Fundamentals and applications of surface plasmon resonance using non-uniform gratings in azobenzene materials

由于偶氮苯发色团独特的光力学行为，光学纳米结构可以在含偶氮苯的固体薄膜上作为表面浮雕进行光刻。在最简单的情况下，均匀的正弦表面浮雕衍射光栅被刻在偶氮苯薄膜上，暴露在劳埃德镜面干涉仪的准直激光干涉图案下。与其他纳米加工技术相比，在偶氮苯薄膜上刻字纳米结构相对便宜，可以在一分钟内完成，并且由一个制造步骤组成，不需要曝光后处理。这些均匀的表面起伏光栅在过去的光子学应用中得到了广泛的应用，例如光通信中有用的平面光波导、分束器、耦合器和光滤光器。基于这类材料的未来应用最终将包括光激活纳米开关和马达，以及光传输纳米颗粒。近年来，我和我的团队研究了偶氮苯材料光电效应的基本原理，并通过开发新型光子器件来利用它们的潜力，例如非均匀衍射光栅，包括直径超过1厘米的恒定和啁啾间距圆形光栅。在我们的光栅上涂上一层薄薄的金属层后，表面等离子体可以在金属层和相邻的介电介质之间的边界上产生。等离子体共振目前是一个热门的研究课题，因为它可以显著提高高优先级技术应用的性能，如太阳能电池、发光二极管、成像仪和传感器。当等离子体激元被激发时，金属-介电边界处的局部电磁场在较窄的波长范围内被高度放大，这为传感和光捕获提供了极好的机会。我和我的团队发表了关于使用非均匀啁啾光栅来扩大表面等离子激元激发带宽的研究论文，关于使用电致伸缩材料主动控制等离子激元信号的研究论文，关于使用偶氮苯纳米结构来增强薄膜太阳能电池的光电流的研究论文，以及关于开发用于检测水中蛋白质和细菌的等离子体生物传感器的研究论文。有趣的是，我们从有机太阳能电池获得了超过300%的功率转换效率提高，取得了令人印象深刻的生物传感体灵敏度超过778 nm每折射率单位，并成功检测大肠杆菌诊断尿路感染。本提案的目标是继续探索偶氮苯材料的光电效应，并制造新的等离子体器件，用于光通信，成像和显微镜，微流体和平面光子电路，水溶液中细菌的生物传感，空气质量远程监测，以及薄膜太阳能电池的效率提高。

Optical nanostructures can be photo-inscribed as surface relief in azobenzene-containing solid thin-films due to the unique photomechanical behaviour of the azobenzene chromophores. In the simplest case, uniform sinusoidal surface relief diffraction gratings are inscribed in azobenzene films upon exposure to a collimated laser interference pattern from a Lloyd mirror interferometer. Compared to other nanofabrication techniques, the inscription of nanostructures in azobenzene films is relatively inexpensive, can be done in under a minute and consists of a single fabrication step with no post-exposure processing. These uniform surface relief gratings have been widely used in the past in photonics applications, such as planar optical waveguides, beam splitters, couplers and light filters useful in optical communications. Futuristic applications based on this class of materials would ultimately include light-activated nano-switches and motors, as well as transport of nanoparticles by light. In recent years, my group and I researched the fundamentals of the photomechanical effect in azobenzene materials, as well as harnessed their potential by developing novel photonics devices, such as non-uniform diffraction gratings, including constant- and chirped-pitch circular gratings over 1 cm in diameter. Upon coating our gratings with a thin metal layer, surface plasmons can be generated at the boundary between the metal layer and an adjacent dielectric medium. Plasmon resonance is currently a hot research topic because it enables significant enhancements in the performance of high-priority technological applications such as solar cells, light emitting diodes, imagers and sensors. When a plasmon is excited, the local electromagnetic fields at the metal-dielectric boundary are highly amplified in a narrow wavelength range, which provides an excellent opportunity for sensing and for light entrapment. My group and I published research papers on the use of non-uniform chirped gratings to widen the surface plasmon excitation bandwidth, on the active control of plasmon signals using an electrostrictive material, on the use of azobenzene nanostructures for photocurrent enhancements in thin-film solar cells, and on the development of plasmonic biosensors for detecting proteins and bacteria in water. Interestingly, we obtained an increase of over 300% in the power conversion efficiency from organic solar cells, achieved an impressive biosensing bulk sensitivity of over 778 nm per refractive index unit, and successfully detected E. coli bacteria for diagnosing urinary tract infections. The objectives of this proposal are to continue exploring the photomechanical effect in azobenzene materials and to fabricate novel plasmonic devices useful in optical communications, imaging and microscopy, microfluidics and planar photonics circuits, biosensing of bacteria in water solutions, air quality remote monitoring, as well as efficiency enhancements in thin-film solar cells.