Madsen Steven J, Esfandyarpour Majid, Brongersma Mark L, Sinclair Robert
Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305-4034 USA.
Geballe Laboratory for Advanced Materials, 476 Lomita Mall, Stanford, California 94305-4045, United States.
ACS Photonics. 2017 Feb 15;4(2):268-274. doi: 10.1021/acsphotonics.6b00525. Epub 2017 Jan 13.
Gold plasmonic nanostructures with several different adhesion layers have been studied with monochromated electron energy loss spectroscopy in the scanning transmission electron microscope (STEM-EELS) and with surface enhanced Raman spectroscopy (SERS). Compared to samples with no adhesion layer, those with 2nm of Cr or Ti show broadened, lower intensity plasmon peaks as measured with EELS. This broadening is observed in both optically active ("bright") and inactive ("dark") plasmon modes. When the former are probed with SERS, the signal enhancement factor is lower for samples with Cr or Ti, another indication of reduced plasmon resonance. This work illustrates the capability of STEM-EELS to provide direct near-field measurement of changes in plasmon excitation probability with nano-scale spatial resolution. Additionally, it demonstrates that applications which require high SERS enhancement, such as biomarker detection and cancer diagnostics, can be improved by avoiding the use of a metallic adhesion layer.
利用扫描透射电子显微镜中的单色电子能量损失谱（STEM-EELS）以及表面增强拉曼光谱（SERS），对具有几种不同粘附层的金等离子体纳米结构进行了研究。与没有粘附层的样品相比，具有2nm铬或钛粘附层的样品，通过EELS测量显示出等离子体峰变宽且强度降低。在光学活性（“明亮”）和非活性（“黑暗”）等离子体模式中均观察到这种展宽现象。当用SERS探测前者时，具有铬或钛的样品的信号增强因子较低，这是等离子体共振降低的另一个迹象。这项工作说明了STEM-EELS能够以纳米级空间分辨率提供等离子体激发概率变化的直接近场测量。此外，它表明，通过避免使用金属粘附层，可以改善诸如生物标志物检测和癌症诊断等需要高SERS增强的应用。
