Optical based thermal probing and characterization

Optical methods are promising tools for small-scale thermal probing and characterization. A lab-developed photothermal (PT) technique provides a noncontact method to characterize the thermal transport along the thickness direction of a multilayered film by analyzing the phase shift of the thermal radiation from the sample’s surface. Aiming to reduce the calibration in the phase shift method, a new amplitude method is developed on the basis of the amplitude of the thermal radiation signal. The new method successfully performs the thermal measurements for chemical vapor deposited SiC films, thermally oxidized SiO2 film on silicon substrates, and spider silk films. Furthermore, weak-sensitivity to the thermal contact resistance enables the amplitude method to lower the effect of thermal contact resistance on thermal conductivity determination. The normalized amplitude ratio of a high frequency to a low frequency provides a reliable way to evaluate the effusivity ratio of the film to that of the substrate. For spider silk films, the contribution to the thermal conductivity from -helices and antiparallel -sheets in silk proteins against the temperature has been studied. Raman spectroscopy is better than PT since its scatterings involve not only the structure information of a sample but also physical properties, like temperature and stress. The edge area of a mechanically cleaved Si wafer is studied using Raman spectroscopy. The appearance of nanocrystals there is proved and it accounts for the abnormal increase in Raman intensity when the grain size of nanocrystals varies from 20 to 10 nm. For transient thermal probing and characterization, a time-domain differential Raman technique is developed using a square-wave modulated laser. The varying duty cycle of the modulation signal realizes controlled heating and