Structural, Electrical and Optical Properties of a Li-doped ZnO Thin Film Fabricated on a Pt(111)/Ti/SiO2/Si(100) Substrate

라그하반,J. W. Kim,장기완,S. S. Kim 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.66 No.7

A Li-doped ZnO (Zn1−xLixO1−δ, x = 0.12) thin film was fabricated on a Pt(111)/Ti/SiO2/Si(100)substrate by using a chemical solution deposition method. The formation of a wurtzite hexagonalstructure was confirmed by an X-ray diffraction and a Raman spectroscopic analysis. Typicalhexagonal microcrystalline grains were observed from the surface morphological studies. Roomtemperatureferroelectricity with a remnant polarization (2Pr) of 0.05 μC/cm2 and a coercive field(2Ec) of 170 kV/cm at an applied electric field of 200 kV/cm was observed in the Li-doped ZnO thinfilm. The measured leakage current density for the thin film was 1.09 × 10−4 A/cm2 at an appliedelectric field of 100 kV/cm. A sharp near-band-edge emission was observed in the photoluminescencespectrum at a wavelength of 375 nm for the thin film.

Studies on the growth, structural, optical, thermal and electrical properties of nonlinear optical cadmium mercury thiocyanate glycol monomethyl ether single crystal

라그하반,A. Bhaskaran,R. Sankar,R. Jayavel 한국물리학회 2010 Current Applied Physics Vol.10 No.2

Single crystals of cadmium mercury thiocyanate glycol monomethyl ether (CMTG) were grown from a mixed solvent of glycol monomethyl ether (GME):water (1:1) by slow evaporation method. The crystal structure and morphology were confirmed by single crystal X-ray diffraction analysis. Presence of functional groups and the coordination of glycol monomethyl ether (GME) and thiocyanate (SCN-) in the CMTG compound were confirmed by FT-IR analysis. Optical transparency of the grown crystal was studied by UV–Vis spectroscopy. Thermal stability and decomposition process were studied by means of TGA and DTA analysis. Dielectric measurement on CMTG single crystal was carried out for various frequency and temperatures. The surface studies by scanning electron microscopy reveals the formation of layer growth pattern indicative of 2D nucleation mechanism. From the second harmonic output power measurement by Kurtz powder method, it is observed that CMTG is a potential material for nonlinear optical applications among the bimetallic thiocyanate adducts series.

Effects of Excessive Bi on the Structure and the Properties of Aurivillius Bi5.25La0.75Fe2Ti3O18 Thin Films

라그하반,김진원,Ji Ya CHOI,김상수,김종우 한국물리학회 2014 새물리 Vol.64 No.7

The effects of excessive Bi on the structural, electrical and multiferroic properties of the La-doped Bi6Fe2Ti3O18 (Bi5.25La0.75Fe2Ti3O18) thin films prepared on Pt(111)/Ti/SiO2/Si(100) substrates by using a chemical solution deposition method are reported. The structures of the thin films were studied by using X-ray diffraction, Raman scattering spectroscopy and scanning electron microscopy. From the experimental comparisons, a low electrical leakage current of 1.84 × 10−5 A/cm2 at 100 kV/cm and enhanced ferroelectric properties, such as a large remnant polarization (2Pr) of 10.5 μC/cm2 and a low coercive field (2Ec) of 400 kV/cm at 485 kV/cm, were observed for the 5% Biexcess La-doped Bi6Fe2Ti3O18 thin film. The formation of a stable bismuth layer-structured phase, a lower c-axis orientation, an optimum crystallinity and a dense microstructure with a smooth surface morphology correlate with the improved electrical and multiferroic properties of the 5% Bi-excessive Bi6Fe2Ti3O18 thin film.

Structural, Electrical and Multiferroic Properties of Nb-doped Bi7Fe3Ti3O21 Thin Films

라그하반,김진원,김상수 한국물리학회 2015 새물리 Vol.65 No.6

The effects of donor Nb5+-ion doping on the structural, electrical, and multiferroic properties of an Aurivillius Bi7Fe3Ti3O21 thin film were investigated. Incorporation of Nb5+-ions into the Ti4+-sites of the Bi7Fe3Ti3O21 thin film resulted in a substantial improvement of its electrical and multiferroic properties. From the study of the electrical properties, the Bi7Fe3Ti2.94Nb0.06O21+δ thin film exhibited a low leakage current density of 5.11×10−6 A/cm2 at 100 kV/cm, which was about one order of magnitude lower than that of the untreated Bi7Fe3Ti3O21 thin film. The ferroelectric P −E hysteresis loops of the Bi7Fe3Ti2.94Nb0.06O21+ thin film showed a large remnant polarization (2Pr) of 20.6 μC/cm2 at 630 kV/cm whereas the 2Pr value measured for the untreated Bi7Fe3Ti3O21 thin film was 3.5 μC/cm2 at 318 kV/cm. Furthermore, a well-saturated magnetic hysteresis loop with an enhanced magnetization was observed for the Bi7Fe3Ti2.94Nb0.06O21+δ thin film at room temperature.

Effects of Nd-doping on the Structural, Electrical, and Multiferroic Properties of Bi7Fe3Ti3O21 Thin Films

라그하반,김진원,최지야,김상수 한국물리학회 2015 새물리 Vol.65 No.4

Aurivillius-phase six-layered Bi7Fe3Ti3O21 (BFTO21) and Nd-doped Bi6.4Nd0.6Fe3Ti3O21 (BNdFTO21) thin films were prepared on Pt(111)/Ti/SiO2/Si(100) substrates by using a chemical solution deposition method in order to investigate their structural, electrical, and multiferroic properties. Doping the Bi sites of the BFTO21 with Nd3+-ions led to remarkable improvements in the electrical and the multiferroic properties. The electrical study of the BNdFTO21 thin film showed a low leakage current density of 4.38 × 10−6 A/cm2 at an applied electric field of 100 kV/cm, which was about one order of magnitude lower than that of the BFTO21 thin film. The ferroelectric P − E hysteresis loop of the BNdFTO21 thin film exhibited a large remnant polarization (2Pr) of 24 μC/cm2 and a low coercive electric field (2Ec) of 154 kV/cm at an applied electric field of 239 kV/cm. Furthermore, the magnetization and the coercive magnetic field that were observed for the BNdFTO21 thin film at room temperature were drastically enhanced compared to those observed for the BFTO21 thin film.

Studies on the structural, optical, dielectric and mechanical properties of non-linear optical manganese mercury Tetrathiocyanate glycol mono methyl ether (MMTG) single crystal

A. Bhaskaran,라그하반,R. MohanKumar,R. Jayavel 한국물리학회 2010 Current Applied Physics Vol.10 No.5

Non-linear optical manganese mercury teterathiocyanate glycol monomethyl ether [MnHg(SCN)4(C3H8O2)] compound was synthesized and single crystals were grown from water-glycol monomethyl ether (1:1) mixed solvent by slow cooling method. Structure and crystallinity of the grown crystal were confirmed by both single crystal and powder X-ray diffraction analysis. Presence of functional groups and coordination of glycol monomethyl ether and thiocyanate in MMTG were confirmed by FT-IR analysis. Optical transmittance and second harmonic generation of the grown crystal were studied by UV–Vis spectrum and Kurtz powder technique. A dielectric study was performed on the MMTG single crystal to study the power dissipation of the material in the presence of alternating electric field. Mechanical behaviour was analysed using Vicker’s microhardness test. Optical surface damage measurement was carried out to confirm the suitability of MMTG crystal for NLO applications.

CNTs 기하학적 파라미터에 따른 폴리머 나노복합재의 퍼콜레이션 임계치 예측 및 전기 전도도 특성 연구

도재혁,나가라잔 라그하반,이종수 대한기계학회 2019 大韓機械學會論文集A Vol.43 No.4

In this study, we investigated the changes in percolation threshold and electrical conductivity for polymer nanocomposites in accordance with geometric parameters of carbon nanotubes(CNTs). CNTs were randomly modeled as line segments, and periodic boundary conditions were applied to the two-dimensional representative volume element (RVE). The entire resistance network of the inner RVE was generated based on the connectivity of intersection points between line segments. The shortest path with the direction of the current between electrodes was used to determine whether percolation occurred. Based on this, the percolation threshold was predicted by conducting a Monte Carlo simulation. The electrical conductivity was predicted using Kirchhoff's current law and the finite element method. We verified the adequacy by comparing our results with other references, and the effects of percolation threshold and electrical conductivity were captured according to geometric parameters. 본 연구에서는 폴리머 나노복합소재에 첨가되는 탄소나노튜브(CNTs)의 기하학적 파라미터에 따른 퍼콜레이션 임계치 예측 및 전기전도도 특성 변화를 관찰하였다. 이를 위해 2차원 대표적 체적 요소(RVE) 내부에 CNTs를 선분으로 난수 모델링을 수행하고 주기경계조건을 적용하였다. CNTs 간의 접촉하는 선분들의 교점과 연결성 정보를 이용하여 RVE 내부의 전체 저항 네트워크를 생성하였다. 두 전극 사이에 흐르는 전류 방향으로 전체 네트워크의 최단 경로를 이용하여 퍼콜레이션 발생 여부를 결정하였다. 이를 기반으로 몬테 카를로 시뮬레이션을 수행해 퍼콜레이션 확률을 예측하고, 키르히호프 전류 법칙과 유한요소법을 이용하여 전기전도도를 예측하였다. 이를 타 참고문헌과 비교하여 그 타당성을 검증하고 CNTs의 기하학적 파라미터가 전기적 특성과 퍼콜레이션 확률에 미치는 영향을 확인하였다.

Structure and Electrical Properties of (La, Zn) Co-doped BiFeO3 Thin Films Prepared by Using Chemical Solution Deposition

김윤장,김해진,김진원,라그하반,김상수 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.3

We prepared pure BiFeO<SUB>3</SUB> (BFO) and (Bi<SUB>0.9</SUB>La<SUB>0.1</SUB>)(Fe<SUB>0.975</SUB>Zn<SUB>0.025</SUB>)O<SUB>3-δ</SUB> (BLFZO) thin films on Pt(111)/Ti/SiO<SUB>2</SUB>/Si(100) substrates by using a chemical solution deposition method. The improved electrical properties were observed in the co-doped BLFZO thin film. The leakage current density of the BLFZO thin film showed four orders lower than that of the pure BFO, 4.17 ?10^-7 A/cm² at 100 kV/cm. The remnant polarization (2<i>P_r</i>) and the coercive electric field (2<i>E_c</i>) of the BLFZO thin film were 97 μC/cm² and 903 kV/cm at applied electric field of 972 kV/cm and at a frequency of 1 kHz and the values were decreased with increasing measurement frequency, 63 μC/cm² and 679 kV/cm at 10 kHz, respectively. Also, after 1.44 ?10¹⁰ cycles the better fatigue endurance was observed in the BLFZO thin film, which is 90% of its initial value. And we confirm that the remnant polarization (2<i>P_r</i>) and the coercive electric field (2<i>E_c</i>) were fairly saturated above measurement frequency of 15 kHz for the BLFZO thin film.

Electrical Properties of Dy, Mn Co-doped BiFeO3 Thin Films Prepared by Using Chemical Solution Deposition

J. W. Kim,라그하반,H. J. Kim,Y. J. Kim,장기완,김상수,이용일,J. M. Lim,D. S. Shin 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.6

The effects of Dy, Mn alone doping and co-doping on the structural, electrical and ferroelectric properties of BiFeO<SUB>3</SUB> thin films were investigated. (Bi_1−xDy_x)(Fe_1−yMn_y)O₃ thin films, with (x, y) = (0, 0), (1, 0), (0, 1), and (1, 1) denoted by BFO, BDyFO, BFMnO, and BDyFMn, respectively, were prepared by using a chemical solution deposition method. All thin films were annealed at 550 → for 30 min by using a conventional annealing process under a nitrogen atmosphere for crystallization. Among the thin films, superior ferroelectric properties were observed in the BDyFMn thin film. The BDyFMn thin film exhibited a low leakage current density (1.8 ≠ 10⁻⁵ A/cm²), well-saturated hysteresis loops, a large remanent polarization (2<i>P_r</i>) of 80 ┢C/cm² (at a 1060-kV/cm applied electric field) and good fatigue endurance.

Effects of Ho- and Ni-doping Alone and of Co-doping on the Structural and the Electrical Properties of BiFeO3 Thin Films

J. W. Kim,라그하반,J. Y. Choi,S. S. Kim 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.66 No.7

The effects of Ho and Ni doping alone and of co-doping with Ho and Ni on thestructural, electrical and ferrolectric properties of BiFeO3 thin films are reported. PureBiFeO3, (Bi0.9Ho0.1)FeO3, Bi(Fe0.98Ni0.02)O3−δ, and (Bi0.9Ho0.1)(Fe0.98Ni0.02)O3−δ thin filmswere prepared on Pt(111)/Ti/SiO2/Si(100) substrates by using a chemical solution depositionmethod. All thin films were annealed at 550◦C for 30 min by using a conventional annealingprocess under a nitrogen atmosphere for crystallization. From the experimental results,the (Bi0.9Ho0.1)(Fe0.98Ni0.02)O3−δ thin film exhibited superior ferroelectric properties. Alower leakage current density and an improved ferroelectric properties were observed in the(Bi0.9Ho0.1)(Fe0.98Ni0.02)O3−δ thin film compared to the BiFeO3 thin film. The improvementscould be explained by the reduction of bismuth and oxygen vacancies, the formation of defectdipoles, and a change in the microstructure.