Optical properties of amorphous thin films of MoO3 deposited by vacuum evaporation

Anwar, M.; Hogarth, C. A.

doi:10.1002/pssa.2211090213

Cited by 72 publications

(35 citation statements)

References 20 publications

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“…The structure of the films and the physical properties have shown to be markedly dependent on the substrate temperature. Anwar et al [6] and Muranaka [11] have suggested that the films of MoO3 and In203 prepared on substrates at a temperature of 270°C or higher are crystalline in character, but the present investigation showed that the mixed MoO3-In203 complex oxide films are amorphous in character at 270 ° C substrate temperature. Anwar et al [16] have studied MoO3 films at higher substrate temperatures and reported the formation of molybdenum species of lower oxidation state (i.e.…”

Section: Discussionmentioning

confidence: 76%

“…Molybdenum boats were used for the evaporation of both MoO3 and In203. All other techniques used to measure film thickness, cleaning of the substrates, raising the substrate temperature, absorption measurements, transmission electron microscopy and annealing the samples in vacuum are the same as described earlier by Anwar and Hogarth [6].…”

Section: Experimental Measurementsmentioning

confidence: 99%

“…Anwar et al [6] have studied the optical properties of MoO3 in thin film form and reported that band gap is decreased with the increase of thickness and substrate deposition temperature. In the present work we report some of the optical properties of MoO3-In203 thin films.…”

Section: Introductionmentioning

confidence: 98%

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The optical absorption edge in amorphous thin films of MoO3-In2O3

Anwar

Hogarth

1989

J Mater Sci

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A study of the effects of changes in composition, film thickness, substrate deposition temperature and annealing on the optical properties of MoO3-1n203 is presented. The results are found to be compatible with the reduction in the value of optical energy gap of these materials as the molar fraction of In203 in the MoO 3 thin film increases. This decrease of optical gap may be attributed to the incorporation of In(Ill) ions in an MoO 3 lattice. The decrease in optical band gap with increasing thickness may be interpreted in terms of the incorporation of oxygen vacancies which are also believed to be the source of conduction electrons in the MoO3-1n203 complex. The decrease of band gap with increasing substrate temperature may be attributed to the enhanced ordering of the samples and the decrease of band gap with annealing may be attributed to a reduction in the concentration of lattice imperfections.

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Section: Discussionmentioning

confidence: 76%

Section: Experimental Measurementsmentioning

confidence: 99%

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The optical absorption edge in amorphous thin films of MoO3-In2O3

Anwar

Hogarth

1989

J Mater Sci

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“…• The loss of transmittance or increase in absorptance in some of the annealed-thin films, over the photon energy range from 0.4 eV to 3.0 eV, is attributed not only to slight grain growth but also to the development of rough surfaces on the top layers of these samples. 46 • The Mo 5+ ions in the Mo 6+ oxide lattice are still responsible for the strong absorption band in the red part of the spectrum.The values of the thermal-activation energy of the reported data have been gauged in the range 0.37-0.41 eV, 22 which, in fact, still cover the semiconducting range. The opticalactivation energy has also been found to be of about 1.5-1.65 eV for the investigated annealed samples, and this is a characteristic signal of intervalence transfer or a polaronic type of absorption.…”

Section: Coloration Bands and Polaronic Modelmentioning

confidence: 99%

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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“…higher electronic conductivities of the molybdenum oxide did result in an improved battery performance. The colour of the sub-stoichiometric MOO3_ x compounds varied from light blue to dark blue [14]. At contrast, the colour of stoichiometric M o O 3 is pure white to light yellow, indicating a low electronic conductivity.…”

Section: Introductionmentioning

confidence: 97%

Sn(II)-Treated MoO3 as cathode material for rechargeable lithium batteries

Hashim

Wrodnigg

Askar

et al. 2002

Ionics

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Abstract.We report on the synthesis and structural, thermal and electrochemical characterisation of reduced molybdenum oxides with layered ~-MoO 3 type structure. The samples have been prepared by reactions of various amounts of water-free tin dichloride with fine-particulated orthorhombic molybdenum trioxide in n-hexane (non-aqueous media) or in aqueous media, which yielded materials with different Sn:Mo ratio. XRD investigations of these materials proved that the crystal structure of the layered o~-MoO 3 has been maintained after the reduction process. No crystalline impurity phases (e.g. tin oxides) could be detected by XRD.The tin-reduced samples exhibited a drastically improved cycling stability and capacity retention on cycling in 1 M LiC104 / propylene carbonate, i.e. the discharge capacities were well above 100 mAh g-~ after 20 cycles whereas the non-treated MoO 3 (reference sample) has retained only about 45 mAh g-~. At higher cycle numbers (approx. cycle 100) the discharge capacity of the reduced molybdenum oxides stabilises at a level of approx. 100 mAh g-1. This significant improvement of the rechargeability may be related to improved electronic conductivity and/or higher structural stabilisation of the layered MoO~ structure either due to (i) a coating of the MoO 3 particles with a protective thin layer of a tin containing compounds, and/or (ii) an amorphisation of the structure after reductive treatment. Further efforts of this study were devoted to a variation of the conductive carbon content in the electrode composition and to changes of cut-~ff voltages and current densities.

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Optical properties of amorphous thin films of MoO3 deposited by vacuum evaporation

Cited by 72 publications

References 20 publications

The optical absorption edge in amorphous thin films of MoO3-In2O3

The optical absorption edge in amorphous thin films of MoO3-In2O3

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

Sn(II)-Treated MoO3 as cathode material for rechargeable lithium batteries

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