讲座主题：Carrier separation and exciton structure in graphene quantum dots and carbon nitride quantum dots

专家姓名：张瑞勤

工作单位：香港城市大学

讲座时间：2023年12月15日 10:00-11:00

讲座地点：腾讯会议：988-447-622

主办单位：kaiyun官方网站下载手机网页

内容摘要：

Graphene quantum dots (GQDs) and Carbon nitride quantum dots (CNQDs), the latest addition to the carbon material family promise numerous novel applications in optical sensing, photo-catalysis, bio-sensing, and photovoltaics. However, understanding the photocatalytic capability of CNQDs compared to the graphene quantum dots (GQDs) have not been investigated thoroughly. In this work, through time-dependent density functional tight binding (TD-DFTB) calculations, it is revealed that due to the ground state frontier molecular orbitals (FMOs) localization, CNQDs have superior carrier charge separation, sensitive to the size of the QD. Strong localization of the FMOs and excited state charge separation was observed in the first excited state due to the relaxation of the structure. The exciton structure reveals spatial confinement to the stretched C-N bonds independent of the size of the QDs while there is no such exciton structure found for GQDs. The optical absorption and emission of CNQDs is sensitive to size and does not show strong variations in the shape of the QD. Our approach provides an explanation for the origin of the enhanced photocatalytic performance of CNQDs over graphene quantum dots (GQDs) and their characteristic exciton localization.

主讲人介绍：

张瑞勤，香港城市大学物理与材料系教授，获德国洪堡基金会贝塞尔研究奖（2004 年）、两项国家自然科学奖（1997和2005年）和一项教育部奖项（1997年），为Journal of Electronic Materials副编辑和AAPPS Bulletin高级编辑，历任香港物理学会主席（2013-2017年）和亚太物理学会(AAPPS)理事（2016年至今），2018年被选为美国物理学会会士(APS Fellow)，2020年起为斯坦福前2%高被引科学家。

张教授将计算物理和实验手段相结合对多学科交叉领域的诸多关键科学和技术问题进行了研究，在发展多体理论和多电子大体系有效计算方法的基础上，系统研究了限域量子态（包括电子、激子和声子）的行为对环境、应力、压力和光的响应和性质的调控，特别是认识到低维体系显著的表面-体积比对量子态性质调控的有效性，成功系统地揭示了低维体系的一系列由表面和应力决定的新颖性质，证明了低维体系的表面和应力效应同量子限域效应同等重要。