The interfacial region between two bulk media in organic semiconductor based devices, such as organic field-effect transistors (OFETs), organic light-emitting diodes, and organic photovoltaics, refers to the region where two different materials such as an organic material and an electrode come in contact with each other. Although the interfacial region contains a significantly smaller fraction of molecules compared to the bulk, it is the primary site where many photoinduced excited state processes occur, such as charge transfer, charge recombination, separation, energy transfer processes, etc. All such photoinduced processes have a dependence on molecular orientation and density of states at the interfaces, therefore having an understanding of the interfacial region is essential. However, conventional spectroscopic techniques, such as surface-enhanced Raman scattering, x-ray photoelectron spectroscopy, atomic force microscopy, etc., face limitations in probing the orientation and density of states of interfacial molecules. Therefore, there is a need for noninvasive techniques capable of efficiently investigating the interfaces. The electronic sum frequency generation (ESFG) technique offers an interface selectivity based on the principle that the second-order nonlinear susceptibility tensor, within the electric dipole approximation, is zero in the isotropic bulk but nonzero at interfaces. This selectivity makes ESFG a promising spectroscopy tool to probe the molecular orientation and density of states at the buried interface. For beginners interested in employing ESFG to study the density of states at the interface, a detailed description of the experimental setup is provided here.

中文翻译：

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开发电子和频发生分光光度计来评估埋地界面。

有机半导体基器件（例如有机场效应晶体管（OFET）、有机发光二极管和有机光伏器件）中两种体介质之间的界面区域是指两种不同材料（例如有机材料和电极）结合的区域。互相接触。尽管与主体相比，界面区域包含的分子比例要小得多，但它是许多光致激发态过程发生的主要位置，例如电荷转移、电荷复合、分离、能量转移过程等。所有这些光致过程都有依赖于界面处的分子取向和状态密度，因此了解界面区域至关重要。然而，传统的光谱技术，如表面增强拉曼散射、X射线光电子能谱、原子力显微镜等，在探测界面分子的取向和态密度方面面临着局限性。因此，需要能够有效研究界面的非侵入性技术。电子和频生成 (ESFG) 技术提供界面选择性，其原理是二阶非线性磁化率张量在电偶极近似内，在各向同性体中为零，但在界面处非零。这种选择性使 ESFG 成为一种有前途的光谱工具，可用于探测埋入界面处的分子取向和态密度。对于有兴趣使用 ESFG 研究界面处态密度的初学者，此处提供了实验设置的详细描述。