Near-Field Enhanced Photochemistry of Single Molecules in a Scanning Tunneling Microscope Junction
Near-Field Enhanced Photochemistry of Single Molecules in a Scanning Tunneling Microscope Junction
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DOI：
10.1021/acs.nanolett.7b03720
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发表时间：
2018-01-01
期刊：
影响因子：
10.8
通讯作者：
Kumagai, Takashi
中科院分区：
文献类型：
--
作者：
Boeckmann, Hannes;Gawinkowski, Sylwester;Kumagai, Takashi
金属纳米结构的光学近场激发可用于增强光化学反应。可见光照射下的增强特别令人感兴趣，因为它可以促进利用阳光来促进光催化化学和能量转换。然而，很少有研究涉及光学近场诱导化学，特别是在单分子水平上。在这封信中，我们报告了扫描隧道显微镜（STM）结中 Cu（111）表面上卟啉的近场增强互变异构化。光诱导的互变异构是由铜基板中的光生载流子介导的。结果表明，与远场诱导过程相比，在金尖端存在的情况下，反应截面显着增强。 Au 尖端的强烈增强发生在红色和近红外光谱范围内，而 W 尖端则显示出较弱的增强，这表明局部等离子体共振的激发有助于该过程。此外，利用 STM 的精确尖端-表面距离控制，可以在隧道状态内外检查近场增强互变异构。我们的结果表明，这种增强归因于通过 STM 结中激发的近场衰减而增加的载流子生成率。此外，光激发隧道电子也有助于隧道状态的过程。
Optical near-field excitation of metallic nanostructures can be used to enhance photochemical reactions. The enhancement under visible light illumination is of particular interest because it can facilitate the use of sunlight to promote photocatalytic chemical and energy conversion. However, few studies have yet addressed optical near-field induced chemistry, in particular at the single-molecule level. In this Letter, we report the near-field enhanced tautomerization of porphycene on a Cu(111) surface in a scanning tunneling microscope (STM) junction. The light-induced tautomerization is mediated by photogenerated carriers in the Cu substrate. It is revealed that the reaction cross section is significantly enhanced in the presence of a Au tip compared to the far-field induced process. The strong enhancement occurs in the red and near-infrared spectral range for Au tips, whereas a W tip shows a much weaker enhancement, suggesting that excitation of the localized plasmon resonance contributes to the process. Additionally, using the precise tip-surface distance control of the STM, the near-field enhanced tautomerization is examined in and out of the tunneling regime. Our results suggest that the enhancement is attributed to the increased carrier generation rate via decay of the excited near-field in the STM junction. Additionally, optically excited tunneling electrons also contribute to the process in the tunneling regime.