Laser-induced Detuning of Quartz Crystal Microbalances in Adsorbing and Non-adsorbing Environments

Light induced modifications in frictional behavior of films of adsorbed molecules constitute an area of current interest in nanotribology, and are potentially observable at room temperature by means of a quartz crystal microbalance (QCM). In order for such studies to be viable, the impact of laser light on a QCM must be established. We report here an investigation of the response of a QCM to green laser light in vacuum, nitrogen, and ethanol gas. Measurements of frequency and amplitude responses of the QCMs were performed, for samples with electrodes composed of AuNi alloys with varying degrees of Ni content. For the adsorbing ethanol films, we observed that the frequency response upon green laser irradiation initially strongly decreased with pressure, but recovered slowly up to the vapor pressure. This effect was more pronounced in electrodes with higher Ni content. QCMs exposed to non-adsorbing nitrogen produced responses of similar magnitude regardless of Ni content, however, we noticed marked changes in the initial response behavior upon illumination. The effects can be explained within the context of the effects of mass uptake, desorption and laser heating [1].
[1] Goodman, L., et al. J. Appl. Phys. 124, 024502 (2018)