bluuebunny/crossref_metadata_2025_split huggingface dataset:
Observation of a Non-stoichiometric Layer at the Silicon Dioxide – Silicon Carbide Interface: Effect of Oxidation Temperature and Post-Oxidation Processing Conditions
Authors: Chang K. C. , Wahab Q. , Porter L. M. 
Published: April 2011

ABSTRACTThermal oxides were grown on n-type 6H-SiC(0001) at 1100 °C for 2 hrs in a wet oxygen ambient after the substrates were cleaned using the complete RCA cleaning process. Metal-oxide-semiconductor (MOS) diodes were then fabricated and subsequently cleaned under different annealing conditions, including re-oxidation-, NO-, and forming gas (10% H2 + 90% N2)-annealing at 950 °C for one hour. Measurements of the interface state densities (Dit) at room temperature showed that post oxidation annealing (POA) reduced the Dit values to a varying degree depending on the specific annealing condition. Annealing in NO and forming gas resulted in the largest reduction in Dit values.Oxides were grown at 950, 1100, and 1250 °C for varying amounts of time without receiving POA. A non-stoichiometric (SixC, x>1) transition layer adjacent to the SiO2/SiC interface has been observed by electron energy loss spectroscopy (EELS). The thickness of this layer was found to increase with oxidation temperature and was not observed at all for a thin oxide grown at 950 °C. The Dit values (close to the conduction band) for diodes with oxides grown at 950°C without POA were lower than the Dit values for the samples oxidized at 1100 °C with any of the POA treatments. While the thickness of the transition layer was found to be dependent on temperature, our results indicate that it is independent of oxide thickness. This transition layer may be associated with the high Dit values and low channel mobilities for SiC MOSFETs.
Structural Properties of 3C-SiC Layers Grown on Si Substrates by Electron Cyclotron Resonance CVD Technique
Authors: Giorgis F. , Chiodoni A. , Cicero G. , Ferrero S. , Mandracci P. , Pirri C. F. , Barucca G. , Calcagno L. , Foti G. , Musumeci P. , Reitano R. 
Published: April 2011

ABSTRACTIn this work we mainly report on the analyses of polycrystalline silicon carbide films grown by Electron Cyclotron Resonance Chemical Vapor Deposition (ECR-CVD) on Si (100) and Si (111) substrates. Structural properties of the films have been analyzed by X-ray diffractometry, transmission electron microscopy and micro-Raman spectroscopy. Samples deposited with optimized deposition conditions, show a polycrystalline columnar structure with lateral crystal dimensions ranging from 300 up to 1400 Å and an orientation close to that of the Si substrates.
Ion Implantation for Silicon Carbide Electronic Devices
Authors: Capano Michael A. 
Published: April 2011

ABSTRACTAs the demands on electronic systems intended for high temperature, high power or high frequency operation increase, silicon-based electronics are being pushed to its fundamental material limits. Consequently, continued improvement in system level performance for these applications requires new semiconductor materials. Silicon carbide (SiC) is a candidate material for the applications listed above, but considerable materials, processing, and device research are still needed before SiC devices are brought to market.This paper concentrates on ion implantation processing of SiC, and attempts to illustrate specific problems associated with ion implantation. Data from a series of experiments relevant to SiC MOSFETs are presented for this purpose. Ion implants into SiC are discussed first to show how a strategy for improving the acceptor activation ratio from less than 1% to nearly 100% is developed. The annealing temperatures (>1600°C) needed to attain high activation ratios lead to severely roughened surfaces. Results from experiments designed to preserve high-quality surfaces have been encouraging from a purely materials perspective. However, these solutions do not translate into improved transport characteristics for SiC MOSFETs. An investigation of inversion layer mobility in 4H-SiC MOSFETs is presented to illustrate this point.
Structural Defects in Ion Implanted 4H-SiC Epilayers
Authors: Persson P. O. Å. , Skorupa W. , Panknin D. , Kuznetsov A. , Hallén A. , Hultman L. 
Published: April 2011

ABSTRACTTransmission electron microscopy (TEM) was used to investigate Al, Ar, C and Si ionimplanted 4H-SiC epilayers. After the implantation the samples were thermally annealed for 30 minutes at 1700°C. During the annealing process dislocation loops are formed and the generation of such dislocation loops upon annealing, is investigated with respect to dopant electrical activation, peak ion concentration and calculated interstitial/vacancy concentrations. It is concluded that the dislocation loops are generated as the result of a combination of residual damage and excess interstitials generated in a “plus one” (+1) process.
Optical Properties of Aluminium and Nitrogen in Compensated 4H-SiC Epitaxial Layers
Authors: Syväjärvi Mikael , Yakimova Rositza , Kakanakova-Georgieva Anelia , Henry Anne , Janzén Erik , Linnarsson Margareta K. 
Published: April 2011

ABSTRACTCompensating impurities affect the device performance but still the fundamental knowledge of this effect in SiC is poor. We demonstrate that the optical properties are affected by compensation effects between the nitrogen donor and aluminium acceptor in 4HSiC epilayers. As demonstrated using low-temperature photoluminescence measurements, the interaction occurs between the impurity bound excitons caused by changes in the aluminium concentration while the nitrogen concentration is constant. The variation is observed over two orders of magnitude in the aluminium concentration. The interplay is also observed in cathodoluminescence measurements between the band edge luminescence and nitrogen-aluminium donor-acceptor pair emission. These observations may be possible to utilize for a non-destructive characterization of compensated epilayers.
Engineering the Al-Ti/p-SiC Ohmic Contact for Improved Performance
Authors: Lin J. Y. , Mohney S. E. , Smalley M. , Crofton J. , Williams J. R. , Isaacs-Smith T. 
Published: April 2011

ABSTRACTThe influence of composition on Al-Ti ohmic contacts to 4H p-SiC was studied. When NA was 7 x 1018 cm−3, contacts with 70 wt.% or more Al became ohmic when annealed at 1000°C for 2 min, whereas when there was 60 wt.% or less Al, the contacts did not become ohmic even when annealed under more severe conditions (longer times and/or higher temperatures). Spiking of the contact metallization always accompanied ohmic behavior and could be correlated with Al-Ti compositions that contain both an Al-rich liquid and solid TiAl3 at 1000°C prior to reaction with SiC or evaporative loss of Al. For the 70 wt.× contacts, a specific contact resistance of 1.5 × 10−4 Ω cm2 was measured along with spiking of the metallization into the SiC with a room-mean-square interfacial roughness of 150 Å and a maximum spiking depth of 1200 Å. Although still a concern, this spiking was less severe than observed for the 90 wt.× composition. A conductive CrB2 cap layer was next demonstrated to retard evaporation of Al during annealing of the Al-Ti contacts with 70 wt.× Al. The cap allowed use of thinner contact layers, reducing the depth of spiking and improving the surface morphology and edge definition of the ohmic contacts, with a one order of magnitude penalty in the specific contact resistance.
Reaction Kinetics of Thermally Stable Contact Metallization on 6H-SiC
Authors: Okojie Robert S. , Lukco Dorothy , Chen Yuan L. , Spry David , Salupo Carl 
Published: April 2011

ABSTRACTThe growth kinetics of thermally stable Ti(100nm)/TaSi2 (200nm)/Pt (300nm) metallization on 6H-SiC was studied after heat treatment in air up to 700°C. Scanning electron microscopy (SEM) of the contact surface morphology reveals a two-dimensional network of features that is attributed to non-uniform oxide growth associated with the multigrain structure of the platinum overlayer. Auger electron spectroscopy (AES) and high-resolution transmission electron microscopy (HRTEM) identified three important reaction zones after initial 30-minute anneal at 600°C in nitrogen. One is the formation of a platinum silicide overlayer resulting from TaSi2 decomposition. The second is titanium silicide formation adjacent to the decomposed TaSi2. The third is pseudo-epitaxial Ti5Si3 at the SiC interface. Specific contact resistance values ranging from 10−4–10−6 Ω-cm2, remained stable after 200 hours at 600°C in air. Activation energies of 1.03eV for platinum silicide oxidation and 1.96eV for Ti5Si3 are obtained from Arrhenius plots.
Comparison Of F2 Plasma Chemistries For Deep Etching Of SiC
Authors: Lee K. P. , Leerungnawarat P. , Pearton S. J. , Ren F. , Chu S. N. G. , Zetterling C.-M. 
Published: April 2011

ABSTRACTA number of F2-based plasma chemistries (NF3, SF6, PF5 and BF3) were investigated for high rate etching of SiC. The most advantageous of these is SF6, based on the high rate (0.6 μm · min−1) it achieves and its relatively low cost compared to NF3. The changes in electrical properties of the near-surface region are relatively minor when the incident ion energy is kept below approximately 75 eV. At a process pressure of 5 mTorr, the SiC etch rate falls-off by ∼15 % in 30 μm diameter via holes compared to larger diameter holes (> 60 μm diameter) or open areas on the mask.
Quantum-Confined Electron Transitions in CdSe Nanocrystals
Authors: Ginger D. S. , Dhoot A. S. , Finlayson C. E. , Greenham N. C. 
Published: April 2011

ABSTRACTWe present quasi-steady-state photoinduced absorption measurements on thin films of colloidal CdSe nanocrystals. We observe an intense, size-dependent absorption peaking in the mid-infrared when the samples are irradiated with visible light. The absorption is accompanied by a bleach in the visible near the position of the first excitonic absorption and persists with a lifetime of milliseconds at room temperature. We characterize the lifetime of the electron state and its cross-section. We attribute this feature to the 1S-1P transition of a delocalized electron. We report a bleaching of the first excitonic transition in electrically excited nanocrystal-based diode structures, and attribute it to charging of the 1S electron state.
Bioconjugates of Luminescent CdSe-ZnS Quantum Dots with Engineered Recombinant Proteins: Novel Self-Assembled Tools for Biosensing
Authors: Goldman Ellen R. , Mattoussi Hedi , Tran Phan T. , Anderson George P. , Mauro J. Matthew 
Published: April 2011

ABSTRACTColloidal semiconductor quantum dots (QDs) are luminescent nanoparticles with size- dependent emission spectra spanning a wide range of wavelengths in the visible and near IR. This property, as well as their higher resistance to photo-degradation compared to organic dye labels, makes QDs potentially suitable for certain biomolecule tagging and multiplexing applications. We describe an electrostatic self-assembly approach for conjugating highly luminescent colloidal CdSe-ZnS core-shell QDs with engineered two-domain recombinant proteins to form conjugates for sensing and imaging applications. The design, preparation, and characterization of high quantum yield IgG antibody-binding protein G bioconjugates using luminescence, electrophoretic gel shift, and affinity assays is reported.
InGaAs Quantum Dots Embedded in p-n Junction on GaAs(311)B Substrate
Authors: Akahane Kouichi , Song Haizhi , Okada Yoshitaka , Kawabe Mitsuo 
Published: April 2011

ABSTRACTWe have evaluated the photoluminescence (PL) properties of quantum dots (QDs) embedded in a p-n junction on GaAs(311)B and were compared with the identical structure grown on GaAs(001). The QDs on these two surfaces were fabricated with a similar size and density by optimizing the growth conditions. The PL emission from the QDs grown on GaAs(001) rapidly disappeared when the excitation power was decreased below 0.4W/cm2, while that from on GaAs(311)B was clearly observable even at a lower excitation power of 0.1W/cm2. From the measurements of PL intensity dependence on temperature and applied electric field, it was found that there are clear differences between the QDs grown on (001) and the QDs grown on (311)B in the recombination rates through non-radiative processes and/or the escape rates of carriers out of QDs to the GaAs host through a tunneling process.
Effects of Spacer Thickness on the Performance of InGaAs/GaAs Quantum Dot Lasers
Authors: Yeh Nien-Tze , Liu Wei-Shen , Chen Shu-Han , Chyi Jen-Inn 
Published: April 2011

ABSTRACTIt is found that the performance of self-assembled In0.5Ga0.5As/GaAs multi-stack quantum dot lasers is sensitive to the GaAs spacer thickness between the dots. Reducing the spacer thickness from 30 nm to 10 nm leads to narrow photoluminescence linewidth, low threshold current, high characteristic temperature and high internal quantum efficiency. This behavior is attributed to inhomogeneous broadening caused by dot size fluctuation related to spacer thickness.
Growth, Structure, Optical and Ultrasonic Investigations of Icosahedral Zn-Mg-Y Quasicrystals
Authors: Sterzel R. , Bruls G. , Kounis A. , Miehe G. , Saitoh K. , Fuess H. , Karpus V. , Babonas G.-J. , Reza L. , Assmus W. 
Published: April 2011

AbstractIt is shown how the history of the growth of an icosahedral Zn-Mg-Y single grain can be determined by measuring the yttrium distribution. The growth mechanism and the stabilization of the icosahedral Zn-Mg-Y, RE (RE = rare earth: Ho, Er, Dy, Gd, Tb) quasicrystals are discussed with respect to structural investigations on related crystalline phases. We also show results of optical and ultrasonic investigations on icosahedral Zn-Mg-Y single crystals. They fit well to the discussed growth and stabilization mechanism.
The Influence of Growth Rate on Porosity in Al-Pd-Mn Icosahedral Quasicrystals.
Authors: Ross Amy R. , Fisher Ian R. , Canfield Paul C. , Lograsso Thomas A. 
Published: April 2011

AbstractGrowth experiments have been carried out to characterize the occurrence and development of porosity in Bridgman and flux grown Al-Pd-Mn icosahedral quasicrystals. The porosity level has been observed to fluctuate between values of 0.0 and 3.75 percent along the length of Bridgman single crystals implying that the development of porosity is affected by the local growth conditions. Experiments were conducted to evaluate the influence of the rate of solidification on the occurrence of porosity. Alloys were solidified with different growth rates, 1mm/hr and >10 mm/hr, using the Bridgman configuration and at different cooling rates, ranging from 0.29°C/hr to 10°C/hr, using the flux growth method. Porosity levels were analyzed via optical image analysis. These experiments indicate that porosity percentages are greatly influenced by cooling rates and crystal size.
Low-Energy Ion Scattering Measurements from an Al-Pd-Mn Quasicrystal
Authors: Bastasz R. , Jenks C. J. , Lograsso T. A. , Ross A. R. , Thiel P. A. , Whaley J. A. 
Published: April 2011

AbstractEnergy-angle distributions of low-energy inert-gas ions scattered from surfaces provide information about surface composition and structure. We have measured energy spectra of He+ scattered from an Al71Pd20Mn9 quasicrystal, which was oriented perpendicular to the 5-fold axis, along various azimuthal directions. Strong scattering signals are seen from Al and Pd, but only a weak Mn signal is observed. From measurements made of He+ at an oblique angle of incidence scattered in the forward direction, we observe a 72° periodicity in the azimuthal dependence of the scattering signal intensity from Al surface atoms. The effect arises from shadowing effects involving neighboring surface atoms and provides direct evidence that Al surface atoms exist in a local environment with 5-fold symmetry. In addition, measuring the variation of the signal intensity with incidence angle provides information about neighboring atom distances, which compare favorably with a model of the quasicrystal surface derived from the bulk structure.
Development of Al-Cu-Fe Quasicrystal-Poly(p-phenylene sulfide) Composites
Authors: Bloom Paul D. , Baikerikar K.G. , Anderegg James W. , Sheares Valerie V. 
Published: April 2011

AbstractQuasicrystalline Al-Cu-Fe powders were used as a novel filler material in poly(p-phenylene sulfide) (PPS). These polymer/quasicrystal composites showed useful properties that may be beneficially exploited in applications such as dry bearings and composite gears. Al-Cu-Fe quasicrystalline filler significantly improved wear resistance to volume loss in polymer-based composites. In addition to improving the composite wear resistance, the Al-Cu-Fe filler showed low abrasion to the 52100 chrome steel counterface. Furthermore, mechanical testing results showed a two-fold increase in the storage modulus of the reinforced composites compared with the polymer samples. In addition, the Al-Cu-Fe filler was compared to its constituent metals, aluminum oxide, and silicon carbide in PPS. Chemical analysis of the wear interface by X-ray spectroscopy indicated the generation of a third body oxide layer during wear. The fabrication in addition to the thermal, mechanical, and wear properties of these unique materials is described.
Synthesis of Bulk Quasicrystals by Spark Plasma Sintering
Authors: Fleury E. , Lee J.H. , Kim S.H. , Song G.S. , Kim J.S. , Kim W.T. , Kim D.H. 
Published: April 2011

AbstractSpark plasma sintering method was applied to Al-Cu-Fe and Al-Si-Cu-Fe gas-atomized powders to prepare almost pore-free cylindrical specimens with icosahedral and 1/1 cubic approximant phases, respectively. This investigation has revealed that a high density could be obtained despite the short period and low temperature imposed during spark plasma sintering. In comparison to hot press technique, these conditions are favorable since they limit the formation of secondary phases and avoid exaggerated grain growth. The Vickers microhardness and fracture toughness of these two alloy systems were found to be larger than those obtained from cast and hot pressed samples, which could be attributed to a strong bonding between powder particles and the small-grained microstructure of the bulk SPS quasicrystalline specimens.
On the Corrosion Mechanisms of Al-Cu-Fe Quasicrystals
Authors: Rüdiger A. , Köster U. 
Published: April 2011

AbstractThe mechanisms of dissolution and passivation of bulk polycrystalline icosahedral Al63Cu25Fe12 during electrolytic corrosion in 0.1 N NaOH and 1 N H2SO4 were studied in detail. In 1 N H2SO4 selective dissolution of Al and Fe occurs at the open circuit potential, which leads to a porous layer of recrystallized fcc Cu; after anodic polarization dissolution of the alloy is followed by redeposition of Cu and formation of Cu2O. In 0.1 N NaOH selective dissolution of Al was observed and a nanocrystalline layer consisting of Cu2O and FeOOH forms at the open circuit potential as well as during anodic polarization up to -150 mVSHE. At higher potentials Cu-ions dissolve into the electrolyte, which allows building up an Al-hydroxide layer. Presumably due to the loss of Al during polarization phase transforma-tions of the quasicrystals (e.g. continuous transformation or precipitation) were observed by transmission electron microscopy.In order to clarify the influence of the quasicrystalline structure on the corrosion, open circuit potentials and current densities of the quasicrystalline and three ternary crystalline phases with different Al-content, but approximately constant ratio Cu:Fe of 2:1 were compared. Lower current densities, but a less noble open circuit potential for the quasicrystals than expected from the trend over the Al-content indicate a small influence of the quasicrystalline structure.
Phase Equilibria at Internal Interfaces of Icosahedral Al–Mn–Pd
Authors: Lück Reinhard , Gödecke Tilo , Beeli Conradin 
Published: April 2011

AbstractHighly faceted microholes (voids) in icosahedral Al-Mn-Pd quasicrystals form during annealing at temperatures between 750 and 830°C via classical Ostwald ripening. The specimens were single-phase icosahedral with a composition of Al71Mn9Pd20. If such a specimen containing voids is cooled to room temperature with a constant cooling rate of typically 0.6 to 5 K/min, the facets of the voids are frequently found to be decorated by a different material. The decorations have typically a morphology similar to fractals. Specimens rapidly quenched after isothermal heat treatments around 830°C never showed similar decorations. By X-ray microanalysis in a scanning electron microscope it has been found that this decoration material is considerably poorer in Al-content that the icosahedral phase, namely: Al60Mn10Pd30. Accordingly, these decorations are precipitations at the surfaces of voids inside a single-phase icosahedral matrix. This implies that these decorations are formed at the void surfaces bya diffusion induced local equilibrium. The local equilibrium can be understood on the basis of the equilbrium results in a single icosahedral phase.
Solidification and Microstructure Control of Mg-rich Alloys in the Mg-Zn-Y Ternary Systemya
Authors: Park E.S. , Yi S. , Ok J.B. , Bae D.H. , Kim W.T. , Kim D.H. 
Published: April 2011

AbstractSolidification microstructures of Mg rich Mg-Zn-Y alloys were studied by using optical microscopy, scanning electron microscopy and transmission electron microscopy. Pseudo eutectic reaction (Liquid→α-Mg + icosahedral phase) takes place during solidification. Alloys containing high Mg content solidifies by primary crystallization ofα-Mg followed by the eutectic reaction at interdendritic region. Mg68Zn28Y4 alloy solidifies by primary crystallization of I-phase followed by theeutectic reaction into a mixture of α-Mg and I-phase. Occasionally D-phase and Mg4Zn7 phases were observed to form with orientation relationships with previously formed I-phase and D-phase, respectively. Thestrength of the alloys increased with increasing the volume fraction of I-phase.
Approximants — the Key to the Structure of Quasicrystals
Authors: Steurer Walter 
Published: April 2011

AbstractThe relationship between approximant structures and quasicrystals is discussed on the example of quantitatively known decagonal quasicrystal and approximant structures in the thoroughly studied system Al-Co-Ni. The binary Al-Co as well as the ternary Al-Co-Ni approximants consist of the same basic pentagonal bipyramidal structure elements as the decagonal phase. The binary Al-Ni approximants, on the other hand, are vacancy ordered superstructures of the AlNi §-phase, which itself is related to the periodic average structure of decagonal Al-Co-Ni. Thus, the decagonal phase may be considered as a compromise between the competing driving forces to form pentagonal structural units on the one side and vacancy ordered superstructures of the AlNi §-phase on the other side. The broad stability range of decagonal Al-Co-Ni can be interpreted in terms of entropy gain by Co/Ni substitutional disorder and phasonic disorder of a part of the Al atoms.
Analysis of Gas Phase Clusters Made from Laser-Vaporized Icosahedral Al-Pd-Mn
Authors: Barrow J.A. , Rexer E.F. , Sordelet D.J. , Besser M.F. , Jenks C.J. , Riley S.J. , Thiel P.A. 
Published: April 2011

AbstractLaser vaporization of an icosahedral Al-Pd-Mn sample with detection by time-of-flight mass spectrometry is used to probe metal clusters made from the alloy. After sample vaporization, clusters form by gas aggregation and may contain several to hundreds of atoms. Multi-photon ionization/fragmentation of these clusters yields mass spectra showing many cluster sizes with enhanced intensity. Clusters are identified at masses near those of pseudo- Mackay and Bergman clusters; however, these clusters do not appear special relative to neighboring clusters. Results of this study and its relationship to the proposed cluster structures in quasicrystalline materials are discussed.