There are two remaining potential problems with a PS film synthesis approach exclusively based on reactive sputtering. The first is linked to the volatility of S and P, even when incorporated in solid-state compounds. For many metal sulfides and phosphides, heating in a non-reactive atmosphere leads to decomposition reactions, typically resulting in preferential loss of S in sulfide films and P in phosphide films. Since temperatures significantly above room temperature are required to crystallize most inorganic materials, the decomposition temperature may be lower than the crystallization temperature for a wide range of targeted PS compounds. The solution to this problem is to ensure high partial pressures of S and P during high-temperature crystallization. Since these species are the gaseous products of decomposition reactions, their intentional addition to the gas mix pushes the decomposition reaction towards the left (i.e., towards the desired solid PS compound) due to Le Chatelier's principle. While relatively high concentrations of S and P in the gas phase could potentially be enforced in the sputter system described above, their partial pressures would still be rather low, because the total pressure in a sputter deposition process is limited to the 10 -6 -10 -5 bar range. Reactive annealing of the sputter-deposited combinatorial libraries in a separate RRTP unit with access to gaseous PH 3 and H 2 S sources and an accessible total pressure up to 1 bar can solve this problem. Another advantage of including an RRTP setup is that it is technically much easier to reach temperatures in excess of 1000 °C and avoid corrosion in an RTP furnace than in a sputter system. In fact, an ex-situ annealing step in a S-containing atmosphere is common practice in sulfide thin film synthesis as it can ensure film crystallization without the loss of sulfur. In many labs, transferring a thin film from deposition equipment to reactive annealing equipment requires exposure to ambient air. This limits the applicability of the two-step film growth process (deposition + annealing) to materials that do not react with oxygen or moisture when they are not crystallized or not fully sulfurized/phosphorized. Sacrificial capping layers can be deposited on top of air-sensitive films to slow down their reaction with air,[115] but this adds complication to the process, and at least a small fraction of the capping layer is likely to be incorporated into the final film and may affect its electronic properties. Transfer of thin-film samples between the deposition and the annealing systems in a glove box under an inert atmosphere (Fig. ) can solve these issues.