Electron and positron work functions of Cr(100)

Abstract

We report measurements of the electron and positron work functions of submonolayer contaminated single crystal surfaces of Cr(100) in ultra high vacuum. The positron work function ø + is obtained by measuring the spectrum of slow positrons reemitted by the Cr(100) surface when it is bombarded with keV energy positrons. The electron work function ø - is measured relative to Al(100) by comparing the target biases at which the slowest emitted positrons are recollected by the target. We obtain ø + = −1.76(10) eV and ø - = 4.46(6) eV for our Cr(100) surface using the value ø - = 4.41(3) eV for Al(100) reported by Grepstad, Gartland and Slagsvold. The ø + value is in agreement with the −2.2 eV calculated by Nieminen and Hodges. The positronium work function for Cr implied by these results is −4.10(10) eV; the positronium negative ion (Ps -) work function for this surface is calculated to be + 0.37(7) eV. A search for Ps - showed that at a 90% confidence level less than one in 10 3 thermalized positrons reaching the Cr surface are emitted as Ps -. The slow positron emission spectrum was observed not to change over the 70–300 K range in contrast to recent theoretical predictions.