ALBERT

Notes: Deep-level transient spectroscopy has been used to characterize n-type In0.48Ga0.52P grown by gas-source molecular beam epitaxy. Only one electron trap was detected in both unintentionally doped and Si-doped material, with the thermal emission energy barrier varying somewhat with measurement conditions. For a bias pulse duration of 10 ms, the emission barrier energy was 0.24±0.03 eV and the capture barrier energy was 0.06±0.02 eV. The trap concentration was less than 3×1014 cm−3 and was found to be independent of Si doping for concentrations up to 4×1018 cm−3 and to oxygen contamination in the range (0.5–1.5)×1018 cm−3.

Notes: Films of thickness 350, 500, and 1100 A(ring) rf-magnetron-sputtered onto Corning 7059 glass at a substrate temperature of 250 °C were patterned into aspect ratios of from 10 to 100 with a fixed width of 10 μm by the photolithographic procedure. Gold pads were formed for electrical contacts. Magnetoresistance ratio, saturation field, and in-plane coercivity were measured. The domain patterns were studied by the Bitter method. Results show that the magnetoresistance ratio increases as film thickness increases. In a 500-A(ring)-thick film, the coercivity decreases from 14 to 9.8 Oe with increasing aspect ratio due to closure domain effects.

Notes: The nematic–isotropic (N–I) phase transition of rod-like molecules is investigated by molecular dynamics (MD) simulation. This study is focused on three different aspects. First, a more realistic model than a hard core system is employed. Second, the MD simulation enables us to calculate time-dependent functions. Last, an isothermal–isobaric (NpT) ensemble is used to consider the change of volume at the N–I transition. The results of MD simulation suggest that the interatomic potential plays an important role in the N–I phase transition of rod-like molecules. The MD simulation of the N–I phase transition of rod-like molecules can predict the "weak first orderedness'' accurately. Both translational and rotational diffusion coefficients of rod-like molecules in the system with a smaller value of σ are larger than those with a larger value of σ, and the calculated rotational reorientation time of rod-like molecules in isotropic phases lies in the 10−11–10−10 s range.

Notes: The mass selected Kr⋅H2O+ cluster is photodissociated in the range 514 to 357 nm using lines from an argon ion laser. Product branching ratios are measured and shown to be a strong function of photon wavelength; Kr+/H2O products dominate at 357 nm (90%) but are equal in intensity to H2O+/Kr products at 514 nm. A small KrH+/OH product is observed at all wavelengths (∼5%), representing the first observation of a photoinduced, intracluster proton transfer reaction. The total cross section is estimated to be ∼2×10−19 cm2 at 514 nm. Laser polarization studies indicated the Kr+/H2O products come from direct accessing of a repulsive upper state (intracluster charge–transfer reaction). Both Kr+(2P3/2) and Kr+(2P1/2) spin–orbit states are formed, but their branching ratio is very strongly dependent on wavelength: 100% Kr+(2P3/2) at 514 nm, 100% Kr+(2P1/2) at 357 nm, and variable amounts of each in between. Analysis of the kinetic energy distribution of Kr+/H2O products indicates H2O is strongly rotationally excited (0.18 to 0.23 eV). This fact, coupled with analysis from an impulsive model for Kr+–H2O dissociation suggests the Kr atom is above (or below) the H2O+ plane in the Kr⋅H2O+ ground state, situated closer to the O end of the molecule. Further analysis of the Kr+/H2O kinetic energy distribution yields the binding energy D00(Kr–H2O+) =0.33± 0.1 eV. Polarization studies indicate H2O+/Kr products arise from a bound upper state. Phase space theory modeling of the kinetic energy distribution indicates the H2O+ product is formed with ∼1.3 eV internal energy. Two models are discussed, one that suggests H2O+(A˜ 2A1) is formed and a second that suggests H2O+ is the chromophore, internally converts to vibrationally hot H2O+(X˜ 2B1) and slowly leaks vibrational energy to the c

Notes: Time-domain reflectometry (TDR) is being used increasingly for measuring the moisture content of porous media. However, successful application for measuring water in soil has been limited to non-deformable soils, and it would be a valuable extension of the technique if it could be used for soils that shrink on drying. We have recently investigated its application to soils rich in clay and organic matter and peats. Here we propose a method for determining moisture content in deformable soils based on the relation between the dielectric constant, K, and the volumetric moisture content, Θ, measured by TDR.Parallel TDR probes with a length of 15 cm and a spacing of 2 cm were placed horizontally in soil cores with a diameter of 20 cm and height of 10 cm taken from a forest. The soil is very porous with large proportions of both silt and clay. The sample weight and travel time of the electromagnetic wave guided by parallel TDR probes were simultaneously measured as a function of time, from saturation to oven-dryness during which the core samples shrank considerably. Vertical and horizontal components of shrinkage were also measured to take the air-exposed region of TDR probe into account in the determination of K. The effect of deformation on volumetric moisture content was formulated for two different expressions, namely actual volumetric moisture content (AVMC) and fictitious (uncorrected) volumetric moisture content (FVMC). The effects of air-exposure and expressions of volumetric moisture content on the relation between K andΘ were examined by fitting the observations with a third-order polynomial. Neglecting the travel time in the air-exposed part or use of the FVMC underestimated the Θ for a given K. The difference was more pronounced between AVMC and FVMC than between two different dielectric constants, i.e. accounting for air-exposure, Kac, and not accounting for air-exposure, Kau. When the existing empirical models were compared with the fitted results, most underestimated the relation based on the AVMC. This indicates that published empirical models do not reflect the effect of deformation on the determination of Θ in our forest soil. Correct use of the Θ expression has more impact on determining moisture content of a deformable soil than the accommodation of travel time through the air-exposed region of TDR probe.

Notes: The magnetic properties of an Fe87Zr7B5Ag1 (at. %) amorphous alloy, which contains an additional insoluble element (Ag) in a small amount, have been investigated as a function of annealing temperatures in order to know its potential applicability as a core material used at high-frequency. As a result, a new excellent soft magnetic material with very high resistivity was developed. The amorphous alloy annealed at a relatively low temperature of Ta=300 °C exhibited a very high initial permeability μi of 146 000 at 1 kHz and 2 mOe, resistivity ρRT of 4.5 μΩ m, and very low coercivity Hc of 20 mOe, respectively. The values obtained are the best ones among various kinds of Fe-based soft amorphous materials reported up to now. Furthermore, the amorphous ribbon heat treated at Ta=300 °C still retained good ductility enough to endure 180° bending, which is very important from the viewpoint of processing for mass production. The phenomenon of good soft magnetic properties presumably arises from the homogenous formation of very fine α-Fe clusters in an amorphous matrix, which can be deduced from the increase of resistivity, and the reduction of magnetostriction caused by the dissolution of Zr and B into the α-Fe cluster. © 1995 American Institute of Physics.

Notes: Intrinsic and generated bulk defects in the gate insulator of silicon insulated gate field effect transistors were examined using a continuous forward-bias pulsed injection technique to inject up to 1017 e/cm2 at 293 and 100 K, for insulator thicknesses ranging between 5.4 and 50.5 nm. The amount of trapping observed at 100 K was about 30 times greater than that at 293 K. The additional trapping at the reduced temperature was determined to come from two sources. One is trapping by existing shallow bulk defects, and the other is an increase in the density of generated bulk defects. The defect generation process is thought to be related to the neutral hole trap becoming unstable during injection, acting as an electron trap. This instability appears to be enhanced as the temperature is reduced to 100 K by a "freeze out'' effect, or by higher energy carriers that result from a reduction in the thermal scattering. The defect generation rate follows a power law, much like a chemical rate equation, i.e., the rate of defect generation is dependent on the injection current density, much like a chemical reaction is dependent on pressure of the reactive species. The charge centroid of the generated defects, measured from the substrate/oxide interface, was determined at both temperatures and the centroid of the shallow electron traps was determined at 100 K. These were found to be in the range of 6–8 nm at 100 K and 10–16 nm at 293 K. Also, a defect free, or tunneling, region of 2–4 nm extent was determined to exist at each interface. This implies that when the oxide thickness decreases to about 4–8 nm, no threshold voltage shift should result from carrier injection at room, or low temperature, and in fact this behavior was observed in these devices (at least up to 1017 e/cm2 injected). It was found that the shallow traps can be rapidly depopulated by subjecting the devices to ordinary white light during normal device use, pointing to a possible method to improve device reliability at 100 K. © 1997 American Institute of Physics.

Notes: The energy distributions of electron emission from a Schottky emitter have been studied at tip temperatures from 1450 to 1800 K and angular current densities from 0.1 to 240 μA/sr. We have observed broadening of the energy distribution, with increase of angular current density and decrease of tip temperature, from 0.4 to 1.32 eV resulting from electron tunneling and electron–electron interaction. Good agreement between the experimental results and predictions from Monte Carlo simulation of the emission process is observed. © 1997 American Institute of Physics.

Notes: A new technique for increasing the laser penetration efficiency of metals has been developed. By amplitude modulating a free-running neodymium:yttrium aluminum garnet laser pulse, the depth of the crater was increased and the threshold energy for reliable hole drilling was decreased significantly. It was observed that the effect of chopping was optimal at 8–12 kHz with a 70% duty cycle. We believe that this improvement is due to an increase in the vapor recoil pressure and reduced plasma screening. Possible acoustic resonance effects have also been considered and will be discussed.