Plasmonic Properties of Gold Nanoparticles Separated from a Gold Mirror by an Ultrathin Oxide
Plasmonic Properties of Gold Nanoparticles Separated from a Gold Mirror by an Ultrathin Oxide
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DOI：
10.1021/nl300351j
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发表时间：
2012-04-01
期刊：
影响因子：
10.8
通讯作者：
Moskovits, Martin
中科院分区：
文献类型：
--
作者：
Mubeen, Syed;Zhang, Shunping;Moskovits, Martin
一段时间以来，已知位于金镜面上方的纳米颗粒（NP）（例如金）几乎与两个紧密耦合的金纳米颗粒一样有效地作为表面增强拉曼散射（SEAS）衬底（当用正确偏振和波长的光照射时）。（1，2）NP-过反射镜（NPOM）结构具有可自顶向下制造的宝贵优点。我们制作了一系列不同的，但薄的原子层沉积的氧化物间隔层的Au-NPOM衬底，并测量了作为间隔层厚度和入射角（AOI）的函数的Sers增强。这些进行了比较，高品质的有限差分时域计算，再现所观察到的间隔厚度和AOI的依赖性忠实。Sers强度预计会受到AOI的强烈影响，因为在NP和镜之间的空间中形成的热点用垂直于镜表面的电磁场分量最有效地激发。有趣的是，我们发现Sers强度在近似60度处达到最大值，并表明这是由于入射场和反射场分量的相干叠加。(3)所观察到的SEAS强度也被证明是非常敏感的氧化物间隔层的介电常数与最强烈的信号时，使用低介电常数的氧化物层（SiO2）获得。
That a nanoparticle (NP) (for example of gold) residing above a gold mirror it almost as effective a surface enhanced Raman scattering (SEAS) substrate (when illuminated with light of the correct polarization and wavelength) as two closely coupled gold nanoparticles has been known for some time.(1,2) The NP-overmirror (NPOM) configuration has the valuable advantage that it is amenable to top-down fabrication. We have fabricated a series of Au-NPOM substrates with varying but thin atomic layer-deposited oxide spacer and measured the SERS enhancement as a Function of spacer thickness and angle of incidence (AOI). These were compared with high-quality finite-difference time-domain calculations, which reproduce the observed spacer thickness and AOI dependences faithfully. The SERS intensity is expected to be strongly affected by the AOI on account for the fact that the hot spot formed in the space between the NP and the mirror is most efficiently excited with an electromagnetic field component that is normal to the surface of the mirror. Intriguingly we find that the SERS intensity maximizes at similar to 60 degrees and show that this is due to the coherent superposition of the incident and the reflected field components.(3) The observed SEAS intensity is also shown to be very sensitive to the dielectric constant of the oxide spacer layer with the most intense signals obtained when using a low dielectric constant oxide layer (SiO2).