Direct Visualization of Plasmonic Hotspots of Silver Nanowire Dimers using SERS

박상민 서울대학교 대학원 2018 국내석사

Visualization of surface plasmon polaritons (SPP) is essential for characterization of plasmonic waveguides which are building blocks for photonic circuits with subwavelength scale. Currently, well-established techniques such as fluorescence- or tip-based microscopy usually improper for being applied to narrow-gap plasmonic structures. In this case, surface-enhanced Raman scattering (SERS) microscopy can be an alternative tool for visualizing highly localized electric field of gap plasmon waveguides. In this work, we report on SERS imaging of chemically synthesized silver nanowire (AgNW) dimers, which shows spatial modulation of intensity patterns along NW-axis. We interpret that such unusual SERS patterns arise from mode beating between two distinct SPP eigenmodes of NW-dimers, generating oscillating intensity distributions. Also, we discuss the validity of the concept that SERS intensity at far-field region directly represents the intensity of local electric field generated from plasmon excitation process, contrary to usual nanoparticle dimers cases.

저차원 물질-금속 나노 하이브리드 구조의 표면 플라즈몬 현상 연구

김민희 인천대학교 대학원 2015 국내석사

Squeezed mode conversion in hybrid surface plasmon polariton waveguide using spin-coated silver film

Ha Thi Vu Anh 성균관대학교 일반대학원 2012 국내석사

We designed, fabricated and characterized a hybrid surface plasmon polariton waveguide (SPP_wg) for mode conversion by using a spin-coating method of an aqueous silver ionic complex solution. The 20-nm-thick silver SPP_wg consists of a straight Insulator-Metal-Insulator waveguide (IMI_wg), a lateral tapered-Insulator-Metal-Insulator-Metal-Insulator (tapered_IMIMI_wg) and a straight IMIMI waveguide (IMIMI_wg). The hybrid SPP_wg for mode conversion is studied theoretically and experimentally at a wavelength of 1550 nm. By using a finite element method, the calculated input mode size at a 6-um-wide and 20-nm-thick IMI_wg and the output mode size at a 3-um-wide and 20-nm-thick IMIMI_wg with a 500-nm-thick central insulator are 8.2 um x 6.1 um and 6.7 um x 4.1 um, respectively. The experimentally measured size of the s0 mode is 12.90 um x 8.08 um at the 6-um-wide and 20-nm-thick IMI_wg. The s0 mode is converted into the Ss0 mode size of 8.08 um x 5.65 um at the 3-um-wide and 20-nm-thick IMIMI_wg with the 500-nm-thick central insulator via the 15-um-long tapered_IMIMI_wg. The coupling loss between this s0 mode and a fundamental mode in a single mode fiber is 1.56 dB/facet caused by a mode size mismatch. The mode size is squeezed by ~2/3 via the 15-um-long-lateral tapered_IMIMI_wg with the 500-nm-thick central insulator. The coupling loss for mode conversion between the straight IMI_wg and the straight IMIMI_wg is 5.49 dB. The hybrid SPP_wg for mode conversion offers an excellent potential in bridging from micron- to sub-micron- scale in nano plasmonic integrated circuits. In addition, the use of the spin-coating method is a very cost-effective solution because the films are formed at a low temperature in a short period of time without requiring a vacuum system.

Gap-plasmon based fluorescence correlation spectroscopy

이홍기 Graduate School, Yonsei University 2020 국내박사

고전 광학에서 입사광은 회절 한계에 의하여 감소될 수 있는 크기에 제한을 받는다. 아베(Abbe) 회절 한계에 따르면 입사광의 크기는 주로 입사광의 파장과 사용된 광학 시스템의 개구 수(numerical aperture, NA)에 의해 결정된다. 이 회절 한계를 극복하기 위해서 다른 방법론이 광학 시스템에 적용되어야 하며 나노 스케일에서의 광 제어를 이루기 위해서 많은 종류의 연구가 수행되어왔다. 본 논문은 플라스모닉스 기술이 회절 한계를 극복한 나노 스케일 영역에서 광신호를 국소화 및 조정하여 높은 신호 대 잡음비(signal-to-noise ratio, SNR) 및 정밀도로 생물학적 정보를 획득할 수 있음을 보였다. 본 논문은 먼저 제 2 장에서 나노 스케일 물질의 플라스몬 특성을 조사하기 위해 박막의 광열 반응을 고려한 반복 계산 방법을 사용하여 금속 나노 구조의 전기장 분포와 열팽창을 분석하였다. 다양한 입사 조건에서 플라스몬 금속 박막의 전기장 향상 및 에너지 흡수의 측정이 가능한 탐침 기반의 측정법을 제시하였다. 또한, 비대칭 다층 계에서의 파동 분산 관계에 의해 설명될 수 있는 금 박막의 누설 방사(leakage radiation, LR)를 조사하였다. LR은 금속 박막의 표면 플라스몬 폴라리톤(surface plasmon polariton, SPP)의 전파를 시각화하며 이를 통하여 금속 표면의 굴절률 분포를 확인할 수 있다. 본 논문은 누설 방사 현미경(leakage radiation microscopy, LRM) 및 표면 플라스몬 공명 현미경(surface plasmon resonance microscopy, SPRM) 기술의 성능을 하드웨어 및 소프트웨어적으로 개선시킬 수 있는 방법에 대하여 논의하였다. 제 3 장은 다양한 크기 및 주기를 가지는 원형, 마름모꼴, 삼각형 모양의 나노 구조에 초단파 펄스가 가해졌을 때 인가되는 국소화된 표면 플라스몬(localized surface plasmon, LSP)에 대하여 살펴본다. 더 나아가, 플라스몬 구조에 인가되는 입사광의 특성을 조정함으로써 회절 한계로 제한된 영역 내에서 근접장 분포의 공간 제어가 가능하며, 고해상도 형광 이미징에 적용이 가능함을 보여주었다. 제 4 장에서는 18 nm 갭을 갖는 플라스몬 나노 구조체 어레이가 형광 상관 분석법 (fluorescence correlation spectroscopy, FCS)의 성능을 개선할 수 있음을 입증하였다. FCS는 형광 신호의 자기 상관 함수로부터 분자의 확산 및 결합 상호 작용과 같은 특성을 조사하는데 용이한 기술로, 특히 세포 내 및 세포막 상의 생체 분자의 운동 특성을 조사하는데 적용된다. FCS는 일반적으로 회절 한계에 의해 제한된 관찰 부피를 사용하여 수행되어 왔다. 예를 들어, 공초점 현미경을 사용한 실험 조건 하에서 FCS는 횡축으로 약 200 nm 및 종축으로 600 nm으로 제한된 관찰 부피를 갖는다. 본 논문에서는, 플라스몬을 사용하여 개선된 형광 상관 분광법(plasmonic-enhanced fluorescence correlation spectroscopy, pFCS)이 생체 분자의 운동 특성 연구에 어떻게 기여할 수 있는지 탐구하였다. p-FCS는 입사광을 나노 갭에 국소화시켜 회절 한계보다 작은 영역에서 생체분자를 관찰할 수 있도록 하였다. 나노 갭 내에 국소화된 전자기장은 근접장 주사 광학 현미경(near-field scanning optical microscopy, NSOM)을 사용하여 실험적으로 확인되었다. 이러한 나노 스케일 영역에서의 전자기장 국소화는 회절한계보다 작은 산란 단면을 가지며 LR의 세기를 증대한다. 본 논문에서는 소실파 내에서 동시에 표면 플라스몬 공명(surface plasmon resonance, SPR) 이미징을 수행할 수 있는 영상장치를 구축하여, 나노 입자를 높은 정밀도로 추적할 수 있게 하였다. 제 2 장과 3 장에서 논의한 바와 같이, 플라스몬 나노 구조체의 근접장 증폭은 형광 여기와 LR 강도 모두를 향상시킬 수 있음을 입증하였다. In classical optics, there is a theoretical limitation of the size to which a focused incident beam can be reduced. The size is mainly governed by the incident wavelength and a numerical aperture of an optical system. To break this diffraction limit, other methodologies should be employed to the optical system and many kinds of research have been performed to achieve a nanoscale light confinement. In this sense, plasmonics can be substantial to manipulate the optical signal within the nanoscale area and collect biological information from the sample with a high signal-to-noise ratio (SNR) and precision. To investigate the plasmonic properties of nanoscale materials, we first analyzed a field distribution and a thermal expansion of metallic nanostructures which were compared with an iterative calculation method considering the opto-thermal response of thin films in Chapter 2. The experimental results had a good agreement with calculation methods. The results have provided direct measurements of optical responses of plasmonic thin films by measuring field enhancements and absorption with various incident conditions. In addition, we have investigated the leakage radiation (LR) of gold thin films which can be explained by the dispersion relation in the asymmetric multi-layered system. We have discussed a good advantage of LR to visualize the surface plasmon polariton (SPP) propagation on gold thin films and how to improve the imaging performance. In Chapter 3, we have explored spatial field localization under ultrashort light pulses based on localized surface plasmon (LSP) by three-dimensional geometrical nanoapertures, which were circular, rhombic, and triangular with various combinations of size and period. Moreover, it was shown that plasmonic nanostructures enable spatial control of near-field distribution within the diffraction-limited area and also applicable to high-resolution fluorescence imaging. In Chapter 4, it was shown that the performance of fluorescence correlation spectroscopy (FCS) could be improved using plasmonic nanostructure arrays which have an 18-nm gap. FCS is a well-known technique that enables molecular detection to obtain biological information such as properties of diffusion and binding interaction by acquiring an autocorrelation of fluorescence fluctuation. FCS is typically conducted using a diffraction-limited volume in which target molecules diffuse. Under the typical experimental condition of confocal microscopy, diffraction-limited FCS has a volume of 200-nm lateral width and 600-nm axial length. We have explored how plasmon-enhanced FCS (p-FCS) was feasible and potential for biomolecular study using lysosomes in the human embryonic kidney (HEK) 293 cells. The p-FCS have provided arrays of sub-diffraction-limited light volume. The field localization within a nanodimer’s gap was confirmed experimentally using near-field scanning optical microscopy (NSOM). Those nanoscale localizations have much smaller scattering cross-section with higher SNR. We have established p-FCS imaging set-up which was able to perform surface plasmon resonance (SPR) imaging simultaneously in the evanescent field, allowing tracking nanoscale molecules with improved precision. As discussed in Chapters 2 and 3, it has been demonstrated that near-field amplification of plasmonic nanostructure had improved both fluorescence excitation and LR intensity. It should be emphasized that plasmonic nanostructures confining electromagnetic field into the nanoscale area have great potential in various biomedical engineering applications. In the dissertation, we have demonstrated near-field and far-field properties of plasmonic nanostructures and their applications for biological studies. The properties and performance of plasmonic nanostructures are expected to be investigated in more extensive areas of research as a critical component of nanotechnology and to find more applications for delivery of nanoscale biomolecular information.

Measurement of photoacoustic signals from nanostructures using a high-resolution photoacoustic microscope

이규승 Graduate School, Yonsei University 2013 국내박사

Light and sound are elementary wave phenomena in nature. They are often used as tools for measuring various properties of materials without any damages. However, light and sound are diminished and scattered as they go through the materials. As a result, the information delivered by the received light or sound is of a low quality and resolutions of the image aquired by those signals are poor. Under such circumstances, the photoacoustic technique provides a useful solution. It minimizes the loss of information and the poor image quality because it uses both light and sound.The photoacoustic technique was discovered by Bell, Tyndall and R?ntgen in the early 1880’s. Sound of any frequency is released from a material when the material absorbs chopped light at the same frequency. Basically, the illuminated material increases in temperature and heats the ambient air. When the light turns off, the material cools down and the temperature of the ambient air decreases. If this process occurs repeatedly, the temperature of the air near the material changes periodically, thus creating sound which is called photoacoustic effect. The photoacoustic effect can be utilized to get images. Photoacoustic imaging is attractive as a non-invasive method. However, in general, photoacoustic imaging system is bulky and expensive due to the equipment required to produce high resolution.In this thesis, a high-resolution photoacoustic microscope (HRPAM) is developed to measure surface plasmon polaritions from nano-metallic structures. For a higher spatial resolution, the HRPAM is built by using a near-field scanning optical microscope (NSOM). With the help of NSOM, light from the aperture with 100 nm in diameter can locally illuminate the sample. A microphone as a sound detector is attached onto the back side of the sample and forms a minimum-volume cell to obtain the sound signals. A continuous wave light from a diode laser works as a light source through an optical chopper with a frequency of several hundred hertz.Conventional AFM or SEM methods can measure the surface shape but cannot find buried materials under the surface. HRPAM can be utilized to find the structures under the surface as well as the surface profile. In particular, it is shown that HRPAM can detect structures under the photoresist materials and find a grating structure under a passivation layer.Surface plasmon polariton effect has also been investigated by utilizing the HRPAM. Due to the energy loss produced by the nano-metallic blocks, the HRPAM image is different from the general surface image. When the light from a NSOM probe tip illuminates the 50-nm thick gold nano-blocks, surface plasmon polaritons are created on the nano-mtallic block surface. Therefore, the greatly reduced peaks and relatively increased photoacoustic signal and phase are observed at the edge and in the middle of the nano-metallic blocks, respectively, due to the radiative process of surface plasmon polaritons. An extraction method to eliminate unwanted background photoacoustic signal and phase is also described.

Exciton Interconversion and transportation in transition metal dichalcogenide materials

Lee, Jubok Sungkyunkwan university 2021 국내박사

엑시톤은 쿨롱 상호작용에 의해 결합된 전자-홀 쌍이다. 이 준입자들은 반도체에서 빛을 방출하고 전자와 마찬가지로 정보 전달체로도 적용되기 때문에 광전자 소자의 기본 구성 요소이다. 단층 전이 금속 디칼코제나이드는 극한의 탄성 변형에 견딜 수 있기 때문에 국소 변형 변조를 통한 효율적인 엑시톤 퍼널효과를 달성하는 이상적인 플랫폼이다. 그러나 지금까지 수행된 연구는 고정 변형 프로필이 있는 기판의 사용에 초점을 맞췄다. 이 연구에서는 주름 형성이 켜지거나 꺼질 수 있도록 유연한 기판에 단층 이황화 텅스텐을 전사하였으며, 외부 변형에 의해 주름의 깊이나 방향이 조절되어 0-57 meV 범위에서 단층 이황화 텅스텐의 띠 간격 모양의 주기적 변조를 완전히 제어할 수 있었다. 나노의 광발광 측정은 단층 이황화 텅스텐의 광여기 엑시톤이 골부위보다 띠 간격이 적은 주름의 상단부위에 축적되었음을 뚜렷하게 입증했다. 2 차원 엑시톤 퍼넬효과의 광범위한 조절결과는 향상된 광전자 성능과 미래의 2 차원 엑시톤 장치에 대한 엑시톤 표류를 제어할 유망한 경로를 시사하였다. 단층 전이 금속 디칼코제나이드는 양자구속효과에 의한 강한 광물질 상호작용으로 인해 2 차원 엑시톤과 플라스몬 사이의 강력한 결합을 보여주기 때문에 플라즈모닉 하이브리드에도 이상적인 플랫폼이다. 엑시톤과 플라스몬 사이의 재구성 가능한 상호 변환은 엑시톤 트랜지스터, 멀티플렉서 및 엑시톤 증폭기와 같은 응용을 가능하게 한다. 이 연구에서는 단층 전이 금속 다이칼코제나이드 위에 중첩된 은 나노선에서 엑시톤-플라스몬 상호 변환에 의해 구현된 광학 논리 원리를 제안한다. 전이 금속 다이칼코제나이드에서 은 나노선의 플라스몬으로 생성된 엑시톤은 최종적으로 은 나노선의 끝에서 출력 신호로 수집된다. 이러한 원리를 이용하여 두 개의 레이저를 사용하여 다양한 논리 소자를 시연하였다. 이러한 결과를 통해 광전자 소자 및 엑시톤 회로에 대한 방법론과 이해를 제시하였다. 국소 변형을 사용하여 엑시톤을 조절 가능한 방식으로 조작할 수 있는 능력은 양자 효율성과 적응성이 강화된 광전자 장치에 적용할 수 있으며, 엑시톤 운송 및 광학 신호 처리결과는 광대역의 파장범위에서 광학적 신호처리의 방법과 광전자 장치에서의 상호 연결의 기초를 보여주었다. An exciton is electron-hole pairs that bounded by the Coulomb interaction. These quasiparticles are fundamental building block of optoelectronic devices because it emits light in semiconductors and also applicable as information carriers just as electrons. Monolayer transition metal dichalcogenides (TMDs) are ideal platform to achieve efficient exciton funneling via local strain modulation because it can withstand extreme elastic strain provides. However, studies conducted thus far have focused on the use of substrates with fixed strain profiles. We prepared 1L-WS2 on a flexible substrate such that the formation of topographic wrinkles could be switched on or off, and the depth or the direction of the wrinkle could be modified by external strain, thereby providing full control of the periodic undulation of the bandgap profile of 1LWS2 in the range of 0–57 meV. Our results of broad tunability of the twodimensional (2D) exciton funneling suggest a promising route to control exciton drift for enhanced optoelectronic performances and future 2D exciton devices. Monolayer transition metal dichalcogenides are also ideal platform for plasmonic hybridization because it shows strong coupling between 2D excitons and plasmons due to strong light-matter interaction by quantum confinement effect. Here, we propose optical logic principles realized by exciton-plasmon interconversion in Ag nanowire (AgNW) overlapped on monolayer TMDs. Excitons generated from TMDs couple to the AgNW plasmons, eventually collected as output signals at the AgNW end. Using two lasers, we demonstrate various kinds of logic devices by modulating excitons. These results are suggesting methodology and understanding for advanced optoelectronic devices and exciton circuit. Ability to manipulate exciton in tunable and switchable manner with local strain engineering is applicable in optoelectronic devices with enhanced quantum efficiency and adaptability. An exciton transportation and optical signal processing capabilities showed clever way of optical operation in subwavelength scale and organized basis of interconnecting in optoelectronic devices.

Infrared nanoscopy study of stacking specific surface plasmon polaritons on few layer graphene

최부건 서울대학교 대학원 2024 국내박사

그래핀은 그 뛰어난 물성으로 차세대 산업을 일굴 신소재로 널리 각광받고 있다. 특히 적외선의 광학적 영역에서 그래핀은 표면에 표면 플라스몬 폴라리톤이라는 빛을 만들어 낼 수 있는데, 이 빛은 뛰어난 전하수송능력, 간단한 실시간 조정 가능성 및 강한 공간적 압축성으로 인해 광전소자 및 광소자로의 이용 가능성에 막대한 주목을 받고 있다. 이러한 그래핀에서의 표면 플라스몬 폴라리톤 특성을 연구하기 위해서는 나노 수준의 공간분해능을 가지는 광학적 관찰 기술이 필히 요구된다. 그러나 일반적으로 광학적 관찰 기술의 공간분해능은 관찰에 사용되는 빛의 파장에 의해 한계가 지어진다. 그래핀에서 표면 플라스몬 폴라리톤의 발생은 수 마이크로미터 이상의 긴 파장을 가지는 중적외선 및 테라헤르츠 파의 영역에서 일어난다. 따라서 표면 플라스몬 폴라리톤의 특성에 의해 표면에서 나노미터 수준으로의 강한 파장 응축이 일어나게 되면, 보통의 광학적 방법으로는 연구가 불가능해지는 것이다. 최근 광학적 관측 한계를 극복하고 나노미터 수준의 공간분해능을 제공하는 현미경들이 개발되면서, 이러한 표면 플라스몬 폴라리톤 특성 연구에 새로운 돌파구가 되어 전세계에서 관련 연구가 활발히 일어나고 있다. 여기 사용되는 대부분의 최신 나노 광학현미경은 근접장이라고 하는 빛에 기반하여 작동한다. 근접장은 광원이 되는 산란체에서 아주 가까운 표면에서만 관측되는 빛으로 나노 수준의 산란체가 존재한다면, 근접장의 크기 또한 나노미터 수준에서 크게 달라지지 않는 특징이 있다. 본 학위 연구 논문에서는 먼저 이와 같은 나노 광학현미경들을 소개한다. 탐침–증강 라만 산란법, 광열–적외선 현미경, 광 유도 힘 현미경, 및 산란형 주사 근접장 광학현미경으로 대표되는 나노 광학현미경 각각의 작동 원리를 밝히고, 이를 통해 이루어져온 지난 연구들에 대해 고찰한다. 또한 각각의 광학 현미경이 현 단계에서 나타내는 한계성에 대해서도 제시한다. 그 후 실제 다층 그래핀의 적층 구조에 따른 특유성을 적외선 산란형 주사 근접장 광학현미경을 이용하여 연구한 내용을 소개한다. 꼬인 2층 그래핀은 첫번째 그래핀 층과 두번째 그래핀 층 사이에 적층 각도에 따라 결정구조 및 띠 구조가 달라진다. 본 논문에서는 임의의 각도로 꼬인 2층 그래핀에 대한 적외선 산란형 주사 근접장 광학현미경 연구를 통해 띠간 전이와 띠내 전이를 빛의 세기와 위상으로 분리하여 시각화하였다. 이 때 각도가 다른 꼬인 2층 그래핀들은 상대적인 전이의 세기 및 위상이 달라 적층 특이성이 나타났으며, 이를 통하여 적외선 나노 영상화를 이용한 적층 구조 구분법의 시초를 마련하였다. 다음으로는 자연적으로 형성된 3층 그래핀의 적층 특이적 표면 플라스몬 폴라리톤의 전파 및 반사에 대해 연구하였다. 표면 플라스몬 폴라리톤의 전파와 반사의 조절은 2차원 광전소자로의 응용에 있어서 매우 중요하다. 그러나 그래핀 위에서의 이들 표면 플라스몬 폴라리톤의 전파는 많은 연구가 이루어져있으나, 반사는 상대적으로 연구가 덜 이루어져왔다. 이 때 표면 플라스몬 폴라리톤은 2가지 서로 다른 경계에서 반사가 일어날 수 있는데, 하나는 그래핀이 끝나 기판과 만나는 경계이고 다른 하나는 서로 다른 광전도도를 가지는 도메인 사이에서 생기는 경계이다. 3층 그래핀은 안정한 2가지의 버널 구조와 삼방정계 구조의 서로 다른 적층 구조를 가지는 가장 간단한 형태의 그래핀이다. 따라서 3층 그래핀의 경우, 두 서로 다른 적층 구조 사이에서의 경계와 삼층 그래핀 자체가 끝나는 경계 2가지 경우에서 표면 플라스몬 폴라리톤의 반사를 연구하고 활용할 수 있는 가장 좋은 물질이다. 본 학위 연구에서는 적외선 나노 영상법을 통하여 띠간 전이 영역에서 3층 그래핀의 적층 구조를 구별하고 띠내 전이 영역에서 적층 특이적 표면 플라스몬 폴라리톤을 직접적으로 시각화하였다. 이 과정에서 그래핀의 광학전도도를 밀접결합근사법을 이용하여 계산하고 실제 3층 그래핀의 광스펙트럼을 계산된 광학전도도를 이용한 점-쌍극자 모델을 통해 이론적으로 재현하는데 성공하였다. 또한 표면 플라스몬 폴라리톤의 전파 파장 또한 적층 특이적 띠내 전이 광학전도도를 통해 완전히 설명되는 것을 보였다. 표면 플라스몬 폴라리톤의 반사에 대해서는 그래핀과 기판 사이의 경계에서 기존에 예상되던 바와는 다르게 적층 구조에 따른 특이성이 나타났으며 또한 같은 적층 구조 내에서도 서로 다른 반사가 일어나고 있음을 확인하였다. 이를 설명하기 위해 그래핀의 광전도도를 이용하여 수치 시뮬레이션을 진행하였다. 그 결과 그래핀과 기판 사이의 경계에서는 매우 국소적인 광전도도의 변화가 존재하고 이 차이로 인하여 반사가 다르게 나타나는 것을 밝혀내었다. 한편 서로 다른 두 적층 구조 사이에서의 표면 플라스몬 반사는 이러한 국소 광전도도의 변화 없이 불연속적인 광전도도의 격차에 의해서 반사가 일어났으며, 이는 기존의 예상과 다르지 않았음을 확인하였다. 위 결과는 서로 다른 적층 구조의 경계적 특성을 이용한 표면 플라스몬 폴라리톤의 반사 세기 및 위상을 조절할 가능성을 시사할 뿐만 아니라 그래핀과 기판 사이의 경계에서도 반사적 특성을 조절할 수 있는 새로운 방법론을 제시한다. Graphene comes into the lime light as a new material opening next generation industries. Especially in infrared optical region, surface plasmon polaritons (SPPs) arise on the surface of graphene. The SPPs on graphene shows high carrier mobility, real time tunability with simple gating or doping, and strong light confinement which make graphene an outstanding candidate of base material for optoelectronic applications. Studies of SPPs on graphene require a tool to measure nanometer scale. However, general optics do not offer the spatial resolution of few nanometers. The limitation is determined by the wavelength of light used to observe the system. As SPPs arise from mid-infrared to terahertz optical region, confined light into nanoscale is impossible to detect. Recently, these so-called diffraction limits are overcome by several microscopies offering below ~10 nm spatial resolution. These accelerate studies considering SPPs on graphene. Near-field light is the key concept of some techniques offering spatial resolution below diffraction limits. The near-field light exists right around small scatterers which act as nano-sized light sources. Therefore, one can generate a point-like light probe by decreasing size of the scatterer. In this article, optical nanoscopy techniques are introduced first. The techniques contain tip-enhanced Raman scattering, photothermal-IR microscopy (also known as AFM-IR), photo-induced force microscopy, and scattering-type scanning near-field optical microscopy (sSNOM). Here, operating principles and recent studies are presented with current limitations. Next, using IR-sSNOM, stacking specificity of few layer graphene (FLG) is shown in the article. First, a twisted bilayer graphene (tBLG) was studied. Twisted bilayer graphenes are known to change physical stackings and band structures by the twisted angle between lower sheet and upper layer. The article directly visualized intraband or interband transition of tBLGs into intensity and phase form of IR- sSNOM signal. The relative transition intensity and phase show stacking specificity. The results opened determination of stacking structures of tBLGs using IR nano-imaging. Also, stacking-specific SPPs propagations and reflections on naturally formed trilayer graphene (TLG) was studied. Controlling propagation and reflection of SPPs on graphene is essential for building ultimate flatland optoelectronic applications. Propagation of SPPs is widely studied recently. However, their reflection is relatively unknown. The reflection could occur at two different boundaries. One is the edge of graphene where graphene is topographically end meeting a substrate. The other is the domain boundary where two different domain of graphene possessing distinct optical conductivities. TLG is the thinnest graphene containing two stable structure: Bernal structure (ABA stacking) and rhombohedral structure (ABC stacking). Therefore, TLG is optimal materials to study two different kinds of reflections of SPPs on graphene. In the article, stacking-specific dielectric contrast of two different stacking structures are demonstrated using IR-sSNOM. Then, SPPs on TLGs are directly visualized at intraband transition region. Optical conductivities which determine optical properties of TLGs are calculated by tight binding approximation. And our point-dipole model successfully reproduced experimental nano-IR spectra of TLGs using the theoretical optical conductivities. SPP wavelengths for ABA-TLG and ABC-TLG are also fully explained by stacking- specific intraband optical conductivities. In case of the SPPs reflection, those from edges of TLG show stacking- and facet- specificities which is unexpected results from previous studies. Numerical electrodynamic studies using optical conductivities of TLGs show that these results might be originated from the existence of local optical conductivities at the edge of TLGs. However, the SPPs reflection at the heterojunction between two different stacking structures shows near ideal reflection and the role of local conductivities is barely observed. The findings suggest the existence of local conductivities at the edge of graphene affecting the reflections of SPPs while domain boundaries between two different stacking structures of TLG are ideal heterojunction with optical conductivity discontinuities. The results may suggest a direction controlling reflections intensity and phase of SPPs not only through manipulating stacking structures but also by using the edges of graphene.

Mixed States of Infrared Light and Matter: Electromagnetic Cavities, Metal Surfaces, and Molecular Vibrations

Erwin, Justin D The Ohio State University ProQuest Dissertations & 2021 해외박사(DDOD)

Fundamental properties of mixed states of light and matter were studied. Mixed states of surface plasmon polaritons (SPP) and the holes of mesh, treated as etalons, are called cavity mediated SPPs herein. This work presents the narrowest measured cavity mediated SPP to date which is accomplished by angle tuning square arrays of microholes in metal film, (3000 lines per inch mesh). The most important results of this work involve mixed states of etalon microcavities and condensed phase molecular vibrations, i.e. vibrational polaritons. Experiments have been conducted on materials in etalon cavities that measure mixed states and related energy splittings. These are first modeled using transfer matrix (TM) calculations that require an accurate complex and frequency dependent index of refraction. In favorable cases, they are further modeled with a cavity quantum electrodynamics (cQED) interaction Hamiltonian. The cQED method allows cavity-vibration coupling to be determined in many systems. However, this work shows the first example of changing the vibration-vibration coupling in a system, liquid acetonitrile, in which the vibrations were already Fermi coupled. Mixed states have also been studied in solvents of water, carbon tetrachloride, and benzene. There is also some preliminary work studying the decomposition reaction of hydrogen peroxide in water, as well as the molecules with CN stretches in liquids and solutions.

(A) study of near-field optical properties and babinet's principle in metallic nano blocks

정은희 Graduate School, Yonsei University 2014 국내박사

Over the past few decades, optics has begun to take over some of the duties of electronics. The primary issue of recent study in electronics has been focused on miniaturization; meanwhile, a similar trend has begun in optics research with the growth of the nano-optics field. One of the key issues in these fields is surface plasmon polaritons (SPPs), propagating light which is bound to the interface between a metal and a dielectric. Electromagnetic (EM) waves in the form of surface plasmons break some of the rules of classical optics such as Babinet’s principle.The purpose of this thesis is to study light propagation and the near-field light evolution analytically and numerically for sub-wavelength metallic nano structures, especially in the optical frequency. It is shown that radiated SPPs are the primary origin of breaking Babinet’s principle in the near-field. First of all, the most simple nano single-block and slit are used to find the condition producing strong SPPs on the metallic surface. In order to verify classical Babinet’s principle, the nano single-block and slit made of carbon black as absorber are investigated. Near-field EM amplitude and intensity are studied for gold nano single-block and slit. Finite difference time domain (FDTD) simulation is used to analyze these optical and electrical properties. As a result, it is found that the strongly excited SPPs radiate and are causative of the invalidity of Babinet’s principle in the near-field. In addition, beam focusing is studied for the case of double-block and slit, which consist of carbon black and gold. Radiated SPPs from each single-block and slit show extraordinarily enhanced transmission at beam focusing point. Using this nano metallic double-block, the boundary regions of three partitions is identified: reactive near-field, intermediated near-field, and far-field regions. These boundaries of the fields are theoretically studied by FDTD, and experimentally observed by near-field scanning optical microscope (NSOM). Although dividing the boundaries is well known in microwave frequency, it has not yet been observed in the visible frequency.Finally, it is found that the radiated SPPs critically affect near-field intensity distributions around metal structures. These techniques using nano metallic blocks are expected to be useful tool not only for analyzing the near-field but also for interpreting the physical behavior of nano-sized metallic structure at visible frequency.

Numerical study of surface plasmon polaritons scattering at a planar metal-dielectric interface by an embedded dielectric nanocube

이서준 서울대학교 대학원 2017 국내석사

Surface plasmon polaritons (SPPs) are localized electromagnetic waves propagating along a planar metal−dielectric interface. SPPs have drawn much attention in a variety of applications, such as light-emitting diodes, solar cells, Raman scattering, chemical or biological sensors, and integrated plasmonic circuits since they are localized electromagnetic waves on a metallic surface with higher local field density. As they have been applied in many applications, the in- and out-coupling of SPPs become important to efficiently excite SPP modes (in-coupling of SPPs), convert SPP modes into far-field radiating modes, electromagnetic waves propagating away from the metal surface to which SPPs are confined (out-coupling of SPPs), or manipulate SPPs (reflection or transmission). Particularly, efficient scattering of SPPs into the far-field radiating modes or reflected or transmitted SPPs is demanded in areas such as thin-film spectroscopy, integrated plasmonic devices, or organic light-emitting diodes (OLEDs). In this numerical study, it is investigated that how SPPs at a planar metal−dielectric interface are scattered by a dielectric nanocube embedded in the metal layer. The scattering properties of the embedded nanocube in terms of cross sections of scattering and absorption, scattering patterns, reflection, and transmission are numerically analyzed employing three-dimensional finite element method based simulations. It is confirmed that this embedded nanocube structural system is capable of wavelength-selective SPPs scattering dependent on the size of the nanocube due to the plasmonic resonant modes that are excited in the nanocube. Moreover, the correlation between the scattering properties of the embedded nanocube and the characteristics of the plasmonic resonant modes found in the embedded nanocube is discussed, showing that a specific plasmonic mode, which similarly appears in each of different-sized nanocubes, is responsible for strong scattering of SPPs. Along with the strong outcoupling of SPPs, the strong reflection also occurs when resonant modes of the embedded nanocube are excited, while the transmission decreases. In addition, the scattering patterns of the scattered waves out-coupled by the embedded nanocube are also discussed. With further development, this study would contribute to efficient scattering of SPPs at a planar interface, which can increase the performance of integrated plasmonic devices and, especially, the efficiency of OLEDs by outcoupling of SPPs into the far field radiating modes by collection of embedded dielectric nanocubes with an appropriately chosen size distribution.