Abstract:A modified spray pyrolysis technique is used for preparing α‐MoO3 thin films after subsequent heat treatment at a relatively low temperature. The spray parameters are selected through a wide variety of elaboration conditions for best photochromic features. Different numbers of spraying and drying cycles are performed to investigate the thickness effect on the structural, morphological, optical, electrical, and photo‐electrical properties of the nanostructured α‐MoO3 films. These film samples are characterized … Show more
“…Similar behavior has been reported in the literature [16,26], whereas MoO 3 thin films have been prepared by a carbonyl chemical vapor deposition process at atmospheric pressure [16] and by sol-gel dip coating technique [26]. Nevertheless, the bandgap values of the film samples are inconsistent with those reported by Gesheva et al [16] and Chibane et al [26]. However, the inconsistency between these data is mainly due to the variety of the starting materials used, the deposition techniques utilized, and the preparation conditions applied [33].…”
Section: Optical Spectroscopic Analysissupporting
confidence: 91%
“…This is well consistent with the experimental observations stated in view of the XRD results, whereas the increase in the LTT temperature promotes crystallinity and consequently enlarge crystallite size that results in a reduction in the oxygen vacancies. Similar observations have been previously reported for α-MoO 3 thin films by Gesheva et al [16] and Chibane et al [26]. But further increase in the LTT temperature up to 625 °C significantly influences the optical properties of the produced α-MoO 3 film samples, making them with high transparency (i.e.…”
Section: Optical Spectroscopic Analysissupporting
confidence: 88%
“…Whereas, the density of oxygen vacancies as structural defects is expected to be abruptly reduced within the well crystallized film samples. Similar behavior has been reported in the literature [16,26], whereas MoO 3 thin films have been prepared by a carbonyl chemical vapor deposition process at atmospheric pressure [16] and by sol-gel dip coating technique [26]. Nevertheless, the bandgap values of the film samples are inconsistent with those reported by Gesheva et al [16] and Chibane et al [26].…”
Section: Optical Spectroscopic Analysissupporting
confidence: 73%
“…Furthermore, molybdenum trioxide has been widely studied a high chemically stable oxide for finding application in sensing [11], catalysis [12] and lithium-ion battery [13]. Many different deposition techniques have been developed to prepare α-MoO 3 thin films, including DC magnetron sputtering [14], laser thermal evaporation technique [15], carbonyl chemical vapor deposition [16], spray pyrolysis technique [17,18], sol-gel dip-coating [19], and spin-coating technique [20]. Amongst these techniques, the sol-gel based techniques (i.e.…”
Spin-coated MoO3 thin films were subsequently subjected to later thermal treatment (LTT) at different temperatures. The x-ray diffraction (XRD) results corroborated that the produced films crystallise in their α-phase with layer structure featured by preferential orientations along the (0k0) planes, and it was also revealed that the thermal energy gained by the later heat treatment plays a major role in enhancing crystallinity enlarging crystallite size. The optical spectroscopic analysis showed that in the visible and near-infrared regions, the average transmission of the film samples remarkably increases with increasing the LTT temperature, whereas the films prepared at 625 °C exhibits an average optical transmission of 79.92%. The optical bandgaps of the film samples were calculated to be of comparable values to the bulk one of α-MoO3 when increasing the LTT temperature from 375 to 525 °C, but it was found to be little greater than the bulk value by further increase in the LTT temperature. The DC electrical results revealed that raising the LTT temperature significantly enhances the electrical resistivity of the film samples, chiefly over the low working-temperatures. These results ascertained the realization of more than one conduction mechanism with different activation energies for the same film, and ramarkable upswings in activation energies were observed by increasing the LTT temperature. The photoconductivity (PC) analysis indicated the occurrence of various trapping processes associated with different photoexcitation energies. The PC analysis also corroborated that the highly resistive thin films exhibit much greater sensitivity to UV illumination compared with the remaining films, whereas the film prepared at the LTT temperature 625 °C presents the higher illumination current at the steady state condition exceeding the dark current value by a factor of 66.01.
“…Similar behavior has been reported in the literature [16,26], whereas MoO 3 thin films have been prepared by a carbonyl chemical vapor deposition process at atmospheric pressure [16] and by sol-gel dip coating technique [26]. Nevertheless, the bandgap values of the film samples are inconsistent with those reported by Gesheva et al [16] and Chibane et al [26]. However, the inconsistency between these data is mainly due to the variety of the starting materials used, the deposition techniques utilized, and the preparation conditions applied [33].…”
Section: Optical Spectroscopic Analysissupporting
confidence: 91%
“…This is well consistent with the experimental observations stated in view of the XRD results, whereas the increase in the LTT temperature promotes crystallinity and consequently enlarge crystallite size that results in a reduction in the oxygen vacancies. Similar observations have been previously reported for α-MoO 3 thin films by Gesheva et al [16] and Chibane et al [26]. But further increase in the LTT temperature up to 625 °C significantly influences the optical properties of the produced α-MoO 3 film samples, making them with high transparency (i.e.…”
Section: Optical Spectroscopic Analysissupporting
confidence: 88%
“…Whereas, the density of oxygen vacancies as structural defects is expected to be abruptly reduced within the well crystallized film samples. Similar behavior has been reported in the literature [16,26], whereas MoO 3 thin films have been prepared by a carbonyl chemical vapor deposition process at atmospheric pressure [16] and by sol-gel dip coating technique [26]. Nevertheless, the bandgap values of the film samples are inconsistent with those reported by Gesheva et al [16] and Chibane et al [26].…”
Section: Optical Spectroscopic Analysissupporting
confidence: 73%
“…Furthermore, molybdenum trioxide has been widely studied a high chemically stable oxide for finding application in sensing [11], catalysis [12] and lithium-ion battery [13]. Many different deposition techniques have been developed to prepare α-MoO 3 thin films, including DC magnetron sputtering [14], laser thermal evaporation technique [15], carbonyl chemical vapor deposition [16], spray pyrolysis technique [17,18], sol-gel dip-coating [19], and spin-coating technique [20]. Amongst these techniques, the sol-gel based techniques (i.e.…”
Spin-coated MoO3 thin films were subsequently subjected to later thermal treatment (LTT) at different temperatures. The x-ray diffraction (XRD) results corroborated that the produced films crystallise in their α-phase with layer structure featured by preferential orientations along the (0k0) planes, and it was also revealed that the thermal energy gained by the later heat treatment plays a major role in enhancing crystallinity enlarging crystallite size. The optical spectroscopic analysis showed that in the visible and near-infrared regions, the average transmission of the film samples remarkably increases with increasing the LTT temperature, whereas the films prepared at 625 °C exhibits an average optical transmission of 79.92%. The optical bandgaps of the film samples were calculated to be of comparable values to the bulk one of α-MoO3 when increasing the LTT temperature from 375 to 525 °C, but it was found to be little greater than the bulk value by further increase in the LTT temperature. The DC electrical results revealed that raising the LTT temperature significantly enhances the electrical resistivity of the film samples, chiefly over the low working-temperatures. These results ascertained the realization of more than one conduction mechanism with different activation energies for the same film, and ramarkable upswings in activation energies were observed by increasing the LTT temperature. The photoconductivity (PC) analysis indicated the occurrence of various trapping processes associated with different photoexcitation energies. The PC analysis also corroborated that the highly resistive thin films exhibit much greater sensitivity to UV illumination compared with the remaining films, whereas the film prepared at the LTT temperature 625 °C presents the higher illumination current at the steady state condition exceeding the dark current value by a factor of 66.01.
“…The reactor of this technique was designed to be composed of a galvanized chamber, and this safety enclosure was attached to a separate control box to control the spray parameters. More details concerning this technique can be found in our previous work [35]. A long optimization process was performed for the MCSP technique, and thus the values of the spray deposition parameters were selected through a wide variety of elaboration conditions.…”
Section: Starting Solutions and Spray-deposition Techniquementioning
Nanostructured SnO2 thin films were synthesized at various substrate temperatures using a modified chemical spray pyrolysis (MCSP) technique. The x-ray diffraction (XRD) patterns confirmed the presence of a rutile SnO2 with tetragonal structure for all the resultant film samples. The XRD results ascertained increase in the grain growth rate and consequent enhancement in crystallinity with increasing the spray-deposition temperature. The optical spectroscopic analysis revealed a significant increase in the optical transmission within the visible region as well as a considerable increase in the optical bandgap by increasing the deposition temperature. However, the spectral distribution of the absorption coefficient ascertained the dominance of direct allowed transition for the SnO2 film samples. The analysis of the current-voltage characteristic curves revealed that the variation of the spray-deposition temperature strongly influences the photosensitivity of the film samples. Based on the electrical results, these film samples reveal a semiconductor behaviour of the transport property over the entire investigated range of the working temperature, with two different conduction mechanisms. The optical and electrical results were combined to evaluate the influence of varying the deposition temperature on the figure of merit (FOM) factor for the SnO2 film samples.
Limited levels of UV exposure can be beneficial to the human body. However, the UV radiation present in the atmosphere can be damaging if levels of exposure exceed safe limits which depend on the individual the skin color. Hence, UV photochromic materials that respond to UV light by changing their color are powerful tools to sense radiation safety limits. Photochromic materials comprise either organic materials, inorganic transition metal oxides, or a hybrid combination of both. The photochromic behavior largely relies on charge transfer mechanisms and electronic band structures. These factors can be influenced by the structure and morphology, fabrication, composition, hybridization, and preparation of the photochromic materials, among others. Significant challenges are involved in realizing rapid photochromic change, which is repeatable, reversible with low fatigue, and behaving according to the desired application requirements. These challenges also relate to finding the right synergy between the photochromic materials used, the environment it is being used for, and the objectives that need to be achieved. In this review, the principles and applications of photochromic processes for transition metal oxides and hybrid materials, photocatalytic applications, and the outlook in the context of commercialized sensors in this field are presented.
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