Seed/catalyst-free growth of zinc oxide nanostructures on multilayer graphene by thermal evaporation

Nanoscale Research Letters, Sep 2014

We report the seed/catalyst-free growth of ZnO on multilayer graphene by thermal evaporation of Zn in the presence of O2 gas. The effects of substrate temperatures were studied. The changes of morphologies were very significant where the grown ZnO structures show three different structures, i.e., nanoclusters, nanorods, and thin films at 600°C, 800°C, and 1,000°C, respectively. High-density vertically aligned ZnO nanorods comparable to other methods were obtained. A growth mechanism was proposed based on the obtained results. The ZnO/graphene hybrid structure provides several potential applications in electronics and optoelectronics.

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Seed/catalyst-free growth of zinc oxide nanostructures on multilayer graphene by thermal evaporation

Nanoscale Research Letters Seed/catalyst-free growth of zinc oxide nanostructures on multilayer graphene by thermal evaporation Nurul Fariha Ahmad 0 Nurul Izni Rusli 3 Mohamad Rusop Mahmood 2 Kanji Yasui 4 Abdul Manaf Hashim 0 1 0 Malaysia-Japan International Institute of Technology , Universiti Teknologi Malaysia, Jalan Semarak, Kuala Lumpur 54100 , Malaysia 1 MIMOS Berhad, Technology Park Malaysia , Kuala Lumpur 57000 , Malaysia 2 Faculty of Electrical Engineering , Universiti Teknologi MARA, Shah Alam, Selangor 40450 , Malaysia 3 School of Electrical System Engineering , Universiti Malaysia Perlis, Kuala Perlis, Perlis 02000 , Malaysia 4 Department of Electrical Engineering, Nagaoka University of Technology , Kamitomioka-machi, Nagaoka, Niigata 940-2137 , Japan We report the seed/catalyst-free growth of ZnO on multilayer graphene by thermal evaporation of Zn in the presence of O2 gas. The effects of substrate temperatures were studied. The changes of morphologies were very significant where the grown ZnO structures show three different structures, i.e., nanoclusters, nanorods, and thin films at 600°C, 800°C, and 1,000°C, respectively. High-density vertically aligned ZnO nanorods comparable to other methods were obtained. A growth mechanism was proposed based on the obtained results. The ZnO/graphene hybrid structure provides several potential applications in electronics and optoelectronics. Graphene; Thermal evaporation; Zinc oxide; Nanostructure; Hybrid integration Background In recent years, strong attentions have been paid in the growth of semiconductor nanostructures on graphene [ 1-5 ] for electronic and optoelectronic applications. Nanostructures such as nanowires, nanorods, nanoneedles, nanosheets, and nanowalls can offer additional functionality to graphene for realizing advanced nanoscale applications in photovoltaics, nanogenerators, field emission devices, sensitive biological and chemical sensors, and efficient energy conversion and storage devices [ 6-8 ]. This is due to the superb properties of nanostructures such as high aspect ratio, extremely large surface-tovolume ratio, and high porosity [ 6-10 ]. Graphene has a great potential for novel electronic devices because of its extraordinary electrical, thermal, and mechanical properties, including carrier mobility exceeding 104 cm2/Vs and a thermal conductivity of 103 W/mK [ 11-14 ]. Therefore, with the excellent electrical and thermal characteristics of graphene layers, growing semiconductor nanostructures on graphene layers would enable their novel physical properties to be exploited in diverse sophisticated device applications. Graphene is a 2D hexagonal network of carbon atoms which is formed by making strong triangular σ-bonds of the sp2 hybridized orbitals. This bonding structure is similar to the (111) plane of zincblende structure and C plane of a hexagonal crystalline structure. With this regard, the growth of semiconductor nanostructures and thin films on graphene is feasible. Recently, there are several works on the growth and application of graphene/semiconductor nanocrystals that show desirable combinations of these properties not found in the individual components [ 15-20 ]. The 1D zinc oxide (ZnO) semiconducting nanostructures are considered to be important multifunctional building blocks for fabricating various nanodevices [ 21,22 ]. Since graphene is an excellent conductor and transparent material, the hybrid structure of ZnO/graphene shall lead to several device applications not only on Si substrate but also on other insulating substrates such as transparent glass and transparent flexible plastic. Owing to the unique electronic and optical properties of ZnO nanostructures, such hybrid structure can be used for sensing devices [ 23-25 ], UV photodetector [26], solar cells [ 27 ], and lightemitting diodes [ 28 ]. ZnO nanostructures have been synthesized by various physical and chemical growth techniques [ 23 ]. These techniques include thermal evaporation [ 5,29 ], hydrothermal [ 2,3 ] and electrochemical deposition [ 4 ], and metal-organic vapor-phase epitaxy (MOVPE) [ 1 ]. In this paper, we report the seed/catalyst-free growth of ZnO structures on multilayer (ML) graphene by thermal evaporation. The dependence of substrate temperatures on the properties of grown structures was studied. Based on the obtained results, a growth mechanism was proposed. Methods A ML graphene on SiO2/Si (Graphene Laboratories Inc, Calverton, NY, USA) was used as a substrate. Figure 1a shows the measured Raman spectra of the ML graphene. The 2D peaks at approximately 2,700 cm−1 of the Raman spectra for graphite as shown by locations 1 and 4 have broader and up-shifted 2D band indicating few layer graphene [ 30 ]. Figure 1b shows the schematic of the experimental setup. The growth was carried out by thermal evaporation technique in dual zone furnace. High-purity metallic Zn powder (99.85%) and oxygen (O2) gas (...truncated)


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Nurul Fariha Ahmad, Nurul Izni Rusli, Mohamad Rusop Mahmood, Kanji Yasui, Abdul Manaf Hashim. Seed/catalyst-free growth of zinc oxide nanostructures on multilayer graphene by thermal evaporation, Nanoscale Research Letters, 2014, pp. 83, Volume 9, Issue 1, DOI: 10.1186/1556-276X-9-83