The results showed that the obtained ZnO NWs have diameters in the range of 300–350 nm with lengths of several tens micrometers. The prepared ZnO NWs are of a single crystal, which have a hexagonal wurtzite crystal structure with c–axis (002) orientation growth perpendicular to the substrate surface. The NW arrays had a good crystal quality with excellent optical properties, indicating a sharp and strong ultraviolet emission at 380 nm, and a weak visible emission at around 516 nm. | Journal of Science and Technology 55 (1B) (2017) 174–184 CATALYST–FREE GROWTH OF WELL–ALIGNED ZnO NANOWIRES ON GRAPHENE/Si SUBSTRATEBY THERMAL EVAPORATION Tran Van Khai*, Cao Xuan Viet, La Thi Thai Ha Faculty of Materials Technology, Ho Chi Minh City University of Technology–VNUHCM 268 Ly Thuong Kiet Street, Ward 14, District 10, Ho Chi Minh City, Vietnam * Email: tvkhai1509@ Received: 30 December 2016; Accepted for publication: 3 March 2017 ABSTRACT Vertically well–aligned ZnO nanowire (NW) arrays with high density were directly synthesized on graphene/Si substrate by thermal evaporation of zinc powder without catalysts or additives. The ZnO NWs were characterized by field emission scanning electron microscopy (FE–SEM), high resolution transmission electron microscopy (HRTEM), X–ray diffraction (XRD), photoluminescence (PL), and Raman spectroscopy. The results showed that the obtained ZnO NWs have diameters in the range of 300–350 nm with lengths of several tens micrometers. The prepared ZnO NWs are of a single crystal, which have a hexagonal wurtzite crystal structure with c–axis (002) orientation growth perpendicular to the substrate surface. The NW arrays had a good crystal quality with excellent optical properties, indicating a sharp and strong ultraviolet emission at 380 nm, and a weak visible emission at around 516 nm. Keywords: graphene, graphene oxide, ZnO nanostructures. 1. INTRODUCTION Two–demensional graphene, a single layer of sp2–bonded carbon atoms arranged in a two– dimensional hexagonal lattice, has attracted tremendous attention in both fundamental studies and practical applications due to its novel structural and exceptional physical, chemical, and mechanical properties [1–2]. Graphene–based sheets have been shown to be very promising for high–performance nanoelectronics, transparent conductors, polymer composites, and microscopy support, etc. Currently, various methods have been developed for production of graphene, including .
