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，间隙天线已被广泛研究并普遍使用，因为其间隙内的耦合电场强烈增强，可以在很宽的范围内进行频谱调谐。许多新兴的纳米光子技术都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高灵敏度传感器的光学纳米天线以及改进的光伏设备。通常，金属纳米结构之间的距离范围从几十纳米到几纳米。直到最近，一些研究小组才成功地产生并测量了亚纳米间隙，这显示了相干量子隧道等新现象。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。尽管如此，在亚纳米尺寸的间隙中实现可重复且稳定的实验条件仍然是一项艰巨的任务，要求很高。此外，迄今为止所展示的方法在许多情况下不适合制备具有预选光频率的共振等离子体耦合，因为它们的等离子体特性由于对随机制备过程的强烈依赖性而不能很好地控制。在目前的工作中，将通过开发机械可控应变结（MCSJ）来修改使用机械可控断裂结（MCBJ）的方法。即使在环境条件下，MCBJ 在测量隧道效应和单分子电导方面也表现出了出色的性能，但遗憾的是对形成的电极间隙几何形状本身的控制较差。 MCSJ 间隙区域中等离激元尖端的形状通过光刻方式预先定义在预拉伸的基板上，随后将可控地释放以接近尖端。这项工作的初始部分致力于对 MCBJ 进行测试测量。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明确的、可调谐的实验装置，用于研究在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机制将得到解决。将收集发光、电子传输和拉曼研究的结果，所有这些结果都在天线几何形状、间隙尺寸、偏置电压和分子桥接变化的情况下在完全相同的系统上进行。因此，该项目旨在对强耦合状态下的等离子体模式分布、渐逝近场的作用、电偏置和分子电导率获得新的见解。