Abstract: A coating apparatus for applying a film to a substrate is provided. The coating apparatus includes a coating chamber, a filament fixture having a filament array, a tensioning device to maintain tension on the filament array to maintain filaments in a planar array during the application or removal of current or heat to the filaments, and a movable stage arranged to hold the substrate to be treated in the coating apparatus in proximity to the filament array so as to maintain a constant thermal gradient across the substrates being treated in the apparatus. An apparatus for applying nanocrystalline diamond to a substrate is also provided.