Incorporation of a binary alloy in an oxide matrix via single source precursor CVD process

Using a Ni-Sn heterometal alkoxide, [Ni2Sn2(O'Bu)(8)], in a chemical vapor deposition (CVD) process, thin films of biphasic composite, Ni3Sn4/SnO2, ha ve been obtained. Due to the presence of two metal atoms in a single molecu le, the decomposition occurs at a molecular level resulting in homogeneous incorporation of intermetallic Ni3Sn4 in an SnO2 matrix. The CVD experiment s performed at different temperatures (450-550 degrees C) show that the obt ained composite results from two chemical processes: (i) disproportionation of Sn(II) species and (ii) the redox reactions ocurring between Sn(II) and Ni(II) species. Fragmentation of the precursor and disproportionation of t he tin(II) component dominate up to 500 degrees C, resulting in the formati on of NiO, Sn(0), and SnO2. Redox reactions are favored at higher temperatu re (550 degrees C) which lead to the formation of the Ni3Sn4 alloy. This al loy-metal oxide composite has been deposited on different substrates (steel , copper, silicon wafer), and no heterogeneity was observed on a micrometer level (energy-dispersive X-ray analysis). Powder X-ray diffraction pattern s of the deposits obtained at 550 degrees C show Ni3Sn4 and SnO2 as the onl y crystalline phases. The scanning electron micrograph images reveal a micr ostructured surface with a fibrous morphology. High-resolution transmission electron microscope investigations show a bimodal mixture where the Ni3Sn4 crystallites (ca. 60-80 nm) are uniformly dispersed in a SnO2 matrix (30-4 5 nm). Well-developed lattice fringes, for both particle types, corroborate the crystalline nature of the two phases, The isomeric shift in the Mossba uer spectrum of the CVD deposit, when compared with the Ni3Sn4 and SnO2 sta ndards, confirms the biphasic nature of the obtained material and shows the composition to be Ni3Sn4/SnO2. Electron spectroscopy for chemical analysis (ESCA) studies performed on both (i) as obtained and (ii) argon sputtered samples established the elemental composition, the oxidation states of the Ni and Sn atoms, and the effect of atmospheric oxidation on the metal atoms located on the surface of the layers. Further characterization of the Ni-S n intermetallic phase was achieved by detailed ESCA and high-resolution tra nsmission electron microscopy (HR-TEM) studies.