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Structural and electronic modification of Ni, Pd, and Fe strained metal overlayers on W(110) and W(100) The interaction of Ag and Al overlayers with InP (110): Surface and diode studies of the effect of Sb interlayers J.

King and Wells have described a convenient technique for measuring adsorption probabilities in ultrahigh vacuum systems equipped with a collimated source and a mass spectrometer for detecting the adsorbate’s ambient partial pressure [Surf. Sci. 29, 454 (1972)]. We describe a method based on similar principles for systems equipped instead with a leak valve for back-filling the chamber and a differentially pumped mass spectrometer with line-of-sight to the adsorbent. The method is demonstrated with measurements of the coverage- and temperature-dependent probability of CO adsorption on Ni(110).

We describe a digital feedforward/feedback controller for the implementation of rapid changes in the temperature of a small, resistively heated metal adsorbent in ultrahigh vacuum. The feedforward loop is based on a second-order model of the system's thermal response, modified by inclusion of a time delay to account for the characteristic time for heal conduction in the adsorbent, and the feedback loop includes proportional and derivative actions. These features allow the temperature of a nickel single crystal, 10 mm diameter and 1 mm thick, to be increased 80 K within approximately 4 s without overshoot, after which desorption rates can be measured at constant surface temperature with a mass spectrometer. The performance of the temperature controller and the advantages of isothermal data collection and analysis are demonstrated with CO desorption from Ni(1lO), for which the functional dependence of the rate on surface coverage at constant temperature identifies clearly the participation of a mobile precursor state in the desorption process.

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