title: Humidity-sensitive electrical conductivity of a Langmuir-Blodgett film of titania nanosheets: surface modification as induced by light irradiation under humid conditions.
abstract: Electrical conductivity of titania nanosheets was investigated for a single-layered Langmuir-Blodgett (LB) film deposited onto a comb-type electrode (5 or 10 microm (electrode spacing) x 8 mm (electrode width)). The photoresponsive electrical properties of the film were investigated by irradiating with a Xe lamp under various atmospheric conditions. The atmosphere was controlled by introducing either oxygen or nitrogen gases containing different amounts of water vapor. As a result, the LB film behaved as an insulator with little photoresponse under dry atmospheric conditions. It became conductive on illuminating with a Xe lamp under a wet oxygen atmosphere. Conductivity increased with the increase of irradiation time (0-30 min) to attain a stationary value in 1 h. The highest conductive state thus attained lasted for several hours in the dark. The impedance of the film was measured over the frequency range of 1 MHz to 50 Hz by varying the relative humidity of an atmosphere from 0 to 100%. The results were analyzed by assuming an equivalent circuit consisting of one resistance (R) with constant Warburg component (W) and one capacitance (C) in parallel. The R component depended remarkably on the relative humidity, while the C component stayed nearly at the constant value. The dependence of R on water vapor (PH2O) was expressed by R = A[PH2O]n with A = constant and n = -2.9. The results were rationalized in terms of the surface modification of titania nanosheets to hydrophilic nature under the illumination of UV light.
authors.affiliation: Graduated School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Tokyo, Japan.
authors.forename: Kazuko
authors.initials: K
authors.lastname: Saruwatari
authors.forename: Hisako
authors.initials: H
authors.lastname: Sato
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Kogure
authors.forename: Takayuki
authors.initials: T
authors.lastname: Wakayama
authors.forename: Masanori
authors.initials: M
authors.lastname: Iitake
authors.forename: Kosho
authors.initials: K
authors.lastname: Akatsuka
authors.forename: Masaaki
authors.initials: M
authors.lastname: Haga
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Sasaki
authors.forename: Akihiko
authors.initials: A
authors.lastname: Yamagishi