Liu Tianji, Besteiro Lucas V, Wang Zhiming, Govorov Alexander O
Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China, Chengdu, China and Department of Physics and Astronomy, Ohio University, Athens, USA.
Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China, Chengdu, China and Centre Énergie Matériaux et Télécommunications, Institut National de la Recherche Scientifique, 1650 Boul. Lionel Boulet, Varennes, QC J3X 1S2, Canada.
Faraday Discuss. 2019 May 1;214:199-213. doi: 10.1039/c8fd00145f. Epub 2019 Mar 4.
The generation of energetic electrons is an effect occurring in any plasmonic nanostructure. However, the number of electrons with high energies generated optically in a plasmonic nanostructure can be relatively small. This is an intrinsic property of the collective plasmon excitations in a Fermi gas of electrons. But the choices of material and geometry have a great impact on the generation rate, and are therefore crucial for designing a nanostructure with a large rate of generation of energetic (hot) electrons. Here we test different plasmonic materials from the point of view of the generation of hot electrons (HEs). Our choice of materials includes both strongly-plasmonic materials (Au, Ag, Cu and Al) and crystals with strongly broadened plasmonic resonances (Pt, TiN and ZrN). Regarding the choice of geometry, we consider two types of nanostructures, single nanocrystals deposited over a dielectric substrate and metastructure absorbers, observing interesting opto-electronic properties. For single nanocrystals, the rate of HE generation is strongly material-dependent since the HE generation rate strongly depends on several physical parameters such as plasmonic enhancement, plasmonic resonance wavelength, Fermi energy, etc. Interestingly, the plasmonic meta-absorbers exhibit a different behaviour. The strongly-plasmonic metals, such as Au, Ag, Cu or Al, show very similar performances, while the materials with damped plasmon resonances demonstrate diverse and reduced rates of HE generation. The physical reason for these different behaviours lies in the dielectric functions of these materials. In the metastructures, plasmonic resonances are in the infrared region and the strongly-plasmonic materials behave as an almost ideal metal, whereas the second group of materials exhibits strong dissipation. This makes the responses from the metastructures made of crystals with damped plasmons strongly dependent on the choice of material. The physical principles described in our study can be useful for designing metastructures and nanodevices based on HEs, which can be used in photo-chemistry and opto-electronics.
高能电子的产生是任何等离子体纳米结构中都会出现的一种效应。然而，在等离子体纳米结构中通过光学方式产生的高能电子数量可能相对较少。这是电子费米气体中集体等离子体激发的一种固有特性。但是材料和几何形状的选择对产生速率有很大影响，因此对于设计具有高能量（热）电子产生速率的纳米结构至关重要。在此，我们从热电子产生的角度测试了不同的等离子体材料。我们选择的材料既包括强等离子体材料（金、银、铜和铝），也包括具有强烈展宽等离子体共振的晶体（铂、氮化钛和氮化锆）。关于几何形状的选择，我们考虑了两种类型的纳米结构，即沉积在介电衬底上的单个纳米晶体和亚结构吸收体，并观察到了有趣的光电特性。对于单个纳米晶体，热电子产生速率强烈依赖于材料，因为热电子产生速率强烈取决于几个物理参数，如等离子体增强、等离子体共振波长、费米能量等。有趣的是，等离子体亚吸收体表现出不同的行为。强等离子体金属，如金、银、铜或铝，表现出非常相似的性能，而具有阻尼等离子体共振的材料则表现出不同且降低的热电子产生速率。这些不同行为的物理原因在于这些材料的介电函数。在亚结构中，等离子体共振处于红外区域，强等离子体材料表现得几乎像理想金属，而第二类材料表现出强烈的耗散。这使得由具有阻尼等离子体的晶体制成的亚结构的响应强烈依赖于材料的选择。我们研究中描述的物理原理对于设计基于热电子的亚结构和纳米器件可能是有用的，这些器件可用于光化学和光电子学。
