【作者】 覃天庞；

【导师】 刘绍军；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2009， 硕士

【摘要】 有序介孔二氧化钛薄膜具有巨大的比表面积和有序的介孔结构,在染料敏化太阳能电池,光催化剂等领域有光明的应用前景,因此被广泛的研究。但是有序介孔二氧化钛薄膜在不同的温度和在不同的气氛下退火,特别是还原性气氛下退火对薄膜结构,以及薄膜中点缺陷对薄膜性能的影响却比较少而且不系统,而这些可能的结构和点缺陷浓度变化极有可能极大地影响薄膜的性能。本文采用TiCl₄和三嵌段共聚物F127分别作为前躯体和结构助进剂,用溶胶凝胶提拉膜方法合成出有序介孔二氧化钛薄膜。合成的薄膜分别在250℃,300℃,350℃,400℃,450℃下退火一个小时。合成的薄膜也分别在N₂,O₂,NH₃,H₂气氛下450℃退火一个小时。采用XRD,SEM和Raman光谱对在不同温度和气氛下退火的薄膜结构进行表征。用Photoluminescence光谱对在不同温度和气氛下退火薄膜的光致发光性能进行表征。XRD,SEM和Raman表征结果表明,合成的薄膜具有序的介孔结构,介孔呈蠕虫状且垂直于薄膜表面。对于在不同温度下退火的薄膜,在300℃以下为非晶态。随着退火温度的提高,薄膜的结晶度不断提高,薄膜的晶粒不断长大,薄膜表面粗糙度变大。薄膜在450℃退火具有完整的锐钛矿结构。对于在不同气氛下退火的有序介孔二氧化钛薄膜,薄膜主要呈锐钛矿结构。且在NH3气氛下薄膜晶粒和表面粗糙度最大,N掺杂进入薄膜;在O₂气氛下薄膜呈相对较多的金红石相。Photoluminescence表征的结果,薄膜都出现带边发光和激子发光带。在不同温度下退火的薄膜,随着退火温度的提高,Photoluminescence的强度不断减小。这是因为薄膜在300℃下为非晶,具有大量的缺陷作为电子空穴的复合中心。随着退火温度的升高,薄膜结晶度不断提高,缺陷不断减少。但是在450℃,薄膜展现一个强的激子发光带,这很可能归于退火温度提高薄膜表面粗糙度的提高产生大量氧空位。在H₂气氛下退火的薄膜具有最大的带边发光和激子发光,这主要归因于薄膜在H₂气氛下退火具有大量的表面缺陷,特别是H₂是还原气氛使薄膜产生大量的氧空位。在O₂气氛下退火的薄膜具有最低的带边发光和机子发光,这主要由于在O₂气氛下退火的薄膜呈相对较多的金红石相。相对于在空气下退火的有序介孔二氧化钛薄膜,在不同气氛下退火的薄膜在带边发光区出现红移,对于NH₃和N₂气氛退火,主要归因于N掺杂。而H₂和O₂气氛是由于产生缺陷能级使能隙变小。这些因退火温度和退火气氛的结构和点缺陷浓度变化对薄膜光致发光性能的影响,对研究和合成高效的染料敏化二氧化钛太阳能电池和高催化活性的二氧化钛薄膜光催化剂都具有有益的参考价值。更多还原

【Abstract】 Ordered mesoporous TiO₂ thin films is studied extensively because they have extremely large specific surface area and ordered mesoporous structure and have promising potential application in dye-sensitized solar cells, photocatalyst fields and so on. However, the changing structure and point defects concentration of ordered mesoporous TiO₂ thin films by annealing at different temperature and annealing in different atmosphere, especially reduction atmosphere is paid less attention. This structure and point defect concentration change of thin films may extremely change the properties of thin films. Here, we employed the TiCl4 and triblock copolymer F127 as precursor and structure-directing agent and synthesized ordered mesoporous TiO₂ thin films by sol-gel dip-coating method. The as-prepared thin films were annealed at 250℃, 300℃, 350℃, 400℃, 450℃in air for 1 hour, respectively. Another group as-prepared thin film were annealed in N₂, O₂, NH₃ and H₂ atmosphere at 450℃for 1 hour, respectively. The structure, crystallinity, crystallite size and surface roughness of thin films were characterized by XRD,SEM and Raman spectra. The emission properties of thin films influenced by different annealing temperature and different annealing atmosphere were characterized by PL spectrum.The results of XRD,SEM and Raman spectra show that the as-prepared thin films have ordered mesostrure. Mesopores are wormlike and normal to thin film surface. As for samples annealed at 250℃, 300℃, 350℃, 400℃, 450℃, thin films are amorphous when the annealing temperature is below 300℃. With the annealing temperature increasing, the crystallinity, crystallite size and surface roughness of thin films increase. Thin films annealed at 450℃were crystallized completely and exhibited the anatase phase. As for ordered mesoporous TiO₂ thin films annealed in N₂, O₂, NH₃ and H₂ atmosphere, they mainly show anatase structure. The crystallite size and surface roughness of thin films annealed in NH3 atmosphere are the largest and that may be attributed to N doped into thin films. More rutile peaks were observed in thin films annealed in O₂. PL results show that thin films all exhibit two emission bands. One is band-band PL, the other is excitonic PL. As for samples annealed in different temperature, with the temperature increasing, the intensity of photoluminescence decreases. It can be ascribed to point defect concentration of thin films decreasing due to the crystallinity of thin films increasing with temperature increasing. But when the annealing temperature is up to 450℃, a strong excitonic emission band appears. It is attributed to the large amount of oxygen vacancies due to the largest surface roughness of thin films annealed at 450℃. Thin films annealed in H2 show the strongest band-band PL and excitonic PL compared to thin films annealed in NH3, N2 and O₂. This is ascribed to the large amount of defect in thin films, especially the large amount of oxygen vacancies generating due to reduced H₂ atmosphere. Thin films annealed in O₂ exhibit the lowest PL intensity. It is ascribed to that they contain more rutile phase. Compared to thin films annealed in air, thin films annealed in N₂, O₂, NH₃ and H₂ atmosphere show the slightly red shift. It can be attributed to N-doped for N₂ and NH₃, generating defect level and decrease the width of band gap for O₂ and H₂. These effects on photoluminescence properties due to the structure and point defect concentration change resulted from different annealing temperature and different annealing atmosphere is of benefit to study and synthesize high quality dye-sensitized solar cells and photocatalyst.更多还原