Abstract-Terahertz slot antenna devices fabricated on silver nanowire network films

J. T. Hong, S. J. Park, Ji-yong Park, Soonil Lee, and Y. H. Ahn

https://www.osapublishing.org/ome/abstract.cfm?uri=ome-7-5-1679&origin=search

We fabricated plasmonic devices operating in the terahertz (THz) frequency range using silver nanowire (AgNW) network films. AgNW films exhibit high conductivity and good transparency in the visible range, with a figure of merit comparable to that of conventional transparent conducting oxide films. The THz conductivity of AgNW films can be improved by post-treatment procedures such as welding using graphene oxide flakes. Using photolithography, we fabricated the slot antenna arrays whose resonance behaviors are determined by geometric parameters such as the length of individual elements. The plasmonic resonance varied with the sheet resistances of the film, enabling us to manipulate the quality factors and the peak position of the resonance, in particular, by controlling the films thickness and by the post-procedures such as the chemical vapor treatment.

© 2017 Optical Society of America

Abstract-Crystallization Kinetics of Lead Halide Perovskite Film Monitored by In-situ Terahertz Spectroscopy

Sae-June Park, Ah-Ram Kim, Jung Taek Hong, Ji-Yong Park, Soonil Lee, and Yeong Hwan Ahn

J. Phys. Chem. Lett., Just Accepted Manuscript

DOI: 10.1021/acs.jpclett.6b02691

Publication Date (Web): January 4, 2017

Copyright © 2017 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/acs.jpclett.6b02691?journalCode=jpclcd

Vibrational modes in the terahertz (THz) frequency range are good indicators of lead halide perovskite's crystallization phase. We performed real-time THz spectroscopy to monitor the crystallization kinetics in lead halide perovskite films. First, THz absorptance was measured while the perovskite film was annealed at different temperatures. During this process, we observed the dynamical phase transition of the perovskite structure from an intermediate phase to the tetragonal phase. By analyzing the Avrami exponent, we observed an abrupt dimensionality switch (of interfacial growth from 1D to 2D) with increasing temperature starting at approximately 90°C. More interestingly, we monitored the laser-induced enhancement of the crystallinity of the pre-annealed perovskite film. The THz absorptance increased initially, then subsequently decayed over a couple of hours, although the enhancement factor varies depending on the film crystallinity. In particular, the Avrami analysis implied that the enhanced crystallization upon light illumination was assisted by the 1D diffusion processes. The perovskite film conductivity increased by the light irradiation more dramatically than the thermal annealing due to percolation threshold behaviors. The activation energy for light-induced crystallization was measured of 2.3 eV, which indicated that enhanced crystallization originated from the photo-induced structural change of residual lead iodide at the grain boundary.

Abstract-Terahertz conductivity of reduced graphene oxide films

J. T. Hong, K. M. Lee, B. H. Son, S. J. Park, D. J. Park, Ji-Yong Park, Soonil Lee, and Y. H. Ahn »View Author Affiliations

http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-21-6-7633

We performed time-domain terahertz (THz) spectroscopy on reduced graphene oxide (rGO) network films coated on quartz substrates from dispersion solutions by spraying method. The rGO network films demonstrate high conductivity of about 900 S/cm in the THz frequency range after a high temperature reduction process. The frequency-dependent conductivities and the refractive indexes of the rGO films have been obtained and analyzed with respect to the Drude free-electron model, which is characterized by large scattering rate. Finally, we demonstrate that the THz conductivities can be manipulated by controlling the reduction process, which correlates well with the DC conductivity above the percolation limit.