Co valence and possible spin transformation in diluted magnetic semiconductors Zn/sub 1-z/Mg/sub z/Co/sub 0.15/O and Zn/sub 1-x/Co/sub x/O

In this paper, possible spin transformation and Co valence in dilute magnetic semiconductors is studied. Polycrystalline samples of Zn/sub 1-x/Co/sub x/O (0.05/spl les/x/spl les/0.17) and Zn/sub 1-z/Mg/sub z/Co/sub 0.15/O are prepared by rapid oxalate decomposition technique. X-ray diffraction is used to determine phase purity of the samples. Co valence state 2+ is determined by X-ray absorption near edge spectroscopy (XANES) using synchrotron irradiation. Magnetic properties measured show that all samples are paramagnetic and magnetization hysteresis measurement indicated that there is no trace of ferromagnetism. From Curie-Weiss fittings at high temperature region, the effective magnetic moment (/spl mu//sub eff/) is 3.87/spl mu//sub B//Co which corresponds to that of tetrahedral Co/sup 2+/ high spin state. When fitting at T approaches 0 K, /spl mu//sub eff/ = 2.82/spl mu//sub B//Co is observed indicating a possible spin state transition to Co/sup 2+/ low spin state

Electrochemical synthesis and characterization of semiconducting Ni(TCNQF4)2(H2O)2(TCNQF4=2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane)

An electrochemical technique has been used to synthesize Ni(TCNQF4)2(H2O)2 (TCNQF4 = 2,3,5,6-tetrafluoro-7,7,8,8- tetracyanoquinodimethane). The method involves the reduction of solid TCNQF4 immobilized on an electrode surface in contact with Ni2+ (aq.)-containing electrolyte. The electrochemically irreversible, but chemically reversible solid–solid TCNQF4/Ni(TCNQF4)2(H2O)2 interconversion process is governed by nucleation and growth kinetics and is represented by the overall reaction: 2TCNQF4 (s, electrode) + Ni2+ (aq.) + 2H2O + 2e h Ni(TCNQF4)2(H2O)2 (s, electrode). Thus, the formation of Ni(TCNQF4)2(H2O)2 involves the oneelectron reduction of TCNQF4 to [TCNQF4]·– coupled with an ingress of Ni2+ (aq.) from the aqueous electrolyte, while the reverse scan represents the oxidation of [TCNQF4]·– to TCNQF4 coupled with the egress of Ni2+ (aq.). Cyclic voltam-mograms for the TCNQF4/Ni(TCNQF4)2(H2O)2 solid–solid phase transformation are independent of the electrode material and the identity of the Ni2+ (aq.) counteranion but are strongly dependent on the concentration of Ni2+ (aq.) and the scan rate. UV/Vis, infrared, and Raman spectra confirm the presence of [TCNQF4]·– in the newly synthesized material. The composition of Ni(TCNQF4)2(H2O)2 was deduced from thermogravimetric and elemental analyses. Scanning electron microscopic images of Ni(TCNQF4)2(H2O)2 electrocrystallized onto the surface of an indium tin oxide electrode show a thin film morphology. Magnetic and conductivity data demonstrate that the complex behaves as a classical paramagnet and is a typical semiconductor with a band gap close to that of an insulator

Reactivity of Reduced [2Fe-2S] Ferredoxins Parallels Host Susceptibility to Nitroimidazoles

The kinetics of the electron transfer reaction between reduced [2Fe-2S] ferredoxins and select nitroimidazole antimicrobial agents is reported. The ferredoxins from the protozoan Trichomonas vaginalis and the cyanobacterium Anabaena sp. strain 7120 were studied because they are the proximal electron donors to nitroimidazoles in these two organisms with significantly different nitroimidazole susceptibilities. The rates of electron transfer from Anabaena ferredoxin to all nitroimidazoles were 1 to 2 orders of magnitude lower than for T. vaginalis ferredoxin. Quantitative structure-activity analysis of the kinetic data showed that the size of the alkyl substituent on the N-1 position of the imidazole ring strongly influenced the magnitude of the electron transfer rate constant. This implies that the distance between the iron-sulfur cluster and the nitro group of the imidazole is the critical variable in determining the rate of electron transfer. A correlation between the magnitude of the one-electron transfer rate constant with the susceptibility of the host organism to the cytotoxic effects of nitroimidazoles was also discovered. These results demonstrate that reductive activation is the most crucial step in determining the toxicity of nitroimidazoles

Synthesis and structural characterization of a TCNQ based organic semi-conducting material with a 2:5 stoichiometry

The tetrabutylammonium complex with a 2:5 stoichiometry, (n-Bu4N)2(TCNQ)5, has been prepared and structurally characterized by X-ray crystallography. Diagnostic bands in the Raman spectrum and signature features in the electrochemistry confirm that the TCNQ moieties are partially charged in the solid state. EPR, magnetic susceptibility, and electrical conductivity measurements are all consistent with (n-Bu4N)2(TCNQ)5 behaving as a quasi-one-dimensional organic semiconductor

Tuning the band gap in silicene by oxidation

Silicene monolayers grown on Ag(111) surfaces demonstrate a band gap that is tunable by oxygen adatoms from semimetallic to semiconducting type. With the use of low-temperature scanning tunneling microscopy, we find that the adsorption configurations and amounts of oxygen adatoms on the silicene surface are critical for band gap engineering, which is dominated by different buckled structures in √13 x √13, 4 x 4, and 2√3 x 2√3 silicene layers. The Si-O-Si bonds are the most energy-favored species formed on √13 x √13, 4 x 4, and 2√3 x 2√3 structures under oxidation, which is verified by in situ Raman spectroscopy as well as first-principles calculations. The silicene monolayers retain their structures when fully covered by oxygen adatoms. Our work demonstrates the feasibility of tuning the band gap of silicene with oxygen adatoms, which, in turn, expands the base of available two-dimensional electronic materials for devices with properties that is hardly achieved with graphene oxide