Au(111)薄膜表面等离激元和热载流子输运性质的理论研究

Theoretical study on surface plasmon and hot carrier transport properties of Au(111) films

厚度低至原子层的金属薄膜具有优越的光吸收能力和导电特性,尤其是在金属薄膜和介质界面激发的表面等离激元,可以很好地捕获光子并产生热载流子,使其在提高太阳能电池的光电转换效率、设计近红外波段的光电探测器和基于表面等离激元的传感器等方面表现出优异的性质.然而,目前还缺少对金属薄膜的表面等离激元和热载流子性质的系统理论研究.本文基于多体第一性原理计算方法,系统地研究了1—5个原子层厚Au(111)薄膜的表面等离激元特性,以及由表面等离激元产生的热载流子的能量分布和输运性质.研究结果表明, Au(111)薄膜具有低损耗的表面等离激元特性.同时,在Au(111)薄膜和介质界面激发的表面等离激元约束程度较强,可以增强局部电场,这在纳米光子学应用中至关重要.此外, Au(111)薄膜具有高热载流子产生效率,且产生的热电子及热空穴能量较高,具有优异的平均自由程和平均自由时间.意外的是,Au(111)薄膜的直流电导率显著优于块体Au.这些结果为Au(111)薄膜在光电子器件和能量转换设备等的设计和制造提供了新的思路和理论基础.

Metal films with a thickness as low as atomic layer have superior light absorption capabilities and conductive properties, especially the surface plasmons excited at the interface between metal film and dielectric can well capture photons and generate hot carriers, making them more efficient in improving the photoelectric conversion efficiency of solar cells, designing photodetectors in the near-infrared band, and sensors based on surface plasmon. However, there is still a lack of systematic theoretical studies on the surface plasmon and hot carrier properties of metal thin films. Based on the many-body first-principles calculation method, in this paper studied systematically are the surface plasmon properties of Au(111) films with thickness in a range from monolayer to 5 monolayers, and the energy distribution and transport properties of hot carriers generated by surface plasmons. The study results show that Au(111) films have low-loss surface plasmon properties.Meanwhile, the surface plasmons excited at the interface between the Au(111) film and the dielectric are strongly confined, which can enhance the local electric field, thus being crucial in nanophotonics applications. In addition, Au(111) film has a high efficiency generating hot carriers, and the generated hot electrons and hot holes are high in energy, and excellent in mean free path and mean free time. Unexpectedly, the direct current conductivity of Au(111) film is significantly better than that of bulk Au. These results provide new ideas and theoretical basis for the design and fabrication of Au(111) films in optoelectronic devices and energy conversion devices.