Abstract-Graphene assisted terahertz metamaterials for sensitive bio-sensing

Hun Lee, Jong-Ho Choe, Chulki Kim,  Sukang Bae, Jin-Soo Kim, Q-Han Park, Minah Seo,



https://www.sciencedirect.com/science/article/pii/S092540052030188X

We report that single-stranded deoxyribonucleic acids (ssDNAs) at very low concentrations can be detected using graphene-combined nano-slot-based terahertz (THz) resonance. A combination of the resonant structure and tuned electro-optical properties of graphene can provide unprecedentedly sensitive biomolecule sensing even using very low energy THz photons, overcoming the huge scale difference of 10,000:1 between the wavelength and the size of the ssDNAs. Ultrahigh sensitivity is obtained by the significant increase in the absorption cross-section of the graphene sheet with the targeted biomolecules, induced by strong THz field enhancement at the resonance frequency inside the slots. Clearly distinguishable THz optical signals were observed between different species of ssDNAs even at the nano-mole level and analyzed quantitatively in terms of the electro-optical properties of the suspended graphene layer modified by the attached ssDNAs without any molecular-specific labeling for the THz regime. Quantitative analysis of ssDNA molecule adsorption was carried based on the change in conductivity using a theoretical THz transmission model.

Abstract-Giant phase retardation of terahertz waves by resonant hyperbolic metasurface

Seojoo Lee, WonTae Kim, Ji-Hun Kang, BongJoo Kang, Fabian Rotermund, Q-Han Park,

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10541/1054122/Giant-phase-retardation-of-terahertz-waves-by-resonant-hyperbolic-metasurface/10.1117/12.2288060.short?SSO=1

Due to the relatively weak birefringence of natural materials in terahertz regime, metasurfaces have been proposed for compact terahertz phase modulators since they show effectively strong birefringence only with ultrathin structures. However, previous designs of metasurface show limited phase modulation reaching only up to the quarter-wavelength phase, and there has been no single metasurface design that works for a terahertz half-waveplate. Here, we present a metasurface that modulates the phase variably up to 180 degrees. The phase modulation is achieved by a hyperbolic metasurface composed of periodically arrayed rectangular metal rings with different periods for horizontal and vertical axis. By controlling each period, we show that our hyperbolic metasurface can possess large positive and negative permittivity values for horizontal and vertical axis and the phase shift can reach up to the 180 degrees. To check the validity of our design, we fabricate reconfigurable metasurface films and demonstrate the phase modulation 90 to 180 degrees. All results show good agreement with numerical simulation results.

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Abstract-Highly sensitive and selective sugar detection by terahertz nano-antennas

• Dong-Kyu Lee
• , Ji-Hun Kang
• , Jun-Seok Lee
• , Hyo-Seok Kim
• , Chulki Kim
• , Jae Hun Kim
• , Taikjin Lee
• ,Joo-Hiuk Son
• , Q-Han Park
•  & Minah Seo

http://www.nature.com/articles/srep15459

Molecular recognition and discrimination of carbohydrates are important because carbohydrates perform essential roles in most living organisms for energy metabolism and cell-to-cell communication. Nevertheless, it is difficult to identify or distinguish various carbohydrate molecules owing to the lack of a significant distinction in the physical or chemical characteristics. Although there has been considerable effort to develop a sensing platform for individual carbohydrates selectively using chemical receptors or an ensemble array, their detection and discrimination limits have been as high in the millimolar concentration range. Here we show a highly sensitive and selective detection method for the discrimination of carbohydrate molecules using nano-slot-antenna array-based sensing chips which operate in the terahertz (THz) frequency range (0.5–2.5 THz). This THz metamaterial sensing tool recognizes various types of carbohydrate molecules over a wide range of molecular concentrations. Strongly localized and enhanced terahertz transmission by nano-antennas can effectively increase the molecular absorption cross sections, thereby enabling the detection of these molecules even at low concentrations. We verified the performance of nano-antenna sensing chip by both THz spectra and images of transmittance. Screening and identification of various carbohydrates can be applied to test even real market beverages with a high sensitivity and selectivity.

Abstract-Observation of terahertz-radiation-induced ionization in a single nano island

Minah Seo,

Ji-Hun Kang,

Hyo-Suk Kim,

Joon Hyong Cho,

Jaebin Choi,

Young Min Jhon,

Seok Lee,

Jae Hun Kim,

Taikjin Lee,

Q-Han Park

& Chulki Kim

http://www.nature.com/srep/2015/150522/srep10280/full/srep10280.html

Terahertz (THz) electromagnetic wave has been widely used as a spectroscopic probe to detect the collective vibrational mode in vast molecular systems and investigate dielectric properties of various materials. Recent technological advances in generating intense THz radiation and the emergence of THz plasmonics operating with nanoscale structures have opened up new pathways toward THz applications. Here, we present a new opportunity in engineering the state of matter at the atomic scale using THz wave and a metallic nanostructure. We show that a medium strength THz radiation of 22 kV/cm can induce ionization of ambient carbon atoms through interaction with a metallic nanostructure. The prepared structure, made of a nano slot antenna and a nano island located at the center, acts as a nanogap capacitor and enhances the local electric field by two orders of magnitudes thereby causing the ionization of ambient carbon atoms. Ionization and accumulation of carbon atoms are also observed through the change of the resonant condition of the nano slot antenna and the shift of the characteristic mode in the spectrum of the transmitted THz waves