Scanning tunneling microscopy/spectroscopy study of V2O5 surface with oxygen vacancies

Oshio, Takanori; Sakai, Yoshiyuki; Ehara, Shaw

doi:10.1116/1.587703

Cited by 21 publications

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“…The existence of oxygen vacancies at the perfect V 2 O 5 (010) surface has been confirmed by experiment [69][70][71][72][73] where scanning tunneling microscopy (STM) and angleresolved X-ray photoelectron spectroscopy (ARXPS) experiments suggest vacancies at vanadyl O(1) sites. [69][70][71] (In the following, we denote a vacancy created by removing oxygen from an O(X) site of the surface by O(X) vac .)…”

Section: Oxygen Vacancies At the Perfect V 2 O 5 (010) Surfacementioning

confidence: 76%

“…[69][70][71] (In the following, we denote a vacancy created by removing oxygen from an O(X) site of the surface by O(X) vac .) In contrast, high resolution electron energy loss spectroscopy (HREELS) data indicate that O(2) vac vacancies are predominant 72 while angleresolved ultraviolet photoelectron spectroscopy (ARUPS) hints at the presence of O(2) vac and/or O(3) vac vacancies.…”

Section: Oxygen Vacancies At the Perfect V 2 O 5 (010) Surfacementioning

confidence: 99%

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Elementary steps of the catalytic NOx reduction with NH3: Cluster studies on reactant adsorption at vanadium oxide substrate

Gruber

Hermann

2013

The Journal of Chemical Physics

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Extended cluster models together with density-functional theory are used to evaluate geometric, energetic, and electronic properties of different adsorbate species that can occur at a vanadium oxide surface where the selective catalytic reduction (SCR) of NO in the presence of ammonia proceeds. Here, we focus on atomic hydrogen, nitrogen, and oxygen, as well as molecular NO and NHx, x = 1, 4, adsorption at a model V2O5(010) surface. Binding sites, oxygen and vanadium, at both the perfect and reduced surface are considered where reduction is modeled by (sub-) surface oxygen vacancies. The reactants are found to bind overall more strongly at oxygen vacancy sites of the reduced surface where they stabilize in positions formerly occupied by the oxygen (substitutional adsorption) compared with weaker binding at the perfect surface. In particular, ammonia, which interacts only weakly with vanadium at the perfect surface, binds quite strongly near surface oxygen vacancies. In contrast, surface binding of the NH4 adsorbate species differs only little between the perfect and the reduced surface which is explained by the dominantly electrostatic nature of the adsorbate interaction. The theoretical results are consistent with experimental findings and confirm the importance of surface reduction for the reactant adsorption forming elementary steps of the SCR process.

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Section: Oxygen Vacancies At the Perfect V 2 O 5 (010) Surfacementioning

confidence: 76%

Section: Oxygen Vacancies At the Perfect V 2 O 5 (010) Surfacementioning

confidence: 99%

Elementary steps of the catalytic NOx reduction with NH3: Cluster studies on reactant adsorption at vanadium oxide substrate

Gruber

Hermann

2013

The Journal of Chemical Physics

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“…This surface exposes vanadyl (V O) double rows along the [010] direction [ Fig. 1(a)], which were observed also with scanning tunneling microscopy (STM) [10,11] and atomic force microscopy [12]. Surprisingly, the V O termination has been found also for the most stable, (0001) surface of V 2 O 3 [4,13,14], whereas the VO 2 110 surface appears to follow the respective bulk termination [1,4,15,16].…”

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confidence: 77%

“…They may involve the formation of mixed valence phases. In addition, several vanadium oxides undergo metal-to-insulator transitions (MIT), e.g., V 2 O 3 at 150 K, VO 2 at 340 K. These complex structural and electronic transformations may play a crucial role in the behavior of vanadia-based systems.Among the surface structures of vanadium oxides [4], the V 2 O 5 001 surface seems to be the most studied [3,[5][6][7][8][9][10][11][12]. This surface exposes vanadyl (V O) double rows along the [010] direction [ Fig.…”

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confidence: 99%

Surface Metal-Insulator Transition on a Vanadium Pentoxide (001) Single Crystal

et al. 2007

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In situ band gap mapping of the V 2 O 5 001 crystal surface revealed a reversible metal-to-insulator transition at 350-400 K, which occurs inhomogeneously across the surface and expands preferentially in the direction of the vanadyl (V O) double rows. Supported by density functional theory and Monte Carlo simulations, the results are rationalized on the basis of the anisotropic growth of vanadyloxygen vacancies and a concomitant oxygen loss driven metal-to-insulator transition at the surface. At elevated temperatures irreversible surface reduction proceeds sequentially as V 2 O 5 001 ! V 6 O 13 001 ! V 2 O 3 0001. DOI: 10.1103/PhysRevLett.99.226103 PACS numbers: 68.47.Gh, 68.35.ÿp, 73.20.ÿr Vanadium oxides represent an important class of materials with high potential in many technological applications based on their diverse temperature-dependent electronic, magnetic, and catalytic properties (e.g., [1][2][3][4] and references therein). There is a large variety of the vanadium oxide phases such as VO (V 2 , rocksalt structure),Depending on the ambient conditions and temperature, phase transformations between these oxides can occur. They may involve the formation of mixed valence phases. In addition, several vanadium oxides undergo metal-to-insulator transitions (MIT), e.g., V 2 O 3 at 150 K, VO 2 at 340 K. These complex structural and electronic transformations may play a crucial role in the behavior of vanadia-based systems.Among the surface structures of vanadium oxides [4], the V 2 O 5 001 surface seems to be the most studied [3,[5][6][7][8][9][10][11][12]. This surface exposes vanadyl (V O) double rows along the [010] direction [ Fig. 1(a)], which were observed also with scanning tunneling microscopy (STM) [10,11] and atomic force microscopy [12]. Surprisingly, the V O termination has been found also for the most stable, (0001) surface of V 2 O 3 [4,13,14], whereas the VO 2 110 surface appears to follow the respective bulk termination [1,4,15,16].Since the thermally induced transformations of vanadium oxides may be initiated at the surface and even be restricted to the surface layers, it is important to study their surface structures in the early stages of transitions when several structures may coexist. In this respect, STM combined with scanning tunneling spectroscopy (STS) can provide direct information on both geometrical and electronic structures of oxide surfaces (see, e.g., [17] ). We here report thermally induced reconstructions observed by STM/STS on a V 2 O 5 001 single crystal surface. Data show that V 2 O 5 , which is not known for the MIT in the bulk, exhibits, however, the MIT at the surface which proceeds through the formation and anisotropic growth of vanadyl-oxygen vacancies and is followed by an irreversible surface reduction. The experimental findings are supported by density functional theory (DFT) and

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“…Vacancies in vanadium oxide have been probed using a variety of spectroscopic techniques, such as scanning tunneling microscopy, 9,26,27 electron energy loss spectroscopy, 28,29 electron paramagnetic resonance studies, 16,12,23 X-ray absorption measurements, 30 and X-ray photoemission spectroscopy (XPS). 15,17 However, most of these techniques either require ultrahigh vacuum (UHV) or controlled environment for operation that makes it difficult to adapt it to 6 in-situ catalytic studies.…”

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confidence: 99%

Defect-induced Burstein-Moss shift in reduced V2O5 nanostructures

et al. 2016

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The main effects of oxygen vacancy defects on the electronic and optical properties of V 2 O 5 nanowires were studied through in-situ Raman, photoluminescence, absorption, and photoemission spectroscopy. Both thermal reduction and electrochemical reduction via lithium insertion leads to the creation of oxygen vacancy defects in the crystal that gives rise to new electronic mid-gap defect states at energy 0.75 eV below the conduction band edge. The defect formation results in delocalization and injection of excess electrons into the conduction band, as opposed to localized electron injection as previously suggested. Contrary to what is seen in most oxides, the presence of vacancy defects leads to band filling and an increase in the optical band gap of V 2 O 5 from 1.95 eV to 2.45 eV, which is attributed to the Burstein-Moss effect. Other observed changes in the optical properties are correlated to the changes in the electronic structure of the oxide as result of defect formation. Further, in-situ Raman measurements during the electrochemical reduction at room temperature show that the oxygen atom that is most readily reduced is the three-fold coordinated oxygen (O3). Reduction of V 2 O 5 through the formation of oxygen vacancy, V O , defects have been studied both by theoretical and experimental studies. 10,11,12,13,14,15 In this work, we address some of the key unanswered questions regarding the correlation between optical properties and electronic structure of The rise of absorbance in the NIR spectral range in reduced oxide is a result of optical excitation of V O defect related mid-gap states. In addition, using in-situ Raman measurements during reduction process, we show that the oxygen atom that most readily participates during electrochemical reduction at room-temperature and gets reduced is the three-fold coordinated oxygen (O3).Vacancies in vanadium oxide have been probed using a variety of spectroscopic techniques, such as scanning tunneling microscopy, 9,26,27 electron energy loss spectroscopy, 28,29 electron paramagnetic resonance studies, 16,12,23 X-ray absorption measurements, 30 and X-ray photoemission spectroscopy (XPS). 15,17 However, most of these techniques either require ultrahigh vacuum (UHV) or controlled environment for operation that makes it difficult to adapt it to 6 in-situ catalytic studies. Here, we use near-infrared photoluminescence (NIR-PL) and Raman spectroscopy that allows for study of vacancy defects and their interaction with redox species under in-operando electrochemical conditions at room temperature, as shown in our recent study. 31 The spectral range of various types of electronic transitions in V 2 O 5 is shown in Fig.1A.Representative PL spectra of stoichiometric and non-stoichiometric V 2 O 5 are shown in Fig.1B.The optical gap of nominally undoped V 2 O 5 is in the range of 1.9-2.5 eV and hence emission spectrum lies in the ultraviolet-to-visible part of the spectral range. In most TMOs, deviation from stoichiometry is a result of the presence of high density ...

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Scanning tunneling microscopy/spectroscopy study of V2O5 surface with oxygen vacancies

Cited by 21 publications

References 0 publications

Elementary steps of the catalytic NOx reduction with NH3: Cluster studies on reactant adsorption at vanadium oxide substrate

Elementary steps of the catalytic NOx reduction with NH3: Cluster studies on reactant adsorption at vanadium oxide substrate

Surface Metal-Insulator Transition on a Vanadium Pentoxide (001) Single Crystal

Defect-induced Burstein-Moss shift in reduced V2O5 nanostructures

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