Electronic Structure of Ce-doped ZrO₂ Film: Study of DFT Calculation and Photoelectron Spectroscopy

Jeong, Kwang Sik,Song, Jinho,Lim, Donghyuck,Kim, Hyungsub,Cho, Mann-Ho The Korean Vacuum Society 2016 Applied Science and Convergence Technology Vol.25 No.1

In this study, we evaluated the change of electronic structure during redox process in cerium-doped $ZrO_2$ grown by sol gel method. By sol-gel method, we could obtain cerium-doped $ZrO_2$ in high oxygen partial pressure and low temperature. After post annealing process in nitrogen ambient, the film is deoxidized. We used spectroscopic and theoretical methods to analysis change of electronic structure. X-ray absorption spectroscopy (XAS) for O K1-edge and Density Functional Theory (DFT) calculation using VASP code were performed to verify the electronic structure of the film. Also, high resolution x-ray photoelectron spectroscopy (HRXPS) for Ce 3d was carried out to confirm chemical bond of cerium doped $ZrO_2$. Through the investigation of the electronic structure, we verified as followings. (1) During reduction process, binding energy of oxygen is increase. Simultaneously, oxidation state of cerium was change to 4+ to 3+. (2) Cerium 4+ and cerium 3+ states were generated at different energy level. (3) Absorption states in O K edge were mainly originated by Ce 4+ $f_0$ and Ce 3+, while occupied states in valance band were mainly originated from Ce 4+ $f_2$.

Electronic Structure and Optical Properties of Inverse-spinel MnCo2O4 Thin Films

김광주,허종욱 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.9

The electronic structure and the optical properties of MnCo2O4 thin films were investigated by using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and spectroscopic ellipsometry (SE) and were compared with those of Co3O4. Polycrystalline films of the spinel oxides were prepared on Al2O3(0001) substrates by using a sol-gel method. XPS investigation indicated that the Mn ions in MnCo2O4 had a valence of +3 and occupied the octahedral sites of the spinel lattice. XRD results revealed that the inverse-spinel MnCo2O4 sample exhibited distortion of the lattice to a tetragonal structure while the Co3O4 sample had a cubic structure. The lattice distortion implies a high-spin t2g3eg1-electron configuration of the octahedral Mn3+ ions, which is susceptible to the Jahn-Teller effect. The dielectric function spectra of MnCo2O4 and Co3O4 measured by using SE in the visible-ultraviolet (1.5–8.5 eV) range exhibited a number of optical absorption structures that could be explained in terms of electronic charge-transfer (CT) transitions between the ions located at different lattice sites. The valence-electronic states involved in the CT transitions were identified from the electronic structure predicted by the XPS analyses.

Structural optimization for thermoelectric properties in Cu-Bi-S pavonite compounds

Hwang, Jae-Yeol,Ahn, Jun Yeon,Lee, Kyu Hyoung,Kim, Sung Wng Elsevier 2017 Journal of Alloys and Compounds Vol.704 No.-

<P><B>Abstract</B></P> <P>We report the enhancement of thermoelectric properties in the complex structured Cu-Bi-S pavonite compounds by optimizing the structural configuration through tuning the Bi-site occupancy, and substitutional doping at interstitial Cu sites by Zn. We verify that electronic transport properties depend on the structural deformation by the Bi site occupancy. Furthermore, we demonstrate that the modification of interstitial site ions enables selective control of thermal conductivity and intrinsically low thermal conductivity can be further suppressed by structural optimization without deteriorating electronic transport properties. We propose that understanding of crystal structure as a basic strategy permits the optimization of thermoelectric properties in the complex structures.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Strong correlation between structure and thermoelectric properties in Cu-Bi-S compounds. </LI> <LI> Electronic transport properties depend on the structural deformation by the Bi site occupancy. </LI> <LI> The modification of interstitial site ions enables selective control of thermal conductivity. </LI> <LI> Intrinsically low thermal conductivity can be further suppressed by structural optimization. </LI> <LI> Understanding of structure as a basic strategy for the optimization of thermoelectric properties. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Electronic Structure of Ce-doped ZrO2 Film: Study of DFT Calculation and Photoelectron Spectroscopy

정광식,송진호,임동혁,김형섭,조만호 한국진공학회 2016 Applied Science and Convergence Technology Vol.25 No.1

In this study, we evaluated the change of electronic structure during redox process in cerium-doped ZrO2 grown by sol gel method. By sol-gel method, we could obtain cerium-doped ZrO2 in high oxygen partial pressure and low temperature. After post annealing process in nitrogen ambient, the film is deoxidized. We used spectroscopic and theoretical methods to analysis change of electronic structure. X-ray absorption spectroscopy (XAS) for O K1-edge and Density Functional Theory (DFT) calculation using VASP code were performed to verify the electronic structure of the film. Also, high resolution x-ray photoelectron spectroscopy (HRXPS) for Ce 3d was carried out to confirm chemical bond of cerium doped ZrO2. Through the investigation of the electronic structure, we verified as followings. (1) During reduction process, binding energy of oxygen is increase. Simultaneously, oxidation state of cerium was change to 4+ to 3+. (2) Cerium 4+ and cerium 3+ states were generated at different energy level. (3) Absorption states in O K edge were mainly originated by Ce 4+ f0 and Ce 3+, while occupied states in valance band were mainly originated from Ce 4+ f2.

Electronic Structure of Ce-doped ZrO₂ Film

Kwang Sik Jeong,Jinho Song,Donghyuck Lim,Hyungsub Kim,Mann-Ho Cho 한국진공학회(ASCT) 2016 Applied Science and Convergence Technology Vol.25 No.1

In this study, we evaluated the change of electronic structure during redox process in cerium-doped ZrO₂ grown by sol gel method. By sol-gel method, we could obtain cerium-doped ZrO₂ in high oxygen partial pressure and low temperature. After post annealing process in nitrogen ambient, the film is deoxidized. We used spectroscopic and theoretical methods to analysis change of electronic structure. X-ray absorption spectroscopy (XAS) for O K1-edge and Density Functional Theory (DFT) calculation using VASP code were performed to verify the electronic structure of the film. Also, high resolution x-ray photoelectron spectroscopy (HRXPS) for Ce 3d was carried out to confirm chemical bond of cerium doped ZrO₂. Through the investigation of the electronic structure, we verified as followings. (1) During reduction process, binding energy of oxygen is increase. Simultaneously, oxidation state of cerium was change to 4+ to 3+. (2) Cerium 4+ and cerium 3+ states were generated at different energy level. (3) Absorption states in O K edge were mainly originated by Ce 4+ f0 and Ce 3+, while occupied states in valance band were mainly originated from Ce 4+ f₂.

Non-cryogenic structure of a chloride pump provides crucial clues to temperature-dependent channel transport efficiency

Yun, Ji-Hye,Li, Xuanxuan,Park, Jae-Hyun,Wang, Yang,Ohki, Mio,Jin, Zeyu,Lee, Wonbin,Park, Sam-Yong,Hu, Hao,Li, Chufeng,Zatsepin, Nadia,Hunter, Mark S.,Sierra, Raymond G.,Koralek, Jake,Yoon, Chun Hong,C American Society for Biochemistry and Molecular Bi 2019 The Journal of biological chemistry Vol.294 No.3

<P>Non-cryogenic protein structures determined at ambient temperature may disclose significant information about protein activity. Chloride-pumping rhodopsin (ClR) exhibits a trend to hyperactivity induced by a change in the photoreaction rate because of a gradual decrease in temperature. Here, to track the structural changes that explain the differences in CIR activity resulting from these temperature changes, we used serial femtosecond crystallography (SFX) with an X-ray free electron laser (XFEL) to determine the non-cryogenic structure of ClR at a resolution of 1.85 Å, and compared this structure with a cryogenic ClR structure obtained with synchrotron X-ray crystallography. The XFEL-derived ClR structure revealed that the all-<I>trans</I> retinal (ATR) region and positions of two coordinated chloride ions slightly differed from those of the synchrotron-derived structure. Moreover, the XFEL structure enabled identification of one additional water molecule forming a hydrogen bond network with a chloride ion. Analysis of the channel cavity and a difference distance matrix plot (DDMP) clearly revealed additional structural differences. B-factor information obtained from the non-cryogenic structure supported a motility change on the residual main and side chains as well as of chloride and water molecules because of temperature effects. Our results indicate that non-cryogenic structures and time-resolved XFEL experiments could contribute to a better understanding of the chloride-pumping mechanism of ClR and other ion pumps.</P>

Characterization of electronic structure in dielectric materials by making use of the secondary electron emission

Uhm, H.S.,Choi, J.H.,Cho, G.,Park, B.J.,Jung, R.J.,Choi, E.H. Elsevier 2013 Current Applied Physics Vol.13 No.2

The methodology of characterizing electronic structure in dielectric materials will be presented in detail. Energy distribution of the electrons emitted from dielectric materials by the Auger neutralization of ions is measured and rescaled for Auger self-convolution, which is restructured from the energy distribution of the emitted electrons. The Fourier transform is very effective for obtaining the density of states from the Auger self-convolution. The MgO layer is tested as an example of this new measurement scheme. The density of states in the valence band of the MgO layer is studied by measuring the energy distribution of the emitted electrons for MgO crystal with three different orientations of (111), (100) and (110). The characteristic energy of @?<SUB>0</SUB> corresponding to the peak density of the states in the band is determined, showing that the (111) orientation has a shallow characteristic energy @?<SUB>0</SUB> = 7.4 eV, whereas the (110) orientation has a deep characteristic energy @?<SUB>0</SUB> = 9.6 eV, consistent with the observed coefficient γ of the secondary electron emission for MgO crystal. Electronic structure in new functional nano-films spayed over MgO layer is also characterized. It is therefore demonstrated that secondary electron emission by the Auger neutralization of ions is highly instrumental for the determination of the density of states in the valence band of dielectric materials. This method simultaneously determines the valence band structure and the coefficient γ of the secondary electron emission, which plays the most important role in the electrical breakdown phenomena.

Characterization of electronic structure in dielectric materials by making use of the secondary electron emission

Han S. Uhm,Joon H. Choi,조광섭,박병주,정난주,최은하 한국물리학회 2013 Current Applied Physics Vol.13 No.2

The methodology of characterizing electronic structure in dielectric materials will be presented in detail. Energy distribution of the electrons emitted from dielectric materials by the Auger neutralization of ions is measured and rescaled for Auger self-convolution, which is restructured from the energy distribution of the emitted electrons. The Fourier transform is very effective for obtaining the density of states from the Auger self-convolution. The MgO layer is tested as an example of this new measurement scheme. The density of states in the valence band of the MgO layer is studied by measuring the energy distribution of the emitted electrons for MgO crystal with three different orientations of (111), (100) and (110). The characteristic energy of ε0 corresponding to the peak density of the states in the band is determined, showing that the (111) orientation has a shallow characteristic energy ε0 =7.4 eV, whereas the (110) orientation has a deep characteristic energy ε0 = 9.6 eV, consistent with the observed coefficient g of the secondary electron emission for MgO crystal. Electronic structure in new functional nano-films spayed over MgO layer is also characterized. It is therefore demonstrated that secondary electron emission by the Auger neutralization of ions is highly instrumental for the determination of the density of states in the valence band of dielectric materials. This method simultaneously determines the valence band structure and the coefficient r of the secondary electron emission, which plays the most important role in the electrical breakdown phenomena.

Elastic and electronic properties of partially ordered and disordered Zr(C₁₋ <i> _x </i>N<i> _x </i>) solid solution compounds: A first principles calculation study

Kim, Jiwoong,Kwon, Hanjung,Kim, Jae-Hee,Roh, Ki-Min,Shin, Doyun,Jang, Hee Dong Elsevier 2015 JOURNAL OF ALLOYS AND COMPOUNDS Vol.619 No.-

<P><B>Abstract</B></P> <P>The elastic properties and electronic structures of partially ordered and disordered Zr(C<SUB>1−</SUB> <I> <SUB>x</SUB> </I>N<I> <SUB>x</SUB> </I>) solid solution compounds were investigated using first principles calculations to understand the effects of nitrogen content and atomic distribution. To obtain a proper exchange–correlation energy, we used local density and generalized gradient approximations with Perdew–Burke–Ernzerhof (LDA and GGA-PBE) parametrization. Partially ordered and disordered structures of Zr(C<SUB>1−</SUB> <I> <SUB>x</SUB> </I>N<I> <SUB>x</SUB> </I>) compounds were expressed using unit cell and special quasi-random structure (SQS) models, respectively. We demonstrated that although the disordered models have P1 symmetry with different model sizes and cell shapes compared with ordered models, they reproduce the equilibrium structure and elastic properties of the Zr(C<SUB>1−</SUB> <I> <SUB>x</SUB> </I>N<I> <SUB>x</SUB> </I>) compounds with B1 (Fm-3m) symmetry. However, clear differences exist in the electronic structures. Therefore, the atomic configuration is essential for calculating the electronic structures of the Zr(C<SUB>1−</SUB> <I> <SUB>x</SUB> </I>N<I> <SUB>x</SUB> </I>) compounds.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Elastic and electronic properties of Zr(C<SUB>1−<I>x</I> </SUB>N<SUB> <I>x</I> </SUB>) compounds by first principles. </LI> <LI> We elucidate the effects of atomic configuration on compound properties. </LI> <LI> Ordered and disordered models are depicted by unit cell and special quasi-random structures. </LI> <LI> Disordered structures are suitable models to estimate compound elastic properties. </LI> <LI> The atomic configuration is essential to obtain accurate electronic structures. </LI> </UL> </P>

Atomic and Electronic Structures of the Ni-induced Phases on Si(111): Scanning Tunneling Microscopy and Spectroscopy Study

심형준,이근섭,김도환,홍석륜,김세훈 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.6

The atomic and electronic structures of Ni-induced phases formed on a Si(111) surface were investigated using scanning tunneling microscopy (STM) and spectroscopy (STS). STM images show the presence of two kinds of the ring clusters ('1x1'-RCs and √19-RCs) which are related to the known '1x1' and √19×√19 phases, respectively. In addition, a new ordered structure having a √7×√7 periodicity with a considerable domain size was also observed to form on the surface. Islands of the √7×√7 structure embedded in the surface of the √19×√19 structure are found to be made by regular packing of the '1x1'-RCs. High-resolution, dual-bias STM images reveal unprecedented atomistic details of both the ring clusters forming the ordered √19×√19 and √7×√7 structures. STS data indicate that the local √7×√7 phase is semiconducting with a gap of about 1 eV. The √19×√19 structure is either metallic or semiconducting with a gap smaller than 0.2 eV. The peaks in the (dI/dV)/(I/V) curves were attributed to the density of the states expected from the existing atomic models of the two ordered structures.