Humidity-sensitive electrical conductivity of a Langmuir-Blodgett film of titania nanosheets: surface modification as induced by light irradiation under humid conditions.
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.
Saruwatari
Kazuko
K
Graduated School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Tokyo, Japan.
Sato
Hisako
H
Kogure
Toshihiro
T
Wakayama
Takayuki
T
Iitake
Masanori
M
Akatsuka
Kosho
K
Haga
Masaaki
M
Sasaki
Takayoshi
T
Yamagishi
Akihiko
A