Application of nanoporous silicon substrates for terahertz spectroscopy
Edwin J. Heilweil, Shu-Zee A. Lo, Gagan Kumar, Thomas E. Murphy
Infrared spectroscopy is a valuable tool for probing and characterizing the macro-molecular motions of complex molecules, including vibrational and phonon modes that cannot be easily accessed through visible spectroscopy. We describe here an improved method for performing high sensitivity and increased spectroscopic resolution measurements of crystallized solids by using nanoporous silicon substrates to capture and concentrate the substance to be analyzed.We compare the results to conventional sampling methods, including dissolution and crystalization on a flat silicon surface and compressed polyethylene pellet spectroscopy. The use of a transparent, nanoporous substrate provides both increased sensitivity and yields sharper spectral features than these conventional approaches. Measurements are reported over the spectral range from 502000 cm1 (1.560 THz), for salicylic acid, dicyanobenzene, glycine, and aspertame.