Influence of oxygen depletion layer on the properties of tin oxide gas-sensing films fabricated by atomic layer deposition

In this paper we report on the influence of film thickness on the electrical and gas-sensing properties of tin oxide thin films grown by atomic layer deposition (ALD) technique. The nature of the carrier and post-flow gases used in ALD was found to have a dramatic influence on the electrical conductance of the deposited films. Up to a film thickness of 50 nm the sheet conductance of the films increased with the thickness, and above 50 nm the sheet conductance was not significantly influenced by the film thickness. This effect was attributed to oxygen depletion at the film surface. When the depth of oxygen depletion (d _dep) was greater than or equal to the film thickness (t), the sheet conductance was thickness dependant. On the other hand, when d _dep≤t, the sheet conductance was independent of the film thickness but depended on the depth of the oxygen depletion. This proposed explanation was verified by subjecting the films to different lengths of post-annealing in an oxygen depleted atmosphere. Gas-sensing functionality of the films with various thicknesses was examined. It was observed that the film thickness had a significant influence on the gas-sensing property of the films. When the thickness was greater than 40 nm, the sensitivity of the films to ethanol was found to follow the widely reported trend, i.e., the sensitivity decreases when the film thickness increases. Below the film thickness of 40 nm the sensitivity decreases as film thickness decreases, and we propose a model to explain this observation based on the increase in resistance due to multiple grain boundaries.     

Study of EIT resonances in an anti-relaxation coated Rb vapor cell

We study the sign of resonances obtained in electromagnetically induced transparency (EIT). Resonances of both kinds—bright (corresponding to enhanced absorption) and dark (corresponding to reduced absorption)—are obtained when the frequency of a probe beam is scanned. The experimental results, presented earlier, use magnetic sublevels of a hyperfine transition in the D₁ line of ⁸⁷Rb along with a magnetic field of 27 G. The atoms are contained in a vapor cell at room temperature, and with anti-relaxation coating on the walls. A quantitative theoretical model, which reproduces the experimental results quite well, is presented for the first time. The model solves the density matrix of the sublevels involved, and uses two regions—one with both the light and magnetic field, and the second without light and just a magnetic field. This ability to have both bright and dark resonances promises applications in sub- and super-luminal propagation of light.     

Single crystal EPR study of Mn(II) doped MgRb2(SO4)2·6H2O: A case of interstitial site

Single crystal electron paramagnetic resonance studies on magnesium rubidium sulphate hexahydrate doped with Mn(II) impurity, in the form of 0.1% of manganous chloride, are carried out at room temperature. The angular variation spectra of the crystal in the three orthogonal planes show that the paramagnetic impurity Mn(II) has entered the host lattice interstitially. The spin Hamiltonian parameters calculated are: g_xx = 1.974, g_yy = 1.928, g_zz = 1.980; A_xx = 9.28, A_yy = 8.58, A_zz = 9.87 mT and D_xx = ‐18.71, D_yy = ‐5.59, D_zz = 24.30 mT. The room temperature and liquid nitrogen temperature study for polycrystalline sample indicate no phase transition. The percentage covalency of Mn–O bond has been estimated to be 11. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

XRD,thermal, FTIR and SEM studies on gel grown γ‐glycine crystals

Glycine is the smallest among amino acids. The polymorphs, α‐ and γ‐forms of glycine were crystallized in silica gel by reduction of solubility method. The grown crystals were characterized by single crystal X‐ray diffraction studies and density determination. Fourier transform infrared spectroscopic studies and thermogravimetric analysis of γ‐glycine were also conducted. Morphological and scanning electron microscopic (SEM) studies were also made and compared with the crystal packing. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

XRD,thermal and FTIR studies on gel grown DL‐Phenylalanine crystals

Phenylalanine [C₉H₁₁NO₂] is one of the essential amino acids in humans. DL‐phenylalanine was crystallized in silica gel under suitable pH conditions by reduction of solubility method. The grown crystals were characterized by density measurement and X‐ray powder diffraction. Fourier transform infrared spectroscopy, and thermogravimetric analysis were also carried out. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Inverse Gaussian Models: Analogues of Symmetry, Skewness and Kurtosis

The inverse Gaussian (IG) family is strikingly analogous to the Gaussian family in terms of having simple inference solutions, which use the familiar ², t and F distributions, for a variety of basic problems. Hence, the IG family, consisting of asymmetric distributions is widely used for modelling and analyzing nonnegative skew data. However, the process lacks measures of model appropriateness corresponding to and ₂, routinely employed in statistical analyses. We use known similarities between the two families to define a concept termed IG-symmetry, an analogue of the symmetry, and to develop IG-analogues ₁ and ₂ of and ₂, respectively. Interestingly, the asymptotic null distributions of the sample versions d ₁, d ₂ of ₁, ₂ are exactly the same as those of their normal counterparts and b ₂. Some applications are discussed, and the analogies between the two families, enhanced during this study are tabulated.     

Synthesis and spectral studies of cobalt(II), nickel(II) and copper(II) complexes of 1-(2-hydroxy-1-naphthyl)-3-(4-X-phenyl)-2-propen-1-ones and their pyridine adducts

Transition Metal Chemistry - Metal(II) chelates of the type ML2nB [M = CoII, NiII and CuII; L = 1-(2-hydroxy-1-naphthyl)-3-(4-X-phenyl)-2-pro-pen-1-one, (X = H, Cl or Me); B = H2O or Py; n = 0, 2]...     

Pressure induced amorphization of AlPO4

AlPO₄ has been compressed to pressures of 16 GPa in a diamond anvil cell and its X-ray diffraction pattern studied by the energy-dispersive technique. The compound is observed to become amorphous at ∼ 12 GPa. This explains the loss of Raman spectrum of AlPO₄ reported by Jayaraman and coworkers (1987).