OPTICAL CHARACTERIZATION OF BOWTIE AND HETERODIMER ANTENNAS: OPTIMIZING DEVICE PROPERTIES FOR SENSING OR PHOTOHARVESTING APPLICATIONS

Open Access
Author:
Wambold, Ray
Graduate Program:
Materials Science and Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
June 24, 2016
Committee Members:
  • Darin Zimmerman, Thesis Advisor
  • Noel Christopher Giebink, Committee Member
  • Venkatraman Gopalan, Committee Member
Keywords:
  • optical antennas
  • plasmonics
  • photonics
Abstract:
The present study investigates the optical characteristics of bowtie and heterodimer antennas designed to operate in the visible to near-infrared spectrum. Two main applications are in mind: a bowtie antenna (BT) device that utilizes field emission or quantum tunneling under an external bias to detect specific frequencies (an optical sensor) and a geometrically-asymmetric heterodimer (HD) that might be used as an optical rectifying device for solar-energy harvesting. We have three main objectives. First, although single devices and arrays of identical devices have been investigated by others, we seek to confirm the optical response of both isolated and strongly-coupled arrays of devices. Second, because the heterodimer device (i.e. the geometric rectifier) has not been extensively studied, we seek further insight into this coupling, since it is an important geometry for solar harvesting via a geometric diode. Third, we investigate how modifying plasmonic devices with Cu atomic layer deposition (ALD) changes the optical response of the devices. Nanoantennas are fabricated on silica employing electron-beam lithography, with gold or palladium as the nanoantenna material. Device arrays are characterized via optical extinction spectroscopy, performed in a confocal microscopy arrangement, and using a broadband light source. Some of the palladium devices then undergo Cu-ALD in order to reduce the gap between the dimer electrodes. We present three experimental studies. The first investigates the effects of varying the device length and the gap between electrodes for relatively isolated nanoantenna; this establishes intra-device interaction properties. The second investigates inter-device interactions. The edge-to-edge distance is varied in the vertical and horizontal directions individually and then both simultaneously. The third demonstrates the effects of adding Cu-ALD on palladium devices. We compare many of our experimental measurements to the results of finite-difference time-domain simulations. These show good agreement with experiment and help unpack the experimental results.