Current Density-Anodic Potential Curves Of Single Crystal GaAs At Low Currents In KOH

Single p-type, GaAs crystals of high purity, Zn doped, were used to determine whether or not the inverse octahedral {111} faces show potential differences and various rates of anodic dissolution. The Ga{111}, As{111}, {110}, and {100} faces, were polished, etched, and etch-polished with concentrated H2SO4 + H2O2, and immersed in IN KOH. The Ga{111} faces were found to be the most noble with respect to rest and anodic dissolution potentials. The potential difference between the inverse {111} faces was as large as 0.14v for the rest and 0.123v for the dissolution potentials. The 4 anodic polarization curves gave nearly parallel Tafel lines, with a slope of 66.0 ± 1 mv/log i, up to current densities of 0.5 ma/cm2. The rate of anodic dissolution of the As{111} faces was 69 X as high as the inverse Ga{111}. The activation energies of dissolution of all 4 faces were equal within experimental limits: 16.7 ± 0.7 kcal mole−1. It is concluded that the slow step in the dissolution of GaAs is a one electron discharge with subsequent steps leading to the formation of Ga(OH)3 to provide a protective coating not readily soluble in KOH. From this point of view all observed phenomena can be explained in a qualitative manner. © 1968, The Electrochemical Society, Inc. All rights reserved

Optical Recording Aspects of rf Magnetron Sputtered Iron-Garnet Films

The intrinsic magneto-optical readout performance in reflection is calculated for bismuth and cobalt-substituted iron-garnet films on a multilayer interference mirror at 800-, 633-, 488-, and 420-nm wavelengths and is compared with that of a trilayer medium composed of an antireflection layer, a rare-earth transition-metal film, and a metallic mirror. It is found, when disregarding inhomogeneities, like irregular domain shape, ripple of the magnetic anisotropy, and surface roughness, that iron garnets are superior to rare-earth transition-metal films at blue to near-ultraviolet wavelengths if operated at thicknesses where optical interference occurs in the magnetic layer. Optical transmittance at these thicknesses is sufficiently high so that multilevel recording media can be conceived. In contrast, the optical absorption of rare-earth transition-metal alloys is much higher so that only thicknesses much above interference conditions are feasible, thus precluding them from multilevel recording. This comparative study is supplemented by calculating the magneto-optical performance in reflection of a recently reported multilayer medium composed of an antireflection coating and a periodically repeated sandwich of 4-Å Co and 9-Å Pt layers. In contrast to conventional rare-earth transition-metal films, the magneto-optical Kerr effects of this material do not degrade when decreasing the wavelength from 800 to 400 nm, but still do not reach the performance of bismuth-iron garnets in the green to ultraviolet spectrum. For the garnet system Y3--xBixFe5O12 the spectra of the real and imaginary parts of the diagonal and off-diagonal component of the dielectric tensor εij are reported in the range of photon energies between 1 and 5 eV, i.e., 1240- and 248-nm wavelengths and a bismuth concentration up x=1.4 Bi3+ atoms per garnet formula. In addition, the off-diagonal components ε′12 and ε″12 are parametrized in terms of paramagnetic optical transitions, taking the spectra for x=1.25 as a typical example. Furthermore, optical and magneto-optical spectra are presented for Co 2+- and Co3+- substituted iron garnets and barium hexaferrite BaFe12O19. Finally, the spectral dependence of the magneto-optical figure of merit 2ΘFp/α of (Y,Bi)3Fe5O12 and amorphous TbFe is compared. Furthermore, high-resolution transmission electron micrographs and x-ray double-crystal diffractograms are presented that elucidate the perfect epitaxial alignment of single-crystalline iron-garnet films and the columnar morphology of polycrystalline iron-garnet films prepared by rf magnetron sputtering. The initial nucleation period of polycrystalline garnet films can be influenced by low-energy ion bombardment for improving the film texture. Under favorable sputtering conditions single- and polycrystalline bismuth-iron garnet films develop a perpendicular magnetic anisotopy. It is not yet clear whether sputtered iron-garnet films can meet the critical requirements on magnetic wall coercivity and magnetic remanence

Hysteretic behaviour in a vacuum deposited submonolayer of single ion magnets

With element-specific X-ray absorption spectroscopy and X-ray magnetic circular dichroism we have investigated submonolayer coverages of TbPc2 and DyPc2 molecules sublimated on highly ordered pyrolytic graphite. We have studied the field dependence of the magnetization of the central lanthanide ion at very low temperatures. Even in zero applied magnetic field we still observe a remanence in the magnetization. Since there are neither intermolecular coupling nor magnetic interactions with the substrate, this remanent behaviour results just from single-ion anisotropy. On the very inert surface of graphite at temperatures between 0.5 K and 2 K the spin relaxation is slow enough to observe a memory effect in the timescale of the experimental measurements

Working Group on Biological Parameters (WGBIOP) 2021

The main objective of the Working Group on Biological Parameters (WGBIOP) is to review the status, issues, developments, and quality assurance of biological parameters used in assessment and management. WGBIOP (1) plans workshops, exchanges, and validation studies on a range of biological varia-bles to review the quality of information supplied for stock assessment and improve quality as-surance and training; (2) investigates data availability and develops documentation and methods to improve communication between data collectors and end-users; (3) delivers new and im-proved functionality for the SmartDots platform. Four otolith exchanges and two workshops were completed in 2020–2021 using SmartDots— eight further exchanges are ongoing. Proposed future exchanges and workshops were reviewed and approved. The development of the SmartDots platform proceeded with the inclusion of the maturity, eggs, atresia, fecundity, and larval identification modules into the software version. A live SmartDots tutorial for event coordinators was conducted. Work to further develop quality assurance guidelines—and review national applications of these—progressed. Age and maturity validation studies were reviewed and a new method for prioritizing future validation work was proposed. Progress with the Stock Identification Database (SID) was reviewed, and the potential for creating a WGBIOP library collection and active involvement of WGBIOP in updating FishBase.org data were evaluated. The importance of identifying and documenting links be-tween all relevant databases and document repositories was identified, and a task to address this was initiated. Work on improving the feedback loop between data collectors and stock assessors on the usage and quality of biological parameters in stock assessment continued. Moving forward, WGBIOP aims to continue collaboration with WGALES and WGSMART on the development of the SmartDots platform, encouraging cross-group sharing of skills and ex-perience to optimize results. WGBIOP aims to improve accessibility to its outputs through up-dates to SID and FishBase.org, and the potential creation of a WGBIOP library collection. WGBIOP hopes to improve two-way communication between data collectors and end-users around the quality and utility of biological parameters used in assessment. WGBIOP also aims to amalgamate all validation activities into one coherent workstream.ICE

Antiferromagnetic coupling of TbPc2 molecules to ultrathin Ni and Co films

The magnetic and electronic properties of single-molecule magnets are studied by X-ray absorption spectroscopy and X-ray magnetic circular dichroism. We study the magnetic coupling of ultrathin Co and Ni films that are epitaxially grown onto a Cu(100) substrate, to an in situ deposited submonolayer of TbPc2 molecules. Because of the element specificity of the X-ray absorption spectroscopy we are able to individually determine the field dependence of the magnetization of the Tb ions and the Ni or Co film. On both substrates the TbPc2 molecules couple antiferromagnetically to the ferromagnetic films, which is possibly due to a super-exchange interaction via the phthalocyanine ligand that contacts the magnetic surface