Abstract
Nonlinear electron scattering is a recently-discovered physical process observed during the localized plasmonic excitation of Ag nanostructures on graphite surface. In the present work, nonlinear electron scattering phenomena is experimentally verified on Au nanostructures by measuring inelastic scattering of electrons field-emitted from tungsten tip. The relative intensity of the electron-energy-loss peak associated with the plasmonic excitation of Au shows again to increase nonlinearly with the electric field generated by the tip-sample bias, demonstrating the generality of nonlinear electron scattering process in plasmonic system. Compared to the nonlinear electron scattering phenomena observed on Ag nanostructures, the nonlinear term for Au nanostructures is about 1 to 2 orders of magnitude smaller, which is in consistent with the field enhancement factor of Au and Ag nanostructures from both the surface-enhanced Raman spectroscopy experiments and the theoretical calculations.
Highlights
Scanning probe electron energy spectroscopy (SPEES) is an emerging technique which can obtain spectroscopy mapping of surface with spatial resolution[1,2,3,4,5,6,7,8]
energy loss spectra (EELS) acquired at 166 μm with five different tip voltages are shown in Fig. 1(a), where the experimental data are denoted as scattered points and the fitted curves are plotted as solid lines
Similar to the phenomena observed on Ag nanostructures[9], the intensity of the localized surface plasmon resonance (LSPR) peak in EELS obtained at relatively low tip voltage is very weak, whereas it is significantly enhanced when the tip voltage increases
Summary
Scanning probe electron energy spectroscopy (SPEES) is an emerging technique which can obtain spectroscopy mapping of surface with spatial resolution[1,2,3,4,5,6,7,8]. It becomes a bottleneck for improving the spatial resolution of this developing technique This difficulty may be overcome by a recently-discovered new physical process, named nonlinear electron scattering, in which the intensity of the inelastic scattering electron signal can be nonlinearly enhanced to the same level of its elastic counterpart, during the excitation of the localized surface plasmon resonance (LSPR) on Ag nanostructures[9]. According to the theoretical explanation[9], extremely high localized electric field is produced by the “hot spots” formed between Ag nanostructures and modulated by the external electric field, which induces nonlinear electron scattering process This is benefited from the large field enhancement factor of Ag nanostructures, as often demonstrated in the surface-enhanced Raman spectroscopy (SERS) experiments[10,11,12,13,14,15,16,17]. This is in accordance with the field enhancement factor of Au and Ag nanostructures obtained by the SERS experiments[21,22,23,24], as well as the theoretical calculations[25]
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