Resonance frequency shift of a CdS nanowire induced by light illumination. (a)–(d) show that the light illumination lowers the resonance frequency from 2106 kHz to 2086 kHz. (a) Resonance at f = 2106 kHz under darkness; (b) resonance disappears under light illumination (wavelength is 405 nm); (c) resonance appears again by tuning frequency to f = 2086 kHz under light illumination; (d) resonance disappears after turning off light illumination. Scale bar: 1 μ m .