0020-1685/02/3804- $27.00 © 2002 MAIK “Nauka /Interperiodica” 0374 Inorganic Materials, Vol. 38, No. 4, 2002, pp. 374–379. Translated from Neorganicheskie Materialy, Vol. 38, No. 4, 2002, pp. 462–467. Original Russian Text Copyright © 2002 by Shatokhin, Putilin, Safonova, Rumyantseva, Gas’kov. INTRODUCTION The catalytic and sensor properties of polycrystal- line semiconducting oxides such as SnO 2 , ZnO, In 2 O 3 , and WO 3 attract considerable interest. The sensitivity and selectivity of these oxides can be enhanced by dop- ing. The sensor behavior of doped materials is, in many respects, governed by the chemical state of the dopant and its distribution between the bulk and surface of the host grains in ceramics and films. Uniform dopant dis- tribution throughout the film bulk is achieved in poly- crystalline films produced by sol–gel processing and spray pyrolysis [1, 2]. To dope the surface layer of films, use is made of physical deposition processes such as magnetron sputtering, vacuum evaporation, and laser ablation [3, 4]. In the last method, a target material is vaporized by a high-power-density laser beam to generate plasma, which expands in vacuum or a buffer gas and condenses on the substrate. This technique offers a number of advantages: the ability to produce films of low-volatility compounds, high deposition rate, additional substrate heating by incident ions, and precise control over the composition of the deposit. At the same time, to produce the desired dopant distribu- tion by laser ablation, it is necessary to know the com- position and energy of the ablated species as functions of laser-irradiation parameters and to optimize the pro- cess variables [5–8]. In this paper, we describe the surface doping of polycrystalline SnO 2 and SnO 2 〈Cu〉 films with palla- dium and examine the effect of the energy density of pulsed KrF laser radiation on the plasma generation process and Pd deposition rate. We also consider the through-thickness dopant distribution in the films and present data on the sensitivity of the resultant Pd/SnO 2 , SnO 2 〈Cu〉, and Pd/SnO 2 〈Cu〉 films to a mixture of 1 vol % H 2 with N 2 . EXPERIMENTAL As an ablation source, we used a focused 248-nm KrF excimer laser beam, with a maximum energy of 0.2 J/pulse and pulse duration of 20 ns, incident on the target surface at 45°. The spot area of the excimer beam was 0.1 mm 2 . The target was mounted in a vac- uum chamber and rotated about the axis normal to its surface by an electric micromotor. The laser energy per pulse was measured using an optoacoustic sensor, cali- brated against a Gentek-500P standard energy detector, and an analog oscilloscope (Fig. 1). The pulse energy was varied from 2.5 to 150 mJ. The deposition rate of Pd films on quartz glass or oxi- dized Si(100) substrates was measured as a function of pulse energy density on the target surface. As targets we Sensor Properties of Pd-Doped SnO 2 Films Deposited by Laser Ablation A. N. Shatokhin, F. N. Putilin, O. V. Safonova, M. N. Rumyantseva, and A. M. Gas’kov Moscow State University, Moscow, 119899 Russia e-mail: felix@org.chem.msu.su Received November 2, 2001 Abstract—Polycrystalline SnO 2 and SnO 2 〈Cu〉 films were surface-doped with palladium using laser ablation. The effect of the energy density of pulsed KrF laser radiation on the plasma generation process and Pd deposi- tion rate was studied, and the depth profiles of Pd in the films were determined. The gas response of the Pd/SnO 2 , SnO 2 〈Cu〉, and Pd/SnO 2 〈Cu〉 films was studied between 200 and 380°C using a mixture of 1 vol % H 2 with N 2 . Surface doping with Pd was found to enhance the hydrogen sensitivity of SnO 2 〈Cu〉 by two orders of magnitude. 1 2 3 4 5 6 Fig. 1. Schematic of the experimental arrangement: (1) KrF laser, (2) vacuum chamber, (3) focusing lens, (4) electric motor, (5) substrate, (6) target.