Selective bond breaking in amorphous hydrogenated silicon by using Duke FEL

In order to study the possibility of influencing the phase containing predominantly Si–H bonds, while having minimal influence on the surrounding materials, samples of a-Si were exposed to Duke-FEL Mark III radiation. The wavelength of the radiation was selected to fit the absorption maximum of stretching vibrations of Si–H bonds (5 μm). By varying the wavelength in the vicinity of 5 μm, the illumination time and the power density, different types and degrees of structural ordering, of Si–H bonds and Si–Si bonds were obtained, and monitored by Raman spectroscopy. By increasing the energy density, at certain level the crystallization occurs. We were able to demonstrate a direct correlation between short and intermediate range ordering and the wavelength and intensity of the radiation. Using 5 μm at 10 kW/cm2 leads to increase in structural disordering. However, increasing power to 60 kW/cm2 improves both short and intermediate order in a-Si : H, as demonstrated by Raman spectroscopy. Further increasing power density by an order of magnitude results in crystallization of the sample.