Electron and positron work functions of Cr(100)

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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 o + 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 o - is measured relative to Al(100) by comparing the target biases at which the slowest emitted positrons are recollected by the target. We obtain o + = −1.76(10) eV and o - = 4.46(6) eV for our Cr(100) surface using the value o - = 4.41(3) eV for Al(100) reported by Grepstad, Gartland and Slagsvold. The o + 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.