Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA.
J Chem Phys. 2011 Jan 21;134(3):034507. doi: 10.1063/1.3543714.
We present results of a combined two-photon photoemission and scanning electron microscopy investigation to determine the electromagnetic enhancement factors of silver-coated spherical nanoparticles deposited on an atomically flat mica substrate. Femtosecond laser excitation of the nanoparticles produces intense photoemission, attributed to near-resonant excitation of localized surface plasmons. Enhancement factors are determined by comparing the respective two-photon photoemission yields measured for single nanoparticles and the surrounding flat surface. For p-polarized, 400 nm (∼3.1 eV) femtosecond radiation, a distribution of enhancement factors is found with a large percentage (67%) of the nanoparticles falling within a median range. A correlated scanning electron microscopy analysis demonstrated that the nanoparticles typifying the median of the distribution are characterized by spherical shapes and relatively smooth silver film morphologies. In contrast, the largest enhancement factors were produced by a small percentage (7%) of particles that displayed silver coating defects that altered the overall particle structure. Comparisons are made between the experimentally measured enhancement factors and previously reported calculations of the localized near-field enhancement for isolated silver nanoparticles.
我们呈现了一项结合双光子光发射和扫描电子显微镜研究的结果，以确定沉积在原子级平坦云母衬底上的银包覆球形纳米粒子的电磁增强因子。纳米粒子的飞秒激光激发产生强烈的光发射，归因于局域表面等离激元的近共振激发。通过比较单个纳米粒子和周围平面各自的双光子光发射产率来确定增强因子。对于 p 偏振的 400nm（约 3.1eV）飞秒辐射，发现增强因子分布有很大比例（67%）的纳米粒子落在中位数范围内。相关的扫描电子显微镜分析表明，代表分布中位数的纳米粒子具有球形和相对光滑的银膜形态。相比之下，最大的增强因子是由一小部分（7%）的粒子产生的，这些粒子的银涂层缺陷改变了整体粒子结构。将实验测量的增强因子与先前报道的孤立银纳米粒子的局域近场增强的计算值进行了比较。
