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Electronic structure and chemisorpti...

Li, Xiaomei.

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Electronic structure and chemisorption properties of chromium and nickel oxides.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Electronic structure and chemisorption properties of chromium and nickel oxides./
作者:	Li, Xiaomei.
面頁冊數:	122 p.
附註:	Source: Dissertation Abstracts International, Volume: 56-03, Section: B, page: 1509.
Contained By:	Dissertation Abstracts International56-03B.
標題:	Condensed matter physics. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=9523194

Electronic structure and chemisorption properties of chromium and nickel oxides.
Li, Xiaomei.

Electronic structure and chemisorption properties of chromium and nickel oxides. - 122 p.

Source: Dissertation Abstracts International, Volume: 56-03, Section: B, page: 1509.

Thesis (Ph.D.)--Yale University, 1994.

Resonant photoemission measurements have been performed on single-crystal Cr$\sb2$O$\sb3$ (1012) surfaces for the first time. A strong resonant enhancement of the highest-lying valence-band states was observed across the Cr 3p $\to$ 3d excitation threshold. In light of the similarity of the resonance in Cr$\sb2$O$\sb3$ with that of the Mott-Hubbard oxides Ti$\sb2$O$\sb3$ and V$\sb2$O$\sb3$, and differences from those of the charge-transfer oxides MnO, Fe$\sb2$O$\sb3$, CoO, NiO and CuO, it is suggested that Cr$\sb2$O$\sb3$ is a Mott-Hubbard insulator. However, configuration-interaction cluster calculations were applied to study the nature of the satellite in the Cr 2p core-level XPS spectrum. It is argued that the satellite can be understood as a charge-transfer satellite, and Cr$\sb2$O$\sb3$ is found to be actually situated at the boundary between the Mott-Hubbard and the charge-transfer regimes. The values of the charge-transfer energy, $\Delta$, the Coulomb correlation energy, U, and the ligand 2p-cation 3d hybridization energy, T, found from fitting the Cr 2p core-level XPS spectrum were used to analyze the valence-band UPS spectrum. The comparison between the experimental spectrum and the theoretical prediction is good.Subjects--Topical Terms:

3173567
Condensed matter physics.

Electronic structure and chemisorption properties of chromium and nickel oxides.
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100 1 $a Li, Xiaomei. $3 3186152
245 1 0 $a Electronic structure and chemisorption properties of chromium and nickel oxides.
300 $a 122 p.
500 $a Source: Dissertation Abstracts International, Volume: 56-03, Section: B, page: 1509.
502 $a Thesis (Ph.D.)--Yale University, 1994.
520 $a Resonant photoemission measurements have been performed on single-crystal Cr$\sb2$O$\sb3$ (1012) surfaces for the first time. A strong resonant enhancement of the highest-lying valence-band states was observed across the Cr 3p $\to$ 3d excitation threshold. In light of the similarity of the resonance in Cr$\sb2$O$\sb3$ with that of the Mott-Hubbard oxides Ti$\sb2$O$\sb3$ and V$\sb2$O$\sb3$, and differences from those of the charge-transfer oxides MnO, Fe$\sb2$O$\sb3$, CoO, NiO and CuO, it is suggested that Cr$\sb2$O$\sb3$ is a Mott-Hubbard insulator. However, configuration-interaction cluster calculations were applied to study the nature of the satellite in the Cr 2p core-level XPS spectrum. It is argued that the satellite can be understood as a charge-transfer satellite, and Cr$\sb2$O$\sb3$ is found to be actually situated at the boundary between the Mott-Hubbard and the charge-transfer regimes. The values of the charge-transfer energy, $\Delta$, the Coulomb correlation energy, U, and the ligand 2p-cation 3d hybridization energy, T, found from fitting the Cr 2p core-level XPS spectrum were used to analyze the valence-band UPS spectrum. The comparison between the experimental spectrum and the theoretical prediction is good.
520 $a Interestingly, defective Cr$\sb2$O$\sb3$ (1012) surfaces are found to preferentially lose Cr upon Ar$\sp+$-ion bombardment, while most of the 3d-transition-metal oxides that have been studied tend to lose O rather than their metal cations. The surface electronic structure is modified by chromium-vacancy surface defects.
520 $a Surface Cr vacancy defects only cause an insignificant change in SO$\sb2$ adsorption characteristics on Cr$\sb2$O$\sb3$ (1012). The SO$\sb2$ adsorption on both nearly perfect and defective Cr$\sb2$O$\sb3$ (1012) surfaces at room temperature is associative and very weak, yielding a small S 2p peak after a large SO$\sb2$ exposure. However, it is found that the reactivity of SO$\sb2$ is somewhat weaker on the defective Cr$\sb2$O$\sb3$ (1012) surface, as compared to that on the cleaved surface. This shows that the role of Cr vacancies in SO$\sb2$ adsorption is very different from that of oxygen vacancies on the other 3d-transition-metal oxides, since surface oxygen vacancies are, in general, known to enhance the reactivity toward SO$\sb2$.
520 $a Unlike Cr$\sb2$O$\sb3$, oxygen-vacancy defects on reduced NiO (100) play an important role in SO$\sb2$ adsorption. SO$\sb2$ reacts only weakly with the stoichiometric NiO (100) surface at room temperature, yielding associatively adsorbed SO$\sb2$ molecules. In contrast, the interaction of SO$\sb2$ with the reduced NiO (100) surface is much stronger. At room temperature, the SO$\sb2$ adsorption on reduced NiO (100) is both associative and dissociative. It was found that the dissociation is due to a thermally activated mechanism that involves adsorption at oxygen-vacancy sites only.
520 $a A simple approach has been developed that includes explicitly the secondary-electron cascade process in the determination of inelastic backgrounds in low-energy electron spectra such as UPS. The new approach fits the spectra much better than does the iterative integral background, which is generally used in higher-energy spectroscopies such as XPS. While the new approach gives a good description of the inelastic background in UPS spectra from transition-metal oxides for low photon energies, discrepancies are found between the computed and actual backgrounds for UPS spectra taken at intermediate photon energies. The reason for this may have to do with experimental parameters. (Abstract shortened by UMI.).
590 $a School code: 0265.
650 4 $a Condensed matter physics. $3 3173567
650 4 $a Inorganic chemistry. $3 3173556
690 $a 0611
690 $a 0488
710 2 $a Yale University. $3 515640
773 0 $t Dissertation Abstracts International $g 56-03B.
790 $a 0265
791 $a Ph.D.
792 $a 1994
793 $a English
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=9523194