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Molecular gas species for gas cluster ion beams (GCIBs), such as carbon dioxide and water, were examined with a range of beam energies and cluster sizes to compare with the "universal relation" of the sputter yield, Y, per cluster atom against incident beam energy, E, per cluster atom of Arn cluster beam using Irganox 1010. In this work, we compare Arn, (CO2)n, and (H2O)n gas clusters to the universal equations for Arn clusters. To discuss molecular gas species for GCIBs, energy per nucleon (E/N) needs to replace energy per atom. We monitored sputter rate, depth resolution, and secondary ion yield as a function of the beam parameters: gas species, beam energy, and cluster size. (H2O)n GCIB shows reduced sputter rates and improved depth resolution with high sensitivity compared to Arn and (CO2)n GCIBs. These initial results indicate the potential to achieve high-depth resolution with high sensitivity and suggest that (H2O)n cluster ion beam has the potential to play a significant role in surface analysis techniques with organic materials. Results also show that no single set of conditions will provide the "best gas cluster ion beam" for all applications. However, it is possible to choose a set of conditions that will be more or less optimal depending on the experimental goals, such as maximizing the sputter rate, depth resolution, and molecular ion yield. In this work, we recommend the following three guidelines for GCIB users to set their own conditions: (1) to maximize the sputter rate, select a smaller cluster (higher E/N), but be aware that this will increase fragmentation and reduce molecular ion yield; (2) to maximize the depth resolution, select a larger cluster (lower E/N), and use (H2O)n GCIB, if possible; and (3) to maximize the molecular ion signal, use the highest beam energy available, and select a cluster with 0.15–0.25 eV/nucleon for Ar and (CO2)n GCIBs or around 0.1 eV/nucleon if using (H2O)n GCIB. These results are valid for XPS, SIMS, and any technique that utilizes GCIBs. [ABSTRACT FROM AUTHOR]

Since carbon nanotubes and onions were discovered, many methods have been proposed for their production. For applications the main requirements are low capital cost, high purity of the produced material, simplicity of technique, and its potential for scale up. Recently a cathodic arc between two graphitic electrodes immersed in liquids has been demonstrated to be a simple method to produce carbon nanoparticles such as nanotubes and onions. In this paper high-resolution transmission electron microscopy is employed to examine the shape of the nanoparticles and the purity of the final material produced under various conditions. In this study we have used an arc discharge in two different liquids—liquid nitrogen and distilled water—and we have changed the grade of the carbon electrodes. The variety in structure, shape, and size of the produced particles is discussed in line with a model proposed to describe the physical process. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A simple method to fabricate high-quality nanoparticles including spherical carbon onions and elongated fullerene-like nanoparticles similar to nanotubes in large quantities without the use of vacuum equipment is reported. The nanoparticles are obtained in the form of floating powder on the water surface following an arc discharge between two graphite electrodes submerged in water. High-resolution transmission electron microscopy (HRTEM) and scanning electron microscopy images confirm the presence of spherical carbon onions with diameters ranging from 4 to 36 nm. The specific surface area of the floating powder was found to be very large, 984.3 m²/g, indicating that the material is promising for gas storage. From the surface area measurements, the mean particle diameter was calculated to be 3.7 nm. This value is close to the lower limit of the carbon onions observed in HRTEM. However, closer HRTEM observations also reveal that some carbon onions are not well crystallized. The large specific surface area can be attributed to the "surface roughness" induced by the defective nature of the carbon onion shells. To explain the formation mechanism of the carbon onions, a model of arc discharge in water with two quenching zones is proposed: (1) the presence of ion current conducive for elongated nanoparticles growth and (2) the absence of ion current for isotropic growth of carbon onions. Based on this model, we propose that the physical characteristics of the product can be controlled. [ABSTRACT FROM AUTHOR]

To clarify the orientational memory site in the hydrogen disproportionation desorption recombination process of Nd[sub 2]Fe[sub 14]B-based anisotropic magnets, high resolution transmission electron microscopy (HRTEM) characterization of hydrogen disproportionated structure of Nd[sub 13.0]Fe[sub 67.9]Co[sub 11.0]Ga[sub 1.0]Zr[sub 0.1]B[sub 7.0] has been performed. In particular, crystallographic orientations of disproportionated products relative to that of parent or original Nd[sub 2]Fe[sub 14]B have been carefully analyzed using partially disproportionated samples. No apparent orientational coherency exists between the disproportionated products of α-Fe, Fe[sub 2]B, and NdH[sub 2] and the parent Nd[sub 2]Fe[sub 14]B. However, nanoscale Nd[sub 2]Fe[sub 14]B particles of 10 to 100 nm in diameter have been detected by HRTEM to be densely present within the disproportionated mixture. Lattice fringe observation has also revealed that the crystallographic axes of the Nd[sub 2]Fe[sub 14]B particles are nearly parallel to those of the original Nd[sub 2]Fe[sub 14]B. It is thus suggested that these Nd[sub 2]Fe[sub 14]B particles be the orientational memory site upon the recombination, which recovers the original orientation leading to the anisotropy formation. [ABSTRACT FROM AUTHOR]

Reports on the growth and characterization of indium arsenide/In[sub1-x]Al[subx]As strained-layer superlattices on gallium arsenide. Growth of the strained-layer superlattices; X-ray diffraction measurements of the superlattices; Measurements conducted to evaluate the strain-induced effects on band structures.

Investigates the effects of indium[sub0.2]aluminum[sub0.8]arsenic buffer layers on the lattice distortions of strained layer superlattices (SLS) by x-ray diffraction. Methods to superimpose the SLS on the large lattice mismatched substrate without defect structures near the interfaces; Determination of alloy compositions and layer thicknesses; Summary of observed and calculated intensities around the reflection and four fitting parameters.

Presents a study which investigated finite-size effects on Raman scattering by longitudinal acoustic (LA) and longitudinal optic phonon (LO) modes in gallium arsenide-aluminum arsenide superlattices. Comparison of the experimental results with theoretical results; Differences between finite-size effects on folded LA phonon modes and confined LO phonon modes; Measurement of Raman scattering.

Presents a photoluminescence study of indium[subx] aluminum[sub1-x] arsenide-gallium arsenide strained layer superlattices. Evaluation of the effects of biaxial strain in the planes perpendicular on the superlattice direction; Method used to interpret the strain effects of band structures; Ways in which strain effects were evaluated.

Studies the lattice-mismatch strains in strained-layer superlattices grown by molecular beam epitaxy. Results and discussion; Conclusion.

Deals with a study that investigated plasma hydrogenation of laser-crystallized and amorphized films. Determination of the hydrogen concentration; Analysis of defect density and hydrogen concentration; Relation between the reduction of defects and the change in the optical properties in laser-amorphized silicon films.

The magnetic properties of fine-grained doubly oriented Si steel sheets of 0.25-0.35 mm in thickness have been investigated. The doubly oriented Si steel sheets with grains of about 0.5 mm in diameter showed a large induction B[SUB8] of about 1.9 T as well as a 35% smaller core loss than the previously studied coarse-grained doubly oriented materials. This decrease in core loss associated with the grain size reduction is primarily due to a large decrease in eddy current loss. The core loss was further decreased by applying tensile stresses and by a reduction in sheet thickness. A tensile-stressed 0.25-mm-thick material showed a small core loss of 0.82 W/kg at 1.7 T and 50 Hz. The material also showed relatively small core losses under alternating fields below 500 Hz. [ABSTRACT FROM AUTHOR]

Quasiballistic electron transport in nanoscale semiconductor structures is investigated to clarify the importance of scatterings under room-temperature operation as reflected in the velocity distribution functions. The analyses are carried out for n+-n-n+ structures based on the semiclassical Boltzmann transport equation (BTE). It is shown that the number of electrons with negative velocity grows exponetially due to scatterings around the top of the electronic potential barrier in the channel region and, thus, the scatterings cannot be neglected even in nanoscale device structures. This is closely related to the mathematical structure of the BTE whose solution exhibits the boundary-layer structure. [ABSTRACT FROM AUTHOR]

We report an observation of ultra-low-frequency self-oscillation of photocurrent in InxGa1-xAs/Al0.15Ga0.85As multiple-quantum-well p–i–n diodes. The photocurrent intensity shows self-oscillations with a characteristic frequency of ∼0.1 Hz at low temperatures under reverse bias voltages. The photocurrent self-oscillation depends on applied bias voltage, temperature, illumination power, and indium content of quantum-well layers. These dependences indicate that the photocurrent self-oscillation is attributed to photogenerated carriers trapped in localized centers within InxGa1-xAs quantum-well regions. [ABSTRACT FROM AUTHOR]

The article informs that among many wide band-gap semiconductor materials, 4H silicon carbide (4H-SiC) has great potential for use as the material for power devices, owing to its crystal maturity and superior electrical properties, such as nearly isotropic mobility and high breakdown electric field. In this article, the electric-field dependence and anisotropy of the impact ionization coefficients of 4H-SiC are obtained. The obtained impact ionization coefficients show large anisotropy; the ionization coefficients in (11&2macr;0) direction are larger than those in the (0001) direction and the asymmetry of the electron and hole-ionization coefficients in the (0001) direction is smaller than that in the (11&2macr;0) direction.

Examines the role of low temperature annealing in improving silicon dioxide/silicon interface. Use of infrared absorption spectroscopy in assessing chemical bonding in silicon dioxide films; Rate of deposition of silicone dioxide films; Concentration of water and hydroxide group in the silicon dioxide films.

Develops a parallel-plate remote plasma reactor containing a metal grid between the powered and the grounded electrode. Measurement of the plasma parameters in radio frequency argon plasmas; Ranges of the electron density; Demonstration of the effective plasma confinement; Approximation of the electron energy distribution function.

High-resolution x-ray diffraction measurements have been carried out in AlxGa1-xAs and InxGa1-xAs grown by the molecular beam epitaxy method on (001) GaAs substrates. The thin epitaxial layers in these lattice-mismatched semiconductor single heterojunctions are uniformly distorted and there is an elastic limit for large x. The epitaxial layer is affected by a thick substrate even over the elastic limit, i.e., the epitaxial layer still shows a strained state beyond the elastic limit. The relationship between the misfit strain and the lattice distortion is discussed. [ABSTRACT FROM AUTHOR]

Raman spectroscopy has been used to study strains in GaAs-In0.2Al0.8As strained-layer superlattices with a fixed layer thickness (100–100 Å) and various InxAl1-xAs buffer layers [x=0 (GaAs in place of AlAs), 0.1, and 0.2]. Strain-induced frequency shifts of the longitudinal optic phonon modes depend on the alloy composition (lattice constant) of the buffer layer. For the GaAs buffer layer (x=0) the mismatch between the superlattice and the buffer layer is accommodated by dislocations near the interface region, while for the In0.2Al0.8As buffer layer the mismatch is accommodated by the tensile strain in the GaAs layers. [ABSTRACT FROM AUTHOR]

The mechanism of Zn diffusion in a GaAs-AlAs superlattice has been studied by measuring the x-ray satellite intensity. The satellite intensity decreases and its width increases with increasng annealing time. The local structure around Zn atom is discussed. [ABSTRACT FROM AUTHOR]

An extended appearance-potential fine-structure measurement of the As-stable GaAs (001) surface has been carried out. The Ga-As, As-As distances of the surface were quantitatively determined for the first time. The surface structure is consistent with that proposed from results of the electron diffraction and photoemission measurements. [ABSTRACT FROM AUTHOR]

We report the development of a fully automatic large-volume 3D electron backscatter diffraction (EBSD) system (ELAVO 3D), consisting of a scanning electron microscope (ZEISS crossbeam XB 1540) with a dedicated sample holder, an adapted polishing automaton (Saphir X-change, QATM), a collaborative robotic arm (Universal Robots UR5), and several in-house built devices. The whole system is orchestrated by an in-house designed software, which is also able to track the process and report errors. Except for the case of error, the system runs without any user interference. For the measurement of removal thickness, the samples are featured with markers put on the perpendicular lateral surface, cut by plasma focused ion beam (PFIB) milling. The individual effects of both 1 μm diamond suspension and oxide polishing suspension polishing were studied in detail. Coherent twin grain boundaries (GBs) were used as an internal standard to check the removal rates measured by the side markers. The two methods for Z-spacing measurements disagreed by about 10%, and the inaccurate calibration of the PFIB system was found to be the most probable reason for this discrepancy. The angular accuracy of the system was determined to be ∼2.5°, which can be significantly improved with more accurate Z-spacing measurements. When reconstructed grain boundary meshes are sufficiently smoothed, an angular resolution of ±4° is achieved. In a 3D EBSD dataset of a size of 587 × 476 × 72 μm 3 , we focused on the investigation of coincidence site lattice ∑9 GBs. While bearing predominantly a pure tilt character, ∑9 GBs can be categorized into three groups based on correlative 3D morphologies and crystallography.