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Electronic and magnetic structure investigation of vanadium doped ZnO nanostructure
Bhardwaj, Richa,Singh, Jitendra Pal,Chae, Keun Hwa,Goyal, Navdeep,Gautam, Sanjeev Elsevier 2018 Vacuum Vol.158 No.-
<P><B>Abstract</B></P> <P>In the present work, vanadium doped ZnO nanostructure, Zn<SUB>1-<I>x</I> </SUB>V<SUB> <I>x</I> </SUB>O (x = 0.00, 0.01, 0.02, 0.03) have been synthesized using sol-gel route. Rietveld refined X-ray diffraction confirms the single wurtzite phase for all the prepared samples with crystallite size ranging from 20 to 40 nm. UV-Diffuse reflectance spectroscopy shows the decrease in band gap energy from 3.20 to 3.17 eV on V doping and and Photoluminescence (PL) measurements has a strong visible emission region in the range 500–700 nm. PL broad peak in the visible region is further deconvoluted to study the defect states in the V:ZnO system. V doped ZnO nanostructure shows the room temperature ferromagnetism measured through Vibrating Sample Magnetometer hysteresis curve. The magnetic moment ( <SUB> μ B </SUB> ) is found to vary from 0.012 to 0.018 <SUB> μ B </SUB> per V-atom as x changes from 0.01 to 0.03 in Zn<SUB>1-<I>x</I> </SUB>V<SUB> <I>x</I> </SUB>O matrix. Magnetic structure properties are correlated with electronic transitions at different atomic levels using near-edge X-ray absorption fine-structure (NEXAFS) spectroscopy. NEXAFS spectral features at O<I>K-</I>, V/Zn <SUB> L 3,2 </SUB> <I>-</I> edge reveals the hybridization of V(3<I>d</I>)-O(2<I>p</I>) orbitals and absence of V-metallic clusters in V:ZnO system. These investigations further envisage the existence of +5 state of vanadium in Zn<SUB>1-<I>x</I> </SUB>V<SUB> <I>x</I> </SUB>O nanostructure.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Zn<SUB>1−<I>x</I> </SUB>V<SUB> <I>x</I> </SUB>O (x = 0.00, 0.01, 0.02, 0.03) synthesis by sol-gel route with crystallite size 20–30 nm. </LI> <LI> PL spectra is deconvoluted that shows the presence of vacancies in the V:ZnO system. </LI> <LI> The hybridized electronic structure of V:ZnO is investigated through NEXAFS. </LI> <LI> Samples show RTFM with magnetic moment varying from 0.012 to 0.018 μ<I>B</I>/V atom for x = 0.01 to 0.03. </LI> <LI> The magnetic structure is discussed through BMP exchange interactions. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Flak, Dorota,Chen, Qianli,Mun, Bongjin Simon,Liu, Zhi,Rę,kas, Mieczysław,Braun, Artur Elsevier 2018 APPLIED SURFACE SCIENCE - Vol.455 No.-
<P><B>Abstract</B></P> <P>Fundamental understanding of charge transfer reaction is essential for the surface and interface engineering of transition metal oxides. In this study the chemical reactivity towards oxygen and hydrogen (13 Pa) under applied thermal conditions (423–673 K), of two polymorphic forms of Fe<SUB>2</SUB>O<SUB>3</SUB> nanoparticles (γ-Fe<SUB>2</SUB>O<SUB>3</SUB> and α-Fe<SUB>2</SUB>O<SUB>3</SUB>) are investigated with the combination of <I>in situ</I> ambient pressure X-ray photoelectron spectroscopy (AP-XPS) and near edge X-ray absorption fine structure spectroscopy (AP-NEXAFS). Our data show that the reactivity of these two polymorphs has a similar character based on the contribution of oxygen vacancy defect states and related material non-stoichiometry. Their exposure to hydrogen at increased temperature results in both cases in the surface reduction. However, γ-Fe<SUB>2</SUB>O<SUB>3</SUB> exhibits more covalent character and undergoes the reduction preferentially with a contribution of metallic Fe<SUP>0</SUP> than Fe<SUP>2+</SUP>, in contrast to α-Fe<SUB>2</SUB>O<SUB>3</SUB>. Further, upon introduction of oxygen at low temperature of 423 K, rapid re-oxidation process takes place at the Fe<SUB>2</SUB>O<SUB>3</SUB> nanoparticles surface. Prepared γ-Fe<SUB>2</SUB>O<SUB>3</SUB> and α-Fe<SUB>2</SUB>O<SUB>3</SUB> nanostructures exhibit in general high n-type and p-type sensor response towards hydrogen, respectively, in a wide concentrations range.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Chemical reactivity investigation of Fe<SUB>2</SUB>O<SUB>3</SUB> polymorph NPs by <I>in situ</I> XPS and NEXAFS. </LI> <LI> Reactivity of Fe<SUB>2</SUB>O<SUB>3</SUB> polymorph NPs is based on the material non-stoichiometry. </LI> <LI> γ-Fe<SUB>2</SUB>O<SUB>3</SUB> more covalent than α-Fe<SUB>2</SUB>O<SUB>3</SUB> in particular upon interaction with H<SUB>2</SUB>. </LI> <LI> γ-Fe<SUB>2</SUB>O<SUB>3</SUB> undergoes reduction preferentially with contribution of Fe<SUP>0</SUP> unlike α-Fe<SUB>2</SUB>O<SUB>3</SUB>. </LI> <LI> Electronic structure changes of Fe<SUB>2</SUB>O<SUB>3</SUB> NPs upon O<SUB>2</SUB> and H<SUB>2</SUB> exposures are reversible. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
NEXAFS 분광법에 의한 Alq<SUB>3</SUB>/Ba과 Alq<SUB>3</SUB>/Au의 계면에서의 전자 천이에 관한 연구
임수용(Su yong Lim),주성후(Sung Hoo Ju),양재웅(Jae Woong Yang) 한국표면공학회 2012 한국표면공학회지 Vol.45 No.1
Tris(8-quinolinolato)aluminum(Ⅲ); Alq3 has been frequently used as an electron transporting layer in organic light-emitting diodes. Either Ba with a low work function or Au with a high work function was deposited on Alq3 layer in vacuum. And then, the behaviors of electron transition at the Alq3/Ba and Alq3/Au interfaces were investigated by using the near edge x-ray absorption fine structure (NEXAFS) spectroscopy. In the each interface, the energy levels of unoccupied obitals were assigned as π<SUP>*</SUP>(LUMO, LUMO+1, LUMO+2 and LUMO+3) and σ<SUP>*</SUP>. And the relative intensities of these peaks were investigated. In an oxygen atom composing Alq3 molecule, the relative intensities for a transition from K-edge to LUMO+2 were largely increased as Ba coverage (ΘBa, 2.7 eV) with a low work function was in-situ sequentially increased on Alq3 layer. In contrast, the relative intensities for the LUMO+2 peak were reduced as Au coverage (ΘAu, 5.1 eV) with a high work function were increased on Alq3 layer. This means that the electron transition by photon in oxygen atom which consists in the unoccupied orbitals in Alq3 molecule, largely depends on work function of a metal. Meanwhile, in the case of electron transition in a carbon atom, as ΘBa was increased on Alq3, the relative intensity from K-edge to π1<SUP>*</SUP> (LUMO and LUMO+1) was slightly decreased, and from K-edge to π2<SUP>*</SUP> (LUMO+2 and LUMO+3) was somewhat increased. This rising of the energy state from π1<SUP>*</SUP> to π2<SUP>*</SUP> exhibits that electrons provided by Ba would contribute to the process of electron transition in the Alq3/Ba interfaces. As shown in above observation, the analyses of NEXAFS spectra in each interface could be important as a basic data to understand the process of electron transition by photon in pure organic materials.
Interaction of SO2 with Oxygen on Ni(100) Studied by XPS and NEXAFS
Chang Min Kim 대한화학회 2006 Bulletin of the Korean Chemical Society Vol.27 No.12
The adsorption and surface reactions of SO2 on Ni(100), c(2x2)_O/Ni (100) and NiO(111)/Ni(100) surfaces have been investigated using X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) technique. On Ni(100), chemisorbed SO2 is formed at 160 K. When SO2 is adsorbed on c(2x2)_O/Ni(100) at 160 K, SO2 reacts with oxygen to form SO3 and trace amount of SO4 species. SO3 is adsorbed on this surface with its C3 axis perpendicular to the surface. On a NiO(111)/Ni(100) surface, both SO3 and SO4 species are formed at 160 K from adsorbed SO2.
Kim, Ki-Jeong,Yang, Sena,Kang, Tai-Hee,Kim, Bong-Soo,Lee, Hang-Gil Korean Chemical Society 2010 Bulletin of the Korean Chemical Society Vol.31 No.7
The electronic and adsorption structure of o-phthalaldehyde (OPA) on the H-Si(100) surface was investigated by using Near Edge X-ray Fine Structure (NEXAFS) and high resolution photoemission spectroscopy (HRPES). We confirmed that the OPA grown on the H-Si(100) surface showed good dependency with about 60 degree tilting angle using NEXAFS and a single O 1s peak by using HRPES. Hydrogen atom passivated on the Si(100) surface was found to be a seed for making one dimensional organic line that uses a chain reaction as the H-Si(100) surface was compared with the hydrogen free Si(100) surface.
Ki-jeong Kim,양세나,Tai-Hee Kang,Bongsoo Kim,Hangil Lee 대한화학회 2010 Bulletin of the Korean Chemical Society Vol.31 No.7
The electronic and adsorption structure of o-phthalaldehyde (OPA) on the H-Si(100) surface was investigated by using Near Edge X-ray Fine Structure (NEXAFS) and high resolution photoemission spectroscopy (HRPES). We confirmed that the OPA grown on the H-Si(100) surface showed good dependency with about 60 degree tilting angle using NEXAFS and a single O 1s peak by using HRPES. Hydrogen atom passivated on the Si(100) surface was found to be a seed for making one dimensional organic line that uses a chain reaction as the H-Si(100) surface was compared with the hydrogen free Si(100) surface.