CONTACT-POTENTIAL MEASURMENTS OF ADSORPTION OF I2, BR2, AND C12 ON BARE AND CESIATED W(100)

The electron-beam retarding potential method has been used to measure the work function changes, Δφ, resulting from the adsorption of I2,Br2, and Cl2 on the (100) face of a tungsten crystal at 300°K. For I2, the work function decreased in the low coverage (i.e., low exposure) range, attaining a minimum of Δφ ≅ - 0.40 eV, and then increased rather abruptly with increasing coverage, reaching Δφ ≅ + 0.08 eV in the high coverage limit. For Br2, the work function increased monotonically with coverage, reaching Δφ ≅ + 0.41 eV rather quickly and then increasing slowly to Δφ ≅ +0.82eV for prolonged exposures. Cl2 also produced a monotonie increase in the work function, the high coverage limit being Δφ ≅ + 0.63 eV. Also included are experimental data on (i) halogen desorption, (ii) electron reflection from clean and halogen-covered W(100), and (iii) the work functions resulting from co-adsorption of I2 + Cs and Cl2 + Cs on W(100). © 1969.