Reflection of Very Slow Electrons

A monoenergetic electron beam from an electrostatic analyzer has been used to measure reflection coefficients of polycrystalline platinum, single-crystal germanium, and single-crystal copper. The lower limit of primary energy is 0.2-0.3 ev. The contact potential difference between target and collector is measured and compensated by the Kelvin method. Targets are cleaned by heating and argon-ion bombardment. Polycrystalline platinum exhibits a maximum at 2.5 ev, and a rise near zero primary energy attributed to a patch effect. Germanium, after ion-bombardment cleaning, exhibits a low reflection coefficient which decreases to a value between 0.05 and 0.10 at the low-energy limit. Copper, after heating and also after ion-bombardment cleaning, shows a reflection coefficient with weak structure, decreasing nearly to zero at the limit of measurement. These results are in general agreement with the predictions of Herring and Nichols regarding the transparency of surface barriers. Observations have also been made on these targets following argon-ion bombardment and exposure to gases.