Nonradiative Investigation of Photodecomposition of Poly(di-n-hexylsilane) Thin Films Using Piezoelectric Photothermal Spectroscopy

To investigate the photodecomposition mechanism of poly(di-n-hexylsilane) (PDHS), the ultraviolet (UV) light irradiation time dependence of the optical absorption (OA) and the piezoelectric photothermal (PPT) signals were measured in vacuum. A strong OA peak at 370 nm and a broad OA band at approximately 320 nm related to the all-trans and helical conformations, respectively, were observed. With increasing UV light irradiation time, their intensities decreased and blue shifts were observed because of the decomposition of Si-Si bonds in the silicon backbone. In the PPT spectrum, a nonradiative recombination peak associated with the all-trans conformation was also observed at 370 nm. When UV light irradiated the sample, in addition to the decrease in the intensity and the blue shift of the PPT peak at 370 nm, new PPT signals at approximately 290 nm were observed. We concluded that these signals were caused by the silicon and/or carbon dangling bonds generated by photodecomposition in vacuum. (C) 2009 The Japan Society of Applied Physics