Adsorption of Potassium on Tungsten

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Abstract
The adsorption of potassium on thermally annealed and field‐evaporated tungsten surfaces was studied by field emission. The φ̄‐ vs‐θ̄ curve has a minimum of 1.78 eV at θ̄=0.83, n̄=3.2×1014 atom/cm2 (which coincides with the minimum of φ110), and approaches φK at θ̄=2–3. Distinct minima also occur for other close‐packed planes, like 211. At θ̄=1, n̄=3.9×1014 atom/cm2, φ̄=1.95 eV the emission pattern is indistinguishable from that of clean tungsten. The average charge per K atom, q̄, varies from 0.27 at low θ to 0.2 electron charges at θ̄=0.8. The value of q on the close‐packed W planes at low coverage may be considerably higher. The activation energy of neutral desorption varied from 2.67 to 2.4 eV over the interval 0<θ̄∼0.4 in order to accommodate more adsorbate in some direct contact with the substrate. The experimental results are shown to be consistent with a model based on delocalized bonding, i.e., metallic adsorption.

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