bluuebunny/crossref_metadata_2025_split huggingface dataset:
Breit-Wigner-Fano Lineshape Analysis of the angential G-band of Metallic Nanotubes
Authors: Brown Sandra D. , Jorio Ado , Corio Paola , Dresselhaus Mildred , Dresselhaus Gene , Kneipp Katrin 
Published: April 2011

AbstractWe present a resonant Raman study of the tangential G-band in metallic SWNTs. By measuring the Raman spectra for isolated SWNTs, we show that the two different lineshapes observed for semiconducting and metallic SWNTs in bundles also occur for isolated SWNTs. A lineshape analysis of the tangential G-band feature for metallic SWNT bundles is presented, showing that only two components are present, the higher frequency component having a Lorentzian lineshape, and the lower one having a Breit–Wigner–Fano (BWF) line-shape. Through comparisons of the Raman tangential G-band spectra from three different diameter distributions of carbon nanotubes, we find that both the frequency and linewidth of the BWF component are diameter dependent.
Structure and Application of Flourinated Carbon Nanofibers
Authors: Hayashi T. , Terrones M. , Kim Y.A. , Nakajima T. , Endo M. 
Published: April 2011

AbstractHigh-resolution transmission electron microscopy (HRTEM) study of heavily fluorinated carbon nanofibers was performed under an ultra high voltage transmission electron microscope (UHVTEM). TEM observation showed rapid transformation of the disordered structure of fluorinated nanofiber to the cylindrical layer structure that is same as the non-fluorinated nanofiber. This observation suggests that electron beam irradiation helps fluorine atoms to dissociate from the carbon atoms. Li-ion secondary battery test cell using fluorinated nanofibers was prepared and the battery performance was tested as a function of cycling.
Single Walled Carbon Nanotubes (SWNTs) as a Gas Sensor
Authors: Pradhan Bhabendra K. , Sumanasekera Gamini U. , Adu Clement K. W. , Romero Hugo , Eklund Peter C. 
Published: April 2011

AbstractA thermoelectric “nano-nose” has been built from tangled bundles of single- walled carbon nanotubes (SWNT). The detector's thermoelectric response [.Delta]S is sensitive to the logarithmic energy derivative of the additional bundle resistivity ([.rho]a) which is identified with the adsorbed molecules. The response is therefore specific to the details of the interaction of the adsorbed molecule with the nanotube wall; even gases such as He, N2 and H2 can be easily detected. Plots of [Δ]S vs. [ρ]a are sensitive to whether oxidation or reduction of the tube wall is taking place, and to whether the gas molecule is physisorbed or chemisorbed. The utility of the sensor stems from the amphoteric nature of the SWNT, the quasi-one-dimensional character of the charge conduction and the high specific surface area of SWNTs.
Electronic and Structural Properties of Carbon Nanotubes Molecular Junction
Authors: Machado M. , Piquini P. , Mota R. , Fazzio A. 
Published: April 2011

AbstractThe electronic and structural properties of finite junctions produced by connecting two C nanotubes, saturated with hydrogens in both edges, are investigated using first-principles calculations, through self-consistent field Hartree-Fock-Roothaan method. The main target of our study is a molecular junction, which connects (10,0) and (6,6) tubes by the introduction of pentagon-heptagon pair defects diametrically opposed in the structure. The charge distributions, the character of the highest occupied molecular orbitals and the densities of states are determined for the finite (10,0) and (6,6) nanotubes and for the formed junction. An energetic analysis is also performed using ab-initio approach and empirical Tersoff potential.
Imaging Oriented Aggregates of Lyotropic Chromonic Mesogenic Dyes by Atomic Force Microscopy
Authors: Schneider Tod , Smith Ashley , Lavrentovich Oleg D. 
Published: April 2011

AbstractWe use a layer-by layer electrostatic assembly technique to obtain aggregates of a chromonic mesogenic dye on mica substrates. The aqueous solutions of dye used for deposition are in the nematic phase. Atomic force microscopy of the dried films reveals that the chromonic molecules adsorb at the charged substrate in the form of ordered aggregates of elongated shape. These elongated aggregates form orientationally ordered arrays. The overall orientation of the array can be changed by shear.
Demonstration of Arrays of Sub-Micrometer Solid-State Fresnel Lenses for Electrons
Authors: Ito Y. , Bleloch A. L. , Brown L. M. 
Published: April 2011

AbstractWe demonstrate the focusing action of a compact solid state pixelated Fresnel phase (PFP) lens for electrons (700 nm in diameter), consisting of an array of holes (“pixelated”) directly drilled by a finely focused electron beam in a thin AlF3 thin film on carbon supporting film. The depths of holes, hence the phase of the exit electron wave is varied as a function of radius from the center of the pattern so that the wavelet from each hole can be in phase on axis at a designated focal point thus producing a lens. An array of two types of lenses, convergent and divergent, with nominal focal length of 1 mm for 200 keV electrons was produced. The estimated full-width-half-maximum of the focus is 8 nm. With improvement of the efficiency, these lenses may find applications in parallel electron-beam lithography, in X-ray optics and in light optics.
FTIR Spectrometry as a Quality Control Method for Surface Engineering of Nanomaterials
Authors: Baraton Marie-Isabelle 
Published: April 2011

AbstractControlled surface engineering of nanopowders cannot be achieved without a specific characterization of the surface chemical groups and the monitoring of the reactions or interactions responsible for the surface modifications. As an example of controlled engineering of nanopowder surfaces, the surface of tin oxide nanoparticles (n-SnO2) is modified by grafting hexamethyldisilazane (HMDS) while the process leading to chemical and electrical modifications of n-SnO2 is monitored in situ by Fourier transform infrared spectrometry. It appears that the effects of the grafting reaction on the surface chemical composition are complex and that a desorption at increasing temperatures leads to strong perturbations of the chemical groups originally grafted on n-SnO2. The present work clarifies the issues related to surface engineering of nanomaterials and elucidates the case of HMDS-grafted n-SnO2.
Chromium Oxide Sub-Micron Particles Fabricated by a Unique Technique: Laser-Induced Solution Deposition
Authors: Zhong Zhenchen 
Published: April 2011

AbstractWe have demonstrated that well-dispersed sub-micron chromium oxide particles can be fabricated by laser-induced solution deposition (LISD) from the solution of CrCl2 solute dissolved in organic solvents containing THF and cyclohexane. The particles are uniform in composition and contain little contamination. The distribution of the particles is narrow in three sizes: 230 nm, 350 nm and 400 nm. We have discussed the kinetics of forming these three kinds of sub-micron particles and the difficulty in obtaining single-phase chromium oxide. We have successfully shown that LISD is a unique technique for fabricating submicron chromium oxide particles with uniform composition and controllable size with narrow particle size distribution. The kinetics (nucleation and growth mechanism) of forming three sizes of particles is discussed.
Characterization of Microcrystalline Si Films by MeV Ion Scattering Techniques
Authors: Bohne W. , Röhrich J. , Selle B. , Birkholz M. , Fenske F. , Fuhs W. , Platen-Schwarzkopf J. , Reinig P. 
Published: April 2011

AbstractRutherford Backscattering Spectroscopy (RBS) and channeling studies with 1.4 MeV−4He ions as well as Heavy-Ion Elastic Recoil Detection Analysis (HI-ERDA) with 230 MeV 129Xe ions have been applied to characterize structural properties and the impurity content of thin Si films. The analytical potential of these ion-beam techniques is demonstrated for two types of samples: (1) μc-Si films prepared by dc magnetron sputtering in a pure Ar plasma and (2) homoepitaxial Si films deposited by low-temperature electron-cyclotron resonance PECVD at the transition from oriented to disordered growth. For μc-Si the atomic area density N.d obtained by RBS was compared with the optical thickness n.d (n=refractive index) derived from the interference structure of IR reflection spectra. It is shown that the ratio R=n.d/N.d of these quantities can serve as a figure of merit for the degree of crystalline order. An apparent similarity was found in the case of the epitaxially grown films between the Si disorder profiles evaluated from the RBS channeling spectra and the hydrogen and oxygen profiles determined by HI-ERDA. This suggests that hydrogen and oxygen are preferentially incorporated in the disordered parts of the films.
Impact of Erbium-Doped Silicon Nanocrystals on the Properties of Polyphenylene Vinylene Films
Authors: Coffer Jeffery L. , Ji Junmin 
Published: April 2011

AbstractThis work describes our initial studies of Er-doped Si nanocrystal/poly(phenylene vinylene) (PPV) composites. Preliminary results have focused on the characterization of these materials via atomic force microscopy (AFM), profilometry, absorption/fluorescence spectroscopies, and current-voltage measurements. A particular point of emphasis here concerns the influence of the Er-doped Si nanocrystals on PPV photoluminescence and carrier transport.
Identification of tetrahedrally coordinated atoms in supercooled liquid silicon
Authors: Brambilla Luigi , Celino Massimo , Cleri Fabrizio , Colombo Luciano , Conversano Roberto , Rosati Mario , Rosato Vittorio 
Published: April 2011

AbstractAn atomic-scale model of liquid silicon has been cooled from high temperatures down in the temperature range between the amorphous and the crystalline melting temperatures by nanosecond scale molecular dynamics simulations with the Stillinger-Weber potential. Tetrahedrally coordinated sites have been identified, in the supercooled liquids, by using a few structural order parameters. The local structure and the stability of these crystalline-like regions (c-type sites and clusters) have been characterized. These have been regarded as candidates for crystalline embryos.
Three-dimensional silicon-based nanostructures in opal matrix: Preparation and properties
Authors: Pevtsov A.B. , Golubev V.G. , Kosobukin V.A. , Kurdyukov D.A. , Medvedev A.V. 
Published: April 2011

AbstractThree-dimensional opal-silicon composites with both direct (a variable extent of filling of opal voids with silicon) and inverted structures have been synthesized. A structural analysis of these fabricated systems is performed. Reflectance spectra from the (111) surface of the composites are measured within the spectral range 400-900 nm. Observed spectral features are interpreted as a manifestation of the [111] direction photonic band gap that is tunable in position and width in the visible and near-infrared spectral ranges.
Electrical transport in porous silicon from improved complex impedance analysis
Authors: Remaki B. , Perichon S. , Lysenko V. , Barbier D. 
Published: April 2011

AbstractAn improved analysis of the electrical transport parameters in meso-porous silicon is presented. Our approach is based on a separate contribution of the crystallites and their interconnections to the total impedance of meso-porous silicon layers. Meso-porous silicon morphology exhibits a columnar structure without quantum confinement. The electrical conduction is thus, partially due to the bulk conductivity within continuous paths of crystallites. The samples were realized on 0.02ω-cm p-type Si substrates. Porous silicon layers of 100µm of thickness and 50% of porosity were inserted in Al/SiO2/porous-Si/Si structures. Their electronic transport parameters were determined using complex impedance measurements. A frequency range of 102 - 107 Hz was used allowing an accurate determination of the impedance components. Combined with thermal stimulation, theses measurements provide a powerful tool for the interpretation of basic properties such as the carriers density in the crystallites and the trapping mechanisms. Our results were interpreted in terms of free carriers conduction in partially compensated crystallites prevailing at low frequencies. At high frequencies (above 10 kHz), the electrical conductivity is mainly controlled by hopping transport on localized states in the chaotic porous structure. Finally, the free carriers mobility, evaluated from SCLC measurement is discussed.
Lateral Superlattices Fabricated with Interferometric Lithography for Nanoscale Device Applications
Authors: Striemer Christopher C. , Fauchet Philippe M. , Tsybeskov Leonid 
Published: April 2011

AbstractTwo-dimensional periodic arrays of inverted pyramid holes with nanometer scale have been patterned on the surface of a (100) silicon wafer and studied for possible application in nanoscale silicon based devices. The surface patterning employed a simple microelectronic processing scheme in which the standing wave intensity pattern from two interfering 458nm laser beams was used to expose holes in a photoresist layer. Subsequent dry etching through an underlying oxide mask layer, followed by a KOH etching step yielded a highly periodic, large area array of inverted pyramids. The pyramid geometry is formed during the anisotropic KOH etch, which stops at the (111) pyramid walls. Therefore, the tips of all inverted pyramids are formed by the intersection of (111) silicon crystal planes and have identical geometry. This study focuses on the use of these features as templates for the controlled crystallization of amorphous silicon layers and also as electric field concentrating “funnels” in MOS-type structures. We will discuss a proposed device in which silicon nanocrystals will be incorporated into the concentrated electric field region at the tip of each inverted pyramid. With this structure, the charging of identical addressable nanocrystals may be possible, leading to the development of practical nanoscale silicon devices.
The Novel Synthesis of Silicon and Germanium Nanocrystallites
Authors: Kauzlarich Susan M. , Liu Qi , Yin Shih-Chieh , Lee Howard W. H. , Taylor Boyd 
Published: April 2011

AbstractInterest in the synthesis of semiconductor nanoparticles has been generated by their unusual optical and electronic properties arising from quantum confinement effects. We have synthesized silicon and germanium nanoclusters by reacting Zintl phase precursors with either silicon or germanium tetrachloride in various solvents. Strategies have been investigated to stabilize the surface, including reactions with RLi and MgBrR (R = alkyl). This synthetic method produces group IV nanocrystals with passivated surfaces. These nanoparticle emit over a very large range in the visible region. These particles have been characterized using HRTEM, FTIR, UV-Vis, solid state NMR, and fluorescence. The synthesis and characterization of these nanoclusters will be presented.
Optical Applications of Macroporous Silicon
Authors: Lehmann Volker 
Published: April 2011

AbstractTwo promising optical applications of macroporous silicon are presented. Due to the high contrast in dielectric constant between the air filled pores and the silicon walls the porous structure exhibits a photonic band gap for infrared radiation perpendicular to the pore axis. By photolithograpic patterning waveguides and optical cavities can be realized in this two-dimensional photonic crystal. Along the pore axis a short-pass filter characteristic is observed for ultraviolet and visible light. Such macropore filters are of high optical quality and may replace conventional filters in imaging systems.
A New Way to Form Three-Dimensional Microstructures by Electrochemical Etching of Silicon
Authors: Kleimann P. , Linnros J. , Juhasz R. 
Published: April 2011

AbstractA new technique of bulk micromachining using anodic etching of (100)-oriented n-type silicon is presented. For particular conditions the transition regime between porous silicon formation and electropolishing enables the formation of high aspect ratio microtips which correspond to inverted macropore structures. This unusual property can be explained by the distortion of current lines near the basis of formed structures. The distortion, which prevents the tip dissolution, is due to the electrical field in the space charge region at the silicon-electrolyte interface. The same property can be used to form three-dimensional microstructures. The position and shape of the structures can be defined by forming steps of a few microns depth, prior tothe electrochemical etching. Then the etching parameters (HF concentration, light intensity, etching current density) are adjusted in order to electropolish the sample except where vertical walls are needed. This enables to form microstructures without a periodic pattern. The feasibility of this technique is demonstrated by forming 100μm wide pores, free-standing beams as well as high aspect ratio micro-needles and micro-tubes.
AlN Acoustic Wave Sensors Using Excimer Laser Micromachining Techniques
Authors: Zhong Feng , Huang Changhe , Auner Gregory W. 
Published: April 2011

ABSTRACTAluminum Nitride (AlN) is a promising piezoelectric material for Acoustic Wave (AW) sensor application due to its high acoustic velocity, linear thermal coefficient and high electromechanical coupling coefficient. Epitaxial AlN thin films were successfully grown on the Sapphire C plane substrate by Plasma Source Molecular Beam Epitaxy (PSMBE). Standard two-port resonator structures were fabricated on the AlN/Sapphire by standard photolithography. Excimer laser micromachining techniques were utilized to fabricate microgroove gratings on the surface of thin film. Beside Surface Acoustic Wave (SAW), Surface Transverse Wave (STW) propagation was also found on the devices with those microgroove and classical metal strip gratings. Laser micromachinined microgroove gratings were found to enhance the propagation of STW. Further, sensors based on STW showed little attenuation in the liquid environment, while sensors based on SAW suffered excess loss when exposed to liquid.
Characterization of GaN MOS Structures Using Photoanodically Grown Oxides with Respect to FET Devices
Authors: Mistele D. , Rotter T. , Ferretti R. , Fedler F. , Klausing H. , Semchinova O.K. , Stemmer J. , Aderhold J. , Graul J. 
Published: April 2011

ABSTRACTPhotoanodically grown Ga2O3 layers were characterized with respect to their suitability as gate dielectrics for GaN based MOSFET Device applications. The Ga2O3 layers were produced in a photoelectrochemical cell using aqueous solutions of KOH. IV characterization of MOS structures show insulating behavior of the oxide layers and CV measurements indicate a small density of states at the oxide/GaN interface. Integrating the wet chemical oxide growth in a MOSFET device fabricating process includes tungsten as gate metal together with H2O2 as etching solution for the gate metal. Source/drain areas were made free of oxide by the alkaline developer of a conventional lithographic step and metallization was done by using the liftoff technique. MOS structures show no inversion mode but strong depletion in reverse biasing mode.
Defect and Stress Control of Algan and Fabrication of High-Efficiency Uv-Led
Authors: Amano H. , Iwaya M. , Nitta S. , Terao S. , Nakamura R. , Ukai T. , Saitoh S. , Kamiyama S. , Wetzel C. , Akasaki I. 
Published: April 2011

ABSTRACTDefects and stress are the most serious issues for growth of AlGaN. Low-temperature deposited (LT -) AlN interlayer between AlGaN and GaN is found to reduce tensile stress during growth, and at the same time suppress the propagation of dislocations having screw components, by which UV-photodetector showing very-low-dark current has been successfully fabricated. However, additional pure-edge dislocations are generated at the LT -interlayer, which resulted in the poor emission property. In addition to the LT -interlayer, lateral growth at the trenched structure was used, thereby achieving crack-free AlGaN and reduction of the density of all types of dislocations in the AlGaN layer. UV light emitting diodes having AlGaN/GaN multi-quantum well active layer was fabricated on the low dislocation density AlGaN. The LED shows strong and sharp UV-emission from GaN-wells.
Fabrication of a High-Power Gan Metal Semiconductor Field-Effect Transistor
Authors: Yoshida Seikoh , Ishii Hirotatsu 
Published: April 2011

ABSTRACTA high-power metal semiconductor field-effect transistor (MESFET) for operating at a very large-current using GaN is reported for the first time. GaN was grown by metalorganic chemical vapor deposition (MOCVD). Sapphire substrates were used for GaN growth. A GaN MESFET with a large size was fabricated. Multi-finger gates were used for large-current operation. The total gate width was 8 cm and the gate length was 2 νm. The electrode materials of the source and the drain were Al/Ti/Au and the schottky electrodes were Pt/Au. The gate, source, and drain were isolated using SiO2. An FET structure was fabricated using a dry-etching technique. Multi-electrode structures were also fabricated using SiO2 for isolating the source, drain, and gate electrodes, respectively. The FET was operated at a current of over 5 A. The breakdown voltage was over 500 V. The transconductance (gm) was about 12 mS/mm. The pinch-off voltage was about -8 V. We confirmed that this GaN MESFET can also be operated at a current of 10 A.
Comprehensive study of anomalous conduction band structure of InxGa1−xAs1-−yNy
Authors: Skierbiszewski C. , Perlin P. , Wisniewski P. , Presz A. , Suski T. , Geisz J. , Jantsch W. , Mars D. 
Published: April 2011

ABSTRACTUsing free standing layer of InGaAsN we have succeeded in measuring the optical absorption in very broad spectral range (0.8-2.5eV). This gave us an insight into the conduction band density of states for the energies higher than the energy gap of this compound. By combining Hall effect measurements with determination of plasma edge frequency in infrared reflectivity for differently doped samples we were able to deduce the density of states, conduction band electrons effective mass and dispersion relation. In particular it turned out that both i) experimentally measured dispersion relation of the conduction band shows extremely high degree of nonparabolicity and consistently ii) the effective mass of electrons is few times larger than that corresponding to GaAs of the same electron concentration. So far the obtained experimental results are in line with recently proposed band anticrossing model of the electronic structure of III-N-V alloys.
Surface Morphology and Composition Characterization at the Initial Stages of AlN Crystal Growth
Authors: Liu B. , Shi Y. , Liu L. , Edgar J.H. , Braski D.N. 
Published: April 2011

ABSTRACTThe morphology and composition of AlN crystals on 6H-SiC (0001) at the initial stage of crystal growth by sublimation re-condensation technique were investigated by SEM and SAM. Discontinuous AlN coverage occurred after 15 minutes growth. The AlN nuclei size, and growth rate increased as temperature increased or pressure decreased. The SiC substrate decomposed leaving hexagonal hillocks; simultaneously, the AlN nucleated on these SiC hillocks apparently rotated by 15° to 30°. The chemical composition of the substrate and different AlN crystal facets were characterized by SAM. The bare substrate area was stoichiometric SiC with insignificant conversion to silicon nitride, while Si and C preferentially incorporated in the AlN at the initial stages of growth on specific crystal planes.
Heteroepitaxy and Characterization of Low-Dislocation-Density GaN on Periodically Grooved Substrates
Authors: Detchprohm T. , Yano M. , Nakamura R. , Sano S. , Mochiduki S. , Nakamura T. , Amano H. , Akasaki I. 
Published: April 2011

ABSTRACTWe have developed a new method to prepare low-dislocation-density GaN by using periodically grooved substrates in a conventional MOVPE growth technique. This new approach was demonstrated for GaN grown on periodically grooved α-Al2O3(0001), 6H-SiC(0001)Si and Si(111) substrates. Dislocation densities were 2×107 cm−2 in low-dislocation-density area.