A Pb MAS-NMR study of Pb-containing glasses

²⁰⁷Pb magic angle spinning (MAS)-NMR spectra have been obtained for various Pb-containing crystalline compounds and high lead glasses. The isotropic chemical shifts were determined for the crystalline samples. The more ionic lead atoms with a coordination number larger than six had relatively small chemical shifts between 0 and 2382 ppm with respect to crystalline Pb(NO₃)₂. On the other hand, the covalent lead atoms with PbO₃ trigonal and PbO₄ square pyramidal configurations gave a multiplet line profile with shifts ranging from about 3000 to 6000 ppm. The lead atoms with different local environments in PbSiO₃ (alamosite) and H-Pb₂SiO₄, for instance, could be clearly distinguished from each other on the basis of the isotropic chemical shift. The NMR spectra for the high lead glasses of composition 67PbO·33SiO₂, 80PbO·20B₂O₃ and 70PbO· 30GaO_1.5 were found to exhibit an extremely broad peak with a shift ranging from about 3000 to 6000 ppm. This shift indicates that, in these glasses, neither such highly ionic lead atoms as found in symmetrical PbO₆ octahedra nor such highly covalent ones as found in PbO₄ square pyramids in the PbO crystal are predominant, but instead PbO₃ trigonal or PbO₄ square pyramids, with two or three other neighboring oxygens at larger distances as found in H-Pb₂SiO₄ or PbSiO₃, are the major lead-oxygen configuration.     

Heavily carbon-doped p-type (In)GaAs grown by gas-source molecular beam epitaxy using diiodomethane

Heavily carbon-doped p-type In_xGa_1−xAs (0≤x<0.49) was successfully grown by gas-source molecular beam epitaxy using diiodomethane (CH₂I₂), triethylindium (TEIn), triethylgallium (TEGa) and AsH₃. Hole concentrations as high as 2.1×10²⁰ cm⁻³ were achieved in GaAs at an electrical activation efficiency of 100%. For In_xGa_1−xAs, both the hole and the atomic carbon concentrations gradually decreased as the InAs mole fraction, x, increased from 0.41 to 0.49. Hole concentrations of 5.1×10¹⁸ and 1.5×10¹⁹ cm⁻³ for x = 0.49 and x = 0.41, respectively, were obtained by a preliminary experiment. After post-growth annealing (500°C, 5 min under As₄ pressure), the hole concentration increased to 6.2×10¹⁸ cm⁻³ for x = 0.49, probably due to the activation of hydrogen-passivated carbon accepters.     

Behavior of Ionic Liquids Around Charged Metal Complexes: Investigation of Homogeneous Electron Transfer Reactions Between Metal Complexes in Ionic Liquids

The second-order electron transfer reaction between the photo-excited triplet state of [Zn(TPP)]* (TPP?=?5,10,15,20-tetraphenylporphyrin) and [Co(sep)]³⁺ (sep?=?sepulchrate?=?1,3,6,8,10,13,16,19-octaazabicyclo[6.6.6]eicosane) was investigated in three ionic liquids (ILs, 1-R-3-methylimidazolium bis(trifluoromethylsulfonyl)imide with R?=?butyl, pentyl, and hexyl) and in acetonitrile. Results of electrochemical and kinetic measurements indicated that ILs dissociate in the vicinity of charged metal complexes and at electrodes, although the dissociated anionic and cationic components of the ILs seem to exist as pairs around the metal complexes. Second-order rate constants for the electron transfer reaction are 1.88?×?10⁹, 3.65?×?10⁷, 2.63?×?10⁷, and 2.01?×?10⁷ kg·mol^?1·s^?1 in acetonitrile and in the butyl, pentyl and hexyl ILs, respectively, at 298 K, after correction of the contribution of diffusion. The average slope of the plot of the logarithmic second-order rate constants observed in acetonitrile and ILs against the logarithmic viscosity of each solvent was ??0.84. However, the slope of the same plot was much steeper (??4.1) when data for only the three ILs were used. Detailed analyses of the experimental results on the basis of the Latner–Levin cross relation and the Marcus theory lead to the conclusion that the solvent properties such as the dielectric constant and refractive index around the polarized/charged transition states are different from those for the bulk ILs: observed self-exchange rate constants did not exhibit the Pekar factor dependence when dielectric constants and refractive indices for bulk ILs are used.     

Focusing effect measurements of artificial dielectric multilayer lens with metal rectangular chips for terahertz wave band

This paper presents the design and fabrication of an artificial multilayer lens comprising ten layers of metal rectangular chips on a cyclo olefin polymer, which has low loss in the terahertz band. Measurements of the focusing effect are also presented. The focusing effect is produced by the rectangular metallic chips which act as an electrical dipole. Simulations are performed using ANSYS HFSS. The lenses are fabricated by laser processing or semiconductor etching. The focusing effect is confirmed by measurement using terahertz near-field microscopy, although some discrepancies are observed between the simulated and measured results.     

Effects of uniaxial pressure and annealing on the resistivity of Ba(Fe1−xCox)2As2

Single crystals of underdoped Ba(Fe_1−xCo_x)₂As₂ were detwinned by applying uniaxial pressure. The anisotropic in-plane resistivity was measured using the Montgomery method without releasing pressure. The resistivity along the a-axis shows metallic behavior down to 5 K, while the resistivity along the b-axis shows an insulator-like behavior in some temperature range. Annealing the sample radically reduces the residual resistivity for x=0, and at the same time the anisotropy becomes much smaller at low temperatures.     

Heat capacity of CeIrSi3 under pressure

We measured the heat capacity of CeIrSi₃ (100 mK<T<6 K) under high pressure up to P=1.38 GPa. The measurements have been used a quasiadiabatic method utilizing a CuBe piston-cylinder pressure cell in a dilution refrigerator. At 0 GPa, a sharp anomaly which indicates the antiferromagnetically transition is observed at T_N=5 K. T_N decreases monotonically with increasing pressure up to P=1.38 GPa. The magnetic entropy is released below T_N only 19% of R ln 2 at 0 GPa. And the magnetic entropy decreases with increasing pressure up to 1.38 GPa, 64% compared to that at 0 GPa.     

Numerical simulations on optoelectronic deep neural network hardware based on self-referential holography

Optical Review - We propose a novel optoelectronic deep neural network (OE-DNN) hardware called the self-referential holographic deep neural network (SR-HDNN). The SR-HDNN features a combination of...