Abstract-THz Biochemical Sensors: Terahertz Biochemical Molecule‐Specific Sensors

Minah Seo, Hyeong‐Ryeol Park,

https://onlinelibrary.wiley.com/doi/10.1002/adom.202070010

The highly sensitive and selective detection of ultrasmall quantities of bio‐chemical substances by using sensing chips, including metallic plasmonic structures and terahertz metamaterials, is conceptually shown. Such terahertz metamaterials have been designed to target the specific absorption peaks of the certain bio‐chemical samples, where molecular‐specific vibration modes exist, and increase the detection sensitivity.

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-Graphene-based crack lithography for high-throughput fabrication of terahertz metamaterials

Sejeong Won, Hyun-June Jung, Dasom Kim, Sang-Hun Lee, DoVan Lam, Hyeon-Don Kim, Kwang-Seop Kim, Seung-Mo Lee, Minah Seo, Dai-Sik Kim, Hak-Joo Lee, Jae-Hyun Kim,



https://www.sciencedirect.com/science/article/abs/pii/S000862231931142X

Terahertz (THz) nanoantennas have significant potential for versatile applications in THz spectroscopy because of their capability for strong electromagnetic field localization. Electron-beam lithography or focused ion beam machining is typically employed to fabricate nanoantenna structures. These nanolithography methods present limitations in the widespread utilization of THz nanoantennas because of their high cost and low productivity. In this work, we proposed graphene-based crack lithography as a high throughput fabrication method for nanoantenna structures. A double-layer graphene interface was introduced to enable independent control of the nanoantenna dimensions and provide graphene-based nanoantenna structures. We analyzed the underlying mechanism of graphene-based cracking and developed an analytical model governing the geometric parameters of the fabricated nanostructures. As a vital application of the fabricated nanoantenna structures, we demonstrated the highly sensitive detection of d-Glucose molecules. Graphene-based crack lithography can provide a cost-effective method for generating nanoantenna structures with the desired characteristics and can accelerate the development of practical applications of electromagnetic metamaterials.

Abstract-Characterization of Degradation in Organic Light Emitting Diodes by Terahertz Spectroscopy

Yeongkon Jeong, Soo Jong Park,  Sang-Hun Lee, Byeong-Kwon Ju,  Young Min Jhon, Minah Seo,

https://ieeexplore.ieee.org/document/8730086

We investigated degradation of organic light emitting diodes (OLED) by terahertz (THz) time-domain spectroscopy. Decreased reflectance at 0.84 THz was observed inferred from the electric degradation of OLED

Abstract-Terahertz optical characteristics of two types of metamaterials for molecule sensing

Yeeun Roh, Sang-Hun Lee, Boyoung Kang, Jeong Weon Wu, Byeong-Kwon Ju, and Minah Seo

Fig. 1 (a) Microscope picture of DSRR metamaterial. (b) THz transmittances of DSRR are shown for different polarization angles of incident THz field. Resonances are shown at 1.2THz for polarization angle 67.5° and 1.4THz for polarization angle 0°. (c) A schematic of THz transmission through DSRR covered with monosaccharide sample droplet.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-13-19042

We investigate spectral responses of two different terahertz (THz) metamaterials of double split ring resonator (DSRR) and the nano slot resonator (NSR) for molecule sensing in low concentration. Two different resonant frequencies of DSRR can be controlled by polarization angle of incident THz beam. For comparison of THz optical characteristics, two NSRs were made as showing the same resonant frequencies as DSRR’s multimode. The monosaccharide molecules of glucose and galactose were detected by these two types of metamaterials matching the resonant frequencies in various concentration. NSR shows higher sensitivity in very low concentration range rather than DSRR, although the behavior was easily saturated in terms of concentration. In contrast, DSRR can cover more broad concentration range with clear linearity especially under high quality factor mode in polarization of 67.5 degree due to the Fano resonance. THz field enhancement distributions were calculated to investigate sensing performance of both sensing chips in qualitative and quantitative manner.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Terahertz wave interaction with metallic nanostructures

Ji-Hun Kang, Dai-Sik Kim,  Minah Seo,

https://www.degruyter.com/downloadpdf/j/nanoph.2018.7.issue-5/nanoph-2017-0093/nanoph-2017-0093.pdf

Understanding light interaction with metallic structures provides opportunities of manipulation of light, and is at the core of various research areas including terahertz (THz) optics from which diverse applications are now emerging. For instance, THz waves take full advantage of the interaction to have strong field enhancement that compensates their relatively low photon energy. As the THz field enhancement have boosted THz nonlinear studies and relevant applications, further understanding of light interaction with metallic structures is essential for advanced manipulation of light that will bring about subsequent development of THz optics. In this review, we discuss THz wave interaction with deep sub-wavelength nano structures. With focusing on the THz field enhancement by nano structures, we review fundamentals of giant field enhancement that emerges from non-resonant and resonant interactions of THz waves with nano structures in both sub- and super- skin-depth thicknesses. From that, we introduce surprisingly simple description of the field enhancement valid over many orders of magnitudes of conductivity of metal as well as many orders of magnitudes of the metal thickness. We also discuss THz interaction with structures in angstrom scale, by reviewing plasmonic quantum effect and electron tunneling with consequent nonlinear behaviors. Finally, as applications of THz interaction with nano structures, we introduce new types of THz molecule sensors, exhibiting ultrasensitive and highly selective functionalities

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, Minah Seo,

http://onlinelibrary.wiley.com/doi/10.1002/adom.201701076/full

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-Ultrasensitive terahertz sensing of gold nanoparticles inside nano slot antennas

Yong-Sang Ryu, Dong-Kyu Lee, Ji-Hun Kang, Sang-Hun Lee, Eui-Sang Yu, and Minah Seo

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-24-30591

We introduce a robust control method of terahertz (THz) transmission by tuning filling factors of Au nanoparticles (AuNPs) inside nano slot antennas. AuNPs in sub-100 nm diameters were spread over the nano slot antennas, followed by sweeping them into the slots. AuNPs can be efficiently localized and inserted into nano slots where the THz fields are greatly enhanced, by a “squeegee” made of the polydimethylsiloxane (PDMS). The sweeping of the AuNPs results in further dramatic reduction of THz transmission by suppressing the fundamental resonance mode of the nano slot, as compared to a typical random dropping case. It definitely works for an accurate THz transmission control, as well as the removal of unwanted ions that occasionally confuse signal accuracy from the target signals. Our approach provides a complete reinterpretation of sample deposition for further steady demands in developing ultrasensitive terahertz (THz) molecule sensors.

© 2017 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Terahertz Nanoprobing of Semiconductor Surface Dynamics

Geunchang Choi, Young-Mi Bahk, Taehee Kang, Yoojin Lee, Byung Hee Son, Yeong Hwan Ahnn,  Minah Seo, Dai-Sik Kim,

http://pubs.acs.org/doi/10.1021/acs.nanolett.7b03289

Most semiconductors have surface dynamics radically different from its bulk counterpart due to surface defect, doping level, and symmetry breaking. Because of the technical challenge of direct observation of the surface carrier dynamics, however, experimental studies have been allowed in severely shrunk structures including nanowires, thin films, or quantum wells where the surface-to-volume ratio is very high. Here, we develop a new type of terahertz (THz) nanoprobing system to investigate the surface dynamics of bulk semiconductors, using metallic nanogap accompanying strong THz field confinement. We observed that carrier lifetimes of InP and GaAs dramatically decrease close to the limit of THz time resolution (∼1 ps) as the gap size decreases down to nanoscale and that they return to their original values once the nanogap patterns are removed. Our THz nanoprobing system will open up pathways toward direct and nondestructive measurements of surface dynamics of bulk semiconductors

Abstract-Terahertz nano probing of semiconductor surface dynamics

Geunchang Choi, Young-Mi Bahk, Taehee Kang, Yoojin Lee, Byung Hee Son, Yeong Hwan Ahn, Minah Seo, and Dai-Sik Kim

http://pubs.acs.org/doi/abs/10.1021/acs.nanolett.7b03289

Most semiconductors have surface dynamics radically different from its bulk counterpart due to surface defect, doping level, and symmetry breaking. Due to the technical challenge of direct observation of the surface carrier dynamics, however, experimental studies have been allowed in severely shrunk structures including nanowires, thin films, or quantum wells where the surface-to-volume ratio is very high. Here, we develop a new type of terahertz (THz) nano probing system to investigate the surface dynamics of bulk semiconductors, using metallic nano gap accompanying strong THz field confinement. We observed that carrier lifetimes of InP and GaAs dramatically decrease close to the limit of THz time resolution (~1 ps) as the gap size decreases down to nano scale, and that they return to their original values once the nano gap patterns are removed. Our THz nano probing system will open up pathways towards direct, and nondestructive measurements of surface dynamics of bulk semiconductors

Abstract-Terahertz transmission control using polarization-independent metamaterials

Sang-Hun Lee, Dong-Kyu Lee, Chulki Kim, Young Min Jhon, Joo-Hiuk Son, and Minah Seo

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-10-11436

We present terahertz (THz) transmission control by several uniquely designed patterns of nano-slot antenna array. Collinearly aligned slot antenna arrays have been usually applied to THz filters with frequency band tunability by their geometry. Normally the amplitude in transmission (reflection) in the collinear alignment case can be varied via rotating the azimuthal angle with a sinusoidal trend, which can limit their utilization and performance only at fixed angle between the alignment of the resonant antennas and incident beam polarization. To pursue a variety of metamaterial uses, here, we present polarization-independent THz filters using variously aligned antenna array (asterisk, chlorophyll, and honeycomb patterns) in such counter-intuitive aspects. Besides, unprecedented multi resonance behaviors were observed in chlorophyll and honeycomb patterns, which can be explained with interferences by adjacent structures. The measured spectra were analyzed by harmonic oscillator model with simplified coupling between slots and their adjacent.

© 2017 Optical Society of America

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