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1

Electrical effect of titanium diffusion on amorphous indium gallium zinc oxide  

NASA Astrophysics Data System (ADS)

In this work, thermal diffusion phenomenon of Ti into amorphous indium gallium zinc oxide (?-IGZO) was carefully investigated with secondary ion mass spectroscopy, I-V, and Rs measurement systems and HSC chemistry simulation tool. According to the experimental and simulated results, the diffused Ti atoms were easily oxidized due to its lowest oxidation free energy. Since oxygen atoms were decomposed from the ?-IGZO during the oxidation of Ti, the number of oxygen vacancies working as electron-donating sites in ?-IGZO was dramatically increased, contributing to the decrease of resistivity (?) from 1.96 ? cm (as-deposited ?-IGZO) to 1.33 × 10-3 ? cm (350 °C annealed ?-IGZO).

Choi, Seung-Ha; Jung, Woo-Shik; Park, Jin-Hong

2012-11-01

2

Origin of deep subgap states in amorphous indium gallium zinc oxide: Chemically disordered coordination of oxygen  

NASA Astrophysics Data System (ADS)

The origin of the deep subgap states in amorphous indium gallium zinc oxide (a-IGZO), whether intrinsic to the amorphous structure or not, has serious implications for the development of p-type transparent amorphous oxide semiconductors. We report that the deep subgap feature in a-IGZO originates from local variations in the oxygen coordination and not from oxygen vacancies. This is shown by the positive correlation between oxygen composition and subgap intensity as observed with X-ray photoelectron spectroscopy. We also demonstrate that the subgap feature is not intrinsic to the amorphous phase because the deep subgap feature can be removed by low-temperature annealing in a reducing environment. Atomistic calculations of a-IGZO reveal that the subgap state originates from certain oxygen environments associated with the disorder. Specifically, the subgap states originate from oxygen environments with a lower coordination number and/or a larger metal-oxygen separation.

Sallis, S.; Butler, K. T.; Quackenbush, N. F.; Williams, D. S.; Junda, M.; Fischer, D. A.; Woicik, J. C.; Podraza, N. J.; White, B. E.; Walsh, A.; Piper, L. F. J.

2014-06-01

3

Electrical effect of titanium diffusion on amorphous indium gallium zinc oxide  

SciTech Connect

In this work, thermal diffusion phenomenon of Ti into amorphous indium gallium zinc oxide ({alpha}-IGZO) was carefully investigated with secondary ion mass spectroscopy, I-V, and R{sub s} measurement systems and HSC chemistry simulation tool. According to the experimental and simulated results, the diffused Ti atoms were easily oxidized due to its lowest oxidation free energy. Since oxygen atoms were decomposed from the {alpha}-IGZO during the oxidation of Ti, the number of oxygen vacancies working as electron-donating sites in {alpha}-IGZO was dramatically increased, contributing to the decrease of resistivity ({rho}) from 1.96 {Omega} cm (as-deposited {alpha}-IGZO) to 1.33 Multiplication-Sign 10{sup -3}{Omega} cm (350 Degree-Sign C annealed {alpha}-IGZO).

Choi, Seung-Ha [School of Electronic and Electrical Engineering, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of); Development Group of Oxide Semiconductor, Samsung Display, Yongin 446-711 (Korea, Republic of); Jung, Woo-Shik [Department of Electrical Engineering, Stanford University, Stanford, California 94305 (United States); Park, Jin-Hong [School of Electronic and Electrical Engineering, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of)

2012-11-19

4

Device characteristics of amorphous indium gallium zinc oxide thin film transistors with ammonia incorporation  

NASA Astrophysics Data System (ADS)

The effect of ammonia gas on amorphous indium gallium zinc oxide thin film transistors is investigated. The ammonia is incorporated into the sputtered a-IGZO film during the deposition process. The results indicate that the sub-threshold swing of the NH 3 incorporated TFTs is significantly improved from 2.8 to 1.0 V/decade, and the hysteresis phenomenon is also suppressed during the forward and reverse sweeping measurement. By X-ray photoelectron spectroscopy analyses, Zn-N and O-H bonds are observed in ammonia incorporated a-IGZO film. Therefore, the improvements in the electrical performance of TFTs are attributed to the passivation of dangling bonds and/or defects by ammonia.

Huang, Sheng-Yao; Chang, Ting-Chang; Chen, Min-Chen; Tsao, Shu-Wei; Chen, Shih-Ching; Tsai, Chih-Tsung; Lo, Hung-Ping

2011-07-01

5

High responsivity of amorphous indium gallium zinc oxide phototransistor with Ta2O5 gate dielectric  

NASA Astrophysics Data System (ADS)

This study investigates the electrical performance of amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) with a Ta2O5 gate dielectric under monochromatic illumination. The relationship between the phototransistor performance and oxygen partial pressure is determined. The oxygen content of the a-IGZO channel significantly affects the electrical and optical characteristics of a-IGZO TFTs. At applied gate biases of 0, 0, and 0.25 V, oxygen partial pressures of 0%, 0.1%, and 0.2% yielded measured device responsivities of 0.23, 0.44, and 4.75 A/W, respectively. Oxygen content can be used to control the mobility of TFTs, which can amplify photocurrent and enhance the responsivity of a-IGZO TFTs with a Ta2O5 gate dielectric.

Chang, T. H.; Chiu, C. J.; Weng, W. Y.; Chang, S. J.; Tsai, T. Y.; Huang, Z. D.

2012-12-01

6

Room-temperature-operated sensitive hybrid gas sensor based on amorphous indium gallium zinc oxide thin-film transistors  

NASA Astrophysics Data System (ADS)

An organic sensing layer is capped onto an amorphous indium gallium zinc oxide (a-IGZO) thin-film transistor (TFT) to form a hybrid sensor. The organic layer, served as a second gate, forms a p-n junction with the a-IGZO film. Oxidizing or reducing vapor molecules act like electron acceptors or electron donors to change the potential of the organic layer and the current of a-IGZO TFT. A sensitive and reversible response to 100 ppb ammonia and 100 ppb acetone is obtained at room temperature. This letter opens a route to develop low-cost large-area bio/chemical sensor arrays based on the emerging a-IGZO TFT technology.

Zan, Hsiao-Wen; Li, Chang-Hung; Yeh, Chun-Cheng; Dai, Ming-Zhi; Meng, Hsin-Fei; Tsai, Chuang-Chuang

2011-06-01

7

Threshold voltage dependence on channel length in amorphous-indium-gallium-zinc-oxide thin-film transistors  

NASA Astrophysics Data System (ADS)

A threshold voltage (Vth) dependence on channel length (L) is reported for amorphous-indium-gallium-zinc-oxide thin-film transistors (TFTs). Vth is found to shift negatively with decreasing L and the negative shift is drastic in TFTs with L < 4 ?m. Combined analysis of current-voltage (I-V) and capacitance-voltage (C-V) curves shows that the Fermi energy (EF) at flat band shifts towards the conduction band (EC) with decreasing L, hence the negative Vth shift. Using the same analysis, the flat band carrier density (nFB) is also found to increase with decreasing L, revealing unintentional doping of the channel by carrier diffusion from the n+ doped source and drain regions as the cause of the negative Vth shift.

Han Kang, Dong; Ung Han, Ji; Mativenga, Mallory; Hwa Ha, Su; Jang, Jin

2013-02-01

8

Surface reactivity and oxygen migration in amorphous indium-gallium-zinc oxide films annealed in humid atmosphere  

NASA Astrophysics Data System (ADS)

An isotope tracer study, i.e., 18O/16O exchange using 18O2 and H218O, was performed to determine how post-deposition annealing (PDA) affected surface reactivity and oxygen diffusivity of amorphous indium-gallium-zinc oxide (a-IGZO) films. The oxygen tracer diffusivity was very high in the bulk even at low temperatures, e.g., 200 °C, regardless of PDA and exchange conditions. In contrast, the isotope exchange rate, dominated by surface reactivity, was much lower for 18O2 than for H218O. PDA in a humid atmosphere at 400 °C further suppressed the reactivity of O2 at the a-IGZO film surface, which is attributable to -OH-terminated surface formation.

Watanabe, Ken; Lee, Dong-Hee; Sakaguchi, Isao; Nomura, Kenji; Kamiya, Toshio; Haneda, Hajime; Hosono, Hideo; Ohashi, Naoki

2013-11-01

9

Microscopic structure and electrical transport property of sputter-deposited amorphous indium-gallium-zinc oxide semiconductor films  

NASA Astrophysics Data System (ADS)

We report on microscopic structures and electrical and optical properties of sputter-deposited amorphous indium-gallium-zinc oxide (a-IGZO) films. From electron microscopy observations and an x-ray small angle scattering analysis, it has been confirmed that the sputtered a-IGZO films consist of a columnar structure. However, krypton gas adsorption measurement revealed that boundaries of the columnar grains are not open-pores. The conductivity of the sputter-deposited a-IGZO films shows a change as large as seven orders of magnitude depending on post-annealing atmosphere; it is increased by N2-annealing and decreased by O2-annealing reversibly, at a temperature as low as 300°C. This large variation in conductivity is attributed to thermionic emission of carrier electrons through potential barriers at the grain boundaries, because temperature dependences of the carrier density and the Hall mobility exhibit thermal activation behaviours. The optical band-gap energy of the a-IGZO films changes between before and after annealing, but is independent of the annealing atmosphere, in contrast to the noticeable dependence of conductivity described above. For exploring other possibilities of a-IGZO, we formed multilayer films with an artificial periodic lattice structure consisting of amorphous InO, GaO, and ZnO layers, as an imitation of the layer-structured InGaZnO4 homologous phase. The hall mobility of the multilayer films was almost constant for thicknesses of the constituent layer between 1 and 6 Å, suggesting rather small contribution of lateral two-dimensional conduction It increased with increasing the thickness in the range from 6 to 15 Å, perhaps owing to an enhancement of two-dimensional conduction in InO layers.

Yabuta, H.; Kaji, N.; Shimada, M.; Aiba, T.; Takada, K.; Omura, H.; Mukaide, T.; Hirosawa, I.; Koganezawa, T.; Kumomi, H.

2014-06-01

10

Highest transmittance and high-mobility amorphous indium gallium zinc oxide films on flexible substrate by room-temperature deposition and post-deposition anneals  

SciTech Connect

Amorphous indium gallium zinc oxide (a-IGZO) thin films of the highest transmittance reported in literature were initially deposited onto flexible polymer substrates at room temperature. The films were annealed in vacuum, air, and oxygen to enhance their electrical and optical performances. Electrical and optical characterizations were done before and after anneals. A partial reversal of the degradation in electrical properties upon annealing in oxygen was achieved by subjecting the films to subsequent vacuum anneals. A model was developed based on film texture and structural defects which showed close agreement between the measured and calculated carrier mobility values at low carrier concentrations (2-6 x 10{sup 19} cm{sup -3}).

Gadre, Mandar J. [School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, Arizona 85287 (United States); Alford, T. L. [School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, Arizona 85287 (United States); Flexible Display Center at Arizona State University, Tempe, Arizona 85284 (United States)

2011-08-01

11

Amorphous Indium Gallium Zinc Oxide Thin-Film Transistors with a Low-Temperature Polymeric Gate Dielectric on a Flexible Substrate  

NASA Astrophysics Data System (ADS)

Amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) with a solution-processed polymeric gate dielectric of cross-linked poly(4-vinylphenol) (c-PVP) film were fabricated on a poly(ethylene terephthalate) (PET) substrate on which an a-IGZO film, as the active channel layer, was deposited by radio frequency (RF) sputtering. The entire TFT fabrication process was carried out at a temperature below 110 °C. The device exhibited an on/off ratio of 1.5× 106 and a high field-effect mobility of 10.2 cm2 V-1 s-1, which is, to our knowledge, the best result ever achieved among a-IGZO TFTs with polymeric gate dielectrics on a plastic substrate.

Hyung, Gun Woo; Park, Jaehoon; Wang, Jian-Xun; Lee, Ho Won; Li, Zhao-Hui; Koo, Ja-Ryong; Kwon, Sang Jik; Cho, Eou-Sik; Kim, Woo Young; Kim, Young Kwan

2013-07-01

12

Scaling down of amorphous indium gallium zinc oxide thin film transistors on the polyethersulfone substrate employing the protection layer of parylene-C for the large-scale integration  

NASA Astrophysics Data System (ADS)

We have investigated the parylene-groups for the device scaling-down as the protection layer of polyethersulfone (PES) substrate. In general, photolithography process on the PES substrate could not be allowed due to its poor chemical resistance. In this work, parylene-C is used as the protection layer. However, adhesion problem is observed caused by the hydrophobic property of parylene-groups. Thereby we additionally used SiO2 as the adhesion layer. Finally, we demonstrated the scaling-down of amorphous indium gallium zinc oxide thin film transistor on a plastic substrate by using lithography technique. Field-effect mobility, threshold voltage, current on-to-off ratio are measured to be 0.84 cm2/V s, 19.7 V, and 7.62×104, respectively.

Chang, Seongpil; Dong, Ki-Young; Park, Jung-Ho; Oh, Tae-Yeon; Kim, Jong-Woo; Lee, Sang Yeol; Ju, Byeong-Kwon

2010-06-01

13

High-Performance Light-Erasable Memory and Real-Time Ultraviolet Detector Based on Unannealed Indium–Gallium–Zinc–Oxide Thin-Film Transistor  

Microsoft Academic Search

A light-erasable memory and a real-time ultraviolet (UV) detector were developed from an amorphous indium–gallium–zinc–oxide (IGZO) thin-film transistor fabricated at room temperature without post-annealing. The natural defects within the IGZO or at the dielectric interface serve as electron traps to support a writing operation (switching down the channel conductance). A negative gate bias accompanied by UV illumination performs an erasing

Wei-Tsung Chen; Hsiao-Wen Zan

2012-01-01

14

Recovery from ultraviolet-induced threshold voltage shift in indium gallium zinc oxide thin film transistors by positive gate bias  

SciTech Connect

The effect of short-duration ultraviolet (UV) exposure on the threshold voltage (V{sub th}) of amorphous indium gallium zinc oxide thin film transistors (TFTs) and its recovery characteristics were investigated. The V{sub th} exhibited a significant negative shift after UV exposure. The V{sub th} instability caused by UV illumination is attributed to the positive charge trapping in the dielectric layer and/or at the channel/dielectric interface. The illuminated devices showed a slow recovery in threshold voltage without external bias. However, an instant recovery can be achieved by the application of positive gate pulses, which is due to the elimination of the positive trapped charges as a result of the presence of a large amount of field-induced electrons in the interface region.

Liu, P.; Chen, T. P.; Li, X. D.; Wong, J. I. [School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798 (Singapore)] [School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798 (Singapore); Liu, Z. [School of Materials and Energy, Guangdong University of Technology, Guangzhou 510006 (China)] [School of Materials and Energy, Guangdong University of Technology, Guangzhou 510006 (China); Liu, Y. [State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, Sichuan 610054 (China)] [State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, Sichuan 610054 (China); Leong, K. C. [GLOBALFOUNDRIES Singapore Pte. Ltd., 60 Woodlands Industrial Park D Street 2, Singapore 738406 (Singapore)] [GLOBALFOUNDRIES Singapore Pte. Ltd., 60 Woodlands Industrial Park D Street 2, Singapore 738406 (Singapore)

2013-11-11

15

Role of incorporated hydrogen on performance and photo-bias instability of indium gallium zinc oxide thin film transistors  

NASA Astrophysics Data System (ADS)

This study examined the effects of hydrogen incorporation in amorphous indium gallium zinc oxide (IGZO) on the performance and photo-bias stability of the resulting thin-film transistors (TFTs). It was found that the threshold voltage of IGZO TFTs was negatively shifted without significant loss of the field-effect mobility and ION/OFF ratio with increasing hydrogen concentration, suggesting that interstitial hydrogen can act as a shallow donor. The hydrogen-doped device, however, showed more negative bias illumination stress (NBIS) instability than the undoped device, which cannot be explained by the simple shallow donor model. This NBIS-induced degradation might be associated with the increased tailing state distribution, which may stem from a hydrogen-related complex defect or compensation.

Kim, Hyo Jin; Park, Se Yeob; Jung, Hong Yoon; Son, Byeong Geun; Lee, Chang-Kyu; Lee, Chul-Kyu; Jeong, Jong Han; Mo, Yeon-Gon; Son, Kyoung Seok; Ryu, Myung Kwan; Lee, Sangyoon; Kyeong Jeong, Jae

2013-02-01

16

Recovery from ultraviolet-induced threshold voltage shift in indium gallium zinc oxide thin film transistors by positive gate bias  

NASA Astrophysics Data System (ADS)

The effect of short-duration ultraviolet (UV) exposure on the threshold voltage (Vth) of amorphous indium gallium zinc oxide thin film transistors (TFTs) and its recovery characteristics were investigated. The Vth exhibited a significant negative shift after UV exposure. The Vth instability caused by UV illumination is attributed to the positive charge trapping in the dielectric layer and/or at the channel/dielectric interface. The illuminated devices showed a slow recovery in threshold voltage without external bias. However, an instant recovery can be achieved by the application of positive gate pulses, which is due to the elimination of the positive trapped charges as a result of the presence of a large amount of field-induced electrons in the interface region.

Liu, P.; Chen, T. P.; Li, X. D.; Liu, Z.; Wong, J. I.; Liu, Y.; Leong, K. C.

2013-11-01

17

High-Performance Indium–Gallium–Zinc Oxide Thin-Film Transistors Based on Anodic Aluminum Oxide  

Microsoft Academic Search

Thin-film transistors (TFTs) based on indium- gallium-zinc oxide (IGZO) active layer and anodic aluminum oxide (Al2O3) gate dielectric were investigated. The anodic Al2O3 gate dielectric possesses low leakage current and relatively high dielectric constant. The IGZO TFT based on anodic Al2O3 shows a mobility of as high as 21.6 cm 2 \\/V · s, an on\\/off current ratio of as

Linfeng Lan; Junbiao Peng

2011-01-01

18

Defect Analysis of the Indium-Gallium-Zinc-Oxygen System for Transparent Oxide Semiconductor Applications  

NASA Astrophysics Data System (ADS)

The defect chemistry of compounds in the InGaO3(ZnO) k (IGZO) system (k=1, 2, and 3) was investigated via analysis of the dependence of conductivity and thermopower on oxygen partial pressure (pO2) at high temperature (750°C), i.e., Brouwer analysis. Defect mechanisms were deduced based on the resulting Brouwer slopes for all the k-phases, the prevailing point defect species were proposed to be the Ga antisite defect (Ga·Zn ionically compensated by indium vacancies (mathrm{V('''}_{In}) ) donors.The validity of the proposed defect mechanism was supported by density functional theory predictions, which calculated intrinsic defect formation energies in crystalline IGZO and also calculated a theory-based Brouwer slope that was in agreement with experiment. The defect chemistry of IGZO was compared to that of the related In2O3(ZnO)k system in order to infer the role of cation composition in governing electrical properties in crystalline IGZO. There is a change from electronic compensation of antisite defects (in crystalline k=3 In2O3(ZnO) k) to ionic compensation for nearly all compositions in the crystalline IGZO phases. The electrical properties of amorphous IGZO (a-IGZO) were investigated in situ as a function of pO2 at moderate temperature (200°C). A sluggish decay in conductivity was observed and attributed to relaxation within the amorphous structure. Upon abrupt change of pO2, two transients were observed in the electrical property response. The initial response was attributed to a rapid change of surface states. The latter transient, with a time constant approximately an order of magnitude larger than the first, was attributed to bulk diffusion of oxygen. Bulk diffusion was confirmed by 18O tracer diffusion measurements by Isotope Exchange Depth Profiling via Secondary Ion Mass Spectrometry. Through the isolation of the bulk component of the overall conductivity change, it was possible to propose an oxygen vacancy defect mechanism for a-IGZO. To the author's knowledge, this is the first instance where in situ conductivity measurements (Brouwer analysis) has been successfully employed study the point defect chemistry in amorphous oxide (semi)conductor films, providing a complementary technique to ab initio calculations.

Adler, Alexander U.

19

High performance indium gallium zinc oxide thin film transistors fabricated on polyethylene terephthalate substrates  

SciTech Connect

High-performance amorphous ({alpha}-) InGaZnO-based thin film transistors (TFTs) were fabricated on flexible polyethylene terephthalate substrates coated with indium oxide (In{sub 2}O{sub 3}) films. The InGaZnO films were deposited by rf magnetron sputtering with the presence of O{sub 2} at room temperature. The n-type carrier concentration of InGaZnO film was {approx}2x10{sup 17} cm{sup -3}. The bottom-gate-type TFTs with SiO{sub 2} or SiN{sub x} gate dielectric operated in enhancement mode with good electrical characteristics: saturation mobility 11.5 cm{sup 2} V{sup -1} s{sup -1} for SiO{sub 2} and 12.1 cm{sup 2} V{sup -1} s{sup -1} for SiN{sub x} gate dielectrics and drain current on-to-off ratio >10{sup 5}. TFTs with SiN{sub x} gate dielectric exhibited better performance than those with SiO{sub 2}. This is attributed to the relatively high dielectric constant (i.e., high-k material) of SiN{sub x}. After more than 500 h aging time at room temperature, the saturation mobility of the TFTs with SiO{sub 2} gate dielectric was comparable to the as-fabricated value and the threshold voltage shift was 150 mV.

Lim, Wantae; Jang, Jung Hun; Kim, S.-H.; Norton, D. P.; Craciun, V; Pearton, S. J. [Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611 (United States); Ren, F. [Department of Chemical Engineering, University of Florida, Gainesville, Florida 32611 (United States); Shen, H. [Sensors and Electron Devices Directorate, Army Research Laboratory, Adelphi, Maryland 20783 (United States)

2008-08-25

20

Fabrication and characterization of indium gallium zinc oxide (IGZO) thin film transistors with (La0.5Y0.5)2O3 gate insulator  

NASA Astrophysics Data System (ADS)

All oxide thin film transistors (TFT) with indium gallium zinc oxide (IGZO) active layer were fabricated by chemical solution deposition (CSD) using aqueous solutions on glass substrate. Bottom source - drain and top gate electrodes were fabricated by thermal deposition technique. Source - drain channel length was patterned 120?m. (La0.5Y0.5)2O3 was used as gate dielectric. Polycrystalline growth of oxides IGZO was confirmed by grazing incidence X-ray diffraction, where as AFM shows nanostructured growth with smooth surface morphology. Current voltage (I-V) characteristics of all oxide TFT revealed very small leakage currents. It is found that (La0.5Y0.5)2O3 dielectric is a promising gate dielectrics and produce TFTs with improved performance and stability compared to polysilicon, La2O3 and Y2O3 gate insulators.

Mistry, Bhaumik V.; Mistry, Jaydeep; Trivedi, U. N.; Joshi, V. G.; Joshi, U. S.

2013-02-01

21

Realization of write-once-read-many-times memory device with O2 plasma-treated indium gallium zinc oxide thin film  

NASA Astrophysics Data System (ADS)

A write-once-read-many-times (WORM) memory devices based on O2 plasma-treated indium gallium zinc oxide (IGZO) thin films has been demonstrated. The device has a simple Al/IGZO/Al structure. The device has a normally OFF state with a very high resistance (e.g., the resistance at 2 V is ˜109 ? for a device with the radius of 50 ?m) as a result of the O2 plasma treatment on the IGZO thin films. The device could be switched to an ON state with a low resistance (e.g., the resistance at 2 V is ˜103 ? for the radius of 50 ?m) by applying a voltage pulse (e.g., 10 V/1 ?s). The WORM device has good data-retention and reading-endurance capabilities.

Liu, P.; Chen, T. P.; Li, X. D.; Liu, Z.; Wong, J. I.; Liu, Y.; Leong, K. C.

2014-01-01

22

Fabrication Process Assessment and Negative Bias Illumination Stress Study of Indium-Gallium-Zinc Oxide and Zinc-Tin Oxide Thin-Film Transistors  

NASA Astrophysics Data System (ADS)

Indium-gallium-zinc oxide (IGZO) and zinc-tin oxide (ZTO) are investigated for thin-film transistor (TFT) applications. Negative bias illumination stress (NBIS) is employed for electrical stability assessment. Unpassivated IGZO and ZTO TFTs suffer from severe NBIS instabilities. Zinc-tin-silicon oxide is found to be an effective passivation layer for IGZO and ZTO TFTs, significantly improving the NBIS stability. NBIS instabilities in unpassivated TFTs are attributed to an NBIS-induced desorption of chemisorbed oxygen from the channel layer top surface, exposing surface oxygen vacancies. A ZTSO layer protects the channel layer top surface from adsorbed gas interactions and also appears to reduce the density of oxygen vacancies. The best device architectures investigated with respect to TFT electrical performance are found to be staggered with aluminum electrodes for unpassivated TFTs and coplanar with ITO electrodes for ZTSO-passivated TFTs. Annealing in wet-O2 is not found to be effective for improving the performance of IGZO or ZTO TFTs or for reducing the post-deposition annealing temperature.

Hoshino, Ken

23

Endurance Characteristics of Amorphous-InGaZnO Transparent Flash Memory With Gold Nanocrystal Storage Layer  

Microsoft Academic Search

The amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT)-based nonvolatile transparent Flash memory devices were fabricated with gold (Au) nanocrystal storage layer. The performance and the reliability of transparent memory devices have been characterized by experiment and technology computer-aided design simulation. This memory device shows a large-enough memory window ?V = 4.7 V at the program\\/erase (P\\/E) voltage VPGM\\/VERS = 35\\/ ?

Jaeman Jang; Jae Chul Park; Dongsik Kong; Dong Myong Kim; Jang-Sik Lee; Byeong-Hyeok Sohn; Il Hwan Cho; Dae Hwan Kim

2011-01-01

24

Multilevel resistive switching memory with amorphous InGaZnO-based thin film  

NASA Astrophysics Data System (ADS)

Multi-level storage capability of resistive random access memory (RRAM) using amorphous indium-gallium-zinc-oxide (InGaZnO) thin film is demonstrated by the TiN/Ti/InGaZnO/Pt device structure under different operation modes. The distinct four-level resistance states can be obtained by varying either the trigger voltage pulse or the compliance current. In addition, the RRAM devices exhibit superior characteristics of programming/erasing endurance and data retention for the application of multi-level nonvolatile memory technology. Physical transport mechanisms for the multi-level resistive switching characteristics are also deduced in this study.

Hsu, Ching-Hui; Fan, Yang-Shun; Liu, Po-Tsun

2013-02-01

25

First-principles study of native point defects in crystalline indium gallium zinc oxide  

NASA Astrophysics Data System (ADS)

Materials in In-Ga-Zn-O system are promising candidates for channel layers of high-performance thin-film transistors (TFTs). We investigated the atomic arrangements and the electronic structures of crystalline InGaZnO4 containing point defects such as oxygen vacancy (VO), interstitial hydrogen (Hi), and interstitial oxygen (Oi) by density functional theory (DFT) using a plane-wave pseudopotential method. The calculations for the atomic structure relaxation suggest that Hi bonds to a lattice oxygen (OO), and Oi occupies a split interstitial site [Oi(split)] forming a chemical bond with OO which is similar to O2 molecule, or Oi occupies an octahedral interstitial site [Oi(oct)]. The electronic structure calculations reveal that VO forms fully occupied states around the middle of the DFT band gap, while Hi does not form a defect level in the band gap but raises the Fermi level above the conduction band minimum. Oi(split) forms fully occupied states above the valence band maximum of the defect-free model (VBM0), while Oi(oct) forms both occupied and unoccupied states above the VBM0. It is thus suggested that VO and Oi(split) are electrically inactive for electrons but work as hole traps, Hi acts as a donor, and Oi(oct) is electrically active, trapping both electrons and holes. These observations imply that VO and Oi(split) do not but Hi and Oi(oct) influence electrical properties of the n-channel TFTs based on the In-Ga-Zn-O semiconductor materials.

Omura, Hideyuki; Kumomi, Hideya; Nomura, Kenji; Kamiya, Toshio; Hirano, Masahiro; Hosono, Hideo

2009-05-01

26

Analysis of electronic structure of amorphous InGaZnO/SiO{sub 2} interface by angle-resolved X-ray photoelectron spectroscopy  

SciTech Connect

The electronic structures of amorphous indium gallium zinc oxide (a-IGZO) on a SiO{sub 2} layers before and after annealing were observed by constant final state X-ray photoelectron spectroscopy (CFS-XPS) and X-ray adsorption near-edge structure spectroscopy (XANES). From the results of angle-resolved CFS-XPS, the change in the electronic state was clearly observed in the a-IGZO bulk rather than in the a-IGZO/SiO{sub 2} interface. This suggests that the electronic structures of the a-IGZO bulk strongly affected the thin-film transistor characteristics. The results of XANES indicated an increase in the number of tail states upon atmospheric annealing (AT). We consider that the increase in the number of tail states decreased the channel mobility of AT samples.

Ueoka, Y.; Ishikawa, Y.; Maejima, N.; Matsui, F.; Matsui, H.; Yamazaki, H.; Urakawa, S.; Horita, M.; Daimon, H.; Uraoka, Y. [Graduate School of Materials Science, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192 (Japan)] [Graduate School of Materials Science, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192 (Japan)

2013-10-28

27

Analysis of electronic structure of amorphous InGaZnO/SiO2 interface by angle-resolved X-ray photoelectron spectroscopy  

NASA Astrophysics Data System (ADS)

The electronic structures of amorphous indium gallium zinc oxide (a-IGZO) on a SiO2 layers before and after annealing were observed by constant final state X-ray photoelectron spectroscopy (CFS-XPS) and X-ray adsorption near-edge structure spectroscopy (XANES). From the results of angle-resolved CFS-XPS, the change in the electronic state was clearly observed in the a-IGZO bulk rather than in the a-IGZO/SiO2 interface. This suggests that the electronic structures of the a-IGZO bulk strongly affected the thin-film transistor characteristics. The results of XANES indicated an increase in the number of tail states upon atmospheric annealing (AT). We consider that the increase in the number of tail states decreased the channel mobility of AT samples.

Ueoka, Y.; Ishikawa, Y.; Maejima, N.; Matsui, F.; Matsui, H.; Yamazaki, H.; Urakawa, S.; Horita, M.; Daimon, H.; Uraoka, Y.

2013-10-01

28

Amorphous InGaZnO ultraviolet phototransistors with double-stack Ga2O3/SiO2 dielectric  

NASA Astrophysics Data System (ADS)

This study investigates the electrical performance of amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors with Ga2O3 gate dielectric and applied on deep-ultraviolet phototransistors. To reduce the leakage current, we introduce the SiO2 interlayer dielectric, which effectively reduces the off-current. Under the illumination of 250 nm, the measured responsivity of the device was 3.2 A/W at an applied gate bias of 0 V. The photo-generated carriers were injected into the channel by the applied electric field and Fowler-Nordheim tunneling. A large photocurrent and responsivity can be obtained which is attributed to the high mobility of the a-IGZO channel.

Chang, T. H.; Chiu, C. J.; Chang, S. J.; Tsai, T. Y.; Yang, T. H.; Huang, Z. D.; Weng, W. Y.

2013-06-01

29

Analysis of temperature-dependent electrical characteristics in amorphous In-Ga-Zn-O thin-film transistors using gated-four-probe measurements  

NASA Astrophysics Data System (ADS)

We analyzed the temperature-dependent electrical characteristics of amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) using a gated-four-probe method (GFP) with temperatures ranging from 93 to 373 K. The intrinsic field-effect mobility and source/drain parasitic resistance were separately extracted using the GFP method. We found that temperature-dependent transfer characteristics originated from the temperature-dependent intrinsic field-effect mobility of the a-IGZO TFTs. The parasitic resistance was also correlated with the intrinsic-field effect mobility, which decreases as the intrinsic field-effect mobility increases, indicating that access parasitic resistance originated from bulk regions rather than metal/semiconductor junction barrier is a key factor to determine the parasitic resistance of a-IGZO TFTs.

Jeong, Jaewook; Jun Lee, Gwang; Kim, Joonwoo; Moon Jeong, Soon; Kim, Jung-Hye

2013-09-01

30

Study of mechanism of stress-induced threshold voltage shift and recovery in top-gate amorphous-InGaZnO4 thin-film transistors with source- and drain-offsets  

NASA Astrophysics Data System (ADS)

Bias instability of top-gate amorphous-indium-gallium-zinc-oxide thin-film transistors with source- and drain-offsets is reported. Positive and negative gate bias-stress (VG_STRESS) respectively induce reversible negative threshold-voltage shift (?VTH) and reduction in on-current. Migration of positive charges towards the offsets lowers the local resistance of the offsets, resulting in the abnormal negative ?VTH under positive VG_STRESS. The reduction in on-current under negative VG_STRESS is due to increase in resistance of the offsets when positive charges migrate away from the offsets. Appropriate drain and source bias-stresses applied simultaneously with VG_STRESS either suppress or enhance the instability, verifying lateral ion migration to be the instability mechanism.

Mativenga, Mallory; Kang, Dong Han; Lee, Ung Gi; Jang, Jin

2012-09-01

31

Nontraditional Amorphous Oxide Semiconductor Thin-Film Transistor Fabrication  

NASA Astrophysics Data System (ADS)

Fabrication techniques and process integration considerations for amorphous oxide semiconductor (AOS) thin-film transistors (TFTs) constitute the central theme of this dissertation. Within this theme three primary areas of focus are pursued. The first focus involves formulating a general framework for assessing passivation. Avoiding formation of an undesirable backside accumulation layer in an AOS bottom-gate TFT is accomplished by (i) choosing a passivation layer in which the charge neutrality level is aligned with (ideal case) or higher in energy than that of the semiconductor channel layer charge neutrality level, and (ii) depositing the passivation layer in such a manner that a negligible density of oxygen vacancies are present at the channel-passivation layer interface. Two AOS TFT passivation schemes are explored. Sputter-deposited zinc tin silicon oxide (ZTSO) appears promising for suppressing the effects of negative bias illumination stress (NBIS) with respect to ZTO and IGZO TFTs. Solution-deposited silicon dioxide is used as a barrier layer to subsequent PECVD silicon dioxide deposition, yielding ZTO TFT transfer curves showing that the dual-layer passivation process does not significantly alter ZTO TFT electrical characteristics. The second focus involves creating an adaptable back-end process compatible with flexible substrates. A detailed list of possible via formation techniques is presented with particular focus on non-traditional and adaptable techniques. Two of the discussed methods, “hydrophobic surface treatment”and “printed local insulator,” are demonstrated and proven effective. The third focus is printing AOS TFT channel layers in order to create an adaptable and additive front-end integrated circuit fabrication scheme. Printed zinc indium aluminum oxide (ZIAO) and indium gallium zinc oxide (IGZO) channel layers are demonstrated using a SonoPlot piezoelectric printing system. Finally, challenges associated with printing electronic materials are discussed. Organic-based solutions are easier to print due to their ability to “stick” to the substrate and form well-defined patterns, but have poor electrical characteristics due to the weakness of organic bonds. Inorganic aqueous-based solutions demonstrate good electrical performance when deposited by spin coating, but are difficult to print because precise control of a substrate's hydrophillic/hydrophobic nature is required. However, precise control is difficult to achieve, since aqueous-based solutions either spread out or ball up on the substrate surface. Thickness control of any printed solution is always problematic due to surface wetting and the elliptical thickness profile of a dispensed solution.

Sundholm, Eric Steven

32

Poole-Frenkel behavior in amorphous oxide thin-film transistors prepared on SiOC  

NASA Astrophysics Data System (ADS)

The electron behavior in amorphous indium-gallium-zinc-oxide thin film transistors (a-IGZO TFTs) depends on the polar characteristics of SiOC, which is used as a gate dielectric. The properties of the interface between the semiconductor and SiOC were defined by using a Schottky contact with a low potential barrier and Poole-Frenkel contacts with a high potential barrier. The leakage current of SiOC, which was used as a gate insulator, decreased at the Poole-Frenkel contacts because of the high potential barrier. The ambipolar properties in the field effect transistor were observed to depend on the various characteristics of SiOC, which ranged from its behaving as an ideal insulator or as a material with a high dielectric constant. The resistance of the a-IGZO channel changed from positive to negative at SiOC, which had the lowest polarity. As to the conduction due to the diffusion current, the mobility increased with increasing carrier concentrations. However, the drift carrier conduction was related to the reduced mobility at higher carrier concentrations. The performance of the transistors was enhanced by the tunneling and the diffusion currents Rather than by the drift current caused by trapping. The Schottky contact and the Poole-Frenkel (PF) contacts at an interface between the IGZO channel and the SiOC were defined according to the heights of potential barriers caused by the depletion layer. The leakage current was very low about 10-12 A at SiOC with PF contacts because of the height of potential barrier was double that with a Schottky contact because the tunneling conductance due to the diffusion current originated from the PF contacts of non-polar SiOC.

Oh, Teresa

2014-05-01

33

High mobility amorphous zinc oxynitride semiconductor material for thin film transistors  

NASA Astrophysics Data System (ADS)

Zinc oxynitride semiconductor material is produced through a reactive sputtering process in which competition between reactions responsible for the growth of hexagonal zinc oxide (ZnO) and for the growth of cubic zinc nitride (Zn3N2) is promoted. In contrast to processes in which the reaction for either the oxide or the nitride is dominant, the multireaction process yields a substantially amorphous or a highly disordered nanocrystalline film with higher Hall mobility, 47 cm2 V-1 s-1 for the as-deposited film produced at 50 °C and 110 cm2 V-1 s-1 after annealing at 400 °C. In addition, it has been observed that the Hall mobility of the material increases as the carrier concentration decreases in a carrier concentration range where a multicomponent metal oxide semiconductor, indium-gallium-zinc oxide, follows the opposite trend. This indicates that the carrier transports in the single-metal compound and the multimetal compound are probably dominated by different mechanisms. Film stability and thin film transistor performance of the material have also been tested, and results are presented herein.

Ye, Yan; Lim, Rodney; White, John M.

2009-10-01

34

Solution processed amorphous InGaZnO semiconductor thin films and transistors  

NASA Astrophysics Data System (ADS)

Amorphous indium gallium zinc oxide (a-IGZO) semiconductor thin films and transistors were deposited on alkali-free glasses by the sol-gel route. The atomic ratio of In:Ga:Zn in the solution was 0.7:0.3:1. In this study, the effects of annealing temperature on the structural, surface condition, optical transmittance, and electrical resistivity of a-IGZO semiconductor thin films were investigated. GIXRD measurements and TEM-NBD analysis indicated that all annealed IGZO thin films had an amorphous phase structure. The dried IGZO sol-gel films annealed at a temperature higher than 425 °C had a flat surface and exhibited high transparency (>89%) in the visible region. According to results from TGA, FT-IR and XPS, the residual organic compounds in the dried IGZO sol-gel films were completely removed at the annealing temperatures higher than 450 °C. Therefore, we chose the 450 °C annealed thin film as the active channel layer in the bottom-gate, bottom-contact (BGBC) thin-film transistor (TFT) in the present study. Current-voltage (I-V) characteristics of the 450 °C annealed a-IGZO TFT revealed that it operated in n-type behavior with a positive threshold voltage (enhancement mode).

Tsay, Chien-Yie; Yan, Tzu-Yi

2014-01-01

35

Fabrication of amorphous InGaZnO thin-film transistor-driven flexible thermal and pressure sensors  

NASA Astrophysics Data System (ADS)

In this work, we present the results concerning the use of amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT) as a driving transistor of the flexible thermal and pressure sensors which are applicable to artificial skin systems. Although the a-IGZO TFT has been attracting much attention as a driving transistor of the next-generation flat panel displays, no study has been performed about the application of this new device to the driving transistor of the flexible sensors yet. The proposed thermal sensor pixel is composed of the series-connected a-IGZO TFT and ZnO-based thermistor fabricated on a polished metal foil, and the ZnO-based thermistor is replaced by the pressure sensitive rubber in the pressure sensor pixel. In both sensor pixels, the a-IGZO TFT acts as the driving transistor and the temperature/pressure-dependent resistance of the ZnO-based thermistor/pressure-sensitive rubber mainly determines the magnitude of the output currents. The fabricated a-IGZO TFT-driven flexible thermal sensor shows around a seven times increase in the output current as the temperature increases from 20 °C to 100 °C, and the a-IGZO TFT-driven flexible pressure sensors also exhibit high sensitivity under various pressure environments.

Park, Ick-Joon; Jeong, Chan-Yong; Cho, In-Tak; Lee, Jong-Ho; Cho, Eou-Sik; Kwon, Sang Jik; Kim, Bosul; Cheong, Woo-Seok; Song, Sang-Hun; Kwon, Hyuck-In

2012-10-01

36

Effect of hydrogen incorporation on the negative bias illumination stress instability in amorphous In-Ga-Zn-O thin-film-transistors  

NASA Astrophysics Data System (ADS)

In amorphous indium-gallium-zinc oxide (a-IGZO) thin film transistors, negative shifts of the threshold voltage commonly occur under negative bias illumination stress (NBIS), and its origin is attributed to hole traps such as O-vacancy (VO) defects. We perform density functional calculations to investigate the effect of hydrogenation on the NBIS instability. We find that hydrogen passivates the electrical activity of VO in form of HO, in which H occupies the vacancy site. The activation energy for dissociating HO into VO and an interstitial H (Hi) is about 1.27 eV, much higher than the migration barrier of about 0.51 eV for Hi diffusion. Kinetic Monte Carlo simulations show that HO defects are quite stable upon post thermal annealing up to 200 °C. Thus, we propose that H incorporation into a-IGZO not only effectively reduces the density of VO defects but also mitigates the NBIS instability in devices fabricated at low temperatures.

Noh, Hyeon-Kyun; Park, Ji-Sang; Chang, K. J.

2013-02-01

37

Toward active-matrix lab-on-a-chip: programmable electrofluidic control enabled by arrayed oxide thin film transistors.  

PubMed

Agile micro- and nano-fluidic control is critical to numerous life science and chemical science synthesis as well as kinetic and thermodynamic studies. To this end, we have demonstrated the use of thin film transistor arrays as an active matrix addressing method to control an electrofluidic array. Because the active matrix method minimizes the number of control lines necessary (m + n lines for the m×n element array), the active matrix addressing method integrated with an electrofluidic platform can be a significant breakthrough for complex electrofluidic arrays (increased size or resolution) with enhanced function, agility and programmability. An amorphous indium gallium zinc oxide (a-IGZO) semiconductor active layer is used because of its high mobility of 1-15 cm(2) V(-1) s(-1), low-temperature processing and transparency for potential spectroscopy and imaging. Several electrofluidic functionalities are demonstrated using a simple 2 × 5 electrode array connected to a 2 × 5 IGZO thin film transistor array with the semiconductor channel width of 50 ?m and mobility of 6.3 cm(2) V(-1) s(-1). Additionally, using the TFT device characteristics, active matrix addressing schemes are discussed as the geometry of the electrode array can be tailored to act as a storage capacitor element. Finally, requisite material and device parameters are discussed in context with a VGA scale active matrix addressed electrofluidic platform. PMID:22134753

Noh, Joo Hyon; Noh, Jiyong; Kreit, Eric; Heikenfeld, Jason; Rack, Philip D

2012-01-21

38

Novel oxide amorphous semiconductors: transparent conducting amorphous oxides  

Microsoft Academic Search

A working hypothesis to find wide gap oxide semiconductors was proposed on the basis of simple considerations. The hypothesis predicts that amorphous double oxides composed of heavy metal cations (HMCs) with an electronic configuration (n ? 1)d10s0 are promising candidates for a novel class of amorphous semiconductors. Electrical and optical properties of three amorphous double oxides composed of the HMCs,

Hideo Hosono; Masahiro Yasukawa; Hiroshi Kawazoe

1996-01-01

39

Electronic structure of oxygen-vacancy defects in amorphous In-Ga-Zn-O semiconductors  

NASA Astrophysics Data System (ADS)

We perform first-principles density functional calculations to investigate the atomic and electronic properties of various O-vacancy (VO) defects in amorphous indium gallium zinc oxides (a-IGZO). The formation energies of VO have a tendency to increase with increasing number of neighboring Ga atoms, whereas they are generally low in the environment surrounded with In atoms. Thus, adding Ga atoms suppresses the formation of O-deficiency defects, which are considered as the origin of device instability in a-IGZO-based thin film transistors. The conduction band edge state is characterized by the In s orbital and insensitive to disorder, in good agreement with the experimental finding that increasing the In content enhances the carrier density and mobility. In a-IGZO, while most VO defects are deep donors, some of the defects act as shallow donors due to local environments different from those in crystalline oxides. As ionized O vacancies can capture electrons, it is suggested that these defects are responsible for positive shifts of the threshold voltage observed under positive gate bias stress. Under light illumination stress, VO defects can be ionized, becoming VO2+ defects due to the negative-U behavior. When electrons are captured by applying a negative bias voltage, ionized VO2+ defects return to the original neutral charge state. Through molecular dynamics simulations, we find that the initial neutral state is restored by annealing, in good agreement with experiments, although the annealing temperature depends on the local environment. Our calculations show that VO defects play an important role in the instability of a-IGZO-based devices.

Noh, Hyeon-Kyun; Chang, K. J.; Ryu, Byungki; Lee, Woo-Jin

2011-09-01

40

Metal-oxide complementary inverters with a vertical geometry fabricated on flexible substrates  

NASA Astrophysics Data System (ADS)

We report on the fabrication of p-channel thin film transistors (TFTs) and vertically stacked complementary inverters comprised of a p-channel copper oxide TFT on top of an n-channel indium gallium zinc oxide TFT fabricated on a flexible polyethersulfone substrate. The p- and n-channel TFTs showed saturation mobility values of 0.0022 and 1.58 cm2/Vs, respectively, yielding inverters with a gain of 120 V/V. This level of performance was achieved by reducing the copper oxide channel thickness, allowing oxygen diffusion into the copper oxide layer at medium processing temperature (150 °C).

Dindar, A.; Kim, J. B.; Fuentes-Hernandez, C.; Kippelen, B.

2011-10-01

41

All solution-processed high-resolution bottom-contact transparent metal-oxide thin film transistors  

Microsoft Academic Search

We report all solution-processed high-resolution bottom-contact indium-gallium-zinc-oxide (IGZO) thin film transistors (TFTs) using a simple surface patterning and dip-casting process. High-resolution nanoparticulate Ag source\\/drain electrodes and a sol-gel processed IGZO semiconductor were deposited by a simple dip-casting along with a photoresist-free, non-relief-pattern lithographic process. The deposited Ag and IGZO solution can be steered into the desired hydrophilic areas by a

Sung Kyu Park; Yong-Hoon Kim; Jeong-In Han

2009-01-01

42

Fabrication and characterization of oxide-based thin film transistors, and process development for oxide heterostructures  

NASA Astrophysics Data System (ADS)

This dissertation is focused on the development of thin film transistors (TFTs) using oxide materials composed of post-transitional cations with (n-1)d 10ns0 (n?4). The goal is to achieve high performance oxide-based TFTs fabricated at low processing temperature on either glass or flexible substrates for next generation display applications. In addition, etching mechanism and Ohmic contact formation for oxide heterostructure (ZnO/CuCrO 2) system is demonstrated. The deposition and characterization of oxide semiconductors (In 2O3-ZnO, and InGaZnO4) using a RF-magnetron sputtering system are studied. The main influence on the resistivity of the films is found to be the oxygen partial pressure in the sputtering ambient. The films remained amorphous and transparent (> 70%) at all process conditions. These films showed good transmittance at suitable conductivity for transistor fabrication. The electrical characteristics of both top- and bottom-gate type Indium Zinc Oxide (InZnO) and Indium Gallium Zinc Oxide (InGaZnO4)-based TFTs are reported. The InZnO films were favorable for depletion-mode TFTs due to their tendency to form oxygen vacancies, while enhancement-mode devices were realized with InGaZnO4 films. The InGaZnO4-based TFTs fabricated on either glass or plastic substrates at low temperature (<100°C) exhibit good electrical properties: the saturation mobility of 5--12 cm2.V-1.s-1 and threshold voltage of 0.5--2.5V. The devices are also examined as a function of aging time in order to verify long-term stability in air. The effect of gate dielectric materials on electrical properties of InGaZnO 4-based TFTs was investigated. The use of SiNx film as a gate dielectric reduces the trap density and the roughness at the channel/gate dielectric interface compared to SiO2 gate dielectric, resulting in an improvement of device parameters by reducing scattering of trapped charges at the interface. The quality of interface is shown to have large effect on TFT performance. Plasma etching process of ZnO was carried out using a variety of plasma chemistries: CH4/H2-, C2H6/H 2-, Cl2-, IBr-, ICl-, BI3- and BBr3/Ar. High fidelity pattern transfer can be achieved with practical etch rate and very smooth surface in methane-based chemistries, although the sidewall is not completely vertical. Threshold energy as low as 60 +/- 20 eV for all plasma chemistries was achieved, confirming that etching is driven by ion-assisted mechanism over the whole range of ion energy. Ohmic contacts to p-CuCrO2 are examined using borides (CrB2 and W2B5), nitrides (TaN and ZrN) and a high temperature metal (Ir). These materials are used as a diffusion barrier in Ni/Au based contacts, i.e., Ni/Au/X/Ti/Au metallization scheme, where X is the refractory material. A minimum specific contact resistance of ˜ 5x10 -4 O.cm2 was achieved for the Ir-containing contacts after annealing at temperature of 500--800°C for 60s in O2 ambient. The presence of Ir diffusion barrier increase the thermal stability of the contacts by ˜ 200 °C compared to conventional Ni/Au contacts. By sharp contrast, the use of other refractory materials led to the poorer thermal stability, with the contact resistance increasing sharply above 400°C.

Lim, Wantae

43

Natural realgar and amorphous AsS oxidation kinetics  

Microsoft Academic Search

The oxidation rates of natural realgar and amorphous synthetic AsS by dissolved oxygen were evaluated using mixed flow reactors at pH 7.2 to 8.8 and dissolved oxygen contents of 5.9 to 16.5 ppm over a temperature range of 25 to 40°C. The ratios of As\\/S are stoichiometric for all amorphous AsS oxidation experiments except for two experiments conducted at pH

Maggy F. Lengke; Regina N. Tempel

2003-01-01

44

Amorphous phase in electrochemically oxidized porous silicon  

Microsoft Academic Search

An amorphous phase has been demonstrated in porous silicon prepared by anodization of silicon wafers. The radial distribution function has been calculated on the basis of the X-ray diffraction pattern recorded from a typical sample. There was revealed an amorphous phase of composition SiO1–6.

Mihai A. Popescu; Valentin N. Chumash; Ion Cojocaru; Vinod K. Jain; Amita Gupta

1996-01-01

45

Acidic amorphous silica prepared from iron oxide of bacterial origin.  

PubMed

Microporous and mesoporous silica derived from biogenous iron oxide is an attractive catalyst for various organic reactions. Biogenous iron oxide contains structural silicon, and amorphous silica remains after iron oxide is dissolved in concentrated hydrochloric acid. The amorphous silica containing slight amounts of iron (Si/Fe = ?150) is composed of ?6-nm-diameter granular particles. The amorphous silica has a large surface area of 540 m(2)/g with micropores (1.4 nm) and mesopores (<3 nm). By using pyridine vapor as a probe molecule to evaluate the active sites in the amorphous silica, it was found that this material has strong Brønsted and Lewis acid sites. When the catalytic performance of this material was evaluated for reactions including the ring opening of epoxides and Friedel-Crafts-type alkylations, which are known to be catalyzed by acid catalysts, this material showed yields higher than those obtained with common silica materials. PMID:23331569

Hashimoto, Hideki; Itadani, Atsushi; Kudoh, Takayuki; Kuroda, Yasushige; Seno, Masaharu; Kusano, Yoshihiro; Ikeda, Yasunori; Nakanishi, Makoto; Fujii, Tatsuo; Takada, Jun

2013-02-01

46

Unveiling the complex electronic structure of amorphous metal oxides  

PubMed Central

Amorphous materials represent a large and important emerging area of material’s science. Amorphous oxides are key technological oxides in applications such as a gate dielectric in Complementary metal-oxide semiconductor devices and in Silicon-Oxide-Nitride-Oxide-Silicon and TANOS (TaN-Al2O3-Si3N4-SiO2-Silicon) flash memories. These technologies are required for the high packing density of today’s integrated circuits. Therefore the investigation of defect states in these structures is crucial. In this work we present X-ray synchrotron measurements, with an energy resolution which is about 5–10 times higher than is attainable with standard spectrometers, of amorphous alumina. We demonstrate that our experimental results are in agreement with calculated spectra of amorphous alumina which we have generated by stochastic quenching. This first principles method, which we have recently developed, is found to be superior to molecular dynamics in simulating the rapid gas to solid transition that takes place as this material is deposited for thin film applications. We detect and analyze in detail states in the band gap that originate from oxygen pairs. Similar states were previously found in amorphous alumina by other spectroscopic methods and were assigned to oxygen vacancies claimed to act mutually as electron and hole traps. The oxygen pairs which we probe in this work act as hole traps only and will influence the information retention in electronic devices. In amorphous silica oxygen pairs have already been found, thus they may be a feature which is characteristic also of other amorphous metal oxides.

?rhammar, C.; Pietzsch, Annette; Bock, Nicolas; Holmstrom, Erik; Araujo, C. Moyses; Grasjo, Johan; Zhao, Shuxi; Green, Sara; Peery, T.; Hennies, Franz; Amerioun, Shahrad; Fohlisch, Alexander; Schlappa, Justine; Schmitt, Thorsten; Strocov, Vladimir N.; Niklasson, Gunnar A.; Wallace, Duane C.; Rubensson, Jan-Erik; Johansson, Borje; Ahuja, Rajeev

2011-01-01

47

Comparison of electrochromic amorphous and crystalline tungsten oxide films  

Microsoft Academic Search

A detailed systematic study of the tungsten oxide thin films has been carried out using WO3 films after they were annealed at progressively increasing temperatures ranging from 350°C to 450°C in oxygen environments. The structural properties of the films were characterized using X-ray diffraction and Raman spectroscopy. The amorphous WO3 films remain as an amorphous phase up to 385°C and

Esra Ozkan; Se-Hee Lee; C. Edwin Tracy; J. Roland Pitts; Satyen K. Deb

2003-01-01

48

Infrared Absorption at Longitudinal Optical Frequency in Amorphous Oxides and Their Mixtures  

Microsoft Academic Search

Infrared absorption at longitudinal optical (LO) frequency was measured in amorphous aluminum oxide, amorphous magnesium oxide and their mixtures. It was found that the LO mode of a mixture of these oxides has a single peak, and its position lies between those of the constituents if two oxides are mixed on the order of angstroms. The LO mode of amorphous

Takeshi Ohwaki; Takashi Onishi

1999-01-01

49

Amorphous tin-cadmium oxide films and the production thereof  

DOEpatents

A tin-cadmium oxide film having an amorphous structure and a ratio of tin atoms to cadmium atoms of between 1:1 and 3:1. The tin-cadmium oxide film may have an optical band gap of between 2.7 eV and 3.35 eV. The film may also have a charge carrier concentration of between 1.times.10.sup.20 cm.sup.-3 and 2.times.10.sup.20 cm.sup.-3. The tin cadmium oxide film may also exhibit a Hall mobility of between 40 cm.sup.2V.sup.-1 s.sup.-1 and 60 cm.sup.2V.sup.-1 s.sup.-1. Also disclosed is a method of producing an amorphous tin-cadmium oxide film as described and devices using same.

Li, Xiaonan; Gessert, Timothy A

2013-10-29

50

Unified interatomic potential and energy barrier distributions for amorphous oxides  

NASA Astrophysics Data System (ADS)

Amorphous tantala, titania, and hafnia are important oxides for biomedical implants, optics, and gate insulators. Understanding the effects of oxide doping is crucial to optimize performance in these applications. However, no molecular dynamics potentials have been created to date that combine these and other oxides that would allow computational analyses of doping-dependent structural and mechanical properties. We report a novel set of computationally efficient, two-body potentials modeling van der Waals and covalent interactions that reproduce the structural and elastic properties of both pure and doped amorphous oxides. In addition, we demonstrate that the potential accurately produces energy barrier distributions for pure and doped samples. The distributions can be directly compared to experiment and used to calculate physical quantities such as internal friction to understand how doping affects material properties. Future analyses using these potentials will be of great value to determine optimal doping concentrations and material combinations for myriad material science applications.

Trinastic, J. P.; Hamdan, R.; Wu, Y.; Zhang, L.; Cheng, Hai-Ping

2013-10-01

51

Multi-scale order in amorphous transparent oxide thin films  

NASA Astrophysics Data System (ADS)

Nominally ``diffraction amorphous'' materials represent a pervasive challenge in establishing classical structure-property relationships. This stems from the difficulty in defining the structure of nominally amorphous materials and experimentally differentiating the short-range (<10 A?) and medium-range (10 to 30 A?) order as a function of process parameters which are important due to their influence on physical, chemical, or transport properties. Herein, we report on the determination of short- and medium-range order in nominally amorphous zinc and tin co-substituted indium oxide In1.4Zn0.3Sn0.3O3 (a-ZITO) thin films grown by pulsed laser deposition. These thin films are being explored as transparent conductors that exhibit changes in transport properties depending on deposition temperature while remaining ``diffraction amorphous.'' Reduced density function (RDF) analysis from electron diffraction accompanied by density functional theory molecular dynamics simulation of a liquid quench suggests ordering at short range. Scanning transmission fluctuation electron microscopy (STFEM) indicates the presence of ordered ZITO regions at medium range. For a-ZITO films grown at different temperatures, RDF analysis showed no significant change in the short range order. However, STFEM revealed notable structural (and symmetry) differences at medium range. The existence of this type of multi-scale local order in amorphous ZITO thin films highlights the importance of a combined approach to unravel the structures of nominally amorphous materials and to understand structure-properties correlations.

Yan, Aiming; Sun, Tao; Borisenko, Konstantin B.; Buchholz, D. Bruce; Chang, Robert P. H.; Kirkland, Angus I.; Dravid, Vinayak P.

2012-09-01

52

Oxide semiconductor film on amorphous insulating surface  

US Patent & Trademark Office Database

Objects are to provide a semiconductor device for high power application in which a novel semiconductor material having high productivity is used and to provide a semiconductor device having a novel structure in which a novel semiconductor material is used. The present invention is a vertical transistor and a vertical diode each of which has a stacked body of an oxide semiconductor in which a first oxide semiconductor film having crystallinity and a second oxide semiconductor film having crystallinity are stacked. An impurity serving as an electron donor (donor) which is contained in the stacked body of an oxide semiconductor is removed in a step of crystal growth; therefore, the stacked body of an oxide semiconductor is highly purified and is an intrinsic semiconductor or a substantially intrinsic semiconductor whose carrier density is low. The stacked body of an oxide semiconductor has a wider band gap than a silicon semiconductor.

2014-04-15

53

Photochemical route for accessing amorphous metal oxide materials for water oxidation catalysis.  

PubMed

Large-scale electrolysis of water for hydrogen generation requires better catalysts to lower the kinetic barriers associated with the oxygen evolution reaction (OER). Although most OER catalysts are based on crystalline mixed-metal oxides, high activities can also be achieved with amorphous phases. Methods for producing amorphous materials, however, are not typically amenable to mixed-metal compositions. We demonstrate that a low-temperature process, photochemical metal-organic deposition, can produce amorphous (mixed) metal oxide films for OER catalysis. The films contain a homogeneous distribution of metals with compositions that can be accurately controlled. The catalytic properties of amorphous iron oxide prepared with this technique are superior to those of hematite, whereas the catalytic properties of a-Fe(100-y-z)Co(y)Ni(z)O(x) are comparable to those of noble metal oxide catalysts currently used in commercial electrolyzers. PMID:23539180

Smith, Rodney D L; Prévot, Mathieu S; Fagan, Randal D; Zhang, Zhipan; Sedach, Pavel A; Siu, Man Kit Jack; Trudel, Simon; Berlinguette, Curtis P

2013-04-01

54

Surface oxidation of amorphous Ni?Zr alloys  

NASA Astrophysics Data System (ADS)

The surface oxidation behaviour of amorphous Ni 64Zr 36 and Ni 91Zr 9 was investigated in situ by XPS and UPS. Oxygen doses up to 2000 L (Langmuir units) were used to study the initial stages of oxidation of the clean surfaces in the temperature range from room temperature to 300°C. XPS core level binding energy shifts of Zr3d lines showed formation of zirconium oxides even at very low exposures. We observed different core level shifts of Zr3d in Ni 64Zr 36 and Ni 91Zr 9 indicating different stoichiometry of the oxides. A pronounced surface segregation of Zr was observed upon oxidation of the alloys. It is shown that this segregation is not a thermal but an oxygen induced phenomenon. The oxidation of Ni is strongly inhibited by Zr. Oxidation of Ni is only observed in Ni 91Zr 9 at 300°C after exposure to more than 1000 L O 2. In the UPS spectra we found a shift of the Ni3d band position towards lower binding energy which can be interpreted as a subsurface Ni enrichment of the amorphous alloys.

Walz, B.; Oelhafen, P.; Güntherodt, H.-J.; Baiker, A.

1989-07-01

55

Universal Medium-Range Order of Amorphous Metal Oxides  

NASA Astrophysics Data System (ADS)

We propose that the structure of amorphous metal oxides can be regarded as a dual-dense-random-packing structure, which is a superposition of the dense random packing of metal atoms and that of oxygen atoms. Our ab initio molecular dynamics simulations show that the medium-range order of amorphous HfO2, ZrO2, TiO2, In2O3, Ga2O3, Al2O3,, and Cu2O is characterized by the pentagonal-bipyramid arrangement of metal atoms and that of oxygen atoms, and prove the validity of our dual-random-sphere-packing model. In other words, we find that the pentagonal medium-range order is universal independent of type of metal oxide.

Nishio, Kengo; Miyazaki, Takehide; Nakamura, Hisao

2013-10-01

56

Bipolar resistive switching in amorphous titanium oxide thin film  

Microsoft Academic Search

Using isothermal and temperature-dependent electrical measurements, we investigated the resistive switching mechanism of amorphous titanium oxide thin films deposited by a plasma-enhanced atomic layer deposition method between two aluminum electrodes. We found a bipolar resistive switching behavior in the high temperature region (> 140 K), and two activation energies of shallow traps, 0.055 eV and 0.126 eV in the ohmic

Hu Young Jeong; Jeong Yong Lee; Min-Ki Ryu; Sung-Yool Choi

2010-01-01

57

Instabilities in Amorphous Oxide Semiconductor Thin-Film Transistors  

Microsoft Academic Search

Thin-film transistors (TFTs) fabricated using amorphous oxide semiconductors (AOS) exhibit good electron mobility (5 to >; 50 cm2\\/V · s), they are transparent, and they can be processed at low temperatures. These new materials show a great promise for high-performance large-area electronics applications such as flexible electronics, transparent electronics, and analog current drivers for organic light-emitting diode displays. Before any

2010-01-01

58

Compositional disorder and transport peculiarities in the amorphous indium oxides  

NASA Astrophysics Data System (ADS)

We present results of the disorder-induced metal-insulator transition (MIT) in three-dimensional amorphous indium-oxide films. The amorphous version studied here differs from the one reported by Shahar and Ovadyahu [Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.46.10917 46, 10917 (1992)] in that it has a much lower carrier concentration. As a measure of the static disorder we use the dimensionless parameter kF?. Thermal annealing is employed as the experimental handle to tune the disorder. On the metallic side of the transition, the low temperature transport exhibits weak-localization and electron-electron correlation effects characteristic of disordered electronic systems. These include a fractional power-law conductivity versus temperature behavior anticipated to occur at the critical regime of the transition. The MIT occurs at a kF??0.3 for both versions of the amorphous material. However, in contrast with the results obtained on the electron-rich version of this system, no sign of superconductivity is seen down to ?0.3 K even for the most metallic sample used in the current study. This demonstrates that using kF? as a disorder parameter for the superconductor-insulator transition (SIT) is an ill defined procedure. A microstructural study of the films, employing high resolution chemical analysis, gives evidence for spatial fluctuations of the stoichiometry. This brings to light that, while the films are amorphous and show excellent uniformity in transport measurements of macroscopic samples, they contain compositional fluctuations that extend over mesoscopic scales. These, in turn, reflect prominent variations of carrier concentrations thus introducing an unusual type of disorder. It is argued that this compositional disorder may be the reason for the apparent violation of the Ioffe-Regel criterion in the two versions of the amorphous indium oxide. However, more dramatic effects due to this disorder are expected when superconductivity sets in, which are in fact consistent with the prominent transport anomalies observed in the electron-rich version of indium oxide. The relevance of compositional disorder (or other agents that are effective in spatially modulating the BCS potential) to other systems near their SIT is discussed.

Givan, U.; Ovadyahu, Z.

2012-10-01

59

Transparent conducting oxides (TCO's) for amorphous silicon solar cells  

NASA Astrophysics Data System (ADS)

The stability of various textured tin oxide and zinc oxide transparent conductors was evaluated against annealing in air, in vacuum or exposed to hydrogen plasma. Only fluorine-doped zinc oxide deposited by atmospheric pressure chemical vapor deposition (APCVD) had stable electrical and optical properties under all conditions. Thin layers of ZnO or TiO2 greatly improved the plasma resistance of SnO2. A new TCO material, niobium-doped titanium dioxide (TiO2:Nb) was able to withstand hydrogen plasmas with only slight increases in its optical absorption and conductivity. Composite TCO's consisting of glass/SnO2:F/TiO2:Nb were shown to provide good electrical contact to amorphous silicon solar cells.

Hegedus, Steven; Liang, Haifan; Gordon, Roy G.

1996-01-01

60

Bipolar resistive switching in amorphous titanium oxide thin films  

Microsoft Academic Search

Using isothermal and temperature-dependent electrical measurements, we\\u000ainvestigated the resistive switching mechanism of amorphous titanium oxide thin\\u000afilms deposited by a plasma-enhanced atomic layer deposition method between two\\u000aaluminum electrodes. We found a bipolar resistive switching behavior in the\\u000ahigh temperature region (> 140 K), and two activation energies of shallow\\u000atraps, 0.055 eV and 0.126 eV in the ohmic

Hu Young Jeong; Jeong Yong Lee; Min-Ki Ryu; Sung-Yool Choi

2009-01-01

61

Water oxidation by amorphous cobalt-based oxides: volume activity and proton transfer to electrolyte bases.  

PubMed

Water oxidation in the neutral pH regime catalyzed by amorphous transition-metal oxides is of high interest in energy science. Crucial determinants of electrocatalytic activity were investigated for a cobalt-based oxide film electrodeposited at various thicknesses on inert electrodes. For water oxidation at low current densities, the turnover frequency (TOF) per cobalt ion of the bulk material stayed fully constant for variation of the thickness of the oxide film by a factor of 100 (from about 15?nm to 1.5??m). Thickness variation changed neither the nanostructure of the outer film surface nor the atomic structure of the oxide catalyst significantly. These findings imply catalytic activity of the bulk hydrated oxide material. Nonclassical dependence on pH was observed. For buffered electrolytes with pKa values of the buffer base ranging from 4.7 (acetate) to 10.3 (hydrogen carbonate), the catalytic activity reflected the protonation state of the buffer base in the electrolyte solution directly and not the intrinsic catalytic properties of the oxide itself. It is proposed that catalysis of water oxidation occurs within the bulk hydrated oxide film at the margins of cobalt oxide fragments of molecular dimensions. At high current densities, the availability of a proton-accepting base at the catalyst-electrolyte interface controls the rate of water oxidation. The reported findings may be of general relevance for water oxidation catalyzed at moderate pH by amorphous transition-metal oxides. PMID:24449514

Klingan, Katharina; Ringleb, Franziska; Zaharieva, Ivelina; Heidkamp, Jonathan; Chernev, Petko; Gonzalez-Flores, Diego; Risch, Marcel; Fischer, Anna; Dau, Holger

2014-05-01

62

Consolidation of amorphous oxide powders using spark plasma sintering  

NASA Astrophysics Data System (ADS)

The objective of this study is to synthesize amorphous oxide powders and sinter the systems close to or at theoretical density for optical transparency while retaining the amorphous structure using the Spark Plasma Sintering (SPS) method. In addition, the parameters that govern the formation of these systems were investigated. The main powder processing techniques are sol-gel, flame-spaying and spherodizing. The systems chosen for this study are alumina-rich rare earth oxides of alumina-lanthana (AL) and alumina-gadolinia (AG). These systems cannot be formed in bulk form by the melt method because of the extremely fast cooling rates needed to maintain the glassy phase. Sintering is an alternative method. Attempts were made by others to form or sinter these systems with little or no success. Amorphous powders of different processing methods and compositions were sintered using SPS at temperatures ranging from 840 to 900°C and pressures from 164 to 742 MPa. For the AL system, the highest transmittance which correlates to the highest relative density without crystallization was obtained with the parameters of 860°C, 742 MPa, and a 200C.min -1 ramp rate and a 4 min hold time for transmittance in the UV/Vis range of more than 40% at 650 nm. In the IR range, the transmittance was above 65%. At lower pressures, e.g. 164 MPA, increasing the hold time increased the transmittance of the sample. Likewise, the AG system showed higher transmittance with increased pressure. Densities of both systems increased with increasing temperature. However, above 880°C, the increase in densities was due to partial crystallization which resulted in the decrease of transmittance. The spherodization process resulted in the crystallization of some of the beads. The transmittance could be improved by removal of the crystallized beads since the amorphous phase sintered to high densities. The flame spray method resulted in nanometric particles which also sintered to high densities. The powders contained silica fibers from the collection process which causes scattering and a reduction of the transmittance. The fast heating rates and short sintering times of the SPS make it possible to sinter amorphous systems at higher temperatures compared to other sintering techniques without crystallization.

Fredrick, Daniela Marisa

63

Comparison Between Crystalline and Amorphous Surfaces of Transition Metal Oxide Water Oxidation Catalysts: a Theoretical Perspective  

NASA Astrophysics Data System (ADS)

Amorphous films of transition-metal oxide water oxidation catalysts (WOCs) often show an enhanced catalytic activity compared to their crystalline counterparts [1-4]. In particular, in the case of cobalt-oxide based WOCs the observed similarity in their electrochemical properties and catalytic activity, under oxidative conditions, has been correlated with the formation of similar amorphous surface morphologies, suggesting the presence of a common, catalytically active amorphous structural motif [3,4]. We present ab initio calculations of cobalt oxide based material surfaces and we compare the electronic properties of crystalline and amorphous surfaces, with the aim of identifying differences related to their different catalytic activity.[4pt] [1] Blakemore, J. D., Schley, N. D., Kushner-Lenhoff, M. N., Winter, A. M., D'Souza, F., Crabtree, R. H., and Brudvig, G. W. Inorg. Chem. 51, 7749 (2012); [2] Tsuji, E., Imanishi, A., Fukui, K.-I. and Nakato, Y. Electrochimica Acta 56, 2009 (2011); [3] Jia, H., Stark, J., Zhou, L. Q., Ling, C., Takeshi, S., and Markin, Z. RSC Advances 2, 10874 (2012); [4] Lee, S. W., Carlton, C., Risch, M., Surendranath, Y., Chen, S., Furutsuki, S., Yamada, A., Nocera, D. G., and Shao-Horn, Y. J. Am. Chem. Soc. 134, 16959 (2012).

Skone, Jonathan H.; Galli, Giulia

2013-03-01

64

Carrier-Induced Lattice Instability in Amorphous Oxide Semiconductors  

NASA Astrophysics Data System (ADS)

Amorphous oxide semiconductors (AOS's) have high electron mobility even in amorphous phase. The AOS-based thin film transistors (TFTs) are nowadays intensively pursued to be adopted into high-resolution flat-panel displays. However, a facing bottleneck of the AOS-based TFT display applications is the instability problem under bias and illumination stress conditions. Especially, by negative bias and illumination stress (NBIS) or only by illumination stress (IS), the threshold voltage of the AOS TFTs is largely negative-shifted. In this work, we study the instability mechanism of the AOS's based on first-principles calculations. The valence band tail states of the AOS's are found to be characterized by the O-O pp?* anti-bonding state. The excited localized-holes thus give lattice instability and form O-O bonds through the pp?-hybridized interaction. The pp?* level is heightened up into the conduction bands along with the O-O bond formation, and two electrons left from the created O-vacancy (VO) occupy the delocalized conduction band states. The O-O and VO complex (a peroxide defect) is found to be a meta-stable donor defect and suggested as an origin of the NBIS and IS instabilities in AOS TFTs. Based on the suggested mechanism, we propose a direction to improve the stability of AOS thin films with optimizing the cation compositions.

Kim, Yong-Sung; Nahm, Ho-Hyun; Kim, Dae-Hwan

2013-03-01

65

Preparation and Crystallization of Tin-doped and Undoped Amorphous Indium Oxide Films Deposited by Sputtering  

Microsoft Academic Search

Tin-doped and undoped amorphous indium oxide films were preparedby dc magnetron sputtering without substrate heating at relativelyhigh total gas pressures and relatively large target-substratedistance. The structural and electrical properties of these filmswere investigated by X-ray diffraction and Hall-effect measurements.The amorphous tin-doped indium oxide (a-ITO) films were crystallizedat a temperature about 30°C higher than that for amorphousindium oxide (a-IO) films.

Pung Keun Song; Hirotaka Akao; Masayuki Kamei; Yuzo Shigesato; Itaru Yasui

1999-01-01

66

Low operating voltage InGaZnO thin-film transistors based on Al2O3 high- k dielectrics fabricated using pulsed laser deposition  

NASA Astrophysics Data System (ADS)

Low-voltage-driven amorphous indium-gallium-zinc-oxide (IGZO) thin-film transistors (TFTs) with an Al2O3 dielectric were fabricated on a Si substrate by using pulsed laser deposition. Both Al2O3 and IGZO thin films are amorphous, and the thin films have very smooth surfaces. The Al2O3 gate dielectric exhibits a very low leakage current density of 1.3 × 10-8 A/cm2 at 5 V and a high capacitance density of 60.9 nF/cm2. The IGZO TFT with a structure of Ni/IGZO/Al2O3/Si exhibits high performance with a low threshold voltage of 1.18 V, a high field effect mobility of 20.25 cm2V-1s-1, an ultra small subthreshold swing of 87 mV/decade, and a high on/off current ratio of 3 × 107.

Geng, G. Z.; Liu, G. X.; Zhang, Q.; Shan, F. K.; Lee, W. J.; Shin, B. C.; Cho, C. R.

2014-05-01

67

A comparison of electrochromic properties of sol–gel derived amorphous and nanocrystalline tungsten oxide films  

Microsoft Academic Search

A pristine acetylated peroxotungstate sol with and without 4wt% of oxalic acid dihydrate (OAD) yielded nanocrystalline and amorphous tungsten oxide (WO3) films respectively by dip coating technique. Contrary to the expected trend, whereby, the nanostructured 4% OAD film with a triclinic modification should have shown superior electrochromic efficiency, its amorphous 0% OAD counterpart exhibits higher optical modulation and coloration efficiency

M. Deepa; D. P. Singh; S. M. Shivaprasad; S. A. Agnihotry

2007-01-01

68

Increased corrosion resistance of stent materials by converting current surface film of polycrystalline oxide into amorphous oxide.  

PubMed

Current efforts of new stent technology have been aimed largely at the improvement of intravascular stent biocompatibility. Among the chemical characteristics of metallic stents, surface oxide corrosion properties are paramount. Using our unique technique, the currently marketed 316 L stainless steel and nitinol stent wires covered with polycrystalline oxide were chemically etched and then passivated to form amorphous oxide. Excellent metallic-stent corrosion resistance with an amorphous oxide surface was demonstrated in our previous in vitro study. For in vivo validation, we compared the corrosion behavior of different oxide surfaces on various forms of test wires in the abdominal aorta of mongrel dogs using open-circuit potential and cyclic anodic polarization measurements. After conduction, the retrieved test wires were observed under scanning electron microscope. No passivity breakdown was found for wires covered with amorphous oxide, while wires with polycrystalline oxide showed breakdown at potentials between +0.2 to + 0.6 V. It has been proven that severe pitting or crevice corrosion occurred on the surface of polycrystalline oxide, while the surface of amorphous oxide was free of degradations in our experiment. We have demonstrated that this amorphous oxide coating on metallic material provides better corrosion resistance, not only in vitro but also in vivo, and it is superior not only in strength safety but also in medical device biocompatibility. PMID:10951371

Shih, C C; Lin, S J; Chung, K H; Chen, Y L; Su, Y Y

2000-11-01

69

Oxidation and carbidation of laser-ablated amorphized Ti particles in carbon monoxide  

NASA Astrophysics Data System (ADS)

IR laser ablation of hexagonal titanium in vacuum leads to amorphization of ablated Ti particles and when carried out in gaseous carbon monoxide it proceeds as reactive ablation involving particles amorphization, oxidation and carbidation. The films deposited in vacuum and in the presence of CO were examined by Fourier transform infrared, Raman and X-ray photoelectron spectroscopy, X-ray and electron diffraction and electron microscopy. The Ti films become oxidized upon contact with air and the Ti/C/O films are composed of Ti-O, Ti-C and C-O bonds-containing structures with Ti in Ti2+-Ti4+ state and incorporating crystalline rutile and elemental carbon. The ablation in vacuum represents a new approach to amorphous titanium and it is judged that hot ablated Ti particles are modified by reactions with CO decomposition products into amorphous Ti oxycarbides which undergo rapid post-pulse amorphization.

Jandová, V?ra; Kup?ík, Jaroslav; Bastl, Zden?k; Šubrt, Jan; Pola, Josef

2013-05-01

70

Probing of 2 dimensional confinement-induced structural transitions in amorphous oxide thin film  

NASA Astrophysics Data System (ADS)

Whereas the atomic structure of surface of crystals is known to be distinct from that of bulk, experimental evidence for thickness-induced structural transitions in amorphous oxides is lacking. We report the NMR result for amorphous alumina with varying thickness from bulk up to 5 nm, revealing the nature of structural transitions near amorphous oxide surfaces/interfaces. The coordination environments in the confined amorphous alumina thin film are distinct from those of bulk, highlighted by a decrease in the fractions of high-energy clusters (and thus the degree of disorder) with thickness. The result implies that a wide range of variations in amorphous structures may be identified by controlling its dimensionality.

Lee, Sung Keun; Ahn, Chi Won

2014-02-01

71

Numerical Design of SiO2 Bridges in Stretchable Thin Film Transistors  

NASA Astrophysics Data System (ADS)

An amorphous indium--gallium--zinc oxide based inverter (a-IGZO inverter) was fabricated. Subsequently, its mechanical characteristics were investigated. A numerical method was adopted to optimize the a-IGZO inverter design. This optimization secured mechanical stability. The curvature at the edge of the SiO2 pad and the thickness of the indium--tin-oxide (ITO) electrode were accounted for in the models. The new model improved the mechanical stability when it was stretched by a total of 5% of its length along the x-axis and did not exhibit fractures or cracks. In contrast, the referenced model fractured under the same condition. It has been verified by both experiments and simulations that newly designed models obtain mechanical stability.

Kim, Byung-Jae; Park, Kyung-Yea; Ahn, Jong-Hyun; Kim, Youn-Jea

2012-01-01

72

Enhanced bias stress stability of a-InGaZnO thin film transistors by inserting an ultra-thin interfacial InGaZnO:N layer  

NASA Astrophysics Data System (ADS)

Amorphous indium-gallium-zinc oxide (a-IGZO) thin film transistors (TFTs) having an ultra-thin nitrogenated a-IGZO (a-IGZO:N) layer sandwiched at the channel/gate dielectric interface are fabricated. It is found that the device shows enhanced bias stress stability with significantly reduced threshold voltage drift under positive gate bias stress. Based on x-ray photoelectron spectroscopy measurement, the concentration of oxygen vacancies within the a-IGZO:N layer is suppressed due to the formation of N-Ga bonds. Meanwhile, low frequency noise analysis indicates that the average trap density near the channel/dielectric interface continuously drops as the nitrogen content within the a-IGZO:N layer increases. The improved interface quality upon nitrogen doping agrees with the enhanced bias stress stability of the a-IGZO TFTs.

Huang, Xiaoming; Wu, Chenfei; Lu, Hai; Ren, Fangfang; Chen, Dunjun; Zhang, Rong; Zheng, Youdou

2013-05-01

73

Investigation of tow-step electrical degradation behavior in a-InGaZnO thin-film transistors with Sm2O3 gate dielectrics  

NASA Astrophysics Data System (ADS)

We investigate the electrical stress-induced instability in amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs) with Sm2O3 gate dielectrics. Tow-step electrical degradation behavior in Sm2O3 a-IGZO TFT devices was found under high gate and drain voltage stress during 1000 s. A typical small positive shift followed by an unusual negative shift of threshold voltage is characterized in our TFT devices. We believe that the positive shift of the threshold voltage is due to charge trapping in the gate dielectric and/or at the channel/dielectric interfaces, while the negative shift of threshold voltage can be attributed to the generation of extra electrons from oxygen vacancies in the a-IGZO channel. We suggested that the amount of oxygen vacancies and the quality of the high-? gate dielectric probably affect the degradation behavior of a-IGZO TFT devices.

Chen, Fa-Hsyang; Her, Jim-Long; Hung, Meng-Ning; Pan, Tung-Ming

2013-07-01

74

Optical, structural and photoelectron spectroscopic studies on amorphous and crystalline molybdenum oxide thin films  

Microsoft Academic Search

Optical, structural and electronic properties of amorphous and crystalline molybdenum oxide thin films have been investigated. As-deposited amorphous films got crystallized into a layered orthorhombic phase on annealing at 350°C. Refractive index (n) and extinction coefficient (k) of as-deposited films and films annealed at 150°C, 240°C and 350°C have been calculated using reflectance and transmittance data. Spectral dependence of absorption

Tarsame S. Sian; G. B. Reddy

2004-01-01

75

Ionic amorphous oxide semiconductors: Material design, carrier transport, and device application  

Microsoft Academic Search

Recently we have reported the room temperature fabrication of transparent and flexible thin film transistors on a polyethylene terephthalate (PET) film substrate using an ionic amorphous oxide semiconductor (IAOS) in an In2O3–ZnO–Ga2O3 system. These transistors exhibit a field effect mobility of ?10cm2 (Vs)?1, which is higher by an order of magnitude than those of hydrogenated amorphous Si and pentacene transistors.

Hideo Hosono

2006-01-01

76

Carrier transport and electronic structure in amorphous oxide semiconductor, a-InGaZnO 4  

Microsoft Academic Search

Carrier transport properties in amorphous oxide semiconductor InGaZnO4 (a-IGZO) thin films were investigated in detail using temperature dependence of Hall measurements. It was found that Hall mobility increased distinctly as carrier concentration increased. Unlikely conventional amorphous semiconductors such as a-Si\\/H, definite normal Hall voltage signals were observed on the films with carrier concentrations (Ne)>1016 cm?3, and Hall mobilities as large

Akihiro Takagi; Kenji Nomura; Hiromichi Ohta; Hiroshi Yanagi; Toshio Kamiya; Masahiro Hirano; Hideo Hosono

2005-01-01

77

Bacterial nanometric amorphous Fe-based oxide: a potential lithium-ion battery anode material.  

PubMed

Amorphous Fe(3+)-based oxide nanoparticles produced by Leptothrix ochracea, aquatic bacteria living worldwide, show a potential as an Fe(3+)/Fe(0) conversion anode material for lithium-ion batteries. The presence of minor components, Si and P, in the original nanoparticles leads to a specific electrode architecture with Fe-based electrochemical centers embedded in a Si, P-based amorphous matrix. PMID:24689687

Hashimoto, Hideki; Kobayashi, Genki; Sakuma, Ryo; Fujii, Tatsuo; Hayashi, Naoaki; Suzuki, Tomoko; Kanno, Ryoji; Takano, Mikio; Takada, Jun

2014-04-23

78

Observation of the amorphous zinc oxide recrystalline process by molecular dynamics simulation  

PubMed Central

The detailed structural variations of amorphous zinc oxide (ZnO) as well as wurtzite (B4) and zinc blende (B3) crystal structures during the temperature elevation process were observed by molecular dynamics simulation. The amorphous ZnO structure was first predicted through the simulated-annealing basin-hopping algorithm with the criterion to search for the least stable structure. The density and X-ray diffraction profiles of amorphous ZnO of the structure were in agreement with previous reports. The local structural transformation among different local structures and the recrystalline process of amorphous ZnO at higher temperatures are observed and can explain the structural transformation and recrystalline mechanism in a corresponding experiment [Bruncko et al., Thin Solid Films 520, 866-870 (2011)].

Lin, Ken-Huang; Sun, Shih-Jye; Ju, Shin-Pon; Tsai, Jen-Yu; Chen, Hsin-Tsung; Hsieh, Jin-Yuan

2013-01-01

79

Observation of the amorphous zinc oxide recrystalline process by molecular dynamics simulation  

NASA Astrophysics Data System (ADS)

The detailed structural variations of amorphous zinc oxide (ZnO) as well as wurtzite (B4) and zinc blende (B3) crystal structures during the temperature elevation process were observed by molecular dynamics simulation. The amorphous ZnO structure was first predicted through the simulated-annealing basin-hopping algorithm with the criterion to search for the least stable structure. The density and X-ray diffraction profiles of amorphous ZnO of the structure were in agreement with previous reports. The local structural transformation among different local structures and the recrystalline process of amorphous ZnO at higher temperatures are observed and can explain the structural transformation and recrystalline mechanism in a corresponding experiment [Bruncko et al., Thin Solid Films 520, 866-870 (2011)].

Lin, Ken-Huang; Sun, Shih-Jye; Ju, Shin-Pon; Tsai, Jen-Yu; Chen, Hsin-Tsung; Hsieh, Jin-Yuan

2013-02-01

80

Optical waveguiding in amorphous tellurium oxide thin films  

Microsoft Academic Search

Optical waveguiding characteristics of amorphous TeO2?x films deposited by reactive sputtering under different O2:Ar gas mixtures are investigated on fused quartz and Corning glass substrates. Infra-red absorption band in the range 641–658 cm?1 confirmed the formation of a Te?O bond, and a 20:80 O2:Ar gas mixture ratio is found to be optimum for achieving highly uniform and transparent films at

Ranu Nayak; Vinay Gupta; A. L Dawar; K Sreenivas

2003-01-01

81

Influence of synthesis conditions on the electrochemical properties of nanostructured amorphous manganese oxide cryogels  

NASA Astrophysics Data System (ADS)

Amorphous manganese oxides have received increasing attention in recent years as intercalation cathodes for rechargeable lithium batteries. The sol-gel method is a versatile method for achieving nanostructured amorphous oxides. In this paper, two different sol-gel routes are investigated, where nanostructured amorphous manganese oxide cryogels are obtained via freeze drying Mn(IV) oxide hydrogels formed in situ. In one route the hydrogels are formed by reaction between a solution of sodium permanganate and a solution of disodium fumarate, and in the other route by reaction between a solution of sodium permanganate and solid fumaric acid. Highly homogeneous monolithic manganese oxide hydrogels are obtained from both synthesis routes with precursor concentrations between 0.1 and 0.2 M. The freeze drying method proves to be an efficient method for obtaining nanostructured amorphous manganese oxide cryogels out of the hydrogels. Depending on the synthesis conditions of the hydrogels, the resultant cryogels can yield very high specific capacities for lithium intercalation and excellent rate performance. The cryogel with the best performance exhibits 289 mAh/g at a C/100 rate and 174 mAh/g at a 2 C rate. Strong dependence of electrochemical properties of the cryogels on the synthesis conditions of the parent hydrogels has been observed. The different electrochemical properties are believed to be due to different surface areas and local structures of the cryogels derived from hydrogels synthesized under different conditions. This strong dependence gives rise to the possibility of achieving promising intercalation materials through tailoring the surface area and the local structure of amorphous manganese oxides by adjusting sol-gel synthesis conditions.

Yang, Jingsi; Xu, Jun John

82

All-amorphous-oxide transparent, flexible thin-film transistors. Efficacy of bilayer gate dielectrics.  

PubMed

Optically transparent and mechanically flexible thin-film transistors (TF-TFTs) composed exclusively of amorphous metal oxide films are fabricated on plastic substrates by combining an amorphous Ta(2)O(5)/SiO(x) bilayer transparent oxide insulator (TOI) gate dielectric with an amorphous zinc-indium-tin oxide (a-ZITO) transparent oxide semiconductor (TOS) channel and a-ZITO transparent oxide conductor (TOC) electrodes. The bilayer gate dielectric is fabricated by the post-cross-linking of vapor-deposited hexachlorodisiloxane-derived films to form thin SiO(x) layers (v-SiO(x)) on amorphous Ta(2)O(5) (a-Ta(2)O(5)) films grown by ion-assisted deposition at room temperature. The a-Ta(2)O(5)/v-SiO(x) bilayer TOI dielectric integrates the large capacitance of the high dielectric constant a-Ta(2)O(5) layer with the excellent dielectric/semiconductor interfacial compatibility of the v-SiO(x) layer in a-ZITO TOS-based TF-TFTs. These all-amorphous-oxide TF-TFTs, having a channel length and width of 100 and 2000 microm, respectively, perform far better than a-Ta(2)O(5)-only devices and exhibit saturation-regime field-effect mobilities of approximately 20 cm(2)/V x s, on-currents >10(-4) A, and current on-off ratios >10(5). These TFTs operate at low voltages (approximately 4.0 V) and exhibit good visible-region optical transparency and excellent mechanical flexibility. PMID:20698566

Liu, Jun; Buchholz, D Bruce; Hennek, Jonathan W; Chang, Robert P H; Facchetti, Antonio; Marks, Tobin J

2010-09-01

83

Influence of DC magnetron sputtering parameters on the properties of amorphous indium zinc oxide thin film  

Microsoft Academic Search

Amorphous or crystalline indium zinc oxide (IZO) thin films, which are highly transparent and conducting, were deposited by DC magnetron sputtering. X-Ray diffraction technique was used for analyzing microstructures of the films, and also differential thermal analysis was performed for observing their crystallization behavior. The IZO thin films prepared were crystallized at much higher temperature than ITO films were. The

Yeon Sik Jung; Ji Yoon Seo; Dong Wook Lee; Duk Young Jeon

2003-01-01

84

PE MOCVD of Thin High Transparent Dielectric Amorphous Films of Aluminium Oxide  

Microsoft Academic Search

Thin transparent amorphous films of aluminum oxide have been obtained using PE MOCVD technique and aluminum P-diketonate as precursor in controlled mixture of gas reagents Ar and 02. The films were depos- ited on glass, quartz and stainless steel substrates at temperature range of 100 -- 250°C. The correlation between electric properties and such deposition parameters as r.f. power Wp,

V. P. Ovsyannikov; G. V. Lashkaryov; E. A. Mazurenko

1995-01-01

85

Effect of the pressure of sputtering atmosphere on the physical properties of amorphous aluminum oxide films  

Microsoft Academic Search

Amorphous aluminum oxide films were prepared by rf-sputtering at various values of the pressure of sputtering atmosphere, and their density, refractive index, Young's modulus and internal stress were measured. The physical properties of the present films depended on the pressure of sputtering atmosphere. The density, refractive index, and Young's modulus decreased with the pressure below about 6.5 Pa, beyond which

Y. Kijima; T. Hanada

2000-01-01

86

Electrical and optical properties of sputtered amorphous vanadium oxide thin films  

NASA Astrophysics Data System (ADS)

Amorphous vanadium oxide (VOx) is a component found in composite nanocrystalline VOx thin films. These types of composite films are used as thermistors in pulsed biased uncooled infrared imaging devices when containing face centered cubic vanadium monoxide phase crystallites, and substantial fractions of amorphous material in the composite are necessary to optimize device electrical properties. Similarly, optoelectronic devices exploiting the metal-to-semiconductor transition contain the room-temperature monoclinic or high-temperature (>68 °C) rutile vanadium dioxide phase. Thin films of VOx exhibiting the metal-to-semiconductor transition are typically polycrystalline or nanocrystalline, implying that significant amounts of disordered, amorphous material is present at grain boundaries or surrounding the crystallites and can impact the overall optical or electronic properties of the film. The performance of thin film material for either application depends on both the nature of the crystalline and amorphous components, and in this work we seek to isolate and study amorphous VOx. VOx thin films were deposited by pulsed dc reactive magnetron sputtering to produce amorphous materials with oxygen contents >=2, which were characterized electrically by temperature dependent current-voltage measurements and optically characterized by spectroscopic ellipsometry. Film resistivity, thermal activation energy, and complex dielectric function spectra from 0.75 to 6.0 eV were used to identify the impact of microstructural variations including composition and density.

Podraza, N. J.; Gauntt, B. D.; Motyka, M. A.; Dickey, E. C.; Horn, M. W.

2012-04-01

87

Electrical properties of amorphous aluminum oxide thin films  

Microsoft Academic Search

Silicon oxide (SiO2) gate length, gate thickness, junction depth, and source\\/drain extension scaling have allowed metal–oxide–semiconductor (MOS) gate dimensions to approach the current ?100nm range. High dielectric constant materials for gate insulation and low resistivity junctions must be developed in order to enable further scaling of these devices. Aluminum oxide (Al2O3), with a bandgap of 9.9eV, is an especially promising

P. Katiyar; C. Jin; R. J. Narayan

2005-01-01

88

P-type conductive amorphous oxides of transition metals from solution processing  

NASA Astrophysics Data System (ADS)

We report a series of solution-processed p-type conductive amorphous Ln-M-O (a-Ln-M-O, where M = Ru, Ir, and Ln is a lanthanide element except Ce) having low resistivities (10-3 to 10-2 ? cm). These oxides are thermally stable to a high degree, being amorphous up to 800 °C, and processable below 400 °C. Their film surfaces are smooth on the atomic scale, and the process allows patterning simply by direct imprinting without distortion of the pattern after annealing. These properties have high potential for use in printed electronics. The electron configurations of these oxides are apparently different from existing p-type oxides.

Li, Jinwang; Kaneda, Toshihiko; Tokumitsu, Eisuke; Koyano, Mikio; Mitani, Tadaoki; Shimoda, Tatsuya

2012-07-01

89

High-k (k=30) amorphous hafnium oxide films from high rate room temperature deposition  

SciTech Connect

Amorphous hafnium oxide (HfO{sub x}) is deposited by sputtering while achieving a very high k{approx}30. Structural characterization suggests that the high k is a consequence of a previously unreported cubiclike short range order in the amorphous HfO{sub x} (cubic k{approx}30). The films also possess a high electrical resistivity of 10{sup 14} {Omega} cm, a breakdown strength of 3 MV cm{sup -1}, and an optical gap of 6.0 eV. Deposition at room temperature and a high deposition rate ({approx}25 nm min{sup -1}) makes these high-k amorphous HfO{sub x} films highly advantageous for plastic electronics and high throughput manufacturing.

Li, Flora M.; Bayer, Bernhard C.; Hofmann, Stephan; Milne, William I.; Flewitt, Andrew J. [Department of Engineering, Electrical Engineering Division, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0FA (United Kingdom); Dutson, James D.; Wakeham, Steve J.; Thwaites, Mike J. [Plasma Quest Ltd., Unit 1B, Rose Estate, Osborn Way, Hook, Hampshire RG27 9UT (United Kingdom)

2011-06-20

90

Polymer light-emitting diodes with amorphous indium-zinc oxide anodes deposited at room temperature  

Microsoft Academic Search

The authors report on the performance of polymer-based light-emitting diodes, LEDs, using amorphous zinc oxide-doped indium oxide, IZO, as anode. In particular, LEDs with poly[(2-methoxy-5-(2?-ethyl-hexyloxy)-1,4-phenylene vinylene] as electroluminescent layer and aluminium cathodes, show higher efficiency with this IZO anode (0.015cd\\/A) than with indium-tin oxide (ITO) (0.010cd\\/A). Inspite of the higher resistance of this IZO electrode, compared with ITO, the fact

Gabriel Bernardo; Gonçalo Gonçalves; Pedro Barquinha; Quirina Ferreira; Graça Brotas; Luís Pereira; Ana Charas; Jorge Morgado; Rodrigo Martins; Elvira Fortunato

2009-01-01

91

Model for determination of mid-gap states in amorphous metal oxides from thin film transistors  

NASA Astrophysics Data System (ADS)

The electronic density of states in metal oxide semiconductors like amorphous zinc oxide (a-ZnO) and its ternary and quaternary oxide alloys with indium, gallium, tin, or aluminum are different from amorphous silicon, or disordered materials such as pentacene, or P3HT. Many ZnO based semiconductors exhibit a steep decaying density of acceptor tail states (trap DOS) and a Fermi level (EF) close to the conduction band energy (EC). Considering thin film transistor (TFT) operation in accumulation mode, the quasi Fermi level for electrons (Eq) moves even closer to EC. Classic analytic TFT simulations use the simplification EC-EF> `several'kT and cannot reproduce exponential tail states with a characteristic energy smaller than 1/2 kT. We demonstrate an analytic model for tail and deep acceptor states, valid for all amorphous metal oxides and include the effect of trap assisted hopping instead of simpler percolation or mobility edge models, to account for the observed field dependent mobility.

Bubel, S.; Chabinyc, M. L.

2013-06-01

92

Seeded growth induced amorphous to crystalline transformation of niobium oxide nanostructures  

NASA Astrophysics Data System (ADS)

A novel high-temperature synthesis of niobium oxide nanostructures has been developed through an amorphous intermediate that crystallizes into anisotropic crystalline structures through a complex mechanism of nucleation-dissolution-selective growth induced by seeded growth. The amorphous materials formed by the thermolysis of niobium oleate transformed into crystalline platelets, wires or bundled wires after the injection of additional niobium oleate at different temperatures. The temperature of the solution during injection of the additional precursor determined the morphology of the formed crystalline structure. The time- and temperature-dependent evolution of the niobium oxide nanostructures demonstrates that amorphous materials progressively turned to crystalline materials. We tuned the size of wires and platelets by the consecutive injection of the precursor solution into the reaction mixture under isothermal conditions. With the sequential injection of the precursor solution, we demonstrate that the anisotropic growth of individual nanowires occurs exclusively along the ends, without the formation of any new nuclei. A mechanism for the transformation of well-defined platelets from wires has been proposed and is due to the exclusive loss of mass at the ends of the wires while growth of the platelets initially occurs along the (001) direction which is then replaced by the (110) face.A novel high-temperature synthesis of niobium oxide nanostructures has been developed through an amorphous intermediate that crystallizes into anisotropic crystalline structures through a complex mechanism of nucleation-dissolution-selective growth induced by seeded growth. The amorphous materials formed by the thermolysis of niobium oleate transformed into crystalline platelets, wires or bundled wires after the injection of additional niobium oleate at different temperatures. The temperature of the solution during injection of the additional precursor determined the morphology of the formed crystalline structure. The time- and temperature-dependent evolution of the niobium oxide nanostructures demonstrates that amorphous materials progressively turned to crystalline materials. We tuned the size of wires and platelets by the consecutive injection of the precursor solution into the reaction mixture under isothermal conditions. With the sequential injection of the precursor solution, we demonstrate that the anisotropic growth of individual nanowires occurs exclusively along the ends, without the formation of any new nuclei. A mechanism for the transformation of well-defined platelets from wires has been proposed and is due to the exclusive loss of mass at the ends of the wires while growth of the platelets initially occurs along the (001) direction which is then replaced by the (110) face. Electronic supplementary information (ESI) available: Additional TEM images, XRD, TGA, and UV-Visible absorption spectra of niobium oxide nanostructures. See DOI: 10.1039/c2nr11803c

Jana, Subhra; Rioux, Robert M.

2012-02-01

93

Dielectric constants of crystalline and amorphous spodumene, anorthite and diopside and the oxide additivity rule  

NASA Astrophysics Data System (ADS)

The dielectric constants and dissipation factors of LiAlSi2O6, CaAl2Si2O8 and CaMgSi2O6 in both the crystalline (?-spodumene, anorthite, and diopside) and amorphous forms were determined at 1 MHz using a two-terminal method and empirically determined edge corrections. The results are: spodumene ?' 11=7.30 tan ?= 0.0007 ?'22=8.463 tan ?= 0.0002 ?'33 =11.12 tan ?= 0.0007 anorthite ?' a *=5.47 tan ?= 0.0009 ?'b *=8.76 tan ?= 0.0010 ?'c *=7.19 tan ?= 0.0013 diopside ?'11=9.69 tan ?= 0.0016 ?'22 = 7.31 tan ?= 0.0007 ?'33=7.29 tan ?= 0.00019 LiAlSi2O6 ?'=8.07 tan ?= 0.047 amorphous CaAl2Si2O8 ?'=7.50 tan ?= 0.0024 amorphous CaMgSi2O6 ?'=8.89 tan ?= 0.0021 amorphous The dielectric properties of a spodumene glass, progressively crystallized at different conditions, were also determined. As the crystallization temperature was increased from 720 to 920° C, ?' increased from 6.22 to 6.44. The dissipation factor, tan ?, remained constant at 0.020. Similarly, as the crystallization time at 750° C increased from 0.5 hr to 6.0 hr, ?' increased from 6.28 to 6.35. The deviations of the measured dielectric polarizabilities as determined from the Clausius-Mosotti equation from those calculated from the sum of oxide polarizabilities according to ? D(mineral, glass) = ? ? D(oxides) are +7.4% for ?-spodumene, +1.2% for diopside, and +28.0, +19.6 and +15.9% for amorphous spodumene, anorthitie and diopside compositions, respectively. Positive deviations in ?-spodumene and anorthite are consistent with lower than normal apparent cation bond valence sums and are believed to be evidence for loosely bonded “rattling” Li and Ca ions. Diopside, with Ca and Mg ions having normal bond valence sums, exhibits no abnormal deviation from additivity. Larger positive deviations in amorphous SiO2, LiAlSi2O6, CaAl2Si2O8 and CaMgSi2O6 are postulated to arise from a combination of loosely bonded cations and disordered O= ions where the oxygen dielectric polarizability increased from its normal value of 2.0 Å3 in well-behaved oxides to 2.2 3.0 Å3 in the amorphous phases.

Shannon, Robert D.; Dickinson, James E.; Rossman, George R.

1992-09-01

94

Exploratory combustion synthesis: amorphous indium yttrium oxide for thin-film transistors.  

PubMed

We report the implementation of amorphous indium yttrium oxide (a-IYO) as a thin-film transistor (TFT) semiconductor. Amorphous and polycrystalline IYO films were grown via a low-temperature solution process utilizing exothermic "combustion" precursors. Precursor transformation and the IYO films were analyzed by differential thermal analysis, thermogravimetric analysis, X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy, and optical transmission, which reveal efficient conversion to the metal oxide lattice and smooth, transparent films. a-IYO TFTs fabricated with a hybrid nanodielectric exhibit electron mobilities of 7.3 cm(2) V(-1) s(-1) (T(anneal) = 300 °C) and 5.0 cm(2) V(-1) s(-1) (T(anneal) = 250 °C) for 2 V operation. PMID:22625409

Hennek, Jonathan W; Kim, Myung-Gil; Kanatzidis, Mercouri G; Facchetti, Antonio; Marks, Tobin J

2012-06-13

95

Inelastic electron scattering in amorphous silicon nitride and aluminum oxide with multiple-scattering corrections  

Microsoft Academic Search

Electron-energy-loss measurements for an amorphous chemical-vapor-deposited silicon nitride film and evaporated sapphire in the broad energy range 1-200 eV are investigated. A method, not requiring the zero-loss peak, to remove the multiple scattering is discussed, applied, and the optical constants obtained. An Elliot-type model used with aluminum oxide gives a valence-exciton binding energy of 1.36+\\/-0.2 eV with a band gap

Peteris Livins; T. Aton; S. E. Schnatterly

1988-01-01

96

Amorphous Oxide Semiconductors for High-Performance Flexible Thin-Film Transistors  

Microsoft Academic Search

Recently, we have demonstrated the potential of amorphous oxide semiconductors (AOSs) for developing flexible thin-film transistors (TFTs). A material exploration of AOSs desired as the channel layer in TFTs is most important for developing high-performance devices. Here, we report our concept of material exploration for AOSs in high-performance flexible and transparent TFTs from the viewpoints of chemical bonding and electronic

Kenji Nomura; Akihiro Takagi; Toshio Kamiya; Hiromichi Ohta; Masahiro Hirano; Hideo Hosono

2006-01-01

97

Amorphous chromia for low-temperature selective catalytic reduction of nitric oxide  

Microsoft Academic Search

This paper reports on high surface area amorphous chromia found to be a highly active and selective catalyst for the reduction of nitric oxide by ammonia in an oxygen excess. A comparison to a VâOâ\\/TiOâ catalyst shows that at a space velocity of 24000 h⁻¹ in 900 ppm NO, 900 ppm NHâ, and 1.8% Oâ, over 90% conversion occurs at

Edward Curry-Hyde; Alfons Baiker

1990-01-01

98

Insitu investigation of the optoelectronic properties of transparent conducting oxide\\/amorphous silicon interfaces  

Microsoft Academic Search

Transparent conducting oxide (TCO)\\/hydrogenated amorphous silicon (a-Si:H) interfaces are investigated combining kinetic ellipsometry and Kelvin probe measurements. It is shown that the correlation between both insitu techniques allows a detailed description of the optoelectronic behavior of these interfaces. The Schottky barrier at the TCO\\/a\\/Si:H interfaces, as revealed by Kelvin probe measurements, is correlated with the chemical reduction of the TCO

B. Drevillon; Satyendra Kumar; P. Roca i Cabarrocas; J. M. Siefert

1989-01-01

99

Investigation on the characteristics of stress-induced hump in amorphous oxide thin film transistors  

NASA Astrophysics Data System (ADS)

In this study, we investigate the instability of amorphous oxide thin film transistors using hafnium-indium-zinc oxide under simultaneous application of light and gate dc-bias. The hump characteristics are observed after negative gate bias and light stress. Based on the positive bias-induced recovery, it is proved that photo-generated holes are trapped in the gate insulator by the electrical field enhanced by the optical energy. Moreover, from simulated electric field distribution, it is clearly revealed that the hole-trapping is localized at the edge regions of the gate insulator along channel width/length directions by electric field crowding, resulting in the hump occurrence.

Kim, Jang Hyun; Kwon, Dae Woong; Chang, Ji Soo; Kim, Sang Wan; Park, Jae Chul; Kim, Chang Jung; Park, Byung-Gook

2011-07-01

100

Oxidative and tribological properties of amorphous and quasicrystalline approximant Al-Cu-Fe thin films.  

PubMed

The origins of the tribological properties and corrosion resistance of amorphous and quasicrystalline approximant alloys have been studied by comparing their properties in thin Al-Cu-Fe alloy films with compositions lying near the quasicrystalline region of the ternary compositional phase diagram. Six sputtered thin films of an Al-Cu-Fe alloy were studied using X-ray diffraction, X-ray photoemission spectroscopy (XPS), and an in situ ultrahigh vacuum (UHV) tribometer. The films were annealed in UHV to induce the formation of orthorhombic, rhombohedral, and amorphous bulk structures. The properties of these thin films were then determined in the same UHV apparatus without exposing the films to air. The rates of surface oxidation by H2O and O2 were measured using XPS. Although the oxidation rates and oxide thicknesses were dependent on the oxidant, they were not sensitive to the structures of the films. Friction was measured between identical samples in sliding contact. The friction coefficients (micros = 0.36 +/- 0.11 to 0.56 +/- 0.08) were comparable to those observed in other experiments using quasicrystals and approximants in UHV; however, there was no strong correlation between the friction coefficients and either the film structure or the degree of surface oxidation. These results suggest that the tribological and corrosion resistance properties of these quasicrystalline approximant alloys are not directly connected to crystalline structure. PMID:16032871

Rampulla, D M; Mancinelli, C M; Brunell, I F; Gellman, A J

2005-05-10

101

Development of Pinhole-Free Amorphous Aluminum Oxide Protective Layers for Biomedical Device Applications  

PubMed Central

This paper describes synthesis of ultrathin pinhole-free insulating aluminum oxide layers for electronic device protection in corrosive liquid environments, such as phosphate buffered saline (PBS) or clinical fluids, to enable emerging biomedical applications such as biomolecular sensors. A pinhole-free 25-nm thick amorphous aluminum oxide layer has been achieved using ultra-high vacuum DC magnetron reactive sputtering of aluminum in oxygen/argon plasma followed by oxygen plasma post-processing. Deposition parameters were optimized to achieve the best corrosion protection of lithographically defined device structures. Electrochemical deposition of copper through the aluminum oxide layers was used to detect the presence (or absence) of pinholes. FTIR, XPS, and spectroscopic ellipsometry were used to characterize the material properties of the protective layers. Electrical resistance of the copper device structures protected by the aluminum oxide layers and exposed to a PBS solution was used as a metric to evaluate the long-term stability of these device structures.

Litvinov, Julia; Wang, Yi-Ju; George, Jinnie; Chinwangso, Pawilai; Brankovic, Stanko; Willson, Richard C.; Litvinov, Dmitri

2013-01-01

102

Tin-based amorphous oxide: A high-capacity lithium-ion-storage material  

SciTech Connect

A high-capacity lithium-storage material in metal-oxide form has been synthesized that can replace the carbon-based lithium intercalation materials currently in extensive use as the negative electrode (anode) of lithium-ion rechargeable batteries. This tin-based amorphous composite oxide (TCO) contains Sn(II)-O as the active center for lithium insertion and other glass-forming elements, which make up an oxide network. The TCO anode yields a specific capacity for reversible lithium adsorption more than 50 percent higher than those of the carbon families that persists after charge-discharge cycling when coupled with a lithium cobalt oxide cathode. Lithium-7 nuclear magnetic resonance measurements evidenced the high ionic state of lithium retained in the charged state, in which TCO accepted 8 moles of lithium ions per unit mole. 15 refs., 5 figs.

Idota, Yoshio; Kubota, Tadahiko [Fujifilm Celltec, Miyagi (Japan)] [Fujifilm Celltec, Miyagi (Japan); Matsufuji, Akihiro [Fuji Photo Film, Kanagawa (Japan)] [and others] [Fuji Photo Film, Kanagawa (Japan); and others

1997-05-30

103

Development of Pinhole-Free Amorphous Aluminum Oxide Protective Layers for Biomedical Device Applications.  

PubMed

This paper describes synthesis of ultrathin pinhole-free insulating aluminum oxide layers for electronic device protection in corrosive liquid environments, such as phosphate buffered saline (PBS) or clinical fluids, to enable emerging biomedical applications such as biomolecular sensors. A pinhole-free 25-nm thick amorphous aluminum oxide layer has been achieved using ultra-high vacuum DC magnetron reactive sputtering of aluminum in oxygen/argon plasma followed by oxygen plasma post-processing. Deposition parameters were optimized to achieve the best corrosion protection of lithographically defined device structures. Electrochemical deposition of copper through the aluminum oxide layers was used to detect the presence (or absence) of pinholes. FTIR, XPS, and spectroscopic ellipsometry were used to characterize the material properties of the protective layers. Electrical resistance of the copper device structures protected by the aluminum oxide layers and exposed to a PBS solution was used as a metric to evaluate the long-term stability of these device structures. PMID:23682201

Litvinov, Julia; Wang, Yi-Ju; George, Jinnie; Chinwangso, Pawilai; Brankovic, Stanko; Willson, Richard C; Litvinov, Dmitri

2013-06-15

104

Preparation and evaluation of amorphous metal oxide magnetic thin films and nanocomposites for spintronics  

NASA Astrophysics Data System (ADS)

In this work, photochemical metalorganic deposition (PMOD) using thin films of metal 2-ethylhexanoates (Mo and Fe) was used to deposit patterned thin films of a-MoO3 and a-Fe 2O3 (where a stands for amorphous) in a positive tone. The mechanism of positive tone PMOD of a-Fe 2O3 was examined by using spectroscopic ellipsometry, which allowed the determination that the development preferentially removed the amorphous iron oxide from the film. The magnetic properties of dense assemblies of spinel ferrite superparamagnetic nanocrystals were studied. This was done for nanocomposite thin films prepared by PMOD containing nanocrystals of one (gamma-Fe2O3 in a-MnO) or two chemical identities (gamma-Fe2O 3+CoFe2O4 in a-Al2O 3 and a-TiO2), and bulk binary mixtures of nanocrystalline powders (gamma-Fe2O3+CoFe 2O4). Based on the magnetic properties of these nanocomposite thin films and powders, a model in which strong, interparticle magnetic interactions affect the magnetic properties is presented. To gain an understanding of the local atomic structure of a-Fe 2O3, X-ray absorption spectroscopy was used to determine the oxidation state and coordination environment of the iron atoms in this amorphous material. It was found the iron is in the +3 oxidation state, and occupied an octahedral environment. Similarly, it was found that octahedral Co2+ and Fe3+ are present in a-CoFe 2O4 and that octahedral Cr3+ is present in a-Cr2O3. The local structure in these amorphous metal oxides a-MOx thin films is also discussed based on an analysis of the extended x-ray absorption fine structure (EXAFS). This represents the first determination of the local structure in a-MOx prepared by PMOD. The magnetic properties of PMOD-prepared a-Fe2 O3, a-CoFe2O4, and a-Cr2O3 thin films were investigated. This work shows that these a-MOx thin films exhibit ferromagnetic properties at room temperature. Prior to this work, no magnetic amorphous iron oxide had previously been reported. Iron(III) 2-ethylhexanoate was used as a precursor for direct-write electron beam induced lithography. The deposition of sub-100 nm iron oxide features was shown. Sub-40 nm nanowires with low line edge and width roughnesses (<3 nm) could be patterned. TEM and AFM inspection also identified free-standing, hollow nanotubes. Keywords. Metal oxide; thin films; magnetic films; magnetic nanocomposite; photolithography; amorphous magnets.

Trudel, Simon

105

Methane combustion over catalysts prepared by oxidation of ternary Pd 15X 10Zr 75 (X = Co, Cr, Cu, Mn and Ni) amorphous alloys  

Microsoft Academic Search

Catalysts for the combustion of methane have been prepared by controlled oxidation of various ternary amorphous alloys with the composition X10Pd15Zr75 (X = Co, Cr, Cu, Mn and Ni). As a reference material, a Pd25Zr75 amorphous alloy was used. The oxidation of the amorphous precursors led, in some cases, to highly active catalysts for the deep oxidation of methane. The

Christian A. Müller; René A. Koeppel; Marek Maciejewski; Josef Heveling; Alfons Baiker

1996-01-01

106

Fundamental steps towards interface amorphization during silicon oxidation: Density functional theory calculations  

NASA Astrophysics Data System (ADS)

Density functional theory calculations reveal a two-step scenario for silicon oxidation nucleation. We detail a quasibarrierless semihexagonal oxide nucleus, involving an unexpected adjacent dimer oxygen bridging bond. It is formed upon O2 chemisorption at 0.5 monolayer on Si(100)-(2×1) . This structure arises from the difficulty to systematically insert oxygen atoms into first neighbor Si-Si bonds. While silanone structures, characterized by a Si=O strand, effectively accommodate oxygen at lower coverages, the stabilization of this hexagonal-like pattern on a cubic substrate at low temperatures and at higher coverages demonstrates the ability of oxygen atoms to deeply modify the arrangement of silicon atoms on the surface and to impose a specific structure. It is believed to offer a key natural pathway toward the formation of an abrupt crystalline semiconductor/amorphous oxide transition.

Hemeryck, A.; Estève, A.; Richard, N.; Djafari Rouhani, M.; Chabal, Y. J.

2009-01-01

107

Transparent conducting oxides (TCO{close_quote}s) for amorphous silicon solar cells  

SciTech Connect

The stability of various textured tin oxide and zinc oxide transparent conductors was evaluated against annealing in air, in vacuum or exposed to hydrogen plasma. Only fluorine-doped zinc oxide deposited by atmospheric pressure chemical vapor deposition (APCVD) had stable electrical and optical properties under all conditions. Thin layers of ZnO or TiO{sub 2} greatly improved the plasma resistance of SnO{sub 2}. A new TCO material, niobium-doped titanium dioxide (TiO{sub 2}:Nb) was able to withstand hydrogen plasmas with only slight increases in its optical absorption and conductivity. Composite TCO{close_quote}s consisting of glass/SnO{sub 2}:F/TiO{sub 2}:Nb were shown to provide good electrical contact to amorphous silicon solar cells. {copyright} {ital 1996 American Institute of Physics.}

Hegedus, S. [Institute of Energy Conversion, University of Delaware, Newark, Delaware 19716 (United States); Liang, H.; Gordon, R.G. [Department of Chemistry, Harvard University, Cambridge, Massachusetts 02138 (United States)

1996-01-01

108

Ni(II) Complexation to Amorphous Hydrous Ferric Oxide: An X-ray Absorption Spectroscopy Study  

SciTech Connect

Ni(II) sorption onto iron oxides and in particular hydrous ferric oxide (HFO) is among the important processes impacting its distribution, mobility, and bioavailability in environment. To develop mechanistic models for Ni, extended X-ray absorption fine structure (EXAFS) analysis has been conducted on Ni(II) sorbed to HFO. Coprecipitation revealed the formation of the metastable {alpha}-Ni(OH){sub 2} at a Ni(II) loading of 3.5 x 10{sup -3} mol g{sup -1}. On the other hand, Ni(II) formed inner-sphere mononuclear bidentate complexes along edges of FeO{sub 6} octahedra when sorbed to HFO surfaces with Ni-O distances of 2.05-2.07 {angstrom} and Ni-Fe distances of 3.07-3.11 {angstrom}. This surface complex was observed by EXAFS study over 2.8 x 10{sup -3} to 10{sup -1} ionic strength, pH from 6 to 7, a Ni(II) loading of 8 x 10{sup -4} to 8.1 x 10{sup 03} mol g{sup -1} HFO, and reaction times from 4 hours to 8 months. The short- and long-range structure analyses suggest that the presence of Ni(II) inhibited transformation of the amorphous iron oxide into a more crystalline form. However, Ni{sup 2+} was not observed to substitute for Fe{sup 3+} in the oxide structure. This study systematically addresses Ni(II) adsorption mechanisms to amorphous iron oxide. The experimentally defined surface complexes can be used to constrain surface complexation modeling for improved prediction of metal distribution at the iron oxide/aqueous interface.

Xu,Y.; Axe, L.; Boonfueng, T.; Tyson, T.; Trivedi, P.; Pandya, K.

2007-01-01

109

Application of wide-bandgap hydrogenated amorphous silicon oxide layers to heterojunction solar cells for high quality passivation  

Microsoft Academic Search

Wide-gap (highly transparent), hydrogenated amorphous silicon oxide (a-SiOx:H) layers are investigated for heterojunction solar cell applications: Intrinsic a-SiOx:H(i) films are formed in order to prove their applicability for surface passivating buffer layers sandwiched between the crystalline silicon (c-Si) and the doped amorphous layer used for the formation of the emitter and the back-surface-field in heterojunction cells. The a-SiOx:H films are

Thomas Mueller; Stefan Schwertheim; Wolfgang R. Fahrner

2008-01-01

110

Amorphous and condensed organic matter domains: the effect of persulfate oxidation on the composition of soil\\/sediment organic matter  

Microsoft Academic Search

The composition of amorphous and condensed soil\\/sediment organic matter (SOM) domains was investigated for one soil sample and four sediment samples. These samples were oxidized with persulfate to remove amorphous SOM, before and after which the composition of SOM was studied by thermogravimetric analysis, pyrolysis-GC\\/MS, and cross polarization magic angle spinning 13C-NMR. Comparison of the SOM composition before and after

Chiel Cuypers; Tim Grotenhuis; Klaas G. J. Nierop; Elena Maneiro Franco; Adrie de Jager; Wim Rulkens

2002-01-01

111

The atomic structure of ternary amorphous TixSi1-xO2 hybrid oxides.  

PubMed

Atomic length-scale order characteristics of binary and ternary amorphous oxides are presented within the framework of ab initio theory. A combined numerically efficient density functional based tight-binding molecular dynamics and density functional theory approach is applied to model the amorphous (a) phases of SiO2 and TiO2 as well as the amorphous phase of atomically mixed TixSi1-xO2 hybrid-oxide alloys over the entire composition range. Short and mid-range order in the disordered material phases are characterized by bond length and bond-angle statistics, pair distribution function analysis, coordination number and coordination polyhedra statistics, as well as ring statistics. The present study provides fundamental insights into the order characteristics of the amorphous hybrid-oxide frameworks formed by versatile types of TiOn and SiOm coordination polyhedra. In a-SiO2 the fourfold crystal coordination of Si ions is almost completely preserved and the atomic structure is widely dominated by ring-like mid-range order characteristics. In contrast, the structural disorder of a-TiO2 arises from short-range disorder in the local coordination environment of the Ti ion. The coordination number analysis indicates a large amount of over and under-coordinated Ti ions (coordination defects) in a-TiO2. Aside from the ubiquitous distortions of the crystal-like coordinated polyhedra, even the basic coordination-polyhedra geometry type changes for a significant fraction of TiO6 units (geometry defects). The combined effects of topological and chemical disorder in a-TixSi1-xO2 alloys lead to a continuos increase in both the Si as well as the Ti coordination number with the chemical composition x. The important roles of intermediate fivefold coordination states of Ti and Si cations are highlighted for ternary a-TixSi1-xO2 as well as for binary a-TiO2. The continuous decrease in ring size with increasing Ti content reflects the progressive loss of mid-range order structure characteristics and the competing roles of network forming and network modifying SiOm and TiOn units in the mixed hybrid oxides. PMID:24848713

Landmann, M; Köhler, T; Rauls, E; Frauenheim, T; Schmidt, W G

2014-06-25

112

Optical and kinetic properties of cathodically deposited amorphous tungsten oxide films  

Microsoft Academic Search

Optical properties and the coloration–decoloration kinetics of electrochromic films of amorphous tungsten oxide (a-WO3), produced by cathodic deposition from a sodium tungstate based aqueous peroxide electrolyte, have been investigated. As films color in 1N H2SO4, sequential appearance of bands with maxima at ?1eV, 1.6eV, 2eV, and 2.4eV is observed in their optical absorption and electrosorption spectra, is the same as

Yu. S. Krasnov; S. V. Volkov; G. Ya. Kolbasov

2006-01-01

113

Amorphous indium zinc oxide thin film transistors with poly-4-vinylphenol gate dielectric layers  

NASA Astrophysics Data System (ADS)

Thin film transistors (TFTs) with amorphous indium zinc oxide (a-IZO) as channel layers and poly-4-vinylphenol as dielectric layers were fabricated. Transmission curves show that the double-layer structure of the a-IZO layer and the poly-4-vinylphenol layer exhibits the antireflection effect. It was found that post heat-treatment at relatively low temperature will improve the electrical performance of the transistors. TFT devices with saturation mobility of 25.4 cm2 V-1 s-1, threshold voltage of 4.0 V, subthreshold swing value of 0.88 V/decade and current on/off ratio of 106 were obtained.

Pu, Haifeng; Li, Guifeng; Feng, Jiahan; Liu, Baoying; Zhang, Qun

2011-09-01

114

The atomic structure of ternary amorphous TixSi1?xO2 hybrid oxides  

NASA Astrophysics Data System (ADS)

Atomic length-scale order characteristics of binary and ternary amorphous oxides are presented within the framework of ab initio theory. A combined numerically efficient density functional based tight-binding molecular dynamics and density functional theory approach is applied to model the amorphous (a) phases of SiO2 and TiO2 as well as the amorphous phase of atomically mixed TixSi1?xO2 hybrid-oxide alloys over the entire composition range. Short and mid-range order in the disordered material phases are characterized by bond length and bond-angle statistics, pair distribution function analysis, coordination number and coordination polyhedra statistics, as well as ring statistics. The present study provides fundamental insights into the order characteristics of the amorphous hybrid-oxide frameworks formed by versatile types of TiOn and SiOm coordination polyhedra. In a-SiO2 the fourfold crystal coordination of Si ions is almost completely preserved and the atomic structure is widely dominated by ring-like mid-range order characteristics. In contrast, the structural disorder of a-TiO2 arises from short-range disorder in the local coordination environment of the Ti ion. The coordination number analysis indicates a large amount of over and under-coordinated Ti ions (coordination defects) in a-TiO2. Aside from the ubiquitous distortions of the crystal-like coordinated polyhedra, even the basic coordination-polyhedra geometry type changes for a significant fraction of TiO6 units (geometry defects). The combined effects of topological and chemical disorder in a-TixSi1?xO2 alloys lead to a continuos increase in both the Si as well as the Ti coordination number with the chemical composition x. The important roles of intermediate fivefold coordination states of Ti and Si cations are highlighted for ternary a-TixSi1?xO2 as well as for binary a-TiO2. The continuous decrease in ring size with increasing Ti content reflects the progressive loss of mid-range order structure characteristics and the competing roles of network forming and network modifying SiOm and TiOn units in the mixed hybrid oxides.

Landmann, M.; Köhler, T.; Rauls, E.; Frauenheim, T.; Schmidt, W. G.

2014-06-01

115

Optimizing amorphous indium zinc oxide film growth for low residual stress and high electrical conductivity  

NASA Astrophysics Data System (ADS)

With recent advances in flexible electronics, there is a growing need for transparent conductors with optimum conductivity tailored to the application and nearly zero residual stress to ensure mechanical reliability. Within amorphous transparent conducting oxide (TCO) systems, a variety of sputter growth parameters have been shown to separately impact film stress and optoelectronic properties due to the complex nature of the deposition process. We apply a statistical design of experiments (DOE) approach to identify growth parameter-material property relationships in amorphous indium zinc oxide (a-IZO) thin films and observed large, compressive residual stresses in films grown under conditions typically used for the deposition of highly conductive samples. Power, growth pressure, oxygen partial pressure, and RF power ratio (RF/(RF + DC)) were varied according to a full-factorial test matrix and each film was characterized. The resulting regression model and analysis of variance (ANOVA) revealed significant contributions to the residual stress from individual growth parameters as well as interactions of different growth parameters, but no conditions were found within the initial growth space that simultaneously produced low residual stress and high electrical conductivity. Extrapolation of the model results to lower oxygen partial pressures, combined with prior knowledge of conductivity-growth parameter relationships in the IZO system, allowed the selection of two promising growth conditions that were both empirically verified to achieve nearly zero residual stress and electrical conductivities >1480 S/cm. This work shows that a-IZO can be simultaneously optimized for high conductivity and low residual stress.

Kumar, Mukesh; Sigdel, A. K.; Gennett, T.; Berry, J. J.; Perkins, J. D.; Ginley, D. S.; Packard, C. E.

2013-10-01

116

Optical constants of amorphous, transparent titanium-doped tungsten oxide thin films.  

PubMed

We report on the optical constants and their dispersion profiles determined from spectroscopic ellipsometry (SE) analysis of the 20%-titanium (Ti) doped of tungsten oxide (WO3) thin films grown by sputter-deposition. The Ti-doped WO3 films grown in a wide range of temperatures (25-500 °C) are amorphous and optically transparent. SE data indicates that there is no significant interdiffusion at the film-substrate interface for a W-Ti oxide film growth of ~90 nm. The index refraction (n) at ? = 550 nm vary in the range of 2.17-2.31 with a gradual increase in growth temperature. A correlation between the growth conditions and optical constants is discussed. PMID:23682744

Ramana, C V; Baghmar, Gaurav; Rubio, Ernesto J; Hernandez, Manuel J

2013-06-12

117

Significant improvement in electronic properties of transparent amorphous indium zinc oxide through yttrium doping  

NASA Astrophysics Data System (ADS)

One big challenge in transparent conducting oxides (TCOs) is to achieve high conductivity and mobility at a low processing temperature. Although optimized conductivity has been achieved in indium zinc oxide (IZO) without doping, it is still interesting to find whether doping can improve conductivity of IZO further. In this paper, we report a low processing temperature achievement of high conductivity and mobility of IZO through yttrium (Y) doping. We found that with different Y doping levels, room temperature fabricated amorphous IZO (a-IZO) samples can be controlled to exhibit either metallic or semiconductor characteristics. Y2O3 is demonstrated to be an effective doping source to achieve conductivity 300% higher than the non-doped IZO sample. Anomalously improved mobility of certain Y2O3-doped IZO samples compared with the non-doped IZO sample is found and analyzed. Besides, a low-temperature resistivity anomaly (semiconductor metal transition) phenomenon is observed and discussed.

Sun, Jian; Yu, Zhigen; Huang, Yanhua; Xia, Yijie; Lai, Weng Soon; Gong, Hao

2014-04-01

118

Crystalline to amorphous phase transition of tin oxide nanocrystals induced by SHI at low temperature  

SciTech Connect

Tin oxide (SnO{sub 2}) thin films were deposited using pulsed laser deposition (PLD) technique on Si substrates. The as-deposited films were irradiated using 100 MeV Ag ions at different fluences ranging from 3x10{sup 13} to 3x10{sup 14} ions/cm{sup 2} at an incidence angle of 75 deg. with respect to surface normal at liquid nitrogen (LN2) temperature. The as-deposited and irradiated films have been characterized using X-ray diffraction (XRD) and atomic force microscopy (AFM) techniques to study the modifications in structural and surface morphological properties. Nanocrystalline film become completely amorphous and nanograins of tin oxide disappeared from the surface as indicated by XRD spectra and AFM micrographs respectively.

Kumar, Vijay; Pratap, Deepti; Jain, Anshul; Agarwal, D. C.; Sulania, I.; Tripathi, A.; Chaudhary, R. J.; Chauhan, R. S. [Department of Physics, R.B.S. College, Agra, U.P.,-282 002 (India); Inter-University Accelerator Centre, New Delhi, -110 067 (India); UGC-DAE CSR, Khandwa Road, Indore, M.P., -452 017 (India); Department of Physics, R.B.S. College, Agra, U.P., -282 002 (India)

2012-06-05

119

Preparation of nanosized LaCoO3 perovskite oxide using amorphous heteronuclear complex as a precursor at low temperature  

Microsoft Academic Search

Nanosized LaCoO3 cobaltite oxide powder with perovskite structure was successfully synthesized at a relatively low calcination temperature using an amorphous heteronuclear complex, LaCo(DTPA)·6H2O, as a precursor. The precursor decomposed completely into cobaltite oxide above 400 °C according to the DTA and TGA results. XPS revealed that the decomposed species was composed of LaCoO3 cobaltite oxide after the precursor was calcined

Yongfa Zhu; Ruiqin Tan; Tao Yi; Shishan Ji; Xiaoyan Ye; Lili Cao

2000-01-01

120

X-ray absorption fine structure study of amorphous metal oxide thin films prepared by photochemical metalorganic deposition  

Microsoft Academic Search

The oxidation state and local geometry of the metal centers in amorphous thin films of Fe2O3 (Fe3+ oxidation state), CoFe2O4 (Co2+\\/Fe3+ oxidation states), and Cr2O3 (Cr3+ oxidation state) are determined using K edge X-ray absorption near-edge structure (XANES) spectroscopy and extended X-ray absorption fine structure (EXAFS) spectroscopy. The metal oxide thin films were prepared by the solid-state photochemical decomposition of

Simon Trudel; E. Daryl Crozier; Robert A. Gordon; Peter S. Budnik; Ross H. Hill

2011-01-01

121

X-ray absorption fine structure study of amorphous metal oxide thin films prepared by photochemical metalorganic deposition  

SciTech Connect

The oxidation state and local geometry of the metal centers in amorphous thin films of Fe{sub 2}O{sub 3} (Fe{sup 3+} oxidation state), CoFe{sub 2}O{sub 4} (Co{sup 2+}/Fe{sup 3+} oxidation states), and Cr{sub 2}O{sub 3} (Cr{sup 3+} oxidation state) are determined using K edge X-ray absorption near-edge structure (XANES) spectroscopy and extended X-ray absorption fine structure (EXAFS) spectroscopy. The metal oxide thin films were prepared by the solid-state photochemical decomposition of the relevant metal 2-ethylhexanoates, spin cast as thin films. No peaks are observed in the X-ray diffraction patterns, indicating the metal oxides are X-ray amorphous. The oxidation state of the metals is determined from the edge position of the K absorption edges, and in the case of iron-containing samples, an analysis of the pre-edge peaks. In all cases, the EXAFS analysis indicates the first coordination shell consists of oxygen atoms in an octahedral geometry, with a second shell consisting of metals. No higher shells are observed beyond 3.5 {angstrom} for all samples, indicating the metal oxides are truly amorphous, consistent with X-ray diffraction results.

Trudel, Simon; Crozier, E. Daryl; Gordon, Robert A.; Budnik, Peter S.; Hill, Ross H. (Calgary); (Simon)

2011-09-06

122

X-ray absorption fine structure study of amorphous metal oxide thin films prepared by photochemical metalorganic deposition  

NASA Astrophysics Data System (ADS)

The oxidation state and local geometry of the metal centers in amorphous thin films of Fe 2O 3 (Fe 3+ oxidation state), CoFe 2O 4 (Co 2+/Fe 3+ oxidation states), and Cr 2O 3 (Cr 3+ oxidation state) are determined using K edge X-ray absorption near-edge structure (XANES) spectroscopy and extended X-ray absorption fine structure (EXAFS) spectroscopy. The metal oxide thin films were prepared by the solid-state photochemical decomposition of the relevant metal 2-ethylhexanoates, spin cast as thin films. No peaks are observed in the X-ray diffraction patterns, indicating the metal oxides are X-ray amorphous. The oxidation state of the metals is determined from the edge position of the K absorption edges, and in the case of iron-containing samples, an analysis of the pre-edge peaks. In all cases, the EXAFS analysis indicates the first coordination shell consists of oxygen atoms in an octahedral geometry, with a second shell consisting of metals. No higher shells are observed beyond 3.5 Å for all samples, indicating the metal oxides are truly amorphous, consistent with X-ray diffraction results.

Trudel, Simon; Daryl Crozier, E.; Gordon, Robert A.; Budnik, Peter S.; Hill, Ross H.

2011-05-01

123

Functionalization of FeCo alloy nanoparticles with highly dielectric amorphous oxide coatings  

NASA Astrophysics Data System (ADS)

FeCo alloy nanoparticles have been prepared by using a two step modified polyol process using Fe(II) chloride and Co acetate tetrahydrate as Fe and Co metal precursors. Tetraethyl silicate, aluminum isopropoxide, and zirconium(IV) acetyl acetonate were used to make amorphous SiO2, Al2O3, and ZrO2 coatings, respectively. X-ray diffraction studies showed that there are no crystalline peaks corresponding to SiO2, Al2O3, and ZrO2 because the oxide coatings of the FeCo core are amorphous in nature. The scanning electron micrograph analysis depicted the cubic nature of the particles with mean particle size of about 45 nm. The maximum saturation magnetization of 205 emu/g was achieved at 300 and 4 K. FeCo nanocomposites were screen printed as films and aligned by using an external magnetic field of 10 kOe. The microwave properties measured by in-plane ferromagnetic resonance at various frequencies indicate a minimum linewidth of ~3700 Oe.

Nguyen, Q.; Chinnasamy, C. N.; Yoon, S. D.; Sivasubramanian, S.; Sakai, T.; Baraskar, A.; Mukerjee, S.; Vittoria, C.; Harris, V. G.

2008-04-01

124

Magnetic properties of Mn-oxide nanoparticles dispersed in an amorphous SiO 2 matrix  

NASA Astrophysics Data System (ADS)

Samples of Mn-oxide nanoparticles dispersed in an amorphous SiO 2 matrix with manganese concentration 0.7 and 3 at% have been synthesized by a sol-gel method. Transmission electron microscopy analysis has shown that the samples contain agglomerates of amorphous silica particles 10-20 nm in size. In silica matrix two types of Mn-rich particles are dispersed, smaller nanoparticles with dimensions between 3 and 10 nm, and larger crystalline areas consisting of aggregates of the smaller nanoparticles. High-temperature magnetic susceptibility study reveals that dominant magnetic phase at higher temperatures is ?-MnO 2. At temperatures below TC=43 K strong ferrimagnetism originating from the minor Mn 3O 4 phase masks the relatively weak magnetism of ?-MnO 2 with antiferromagnetic interactions. Magnetic field dependence of the maximum in the zero-field-cooled magnetization for both the samples in the vicinity of 40 K, and a frequency shift of the real component of the ac magnetic susceptibility in the sample with 3 at% Mn suggest that the magnetic moments of the smaller Mn 3O 4 nanoparticles with dimensions below 10 nm are exposed to thermally activated blocking process just below the Curie temperature TC. Appearance of a maximum in the zero-field-cooled magnetization for both the samples below 10 K indicates possible spin glass freezing of the magnetic moments at low temperatures which might occur in the geometrically frustrated Mn sublattice of the ?-MnO 2 crystal structure.

Milivojevi?, D.; Babi?-Stoji?, B.; Jokanovi?, V.; Jagli?i?, Z.; Makovec, D.

2011-03-01

125

Amorphous Calcium Phosphate Based Composites: Effect of Surfactants and Poly(ethylene oxide) on Filler and Composite Properties  

Microsoft Academic Search

The uncontrolled aggregation of amorphous calcium phosphate (ACP) particulate fillers and their uneven distribution within polymer matrices can have adverse effects on the properties of ACP composites. In this article, we assessed the influence of nonionic and anionic surfactants and poly(ethylene oxide) (PEO) introduced during the preparation of ACP on the particle size distribution and compositional properties of ACP. In

J. M. Antonucci; D. W. Liu; D. Skrtic

2007-01-01

126

Stoichiometric analysis of compositionally graded combinatorial amorphous thin film oxides using laser-induced breakdown spectroscopy.  

PubMed

Laser-induced breakdown spectroscopy (LIBS) is a recently developed locally destructive elemental analysis technique that can be used to analyze solid, liquid, and gaseous samples. In the system explored here, a neodymium-doped yttrium aluminum garnet laser ablates a small amount of the sample and spectral emission from the plume is analyzed using a set of synchronized spectrometers. We explore the use of LIBS to map the stoichiometry of compositionally graded amorphous indium zinc oxide thin-film libraries. After optimization of the experimental parameters (distance between lens and samples, spot size on the samples, etc.), the LIBS system was calibrated against inductively coupled plasma atomic emission spectroscopy which resulted in a very consistent LIBS-based elemental analysis. Various parameters that need to be watched closely in order to produce consistent results are discussed. We also compare LIBS and x-ray fluorescence as techniques for the compositional mapping of libraries. PMID:20687701

Widjonarko, N Edwin; Perkins, John D; Leisch, Jennifer E; Parilla, Philip A; Curtis, Calvin J; Ginley, David S; Berry, Joseph J

2010-07-01

127

Stoichiometric analysis of compositionally graded combinatorial amorphous thin film oxides using laser-induced breakdown spectroscopy  

SciTech Connect

Laser-induced breakdown spectroscopy (LIBS) is a recently developed locally destructive elemental analysis technique that can be used to analyze solid, liquid, and gaseous samples. In the system explored here, a neodymium-doped yttrium aluminum garnet laser ablates a small amount of the sample and spectral emission from the plume is analyzed using a set of synchronized spectrometers. We explore the use of LIBS to map the stoichiometry of compositionally graded amorphous indium zinc oxide thin-film libraries. After optimization of the experimental parameters (distance between lens and samples, spot size on the samples, etc.), the LIBS system was calibrated against inductively coupled plasma atomic emission spectroscopy which resulted in a very consistent LIBS-based elemental analysis. Various parameters that need to be watched closely in order to produce consistent results are discussed. We also compare LIBS and x-ray fluorescence as techniques for the compositional mapping of libraries.

Widjonarko, N. Edwin [Department of Physics, 390 UCB, University of Colorado, Boulder, Colorado 80309-0390 (United States); National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, Colorado 80401 (United States); Perkins, John D.; Leisch, Jennifer E.; Parilla, Philip A.; Curtis, Calvin J.; Ginley, David S.; Berry, Joseph J. [National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, Colorado 80401 (United States)

2010-07-15

128

Improved stability of amorphous zinc tin oxide thin film transistors using molecular passivation  

NASA Astrophysics Data System (ADS)

The role of back channel surface chemistry on amorphous zinc tin oxide (ZTO) bottom gate thin film transistors (TFTs) has been characterized by positive bias-stress measurements and x-ray photoelectron spectroscopy. Positive bias-stress turn-on voltage shifts for ZTO-TFTs were significantly reduced by passivation of back channel surfaces with self-assembled monolayers of n-hexylphosphonic acid when compared to ZTO-TFTs with no passivation. These results indicate that adsorption of molecular species on the exposed back channel of ZTO-TFTs strongly influence observed turn-on voltage shifts, as opposed to charge injection into the dielectric or trapping due to oxygen vacancies.

Rajachidambaram, M. S.; Pandey, A.; Vilayurganapathy, S.; Nachimuthu, P.; Thevuthasan, S.; Herman, G. S.

2013-10-01

129

Amorphous silicon waveguides grown by PECVD on an Indium Tin Oxide buried contact  

NASA Astrophysics Data System (ADS)

Low-loss hydrogenated amorphous silicon (?-Si:H) waveguides were realized by plasma enhanced chemical vapour deposition (PECVD) on a transparent conductive oxide (TCO) layer which is intended to provide the buried contact in active devices, e.g. switches and modulators. In particular we propose a technological solution to overcome both the strong reduction in optical transmittance due to the very high extinction coefficient of metal contacts and, at the same time, the optical scattering induced by the texturization effect induced in ?-Si:H films grown on TCO. The realized waveguides were characterized in terms of propagation losses at 1550 nm and surface roughness. The experimental performances have been compared to those obtained through calculations using an optical simulation package. The results are found to be in agreement with the experimental data.

Rao, Sandro; Della Corte, Francesco G.; Summonte, Caterina

2012-06-01

130

Reaction of Formic Acid over Amorphous Manganese Oxide Catalytic Systems: An In Situ Study  

SciTech Connect

The interaction of formic acid with amorphous manganese oxide (AMO) is investigated using in situ photoelectron and infrared spectroscopy techniques. Soft X-ray photoelectron spectroscopy (sXPS) and in situ FTIR illustrate two possible modes of formate bound species at the AMO surface. Two peaks in the IR region from 1340-1390 cm{sup -1} are indicative of formate species bound to the surface in a bidentate configuration. However, a 224 cm{sup -1} band gap between v{sub s}OCO and v{sub as}OCO suggests formate is bound in a bridging configuration. Temperature-programmed desorption studies confirm the formate bound species desorbs as carbon dioxide from the surface at multiple binding sites. At temperatures above 700 K, the presence of K{sup +} {hor_ellipsis} OC complex suggests the bound species interacts at vacant sites related to framework oxygen and cation mobility.

J Durand; S Senanayake; S Suib; D Mullins

2011-12-31

131

Reaction of Formic Acid over Amorphous Manganese Oxide Catalytic Systems: An In Situ Study  

SciTech Connect

The interaction of formic acid with amorphous manganese oxide (AMO) is investigated using in situ photoelectron and infrared spectroscopy techniques. Soft X-ray photoelectron spectroscopy (sXPS) and in situ FTIR illustrate two possible modes of formate bound species at the AMO surface. Two peaks in the IR region from 1340-1390 cm{sup -1} are indicative of formate species bound to the surface in a bidentate configuration. However, a 224 cm{sup -1} band gap between v{sub s}OCO and v{sub as}OCO suggests formate is bound in a bridging configuration. Temperature-programmed desorption studies confirm the formate bound species desorbs as carbon dioxide from the surface at multiple binding sites. At temperatures above 700 K, the presence of K{sup +} {hor_ellipsis} OC complex suggests the bound species interacts at vacant sites related to framework oxygen and cation mobility.

Durand, Jason [University of Connecticut; Senanayake, Sanjaya D [ORNL; Mullins, David R [ORNL; Suib, Steven [ORNL

2010-01-01

132

Improved Stability Of Amorphous Zinc Tin Oxide Thin Film Transistors Using Molecular Passivation  

SciTech Connect

The role of back channel surface chemistry on amorphous zinc tin oxide (ZTO) bottom gate thin film transistors (TFT) have been characterized by positive bias-stress measurements and x-ray photoelectron spectroscopy. Positive bias-stress turn-on voltage shifts for ZTO-TFTs were significantly reduced by passivation of back channel surfaces with self-assembled monolayers of n-hexylphosphonic acid (n-HPA) when compared to ZTO-TFTs with no passivation. These results indicate that adsorption of molecular species on exposed back channel of ZTO-TFTs strongly influence observed turn-on voltage shifts, as opposed to charge injection into the dielectric or trapping due to oxygen vacancies.

Rajachidambaram, Meena Suhanya; Pandey, Archana; Vilayur Ganapathy, Subramanian; Nachimuthu, Ponnusamy; Thevuthasan, Suntharampillai; Herman, Gregory S.

2013-10-21

133

Exchange bias effect in partially oxidized amorphous Fe-Ni-B based metallic glass nanostructures  

NASA Astrophysics Data System (ADS)

The magnetic properties of amorphous Fe-Ni-B based metallic glass nanostructures were investigated. The nanostructures underwent a spin-glass transition at temperatures below 100 K and revealed an irreversible temperature following the linear de Almeida-Thouless dependence. When the nanostructures were cooled below 25 K in a magnetic field, they exhibited an exchange bias effect with enhanced coercivity. The observed onset of exchange bias is associated with the coexistence of the spin-glass phase along with the appearance of another spin-glass phase formed by oxidation of the structurally disordered surface layer, displaying a distinct training effect and cooling field dependence. The latter showed a maximum in exchange bias field and coercivity, which is probably due to competing multiple equivalent spin configurations at the boundary between the two spin-glass phases.

Thomas, S.; Pookat, G.; Nair, S. S.; Daniel, M.; Dymerska, B.; Liebig, A.; Al-Harthi, S. H.; Ramanujan, R. V.; Anantharaman, M. R.; Fidler, J.; Albrecht, M.

2012-06-01

134

Advantages of using amorphous indium zinc oxide films for window layer in Cu(In,Ga)Se 2 solar cells  

Microsoft Academic Search

The advantages of using indium zinc oxide (IZO) films instead of conventional Ga-doped zinc oxide (ZnO:Ga) films for Cu(In,Ga)Se2 (CIGS) solar cells are described. The electrical properties of IZO are independent of film thickness. IZO films have higher mobility (30–40cm2\\/Vs) and lower resistivity (4–5×10?4?cm) compared to ZnO:Ga films deposited without intentional heating, because the number of grain boundaries in amorphous

Moe Warasawa; Akira Kaijo; Mutsumi Sugiyama

135

Preparation of amorphous electrochromic tungsten oxide and molybdenum oxide by plasma enhanced chemical vapor deposition  

Microsoft Academic Search

Preliminary experiments have been performed to probe the feasibility of using plasma enhanced chemical vapor deposition (PE--CVD) to prepare electrochromic thin films of tungsten oxide and molybdenum oxide by plasma reaction of WFâ, W(CO)â, and Mo(CO)â with oxygen. Thin films produced in a 300 W, electrodeless, radio-frequency (rf), capacitive discharge were found to be electrochromic when tested with either liquid

C. E. Tracy; D. K. Benson

1986-01-01

136

Influence of deposition temperature and amorphous carbon on microstructure and oxidation resistance of magnetron sputtered nanocomposite Crsbnd C films  

NASA Astrophysics Data System (ADS)

It is known that mechanical and tribological properties of transition metal carbide films can be tailored by adding an amorphous carbon (a-C) phase, thus making them nanocomposites. This paper addresses deposition, microstructure, and for the first time oxidation resistance of magnetron sputtered nanocomposite Crsbnd C/a-C films with emphasis on studies of both phases. By varying the deposition temperature between 20 and 700 °C and alternating the film composition, it was possible to deposit amorphous, nanocomposite, and crystalline Crsbnd C films containing about 70% C and 30% Cr, or 40% C and 60% Cr. The films deposited at temperatures below 300 °C were X-ray amorphous and 500 °C was required to grow crystalline phases. Chronoamperometric polarization at +0.6 V vs. Ag/AgCl (sat. KCl) in hot 1 mM H2SO4 resulted in oxidation of Crsbnd C, yielding Cr2O3 and C, as well as oxidation of C. The oxidation resistance is shown to depend on the deposition temperature and the presence of the a-C phase. Physical characterization of film surfaces show that very thin C/Cr2O3/Crsbnd C layers develop on the present material, which can be used to improve the oxidation resistance of, e.g. stainless steel electrodes.

Nygren, Kristian; Andersson, Matilda; Högström, Jonas; Fredriksson, Wendy; Edström, Kristina; Nyholm, Leif; Jansson, Ulf

2014-06-01

137

Amorphous Nb/Fe-oxide ion-storage films for counter electrode applications in electrochromic devices  

SciTech Connect

The electrochromic properties of mixed Nb/Fe-oxide films with amorphous structure which were prepared via the sol-gel route were determined. Films with Nb/Fe molar concentration ratios 0.2:1, 0.4:1, and 1:1 exhibit ion-storage capacities up to 18 mC/cm{sup 2} depending on Nb/Fe molar ratio. Electrochromically films behave as optically passive electrodes with a coloration efficiency of nearly zero at {lambda} > 480 nm, while at shorter wavelengths a relatively strong anodic coloring was observed, yielding negative coloration efficiencies up to {minus}20 cm{sup 2}/C. Coloring/bleaching changes of films are correlated with the ex situ IR spectroscopic measurements of charged/discharged films showing distortions of the film structure with Li{sup +} ion insertion/extraction reactions. Electrochemical stability of Nb/Fe (0.4:1)-oxide films was tested up to 2,000 cycles in a sol-gel electrochromic device consisting of sol-gel-derived WO{sub 3} films and hybrid organic/inorganic ionic conductor with ionic conductivity of about 10{sup {minus}4} S/cm serving for lamination of the electrodes.

Orel, B.; Macek, M.; Lavrencic-Stangar, U. [National Inst. of Chemistry, Ljubljana (Slovenia); Pihlar, B. [Univ. of Ljubljana (Slovenia). Faculty of Chemistry

1998-05-01

138

Quantitative analysis of amorphous indium zinc oxide thin films synthesized by Combinatorial Pulsed Laser Deposition  

NASA Astrophysics Data System (ADS)

The use of amorphous and transparent oxides is a key for the development of new thin film transistors and displays. Recently, indium zinc oxide (IZO) was shown to exhibit high transparency in the visible range, low resistivity, and high mobility. Since the properties and the cost of these films depend on the In/(In + Zn) values, the measurement of this ratio is paramount for future developments and applications. We report on accurate analysis of the elemental composition of IZO thin films synthesized using a Combinatorial Pulsed Laser Deposition technique. The monitoring of the thin films elemental composition by Laser-Induced Breakdown Spectroscopy was chosen in view of further in situ and real-time technological developments and process control during IZO fabrication. Our analytical approach is based on plasma modeling, the recorded spectra being then compared to the spectral radiance computed for plasmas in local thermal equilibrium. The cation fractions measured were compared to values obtained by complementary measurements using energy dispersive X-ray spectroscopy and Rutherford backscattering spectrometry. Spectroscopic ellipsometry assisted the scientific discussion. A good agreement between methods was found, independently of the relative fraction of indium and zinc that varied from about 65 to 90 and 35 to 10 at%, respectively, and the measurement uncertainties associated to each analytical method.

Axente, E.; Socol, G.; Beldjilali, S. A.; Mercadier, L.; Luculescu, C. R.; Trinca, L. M.; Galca, A. C.; Pantelica, D.; Ionescu, P.; Becherescu, N.; Hermann, J.; Craciun, V.

2014-04-01

139

Modeling the adsorption of mercury(II) on (hydr)oxides. 1: Amorphous iron oxide and {alpha}-quartz  

SciTech Connect

In this study, the authors provide a single model capable of describing the behavior of mercury(II) at two different solid/water interfaces. Mercury(II) sorption on amorphous ferric oxide (HFO) and {alpha}-SiO{sub 2} can be simulated using the surface complexation approach. In both cases, experiments are best reproduced when ternary surface complexes between the surface ({triple_bond}S-OH{sup 0}), Hg{sup 2+}, OH{sup {minus}} or Cl{sup {minus}} are included in the model. Sorption of ternary surface complexes predominates in the case of {alpha}-SiO{sub 2}. In addition, in the case of HFO, additional precipitation reactions of a nonideal Hg(OH){sub 2}-Fe(OH){sub 3} solid solution are needed at high sorbate to sorbent ratios. The modeling leads to a new set of surface complexation constants for the interaction between Hg{sup 2+} and these oxide surfaces which are described herein.

Tiffreau, C.; Luetzenkirchen, J.; Behra, P. [Univ. Louis Pasteur, Strasbourg (France). Inst. de Mecanique des Fluides] [Univ. Louis Pasteur, Strasbourg (France). Inst. de Mecanique des Fluides

1995-06-01

140

Stabilization of FGD gypsum for its disposal in landfills using amorphous aluminium oxide as a fluoride retention additive.  

PubMed

The applicability of amorphous aluminium oxide as a fluoride retention additive to flue gas desulphurisation (FGD) gypsum was studied as a way of stabilizing this by-product for its disposal in landfills. Using a batch method the sorption behaviour of amorphous aluminium oxide was evaluated at the pH (about 6.5) and background electrolyte conditions (high chloride and sulphate concentrations) found in FGD gypsum leachates. It was found that fluoride sorption on amorphous aluminium oxide was a very fast process with equilibrium attained within the first half an hour of interaction. The sorption process was well described by the Langmuir model, offering a maximum fluoride sorption capacity of 61.7 mg g(-1). Fluoride sorption was unaffected by chloride co-existing ions, while slightly decreased (about 20%) by competing sulphate ions. The use of amorphous aluminium oxide in the stabilization of FGD gypsum proved to greatly decreased its fluoride leachable content (in the range 5-75% for amorphous aluminium oxide doses of 0.1-2%, as determined by the European standard EN 12457-4 [EN-12457-4 Characterization of waste-leaching-compliance test for leaching of granular waste materials and sludges-Part 4: one stage batch test at a liquid to solid ratio of 10 l/kg for materials with particle size below 10mm (without or with size reduction)]), assuring the characterization of this by-product as a waste acceptable at landfills of non-hazardous wastes according to the Council Decision 2003/33/EC [Council Decision 2003/33/EC of 19 December 2002. Establishing criteria and procedures for the acceptance of waste at landfills pursuant to Article 16 of and Annex II to Directive 1999/31/EC] on landfill of wastes. Furthermore, as derived from column leaching studies, the proposed stabilization system proved to be highly effective in simulated conditions of disposal, displaying a fluoride leaching reduction value about 81% for an amorphous aluminium oxide added amount of 2%. PMID:17509651

Alvarez-Ayuso, E; Querol, X

2007-09-01

141

Comparative Electrochemical Analysis of Crystalline and Amorphous Anodized Iron Oxide Nanotube Layers as Negative Electrode for LIB.  

PubMed

This work is a comparative study of the electrochemical performance of crystalline and amorphous anodic iron oxide nanotube layers. These nanotube layers were grown directly on top of an iron current collector with a vertical orientation via a simple one-step synthesis. The crystalline structures were obtained by heat treating the as-prepared (amorphous) iron oxide nanotube layers in ambient air environment. A detailed morphological and compositional characterization of the resultant materials was performed via transmission electron microscopy (TEM), field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and Raman spectroscopy. The XRD patterns were further analyzed using Rietveld refinements to gain in-depth information on their quantitative phase and crystal structures after heat treatment. The results demonstrated that the crystalline iron oxide nanotube layers exhibit better electrochemical properties than the amorphous iron oxide nanotube layers when evaluated in terms of the areal capacity, rate capability, and cycling performance. Such an improved electrochemical response was attributed to the morphology and three-dimensional framework of the crystalline nanotube layers offering short, multidirectional transport lengths, which favor rapid Li(+) ions diffusivity and electron transport. PMID:24964233

Pervez, Syed Atif; Kim, Doohun; Farooq, Umer; Yaqub, Adnan; Choi, Jung-Hee; Lee, You-Jin; Doh, Chil-Hoon

2014-07-23

142

In–Ga–Zn–O thin film transistor with HfO{sub 2} gate insulator prepared using various O{sub 2}/(Ar + O{sub 2}) gas ratios  

SciTech Connect

We have investigated the effect of the deposition of an HfO{sub 2} thin film as a gate insulator with different O{sub 2}/(Ar + O{sub 2}) gas ratios using RF magnetron sputtering. The HfO{sub 2} thin film affected the device performance of amorphous indium–gallium–zinc oxide transistors. The performance of the fabricated transistors improved monotonously with increasing O{sub 2}/(Ar + O{sub 2}) gas ratio: at a ratio of 0.35, the field effect mobility of the amorphous InGaZnO thin film transistors was improved to 7.54 cm{sup 2}/(V s). Compared to those prepared with an O{sub 2}/(Ar + O{sub 2}) gas ratio of 0.05, the field effect mobility of the amorphous InGaZnO thin film transistors was increased to 1.64 cm{sup 2}/(V s) at a ratio of 0.35. This enhancement in the field effect mobility was attributed to the reduction of the root mean square roughness of the gate insulator layer, which might result from the trap states and surface scattering of the gate insulator layer at the lower O{sub 2}/(Ar + O{sub 2}) gas ratio.

Jo, Young Je [WCU Department of Printed Electronics, Sunchon National University, Chonnam 540-742 (Korea, Republic of)] [WCU Department of Printed Electronics, Sunchon National University, Chonnam 540-742 (Korea, Republic of); Lee, In-Hwan [School of Advanced Materials Engineering, Chonbuk National University, Chonju 561-756 (Korea, Republic of)] [School of Advanced Materials Engineering, Chonbuk National University, Chonju 561-756 (Korea, Republic of); Kwak, Joon Seop, E-mail: jskwak@sunchon.ac.kr [WCU Department of Printed Electronics, Sunchon National University, Chonnam 540-742 (Korea, Republic of)

2012-10-15

143

Sol–gel synthesized powder and pulsed laser deposited film of amorphous indium zinc oxides doped with Fe  

Microsoft Academic Search

Amorphous indium and zinc oxides (IZO) doped with various concentration of Fe were prepared by a sol–gel method. 1% Fe doping\\u000a indicated the ferromagnetic behavior and showed the magnetic relaxation peaks in addition to a paramagnetic doublet. The films\\u000a on glass plate were deposited by pulsed laser ablation under 10???6 Torr, using IZO powder with 5% Fe. After annealing at 400?C

K. Nomura; Y. Suzuki; S. Iio; T. Yajima; Y. Yamada; Y. Hirose; T. Hasegawa

2008-01-01

144

Carrier concentration dependence of Ti\\/Au specific contact resistance on n-type amorphous indium zinc oxide thin films  

Microsoft Academic Search

Ti(200 A˚)\\/Au(800 A˚) Ohmic contacts to n-type amorphous indium zinc oxide (IZO) films with carrier concentrations of (1×1015)-(5×1020) cm-3 showed as-deposited specific contact resistances in the range of (3×10-1)-(1×10-4) Omega cm2. Postgrowth annealing from 200 to 500 °C resulted in significant improvement in contact resistances due to increase of the carrier concentration in the near surface region of IZO layer,

Wantae Lim; D. P. Norton; Jung Hun Jang; V. Craciun; S. J. Pearton; F. Ren

2008-01-01

145

Sol–gel synthesized powder and pulsed laser deposited film of amorphous indium zinc oxides doped with Fe  

Microsoft Academic Search

Amorphous indium and zinc oxides (IZO) doped with various concentration of Fe were prepared by a sol–gel method. 1% Fe doping\\u000a indicated the ferromagnetic behavior and showed the magnetic relaxation peaks in addition to a paramagnetic doublet. The films\\u000a on glass plate were deposited by pulsed laser ablation under 10???6 Torr, using IZO powder with 5% Fe. After annealing at 400?C

K. Nomura; Y. Suzuki; S. Iio; T. Yajima; Y. Yamada; Y. Hirose; T. Hasegawa

146

Origins of High Mobility and Low Operation Voltage of Amorphous Oxide TFTs: Electronic Structure, Electron Transport, Defects and Doping  

Microsoft Academic Search

Amorphous oxide semiconductors (AOSs) are expected as new channel materials in thin-film transistors (TFTs) for large-area and\\/or flexible flat-panel displays and other giant-microelectronics devices. So far, many prototype displays have been demonstrated in these four years since the first report of AOS TFT. The most prominent feature of AOS TFTs is that they operate with good performances even if they

Toshio Kamiya; Kenji Nomura; Hideo Hosono

2009-01-01

147

Catalytic properties of mesoporous amorphous silicates of rare-earth elements in the methane oxidative coupling reaction  

Microsoft Academic Search

The influence of the composition of new materials—mesoporous amorphous lanthanide silicates—on the features of their porous\\u000a structure and the effectiveness of the oxidative coupling of methane (single-stage production of ethylene, ethane, and their\\u000a homologues from methane) is revealed. The synergistic effect in this reaction of La and Ce ions introduced into the silicate\\u000a matrix at the sol-gel synthesis stage, which

A. G. Dedov; A. S. Loktev; N. O. Tel’pukhovskaya; K. V. Parkhomenko; M. N. Kartasheva; M. V. Gerashchenko; I. I. Moiseev

2010-01-01

148

Low-loss amorphous silicon waveguides grown by PECVD on indium tin oxide  

NASA Astrophysics Data System (ADS)

Low-loss hydrogenated amorphous silicon (?-Si:H) waveguides were realized by plasma enhanced chemical vapour deposition (PECVD) on a transparent conductive oxide (TCO) layer which is intended to provide the buried contact for the application of an external bias in active devices, e.g. switches and modulators. In particular we propose a technological solution to overcome both the strong reduction in optical transmittance due to the very high extinction coefficient of metal contacts and, at the same time, the optical scattering induced by the texturization effect induced in ?-Si:H films grown on TCO. The very high optical propagation losses were minimized by depositing a spin-on-glass (SOG) layer between the ?-Si:H core-layer and the TCO bottom contact. In this case, propagation losses of 2.5 dB/cm at 1550 nm were measured. All the fabricated samples were optically characterized and the surface roughness was accurately measured using a mechanical profilometer. We observed that, for an ?-Si:H core-layer directly deposited on the TCO contact, the surface roughness is of the order of 100 nm leading to totally opaque waveguides. The experimental performances have been compared to those obtained through calculations using an optical simulation package. The results are found to be in agreement with the experimental data.

Rao, S.; Della Corte, F. G.; Summonte, C.

2010-09-01

149

Hydrogen evolution from a copper(I) oxide photocathode coated with an amorphous molybdenum sulphide catalyst  

NASA Astrophysics Data System (ADS)

Concerns over climate change resulting from accumulation of anthropogenic carbon dioxide in the atmosphere and the uncertainty in the amount of recoverable fossil fuel reserves are driving forces for the development of renewable, carbon-neutral energy technologies. A promising clean solution is photoelectrochemical water splitting to produce hydrogen using abundant solar energy. Here we present a simple and scalable technique for the deposition of amorphous molybdenum sulphide films as hydrogen evolution catalyst onto protected copper(I) oxide films. The efficient extraction of excited electrons by the conformal catalyst film leads to photocurrents of up to -5.7mAcm-2 at 0V versus the reversible hydrogen electrode (pH 1.0) under simulated AM 1.5 solar illumination. Furthermore, the photocathode exhibits enhanced stability under acidic environments, whereas photocathodes with platinum nanoparticles as catalyst deactivate more rapidly under identical conditions. The work demonstrates the potential of earth-abundant light-harvesting material and catalysts for solar hydrogen production.

Morales-Guio, Carlos G.; Tilley, S. David; Vrubel, Heron; Grätzel, Michael; Hu, Xile

2014-01-01

150

Hydrogen evolution from a copper(I) oxide photocathode coated with an amorphous molybdenum sulphide catalyst.  

PubMed

Concerns over climate change resulting from accumulation of anthropogenic carbon dioxide in the atmosphere and the uncertainty in the amount of recoverable fossil fuel reserves are driving forces for the development of renewable, carbon-neutral energy technologies. A promising clean solution is photoelectrochemical water splitting to produce hydrogen using abundant solar energy. Here we present a simple and scalable technique for the deposition of amorphous molybdenum sulphide films as hydrogen evolution catalyst onto protected copper(I) oxide films. The efficient extraction of excited electrons by the conformal catalyst film leads to photocurrents of up to -5.7?mA?cm(-2) at 0?V versus the reversible hydrogen electrode (pH 1.0) under simulated AM 1.5 solar illumination. Furthermore, the photocathode exhibits enhanced stability under acidic environments, whereas photocathodes with platinum nanoparticles as catalyst deactivate more rapidly under identical conditions. The work demonstrates the potential of earth-abundant light-harvesting material and catalysts for solar hydrogen production. PMID:24402352

Morales-Guio, Carlos G; Tilley, S David; Vrubel, Heron; Grätzel, Michael; Hu, Xile

2014-01-01

151

Oxygen partial pressure influence on the character of InGaZnO thin films grown by PLD  

NASA Astrophysics Data System (ADS)

The amorphous oxide semiconductors (AOSs) are promising for emerging large-area optoelectronic applications because of capability of large-area, uniform deposition at low temperatures such as room temperature (RT). Indium-gallium-zinc oxide (InGaZnO) thin film is a promising amorphous semiconductors material in thin film transistors (TFT) for its excellent electrical properties. In our work, the InGaZnO thin films are fabricated on the SiO2 glass using pulsed laser deposition (PLD) in the oxygen partial pressure altered from 1 to 10 Pa at RT. The targets were prepared by mixing Ga2O3, In2O3, and ZnO powder at a mol ratio of 1: 7: 2 before the solid-state reactions in a tube furnace at the atmospheric pressure. The targets were irradiated by an Nd:YAG laser(355nm). Finally, we have three films of 270nm, 230nm, 190nm thick for 1Pa, 5Pa, 10Pa oxygen partial pressure. The product thin films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), Hall-effect investigation. The comparative study demonstrated the character changes of the structure and electronic transport properties, which is probably occurred as a fact of the different oxygen partial pressure used in the PLD.

Lu, Yi; Wang, Li

2012-11-01

152

Solution-processed amorphous niobium oxide as a novel electron collection layer for inverted polymer solar cells  

NASA Astrophysics Data System (ADS)

Amorphous niobium oxide (NbOx) as an electron collection layer in inverted polymer solar cells was prepared by a solution process. The power conversion efficiency of inverted polymer solar cells based on a blend of poly(3-hexylthiophene) and [6,6]-phenyl C61 butyric acid methyl ester was improved to 2.22% by inserting an NbOx layer between the active layer and indium tin oxide electrode. An energy level diagram of component materials in the inverted polymer solar cell indicated that the NbOx layer works as both an electron collection layer and hole blocking layer in polymer solar cells.

Hamada, Keisuke; Murakami, Naoya; Tsubota, Toshiki; Ohno, Teruhisa

2013-10-01

153

High-performance solution-processed amorphous zinc-indium-tin oxide thin-film transistors.  

PubMed

Films of the high-performance solution-processed amorphous oxide semiconductor a-ZnIn(4)Sn(4)O(15), grown from 2-methoxyethanol/ethanolamine solutions, were used to fabricate thin-film transistors (TFTs) in combination with an organic self-assembled nanodielectric as the gate insulator. This structurally dense-packed semiconductor composition with minimal Zn(2+) incorporation strongly suppresses transistor off-currents without significant mobility degradation, and affords field-effect electron mobilities of approximately 90 cm(2) V(-1) s(-1) (104 cm(2) V(-1) s(-1) maximum obtained for patterned ZITO films), with I(on)/I(off) ratio approximately 10(5), a subthreshhold swing of approximately 0.2 V/dec, and operating voltage <2 V for patterned devices with W/L = 50. The microstructural and electronic properties of ZITO semiconductor film compositions in the range Zn(9-2x)In(x)Sn(x)O(9+1.5x) (x = 1-4) and ZnIn(8-x)Sn(x)O(13+0.5x) (x = 1-7) were systematically investigated to elucidate those factors which yield optimum mobility, I(on)/I(off), and threshold voltage parameters. It is shown that structural relaxation and densification by In(3+) and Sn(4+) mixing is effective in reducing carrier trap sites and in creating carrier-generating oxygen vacancies. In contrast to the above results for TFTs fabricated with the organic self-assembled nanodielectric, ZnIn(4)Sn(4)O(15) TFTs fabricated with SiO(2) gate insulators exhibit electron mobilities of only approximately 11 cm(2) V(-1) s(-1) with I(on)/I(off) ratios approximately 10(5), and a subthreshhold swing of approximately 9.5 V/dec. PMID:20662515

Kim, Myung-Gil; Kim, Hyun Sung; Ha, Young-Geun; He, Jiaqing; Kanatzidis, Mercouri G; Facchetti, Antonio; Marks, Tobin J

2010-08-01

154

Ketjenblack carbon supported amorphous manganese oxides nanowires as highly efficient electrocatalyst for oxygen reduction reaction in alkaline solutions.  

PubMed

A composite air electrode consisting of Ketjenblack carbon (KB) supported amorphous manganese oxide (MnOx) nanowires, synthesized via a polyol method, is highly efficient for the oxygen reduction reaction (ORR) in a Zn-air battery. The low-cost and highly conductive KB in this composite electrode overcomes the limitations due to low electrical conductivity of MnOx while acting as a supporting matrix for the catalyst. The large surface area of the amorphous MnOx nanowires, together with other microscopic features (e.g., high density of surface defects), potentially offers more active sites for oxygen adsorption, thus significantly enhancing ORR activity. In particular, a Zn-air battery based on this composite air electrode exhibits a peak power density of ?190 mW/cm2, which is far superior to those based on a commercial air cathode with Mn3O4 catalysts. PMID:22050041

Lee, Jang-Soo; Park, Gi Su; Lee, Ho Il; Kim, Sun Tai; Cao, Ruiguo; Liu, Meilin; Cho, Jaephil

2011-12-14

155

Characterization of magnetoimpedance on polycrystalline and amorphous chromium oxides bilayered thin films  

Microsoft Academic Search

The impedance of chemical vapor deposited CrO2 and Cr2O3 bilayered thin films, composed of polycrystalline and amorphous structure, have been systematically studied in function of frequency and temperature. In the polycrystalline-CrO2\\/amorphous-Cr2O3 bilayer, the real part of impedance at low frequency (f<300 kHz) demonstrates a sharp transition at temperature around 330 K, with a specific feature of positive temperature coefficient, similar

C. M. Fu; C. J. Lai; H. S. Hsu; Y. C. Chao; J. C. A. Huang; C.-C. Wu; S.-G. Shyu

2002-01-01

156

Transport behavior across the field-driven superconductor-insulator transition in amorphous indium oxide films  

NASA Astrophysics Data System (ADS)

Superconductor-insulator transition (SIT) in two-dimensional (2D) thin films is a beautiful realization of a zero temperature quantum phase transition (QPT) and has been explored both theoretically and experimentally over the last two decades. In addition to the several intrinsic ways (such as thickness) of tuning the transition, external magnetic field has been used to tune from one ground state to another in various condensed matter systems. Amorphous indium oxide thin films, with their unique capability of tuning the disorder level in the system easily, have been proven to be an excellent model system to study the transport mechanisms near and across the SIT in 2D. In this thesis, magnetic field-driven SIT in 2D films of amorphous InO x is studied. The goal of this work is to understand the microscopic transport mechanisms responsible for driving the SIT when the magnetic field direction is continually varied from being perpendicular to the sample plane to parallel. Applying a perpendicular magnetic field resulting in a clear field-driven SIT and a magneto-resistance peak on the insulating side in InO x films have been previously understood in a bosonic picture put forward by M. P. A. Fisher and coworkers. However, this boson-vortex duality picture is expected to give rise to markedly different transport characteristics when the magnetic field is applied parallel to the sample plane. Features found in the parallel-field transport data however can also be explained by the bosonic picture, thereby questioning the applicability of the hitherto successful models to the physics of SIT. An isotropic magnetic field value, where the sample has the exact same resistance irrespective of the angle between the sample plane and magnetic field direction, is found. This isotropic point lies at field values above the critical field (Bc) of the SIT (in both perpendicular and parallel configurations) and above the magnetoresistance peak. The isotropic point is very weakly dependent on disorder levels and is temperature-independent. These observations suggest a possible fermionic role in the conduction near the quantum critical point of the SIT and would require newer models to be developed to completely understand the physics. Current-voltage characteristics measured in superconducting samples (below Bc) show that the true superconducting behavior (with a critical current to conduction) appears only in the B = 0 limit. Especially, application of a small magnetic field (˜ 0.2 T) drives the system into a flux flow regime and hence dissipative. The role of this dissipative channel in the superconducting phase in driving the SIT is not well understood. Competing roles of dissipation and bosonic mechanisms need to be treated simultaneously to decipher the underlying physics. When magnetic field is applied to a mesoscopic scale superconducting film, the film breaks into puddles of superconductors and insulators, thereby suggesting percolation-type transport behavior near the quantum critical point. Interestingly, the nonuniform nature of conduction occurs only in magnetic fields below and above Bc at very low temperature below ˜ 400 mK and the sample is completely homogeneous at B c. A complete understanding of the scale of inhomogeneous regions and their role in driving the QPT are still unclear. And the results presented suggest that more experimental and theoretical efforts are needed for understanding the physics near the QPT clearly.

Kim, Min-Soo

157

Modeling the adsorption of mercury(II) on (hydr)oxides. 2: {alpha}-FeOOH (goethite) and amorphous silica  

SciTech Connect

The surface complexation model is used to describe sorption experiments of inorganic mercury(II) in the presence of an amorphous silica, Aerosil 200, or an iron (hydr)oxide, the goethite {alpha}-FeOOH (Bayferrox 910). In the simulations, one assumes the formation of a monodentate surface complex {triple_bond}S{single_bond}OHgOH and {triple_bond}S{single_bond}OHgCl, when chlorides are present in solution. Participation of the complex {triple_bond}S{single_bond}OHgCl has been especially evidenced. Comparisons with other data from the literature have been made to investigate the influence of the nature of the oxide on the mechanism of mercury(II) adsorption. X-ray photoelectron spectroscopy was used to characterize the surface of the (hydr)oxides prior to adsorption and to observe when possible the mercury surface compounds.

Bonnissel-Gissinger, P.; Alnot, M.; Ehrhardt, J.J. [CNRS-Univ. Henri Poincare, Villers-les-Nancy (France). Lab. de Chimie Physique pour l`Environnement] [CNRS-Univ. Henri Poincare, Villers-les-Nancy (France). Lab. de Chimie Physique pour l`Environnement; Lickes, J.P. [Univ. Libre de Bruxelles, Brussels (Belgium). Service de Chimie Analytique] [Univ. Libre de Bruxelles, Brussels (Belgium). Service de Chimie Analytique; Behra, P. [Univ. Louis Pasteur-CNRS, Strasbourg (France). Inst. de Mecanique des Fluides] [Univ. Louis Pasteur-CNRS, Strasbourg (France). Inst. de Mecanique des Fluides

1999-07-15

158

Electrical and optical characteristics of Co-sputtered amorphous Ce-doped indium-zinc-oxide thin-film transistors  

NASA Astrophysics Data System (ADS)

We report the electrical and the optical characteristics of amorphous cerium-gallium-zinc-oxide (a-CIZO) thin-film transistors (TFTs) as a function of the cerium content inside the a-CIZO channel layers. The a-CIZO films were systematically prepared by using a co-sputtering method with a combination of RF-sputtered indium-zinc-oxide (IZO) at a fixed power of 50 W and cerium-oxide (CeO2) at powers from 15 to 30 W. The Ce content in the CIZO layers increased with increasing RF power on the CeO2 target. The a-CIZO TFT at the optimum power of 15 W exhibited a mobility of 2.5 cm2/Vsec, a threshold voltage ( V T ) of 0.22 V, ?V T shifts of less than 5.2 V under negative bias stress, and a Ion/Ioff ratio of 2.40 × 1010.

Koo, Ja Hyun; Kang, Tae Sung; Kim, Tae Yoon; Hong, Jin Pyo

2013-02-01

159

Local environment of iron in heavy ion-irradiated amorphous magnetic oxides by Moessbauer and x-ray absorption spectroscopy  

SciTech Connect

Moessbauer and X-ray absorption spectroscopies of some crystallized iron oxides, Fe{sub 2}O{sub 3}, FePO{sub 4}, Fe{sub 3}PO{sub 7}, and SrMn{sub 1.85}Fe{sub 0.15}O{sub 2.5}, the garnet Y{sub 3}Fe{sub 5}O{sub 12}, and the barium hexaferrite BaFe{sub 12}O{sub 19} have been undertaken in order to look at the local order around iron in Y{sub 3}Fe{sub 5}O{sub 12} and BaFe{sub 12}O{sub 19} materials amorphized by irradiation with high energy (27 MeV/n) xenon ions accelerated by GANIL. Simulations of the Moessbauer spectra suggested the presence of fivefold coordinated iron in the amorphous irradiated compounds with a distribution of magnetic interactions due to the variations of the number of iron second neighbors. The XANES spectra at the Fe-K edge confirmed the fivefold coordination of iron in the amorphous ferrites, show that the local structure around iron appears to be similar although the original structures were different, and appear close to the one observed in the Fe{sub 3}PO{sub 7} compound in which iron stands in a trigonal bipyramidal environment.

Studer, F.; Houpert Ch. (Crismat, Caen (France)); Toulemonde, M. (Ciril,Caen (France)) Dartyge E. (Lure, Orsay, (France))

1991-04-01

160

Influence of the borohydride concentration on the composition of the amorphous Fe–B alloy produced by chemical reduction of synthetic, nano-sized iron-oxide particles  

Microsoft Academic Search

Amorphous Fe–B alloys can be prepared at room temperature by reduction with borohydride of iron-oxide particles in suspension. By varying the borohydride concentration, amorphous Fe–B alloys with boron contents between 2 and 13at.% have been produced by reduction of synthetic (nano-sized particles) and natural (micro-sized) hematite (?-Fe2O3) using sodium borohydride (NaBH4). The results presented in this paper were obtained from

V. G. de Resende; E. De Grave; G. M. da Costa; J. Janssens

2007-01-01

161

Structure of amorphous oxide ceramics by nuclear magnetic resonance spectroscopy and molecular dynamics simulations  

NASA Astrophysics Data System (ADS)

Molecular dynamics (MD) simulations have been used to study the structure and dynamics of sodium tetrasilicate (Na2Si4O9 ) liquid as a function of pressure, ranging from I atmosphere to 100 GPa, at a temperature of 6000 K. The calculated self-diffusivity of the ions increases with increasing pressure, up to a maximum of approximately 10--15 GPa. Above this pressure, the O2- diffusivity decreases slightly with increasing pressure. The results of the simulations allow the distinction of two different mechanisms for the pressure-induced coordination change of silicon. The first, occurring at lower pressures, involves the formation of V-coordinated silicon, via reaction with non-bridging oxygens. The high pressure mechanism involves a reaction of bridging oxygens, which results in the formation of III-coordinated oxygen. MD simulations were carried out in order to investigate the structure and transport properties of boron oxide melt, as a function of pressure. The simulations show a rapid initial increase in the diffusion coefficients of boron and oxygen ions to ˜5--7 GPa, followed by a slower increase from 7--14 GPa. The increase in ion diffusivities is correlated with an increase in the proportion of BO4 to BO3 units. These results can be used to help rationalize an increase in growth rate of boron suboxide (B6O) crystals, observed from B2O3-B 6O melts in the 0--4 GPa pressure range. Structural characterization has also been carried out on a decomposed alumina ceramic precursor material, which is synthesized via thermal decomposition of an aluminum nitrate, nanohydrate [Al(NO3)3·9H 2O] salt to yield an x-ray amorphous, water-soluble precursor. Characterization of the solid precursor is presented, along with an in-depth study on the aluminum speciation in solution. Although the solid precursor contains entirely VI-coordinated aluminum, the solution phase contains IV-, V-, and VI-coordinated aluminum, whose relative abundance does not change with increasing thermal decomposition of the starting material. Furthermore, it is the change in solution concentration which alters the relative ratios of the structural units present in solution.

Diefenbacher, Jason Ross

162

Amorphous iron-(hydr) oxide networks at liquid/vapor interfaces: In situ X-ray scattering and spectroscopy studies  

SciTech Connect

Surface sensitive X-ray reflectivity (XR), fluorescence (XF), and grazing incidence X-ray diffraction (GIXD) experiments were conducted to determine the accumulation of ferric iron Fe (III) or ferrous iron Fe (II) under dihexadecyl phosphate (DHDP) or arachidic acid (AA) Langmuir monolayers at liquid/vapor interfaces. Analysis of the X-ray reflectivity and fluorescence data of monolayers on the aqueous subphases containing FeCl3 indicates remarkably high levels of surface-bound Fe (III) in number of Fe3þ ions per molecule (DHDP or AA) that exceed the amount necessary to neutralize a hypothetically completely deprotonated monolayer (DHDP or AA). These results suggest that nano-scale iron (hydr) oxide complexes (oxides, hydroxides or oxyhydroxides) bind to the headgroups and effectively overcompensate the maximum possible charges at the interface. The lack of evidence of in-plane ordering in GIXD measurements and strong effects on the surface-pressure versus molecular area isotherms indicate that an amorphous network of iron (hydr) oxide complexes contiguous to the headgroups is formed. Similar experiments with FeCl2 generally resulted with the oxidation of Fe (II)–Fe (III) which consequently leads to ferric Fe (III) complexes binding albeit with less iron at the interface. Controlling the oxidation of Fe (II) changes the nature and amount of binding significantly. The implications to biomineralization of iron (hydr) oxides are briefly discussed.

Wang, W.; Pleasants, J.; Bu, W.; Park, R.Y.; Kuzmenko, I.; Vaknin, D.

2012-06-23

163

Role of Hydrophobicity in Adhesion of the Dissimilatory Fe(III)-Reducing Bacterium Shewanella alga to Amorphous Fe(III) Oxide  

PubMed Central

The mechanisms by which the dissimilatory Fe(III)-reducing bacterium Shewanella alga adheres to amorphous Fe(III) oxide were examined through comparative analysis of S. alga BrY and an adhesion-deficient strain of this species, S. alga RAD20. Approximately 100% of S. alga BrY cells typically adhered to amorphous Fe(III) oxide, while less than 50% of S. alga RAD20 cells adhered. Bulk chemical analysis, isoelectric point analysis, and cell surface analysis by time-of-flight secondary-ion mass spectrometry and electron spectroscopy for chemical analysis demonstrated that the surfaces of S. alga BrY cells were predominantly protein but that the surfaces of S. alga RAD20 cells were predominantly exopolysaccharide. Physicochemical analyses and hydrophobic interaction assays demonstrated that S. alga BrY cells were more hydrophobic than S. alga RAD20 cells. This study represents the first quantitative analysis of the adhesion of a dissimilatory Fe(III)-reducing bacterium to amorphous Fe(III) oxide, and the results collectively suggest that hydrophobic interactions are a factor in controlling the adhesion of this bacterium to amorphous Fe(III) oxide. Despite having a reduced ability to adhere, S. alga RAD20 reduced Fe(III) oxide at a rate identical to that of S. alga BrY. This result contrasts with results of previous studies by demonstrating that irreversible cell adhesion is not requisite for microbial reduction of amorphous Fe(III) oxide. These results suggest that the interaction between dissimilatory Fe(III)-reducing bacteria and amorphous Fe(III) oxide is more complex than previously believed.

Caccavo, F.; Schamberger, P. C.; Keiding, K.; Nielsen, P. H.

1997-01-01

164

Amorphous Transparent Conducting Oxides (TCOs) Deposited at T 100<= ..deg.. C (Presentation)  

SciTech Connect

The summary of this report is that amorphous InZnO (a-IZO) is a very versatile TCO with: (1) low process temperatures ({approx} 100 C); (2) easy to make by sputtering; (3) excellent optical and electronic properties; (4) very smooth etchable films; and (5) remarkable thermal processing stability.

Perkins, J.; van Hest, M.; Teplin, C.; Alleman, J.; Dabney, M.; Gedvilas, L.; Keyes, B.; To, B.; Ginley D.

2006-05-01

165

Radiation-induced amorphization resistance and radiation tolerance in structurally related oxides  

Microsoft Academic Search

Ceramics destined for use in hostile environments such as nuclear reactors or waste immobilization must be highly durable and especially resistant to radiation damage effects. In particular, they must not be prone to amorphization or swelling. Few ceramics meet these criteria and much work has been devoted in recent years to identifying radiation-tolerant ceramics and the characteristics that promote radiation

Kurt E. Sickafus; Robin W. Grimes; James A. Valdez; Antony Cleave; Ming Tang; Manabu Ishimaru; Siobhan M. Corish; Christopher R. Stanek; Blas P. Uberuaga

2007-01-01

166

Preparation and properties of amorphous titania-coated zinc oxide nanoparticles  

SciTech Connect

Amorphous TiO{sub 2}-coated ZnO nanoparticles were prepared by the solvothermal synthesis of ZnO nanoparticles in ethanol and the followed by sol-gel coating of TiO{sub 2} nanolayer. The analyses of X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed that the resultant ZnO nanoparticles were hexagonal with a wurtzite structure and a mean diameter of about 60 nm. Also, after TiO{sub 2} coating, the TEM images clearly indicated the darker ZnO nanoparticles being surrounded by the lighter amorphous TiO{sub 2} layers. The zeta potential analysis revealed the pH dependence of zeta potentials for ZnO nanoparticles shifted completely to that for TiO{sub 2} nanoparticles after TiO{sub 2} coating, confirming the formation of core-shell structure and suggesting the coating of TiO{sub 2} was achieved via the adhesion of the hydrolyzed species Ti-O{sup -} to the positively charged surface of ZnO nanoparticles. Furthermore, the analyses of Fourier transform infrared (FTIR) and Raman spectra were also conducted to confirm that amorphous TiO{sub 2} were indeed coated on the surface of ZnO nanoparticles. In addition, the analyses of ultraviolet-visible (UV-VIS) and photoluminescence (PL) spectra revealed that the absorbance of amorphous TiO{sub 2}-coated ZnO nanoparticles at 375 nm gradually decreased with an increase in the Ti/Zn molar ratio and the time for TiO{sub 2} coating, and the emission intensity of ZnO cores could be significantly enhanced by the amorphous TiO{sub 2} shell. - Graphical abstract: Amorphous titania-coated ZnO nanoparticles with a core-shell structure were prepared. It was found that the emission intensity of ZnO cores could be significantly enhanced by the amorphous TiO{sub 2} shell.

Liao Minhung [Applied Science and Technology Research Center, Department of Cosmetology and Styling, Transworld Institute of Technology, Douliu 640, Yulin, Taiwan (China)]. E-mail: liaomh@mail.tit.edu.tw; Hsu, C.-H. [Department of Chemical Engineering, National Cheng Kung University, Tainan, Taiwan 701 (China); Chen, D.-H. [Department of Chemical Engineering, National Cheng Kung University, Tainan, Taiwan 701 (China)]. E-mail: chendh@mail.ncku.edu.tw

2006-07-15

167

Structural and electrical characteristics of high-? Er2O3 and Er2TiO5 gate dielectrics for a-IGZO thin-film transistors  

PubMed Central

In this letter, we investigated the structural and electrical characteristics of high-? Er2O3 and Er2TiO5 gate dielectrics on the amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT) devices. Compared with the Er2O3 dielectric, the a-IGZO TFT device incorporating an Er2TiO5 gate dielectric exhibited a low threshold voltage of 0.39 V, a high field-effect mobility of 8.8 cm2/Vs, a small subthreshold swing of 143 mV/decade, and a high Ion/Ioff current ratio of 4.23 × 107, presumably because of the reduction in the oxygen vacancies and the formation of the smooth surface roughness as a result of the incorporation of Ti into the Er2TiO5 film. Furthermore, the reliability of voltage stress can be improved using an Er2TiO5 gate dielectric.

2013-01-01

168

Flexible double gate a-IGZO TFT fabricated on free standing polyimide foil  

NASA Astrophysics Data System (ADS)

In this paper, the concept of double gate transistors is applied to mechanically flexible amorphous indium-gallium-zinc-oxide (a-IGZO) thin film transistors (TFTs) fabricated on free standing plastic foil. Due to the temperature sensitivity of the plastic substrate, a-IGZO is a suitable semiconductor because it provides carrier mobilities around 10 cm2/Vs when deposited at room temperature. Double gate TFTs with connected bottom and top gate are compared to bottom gate reference TFTs fabricated on the same substrate. Double gate a-IGZO TFTs exhibit a by 78% increased gate capacitance, a by 700 mV higher threshold voltage, and therefore an up to 92% increased transconductance when characterized at the same gate voltage above threshold (over-bias voltage). The subthreshold swing and the on/off current ratios are improved as well, and reach excellent values of 69 mV/dec and 2 × 109, respectively. The mechanical flexibility of double gate TFTs compared to bottom gate TTFs is investigated, and device operation is shown while the double gate TFT is exposed to tensile strain of 0.55%, induced by bending to a radius of 5 mm.

Münzenrieder, Niko; Zysset, Christoph; Petti, Luisa; Kinkeldei, Thomas; Salvatore, Giovanni A.; Tröster, Gerhard

2013-06-01

169

Amorphous silica nanoparticles trigger nitric oxide/peroxynitrite imbalance in human endothelial cells: inflammatory and cytotoxic effects  

PubMed Central

Background The purpose of this study was to investigate the mechanism of noxious effects of amorphous silica nanoparticles on human endothelial cells. Methods Nanoparticle uptake was examined by transmission electron microscopy. Electrochemical nanosensors were used to measure the nitric oxide (NO) and peroxynitrite (ONOO?) released by a single cell upon nanoparticle stimulation. The downstream inflammatory effects were measured by an enzyme-linked immunosorbent assay, real-time quantitative polymerase chain reaction, and flow cytometry, and cytotoxicity was measured by lactate dehydrogenase assay. Results We found that the silica nanoparticles penetrated the plasma membrane and rapidly stimulated release of cytoprotective NO and, to a greater extent, production of cytotoxic ONOO?. The low [NO]/[ONOO?] ratio indicated increased nitroxidative/oxidative stress and correlated closely with endothelial inflammation and necrosis. This imbalance was associated with nuclear factor ?B activation, upregulation of key inflammatory factors, and cell death. These effects were observed in a nanoparticle size-dependent and concentration-dependent manner. Conclusion The [NO]/[ONOO?] imbalance induced by amorphous silica nanoparticles indicates a potentially deleterious effect of silica nanoparticles on vascular endothelium.

Corbalan, J Jose; Medina, Carlos; Jacoby, Adam; Malinski, Tadeusz; Radomski, Marek W

2011-01-01

170

Good electrical and mechanical properties induced by the multilayer graphene oxide sheets incorporated to amorphous carbon films  

NASA Astrophysics Data System (ADS)

Multilayer graphene oxide nanosheets were fabricated using commercially available expanded graphite by simple ultrasonic treatment and then were incorporated into the amorphous carbon matrix as fillers by electrochemical deposition. The electrical conductivity of the films was strongly improved due to the contribution of the multilayer graphene oxide sheets. Moreover, the Young's modulus, hardness and elastic recovery of the composite films were measured to be about 171.1 GPa, 10.1 GPa and 81.4%, respectively, compared to 137.4 GPa, 5.1 GPa and 44.3% of undoped a-C:H films prepared at the same conditions. Additionally, the friction coefficient was tested to be 0.15 (0.5 N, 2 Hz) and the antiwear life was prolonged to about 200 s while the undoped DLC films obtained at the same condition were easy to be frazzled.

Zhang, Junyan; Yu, Yuanlie; Huang, Deming

2010-07-01

171

Photoresist-free fully self-patterned transparent amorphous oxide thin-film transistors obtained by sol-gel process.  

PubMed

We demonstrated self-patterned solution-processed amorphous oxide semiconductor thin-film transistors (TFTs) using photosensitive sol-gels. The photosensitive sol-gels were synthesized by adding ?-diketone compounds, i.e., benzoylacetone and acetylacetone, to sol-gels. The chemically modified photosensitive sol-gels showed a high optical absorption at specific wavelengths due to the formation of metal chelate bonds. Photoreactions of the modified solutions enabled a photoresist-free process. Moreover, Zn-Sn-O with a high Sn ratio, which is hard to wet-etch using conventional photolithography due to its chemical durability, was easily patterned via the self-patterning process. Finally, we fabricated a solution-processed oxide TFT that included fully self-patterned electrodes and an active layer. PMID:24686314

Lim, Hyun Soo; Rim, You Seung; Kim, Hyun Jae

2014-01-01

172

Amorphous semiconducting and conducting transparent metal oxide thin films and production thereof  

Microsoft Academic Search

Metal oxide thin films and production thereof are disclosed. An exemplary method of producing a metal oxide thin film may comprise introducing at least two metallic elements and oxygen into a process chamber to form a metal oxide. The method may also comprise depositing the metal oxide on a substrate in the process chamber. The method may also comprise simultaneously

John Perkins; David Ginley; Matthew Taylor; George A. Neuman; Henry A. Luten; Jeffrey A. Forgette; John S. Anderson

2010-01-01

173

Amorphous Indium-Zinc-Oxide Transparent Conductors for Thin Film PV  

Microsoft Academic Search

Amorphous InZnO's (a-IZO) basic PV applicability has now been demonstrated in prototype CIGS, Si Heterojunction (SiHJ) and organic photovoltaics (OPV). However, to move beyond initial demonstration devices, improved TCO properties and processibility of the a-IZO films are needed. Here, RF-superimposed DC sputtering was used to improve the reliable deposition of a-IZO with conductivity Ï >; 3000 S\\/cm.

J. Perkins; T. Gennett; M. Galante; D. Gillaspie; D. Ginley

2011-01-01

174

Amorphous Indium-Zinc-Oxide Transparent Conductors for Thin Film PV: Preprint  

Microsoft Academic Search

Amorphous InZnO's (a-IZO) basic PV applicability has now been demonstrated in prototype CIGS, Si Heterojunction (SiHJ) and organic photovoltaics (OPV). However, to move beyond initial demonstration devices, improved TCO properties and processibility of the a-IZO films are needed. Here, RF-superimposed DC sputtering was used to improve the reliable deposition of a-IZO with conductivity > 3000 S\\/cm.

J. Perkins; T. Gennett; M. Galante; D. Gillaspie; D. Ginley

2011-01-01

175

Room-temperature fabrication of transparent flexible thin-film transistors using amorphous oxide semiconductors  

Microsoft Academic Search

Transparent electronic devices formed on flexible substrates are expected to meet emerging technological demands where silicon-based electronics cannot provide a solution. Examples of active flexible applications include paper displays and wearable computers. So far, mainly flexible devices based on hydrogenated amorphous silicon (a-Si:H) and organic semiconductors have been investigated. However, the performance of these devices has been insufficient for use

Kenji Nomura; Hiromichi Ohta; Akihiro Takagi; Toshio Kamiya; Masahiro Hirano; Hideo Hosono

2004-01-01

176

Preparation and evaluation of amorphous metal oxide magnetic thin films and nanocomposites for spintronics  

Microsoft Academic Search

In this work, photochemical metalorganic deposition (PMOD) using thin films of metal 2-ethylhexanoates (Mo and Fe) was used to deposit patterned thin films of a-MoO3 and a-Fe 2O3 (where a stands for amorphous) in a positive tone. The mechanism of positive tone PMOD of a-Fe 2O3 was examined by using spectroscopic ellipsometry, which allowed the determination that the development preferentially

Simon Trudel

2008-01-01

177

Functionalization of FeCo alloy nanoparticles with highly dielectric amorphous oxide coatings  

Microsoft Academic Search

FeCo alloy nanoparticles have been prepared by using a two step modified polyol process using Fe(II) chloride and Co acetate tetrahydrate as Fe and Co metal precursors. Tetraethyl silicate, aluminum isopropoxide, and zirconium(IV) acetyl acetonate were used to make amorphous SiO2, Al2O3, and ZrO2 coatings, respectively. X-ray diffraction studies showed that there are no crystalline peaks corresponding to SiO2, Al2O3,

Q. Nguyen; C. N. Chinnasamy; S. D. Yoon; S. Sivasubramanian; T. Sakai; A. Baraskar; S. Mukerjee; C. Vittoria; V. G. Harris

2008-01-01

178

Amorphous Indium-Zinc-Oxide Transparent Conductors for Thin Film PV: Preprint  

SciTech Connect

Amorphous InZnO's (a-IZO) basic PV applicability has now been demonstrated in prototype CIGS, Si Heterojunction (SiHJ) and organic photovoltaics (OPV). However, to move beyond initial demonstration devices, improved TCO properties and processibility of the a-IZO films are needed. Here, RF-superimposed DC sputtering was used to improve the reliable deposition of a-IZO with conductivity > 3000 S/cm.

Perkins, J.; Gennett, T.; Galante, M.; Gillaspie, D.; Ginley, D.

2011-07-01

179

Complex nanospherulites of zinc oxide and native amorphous boron in the lunar regolith from Mare Crisium  

NASA Astrophysics Data System (ADS)

During the study of tea-colored impact glass fragments from the sample of lunar regolith delivered to Earth by the Luna 24 automatic station by transmission electron microscopy, the composition variations of the previously described high-carbonaceous film, the presence of at least three composition types of glasses, and unusual nanospherulites with Zn-B-N-O composition were discovered. As a part of a nonuniform high-carbonaceous oxygen-bearing film, sites enriched in either Na, S, Si, or Ca were detected. All these sites, as well as the whole film, are electron-amorphous; however, crystalline graphite was also found. Two types of nanospherulites are composed of amorphous ZnO and regular interstratifications of crystalline ZnO and amorphous boron layers with insignificant participation of adsorbed nitrogen. It is supposed that the formation of zinc-boron nanospherulites was caused by a fast-flowing explosive process and probably was modulated by high-frequency acoustic oscillations in a cloud of evaporated high-temperature ionized gas during the impact event.

Mokhov, A. V.; Kartashov, P. M.; Gornostaeva, T. A.; Asadulin, En. E.; Bogatikov, O. A.

2013-01-01

180

The amorphous oxides MnV 2O 6 + ? (0 < ? < 1) as high capacity negative electrode materials for lithium batteries  

NASA Astrophysics Data System (ADS)

MnV 2O 6 + ? · nH 2O (0 < ? < 1) amorphous oxides were prepared by a two-step process including the precipitation of a crystallized precursor MnV 2O 6 · 4H 2O and its ozonation at temperatures below 100 °C. Their characterization by spectroscopic techniques (XAS and EELS) shows that V 5+ retains a VO 5 environment and that Mn, which remains in octahedral coordination, is oxidized to Mn 4+ mainly. MnV 2O 6 + ? compounds insert reversibly large amounts of Li per formula unit (e.g. Li 12MnV 2O 6.96) at low voltage. After the first insertion/de-insertion cycle, subsequent cycles correspond to fully reversible lithium insertion between the two compositions: Li ?MnV 2O 6 + ? ( ? ? 2) and Li 12MnV 2O 6 + ? (from 600 to 900 mAh/g). Investigations on the Li derivatives by XAS and EELS show that during the insertion/de-insertion cycles the V oxidation state varies reversibly between +5 and +3. Mn 4+ cations are reduced to Mn 2+ upon the first discharge. During the subsequent cycles the average Mn oxidation state varies reversibly between +2 and about +2.6. It clearly appears that the electron transfer from Li to the host matrix decreases with increasing x in Li xMnV 2O 6 + ?.

Piffard, Y.; Leroux, F.; Guyomard, D.; Mansot, J.-L.; Tournoux, M.

181

First-principles study of the mechanical and optical properties of amorphous hydrogenated silicon and silicon-rich silicon oxide  

NASA Astrophysics Data System (ADS)

We use first-principles density-functional theory (DFT) calculations to predict mechanical and optical property variation with composition for hydrogenated amorphous Si (a-Si:H) ( at.%H=0 , 5.9, 11.1, and 15.8) and a-SiOx ( x=0 , 0.5, 1.0, 1.5, and 2.0). A better understanding of the properties of a-Si:H and amorphous silicon oxide (a-SiOx) is technologically important, particularly for photovoltaic and optoelectronic device applications, respectively. However, relatively little reliable property information is available for these amorphous materials except for the well-studied end-point cases of a-Si and a-SiO2 . Our DFT calculations within the generalized gradient approximation predict that addition of H to a-Si monotonically reduces the elastic modulus (Y) by 18% and bulk modulus (B) by 16% as H incorporation increases to 15.8at.% in a-Si:H. Similarly, addition of O to a-Si monotonically reduces Y by 35% and B by 38% as x increases to 2.0 in a-SiOx . Our optical spectra for the complex dielectric function, ?(?) , exhibit intensity reduction in the E2 transition peak of Im[?(?)] and reduction in the low-frequency dielectric constant {?o=lim??0Re[?(?)]} as either H or O are added to a-Si while the a-SiOx spectra additionally resolve a vivid blueshift of both the fundamental absorption edge and E2 transition energy as O content increases. Considering the large variation in reported experimental measurements and the limited availability of previous computational results, our property predictions provide valuable insight into the mechanical and optical behavior of a-Si:H and a-SiOx materials.

Bondi, Robert J.; Lee, Sangheon; Hwang, Gyeong S.

2010-05-01

182

Amorphous stability of HfO 2 based ternary and binary composition spread oxide films as alternative gate dielectrics  

NASA Astrophysics Data System (ADS)

A ternary alloyed thin film library of HfO 2-Y 2O 3-Al 2O 3 was grown on a Si(1 0 0) substrate in a few hours by a new pulsed laser deposition (PLD) system installed with a masking and substrate rotating scheme. This specially designed combinatorial ternary composition spread method enabled us to fabricate continuous ternary and binary composition spread film libraries. It is noteworthy that the library made by this system is addressable; each film composition covers the full range (from 0 to 100%) and can be directly correlated with the film location in the ternary and binary phase diagram. Rapid permittivity measurement on the film libraries was carried out by a scanning microwave microscope, while the crystal structure was by a combinatorial X-ray diffractometer (XRD). The (HfO 2) 6(Y 2O 3) 1(Al 2O 3) 3 ternary composition area in an amorphous phase was found to have a dielectric constant higher than HfO 2-Y 2O 3 binary area. This ternary oxide is promising as amorphous gate dielectric material.

Hasegawa, K.; Ahmet, P.; Okazaki, N.; Hasegawa, T.; Fujimoto, K.; Watanabe, M.; Chikyow, T.; Koinuma, H.

2004-02-01

183

Temperature-Dependent Tunnelling into Amorphous Silicon.  

National Technical Information Service (NTIS)

Conductance measurements are presented for junctions of the type metal-oxide-amorphous silicon, where the oxide is sufficiently thin to permit tunnelling. The conductance exhibits a temperature dependence essentially identical to that for amorphous silico...

C. J. Mogab D. Adler J. A. Sauvage

1972-01-01

184

Magnesium-Aluminum-Zirconium Oxide Amorphous Ternary Composite: A Dense and Stable Optical Coating  

NASA Technical Reports Server (NTRS)

In the present work, the process parameter dependent optical and structural properties of MgO-Al(2)O(3)-ZrO(2) ternary mixed-composite material have been investigated. Optical properties were derived from spectrophotometric measurements. The surface morphology, grain size distributions, crystallographic phases and process dependent material composition of films have been investigated through the use of Atomic Force Microscopy (AFM), X-ray diffraction analysis and Energy Dispersive X- ray (EDX) analysis. EDX analysis made evident the correlation between the optical constants and the process dependent compositions in the films. It is possible to achieve environmentally stable amorphous films with high packing density under certain optimized process conditions.

Sahoo, N. K.; Shapiro, A. P.

1998-01-01

185

Electronic Structure of O-vacancy in Amorphous Zinc-Tin Oxides  

NASA Astrophysics Data System (ADS)

We study the atomic and electronic structure of O-vacancy (VO) in amorphous Zn-Sn-O (a-ZTO) through density functional calculations. Some of O-vacancies are spontaneously ionized, donating electrons to the conduction band, while most VO defects act as deep donors. When VO is ionized, severe outward relaxations occur, increasing the stability of VO+2. From the formation energies, the charge transition level of VO is found to be shallower in a-ZTO, as compared to crystalline phase. We suggest that VO causes persistent photoconductivity in a-ZTO.

Ryu, Byungki; Chang, Kee Joo

2011-12-01

186

Comparison of amorphous iridium water-oxidation electrocatalysts prepared from soluble precursors.  

PubMed

Electrodeposition of iridium oxide layers from soluble precursors provides a route to active thin-layer electrocatalysts for use on water-oxidizing anodes. Certain organometallic half-sandwich aqua complexes of iridium form stable and highly active oxide films upon electrochemical oxidation in aqueous solution. The catalyst films appear as blue layers on the anode when sufficiently thick, and most closely resemble hydrous iridium(III,IV) oxide by voltammetry. The deposition rate and cyclic voltammetric response of the electrodeposited material depend on whether the precursor complex contains a pentamethylcyclopentadieneyl (Cp*) or cyclopentadienyl ligand (Cp), and do not match, in either case, iridium oxide anodes prepared from non-organometallic precursors. Here, we survey our organometallic precursors, iridium hydroxide, and pre-formed iridium oxide nanoparticles. From electrochemical quartz crystal nanobalance (EQCN) studies, we find differences in the rate of electrodeposition of catalyst layers from the two half-sandwich precursors; however, the resulting layers operate as water-oxidizing anodes with indistinguishable overpotentials and H/D isotope effects. Furthermore, using the mass data collected by EQCN and not otherwise available, we show that the electrodeposited materials are excellent catalysts for the water-oxidation reaction, showing maximum turnover frequencies greater than 0.5 mol O(2) (mol iridium)(-1) s(-1) and quantitative conversion of current to product dioxygen. Importantly, these anodes maintain their high activity and robustness at very low iridium loadings. Our organometallic precursors contrast with pre-formed iridium oxide nanoparticles, which form an unstable electrodeposited material that is not stably adherent to the anode surface at even moderately oxidizing potentials. PMID:22725667

Blakemore, James D; Schley, Nathan D; Kushner-Lenhoff, Maxwell N; Winter, Andrew M; D'Souza, Francis; Crabtree, Robert H; Brudvig, Gary W

2012-07-16

187

Characteristics of hollow microtubes consisting of amorphous iron oxide nanoparticles produced by iron oxidizing bacteria, Leptothrix ochracea  

Microsoft Academic Search

Some features of characteristic iron oxide sheaths which the iron oxidizing bacteria Leptothrix ochracea (L. oceracea) formed were studied in order to make clear their morphology microstructure, chemical composition, and crystal structure through scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX), and X-ray diffraction (XRD). Each sheath was a hollow tube with average outer and inner diameters of 1.1

H. Hashimoto; S. Yokoyama; H. Asaoka; Y. Kusano; Y. Ikeda; M. Seno; J. Takada; T. Fujii; M. Nakanishi; R. Murakami

2007-01-01

188

Ultrathin (1×2)-Sn layer on GaAs(100) and InAs(100) substrates: A catalyst for removal of amorphous surface oxides  

NASA Astrophysics Data System (ADS)

Amorphous surface oxides of III-V semiconductors are harmful in many contexts of device development. Using low-energy electron diffraction and photoelectron spectroscopy, we demonstrate that surface oxides formed at Sn-capped GaAs(100) and InAs(100) surfaces in air are effectively removed by heating. This Sn-mediated oxide desorption procedure results in the initial well-defined Sn-stabilized (1×2) surface even for samples exposed to air for a prolonged time. Based on ab initio calculations we propose that the phenomenon is due to indirect and direct effects of Sn. The Sn-induced surface composition weakens oxygen adsorption.

Laukkanen, P.; Punkkinen, M. P. J.; La?Ng, J.; Tuominen, M.; Kuzmin, M.; Tuominen, V.; Dahl, J.; Adell, J.; Sadowski, J.; Kanski, J.; Polojärvi, V.; Pakarinen, J.; Kokko, K.; Guina, M.; Pessa, M.; Väyrynen, I. J.

2011-06-01

189

Comparative study of transparent rectifying contacts on semiconducting oxide single crystals and amorphous thin films  

NASA Astrophysics Data System (ADS)

We demonstrate fully transparent, highly rectifying contacts (TRC) on amorphous GaInZnO and compare them to TRC fabricated on single crystalline bulk ZnO and heteroepitaxial ZnO thin films. The contacts' transparency in the visible spectral range exceeds 70%. From numerical simulations, we conclude that thermionic emission is the dominating transport mechanism, however, for several samples with low net doping density diffusion theory must be applied. The detailed investigation of the rectification properties of the TRC using temperature-dependent current-voltage and capacitance-voltage measurements reveals that barrier inhomogeneities govern the IV-characteristics of all diodes irrespective of the sample crystallinity. Assuming a Gaussian barrier height distribution, the extracted mean barrier heights typically range between 1.1 and 1.3 V. The width of the barrier distribution correlates with the mean barrier height and ranges from 110 to 130 mV. By compiling literature data, we found that this correlation holds also true for Schottky diodes on elemental and III-V semiconductors.

Lajn, Alexander; von Wenckstern, Holger; Grundmann, Marius; Wagner, Gerald; Barquinha, Pedro; Fortunato, Elvira; Martins, Rodrigo

2013-01-01

190

Structure, Morphology, and Optical Properties of Amorphous and Nanocrystalline Gallium Oxide Thin Films  

SciTech Connect

Ga2O3 thin films were produced by sputter deposition by varying the substrate temperature (Ts) in a wide range (Ts=25-800 oC). The structural characteristics and optical properties of Ga2O3 films were evaluated using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS), Rutherford backscattering spectrometry (RBS) and spectrophotometric measurements. The effect of growth temperature is significant on the chemistry, crystal structure and morphology of Ga2O3 films. XRD and SEM analyses indicate that the Ga2O3 films grown at lower temperatures were amorphous while those grown at Ts?500 oC were nanocrystalline. RBS measurements indicate the well-maintained stoichiometry of Ga2O3 films at Ts=300-700 oC. The spectral transmission of the films increased with increasing temperature. The band gap of the films varied from 4.96 eV to 5.17 eV for a variation in Ts in the range 25-800 oC. A relationship between microstructure and optical property is discussed.

Kumar, S. Sampath; Rubio, E. J.; Noor-A-Alam, M.; Martinez, G.; Manandhar, Sandeep; Shutthanandan, V.; Thevuthasan, Suntharampillai; Ramana, C.V.

2013-02-15

191

Photochromism of amorphous molybdenum oxide films with different initial Mo5+ relative concentrations  

NASA Astrophysics Data System (ADS)

We report the effect of deposition conditions on the intrinsic color and photochromic properties of amorphous MoO3 thin films (a-films) deposited by R.F. unbalanced magnetron sputtering. Optical transmission spectroscopy was used to measure optical properties of the films. The conversion between Mo6+ and Mo5+ for as-deposited and UV irradiated films was characterized using XPS. Raman spectroscopy was used to confirm that the results of XPS were consistent with the bulk of the films. It is shown that absorption coefficient of as-deposited films increases with Mo5+ content. The temporal evolution of absorption coefficients for all films under UV light irradiation is measured using optical transmission spectroscopy. The largest change in absorption was observed for the film with the highest initial Mo5+ content. The temporal evolution of absorption coefficients for all the films shows initial fast rise within first minute of irradiation. XPS and Raman results show that for all films Mo5+ content increases as a result of UV irradiation except for the film with the highest initial Mo5+ content, for which the Mo5+ content decreases relative to Mo6+ despite the fact that the absorption of the film continues to rise. Further understanding of this mechanism is important since it will lead to enhanced photochromism and extend the photo-colorability of the films beyond the point at which the conversion of Mo6+ to Mo5+ is saturated.

Rouhani, Mehdi; Foo, Yong L.; Hobley, Jonathan; Pan, Jisheng; Subramanian, Gomathy Sandhya; Yu, Xiaojiang; Rusydi, Andrivo; Gorelik, Sergey

2013-05-01

192

Light induced instability mechanism in amorphous InGaZn oxide semiconductors  

NASA Astrophysics Data System (ADS)

A model of the negative bias illumination stress instability in InGaZn oxide is presented, based on the photo-excitation of electrons from oxygen interstitials. The O interstitials are present to compensate hydrogen donors. The O interstitials are found to spontaneously form in O-rich conditions for Fermi energies at the conduction band edge, much more easily that in related oxides. The excited electrons give rise to a persistent photoconductivity due to an energy barrier to recombination. The formation energy of the O interstitials varies with their separation from the H donors, which leads to a voltage stress dependence on the compensation.

Robertson, John; Guo, Yuzheng

2014-04-01

193

Packing and the structural transformations in liquid and amorphous oxides from ambient to extreme conditions.  

PubMed

Liquid and glassy oxide materials play a vital role in multiple scientific and technological disciplines, but little is known about the part played by oxygen-oxygen interactions in the structural transformations that change their physical properties. Here we show that the coordination number of network-forming structural motifs, which play a key role in defining the topological ordering, can be rationalized in terms of the oxygen-packing fraction over an extensive pressure and temperature range. The result is a structural map for predicting the likely regimes of topological change for a range of oxide materials. This information can be used to forecast when changes may occur to the transport properties and compressibility of, e.g., fluids in planetary interiors, and is a prerequisite for the preparation of new materials following the principles of rational design. PMID:24982151

Zeidler, Anita; Salmon, Philip Stephen; Skinner, Lawrie Basil

2014-07-15

194

Packing and the structural transformations in liquid and amorphous oxides from ambient to extreme conditions  

PubMed Central

Liquid and glassy oxide materials play a vital role in multiple scientific and technological disciplines, but little is known about the part played by oxygen–oxygen interactions in the structural transformations that change their physical properties. Here we show that the coordination number of network-forming structural motifs, which play a key role in defining the topological ordering, can be rationalized in terms of the oxygen-packing fraction over an extensive pressure and temperature range. The result is a structural map for predicting the likely regimes of topological change for a range of oxide materials. This information can be used to forecast when changes may occur to the transport properties and compressibility of, e.g., fluids in planetary interiors, and is a prerequisite for the preparation of new materials following the principles of rational design.

Zeidler, Anita; Salmon, Philip Stephen; Skinner, Lawrie Basil

2014-01-01

195

Electron weak localization, and electron–phonon interaction in amorphous zinc-doped indium oxide films  

Microsoft Academic Search

We have systematically investigated the temperature dependence of resistivity ? and Hall coefficient RH of indium zinc oxide films with thickness d=350 nm in the temperature range 2.0 K to 300 K. Specimen films with ??3?17 ?? m (300 K) show metallic characteristics (??T) at temperatures above 100 K. At low temperatures below 20 K, the resistivity slightly increases with decreasing temperature because of the quantum effects

K. Makise; M. Funaki; B. Shinozaki; K. Yano; Y. Shimane; K. Inoue; H. Nakamura

2008-01-01

196

Local coordination structure and electronic structure of the large electron mobility amorphous oxide semiconductor In-Ga-Zn-O: Experiment and ab initio calculations  

Microsoft Academic Search

Ionic amorphous oxide semiconductors (IAOSs) are new materials for flexible thin film transistors that exhibit field-effect mobilities of ˜10cm2V-1s-1 [K. Nomura , Nature 488, 432 (2004)]. The local coordination structure in an IAOS, In-Ga-Zn-O ( a -IGZO), was examined using extended x-ray absorption fine structure analysis combined with ab initio calculations. The short-range ordering and coordination structures in a -IGZO

Kenji Nomura; Toshio Kamiya; Hiromichi Ohta; Tomoya Uruga; Masahiro Hirano; Hideo Hosono

2007-01-01

197

Solid-state photoelectrochemical device based on poly(3-hexylthiophene) and an ion conducting polymer electrolyte, amorphous poly(ethylene oxide) complexed with I 3 ?\\/I ? redox couple  

Microsoft Academic Search

The photoelectrochemical properties of a solid-state photoelectrochemical cell (PEC) based on poly(3-hexylthiophene), P3HT, and an ion-conducting polymer electrolyte, amorphous poly(ethylene oxide), POMOE, complexed with I3?\\/I? redox couple has been constructed and studied. The current–voltage characteristics in the dark and under white light illumination, transient photocurrent and photovoltage studies, photocurrent action spectra for front and back side illuminations and an open-circuit

Mosissa Adi; Teketel Yohannes; Theodros Solomon

2004-01-01

198

A Study of the Liquid Crystal Alignment Mechanism of Bond-Breaking Via Ion-Beam Irradiation of an Amorphous Aluminum-Oxide Surface  

Microsoft Academic Search

In this paper, we study the Ion-beam (IB) irradiated amorphous (a)-aluminum oxide (Al O ) inorganic layer deposited by RF magnetron sputtering as an liquid crystal (LC) alignment layer. Uniformly vertical-aligned (VA)-LC on a-Al O surface resulted from IB irradiation energy above 1800 eV. We assumed that LC molecular orientation depends on the intensity of Al 2p, O 1s peaks,

Dai-Hyun Kim; Hae-Yoon Jung; Young-Gu Kang; Young-Hwan Kim; Hong-Gyu Park; Byoung-Yong Kim; Dae-Shik Seo

2011-01-01

199

Facile Alignment of Amorphous Poly(ethylene oxide) Microdomains in a Liquid Crystalline Block Copolymer Using Magnetic Fields  

NASA Astrophysics Data System (ADS)

Large area microdomain alignment in poly(ethylene oxide-b-methacryalte/LC) diblock copolymers was successfully accomplished in the melt state by application of a 6 T magnetic field while cooling from elevated temperatures. Small angle X-ray scattering demonstrated that both lamellar and cylindrical PEO microdomains oriented with their interfaces along the applied field while the smectic layers of the liquid crystalline mesophase are perpendicular to the field. This is in agreement with the positive diamagnetic anisotropy of the cyano-biphenyl mesogen and a homogeneous anchoring condition at the inter-material dividing surface (IMDS) between the two blocks. Addition of homopolymer acrylic acid and LiClO4 suppress PEO crystallinity and produce stronger segregation between the polymer blocks leading to improved order. Our experiments demonstrate the creation of well aligned arrays of amorphous PEO domains over large length scales and offer a route to functional materials, in particular for selective transport applications such as solid ionic electrolytes.

Osuji, Chinedum; Gopinadhan, Manesh; Majewski, Pawel

2010-03-01

200

Reduction of tail state on boron doped hydrogenated amorphous silicon oxide films prepared at high hydrogen dilution.  

PubMed

In this report, we have investigated on the defect state of diborane (B2H6) doped wide bandgap hydrogenated amorphous silicon oxide (p-type a-SiO:H) films prepared using silane (SiH4), hydrogen (H2) and nitrous oxide (N2O) in a radio frequency (RF) plasma enhanced chemical vapor deposition (PECVD) system with different hydrogen dilutions. The films prepared with higher hydrogen dilution show lower Urbach energy (Eu), lower microstructure (R*), lower short and medium range disorder (omegaTO, Gamma(TO), I(TA)/I(TO), I(LA)/I(TO)), higher dark conductivity (sigma d) and higher refractive index (n) with high optical gap (Eg). Eu decreases from 248 meV to 153 meV, and R* decreases from 0.46 to 0.26, Raman peak omegaTO-TO mode position shifts from 480.24 to 483.28, GammaTO-full width half maximum of omegaTO decreases from 78.16 to 63.87, I(TA)/I(TO)-the ratio of integrated area of TA and TO mode decreases from 0.624 to 0.474, I(LA)/I(TO)-the ratio of integrated area of LA and TO mode deceases from 0.272 to 0.151, sigma d increases from 4.6 x 10(-7) S/cm to 1.1 x 10(-6) S/cm, n increases from 3.70 to 3.86. Reduced Nd, Eu and R* at wide Eg indicates that the films are more useful for solar cell window layer. Applying this layer to a single junction solar cell shows open circuit voltage (Voc) = 0.80 V, short circuit current density (Jsc) = 16.3 mA/cm2, fill factor (FF) = 72%, efficiency (eta) = 9.4%. PMID:24266147

Park, Jinjoo; Iftiquar, S M; Lee, Sunwha; Park, Hyeongsik; Shin, Chonghoon; Jung, Junhee; Lee, Youn-Jung; Balaji, Nagarajan; Yi, Junsin

2013-12-01

201

High-stability oxygen sensor based on amorphous zinc tin oxide thin film transistor  

NASA Astrophysics Data System (ADS)

This research presents a sol-gel derived zinc tin oxide thin film transistor (TFT) as a high-stability oxygen sensor. Due to its high sensitivity, oxygen has been traditionally regarded as having a negative influence on the electrical characteristics of zinc-based TFTs; however, TFTs can also act as an oxygen sensor. After illumination with visible light in oxygen-rich ambient, a significant increase in drain current of nearly 104 times occurs with fixed gate and drain voltages. It is expected that an optimized method of illumination can help to reset the electrical characteristics or distinguish the on/off state of this reliable oxygen sensor.

Chen, Yu-Chun; Chang, Ting-Chang; Li, Hung-Wei; Chung, Wan-Fang; Wu, Chang-Pei; Chen, Shih-Ching; Lu, Jin; Chen, Yi-Hsien; Tai, Ya-Hsiang

2012-06-01

202

Electrodeposited amorphous manganese oxide nanowire arrays for high energy and power density electrodes  

NASA Astrophysics Data System (ADS)

Arrays of manganese oxide nanowires were electrodeposited into anodized alumina membranes. These nanowire arrays were investigated in terms of their structural and electrochemical properties as cathodes for high energy and high power density Li ion batteries. The nanowire arrays were assembled with a Li counter electrode and non-aqueous electrolyte to form secondary batteries. These cells were capable of multiple charge/discharge cycles, with a cathode specific capacity of approximately 300 mA h/g. Though the cathodes were fabricated without any binder or conductive additives, the electrodes could be discharged at current densities up to 0.1 mA/cm 2 before the onset of any significant polarization.

West, W. C.; Myung, N. V.; Whitacre, J. F.; Ratnakumar, B. V.

203

Behaviors of InGaZnO thin film transistor under illuminated positive gate-bias stress  

NASA Astrophysics Data System (ADS)

In this letter, we investigate the impact of the light illumination on the stability of indium-gallium-zinc oxide thin film transistors under positive gate-bias stress. The noticeable decrease in threshold voltage (Vt) shift more than 5.5 V under illuminated positive gate-bias stress indicates a superior reliability in contrast with the dark stress. The accelerated Vt recovery characteristic compared with dark recovery demonstrates that the charge detrapping effect was enhanced under illumination. Furthermore, the average effective energy barrier of charge trapping and detrapping was derived to verify that illumination can excite the trapped charges and accelerate the charge detrapping process.

Chen, Te-Chih; Chang, Ting-Chang; Tsai, Chih-Tsung; Hsieh, Tien-Yu; Chen, Shih-Ching; Lin, Chia-Sheng; Hung, Ming-Chin; Tu, Chun-Hao; Chang, Jiun-Jye; Chen, Po-Lun

2010-09-01

204

Monochromatic light-assisted erasing effects of In-Ga-Zn-O thin film transistor memory with Al2O3/Zn-doped Al2O3/Al2O3 stacks  

NASA Astrophysics Data System (ADS)

We studied how electrical erasing of indium gallium zinc oxide-thin-film-transistor memory was improved by adding concurrent irradiation with monochromatic light (ML). At fixed gate bias, irradiating at wavelengths of ?500 nm increased the erasing window (?Vth-e) significantly: At a gate bias of -20 V and an erasing time of 5 min, ML irradiation at 400 nm increased ?Vth-e from 0.29 to 3.21 V. ?Vth-e increased incrementally with gate bias, erasing time, and ML power density, particularly at short ML wavelengths. Analyzing our experimental results, we discuss the underlying erasure mechanisms.

Chen, Sun; Zhang, Wen-Peng; Cui, Xing-Mei; Ding, Shi-Jin; Sun, Qing-Qing; Zhang, Wei

2014-03-01

205

Effects of ionic liquids on cation dynamics in amorphous polyethylene oxide electrolytes.  

PubMed

We perform extensive molecular dynamics simulations of a poly(ethylene oxide)-based polymer electrolyte material containing lithium bis(trifluoromethanesulfonyl)imide salt for a wide temperature regime above and below the experimental crystallization temperature with and without N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide ionic liquid (IL). The impact of the IL-concentration on the cation dynamics is studied. The increase of the cation mobility upon addition of IL is significant but temperature-independent. This can be related to distinct variations of the underlying transport properties as expressed within the previously introduced transport model of polymer electrolytes. Even for the largest IL concentration the transport model perfectly predicts the non-trivial time-dependence of the cationic mean square displacement for all temperatures. Finally, we compare our numerical and theoretical findings with the results of recent nuclear magnetic resonance experiments. In this way we can exclusively relate the strong experimentally observed dependence of the low-temperature Li-diffusivity on the IL concentration to the impact of IL on crystallization. PMID:24437910

Chattoraj, Joyjit; Diddens, Diddo; Heuer, Andreas

2014-01-14

206

Effects of ionic liquids on cation dynamics in amorphous polyethylene oxide electrolytes  

NASA Astrophysics Data System (ADS)

We perform extensive molecular dynamics simulations of a poly(ethylene oxide)-based polymer electrolyte material containing lithium bis(trifluoromethanesulfonyl)imide salt for a wide temperature regime above and below the experimental crystallization temperature with and without N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide ionic liquid (IL). The impact of the IL-concentration on the cation dynamics is studied. The increase of the cation mobility upon addition of IL is significant but temperature-independent. This can be related to distinct variations of the underlying transport properties as expressed within the previously introduced transport model of polymer electrolytes. Even for the largest IL concentration the transport model perfectly predicts the non-trivial time-dependence of the cationic mean square displacement for all temperatures. Finally, we compare our numerical and theoretical findings with the results of recent nuclear magnetic resonance experiments. In this way we can exclusively relate the strong experimentally observed dependence of the low-temperature Li-diffusivity on the IL concentration to the impact of IL on crystallization.

Chattoraj, Joyjit; Diddens, Diddo; Heuer, Andreas

2014-01-01

207

Ce-Ti amorphous oxides for selective catalytic reduction of NO with NH3: confirmation of Ce-O-Ti active sites.  

PubMed

The amorphous Ce-Ti mixed oxides were reported to be catalysts for selective catalytic reduction of NO(x) with NH(3), in which Ce and not Ti acts as their solvent in spite of the fact that Ce is low in content. The amorphous catalysts were characterized by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM) equipped with selective area electron diffraction (SAED). The Ce-Ti amorphous oxide shows higher activity than its crystalline counterpart at lower temperatures. Moreover, the presence of small CeO(2) crystallites as for the impregnated sample is deleterious to activity. The Ce-O-Ti short-range order species with the interaction between Ce and Ti in atomic scale was confirmed for the first time to be the active site using temperature programmed reduction with H(2) (H(2)-TPR), in situ FTIR spectra of NO adsorption, X-ray photoelectron spectroscopy (XPS), and X-ray absorption fine-structure (XAFS). Lastly, the Ce-O-Ti structure was directly observed by field-emission TEM (FETEM). PMID:22888951

Li, Ping; Xin, Ying; Li, Qian; Wang, Zhongpeng; Zhang, Zhaoliang; Zheng, Lirong

2012-09-01

208

Surface Complexation of Pb(II) on Amorphous Iron Oxide and Manganese Oxide: Spectroscopic and Time Studies  

SciTech Connect

Hydrous Fe and Mn oxides (HFO and HMO) are important sinks for heavy metals and Pb(II) is one of the more prevalent metal contaminants in the environment. In this work, Pb(II) sorption to HFO (Fe{sub 2}O{sub 3}{center_dot}nH{sub 2}O, n=1-3) and HMO (MnO{sub 2}) surfaces has been studied with EXAFS: mononuclear bidentate surface complexes were observed on FeO{sub 6} (MnO{sub 6}) octahedra with Pb{single_bond}O distance of 2.25-2.35 Angstroms and Pb{single_bond}Fe(Mn) distances of 3.29-3.36 (3.65-3.76) Angstroms. These surface complexes were invariant of pH 5 and 6, ionic strength 2.8x10{sup -3} to 1.5x10{sup -2}, loading 2.03x10{sup -4} to 9.1 x 10{sup -3} mol Pb/g, and reaction time up to 21 months. EXAFS data at the Fe K-edge revealed that freshly precipitated HFO exhibits short-range order; the sorbed Pb(II) ions do not substitute for Fe but may inhibit crystallization of HFO. Pb(II) sorbed to HFO through a rapid initial uptake ({approx}77%) followed by a slow intraparticle diffusion step ({approx}23%) resulting in a surface diffusivity of 2.5x10{sup -15} cm{sup 2}/s. Results from this study suggest that mechanistic investigations provide a solid basis for successful adsorption modeling and that inclusion of intraparticle surface diffusion may lead to improved geochemical transport depiction.

Xu,Y.; Boonfueng, T.; Axe, L.; Maeng, S.; Tyson, T.

2006-01-01

209

X-ray absorption spectroscopy elucidates the impact of structural disorder on electron mobility in amorphous zinc-tin-oxide thin films  

NASA Astrophysics Data System (ADS)

We investigate the correlation between the atomic structures of amorphous zinc-tin-oxide (a-ZTO) thin films grown by atomic layer deposition (ALD) and their electronic transport properties. We perform synchrotron-based X-ray absorption spectroscopy at the K-edges of Zn and Sn with varying [Zn]/[Sn] compositions in a-ZTO thin films. In extended X-ray absorption fine structure (EXAFS) measurements, signal attenuation from higher-order shells confirms the amorphous structure of a-ZTO thin films. Both quantitative EXAFS modeling and X-ray absorption near edge spectroscopy (XANES) reveal that structural disorder around Zn atoms increases with increasing [Sn]. Field- and Hall-effect mobilities are observed to decrease with increasing structural disorder around Zn atoms, suggesting that the degradation in electron mobility may be correlated with structural changes.

Siah, Sin Cheng; Lee, Sang Woon; Lee, Yun Seog; Heo, Jaeyeong; Shibata, Tomohiro; Segre, Carlo U.; Gordon, Roy G.; Buonassisi, Tonio

2014-06-01

210

Electric charging/discharging characteristics of super capacitor, using de-alloying and anodic oxidized Ti-Ni-Si amorphous alloy ribbons  

PubMed Central

Charging/discharging behaviors of de-alloyed and anodic oxidized Ti-Ni-Si amorphous alloy ribbons were measured as a function of current between 10 pA and 100 mA, using galvanostatic charge/discharging method. In sharp contrast to conventional electric double layer capacitor (EDLC), discharging behaviors for voltage under constant currents of 1, 10 and 100 mA after 1.8 ks charging at 100 mA show parabolic decrease, demonstrating direct electric storage without solvents. The supercapacitors, devices that store electric charge on their amorphous TiO2-x surfaces that contain many 70-nm sized cavities, show the Ragone plot which locates at lower energy density region near the 2nd cells, and RC constant of 800 s (at 1 mHz), which is 157,000 times larger than that (5 ms) in EDLC.

2014-01-01

211

Local coordination structure and electronic structure of the large electron mobility amorphous oxide semiconductor In-Ga-Zn-O: Experiment and ab initio calculations  

NASA Astrophysics Data System (ADS)

Ionic amorphous oxide semiconductors (IAOSs) are new materials for flexible thin film transistors that exhibit field-effect mobilities of ˜10cm2V-1s-1 [K. Nomura , Nature 488, 432 (2004)]. The local coordination structure in an IAOS, In-Ga-Zn-O ( a -IGZO), was examined using extended x-ray absorption fine structure analysis combined with ab initio calculations. The short-range ordering and coordination structures in a -IGZO are similar to those in the corresponding crystalline phase, InGaZnO4 , and edge-sharing structures consisting of In-O polyhedra remain in the amorphous structure. The In3+ 5s orbitals form an extended state with a band effective mass of ˜0.2me at the conduction band bottom.

Nomura, Kenji; Kamiya, Toshio; Ohta, Hiromichi; Uruga, Tomoya; Hirano, Masahiro; Hosono, Hideo

2007-01-01

212

The nature and composition of amorphous material and free oxides in some temperate region and tropical soils  

Microsoft Academic Search

Amorphous clay separated from pedons of a highly weathered soil previously classified as Oxisol and an Ultisol of the Southern States and, from the surface horizons of an Oxisol and two Andepts of the tropics were studied by chemical, DTA, infrared and X?ray analysis.Considerable amounts of amorphous material, 20–37% in temperate region and 29–40% in tropical soils, were extracted by

K. H. Tan; H. F. Perkins; R. A. McCreery

1970-01-01

213

Electron tunnelling into amorphous germanium and silicon.  

NASA Technical Reports Server (NTRS)

Measurements of tunnel conductance versus bias, capacitance versus bias, and internal photoemission were made in the systems aluminum-oxide-amorphous germanium and aluminium-oxide-amorphous silicon. A function was extracted which expresses the deviation of these systems from the aluminium-oxide-aluminium system.

Smith, C. W.; Clark, A. H.

1972-01-01

214

Researches on Amorphous Perovskite.  

National Technical Information Service (NTIS)

Researches on amorphous perovskite were conducted and thereby the quenching production of fragile oxide by a soft roller method was made possible. The film of KNbO(sub 3) added with other materials were produced by this method. These films have the possib...

1988-01-01

215

Large-scale complementary macroelectronics using hybrid integration of carbon nanotubes and IGZO thin-film transistors.  

PubMed

Carbon nanotubes and metal oxide semiconductors have emerged as important materials for p-type and n-type thin-film transistors, respectively; however, realizing sophisticated macroelectronics operating in complementary mode has been challenging due to the difficulty in making n-type carbon nanotube transistors and p-type metal oxide transistors. Here we report a hybrid integration of p-type carbon nanotube and n-type indium-gallium-zinc-oxide thin-film transistors to achieve large-scale (>1,000 transistors for 501-stage ring oscillators) complementary macroelectronic circuits on both rigid and flexible substrates. This approach of hybrid integration allows us to combine the strength of p-type carbon nanotube and n-type indium-gallium-zinc-oxide thin-film transistors, and offers high device yield and low device variation. Based on this approach, we report the successful demonstration of various logic gates (inverter, NAND and NOR gates), ring oscillators (from 51 stages to 501 stages) and dynamic logic circuits (dynamic inverter, NAND and NOR gates). PMID:24923382

Chen, Haitian; Cao, Yu; Zhang, Jialu; Zhou, Chongwu

2014-01-01

216

Laser Fired Aluminum Emitter for High Efficiency Silicon Photovoltaics Using Hydrogenated Amorphous Silicon and Silicon Oxide Dielectric Passivation  

NASA Astrophysics Data System (ADS)

This thesis proposes and demonstrates a hydrogenated amorphous silicon passivated, inverted photovoltaic device on n-type silicon, utilizing a Laser Fired Emitter on a rear i-a- Si:H/SiO x dielectric stack. This novel low-temperature-fabricated device architecture constitutes the first demonstration of an LFE on a dielectric passivation stack. The optimization of the device is explored through Sentaurus computational modeling, predicting a potential efficiency of >20%. Proof of concept devices are fabricated using the DC Saddle Field PECVD system for the deposition of hydrogenated amorphous silicon passivation layers. Laser parameters are explored highlighting pulse energy density as a key performance determining factor. Annealing of devices in nitrogen atmosphere shows performance improvements albeit that the maximum annealing temperature is limited by the thermal stability of the passivation. A proof of concept device efficiency of 11.1% is realized forming the basis for further device optimization.

Fischer, Anton

217

Electronic structure and transport properties in the transparent amorphous oxide semiconductor 2 CdO.GeO2  

Microsoft Academic Search

An amorphous 2 CdO.GeO2 thin film with a band gap of 3.4 eV can be converted from an insulator (conductivity ~10-9 S cm-1) into a degenerate semiconductor (~102 S cm-1) by carrier doping with ion implantation without significant loss in visible transparency. An interesting feature of this material's transport property is its Hall mobility: a pn sign anomaly, which is

Satoru Narushima; Masahiro Orita; Masahiro Hirano; Hideo Hosono

2002-01-01

218

Effective-Time of Pulsed Photothermal Heating for Polycrystalline Nucleation of Perovskite Oxide Films from an Amorphous Matrix  

NASA Astrophysics Data System (ADS)

For making a photoinduced crystal growth method more universal, we have investigated the key parameters for polycrystalline nucleation from an amorphous matrix of LaMnO3 with focus on the pulsed photothermal heating time under excimer laser irradiation. We have clearly demonstrated that effective annealing time (teff) was very important for the crystallization under the excimer laser irradiation. The teff is defined as the time in which the temperature at the film surface increases over the effective annealing temperature for the crystallization of LaMnO3. The threshold of the teff value for initial crystal nucleation was evaluated to be approximately 60 ns for this material.

Nakajima, Tomohiko; Tsuchiya, Tetsuo; Ichihara, Masaki; Nagai, Hideaki; Kumagai, Toshiya

2009-02-01

219

Cost-Effective and Self-Textured Gallium-Doped Zinc Oxide Front Contacts for Hydrogenated Amorphous Silicon Thin-Film Solar Cells  

NASA Astrophysics Data System (ADS)

We adopt a economical and original method to fabricate self-textured gallium-doped zinc oxide (GZO) front contacts for hydrogenated amorphous silicon (a-Si:H) single-junction solar cells. This technique involves an atmospheric-pressure plasma jet (APPJ) and a dc sputtering process. The electro-optical characteristics of the textured GZO films are mainly controlled by the haze of organosilicon underlayers deposited by the APPJ. The films exhibit an average optical transmittance of about 80% and resistivity below 9.91× 10-4 ? cm. Moreover, compared with flat solar cells, textured cells fabricated on moderate GZO front contacts show 7.9 and 10.9% enhancements in conversion efficiency and short-circuit current density, respectively.

Yu, Shu-Hung; Ho, Po-Ching; Lee, Chia-Ling; Bi, Chien-Chung; Yeh, Chih-Hung; Chang, Chun-Yen

2013-02-01

220

Phosphonic acid self-assembled monolayer and amorphous hafnium oxide hybrid dielectric for high performance polymer thin film transistors on plastic substrates  

NASA Astrophysics Data System (ADS)

A vacuum-free solution processed hybrid dielectric composed of an n-octadecyl-phosphonic acid self-assembled monolayer on amorphous sol-gel processed hafnium oxide (HfOx) is demonstrated for low-voltage polymer semiconductor-based thin film transistors (TFTs). The phosphonic acid/HfOx hybrid dielectric provides high capacitance (0.41 ?F/cm2), low leakage current (5×10-8 A/cm2), and is compatible with plastic substrates. The utility of this dielectric is demonstrated by fabricating high performance polymer TFTs based on a spin coated thiophene-thiazolothiazole copolymer with operating voltages under -2 V, negligible hysteresis, subthreshold slopes as low as 100 mV/dec, and hole mobilities up to 0.11 cm2 V s.

Acton, Orb; Osaka, Itaru; Ting, Guy; Hutchins, Daniel; Ma, Hong; McCullough, Richard D.; Jen, Alex K.-Y.

2009-09-01

221

Light-extraction enhancement in GaN-based light-emitting diodes using grade-refractive-index amorphous titanium oxide films with porous structures  

SciTech Connect

Amorphous titanium oxide (a-TiO{sub x}:OH) films prepared by plasma-enhanced chemical-vapor deposition at 200 and 25 deg. C are in turn deposited onto the GaN-based light-emitting diode (LED) to enhance the associated light extraction efficiency. The refractive index, porosity, and photocatalytic effect of the deposited films are correlated strongly with the deposition temperatures. The efficiency is enhanced by a factor of {approx}1.31 over that of the uncoated LEDs and exhibited an excellent photocatalytic property after an external UV light irradiation. The increase in the light extraction is related to the reduction in the Fresnel transmission loss and the enhancement of the light scattering into the escape cone by using the graded-refractive-index a-TiO{sub x}:OH film with porous structures.

Liu, D.-S.; Lin, T.-W.; Huang, B.-W.; Juang, F.-S.; Lei, P.-H. [Institute of Electro-Optical and Materials Science, National Formosa University, Huwei 63201, Taiwan (China); Hu, C.-Z. [Chilin Technology Co. Ltd., Tainan County 71758, Taiwan (China)

2009-04-06

222

Stability of amorphous hydrous manganese oxide in contrasting soils and implications for its use in chemical stabilization of metals/metalloids in contaminated soil environments  

NASA Astrophysics Data System (ADS)

Amorphous manganese oxides are known to be efficient sorbents in soils and thus useful in remediation technologies. A novel amorphous hydrous manganese oxide (HMO) was prepared by a modified procedure generally used for birnessite synthesis. Its long-term stability in view of possible applications for chemical stabilization of metals/metalloids in polluted soils was evaluated. HMO was sealed in experimental bags prepared from polyamide fabric (pore size 1 um) and placed in the pots containing 200 g of soil. Three contrasting soils were used (two cambisols with pH values of 4.2 and 5.4, respectively, and a chernozem with a pH of 7.3). Each pot was equipped with a rhizon pore water sampler and the water content was maintained at 80% WHC throughout the experiment. HMO and pore waters were sampled after 1, 7, 15, 30, 45, 60, 75 and 90 days of incubation. Up to 113 mg Mn/L was released into pore water at the beginning of the experiment in more acidic soils indicating a slight dissolution of HMO surfaces. Manganese release into the pore water stabilized after 15 days in agreement with mass loss measurements. Mass loss decreased again after 60 days of the incubation for the neutral soil due to the formation of secondary rhodochrosite (MnCO3) detected on the HMO surfaces by X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM). The efficiency of HMO for trace metal retention in soils (e.g., Zn) slightly decreased after 60 days, probably due to the mineralogical transformation of the sorbent leading to decrease of binding surfaces. Nevertheless, only approximately 10% of HMO dissolved after 90 days of experiment showing that this sorbent can be relatively stable in the studied soils. Its binding capacity for metals/metalloids should be further tested in soils with elevated contaminant concentrations.

Ettler, V.; Knytl, V.; Komarek, M.; Della Puppa, L.; Mihaljevic, M.; Sebek, O.

2012-04-01

223

Experimental approach and atomistic simulations to investigate the radiation tolerance of complex oxides: Application to the amorphization of pyrochlores  

NASA Astrophysics Data System (ADS)

Both experimental approach and atomistic simulations are performed in order to investigate the influence of the composition of pyrochlores on their radiation tolerance. Therefore, Gd2Ti2O7 and Gd2Zr2O7 were irradiated with 4 MeV Au and 92 MeV Xe ions in order to study the structural changes induced by low and high-energy irradiations. XRD results show that, for both irradiations, the structural modifications are strongly dependent on the sample composition: Gd2Ti2O7 is readily amorphized, whereas Gd2Zr2O7 is transformed into a radiation-resistant anion-deficient fluorite structure. Using atomistic simulations with new interatomic potentials derived from the SMTB-Q model, the lattice properties and the defect formation energies were calculated in Gd2Ti2O7 and Gd2Zr2O7. Calculations show that titanates have a more covalent character than zirconates. Moreover, in Gd2Ti2O7 the formation of cation antisite defects leads to strong local distortions around Ti-defects and to a decrease of the Ti coordination number, which are not observed in Gd2Zr2O7. Thus, the radiation resistance is related to the defect stability: the accumulation of structural distortions around Ti-defects could drive the Gd2Ti2O7 amorphization induced by irradiation.

Sattonnay, G.; Thomé, L.; Sellami, N.; Monnet, I.; Grygiel, C.; Legros, C.; Tetot, R.

2014-05-01

224

X-ray absorption, photoemission spectroscopy, and Raman scattering analysis of amorphous tantalum oxide with a large extent of oxygen nonstoichiometry.  

PubMed

The electronic structure and modification of the local interatomic structure of a reactive sputtered amorphous tantalum oxide (a-TaO(x)) thin film with the variation of oxygen nonstoichiometry, x in a-TaO(x) have been investigated by X-ray absorption spectroscopy (XAS), X-ray photoemission spectroscopy (XPS), Raman scattering spectroscopy, and Rutherford back scattering spectroscopy. A parallel chemical shift of Ta4f(7/2) and O1s core levels observed with the variation of x indicates the Fermi level shift by reduction and oxidation in the framework of the rigid band model. Extended X-ray absorption fine structure (EXAFS) suggests both the increase of average coordination number of the first Ta-O shell in polyhedra and a considerable reduction of the average Ta-O bond length with the increase of x. The relative intensity of Raman shift peaks at 670 cm(-1) and 815 cm(-1), corresponding to Ta-O stretching of TaO(6) octahedra and TaO(5) probably with a pyramidal form, respectively, drastically changes between x = 2.47 to 1.86, suggesting the change in the predominant polyhedron from TaO(6) to TaO(5) with a modification in multiplicity of oxygen by the reorganization of the polyhedral network. PMID:21863188

Tsuchiya, Takashi; Imai, Hideto; Miyoshi, Shogo; Glans, Per-Anders; Guo, Jinghua; Yamaguchi, Shu

2011-10-14

225

Polymeric Systems for Amorphous ?9-Tetrahydrocannabinol Produced by a Hot-Melt Method. Part II: Effect of Oxidation Mechanisms and Chemical Interactions on Stability  

PubMed Central

The objectives of the present research investigations were to (i) elucidate the mechanism for the oxidative degradation of ?9-tetrahydrocannabinol (THC) in polymer matrix systems prepared by a hot-melt fabrication procedure, and (ii) study the potential for controlling these mechanisms to reduce the degradation of THC in solid dosage formulations. Various factors considered and applied included drug-excipient compatibility, use of antioxidants, cross-linking in polymeric matrices, microenvironment pH, and moisture effect. Instability of THC in polyethylene oxide (PEO)-vitamin E succinate (VES) patches was determined to be due to chemical interaction between the drug and the vitamin as well as with the atmospheric oxygen. Of the different classes and mechanisms of antioxidants studied, quenching of oxygen by reducing agents, namely, ascorbic acid was the most effective in stabilizing THC in PEO-VES matrices. Only 5.8% of the drug degraded in the ascorbic acid-containing patch as compared to the control (31.6%) after 2 months of storage at 40°C. This coupled with the cross-linking extent and adjustment of the pH microenvironment, which seemed to have an impact on the THC degradation, might be effectively utilized towards stabilization of the drug in these polymeric matrices and other pharmaceutical dosage forms. These studies are relevant to the development of a stable transmucosal matrix system for the therapeutic delivery of amorphous THC.

MUNJAL, MANISH; ELSOHLY, MAHMOUD A.; REPKA, MICHAEL A.

2010-01-01

226

Chemical mechanical planarization of amorphous Ge2Sb2Te5 using KClO4 as oxidizer in acidic slurry  

NASA Astrophysics Data System (ADS)

Amorphous Ge2Sb2Te5 (a-GST) chemical mechanical planarization (CMP) using KClO4 as the oxidizer in an acidicslurry is investigated in the present work. It is shown that the removal rate (RR ) of the a-GST firstly increases and thentends to saturate when the KClO4 concentration is greater than 0.8 wt%, but the static etch rate (SER) linearly increasesfrom low to high KClO4 concentration. To understand the oxidation-reaction capability of Ge, Sb and Te, depth profilesof composition of elements and etch morphology of a-GST immersed in the slurry for some time are measured,respectively. It is found that selective corrosion occurs among Ge, Sb and Te, and an accumulation of Te and loss of Gein a-GST surface region are obvious observed, especially at high KClO4 concentrations. Temperature dependent sheetresistance measurements of all the samples pre- and post-CMP reveal a similar trend, which implies a-GST CMP is ableto keep its characteristic well.

He, Aodong; Song, Zhitang; Bo, Liu; Zhong, Min; Weili, Liu; Wang, Liangyong; Yan, Weixia; Lei, Yu; Wu, Guangping

227

Investigation of the effects of deposition parameters on indium-free transparent amorphous oxide semiconductor thin-film transistors fabricated at low temperatures for flexible electronic applications  

NASA Astrophysics Data System (ADS)

Low temperature gallium tin zinc oxide (GSZO) based thin film transistors fabricated on silicon has been investigated as a potential indium free transparent amorphous oxide semiconductor thin film transistor (TAOS TFT) with potential device applications on plastic substrates. A comprehensive and detailed study on the performance of GSZO TFTs has been carried out by studying the effects of processing parameters such as deposition temperature and annealing temperature/duration, as well as the channel thickness with all temperatures held below 150 °C. Variety of characterization techniques, namely Rutherford backscattering (RBS), x-ray photoelectron spectroscopy (XPS) and x-ray reflectivity (XRR) in addition to I-V and C-V measurements were employed to determine the effects of the above parameters on the composition and quality of the channel. Optimized TFT characteristics of ID=3×10-7 A, ION/OFF =2×106, VON ~ -2 V, SS ~ 1 V/dec and ?FE = 0.14 cm2/V· s with a ?VON of 3.3 V under 3 hours electrical stress were produced.

Alston, Robert; Iyer, Shanthi; Bradley, Tanina; Lewis, Jay; Cunningham, Garry; Forsythe, Eric

2014-02-01

228

Controlled aluminum-induced crystallization of an amorphous silicon thin film by using an oxide-layer diffusion barrier  

NASA Astrophysics Data System (ADS)

Aluminum-induced crystallization (AIC) of amorphous silicon with an Al2O3 diffusion barrier was investigated for controlling Si crystallization and preventing layer exchange during the annealing process. An Al2O3 layer was deposited between the a-Si and the Al films (a-Si/Al2O3/Al/Glass) and was blasted with an air spray gun with alumina beads to form diffusion channels between the Si and the Al layers. During the annealing process, small grain Si x Al seeds were formed at the channels. Then, the Al2O3 diffusion barrier was restructured to close the channels and prevent further diffusion of Al atoms into the a-Si layer. A polycrystalline Si film with (111), (220) and (311) crystallization peaks in the X-ray diffraction pattern was formed by annealing at 560 °C in a conventional furnace. That film showed a p-type semiconducting behavior with good crystallinity and a large grain size of up to 14.8 µm. No layer conversion occurred between the Si and the Al layers, which had been the fundamental obstacle to the applications in the crystallization of a-Si films by using the AIC method.

Hwang, Ji-Hyun; Kwak, Hyunmin; Kwon, Myeung Hoi

2014-03-01

229

Amorphous Magnetic Insulators for Microwave Device Applications.  

National Technical Information Service (NTIS)

Results of our studies on thin films of amorphous magnetic oxides are summarized in this report. The main emphasis of the program was on the preparation and magnetic characterization of amorphous BiFeO3 films substituted with nonmagnetic perovskites, zinc...

G. Srinivasan

1992-01-01

230

An XPS Study of Amorphous Thin Films of Mixed Oxides In2O3-SnO2 System Deposited by Co-Evaporation  

NASA Astrophysics Data System (ADS)

XPS core level measurements are used to observe the surface changes in amorphous thin films of mixed oxides In2O3-SnO2 system deposited by co-evaporation. The effects of changes in composition (in mol%), film thickness, substrate temperature, post-deposition annealing, and etching with Ar+ ions on the binding energies of In(3d) and Sn(3d) doublets in mixed oxides In2O3-SnO2 system are presented. XPS core level In(3d) and Sn(3 d) spectra at various compositions exhibit the characteristic 3d5 / 2 and 3d3 / 2 doublets. The positions of the In(3d) and Sn(3d) lines are those as expected for In3+ ions in In2O3 and Sn4+ ions in SnO2. The initial decrease in binding energy with an increase in Sn content in In2O3 lattice is caused by the Sn atom substitution of In atom, giving out one extra electron. The increase in binding energy above the critical Sn content (10 mol% SnO2) is caused by the defects formed by Sn atoms, which act as carrier traps rather than electron donors. The decrease in binding energy with film thickness is caused by the increase in free-carriers density, which is generated by oxygen vacancy acting as two electrons donor. The decrease in binding energy with a substrate and annealing temperatures is due either to the severe deficiency of oxygen, which deteriorates the film properties and reduces the mobility of the carriers or to the diffusion of Sn atoms from interstitial locations into the In cation sites and the formation of indium and tin species of lower valence states so that the In3+ and the Sn4+ oxidation states may be changed to the In2+ and the Sn2+ oxidation states respectively. The new oxidation states, In2+ and Sn2+, formed due to ion etching and annealing the samples can be attributed to the internal electron transfer from oxygen 2p to the In 5s and Sn 5s levels both in In2O3 and SnO2.

Anwar, M.; Ghauri, I. M.; Siddiqi, S. A.

231

Resistance switching in amorphous and crystalline binary oxides grown by electron beam evaporation and atomic layer deposition  

Microsoft Academic Search

Resistance switching random access non-volatile memories (ReRAM) could represent the leading alternative to floating gate technology for post 32nm technology nodes. Among the currently investigated materials for ReRAM, transition metal binary oxides, such as NiO, CuxO, ZrOx, TiO2, MgO, and Nb2O5 are receiving increasing interest as they offer high potential scalability, low-energy switching, thermal stability, and easy integration in CMOS

S. Spiga; A. Lamperti; C. Wiemer; M. Perego; E. Cianci; G. Tallarida; H. L. Lu; M. Alia; F. G. Volpe; M. Fanciulli

2008-01-01

232

Amorphous TiO? coatings stabilize Si, GaAs, and GaP photoanodes for efficient water oxidation.  

PubMed

Although semiconductors such as silicon (Si), gallium arsenide (GaAs), and gallium phosphide (GaP) have band gaps that make them efficient photoanodes for solar fuel production, these materials are unstable in aqueous media. We show that TiO2 coatings (4 to 143 nanometers thick) grown by atomic layer deposition prevent corrosion, have electronic defects that promote hole conduction, and are sufficiently transparent to reach the light-limited performance of protected semiconductors. In conjunction with a thin layer or islands of Ni oxide electrocatalysts, Si photoanodes exhibited continuous oxidation of 1.0 molar aqueous KOH to O2 for more than 100 hours at photocurrent densities of >30 milliamperes per square centimeter and ~100% Faradaic efficiency. TiO2-coated GaAs and GaP photoelectrodes exhibited photovoltages of 0.81 and 0.59 V and light-limiting photocurrent densities of 14.3 and 3.4 milliamperes per square centimeter, respectively, for water oxidation. PMID:24876492

Hu, Shu; Shaner, Matthew R; Beardslee, Joseph A; Lichterman, Michael; Brunschwig, Bruce S; Lewis, Nathan S

2014-05-30

233

Analysis of conducting-system frequency response data for an interfacial amorphous phase of copper-core oxide-shell nanocomposites  

NASA Astrophysics Data System (ADS)

Complex electrical-conductivity experimental data sets for the interfacial amorphous phase in copper-core-copper-oxide-shell nanostructured composites have been analyzed using two Kohlrausch-related frequency response models recently developed for analysis of the dispersive electrical response of conductive materials. Such analysis has been carried out for both the precursor (herein referred to as the reference) glass as well as the glass in which the core-shell nanostructure was developed after suitable heat treatment. Complex nonlinear-least-squares data fitting at each temperature employed composite Kohlrausch models that included electrode effects. Because of the lack of sufficient high-frequency data, it was necessary to use fixed, rather than free, values of the shape parameter ?1 of the model. On the basis of topological considerations, its values were set at 1/3 and 2/3 for the reference glass and the core-shell structured glass, respectively. The activation energies of resistivity for the reference and the treated glasses were found to have values of about 2 and 0.4 eV, respectively, indicating two different mechanisms of electrical conduction. A blocking-electrode measurement on the reference glass indicated the presence of an electronic as well as an ionic component of the electrical conductivity, with the ionic part dominating at the temperatures for which the present analyses were carried out.

MacDonald, J. R.; Basu, S.; Chakravorty, D.

2005-06-01

234

Damage-free back channel wet-etch process in amorphous indium-zinc-oxide thin-film transistors using a carbon-nanofilm barrier layer.  

PubMed

Amorphous indium-zinc-oxide thin film transistors (IZO-TFTs) with damage-free back channel wet-etch (BCE) process were investigated. A carbon (C) nanofilm was inserted into the interface between IZO layer and source/drain (S/D) electrodes as a barrier layer. Transmittance electron microscope images revealed that the 3 nm-thick C nanofilm exhibited a good corrosion resistance to a commonly used H3PO4-based etchant and could be easily eliminated. The TFT device with a 3 nm-thick C barrier layer showed a saturated field effect mobility of 14.4 cm(2) V(-1) s(-1), a subthreshold swing of 0.21 V/decade, an on-to-off current ratio of 8.3 × 10(10), and a threshold voltage of 2.0 V. The favorable electrical performance of this kind of IZO-TFTs was due to the protection of the inserted C to IZO layer in the back-channel-etch process. Moreover, the low contact resistance of the devices was proved to be due to the graphitization of the C nanofilms after annealing. In addition, the hysteresis and thermal stress testing confirmed that the usage of C barrier nanofilms is an effective method to fabricate the damage-free BCE-type devices with high reliability. PMID:24969359

Luo, Dongxiang; Zhao, Mingjie; Xu, Miao; Li, Min; Chen, Zikai; Wang, Lang; Zou, Jianhua; Tao, Hong; Wang, Lei; Peng, Junbiao

2014-07-23

235

Effects of contact resistance on the evaluation of charge carrier mobilities and transport parameters in amorphous zinc tin oxide thin-film transistors  

NASA Astrophysics Data System (ADS)

Accurate determination of the charge transport characteristics of amorphous metal-oxide transistors requires the mitigation of the effects of contact resistance. The use of additional electrodes as voltage probes can overcome contact resistance-related limitations and yields accurate charge carrier mobility values, trap depths and temperature and carrier density dependencies of mobility as well as trap depths. We show that large differences in measured charge carrier mobility values are obtained when such contact resistances are not factored out. Upon exclusion of the contact resistance, the true temperature dependence of charge carrier mobility appears in the form of two clearly distinct mobility regimes. Analyzing these revealed mobility regions leads to a more accurate determination of the underlying transport physics, which shows that contact resistance-related artefacts yield incorrect trends of trap depth with gate voltage, potentially leading to a misconstruction of the charge transport picture. Furthermore, a comparison of low- and high-mobility samples indicates that the observed effects are more general.

Schulz, Leander; Yun, Eui-Jung; Dodabalapur, Ananth

2014-06-01

236

Electrocatalytic oxidation of formic acid and methanol at the amorphous Pt sub 66 Sb sub 34 electrode  

SciTech Connect

The electrocatalytic activity of Pt{sub 66}Sb{sub 34} rapidly quenched alloy (glassy metal) towards oxidation of HCOOH and CH{sub 3}OH has been investigated. The studies have been carried out in an apparatus in which combined surface analysis electrochemistry experiments can be performed. The electrodes were cleaned by standard UHV procedures, and their surface composition was analyzed using Auger electron spectroscopy before each electrochemical experiment. The electrocatalytic activity of the material has been directly correlated with the surface composition of the alloy. The rapidly quenched Pt{sub 66}Sb{sub 34} is a single-phase alloy of homogeneous composition, free from grain boundaries. No surface segregation or leaching of alloy elements were observed during experiments which lasted several hours. Its surface composition displayed a long term stability. The rate of CH{sub 3}OH and HCOOH oxidation at this material is about 5 to 20 times higher than that at a pure, smooth, polyoriented Pt electrode. It has been shown that the enhanced catalytic activity of the glassy alloy is a complex function of electronic, geometric, and synergistic effects.

Sun, S.G.; Lipkowski, J. (Dept. of Chemistry, Univ. of Guelph, Guelph, Ontario N1G 2W1 (CA)); Altounian, Z. (Physics Dept., McGill Univ., Montreal, Quebec H3A 2T8 (CA))

1990-08-01

237

The effect of B{sub 2}O{sub 3} addition on the crystallization of amorphous TiO{sub 2}-ZrO{sub 2} mixed oxide  

SciTech Connect

The effect of B{sub 2}O{sub 3} addition on the crystallization of amorphous TiO{sub 2}-ZrO{sub 2} mixed oxide was investigated by X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG/DTA). TiO{sub 2}-ZrO{sub 2} mixed oxide was prepared by co-precipitation method with aqueous ammonia as the precipitation reagent. Boric acid was used as a source of boria, and boria contents varied from 2 to 20 wt%. The results indicate that the addition of small amount of boria (<8 wt%) hinders the crystallization of amorphous TiO{sub 2}-ZrO{sub 2} into a crystalline ZrTiO{sub 4} compound, while a larger amount of boria ({>=}8 wt%) promotes the crystallization process. FT-IR spectroscopy and {sup 11}B MAS NMR results show that tetrahedral borate species predominate at low boria loading, and trigonal borate species increase with increasing boria loading. Thus it is concluded that highly dispersed tetrahedral BO{sub 4} units delay, while a build-up of trigonal BO{sub 3} promote, the crystallization of amorphous TiO{sub 2}-ZrO{sub 2} to form ZrTiO{sub 4} crystals. - Graphical abstract: The addition of small amount of boria (<8 wt%) hinders the crystallization of amorphous TiO{sub 2}-ZrO{sub 2} into a crystalline ZrTiO{sub 4} compound, while the larger amount of boria ({>=}8 wt%) promotes the crystallization process.

Mao Dongsen [Research Institute of Applied Catalysis, Department of Chemical Engineering, Shanghai Institute of Technology, Number 120, Caobaolu, Shanghai 200235 (China)], E-mail: dsmao1106@yahoo.com.cn; Lu Guanzhong [Research Institute of Applied Catalysis, Department of Chemical Engineering, Shanghai Institute of Technology, Number 120, Caobaolu, Shanghai 200235 (China)

2007-02-15

238

Low-temperature photo-activated inorganic electron transport layers for flexible inverted polymer solar cells  

NASA Astrophysics Data System (ADS)

A simple and versatile route of forming sol-gel-derived metal oxide n-type electron transport layers (ETLs) for flexible inverted polymer solar cells (PSCs) is proposed using low-temperature photochemical activation process. The photochemical activation, which is induced by deep ultraviolet irradiation on sol-gel films, allows formation of metal oxide n-type ETLs such as zinc oxide (ZnO) and indium gallium zinc oxide films at a low temperature. Compared to poly(3-hexylthiophene)/phenyl-C61-butyric acid methyl ester inverted PSCs with thermally annealed ZnO ETLs (optimized efficiency of 3.26 ± 0.03 %), the inverted PSCs with photo-activated ZnO ETLs showed an improved efficiency of 3.60 ± 0.02 %. The enhanced photovoltaic property is attributed to efficient charge collection from low overall series resistance and high surface area-to-geometric area ratio by the photo-activated ZnO ETLs.

Lee, Jung-Wook; Lee, Soo-Hyoung; Kim, Yong-Hoon; Park, Sung Kyu

2014-04-01

239

Amorphous metal composites  

DOEpatents

An improved amorphous metal composite and process of making the composite. The amorphous metal composite comprises amorphous metal (e.g. iron) and a low molecular weight thermosetting polymer binder. The process comprises placing an amorphous metal in particulate form and a thermosetting polymer binder powder into a container, mixing these materials, and applying heat and pressure to convert the mixture into an amorphous metal composite.

Byrne, Martin A. (Troy, NY); Lupinski, John H. (Scotia, NY)

1984-01-01

240

Development of a Two-Phase Structural and Optical Model for Understanding the Fundamental Electrochromic Processes in Amorphous Tungsten Oxide Thin Films.  

NASA Astrophysics Data System (ADS)

The evolution of a dense columnar morphology with a related void network structure is a natural result of random ballistic aggregation of atoms during the thin film growth process under low adatom mobility conditions. Thin film properties and applications (e.g. magneto-optic materials and a-Si:H solar cells) are often dominated by this anisotropic morphology. Electrochromism is a phenomenon in which the optical properties of a material change due to the stimulus of an applied electric field. Tungsten oxide (WO _3) is probably the most widely studied electrochromic (EC) material, and is the primary material used as the active layer in EC applications. Although it has been shown that the structure of a-WO_3 thin films is dominated by dense columnar regions and an anisotropic void network, little work has been done on the structure of a-WO_3 as it relates to the EC properties. Amorphous WO_3 thin films have been prepared by reactive dc-magnetron sputtering under different deposition conditions. Through the use of plasma diagnostics, scanning electron microscopy, EC coloration experiments, and spectroscopic ellipsometry, the effect of preparation conditions on film morphology and EC properties have been studied. The results of this study show that a-WO_3 thin films are dominated by a columnar morphology and an intercolumnar void network that strongly influence the EC properties. In addition, real-time spectroscopic ellipsometry (RTSE) experiments on the WO_3 EC coloration process have been performed for the first time. In studies of very thin (~150 A) films by RTSE, the formation of hydrogen tungsten bronze rm(H _{x}WO_3) is controlled by reaction-limited kinetics, and thus it was possible to extract optical dielectric function spectra at different stages of the coloration process. These spectra can be understood in terms of a two-phase physical mixture of WO_3 and rm H_ {x}WO_3 components with relative volume fractions determined in a regression analysis of the spectra. Based on these results, a two-phase model is presented to describe EC processes in a-WO_3. This model sheds light on the fundamental optical and kinetic mechanisms while consistently explaining the morphological dependence of the EC properties.

Witham, Howard Stanley

241

Three-dimensionally stacked flexible integrated circuit: Amorphous oxide/polymer hybrid complementary inverter using n-type a-In-Ga-Zn-O and p-type poly-(9,9-dioctylfluorene-co-bithiophene) thin-film transistors  

NASA Astrophysics Data System (ADS)

A three-dimensional vertically-stacked flexible integrated circuit is demonstrated based on hybrid complementary inverters made of n-type In-Ga-Zn-O (a-IGZO) amorphous oxide thin-film transistors (TFTs) and p-type poly-(9,9-dioctylfluorene-co-bithiophene) (F8T2) polymer TFTs, where all the fabrication processes were performed at temperatures <=120 °C. Saturation mobilities of the a-IGZO TFT and the F8T2 TFT are ~3.2 and ~1.7×10-3 cm2 V-1 s-1, respectively, from which we chose the appropriate dimensions of the TFTs so as to obtain a good balance for the inverter operation. The maximum voltage gain is ~67, which is better than those reported for organic/oxide hybrid complementary inverters.

Nomura, Kenji; Aoki, Takashi; Nakamura, Kiyoshi; Kamiya, Toshio; Nakanishi, Takashi; Hasegawa, Takayuki; Kimura, Mutsumi; Kawase, Takeo; Hirano, Masahiro; Hosono, Hideo

2010-06-01

242

Theory of amorphous ices.  

PubMed

We derive a phase diagram for amorphous solids and liquid supercooled water and explain why the amorphous solids of water exist in several different forms. Application of large-deviation theory allows us to prepare such phases in computer simulations. Along with nonequilibrium transitions between the ergodic liquid and two distinct amorphous solids, we establish coexistence between these two amorphous solids. The phase diagram we predict includes a nonequilibrium triple point where two amorphous phases and the liquid coexist. Whereas the amorphous solids are long-lived and slowly aging glasses, their melting can lead quickly to the formation of crystalline ice. Further, melting of the higher density amorphous solid at low pressures takes place in steps, transitioning to the lower-density glass before accessing a nonequilibrium liquid from which ice coarsens. PMID:24858957

Limmer, David T; Chandler, David

2014-07-01

243

Nanocrystal dispersed amorphous alloys  

NASA Technical Reports Server (NTRS)

Compositions and methods for obtaining nanocrystal dispersed amorphous alloys are described. A composition includes an amorphous matrix forming element (e.g., Al or Fe); at least one transition metal element; and at least one crystallizing agent that is insoluble in the resulting amorphous matrix. During devitrification, the crystallizing agent causes the formation of a high density nanocrystal dispersion. The compositions and methods provide advantages in that materials with superior properties are provided.

Perepezko, John H. (Inventor); Allen, Donald R. (Inventor); Foley, James C. (Inventor)

2001-01-01

244

Performance enhancement of n-channel inversion type In{sub x}Ga{sub 1-x}As metal-oxide-semiconductor field effect transistor using ex situ deposited thin amorphous silicon layer  

SciTech Connect

Significant enhancement in metal-oxide-semiconductor field effect transistor (MOSFET) transport characteristics is achieved with In{sub x}Ga{sub 1-x}As (x=0.53, x=0.20) channel material using ex situ plasma enhanced chemical vapor deposited amorphous Si layer. In{sub x}Ga{sub 1-x}As MOSFETs (L=2 {mu}m, V{sub gs}-V{sub t}=2.0 V) with Si interlayer show a maximum drain current of 290 mA/mm (x=0.53) and 2 {mu}A/mm (x=0.20), which are much higher compared to devices without a Si interlayer. However, charge pumping measurements show a lower average interface state density near the intrinsic Fermi level for devices without the silicon interlayer indicating that a reduction in the midgap interface state density is not responsible for the improved transport characteristics.

Sonnet, A. M.; Hinkle, C. L.; Jivani, M. N.; Chapman, R. A. [Department of Electrical Engineering, University of Texas at Dallas, Richardson, Texas 75080 (United States); Pollack, G. P.; Wallace, R. M. [Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas 75080 (United States); Vogel, E. M. [Department of Electrical Engineering, University of Texas at Dallas, Richardson, Texas 75080 (United States); Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas 75080 (United States)

2008-09-22

245

Pulmonary inflammation in rats after intratracheal instillation of quartz, amorphous SiO2, carbon black, and coal dust and the influence of poly-2-vinylpyridine-N-oxide (PVNO).  

PubMed

Effects of poly-2-vinylpyridine-N-oxide (PVNO) were investigated in numerous in vivo and in vitro studies published in the nineteen sixties and seventies. These studies showed that PVNO inhibited development of fibrosis from quartz dust and improved lung clearance of quartz after inhalation exposure. Ameliorating effects of PVNO were observed also for pulmonary damage from colloidal SiO2 and organic substances, and the fibrogenic inflammation caused by carrageenan. Although it is not proven that silicosis is a precondition for quartz-induced lung tumours, we investigated the hypothesis that PVNO could reduce the lung tumour risk from quartz in rats. A carcinogenicity study was therefore started in rats with the main focus on the quantitative relationships among pulmonary inflammation, fibrosis and neoplasia caused by intratracheal instillation of 3 mg quartz DQ 12 with or without additional subcutaneous PVNO treatment. Other study groups were treated with multiple dust instillations, i.e. 30 instillations of 0.5 mg amorphous SiO2 at intervals of 2 weeks, 10 instillations of 0.5 mg of ultrafine carbon black or 1 mg coal at weekly intervals. The analyses of the bronchoalveolar lavage fluid (BALF) 9 months after start of the life-time study showed that the aim of producing similar levels of increased enzyme concentrations in the four groups treated with quartz/PVNO, amorphous SiO2, carbon black and coal was achieved. A 2.5- to 7.7-fold increase for lactate dehydrogenase (LDH), total protein, alkaline phosphatase and gamma-glutamyl transferase (gamma-GT) was found in these groups as compared to the control. In contrast, quartz treatment without PVNO increased the LDH level up to 24-fold and of total protein to 13-fold. However, the cell counts in the BALF were not so much different in all five groups, i.e. quartz without PVNO (leukocytes: 480.000, PMN: 190.000), quartz with PVNO (leukocytes: 300.000, PMN: 100.000), amorphous SiO2 (leukocytes: 570.000, PMN: 315.000), carbon black (leukocytes: 390.000, PMN: 150.000) and coal (leukocytes: 200.000, PMN: 65.000). Histopathological investigations after four weeks and three months revealed that the used PVNO sample was active in the quartz and amorphous SiO2 groups and markedly reduced the incidences or severity of several pulmonary changes such as macrophage accumulation, inflammatory cell infiltration, interstitial fibrosis, bronchiolo-alveolar hyperplasia, alveolar lipoproteinosis and amorphous SiO2 -induced granulomatous alveolitis/interstitial fibrotic granulomas. Also in the lung-associated lymph nodes (LALN), PVNO treatment significantly reduced the incidence and severity of inflammation in both quartz and amorphous SiO2 groups as evidenced by the presence of well-circumscribed aggregates of intact particle-laden macrophages without signs of degeneration and accompanying granulocytic infiltration and fibrosis. Immunological investigations at the 9 months timepoint on the in vitro production of reactive nitrogen (RNI) or oxygen (ROI) intermediates and tumour necrosis factor (TNF-alpha) from BALF-derived cells indicated a diminished responsiveness to LPS in all particle treatment groups. A diminished production of ROI was also found in the quartz, carbon black, and coal dust groups, respectively, as compared to the values seen in the quartz/PVNO- and amorphous SiO2 treated groups. Treatment with quartz plus PVNO restored the capability of the cells to respond to LPS as compared to the treatment with quartz alone. TNF-alpha production was diminished in the groups treated with quartz, carbon black, and coal dust alone whereas in the quartz/PVNO- and amorphous SiO2-treated groups an elevated TNF-alpha production was seen. These results led to the conclusion that only amorphous SiO2 did not affect the "normal" ability of the cells to respond to LPS and that PVNO protected the cells from a toxic effect of the quartz particles. PMID:12211632

Ernst, Heinrich; Rittinghausen, Susanne; Bartsch, Wilfried; Creutzenberg, Otto; Dasenbrock, Clemens; Görlitz, Bernd-Detlef; Hecht, Matthias; Kairies, Ulf; Muhle, Hartwig; Müller, Meike; Heinrich, Uwe; Pott, Friedrich

2002-08-01

246

MIT Amorphous Computing  

NSDL National Science Digital Library

This site covers the interesting new frontier of molecular computing, which links molecular biology with computer science. It is Massachusetts Institute of Technology's (MIT's) Amorphous Computing homepage. Amorphous computing is defined by the MIT amorphous computer engineers as "methods for instructing myriads of programmable entities to cooperate to achieve particular goals," and sometimes involves the use of organic molecules. In the News, Research, and Demos are among the pages available at the site. The demonstration of "gunk" software is particularly informative and unusual (HSLIM software required).

247

Melting of Amorphous Si.  

National Technical Information Service (NTIS)

The prediction by Turnbull and his colleagues that amorphous Si and Ge undergo first order melting transitions at temperatures T/sub al/ substantially beneath the crystalline melting temperature T/sub cl/ has stimulated much work. Structural, calorimetric...

J. M. Poate P. S. Peercy M. O. Thompson

1985-01-01

248

Amorphous diamond films  

DOEpatents

Amorphous diamond films having a significant reduction in intrinsic stress are prepared by biasing a substrate to be coated and depositing carbon ions thereon under controlled temperature conditions. 1 fig.

Falabella, S.

1998-06-09

249

Fabrication of solution-processed amorphous indium zinc oxide thin-film transistors at low temperatures using deep-UV irradiation under wet conditions  

NASA Astrophysics Data System (ADS)

We fabricated solution-processed indium zinc oxide (IZO) thin film transistors (TFTs) at annealing temperatures as low as 250 °C using deep UV (DUV) irradiation in water vapor medium. The DUV light decomposed the carbon compounds in the IZO films, and the hydroxyl radicals generated when water vapor reacted with ozone effectively oxidized the films. These phenomena were confirmed by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Finally, we fabricated DUV-treated IZO TFTs in water-vapor medium at 250 °C with a mobility of 1.2 cm2/Vs and an on/off current ratio of 2.66 × 106.

Park, Jee Ho; Chae, Soo Sang; Yoo, Young Bum; Lee, Ji Hoon; Lee, Tae Il; Baik, Hong Koo

2014-03-01

250

Amorphous Hydrogenated Carbon Nanofilm  

Microsoft Academic Search

Amorphous hydrogenated carbon (a-C:H) nanofilm is a metastable form of amorphous carbon with significant sp3 bonding. a-C:H\\u000a is a semiconductor with a high mechanical hardness, chemical inertness, and optical transparency. This chapter will describe\\u000a the deposition methods, deposition mechanisms, characterization methods, electronic structure, gap states, defects, doping,\\u000a luminescence, field emission, mechanical properties, and some applications of a-C:H. The films have

Dechun Ba; Zeng Lin

251

Depth analysis of subgap electronic states in amorphous oxide semiconductor, a-In-Ga-Zn-O, studied by hard x-ray photoelectron spectroscopy  

NASA Astrophysics Data System (ADS)

In a previous work, we examined subgap states in highly doped amorphous In-Ga-Zn-O (a-IGZO) films by hard x-ray photoelectron spectroscopy (HX-PES) and found they had subgap electronic states above the valence band maximum (VBM) with the densities > 5 × 1020 cm-3 and just below the Fermi level with the densities > 5 × 1019 cm-3 [K. Nomura, T. Kamiya, H. Yanagi, E. Ikenaga, K. Yang, K. Kobayashi, M. Hirano, and H. Hosono, Appl. Phys. Lett. 92, 202117 (2008)] however, their electron densities (Ne > 3 × 1019 cm-3) are rather high and not compatible with rational properties required for active channel layers in thin-film transistors (TFTs). In this work, we report the effects of Ne and thermal annealing on the subgap states in order to provide the data useful for actual TFTs. It was found that the low-Ne a-IGZO films had extra subgap states above VBM similar to the previous report, but their densities were as small as ~2.0 × 1020 cm-3 for the highly resistive, wet-annealed a-IGZO films. Angle-dependent HX-PES revealed that the subgap states above VBM concentrate in the surface region. The O 1s peak indicated that the wet annealing suppressed the generation of subgap states by terminating these states with -OH bonds. The subgap states below EF were observed commonly in all the samples including ZnO, crystalline (c-) IGZO and a-IGZO. It is concluded that these states below EF are neither related to the disordered structures of a-IGZO nor to their TFT characteristics. It is considered that these states are related to the metastable states created by the high-energy photons in vacuum.

Nomura, Kenji; Kamiya, Toshio; Ikenaga, Eiji; Yanagi, Hiroshi; Kobayashi, Keisuke; Hosono, Hideo

2011-04-01

252

Kinetic rates of amorphous As 2S 3 oxidation at 25 to 40°C and initial pH of 7.3 to 9.4  

NASA Astrophysics Data System (ADS)

The experimental studies of As 2S 3 (am) oxidative dissolution were investigated by use of particle sizes of 8 to 44 ?m in a mixed flow reactor at 25 to 40°C and initial pH 7.3 to 9.4 to determine the effect of dissolved oxygen content, temperature, sulfate, and pH at 0.01 M ionic strength. Most experiments ran for ˜30 h; however, some longer (52 h) and shorter (6-10 h) experiments were also conducted. In most experiments, the As and S release rates had reached an apparent steady state after 20 h. For most experiments, oxidation became stoichiometric after a steady state condition was achieved. The arsenic and sulfur release rates after 20 h in most experiments are in the order of 2.70 × 10 -10 to 4.90 × 10 -9 mol m -2 s -1 in the presence of oxygen. The rate laws of As 2S 3 (am) oxidation were only determined for experiments that ran for ˜30 h at 25 to 40°C and steady state pH 6.9 to 7.9 and are given as follows: Rate law: Activation energy:R( As) =10 -16.77[ DO] 0.42[ H+] -1.26 16.8±5.0 kJ mol-1R( S) =10 -16.99[ DO] 0.35[ H+] -1.25 16.3±5.4 kJ mol-1, where R is the rate of As 2S 3 (am) destruction (mol m -2s -1), [DO] is the concentration of dissolved oxygen (M), and [H +] is the concentration of protons (M). The low activation energy of As 2S 3 (am) oxidative dissolution indicates diffusion control as the dominant mechanism. Moreover, most solid surfaces after the experiments appear smooth and undisturbed. In all experiments, As(III) is present in proportions ranging from ˜49 to 92% of total As at steady-state conditions. Sulfur oxyanions occurred as sulfate (SO 42-), sulfite (SO 32-), and polythionates (S nO 62-) where polythionates are found to be the dominant sulfur species. The acid generated from As 2S 3 (am) at 25°C and pH 7 to 9 can be expressed as follows: [ H+] prod=7.89[ H+] initial+(2.37×10 -7), where [H +] prod is the proton release from the oxidation of As 2S 3 (am) (mol/g), [H +] initial is the initial amount of proton, and 2.37 × 10 -7 is an empirical factor.

Lengke, Maggy F.; Tempel, Regina N.

2001-07-01

253

4.0-inch Active-Matrix Organic Light-Emitting Diode Display Integrated with Driver Circuits Using Amorphous In-Ga-Zn-Oxide Thin-Film Transistors with Suppressed Variation  

NASA Astrophysics Data System (ADS)

We have newly developed a 4.0-in. quarter video graphics array (QVGA) active-matrix organic light-emitting diode (AMOLED) display integrated with gate and source driver circuits using amorphous In-Ga-Zn-oxide (IGZO) thin-film transistors (TFTs). Focusing on a passivation layer in an inverted staggered bottom gate structure, the threshold voltage of the TFTs can be controlled to have “normally-off” characteristics with suppressed variation by using a SiOx layer formed by sputtering with a low hydrogen content. In addition, small subthreshold swing S/S of 0.19 V/decade, high field-effect mobility ?FE of 11.5 cm2 V-1 s-1, and threshold voltage Vth of 1.27 V are achieved. The deposition conditions of the passivation layer and other processes are optimized, and variation in TFT characteristics is suppressed, whereby high-speed operation in gate and source driver circuits can be achieved. Using these driver circuits, the 4.0-in. QVGA AMOLED display integrated with driver circuits can be realized.

Hiroki Ohara,; Toshinari Sasaki,; Kousei Noda,; Shunichi Ito,; Miyuki Sasaki,; Yuta Endo,; Shuhei Yoshitomi,; Junichiro Sakata,; Tadashi Serikawa,; Shunpei Yamazaki,

2010-03-01

254

Formation of amorphous materials  

DOEpatents

Metastable amorphous or fine crystalline materials are formed by solid state reactions by diffusion of a metallic component into a solid compound or by diffusion of a gas into an intermetallic compound. The invention can be practiced on layers of metals deposited on an amorphous substrate or by intermixing powders with nucleating seed granules. All that is required is that the diffusion of the first component into the second component be much faster than the self-diffusion of the first component. The method is practiced at a temperature below the temperature at which the amorphous phase transforms into one or more crystalline phases and near or below the temperature at which the ratio of the rate of diffusion of the first component to the rate of self-diffusion is at least 10.sup.4. This anomalous diffusion criteria is found in many binary, tertiary and higher ordered systems of alloys and appears to be found in all alloy systems that form amorphous materials by rapid quenching. The method of the invention can totally convert much larger dimensional materials to amorphous materials in practical periods of several hours or less.

Johnson, William L. (Pasadena, CA); Schwarz, Ricardo B. (Westmont, IL)

1986-01-01

255

Far-infrared spectra of amorphous titanium dioxide films  

Microsoft Academic Search

The amorphous TiO2 film structure on an aluminum substrate was studied by far infrared reflection–absorption spectroscopic (IRAS) analysis. The transverse (TO) and longitudinal (LO) optical modes of the amorphous oxide films were studied experimentally and through simulation. These optical modes were compared to those of the corresponding crystal. While TO modes of the films correspond to those of the crystal,

G. Scarel; C. R. Aita; H. Tanaka; K. Hisano

2002-01-01

256

Resonance tunneling in binary amorphous films  

Microsoft Academic Search

In the experiments described, several conductivity peaks were observed on both branches of the current-voltage curve of amorphous binary films having the structure of anthracene\\/aluminum oxide. The conductivity is attributed to electron tunneling across the space-charge layer. The tunnel current is split into a noise and resonance component, and an expression for the noise component dependent on the permeability of

O. P. Fedchuk; M. V. Vitiuk

1976-01-01

257

Mineralizing action of iron in amorphous silica  

Microsoft Academic Search

The mineralizing action of iron in amorphous silica was investigated by firing mixtures of silica gel and iron oxides at 1100 and 1150°C. Silica gel did not crystallize in the absence of ferrous ion below 1200°C. When silica gel mixed with ferrous oxalate was heated at 1100°C in a mildly reducing atmosphere(N2, CO2, CO), quartz, cristobalite and ferrous silicate (Fe2SiO4)

Hayato Nanri; Nobuyuki Takeuchi; Shingo Ishida; Koji Watanabe; Mitsuru Wakamatsu

1996-01-01

258

Crystalline Amorphous Semiconductor Superlattice  

NASA Astrophysics Data System (ADS)

A new class of superlattice, crystalline amorphous superlattice (CASL), by alternatively depositing two semiconductor materials, is proposed. CASL displays three states depending on the component materials’ phase: both polycrystalline phases, both amorphous phases, and one polycrystalline phase while another amorphous phase. Using materials capable of reversible phase transition, CASL can demonstrate reversibility among three states. GeTe/Sb2Te3 CASL has been synthesized and proved by x-ray reflectometry and TEM results. The reversible transition among three states induced by electrical and laser pulse was observed. The changes in the optical absorption edge, electrical resistivity, thermal conductivity, and crystallization temperature as a function of layer thickness are interpreted as quantum or nanoeffects. The unique properties of CASL enable the design of materials with specific properties.

Chong, T. C.; Shi, L. P.; Wei, X. Q.; Zhao, R.; Lee, H. K.; Yang, P.; Du, A. Y.

2008-04-01

259

Structural Amorphous Steels  

NASA Astrophysics Data System (ADS)

Recent advancement in bulk metallic glasses, whose properties are usually superior to their crystalline counterparts, has stimulated great interest in fabricating bulk amorphous steels. While a great deal of effort has been devoted to this field, the fabrication of structural amorphous steels with large cross sections has remained an alchemist’s dream because of the limited glass-forming ability (GFA) of these materials. Here we report the discovery of structural amorphous steels that can be cast into glasses with large cross-section sizes using conventional drop-casting methods. These new steels showed interesting physical, magnetic, and mechanical properties, along with high thermal stability. The underlying mechanisms for the superior GFA of these materials are discussed.

Lu, Z. P.; Liu, C. T.; Thompson, J. R.; Porter, W. D.

2004-06-01

260

Amorphous and Ultradisperse Crystalline Materials.  

National Technical Information Service (NTIS)

The book sums up experimental and theoretical findings on amorphous and ultradisperse crystalline materials, massive and film types. Present-day concepts on the structure of amorphous materials, temperature stability of these materials, characteristics of...

K. A. Osipov

1974-01-01

261

Properties of Al2O3: nc-Si nanostructures formed by implantation of silicon ions into sapphire and amorphous films of aluminum oxide  

NASA Astrophysics Data System (ADS)

Photoluminescence, infrared Fourier spectroscopy, Raman scattering, transmission electron microscopy, and electron diffraction were used to study the luminescent, optical, and structural properties of aluminum oxide layers (sapphire and films of Al2O3 deposited on silicon) implanted with Si+ to produce silicon nanocrystals. It is established that, in both cases, a high-temperature annealing of heavily implanted samples brings about the formation of silicon nanocrystals. However, the luminescent properties of the nanocrystals are strongly dependent on the type of pristine matrix; namely, nanocrystals in Al2O3 films emit light in the spectral range typical of Si quantum dots (700-850 nm), whereas in sapphire this photoluminescence is not observed. This difference is interpreted as being due to the fact that local stresses arise in the nanocrystal/sapphire system and break chemical bonds at the interface between the phases, whereas in Al2O3 films stresses are relaxed.

Tetelbaum, D. I.; Mikhaylov, A. N.; Belov, A. I.; Ershov, A. V.; Pitirimova, E. A.; Plankina, S. M.; Smirnov, V. N.; Kovalev, A. I.; Turan, R.; Yerci, S.; Finstad, T. G.; Foss, S.

2009-02-01

262

Hydrogenated amorphous semiconductors  

SciTech Connect

Solar cells based on hydrogenated amorphous silicon are now made from a variety of materials including alloys and microcrystalline films. Research aimed at improving cell efficiency should emphasize studies of alloys and metastable defects. We discuss several research topics related to the growth, structure, and electronic properties of these materials, which should lead to improved photovoltaic devices. 29 refs., 8 figs.

Paul, W. (Harvard Univ., Cambridge, MA (United States)); Street, R.A. (Xerox Palo Alto Research Center, CA (United States)); Wagner, S. (Princeton Univ., NJ (United States))

1993-01-01

263

Hydrogenated Amorphous Silicon  

Microsoft Academic Search

Divided roughly into two parts, the book describes the physical properties and device applications of hydrogenated amorphous silicon. The first section is concerned with the atomic and electronic structure, and covers growth defects and doping and defect reactions. The emphasis is on the optical and electronic properties that result from the disordered structure. The second part of the book describes

1991-01-01

264

Amorphous semiconductor solar cell  

DOEpatents

A solar cell comprising a back electrical contact, amorphous silicon semiconductor base and junction layers and a top electrical contact includes in its manufacture the step of heat treating the physical junction between the base layer and junction layer to diffuse the dopant species at the physical junction into the base layer.

Dalal, Vikram L. (Newark, DE)

1981-01-01

265

Room-temperature low-voltage electroluminescence in amorphous carbon nitride thin films  

Microsoft Academic Search

White-blue electroluminescent emission with a voltage bias less than 10 V was achieved in rf sputter-deposited amorphous carbon nitride (a-CN) and amorphous silicon carbon nitride (a-SiCN) thin-film-based devices. The heterojunction structures of these devices consist of: Indium tin oxide (ITO), used as a transparent anode; amorphous carbon film as an emission layer, and aluminum as a cathode. The thickness of

R. Reyes; C. Legnani; P. M. Ribeiro Pinto; M. Cremona; P. J. G. de Araújo; C. A. Achete

2003-01-01

266

Amorphous silicon radiation detectors  

DOEpatents

Hydrogenated amorphous silicon radiation detector devices having enhanced signal are disclosed. Specifically provided are transversely oriented electrode layers and layered detector configurations of amorphous silicon, the structure of which allow high electric fields upon application of a bias thereby beneficially resulting in a reduction in noise from contact injection and an increase in signal including avalanche multiplication and gain of the signal produced by incoming high energy radiation. These enhanced radiation sensitive devices can be used as measuring and detection means for visible light, low energy photons and high energy ionizing particles such as electrons, x-rays, alpha particles, beta particles and gamma radiation. Particular utility of the device is disclosed for precision powder crystallography and biological identification.

Street, Robert A. (Palo Alto, CA); Perez-Mendez, Victor (Berkeley, CA); Kaplan, Selig N. (El Cerrito, CA)

1992-01-01

267

Amorphous silicon radiation detectors  

DOEpatents

Hydrogenated amorphous silicon radiation detector devices having enhanced signal are disclosed. Specifically provided are transversely oriented electrode layers and layered detector configurations of amorphous silicon, the structure of which allow high electric fields upon application of a bias thereby beneficially resulting in a reduction in noise from contact injection and an increase in signal including avalanche multiplication and gain of the signal produced by incoming high energy radiation. These enhanced radiation sensitive devices can be used as measuring and detection means for visible light, low energy photons and high energy ionizing particles such as electrons, x-rays, alpha particles, beta particles and gamma radiation. Particular utility of the device is disclosed for precision powder crystallography and biological identification. 13 figs.

Street, R.A.; Perez-Mendez, V.; Kaplan, S.N.

1992-11-17

268

Amorphous Carbon Nanospheres  

SciTech Connect

Amorphous carbon nanosphere used as the anode material for Li-intercalation in Lithium-ion energy storage. This structure was obtained through a thermal annealing process at a temperature of 3000 degree Kelvin, simulated using the LAMMPS molecular dynamics code on the LCRC Fusion resource. Science: Kah Chun Lau, Larry Curtiss, Argonne National Laboratory Visualization: Aaron Knoll, Mark Hereld, Michael E. Papka, Argonne National Laboratory

None

2012-01-01

269

Amorphous silicon solar cells  

Microsoft Academic Search

Amorphous silicon solar cells have been fabricated in several different structures: heterojunctions, p-i-n junctions, and Schottky barrier devices. The procedures used in constructing the various solar cells are discussed, and their photovoltaic properties are compared. At present, the highest conversion efficiency (5.5 percent) has been obtained with a Schottky barrier cell, and this structure appears to offer the best promise

D. E. Carlson

1977-01-01

270

Nucleation and crystallization characteristics of phosphorus-doped amorphous silicon slit nano wire  

Microsoft Academic Search

Nucleation and crystallization characteristics of phosphorus-doped amorphous silicon (a-Si) 'slit nano wire' are studied, which is fabricated by conformal filling of a 100 nm wide trench by HLD (High temperature Low pressure chemical vapor Deposition) oxide, and measures about 10 nm in width and height. Nucleation rate and crystallization rate of the amorphous silicon layer, with a phosphorus doping concentration

Yasuo Wada; Takashi Kobayashi; Tokuo Kure; Toshiyuki Yoshimura; Yoshimi Sudou; Yasushi Gotou; Seiichi Kondo

1994-01-01

271

Amorphous alumina coatings: processing, structure and remarkable barrier properties.  

PubMed

Amorphous aluminium oxide coatings were processed by metalorganic chemical vapour deposition (MOCVD); their structural characteristics were determined as a function of the processing conditions, the process was modelled considering appropriate chemical kinetic schemes, and the properties of the obtained material were investigated and were correlated with the nanostructure of the coatings. With increasing processing temperature in the range 350 degrees C-700 degrees C, subatmospheric MOCVD of alumina from aluminium tri-isopropoxide (ATI) sequentially yields partially hydroxylated amorphous aluminium oxides, amorphous Al2O3 (415 degrees C-650 degrees C) and nanostructured gamma-Al2O3 films. A numerical model for the process allowed reproducing the non uniformity of deposition rate along the substrate zone due to the depletion of ATI. The hardness of the coatings prepared at 350 degrees C, 480 degrees C and 700 degrees C is 6 GPa, 11 GPa and 1 GPa, respectively. Scratch tests on films grown on TA6V titanium alloy reveal adhesive and cohesive failures for the amorphous and nanocrystalline ones, respectively. Alumina coating processed at 480 degrees C on TA6V yielded zero weight gain after oxidation at 600 degrees C in lab air. The surface of such low temperature processed amorphous films is hydrophobic (water contact angle 106 degrees), while the high temperature processed nanocrystalline films are hydrophilic (48 degrees at a deposition temperature of 700 degrees C). It is concluded that amorphous Al2O3 coatings can be used as oxidation and corrosion barriers at ambient or moderate temperature. Nanostructured with Pt or Ag nanoparticles, they can also provide anti-fouling or catalytic surfaces. PMID:22097590

Samélor, Diane; Lazar, Ana-Maria; Aufray, Maëlenn; Tendero, Claire; Lacroix, Loïc; Béguin, Jean-Denis; Caussat, Brigitte; Vergnes, Hugues; Alexis, Joël; Poquillon, Dominique; Pébère, Nadine; Gleizes, Alain; Vahlas, Constantin

2011-09-01

272

Amorphous silicon carbide TFTs  

NASA Astrophysics Data System (ADS)

In this paper we present and characterize a-Si 1- xC x:H thin film transistors, TFTs, fabricated by PECVD deposition. Precise modeling and parameter extraction for these devices was done using a unified procedure previously developed by us for amorphous, polycrystalline, nanocrystalline and organic TFTs. The behavior with temperature and stress of the extracted parameters is analyzed to determine similarities and differences with respect to a-Si:H TFTs. Electrical simulation allowed to estimate the localized traps energy distribution.

Estrada, M.; Cerdeira, A.; Resendiz, L.; García, R.; Iñiguez, B.; Marsal, L. F.; Pallares, J.

2006-03-01

273

Optical multilayers with an amorphous fluoropolymer  

SciTech Connect

Multilayered coatings were made by physical vapor deposition (PVD) of a perfluorinated amorphous polymer, Teflon AF2400, together with other optical materials. A high reflector at 1064 run was made with ZnS and AF2400. An all-organic 1064-nm reflector was made from AF2400 and polyethylene. Oxide (HfO{sub 2}, SiO{sub 2}) compatibility was also tested. Each multilayer system adhered to itself. The multilayers were influenced by coating stress and unintentional temperature rises during PVD deposition.

Chow, R.; Loomis, G.E.; Lindsey, E.F.

1994-07-01

274

Molecular dynamics in amorphous ergocalciferol  

NASA Astrophysics Data System (ADS)

While developing new pharmaceutical products based on drug substances in their amorphous form, the molecular mobility of amorphous active ingredients have to be characterized in detail. The molecular mobility in the supercooled liquid and glassy states of ergocalciferol is studied using broadband dielectric spectroscopy over wide frequency and temperature ranges. Dielectric studies revealed a number of relaxation process of different molecular origin.

Mohamed, Sahra; Thayyil, M. Shahin; Capaccioli, S.

2014-04-01

275

Compensated amorphous silicon solar cell  

DOEpatents

An amorphous silicon solar cell incorporates a region of intrinsic hydrogenated amorphous silicon fabricated by a glow discharge wherein said intrinsic region is compensated by P-type dopants in an amount sufficient to reduce the space charge density of said region under illumination to about zero.

Carlson, David E. (Yardley, PA)

1980-01-01

276

Compensated amorphous silicon solar cell  

DOEpatents

An amorphous silicon solar cell including an electrically conductive substrate, a layer of glow discharge deposited hydrogenated amorphous silicon over said substrate and having regions of differing conductivity with at least one region of intrinsic hydrogenated amorphous silicon. The layer of hydrogenated amorphous silicon has opposed first and second major surfaces where the first major surface contacts the electrically conductive substrate and an electrode for electrically contacting the second major surface. The intrinsic hydrogenated amorphous silicon region is deposited in a glow discharge with an atmosphere which includes not less than about 0.02 atom percent mono-atomic boron. An improved N.I.P. solar cell is disclosed using a BF.sub.3 doped intrinsic layer.

Devaud, Genevieve (629 S. Humphrey Ave., Oak Park, IL 60304)

1983-01-01

277

Thermochemistry of amorphous and crystalline zirconium and hafnium silicates.  

NASA Astrophysics Data System (ADS)

Calorimetric investigation of amorphous and crystalline zirconium and hafnium silicates was performed as part of a research program on thermochemistry of alternative gate dielectrics. Amorphous hafnium and zirconium silicates with varying SiO2 content were synthesized by a sol-gel process. Crystalline zirconium and hafnium silicates (zircon and hafnon) were synthesized by solid state reaction at 1450 °C from amorphous gels and grown as single crystals from flux. High temperature oxide melt solution calorimetry in lead borate (2PbO.B2O3) solvent at 800 oC was used to measure drop solution enthalpies for amorphous and crystalline zirconium and hafnium silicates and corresponding oxides. Applying appropriate thermochemical cycles, formation enthalpy of crystalline ZrSiO4 (zircon) from binary oxides (baddeleite and quartz) at 298 K was calculated as -23 +/-2 kJ/mol and enthalpy difference between amorphous and crystalline zirconium silicate (vitrification enthalpy) was found to be 61 +/-3 kJ/mol. Crystallization onset temperatures of amorphous zirconium and hafnium silicates, as measured by differential scanning calorimetry (DSC), increased with silica content. The resulting crystalline phases, as characterized by X-ray diffraction (XRD), were tetragonal HfO2 and ZrO2. Critical crystallite size for tetragonal to monoclinic transformation of HfO2 in the gel was estimated as 6 +/-2 nm from XRD data Crystallization enthalpies per mole of hafnia and zirconia in gels decrease slightly together with crystallite size with increasing silica content, for example from -22 to -15 +/-1 kJ per mol of HfO2 crystallized at 740 and 1006 °C from silicates with 10 and 70 mol Applications of thermal analyses and solution calorimetry techniques together with first-principles density functional calculations to estimate interface and surface energies are discussed.

Ushakov, S.; Brown, C. E.; Navrotsky, Alexandra; Boatner, L. A.; Demkov, A. A.; Wang, C.; Nguyen, B.-Y.

2003-03-01

278

Potential of amorphous and microcrystalline silicon solar cells  

Microsoft Academic Search

Low pressure chemical vapour deposition (LP-CVD) ZnO as front transparent conductive oxide (TCO), developed at IMT, has excellent light-trapping properties for a-Si:H p-i-n single-junction and ‘micromorph’ (amorphous\\/microcrystalline silicon) tandem solar cells. A stabilized record efficiency of 9.47% has independently been confirmed by NREL for an amorphous silicon single-junction p-i-n cell (?1 cm2) deposited on LP-CVD ZnO coated glass. Micromorph tandem

J. Meier; J. Spitznagel; U. Kroll; C. Bucher; S. Faÿ; T. Moriarty; A. Shah

2004-01-01

279

Methods of amorphization and investigation of the amorphous state.  

PubMed

The amorphous form of pharmaceutical materials represents the most energetic solid state of a material. It provides advantages in terms of dissolution rate and bioavailability. This review presents the methods of solid- -state amorphization described in literature (supercooling of liquids, milling, lyophilization, spray drying, dehydration of crystalline hydrates), with the emphasis on milling. Furthermore, we describe how amorphous state of pharmaceuticals differ depending on the method of preparation and how these differences can be screened by a variety of spectroscopic (X-ray powder diffraction, solid state nuclear magnetic resonance, atomic pairwise distribution, infrared spectroscopy, terahertz spectroscopy) and calorimetry methods. PMID:24152894

Einfal, Tomaž; Planinšek, Odon; Hrovat, Klemen

2013-09-01

280

Bulk amorphous materials  

SciTech Connect

This is the final report for a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The objective of this work was to develop the competency for the synthesis of novel bulk amorphous alloys. The authors researched their synthesis methods and alloy properties, including thermal stability, mechanical, and transport properties. The project also addressed the development of vanadium-spinel alloys for structural applications in hostile environments, the measurement of elastic constants and thermal expansion in single-crystal TiAl from 300 to 750 K, the measurement of elastic constants in gallium nitride, and a study of the shock-induced martensitic transformations in NiTi alloys.

Schwarz, R.B.; Archuleta, J.I.; Sickafus, K.E. [and others

1998-12-01

281

Adsorption of selenium by amorphous iron oxyhydroxide and manganese dioxide  

NASA Astrophysics Data System (ADS)

This work compares and models the adsorption of selenium and other anions on a neutral to alkaline surface (amorphous iron oxyhydroxide) and an acidic surface (manganese dioxide). Selenium adsorption on these oxides is examined as a function of pH, particle concentration, oxidation state, and competing anion concentration in order to assess how these factors might influence the mobility of selenium in the environment. The data indicate that 1) amorphous iron oxyhydroxide has a greater affinity for selenium than manganese dioxide, 2) selenite [Se(IV)] adsorption increases with decreasing pH and increasing particle concentration and is stronger than selenate [Se(VI)] adsorption on both oxides, and 3) selenate does not adsorb on manganese dioxide. The relative affinity of selenate and selenite for the oxides and the lack of adsorption of selenate on a strongly acidic surface suggests that selenate forms outer-sphere complexes while selenite forms inner-sphere complexes with the surfaces. The data also indicate that the competition sequence of other anions with respect to selenite adsorption at pH 7.0 is phosphate > silicate > molybdate > fluoride > sulfate on amorphous iron oxyhydroxide and molybdate ? phosphate > silicate > fluoride > sulfate on manganese dioxide. The adsorption of phosphate, molybdate, and silicate on these oxides as a function of pH indicates that the competition sequences reflect the relative affinities of these anions for the surfaces. The Triple Layer surface complexation model is used to provide a quantitative description of these observations and to assess the importance of surface site heterogeneity on anion adsorption. The modeling results suggest that selenite forms binuclear, innersphere complexes with amorphous iron oxyhydroxide and monodentate, inner-sphere complexes with manganese dioxide and that selenate forms outer-sphere, monodentate complexes with amorphous iron oxyhydroxide. The heterogeneity of the oxide surface sites is reflected in decreasing equilibrium constants for selenite with increasing adsorption density and both experimental observations and modeling results suggest that manganese dioxide has fewer sites of higher energy for selenite adsorption than amorphous iron oxyhydroxide. Modeling and interpreting the adsorption of phosphate, molybdate, and silicate on the oxides are made difficult by the lack of constraint in choosing surface species and the fact that equally good fits can be obtained with different surface species. Finally, predictions of anion competition using the model results from single adsorbate systems are not very successful because the model does not account for surface site heterogeneity. Selenite adsorption data from a multi-adsorbate system could be fit if the equilibrium constant for selenite is decreased with increasing anion adsorption density.

Balistrieri, Laurie S.; Chao, T. T.

1990-03-01

282

Adsorption of selenium by amorphous iron oxyhydroxide and manganese dioxide  

USGS Publications Warehouse

This work compares and models the adsorption of selenium and other anions on a neutral to alkaline surface (amorphous iron oxyhydroxide) and an acidic surface (manganese dioxide). Selenium adsorption on these oxides is examined as a function of pH, particle concentration, oxidation state, and competing anion concentration in order to assess how these factors might influence the mobility of selenium in the environment. The data indicate that 1. 1) amorphous iron oxyhydroxide has a greater affinity for selenium than manganese dioxide, 2. 2) selenite [Se(IV)] adsorption increases with decreasing pH and increasing particle concentration and is stronger than selenate [Se(VI)] adsorption on both oxides, and 3. 3) selenate does not adsorb on manganese dioxide. The relative affinity of selenate and selenite for the oxides and the lack of adsorption of selenate on a strongly acidic surface suggests that selenate forms outer-sphere complexes while selenite forms inner-sphere complexes with the surfaces. The data also indicate that the competition sequence of other anions with respect to selenite adsorption at pH 7.0 is phosphate > silicate > molybdate > fluoride > sulfate on amorphous iron oxyhydroxide and molybdate ??? phosphate > silicate > fluoride > sulfate on manganese dioxide. The adsorption of phosphate, molybdate, and silicate on these oxides as a function of pH indicates that the competition sequences reflect the relative affinities of these anions for the surfaces. The Triple Layer surface complexation model is used to provide a quantitative description of these observations and to assess the importance of surface site heterogeneity on anion adsorption. The modeling results suggest that selenite forms binuclear, innersphere complexes with amorphous iron oxyhydroxide and monodentate, inner-sphere complexes with manganese dioxide and that selenate forms outer-sphere, monodentate complexes with amorphous iron oxyhydroxide. The heterogeneity of the oxide surface sites is reflected in decreasing equilibrium constants for selenite with increasing adsorption density and both experimental observations and modeling results suggest that manganese dioxide has fewer sites of higher energy for selenite adsorption than amorphous iron oxyhydroxide. Modeling and interpreting the adsorption of phosphate, molybdate, and silicate on the oxides are made difficult by the lack of constraint in choosing surface species and the fact that equally good fits can be obtained with different surface species. Finally, predictions of anion competition using the model results from single adsorbate systems are not very successful because the model does not account for surface site heterogeneity. Selenite adsorption data from a multi-adsorbate system could be fit if the equilibrium constant for selenite is decreased with increasing anion adsorption density. ?? 1990.

Balistrieri, L. S.; Chao, T. T.

1990-01-01

283

Low Temperature Thermal Properties of Amorphous Polymer Blends.  

NASA Astrophysics Data System (ADS)

Thermal conductivity (kappa) and specific heat ({rm C}_ p) of amorphous polymer blends of polystyrene (PS) and polyphenylene oxide (PPO) with a wide range of compositions have been measured for 2K < T < 100K. The results show general features expected of amorphous solids: a peak in {rm C }_ p/T^ 3 below about 10K and a plateau in kappa up to about 6K. The {rm C}_ p/T^ 3 is enhanced, and the kappa value for the plateau region is depressed for the PPO rich compositions. The results are discussed in terms of a new model that describes phonon localization in polymers at temperatures above 20K. This "ter-tra" model for phonon localization in polymers fits our kappa and {rm C}_ p data within experimental error. The results are also analyzed in terms of the fractal model for the medium range structure of amorphous polymers.

Giedd, Ryan Evan

284

Structural relaxation in amorphous silicon carbide  

Microsoft Academic Search

High purity single crystal and chemically vapor deposited (CVD) silicon carbide have been amorphized under fast neutron irradiation. The gradual transition in physical properties from the as-amorphized state to a more relaxed amorphous state prior to crystallization is studied. For the three bulk properties studied: density, electrical resistivity, and thermal conductivity, large property changes occur upon annealing between the amorphization

L. L. Snead; S. J. Zinkle

2002-01-01

285

Compensated amorphous-silicon solar cell  

Microsoft Academic Search

An amorphous silicon solar cell including an electrically conductive substrate, a layer of glow discharge deposited hydrogenated amorphous silicon having regions of differing conductivity with at least one region of intrinsic hydrogenated amorphous silicon. The layer of hydrogenated amorphous silicon has opposed first and second major surfaces where the first major surface contacts the elecrically conductive substrate and an electrode

Devaud

1982-01-01

286

Generalized melting criterion for amorphization.  

National Technical Information Service (NTIS)

We present a thermodynamic model of solid-state amorphization based on a generalization of the well-known Lindemann criterion. The original Lindemann criterion proposes that melting occurs when the root-mean-square amplitude of thermal displacement exceed...

R. Devanathan N. Q. Lam P. R. Okamoto M. Meshii

1992-01-01

287

Fabrication of amorphous diamond films  

DOEpatents

Amorphous diamond films having a significant reduction in intrinsic stress are prepared by biasing a substrate to be coated and depositing carbon ions thereon under controlled temperature conditions. 1 fig.

Falabella, S.

1995-12-12

288

Excitations of Amorphous Solid Helium  

NASA Astrophysics Data System (ADS)

We present neutron scattering measurements of the dynamic structure factor, S(Q,?), of amorphous solid helium confined in 47 \\ptilde ore diameter MCM-41 at pressure 48.6 bar. At low temperature, T = 0.05 K, we observe S(Q,?) of the confined quantum amorphous solid plus the bulk polycrystalline solid between the MCM-41 powder grains. No liquid-like phonon-roton modes, other sharply defined modes at low energy (?< 1.0 meV) or modes unique to a quantum amorphous solid that might suggest superflow are observed. Rather the S(Q,?) of confined amorphous and bulk polycrystalline solid appear to be very similar. At higher temperature (T> 1 K), the amorphous solid in the MCM-41 pores melts to a liquid which has a broad S(Q,?) peaked near ?˜ 0 characteristic of normal liquid ^4He under pressure. Expressions for the S(Q,?) of amorphous and polycrystalline solid helium are presented and compared. In previous measurements of liquid ^4He confined in MCM-41 at lower pressure the intensity in the liquid roton mode decreases with increasing pressure until the roton vanishes at the solidification pressure (38 bars), consistent with no roton in the solid observed here

Bossy, Jacques; Ollivier, Jacques; Schober, Helmut; Glyde, Henry R.

2013-03-01

289

Excitations of amorphous solid helium  

NASA Astrophysics Data System (ADS)

We present neutron scattering measurements of the dynamic structure factor S(Q,?) of amorphous solid helium confined in 47-Å pore diameter MCM-41 at pressure 48.6 bars. At low temperature T=0.05 K, we observe S(Q,?) of the confined quantum amorphous solid plus the bulk polycrystalline solid between the MCM-41 powder grains. No liquidlike phonon-roton modes, other sharply defined modes at low energy (?< 1.0 meV), or modes unique to a quantum amorphous solid that might suggest superflow are observed. Rather, the S(Q,?) of confined amorphous and bulk polycrystalline solid appear to be very similar. At higher temperature (T> 1 K), the amorphous solid in the MCM-41 pores melts to a liquid which has a broad S(Q,?) peaked near w?0, characteristic of normal liquid 4He under pressure. Expressions for the S(Q,?) of amorphous and polycrystalline solid helium are presented and compared. In previous measurements of liquid 4He confined in MCM-41 at lower pressure, the intensity in the liquid roton mode decreases with increasing pressure until the roton vanishes at the solidification pressure (38 bars), consistent with no roton in the solid observed here.

Bossy, Jacques; Ollivier, Jacques; Schober, Helmut; Glyde, H. R.

2012-12-01

290

Synthesis of Fe–Ni–B–Si–Nb amorphous and crystalline composite coatings by laser cladding and remelting  

Microsoft Academic Search

Amorphous and nanocrystalline composite coatings are synthesized by laser cladding and remelting. The result of X-ray diffraction shows that an amorphous structure and some crystalline phases occur in the coatings. The microstructure of the coatings is different with different amounts of Si in the coatings. The fracture appearance suggests that brittle fracture occurs in coatings. There are some oxides, borides

Peilei Zhang; Hua Yan; Chengwu Yao; Zhuguo Li; Zhishui Yu; Peiquan Xu

2011-01-01

291

Dissolution rates of amorphous Al- and Fe-phosphates and their relevance to phosphate mobility on Mars  

NASA Astrophysics Data System (ADS)

Phosphate is an essential element for life on Earth, and therefore if life exists or ever existed on Mars it may have required phosphate. Amorphous Al- and Fe-phosphates rapidly precipitate from acidic solutions and amorphous Al-phosphates likely control phosphate concentrations in some natural waters on Earth. Amorphous phases may be even more important on Mars than on Earth, and amorphous phosphates are therefore likely important in the phosphate cycle on Mars. Despite this importance, however, few dissolution rates exist for amorphous Al- and Fe- phosphates. In this study, dissolution rates of amorphous Al- and Fe-phosphates were measured in flow-through reactors from steady state concentrations of Al, Fe and P. A pH--dependent rate law was calculated from the dissolution rates log R = log k -- npH, where R is the dissolution rate, k is intrinsic rate constant and n is the rate dependence on pH. For amorphous Al-phosphate, log k = -6.539 +/- 1.529, and n = 2.391 +/- 0.493. For amorphous Fe-phosphate, log k = -13.031 +/- 0.558, and n = 1.376 +/- 0.221. Amorphous Al-phosphate dissolves stoichiometrically under all conditions, and amorphous Fe-phosphate dissolves non-stoichiometrically, approaching stoichiometric dissolution as pH decreases, due potentially to Fe-oxides precipitating and armoring grain surfaces. Perhaps due to these effects, amorphous Al-phosphate dissolution rates are approximately three orders of magnitude faster than amorphous Fe-phosphate dissolution rates. Amorphous Al-phosphate dissolution rates measured in this study are also faster than published variscite dissolution rates. Dissolution rates of amorphous Al- and Fe-phosphates in this study therefore imply rapid phosphate release into acidic environments, suggesting phosphate mobility under Mars-relevant conditions.

Tu, Valerie M.

292

Processing Bi-Pb-Sr-Ca-Cu-O superconductors from amorphous state  

NASA Technical Reports Server (NTRS)

The bismuth based high T sub c superconductors can be processed via an amorphous Bi-Pb-Sr-Ca-Cu oxide. The amorphous oxides were prepared by melting the constituent powders in an alumina crucible at 1200 C in air followed by pouring the liquid onto an aluminum plate, and rapidly pressing with a second plate. In the amorphous state, no crystalline phase was identified in the powder x ray diffraction pattern of the quenched materials. After heat treatment at high temperature the amorphous materials crystallized into a glass ceramic containing a large fraction of the Bi2Sr2Ca2Cu3O(x) phase T sub c = 110 K. The processing method, crystallization, and results of dc electrical resistivity and ac magnetic susceptibility measurements are discussed.

Chiang, C. K.; Wong-Ng, W.; Cook, L. P.; Freiman, S. W.; Hwang, N. M.; Vaudin, M.; Hill, M. D.; Shull, R. D.; Shapiro, A. J.; Swartzendruber, L. J.

1991-01-01

293

Electron back-scattered diffraction of crystallized vanadium dioxide thin films on amorphous silicon dioxide  

Microsoft Academic Search

Crystalline films and isolated particles of vanadium dioxide (VO2) were obtained through solid phase crystallization of amorphous vanadium oxide thin films sputtered on silicon dioxide. Electron back-scattered diffraction (EBSD) was used to study the crystals obtained in the thin films, to differentiate them from different vanadium oxide stoichiometries that may have formed during the annealing process, and to study their

Felipe Rivera; Laurel Burk; Robert Davis; Richard Vanfleet

294

Inhibitory Effect of Soil Organic Matter on the Crystallization of Amorphous Ferric Hydroxide  

Microsoft Academic Search

SOILS and sediments often contain large quantities of hydrous ferric oxide which, according to X-ray analysis, cannot be accounted for by crystalline forms of iron oxide. This is surprising in view of the fact that crystallization in vitro of freshly prepared amorphous ferric hydroxide to goethite or haematite is virtually complete after a few months or years, even at room

U. Schwertmann

1966-01-01

295

Influence of irradiation spectrum and implanted ions on the amorphization of ceramics  

SciTech Connect

Polycrystalline Al2O3, magnesium aluminate spinel (MgAl2O4), MgO, Si3N4, and SiC were irradiated with various ions at 200-450 K, and microstructures were examined following irradiation using cross-section TEM. Amorphization was not observed in any of the irradiated oxide ceramics, despsite damage energy densities up to {similar_to}7 keV/atom (70 displacements per atom). On the other hand, SiC readily amorphized after damage levels of {similar_to}0.4 dpa at room temperature (RT). Si3N4 exhibited intermediate behavior; irradiation with Fe{sup 2+} ions at RT produced amorphization in the implanted ion region after damage levels of {similar_to}1 dpa. However, irradiated regions outside the implanted ion region did not amorphize even after damage levels > 5 dpa. The amorphous layer in the Fe-implanted region of Si3N4 did not appear if the specimen was simultaneoulsy irradiated with 1-MeV He{sup +} ions at RT. By comparison with published results, it is concluded that the implantation of certain chemical species has a pronounced effect on the amorphization threshold dose of all five materials. Intense ionizing radiation inhibits amorphization in Si3N4, but does not appear to significantly influence the amorphization of SiC.

Zinkle, S.J.; Snead, L.L.

1995-12-31

296

Optimization of transparent and reflecting electrodes for amorphous silicon solar cells. Annual subcontract report, April 1, 1994--March 31, 1995.  

National Technical Information Service (NTIS)

Transparent and reflecting electrodes are important parts of the structure of amorphous silicon solar cells. We report improved methods for depositing zinc oxide, deposition of tin nitride as a potential reflection-enhancing diffusion barrier between the ...

R. G. Gordon

1995-01-01

297

Tribological properties of aligned film of amorphous carbon nanorods on AAO membrane in different environments  

Microsoft Academic Search

The aligned film of amorphous carbon nanorods was synthesized by chemical vapor deposition at 650°C with the Co catalyst on a porous anodic aluminum oxide (AAO) membrane. The morphology and microstructure of the aligned film of amorphous carbon nanorods were examined by field emission SEM, TEM and Raman spectroscopy. The tests sliding against a quenched-and-tempered GCr15 steel were conducted using

J. P. Tu; C. X. Jiang; S. Y. Guo; X. B. Zhao; M. F. Fu

2005-01-01

298

Magnetic Behavior and Chemical Shift of Amorphous Cr2O3  

Microsoft Academic Search

The chemical shift in cristalline and amorphous Cr2O3 was determined from the X-ray absorption Cr K edge spectra. The measurements of the temperature dependence of the reciprocal susceptibility between 100 and 1200 K show an antiferromagnetic behavior for the cristalline sample, with the Neel temperature at 318 K, and a linear dependence (Curie-Weiss law) with thetap<0, for the amorphous oxide.

I. Pop; M. Andrecut; I. Burda; C. Oprea; C. Andrecut

1997-01-01

299

High performance amorphous steel coating prepared by HVOF thermal spraying  

Microsoft Academic Search

Amorphous steel coating with a composition of Fe48Cr15Mo14C15B6Y2 was prepared by means of high velocity oxygen fuel (HVOF) thermal spraying. Microstructural analysis gives the information about porosity, oxidation and nanocrystal precipitation. Properties including the hardness, wear, corrosion and magnetic behaviors of the coating were examined. It was shown that the microhardness and wear resistance of the coating are superior to

H. S. Ni; X. H. Liu; X. C. Chang; W. L. Hou; W. Liu; J. Q. Wang

2009-01-01

300

Amorphous-silicon cell reliability testing  

NASA Technical Reports Server (NTRS)

The work on reliability testing of solar cells is discussed. Results are given on initial temperature and humidity tests of amorphous silicon devices. Calibration and measurement procedures for amorphous and crystalline cells are given. Temperature stress levels are diagrammed.

Lathrop, J. W.

1985-01-01

301

Tandem junction amorphous silicon solar cells  

DOEpatents

An amorphous silicon solar cell has an active body with two or a series of layers of hydrogenated amorphous silicon arranged in a tandem stacked configuration with one optical path and electrically interconnected by a tunnel junction. The layers of hydrogenated amorphous silicon arranged in tandem configuration can have the same bandgap or differing bandgaps.

Hanak, Joseph J. (Lawrenceville, NJ)

1981-01-01

302

Buried oxide layer in silicon  

DOEpatents

A process for forming Silicon-On-Insulator is described incorporating the steps of ion implantation of oxygen into a silicon substrate at elevated temperature, ion implanting oxygen at a temperature below 200.degree. C. at a lower dose to form an amorphous silicon layer, and annealing steps to form a mixture of defective single crystal silicon and polycrystalline silicon or polycrystalline silicon alone and then silicon oxide from the amorphous silicon layer to form a continuous silicon oxide layer below the surface of the silicon substrate to provide an isolated superficial layer of silicon. The invention overcomes the problem of buried isolated islands of silicon oxide forming a discontinuous buried oxide layer.

Sadana, Devendra Kumar (Pleasantville, NY); Holland, Orin Wayne (Lenoir, TN)

2001-01-01

303

Electronic Structure of Amorphous Ge.  

National Technical Information Service (NTIS)

The electronic spectrum of amorphous Ge is examined in view of the recent Letter of Brust. Using Burst's calculations, it is shown that even a partial retention of k as a quantum number results in prediction of a strong modulation in photoemission energy-...

T. M. Donovan W. E. Spicer

1970-01-01

304

Planar anisotropy in amorphous semiconductors  

Microsoft Academic Search

Theoretical work has been carried out towards the planar (non-axial) anisotropy in amorphous semiconductors. The spontaneous polarization (Ps) vector seems to move into the plane leaving the axial characters. The work has been done in zero and non-zero electric field modes. Existence of easy, hard axes and the existence of cones have been demonstrated. In the case of cones Ps

W. I. Khan; A. E. Rakhshani; A. Y. M. Al-Qenaie

1996-01-01

305

Planar anisotropy in amorphous semiconductors  

Microsoft Academic Search

Theoretical work has been carried out towards the planar (non-axial) anisotropy in amorphous semiconductors. The spontaneous polarization (Ps) vector seems to move into the plane leaving the axial characters. The work has been done in zero and non-zero electric field modes. Existence of easy, hard axes and the existence of cones have been demonstrated. In the case of cones, Ps

W. I. Khan; A. E. Rakhshani; A. Y. M. Al-Qenaie

1996-01-01

306

Thorium sorption on amorphous silica  

Microsoft Academic Search

The sorption of Th on amorphous colloidal particles of Si02 (Aerosil OX 200) has been studied in perchlorate media in order to obtain quantitative information on the sorption of The on silica. In order to quantify the pH dependence of the charge of the silica surface, potentiometric surface titrations of the silica particles have also been made. The results from

Erik Östhols

1995-01-01

307

Microstructure and surface chemistry of amorphous alloys important to their friction and wear behavior  

NASA Technical Reports Server (NTRS)

An investigation was conducted to examine the microstructure and surface chemistry of amorphous alloys, and their effects on tribological behavior. The results indicate that the surface oxide layers present on amorphous alloys are effective in providing low friction and a protective film against wear in air. Clustering and crystallization in amorphous alloys can be enhanced as a result of plastic flow during the sliding process at a low sliding velocity, at room temperature. Clusters or crystallines with sizes to 150 nm and a diffused honeycomb-shaped structure are produced on the wear surface. Temperature effects lead to drastic changes in surface chemistry and friction behavior of the alloys at temperatures to 750 C. Contaminants can come from the bulk of the alloys to the surface upon heating and impart to the surface oxides at 350 C and boron nitride above 500 C. The oxides increase friction while the boron nitride reduces friction drastically in vacuum.

Miyoshi, K.; Buckley, D. H.

1983-01-01

308

Thermal conductivity accumulation in amorphous silica and amorphous silicon  

NASA Astrophysics Data System (ADS)

We predict the properties of the propagating and nonpropagating vibrational modes in amorphous silica (a-SiO2) and amorphous silicon (a-Si) and, from them, thermal conductivity accumulation functions. The calculations are performed using molecular dynamics simulations, lattice dynamics calculations, and theoretical models. For a-SiO2, the propagating modes contribute negligibly to thermal conductivity (6%), in agreement with the thermal conductivity accumulation measured by Regner et al. [Nat. Commun. 4, 1640 (2013), 10.1038/ncomms2630]. For a-Si, propagating modes with mean-free paths up to 1 ?m contribute 40% of the total thermal conductivity. The predicted contribution to thermal conductivity from nonpropagating modes and the total thermal conductivity for a-Si are in agreement with the measurements of Regner et al. The accumulation in the measurements, however, takes place over a narrower band of mean-free paths (100 nm-1 ?m) than that predicted (10 nm-1 ?m).

Larkin, Jason M.; McGaughey, Alan J. H.

2014-04-01

309

Physicochemical determinants in the cellular responses to nanostructured amorphous silicas.  

PubMed

Amorphous silicas, opposite to crystalline polymorphs, have been regarded so far as nonpathogenic, but few studies have addressed the toxicity of the wide array of amorphous silica forms. With the advent of nanotoxicology, there has been a rising concern about the safety of silica nanoparticles to be used in nanomedicine. Here, we report a study on the toxicity of amorphous nanostructured silicas obtained with two different preparation procedures (pyrolysis vs. precipitation), the pyrogenic in two very different particle sizes, in order to assess the role of size and origin on surface properties and on the cell damage, oxidative stress, and inflammatory response elicited in murine alveolar macrophages. A quartz dust was employed as positive control and monodispersed silica spheres as negative control. Pyrogenic silicas were remarkably more active than the precipitated one as to cytotoxicity, reactive oxygen species production, lipid peroxidation, nitric oxide synthesis, and production of tumor necrosis factor-?, when compared both per mass and per unit surface. Between the two pyrogenic silicas, the larger one was the more active. Silanols density is the major difference in surface composition among the three silicas, being much larger than the precipitated one as indicated by joint calorimetric and infrared spectroscopy analysis. We assume here that full hydroxylation of a silica surface, with consequent stable coverage by water molecules, reduces/inhibits toxic behavior. The preparation route appears thus determinant in yielding potentially toxic materials, although the smallest size does not always correspond to an increased toxicity. PMID:22491428

Gazzano, Elena; Ghiazza, Mara; Polimeni, Manuela; Bolis, Vera; Fenoglio, Ivana; Attanasio, Angelo; Mazzucco, Gianna; Fubini, Bice; Ghigo, Dario

2012-07-01

310

Optical dispersion relations for amorphous semiconductors and amorphous dielectrics  

Microsoft Academic Search

An expression for the imaginary part, k, of the complex index of refraction, N=n-ik, for amorphous materials is derived as a function of photon energy E: k(E)=A(E-Eg)2\\/(E2-BE+C) where A, B, and C are positive nonzero constants characteristic of the medium such that 4C-B2>0. Eg represents the optical energy band gap. The real part, n, of the complex index of refraction

A. R. Forouhi; I. Bloomer

1986-01-01

311

Amorphous metal-organic frameworks.  

PubMed

Conspectus Crystalline metal-organic frameworks (MOFs) are porous frameworks comprising an infinite array of metal nodes connected by organic linkers. The number of novel MOF structures reported per year is now in excess of 6000, despite significant increases in the complexity of both component units and molecular networks. Their regularly repeating structures give rise to chemically variable porous architectures, which have been studied extensively due to their sorption and separation potential. More recently, catalytic applications have been proposed that make use of their chemical tunability, while reports of negative linear compressibility and negative thermal expansion have further expanded interest in the field. Amorphous metal-organic frameworks (aMOFs) retain the basic building blocks and connectivity of their crystalline counterparts, though they lack any long-range periodic order. Aperiodic arrangements of atoms result in their X-ray diffraction patterns being dominated by broad "humps" caused by diffuse scattering and thus they are largely indistinguishable from one another. Amorphous MOFs offer many exciting opportunities for practical application, either as novel functional materials themselves or facilitating other processes, though the domain is largely unexplored (total aMOF reported structures amounting to under 30). Specifically, the use of crystalline MOFs to detect harmful guest species before subsequent stress-induced collapse and guest immobilization is of considerable interest, while functional luminescent and optically active glass-like materials may also be prepared in this manner. The ion transporting capacity of crystalline MOFs might be improved during partial structural collapse, while there are possibilities of preparing superstrong glasses and hybrid liquids during thermal amorphization. The tuning of release times of MOF drug delivery vehicles by partial structural collapse may be possible, and aMOFs are often more mechanically robust than crystalline materials, which is of importance for industrial applications. In this Account, we describe the preparation of aMOFs by introduction of disorder into their parent crystalline frameworks through heating, pressure (both hydrostatic and nonhydrostatic), and ball-milling. The main method of characterizing these amorphous materials (analysis of the pair distribution function) is summarized, alongside complementary techniques such as Raman spectroscopy. Detailed investigations into their properties (both chemical and mechanical) are compiled and compared with those of crystalline MOFs, while the impact of the field on the processing techniques used for crystalline MOF powders is also assessed. Crucially, the benefits amorphization may bring to existing proposed MOF applications are detailed, alongside the possibilities and research directions afforded by the combination of the unique properties of the amorphous domain with the versatility of MOF chemistry. PMID:24707980

Bennett, Thomas D; Cheetham, Anthony K

2014-05-20

312

New amorphous thin-film lithium electrolyte and rechargeable microbattery  

SciTech Connect

Sputtering of Li{sub 3}PO{sub 4} in pure N{sub 2} results in the formation of an amorphous lithium electrolyte that is stable in contact with lithium and has electrical properties that are suitable for application in a thin-film cell. Thin-film rechargeable lithium cells have been fabricated and characterized using this electrolyte between a lithium anode and an amorphous vanadium oxide cathode. The open circuit voltage of the cell is 3.6 to 3.7 V, and it has a capacity of 130 {mu}Ah/cm{sup 2} when discharged to 1.5 V. The ac impedance of the cells measured at different stages of discharge indicate a significant decrease in internal resistance at about the midpoint of the discharge.

Bates, J.B.; Gruzalski, G.R.; Dudney, N.J.; Luck, C.F.

1992-02-01

313

Structural Relaxation In Amorphous Materials  

Microsoft Academic Search

\\u000a In the glass transition region the molecular rearrangements slow down considerably. Then the macroscopic properties of the\\u000a amorphous material changes on a scale of minutes and they can easily be observed. If a such material is equilibrated at temperature\\u000a T\\u000a \\u000a o\\u000a in the glass transition region and then suddenly cooled to temperature T, the volume will change as shown in

J. Mállek; J. Shán?lová

314

Impedance spectroscopic analysis on effects of partial oxidation of TiN bottom electrode and microstructure of amorphous and crystalline HfO2 thin films on their bipolar resistive switching.  

PubMed

The electrical resistance switching (RS) properties of amorphous HfO2 (a-HfO2) and crystalline HfO2 (c-HfO2) thin films grown on a TiN substrate via atomic layer deposition were examined using DC current-voltage (I-V) sweep and AC impedance spectroscopic (IS) analyses. The rapid thermal annealing of the a-HfO2 film at 500 °C under a N2 atmosphere for 5 min crystallized the HfO2 film and induced an interfacial TiON barrier layer. The a-HfO2 sample showed fluent bipolar RS performance with a high on/off ratio (? 500), whereas the c-HfO2 sample showed a much lower on/off ratio (

Yoon, Ji-Wook; Yoon, Jung Ho; Lee, Jong-Heun; Hwang, Cheol Seong

2014-06-21

315

Impedance spectroscopic analysis on effects of partial oxidation of TiN bottom electrode and microstructure of amorphous and crystalline HfO2 thin films on their bipolar resistive switching  

NASA Astrophysics Data System (ADS)

The electrical resistance switching (RS) properties of amorphous HfO2 (a-HfO2) and crystalline HfO2 (c-HfO2) thin films grown on a TiN substrate via atomic layer deposition were examined using DC current-voltage (I-V) sweep and AC impedance spectroscopic (IS) analyses. The rapid thermal annealing of the a-HfO2 film at 500 °C under a N2 atmosphere for 5 min crystallized the HfO2 film and induced an interfacial TiON barrier layer. The a-HfO2 sample showed fluent bipolar RS performance with a high on/off ratio (~500), whereas the c-HfO2 sample showed a much lower on/off ratio (<~10), but its switching uniformity was better than that of a-HfO2. Such critical differences can be mainly attributed to the absence and presence of the TiON barrier layer in the a-HfO2 and c-HfO2 samples, respectively. The AC IS especially enabled the resistance states of the HfO2/Pt interface and the HfO2/TiN interface to be separately examined during one complete switching cycle of each sample. Although the Pt/c-HfO2 interface has a Schottky barrier in the pristine state, it disappeared once the c-HfO2 was electroformed and was not recovered even after the reset step. In contrast, the Pt/a-HfO2 interface partly recovered the Schottky barrier after the reset.

Yoon, Ji-Wook; Yoon, Jung Ho; Lee, Jong-Heun; Hwang, Cheol Seong

2014-05-01

316

Anodic oxidation of vanadium and properties of vanadium oxide films  

NASA Astrophysics Data System (ADS)

Thin films of amorphous vanadium oxide have been prepared by electrochemical anodic oxidation. The phase composition of anodic films on vanadium has been shown to depend on the oxidation conditions (electrolyte composition, oxidation current, and time), and the stoichiometry can be controlled from V O2 to V2O5. Physical properties of the oxide films, including the metal-insulator transition in amorphous V O2, are studied. In addition, it is shown that non-equilibrium electrochemical oxidation leads to the formation of metastable vanadium oxides with extremely high sensitivity to laser ({\\sim }1~{\\mathrm {mJ~cm^{-2}}} ) and electron-beam ({\\sim }10~\\micmu {\\mathrm {C~cm}}^{-2} ) irradiation. Such films are of considerable technical interest, particularly because of potential applications as an efficient resist material for both photonanolithography and electron-beam nanolithography.

Stefanovich, G. B.; Pergament, A. L.; Velichko, A. A.; Stefanovich, L. A.

2004-06-01

317

Crystallisation of crystallizable and amorphous polymer mixtures and peculiarities of their structure: an NMR study.  

PubMed

After isothermal crystallization of the crystallizable poly(ethylene oxide)/amorphous poly(propylene oxide) mixture, partially crystalline structures were formed. They present a specific heterogeneous medium with a hard frame composed of the crystal phase. The isothermal crystallization of the mixture and molecular self-diffusion processes in the amorphous phase of the crystallized mixture was studied by nuclear magnetic resonance relaxation and nuclear magnetic resonance (NMR) with pulsed field gradient. The temporal dependencies of the apparent self-diffusion coefficient were analyzed and the heterogeneity sizes were estimated. The dependence of the heterogeneity size on the crystallization temperature can be qualitatively described by parameter delta, which includes the linear growth rate of the crystal and diffusion coefficient of the amorphous (more mobile) component. PMID:9803925

Filippov, A V; Smirnov, V S; Doroginizkij, M M

1998-01-01

318

Amorphous lercanidipine hydrochloride and uses thereof  

US Patent & Trademark Office Database

The invention provides a substantially pure amorphous lercanidipine hydrochloride having a purity of at least 95% pure, preferably at least about 97% pure, more preferably at least about 99% pure, and still more preferably at least about 99.5% pure. The invention further relates to methods of preparing substantially pure amorphous lercanidipine, as well as methods of providing rapid relief from hypertension by administering the substantially pure amorphous lercanidipine hydrochloride of the present invention to a patient in need of such treatment.

2010-10-26

319

Selective laser sintering of amorphous metal powder  

Microsoft Academic Search

For the first time, selective sintering of amorphous PtCuNiP powder with a pulsed Nd:YAG laser has been studied. Upon pulsed interaction, the grains melt only superficially to build necks between the grains. Depending on the laser parameters, the sintered material can be crystallized or retained amorphous. By contrast with crystalline powder, laser sintering of amorphous powder is achieved at substantially

P. Fischer; A. Blatter; V. Romano; H. P. Weber

2005-01-01

320

Structure, cell response and biomimetic apatite induction of gradient TiO 2-based\\/nano-scale hydrophilic amorphous titanium oxide containing Ca composite coatings before and after crystallization  

Microsoft Academic Search

Chemical treatment was used to modify the surface of microarc oxidized (MAO) coating containing Ca and P. And the chemically treated MAO (C-MAO) coating was further heat-treated at 400–800°C. The average roughness of the MAO and C-MAO coatings is about 250nm; further heat treatment improved the roughness of the C-MAO coating. The chemical and heat treatment enhanced the wetting ability

Daqing Wei; Yu Zhou; Chunhui Yang

2009-01-01

321

Chromic mechanism in amorphous WO{sub 3} films  

SciTech Connect

The authors propose a new model for the chromic mechanism in amorphous tungsten oxide films (WO{sub 3{minus}y}{center_dot}nH{sub 2}O). This model not only explains a variety of seemingly conflicting experimental results reported in the literature that cannot be explained by existing models, it also has practical implications with respect to improving the coloring efficiency and durability of electrochromic devices. According to this model, a typical as-deposited tungsten oxide film has tungsten mainly in W{sup 6+} and W{sup 4+} states and can be represented as W{sub 1{minus}y}{sup 6+} W{sub y}{sup 4+}O{sub 3{minus}y}{center_dot}nH{sub 2}O. The proposed chromic mechanism is based on the small polaron transition between the charge-induced W{sup 5+} state and the original W{sup 4+} state instead of the W{sup 5+} and W{sup 6+} states as suggested in previous models. The correlation between the electrochromic and photochromic behavior in amorphous tungsten oxide films is also discussed.

Zhang, J.G.; Benson, D.K.; Tracy, C.E.; Deb, S.K.; Czanderna, A.W. [National Renewable Energy Lab., Golden, CO (United States)] [National Renewable Energy Lab., Golden, CO (United States); Bechinger, C. [Universitaet Konstanz (Germany)] [Universitaet Konstanz (Germany)

1996-11-01

322

Amorphous silicon based radiation detectors  

SciTech Connect

We describe the characteristics of thin(1 {mu}m) and thick (>30{mu}m) hydrogenated amorphous silicon p-i-n diodes which are optimized for detecting and recording the spatial distribution of charged particles, x-rays and {gamma} rays. For x-ray, {gamma} ray, and charged particle detection we can use thin p-i-n photosensitive diode arrays coupled to evaporated layers of suitable scintillators. For direct detection of charged particles with high resistance to radiation damage, we use the thick p-i-n diode arrays. 13 refs., 7 figs.

Perez-Mendez, V.; Cho, G.; Drewery, J.; Jing, T.; Kaplan, S.N.; Qureshi, S.; Wildermuth, D. (Lawrence Berkeley Lab., CA (United States)); Fujieda, I.; Street, R.A. (Xerox Palo Alto Research Center, CA (United States))

1991-07-01

323

Optimization of Conductivity and Transparency in Amorphous In-Zn-O Transparent Conductors: Preprint  

SciTech Connect

Amorphous mixed metal oxide TCOs are of increasing interest due to the excellent opto-electronic properties and smoothness (RRMS < 0.5 nm) obtained for sputtered films deposited at less than 100 ..deg..C. Here, we have investigated the combined materials phase space of oxygen stoichiometry and metals composition (In:Zn ratio) and made two key discoveries.

Perkins, J.; Berry, J.; van Hest, M.; Alleman, J.; Dabney, M.; Gedvilas, L.; Ginley, D. S.; Leenheer, A.; O'Hayre, R.

2008-05-01

324

Fabrication of transparent conducting amorphous Zn–Sn–In–O thin films by direct current magnetron sputtering  

Microsoft Academic Search

Amorphous ZnO–SnO2–In2O3 films were grown by direct current magnetron sputtering from vacuum hot pressed ceramic oxide targets of Zn:In:Sn cation ratios 1:2:1 and 1:2:1.5 onto glass substrates. X-ray diffraction analysis showed that the microstructure remained amorphous during annealing at 200 °C for up to 5 hours. By monitoring the electrical resistivity, oxygen content and substrate temperature were optimized during deposition. The optimal

Cleva W. Ow-Yang; Hyo-young Yeom; David C. Paine

2008-01-01

325

Transformation evolution and infrared absorption spectra of amorphous and crystalline nano-Al 2O 3 powders  

Microsoft Academic Search

Amorphous and crystalline nano-Al2O3 powders were prepared by direct oxidation and hydrolysis of pure aluminum, respectively. The results by XRD and DTA measurements revealed that after annealing at 1370 K, the evolution in the amorphous nano-Al2O3 powder involved a low temperature relaxation followed by a simple ?- to ?-Al2O3 transition. On the other hand, the ?- to ?- to ?-A2O3

T. S. Gu; G. M. Lin

1997-01-01

326

In situ analysis of aluminum enhanced crystallization of hydrogenated amorphous silicon (aSi:H) using X-ray diffraction  

Microsoft Academic Search

Deposition of polysilicon at low temperatures is important for the low cost production of electronic devices, especially solar cells and active matrix liquid crystal displays (AMLCD). In this paper in situ X-ray diffraction studies of aluminum enhanced crystallization of hydrogenated amorphous silicon (a-Si:H) at low temperatures is reported. Hydrogenated amorphous silicon films were deposited on oxidized silicon substrates. Aluminum was

F. A Khalifa; H. A Naseem; J. L Shultz; W. D Brown

1999-01-01

327

Magnetic and Structural Characteristics of Amorphous and Crystalline alpha-Al2O3 High TC Superconductors  

Microsoft Academic Search

The amorphous and crystalline alpha-Al2O3 oxides were investigated from magnetic and structural point of view. The temperature dependence of the magnetic susceptibility experiences double diamagnetic transition. First diamagnetic-paramagnetic transition is connected with the superconductor-paramagnetic transition, and the second is connected with the diamagnetic-normal state transition of alpha-Al2O3-amorphous and crystalline phase. The crystalline alpha-Al2O3 phase has the critical temperature Tc(chi =

Iuliu Pop; Camelia Oprea; Ioan Burda; Olivia Pop

1997-01-01

328

Catalytic applications of amorphous alloys: Expectations, achievements, and disappointments  

NASA Astrophysics Data System (ADS)

This review intends to summarize the major achievements in the application of amorphous alloys as precursors of catalyst materials. This non-traditional catalyst preparation method may provide supported catalysts with novel chemical and structural properties. Selected examples for both glassy alloy precursors and those fabricated by mechanochemistry include CO oxidation over binary and ternary alloys, dehydrogenation over Cu-M (M = Ti, Zr or Hf), one-step synthesis of methyl isobutyl ketone, and selective hydrogenation of unsaturated carbonyl compounds. Ni alloys for methanation developed for the project to solve global warming by recycling carbon dioxide are also discussed.

Molnár, Árpád

2011-07-01

329

Nonclassical crystallization of amorphous iron nanoparticles by radio frequency methods  

NASA Astrophysics Data System (ADS)

Amorphous iron nanoparticles were synthesized using an aqueous reduction in iron(II) sulfate with sodium borohydride and sodium citrate. Various radio frequency (rf) exposure times were investigated in order to determine trends in nonclassical crystallization. RF times from 15 to 300 s revealed an increase in crystallite size from 5 to 60 nm, as determined by powder x-ray diffraction. Also, solvent optimization revealed that ethanol produced the largest trends for increasing crystallite size without total oxidation of the samples. Magnetic characterization by room temperature vibrating sample magnetometry and high resolution transmission microscopy was performed to verify magnetic properties and particle morphology.

Carroll, K. J.; Pitts, J. A.; Zhang, Kai; Pradhan, A. K.; Carpenter, E. E.

2010-05-01

330

XRD Technique: A way to disseminate structural changes in iron-based amorphous materials  

SciTech Connect

Prevention of corrosion is a vital goal for the Department of Defense when billions of dollars are spent every year. Corrosion resistant materials have applications in all sort of military vehicles, and more importantly in naval vessels and submarines which come in contact with the seawater. It is known that corrosion resistance property can be improved by the used of structurally designed materials in the amorphous state where the atoms are arranged in a non-periodic fashion and specific atoms, tailored to the required properties can be interjected into the matrix for specific application. The XRD techniques reported here is to demonstrate the optimal conditions for characterization of these materials. The samples, which normally contain different compositions of Fe, Cr, B, Mo, Y, Mn, Si and W, are in the form of powders, ribbons and coatings. These results will be compared for the different forms of the sample which appears to correlate to the cooling rate during sample processing. In most cases, the materials are amorphous or amorphous with very small amount of crystallinity. In the ribbon samples for different compositions we observed that the materials are essentially amorphous. In most cases, starting from an amorphous powder sample, the coatings are also observed to be amorphous with a small amount of iron oxide on the surface, probably due to exposure to air.

Saw, C K; Lian, T; Day, D; Farmer, J

2007-05-24

331

Hydrogen effusion from tritiated amorphous silicon  

NASA Astrophysics Data System (ADS)

Results for the effusion and outgassing of tritium from tritiated hydrogenated amorphous silicon (a-Si:H:T) films are presented. The samples were grown by dc-saddle field glow discharge at various substrate temperatures between 150 and 300 °C. The tracer property of radioactive tritium is used to detect tritium release. Tritium effusion measurements are performed in a nonvacuum ion chamber and are found to yield similar results as reported for standard high vacuum technique. The results suggest for decreasing substrate temperature the growth of material with an increasing concentration of voids. These data are corroborated by analysis of infrared absorption data in terms of microstructure parameters. For material of low substrate temperature (and high void concentration) tritium outgassing in air at room temperature was studied, and it was found that after 600 h about 0.2% of the total hydrogen (hydrogen+tritium) content is released. Two rate limiting processes are identified. The first process, fast tritium outgassing with a time constant of 15 h, seems to be related to surface desorption of tritiated water (HTO) with a free energy of desorption of 1.04 eV. The second process, slow tritium outgassing with a time constant of 200-300 h, appears to be limited by oxygen diffusivity in a growing oxide layer. This material of lowest H stability would lose half of the hydrogen after 60 years.

Kherani, N. P.; Liu, B.; Virk, K.; Kosteski, T.; Gaspari, F.; Shmayda, W. T.; Zukotynski, S.; Chen, K. P.

2008-01-01

332

Photoemission Studies on Bulk Amorphous Steels  

NASA Astrophysics Data System (ADS)

The recent availability of bulk amorphous metals (BMGs) promises interesting new applications for the near future based on the superior structural, physical, and chemical properties of such materials compared to conventional steels. In order to shed light on local atomic and electronic structure photoemission studies have been performed on BMGs containing Fe, Cr, Mo, C, B, and Er. Progressing from ternary to penternary alloys we studied changes in the local electronic environment in a systematic manner by means of core-level and valence band spectroscopy. Step-by-step ion irradiation revealed differences in surface and bulk elemental composition and bonding. In particular the bonding state of B changes from oxide (surface) to boride (bulk). Iron exhibits the most prominent spectral changes of all the metal constituents, showing significantly higher core-level binding energies in penternary alloys than in ternary and quaternary compounds. Investigations of the Fe 3s multiplet splitting indicates a dependence of the splitting energy on the abundance of erbium in the alloy. Future experiments will focus on bulk material properties by preparing alloy surfaces in vacuum and addressing the constituents' chemical environment in more detail.

Buettner, Michael; Mun, B. Simon; Oelhafen, Peter; Reinke, Petra

2007-03-01

333

Amorphous silicon optical waveguides and Bragg mirrors  

NASA Astrophysics Data System (ADS)

We study 200 nm thick hydrogenated amorphous silicon (a-Si:H) optical strip waveguides fabricated by Plasma Enhanced Chemical Vapor Deposition (PECVD) technique over PECVD silicon oxide on top of standard silicon wafer. The layer of a-Si:H is etched by Reactive Ion Etching (RIE). The ability to deposit a-Si:H at low temperatures (~250°C) by PECVD renders it a promising material for integration of optical waveguides with microelectronics. Waveguides with width varying from 2 ?m to 10 ?m exhibit low loss. Material refractive index data of a-Si:H is measured by reflectometry and is used in simulations. A high refractive index contrast between a-Si:H and air allows tight optical confinement of modes. We demonstrate Bragg gratings fabricated by e-beam writing technology on top of the waveguides. The period of the grating is approximately 300 nm and the depth of the grooves is about 30 nm. The grating on top of the waveguide act as mirror.

Khanna, A.; Mulot, M.; Arpiainen, S.; Säynätjoki, A.; Ahopelto, J.; Honkanen, S.; Lipsanen, H.

2008-05-01

334

Structural Studies of Amorphous Polyaniline Films  

NASA Astrophysics Data System (ADS)

Polyaniline (PANI) is a versatile conducting polymer well-known for its diversity of structural forms, facile doping methodologies (especially through acid-base chemistry) and extensive range of potential applications. This talk focuses on x-ray scattering studies which probe the local (1Å to 10Åmolecular structure and structural evolution within amorphous polyaniline films in both the emeraldine base (EB) oxidation state and after protonic acid doping to yield the emeraldine salt (ES) form. Using radial distribution function analysis of this x-ray scattering data in combination with linked-atom structure factor refinement schemes it is possible to ascertain key components of the PANI main chain structure and that of the interchain packing. In general, the intrachain ordering is found to be significantly better than that of the interchain structure. Halogenic acid doping to give ES is found to yield discernable changes in both the intrachain and interchain structures. Furthermore, refinement of anomalous scattering data (in the case of HBr doping) enables a partial determination of the halogen acid anion location within the PANI host matrix. These findings shed light on the doping-induced variations of important physical properties in these films including charge and mass transport. Work supported by the National Science Foundation through DMR Grant No. 9305289.

Winokur, Michael J.

1996-03-01

335

Fluorination of amorphous thin-film materials with xenon fluoride  

DOEpatents

A method is disclosed for producing fluorine-containing amorphous semiconductor material, preferably comprising amorphous silicon. The method includes depositing amorphous thin-film material onto a substrate while introducing xenon fluoride during the film deposition process.

Weil, R.B.

1987-05-01

336

Fluorination of amorphous thin-film materials with xenon fluoride  

DOEpatents

A method is disclosed for producing fluorine-containing amorphous semiconductor material, preferably comprising amorphous silicon. The method includes depositing amorphous thin-film material onto a substrate while introducing xenon fluoride during the film deposition process.

Weil, Raoul B. (Haifa, IL) [Haifa, IL

1988-01-01

337

Oxygen diffusion through Al-doped amorphous SiO 2  

Microsoft Academic Search

Oxygen (O) diffusion through pure and aluminum (Al)-doped amorphous silica is investigated by using secondary ion mass spectrometry\\u000a to profile the diffusion of an18O tracer. The oxides are formed by the thermal oxidation of polymer-derived SiCN and SiAlCN ceramics. The authors demonstrate\\u000a that a small amount of Al dopant can significantly inhibit both the interstitial and network diffusion of O.

Yiguang Wang; Yongho Sohn; Linan An; Yi Fan; Ligong Zhang

2006-01-01

338

Crystallization of amorphous silicon thin films using nanoenergetic intermolecular materials with buffer layers  

Microsoft Academic Search

Optimization of the crystallization of amorphous silicon (a-Si) using a mixture of nanoenergetic materials of iron oxide\\/aluminum (Fe2O3\\/Al) was studied. To achieve high-quality polycrystalline Si (poly-Si) thin films, silicon oxide (SiO2) and silver (Ag) layer were deposited on the a-Si as buffer layers to prevent the metal diffusion in a-Si during thermite reaction and to transport the thermal energy released

Choong Hee Lee; Tae Hoon Jeong; Do Kyung Kim; Woong Hee Jeong; Myung-Koo Kang; Tae Hyung Hwang; Hyun Jae Kim

2009-01-01

339

Magneto-optical effect spectra of rare-earth-transition-metal amorphous films  

Microsoft Academic Search

Some results of the magneto-optical effect spectra of rare-earth-transition-metal amorphous films are presented. These results suggest that the polarity reversal of the Kerr hysteresis loops on the surface of the films after annealing with limited oxidation is sometimes not due to the magnetic origin but may be mainly due to the change of the optical properties of the oxide surface

D. F. Shen; T. Numata; Y. Sakurai; K. Sato

1983-01-01

340

Ductile crystalline-amorphous nanolaminates  

PubMed Central

It is known that the room-temperature plastic deformation of bulk metallic glasses is compromised by strain softening and shear localization, resulting in near-zero tensile ductility. The incorporation of metallic glasses into engineering materials, therefore, is often accompanied by complete brittleness or an apparent loss of useful tensile ductility. Here we report the observation of an exceptional tensile ductility in crystalline copper/copper–zirconium glass nanolaminates. These nanocrystalline–amorphous nanolaminates exhibit a high flow stress of 1.09 ± 0.02 GPa, a nearly elastic-perfectly plastic behavior without necking, and a tensile elongation to failure of 13.8 ± 1.7%, which is six to eight times higher than that typically observed in conventional crystalline–crystalline nanolaminates (<2%) and most other nanocrystalline materials. Transmission electron microscopy and atomistic simulations demonstrate that shear banding instability no longer afflicts the 5- to 10-nm-thick nanolaminate glassy layers during tensile deformation, which also act as high-capacity sinks for dislocations, enabling absorption of free volume and free energy transported by the dislocations; the amorphous–crystal interfaces exhibit unique inelastic shear (slip) transfer characteristics, fundamentally different from those of grain boundaries. Nanoscale metallic glass layers therefore may offer great benefits in engineering the plasticity of crystalline materials and opening new avenues for improving their strength and ductility.

Wang, Yinmin; Li, Ju; Hamza, Alex V.; Barbee, Troy W.

2007-01-01

341

Narrow Band Gap Amorphous Silicon Semiconductors.  

National Technical Information Service (NTIS)

Disclosed is a narrow band gap amorphous silicon semiconductor comprising an alloy of amorphous silicon and a band gap narrowing element selected from the group consisting of Sn, Ge, and Pb, with an electron donor dopant selected from the group consisting...

A. Madan A. H. Mahan

1985-01-01

342

Method of making amorphous metal composites  

DOEpatents

The process comprises placing an amorphous metal in particulate form and a low molecular weight (e.g., 1000-5000) thermosetting polymer binder powder into a container, mixing these materials, and applying heat and pressure to convert the mixture into an amorphous metal composite.

Byrne, Martin A. (Troy, NY); Lupinski, John H. (Scotia, NY)

1982-01-01

343

Electronic Structure of Amorphous Silicon Nanoclusters  

Microsoft Academic Search

The electronic structure of amorphous silicon nanoclusters is calculated within the empirical tight-binding approximation. The electronic states are classified into three groups: extended and weakly and strongly localized. The last category practically disappears in hydrogenated amorphous silicon clusters for which the blueshift is comparable to what is predicted for crystallites. The radiative recombination rates are comparable for small clusters \\\\(~1

G. Allan; C. Delerue; M. Lannoo

1997-01-01

344

Electron beam recrystallization of amorphous semiconductor materials  

NASA Technical Reports Server (NTRS)

Nucleation and growth of crystalline films of silicon, germanium, and cadmium sulfide on substrates of plastic and glass were investigated. Amorphous films of germanium, silicon, and cadmium sulfide on amorphous substrates of glass and plastic were converted to the crystalline condition by electron bombardment.

Evans, J. C., Jr.

1968-01-01

345

Ab initio prediction of amorphous B84.  

PubMed

To explore the possible existence of boron clusters without carbon analogs, we study B(84) cluster as a prototypical system by ab initio calculations. Structures of several isomer forms of B(84) are optimized. Among these isomers, a group of amorphous (disordered) structures are found to be the most stable. Different from the high-symmetry isomers, the amorphous B(84) clusters are more stable than the fullerene B(80) in terms of cohesive energy per atom. These amorphous structures can be distinguished from other high-symmetry structures experimentally via, for example, infrared spectra. The radial and angular distribution functions of amorphous B(84) structures are more diffuse than those of high-symmetry structures. On the basis of these findings, we propose that amorphous structures may be generic for boron and dominate boron clusters in a range of cluster scale. PMID:20095546

Shang, Bo; Yuan, Lan-Feng; Zeng, Xiao Cheng; Yang, Jinlong

2010-02-18

346

Compensated amorphous-silicon solar cell  

DOEpatents

An amorphous silicon solar cell including an electrically conductive substrate, a layer of glow discharge deposited hydrogenated amorphous silicon having regions of differing conductivity with at least one region of intrinsic hydrogenated amorphous silicon. The layer of hydrogenated amorphous silicon has opposed first and second major surfaces where the first major surface contacts the elecrically conductive substrate and an electrode for electrically contacting the second major surface. The intrinsic hydrogenated amorphous silicon region is deposited in a glow discharge with an atmosphere which includes not less than about 0.02 atom percent mono-atomic boron. An improved N.I.P. solar cell is disclosed using a BF/sub 3/ doped intrinsic layer.

Devaud, G.

1982-06-21

347

Amorphous Solid without Low Energy Excitations  

SciTech Connect

We have measured the low temperature internal friction (Q{sup -1}) of amorphous silicon (a-Si) films. {ital e}-beam evaporation or {sup 28}Si{sup +} implantation leads to the temperature-independent Q{sup -1}{sub 0} plateau common to all amorphous solids. For hydrogenated amorphous silicon with 1 at. {percent} H produced by hot wire chemical vapor deposition, however, Q{sup -1}{sub 0} is over 200 times smaller than for {ital e}-beam {ital a}-Si. This is the first observation of an amorphous solid without any significant low energy excitations. It offers the opportunity to study amorphous solids containing controlled densities of tunneling defects, and thus to explore their nature. {copyright} {ital 1997} {ital The American Physical Society}

Liu, X.; White, B.E. Jr.; Pohl, R.O. [Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853-2501 (United States)] [Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853-2501 (United States); Iwanizcko, E.; Jones, K.M.; Mahan, A.H.; Nelson, B.N.; Crandall, R.S. [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States)] [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States); Veprek, S. [Institute for Chemistry of Inorganic Materials, Tech.Univ.Munich, D-85747 Garching (Germany)] [Institute for Chemistry of Inorganic Materials, Tech.Univ.Munich, D-85747 Garching (Germany)

1997-06-01

348

Amorphous ice: density and reflectivity.  

PubMed

Amorphous ice prepared under a wide range of conditions has a density, determined from its buoyancy in liquid oxygen, of 0.94+/-0.02 gram per cubic centimeter, the same as that of ordinary hexagonal ice, with no indication of the glassy superdense ice (2.32 grams per cubic centimeter) reported recently. The diffuse reflectivity shows a small increase as the ice crystallizes at 153 degrees K. This increase is followed by a much larger increase (probably associated with crystal growth) as the sample warms, and the reflectivity reaches a maximum well below the melting temperature. Although the ice deposits appear translucent, the specular reflectivity is low, thus indicating a dull rather than a glassy surface. PMID:17737992

Ghormley, J A; Hochanadel, C J

1971-01-01

349

Research on stable, high-efficiency amorphous silicon multijunction modules  

NASA Astrophysics Data System (ADS)

This report describes a contract to produce multijunction modules based entirely on amorphous silicon alloys, the modules having an aperture area of at least 900 sq cm and a stable, reproducible conversion efficiency of at least 6.5 percent after 600 hours of light exposure (air mass 1.5) at 50 C. The work focussed on (1) producing opto-electronic-grade amorphous silicon material for band gaps of about 1.7 and 1.9 eV by changing the hydrogen content in the film bonded to the silicon, (2) studying and obtaining data on the light stability of single-junction p-i-n solar cells with gaps of about 1.7 and 1.9 eV, and (3) analyzing losses in a silicon/silicon multijunction cell. New results are reported on an indium tin oxide (ITO)/silver back contact and the deposition of granular tin oxide by atmospheric-pressure chemical vapor deposition. Progress toward module fabrication at the end of six months has been good, with the demonstration of 5.4 percent initial efficiency in a silicon/silicon multijunction submodule with an aperture area of 4620 sq cm and incorporating devices with 2nd-junction i-layer thicknesses of about 3500 A. A single-junction silicon submodule with an aperture area of 4620 sq cm, a thickness of about 3500 A, and an initial efficiency of 6.5 percent was demonstrated.

Bhat, P. K.; Brown, S.; Hollingsworth, R.; Shen, D. S.; Delcueto, J.; Iwanicko, E.; Marshall, C.; Dehart, C.; Mentor, D.; Benson, A.

1991-04-01

350

One-dimensional growth mechanism of amorphous boron nanowires  

NASA Astrophysics Data System (ADS)

High-density of arrays of self-oriented boron nanowires grown on silicon substrates were synthesized by radio-frequency magnetron sputtering with a target of highly pure boron and boron oxide mixture using argon as the sputtering atmosphere. TEM studies show that the conventional growth mechanisms such as Frank screw-dislocation mechanism and the vapor-liquid-solid mechanisms are not suitable for the one-dimensional growth of boron nanowires. The oxide-assisted cluster-solid mechanism for the Si and Ge crystalline nanowires is not completely suitable for our case. The vapor-cluster-solid mechanism is proposed for the well-aligned growth of the amorphous boron nanowires.

Wang, Y. Q.; Duan, X. F.; Cao, L. M.; Wang, W. K.

2002-06-01

351

Crystalline to amorphous transformation in silicon  

SciTech Connect

In the present investigation, an attempt was made to understand the fundamental mechanism of crystalline-to-amorphous transformation in arsenic implanted silicon using high resolution electron microscopy. A comparison of the gradual disappearance of simulated lattice fringes with increasing Frenkel pair concentration with the experimental observation of sharp interfaces between crystalline and amorphous regions was carried out leading to the conclusion that when the defect concentration reaches a critical value, the crystal does relax to an amorphous state. Optical diffraction experiments using atomic models also supported this hypothesis. Both crystalline and amorphous zones were found to co-exist with sharp interfaces at the atomic level. Growth of the amorphous fraction depends on the temperature, dose rate and the mass of the implanted ion. Preliminary results of high energy electron irradiation experiments at 1.2 MeV also suggested that clustering of point defects occurs near room temperature. An observation in a high resolution image of a small amorphous zone centered at the core of a dislocation is presented as evidence that the nucleation of an amorphous phase is heterogeneous in nature involving clustering or segregation of point defects near existing defects.

Cheruvu, S.M.

1982-09-01

352

Photonic crystals, amorphous materials, and quasicrystals  

NASA Astrophysics Data System (ADS)

Photonic crystals consist of artificial periodic structures of dielectrics, which have attracted much attention because of their wide range of potential applications in the field of optics. We may also fabricate artificial amorphous or quasicrystalline structures of dielectrics, i.e. photonic amorphous materials or photonic quasicrystals. So far, both theoretical and experimental studies have been conducted to reveal the characteristic features of their optical properties, as compared with those of conventional photonic crystals. In this article, we review these studies and discuss various aspects of photonic amorphous materials and photonic quasicrystals, including photonic band gap formation, light propagation properties, and characteristic photonic states.

Edagawa, Keiichi

2014-06-01

353

Electron beam cutting in amorphous alumina sheets  

SciTech Connect

We have found that nanometer diameter holes and slots can be cut in thin sheets of amorphous alumina using an intense electron beam. The holes, formed by a nonthermal process, are uniform in diameter, are surrounded by metallic aluminum, and can penetrate a 100-nm sheet in a few seconds. The amorphous alumina sheets are formed by anodization of electropolished high purity aluminum. The electron beam cutting seems very similar to the process reported in the metal ..beta..-aluminas. Since uniform, stable, and easily handled sheets of amorphous alumina can be fabricated and electron beam cut, this process is now practical for nanolithography as well as many other applications.

Mochel, M.E.; Eades, J.A.; Metzger, M.; Meyer, J.I.; Mochel, J.M.

1984-03-01

354

Latent ion tracks in amorphous silicon  

NASA Astrophysics Data System (ADS)

We present experimental evidence for the formation of ion tracks in amorphous Si induced by swift heavy-ion irradiation. An underlying core-shell structure consistent with remnants of a high-density liquid structure was revealed by small-angle x-ray scattering and molecular dynamics simulations. Ion track dimensions differ for as-implanted and relaxed Si as attributed to different microstructures and melting temperatures. The identification and characterization of ion tracks in amorphous Si yields new insight into mechanisms of damage formation due to swift heavy-ion irradiation in amorphous semiconductors.

Bierschenk, T.; Giulian, R.; Afra, B.; Rodriguez, M. D.; Schauries, D.; Mudie, S.; Pakarinen, O. H.; Djurabekova, F.; Nordlund, K.; Osmani, O.; Medvedev, N.; Rethfeld, B.; Ridgway, M. C.; Kluth, P.

2013-11-01

355

Comprehensive phase characterization of crystalline and amorphous phases of a Class F fly ash  

SciTech Connect

A comprehensive approach to qualitative and quantitative characterization of crystalline and amorphous constituent phases of a largely heterogeneous Class F fly ash is presented. Traditionally, fly ash composition is expressed as bulk elemental oxide content, generally determined by X-ray fluorescence spectroscopy. However, such analysis does not discern between relatively inert crystalline phases and highly reactive amorphous phases of similar elemental composition. X-ray diffraction was used to identify the crystalline phases present in the fly ash, and the Rietveld quantitative phase analysis method was applied to determine the relative proportion of each of these phases. A synergistic method of X-ray powder diffraction, scanning electron microscopy, energy dispersive spectroscopy, and multispectral image analysis was developed to identify and quantify the amorphous phases present in the fly ash.

Chancey, Ryan T., E-mail: rchancey@architecturalengineers.co [Nelson Architectural Engineers, Plano, TX 75093 (United States); Stutzman, Paul [National Institute for Standards and Technology, Gaithersburg, MD 20899 (United States); Juenger, Maria C.G.; Fowler, David W. [University of Texas at Austin, Austin, TX 78712 (United States)

2010-01-15

356

Dielectric enhancement in amorphous TaxGe1-xOy thin films  

NASA Astrophysics Data System (ADS)

We report that the dielectric constant can be increased in amorphous thin film TaxGe1-xOy over pure amorphous Ta2O5. With only 3% substitution of Ge for Ta the relative dielectric constant ?r rises to 30.5, a 40% increase over the value obtained for pure amorphous Ta2O5 films deposited under identical conditions (?r=22). No enhancement is observed in the optical dielectric constant (i.e., refractive index). This suggests that the enhancement is dominated by the effects in the ionic polarizability rather than the electronic polarizability. This system represents a valuable opportunity to explore the sensitive relationship between bonding and electronic properties in amophous oxides.

Naoi, Taro A.; Barron, Sara C.; Noginov, Maxim M.; van Dover, R. B.

2012-08-01

357

Pressure-induced amorphous-to-amorphous configuration change in Ca-Al metallic glasses  

PubMed Central

Pressure-induced amorphous-to-amorphous configuration changes in Ca-Al metallic glasses (MGs) were studied by performing in-situ room-temperature high-pressure x-ray diffraction up to about 40?GPa. Changes in compressibility at about 18?GPa, 15.5?GPa and 7.5?GPa during compression are detected in Ca80Al20, Ca72.7Al27.3, and Ca66.4Al33.6 MGs, respectively, whereas no clear change has been detected in the Ca50Al50 MG. The transfer of s electrons into d orbitals under pressure, reported for the pressure-induced phase transformations in pure polycrystalline Ca, is suggested to explain the observation of an amorphous-to-amorphous configuration change in this Ca-Al MG system. Results presented here show that the pressure induced amorphous-to-amorphous configuration is not limited to f electron-containing MGs.

Lou, H. B.; Fang, Y. K.; Zeng, Q. S.; Lu, Y. H.; Wang, X. D.; Cao, Q. P.; Yang, K.; Yu, X. H.; Zheng, L.; Zhao, Y. D.; Chu, W. S.; Hu, T. D.; Wu, Z. Y.; Ahuja, R.; Jiang, J. Z.

2012-01-01

358

Optimization of transparent and reflecting electrodes for amorphous-silicon solar cells. Final subcontract report, 1 May 1991--30 April 1994  

SciTech Connect

Fluorine-doped zinc oxide was shown to have the lowest absorption loss of any of the known transparent conductors. An apparatus was constructed to deposit textured, transparent, conductive, fluorine-doped zinc oxide layers with uniform thickness over a 10 cm by 10 cm area, using inexpensive, high-productivity atmospheric pressure chemical vapor deposition. Amorphous silicon solar cells grown on these textured films show very high peak quantum efficiencies (over 90%). However, a significant contact resistance develops at the interface between the amorphous silicon and the zinc oxide. Transparent, conductive gallium-doped zinc oxide films were grown by APCVD at a low enough temperature (260{degree}C) to be deposited on amorphous silicon as a final conductive back contact to solar cells. A quantum-mechanical theory of bonding was developed and applied to some metal oxides; it forms a basis for understanding TCO structures and the stability of their interfaces with silicon.

Gordon, R.G.; Hu, J.; Lacks, D.; Musher, J.; Thornton, J.; Liang, H. [Harvard Univ., Cambridge, MA (United States)

1994-07-01

359

Corrosion resistant amorphous metals and methods of forming corrosion resistant amorphous metals  

DOEpatents

A system for coating a surface comprises providing a source of amorphous metal, providing ceramic particles, and applying the amorphous metal and the ceramic particles to the surface by a spray. The coating comprises a composite material made of amorphous metal that contains one or more of the following elements in the specified range of composition: yttrium (.gtoreq.1 atomic %), chromium (14 to 18 atomic %), molybdenum (.gtoreq.7 atomic %), tungsten (.gtoreq.1 atomic %), boron (.ltoreq.5 atomic %), or carbon (.gtoreq.4 atomic %).

Farmer, Joseph C. (Tracy, CA); Wong, Frank M. G. (Livermore, CA); Haslam, Jeffery J. (Livermore, CA); Yang, Nancy (Lafayette, CA); Lavernia, Enrique J. (Davis, CA); Blue, Craig A. (Knoxville, TN); Graeve, Olivia A. (Reno, NV); Bayles, Robert (Annandale, VA); Perepezko, John H. (Madison, WI); Kaufman, Larry (Brookline, MA); Schoenung, Julie (Davis, CA); Ajdelsztajn, Leo (Walnut Creek, CA)

2009-11-17

360

Crystallization of amorphous solid films  

NASA Astrophysics Data System (ADS)

Below ˜130 K, H2O can exist for prolonged periods in a thermodynamically unstable, non-crystalline solid form known as amorphous solid water (ASW). When warmed to above 135 K, ASW crystallizes to the thermodynamically favored state, cubic ice I, on a laboratory time scale. Despite the relevance of ASW crystallization to a variety of scientific problems ranging from astrophysical phenomena to cryopreservation, the kinetics of this transformation are largely uncharacterized, and its mechanism is not fully understood. In the present work, the crystallization kinetics of vapor-deposited, nonporous ASW films less than one micron thick are investigated experimentally near 140 K. The amorphous to crystalline transition is characterized using a probe molecule, chlorodifluoromethane (CHF2Cl), whose adsorbed states and hence desorption kinetics are sensitive to the crystallinity of solid water surfaces. The transformation kinetics of very thick ASW films are found to be both independent of specimen size and consistent with simultaneous homogeneous nucleation and isotropic growth of crystalline ice grains. As the ASW film thickness is reduced from 385 nm to 55 nm, however, the rate of surface crystallization decelerates, in apparent conflict with a homogeneous nucleation and growth mechanism. In an attempt to explain this behavior, a geometrical model of phase transition kinetics at the surface of solids, with special consideration of finite specimen size in one dimension, is constructed. For materials in which nucleation occurs spatially randomly, phase change is predicted to decelerate when film thickness is reduced below the mean crystal grain size. This phenomenon originates from a reduction in the number of crystallites available to transform the surface as the sample becomes thinner. Good quantitative agreement between this simple model and the experimental data is attained using a minimum of kinetic parameters, suggesting it captures the essential physics of ASW crystallization. These model fits also yield preliminary estimates of crystalline ice growth and nucleation rates. Finally, an experimental protocol and corresponding model of phase change that together permit accurate quantification of nucleation and growth kinetics (when both processes occur simultaneously) is developed. Using the outlined methodology, crystalline ice growth and nucleation rates near 140 K are found to be ˜1 A/s and ˜1010 cm-3s -1, respectively, and to exhibit Arrhenius temperature dependencies with activation energies of ˜50 and ˜170 kJ/mol.

Safarik, Douglas Joseph

2003-06-01

361

Hydrogenated Amorphous Silicon-Germanium Alloys.  

National Technical Information Service (NTIS)

This report describes the effects of the germanium fraction in hydrogenated amorphous silicon-germanium alloys on various parameters, especially those that are indicators of film quality, and the impact of deposition methods, feedgas mixtures, and other d...

W. Luft

1988-01-01

362

The microscope structures of amorphous phosphorus  

NASA Astrophysics Data System (ADS)

The microscopic structures of thin films of amorphous phosphorus have been investigated by Raman scattering. The thin films were deposited by vacuum evaporation at substrate temperatures T s between 300 and 510K. The Raman spectra of the films were compared with vibrational spectra of different allotropes of phosphorus: orthohombic black P, bulk amorphous red P and Hittorf's P. The structure of the films with T s ? 300K is built up of double layers similar to those of orthorhombic black P. For T s?510K the thin films have a structure similar to bulk amorphous red P based on the pentagonal tubes of Hittorf's P. A continuous transformation from one structure to the other is indicated by the Raman spectra of the films at intermediate T s. The Raman measurements support early determinations of the structures of amorphous phosphorus inferred from radial distribution functions.

Olego, D. J.; Baumann, J. A.; Schachter, R.

1985-03-01

363

Medical imaging applications of amorphous silicon.  

National Technical Information Service (NTIS)

Two dimensional hydrogenated amorphous silicon (a-Si:H) pixel arrays are good candidates as flat-panel imagers for applications in medical imaging. Various performance characteristics of these imagers are reviewed and compared with currently used equipmen...

A. Mireshghi J. S. Drewery W. S. Hong T. Jing S. N. Kaplan

1994-01-01

364

Amorphous Semiconductor Thin Films, an Introduction  

SciTech Connect

The field of amorphous semiconductors is so large that I cannot do it justice, but I hope this short column gives you some insight into the properties and materials available, and the issues involved.

Martin, Peter M.

2003-12-01

365

Future of amorphous silicon photovoltaic technology.  

National Technical Information Service (NTIS)

Amorphous silicon modules are commercially available. They are the first truly commercial thin-film photovoltaic (PV) devices. Well-defined production processes over very large areas (>1 m(sup 2)) have been implemented. There are few environmental issues ...

R. Crandall W. Luft

1995-01-01

366

Amorphization and reduction of thermal conductivity in porous silicon by irradiation with swift heavy ions  

NASA Astrophysics Data System (ADS)

In this article, we demonstrate that the thermal conductivity of nanostructured porous silicon is reduced by amorphization and also that this amorphous phase in porous silicon can be created by swift (high-energy) heavy ion irradiation. Porous silicon samples with 41%-75% porosity are irradiated with 110 MeV uranium ions at six different fluences. Structural characterisation by micro-Raman spectroscopy and SEM imaging show that swift heavy ion irradiation causes the creation of an amorphous phase in porous Si but without suppressing its porous structure. We demonstrate that the amorphization of porous silicon is caused by electronic-regime interactions, which is the first time such an effect is obtained in crystalline silicon with single-ion species. Furthermore, the impact on the thermal conductivity of porous silicon is studied by micro-Raman spectroscopy and scanning thermal microscopy. The creation of an amorphous phase in porous silicon leads to a reduction of its thermal conductivity, up to a factor of 3 compared to the non-irradiated sample. Therefore, this technique could be used to enhance the thermal insulation properties of porous Si. Finally, we show that this treatment can be combined with pre-oxidation at 300 °C, which is known to lower the thermal conductivity of porous Si, in order to obtain an even greater reduction.

Newby, Pascal J.; Canut, Bruno; Bluet, Jean-Marie; Gomès, Séverine; Isaiev, Mykola; Burbelo, Roman; Termentzidis, Konstantinos; Chantrenne, Patrice; Fréchette, Luc G.; Lysenko, Vladimir

2013-07-01

367

Short channel device performance of amorphous InGaZnO thin film transistor  

NASA Astrophysics Data System (ADS)

Short channel device performance of deep-submicron gate length oxide thin film transistor (TFT) with amorphous InGaZnO (a-IGZO) active semiconductor is presented. Remarkable electrical properties of short channel oxide TFT were achieved utilizing crucial structure and material optimization such as self aligned gate structure with homo junction, multi-channel with rounded corners, and high-? gate dielectric. It was found that various device performance parameters of short channel-oxide TFTs were significantly influenced by materials, processes, and structural geometry, which should be more carefully designed.

Jeon, Sanghun; Benayad, Anass; Ahn, Seung-Eon; Park, Sungho; Song, Ihun; Kim, Changjung; Chung, U.-In

2011-08-01

368

Elastic properties of amorphous and nanocrystalline silicon  

Microsoft Academic Search

We review the present status of the elastic properties of amorphous silicon (a-Si) and germanium (a-Ge) thin films produced by either plasma-assisted chemical-vapor-deposition (PECVD) or hot-wire (cat) CVD (HWCVD). Using an extremely sensitive c-Si mechanical oscillator, we measure the low temperature oscillator damping for a variety of amorphous and nanocrystalline Si thin films deposited on the oscillator and thus determine

Richard S Crandall; Xiao Liu

2001-01-01

369

Tests Of Amorphous-Silicon Photovoltaic Modules  

NASA Technical Reports Server (NTRS)

Progress in identification of strengths and weaknesses of amorphous-silicon technology detailed. Report describes achievements in testing reliability of solar-power modules made of amorphous-silicon photovoltaic cells. Based on investigation of modules made by U.S. manufacturers. Modules subjected to field tests, to accelerated-aging tests in laboratory, and to standard sequence of qualification tests developed for modules of crystalline-silicon cells.

Ross, Ronald G., Jr.

1988-01-01

370

A magnetic sensor with amorphous wire.  

PubMed

Using a FeCoSiB amorphous wire and a coil wrapped around it, we have developed a sensitive magnetic sensor. When a 5 mm long amorphous wire with the diameter of 0.1 mm was used, the magnetic field noise spectrum of the sensor was about 30 pT/ÖHz above 30 Hz. To show the sensitivity and the spatial resolution, the magnetic field of a thousand Japanese yen was scanned with the magnetic sensor. PMID:24940865

He, Dongfeng; Shiwa, Mitsuharu

2014-01-01

371

A Magnetic Sensor with Amorphous Wire  

PubMed Central

Using a FeCoSiB amorphous wire and a coil wrapped around it, we have developed a sensitive magnetic sensor. When a 5 mm long amorphous wire with the diameter of 0.1 mm was used, the magnetic field noise spectrum of the sensor was about 30 pT/?Hz above 30 Hz. To show the sensitivity and the spatial resolution, the magnetic field of a thousand Japanese yen was scanned with the magnetic sensor.

He, Dongfeng; Shiwa, Mitsuharu

2014-01-01

372

Potential of amorphous silicon for solar cells  

Microsoft Academic Search

.   This paper reviews recent developments in the field of amorphous-silicon-based thin-film solar cells and discusses potentials\\u000a for further improvements. Creative efforts in materials research, device physics, and process engineering have led to highly\\u000a efficient solar cells based on amorphous hydrogenated silicon. Sophisticated multijunction solar cell designs make use of\\u000a its unique material properties and strongly suppress light induced degradation.

B. Rech; H. Wagner

1999-01-01

373

Amorphization of sapphire during ion beam mixing  

Microsoft Academic Search

Earlier studies indicated that implantation of zirconium into sapphire at room temperature produced an amorphous layer at a critical composition of approximately 6.5% (cation). Further insight into the amorphization of sapphire has been provided by ion beam mixing studies. Bi-layer couples of ~ 80 nm thick polycrystalline ZrO2 films deposited on the (0001) face of alpha-Al2O3 single crystals were irradiated

D. L. Joslin; C. J. McHargue; C. W. White; N. D. Evans

1994-01-01

374

Amorphization of sapphire during ion beam mixing  

Microsoft Academic Search

Earlier studies indicated that implantation of zirconium into sapphire at room temperature produced an amorphous layer at a critical composition of approximately 6.5% (cation). Further insight into the amorphization of sapphire has been provided by ion beam mixing studies. Bi-layer couples of approx. 80 nm thick polycrystalline ZrO2 films deposited on the (0001) face of alpha-Al2O3 single crystals were irradiated

D. L. Joslin; C. J. McHargue; C. W. White; N. D. Evans

1994-01-01

375

Can amorphization take place in nanoscale interconnects?  

PubMed

The trend of miniaturization has highlighted the problems of heat dissipation and electromigration in nanoelectronic device interconnects, but not amorphization. While amorphization is known to be a high pressure and/or temperature phenomenon, we argue that defect density is the key factor, while temperature and pressure are only the means. For nanoscale interconnects carrying modest current density, large vacancy concentrations may be generated without the necessity of high temperature or pressure due to the large fraction of grain boundaries and triple points. To investigate this hypothesis, we performed in situ transmission electron microscope (TEM) experiments on 200 nm thick (80 nm average grain size) aluminum specimens. Electron diffraction patterns indicate partial amorphization at modest current density of about 10(5) A cm(-2), which is too low to trigger electromigration. Since amorphization results in drastic decrease in mechanical ductility as well as electrical and thermal conductivity, further increase in current density to about 7 × 10(5) A cm(-2) resulted in brittle fracture failure. Our molecular dynamics (MD) simulations predict the formation of amorphous regions in response to large mechanical stresses (due to nanoscale grain size) and excess vacancies at the cathode side of the thin films. The findings of this study suggest that amorphization can precede electromigration and thereby play a vital role in the reliability of micro/nanoelectronic devices. PMID:22322399

Kumar, S; Joshi, K L; van Duin, A C T; Haque, M A

2012-03-01

376

Thorium sorption on amorphous silica  

NASA Astrophysics Data System (ADS)

The sorption of Th on amorphous colloidal particles of Si0 2 (Aerosil OX 200) has been studied in perchlorate media in order to obtain quantitative information on the sorption of The on silica. In order to quantify the pH dependence of the charge of the silica surface, potentiometric surface titrations of the silica particles have also been made. The results from the studies were modelled using a surface complexation model with a diffuse layer correction for electrostatic terms. The sorption and surface charge data can be explained by the following surface complexation reactions: ?Si0H ??SiO - + H + log Q aint=-6.9±0.1 2?SiOH + Th 4+ ? (?SiO) 2Th 2+ + 2H + log Q 1int = -1.9±0.4 The errors are given as three standard deviations in the fitted constants. According to model predictions, which are confirmed by literature data, the sorption of Th on silica will only be important in the pH range 3-6.

Östhols, Erik

1995-04-01

377

In Situ Laser Synthesis of Fe-Based Amorphous Matrix Composite Coating on Structural Steel  

NASA Astrophysics Data System (ADS)

Iron-based amorphous materials, owing to their very high hardness, elastic modulus, wear resistance, and corrosion resistance, can be potential materials for surface modification and engineering of many structural alloys. The current study focuses on a novel functional coating, synthesized via laser cladding of an iron-based (Fe48Cr15Mo14Y2C15B) amorphous precursor powder, on AISI 4130 steel substrate, using a continuous-wave diode-pumped ytterbium laser. The coatings were characterized by different techniques like X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). SEM and TEM studies indicated the presence of Fe-based nanocrystalline dendrites intermixed within an amorphous matrix. A three-dimensional thermal modeling approach based on COMSOL Multiphysics (COMSOL Inc., Burlington, MA) was used to approximately predict the temperature evolution and cooling rates achieved during laser processing. The mechanisms for the formation of crystalline phases and the morphological changes in the microstructure were studied based on the thermal model developed. Although the thermal model predicted substantially high cooling rates as compared to the critical cooling rate required for retaining an amorphous phase, the formation of crystalline phases is attributed to formation of yttrium oxide, reducing the glass-forming ability, and formation of different oxide phases that act as heterogeneous nucleation sites resulting in the composite microstructure.

Katakam, Shravana; Hwang, Jun Y.; Paital, Sameer; Banerjee, Rajarshi; Vora, Hitesh; Dahotre, Narendra B.

2012-12-01

378

From amorphous to crystalline silicon nanoclusters: structural effects on exciton properties  

NASA Astrophysics Data System (ADS)

Synchrotron x-ray absorption spectroscopy (XAS) and electron spin resonance (ESR) experiments were performed to determine, in combination with Raman spectroscopy and x-ray diffraction (XRD) data from previous reports, the structure and paramagnetic defect status of Si-nanoclusters (ncls) at various intermediate formation stages in Si-rich Si oxide films having different Si concentrations (y = 0.36-0.42 in SiyO1-y), fabricated by electron cyclotron resonance plasma-enhanced chemical vapor deposition and isochronally (2 h) annealed at various temperatures (Ta = 900-1100?°C) under either Ar or (Ar + 5%H2) atmospheres. The corresponding emission properties were studied by stationary and time dependent photoluminescence (PL) spectroscopy in correlation with the structural and defect properties. To explain the experimental data, we propose crystallization by nucleation within already existing amorphous Si-ncls as the mechanism for the formation of the Si nanocrystals in the oxide matrix. The cluster-size dependent partial crystallization of Si-ncls at intermediate Ta can be qualitatively understood in terms of a ‘crystalline core-amorphous shell’ Si-ncl model. The amorphous shell, which is invisible in most diffraction and electron microscopy experiments, is found to have an important impact on light emission. As the crystalline core grows at the expense of a thinning amorphous shell with increasing Ta, the PL undergoes a transition from a regime dominated by disorder-induced effects to a situation where quantum confinement of excitons prevails.

Borrero-González, L. J.; Nunes, L. A. O.; Guimarães, F. E. G.; Wojcik, J.; Mascher, P.; Gennaro, A. M.; Tirado, M.; Comedi, D.

2011-12-01

379

Radiation Response of Rhombohedral Oxides  

SciTech Connect

The radiation response of three rhombohedral oxides, namely, sapphire ({alpha}-Al{sub 2}O{sub 3}), ilmenite (FeTiO{sub 3}), and geikielite (MgTiO{sub 3}), has been examined by irradiating electron transparent samples with 1 MeV Kr(+) and 1.5 MeV Xe(+)ions. The microstructural changes during irradiation were observed in situ in a high-voltage electron microscope using electron diffraction and microscopy. The irradiation conditions were designed to minimize beam heating and chemical effects due to the implanted ion. Of the three oxides studied, ilmenite is the most susceptible to radiation-induced amorphization while sapphire is the least susceptible. In all three materials, the critical temperature for amorphization was below 300 K indicating good room temperature resistance to amorphization by energetic beams.

Devanathan, R.; Weber, W.J. [Pacific Northwest National Lab., Richland, WA (United States); Mitchell, J.N.; Sickafus, K.E.; Nastasi, M. [Los Alamos National Lab., NM (United States)

1997-12-31

380

Amorphous silica nanoparticles impair vascular homeostasis and induce systemic inflammation.  

PubMed

Amorphous silica nanoparticles (SiNPs) are being used in biomedical, pharmaceutical, and many other industrial applications entailing human exposure. However, their potential vascular and systemic pathophysiologic effects are not fully understood. Here, we investigated the acute (24 hours) systemic toxicity of intraperitoneally administered 50 nm and 500 nm SiNPs in mice (0.5 mg/kg). Both sizes of SiNPs induced a platelet proaggregatory effect in pial venules and increased plasma concentration of plasminogen activator inhibitor-1. Elevated plasma levels of von Willebrand factor and fibrinogen and a decrease in the number of circulating platelets were only seen following the administration of 50 nm SiNPs. The direct addition of SiNPs to untreated mouse blood significantly induced in vitro platelet aggregation in a dose-dependent fashion, and these effects were more pronounced with 50 nm SiNPs. Both sizes of SiNPs increased lactate dehydrogenase activity and interleukin 1? concentration. However, tumor necrosis factor ? concentration was only increased after the administration of 50 nm SiNPs. Nevertheless, plasma markers of oxidative stress, including 8-isoprostane, thiobarbituric acid reactive substances, catalase, and glutathione S-transferase, were not affected by SiNPs. The in vitro exposure of human umbilical vein endothelial cells to SiNPs showed a reduced cellular viability, and more potency was seen with 50 nm SiNPs. Both sizes of SiNPs caused a decrease in endothelium-dependent relaxation of isolated small mesenteric arteries. We conclude that amorphous SiNPs cause systemic inflammation and coagulation events, and alter vascular reactivity. Overall, the effects observed with 50 nm SiNPs were more pronounced than those with 500 nm SiNPs. These findings provide new insight into the deleterious effect of amorphous SiNPs on vascular homeostasis. PMID:24936130

Nemmar, Abderrahim; Albarwani, Sulayma; Beegam, Sumaya; Yuvaraju, Priya; Yasin, Javed; Attoub, Samir; Ali, Badreldin H

2014-01-01

381

Amorphous silica nanoparticles impair vascular homeostasis and induce systemic inflammation  

PubMed Central

Amorphous silica nanoparticles (SiNPs) are being used in biomedical, pharmaceutical, and many other industrial applications entailing human exposure. However, their potential vascular and systemic pathophysiologic effects are not fully understood. Here, we investigated the acute (24 hours) systemic toxicity of intraperitoneally administered 50 nm and 500 nm SiNPs in mice (0.5 mg/kg). Both sizes of SiNPs induced a platelet proaggregatory effect in pial venules and increased plasma concentration of plasminogen activator inhibitor-1. Elevated plasma levels of von Willebrand factor and fibrinogen and a decrease in the number of circulating platelets were only seen following the administration of 50 nm SiNPs. The direct addition of SiNPs to untreated mouse blood significantly induced in vitro platelet aggregation in a dose-dependent fashion, and these effects were more pronounced with 50 nm SiNPs. Both sizes of SiNPs increased lactate dehydrogenase activity and interleukin 1? concentration. However, tumor necrosis factor ? concentration was only increased after the administration of 50 nm SiNPs. Nevertheless, plasma markers of oxidative stress, including 8-isoprostane, thiobarbituric acid reactive substances, catalase, and glutathione S-transferase, were not affected by SiNPs. The in vitro exposure of human umbilical vein endothelial cells to SiNPs showed a reduced cellular viability, and more potency was seen with 50 nm SiNPs. Both sizes of SiNPs caused a decrease in endothelium-dependent relaxation of isolated small mesenteric arteries. We conclude that amorphous SiNPs cause systemic inflammation and coagulation events, and alter vascular reactivity. Overall, the effects observed with 50 nm SiNPs were more pronounced than those with 500 nm SiNPs. These findings provide new insight into the deleterious effect of amorphous SiNPs on vascular homeostasis.

Nemmar, Abderrahim; Albarwani, Sulayma; Beegam, Sumaya; Yuvaraju, Priya; Yasin, Javed; Attoub, Samir; Ali, Badreldin H

2014-01-01

382

Origin of ferromagnetism enhancement in bi-layer chromium-doped indium zinc oxides  

NASA Astrophysics Data System (ADS)

This work demonstrates that by controlling the rapid thermal annealing temperature, amorphous chromium-doped indium zinc oxide films develop an amorphous-crystalline bi-layer structure and show magnetization up to ~30 emu/cm3. The crystalline layer arises from significant out-diffusion of Zn from surfaces, leading to a large difference in the Zn:In ratio in amorphous and crystalline layers. Doped Cr ions in amorphous and crystalline layers form different valence configurations, creating a charge reservoir which transfers electrons through amorphous-crystalline interfaces and in turn enhances ferromagnetism.

Hsu, C. Y.

2012-08-01

383

Drift mobilities in amorphous silicon  

SciTech Connect

The author studied the nonlinear effects of the electric field on the drift mobilities of both electrons and holes in a series of undoped hydrogenated amorphous silicon (a-Si:H) and silicon-germanium alloy specimens. The author measured the transient photocurrents in pin diode structures as a function of electric field and temperature. Time-of-flight and charge collection measurements were conducted from which we concluded that the quantum efficiency for photo-carrier generation varied less than 10% for all specimens in this temperature and electric field range. In all cases transport was dispersive, but no evidence for field-dependence of the dispersion itself was found. The characteristic electric field for the onset of nonlinear electron transport increased with Ge concentration. In a-Si:H the author found a slight evidence for nonlinear transport of holes. The author presents a photocharge transient technique which allowed probing of the drift of electrons in several undoped a-Si:H specimens. The author found a unique feature of the transient photocharge associated with the thermal emission of the trapped electrons, strongly indicating that recombination occurs well after deep-trapping. The temperature dependence of the emission time revealed the mean energy of the trap distribution and the attempt-to-escape frequency associated with this trap. The author analyzed transient photocurrent and time-of-flight measurements in undoped a-Si:H for photocarrier motion both parallel and perpendicular to the thin-film growth axis. The author found a good agreement of the electron drift-mobility measurements and the electron mobility-lifetime product estimates for the two field directions for fifteen specimens. The data exclude an electron transport anisotropy in a-Si:H greater than a factor of two.

Antoniadis, H.

1992-01-01

384

The photoluminescence in electrochemically oxidized porous silicon  

Microsoft Academic Search

Some oxidized porous silicon samples exhibit an amorphous phase with the approximate composition SiO1.6. The particular features of the photoluminescence spectra were tentatively ascribed to the contribution of the interface between silicon and the non-stoichiometric oxide

M. Popescu; V. Chumash; I. Cojocaru; S. Zamfira; V. K. Jain; A. Gupta

1995-01-01

385

Characterization of High- k Gate Dielectric with Amorphous Nanostructure  

NASA Astrophysics Data System (ADS)

In the present study, Zr x La1- x O y amorphous nanostructures were prepared by the sol-gel method such that the Zr atomic fraction ( x) ranged from 0% to 70%. An analytical model is described for the dielectric constant ( k) of Zr x La1- x O y nanostructures in a metal-oxide-semiconductor (MOS) device. The structure and morphology of Zr x La1- x O y film was studied using x-ray diffraction, scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. Elemental qualitative analysis was performed using energy-dispersive x-ray spectra and a map that confirmed the findings. Preliminary information on the influence of thermal annealing on the morphological control of Zr x La1- x O y amorphous nanostructures is presented. The dielectric constant of the crystalline Zr0.5La0.5O y thin film is about 36. Electrical property characterization was performed using a metal-dielectric-semiconductor structure via capacitance-voltage and current density-voltage measurements.

Bahari, Ali; Gholipur, Reza

2013-12-01

386

Electron-beam-assisted superplastic shaping of nanoscale amorphous silica  

PubMed Central

Glasses are usually shaped through the viscous flow of a liquid before its solidification, as practiced in glass blowing. At or near room temperature (RT), oxide glasses are known to be brittle and fracture upon any mechanical deformation for shape change. Here, we show that with moderate exposure to a low-intensity (<1.8×10?2 A cm?2) electron beam (e-beam), dramatic shape changes can be achieved for nanoscale amorphous silica, at low temperatures and strain rates >10?4 per second. We show not only large homogeneous plastic strains in compression for nanoparticles but also superplastic elongations >200% in tension for nanowires (NWs). We also report the first quantitative comparison of the load-displacement responses without and with the e-beam, revealing dramatic difference in the flow stress (up to four times). This e-beam-assisted superplastic deformability near RT is useful for processing amorphous silica and other conventionally-brittle materials for their applications in nanotechnology.

Zheng, Kun; Wang, Chengcai; Cheng, Yong-Qiang; Yue, Yonghai; Han, Xiaodong; Zhang, Ze; Shan, Zhiwei; Mao, Scott X; Ye, Miaomiao; Yin, Yadong; Ma, Evan

2010-01-01

387

The XRD Amorphous Component in John Klein Drill Fines at Yellowknife Bay, Gale Crater, Mars  

NASA Technical Reports Server (NTRS)

Drill fines of mudstone (targets John Klein and Cumberland) from the Sheepbed unit at Yel-lowknife Bay were analyzed by MSL payload elements including the Chemistry and Mineralogy (CheMin), APXS (Alpha Particle X-Ray Spectrometer), and Sample Analysis at Mars (SAM) instruments. CheMin XRD results show a variety of crystalline phases including feldspar, pyroxene, olivine, oxides, oxyhydroxides, sulfates, sulfides, a tri-octahedral smectite, and XRD amorphous material. The drill fines are distinctly different from corresponding analyses of the global soil (target Rocknest) in that the mudstone samples contained detectable phyllosilicate. Here we focus on John Klein and combine CheMin and APXS data to calculate the chemical composition and concentration of the amorphous component. The chemical composition of the amorphous plus smectite component for John Klein was calculated by subtracting the abundance-weighted chemical composition of the individual XRD crystalline components from the bulk composition of John Kline as measured by APXS. The chemical composition of individual crystalline components was determined either by stoichiometry (e.g., hematite and magnetite) or from their unit cell parameters (e.g., feldspar, olivine, and pyroxene). The chemical composition of the amorphous + smectite component (approx 71 wt.% of bulk sample) and bulk chemical composition are similar. In order to calculate the chemical composition of the amorphous component, a chemical composition for the tri-octahedral smectite must be assumed. We selected two tri-octahedral smectites with very different MgO/(FeO + Fe2O3) ratios (34 and 1.3 for SapCa1 and Griffithite, respectively). Relative to bulk sample, the concentration of amorphous and smectite components are 40 and 29 wt.% for SapCa1 and 33 and 36 wt.% for Griffithite. The amount of smectite was calculated by requiring the MgO concentration to be approx 0 wt.% in the amorphous component. Griffithite is the preferred smectite because the position of its 021 diffraction peak is similar to that reported for John Klein. In both cases, the amorphous component has low SiO2 and MgO and high FeO + Fe2O3, P2O5, and SO3 concentrations relative to bulk sample. The chemical composition of the bulk drill fines and XRD crystalline, smectite, and amorphous components implies alteration of an initially basaltic material under near neutral conditions (not acid sulfate), with the sulfate incorporated later as veins of CaSO4 injected into the mudstone.

Morris, Richard V.; Ming,, Douglas W.; Blake, David; Vaniman, David; Bish, David L; Chipera, Steve; Downs, Robert; Morrison, Shaunna; Gellert, Ralf; Campbell, Iain; Treiman, Alan H.; Achilles, Cherie; Bristow, Thomas; Crisp, Joy A.; McAdam, Amy; Archer, Paul Douglas; Sutter, Brad; Rampe, Elizabeth B.

2013-01-01

388

Surface smoothing effect of an amorphous thin film deposited by atomic layer deposition on a surface with nano-sized roughness  

NASA Astrophysics Data System (ADS)

Previously, Lau (one of the authors) pointed out that the deposition of an amorphous thin film by atomic layer deposition (ALD) on a substrate with nano-sized roughness probably has a surface smoothing effect. In this letter, polycrystalline zinc oxide deposited by ALD onto a smooth substrate was used as a substrate with nano-sized roughness. Atomic force microscopy (AFM) and cross-sectional transmission electron microscopy (XTEM) were used to demonstrate that an amorphous aluminum oxide thin film deposited by ALD can reduce the surface roughness of a polycrystalline zinc oxide coated substrate.

Lau, W. S.; Zhang, J.; Wan, X.; Luo, J. K.; Xu, Y.; Wong, H.

2014-02-01

389

Amorphous water-soluble derivatives of cyclodextrins: nontoxic dissolution enhancing excipients.  

PubMed

Dissolution properties of drugs may be improved by their conversion to an amorphous state or by complexation with cyclodextrins. The present report describes the preparation of cyclodextrin derivatives which are intrinsically amorphous, and water-soluble, and their use as complexation agents. Such derivatives were prepared by condensation of alpha-, beta-, or gamma-cyclodextrins with epoxides (propylene oxide, isobutylene oxide, epichlorohydrin, 1,4-butanediol diglycidyl ether). The condensation products effectively solubilized estradiol, progesterone, or testosterone in water; these solutions, upon freeze-drying, yielded solids which could be directly compressed to tablets which dissolve completely within minutes. Condensation products of cyclodextrins did not have any untoward or toxic effects when administered chronically to mice per os for a 16-week period. PMID:4067854

Pitha, J; Pitha, J

1985-09-01

390

Mechanisms and effects of wear on amorphous carbon thin films  

NASA Astrophysics Data System (ADS)

Amorphous carbon thin films, which are commonly used as protective layers for magnetic hard disks, experience wear during the operation of a hard disk. During sliding between these carbon films and the read-write head's slider tribochemical reactions occur, which have been predicted to remove carbon oxides. The tribochemical reactions have been investigated in this study through the use of a novel mass-spectroscopy tribotester. We have observed that the dominant species produced during sliding is COsb2, in both dry nitrogen and oxygen environments, and that the generation rate is ten times higher in oxygen. With the use of this tester, we have also investigated the effect of the slider material, which consists of alumina titanium-carbide (Alsb2Osb3-TiC), on the carbon dioxide evolution. By depositing a thin barrier coating of carbon (50A) on the slider surface, we found that the production of carbon dioxide was an order of magnitude lower than with uncoated sliders. Thermogravimetric analysis (TGA) of the slider material corroborates its role in enhancing the gasification of carbon. We have also explored the effect of wear on the microstructural features of carbon. With the aid of transmission electron spectroscopy (TEM) and electron-energy loss spectroscopy (EELS), we have found that the graphitic content of the amorphous carbon layer increases in the initial stages of wear. We also explored the temperatures achieved during sliding by comparing the microstructure of the worn carbon to that of unworn thermally-annealed carbon. Using additional techniques of Raman spectroscopy and NEXAFS, we found analogous less-randomly ordered microstructures at anneal temperatures of 300-500sp°C. We also explored the role of the magnetic layer (cobalt-platinum-chromium alloy) in the graphitization of amorphous carbon. With in situ heating and cooling TEM observations of the carbon/magnetic layer interface, we found that the microstructure of the carbon becomes more graphitic at low temperatures when in the presence of the magnetic layer. Crystallization temperatures of amorphous carbon, determined by calorimetry, occur in the range of 500-600sp°C when the carbon is in contact with this layer. TEM observations suggest carbon diffuses into the magnetic layer upon heating and precipitates as graphite upon cooling. We conclude that the wear mechanism includes frictional heating combined with metal-induced graphitization.

Ramirez, Ainissa Gweneth

391

Some correlations for duffusion in amorphous alloys  

SciTech Connect

Diffusion of several impurity atoms (Cu, Al, Au, and Sb) has been studied in Zr/sub 61/Ni/sub 39/ and Fe/sub 82/B/sub 18/ amorphous alloys. A definite correlation between the diffusion coefficient (D) and the atomic size of the diffusant is seen for the metal-metal (M-M) alloy, while it is not clear for the metal-metalloid (M-Me) alloy. Based on the present data, as well as other published data in binary amorphous alloys, empirical correlations have been found between (i) the activation energy (/ital Q/) and the energy required to form a hole of the size of the diffusing atom in the host alloy, and (ii) the pre-exponential factor (/ital D//sub 0/) and /ital Q/. While the former correlation is seen only for binary M-M type of amorphous alloys, the latter correlation is more general and holds for all types of amorphous alloys. Based on the correlation between /ital D//sub 0/ and /ital Q/, it is proposed that there are two distinct mechanisms of diffusion in amorphous alloys.

Sharma, S. K.; Banerjee, S.; Kuldeep; Jain, A. K.

1989-05-01

392

Offset for protection against amorphous pips  

SciTech Connect

This patent describes in an optical recording system including optical means for writing information on an optical recording medium, an improvement for affecting an amorphous pip representative of a portion of an optical recording medium that is in an amorphous state. It comprises: first means for receiving a read signal representative of information provided on the optical recording medium. The read signal including a first portion representative of an unchanged portion of the optical recording medium and a second portion having a pip representative of at least one of the following: a hole and an amorphous portion of the optical recording medium; and second means communicating with the first means for inputting an offset signal to the first means. The offset signal being representative of a pip produced by an amorphous portion of the optical recording medium. The first means includes means, using the offset signal, for affecting the second portion of the read signal and not other portions of the read signal, in order to prevent the second portion from being detected as a pip due to a hole when it is a pip due to an amorphous portion.

Bracht, R.R.; Verboom, J.J.

1989-11-21

393

Novel Internal Friction of Amorphous Solids  

NASA Astrophysics Data System (ADS)

Owing to the great sensitivity of the double-paddle oscillators, we have recently measured the low-temperature internal friction of amorphous silicon films (X. Liu, B. E. White, Jr., R. O. Pohl, E. Iwanizcko, K. M. Jones, A. H. Mahan, B. N. Nelson, R. S. Crandall, S. Veprek, Phys. Rev. Lett. 78), 4418 (1997). While e-beam evaporation, sputtering, or Si^+ ion implantation produce a-Si films with similar tunneling states as in all amorphous solids, hydrogenated a-Si films with 1 at.% H prepared by hot-wire chemical vapor deposition show no sign of any significant low energy excitations. This observation offers an exciting opportunity to study the structural origin of the low energy excitations common to amorphous solids. A possible explanation is that in the hydrogenated films the amorphous structure is closer to the fourfold coordinated continuous random network expected in amorphous Si, and thus the lattice is more constrained, resulting in the absence of tunneling states.

Liu, Xiao

1998-03-01

394

Silicon carbide amorphization by electron irradiation  

SciTech Connect

Observations made more than ten years ago showed that SiC could be made amorphous at cryogenic temperatures by in-situ 300kV electron irradiation. However, high voltage electron microscope (HVEM) results indicate a threshold voltage of 725 kV for amorphization of SiC at 140 K. In addition, a recent review exposes the considerable uncertainty in the literature regarding displacement energies for SiC. Therefore, further experiments have been performed in a Philips CM30 (LaB{sub 6} cathode) with a Gatan double-tilt cooling holder in an attempt to determine the threshold voltage for amorphization at {approximately} 140 K. Sintered {alpha}-SiC (defected 6H polytype), beam direction B = <11{bar 2}0>, and probes containing {approximately} 75 nA in {approximately} 0.5 {micro}m, were used. Amorphization occurred in <10 min at 300 kV and after {approximately} 60 min at 180 kV; visible darkening occurred at lower voltages and doses. Similar behavior occurred for B = [0001]. The critical dose for amorphization was measured as a function of accelerating voltage. Probe current profiles were measured by post-specimen scanning (CM30 SCIM mode with 100 {micro}m diameter Gatan STEM detector) images of the focused probes positioned in a hole, and probe currents were measured from the exposure time, which had previously been calibrated with a Faraday cup.

Bentley, J.

1998-02-01

395

A novel amorphous CoSnxOy decorated graphene nanohybrid photocatalyst for highly efficient photocatalytic hydrogen evolution.  

PubMed

A novel amorphous cobalt tin composite oxide decorated with graphene nanohybrid (CoSnxOy/G) sensitized by Eosin Y (EY) exhibited excellent photocatalytic hydrogen evolution activity (974.6 ?mol for 3 h) under visible light irradiation. The highest AQE of EY-CoSnxOy/G of 20.1% was achieved at 430 nm. PMID:24709900

Kong, Chao; Min, Shixiong; Lu, Gongxuan

2014-05-21

396

Fabrication and characterization of amorphous lithium electrolyte thin films and rechargeable thin-film batteries  

Microsoft Academic Search

Amorphous oxide and oxynitride lithium electrolyte thin films were synthesized by r.f. magnetron sputtering of lithium silicates and lithium phosphates in Ar, Ar + O2, Ar + N2, or N2. The composition, structure, and electrical properties of the films were characterized using ion and electron beam, X ray, optical, photoelectron, and a.c. impedance techniques. For the lithium phosphosilicate films, lithium

J. B. Bates; N. J. Dudney; G. R. Gruzalski; R. A. Zuhr; A. Choudhury; C. F. Luck; J. D. Robertson

1993-01-01

397

Processing Bi-Pb-Sr-Ca-Cu-O superconductors from amorphous state  

Microsoft Academic Search

Researchers produced superconducting ceramics of the Bi-Pb-Sr-Ca-Cu-O system started from a glass. To form the glass, the mixed oxide powder was melted at 1200 C in air. The liquid was quenched rapidly by pouring it onto an aluminum plate and rapidly pressing with another plate. The quenched compound was in the form of black amorphous solid, whose x-ray powder pattern

C. K. Chiang; S. W. Freiman; W. Wong-Ng; N. M. Hwang; A. J. Shapiro; M. D. Hill; L. P. Cook; R. D. Shull; L. J. Swartzendruber; L. H. Bennett

1990-01-01

398

A Electron Tunneling Study of TIN(1-X) Copper(x) Amorphous Thin Films  

Microsoft Academic Search

Amorphous Sn_{1-x}Cu _{x} thin films (0.08 <= x <= 0.41) were prepared by e-beam deposition onto a liquid helium temperature substrate in an ultra-high vacuum system to form tunnel junctions in an aluminum - aluminum oxide - superconductor configuration. Measurements of film resistance, transition temperature, crystallization temperature, and energy gap were made. The Eliashberg function, alpha^2F(omega), was derived from tunneling

Paul Willard Watson III

1993-01-01

399

Molecular dynamics study of structural properties of amorphous Al2O3  

Microsoft Academic Search

The structural properties of amorphous aluminum oxide (Al2O3) have been investigated by means of the molecular dynamics technique. The simulations were done in a microcanonical ensemble, using a pairwise potential, on systems with up to 1800 particles. Three different systems, at densities ranging from 3.0 to 3.3 g\\/cm3, were prepared by quenching from the melt. The network topology of our

Gonzalo Gutiérrez; Börje Johansson

2002-01-01

400

Template confined synthesis of amorphous carbon nanotubes and its confocal Raman microscopy  

NASA Astrophysics Data System (ADS)

Amorphous carbon nanotubes (aCNTs) were synthesized by AAO (anodic aluminum oxide) template at a temperature 500 °C in nitrogen atmosphere using the citric acid as a carbon source without the help of any catalyst particles. Morphological analysis of the as prepared samples was carried out by field emission scanning electron microscopy (FESEM). Confocal Raman imaging has been studied and an attempt has been made to find out the graphitic (sp2) and disordered phase of the CNTs.

Maity, Supratim; Roychowdhury, Tuhin; Chattopadhyay, Kalyan Kumar

2014-04-01

401

Optimization of ZnO Films for Amorphous Silicon Solar Cells  

Microsoft Academic Search

ZnO films prepared by the metalorganic chemical vapor deposition (MOCVD) method were applied to amorphous silicon (a-Si) solar cells as a transparent conductive oxide (TCO). The B2H6 flow rate and the thickness of the film were optimized at 0.5 mumol\\/min and 2.0 mum, respectively. We also proposed a preannealing technique of the ZnO film before fabrication of a-Si solar cells,

Katsuya Tabuchi; Wilson W. Wenas; Akira Yamada; Makoto Konagai; Kiyoshi Takahashi

1993-01-01

402

Characterization of Amorphous High-k Thin Films by EXAFS and GIXS  

SciTech Connect

Silicon and nitrogen incorporated Hf oxide (HfSiON) is considered to be a promising alternative gate insulator for next-generation MOSFETs. EXAFS and GIXS (Grazing Incidence X-ray Scattering) have been applied to the characterization of amorphous HfSiON films at SPring-8. Novel cluster models have been suggested based on the analogy to the ordered states for the Zr-O-N ternary system.

Takemura, Momoko; Yamazaki, Hideyuki; Ohmori, Hirobumi; Yoshiki, Masahiko; Takeno, Shiro; Ino, Tsunehiro; Nishiyama, Akira [Corporate R and D Center, Toshiba Corporation 1, Komukai Toshiba-cho, Saiwai-ku, Kawasaki 212-8582 (Japan); Sato, Nobutaka [Toshiba Nanoanalysis Corporation, 1, Komukai Toshiba-cho, Saiwai-ku, Kawasaki 212-8583 (Japan); Hirosawa, Ichiro; Sato, Masugu [JASRI/SPring-8, 1-1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198 (Japan)

2007-01-19

403

Fabrication and characterization of amorphous lithium electrolyte thin films and rechargeable thin-film batteries  

SciTech Connect

Research on the deposition and characterization of amorphous lithium electrolyte and vanadium oxide thin films was undertaken with the goal of developing a thin-film rechargeable lithium battery. Most of this effort has focused on the electrolyte film, with less but increasing attention given to the cathode. Recent studies on these films and rechargeable thin-film lithium cells will be reviewed in this paper.

Bates, J.B.; Dudney, N.J.; Gruzalski, G.R.; Zuhr, R.A.; Choudhury, A.; Luck, C.F. [Oak Ridge National Lab., TN (United States); Robertson, J.D. [Kentucky Univ., Lexington, KY (United States)

1992-02-01

404

Sub1.3 nm Amorphous Tantalum Pentoxide Gate Dielectrics for Damascene Metal Gate Transistors  

Microsoft Academic Search

The formation process of amorphous tantalum pentoxide (Ta2O5) gate dielectrics was developed for sub-0.1 mum damascene metal gate transistors. Ta2O5 film deposition at high temperature (550°C) on ultrathin (1 nm) oxynitride interface layer improves the surface morphology and decreases the carbon contamination in films. Elimination of post-deposition annealing suppresses the increase of interface layer thickness, and hence, ultrathin equivalent oxide

Seiji Inumiya; Atsushi Yagishita; Tomohiro Saito; Masaki Hotta; Yoshio Ozawa; Kyoichi Suguro; Yoshitaka Tsunashima; Tsunetoshi Arikado

2000-01-01

405

Electrochemical properties of amorphous comb-shaped composite PEO polymer electrolyte  

Microsoft Academic Search

The electrochemical behaviour of a polyethylene oxide (PEO)-based composite polymer electrolyte are studied. The crystallinity of the PEO is suppressed by using a comb-shaped polymer to improve polymer chain mobility. An amorphous comb-shaped polymer, ‘TEC-24’, with a side-chain content of 24mol%, is designed and fine silica powder is dispersed within it to enhance the mechanical properties above the melting point.

J.-S Chung; H.-J Sohn

2002-01-01

406

Boron adsorption on aluminum and iron oxide minerals  

Microsoft Academic Search

Boron adsorption behavior was investigated on various crystalline and x-ray amorphous Al and Fe oxide minerals. Adsorption increased at low pH, exhibited a peak in the pH range 7 to 8, and decreased at high pH. The magnitude of B adsorption was much greater for the x-ray amorphous materials. Since B adsorbs specifically on Al and Fe oxide minerals, the

S. Goldberg; R. A. Glaubig

2008-01-01

407

Amorphous Diamond MEMS and Sensors  

SciTech Connect

This report describes a new microsystems technology for the creation of microsensors and microelectromechanical systems (MEMS) using stress-free amorphous diamond (aD) films. Stress-free aD is a new material that has mechanical properties close to that of crystalline diamond, and the material is particularly promising for the development of high sensitivity microsensors and rugged and reliable MEMS. Some of the unique properties of aD include the ability to easily tailor film stress from compressive to slightly tensile, hardness and stiffness 80-90% that of crystalline diamond, very high wear resistance, a hydrophobic surface, extreme chemical inertness, chemical compatibility with silicon, controllable electrical conductivity from insulating to conducting, and biocompatibility. A variety of MEMS structures were fabricated from this material and evaluated. These structures included electrostatically-actuated comb drives, micro-tensile test structures, singly- and doubly-clamped beams, and friction and wear test structures. It was found that surface micromachined MEMS could be fabricated in this material easily and that the hydrophobic surface of the film enabled the release of structures without the need for special drying procedures or the use of applied hydrophobic coatings. Measurements using these structures revealed that aD has a Young's modulus of {approx}650 GPa, a tensile fracture strength of 8 GPa, and a fracture toughness of 8 MPa{center_dot}m {sup 1/2}. These results suggest that this material may be suitable in applications where stiction or wear is an issue. Flexural plate wave (FPW) microsensors were also fabricated from aD. These devices use membranes of aD as thin as {approx}100 nm. The performance of the aD FPW sensors was evaluated for the detection of volatile organic compounds using ethyl cellulose as the sensor coating. For comparable membrane thicknesses, the aD sensors showed better performance than silicon nitride based sensors. Greater than one order of magnitude increase in chemical sensitivity is expected through the use of ultra-thin aD membranes in the FPW sensor. The discoveries and development of the aD microsystems technology that were made in this project have led to new research projects in the areas of aD bioMEMS and aD radio frequency MEMS.

SULLIVAN, JOHN P.; FRIEDMANN, THOMAS A.; ASHBY, CAROL I.; DE BOER, MAARTEN P.; SCHUBERT, W. KENT; SHUL, RANDY J.; HOHLFELDER, ROBERT J.; LAVAN, D.A.

2002-06-01

408

Hydrogenated amorphous carbon grains in Comet Halley  

SciTech Connect

Recent IR observations of Comets Halley, Wilson, and Bradfield have shown the existence of an emission feature falling at around 3.4 microns. In this paper, it is shown that a good fit of both the IR continuum and the band can be obtained by assuming a simple thermal emission model based upon the optical properties of hydrogenated amorphous carbon (HAC) grains, measured in laboratory. The best fits of P/Halley's spectra are obtained for HAC dust amounts which appear consistent with the constraints imposed by the observed production rates. The presence of amorphous carbon solid particles is also supported on the basis of in situ mass spectrometry measurements performed by the Vega 1/2 and Giotto spacecraft in the environment of P/Halley. At present, it appears reasonable to suggest that amorphous carbon grains are able to match the observations and can be considered among likely candidates for cometary materials. 51 refs.

Colangeli, L.; Schwehm, G.; Bussoletti, E.; Fonti, S.; Blanco, A. (Cassino Universita (Italy) ESA, Space Science Dept., Noordwijk (Netherlands) Osservatorio Astronomico di Capodimonte, Naples (Italy) Lecce Universita (Italy))

1990-01-01

409

IUE observations of amorphous hot galaxies  

NASA Technical Reports Server (NTRS)

Blue amorphous galaxies are star-forming, irregularlike systems which lack the spatially distinct OB stellar groups that are characteristic of most late-type galaxies. In order to better understand the nature of star-formation processes in these unusual galaxies, short-wavelength IUE spectra of the amorphous galaxies NGC 1705 and NGC 1800 have been obtained. It is found that NGC 1705 contains a normal mix of OB stars, which is consistent with the nearly constant recent star-formation rate inferred from new optical data. NGC 1800 is likely to have similar properties, and blue galaxies with amorphous structures thus do not show evidence for anomalies in stellar populations. The UV spectra of these galaxies and a variety of other hot extragalactic stellar systems in fact have similar characteristics, which suggests OB stellar populations are often homogeneous in their properties.

Lamb, S. A.; Hjellming, M. S.; Gallagher, J. S., III; Hunter, D. A.

1985-01-01

410

Amorphous Polymeric Nitrogen from Dynamic Shock Simulation  

NASA Astrophysics Data System (ADS)

In recent years there has been significant interest in polymeric phases of nitrogen at low pressure for potential application as an energetic material. This interest was bolstered by experimental evidence of metastable amorphous polymeric nitrogen at low pressure.ootnotetextGoncharov, A. F. et al., Phys. Rev. Lett. 85, 1262 (2000)^,ootnotetextEremets, M. I. et al., Nature 411, 170 (2001) While considerable theoretical work has been done on many crystal phases of nitrogen, simulating amorphous polymeric nitrogen has been more challenging. Starting from first principles dynamic shock simulation of cubic-gauche nitrogenootnotetextMattson, William D. and Balu, Radhakrishnan, Phys. Rev. B 83, 174105 (2011) we demonstrate a form of polymeric nitrogen at low pressure that may be directly related to amorphous polymeric nitrogen.

Beaudet, Todd; Mattson, William; Rice, Betsy

2012-02-01

411

Synthesis and photocurrent of amorphous boron nanowires.  

PubMed

Although theoretically feasible, synthesis of boron nanostructures is challenging due to the highly reactive nature, high melting and boiling points of boron. We have developed a thermal vapor transfer approach to synthesizing amorphous boron nanowire using a solid boron source. The amorphous nature and chemical composition of boron nanowires were characterized by high resolution transmission electron microscopy, selected area electron diffraction, and electron energy loss spectroscopy. Optical properties and photoconduction of boron nanowires have not yet been reported. In our investigation, the amorphous boron nanowire showed much better optical and electrical properties than previously reported photo-response of crystalline boron nanobelts. When excited by a blue LED, the photo/dark current ratio (I/I0) is 1.5 and time constants in the order of tens of seconds. I/I0 is 1.17 using a green light. PMID:25061013

Ge, Liehui; Lei, Sidong; Hart, Amelia H C; Gao, Guanhui; Jafry, Huma; Vajtai, Robert; Ajayan, Pulickel M

2014-08-22

412

Rigid Amorphous Fraction in PLA Electrospun Fibers  

NASA Astrophysics Data System (ADS)

Electrospun fibers of poly(lactic acid) (PLA) were formed by adopting a high-speed rotating wheel as the counter-electrode. The molecular orientation, crystallization mechanism, and phase structure and transitions of the aligned ES fibers were investigated. Using thermal analysis and wide angle X-ray scattering (WAXS), we evaluated the confinement that exists in as-spun amorphous, and heat-treated semicrystalline, fibers. Differential scanning calorimetry confirmed the existence of a constrained amorphous phase in as-spun aligned fibers, without the presence of crystals or fillers to serve as fixed physical constraints. Using WAXS, for the first time the mesophase fraction, consisting of oriented amorphous PLA chains, was quantitatively characterized in nanofibers.

Cebe, Peggy; Ma, Qian; Simona Cozza, Erika; Pyda, Marek; Mao, Bin; Zhu, Yazhe; Monticelli, Orietta

2013-03-01

413

Research on stable, high-efficiency amorphous silicon multijunction modules  

SciTech Connect

This report describes a contract to produce multijunction modules based entirely on amorphous silicon alloys, the modules having an aperture area of at least 900 cm{sup 2} and a stable, reproducible conversion efficiency of at least 6.5% after 600 hours of light exposure (air mass 1.5) at 50{degrees} C. The work focussed on (1) producing opto-electronic-grade amorphous silicon material for band gaps of about 1.7 and 1.9 eV by changing the hydrogen content in the film bonded to the silicon, (2) studying and obtaining data on the light stability of single-junction p-i-n solar cells with gaps of about 1.7 and 1.9 eV, and (3) analyzing losses in a silicon/silicon multijunction cell. We report new results on an indium tin oxide (ITO)/silver back contact and the deposition of granular tin oxide by atmospheric-pressure chemical vapor deposition. Progress toward module fabrication at the end of six months has been good, with the demonstration of 5.4% initial efficiency in a silicon/silicon multijunction submodule with an aperture area of 4620 cm{sup 2} and incorporating devices with 2nd-junction i-layer thicknesses of about 3500 {angstrom}. We also demonstrated a single-junction silicon submodule with an aperture area of 4620 cm{sup 2}, a thickness of about 3500 {angstrom}, and an initial efficiency of 6.5%. 4 refs., 39 figs., 5 tabs.

Bhat, P.K.; Brown, S.; Hollingsworth, R.; Shen, D.S.; del Cueto, J.; Iwanicko, E.; Marshall, C.; DeHart, C.; Mentor, D.; Benson, A.; Matovich, C.; Sandwisch, J. (Glasstech Solar, Inc., Golden, CO (USA))

1991-04-01

414

Co-rich magnetic amorphous films and their application in magnetoelectronics  

NASA Astrophysics Data System (ADS)

Three kinds of Co-rich magnetic amorphous films of CoFeB, CoFeNiSiB, and CoFeHfO were prepared by magnetron sputtering and applied as soft ferromagnetic (FM) electrodes in tunneling magnetoresistance (TMR) devices. Initial results exhibit a large room-temperature TMR effect of approximately 50%. The high effect can be attributed to interfacial coherence between the amorphous barrier-electrode layers and, accordingly, suggests a high local spin polarization possibly associated with strong nearest-neighbor spin correlations of the magnetic atoms. The magnetotransport behavior may be governed by details of the local spin environment in magnetic amorphous electrodes due to their short electron mean-free path (˜3-5Å) . The annealing effect on TMR was found to be more pronounced due to the atomic cooperative structural relaxation and more thermally stable compared with the polycrystalline electrode junctions. Additionally, the use of the magnetic oxide electrode CoFeHfO has shown that the relevant FM electrode-barrier interface becomes insensitive to the oxygen, which simplifies the oxidation process used for the oxide barrier fabrication.

Luo, Y.; Esseling, M.; Käufler, A.; Samwer, K.; Dimopoulos, T.; Gieres, G.; Vieth, M.; Rührig, M.; Wecker, J.; Rudolf, C.; Niermann, T.; Seibt, M.

2005-07-01

415

Mechanical-contact-induced transformation from the amorphous to the partially crystalline state in metallic glass  

NASA Technical Reports Server (NTRS)

Friction and wear tests were conducted with 3.2- and 6.4-millimeter-diameter aluminum oxide spheres sliding, in reciprocating motion, on a Fe67Co18B14Si1 metallic foil. Crystallites with a size range of 10 to 150 nanometers were produced on the wear surface of the amorphous alloy. A strong interaction between transition metals and metalloids such as silicon and boron results in strong segregation during repeated sliding, provides preferential transition metal-metalloid clustering in the amorphous alloy, and subsequently produces the diffused honeycomb structure formed by dark grey bands and primary crystals, that is, alpha-Fe in the matrix. Large plastic flow occurs on an amorphous alloy surface with sliding and the flow film of the alloy transfers to the aluminum oxide pin surface. Multiple slip bands due to shear deformation are observed on the side of the wear track. Two distinct types of wear debris were observed as a result of sliding: an alloy wear debris, and/or powdery-whiskery oxide debris.

Miyoshi, K.; Buckley, D. H.

1984-01-01

416

Microstructure and surface chemistry of amorphous alloys important to their friction and wear behavior  

NASA Technical Reports Server (NTRS)

An investigation was conducted to examine the microstructure and surface chemistry of amorphous alloys, and their effects on tribological behavior. The results indicate that the surface oxide layers present on amorphous alloys are effective in providing low friction and a protective film against wear in air. Clustering and crystallization in amorphous alloys can be enhanced as a result of plastic flow during the sliding process at a low sliding velocity, at room temperature. Clusters or crystallines with sizes to 150 nm and a diffused honeycomb-shaped structure are produced on sizes to 150 nm and a diffused honeycomb-shaped structure are produced on the wear surface. Temperature effects lead to drastic changes in surface chemistry and friction behavior of the alloys at temperatures to 750 C. Contaminants can come from the bulk of the alloys to the surface upon heating and impart to the surface oxides at 350 C and boron nitride above 500 C. The oxides increase friction while the boron nitride reduces friction drastically in vacuum.

Miyoshi, K.; Buckley, D. H.

1986-01-01

417

Mechanical contact induced transformation from the amorphous to the crystalline state in metallic glass  

NASA Technical Reports Server (NTRS)

Friction and wear tests were conducted with 3.2- and 6.4-millimeter-diameter aluminum oxide spheres sliding, in reciprocating motion, on a Fe67Co18B14Si1 metallic foil. Crystallites with a size range of 10 to 150 nanometers were produced on the wear surface of the amorphous alloy. A strong interaction between transition metals and metalloids such as silicon and boron results in strong segregation during repeated sliding, provides preferential transition metal-metalloid clustering in the amorphous alloy, and subsequently produces the diffused honeycomb structure formed by dark grey bands and primary crystals, that is, alpha-Fe in the matrix. Large plastic flow occurs on an amorphous alloy surface with sliding and the flow film of the alloy transfers to the aluminum oxide pin surface. Multiple slip bands due to shear deformation are observed on the side of the wear track. Two distinct types of wear debris were observed as a result of sliding: an alloy wear debris, and/or powdery-whiskery oxide debris.

Miyoshi, K.; Buckley, D. H.

1984-01-01

418

Amorphous carbon enhancement of hydrogen penetration into UO2  

NASA Astrophysics Data System (ADS)

The interaction of D2 and H2O (humidity) with amorphous carbon covered UO2 vs. clean UO2 was studied using Secondary Ion Mass Spectrometry (SIMS) and X-ray Photoelectron Spectroscopy (XPS). It was found that SIMS depth profiles of the carbon covered side vs. the bare oxide, show significant higher intensities of H- and D- for the first, through the carbon layer and beneath it. The presence of a thin carbon layer on a UO2 surface caused a significant buildup of hydroxyl, probably adsorbed on the carbon, but maybe also beneath the layer, in the presence of atmospheric humidity. Exposure of the carbon covered oxide to D2 on a UHV annealed surface also caused a growth of the hydroxyl. It is concluded that the carbon surface strongly enhances the dissociation of water vapor as well as that of hydrogen and the penetration of the dissociation products to the oxide, as compared to the bare UO2 surface. The contribution of the latter, beneath the carbon, should be verified or ruled out by further experiments.

Zalkind, S.; Shamir, N.; Gouder, T.; Akhvlediani, R.; Hoffman, A.

2014-06-01

419

Amorphization strategy affects the stability and supersaturation profile of amorphous drug nanoparticles.  

PubMed

Amorphous drug nanoparticles have recently emerged as a promising bioavailability enhancement strategy of poorly soluble drugs attributed to the high supersaturation solubility generated by the amorphous state and fast dissolution afforded by the nanoparticles. Herein we examine the effects of two amorphization strategies in the nanoscale, i.e., (1) molecular mobility restrictions and (2) high energy surface occupation, both by polymer excipient stabilizers, on the (i) morphology, (ii) colloidal stability, (iii) drug loading, (iv) amorphous state stability after three-month storage, and (v) in vitro supersaturation profiles, using itraconazole (ITZ) as the model drug. Drug-polyelectrolyte complexation is employed in the first strategy to prepare amorphous ITZ nanoparticles using dextran sulfate as the polyelectrolyte (ITZ nanoplex), while the second strategy employs pH-shift precipitation using hydroxypropylmethylcellulose as the surface stabilizer (nano-ITZ), with both strategies resulting in >90% ITZ utilization. Both amorphous ITZ nanoparticles share similar morphology (?300 nm spheres) with the ITZ nanoplex exhibiting better colloidal stability, albeit at lower ITZ loading (65% versus 94%), due to the larger stabilizer amount used. The ITZ nanoplex also exhibits superior amorphous state stability, attributed to the ITZ molecular mobility restriction by electrostatic complexation with dextran sulfate. The higher stability, however, is obtained at the expense of slower supersaturation generation, which is maintained over a prolonged period, compared to the nano-ITZ. The present results signify the importance of selecting the optimal amorphization strategy, in addition to formulating the excipient stabilizers, to produce amorphous drug nanoparticles having the desired characteristics. PMID:24669821

Cheow, Wean Sin; Kiew, Tie Yi; Yang, Yue; Hadinoto, Kunn

2014-05-01

420

Short range order in amorphous polycondensates  

SciTech Connect

The static coherent structure factors S(Q) of the polymer glass Bisphenol-A-Polycarbonate and its chemical variation Bisphenol-A- Polyctherkctone- both in differently deuterated versions- have been measured by spin polarized neutron scattering. The method of spin polarization analysis provided an experimental separation of coherent and incoherent scattering and a reliable intensity calibration. Results are compared to structure factors calculated for model structures which were obtained by ``amorphous cell`` computer simulations. In general reasonable agreement is found between experiment and simulation; however, certain discrepancies hint at an insufficient structural relaxation in the amorphous cell method. 15 refs, 1 fig, 1 tab.

Lamers, C.; Richter, D.; Schweika, W. [Forschungszentrum Juelich GmbH (Germany). Inst. fuer Festkoerperforschung; Batoulis, J.; Sommer, K. [Bayer AG, Leverkusen (Germany); Cable, J.W. [Oak Ridge National Lab., TN (United States); Shapiro, S.M. [Brookhaven National Lab., Upton, NY (United States)

1992-12-01

421

Structure and mobility on amorphous silicon surfaces  

NASA Astrophysics Data System (ADS)

The structure and dynamics of amorphous surfaces are poorly understood. The present work develops methods employing classical molecular dynamics (MD) simulations to elucidate these phenomena on amorphous silicon. Careful relaxation of the initial ensemble and taking account of exchange with the bulk yield surface diffusion coefficients in good agreement with experiment. Randomly oriented dimer pairs dominate the surface structure. Diffusion proceeds by several pathways, which all differ in basic character from those typically observed on crystalline silicon. The primary pathways involve single atoms and dimer pairs, which typically move only one or two atomic diameters before reincorporating into the surface. Frequent vertical migration takes place between the first two atomic layers.

Dalton, A. S.; Seebauer, E. G.

2004-02-01

422

Hysteresis in stress cycling of amorphous ribbons  

NASA Astrophysics Data System (ADS)

The permeability of soft amorphous ribbons shows significant hysteresis through stress cycling. The response of a circuit incorporating an amorphous CoFeNiSiB based ribbon, as a function of longitudinal stress, with a longitudinal excitation field, is measured. The behaviour of the stress impedance is related to domain wall behaviour, at a range of different frequencies, through a simple model of eddy currents in sheets. It is suggested that changes in the pinning mechanism have a profound effect on the measured impedance.

Tomka, G. J.; Milne, J.; Tweed, S.; Thomas, O.

2004-05-01

423

Phonon excitations in multicomponent amorphous solids  

SciTech Connect

The method of two-time temperature-dependent Green's functions is used to investigate phonon excitations in multicomponent amorphous solids. The equation obtained for the energy spectrum of the phonon excitations takes into account the damping associated with scattering of phonons by structure fluctuations. The quasicrystal approximation is considered, and as an example explicit expressions are obtained for the case of a two-component amorphous solid for the frequencies of the acoustical and optical modes and for the longitudinal and transverse velocities of sound. The damping is investigated.

Vakarchuk, I.A.; Migal', V.M.; Tkachuk, V.M.

1988-11-01

424

Thermal conductivity of sputtered amorphous Ge films  

NASA Astrophysics Data System (ADS)

We measured the thermal conductivity of amorphous Ge films prepared by magnetron sputtering. The thermal conductivity was significantly higher than the value predicted by the minimum thermal conductivity model and increased with deposition temperature. We found that variations in sound velocity and Ge film density were not the main factors in the high thermal conductivity. Fast Fourier transform patterns of transmission electron micrographs revealed that short-range order in the Ge films was responsible for their high thermal conductivity. The results provide experimental evidences to understand the underlying nature of the variation of phonon mean free path in amorphous solids.

Zhan, Tianzhuo; Xu, Yibin; Goto, Masahiro; Tanaka, Yoshihisa; Kato, Ryozo; Sasaki, Michiko; Kagawa, Yutaka

2014-02-01

425

Anisotropy of losses in amorphous ribbons  

NASA Astrophysics Data System (ADS)

The soft magnetic properties of amorphous ribbons are expected to be anistropic because of the shear deformation during the melt spinning procedure. In this paper the losses of an Fe 80B 14Si 6 amorphous ribbon were measured on stripes which were cut either parallel or perpendicular to the ribbon axis. The dependence of the losses as a function of peak induction and frequency suggests that there is an easy axis of magnetization parallel to the ribbon axis. After stress relief annealing this anisotropy is reduced. That is why this anisotropy is assumed to be due to internal stress introduced upon quenching.

Roth, S.; Habiger, D.-U.

1986-10-01

426

Neutron scattering studies of amorphous Invar alloys  

SciTech Connect

This paper reviews recent inelastic neutron scattering experiments performed to study the spin dynamics of two amorphous Invar systems: Fe/sub 100-x/B/sub x/ and Fe/sub 90-x/Ni/sub x/Zr/sub 10/. As in crystalline Invar Fe/sub 65/Ni/sub 35/ and Fe/sub 3/Pt, the excitation of conventional long-wavelength spin waves in these amorphous systems cannot account for the relatively rapid change of their magnetization with temperature. These results are discussed in terms of additional low-lying excitations which apparently have a density of states similar to the spin waves.

Fernandez-Baca, J.A.

1989-01-01

427

Superhydrophobic amorphous carbon/carbon nanotube nanocomposites  

NASA Astrophysics Data System (ADS)

Superhydrophobic amorphous carbon/carbon nanotube nanocomposites are fabricated by plasma immersion ion implantation with carbon nanotube forests as a template. The microstructure of the fabricated nanocomposites shows arrays of carbon nanotubes capped with amorphous carbon nanoparticles. Contact angle measurements show that both advancing and receding angles close to 180° can be achieved on the nanocomposites. The fabrication here does not require patterning of carbon nanotubes or deposition of conformal coatings with low surface energy, which are usually involved in conventional approaches for superhydrophobic surfaces. The relationship between the observed superhydrophobicity and the unique microstructure of the nanocomposites is discussed.

Han, Z. J.; Tay, B. K.; Shakerzadeh, M.; Ostrikov, K.

2009-06-01

428

Amorphous Insulator Films With Controllable Properties  

NASA Technical Reports Server (NTRS)

In experiments described in report, amorphous hydrogenated carbon films grown at room temperature by low-frequency plasma deposition, using methane or butane gas. Films have unique array of useful properties; (a) adhere to wide variety of materials; (b) contain only carbon and hydrogen; (c) smooth and free of pinholes; (d) resistant to attack by moisture and chemicals; and (e) have high electric-breakdown strength and electrical resistivity. Two of optical properties and hardness of this film controlled by deposition conditions. Amorphous a-C:H and BN films used for hermetic sealing and protection of optical, electronic, magnetic, or delicate mechanical systems, and for semiconductor field dielectrics.

Alterovitz, Samuel A.; Warner, Joseph D.; Liu, David C.; Pouch, John J.

1987-01-01

429

Amorphization of ?-quartz and comparative study of defects in amorphized quartz and Si nanocrystals embedded in amorphous silica  

NASA Astrophysics Data System (ADS)

Ion irradiation of ?-quartz renders the crystal SiO 2 structure amorphous. The enormous amount of structural defects produced after ion irradiation give a chance for photoactive intrinsic defects to be formed. These may be responsible for the photoluminescence in irradiated ?-quartz. On the other hand, the radiation defects are not stable, and thus, an alternative structure where the defects of interest can be stabilized is required. The stabilization of the defects can be achieved in the structures of amorphous silica with embedded Si nanocrystals (NC), thanks to the unique structure of the formed interface. By means of Molecular Dynamics (MD), we analyze defects in both amorphized ?-quartz and Si-NC/a-SiO 2 interfaces formed by 1.1, 2.4 and 4 nm diameter NC's. In the simulation, we employ a classical interatomic potential and a potential, which takes into consideration a charge transfer between Si and O atoms. We show that although the number of silanone bonds Si dbnd O in irradiated quartz is higher, they are also found in a Si-NC/a-SiO 2 interface without the necessity of preceding irradiation of the sample. We also compare the defects in irradiation-amorphized quartz and the three sizes of Si-NC/a-SiO 2 interfaces. Analysis of the charges showed that the charge state of coordination defects depends on the type of atoms in the near neighborhood.

Djurabekova, Flyura; Backholm, Matilda; Backman, Marie; Pakarinen, Olli H.; Keinonen, Juhani; Nordlund, Kai; Shan, Tzu-Ray; Devine, Bryce D.; Sinnott, Susan B.

2010-10-01

430

New Amorphous Silicon Alloy Systems  

NASA Astrophysics Data System (ADS)

The properties of hydrogenated amorphous silicon (a-Si:H) have been modified by alloying with Al, Ga and S respectively. The Al and Ga alloys are in effect quaternary alloys as they were fabricated in a carbon-rich discharge. The alloys were prepared by the plasma assisted chemical vapor deposition (PACVD) method. This method has several advantages, the major one being the relatively low defect densities of the resulting materials. The PACVD system used to grow the alloy films was designed and constructed in the laboratory. It was first tested with known (a-Si:H and a-Si:As:H) materials. Thus, it was established that device quality alloy films could be grown with the home-made PACVD setup. The chemical composition of the alloys was characterized by secondary ion mass spectrometry (SIMS), and electron probe microanalysis (EPMA). The homogeneous nature of hydrogen distribution in the alloys was established by SIMS depth profile analysis. A quantitative analysis of the bulk elemental content was carried out by EPMA. The analysis indicated that the alloying element was incorporated in the films more efficiently at low input gas concentrations than at the higher concentrations. A topological model was proposed to explain the observed behavior. The optical energy gap of the alloys could be varied in the 0.90 to 1.92 eV range. The Al and Ga alloys were low band gap materials, whereas alloying with S had the effect of widening the energy gap. It was observed that although the Si-Al and Si-Ga alloys contained significant amounts of C and H, the magnitude of the energy gap was determined by the metallic component. The various trends in optical properties could be related to the binding characteristics of the respective alloy systems. A quantitative explanation of the results was provided by White's tight binding model. The dark conductivity-temperature dependence of the alloys was examined. A linear dependence was observed for the Al and Ga systems. Electronic conduction in the S-alloys appeared to proceed by a two step mechanism. The thermal activation energies for the high Al content and S-alloys were close to half the band gap value. The photoresponse of the films was determined from the light to dark conductivity ratio. The best photoresponse (sigma_ {L}/sigma_{D} = 4 times 10^2) was obtained for the Si-S alloys showing that they are promising electrode materials for solar cell application. A single unit photovoltaic electrolyzer was constructed by combining a-Si:H solar cells with an electrolysis cell. Several different configurations ((PIN), (PIN)^2 , and (PIN)^3) of the solar cells were tested. Both electric power and chemical energy (H_2) could be simultaneously drawn from the electrolyzer.

Kapur, Mridula N.

1990-01-01

431

Oxidation of aluminum nanoclusters  

SciTech Connect

The dynamics of oxidation of aluminum nanoclusters (20 nm diameter) is investigated using a parallel molecular dynamics approach based on variable charge interatomic interactions due to Streitz and Mintmire that include both ionic and covalent effects. Simulations are performed for both canonical ensembles for molecular oxygen (O{sub 2}) environments and microcanonical ensembles for molecular (O{sub 2}) and atomic (O{sub 1}) oxygen environments. Structural and dynamic correlations in the oxide region are calculated, as well as the evolution of charges, surface oxide thickness, diffusivities of atoms, and local stresses. In the microcanonical ensemble, the oxidizing reaction becomes explosive in both molecular and atomic oxygen environments due to the enormous energy release associated with Al-O bonding. Local stresses in the oxide scale cause rapid diffusion of aluminum and oxygen atoms. Analyses of the oxide scale reveal significant charge transfer and a variation of local structures from the metal-oxide interface to the oxide-environment interface. In the canonical ensemble, oxide depth grows linearly in time until {approx}30 ps, followed by saturation of oxide depth as a function of time. An amorphous oxide layer of thickness {approx}40 A is formed after 466 ps, in good agreement with experiments. The average mass density in the oxide scale is 75% of the bulk alumina density. Evolution of structural correlation in the oxide is analyzed through radial distribution and bond angles. Through detailed analyses of the trajectories of O atoms and their formation of OAl{sub n} structures, we propose a three-step process of oxidative percolation that explains deceleration of oxide growth in the canonical ensemble.

Campbell, Timothy J. [Collaboratory for Advanced Computing and Simulations, Department of Materials Science and Engineering, Department of Physics and Astronomy, Department of Computer Science, University of Southern California, Los Angeles, California 90089-0242 (United States); Mississippi State University, Stennis Space Center, Mississippi 39529 (United States); Aral, Gurcan; Kalia, Rajiv K.; Nakano, Aiichiro; Vashishta, Priya [Collaboratory for Advanced Computing and Simulations, Department of Materials Science and Engineering, Department of Physics and Astronomy, Department of Computer Science, University of Southern California, Los Angeles, California 90089-0242 (United States); Ogata, Shuji [Graduate School of Engineering, Nagoya Institute of Technology, Nagoya 466-8555 (Japan)

2005-05-15

432

The XRD Amorphous Component in John Klein Drill Fines at Yellowknife Bay, Gale Crater, Mars  

NASA Astrophysics Data System (ADS)

Drill fines of mudstone (targets John Klein and Cumberland) from the Sheepbed unit at Yel-lowknife Bay were analyzed by MSL payload elements including the Chemistry and Mineralogy (CheMin), APXS (Alpha Particle X-Ray Spectrometer), and Sample Analysis at Mars (SAM) instruments. CheMin XRD results show a variety of crystalline phases including feldspar, pyrox-ene, olivine, oxides, oxyhydroxides, sulfates, sulfides, a tri-octahedral smectite, and XRD amorphous material. The drill fines are distinctly different from corresponding analyses of the global soil (target Rocknest) in that the mudstone samples contained detectable phyllosilicate. Here we focus on John Klein and combine CheMin and APXS data to calculate the chemical composition and concentration of the amorphous component. The chemical composition of the amorphous plus smectite component for John Klein was cal-culated by subtracting the abundance-weighted chemical composition of the individual XRD crystalline components from the bulk composition of John Kline as measured by APXS. The chemical composition of individual crystalline components was determined either by stoichiome-try (e.g., hematite and magnetite) or from their unit cell parameters (e.g., feldspar, olivine, and pyroxene). The chemical composition of the amorphous + smectite component (~71 wt.% of bulk sample) and bulk chemical compositon are similar. In order to calculate the chemical composition of the amorphous component, a chemical composition for the tri-octahedral smectite must be assumed. We selected two tri-octahedral smectites with very different MgO/(FeO + Fe2O3) ratios (34 and 1.3 for SapCa1 and Griffithite, respectively). Relative to bulk sample, the concentration of amorphous and smectite components are 40 and 29 wt.% for SapCa1 and 33 and 36 wt.% for Griffithite. The amount of smectite was calculated by requiring the MgO concentration to be~0 wt.% in the amporphous component. Griffithite is the preferred smectite because the position of its 02l diffraction peak is similar to that reported for John Klein. In both cases, the amorphous component has low SiO2 and MgO and high FeO + Fe2O3, P2O5, and SO3 concentrations relative to bulk sample. The chemical composition of the bulk drill fines and XRD crystalline, smectite, and amorphous components implies alteration of an initially basaltic material under near neutral conditions (not acid sulfate), with the sulfate incorporated later as veins of CaSO4 injected into the mudstone.

Morris, R. V.; Ming, D. W.; Blake, D.; Vaniman, D.; Bish, D. L.; Chipera, S.; Downs, R.; Morrison, S.; Gellert, R.; Campbell, I.; Treiman, A. H.; Achilles, C.; Bristow, T.; Crisp, J. A.; McAdam, A.; Archer, P. D.; Sutter, B.; Rampe, E. B.; Team, M.

2013-12-01

433

Swift heavy ion irradiation-induced amorphization of La2Ti2O7  

NASA Astrophysics Data System (ADS)

Polycrystalline La2Ti2O7 powders have been irradiated with 2.0 GeV 181Ta ions up to a fluence of 1 × 1013 ions/cm2. Radiation-induced structural modifications were analyzed using synchrotron-based X-ray diffraction (XRD), small angle X-ray scattering (SAXS), Raman spectroscopy and transmission electron microscopy (TEM). An increase in the amorphous fraction as a function of fluence was revealed by XRD and Raman analyses and is evidenced by the reduction in intensity of the sharp Bragg maxima from the crystalline regions. Concurrently, diffraction maxima and vibrational absorption bands broaden with the increasing amorphous fraction. The cross-section for the crystalline-to-amorphous transformation (ion tracks) was determined by quantitative analysis of XRD patterns yielding a track diameter of d = 7.2 ± 0.9 nm. Slightly larger track diameters were obtained directly from TEM images (d = 10.6 ± 0.8 nm) and SAXS analysis (d = 10.6 ± 0.3 nm). High-resolution TEM images revealed that single tracks are entirely amorphous without any outer crystalline, disordered shell as found in pyrochlore oxides of the same stoichiometry. The large ratio of ionic radii of the A- and B-site c