Troglia Alessandro, Bigi Chiara, Vobornik Ivana, Fujii Jun, Knez Daniel, Ciancio Regina, Dražić Goran, Fuchs Marius, Sante Domenico Di, Sangiovanni Giorgio, Rossi Giorgio, Orgiani Pasquale, Panaccione Giancarlo
Istituto Officina dei Materiali (IOM)-CNR, Laboratorio TASC in Area Science Park, S.S. 14 Km 163.5, Trieste, 34149, Italy.
Dipartimento di Fisica, Universitá di Milano, Via Celoria 16, Milano, 20133, Italy.
Adv Sci (Weinh). 2022 May;9(16):e2105114. doi: 10.1002/advs.202105114. Epub 2022 Apr 5.
The formation and the evolution of electronic metallic states localized at the surface, commonly termed 2D electron gas (2DEG), represents a peculiar phenomenon occurring at the surface and interface of many transition metal oxides (TMO). Among TMO, titanium dioxide (TiO ), particularly in its anatase polymorph, stands as a prototypical system for the development of novel applications related to renewable energy, devices and sensors, where understanding the carrier dynamics is of utmost importance. In this study, angle-resolved photo-electron spectroscopy (ARPES) and X-ray absorption spectroscopy (XAS) are used, supported by density functional theory (DFT), to follow the formation and the evolution of the 2DEG in TiO thin films. Unlike other TMO systems, it is revealed that, once the anatase fingerprint is present, the 2DEG in TiO is robust and stable down to a single-unit-cell, and that the electron filling of the 2DEG increases with thickness and eventually saturates. These results prove that no critical thickness triggers the occurrence of the 2DEG in anatase TiO and give insight in formation mechanism of electronic states at the surface of TMO.
通常被称为二维电子气（2DEG）的局域在表面的电子金属态的形成与演化，是许多过渡金属氧化物（TMO）的表面和界面处发生的一种特殊现象。在过渡金属氧化物中，二氧化钛（TiO₂），特别是其锐钛矿多晶型，是开发与可再生能源、器件和传感器相关的新型应用的典型体系，其中了解载流子动力学至关重要。在本研究中，采用角分辨光电子能谱（ARPES）和X射线吸收光谱（XAS），并辅以密度泛函理论（DFT），来追踪TiO₂薄膜中二维电子气的形成与演化。与其他过渡金属氧化物体系不同，研究发现，一旦存在锐钛矿特征，TiO₂中的二维电子气在单胞厚度下仍稳健且稳定，并且二维电子气的电子填充随厚度增加并最终饱和。这些结果证明，没有临界厚度会触发锐钛矿TiO₂中二维电子气的出现，并深入了解过渡金属氧化物表面电子态的形成机制。
