bluuebunny/crossref_metadata_2025 huggingface dataset:
CIGS2 Thin Film Solar Cells on Stainless Steel Foil
Authors: Dhere Neelkanth G. , Ghongadi Shantinath R.
Published: April 2011

CuIn1−xGaxS2 (CIGS2) thin-film solar cells are of interest for space power applications because of the near optimum bandgap for AM0 solar radiation in space. CuIn1−xGaxSe2−ySy (CIGS) and CIGS2 solar cells are expected to be superior to Si and GaAs solar cells for the space missions especially in terms of the performance at the end of low earth orbit (LEO) mission. Ultra-lightweight thin-film solar cells deposited on flexible stainless steel (SS) foils have a potential for achieving high specific power.

Magnetron-sputter-deposition parameters of molybdenum back-contact layer were optimized so as to minimize residual stress. Cu-rich Cu-Ga/In layers were sputter-deposited on unheated Mo-coated SS foils from CuGa(22%) and In targets. Well-adherent, large (3 μm), compact-grain Cu-rich CIGS2 films were obtained by sulfurization in a Ar:H2S 1:0.04 mixture and argon flow rate of 650 sccm, at the maximum temperature of 475° C for 60 minutes with intermediate 30 minute annealing step at 120° C. p-type CIGS2 thin films were obtained by etching away the Cu- rich layer segregated at the surface in a dilute KCN solution. XRD analysis of a CIGS2 film on SS foil revealed growth of chalcopyrite CIGS2 phase having ao= 5.519 Å and co= 11.125 Å and {112} preferred orientation. Positive SIMS depth profile of CIGS2 film showed gallium concentration increasing toward the back contact.

Solar cells were completed by deposition of CdS heterojunction partner layer by chemical bath deposition, transparent-conducting ZnO/ZnO:Al window bilayer by RF sputtering, and vacuum deposition of Ni/Al contact fingers through metal mask. PV parameters of a CIGS2 solar cell on SS flexible foil measured under AM 0 conditions at the NASA GRC were: Voc = 802.9 mV, Jsc = 25.07 mA/cm2, FF = 60.06%, and η = 8.84%. For this cell, AM 1.5 PV parameters measured at NREL were: Voc = 788 mV, Jsc = 19.78 mA/cm2, FF = 59.44%, η = 9.26%. Quantum efficiency curve showed a sharp QE cutoff equivalent to CIGS2 bandgap of ∼1.50 eV, fairly close to the optimum value for efficient AM0 PV conversion in the space.
Alloying and selenization of Cu-In stacked layers evaporated onto large areas
Authors: Caballero Raquel , Guillén Cecilia , Bayón Rocío
Published: April 2011

In this work, Cu and In thin films, as precursors for CuInSe2 (CIS) formation, have been deposited on glass substrate up to 30 × 30 cm2 area using an electron beam evaporator in sequential processes. In order to obtain a similar global composition, three types of sequential processes of evaporation: A) Cu/In/Cu/In, B) Cu/In/Cu/In/Cu/In and C) In/Cu/In/Cu have been tested. As-grown thin films were studied at room temperature and after 120° C annealing. XRD analysis of these films showed mainly the CuIn2−x (0≤ × ≤ 1) phase at room temperature, and Cu11In9 after annealing at 120° C. After alloying, the films were selenized at temperature between 250° and 400° C in vacuum using elemental selenium vapour. XRD of the selenized thin films corresponding to In/Cu/In/Cu sequence and previously annealing at 120° C, showed the major presence of the polycrystalline chalcopyrite structure CuInSe2 with preferential orientation (112) plane at temperature as low as 250° C. From SEM studies and profilometer measurements a decrease in the mean roughness could be observed after annealing at 120° C. In contrast the resistivity of the films increased.
Improvement in Diffusion Length Estimation using the Photocurrent-Capacitance Method in CuInSe2-based Cells
Authors: Champness Clifford H.
Published: April 2011

The experimental technique in the photocurrent-capacitance method of estimating minority diffusion lengths, as applied to CuInSe2-based photovoltaic cells, has been improved, principally by replacing the earlier chopped light and monochromator technique by one employing a steady strong stable light source and a long pass optical filter. The filter requires an absorption edge at an appropriate wavelength to provide the penetrating light at sufficient intensity, which has been found to be 1.1 μm for CuInSe2 cells and 1.0 μ for Cu(In,Ga)Se2 cells. In addition, the parallel capacitance is determined with reverse bias under the same illumination as that during the photocurrent measurements and at a suitable frequency, such as 10 kHz. With these changes, the technique has been found to be more tolerant to cell imperfections and reproducible estimates of diffusion length have been obtained on CuInSe2 and Cu(In,Ga)Se2 cells.
Photoelectrochemical Study of State of Art Copper Indium Gallium Diselenide Thin Films
Authors: Clolus E. , Galtayries A. , Canava B. , Guillemoles J. F. , Lincot D.
Published: April 2011

State of the art CIGS thin films have been studied by means of the semiconductorelectrolyte junction. They appear as chemically robust allowing to use aggressive electrolyte compositions as for instance more acidic pH, down to 0 in sulfuric acid environment. In these electrolytes, reliable capacitance and photo-current related characterization techniques have been used. It has been shown that a short treatment in a gold (III) solution can facilitate the characterizations, and stabilize the surface composition. These results tend towards settling a standardized electrochemical testing procedure for CIGS layers
High Permittivity Oxide Gate Stacks on Silicon Incorporating UHV Silicon Nitride Interfacial Layers
Authors: Shriver Mark A. , Gabrys Ann M. , Higman T. K. , Campbell S. A.
Published: April 2011

Current high permittivity material deposition techniques produce a low permittivity oxide interfacial layer consequently increasing the equivalent oxide thickness. This interfacial oxide layer can be prevented by initially growing a thin nitride layer to act as a diffusion barrier. The interfacial nitride layer must also have low interface state densities comparable to state-of-the-art SiO2 insulators in order to be suitable for MOSFETs. The nitride layer used in this study was formed by thermal nitridation in a UHV system, with the subsequent high permittivity deposition done in an adjoining system. After forming capacitors from these films, capacitance vs. voltage (C-V) techniques were used to determine the interface state density and equivalent oxide thickness of the films. Gate stack films were produced on Si(100) and Si(111) and the results are compared. Gate stacks on Si(100) show a slight increase in stretchout in the high frequency C-V curves for both n-type and p-type samples. Initial data suggests that Si(111) has a lower interface state density than the Si(100) gate stacks. This may be attributed to the Si3N4layer on Si(111) being epitaxial nitride.
Development of Polycide Application and Control of Process Conditions on DCS Based WSix
Authors: Park Young-Kyou , Won Jaihyung , Park Ju-Hwan , Park Jung-Ho
Published: April 2011

Dichlorosilane based CVD WSix is deposited by the reaction of tungsten fluoride (WF6) and dichlorosilane (SiH2Cl2; DCS). The reaction is thermodynamically favorable and results in WSix film with less fluorine (F) concentration than monosilane (SiH4; MS) based WSix. DCS based WSix shows less expansion of gate oxide and better step coverage than monosilane based WSix. Due to its DCS based stable film stoichiometry, WSix has low resistivity and therefore has been widely applied in ULSI memory devices. However, DCS is a source of chlorine, which is a major impurity. This means special considerations have to be made when using DCS based WSix in comparison with MS based WSix. This work provides evaluation and control of chlorine behaviors in DCS based WSix film.
CoSi2 formation using a Ti capping layer - The influence of processing conditions on CoSi2 nucleation.
Authors: Detavernier C. , Van Meirhaeghe R.L. , Maex K.
Published: April 2011

A reactive Ti capping layer is needed to getter oxygen contamination and to make the cobalt silicidation reaction a more robust process. However, the presence of a Ti capping layer induces two other effects (in addition to the beneficial gettering of oxygen impurities): the formation temperature of CoSi2 is increased and the CoSi2 layer has a strong (220) preferential orientation. Because of the current technological importance of the Ti/Co/Si system, we have made a detailed investigation of the influence of several process parameters (annealing temperature, selective etching, layer thickness) on the nucleation of CoSi2 in the Ti/Co/Si system. Moreover, it is shown that the addition of Ni (i.e. a Ti/Co/Ni/Si or Ti/Ni/Co/Si structure) causes a decrease of the CoSi2 nucleation temperature.
Stress evolution in a Ti/Al(Si,Cu) dual layer during annealing
Authors: Bostrom Ola , Gergaud Patrice , Thomas Olivier , Boivin Philippe
Published: April 2011

Mechanical stress and stress evolution in interconnections may cause reliability problems in IC circuits. It is thus of great importance to understand the origin of this stress.

In this paper, the stress evolution during the solid state reaction between blanket titanium and aluminum films has been studied by in-situ substrate curvature measurements. Whereas the formation of TiAl3 is expected to induce large tensile stress because of a global volume decrease of 6-8%, curvature measurements of titanium/aluminum dual layers during annealing at 450°C suggests the formation of a compressive compound.

The evolution of the average force per unit width of the layer during the solid state reaction is interpreted on the basis of a phenomenological model used to describe stress evolution during silicide formation.
Study of the Yielding and Strain Hardening Behavior of a Copper Thin Film on a Silicon Substrate Using Microbeam Bending
Authors: Florando Jeffrey N. , Nix William D.
Published: April 2011

Recently a new microbeam bending technique utilizing triangular beams was introduced. For this geometry, the film on top of the beam deforms uniformly when the beams are deflected, unlike the standard rectangular geometry in which the bending is concentrated at the support. The yielding behavior of the film can be modeled using average stress-strain equations to predict the stress-strain relation for the film while attached to its substrate. This model has also been used to show that the gradint of stress and strain through the thickness of the film, which occurs during beam bending, does not obscure the measurement of the yield stress in our analysis.

Utilizing this technique, the yielding and strain hardening behavior of bare Cu thin films has been investigated. The Cu film was thermally cycled from room temperature to 500 °C, and from room temperature to –196°C. The film was tested after each cycle. The thermal cycles were performed to examine the effect of thermal processing on the stress-strain behavior of the film.
Bonding, Splitting and Thinning by Porous Si in ELTRAN®; SOI-Epi Wafer™
Authors: Yamagata Kenji , Yonehara Takao
Published: April 2011

ELTRAN is a unique technique to produce the SOI wafers using a porous Si material in semiconductor process. In ELTRAN process, it is required to form the porous Si layer on entire wafer surface uniformly, stably and mass productively without contaminations. In this investigation, we have carried out the simulation of current density distribution to unify the porous layer thickness by finite element method. Canon designed and completed an automatic anodization apparatus. As a result, we could produce the 8 and 6 inches porous Si wafers and ELTRAN SOI wafers stably. And we also developed successfully 300mm ELTRAN SOI wafers with excellent SOI film thickness uniformity.
Transfer and handling of thin semiconductor materials by a combination of wafer bonding and controlled crack propagation
Authors: Bagdahn J. , Katzer D. , Petzold M. , Wiemer M. , Alexe M. , Dragoi V. , Goesele U.
Published: April 2011

Direct waferbonding is an appropriate technology to join two or more wafers of the same or of different materials. Waferbonding can be used to stiffen thin wafers during fabrication. However, conventional fabrication processes lead to an increase of the bond strength, which inhibits the required de-bonding. The propagation of cracks, which is based on a subcritical crack growth in the bonded interface, was used to cleave the bonded wafers. The subcritical crack growth is limited to the bonded interface, since the adjacent bulk semiconductor materials are inherently resistant to subcritical crack growth. The process allows the separation of Si-Si and Si-GaAs wafers after annealing. Wafer-bonded SOI wafers can also be separated with this technology even if they were annealed at 1100°C. The first examples for wafer stiffening during fabrication and wafer transfer using the developed approach will be presented.
Single-Axis Projection Scheme for Conducting Sequential Lateral Solidifica-tion of Si Films for Large-Area Electronics
Authors: Limanov Alexander , Borisov Vladimir
Published: April 2011

This paper deals with some results of research in SLS performed in the excimer laser laboratory of TRINITI research institute, Russia, where different types of excimer lasers have been developed and manufactured. The research used a new simple SLS approach based on single-axis (i.e., cylinder) projection optics. The method employs a long single melting line extended many centimeters in length. The line is formed by projection through a single slit in a bulk metal mask. Some aspects of the efficiency, potential, and technical challenge of the method are discussed. This method is particularly useful with low pulse energy and high frequency excimer lasers, and one of the most efficient ways of providing directionally crystallized Si films over a large area. Several types of excimer lasers were tested for the SLS technique. It was found that among various parameters, pulse duration is a more important one, e.g., an increase in pulse duration from 25 to 150 ns results in enlargement of lateral growth distance by about three times.
Electrical Properties of Srta2O6 Thin Films Deposited by Plasma Enhanced Atomic Layer Deposition (Peald)
Authors: Lee Won-Jae , Shin Chang-Ho , You In-Kyu , Yang Il-Suk , Ryu Sang-Ouk , Yu Byoung-Gon , Cho Kyoung-Ik , Yoon Soon-Gil , Lee Chun-Su
Published: April 2011

The SrTa2O6 (STO) thin films were prepared by plasma enhanced atomic layer deposition (PEALD) with alternating supply of reactant sources, Sr[Ta(C2H5O)5(C4H10NO)]2 {Strontium bis-[tantalum penta-ethoxide dimethyllaminoethoxide]; Sr(Ta(OEt)5▪dmae)2} and O2plasma. It was observed that the uniform and conformal STO thin films were successfully deposited using PEALD and the film thickness per cycle was saturated at about 0.8 nm at 300°C. Electrical properties of SrTa2O6 (STO) thin films prepared on Pt/SiO2/Si substrates with annealing temperatures have been investigated. While the grain size and dielectric constant of STO films increased with increasing annealing temperature, the leakage current characteristics of STO films slightly deteriorated. The leakage current density of a 40nm-STO film was about 5×10−8A/cm2 at 3V.
Electron Transmission Through Modified Schottky Barriers
Authors: Jensen Kevin L.
Published: April 2011

The effects of a Coulomb-like potential in the Schottky barrier existing between a material-diamond interface is analyzed. The inclusion is intended to mimic the effects of an ionized trap within the barrier, and therefore to account for charge injection into the conduction band of diamond via a Poole-Frenkel transport mechanism. The present treatment is to provide a qualitative account of the increase in current density near the inclusion, which can be substantial. The model is first reduced to an analytically tractable one-dimensional tunneling problem addressable by an Airy Function approach in order to investigate the nature of the effect. A more comprehensive numerical approach is then applied. Finally, statistical arguments are used to estimate emission site densities using the results of the aforementioned analysis.
Advanced Excimer-Laser Recrystallization Technology for Crystal-Si Thin-Film Devices
Authors: Matsumura Masakiyo
Published: April 2011

This paper reviews an excimer-laser annealing (ELA) method of Si thin-films on glass studied in the Tokyo Institute of Technology, aiming at position-controlled ultra-large grain growth with high packing density by a single shot irradiation of a laser-light pulse. Key concepts are (I) 2-D modulation of the laser light intensity on the sample surface, (II) reduction of the heat removal rate from the molten Si thin layer of high temperature, and (III) enlargement of the effective specific-heat while keeping the effective thermal-conductivity low for annealed layers. There were two possible solutions for the condition (I). The first solution is of an application of a cross-coupled phase-shifter formed on a transparent quartz plate. The second solution is of a half-tone phase-modulation method (PAMELA method) using semi-transparent thin films on quartz substrate with phase-shifter. The condition (II) is satisfied by changing the SiO2 underlayer to the porous or organic silica underlayer for reducing vertical heat flow flux to the cool underlayer, and by thinning the Si layer for reducing heat flow flux along the highly conductive Si layer. The condition (III) is satisfied, by the SiON capping layer for a KrF excimer laser, and by the SiOC capping layer for a XeCl excimer laser, since they have a reasonable light absorption coefficient, low thermal conductivity, large specific-heat and sufficient heat tolerance.
A New Poly-Si TFT Employing XeCl Excimer Laser Annealing with Pre-patterned Al Laser Beam Mask
Authors: Han Min-Koo , Jung Sang-Hoon , Jeon Jae-Hong
Published: April 2011

We report new lateral grain growth mechanism by XeCl excimer laser annealing on a-Si film with pre-patterned Al layer. 2000Å-thick Al pattern on 800Å-thick PECVD a-Si film successfully reflects the incident laser beam and results in temperature gradient during the recrystallization process. The TEM images show that grain growth near the boundary between the liquid and the solid region exhibits a different mechanism compared with the conventional ELA. About 1.5 m-long lateral grain has been successfully obtained by single laser irradiation

A poly-Si TFT with single grain boundary in the channel has been fabricated by the proposed excimer laser annealing. An excellent device characteristics such as mobility more than 250cm2/Vsec, high On/Off current ratio of 6.3×106 and low threshold voltage less than 1 V has been obtained. The experimental results show that the mobility, threshold voltage and sub-threshold slope of proposed TFTs are superior to those of the conventional TFTs.
Polycrystalline Lead Iodide Films: Optical, Electrical and X-ray Counting Characterization
Authors: Fornaro L. , Saucedo E. , Mussio L. , Gancharov A. , Guimaraes F. , Hernandes A.
Published: April 2011

Lead iodide purified by zone refining and repeated sublimation was used for growing Polycrystalline films by physical vapor deposition. Palladium film was deposited as rear contact onto glass and alumina substrates 2.5 × 2.5 cm2 in size. Onto it, lead iodide polycrystalline films were grown by sublimation at 390 °C and 5 × 10−5 mm Hg, substrate temperatures of about 200 °C and deposition times of about 10 days. Film thickness was measured by X-ray transmission at 59.5 keV giving values from 35 to 50 μm (5%). Optical and atomic force microscopy were performed to the films giving an average grain size of (80±20) μm. Low temperature photoluminescence was performed and peak position and broadness confirmed the high purity of starting materials. Films were characterized by X-ray diffraction, giving an [ΣI (0 0 l)] / [ΣI (h k l)] relation of 0.8 that indicates a strong growth preferred orientation along c axis. Front palladium thermal deposition contacts and acrylic encapsulation were done and apparent resistivity (2 × 1014 Ω. cm) and current density (7 pA/cm2 (30 V)) were obtained. X-ray film response was checked by irradiating with 241Am and an X-ray beam. Finally, film and detector characterizations were correlated with starting material, deposition parameters and previous results for the same and alternative materials like mercuric iodide.
Properties of ZnO Thin Films Deposited by Spray Pyrolysis and Magnetron Sputtering
Authors: Nunes Patrícia , Fortunato Elvira , Martins Rodrigo
Published: April 2011

In this work we present a study of the properties of ZnO thin films produced by spray pyrolysis and r.f. magnetron sputtering. Before the annealing treatment the properties of the films are very similar, which means that the films produced by both techniques could be used on optoelectronic devices. However spray pyrolysis is a more simple and cheap technique than sputtering, but with this last technique the thin films exhibit a higher uniformity.
Self-Assembly CoSi2-Nanostructures for Fabrication of Schottky Barrier MOSFETs on SOI
Authors: Kluth Patrick , Zhao Qing-Tai , Winnerl Stephan , Mantl Siegfried
Published: April 2011

A new self-assembly patterning method for generation of epitaxial CoSi2 nanostructures was used to fabricate 70 nm gate-length Schottky barrier metal oxide semiconductor field effect transistors (SBMOSFETs) on silicon-on-insulator (SOI) substrates. This technique involves only conventional optical lithography and standard silicon processing steps. It is based on anisotropic diffusion of Co/Si atoms in a strain field during rapid thermal processing. The strain field is generated along the edges of a mask consisting of 20 nm SiO2 and 300 nm Si3N4. Single-crystalline CoSi2 layers grown by molecular beam allotaxy (MBA) on thin SOI substrates were patterned using this technique. During rapid thermal oxinitridation (RTON) of the masked silicide structure, a well defined separation of the silicide layer forms along the edge of the mask. These highly uniform gaps define the channel region of the fabricated device. The separated silicide layers act as metal source and drain. During the RTON-step a 6 nm thin SiO2 is formed on top of the gap which is used as a gate oxide. The SBMOSFETs can be driven as both p-channel and n-channel devices without complementary substrate doping and show good I-V characteristics.
White Light Luminescence from Nano-ZnS Doped Porous Silicon
Authors: Cheah K. W. , Xu Ling , Huang Xinfan
Published: April 2011

Nano-ZnS was deposited into porous silicon. By varying the concentration of Zn2+ ion solution during nano-ZnS formation, the amount of nano-ZnS in porous silicon host can be controlled. The doped porous silicon exhibited a gradual shift in its photoluminescence peak from red to blue as a function of the nano-ZnS coverage. At an optimum doping, white light photoluminescence was obtained. A study in the luminescence lifetime showed that the radiative recombination at the blue end of the visible spectrum was due to nano-ZnS, whereas, luminescence emission at the red end of the visible spectrum came from porous silicon. The latter luminescence was due to in part tunneling of excited electrons from nanoZnS into porous silicon and in part direct excitation of porous silicon layer. Time-resolved photoluminescence also showed that radiative recombination was effectively dominated by the nano-ZnS. Photoluminescence excitation result revealed the presence of two excitation levels; one belonged to nano-ZnS at near uv region, and another at about 520 nm from the surface states of porous silicon and nano-ZnS. The doping of nano-ZnS into porous silicon demonstrates that luminescence color tuning is possible when an appropriate functional material is introduced into porous silicon.
Microsensors for Automotive Applications – Metrology and Test
Authors: Flik Gottfried , Eisenschmid Heinz , Raudzis Carsten , Schatz Frank , Schoenenborn Winfried , Trah Hans-Peter
Published: April 2011

According to market surveys automotive microsensors will evolve into a multi-billion dollar business by 2005. Key roles are attributed to inertial sensors for passenger safety systems, and mass flow and pressure sensors for engine management systems. Thin film techniques together with silicon bulk or surface micromachining have been established as preferential processes to achieve reduction of sensor size, weight and cost along with improvements of sensor functionality and reliability. Enhanced sensor performance often pushes the limits of process technology and therefore the need arises very early in the MEMS design process to identify materials and geometry related parameters which are critical with respect to their tolerance band specifications. In order to control these critical parameters, automated wafer level test procedures need to be developed (based preferentially on electrical quantities) and additionally considered for in the sensor design phase (design for test). In analogy to microelectronics 2D wafer maps of critical parameters may give hints on how to improve process stability and how to adapt the sensor design in order to optimize yield. Examples of critical model parameter variations include thermal conductivity, thickness, and shear modulus of thin films.
Mechanisms of Fatigue in Polysilicon Mems Structures
Authors: Shrotriya P. , Allameh S. , Butterwick A. , Brown S. , Soboyejo W.O.
Published: April 2011

Fatigue crack initiation is shown to be associated with the stress-assisted evolution of a surface silica layer that forms during the normal exposure of unpassivated polysilicon surfaces to lab air In-situ atomic force microscopy (AFM) techniques are used to reveal the evolution of overall surface topology during incremental cyclic deformation to failure. Linear perturbation analysis of stress-assisted dissolution is then utilized to predict the evolution of the surface morphology. The predictions from the perturbation analysis are shown to be consistent with measured surface morphologies obtained using AFM techniques.
Characteristics of Thick Sol-Gel Lead Zirconate Titanate Films for Angular Rate Sensor Application
Authors: Lee S. H. , Iijima T. , Nakamura K. , Tanaka S. , Esashi M.
Published: April 2011

In this study, thick sol-gel PZT(Pb(Zr1−xTix)O3) films were fabricated and their characteristics were investigated for angular rate sensor applications. The crack-free thick sol-gel PZT films were successfully deposited on silicon substrates by multiple spin-coating technique combined with rapid thermal annealing(RTA). The thickness of the PZT films is 1.5 νm, which is required by a vibration angular rate sensor for a good actuation and sensing. The remnant polarization of the PZT films is 12.0νC/cm2. The PZT films were applied to the vibration angular rate sensor structure, and the vibration of 1.78νm in amplitude at the resonant frequency of 35.8kHz was obtained. In this case, the driving voltage of 5Vp-p by bulk piezoelectric materials was applied to the driving electrode with out of phase signal through voltage and inverting amplifier.

The oscillating output voltage obtained by external actuation using a stacked piezo-actuator showed the values of 0.76V and 0.87V in outer/inner driving electrode at driving voltage of 5Vp-p.
A Constitutive Model for the Mechanical Behavior of Single Crystal Silicon at Elevated Temperature
Authors: Moon H.-S. , Anand L. , Spearing S. M.
Published: April 2011

Silicon in single crystal form has been the material of choice for the first demonstration of the MIT microengine project. However, because it has a relatively low melting temperature, silicon is not an ideal material for the intended operational environment of high temperature and stress. In addition, preliminary work indicates that single crystal silicon has a tendency to undergo localized deformation by slip band formation. Thus it is critical to obtain a better understanding of the mechanical behavior of this material at elevated temperatures in order to properly exploit its capabilities as a structural material. Creep tests in simple compression with n-type single crystal silicon, with low initial dislocation density, were conducted over a temperature range of 900 K to 1200 K and a stress range of 10 MPa to 120 MPa. The compression specimens were machined such that the multi-slip <100> or <111> orientations were coincident with the compression axis. The creep tests reveal that response can be delineated into two broad regimes: (a) in the first regime rapid dislocation multiplication is responsible for accelerating creep rates, and (b) in the second regime an increasing resistance to dislocation motion is responsible for the decelerating creep rates, as is typically observed for creep in metals. An isotropic elasto-viscoplastic constitutive model that accounts for these two mechanisms has been developed in support of the design of the high temperature turbine structure of the MIT microengine.
Superconducting Properties of High-Jc MgB2 Coatings
Authors: Christen D. K. , Cantoni C. , Thompson J. R. , Paranthaman M. , Chisholm M. F. , Kerchner H. R. , Christen H. M.
Published: April 2011

We report the fabrication and superconducting properties of ∼0.5 μm thick, fine-grained polycrystalline coatings of MgB2 on single-crystal substrate surfaces. The films exhibit large critical current densities, implying little effect from the grain boundaries. Analyses for thermal activation effects are inconclusive, and evidence is presented that the irreversibility line is dominated by the combined influences of Hc2 anisotropy and polycrystallinity. Comparative studies of the magnetic persistent currents and electrical transport properties reveal excellent agreement over a wide range of temperature and magnetic field. This result is contrary to similar comparisons on high-temperature cuprates, where disparities arise from the effects of large flux creep and the diverse electric field regimes probed by the two techniques. The MgB2 films exhibit extremely sharp voltage-current relations away from the irreversibility line, in qualitative agreement with observed large Jc values and low rates of magnetic flux creep.
The Synthesis and Performance of MgB2
Authors: Meng R. L. , Lorenz B. , Xue Y. Y. , Pham D. , Cmaidalka J. , Meen J. K. , Sun Y. Y. , Chu C. W.
Published: April 2011

We have studied the kinetics of the chemical reaction between Mg and B by differential thermal analysis. There are two exothermal peaks observed at 500 and 650 °C. We speculate that the first exothermal peak is mainly related to the chemical reaction between Mg and oxygen, forming MgO. The second exothermal peak, which coincides with the melting point of Mg, clearly indicates the chemical reaction between Mg and B. The effect of synthesis conditions and defects on the transport property of MgB2 has been investigated. A correlation between the microstrain, the lattice parameters, and the Mg concentration were observed and are discussed.
Bond-Length Fluctuations in the Copper-Oxide Superconductors
Authors: Goodenough John B.
Published: April 2011

The phase diagram of La2-xSrxCuO4 is interpreted. From the virial theorem, it is argued that the cross-over from localized to itinerant electronic behavior in the range 0 < x < 0.3 is characterized by fluctuations between two equilibrium Cu-O bond lengths. Cooperative local fluctuations give rise to one-hole correlation bags of 5 to 6 copper centers on the underdoped side, to strong-correlation fluctuations in an itinerant-electron matrix on the overdoped side. Spinodal phase segregation between an antiferromagnetic, insulating parent phase and the superconductive phase occurs in the underdoped compositions, between the superconductive phase and the metallic overdoped phase on the other side of the phase diagram. Ordering of the fluctuations into a travelling bipolaronic charge-density/spin-density wave of composition x ≈?1/6 yields heavy fermions of symmetry (x2− y2) coexisting with light electrons; the high-temperature superconductive pairs are condensed out from the heavy fermions.
Real-time Degradation Study of HgBa2CaCu2O6+δ?Thin Film Using Near-field Scanning Microwave and Optical Dual Probe
Authors: Aga Roberto S. , Xie Yi-Yuan , Wu Judy Z.
Published: April 2011

All high- Tc superconductors are susceptible to humid environment. The mechanism behind this degradation process is not yet well known or even described. In an attempt to understand the mechanism, we studied the real-time degradation process of HgBa2CaCu2O6+δ (Hg-1212) thin film using scanning probe microscopy (SPM) techniques. A newly developed near-field scanning microwave and optical dual probe was employed to map simultaneously the spatial variation of microwave sheet resistance and optical transmittance of a sample. Mapping was performed at a regular time interval while the sample was exposed to a very high level of humidity (85%-90%). In a separate experiment, atomic force microscope (AFM) was used to monitor the surface roughness of a sample subjected to the same level of humidity. Results indicate that the degradation process of Hg-1212 involves the gradual transformation of the material into a colorless insulator accompanied by continuous surface deformations.
Preparation of Bi-2212/Ag Tapes by Electrodeposition
Authors: Chen Jun , Bhattachary Raghu , Padmanabhanl Ramakrishnan , Blaugher Richard
Published: April 2011

Bi-2212 precursor films were deposited on both sides of polycrystalline Ag tapes by electrodeposition. After a melt-solidification process in flowing oxygen atmosphere, c-axis textured Bi-2212 films with Jc( 0T, 4.2K) up to 820,000 A/ cm2 were obtained. A post annealing in flowing nitrogen at 475°C for 25 minutes increased Tc from 72 K to 92 K, and Jc(H=0T) > 17, 000A/ cm2 was observed at 60 K. No scaling behavior of the pinning force was observed, indicating more than one pinning mechanism in thus obtained Bi-2212/Ag tapes.
Preparation and Electronic Device Properties of Single Crystalline La2−xSrxCuO4Superconducting Film
Authors: Islam A. T. M. Nazmul , Ashizawa K. , Watauchi S. , Tanaka I.
Published: April 2011

We have grown La2−xSrxCuO4 single-crystalline films on atetra-axis oriented Zn doped La2CuO4 single crystals by IR-LPE technique. The films show thickness dependence of Tc,onset, but films of thickness below 80μm doesn't show zero resistance down to 4.2K. The I-V characteristics showed reduced voltage jump than usual and small hysteresis. This phenomenon resembles with the characteristics of resistively and capacitively shunted intrinsic Josephson junctions (RCSJ)
Thermoelectric Potential of Bi and Bi1−x Sbx Nanowire Arrays
Authors: Dresselhaus M. S. , Lina Y.-M. , Rabin O. , Cronin S. B. , Black M. R. , Ying J. Y.
Published: April 2011

The potential of Bi and Bi1−x Sbx nanowire arrays for thermoelectric applications is discussed. The advantages of bismuth as a low dimensional thermoelectric material are enumerated and the role of modeling is emphasized. The advantages of using the Sb concentration as well as the wire diameter as materials parameters for optimizing the thermoelectric performance of these nanowires are discussed, with particular emphasis given to the development of a high performance p-type nanowire thermoelectric material.
Molecular-dynamics studies on solid phase epitaxy of guest-free silicon clathrates
Authors: Munetoh Shinji , Moriguchi Koji , Motooka Teruaki , Kamei Kazuhito
Published: April 2011

Dynamical phenomena during the solid phase epitaxy (SPE) of guest-free Si clathrates (Si34 and Si46) via molecular-dynamics (MD) simulations using the Tersoff potential have been reported. The activation energy of SPE for Si34 has been found to correspond with the experimental value for the cubic diamond phase (c-Si; approximately 2.7eV), while the SPE rates of Si46 are much lower than that of c-Si. The structural transition from Si46 (type-I) to Si34 (type-II) can be also observed during the Si46 [001] SPE. The present results suggest that it is worthwhile to intensify experimental studies concerning crystal growth techniques of clathrate materials and these interesting Si forms may open up a new field in “silicon technologies”.
Electrical Transport Properties of Rare Earth Doped Pentatellurides
Authors: Lowhorn Nathan D. , Tritt Terry M. , Littleton R. T. , Abbott Edward E. , Kolis J. W.
Published: April 2011

The transition metal pentatellurides HfTe5 and ZrTe5 exhibit a broad resistive anomaly as a function of temperature. This behavior is also reflected in the thermopower as it changes from a large positive value below room temperature to a large negative value at lower temperatures with the zero crossing corresponding well with the peak temperature of the resistive anomaly. The large values of the thermopower at low temperatures (T ≈ 150 K) have made these materials attractive for investigation for potential low temperature thermoelectric applications. The magnitude of the resistive peak and the peak temperature are highly sensitive to doping as well as external influences such as magnetic field and pressure. In this study we examine the effect of doping with various rare earth elements (RE = Ce, Sm and Dy) and the subsequent effects on the electrical resistivity and the thermopower. These results will be discussed in relation to the thermoelectric performance of these materials.
Mechanical Characterization of Functionally Graded Materials with a Yield Strength Gradient
Authors: Nayebi A. , Mauvoisin G. , Bartier O. , Abdi R. El
Published: April 2011

An elasto-plastic spherical indentation study on materials with a yield strength gradient, like steels which have undergone thermal hardening such as nitriding, is carried out using both experimental and finite element methods. A theory based on the evolution of hardness, is proposed to determine the yield stress and hardness profiles for materials with a decreasing yield stress with depth.

Results for carbo-nitriding steels obtained by the standard Vickers micro hardness technique are compared with those obtained by the proposed method.
Characterization of the Degraded Microstructures of a Platinum Aluminide Coating
Authors: Kim Hyungjun , Walter Mark E.
Published: April 2011

To investigate phase evolution of β-(Ni,Pt)Al/γ-(Ni3Al) in thermal barrier coating bond coat systems, specimens were subjected to 1200°C cyclic and isothermal heating. By removing the thermally grown oxide (TGO) after every 10 hours of heating, aluminum (Al) depletion from the bond coat was accelerated. Non-accelerated and accelerated Al-depletion samples were examined with scanning electron microscopy after every 10 hours of cyclic and isothermal heating. Observations from after the first 10 hours of thermal exposure show distinct microstructural differences. After 50 hours of heating, cyclic accelerated Al-depletion samples show more distinct grain boundaries and a higher proportion of-(Ni3Al) phase than isothermalaccelerated Al-depletion samples. Through instrumented micro-indentation, trends in elastic modulus were determined for isothermal and cyclic accelerated Al-depletion specimens.
Functionally Graded Materials produced with High Power Lasers
Authors: Hosson Jeff Th. De , Pei Yutao
Published: April 2011

With a well-controlled laser melt injection (LMI) process, for the first time the feasibility is demonstrated to produce SiC particles (SiCp) reinforced Ti6Al4V functionally graded materials (FGMs). SiCp are injected just behind the laser beam into the extended part of the laser melt pool that is formed at relatively high beam scanning velocities. The process allows for the minimization of the decomposition reaction between SiCp and Ti6Al4V melt, and also leads to FGMs of SiCp/Ti6Al4V instead of a homogeneous composite layer on Ti6Al4V substrates. An injection model is designed based on the temperature/viscosity field of the laser pool for a deeper understanding the mechanism of formation of the FGMs with LMI. The model is based on finite element calculations of the temperature field in the melt pool, physical considerations of the LMI process and it is supported by experimental observations. Three types of reaction layers are observed around SiCp, namely a thin monocrystalline TiC layer, a cellular polycrystalline TiC layer and a thick mixed layer of TiC with Ti5Si3. Among them, only the monocrystalline TiC layer exhibits particular orientation relationships to the SiCp lattice, i.e. (111)TiC//(0001)SiC and <110>TiC//<1100>SiC or (111)TiC // (1012)SiC and <110>TiC//<1210>SiC. These two kinds of TiC reaction layers act as a barrier against the interfacial reaction and its swift formation during rapid cooling hinders the dissolution of SiCp in the Ti-melt.
Interfacial Force Microscopy and its Application in Metal Matrix Composites
Authors: Liebig Berthold E. , Chantis Athanasios , Steffan Craig E. , Puszynski Jan A. , Winter Robb M.
Published: April 2011

Metal matrix composites (MMCs) combine the properties of metal and ceramic or intermetallic materials. Common examples of metal matrix composites are Cu-Al2O3, SiCw-Al, Al-Al2O3, Al-B4C, and Ni-NiAl3. Mechanical or thermal properties, such as strain-stress behavior, or thermal expansion coefficient can be tailored by changing the content of the reinforcing phase. The most common techniques of measuring mechanical properties of composite materials rely on macroscopic approach. During the past fifteen years, a significant effort has been made to develop various techniques of measuring mechanical properties on a microscopic level. These techniques include atomic force microscope (AFM) and depth sensing indentation techniques, based on Hertzian contact mechanics. However, it is still a challenge to measure reliably and quantitatively the Young's modulus and Poisson's ratio of individual phases as well as properties at the interfaces. This presentation will focus on fundamental aspects of measuring of mechanical properties of metal matrix composites at nano-scale using Interfacial Force Microscopy (IFM). The IFM is a scanning probe microscope, which utilizes a unique self-balancing capacitance force sensor. Force-displacement curves obtained with the IFM are analyzed using Hertzian contact mechanics to extract the Young's moduli of the individual phases and interface region with high spatial resolution. The properties of Cu-Al2O3, Al-SiCp composites will be discussed in detail. Furthermore, a comparison of experimental data with mechanical properties calculated from first principles will be discussed.
A Nanoscratch Method for Assessing Wear of Metal Carbide-Metal Nacreous Nanostructures
Authors: Obbard Rachel W. , Gross Todd S.
Published: April 2011

The wear resistance of metal carbide-metal nacreous nanostructures is compared to that of a solid metal carbide hard coating. A reciprocating nanoscratch method has been developed which allows the assessment of wear resistance of the film independent of substrate type or film-substrate adhesion. A series of nominally 1 micron thick TiC-based multilayer films on Si substrates were produced using RF magnetron sputtering. A scratch protocol consisting of 70 reciprocal scratches each 9.5 m m in length was applied. Data reduction techniques were used to remove the effects of sample tilt and drift. The resulting normal displacement as a function of scratch cycles is used to compare the wear of different films on Si <111> substrates. Specific wear characteristics related to film morphology are examined. This investigation showed that this nanoscratch technique holds promise as a thin film wear characterization technique.
Effect of Co Seed Layers on the Magnetic Anisotropy of Au/Co Metallic Multilayers
Authors: Kamiko Masao , Mizuno Hiroyuki , Lu Guang-Hong , Zhou Yao-Min , Yamamoto Ryoichi
Published: April 2011

Au/Co(111) multilayers and a Au buffer layer were grown by MBE on Al2O3(0001) substrates using a thin Co seed layer. The influence of the Co layer on the structure of the Au/Co multilayers was studied by X-ray diffraction and reflection high-energy electron diffraction (RHEED), and compared to its effect on the magnetic anisotropy. The Au buffer layer grown on Al2O3(0001) substrates display a large fraction of (111) fiber texture, giving rise to a lack of lateral continuity in the film. The initial deposition of a few monolayers of Co onto Al2O3(0001) substrates prior to deposition of the Au buffer layer yielded (111) epitaxial films with no texture. The use of this seeded epitaxy results in a highly improved structural quality of Au/Co(111) multilayers. From the results of Low-angle X-ray diffraction and RHEED observations, we confirmed that the interfaces of Au/Co multilayers with Co seed layer are sharper than those without Co seed layer. It cleary shows that the use of Co seed layer improved the periodicity of Au/Co multilayers. The magnetic anisotropy energy of Au/Co multilayers increased by using the Co seed layer, and the high quality of structure results larger perpendicular magnetic anisotropy.
Chemically Amplified Resist Approaches for E-beam Lithography Mask Fabrication
Authors: Maldonado J.R. , Angelopoulos M. , Huang W. , Brainard R. L. , Guevremont J. M. , Tan Z.
Published: April 2011

This paper describes stable, high sensitivity (5-10 μC/cm2 at 50 kV) e-beam resist systems utilizing chemical amplification suitable for mask fabrication for device generations below 100 nm. In particular, two resist systems with improved performance for mask fabrication developed in a joint program by Etec, IBM and Shipley will be described: a Si- doped version of the IBM KRS-XE resist (now commercially available) developed at IBM Research, and a new MANA resist developed at Shipley. Commercialization issues for mask e-beam resists also will be discussed.
Charge Transport in Mesoscopic Carbon Network Structures
Authors: Ksenevich V. , Galibert J. , Samuilov V. , Seo Y.-S. , Sokolov J. , Rafailovich M.
Published: April 2011

The charge transport and quantum interference effects in low-dimensional mesoscopic carbon networks prepared using self-assembling were investigated. The mechanism of conduction in low-dimensional carbon networks was found to depend on the annealing temperature of the nitrocellulose precursor. The charge transport mechanism for carbon networks obtained at Tann=750 0C was found to be the hopping conductivity in the entire investigated temperature range. The Coulomb gap near the Fermi level in the density of states was observed in the investigated carbon networks. The width of the Coulomb gap was found to be decreased with the annealing temperature of the carbon structures. The crossover from the strong localization to the weak localization regime of the charge transport in the carbon structures, obtained at Tann=950 0C and Tann=1150 0C, was observed in the temperature range T>100 K and T>20 K, respectively.
Nanoscale Control of the Polymer-Fullerene Interface in Photovoltaic Devices by Thermally-Controlled Interdiffusion
Authors: Drees M. , Davis R.M. , Marciu D. , Premaratne K. , Graupner W. , Miller M. , Heflin J.R.
Published: April 2011

Ultrafast photoinduced charge transfer from conjugated polymers to fullerenes has led to extensive studies of these systems as photovoltaic devices. The charge transfer process prevents radiative electron-hole recombination, resulting in free, mobile charges. A limiting factor is the exciton diffusion distance, which is of the order of 10 nm. If the fullerene is not within this distance of the optical excitation site, no charge separation will take place. The simplest system for such devices is a bilayer system in which a film of C60 is sublimed onto a spin-cast film of MEH-PPV, for example. We describe studies in which the polymer is heated above the glass transition temperature in an inert environment, inducing an interdiffusion of the polymer and the fullerene layers. With this process, a controlled, bulk, gradient heterojunction is created. The photoluminescence and the short circuit currents of the devices show a dramatic decrease in photoluminescence and concomitant increase in short circuit currents, demonstrating the improved interface.