Progression of reduction of MoO3 observed in powders and solution-processed films

Inzani, Katherine; Nematollahi, Mohammadreza; Selbach, Sverre M.; Grande, Tor; Vullum‐Bruer, Fride

doi:10.1016/j.tsf.2017.02.029

Cited by 34 publications

(12 citation statements)

References 59 publications

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“…In the case of the SCM and SMC designs, E gap drops in the same range from 2.74 to 2.60 eV and from 2.82 to 2.70 eV, respectively (see Figure a). For MoO 3 thin films, the slight increase in E gap with the annealing temperature has also been observed by other groups, which have deposited this oxide by different synthesis techniques. − This effect has been associated with a structural rearrangement of the MoO 3 lattice, specifically a reduction of point defects . In addition, our group recently found that the crystallization process in MoO 3 takes place at higher temperatures, with respect to annealing in air, when the thermal treatments are performed in inert atmospheres. , This information implies that, for the SMC system, the CdSe layer causes a slow rearrangement process in the MoO 3 lattice as compared to the case where MoO 3 is directly exposed to oxygen.…”

Section: Resultssupporting

confidence: 63%

“…30−32 This effect has been associated with a structural rearrangement of the MoO 3 lattice, specifically a reduction of point defects. 30 In addition, our group recently found that the crystallization process in MoO 3 takes place at higher temperatures, with respect to annealing in air, when the thermal treatments are performed in inert atmospheres. 25,33 This information implies that, for the SMC system, the CdSe layer causes a slow rearrangement process in the MoO 3 lattice as compared to the case where MoO 3 is directly exposed to oxygen.…”

Section: Resultsmentioning

confidence: 99%

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Effect of a CdSe Layer on the Thermo- and Photochromic Properties of MoO₃ Thin Films Deposited by Physical Vapor Deposition

et al. 2019

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The influence of a cadmium selenide (CdSe) layer on the thermochromic and photochromic properties of molybdenum trioxide (MoO 3 ) thin films was studied. The films were deposited on glass substrates by thermal evaporation in vacuum using two different bilayer configurations, namely, substrate/MoO 3 /CdSe (SMC) and substrate/CdSe/MoO 3 (SCM). The film thicknesses for the MoO 3 and CdSe layers were ca. 250 and 20 nm, respectively. The thermochromic effect was evaluated in the annealing temperature range from 25 to 225 °C, in the presence of air. The characteristic optical absorption band attributed to the color center formation, centered at 820 nm, indicated enhanced thermo-and photochromic effects for both bilayer systems relative to monolayer MoO 3 thin films. For the thermochromic effect, this improvement was more pronounced when CdSe was the upper layer, i.e., for the SMC system. Regarding the photochromic effect, the films were irradiated with UV light for several exposure times within the lapse of 30−180 min. While both bilayer systems presented better photochromic response than pure MoO 3 thin films, the SCM system exhibited better photochromic response. These results are explained in terms of the optical, structural, and surface chemistry properties of the films.

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Section: Resultssupporting

confidence: 63%

Section: Resultsmentioning

confidence: 99%

Effect of a CdSe Layer on the Thermo- and Photochromic Properties of MoO₃ Thin Films Deposited by Physical Vapor Deposition

et al. 2019

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“…The evolution of reduced phases is in agreement with a previous work on the progression of reduction of MoO3. 58 It should be noted that the band gaps given by the Tauc analysis in the previous work include the contributions from the sub-band gap states, such that the Tauc band gap decreases with the onset of reduced phases. Here, the optical analysis accounts for the sub-band gap states with the Gaussian oscillator.…”

Section: Resultsmentioning

confidence: 93%

Tailoring properties of nanostructured MoO3−x thin films by aqueous solution deposition

Inzani

Nematollahi

Selbach

et al. 2018

Applied Surface Science

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Molybdenum oxide films are required for a large range of optical, electronic and catalytic applications, and optimal film characteristics are similarly broad. Furthermore, the layered crystal structure of MoO3 is suited to nanostructuring, which can be adapted to enhance the film properties. Here, we present a simple, aqueous route to MoO3 thin films and attain nanostructured morphologies by control of solution parameters. Smooth and homogeneous thin films were achieved by control of the molecular species in solution by pH. The sensitivity of film quality to pH was demonstrated with the addition of PVA to the solution, which resulted in large spherical particulates on the surface. Film thickness was adjusted from 10 to 60 nm, whilst maintaining good film quality, by changing the solution concentration. Moreover, the grain size and nanocrystallite orientation varied with solution concentration. The importance of film morphology is revealed in the compositional changes of the films during hydrogen reduction, with differences in breakdown of film coverage and growth of reduced phases. Furthermore, spectroscopic ellipsometry was used to determine the optical properties of the films. This revealed changes in the dielectric function and band gap that were dependent on the level of reduction. The nanoscale morphologies presented demonstrate the potential to precisely control film morphology, dimensions, oxygen stoichiometry and phase composition by a low-cost wet chemical route.

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“…Formation of these reduced species involves a lattice rearrangement from corner-shared octahedra to an edge-shared octahedra with a shear structure. , Spevack and McIntyre reported that temperatures near 730 °C were required in order to reduce MoO 3 thin films, originally synthesized at a low temperature (250 °C), to MoO 2 . Inzani and co-workers investigated the reduction of MoO 3 powders and solution-processed films under dilute (5%) hydrogen gas. Shear defects, nucleation, and growth of reduced phases within the MoO 3 matrix were investigated.…”

Section: Introductionmentioning

confidence: 99%

“…2,19 Spevack and McIntyre 19 reported that temperatures near 730 °C were required in order to reduce MoO 3 thin films, originally synthesized at a low temperature (250 °C), to MoO 2 . Inzani and co-workers 20 MoO 3 powders and solution-processed films under dilute (5%) hydrogen gas. Shear defects, nucleation, and growth of reduced phases within the MoO 3 matrix were investigated.…”

Section: ■ Introductionmentioning

confidence: 99%

Polyelectrolyte-Assisted Oxygen Vacancies: A New Route to Defect Engineering in Molybdenum Oxide

et al. 2018

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The presence of oxygen vacancy sites fundamentally affects physical and chemical properties of materials. In this study, a dipole-containing interaction between poly(diallyldimethylammonium chloride) PDDA and α-MoO is found to enable high-concentrations of surface oxygen vacancies. Thermal annealing under Ar resulted in negligible reduction of MoO to MoO with x = 0.03 at 600 °C. In contrast, we show that the thermochemical reaction with PDDA polyelectrolyte under Ar can significantly reduce MoO to MoO with x = 0.36 (MoO) at 600 °C. Thermal annealing under H gas enhanced the substoichiometry of MoO from x = 0.62 to 0.98 by using PDDA at the same conditions. Density functional theory calculations, supported by experimental analysis, suggest that the vacancy sites are created through absorption of terminal site oxygen (O) upon decomposition of the N-C bond in the pentagonal ring of PDDA during the thermal treatment. O atoms are absorbed as ionic O and neutral O, creating Mo-v and Mo-v vacancy bipolarons and polarons, respectively. X-ray photoemission spectroscopy peak analysis indicates the ratio of charged to neutral molybdenum ions in the PDDA-processed samples increased from Mo/Mo = 1.0 and Mo/Mo = 3.3 when reduced at 400 °C to Mo/Mo = 3.7 and Mo/Mo = 2.6 when reduced at 600 °C. This is consistent with our ab initio calculation where the Mo-v formation energy is 0.22 eV higher than that for Mo-v in the bulk of the material and 0.02 eV higher on the surface. This study reveals a new paradigm for effective enhancement of surface oxygen vacancy concentrations essential for a variety of technologies including advanced energy conversion applications such as electrochemical energy storage, catalysis, and low-temperature thermochemical water splitting.

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Progression of reduction of MoO3 observed in powders and solution-processed films

Cited by 34 publications

References 59 publications

Effect of a CdSe Layer on the Thermo- and Photochromic Properties of MoO₃ Thin Films Deposited by Physical Vapor Deposition

Effect of a CdSe Layer on the Thermo- and Photochromic Properties of MoO₃ Thin Films Deposited by Physical Vapor Deposition

Tailoring properties of nanostructured MoO3−x thin films by aqueous solution deposition

Polyelectrolyte-Assisted Oxygen Vacancies: A New Route to Defect Engineering in Molybdenum Oxide

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Progression of reduction of MoO3 observed in powders and solution-processed films

Cited by 34 publications

References 59 publications

Effect of a CdSe Layer on the Thermo- and Photochromic Properties of MoO3 Thin Films Deposited by Physical Vapor Deposition

Effect of a CdSe Layer on the Thermo- and Photochromic Properties of MoO3 Thin Films Deposited by Physical Vapor Deposition

Tailoring properties of nanostructured MoO3−x thin films by aqueous solution deposition

Polyelectrolyte-Assisted Oxygen Vacancies: A New Route to Defect Engineering in Molybdenum Oxide

Contact Info

Product

Resources

About

Effect of a CdSe Layer on the Thermo- and Photochromic Properties of MoO₃ Thin Films Deposited by Physical Vapor Deposition

Effect of a CdSe Layer on the Thermo- and Photochromic Properties of MoO₃ Thin Films Deposited by Physical Vapor Deposition