Library

Notes: The microstructural origin of magnetic anisotropy in a magnetron in-line sputter-deposited CoPtCr/Cr magnetic thin-film disk was examined by mapping magnetic properties and microstructure. The film coercivity (Hc), remanence-thickness product (Mrδ), and coercivity squareness (S*) were determined as a function of radial (r) and angular (θ) co-ordinates using a transfer curve magnetometer. The observed variations in Hc, Mrδ, and S* across the disk were 85 Oe, 0.15 emu/cm2, and 0.03, respectively. The angular variation in magnetic properties showed a sinusoidal pattern with the maxima corresponding to the regions where the tracks were parallel (θ=270°) to the pallet movement direction. High-resolution scanning transmission electron microscopy showed subtle differences in the Co-alloy grain morphology and crystallographic orientation between θ=270° and θ=360° locations. The grains were equiaxed in general except for a small fraction of grains elongated in the direction of pallet movement. Lattice images clearly showed that about 45% of the Co-alloy grains had in-plane c axes and a preferred alignment of the c axes along the texture groove. A greater preference for the c axes to lie along the texture line was observed for the θ=270° location. A coherency stress-based model is proposed to explain the preferred c-axis alignment. While the crystalline anisotropy appears to be the main factor responsible for the magnetic anisotropy, both crystalline and shape anisotropies contribute to the magnetic anisotropy variations.

Notes: Abstract: The relationship between extracellular signal-regulated protein kinase (ERK) activation and process extension in cultured bovine oligodendrocytes (OLGs) was investigated. Process extension was induced through the exposure of cultured OLGs to phorbol 12-myristate 13-acetate (PMA), an activator of protein kinase C (PKC), for various intervals. During the isolation of these OLGs from bovine brain, the original processes were lost. Therefore, any reinitiation of process extension via PMA stimulation was easily discernible through morphological monitoring. It was found that exposure of OLGs to PMA for 10 min was enough to induce OLG process extension 24–72 h later. Furthermore, this extension was still evident at least 1 week after the initial PMA stimulation, indicating that OLGs do not need continuous PKC activation to sustain process extension. Control and PMA-stimulated OLGs were also subjected to immunocytochemistry using an anti-ERK antibody selective for the mitogen-activated protein kinases p42 Erk2 (ERK2) and p44 Erk1 (ERK1) isoforms. ERK immunoreactivity in the nucleus was evident after PMA stimulation of OLGs but not in control OLGs. In parallel experiments, the control and PMA-stimulated OLGs were purified by Mono Q fractionation and subjected to ERK phosphotransferase assays using [γ-32P]ATP and either myelin basic protein (MBP) or a synthetic peptide substrate based on the Thr97 phosphorylation site in MBP. These assays indicated that in PMA-treated OLGs, ERK activation was at least 12-fold higher than in control OLGs. Anti-ERK and anti-phosphotyrosine western blots of the assay fractions verified an enhanced phosphorylation of ERK1 and ERK2 in PMA-treated fractions relative to control fractions. When OLGs were pretreated for 15 min with the ERK kinase (MEK) inhibitor PD 098059 before PMA stimulation, they exhibited a 67% decrease in ERK activation as compared with cells treated with PMA alone. Furthermore, these MEK inhibitor-pretreated cells were still viable but showed no process extensions up to 1 week later. Therefore, we propose that a threshold level of ERK activity is required for the initiation of OLG process extension.

Notes: Hot-filament-assisted chemical vapor deposition has been used to study the growth morphology of synthetic diamond deposited on silicon substrate in a dilute (1 vol %) CH3COCH3/H2 at high substrate temperature (about 777 °C). Scanning electron microscope pictures of the diamond particles show that the surfaces of synthetic diamond consist of rough-octahedral (111) faces and smooth-cubic (100) faces, which is cubo-octahedron. And also the (110) facets on the octahedral face are observed. The relative growth rate of (111) faces to that of (100) faces in the cubo-octahedron is double that derived from the calculated specific surface energy. So the apparent growth rate of the octahedral face must be explained by the growths of two constituent crystallographic planes of (100) and (110). The observed roughness of (111) faces arises from the competing growths of (100) and (110) planes. The (110) faces separate the (111) faces into three (110) planes. For the study of diamond crystal growth during deposition, it is suggested that the growth mechanism of cubo-octahedral diamond is the competing growths of (100) and (110) crystallographic planes.

Notes: The crystallization behavior of amorphous Ge2Sb2Te5 thin films were investigated by using differential scanning calorimetry, x-ray diffraction, and optical reflectivity measurements. The analysis of in situ ellipsometry isotherm Ge2Sb2Te5 films based on the Johnson–Mehl–Avrami equation revealed that the crystallization process near 150 °C was a two-step process. In this alloy thin film, the kinetic exponents in the Johnson–Mehl–Avrami equation were about 4.4 for the first stage and 1.1 for the second stage. A kinetic model based on the cascaded crystallization is proposed. The proposed model showed good agreement with the experimental results obtained by transmission electron microscopy and x-ray diffraction. © 1999 American Institute of Physics.

Notes: We present direct observation of self-focusing near the diffraction limit by measuring the beam-spot size with a scanning fiber probe tip. We have used the polycrystalline silicon film, which exhibits a reverse-saturation (Im χ(3)(approximate)8×10−3 esu) and self-focusing (Re χ(3)(approximate)2×10−2 esu), as measured by the conventional z-scan method with He–Ne laser. It is observed that the beam radius of about its wavelength becomes smaller as the input laser intensity is increased, which indicates that the self-focusing effect dominates over the reverse saturation in the 300-nm-thick sample. © 2001 American Institute of Physics.

Notes: Abstract Microstructures of pyrolytic carbons deposited in a tumbling bed from propane gas have been examined by polarized light microscopy, scanning electron microscopy, and transmission electron microscopy. Isotropic, laminar, and columnar structures were obtained. These structural varieties, which could be produced by changes in the deposition conditions and the substrate geometry, Were investigated to select more reasonable deposition mechanism. Two essential factors are found directly related to determine the microstructure of pyrolytic carbon. [)ne is the degree of supersaturation of pyrolysis products in a gas phase. The other is the gas flow pattern of recirculation within a deposition zone. The overall deposition process of pyrolytic carbon can be explained by the factors independent of various coating systems. This paper gives the experimental evidences that the above two factors are inter-related and simultaneously contribute to form pyrolytic carbons, and the cracks formed in deposits are closely related to their fracture mechanism. Due to the cracks the fractured surfaces of isotropic deposits are round and those of columnar deposits are laminated. Laminar deposits have both round and laminated fracture surfaces.