Resonant piezoelectric optoacoustic detection of surface and bulk phase transitions

Y.CESA; N. MINGOLO; JMC LARRIERA; O.E. MARTÍNEZ

SURFACE AND COATINGS TECHNOLOGY

ELSEVIER SCIENCE SA

Año: 1999 vol. 122 p. 28 - 32

0257-8972

A new technique for optoacoustic determination of phase transitions is described, based on the resonant piezoelectric detection of the acoustic signal generated by the thermal excitation of the sample by means of a low power modulated diode laser. The technique does not make use of a gas cell and a microphone, but instead uses a piezoelectric detector in contact with the sample holder and a diode laser modulated at the resonant frequency of the detector. The signal is filtered by a phase-sensitive amplifier (lock-in), providing information on the amplitude and phase of the acoustic wave. It is shown that the technique is particularly sensitive to glass-crystalline transitions, with a distinctive decrease in the phase of the signal attributed to the large decrease in the heat capacity upon crystallization of the glass. The high sensitivity of the method should make it particularly adequate for the determination of the stability of amorphous films over crystalline substrates or glassed surfaces. (C) 1999 Elsevier Science S.A. All rights reserved.