Scanning tunneling microscope light emission: Effect of the strong dc field on junction plasmons
Scanning tunneling microscope light emission: Effect of the strong dc field on junction plasmons
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DOI：
10.1103/physrevb.94.035443
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发表时间：
2016-07-26
影响因子：
3.7
通讯作者：
Mitra, J.
中科院分区：
文献类型：
--
作者：
Kalathingal, Vijith;Dawson, Paul;Mitra, J.
所观察到的能量的局部表面等离子体激元（LSPs）的尖端样品交界处的扫描隧道显微镜，确定在光输出的光谱峰激发，是非常显着的红移相对于使用标准的光学数据的尖端和样品材料，在这种情况下，金的计算。我们认为，这种异常依赖于极端的字段在亚纳米隧道附近的尖端和样品，在整个直流偏置（1-2 V）的应用。有限元建模分析的金纳米球-平面（NS-P）的组合，在隧道附近，至关重要的是，在一个高的静电场（类似于10（9）V/m）的存在。有人认为，强直流电场诱导的非线性校正的介电函数的金通过一个大的背景极化率的影响，通过非线性，chi（（3））的磁化率的贡献。当输入到模型系统中时，修改后的光学数据改变了NS-P系统的LSP腔模式，与原始金NS-P系统相比，确实揭示了能量的大红移。净结果可以被认为等同于降低体等离子体能量，物理解释是隧穿环境的强场导致表面电荷屏蔽，有效地降低了可用于参与等离子体振荡的自由电子的密度。
The observed energies of the localized surface plasmons (LSPs) excited at the tip-sample junction of a scanning tunneling microscope, as identified by spectral peaks in the light output, are very significantly redshifted with respect to calculations that use standard optical data for the tip and sample material, gold in this case. We argue that this anomaly depends on the extreme field in the sub-nm tunneling proximity of the tip and the sample, across which a dc bias (1-2 V) is applied. Finite element modeling analysis is presented of a gold nanosphere-plane (NS-P) combination in tunneling proximity and, crucially, in the presence of a high static electric field (similar to 10(9) V/m). It is argued that the strong dc field induces nonlinear corrections to the dielectric function of the gold via the effect of a large background polarizability through the nonlinear, chi((3)) susceptibility contribution. When fed into the model system the modified optical data alters the LSP cavity modes of the NS-P system to indeed reveal a large redshift in energy compared to those of the virgin gold NS-P system. The net outcome may be regarded as equivalent to lowering the bulk plasmon energy, the physical interpretation being that the intense field of the tunneling environment leads to surface charge screening, effectively reducing the density of free electrons available to participate in the plasmon oscillations.