Achievement

IGERT trainee Michael Riley from Chemical Engineering department led an effort working with Physics IGERT faculty to create 30 and 45 micron thick, graded index Si films in the form of nano-spirals on Si substrate using dynamic oblique angle deposition technique. They showed that the success of producing such a thick film without delamination from the Si substrate is primarily due to nano-porous nature of the film which effectively eliminates the stress generated during growth. An effective refraction index of 2.1 and 1.9 were extracted from the terahertz time domain reflectivity data, which corresponds to 57% and 51% porosity for the 30 and 45 micron thick films, respectively. The gradient of porosity through the film was modeled to describe quantitatively the terahertz reflectance data. The feasibility of using such a film as THz antireflection coating in the 0.2 to 2.0 THz regime was explored.