bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optical-based Flux Monitoring of Atomic Antimony Sources for Molecular Beam Epitaxy
Authors: Brewer P. D. , Killeen K. P. 
Published: April 2011

AbstractIn this paper we discuss the use of optical-based flux monitoring (OFM) for real-time control of atomic antimony fluxes for applications in molecular beam epitaxy. Atomic antimony beams were generated using a two-zone cracking effusion cell. The product distribution of the source was characterized using a time-of-flight mass spectrometer employing resonance-enhanced laser ionization. A double-pass OFM system has been developed to monitor the atomic antimony beam that is capable of precise flux measurement during MBE growth.
Real-Time Composition And Thickness Control Techniques In A Metalorganic Chemical Vapor Deposition Process
Authors: Gaffneyt M. S. , Reavesl C. M. , Holmes A. L , Smith R. S. , DenBaars S. P. 
Published: April 2011

AbstractMetalorganic chemical vapor deposition (MOCVD) is a process used to manufacture electronic and optoelectronic devices that has traditionally lacked real-time growth monitoring and control. We have developed control strategies that incorporate monitors as real-time control sensors to improve MOCVD growth. An analog control system with an ultrasonic concentration monitor was used to reject bubbler concentration disturbances which exist under normal operation, during the growth of a four-period GaInAs/InP superlattice. Using X-ray diffraction, it was determined that the normally occurring concentration variations led to a wider GaInAs peak in the uncompensated growths as compared to the compensated growths, indicating that closed loop control improved GaInAs composition regulation. In further analysis of the X-ray diffraction curves, superlattice peaks were used as a measure of high crystalline quality. The compensated curve clearly displayed eight orders of satellite peaks, whereas the uncompensated curve shows little evidence of satellite peaks.
Near Field Scanning Optical Microscopy and Spectroscopy of Electronic Materials and Structures
Authors: Duncan W. M. 
Published: April 2011

AbstractA Near Field Scanning Optical Microscope (NSOM) with spectroscopic capability is applied to imaging semiconductor and microelectronic structures. NSOM combined with spectroscopic analysis provides physical and chemical information of thin films and defects with ultra high spatial resolution. We have studied epitaxial and bulk samples and partially fabricated SiO2/Si CMOS structures to investigate the spatial resolution and imaging modes of NSOM. Reflected intensity contrast in NSOM yields images of defect networks in InGaAs/InAlAs/GaAs epitaxial layers and shows thickness variations in SiO2 films on Si. Surface topological changes observed in NSOM demonstrate a spatial resolution of significantly better than 0.25 μm. Fluorescence imaging is examined for chemically identifying materials and defects.
Imaging of Silicon Carrier Dynamics with Near-Field Scanning Optical Microscopy
Authors: Rosa A. H. La , Yakobson B. I. , Hallen H. D. 
Published: April 2011

AbstractA contactless high spatial resolution technique has been developed to characterize semiconductor materials using the Near-Field Scanning Optical Microscope. The technique can be used to non-invasively measure: surface topography, defect content, and carrier lifetime variations in silicon. The success of the technique relies on the sensitive detection of changes in infrared transmission induced by local generation of free carriers using pulsed visible radiation. Here we extend the application of this technique to characterize silicon on insulator materials. We also include computer simulation results to address the role played by diffusion in the ultimate lateral resolution that can be achieved using this technique.
Quantitative Photoreflectance Experiments on Indium Phosphide Surfaces and Structures
Authors: Hildebrandt S. , Schreiber J. , Kuzmenko R. , Gansha A. , Kircher W. , Höring L. 
Published: April 2011

AbstractPhotoreflectance (PR) modulation spectroscopy is a widely used optical technique on GaAs but it has been applied much more rarely on InP being an equally important optoelectronic compound semiconductor. Typical PR spectral lineshapes in the fundamental gap region of various InP materials are investigated. Spectral components such as Franz-Keldysh oscillations, lowfield features, and epilayer interference phenomena are analyzed. Current applications concern the determination of the surface electric field, investigations of ion etching and hydrogenation processing, and the characterization of homo- and strained heteroepitaxial layers by means of synchronous phase and complex fitting analysis.
Origin of the 1.3 eV Transition in InP/InAlAs/InP Heterostructure
Authors: Benyattou T. , Garcia-Perez M. A. , Moneger S. , Guillot G; , Caneau C. 
Published: April 2011

AbstractWe report in this paper results from photoluminescence studies on InP/AlInAs/InP double heterostructure. We particuliary focus on the 1.26 eV recombination (also refered as the 1.3 eV transition) that originates from the inverse interface. We will show that its optical properties is related to the non commutativity of the AlInAs/InP band offset.
Three-Dimensional Active Gratings for Light Emission Control
Authors: Romanov S. G. , Fokin A. , Butko V. , Johnson N. P. , Torres C. M. Sotomayor 
Published: April 2011

AbstractThree dimensional lattices of semiconductor nanostructures were prepared using porous artificial opals as templates. Opals are natural gratings for visible light, and the template forces the semiconductor to follow the size (typically 100 nm) and symmetry (fcc) of their void-like lattice. The purpose of using this material is to match the wavelength of the emitted light from the semiconductor component with one of the lattice's own modes to enhance the luminescence efficiency. TiO2 was grown using in-cavity, multiple step synthesis by CVD. The band gap of the composite is near 3 eV. Raman scattering, absorption and photoluminescence (PL) spectra were examined for various amounts of TiO2 in opal. Transmission of the PL through the composite shows an intensity decrease at 2.15 eV which is not in the region of interband absorption of composite components. This corresponds to the structure possessing an overall refractive index between that of opal (1.45) and rutile (2.3) of 1.8.
Real Time Measurement of Epilayer Strain Using a Simplified Wafer Curvature Technique
Authors: Floro J. A. , Chason E. , Lee S. R. 
Published: April 2011

AbstractWe describe a technique for measuring thin film stress using wafer curvature that is robust, compact, easy to setup, and sufficiently sensitive to serve as a routine diagnostic of semiconductor epilayer strain in real time during MBE or CVD growth. We demonstrate, using growth of SiGe alloys on Si, that the critical thickness for misfit dislocation can clearly be resolved, and that the subsequent strain relaxation kinetics during growth or post-growth annealing are readily obtained.
Combined Room Temperature Photoluminescence And High Resolution X-Ray Diffraction Mapping Of Semiconductor Wafers
Authors: Cockerton S , Cooke M L , Bowen D K , Tanner B K 
Published: April 2011

AbstractWe describe the characteristics and performance of a combined desk-side high resolution X-ray diffractometer and room temperature photoluminescence spectrometer designed for rapid mapping of compound semiconductors in a production line context. The combined data for AIGaAs on GaAs suggest that recent measurements of the lattice constant and the Poisson ratio of AlAs may be more reliable than earlier published values. We illustrate the instrument performance in showing that for lattice matched ternary GaInP on GaAs systems, the X-ray rocking curve maps are much more sensitive to composition variation than the photoluminescence spectra.
Characterization Of Micropipes And Other Defect Structures In 6H-SiC Through Fluorescence Microscopy
Authors: Vetter W. D. , Dudley M. , Wong T.- F. , Frderich J. T. 
Published: April 2011

AbstractCrystals of silicon carbide, and other polytypic materials often have micropipes associated with screw dislocations of large Burgers vectors running along their axial dimensions. These defects are considered the most deleterious to the performance of SiC semiconductor devices.Optical micrographs of micropipes in silicon carbide crystals are ordinarily faint. To obtain micrographs showing higher contrast and detail, laser scanning confocal microscopy (LSCM) and simple fluorescence microscopy were used on 6H-SiC single crystals after infiltrating them with a low-viscosity epoxy containing a fluorescent dye. “Staining” the micropipes rendered them much more visible both in fluorescence and conventional optical microscopies. Details of their structures and shapes were revealed, and their dimensions were measured accurately, using LSCM and other, less sophisticated, fluorescence microscopies. Other voids present, such as microcracks, were also visualized. Observations by this optical technique were related to information obtained by synchrotron white beam x-ray topography.
Brillouin Light Scattering Determination of the Glass Transition in Thin, Freely-Standing Poly(styrene) Films
Authors: Forrest J. A. , Dalnoki-Veress K. , Dutcher J. R. , Rowat A. C. , Stevens J. R. 
Published: April 2011

ABSTRACTWe have used Brillouin light scattering (BLS) to measure the glass transition temperature of thin, freely-standing poly(styrene) (PS) films. The freely-standing films were prepared by spincoating solutions of PS in toluene onto glass substrates, annealing the supported films in vacuum, and then using a water surface transfer technique to place the films across a 3 mm diameter orifice. Ellipsometry measurements of similar floated films transferred to Si(001) wafers allow the determination of the film thicknesses. Atomic force microscopy measurements revealed that the films have an rms roughness of less than 10 A˚. With the freely-standing films placed in an optical furnace, we performed BLS measurements of the films using a high-contrast, multipassed, tandem Fabry-Perot interferometer. We obtained a reliable, reproducible measure of the glass transition temperature, Tg, from the large changes in the frequencies of the thermally-excited, viscoelastic, film-guided waves within the PS films as the films were heated above Tg. BLS results for bulk PS and a 1800 A˚ thick, freely-standing PS film are presented. We find the same glass transition temperature for the 1800 A˚ thick film as the bulk PS sample. This Tg value is the same as that obtained using differential scanning calorimetry (DSC).
Relaxation Behavior in Polystyrene Near and Above the Glass Transiton Studied by Ultrasonic Technique
Authors: Sahnoune A. , Piché L. 
Published: April 2011

ABSTRACTWe report measurements of the temperature and pressure dependence of ultrasonic modulus in polystyrene between 340 and 550 K and applied pressures up to 775 bar. The real and imaginary parts of the modulus are analyzed within the Havriliak-Negami model and very good agreement is found over the entire temperature and pressure ranges. Using the Vogel-Tammann-Fulcher equation for the relaxation time, the Kauzmann temperature TK and the fragility parameter D of polystyrene were determined. The value of D indicates that polystyrene is a fragile-glass former.
The Role of Stochastic Noise on the Glass Transition
Authors: Perez-Cardenas Fernando C. , Gan Hao 
Published: April 2011

ABSTRACTGlasses are amorphous solids that exhibit an intricate structural relaxation. A broad relaxation time spectrum always emerges when these systems are perturbed. By using a Langevin-type differential equation to describe the structure dynamicsof these materials, it is depicted how the broad relaxation time spectrum arises due to the stochastic noise and how this affects the system's structure evolution as it is cooled down into the glass transition region. This stochastic model provides a macroscopic as well a microscopic view of the glass relaxation process.
An Experimental Study of the Dynamics of Contact Lines
Authors: Kumar S. , Robbins M. O. , Reich D. H. 
Published: April 2011

ABSTRACTWe have studied the dynamics of contact lines formed by water-alkane interfaces in capillaries with random surface disorder. We find that the contact-line velocity V scales with the applied capillary pressure P as V∼ (P – Pt)ζ over two decades in V. This is consistent with a critical depinning transition. We obtain this result by using a sensitive ac differential-pressure measurement technique to measure dP/dV. We find that dP/dV αV−0 8 (5) implying that 1/ζ = 0. 20 (5).
Simulation of Dynamics of Solid-Liquid Transition
Authors: Kogure Y. , Masuyama H. , Doyama M. 
Published: April 2011

ABSTRACTMolecular dynamics simulations on the solid-liquid transition of copper crystals have been performed. The configulation and the motion of atoms are monitored by RDF. It is seen that the height of the first peak in the RDF, which located at the nearest neighbour distance, decreased drastically as the temperature is increased.
Pinning of Water Imbibition Front In Porous Media
Authors: Wong Po-Zen , Delker Thomas , Hott Morgan , Pengra David B. 
Published: April 2011

ABSTRACTWe report a study of the dynamics of capillary rise of water in a column of glass beads. The water column height h is measured as a function of time t. Analyzing the late-time data in terms of critical pinning, dh/dt α (P − Pa)β, we find an anomalously large exponent β. A similar measurement for contact line pinning in capillary tubes indicates β < 1. We discuss these findings in light of recent theories for domain wall pinning in the random-field Ising model and suggest a new equation of motion which corresponds to the Wolf-Villain model with quenched noise.
Growth Equation with a Conservation Law
Authors: Lauritsen Kent Bækgaard 
Published: April 2011

ABSTRACTWe investigate an interface growth equation with a conservation law. The interaction is characterized by an integral kernel. The equation contains the Kardar-Parisi-Zhang, Sun-Guo-Grant, and Molecular-Beam Epitaxy growth equations as special cases and allows for a unified investigation of growth equations. We perform a dynamic renormalization-group analysis and determine the scaling behavior and universality classes for such growth models with a conservation law.
Morphology of the Fungus Aspergillus Oryzae and Nidulans
Authors: Miyazima Sasuke , Matsuura Shu 
Published: April 2011

ABSTRACTA variety of growth manner of the fungus Aspergillus oryzae and nidulans under varying environmental conditions such as the nutrient concentration, and medium stiffness are investigated, ranging from a homogeneous Eden-like to a ramified DLA-like pattern. The roughness σ(i, h) of the growth front of the band-shaped colony, where h is the mean front height within l of the l horizontal range, satisfies the self-affine fractal relation under favorable environmental conditions.
Stereological Estimation of Fractal Number of Fracture Planes in Concrete
Authors: Stroeven P. 
Published: April 2011

ABSTRACTConcrete is a man-made material containing a particulate filler designed on the basis of a sieve curve. In case of river aggregate, the particles are approximately spherical and smoothtextured. The particle-matrix interface is mostly the weakest chain link in the mechanical system. This implies damage evolution to start at particle-matrix interfaces. In case of direct tension, these interface cracks will be on average perpendicular to the loading direction. In case of direct compression, they will be parallel to the loading direction. A single fracture surface is formed in tension and a series of fracture surfaces in compression. They are the result of crack concentration within a process zone, in which the engineering crack closely meanders around a dividing plane. This allows to model these fracture surfaces on different resolution levels. It is shown, using stereological notions, that the very phenomenon is of a non-ideal fractal nature. Estimates for fractal dimension of fracture surfaces in concretes based on sieve curves at the border of the practical range are found to closely match experimental data reported in the literature.
Fractal and Dendritic Growth of Surface Aggregates
Authors: Brune H. , Bromann K. , Kern K. , Jacobsen J. , Stoltze P. , Jacobsen K. , Nørskov J. 
Published: April 2011

ABSTRACTThe similarity of patterns formed in non-equilibrium growth processes in physics, chemistry and biology is conspicuous and many attempts have been made to discover common mechanisms underlying their growth. The central question in this context is what causes some patterns to be dendritic, as e.g. snowflakes, while others grow fractal (randomly ramified). Here we report a crossover from fractal to dendritic patterns for growth in two dimensions: the diffusion limited aggregation of Ag atoms on a Pt(111) surface as observed by means of variable temperature STM. The microscopic mechanism of dendritic growth can be analyzed for the present system. It originates from the anisotropy of the diffusion of adatoms at corner sites which is linked to the trigonal symmetry of the substrate. This corner diffusion is observed to be active as soon as islands form, therefore, the classical DLA clusters with the hit and stick mechanism do not form. The ideas on the mechanism for dendritic growth have been verified by kinetic Monte-Carlo simulations which are in excellent agreement with experiment.
Why are computer simulations of growth useful?
Authors: Jensen Pablo , Bardotti Laurent , Barabási Albert-László , Larralde Hernán , Havlin Shlomo , Stanley H. Eugene 
Published: April 2011

ABSTRACTWe show how computer simulations can give unique information on the growth of nanostructures and thin films. Specifically, they can predict the morphologies and the island size distributions corresponding to different growth mechanisms. This information cannot be obtained from other approaches such as mean-field mathematical theories or scaling analysis. Special attention is given to the effects of small cluster mobility on experimental results.
Fractal Analysis of the Microstructure of Aisi 304 Steel.
Authors: Hinojosa M. , Trejo V. , Ortiz U. 
Published: April 2011

ABSTRACTThe present work reports the results of fractal analysis of the grain boundaries of AISI 304 stainless steel. Microstructure in the non deformed condition is compared against microstructure with 50% tensile strain. Observations were made by optical microscopy, magnifications used were 50, 100, 200, 400, and 1000x. Measurements were made over digitized images using image analysis. Fractal dimension of the grain boundaries were obtained using Richardson plots of perimeter against yardstick length. Our results agree well with reported values for different natural fractal curves. We found that, in general, grains exhibit two different fractal dimensions: one structure dimension that gives information about the morfology of the grain and one texture dimension which accounts for the fine details of the grain boundary.
Evaluation of Inaccessible Pore Structures in Random Porous Solids
Authors: Yoshizawa N. , Yamada Y. , Shiraishi M. , Kaneko K. , Setoyama N. 
Published: April 2011

ABSTRACTA fine pore characterization method is investigated for a disordered solid including inaccessible pores. Here inaccessible pores denote ones into which N2 molecule cannot access at 77 K. Activated carbons prepared differently are examined. The basic idea of the method is as follows: (1) Pores are classified into effective micropores (further devided into smaller and larger micropores distinguished from DR (Dubinin-Radushkevich) analysis and inaccessible pores. (2) Volume fraction is determined for each type of pore considering densities. (3) Debye-Bueche plot derived from SAXS analysis is used to estimate the average transversal length of solid part and pore, respectively, convinedwith their volume fractions obtained from (1) and (2). (4) In case of a porous systemwith a symmetrical shape of pores, relative number and size of inaccessible pore to effective micropore are calculated.
Solid Electrolytes: Microstructural Characterization by Conductivity Spectroscopy
Authors: Funke K. 
Published: April 2011

ABSTRACTIn conductivity spectroscopy, ionic conductivities of solid electrolytes are measured continuously from a few Hertz up to the mid-infrared, i.e., in a frequency range covering more than twelve decades. In this paper we present experimental conductivity spectra of various cryst alline and glassy ionic conductors. Tracing the characteristic patterns of the spectra back to their generic processes provides a powerful means for probing the motion of the ions on atomic scales of space and time. The technique is particularly useful for exploring the single-particle potentials felt by the ions and, hence, for elucidating details of the surrounding structure. In our examples we discuss widths, anisotropies, and geometrical arrangements of sites in crystals as well as the existence of non-equivalent sites in glass.
Electrical Characterization of Impurities in and Contacts on Mercuric Iodide
Authors: Van Scyoc J. M. , Gilbert T. S. , James R. B. 
Published: April 2011

ABSTRACTMercuric iodide (HgI2) is a semiconductor that has shown great promise for use in roomtemperature high-resolution x-ray and gamma-ray spectrometers. Its widespread usage has been limited, however, by low yield and long-term reliability problems. The processing of this material is still in its infancy compared to silicon, so research efforts continue to pursue the root causes of device failures. Two likely sources of performance limitations are impurities and poor contacts. Significant efforts have been expended in developing and using various purification schemes. However, quantitative chemical analyses have shown that several metallic impurities still exist at the high ppb level. In addition, it has not yet been definitively determined which impurities are most problematic and at what level they have a detrimental effect. Leakage currents and currentvoltage measurements have been used to study the movement of mobile impurity-related defect centers in the bulk mercuric iodide. In particular, this method has been used to quantify the drift of metallic impurities, such as Ag and Cu, which are known to or believed to degrade HgI2 detectors. Four-point-probe sheet resistance measurements have been used to study the stability of contacts and the formation of reaction layers. In particular, such measurements have revealed that the Pd contacts currently used for the highest quality detectors are not as stable as previously thought, as the films of Pd react with the HgI2 to form the amalgam PdHg.