Theoretical models of Schottky-barrier height formation are reviewed. A particular emphasis is placed on the examination of how these models agree with general physical principles. New concepts on the relationship between interface dipole and chemical bond formation are analyzed, and shown to offer a coherent explanation of a wide range of experimental data.

Recent advances in Schottky barrier concepts

The development of optically transparent and mechanically flexible electronic circuitry is an essential step in the effort to develop next-generation display technologies, including 'see-through' and conformable products. Nanowire transistors (NWTs) are of particular interest for future display devices because of their high carrier mobilities compared with bulk or thin-film transistors made from the same materials, the prospect of processing at low temperatures compatible with plastic substrates, as well as their optical transparency and inherent mechanical flexibility. Here we report fully transparent In(2)O(3) and ZnO NWTs fabricated on both glass and flexible plastic substrates, exhibiting high-performance n-type transistor characteristics with approximately 82% optical transparency. These NWTs should be attractive as pixel-switching and driving transistors in active-matrix organic light-emitting diode (AMOLED) displays. The transparency of the entire pixel area should significantly enhance aperture ratio efficiency in active-matrix arrays and thus substantially decrease power consumption.

/pdf/fabrication-of-fully-transparent-nanowire-transistors-for-2xzvorp9x2.pdf

Fabrication of fully transparent nanowire transistors for transparent and flexible electronics

In order to make sound decisions regarding arsenate contamination in soil and water environments, it is necessary to have a thorough understanding of the mechanisms of arsenate sorption and desorption over extended periods. The major objectives of this study were to determine the effects of aging or residence time on the kinetics of arsenate sorption and desorption on goethite, and to combine spectroscopic x-ray absorption fine structure (XAFS) and macroscopic studies in order to determine sorption and desorption mechanisms over time at pH 4 and 6. Sorption studies, conducted from 4 min to 12 mo, showed that arsenate sorption on goethite increased with time. Sorption was initially rapid, with over 93% arsenate being sorbed in a 24-h period at pH 6. Similar arsenate adsorption behavior was observed at pH 4. Analysis of the samples with extended x-ray absorption fine structure (EXAFS) revealed that there exist two distinct atomic shells surrounding the adsorbed As. The closest atomic shell was identified as an O atom, the next shell out was identified as an Fe atom. The As-Fe bond distance of 3.30 A, derived from XAFS data, is indicative of a bidentate binuclear bond forming between the arsenate atoms and the goethite surface. This is in agreement with the findings of previous researchers. Analysis of the As EXAFS from samples incubated for various periods indicated that the molecular environment did not change over time. Complimentary desorption kinetic studies showed that when aging was increased, there was no significant change in the amount of arsenate desorbed from goethite by PO 4 3- . Initially, desorption was quite rapid with >35% of the total adsorbed As being desorbed within 24 h at pH 6. After the initial rapid desorption, only a small amount of additional desorption occurred at longer times. A significant amount of arsenate remained bound to the goethite after 5 mo of desorption even though the PO 4 3 desorptive solution was three times stronger than the initial arsenate sorptive solution. Sulfate was much less effective at promoting arsenate desorption; at pH 6, no more than 2.5% of the total sorbed arsenate desorbed over a 5-mo period. Desorption results at pH 4 were similar to the desorption behavior at pH 6. The XAFS analyses of PO 4 3- desorbed arsenate samples showed that the molecular environment of the adsorbed arsenate did not change.

/pdf/residence-time-effects-on-arsenate-adsorption-desorption-13ei72q4ie.pdf

Residence time effects on arsenate adsorption/desorption mechanisms on goethite

Crystal chemistry of trace elements in natural and synthetic goethite

http://xraysweb.lbl.gov/uxas/Publicatons/Papers/pdfs/Takahashi-GCA.pdf

Chemical and structural control of the partitioning of Co, Ce, and Pb in marine ferromanganese oxides

We succeed in preparing anisotropic magnetic powders with high performance based on the NdFe10.5Mo1.5Nx nitrides. The properties of these materials are favorable for permanent magnet application. The domain structures of the NdFe10.5Mo1.5 and NdFe10.5Mo1.5Nx were studied by using magnetic force microscopy. Upon nitrogenation, a domain structure transition from complex maze to simple stripe was found. This transition is due to the strongly uniaxial magnetocrystalline anisotropy induced by interstitial nitrogen atoms. Together with magnetic measurements, we have calculated the domain wall energy γ, exchange constant A, domain wall thickness δ, and critical single-domain particle size Dc of NdFe10.5Mo1.5 and NdFe10.5Mo1.5Nx.

Magnetic properties and magnetic domain structures of NdFe10.5Mo1.5 and NdFe10.5Mo1.5Nx

Neutron diffraction was used to determine the crystallographic structures of the ${\mathrm{YFe}}_{10}{\mathrm{Mo}}_{2}$ and ${\mathrm{YFe}}_{10}{\mathrm{Mo}}_{2}X$ $(X$=H,N). The spin-polarized muffin-tin-orbital method was applied to calculate the electronic structures of ${\mathrm{YFe}}_{10}{\mathrm{Mo}}_{2}X$ $(X$=H,B,C,N,O,F) and ${\mathrm{YFe}}_{10}{\mathrm{Mo}}_{2}E$, which is ${\mathrm{YFe}}_{10}{\mathrm{Mo}}_{2}$ with an empty sphere insertion. Both N and H atoms were found to reside on the interstitial $2b$ sites. The magnetovolume effect and chemical bonding effect of interstitial $X$ atoms are investigated by a systematic analysis of the local magnetic moments ${\ensuremath{\mu}}_{\mathrm{loc}},$ Fermi-contact hyperfine fields ${(H}_{\mathrm{FC}})$, and isomer shifts (IS) at different Fe sites in ${\mathrm{YFe}}_{10}{\mathrm{Mo}}_{2}X$ $(X$=H,B,C,N,O,F) and ${\mathrm{YFe}}_{10}{\mathrm{Mo}}_{2}E$. It is found that the insertion of the $X$ atom changes not only Fe-Fe interaction, but also Fe-$X$ interaction, and the latter is dependent on the chemical properties of $X$ atoms. It can be concluded that, based on our results, the chemical bonding effect in $R\ensuremath{-}(\mathrm{F}\mathrm{e},\mathrm{M}{)}_{12}\ensuremath{-}X$ is determined by the features of the Fe-$X$ bonds. The role of the $X$ atom is not only to increase the magnetic moments and hyperfine fields through magnetovolume effects, but also to affect those by chemical-bonding effects. The chemical-bonding effect is strongly dependent on the $X$ atom.

Ab initio calculation of interstitial-atom effects in YFe10Mo2X (X=E,H,B,C,N,O,F)

The structure and magnetic properties of RFe12−xMox series and their nitrides with R=Y,Gd,Nd and x=0.8,1.0,1.5,2.0,2.5 have been studied by x‐ray‐diffraction and magnetic measurements. It is found that with the increment of Mo content x, the lattice parameters increase, whereas the saturation magnetization, Curie temperature, and anisotropy field decreases in the RFe12−xMox series. Upon nitrogenation lattice parameters, saturation magnetization, and Curie temperature increase. Correspondingly, the easy c‐axis magnetocrystalline anisotropy of the Fe sublattice decreases in YFe12−xMoxNy and GdFe12−xMoxNy but increases in NdFe12−xMoxNy although its variation with the Mo content is the same as in their original counterparts. NdFe12−xMoxNy compound in the low Mo content shows great potential for permanent magnet applications.

Variation of magnetic properties as a function of Mo content in the RFe12−xMox series and their nitrides (R=Y, Nd, Gd)

The structural and magnetic properties of the compounds and their nitrides have been studied by means of neutron diffraction and crystal-field calculation. Neutron diffraction studies show that the compounds and their nitrides exhibit -type structure, The vanadium atoms occupy 8i sites, and the nitrogen atoms occupy the 2b sites. It is also found that the direction of the magnetic moments changes from that of the ab-plane to that of the c-axis upon nitrogenation, which is consistent with the results of calculations based on crystal-field theory and the single-ion model.

Neutron diffraction studies of and

A series of Y(Fe, M) 12 compounds and their hydrides and nitrides, where M  Ti, V, Mo, Cr, W, were prepared single phase. The effects of interstitial H and N atoms on the structural and magnetic properties have been studied by using the X-ray diffraction and magnetic measurements. The hydrides and nitrides still retain the tetragonal structure, but the unit cell volumes are expanded compared to their original counterparts. The saturation magnetization and Curie temperature are increased by both hydrogenation and nitrogenation, whereas the easy c -axis anisotropy related to the Fe-sublattice is enhanced in the hydrides but decreased in the nitrides.

Weihua Mao

Papers

Magnetic properties and magnetic domain structures of NdFe10.5Mo1.5 and NdFe10.5Mo1.5Nx

Ab initio calculation of interstitial-atom effects in YFe10Mo2X (X=E,H,B,C,N,O,F)

Variation of magnetic properties as a function of Mo content in the RFe12−xMox series and their nitrides (R=Y, Nd, Gd)

Neutron diffraction studies of and

Structural and magnetic properties of H and N modified Y(Fe, M)12 compounds (M Ti, V, Mo, Cr, W)