bluuebunny/crossref_metadata_2025 huggingface dataset:
Amelogenin Nanospheres Modulate Crystal Habit of Octacalcium Phosphate and Hydroxyapatite Crystals in In Vitro Model Systems
Authors: J. Moradian-Oldak , H.B. Wen , A.G. Fincham , M. Iijima
Published: April 2011

This paper is a short review of recent studies, which were undertaken to investigate interactions of amelogenin with octacalcium phosphate (OCP), and apatite. OCP crystals were grown using two independent experimental systems; (a) in a 10% gelatin gel, containing 0-2% amelogenin, where the crystals were formed in a double-diffusion chamber, and (b) in a 10% pure amelogenin gel, where crystal growth took place in between a cation-selective and a dialysis membrane. Apatite crystals were grown from a supersaturated calcifying solution on a bioactive glass in the absence (SCSB) and the presence of amelogenin (SCSrM179). It was found that OCP crystals formed in 10% gelatin gel containing 1-2% amelogenin were longer (3-5 times larger in aspect ratio) than the OCP crystals formed in 10% gelatin without amelogenin. A profound effect was that found in the cation selective membrane system when 10% amelogenin inhibited the growth morphology in a specific manner. Affected crystals had a length to width ratio twice larger than that of control crystals while the width to thickness ratio was about 1/12 of that of the control crystals. Amelogenin promoted the formation of bundles of lengthwise apatite crystals, which were all oriented parallel to their c axes when grown on SCSrM179. It was found that individual apatite crystals within those bundles adopted an elongated, curved shape. The data presented here suggest that amelogenin nanospheres modulate the growth morphology of apatite and OCP crystals and indicate significant functional roles for amelogenin proteins during the in vivo oriented growth of enamel crystallites.
Influence of external temperature field to period of eutectic pattern
Authors: A.P. Gus'kov
Published: April 2011

We used a mathematical model of crystal growth of [1] for the description of an eutectic pattern [2]. But the stationary problem gives physically unrealizable solutions (fig. 1) for values of system parameters corresponding to real experiments. Now known models [1,3-7] of crystal growth, used for a research of the interface stability of directed crystallization, not take into account of an external temperature field too. As examples of application of these models the regimes of crystal growth are usually used. The purpose of this work - to construct a model of a binary melt crystallization taking into account an external temperature field. Within the framework of this model we deduce analytical dependence of period of the eutectic structure on parameters of the system. We demonstrate, that for real parameters of the system, the parameters of the external temperature field weakly influence period of the eutectic pattern. This outcome is observed in experiments. We also explain the reason of joint emerging eutectic and dendrite of a structure for want of growth of eutectic crystals. We also explain the reason of joint both eutectic growth and dendrite growth under eutectic growth.
Intrasectoral Zoning of Proteins and Nucleotides in Simple Crystalline Hosts
Authors: Kurimoto Miki , Bastin Loyd D. , Fredrickson Daniel , Gustafson Pamela N. , Jang Sei-Hum , Kaminsky Werner , Lovell Scott , Mitchell Christine A. , Chmielewski Jean , Kahr Bart
Published: April 2011

Oriented gases of biopolymers in simple, single crystal hosts might be used to measure anisotropic molecular properties of analytes that could not otherwise be crystallized. Here we show two types of crystals as examples of the single crystal matrix isolation of biopolymers: green fluorescent protein in α-lactose monohydrate as a model system for studying the kinetic stabilization of biopharmaceuticals, and adenosine phosphates in potassium dihydrogen phosphate, a first step in the matrix isolation of oligonucleotides. In each case, the hosts undergo compositional zoning – both intersectoral and intrasectoral – during growth from solution. Intrasectoral zoning is evident by the selective luminescence of adjacent vicinal slopes of growth active hillocks. Nucleotides furthermore distinguish between symmetry related growth sectors enantioselectively.
Growth of the {101} face of KDP crystals in the presence of dye Chicago Sky Blue
Authors: Gliko Olga A. , Zaitseva Natalia P. , Rashkovich Leonid N.
Published: April 2011

In situ interference technique is used for a study of morphology and growth kinetics of a pyramidal face of KDP crystals with dye Chicago Sky Blue. It is shown that the impurity is captured by a crystal when its concentration in the solution exceeds a certain temperature depended value. In the presence of impurity the face loses its stability with increasing of supersaturation. Further increase of supersaturation leads to the restore and subsequent loss of stability. The experimental results are interpreted in the framework of earlier developed model for a crystal growth in the presence of the easily desorbed mobile impurity. The parameters characterizing the adsorption behavior of mobile impurity and its capture have been determined.
Low-Temperature CVD Carbon Coatings on Glass Plates for Flat Panel Display Applications
Authors: Tzeng Yonhua , Liu Chao , Cutshaw Calvin , Chen Zheng
Published: April 2011

Low-temperature chemical vapor deposition processes were studied for coating carbon films on metal-coated glass plates. Thermal CVD in hydrocarbon mixtures was used for carbon deposition at temperatures between 300°C and 550°C. Carbon deposited on metal coated glass plates were examined by SEM and analyzed using a pin to disk setup in an ultra high vacuum chamber for measuring the electron emission characteristics. Using a one-millimeter diameter tungsten rod with a hemispherical tip as the anode while the carbon coatings as the cathode, current-voltage characteristics of the carbon coatings were measured and used for calculating the electric field at which electron emission started as well as calculating the field enhancement factor of the carbon coatings. Field emission of electrons from carbon coatings starting from an electric field as low as 1.4 volts per micrometer has been achieved.
Very low field electron emission from Hot Filament CVD grown microcrystalline diamond
Authors: Satyanarayana B.S. , Peng X.L. , Adamopoulos G. , Robertson J. , Milne W.I. , Clyne T.W.
Published: April 2011

Very low threshold field emission from undoped microcrystalline diamond films grown by the hot filament chemical vapour deposition process (HFCVD) is reported. The effect of crystal size, methane concentration and the temperature has been studied. The microcrystalline diamond films grown using 3% methane (CH4) / hydrogen (H2) gas mixture ratio under varying deposition temperatures exhibit very low emission threshold fields. The threshold fields varied from 0.4 V/ [.proportional]m to 1 V/[.proportional]m for an emission current density of 1 [.proportional]A/cm2. A correlation between the emission characteristics and the material properties is presented. These films exhibit an emission site density of ∼ 104−105/cm2 at an applied field of 3 V/[.proportional]m.
Single-Shot Excimer-Laser Crystallization of an Ultra-Large Si Thin-Film Disk
Authors: Nakata Mitsuru , Oh Chang-Ho , Matsumura Masakiyo
Published: April 2011

An excimer-laser-induced large-grain growth method has been proposed which utilizes non-uniform heat diffusion along the Si thin-film and also along the underlayer. A single-shot of KrF excimer-laser light pulse with uniform intensity could crystallize a circularly pre-patterned Si thin-film of 20νm in diameter, much larger than TFT feature size in present AM-LCD panels.
Sub-grain Boundary Spacing in Directionally Crystallized Si Films Obtained via Sequential Lateral Solidification
Authors: Crowder M. A. , Limanov A. B. , Im James S.
Published: April 2011

In this paper, we report on the average linear density of sub-grain boundaries that are found in directionally solidified microstructures obtained via sequential lateral solidification of Si thin films. Specifically, we have characterized the dependence of the sub-grain boundary density on the film thickness, incident energy density, and per-pulse translation distance. The investigation was confined to analyzing directionally solidified microstructures obtained using straight-line beamlets. It is found that the average spacing of the sub-grain boundaries depended approximately linearly on the film thickness, where it varied from 0.28m at a thickeness of 550Å to ∼0.75μm at 2,000 Å. In contrast, variations in either the energy density or the per-pulse translation distance within the investigated SLS process parameter domain were found to have a negligible effect on the spacing. Discussion is provided on a preliminary model that invokes polygonization of thermal-stress generated dislocations, and on implications of the dependence of device performance on the film thickness.
Applications of Ion Track Lithography in Vacuum Microelectronics
Authors: Musket Ronald G.
Published: April 2011

When a high-velocity (i.e., typically > 0.1 MeV/amu) ion passes through a material it can change the properties of the material within a cylindrical zone centered on the essentially straight trajectory of the ion. The electronic bonding, phase, and density are among the properties modified in the zone, which is called a latent nuclear, or ion, track. Because the diameters of latent ion tracks are typically less than 20 nm, selective chemical etching is generally employed to improve the detection and assessment of the tracks. Historically, etched nuclear tracks have been used mainly for nuclear particle identification, geochronology, measurement of extremely low-dose radiation levels, and creation of membrane filters.
Fabrication and Characterization of Singly-Addressable Arrays of Polysilicon Field-Emission Cathodes.
Authors: Chubun N.N. , Chakhovskoi A.G. , Hunt C.E. , Hajra M.
Published: April 2011

Polysilicon is a promising candidate material for field-emission microelectronics devices. It can be competitive for large-size, cost-sensitive applications such as flat-panel displays and micro electro-mechanical systems. Singly-addressable arrays of field-emission cells were fabricated in a matrix configuration using a subtractive process on Polysilicon-On-Insulator substrates. Matrix rows were fabricated as insulated polycrystalline silicon strips with sharp emission tips; and matrix columns were deposited as gold thin film electrodes with round gate openings. Ion implantation has been used to provide the required conductivity of the poly-Si layer. To reduce radius of curvature of the polysilicon tips, a sharpening oxidation process was used. The final device had polysilicon emission tips with end radii smaller than 15 nm, surrounded by gate apertures of 0.4 μm in diameter. Field emission properties of the cathodes were measured at a pressure of about 10-8 Torr, to emulate vacuum conditions available in sealed vacuum microelectronics devices. It was found that an emission current of 1 nA appears at a gate voltage of 25 V and can be increased up to 1μA at 70 V. Over this range of current, no “semiconductor” deviation from the Fowler-Nordheim equation was observed. I-V characteristics measured in cells of a 10x10 matrix, with a cell spacing of 50 μm demonstrated good uniformity and reproducibility.
Theory and Modelling of Field-Induced Electron Emission
Authors: Forbes Richard G.
Published: April 2011

This paper addresses issues in the theory of field-induced electron emission. First, it summarises our present understanding of the theory of Fowler-Nordheim (FN) plots, and shows the relationship between a recent precise (in standard FN theory) approach to the interpretation of the FN-plot intercept and older approximate approaches. Second, it comments on the interpretation of FN plots taken from semiconductor field emitters. Third, it summarises the main points of a recent hypothesis about the mechanism of field-induced emission from carbonbased films and other electrically nanostructured heterogeneous (ENH) materials. Weaknesses in previous hypotheses are noted. It is hypothesised that thin films of all ENH materials, when deposited on a conducting substrate, will emit electrons in appropriate circumstances. Such films emit electrons at low macroscopic fields because they contain conducting nanostructureinsidethem: this structure generates sufficient geometrical field enhancement near the film/vacuum interface that more-or-less normal Fowler-Nordheim emission can occur. In connection with experiments on amorphous carbon films carried out by a group in Fribourg, it is shown that nanostructure of the size measured by scanning probe techniques should be able to generate field enhancement of the size measured in field electron spectroscopy experiments. This result provides a quantitative corroboration of other work suggesting that emission from amorphous carbon films is primarily due to geometrical field enhancement by nanostructures inside the film. Some counter-arguments to the internal-field-enhancement hypothesis are considered and disposed of. Some advantages of ENH materials as broad-area field emission electron sources are noted; these include control of material design.
Silicon Field Emission Arrays Coated with CoSi2 Layer Grown by Reactive Chemical Vapor Deposition
Authors: Han Byung Wook , Rhee Hwa Sung , Ahn Byung Tae , Lee Nam Yang
Published: April 2011

We prepared Si emitters coated with an MOCVD CoSi2 layer to improve the emission properties. The CoSi2 layer was grown in situ by reactive chemical vapor deposition of cyclopentadienyl dicarbonyl cobalt at 650 °C. The CoSi2 layer was conformally coated on the Si emitter tips and had a twinned structure at the epitaxial CoSi2/Si interface. The CoSi2-coated Si emitters showed an enhanced emission due to the increase of the number of emitting site from Fowler-Nordheim plot. The fluctuation of emission current was reduced by CoSi2 coating. But the long-term stability was not much improved.
Large and Stable Field-Emission Current from Heavily Si-Doped AlN Grown by MOVPE
Authors: Kasu Makoto , Kobayashi Naoki
Published: April 2011

We investigated electron field emission (FE) from heavily Si-doped AlN grown by metalorganic vapor phase epitaxy. We found that, as the Si-dopant density increases, the threshold electric field decreases, which indicates that electrons are supplied to the surface effectively as a result of Si doping. We show that heavily Si-doped AlN has a maximum FE current of 347 μA (the maximum current density of 11 mA/cm2), stable FE current (fluctuation: 3%), and a threshold electric field of 34 V/μm. We observed visible light emission (luminance: about 1200 cd/m2) from phosphors excited by the field-emitted electrons.
Silicon Field Emitter Array by Fast Anodization Method
Authors: Fung Y.M. , Cheung W.Y. , Wilson I.H. , Xu J.B. , Wong S.P.
Published: April 2011

A new fast fabrication method entailing, two step anodization of silicon with different HF solutions was used to form a high aspect ratio silicon Field Emitter Array on n-type silicon (resistivity of 0.01cm). A Silicon oxide mask was used to define the field emitter array. The silicon substrate was pre-anodized with low current density for 1 minute in the dark and then anodized in HF:H2O:Ethanol solution. Finally, the porous silicon was removed by isotropic solution etching. The turn-on voltage of the fabricated field emitters was approximately 27V/μm when the emission current density reaches 1μA/cm2. This compares with the turn-on field of about 35V/μm on silicon tip array fabricated by using an isotropic etching solution of HNO3. We obtained field emitter arrays with good uniformity and reproducibility.
Field Emission Structure with Shottky-Barrier Electrode
Authors: Genelev Andrey P. , Levitsky Alexey A. , Zasemkov Vladimir S.
Published: April 2011

We analyze a non-traditional version of semiconductor field emission structure, based on silicon cones arrays and destined for application in low-voltage vacuum microelectronics devices. In proposed construction, the gate electrode is used as Shottky-barrier contact on silicon tips. Due to Shottkybarrier contact we have obtained depletion layer in tip body under the gate electrode. Therefore variation of the gate electric potential provides the emitter current modulation. Experimental structures were fabricated with about 28000 silicon cones per 1 mm2 by reactive ion etching through a silica mask. Using a quasi two-dimensional model, we have computed these emitter structures. The model takes into account non-uniformity of silicon cone cross-section. Here, we study the influence of emitter tips parameters on the structure performance. Initial results prove the possibility of cathode current electric control with the gate electrode potential. Additionally we have obtained some other electric parameters of the emitter with the Shottky-barrier contact. The results of numerical analysis and experimental study provide a guide for design of proposed field emitter structure.
Field emission from heterostructured nanoseeded diamond and nanocluster carbon cathodes
Authors: Satyanarayana B.S. , Nishimura K. , Hiraki A. , Milne W.I.
Published: April 2011

Novel heterostructured cold cathodes made of nanoseeded diamond and cathodic arc process grown nanocluster carbon films, were studied. The nanocrystalline diamond with varying diamond concentration was first coated on to the substrate. The nanocluster carbon films were then deposited on the nanoseeded diamond coated substrates using the cathodic arc process at room temperature. The resultant heterostructured microcathodes were observed to exhibit electron emission currents of 1μA/cm2 at low fields of 1.2 - 5 V/μm. Further some of the samples seem to exhibit I-V characteristics with a negative differential resistance region at room temperature conditions. This negative differential resistance or the resonant tunneling behaviour was observed to be dependent on the nanoseeded diamond concentration.
Work function of carbon nanotubes
Authors: Shiraishi Masashi , Ata Masafumi
Published: April 2011

The work functions of multi- and single-walled carbon nanotubes are found to be 4.95eV and 5.10eV respectively. The measurements were carried out using the photoelectron emission (PEE) method, which allows easy and precise measurements to be made in air. We have found that the work function of the nanotubes is 0.1–0.2eV larger than that of highly oriented pyrolytic graphite (HOPG) of which the valence state is σ–Φ orthogonal. This result is ascribable to reflection of the σ–Φ⊏ mixed valence state in the case of carbon nanotubes. The experimental data were well reproduced in ab-initio calculations on planar and cylindrical conjugated states.
Monte Carlo Simulation of Amphiphile Self-Assembly during Dip Coating
Authors: Rankin Stephen E. , Malanoski Anthony P. , van Swol Frank
Published: April 2011

Fascinating nanostructured porous materials have recently been synthesized by evaporation-driven coassembly of ceramic precursors and amphiphiles. To expand our understanding of this process, we examine the influence of interfaces on self-assembly process using equilibrium lattice-based Monte Carlo simulations of ternary amphiphile-solvent mixtures. The simulations are able to predict the existence of all significant lyotropic mesophases, including lamellae, hexagonal closepacked cylinders, and cubic phases such as the gyroid. In the presence of walls that attract the majority solvent, the amphiphiles are confined to a smaller region of space, and experience a higher local concentration than the bulk concentration. This can lead to early transitions between mesophases. On the other hand, when the surface repels the majority solvent, amphiphiles tend to adsorb at the walls, and the local effective concentration in solution is lower. This can delay mesophase formation. When the amphiphile concentration is high enough that mesophases form in the bulk solution, however, either type of strongly attracting wall will align the mesophase (lamellae or hexagonal channels) parallel to the walls. In contrast, neutral walls (with no preferential interaction with either component) align mesophases perpendicular to themselves, which could be an interesting route to pores aligned normal to a film.
Nanosphere Lithography: Self-Assembled Photonic and Magnetic Materials
Authors: Haes Amanda J. , Haynes Christy L. , Van Duyne Richard P.
Published: April 2011

Early work with size-tunable periodic particle arrays (PPAs) fabricated by nanosphere lithography (NSL) demonstrated that the localized surface plasmon resonance (LSPR) could be tuned throughout the visible region of the spectrum. Further developments of the NSL technique have produced a myriad of nanoparticle configurations. Presented in this paper are several array types and examples of their utility in current applications. Both the sensitivity and tunability of the LSPR have been firmly established using single layer PPAs. Magnetic force microscopy (MFM) has been used to show that double layer PPAs act as single domain magnets and give strong MFM contrast. Angle-resolved NSL has produced nanogap and nano-overlap structures with manipulation resolution of one nanometer. Nanowell structures extend the original twodimensional structure into the third dimension. Exploitation of this flexible, materials-general NSL technique allows for investigation of the catalytic, electrochemical, magnetic, optical and thermodynamic properties of nanoparticles.
New Method For First Principles Modeling of Electron Transport through Nanoelectronic Devices.
Authors: Brandbyge Mads , Stokbro Kurt , Taylor Jeremy , Mozos Jose-Luis , Ordejón Pablo
Published: April 2011

In this paper we present a new theoretical method for modeling electron transport through nanostructures under non-equilibrium conditions. The electronic structure of the nanostructures are modeled from first principles and are described selfconsistently under the non-equilibrium conditions by means of a Green's function technique. The method is used to calculate the electron transport through benzene-dithiolate connected to two gold chains.
Sub-100 nm Patterning of Aluminum Film by AFM Local Oxidation
Authors: Notargiacomo Andrea , Foglietti Vittorio , Evangelisti Florestano
Published: April 2011

We have investigated the local oxidation of an aluminum film to fabricate aluminum and aluminum oxide masks on Si and SiGe substrates. The local oxidation is made by negatively biasing the probe of an atomic force microscope operating in contact mode. The masks are defined by removing the unwanted material using highly selective etching solutions at room temperature. The produced aluminum-based masks can withstand reactive ion etching processes using fluorinated gases mixtures. We report examples of sub-100 nm pattern transfer on the substrate using the AFM fabricated masks. Preliminary observations suggest to use the sputtered aluminum films for which the anodization is found more efficient than for e-beam evaporated aluminum.
Growth Mechanism of Chains of Silicon Nanocrystallites
Authors: Kohno Hideo , Tanaka Koji , Takeda Seiji
Published: April 2011

The growth mechanism of chains of silicon nanocrystallites was investigated. Energy-filtered transmission electron microscopy observations provided strong evidence that the chains were formed as a result of surface oxidation of silicon nanowires. In addition, the periodic instability in the wetting property of molten catalysts was simulated numerically.
Chemical stability studies of thermally-carbonized porous silicon
Authors: Salonen J. , Lehto V-P. , Björkqvist M. , Laine E. , Niinistö L.
Published: April 2011

We have studied chemical stability of thermally-carbonized porous silicon (PS). The initial hydrogen termination of PS has been replaced by carbon using thermal dissociation of acetelyne molecules. This kind of carbonized surface has been found to be at least as stable in humid atmosphere as a thermally-oxidized PS surface. It is also found to be stable in an aqueous KOH and HF. In-vitro studies of tissue compatible in simulated human fluid indicate improved stability and that the carbonized surface could be bioactive.
Diffusion Length Measurements of Minority Carriers in Si-SiO2Using the Photo-Grating Technique
Authors: Posada Y. , Balberg I. , Fonseca L.F. , Resto O. , Weisz S.Z.
Published: April 2011

We have studied the microstructure, the transport and the phototransport properties of the Si crystallites network in Si-SiO2composites. We have found that in our co-sputtered samples the average crystallite diameter, d, decreases from 40 to 5 nm as the content of the silicon, x, decreases from 80 to 40 volume%, and that the percolation of the network sets is at x ≈ 40 vol%. A simultaneous study of the photoluminescence (PL) shows the, quantum confinement, expected red shift of its peak with increasing d. On the other hand the very strong observed decrease of the PL intensity with x is interpreted here as due to a deconfinement effect that is dominated by the increase in the cluster size of connected Si crystallites. The results suggest that a closed random packing of the Si crystallites will be the preferred network for high intensity electroluminescence.
Modeling Carrier Transport in Oxide-Passivated Nanocrystalline Silicon Leds
Authors: Hirschman Karl D. , Fauchet Philippe M.
Published: April 2011

This report presents an investigation on carrier transport in LED structures based on oxide passivated nanocrystalline silicon (OPNSi), formed by oxidation of porous silicon. This material, like its precursor, can luminesce quite efficiently while demonstrating several advantages in stability (i.e. chemical, thermal, electrical and electroluminescence). OPNSi can be best described as a porous glass structure with defects that facilitate transport, and remaining embedded nanocrystals of silicon that support light emission. Although this study does not provide a direct measurement of the density of states in OPNSi, the following transport study suggests a high density of states having a broad energy distribution that readily exchange charge with the silicon electrodes. Experimental data also suggests the existence of deeper trap centers that do not facilitate transport, yet influence transport behavior significantly. The device operation is explained by bipolar injection from an electron-injection cathode and a hole-injection anode into the semi-insulating OPNSi layer. The device is modeled as a “field effect diode”, where untraditional concepts are applied in the interpretation of experimental observations. Extensive electrical characterization of OPNSi LEDs has lead to the development of a comprehensive transport model that is self-consistent with all experimental observations.
Prorerties of Nanostructured Porous Semiconductors Studied Via Noise Spectroscopy
Authors: Parkhutik Vitali
Published: April 2011

Formation of porous layers via localized corrosion of semiconductors is a reliable method to produce nano-structured semiconducting materials. The formation process is assisted by strong fluctuations (noise) of the anodic potential or current applied to the corroding material. Electrical and optical characteristics of nanoparticles are also quit noisy. The noise is a result of heterogeneity of the electrochemical reactions involved into the formation of pores and pits, transient phenomena in the formed porous layers, their exchange by energy with environment, etc. Therefore, analyzing the noise would be useful to understand the nature of the formation processes and properties of nanoparticles.

Here we present the results of studying the formation of porous silicon and electrical properties of the formed porous layers with the help of so-called Flicker-Noise Spectroscopy (FNS), method allowing to quantify and analyze the information contained in noisy signals. The method is different from existing approaches in that it allows not only to represent the noisy signals but estract physically meaning information from them. It is shown that using the FNS approach one can extract useful information on the kinetics of the electrochemical and electrical processes.
Analyses of Ballistic Electron Transport in Nanocrystalline Porous Silicon
Authors: Kojima Akira , Sheng Xia , Koshida Nobuyoshi
Published: April 2011

The characteristics of ballistic electron transport in porous silicon (PS) are investigated in terms of the electron emission from PS diodes and the energy distribution of emitted electrons. The energy distributions show a behavior of ballistic electron emission that is quite different with the Maxwellian distribution. This is clearly observed at low temperatures below 150 K where the electrical conduction in PS is dominated by the tunneling mode. At 100 K, the peak position of distribution curve becomes more close to the energy corresponding to the energy gain expected from ballistic transport without any scattering losses. The simulated energy distribution suggests that the electrons having higher energies in a non-equilibrium state travel ballistically in PS via field-induced tunneling process. These results support that electrons can travel ballistically in nanocrystalline layer under a high electric field. The observed ballistic transport indicates the further technological potential of silicon nanocrystallites.
A Novel Solid-State Light-Emitting Device Based on Ballistic Electron Excitation
Authors: Nakajima Y. , Kojima A. , Koshida N.
Published: April 2011

The concept of a novel solid-state light-emitting device is proposed on a basis of our previous report that the nanocrystalline porous silicon (PS) diode with a well-controlled structure operate as an efficient ballistic electron emitter. This device is composed of a semitransparent thin Au film, a fluorescent thin film, a PS layer, and n-type Si substrate. When a positive bias voltage is applied to the Au electrode, visible luminescence is emitted of which band corresponds to that of the deposited fluorescent material. The optoelectronic characteristics suggest that the light emission is based on direct excitation of fluorescent film by ballistic electrons generated in the PS layer. This result indicates another possibility of nanocrystalline silicon for photonic applications.
Photoluminescence from amorphous SiO2/Silicon/amorphous SiO2single quantum well structures
Authors: Wang Y.Q. , Ishikawa Y. , Shibata N.
Published: April 2011

Amorphous silicon dioxide/silicon/amorphous silicon dioxide single quantum well structures were fabricated by oxygen implantation followed by thermal oxidation. No photoluminescence (PL) was observed from the as grown samples. We found that annealing in hydrogen allows the single quantum well (SQW) structures to emit two-peak (blue and yellow) PL at room temperature (RT). The blue PL (2.9 eV) does not change with the thickness of Si layers or the temperature. The yellow peak varied from 2.0 eV to 2.4 eV with thinning of the Si layer from 5 nm to 0.5 nm. Lowering the temperature also changed the yellow peak position of the 1.5 nm Si-SQW structure from 2.3 eV (RT) to 2.6 eV (8.4 K). We conclude that the blue PL is from SiO2 and the yellow PL is caused by a recombination process in the Si-SQW.
The Effect of Surface Roughness on Photoluminescence of Porous Silicon
Authors: Ogawa Shunsuke , Uehara Nobutomo , Ohmukai Masato , Tsutsumi Yasuo
Published: April 2011

We studied the effect of surface roughness of Si wafers on porous silicon by means of photoluminescence (PL), Fourier transformed infrared (FTIR) absorption and Raman spectroscopy. We prepared several kinds of Si wafers with a different surface roughness, and then the anodization was performed at a same condition. PL spectra show a blue shift with the increase of surface roughness. The particle size of porous silicon nanostructure becomes the smaller with increasing surface roughness at the same time. On the other hand, FTIR absorption spectra show no difference regardless of surface roughness. The PL emission dependent on the surface roughness originates from a quantum size effect. We infer that the surface roughness causes the concentration of the current during anodization in the area where the radius of the curvature at the surface is small.
A novel, nanocrystal (nc) based non-volatile memory device
Authors: Blauwe Jan W. De , Green Marty L. , Sorsch Tom W. , Weber Garry R. , Bude Jeff D. , Kerber Andi , Klemens Fred , Kim Young , Ostraat Michele L. , Flagan Richard C. , Atwater Harry A.
Published: April 2011

This paper describes the fabrication, and structural and electrical characterization of a new, aerosol-nanocrystal floating-gate FET, aimed at non-volatile memory (NVM) applications. This aerosol- nanocrystal NVM device features program/erase characteristics comparable to conventional stacked gate NVM devices, excellent endurance (>105 P/E cycles), and long-term non-volatility in spite of a thin bottom oxide (55-60Å). In addition, a very simple fabrication process makes this aerosol-nanocrystal NVM device a potential candidate for low cost NVM applications.
AC Operation of GaN:Er Thin Film Electroluminescent Display Devices
Authors: Heikenfeld J. , Steckl A. J.
Published: April 2011

Thin-film electroluminescence has been obtained from GaN:Er deposited directly on amorphous dielectric layers. Electroluminescent device (ELD) structures consisting of a dielectric/GaN/dielectric were formed on p+-Si substrates. In contrast to previous GaN:Er ELDs which used epitaxial growth conditions on crystalline substrates and were operated under DC bias, these ELDs were operated under AC bias. A maximum luminance value of 300, 60, and 15 cd/m2 has been achieved from GaN:Er and AlGaN:Er AC-ELDs biased at 180 V and 100, 10, and 1 kHz, respectively. The emission spectra, which originate from Er3+ 4f-4f transitions, consist of dominant visible emission at ∼537/558 nm and infra-red (IR) emission at 1.5 μm. A violet emission peak at 415 nm indicates that hot carriers can gain up to ∼3 eV energy for an applied voltage corresponding to 1.5 MV/cm applied field. The emitted intensity initially increases linearly with frequency, followed by a trend towards saturation. The frequency for 3 dB reduction from the linear relation is at ∼65 kHz for visible emission and ∼8 kHz for infrared emission. The saturation trends can be explained in terms of the spontaneous emission lifetimes of the visible (∼10 μs) and IR (∼1ms) Er3+ emissions.
Electrical Properties of InN Grown by RF-MBE
Authors: Saito Yoshiki , Teraguchi Nobuaki , Suzuki Akira , Yamaguchi Tomohiro , Araki Tsutomu , Nanishi Yasushi
Published: April 2011

InN films with excellent surface morphology were grown by controlled the V/III ratio of InN epitaxal layer. It was found they were single crystal of InN films with wurtzite structure by X-ray diffraction (XRD) measurement and reflection high-energy electron diffraction (RHEED) observation. Hall mobility as high as 760 cm2/Vs was achieved for InN film grown at 550°C with 240 W of RF plasma power with a carrier density of 3.0×1019 cm−3 at room temperature. To our knowledge, this electron mobility is the highest value ever reported.
Profiling electric fields in GaN/InGaN/GaN single quantum wells by electron holography
Authors: Cai Juan , Mccartney M. R. , Ponce F. A.
Published: April 2011

We use electron holography to profile the local internal potential due to spontaneous polarization and piezoelectric effects in strained quantum well structures of wurtzitic group III nitrides. Profiles of the electrostatic potential across a GaN/InxGa1−xN/GaN quantum well structure show the existence of internal electric fields of about –2.2 ± 0.6 MV/cm, and a potential drop across the quantum well of 0.6 ± 0.16 V. The electric fields indicate an average indium composition of 15% in the quantum well, for a thickness of 2.7 nm. This indium composition compares well with measurements by energy-disperse spectroscopy of 18 ± 2 %. Screening effect is not observed under these experimental conditions.
Group-III Nitride Quantum Heterostructures Emitting in the whole Visible Range
Authors: Grandjean Nicolas , Damilano Benjamin , Massies Jean
Published: April 2011

Group-III nitride quantum wells (QWs) and quantum dots (QDs) have been grown by molecular beam epitaxy (MBE). Their optical properties are shown to be governed by the presence of a huge internal polarization field. For example, GaN/AlN QDs emit from the blue to the orange due to the giant quantum confined Stark effect (QCSE) induced by a built- in electric field of 4 MV/cm. Another consequence of the QCSE is to drastically reduces the oscillator strength of the ground state transition and thereby to increase by several orders of magnitude its radiative lifetime. Despite the very large density of dislocations in nitride layers, which induce non-radiative recombinations, carrier localization enhances the photoluminescence (PL) efficiency. This is demonstrated by GaN/AlN QDs grown on silicon substrates exhibiting strong PL intensity at room temperature. InGaN/GaN QWs with In composition of 20% also display 300 K PL peaking through the whole visible spectrum (0.4-0.66 νm). This is achieved by varying the QW thickness from 1.5 to 5.5 nm, the red-shift resulting from an internal electric field of 2.5 MV/cm. For InGaN/GaN QWs emitting at 2.8-2.9 eV, the PL efficiency at 300 K is larger than 10 %. This is ascribed to carrier localization, which is not due to InGaN phase separation that would form QDs, as revealed by transmission electron microscopy. Another origin of the carrier localization in InGaN/GaN QWs is then discussed.
Effect of N2 Plasma Treatments on Dry Etch Damage in n- and p-type GaN
Authors: Kent D.G. , Lee K.P. , Zhang A.P. , Luo B. , Overberg M.E. , Abernathy C.R. , Ren F. , Mackenzie K.D. , Pearton S.J. , Nakagawa Y.
Published: April 2011

The extent of damage recovery by N2 plasma treatment of previously damaged n- and p-GaN has been examined using current-voltage (I-V) characteristics from Schottky diodes. There are two contributions to the observed improvement in the I-V characteristics, namely a simple annealing effect and also a chemical effect from reactive nitrogen. However the N2 plasma treatment does not fully restore the initial electrical properties of the near-surface region.
Microstructure of GaN Grown on (1120) Sapphire
Authors: Ruterana P. , Wickenden A. E. , Twigg M. E. , Koleske D.D. , Henry R. L. , Tottereau O.
Published: April 2011

Most of the work done on GaN has taken into account layers grown on the (0001) sapphire. However one would expect the growth on (1120) to lead to different structural defects. As has been shown, in one direction, the mismatch is rather small. In this work, we have carried out structural analysis of layers and interfacial relationship. Inside the layers, the density of defects is comparable to that found conventionally in layers grown on top of (0001) sapphire. The growth mode is also mosaic with a grain size of a few microns. One interesting result is the interface structure, which differs from conventional growth where a flat or stepped interface is formed with a large distance between steps. In this case, the interface is found to be rough at the atomic scale so that this roughness has a random distribution. Moreover, the misfit dislocation spacing is 1nm which is only half the dislocation spacing found in GaN growth on (0001) sapphire.
Fabrication of GaN layer with Low Dislocation Density using Facet controlled ELO technique
Authors: Miyake H. , Mizutani H. , Hiramatsu K. , Iyechika Y. , Honda Y. , Maeda T.
Published: April 2011

GaN layers with low dislocation density have been fabricated be means of facet-controlled epitaxial lateral overgrowth (FACELO) via low-pressure metalorganic vapor phase epitaxy (LP-MOVPE). The distribution of the dislocations in FACELO GaN was inspected by observation of InGaN growth pits. For FACELO with {11-20} facets as the first step, the dislocations concentrate only in the window region. For FACELO with {11-22} facets as the first step, the dislocations exist only in the coalescence region. The double FACELO, which was FACELO with {11-20} on FACELO with {11-22}, was demonstrated and dislocation density of less than 105 cm−2 was achieved.
Effect of Thermal Annealing on the Photoluminescence Properties of a GaInNAs/GaAs Single Quantum Well
Authors: Grenouillet Laurent , Bru-Chevallier Catherine , Guillot Gérard , Gilet Philippe , Ballet Philippe , Duvaut Philippe , Chenevas-Paule Andrè , Million Alain
Published: April 2011

We report on the effect of thermal annealing on the photoluminescence properties of a Ga0.65In0.35N0.02As0.98/GaAs single quantum well. Thermal annealing is shown to decrease the strong nitrogen-induced localization effects observed at low temperatures and to reduce the full width at half maximum of the emission peak. It also induces a strong blue shift of the emission peak energy, which is thought not to arise from an In-Ga interdiffusion alone, as it is much larger than in a nitrogen-free reference single quantum well.
Photoluminescence Studies of p-type GaN:Mg Co-doped with Oxygen
Authors: Korotkov R. Y. , Gregie J. M. , Wessels B. W.
Published: April 2011

The low temperature photoluminescence (PL) of Mg-doped GaN co-doped with oxygen is investigated. Two PL bands are observed at low temperature at 2.5 and 2.8 eV in the p-type oxygen co-doped samples. Both the 2.5 eV and 2.8 eV bands are attributed to donor-acceptor (DA) transitions involving deep donors of different origin and a shallow MgGa acceptor. The integrated intensity of the 2.8 eV band in p-type GaN decreases as the oxygen partial pressure is increased. The decrease is attributed to reduced compensation by deep native donors. The two bands are not formed in n-type (n > 1019 cm−3) GaN:Mg over-doped with oxygen indicating that the deep donors responsible for these transitions have high formation energies in n-type material.
Group III-Nitride Based VCSEL for Applications at the Wavelength of 400nm
Authors: Linnik M. , Christou A.
Published: April 2011

Short wavelength Vertical Cavity Surface Emitting Laser based on the group III nitrides, GaN, AlN, InN, and their ternary alloys is reported. Optical properties such as band gap and index of refraction of the nitride binary compound were calculated based on the fitting of the experimental data and the first principle calculations. The ternary alloy optical properties were determined in the same manner but based on the binary compound data. The active region containing InGaN strained multiple quantum wells is formed between two Distributed Bragg Reflectors. GaInN/AlN material systems are shown to be the most suitable for highly reflective Bragg mirrors with minimized number of layers. LiGaO2 substrate is proposed for GaN growth due to its small lattice mismatch with GaN (about 0.9%) and its ability to provide a good thermal matching between the two materials. We report VCSEL calculations on threshold current and emission spectra.
A Generalized Roosbroeck-Schockley Relation for III-Nitrides in Far-from-Equilibrium Conditions
Authors: Vasconcellos A. R. , Luzzi R. , Rodríguez C. G. , Freire V. N. , Costa A. P. da
Published: April 2011

We consider the behavior of the absorption coefficient and luminescence spectrum in the steady state when III-nitrides semiconductors (compounds GaN, AlN, and InN) are in far-fromequilibrium conditions created by an electric field. We analyze the high frequency part of the spectra obtaining a generalization of the Roosbroeck-Schockley relation, δRS(ω, EF), the ratio between the frequency dependent luminescence I(ω) and the absorption coefficient α(ω), for nonequilibrium conditions which are dependent on the electric field intensity EF. We show that the carrier's temperature within a small error is proportional to d ln[δRS(ω, EF)]/dω.
High electron mobility in free-standing GaN substrates
Authors: Saxler A. , Look D. C. , Elhamri S. , Sizelove J. , Cull D. , Mitchel W. C. , Callahan M. , Bliss D. , Bouthillette L. , Wang Sheng-Qi , Sung C. M. , Park S. S. , Lee K. Y.
Published: April 2011

High peak electron mobilities were observed in free-standing c-plane GaN substrates. Two layers, a low mobility degenerate layer and a high mobility bulk layer, were present in these samples. The carrier concentrations and mobilities for the layers were extracted using two methods: 1) magnetic field dependent Hall effect analysis and 2) a simple two carrier model with the assumption that one of the layers is degenerate. In addition, measurements were performed after etching away the degenerate layer. The mobility of the bulk layer is found to peak at nearly 8000 cm2/Vs at 60K using the magnetic field dependent Hall effect data. Record room temperature mobility for bulk GaN of 1190 cm2/V s was measured.
Phonon Lifetimes and Phonon Decay Channels in Single Crystalline Bulk Aluminum Nitride
Authors: Kuball M. , Hayes J.M. , Shi Ying , Edgar J.H.
Published: April 2011

We report on the Raman analysis of the phonon lifetimes and phonon decay channels of the A1(LO), E1(LO) and E2(high) phonons of single crystalline bulk AlN grown by the sublimationrecondensation method. The temperature dependence of the phonon lifetimes was investigated from 10K to 1275K. Our experimental results show that amongst the various possible decay channels, the A1(LO) phonons of AlN decay primarily into two phonons of equal energy (Klemens model), most likely longitudinal-acoustic (LA) phonons. AlN is therefore in great contrast to GaN, where a symmetric decay of the A1(LO) phonons is not possible due to a large energy gap between the acoustic and optical phonon branches. For the E2(high) phonon, we find an asymmetric phonon decay into a high-energy and a low-energy phonon. Possible decay channels of the E2(high) phonon include combinations of E2(low) and acoustic phonons. For the E1(LO) phonons, the temperature dependence of the phonon lifetime is consistent with a symmetric phonon decay. Phonon lifetimes of the A1(LO), the E1(LO) and the E2(high) phonon of 0.75ps, 1.2ps and 2.9ps, respectively, were measured at 10K.
Smoothening of (001) and (111) Cu films epitaxially grown on Si substrates
Authors: Lukaszew Rosa Alejandra , Uher Ctirad , Clarke Roy
Published: April 2011

We report an in-situ study of the MBE growth of Cu films on hydrogen-terminated Si (001) and (7×7) reconstructed Si(111) substrates. Using correlated RHEED and STM data, we find a dramatic smoothing of epitaxial Cu(001) surfaces by annealing the as- grown films in the 120-160oC temperature range and somewhat less so for the Cu (111) films. Our measurements reveal a lower activation energy (0.40 ± 0.04 eV) for inter- terrace mass transport in Cu(001) than for Cu(111) (1.10 ± 0.03 eV) the former possibly influenced by the presence of hydrogen. Scaling analysis of the subsequent Cu growth on the annealed smooth surfaces yields a coarsening exponent of 1/4 for the (001) oriented films while this exponent is 1/3 for the (111) films, providing for the first time experimental data for the same system in these two orientations.
Mechanism of Interfacial Coarsening in Molecular Beam Epitaxy Growth on (001) Surfaces
Authors: Golubovic Leonardo , Moldovan Dorel
Published: April 2011

We theoretically address epitaxial growth on (001) crystalline surfaces symmetry, in the regime when pyramids are formed across the growing interface due to Schwoebel step-edge barriers. We develop a kinetic scaling theory that analytically explains numerous experiments and simulations suggesting that pyramid size grows, via coarsening, as a fourth root of the deposition time. Pyramid dynamics is elucidated in terms of pyramid edges that form a growing self-organized square lattice across the growing interface. The edge lattice of pyramids is disordered by topological defects that are characterized here as dislocations. We show that pyramid coarsening is mediated by climb-motion of the dislocations of the edge lattice.