The results offer useful insight into the synthesis of nanowires. A change in a variable can have an effect on the growth and size of a nanowire. In this research, the variables, pressure and type of substrate were altered. These alterations did exhibit an effect on the size and growth of the nanowires.
As demonstrated by the data, there is a change in growth at different pressures and on different substrates. The pressure that demonstrates the greatest nanowire growth across the substrate whether colloidal or sputtered substrate was at around 200 torr. While more growth occurred across the substrate, a line layer of nanowires are observed. However at 300 torr, a more dense region is observed along the edge of the substrate as the precursor first comes in contact and nucleation begins. This region has longer and more uniform wires on the sputtered and colloidal substrates. At 400 torr on the sputter, little uniform nanowires are observed across the substrate and more belts were produced than any other substrate. When the optimum condtions are not met, liitle to no nanowires are observed and may result in undesirable material as shown on the colloidal substrate at 400 torr.
When observing the different substrate, the colloid synthesized smaller and more uniform nanowires and little to no nanobelts as opposed to the sputtered substrates. This is because the colloids, Au nanoparticles, offer a nucleation site for CdS growth and the size of the wires can be controlled.
Other factors can effect the synthesis of nanowires.
1. The position of the precursor on the ring can effect the growth of the nanowires. If the precursor is clumped together, very little growth will occur or more belts maybe observed. This can also occur if too little or too much precursor is used. The best results are obtained when the recommended amount is used and the precursor is placed uniformly in a line when added to the glass ring. When added in this fashion, the precursor is dispensed uniformly over a given amount of time and optimal growth of nanowires can be achieved.
2. The initial location of the precursor is very important. The position of the glass ring is critical to prevent the evaporation of the precursor before the optimal temperature is reached. If this is not adhered to, evaporation of the precursor may occur and very little product will be produced.
3. When the glass ring is positioned properly, the time in which the material is dispensed is also important. When added at 1 minute intervals, growth was optimal and uniform nanowires were observed. When added at 3 minute intervals, only a film of precursor is observed.
4. As mentioned previously, the coating on the silicon wafer, a single silicon crystal, will effect the type of nanowires synthesized. Sputter coating will generate thicker nanowires and a greater chance in the formation of nanobelts, while colloidal coating will generate more uniform nanowires and also serves to aid in obtaining a desired size of nanowires.