纳米柱状多孔WO_(3-x)/TiO_(2)薄膜的电致变色性能

Electrochromic Properties of Nano-columnar Porous WO_(3-x)/TiO_(2) Thin Films

采用反应磁控溅射在掠射角度α=0°和α=80°的条件下制备氧化钨(WO_(3-x))薄膜,然后在其表面沉积二氧化钛(TiO_(2))。利用X射线衍射仪(XRD)、场发射扫描电镜(FE-SEM)和X射线光电子能谱仪(XPS)对WO_(3-x)/TiO_(2)薄膜的晶体结构、表面/断面形貌以及表面化学成分进行表征。在三电极体系1 mol/L LiClO_(4)/PC溶液中,采用电化学工作站和紫外-可见分光光度计测试了WO_(3-x)/TiO_(2)薄膜的电致变色性能。XRD结果表明,WO_(3-x)/TiO_(2)薄膜为非晶态结构,与掠射角度无关。当掠射角度为80°时,获得了纳米柱状多孔薄膜。从W 4f和Ti 2p的XPS谱图确认氧化钨为亚化学计量比的WO_(3-x),而氧化钛为满足化学计量比的TiO_(2)。与致密薄膜相比,纳米柱状多孔薄膜需要较低的驱动电压且具有较快的响应速度。纳米柱状多孔薄膜的电荷容量为83.78 mC,是致密薄膜电荷容量30.83 mC的2倍以上。在±1.2 V驱动电压下,注入和脱出离子扩散速率分别为D_(in)=5.69×10^(-10)cm^(2)/s和D_(de)=5.08×10^(-10)cm^(2)/s。与纯WO_(3)薄膜相比,WO_(3-x)/TiO_(2)薄膜的电致变色循环稳定性更好。纳米柱状多孔薄膜在可见光范围内具有较大的光调制幅度,因此其光密度变化(ΔOD)大于致密薄膜。

Tungsten oxide(WO_(3-x))thin films were fabricated by reactive magnetron sputtering at glancing angleα=0°orα=80°,and then titanium oxide(TiO_(2))was deposited on it.X-ray diffraction(XRD),field emission scanning electron microscopy(FE-SEM)and X-ray photoelectron spectroscopy(XPS)were employed to characterize the crystal structure,surface/cross-section morphologies,and surface chemical composition of the WO_(3-x)/TiO_(2) thin films.Electrochromic properties of the WO_(3-x)/TiO_(2) thin films were measured by electrochemical workstation in three-electrode system with 1 mol/L LiClO_(4)/PC solution and UV-Vis spectrophotometer.Results reveal that the WO_(3-x)/TiO_(2) thin films present totally amorphous structure independent on glancing angles.As the glancing angle is kept at 80°,the nano-columnar porous thin film is obtained.Substoichiometric tungsten oxide(WO_(3-x))and stoichiometric titanium oxide(TiO_(2))are confirmed by XPS spectra of W 4f and Ti 2p,respectively.Compared with the dense thin film,the nano-columnar porous film needs a lower driving potential and presents faster response.The charge capacity of the nano-columnar porous film is calculated to be 83.78 mC,which is over twice higher than 30.83 mC of the dense film.The intercalation and deintercalation ion diffusion rates are determined to be D_(in)=5.69×10^(-10) cm^(2)·s^(-1) and D_(de)=5.08×10^(-10) cm^(2)·s^(-1) at the applied potential±1.2 V,respectively.The electrochromic cycle of the nano-columnar porous WO_(3-x)/TiO_(2) thin film is more stable than that of pure WO_(3) thin film.The optical density variation(ΔOD)of the nano-columnar porous thin film is larger than that of the dense thin film due to the larger optical modulation amplitude in the whole visible wavelengths.