Lyu Xiaying, Li Yaolong, Li Xiaofang, Liu Xiulan, Xiao Jingying, Xu Weiting, Jiang Pengzuo, Yang Hong, Wu Chengyin, Hu Xiaoyong, Peng Liang-You, Gong Qihuang, Yang Shengxue, Gao Yunan
State Key Laboratory for Mesoscopic Physics & Department of Physics, Collaborative Innovation Center of Quantum Matter and Frontiers Science Center for Nano-optoelectronics, Beijing Academy of Quantum Information Sciences, Peking University, Beijing 100871, China.
School of Materials Science and Engineering, Beihang University, Beijing 100191, China.
Nanoscale. 2024 May 16;16(19):9317-9324. doi: 10.1039/d4nr00281d.
For atomically thin two-dimensional materials, variations in layer thickness can result in significant changes in the electronic energy band structure and physicochemical properties, thereby influencing the carrier dynamics and device performance. In this work, we employ time- and energy-resolved photoemission electron microscopy to reveal the ultrafast carrier dynamics of PdSe with different layer thicknesses. We find that for few-layer PdSe with a semiconductor phase, an ultrafast hot carrier cooling on a timescale of approximately 0.3 ps and an ultrafast defect trapping on a timescale of approximately 1.3 ps are unveiled, followed by a slower decay of approximately tens of picoseconds. However, for bulk PdSe with a semimetal phase, only an ultrafast hot carrier cooling and a slower decay of approximately tens of picoseconds are observed, while the contribution of defect trapping is suppressed with the increase of layer number. Theoretical calculations of the electronic energy band structure further confirm the transition from a semiconductor to a semimetal. Our work demonstrates that TR- and ER-PEEM with ultrahigh spatiotemporal resolution and wide-field imaging capability has great advantages in revealing the intricate details of ultrafast carrier dynamics of nanomaterials.
对于原子级薄的二维材料，层厚度的变化会导致电子能带结构和物理化学性质发生显著变化，从而影响载流子动力学和器件性能。在这项工作中，我们采用时间分辨和能量分辨光发射电子显微镜来揭示不同层厚度的PdSe的超快载流子动力学。我们发现，对于具有半导体相的少层PdSe，揭示了在大约0.3皮秒时间尺度上的超快热载流子冷却和在大约1.3皮秒时间尺度上的超快缺陷俘获，随后是大约几十皮秒的较慢衰减。然而，对于具有半金属相的块状PdSe，仅观察到超快热载流子冷却和大约几十皮秒的较慢衰减，而缺陷俘获的贡献随着层数的增加而受到抑制。电子能带结构的理论计算进一步证实了从半导体到半金属的转变。我们的工作表明，具有超高时空分辨率和宽场成像能力的时间分辨和能量分辨光发射电子显微镜在揭示纳米材料超快载流子动力学的复杂细节方面具有很大优势。
