The growth of gold nanoparticles and ZnO nanorods in atom beam co-sputtered Au-ZnO nanocomposite (NC) system by annealing at two different ambient conditions is demonstrated in this work. Annealing in a furnace at 600 °C (air environment) confirmed the formation of ZnO nanorods surrounded with Au nanoparticles. In-situ annealing inside a transmission electron microscope (TEM) led to the formation of gold nanocrystals with different polygonal shapes. TEM micrographs were obtained in real time at intermediate temperatures of 300 °C, 420 °C, and 600 °C under vacuum. The growth mechanisms of Au nanocrystals and ZnO nanorods are discussed in the framework of Au-Zn eutectic and Zn-melting temperatures in vacuum and air, respectively. Current-voltage responses of Au-ZnO NC nanorods in dark as well as under light illumination have been investigated and photoswitching in Au-ZnO NC system is reported. The photoswitching has been discussed in terms of Au-ZnO band-diagram.

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See supplementary material at http://dx.doi.org/10.1063/1.4752469. The supplementary figures present further detailed informations about different properties of this Au-ZnO nanocomposite. Figure S1 show the SPR tunability of Au-ZnO nanocomposite at different temperatures. A single NC sample was subsequently annealed upto 900 °C (with step of 100 °C) and at each step the SPR was measured. The SPR peak goes 510 nm to 616 nm after annealing upto 600 °C and beyond 600 °C it switches back to 545 nm (at 900 °C). Subsequently XRD measurements were also performed and shown as Figure S2. Initially with increase in temperature (upto 400 °C) the ZnO matrix is amorphous and Au NPs are in face centered cubic (FCC) phase. Above 400 °C, a slight improvement in the crystalline nature of ZnO matrix occurs as can be seen by (100) and (101) peaks corresponding to XRD spectrum at 500 °C. With further increase in temperature upto 700 °C the intensities of HCP (100) and (101) peaks improve. Annealing beyond 700 °C the HCP (101) peak disappears and HCP-(002) phase appears. Figure S3 shows the change in bandgap and shift in SPR peak in Au-ZnO NC at different annealing temperatures (same sample). The bandgap was estimated using Tauc plot from UV-Visible spectrum. It shows that bandgap decreases with increase in temperature. Figures S4 to S9 show the detailed TEM and HRTEM investigations of Au ZnO NC. Figure S4 demonstrates that TEM images of pristine and annealed (inside TEM) Au-ZnO NC at 300 °C and 420 °C temperature. Figure S5 illustrates different shapes (rhombohedral, triangular, rod, hexagonal and pentagonal) Au NPs grown after in-situ heating inside TEM at 600 °C. Figure S6 shows the scanning transmission electron microscopy images of Au-ZnO nanocomposite (in situ at 600 °C inside TEM). The elemental maps corresponding to Au, Zn and O elements on a trapezoidal Au NP (after in-situ annealing) are depicted in fig. S7. Figure S8 and S9 show TEM and HRTEM images from Au-ZnO NC nanorods sample annealed at 600 °C in air.

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