Electrical Detection of Oscillations in Micro- and Nano- Cantilevers Using Harmonic Detection of Resonance
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0888-V02-03.1
Electrical Detection of Oscillations in Micro- and Nano- Cantilevers Using Harmonic Detection of Resonance
J. Gaillard, R. Ciocan, M. Skove and A. M. Rao Department of Physics and Astronomy, Clemson University, Clemson, SC 29634 ABSTRACT Accurate determination of the resonant frequency, phase and quality factor in micro and nano-mechanical oscillators permits the detection of: (i) trace amounts of specific adsorbed molecules which affect the resonant frequency; (ii) pressure variations which affect the mechanical damping of the oscillator; or (iii) the temperature dependence of the elastic properties of the oscillator through a shift in the resonant frequency. To date, electrical detection of oscillations in cantilevered multiwalled carbon nanotubes (MWNTs) has eluded researchers in the field. Electrical detection allows a simple means for measuring the resonance frequency, phase and quality factor of cantilevers built into integrated circuits, or cantilevers whose response can be monitored as a function of any external parameter such as temperature or pressure. To this end, we described a fully electrical (actuation and detection) method termed harmonic detection of resonance (HDR) to measure mechanical oscillations in ambient conditions for two systems: Si-based micro- and MWNT based nano-cantilevers. Furthermore, we demonstrate that the resonant frequency in micro- and nano-cantilevers can be tuned without appreciable change in the quality factor which suggests that HDR is an ideal platform in device design and applications. INTRODUCTION Recently, a doubly clamped single walled carbon nanotube (SWNT) was electrically actuated and its resonant frequency was detected using a mixer technique1. Although this technique is valuable for a beam in a guitar-like configuration, it cannot be applied to a cantilevered nanostructure. Alternatively, a technique for detecting nanoscale displacements has been demonstrated using a single electron transistor2. However, this device operates at low temperatures (30 mK) and a relatively high magnetic field (8 T). Electrically induced mechanical oscillations in MWNTs have also been recorded using non-electrical detection methods that involved the use of a transmission electron microscope3, scanning electron microscope4, field emission microscope5, or an optical microscope6,7. For realistic applications, the resonating system must be portable and therefore a capacitive readout of the mechanical motion is ideal. Implementing a capacitive readout method is challenging due to a large interfering signal at the driving frequency which comes from the inherent parasitic capacitance in the circuits that contain the oscillator and its counter electrode. We find that by locking into higher harmonics of the driving frequency, the parasitic capacitance can be avoided, facilitating the measurement of dynamic capacitance with high sensitivity in micro- and nano-cantilevers.
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EXPERIMENTAL In our studies, we manipulate a cantilever over a dark field microscope as report
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