The growth of ultrathin films of vanadium oxide on TiO2()

Agnoli, Stefano; Sambi, Mauro; Granozzi, G.; Castellarin‐Cudia, Carla; Surnev, S.; Ramsey, Michael G.; Netzer, F.P.

doi:10.1016/j.susc.2004.05.118

Cited by 31 publications

(62 citation statements)

References 19 publications

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“…[17][18][19][20][21] This process is similar in nature to Al Cho's early GaAs films grown using "epitaxy by periodic annealing;" 22 epitaxy by periodic annealing has also been used to grow epitaxial SrTiO 3 on Si. 23,24 No electrical transport measurements on the VO 2 films made by this procedure were reported by Sambi et al [17][18][19][20][21] Our films grown on TiO 2 (001) substrates by MBE following this procedure [17][18][19][20][21] were epitaxial, but did not exhibit an MIT. Only after utilizing ~ 80% pure distilled ozone 25 in place of molecular oxygen was an MIT observed.…”

Section: -13mentioning

confidence: 99%

Epitaxial growth of VO2 by periodic annealing

Tashman

Lee

Paik

et al. 2014

Applied Physics Letters

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We report the growth of ultrathin VO 2 films on rutile TiO 2 (001) substrates via reactive molecular-beam epitaxy. The films were formed by the cyclical deposition of amorphous vanadium and its subsequent oxidation and transformation to VO 2 via solid-phase epitaxy.Significant metal-insulator transitions were observed in films as thin as 2.3 nm, where a resistance change ΔR/R of 25 was measured. Low angle annular dark field scanning transmission electron microscopy was used in conjunction with electron energy loss spectroscopy to study the film/substrate interface and revealed the vanadium to be tetravalent and the titanium interdiffusion to be limited to 1.6 nm. Page 4 of 25The huge metal-insulator transition (MIT) exhibited by VO 2 in the vicinity of roomtemperature has made it a material of interest for uncooled microbolometer arrays, 1 gas sensing, 2 optical limiting, 3 and most recently MIT transistors. 4,5 In bulk single crystals this MIT occurs at a transition temperature (T c ) of 340 K and is accompanied by a change in structure from a hightemperature tetragonal form, to a low-temperature monoclinic form. 6 The change in resistivity through this transition in bulk VO 2 single crystals has been measured to be five orders of magnitude with a temperature hysteresis 0.5-1 K. 7 The change in resistivity in thick films (>100 nm) can be as high as four orders of magnitude, [8][9][10] but in thin films (<10 nm) is less than three orders of magnitude in all reports to date. 11-13While VO 2 presents an opportunity for emergent switching devices and sensors, its large carrier concentration (~10 In this paper we describe a process for the growth of ultrathin VO 2 films by reactive molecular-beam epitaxy (MBE) and show that they exhibit clear MITs in films as thin as 2.3 nm.We investigate the properties of these films with four-circle x-ray diffraction (XRD), low-angle annular dark field (LAADF) scanning transmission electron microscopy (STEM), electron energy loss spectroscopy (EELS), and electronic transport measurements. We also describe a standardized method for calculating the magnitude, hysteresis, and T c of these transitions using Savitsky-Golay smoothing derivatives. 16 All films in this paper were grown by MBE in a Veeco Gen10. X-ray diffraction spectra were collected with a Rigaku Smartlab system utilizing Cu Κ α1 radiation with a 220 Ge twobounce incident-beam monochromator and a 220 Ge two-bounce diffraction side analyzer crystal. STEM images were taken with an FEI Tecnai G 2 F20. VO 2 film thicknesses were calculated with data from Rutherford backscattering spectrometry (RBS) assuming the calibration films had bulk VO 2 density. Electrical transport data was taken using the standard four-contact van der Pauw method in a Quantum Design Physics Property Measurement System (PPMS) with contacts made using gold wire and silver paint. All growth temperatures were measured using a thermocouple in the substrate cavity, but not in contact with the substrate.During growth the film was monitored using reflection ...

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Section: -13mentioning

confidence: 99%

Epitaxial growth of VO2 by periodic annealing

Tashman

Lee

Paik

et al. 2014

Applied Physics Letters

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“…To elucidate the ODH reaction mechanism over vanadia on a molecular level, different model systems have been invoked that range from single crystals [22,23] and thin films prepared on TiO 2 [24][25][26], W(110) [27] , Au(111) [27][28][29][30][31] , Rh(111) [32][33][34] , and Cu 3 Au(100) [35][36][37] to vanadia particles deposited onto oxide substrates [21,38,39] including ceria [40][41][42]. In addition to experimental investigations, density functional theory h as been employed to explore the structural characteristics and reactivity towards methanol of model vanadia systems [43][44][45][46][47][48].…”

Section: Introductionmentioning

confidence: 99%

Relating methanol oxidation to the structure of ceria-supported vanadia monolayer catalysts

Abbott

Uhl

Baron

et al. 2010

Journal of Catalysis

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Abstract.Vanadia "monolayer"-type catalysts supported on reducible oxides such as ceria previously have shown high activity for the selective oxidation of alcohols. Here, a model system consisting of vanadia particles deposited on well-ordered CeO 2 (111) thin films has been employed. Scanning tunneling microscopy (STM), photoelectron spectroscopy (PES), and infrared reflection absorption spectroscopy (IRAS) were used to characterize the VO x /CeO 2 surface as a function of vanadia loading. The formation of isolated monomeric species as well as two-dimensional vanadia islands that wet the ceria support was directly observed by STM. The vanadia species exhibit V in a +5 oxidation state and expose vanadyl (V=O) groups with stretching vibrations that blue -shift from ~1005 cm -1 , to ~1040 cm -1 with increasing coverage.Temperature programmed desorption (TPD) of methanol revealed three peaks for formaldehyde production. One is correlated with reactivity on the ceria support (565-590 K). Another is correlated with reactivity on large vanadia particles (475-505 K) similar to that previously observed on vanadia/silica and vanadia/alumina model systems. A low temperature reaction pathway (~370 K) is observed at low coverage, which is assigned to the reactivity of isolated vanadia species surrounded by a reduced ceria surface. It is concluded that strong support effects reported in the literature for the real catalysts are likely related to the stabilization of small vanadia clusters by reducible oxide supports.

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“…The rutile phase has been more extensively studied than the two others and several microscopic studies were carried out under ultra-high vacuum (UHV) conditions and 3 with preliminary treatments (Ar + -ion bombardment, irradiation, high temperature), allowing a detailed knowledge of some selected crystallographic faces at the atomic level in terms of relaxation, reconstruction and defects [6][7][8][9][10][11][12]. Then, many metal and metal oxide overlayer growth [13][14][15][16][17][18], organic and inorganic molecule adsorptions [19][20][21][22][23][24][25][26], have also been studied and the surface chemistry on this phase was abundantly investigated. Among the low index faces naturally present in the rutile phase powder, the (110) face was found as the most stable one [27,28] and thus has been much more studied than the others.…”

Section: Introductionmentioning

confidence: 99%

Combined investigation of water sorption on TiO2 rutile (110) single crystal face: XPS vs. periodic DFT

et al. 2007

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XPS and periodic DFT calculations have been used to investigate water sorption on the TiO 2 rutile (110) face. Two sets of XPS spectra were collected on the TiO 2 (110) single crystal 2 clean and previously exposed to water: the first set with photoelectrons collected in a direction parallel to the normal to the surface; and the second set with the sample tilted by 70°, respectively. This tilting procedure promotes the signals from surface species and reveals that the first hydration layer is strongly coordinated to the surface and also that, despite the fact that the spectra were recorded under ultra-high vacuum, water molecules subsist in upper hydration layers. In addition, periodic DFT calculations were performed to investigate the water adsorption process to determine if molecular and/or dissociative adsorption takes place.The first step of the theoretical part was the optimisation of a dry surface model and then the investigation of water adsorption. The calculated molecular water adsorption energies are consistent with previously published experimental data and it appears that even though it is slightly less stable, the dissociative water sorption can also take place. This assumption was considered, in a second step, on a larger surface model where molecular and dissociated water molecules were adsorbed together with different ratio. It was found that, due to hydrogen bonding stabilisation, molecular and dissociated water molecules can coexist on the surface if the ratio of dissociated water molecules is less than ≈ 33 %. These results are consistent with previous experimental works giving a 10-25 % range.

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The growth of ultrathin films of vanadium oxide on TiO2()

Cited by 31 publications

References 19 publications

Epitaxial growth of VO2 by periodic annealing

Epitaxial growth of VO2 by periodic annealing

Relating methanol oxidation to the structure of ceria-supported vanadia monolayer catalysts

Combined investigation of water sorption on TiO2 rutile (110) single crystal face: XPS vs. periodic DFT

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