bluuebunny/crossref_metadata_2025_split huggingface dataset:
All-Printed Inorganic Logic Elements Fabricated by Liquid Embossing
Authors: Bulthaup Colin , Wilhelm Eric , Hubert Brian , Ridley Brent , Jacobson Joe 
Published: April 2011

AbstractThe liquid embossing process, devices made by this process, and their characteristics are presented. Structures fabricated and discussed here include: conductive lines with cross line resistance greater than 100 GΩ and resistivities 4 times that of the bulk material, multilayer structures with etched sacrificial materials, vias that conduct through an embossed insulating layer, photodetectors made with nanocrystal solutions of CdSe, and all printed inorganic field effect transistors.
Using Layered Manufacturing to Create Textured Microstructures in Si3N4 Ceramics
Authors: Rangarajan S. , Harper B. , McCuiston R. , Safari A. , Kalman Z. , Mayo W. , Danforth S. C. , Gasdaska C. 
Published: April 2011

AbstractIn recent years, seeding has been shown to be an effective method to create textured microstructures in Si 3N4, Al2O3 and PZT ceramics. The objective of this research is to create anisotropic and textured Si3N4 parts using the Fused Deposition of Ceramics (FDC) process. This technique is currently being developed to fabricate high performance structural Si 3N4 based components. In order to create the textured microstructures, rod-like β-Si3N4 seed particles are introduced into the FDC feedstock filaments. In this study, anisometric β-Si3N4 seeds were introduced into the starting α-Si3N4 powder (Honeywell's AS800 grade) at a 10 vol.% loading. The effects of the seeds (aspect ratio ∼4) on the viscosity and resultant microstructure were evaluated using capillary rheology, scanning electron microscopy, coefficient of thermal expansion (CTE) measurements, and x-ray diffraction. It is observed that the seeds do align during filament extrusion and a significant texture has been detected by x-ray diffraction and CTE measurements in FDC feedstock filaments and sintered FDC parts.
Investigation into Freeform Fabrication of Multi-Material Parts by 3D Welding and Milling Process
Authors: Song Yong-Ak , Park Sehyung 
Published: April 2011

AbstractSolid Freeform Fabrication (SFF) gives engineers a new freedom to build parts which have proved impossible to manufacture using conventional techniques. However, the surface finish nd accuracy of SFF parts are still lower than those of parts which have been machined in conventional operations. A process combination of additive and subtractive techniques is currently being developed in order to overcome this problem. The hybrid approach called “3D Welding and Milling” uses welding as an additive and conventional milling as a subtractive technique, thereby exploiting the advantages of both processes. In this paper, the attempt was made to build multi-material parts, especially molds, by using two different deposition strategies. The results show that it is a feasible approach to build multi-material metal parts directly.
Dimensionally Accurate Mold Inserts and Metal Components by Direct Metal Laser Sintering
Authors: Lind Jan-Erik , Kotila Juha , Syvänen Tatu , Nyrhilä Olli 
Published: April 2011

AbstractOne of the main deficiencies in today‘s rapid tooling techniques is the capability of producing only near net-shape parts. Direct Metal Laser Sintering (DMLS) is a technique that enables the fabrication of true net-shape parts in just a few hours with only minimum postprocessing. The DMLS is a laser-based rapid tooling process developed in Europe by Rapid Product Innovations (formerly Electrolux Rapid Development Finland) and EOS GmbH Germany. Rapid Product Innovations was also the first to implement this technology to functional prototyping by using two proprietary bronze-based powders and a new steel-based powder. The technique enables the fabrication of tailored microstructures from porous matrix to near full density. Thus, functionally gradient structures can be fabricated, i.e. material is sintered to full density only where it is needed. This paper describes the philosophy of fabricating true net-shape mold inserts and metal components, but also concentrates on how to maintain the dimensional accuracy even after the post-processing. The study shows that even +/− 0.05 mm accuracy can be obtained. The results of the study also illustrate the beneficial effects of reduced layer thickness and post-processing on the surface roughness and mechanical properties as well as the suitability of various conventional and non-conventional coatings. With reduced layer thickness, the step-shaped effect of the layers was no longer visible. The surface was even further improved by shot peening and coating. In addition, case studies from injection molding, pressure die-casting and direct metal component fabrication are presented.
Selective Laser Sintering of Zirconia
Authors: Harlan Nicole R. , Bourell David , Park Seok-Min , Beaman Joseph J. 
Published: April 2011

AbstractA combination of Selective Laser Sintering and colloidal infiltration has been used to create partially stabilized zirconia molds for titanium casting. The mold material system was chosen for its low reactivity with molten titanium and thermal shock resistance. The base material, stabilized zirconia mixed with a copolymer binder, was pre-processed before laser sintering into the desired green shape. The average density of the fired parts could be increased to twice that of the green density. Hole sizes as small as 180 m are possible in thin ceramic components.
Matrix Assisted Pulsed Laser Evaporation Direct Write (MAPLE DW): A New Method to Rapidly Prototype Active and Passive Electronic Circuit Elements
Authors: Fitz-Gerald J.M. , Chrisey D.B. , Piqu A. , Auyeung R.C.Y. , Mohdi R. , Young H.D. , Wu H.D. , Lakeou S. , Chung R. 
Published: April 2011

AbstractWe demonstrate a novel laser-based approach to perform rapid prototyping of active and passive circuit elements called MAPLE DW. This technique is similar in its implementation to laser induced forward transfer (LIFT), but different in terms of the fundamental transfer mechanism and materials used. In MAPLE DW, a focused pulsed laser beam interacts with a composite material on a laser transparent support transferring the composite material to the acceptor substrate. This process enables the formation of adherent and uniform coatings at room temperature and atmospheric pressure with minimal post-deposition modification required, i.e., ≤ 400°C thermal processing. The firing of the laser and the work piece (substrate) motion is computer automated and synchronized using software designs from an electromagnetic modeling program validating that this technique is fully CAD/CAM compatible. The final properties of the deposited materials depend on the deposition conditions and the materials used, but when optimized, the properties are competitive with other thick film techniques such as screenprinting. Specific electrical results for conductors are < 5X the resistivity of bulk Ag, for BaTiO3/TiO2 composite capacitors the k can be tuned between 4 and 100 and losses are < 1-4%, and for polymer thick film resistors the compositions cover 4 orders of magnitude in sheet resistivity. The surface profiles and fracture cross-section micrographs of the materials and devices deposited show that they are very uniform, densely packed and have minimum resolutions of ∼10 µm. A discussion of how these results were obtained, the materials used, and methods to improve them will be given.
The Inverse Hall-Petch Effect—Fact or Artifact?
Authors: Koch Carl C. , Narayan J. 
Published: April 2011

ABSTRACTThis paper critically reviews the data in the literature which gives softening—the inverse Hall-Petch effect—at the finest nanoscale grain sizes. The difficulties with obtaining artifactfree samples of nanocrystalline materials will be discussed along with the problems of measurement of the average grain size distribution. Computer simulations which predict the inverse Hall-Petch effect are also noted as well as the models which have been proposed for the effect. It is concluded that while only a few of the experiments which have reported the inverse Hall-Petch effect are free from obvious or possible artifacts, these few along with the predictions of computer simulations suggest it is real. However, it seems that it should only be observed for grain sizes less than about 10 nm.
Vibrational Properties of Silver Nanoparticles and Nanocrystalline Materials
Authors: Meyer Ralf 
Published: April 2011

ABSTRACTThe vibrational density of states of silver in the form of a free cluster, a single crystal and a nanocrystalline material has been calculated with the help of molecular-dynamics simulations. The model for the nanocrystalline material was derived by the simulation of pressureless sintering of nanometer sized silver particles. The results show a broadening of the vibrational density of states in the case of the cluster and the nanocrystalline material.
Optical Properties of Nanoparticle Pair Structures
Authors: Sandrock Marie L. , El-Kouedi Mahnaz , Gluodenis Maryann , Foss Colby A. 
Published: April 2011

AbstractThe synthesis of nanoparticle pair structures via porous host electrochemical template synthesis reviewed. Electrochemical template synthesis offers two advantages over solution methods, namely: 1) control over particle pair structure and orientation; and 2) control over geometry, size and composition of each member of the particle pair. These features of electrochemical template synthesis allow for straightforward comparison of experimental and theoretical spectra. Orientation control allows for the evaluation of second order nonlinear optical properties of centrosymmetric and non-centrosymmetric nanoparticle pair systems. The dependence of Second Harmonic Generation intensity on particle pair shape size and orientation is discussed. The synthesis and linear spectra of metal-semiconductor nanoparticle pair structures are also discussed, with emphasis on interparticle physical and electromagnetic interactions.
Strain Anisotropies in Core/Shell Magnetic Nanostructures
Authors: Papaefthymiou Georgia C. 
Published: April 2011

AbstractThe magnetic properties of nanosized iron-oxo molecular clusters have been investigated via Mössbauer spectroscopy and compared to those of silica coated iron-oxide nanoparticles. The clusters, prepared by controlled hydrolytic iron polymerization reactions, contain a ∼ 1.2 nm diameter magnetic core of spin-coupled iron ions surrounded by a shell of benzoate ligands. The nanoparticles, prepared via sol-gel synthesis, contain a ∼ 4.0 nm average diameter γ-Fe2O3 core coated by a shell of SiO2. Both systems exhibit magnetic bistability at low temperatures with estimated magnetic anisotropy constants of Keff = 0.63x105 J/m3 for the clusters and Keff = 0.55 ×105 J/m3 for the particles. The similar values of Keff indicate that these two systems experience similar degrees of strain at the core/shell interface. This is further supported by the values of the quadrupole splitting, ΔEQ=0.77 mm/s for the clusters and ΔEQ=0.75 mm/s for the particles, pointing to same degree of distortion from pure octahedral or tetrahedral symmetry at the iron coordination sites for either system. Implications of these observations for the surface atomic structure of γ-Fe2O3 nanoparticles are discussed.
Polymeric Surfactants Based on Oleic Acid— Lamellar Liquid Crystal Polymerization of Sodium Oleate/Water/Hexadecane/4-Allyl-1, 6-Heptadiene-4-ol System And Sodium Oleate/Water/Hexadecane/Pentaerythritol Triarylate System
Authors: Fu Qinghong 
Published: April 2011

AbstractThe lamellar liquid crystalline (LLC) regions of sodium oleate (NaOL)/ water/hexadecane/4-allyl-1,6-heptadiene-4-ol (AHD-ol) system and sodium oleate (NaOL) /water/hexadecane/pentaerythritol triacrylate (PETA) system were determined when the weight ratio of NaOL to hexadecane was kept at 90:10. Copolymerization was accomplished in the LLC phases of the above systems. AHD-ol and PETA acted as the cross-linking agents between the double bonds on NaOL backbones in their systems respectively. Interlayer spacing determinations showed that the cross-linking agents, AHD-ol and PETA, were solubilized in the middle of the NaOL hydrocarbon chains in each LLC system. As a result, the copolymerization reactions were confined within each monolayer of the amphiphilic bilayer. The systems after the copolymerization were a mixture of water and LLC phase for the former system and a mixture of LLC phase and solid particles for the latter one. The aqueous solutions of copolymers exhibited surface activity, but with both higher CMC and surface tension values than NaOL aqueous solutions.
Fabrication and Characterization of Chromium Oxide Nanoparticles/Thin Films
Authors: Zhong Zhenchen , Cheng Ruihua 
Published: April 2011

AbstractWell-dispersed nanoscale textured chromium oxide particles/thin films can be fabricated under certain conditions by laser-induced solution deposition (LISD) from organic solutions and by using selective organometallic chemical vapor deposition (OMCVD). The fabricated nanoparticles/thin films are characterized by scanning electron microscope (SEM), EDX, X-ray diffraction, and magnetic measurements. We have successfully demonstrated that the LISD and OMCVD are unique techniques for fabricating uniformly-distributed thin films but anistropic chromium oxide particles, which can be used in electro-magnetic devices. The magnetization measurements show that both types of chromium oxides are presented and that the Curie temperature Tc and the saturation magnetization field may be adjustable by controlling the stoichiometry.
Accurate Dry Etching with Fluorinated Gas for Two-dimensional Si Photonic Crystal
Authors: Takahashi Chiharu , Takahashi Jun-Ichi , Notomi Masaya , Yokohama Itaru 
Published: April 2011

AbstractAnisortopic Si dry etching is usually carried out with chlorinated gases for electronic devices such as Si-LSIs. We had another look at Si dry etching with fluorinated gases in order to obtain an ideal air hole for two-dimensional Si photonic crystal. We simulated vertical Si etching, and showed the possibility that single crystal Si can be etched vertically with high selectivity to the etching mask using fluorinated gases. We investigated ECR etching with an SF6-CF4 mixture, and vertical Si etching was achieved at room temperature. High Si/Ni selectivity above 100 was also obtained. Two-dimensional Si photonic crystal with a photonic band gap between 1.25 and 1.51 μm was produced using SF6-CF4 ECR plasma and a thin Ni mask.
Stress Effects in p-Type AlGaN/GaN Heterostructures
Authors: Sutandi Agustinus , Ruden P. Paul , Brennan Kevin F. 
Published: April 2011

AbstractThe physics of bulk wurtzite-structure III-nitride materials and of III-nitride heterostructures includes many phenomena that can be modulated by the application of stress. In particular, p-type material is expected to display a rich variety of piezo-resistive and piezo-optic effects that originate from the stress-induced modulation of lattice polarization charges, of valence band energies, and of bulk, surface, and interface defect states in the band gap. Here we focus on the expected effects of in-plane uniaxial on p-channel AlGaN/GaN heterostructures grown along the hexagonal axis on sapphire substrates. The valence band structure in the channel region is calculated self-consistently in the framework of a six-band Rashba-Sheka-Pikus (RSP) Hamiltonian. Stress-effects are included (in linear elastic theory) through deformation potentials and through the modulation of interfacial polarization charges associated with the piezoelectric nature of the constituent materials.
HTCVD growth of semi-insulating 4H-SiC crystals with low defect density
Authors: Ellison A. , Magnusson B. , Hemmingsson C. , Magnusson W. , Iakimov T. , Storasta L. , Henry A. , Henelius N. , Janzén E. 
Published: April 2011

ABSTRACTThe development of a novel SiC crystal growth technique, generically described as High Temperature Chemical Vapor Deposition (HTCVD) is reviewed. The structural, optical and electrical properties of 4H-SiC semi-insulating substrates are investigated with the aim of providing optimal microwave device performances. In particular, alternative compensation mechanisms to vanadium doping in S.I substrates are investigated to eliminate substrate induced trapping effects. Carried out at temperatures above 2100°C, the HTCVD technique uses, as in CVD, gas precursors (silane and a hydrocarbon) as source materials. The growth process can be described as “Gas Fed Sublimation” and proceeds by the gas phase nucleation of Six-Cy clusters, followed by their sublimation into active species that are condensed on a seed. Crystals with diameters up to 45 mm have been obtained with growth rates of 0.6 mm/h. The use of specific process steps, such as in-situ seed surface preparation and micropipe closing are presented and high resistivity wafers with micropipe densities down to 10 cm−2 are demonstrated. 4H-SiC substrates prepared from undoped crystals (with vanadium concentration lower than 5×1014 cm−3) exhibit semi-insulating behavior with a room temperature resistivity of the order of 1010Ω?cm. Infrared absorption measurements show that two types of semi-insulating crystals can be grown, with a spectrum either dominated by the Si-vacancy, or by a previously unreported defect labeled UD-1. These two types of semi-insulating wafers are also differentiated by the temperature dependence of their resistivity, with activation energies of 0.85 and 1.4±0.1 eV, respectively, and by the stability of their resistivity upon an annealing at 1600°C. Initial MESFET devices processed on HTCVD grown substrates show better DC characteristics than devices processed on vanadium doped substrates.
Growth and Characterisation of 4H-SiC MESFET structures grown by Hot-Wall CVD
Authors: Forsberg U. , Henry A. , Danielsson Ö. , Rorsman N. , Eriksson J. , Wahab Q. , Storasta L. , Linnarsson M. K. , Janzén E. 
Published: April 2011

ABSTRACTMetal semiconductor field effect transistor, MESFET, structures have been grown in a hot-wall CVD reactor. Using trimethylaluminium and nitrogen as dopant sources, p- and n-type epitaxial layers were grown on semi insulating substrates. A comprehensive characterization study of thickness and doping of these structures has been performed by using scanning electron microscopy, secondary ion mass spectrometry, capacitance-voltage measurements. Each technique is discussed concerning its advantage and disadvantage. Some transistor properties of MESFETs processed on the grown material are presented.
Optimization of the carbonized buffer layer for the growth of high quality single crystal SiC on Si
Authors: Cloitre T. , Moreaud N. , Vicente P. , Sadowski M. , Moret M. , Aulombard R. L. 
Published: April 2011

ABSTRACTCarbonized buffer layers were formed on Si (100) nominally oriented substrates with propane diluted in palladium purified hydrogen in a cold wall vertical reactor. Subsequent SiC layers were grown using silane and propane at atmospheric pressure. The growth temperature was ranging from 1150°C to 1350°C. The layers obtained were characterized by LT photoluminescence, IR reflectivity, X-ray diffraction, micro-Raman on cleaved edges, AFM imaging, and optical microscopy. Drastic influence on the layer surface morphology was evidenced depending on the transition step between the carbonization and the SiC epitaxial growth. As a result, we have developed a carbonization process leading to very high quality 3CSiC films grown at 1250°C.
Oxidation study of hydrogenated amorphous silicon carbide films
Authors: Choi W. K. , Lee L. P. , Leoy C. C. 
Published: April 2011

ABSTRACTWe present results of an oxidation study of a-Si1−xCx:H films prepared by the plasma enhanced chemical vapor deposition of silane and acetylene. The composition (i.e. x) of the samples was determined by the flow rates of silane and acetylene. Oxidation was carried out at 400 to 850°C in dry oxygen ambient. The infrared (IR) spectra of the as-prepared films showed the intensity of the Si-C peak decreases and the Si-CH3 peak increases as x increases. The Si-H peak shifts to higher frequency as x increases. Note that the incorporation of CH3 radicals in a-Si1−xCx:H films has shown to introduce voids and increased the porosity of the films. The IR spectra of the oxidized samples showed clear Si-O stretching and rocking/wagging modes for all films. We suggest that the growth of oxide on a-Si1−xCx:H is a result of voids that facilitate the diffusion of oxidants into the film. We shown that the activation energy, obtained from the linear rate region of the oxide growth, was far less than the dissociation energies of the Si-Si, Si-C and Si-H bonds. We suggest that this could be due to the amorphous nature of the samples that caused the various chemical bonds to be weaker during oxidation.
Impurity Activation in N+ Ion-Implanted 6H-SiC with Pulsed Laser Annealing Method
Authors: Eryu O. , Aoyama K. , Abe K. , Nakashima K. 
Published: April 2011

ABSTRACTWe have succeeded in pulsed laser annealing of N+ ion-implanted n-type 6H-SiC for increasing the carrier density near surface in order to decrease contact resistance, which induces little redistribution of implanted impurities after laser irradiation. By repeated laser irradiation at low energy density, the ion–implanted impurities were electrically activated without melting the surface region. SiC substrates with impurity concentration of 2×1018 /cm3 were implanted with 30 keV N+ ions with dose of 4.7×1013/cm2. After pulsed laser annealing, a contact resistance was measured to be 5.7×10−5 Ωcm2 using Al electrode on the N+ -implanted layer.
Fabrication of 3.4kV high voltage n-type 4H-SiC Schottky barrier diodes using thick epitaxial layers
Authors: Tsuji Takashi , Fujisawa Hiroyuki , Ogino Shinji , Tsuchida Hidekazu , Kamata Isaho , Jikimoto Tamotsu , Izumi Kunikazu 
Published: April 2011

ABSTRACTFabrication and evaluation of high voltage n-type 4H-SiC Schottky barrier diodes (SBDs) using 27μm thick epitaxial layers were presented. To achieve the ideal value of the breakdown voltage, various parameters of junction termination extension (JTE) were investigated. We concluded that the termination of triple rings with the concentrations of 6×1017, 3×1017, 1.5×1017cm−1 outwardly was best with the simulations. The SBDs with this termination showed the blocking voltage up to 3.4kV, which is almost the ideal value. We also investigated the distribution of leakage currents at -600V in SBDs with various diameters up to 4mm. High yield was obtained in the SBDs with the diameters below 2mm. The SBDs with high leakage currents showed the excess currents in the low forward voltage region and lots of bright spots could be observed by optical beam induced current analysis.