bluuebunny/crossref_metadata_2025_split huggingface dataset:
7Li MAS NMR Studies of Lithiated Manganese Dioxide Tunnel Structures: Pyrolusite and Ramsdellite
Authors: Paik Younkee , Lee Young J. , Wang Francis , Bowden William , Grey Clare P. 
Published: April 2011

ABSTRACTThe one-dimensional 1×1 and 1×2 tunnel structures of manganese dioxides, pyrolusit(β-MnO2) and ramsdellite (R-MnO2), respectively, were chemically intercalated with LiI. Two 7Li resonances were observed in lithiated pyrolusite. One isotropic resonance arising at 110 ppm shows a short spin-lattice relaxation time (T1 ∼ 3 ms) and was assigned to Li+ ions in the 1×1 tunnel structure. The other isotropic resonance arising at 4 ppm shows a long spin-lattice relaxation time (T1 ∼ 100 ms) and was assigned to Li+ ions in diamagnetic local environments in the form of impurities such as Li2O or on the surface of the MnO2 particles. Three 7Li resonances were observed in lithiated ramsdellite at very different frequencies (600, 110 and 0 ppm). The resonance at 600 ppm, which is observed at low lithium intercalation levels, is assigned toLi+ ions coordinated to both Mn(III) and Mn(IV) ions in the 1×2 tunnels, while the resonanceat 110 ppm is due to Li+ ions coordinated to Mn(III) ions and appears at higher Li levels. The resonance at 0 ppm is associated with a long spin-lattice relaxation time (T1 ∼ 100 ms) and is also assignedto Li+ ions in diamagnetic impurities.
Microporous Ruthenium Oxide Films for Energy Storage Applications
Authors: Zheng J.P. , Fang Q.L. 
Published: April 2011

ABSTRACTHighly porous ruthenium oxide films were prepared using ruthenium ethoxide solution at low temperatures. The specific capacitance of the ruthenium oxide film electrode made with ruthenium ethoxide solution is much higher than that made using the traditional ruthenium chloride solution. It was found that amorphous ruthenium oxide films with high porosity could be formed at temperatures of 100-200 °C. At temperatures above 250 °C, crystalline ruthenium oxide films were formed. Electrochemical capacitors were made with ruthenium oxide film electrodes and were tested under constant current charging and discharging. The maximum specific capacitance of 593 F/g was obtained from the electrode prepared at 200 °C. The interfacial capacitance increased linearly with increasing film thickness. A value of interfacial capacitance as high as 4 F/cm2 was obtained from the electrode prepared at 200 °C.
Formation and Erosion of WC under W+ Irradiation of Graphite
Authors: Roth J. , Toussaint U. v. , Schmid K. , Luthin J. , Eckstein W. , Zuhr R. A. , Hensley D.K. 
Published: April 2011

ABSTRACTThe bombardment of C with 100 keV and 1 MeV W at normal incidence is studied as a function of the incident W fluence experimentally and by computer simulation with the program TRIDYN. Calculated oscillations in the amount of retained W and in the target weight change are confirmed experimentally for 100 keV at room temperature. XPS investigations show W2C formation during ion implantation already at room temperature. RBS depth profiles for 1 MeV bombardment show W mobility and surface segregation even at liquid nitrogen (LN2) temperatures. At elevated temperatures W clusters to form nano-particles at the surface and the oscillations in the retained amount of W disappear.
Thermodynamic Model of the Role of Hydrogen Dilution in Plasma Deposition of Microcrystalline Silicon
Authors: Robertson J 
Published: April 2011

ABSTRACTHydrogen dilution is used to promote the nucleation and growth of microcrystalline Si (μc-Si) by plasma enhanced chemical vapour deposition (PECVD). The free energy of μc-Si and hydrogenated amorphous silicon (a-Si:H) is analysed as a function of Si:H composition in order to derive the effect of hydrogen dilution. It is shown that increasing the hydrogen content of the a-SiHx precursor phase increases the relative stability of μc-Si slightly, but strongly increases the driving force for nucleation. The higher stability of μc-Si is the fundamental origin of the higher etch rates of a-Si:H, while surface mobility models do not account for sub-surface nucleation of μc-Si.
The Staebler-Wronski Effect and 1/f Noise in Amorphous Silicon
Authors: Belich T. J. , Kakalios J. 
Published: April 2011

ABSTRACTExperimental measurements of the Q-function (a comparison of the conductivity and thermopower activation energies) and the non-Gaussian statistical character of the 1/f noise in n-type doped a-Si:H as a function of light soaking (the Staebler-Wronski effect) are reported. There is a significant decrease in the non-Gaussian statistical character of the 1/f noise following light soaking of a device quality film, consistent with a slight increase in the long-range disorder. However, there is no change in the Q-function following light exposure, indicating that there is no significant increase in the long-range disorder.
Assessment of the Use of Microcrystalline Silicon Materials Grown at Rates Near 15 Å/s as i-layer Material for Single and Multi-Junction Solar Cells
Authors: Jones S.J. , Crucet R. , Capangpangan R. , Izu M. , Banerjee A. 
Published: April 2011

ABSTRACTA microwave-based technique has been used to prepare microcrystalline Si (µc-Si) materials rates near 15 Å/s. The use of these materials as intrinsic layers (i-layers) for single and multi-junction devices has been assessed. Since the high deposition rates allow for fabrication of the required thicker µc-Si i-layers in a similar amount of time to that used for high quality a-SiGe i-layers (rates of 1-3 Å/s), the materials are attractive, low cost replacements for a-SiGe bottom cell i-layers in a-Si/a-SiGe and a-Si/a-SiGe/a-SiGe multi-junction cells. Single-junction nip, a-Si/µc-Si and a-Si/a-SiGe/µc-Si devices have been fabricated. For these devices, the doped and amorphous layers were deposited using conventional rf glow discharge processes and deposition equipment separate from that used to fabricate the µc-Si materials. 7.0% efficiencies have been achieved for single-junction devices while pre-light soaked 9.8 and 11.4% efficiencies have been achieved for the tandem and triple-junction devices, respectively. The single-junction devices exhibit a degradation of only 0-2% after long term (1000 hrs.) of light soaking demonstrating a high degree of stability. Based on the present status, the µc-Si material prepared at high rates qualifies as a reasonable candidate for the i-layer of a bottom cell of a triple-junction device. Improvements in the performance, particularly the FF, will be needed before use in single-junction and tandem devices can be considered.
Improvement In Electrical Properties of Polycrystalline Silicon Films by The H2O Vapor Annealing Method
Authors: Sameshima Toshiyuki , Asada Katsimi , Tsunoda Yoshiyuki , Kaneko Yoshiyasu 
Published: April 2011

ABSTRACTImprovement of electrical properties by heat treatment with high-pressure H2O vapor was discussed for 7.4×1017cm−3 phosphorus-doped pulsed laser crystallized silicon films. The analysis of the electrical conductivity resulted in that 1.3×106-Pa-H2O vapor annealing at 270°C for 3 h reduced the density of defect states from 5.5 ×1018 cm−3(as crystallized) to 5.0×1017 cm−3 for tail states and from 1.0×1018 cm−3(as crystallized) to 3.0×1017 cm−3 for deep level defect states. The potential barrier height at grain boundaries decreased from 0.34 eV (as crystallized) to 0.05 eV by the heat treatment. The combination of oxygen plasma with high-pressure H2O vapor annealing effectively reduced the densities of defect tail sates as well as deep level defect states. It achieved a high performance of thin film transistors with a threshold voltage of 1.3 V and an effective mobility of 160 cm2/Vs.
Towards an All-Hot-Wire TFT: Silicon Nitride and amorphous Silicon deposited by Hot-Wire Chemical Vapor Deposition
Authors: Stannowski B. , Veen M.K. van , Schropp R.E.I. 
Published: April 2011

ABSTRACTWe present thin-film transistors with both amorphous silicon and silicon nitride deposited by hot-wire chemical vapor deposition. Hot-wire amorphous silicon with good electrical properties was deposited from the decomposition of silane at a substrate temperature of 250°C. For Hot-wire silicon nitride we used silane and ammonia at a substrate temperature of 340°C. In this paper we address structural and electrical properties of this material. A high ammonia flow results in porous films that exhibit post-deposition oxidation. By limiting the ammonia/silane ratio to 30, compact layers with a hydrogen content of only 10 at.% and a refractive index of 1.95 are obtained. Using this layer as gate dielectric results in thin-film transistors with good switching behavior and a field-effect mobility of 0.3 cm2/Vs.
Jet-printed Fabrication of a-Si:H Thin-film Transistors and Arrays
Authors: Wong W.S. , Ready S. , Matusiak R. , White S.D. , Lu J.-P. , Lau R. , Ho J. , Street R.A. 
Published: April 2011

ABSTRACTPhase-change wax-based printed masks were used to fabricate a-Si:H thin-film transistors (TFTs) in place of conventional lithography. Wax-mask features with a minimum feature size of ∼20 [.proportional]m was achieved using an acoustic-ink-printing process. Bottom-gate TFTs with source-drain contacts overlapping the channel were created using a four-mask process. The TFTs have I-V characteristics comparable to photolithographically patterned devices, with mobility of 0.6-1 cm2/V·s, threshold voltage of 2-3 V, and on/off ratios exceeding 107, for devices with channel lengths below 50[.proportional]m.
Illumination Dependence of Microcrystalline PIN Diodes
Authors: Brammer Torsten , Birmans Franz , Krause Mathias , Stiebig Helmut , Wagner Heribert 
Published: April 2011

ABSTRACTNumerical simulations of the current-voltage characteristics of PECVD-microcrystalline silicon based p-i-n diodes were performed to study the affect of defect density and mobility on solar cell performance. Depending on the combination of both parameters the ideality factor increases or decreases with applied forward bias. The reason is the variable contribution of volume recombination to the total diode current and space charge stored in defect states. The decrease in dark current with reduced hydrogen dilution can partly be attributed to a decrease in recombination centers by the same factor as predicted for midgap defect states by the analytic diode theory. Microcrystalline silicon solar cells deposited in the highly crystalline regime (high H-dilution) are limited by recombination of photogenerated carriers and high dark current. Both can be attributed to a large number of recombination centers. The fill factor of our state-of-theart solar cell is limited by the dark current for small illumination intensities, by series resistance for high illumination levels and by both at its maximum under AM1.5 illumination. Short-circuit current and open-circuit voltage pairs measured under intensities from 10-6 to 30 suns reveal a diode characteristic corresponding to an ideality factor of one at large forward bias.
Ex situ and in situ defect density measurements of a-Si:H by means of the cavity ring down absorption technique
Authors: Smets A.H.M. , van Helden J.H. , van de Sanden M.C.M. 
Published: April 2011

ABSTRACTFor the first time it is demonstrated that the surface defect density can be measured using the cavity ring down (CRD) absorption technique and it is shown that CRD is more sensitive for surface defects than dual beam photoconductivity (DBP) technique. Ex situ measurements have shown that the surface defects of the oxidized a-Si:H surface are distributed over a surface region with thickness W(d). The obtained surface defect density is 1.0 × 1012 up to 1.4 × 1012 cm-2. During growth the a-Si:H surface defect density region has at least a thickness of 15 nm. During deposition of 15 nm a-Si:H the surface density increases up to a not yet saturated value of 1×1013 cm-2.
Study of Defects in Hydrogenated Amorphous Silicon by Constant Photocurrent Method and Positron Annihilation
Authors: Amaral A. , Lavareda G. , de Carvalho C. Nunes , Brogueira P. , Gordo P. M. , Subrahmanyam V. S. , Gil C. Lopes , Naia M.. Duarte , de Lima A. P. 
Published: April 2011

ABSTRACTThe influence of the power density, PD, on the density and structure of defects of undoped a-Si:H thin films, deposited by rf-PECVD, is studied by constant photocurrent method, CPM, and by slow positron beam spectroscopy, respectively. Deep defect density, NDD, remains approximately constant at 10-16 cm-3, typical of device quality material, for PD in the range 7 - 20 mW.cm-3 calculated from CPM. NDD increases roughly one order of magnitude for both low and for high power densities. Positron annihilation spectroscopy reveals the presence of two kinds of vacancy type defects in the films: large vacancy clusters or voids for PD ∼ 7 mW.cm-3 and small vacancy type defects as PD increases to ∼30 mW.cm-3. The relative abundance of the structural defects is shown to be controlled by the power density used during the deposition without affect the electronic deep defect density, significantly.
Charge carrier transport in a-Si:H/c-Si heterojunctions
Authors: Aichberger Susanne von , Wünsch Frank , Kunst Marinus 
Published: April 2011

ABSTRACTContactless transient photoconductivity measurements of a-Si:H / c-Si heterojunctions are presented. It is shown that n a-Si:H / n c-Si junctions furnish an excellent passivation of the n c-Si surface. For i a-Si:H / n c-Si junctions the passivation is better for thicker films, whereas for very thin films (10 nm or less) a deviating behaviour probably due to inhomogeneities is observed. For the p a-Si:H / n c-Si junction separation of excess charge carriers in the space charge region is observed leading to a slowly decaying tail of the signal. This separation is also observed in thick i a-Si:H / n c-Si samples where electrons are injected from the a-Si:H film in the c-Si substrate.
High Electron Mobility TFTs of Nanocrystalline Silicon Deposited at 150°oC on Plastic Foil
Authors: Cheng I-Chun , Wagner Sigurd , Bae Sanghoon , Fonash Stephen J. 
Published: April 2011

ABSTRACTTop gate n-channel thin film transistors (TFTs) of nanocrystalline silicon (nc-Si:H) were fabricated on Kapton polyimide film substrates at a maximum process temperature of 15°C. These are thefirst nc-Si:H TFTs ever made on a plastic substrate. Both intrinsic and n+ source/drain layers were directly deposited at 80 MHz excitation frequency for high growth rate. Coplanar TFTs with top source/drains and staggered TFTs with bottom source/drains were made. The coplanar top gate and top source/drain structures have linear electron mobility of ∼ 30 cm2V-1s-1 and ON/OFF ratio up to ∼ 105. TFTs with the top gate and bottom source/drain structure made to date have linear mobility of up to ∼ 12 cm2V-1s-1 and ON/OFF ratio of ∼105.
T-Site Trapped Molecular Hydrogen in Hot Wire a-Si:H
Authors: Herberg J. , Fedders P. A. , Leopold D. J. , Norberg R. E. , Schropp R. E. 
Published: April 2011

ABSTRACTProton NMR and proton-29Si double resonance NMR have been performed on hot wire a-Si:H films deposited from SiH4. Results are compared with those from conventional plasma enhanced chemical vapor deposition a-Si:H. Proton nutational angle studies and proton-29Si spin-echo double resonance (SEDOR) signals at 80 and 294 K indicate that a significant proton resonance population arises from T-site-trapped molecular H2. The hot wire films also display a ≥80 kHz FWHM uperbroad proton line and a sharp feature diamagnetically shifted by 25 ppm.
High rate growth of device grade silicon thin films for solar cells
Authors: Kondo M. , Suzuki S. , Nasuno Y. , Matsuda A. 
Published: April 2011

ABSTRACTWe have developed a plasma enhanced chemical vapor deposition (PECVD) technique for high-rate growth of µc-Si:H at low temperatures using hydrogen diluted monosilane source gas under high-pressure depletion conditions. It was found that material qualities deteriorate, e.g. crystallinity decreases and defect density increases with increasing growth rate mainly due to ion damage from the plasma. We have found that deuterium dilution improves not only the crystallinity but also defect density as compared to hydrogen dilution and that deuterium to hydrogen ratio incorporated in the film has a good correlation with crystallinity. The advantages of the deuterium dilution are ascribed to lower ion bombardment due to slower ambipolar diffusion of deuterium ion from the plasma. Further improvement of material quality has been achieved using a triode technique where a mesh electrode inserted between cathode and anode electrodes prevents from ion bombardment. In combination with a shower head cathode, the triode technique remarkably improves the crystallinity as well as defect density at a high growth rate. As a consequence, we have succeeded to obtain much better crystallinity and uniformity at 5.8 nm/s with a defect density of 2.6×1016cm−3. We also discuss the limiting factors of growth rate and material quality for µc-Si solar cells.
Directional Field Aided Lateral Crystallization of Amorphous Silicon Thin Films
Authors: Izmajlowicz Marek A. T. , Morrison Neil A. , Flewitt Andrew J. , Milne William I. 
Published: April 2011

ABSTRACTFor application to active matrix liquid crystal displays (AMLCDs), a low temperature (< 600 °C) process for the production of polycrystalline silicon is required to permit the use of inexpensive glass substrates. This would allow the integration of drive electronics onto the display panel. Current low temperature processes include excimer laser annealing, which requires expensive equipment, and solid phase crystallization, which requires high temperatures. It is known that by adding small amounts of metals such as nickel to the amorphous silicon the solid phase crystallization temperature can be significantly reduced. The rate of this solid phase metal induced crystallization is increased in the presence of an electric field. Previous work on field aided crystallization has reported crystal growth that either proceeds towards the positive terminal or is independent of the direction of the electric field. In this work, extensive investigation has consistently revealed directional crystallization, from the positive to the negative terminal, of amorphous silicon thin films during heat treatment in the presence of an electric field. This is the first time that this phenomenon has been reported. Models have been proposed for metal induced crystallization with and without an applied electric field in which a reaction between Ni and Si to produce NiSi is the rate-limiting step. The crystallization rate is increased in the presence of an electric field through the drift of positive Ni ions.
Ge Island evolution during growth, in-situ anneal, and Si capping in an industrial CVD reactor
Authors: Loo Roger , Meunier-Beillard Philippe , Dentel Didier , Goryll Michael , Vanhaeren Danielle , Vescan Lili , Bender Hugo , Caymax Matty , Vandervorst Wilfried 
Published: April 2011

ABSTRACTSi based nanostructures such as Ge or Si1-xGex dots embedded in Si receive a lot of attention. This interest is driven by the reduction of device sizes as well as by their possible use in opto-electronic applications, as a possible solution to improve the radiative light emission. In this paper we give a detailed overview of the growth kinetics as observed for Ge growth in a standard production oriented chemical vapor deposition system. The island morphology and density are controlled by varying the growth conditions or by applying a thermal anneal after the island growth. Island densities up to 2.3x1010 cm−2 have been obtained for depositions at 650°C. With increasing deposition time, the usual change-over from monomodal to bimodal island distribution is pointed out and this change-over depends on the critical island diameter, which decreases with decreasing growth temperature. Applying a thermal budget after the island growth initiates Ge surface diffusion and Si diffusion from the substrate through the islands. This results in an enhancement of the island diameter and height, and also in a reduction of island density. Furthermore, depending on the island distribution after Ge deposition, a transition from pyramid to dome or visa versa is observed after the in-situ anneal. Optical device structures require a Si cap layer. However, Si capping at 700°C, leads to a nearly total dissolution of small islands and a truncation of bigger dome-shaped islands. This can be prevented by reducing the deposition temperature and by changing the Si gas source. Clear island luminescence, is observed up to 200K and lies in the spectral range of 1.35-1.50μm, which is interesting from the point of view of applications. In particular, this shows the potential of this material system for opto-electronic device applications. In spite of the fact that the observed PL intensity is comparable to the best reported values, we could further enhance it by a thermal treatment in a H2 plasma.
Morphology, Phonon Confinement and Properties of a-Si:H Films
Authors: Ligatchev Valeri 
Published: April 2011

ABSTRACTIt is usually assumed that optical and electrical properties of amorphous semiconductors are determined by the short-range-order (SRO) parameters of atomic structure. The SRO parameters behavior is considered here as governed by morphology geometrical parameters (MGP) variations. Generalized Skettrup model is developed for a quantitative description of the MGP influence on the density of electron states distribution N(E). Common N(E) relation for the power, exponential and the ‘defect’ regions of the dependence is derived both for adiabatic (optical) and non-adiabatic (thermal) electron excitation processes. The simulated (by the N(E) convolution) spectral dependence of the opti-cal absorption coefficient contains the Tauc, Urbach and the ‘defect’ parts. The optical gap and the Urbach tail slope energies are typical for the ‘device quality’ a-Si:H films at the average morphology geometrical parameters values of order of 1 μm. Nearly linear the optical gap versus the Urbach tail slope energies dependence is obtained at the mor-phology geometrical parameters and temperature changes. Good agreement of experi-mental and the simulation results is achieved for a-Si:H films, prepared both by the RF sputtering and by the silane decomposition.
Nanoparticle Oxides Precursor Inks for Thin film Copper Indium Gallium Selenide (CIGS) Solar Cells
Authors: Kapur Vijay K. , Fisher Matthew , Roe Robin 
Published: April 2011

ABSTRACTThe paper describes ISET's patented non-vacuum process for low cost mass production of CIGS solar cells. In this process, the water based precursor inks of mixed oxides are deposited on various conducting substrates by a variety of non-vacuum coating techniques. The oxides are converted to CIGS by annealing and the device is completed by deposition of CdS by CBD followed by ZnO deposition by MOCVD. Small area solar cells with efficiency >13% have been fabricated by this process. The advantages of this non-vacuum process are: high compositional control of the absorber layer, high materials utilization and low cost.
Fabrication of Light weight Flexible CIGS solar Cells for Space Power Applications
Authors: Kapur Vijay K. , Fisher Matthew , Roe Robin 
Published: April 2011

ABSTRACTA novel, non-vacuum and a patented process developed by ISET for manufacturing terrestrial CIGS solar cells was successfully applied to fabricate CIGS solar cells on flexible 50 μm thick Mo foil for space power applications. Solar cells of area 5.0 cm2 were fabricated with their AM0 efficiency approaching 9.0% with an estimated power density of 250 watts/kg. With further improvements it is possible to fabricate CIGS solar cells with AM0 efficiencies approaching 13%. This process can be used to fabricate low cost, light-weight CIGS solar cells on a variety of flexible substrates much lighter than Mo foil to achieve power densities approaching 1.0 kW/kg.