Optically addressing a large number of cantilevers

A heterodyne laser Doppler interferometer operating up to 100 MHz with an optical vibration excitation function was implemented to enable frequency detection of nanocantilevers. By using the stimulant of a network analyzer to sweep the modulation frequency of the laser diode used for photothermal vibration excitation, cantilevers measuring as narrow as 100 nm could be excited, and its natural frequency synchronously measured with the analyzer. Due to the gradient in frequency of the cantilevers, frequency shift of each cantilever could be addressed without the need for precise laser spot positioning, wiring to the cantilevers or multiplexing. Since the method is well adapted for a large number of cantilevers, we are currently fabricating a cantilever array with 88 or more cantilevers within one row, and optics to allow sweeping of the laser spot in phase with the frequency sweep. Preliminary results on frequency measurement and mass detection will be reported.