Plasmons: quanta for micro-region temperature measurement

Abstract

An analysis is made of the shifts in the plasmon loss energies for a 1 keV electron beam scattered from pure tin as a function of temperature in ultra-high vacuum. The plasmons in tin are free-electron like and the thermal shifts are shown to arise from the volume expansion and consequent reduction in electron density as the temperature rises. The shifts for the volume plasmon of 0.49 meVK⁻¹ in the solid state, and 0.60 meVK⁻¹ in the liquid state, may be measured fairly readily to an accuracy better than 10 meV and hence provide a temperature measurement to better than 20 K. In the study of solid surfaces in an ultra-high vacuum scanning electron microscope, by a choice of electron beam energy, this method may be used to define the temperature in the outermost 1 nm at a solid surface with a lateral region limited only by the electron probe size. This may be less than 100 nm in modern surface analysis instruments and involve power of less than 10 nW. In the study of thin films by transmission electron microscopy, the temperature may be determined with a spatial resolution close to that of the imaging and involve even lower power inputs than for solid surfaces.