bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth of Co-evaporated Cu(In,Ga)Se2 – The Influence of Rate Profiles on Film Morphology
Authors: Bodegård M. , Kessler J. , Lundberg O. , Schöldström J. , Stolt L.
Published: April 2011

The influence of the evaporation rate profiles on the microstructure of co-evaporated Cu(In,Ga)Se2, (CIGS), is discussed. The influence of Cu excess in the beginning of the CIGS growth has been investigated. In addition, the Ga rate has been varied in order to create bandgap grading in the CIGS film. By studying CIS and CGS films separately and as CGS/CIS stacks results on interdiffusion of In and Ga interdiffusion have been obtained. The resulting thin films are investigated mainly using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). Solar cell devices were prepared and IV measurements performed on samples with varying CIGS deposition parameters.
Ion beam assisted deposition of Cu(In,Ga)Se2 films for thin film solar cells
Authors: Lippold Gerd , Neumann Horst , Schindler Axel
Published: April 2011

We report on a novel ion beam selenization process. The reactive chalcogen component Se and a significant part of the thermal energy needed for CIGS formation is delivered directly into the growing surface by a low energy Se ion beam from a broad beam ion source. This highly controllable technique with respect to ion energy, dose and uniformity and with scale- up capabilities can be used in two ways either for selenization of metallic Cu/(In,Ga) thin film stacks or in co-deposition. In the case of co-deposition the CIGS growth temperature can be reduced to < 400°C

Besides the description of the method we present results of Se ion beam analysis and properties of CIGS thin films, produced by the novel selenization process.
Electronic Properties of Cu-In-S Solar Cells on Cu-Tape Substrate
Authors: Konovalov Igor , Penndorf Jürgen , Winkler Michael , Tober Olaf
Published: April 2011

Thin film solar cells obtained by the “CIS on copper tape” technique are investigated. This technique promises a high throughput capability, but the efficiency of the cells is still about 5 % only. The model of the band structure of the absorber has been introduced into the model of the whole cell. Parameters of the model were determined experimentally by use of quantitative EBIC profiling, C-V doping profiling, Hall measurements, and AFM. The structure has been simulated using SCAPS-1D software. Results of the simulation show a good correlation to the measured I-V and DSR data of the cell. The benefits and drawbacks of the cell structure as well as factors limiting its efficiency are discussed.
Voltage Dependent Carrier Collection in CdTe Solar Cells
Authors: Bätzner D.L. , Agostinelli Guido , Romeo A. , Zogg H. , Tiwari A.N.
Published: April 2011

The measurement of quantum efficiency with bias voltage is a powerful tool to characterize CdTe/CdS solar cell. As the quantum efficiency changes drastically with bias it will be referred to as Apparent Quantum Efficiency AQE. The AQE gives insight to the spectral contents of the cell current and therefore resolves the spatial carrier collection in the cell at each working point. So it is possible to understand the influence of the junctions and changing resistances in the cell. The photoconductivity of CdS facilitates AQE well above unity, i.e. up to 100, at high forward bias. The spectral sensitivity of the CdS photoconductivity affects the cell current strongly. This can explain the dependence of fill factor and roll-over of the I-V characteristics on the spectral content of illumination. Further more back contact junction influence and defect related features, such as sub band gap generation, are evident in the AQE for high forward bias.
Interface Defects in GIGS-based Solar Cells from Coupled Electrical and Chemical Points of View
Authors: Canava B. , Vigneron J. , Etcheberry A. , Saad S. Ould , Djebbour Z. , Mencaraglia D. , Guillemoles J.F. , Lincot D.
Published: April 2011

Chemistry of co-evaporated CIGS surfaces submitted to chemical treatments relevant to fabrication steps were investigated by XPS and admittance spectroscopy. A Se XPS signal specific of the CIGS surfaces was identified. Surface states seen by Admittance and surface chemistry are seen to change significantly during the elaboration steps. Consequences for device elaboration are briefly discussed.
Absorption and photoluminescence studies of lightly alloyed CdTe(S) and CdS(Te)
Authors: Shvydka Diana , Compaan A.D. , Price K.J.
Published: April 2011

CdTe-rich and CdS-rich alloy films were deposited at temperatures less than 300C using an rf sputtering technique. Transmission-reflection and photoluminescence measurements were conducted to study the near-band edge properties of this ternary system for films of different compositions at room temperature and at 10K. Results were compared to data on defect states introduced in CdTe single crystal by annealing at several different overpressure conditions, including CdS and CdCl2 overpressures. A below-band-gap photoluminescence excitation technique was used to study systematically the effect of different steps in the production of the complete solar cell on band gap states of CdSxTe1−x alloys as well as pure binary constituents.
Current Transport in CuInS2 Solar Cells Depending on Absorber Preparation
Authors: Reiβ Joachim , Malmström Jonas , Werner Axel , Henge Imke , Klenk Reiner , Lux-Steiner Martha Ch.
Published: April 2011

According to our model for the current transport in CuInS2/CdS/ZnO solar cells presented previously, the dominant recombination under illumination occurs at the CuInS2/CdS interface. In this contribution we expand this model for cells where the absorber has been prepared in different sequential processes by using results from jV curve measurements performed at varied temperature and illumination. We find that in contrast to CuInSe2 and CuGaSe2 solar cells from the Ångström Solar Center the CuInS2 cells exhibit a qualitative change in the dominant recombination mechanism between the dark and under illumination. The dominant recombination mechanism under illumination appears to be affected by absorber preparation parameters.
Alternating Layer Chemical Vapor Deposition (ALD) of Metal Silicates and Oxides for Gate Insulators
Authors: Gordon Roy G. , Becker Jill , Hausmann Dennis , Suh Seigi
Published: April 2011

A new process was developed for deposition of the silicates and oxides of metals such as zirconium and hafnium at low substrate temperatures (100–300°C). The silicon and oxygen source is tris(tert-butoxy)silanol, (tBuO)3SiOH, and the metal precursors are metal amides. A typical reaction is

ZrL4 + 2 (tBuO)3SiOH → ZrSi2O6 + 4HL + 6H2C=C(CH3)2 + 2 H2O

in which the ligand L is ethylmethylamide, -NEtMe. The precursor vapors were alternately pulsed into a heated reactor, yielding about 0.3 to 0.7 nm of metal silicate film for each cycle. Replacing the silanol pulses with water pulses yields pure metal oxides with a thickness of about 0.1 to 0.15 nm per cycle. The silicon content of the films can be adjusted to any desired value by replacing some of the silanol pulses by water pulses. This new process has a number of advantages over previous methods for depositing metal silicates. Uniformity of thickness and stoichiometry are readily achieved. The deposition atmosphere is non-oxidizing, so that formation of low-k interfacial oxides between the deposited layer and a silicon substrate is minimized. The new halogen-free precursors avoid halogen contamination of films and corrosion of deposition systems. This process is a promising method for forming the next generation of ultra-thin high-k gate dielectrics in silicon-based microelectronics.
Promising Gate Stacks with Ru & RuO2 Gate Electrodes and Y-silicate Dielectrics
Authors: Zhong Huicai , Heuss Greg , Suh You-Seok , Hong Shin-Nam , Misra Veena , Kelly Jason , Parsons Gregory
Published: April 2011

In this work, we studied the electrical and thermal stability of Ru and RuO2 electrode on Y-silicate dielectrics in contrast to ZrO2 and Al2O3 dielectrics. Very low resistivity Ru and rutile stoichiometric RuO2 films, deposited via reactive sputtering, were evaluated as gate electrodes on ultrathin Y-silicate, ZrO2 and Al2O3 films for Si-MOS devices. Thermal and chemical stability of the electrodes was studied at annealing temperatures up to 800°C in N2 and subsequently forming gas anneal. XRD and XPS were measured to study grain structure and interface reactions. The morphology of the films was tested by atomic force microscopy (AFM). Electrical properties were evaluated via MOS capacitors. The role of oxygen inside dielectrics was studied by comparing equivalent oxide thickness change as a function of annealing temperature for capacitors with Y-silicate, ZrO2and Al2O3 dielectrics. Good stability of Ru and RuO2 gate electrodes on all dielectrics studied was found. Flatband voltage and gate current as a function of annealing temperature was also studied. It was found that capacitors with Y-silicate after high-temperature anneal had less positive flatband voltage shift than ZrO2 and Al2O3. For capacitors with Ru gate electrode, the significant flatband voltage shift after high temperature anneal could be partially removed by a forming gas anneal.
Effect of Pre-cooling Treatment on the Formation of C54 Phase Titanium Silicide
Authors: Zhangand Lin , Lee YongKeun
Published: April 2011

In this paper, the effect of pre-cooling treatment on the low resistivity C54 phase titanium silicide film growth was investigated. Our experimental results and micro-structural analysis show that, by introducing such cooling treatment into the titanium silicide process to precede the conventional rapid thermal annealing, the low resistivity C54 phase formation can be enhanced. Defects at the Si/Ti interface caused by the thermal mismatch between titanium and silicon layers during the cooling treatment were found to contribute to the increase of the C49 nucleus sites. This help to supply more C49 grain boundaries and triple junction sites at which the C54 phase could nucleate. This discovery has the potential to reduce the complexity and cost associated with forming low resistivity titanium silicide on sub-micron structures for future ULSI application.
Molybdenum Gate Electrode Technology For Deep Sub-Micron CMOS Generations
Authors: Ranade Pushkar , Lin Ronald , Lu Qiang , Yeo Yee-Chia , Takeuchi Hideki , King Tsu-Jae , Hu Chenming
Published: April 2011

Continued scaling of CMOS technology beyond the 100 nm technology node will rely on fundamental changes in transistor gate stack materials [1]. Refractory metals and their metallic derivatives are among the only candidates suitable for use as transistor gate electrodes. In earlier publications, Mo has been proposed as a potential candidate for use as a MOSFET gate electrode and the implantation of nitrogen ions into the Mo film has been observed to lower the interfacial work function of Mo [2,3]. This observation indicates the potential application of Mo as a CMOS gate electrode. In this paper, the dependence of the interfacial work function on the nitrogen implant parameters (viz. energy and dose) is discussed. In general, metal work functions at dielectric interfaces depend on the permittivity of the dielectric [3,4,5]. This dependence of the gate work function on dielectric permittivity presents a significant challenge for the integration of metal gate electrodes into future CMOS technology. In light of this, the ability to engineer the Mo gate work function over a relatively large range makes it an attractive candidate for this application.
Silicide Formation for Ni and Pd Bilayers on Si(100) Substrates
Authors: Qu Xin-Ping , Detavernier C. , Van Meirhaeghe R. L. , Cardon F.
Published: April 2011

The silicide formation for Ni/Pd and Pd/Ni bilayers on Si(100) substrates was investigated. X-ray diffraction and photoelectron spectroscopy (XPS) depth profiling have been applied to study the phase formation of the silicide. We found that with addition of Pd into Ni/Si, a uniform layer of ternary Ni1−xPdxSi layer formed and kept stable for a wide temperature range. The lattice parameter of Ni1−xPdxSi as a function of Pd addition was calculated. The nucleation temperature of NiSi2 was delayed due to the addition of Pd. The higher the Pd addition, the larger the increase in NiSi2 nucleation temperature. We also studied the effect on the addition of Ni to the Pd/Si reaction. For pure Pd/Si reaction PdSi nucleated from Pd2Si at 750°C or above. For Ni/Pd/Si reaction, Pd2Si changed to Ni1−xPdxSi at temperature lower than 750°C due to the incorporation of Ni. The phenomena were explained by classic nucleation theory taking into account the effect of mixing entropy effect.
“Reverse” Stress Relaxation in cu Thin Films
Authors: Spolenak R. , Volkert C. A. , Ziegler S. , Panofen C. , Brown W.L.
Published: April 2011

In this study we present investigation on the anelastic behavior of sputtered 1 [.proportional]m thin Cu films. Most of the literature that reports on the mechanical properties of thin metallic films is based on substrate curvature measurements. We have developed a new version of a bulge tester that combines the capacitive measurement of the bulge deflection of a membrane with a resonance frequency measurement of the residual stress in the membrane. A Cu membrane is plastically deformed to a pre-determined strain by controlled gas-pressure bulging of the membrane. After the bulging stress is removed, the residual tensile stress, which has been decreased by the plastic deformation, is then determined by measuring the resonant frequency as a function of time. Immediately after plastic straining, the residual (tensile) stress of membranes was observed to increase. At room temperature a maximum stress was typically reached in the order of an hour. At still longer times the stress decreased again as a result of creep. The transient increase in stress following plastic straining grew larger as the amount of plastic strain produced by bulging was increased. With higher temperatures the transient became both faster and larger. A model is presented that based on the mechanism of thermally activated glide separates the microstructure in a class of “soft” and “hard” grains solving the issue of an “apparent” increase in strain energy as a function of time after deformation.
Optical study of SiGe films grown with low temperature Si buffer
Authors: Luo Y. H. , Wan J. , Liu J. L. , Wang K. L.
Published: April 2011

In this work, SiGe films on low temperature Si buffer layers were grown by solid-source molecular beam epitaxy and characterized by atomic force microscope, photoluminescence and Raman spectroscopy. Effects of the growth temperature and the thickness of the low temperature Si buffer were studied. It was demonstrated that using proper growth conditions of the low temperature Si buffer, the Si buffer became tensily strained and gave rise to the compliant effect. High-quality SiGe films with low threading dislocation density have been obtained.
X-Ray Diffuse Scattering from Misfit Dislocation at Buried Interface
Authors: Li Kaile , Miceli Paul F. , Lavoie Christian , Tiedje Tom , Kavanagh Karen L.
Published: April 2011

Motivated by x-ray scattering experiments on heteroepitaxially grown thin films, we present model calculations of the diffuse x-ray scattering arising from misfit dislocations. The model is based on the elastic displacements from dislocations whose positions are spatially uncorrelated. These numerical results give support to a phenomenological model [Phys. Rev. B 51, 5506 (1995)] that predicts the scaling of diffuse scattering intensity with perpendicular wavevector, Qz. At low Qz the diffuse width scales inversely with the defect size, which is given by the film thickness due to the effect of the elastic image field, whereas at high Qz the diffuse width is mosaic-like, scaling with Qz. New experimental results for InxGa1−xAs/GaAs are also presented and compared to the model. The calculations are in good agreement with these experiments, as well as other measurements in the literature for high and low dislocation density.
Si/GaAs heterostructures fabricated by direct wafer bonding
Authors: Dragoi Viorel , Alexe Marin , Reiche Manfred , Radu Ionut , Thallner Erich , Schaefer Christian , Lindner Paul
Published: April 2011

Si/GaAs heterostructures were obtained by a low temperature direct wafer bonding (DWB) method which uses spin-on glass (SOG) intermediate layers. The use of intermediate SOG layers allows the fabrication of Si/GaAs heterostructures at processing temperatures lower than 200°C. The achieved bonding energy permits thinning down to a few microns of Si and GaAs wafers, respectively, using grinding procedures followed by chemical mechanical polishing (CMP). After thinning, the heterostructures sustained annealing temperatures of 450°C without damaging of the bonded interface. The above bonding procedure was successfully applied for bonding GaAs wafers to Si wafers with structured surfaces. A technology was developed based on this bonding method for producing universal GaAs-on-Si or Si-on-GaAs substrates.
Multiple Wafer Bonding for MEMS Applications
Authors: Reiche M. , Haueis M. , Dual J. , Cavalloni C. , Buser R.
Published: April 2011

Most of the microelectromechanical systems (MEMS) require a 3-dimensional architecture which can efficiently be realized by multiple semiconductor wafer direct bonding. The present paper demonstrates the method on a force sensor for high resolution measurements of static loads. To minimize temperature stress an all-in silicon solution was developed in contrast to micromachined resonant force sensors published already in the literature.

The presented force sensor integrates load coupling, the excitation and detection of the vibration of the microresonator in one and the same single crystal silicon package. First measurements proved a sensitivity of 26 Hz/N and a resolution better than 3 mN.
Numerical Modeling of High Repetition Rate Pulsed Laser Crystallization of Silicon Films on Glass
Authors: Köhler Jürgen R. , Dassow Ralf , Werner Jürgen H.
Published: April 2011

This contribution investigates the crystallization behavior of amorphous silicon films on glass by using pulsed lasers with very high repetition rates up to 100 kHz. We determine the influence of the laser repetition rate f and of the film thickness d on the grain width g of the resulting polycrystalline silicon films. Our experimental results indicate a strong dependence of the grain width g on film thickness d as well as on the repetition rate f of the laser. The grain width rises from g = 0.27 µm to g = 3.59 µm if the film thickness increases from d = 50 nm to d= 300 nm and the repetition rate f from f = 20 kHz to 100 kHz. We use a purpose developed two- dimensional finite difference numerical model to calculate the evolution of the temperature in the silicon film and in the glass substrate. An increase of both, the film thickness d, and the repetition rate f decrease the solidification velocity v of the film. A comparison of the solidification velocity vs and the measured grain width g shows a linear correlation.
(001)-Textured Laser-Crystallized Silicon thin Films on Glass Substrates
Authors: Nerding M. , Christiansen S. , Esser G. , Urmoneit U. , Otto A. , Strunk H.P.
Published: April 2011

We investigate the microstructure of polycrystalline silicon films (grain size, texture and grain boundary population) on glass substrates. These films are produced from amorphous silicon precursor layers by scanning the raw beam of a continuous wave Ar+- ion laser operated at a wavelength of 514 nm over the amorphous silicon thereby crystallizing it. The materials applicability for devices in large area electronics strongly depends on the orientation of the surface normal, the average grain size and the defect density and population. Transmission electron microscopy together with electron back-scattering diffraction analysis of the crystallized layers reveal grain widths of about 10μm and grain lengths of several 10 μm. Under certain procesing conditions a preferred (001)-surface normal orientation (texture) forms. The grain boundary population is dominated in the textured films by coincidence boundaries, essentially twin boundaries of first and second order as well as Σ=5 boundaries.
Single-Crystal Thin Film Transistor by Grain-Filter Location-Controlled Excimer-Laser Crystallization
Authors: Dijk Barry D. van , Wilt Paul Ch. Van der , Bertens G. J. , Nanver Lis.K. , Ishihara Ryoichi
Published: April 2011

Thin film transistors (TFTs) are fabricated inside a large, location-controlled, silicon grain, fabricated with the grain-filter method. In a first experiment TFTs with high field-effect mobility for electrons of 430 cm2/Vs are fabricated. The off-current and subthreshold swing have high values of 60 pA and 1.2 V/dec, respectively. The grain-filter is improved by doping the channel and by planarizing the grain-filter by chemical mechanical polishing (CMP). TFTs fabricated in CMP-planarized grain-filters have mobility, off-current, and subthreshold swing of 430 cm2/Vs, 0.3 pA, and 0.29 V/dec, respectively, which compares well with the characteristics for SOI TFTs.
High Quality Poly-Si Film and Transistor Formed by Nickel-Induced- Lateral-Crystallization and Pulsed-Rapid-Thermal-Annealing
Authors: Leung T.C. , Cheng C.F. , Poon M.C.
Published: April 2011

Nickel Induced Lateral Crystallization (NILC) and Pulsed Rapid Thermal Annealing (PRTA) have been used to study new low temperature and high quality poly-silicon (poly-Si) films and thin film transistors (TFTs). The growth rate of poly-Si films has been found to greatly increase from 0.025μm/minute to 1.07μm/minute, and the drain current and performance of TFTs have increased by around 75%. The new poly-Si technology has good potential to apply in high performance, large area, fast throughput, low cost and even low temperature device applications.
Study of Crystal Growth in Grain-Filters for Location-Controlled Excimer Laser Crystallization
Authors: Wilt Paul Ch. van der , Dijk B.D. van , Bertens G.J. , Ishihara R.
Published: April 2011

Amorphous silicon films were transformed into large-grain polycrystalline silicon films by excimer laser induced rapid melting and solidification. Growth is seeded by residual unmolten silicon left in a grid of holes made in the underlying silicon oxide layer. Growth thus starts with a vertical growth phase, during which occlusion of grains occurs, ideally filtering out only a single grain that subsequently seeds the lateral growth. Yield was increased by sharpening the edges of the hole to improve the filtering mechanism and very uniform polycrystalline layers were obtained. Furthermore, simulations were performed to analyze parameters such as growth velocity and melt depth. It was found that heat from laser light absorbed in the neighborhood of the hole strongly contributes to melt depth and thus to the filtering mechanism. Substrate heating or longer pulse durations can be utilized to ensure the occlusion of grains during vertical growth, to reduce thermal stresses, and to increase grain size to a value sufficient for single crystal thin-film transistors.
The Study of the Formation of Thin SOI Structure by SIMOX with Water Plasma
Authors: Jing Chen , Meng Chen , Xiang Wang , Yemin Dong , Zhihong Zheng , Xi Wang
Published: April 2011

The biggest drawback of the widely application of SIMOX-SOI material is the low yield and the high cost which mainly due to the long implantation time by conventional beamline implanter. An implanter without an ion mass analyzer is used to fabricate SOI materials by H2O+, HO+, and O+ ions implantation using water plasma. Based on the consideration that the masses of the three ions of are quite close, their depth profiles in as-implanted wafers will not disperse much, which makes it possible for the formation of a single buried oxide layer by choosing the appropriate energy and dose. The results show that it exits a dose window at fixed implantation energy to form desirable thin or ultra-thin SOI structure with the buried oxide layer free of silicon islands. Compared to conventional SIMOX method, the sample implanted at the same dose and energy has thicker BOX layer. This probably caused by the heavy oxygen damaged region with hydrogen-induced defects in as-implanted wafer appears to be the adsorption center for the outside oxygen to diffuse into the silicon during the high-temperature annealing process.
Experimental Study on the Role of Hydrogen in the Breakdown of Low-Temperature Si Epitaxy
Authors: Platen-Schwarzkopf J. , Bohne W. , Fuhs W. , Lips K. , Röhrich J. , Selle B. , Sieber I.
Published: April 2011

Homoepitaxial Si layers were grown on Si(100) at temperatures of 325 - 500 °C by Electron-Cyclotron Resonance Plasma-Enhanced Chemical Vapor Deposition (ECR PECVD) from a gas mixture of SiH4,H2 and Ar. Ar was added in order to realize high growth rates where the breakdown of epitaxy was well observed. Si disorder depth profiles derived from RBS channeling spectra were compared with hydrogen depth distributions measured by Heavy-Ion Elastic Recoil Detection Analysis (HI-ERDA) and Secondary Ion Mass Spectroscopy (SIMS). The results suggest that the transition from epitaxial to amorphous growth proceeds through two stages: (1) a highly defective but still ordered growth with the defect density increasing as the growth proceeds and (2) the formation of conically shaped precipitates of amorphous Si. Both regions act as an increasingly effective sink for excessive hydrogen which diffuses from the growth surface into the bulk of the sample. In perfectly grown epitaxial films, where the overall concentration of excessive hydrogen was low, the hydrogen diffusion tail was found to extend far beyond the interface into the Si substrate.
A Self-Aligned Silicide Process for Thin Silicon-on-Insulator MOSFETs and Bulk MOSFETs with Shallow Junctions
Authors: Cohen G. M. , Cabral C. , Lavoie C. , Solomon P. M. , Guarini K.W. , Chan K.K. , Roy R.A.
Published: April 2011

We discuss a modified self-aligned silicide (salicide) process that uses a silicon cap to reduce the substrate silicon consumption by 50% as compared with a conventional salicide process. We have used a metal-silicon mixture to form the metal-rich phase reliably in the first anneal. After etching the unreacted mixture we deposit a silicon cap. This forces the metal to react with the silicon cap as well as with the substrate during the second anneal, thus minimizing silicon consumption from the substrate. The unreacted portion of the silicon cap is selectively etched, leaving a structure with a raised source and drain. We expect this process to be useful for forming silicide on shallow junctions and thin SOI films, where silicon consumption is constrained.
Neutron Irradiation-Induced Dimensional Changes in MEMS Glass Substrates
Authors: Allred Clark L. , Borenstein Jeffrey T. , Hobbs Linn W.
Published: April 2011

A study is made of radiation-induced expansion/compaction in Pyrex and Hoya SD-2 glasses, which are used as substrates for MEMS devices. Glass samples were irradiated with a neutron fluence composed primarily of thermal neutrons, and a flotation technique was employed to measure the resulting density changes in the glass. Transport of Ions in Matter (TRIM) calculations were performed to relate fast (∼1 MeV) neutron atomic displacement damage to that of boron thermal neutron capture events, and measured density changes in the glass samples were thus proportionally attributed to thermal and fast neutron fluences. The trend for strain with thermal neutron fluence (n/cm2) was found to be a linear compaction of -2.8×10−20 for Pyrex and -1.0×10−21 for Hoya SD-2. For fast neutron fluence, the trend for strain was also linear: -6.1×10−21for Pyrex and -7.9×10−22 for Hoya SD-2. The measured radiation-induced compaction of Pyrex is found to agree with that of previous studies. To our knowledge, this work represents the first study of compaction in Hoya SD-2 with neutron fluence. Hoya SD-2 is of considerable importance to MEMS, owing to its close thermal expansivity match to silicon from 25-500 C.
Issues with Gold Electroplating for Microelectromechanical System Applications
Authors: Kondoleon Caroline A. , Marinis Thomas F.
Published: April 2011

Electro-plated gold films are used extensively in packaging of MEM sensors to make connections to signal conditioning electronics. Over the past two years, production lots of gold plated substrates, procured from various vendors, failed an accelerated aging qualification test. In this test, 0.0025 [mm] diameter aluminum wires were ultrasonically welded to the film, aged at 120°C for 48 hours, and then pulled to destruction. The criterion for passing this test was that the wires should break both before and after aging. In the defective lots, the wires lifted off of the gold film after aging. Analysis of these defective films by SEM, Auger, and TOF-SIMS suggested that residues, deposited from the plating bath, concentrated beneath the bond as the gold and aluminum reacted to form an inter-metallic compound during aging. A combination, etch and cleaning treatment was developed for defective substrates, which removed a sufficient amount of residues from the gold to pass the qualification test.
Microstructuring of Silica and Polymethylmethacrylate Glasses by Femtosecond Irradiation for MEMS Applications
Authors: Juodkazis Saulius , Yamasaki Kazuhiko , Marcinkeviĉius Andrius , Mizeikis Vygantas , Matsuo Shigeki , Misawa Hiroaki , Lippert Thomas
Published: April 2011

We report the fabrication of complex 3D microstructures in silica and polymethyl- methacrylate glass by a combination of femtosecond laser microfabrication and chemical wet etching techniques. It is demonstrated that fabrication of interconnected network of channels having lengths of about 200 νm, and diameters as small as 10 νm is possible due to the enhanced etching selectivity (typically 20 - 60) in the laser-irradiated regions. Thus, it becomes feasible to form 3D micro-fluidic and photonic crystal structures in transparent glass-like materials using this approach. In addition, preliminary results on microstructuring of rubber are presented.
Fabrication of High Jc YBa2Cu3O7-δ Coated Conductors Using Sol-Gel Buffer Layers On Nickel and Nickel Alloy Substrates
Authors: Sathyamurthy S. , Paranthaman M. , Kang B. W. , Zhai H. Y. , Aytug T. , Christen H. M. , Specht E. D. , Kowalewski M. M. , Goyal A. , Martin P. M.
Published: April 2011

Sol-gel processing of La2Zr2O7 (LZO) buffer layers on biaxially textured Ni-3 at.% W alloy substrates using a continuous reel-to-reel dip-coating unit has been studied. The epitaxial LZO films obtained have a strong cube texture and uniform microstructure. The effect of increasing the annealing speed on the texture, microstructure and the carbon content retained in the film were studied. On top of the LZO films, epitaxial layers of Yttria Stabilized Zirconia (YSZ) and Ceria (CeO2) were deposited using rf sputtering, and YBa2Cu3Ox (YBCO) films were then deposited using Pulsed Laser Deposition (PLD). A critical current density (Jc) of 1.9 MA/cm2 at 77K and self-field and 0.34 MA/cm2 at 77K and 0.5T have been obtained on these films. These values are comparable to those obtained on YBCO films deposited on all-vacuum deposited buffer layers, and are the highest ever obtained using solution seed layers. The use of all-solution buffers for coated conductor processing has also been explored. A critical current density of 1.1 MA/cm2 at 77 K and self-field was obtained on YBCO films grown be PLD on LZO buffered nickel substrates.
Characterizing Transport Current Defects in 1-cm-Wide YBa2Cu3O7-δ Coated Conductors
Authors: Brown G. W. , Hawley M. E. , Peterson E. J. , Coulter J. Y. , Dowden P. C. , Arendt P. N. , Foltyn S. R. , Mueller F. M.
Published: April 2011

We have used a low temperature magnetic imaging system to determine current pathways in 5 cm long “good” and “bad” regions of a 1-cm-wide YBa2Cu3O7-δ coated conductor. The good and bad regions were identified with 4 point probe measurements taken at 1 cm intervals along the tape length. The current density map from the good region showed the expected edge peaked structure, similar to that seen in previous work on high quality test samples grown on single crystal substrates. The structure was also consistent with theoretical understanding of thin film superconductors where demagnetizing effects are strong. The maps from the bad region showed that the current was primarily confined to the right half of the sample. The left half carried only a small current that reached saturation quickly. Effectively halving the sample width quantitatively explains the critical current measured in that section. Spatially resolved x-ray analysis with 1 mm resolution was used to further characterize the bad section and suggested an abnormally large amount of a-axis YBCO present. This may be the result of non-uniform heating leading to a low deposition temperature in that area.
In-situDeposition of Superconducting MgB2 Films
Authors: Stelmashenko N. , Yates K. A. , Tsaneva V. N. , Kambara M. , Cardwell D. A. , Blamire M. G.
Published: April 2011

The discovery of superconductivity in MgB2 has been followed by many papers reporting attractive thin film properties. In most cases these have involved the deposition of precursor films followed by in-situ or ex-situ post annealing in a Mg-rich atmosphere. Although simple device structures have been fabricated from such films, it is desirable for a number of reasons that a heterostructure device technology be developed. Heterostructure growth is likely to require in-situ growth, preferably without post-annealing. To achieve this, low oxygen and high Mg background pressures are required in the vicinity of the sample. By using a novel heater geometry we have been able to grow superconducting MgB2 films from Mg-rich targets at temperatures below 500 °C. This paper reports the growth method, and structural and electrical characterization of the films.
Observation of Vortices and Columnar Defects by 1-MV Lorentz Microscopy II
Authors: Kamimura O. , Kasai H. , Matsuda T. , Harada K. , Tonomura A. , Okayasu S. , Sasase M. , Nakayama Y. , Shimoyama J. , Kishio K. , Hanaguri T. , Kitazawa K.
Published: April 2011

Two types of shape and contrast features of superconducting vortices in a Lorentz micrograph were obtained by the newly developed 1-MV field-emission transmission electron microscope on a Bi2Sr2CaCu2O8+8(Bi-2212) thin specimen containing tilted columnar defects. The shape and contrast features could be consistently interpreted by the simulation that some vortices were pinned along tilted columnar defects and others were unpinned. The interesting property for temperature change of vortex core inside the material was also observed.
Intrinsic Josephson Junctions on High-quality BSCCO-2212/2223 Superlattice Thin Films Grown by MOCVD
Authors: Endo K. , Sato H. , Yoshizawa T. , Abe K. , Itoh J. , Kajimura K. , Akoh H.
Published: April 2011

We report on the successful preparation of intrinsic Josephson junctions on high-quality BSCCO-2212/2223 superlattice thin films grown by MOCVD. The surface of as-grown films was very smooth with the roughness of the order of a half unit cell. Mesas were effectively structured on the film by the liquid-nitrogen-cooled dry etching method. A typical I-V characteristic in the c-axis direction of a BSCCO film shows the hysteresis and multiple resistive branches. The number of branches is consistent with that of junctions calculated from the height of a mesa structure. This indicates that BSCCO-2212/2223 superlattice films consist of a series array of S(CuO2 bilayer) / I(SrO, BiO layers) / S(CuO2 trilayer) junction. The formation of stacked Josephson junctions was also confirmed by the temperature dependence and the magnetic field dependence of Ic.
Effect of High Magnetic Field during Melt-Solidification Process on Crystal Alignment of REBCO Bulk
Authors: Yamagiwa R. , Horii S. , Eto H. , Otzschi K. , Shimoyama J. , Kishio K.
Published: April 2011

Disk-shaped samples of REBa2Cu3Oy ( RE123, RE = Y, Ho ) with 40%-by-molar RE2BaCuO5 (RE211, same RE of RE123 ) were melt-solidified without seeding under various magnetic fields (μ0Ha = 0 ˜ 8 T) and at various cooling rates ( Cr = 5.0, 10.0°C/h) in ambient atmosphere. Crystal alignment was evaluated by the X-ray diffraction, magnetization measurement using a SQUID magnetometer and observation of microstructure using a scanning electron microscope and a polarizing microscope. The melt grown RE123 crystals were c-axis-aligned under magnetic fields parallel to the applied field, (Ha), while the effect of alignment were systematically changed by the conditions of cooling rate and RE elements and the magnitude of Ha. The best c-axis-aligned sample showed that the value of anisotropy ( where the ratio of ΔMH//Ha /ΔMH⊥Ha) was approximately 20 at 85K and at μ0H = 0.3 T for the condition of RE = Y, Cr = 5.0°C/h, μ0Ha = 8 T.
Phase Relationships and Phase Formation in the System BaF2-BaO-Y2O3-CuOx-H2O
Authors: Wong-Ng W. , Cook L. P. , Suh J. , Levin I. , Vaudin M. , Feenstra R. , Cline J. P.
Published: April 2011

The interplay of melting equilibria and reaction kinetics is important during formation of the Ba2YCu3O6+x (Y-213) phase from starting materials in the quaternary reciprocal system Ba,Y,Cu//O,F. For experimental investigation of the process we used a combination of differential thermal analysis (DTA) for study of melting equilibria, and in-situ high-temperature x-ray diffraction (HTXRD) for study of the phase formation and reaction kinetics. DTA investigation of compositions spaced along compositional vectors extending from the oxide end to the fluoride end of the reciprocal system have given evidence of low melting liquids (∼600 °C) near the fluorine-rich end. Work is continuing to determine whether similar thermal events observed in the interior of the system also indicate low temperature liquids, and on the extent to which low-melting liquids could be involved in Y-213 phase formation. HTXRD investigations have been initiated on the conversion of 0.3 μm and 1.0 μm thick BaF2-Y-Cu precursor films to Y-213 in the presence of water vapor. Preliminary results indicated that the thickness of film has a strong influence on the texture of the Y-213 film: a 0.3 μm film showed mainly (001) texture, whereas a 1.0 μm film showed a greater volume fraction of (h00) texture. While the HTXRD method cannot directly reveal the presence of liquid, we are working to combine DTA and HTXRD data for a unified picture of Y-213 phase formation during the “BaF2 ex-situ” process for coated-conductor fabrication.
Theoretical Considerations for Finding New Thermoelectric Materials
Authors: Singh David J.
Published: April 2011

This paper reviews the connections between the transport properties underlying the thermoelectric performance of a material and microscopic quantities, particularly as they may be obtained from first principles calculations. These are illustrated using examples from work on skutterudites. The results are used to suggest yet to be explored avenues for achieving higher thermoelectric performance within this class of materials.
Synthesis and Properties of Lead Selenide Nanocrystal Solids
Authors: Chen Feng , Stokes Kevin L. , Zhou Weilie , Fang Jiye , Murray Christopher B.
Published: April 2011

We present results of our investigation of the synthesis, structural properties and electrical transport properties of lead selenide (PbSe) nanoparticle-derived solids. Stable colloidal solutions containing crystalline PbSe particles with sizes on the order of 5-10 nm were synthesized using an organometallic lyothermal growth method in high-temperature organic solvents (100∼200 °C). The nanoparticle powders have been characterized by X-ray scattering (WAXS/SAXS), electron microscopy and optical absorption. Thin lms were formed by controlled precipitation of the nanoparticles from solution onto insulating substrates. Electrical resistance (R) and Seebeck coecient (S) for conductive PbSe lms from dierent annealing conditions were studied and compared. We were able to obtain conductive PbSe lms from colloids by low temperature annealing which did not disturb the nanoparticle self-assembly.
Multinuclear NMR and Powder X-ray Diffraction Studies of Si and Sn Clathrates of Alkali Metals: Vacancies, Disorder and Knight Shifts
Authors: Ferguson Michael J. , Moudrakovski Igor L. , Ratcliffe Christopher I. , Tse John S.
Published: April 2011

The Structure I type binary metal clathrates of K/Si, Rb/Si and Cs/Sn have been synthesised and studied by powder X-ray diffraction and solid state NMR. Rietveld analysis shows that in all three materials some of the cages are empty, and that in the Cs/Sn clathrate there are vacancies in the Sn framework. The NMR results yield Knight shifts for 29Si and 39K and confirm that the Cs/Sn clathrate is not conducting. Many of the features of the NMR spectra can be understood in terms of the distributions of atom vacancies.
Experimental Thermopower of Quantum Wires
Authors: Vedernikov M. V. , Uryupin O. N. , Goltsman B. M. , Ivanov Yu. V. , Kumzerov Yu. A.
Published: April 2011

Experimental investigation of thermoelectric properties of nanowires with diameter of about 5 nm was carried out. Chrysotile asbestos (a natural mineral) was used for a sample preparation. Its nano-sized channels were filled under pressure by melted InSb or Te. The measurements showed that temperature dependences of electrical resistance and thermopower of produced quantum wires differ considerably from corresponding dependences of bulk materials. It is possible to conclude that the results obtained are better described by Lattinger liquid model than by usual Fermi gas one.
Formation, Crystal Structure and Physical Properties of Novel Thermoelectric Skutterudites: EuyFe4−xNixSb12
Authors: Grytsiv Andriy , Rogl Peter , Berger Stefan , Paul Christoph , Bauer Ernst , Godart Claude , Saccone Adriana , Ferro Ricardo , Kaczorowski Darek
Published: April 2011

Quantitative X-ray powder Rietveld refinements for a series of alloys from the solid solution EuyFe4−xNixSb12, synthesized by argon arc-melting followed by long term annealing, established in all cases isotypism with the partially filled skutterudite-type structure, LaFe4P12. The Eucontent of the samples was determined from the combined data obtained results of Rietveld refinements and electron microprobe measurements. These investigations confirmed a systematic trend for the Eu-occupancy y in the parent lattice, revealing a gradual decrease of the maximum Eu-content from practically full occupancy, y = 0.83, in Eu0.83Fe4Sb12 to y ∼ 0.5 for Eu∼0.5Fe2Ni2Sb12. Eu0.83Fe4Sb12 orders magnetically below 84 K and the transition temperature decreases as a function of Fe/Ni substitution. As a further consequence of the Fe/Ni substitution electronic transport crosses over from a hole conductivity regime into electron dominated behaviour. Concomitantly, the transition metal exchange increases the Seebeck coefficient significantly, hence the figure of merit enhances.
BN protective coating for high temperature applications
Authors: Bathe Ravi , Vispute R.D. , Habersat Daniel , Takeuchi Ichiro , Sharma R.P. , Venkatesan T. , Zheleva T.S. , Jones Ken
Published: April 2011

We report on the fabrication, characterization, and processing of boron nitride films for use in high temperature applications such as field passivation, capping layers for thermal annealing of SiC, and protecting metallic filaments from their working environments. The BN films have been fabricated by pulsed laser deposition and spray techniques. The deposited films were characterized by X-ray Diffraction, Fourier Transform Infrared Spectroscopy, Ultraviolet-Visible Spectroscopy, Rutherford Backscattering Spectrometry and Transmission Electron Microscopy. The BN films deposited in the temperature range of 200-500°C have been found to be poorly crystalline, whereas the films fabricated above 600°C have been found to be microcrystalline. The as-deposited films were annealed at various temperatures ranging from 900°C to 1700°C in order to densify the films and study the applicability of the coatings. An AlN buffer layer was also applied in a few cases to improve chemical bonding with the substrate. Adhesion of the films with the heater components was greatly improved for high temperature annealed samples due to good interfacial bonding with the substrate material. Our results on the properties of BN films with an emphasis on characterization, processing, and implications for high temperature applications are discussed.
Hydrogen Free, High sp3 Content DLC Films Produced by Pulsed Laser Ablation of Amorphous Graphite
Authors: Haverkamp J. , Mayo R. M. , Narayan J. , Jin C.
Published: April 2011

Pulsed laser deposition is a unique technique for the deposition of a wide variety of thin films. These films include magnetic and optical films, novel semiconductors, high temperature superconductors, and diamond-like carbon films. Amorphous Carbon material is evaporated from a solid target and ionized by a high-energy KrF laser and ejected as a plasma plume. The plume expands outwards and deposits the target material on a silicon substrate. Plasma and flow parameters in this plume determine the quality of the film deposited on the substrate. In these experiments, a quadruple Langmuir probe is used to determine various plasma properties in the plume as a function of laser energy density on target, laser spot size on the target and probe position from target. These properties include electron temperature, ion flow speed, ion kinetic energy, plume peaking parameter, and ion density. Film analysis was conducted by electron energy loss spectroscopy (EELS) indicating that DLC films have been successfully deposited with an sp3 concentration as exceeding 72%.
Bio-compatible Thin Films on Rare Earth Based Permanent Magnets
Authors: Vasilescu Ecaterina , Drob Paula , Raducanu Doina , Angelescu Lucia , Iliuc Constantin
Published: April 2011

The item of the paper is focussed on some bio-compatible coatings for rare earth based permanent magnets, which are used as dental materials for prosthetic devices as retention units. The studied alloy belongs to Nd-Fe-B system with some Dy and Al content. The double-layer coatings had different chemical compositions; first layer: Ag30-Cr70, Co30-Cr70, Stainless Steel and the second layer: titanium nitride (TiN). Data about corrosion behavior, wear resistance and adhesion are presented. The corrosion resistance of these coatings was tested in artificial saliva, using electrochemical potentiostatic and potentiodynamic polarization techniques. The stability in the corrosion media, the localized corrosion susceptibility and the corrosion rates were determined. It resulted that the Nd30-Dy5-Fe-Al0.4-B alloy with Ag30-Cr70 + TiN film is very stable in artificial saliva. The wear behavior of the coatings in different conditions of contact and load was tested, also. The adhesion was determined by scratching test.
Structural and Tribological Properties of TiC/C/Ag Coatings in Vacuum and Ambient Environments
Authors: Endrino Jose L. , Nainaparampil Jose J. , Krzanowski James E.
Published: April 2011

TiC/C/Ag coatings were deposited by magnetron sputtering pulsed laser deposition (MSPLD) combining sputtering from a custom made Ti-Ag (60:40) target with the ablation of carbon. Energy disperse spectroscopy (EDS) was used to determine the elemental composition, and x-ray diffraction (XRD) and cross-sectional scanning electron microscopy (XSEM) to examine the structure of the films. Hardness and reduced modulus measurements were acquired using a nanoindentation technique. The pin-on-disk friction test was used to study the friction behavior of the deposited samples in high vacuum and ambient conditions. Variations in the laser energy and the power of the sputtering gun yielded a set of samples with carbon content that ranged from 15.0 to 95.6 percent. The hardest samples with the highest reduced modulus were those with a moderate carbon content and that were shown to form a titanium carbide phase. Tribological results indicated that there is an optimum composition of a TiC/C/Ag coating (~25 at.% carbon) for which it can be reversible and provide lubrication in both ambient and vacuum.