With the advances in electronics and communication devices over the last several decades, radio-frequency antennas have miniaturized from externally mounted “rabbit ears” on our grandma’s televisions to devices small enough to be concealed within the body of the cellphone itself, corresponding to the carrier frequencies used from on the order of hundreds of MHz to a few GHz. Optical nanoantennas, also called plasmonic nanoantennas, just like their radio-frequency equivalents, efficiently couples the energy of light - an electromagnetic wave oscillating at THz frequencies to a confined region within their feed gap of subwavelength dimension, far beyond the classical diffraction limit. The resonant optical interaction of metallic nanoantennas in their near-field produces strong electromagnetic field confinement, and the gap-width dependent optical scattering intensity opens a regime in sensing applications on the nanoscale. In this thesis, we first explore the optical interaction between two optical antennas- a metallic apertureless near-field optical microscope (a-NSOM) tip and a metal-coated nanomechanical resonator (NMR) over nanoscale distance that vary in a harmonic or transient fashion to demonstrate local measurement of mechanical vibrations in NMRs with nanoscale spatial resolution and nanosecond temporal resolution. In the measurement, a plasmonic nanofocusing element is integrated with the a-NSOM probe for efficient concentration of propagating surface plasmon polaritons (SPPs) at the apex of probe tip, and efficient confinement of light in the gap between the probe-tip and surface of the NMR. Using this technique, we measured the surface vibrations of suspended metal-coated silicon NMRs with a minimum detectable root-mean-squared displacement sensitivity of 0.3pm/√Hz. In addition, the plasmonic aNSOM technique is used for local measurement of motion in a NMR actuated by a harmonic photothermal source to demonstrate all-optical actuation and detection of mechanical vibrations in micro- and nanostructures with sub-wavelength lateral spatial resolution. Owing to the strong concentration of light at the plasmonic probe, significant heating of the tip and a sample positioned in the optical near-field is expected. We subsequently investigated the local heating produced by the plasmonic nanofocusing probe under steady state conditions using the tip-enhanced Raman approach. This study has implications for exploring the plasmonic nanofocusing probe in heat assisted nanofabrication and fundamental studies of nanoscale heat transport in materials. In order to push forward the temporal resolution of our technique to picosecond scale, corresponding to the measured frequencies exceeding 100GHz, the pump probe technique is then incorporated with the a-NSOM probe for detection of ultrahigh frequency phonon or acoustic vibrations in isolated nanostructures. This newly developed technique allows us to investigate mechanical vibrations in laterally patterned gold nanodots on glass substrates followed by transient optical excitation. With this technique, quantitative information on a single nanostructure with high temporal and spatial resolution can be obtained. Finally, using the optical field concentration of plasmonic nanoantennas as inspiration, a novel class of pillar nanoantennas (P-NAs) is designed, and their plasmon response is utilized for polarization selective detection of complex acoustic phonon vibration modes. This study have important implications in the development of, high speed opto-acoustic modulators, reconfigurable nanomechanical plasmonic metastructures, and ultrafast transducers for detection of acoustic vibrations.

Last modified

• 03/29/2018

Creator

• Xiang Chen

DOI

• https://doi.org/10.21985/N2MQ23

Subject

• Mechanical Engineering

Keyword

• ultrafast
• opto-mechanical
• nanoantenna
• plasmonic
• a-NSOM
• NMRs

Date created

• 2017-01-01

Resource type

• Dissertation

Rights statement

• In Copyright