Photothermal Reflectance
Photothermal Reflectance (PTR) is utilized for measuring thin films and nanostructures. PTR is a pump and probe technique in which the pump source (Nd:YAG laser) provides thermal energy to the sample whereas the probe (He-Ne laser) senses the reflectivity change at the sample’s surface. To enhance heat absorption, a layer of gold film is deposited on top of the thin layer sample.
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Photothermal Reflectance (PTR) is utilized for measuring thin films and nanostructures. PTR is a pump and probe technique in which the pump source (Nd:YAG laser) provides thermal energy to the sample whereas the probe (He-Ne laser) senses the reflectivity change at the sample’s surface. To enhance heat absorption, a layer of gold film is deposited on top of the thin layer sample.
The measurement begins with the Nd:YAG laser pulse(~8 ns) incident on the sample surface. The sample surface temperature rises sharply, and then relaxes with time. This gives rise to a temperature profile which depends on the thermal properties of the underlying films and the thermal resistance between the layers. The heating up of the sample induces a change in the refractive index on the surface. The probe beam is focused on the center of the pump spot to monitor the induced changes. Since the temperature and the reflectivity of gold are inversely related, the temperature profile can be obtained by capturing the changes in the reflected probe beam. The latter is acquired using a photodetector and the signals are displayed on an oscilloscope. A typical captured profile, which has been normalized and inverted, is shown below. To extract the thermal properties form the obtained signal, analytical expression of heat conduction is used to curve fit the measured data.
We measured thermal properties of thin film ranging from 20 nm to a few microns thickness. With sufficient samples, it is also possible to measure thermal contact resistance across interface. Interested party that wants their thin film/nanostructures to be measured can contact us for the requirement needed for their samples.
