Fabrication of a multi-layered carbon nanotube/SiC stack structure

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Abstract

A multi-layered carbon nanotube (CNT)/SiC stack structure was fabricated by repeated alternate deposition and surface decomposition of SiC. The newly deposited 3C-SiC layer on the CNT film had good crystallinity; the CNTs produced by the decomposition of the 3C-SiC were as mostly aligned as the CNTs produced from pristine 6H-SiC. By appropriate choice of deposition and decomposition conditions we demonstrated that it is possible to produce alternating CNT and SiC layers with a controlled thickness.

Introduction

Since their discovery, carbon nanotubes (CNTs) have attracted great attention for various applications based on their specific electrical [1], [2], [3], [4] and mechanical properties [5], [6], [7], [8], [9]. The quantity and quality of CNTs required for actual applications have improved through the development of various synthetic approaches, such as arc-discharge [10], [11], laser evaporation [12] and chemical vapor deposition methods [13], [14], [15], [16].

We have previously reported that aligned CNTs self-organize and completely cover a SiC surface via the selective evaporation of SiO gas due to active oxidation of SiC in a vacuum at high temperature [17], [18], [19]. We refer to this approach as the “SiC surface decomposition method”. The CNTs fabricated by this method are well-aligned, highly dense and homogeneous, and were confirmed to be exclusively of the zigzag type by selective area electron diffraction [20]. These characteristics indicate that such CNTs have potential as a variable band gap semiconductor material through controlling the diameter. Furthermore, these CNTs are connected directly to SiC, a next-generation semiconductor with a wide band gap.

From the point of view of creating a novel semiconductor device, in this work we have tried to fabricate a SiC/CNT stacking layer structure, in which CNT and SiC films are stacked alternately on the SiC substrate by repeated deposition and decomposition.

Section snippets

Experimental procedure

Firstly, 230 nm long CNTs oriented on SiC substrates were prepared by the surface decomposition method. 6H-SiC ( 0 0 0 1¯) surfaces were heated to 1700 °C and held at that temperature for 0.5 h in a vacuum of 1.0×10−4 Torr in an electric furnace with an electric resistance carbon heater.

Secondly, the obtained CNTs/6H-SiC substrates were loaded with SiO2 and C powders with the ratio of 1:1.67 in a carbon crucible. The crucible has a cap with a small hole for evacuation and to maintain a partial pressure

Results and discussion

Aligned CNTs grow via the following active oxidation reaction (1) employing residual CO gas produced in a vacuum of 1.0×10−4 Torr in the furnace with the electric resistance carbon heater, as described in our previous paper [17], [18]:SiC (s)+CO (g)→SiO (g)↑+C (s)

Fig. 1(a) and (a′) shows a TEM image and an AFM image of the CNT film firstly formed on the 6H-SiC substrate by annealing at 1700 °C for 0.5 h. Well-aligned multi-walled CNTs 230 nm long are synthesized as shown in Fig. 1(a). The diameter

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