SPIE fellow visits UNC Charlotte

“BROADBAND TERAHERTZ CONDUCTIVITY AND OPTICAL TRANSMISSION OF INDIUM-TIN-OXIDE (ITO) NANOMATERIALS”

EVENT DATE: Tuesday, October 1, 2013
LUNCH WITH THE SPEAKER : 11:30am – 12:30pm * 238 Grigg
SEMINAR – 12:45 – 1:45pm * 132 Grigg

Abstract

Time-domain terahertz spectroscopy (THz-TDS) provides a non-contact method for characterizing the electrical and dielectric properties of technologically important materials, e.g., transparent and conducting Indium Tin Oxide (ITO) thin films, which are widely used in optoelectronic devices. Recently, ITO nanomaterials have attracted a lot of attention, because of its omidirectional and wideband anti-reflection characteristics. Indium-tin-oxide (ITO) nanorods (NRs) and nanowhiskers (NWhs) were fabricated by an electron-beam glancing-angle deposition (GLAD) system. Two terahertz (THz) time-domain spectrometers (TDS) with combined spectral coverage from 0.15 to 9.00 THz were used. These allow accurate determination of the optical and electrical properties of such ITO nanomaterials in the frequency range from 0.20 to 4.00 THz. Together with Fourier transform infrared spectroscopic (FTIR) measurements, we found that the THz and far-infrared transmittance of these nanomaterials can be as high as 70% up to 15 THz, as opposed to about 9% for sputtered ITO thin films. The complex conductivities of ITO NRs, NWhs as well films are well fitted by the Drude-Smith model. Taking into account that the volume filling factors of both type of nanomaterials are nearly same, mobilities, and DC conductivities of ITO NWhs are higher than those of NRs due to less severe carrier localization effects in the former. On the other hand, mobilities of sputtered ITO thin films are poorer than ITO nanomaterials because of larger concentration of dopant ions in films, which causes stronger carrier scattering. We note further that consideration of the extreme values of Re{σ} and Im{σ} as well the inflection points, which are functions of the carrier scattering time (τ) and the expectation value of cosine of the scattering angle (γ), provide additional criteria for accessing the accuracy of the extraction of electrical parameters of non-Drude-like materials using THz-TDS. Our studies so far indicate ITO NWhs with heights of ~1000 nm show outstanding transmittance and good electrical characteristics. Improved performance of a liquid-crystal-based THz phase shifter using ITO NWhs as electrodes will be shown as an example.

Biography
Ci-Ling Pan graduated from Tunghai University, Taichung, Taiwan (B.S., 1971) and Colorado State University (CSU), Ft. Collins, Colorado, USA (M.S., 1975 and Ph.D., 1979). All of his degrees are in Physics. Since 2009, He is a Tsing Hua Chair Professor, the Department of Physics, National Tsing Hua University (NTHU), Hsinchu, Taiwan. Currently, Prof. Pan is the department chair. He also held joint appointment in the Institute of Photonics Technologies and served as Director of the Photonics Research Center of NTHU. Prof. Pan taught at National Chiao Tung University, Taiwan, 1981-2009. He was a visiting professor at Osaka University and the Chinese University of Hong Kong in 2004 and 2008, respectively. Prof. Pan was the first coordinator for the Optics and Photonics Program of the National Science Council (NSC) (1996 to 1999), Taiwan. He is a permanent member of the Physical Society (PSROC), the Optical Engineering Society (ROCOES, now the Taiwan Photonics Society), The Chinese Institute of Engineers of Taiwan, the Republic of China. Prof. Pan is a Fellow of APS, IEEE, OSA and SPIE, PSROC and PSC (Photonics Society of Chinese Americans). He has also received numerous honors in Taiwan, e.g., the prestigious Outstanding Scholarship Award of the Ministry of Education.
Prof. Pan has worked on a wide spectrum of topics in optics, lasers and related fields, including single-atom detection, nonlinear optics, frequency-stabilized lasers and precision optical instrumentation including near-field microscopy, interferometry and optical fiber sensors during his career. In particular, his group has made significant contributions on ultrafast optoelectronic material and devices based on arsenic-ion-implanted GaAs; cw and mode-locked tunable dual- and multiple- wavelengths lasers; picosecond and femtosecond laser mode-locking dynamics and laser-diode-based techniques for optical-microwave interactions and high-speed instrumentation. Recent research highlights include pioneering the field of liquid crystal THz photonics, femtosoeocnd-laser recrystallization and activation of silicon as well as novel THz generators and detectors. The latter were used in diverse applications such as diagnostics of technologically important materials for photovoltaics, assessing burn trauma and optical-network-compatible W-band (100 GHz or 0.1 THz) wireless communication Link at a data rate beyond 20 Gbit/s.