López-Camacho E, Fernández M, Gómez-Aleixandre C
Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, 28049 Madrid, Spain.
Nanotechnology. 2008 Jul 30;19(30):305602. doi: 10.1088/0957-4484/19/30/305602. Epub 2008 Jun 12.
SiC/SiO(2) nanocables, consisting of a crystalline SiC core surrounded by an amorphous silica shell, have been grown by thermal chemical vapour deposition (CVD) at 950 °C on Ni-covered silicon substrates. The addition of methane to a 375 Torr hydrogen atmosphere, after heating the substrate in argon, leads to the growth of the SiC/SiO(2) nanocables, by the carbothermal reduction of silicon oxide as the initial stage. The growth mechanism follows the model previously proposed by us for a reducing medium. From the results obtained, several effects of hydrogen on the deposition process have been established: (a) reduction of the nickel nucleation sites, thus favouring the formation of SiC from the initial stage; (b) oxygen removal in the medium hindering the oxidative effect over the SiO and C species, thus promoting the nanocable growth, and (c) increase of the SiO concentration in the neighbourhood of the active nucleation sites. In addition, it is important to mention that SiC/SiO(2) nanocables, following the already proposed model, are obtained uniquely in a narrow hydrogen pressure range. At high hydrogen pressure, the unexpected formation of silica nanowires together with the SiC/SiO(2) nanocables has been detected.
碳化硅/二氧化硅纳米电缆由结晶碳化硅芯和非晶二氧化硅壳组成，通过热化学气相沉积（CVD）在950°C下在镀镍硅衬底上生长而成。在氩气中加热衬底后，向375托的氢气气氛中添加甲烷，通过氧化硅的碳热还原作为初始阶段，导致碳化硅/二氧化硅纳米电缆的生长。生长机制遵循我们先前为还原介质提出的模型。从获得的结果来看，已经确定了氢气对沉积过程的几种影响：（a）减少镍成核位点，从而从初始阶段就有利于碳化硅的形成；（b）去除介质中的氧气，阻碍对二氧化硅和碳物种的氧化作用，从而促进纳米电缆的生长；（c）增加活性成核位点附近的二氧化硅浓度。此外，需要指出的是，按照已提出的模型，碳化硅/二氧化硅纳米电缆仅在狭窄的氢气压力范围内获得。在高氢气压力下，已检测到二氧化硅纳米线与碳化硅/二氧化硅纳米电缆意外形成。
