Optical and Optoacoustic Inspection of Niobium Trisulfide Whiskers

Transition metal trichalcogenide niobium trisulfide (NbS3) is a unique material that is still of interest, and its device applications have been explored. In this study, we determined the optical and optoacoustic parameters of NbS3 whiskers using a nondestructive, noninvasive, and noncontact method based on laser ultrasonics. In order to inspect and determine the parameters of the type IV NbS3 whiskers, the polarization-dependent transient relative reflectivity changes of the sample surface were monitored and analyzed based on a well-established optical detection theory of ultrasonics. Using simple calculations and curve fitting, the velocity of sound v, polarization-dependent complex refractive index ñ, ultrasonic attenuation coefficient α, and photoelastic constant dñ/dη were determined. Further, using laser ultrasonics combined with nanoindentation, Young's modulus Y and Poisson's ratio σ were estimated. This study demonstrates the potential of picosecond laser ultrasonics in the material characterization of microcrystals for nanodevice applications.