title: Dynamic near-field optical interaction between oscillating nanomechanical structures.
abstract: Near-field optical techniques exploit light-matter interactions at small length scales for mechanical sensing and actuation of nanomechanical structures. Here, we study the optical interaction between two mechanical oscillators--a plasmonic nanofocusing probe-tip supported by a low frequency cantilever, and a high frequency nanomechanical resonator--and leverage their interaction for local detection of mechanical vibrations. The plasmonic nanofocusing probe provides a confined optical source to enhance the interaction between the two oscillators. Dynamic perturbation of the optical cavity between the probe-tip and the resonator leads to nonlinear modulation of the scattered light intensity at the sum and difference of their frequencies. This double-frequency demodulation scheme is explored to suppress unwanted background and to detect mechanical vibrations with a minimum detectable displacement sensitivity of 0.45 pm/Hz(1/2), which is limited by shot noise and electrical noise. We explore the demodulation scheme for imaging the bending vibration mode shape of the resonator with a lateral spatial resolution of 20 nm. We also demonstrate the time-resolved aspect of the local optical interaction by recording the ring-down vibrations of the resonator at frequencies of up to 129 MHz. The near-field optical technique is promising for studying dynamic mechanical processes in individual nanostructures.
authors.affiliation: Mechanical Engineering Department, Northwestern University, Evanston, IL 60208.
authors.forename: Phillip
authors.initials: P
authors.lastname: Ahn
authors.affiliation: Mechanical Engineering Department, Northwestern University, Evanston, IL 60208.
authors.forename: Xiang
authors.initials: X
authors.lastname: Chen
authors.affiliation: Mechanical Engineering Department, Northwestern University, Evanston, IL 60208.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: Mechanical Engineering Department, Northwestern University, Evanston, IL 60208.
authors.forename: Matthew
authors.initials: M
authors.lastname: Ford
authors.affiliation: Center for Nanoscale Materials, Argonne National Laboratory, Argonne, IL 60439-4806.
authors.forename: Daniel
authors.initials: D
authors.lastname: Rosenmann
authors.affiliation: Center for Nanoscale Materials, Argonne National Laboratory, Argonne, IL 60439-4806.
authors.forename: Ii Woong
authors.initials: IW
authors.lastname: Jung
authors.affiliation: Mechanical Engineering Department, Northwestern University, Evanston, IL 60208.
authors.forename: Cheng
authors.initials: C
authors.lastname: Sun
authors.affiliation: 1] Mechanical Engineering Department, Northwestern University, Evanston, IL 60208 [2] Civil and Environmental Engineering Department, Northwestern University, Evanston, IL 60208.
authors.forename: Oluwaseyi
authors.initials: O
authors.lastname: Balogun