Application of nanoporous silicon substrates for terahertz spectroscopy
Published/Posted: January 1, 2013
Authors: Lo, S.-Z. A.; Kumar, G.; Murphy, T. E.; Heilweil, E. J.
DOI: 10.1364/OME.3.000114Abstract: Mid to far-infrared (terahertz) spectroscopy is a valuable tool for probing and characterizing macromolecular structures and motions of complex molecules, including low frequency vibrational and phonon modes in condensed phases. We describe here an improved and readily implemented method for performing terahertz spectroscopic measurements by using a nanoporous silicon substrate to capture and concentrate the substance to be analyzed. We compare the results to conventional sampling methods, including dissolution and crystallization on a flat silicon surface and dispersing crystallites in compressed polyethylene pellets, and show that the use of a transparent, nanoporous substrate provides both increased sensitivity and yields sharper spectral features than conventional solid-state sampling approaches. FTIR measurements are reported over the spectral range from 50–2000 cm−1 (1.5–60 THz), for salicylic acid, dicyanobenzene, glycine, and aspartame.