Ferromagnetism in Zn1−xCrxTe (x = 0.050.15) films grown on GaAs(1 0 0) substrate

Devaraj Soundararajan,고장면,Devanesan Mangalaraj,Devaraj Nataraj,Lev Dorosinskii,Jaime Santoyo-Salazar 한국물리학회 2010 Current Applied Physics Vol.10 No.3

Zn1-xCrxTe (x = 0.05, 0.15) films were grown on GaAs(1 0 0) substrate by thermal evaporation method. X-ray diffraction analysis showed the presence of ZnCrTe phase without any secondary phase. The surface was analyzed by high resolution magnetic force microscope and profile measurements showed orientation of magnetic domains in the range of 0.5–2 nm with increase of Cr content. Magnetic moment–magnetic field measurements showed a characteristic hysteresis loop even at room temperature. The Curie temperature was estimated to be greater than 300 K. From the electron spin resonance spectra, the valence state of Cr in ZnTe was found to be +2 with d2 electronic configuration. Hall effect study was done at room temperature and the result showed the presence of p-type charge carriers and hole concentration was found to increase from 5.95 × 1012 to 6.7 × 1012 m-3 when Cr content increases. We deduce the origin of ferromagnetic behavior based on the observed experimental results.

Ferromagnetic Domain Behaviors in Mn doped ZnO Film

Devaraj Soundararajan,Jaime Santoyo-Salazar,Jang-Myoun Ko,Ki Hyeon Kim 한국자기학회 2011 Journal of Magnetics Vol.16 No.3

Mn doped ZnO films were prepared on Si (100) substrates using sol-gel method. The prepared films were annealed at 550℃ for decomposition and oxidation of the precursors. XRD analysis revealed the presence of ZnMnO hexagonal wurtzite phase along with the presence of small quantity of ZnMn₂O₃ secondary phase and poor crystalline nature. The 2D, 3D views of magnetic domains and domain profiles were obtained using magnetic force microscopy at room temperature. Rectangular shaped domains with an average size of 4.16 ㎚ were observed. Magnetic moment measurement as a function of magnetic field was measured using superconducting quantum interference device (SQUID) magnetometry at room temperature. The result showed the ferromagnetic hysteresis loop with a curie temperature higher than 300 K.

Soybean Protein: A Natural Source for the Production of Green Silver Nanoparticles

Devaraj Sasikala,Kasivelu Govindaraju,Selvaraj Tamilselvan,Ganesan Singaravelu 한국생물공학회 2012 Biotechnology and Bioprocess Engineering Vol.17 No.6

The ethnopharmacological approach to the production of nanoparticles is directly related to the creation of an important symbiosis between nanoscience and medical science. Production of nanoparticles under ecofriendly conditions is of significance to address growing concerns on the overall toxicity of nanoparticles for medical and biotechnological applications. The present investigation demonstrates silver nanoparticles production capabilities of a miracle bean soybean Glycine max. We found that a single protein of soybean with a molecular weight of 51 kDa stabilizes the newly formed silver nanoparticles. The electroeluted protein has confirmed the bioreduction property of silver ions.

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.

Numerical Analysis of Nanogap Effects in Metallic Nano-disk and Nano-sphere Dimers: High Near-field Enhancement with Large Gap Sizes

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>

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.

In-situ growth of 3D Cu-MOF on 1D halloysite nanotubes/reduced graphene oxide nanocomposite for simultaneous sensing of dopamine and paracetamol

Devaraj Manoj,Saravanan Rajendran,Tuan K.A. Hoang,Sabah Ansar,주상우,Yasser Vasseghian,Matias Soto-Moscoso 한국공업화학회 2022 Journal of Industrial and Engineering Chemistry Vol.112 No.-

Three-dimensional (3D) metal–organic frameworks (MOFs) a class of porous materials with tunablestructure and surface functionality has arisen as electrode materials especially, for electrochemical sensingof analytes. However, MOFs possess intrinsic drawbacks such as poor conductivity with an agglomerationof particles, which restricted the electrochemical signal response in terms of sensitivity anddetection limits. In this regard, the present work aims to develop conducting Cu-MOF on HNTs, a goodsubstate for in-situ growth of MOF nanostructures due to the existence of abundant negatively chargedSi-OH that can help the growth of nanosized MOFs. The negatively charged siloxane (Si-O-Si) groupson the surface of HNTs can be attracted by positive charged Cu2+ ions present in the reaction mixturethrough strong electrostatic attraction. When subjected to hydrothermal treatment, the Cu2+ ions canform nano-sized Cu-MOF particles with assistance from 2-methylimidazole. Moreover, the presence ofgraphene oxide (GO) can improve the electrical conductivity, large surface area, and thus resulting inthe formation of conducting Cu-MOF/HNTs/rGO nanocomposite. Owing to the synergetic desirable propertiesof active metal sites and high porosity offered by Cu-MOF, the high conductivity of rGO, and thelarge surface area of HNTs, the resultant Cu-MOF/HNTs/rGO modified GC electrode demonstrates superiorelectrochemical signal response towards dopamine and paracetamol. Moreover, the developed sensorexhibits wide linear ranges of 0.1 lM–130 lM and 0.5–250 lM, with a low detection limit of 0.03 lMand 0.15 lM for dopamine and paracetamol, respectively.

Influence of cavity geometry towards plasmonic gap tolerance and respective near-field in nanoparticle-on-mirror

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.

Carbon‑based microelectrodes for environmental remediation: progress, challenges and opportunities

Devaraj Manoj,Rajendran Saravanan,Atchudan Raji,Arumugam Thangamani 한국탄소학회 2023 Carbon Letters Vol.33 No.6

The need for high-performance environmental remediation has increased due to the environment’s ongoing degradation in the form of significant growth in industrialization and urbanization. Therefore, the toxic heavy metals can easily enter into environmental as well as foods and thus the search of clean water for drinking, household and irrigation purposes is of crucial importance. To meet this challenge, microelectrodes are flexible, low-cost and easier for fabrication has become the strong role in the detection of heavy metals with high sensitivity towards higher adsorption of heavy metals from contaminated water. To improve the sensitivity of the microelectrodes, carbon-based microelectrodes decorated with nanomaterials have been explored for the detection of metal ions thereby their presence in trace levels can be estimated. The aim of the present review is to summarize the recent developments in carbon-based microelectrodes for the electrochemical determination of heavy metals. It is followed by the various nanomaterials decorated on the carbon microelectrodes for detection of heavy metals was systematically discussed. Finally, the application and the future perspectives in the development of smart electrochemical sensing is provided. This short review will provide the useful information for the recent development in microelectrodes and also guide the pathway for the detection of heavy metals.

Design for an efficient single photon source based on a single quantum dot embedded in a parabolic solid immersion lens

Devaraj, Vasanthan,Baek, Jongseo,Jang, Yudong,Jeong, Hyuk,Lee, Donghan The Optical Society 2016 Optics express Vol.24 No.8