Measurement of the positron work functions of polycrystalline Fe, Mo, Ni, Pt, Ti, and V.

Abstract

We report measurements of the positron work functions ${\mathrm{\ensuremath{\varphi}}}^{+}$ of polycrystalline samples of Fe, Mo, Ni, Pt, Ti, and V. The positron work functions were obtained by measuring the energy spectrum of slow positrons reemitted by the metal surfaces when bombarded with keV-energy positrons. Two methods were used to extract the work functions. The first method provides an absolute measurement. The second method infers the positron work function from measurements of \ensuremath{\Sigma}=${\mathrm{\ensuremath{\mu}}}^{+}$+${\mathrm{\ensuremath{\mu}}}^{\mathrm{\ensuremath{-}}}$ (where ${\mathrm{\ensuremath{\mu}}}^{+}$ and ${\mathrm{\ensuremath{\mu}}}^{\mathrm{\ensuremath{-}}}$ are the positron and electron chemical potentials, respectively) relative to the value of \ensuremath{\Sigma} for Cu and to the values of the electron work function for the surface. The second method (which circumvents many of the systematic problems of the first method since the values of \ensuremath{\Sigma} are independent of crystal face and surface contamination) gives ${\mathrm{\ensuremath{\varphi}}}_{\mathrm{Fe}}^{+}$=-1.2(2) eV, ${\mathrm{\ensuremath{\varphi}}}_{\mathrm{MO}}^{+}$=-2.2(2) eV, ${\mathrm{\ensuremath{\varphi}}}_{\mathrm{Ni}}^{+}$=-1.2(2) eV, ${\mathrm{\ensuremath{\varphi}}}_{\mathrm{Pt}}^{+}$=-1.8(2) eV, ${\mathrm{\ensuremath{\varphi}}}_{\mathrm{V}}^{+}$=-0.6(2) eV, and ${\mathrm{\ensuremath{\varphi}}}_{\mathrm{Ti}}^{+}$>0. Our results are compared to theoretical predictions and to previous measurements.