Two-detector measurement system of pulse photothermal radiometry for the investigation of the thermal properties of thin films

Abstract

Pulsed photothermal radiometry, a method developed in previous work for thin film thermal effusivity measurements, is now further developed for the determination of thin film thermal conductivity and volumetric specific heat. The present setup consists of a nanosecond laser source and two infrared (IR) detectors for temperature response measurement. The two detectors have different sizes and frequency bandwidths enabling accurate measurement of the surface temperature both in very short (ns) and long (μs) times after the laser pulse. This enables measurement of the apparent effusivity of both the thin film and substrate. The position in time of the transition region between the film and substrate effusivity is essential for recalculation of the thermal conductivity and volumetric specific heat from the measured thermal effusivity. The presented experimental system was applied to the investigation of the thermal properties of TiO2 and Si-B-C-N thin films. The different thermal conductivity of the TiO2 films correlates well with their different phase structures. The Si-B-C-N films show a slightly different thermal conductivity and specific heat capacity for different atomic compositions.