Mechanically controllable strain junctions: targeting quantum effects and strong plasmonic coupling in ultra-narrow gaps

机械可控应变结：针对超窄间隙中的量子效应和强等离子体耦合

• 批准号: 287911648
• 负责人: Dr. Kai Braun
• 金额: --
• 依托单位: Institut für Physikalische und Theoretische Chemie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2015
• 资助国家: 德国
• 起止时间: 2014-12-31 至 2019-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/287911648?language=en
• 关键词: Mechanically; controllable; strain; junctions; targeting

Within the last decade gap antennas have been widely studied and are commonly used due to the strongly enhanced coupled electrical fields within their gap, which can be spectrally tuned over a wide range. Many emerging nano-photonic technologies depend on the careful control of this plasmonic coupling, including optical nanoantennas for high-sensitivity sensors in chemical and biological applications and improved photovoltaic devices. Typically the distances between the metallic nanostructures range from several tens of nm down to a few nm. Only recently several groups managed to produce and measure sub-nanometer gaps, which show new phenomena such as coherent quantum tunnelling. These effects could become crucial in nanoscale optoelectronics and may pave the way to single molecule opto-electronics.Nevertheless, achieving reproducible and stable experimental conditions with sub-nanometer sized gaps remains a challenging task in high demand. In addition, the methods demonstrated so far are in many cases not suitable for preparing resonant plasmonic coupling with a preselected optical frequency, since their plasmonic properties are not very well-controllable due to a strong dependence on the random preparation processes. In the present work, the approach of using mechanically controllable break junctions (MCBJs) will be revised by developing mechanically controllable strain junctions (MCSJs). MCBJs have shown great performance in measuring tunneling effects and single molecule conductance even at ambient conditions, but unfortunately exhibit poor control of the formed electrode gap geometry itself. The shape of the plasmonic tips in the gap region of a MCSJ is lithographically pre-defined on a pre-stretched substrate, which afterwards will be controllably released to approach the tips.The initial part of this work is dedicated to test measurements on MCBJs. These experiments are used to validate the stretching control setup and establish a link to literature results. The objectives of this project are to develop a well-defined, tunable experimental setup for investigating the interplay between the optical and electronic properties of a nano-gap between metal antennas under wide parameter variation, both for pure gaps and for gaps bridged by molecules, with sub-nanometer control under ambient conditions. With this setup the regime of strong coupling and quantum plasmonics will be addressed. The results from luminescence, electronic transport and Raman studies, all on exactly the same system under variation of antenna geometry, gap size, bias voltage, and molecular bridging will be collected. The project thus aims at gaining new insight into the plasmonic mode distribution, role of the evanescent near-field, electrical biasing, and molecular conductivity in the strong coupling regime.

在过去的十年中，间隙天线已经被广泛研究，并且由于其间隙内的强烈增强的耦合电场而被普遍使用，其可以在宽范围内进行频谱调谐。许多新兴的纳米光子技术依赖于对这种等离子体耦合的仔细控制，包括用于化学和生物应用中的高灵敏度传感器的光学纳米天线以及改进的光伏器件。通常，金属纳米结构之间的距离范围从几十nm下至几nm。直到最近，几个研究小组才成功地制造和测量了亚纳米间隙，这些间隙显示了新的现象，如相干量子隧穿。这些效应可能在纳米级光电子学中变得至关重要，并可能为单分子光电子学铺平道路。然而，实现具有亚纳米尺寸间隙的可重复且稳定的实验条件仍然是一项具有挑战性和高需求的任务。此外，迄今为止所展示的方法在许多情况下不适合于制备具有预选光学频率的共振等离子体激元耦合，因为它们的等离子体激元性质由于对随机制备过程的强烈依赖性而不是非常好地可控。在目前的工作中，使用机械可控断裂结（MCBJ）的方法将被修改，通过开发机械可控应变结（MCSJ）。MCBJ即使在环境条件下也在测量隧穿效应和单分子电导方面表现出很好的性能，但不幸的是，对所形成的电极间隙几何形状本身的控制较差。MCSJ的差距区域中的等离子体尖端的形状是在预拉伸的衬底上光刻预定义的，之后将可控地释放以接近尖端。这些实验用于验证拉伸控制设置，并建立与文献结果的链接。该项目的目标是开发一个定义明确，可调的实验装置，用于研究宽参数变化下金属天线之间的纳米间隙的光学和电子特性之间的相互作用，无论是纯间隙还是分子桥接的间隙，在环境条件下进行亚纳米控制。通过这种设置，强耦合和量子等离子体激元的制度将得到解决。从发光，电子传输和拉曼研究的结果，所有的天线的几何形状，间隙大小，偏置电压和分子桥接的变化下完全相同的系统将被收集。因此，该项目的目的是获得新的洞察力的等离子体模式分布，倏逝近场，电偏置和分子电导率在强耦合制度的作用。