Wavelength Dependence of Photoinduced Microcantilever Bending in the UV-VIS Range

Micromechanical devices such as microcantilevers (MC) respond to irradiationwith light by at least two different, photon-mediated processes, which induce MC bendingas a consequence of differential surface stress. The first and slow bending is due to theabsorption of photons, whose energy is transformed into heat and causes bending ofbimetallic microcantilevers due to thermal expansion. The second type of deflection is fastand caused by photons of sufficient energy to promote electrons across the Schottky barrierand thus create charge carriers, resulting in photoinduced stress that causes MC bending. Inthis study, the MC bending response to irradiation with light of wavelengths ranging from250 to 700 nm was investigated. Measurements of the immediate mechanical response tophotoinduced stress as a function of the wavelength of incident light provide an avenue tothe determination of the cut-off wavelength/energy of the Schottky barrier in the MCdevices under investigation. For a gold coated Si3Ni4 microcantilever we measured a cutoffwavelength of 1206 nm, which lies in the range of the literature value of 1100 nm.