Thin films polysilanes

Thin films of this polymer generate third harmonic radiation upon irradiation at 1064 nm, believed to be due to a three-photon resonance. Thus polysilane polymers may eventually find use in laser technology. 

N Tanigaki, H Kyotani, M Wada, A Kaito, Y Yoshida, EM Han, K Abe, and K Yase, Oriented thin films of conjugated polymers polysilanes and polyphenylenes, Thin Solid Films, 331 229-238, 1998. 

Detailed information on the conformation and orientation of polysilane thin films has been obtained by anisotropic PL.80 The alignment of poly (methylphenylsilane-co-methacryloxypropyltriethoxysilane) [P(MPS-co-MPTES)] adsorbed on silica substrates has been studied at 14 K using an attenuated He-Cd polarized laser beam (X = 325 nm) as the excitation source. Laser irradiation decreases the PL intensity, blue shifts the PL peak position... 

UV light induced refractive index change has been observed in organic polysilane (PS)-silica and PS-titania hybrid thin films prepared by the sol-gel method.135 The magnitude of the refractive index change was found to be 0.16 for 50 wt % PS-silica and 0.18 for 50 wt % PS-titania hybrid thin films. It was demonstrated that the refractive index change of the hybrid thin films is due to the photodecomposition of PS. These findings indicate potential usefulness of the hybrid thin films as optical devices with refractive index modulated structures. 

Nonlinear optical properties have recently been observed for the polysilane (PhMeSi) 132, suggesting that polysilanes may eventually find use in optical technology. Irradiation of a thin film of the polysilane at 1064 nm gave rise to efficient third-harmonic generation, while irradiation at 1907 cm-1 produced no nonlinear signal. The third-harmonic resonance is believed to be due to a three-photon process, but its origin is uncertain. Farther research will undoubtedly be carried out on this new phenomenon. 

It should be mentioned that these silicon-backbone polymers are highly absorptive, and must therefore be used in very thin films ( 30 nm), which can be prone to defects. Also, the principal electronic transition in these polysilane (with two-dimensional silicon backbone) and polysilane (three-dimensional silicon backbone) polymers when irradiated at 193 nm is most likely a (t-ct transition involving the all-silicon backbone. Due to this excitation, reaction pathways leading to scission of the Si-Si bonds lead to photodegradation of the polymer. 

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