Atomic/molecular layer deposited crystalline metal-organic thin films based on low-valent metals

Crystalline metal-organic thin films offer promising solutions for the diverse needs of miniature electronic devices, requiring functional or smart materials for sensing, energy storage, or gas capture. The semiconductor industry has widely employed atomic layer deposition (ALD) of thin films in applications that require ultra-thin and high-quality coatings on demanding surfaces. The advantage of the ALD method is the controllability of the thin film growth with atomic-level precision, as well as the uniformity of the resulting coating on large and complex structures. However, with the goal of continuously improving the performances of nanoscale devices, studies on more complex thin-film materials are needed. Thin-film materials with unique physical or chemical properties can be achieved by combining the organic linking molecules and metal counterparts, which is possible by atomic/molecular layer deposition (ALD/MLD). In this thesis, 19 different ALD/MLD processes based on low-valent metals together with aromatic organic counterparts were studied. The most important finding was that the ALD/MLD technique can be used to directly produce a variety of in-situ crystalline metal-organic thin-film materials, including materials that have not been previously fabricated by any other method. The research also provides valuable insight for designing such ALD/MLD processes: metal precursors with fewer and smaller ligands can promote the formation of an in-situ crystalline thin-film structure. A significant observation from the application point of view was that some of the in-situ crystalline thin-film structures discovered by the ALD/MLD technique can serve as guest-matrix structures and host intercalated metal ions or reversibly adsorb water molecules without disrupting the fundamental crystal structure. Currently, there are already 50 original ALD/MLD publications where thin-film structures show either in-situ or post-deposition treated crystallinity. Since the field of metal-organic thin films is still in its early stage, the ALD/MLD technique offers plenty of possibilities for developing novel and functional thin films.