Negative Work Function of Thermal Positrons in Metals

Abstract

Theoretical study shows that thermalized positrons are thrown out of a metal with an energy of the order of several eV. This phenomenon is shown to be closely related to the electron work function of metals. Since energy is emitted when positrons leave the metal surface, it is named "negative work function." The negative work function of thermal positrons is ${\ensuremath{\Phi}}^{p}\ensuremath{\simeq}\ensuremath{\Delta}{\ensuremath{\varphi}}^{e}\ensuremath{-}{\ensuremath{\mu}}_{c}^{p}+O(\frac{{N}_{p}}{N})$, where ${N}_{p}$ and $N$ are the total number of positrons and electrons, respectively, in the metal. $\ensuremath{\Delta}{\ensuremath{\varphi}}^{e}$ is the electrostatic potential across the metal surface due to the double layer taken from the electron work-function calculation, and ${\ensuremath{\mu}}_{c}^{p}$ is the correlation contribution to the positron chemical potential at the mean electrostatic potential.