Haq Atta Ul, Buerkle Marius, Askari Sadegh, Rocks Conor, Ni Chengsheng, Švrček Vladimir, Maguire Paul, Irvine John T S, Mariotti Davide
Nanotechnology & Integrated Bioengineering Centre (NIBEC), Ulster University, Shore Road, Newtownabbey BT37 0QB, United Kingdom.
National Institute of Advanced Industrial Science and Technology (AIST), Central 2, Tsukuba 305-8568, Japan.
J Phys Chem Lett. 2020 Mar 5;11(5):1721-1728. doi: 10.1021/acs.jpclett.9b03828. Epub 2020 Feb 18.
The knowledge of band edges in nanocrystals (NCs) and quantum-confined systems is important for band alignment in technologically significant applications such as water purification, decomposition of organic compounds, water splitting, and solar cells. While the band energy diagram of bulk silicon carbides (SiCs) has been studied extensively for decades, very little is known about its evolution in SiC NCs. Moreover, the interplay between quantum confinement and surface chemistry gives rise to unusual electronic properties and remains barely understood. Here, we report for the first time the complete band energy diagram of SiC NCs synthesized such that they span the regime from strong to intermediate to weak quantum confinement. The absolute positions of the highest occupied (HOMO) and lowest unoccupied (LUMO) molecular orbitals show clear size dependence. While the HOMO level follows the expected behavior for quantum-confined electronic states, the LUMO energy shifts below the bulk conduction band minimum, which cannot be explained by a simple quantum confinement caused by the size effect. We show that this effect is a result of the interplay between quantum confinement and the formation of surface states due to partial and site-selective oxygen passivation.
了解纳米晶体（NCs）和量子受限系统中的能带边缘对于诸如水净化、有机化合物分解、水分解和太阳能电池等具有重要技术意义的应用中的能带对准至关重要。尽管块状碳化硅（SiC）的能带能量图已经被广泛研究了几十年，但对于其在SiC纳米晶体中的演化却知之甚少。此外，量子限制和表面化学之间的相互作用产生了不寻常的电子特性，并且仍然几乎不为人所理解。在这里，我们首次报告了合成的SiC纳米晶体的完整能带能量图，这些纳米晶体涵盖了从强量子限制到中等量子限制再到弱量子限制的范围。最高占据分子轨道（HOMO）和最低未占据分子轨道（LUMO）的绝对位置显示出明显的尺寸依赖性。虽然HOMO能级遵循量子受限电子态的预期行为，但LUMO能量移至块状导带最小值以下，这不能用由尺寸效应引起的简单量子限制来解释。我们表明，这种效应是量子限制与由于部分和位点选择性氧钝化导致的表面态形成之间相互作用的结果。
