Reaction mechanism and optimal conditions for preparation of high-quality vanadium oxide films by organic sol–gel for optoelectronic applications

Abstract

Although vanadium oxides (VO x ) are important functional materials for academic research and industrial applications, the reaction mechanism of VO x prepared by organic sol–gel remains unclear. In order to investigate this mechanism, VO x organic sols were reacted at different temperatures, by which various VO x thin films were prepared. The products were systematically characterized by infrared spectroscopy, Raman spectroscopy, UV–vis spectroscopy, thermogravimetric analysis, scanning electron microscopy, x-ray diffraction, and a high resistance meter. Results reveal that vanadium alkoxides are created through an alcoholysis reaction of V2O5 powder and isobutyl alcohol, and then a condensation reaction of the vanadium alkoxides leads to the formation of VO x networks. The as-prepared sols are strongly temperature-dependent, causing different chemical structures and physical properties for the resulting VO x films. Particularly, a moderate temperature of 110 °C prompts both alcoholysis and condensation reactions, and thus the VO x films that are produced by the sol reacted at 110 °C possess a low resistivity of 23 Ω cm, a high temperature coefficient resistance (TCR) of −3.2% K−1, and a low average transmittance of 54% in 580–1100 nm, compared with those prepared by the sols reacted at lower or higher temperatures. Therefore, 110 °C is a desirable sol temperature for producing VO x films serving as high-quality bolometric materials for uncooled infrared detectors. This work discloses not only the reaction mechanism of VO x films prepared by organic sol–gel, but also the route to yield desirable VO x films for optoelectronic applications.

Single-Walled Carbon Nanotube-Controlled Meyer–Neldel Rules in Vanadium Oxide Films for Applications as Thermistor Materials in Sensors and Detectors

“…This suggests that the chemical reactions for VO x organic gels during annealing in atmosphere at high temperatures are different from those for pure VO x in the similar conditions. For pure VO x , more O atoms in air will chemically react with V, thus causing the formation of VO x with higher valence states of V. But if VO x organic gel is heated, the decomposition of the VO x organic gel leads to the creations of numerous reductive gases, such as CO, H, R • radicals, and so forth . Such reductive gases suppress the chemical reactions of O 2 in air with V, and thus lower valence states of V are formed, as in our cases.…”

“…For pure VO x , more O atoms in air will chemically react with V, thus causing the formation of VO x with higher valence states of V. But if VO x organic gel is heated, the decomposition of the VO x organic gel leads to the creations of numerous reductive gases, such as CO, H, R • radicals, and so forth. 28 Such reductive gases suppress the chemical reactions of O 2 in air with V, and thus lower valence states of V are formed, as in our cases. Therefore, it was previously observed that annealing of VO x organic gel in atmosphere at higher temperature leads to the formation of VO x with lower valence states of V. 29 The XRD patterns of the VO x films annealed at different T (Figure 3) reveal transitions from VO x organic gels to amorphous VO x at low annealing T, and further to crystalline VO x at higher T, as observed by Livage.…”

“…If the annealing T is increased to 340 °C, a sharp peak at 12.4°, assigned to the (200) plane of V 2 O 5 , appears. But at a higher T of 370 °C, besides a much stronger peak at 12.4° for V 2 O 5 , another obvious but relatively weak peak at 17.5°, corresponding to the (301) plane of V 4 O 9 , was simultaneously detected, indicating enhanced crystallinity and partial reduction of V 5+ to low valence states of V, resulted from decomposition of the network structures of VO x organic gels and reconstruction of the V–O bonds . This suggests that the chemical reactions for VO x organic gels during annealing in atmosphere at high temperatures are different from those for pure VO x in the similar conditions.…”

“…But at a higher T of 370 °C, besides a much stronger peak at 12.4°for V 2 O 5 , another obvious but relatively weak peak at 17.5°, corresponding to the (301) plane of V 4 O 9 , was simultaneously detected, indicating enhanced crystallinity and partial reduction of V 5+ to low valence states of V, resulted from decomposition of the network structures of VO x organic gels and reconstruction of the V−O bonds. 28 This suggests that the chemical reactions for VO x organic gels during annealing in atmosphere at high temperatures are different from those for pure VO x in the similar conditions. For pure VO x , more O atoms in air will chemically react with V, thus causing the formation of VO x with higher valence states of V. But if VO x organic gel is heated, the decomposition of the VO x organic gel leads to the creations of numerous reductive gases, such as CO, H, R • radicals, and so forth.…”

Localized surface plasmons in platinum aluminide semi-shells

“…The alkali metals, lithium, potassium and sodium, can also sustain very strong plasmon resonances [8] but are extremely chemically reactive. For all these reasons there has been interest in trying to identify new materials that could be used in plasmonic applications [9][10][11][12][13][14][15][16].…”