Structural Evolution of MoO3 Thin Films Deposited on Copper Substrates upon Annealing: An X-ray Absorption Spectroscopy Study

Abstract

Structural changes of MoO3 thin films deposited on thick copper substrates upon annealing at different temperatures were investigated via ex situ X-Ray Absorption Spectroscopy (XAS). From the analysis of the X-ray Absorption Near-Edge Structure (XANES) pre-edge and Extended X-ray Absorption Fine Structure (EXAFS), we show the dynamics of the structural order and of the valence state. As-deposited films were mainly disordered, and ordering phenomena did not occur for annealing temperatures up to 300 °C. At ~350 °C, a dominant α-MoO3 crystalline phase started to emerge, and XAS spectra ruled out the formation of a molybdenum dioxide phase. A further increase of the annealing temperature to ~500 °C resulted in a complex phase transformation with a concurrent reduction of Mo6+ ions to Mo4+. These original results suggest the possibility of using MoO3 as a hard, protective, transparent, and conductive material in different technologies, such as accelerating copper-based devices, to reduce damage at high gradients.

A Two‐dimensional Amorphous Plasmonic Heterostructure of Pd/MoO3‐x for Enhanced Photoelectrochemical Water Splitting Performance

“…The more positive and higher line intensities represent the positive oxidation state of Mo in MoO 3‐x , compared with that of Mo foil, resulting from Mo−O bonds leading the electron transfer from Mo to O [7b] . For Pd/MoO 3‐x, the higher intensity of the pre‐edge peak feature indicating that the valence of Mo is increased, which is in agreement with more Mo 6+ state in Mo XPS of Pd/MoO 3‐x [18] . The XANES spectral shape of nanosheets shows apparent broadening, implying the larger structural disorder for MoO 3‐x .…”

Metal‐Organic Fragments with Adhesive Excipient and Their Utilization to Stabilize Multimetallic Electrocatalysts for High Activity and Robust Durability in Oxygen Evolution Reaction

“…In the XANES spectra, the intense pre‐edge peak at 20 005 eV implies that hexavalent Mo promoted the 1s–4d quadruple transition. [ 29 ] The k 3 ‐weighted normalized EXAFS spectra supported the presence of MoO bonds within octahedrally coordinated mononuclear MoO 6 without additional shells. Therefore, mononuclear MoO 6 was the dominant compound deciding the morphology and composition and played the most crucial role in forming FeNiMo.…”

Incorporating MoO3 Patches into a Ni Oxyhydroxide Nanosheet Boosts the Electrocatalytic Oxygen Evolution Reaction

“…As shown in Figure d, the absorption edges of the Mo K-edge XANES spectra for MoO 2 , MoO 3 , and NiMoNS locate at higher energies than that of Mo-foil. This is understandable, considering that the Mo in MoO 2 , MoO 3 , and NiMoNS are in oxidation states. − A pre-peak at 19 995 eV appears on the Mo K-edge XANES spectrum for MoO 3 , and is caused by the mixing of the 2p orbital of O atom with the 5p and 4d orbitals of Mo atom in MoO 3 . − The pre-peak at 19 995 eV is not observed for MoO 2 . On the Mo K-edge XANES spectrum of NiMoNS, the pre-peak at 19 995 eV is present but becomes smaller than that of MoO 3 , implying that parts of Mo 6+ are reduced to Mo 5+ on NiMoNS. − In EXAFS spectra (Figure e), the peaks of NiMoNS locate between MoO 2 and MoO 3 .…”