Apparatus for promoting heat transfer between a first volume (chamber volume) and a second volume (expandable, substrate support platform volume). Specifically, the apparatus comprises: a chamber defining a chamber volume that contains a chamber atmosphere, e.g., a partial vacuum; a substrate support platform that defines an expandable volume that contains a heat transfer medium, e.g., air; and a seal that isolates the chamber volume from the heat transfer medium. The substrate support platform further comprises: a substrate support platen that has a first surface located within the chamber volume and a second surface located within the expandable volume; a housing sealed to the second surface of the substrate support platen; and a expandable member such as a bellows, attached to the housing, to provide for expansion of the expandable volume that is defined by the housing and the bellows. The housing is typically fabricated of metal and the substrate support is typically fabricated of ceramic. The seal forms a hermetic junction between the ceramic substrate support and the metal housing.