bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chemical Reactions on the Surface of SnO2 Nanosized Powders at the Origin of the GaS Sensing Properties: FTIR Investigation
Authors: Baraton M.-I. , Merhari L. 
Published: April 2011

ABSTRACTThe surface chemical reactions at the origin of the CO detection by SnO2-based sensors are investigated by Fourier transform infrared spectrometry for two different SnO2 particle sizes. Knowing that the variations of the infrared energy transmitted by the sample versus surrounding gases are related to the variations of the electrical conductivity, correlation of surface chemical reactions with the sensor response is established and discussed.
Morphological Stability of Ni(Al)/Ni3Al Nanolaminate Composites
Authors: Fain Jason P. , Banerjee Rajarshi , Josell Daniel , Anderson Peter M. , Fraser Hamish , Tymiak Natalia , Gerberich William 
Published: April 2011

ABSTRACTThis manuscript discusses the morphological instability observed when multilayered samples with alternating layers of Γ-Ni(Al)/γ-Ni3Al are exposed to 800C for approximately 100 hours. Samples with 20nm/20nm or 120nm/120nm layer thickness and <001> or <Ill> crystal orientation to the interface normal were tested. Pinching off of layers is strongly affected by crystal orientation and layer thickness. Corresponding modeling suggests that the stability of this system is sensitive to fluctuations in the volume fraction of the two phases, the aspect ratio of columnar grains in the layers, and whether coherent or semi-coherent interfaces are present.
Measuring the Dielectric Properties of Nanostructures using Optical Reflection and Transmission: Bismuth Nanowires in Porous Alumina
Authors: Black M. R. , Lin Y. M. , Dresselhaus M. S. , Tachibama M. , Fang S. , Rabin O. , Ragot F. , Eklund P. C. , Dunn Bruce 
Published: April 2011

ABSTRACTThis paper develops a method to deduce the dielectric function of nanostructures smaller than the chosen wavelength of light. It modifies the Maxwell - Garnett Effective Medium Theory equations to calculate the dielectric function of a metal embedded inside a dielectric. Specifically, reflection and transmission measurements of an array of bismuth nanowires in an anodized porous alumina template are used to calculate the frequency - dependent di-electric function of the nanowires. The spectra are taken using Fourier transform infrared spectroscopy covering the 500 to 4000 cm−1 frequency range. These data are used to determine the real and imaginary parts of the dielectric function of the composite materials. Next, the percentage of the total volume occupied by either Bi or air in the porous alumina (the “filling factor”) was found by scanning electron microscopy. The modified Maxwell-Garnett (M-G) equations specify how to use the filling factor and the dielectric function of the composite material to calculate the dielectric function of the alumina. Finally, the modified M-G equations are used a second time to calculate the dielectric function of Bi nanowires using the dielectric function of alumina, the dielectric function of the filled template, and the filling factor. The resulting dielectric function of Bi nanowires is then compared to theoretical predictions.
Colossal Hopping Magnetoresistance of GaAs/ErAs Nanocomposites
Authors: Petukhov A. G. , Foygel M. , Chantis A. 
Published: April 2011

ABSTRACTA theory of bound magnetic polaron (BMP) hopping, driven by thermodynamic fluctuations of the local magnetization, has been developed. It is based on a two-site model of BMP's. The BMP hopping probability rate was calculated in the framework of the “Golden Rule” approach by using the Ginzburg-Landau effective Hamiltonian method. The theory explains the main features of hopping resistivity observed in a variety of experiments in dilute magnetic semiconductors and magnetic nanocomposites, namely: (a) negative giant magnetoresistance, the scale of which is governed by a magnetic polaron localization volume, and (b) low magnetic field positive magnetoresistance, which usually preceeds negative magnetoresistance.
Magnetic Hardening Induced by Exchange Coupling in Mechanically Milled Antiferromagnetic - Ferromagnetic Composites
Authors: Sort J. , Nogués J. , Amils X. , Suriñach S. , Muñoz J.S. , Baró M.D. 
Published: April 2011

ABSTRACTMechanical milling has been used to synthesize ferromagnetic (FM, Co) - antiferromagnetic (AFM, NiO) composites. The coercivity, HC, and energy product, BHMax, of these composites can be enhanced at room temperature after appropriate heat treatments above the Néel temperature of the AFM, TN. Although the maximum Hcis achieved for the (NiO)1: 1 (Co) weight ratio, BHMaxis further enhanced for the (NiO)2:3(Co) ratio, where higher saturation magnetization is obtained due to the larger amount of FM. Exchange coupling, responsible for these effects, decreases as the temperature is increased and vanishes close to TN. The thermal stability of the coercivity enhancement remains rather insensitive to the somewhat broad distribution of blocking temperatures of this system.
Study of the Luminescence of Eu-Doped Nanocrystalline Si/SiO2 Systems Prepared by RF Co-Sputtering
Authors: Nery G.A. , Mahfoud A. , Fonseca L.F. , Liu H. , Resto O. , Weisz S.Z. 
Published: April 2011

ABSTRACTWe prepared Eu-doped films of Si nanoparticles embedded in SiO2 using pellets of Eu2O3 by sputtering. We studied their photoemission, transmission and fluorescence to obtain data about their composition and particle size and the Eu interaction characteristics. We were able to incorporate Eu(III) into the Si nanoparticle / SiO2 host. We also found we obtained Eu(II) in the process. We found a lowering of photoluminescence intensity with lowering of temperature. An as yet unanswered question is the reason for the intense whitish luminescence found in some regions of the samples. Some involvement with Eu(II) is suspected. Eu(IIl) related peaks were only observed where the size distribution peak of the nanoparticles was lower than 1.3nm. Whitish luminescence was related to peak sizes ranging from 1.1nm to 1.4nm. Annealing the samples had clear effects upon their photoluminescence, but did not necessarily involve changes in particle sizes, nor were these size changes necessary to increase luminescence. The Eu doping has a tendency to halt the annealing effects on size and, when changes did occur, the particles generally became smaller.
Can We Determine the Barrier Resistance for Electron Transport in Ligand Stabilized Nanoparticles from Integral Conductance Measurements?
Authors: Simon U. 
Published: April 2011

ABSTRACTBy means of integral temperature dependent conductance measurements, the effective capacitance of ligand stabilized nanoparticles, arranged in dense packings or networks, can be deduced from the activation energy of the charge transport, for which the use of the Landauer formula is proposed. According to this, the barrier resistance in ligand stabilized nanoparticle arrangements depends predominantly on the inter particle spacing rather than on the chemical composition of the molecules. Comparison with data of the single molecule resistance determined by local probe techniques or by theoretical methods shows remarkable aggreement.
Stoichiometry Control in Molecular Beam Deposited Nanocrystalline SnO2 and TiO2 Thin Films
Authors: Hoche H. , Hahn H. , Edelman F. , Nagel R. , Werner P. 
Published: April 2011

ABSTRACTMolecular beam deposition (MB) of thin film metal oxide is prospective for application in gas sensor technology due to the well-controlled oxide molecular fluxes during creation of multi-oxide structures with improved characteristics. However, the MB process leads to some oxygen deficiency in the oxide. Further application of the MB technology (and, in general, the e-beam oxide deposition in vacuum) for processing of sensor structures needs the control and correction of the oxygen stoichiometry by adding in-situ atomic oxygen to the growing material or via the thin film oxidation after deposition.Thin films (50 to 500 nm) of SnOx and TiOx were deposited on SiO2/(001)Si substrates at 100°C by MB from SnO2 and TiO2 sources. The film stoichiometry in the as-deposited state and after annealing in vacuum and in oxygen is characterized by XRD, TEM and RBS. Oxygen annealing transformed the strongly non-stoichiometric SnO (Romarchite) in the as-deposited state to Cassiterite, SnO2. Structure transformations in the TiO2 films during annealing are also discussed.
Structure and Magnetic Property Correlation in Nanocrystalline SmFe9
Authors: Djega-Mariadassou C. , Bessais L. 
Published: April 2011

ABSTRACTSmxFe100−x samples with x = 7.6, 10.5 and 12.5 were prepared by high energy ball-milling and subsequent annealing at various temperature Ta, 600 < Ta < 1200 °C. Rietveld analysis coupled to Curie temperature measurements and M6ssbauer spectroscopy revealed for 600 < Ta < 900 °C an hexagonal phase P6/mmm derived from TbCu7 with stoichiometry SmFe9. At Ta > 900 °C, the ordered R3m Sm2Fe17 structure is obtained so that SmFe9 appears as the out-of-equilibrium precursor of Sm2Fe17. The Curie temperature and hyperfine field augmentation found for SmFe9 results from an increase of the interatomic distance in the Fe-Fe dumbbell, responsible for a reduction of the negative exchange interaction.
Pulsed Magnetic Field Induced 3-D Islanding of Oxygen Contained Clusters in Cz-Si Crystals
Authors: Levin M. N. , Zon B. A. 
Published: April 2011

AbstractEffect of pulsed magnetic field induced self-organized generation of 3-D spatially regular structures of oxygen-vacancy contained clusters of nanometer scale has been observed in silicon crystals grown by Czochralski method (Cz-Si). The effect has been studied by means of ultra-soft X-ray spectroscopy, scanning tunneling microscopy and potential probe measurements. Mechanisms responsible for the effect have been discussed.
Growth and Decay of Germanium Islands on Silicon Studied by High Temperature Stm
Authors: Kästner M. , Voigtländer B. 
Published: April 2011

AbstractWe use a scanning tunneling microscope (STM) capable of imaging the growing layer at high temperature during molecular beam epitaxy (MBE) to study the epitaxial growth of Germanium on Silicon and the decay of Ge islands. The periodicity of the (2×N) reconstruction of two-dimensional Ge layers on Si(001) is measured as function of the Ge coverage. Strain energy drives the formation of the (2×N) reconstruction and Si/Ge intermixing. A comparison to total energy calculations predicting the periodicity of the (2×N) reconstruction is used to estimate the amount of Si-Ge intermixing near the surface. The evolution of the size and shape of individual “hut clusters” is measured and explained by kinetically self-limiting growth. The relaxation of kinetically a determined morphology towards equilibrium is followed for a Ge layer on Si(111). Strained two-dimensional as well as partially relaxed three-dimensional islands dissolve and are soaked up by larger three-dimensional islands which are dislocated and therefore fully relaxed.
In Situ Measurements of Stress Relaxation During Strained Layer Heteroepitaxy
Authors: Chason E. , Yin J. , Tetz K. , Beresford R. , Freund L. B. , Gonzalez M. Ujue , Floro J. A. 
Published: April 2011

AbstractWe present real-time measurements of stress relaxation kinetics during epitaxial growth obtained using a wafer-curvature-based technique optimized for in situ studies. Depending on the temperature and misfit strain, different mechanisms of stress relaxation are observed. In heterolayers of InGaAs grown on GaAs (001) substrates, relaxation occurs by a dislocationmediated mechanism. In SiGe layers grown on Si (001) substrates at elevated temperature, relaxation occurs by the formation of islands on the surface. These islands elastically relax misfit stress without the introduction of dislocations at the island-substrate interface.
Spontaneous Formation of Arrays of Strained Islands: Thermodynamics Versus Kinetics
Authors: Shchukin V. A. , Ledentsov N. N. , Bimberg D. 
Published: April 2011

AbstractOptions are discussed which allow to distinguish equilibrium arrays of strained islands from kinetically-controlled arrays. Finite-temperature thermodynamic theory is developed for equilibrium arrays of two-dimensional monolayer-high islands in heteroepitaxial systems at submonolayer coverage. It is shown that the entropy contribution to the Helmholtz free energy of the system favors formation of small islands and results in the shrinkage of the islands with increasing temperature. The average size of islands decreases tremendously with respect to zero-temperature size at temperatures far below the characteristic energy of island formation. Such a temperature dependence can be the basis for decisive experiments aimed to distinguish between thermodynamic and kinetic effects on the formation of arrays of 2D islands. The theory is able to explain results of high-resolution electron microscopy of submonolayer arrays of InAs/GaAs(001) islands. Their formation is predominantly influenced by thermodynamics.
CuPt-B Ordered Microstructures in GaInP and GaInAs Films
Authors: Ahrenkiel S. P. , Jones K. M. , Matson R. J. , Al-Jassim M. M. , Zhang Y. , Mascarenhas A. , Friedman D. J. , Arent D. J. , Olson J. M. , Hanna M. C. 
Published: April 2011

AbstractWe examine CuPt-B atomic sublattice ordering in Ga0.51In0.49P (GaInP) and Ga0.47In0.53As (GaInAs) III-V alloy films grown by atmospheric- and low-pressure metalorganic chemical vapor deposition on singular and vicinal (001) substrates. The influences of growth conditions and substrate miscut on double- and single-variant ordered microstructures are investigated using transmission electron microscopy (TEM). Relatively thick (>1–2 litm) double-variant ordered GalnP and GaInAs films show complementary superdomain formation. Single-variant ordered films on <111>B-miscut substrates contain single-phase domains, separated by antiphase boundaries (APBs). The appearance of APBs in TEM dark-field images is anticipated from electron diffraction theory.
Single and Double Variant Cupt-B Ordered GalnAs
Authors: Forrest R. L. , Meserole E. D. , Nielsen R. T. , Goorsky M. S. , Zhang Y. , Mascarenhas A. , Hanna M. , Francoeur S. 
Published: April 2011

AbstractNominally lattice-matched GaInAs layers grown by metal organic vapor phase epitaxy on InP substrates have been studied using high-resolution x-ray diffraction (HRXRD) to determine the growth conditions under which ordering is introduced. HRXRD provides an independent means to quantify the order parameter of semiconductor heterostructures as well as the ordering on different {111} planes, i.e., double variant ordering. This independent means to determine ordering provides for a better understanding of the effects of ordering on the electronic and optical properties. Double variant ordering was observed for epitaxial layers grown on exact (001) InP substrates, with an order parameter of about 0.1 in both variants. For substrates that were miscut by 6 degrees, single variant ordering was detected. In these cases, an order parameter as high as 0.66 was measured for certain growth conditions. The layers grown on vicinal substrates are all of high crystalline quality, those on (001) substrates exhibit some mosaic spread.
Local Order of Te Impurity Atoms in Heavily Doped GaAs:Te and Accompanying Electron Localization Effect
Authors: Slupinski T. , Zielinska-Rohozinska E. 
Published: April 2011

AbstractWe show the results of joined studies of the free electron concentration and x-ray diffuse scattering from heavily doped GaAs:Te single crystal as a function of controlled annealings at high temperatures 700–1200°C and Te concentration 1018− 2 1019 cm−3 from the range, where the free electron concentration saturates. Changes of electron concentration caused by annealings are accompanied by structural changes, both being in a high coincidence and reversible versus annealing temperature On a basis of the microscopic model of x-ray diffuse scattering from a solid solution, newly proposed here, we argue that impurity atom pairs arise, locally in a crystal, when the free electron concentration is lowered by annealing. We suppose that the electron localization is caused by impurity atom pairs, supporting recently published results.
The Initial Stages of Growth of Ordered GaInP and GaInAs Grown by Metal Organic Vapor Phase Epitaxy
Authors: Hanna M. C. , Mascarenhas A. , Cheong Hyeonsik M. 
Published: April 2011

AbstractWe have used atomic force microscopy (AFM) and Raman spectroscopy to investigate the development of the surface morphology of (001) direct and vicinal GaInP and GaInAs grown under conditions to produce strong CUPtB ordering. Raman spectroscopy provided direct evidence of CuPtB ordering in layers as thin as 10 nm for GaInP and 5 nm for GaInAs. We find that the morphology of GaInP and GaInAs on (001)6B substrates consists of ridges, which are aligned predominately along the [110] direction (A-direction). These ridges are well developed even at layer thicknesses of 2 nm, and their sides consist of step-bunches and near (001) terraces. On (001) direct substrates, the GaInP morphology is similar to that obtained on 6B substrates, although the step bunches have no preferential orientation, while GaInAs (001) growth proceeds by a combination of 2D-island and step flow growth. We discuss possible reasons for the differences in the morphology of ordered GaInP and GaInAs. The results of this work suggest it may be difficult to produce abrupt heterointerfaces in structures containing ordered GalnP and GaInAs alloys.
The Nature and Origin of Lateral Composition Modulations in Short-Period Strained-Layer Superlattices
Authors: Norman A. G. , Ahrenkiel S. P. , Moutinho H. R. , Ballif C. , Al-Jassim M. M. , Mascarenhas A. , Follstaedt D. M. , Lee S. R. , Reno J. L. , Jones E. D. , Mirecki-Millunchick J. , Twesten R. D. 
Published: April 2011

AbstractThe nature and origin of lateral composition modulations in (AlAs)m(InAs)nshort-period strained-layer superlattices grown by molecular beam epitaxy on InP substrates have been investigated by x-ray diffraction, atomic force microscopy, and transmission electron microscopy. Strong modulations were observed for growth temperatures between ≈ 540 and 560° C. The maximum strength of modulations was found for SPS samples with InAs mole fraction x (= n/(n+m)) close to ≈ 0.50 and when n≈m≈2. The modulations were suppressed at both high and low values of x. For x > 0.52 (global compression), the modulations were along the <100> directions in the (001) growth plane. For x < 0.52 (global tension), the modulations were along the two <310> directions rotated ≈ ±27° from [110] in the growth plane. The remarkably constant wavelength of the modulations, between ≈ 20–30 nm, and the different modulation directions observed, suggest that the origin of the modulations is due to surface roughening associated with the high misfit between the individual SPS layers and the InP substrate. Highly uniform unidirectional modulations have been grown by control of the InAs mole fraction and growth on suitably offcut substrates, which show great promise for application in device structures.
Formation of Direct Energy Gap Group IV Semiconductor Alloys and Quantum Dot Arrays in SnxSi1−x /Si and SnxGe1−x/Ge Alloy Systems
Authors: Atwater Harry A. , Ragan Regina , Min Kyu S. 
Published: April 2011

AbstractThe narrow gap semiconductor alloys SnxGe1−x, and SnxSi1−x offer the possibility for engineering tunable direct energy gap Group IV semiconductor materials. For pseudomorphic SnxGe1−x, alloys grown on Ge (001) by molecular beam epitaxy, an indirect-to-direct bandgap transition with increasing Sn composition is observed, and the effects of misfit on the bandgap analyzed in terms of a deformation potential model. Key results are that pseudomorphic strain has only a very slight effect on the energy gap of SnxGe1−x, alloys grown on Ge (001) but for SnxGe1−x alloys grown on Ge (111) no indirect-to-direct gap transition is expected. In the SnxSi1−x system, ultrathin pseudomorphic epitaxially-stabilized α-SnxSi1−x alloys are grown on Si (001) substrates by conventional molecular beam epitaxy. Coherently strained oa-Sn quantum dots are formed within a defect-free Si (001) crystal by phase separation of the thin SnxSi1−x layers embedded in Si (001). Phase separation of the thin alloy film, and subsequent evolution occurs via growth and coarsening of regularly-shaped α-Sn quantum dots that appear as 4–6 nm diameter tetrakaidecahedra with facets oriented along elastically soft [100] directions. Attenuated total reflectance infrared absorption measurements indicate an absorption feature due to the α-Sn quantum dot array with onset at ˜0.3 eV and absorption strength of 8 × 103 cm−1, which are consistent with direct interband transitions.
Self-Assembled Iii-Phospide Quantum Dots Grown by Metalorganic Chemical Vapor Deposition
Authors: Ryou Jae-Hyun , Chowdhury Uttiya , Dupuis Russell D. , Reddy Chavva V. , Narayanamurti Venkatesh , Mathes David T. , Hull Robert 
Published: April 2011

AbstractWe report InP self-assembled quantum dots embedded in In0.51Al0.49P grown by metalorganic chemical vapor deposition. Growth parameters are altered to study the InP quantum-dot growth characteristics under various growth conditions. Quantum-dot morphology is characterized using atomic-force microscopy. Also, photoluminescence studies of the light-emitting properties are performed. Direct-bandgap ternary InxAlI−xP (x=˜0.7, ˜0.85) self-assembled quantum dots are also grown and compared with InP quantum dots.
Shape Reversal of Ge/Si Domes to Pyramids Via Si-Ge Intermixing and Strain Reduction
Authors: Henstrom William L. , Liu Chuan-Pu , Gibson J. Murray 
Published: April 2011

AbstractAt 650°C, Si freely intermixes with Ge in the dome islands causing a reduction in the strain of the islands and an increase in island size. The shape reversal of Ge/Si domes to pyramids is investigated by analysis of the strain and size changes that occur on an island by island basis. This was carried out for anneal times of 0, 20, 40 and 60 minutes. Transition islands were observed consistent with previous work[1], which are partially domes and partially pyramids. These islands demonstrated a strain gradient, having a slightly lower strain on the side that has transformed to a pyramid. Cross-sectional STEM was then used to show that this strain gradient is associated with a non-uniform Si intermixing in the islands.
Systematic Studies of Fullerene Derivative Electron Beam Resists
Authors: Robinson A. P. G. , Palmer R. E. , Tada T. , Kanayama T. , Shelley E. J. , Philp D. , Preece J. A. 
Published: April 2011

AbstractWe report systematic studies of the response of C60 derivatives to electron beam irradiation. Films of fourteen different mono, tris and tetra adduct methanofullerene C60 derivatives were produced by spin coating on hydrogen terminated silicon substrates. Exposure of the films to a 20 keV electron beam substantially altered the dissolution rate of the derivative films in organic solvents such as monochlorobenzene. All of the derivatives exhibited negative tone resist behaviour with sensitivities between ∼ 8.5 × 10-4 and ∼ 4 × 10-3 C/cm2 107, much higher than that of C60. Features with widths of ∼ 20 nm were produced using these compounds, and the etch ratios of the compounds were found to be more than twice those of a standard novolac based resist (SAL601).