SYNTHESIS AND CHARACTERIZATION OF In2S3 AND InN NANOWIRES BY CHEMICAL VAPOR DEPOSITION
Research Area Nanowire synthesis
Status Finished
Degree Master
Directors Andreas Othonos Matthew Zervos
Students Polina Papageorgiou
Proposed start date 2009-01-12
Proposed end date 2011-05-31
Description:

In the present project we achieved the growth of indium sulphide nanowires (NWs) on Si via the reaction of In and InCl3 with H2S using chemical vapor deposition at  temperatures as low as 250 °C. We find that the growth of InS NWs via the direct reaction of In with H2S is hindered by the formation of a vapor limiting shell around  the source of In. A low yield of InS NWs with diameters of ≈ 100 nm, lengths up to ≈ 5 μm and hexagonal crystals measuring ≈ 500 nm across, were obtained between 500 - 600°C, but their growth was not uniform or reproducible. These exhibited weak, but nevertheless clear peaks, in the X-ray diffraction (XRD) spectrum  corresponding to tetragonal β-In2S3 and orthorhombic InS. No NWs were obtained for T≤ 500 °C while for T> 600 °C we obtained a polycrystalline layer with oriented grains of triangular shape. In contrast, a high yield of InS NWs with diameters ≤ 200 nm and lengths up to ≈ 2 μm were obtained at temperatures as low as 250 °C via  the reaction of In and InCl3 with H2S. The sublimation of InCl3 enhances the vapor pressure of In and the growth of InS NWs, which organize themselves in urchin like structures at 300 °C, exhibiting very intense peaks in the XRD spectrum, corresponding mainly to orthorhombic InS. Optical transmission measurements through the  InS NWs gave a bandgap of 2.4eV.

In addition we have grown In2O3 nanowires (NWs) with diameters of 50 nm and lengths ≥2 μm on Si(001) via the wet oxidation of In at 850 °C using Au as a catalyst.  These exhibited clear peaks in the X-ray diffraction corresponding to the body centred cubic crystal structure of In2O3 while the photoluminescence (PL) spectrum at  300 K consisted of two broad peaks, centred around 400 and 550 nm. The post-growth nitridation of In2O3 NWs was systematically investigated by varying the nitridation temperature between 500 and 900 °C, flow of NH3 and nitridation times between 1 and 6 h. The NWs are eliminated above 600 °C while long nitridation times at 500 and 600 °C did not result into the efficient conversion of In2O3 to InN. We find that the nitridation of In2O3 is effective by using NH3 and H2 or a two-step temperature nitridation process using just NH3 and slower ramp rates. We discuss the nitridation mechanism and its effect on the PL.

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