Novel growth of carbon nanotubes on nickel nanowires Norani Muti Mohamed a,b, ⁎, Muhammad Imran Irshad a,b , Mohamed Zaki Abdullah c , Mohamed Shuaib Mohamed Saheed a,b a Centre of Innovative Nanostructure & Nanodevices (COINN), Universiti Teknologi PETRONAS, 32610 Bandar Seri Iskandar, Perak Darul Ridzuan, Malaysia b Department of Fundamental & Applied Sciences, Universiti Teknologi PETRONAS, 32610 Bandar Seri Iskandar, Perak Darul Ridzuan, Malaysia c Department of Mechanical Engineering, Universiti Teknologi PETRONAS, 32610 Bandar Seri Iskandar, Perak Darul Ridzuan, Malaysia abstract article info Article history: Received 1 December 2015 Received in revised form 28 January 2016 Accepted 29 January 2016 Available online 30 January 2016 A novel growth phenomenon is presented in this paper where carbon nanotubes (CNT) were grown successfully on nickel (Ni) nanowire using chemical vapour deposition technique. The decomposed carbon from ethylene diffused through the surface of nanowires and precipitated into hollow cylindrical carbon structures. Nanotubes of various lengths are found to have grown along the length of the outer side of the nanowires and were firmly rooted to their walls. The presence of a thin layer of oxide (~3 nm) on the top surface of nanowires is believed to have promoted the growth of CNT. Raman, X-ray photoelectron (XPS) and electron energy loss spectroscopy (EELS) were conducted in order to understand the formation of nanotubes and verify their presence, their level of crystallinity and chemical bonding structure with nanowires. This hybrid nanostructure is also found to have ferromagnetic behaviour, which can be applied in devices such as magnetic sensors and spintronic devices that combine the unique properties of CNT and Ni nanowires. © 2016 Elsevier B.V. All rights reserved. Keywords: Anodized aluminium oxide (AAO) Carbon nanotubes Electrodeposition Nickel nanowires 1. Introduction There have been various reports on the synthesis [1,2], growth mechanism [3,4], and the applications of carbon nanotubes (CNT) film on solid substrate with continuous or island-like metallic nanoparticles which acts as the nucleation seeds for nanotubes growth. Although the growth mechanism of CNT is still being heavily debated, most of the researchers agree on two practical growth methods of, which are base and tip growth [5,6]. Tip growth occurred when the decomposed carbon diffused and precipitated through the catalyst and lifted the particles during the extrusion. Catalyst particles will fail to be lifted up for base growth due to their strong interaction with the underlying substrate. In both cases, the surface tension between the catalyst and substrate plays a crucial part and the catalyst particles are assumed to be in the shape of island-like nanoparticles. These nanoparticles act as nucleation seeds for the growth of nanotubes. Yen et al. [7] have reported the use of short nanowires as core mate- rial to grow carbon nanotubes around it for field emission applications. Fabrication of the metal-filled CNT was achieved using inductively coupled plasma chemical vapour deposition (ICP-CVD). Hekmat et al. [8] have synthesized carbon nanotubes on the top of nickel nanowire forest. This hybrid structure consisted of carbon nanotubes with high content of amorphous carbon to act as electrode for super-capacitor applications. However, there is no work reported so far in which CNT have been grown in such a way that they are rooted on the outer surface of individual metal nanowires. This research gap has motivated to further study on hybrid nanostructure of nickel and carbon nanotube in order to understand the mechanism involved. In this paper, the growth of nanotubes over the outer surface of individual metallic Ni nanowires is shown for the first time. This is unique since the nucleation seeds originated from long, thin (nanometre sized diameter) nanowires instead of nanoparticles. The interaction between the decomposed carbon and the surface of nanowires and subsequent graphitization of carbon atoms to form hollow cylindrical structure will be studied and discussed. 2. Methodology As reported earlier [9–11], good quality Ni nanowires were produced using electrodeposition method assisted by anodized aluminium oxide (AAO) template. This method was adopted because of its unparalleled advantages such as low production cost, high purity of the products and large-scale production with controlled geometry and morphology [12–14]. For the growth of CNT, chemical vapour deposition (CVD) tech- nique was used as it produces higher yield and purity, and the only method that offers better control of growth parameters [15]. Electro- chemically synthesized Ni nanowires used as the sites for the growth of CNT are shown in Fig. 1. The grown nanowires are polycrystalline in nature with typical diameter of around 100 nm as reported earlier [9]. Diamond & Related Materials 65 (2016) 59–64 ⁎ Corresponding author at: Centre of Innovative Nanostructure & Nanodevices (COINN), Universiti Teknologi PETRONAS, 32610 Bandar Seri Iskandar, Perak Darul Ridzuan, Malaysia. E-mail address: noranimuti_mohamed@petronas.com.my (N.M. Mohamed). http://dx.doi.org/10.1016/j.diamond.2016.01.026 0925-9635/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Diamond & Related Materials journal homepage: www.elsevier.com/locate/diamond