Tzschoppe Michael, Huck Christian, Hötzel Fabian, Günther Benjamin, Mamiyev Zamin, Butkevich Andrey, Ulrich Constantin, Gade Lutz H, Pucci Annemarie
Kirchhoff Institute for Physics, Heidelberg University, Heidelberg, Germany.
J Phys Condens Matter. 2019 May 15;31(19):195001. doi: 10.1088/1361-648X/ab0710. Epub 2019 Feb 14.
The plasmonic signals of quasi-1D electron systems are a clear and direct measure of their metallic behavior. Due to the finite size of such systems in reality, plasmonic signals from a gold-induced superstructure on Si(5 5 3) can be studied with infrared spectroscopy. The infrared spectroscopic features have turned out to be extremely sensitive to adsorbates. Even without geometrical changes of the surface superstructure, the effects of doping, of the adsorbate induced electronic surface scattering, and of the electronic polarizability changes on top of the substrate surface give rise to measurable changes of the plasmonic signal. Especially strong changes of the plasmonic signal have been observed for gold, oxygen, and hydrogen exposure. The plasmonic resonance gradually disappears under these exposures, indicating the transion to an insulating behavior, which is in accordance with published results obtained from other experimental methods. For C and, as shown here for the first time, TAPP-Br, the plasmonic signal almost retains its original intensity even up to coverages of many monolayers. For C, the changes of the spectral shape, e.g. of electronic damping and of the resonance position, were also found to be marginal. On the other hand, TAPP-Br adsorption shifts the plasmonic resonance to higher frequencies and strongly increases the electronic damping. Given the dispersion relation for plasmonic resonances of 1D electron systems, the findings for TAPP-Br indicate a push-back effect and therefore stronger confinement of the free charge carriers in the quasi-one-dimensonal channel due to the coverage by the flat TAPP-Br molecules. On the gold-doped Si(5 5 3)-Au surface TAPP-Br acts as counter dopant and increases the plasmonic signal.
准一维电子系统的等离子体信号是其金属行为的一种清晰而直接的度量。由于这类系统在实际中尺寸有限，因此可以利用红外光谱研究硅（5 5 3）上金诱导超结构的等离子体信号。结果表明，红外光谱特征对吸附质极其敏感。即使表面超结构没有几何变化，掺杂、吸附质诱导的电子表面散射以及衬底表面上方电子极化率变化的影响也会导致等离子体信号发生可测量的变化。在金、氧和氢暴露的情况下，观察到等离子体信号有特别强烈的变化。在这些暴露条件下，等离子体共振逐渐消失，这表明转变为绝缘行为，这与其他实验方法得到的已发表结果一致。对于碳以及首次在此展示的四氨基苯基溴化卟啉（TAPP-Br），即使覆盖许多单层，等离子体信号几乎仍保持其原始强度。对于碳，还发现光谱形状的变化，例如电子阻尼和共振位置的变化很小。另一方面，TAPP-Br的吸附将等离子体共振移向更高频率，并强烈增加电子阻尼。根据一维电子系统等离子体共振的色散关系，TAPP-Br的研究结果表明存在一种推回效应，因此由于平面TAPP-Br分子的覆盖，准一维通道中的自由电荷载流子受到更强的限制。在金掺杂的硅（5 5 3）-金表面上，TAPP-Br起到反掺杂剂的作用并增加等离子体信号。
