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

由于偶氮苯发色团的可逆跨顺式光致异构化，在含偶氮苯的固体薄膜中，全息纳米结构可以作为表面浮雕被光诱导。在最简单的情况下，当曝光于准直激光干涉图案时，线性表面浮雕衍射栅刻在偶氮薄膜上。在偶氮薄膜上刻写纳米结构只需几分钟，只需一步就可以完成。这使得它们与其他纳米制造技术相比具有很大的优势。所得到的纳米结构随着时间的推移是稳定的，并且可以根据应用的不同而被其他材料覆盖。我的团队最近开发了一种新的实验技术，将非线性表面浮雕结构刻在偶氮薄膜上。例如，我们成功地将柱面和球面透镜的全息表示写成了啁啾间距衍射光栅。这些光栅会像真实的物理透镜一样聚焦探测光束。我们还设计并制作了一种新颖的锥形夹具，可以同时制作等间距和啁啾间距的圆形表面浮雕光栅。在这些新颖的非线性纳米结构上涂上一层薄的金属层，就可以产生表面等离子激元。这些等离子体是在金属层和相邻介质之间的边界上传播的共振电磁波。在等离子体激元的激发下，边界上的局部电磁场被高度放大。这些场可以延伸到界面上方和下方200纳米，这导致光捕获并增强了整个介质层的透射率。如果同时满足几个参数，通常会产生表面等离子激元。这使得它们可以同等地用作传感器。该方案的目的是研究和优化偶氮薄膜上新型非线性纳米结构中表面等离子激元的产生。我们将研究在圆形栅中激发最强等离子体所需的各种参数。我们还将对啁啾间距光栅进行优化，以获得最佳的光带宽激励，并将其用作等离子体能量集中器。这些光栅将被整合到薄膜太阳能电池和有机发光二极管中，作为介电介质。其目标是在宽的光带宽和所有的光偏振下实现实质性的和可控的表面等离子激元增强。这将通过对纳米结构的形状及其对等离子体激发的影响的系统研究来完成。这些纳米结构还将被研究在传感应用方面的潜在用途，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.