Surface Structures of Silicon and Germanium

Si and Ge were cleaved on the (111) plane under ultra high vacuum and exposed to O and subsequent heat treatment. LEED and spot photometric measurements were taken. Cleaved surfaces for both Si and Ge gave the expected (2 x 1) structure. Results for O exposure were qualitatively for Si and Ge. The 1/2 orders disappeared after exposure to approx = 10 exp - exp 7. Integral orders started to weaken at 10 exp -6 to 10 exp - exp 2 torr min., disappearing at 10 exp -1 torr min. Heat treatment of Si at 900 deg C for several seconds restored the integral orders and further heating gave a new pattern with 1/3 orders. Exposure to 2 x 10 exp -6 torr min O without further heating weakened the fractional orders and at 10 exp -5 torr min they disappeared. Integral orders remained after further heating in O. For Ge integral orders were not restored after 0 exposure until heat treatment had continued at 550 deg C for several min. The (1 x 1) structure disappeared after heating at 590 deg C in 7 x 10 exp -1 torr O and further heating at 590 deg C without O restored the integral order Variations of intensity with voltage were measured for the (00) and (20) spots. The results supported a model proposed by Haneman (Phys. Rev., 1968, 170, 705) involving two kinds of atom sites on the cleaved surface. 20 ref.--E.J.S.

Oxide-based bifunctional oxygen electrode for rechargeable metal/air batteries

Statistical methods for optimizing the morphology of oxide-based, bifunctional oxygen electrodes for use in rechargeable metal/air batteries are examined with regard to binder composition, compaction time, and compaction load. Results show that LaNiO3 with PTFE binder in a nickel mesh envelope provides a satisfactory electrode.

Low-temperature polymer precursor-based synthesis of nanocrystalline particles of lanthanum calcium manganese oxide (La0.67Ca0.33MnO3) with enhanced ferromagnetic transition temperature

We report a simple modified polymeric precursor route for the synthesis of highly crystalline and homogenous nanoparticles of lanthanum calcium manganese oxide (LCMO). The LCMO phase formation was studied by thermal analysis, x-ray powder diffraction, and infrared spectroscopy at different stages of heating. These nanocrystallites (average particle size of 30 nm) possess ferromagnetic-paramagnetic transition temperature (T-c) of 300 K, nearly 50 K higher than that of a single crystal. The Rietveld analysis of the powder x-ray diffraction data of the nanopowders reveals significant lattice contraction and reduction in unit cell anisotropy-these structural changes are correlated to the enhancement in T-c.

Microwave irradiation-assisted method for the deposition of adherent oxide films on semiconducting and dielectric substrates

We report a method for the deposition of thin films and thick coatings of metal oxides through the liquid medium, involving the micro waveirradiation of a solution of a metal-organic complex in a suitable dielectric solvent. The process is a combination of sol-gel and dip-coating methods, wherein coatings can be obtained on nonconducting and semiconducting substrates, within a few minutes. Thin films of nanostructured ZnO (wurtzite) have been obtained on Si(100), glass and polymer substrates, the nanostructure determined by process parameters The coatings are strongly adherent and uniform over 15 mm x 15 mm, the growth rate similar to 0.25 mu m/min Coatings of nanocrystalline Fe2O3 and Ga2O3 have also been obtained The method is scalable to larger substrates, and is promising as a low temperature technique for coating dielectric substrates, including flexible polymers. (C) 2010 Elsevier B.V. All rights reserved.

Electron microscopic investigation of high-temperature oxide superconductors

Electron microscopic investigations have been carried out on superconducting YBa2Cu3 O7−δ, NdBa2Cu3 O7−δ and related oxides. All these orthorhombic oxides exhibit twin domains. Based on high resolution electron microscopy, it is shown that there is no significant change in the structure across the twins. Oxides of the La2−x Sr x (Ba x )CuO4 system do not show twins, but exhibit other types of defects. Twins appear to be characteristic of only the orthorhombic 123 structures.

2,4-Lutidine-1-oxide complexes of lanthanide perchlorates

2,4-Lutidine-1-oxide (2,4-LutO) complexes of lanthanide perchlorates of the formulae Ln2(2,4-LutO)13(ClO4)6 (Ln = Pr and Nd) and Ln2(2,4-LutO)15 (ClO4)6 (Ln = La, Tb, Dy, Ho and Yb) have been prepared and characterised by chemical analysis, IR, NMR, conductance and electronic spectral data. Proton NMR data along with the IR data show that the ligand coordinates to the metal ion through the oxygen. Conductance data of the complexes in acetone and nitrobenzene indicate that the perchlorate is not coordinated to the metal ion.

Growth of titanium oxide overlayers by thermal oxidation of titanium

This paper describes a theoretical model for the growth of titanium oxide by thermal oxidation of titanium. It is shown that this model can explain the formation of layers of different oxides of titanium and the changes in these layers with variations in the conditions of oxidation. Some experimental X-ray diffraction results which support the model are also given.

High contrast laser writing in insitu textured germanium films via a novel chemical oxide formation

A high contrast laser writing technique based on laser induced efficient chemical oxidation in insitu textured Ge films is demonstrated. Free running Nd-YAG laser pulses are used for irradiating the films. The irradiation effects have been characterised using optical microscopy, electron spectroscopy and microdensitometry. The mechanism for the observed contrast has been identified as due to formation of GeO2 phase upon laser irradiation using X-ray initiated Auger spectroscopy (XAES) and X-ray photoelectron spectroscopy (XPS). The contrast in the present films is found to be nearly five times more than that known due to GeO phase formation in similar films.

Delamination and solvothermal decomposition of layered zinc hydroxysalt: Formation of bimodal zinc oxide nanostructures

Dodecylsulphate-intercalated zinc hydroxysalt, Zn-5(OH)(8)(DS)(2)center dot mH(2)O delaminates to give monolayer colloidal dispersions in alcohols such as 1-butanol and ethylene glycol. The extent of delamination and the stability of the colloidal dispersion are comparable to those of layered double hydroxides. The solvothermal decomposition of the colloidal dispersion of the hydroxysalt in ethylene glycol yields a bimodal ZnO having a nanotubular structure decorated with nanosheets. (C) 2010 Elsevier Masson SAS. All rights reserved.

Investigations on Bi2CuO4: a quasi-one-dimensional oxide system

The potential of Bi2CuO4 as the first oxide system to show a linear-chain magnetic behaviour is examined. Electron diffraction studies do not resolve the previously reported ambiguity regarding its space group. The magnetic susceptibility data at high temperatures are best fitted to a uniform antiferromagnetic spin-1/2 Heisenberg chain. At low temperatures, however, neither the uniform nor the alternating Heisenberg antiferromagnetic model fits the data. Magnetic susceptibility data over the entire temperature range can be fitted if one assumes dimeric units with a nearly degenerate second singlet state close to the ground state, these states being separated from an excited triplet state by an energy gap. A simple heuristic model of a dimer that gives such an energy level spectrum is examined.

Neutralization of phosphorus in polycrystalline silicon by hydrogenation

Experimental evidence that phosphorus in silicon is neutralized by hydrogenation is presented by measuring changes in sheet resistance and Hall mobility carrier in heavily phosphorus‐doped polycrystalline films.