Controlled beam dry etching of InP by using Br2-N2 Gas

Indium phosphide dry etching is carried out using a reactive beam extracted from a Br₂-N₂ gas discharge plasma. Keeping the N₂ gas pressure constant at 0.23 mTorr, the Br₂ gas pressure was varied from 0 to 0.1 mTorr and the sample temperature was varied from 40 to 200°C. The etched shapes and etching rates are investigated in terms of the etching beam composition. Two distinct types of etching mechanisms come into play depending on the Br₂ gas pressure. Smooth vertical side walls and a temperature independent etching rate can be obtained at a Br₂ gas pressure of 0.04 mTorr or less and a temperature above 100°C, where the etching is induced by the ambient Br₂ gas species and N₂ beam. Undercut etching with a temperature dependent etching rate is seen at a Br₂ gas pressure of 0.07 mTorr or higher, where the etching beam contains both N₂ and Br₂ gas species. Neutralized Br species generated by the discharge of the Br₂ gas are shown to form the undercut. A waveguide corner mirror with a loss of less than 1 dB is made by using an etching beam with no neutralized Br species.     

The effect of pre-stressing and annealing on the young's modulus of some nuclear graphites

Studies have been made on the decrease in the dynamic Young's modulus of some nuclear graphites caused by pre-stressing or cyclic loading in compressive mode and its recovery due to annealing up to 2000 °C. It is found that the decrease in the modulus is well represented by the formulae, $\text{E}\text{E}{}_0\text{= ? Aσ}{}^2\text{+B}$ for ex-truded graphites and $\text{(E ? E}{}_{\mathrm{c}}\text{)}\text{(E}{}_0\text{?E}{}_{\mathrm{c}}\text{) = B}\text{exp}\text{( ? Aσ}{}^2\text{)}$ for moulded ones, where E, E_c and E₀ are the modulus at a pre-stress σ, that at pre-stress equal to fracture stress and that with no pre-stressing, respectively. A and B are constants. Annealing experiments show that the moduli of extruded graphites recover almost completely below 1000 °C, while in the case of moulded graphites complete recovery is not attained even at 2000 °C. The activation energy obtained for the recovery of an extruded graphite below 1000 °C is about 0.6 eV.     

Structures and purification of boron nitride nanotubes synthesized from boron-based powders with iron particles

Boron nitride (BN) nanotubes, nanohorns and nanocoils were synthesized by annealing Fe₄N/B, FeB and Fe/B powders at 1000 °C for 1–24 h in nitrogen gas atmosphere, and large amounts of BN nanotubes were obtained by annealing Fe₄N/B. The growth mechanism and atomic structures were investigated on cup-stacked BN nanotubes synthesized from Fe₄N/B by X-ray diffraction, high-resolution electron microscopy, electron diffraction and energy dispersive X-ray spectroscopy. As-produced BN soot was purified by removing non-BN nanomaterials such as metal catalyst particles and unreacted boron, and high purity BN nanotubes were obtained.     

Formation and atomic structures of boron nitride nanohorns

Boron nitride (BN) nanohorns were synthesized by an arc-melting method, and atomic structure models for BN nanohorns with tetragonal BN rings were proposed from high-resolution electron microscopy. Stability and electronic structures of the BN nanohorns were investigated by molecular orbital/mechanics calculations. The calculation showed that multiwalled BN nanohorns would be stabilized by stacking of BN nanohorns. The energy gap of BN nanohorn was calculated to be 0.8 eV, which is lower compared to those of BN clusters and nanotubes.     

Three-dimensional atomic imaging of Y and (B12)13 clusters in YB56 by HREM and crystallographic image processing

The three-dimensional atomic image of YB₅₆ was obtained by inverse Fourier transformation of three-dimensional phases and amplitudes in three high-resolution images along [100], [110] and [111] of YB₅₆ crystals. After crystallographic image processing, the image directly showed the three-dimensional potential map of the crystal, which showed (B₁₂)₁₃ clusters and Y atom positions. The present method would be useful for three-dimensional structure analysis in nanoscale regions.     

Design of Synthetic Polymer Nanoparticles that Capture and Neutralize a Toxic Peptide

Designed polymer nanoparticles (NPs) capable of binding and neutralizing a biomacromolecular toxin are prepared. A library of copolymer NPs is synthesized from combinations of functional monomers. The binding capacity and affinity of the NPs are individually analyzed. NPs with optimized composition are capable of neutralizing the toxin even in a complex biological milieu. It is anticipated that this strategy will be a starting point for the design of synthetic alternatives to antibodies.     

Influence of high temperature exposure on the properties of alumina short fibre reinforced AA6061 alloy

Influences of high temperature exposure on the mechanical properties and microstructures of AA6061 alloy matrix composites containing 15 vol % alumina short fibre (FRM) have been examined. When the exposure temperature exceeded 853 K, the degradation in fracture strength of the FRM became remarkable. During the heat treatment, magnesium, which is one of the strengthening elements of the matrix, segregated on the surface of alumina fibres to form a spinel and vaporized from the specimen surface in the vacuum. Therefore, degradation in the strength of the FRM was caused by weakening of the matrix due to the dissipation of magnesium from the matrix. Appropriate conditions for joining the FRM were also discussed.     

Tumor growth modulation by sense and antisense vascular endothelial growth factor gene expression: effects on angiogenesis, vascular permeability, blood volume, blood flow, fluorodeoxyglucose uptake, and proliferation of human melanoma intracerebral xenografts

Vascular endothelial growth factor (VEGF), also known as vascular permeability factor, has been investigated as a potent mediator of brain tumor angiogenesis and tumor growth. We evaluated the effect of VEGF expression on the pathophysiology of tumor growth in the brain. Human SK-MEL-2 melanoma cells, with minimal VEGF expression, were stably transfected with either sense or antisense mouse VEGF cDNA and used to produce intracerebral xenografts. Vascular permeability, blood volume, blood flow, and tumor fluorodeoxyglucose metabolism were assessed using tissue sampling and quantitative autoradiography. Tumor proliferation was assessed by measuring bromodeoxyuridine labeling indices. Tumor vascular density and morphological status of the blood-brain barrier were evaluated by immunohistochemistry. SK-MEL-2 cells transfected with sense VEGF (V+) expressed large amounts of mouse and human VEGF protein; V+ cells formed well-vascularized, rapidly growing tumors with minimal tumor necrosis. V+ tumors had substantial and significant increases in blood volume, blood flow, vascular permeability, and fluorodeoxyglucose metabolism compared to wild-type and/or V- (antisense VEGF) tumors. VEGF antisense transfected V- expressed no detectable VEGF protein and formed minimally vascularized tumors. V- tumors had a very low initial growth rate with central necrosis; blood volume, blood flow, vascular permeability, and glucose metabolism levels were low compared to wild-type and V+ tumors. A substantial inhibition of intracerebral tumor growth, as well as a decrease in tumor vascularity, blood flow, and vascular permeability may be achieved by down-regulation of endogenous VEGF expression in tumor tissue. VEGF-targeted antiangiogenic gene therapy could be an effective component of a combined strategy to treat VEGF-producing brain tumors.     

Formation of WSi-based ohmic contacts to n-type GaAs

An outcome of the indirect doping concept conceived recently in NiGe-based Ohmic contacts has led to the development of annealed WSi-based Ohmic contacts to n-type GaAs for the first time. It was concluded that simultaneous addition of a “direct doping element” of Si in WSi_2.7 and an “indirect doping element (M)” such as Au, Pd, Cu, or Ag, was essential. The M(5 nm)/WSi_2.7(20nm)/W(50 nm) contacts showed Ohmic behavior after annealing with the lowest contact resistances of 0.4 Ω mm (6×10⁻⁶ cm²). In addition, the WSi-based contacts with a small amount of Au showed good thermal stability at 400 °C after contact formation. Microstructural analysis of the WSi contacts with Au showed formation of β-AuGa and WSi₂ compounds, which indicates that the Ohmic behavior would be due to heavy doping of Si at the GaAs surface induced by Ga out-diffusion. The mechanism of Ohmic contact formation of the present contacts agreed very well with that of the NiGe-based Ohmic contacts.