Department of Electrical and Computer Engineering, University of Houston, 4800 Calhoun Road, Houston, TX 77204-4005, USA.
Nanoscale. 2014 Jul 21;6(14):8199-207. doi: 10.1039/c4nr01645a.
Plasmonic metal nanostructures have shown great potential in sensing, photovoltaics, imaging and biomedicine, principally due to the enhancement of local electric field by light-excited surface plasmons, i.e., collective oscillation of conduction band electrons. Thin films of nanoporous gold have received a great deal of interest due to the unique 3-dimensional bicontinuous nanostructures with high specific surface area. However, in the form of semi-infinite thin films, nanoporous gold exhibits weak plasmonic extinction and little tunability in the plasmon resonance, because the pore size is much smaller than the wavelength of light. Here we show that by making nanoporous gold in the form of disks of sub-wavelength diameter and sub-100 nm thickness, these limitations can be overcome. Nanoporous gold disks not only possess large specific surface area but also high-density, internal plasmonic "hot-spots" with impressive electric field enhancement, which greatly promotes plasmon-matter interactions as evidenced by spectral shifts in the surface plasmon resonance. In addition, the plasmonic resonance of nanoporous gold disks can be easily tuned from 900 to 1850 nm by changing the disk diameter from 300 to 700 nm. Furthermore, nanoporous gold disks can be fabricated as either bound on a surface or as non-aggregating colloidal suspension with high stability.
等离子体金属纳米结构在传感、光伏、成像和生物医学等领域具有巨大的应用潜力，主要是由于光激发表面等离激元（即导带电子的集体振荡）增强了局部电场。纳米多孔金薄膜因其具有独特的三维双连续纳米结构和高比表面积而受到广泛关注。然而，在半无限薄的薄膜形式下，纳米多孔金表现出较弱的等离子体消光和等离子体共振的可调谐性，因为孔径远小于光的波长。在这里，我们表明，通过将纳米多孔金制成亚波长直径和亚 100nm 厚度的圆盘形式，可以克服这些限制。纳米多孔金圆盘不仅具有大的比表面积，而且具有高密度的内部等离子体“热点”，具有令人印象深刻的电场增强，这大大促进了等离子体-物质相互作用，如表面等离子体共振的光谱位移所证明的那样。此外，通过将圆盘直径从 300nm 改变到 700nm，纳米多孔金圆盘的等离子体共振可以轻松地从 900nm 调谐到 1850nm。此外，纳米多孔金圆盘可以制备成与表面结合的形式或作为具有高稳定性的非聚集胶体悬浮液。
