Ji Zhiqiang, Dervishi Enkeleda, Doorn Stephen K, Sykora Milan
Chemistry Division , Los Alamos National Laboratory , Los Alamos , New Mexico 87545 , United States.
Materials Physics and Applications Division, Center for Integrated Nanotechnologies , Los Alamos National Laboratory , Los Alamos , New Mexico 87545 , United States.
J Phys Chem Lett. 2019 Mar 7;10(5):953-959. doi: 10.1021/acs.jpclett.9b00119. Epub 2019 Feb 18.
The electronic structure of a series of bottom-up synthesized graphene quantum dots (GQDs) smaller than 2 nm was investigated by spectroelectrochemistry, yielding insights not previously available from ensemble-level studies. The results show that for the strongly confined GQDs the dependence of the band gap on the GQD size deviates from the prediction of the standard Dirac Fermion model but agrees well with the models explicitly accounting for the electron-electron and electron-hole interactions. The HOMO/LUMO energy levels are found to be distributed nearly symmetrically around the 0 V value versus normal hydrogen electrode (NHE), becoming more positive/negative, respectively, with increasing GQD size. The exciton binding energies are found to follow power dependence on the number of carbon atoms per GQD, with the experimental values falling within the range of ∼0.1 to ∼0.6 eV. Given the broad accessibility of the described experimental tools and methods, our work opens a path to a more systematic examination of quantum confinement effects in GQDs.
通过光谱电化学研究了一系列尺寸小于2 nm的自下而上合成的石墨烯量子点（GQD）的电子结构，获得了此前在整体水平研究中无法获得的见解。结果表明，对于强受限的GQD，带隙对GQD尺寸的依赖性偏离了标准狄拉克费米子模型的预测，但与明确考虑电子-电子和电子-空穴相互作用的模型非常吻合。发现相对于标准氢电极（NHE），最高占据分子轨道（HOMO）/最低未占分子轨道（LUMO）能级在0 V值附近几乎对称分布，随着GQD尺寸的增加，分别变得更正/更负。发现激子结合能与每个GQD中的碳原子数呈幂次依赖关系，实验值落在0.1至0.6 eV范围内。鉴于所描述的实验工具和方法具有广泛的可及性，我们的工作为更系统地研究GQD中的量子限制效应开辟了一条道路。
