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- 검색키워드
- 저자 : ( Narendra S Parmar ) (검색결과 4 건)
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Parmar, Narendra S.,Choi, Ji-Won,Boatner, Lynn A.,McCluskey, Matthew D.,Lynn, Kelvin G. Elsevier 2017 JOURNAL OF ALLOYS AND COMPOUNDS Vol.729 No.-
<P><B>Abstract</B></P> <P>Research is described here that is directed toward obtaining <I>p</I>-type ZnO crystals either by doping or by creating native defects. Theoretically, zinc vacancies are shallow acceptors that should allow for <I>p</I>-type conduction. Bulk ZnO crystals can be grown by chemical vapor transport (CVT), melt solidification, and hydrothermal methods. Here we have explored annealing processes with the goal of creating zinc vacancies in bulk ZnO crystals. Positron annihilation spectra reveal the reproducible formation of high concentrations (>10<SUP>20</SUP> cm<SUP>−3</SUP>) of isolated zinc vacancies (<I>V</I> <SUB>Zn</SUB>) in oxygen-annealed, CVT-grown ZnO crystals in the ∼100–150 nm near-surface. Melt- and hydrothermally grown samples, in contrast, show insignificant levels of zinc vacancy creation. Photoluminescence (PL) emission spectra indicate a <I>V</I> <SUB>Zn</SUB>(0/-1) acceptor level at ∼ 155–165 meV; red PL (∼1.7 eV) emission, related to the <I>V</I> <SUB>Zn</SUB>(-1/-2) level, was also observed. Infrared absorption spectroscopy reveals the presence of a zinc vacancy complex with a hole binding energy range of 420–450 meV – and with a continuum suggesting a <I>p</I>-type region. XPS measurements support the deficiency of Zn after oxygen annealing the CVT-grown ZnO single crystal.</P> <P><B>Highlights</B></P> <P> <UL> <LI> CVT, hydrothermally and Melt-grown ZnO crystals were investigated. </LI> <LI> Isolated V<SUB>Zn</SUB> > 10<SUP>20</SUP> cm<SUP>−3</SUP> were formed in oxygen annealed CVT ZnO crystals. </LI> <LI> PL emission indicate a V<SUB>Zn</SUB>(0/-1) acceptor level at ∼ 155–165 meV. </LI> <LI> FTIR reveals zinc vacancy complex with a hole binding energy ∼ 420–450 meV. </LI> <LI> XPS data support the deficiency of Zn in oxygen annealed CVT ZnO crystals. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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Cho, Yoonho,Parmar, Narendra S.,Nahm, Sahn,Choi, Ji-Won Elsevier 2017 Ceramics international Vol.43 No.9
<P><B>Abstract</B></P> <P>In the quest of promising Indium free amorphous transparent conducting oxide (TCO), Zn-doped SnO<SUB>2</SUB>/Ag/Zn-doped SnO<SUB>2</SUB> (OMO) multilayer films were prepared on flexible polyethylene terephthalate (PET) substrates by RF sputtering at room temperature (RT). Growth parameters were optimized by varying sputtering power and working pressure, to have high electrical conductivity and optical transmittance. Optimization of the thickness of each layer was done by Essential Macleod Program (EMP) simulation to get the higher transmission through OMO multilayer. The sheet resistance and transmittance of 3at% Zn-doped SnO<SUB>2</SUB> thin film (30nm) were 2.23 kΩ/□, (ρ ~ 8.92×10<SUP>−3</SUP> Ω∙cm) and 81.3% (at λ ~ 550nm), respectively. By using optimized thicknesses of Zn-doped SnO<SUB>2</SUB> (30nm) and Ag (12nm) and optimized growth condition Zn-doped SnO<SUB>2</SUB>/Ag/Zn-doped SnO<SUB>2</SUB> multilayer thin films were deposited. The low sheet resistance of 7.2 Ω/□ and high optical transmittance of 85.1% in the 550nm wavelength region was achieved with 72nm multilayer film.</P>
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투명 박막 리튬이차전지를 위한 LiNiPO<sub>4</sub> 박막의 광학 및 전기화학적 특성
이현석 ( Hyunseok Lee ),( Narendra S Parmar ),김광범 ( Kwang-bum Kim ),최지원 ( Ji-won Choi ) 한국센서학회 2018 센서학회지 Vol.27 No.1
Transparent olivine LiNiPO4 thin films on sapphire substrates were fabricated by radio frequency (RF) magnetron sputtering. The Xray diffraction patterns show these thin films have the phase of LiNiPO<sub>4</sub> with an ordered olivine structure indexed to the orthorhombic Pmna space group. LiNiPO<sub>4</sub> thin films deposited on sapphire substrates exhibit transmittance of about 83 %. It was confirmed that the LiNiPO<sub>4</sub> thin film exhibits a high potential of 5 V-class.
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Carbon-free Mn-doped LiFePO<sub>4</sub> cathode for highly transparent thin-film batteries
Lee, HyunSeok,Kim, Sangtae,Parmar, Narendra Singh,Song, Jong-Han,Chung, Kyung-yoon,Kim, Kwang-Bum,Choi, Ji-Won Elsevier Sequoia 2019 Journal of Power Sources Vol. No.
<P><B>Abstract</B></P> <P>The search for transparent battery cathodes primarily focuses on patterned electrodes with feature sizes below the optical absorption limit. This significantly limits the electrode capacity, as a large electrode area remains unused to maintain transparency. Herein, we report transparent olivine LiFe<SUB>0.77</SUB>Mn<SUB>0.23</SUB>PO<SUB>4</SUB> thin-film electrodes discovered through high-throughput continuous-composition-spread sputtering. After investigating six different Mn doping ratios, we found the optimal Mn-doped olivine composition with an enhanced discharge capacity of 45.7 μA h/cm<SUP>2</SUP>∙μm without using excessive nanosized features or carbon coating. The thin-film electrode exhibits a clear redox activity for both Fe<SUP>3+/2+</SUP> and Mn<SUP>3+/2+</SUP>, resulting in an enhanced average voltage over LiFePO<SUB>4</SUB> composition. A 250-nm-thick film exhibits an optical transmittance of over 80% in the visible region. The results in this study demonstrates that transparent cathode thin films can be developed based on phospho-olivines via doping strategies with high-throughput continuous-composition-spread sputtering methods.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Exploration of carbon-free transparent LiFe<SUB>1-<I>x</I> </SUB>Mn<SUB> <I>x</I> </SUB>PO<SUB>4</SUB> thin films by CCS. </LI> <LI> The capacity of carbon-free LiFe<SUB>0.77</SUB>Mn<SUB>0.23</SUB>PO<SUB>4</SUB> thin films is 45.7 μA h/cm<SUP>2</SUP>∙μm. </LI> <LI> Transmittance of Carbon-free LiFe<SUB>0.77</SUB>Mn<SUB>0.23</SUB>PO<SUB>4</SUB> thin film exhibits 82%. </LI> <LI> Carbon-free LiFe<SUB>0.77</SUB>Mn<SUB>0.23</SUB>PO<SUB>4</SUB> is suitable for transparent thin film batteries. </LI> </UL> </P>
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