Real-space observation of xenon adsorption and desorption kinetics on graphite (0 0 0 1) by photoemission electron microscopy

Abstract

The growth and desorption of Xe monolayers on the basal plane of graphite has been investigated by real-space imaging using photoemission electron microscopy. Adsorption kinetics was studied at different substrate temperatures (39–65 K), corresponding to different growth modes. Coexisting phases showed up as different grey values in the image. Typical domain sizes of the 2D solid phases around 60 K are of the order of one to several μm. The domains exhibit an elongated shape with their long axis oriented preferentially parallel to step edges of the substrate. With increasing coverage the brightness of the domains increases, the 2D gas-phase regions shrink and finally disappear at high coverage, in agreement with the phase diagram of Xe films. The saturated monolayer at 60 K shows a “wave-like” structure indicating coexistence of the commensurate (√3×√3) R30° and an incommensurate 2D solid phase. Desorption kinetics has been studied at temperatures between 70 and 75 K. The close-packed monolayer breaks up into many small islands, again oval-shaped and oriented along the step edges, which in turn loose intensity, shrink and finally disappear at 74.4 K. The line scans and histograms of the grey values reveal that during desorption the islands of the commensurate phase persist down to low coverages and the incommensurate and 2D gas phase decrease in 2D Xe density.