Abstract
Secondary electron yield (SEY) curves in the 0-1000 eV range were measured on polycrystalline Ag, Au and Cu samples. The metals were examined as introduced in the ultra-high vacuum chamber and after having been cleaned by Ar+ ion sputtering. The comparison between the curves measured on the clean samples and in the presence of contaminants, due to the permanence in atmosphere, confirmed that the SEY behavior is strongly influenced by the chemical state of the metal surface. We show that when using very slow primary electrons the sample work function can be determined with high accuracy from the SEY curves. Moreover we prove that SEY is highly sensitive to the presence of adsorbates even at submonolayer coverage. Results showing the effect of small quantities of CO adsorbed on copper are presented. Our findings demonstrate that SEY, besides being an indispensable mean to qualify technical materials in many technological fields, can be also used as a flexible and advantageous diagnostics to probe surfaces and interfaces.
Highlights
The accurate determination of the secondary electron yield (SEY) of the materials exposed to radiation is a key issue in the technical design of new particle accelerators.[1,2,3,4,5,6] The prevision and the minimization of SEY is a strict requirement to limit electron cloud phenomena and favor the stability of machine performances.[7,8,9] Analogous criticality concerns microwave and RF components for space applications that find one of their most important functional limitations in the multipactor and corona breakdown discharges.[10]
The urgency of these questions has led to diffuse investigations and the importance of the factors related to intrinsic material properties,[11,12] morphology,[13,14] chemical state[15] and temperature[16,17] in determining the actual SEY behavior of materials hit by electron fluxes has been well assessed
After surface cleaning by Ar+ sputtering the level of contamination is brought below the XPS detection limit and correspondingly the SEY decreases for all three metals
Summary
The accurate determination of the secondary electron yield (SEY) of the materials exposed to radiation is a key issue in the technical design of new particle accelerators.[1,2,3,4,5,6] The prevision and the minimization of SEY is a strict requirement to limit electron cloud phenomena and favor the stability of machine performances.[7,8,9] Analogous criticality concerns microwave and RF components for space applications that find one of their most important functional limitations in the multipactor and corona breakdown discharges.[10]. E. the maximum of the SEY curve, the corresponding primary electron energy and the first crossover energy at which the SEY crosses unit. For a sample exposed to an electron beam the SEY curve is evaluated in terms of the standard parameters that describe the overall response of the material to external excitation, δmax, Emax and E0, 1,6 i. In this approach the very low energy part of the SEY curve is currently neglected essentially because its contribution to the total SEY is not quantitatively relevant. The modification induced in the LE-SEY and SEY curves by controlled low temperature (∼10 K) adsorption of the residual gases and of carbon monoxide (CO), highlighting the effects due to surface adsorbates even at submonolayer coverage
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