Thermal-diffusivity measurements of ultrahigh thermal conductors with use of scanning photothermal rate-window spectrometry: Chemical-vapor-deposition diamonds

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Abstract
A comprehensive study of a photothermal rate-window spectrometry for thermal-diffusivity measurements of ultrahigh thermal conductors, using either a dual-channel boxcar averager or a lock-in amplifier, is presented. Theoretical analysis of infrared radiometric transients and techniques to extract the diffusivities of materials from the transient are discussed. By exploiting the derivative signal nature of the rate-window methodology, one can measure the thermal diffusivity of the sample with superior signal-to-noise (S/N) ratio from the maximum position of the radiometric rate-window signal. Our measurements of thermal diffusivities of chemical-vapor-deposition diamonds made by the hot-filament process as a function of temperature between 60 and 300 K are the first such photothermal data obtained completely nonintrusively and they illustrate the unique potential of this measurement methodology for the nondestructive, noncontact photothermal investigation of ultrahigh thermal-conductor thermophysics, largely inaccessible by other diagnostic probes.