Phase transitions are central to many major discoveries in condensed matter physics. Controlling such transitions on the level of a discrete number of atoms or molecules therefore is of both scientific and technological interest. We report ‘phase transitions’ of Xe condensates in on-surface confinements induced by temperature changes and by local probe excitation. The pores of a metal-organic network occupied with 1 up to 9 Xe atoms have been investigated in their propensity to undergo ‘condensed solid’ to ‘confined fluid’ transitions. Different transition temperatures are identified which depend on the number of Xe atoms in the condensate and relate to the stability of the Xe clustering in the condensed ‘phase’. This work reveals the feature-rich transition behaviour of discrete, confined planar condensates which provide a showcase towards future ‘phase-transition’ storage media patterned by self-assembly. Also this work opens the door to real space investigations of reversible solid to fluid transitions of ‘magic cluster’ condensates in an array of very well defined quantum confinements as they are of fundamental interest.
 Aisha Ahsan et al., small (2018).
 Sylwia Nowakowska et al., Nature Communications, 6, 6071 (2015)