Article: De Alba, R; Abhilash, TS; Rand, RH; Craighead, HG; Parpia, JM; “Low-Power Photothermal Self-Oscillation of Bimetallic Nanowires”, Nano Letters, 17 (7):3995-4002
Abstract: We investigate the nonlinear mechanics of a bimetallic, optically absorbing SiN-Nb nanowire in the presence of incident laser light and a reflecting Si mirror. Situated in a standing wave of optical intensity and subject to photothermal forces, the nanowire undergoes self-induced oscillations at low incident light thresholds of <1 mu W due to engineered strong temperature-position (T-z) coupling. Along with inducing Self-oscillation, laser light causes large changes to the mechanical resonant frequency omega(0) and equilibrium position z(0) that cannot be neglected. We present experimental results, and a theoretical model for the motion under laser illumination. In the model; we solve-the governing nonlinear differential equations by perturbative means to show that self-oscillation amplitude is set by the competing effects of direct T-z coupling and 2 omega(0) parametric excitation due to T-omega(0) coo coupling. We then-study the linearized equations of motion to show, that the optimal thermal time constant tau for photothermal feedback is tau -> infinity rather than the previously reported omega(0) tau = 1. Lastly, we demonstrate photothermal quality factor (Q) enhancement of driven motion as a means to counteract air damping. Understanding photothermal effects on nano- and micromechanical devices, as well as nonlinear aspects of optics-based motion detection) can:enable new device applications as oscillators or other-electronic elements with smaller device footprints and less stringent ambient vacuum requirements.
Funding Acknowledgement: Cornell Center for Materials Research; NSF [DMR-1120296, DMR-1202991, ECCS-1542081]
Funding Text: We thank A. T. Zehnder for guidance in applying beam-theory to our supporting cantilevers, as well as other helpful discussions. This work was supported in part by the Cornell Center for Materials Research with funding from the NSF under DMR-1120296 and by the NSF under DMR-1202991. Devices were fabricated at the Cornell NanoScale Facility, a member of the National Nanotechnology Coordinated Infrastructure (NNCI), which is supported by the NSF under ECCS-1542081.