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

Micromechanical devices such as microcantilevers (MC) respond to irradiation with light by at least two different, photon-mediated processes, which induce MC bending as a consequence of differential surface stress. The first and slow bending is due to the absorption of photons, whose energy is transformed into heat and causes bending of bimetallic microcantilevers due to thermal expansion. The second type of deflection is fast and caused by photons of sufficient energy to promote electrons across the Schottky barrier and thus create charge carriers, resulting in photoinduced stress that causes MC bending. In this study, the MC bending response to irradiation with light of wavelengths ranging from 250 to 700 nm was investigated. Measurements of the immediate mechanical response to photoinduced stress as a function of the wavelength of incident light provide an avenue to the determination of the cut-off wavelength/energy of the Schottky barrier in the MC devices under investigation. For a gold coated Si(3)Ni(4) microcantilever we measured a cutoff wavelength of 1206 nm, which lies in the range of the literature value of 1100 nm.