小分子吸附调控Ti掺杂石墨烯电子结构和磁性的密度泛函理论研究
A DFT study on tuning electronic structure and magnetic property of Ti doped graphene by small gas adsorption

本文采用基于密度泛函理论的第一性原理方法，研究了气体分子CO、NO、NO2和SO2吸附对Ti掺杂石墨烯(TiG)电子结构和磁性的调制。研究表明：TiG对CO、NO、NO2和SO2分子的吸附作用较强，各分子与Ti原子键合并形成Ti-X键(X代表C、O、N原子)；各分子的吸附可导致Gas@TiG体系电磁性质明显改变：CO分子吸附基底后，虽未能引起CO@TiG体系电子性质改变和磁性的产生，却能够有效调控该体系的带隙宽度；不同于CO分子，NO、NO2和SO2分子的吸附使得半导体性的TiG基底转变为金属特性，但各体系磁性表征不同：NO@TiG发生完全自旋极化，即NO分子与基底上均有自旋分布，且二者的自旋方向相同；顺磁性的NO2分子吸附于TiG基底时磁性消失； SO2分子吸附于TiG基底后自身产生磁性，但基底几乎未发生自旋极化，SO2@TiG呈现自旋极化的局域分布特征。由此，依据分子吸附后体系电磁性质特征的不同，可辨识被测气体分子。此项研究结果为高灵敏度和高选择性的石墨烯基气体传感器的设计提供理论参考。
Modulating the electronic structure and magnetic property of Ti doped graphene (TiG) by the adsorption of gas molecules (CO，NO, NO2 and SO2 ) is investigated by first-principles based on density functional theory. It is found that CO, NO, NO2 and SO2 molecules are strongly adsorbed on TiG through the formation of Ti-X (X=C, O, N) bonds. Each gas adsorption induces significant changes in electronic and magnetic property of Gas@TiG system. CO adsorbing can not lead to change of electronic property and production of magnetic for CO@TiG system but effectively tune its band gap；Different from CO molecule, the substrate of TiG is transformed from semiconductor to metal via the adsorption of NO, NO2 and SO2 molecules. However, NO@TiG shows complete spin polarization, namely, there is spin distribution on NO and the substrate and both of them have the same spin direction; Paramagnetic NO2 molecule has no magnetic after the gas adsorption on TiG; For SO2@TiG, SO2 produces magnetic and there is no spin polarization on the substrate, the system presents local polarization characteristic. So the detected gas molecules can be identified according to the different electronic and magnetic properties of the system caused by gas adsorption. Our work provide theoretical reference to design highly sensitive and selective graphene-based gas sensor.