Controlled synthesis of Zirconium Oxide on graphene nanosheets by atomic layer deposition and its growth mechanism Jian Liu a , Xiangbo Meng b , Yuhai Hu a , Dongsheng Geng a , Mohammad Norouzi Banis a , Mei Cai c , Ruying Li a , Xueliang Sun a, * a Department of Mechanical and Materials Engineering, University of Western Ontario, London, ON, Canada N6A 5B9 b Department of Chemistry, Brookhaven National Laboratory, Upton, NY 11973, USA c General Motors R&D Center, Warren, MI 48090-9055, USA ARTICLE INFO Article history: Received 16 June 2012 Accepted 6 September 2012 Available online 15 September 2012 ABSTRACT Zirconium Oxide (ZrO 2 ) was deposited on graphene nanosheets (GNS) by atomic layer depo- sition (ALD) using tetrakis(dimethylamido)zirconium(IV) and water as precursors. The results indicated that both morphology and crystallinity of the deposited ZrO 2 were con- trollable in a temperature range of 150–250 °C. At all the temperatures studied, ZrO 2 nano- particles were formed with lower number of ALD cycles (<10 cycles at 150 °C and <30 cycles at 200 and 250 °C), while ZrO 2 thin films were achieved uniformly with higher number of ALD cycles (>10 cycles at 150 °C and >30 cycles at 200 and 250 °C). The crystallinity of the deposited ZrO 2 was highly dependent on the deposition temperature. The ZrO 2 deposited at 150 °C exhibited mainly amorphous nature, whereas that prepared at 250 °C consisted of crystalline phase. At 200 °C, a mixture of amorphous and crystalline ZrO 2 appeared in the ZrO 2 –GNS nanocomposite. In all cases, the growth of ZrO 2 on GNS showed a transfor- mation from an ‘‘island growth’’ mode to a ‘‘layer-by-layer growth’’ mode with increasing ALD cycle. Cyclic voltammetry measurement demonstrated that 10-cycle ZrO 2 –GNS nano- composite exhibited evident electrochemical capacitance characteristics. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction As a two-dimensional (2D) nanostructure composed of sp 2 hybridized carbon, graphene has been drawing worldwide attention since its discovery in 2004 [1]. It possesses high ther- mal conductivity (5000 W m 1 K 1 ) [2], excellent electric conductivity (200,000 cm 2 V 1 s 1 ) [3], large surface area (the- oretical valve, 2630 m 2 g 1 ) [4], and strong mechanical strength [5]. These outstanding properties promise graphene in a wide range of potential applications, such as electronics [6], supercapacitors [4], lithium ion batteries [7,8], fuel cells [9], solar cells [10,11] and bioscience/biotechnologies [12]. Recently, there is increasing interest in using graphene as a building block to fabricate multifunctional nanocomposites, which combine desired properties of each component. So far, polymer, metal, or metal oxides have been incorporated into graphene for various applications [13–20]. In particular, metal oxides supported by graphene represent one kind of nanocomposites with unique mechanical, catalytic, and elec- trochemical properties [15–23]. For example, TiO 2 –graphene nanocomposites were used for hydrogen evolution from water photocatalytic splitting [16]. SnO 2 –graphene nanocom- posites showed enhanced cyclic performance and lithium storage capacity [18]. In addition, Co 3 O 4 grown on graphene 0008-6223/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.carbon.2012.09.007 * Corresponding author: Fax: +1 519 661 3020. E-mail addresses: xsun@eng.uwo.ca, xsun9@uwo.ca (X. Sun). CARBON 52 (2013) 74 – 82 Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/carbon