Monday, January 22, 2018

Abstract-Enhanced Terahertz Shielding of MXenes with Nano-Metamaterials

Geunchang Choi, Faisal Shahzad, Young-Mi Bahk, Young Min Jhon, Hyunchul Park, Mohamed Alhabeb, Babak Anasori, Dai-Sik Kim, Chong Min Koo, Yury Gogotsi,

Terahertz (THz) shielding becomes increasingly important with the growing development of THz electronics and devices. Primarily materials based on carbon nanostructures or polymer–carbon nanocomposites have been explored for this application. Herein, significantly enhanced THz shielding efficiencies for 2D titanium carbide (Ti3C2 MXene) thin films with nanoscale THz metamaterials are presented. Nanoscale slot antenna arrays with strong resonances at certain frequencies enhance THz electromagnetic waves up to three orders of magnitude in transmission, which in turn enormously increases the shielding performance in combination with MXene films. Drop-casting of a colloidal solution of MXene (a few micrograms of dry material) can produce an ultrathin film (several tens of nanometers in thickness) on a slot antenna array. Consequently, THz waves strongly localized in the near-field regime by the slot antenna undergo enhanced absorption through the film with a magnified effective refractive index. Finally, the combination of an ultrathin MXene film and a nano-metamaterial shows excellent shielding performance in the THz range.

Abstract-Highly-sensitive plasmonic nano-ring transistor for monolithic terahertz active antenna

 Min Woo Ryu,  Ramesh Patel,  Esan Jang, Sang Hyo Ahn, Hyeong Ju Jeon, Mun Seok Choe, Eunmi Choi,  Ki Jin Han,  Kyung Rok Kim

We report a highly-sensitive plasmonic nano-ring transistor for monolithic terahertz (THz) active antenna. By designing an ultimate asymmetric transistor on a metal-gate structure, more enhanced (180 times) channel charge asymmetry has been obtained in comparison with a bar-type asymmetric transistor of our previous work. In addition, by exploiting ring-type transistor itself as a monolithic circular active antenna, which is designed for a 0.12-THz resonance frequency, we experimentally demonstrated the highly-enhanced responsivity (RV) > 1 kV/W (× 5) and reduced noise-equivalent power (NEP) <; 10 pW/Hz0.5 (× 1/10).

Abstract-Broadband gate-tunable terahertz plasmons in graphene heterostructures

Baicheng Yao, Yuan Liu, Shu-Wei Huang, Chanyeol Choi, Zhenda Xie, Jaime Flor Flores, Yu Wu, Mingbin Yu, Dim-Lee Kwong, Yu Huang, Yunjiang Rao, Xiangfeng Duan,  Chee Wei Wong,

Graphene, a unique two-dimensional material comprising carbon in a honeycomb lattice1, has brought breakthroughs across electronics, mechanics and thermal transport, driven by the quasiparticle Dirac fermions obeying a linear dispersion2,3. Here, we demonstrate a counter-pumped all-optical difference frequency process to coherently generate and control terahertz plasmons in atomic-layer graphene with octave-level tunability and high efficiency. We leverage the inherent surface asymmetry of graphene for strong second-order nonlinear polarizability4,5, which, together with tight plasmon field confinement, enables a robust difference frequency signal at terahertz frequencies. The counter-pumped resonant process on graphene uniquely achieves both energy and momentum conservation. Consequently, we demonstrate a dual-layer graphene heterostructure with terahertz charge- and gate-tunability over an octave, from 4.7 THz to 9.4 THz, bounded only by the pump amplifier optical bandwidth. Theoretical modelling supports our single-volt-level gate tuning and optical-bandwidth-bounded 4.7 THz phase-matching measurements through the random phase approximation, with phonon coupling, saturable absorption and below the Landau damping, to predict and understand graphene plasmon physics.

Abstract-A 177–205 GHz 249 mW CMOS-Based Integer-N Frequency Synthesizer Module for Planetary Exploration

Adrian Tang, Yanghyo Kim,   Theodore Reck, Yiwu Tang,  Yinuo Xu, Goutam Chattopadhyay,   Brian Drouin,  Imran Mehdi,

This letter discusses the development of a 177–205 GHz CMOS synthesizer module to support planetary science THz instrumentation. The developed synthesizer chip employs a CMOS system-on-chip device containing a 50 GHz phase-locked loop with programmable divider and both 100 and 200 GHz frequency doublers to provide the output carrier. The chip also contains a power sensor for calibration of output power and a dosimeter and thermometer for environmental monitoring of radiation and temperature. The chip is integrated into a board with a microcontroller and USB interface for providing frequency commands and sensor readback. The module is shown to deliver at least 10 μW across the 177–205 GHz lock range while consuming 249 mW of dc power.

Sunday, January 21, 2018

Abstract-Tunable multiband directional electromagnetic scattering from spoof Mie resonant structure

We demonstrate that directional electromagnetic scattering can be realized from a artificial Mie resonant structure which supports electric and magnetic dipole modes simultaneously. The directivity of the far-field radiation pattern can be switched by changing the incident light wavelength as well as tailoring the geometric parameters of the structure. Particularly, the electric quadrupole at higher frequency contribute significantly to the scattered fields, leading to enhancement of the directionality. In addition, we further design a quasiperiodic spoof Mie resonant structure by alternately inserting two materials into the slits. The results show that multi-band directional light scattering are realized by exciting multiple electric and magnetic dipole modes with different frequencies in the quasiperiodic structure. The presented design concept is general from microwave to terahertz region and can be applied for various advanced optical devices, such as antenna, metamaterial and metsurface.