Third-order Nonlinear Optical Properties of Regioregular Poly(3-Hexylthiophene) Thin Films on Quartz Glasses Modified by Hexamethyldisilazane

Abstract

Regioregular poly(3-hexylthiophene) [RR-P3HT] thin films were prepared on fused quartz glasses by spin-coating and drop-casting from the chloroform solutions. The effect of surface modification of quartz glass by hexamethyldisilazane (HMDS) on the RR-P3HT film structures was investigated. Film structures and morphologies were characterized by UV-visible absorption spectra, out-of-plane X-ray diffraction (XRD) and atomic force microscopy (AFM). The third-order nonlinear optical (NLO) susceptibilities Χ(3)(-3ω; ω, ω, ω) of the RR-P3HT films were determined by the third harmonic generation (THG) technique with an incident wavelength of 1064 nm. The drop-cast film shows enhanced Χ(3) of about three times of that of the spin-coated one, and HMDS treatment can increase the Χ(3) further to about 30 percent higher than the untreated one, keeping all the film thicknesses around 140 nm These results revealed the deposition method and surface modification effects on the RR-P3HT film structures, and the importance of higher ordering (enhanced inter-molecular interactions through π-π stacking) and increased crystallinity to the enhancement of the Χ(3) of the polymeric films for their applications in NLO devices.