Diamantopoulos Nikolaos C, Barnasas Alexandros, Garoufalis Christos S, Anyfantis Dimitrios I, Bouropoulos Nikolaos, Poulopoulos Panagiotis, Baskoutas Sotirios
Materials Science Department, University of Patras, 26504 Patras, Greece.
Foundation for Research and Technology Hellas, Institute of Chemical Engineering and High Temperature Chemical Processes, 26504 Patras, Greece.
Nanomaterials (Basel). 2020 Nov 29;10(12):2379. doi: 10.3390/nano10122379.
Thin Titanium films were fabricated on quartz substrates by radio frequency magnetron sputtering under high vacuum. Subsequent annealing at temperatures of 600 ∘C in air resulted in single-phase TiO2 with the structure of rutile, as X-ray diffraction experiment demonstrates. Atomic-force microscopy images verify the high crystalline quality and allow us to determine the grain size even for ultrathin TiO2 films. Rutile has a direct energy band gap at about 3.0-3.2 eV; however, the transitions between the valence and conduction band are dipole forbidden. Just a few meV above that, there is an indirect band gap. The first intense absorption peak appears at about 4 eV. Tauc plots for the position of the indirect band gap show a "blue shift" with decreasing film thickness. Moreover, we find a similar shift for the position of the first absorbance peak studied by the derivative method. The results indicate the presence of quantum confinement effects. This conclusion is supported by theoretical calculations based on a combination of the effective mass theory and the Hartree Fock approximation.
通过射频磁控溅射在高真空条件下于石英衬底上制备了薄钛膜。如X射线衍射实验所示，随后在空气中600℃的温度下退火得到了具有金红石结构的单相TiO₂。原子力显微镜图像证实了其高结晶质量，甚至对于超薄TiO₂薄膜，也能让我们确定晶粒尺寸。金红石在约3.0 - 3.2 eV处有直接能带隙；然而，价带和导带之间的跃迁是偶极禁戒的。在其上方仅几meV处，存在一个间接能带隙。第一个强吸收峰出现在约4 eV处。间接能带隙位置的陶克图显示随着薄膜厚度减小出现“蓝移”。此外，我们通过导数法研究发现第一个吸光度峰的位置也有类似的移动。结果表明存在量子限制效应。这一结论得到了基于有效质量理论和哈特里 - 福克近似相结合的理论计算的支持。
