The European Physical Journal Applied Physics

Table of Contents - April 2002 - Volume 18, Issue 01  

Organic Materials and Devices

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

K. I. Gnanasekara1a2, B. Rambabua1a2 and K. C. Langrya3

Surface Science, Spectroscopy and Solid State Ionics Laboratory, Department of Physics, Southern University

A&M College, Bâton Rouge, Louisiana 70813, USA

Chemical and Biological Detection Group, Lawrence Livermore National Laboratory, Livermore, California 94550, USA

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 ${\rm SnO}_2 \cong 3.07$  nm at 293 K and the critical grain size is therefore 2 × Debye length, which is 6 nm.)

(Received April 28 2001)

(Revised November 15 2001)

(Accepted December 17 2001)

(Online publication April 15 2002)

PACS:

  • 07.07.Df – Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing;
  • 81.15.Fg – Laser deposition;
  • 73.61.Jc – Amorphous semiconductors; glasses

Rambabu@grant.phys.subr.edu