We explore the incident energy dependence of the electronic excitation spectra of Au and Ag films in scanning probe energy loss spectroscopy (SPELS) and also high resolution electron energy loss spectroscopy. We show that the spectra obtained in SPELS depend strongly on the incident electron beam energy. In the case of Au, interband transitions mask the surface plasmon unless the field emission voltage is reduced to ∼100 V, whereas there is a clear surface plasmon peak above 300 V for Ag.
The magic of SPELS: Scanning probe energy loss spectroscopy (SPELS) can be viewed as a hybrid (see figure) between scanning tunneling microscopy (STM) and electron energy loss spectroscopy (EELS). As the spatial resolution of SPELS is in the 10‐nm regime, the way is opened to true nanometer‐scale band‐structure measurements.
Secondary-electron emission (SEE) spectra have been obtained with the Scanning Probe Energy Loss Spectrometer at a tip-sample distance of only 50 nm. Such short working distances are required for the best theoretical spatial resolution (<10 nm). The SEE spectra of graphite, obtained as a function of tip bias voltage, are shown to correspond to unoccupied states in the electronic band structure. The SEE spectra of thin gold films demonstrate the capability of identifying (carbonaceous) surface contamination with this technique.
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