bluuebunny/crossref_metadata_2025 huggingface dataset:
Recursive Image Charge Approach for Quantitative Characterization of Dielectric Thin Film Library Using Scanning Tip Microwave Near-field Microscopy
Authors: Gao Chen , Hu Bo , Huang Mengming , Zhang Pu , Liu Wen-han
Published: April 2011

We developed a recursive image charge approach for quantitative characterizations of dielectric thin films using the scanning tip microwave near-field microscope. With this method, frequency shift of the microscope as functions of the dielectric constant and the thickness of a film can be effectively computed in a recursive way. We believe that this approach can promote the high-throughput characterization of the dielectric libraries.
Order-disorder transition in the Cd-Ca cubic approximant
Authors: Widom M. , Mihalkovič M.
Published: April 2011

Recent experiments discovered an order-disorder transition occuring at low temperatures in large unit 1/1 cell cubic approximants of the stable Cd-based binary alloy quasicrystals. The transition is related to correlations among orientational degrees of freedom whose separations are around 12 Å. We analyze the interactions between the degrees of freedom using ab-initio calculations for Cd-Ca alloys and derive an equivalent antiferromagnetic Ising model which shows a similar phase transition. However, the calculated transition temperature is higher than observed experimentally, indicating that the actual structure and its order-disorder transition are more complex than originally proposed. A side-benefit of our study is the discovery of a canonical-cell decoration model for the Cd-Ca icosahedral phase.
Structural Evolution of Cold Rolled Multi-Layers in the Al-Cu-Fe Ternary System
Authors: Park J. S. , Fleury E. , Kim J. H. , Chang H. J. , Kim W. T. , Kim D. H.
Published: April 2011

Samples with a target composition of Al62.5Cu25Fe12.5 (at.%) have been produced from the repeated cold rolling and folding (R&F) process of Al, Cu and Fe elemental foils. Upon early increments of the R&F cycle, the mechanically-induced process led to the fragmentation of the initial foils, which resulted in the dispersion of elemental Fe layers through the refined Al and Cu layers. After 40 R&F cycles the Al2Cu phase was detected, while Fe did not contribute to the formation of compounds. Thermal analyses suggested that the formation and dissolution of the Al2Cu and Al7Cu2Fe phases are critical steps for the synthesis of the i-phase during post-R&F treatment. Annealing between 650° and 750°C enabled the formation of the stable i-phase and resulted in high values of the microhardness.
Electrocodeposited Quasicrystalline Coatings for Non-Stick Wear Resistant Cookware
Authors: Minevski Zoran , Tennakoon Charles L. , Anderson Kelvin C. , Nelson Carl J. , Burns Frederick C. , Sordelet Daniel J. , Haering Chad W. , Pickard Don W.
Published: April 2011

Lynntech, Inc has successfully researched and demonstrated a unique method for the manufacture of quasicrystalline (QC) coatings that utilizes the process of electrocodeposition. The purpose of this study was to optimize the physical-mechanical properties of the QC coatings. All metal substrates were aluminum alloy Al-3004 and codeposition was performed using Al65Cu23Fe12 QC powders in nickel plating solutions. X-ray diffraction spectroscopy was performed in order to verify the attachment of quasicrystals to the aluminum alloy substrate and coated samples displayed identical spectra to those of raw QC powders. The average contact angle θ was 117.2° for electrocodeposited QC coatings. Friction was monitored during pin-on-disk wear tests and QC coated samples had coefficients of friction as low as 0.01 and an average value of 0.05 with samples showing no visible wear scar. Lynntech's electrocodeposited quasicrystalline coatings withstand high temperatures and exhibit low wear and friction characteristics with a low surface energy making them ideal for cookware, as well as various other applications such as bearings, landing gear and engine parts, where thermal and mechanical conditions are prime importance.
Thermoelectric properties of the Al-TM-Si (TM = Mn, Re) 1/1-cubic approximant
Authors: Takeuchi Tsunehiro , Otagiri Toshio , Sakagami Hiroki , Mizutani Uichiro
Published: April 2011

The electrical resistivity, thermoelectric power, and thermal conductivity were investigated for the Al71.6-xMn 17.4Six and Al71.6-xRe 17.4Six (7 ≤ x ≤ 12) 1/1-cubic approximants. A large thermoelectric power ranging from -40 to 90 μV/K and a low thermal conductivity less than 3 W/K·cm were observed at room temperatures. The electrical resistivity at room temperature for these approximants was kept below 4,000 μΩcm, that is much smaller than that in the corresponding quasicrystals. As a result of the large thermoelectric power, the low thermal conductivity, and the low electrical resistivity, large dimensionless figure of merit ZT = 0.10 (n-type) and 0.07 (p-type) were achieved for the Al71.6Re17.4Si11 and Al71.6Mn17.4Si11 at room temperature, respectively.
Constitutive model of quasicrystal plasticity: Strain-rate and temperature dependence
Authors: Heggen Marc , Feuerbacher Michael
Published: April 2011

A constitutive model describing the plasticity of icosahedral quasicrystals [1] was applied to icosahedral Al-Pd-Mn over a wide range of experimental deformation conditions. The model incorporates the evolution of two microstructural parameters: The first, as in crystals, is the dislocation density; the second is a quasicrystal-specific order parameter that accounts for deformation-induced disordering and thermally activated reordering of the quasicrystal structure. Significant strain-rate dependence was found which can be understood by the interactive evolution of these two microstructural parameters. The present work shows that the constitutive model comprehensively describes the features of quasicrystal plasticity over a wide range of experimental conditions.
Low temperature deformation mechanisms of icosahedral AlPdMn quasicrystals.
Authors: Texier Michael , Bonneville Joël , Proult Anne , Rabier Jacques , Thilly Ludovic
Published: April 2011

Confining pressure techniques, that superimpose a shear stress on an isostatic component, allowed us to plastically deform AlPdMn specimens at temperatures below the brittle-to-ductile transition temperature obtained using conventional uniaxial deformation tests at usual strain-rates. Microstructural observations associated with these low deformation temperatures are reported. They provide new insights on the elementary deformation mechanisms that control plasticity in this non-periodic structure.
Influence of Al on Quasicrystal Formation in Zr-Ti-Nb-Cu-Ni-Al Metallic Glasses
Authors: Scudino Sergio , Eckert Jürgen , Kühn Uta , Breitzke Hergen , Lüders Klaus , Schultz Ludwig
Published: April 2011

The effect of Al on the crystallization behavior of (Zr0.616Ti0.087Nb0.027Cu0.15Ni0.12)100–xAlx melt-spun glassy ribbons with x = 7.5, 5, 2.5 and 0 was investigated by differential scanning calorimetry, x-ray diffraction and transmission electron microscopy. The devitrification of the ribbons is characterized by the formation of a metastable quasicrystalline phase during the first stage of the crystallization process even for the alloy with x = 0. Therefore, Al is not essential for quasicrystal formation in the present alloys. However, it affects the properties of the amorphous as well as of the quasicrystalline phase. With decreasing Al content, the temperature range of stability of the quasicrystalline phase increases whereas the thermal stability of the amorphous phase decreases together with a slight decrease of the extension of the supercooled liquid region. Thus, it is concluded that although the addition of Al improves the stability of the glassy phase, it has no beneficial effect on the formation of quasicrystals.
Local Structural Variations in Al72Ni20Co8 Decagonal Quasicrystals
Authors: Yan Yanfa , Pennycook S. J.
Published: April 2011

We investigate local structural variations in Al72Ni20Co8 quasicrystals using first principles density-functional total-energy calculations. We find that local chemical fluctuation can cause large structural variations on the central rings of the 2-nm clusters. Such structure variations may result in ambiguities at the central rings in high-resolution electron microscopy images of Al72Ni20Co8 decagonal quasicrystals.
Orientation relationship between metallic thin films and quasicrystalline substrates.
Authors: Fournée V. , Rossa A. R. , Lograsso T. A. , Thiel P. A.
Published: April 2011

We present experimental results on the structure of Ag thin films grown on high-symmetry surfaces of both quasicrystals and approximants. For coverages above ten monolayers, Ag form fcc nanocrystals with (111) plane parallel to the surface plane. Depending on the substrate surface symmetry, the Ag nanocrystals exist in one, two or five different orientations, rotated by a multiple of 2π/30. The orientation relationship between crystalline films and substrates appears to be determined by the following principles: high atomic density rows of the adsorbate are aligned along high atomic density rows of the substrate.
Cleavage Planes of Icosahedral Quasicrystals: A Molecular Dynamics Study
Authors: Rösch Frohmut , Rudhart Christoph , Gumbsch Peter , Trebin Hans-Rainer
Published: April 2011

The propagation of mode I cracks in a three-dimensional icosahedral model quasicrystal has been studied by molecular dynamics techniques. In particular, the dependence on the plane structure and the influence of clusters have been investigated. Crack propagation was simulated in planes perpendicular to five-, two- and pseudo-twofold axes of the binary icosahedral model.

Brittle fracture without any crack tip plasticity is observed. The fracture surfaces turn out to be rough on the scale of the clusters. These are not strictly circumvented, but to some extent cut by the dynamic crack. However, compared to the flat seed cracks the clusters are intersected less frequently. Thus the roughness of the crack surfaces can be attributed to the clusters, whereas the constant average heights of the fracture surfaces reflect the plane structure of the quasicrystal. Furthermore a distinct anisotropy with respect to the in-plane propagation direction is found.
Effects of Positive Feedback on Crystallization Kinetics and Recalescence
Authors: Bossuyt Sven , Lindsay Greer A.
Published: April 2011

In bulk metallic glasses cooled at nearly the critical cooling rate for glass formation, nucleation is observed to be spatially localized; nanocrystals are clustered together in spherical regions. This implies that a positive feedback mechanism locally increases the nucleation rate in the vicinity of other nucleation events. Linear stability analysis and computer simulation of differential equations describing crystal nucleation and growth are used to theoretically examine the plausibility of different potential feedback mechanisms. It is shown that interactions between different crystallizing phases can lead to counter-intuitive composition dependence of the crystallization kinetics in the case of non-polymorphic crystallization.
Modifications of the phase selection during the crystallization of amorphous Al-Y-Fe
Authors: Boucharat N. , Rösner H. , Hebert R. J. , Perepezko J. H. , Wilde G.
Published: April 2011

The effect of thermal treatments, plastic deformation and inoculation of quenched Al88Y7Fe5glasses with immiscible Pb and In on their crystallization behavior has been studied based on calorimetric and microstructural analyses. The results demonstrate the effect of the plastic deformation and of the inoculants to promote nanocrystallization. Moreover, the formation of a pronounced concentration gradient at the growing nanocrystal interface provides for the kinetic stability of the nanostructure and the modification of the phase evolution sequence of the crystallization reactions.
Metallic glass fluid flow during welding using self-propagating reactive multilayer foils
Authors: Swiston Albert J. , Weihs Timothy P. , Knio Omar M. , Hufnagel Todd C.
Published: April 2011

We use a fluid mechanics model to analyze glass fluid flow during the welding of bulk metallic glasses with reactive multilayer foils acting as local heat sources. The resulting welded joints were shear tested, and fracture surfaces were analyzed by optical microscopy. Fracture surfaces of failed metallic glass joints show distinct regions of metal-metal veins that indicate effective metallurgical bonding. We observe a monotonic increase in the failure strength of the joints with the fraction of the joint composed of such veins. For the strongest joint tested (shear strength of 420 MPa), nearly 60% of the fracture surface is comprised of metal-metal veins. We have developed a qualitative fluid mechanics explanation of the welding process, in which shear stresses (due to pressure applied during joining) push the reactive foil from the joint interface and create the metal-metal veins. The welding process is more effective at higher joining pressure and greater foil thickness, leading to increased joint strength.
Thermodynamics of The Pd43Ni10Cu27P20 Bulk Metallic Glass Forming Alloy
Authors: Kuno Masahiro , Shadowspeaker Ludi A. , Schroers Jan , Busch Ralf
Published: April 2011

The thermodynamics of the bulk metallic glass forming Pd43Ni10Cu27P20 alloy were investigated with differential scanning calorimetry (DSC). The specific heat capacity of the undercooled liquid with respect to the crystalline mixture was measured in the DSC simultaneously with the enthalpy of crystallization over the entire supercooled liquid region. The enthalpy, entropy, and Gibbs free energy change between the liquid and the crystalline mixture was determined from the specific heat capacity data. The calculated enthalpy function closely matched the enthalpies of crystallization that were measured in the DSC, which verifies the validity of the thermodynamic model used. A small Gibbs free energy difference between undercooled liquid and crystalline mixture was found for decreasing temperature in Pd43Ni10Cu27P20 when compared to other glass forming alloys. This reflects a small driving force for crystallization when undercooling this alloy and is the main contributing factor for its high glass forming ability.
The Thermal Shear-Transformation-Zone Theory: Homogeneous Flow and Superplasticity in Bulk Metallic Glasses
Authors: Falk Michael L. , Langer James S. , Pechenik Leonid
Published: April 2011

We present an extended version of our earlier shear-transformation-zone theory of amorphous plasticity that takes into account thermally assisted molecular rearrangements. As in the previous low-temperature theory a transition is predicted between jammed and flowing states at a well defined yield stress. In the new theory the jammed state below the yield stress exhibits thermally assisted creep. The theory accounts for the experimentally observed strain-rate dependence of the viscosity of a bulk metallic glass. In particular it models the onset of superplastic behavior at high strain rates as the system approaches the yield stress. The theory also captures many of the details of the transient stress-strrain response of the metallic glass at temperatures near the glass transition.
High-density liquid-like component facilitates plastic flow in a model amorphous silicon system
Authors: Demkowicz Michael J. , Argon Ali S.
Published: April 2011

Molecular dynamics simulations show that plastic deformation behavior of model Stillinger-Weber amorphous Si is very sensitive to the density of the initial unstressed state. Low-density systems exhibit a pronounced yield phenomenon, strain softening, and a dramatic drop in pressure during deformation at constant volume. This behavior is explained by the interplay in every system of the prevailing solid-like and liquid-like components, with the latter being denser and more amenable to plastic flow.
Free Volume Changes and Crack Tip Deformation in Bulk Metallic Glass Alloys and their Composites
Authors: Kanungo Biraja P. , Lambert Matthew J. , Flores Katharine M.
Published: April 2011

The free volume changes associated with deformation of metallic glasses play an important role in strain localization in shear bands. However the details of these structural changes during inhomogeneous deformation are unclear. In this study, the free volume changes in Cu60Zr30Ti10 and Zr58.5Cu15.6Ni12.8Al10.3Nb2.8 bulk metallic glasses were examined and quantified using differential scanning calorimetry following rolling and low temperature annealing. It was found that the height of the endothermic peak associated with the glass transition decreased following deformation whereas annealing resulted in an increase in the peak height. Additionally, the exothermic event associated with structural relaxation prior to the glass transition occurred at a lower temperature after rolling in the Zr-based system. Surprisingly, a similar shift in the onset temperature was not observed in the Cu-based system, suggesting a different structural relaxation mechanism. The Zr-based system was successfully modeled and the results indicated that the free volume increased ∼4% with inhomogeneous deformation and decreased ∼14% with annealing, consistent with expectations. In an effort to further characterize strain localization in shear bands, the development of a crack tip damage zone in a Zr-based bulk metallic glass composite was studied using scanning electron and atomic force microscopy. The first shear band developed at an angle of ∼60° from the crack propagation direction. This is discussed in light of the Mohr-Coulomb yield criterion for metallic glasses. The reinforcement phase arrested the growth of individual shear bands, while accumulated damage resulted in the shear bands cutting through the crystalline phase, ultimately resulting in crack branching and failure.
Microstructure of Ti-Based, Dendrite/Nanostructured-Matrix Composites
Authors: Woodcock Thomas G. , Mato Sonia , Alcalá Germán , He Guo , Wang Yinmin , Ma En , Dai Qunlong , Sui Manling , Löser Wolfgang , Eckert Jürgen , Schultz Ludwig
Published: April 2011

Electron microscopy of the composite-forming alloys Ti60Cu14Ni12Sn4Nb10 and Ti60Cu14Ni12Sn4Ta10, shows that for both alloys, the microstructure consists of an array of micron-scale dendrites surrounded by a nanoscale binary eutectic. In the Ta-containing alloy, one of the eutectic phases has been identified as having a bcc crystal structure similar to that of the dendrites. In the Nb-containing alloy, one of the eutectic phases has been found to have a similar composition to that of the dendrites. Further detailed structural and compositional characterization is needed in order to understand the solidification behaviour of such materials. This knowledge may then be used to improve the casting conditions and subsequent mechanical properties of the materials.
Structural Relaxation and Crystallization in a Pd40Cu30Ni10P20 Bulk Metallic Glass
Authors: Raghavan R. , Ramamurty U. , Basu J. , Ranganathan S. , Nishiyama N.
Published: April 2011

The stability of a Pd40Cu30Ni10P20 bulk metallic glass (BMG) against structural relaxation is investigated by isothermal and isochronal annealing heat treatments below and above its glass transition temperature, Tg, for varying periods. Differential scanning calorimetry (DSC) of the annealed samples shows an excess endotherm at Tg, irrespective of the annealing temperature. This recovery peak evolves exponentially with annealing time and is due to the destruction of anneal-induced compositional short range ordering. The alloy exhibits a high resistance to crystallization on annealing below Tg and complex Pd- and Ni-phosphides evolve on annealing above Tg.
(Selective) Epitaxial Growth of Strained Si to Fabricate Low Cost and High Performance CMOS Devices
Authors: Loo R. , Delhougne R. , Meunier-Beillard P. , Caymax M. , Verheyen P. , Eneman G. , Wolf I. De , Janssens T. , Benedetti A. , Meyer K. De , Vandervorst W. , Heyns M.
Published: April 2011

Tensile strained Si on SiGe Strain Relaxed Buffers (SRB) is an interesting candidate to increase both electron and hole mobility which results in improved device performance. Most of this work was/is based on thick (several μm), step-graded SRBs with or without Chemical Mechanical Polishing (CMP) planarisation. This approach bears several disadvantages such as issues with STI formation in the thick SiGe structure, and considerable self-heating effects due to the lower thermal conductivity of the SiGe material. Further, pMOS improvement requires SRBs with high Ge contents (> 30 %), which complicates device fabrication even more. To overcome these issues, we developed a new and cost efficient type of thin SRB (∼200 nm). The concept is based on the introduction of a thin carbon-containing layer during growth of a constant composition SiGe layer. The process relies on standard Chemical Vapor Deposition epitaxial technology without need for CMP. It is designed to allow both non-selective growth on blanket wafers and selective growth in the active area of structured wafers with Shallow Trench Isolation (STI). The selective epitaxial process for strained Si on thin SRBs proposed here, allows relatively simple and cost-effective fabrication of strained Si layers on existing STI structures without any process modification. Further, it offers a very flexible fabrication scheme to independently improve nMOS and pMOS devices. The SRB quality is comparable to the best reported in literature so far, with 70 % and 53 % mobility enhancements for long channel nMOSFETs on 22 % Ge SRBs grown on blanket and STI patterned wafers, respectively.
Strained Silicon On Insulator wafers made by the Smart Cut™ technology
Authors: Ghyselen B. , Bogumilowicz Y. , Aulnette C. , Abbadie A. , Osternaud B. , Besson P. , Daval N. , Andrieu F. , Cayrefourq I. , Moriceau H. , Ernst T. , Tiberj A. , Rayssac O. , Blondeau B. , Mazure C. , Lagahe-Blanchard C. , Pocas S. , Cartier A.-M. , Hartmann J.-M. , Leduc P. , Nardo C. Di , Lugand J.-F. , Fournel F. , Semeria M.-N. , Kernevez N. , Campidelli Y. , Kermarrec O. , Morand Y. , Rivoire M. , Bensahel D. , Paillard V. , Vincent L. , Claverie A. , Boucaud P.
Published: April 2011

Strained Silicon On Insulator wafers are today envisioned as a natural and powerfulenhancement to standard SOI and/or bulk-like strained Si layers. For MOSFETs applications, thisnew technology potentially combines enhanced devices scalability allowed by thin films andenhanced electron and hole mobility in strained silicon. This paper is intended to demonstrate byexperimental results how a layer transfer technique such as the Smart Cut™ technology can be usedto obtain good quality tensile Strained Silicon On insulator wafers. Detailed experiments andcharacterizations will be used to characterize these engineered substrates and show that they arecompatible with the applications.
Strain Mapping in SiGe by Visible Raman Spectroscopy
Authors: Pajcini Vasil
Published: April 2011

Heterogeneous strain in Si/SiGe for CMOS mobility enhancement may result in device yield losses or IC performance limitations. This lateral heterogeneity in strain can be uniquely measured by Raman spectroscopy. UV Raman and Visible Raman can measure this heterogeneity respectively in the thin Si cap and in the SiGe underlayer. Both UV and Visible Raman are useful. While UV Raman is optimized for the Si channel layer, Visible Raman of the SiGe underlayer provides diagnostic information when trying to understand and reduce the heterogeneity in the Si channel. In principle Visible Raman can also measure the heterogeneity of the strain in the Si channel, but in practice this is very time consuming and not as sensitive as UV Raman. This paper focuses on the kind of heterogeneity strain information available from Visible Raman.
Physical characterization of HfO2 deposited on Ge substrates by MOCVD
Authors: Elshocht S. Van , Brijs B. , Caymax M. , Conard T. , Gendt S. De , Kubicek S. , Meuris M. , Onsia B. , Richard O. , Teerlinck I. , Steenbergen J. Van , Zhao C. , Heyns M.
Published: April 2011

Germanium is because of its intrinsically higher mobility than Si, currently under consideration as an alternative approach to improve transistor performance. Germanium oxide, however, is thermodynamically unstable, preventing formation of the gate dielectric by simple oxidation. At present, high-k dielectrics might be considered as an enabling technology as much progress has been made in the deposition of thin high-quality layers.

In this paper, we study the growth and physical properties of HfO2 deposited on Ge by MOCVD, using TDEAH and O2 as precursors, and compare the results to similar layers deposited on silicon substrates. Our results show that the physical properties of MOCVDdeposited HfO2 layers on Ge are very similar to what we have observed in the past for Si. Unfortunately, some of the negative aspects observed for Si, such as diffusion of substrate material in the high-k layer, a low density for thinner layers, or a rough top surface, are also observed for the case of Ge. However, careful surface pretreatments such as NH3 annealing the Ge substrate prior to deposition, can greatly improve the physical properties. An important observation is the very thin interfacial layer between HfO2 and Ge substrate, allowing a more aggressive scaling for Ge.
Island Scaling Effects on Photoluminescence of Strained SiGe/Si (100)
Authors: Peterson Rebecca L. , Yin Haizhou , Sturm J. C.
Published: April 2011

The fabrication of electronic devices on semiconductor islands is becoming increasingly common because of silicon-on-insulator technology and/or because of strain engineering in compliant substrate approaches. While photoluminescence can be an accurate probe of Ge content and strain, in islands it can be affected by the presence of the island edges. Here we present data and a model showing that for high quality SiGe, edge effects are critical for sizes under ∼20 μm. These effects can be mitigated by regrowing epitaxial silicon to passivate the recombination states on the island edges.
The Role of Preamorphization and Activation for Ultra Shallow Junction Formation on Strained Si Layers Grown on SiGe Buffer
Authors: Pawlak B.J. , Vandervorst W. , Lindsay R. , Wolf I. De , Roozeboom F. , Delhougne R. , Benedetti A. , Loo R. , Caymax M. , Maex K. , Cowern N.E.B.
Published: April 2011

In advanced CMOS technology nodes one may achieve further enhancement of device performance by carrier mobility modification in the transistor channel. The carrier mobility enhancement can be realized by formation of strained silicon layers on a Si1−xGex strain relaxed buffer. Formation of source and drain extensions on such structures need to satisfy one additional requirement, the formation process, including the activation related thermal budget should not relax the strain in the channel. In this paper we separately investigate the role of amorphization during implantation, different doping impurities and thermal budget on the junction and the transistor channel regions properties. Two approaches of dopant activation are discussed: low temperature solid phase epitaxial regrowth and high temperature conventional spike.
Epitaxial La0.67(Sr,Ca)0.33MnO3 Films on Si for IR Bolometer Applications
Authors: Grishin A.M. , Khartsev S.I. , Kim J.-H. , Lu Jun
Published: April 2011

We report on processing and properties of La0.67(Sr,Ca)0.33MnO3(LSCMO) films grown by pulsed laser deposition technique on Si(001) substrates buffered with Bi4Ti3O12/CeO2/YSZ heteroepitaxial layers. X-ray diffraction shows cube-on-cube growth of epitaxial Bi4Ti3O12/CeO2/YSZ/Si heterostructure whereas the LSCMO layer grows in the “diagonal-on-side” manner onto the Bi4Ti3O12 (BTO) template. High resolution TEM images demonstrate sharp interfaces between the buffer layers and LSCMO film as well as rare misfit dislocations on the CeO2/YSZ interface. LSCMO film processing conditions have been optimized to get maximum temperature coefficient of resistivity TCR = 4.4%K-1 and colossal magnetoresistance(CMR) ‘Delta;ρ/ρ ∼ 2.9%kOe-1 @ 294K. Almost ultimate CMR performance at room temperature has been achieved due to successive improvement of c-axisorientation of layers: full widths at half-maximum (FWHM) 0.65, 0.58, 0.65, 1.13 and 0.18 degrees in LSCMO/BTO/CeO2/YSZ/Si stack, respectively. Characterization of electrical noise in CMR film yields noise equivalent temperature difference (NETD) as low as 1.2 ‘mu;K/√Hz @ 30Hz and 294K.
Preparations and Evaluations of Magnetoelectric Thin Films for Josephson Field Effect Transistor
Authors: Iwata Nobuyuki , Matsuo Koji , Ootsuka Noriaki , Yamamoto Hiroshi
Published: April 2011

We proposed the magnetoelectric (ME) effect as a new function of oxides electronic devices. The ME effect is characterized by the appearance of an induced magnetization with electric field applied and also is true in the opposite way. As one of the oxides devices we proposed a new type of Josephson field effect transistor (JFET) as adopting the ME materials to a gate insulator. In such the device, considering the Fraunhofer pattern, large IC modulation was expected by the induced magnetic field. Representative ME material, Cr2O3 films were deposited on Josephson junctions which were formed bygrain boundaries in YBa2Cu3OX (YBCO) films grown on MgO substrates. The multilayered films, Cr2O3 /YBCO and Cr2O3 / Y2O3 / YBCO were studied as the model of JFET.
Two-Dimensional Electronic Structures in Layered Oxychalcogenide Semiconductors, LaCuOCh (Ch=S, Se, Te) and La2CdO2Se2
Authors: Kamiya Toshio , Ueda Kazushige , Hiramatsu Hidenori , Ohta Hiromichi , Hirano Masahiro , Hosono Hideo
Published: April 2011

Electronic structures of layered oxychalcogenides, LaCuOCh (Ch=S, Se, Te) and La2CdO2Se2, were studied using ab-initio band calculations in relation to their optical and electronic properties. It was found that the dispersions of the top valence bands are much smaller in Γ-Z direction than in Γ-X direction, indicating that the electronic structure is highly two-dimensional, and that holes are confined in the CuCh or CdSe layers. The two-dimensional electronic structure is supported experimentally by staircase-like structure observed in optical absorption spectra at 10 K associated with two excitonic absorption peaks split by spin-orbit interaction of Ch ions. La2CdO2Se2has the largest bandgap due to the two-dimensional network structure of CdSe tetrahedra.
Nanoscale Etching of Metallic Perovskites Using STM
Authors: Dahl Ø. , Hallsteinsen S. , Grepstad J. K. , Borg A. , Tybell T.
Published: April 2011

In the present work we use a scanning tunneling microscope to modify the surface structure of epitaxial SrRuO3 thin films. Point and line etching experiments were carried out in ultra-highvacuum, using tungsten tips. The point etchings showed that pulses fired at small (< 4.5V) bias voltages did not bring about any physical modifications of the film surface, while voltages in excess of4.5 V led to etched holes accompanied by mounds. Moreover, well-defined line etching was achieved with atypical depth of approximately two unit cells and linewidths as small as 5 nm. The experiments demonstrate that a scanning tunneling microscope can be used for nanometer-scale patterning of SrRuO3 thin film surfaces.
Non-metastable recombination induced reactions involving hydrogen in SiC
Authors: Koshka Yaroslav , Krishnan Bharat , Mazzola Michael S.
Published: April 2011

A brief survey of some of the recent results of recombination-induced defect reactions involving hydrogen in 4H and 6H-SiC is given. A variety of outcomes of such reactions have been observed in hydrogenated 4H and 6H-SiC polytypes under optical excitation at reduced temperature. A few different non-metastable hydrogen-defect complexes can form, including hydrogen complexes with Al and B acceptors, hydrogen complex with Si vacancy, as well as some other non-identified complexes. Electrical measurements indicated strong recombination-induced passivation of the electrical activity of aluminum and boron acceptors in SiC. This passivation resulted in the reduction of the net free hole concentration and even inversion of the conductivity type. It is suggested that optical excitation causes a long-range migration of hydrogen followed by its capture in one or another kind of defect complexes. Further insight in the formation of specific complexes as a result of recombination-induced defect reactions is provided by thermal admittance spectroscopy. Energy gap levels in the regions that remained p-type after hydrogenation as well as in the regions where the conductivity was inverted by the recombination-induced passivation are investigated.
Infrared Spectroscopy of Hydrogen in ZnO
Authors: Mccluskey M.D. , Jokela S.J.
Published: April 2011

Zinc oxide (ZnO) has shown great promise as a wide band gap semiconductor with optical, electronic, and mechanical applications. Recent first-principles calculations and experimental studies have shown that hydrogen acts as a shallow donor in ZnO, in contrast to hydrogen's usual role as a passivating impurity. The structures of such hydrogen complexes, however, have not been determined. To address this question, we performed vibrational spectroscopy on bulk, single-crystal ZnO samples annealed in hydrogen (H2) or deuterium (D2) gas. Using infrared (IR) spectroscopy, we have observed O-H and O-D stretch modes at 3326.3 cm−1 and 2470.3 cm−1 respectively, at a sample temperature of 14 K. These frequencies are in good agreement with the theoretical predictions for hydrogen and deuterium in an antibonding configuration, although the bond-centered configuration cannot be ruled out. The IR-active hydrogen complexes are unstable, however, with a dissocation barrier on the order of 1 eV.
Hydrogen Bonding in ZnO
Authors: Nickel N. H. , Brendel K.
Published: April 2011

Hydrogen effusion measurements reveal that the total hydrogen concentration in ZnO ranges from 5.2×1016 cm−3 for single crystal ZnO to 3×1021 cm−3 for polycrystalline ZnO thin-fims. From the H effusion spectra the hydrogen chemical potential is determined as a function of the H concentration that can be related th the H density-of-states distribution. Single crystal ZnO exhibiting the lowest H concentration reveals six peaks in the H density-of-states located between 0.59 and 1.4 eV below the H transport site. With increasing H concentration the amount of H accommodated with binding energies larger than 1.0 eV increases significantly.
Anharmonicity in the Vibrational Modes Associated with H-H, N-H, O-H, and C-H bonds
Authors: Limpijumnong Sukit
Published: April 2011

The anharmonic contributions to the vibrational frequency of various H-H, N-H, O-H, and C-H bond configurations are investigated using first principles calculations. While harmonic approximation can be accurately used to calculate the local vibrational mode of most microscopic configurations, the configurations involving strong X-H bond are exceptions because of the exceptionally light mass of the H atom. We will explicitly present the magnitude of the anharmonic contributions to the total frequencies associated with X-H bonds in free molecules as well as in semiconductors defects.
Impact of Hydrogen Plasma Treatment on Gettering by He Implantation-Induced Cavities in Silicon
Authors: Alquier D. , Ntsoenzok E. , Liu C.L. , Vengurlekar A. , Ashok S.
Published: April 2011

The use of gettering techniques, with precise location of the gettering regions, has become crucial for device manufacturing. Helium-induced cavities have been shown to getter metallic impurities very effectively, but suffer from the drawback of requiring relatively high He doses. In this work, He-implanted Cz wafers of varying resistivity were subjected to hydrogen plasma hydrogenation prior to the cavity-formation anneal. We focus our studies on the cavity layer interactions with metal impurities. XTEM images reveal that hydrogenation increases the cavity radius. Our SIMS results show that the doping level has no influence on the metal gettering efficiency while the addition of plasma hydrogenation tends to decrease it. However, the efficiency can be controlled with the cavity radius which is interesting for future applications of the technique.
Hydrogen passivation of bulk defects and surface in silicon
Authors: Martinuzzi Santo , Palais Olivier
Published: April 2011

Monocrystalline and multicrystalline silicon wafers were investigated with boron doping levels in the range 1015 cm−3 to 1016 cm−3, respectively. Hydrogenation of the samples resulted from hydrogen-rich silicon nitride deposition by plasma enhanced chemical vapour deposition on the surface of the wafers. Passivation effects are observed after annealing and evaluated using minority carrier diffusion length (L) measurements, light beam induced current scan maps and lifetime (τ) measurements, by the contact-less phase shift technique. When applied at various excitation frequencies the phase shift technique leads evaluate the surface recombination velocity (S) and the actual bulk lifetime.

It was found, in multicrystalline silicon that isolated intragrain defects are well passivated while at grain boundaries and dislocation clusters deep levels are transformed into shallow levels. As a consequence L increases up to 80 % after firing the samples which the back surface was covered by a 2 μm thick aluminium layer. S decreases below 500 cm/s at the front surface covered by the hydrogen rich silicon nitride layer.
How much hydrogen and voids are energetically stable in silicon thin films?
Authors: Morral Anna Fontcuberta i , Vach Holger , Cabarrocas Pere Roca i
Published: April 2011

We have developed a model to account for the effects of hydrogen and voids on the structural stability of silicon thin films. The model is based on both experiments and theory. First, hydrogenated amorphous silicon films (a-Si:H) with various hydrogen contents were obtained by Plasma Enhanced Chemical Vapor Deposition. A linear correlation between hydrogen content and void fraction was observed. By tuning the deposition conditions, polymorphous silicon films with hydrogen contents up to 15%, very small void fractions (0.5%) and excellent electronic properties were also obtained. Density Functional Theory (DFT) calculations were performed to determine the formation energy for four types of silicon tetrahedra of the form Si-SinH4−n (n=1, 2, 3, 4). In our model, these tetrahedral units are considered as the building blocks of the silicon thin films. Considering a homogeneous distribution of hydrogen in the solid, the proportion of the different SiSinH4−n tetrahedra as a function of the hydrogen concentration was calculated. Then, the formation energy of hydrogenated amorphous silicon (a-Si:H) was calculated as a function of the hydrogen content and for various porosities. The model predicts that hydrogen incorporation does render the a-Si:H structure unstable for different hydrogen contents depending on the void fraction. Our results show that polymorphous silicon films with hydrogen concentrations up to 15% can be as stable as standard amorphous silicon with 2% hydrogen content, provided that the presence of hydrogen is not associated with the incorporation of porosity in the film.
SiC Power Devices – An Overview
Authors: Agarwal Anant , Das Mrinal , Krishnaswami Sumithra , Palmour John , Richmond James , Ryu Sei-Hyung
Published: April 2011

An overview of SiC Power Devices is provided. Progress in 1200 V SiC Schottky diodes, 1200 V SiC BJTs, 10-20 kV SiC PiN diodes and 2 kV SiC Power MOSFETs will be described. SiC Schottky diodes have already been commercialized. The next step of inserting these diodes in Si IGBT modules is happening now. Emphasis is placed on the problems and issues at the SiC device/process interface which need to be urgently addressed such as the roughness created during the implant anneals, reliability of the gate oxide under positive and negative bias, low current gain of the BJTs, forward voltage instability in the pn junctions etc. Overcoming these issues in the near future will be critical to the successful commercialization of SiC devices.
Epitaxial Growth of 3C-SiC on T-shape columnar Si Substrates
Authors: Nishino S. , Shoji A. , Nishiguchi T. , Ohshima S.
Published: April 2011

Cubic silicon carbide (3C-SiC) is a suitable semiconductor material for high temperature, high power and high frequency electronic devices, because of its wide bandgap, high electron mobility and high saturated electron drift velocity. The usage of Si substrates has the advantage of large area substrates for the growth of 3C-SiC layers. However, large lattice mismatch between 3C-SiC and Si (>20%) has caused the generation of defects such as misfit dislocations, twins, stacking faults and threading dislocations at the SiC/Si interface. Lateral epitaxial overgrowth (ELOG) of 3C-SiC on Si substrates using SiO2 has been reported to reduce the defect density. In this report, epitaxial growth of 3C-SiC on T-shape patterned (100) Si substrates has been investigated to reduce interfacial defects.
Status of 4H-SiC Substrate and Epitaxial Materials for Commercial Power Applications
Authors: Powell A.R. , Sumakeris J.J. , Leonard R.T. , Brady M.F. , Müller St.G. , Tsvetkov V.F. , Hobgood H.McD , Burk A.A. , Paisley M.J. , Glass R.C. , Carter C.H.
Published: April 2011

The performance enhancements offered by the next generation of SiC high power devices offer potential for enormous growth in SiC power device markets in the next few years. For this growth to occur, it is imperative that substrate and epitaxial material quality increases to meet the needs of the targeted applications. We will discuss the status and requirements for SiC substrates and epitaxial material for power devices such as Schottky and PiN diodes. For the SiC Schottky device where current production is approaching 50 amp devices, there are several material aspects that are key. These include; wafer diameter (3-inch and 100-mm), micropipe density (<0.3 cm−2 for 3-inch substrates and 16 cm−2 for 100-mm substrates), epitaxial defect densities (total electrically active defects <1.5 cm−2), epitaxial doping and epitaxial thickness uniformity. For the PiN diodes the major challenge is the degradation of the Vf characteristics due to the introduction of stacking faults during the device operation. We have demonstrated that the stacking faults are often generated from basal plane dislocations in the active region of the device. Additionally we have demonstrated that by reducing the basal plane dislocation density, stable PiN diodes can be produced. At present typical basal plane dislocation densities in our epitaxial layers are 100 to 500 cm−2; however, we have achieved basal plane dislocation densities as low as 4 cm−2 in epitaxial layers grown on 8° off-axis 4H-SiC substrates.
The Effect of Doping Concentration and Conductivity Type on Preferential Etching of 4H-SiC by Molten KOH
Authors: Gao Ying , Zhang Zehong , Bondokov Robert , Soloviev Stanislav , Sudarshan Tangali
Published: April 2011

Molten KOH etchings were implemented to delineate structural defects in the n- and ptype 4H-SiC samples with different doping concentrations. It was observed that the etch preference is significantly influenced by both the doping concentrations and the conductivity types. The p-type Si-face 4H-SiC substrate has the most preferential etching property, while it is least for n+ samples. It has been clearly demonstrated that the molten KOH etching process involves both chemical and electrochemical processes, during which isotropic etching and preferential etching are competitive. The n+ 4H-SiC substrate was overcompensated via thermal diffusion of boron to p-type and followed by molten KOH etching. Three kinds of etch pits corresponding to threading screw, threading edge, and basal plane dislocations are distinguishably revealed. The same approach was also successfully employed in delineating structural defects in (0001) C-face SiC wafers.
Room-temperature Photoluminescence at 1540 nm from Amorphous Silicon Carbide Films Implanted with Erbium
Authors: Gallis Spyros , Efstathiadis Harry , Huang Mengbing , Kaloyeros Alain E. , Nyein Ei Ei , Hommerich Uwe
Published: April 2011

In the present work, strong room-temperature photoluminescence (PL) at 1540 nm is reported from erbium-implanted and post-annealed amorphous silicon carbide (a-SiC:Er) films. The stoichiometric SiC films were grown by thermal chemical vapor deposition (TCVD) at 800°C, and then implanted to Er fluence of 3×1015 ions/cm2 using 380 keV implantation energy. Post-implantation annealing was carried out at the temperature range of 550°C to 1350°C in argon (Ar) ambient. The resulting SiC films were characterized by Auger electron spectroscopy (AES), Rutherford backscattering (RBS), Fourier transform infrared spectroscopy (FTIR), nuclear reaction analysis (NRA), x-ray diffraction (XRD), and high-resolution transmission electron microscope (HRTEM). Clear PL behavior was seen from the annealed a-SiC:Er samples, even at room temperature, with PL intensity reaching a maximum for samples annealed at 900°C.

Additional studies of thermal quenching of Er luminescence from a-SiC:Er samples annealed at 900°C indicated that as the sample temperature increased from 14K to room temperature, the luminescence intensity at 1540 nm dropped by a factor of ∼ 3.6. Moreover, the PL spectra of the a-SiC:Er samples did not exhibit any defect-generated luminescence. It is suggested that the lower density of Si and C vacancies in the stoichiometric a-SiC:Er, as compared to its non-stoichiometric a-Si1-xCx counterpart, along with the incorporation of a higher Er dopant concentration, can effectively diminish defect-produced luminescence and lead to a significant improvement in PL performance.

These properties suggest that stoichiometric a-SiC:Er may be a good candidate for producing optoelectronic devices operating in the 1540 nm region.
Morphology-Controlled Synthesis of Nanostructured Silicon Carbide
Authors: Guo Xiang-Yun , Jin Guo-Qiang , Hao Ya-Juan
Published: April 2011

Phenolic resin and tetraethoxysilane were used to prepare a binary carbonaceous silicon xerogel, the precursor of silicon carbide (SiC). By employing different additives in the sol-gel process, a series of xerogel precursors with differently chemical composition were obtained. Heating these xerogels to 1250°C, nanostructured β-SiC with various morphologies including nanowires, nanofibers, nanoparticles and mesoporous SiC were produced via carbothermal reduction. The preparation method of the xerogels was presented and the influences of different additives on the sol-gel process and the SiC formation were discussed in this paper.
Fabrication and Initial Characterization of 600 V 4H-SiC RESURF-type JFETs
Authors: Hatsukawa Satoshi , Iiyama Michitomo , Fujikawa Kazuhiro , Ito Atsushi
Published: April 2011

A RESURF-type JFET is a suitable structure as a lateral switching device with a breakdown voltage of above 600 V for an inverter module which drives motors of an electric or hybrid automobile. In this study, 600 V RESURF-type JFETs were fabricated to investigate the operation and characteristics. The drift region between the drain and the source areas has a double RESURF structure to reduce the on-resistance. At first, small devices were fabricated. The width and length of the channel are 200 μm and 10 μm, respectively. The distance between the drain and the gate areas, which is the drift length, is 15 μm. The saturation current normally-off device is about 0.6 mA at a gate voltage of 3 V. The specific on-resistance is about 160mωcm2. The maximum breakdown voltage is 720 V. Next, large ones were fabricated. The width of the channel is 80 mm. The saturation current normally-on device is about 0.5 A at a gate voltage of 2 V. The specific on-resistance is about 200mωcm2. The maximum breakdown voltage is 250 V.