Controlling the Energy-Level Alignment of Silicon Carbide Nanocrystals by Combining Surface Chemistry with Quantum Confinement

Atta Ul Haq, Marius Buerkle, Sadegh Askari, Conor Rocks, Chengsheng Ni, Vladimir Švrček, Paul Maguire, John T. S. Irvine, Davide Mariotti

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Abstract

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.
Original languageEnglish
Pages (from-to)1721-1728
Number of pages8
JournalJournal of Physical Chemistry Letters
Volume11
Issue number5
DOIs
Publication statusPublished - 10 Feb 2020

Keywords

  • Oxygen
  • Energy
  • Transmission electron microscopy
  • Quantum confinement
  • Electrical conductivity

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