Basak Tista, Basak Tushima
Mukesh Patel School of Technology Management and Engineering, NMIMS University, Mumbai 400056, India.
Department of Physics, Mithibai College, Mumbai 400056, India.
J Phys Condens Matter. 2020 Aug 11;32(44). doi: 10.1088/1361-648X/aba012.
The electronic and optical properties of graphene quantum dots can be significantly tailored by doping it with heteroatoms, thus extending its potential applications. In this work, we have employed time-dependent density functional theory to systematically explore the effect of introduction of nitrogen atoms in varying concentration at pyridinic and graphitic configuration in armchair and zigzag-edged triangular shaped graphene quantum dots (TQDs) of different sizes. Our results indicate that the electronic band-gap in these N-doped systems can be effectively tuned by varying the configuration as well as concentration of dopants and nature of edge-termination. The variation of electronic band-gap is critically determined by the localized/delocalized nature of molecular orbitals and presence of additional energy levels due to dopant nitrogen atoms. However, the significance of these extra energy levels in modulating the optical properties (appearance of characteristic N-dopant absorption peaks) becomes conspicuous only for specific configuration and concentration of nitrogen atoms. In addition, our studies have attributed the strong dependence of blue/red-shift of absorption spectra and variation in the peak profile to position as well as concentration of dopant atoms and edge-termination pattern. Further, it is observed that the effect of increasing size of TQDs on the strength of most intense absorption peak of pyridinic N-doped TQDs is remarkably different from graphitic N-doped systems. This selective manipulation of optical properties in TQDs due to different N-doping pattern can open up new frontiers for rational design of novel optoelectronic devices.
通过用杂原子对石墨烯量子点进行掺杂，可以显著调整其电子和光学性质，从而拓展其潜在应用。在这项工作中，我们采用含时密度泛函理论，系统地探究了在不同尺寸的扶手椅型和锯齿型边缘三角形石墨烯量子点（TQDs）中，以吡啶型和石墨型构型引入不同浓度氮原子的影响。我们的结果表明，在这些氮掺杂体系中，通过改变掺杂剂的构型、浓度以及边缘终止的性质，可以有效地调节电子带隙。电子带隙的变化主要由分子轨道的定域/离域性质以及掺杂氮原子导致的额外能级的存在所决定。然而，这些额外能级在调节光学性质（特征性氮掺杂吸收峰的出现）方面的重要性，仅在特定的氮原子构型和浓度下才会显著体现。此外，我们的研究认为，吸收光谱的蓝移/红移以及峰形变化对掺杂原子的位置和浓度以及边缘终止模式有很强的依赖性。进一步观察发现，TQDs尺寸增大对吡啶型氮掺杂TQDs最强吸收峰强度的影响，与石墨型氮掺杂体系显著不同。由于不同的氮掺杂模式而对TQDs光学性质进行的这种选择性调控，可为新型光电器件的合理设计开辟新的途径。
