Plasmonic Non-linear Surface Relief Nano-structures in Azobenzene-Containing Materials and Their Applications

在含偶氮苯的固体薄膜中，由于偶氮苯发色团的可逆反式光异构化，全息纳米结构可以被光诱导为表面浮雕。在最简单的情况下，暴露于准直激光干涉图样后，在偶氮薄膜上刻上线性表面浮雕衍射光栅。在偶氮薄膜上刻写纳米结构可以在几分钟内完成，并且由一个制造步骤组成。这使得它们与其他纳米制造技术相比具有很高的优势。由此产生的纳米结构随着时间的推移是稳定的，并且可以根据应用情况涂上其他材料。我的小组最近开发了新的实验技术，在偶氮薄膜上刻写非线性表面浮雕结构。例如，我们成功地将圆柱透镜和球面透镜的全息表示刻为啁啾间距衍射光栅。这些光栅聚焦探测光束，就像一个真正的物理透镜。我们还设计并制造了一种新型的锥形夹具，可以生产恒定螺距和啁啾螺距圆形表面浮雕光栅。在这些新颖的非线性纳米结构上涂上一层薄薄的金属层，就可以产生表面等离子体。这些等离子体是共振电磁波，在金属层和邻近的介电介质之间的边界传播。等离激元激发后，边界处的局部电磁场被高度放大。这些电场可以延伸到界面上下200纳米，这导致光困住并增强了整个介电层的传输。如果同时满足几个参数，通常会产生表面等离子体。这使得它们同样可以用作传感器。本研究的目的是研究和优化这些新型非线性纳米结构在偶氮薄膜上表面等离子体的产生。我们将研究激发圆形光栅中最强等离子体所需的各种参数。我们还将优化啁啾间距光栅，以获得最佳的光带宽激发，并利用它们作为等离子体能量集中器。这些光栅将被集成到薄膜太阳能电池和有机发光二极管中，它们将充当介电介质。目标是在宽光带宽和所有光偏振中实现实质性和可控的表面等离子体增强。这将通过系统地研究纳米结构的形状及其对等离子激元激发的影响来完成。这些纳米结构也将研究它们在传感应用中的潜在用途，特别是生物传感器。

Holographic nanostructures can be photo-induced as surface-relief in azobenzene-containing solid thin-films due to the reversible trans-cis photo-isomerization of the azobenzene chromophores. In the simplest case, linear surface-relief diffraction gratings are inscribed on azo thin-films upon exposure to a collimated laser interference pattern. The inscription of nanostructures on azo films can be done in a few minutes and consists of a single fabrication step. This makes them highly advantageous compared to other nanofabrication techniques. The resulting nanostructures are stable over time and can be coated with other materials, depending on the application. My group has recently developed new experimental techniques to inscribe non-linear surface-relief structures on azo films. For example, we successfully inscribed holographic representations of cylindrical and spherical lenses as chirped-pitch diffraction gratings. These gratings focalized a probing light beam just like a real physical lens. We also designed and fabricated a novel conical fixture that enabled the production of both constant-pitch and chirped-pitch circular surface-relief gratings. Upon coating these novel non-linear nanostructures with a thin metallic layer, surface plasmons could be generated. These plasmons are resonant electromagnetic waves that propagate at the boundary between the metal layer and an adjacent dielectric medium. Upon excitation of the plasmon, the local electromagnetic fields at the boundary are highly amplified. These fields could extend up to 200 nanometers above and below the interface and this results in light entrapment and enhanced transmission throughout the dielectric layer. Surface plasmons are normally generated if several parameters are simultaneously satisfied. This allows them to be equally used as sensors. The objective of this proposal is to study and optimize the generation of surface plasmons in those novel non-linear nanostructures which where inscribed on azo thin-films. We will study the various parameters required to excite the strongest plasmons in circular gratings. We will also optimize the chirped-pitch gratings for optimal light bandwidth excitations, as well as utilize them as plasmonic energy concentrators. These gratings will be incorporated in thin-film solar cells and organic light emitting diodes, which will act as the dielectric media. The goal is to achieve substantial and controllable surface plasmon enhancements over a wide light bandwidth as well as in all light polarizations. This will be done by methodical studies on the nanostructures' shape and their influence on the plasmon excitation. These nanostructures will also be studied for their potential use in sensing applications, particularly biosensors.