Using Heterodyne-Detected Electronic Sum Frequency Generation To Probe the Electronic Structure of Buried Interfaces
Using Heterodyne-Detected Electronic Sum Frequency Generation To Probe the Electronic Structure of Buried Interfaces
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利用外差检测电子和频产生来探测埋入界面的电子结构
DOI：
10.1021/acs.jpcc.7b05514
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
Roberts, Sean T.
中科院分区：
文献类型：
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作者：
Moon, Aaron P.;Pandey, Ravindra;Bender, Jon A.;Cotton, Daniel E.;Renard, Benny A.;Roberts, Sean T.
有机半导体（OSC）因其高消光系数、加工优势以及显示单线态激子裂变等独特现象的能力而成为颇具吸引力的光电材料。然而，采用 OSC 作为有源电子元件仍然具有挑战性，因为这需要在 OSC 和其他材料之间形成结。这种结点会扭曲 OSC 的电子特性，使能量和电荷在结点上的传输变得复杂。为了研究这些结点，我们的小组采用了一种界面选择技术，即电子和频发生光谱 (ESFG)，但将 ESFG 应用于 OSC 薄膜的一个复杂问题是它们必须有两个界面，每个界面都可以产生信号。在传统的ESFG测量中，关于ESFG信号的相位的信息丢失。然而，该信息可以通过外差检测（HD）技术来恢复。在这里，我们提出的实验和模型计算说明了 HD-ESFG 相对于传统 ESFG 测量在 OSC 薄膜研究中所提供的一些关键优势。具体来说，我们报告了在 SiO2 上生长的 N,N'-二甲基-3,4,9,10-苝二甲酰亚胺 (C1-PDI) 薄膜的 HD-ESFG 光谱。为了实现这些测量，我们构建了一个 HD-ESFG 光谱仪，它使用公共路径光学器件来在多个小时内保持高度的相位稳定性。我们发现，HD-ESFG 不仅对 ESFG 光谱中的弱特征具有更高的灵敏度，而且这些测量中包含的相位信息有助于选择性地隔离来自特定薄膜界面的信号。有趣的是，我们发现 C1-PDI 的 HD-ESFG 光谱中的共振与本体 C1-PDI 薄膜的线性吸收光谱中的共振显着偏移，这表明薄膜界面处分子的分子间堆积与本体不同。
Organic semiconductors (OSCs) are attractive optoelectronic materials due to their high extinction coefficients, processing advantages, and ability to display unique phenomena such as singlet exciton fission. However, employing OSCs as active electronic components remains challenging, as this necessitates forming junctions between OSCs and other materials. Such junctions can distort the OSC’s electronic properties, complicating the transfer of energy and charge across them. To investigate these junctions, our group has employed an interface-selective technique, electronic sum frequency generation spectroscopy (ESFG), yet one complication in applying ESFG to thin OSC films is they necessarily have two interfaces that can each produce signals. In a conventional ESFG measurement, information regarding the phase of the ESFG signal is lost. However, this information can be recovered with heterodyne detection (HD) techniques. Here, we present experiments and model calculations that illustrate some key advantages offered by HD-ESFG over conventional ESFG measurements for the study of OSC films. Specifically, we report HD-ESFG spectra ofN,N′-dimethyl-3,4,9,10-perylenedicarboximide (C1-PDI) thin films that have been grown on SiO2. To implement these measurements, we have constructed an HD-ESFG spectrometer that uses common path optics to maintain a high degree of phase stability over multiple hours. We find that not only does HD-ESFG offer increased sensitivity to weak features in ESFG spectra, but the phase information included in these measurements aids in selectively isolating signals that arise from a specific film interface. Interestingly, we find that resonances in HD-ESFG spectra of C1-PDI are significantly shifted from those in linear absorption spectra of bulk C1-PDI films, suggesting that the intermolecular packing of molecules at film interfaces differs from the bulk.