bluuebunny/crossref_metadata_2025 huggingface dataset:
Stereological Corrections for Grain Boundary Number Fractions in Three Dimensions
Authors: Reed Bryan W. , Kumar Mukul
Published: April 2011

Two-dimensional (2D) cross sections through three-dimensional (3D) polycrystalline materials present a biased picture of the statistical properties of grain boundary networks. These properties are essential to many practical applications such as grain boundary engineering. We show a simple correction that will partly correct for the sampling biases by removing the effect of the correlation between grain boundary type and grain boundary area. This correction alters number fraction estimates by as much as ∼60% for σ3 boundaries in the highly-twinned copper samples we consider. We also estimate the bias introduced by the correlation between boundary type and boundary shape, which for many materials represents perhaps a 10% shift in the measured statistics, so that the simple method we propose should correct for the majority of the bias in favorable cases.

This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes.
Atomic Force Microscopy and Spectroscopy of Self-Assembled InAsSb Quantum Dots grown on InP Substrates by MOCVD
Authors: Sin Yongkun , Kim Hyun I. , Stupian Gary W. , Qiu Yueming
Published: April 2011

InAsSb quantum dot (QD) lasers are promising light sources with emission wavelengths beyond 2μm as recently demonstrated. We report the first detailed atomic force microscope (AFM) characterization of uncapped InAsSb quantum dots self-assembled on GaAs/In0.53Ga0.47As layers. These quantum dot structures are grown on (100) InP substrates by metal organic chemical vapor deposition (MOCVD). Growth conditions are chosen to maximize photoluminescence intensity and to obtain high output powers from Fabry-Perot lasers with one stack of InAsSb QDs. Conductive AFM is employed to simultaneously study topography, current image, and current-voltage (I-V) characteristics from various InAs1-ySby QDs with y varied between 0 and 0.25. Typical dot density is 4–5×1010/cm2 and dots are estimated to have a lateral dimension at the base of ∼40nm and a height of 2–5nm. I-V characteristics measured from individual InAsSb QDs are compared to those from InAs QDs. Also reported are electronic properties including energy band gaps of InAs and InAsSb QDs.
Intersubband Transitions in In0.3 Ga0.7As/GaAs Multiple Quantum Dots of Varying Dot-Sizes
Authors: Chua Y. C. , Liang Jie , Passmore B. S. , DeCuir E. A. , Manasreh M. O. , Wang Zhiming , Salamo G. J.
Published: April 2011

The optical absorption spectra of intersubband transitions in In0.3Ga0.7As/GaAs multiple quantum dots (MQDs) grown by molecular beam epitaxy were investigated. By varying the number of In0.3Ga0.7As monolayers deposited, a series of samples with varying dot sizes ranging from 10 – 50 monolayers were obtained. The quantum dots grown with size less than 15 monolayers or more than 50 monolayers did not yield any observable measurements of intersubband transition. This suggests that there exist a critical upper and lower limit of In0.3Ga0.7As quantum dots for infrared detectors. A wavelength range of 8.60 – 13.70 μm is achieved for structures grown with the above monolayers range. The theoretical line-shape of the intersubband transition absorption was compared to the experimental measurements. From the lineshape, it was deduced that bound-to-continuum transtition is present in thick quantum dots and bound-to-bound transition is present in thinly grown quantum dots.
Pt/Au and W/Pt/Au Schottky Contacts to Bulk n-ZnO.
Authors: Ip Kelly , Gila Brent , Onstine Andrea , Lambers Eric , Heo Young-Woo , Norton David , Pearton Stephen , LaRoche Jeffrey , Ren Fan
Published: April 2011

UV-ozone cleaning prior to metal deposition of either e-beam Pt contacts or sputtered W contacts on n-type single-crystal ZnO is found to significantly improve their rectifying characteristics. Pt contacts deposited directly on the as-received ZnO surface are Ohmic but show rectifying behavior with ozone cleaning. The Schottky barrier height of these Pt contacts was 0.70 eV, with ideality factor of 1.5 and a saturation current density of 6.2 × 10−6 A·cm−2. In contrast, the as-deposited W contacts are Ohmic, independent of the use of ozone cleaning. Post-deposition annealing at 700 °C produces rectifying behavior with Schottky barrier heights of 0.45 eV for control samples and 0.49 eV for those cleaned with ozone exposure. The improvement in rectifying properties of both the Pt contacts is related to removal of surface carbon contamination from the ZnO.
Short-Period Strain-balanced GaAs1-x Nx/InAs(N) Superlattices Lattice-matched to InP(001): a new material for 0.4–0.6 eV mid IR applications
Authors: Bhusal L. , Alemu A. , Freundlich A.
Published: April 2011

A theoretical and experimental investigation of electronic band structure (Γ-point) of strain balanced GaAs1-xNx/InAs1-xNx short period superlattice on InP is performed. A six-band Kane Hamiltonian and band anti-crossing models, modified for the strain effects are used to describe the electronic states of the highly strained zincblende GaAs1-xNx and InAs1-xNx ternaries. Operating wavelengths of these heterostructures are predicted to extend beyond 2 μm. Preliminary photoluminescence results of the chemical beam epitaxially grown sample are shown to be consistent with the theoretical predictions.
Vertical and in-plane electrical transport in InAs/InP semiconductor nanostructures
Authors: Vicaro K. O. , Bortoleto J. R. R. , Gutiérrez H. R. , Nieto L. , von Zuben A. A. G. , Seabra A. C. , Schulz P. A. , Cotta M. A.
Published: April 2011

Vertical and in-plane electrical transport in InAs/InP semiconductors wires and dots have been investigated by conductive atomic force microscopy (C-AFM) and electrical measurements in processed devices. Localized I-V spectroscopy and spatially resolved current images (at constant bias), carried out using C-AFM in a controlled atmosphere at room temperature, show different conductances and threshold voltages for current onset on the two types of nanostructures. The processed devices were used in order to access the in-plane conductance of an assembly with a reduced number of nanostructures. On these devices, signature of two-level random telegraph noise (RTN) in the current behavior with time at constant bias is observed. These levels for electrical current can be associated to electrons removed from the wetting layer and trapped in dots and/or wires. A crossover from conduction through the continuum, associated to the wetting layer, to hopping within the nanostructures is observed with increasing temperature. This transport regime transition is confirmed by a “temperature-voltage” phase diagram.
Preparation and luminescent properties of SrS:Ce by addition of sulphur as a co-activator in SrSO4:Ce(SO4)2.4H2O by carbothermal reduction.
Authors: Thiyagarajan P. , Kottaisamy M. , Sethupathi K. , Rao M. S. R.
Published: April 2011

Ce activated SrS has been prepared from SrSO4:Ce(SO4)2.4H2O by ecologically acceptable carbothermal reduction in the absence of inert gas and hazardous H2S environment. The mixtures were fired at 900°C to find out the feasibility of the reduction reaction. In order to understand the compensator behavior we tried with sulfur and various fluxes viz., NH4Cl, NaCl. The materials synthesized were characterized by XRD, photoluminescence emission (PL) and excitation spectroscopy (PLE) and SEM. The characterization results showed the formation of SrS at 900°C with an increase in luminescence intensity after the addition of sulfur as a co-activator. The bright blue-green emission observed at 480nm and 540nm corresponds to energy bands originating from 2T2g (5d) to 2F7/2, 2F5/2(4f) of Ce3+ transitions. The excitation spectrum shows a fundamental absorption of SrS host crystal lattice in the lower wavelength region at 283 nm and Ce at 430 nm.
Heterostructures with Strained InGaAs Quantum Wells for RCE Photodiode Applications in the 1.8–2 μm Spectral Range
Authors: Zynek Jadwiga , Jasik Agata , Gaca Jaroslaw , Wojcik Marek , Strupinski Wlodzimierz , Rutkowski Jaroslaw , Wnuk Artur , Klima Krzysztof
Published: April 2011

The results of the work on the technology and characterization methods of resonant cavity enhanced (RCE) photodiode heterostructures with strained InxGa1–xAs quantum wells (0.65≤x≤0.82), designed for the 1.8 - 2 μm spectral range, are presented. The heterostructures grown on InP by metalorganic chemical vapor deposition have been investigated by high-resolution X-ray diffraction with synchrotron source, transmission electron microscopy, photoluminescence and reflectivity spectra measurements. Non-resonant photodiodes fabricated from these epitaxial structures exhibit dark current densities below 10-6 A/cm2 and quantum efficiencies above 1 % (even without bias). These quantum efficiency values are a good basis for the resonant cavity enhancement. The optical field enhancement at quantum wells has been examined in resonant heterostructures before processing.
Electronic and Optical Properties of SiGe alloys within first-principles schemes
Authors: Cappellini G. , Satta G. , Palummo M. , Onida G.
Published: April 2011

We present first-principles calculated electronic and optical properties of some SiGe alloys. The ground-state, electronic excitations and optical properties have been calculated with Ge and Si atoms arranged in different ways among the sites of a diamond-type lattice. For the ground state a DFT-LDA scheme and for the electronic excitations a DFT-GW approach have been respectively used. For the optical properties the DFT-LDA-RPA scheme has been applied for alloys going in composition from Si(100%) to Ge(100%): obtained results have been compared with existing experimental and theoretical data. For the noticeable Si(50%)Ge(50%) alloy also two-particle effects have been evaluated using the Bethe-Salpeter equation.
Novel Noncontact Thickness Metrology for Partially Transparent and Nontransparent Wafers for Backend Semiconductor Manufacturing
Authors: Walecki Wojciech J. , Souchkov Vitali , Lai Kevin , Van Phuc , Santos Manuel , Pravdivtsev Alexander , Lau S. H. , Koo Ann
Published: April 2011

Single probe infrared low coherence optical interferometry has been proven to be an effective tool for characterization of thin and ultra-thin semiconductor Si and compound materials wafers. Its application was however limited to wafers transparent at probing wavelength, and having relatively smooth surfaces. Purpose of this paper is to present an extension of low coherence interferometry to characterization of non-transparent wafers, and wafers with rough surfaces.
Dielectric Properties of Semiconductors by TDDFT in Real-Space and Real-Time Approach
Authors: Zempo Yasunari , Akino Nobuhiko
Published: April 2011

The dielectric responses of semiconductors such as C, Ge, Si, and AlGaAs are studied by the time-dependent density-functional theory. In our study, the real-space grid representation of the electron wave functions is used and the real-time approach is employed for the dynamics of the system. Both the static and dynamic dielectric functions are calculated, and we yielded that the static dielectric constants ε(0) are especially in good agreement with the experimental values. The effect of Al-component in the compound semiconductor AlxGa1−xAs is also studied. The peaks of the imaginary part of the dielectric function change with the band separation as a function of the Al-component. Furthermore, the static dielectric constants show the expected change due to the band separation as a function of the Al-component.
Fabrication of Silicon Nitride Film using Pure Nitrogen Plasma Generated near Atmospheric Pressure for III-V Semiconductor Fabrication
Authors: Hayakawa R. , Yoshimura T. , Nakae M. , Uehara T. , Ashida A. , Fujimura N.
Published: April 2011

Stable discharging of pure nitrogen can be maintained even at atmospheric pressure when alternative pulsed voltage is applied between two parallel plate electrodes. From optical emission spectroscopy, strong emissions from the N2 2nd positive system, weak emissions from N2 Herman's infrared system and N2 1st positive system were observed. The emission intensities from the N2 2nd positive system and the N2 Herman's infrared system increase with increasing the nitrogen gas pressure, whereas the emission intensities from the N2+ 1st negative system and N2 1st positive system decrease. The thickness of the silicon nitride film fabricated at 500 Torr was 1.6 nm at a nitridation temperature as low as 25°C, regardless of the nitridation temperature and nitridation time. From these results, we conclude that N2(C3IIu) plays an important role for the excellent reactivity of the nitrogen plasma generated near atmospheric pressure.
Electroluminescence from GalnN Quantum Wells Grown on Non-(0001) Facets of Selectively Grown GaN Stripes
Authors: Neubert Barbara , Habel Frank , Bruckner Peter , Scholz Ferdinand , Riemann Till , Christen Jürgen
Published: April 2011

Non (0001) GalnN QWs have been grown by low pressure MOVPE on side facets of triangular shaped selectively grown GaN stripes. By analysing low temperature photo- and cathodoluminescence and room temperature electroluminescence, we found strong indications, that both, In and Mg are less efficiently incorporated on these side facets compared to the common (0001) plane with even lower efficiency for stripes running along (1–100) compared to (11–20). Nevertheless, we observed strong light emission from these quantum wells, supposed to be at least partly caused by the reduced piezo-electric field.
Comparative Study of GaN Based Light Emitting Devices Grown on Sapphire and GaN Substrates
Authors: Figge Stephan , Dennemarck Jens , Alexe Gabriela , Hommel Detlef
Published: April 2011

The homoeptaxial growth of GaN based devices has advantages against the heteroepi-taxial realization on substrates such as sapphire or SiC, since heteroepitaxy implies a lot of problems like lattice mismatch, different thermal expansion coefficients, and needs an extensive optimization of the growth at the heterointerface. In this paper we will discuss GaN based light emitting devices grown by homoepitaxy in comparison to devices grown on sapphire. We will show the differences in device performance, device processing and the influence of the thermal resistivity on the devices.
Resonant-Raman Scattering of ZnO Crystallites: the Quasi Nature of the LO Mode
Authors: Chen Xiang-Bai , Morrison John L. , Huso Jesse , Metzger Jonathan G. , Bergman Leah , Efrima Shlomo
Published: April 2011

The Raman modes of ZnO crystallites of the wurtzite structure were investigated via micro-Raman scattering at resonant and out-of-resonant conditions. The E2 mode was the predominant mode in the spectra for out-of-resonant conditions. For the resonant conditions one mode at the spectral range of the LO's of ZnO single crystal was the predominant mode: its frequency was found to be at ∼ 580 cm−1. The A1(LO) and the E1(LO) modes of a reference ZnO single crystal were found to be 568 cm−1 and 586 cm−1 respectively. Two possible mechanisms were considered that may explain the mode frequency of the crystallites: it can be regarded as a confined E1(LO) mode or as a quasi-LO mode. The UV-photoluminescence of the crystallites was found to have the same energy as that of the single crystal ∼ 3.3 eV, indicating the lack of size-confinement of the electronic states in the crystallites, and inter alia that of the phonon states. Our analysis indicated that the observed frequency can be explained in terms of Loudon's model of a quasi-mode behavior which is due to the crystallites tilt.
Vapor-liquid-solid Growth of III-Nitride Nanowires and Heterostructures by Metal-Organic Chemical Vapor Deposition
Authors: Su J. , Gherasimova M. , Cui G. , Han J. , Lim S. , Ciuparu D. , Pfefferle L. , He Y. , Nurmikko A. V. , Broadbridge C. , Lehman A. , Onuma T. , Kurimoto M. , Chichibu S. F.
Published: April 2011

We report flexible synthesis of III-Nitride nanowires and heterostructures by metal-organic chemical vapor deposition (MOCVD) via a catalytic vapor-liquid-solid (VLS) growth mechanism. Indium is used as an in-situ catalyst to facilitate and sustain the stability of liquid phase droplet for VLS growth based on thermodynamic consideration. The employment of mesoporous molecular sieves (MCM-41) helps to prevent the coalescence of catalyst droplets and to promote nucleation statistics. Cathodoluminescence (CL) of GaN nanowires shows near band-edge emission at 370nm, and strong E2 phonon peak is observed at room temperature in Raman scattering spectra. Both binary GaN and AlN nanowires have been synthesized by MOCVD. Three-dimensional AlN/GaN trunk-branch nanostructures are reported to illustrate the versatility of incorporating the VLS mechanism into MOCVD process.
Effect of the polar surface on GaN nanostructure morphology and growth orientation
Authors: Nam C. Y. , Tham D. , Fischer J. E.
Published: April 2011

Wurtzite gallium nitride nanostructures were synthesized by catalyst-free thermal reaction of gallium oxide and ammonia. Depending on ammonia flow rate the resulting morphology varied. At 75 sccm only nanowires were obtained, while polyhedral crystals and nanobelts were observed at 175 sccm. From scanning electron microscopy and transmission electron microscopy, both thin smooth and thick corrugated nanowires were observed. The growth orientations of most of the smooth ones, as well as the nanobelts, were perpendicular to the c-axis (<0001>), while the corrugated nanowires and the large polyhedra grew parallel to <0001>. We propose a model to explain these variations of morphology and growth orientation in terms of the Ga/N ratio and the different characteristic length of {0001} polar surface in each morphology.
Initial Stages of Growth of Gallium Nitride via Iodine Vapor Phase Epitaxy
Authors: Mecouch WJ , Rodriguez BJ , Reitmeier ZJ , Park J-S , Davis RF , Sitar Z
Published: April 2011

Thin layers of GaN have been deposited on 1μm thick MOVPE GaN(0001) thin film substrates using a novel vertical iodine vapor phase epitaxy system. The system features three concentric flow zones that separate the reactant gasses until they reach the substrate. Hydrogen flows through the innermost zone to deliver iodine vapor from an external bubbler to the molten Ga maintained at ∼1050°C and GaI to the substrate; high-purity ammonia flows through the outermost zone; nitrogen flows through the middle zone to prevent reaction between the growth species at the GaI nozzle. GaN growth was found to be a function of time, with decreasing concentration of iodine the likely cause of a decrease in growth rate at longer growth times. The step-and-terrace microstructure of the MOVPE seeds was replaced with a smooth morphology film after the shortest growth experiment. Star-shaped features with hexagonal symmetry grew on the surface with increasing growth time. These features became the tops of hexagonal pyramids; these pyramids grew competitively and dominated the final growth surface. The surface of the films grown for the longest period contained a step-and-terrace microstructure; however, the density of steps of was lower than that on the surface of underlying MOVPE substrate.
Optimization of p-type AlGaN/GaN and GaN/InGaN Superlattice Design for Enhanced Vertical Transport
Authors: Kauser M. Z. , Osinsky A. , Dong J. W. , Hertog B. , Dabiran A. , Chow P. P.
Published: April 2011

We report on p-type AlGaN/GaN and GaN/InGaN superlattice (SL) designs with significantly improved vertical and lateral electrical conductivity (σV and σL). Composition-graded p–AlGaN layers were used to produce eight fold reduction in barrier height and a ∼40% increase in the sheet hole density in the p-GaN wells compared to typical SL structures. Thirteen orders of magnitude and 35 times improvement is obtained for σV and σL compared to typical SL and bulk p-GaN, respectively. A similar approach for p-GaN/InGaN SL resulted in seven fold reduction in barrier height and a ∼30% increase in the sheet hole density in the p-InGaN wells compared to a typical SL structures. σL is strongly dependent on hole mobility in the well and about 19 times improvement is obtained for the optimized design, SL-B, with μp=30 cm2 V-1s-1 compared to bulk-InGaN. More than 10 orders of magnitude improvement in σV is obtained for SL-B compared to modulation doped SL.
RF-MBE Growth of InN Dots on N-polar GaN Grown on Vicinal c-plane Sapphire
Authors: Hashimoto Naoki , Kikukawa Naohiro , Che Song-Bek , Ishitani Yoshihiro , Yoshikawa Akihiko
Published: April 2011

We have grown InN quantum dots (QDs) on nitrogen-polarity (N-polarity) GaN under-layer by the radio-frequency plasma-assisted molecular beam epitaxy (RF-MBE), and systematically investigated growth mechanism of the InN dots. The InN QDs with the N-polarity could be grown at about 500°C, which was much higher than that of previous reports on InN dots grown by MBE. When the nominal coverage of InN became more than 1 mono-layer (ML), lattice relaxation of InN occurred and high density InN dots were uniformly formed. These results indicated that InN dots were formed by Stranski-Krastanov (S-K) growth mode. For the InN deposition above about 8ML, InN dots tended to coalesce and resulted in remarakable decrease of the dots density.
Photoluminescence Study of Plastically Deformed GaN
Authors: Yonenaga I. , Makino H. , Itoh S. , Goto T. , Yao T.
Published: April 2011

We report the photoluminescence characteristics of fresh dislocations introduced by the plastic deformation in GaN bulk crystals. GaN crystals prepared from free standing wafers grown by the HVPE technique were compressed plastically at 900 to 1000°C. In the deformed crystals (a/3) (1120) dislocations on the (1110) prismatic plane, corresponding to the so-called threading dislocations, were observed in TEM. In the PL studies at 11K the intensity of the near band-edge luminescence decreased drastically in the deformed GaN by about 1/12 than that of the as-grown GaN, which seems to imply the introduction of a high density of non-radiative reco!m bination centers into GaN! during the plastic deformation. By the plastic deformation the yellow band luminescence decreased remarkably meanwhile the red band and other new luminescence developed relatively. It is found that dislocations do not originate to the yellow luminescence but the red luminescence.
Micro-photoluminescence studies of excitonic and multiexcitonic states of quantum dot-like localization centers in InGaN/GaN structures
Authors: Sebald K. , Lohmeyer H. , Gutowski J. , Einfeldt S. , Roder C. , Hommel D.
Published: April 2011

We present micro-photoluminescence measurements on unstructured InGaN/GaN quantum well samples. Single sharp emission lines were observed and their optical properties were studied as a function of temperature and excitation density. The experimental findings such as the independence of their spectral position on the excitation density and the observation of binding and antibinding multiexcitonic states give clear evidence for the existence of strong localization centers in the InGaN quantum well, which exhibit the same characteristics as they are known for quantum dot structures.
Ultrafast All-optical Switches Based on Intersubband Transitions in GaN/AlN Multiple Quantum Wells for Tb/s Operation
Authors: Dawlaty Jahan M. , Rana Farhan , Schaff William J.
Published: April 2011

Theoretical and experimental results on ultra-fast all-optical switches based on intersubband transitions for Tb/s operation are presented. Designs for engineering intersubband transitions (ISBT) in GaN/AlN quantum wells near communication wavelengths (∼1.55 μm) and for realizing all-optical switches requiring small pulse energies are discussed. Optimized designs show all-optical switching at Tb/s data rates with pulse energies as small as 200 fJ. Experimental realization of narrow line-width ISBT in GaN/AlN superlattices is also demonstrated.
Synthesis and Properties of GaxMn1-xN films
Authors: Zhang R. , Yu Y. Y. , Xiu X. Q. , Xie Z. L. , Gu S. L. , Shen B. , Shi Y. , Zheng Y. D.
Published: April 2011

ABSTRATCT:

Mn-doped GaN films were grown by hydride vapor phase epitaxy(HVPE). structural measurements show that Mn may substitute Ga atoms in the GaN lattice. Ferromagnetism is observed in these HVPE grown Mn-doped GaN films, which may come from the GaxMn1−xN phase in the films.
Multi-color luminescence from nanocrystalline silicon
Authors: Kunii Hiroshi , Sato Keisuke , Hirakuri Kenji , Izumi Tomio
Published: April 2011

We have investigated correlation between luminescence property and particle size of nanocrystalline silicon (nc-Si) fabricated by controlling Si concentration in an amorphous SiOx (a-SiOx) films. The Si concentration in the a-SiOx film was increased with increasing a RF power and lowering a gas pressure. The increase of Si concentration led to expansion of the particle size of nc-Si. The particle size of nc-Si was varied from 1.8 nm up to 3.5 nm for the sample introduced the Si concentration from 0.7 % up to 9 %. The luminescent color from nc-Si grains, which differs in size, showed a red/green/blue lights.
Surface Cusp Formation in Si Homoepitaxy
Authors: Baribeau J.-M. , Wu X. , Beaulieu M. , Lockwood D.J. , Rowell N.L.
Published: April 2011

We report a study of the surface morphology and microstructure of Si epitaxial layers grown by MBE on (001) Si at temperatures at which epitaxy breakdown is observed. For films grown in the 400 - 450 °C temperature range the epitaxy breakdown is very sluggish and characterized by a columnar growth and the formation of surface cusps. We have used atomic force microscopy to study the shape, size and distribution of those surface cusps. Surface cusps are of square shape with sides predominantly oriented along <110> directions and are typically of 50 nm size and 5 nm depth. The cusps can be very regular in size and their surface density (typically of 109-1010 cm-2) is dependent on the growth temperature. The epitaxial Si in this temperature regime exhibits a residual strain of the order of -5 × 10−5 in the growth direction. Photoluminescence (PL) from cusped Si films is characterized by a broad PL at low energy possibly due to impurities incorporation at low growth temperatures. We have observed that Ge self-assembled dots can be grown on cusped surfaces. Large area AFM measurements reveal that surface cusps are “decorated” by clusters of large dome-like Ge dots, while a lower density of smaller dome and pyramid shape islands are seen away from the cusps.
Thermal Conductivity of Porous Silicon Evaluated from Phase Characteristics of Photoacoustic Spectroscopy
Authors: Ohmukai Masato , Shimizu Hirokazu , Tsutsumi Yasuo
Published: April 2011

Porous silicon (PS), well known as a visible luminescent material, has been revealed to be an attractive candidate for an ultrasonic emitter recently. Since the ultrasonic emission is based on a thermal process it is important to evaluate thermal properties of PS. We then evaluated the thermal conductivity of PS from the phase delay in a photoacoustic (PA) signal. We report the dependence of thermal conductivity on anodization time in forming PS.
Metal-free Growth of Si/SiO2 Nanowires by Annealing SiOx (x<2) Films Deposited by PECVD
Authors: Wang Xiaoxin , Zhang Jianguo , Wang Qiming
Published: April 2011

A new metal catalysis-free method of fabricating Si or SiO2 nanowires (NWs) compatible with Si CMOS technology was proposed by annealing SiOx (x<2) films deposited by plasma -enhanced chemical vapor deposition (PECVD). The effects of the Si content (x value) and thickness of SiOx films, the annealing process and flowing gas ambient on the NW growth were studied in detail. The results indicated that the SiOx film of a thickness below 300 nm with × value close to 1 was most favorable for NW growth upon annealing at 1000–1150°C in the flowing gas mixture of N2 and H2. NWs of 50–100nm in diameter and tens of micrometers in length were synthesized by this method. The formation mechanism was likely to be related to a new type of oxide assisted growth (OAG) mechanism, with Si nanoclusters in SiOx films after phase separation serving as the nuclei for the growth of NWs in SiOx films>200nm, and SiO molecules from thin SiOx film decomposition inducing the NW growth in films<100nm. An effective preliminary method to control NW growth direction was also demonstrated by etching trenches in SiOx films followed by annealing.
Growth and Characterization of SiOx nanowires by VLS and SLS growth mechanism
Authors: Rho Dae-Ho , Kim Jae-Soo , Byun Dong-Jin , Yang Jae-Woong , Lee Jae-Hoon , Kim Na-Ri
Published: April 2011

ABSTRCT:

SiOx nanowire were synthesized using VLS (vapor-liquid-solid) and SLS (ssolid-liquid-solid) growth mechanism. Grown nanowires had a different shapes by the kind of substrates and kind of catalysts. Diameters and lengths of grown nanowires were varied with growth conditions. By vapor evaporation method, used substrates effected growth scheme and density of nanowires because of differences of catalyst nucleation characteristics. Grown nanowires showed different microstructures and optical properties. By catalyst evaporation method, various shapes of SiOx nanowires were grown. These shapes of nanowire were formed by the typical reaction of catalyst and Si source. Measured optical properties show blue luminescence about 430nm because of oxygen defects in the nannowire.
Evolution of the Luminescence Spectrum During the Dry and Steam Oxidation of SiGe Films
Authors: Rodríguez A. , Sangrador J. , Rodríguez T. , Prieto A. C. , Avella M. , Jiménez J.
Published: April 2011

The luminescence emission arising from SiGe layers oxidized in dry or wet atmospheres has been studied and the results obtained in both cases have been compared. Additional characterization of the samples by Raman and FTIR spectroscopies, which give information on the remaining SiGe layer and on the composition of the growing oxides respectively, have allowed the luminescence and the structural features of the samples at each stage of the oxidation processes to be correlated. SiGe layers of two different thickness have been used in order to clearly establish the origin of the different emissions, eliminating the contribution of the oxide and linking them to the presence of nanoparticles.
Double Interface Coatings on Silicon Carbide Fibers
Authors: Nable Jun C. , Nosheen Shaneela , Suib Steven L. , Galasso Francis S. , Kmetz Michael A.
Published: April 2011

Interface coatings on fibers are important in ceramic matrix composites. In addition to providing toughness, the interface coating must also protect the reinforcing ceramic fibers from corrosive degradation. A double interface coating has been applied onto silicon carbide fibers. The double interface coating is comprised of a combination of nitride and oxide coatings. Among the nitrides, boron nitride and titanium nitride were utilized. These nitrides were deposited by CVD. The metal oxides of choice were aluminum oxide and zirconium oxide which were applied onto the nitride coatings by MOCVD. The phases on the coated fibers were determined by XRD. The surface coating microstructures were observed by SEM. The effect of the coatings on the tensile strengths was determined by Instron tensile strength measurements.
Formation of High-Resistivity Silver-Silicon Dioxide Composite Thin Films Using Sputter Deposition.
Authors: Shover Ann Marie , Harper James M.E. , Dellas Nicholas S. , MoberlyChan Warren J.
Published: April 2011

Composite Ag-SiO2 thin films were deposited to examine the stability of materials with high resistivity above 5000 μΩ-cm. We found that the resistivity increases exponentially with SiO2 volume fractions larger than 0.50 which is consistent with a tunneling conductivity mechanism. In order to obtain a broad composition range, these films were deposited on a stationary substrate placed above Ag and SiO2 sputtering sources. This configuration allowed compositions ranging from 0.8 to 56.3% SiO2 to be deposited on the same sample. Resistance measurements were made using a four-point probe and a profilometer was used to measure thickness. Predicted values of thickness and composition were obtained by calibrating deposition rates from the separate sources, and were verified using Rutherford Backscattering Spectroscopy. Electron microscopy analysis revealed Ag agglomerating on the surface of the film. Because of the high mobility of Ag, the films should be capped to prevent Ag agglomeration. The results of this research demonstrate that high-resistivity thin films can be grown using Ag-SiO2 composites.
Comparison of Hardness Enhancement and Wear Mechanisms in Low Temperature Nitrided Austenitic and Martensitic Stainless Steel
Authors: Mändl S. , Manova D. , Hirsch D. , Neumann H. , Rauschenbach B.
Published: April 2011

Energetic nitrogen implantation into austenitic stainless steel or nickel alloys leads to the formation of a very hard and wear resistant surface layer with an expanded lattice, while similar results are reported for selected martensitic steels. A comparison of the phase formation under identical process conditions at 380 °C using an austenitic (304) and a martensitic (420) steel grade (in an annealed ferrite/cementite condition) shows that the initial microstructure is retained in both of them. As the formation of dislocations and stacking faults cannot account for the dramatic hardness increase, the build-up of compressive stress is proffered as an explanation covering these two steel types. Furthermore the energetic nitrogen implantation apparently stabilizes the expanded lattice with suppressing the chemical transition to iron nitrides and, for steel 420, the metallurgical transition towards austenite at high nitrogen contents.
Buckling failure of compressive loaded hard layers in flexible devices
Authors: Bouten Piet C.P. , van Gils Marcel A.J.
Published: April 2011

Substrate materials for flexible devices are multi-layer composite structures. On top of a base polymer functional inorganic layers such as permeation barriers and conductive layers are applied. Due to the thermal mismatch between polymer and inorganic layer, the layer is compressive loaded at ambient conditions. A characteristic failure mode, occurring with compressive loaded thin layers, is buckling failure. The interface between adjacent layers fails locally, and the thin top layer bends outwards. The buckles have a characteristic width and height. These sizes are used to analyse the compressive strain, present in the layer before failure, and the adhesion quality of the failed interface. A buckle map is introduced to guide this analysis.
Si(100) Nitridation by Remote Plasmas for Enhanced High-κ Gate Performance
Authors: Chen P. , Klein T. M.
Published: April 2011

Hafnium oxide is the leading high-κ candidate for next generation CMOS devices, however, it is plagued by problems such as a propensity to react with the Si(100) substrate, to crystallize, and to have fixed and trapped charges and low transistor mobilities. A remote N2/He plasma was used as a reactant during MOCVD with Hf (IV) t-butoxide which incorporates 6 at.% nitrogen located at the film-substrate interface and reduces the interdiffusion problem upon anneal [1]. A new process for pretreating the silicon wafer with a N2/He plasma was developed to improve nitrogen concentrations at the interface and reduce interdiffusion further. Films deposited with N2/He plasma and the pretreatment method were compared to O2/He plasma deposited films and N2/He plasma deposited films without the nitridation step. It is shown that a 16Å interface SiNx layer is sufficient to prevent reaction during a 1000°C Ar/O2 anneal at atmosphere and an intermediate annealing step is crucial for desired reduction in interdiffion. Thick films show some crystalline peaks by XRD which are suppressed using the N2 process. Electrical measurements on thick films show the pretreatment process results in the lowest leakage current density and the highest dielectric constant of 21.5.
Biodegradable Microfluidic Scaffolds for Vascular Tissue Engineering
Authors: Bettinger C. J. , Borenstein J. T. , Langer R. S.
Published: April 2011

This work describes the integration of novel microfabrication techniques for vascular tissue engineering applications in the context of a novel biodegradable elastomer. The field of tissue engineering and organ regeneration has been borne out of the high demand for organ transplants. However, one of the critical limitations in regeneration of vital organs is the lack of an intrinsic blood supply. This work expands on the development of scaffolds for vascular tissue engineering applications by employing microfabrication techniques. Unlike previous efforts, this work focuses on fabricating single layer and three-dimensional scaffolds from poly(glycerol-sebacate) (PGS), a novel biodegradable elastomer with superior mechanical properties. The transport properties of oxygen and carbon dioxide in PGS were measured through a series of time-lag diffusion experiments. The results of these measurements were used to calculate a characteristic length scale for oxygen diffusion limits in solid PGS scaffolds. Single layer and three-dimensional microfluidic scaffolds were then produced using fabrication techniques specific for PGS. This work has resulted in the fabrication of solid PGS-based scaffolds with biomimetic fluid flow and capillary channels on the order of 10 microns in width. Fabrication of complex, three-dimensional microfluidic PGS scaffolds was also demonstrated by stacking and bonding multiple microfluidic layers.
Bioreactor Based Bone Tissue Engineering: Influence of Wall Collision on Osteoblast Cultured on Polymeric Microcarrier Scaffolds in Rotating Bioreactors
Authors: Yu Xiaojun , Botchwey Edward A. , Levine Elliot M. , Pollack Solomon R. , Laurencin Cato T.
Published: April 2011

Rotating bioreactors have been used to overcome the limitations of passive nutrient diffusion in three-dimensional (3D) constructs for tissue engineering of bone. It is hypothesized that conventional scaffolds undergo repeated wall collisions in rotating bioreactors, which may disrupt bone tissue formation. In this study, we investigated the effects of wall collision on osteoblastic cells cultured on a microsphere based scaffold of varying densities in comparison to water. The conventional heavier than water (HTW; density > 1 g/cm3) scaffolds were fabricated by sintering HTW microspheres of 85:15 poly (lactide-co-glycolide) (PLAGA), and mixed scaffolds were designed by mixing lighter than water (LTW; density < 1 g/cm3) and HTW microspheres of PLAGA. We quantified average velocities of the two types of scaffolds using a particle tracking system, and no significant difference in average velocities was observed between the two types of scaffolds. However, HTW scaffolds have frequent wall collision and mixed scaffolds can avoid wall collision in bioreactors. When human Saos-2 osteoblast like cells were cultured on the scaffolds in bioreactors for 16 days, bone cell proliferation and cell differentiation on HTW scaffolds were significantly inhibited as compared to those cultured on mixed scaffolds in rotating bioreactors. These results indicate that collision between scaffolds and bioreactor wall is a confounding factor in osteoblastic cell proliferation and differentiation. These studies provide a foundation for development of 3D scaffolds for tissue engineering of bone in rotating bioreactors.
Effect of Impressing Rate of Field on Polarization Reversal in Mg Doped Near Stoichiometric Lithium Tantalate Single Crystals
Authors: Ganesamoorthy Sarveswaran , Nakamura Masaru , Takekawa Shunji , Kumaragurubaran Somu , Terabe Kazuya , Kitamura Kenji
Published: April 2011

The coercive field measured from ferroelectric hysteresis loop for pure and Mg:SLT (0.5 mol% doped) crystals were found to be independent of ramp rate of voltage, while it depends strongly on ramp rate for Mg:SLT (1 mol% doped) crystals. The measured coercive field decreased monotonously depending on the Mg concentration and low Ec value of 6 kV/cm is obtained for Mg(1.0 mol%)SLT crystal. Internal field of about 1 kV/cm present in pure SLT completely gets vanished in Mg(1.0 mol%)SLT. Spontaneous polarization is insensitive to the Mg addition. The origin of the internal field and large changes in switching fields appear largely to be dependent on the [Li]/[Li+Ta] ratio in crystals. On repeated cycling, the coercive field is found to have a marginal variation in pure and Mg doped SLT crystals.
New Magnetic Zintl Phases in Eu-In-P System
Authors: Jiang Jiong , Payne Amy C. , Kauzlarich Susan M.
Published: April 2011

Single crystals of two new compounds, Eu3InP3 and Eu3In2P4, were prepared by In flux synthesis. Eu3InP3 crystallizes in the Pnma orthorhombic space group with a = 12.6517(15) Å, b = 4.2683(5) Å, c = 13.5643(14) Å, and Z = 4 while Eu3In2P4 belongs to Pnnm space group, a = 6.6999(6) Å, b = 16.1019(13) Å, c = 4.2725(4) Å, and Z = 2. These two compounds are isotypic to the main group compounds Sr3InP3 and Sr3In2P4 respectively. Both structures consist of distorted In-P tetrahedra and isolated Eu2+ ions. In Eu3InP3 these tetrahedra share corners to form one-dimensional chains. The Eu2+ ions occupy three different sites, and form a complicated network containing some triangles. In Eu3In2P4 these tetrahedra form edge-shared dimers, and these dimers form chains. Eu3InP3 shows unusual magnetic properties: there are three magnetic ordering transitions at 14 K, 10.4 K, and around 5 K and the magnetization curve shows steps in the low temperature region. Eu3In2P4 magnetically orders at 14.5 K. Its magnetization curve saturates at around 1T. Eu3InP3 and Eu3In2P4 are both semiconductors.
Effect of growth parameters on refractive index and film composition of plasma enhanced chemical vapor deposition silicon oxynitride films
Authors: Naskar S. , Bower C. A. , Yadon L. N. , Wolter S.D. , Stoner B.R. , Glass J.T.
Published: April 2011

The importance of silicon oxynitride (SiOxNy) for optoelectronic device applications is ever increasing owing to its tunable refractive index. In this research, the influence of deposition conditions on film properties, correlated with film composition and bonding, have been investigated. Thick SiOxNy films were deposited in a plasma enehanced chemical vapor deposition reactor using silane (SiH4) and nitrous oxide (N2O) as precursor gases. To investigate the influence of deposition conditions on film properties, three different parameters were studied; gas flow ratio, RF plasma mixed frequency ratio and RF power. Several different SiOxNy films were deposited at varying conditions. The temperature and pressure were maintained at 350°C and 1 Torr during all the experimental runs. The films were characterized for refractive index, growth rate and residual stress. The refractive index and the thickness of the films were measured using a prism-coupling technique. For composition analysis, x-ray photoelectron spectroscopy studies and elastic recoil detection analysis were undertaken. The materials analysis was used to determine the correlation between growth parameters and material chemistry. In addition, the correlation between material chemistry and refractive index was also investigated.
Effect of Al Additions on the Synthesis of Single-Phase Ti3SiC2
Authors: Sun ZhengMing , Yang Songlan , Hashimoto Hitoshi , Barsoum Michel W.
Published: April 2011

Powder mixtures of 3Ti/SiC/C/xAl with different Al contents (x=0∼0.2) were reactively sintered by pulse discharge sintering (PDS) process, to reveal the effect of Al addition on the single-phase bulk Ti3SiC2 synthesis. It was found that the optimal sintering temperature for the Ti3SiC2 synthesis is greatly decreased by the Al addition. Almost single-phase bulk Ti3SiC2 material can be synthesized from 3Ti/SiC/C/0.15Al and 3Ti/SiC/C/0.20Al powder mixtures at temperature as low as 1200°C for 15 min by PDS. And the optimal temperature range for the Ti3SiC2 formation is enlarged obviously by the Al addition.
Synthesis and Properties of [B/C] Layered Compounds.
Authors: Mori Takao
Published: April 2011

We report synthesis and properties of layered compounds with 2D boron-and-carbon-mixed-atomic-layers which are related to topics of recent high interest. The previous discovery of the first [B/C] graphite intercalation-like compound Sc2B1.1C3.2 and evaluation of reported high temperature ferromagnetism in CaB2C2 are reviewed. MgB2 related [B/C] compounds MgB2C2 and LiBC were synthesized and hole doping carried out in search for superconducting materials with high TC. Superconductivity was not observed for any of the compounds above 1.8 K, but (Mg, Li)B2C2 is demonstrated to be the most promising system, with an insulator to metal transition indicated to be induced.
Synthesis of InP and InAs quantum rods using Indium Acetate and Myristic acid
Authors: Shweky Itzhak , Aharoni Assaf , Mokari Taleb , Nadler Moshe , Rothenberg Eli , Popov Inna , Banin Uri
Published: April 2011

The development of solution based synthesis approaches for preparing nanocrystals of III-V semiconductor presents a significant & important challenge especially with relation to shape control to achieve rod growth. To this end, a novel approach for synthesis of soluble semiconductor quantum rods using metal nanoparticles to direct and catalyze one-dimensional growth is developed. The synthesis method is useful in particular for III-V semiconductor with cubic lattice, where the utilization of surfactant-controlled rod-growth is not easily realized. The growth takes place via the solution–liquid–solid (SLS) mechanism where proper precursors are injected into a coordinating solvent as we reported in earlier work for InAs nanorods. Herein, we report the synthesis of high quality InP nanorods using Indium Acetate and myristic acid with gold nanoparticles as the catalysts in the SLS growth mode. A similar route was successfully developed for the growth of InAs nanorods. We find that the amount of Au catalyst in the reaction is an important parameter to achieving shape control. Transmission electron microscope (TEM) images of InP and InAs nanocrystals revealed that the crystals are mostly rod-shaped. XRD measurements, absorption spectra were preformed for the nanorods characterization.
The Chemical Bonding of Organic-Inorganic in Hybrid Compounds
Authors: Dai Yadong , Guo Liling , Hu Minjie , Shi Kunyu , Min Xinmin , Cao Minhe , Liu Hanxing
Published: April 2011

As has been discussed, research on the electronic structure between organic and inorganic atoms in hybrid compounds has become important. In our study, DV—Xα method was employed to calculate the electronic structure of the hybrid compound. The information obtained from the calculation included orbit charge, bonding order, Fermi energy, density of the state, etc. The influence of organic and inorganic parts on the energy band structure of the hybrid compound was discussed based on the calculation results of Fermi energy and density of state. The chemical bonding between organic and inorganic parts in the hybrid compound was also analyzed in detail according to the orbital charges and bond orders.