An apparatus for coating specimens includes a reaction chamber and a plurality of reaction modules in the reaction chamber for containing specimens to be coated, where each reaction module includes a module inlet and a module outlet. A plurality of conduits are configured to be in fluid communication with at least one gas source external to the reaction chamber, and each of the conduits terminates in one of the reaction modules for delivery of gaseous reagents to the specimens to be coated. The module outlets are in fluid communication with the reaction chamber for expulsion of gaseous reaction products from the reaction modules.