bluuebunny/crossref_metadata_2025 huggingface dataset:
Transparent p- and n-Type Conductive Oxides With Delafossite Structure
Authors: Yanagi Hiroshi , Ueda Kazushige , Ibuki Shuntaro , Hase Tomomi , Hosono Hideo , Kawazoe Hiroshi
Published: April 2011

Thin films of CuAlO2, CuGaO2 and AglnO2 with delafossite structure were prepared on sapphire substrates by pulsed laser deposition method. The resulting CuA102 thin films exhibited p-type conduction and the electrical conductivity at room temperature was 0.3 Scm−1. CuGaO2 thin films were grown epitaxially on μ-Al2O3 (001) surface and showed p-type conduction (conductivity at room temperature = 0.06 S cm−1). The optical band gap was estimated to be ∼3.5 eV for CuAlO2 or ∼3.6 eV for CuGaO2. On the other hand, the thin film of Sn doped AglnO2 exhibited n-type conduction. The optical band gap and electrical conductivity at room temperature were ∼4.1 eV and 70 S cm−1, respectively. The recent work demonstrates the validity of our chemical design concept for p- and n-type transparent conducting oxides, providing an opportunity for realization of transparent p-n junction using delafossite-type oxides.
Buried Oxide Channel Field Effect Transistor
Authors: Misewich J.A. , Schrott A.G.
Published: April 2011

A room temperature oxide channel field effect transistor with the channel on the surface was recently demonstrated at IBM which showed switching characteristics similar to conventional silicon FETs. In this paper we introduce a new architecture for the oxide channel transistor where the oxide channel material is buried below the gate oxide layer. This buried channel architecture has several significant advantages over the surface channel design in coupling capacitance, channel mobility, and channel stability. We will discuss the design and fabrication of the buried channel oxide FET and we will present results from these devices which demonstrate a higher transconductance.
Work Function Study for the Search of Efficient Target Materials for Use in Hyperthermal Surface Ionization Using a Scanning Kelvin Probe
Authors: Petermann U. , Baikie I.D. , Lägel B. , Dirscherl K.M.
Published: April 2011

In order to search for efficient target materials for use in Hyperthermal Surface lonisation (HSI), a new mass spectroscopy ionisation technique, we have performed a study of high and low work function (ø) surfaces as part of an ongoing project. HSI relies on high and low work function surfaces for the production of positive (pHSI) and negative (nHSI) ions, respectively.

Using a novel UHV Scanning Kelvin Probe we have followed the oxidation kinetics of polycrystalline Re at different temperatures and examined the effects of oxidation, flash annealing and sputter-anneal cleaning cycles via high resolution work function topographies. Our results indicate that oxidised Re is the best candidate for pHSI in terms of ionisation efficiency and ø change. The peak work function change of 2.05 eV occurred at 900 K to 950K.

For the nHSI materials Calcium exhibited the best performance with respect to the ionisation efficiency indicating a wf of 2.9 eV. We will present data in terms of mass fragmentation using an HSI-Time-of-Flight (TOF) system and time stability of the work function.
Volatile, Fluorine-Free β-Ketoiminate Precursors for MOCVD Growth of Lanthanide Oxide Thin Films
Authors: Edleman N.L. , Belot J.A. , Babcock J.R. , Metz A.W. , Metz M.V. , Stern C.L. , Marks T.J.
Published: April 2011

Lanthanide oxide thin films are of increasing scientific and technological interest to the materials science community. A new class of fluorine-free, volatile, low-melting lanthanide precursors for the metal-organic chemical vapor deposition (MOCVD) of these films has been developed. Initial results from a full synthetic study of these lanthanide-organic complexes are detailed.
Preparation and Characterization of Epitaxial Bi2WO6 Thin Films Prepared by a Sol-Gel Process
Authors: Nishio Keishi , Kudo Chikako , Nagahama Tsutomu , Manabe Takaaki , Yamaguchi Iwao , Watanabe Yuichi , Tsuchiya Toshio
Published: April 2011

We have succeeded in an epitaxial growth of bismuth tungstate (Bi2WO6, BWO) thin films, one of the bismuth layer-structure ferroelectrics (BLSF), on SrTiO3 (001) single crystal substrates by a spin coating process. BLSF are known to be one of the promising materials for ferroelectric random access memory (FeRAM) devices. A homogeneous coating solution was prepared with tungsten hexachloride and bismuth 2-ethylhexanoate as raw materials, and 2-(2-methoxyethoxy) ethanol and formamide as solvents. The as-coated thin films were sintered at temperatures from 500 to 800°C for lh in air. BWO crystallized at temperatures above 500°C. Any crystal phase was not observed in the thin films except for (001) phases of BWO in the XRD patterns. It was confirmed that the thin film was growing epitaxially by measurement of XRD pole figure. The crystallographic relationship of the film and substrate was BWO(001)//STO(001), BWO[110]//STO[100].
Effects of the Heat-Treatment Conditions on Microstructures of YbBa2Cu3O7-σ Superconducting Films Formed by the Dipping-Pyrolysis Process
Authors: Shibata J. , Yamagiwa K. , Hirabayashi I. , Hirayama T. , Ikuhara Y.
Published: April 2011

YbBa2Cu3O7-σ(Yb123) films were formed on SrTiO3(STO)(001) and LaAlO3(LAO)(001) substrates by the dipping-pyrolysis process. Using transmission electron microscopy, we investigated effects of the heat-treatment conditions in the processes of the dipping-pyrolysis method on microstructures of these films. As a result, we found that the high heating rates at the initial and final heat-treatments are necessary for achieving the epitaxial growth of the superconducting films.
Micro Pattern of TiO2 Thin Film Formation by Direct Synthesis From Aqueous Solution and Transcription of Resist Pattern
Authors: Yao Takeshi , Uchimoto Yoshiharu , Yabe Hiroki
Published: April 2011

Direct synthesis from aqueous solution (DSAS) is the method for synthesizing ceramic oxides in crystalline state directly from aqueous solution at ordinary temperature and ordinary pressure. DSAS is advantageous because of the applicability to making films with wide areas and/or complicated shapes with no requirement of vacuum or high temperature. Micro patterning of materials having high dielectric constant is important for manufacturing electronic devices such as dynamic random access memory, ferroelectric random access memory and so on. By using DSAS, TiO2 thin film was formed on the glass plate surface where micro pattern had been printed by commercial organic photoresist material. Then the resist material was dissolved off by acetone or ethanol with the TiO2 thin film just on. From SEM observation, it is indicated that micro pattern of TiO2 thin film transcribing the resist pattern with minimum line width of I νm was obtained. This method will be applicable to the construction of highly integrated dielectric devices.
New Structure Model for Lithium Nickel Batteries
Authors: Monge M.A. , Gutiérrez-Puebla E. , Rasines I. , Campa J.A.
Published: April 2011

After growing black colored single crystals of LixNi1−xO (x = 0.27) and solving its crystal structure, a model is proposed as an alternative to the structural type admitted for LixNi1−xO. The new rhombohedral cell consists of a cubic close packing of oxygens in which the alternation of two kind of mixed layers containing Li and Ni in different ratios can be detected along the c direction. This model implies a Li order incompatible with the alternation of Ni layers, one of them pure and the other containing some Li. The results of magnetization measurements look consistent with the new structural type, and reveal that LixNi1−xO behaves as mictomagnetic.
Materials Design for the Low-Resistivity in p-Type ZnO and Transparent Ferromagnet With Transition Metal Atom Doped ZnO: Prediction vs. Experiment
Authors: Sato K. , Katayama-Yoshida H. , Yamamoto T.
Published: April 2011

We propose a new valence control method of codoping with doping Ga (or In, Al) donor and N acceptor at the same time for the fabrication of a low-resistivity p-type ZnO based upon the ab initio calculation. We compare our predicted materials design to fabricate a low resistivity p-type ZnO with the recent successful codoping. Based upon the success in the valence control of ZnO, we propose a materials design to fabricate the ferromagnetic Mn-doped p-type ZnO upon codoping. It is shown that the anti-ferromagnetic state is more stable than the ferromagnetic ones due to the anti-ferromagnetic super-exchange interaction, if we have no mobile holes. Upon codoping with the mobile holes, it is shown that the ferromagnetic state becomes more stable than the anti-ferromagnetic ones due to the ferromagnetic double-exchange interaction. However, it is shown that the anti-ferromagnetic state is more stable upon electron doping due to the anti-ferromagnetic super-exchange interaction. We calculate the chemical trends of the magnetic state in V-, Cr-, Fe-, Co-, and Ni-doped (25 at%) in ZnO, and predict that all of these materials show the ferromagnetic ground states without electron and hole doping.
Laser Direct Write of Conducting and Insulating Tracks in Silicon Carbide
Authors: Sengupta D.K. , Quick N.R. , Kar A.
Published: April 2011

Conventional direct write processes are multi-step requiring at least one additional process to change conductive properties. A direct conversion technique that uses lasers to irradiate silicon carbide, providing tracks which are highly conductive has been demonstrated. It was found that laser irradiation of insulating silicon carbide films could cause a drop from 1011 to 10−4 ohm-cm in a 4-point resistance test. However, in the presence of pure oxygen, laser-irradiated silicon carbide conductor and semiconductor samples exhibit insulating characteristics. Pattern formation was achieved by a computer program controlled galvo-mirror. The pads, 0.4 cm × 0.7 cm were formed by beam rastering with an overlap of 30% of the 0.025 cm beam diameter. This computer assisted processing allows the design of patterns using conventional CAD/CAE technologies and smart material behavior via selective and controlled electrical property transitions by laser irradiation
Focused Electron Beam Induced Deposition of Gold and Rhodium
Authors: Hoffmann P. , Utke I. , Cicoira F. , Dwir B. , Leifer K. , Kapon E. , Doppelt P.
Published: April 2011

Electron beam induced deposition with two noble metal precursors (Rhodium and Gold) having the same halogeno and trifluorophosphine ligands is presented. The deposit geometry of lines and freestanding bridges is discussed with respect to electron energy, beam shape, and backscattered electron distribution. Electron beam heating effects are estimated to be negligible in our deposition conditions. Using PF3AuCl, lines of percolating gold grains were deposited with electrical resistivities as low as 22μωcm at room temperature (Au: 2.2μωcm). Auger electron analysis shows about 60at% Rh in deposits obtained with [RhCI(PF3)2]2, however the resistivity of 1ωcm is high compared to 4.5μωcm of pure Rh.
Computational Modeling of Direct Print Microlithography
Authors: Darhuber A. A. , Miller S. M. , Troian S. M. , Wagner S.
Published: April 2011

Using a combination of experiment and simulations, we have studied the equilibrium shapes of liquid microstructures on flat but chemically heterogeneous substrates. The surface patterns, which define regions of different surface energy, induce deformations of the liquid-solid contact line, which in turn can either promote or impede capillary break-up and bulge formation. We study numerically the influence of the adhesion energies on the hydrophilic and hydrophobic surface areas, the pattern geometry and the deposited fluid volume on the liquid surface profiles
Deposition of Ceramic Materials Using Powder and Precursor Vehicles Via Direct Write Processing
Authors: Rack P.D. , Fitz-Gerald J.M. , Geiculescu A.C. , Rack H.J. , Piqué A. , Auyeung R.C.Y. , Chrisey D.B.
Published: April 2011

Dry powder and sol gel ceramic films were deposited using a Matrix Assisted Pulsed Laser Evaporation Direct Write (MAPLE-DW) technique developed at NRL for optical and electrical device applications. The MAPLE-DW technique uses a high-energy focussed photon source in combination with a “ribbon” to fabricate materials onto a range of substrates at room temperature without material degradation. Two different classes of materials were processed in this research, (1) ceramic dry powder materials and (2) sot gel precursor materials. Cathodoluminescent measurements demonstrated that the efficiencies of the transferred phosphor materials were not degraded during the laser transfer process. Scanning electron microscopy and 3-D surface profilometry of the ribbon after the MAPLE-DW process revealed a 90–95% transfer efficiency for the dry powders. Scanning electron microscopy and energy dispersive spectroscopy revealed that the sol gel materials also transferred with an efficiency in the 90-95% range. Three distinct regions were identified on the so gel ribbon after the laser transfer process. The regions suggest that the matrix absorbing layer and the sol gel materials are completely removed for the areas irradiated by the laser pulse, and in a second so-called “heat affected region,” only the sol gel material is ejected from the ribbon.
Material Systems Used by Micro Dispensing and Ink Jetting Technologies
Authors: Zhang Jie , Shmagin Irina , Skinner James , Szczech John , Gamota Daniel
Published: April 2011

In today's electronic industry, manufacturers are continuously improving capital utilization, developing flexible manufacturing processes, reduce changeover time and improving yield and throughput. Interest in rapid prototyping and 3-D fabrication capabilities are rapidly increasing, and a number of candidate direct writing technologies are in development to meet these demands.

This work studies material systems used by data driven materials deposition (DDMD) technologies for potential low temperature reel-to-reel high volume manufacturing on low cost substrates. Characterization results of fabricated discrete and RF devices using commercially available micro dispensing and ink jet systems will be discussed. Material rheological properties, deposition process characterization, deposition repeatability, fabricated device reliability and electrical performance will be presented. The test vehicles contain resistors and capacitors, transmission lines, open and short series stub filters, and half-wavelength resonators. The material/substrate compatibility will be demonstrated through environmental conditioning of the test vehicles. In addition, a cost estimate for using micro dispensing technologies was conducted to compare current manufacturing technologies to DDMD.
Laser Direct-Write of Materials for Microelectronics Applications
Authors: Rahman K. M. A. , Wells D. N. , Duignan M. T.
Published: April 2011

We demonstrate a laser direct-write method, a maskless process that transfers material directly from a ribbon to a substrate. This process offers the promise of fabricating passive electronic micro-components at a high speed with high spatial resolution. We are developing a workstation implementing this direct-write method, which integrates deposition, direct laser sintering, and micromachining capability on a single machine. Using this workstation we have deposited micro-patterns of conducting lines and resistors on alumina and polyimide substrates under ambient conditions that exhibit good electrical properties and substrate adhesion. From preliminary studies of laser sintering it was found that a wide range of sintering conditions may be used to arrive at silver conducting lines (∼60 µm × 10 µm) on alumina substrate with resistivity in the range of 5 to 10 times the resistivity of bulk silver. Preliminary results also indicate direct laser sintering of cermet resistor material can yield reproducible resistance values.
Calculation of Hamaker Constants in Nonaqueous Fluid Media
Authors: Bell Nelson , Dimos Duane
Published: April 2011

Calculations of the Hamaker constants representing the van der Waals interactions between conductor, resistor and dielectric materials are performed using Lifshitz theory. The calculation of the parameters for the Ninham-Parsegian relationship for several non-aqueous liquids has been derived based on literature dielectric data. Discussion of the role of van der Waals forces in the dispersion of particles is given for understanding paste formulation. Experimental measurements of viscosity are presented to show the role of dispersant truncation of attractive van der Waals forces.
Modeling and Optimization of Novel Actuators Produced by Solid Freeform Fabrication
Authors: Cheeseman B.A. , Ruan X.P. , Safari A. , Danforth S.C. , Chou T.W.
Published: April 2011

The ability of Solid Freeform Fabrication (SFF) to produce complex piezoceramic architectures has enabled the development of novel designs for PZT actuators. Recently, it has been shown that through the intelligent application of actuator geometry, poling direction, piezoelectric material, and electric field direction, the force and displacement output of a piezoelectric actuator could be optimized. The current investigation examines several piezoceramic actuator geometries, including dome, spiral and a telescoping shaped actuators. Using finite element analysis (FEA), parametric studies are performed to identify some key issues in the optimization of actuator performance. Results of the dome study indicate that an actuator having a tangentially alternating poling direction and applied electric field exhibits a much larger displacement when compared to dome actuators having either a through-the-thickness or tangential poling direction. Analysis of spiral actuators indicates that the spiral geometry results in pronounced displacement amplification when compared to the displacement of an equivalent length piezoelectric strip. In summary, some remarks will be made on the optimal use of piezoelectric material properties and actuator geometry in actuator design.
Automated Fabrication of Ceramic Electronic Packages by Stereo-Photolithography
Authors: Zimbeck W.R. , Jang J. H. , Schulze W. , Rice R. W.
Published: April 2011

Significant cost and timesavings can be realized by applying automated freeform fabrication techniques to the fabrication of ceramic electronic packaging. The widely used thick film/screen printing approach for ceramic packaging involves multiple separate processing stations to build up a multilayer package with embedded electrical connectivity. The current process steps include tape casting, conductor pattern screen-printing, punching/filling of vias, dicing, alignment and lamination. The development of low and high temperature co-fire ceramic systems (LTCC and HTCC) has streamlined the firing process, but significant inefficiencies remain in constructing the green state package, such that prototyping of ceramic packages is often very expensive with substantial lead times. This paper describes an integrated approach that combines the automated three-dimensional capabilities of stereolithography of ceramics and metals with the high resolution and precision of advanced photolithography systems. The process utilizes photocureable resins filled with sinterable ceramic and metal particles, which are applied layer-by-layer and photopatterned to build up a multilayer package. Materials development has focused on a glass-ceramic dielectric, a silver conductor and a barium titanate dielectric. Resin rheology and photocuring characteristics, thermal processing and sintered properties of the materials are described. A breadboard processing system was constructed and the results of fabricating test circuits are presented.
Microstructural Study of Laser Formed Ti-6Al-4V
Authors: Kelly S.M. , Kampe S.L. , Crowe C.R.
Published: April 2011

A microstructural evaluation of as-deposited LasformedSM Ti-6Al-4V, a Laser Additive Manufacturing (LAM) process, is the subject of the current work. Distinct features of the macrostructure include: large columnar prior-β grains (the initial solid to form upon cooling from the melt) have grown through multiple deposited layers due to epitaxial growth from previously solidified layers; a well defined heat affected zone; the presence of “layer bands,” which are speculated to be a result of macrosegregation in the solidifying melt puddle and/or the complex thermal history that the part received as it was built, layer by layer. The microstructure of the layer band consists of larger colonies of acicular α outlined in transformed β, whereas the adjacent material consists of smaller colonies having the same type of structure.
Processing-Structure-Property Relations of Polymer-Polymer Composites Formed by Cryogenic Mechanical Alloying for Selective Laser Sintering Applications
Authors: Schultz J. P. , Martin J. P. , Kander R. G. , Suchicital C. T. A.
Published: April 2011

Cryogenic mechanical alloying (CMA) has been shown to be an effective means for producing composite powders for selective laser sintering (SLS). Unlike composite particles made by a coating process, both phases are continuous throughout the particles formed by CMA. Consolidation of these composite particles via SLS offers the possibility of forming parts with a co-continuous microstructure. In this research, the microstructure of mechanically alloyed polymer-polymer composites for use in the SLS process is investigated using transmission electron microscopy. By varying the charge ratio and milling time of the CMA process, the phase domain size of the resulting composite powder can be manipulated. This ongoing work explores the microstructural evolution as the composite powders are consolidated via SLS into macroscopic parts, as well as the relationships between microstructure and bulk properties.
Mechanical Spectroscopy of Nanocrystalline Metals
Authors: Bonetti E. , Pasquini L. , Savini L.
Published: April 2011

The mechanical behavior of nanocrystalline iron and nickel prepared by mechanical attrition and inert gas condensation was investigated using mechanical spectroscopy techniques in the quasi static-and low frequency dynamic stress-strain regimes. The measures were performed on samples previously stabilized by thermal annealing at low homologous temperatures. The results of elastic energy dissipation, creep, and creep recovery measurements performed in the low strain regime (ε = 10−5−10−3) allowed to trace a phenomenological picture of the anelastic and viscoplastic behavior of nanocrystalline Ni and Fe in the 300-450 K range with different grain sizes and interfaces disorder degree. Activation energies of the thermally activated anelastic and plastic mechanisms responsible for the mechanical behavior have been evaluated.
Dislocations in Submicron Grain Size and Nanocrystalline Copper
Authors: Ungár T. , Tichy G. , Sanders P. G. , Weertman J. R.
Published: April 2011

Using the dislocation model of strain anisotropy in X-ray diffraction peak profile analysis it is shown that in nanocrystalline copper produced by inert gas condensation dislocations are present, at least, down to average grain sizes of the order of 20 nm. Based on the analysis of the dislocation contrast factors it is suggested that with decreasing grain size the proportion of Lomer-Cottrell type dislocations increases.
Logarithmic Relaxation of Resistance in Time of Annealed and Plastically Deformed Au80Fe20
Authors: Allia P. , Baricco M. , Bosco E. , Coisson M. , Falletti D. , Selvaggini V. , Tiberto P. , Vinai F.
Published: April 2011

Rapidly solidified Au80Fe20 ribbons were prepared either by melt spinning or by solidstate quenching of a homogenised master alloy. The as-quenched sample displays a paramagnetic behavior indicating a perfect solid solution of Fe in the Au matrix. Subsequent anneals have been performed to induce the precipitation of Fe particles. X-ray diffraction technique have been exploited to determine the alloy microstructure. The structural stability have been studied by measuring electrical properties in isothermal and tempering condition. The variation of magnetisation and electrical resistance have been measured after submitting the samples to plastic deformation. A logarithmic relaxation of the electrical resistance is observed in all studied samples after deformation. Magnetic hysteresis loops have been measured in as-quenched and annealed samples at different temperatures. X-ray diffraction and magnetic measurements indicate that thermal treatments have been successful in inducing the precipitation of both bcc and fcc Fe clusters.
Monte Carlo Simulations of Grain Boundary Sliding and Migration: Effect of Temperature and Vacancy
Authors: Ballo P. , Kioussis N. , Lu Gang
Published: April 2011

We have carried out Monte Carlo (MC) simulations using the embedded atom potential to study the sliding and migration of the σ5 [001] (210) tilt grain boundary (GB) in aluminum and the effect of vacancies on the sliding properties. We find that the simulated annealing allows the system to gradually anneal to a global-minimum configuration, thus increasing the number of migrations and reducing the GB sliding energy barriers to about a factor of three compared to the corresponding “static” values. The distribution of atomic energies as a function of GB displacement, provide insight into which atoms are responsible for the GB migration. The vacancy formation energy is found to be lower when the vacancy is placed on the first layer to the boundary, in excellent agreement with ab initio electronic structure calculations. The sliding and migration properties depend very sensitively on the position of the vacancy in the GB core.
Coherency Strain and a New Yield Criterion
Authors: Jayaweera N.B. , Downes J.R. , Dunstan D.J. , Bushby A.J. , Kidd P. , Kelly A.
Published: April 2011

We have studied the onset of plasticity in coherently-strained semiconductor superlattices, using nano-indentation with spherical indenter tips to observe the full stress-strain curve. The yield pressure is reduced by as much as a factor of two by the presence of the coherency strain. By varying the thicknesses and strains of the superlattice layers, we provide a proof that yield commences over a finite volume. It is properties averaged or summed over this volume which determine the yield pressure. We show that the relevant yield criterion for our experimental data is the rate of change of elastic strain energy with plastic relaxation, integrated over a volume of the order of a micron across. This result is expected to be valid for other systems with highly inhomogenous strain fields, and hence to be applicable to modelling of point contact, and to the design and understanding of structural materials which have coherently-strained microstructure.
Correlations of Microstructure and TEM Observations of Plasticity in Metallic Nanolaminates
Authors: Kramer Donald E. , Foecke Tim
Published: April 2011

Nanolaminate materials exhibit increases in hardness and yield strength beyond those expected according to rule of mixtures calculations. Several models have been proposed to explain this enhancement of strength, but conclusive experimental verification is hindered by the complex interaction between ingrown defects, in-plane microstructure and compositional modulation. In this study, mechanisms of plastic deformation in nanolaminates are investigated by in situ TEM straining of epitaxial Cu/Ni nanolaminates grown on Cu (001) single crystal substrates. Two distinct types of deformation are observed. Initial plastic deformation is accommodated by motion of “Orowan” and threading dislocations in a uniform and random fashion. As the stress levels increase, fracture occurs creating a mixed mode crack. Subsequent observations suggest that intense plastic deformation occurs over many bilayers in the direction of crack growth, but is contained to within one or two bilayers in a direction normal to the crack faces.
Interaction Between Dislocations and Misfit Interface
Authors: Kuronen A. , Kaski K. , Perondi L. F. , Rintala J.
Published: April 2011

Mechanisms responsible for the formation of a misfit dislocation in a lattice-mismatched system have been studied using Molecular Dynamics simulations of a two-dimensional Lennard-Jones system. Results show clearly how the strain due to the lattice-mismatched interface acts as a driving force for migration of dislocations in the substrate and the overlayer and nucleation of dislocations in the overlayer edges. Moreover, we observe dislocation reactions in which the gliding planes of dislocations change such that they can migrate to the interface.
New Ceramic Composite from a Multioxide Eutectic Melt
Authors: Calderon-Moreno Jose M. , Yoshimura Masahiro
Published: April 2011

New high temperature ceramic eutectic composites have been obtained. The composite is self-assembled in one quick step by rapid supercooling of the multioxide alumina-YAG-zirconia eutectic in an arc-image lamp furnace. The new material will find applications as in-situ coating and component for use at ultra-high temperature. Periodic self-assembled layered structures kinetically forced to solidify with interspacing in the submicron range will result in very interesting properties and applications for high temperature multioxide oxide eutectic composites, offering the challenge of design of layered nanostructures tailored to specific applications by kinetic control during solidification.
Structural and Optical Properties of Gold In MgO: Effects of Shape And The Interface
Authors: Bryant Elana M. , Ueda Akira , Mu Richard R. , Wu Marvin H. , Meldrum Alkiviathes , Henderson Don O.
Published: April 2011

The fundamental studies of metallic nanoparticles embedded in various host materials have been made. The host-guest interaction causes the shapes of embedded nanoparticles, and the surface plasmon resonances of the metallic nanoparticles are affected by the host materials. The control of the surface plasmon resonance condition is a challenging question. We will discuss the interface effect of the systems where gold nanoparticles were fabricated between materials of MgO and SiO2.
Matrix-Assisted Synthesis of Palladium Nanocage and Nanowires
Authors: Cheon Jinwoo , Lee Kyung-Bok , Kang Hongkyu , Oh S. J. , Ri H.-C.
Published: April 2011

Our study describes the synthesis of novel nanoscale Pd cage and wires whose sizes and shapes are templated by mesoporous matrices. The templates used are cubic phase MCM-48 and hexagonal phase CnMCM-41 (n = 16, and 22), SBA-15, which have pore diameters of ∼3, ∼3.8, ∼4.7, and ∼9 nm, respectively. For Pd@MCM-48, the Pd metal forms spherical domains (∼38 nm) consisting of three dimensionally interconnected into Pd arrays; for Pd@SBA-15 and Pd@MCM-41, the Pd metal forms of one-dimensional wires. Etching out the matrix produces porous Pd cages (pore sizes of ∼1.5 - 2.0 nm) with retaining original domain sizes of ∼38 nm; similarly Pd@SBA-15 and Pd@MCM-41 afford freestanding Pd nanowires. All the materials are examined by TEM, XRD, BET, and EDAX analysis. Furthermore, the thermal behavior of Pd nanowire is briefly described.
Nanosphere Lithography: Synthesis and Application of Nanoparticles with Inherently Anisotropic Structures and Surface Chemistry
Authors: Haynes Christy L. , Haes Amanda J. , Duyne Richard P. Van
Published: April 2011

Early work with size-tunable periodic particle arrays (PPAs) fabricated by nanospherelithography (NSL) demonstrated that the localized surface plasmon resonance (LSPR) could be tuned throughout the visible region of the spectrum. The LSPR is sensitive to changes in nanoparticle aspect ratio and local dielectric environment. This property has recently been exploited to develop a novel method of measuring surface-enhanced Raman scattering (SERS) excitation profiles. Single layer PPAs consist of size-tunable anisotropic nanoparticles that can be modified to exhibit anisotropic surface chemistry. This work demonstrates multiple schemes for PPA modification using self-assembled monolayers and colloid decoration. Nanoparticle anisotropy can be further exploited with the recent combination of NSL and reactive ion etching (RIE); this extends the two-dimensional PPA structure into the third dimension.
Microstructural and Magnetic Properties of Core-Shell Ni-Ce Nanocomposite Particles Assemblies
Authors: Sun Xiang-Cheng , Toledo J. A. , Yacaman M. Jose
Published: April 2011

Novel magnetic core-shell Ni-Ce nanocomposite particles (15-50 nm) are presented. SEM observation indicates a strongly ferromagnetic interacting order with chain-like features among Ni-Ce nanocomposite particle assemblies. Typical HREM image demonstrates that many planar defects (i. e. stacking faults) exist in large Ni core zone (10-45 nm ); the innermost NiCe alloy and outermost NiO oxide exist in the thin shell layers ( 3-5 nm ). Nano-diffraction patterns show an indication of well-defined spots characteristic and confirm the nature of this core-shell nanocomposite particles. Superparamagnetic relaxation behavior above average blocking temperature (TB =170K) for Ni-Ce nanocomposite particles assemblies have been exhibited, this superparamagnetic behavior is found to be modified by interparticle interactions, which depending on the applied field; size distribution and coupling with the strong interparticle interaction. In addition, an antiferromagnetic order occurs with a Neél temperature TN of about 11K due to Ce ion magnetic order fuction. A spin-flop transition is also observed below TN at a certain applied field and low temperature.
Nonlinear Optical Responses of Spin-Coated Vanadium Oxide Films
Authors: Ando Masanori , Kadono Kohei , Kamada Kenji , Ohta Koji , Delouis Jean-François , Nakatani Keitaro , Delaire Jacques
Published: April 2011

We report on the third-order nonlinear optical responses of V2O5 films prepared by pyrolysis of spin-coated films of vanadium 2-ethylhexanoate. Temporal behavior of third-order optical nonlinearity of the spin-coated V2O5 films was examined at a wavelength of 532 nm by the degenerate four-wave mixing (DFWM) technique using a mode locked Nd/YAG laser (35 ps fwhm). Fast relaxation with a lifetime of 25 ps and slow relaxation with a lifetime of 150 ps were observed. The nonlinear transmission experiment on the spin-coated V2O5 films using the same laser source showed that the transmittance decreased with increasing intensity of the incident light. The intensity-dependent absorption coefficients (β) were roughly estimated to be 3.5×10−5 cm/W. Transient absorption properties of the V2O5 film were measured by use of the second and third harmonics of a Q switched Nd/YAG laser (10 ns fwhm). The results observed for the nonlinear transmission and the transient absorption suggest that induced absorption would contribute to the third-order optical nonlinearity of the V2O5 films with fast response times, and also suggest that the V2O5 films have potentiality for use as optical power limiting materials.
SiC Crystal Growth from the Vapor and Liquid Phase
Authors: Hofmann Dieter , Bickermann Matthias , Ebling Dirk , Epelbaum Boris , Kadinski Lev , Selder Markus , Straubinger Thomas , Weingaertner Roland , Wellmann Peter , Winnacker Albrecht
Published: April 2011

The status of SiC vapor growth technique (PVT) is reviewed and related innovative aspects are introduced. Problems of the preparation of SiC crystals with uniform electronic properties are addressed, especially the growth of semiinsulating SiC. An overview about the performance of numerical modeling is given as tool for the optimization of the PVT process. Development activities in the field of liquid phase processing for the preparation of SiC bulk crystals and micropipe healing are presented. Finally recent results on the present understanding of filamentary void formation/elimination (micropipes, macrodefects) are summarized.
Heat and mass transfer simulation of SiC boule growth by sublimation
Authors: Pons Michel , Moulin Cecile , Dedulle Jean-Marc , Pisch Alexandre , Pelissier Bernard , Blanquet Elisabeth , Anikin Michail , Pernot Etienne , Madar Roland , Bernard Claude , Faure Christian , Billon Thierry , Feuillet Guy
Published: April 2011

An accurate modelling and simulation of the sublimation growth process needs a software taking into account a multitude of highly coupled phenomena: fluid mechanics, convective, conductive and radiative heat transfer, electromagnetic, multicomponent species transport, homogeneous and heterogeneous reactivity and finally thermal and transport databases. The objective of this paper is to combine modelling trends with experimental results to propose explanations and solutions to growth problems. Finally, a simple and generic mechanical approach will show the relations between the density of dislocations and the temperature field.
Challenges and State-of-the-Art of Oxides on SiC
Authors: Lipkin Lori , Das Mrinal , Palmour John
Published: April 2011

Single crystal SiC is a wide band-gap semiconductor with material characteristics that make it quite suitable for high voltage and high current applications. However, these devices are currently limited by their passivation. Significant improvements have been made with oxides on SiC. The most notable oxide processes are the re-oxidation anneal, a stacked ONO dielectric, and nitridation using an NO or N2O anneal. Additional improvements in lateral MOSFET mobility have been achieved using a surface channel implant, and lower temperature implant activation anneals. However, the passivation remains a significant limitation for SiC power devices.
Nitrogen Passivation of the Interface States Near the Conduction Band Edge in 4H-Silicon Carbide
Authors: Williams J. R. , Chung G. Y. , Tin C. C. , McDonald K. , Farmer D. , Chanana R. K. , Weller R. A. , Pantelides S. T. , Holland O. W. , Das M. K. , Lipkin L. A. , Feldman L. C.
Published: April 2011

This paper describes the development of a nitrogen-based passivation technique for interface states near the conduction band edge [Dit(Ec)] in 4H-SiC/SiO2. These states have been observed and characterized in several laboratories for n- and p-SiC since their existence was first proposed by Schorner, et al. [1]. The origin of these states remains a point of discussion, but there is now general agreement that these states are largely responsible for the lower channel mobilities that are reported for n-channel, inversion mode 4H-SiC MOSFETs. Over the past year, much attention has been focused on finding methods by which these states can be passivated. The nitrogen passivation process that is described herein is based on post-oxidation, high temperature anneals in nitric oxide. An NO anneal at atmospheric pressure, 1175°C and 200–400sccm for 2hr reduces the interface state density at Ec-E ≅0.1eV in n-4H-SiC by more than one order of magnitude - from > 3×1013 to approximately 2×1012cm−2eV−1. Measurements for passivated MOSFETs yield effective channel mobilities of approximately 30–35cm2/V-s and low field mobilities of around 100cm2/V-s. These mobilities are the highest yet reported for MOSFETs fabricated with thermal oxides on standard 4H-SiC and represent a significant improvement compared to the single digit mobilities commonly reported for 4H inversion mode devices. The reduction in the interface state density is associated with the passivation of carbon cluster states that have energies near the conduction band edge. However, attempts to optimize the the passivation process for both dry and wet thermal oxides do not appear to reduce Dit(Ec) below about 2×1012cm−2eV−1 (compared to approximately 1010cm−2eV−1 for passivated Si/SiO2). This may be an indication that two types of interface states exist in the upper half of the SiC band gap – one type that is amenable to passivation by nitrogen and one that is not. Following NO passivation, the average breakdown field for dry oxides on p-4H-SiC is higher than the average field for wet oxides (7.6MV/cm compared to 7.1MV/cm at room temperature). However, both breakdown fields are lower than the average value of 8.2MV/cm measured for wet oxide layers that were not passivated. The lower breakdown fields can be attributed to donor-like states that appear near the valence band edge during passivation.
Profiling of the SiO2 - SiC Interface Using X-ray Photoelectron Spectroscopy
Authors: Ghosh R. N. , Ezhilvalavan S. , Golding B. , Mukhopadhyay S. M. , Mahadev N. , Joshi P. , Das M. K. , Jr J. A. Cooper
Published: April 2011

The implementation of SiC based sensors and electronics for operation in chemically harsh, high temperature environments depends on understanding the SiO2/SiC interface in field effect devices. We have developed a technique to fabricate wedge polished samples (angle ∼ 1×10−4 rad) that provides access to the SiO2/SiC interface via a surface sensitive probe such as xray photoelectron spectroscopy (XPS). Lateral scanning along the wedge is equivalent to depth profiling. Spatially resolved XPS images of the O 1s and Si 2p core levels were obtained of the interfacial region. Samples consist of device-quality thermally grown oxides on 4H-SiC single crystal substrates. The C 1s spectrum suggests the presence of a graphitic layer on the nominally bare SiC surface following thermal oxidation.
Influence of Interface States on Output Characteristics of 4H-SiC MESFETs on Semi–Insulating Substrates
Authors: Sghaier Nabil , Souifi Abdel K. , Bluet Jean-Marie , Berenguer Manuel , Guillot Gérard , Noblanc Olivier , Brylinski Christian
Published: April 2011

The aim of this work is to study the origin of parasitic phenomena in the output characteristics of 4H-SiC MESFETs on semi-insulating (SI) substrates with various buffer layers. Ids-Vds measurements as a function of temperature have first been performed. Different parasitic effects such as kink effect, hysteresis effect when the gate voltage is successively increased or decreased, or changes in the output characteristics after a high drain polarization are presented. Random Telegraph Signal (RTS) measurements and frequency dispersion of the output conductance have next been realized. From the obtained results, we propose that the parasitic effect on the output characteristics are correlated with the presence of deep levels located near the semi -insulating substrate interface. The main observed trap is tentatively attributed to the presence of Vanadium in the SI substrate.
Short-Channel Effect Suppression In Silicon Carbide Power Mesfets
Authors: Konstantinov A. , Saroukhan A-M. , Karlsson S. , Harris C. , Litwin A.
Published: April 2011

We demonstrate that the performance of silicon carbide MESFETs is largely determined by short-channel effects. Parasitic bipolar transistor turn-on limits the operation voltage to a small fraction of the theoretically expected value for an ideal device. Tradeoffs are shown to exist between optimum gate length and on-state current on one hand, and the maximum blocking voltage on the other hand. Composite p-buffers with an elevated doping in the vicinity of the active layer considerably increase the operation voltage. Silicon carbide MESFETs utilizing composite buffers are reported.
Quality of Thermally Grown Oxides in 4H-SiC over Nitrogen or Phosphorus Implanted Regions
Authors: Khan I. A. , Um B. , Matin M. , Capano M. A. , Cooper J. A.
Published: April 2011

Current SiC metal-oxide-semiconductor-field-effect-transistors (MOSFETs) have regions of the gate electrode that overlaps the source/drain contact implant. The source/drain region is electrically isolated from this gate electrode extension by the gate insulator. Typically, the gate insulator is established through a controlled thermal oxidation step. The performance of the electrical isolation between the gate electrode and the source/drain implant region is studied using MOS systems for the nitrogen and phosphorus implant species. The dielectric strength of thermal oxide grown over a phosphorus implanted region is about four times lower than a non-implanted region and about two times lower than the nitrogen implanted region for the same implant and anneal conditions.
Al/Ni And Al/Ti Ohmic Contact To P-type SiC Diffused Layer
Authors: Wang Xaiobin , Soloviev Stanislav , Gao Ying , Straty G. , Sudarshan Tangali , Williams John R. , Crofton John
Published: April 2011

Ohmic contacts to p-type SiC were fabricated by depositing Al/Ni and Al/Ti followed by high temperature annealing. A p-type layer was fabricated by Al or B diffusion from vapor phase into both p-type and n-type substrates. The thickness of the diffused layer was about 0.1–0.2 μm with surface carrier concentration of about 1.0×1019cm−3. Metal contacts to a p-type substrate with a background doping concentration of 1.2×1018cm−3, without a diffusion layer, were also formed. The values of specific contact resistance obtained by Circular Transmission Line Method (CTLM) and Transfer Length Method (TLM) for the n-type substrate, and by Cox & Strack method for p-type substrate, respectively, varied from 1.3×10−4Ωcm2 to 8.8×10−3 Ωcm2. The results indicate that the specific contact resistance could be significantly reduced by creating a highly doped diffused surface layer.
Optical Absorption of Doped and Undoped Bulk SiC
Authors: Miller K. , Zhou Q. , Chen J. , Manasreh M. O. , Feng Z. C. , Ferguson I.
Published: April 2011

Optical absorption spectra of undoped, n-type, and semi-insulating 6H and 4H bulk silicon carbide (SiC) were obtained in the spectral region of 200 – 3200 nm (6.20 – 0.3875 eV). Several features were observed in the absorption spectra collected for various samples. A sharp peak below the band gap was observed in 4H SiC. The intensity of this peak was observed to increase in samples that exhibit larger absorption due to free carriers, which leads us to conclude that the defect responsible for this peak is also the source of the free carriers in the materials. Additionally, a series of optical absorption peaks separated by approximately 21 meV were observed around 0.9185 eV (1350 nm). These peaks are zero phonon lines of intraband transitions in the VSi 3d shell. The optical absorption near the band edge was observed to be sample dependent. The variation of the band gap as a function of temperature is also observed to be sample dependent.
Annealing Study of Ga Implanted p-Type 6H-SiC for Ohmic Contact Metallizations
Authors: Prenatt M. , Iliadis A. A. , Vispute R. D. , Wood M. C. , Derenge M. , Geil B. , Jones K. A.
Published: April 2011

Shallow implantations of Ga ions were performed on p-type 6H-SiC by conventional broad area implantation, and the physical and electrical properties of the Ga-SiC system upon high temperature annealing were examined, in order to understand the role of Ga in ohmic contact formation. The shallow implantation depth (30 nm) and high Ga doses ranging between 1×1015 and 1×1016 cm−2, resulted in heavy surface damage as observed by atomic force microscopy surveys. Samples annealed using a sacrificial SiC wafer as a capping layer, showed no improvement in surface roughness for annealing up to 1300 °C, while at 1500 °C, surface roughness was markedly changed. At 1600 °C the surface re-crystallized back to the stepped terraced morphology of the un-implanted surface but with significantly larger step and terrace size. At this annealing temperature, heavy Ga loss from the surface was observed. Samples annealed at 1500 °C using an AlN capping layer, showed significant outdiffusion of Si into the AlN layer, and redistribution of Ga within the SiC surface. The contact resistance of as-implanted and annealed samples using the sacrificial SiC wafer, were measured by the TLM method. Although contact resistance was found to decrease with increasing annealing temperature, sheet resistance increased, and contact resistance values were higher than expected, indicating that the heavy loss of Ga atoms contributed to the increased levels of contact resistance.