Current Nanoscience, 2012, 8, 161-169 161 Taguchi Method Optimization of Parameters for Growth of Nano Dimensional SiC Wires by Chemical Vapor Deposition Technique Jyoti Prakash 1* , Sunil K. Ghosh 2 , D. Sathiyamoorthy 1 , R. Venugopalan 1 and B. Paul 3 1 Powder Metallurgy Division, Bhabha Atomic Research Centre, Trombay, Mumbai-400085, India; 2 Bio-Organic Division, Bhabha Atomic Research Centre, Trombay, Mumbai-400085, India 3 Materials Processing Division, Bhabha Atomic Research Centre, Trom- bay, Mumbai-400085, India Abstract: SiC wires of different morphology were grown using methyltrichlorosilane (MTS) and hydrogen by chemical vapor deposition under ambient pressure. Taguchi method has been used to design experiments to get the optimum parameters for growing SiC wires of diameter in nanometer range. Results from XRD and SEM analyses showed the growth of -SiC wires having different morphology. At higher temperature (1500 °C), the growth of SiC grains was observed rather than wires. The optimum deposition conditions for uniform diameter growth of SiC nano wires, smoothness of the surface and homogeneous growth of SiC on the surface have been obtained. The hydrogen to MTS flow rate ratio should be above 20 for the growth of SiC wires of nanometer diameter. The deposition temperature for the growth of crystalline SiC wires should be 1100-1300 °C. The total flow rate of carrier gas comprising of argon and hydrogen for a particular H2/MTS flow rate ratio is critical for morphological outcome of SiC. In the present study it was 2 lpm for H2/MTS flow rate ra- tio 14 to obtain wire morphology. When the total gas flow rate was increased to 6 lpm for the same H2/MTS flow rate ratio 14, the wire morphology of SiC disappeared and the formation of grains occurred. The optimum deposition temperature i.e. 1300 °C was kept con- stant and further experiments were conducted by changing H2/MTS mole ratio to verify morphological outcome of SiC. A plausible mechanism has been suggested for the above observations using vapor-solid mechanism. Keywords: CVD process, Nanowires, Nanorods, Silicon carbide, SEM, Taguchi method, VL mechanism. 1. INTRODUCTION Recently, one-dimensional silicon carbide (SiC) nanostructures have become an important area of research due to their potential applications in mesoscopic research and nanostructured composite materials [1]. The synthesis, formation mechanism and properties of SiC continued to attract growing attention due to its excellent mechanical, thermal and electronic properties [2-4]. One dimen- sional SiC materials possess shape-induced unique electrical and optical properties, as well as better elasticity and strength than those in the bulk SiC. Due to these properties, SiC is considered as a promising material for applications in reinforcement material such as C/C composites, biomaterials, high-temperature semi-conducting devices, light weight/high strength structure and catalysis fields, especially for use in harsh environments [5,6]. To date, SiC nanostructures with various shapes, including SiC nanobelts [7], nanorods [8], nanowires and nanotubes [9,10], have been successfully synthesized. Several growth techniques have been used to synthesize the SiC wires of different dimensions. Amongst them, the catalytical chemical vapor deposition (CCVD) [11], metal-organic chemical vapor deposition (MOCVD) [12], carbothermal reduction process [13] and carbon nanotube confined growth [14] are very common. It is necessary to explore a simpler and more effective way for smooth and homogeneous growth of SiC nanostructures for further practical applications. Chemical vapor deposition (CVD) process is the most suitable and widely used method for the production of wires of different shapes with high purity and homogeneous coatings. In the present studies we demonstrate a simple but effective CVD synthesis route for the growth of homogeneous and smooth SiC wires and application of Taguchi method to optimize the pa- rameters for growth of nano dimensional SiC wires. The various operating parameters that effect the growth of SiC wires are *Address for correspondence to this author at the Powder Metallurgy Divi- sion, Bhabha Atomic Research Centre, Trombay, Mumbai-400085, India; Tel: +91-22-25590499; Fax: +91-22-27840031; E-mail: jprakash@barc.gov.in temperature of synthesis, MTS flow rate, hydrogen flow rate and total gas flow rate. All these parameters were varied at three differ- ent levels. So, this is a four-factor three-level system. In full facto- rial design, either 34 or 81 number of experiments needed to be carried out to get the necessary informations whereas Taguchi method allowed us to complete the study in nine experiments only. With the help of these nine experiments, the parameters for synthe- sizing pure nano SiC wires have been optimized. Further experi- ments have been carried out by varying hydrogen to MTS ratio to observe its effect on the growth diameters of SiC keeping other optimized parameters constant. 2. TAGUCHI METHOD Taguchi designed a robust multi-parameter optimization proce- dure [15] for identification and optimization of dominant process parameters with minimum number of experiments. The method is based on an orthogonal array [16] of experiments, which is a mini- mal set of experiments with various combinations of parameter levels. Output of the orthogonal array is used to optimize an objec- tive function, which indicates the relative influences of various parameters on the formation of the desired product. There are three types of objective function i.e. larger-the-better, smaller-the-better and nominal-the-best. The influences are commonly referred in terms of S/N (signal to noise) ratio as shown in Eq.1 where is the objective function to be optimized, μ is the measured signal (e.g. diameter of SiC wires) and is the standard deviation of the signal to noise ratio. μ 2 2 (1) For optimization of deposition rate and growth diameter of SiC wires, smaller-the-better type of objective function was used. In this case, the exact relation between S/N ratio and the signal is given by Eq. 2 where y i is the signal (deposition rate or diameter of SiC wires) measured in each experiment averaged over “n” repetitions. S N (dB) = 10 log( 1 n ) y i 2 i n (2) 1 7 - /12 $58.00+.00 © 2012 Bentham Science Publishers