bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determination of Nano Fluctuations in Surface Oxides of GaSb With Br-IBAE
Authors: Krishnaswami K. , Krejca B. , Vangala S.R. , Santeufemio C. , Allen L.P. , Ospina M. , Liu X. , Sung C. , Vaccaro K. , Goodhue W.D. 
Published: April 2011

ABSTRACTHigh-quality substrates with thin uniform oxide layers are critical to the development of low-power epitaxy-based GaSb electronic and electro-optic devices. In this material system, the thickness and elemental composition of the oxide layers are a strong function of the surface preparation method. Here, a figure of merit for quantifying the thickness and thickness variations of an oxide layer on GaSb has been developed using bromine ion beam assisted etching (Br-IBAE). Furthermore, the overall thickness and composition of the oxide determines the etch depth for a fixed set of Br-IBAE parameters. The etch rate in GaSb was determined to be ∼395nm/min and that of its surface oxides was measured to be between 1.86 to 4.2nm/min. Hence, due to the difference in etch rates, nano fluctuations of the oxide thickness at the oxide surface and at the substrate/oxide interface, result in amplified roughness fluctuations in the etched GaSb substrate. The average roughness of Br-IBAE etched surfaces is used as figures of merit to quantify the uniformity and smoothness of the oxide layer. To demonstrate this, GaSb surfaces with various oxide layers and thicknesses were identically etched and their surface roughness measured using atomic force microscopy (AFM). This novel technique can generally be extended to a number of material systems.
Atomic-scale investigation of the dielectric screening at the interface between silicon and its oxide
Authors: Giustino Feliciano , Pasquarello Alfredo 
Published: April 2011

ABSTRACTWe investigate the dielectric screening across the Si-SiO2 interface using a first-principle approach. By determining the profile of the microscopic polarization and the effective polarizabilities of SiOn (n = 0,‥4) structural units, we show that the variation of the local screening across the interface relates to the chemical grading. The oxide region near the Si substrate shows the same dielectric permittivity as bulk SiO2 as long as the oxide is locally stoichiometric. The suboxide region carries an enhanced permittivity, with a value intermediate between those corresponding to bulk Si and SiO2. The implications of these findings for the scalability of the equivalent oxide thickness in high-κ gate stacks are discussed.
Precise Characterization of Silicon on Insulator (SOI) and Strained Silicon on Si1−xGex on Insulator (SSOI) Stacks with Spectroscopic Ellipsometry
Authors: Sun Lianchao , Fouere Jean-Claude 
Published: April 2011

ABSTRACTFurther improvements in CMOS circuit performance such as switching speed and power reduction will rely on the use of silicon on insulator (SOI) substrates with decreased functional layer thicknesses. According to the International Technology Roadmap for Semiconductors (ITRS), the silicon and buried SiO2 (BOX) layer thicknesses for a fully depleted device should be in the ranges of 10–16nm and 24 – 40nm by 2005, respectively. A key issue for fully-depleted CMOS transistors is control of such ultra-thin layer thicknesses and their uniformity along with other parameters such as surface and interface roughness. This poses a challenge to metrology, especially to conventional reflectometry technique because the layer thicknesses must be determined with angstrom precision for both silicon cap and SiO2 box layer.Spectroscopic ellipsometry (SE) is an optical and non destructive technique for determining thin film thickness and material optical properties. Because ellipsometry measures the change in the polarization state for both the amplitude ratio of the p to s polarizations, and in the phase retardation, it provides a precise way to characterize such ultra thin SOI stacks. Comprehensive characterization results for a number of thin and ultra thin SOI stacks with different thickness ranges will be presented together with measurement repeatability results relevant to the film thickness process tolerances. In addition, characterization results for advanced device applications such as strained silicon-on- Si1−xGex-on-insulator (SSOI) will also be shown, demonstrating the use and capability of spectroscopic ellipsometry for precise determination of layer thickness, material composition, interfacial layers, etc. Principles and advantages of the technique will also be discussed in the presentation.
A New Mechanistic Diagram for Molecularly Imprinted Polymers
Authors: Spivak David A. 
Published: April 2011

ABSTRACTA new mechanistic diagram describing the non-covalent molecular imprinting process is put forth in the text. A significant consequence of the new mechanistic picture is that the pre-polymer complex structure does not necessarily reflect the structure of the final binding sites in the polymer. Two independent studies are presented in combined form that support the suggested changes to the mechanistic diagram. In the first study, the maximum number of functional groups surrounding the template molecule in solution are shown to be less than the average number of functional groups in the binding sites of the polymers. In the second study, shape selectivity is shown to be an important contributor to molecular recognition by the imprinted polymers; which is significant because contributions of shape cannot be predicted by the solution phase pre-polymer complex.
Development of a high throughput synthesis technique for the optimization of MIPs for 17β-Estradiol
Authors: Dirion B. , Schillinger E. , Sellergren B. 
Published: April 2011

ABSTRACTA high throughput synthesis technique was developed for the combinatorial optimization of polymers imprinted with 17□-Estradiol. This incorporated a liquid handling robot for the rapid dispensing of monomers, templates, solvents and initiator into the reaction vessels of a 96-well plate. A library of 80 polymers, each ca 80mg, was prepared using functional monomers containing acid functionalities (methacrylic acid (MAA), trifluoromethylacrylic acid (TFMAA)), basic functionalities (2-vinylpyridine (2-Vpy), 4-vinylpyridine (4-Vpy), diethyl-2-aminoethylmethycrylate (DEAEMA)) or neutral functional groups (2-hydroxyethylmethacrylate (HEMA), methacrylamide (MAAM), N-vinylpyrrolidone (NVP), acetoxystyrene (AST)). Four replicas each of imprinted and nonimprinted polymers were made for each functional monomer using ethyleneglycoldimethacrylate (EDMA) as crosslinking monomer and acetonitrile as solvent. Polymer washing and exchange of incubation solutions could be effectively carried out after transfer of the polymers to solvent resistant filter plates. The binding properties of the polymers could then be rapidly assessed in the batch mode by quantifying non-bound fractions in parallel using a fluorescence monochromator plate reader. These data showed an acceptable agreement with the data from a corresponding HPLC evaluation of the rebinding solutions. In agreement with other reports, the acid functional monomers MAA and TFMAA, the basic DEAEMA and the neutral MAAM exhibited the highest imprinting factors.
Phase Inversion Molecularly Imprinting of Uracil Targeted Membranes Made of Polyacrylonitrile Copolymers Having Methacrylic Acid and Acrylic Acid Segments for Recognition and Permselective Binding
Authors: Xia Shao Ling , Wang Hong Ying , Kobayashi Takaomi 
Published: April 2011

ABSTRACTPolyacrylonitrile having methacrylic acid [P(AN-co-MAA)] and acrylic acid [P(AN-co-AA)] was used for phase inversion imprinting of uracil (URA). Resultant imprinted membranes had porous morphology and showed permselective binding of URA, when 32 μM URA aqueous solution was permeated under pressure gradient of 100 Pa across the membrane. Under the circumstance, the imprinted P(AN-co-MAA) membrane bound 7.9 μmol/g of URA with 8.4×10−6 m3/m2·s of volume flux. The imprinted P(AN-co-AA) membrane showed loose selectivity relative to the P(AN-co-MAA) membrane. Binding behavior of URA and dimethyluracil (DMURA) was also compared in both imprinted membranes. Evidence was presented that P(AN-co-MAA) with methacrylic segments was effective for URA imprinting and resulted in high URA selectivity in the permselective binding experiments.
Control of Morphology and Growth Direction of Gallium Nitride Nanostructures
Authors: Bae Seung Yong , Seo Hee Won , Park Jeunghee 
Published: April 2011

ABSTRACTVarious shaped single-crystalline gallium nitride (GaN) nanostructures were produced by chemical vapor deposition method in the temperature range of 900–1200 °C. Scanning electron microscopy, transmission electron microscopy, electron diffraction, x-ray diffraction, electron energy loss spectroscopy, Raman spectroscopy, and photoluminescence were used to investigate the structural and optical properties of the GaN nanostructures. We controlled the GaN nanostructures by the catalyst and temperature. The cylindrical and triangular shaped nanowires were synthesized using iron and gold nanoparticles as catalysts, respectively, in the temperature range of 900 – 1000 °C. We synthesized the nanobelts, nanosaws, and porous nanowires using gallium source/ boron oxide mixture. When the temperature of source was 1100 °C, the nanobelts having a triangle tip were grown. At the temperature higher up to 1200 °C the nanosaws and porous nanowires were formed with a large scale. The cylindrical nanowires have random growth direction, while the triangular nanowires have uniform growth direction [010]. The growth direction of the nanobelts is perpendicular to the [010]. Interestingly, the nanosaws and porous nanowires exhibit the same growth direction [011]. The shift of Raman, XRD, and PL bands from those of bulk was correlated with the strains of the GaN nanostructures.
Surface States in Passivated, Unpassivated and Core/Shell Nanocrystals: Electronic Structure and Optical Properties
Authors: Bryant Garnett W. , Jaskolski W. 
Published: April 2011

ABSTRACTSurface effects significantly influence the functionality of semiconductor nanocrystals. A theoretical understanding of these surface effects requires models capable of describing surface details at an atomic scale, passivation with molecular ligands, and few-monolayer capping shells. We present an atomistic tight-binding theory of the electronic structure and optical properties of passivated, unpassivated and core/shell nanocrystals to study these surface effects.
Degree of Asymmetry of CdSe Quantum Dots Grown in Glass Probed by Four Wave Mixing
Authors: Filin A. I. , Babocsi K. , Schmitt M. , Persans P. D. , Kiefer W. , Kulakovskii V. D. 
Published: April 2011

ABSTRACTInformation about quantum dot (QD) asymmetry is derived by analyzing the polarization properties of the time-integrated four wave mixing (FWM) signal. The lowering of QD symmetry results in the splitting of bright J= +/-1 exciton states. This causes the polarization oscillation of circularly excited excitons between these two split states. In a QD ensemble with a random distribution in the exciton level splitting, this results in the decay of the difference in FWM signals observed in scattering of σ+ and σ+ polarized light on the population grating created by two σ+ pulses, the decay time reflecting the degree of QD asymmetry. We have investigated the decay time of the difference in two polarized signals for quantum dots of equal size, grown in a glass matrix under different conditions. Increasing growth temperature and decreasing growth time lead to lowering of QD symmetry. We discuss this experimental result in terms of kinetics of nanoparticle growth in glass.
Vapor-Phase Synthesis and Surface Functionalization of ZnSe Nanoparticles in a Counterflow Jet Reactor
Authors: Sarigiannidis Christos , Petrou Athos , Mountziaris T. J. 
Published: April 2011

ABSTRACTCompound semiconductor nanocrystals (quantum dots) exhibit unique size-dependent optoelectronic properties making them attractive for a variety of applications, including ultrasensitive biological detection, high-density information storage, solar energy conversion, and photocatalysis. There is presently a great need for developing scalable techniques that allow efficient synthesis, size control, and functionalization of quantum dots, without a loss of the desirable optical properties. We report experimental results on the properties and surface modification of ZnSe nanoparticles grown by a continuous vapor-phase technique utilizing an axisymmetric counterflow jet reactor. Luminescent ZnSe nanocrystals were obtained at room temperature by reacting vapors of dimethylzinc:triethylamine adduct with hydrogen selenide, diluted in a hydrogen carrier gas. The two reactants were supplied from opposite inlets of the counterflow jet configuration and initiated particle nucleation in a region near the stagnation point of the laminar flow field. Surface modification of nanoparticles by adsorption of 1-pentanethiol was used to control the rate of particle coalescence. The counterflow jet technique can be scaled up for commercial production and is compatible with other vapor-phase processing techniques used in the microelectronics industry.
Synthesis and Size Control of Luminescent II-VI Semiconductor Nanocrystals by a Novel Microemulsion-Gas Contacting Technique
Authors: Karanikolos Georgios N. , Alexandridis Paschalis , Petrou Athos , Mountziaris T. J. 
Published: April 2011

ABSTRACTA scalable, room-temperature technique for controlled synthesis of luminescent II-VI nanocrystals has been developed by using the dispersed phase of stable, well-characterized microemulsions as templates for nanoparticle synthesis. The microemulsions were formed by self-assembly of poly (ethylene oxide)-poly (propylene oxide)-poly (ethylene oxide) (PEO-PPO-PEO) amphiphilic block copolymer and heptane in formamide. By adjusting the surfactant to dispersed phase ratio, stable microemulsions were obtained with droplet diameter of ∼40nm. These microemulsions avoid problems or rapid droplet-droplet coalescence that hamper reverse micelles and lead to polydisperse particle populations. Luminescent ZnSe quantum dots were synthesized by reacting diethylzinc (dissolved in the heptane dispersed phase) with hydrogen selenide gas (diluted in hydrogen). The gas was bubbled through the microemulsion, dissolved in the formamide, and diffused to the nanodroplet interfaces to react with diethylzinc. The experiments indicate that a single nanocrystal is formed in each nanodroplet by coalescence of clusters (nuclei) and smaller crystals. The energy released during coalescence is sufficient to anneal the clusters into high-quality crystals. The process allows precise control of nanocrystal size by adjusting the initial concentration of diethylzinc in heptane. The “as grown” nanocrystals exhibit size-dependent luminescence, narrow and symmetric emission, good monodispersity (confirmed by TEM analysis), and excellent photochemical stability. The technique is currently being extended to the synthesis of CdSe nanocrystals with promising preliminary results.
Preparation of Tungsten Bronze Nanowires
Authors: Qi Hang , Wang Cuiying , Liu Jie 
Published: April 2011

ABSTRACTTwo simple techniques to prepare tungsten bronze nanowires are reported in this paper. Tungsten bronze nanowires with a diameter of less than 100nm and a length of more than 10 μm have been successfully prepared by employing these techniques. A Vapor-Liquid-Solid (VLS) mechanism has been proposed to explain the growth of these tungsten bronze nanowires.
A Novel Tick Film Nanocrystalline Y2O3:Eu3+ Phosphor Synthesized by Post-Dispersion Treatment at Low Temperature
Authors: Hong Sung-Jei , Kwak Min-Gi , Moon Dae-Gyu , Kim Won-Keun , Han Jeong-In 
Published: April 2011

ABSTRACTIn this study, a novel thick film nanocrystalline phosphor is synthesized by using postdispersion treatment at low temperature. The post-dispersion treatment is to prevent the agglomeration between the precursors by mixing the organic dispersing agent with them before heat-treatment. The mean size of the particle heat-treated at 500°C is 4nm. Also, europium is uniformly distributed in the yttrium oxide with deviation below 0.5%. The nanocrystalline phosphor is principally composed of cubic structure having preferred orientation of <222>, <440>, and <400>. The photoluminescence properties of the nanocrystalline phosphor characterized with monochrometric systems reveals that the main PL peak is detected at 611 nm, and thick film nanocrystalline phosphor with 15wt% europium exhibits better properties.
Quantum Calculations of Carbon Nanotube Charging and Capacitance
Authors: Pomorski Pawel , Pastewka Lars , Roland Christopher , Guo Hong , Wang Jian 
Published: April 2011

ABSTRACTAlthough it has long been known that the classical notions of capacitance are altered at the nanoscale, few first principles calculations of these properties exist for real material systems. With a recently developed ab initio formalism, which combines nonequilibrium Greens function techniques with real-space density functional calculations, we have investigated charging effects for carbon nanotube systems, which are described by the capacitance coefficients. Specifically, the capacitance matrix of two nested nanotube armchair nanotubes, the insertion of one nanotube into another, and the properties of a nanotube acting as a probe over a flat aluminum surface were considered.
Design of Water-Soluble Quantum Dots with Novel Surface Ligands for Biological Applications
Authors: Tetsuo Uyeda H. , Medintz Igor L. , Mattoussi Hedi 
Published: April 2011

ABSTRACTWe have designed a series of organic oligo- and polyethylene glycol (PEG) based surface capping ligands that allow for QD manipulation in aqueous media. We utilized readily available thioctic acid and various oligo- and polyethylene glycols in simple esterification schemes, followed by reduction of the dithiolane to produce multi-gram quantities of capping substrates. Cap exchange of the native trioctyl-phosphine and -phosphine oxide based ligands with the PEG-terminated dithiol-alkyl cap readily resulted in aqueous dispersions of QDs that were homogeneous and stable in various pH ranges over an extended period of time. Mixed surface capping strategies utilizing ratios of dihydrolipoic acid to the pegylated dihydrolipoic acid were also prepared. We anticipate that such systems should allow one to covalently attach amine containing biomolecules to nanoparticle systems bearing carboxylates, employing known coupling agents, such as (dimethylamino) propyl-3-ethyl-carbodiimide (EDC). This design and conjugation strategy may facilitate the development of a new generation of QD-bioconjugates, which can be directly utilized in bio-related applications such as sensing and cellular imaging.
Optimization of Quantum Dot – Nerve Cell Interfaces
Authors: Winter Jessica , Schmidt Christine , Korgel Brian 
Published: April 2011

ABSTRACTNerve cells communicate by passing electrical signals through extensions from their cell bodies. Micron-scale devices such as microelectrode arrays and field effect transistors have already been used to externally manipulate these signals. However, these devices are almost as large as the cell body of the neuron. In order to make functional electrical connections to nerve extensions or their component ion channels that propagate signals, it will be necessary to utilize increasingly smaller components. We propose the use of semiconductor quantum dots, which can be optically activated, as a potential means of perturbing the nerve membrane potentials. As a first step, we have created qdot-neuron interfaces with cadmium sulfide quantum dots. The qdots may be attached to cells either non-specifically or through selected interactions exploiting biorecognition molecules attached to the qdot particle surface. We have investigated the effect of altered synthesis conditions including pH, concentration, reactant ratio, ligand length, ligand R group, and ligand concentration on the nature and quality of qdot-cell binding. We discuss the effect of these altered synthesis conditions on particle fluorescence intensity and color. Additionally, we studied the interaction of these particles with cells and determined that larger particles are more likely to bind non-specifically than smaller particles produced with the same amount of passivating ligand. It is possible this results from reduced surface area coverage of passivating chemical. Finally, we have produced particles passivated with the biorecognition peptide CGGGRGDS in the absence of other chemical stabilizers and characterized their surfaces using NMR and IR.
Growth Structure, and Optical Properties of III-Nitride Quantum Dots
Authors: Morkoç Hadis , Neogi Arup , Kuball Martin 
Published: April 2011

ABSTRACTQuasi-zero-dimensional (0D) semiconductors have been the subject of considerable interest which is stemmed from their unique physical properties which in turn are conducive to devices such as low threshold lasers and light polarization insensitive detectors, in addition to exciting basic physical phenomena. A laboratory analogue of 0D systems is semiconductor quantum dots (QDs) wherein the electronic states are spatially localized and the energy is fully quantized, loosely similar to an atomic system, making it more stable against thermal perturbations. In addition, the electronic density of states near the band gap is higher than in 3D and 2D systems, leading to a higher probability for optical transitions. Furthermore, the electron localization may dramatically reduce the scattering of electrons by bulk defects and reduce the rate of non-radiative recombination. Semiconductor based and metal based dots have been produced, the former via self-assembly and also by lithographic methods in many II-VI, III-V, and group IV semiconductor. The aim of this paper is focused on III-Nitride based quantum dots covering their production and optical properties, as well as reporting on the GaN quantum dots produced by molecular beam epitaxy utilizing standard, ripening, metal spray followed by nitridation methods.
Anisotropy in Thermoelectric Properties of CsBi4Te6
Authors: Chung Duck-Young , Mahanti S. D. , Chen Wei , Uher Citrad , Kanatzidis Mercouri G. 
Published: April 2011

ABSTRACTCsBi4Te6 (ZT ∼ 0.8 at 225 K) shows highly anisotropic features in its crystal morphology and structure as expressed by the parallel infinite [Bi4Te6] rods which are linked via Bi-Bi bonds. Band calculations also point to a significant anisotropy in the carrier effective masses, and for this reason we examined the anisotropic thermoelectric properties of CsBi4Te6. The electrical conductivity, thermopower and thermal conductivity were measured along the three different crystallographic directions of the monoclinic structure of CsBi4Te6. These measurements were performed on samples with different degrees of doping. The strong charge transport anisotropy of these samples was confirmed and also observed that the thermopower values along the c-axis direction (which is perpendicular to the layer of Cs atoms) was negative (-80 μV/K) while those along the needle direction (b-axis) and parallel to the [Bi4Te6] layers (a-axis) were p-type (50–100 μV/K at room temperature. Other anisotropic features in the crystal growth habit, electronic band structure, and electrical and thermal conductivities are also presented.
Electronic Structure and Thermoelectric Properties of AxMo3Sb5Te2
Authors: Soheilnia Navid , Kleinke Holger 
Published: April 2011

ABSTRACTMo3Sb7 may be chemically modified to become semiconducting by replacing two Sb atoms with two Te atoms (per formula unit). This material may be an attractive candidate for the thermoelectric energy conversion, as its thermal conductivity may be lowered by creating the rattling effect upon intercalation of small cations, and its band structure may be tailored, i.e. the band gap size modified. The higher the Te content and the higher the cation amount, the smaller is the band gap, which can virtually reach any value below 0.5 eV.