TY - JOUR
T1 - Controlling the Energy-Level Alignment of Silicon Carbide Nanocrystals by Combining Surface Chemistry with Quantum Confinement
AU - Haq, Atta Ul
AU - Buerkle, Marius
AU - Askari, Sadegh
AU - Rocks, Conor
AU - Ni, Chengsheng
AU - Švrček, Vladimir
AU - Maguire, Paul
AU - Irvine, John T. S.
AU - Mariotti, Davide
PY - 2020/3/5
Y1 - 2020/3/5
N2 - 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.
AB - 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.
KW - Oxygen
KW - Energy
KW - Transmission electron microscopy
KW - Quantum confinement
KW - Electrical conductivity
UR - https://pure.ulster.ac.uk/en/publications/controlling-the-energy-level-alignment-of-silicon-carbide-nanocry
UR - http://www.scopus.com/inward/record.url?scp=85080072964&partnerID=8YFLogxK
U2 - 10.1021/acs.jpclett.9b03828
DO - 10.1021/acs.jpclett.9b03828
M3 - Article
C2 - 32040322
SN - 1948-7185
VL - 11
SP - 1721
EP - 1728
JO - Journal of Physical Chemistry Letters
JF - Journal of Physical Chemistry Letters
IS - 5
ER -