Abstract
A compact proximal retarding field analyzer for scanning probe energy loss spectroscopy measurements is described. Using the scanning tunneling microscope (STM) tip as a field emission (FE) electron source in conjunction with this analyzer, which is placed at a glancing angle to the surface plane, FE sample current and electron reflectivity imaging may be performed simultaneously. This is demonstrated in measurements of Ag nanostructures prepared on graphite by electron-beam lithography, where a material contrast of 13% is observed, with a lateral resolution of 25 nm, between the silver and graphite in electron reflectivity images. Topological contrast mechanisms such as edge enhancement and shadowing are also observed, giving rise to additional features in the electron reflectivity images. The same instrument configuration has been used to measure electron energy loss spectra on bare graphite, where the zero loss peak, π band plasmon loss peak and secondary electron peaks are observed. Using this simple and compact analyzer an STM, with sufficient open access to the tip-sample junction, may easily be augmented to provide simultaneous elemental and topographic mapping, supplementing STM image measurements with FE sample current and electron reflectivity images, as well as electron energy loss spectroscopy measurements, in the same instrument.
Highlights
Scanning tunneling microscopy (STM) has become firmly established as a mature technique for surface characterization since it was first demonstrated more than three decades ago [1]
To investigate the performance of the retarding field analyzer (RFA) for scanning probe energy loss spectroscopy (SPELS) measurements, electron energy loss spectra were measured on bare highly oriented pyrolytic graphite (HOPG)
When positioned close to the sample surface at a glancing angle and used in conjunction with field emitted electrons from the scanning tunneling microscope (STM) tip, material contrast with a resolution of 25 nm can be routinely observed in electron reflectivity images of Ag nanostructures produced by Electron beam lithography (EBL) on HOPG
Summary
Scanning tunneling microscopy (STM) has become firmly established as a mature technique for surface characterization since it was first demonstrated more than three decades ago [1]. Festy et al [7] showed that edge enhancement and shadowing effects were important contrast mechanisms in backscattered electron images measured with a retarding field analyzer (RFA) placed at a glancing angle (
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