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Vasanthan Devaraj,정나나,이종민,황윤회,손종렬,오진우 한국물리학회 2019 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.75 No.4
Conventionally, in plasmonics, experimentally developed nanoparticle on a metallic mirror design is used to mimic the free space dimer metallic nanoparticles. Numerous theoretical simulations considering free space dimer were carried out and their plasmonic properties were applied to nanoparticle on a metallic mirror design. In this work, with the help of three-dimensional finite element method simulation we directly compared the free space dimer and nanoparticle on a metallic mirror designs and analyzed their plasmonic properties. Although there are similarities in their generalized near field enhancement properties, we observe significant differences as well. With the help of three-dimensional surface charge density mappings, we explain the origin of these differences, as cross-sectional amplitude of electric field profiles has limitation in understanding such complex plasmonic mode(s). We hope our study will be helpful in understanding the origin of complex plasmonic modes, and sub-wavelength optical properties for the development of the efficient light devices.
수치해석적으로 분석한 오각형 나노선과 원형 나노선을 사용한 나노갭 구조의 근거리장 특성
DEVARAJ VASANTHAN,이종민,김춘태,김원근,오진우 한국물리학회 2019 새물리 Vol.69 No.1
When a nanogap was formed by using a metal nanowire, the dependences of the electric field characteristics on the shape of the nanowire were calculated by using a 3-dimensional finite-difference time-domain method. The nanogaps formed by using pentagon-shaped nanowires had electric field enhancement characteristics similar to those of the nanogaps formed by using circular nanowires, but the stability of the resonance wavelength was superior. The excellent resonance wavelength stability means that the resonance wavelength does not vary greatly with the difference in the nanogap spacing. This method is advantageous for fabricating a device with stable resonance characteristic in-spite of geometrical errors and can be commercialized at low fabrication cost. Surface plasmon-mode information, which can be indirectly identified in the electric field's shape, is discussed to explain the cause of such stability. 금속 나노선으로 나노갭을 형성하였을 때 나노선의 형태에 따른 전기장 특성을 3차원 유한 차분 시간 영역 방법으로 계산하고 그 결과를 분석하였다. 오각형 나노선으로 형성한 나노갭의 경우 원형 나노선으로 형성한 나노갭에 비해 전기장 증강 특성은 유사하지만 공명 파장의 안정성은 더 우수한 특성을 보임을 발견하였다. 공명 파장 안정성이 우수하다는 것은 나노갭 간격 차이에 따라 공명 파장이 크게 변하지 않음을 말한다. 저비용 공정 방법으로 나노갭을 형성하면 수 nm 정도 분포가 항상 발생하지만 공명 파장 안정성이 우수하기 때문에 상용화 가능한 소자를 개발할 때 도움이 된다. 전기장 모양도에서 간접적으로 확인할 수 있는 표면 플라즈몬 모드 정보를 통해 이런 안정성이 나타나는 원인을 논의하였다.
Unveiling facet effects in metallic nanoparticles to design an efficient plasmonic nanostructure
Devaraj Vasanthan,Lee Il Hyun,Kim Minjun,Nguyen Thanh Mien,Son Jong Pil,Lee Jong-Min,Lee Donghan,Kim Kwang Ho,오진우 한국물리학회 2022 Current Applied Physics Vol.44 No.-
We investigated the role of nanoparticle surface morphology (facets) in estimating the plasmonic properties of nanoparticle-on-a-mirror design or NPOM in the presence of a thicker (20 nm) dielectric layer. Nanoparticle surface morphology differences ranging from smoother surface to multi-facets in the form of a sphere (NSOM), cube (NCOM), and singe bottom faceted sphere (SBF-NSOM) shapes have been employed. Three significant optical properties were observed. Better longer wavelength near-field and far-field resonance spectral positions from NCOM are achieved. Near-field enhancement extracted from SBF-NSOM outperformed NCOM by more than ~ two times. Plasmonic gap mode enhancement is absent for NSOM in the presence of a larger dielectric layer. The availability of plasmonic gap modes in NCOM and SBF-NSOM, even at a 20 nm thick dielectric layer, is highly beneficial for various plasmonic applications. These differences in optical properties are understood by the role of NP facets in influencing the plasmonic cavity region.
Devaraj, Vasanthan,Choi, Jongwan,Kim, Chang-Seok,Oh, Jin-Woo,Hwang, Yoon-Hwae 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.72 No.5
<P>Various gap sizes are investigated numerically to extract the local electric field enhancement from a gold sphere and disk dimer systems. Our simulations predict that a metallic disk dimer system(s) exhibit large local electric field enhancements at larger gap sizes (20 nm, 40 nm) as compared to that of sphere dimer designs (gap size = 8 nm, 14 nm). These gap size differences similar to 2.5 -3.3 times larger as compared to that of sphere dimer systems, facilitates the device fabrication. These numbers are obtained by the influence of uniform gap size distribution as a function of total volume '+/- Z direction'. Such geometry, by achieving good local electric field enhancement from larger gap size, will enhance the variety of potential applications in the field of plasmonics, sensors, single molecule detection, surface enhanced spectroscopy, and so on.</P>
Fabrication of Ultra-smooth 10 nm Silver Films without Wetting Layer
Vasanthan Devaraj,Jongmin Lee,Jongseo Baek,Donghan Lee 한국진공학회(ASCT) 2016 Applied Science and Convergence Technology Vol.25 No.2
Using conventional deposition techniques, we demonstrate a method to fabricate ultra-smooth 10 nm silver films without using a wetting layer or co-depositing another material. The argon working pressure plays a crucial role in achieving an excellent surface flatness for silver films deposited by DC magnetron sputtering on an InP substrate. The formation of ultra-smooth silver thin films is very sensitive to the argon pressure. At the optimum deposition condition, a uniform silver film with an rms surface roughness of 0.81 nm has been achieved.
Vasanthan Devaraj,장유동,이동한 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.68 No.8
Various geometries are investigated numerically to extract the maximum number of photons to the airside from a single quantum dot embedded in a metal/dielectric cladded GaAs cylindrical structure. At the optimum cylindrical diameter, we predict that 80% of the photons can be extracted to the air side with a photon collection efficiency of 39% (68%) for a numerical aperture of 0.5 (0.8). These numbers are obtained as the influences of the internal modes and the multimode contributions are minimized at and around the target wavelength. Such geometry, by achieving good photon extraction and collection, will enhance nonclassical light generation at near infrared wavelengths.
DEVARAJ VASANTHAN,이종민,오진우 한국물리학회 2020 Current Applied Physics Vol.20 No.12
In this work, we emphasize the importance of cavity geometry along with nanoparticle shape and plasmonic nanogap (based on a nanoparticle on a metallic film (NPOM) design) which plays significant role in understanding the complex plasmonic mode characteristics involving nanoparticle and gap mode resonances. The cross-section imprint of planar cavity on metallic film plays decisive role in near field enhancement properties at similar NP size and plasmonic nanogap conditions for spherical and cubical NPOM systems. By mimicking the NPOM structure to metal-insulator-metal design, we understand the resonant emission differences for the respective plasmonic modes. Influence of dominant and weaker gap mode resonances resulted in an interesting optical behavior (fluctuations in near field enhancement strength) in NP mode in case of cubical nanostructures. By such extensive investigation and interpretation of sub-wavelength complex plasmonic mode characteristics, various practical applications in plasmonics field can be accomplished.