Surface Analysis (SESSA). This database provides data for the many parameters needed in quantitative Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). In addition, AES and XPS spectra can be simulated for layered samples. The simulated spectra, for layer compositions and thicknesses specified by the user, can be compared with measured spectra. The layer compositions and thicknesses can then be adjusted to find maximum consistency between simulated and measured spectra. In this way, AES and XPS can provide more detailed characterization of multilayer thin-film materials. We report on the use of SESSA for determining the thicknesses of HfO2, ZrO2, HfSiO4, and ZrSiO4 films on Si by angle-resolved XPS. Practical effective attenuation lengths (EALs) have been computed from SESSA as a function of film thickness and photoelectron emission angle (i.e., to simulate the effects of tilting the sample). These EALs have been compared with similar values obtained from the NIST Electron Effective-Attenuation-Length Database (SRD 82). Generally good agreement was found between corresponding EAL values, but there were differences for film thicknesses less than the inelastic mean free path of the photoelectrons in the overlayer film. These differences are due to a simplifying approximation in the algorithm used to compute EALs in SRD 82. SESSA, with realistic cross sections for elastic and inelastic scattering in the film and substrate materials, is believed to provide more accurate EALs than SRD 82 for thin-film thickness measurements, particularly in applications where the film and substrate have different electron-scattering properties.

Powell, C. J.; Smekal, W.; Werner, W. S. M.

2005-09-01

228

Effect of rapid thermal annealing on strain in ultrathin strained silicon on insulator layers  

E-print Network

Effect of rapid thermal annealing on strain in ultrathin strained silicon on insulator layers T. S March 2003; accepted 4 June 2003 The fabrication of ultrathin strained silicon directly on insulator is demonstrated and the thermal stability of these films is investigated. Ultrathin ( 13 nm) strained silicon

229

Interfacial diffusion behavior in Ni-BaTiO 3 MLCCs with ultra-thin active layers  

NASA Astrophysics Data System (ADS)

The interfacial structure and diffusion behavior between the dielectric layers (BaTiO3) and internal electrode layers (Ni) in X5R-type multilayer ceramic capacitors (MLCCs, from -55C to 85C, at a temperature capacitance coefficient within 15%) with ultra-thin active layers ( T = 1-3 m) have been investigated by several microstructural techniques (SEM/TEM/HRTEM) with energy-dispersive x-ray spectroscopy (EDS). In the MLCC samples with different active layer thicknesses (1-3 m), weak interfacial diffusion was observed between BaTiO3 and Ni. It was also found that the diffusion capability of Ni into the BaTiO3 layer was stronger than that of BaTiO3 to the Ni electrode, which indicated that the diffusion of Ni was the dominant factor for the interfacial diffusion behavior in the ultra-thin layered MLCCs. The mechanism of Ni diffusion is discussed in this study as well.

Gong, Huiling; Wang, Xiaohui; Tian, Zhibin; Zhang, Hui; Li, Longtu

2014-03-01

230

Improved Dielectric Films For Capacitors  

NASA Technical Reports Server (NTRS)

Dielectric films made from blends of some commercially available high-dielectric-constant cyanoresins with each other and with cellulose triacetate (CTA) have both high dielectric constants and high breakdown strengths. Dielectric constants as high as 16.2. Films used to produce high-energy-density capacitors.

Yen, Shiao-Ping S.; Lewis, Carol R.; Cygan, Peter J.; Jow, T. Richard

1994-01-01

231

Advanced Physics: Capacitors and Dielectrics  

NSDL National Science Digital Library

Click-drag the dielectric blocks, dielectric constants k1= 2.4 and k2, respectively, into the capacitor (charge given in mC and position given in centimeters). Observe how the electric field and the charge on the capacitor and the dielectric change when you move the dielectric.

Christian, Wolfgang; Belloni, Mario

2006-01-19

232

Effects of strained layer near SiO2-Si interface on electrical characteristics of ultrathin gate oxides  

NASA Astrophysics Data System (ADS)

Ultrathin gate oxides formed by different process technologies are investigated in detail. The following important evidence is found: the discrepant result on the two time-dependent dielectric breakdown (TDDB) lifetime measurements, the constant-current stress, and the constant-voltage stress. The discrepancy is due mainly to the difference in the oxide leakage characteristics. Apparent changes in the activation energy and the defect generation rate during the TDDB testing are also experimentally observed for the two oxides formed by different process technologies. From the analysis based on the x-ray photoelectron spectroscopy by means of the oxide etch by dilute HF and the Fourier-transform infrared attenuated total reflection method, we consider that the above phenomena are induced by the difference in the built-in compressive strain of the Si-O network near the SiO2 and Si interface.

Eriguchi, Koji; Harada, Yoshinao; Niwa, Masaaki

2000-02-01

233

Versatile ultrathin nanoporous silicon nitride membranes.  

PubMed

Single- and multiple-nanopore membranes are both highly interesting for biosensing and separation processes, as well as their ability to mimic biological membranes. The density of pores, their shape, and their surface chemistry are the key factors that determine membrane transport and separation capabilities. Here, we report silicon nitride (SiN) membranes with fully controlled porosity, pore geometry, and pore surface chemistry. An ultrathin freestanding SiN platform is described with conical or double-conical nanopores of diameters as small as several nanometers, prepared by the track-etching technique. This technique allows the membrane porosity to be tuned from one to billions of pores per square centimeter. We demonstrate the separation capabilities of these membranes by discrimination of dye and protein molecules based on their charge and size. This separation process is based on an electrostatic mechanism and operates in physiological electrolyte conditions. As we have also shown, the separation capabilities can be tuned by chemically modifying the pore walls. Compared with typical membranes with cylindrical pores, the conical and double-conical pores reported here allow for higher fluxes, a critical advantage in separation applications. In addition, the conical pore shape results in a shorter effective length, which gives advantages for single biomolecule detection applications such as nanopore-based DNA analysis. PMID:19948951

Vlassiouk, Ivan; Apel, Pavel Y; Dmitriev, Sergey N; Healy, Ken; Siwy, Zuzanna S

2009-12-15

234

Internal Structure of Ultrathin Diblock Copolymer Brushes  

NASA Astrophysics Data System (ADS)

Diblock copolymer brushes (DCBs) have garnered enormous interest in recent years due to their stimuli-responsive behavior. Although the synthesis of DCBs has been widely studied, the internal brush structure of these films is still not clear. We have resolved the internal structure of ultrathin DCBs using neutron reflectivity and grazing incidence small-angle X-ray scattering (GISAXS). DCBs of deuterated polystyrene (dPS) and poly(methyl acrylate) (PMA) with dPS adjacent to the substrate (d-PS-b-PMA) or with PMA adjacent to the substrate (PMA-b-dPS) and having different thicknesses were synthesized using atom transfer radical polymerization. It was found that internal brush structure depends strongly on the block sequence and the value of XN. For the thinnest films a model of two layers with an interfacial region of finite width provides a good description of the data. For dPS-b-PMA films that are thicker and of sufficiently asymmetric composition, a third layer must be included. The necessity of including a third layer is consistent with the presence of a lateral ordering of some type in the center of the brush, as evidenced by correlation peaks in the GISAXS data. The interface width is found to be smaller for PMA-b-dPS than for dPS-b-PMA brushes.

Akgun, Bulent; Brittain, William J.; Foster, Mark D.; Majkrzak, Charles F.; Li, Xuefa; Wang, Jin

2006-10-01

235

Crystallization Properties of Ultrathin Phase Change Films  

SciTech Connect

The crystallization behavior of ultrathin phase change films was studied using time-resolved x-ray diffraction (XRD). Thin films of variable thickness between 1 and 50?nm of the phase change materials Ge2Sb2Te5 (GST), N-doped GST, Ge15Sb85, Sb2Te, and Ag- and In-doped Sb2Te were heated in a He atmosphere, and the intensity of the diffracted x-ray peaks was recorded. It was found for all materials that the crystallization temperature increases as the film thickness is reduced below 10?nm. The increase depends on the material and can be as high as 200? C for the thinnest films. The thinnest films that show XRD peaks are 2?nm for GST and N-GST, 1.5?nm for Sb2Te and AgIn-Sb2Te, and 1.3?nm for GeSb. This scaling behavior is very promising for the application of phase change materials to solid-state memory technology.

Raoux,S.; Jordan-Sweet, J.; Kellock, A.

2008-01-01

236

Dewetting of ultrathin surfactant-covered films  

NASA Astrophysics Data System (ADS)

Many industrially and technologically important situations involve thin films covered with either pre-existing or introduced surfactant, which can potentially affect dewetting and spreading processes. The two-dimensional dewetting dynamics of ultrathin liquid films are studied here in the presence of insoluble surfactant; surfactants can drive a flow due to surface tension gradients and additionally the coefficients of the intermolecular potential, which are usually assumed to be constant, can depend on the surfactant concentration. Coupled evolution equations for the film height and surfactant concentration are derived using lubrication theory. These equations are parameterized by a Marangoni parameter, M, and the equilibrium film thickness, lc, obtained by setting the intermolecular potential to zero. A linear stability analysis of these equations shows that the presence of surfactant can widen the band of unstable wave numbers and that, for relatively large lc, the selected wave number is minimized for a certain value of M. Numerical simulations of the evolution equations show that initially nonuniform distributions of surfactant can destabilize clean spinodally stable films. Our results also show that it is possible to destabilize these films using uniform initial surfactant distributions, although this is only possible when the intermolecular potential coefficients are concentration dependent.

Warner, M. R. E.; Craster, R. V.; Matar, O. K.

2002-11-01

237

Swelling of ultrathin crosslinked polyamide water purification membranes  

NASA Astrophysics Data System (ADS)

Polyamide (PA) ultrathin films represent the state-of-the-art nanofiltration and reverse osmosis membranes used in water desalination. The performance of these materials, such as permselectivity, is intimately linked with extent of swelling of the PA network. Thus, quantifying their swelling behavior would be a useful and simple route to understanding the specific network structural parameters that control membrane performance. In this work, we measure the swelling behavior of PA ultrathin films using X-ray reflectivity as a function of water hydration. By applying the Flory-Rehner theory used to describe the swelling behavior of polymer networks, we quantify the PA network properties including Flory interaction parameter and the monomer units between crosslinks. Finally, we demonstrate application of this measurement approach for characterizing the network properties of different types of PA ultrathin films relevant to water purification and discuss the relationship between network and transport properties.

Chan, Edwin; Stafford, Christopher

2013-03-01

238

Ultrathin plasmonic nanogratings for rapid and highly-sensitive detection  

E-print Network

We developed a nanoplasmonic sensor platform employing the extraordinary optical properties of one-dimensional nanogratings patterned on 30nm-thick ultrathin Ag films. Excitation of Fano resonances in the ultrathin Ag nanogratings results in transmission spectra with high amplitude, large contrast, and narrow bandwidth, making them well-suited for rapid and highly-sensitive sensing applications. The ultrathin nanoplasmonic sensor chip was integrated with a polydimethylsiloxane (PDMS) microfluidic channel, and the measured refractive index resolution was found to be 1.46x10-6 refractive index units (RIU) with a high temporal resolution of 1 sec. This compares favorably with commercial prism-based surface plasmon resonance sensors, but is achieved using a more convenient collinear transmission geometry and a significantly smaller sensor footprint of 50x50um2. In addition, an order-of-magnitude improvement in the temporal and spatial resolutions was achieved relative to state-of-the-art nanoplasmonic sensors, fo...

Zeng, Beibei; Bartoli, Filbert J

2014-01-01

239

Cast dielectric composite linear accelerator  

DOEpatents

A linear accelerator having cast dielectric composite layers integrally formed with conductor electrodes in a solventless fabrication process, with the cast dielectric composite preferably having a nanoparticle filler in an organic polymer such as a thermosetting resin. By incorporating this cast dielectric composite the dielectric constant of critical insulating layers of the transmission lines of the accelerator are increased while simultaneously maintaining high dielectric strengths for the accelerator.

Sanders, David M. (Livermore, CA); Sampayan, Stephen (Manteca, CA); Slenes, Kirk (Albuquerque, NM); Stoller, H. M. (Albuquerque, NM)

2009-11-10

240

Thin dielectric degradation during silicon selective epitaxial growth process  

NASA Astrophysics Data System (ADS)

A fundamental issue in silicon selective epitaxial growth (SEG) processes is the impact of the pre-epitaxy silicon surface treatments and the SEG ambient on the properties of thin insulating materials exposed to the preclean environment. In this study, we compare pinhole formation in 10-50 nm thermal oxides with more robust oxide/nitride composites of similar thickness. The degradation of thin thermal oxide is attributed to pinhole formation and expansion in the ultrathin oxide layers during ex situ pre-epi surface treatments, in situ H2 prebake, and selective epitaxial deposition process. The superior resistance of oxide/nitride/oxide (ONO) structures to dielectric degradation may be attributed to the existence of the sandwiched silicon nitride layer which suppresses the mechanism of oxide decomposition during the pre-epitaxy wet cleaning, and the selective epitaxial growth processes.

Shih, Yang-Chin; Zhang, Guobiao; Hu, Chenming; Oldham, William G.

1995-10-01

241

Dielectric Stimulated Wakefield Accelerator  

Microsoft Academic Search

Wakefield acceleration in a dielectric-loaded waveguide has been previously analyzed and tested.(M. Rosing and W. Gai, Phys. Rev. D 42), 1829 (1990).^,3 We note that a dielectric geometry can be found in which the wakefield is a nearly-periodic function of z - ct, and that the multi-mode wakefield period and interbunch spacing can coincide. Thus, superposition of wakes can occur.

T. B. Zhang; J. L. Hirshfield; T. C. Marshall; B. Hafizi

1997-01-01

242

Method for laser welding ultra-thin metal foils  

DOEpatents

A method for simultaneously cutting and welding ultra-thin foils having a thickness of less than 0.002 inches wherein two ultra-thin films are stacked and clamped together. A pulsed laser such as of the Neodymium: YAG type is provided and the beam of the laser is directed onto the stacked films to cut a channel through the films. The laser is moved relative to the stacked foils to cut the stacked foils at successive locations and to form a plurality of connected weld beads to form a continuous weld.

Pernicka, John C. (Fort Collins, CO); Benson, David K. (Golden, CO); Tracy, C. Edwin (Golden, CO)

1996-01-01

243

Method for laser welding ultra-thin metal foils  

DOEpatents

A method for simultaneously cutting and welding ultra-thin foils having a thickness of less than 0.002 inches wherein two ultra-thin films are stacked and clamped together. A pulsed laser such as of the Neodymium: YAG type is provided and the beam of the laser is directed onto the stacked films to cut a channel through the films. The laser is moved relative to the stacked foils to cut the stacked foils at successive locations and to form a plurality of connected weld beads to form a continuous weld. 5 figs.

Pernicka, J.C.; Benson, D.K.; Tracy, C.E.

1996-03-26

244

Enhanced charge storage of ultrathin polythiophene films within porous nanostructures.  

PubMed

In a single step polymerization and coating, oxidative chemical vapor deposition (oCVD) has been used to synthesize unsubstituted polythiophene. Coatings have been conformally coated within porous nanostructures of anodized aluminum oxide, titanium dioxide, and activated carbon. Significant enhancement in charge capacity has been found with ultrathin polythiophene coatings that preserve the surface area and pore space of the nanostructures. Pseudocapacitors consisting of ultrathin polythiophene coated within activated carbon yielded increases of 50 and 250% in specific and volumetric capacitance compared with bare activated carbon. Devices were stable up to the 5000 cycles tested with only a 10% decrease in capacitance. PMID:24840296

Nejati, Siamak; Minford, Thomas E; Smolin, Yuriy Y; Lau, Kenneth K S

2014-06-24

245

Ultrathin metals and nano-structuring for photonic applications  

NASA Astrophysics Data System (ADS)

Ultrathin materials and nano-structuring are becoming essential for the functionalization of optical surfaces. In the talk we will show how ultrathin metals can be exploited to create competitive transparent electrodes. At the same time they can be used to create nanostructured surfaces through mass scalable dewetting and etching techniques. After presenting the techniques, we will focus on the applications made possible by these materials and technologies, including self-cleaning or easy-to-clean display screens, efficient indium-free light emitting diodes and solar cells, antireflective structures for the laser industry and super-wetting surfaces for biology.

Formica, Nadia; Carrilero, Albert; Chen, Tong Lai; Ghosh, Dhriti S.; Mazumder, Prantik; Pruneri, Valerio

2014-03-01

246

Long-term reliability degradation of ultrathin dielectric films due to heavy-ion irradiation  

Microsoft Academic Search

High-energy ion-irradiated 3.3-nm oxynitride film and 2.2-nm SiO2-film MOS capacitors show premature breakdown during subsequent electrical stress. This degradation in breakdown increases with increasing ion linear energy transfer (LET), increasing ion fluence, and decreasing oxide thickness. The reliability degradation due to high-energy ion-induced latent defects is explained by a simple percolation model of conduction through SiO2 layers with irradiation and\\/or

B. K. Choi; D. M. Fleetwood; R. D. Schrimpf; Lloyd W. Massengill; K. F. Galloway; M. R. Shaneyfelt; T. L. Meisenfieimer; P. E. Dodd; J. R. Schwank; Y. M. Lee; R. S. John; G. Lucovsky

2002-01-01

247

Aperture excited dielectric antennas  

NASA Technical Reports Server (NTRS)

The results of a comprehensive experimental and theoretical study of the effect of placing dielectric objects over the aperture of waveguide antennas are presented. Experimental measurements of the radiation patterns, gain, impedance, near-field amplitude, and pattern and impedance coupling between pairs of antennas are given for various Plexiglas shapes, including the sphere and the cube, excited by rectangular, circular, and square waveguide feed apertures. The waveguide excitation of a dielectric sphere is modeled using the Huygens' source, and expressions for the resulting electric fields, directivity, and efficiency are derived. Calculations using this model show good overall agreement with experimental patterns and directivity measurements. The waveguide under an infinite dielectric slab is used as an impedance model. Calculations using this model agree qualitatively with the measured impedance data. It is concluded that dielectric loaded antennas such as the waveguide excited sphere, cube, or sphere-cylinder can produce directivities in excess of that obtained by a uniformly illuminated aperture of the same cross section, particularly for dielectric objects with dimensions of 2 wavelengths or less. It is also shown that for certain configurations coupling between two antennas of this type is less than that for the same antennas without dielectric loading.

Crosswell, W. F.; Chatterjee, J. S.; Mason, V. B.; Tai, C. T.

1974-01-01

248

In situ transmission electron microscopy study of dielectric breakdown of surface oxides during electric field-assisted sintering of nickel nanoparticles  

NASA Astrophysics Data System (ADS)

The removal of ultra-thin oxide surface layers on nanometric nickel particles is investigated in the framework of electric field-induced dielectric breakdown. In situ transmission electron microscopy was used to directly apply electrical biasing to agglomerates of nanoparticles during simultaneous imaging of the contact area between two adjacent particles. The applied electrical field initiated dielectric breakdown of the surface layers through percolation of oxygen vacancies and the migration of oxygen away from the particle contact, which leads to the formation of metallic necks and their subsequent growth. The experimental results represent direct evidence for surface cleaning effects during electric field-assisted sintering.

Bonifacio, Cecile S.; Rufner, Jorgen F.; Holland, Troy B.; van Benthem, Klaus

2012-08-01

249

Dielectric nonlinearity of ferroelectrics  

NASA Astrophysics Data System (ADS)

The ac field dependence of the dielectric constant and first order reversal curves (FORC) distribution were employed to quantify the effect of dielectric thickness, grain size, oxygen vacancy concentration, and microstructural heterogeneity on the dielectric nonlinearity of PbZr0.52Ti0.48O 3 thin films and BaTiO3-based ceramics on a wide electric field range. With the FORC distribution, the dielectric properties were calculated using Preisach model. The FORC distribution of PbZr0.52Ti0.48O3 thin films was characterized as a function of film thickness. It was found that the thickness dependence of the small field dielectric constant is due primarily to differences in the domain wall contributions to the properties. The irreversible FORC distribution decreased and the switching fields increased as the thickness decreased. Prediction of the polarization-electric field curves and the ac field dependence of the dielectric constant were found to give a good fit to the experimental results. Some discrepancies remain in the high field dielectric constant, probably caused by its definition. The dielectric nonlinearity of BaTiO3 ceramics with grain sizes from 1.2 to 76 microm was investigated. Defect dipoles in samples with large grains led to pinching of minor polarization-electric field loops as well as a threshold field in the ac field dependence of the dielectric constant and loss. For samples with small grains, a sublinear ac field dependence was observed. The irreversible FORC distributions characterizing the responses showed two strong and narrow peaks for large-grained samples and a weak, broad peak centered near the origin for samples with small grains. As the grain size decreased, the reversible FORC distribution at zero-bias field increased. No grain size dependence of the reversible FORC distributions was observed at high dc electric fields. These results indicate that the grain size dependence of the small field dielectric constant is attributable to a domain wall contribution and long-range domain wall motion suppressed while short-range domain wall motion enhanced as the grain size decreased. The effect of the oxygen vacancies on the dielectric nonlinearity of formulated and undoped BaTiO3 ceramics was investigated by changing oxygen partial pressure during firing. For the formulated ceramics, the dielectric constant of both oxygen and air fired samples increased almost linearly with the amplitude of the ac driving field. Formulated BaTiO3 samples sintered in a reducing atmosphere produced a sub-linear increase in the permittivity with the ac field amplitude. For undoped BaTiO3 ceramics, the dielectric constant increased sub-linearly over a wide range of oxygen partial pressures during firing. It is proposed for the formulated ceramics that the dopant-oxygen vacancy defect dipoles in the shell region accounted for the curvature in the field dependence of the permittivity. These defects appear to add a concentration of weak pinning centers to the potential energy profile through which domain walls move. FORC distributions as well as the ac field dependence of the dielectric constant were investigated for model BaTiO3-based multilayer ceramic capacitors with dielectric layer thicknesses from 2.2 microm to 8.6 microm and those in which the grain size of the dielectrics varied from 0.28 microm to 0.39 microm while the layer thickness was held constant. In both cases, core-shell microstructures were observed. It was found that as the dielectric thickness decreased, the small and high electric field dielectric constants decreased, as did the peaks near the origin in the irreversible and reversible parts of the FORC distribution. The reversible FORC distributions of all the parts did not converge at high bias. These results indicate that the thickness dependence is attributable to a low dielectric constant interfacial layer and/or Schottky depletion layer at dielectric-electrode interfaces. It was also found that the high field dielectric constant, the peak in the irreversible FORC distribution at the origin, and the rever

Fujii, Ichiro

250

Novel MOCVD processes for nanoscale dielectric and ferroelectric thin films  

NASA Astrophysics Data System (ADS)

Nanoscale oxide thin films such as Ba1-xSrxTiO3 (BST), PbZr1-xTixO3 (PZT) and SrBi2(Ta1-xNbx)2O9 (SBTN) that have high dielectric constant and excellent ferroelectric properties have been receiving greatly increased attention, specially for high density memories in next generation integrated circuits. However, most MOCVD precursors for dielectric and ferroelectric film growth have a very low vaporization pressure and poor thermal stability at elevated temperatures. Moreover, when the film thickness is decreased, the apparent bulk-like properties of thin films tend to worsen due to the increased influence of the interface. In order to solve the problems, novel MOCVD techniques including the development of a new liquid delivery, plasma (ECR or RF) enhanced deposition, TurboDisc technology and two step process were developed. The thickness uniformity, composition uniformity and dielectric and ferroelectric property uniformity of BST, PZT and SBT thin films on 6' Si and Pt wafers are also investigated. Experimental results showed that the new liquid delivery system can improve process reproducibility and increase deposition rates, and the growth reactor with high speed rotation system can deposit homogeneous ultra-thin films on large size substrates, and plasma enhanced MOCVD can reduce the deposition temperature and increase the deposition rate to decrease growth temperature without compromising the quality of the material, and the two step processes can be used to improve interface mismatch between film and substrate. Therefore, high quality dielectric and ferroelectric thin films with nanoscale thickness can be obtained.

Li, Tingkai; Zawadzki, Peter A.; Stall, Richard A.

1997-09-01

251

Dynamic response of ultrathin highly dense ZIF-8 nanofilms.  

PubMed

Ultrathin ZIF-8 nanofilms are prepared by facile step-by-step dip coating. A critical withdrawal speed allows for films with a very uniform minimum thickness. The high refractive index of the films denotes the absence of mesopores. The dynamic response of the films to CO2 exposure resembles behaviour observed for non-equilibrium organic polymers. PMID:25142780

Cookney, Joanna; Ogieglo, Wojciech; Hrabanek, Pavel; Vankelecom, Ivo; Fila, Vlastimil; Benes, Nieck E

2014-09-01

252

ANALYSIS AND DESIGN OF AN ULTRA-THIN METAMATERIAL ABSORBER  

Microsoft Academic Search

This paper presents a class of ultra-thin metamaterial absorbers, which consists of periodic microstrip lines on top of a planar lossy substrate backed by a conducting metallic plate. A highly efficient full-wave analysis method was developed to solve the electromagnetic response of the absorbers. The influence of electromagnetic properties of the substrate and physical dimensions of the microstrip lines were

Ruifeng Huang; Zheng-Wen Li; Ling Bing Kong; Lie Liu; Serguei Matitsine

2009-01-01

253

Thickness-dependent spontaneous dewetting morphology of ultrathin Ag films  

Microsoft Academic Search

We show here that the morphological pathway of spontaneous dewetting of ultrathin Ag films on SiO2 under nanosecond laser melting is dependent on film thickness. For films with thickness h of 2 nm <= h <= 9.5 nm, the morphology during the intermediate stages of dewetting consisted of bicontinuous structures. For films with 11.5 nm <= h <= 20 nm,

H. Krishna; R. Sachan; J. Strader; C. Favazza; M. Khenner; R. Kalyanaraman

2010-01-01

254

Thickness-dependent spontaneous dewetting morphology of ultrathin Ag films  

Microsoft Academic Search

We show here that the morphological pathway of spontaneous dewetting of ultrathin Ag films on SiO2 under nanosecond laser melting is dependent on film thickness. For films with thickness h of 2 nm ? h ? 9.5 nm, the morphology during the intermediate stages of dewetting consisted of bicontinuous structures. For films with 11.5 nm ? h ? 20 nm,

H. Krishna; R. Sachan; J. Strader; C. Favazza; M. Khenner; Ramki Kalyanaraman

2010-01-01

255

Synthesis and Characterization of Zirconium Tungstate Ultra-Thin Fibers  

SciTech Connect

This study reports an innovative method of electrospinning followed by pyrolysis to synthesize zirconium tungstate (ZrW2O8), a material with negative coefficient of thermal expansion (CTE), in ultra-thin fiber form. Morphologies and microstructures of the as-electrospun precursor fibers, the heat-treated intermediate fibers, and the final ZrW2O8 ultra-thin fibers were characterized by SEM, XRD, and TEM. The ZrW2O8 ultra-thin fibers had diameters in the sub-micrometer range with aspect ratios larger than 100; these fibers were polycrystalline, and consisted of single crystalline ZrW2O8 crystallites with sizes of 30-50 nm and surface roughness of several nanometers. The ZrW2O8 ultra-thin fibers are expected to outperform spherically, cylindrically, and/or irregularly shaped polycrystalline ZrW2O8 particles for the development of composites with precisely controlled CTEs. Additionally, this reported method could be utilized as a general approach to convert nano-scaled inorganic particles into fibers.

Zhang, Lifeng [South Dakota School of Mines and Technology; Howe, Jane Y [ORNL; Fong, Hao [South Dakota School of Mines and Technology; Zhang, Yan [Anhui Normal University, People's Republic of China

2009-01-01

256

Ultrathin oxide films and interfaces for electronics and spintronics  

Microsoft Academic Search

Oxides have become a key ingredient for new concepts of electronic devices. To a large extent, this is due to the profusion of new physics and novel functionalities arising from ultrathin oxide films and at oxide interfaces. We present here a perspective on selected topics within this vast field and focus on two main issues. The first part of this

Manuel Bibes; Javier E. Villegas; Agnes Barthelemy

2011-01-01

257

Dielectric Thin Films.  

NASA Astrophysics Data System (ADS)

Thin film technology is pervasive in the fabrication of all high performance integrated circuits. Success of this technology is due to its capability to achieve high volumetric efficiency by reducing the physical size of each element without disrupting its electrical performance. Along with other thin films, considerable attention has been paid in the area of ferroelectric thin films for device applications. Generally these films are amorphous in nature and an annealing process is required to enhance the crystallinity of the film. Measurement of dielectric properties of these films showed an increase in the values of dielectric constant and a decrease of coercive fields and annealing. Thus a larger volume efficiency can be achieved with ferroelectric materials. We chose to investigate ferroelectric antimony sulphur iodide (SbSI) and bismuth titanate (Bi(,4)Ti(,3)O(,12)) for dielectric thin film applications. SbSI is a member of the large family of A('V)B('VI)C('VII) ferroelectric compounds with a large anisotropy in the dielectric properties and a phase transition temperature at 20(DEGREES)C. It has a dielectric constant as high as 6.0 x 10('4) and a large pyroelectric coefficient of 60 x 10('3) (mu)c/m('2) (DEGREES)C at the phase transition. It also has very interesting piezoelectric properties. SbSI thin films were prepared by the vacuum thermal evaporation method. The c-axis oriented SbSI films were prepared by the recrystallization of as-grown films using a suitable annealing process. Bi(,4)Ti(,3)O(,12) is a member of the bismuth oxide layer structure family. The high Curie temperature (675(DEGREES)C) and mica-like morphology of the sheet structure suggest the potentiality of Bi(,4)Ti(,3)O(,12) as a stable thin film dielectric with high dielectric strength. Crystalline Bi(,4)Ti(,3)O(,12) films were deposited by RF sputtering in argon:oxygen gas atmosphere using heated substrates. Dielectric measurements on these films showed that SbSI thin films can be made reproducibly with the capacitance ranging up to 0.6 (mu)F/cm('2). Cracks due to high stress and pin-holes in films deteriorate the dielectric properties. On the other hand Bi(,4)Ti(,3)O(,12) films prepared on hot substrates showed permittivity (epsilon)(,R) > 200 and tan (delta) < 2%, suggesting the potential use of this material in thin film capacitors.

Ghosh, Prasanta K.

258

Determination of dielectric constant of dielectric particles using negative dielectrophoresis  

Microsoft Academic Search

The dielectric constant of dielectric particles is determined using negative dielectrophoresis (DEP). A pair of cylindrical electrodes is employed to produce a non-uniform electric field that levitates a dielectric particle. Because the electrode structure is simple, we obtain explicit equations for the electric field, the potential energy, the stable levitation height, and the effective polarizability. Measuring the height of the

Sang-Wook Lee; Yong-Wook Kim; Yong-Kweon Kim

1996-01-01

259

PREFACE: Dielectrics 2013  

NASA Astrophysics Data System (ADS)

This volume records the 42nd Dielectrics Group Proceedings of the Dielectrics Conference that took place at the University of Reading UK from 10-12 April 2013. The meeting is part of the biennial Dielectrics series of the Dielectrics Group, and formerly Dielectrics Society, and is organised by the Institute of Physics. The conference proceedings showcase some of the diversity and activity of the Dielectrics community worldwide, and bring together contributions from academics and industrial researchers with a diverse background and experiences from the Physics, Chemistry and Engineering communities. It is interesting to note some continuing themes such as Insulation/HV Materials, Dielectric Spectroscopy, Dielectric Measurement Techniques and Ferroelectric materials have a growing importance across a range of technologically important areas from the Energy sector to Materials research, Semiconductor and Electronics industries, and Metrology. We would like to thank all of our colleagues and friends in the Dielectrics community who have supported this event by contributing manuscripts and participating in the event. The conference has provided excellent networking opportunities for all delegates. Our thanks go also to our theme chairs: Dr Stephen Dodd (University of Leicester) on Insulation/HV Materials, Professor Darryl Almond (University of Bath) on Dielectric Spectroscopy, Dr John Blackburn (NPL) on Dielectric Measurement Techniques and Professor Anthony R West (University of Sheffield) on Ferroelectric Materials. We would also like to thank the other members of the Technical Programme Committee for their support, and refereeing the submitted manuscripts. Our community would also like to wish a full recovery to our plenary speaker Prof John Fothergill (City University London) who was unexpectedly unable to give his talk as well as thank Professor Alun Vaughan for stepping in and giving an excellent plenary lecture in his place at such very short notice. We are also pleased to express our thanks to the Conference Department of the Institute of Physics for their invaluable support in organizing this event. We are especially grateful to Dawn Stewart for her responsive and day-to-day handling of this conference, as well as Claire Garland for help in planning and managing this international event. We would also like to thank Dr Steve Welch, Director at ESP Central Ltd, representing the interest of the Electronics, Sensors, Photonics Knowledge Transfer Network, as well as Paul Naylor and Susan Matos for their contribution towards the KTN session of the Conference. Finally, we would like to thank Solartron Analytical, Ametek and Princeton Applied Research for demonstrating precision electrochemical impedance spectroscopy measurement techniques at the conference. We hope that the wider Dielectrics community will find these proceedings of interest and will use them as reference text in their future work. Programme committee R Pethig, University of Edinburgh J Blackburn, National Physical Laboratory J Swingler, Heriot Watt University S Hadjiloucas, University of Reading A West, University of Sheffiled M Hughes, University of Surrey S Dodd, University of Leicester D Almond, University of Bath M Cain, National Physical Laboratory D J Swaffield, University of Southampton N Green, University of Southampton A Vaughan, University of Southampton Sillas Hadjiloucas and John Blackburn (Summer 2013)

Hadjiloucas, Sillas; Blackburn, John

2013-11-01

260

Thermally switchable dielectrics  

DOEpatents

Precursor polymers to conjugated polymers, such as poly(phenylene vinylene), poly(poly(thiophene vinylene), poly(aniline vinylene), and poly(pyrrole vinylene), can be used as thermally switchable capacitor dielectrics that fail at a specific temperature due to the non-conjugated precursor polymer irreversibly switching from an insulator to the conjugated polymer, which serves as a bleed resistor. The precursor polymer is a good dielectric until it reaches a specific temperature determined by the stability of the leaving groups. Conjugation of the polymer backbone at high temperature effectively disables the capacitor, providing a `built-in` safety mechanism for electronic devices.

Dirk, Shawn M.; Johnson, Ross S.

2013-04-30

261

Multilayer dielectric diffraction gratings  

DOEpatents

The design and fabrication of dielectric grating structures with high diffraction efficiency used in reflection or transmission is described. By forming a multilayer structure of alternating index dielectric materials and placing a grating structure on top of the multilayer, a diffraction grating of adjustable efficiency, and variable optical bandwidth can be obtained. Diffraction efficiency into the first order in reflection varying between 1 and 98 percent has been achieved by controlling the design of the multilayer and the depth, shape, and material comprising the grooves of the grating structure. Methods for fabricating these gratings without the use of ion etching techniques are described.

Perry, Michael D. (Livermore, CA); Britten, Jerald A. (Oakley, CA); Nguyen, Hoang T. (Livermore, CA); Boyd, Robert (Livermore, CA); Shore, Bruce W. (Livermore, CA)

1999-01-01

262

Low-Dielectric Polyimides  

NASA Technical Reports Server (NTRS)

New process developed to produce aromatic condensation polyimide films and coatings having dielectric constants in range of 2.4 to 3.2. Materials better electrical insulators than state-of-the-art commercial polyimides. Several low-dielectric-constant polyimides have excellent resistance to moisture. Useful as film and coating materials for both industrial and aerospace applications where high electrical insulation, resistance to moisture, mechanical strength, and thermal stability required. Applicable to production of high-temperature and moisture-resistance adhesives, films, photoresists, and coatings. Electronic applications include printed-circuit boards, both of composite and flexible-film types and potential use in automotive, aerospace, and electronic industries.

St. Clair, Anne K.; St. Clair, Terry L.; Winfree, William P.; Emerson, Bert R., Jr.

1989-01-01

263

Self-assembly of large-scale and ultrathin silver nanoplate films with tunable plasmon resonance properties.  

PubMed

We describe a rapid, simple, room-temperature technique for the production of large-scale metallic thin films with tunable plasmonic properties assembled from size-selected silver nanoplates (SNPs). We outline the properties of a series of ultrathin monolayer metallic films (8-20 nm) self-assembled on glass substrates in which the localized surface plasmon resonance can be tuned over a range from 500 to 800 nm. It is found that the resonance peaks of the films are strongly dependent on the size of the nanoplates and the refractive index of the surrounding dielectric. It is also shown that the bandwidth and the resonance peak of the plasmon resonance spectrum of the metallic films can be engineered by simply controlling aggregation of the SNP. A three-dimensional finite element method was used to investigate the plasmon resonance properties for individual SNPs in different dielectrics and plasmon coupling in SNP aggregates. A 5-17 times enhancement of scattering from these SNP films has been observed experimentally. Our experimental results, together with numerical simulations, indicate that this self-assembly method shows great promise in the production of nanoscale metallic films with enormous electric-field enhancements at visible and near-infrared wavelengths. These may be utilized in biochemical sensing, solar photovoltaic, and optical processing applications. PMID:21955107

Zhang, Xiao-Yang; Hu, Anming; Zhang, Tong; Lei, Wei; Xue, Xiao-Jun; Zhou, Yunhong; Duley, Walt W

2011-11-22

264

Surface-sensitive UHV dielectric studies of nanoscale organic thin films: Adsorption, crystallization, and sublimation  

NASA Astrophysics Data System (ADS)

Nanoscale systems are small collections of atoms or molecules, which as a result of their limited extent, show measurable thermodynamic deviations from bulk samples of the same species. The deviations may result from purely finite-size effects, or may be due to an increased significance of the interaction between the nanoscale system and its container. Ultra-thin (<100 nm) films of organic molecules adsorbed on surfaces afford unique opportunities to study the interplay of forces relevant to nanoscale physics. This thesis describes the development of a novel ultra-high vacuum apparatus to study the behavior of adsorbed polar molecules via dielectric spectroscopy (UHV-DS). Ultra-thin films are grown and characterized in-situ. The use of interdigitated electrode capacitors and a ratio-transformer bridge technique yields resolutions of 1 aF and 10-5 ppm in the capacitance and loss tangent, respectively. Typical sensitivity is 10 aF per monolayer at 80 K. Results are given for studies on water, methanol, and Cp* (a synthetic molecular rotor). The desorption event in the dielectric spectra is correlated with thermal desorption spectroscopy. During growth of methanol films, we observe partial crystallization for temperatures above ? 100 K. Crystallization is also observed upon heating glassy films grown at 80 K. Finally, we discuss UHV-DS as a probe for solid thin-film vapor pressure measurements, and show that our data on methanol compare favorably with those in the literature.

Underwood, Jason M.

265

Dielectrically Loaded Biconical Antennas  

Microsoft Academic Search

Biconical antennas are of great interest to those who deal with broadband applications including the transmission\\/reception of pulses. In particular, wide-angle conical antennas are an attractive choice in many applications including Electronic Support Measures (ESM) and the measurements of transient surface currents and charge densities on aircraft. Dielectric loading in the interior region of a conical antenna can be used

Fouad Ahmed Nusseibeh

1995-01-01

266

Folded dielectric elastomer actuators  

Microsoft Academic Search

Polymer-based linear actuators with contractile ability are currently demanded for several types of applications. Within the class of dielectric elastomer actuators, two basic configurations are available today for such a purpose: the multi-layer stack and the helical structure. The first consists of several layers of elementary planar actuators stacked in series mechanically and parallel electrically. The second configuration relies on

Federico Carpi; Claudio Salaris; Danilo DeRossi

2007-01-01

267

Helical dielectric elastomer actuators  

Microsoft Academic Search

This paper presents a new type of contractile polymer-based electromechanical linear actuator. The device belongs to the class of dielectric elastomer actuators, which are typically capable of undergoing large deformations induced by an applied electric field. It is based on a novel helical configuration, suitable for the generation of electrically driven axial contractions and radial expansions. The architecture, the principle

Federico Carpi; Antonio Migliore; Giorgio Serra; Danilo DeRossi

2005-01-01

268

Molds for cable dielectrics  

DOEpatents

Molds for use in making end moldings for high-voltage cables are described wherein the dielectric insulator of a cable is heated and molded to conform to a desired shape. As a consequence, high quality substantially bubble-free cable connectors suitable for mating to premanufactured fittings are made. 5 figs.

Roose, L.D.

1996-12-10

269

Molds for cable dielectrics  

DOEpatents

Molds for use in making end moldings for high-voltage cables are described wherein the dielectric insulator of a cable is heated and molded to conform to a desired shape. As a consequence, high quality substantially bubble-free cable connectors suitable for mating to premanufactured fittings are made.

Roose, Lars D. (Albuquerque, NM)

1996-01-01

270

Lunar permafrost - Dielectric identification.  

NASA Technical Reports Server (NTRS)

A simulator of lunar permafrost at 100 K exhibits a dielectric relaxation centered at approximately 300 hertz. If permafrost exists in the moon between 100 and 213 K, it should present a relaxation peak at approximately 300 hertz. For temperatures up to 263 K it may go up to 20 kilohertz.

Alvarez, R.

1973-01-01

271

Ternary gas dielectrics  

SciTech Connect

Recent findings on ternary gas dielectrics comprising N/sub 2/ + SF/sub 6/ or CHF/sub 3/ + SF/sub 6/ and small amounts (1 to 30%) of a strongly electron-attaching perfluorocarbon (PFC) are presented and discussed. Breakdown strengths of such ternary gas dielectrics under cylindrical and point-plane nonuniform dc fields and under impulse stress for total pressures varying from 50 to 600 kPa are reported, along with results on the decomposition products of the SF/sub 6/ + PFC binary components of the ternary mixtures. On the basis of these data, ternary gas dielectrics are identified which have high dielectric strengths, are relatively free of carbonization, could reduce SF/sub 6/ toxicity and corrosion problems, and possess improved dc highly nonuniform field and impulse withstand capabilities. A number of these have dew points comparable to or better than pure SF/sub 6/ over practical pressure ranges and can be economically attractive if the large-scale production of PFCs reduces their present extremely small-scale production cost by a factor of approx. 5 to 10.

Chrisophorou, L.G.; James, D.R.; Sauers, I.; Pace, M.O.; Pai, R.Y.; Fatheddin, A.

1982-01-01

272

Znic Oxide Nanowires with Ultra-Thin and Low-Resistance Seed Layer  

Microsoft Academic Search

We report the zinc oxide (ZnO) nanowires with ultra-thin seed layer by low-cost hydrothermal method. The ultra-thin seed layer consists of ZnO thin film, which is fabricated by sol-gel method and then etched to reduce the thickness by diluted HCI. The resistance along the vertical direction of the ultra-thin seed layer on the indium tin oxide (ITO) glass decreases during

Wen-Yan Su; Ching-Fuh Lin

2008-01-01

273

Characterization of dielectric breakdown behavior by in situ transmission electron microscopy  

NASA Astrophysics Data System (ADS)

Dielectric breakdown (BD) is the loss of capacitance upheld by an insulating material through defect formation and charge trapping. Dielectric BD is well-studied in the framework of reliability physics for semiconductor applications, and presents itself as a viable mechanism during materials processing by electric field assisted sintering (EFAS). So far a mechanistic understanding of dielectric BD is incomplete due to the limitations in nanoscale defect characterization techniques. The recent development of novel in situ transmission electron microscopy (TEM) capabilities enables the atomic-scale characterization of dielectric BD mechanisms, which was the subject of this dissertation. As the technology of semiconductor devices moves toward the sub-25 nm technology the electronic properties of gate oxide layers are affected eventually leading to device failure by dielectric BD. This study aimed to provide a systematic approach of simultaneous imaging and local application of electrical stress using in situ TEM by contacting an electrically biased Scanning Tunnelling Microscopy (STM) probe directly to the TEM sample. This experimental setup therefore allows a correlation of electrical signatures with defect structure evolution. In situ TEM experiments carried out with a single SiO2-based field effect transistor resulted to catastrophic failure of the dielectric layer consistent with descriptions of soft dielectric breakdown (SBD) and hard dielectric breakdown (HBD). A variety of in situ TEM techniques was further utilized to investigate whether electric field induced dielectric breakdown may contribute to densification of metallic powder particles during EFAS. In situ heating and STM-TEM experiments were systematically applied to separately study thermal and athermal effects during densification, respectively. Nanometric metal powders used for sintering typically possess surface oxides that affect the thermodynamics and kinetics of neck formation during the initial stage of sintering. The thermal effects were found to be driven by reduction-oxidation reactions of nickel oxide with carbon. The presence of carbon promotes the removal of surface oxides at lower temperatures and, therefore, can accelerate densification. By the controlled application of electrical bias, EFAS conditions were reproduced during in situ TEM and revealed reduction of ultra-thin nickel oxide surface layers by electric field-induced dielectric breakdown. The results provide evidence for previously suggested effects of local electric field amplification at inter-particle contact areas, which, hence, triggers surface cleaning through electric field-induced dielectric breakdown.

Bonifacio, Cecile Semana

274

Structure-dependent mechanical properties of ultrathin zinc oxide nanowires  

PubMed Central

Mechanical properties of ultrathin zinc oxide (ZnO) nanowires of about 0.7-1.1 nm width and in the unbuckled wurtzite (WZ) phase have been carried out by molecular dynamics simulation. As the width of the nanowire decreases, Young's modulus, stress-strain behavior, and yielding stress all increase. In addition, the yielding strength and Young's modulus of Type III are much lower than the other two types, because Type I and II have prominent edges on the cross-section of the nanowire. Due to the flexibility of the Zn-O bond, the phase transformation from an unbuckled WZ phase to a buckled WZ is observed under the tensile process, and this behavior is reversible. Moreover, one- and two-atom-wide chains can be observed before the ZnO nanowires rupture. These results indicate that the ultrathin nanowire possesses very high malleability. PMID:21711876

2011-01-01

275

Competing weak localization and weak antilocalization in ultrathin topological insulators.  

PubMed

We demonstrate evidence of a surface gap opening in topological insulator (TI) thin films of (Bi(0.57)Sb(0.43))(2)Te(3) below six quintuple layers through transport and scanning tunneling spectroscopy measurements. By effective tuning the Fermi level via gate-voltage control, we unveil a striking competition between weak localization and weak antilocalization at low magnetic fields in nonmagnetic ultrathin films, possibly owing to the change of the net Berry phase. Furthermore, when the Fermi level is swept into the surface gap of ultrathin samples, the overall unitary behaviors are revealed at higher magnetic fields, which are in contrast to the pure WAL signals obtained in thicker films. Our findings show an exotic phenomenon characterizing the gapped TI surface states and point to the future realization of quantum spin Hall effect and dissipationless TI-based applications. PMID:23198980

Lang, Murong; He, Liang; Kou, Xufeng; Upadhyaya, Pramey; Fan, Yabin; Chu, Hao; Jiang, Ying; Bardarson, Jens H; Jiang, Wanjun; Choi, Eun Sang; Wang, Yong; Yeh, Nai-Chang; Moore, Joel; Wang, Kang L

2013-01-01

276

Ultrathin aluminum sample cans for single crystal inelastic neutron scattering  

SciTech Connect

Single crystal inelastic neutron scattering measurements are often performed using a sample environment for controlling sample temperature. One difficulty associated with this is establishing appropriate thermal coupling from the sample to the temperature controlled portion of the sample environment. This is usually accomplished via a sample can which thermally couples the sample environment to the sample can and the sample can to the sample via an exchange gas. Unfortunately, this can will contribute additional background signal to ones measurement. We present here the design of an ultrathin aluminum sample can based upon established technology for producing aluminum beverage cans. This design minimizes parasitic sample can scattering. Neutron scattering measurements comparing a machined sample can to our beverage can design clearly indicate a large reduction in scattering intensity and texture when using the ultrathin sample can design. We also examine the possibility of using standard commercial beverage cans as sample cans.

Stone, Matthew B [ORNL; Loguillo, Mark [ORNL; Abernathy, Douglas L [ORNL

2011-01-01

277

Ultrathin and lightweight organic solar cells with high flexibility  

NASA Astrophysics Data System (ADS)

Application-specific requirements for future lighting, displays and photovoltaics will include large-area, low-weight and mechanical resilience for dual-purpose uses such as electronic skin, textiles and surface conforming foils. Here we demonstrate polymer-based photovoltaic devices on plastic foil substrates less than 2??m thick, with equal power conversion efficiency to their glass-based counterparts. They can reversibly withstand extreme mechanical deformation and have unprecedented solar cell-specific weight. Instead of a single bend, we form a random network of folds within the device area. The processing methods are standard, so the same weight and flexibility should be achievable in light emitting diodes, capacitors and transistors to fully realize ultrathin organic electronics. These ultrathin organic solar cells are over ten times thinner, lighter and more flexible than any other solar cell of any technology to date.

Kaltenbrunner, Martin; White, Matthew S.; G?owacki, Eric D.; Sekitani, Tsuyoshi; Someya, Takao; Sariciftci, Niyazi Serdar; Bauer, Siegfried

2012-04-01

278

Tunable ultrathin mantle cloak via varactor-diode-loaded metasurface.  

PubMed

We propose a tunable strategy for the ultrathin mantle cloak via metasurface. The tunable cloak is implemented by loading varactor diodes between two neighboring horizontal metallic strips which constitute the metasurface. We demonstrate that the varactor diodes enable the capacitive reactance of the metasurface to be tunable from -157 ? to -3 ? when the DC bias voltage is properly changed. The active metasurface is then explored to cloak conformally a conducting cylinder. Both numerical and experiment results show that the cloaking frequency can be continuously controlled from 2.3 GHz to 3.7 GHz by appropriately adjusting the bias voltage. The flexible tunability and good cloaking performance are further examined by the measured field distributions. The advanced features of tunability, low profile, and conformal ability of the ultrathin cloak pave the way for practical applications of cloaking devices. PMID:24921534

Liu, Shuo; Xu, He-Xiu; Zhang, Hao Chi; Cui, Tie Jun

2014-06-01

279

Ultrathin and lightweight organic solar cells with high flexibility.  

PubMed

Application-specific requirements for future lighting, displays and photovoltaics will include large-area, low-weight and mechanical resilience for dual-purpose uses such as electronic skin, textiles and surface conforming foils. Here we demonstrate polymer-based photovoltaic devices on plastic foil substrates less than 2 ?m thick, with equal power conversion efficiency to their glass-based counterparts. They can reversibly withstand extreme mechanical deformation and have unprecedented solar cell-specific weight. Instead of a single bend, we form a random network of folds within the device area. The processing methods are standard, so the same weight and flexibility should be achievable in light emitting diodes, capacitors and transistors to fully realize ultrathin organic electronics. These ultrathin organic solar cells are over ten times thinner, lighter and more flexible than any other solar cell of any technology to date. PMID:22473014

Kaltenbrunner, Martin; White, Matthew S; G?owacki, Eric D; Sekitani, Tsuyoshi; Someya, Takao; Sariciftci, Niyazi Serdar; Bauer, Siegfried

2012-01-01

280

Magnetic excitations in ultrathin magnetic films: Temperature effects  

NASA Astrophysics Data System (ADS)

The idea of investigating large wave-vector magnetic excitations in ultrathin films by spin-polarized electron spectroscopy is briefly reviewed. The historical background of the paper is based on the personal experience of the authors who collaborated and discussed with Douglas Mills regarding this subject. Douglas Mills' impact on the understanding of fundamental mechanisms involved in the excitation process and the development of the theory of magnetic excitations is outlined. In addition, the temperature effects on the large wave-vector magnetic excitations in ultrathin Fe films are addressed. The experimental results of magnon excitations in the pseudomorphic Fe monolayer on W(110) are presented. The temperature dependence of the magnon dispersion relation is discussed.

Zakeri, Kh.; Prokop, J.; Zhang, Y.; Kirschner, J.

2014-12-01

281

Loading and release of charged dyes using ultrathin hydrogels.  

PubMed

The anionic dyes methyl orange (MO) and allura red (AR) were used as model drugs to assess the loading and release by layer-by-layer assembled ultrathin hydrogels prepared via the amide formation of poly(acrylic acid-co-N-isopropylacrylamide) with AAc contents of 5, 10, and 15 mol % plus poly(vinylamine hydrochloride). The amount of MO loaded was potentially controlled by changing the dye concentrations, film thickness, and AAc content of the copolymers. The release of AR was controlled by the NaCl concentration and pH. We conclude that the polymeric matrices of ultrathin hydrogels have great potential for the loading and release of charged drugs. PMID:16089378

Serizawa, Takeshi; Matsukuma, Daisuke; Akashi, Mitsuru

2005-08-16

282

Ultrathin and lightweight organic solar cells with high flexibility  

PubMed Central

Application-specific requirements for future lighting, displays and photovoltaics will include large-area, low-weight and mechanical resilience for dual-purpose uses such as electronic skin, textiles and surface conforming foils. Here we demonstrate polymer-based photovoltaic devices on plastic foil substrates less than 2??m thick, with equal power conversion efficiency to their glass-based counterparts. They can reversibly withstand extreme mechanical deformation and have unprecedented solar cell-specific weight. Instead of a single bend, we form a random network of folds within the device area. The processing methods are standard, so the same weight and flexibility should be achievable in light emitting diodes, capacitors and transistors to fully realize ultrathin organic electronics. These ultrathin organic solar cells are over ten times thinner, lighter and more flexible than any other solar cell of any technology to date. PMID:22473014

Kaltenbrunner, Martin; White, Matthew S.; Glowacki, Eric D.; Sekitani, Tsuyoshi; Someya, Takao; Sariciftci, Niyazi Serdar; Bauer, Siegfried

2012-01-01

283

Ultra-thin lubricating films under transient conditions  

NASA Astrophysics Data System (ADS)

The mechanism of fluid film lubrication in ultra-thin conjunctions under counterformal concentrated circular point contacts is discussed in this paper. The significance of squeeze film action in increased load carrying capacity is highlighted. The numerical predictions made in acceleration-deceleration motion of a ball against a flat race is found to conform with the experimental findings of other research workers for polar branched lubricants down to a film thickness in the region of 20 nm. This conformance with the experimental findings has enabled a fundamental understanding of the multi-physics of film formation when conditions promoting the formation of ultra-thin films of the order of few nanometres have been employed, with the use of a non-polar lubricant. This paper provides the first ever solution of the combined effect of viscous, surface and molecular forces under transient conditions.

Al-Samieh, M.; Rahnejat, H.

2001-09-01

284

Gate Last Indium-Gallium-Arsenide MOSFETs with Regrown Source-Drain Regions and ALD Dielectrics  

NASA Astrophysics Data System (ADS)

III-V-based MOSFETs have the potential to exceed the performance of silicon-based MOSFETs due to the semiconductor's small electron effective mass. Modern silicon-based MOSFETs with 22 nm gate lengths utilize high-k gate insulators and non-planar device geometries to optimize device performance. III-V HEMT technology has achieved similar gate lengths, but large source-drain access resistances and the lack of high-quality gate insulators prevent further device performance scaling. Sub-22 nm gate length III-V MOSFETs require metal-semiconductor contact resistivity to be less than 1 ohm-micron squared, gate insulators with less than 1 nm effective oxide thickness, and semiconductor-insulator interface trap densities less than 2E12 per square centimeter per electron volt. This dissertation presents InGaAs-based III-V MOSFET process flows and device results to assess their use in VLSI circuits. Previous III-V MOSFET results focused on long (>100 nm) gate lengths and ion implantation for source-drain region formation. Scaling III-V MOSFETs to shorter gate lengths requires source-drain regions that have low sheet resistance, high mobile charge densities, and low metal-semiconductor contact resistance. MBE- and MOCVD-based raised epitaxial source-drain regrowth meet these requirements. MBE InAs source-drain regrowth samples have shown 0.5 to 2 ohm-micron squared metal semiconductor contact resistivities. MOCVD InGaAs source-drain regrowth samples have shown < 100 ohm-micron single-sided access resistance to InGaAs MOSFETs. Gate insulators on III-V materials require large conduction band offsets to the channel, high dielectric permittivities, and low semiconductor-insulator interface trap densities. An in-situ hydrogen plasma / trimethylaluminum treatment has been developed to lower the gate semiconductor-insulator interface trap density. This treatment, done immediately before gate insulator deposition, has been shown to lower MOS capacitor interface trap densities by more than a factor of two. Devices using gate-first MBE regrowth, gate-last MBE regrowth, and gate-last MOCVD regrowth were fabricated and resulting devices characterized. 65 nm gate length gate-first MBE regrowth devices employing a 2.2 nm EOT Al 2O3 gate insulator show peak transconductances of 0.3 mS/micron at 1 V Vds. Gate-first FET performance scaling is limited by processed-induced damage and ungated access regions. 64 nm gate length gate-last MBE regrowth devices employing a 1.21 nm EOT Al2O 3 / HfO2 bi-layer gate insulator show peak transconductances of 1.4 mS/micron at 0.5 V Vds. Other gate-last MBE samples had long channel subthreshold swings as low as 117 mV/dec. 48 nm gate length gate-last MOCVD MOSFETs employing a 0.8 nm EOT HfO2 gate insulator and digital channel etching show peak transconductances of 2 mS/micron at 0.5 V Vds, with long channel devices having 97 mV/dec subthreshold swing.

Carter, Andrew Daniel

285

Electrical Transport of Spin Polarized Carriers in Disordered Ultrathin Films  

Microsoft Academic Search

Glass like behavior of electrical transport relaxation has been induced in quench-condensed ultrathin films of amorphous Bismuth by application of a parallel magnetic field. This effect is found in films well on the insulating side of the superconductor-insulator transition, and disappears as thickness is increased. We propose that this behavior is caused by space-charge-limited current flow, which is induced by

Anand Bhattacharya; Luis Hernandez; Kevin Parendo; Allen Goldman

2003-01-01

286

Excess drain noise simulation in ultrathin oxides MOSFETs  

Microsoft Academic Search

This work presents a simple analytical model for the low frequency noise in ultrathin oxide MOSFETs of advanced bulk CMOS\\u000a technology. The developed formulations of the gate leakage and drain current noise are based on a flat band voltage concept\\u000a and analyzed with respect to noise measurements. Its proves very effective in describing the overall drain current noise as\\u000a well

T. Contaret; G. Ghibaudo; A. Ferron; F. Buf

2006-01-01

287

Ultrathin magnetic films: Electrochemistry versus molecular-beam epitaxy  

Microsoft Academic Search

Ultrathin Co films have been electrodeposited on Cu(001) from an aqueous Na2SO4\\/CoSO4 electrolyte under cleanliness conditions equivalent to ultrahigh vacuum of 510-10 mbar. Films thicker than 1.5 ML show in-plane magnetization and square hysteresis loops. The saturation magnetization increases linearly with film thickness. The magnetization vanishes below 1.5 ML in agreement with molecular-beam epitaxy (MBE) films at 300 K. The

W. Schindler; J. Kirschner

1997-01-01

288

Giant room-temperature elastocaloric effect in ferroelectric ultrathin films.  

PubMed

Environmentally friendly ultrathin BaTiO3 capacitors can exhibit a giant stress-induced elastocaloric effect without hysteresis loss or Joule heating. By combining this novel elastocaloric effect with the intrinsic electrocaloric effect, an ideal refrigeration cycle with high performance (temperature change over 10 K with a wide working-temperature window of 60 K) at room temperature is proposed for future cooling applications. PMID:25042767

Liu, Yang; Infante, Ingrid C; Lou, Xiaojie; Bellaiche, Laurent; Scott, James F; Dkhil, Brahim

2014-09-17

289

Ultrathin amorphous manganese dioxide nanosheets synthesized with controllable width.  

PubMed

We present a one-step synthesis process for ultrathin non-crystalline MnO2 nanosheets. Their thickness is about 2 nm and the width varies from 5 to 20 nm. They induce a higher capacitance than zero-dimensional spheres or one-dimensional rods. When heat treated at elevated temperature MnO2 nanosheets partly grow into crystalline Mn2O3 rods. PMID:23851984

Xu, Chengjun; Shi, Shan; Sun, Yige; Chen, Yanyi; Kang, Feiyu

2013-08-25

290

Stable multilayer ultrathin film containing covalently attached colloidal Ag nanoparticles  

Microsoft Academic Search

Stable multilayer ultrathin films were constructed by alternate deposition of nitro-diazoresin (NDR) and Ag nanoparticles (Ag-NPs) followed by UV irradiation. The absorbance of the un-irradiated film at 385 and 412 nm, which is the characteristic absorption of -N2+ of NDR and Ag-NPs respectively, increases linearly with the fabrication cycle. This result shows that the layer-by-layer electrostatic deposition of NDR and

Conghua Lu; Shuo Bai; Dongbai Zhang; Lan Huang; Jiming Ma; Chuanqiou Luo; Weixiao Cao

2003-01-01

291

Organic field-effect transistors with ultrathin gate insulator  

Microsoft Academic Search

We have used a commercially available Mylar film coated with a thin (?60nm) layer of aluminium and an ultrathin (?3.5nm) SiO2 layer as flexible substrate for the manufacture of bottom-gate organic field-effect transistors (OFETs). We show that the SiO2 layer has insulating properties with a breakdown voltage of 1.6V and a capacitance of ?1?F\\/cm2. We have manufactured organic field-effect transistors

L. A Majewski; R Schroeder; M Grell

2004-01-01

292

Magnetism and surface structure of atomically controlled ultrathin metal films  

NASA Astrophysics Data System (ADS)

We review the correlation of magnetism and surface structure in ultrathin metal films, including the tailoring of novel magnetic properties using atomic scale control of the nanostructure. We provide an overview of modern fabrication and characterization techniques used to create and explore these fascinating materials, and highlight important phenomena of interest. We also discuss techniques that control and characterize both the magnetic and structural properties on an atomic scale. Recent advances in the development and applications of these techniques allow nanomagnetism to be investigated in an unprecedented manner. A system cannot necessarily retain a two-dimensional structure as it enters the ultrathin region, but it can transform into a three-dimensional, discontinuous structure due to the Volmer-Weber growth mechanism. This structural transformation can give rise to superparamagnetism. During this evolution, competing factors such as interparticle interactions and the effective magnetic anisotropy govern the magnetic state. These magnetic parameters are influenced by the nanostructure of the film. In particular, controlling the magnetic anisotropy is critical for determining the magnetic properties. Surface effects play especially important roles in influencing both the magnitude and direction of the magnetic anisotropy in ultrathin films. By properly altering the surface structure, the strength and direction of the magnetic anisotropy are controlled via spin-orbit and/or dipole interactions.

Shiratsuchi, Yu; Yamamoto, Masahiko; Bader, S. D.

293

Magnetism and surface structure of atomically controlled ultrathin metal films.  

SciTech Connect

We review the correlation of magnetism and surface structure in ultrathin metal films, including the tailoring of novel magnetic properties using atomic scale control of the nanostructure. We provide an overview of modern fabrication and characterization techniques used to create and explore these fascinating materials, and highlight important phenomena of interest. We also discuss techniques that control and characterize both the magnetic and structural properties on an atomic scale. Recent advances in the development and applications of these techniques allow nanomagnetism to be investigated in an unprecedented manner. A system cannot necessarily retain a two-dimensional structure as it enters the ultrathin region, but it can transform into a three-dimensional, discontinuous structure due to the Volmer-Weber growth mechanism. This structural transformation can give rise to superparamagnetism. During this evolution, competing factors such as interparticle interactions and the effective magnetic anisotropy govern the magnetic state. These magnetic parameters are influenced by the nanostructure of the film. In particular, controlling the magnetic anisotropy is critical for determining the magnetic properties. Surface effects play especially important roles in influencing both the magnitude and direction of the magnetic anisotropy in ultrathin films. By properly altering the surface structure, the strength and direction of the magnetic anisotropy are controlled via spin-orbit and/or dipole interactions.

Shiratsuchi, Yu.; Yamamoto, M.; Bader, S. D.; Materials Science Division; Osaka Univ.

2007-01-01

294

Temperature switchable polymer dielectrics.  

SciTech Connect

Materials with switchable states are desirable in many areas of science and technology. The ability to thermally transform a dielectric material to a conductive state should allow for the creation of electronics with built-in safety features. Specifically, the non-desirable build-up and discharge of electricity in the event of a fire or over-heating would be averted by utilizing thermo-switchable dielectrics in the capacitors of electrical devices (preventing the capacitors from charging at elevated temperatures). We have designed a series of polymers that effectively switch from a non-conductive to a conductive state. The thermal transition is governed by the stability of the leaving group after it leaves as a free entity. Here, we present the synthesis and characterization of a series of precursor polymers that eliminate to form poly(p-phenylene vinylene) (PPV's).

Johnson, Ross Stefan

2010-08-01

295

Temperature switchable polymer dielectrics.  

SciTech Connect

Materials with switchable states are desirable in many areas of science and technology. The ability to thermally transform a dielectric material to a conductive state should allow for the creation of electronics with built-in safety features. Specifically, the non-desirable build-up and discharge of electricity in the event of a fire or over-heating would be averted by utilizing thermo-switchable dielectrics in the capacitors of electrical devices (preventing the capacitors from charging at elevated temperatures). We have designed a series of polymers that effectively switch from a non-conductive to a conductive state. The thermal transition is governed by the stability of the leaving group after it leaves as a free entity. Here, we present the synthesis and characterization of a series of precursor polymers that eliminate to form poly(p-phenylene vinylene) (PPV's).

Kholwadwala, Fenil Manish; Johnson, Ross Stefan; Dirk, Shawn M.

2010-06-01

296

Microwave dielectric resonators  

NASA Astrophysics Data System (ADS)

A historical review and a status report on the state of the art of microwave dielectric resonators are presented. Early experimental works predating practical applications are noted, including work on rutile in the 1960s and the breakthrough development of stable low-less barium tetratitanate ceramics. Topics include: theory of operation, coupling to microwave structures, ceramic materials, applications, various filters, diode oscillators, and FET or bipolar transistor oscillators.

Fiedziuszko, S. J.

1986-09-01

297

Stimulated dielectric wakefield accelerator  

Microsoft Academic Search

A dielectric-lined waveguide can be built that supports multi-mode, nearly non-dispersive propagation; wherein a superposition of TM0n wakefields is shown to result in highly peaked axial electric fields localized on each driving bunch in a periodic sequence. This allows stimulated emission of wakefield energy to occur at a rate which is much larger than the coherent spontaneous emission from a

T.-B. Zhang; J. L. Hirshfield; T. C. Marshall; B. Hafizi

1997-01-01

298

Additive manufacturing of graded dielectrics  

NASA Astrophysics Data System (ADS)

A method for the fabrication of graded dielectrics within a structural composite is presented. This system employs an ultrasonic powder deposition head to print high dielectric powders onto a woven fabric composite substrate. It is shown how this system can integrate 3D variations of dielectric properties at millimeter resolution within a mechanically rugged substrate. To conclude, the systems practical application is demonstrated with experimental results from a graded index lens.

Roper, David A.; Good, Brandon L.; McCauley, Raymond; Yarlagadda, Shridhar; Smith, Jared; Good, Austin; Pa, Peter; Mirotznik, Mark S.

2014-04-01

299

Transmission properties of terahertz pulses through an ultrathin subwavelength silicon hole array  

E-print Network

Transmission properties of terahertz pulses through an ultrathin subwavelength silicon hole array 30 March 2005 We demonstrate extraordinary THz transmission of an array of subwavelength apertures patterned on ultrathin highly doped silicon by reactive ion etching. The zero-order transmission spectra

300

Near-Infrared Surface Plasmon Resonance Measurements of Ultrathin Films. 2. Fourier  

E-print Network

Near-Infrared Surface Plasmon Resonance Measurements of Ultrathin Films. 2. Fourier Transform SPR to the study of ultrathin organic films adsorbed onto gold surfaces utilizing near-infrared (NIR) excitation reflectivity spectrum from a prism/gold film/water as- sembly at a fixed angle of incidence approximately 1

301

Multi-resonant absorption in ultra-thin silicon solar cells with metallic nanowires  

E-print Network

trapping in microcrystalline silicon solar cells with textured substrates," Prog. Photovolt. Res. Appl. 11Multi-resonant absorption in ultra-thin silicon solar cells with metallic nanowires In`es Massiot,1 in flat and ultra-thin amorphous silicon solar cells with a one-dimensional silver grating embedded

Paris-Sud XI, Université de

302

Light trapping in ultrathin plasmonic solar cells Vivian E. Ferry,1,2,*  

E-print Network

, and J. Bailat, "Thin-film Silicon Solar Cell Technology," Prog. Photovolt. Res. Appl. 12(23), 113Light trapping in ultrathin plasmonic solar cells Vivian E. Ferry,1,2,* Marc A. Verschuuren,3, and measurement of ultrathin film a-Si:H solar cells with nanostructured plasmonic back contacts, which

Polman, Albert

303

Physical Review B 66, 024419 (2002) Anisotropy of ultrathin ferromagnetic films and the spin reorientation transition  

E-print Network

Physical Review B 66, 024419 (2002) Anisotropy of ultrathin ferromagnetic films and the spin relative to the film. These coefficients are then studied experimentally (for a review see Ref. 6 on the direction of the magne- tization of ultrathin ferromagnetic films in the ground-state is studied. The ground

Usadel, K. D.

304

Ultrathin, high-efficiency, broad-band, omni-acceptance, organic solar cells enhanced by  

E-print Network

Ultrathin, high-efficiency, broad-band, omni- acceptance, organic solar cells enhanced by plasmonic and demonstration of a new ultra-thin high- efficiency organic solar cell (SC), termed "plasmonic cavity: Three of central challenges in solar cells are high light coupling into solar cell, high light trapping

305

Ballistic transport in ultrathin films and channels with random rough walls  

E-print Network

Ballistic transport in ultrathin films and channels with random rough walls A.E.Meyerovich y and S: Ballistic transport in ultrathin films and channels with random rough walls December 4, 1996 y To whom.Mathews Ave., Urbana, IL 61801, USA #12; 2 1. Introduction Repeated collisions of ballistic particles

Meyerovich, Alex

306

White Organic Light-Emitting Diodes with fine chromaticity tuning via ultrathin layer position shifting  

E-print Network

White Organic Light-Emitting Diodes with fine chromaticity tuning via ultrathin layer position : Non-doped white organic light-emitting diodes using an ultrathin yellow-emitting layer of rubrene (5. In particular, White OLEDs (WOLEDs) are of foremost interest for lighting and display applications1 . To achieve

Paris-Sud XI, Université de

307

Defects in Ultra-Thin Oxygen Implanted Silicon-on-Insulator Materials  

NASA Astrophysics Data System (ADS)

Dielectric isolation of the active components in integrated circuits becomes increasingly important as silicon devices are scaled down into the submicron regime. In their fabrication, silicon-on-insulator (SOI) substrates have many advantages over bulk silicon substrates, including low power consumption, and greater packing densities of device components. Of the several SOI technologies, the most advanced is the synthesis of a buried oxide layer (BOX) by an oxygen implantation technique that is called SIMOX (Separation by Implantation of Oxygen). Two major processing steps in creating SIMOX are (1) implantation of oxygen and (2) high temperature annealing to restore the crystalline order from the implantation damage. Conventional SIMOX material has top silicon and BOX layers of 200nm and 400nm thickness, respectively. The dimensions of the stack can be adjusted by variation of the process parameters since the thickness of the buried oxide layer depends on the dose of oxygen ions implanted, and that of the top silicon layer on the implantation energy. In recent developments, implantation dose and energy have been reduced, resulting in ultra-thin layers that offer cost savings and improved performance of the SIMOX substrate. However, the smaller dimensions one fifth that of conventional SIMOX - present several challenges since defects and interfaces are much closer to the surface, and slight variations of processing parameters can be detrimental to the final products. Our study investigates various types of defects generated by implantation and their evolution through the intermediate temperature and high temperature annealing. The defects include multiple stacking faults, oxide precipitates, and silicon islands. Their growth, characteristics, and density as a function of implantation energy, oxygen dose, annealing temperature, and time will be discussed.

Seraphin, Supapan; Jeoung, Jun Sik; Johnson, Benedict

2001-11-01

308

Low voltage stress-induced leakage current in 1.4 2.1 nm SiON and HfSiON gate dielectric layers  

NASA Astrophysics Data System (ADS)

This work examines stress-induced leakage current (SILC) in both ultrathin silicon oxynitride and hafnium silicate dielectric layers for future MOS technology nodes. SILC is confirmed to be sense voltage dependent and is observed to have a dependence on bulk oxide traps for both dielectric layers. A possible explanation for the sense voltage dependence is provided. SILC is found to be a greater problem in the HfSiON layers, because of its magnitude relative to the initial current. This results in the leakage current density quickly becoming greater than that for SiON. The SILC is found to have a transient component in the HfSiON layers, indicating the presence of slow electron traps. Finally, the correlation between SILC and drive current reduction is demonstrated. It is concluded that in the high-k layers investigated in this study, SILC seems more of a problem than dielectric breakdown.

O'Connor, Robert; McDonnell, Stephen; Hughes, Greg; Degraeve, Robin; Kauerauf, Thomas

2005-08-01

309

Supercritically exfoliated ultrathin vanadium pentoxide nanosheets with high rate capability for lithium batteries.  

PubMed

Ultrathin V2O5 nanosheets were successfully prepared through supercritical solvothermal reaction followed by annealing treatment. The formation of ultrathin nanosheets is owing to Ostwald ripening and the effect of supercritical fluids. As cathode material for lithium batteries, the ultrathin V2O5 nanosheets exhibit a capacity of 108 mA h g(-1) at a high rate of up to 10 C at 2.4-4 V and excellent cyclability with little capacity loss after 200 cycles. The enhanced rate performance is attributed to the shortened diffusion distance and the increased electrode-electrolyte contact area of the ultrathin nanosheet structure. It is also demonstrated that the supercritical solvothermal method is effective and facile to scalably synthesize ultrathin nanomaterials for lithium batteries. PMID:23963528

An, Qinyou; Wei, Qiulong; Mai, Liqiang; Fei, Jiayang; Xu, Xu; Zhao, Yunlong; Yan, Mengyu; Zhang, Pengfei; Huang, Shizhe

2013-10-21

310

Wakefields in a dielectric tube with frequency dependent dielectric constant  

E-print Network

Dielectric laser driven accelerators could operate at a fundamental mode frequency where consideration must be given to the frequency dependence of the dielectric constant when calculating wakefields. Wakefields are calculated for a frequency dependence that arises from a single atomic resonance. Causality is considered, and the effect on the short range wakefield is calculated.

Siemann, Robert

2005-01-01

311

Wakefields in a Dielectric Tube with Frequency Dependent Dielectric Constant  

Microsoft Academic Search

Laser driven dielectric accelerators could operate at a fundamental mode frequency where consideration must be given to the frequency dependence of the dielectric constant when calculating wakefields. Wakefields are calculated for a frequency dependence that arises from a single atomic resonance. Causality is considered, and the effects on the short range wakefields are calculated.

R. H. Siemann; A. W. Chao

2005-01-01

312

Wakefields in a Dielectric Tube with Frequency Dependent Dielectric Constant  

SciTech Connect

Laser driven dielectric accelerators could operate at a fundamental mode frequency where consideration must be given to the frequency dependence of the dielectric constant when calculating wakefields. Wakefields are calculated for a frequency dependence that arises from a single atomic resonance. Causality is considered, and the effects on the short range wakefields are calculated.

Siemann, R.H.; Chao, A.W.; /SLAC

2005-05-27

313

New silicone dielectric elastomers with a high dielectric constant  

Microsoft Academic Search

Dielectric elastomers (Des) are a type of EAPs with unique electrical properties and mechanical properties: high actuation strains and stresses, fast response times, high efficiency, stability, reliability and durability. The excellent figures of merit possessed by dielectric elastomers make them the most performing materials which can be applied in many domains: biomimetics, aerospace, mechanics, medicals, etc. In this paper, we

Zhen Zhang; Liwu Liu; Jiumin Fan; Kai Yu; Yanju Liu; Liang Shi; Jinsong Leng

2008-01-01

314

Dielectric dispersion and dielectric friction in electrolyte solutions. I  

Microsoft Academic Search

A self-consistent, kinetic theory of ion-solvent interactions is developed within the framework of continuum mechanics. It is shown that the hydrodynamic coupling between viscous momentum transport and dielectric relaxation leads not only to a theory of ion mobility but also to a description of the dielectric properties of electrolyte solutions. The concept of kinetic polarization deficiency is introduced, whereby the

J. Hubbard; L. Onsager

1977-01-01

315

Slow DNA transport through nanopores in hafnium oxide membranes.  

PubMed

We present a study of double- and single-stranded DNA transport through nanopores fabricated in ultrathin (2-7 nm thick) freestanding hafnium oxide (HfO2) membranes. The high chemical stability of ultrathin HfO2 enables long-lived experiments with <2 nm diameter pores that last several hours, in which we observe >50 000 DNA translocations with no detectable pore expansion. Mean DNA velocities are slower than velocities through comparable silicon nitride pores, providing evidence that HfO2 nanopores have favorable physicochemical interactions with nucleic acids that can be leveraged to slow down DNA in a nanopore. PMID:24083444

Larkin, Joseph; Henley, Robert; Bell, David C; Cohen-Karni, Tzahi; Rosenstein, Jacob K; Wanunu, Meni

2013-11-26

316

Ground state configurations in antiferromagnetic ultrathin films with dipolar anisotropy  

NASA Astrophysics Data System (ADS)

The formalism developed in a previous work to calculate the dipolar energy in quasi-two-dimensional crystals with ferromagnetic order is now extended to collinear antiferromagnetic order. Numerical calculations of the dipolar energy are carried out for systems with tetragonally distorted fcc [001] structures, the case of NiO and MnO ultrathin film grown in non-magnetic substrates, where the magnetic phase is a consequence of superexchange and dipolar interactions. The employed approximation allows to demonstrate that dipolar coupling between atomic layers is responsible for the orientation of the magnetization when it differs from the one in a single layer. The ground state energy of a given NiO or MnO film is found to depend not only on the strain, but also on how much the interlayer separation and the 2D lattice constant are changed with respect to the ideal values corresponding to the non-distorted cubic structure. Nevertheless, it is shown that the orientation of the magnetization in the magnetic phase of any of these films is determined by the strain exclusively. A striped phase with the magnetization along the [112] direction appears as the ground state configuration of NiO and MnO ultrathin films. In films with equally oriented stripes along the layers this magnetic phase is twofold degenerate, while in films with multidomain layers it is eightfold degenerate. These results are not in contradiction with experimentally observed out-of-plane or in-plane magnetization of striped phases in NiO and MnO ultrathin films.

Len, H.

2013-02-01

317

Energy harvesting using dielectric elastomers  

Microsoft Academic Search

Dielectric Elastomers are well known for there performance as actuators, but these materials can be used effectively as generators. Research on this field have received considerable attention lately, several prototypes were built like wavepower and human kinetic power generators. The focus of this paper is how the dielectric elastomer can be used as generator. The paper presents a dynamic model

Balazs Czech; Rick van Kessel; Pavol Bauer; Jan Abraham Ferreira; Ambroise Wattez

2010-01-01

318

Materials for dielectric elastomer actuators  

Microsoft Academic Search

Dielectric elastomer actuators consist of an elastomer film sandwiched between compliant electrodes. They work as electrostatic actuators: when a large electric field is applied over the electrodes, the rubber is compressed and the elastomer film elongates in the film plane. The performance of dielectric elastomer actuators (DEA), when a constant potential is applied, is expressed in a universal equation where

Peter Sommer-Larsen; Anne L. Larsen

2004-01-01

319

Dielectric elastomer actuators Guggi Kofod  

E-print Network

Dielectric elastomer actuators Guggi Kofod Ph.D. thesis, September 2001 The Technical University. The theories of elasticity and Maxwell stress are combined, in the special case of a dielectric elastomer-strained silicone elastomer films, providing stable compliant electrodes. Procedures for manufacturing of DEA

320

Electric fields in irradiated dielectrics  

NASA Technical Reports Server (NTRS)

An existing model for quantitatively predicting electric field build-up in dielectrics is used to demonstrate the importance of material parameters. Results indicate that electron irradiation will produce 10 to the 6th power V/cm in important materials. Parameters which can alter this build-up are discussed. Comparison to known irradiation induced dielectric charging experiments is discussed.

Frederickson, A. R.

1979-01-01

321

Degradation Of Reflectors And Dielectrics  

NASA Technical Reports Server (NTRS)

Report describes important degrading effects of atmosphere and outer-space environments on reflective surfaces and dielectrics. For reflective surfaces, terrestrial effects include soiling on glass surfaces and changing with time. Space effects include ultraviolet enhancement of contamination and possible surface erosion due to solar radiation, impact of debris, and interactions with atomic oxygen. Dielectrics similarly affected in both environments.

Bouquet, Frank L.; Cuddihy, Edward F.; Maag, Carl R., Jr.

1987-01-01

322

Electric-field-induced domain evolution in ferroelectric ultrathin films.  

PubMed

The electric-field-induced evolution of the recently discovered periodic 180 degree nanostripe domain structure is predicted in epitaxial Pb(Zr0.5Ti0.5)O3 ultrathin films from first principles. This evolution involves (1) the lateral growth of majority dipole domains at the expense of minority domains with the overall stripe periodicity remaining unchanged, (2) the creation of surface-avoiding nanobubbles, and (3) the formation of a single monodomain state. Analogies and differences (i) with ferroelectric thin films made of BaTiO3 and (ii) with ferromagnetic thin films under magnetic field are discussed. PMID:16712035

Lai, Bo-Kuai; Ponomareva, I; Naumov, I I; Kornev, I; Fu, Huaxiang; Bellaiche, L; Salamo, G J

2006-04-01

323

Ultrathin ?-FeOOH and ?-Fe2O3 nanowires  

NASA Astrophysics Data System (ADS)

We report the facile synthesis of ultrathin ?-FeOOH and ?-Fe2O3 nanowires with diameter of 2-3 nm. The ?-FeOOH nanowires show the unique optical properties attributed to the size- and shape-related quantum confinement effect. Upon heat treatment, they are transformed into ?-Fe2O3 nanowires, which exhibit the different magnetic properties compared with the previously reported ?-Fe2O3 nanostructures synthesized in silica matrices. The ?-Fe2O3 nanowires also exhibit high catalytic efficiency and hold potential for environmental-remediation applications.

Li, Shaozhou; Gan, Chee Lip

2014-11-01

324

1% solar cells derived from ultrathin carbon nanotube photoabsorbing films  

NASA Astrophysics Data System (ADS)

Using a carbon nanotube photoabsorbing film <5 nm in thickness, we demonstrate a 1% solar cell. Specifically, polymer wrapped, highly monochiral (7, 5) nanotubes are implemented in a bilayered heterojunction with acceptor C60. The nanotubes drive 63% of the conversion, several times stronger than previously demonstrated. Peak external quantum efficiency (QE) of 43% at the nanotube bandgap (1055 nm) and power conversion efficiency of 0.95% and 1.02% at 1.0 and 1.5 suns, respectively, are achieved. The high internal QE from the ultrathin layers suggests that nanostructured or multijunction cells exploiting multiple nanotube layers will be many times more efficient.

Shea, Matthew J.; Arnold, Michael S.

2013-06-01

325

Low-threshold optical bistabilities in ultrathin nonlinear metamaterials.  

PubMed

Optical bistability typically occurs only when the optical thickness in the device or the input light power is unfavorably large. Here we show that, for a class of plasmonic metamaterials consisting of ultrathin holey metallic plates filled with nonlinear materials, the optical bistability can occur with an ultralow excitation power. We present a realistic design working at 0.2THz and perform full-wave simulations to quantitatively study its optical bistability properties. An analytical model is developed to explain the inherent physics and provides a general design guideline for future development. PMID:24876015

Tang, Shiwei; Zhu, Baocheng; Xiao, Shiyi; Shen, Jung-Tsung; Zhou, Lei

2014-06-01

326

Electronic structure of erbium suicide ultra-thin films  

NASA Astrophysics Data System (ADS)

The electronic structure of erbium silicide ultra-thin films epitaxially grown on Si(111) has been studied by means of angle-resolved ultra-violet photoemission spectroscopy (ARUPS) in the coverage range 0.2-4 monolayers (ML). Some peaks probably related to the silicide surface atomic structure are observed at any coverage. Features that appear at normal emission in connection with an R3 superstructure are ascribed to vacancy-induced states in the silicon surface plane. No true interface states could be identified in this study.

Veuillen, J.-Y.; Tan, T. A. Nguyen; Lollman, D. B. B.

1993-08-01

327

Low thermal conductivity in ultrathin carbon nanotube (2, 1)  

PubMed Central

Molecular dynamic simulations reveal that the ultrathin carbon nanotube (CNT) (2, 1) with a reconstructed structure exhibits a surprisingly low thermal conductivity, which is only ~1630% of those in regular CNTs, e.g. CNT (2, 2) and (5, 5). Detailed lattice dynamic calculations suggest that the acoustic phonon modes greatly soften in CNT (2, 1) as compared to regular CNTs. Moreover, both phonon group velocities and phonon lifetimes strikingly decrease in CNT (2, 1), which result in the remarkable reduction of thermal conductivity. Besides, isotope doping and chemical functionalization enable the further reduction of thermal conductivity in CNT (2, 1). PMID:24815003

Zhu, Liyan; Li, Baowen

2014-01-01

328

Chemical surface deposition of ultra-thin semiconductors  

DOEpatents

A chemical surface deposition process for forming an ultra-thin semiconducting film of Group IIB-VIA compounds onto a substrate. This process eliminates particulates formed by homogeneous reactions in bath, dramatically increases the utilization of Group IIB species, and results in the formation of a dense, adherent film for thin film solar cells. The process involves applying a pre-mixed liquid coating composition containing Group IIB and Group VIA ionic species onto a preheated substrate. Heat from the substrate causes a heterogeneous reaction between the Group IIB and VIA ionic species of the liquid coating composition, thus forming a solid reaction product film on the substrate surface.

McCandless, Brian E. (243 W. Main St., Elkton, MD 21921); Shafarman, William N. (1905 N. Van Buren St., Wilmington, DE 19802)

2003-03-25

329

Dielectric Breakdown Lightning Model  

NSDL National Science Digital Library

The Dielectric Breakdown Lightning Model implements a common method for modeling lightning using a grid with regions of varying electric potential to simulate the electrical charge buildup during a lightning storm. To simulate the source of the lightning in the cloud, we set the potential to zero and place a small region of negative charge near the top of the grid. Along the bottom of the grid, we set the boundary potential to one to simulate the positive charge on the ground. All other grid points are given an initial electric potential equal to 0.5. After solving Laplace's equation, we examine all the grid points that are adjacent to a negative charge. We choose one adjacent point as the new growth site for the lightning, representing a point where the air is ionized and lightning will develop. The Dielectric Breakdown Lightning Model was developed as a final project in a sophomore-level Computational Physics course (Phy 200) using the Easy Java Simulations (EJS) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the jar file will run the program if Java is installed. You can modify this simulation if you have EJS installed by right-clicking within the map and selecting "Open Ejs Model" from the pop-up menu item.

Castle, Sam

2012-06-16

330

Dielectric Composites for Naval Applications  

NASA Astrophysics Data System (ADS)

As an integral part of the U.S. Navy's all-electric ship effort, the Naval Research Laboratory (NRL) has been developing advanced dielectrics to provide viable solutions for high energy density capacitors as well as high-dielectric-constant (K) filter capacitors. Our group at NRL has focused on ceramic and ceramic-based composite dielectrics, which are characterized by the high dielectric constant (from 200 to 4000) relative to polymer materials (typically <5) and high breakdown strengths (>200 kV/cm). This article details three approaches to creating high energy density and high-K-filter capacitor materials. These approaches use different processing routes to produce ceramic-based composite dielectrics and include freeze-casting, glass-ceramic, and nanocomposite technologies.

Gorzkowski, E. P.; Pan, M.-J.

2013-12-01

331

Dielectric Actuation of Polymers  

NASA Astrophysics Data System (ADS)

Dielectric polymers are widely used in a plurality of applications, such as electrical insulation, dielectric capacitors, and electromechanical actuators. Dielectric polymers with large strain deformations under an electric field are named dielectric elastomers (DE), because of their relative low modulus, high elongation at break, and outstanding resilience. Dielectric elastomer actuators (DEA) are superior to traditional transducers as a muscle-like technology: large strains, high energy densities, high coupling efficiency, quiet operation, and light weight. One focus of this dissertation is on the design of DE materials with high performance and easy processing. UV radiation curing of reactive species is studied as a generic synthesis methodology to provide a platform for material scientists to customize their own DE materials. Oligomers/monomers, crosslinkers, and other additives are mixed and cured at appropriate ratios to control the stress-strain response, suppress electromechanical instability of the resulting polymers, and provide stable actuation strains larger than 100% and energy densities higher than 1 J/g. The processing is largely simplified in the new material system by removal of the prestretching step. Multilayer stack actuators with 11% linear strain are demonstrated in a procedure fully compatible with industrial production. A multifunctional DE derivative material, bistable electroactive polymer (BSEP), is invented enabling repeatable rigid-to-rigid deformation without bulky external structures. Bistable actuation allows the polymer actuator to have two distinct states that can support external load without device failure. Plasticizers are used to lower the glass transition temperature to 45 C. Interpenetrating polymer network structure is established inside the BSEP to suppress electromechanical instability, providing a breakdown field of 194 MV/m and a stable bistable strain as large as 228% with a 97% strain fixity. The application of BSEP in tactile display is investigated by the prototyping of a large scale refreshable Braille display device. Braille is a critical way for the vision impaired community to learn literacy and improve life quality. Current piezoelectrics-based refreshable Braille display technologies are limited to up to 1 line of Braille text, due to the bulky size of bimorph actuators. Based on the unique actuation feature of BSEP, refreshable Braille display devices up to smartphone-size have been demonstrated by polymer sheet laminates. Dots in the devices can be individually controlled via incorporated field-driven BSEP actuators and Joule heater units. A composite material consisting of silver nanowires (AgNW) embedded in a polymer substrate is brought up as a compliant electrode candidate for BSEP application. The AgNW composite is highly conductive (Rs: 10 ?/sq) and remains conductive at strains as high as 140% (Rs: <10 3 ?/sq). The baseline conductivity has only small changes up to 90% strain, which makes it low enough for both field driving and stretchable Joule heating. An out-of-plane bistable area strain up to 68% under Joule heating is achieved.

Niu, Xiaofan

332

An electrode-free method of characterizing the microwave dielectric properties of high-permittivity thin films  

NASA Astrophysics Data System (ADS)

A thin dielectric resonator consisting of a dielectric substrate and the thin film deposited upon it is shown to suffice for microwave characterization and dielectric parameter measurement of high-permittivity thin films without electrodes. The TE01? resonance mode was excited and measured in thin (down to 0.1 mm) rectangular- or disk-shaped low-loss dielectric substrates (D 10 mm) with permittivity ?'?10 inserted into a cylindrical shielding cavity or rectangular waveguide. The in-plane dielectric permittivity and losses of alumina, DyScO3, SmScO3, and (LaAlO3)0.29(SrAl1/2Ta1/2O3)0.71 (LSAT) substrates were measured from 10 to 18 GHz. The substrate thickness optimal for characterization of the overlying thin film was determined as a function of the substrate permittivity. The high sensitivity and efficiency of the method, i.e., of a thin dielectric resonator to the dielectric parameters of an overlying film, was demonstrated by characterizing ultrathin strained EuTiO3 films. A 22 nm thick EuTiO3 film grown on a (100) LSAT substrate and strained in biaxial compression by 0.9% exhibited an increase in microwave permittivity at low temperatures consistent with it being an incipient ferroelectric; no strain-induced ferroelectric phase transition was seen. In contrast, a 100 nm thick EuTiO3 film grown on a (110) DyScO3 substrate and strained in biaxial tension by 1% showed two peaks as a function of temperature in microwave permittivity and loss. These peaks correspond to a strain-induced ferroelectric phase transition near 250 K and to domain wall motion.

Bovtun, V.; Pashkov, V.; Kempa, M.; Kamba, S.; Eremenko, A.; Molchanov, V.; Poplavko, Y.; Yakymenko, Y.; Lee, J. H.; Schlom, D. G.

2011-01-01

333

Ultra-thin, light-trapping silicon solar cells  

NASA Technical Reports Server (NTRS)

Design concepts for ultra-thin (2 to 10 microns) high efficiency single-crystal silicon cells are discussed. Light trapping allows more light to be absorbed at a given thickness, or allows thinner cells of a given Jsc. Extremely thin cells require low surface recombination velocity at both surfaces, including the ohmic contacts. Reduction of surface recombination by growth of heterojunctions of ZnS and GaP on Si has been demonstrated. The effects of these improvements on AM0 efficiency is shown. The peak efficiency increases, and the optimum thickness decreases. Cells under 10 microns thickness can retain almost optimum power. The increase of absorptance due to light trapping is considered. This is not a problem if the light-trapping cells are sufficiently thin. Ultra-thin cells have high radiation tolerance. A 2 microns thick light-trapping cell remains over 18 percent efficient after the equivalent of 20 years in geosynchronous orbit. Including a 50 microns thick coverglass, the thin cells had specific power after irradiation over ten times higher than the baseline design.

Landis, Geoffrey A.

1989-01-01

334

Weak anti-localization in ultrathin Sb(111) films  

NASA Astrophysics Data System (ADS)

We report the first studies of localization in ultrathin Sb films. Sb is a topological semi-metal with a negative bandgap of 180meV, however it is anticipated that in ultra-thin films, quantum confinement will open the bulk gap, such that transport is dominated by the topological surface states. We have studied the magneto-transport of nominally 4.5nm thick films of Sb(111) grown via molecular beam epitaxy at a temperature of 300C on nearly lattice matched epilayers. The longitudinal resistance shows positive magneto-resistance, well described by the standard weak anti-localization (WAL) theory of Hikami, Larkin and Nagaoka. The WAL response is consistent with that of a single conducting channel with a phase breaking length of 200nm at 1.8K. Scanning electron microscopy shows that the Sb growth proceeded by a Volmer-Weber (islanding) process resulting in disordered films. More recent growths performed at lower temperature have yielded significantly less resistive, smoother and thinner films for which transport measurements are ongoing.

Cairns, S.; McGlohon, N.; Robison, C.; Keay, J.; Gaspe, C. K.; Wickramasinghe, K. S.; Mishima, T. D.; Santos, M. B.; Murphy, S. Q.

2013-03-01

335

Optical properties of magnetically doped ultrathin topological insulator slabs  

NASA Astrophysics Data System (ADS)

Starting from a three-dimensional Hamiltonian, we study the optical properties of ultrathin topological insulator slabs for which the coupling between Dirac fermions on opposite surfaces results in two degenerated gapped hyperbolic bands. The gap is a threshold for the optical absorption and translates in a peak in the imaginary part of the optical conductivity. An exchange field applied perpendicular to the slab splits the degenerated hyperbolic bands and a double step structure comes out in the optical absorption, whereas a double peak structure appears in the imaginary part of the longitudinal optical conductivity. The exchange field breaks time-reversal symmetry and for exchange fields larger than the surfaces coupling gap, the zero frequency Hall conductivity is quantized to e2/h. This result implies large values of the Kerr rotation angle and a quantization of the Faraday angle. In ultrathin slabs, the absence of light multiple scattering and bulk conductivity makes the Kerr angle remain rather large in a wide range of frequencies.

Lasia, Martha; Brey, Luis

2014-08-01

336

Supersonically blown ultrathin thorny devil nanofibers for efficient air cooling.  

PubMed

The effect of the supersonically blown below-74 nm nanofibers on cooling of high-temperature surfaces is studied experimentally and theoretically. The ultrathin supersonically blown nanofibers were deposited and then copper-plated, while their surfaces resembled those of the thorny-devil nanofibers. Here, we study for the first time the enhancement of surface cooling in gas in the cases of the forced and natural convection with the help of ultrathin thorny-devil nanofibers. These polymer core-metal shell nanofibers in nanometric scale possess a relatively high thickness of the metal shell and a high effective thermal conductivity, which facilitates heat transfer. The additional surface temperature reduction close to 5 C in the case of the forced convection in the impinging air jet and close to 17 C in the case of the natural convection was achieved. Correspondingly, an increase in the value of the heat transfer coefficient of about 41% in the forced convection, and about 20% in the natural convection was achieved due to the presence of the thorny devil electrospun and/or supersonically blown nanofibers. PMID:25017392

An, Seongpil; Lee, Changmin; Liou, Minho; Jo, Hong Seok; Park, Jung-Jae; Yarin, Alexander L; Yoon, Sam S

2014-08-27

337

The Calorimetric Glass Transition of Polystyrene Ultrathin Films  

NASA Astrophysics Data System (ADS)

The glass transition temperature (Tg) for nanoconfined materials have been widely studied since the early 1990s. For supported polystyrene ultrathin films, Tg differs from bulk value. Recent work has attributed nanoconstrained Tg effects to artifact. In this study, we attempted to resolve this controversy and measure Tg for single polystyrene ultrathin films using Flash DSC. Films have been prepared in two ways: spincast films placed on a layer of inert oil or grease and films directly spincast on the back of the calorimetric chip. For the films on oil or on grease, the 160 nm thick films show no Tg depression. On the other hand, thinner films on oil and on grease show a Tg depression which decreases with increasing cooling rate. The depression reverts to the bulk values over the course of a day at 160 ^oC due to dewetting and thickening. For directly spincast films, no Tg depression is observed, consistent with results from other nanocalorimetry work. Our results are consistent with literature results that Tg decreases with decreasing substrate surface energy, and they also demonstrate that the Tg depression observed is not due to degradation or to plasticization effects.

Gao, Siyang; Koh, Yung P.; Simon, Sindee S.

2013-03-01

338

Thickness dependence of elastic modulus and hardness of on-wafer low-k ultrathin polytetrafluoroethylene films  

SciTech Connect

Elastic modulus and hardness of on-wafer low-k dielectric polytetrafluoroethylene films in the thickness range of 48.1 to 1,141 nm have been investigated using the dynamic contact module (DCM) in a frequency-specific depth-sensing indentation. It was observed that, when the film thickness is less than 500 nm, both the modulus and hardness of the films decrease sharply as the thickness of the film increases. However, when the films are thicker than 500 nm, the modulus and hardness are practically independent of the film thickness, and equal to approximately 2.3 Pa and 58 MPa, respectively. These values are about 5 times of the values obtained from the corresponding bulk sample. The significant increase in mechanical strength is probably resulted from a molecular reorganization in thin/ultrathin polymer films, often observed in polymeric materials. The present findings suggest that the chemical-mechanical polishing (CMP) characteristics of polytetrafluoroethylene films are thickness dependent.

Wang, J.; Shi, F.G.; Nieh, T.G.; Zhao, B.; Brongo, M.R.; Qu, S.; Rosenmayer, T.

2000-03-17

339

Dielectric elastomer cantilever beam sensor  

NASA Astrophysics Data System (ADS)

Dielectric elastomer sensors are a recent type of mechanical sensors utilized to detect forces, pressures and deformations. The sensors have several advantages compared with traditional sensors including high elasticity, capacitive sensing and inexpensive fabrication. In this paper, a new sensing device for measuring small concentrated force is proposed. The device deploys the dielectric membrane on the surface of cantilever beam of constant strength. The dielectric membrane is a capacitance sensor built with dielectric polymer coated with soft electrodes. The change in strain arising from the cantilever beam with concentrated force at free end can be quickly transferred to the dielectric membrane. The strain variation of the dielectric membrane induces the change in the capacitance of the membrane. Tests on the device show that the concentrated force at the free end of the cantilever beam is approximately proportional to the change in the capacitance. According to the relation, the unknown concentrated force can be obtained accurately by measuring the change in the capacitance of the dielectric membrane. The new device is capable of monitoring small concentrated force with prominent sensitivity.

Ni, Na; Zhang, Ling; Zhou, Jinxiong; Wang, Yin; Liu, Fan

2014-03-01

340

Ultrathin multi-band planar metamaterial absorber based on standing wave resonances.  

PubMed

We present a planar waveguide model and a mechanism based on standing wave resonances to interpret the unity absorptions of ultrathin planar metamaterial absorbers. The analytical model predicts that the available absorption peaks of the absorber are corresponding to the fundamental mode and only its odd harmonic modes of the standing wave. The model is in good agreement with numerical simulation and can explain the main features observed in typical ultrathin planar metamaterial absorbers. Based on this model, ultrathin planar metamaterial absorbers with multi-band absorptions at desired frequencies can be easily designed. PMID:23262721

Peng, Xiao-Yu; Wang, Bing; Lai, Shumin; Zhang, Dao Hua; Teng, Jing-Hua

2012-12-01

341

Graphene-graphite oxide field-effect transistors.  

PubMed

Graphene's high mobility and two-dimensional nature make it an attractive material for field-effect transistors. Previous efforts in this area have used bulk gate dielectric materials such as SiO(2) or HfO(2). In contrast, we have studied the use of an ultrathin layered material, graphene's insulating analogue, graphite oxide. We have fabricated transistors comprising single or bilayer graphene channels, graphite oxide gate insulators, and metal top-gates. The graphite oxide layers show relatively minimal leakage at room temperature. The breakdown electric field of graphite oxide was found to be comparable to SiO(2), typically ~1-3 10(8) V/m, while its dielectric constant is slightly higher, ? ? 4.3. PMID:22380722

Standley, Brian; Mendez, Anthony; Schmidgall, Emma; Bockrath, Marc

2012-03-14

342

Thermo-switchable polymer dielectrics.  

SciTech Connect

We are interested in utilizing the thermo-switchable properties of precursor poly(p-phenylene vinylene) (PPV) polymers to develop capacitor dielectrics that will fail at specific temperatures due to the material irreversibly switching from an insulator to a conducting polymer. By utilizing different leaving groups on the polymer main chain, the temperature at which the polymer transforms into a conductor can be varied over a range of temperatures. Electrical characterization of thin-film capacitors prepared from several precursor PPV polymers indicates that these materials have good dielectric properties until they reach elevated temperatures, at which point conjugation of the polymer backbone effectively disables the device. Here, we present the synthesis, dielectric processing, and electrical characterization of a new thermo-switchable polymer dielectric.

Kholwadwala, Fenil Manish; Johnson, Ross Stefan; Dirk, Shawn M.

2010-11-01

343

Infrared cubic dielectric resonator metamaterial.  

SciTech Connect

Dielectric resonators are an effective means to realize isotropic, low-loss optical metamaterials. As proof of this concept, a cubic resonator is analytically designed and then tested in the long-wave infrared.

Sinclair, Michael B.; Brener, Igal; Peters, David William; Ginn, James Cleveland, III; Ten Eyck, Gregory A.

2010-06-01

344

Fractal Dimension of Dielectric Breakdown  

Microsoft Academic Search

It is shown that the simplest nontrivial stochastic model for dielectric breakdown naturally leads to fractal structures for the discharge pattern. Planar discharges are studied in detail and the results are compared with properly designed experiments.

L. Niemeyer; L. Pietronero; H. J. Wiesmann

1984-01-01

345

Unified theory for perfect absorption in ultrathin absorptive films with constant tangential electric or magnetic fields  

NASA Astrophysics Data System (ADS)

The maximal absorption rate of ultrathin films is 50% under the condition that the tangential electric (or magnetic) field is almost constant across the film in a symmetrical environment. However, with certain reflectors, the absorption rate can be greatly increased, even to perfect absorption (100%). In this paper, we explicitly derive the general conditions of the ultrathin absorptive film parameters to achieve perfect absorption with general types of reflectors under the condition that the tangential electric (or magnetic) field is almost constant across the film. We find that the parameters of the film can be classified into three groups, exhibiting (1) a large permittivity (permeability), (2) a near-zero permeability (permittivity), or (3) a suitable combination of permittivity and permeability, respectively. Interestingly, the latter two cases demonstrate extraordinary absorption in ultrathin films with almost vanishing losses. Our paper serves as a guide for designing ultrathin perfect absorbers with general types of reflectors.

Luo, Jie; Li, Sucheng; Hou, Bo; Lai, Yun

2014-10-01

346

Spontaneous emission in dielectric nanoparticles  

Microsoft Academic Search

An analytical expression is obtained for the radiative-decay rate of an excited optical center in an ellipsoidal dielectric\\u000a nanoparticle (with sizes much less than the wavelength) surrounded by a dielectric medium. It is found that the ratio of the\\u000a decay rate A\\u000a nano of an excited optical center in the nanoparticle to the decay rate A\\u000a bulk of an excited

K. K. Pukhov; T. T. Basiev; Yu. V. Orlovskii

2008-01-01

347

Reflected wavefront manipulation based on ultrathin planar acoustic metasurfaces  

PubMed Central

The introduction of metasurfaces has renewed the Snell's law and opened up new degrees of freedom to tailor the optical wavefront at will. Here, we theoretically demonstrate that the generalized Snell's law can be achieved for reflected acoustic waves based on ultrathin planar acoustic metasurfaces. The metasurfaces are constructed with eight units of a solid structure to provide discrete phase shifts covering the full 2? span with steps of ?/4 by coiling up the space. By careful selection of the phase profiles in the transverse direction of the metasurfaces, some fascinating wavefront engineering phenomena are demonstrated, such as anomalous reflections, conversion of propagating waves into surface waves, planar aberration-free lens and nondiffracting Bessel beam generated by planar acoustic axicon. Our results could open up a new avenue for acoustic wavefront engineering and manipulations. PMID:23986034

Li, Yong; Liang, Bin; Gu, Zhong-ming; Zou, Xin-ye; Cheng, Jian-chun

2013-01-01

348

Swelling and surface modification of ultrathin chitosan films  

NASA Astrophysics Data System (ADS)

Chitosan is a biodegradable polysaccharide derived from seashell waste products. The high water absorbency and biocompatibility of chitosan have enabled its use as a hydrogel in specialty biomedical applications. We present the results of several experiments focused on characterizing properties of ultrathin films of chitosan critical to their use in techniques such as wound dressings, medical implants and drug delivery systems. Uniform thin films with thicknesses of 15 to 600 nm and rms roughness of the order of 1 nm were prepared using techniques previously developed in our research group. The swelling of these films in the presence of high humidity has been characterized using reflection ellipsometry, atomic force microscopy and quartz crystal microbalance techniques. The effects of exposure to elevated temperature and UV/ozone (a common surface modification technique) on the surface properties such as hydrophobicity are described.

Murray, Chris

2005-03-01

349

Ultrathin nanostructured metals for highly transmissive plasmonic subtractive color filters.  

PubMed

Plasmonic color filters employing a single optically-thick nanostructured metal layer have recently generated considerable interest as an alternative to colorant-based color filtering technologies, due to their reliability, ease of fabrication, and high color tunability. However, their relatively low transmission efficiency (~30%) needs to be significantly improved for practical applications. The present work reports, for the first time, a novel plasmonic subtractive color filtering scheme that exploits the counter-intuitive phenomenon of extraordinary low transmission (ELT) through an ultrathin nanostructured metal film. This approach relies on a fundamentally different color filtering mechanism than that of existing plasmonic additive color filters, and achieves unusually high transmission efficiencies of 60 ~ 70% for simple architectures. Furthermore, owing to short-range interactions of surface plasmon polaritons at ELT resonances, our design offers high spatial resolution color filtering with compact pixel size close to the optical diffraction limit (~?/2), creating solid applications ranging from imaging sensors to color displays. PMID:24100869

Zeng, Beibei; Gao, Yongkang; Bartoli, Filbert J

2013-01-01

350

Ultrathin Nanostructured Metals for Highly Transmissive Plasmonic Subtractive Color Filters  

NASA Astrophysics Data System (ADS)

Plasmonic color filters employing a single optically-thick nanostructured metal layer have recently generated considerable interest as an alternative to colorant-based color filtering technologies, due to their reliability, ease of fabrication, and high color tunability. However, their relatively low transmission efficiency (~30%) needs to be significantly improved for practical applications. The present work reports, for the first time, a novel plasmonic subtractive color filtering scheme that exploits the counter-intuitive phenomenon of extraordinary low transmission (ELT) through an ultrathin nanostructured metal film. This approach relies on a fundamentally different color filtering mechanism than that of existing plasmonic additive color filters, and achieves unusually high transmission efficiencies of 60 ~ 70% for simple architectures. Furthermore, owing to short-range interactions of surface plasmon polaritons at ELT resonances, our design offers high spatial resolution color filtering with compact pixel size close to the optical diffraction limit (~?/2), creating solid applications ranging from imaging sensors to color displays.

Zeng, Beibei; Gao, Yongkang; Bartoli, Filbert J.

2013-10-01

351

Ultrathin broadband nearly perfect absorber with symmetrical coherent illumination.  

PubMed

As highlighted by recent articles [Phys. Rev. Lett. 105, 053901 (2010) and Science 331, 889-892 (2011)], the coherent control of narrowband perfect absorption in intrinsic silicon slab has attracted much attention. In this paper, we demonstrate that broadband coherent perfect absorber (CPA) can be achieved by heavily doping an ultrathin silicon film. Two distinct perfect absorption regimes are derived with extremely broad and moderately narrow bandwidth under symmetrical coherent illumination. The large enhancement of bandwidth may open up new avenues for broadband applications. Subsequently, interferometric method is used to control the absorption coherently with extremely large contrast between the maximum and minimum absorptance. Compared with the results in literatures, the thin film CPAs proposed here show much more flexibility in both operation frequency and bandwidth. PMID:22330464

Pu, Mingbo; Feng, Qin; Wang, Min; Hu, Chenggang; Huang, Cheng; Ma, Xiaoliang; Zhao, Zeyu; Wang, Changtao; Luo, Xiangang

2012-01-30

352

Dendrimer-mediated hydrothermal synthesis of ultrathin gold nanowires  

NASA Astrophysics Data System (ADS)

We report the use of poly(amidoamine) dendrimers as stabilizers to synthesize ultrathin Au nanowires (NWs) with a diameter of 1.3 nm via a hydrothermal approach. The formation of uniform Au NWs was optimized by varying the Au/Ag salt molar ratio, dendrimer stabilizers, and reaction solvent, temperature, and time. A novel growth mechanism involving a synergic facet-dependent deposition/reduction of Ag(I) and oriented migration of Au atoms is proposed based on density functional theory calculations and the experimental results. This work can significantly expand the scope of dendrimers as stabilizers to generate metal NWs in aqueous solution that may be further functionalized for different applications.

Liu, Hui; Cao, Xiaoming; Yang, Jianmao; Gong, Xue-Qing; Shi, Xiangyang

2013-11-01

353

Ultrathin Nanostructured Metals for Highly Transmissive Plasmonic Subtractive Color Filters  

PubMed Central

Plasmonic color filters employing a single optically-thick nanostructured metal layer have recently generated considerable interest as an alternative to colorant-based color filtering technologies, due to their reliability, ease of fabrication, and high color tunability. However, their relatively low transmission efficiency (~30%) needs to be significantly improved for practical applications. The present work reports, for the first time, a novel plasmonic subtractive color filtering scheme that exploits the counter-intuitive phenomenon of extraordinary low transmission (ELT) through an ultrathin nanostructured metal film. This approach relies on a fundamentally different color filtering mechanism than that of existing plasmonic additive color filters, and achieves unusually high transmission efficiencies of 60 ~ 70% for simple architectures. Furthermore, owing to short-range interactions of surface plasmon polaritons at ELT resonances, our design offers high spatial resolution color filtering with compact pixel size close to the optical diffraction limit (~?/2), creating solid applications ranging from imaging sensors to color displays. PMID:24100869

Zeng, Beibei; Gao, Yongkang; Bartoli, Filbert J.

2013-01-01

354

A novel ultrathin and broadband microwave metamaterial absorber  

NASA Astrophysics Data System (ADS)

In this paper, the design, simulation, fabrication, and measurement of an ultrathin and broadband microwave metamaterial absorber (MMA) based on a double-layer structure are presented. Compared with the prior work, our structure is simple and polarization insensitive. The broadband MMA presents good absorption above 90% between 8.85 GHz and 14.17 GHz, with a full width at half maximum (FWHM) absorption bandwidth of 6.77 GHz and a relative FWHM absorption bandwidth of 57.3%. Moreover, the structure has a thickness of 1.60 mm (only ?/20 at the lowest frequencies). The experimental results show excellent absorption rates which are in good correspondence with the simulated results. The broadband absorber is promising candidates as absorbing elements in scientific and technical applications because of its broadband absorption and polarization insensitive.

Wang, Bei-Yin; Liu, Shao-Bin; Bian, Bo-Rui; Mao, Zhi-Wen; Liu, Xiao-Chun; Ma, Ben; Chen, Lin

2014-09-01

355

Dendrimer-mediated hydrothermal synthesis of ultrathin gold nanowires  

PubMed Central

We report the use of poly(amidoamine) dendrimers as stabilizers to synthesize ultrathin Au nanowires (NWs) with a diameter of 1.3?nm via a hydrothermal approach. The formation of uniform Au NWs was optimized by varying the Au/Ag salt molar ratio, dendrimer stabilizers, and reaction solvent, temperature, and time. A novel growth mechanism involving a synergic facet-dependent deposition/reduction of Ag(I) and oriented migration of Au atoms is proposed based on density functional theory calculations and the experimental results. This work can significantly expand the scope of dendrimers as stabilizers to generate metal NWs in aqueous solution that may be further functionalized for different applications. PMID:24212329

Liu, Hui; Cao, Xiaoming; Yang, Jianmao; Gong, Xue-Qing; Shi, Xiangyang

2013-01-01

356

Electronic and magnetic properties of ultrathin Au/Pt nanowires.  

PubMed

We have reported the synthesis of Au(25)Pt(75) and Au(48)Pt(52) alloyed ultrathin nanowires with average widths of less than 3 nm via a wet chemistry approach at room temperature. Using a combination of techniques, including scanning transmission electron microscopy equipped with X-ray energy dispersive spectroscopy, ultraviolet-visible spectroscopy, and X-ray absorption near-edge structure and extended X-ray absorption fine structure spectroscopies, we identified the stoichiometry-dependent heterogeneous crystalline structures, as well as electronic structures with respect to the charge transfer between Pt and Au within both nanowires. In particular, we observed d-charge depletion at the Au site and the d-charge gain at the Pt site in Au(48)Pt(52) nanowires, which accounted for its ferromagnetic magnetic behavior, in contrast to the paramagnetism and diamagnetism appearing respectively in bulk Pt and Au. PMID:19645434

Teng, Xiaowei; Feygenson, Mikhail; Wang, Qi; He, Jiaqing; Du, Wenxin; Frenkel, Anatoly I; Han, Weiqiang; Aronson, Meigan

2009-09-01

357

Electronic and Magnetic Properties of Ultrathin Au/Pt Nanowires  

SciTech Connect

We have reported the synthesis of Au25Pt75 and Au48Pt52 alloyed ultrathin nanowires with average widths of less than 3 nm via a wet chemistry approach at room temperature. Using a combination of techniques, including scanning transmission electron microscopy equipped with X-ray energy dispersive spectroscopy, ultraviolet-visible spectroscopy, and X-ray absorption near-edge structure and extended X-ray absorption fine structure spectroscopies, we identified the stoichiometry-dependent heterogeneous crystalline structures, as well as electronic structures with respect to the charge transfer between Pt and Au within both nanowires. In particular, we observed d-charge depletion at the Au site and the d-charge gain at the Pt site in Au48Pt52 nanowires, which accounted for its ferromagnetic magnetic behavior, in contrast to the paramagnetism and diamagnetism appearing respectively in bulk Pt and Au.

Teng, X.; Feygenson, M; Wang, Q; He, J; Du, W; Frenkel, A; Han, W; Aronson, M

2009-01-01

358

Competing weak localization and weak antilocalization in ultrathin topological insulators  

NASA Astrophysics Data System (ADS)

We demonstrate the evidences of a surface gap opening in (Bi0.57Sb0.43)2Te3 samples for film thickness below 6 quintuple layers, through magnetotransport and scanning tunneling spectroscopy measurements. By tuning Fermi level position relative to the gap, the striking crossover between weak antilocalization and weak localization is observed in nonmagnetic 4 and 5 QL films at low field region, a characteristic feature of quantum interferences competition, possibly owing to the change of net Berry phase. Furthermore, when the Fermi level is swept into the surface gap, the overall unitary behaviors are revealed at higher magnetic field, which are in contrast to the pure WAL signals obtained in thicker films. Besides, the surface bandgap of ultrathin film is also determined by low temperature STS measurements. Our findings show an exotic phenomenon characterizing the gapped TI surface states and point to the future realization of quantum spin Hall effect and dissipationless TI-based applications.

Lang, Murong; He, Liang; Kou, Xufeng; Upadhyaya, Pramey; Fan, Yabin; Chu, Hao; Yeh, Nai-Chang; Wang, Kang

2013-03-01

359

Crossover behavior in hydrogen sensing mechanism for palladium ultrathin films.  

SciTech Connect

Palladium has been extensively studied as a material for hydrogen sensors because of the simplicity of its reversible resistance change when exposed to hydrogen gas. Various palladium films and nanostructures have been used, and different responses have been observed with these diverse morphologies. In some cases, such as with nanowires, the resistance will decrease, whereas in others, such as with thick films, the resistance will increase. Each of these mechanisms has been explored for several palladium structures, but the crossover between them has not been systematically investigated. Here we report on a study aimed at deciphering the nanostructure-property relationships of ultrathin palladium films used as hydrogen gas sensors. The crossover in these films is observed at a thickness of {approx} 5 nm. Ramifications for future sensor developments are discussed.

Darling, S. B.; Ramanathan, M.; Skudlarek, G.; Wang, H. H.; Illinois Math and Science Academy

2010-01-01

360

Glass transition in Ultrathin Polymer Films : A Thermal Expansion Study  

E-print Network

Glass transition process gets affected in ultrathin films having thickness comparable to the size of the molecules. We observe systematic broadening of glass transition temperature (Tg) as the thickness of the polymer film reduces below the radius of gyration but the change in the average Tg was found to be very small. Existence of reversible negative and positive thermal expansion below and above Tg increased the sensitivity of our thickness measurements performed using energy dispersive x-ray reflectivity. A simple model of Tg variation as a function of depth expected from sliding motion could explain the results. We observe clear glass transition even for 4 nm polystyrene film that was predicted to be absent from ellipsometry measurements of thicker films.

M. Bhattacharya; M. K. Sanyal; Th. Geue; U. Pietsch

2005-01-19

361

Colloidal synthesis of ultrathin two-dimensional semiconductor nanocrystals.  

PubMed

2D semiconductor quantum wells have been recognized as potential candidates for various quantum devices. In quantum wells, electrons and holes are spatially confined within a finite thickness and freely move in 2D space. Much effort has focused on shape control of colloidal semiconductor nanocrystals(NCs), and synthesis of 2D colloidal NCs has been achieved very recently. Here, recent advances in colloidal synthesis of uniform and ultrathin 2D CdSeNCs are highlighted. Structural and optical property characterization of these quantum-sized 2D CdSe NCs is discussed. Additionally, 2D CdSe NCs doped with Mn 2+ ions for dilute magnetic semiconductors (DMS) are presented.These 2D CdSe-based NCs can be used as model systems for studying quantum-well structures. PMID:21894625

Son, Jae Sung; Yu, Jung Ho; Kwon, Soon Gu; Lee, Jihwa; Joo, Jin; Hyeon, Taeghwan

2011-07-26

362

Unidirectional phase singularity in ultrathin metamaterials at exceptional points  

NASA Astrophysics Data System (ADS)

Scattering properties of light in metamaterials are similar to those in open quantum systems. Here we propose an ultrathin tailored metamaterial designed to show that one-way zero reflection yielding to topologically stable phase dislocation is responsible for the exceptional point, one of the most important degeneracies in the non-Hermitian Hamiltonian. In order to bridge the exotic macroscopic optical phenomenon occurring in metamaterials, a phenomenological model under microscopic view is developed and good agreement with the full-blown numerical simulation is found. Our investigation uncovers the capabilities of metamaterials to exhibit extreme optical properties and to provide us with many potential applications such as the suppression of undesired scattering signals in the spectral band ranging from microwaves to visible light.

Kang, Ming; Cui, Hai-Xu; Li, Teng-Fei; Chen, Jing; Zhu, Weiren; Premaratne, Malin

2014-06-01

363

Selective and efficient electrochemical biosensing of ultrathin molybdenum disulfide sheets  

NASA Astrophysics Data System (ADS)

Atomically thin molybdenum disulfide (MoS2) sheets were synthesized and isolated via solvent-assisted chemical exfoliation. The charge-dependent electrochemical activities of these MoS2 sheets were studied using positively charged hexamine ruthenium (III) chloride and negatively charged ferricyanide/ferrocyanide redox probes. Ultrathin MoS2 sheet-based electrodes were employed for the electrochemical detection of an important neurotransmitter, namely dopamine (DA), in the presence of ascorbic acid (AA). MoS2 electrodes were identified as being capable of distinguishing the coexistence of the DA and the AA with an excellent stability. Moreover, the enzymatic detection of the glucose was studied by immobilizing glucose oxidase on the MoS2. This study opens enzymatic and non-enzymatic electrochemical biosensing applications of atomic MoS2 sheets, which will supplement their established electronic applications.

Narayanan, Tharangattu N.; Vusa, Chiranjeevi S. R.; Alwarappan, Subbiah

2014-08-01

364

Dielectric and permeability  

NASA Technical Reports Server (NTRS)

Using the unabridged Maxwell equations (including vectors D, E and H) new effects in collisionless plasmas are uncovered. In a steady state, it is found that spatially varying energy density of the electric field (E perpendicular) orthogonal to B produces electric current leading, under certain conditions, to the relationship P perpendicular+B(2)/8 pi-epsilon E perpendicular(2)/8 pi = constant, where epsilon is the dielectric constant of the plasma for fields orthogonal to B. In steady state quasi-two-dimensional flows in plasmas, a general relationship between the components of electric field parallel and perpendicular to B is found. These effects are significant in goephysical and astrophysical plasmas. The general conditions for a steady state in collisionless plasma are deduced. With time variations in a plasma, slow compared to ion-gyroperiod, there is a general current, (j*), which includes the well-known polarisation current, given by J*=d/dt (ExM)+(PxB)xB B(-2) where M and P are the magnetization and polarization vectors respectively.

Cole, K. D.

1982-01-01

365

Metal-dielectric interactions  

NASA Technical Reports Server (NTRS)

Metal direlectric surface interactions and dielectric films on metal substrates were investigated. Since interfacial interaction depends so heavily on the nature of the surfaces, analytical surface tools such as Auger emission spectroscopy, X-ray photoelectron spectroscopy and field ion microscopy were used to assist in surface and interfacial characterization. The results indicate that with metals contacting certain glasses in the clean state interfacial, bonding produces fractures in the glasses while when a film such as water is present, fractures occur in the metal near the interface. Friction forces were used to measure the interfacial bond strengths. Studies with metals contacting polymers using field ion microscopy revealed that strong bonding forces could develop being between a metal and polymer surface with polymer transferring to the metal surface in various ways depending upon the forces applied to the surface in contact. With the deposition of refractory carbides, silicides and borides onto metal and alloy substrates the presence of oxides at the interface or active gases in the deposition plasma were shown to alter interfacial properties and chemistry. Auger ion depth profile analysis indicated the chemical composition at the interface and this could be related to the mechanical, friction, and wear behavior of the coating.

Buckley, D. H.

1979-01-01

366

PHYSICAL REVIEW B 83, 195305 (2011) Enhanced spin relaxation in an ultrathin metal film by the Rashba-type surface  

E-print Network

PHYSICAL REVIEW B 83, 195305 (2011) Enhanced spin relaxation in an ultrathin metal film/Ag-terminated ultrathin Ag(111) films by the micro-four-point probe method as a function of the applied magnetic field in the ultrathin film significantly. DOI: 10.1103/PhysRevB.83.195305 PACS number(s): 73.63.Hs, 72.15.Rn, 79.60.-i

Hasegawa, Shuji

367

Dielectric behaviors and high energy storage density of nanocomposites with core-shell BaTiO3@TiO2 in poly(vinylidene fluoride-hexafluoropropylene).  

PubMed

Nanocomposites comprising a P(VDF-HFP) polymer matrix and core-shell structured nanoparticle fillers were prepared, in which a crystalline, ultrathin TiO2 shell layer encapsulates BaTiO3 nanoparticles. A large dielectric constant (>110) was obtained, which was unexpectedly more than 3 times higher than that of the nanocomposite without the TiO2 shell layer. The significant improvement in electric polarization is attributed to the highly interactive interfaces among the multiple dielectric materials with the introduction of the intermediate TiO2 layer, which also improves the breakdown field (>340 MV m(-1)). Thus a resulting dielectric energy density of 12.2 J cm(-3) is achieved, among the highest energy densities for polymer-ceramic composites. PMID:23999532

Rahimabady, Mojtaba; Mirshekarloo, Meysam Sharifzadeh; Yao, Kui; Lu, Li

2013-10-14

368

Elastomer dielectric for pulse power  

SciTech Connect

Selected elastomer dielectrics are characterized as high-voltage insulators for use in pulse power systems. Silicone, ethylene-propylene rubber and polyurethene were tested, but most of the data is for silicone. The particular power system developed uses a formed silicone insulator 76 cm in dia. and 3 mm thick as the major insulator between capacitors, railgap switches, load, and return conductor. The capacitor array is dc charged to 50 kV, and has an on-load current risetime of 5 x 10/sup 12/ A/s and 1 Ma peak current. The results showed that the use of an elastomer dielectric made possible the construction of a pulser one order of magnitude smaller than previously constructed pulsers having the same current characteristics. Also, use of the elastomer dielectrics in pulse power systems leads to improved production techniques and system reliability. (LCL)

Bradley, L.P.; Orham, E.L.; Stowers, I.F.; Braucht, J.R.

1980-05-30

369

Study of transport properties in graphene monolayer flakes on SiO[sub 2] substrates  

E-print Network

We investigate the carrier mobility in monolayer and bilayer graphene with a top HfO2dielectric, as a function of the HfO2film thickness and temperature. The results show that the carrier mobility decreases during the ...

Tirado, J. M.

370

Dielectric characterization of unstabilized aggregate base materials  

E-print Network

investigates the correlation of dielectric values obtained using the dielectric probe in the laboratory with those calculated from GPR measurements of granular base materials beneath different pavement surfaces in field conditions. The influence of the type...

Guthrie, William Spencer

2012-06-07

371

Electric and Magnetic Walls on Dielectric Interfaces  

E-print Network

Sufficient conditions of the existence of electric or magnetic walls on dielectric interfaces are given for a multizone uniform dielectric waveguiding system. If one of two adjacent dielectric zones supports a TEM field distribution while the other supports a TM (TE) field distribution, then the common dielectric interface behaves as an electric (magnetic) wall, that is, the electric (magnetic) field line is perpendicular to the interface while the magnetic (electric) field line is parallel to the interface.

Changbiao Wang

2010-07-20

372

First-principles study of structural, vibrational, and lattice dielectric properties of hafnium oxide Xinyuan Zhao and David Vanderbilt  

E-print Network

, Piscataway, New Jersey 08854-8019 Received 25 February 2002; published 13 June 2002 Crystalline structures-wave basis. The structures of low-pressure HfO2 polymorphs are carefully studied with both the local agreement. After calculating the Born effective charge tensors and the force-constant matrices by finite

Vanderbilt, David

373

Quantum dots formed by ultrathin insertions in wide-gap matrices N.N. Ledentsova,1,*, I.L. Krestnikov1a  

E-print Network

Quantum dots formed by ultrathin insertions in wide-gap matrices N.N. Ledentsova,1,*, I on experimental and theoretical studies on a new type of quantum-dot (QD) structures obtained using ultrathin, i: Semiconductor low-dimensional structures; Quantum dots; Ultrathin-layer insertions in wide-gap semiconductors 1

Nabben, Reinhard

374

Cellulose Triacetate Dielectric Films For Capacitors  

NASA Technical Reports Server (NTRS)

Cellulose triacetate investigated for use as dielectric material in high-energy-density capacitors for pulsed-electrical-power systems. Films of cellulose triacetate metalized on one or both sides for use as substrates for electrodes and/or as dielectrics between electrodes in capacitors. Used without metalization as simple dielectric films. Advantages include high breakdown strength and self-healing capability.

Yen, Shiao-Ping S.; Jow, T. Richard

1994-01-01

375

Dielectric elastomers of interpenetrating networks Zhigang Suoa  

E-print Network

Dielectric elastomers of interpenetrating networks Zhigang Suoa and Jian Zhu School of Engineering. doi:10.1063/1.3272685 Subject to an electric field, a membrane of a dielectric elastomer reduces of the dielectric elastomer is under- stood in terms of three quantities: the modulus , the permit- tivity

Suo, Zhigang

376

Dielectric investigation of some woven fabrics  

Microsoft Academic Search

In this paper, we have investigated the temperature dependence of dielectric properties (relative dielectric permeabilities and dielectric tangents of losses) for woven fabrics of hemp, jute, flax, cotton, polyester (PES), cotton-PES mixture, and wool. The measurements have been carried out at a temperature range from -50 to 50 C in the electric periodic field at a frequency 1 MHz in

Dragana D. Cerovic; Jablan R. Dojcilovic; Koviljka A. Asanovic; Tatjana A. Mihajlidi

2009-01-01

377

Dielectric investigation of some woven fabrics  

Microsoft Academic Search

In this paper, we have investigated the temperature dependence of dielectric properties (relative dielectric permeabilities and dielectric tangents of losses) for woven fabrics of hemp, jute, flax, cotton, polyester (PES), cotton-PES mixture, and wool. The measurements have been carried out at a temperature range from ?50 to 50 C in the electric periodic field at a frequency 1 MHz in

Dragana D. Cerovic; Jablan R. Dojcilovic; Koviljka A. Asanovic; Tatjana A. Mihajlidi

2009-01-01

378

Linearly tapered slot antenna with dielectric superstrate  

NASA Technical Reports Server (NTRS)

The effect of dielectric superstrate on a linearly tapered slot antenna (LTSA) was investigated experimentally. It was observed that the dielectric superstrate improves the directivity but generally at the expense of higher sidelobe level. The dielectric superstrate could be used to reduce the physical length and to improve the radiation characteristics of the LTSA.

Simons, Rainee N.; Lee, Richard Q.

1993-01-01

379

Ultra-thin solid oxide fuel cells: Materials and devices  

NASA Astrophysics Data System (ADS)

Solid oxide fuel cells are electrochemical energy conversion devices utilizing solid electrolytes transporting O2- that typically operate in the 800 -- 1000 C temperature range due to the large activation barrier for ionic transport. Reducing electrolyte thickness or increasing ionic conductivity can enable lower temperature operation for both stationary and portable applications. This thesis is focused on the fabrication of free standing ultrathin (<100 nm) oxide membranes of prototypical O 2- conducting electrolytes, namely Y2O3-doped ZrO2 and Gd2O3-doped CeO2. Fabrication of such membranes requires an understanding of thin plate mechanics coupled with controllable thin film deposition processes. Integration of free standing membranes into proof-of-concept fuel cell devices necessitates ideal electrode assemblies as well as creative processing schemes to experimentally test devices in a high temperature dual environment chamber. We present a simple elastic model to determine stable buckling configurations for free standing oxide membranes. This guides the experimental methodology for Y 2O3-doped ZrO2 film processing, which enables tunable internal stress in the films. Using these criteria, we fabricate robust Y2O3-doped ZrO2 membranes on Si and composite polymeric substrates by semiconductor and micro-machining processes, respectively. Fuel cell devices integrating these membranes with metallic electrodes are demonstrated to operate in the 300 -- 500 C range, exhibiting record performance at such temperatures. A model combining physical transport of electronic carriers in an insulating film and electrochemical aspects of transport is developed to determine the limits of performance enhancement expected via electrolyte thickness reduction. Free standing oxide heterostructures, i.e. electrolyte membrane and oxide electrodes, are demonstrated. Lastly, using Y2O3-doped ZrO2 and Gd2O 3-doped CeO2, novel electrolyte fabrication schemes are explored to develop oxide alloys and nanoscale compositionally graded membranes that are thermomechanically robust and provide added interfacial functionality. The work in this thesis advances experimental state-of-the-art with respect to solid oxide fuel cell operation temperature, provides fundamental boundaries expected for ultrathin electrolytes, develops the ability to integrate highly dissimilar material (such as oxide-polymer) heterostructures, and introduces nanoscale compositionally graded electrolyte membranes that can lead to monolithic materials having multiple functionalities.

Kerman, Kian

380

Pyroelectricity in alternating ultrathin organized molecular films incorporating barium ions  

NASA Astrophysics Data System (ADS)

Pyroelectric properties in alternating DAEP/NC Langmuir-Blodgett (LB) films and effects of incorporating the barium cations on pyroelectric behaviors have been investigated. Its pyroelectric coefficient measured is found to be 58?C m-2 K-1at 300K. The dielectric properties have been measured and used to determine the figures of merit in thermal devices. Relative permittivity ?r and dielectric loss values tan? of pyroelectric films (in the range of 1KHz - 100KHz) are 2.34~1.96 and 0.08~0.04, respectively. These data give a maximum pyroelectric figure of merit of 150?C m-2 K-1 in the alternating LB films incorporating barium ions. The effects of different deposition on pyroelectric properties are also discussed in this paper. It is indicated that the alternating LB films is promising in the field of pyroelectricity and pyroelectric infrared detector.

Ma, Shihong; Li, Shuhong; Lu, Xingze; Wang, Wencheng; Wang, Genshui; Liu, Pulin; Guo, Shaoling; Chu, Junhao

2002-12-01

381

Ultrathin Nickel Hydroxide and Oxide Nanosheets: Synthesis, Characterizations and Excellent Supercapacitor Performances  

NASA Astrophysics Data System (ADS)

High-quality ultrathin two-dimensional nanosheets of ?-Ni(OH)2 are synthesized at large scale via microwave-assisted liquid-phase growth under low-temperature atmospheric conditions. After heat treatment, non-layered NiO nanosheets are obtained while maintaining their original frame structure. The well-defined and freestanding nanosheets exhibit a micron-sized planar area and ultrathin thickness (<2 nm), suggesting an ultrahigh surface atom ratio with unique surface and electronic structure. The ultrathin 2D nanostructure can make most atoms exposed outside with high activity thus facilitate the surface-dependent electrochemical reaction processes. The ultrathin ?-Ni(OH)2 and NiO nanosheets exhibit enhanced supercapacitor performances. Particularly, the ?-Ni(OH)2 nanosheets exhibit a maximum specific capacitance of 4172.5 F g-1 at a current density of 1 A g-1. Even at higher rate of 16 A g-1, the specific capacitance is still maintained at 2680 F g-1 with 98.5% retention after 2000 cycles. Even more important, we develop a facile and scalable method to produce high-quality ultrathin transition metal hydroxide and oxide nanosheets and make a possibility in commercial applications.

Zhu, Youqi; Cao, Chuanbao; Tao, Shi; Chu, Wangsheng; Wu, Ziyu; Li, Yadong

2014-08-01

382

Ultrathin InAs nanowire growth by spontaneous Au nanoparticle spreading on indium-rich surfaces.  

PubMed

Ultrathin InAs nanowires (NWs) can enable true one-dimensional electronics. We report a growth phenomenon where a bimodal size distribution (?? nm and ?5 nm in diameter) of InAs NWs can be achieved from gold (Au) nanoparticles of a single size, ? (? = 50-250 nm). We determine that ultrathin InAs NW growth is seeded by ultra-small Au nanoparticles shed from the large Au seeds upon indium (In) introduction into the growth system and formed prior to the supersaturation of In in Au. The Au spreading phenomenon is explained by the balancing of Gibbs free energy lowering from In-Au mixing and the surface tension increase. Ultrathin InAs NWs formed in this way exhibit a perfect wurtzite structure with no stacking faults. We have observed InAs NWs with diameters down to ?2 nm using our growth method. Passivating the ultrathin InAs NWs with an AlAs shell, subsequently oxidized in air, results in physical deformation of the InAs core, demonstrating the mechanical pliability of these ultrathin NWs. PMID:25383665

Jung, Kyooho; Mohseni, Parsian K; Li, Xiuling

2014-12-21

383

Separation of CO2 Using Ultra-Thin Multi-Layer Polymeric Membranes for Compartmentalized Fiber Optic Sensor Applications  

E-print Network

Separation of CO2 Using Ultra-Thin Multi-Layer Polymeric Membranes for Compartmentalized Fiber of the author. #12;iii Supervisory Committee Separation of CO2 Using Ultra-Thin Multi-Layer Polymeric Membranes sequestration is the most stable option for long-term storage of carbon dioxide (CO2), with significant CO2

Victoria, University of

384

CO Gas Sensing by Ultrathin Tin Oxide Films Grown by Atomic Layer Deposition Using Transmission FTIR Spectroscopy  

E-print Network

CO Gas Sensing by Ultrathin Tin Oxide Films Grown by Atomic Layer Deposition Using Transmission measured by using transient experiments. The ultrathin SnOx ALD films with a thickness of 10 ? were able conductivity of semiconductor metal oxides for gas detection started with the original work of Seiyama on ZnO1

George, Steven M.

385

PHYSICAL REVIEW B 83, 144504 (2011) Persistence of superconductivity in niobium ultrathin films grown on R-plane sapphire  

E-print Network

PHYSICAL REVIEW B 83, 144504 (2011) Persistence of superconductivity in niobium ultrathin films ultrathin films (from 2 to 10 nm) deposited in ultrahigh vacuum on atomically flat R-plane sapphire wafers. A textured polycrystalline morphology is observed for the thinnest films, showing that heteroepitaxy

Canet, Léonie

386

Improved high-field reliability for a SiC metal-oxide-semiconductor device by the incorporation of nitrogen into its HfTiO gate dielectric  

NASA Astrophysics Data System (ADS)

Materials with high dielectric constant (k) have been used in SiC-based metal-oxide-semiconductor (MOS) devices to reduce the electric field in the gate dielectric and thus suppress a high-field reliability problem. In this work, high-k gate dielectrics HfxTi1-xO2 and HfxTi1-xON are applied in SiC MOS devices and an ultrathin thermally grown SiO2 is used as an interlayer between SiC and the high-k materials to block electron injection from SiC into the low-barrier high-k materials. Incorporating nitrogen into the Hf-Ti oxide (by adding nitrogen gas during its sputtering) stacked with a SiO2 interlayer (HfxTi1-xO/SiO2) results in a better gate dielectric for the MOS capacitor, such as smaller frequency dispersion in the capacitance-voltage curve, less oxide charges, and better interface quality. Moreover, the nitrogen incorporation increases the dielectric constant of the oxide, but causes higher dielectric leakage, which can be suppressed by the SiO2 interlayer. High-field stress under constant electric field is performed on the stacked/nonstacked Hf-Ti oxides and oxynitrides, and it turns out that the two oxynitrides show a much smaller flatband shift and a less stress-induced leakage current compared with the two oxides. Based on these results, the HfxTi1-xON/SiO2 stack could be a promising high-k gate dielectric for SiC MOS devices with enhanced reliability.

Lin, L. M.; Lai, P. T.

2007-09-01

387

Aminosilanization nanoadhesive layer for nanoelectric circuits with porous ultralow dielectric film.  

PubMed

An ultrathin layer is investigated for its potential application of replacing conventional diffusion barriers and promoting interface adhesion for nanoelectric circuits with porous ultralow dielectrics. The porous ultralow dielectric (k ? 2.5) substrate is silanized by 3-aminopropyltrimethoxysilane (APTMS) to form the nanoadhesive layer by performing oxygen plasma modification and tailoring the silanization conditions appropriately. The high primary amine content is obtained in favor of strong interaction between amino groups and copper. And the results of leakage current measurements of metal-oxide-semiconductor capacitor structure demonstrate that the aminosilanization nanoadhesive layer can block copper diffusion effectively and guarantee the performance of devices. Furthermore, the results of four-point bending tests indicate that the nanoadhesive layer with monolayer structure can provide the satisfactory interface toughness up to 6.7 0.5 J/m(2) for Cu/ultralow-k interface. Additionally, an annealing-enhanced interface toughness effect occurs because of the formation of Cu-N bonding and siloxane bridges below 500 C. However, the interface is weakened on account of the oxidization of amines and copper as well as the breaking of Cu-N bonding above 500 C. It is also found that APTMS nanoadhesive layer with multilayer structure provides relatively low interface toughness compared with monolayer structure, which is mainly correlated to the breaking of interlayer hydrogen bonding. PMID:23749192

Zhao, Zhongkai; He, Yongyong; Yang, Haifang; Qu, Xinping; Lu, Xinchun; Luo, Jianbin

2013-07-10

388

Dielectric THz waveguides  

NASA Astrophysics Data System (ADS)

In this thesis we have explored a wide variety of dielectric waveguides that rely on many different waveguiding mechanisms to guide THz (far-infrared) radiation. We have explored both theoretically and experimentally a large number of waveguide designs with the aim of reducing propagation and bending losses. The different waveguides can be classified into two fundamentally different strategies for reducing the propagation loss: small-core single-mode evanescent-field fibers or large hollow-core multi-mode tubes. Our focus was first set on exploring the small-core evanescent-field fiber strategy for reducing propagation losses. Following initial theoretical work in our group, much effort was spent on the fabrication and measurement of evanescent porous subwavelength diameter plastic fibers, in an attempt to further reduce the propagation losses. The fabrication of such fibers is a challenge and many novel techniques were devised to enable fiber drawing without hole collapse. The first method sealed the holes of an assembly of polymer tubes and lead to fibers of relatively low porosity (25% air within the core) due to reduction in hole size during fiber drawing. The second method was a novel sacrificial polymer technique whereby drawing a completely solid fiber prevented any hole collapse and the subsequent dissolution of the sacrificial polymer revealed the holes in the fiber. The third method was a combination of preform casting using glass molds and drawing with pressurized air within the holes. This led to fibers of record porosity (86% air). The measurement of these porous fibers began with a collaboration with a group from the university of Sherbrooke. At the time, the only available detector was a frequency integrating liquid-helium-cooled bolometer (powermeter). A novel directional coupler method for measuring the losses of subwavelength fibers was developed whereby an evanescent coupler is formed by bringing a probe fiber in proximity to the sample fiber. By translating the coupling probe fiber along the length of the sample the propagation loss could be estimated in a non-destructive way. Because of the low-pass frequency filtering of the probe fiber and the frequency integration of the detector, the results required careful interpretation and spectral information was limited to the vicinity of 0.2 THz. Subsequent transmission experiments using the adjustable THz-TDS setup enabled the measurement of the full loss spectrum and confirmed the very low propagation loss (< 0.02 cm-1) of the porous subwavelength fibers, among some of the lowest reported losses to date. These measurements further demonstrated that the addition of porosity blue-shifted absorption losses, by virtue of increasing the fraction of power guided in air, thus enabling transmission at higher frequencies and with a wider transmission peak than non-porous subwavelength fibers. Much effort was also spent on exploring the hollow-core waveguide strategy with the development of large hollow-core Bragg fibers. Owing to the similarities in the refractive indices of polymers in the THz regime, two different methods were proposed and implemented for increasing the refractive index contrast between the layers of the Bragg reflector. The first method consisted of co-rolling a polymer film with powder particles in order to create air layers. The second method consisted in rolling a bi-layer of a TiO2 doped polyethylene film and a pure polyethylene film. Despite the increased index contrast between the doped and undoped layers, the overall propagation loss was larger than that of the air-polymer Bragg fiber due to the high absorption loss of the TiO2 doped film. Although much prior work had been done by others on planar THz Bragg reflectors this is the first implementation of a THz Bragg fiber. Unfortunately, in their current implementation the fibers are either too lossy or mechanically unstable. (Abstract shortened by UMI.)

Dupuis, Alexandre

389

Dynamic response of dielectric elastomers  

Microsoft Academic Search

Dielectric elastomers have received a great deal of attention recently for effectively transforming electrical energy to mechanical work. Their large strains and conformability make them enticing materials for many new types of actuators. Unfortunately, their non-linear material behavior and large deformations make actual devices difficult to model. However, the reason for this difficulty can also be used to design actuators

Eric M. Mockensturm; Nakhiah Goulbourne

2006-01-01

390

On designing dielectric elastomer actuators  

Microsoft Academic Search

Subject to a voltage, a dielectric elastomer can deform substantially, making it a desirable material for actuators. Designing such an actuator, however, has been challenging due to nonlinear equations of state, as well as multiple modes of failure, parameters of design, and measures of performance. This paper explores these issues, using a spring-roll actuator as an example. We formulate the

Mickael Moscardo; Xuanhe Zhao; Zhigang Suo; Yuri Lapusta

2008-01-01

391

Hydrostatically Coupled Dielectric Elastomer Actuators  

Microsoft Academic Search

Within the emerging field of polymer-based mechatronics, soft materials showing intrinsic electromechanical transduction properties are being largely studied to develop new types of actuators. Among them, so-called dielectric elastomer (DE) actuators are one of the most promising. This paper presents a new class of such devices, which uses an incompressible fluid to mechanically couple an active part to a passive

Federico Carpi; Gabriele Frediani; Danilo De Rossi

2010-01-01

392

Dielectric nanocomposites with insulating properties  

Microsoft Academic Search

Polymer nanocomposites possess promising high performances as engineering materials, if they are prepared and fabricated properly. Some work has been recently done on such polymer nanocomposites as dielectrics and electrical insulation. This was reviewed in 2004 based on the literatures published up to 2003. New significant findings have been added since then. Furthermore, a multi-core model with the far-distance effect,

Toshikatsu Tanaka

2005-01-01

393

Coherent multimoded dielectric wakefield accelerators  

Microsoft Academic Search

There has recently been a study of the potential uses of multimode dielectric structures for wakefield acceleration [1]. This technique is based on adjusting the wakefield modes of the structure to constructively interfere at certain delays with respect to the drive bunch, thus providing an accelerating gradient enhancement over single mode devices. In this report we examine and attempt to

J Power; W Gai; P Schoessow

1998-01-01

394

Coherent multimoded dielectric wakefield accelerators  

Microsoft Academic Search

There has recently been a study of the potential uses of multimode dielectric structures for wakefield acceleration [1]. This technique is based on adjusting the wakefield modes of the structure to constructively interfere at certain delays with respect to the drive bunch, thus providing an accelerating gradient enhancement over single mode devices. In this report we examine and attempt to

J. Power; W. Gai; P. Schoessow

1999-01-01

395

End moldings for cable dielectrics.  

National Technical Information Service (NTIS)

End moldings for high-voltage cables are described wherein the dielectric insulator of the cable is heated and molded to conform to a desired shape. As a consequence, high quality substantially bubble- free cable connectors suitable for mating to premanuf...

L. D. Roose

1993-01-01

396

Dielectric properties of Ekibastuz coal  

SciTech Connect

An investigation was carried out into the relationships between the dielectric loss angle of an Ekibastuz brown coal, its moisture and ash and the electric field frequency. It has been demonstrated that it is, in principle, possible to measure the ash and moisture contents of this coal by a high-frequency multi-parameter method.

Protopopov, O.A.

1984-01-01

397

Ceramic capacitor and dielectric compositions  

SciTech Connect

A dielectric composition, for use in the manufacture of ceramic capacitors, and comprised of barium titanate (BaTiO/sub 3/) with small additions of niobium pentoxide (Nb/sub 2/O/sub 5/) and gadolinium sesquioxide (Gd/sub 2/O/sub 3/).

Alexander, J. H.

1985-06-25

398

Fundamental studies of diffusion barriers for copper metallization and atomic layer deposited high-kappa films  

NASA Astrophysics Data System (ADS)

Copper is used as interconnect material due to its lower resistivity, higher melting point and higher electromigration resistance than those of Al. However, Cu diffuses rapidly into Si and SiO2, to form Cu-silicides at temperatures as low as 200C. Being highly resistive, Cu-silicides are detrimental in the performance of the integrated circuits. The continued downscaling of device dimensions has placed a high priority on the development of thin diffusion barrier layers in copper metallization. The effectiveness and performance of Mo-based bi-layers, such as Mo/WN, Mo/Ti, and Mo/TiN, and a ternary single layer, Mo-V nitride, deposited using magnetron sputtering are investigated in this work. The Cu/barrier film(s)/Si structures are annealed at high temperatures in N2 and the interactions between the layers along with the possible formation of any anneal-induced reaction products are evaluated using different techniques. The formation of Cu3Si due to the intermixing of Cu and Si is indicative of barrier breakdown. The decreasing device dimensions in microelectronic circuits set high demands for film conformality as the barrier layer thickness is anticipated to decrease to 1.9 nm for the 25 nm node (by 2015). In order to meet future requirement of ultrathin barriers, the apparently counter-intuitive approach of using insulating films, such as HfO2 and Al2O 3, deposited using atomic layer deposition (ALD) technique has been studied and revealed interesting and promising results. In microelectronics fabrication, there is also a need for thin films with high dielectric constant (kappa) in order to continue device dimension reduction of logic and memory devices. With conventional SiO2 based materials, continued scale minimization mandates single digit atomic layer thicknesses of the dielectric layers that lead to the ultimate limitation of quantum mechanical tunneling. To overcome this limitation, high-kappa metal oxides have been recognized as future gate dielectrics. Both HfO 2 and Y2O3 films have held promise due to their compatibility with silicon, high kappa values and large band gaps. The structural properties of HfO2 and Y2O3 films, deposited at optimal ALD conditions, have therefore been investigated. Also, the effect of Y2O3 incorporation in the structural phase transition of HfO2-Y2O3 nanolaminate films has been evaluated.

Majumder, Prodyut

399

Structure and macroscopic tackiness of ultrathin pressure sensitive adhesive films.  

PubMed

Ultrathin layers of the statistical copolymer P(nBA-stat-MA) with a majority of n-butyl acrylate (nBA) and a minority of methyl acrylate (MA) are characterized with respect to the film morphology and the mechanical response in a probe tack test. The probed copolymer can be regarded as a model system of a pressure sensitive adhesive (PSA). The films are prepared by spin-coating which enables an easy thickness control via the polymer concentration of the solution. The film thickness is determined with x-ray reflectivity (XRR) and white light interferometry (WLI). Grazing incidence small angle x-ray scattering (GISAXS) provides detailed and statistically significant information about the film morphology. Two types of lateral structures are identified and no strong correlation of these structures with the PSA film thickness is observed. In contrast, prominent parameters of the probe tack test, such as the stress maximum and the tack energy, exhibit an exponential dependence on the film thickness. PMID:22817560

Diethert, Alexander; Krstgens, Volker; Magerl, David; Ecker, Katharina; Perlich, Jan; Roth, Stephan V; Mller-Buschbaum, Peter

2012-08-01

400

Comparison of thermal and chemical treatments of ultrathin chitosan films  

NASA Astrophysics Data System (ADS)

Chitosan is a biodegradable polysaccharide derived from seashell waste products. The high water absorbency and biocompatibility of chitosan have enabled its use as a hydrogel in specialty biomedical applications. Chitosan can be dissolved in weakly acidic solutions enabling its use in applications such as films and gels, which can be converted into chitin by a chemical process known as acetylation. We present the results of several experiments in which changes in the thickness, index of refraction and molecular environment in response to changes in relative humidity for ultrathin films of chitosan are examined as a function of exposure to temperatures above 150 degrees Celsius. Measurements made by ellipsometry and FTIR spectroscopy indicate that changes in the thickness and index of refraction of the films are accompanied by a change in the infrared absorption spectra similar to that associated with acetylation, which is typically accomplished by exposure of chitosan to acetic anhydride. We believe that these changes are responsible for reduced equilibrium water content in the films at all relative humidity values studied, and may offer a simple method for converting chitosan into a chitin-like material.

Murray, Chris; Dutcher, John

2006-03-01

401

Three-dimensional Ultrathin Planar Lenses by Acoustic Metamaterials.  

PubMed

Acoustic lenses find applications in various areas ranging from ultrasound imaging to nondestructive testing. A compact-size and high-efficient planar acoustic lens is crucial to achieving miniaturization and integration, and should have deep implication for the acoustic field. However its realization remains challenging due to the trade-off between high refractive-index and impedance-mismatch. Here we have designed and experimentally realized the first ultrathin planar acoustic lens capable of steering the convergence of acoustic waves in three-dimensional space. A theoretical approach is developed to analytically describe the proposed metamaterial with hybrid labyrinthine units, which reveals the mechanism of coexistence of high refractive index and well-matched impedance. A hyperbolic gradient-index lens design is fabricated and characterized, which can enhance the acoustic energy by 15?dB at the focal point with very high transmission efficiency. Remarkably, the thickness of the lens is only approximately 1/6 of the operating wavelength. The lens can work within a certain frequency band for which the ratio between the bandwidth and the center frequency reaches 0.74. By tailoring the structure of the metamaterials, one can further reduce the thickness of the lens or even realize other acoustic functionalities, opening new opportunity for manipulation of low-frequency sounds with versatile potential. PMID:25354997

Li, Yong; Yu, Gaokun; Liang, Bin; Zou, Xinye; Li, Guangyun; Cheng, Su; Cheng, Jianchun

2014-01-01

402

Three-dimensional Ultrathin Planar Lenses by Acoustic Metamaterials  

NASA Astrophysics Data System (ADS)

Acoustic lenses find applications in various areas ranging from ultrasound imaging to nondestructive testing. A compact-size and high-efficient planar acoustic lens is crucial to achieving miniaturization and integration, and should have deep implication for the acoustic field. However its realization remains challenging due to the trade-off between high refractive-index and impedance-mismatch. Here we have designed and experimentally realized the first ultrathin planar acoustic lens capable of steering the convergence of acoustic waves in three-dimensional space. A theoretical approach is developed to analytically describe the proposed metamaterial with hybrid labyrinthine units, which reveals the mechanism of coexistence of high refractive index and well-matched impedance. A hyperbolic gradient-index lens design is fabricated and characterized, which can enhance the acoustic energy by 15 dB at the focal point with very high transmission efficiency. Remarkably, the thickness of the lens is only approximately 1/6 of the operating wavelength. The lens can work within a certain frequency band for which the ratio between the bandwidth and the center frequency reaches 0.74. By tailoring the structure of the metamaterials, one can further reduce the thickness of the lens or even realize other acoustic functionalities, opening new opportunity for manipulation of low-frequency sounds with versatile potential.

Li, Yong; Yu, Gaokun; Liang, Bin; Zou, Xinye; Li, Guangyun; Cheng, Su; Cheng, Jianchun

2014-10-01

403

Three-dimensional Ultrathin Planar Lenses by Acoustic Metamaterials  

PubMed Central

Acoustic lenses find applications in various areas ranging from ultrasound imaging to nondestructive testing. A compact-size and high-efficient planar acoustic lens is crucial to achieving miniaturization and integration, and should have deep implication for the acoustic field. However its realization remains challenging due to the trade-off between high refractive-index and impedance-mismatch. Here we have designed and experimentally realized the first ultrathin planar acoustic lens capable of steering the convergence of acoustic waves in three-dimensional space. A theoretical approach is developed to analytically describe the proposed metamaterial with hybrid labyrinthine units, which reveals the mechanism of coexistence of high refractive index and well-matched impedance. A hyperbolic gradient-index lens design is fabricated and characterized, which can enhance the acoustic energy by 15?dB at the focal point with very high transmission efficiency. Remarkably, the thickness of the lens is only approximately 1/6 of the operating wavelength. The lens can work within a certain frequency band for which the ratio between the bandwidth and the center frequency reaches 0.74. By tailoring the structure of the metamaterials, one can further reduce the thickness of the lens or even realize other acoustic functionalities, opening new opportunity for manipulation of low-frequency sounds with versatile potential. PMID:25354997

Li, Yong; Yu, Gaokun; Liang, Bin; Zou, Xinye; Li, Guangyun; Cheng, Su; Cheng, Jianchun

2014-01-01

404

Thickness-dependent spontaneous dewetting morphology of ultrathin Ag films.  

PubMed

We show here that the morphological pathway of spontaneous dewetting of ultrathin Ag films on SiO2 under nanosecond laser melting is dependent on film thickness. For films with thickness h of 2 nm < or = h < or = 9.5 nm, the morphology during the intermediate stages of dewetting consisted of bicontinuous structures. For films with 11.5 nm < or = h < or = 20 nm, the intermediate stages consisted of regularly sized holes. Measurement of the characteristic length scales for different stages of dewetting as a function of film thickness showed a systematic increase, which is consistent with the spinodal dewetting instability over the entire thickness range investigated. This change in morphology with thickness is consistent with observations made previously for polymer films (Sharma and Khanna 1998 Phys. Rev. Lett. 81 3463-6; Seemann et al 2001 J. Phys.: Condens. Matter 13 4925-38). Based on the behavior of free energy curvature that incorporates intermolecular forces, we have estimated the morphological transition thickness for the intermolecular forces for Ag on SiO2. The theory predictions agree well with observations for Ag. These results show that it is possible to form a variety of complex Ag nanomorphologies in a consistent manner, which could be useful in optical applications of Ag surfaces, such as in surface enhanced Raman sensing. PMID:20299723

Krishna, H; Sachan, R; Strader, J; Favazza, C; Khenner, M; Kalyanaraman, R

2010-04-16

405

Wrinkling of atomic planes in ultrathin Au nanowires.  

PubMed

A detailed understanding of structure and stability of nanowires is critical for applications. Atomic resolution imaging of ultrathin single crystalline Au nanowires using aberration-corrected microscopy reveals an intriguing relaxation whereby the atoms in the close-packed atomic planes normal to the growth direction are displaced in the axial direction leading to wrinkling of the (111) atomic plane normal to the wire axis. First-principles calculations of the structure of such nanowires confirm this wrinkling phenomenon, whereby the close-packed planes relax to form saddle-like surfaces. Molecular dynamics studies of wires with varying diameters and different bounding surfaces point to the key role of surface stress on the relaxation process. Using continuum mechanics arguments, we show that the wrinkling arises due to anisotropy in the surface stresses and in the elastic response, along with the divergence of surface-induced bulk stress near the edges of a faceted structure. The observations provide new understanding on the equilibrium structure of nanoscale systems and could have important implications for applications in sensing and actuation. PMID:25004463

Roy, Ahin; Kundu, Subhajit; Mller, Knut; Rosenauer, Andreas; Singh, Saransh; Pant, Prita; Gururajan, M P; Kumar, Praveen; Weissmller, J; Singh, Abhishek Kumar; Ravishankar, N

2014-08-13

406

Ultrathin-layer chromatography nanostructures modified by atomic layer deposition.  

PubMed

Stationary phase morphology and surface chemistry dictate the properties of ultrathin-layer chromatography (UTLC) media and interactions with analytes in sample mixtures. In this paper, we combined two powerful thin film deposition techniques to create composite chromatography nanomaterials. Glancing angle deposition (GLAD) produces high surface area columnar microstructures with aligned macropores well-suited for UTLC. Atomic layer deposition (ALD) enables precise fabrication of conformal, nanometer-scale coatings that can tune surfaces of these UTLC films. We coated ?5?m thick GLAD SiO2 UTLC media with <10nm thick ALD metal oxides (Al2O3, ZrO2, and ZnO) to decouple surface chemistry from the underlying GLAD scaffold microstructure. The effects of ALD coatings on GLAD UTLC media were investigated using transmission electron microscopy (TEM), gas adsorption porosimetry, and lipophilic dye separations. The results collectively show that the most significant changes occur over the first few nanometers of ALD coating. They further demonstrate independent control of film microstructure and surface characteristics. ALD coatings can enhance complex GLAD microstructures to engineer new composite nanomaterials potentially useful in analytical chromatography. PMID:23768654

Jim, S R; Foroughi-Abari, A; Krause, K M; Li, P; Kupsta, M; Taschuk, M T; Cadien, K C; Brett, M J

2013-07-19

407

Transient coexisting nanophases in ultrathin films confined between corrugated walls  

SciTech Connect

Grand-canonical Monte Carlo and microcanonical molecular dynamics methods have been used to simulate an ultrathin monatomic film confined to a slit-pore [i.e., between solid surfaces (walls)]. Both walls comprise atoms rigidly fixed in the face centered cubic (100) configuration; one wall is smooth on a nanoscale and the other is corrugated (i.e., scored with regularly spaced rectilinear grooves one to several nanometers wide). Properties of the film have been computed as a function of the lateral alignment (registry), with the temperature, chemical potential, and distance between the walls kept constant. Changing the registry carries the film through a succession of equilibrium states, ranging from all solid at one extreme to all fluid at the other. Over a range of intermediate registries the film consists of fluid and solid portions in equilibrium, that is fluid-filled nanocapillaries separated by solid strips. The range of registries over which such fluid--solid equilibria exist depends upon the width of the grooves and the frequency of the corrugation. For grooves of width comparable to the range of the interatomic potential, fluid and solid phases cease to coexist. In the limit of very wide grooves the character of the film is similar to that of the film confined by strictly smooth walls. The rich phase behavior of the confined film due to the coupling between molecular (registry) and nano (corrugation) scales has obvious implications for boundary lubrication.

Curry, J.E.; Zhang, F.; Cushman, J.H. (Lilly Hall of Life Sciences, Purdue University, West Lafayette, Indiana 47907 (United States)); Schoen, M. (Institut fuer Theoretische Physik, Technische Universitaet Berlin, Hardenbergstr. 36, 10623 Berlin (Germany)); Diestler, D.J. (Department of Agronomy, Keim Hall, University of Nebraska-Lincoln, Lincoln, Nebraska 68583-0915 (United States))

1994-12-15

408

The physical and chemical properties of ultrathin oxide films.  

PubMed

Thin oxide films (from one to tens of monolayers) of SiO2, MgO, NiO, Al2O3, FexOy, and TiO2 supported on refractory metal substrates have been prepared by depositing the oxide metal precursor in a background of oxygen (ca 1 x 10(-5) Torr). The thinness of these oxide samples facilitates investigation by an array of surface techniques, many of which are precluded when applied to the corresponding bulk oxide. Layered and mixed binary oxides have been prepared by sequential synthesis of dissimilar oxide layers or co-deposition of two different oxides. Recent work has shown that the underlying oxide substrate can markedly influence the electronic and chemical properties of the overlayer oxide. The structural, electronic, and chemical properties of these ultrathin oxide films have been probed using Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), electron energy loss spectroscopy (ELS), ion-scattering spectroscopy (ISS), high-resolution electron energy loss spectroscopy (HREELS), infrared reflectance absorption spectroscopy (IRAS), temperature-programmed desorption (TPD), scanning tunneling microscopy (STM), and scanning tunneling spectroscopy (STS). PMID:15012439

Street, S C; Xu, C; Goodman, D W

1997-01-01

409

Ultrathin organic solar cells with graphene doped by ferroelectric polarization.  

PubMed

Graphene has been employed as transparent electrodes in organic solar cells (OSCs) because of its good physical and optical properties. However, the electrical conductivity of graphene films synthesized by chemical vapor deposition (CVD) is still inferior to that of conventional indium tin oxide (ITO) electrodes of comparable transparency, resulting in a lower performance of OSCs. Here, we report an effective method to improve the performance and long-term stability of graphene-based OSCs using electrostatically doped graphene films via a ferroelectric polymer. The sheet resistance of electrostatically doped few layer graphene films was reduced to ?70 ?/sq at 87% optical transmittance. Such graphene-based OSCs exhibit an efficiency of 2.07% with a superior stability when compared to chemically doped graphene-based OSCs. Furthermore, OSCs constructed on ultrathin ferroelectric film as a substrate of only a few micrometers show extremely good mechanical flexibility and durability and can be rolled up into a cylinder with 7 mm diameter. PMID:24521002

Kim, Keumok; Bae, Sang-Hoon; Toh, Chee Tat; Kim, Hobeom; Cho, Jeong Ho; Whang, Dongmok; Lee, Tae-Woo; zyilmaz, Barbaros; Ahn, Jong-Hyun

2014-03-12

410

Hysteresis and anisotropy in ultrathin Fe/Si(001) films  

NASA Astrophysics Data System (ADS)

It is challenging to investigate the magnetic anisotropy of Fe/Si(001) film in the case a limited magnetic field strength, when both coherent rotation and domain wall displacement coexist in the magnetization reversal process. Owing to the domain wall displacement, the magnetization reversal switching field is far lower than the magnetic anisotropy field, and, consequently, only the magnetization reversal process near easy axis can be treated as coherent rotation. Here, we record the slope of the magnetic torque curve of an iron film grown on a Si(001) substrate measured near the easy axis by anisotropic magnetoresistance (AMR) to separate the coherent rotation of magnetization reversal process from domain wall displacement. Furthermore, the magnitudes of various magnetic anisotropy constants were derived from the magnetic torque curves. Our work suggests that the AMR at low fields can clearly separate the detailed contributions of various magnetic anisotropies when domain wall displacement existed in Fe(001) ultrathin film. We also report on the hysteresis behavior of such films as measured by magneto-optic Kerr effect.

Ye, Jun; He, Wei; Wu, Qiong; Hu, Bo; Tang, Jin; Zhang, Xiang-Qun; Chen, Zi-Yu; Cheng, Zhao-Hua

2014-09-01

411

Dispersion compensation for an ultrathin metal film using LCDCCD system  

NASA Astrophysics Data System (ADS)

A dispersion compensation method is introduced to correct the distorted image passing through an ultrathin metal film. An LCDCCD system is modeled by the back propagation network and used to evaluate the transmittance of the ultrathin metal film. Training samples for the network come from 729 images captured by shooting test patches, in which the RGB values are uniformity distributed between 0 and 255. The RGB value of the original image that will be distorted by the dispersion is first transformed by mapping from the LCD to the CCD, multiplied by the inverse matrix of the transmittance matrix, and finally transformed by mapping from the CCD to the LCD, then the corrected image is obtained. In order to verify the effectiveness of the proposed method, ultrathin aluminum films with different thicknesses are evaporated on glass substrates and laid between the CCD and LCD. Experimental results show that the proposed method compensates for the dispersion successfully.

Dai, Yu; Zhang, Jian-Xu

2012-10-01

412

Rapid and highly sensitive detection using Fano resonances in ultrathin plasmonic nanogratings  

NASA Astrophysics Data System (ADS)

We developed a nanoplasmonic sensor platform employing the extraordinary optical properties of one-dimensional nanogratings patterned on 30 nm-thick ultrathin Ag films. Excitation of Fano resonances in the ultrathin Ag nanogratings results in transmission spectra with high amplitude, large contrast, and narrow bandwidth, making them well-suited for rapid and highly sensitive sensing applications. The ultrathin nanoplasmonic sensor chip was integrated with a polydimethylsiloxane microfluidic channel, and the measured refractive index resolution was found to be 1.46 10-6 refractive index units with a high temporal resolution of 1 s. This compares favorably with commercial prism-based surface plasmon resonance sensors, but is achieved using a more convenient collinear transmission geometry and a significantly smaller sensor footprint of 50 50 ?m2. In addition, an order-of-magnitude improvement in the temporal and spatial resolutions was achieved relative to state-of-the-art nanoplasmonic sensors, for comparable detection resolutions.

Zeng, Beibei; Gao, Yongkang; Bartoli, Filbert J.

2014-10-01

413

Laser cutting of ultra-thin glasses based on a nonlinear laser interaction effect  

NASA Astrophysics Data System (ADS)

Glass panel substrates have been widely used in consumer electronics such as in flat panel TVs, laptops, and cell phones. With the advancement in the industry, the glass substrates are becoming thinner and stronger for reduced weight and volume, which brings great challenges for traditional mechanical processes in terms of cut quality, yield, and throughput. Laser glass cutting provides a non-contact process with minimum impact and superior quality compared to the mechanical counterparts. In this paper, we presented recent progresses in advanced laser processing of ultra-thin glass substrates, especially laser-cutting of ultra-thin glasses by a high power laser through a nonlinear interaction effect. Our results indicate that this technique has great potential of application for mass production of ultra-thin glass substrates.

Chen, Jian; Wu, Zhouling

2013-07-01

414

Spectroscopic Studies of O-Vacancy Defects in Transition Metal Oxides  

SciTech Connect

Dielectrics comprised of nano-crystalline HfO{sub 2} in gate stacks with thin SiO{sub 2}/SiON interfacial transition regions display significant asymmetries with respect to trapping of Si substrate injected holes and electrons. Based on spectroscopic studies, and guided by ab initio theory, electron and hole traps in HfO{sub 2} and other transition metal elemental oxides are assigned to O-atom divacancies clustered at internal grain boundaries of nano-crystalline films. Engineering solutions in which grain boundary defects are suppressed include: (i) ultra-thin, <2 nm, HfO{sub 2} fims, (ii) chemically phase separated high HfO2 content silicate films, and (iii) non-crystalline Zr/Hf Si oxynitride films.

Lucovsky, G.; Luning, J.; Fleming, L.B.; Ulrich, M.D.; Rowe, J.E.; Seo, H.; Lee, S.; Lysaght, P.; Bersuker, G.

2009-06-03

415

Templated 3D Ultrathin CVD Graphite Networks with Controllable Geometry: Synthesis and Application As Supercapacitor Electrodes.  

PubMed

Three-dimensional ultrathin graphitic foams are grown via chemical vapor deposition on templated Ni scaffolds, which are electrodeposited on a close-packed array of polystyrene microspheres. After removal of the Ni, free-standing foams composed of conjoined hollow ultrathin graphite spheres are obtained. Control over the pore size and foam thickness is demonstrated. The graphitic foam is tested as a supercapacitor electrode, exhibiting electrochemical double-layer capacitance values that compare well to those obtained with the state-of-the-art 3D graphene materials. PMID:25318008

Hsia, Ben; Kim, Mun Sek; Luna, Lunet E; Mair, Nisha R; Kim, Yongkwan; Carraro, Carlo; Maboudian, Roya

2014-11-12

416

Reduction of charge fluctuation energies in ultrathin NiO films on Ag(001)  

NASA Astrophysics Data System (ADS)

As the film becomes atomically thin, the on-site Coulomb interaction energy between two 3p holes of the NiO films on Ag(001) U (Ni 3p) significantly decreases as revealed by both X-ray photoelectron and Auger electron spectroscopies. The reduction of U (Ni 3p) for the ultrathin films is well accounted for by varied image potentials and polarization energies in the films from their bulk values. The present results confirm a previous model predicting the reduction of charge fluctuation energies in ultrathin oxide films on highly polarizable substrates due to the extra-atomic relaxations.

Yang, Seolun; Park, H.-K.; Kim, J.-S.; Phark, S.-H.; Chang, Young Jun; Noh, T. W.; Hwang, H.-N.; Hwang, C.-C.; Kim, H.-D.

2013-10-01

417

Growth behaviors of ultrathin ZnSe nanowires by Au-catalyzed molecular-beam epitaxy  

SciTech Connect

Ultrathin ZnSe nanowires grown by Au-catalyzed molecular-beam epitaxy show an interesting growth behavior of diameter dependence of growth rates. The smaller the nanowire diameter, the faster is its growth rate. This growth behavior is totally different from that of the nanowires with diameters greater than 60 nm and cannot be interpreted by the classical theories of the vapor-liquid-solid mechanism. For the Au-catalyzed nanowire growth at low temperatures, we found that the surface and interface incorporation and diffusion of the source atoms at the nanowire tips controlled the growth of ultrathin ZnSe nanowires.

Cai, Y.; Wong, T. L.; Chan, S. K.; Sou, I. K.; Wang, N. [Department of Physics and the Institute of Nano Science and Technology, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong (China); Su, D. S. [Department of Inorganic Chemistry, Fritz-Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin (Germany)

2008-12-08

418

Dielectric breakdown of cell membranes.  

PubMed

With human and bovine red blood cells and Escherichia coli B, dielectric breakdown of cell membranes could be demonstrated using a Coulter Counter (AEG-Telefunken, Ulm, West Germany) with a hydrodynamic focusing orifice. In making measurements of the size distributions of red blood cells and bacteria versus increasing electric field strength and plotting the pulse heights versus the electric field strength, a sharp bend in the otherwise linear curve is observed due to the dielectric breakdown of the membranes. Solution of Laplace's equation for the electric field generated yields a value of about 1.6 V for the membrane potential at which dielectric breakdown occurs with modal volumes of red blood cells and bacteria. The same value is also calculated for red blood cells by applying the capacitor spring model of Crowley (1973. Biophys. J. 13:711). The corresponding electric field strength generated in the membrane at breakdown is of the order of 4 . 10(6) V/cm and, therefore, comparable with the breakdown voltages for bilayers of most oils. The critical detector voltage for breakdown depends on the volume of the cells. The volume-dependence predicted by Laplace theory with the assumption that the potential generated across the membrane is independent of volume, could be verified experimentally. Due to dielectric breakdown the red blood cells lose hemoglobin completely. This phenomenon was used to study dielectric breakdown of red blood cells in a homogeneous electric field between two flat platinum electrodes. The electric field was applied by discharging a high voltage storage capacitor via a spark gap. The calculated value of the membrane potential generated to produce dielectric breakdown in the homogeneous field is of the same order as found by means of the Coulter Counter. This indicates that mechanical rupture of the red blood cells by the hydrodynamic forces in the orifice of the Coulter Counter could also be excluded as a hemolysing mechanism. The detector voltage (or the electric field strength in the orifice) depends on the membrane composition (or the intrinsic membrane potential) as revealed by measuring the critical voltage in E. coli B harvested from the logarithmic and stationary growth phases. The critical detector voltage increased by about 30% for a given volume on reaching the stationary growth phase. PMID:4611517

Zimmermann, U; Pilwat, G; Riemann, F

1974-11-01

419

Dielectric Breakdown of Cell Membranes  

PubMed Central

With human and bovine red blood cells and Escherichia coli B, dielectric breakdown of cell membranes could be demonstrated using a Coulter Counter (AEG-Telefunken, Ulm, West Germany) with a hydrodynamic focusing orifice. In making measurements of the size distributions of red blood cells and bacteria versus increasing electric field strength and plotting the pulse heights versus the electric field strength, a sharp bend in the otherwise linear curve is observed due to the dielectric breakdown of the membranes. Solution of Laplace's equation for the electric field generated yields a value of about 1.6 V for the membrane potential at which dielectric breakdown occurs with modal volumes of red blood cells and bacteria. The same value is also calculated for red blood cells by applying the capacitor spring model of Crowley (1973. Biophys. J. 13:711). The corresponding electric field strength generated in the membrane at breakdown is of the order of 4 106 V/cm and, therefore, comparable with the breakdown voltages for bilayers of most oils. The critical detector voltage for breakdown depends on the volume of the cells. The volume-dependence predicted by Laplace theory with the assumption that the potential generated across the membrane is independent of volume, could be verified experimentally. Due to dielectric breakdown the red blood cells lose hemoglobin completely. This phenomenon was used to study dielectric breakdown of red blood cells in a homogeneous electric field between two flat platinum electrodes. The electric field was applied by discharging a high voltage storage capacitor via a spark gap. The calculated value of the membrane potential generated to produce dielectric breakdown in the homogeneous field is of the same order as found by means of the Coulter Counter. This indicates that mechanical rupture of the red blood cells by the hydrodynamic forces in the orifice of the Coulter Counter could also be excluded as a hemolysing mechanism. The detector voltage (or the electric field strength in the orifice) depends on the membrane composition (or the intrinsic membrane potential) as revealed by measuring the critical voltage in E. coli B harvested from the logarithmic and stationary growth phases. The critical detector voltage increased by about 30% for a given volume on reaching the stationary growth phase. PMID:4611517

Zimmermann, U.; Pilwat, G.; Riemann, F.

1974-01-01

420

Comparative Study of HfTa-based gate-dielectric Ge metal-oxide-semiconductor capacitors with and without AlON interlayer  

NASA Astrophysics Data System (ADS)

The electrical properties and high-field reliability of HfTa-based gate-dielectric metal-oxide-semiconductor (MOS) devices with and without AlON interlayer on Ge substrate are investigated. Experimental results show that the MOS capacitor with HfTaON/AlON stack gate dielectric exhibits low interface-state/oxide-charge densities, low gate leakage, small capacitance equivalent thickness (1.1 nm), and high dielectric constant (20). All of these should be attributed to the blocking role of the ultrathin AlON interlayer against interdiffusions of Ge, Hf, and Ta and penetration of O into the Ge substrate, with the latter effectively suppressing the unintentional formation of unstable poor-quality low- k GeO x and giving a superior AlON/Ge interface. Moreover, incorporation of N into both the interlayer and high- k dielectric further improves the device reliability under high-field stress through the formation of strong N-related bonds.

Xu, J. P.; Zhang, X. F.; Li, C. X.; Chan, C. L.; Lai, P. T.

2010-04-01

421

High thermal robustness of molecularly thin perovskite nanosheets and implications for superior dielectric properties.  

PubMed

A systematic study has been conducted to examine the thermal stability of layer-by-layer assembled films of perovskite-type nanosheets, (Ca2Nb3O10(-))n (n = 1-10), which exhibit superior dielectric and insulating properties. In-plane and out-of-plane X-ray diffraction data as well as observations by atomic force microscopy and transmission electron microscopy indicated the high thermal robustness of the nanosheet films. In a monolayer film with an extremely small thickness of ?2 nm, the nanosheet was stable up to 800 C, the temperature above which segregation into CaNb2O6 and Ca2Nb2O7 began. The critical temperature moderately decreased as the film thickness, or the number of nanosheet layers, increased, and reached 700 C for seven- and 10-layer films, which is comparable to the phase transformation temperature for a bulk phase of the protonic layered oxide of HCa2Nb3O101.5H2O as a precursor of the nanosheet. This thermal stabilization of perovskite-type nanosheets should be associated with restricted nucleation and crystal growth peculiar to such ultrathin 2D bound systems. The stable high-k dielectric response (?r = 210) and highly insulating nature (J < 10(-7) A cm(-2)) remained substantially unchanged even after the nanosheet film was annealed up to 600 C. This study demonstrates the high thermal stability of 2D perovskite-type niobate nanosheets in terms of structure and dielectric properties, which suggests promising potential for future high-k devices operable over a wide temperature range. PMID:24797417

Li, Bao-Wen; Osada, Minoru; Ebina, Yasuo; Akatsuka, Kosho; Fukuda, Katsutoshi; Sasaki, Takayoshi

2014-06-24

422

Validity of Yubero-Tougaard theory to quantitatively determine the dielectric properties of surface nanofilms  

NASA Astrophysics Data System (ADS)

Reflection electron energy-loss spectroscopy (REELS) at low energies is very surface sensitive and can be used to characterize the electronic properties of ultrathin films and surface nanostructures. To extract reliable quantitative information from a REELS experiment it is essential to have accurate theoretical algorithms. In this paper, we have studied the validity of a theoretical method proposed by Yubero and Tougaard [Phys. Rev. B 46, 2486 (1992); Phys. Rev B 53, 9719 (1996)] to determine the dielectric function ? by using an analysis of an effective experimental REELS cross section determined by the Tougaard-Chorkendorff algorithm [Phys Rev B 35, 6570 (1987)]. To this end, REELS experiments with electrons incident normal to the surface were carried out for a wide range of exit angles (35-74 to the surface normal) and energies 200, 500, and 1000eV for several materials (Cu, Ag, Au, and Fe). We find that the theory is in very good agreement with experiment for all geometries and energies studied. It is important to note that for a given element, the same ? is used for all geometries and energies and that this ? is determined by the analysis. The fact that the theory applies at energies at least down to 200eV where the inelastic mean free path (?) is 0.5nm implies that the method can be used to determine the dielectric properties of nanofilms, and the additional fact that the theory can predict the variation with angle suggests that the method might also be used to determine the dielectric properties of nanostructures.

Hajati, Shaaker; Romanyuk, Oleksandr; Zemek, Josef; Tougaard, Sven

2008-04-01

423

Low dielectric constant materials and processes for interlayer dielectric applications  

NASA Astrophysics Data System (ADS)

At 0.18 microns and below minimum device dimensions in Ultra Large Scale Integrated Circuits, signal net parasitic delay amounts to 80% of the overall path delay. This leads to serious problems relating to signal timing, crosstalk, noise and power consumption. Although Copper is being used as an alternative to Aluminum interconnects to reduce the resistive component of the RC delays, finding a suitable material to replace Silicon Dioxide (SiO2) as the interlayer dielectric poses serious challenges. Most of the inorganic candidates are variants of SiO2, while the most prominent among polymeric materials belong to the polyparaxylylene family. The primary disadvantage of polyparaxylylene materials is their low thermal stability. While SiO2 based inorganic films exhibit excellent thermal stability, they offer only incremental improvement in the dielectric constant. The thin film deposition technique for these materials is important as it directly impacts the cost of manufacturing. Chemical Vapor Deposition is known to make high purity, conformal thin films, and is compatible with current silicon manufacturing technology. This research is primarily focused to develop materials which have (i) Low dielectric Constant; (ii) High thermal stability, and to deposit them using Chemical Vapor Deposition technique. The vision was to develop a composite thin film material with the thermal stability of SiO2 and the low dielectric constant of paraxylylenes. The first objective of this research was to develop a technique to deposit SiO2 films at near room temperatures. Thin conformal films of SiO2 were deposited at temperatures around 50C using Di-acetoxy-di-tertiary-butoxy silane (DADBS) as the precursor. The thermal stability, optical and electrical properties of the codeposited thin films were systematically studied. It was possible to control the composition of these films smoothly and these films were shown to be of nanocomposite type. However, the thermal stability of these nanocomposite thin films was only marginally better than that of paraxylylenes. These films were then heat treated under oxygen to 'burn off' the polymer content. It was shown that annealing these films in oxygen environment leaves porous SiO 2 which exhibits the thermal stability of SiO2 and the porosity results in lower dielectric constant.

Vedula, Ramakrishna

424

Polarity-adjustable reversed phase ultrathin-layer chromatography.  

PubMed

Reversed phase thin layer chromatography (TLC) or high performance thin layer chromatography (HPTLC) plates modified with C18, C8 or C2 to provide the silica-gel stationary phase with different polarities are available on the market, however, reversed phase plates with tunable polarity have not been reported. Given the limited variety of reversed phase plates, mobile phase composition optimization is necessary to obtain better separation of analytes with similar characteristics, which is often a time consuming step. We present polarity-adjustable reversed phase ultrathin-layer chromatography (UTLC) plates, which simplifies the mobile phase screening process and greatly expands the selection of reversed phase plates. The plates were fabricated on glass substrates with SiO(2) nanopillars deposited using the glancing angle deposition (GLAD) technique. SiO(2) nanopillars were functionalized with octadecyltrichlorosilane to generate a super hydrophobic stationary phase. Unlike commercial silica-gel based stationary phases, the isolated nanopillar architecture presented here exposes a high surface area to post-fabrication surface treatments. In our work, an O(2) plasma treatment at different powers, pressures and exposure times was used to shorten the silane carbon chain and introduce COOH groups to the surface, producing plates with finely tunable polarities. Separation of a model dye mixture of Sudan blue and Sudan IV confirmed the tuning of surface polarities by measurement of retention behavior changes. The dye elution order reversed as a result of the change in surface polarity. When the same plasma treatment process was tested on commercial reversed phase plates, separation behavior did not change because the disordered and tortuous silica gel restricts the accessible surface area. Plasma treatment of GLAD structures with highly accessible surfaces improved control over interfacial properties, producing better reverse phase separations. PMID:23116804

Hall, J Z; Taschuk, M T; Brett, M J

2012-11-30

425

Ultrathin single and multi-channel fiberscopes for biomedical imaging  

NASA Astrophysics Data System (ADS)

Ultrathin fiberscopes typically have an imaging channel and an illumination channel and are available in diameters ranging from 0.5 mm to 2.5 mm. The minimum diameter can be reduced by combining the illumination and imaging paths into a single fiberoptic channel. Constructing a single channel fiberscope requires a technique of illuminating the tissue, while minimizing the Fresnel reflections and scatter within the common illumination and detection channel. A single channel fiberscope should image diffusely reflected light from tissue illuminated with light filtered for the visible wavelength range (450 - 650 nm). Simply combining the illumination and collection paths via a beamsplitter results in a low object to background signal ratio. The low contrast image is due to a low collection efficiency of light from the object as well as a high background signal from the Fresnel reflection at the proximal surface of the fiber bundle, where the illumination enters the fiber bundle. The focus of the dissertation is the investigation of methods to reduce the background signal from the proximal surface of the fiber bundle. Three systems were tested. The first system uses a coherent fiber bundle with an ar-coating on the proximal face. The second system incorporates crossed polarizers into the light path. In addition, a technique was developed, whereby a portion of the image numerical aperture is devoted to illumination and a portion to image signal detection. This technique is called numerical aperture sharing (NA sharing). This dissertation presents the design, construction, testing, and comparison of the three single channel fiberscopes. In addition, preliminary results of a study aimed at the usefulness of broadband diffuse reflectance imaging for the identification and tracking of disease progression in mouse esophagus are presented.

Kano, Angelique Lynn

426

Evaluation of preferable insertion routes for esophagogastroduodenoscopy using ultrathin endoscopes  

PubMed Central

AIM: To evaluate the discomfort associated with esophagogastroduodenoscopy (EGD) using an ultrathin endoscope through different insertion routes. METHODS: This study (January 2012-March 2013) included 1971 consecutive patients [male/female (M/F), 1158/813, 57.5 11.9 years] who visited a single institute for annual health checkups. Transnasal EGD was performed in 1394 patients and transoral EGD in 577. EGD-associated discomfort was assessed using a visual analog scale score (VAS score: 0-10). RESULTS: Multivariate analysis revealed gender (M vs F: 4.02 2.15 vs 5.06 2.43) as the only independent predictor of the VAS score in 180 patients who underwent EGD for the first time; whereas it revealed gender (M vs F 3.60 2.20 vs 4.84 2.37), operator, age group (A: < 39 years; B: 40-49 years; C: 50-59 years; D: 60-69 years; E: > 70 years; A/B/C/D/E: 4.99 2.32/4.34 2.49/4.19 2.31/3.99 2.27/3.63 2.31), and type of insertion as independent predictors in the remaining patients. Subanalysis for gender, age group, and insertion route revealed that the VAS score decreased with age regardless of gender and insertion route, was high in female patients regardless of age and insertion route, and was low in males aged over 60 years who underwent transoral insertion. CONCLUSION: Although comprehensive analysis revealed that the insertion route may not be an independent predictor of the VAS score, transoral insertion may reduce EGD-associated discomfort in elderly patients. PMID:24803817

Ono, Satoshi; Niimi, Keiko; Fujishiro, Mitsuhiro; Takahashi, Yu; Sakaguchi, Yoshiki; Nakayama, Chiemi; Minatsuki, Chihiro; Matsuda, Rie; Hirayama-Asada, Itsuko; Tsuji, Yosuke; Mochizuki, Satoshi; Kodashima, Shinya; Yamamichi, Nobutake; Ozeki, Atsuko; Matsumoto, Lumine; Ohike, Yumiko; Yamazaki, Tsutomu; Koike, Kazuhiko

2014-01-01

427

End moldings for cable dielectrics  

DOEpatents

End moldings for high-voltage cables are described wherein the dielectric insulator of the cable is heated and molded to conform to a desired shape. As a consequence, high quality substantially bubble-free cable connectors suitable for mating to premanufactured fittings are made. Disclosed is a method for making the cable connectors either in the field or in a factory, molds suitable for use with the method, and the molded cable connectors, themselves.

Roose, Lars D. (Albuquerque, NM)

2000-01-01

428

Coherent multimoded dielectric wakefield accelerators.  

SciTech Connect

There has recently been a study of the potential uses of multimode dielectric structures for wakefield acceleration [1]. This technique is based on adjusting the wakefield modes of the structure to constructively interfere at certain delays with respect to the drive bunch, thus providing an accelerating gradient enhancement over single mode devices. In this report we examine and attempt to clarify the issues raised by this work in the light of the present state of the art in wakefield acceleration.

Power, J.

1998-07-16

429

Coherent multimoded dielectric wakefield accelerators  

SciTech Connect

There has recently been a study of the potential uses of multimode dielectric structures for wakefield acceleration. This technique is based on adjusting the wakefield modes of the structure to constructively interfere at certain delays with respect to the drive bunch, thus providing an accelerating gradient enhancement over single mode devices. In this report we examine and attempt to clarify the issues raised by this work in the light of the present state of the art in wakefield acceleration.

Power, J.; Gai, W.; Schoessow, P. [Argonne National Laboratory, High Energy Physics Division, 9700 S Cass Ave, Argonne, Illinois 60439 (United States)

1999-07-12

430

Microwave dielectric spectrum of rocks  

NASA Technical Reports Server (NTRS)

A combination of several measurement techniques was used to investigate the dielectric properties of 80 rock samples in the microwave region. The real part of the dielectric constant, epsilon', was measured in 0.1 GHz steps from 0.5 to 18 GHz, and the imaginary part, epsilon'', was measured at five frequencies extending between 1.6 and 16 GHz. In addition to the dielectric measurements, the bulk density was measured for all the samples and the bulk chemical composition was determined for 56 of the samples. The study shows that epsilon' is frequency-dependent over the 0.5 to 18 GHz range for all rock samples, and that the bulk density rho accounts for about 50 percent of the observed variance of epsilon'. For individual rock types (by genesis), about 90 percent of the observed variance may be explained by the combination of density and the fractional contents of SiO2, Fe2O3, MgO, and TiO2. For the loss factor epsilon'', it was not possible to establish statistically significant relationships between it and the measured properties of the rock samples (density and chemical composition).

Ulaby, F. T.; Bengal, T.; East, J.; Dobson, M. C.; Garvin, J.; Evans, D.

1988-01-01

431

Dielectric relaxation of samarium aluminate  

NASA Astrophysics Data System (ADS)

A ceramic SmAlO3 (SAO) sample is synthesized by the solid-state reaction technique. The Rietveld refinement of the X-ray diffraction pattern has been done to find the crystal symmetry of the sample at room temperature. An impedance spectroscopy study of the sample has been performed in the frequency range from 50 Hz to 1 MHz and in the temperature range from 313 K to 573 K. Dielectric relaxation peaks are observed in the imaginary parts of the spectra. The Cole-Cole model is used to analyze the dielectric relaxation mechanism in SAO. The temperature-dependent relaxation times are found to obey the Arrhenius law having an activation energy of 0.29 eV, which indicates that polaron hopping is responsible for conduction or dielectric relaxation in this material. The complex impedance plane plot of the sample indicates the presence of both grain and grain-boundary effects and is analyzed by an electrical equivalent circuit consisting of a resistance and a constant-phase element. The frequency-dependent conductivity spectra follow a double-power law due to the presence of two plateaus.

Sakhya, Anup Pradhan; Dutta, Alo; Sinha, T. P.

2014-03-01

432

Ultra-thin resistive switching oxide layers self-assembled by field-induced oxygen migration (FIOM) technique  

PubMed Central

High-performance ultra-thin oxide layers are required for various next-generation electronic and optical devices. In particular, ultra-thin resistive switching (RS) oxide layers are expected to become fundamental building blocks of three-dimensional high-density non-volatile memory devices. Until now, special deposition techniques have been introduced for realization of high-quality ultra-thin oxide layers. Here, we report that ultra-thin oxide layers with reliable RS behavior can be self-assembled by field-induced oxygen migration (FIOM) at the interface of an oxide-conductor/oxide-insulator or oxide-conductor/metal. The formation via FIOM of an ultra-thin oxide layer with a thickness of approximately 25?nm and 2.5% excess oxygen content is demonstrated using cross-sectional transmission electron microscopy and secondary ion mass spectroscopy depth profile. The observed RS behavior, such as the polarity dependent forming process, can be attributed to the formation of an ultra-thin oxide layer. In general, as oxygen ions are mobile in many oxide-conductors, FIOM can be used for the formation of ultra-thin oxide layers with desired properties at the interfaces or surfaces of oxide-conductors in high-performance oxide-based devices. PMID:25362933

Lee, Sangik; Hwang, Inrok; Oh, Sungtaek; Hong, Sahwan; Kim, Yeonsoo; Nam, Yoonseung; Lee, Keundong; Yoon, Chansoo; Kim, Wondong; Park, Bae Ho

2014-01-01

433

Temperature Dependence of Dielectric Constants of Cubic Ionic Compounds  

Microsoft Academic Search

The temperature and pressure dependence of the dielectric constant of a number of cubic halides and oxides with a broad range of dielectric constants have been determined. For low-? compounds the dielectric constant increases with increasing temperature, whereas for high-? compounds the dielectric constant decreases with increasing temperature. Hydrostatic pressure lowers the value of the dielectric constant for all compounds

A. J. Bosman; E. E. Havinga

1963-01-01

434

A self-healing dielectric elastomer actuator  

NASA Astrophysics Data System (ADS)

Dielectric elastomer actuators that can provide muscle-like actuation are unable to self-heal like real muscle tissue. This severely limits dielectric elastomer reliability and robustness. This paper describes a way to instill self-healing into the DE by using a two-phase dielectric consisting of an open-cell silicone sponge saturated with silicone oil. When the dielectric is breached, the oil is able to flow back into any void, re-establishing the dielectric structure. The sponge holds the oil in place and provides dimensional stability, while the oil ensures the integrity of the dielectric layer. The operation of this has been demonstrated in a prototype DE actuator that continued to function despite being perforated multiple times with a sharp object.

Hunt, Stacy; McKay, Thomas G.; Anderson, Iain A.

2014-03-01

435

Dielectric relaxation of high-k oxides  

PubMed Central

Frequency dispersion of high-k dielectrics was observed and classified into two parts: extrinsic cause and intrinsic cause. Frequency dependence of dielectric constant (dielectric relaxation), that is the intrinsic frequency dispersion, could not be characterized before considering the effects of extrinsic frequency dispersion. Several mathematical models were discussed to describe the dielectric relaxation of high-k dielectrics. For the physical mechanism, dielectric relaxation was found to be related to the degree of polarization, which depended on the structure of the high-k material. It was attributed to the enhancement of the correlations among polar nanodomain. The effect of grain size for the high-k materials' structure mainly originated from higher surface stress in smaller grain due to its higher concentration of grain boundary. PMID:24180696

2013-01-01

436

Electromechanics of dielectric particles in dielectric liquids acted on by a microelectrode array  

E-print Network

Arrays of microelectrodes were used to apply forces to dielectric (soda lime glass) spheres in a thin (200 micrometer thick) layer of a dielectric liquid polymer (EOPN 8021). The microelectrodes were fabricated using standard photolithographic...

Seo, Cheong Soo

2006-04-12

437

Electromechanical coupling in dielectric elastomer actuators  

Microsoft Academic Search

In this paper the electromechanical coupling in dielectric elastomer actuators is investigated. An equation proposed by Pelrine et al. [R.E. Pelrine, R.D. Kornbluh, J.P. Joseph, Electrostriction of polymer dielectrics with compliant electrodes as a means of actuation, Sens. Actuators A 64 (1998) 7785] is commonly used for the calculation of the electrostatic forces in dielectric elastomer systems. This equation is

Michael Wissler; Edoardo Mazza

2007-01-01

438

Investigation of dielectric overlay microstrip circuits  

E-print Network

capacitance. The advantage of this method is that it provides a closed-form solution. However, this method in its current form is limited to a specific structure containing four dielectric layers. The second method that is well suited to the overlay... capacitances. The first is the capacitance of the structure with all dielectrics replaced by air, this is denoted by C . The second capacitance is that where the dielectrics are present, denoted by C. From these two capacitances, the characteristic impedance...

Klein, James Louis

2012-06-07

439

Dielectric constant microscopy for biological materials  

NASA Astrophysics Data System (ADS)

This paper describes the work on the development of Dielectric Constant Microscopy for biological materials using double pass amplitude modulation method. The dielectric constant information can be obtained at nanometer scales using this technique. Electrostatic force microscopy images of biological materials are presented. The images obtained from the EFM technique mode clearly show inversion contrast and gives the spatial variation of tip-sample capacitance. The EFM images are further processed to obtain dielectric constant information at nanometer scales.

Valavade, A. V.; Kothari, D. C.; Lbbe, C.

2013-02-01

440

Test results of a prototype dielectric microcalorimeter  

NASA Astrophysics Data System (ADS)

The initial development work on a dielectric microcalorimeter is presented. It focuses on the dielectric properties of the ferroelectric material KTa(1-x)Nb(x)O3 (KTN). Measurements of the temperature dependent dielectric constant are given together with the first alpha particle detection results from a prototype composite microcalorimeter operating at 1.3 K. A nonthermal mechanism for detecting 6 MeV alpha particles in a monolithic KTN sample is also reported.

Pfafman, T. E.; Silver, E.; Labov, S.; Beeman, J.; Goulding, F.; Hansen, W.; Landis, D.; Madden, N.

1990-11-01