A scanning probe microscopy study of the (001) surfaces of V2O5 and V6O13

Smith, Richard L.; Rohrer, Gregory S.; Lee, K.S.; Seo, Dong‐Kyun; Whangbo, M.‐H.

doi:10.1016/s0039-6028(96)00858-8

Cited by 58 publications

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References 45 publications

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

et al. 2007

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“…The calibration was checked for consistency with the scanners on other microscopes in our laboratory, which have been calibrated using surface crystallographic features. 16 The second consideration was the information density of the images from which the measurements were made. The topographic data were collected pixelby-pixel, and the lateral resolution limit was determined by the pixel spacing.…”

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confidence: 99%

Measuring the Influence of Grain‐Boundary Misorientation on Thermal Groove Geometry in Ceramic Polycrystals

Saylor

Rohrer

1999

Journal of the American Ceramic Society

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116

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We have used electron backscattered diffraction patterns to determine the misorientation of 201 adjacent pairs of grains in a magnesia polycrystal. The width and depth of the thermal grooves formed by these same grain boundaries were also measured by atomic force microscopy (AFM). By simulating the errors associated with the AFM observations and comparing our observations to existing data for magnesia and alumina, we show that, under appropriate experimental conditions, surface dihedral angles, relative grain-boundary energies, and surface diffusivities determined from AFM measurements are consistent with data acquired by more laborious techniques. Correlation of the grain-boundary misorientation and thermal groove geometry leads to the observation that grain boundaries with small misorientations, regardless of the rotation axis, have shallow thermal grooves and relatively low grain-boundary energies. Furthermore, numerous boundaries with relatively large misorientations but shallow thermal grooves correspond to special boundaries near coincident-sitelattice (CSL) misorientations. Finally, the data set indicates that factors other than the boundary misorientation, such as anisotropy of the surface energy and the grain-boundary tangent plane, play a role in determining the groove geometry.

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“…Such total electrondensity plots, calculated using the extended Hückel tightbinding (EHTB) electronic band-structure method [6], have been necessary to explain the observed STM and AFM images of a large number of organic conducting salts, transition-metal chalcogenides and transition-metal halides [4,5]. In ambient conditions, our previous observations of V 2 O 5 (0 0 1) single crystal surface [7,8] give result which is some different from the ideal surface as observed by Smith et al [9]; however, it is important to notice that sample used by Smith et al was doped with Na and it is well known that some alkali atoms remain in the first layers of the bulk [10] and so surface behaviours can be modified. Accordingly, we were interested by the investigation of the clean and lithiated V 2 O 5 (0 0 1) single crystal surface in order to examine the influence of the simplest alkali atoms (here the lithium) on the catalytic properties of the (0 0 1) plane.…”

Section: Introductionmentioning

confidence: 97%