bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structure of InAs Quantum Dots in Si Matrix Investigated by High Resolution Electron Microscopy
Authors: Zakharov N. D. , Werner P. , Ustinov V. M. , Kovsh A.R. , Cirlin G. E. , Smolski O.V. , Denisov D.V. , Alferov Zh. I. , Ledentsov N. N. , Heitz R. , Bimberg D. 
Published: April 2011

ABSTRACTQuantum dot structures containing 2 and 7 layers of small coherent InAs clusters embedded into a Si single crystal matrix were grown by MBE. The structure of these clusters was investigated by high resolution transmission electron microscopy. The crystallographic quality of the structure severely depends on the substrate temperature, growth sequence, and the geometrical parameters of the sample. The investigation demonstrates that Si can incorporate a limited volume of InAs in a form of small coherent clusters about 3 nm in diameter. If the deposited InAs layer exceeds a critical thickness, large dislocated InAs precipitates are formed during Si overgrowth accumulating the excess of InAs.
Spontaneous Self-Embedding of Three-Dimensional SiGe Islands
Authors: Mateeva E. , Sutter P. , Lagally M. G. 
Published: April 2011

ABSTRACTIt is shown that. under appropriate conditions, high-Ge-concentration coherent 3D SiGe islands grown on Si(100) self-embed in a matrix of low-Ge-concentration alloy. The process may be more generally useful for preserving the shape of self-assembled “quantum dot” islands during embedding in a matrix material.
Dynamics of the Growth of InAs Quantum Dots on GaAs(001) Substrates
Authors: Westwood D.I. , Brown I.H. , Linsell D.N.J. , Matthai C.C. 
Published: April 2011

ABSTRACTStandard rate equation models of island formation in the InAs/GaAs(001) system have been reassessed in terms of new experimental evidence from real time in-situ reflectance anisotropy spectroscopy (RAS) measurements. These measurements have revealed the behaviour and role of the wetting layer in the modified Stranski-Krastanov growth mode during molecular beam epitaxial growth showing that it can continue to significantly increase in thickness following the onset of islanding. The presence of two dimensional (2D) islands, which act as precursors to three dimensional (3D) islands (the quantum dots) in conventional models, does in principle allow an extension of the “wetting layer”. However, it has been found necessary to extend the standard model to include extra terms that allow material to be incorporated into (and detach from) the wetting layer and which cannot convert to 3D islands. With this improved model, it is found possible to achieve agreement with the RAS measurements.
Doping and Oxidation Effects in Raman Spectra of Manganites
Authors: Podobedov V. B. , Weber A. , Dezanneau G. , Pignard S. , Kreizel J. , Vincent H. 
Published: April 2011

AbstractRaman scattering from LayRxMnO3-δ compounds (single crystals, ceramics, films) was studied as a function of kind (R) and amount (x) of dopant as well as of oxygen deficit (δ). For x = 0.1 to 0.55, a nearly linear Raman shift of the Ag mode from 240 to 125 cm−1 was observed in Srdoped compounds. While the intensity of disorder-induced Raman bands was found to be sensitive to the oxygen content, the symmetry allowed related Raman modes exhibit the changes in the frequency. As an indication of deposition conditions, lowering of a symmetry of the film structures with respect to single crystals and ceramics was detected. We discuss the physical nature of the observed effects and show how Raman data can be used for the optical characterization of manganite samples.
Liquid Compounds for CVD of Alkaline Earth Metals
Authors: Gordon Roy G. , Barry Seán T. , Liu Xinye , Teff Daniel J. 
Published: April 2011

AbstractThe first room-temperature liquid compounds useful for the CVD of alkaline earth metalcontaining oxides were prepared by reacting metal (Mg, Ca, Sr, and Ba) beta-diketonates with novel polyamine ligands. The compounds are monomeric and can be completely flash-vaporized without leaving any non-volatile residue detectable at the parts-per-million level. A stable, solvent-free liquid mixture was formed by mixing new liquid barium, strontium and titanium compounds. CVD experiments using direct liquid injection of this liquid mixture deposited films of barium strontium titanate. This approach should also be applicable to the deposition of many other multicomponent oxides containing alkaline earth metals: ferroelectrics (strontium bismuth tantalate), metallic conductors (strontium vanadium oxide, lanthanum strontium cobalt oxide), phosphors (calcium tungstate), non-linear optical materials (beta-barium borate), magnetic oxides (barium ferrite), colossal magnetoresistive materials (lanthanum strontium manganese oxide), high Tc superconductors (yttrium barium copper oxide, bismuth calcium strontium copper oxide) and microwave dielectrics (barium magnesium tantalate).
Factors Controlling Transport Properties of Interfaces in High-Tc Superconductors
Authors: Hilgenkamp H. , Schulz R. R. , Schneider C. W. , Goetz B. , Schmehl A. , Bielefeldt H. , Mannhart J. 
Published: April 2011

AbstractA comprehensive understanding of the transport properties of interfaces in high-Tc cuprates been obtained by considering their microstructure, the possibility of bending of the electronic
band structure in these materials, and the predominant dx2-y2 -symmetry of the order parameter in most high-Tc cuprates. These factors are of central importance for the critical current density and the normal state resistivity of grain boundaries and their dependencies on boundary misorientation and on applied magnetic and electrical fields. In addition, some of these factors play an important role for the transport properties of other interfaces involving high-Tc superconductors, such as superconductors-normal metal contacts.Based on the improved understanding of the mechanisms controlling interface transport properties, we have been able to meet a long-standing challenge in high-Tc superconductivity and have increased the critical current densities of grain boundaries by large factors, using appropriate doping.
Optical Properties of AlGaAsSb, AlGalnP, AlGaInAs, and GaInAsP for Optoelectronic Applications
Authors: Linnik M. , Christou A. 
Published: April 2011

ABSTRACTThe authors present calculations of quaternary III–V semiconductor alloy optical properties and the comparison of the theoretical data with available experimental results for AlGaAsSb, AlGaInP, AlGaInAs, and GaInAsP alloys. The investigation includes material's energy bandgap and refractive index calculations as a function of the incident wavelength in the transparent region, as well as the composition of the alloy. Optimization of the quaternary alloy refractive indices was obtained from a semi-empirical dielectric function calculations based on the interband transition contributions.
A Three-Dimensional Computer Model for Simulation of Light-Trapping Effects in Porous Silicon
Authors: Charbel Peter T. , Zheng Jim P. 
Published: April 2011

ABSTRACTIt has been demonstrated that porous silicon can be used to enhance the sensitivity, spectral bandwidth, and light acceptance angle of photodiodes. In an attempt to better understand light trapping effects in porous silicon, a three-dimensional model was used to approximate the surface geometry of porous silicon. It was found that the main contributing factor to the observed high efficiencies is the shape of the pores. The general shape resembles cylindrical shaped sections, whose radii are in the micron range. The results of the computer simulation were compared to actual experimental results where porous silicon was tested under variable conditions of lighting and porosity. The comparison shows that the simulation gives a good approximation of the behavior of porous silicon. Although the simulation does not perfectly match experimental values, it does provide the insight that the surface geometry of porous silicon is the main contributing factor to its efficiency in trapping light.
First-Principles Study of Optical Excitations in Alpha Quartz
Authors: Chang Eric K. , Rohlfing Michael , Louie Steven G. 
Published: April 2011

ABSTRACTThe properties of silicon dioxide have been studied extensively over the years. However, there still remain major unanswered questions regarding the nature of the optical spectrum and the role of excitonic effects in this technologically important material. In this work, we present an ab initio study of the optical absorption spectrum of alpha-quartz, using a newly developed first-principles method which includes self-energy and electron-hole interaction effects. The quasiparticle band structure is computed within the GW approximation to obtain a quantitative description of the single-particle excitations. The Bethe-Salpeter equation for the electron-hole excitations is solved to obtain the optical spectrum and to understand the spatial extent and physical properties of the excitons. The theoretical absorption spectrum is found to be in excellent agreement with the measured spectrum. We show that excitonic effects are crucial in the frequency range up to 5 eV above the absorption threshold.
Influence of The Alloy Composition on The Thermodynamic Parameters of Nucleation and Growth of SiGe
Authors: Olivares J. , Rodríguez A. , Sangrador J. , Rodríguez T. , Martín P. , Jiménez J. , Ballesteros C. , Castro M. 
Published: April 2011

AbstractThe influence of the germanium fraction on the parameters of the solid phase crystallization of amorphous silicon-germanium has been studied. Layers of different compositions were deposited by LPCVD at 450 °C and crystallized at 525, 550, 575 and 600 °C. The crystalline fraction was determined as a function of the annealing time for each germanium fraction and temperature. The incubation and the characteristic crystallization times were obtained by fitting the crystalline fraction to Avrami's model. The values of the diffusion activation energy were obtained for different compositions. The dependence of the nucleation rate and the growth velocity on the germanium fraction and the temperature was studied. The three parameters decrease as the Ge fraction increases; though the stronger dependence corresponds to the nucleation rate. The dependences on the composition and the temperature were analyzed in the frame of a conventional nucleation and growth model and their relationship with the corresponding free energies was discussed.
Transitory Metastable Phases in Refractory Metals-Based Systems Solidified by Drop-Tube Processing: A First-Principles Approach
Authors: Berne C. , Pasturel A. , Sluiter M. , Vinet B. 
Published: April 2011

AbstractThe solidification path of highly undercooled refractory metals and their alloys solidified in a ultra high vacuum drop-tube is shown to involve transitory metastable phases. First-principles calculations of structural stability are used to determine the possibility of obtaining metastable phases in these systems, with a view to relate this metastability with the site occupation in the σ phase in the case of the ReTa system.
Premonitory Martensitic Surface Relief Via Novel X-Ray Diffuse and Laser Light Reflectivity from The (001)-Surface of A Ni63Al37Single Crystal
Authors: Klemradt U. , Aspelmeyer M. , Abe H. , Wood L.T. , Moss S.C. , Dimasi E. , Peisl J. 
Published: April 2011

AbstractBoth x-ray diffuse reflectivity and laser light scattering have been used to investigate the temperature-dependent surface behavior of a Ni63Al37single crystal on different length scales. In-situ experiments were performed above the conventional martensitic start temperature Ms to search for premartensitic phenomena. X-ray experiments showed the presence of a surface precursor with second-order (continuous) character several 10 K above Ms. This premonitory effect corresponds to a height-height-correlation function which changes on the nanometer scale as the martensitic transformation is approached. At the martensitic transformation, the surface morphology changed from nanoscopic roughness to macroscopic relief within a temperature interval of less than 1 K via intermediate stages. Laser light scattering was employed to study time-dependent aspects of the athermal martensitic transformation above Ms. The occurrence of a martensitic transformation on isothermal holding after a certain incubation period was observed in Ni-Al for the first time. The measured incubation times increased by four orders of magnitude within a temperature interval of 0.5 K.
Particle Coarsening in Multiphase Ternary Systems
Authors: Holmes W.C. , Hoyt J.J. 
Published: April 2011

AbstractParticle Coarsening in ternary, multiphase -multicomponent, systems is quite different than its binary counterpart in that the presence of one phase can affect the coarsening behavior of another. We have shown by analytic analysis and numerical simulation that the interaction between two coexisting phases depends on: solution thermodynamics, diffusivities, and equilibrium concentration differences between matrix and precipitate phases. Therefore, different ternary systems create different cross phase interactions which affect coarsening behavior. For example, spatial correlations between the two coarsening phases are a strong function of this interaction and can lead to spatial ordering between the two phases. Also, specific ternary systems can produce kinetic instabilities and pattern formation.
A Raman Study of a Metastable Crystalline State in Amorphous SiGe Layers Under cw Laser Illumination: Influence of the Temperature
Authors: Martin P. , Olivares J. , Rodriguez A. , Sangrador J. , Jinenez J. , Rodriguez T. 
Published: April 2011

AbstractA metastable crystalline state was observed in amorphous SiGe/Si layers under illumination with a cw laser beam (514.5 nm) with power density below the crystallization threshold. The observation of this state was temperature dependent and it was reversible. The structural properties of this metastable crystallization were studied by Raman spectroscopy.
A Comparison Between the Calculated and Experimental Effects of Enhanced Precursor Translational Kinetic Energy on SiC Growth on Si(100) and Si(L11) from Hexamethyldisilane
Authors: Beck D. W. , Li Q. , Kordesch M. E. 
Published: April 2011

AbstractSilicon Carbide thin films were grown on Si(100) and (111) substrates at 1050EC using a pulsed supersonic beam of hexamethyldisilane (HMDS) in hydrogen. X-ray diffraction analysis shows that these films contain only the 3C cubic polytype, determined mainly by the SiC(111) diffraction peak at 22 = 35.6E, the SiC(200) peak at 22 = 41.4E and the SiC(220) peak at 22 = 60.OE.The angle of incidence of the HMDS/hydrogen beam could be varied through an angle of 0 to 90E without displacing the specimen from the focal point of the beam. On the Si(100) surface, the film growth texture was monitored by measuring the ratio of the SiC(111) to (200) diffraction peak intensity for beam incidence angles of 0, 30, 45 and 60E. On Si(111). The SiC(111)/(220) ratio was monitored. An 8-fold increase in the incident translational kinetic energy of the precursor molecules can be achieved at the highest glancing angle. In general, the effects of enhanced translational kinetic energy on SiC film growth were insignificant, in agreement with calculations of the sticking probability for SiC homoepitaxial growth with seeded beams on SiC [1]. Further examination of the films with SEM and AFM revealed the growth of epitaxial islands at low coverages, and the process of island coalescence.
In Situ Observation of Melting and Solidification
Authors: Saka H. , Arai S. , Muto S. , Miyai H. , Tsukimoto S. 
Published: April 2011

AbstractMelting and solidification of metallic materials have been observed directly using an in-situ heating experiment in an electron microscope. In pure Al melting initiates at the surface, while in a eutectic alloy melting initiates preferentially at eutectic interfaces and grain boundaries. The atomic structure of a solidliquid interface was identified by comparing an experimental image with computed ones.
Experimental Methods and Data Analysis for Fluctuation Microscopy
Authors: Voyles P. M. , Treacy M. M. J. , Gibson J. M. , Jin H-C. , Abelson J. R. 
Published: April 2011

AbstractWe have developed a new electron microscopy technique called fluctuation microscopy which is sensitive to medium-range order in disordered materials. The technique relies on quantitative statistical analysis of low-resolution dark-field electron micrographs. Extracting useful information from such micrographs involves correcting for the effects of the imaging system, incoherent image contrast caused by large scale structure in the sample, and the effects of the foil thickness.
The Atomic Structure of Mosaïc Grain Boundary Dislocations in GaN Epitaxial Layers
Authors: Potin V. , Nouet G. , Ruterana P. , Pond R.C. 
Published: April 2011

AbstractThe studied GaN layers are made of mosaYc grains rotated around the c-axis by angles in the range 0-25°. Using high-resolution electron microscopy, anisotropic elasticity calculations and image simulation, we have analyzed the atomic structure of the edge threading dislocations. Here, we present an analysis of the Σ = 7 boundary using circuit mapping in order to define the Burgers vectors of the primary and secondary dislocations. The atomic structure of the primary ones was found to exhibit 5/7 and 8 atom cycles.
Energy Dispersive X-ray Spectrometry With the Transition Edge Sensor Microcalorimeter: A Revolutionary Advance in Materials Microanalysis
Authors: Newbury Dale , Wollman David , Irwin Kent , Hilton Gene , Martinis John 
Published: April 2011

AbstractThe NIST microcalorimeter energy dispersive x-ray spectrometer provides important advances in x-ray spectrometry. The high spectral resolution, approaching 2 eV for photon energies below 2 keV, the wide photon energy coverage, 250 eV to 10 keV, and the energy dispersive operation enable a wide range of materials characterization problems to be addressed. This performance is especially critical to high spatial resolution, low-voltage x-ray microanalysis performed with the field-emission gun scanning electron microscope.
Isomeric Higher and Smaller Fullerenes: A Profound Enthalpy/Entropy Interplay
Authors: Zhao X. , Slanina Z. , Ōsawa E. 
Published: April 2011

ABSTRACTComputations of isomeric fullerenes are performed at semiempirical and ab initio quantum-chemical levels: C36, C72, C88. C36 fullerenes and quasi-fullerenes are computed at the SAM1 level, and then at the B3LYP/6-31G* level. Altogether 598 cages are considered. The SAM1 method is also applied to C72, i.e., the solitary isolated-pentagon-rule (IPR) structure and several non-IPR isomers. Finally, the complete set of thirty five topologically different IPR isomers of C88 is computed. In all the cases, energetics is combined with entropy contributions based on the harmonic-oscillator and rigid-rotator model. Considerable temperature effects on the relative stabilities in the systems are found. Relationships to available observed data are discussed throughout and a good agreement is found.
Formation of Nanotube-Based Quantum Dots With Strain and Addimers
Authors: Orlikowski D. , Nardelli M. Buongiorno , Bernholc J. , Roland C. 
Published: April 2011

ABSTRACTWe present the results of a large-scale molecular dynamics investigation of addimers on strained carbon nanotubes. We find that addimers induce a new set of transformations that lead to the formation of extended defects that are actually short segments of tubes of altered helicity. As these defects wrap themselves about the circumference of the nanotube, this suggests that the combination of addimers and strain may well lead to the formation of nanotube-based quantum dots. The formation of these quantum dots is most favorable for the (n.O) zigzag tubes. For these tubes, addimers induce plastic transformations in tubes that normally display brittle behavior.
Partial Carbonization of Aromatic Polyimide Films
Authors: Doyama M. , Ichida A. , Inoue Y. , Kogure Y. , Nozaki T. , Yamada S. 
Published: April 2011

ABSTRACTAromatic polyimide films are partially carbonized between 700°C and 1000°C. Electrical conductivity and Hall coeficient have been measured. Electrical conductivity is higher at higher measuring temperatures. The electrical conductivity σ can be expressed as σ= σ0exp (–E /kT), where k is the Boltzman constant. T is the absolute temperature. E depends upon the carborized temperature. The experimental data show the Hall coefficient RH is negative, and this implies the carriers are negatively charged, i.e. electrons. The specimens are n-type semiconductors. The carrier density η can be expressed by η= A1 exp (–E1/κT) and carrier mobility μ can be expressed by μ = A1exp ( E2/κT). E, E1andE2 depend upon the carbonized temperature
Properties of Ion Beam Deposited Tetrahedral Fluorinated Amorphous Carbon Films (ta-C:F)
Authors: Ronning C. , Merk R. , Feldermann H. , Harbsmeier F. , Hofsäss H. 
Published: April 2011

ABSTRACTWe have studied the growth and the properties of ta-C:F films prepared by the deposition of mass separated 12C+ and 19F+ ions as a function of the F concentration CF. The films are always strongly F-deficient due to the formation of volatile CFx, molecules during the deposition process. CF ≈ 25 at.% is obtained for an ion charge ratio of C+:F+ = 1:1. The mass density strongly decreases from 2.9 g/cm3 for ta-C to 1.1 g/cm3 for films with CF ≈ 23 at.%, whereas the electron density related plasmon energy only varies slightly between 31.8 eV and 29 eV. Therefore, films with small CF have both a high mass and high electron density resulting in diamond-like properties. The discrepancy between low mass density and high electron density for films with large cF can be explained by voids. The thickness and composition of films with CF below 20 at.% remains unchanged for vacuum annealing to temperatures of 600 °C for 10 minutes. Loss of F was observed for films with cF above 20 at.%. The compressive film stress decreases with increasing CF, and is further reduced by annealing.
Fluorine Incorporation Into Hard Amorphous Hydrogenated Carbon Films Deposited by PECVD
Authors: Freire F. L. , Jacobsohn L. G. , Franceschini D. F. 
Published: April 2011

ABSTRACTThe incorporation of fluorine into amorphous hydrogenated carbon films deposited by the plasma enhanced chemical vapor deposition technique (PECVD) was investigated. Different mixtures of CH4 and CF4 were employed as the plasma atmosphere, with the partial pressure of CF4 ranging from 0 to 100 %. For all depositions, the self-bias was kept at –350 V. In the case of atmospheres richer than ∼80 % of CF4, no film deposition but substrate erosion was observed. The composition of the films was determined by Ion Beam Analysis (IBA), revealing that fluorine is incorporated into the amorphous network by replacing hydrogen. Infrared (IR) transmission measurements confirmed these results. It was also found that the incorporation of fluorine has the effect of reducing both the internal stress and hardness due to atomic density reduction.
Effect of Argon Addition on Nitrogen Containing Carbon Films Prepared by Hot Carbon Filament CVD
Authors: Watanabe Yoshihisa , Ohnita Shinobu , Kitazawa Nobuaki , Nakamura Yoshikazu 
Published: April 2011

ABSTRACTNitrogen containing amorphous carbon (a-CNx) films were prepared on silicon single crystal substrates by heating a carbon filament in low pressure nitrogen atmosphere and the effects of argon addition to nitrogen atmosphere were studied by changing the argon fraction under the total pressure of 100 Pa. The growth rate of the films is found to decrease with increasing the argon fraction. x-ray photoelectron spectroscopy shows that the films are composed of carbon and nitrogen and the optimal fraction of argon addition is observed for increasing the nitrogen concentration. Observations by atomic force microscopy reveal that the film surfaces are covered with particle-like features and the size of the features decreases drastically by argon addition. It is concluded that argon addition to the reactant gas is effective in synthesizing a-CNx films with the smooth surface and high nitrogen concentration