THEORETICAL MODELING OF OBLIQUELY CROSSED PHOTOTHERMAL DEFLECTION FORTHERMAL-CONDUCTIVITY MEASUREMENTS OF THIN-FILMS

A three-dimensional theoretical model has been developed to calculate the normal probe beam deflection of the obliquely crossed photothermal deflection configuration in samples which consist of thin films depos ited on substrates. Utilizing the dependence of the normal component o f probe beam deflection on the cross-point position of the excitation and probe beams, the thermal conductivity of the thin film can be extr acted from the ratio of the two maxims of the normal deflection amplit ude, which occurs when the cross-point is located near both surfaces o f the sample. The effects of other parameters, including the intersect angle between the excitation and the probe beams in the sample, the m odulation frequency of the excitation beam, the optical absorption and thickness of the thin films, and the thermal properties of substrates on the thermal conductivity measurement of the thin film, are discuss ed. The obliquely crossed photothermal deflection technique seems to b e well suited for thermal conductivity measurements of thin films with a high thermal conductivity but a low optical absorption, such as dia mond and diamond-like carbon, deposited on substrates with a relativel y low thermal conductivity.