Polycrystalline In2O3 films with high crystallinity were prepared by annealing the amorphous In2O3 films deposited at room temperature by using dc/rf sputtering method. General electronic behaviors of both these amorphous and polycrystalline films have been investigated by means of Hall effect and resistivity measurements at temperatures between 4.2 and 300K. For the amorphous films, ionized impurity scattering dominates the electronic transport, and Hall mobility agrees well with the theory of degenerate semiconductors with divalent impurity scattering centers. On the other hand, the conduction mechanism of the polycrystalline films is governed dominantly by phonon scattering, since these films exhibit a clearly positive temperature coefficient of resistivity with the maximum Hall mobility of 150cm2∕Vs at 300K and 230cm2∕Vs at 4.2K, with little change in carrier concentration between these temperatures. Conductivity of both the amorphous and polycrystalline films is found to show a linear relationship in a double-logarithmic plot against carrier concentration between 4×1015 and 5×1020cm−3, a typical behavior of the impurity semiconductors with parabolic conduction band. For each set of films with the same thermal history, Hall mobility is found to vary on a convex upward curve with respect to carrier concentration. This behavior suggests a general and strong correlation of the structural defects introduced upon deposition and localization of conduction electrons with electron mobility, which led to a proposition of three categories for temperature coefficient of resistivity with major transport mechanisms of phonon scattering, divalent impurity scattering, and weak localization, respectively.
The question of how to design a water-soluble globular protein remains. We report here the synthesis of a native-like and pore-forming small globular protein (SGP, 69 amino acid residues). The protein was designed to have four helices: a Trp-containing short hydrophobic helix in the middle surrounded by three Tyr-containing long basic amphiphilic helices. Size-exclusion chromatography and CD measurements indicated that in buffer solution SGP is monomeric with a 50% helical structure. SGP did not completely denature even at high temperature (90 degrees C) and at relatively high Gu x HCl concentration so that the denaturant concentration at the midpoint of the transition is 5 M. Dye binding studies and fluorescence energy transfer experiments showed that SGP possesses a hydrophobic binding site and its Trp of the central helix is present at a relatively hydrophobic region and accepts the energy from Tyr(s) in other amphiphilic helices, indicating that SGP takes a stable globular-like structure in aqueous solution. From the depth-dependent fluorescent studies using egg PC liposomes containing n-doxyl fatty acids and brominated phospholipid as quenchers, it was found that the hydrophobic central alpha-helix is able to enter spontaneously into the lipid bilayers and the Trp in the central alpha-helix is located at about the middle of the alkyl chain in the outer layer of the phospholipid bilayer. The peptide is also able to increase the membrane permeability with two modes of current (basal current and single ion channel) in planar phospholipid bilayers, indicating the spontaneous insertion of the protein into the lipid bilayer (basal current) and then the formation of a uniform size of channel pore (14 pS). SGP is useful as a basic and starting model to find good amino acid sequences that fold to a desired protein structure and to search translocation mechanisms from aqueous solution into lipid bilayers.
The etching rate difference of magnetic materials with respect to the aspect ratio (AR) has been investigated using CO/NH3 plasma with a Ta mask for high-density integration of magnetic random access memory devices. The etching depth difference of magnetic stack films as a function of etching times reveals that the etching rate is suddenly reduced at AR > 0.7, and the occurrence of etch stop has been confirmed. From the scanning transmission electron microscope–energy dispersive x-ray spectroscopy results, Ta deposition, which proceeds from the Ta mask to the bottom space of the pattern, induces this etch stop. The roof mask structure, which has a concavity directly under the Ta mask to reduce the amount of Ta deposition, can improve the etch stop, and a fine magnetic stack film pattern with AR = 2.3 can be fabricated.
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