Study On The Electrodeposition And Fundamental Theory Of2D Zinc, ZnO And Mg_xZn_1-xO Nano-Films

Zinc has been widely uesd in indurstrial applications. This thesis focuses on Zincand its oxide ZnO. Ultrathin transition-metal films formed on foreign solid surfaceshave received increasing attention during the past years. Considerable theoretical andexperimental efforts have been devoted to the zinc underpotential deposition （UPD）process. Besides, ZnO is a direct-gap semiconductor material with a wurtzite structure.Due to its various advantages, such as abundance, non-toxicity, good stability in plasmaetc, it is considered as the most promising substitute transparent conductive oxide（TCO）for widely used, scarce and expensive ITO. ZnO thin film can be widely applied inopto-electronic fields such as solar cell, liquid crystal display, light-emitting devices,gas sensor etc, so it has gained great attention in recent years. Comparing to traditionalmethods for the fabrication of compound semiconductor films, electrochemicaldeposition method presents several advantages as: simple, economical and efficient. Themain aspects of this work are as following:The UPD of zinc from very alkaline media on Au substrate has been studied byfirst-principles density functional theory （DFT） calculations and electrochemicalmethods. The results showed that zinc can be deposited to Au surface by UPD. Theanalysis of the experimental data clearly showed the presence of UPD process thatstarted at-0.935V vs.SCE, and the variation in the metalion concentration may affectthe kinetics of the UPD process.The potentiostatic transients exhibit a two-dimensional（2D） instantaneous nucleation and growth mechanism, which limited by theincorporation of adatoms. Specific hydroxyl adsorption exerts an important influence oncourse of upd of zinc on Au.ZnO thin films have been prepared on indium tin oxide （ITO） substrate byelectrochemical deposition. These films were mainly studied in terms of the influence ofapplied conditions such as deposition voltage, time, temperature and concentration ontheir structural and optical properties. The optimal deposition conditions are: deposit theZnO films in≤0.1mol/L Zn（NO₃）₂aqueous solution, which temperature regulated at65°C, ranging the deposition time from10to minute, and the deposition voltage isapproximately-1.0V. It is conducive to the formation of low-dimensional ZnOnanostructures by adding suitable surfactants or Cl.Using first-principles methods based on density functional theory and pseudopotentials, a study related to native point defects in ZnO and electronic structureof Mg-doped ZnO has been performed. The Mg_xZn_1-xO （0≤x≤0.250） films wereprepared on indium tin oxide （ITO） substrate using the optimal electrochemicaldeposition conditions. The calculated conclusions reveal that oxygen antisites, oxygeninterstitials and zinc vacancies behave as acceptors while zinc antisites and zincinterstitials are donors. Furthermore, the formation energy of zinc interstitials is smallest.As a result, the zinc interstitials are the main reason why the undoped ZnO is n typesemiconductor. The result indicated the Mg_xZn_1-xO film is maintaining the ZnO hexagonspiauterite structure, and the band gap of ZnO broadens with increasingMg-dopingconcentrations. Our work shows that the bottom of conduction band is determined bythe Zn4s electron states which can shift to a higher energy due to Mg-doping.