이온성 유기결정 물질의 테라헤르츠파 발생 감소 원인에 대한 이론적 연구

김종택 ( Kim Jongtaek ) 공군사관학교 2019 空士論文集 Vol.70 No.-

테라헤르츠(terahertz, THz)파는 적외선보다 낮은 에너지를 가지므로 인체에 무해하며, 분자뿐만 아니라 분자들의 상호작용에 까지 관여하므로 의료/의약품/보안 등의 분야에서 검사 및 탐지에 X-ray를 대체하여 유용하게 사용될 수 있지만, 자연적으로는 거의 존재하지 않아 인공적 발생이 필요한 광원(light source)이다. 본 연구에서는 지금까지 개발된 유기결정 중 가장 큰 테라헤르츠파 발생효율을 타내내는 HMQ-TMS 물질의 부분적인 테라헤르츠파 발생효율 감소의 원인을 미시적분자 수준에서 화학시뮬레이션 방법을 통해 분석하였다. 단분자를 대상으로 한 시뮬레이션 결과는 실험 결과와는 다소 차이를 보였지만, 다음의 몇 가지 흥미로운 사실을 알 수 있었다. 낮은(2THz 이하) 에너지 영역에서의 테라헤르츠파 흡수는 기능기의 회전과 링 간 대단위 비틀림 또는 굽힘 진동과 관련이 있으며 음이온이 주된 역할을 하고, 중간 에너지 영역에서는 기능기의 회전 및 이와 연동된 링의 탈평면 나비 날개짓 진동이 관련이 있으며 양이온과 음이온이 관여되어 있고, 높은(7THz 이상) 에너지 영역에서는 기능기의 회전과 연동된 링의 탈평면 소단위 분절적 진동이 관련되어 있으며 주로 음이온이 관여된 것으로 확인되었다. 이러한 연구결과는 연구자들이 해당 진동을 억제하는 방향으로 분자를 다자인하여 보다 높은 효율을 갖는 테라헤르츠파 발생물질을 개발하는데 유용한 정보를 제공할 것으로 기대된다. 아울러, 향후에는 분자 간 상호작용이 고려된 고체진동 시뮬레이션 연구를 위해 물리, 화학, 수학, 전산 분야의 학제 간 연구가 추가적으로 이루어질 필요가 있다. Terahertz-wave with energy lower than infra-red is harmless to human body and involved to interaction between molecular vibrations as well as each vibration, so that it has a potential use for inspection or detection concerning medicine, drug, security, etc. In nature, however, terahertz-wave is not found with enough energy for its use. It must be artificially generated. This study has examined through chemical simulation at the microscopic molecular level the cause of partial decrease of terahertz-wave generation efficiency for HMQ-TMS which shows the highest efficiency among organic crystals developed until now. Although the results of molecular simulation exhibit a little difference from those of experiment, they still provide some interesting findings. Terahertz-wave absorption of HMQ-TMS is commonly involved in the rotation of functional groups over all energy regions. In addition, the torsion or bending motion between large ring units is involved in low energy absorption below 2THz, the out-of-plane butterfly motion of ring units in medium energy absorption, and the out-of-plane segmental motion within ring units in relatively high energy absorption above 7THz. It is expected that the results of this study help the researchers to develop a new highly-efficient terahertz-wave generation materials through molecular design suppressing the vibrations concerned with the decrease of terahertz-wave generation. In the future, the interdisciplinary research between chemistry, physics, mathematics, and computer science is needed for the solid-state simulation research incorporating interaction between the target molecule and neighboring molecules

이온성 유기결정(HMB-TMS)의 테라헤르츠파 흡수 특성에 대한 분자클러스터 이론적 연구

김종택 ( Kim Jongtaek ) 공군사관학교 2020 空士論文集 Vol.71 No.1

테라헤르츠(terahertz, THz)파는 전자기 스펙트럼에서 광파의 하단인 적외선과 전자파의 상단인 마이크로파 사이에 위치하여 두 가지 특성을 모두 가지며 에너지가 낮아 인체에 무해한 광원이다. 이러한 이유로 테라헤르츠파는 반도체 비파괴 검사, 공항 검색대 위험물/폭발물 탐지, 제약/의료분야 약물 검사 및 암진단 등에 광범위하게 활용될 수 있다. 하지만, 자연적으로 존재하지 않기 때문에 인위적 발생이 필요하다. 최근 고효율 테라헤르츠파를 발생시키기 위한 노력들이 이어지고 있으며 유기물질이 무기물질에 비해 우수한 성능을 보이고 있다. 본 연구에서는 유기물질 중에 이전에 개발된 이온성 유기결정의 테라헤르츠파 발생 성능을 향상시키기 위해 양이온의 구조를 일부 변형하여 새로이 개발된 HMB-TMS[(2-(4-hydroxy-3-methoxystyryl)-3-methylbenzothiazol-3-ium)-(2,4,6-trimethylbenzenesulfonate)] 유기결정이 예상과는 다르게 자체 흡수에 의해 테라헤르츠파 발생이 감소하는 현상을 화학시뮬레이션으로 분석하였다. 그 결과, 테라헤르츠파 흡수에 양이온이 주로 관여하고 음이온은 크게 영향을 미치지 않는 것으로 나타났으며 HMB 양이온의 전자 받게 부위 질소 양이온에 붙어 있는 메틸(-N+-CH3)의 회전진동과 탈평면 굽힘진동에 의해 유발되는 양이온의 파이 공액결합(π-conjugation) 붕괴가 주된 원인으로 작용함을 알 수 있었다. 이러한 결과는 실험분야 연구자들이 고효율 테라헤르츠파 발생 물질을 개발하는데 유용한 정보를 제공할 것으로 기대된다. The terahertz(THz) wave is located in the electromagnetic spectrum between infrared and microwave, which has both characteristics. It is a light source that is very low in energy and harmless to the human body. For these reasons, it can be widely used for semiconductor non-destructive testing, detection of hazardous/explosive materials at airport checkpoints, and pharmaceutical drug testing as well as medical cancer diagnosis. However, since it does not exist in the natural world, artificial generation is needed. Hence, many efforts have been made to generate high-efficiency terahertz waves. Among them, organic materials have shown better performance compared to inorganic materials. In this study, chemical simulation analyzes the reduction of terahertz wave generation in a newly developed HMB-TMS organic crystal by self-absorbing, which is contrary to our expectation. The results show that the main causes are the rotational vibration and the out-of-plane bending vibration of the methyl attached to the positive nitrogen(-N+-CH3) of the HMB cation which leads to the π-conjugation collapse of the cation. In addition, it was found through the simulation of cation-anion dimer vibrations that the terahertz-wave absorption is mainly concerned with the cation than the anion. These results are expected to provide chemists in the field of crystal engineering useful information to develop more efficient THz-wave generating materials.

Terahertz Quantum Plasmonics of Nanoslot Antennas in Nonlinear Regime

Kim, Joon-Yeon,Kang, Bong Joo,Park, Joohyun,Bahk, Young-Mi,Kim, Won Tae,Rhie, Jiyeah,Jeon, Hyeongtag,Rotermund, Fabian,Kim, Dai-Sik American Chemical Society 2015 NANO LETTERS Vol.15 No.10

<P>Quantum tunneling in plasmonic nanostructures has presented an interesting aspect of incorporating quantum mechanics into classical optics. However, the study has been limited to the subnanometer gap regime. Here, we newly extend quantum plasmonics to gap widths well over 1 nm by taking advantage of the low-frequency terahertz regime. Enhanced electric fields of up to 5 V/nm induce tunneling of electrons in different arrays of ring-shaped nanoslot antennas of gap widths from 1.5 to 10 nm, which lead to a significant nonlinear transmission decrease. These observations are consistent with theoretical calculations considering terahertz-funneling-induced electron tunneling across the gap.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2015/nalefd.2015.15.issue-10/acs.nanolett.5b02505/production/images/medium/nl-2015-02505j_0003.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl5b02505'>ACS Electronic Supporting Info</A></P>

테라 헤르츠 시스템 설계 방법에 대한 고찰

김병욱 영산대학교 2008 영산논총 Vol.18 No.-

A design methodology based on device models, compact models, and system models, is proposed for the terahertz systems. The problems arisen from the operation of terahertz frequencies in the system are seriously studied to treat the device models, and the importance of constructing compact modeling technologies is emphasized for reusing conventional electronics design automation technologies. The compact model carries physical parameters out of the device model, that involves both classical and quantum mechanical effects, to connect directly with the system model for the purpose of reusing EDA(electronics design automation) design flow and getting free system design methodologies from the influence of the problems arisen from the operation of terahertz frequencies in the system.

A terahertz performance of hybrid single walled CNT based amplifier with analytical approach

Kumar, Sandeep,Song, Hanjung Elsevier 2018 Solid-state electronics Vol.139 No.-

<P><B>Abstract</B></P> <P>This work is focuses on terahertz performance of hybrid single walled carbon nanotube (CNT) based amplifier and proposed for measurement of soil parameters application. The proposed circuit topology provides hybrid structure which achieves wide impedance bandwidth of 0.33 THz within range of 1.07-THz to 1.42-THz with fractional amount of 28%. The single walled RF CNT network executes proposed ambition and proves its ability to resonant at 1.25-THz with analytical approach. Moreover, a RF based microstrip transmission line radiator used as compensator in the circuit topology which achieves more than 30 dB of gain. A proper methodology is chosen for achieves stability at circuit level in order to obtain desired optimal conditions. The fundamental approach optimizes matched impedance condition at (50+j0) Ω and noise variation with impact of series resistances for the proposed hybrid circuit topology and demonstrates the accuracy of performance parameters at the circuit level. The chip fabrication of the proposed circuit by using RF based commercial CMOS process of 45 nm which reveals promising results with simulation one. Additionally, power measurement analysis achieves highest output power of 26 dBm with power added efficiency of 78%. The succeed minimum noise figure from 0.6 dB to 0.4 dB is outstanding achievement for circuit topology at terahertz range. The chip area of hybrid circuit is 0.65 mm<SUP>2</SUP> and power consumption of 9.6 mW.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Hybrid CNT based amplifier performance at terahertz. </LI> <LI> To achieved wide impedance bandwidth up to 0.33-THz. </LI> <LI> Proposed circuit occupies less chip area. </LI> <LI> Noise figure of 0.4 dB is outstanding achievements. </LI> <LI> Power Measurement reveals highest PAE of 78%. </LI> </UL> </P>

데이터 처리를 통한 테라헤르츠 (THz) 파의 2차원 이미지 개선

손채화,진윤식,전석기,김근주,정순신,정원용,Shon, Chae-Hwa,Jin, Yun-Sik,Jeon, Seuk-Gy,Kim, Keun-Ju,Jung, Sun-Shin,Yong, Chong-Won 한국광학회 2005 한국광학회지 Vol.16 No.6

테라헤르츠(terahertz: THz) 파를 이용한 2차원(2D) 투과 이미지의 개선 특성에 대해서 보고한다. THz 파 투과 신호의 진폭과 위상을 이용하여 다양한 시료에 대한 2차원 이미지를 얻었다. THz 파의 진폭과 위상 정보를 조합하는 새로운 방법을 제안하였고, 이 방법을 이용하여 피크 값의 크기 혹은 위상 중 어느 한가지만을 이용한 이미지보다 나은 이미지를 얻을 수 있었다. 또한 호모몰픽 필터링(homomorphic filtering) 디지틸 이미지 처리(digital image processing) 가 노이즈를 저감시키는데 효율적이고 나은 품질의 이미지도 얻을 수 있음을 보인다. 이 결과를 이용하여 향후 실시간 이미징에 응용 가능하다. Two-dimensional (2D) images that are produced by terahertz (THz) irradiation we presented. It is possible to obtain 2D image of various materials by observing the amplitude and the phase of the THz signals which go through them. Better images are produced by combining the amplitude and phase of the signal rather than using only one of these. Homomorphic filtering that is one elf the well-known technique of digital image signal processing is effective to reduce the noise signal and can provide better quality images. The results can be applied to real-time imaging afterwards.

테라헤르츠를 이용하여 글자를 읽어내기 위한 전처리 과정에 대한 연구

박인호,김성윤,김영섭,이용환 한국반도체디스플레이기술학회 2017 반도체디스플레이기술학회지 Vol.16 No.2

Recently, ancient documents are actively studied and discussed. However, ancient documents has a few problems on interpretation. The antique documents are too fragile to hand over. So, some studies have been carried out using terahertz to read ancient documents without damaging them. Three techniques are necessary to read letters using terahertz. First, PPEX algorithm, which distinguishes pages. Second, TGSI technique, which distinguishes text from paper on a page. Third, CCSC algorithm, which transforms signals to letters. In this paper, we will describe the preprocessing process to facilitate the recognition of letters before applying the post processing as we mentioned above. Histogram equalization, Histogram stretching and the Sobel filter were applied to the preprocessing

Terahertz-Wave Vibrometer Using a Phase-Noise-Compensated Self-Heterodyne System

Hajun Song,Jong-In Song IEEE 2016 IEEE photonics technology letters Vol.28 No.3

<P>A terahertz (THz) vibrometer based on a photomixing self-heterodyne system for measuring the vibration of an object behind an opaque barrier is reported. The proposed THz vibrometer employs a phase noise compensation technique to reduce the phase noise of the system and thereby improves the signal-to-noise ratio (SNR) of the system. In this letter, the performance of THz vibrometers with and without the phase noise compensation technique is compared. The proposed THz vibrometer employing a phase noise compensation technique shows an improved SNR and larger bandwidth compared with those of the conventional THz vibrometer using a Golay cell.</P>

Terahertz-Triggered Phase Transition and Hysteresis Narrowing in a Nanoantenna Patterned Vanadium Dioxide Film

Thompson, Zachary J.,Stickel, Andrew,Jeong, Young-Gyun,Han, Sanghoon,Son, Byung Hee,Paul, Michael J.,Lee, Byounghwak,Mousavian, Ali,Seo, Giwan,Kim, Hyun-Tak,Lee, Yun-Shik,Kim, Dai-Sik American Chemical Society 2015 NANO LETTERS Vol.15 No.9

<P>We demonstrate that high-field terahertz (THz) pulses trigger transient insulator-to-metal transition in a nanoantenna patterned vanadium dioxide thin film. THz transmission of vanadium dioxide instantaneously decreases in the presence of strong THz fields. The transient THz absorption indicates that strong THz fields induce electronic insulator-to-metal transition without causing a structural transformation. The transient phase transition is activated on the subcycle time scale during which the THz pulse drives the electron distribution of vanadium dioxide far from equilibrium and disturb the electron correlation. The strong THz fields lower the activation energy in the insulating phase. The THz-triggered insulator-to-metal transition gives rise to hysteresis loop narrowing, while lowering the transition temperature both for heating and cooling sequences. THz nanoantennas enhance the field-induced phase transition by intensifying the field strength and improve the detection sensitivity via antenna resonance. The experimental results demonstrate a potential that plasmonic nanostructures incorporating vanadium dioxide can be the basis for ultrafast, energy-efficient electronic and photonic devices.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2015/nalefd.2015.15.issue-9/acs.nanolett.5b01970/production/images/medium/nl-2015-01970q_0007.gif'></P>

In-situ thickness measurement of epoxy molding compound in semiconductor package products using a Terahertz-Time of Flight System

Park, Dong-Woon,Oh, Gyung-Hwan,Kim, Dug-Joong,Kim, Hak-Sung Elsevier 2019 NDT AND E INTERNATIONAL Vol.105 No.-

<P><B>Abstract</B></P> <P>Refractive index and thickness of an epoxy molding compound (EMC) were successfully measured without any advance knowledge of properties of material using the Terahertz-Time of Flight System (THz-TFS). The theoretical analysis for calculation of the refractive index and thickness of EMC was conducted considering two time-delay values of emission and detection mode (normal reflection mode and transmission mode). By combining two time-delay values from the normal reflection and transmission modes, the refractive index of EMC could be directly deduced without any parameter of the properties of specimen. The thickness of EMC mold could be simultaneously calculated by using only THz time-delay values. The thickness measurement results using THz-TFS were verified with the thickness measured through scanning electron microscopy (SEM).</P>