bluuebunny/crossref_metadata_2025 huggingface dataset:
Lithium deintercalation in LiNi0.30Co0.70O2: Redox processes, electronic and ionic mobility as characterized by7Li MAS NMR and electrical properties
Authors: Carlier D. , Ménétrier M. , Delmas C.
Published: April 2011

LiNi1-yCoyO2 materials are particularly interesting as positive electrode in lithium-ion batteries. Their 7Li MAS NMR spectra are sensitive to the presence of paramagnetic Ni3+ cations as nearest and next-nearest neighbors. These contact shift (or Fermi contact) interactions are used to yield information on the lithium environment in terms of paramagnetic cations.

Electrochemically deintercalated LixNi0.30Co0.70O2 phases have been characterized by XRD, 7Li MAS NMR, electronic conductivity and thermoelectronic power. Ni3+ oxidation to Ni4+ occurs at the beginning of deintercalation, leading to a Ni3+/Ni4+ hopping which causes an exchange of the 7Li NMR signals of the Li ions interacting with nickel. For higher deintercalation amounts, the signal due to Li ions with only cobalt as first and second neighbor is also involved in the exchange upon heating, showing the onset of ionic hopping. For x close to 0.70, an increase of the NMR shift with temperature is observed, which is assigned to a hopping between Ni4+ and Co3+. Therefore, the question as to which ion is actually oxidized during deintercalation is somewhat irrelevant around this composition. Finally, for x < 0.70, the presence of Ni hinders a true long-range electronic delocalisation between Co4+/Co3+ (LS) as it happens in LixCoO2(x < 0.70). However, electrons are clearly delocalized in restricted zones, as seen from NMR and thermoelectronic power coefficient.
Quantitative Modelling of Nucleation Kinetics in Experiments for Poly-Si Growth on Sio2 by Hot-Wire Chemical Vapor Deposition
Authors: Swiatek Maribeth , Holt Jason K. , Atwater Harry A.
Published: April 2011

We apply a rate-equation pair binding model of nucleation kinetics [1] to the nucleation of Si islands grown by hot-wire chemical vapor deposition on SiO2 substrates. Previously, we had demonstrated an increase in grain size of polycrystalline Si films with H2 dilution from 40 nm using 100 mTorr of 1% SiH4 in He to 85 nm with the addition of 20 mTorr H2. [2] This increase in grain size is attributed to atomic H etching of Si monomers rather than stable Si clusters during the early stages of nucleation, decreasing the nucleation density. Atomic force microscopy (AFM) measurements show that the nucleation density increases sublinearly with time at low coverage, implying a fast nucleation rate until a critical density is reached, after which grain growth begins. The nucleation density decreases with increasing H2 dilution (H2:SiH4), which is an effect of the etching mechanism, and with increasing temperature, due to enhanced Si monomer diffusivity on SiO2. From temperature-dependent measurements, we estimate the activation energy for surface diffusion of Si monomers on SiO2 to be 0.47 ± 0.09 eV. Simulations of the temperature-dependent supercritical cluster density lead to an estimated activation energy of 0.42 eV ± 0.01 eV and a surface diffusion coefficient prefactor of 0.1 ± 0.03 cm2/s. H2-dilution-dependent simulations of the supercritical cluster density show an approximately linear relationship between the H2 dilution and the etch rate of clusters.
Changes in hydrogenated amorphous silicon upon extensive light-soaking at elevated temperature
Authors: Hata N. , Fortmann C. M. , Matsuda A.
Published: April 2011

Previously a through the substrate ellipsomtery technique was used to study the high temperature dynamics of light induced reversible changes in amorphous silicon thin films [1]. Since this technique was based on above gap optical changes it is sensitive to the structural aspects of the light induced effects, differently from the below-gap absorption techniques which detect dangling-bond defect states [2-3]. It was found that high intensity light soaking at an elevated temperature causes surprising large, reversible, changes [1]. By comparing these optical changes with the changes in dangling bond concentrations probed by electronic and below gap methods, a fuller picture of temperature dependent light-induced defect creation and annealing dynamics emerges. A high temperature high intensity light soaking method is developed which reduces saturation times, decreases the saturated dangling bond density, as well as decreases the annealing activation energy. These results are discussed in terms of the coupling between network disorder and its relaxation with respect to defect concentrations at high temperature.
Importance of Defect Density near the p-i Interface for a-Si:H Solar Cell Performance
Authors: Korevaar B.A. , Smit C. , Swaaij R.A.C.M.M. van , Schram D.C. , Sanden M.C.M. van de
Published: April 2011

A cascaded arc expanding thermal plasma is used to deposit intrinsic hydrogenated amorphous silicon at growth rates larger than 2 Å/s. Implementation into a single junction p-i-n solar cell resulted in initial efficiencies of ∼7%, although all the optical and initial electrical properties of the individual layers are comparable with RF-PECVD deposited films. The somewhat lower efficiency is due to a smaller fill factor. Spectral response measurements, illuminated J,V- measurements, and simulations indicate that a higher local defect density in the region near the p-i interface might be responsible for the smaller fill factor in comparison with conventional low- rate RF-PECVD. The higher defect density is most likely caused by the initial growth in the first 10 to 50 nm. Therefore, controlled initial growth of the intrinsic layer is suggested for good solar cell performance.
Controlling The Lateral Photoeffect In a-Si:H Heterojunction Structures: The Influence of The Band Offset Analysed Through A Numerical Simulation
Authors: Fantoni A. , Fernandes M. , Louro P. , Schwarz R. , Vieira M.
Published: April 2011

When an a-Si:H p-i-n structure is locally illuminated by a light spot, the non uniformity of light causes the appearance of a gradient in the carrier concentration between the illuminated and the dark zone. Carrier start to flow in agreement with such gradients, and when equilibrium is reached, the lateral diffusion process is counterbalanced by the appearance of a lateral component of the electric field vector in addition to the transverse usual one. The lateral fields act as a gate for the lateral flow of the carriers and small lateral currents appears at the transition region between the illuminated and the dark zone.

Such lateral photoeffect depends on the incident light wavelength, light intensity and on the device operation condition (mainly the applied bias). The introduction of carbon in the doped layers modifies the intensity and the extension of these lateral effects through the potential barriers deriving from the band banding at the interfaces.

We have used the 2D numerical simulator ASCA to analyze the behavior of an a-Si:H p-i-n structure under local illumination with the goal of observing the appearance of the lateral components of the electric field and current density vectors. Different homo and heterojunctions have been simulated, outlining how the band offset at the interfaces influences the induced lateral photoeffect and aiming to explain how a correct device design and engineering can, depending on the foreseen application, alternatively enhance or reduce the intensity of such lateral effects.
Photocapacitance of Hydrogenated Amorphous Silicon Phototransistors
Authors: Caputo D. , Cesare G. de , Lemmi F. , Nascetti A. , Palma F. , Roca F. , Tucci M.
Published: April 2011

Amorphous silicon-based phototransistors are studied as an alternative solution to replace pixel-level amplifiers simplifying large-area imaging systems. We report electrical characterization by means of current-voltage and capacitance measurements. The measured capacitance increases with decreasing frequency of the probe signal and values largely exceeding the geometrical one at low frequencies have been achieved both in the dark and under illumination. In particular, values in excess of 200 μF/cm2 are measured under 220 μW/cm2 illumination at 600 nm at 100 mHz. The capacitance dependence on frequency is interpreted in terms of trapping and release kinetics processes in the base and of the gain of the device.
Control of Medium Range Order in Amorphous Silicon via Ion and Neutral Bombardment
Authors: Gerbi Jennifer E. , Voyles Paul. M. , Treacy Michael M. J. , Gibson J. Murray , Chen Wangchun , Heuser Brent J. , Abelson J. R.
Published: April 2011

We have observed the existence of medium range order via fluctuation microscopy in amorphous silicon grown at 230°C. We hypothesize that this structure develops during the highly non-equilibrium growth process; high densities of ordered surface nuclei are produced which are subsequently buried and forced into an unfavorable energy state. These nm sized regions are distorted in the bulk due to strain, but remain topologically crystalline. In this work, we alter the growth energetics both at the surface and sub-surface during magnetron sputter film deposition with two kinds of particle bombardment, respectively: a controllable flux of low-energy (20eV) Ar+ ions, and higher energy (100eV) D vs. H neutrals. With this method, we demonstrate for the first time control over the intensity of this medium-range structural order at a constant substrate temperature as seen primarily with fluctuation electron microscopy, but also Raman scattering, spectroscopic ellipsometry, and SAXS. We suggest that these bombardments can increase adspecie surface mobility or drive local sub-surface restructuring (“kinetic annealing”), thus increasing or decreasing the size, density and/or strength of the ordered regions.
Determination of the Mobile-Hydrogen Charge State in Hydrogenated Amorphous Silicon
Authors: Nelsona Brent P. , Xu Yueqin , Reedy Robert C. , Crandall Richard S. , Mahan A. Harv , Branz Howard M.
Published: April 2011

We find that hydrogen diffuses as H+, H0, or H- in hydrogenated amorphous silicon depending on its location within the i-layer of a p-i-n device. We annealed a set of five p-i-n devices, each with a thin deuterium-doped layer at a different location in the i-layer, and observed the D-diffusion using secondary ionmass spectrometry (SIMS). When H-diffuses in a charged state, electric fields in the device strongly influence the direction and distance of diffusion. When D is incorporated into a device near the p-layer, almost all of the D-diffusion occurs as D+, and when the D is incorporated near the n-layer, most of the D-diffusion occurs as D-. We correlate the preferential direction of D-motion at given depth within the i-layer, with the local Fermi level (as calculated by solar cell simulations), to empirically determine an effective correlation energy for mobile-H electronic transitions of 0.39 ± 0.1 eV. Using this procedure, the best fit to the data produces a disorder broadening of the transition levels of ∼0.25 eV. The midpoint between the H0/+ and the H0/- transition levels is ∼0.20 ± 0.05 eV above midgap.
EVALUATION OF MICROCRYSTALLINE SILICON FILMS DEPOSITED BY ULTRAFAST THERMAL PLASMA CVD
Authors: Chae Yongkee , Ohno Hiromasa , Eguchi Keisuke , Yoshida Toyonobu
Published: April 2011

This research is the first attempt at applying thermal plasma chemical vapor deposition (TPCVD) for the ultrafast deposition of Si films for solar cells. A conventional deposition process of Si films, such as plasma-enhanced chemical vapor deposition (PECVD), is capable of a maximum deposition rate of approximately 5 Å/s and it takes a relatively long time to deposit an intrinsic layer. In this paper we report a novel ultrafast deposition approach using dc-rf hybrid TPCVD. The extreme improvement of stability, controllability, and cleanliness of the process enabled the deposition of microcrystalline Si films at the ultrafast rate of over 1000 nm/s, which is about 2000 times faster than that by conventional CVD. Moreover, a minimum defect density of 7.2×1016 cm−3was achieved by post-treatment of the film in 2 Torr H2/Ar plasma. Monte-Carlo simulation and step coverage analysis suggested that the precursor is an approximately 1 nm cluster with a sticking probability of about 0.6. The success of this research will lead to the development of commercially viable technology in a roll-to-roll system in the near future, and will fundamentally change the established concepts of Si deposition technology.
Ion-assisted Sputter Deposition of Microcrystalline Silicon Films with Pulsed-DC Plasma Excitation
Authors: Reinig P. , Fenske F. , Selle B. , Fuhs W.
Published: April 2011

We have applied a novel Ion-Assisted Sputter Deposition (IASD) method to deposit microcrystalline silicon (µc-Si) thin films with high deposition rates. An unbalanced magnetron sputter source together with an asymmetrical bipolar pulsed-DC plasma excitation operating in the frequency range 50-250 kHz was used for realizing high ion fluxes to the growing film. µc-Si films of high crystallinity are obtained at T > 400 °C with growth rates of up to 90 nm/min. The crystallinity of the films is characterized by the thickness-independent ratio of the optical thickness n·d determined by FTIR measurements and the atomic area density N·d as given by RBS analysis.
Stability and Nanostrucure of Heterogeneous Amorphous Silicon Thin-Film Synthesized Under High Chamber Pressure (500 To 2200 Mtorr) Regime of Rf Pecvda
Authors: Middya A. R. , Hamma S. , Hazra S. , Ray S. , Longeaud C.
Published: April 2011

We report on improvement in stability of a new type of amorphous silicon films, synthesized (growth rate > 0.1 nm/s) by driving the plasma condition close to the powder regime (or “γ-regime”) of rf PECVD. These films exhibit high mobility-lifetime products [(μτ)annld ∼ 10−4 cm2/V, σph/σd ∼ 5-10×105, Ea ≍ 0.7 - 0.9 eV ], compact network structure [CH ≍ 7 to 8 at%, nanovoid density < 0.01 %, ρ ≍ 2.23 ± 0.01 gm/cm3], new features of optical properties and density-of-state (DOS) above EF is significantly lower than that of state-of-the art films. The kinetics of light-induced (AM 1.5) degradation of μτ is very fast and saturated μτ ∼ 10−6cm2/V, a value similar to that of conventional a-Si:H films at annealed state. The improved stability of “new” a-Si films, henceforth it will be denoted as “quasi-amorphous silicon (qm-Si) thin- film”, will be correlated with its specific nanostructure.
Novel ‘Photochemical deposition’ and conventional ‘Electrochemical deposition’ of CdS and HgxCd1−xTe thin films and their characterization for solar cell device applications
Authors: Kumaresan R. , Ichimura M. , Babu S.Moorthy , Ramasamy P.
Published: April 2011

Solar cell devices of the structures CdS/CdTe and CdS/HgCdTe, based on II-VI semiconductor thin films have been fabricated and analyzed. CdS thin films were deposited by the recently established novel deposition technique, namely, 'Photochemical deposition' and the Cd rich HgxCd1−xTe films used for the device fabrication were deposited by the conventional ‘electrochemical deposition’ technique. First solar cell devices of the structures CdS/CdTe and CdS/HgCdTe using photochemically deposited CdS films, were fabricated and analyzed for the conversion efficiency.
Design, Actual Performance, and Electrical Stability of CISCuT-Based Quasi-Endless Solar Cell Tapes
Authors: Winkler Michael , Penndorf Jürgen , Griesche Joachim , Konovalov Igor , Tober Olaf
Published: April 2011

Solar cells based on Cu-In-S-phase absorber layers on a quasi-endless copper tape were made in a series of consecutive roll-to-roll processes, for which a base line has recently been set up. The so called “as grown cell absorber”, which consists of a stack of CuIn5S8 and CuInS2 layers, is completed to a solar cell by a CuI buffer layer of about 70 nm thickness and a 1 μm thick ZnO-TCO window layer. The design of the whole cell including the phase constitution of the absorber layer and the actual standard electrical characteristics will be presented. Considering the first stability tests and the experimental possibilities of the base line, an outlook will be given concerning the ability and perspectives of using these cell tapes for module production.
Influence of atomic hydrogen on intrinsic defects in CuInSe2
Authors: Otte Karsten , Lippold Gerd , Frank Wilfried , Wenzel Axel , Krauser Johann , Weidinger Alois , Schindler Axel
Published: April 2011

Hydrogen with an energy of 300 eV was implanted into single crystalline CuInSe2samples at temperatures of 200 °C and 300 °C during implantation. We found that the hydrogen is not limited to the expected implantation depth but diffuses into the bulk of the sample. The hydrogen concentration ranges from 1019H/cm3in a depth of about 300 nm up to some 1021H/cm3next to the surface and resembles a diffusion profile. The hydrogen induced change of composition was not only at the surface, but also up to a depth of about 200 nm similar to that of the hydrogen profile. Mainly a Cu deficiency after hydrogen implantation could be observed and is explained as the passivation of VCuby hydrogen and the additional production of VCuby the induced band-bending.
Effect of CdTe thickness reduction in high efficiency CdS/CdTe solar cells
Authors: Gupta Akhlesh , Matulionis I. , Drayton J. , Compaan A.D.
Published: April 2011

High efficiency CdTe solar cells are typically grown with CdTe thicknesses from 3 to 15 μm, although the thickness required for 90% absorption of the incident irradiation at 800 nm is only ∼1 μm. In this paper, we present the effect of CdTe thickness reduction on the performance of CdS/CdTe solar cells in which both the CdS and CdTe films were grown by sputtering. We produced a series of cells with different CdTe thickness (from 0.5 to 3.0 μm), and held the CdS thickness and back-contact-processing constant. The effect of CdTe thickness reduction on the diffusion of CdS into CdTe was studied using optical absorption and x-ray diffraction techniques. Only slight decreases occur in open-circuit voltage, short-circuit current, and fill factor with decrease in CdTe film thickness to 1.0 μm. Almost 10% efficient cells were obtained with 1 μm CdTe. Below 1 μm, all cell parameters decrease more rapidly, including the red quantum efficiency.
Importance of electron current in p-type CdTe in CdS/CdTe thin film solar cells at forward bias
Authors: Beier Jutta , Köntges Marc , Nollet Peter , Degrave Stefaan , Burgelman Marc
Published: April 2011

In previous work [1,2], we modeled the cross-over of the I-V curves of thin film CdS/CdTe solar cells in terms of an electron (minority carrier) current in the vicinity of the back contact. In this work, we focus on the necessary extension of this analytical model based on a series of measurement results. Especially the wavelength and voltage dependence of the current at forward bias is illustrated in these measurements. The various possible causes for this kind of behavior are discussed and modeled. The extensions to the previous model, needed to describe the voltage and wavelength dependent behavior of I-V curves of real CdTe/CdS solar cells, are proposed.
Characterisation of TiO2films grown at low temperatures for alternative gate dielectric application
Authors: Zhang Jun-Ying , Boyd Ian W.
Published: April 2011

In this paper we report the growth of thin titanium oxide films on Si (100) and quartz at low temperatures (≤350°C) by photo-induced chemical vapor deposition (photo-CVD) with 222 nm UV radiation using a novel injection liquid source, which overcomes the reproducible problem in conventional bubblers. The properties of the films formed have been studied using ellipsometry, UV spectrophotometry and Fourier transform infrared spectroscopy (FTIR) measurements. Nanostructured films were observed by atomic force microscopy (AFM). It was found that crystalline TiO2films could be formed at deposition temperatures as low as 210°C by x-ray di ffraction (XRD). The influence of the deposition temperature on the film is discussed. The refractive index as high as 2.5 can be obtained at a deposition temperature of 350°C, while an optical transmittance of between 80-95% in the visible region of the spectrum was obtained at different deposition temperatures. Physical and optical characterization both reveal good film qualities, rendering this technique promising for a wide range of industrial application in low temperature microelectronic and optoelectronic material processing as well as for many heat sensitive compounds.
Discrete dislocation sim ulation of thin film plasticit y
Authors: von Blanckenhagen B. , Gumbsch P. , Arzt E.
Published: April 2011

A discrete dislocation dynamics sim ulation is used to investigate dislocation motion in the confined geometry of a polycrystalline thin film. The repeated activ ation of a Frank-Read source is sim ulated. The stress to activate the sources and to initiate plastic fiow is significantly higher than predicted by models where the dislocations extend o ver the entire film thic kness. An efiective source size, which scales with the grain dimensions, yields fiow stresses in reasonable agreemen t with experimen ts. The infiuence of dislocations deposited at interfaces is investigated by comparing calculations for a film sandwic hed between a substrate and a capping layer with those for a free standing film.
Solid Solution Alloy Effects on Microstructure and Indentation Hardness in Pt-Ru Thin Films
Authors: Hyun Seungmin , Kraft Oliver , Vinci Richard P.
Published: April 2011

The elastic moduli and flow stresses of as-deposited Pt and Pt-Ru solid solution thin films were investigated by the nanoindentation method. The influence of solid solution alloying was explored by depositing Pt-Ru solid solution thin films with various compositions onto Si substrates. The 200 nm films were prepared by DC magnetron cosputtering with a Ru composition range from 0 to 20wt%. As expected, the modulus and the flow stress both increased significantly with an increase in Ru. The experimental results compare favorably to predictions based on a simple dislocation motion model consisting of three strengthening terms: substrate constraint, grain size strengthening and solid solution strengthening.
Temperature and Strain Rate Dependence of Deformation-Induced Point Defect Cluster Formation in Metal Thin Foils
Authors: Yasunaga K. , Matsukawa Y. , Komatsu M. , Kiritani M.
Published: April 2011

The mechanism of plastic deformation in thin metal foils without involving dislocations was examined by investigating the variations in vacancy cluster formation during deformation for a range of deformation speeds and temperatures. The deformation morphology was not seen to change appreciably over a very wide range of strain rate, 10-4/s – 106/s, whereas the number density of vacancy clusters was observed to increase with increasing strain rate up to saturation value that is dependent on materials and temperature. The density of vacancy clusters decreased to zero with decreasing deformation speed. The strain rate at which the density of vacancy clusters begins to decrease was found to be proportional to the vacancy mobility, suggesting that the vacancies are generated as dispersed vacancies and escape to the specimen surfaces during slow deformation without forming clusters. A very long tail in the distribution of the density of vacancy clusters towards lower strain rates was reasonably attributed to the generation of small vacancy complexes due to deformation. These results give valuable information that can be used to establish new models for plastic deformation of crystalline metals without involving dislocations.
Misfit Dislocation Introduction During The Epitaxial Growth of Inas Islands on Gap
Authors: Gopal Vidyut , Vasiliev Alexander L. , Kvam Eric P.
Published: April 2011

The initial growth of InAs on 11% lattice mismatched GaP substrates by molecular beam epitaxy was investigated. High resolution transmission electron microscopy (HREM) images showed that the InAs grew in the form of three-dimensional islands of dissimilar sizes. Mismatch induced strain relief was effected by the direct introduction of (mostly) edge dislocations at the corners of the islands. An examination of HREM images of several islands revealed that the island aspect ratio decreased with the introduction of misfit dislocations. Strain relaxation in the smaller, relatively dislocation-free islands occurred by elastic deformation of InAs lattice planes, which was more effective far from the constrained island-substrate interface. As a result, these islands grew taller and narrower, with a gradient in the elastic strain energy. However, a higher aspect ratio resulted in a higher surface area – to – volume ratio, and increased the surface energy of the InAs islands. Consequently, there was a driving force for the reduction of the aspect ratio if an alternate avenue for strain relaxation existed. The alternate route was plastic deformation by the introduction of misfit dislocations. As the island grew, the strain at the island corners increased, and beyond a critical value, misfit dislocations were added. These dislocations relieved strain at the heterointerface, and promoted the islands to grow laterally, i.e., the aspect ratio decreased. Islands coalesced, and a continuous layer resulted by a nominal thickness of 3 nm. Thus, the morphology of InAs islands grown on GaP was determined by the balance between elastic and plastic deformation.
Wafer Bonding of Silicon Carbide and Gallium Nitride
Authors: Lee Jaeseob , Cook T. E. , Bryan E. N. , Hartman J. D. , Davis R. F. , Nemanich R. J.
Published: April 2011

Wafer bonding of SiC and GaN may prove important in the formation of high power heterojunction devices. Results of bonding SiC (C or Si surface) onto GaN (Ga surface) are presented. The samples were n-type 6H SiC and epitaxial n-type 2H(wurzite) GaN grown on SiC. The results demonstrate bonding for both possibilities, but the bonding of the C surface SiC to Ga surface GaN is more readily accomplished. A lower resistance was found for the C-face SiC/Ga-face GaN. The results indicate that the polarity of the interface is important for bonding of these materials.
Orientation and Boron Concentration Dependence of Si Layer Transfer by Mechanical Exfoliation
Authors: Henttinen Kimmo , Suni Tommi , Nurmela Arto , Airaksinen Veli-Matti , Suni Ilkka , Lau S.S
Published: April 2011

Mechanical exfoliation strength has been measured in hydrogen implanted <100>, <111> and <110> oriented Si wafers using the crack opening method. The bonding temperature required for exfoliation increases in the order <100>, <111> and <110>. The same method has been applied to study the influence of boron doping on mechanical exfoliation in <100> Si wafers. The required bonding temperature to exfoliate mechanically decreases with increasing doping level independent of the electrical activation of boron. The enhanced crystallization rate of boron doped Si is suggested as a plausible explanation for the result.
Excimer Laser Annealing Effect on MILC Polycrystalline Silicon Film
Authors: Park Kee-Chan , Song In-Hyuk , Jung Sang-Hoon , Han Min-Koo
Published: April 2011

XeCl excimer laser was irradiated on metal induced laterally crystallized (MILC) polycrystalline silicon (poly-Si) film in order to eliminate the intra-grain defects of MILC poly-Si film which incorporated 2 μm wide metal induced crystallized (MIC) poly-Si line pattern. On the irradiation of the laser beams, different melt and recrystallization phenomena were observed in the MILC and the MIC poly-Si region due to the Ni content difference in each film. The transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS) measurements indicated that the melting temperature of the poly-Si film decreased as the Ni content increased. With the laser irradiation energy density of 370 mJ/cm2, 2 μm long defect-free poly-Si grain was successfully grown in the MILC poly-Si due to the melting temperature variation at the MILC-MIC poly-Si boundary.
PECVD Amorphous Silicon Nitride at 120°C for a-Si:H TFTs.
Authors: Stryahilev Denis , Sazonov Andrei , Nathan Arokia
Published: April 2011

The effect of a-SiNx films stoichiometry and their physical properties on the electrical integrity and masking ability is studied. The films are deposited at 120° C by 13.56 MHz PECVD from SiH4+NH3 + N2 gas mixture. They have the N/Si ratio of 1.4 to 1.7 and hydrogen concentration of 25 to 40 at.%. The electrical characterization was carried out by I-V measurements. An electrical resistivity of ∼1016 Ohm-cm and breakdown voltage of 5.5 MV/cm have been achieved for our PECVD nitride films. The performance of a-Si:H TFTs with these silicon nitride as the gate dielectric and passivation layer has been also evaluated.
Emission Properties of Nanostructured Carbon Field-Emission Cathodes
Authors: Chakhovskoi A.G , Chubun N.N , Hunt C.E. , Obraztsov A.N , Volkov A.P.
Published: April 2011

Planar field-emission cathode structures consisting of nanostructured carbon flakes have been investigated as an electron source for flat panel display application.

Layers of nanoflakes were grown on silicon and molybdenum substrates using a high- temperature pyrolitic plasma-assisted CVD method. The result is a vertically oriented nanocluster layer of 1-2 micrometer height chemically bonded with the substrates. Additional orientation of the flakes, occurring during the first activation of the cathodes, was observed.

Field emission properties of the emitters were studied in a vacuum chamber and in sealed flat-panel prototype devices with non-patterned low-voltage phosphor screens. Emitters with an area up to 1 square inch were tested under DC currents up to 100 microamps in diode mode. Anode bias up to 1.5 kV was applied. Current fluctuations of 1-2% were achieved using loading resistor.
Effects of Process Conditions on the Performance of Large Grain Poly-Silicon on Insulator (LPSOI) MOSFET for Advanced CMOS Applications
Authors: Shivani S. , Ng K. L. , Cheng C. F. , Poon M. C. , Chan Mansun
Published: April 2011

Effects of process annealing temperature on Metal-Induced-Lateral-Crystallization (MILC) growth rate and quality of MILC polysilicon formed were studied. Raman spectrum analysis was employed for material characterization. MILC polysilicon layer, which was formed by applying an optimum annealing condition together with post high temperature annealing, could be used to fabricate Thin-Film-Transistor (TFT) with considerably electrical improvements. This reflected that good quality of the polysilicon layer. It is believed that the proposed MILC formation method can be empolyed to produce large grain polysilicon on insulator (LPSOI) for advanced devices and circuits' fabrication.
Positron Annihilation Lifetime Spectroscopy (Pals) Application in Metal Barrier Layer Integrity for Porous Low-K Materials
Authors: Lin Simon , Sun Jia-Ning , Gidley David W. , Wetzel Jeffrey T. , Monnig K.A. , Ryan E. Todd , Jang Simon , Yu Douglas , Liang M.S.
Published: April 2011

Positron Annihilation Lifetime Spectroscopy (PALS) (1, 2) is a useful tool to pre-screen metal barrier integrity for Si-based porous low-k dielectrics. Pore size of low-k, thickness of metal barrier Ta, positronium (Ps) leakage from PALS, trench sidewall morphology, electrical test from one level metal (1LM) pattern wafer and Cu diffusion analysis were all correlated. Macro-porous low-k (pore size >= 200A) and large scale meso-porous low-k (>50∼200A) encounter both Ps leakage and Cu diffusion into low-k dielectric in the 0.25μmL/0.3μmS structures when using SEMATECH in-house PVD Ta 250A as barrier layer. For small scale meso-porous (>20∼50A) and micro-porous (<=20A) low-k, no Ps leakage and no Cu diffusion into low-k were observed even with PVD Ta 50A, which is proved also owing to sidewall densification to seal all sidewall pores due to plasma etch and ash. For future technology, smaller pore size of porous Si-based low-k (=< 50A) will be preferential for dense low-k like trench sidewall to avoid metal barrier integrity due to coverage problems from sidewall pores.
Plasticity Length Scale in LIGA Nickel MEMS Structures
Authors: Lou J. , Shrotriya P. , Allameh S. , Yao N. , Buchheit T. , Soboyejo W.O.
Published: April 2011

The plasticity length scale parameters associated with rotational and stretch gradients in LIGA nickel MEMS structures plated from sulfamate bath are presented in this paper. These are obtained from micro-bend and micro-tensile experiments on LIGA nickel films with different thicknesses. The composite length-scale parameter, lc is measured to be ∼ 4.8 νm for as-plated films (25, 50, 100 and 175 νm thick). The implications of the results are then discussed for the modeling of plasticity in LIGA nickel structures.
New MEMS Technology Using Multi-Layer NILC Poly-Si and NiSi Films
Authors: Cheung W. M. , Cheng C. F. , Poon M. C. , Qin M. , Yuen C. Y. , Chan Mansun
Published: April 2011

A novel MEMS technology using multi-layer poly-silicon (poly-Si) is proposed. The poly-Si film is formed from the new Nickel-Induced-Lateral-Crystallization (NILC) method and has very large grain (>10νm) and near crystal quality. 700 nm thermal oxide was grown on a Si wafer. 100 nm LPCVD amorphous Si was deposited and followed by a 50 Å Ni deposition. The a-Si was crystallized at 550°C for 65 hours and subsequent 800°C for 2 hours to form the first (lower) NILC poly-Si layer. N-channel TFTs were fabricated on the NILC polysilicon layer. The process was repeated and a second (upper) polysilicon layer and TFTs were formed on top of the first polysilicon layer.

The lower polysilicon has slightly larger grains and better material quality. Thin-film- transistors (TFT) fabricated on the 3-dimensional (3-D) poly-Si layers have I-V characteristics similar to (>40%) silicon-on-insulator TFTs. While TFTs on lower layer have better mobility and device properties, TFTs on upper layer have better uniformity. The accumulated heating and other effects have also been studied.
Aluminum-Silicon and Gold-Silicon Eutectics: New Opportunities for MEMS Technologies
Authors: Iliescu Ciprian , Poenar Daniel P. , Nanyang Jianmin Miao
Published: April 2011

Our practical experiments highlight that aluminum-silicon (Al-Si) and gold-silicon (Au- Si) eutectics are fairly inert to the attack of both anisotropic and isotropic wet etchants of Si (e.g. KOH or HF/HNO3 solutions). Therefore, these interfacial eutectics can be used as etch-stop layers in wet etching-based bulk micromachining. This paper presents how Al-Si and Au-Si eutectic layers may be employed for applications whose production involves such operations (e.g. high-pressure sensors) and will discuss three major directions of interest: eutectic formation, diaphragm generation and application of the eutectic layer in a pressure sensor.
Materials Issues in the Application of Silicon Nitride Films in Silicon MEMS
Authors: Moore David F. , Bostock Roger M. , Boyle Paul , Conradie Ewan H.
Published: April 2011

This paper reviews bulk micromachining of Si, with particular reference to the microassembly and packaging of optical and electronic components. Taking as an example the use of 2.3 [.proportional]m thick silicon nitride microclips to hold an optic fibre in place in a silicon V-groove, the potential of thin film packaging is briefly assessed. The fabrication process is to: [i] deposit a controlled stress silicon nitride layer onto a blank (100) oriented silicon wafer by chemical vapour deposition (standard LPCVD but silicon rich); [ii] pattern the silicon nitride clip mask shape by optical lithography and reactive ion etching; and [iii] remove the underlying silicon to form a V-shaped groove with an anisotropic liquid etch process using the silicon nitride as a mask. From the measured deflection of a silicon nitride beam when a force is applied, the Young's modulus is 400 GPa. The beams are rugged and a clipping force of 10 N per metre of optic fibre length is achieved.

This approach to applying the mechanical properties of thin films is compatible with standard thin film technology, enables precise microassembly, and has great potential to reduce manufacturing costs in a wide range of sensors and microsystems. In some applications high temperature processing must be avoided, even early on in the manufacturing process. Using low temperature processing, robust clips from silicon nitride made by plasma enhanced chemical vapour deposition (PECVD and hydrogen rich) are made, but the Young's modulus of this material is typically 40 GPa and the clipping force is correspondingly small. The paper concludes by assessing the prospects for other thin film materials in mechanical MEMS and packaging.
Thin Film Superconducting MgB2 Grown by MBE without Post-Anneal
Authors: Jo William , Huh Jeong-Uk , Ohnishi Tsuyoshi , Marshall Ann F. , Beasley Malcolm R. , Hammond Robert H.
Published: April 2011

We report the synthesis of superconducting MgB2 thin films grown in-situ by molecular beam epitaxy (MBE). Mg-rich fluxes are deposited with B-flux by electron beam evaporation onto c- and r-plane sapphire substrates. Deposition temperature is varied between 260 ∼ 320 °C. Base pressure of the MBE chamber is at low 10-10 Torr, rising to 10-8 Torr during deposition due mostly to the presence of hydrogen and nitrogen. Asgrown MgB2 films show superconducting transition at ∼ 34 K with ΔTc < 1 K. The films on c-plane sapphire substrates exhibit c-axis oriented peaks of MgB2, and full-width at half maximum of 3 degree in their rocking curves. Azimuthal phi-scan of the MgB2(101) peak shows 12-fold symmetric peaks, which is confirmed by selected area diffraction pattern in transmission electron microscopy (TEM). Plan-view TEM shows hexagonal-shaped grain growth with grain size of about 400 Å.
High-Temperature Superconductivity in Graphite-Sulfur Composites: Theoretical Analysis
Authors: Galvão D. S. , Laks B. , Silva R. R. da , Torres J. H. S. , Kopelevich Y.
Published: April 2011

Recently superconductivity in graphite-sulfur composites was experimentally observed. In this work we have analyzed the electronic structure changes associated with the presence of sulfur atoms in one and two dimensional graphite layers. We have considered ordered and disordered sulfur atoms distributions in many configurations. The density of states (DOS) of these structures were obtained using the negative factor counting (NFC) technique coupled to a tight-binding hamiltonian (Hückel type). Our results indicate that the incorporation of sulfur atoms at edge graphite layers (changing their global geometric curvature and increasing the DOS at the Fermi level) might be in the origin of the graphite superconductivity.
The Effect of Sheath Materials on the Superconductivity of MgB2
Authors: Zhu W. , Watson D. R. , Cave J. R.
Published: April 2011

Inconel, tantalum and a silver-palladium alloy were used to fabricate MgB2tapes. The tapes, made by the Powder In Tube (PIT) method, were heat-treated at 800°C and 900°C in 1 atmosphere of flowing argon. The microstructure and phase composition of the tapes were examined by Scanning Electron Microscopy (SEM) and X-Ray Diffractometry (XRD). Critical temperatures (Tc) and magnetization-applied magnetic field (M-H) curves were measured by SQUID magnetometry. It is found that between 800–900°C inconel and tantalum sheaths have no effect on the Tc,inductive of the material. However, under certain processing conditions, the silver-palladium sheath can decrease the Tcor destroy the superconductivity completely. The inconel sheathed tape was found to have better superconducting properties than the tantalum and silver-palladium sheathed tapes. Consistency checks have been applied to verify the validity of the Bean Model in obtaining the critical current density (Jc) from magnetization data. The inconel sheathed tape is estimated to have a magnetization Jc(5K, ∼0.5 T) of 1.4 × 105A/cm2.
Pulsed Laser Deposition of Y1Ba2Cu3O7-δ?Thin Films in High Oxygen Partial Pressures
Authors: Haugan Timothy J. , Barnes Paul N. , Nekkanti Rama M. , Maartense Iman , Brunke Lyle B. , Murphy John P.
Published: April 2011

Pulsed laser deposition of Yba2Cu3O7-δ?(YBCO) coated conductors was studied for the range of P(O2) from 120 mTorr to 1200 mTorr, higher than typically used oxygen partial pressures during deposition. The purpose of the investigation was to determine the sensitivity of YBCO film quality to varying P(O2) for scaled-up fabrication of long-length coated conductors. Deposition at high P(O2) (≥?400 mTorr) gave very high and more consistent critical temperatures (Tc ≈?92 ±?0.4 °K) than results obtained at lower oxygen partial pressures (≤?200 mTorr) as determined by magnetic susceptibility measurements. Typically, the lower partial pressures are used although the laser fluence used in this research (3.2 J/cm2) is higher than typical. Transport Jc's were consistantly high for a wide range of oxygen pressures, 5–8 ×?106 A/cm2 at 77 K, self-field for P(O2) = 200–1200 mTorr. These results indicate that pulsed laser deposition of YBCO is relatively insensitive to P(O2) at the higher pressures of oxygen considered.
Texture by the kilometer
Authors: Specht E. D. , List F. A.
Published: April 2011

A novel x-ray diffractometer has been used to characterize the texture of 2 km of textured tape in segments up to 20 m long. Techniques have been developed for the study of the uniformity of texture and for the detection of second phases, deviations from cube texture, and the sharpness of cube texture, in metal substrates, oxide buffer layers, and YBa2Cu3O7 (YBCO) superconductors.
Engineered Microstructures and Transport Properties in YBCO Coated Conductors
Authors: Holesinger T. G. , Gibbons B. J. , Coulter J. Y. , Foltyn S. R. , Groves J. R. , Arendt P. N.
Published: April 2011

Each process used to deposit or make the bi-axially textured template, buffer layer(s), and the superconductor in a coated conductor creates interfaces along which defects or interfacial reactions may result. These defects can be additive and propagate through the entire film structure to affect the growth and properties of the superconducting film. Defects within the films and their corresponding transport properties have been correlated with the differences in the thickness of the underlying buffer layer material. This knowledge can be used to control and engineer the structure of the coated conductor to maximize critical current densities.
Overview of Various Strategies and Promising New Bulk Materials for Potential Thermoelectric Applications
Authors: Tritt Terry M.
Published: April 2011

Recently, there has been a renewed interest in thermoelectric material research. There are a number of different systems of potential thermoelectric (TE) materials that are under investigation by various research groups. Some of these research efforts focus on minimizing lattice thermal conductivity while other efforts focus on materials that exhibit large power factors. An overview of some of the requirements and strategies for the investigation and optimization of a new system of materials for potential thermoelectric applications will be discussed. Some of the newer concepts such as low-dimensional systems and Slack's phononglass, electron-crystal concept will be discussed. Current strategies for minimizing lattice thermal conductivity and also minimum requirements for thermopower will be presented. The emphasis of this paper will be to identify some of the more recent promising bulk materials and discuss the challenges and issues related to each. This paper is targeted more at “newcomers” to the field and does not discuss some of the very interesting results that are being reported in the thin film and superlattice materials. Some of the bulk materials which will be discussed include complex chalcogenides (e.g.CsBi4Te6 and pentatellurides such as the Zr1−XHfXTe5 system), half-Heusler alloys (e.g. TiNiSn1−XSbX), ceramic oxides (NaCo4O2), skutterudites (e.g. YbXCo4−XSb12 or EuXCo4−XSb12) and clathrates (e.g. Sr8Ga16Ge30). Each of these systems is distinctly different yet each exhibits some prospect as a potential thermoelectric material. Results will be presented and discussed on each system of materials.
Thermoelectric Transport Properties of Individual Bismuth Nanowires
Authors: Cronin Stephen B. , Lin Yu-Ming , Rabin Oded , Black Marcie R. , Dresselhaus Gene , Dresselhaus Mildred S.
Published: April 2011

We developed a method for making 4-point contacts to Bi nanowires with a thick oxide coat using a combination of lithographic and focused ion beam (FIB) techniques. The resistivity of Bi nanowires with diameters in the range 70-200nm is found to increase with decreasing wire diameter. In contrast to bulk Bi, the temperature dependence of the resistivity is found to decrease monotonically with increasing temperature. The results are explained on the basis of increased scattering in the nanowire and the known temperature dependence of the electronic properties of bulk Bi. A large magneto-resistance was also measured, indicating a high crystalline quality of the nanowires. A large spread in the measured values of the resistivity indicates significant systematic error in the measurement technique. Possible sources for error are discussed.
Thermoelectric Module For Low Temperature Applications
Authors: Lal Sangeeta , Loo Sim , Chung Duck-Young , Kyratsi Theodora , Kanatzidis Mercouri G. , Cauchy Charles , Hogan Timothy P.
Published: April 2011

The possibility of a prototype thermoelectric cooling device for operation near liquid nitrogen temperatures has been explored. In these devices, the figure of merit involves a combination of the properties of the two branches of the module. Here, we investigate the fabrication of a module with a new low temperature material, CsBi4Te6 (p-type), and the best known low temperature n-type materials Bi85Sb15. Transport measurements for each of these materials show high performance at low temperatures. Known values for the figure of merit Zmax of CsBi4Te6 is 3.5 × 10−3 K−1 at 225K and for Bi85Sb15 is 6.5 × 10−3 K−1 at 77K. At 100K these values drop to 2.0×10−3 K−1 for CsBi4Te6 and 6.0×10−3 K−1 for Bi85Sb15. Theoretical simulations based on these data show a cooling of δT = 12K at 100K, which is almost three times the efficiency of a Bi2Te3 module at that temperature. We present transport measurements of elements used in the fabrication of a low temperature thermoelectric module and properties of the resulting module.
Investigation of i-AlCuFe Quasicrystals and their ω and β Approximants as Thermoelectric Materials
Authors: Alboni P. N. , Pope A. L. , Tritt T. M. , Ross A. R. , Jenks C. , Sordelet D.
Published: April 2011

In the search for new thermoelectric materials, quasicrystals have been investigated due to their inherently low thermal conductivity. Crystalline phases called approximants which are closely related to the quasicrystals, however, have largely been ignored. These approximants have similar structure, yet the periodicity of a crystal. In this paper, we have investigated an icosahedral i-AlCuFe quasicrystalline phase as well as two of its corresponding approximant phases (ω and β). Electrical and thermal transport properties of these materials are presented. The viability of the i-AlCuFe quasicrystalline system and the ω and β approximant phases as thermoelectric materials is discussed.
Thermoelectric Nanowires by Electrochemical Deposition
Authors: Rabin Oded , Lin Yu-Ming , Cronin Stephen B. , Dresselhaus Mildred S.
Published: April 2011

Nanowires made of thermoelectric-relevant materials were grown by electrochemical deposition. Their diameter and ordering are dictated by the porous alumina template that is fabricated on the working electrode prior to the deposition. The composition of the nanowires is controlled by the composition of the electrolyte and the deposition potential. This technique offers unique opportunities regarding the range of geometries and materials that can be employed. The structural and transport properties of these wires will be presented, and comparison will be made to nanowires synthesized by other techniques.