Theoretical studies of light emission from molecular junctions

分子连接发光的理论研究

• 批准号: 338583897
• 负责人: Dr. Safa Golrokh Bahoosh, Ph.D.
• 金额: --
• 依托单位: Arbeitsgruppe Theorie des Quantentransports
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2017
• 资助国家: 德国
• 起止时间: 2016-12-31 至 2020-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/338583897?language=en
• 关键词: Theoretical; studies; light; emission; molecular

The interaction of electrons with collective electromagnetic modes and the coupling of these modes to photons provide a unique probe for tip-surface interactions involving inelastic electron tunneling excitations of local plasmon modes and has become an important topic bridging nanoelectronics and plasmonics. STM-induced light emission due to the damping of the surface plasmon polaritons revealed a strong correlation between the light emission intensity and the current fluctuations at optical frequencies. However, the role of the molecule and how it effects the STM-induced light emission remains debated.My main objective is to describe the emission of plasmonic light in molecular junctions at lower photon energies compare to the applied bias as well as the emitted light at photonenergies which exceed the applied bias significantly . The former will be investigatedby exploring the characteristics of frequency-dependent non-symmetrized current-current correlation function for different quantum models. While I will formulate my theory for a general multilevel system, I will in conceptual studies concentrate on single and two-level models. The two-level model are of particular interest. They constitute a minimal model for a molecular junction, they can treat both Fano resonance and describe transport through dominant HOMO and LUMO levels.Furthermore, I will develop a microscopic theory for plasmonic light emission in molecular junctions based on the Keldysh nonequilibrium Green's function (NEGF) formalism taking into account an energy-dependent transmission and by considering single level and two-level transport, especially to explain the experimentally observed above-threshold emission. Particularly, the possibility of three- and four-electron scattering processes and the relevant self-energy diagrams due to these higher order corrections will be identified.Finally, using a multiscale quantum mechanics/electromagnetics (QM/EM) method, the shot noise characteristics and the light emission rate of such junctions will be calculated quantitatively. To this aim, the QM region is simulated using the DFT method in combination with NEGF, while the EM region is simulated by implementation of Maxwell's equations. QM and EM calculations communicate with each other through the interface by means of boundary conditions between the two regions and are solved iteratively until self-consistency achieved.

电子与集体电磁模式的相互作用以及这些模式与光子的耦合为涉及局部等离子体激元模式的非弹性电子隧穿激发的尖端-表面相互作用提供了独特的探针，并且已经成为连接纳米电子学和等离子体激元学的重要课题。STM诱导的光发射由于表面等离子体激元的阻尼揭示了光发射强度和在光学频率的电流波动之间的强相关性。然而，分子的作用以及它如何影响STM诱导的光发射仍然存在争议，我的主要目标是描述在较低的光子能量下的分子结中的等离子体激元光的发射与所施加的偏压相比，以及在光子能量显著超过所施加的偏压的情况下的发射光。前者将通过研究不同量子模型下频率依赖的非对称电流-电流关联函数的特性来研究。虽然我将制定我的理论，为一般的多级系统，我将在概念上的研究集中在单和两个层次的模型。两级模型特别令人感兴趣。它们构成了分子结的最小模型，它们可以处理Fano共振并通过主要HOMO和LUMO能级描述传输。此外，我将基于Keldysh非平衡绿色函数（NEGF）形式主义，考虑到能量依赖的传输，并考虑单能级和两能级传输，特别是解释实验上观察到的阈上发射。最后，利用多尺度量子力学/电磁学（QM/EM）方法，定量计算了这种结的散粒噪声特性和发光率。为此，QM区域使用DFT方法结合NEGF进行模拟，而EM区域通过实施麦克斯韦方程进行模拟。QM和EM计算通过两个区域之间的边界条件通过接口相互通信，并迭代求解，直到实现自洽。