Electric-Field Gradients at Group-III Sites on GaAs and InAs (111)B Surfaces

We report a comparison of electric-field gradients (EFGs) measured at the group-III sites on epitaxially-grown surfaces of 2×2-reconstructed GaAs and InAs crystals. For this purpose, we used ¹¹¹In→¹¹¹Cd perturbed-angular-correlation (PAC) spectroscopy. Sharp spectral lines characterize the perturbation functions corresponding to both surfaces. On GaAs surface, we observe only one well-defined nuclear electric-quadrupole interaction (NQI); and on the InAs surface, we observe a primary and a secondary NQI. Very similar but experimentally-distinguishable values of the EFG-parameters characterize the primary interactions corresponding to the GaAs and InAs surfaces. Specifically, for the GaAs and InAs surfaces, ω _Q =28.0±0.2 Mrad s⁻¹ and η=0.43±0.02 and ω _Q =28.8±0.2 Mrad s⁻¹ and η=0.39±0.02, and the angles between EFG z-axis and the (111) direction are 65°±3° and β=53°±3°, respectively. These unexpected results indicate that the so-called lattice contribution to the EFG is not significant. Moreover, for the primary NQIs on both surfaces, the similar parameter values demonstrate that chemical differences between the ¹¹¹In probe and the indigenous Ga surface atoms cause no large quantitative effects. This information indicates that impurity probes and PAC spectroscopy can be used effectively to investigate III–V surfaces. This revised version was published online in September 2006 with corrections to the Cover Date.     

Conformational Analysis of (S)-4,5,6,7-Tetrahydro-5-Methylimidazo [4,5,1-jk][1,4]-Benzodiazepin-2(1H)-one (R78362)

The solution and solid state conformation of (S)-4,5,6,7-tetrahydro-5-methylimidazo [4,5,1-jk][1,4]-benzodiazepin-2(1H)-one (R78362) have been investigated by low temperature NMR and x-ray diffraction studies. The ¹H NMR spectrum of R78362 shows no evidence of the presence of multiple conformers in the temperature range 340K - 177K. Molecular mechanisms and semiempirical molecular orbital calculations suggest that the nitrogen and ring inversion barriers of R78362 are small and thus a time-averaged ¹H NMR spectrum is probably occurring at 298K. The x-ray diffraction data indicated that there were two independent molecules in the asymmetric unit of the crystal. The two molecules had similar conformations with the benzoimidazole ring being planar and the diazepine ring in a “half-chair” conformation.     

Search for f(J)(2220) in radiative J/ψ decays

We present a search for f(J)(2220) production in radiative J/ψ→γf(J)(2220) decays using 460 fb?1 of data collected with the BABAR detector at the SLAC PEP-II e(+)e? collider. The f(J)(2220) is searched for in the decays to K(+)K? and K(S)?K(S)?. No evidence of this resonance is observed, and 90% confidence level upper limits on the product of the branching fractions for J/ψ→γf(J)(2220) and f(J)(2220)→K(+)K?(K(S)?K(S)?) as a function of spin and helicity are set at the level of 10??, below the central values reported by the Mark III experiment.     

Antenna length and polarization response of antenna-coupled MOM diode infrared detectors

This work focuses on the fabrication and response of dipole antenna-coupled metal–oxide–metal diode detectors to long-wave infrared radiation. The detectors are fabricated using a single electron beam lithography step and a shadow evaporation technique. The detector’s characteristics are presented, which include response as a function of incident infrared power and polarization angle. In addition, the effect of dipole antenna length on detection characteristics for 10.6 μm radiation has been measured to determine resonant lengths. The response of the detector shows a first resonance at a dipole length of 3.1 μm, a second resonance at 9.3 μm, and third at 15.5 μm. The zeros intermediate to the resonances are also evident.     

Characterization of Standard Reference Material 2941, uranyl-ion-doped glass, spectral correction standard for fluorescence

Standard Reference Material^® (SRM^®) 2941 is a cuvette-shaped, uranyl-ion-doped glass, recommended for use for relative spectral correction of emission and day-to-day performance validation of fluorescence spectrometers. Properties of this standard that influence its effective use or contribute to the uncertainty in its certified emission spectrum have been explored here. These properties include its photostability, absorbance, dissolution rate in water, anisotropy, temperature coefficient of fluorescence intensity, and fluorescence lifetimes. The expanded uncertainties in the certified spectrum are about 4% around the peak maximum at 526 nm, using an excitation wavelength of 427 nm. The SRM also exhibits a strong resistance to photodegradation, with no measurable decrease in fluorescence intensity even after 8 h of laser irradiation.     

Addition reaction and characterization of chlorotris(triphenylphosphine)iridium(I) on silicon(1 1 1) surfaces

Studies were performed to determine the chemical addition of a metal complex molecule, chlorotris(triphenylphosphine)iridium(I), on hydrogen passivated Si(1 1 1) surfaces to form a self-assembled monolayer (SAM). The iridium complex was synthesized prior to chemical addition, for which modified reaction conditions were chosen. Following addition, the silicon surfaces were characterized with X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV). The XPS results revealed that the surfaces consisted of the expected elemental percentages and that the iridium has a slightly higher success rate at attaching to oxide-free surfaces. XPS data also strongly indicate that the iridium complex remained intact upon chemisorption and did not decompose during the addition reaction. CV data show a difference between iridium treated surfaces and control samples. Hydrogen passivated wafers with iridium complex were much more conductive than those which were terminated with just an oxide or with an oxide and iridium complex. Furthermore, no free iridium reagent was detected as an additional feature in the current profile, indicating there was no physisorbed layer.     

THE PREPARATION OF TRIALKYL PHOSPHITES DIRECTLY FROM THE ELEMENT

Abstract

The reaction between finely divided white phosphorus and several alkoxide ions in the presence of tetrachloromethane and excess of alcohol has been investigated under a variety of conditions. High yields of trialkylphosphite are obtained when two equivalents of alkoxide are used. With one equivalent of alkoxide, dialkylphosphonate is formed in comparable yield. Maximum yields of triester are obtained within 1–3 h at room temperature. Prolonged treatment results in the conversion of trialkylphosphite to phosphate by reaction with tetrachloromethane. Phenolate ions are unreactive under the same experimental conditions. The mechanism of the reaction is discussed.     

Hemostatic efficacy and tissue reaction of oxidized regenerated cellulose hemostats

Oxidized regenerated cellulose (ORC) has been used as an absorbable hemostat since World War II. In the present study, hemostasis time was determined in a spleen incision model in swine. The effect of mass on absorbable hemostat efficacy and hemostasis time was evaluated by standardizing the ORC materials on a mass basis. The median hemostasis time for a single layer of the new nonwoven ORC was as much as 51 % shorter than woven ORC (P < 0.001). The mean hemostasis time for nonwoven ORC was not affected by the mass of hemostat applied to the wound. The hemostatic efficacy of woven ORC increased with the mass (layers) of hemostat applied to the wound. Nonwoven ORC is significantly faster in achieving hemostasis than woven ORC, and its hemostatic efficacy is not influenced by the mass of material applied. Tissue reaction was minimal and the material was fully absorbed by 14 days.