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The Synchrotron Radiation Study Of The Optoelectronic Properties In Tungsten Trioxide And The Related Device Applications

Posted on:2024-01-16Degree:DoctorType:Dissertation
Country:ChinaCandidate:C L HuFull Text:PDF
GTID:1520306932457114Subject:Nuclear Science and Technology
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Tungsten trioxide(WO3)is a traditional transition metal oxide that has attracted substantial attention due to its potential applications in various fields such as electrochromics,photodegradation catalysis,energy storage batteries,and gas detection.Nornally WO3 shows rich crystal and phase structures,which can be interconverted with different temperature,leading to changeable energy gaps from 2.6 eV to 3.2 eV.Furthermore,the intercalation of extrinsic ions will cause metal-insulating phase transitions in WO3,accompanied by significant changes of the macroscopic properties,such as crystal structure,visible and infrared light transmittance and so on.These phasechange characteristics of WO3 modulated by ion doping show widely potential applications in intelligent display,electrochromism,memristor neural network,gas sensors and photocatalysis.The current thesis focuses on WO3 thin films,and systematically investigates the physicochemical process and electron state evolution of WO3 doped with Li+or H+by using the combination of in-situ electrical and optical tests,the synchrotron radiation spectroscopy characterizations and the first-principles calculations.Based on these studies,the device applications of WO3 thin film are developed,including the rewritable grating device based on WO3 periodic metalinsulating phase structures,the electric field modulated WO3 electrochromic smart window with enhanced performance,and the erasing circuits with WO3 material.The main results and findings of the thesis can be summarized as follows:(1)Rewritable gratings based on WO3 periodic metal-insulating phase structures.It is known that the fabrication of conventional relief gratings has become matured,while the obtained grating device has fixed periodicity and optical characteristics,which cannot be modulated or reprocessed subsequently.Based on the electron-proton synergistic doping technique initially proposed in our group,we can realize the selective hydrogenation-induced electron doping in WO3 film within the micrometer scale to produce the periodic metal-insulating phase stripes,thus leading to a modulated gratings device.The obtained WO3 grating device shows the unique advantages of periodically controllable and reusable properties,since it can be restored to the initial state by convenient annealing treatment just in air condition.In addition,by using the synchrotron radiation photoelectron spectroscopy(XPS),synchrotron infrared spectroscopy and first-principles calculations,we have revealed the process of WO3 phase transition induced by hydrogenation doping and the microscopic mechanism of hydrogenated electron doping induced phase changes in WO3 film.(2)WO3 electrochromic smart window with enhanced performance.For the WO3 smart window based on aqueous electrolyte,the electrochromic performance and response time are closely associated with the ion transport characteristics at the liquid/solid interface.In the current thesis,we have proposed a strategy to modify the traditional aqueous Li+/H+electrolytes by adding specific inert metal ions.The addition of inert metal ions to the aqueous electrolyte not only enhances the electrochromic performance,but also greatly broadens the electrochemical window,thereby avoiding the hydrogen bubbles generation during the electrochemical reaction.In addition,the inert metal ions in the electrolyte will involve the reversible electroplating process,resulting in an enhanced optical modulation in the visible band(500 nm and 700 nm)up to 77.5%and 70.4%,respectively.The device exhibits high stability and electrochromic efficiency after 1000 cycles.The synchrotron radiation based XPS tests have revealed that the chemical state change in WO3 is closely related to the ion intercalation driven by the electric field.(3)Erasing circuits with WO3 thin film.It is revealed that Li+or H+insertion into WO3 with high concentration can modulate it from the insulating state to metallic state,leading to the increased conductivity by six orders of magnitude.Combining the traditional lithographic technique and electron-proton synergistic doping route in an acid solution,selective hydrogenation of WO3 within the micron scale has been experimentally realized,leading to the reversible HxWO3 conductive nanowire and rewritable WO3 micro-nano circuit.This adjustable microcircuit fabrication method provides a good electrode template preparation process for microstructure electrical measurement,which not only avoids the complex lithography,etching,and plating electrode prepration during the electric measurements for microstructured sample,but also can be recycled used by high-temperature annealing treatment.
Keywords/Search Tags:tungsten trioxide, metal-insulator transition, magnetron sputtering, hydrogen doping, Synchrotron soft X-ray spectroscopy, Synchrotron infrared spectroscopy
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