Scanning fast photothermal radiometry

The thermal characterization at micro or nano scale is of great interest for numerous of technical and technological applications. Assessment of heat transfer at microscale permits understanding behavior and design of different kind of systems like microelectronic or micro-electro-mechanical devices or effective properties of composite materials.
In this context, at I2M laboratory, we use widely the photothermal methods for thermal characterization of thin layer materials. One of these methods is the modulated photothermal radiometry (MPTR) which is well adapted to measure the out of plane thermal properties of thin films. The modulated photothermal radiometry is a contactless measurement technique based on monitoring the emitted infrared radiation from the surface of the sample consequently to a periodic photothermal excitation. The photothermal power from a modulated laser source is absorbed by the surface of the sample leading to an increase in the temperature at the heating area. This results in an increase in the infrared emitted radiation and assuming small temperature increase the emitted radiation can be linearized. On this way an indirect measurement of the temperature at the sample surface is obtained. In this work, we intend to develop a fast photothermal radiometry with several tenth of microns in resolution in order to enable the in plane thermal characterization. With the use an optical arrangement we manage the formation of the heating and measurement spots at the sample surface. The heating spot of 15 μm in diameter is formed by focusing the laser; the measurement spot of 50 μm in dimeter is an image of the detector over the sample surface. The sample mounted over a translation stage permits it’s scanning with micrometric precision. The use of modulated excitation allows exploring the frequencies up to 50 kHz. Under this configuration the in plane and out of plane heat conduction is possible to be assessed.