a seal when in the closed position during which time annealing takes place within the gap of the chamber in a further aspect the present invention provides a method of forming a group ibiiiavia compound layer on a surface of a flexible roll application_number US 54959006 A description reaction of precursors comprising group ib material s group iiia material s and optionally group via material s or components with group via material s may be achieved in various ways these techniques involve heating the precursor layer to a temperature range of 350 600 u00b0 c in the presence of at least one of se s and te provided by sources such as solid se solid s solid te h 2 se gas h 2 s gas h 2 te gas se vapors s vapors te vapors etc for periods ranging from 1 minute to 1 hour the se s te vapors may be generated by heating solid sources hydride gases such as h 2 se and h 2 s may be bottled gases such hydride gases and short lifetime gases such as h 2 te may also be generated in situ for example by electrolysis in aqueous acidic solutions of cathodes comprising s se and or te and then provided to the reactors electrochemical methods to generate these hydride gases are suited for in situ generation precursor layers may be exposed to more than one group via materials either simultaneously or sequentially for example a precursor layer comprising cu in ga and se may be annealed in presence of s to form cu in ga s se 2 the precursor layer in this case may be a stacked layer comprising a metallic.