Growth mode and phase transitions of multilayer nitrogen on graphite

The nitrogen-on-graphite growth process above the monolayer was studied by ac heat-capacity technique. The evolution of the heat-capacity peaks due to the orientational-ordering transitions as a function of coverage indicates regions of coexistence of the single and bilayer films and of the bilayer and trilayer films. Between regions of coexistence pure bilayer and trilayer films are found. The data also show clear evidence that near 30 K, only a maximum of three layers can form on the graphite surface when the bulk clusters start to grow. In addition, a sharp heat-capacity peak at 23.4 K was found for coverages above two layers. This peak is related to structural transition in the three-layer system and is probably a layering transition from a two-layer plus bulk system for T<23.4 K to a three-layer plus bulk system for T>23.4 K.