Structure of amorphous thin films of WO3 and MoO3

Ramāns, G. M.; Gabrusenoks, J.; Lūsis, A.; Patmalnieks, Aloizijs

doi:10.1016/s0022-3093(87)80504-5

Cited by 49 publications

(16 citation statements)

References 4 publications

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“…This result was expected because, owing to efficient cooling, the substrate temperature was far below the temperatures usually reported for the tungsten oxide amorphous-crystalline transition ͑typically 350-370°C͒. 9 In all our depositions, the temperature of the copper substrate holder did not exceed 45°C, although the substrate temperatures were probably greater than this, due to the lower thermal conductivities of silicon and glass compared to that of copper.…”

Section: Resultssupporting

confidence: 47%

Tungsten Oxide Films of High Electrochromic Efficiencies Obtained by Deposition

Scarmínio

Moraes

Dias

et al. 2003

Electrochem. Solid-State Lett.

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Amorphous tungsten oxide films of high electrochromic efficiency were produced by a chemical vapor deposition technique in which the precursors of film formation are generated at the surface of a heated tungsten filament by reactions of tungsten with oxygen. The film deposition rate was determined as a function of the filament temperature and oxygen pressure. Molecular structure investigations using X-ray photoelectron spectroscopy revealed that the tungsten oxide was in the WO 3 stoichiometry. The electrochromic properties of the films were studied for Li ϩ intercalation. Optical efficiencies as high as 78 and 125 cm 2 /C at 632.8 and 950 nm, respectively, and absorbance changes from 0.07 to 1.1 were measured between the bleached and the colored states at 632.8 nm.Tungsten oxide films find application in electrochromic devices, 1 gas sensors, 2 and electrocatalysis. 3 The electrochromic effect, particularly, has been extensively investigated in these films as they present one of the best optical performances among the inorganic electrochromic compounds. 4,5 Several deposition techniques such as sputtering, 6 thermal evaporation, 7 and plasma-enhanced chemical vapor deposition 8 have been used to obtain electrochromic tungsten oxide films. Recently, we developed a new deposition method, called hot filament metal oxide deposition ͑HFMOD͒, using a tungsten filament heated in a rarefied oxygen atmosphere. The film is formed on a substrate positioned near the filament and the deposition rate is controlled by the filament temperature and the oxygen pressure. Both the thermochemistry of the process and the kinetics of film formation are currently under investigation. It is clear, however, that the film is formed from volatile W x O y precursors generated on the heated tungsten surface in reactions between oxygen and tungsten.This work describes the electrochromic properties of tungsten oxide films obtained by HFMOD. Because the deposition rate is of practical interest in thin-film deposition and the crystalline and molecular structure usually play important roles in electrochromic properties, this paper also includes studies of these parameters. The deposition rate was investigated as a function of the filament temperature and oxygen pressure while the crystalline and molecular structure were characterized by X-ray diffractometry ͑XRD͒ and X-ray photoelectron spectroscopy ͑XPS͒, respectively. The electrochromic properties of the coatings were studied for Li ϩ intercalation, using an electrochemical cell coupled with an optical setup. The films exhibited wide changes in optical absorbance, excellent optical and electrochemical reversibility, and very large electrochromic efficiencies. Figure 1 is a schematic representation of the deposition apparatus ͑tungsten filament, substrate, and other accessories͒ mounted inside a vacuum chamber. The filament was heated resistively by a current supply to high temperatures while oxygen was admitted into the chamber via an electronic mass flowmeter. Pressure measurements were made u...

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Section: Resultssupporting

confidence: 47%

Tungsten Oxide Films of High Electrochromic Efficiencies Obtained by Deposition

Scarmínio

Moraes

Dias

et al. 2003

Electrochem. Solid-State Lett.

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“…Now let us review the coloration spectra of the reported molybdenum bronzes within the framework of the polaron model with some more lucidity. On the basis of infrared, 104 and Raman data, 105,106 which supports electron localization, 28,107,108 optical coloration data can either be interpreted in terms of the intervalence charge-transfer transition mechanism 11,101,109 or in terms of polaronic-absorption processes. 15,47 However, the evidences for small polarons have been reported in amorphous H x WO 3 by Wittwer et al, 15 Schirmer et al, 47 and Yoshimura.…”

Section: Summary and Discussionmentioning

confidence: 83%

Optical and electrochromic properties of annealed lithium-molybdenum-bronze thin films

Hussain

2002

Journal of Elec Materi

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Optical band gaps, Urbach inverse slopes, and coloration bands of various samples of annealed, microcrystalline Li x MoO 3 -bronze thin films in the concentration range 0 Ͻ x Ͻ 0.6 were determined over the photon energy range from 0.4 eV to 4.2 eV. On investigation, it is learned that the measured, optical band gaps do not shift rigidly over the annealing temperature range 293 Յ T Յ 423 K and, therefore, do not reveal the Burstein-Moss effect or reflect any stable, crystallographic phase transformation during any investigated annealing cycle. A model relating the temperature-dependent optical gap to the real part of the refractive index has also been developed, and this model fits very well to the annealed data within a maximum error of about 20%. Next, using an oscillator model, a phonon energy of ϳ0.08 eV was obtained, which is very close to the characteristic phonon energy of the material, MoO 3 . Using this model, it becomes more certain that the contributions to the Urbach absorption edge for the annealed-molybdenum bronzes are coming from the structural and compositional disorder. In another finding, it was found that the absorption-peak energy for the annealed data was about 1.5-1.6 eV, which is still broad and asymmetrical, and therefore, it is almost of the Mo 6ϩ (or Mo 4ϩ )-Mo 5ϩ intervalence or polaronic type. Using the polaron model, the half-bandwidth of the coloration bands of investigated, annealed Li x MoO 3 -thin films was found to be almost constant, which is consistent with the nonrigid band behavior.

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“…For such reasons different spectra are obtained by using different deposition techniques, or even changing the parameters within a chosen method. However, the common features of the amorphous films are a broad band peaked at slightly below 800 cm -~ and another one at about 950 cm -~, usually attributed to the terminal W-O bonds [10][11][12][13]. Our pure WO3 films, obtained by reactive sputtering with the parameters listed above, show high intensity ratio between the 950 cm -a band and the broad band at about 800 cm -~, attributed to the bulk W-O bond vibrations.…”

Section: Raman Measurementsmentioning

confidence: 74%

Sputtering deposition and characterization of Ru-doped WO3 thin films for electrochromic applications

Cazzanelli

Castriota

Kalendarev

et al. 2003

Ionics

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Abstract. Mixed tungsten-ruthenium oxide thin films were prepared for the first time by de magnetron co-sputtering technique and were studied by cyclic voltammetry, optical transmission measurements, Raman spectroscopy and the W L 3 and Ru K edges X-ray absorption spectroscopy (XAS) in comparison with pure WO3 films. The Ru concentration was varied in the range from 0 to 28 at.%. XAS results suggest that the average local structure around both tungsten and ruthenium ions remains unchanged within experimental accuracy in all samples, moreover, for tungsten ions, it resembles that of pure WO3 films. However, the presence of the ruthenium ions affects the electrochemical and optical properties of the films. Our results suggest that mixed films are formed by tungsten trioxide grains surrounded by ruthenium oxide phase.

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Structure of amorphous thin films of WO3 and MoO3

Cited by 49 publications

References 4 publications

Tungsten Oxide Films of High Electrochromic Efficiencies Obtained by Deposition

Tungsten Oxide Films of High Electrochromic Efficiencies Obtained by Deposition

Optical and electrochromic properties of annealed lithium-molybdenum-bronze thin films

Sputtering deposition and characterization of Ru-doped WO3 thin films for electrochromic applications

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