Alpa Y. Shah

Aerosol assisted chemical vapour deposition of germanium thin films using organogermanium carboxylates as precursors and formation of germania films

Diethyl germanium bis-picolinate, [Et2Ge(O2CC5H4N)2], and trimethyl germanium quinaldate, [Me3Ge(O2CC9H6N)], have been used as precursors for deposition of thin films of germanium by aerosol assisted chemical vapour deposition (AACVD). The thermogravimetric analysis revealed complete volatilization of complexes under nitrogen atmosphere. Germanium thin films were deposited on silicon wafers at 700°C employing AACVD method. These films on oxidation under an oxygen atmosphere at 600°C yield GeO2. Both Ge and GeO2 films were characterized by XRD, SEM and EDS measurements. Their electrical properties were assessed by current–voltage (I–V) characterization.

Diorganotin(IV) 4,6-dimethyl-2-pyrimidyl selenolates: synthesis, structures and their utility as molecular precursors for the preparation of SnSe2 nano-sheets and thin films

The complexes of composition [R2Sn{SeC4H(Me-4,6)2N2}2] (R = Me, Et, nBu or tBu) have been isolated by the reaction of R2SnCl2 with NaSeC4H(Me-4,6)2N2. The treatment of [R2Sn{SeC4H(Me-4,6)2N2}2] with R2SnCl2 afforded chloro complexes [R2SnCl{SeC4H(Me-4,6)2N2}] (R = Me, nBu or tBu). These complexes were characterized by elemental analyses and NMR (1H, 13C, 77Se, 119Sn) spectroscopy. The molecular structures of [tBu2Sn{SeC4H(Me-4,6)2N2}2] and [tBu2SnCl{SeC4H(Me-4,6)2N2}] were established by single crystal X-ray diffraction analyses. Thermolysis of [R2Sn{SeC4H(Me-4,6)2N2}2] (R = Et, nBu or tBu) in oleylamine (OLA) afforded the nanocrystalline hexagonal phase of SnSe2. Thin films of SnSe2 were deposited on silicon wafers by AACVD of [tBu2Sn{SeC4H(Me-4,6)2N2}2]. The nanostructures and thin films were characterized by solid state diffuse reflectance spectroscopy, XRD, EDX, SEM and TEM techniques. The solid state diffuse reflectance measurements of the nanosheets showed direct and indirect band gaps in the ranges of 1.76–2.30 eV and 1.38–1.49 eV, respectively, which are blue shifted relative to bulk tin selenide.

Structural differences in the luminescence properties of lanthanide doped orthorhombic and monoclinic phases of Y2GeO5

Stable monoclinic and metastable orthorhombic phases of Y2GeO5 have been prepared and characterized by XRD and FT-IR. Changes in the local environment around the Y3+ ions in both phases have been probed by Eu3+ doping of the lattices and subsequent measurement of their luminescence properties. The XRD and FT-IR studies revealed that Y2O2 chains exist in the metastable orthorhombic Y2GeO5 phase, while edge-shared distorted YO6 octahedra and YO7 pentagonal bi-pyramids constitute the monoclinic Y2GeO5 lattice. Detailed luminescence studies, including the experimentally evaluated Judd–Ofelt parameters (Ω2 and Ω4 values), have confirmed that the polarisability around the Y3+/Eu3+ ions and the associated electric dipole transition probabilities are higher in the metastable orthorhombic Y2GeO5 phase in comparison to the thermodynamically stable monoclinic Y2GeO5. This has been attributed to the lower symmetry of the electronic environment around the Y3+/Eu3+ ions, and the larger Y⋯Y average separation in the metastable form than that of stable monoclinic Y2GeO5.