Emitted secondary Electrons: In vacuo plasmon energy gain observation using a Three-Point probe method.

[Display omitted] • A new type of vacuo plasmon energy gain observation technique: a three-point method. • Enlarging the surface plasmon energy gain structure in SE spectra. • Clearly observed surface plasmon energy gain structure of Au and Ag. • Potential for developing a new physical image for surface plasmons in vacuum. A surface plasmon energy gain for emitted secondary electrons (SEs) was recently observed in SE spectroscopy measurements from a tailor-made nanostructured Au specimen as a satellite on the high energy side of the vacuum level. However, thus far, this plasmon energy gain phenomenon has been observed only for Au samples because surface plasmons in Au arise at 2.3 eV, which is relatively far from the strong background cascade peak of SEs. Here, we report a brand-new three-point probe method, for enlarging the surface plasmon energy gain structure in SE spectra. Using this scheme, three different SE energy spectra were measured from nanostructured samples of Au and Ag. By combining their spectra, the surface plasmon energy gain structure of Au and Ag can be clearly observed. The observed structures revealed that the plasmon energy gain process for SEs contributing to a potentially observable feature in a spectrum occurs only in vacuum above the sample surface and is naturally related only to surface plasmons. This unusual plasmon energy gain phenomenon observed by the three-point probe method suggests the potential for development of a new physical image directly in space based on surface plasmons in vacuum above the surface of a medium. [ABSTRACT FROM AUTHOR]