Role of photostriction and photothemal effects in photon induced deflection of Si microcantilevers

Highlights: • Photo induced deflection is studied in response to laser radiation (He-Ne – 6328 A⁰) on uncoated, Au and Al coated Si microcantilevers to examine the induced stress contribution from photothermal and photostriction phenomenon. • The observed deflections in different MCs and their time response from these two mechanisms, i.e. thermal stress and photostriction, were analyzed using an optical readout scheme in an atomic force microscope. • Laser was made to incident on both sides of the MCs by flipping to understand the cause of deflection and results were compared in terms of deflection magnitude, direction and response time. • It is shown that an upward deflection with a fast response, independent of laser exposing side, and is attributed to photostriction effect in uncoated Si microcantilevers while photothermal effect dominated in bimaterial (metal coated) microcantilevers with a relatively slow response with deflection dependent on the laser exposing side. Laser beam (He-Ne – 6328 A⁰) induced deflection in uncoated, Au, and Al coated Si microcantilevers (MCs) of various dimensions was studied, using an AFM head, to examine the induced stress contribution from photothermal and photostriction phenomenon. The laser beam was made to incident sequentially on front and back surfaces of the MC, by flipping it, and results were compared in terms of deflection magnitude, direction of bending and response time. In case of uncoated MCs, it was observed that the induced deflection was always in the direction of the incident laser beam with a fast response. In contrast, in metal (Au, Al) coated MCs, deflection direction was found to be dependent on laser beam exposure side with two orders of enhanced deflection sensitivity and slow response time. The former is attributed to photostriction effect while the latter is explained on the basis of photothermal effect in bimetallic MCs. Flipping experiments on bimettalic MCs, further revealed that stress contribution from these two source mechanisms crucially depends on MC dimensions and direction of laser exposure.