Unusual high sensitivity in highly oriented laser ablated thin films of SnO₂ on (1102) sapphire and (100) LaAlO₃

¹ Surface Science, Spectroscopy and Solid State Ionics Laboratory, Department of Physics, Southern University
² A&M College, Bâton Rouge, Louisiana 70813, USA
³ Chemical and Biological Detection Group, Lawrence Livermore National Laboratory, Livermore, California 94550, USA

Corresponding author: Rambabu@grant.phys.subr.edu

Received: 28 April 2001
Revised: 15 November 2001
Accepted: 17 December 2001
Published online: 15 April 2002

Abstract

A systematic investigation on growth and sensor characteristics of SnO₂ thin films of different orientations is reported for the first time. Thin films were grown by pulsed laser (KrF; λ = 248 nm) ablation technique under in-situ conditions. Films deposited at 525 °C on (1102) sapphire were predominantly (101) orientated whereas those deposited on (100) LaAlO₃ were highly a-axis orientated. Sensors made of predominantly (101) oriented films exhibited more than two orders magnitude change in resistance even for 100 ppm of H₂ in air at 310 °C. The response and retracing times of the sensor were remarkably short respectively 30 and 200 s. Sensors made of a-axis oriented films also exhibited similar sensitivity and response time for the same quantity of both H₂ and LPG. However, the retrace time was very long typically about 20 min. Atomic force microscopic (AFM) investigation reveals that the films are highly granular with an average size of about 100–150 nm which is ten times larger than the critical size of 6 nm, a criterion required for high sensitivity. (The Debye length of  nm at 293 K and the critical grain size is therefore 2 × Debye length, which is 6 nm.)