Du Wei, Chen Xiaoping, Wang Tao, Lin Qianqi, Nijhuis Christian A
Department of Chemistry, National University of Singapore, 3 Science Drive 3, 117543 Singapore, Singapore.
Fujian Provincial Key Laboratory of Modern Analytical Science and Separation Technology, College of Chemistry, Chemical Engineering and Environment, Minnan Normal University, Zhangzhou 363000, China.
J Am Chem Soc. 2024 Aug 7;146(31):21642-21650. doi: 10.1021/jacs.4c05544. Epub 2024 Jun 28.
Plasmon excitation in molecular tunnel junctions is interesting because the plasmonic properties of the device can be, in principle, controlled by varying the chemical structure of the molecules. The plasmon energy of the excited plasmons usually follows the quantum cutoff law, but frequently overbias plasmon energy has been observed, which can be explained by quantum shot noise, multielectron processes, or hot carrier models. So far, clear correlations between molecular structure and the plasmon energy have not been reported. Here, we introduce halogenated molecules (HS(CH)X, with X = H, F, Cl, Br, or I) with polarizable terminal atoms as the tunnel barriers and demonstrate molecular control over both the excited plasmon intensity and energy for a given applied voltage. As the polarizability of the terminal atom increases, the tunnel barrier height decreases, resulting in an increase in the tunneling current and the plasmon intensity without changing the tunneling barrier width. We also show that the plasmon energy is controlled by the electrostatic potential drop at the molecule-electrode interface, which depends on the polarizability of the terminal atom and the metal electrode material (Ag, Au, or Pt). Our results give new insights in the relation between molecular structure, electronic structure of the molecular junction, and the plasmonic properties which are important for the development of molecular scale plasmonic-electronic devices.
分子隧道结中的等离激元激发很有趣，因为原则上该器件的等离激元特性可通过改变分子的化学结构来控制。受激等离激元的等离激元能量通常遵循量子截止定律，但经常观察到过偏置等离激元能量，这可以用量子散粒噪声、多电子过程或热载流子模型来解释。到目前为止，尚未报道分子结构与等离激元能量之间有明确的相关性。在此，我们引入具有可极化端原子的卤化分子（HS(CH)X，其中X = H、F、Cl、Br或I）作为隧道势垒，并证明在给定施加电压下，分子对受激等离激元强度和能量都有控制作用。随着端原子极化率的增加，隧道势垒高度降低，导致隧穿电流和等离激元强度增加，而隧穿势垒宽度不变。我们还表明，等离激元能量由分子 - 电极界面处的静电势降控制，这取决于端原子的极化率和金属电极材料（Ag、Au或Pt）。我们的结果为分子结构、分子结的电子结构与等离激元特性之间的关系提供了新的见解，这对于分子尺度等离激元 - 电子器件的发展很重要。
