Ultra high sensitive detection of mechanical resonances of nanowires by field emission microscopy

We present here highly sensitive measurements of nanowire mechanical resonances by analyzing Field Emission Microscopy (FEM) images from the nanowires while they are excited by sinusoidally time-varying voltages. Numerical analysis of the image blurring during frequency sweeps through resonances are shown to allow detection with ≃100× higher sensitivity as compared to our previous measurements where they were detected by the changes in the total field emission (FE) current. Furthermore since FEM approximately measures the end angle of the nanowire, this detection is more sensitive to higher resonance modes which in general have much smaller amplitudes. Observation of the mechanical response of SiC nanowires in FEM shows that they almost always present non linear mechanical behavior with large hysteresis and abrupt jump effects in their frequency response that are related to the large applied electric field. We approach the linear regime by reducing the excitation voltage and by using the sensitive image detection method.