Atomic/Molecular Layer Deposition for Designer's Functional Metal–Organic Materials

Atomic layer deposition (ALD) for high-quality conformal inorganic thin films is one of the cornerstones of modern microelectronics, while molecular layer deposition (MLD) is its less-exploited counterpart for purely organic thin films. Currently, the hybrid of these two techniques, i.e., ALD/MLD, is strongly emerging as a state-of-the-art gas-phase route for designer's metal–organic thin films, e.g., for the next-generation energy technologies. The ALD/MLD literature comprises nearly 300 original journal papers covering most of the alkali and alkaline earth metals, 3d transition metals, and lanthanides as the metal component and a variety of aliphatic, aromatic, and natural organic components. Some of these ALD/MLD processes yield in situ crystalline coordination-polymer- or metal–organic-framework-like structures. Another attractive aspect is that many of the metal–organics realized through ALD/MLD are fundamentally new materials, and even unaccessible through conventional synthesis. Here, the current state of research in the field is presented, by i) providing a comprehensive account of the ALD/MLD processes so far developed, ii) addressing the constraints/possibilities for growing in situ crystalline metal–organic films, iii) highlighting some intriguing ALD/MLD materials and their application potential, and iv) making a brief outlook to the future perspectives and challenges in the field.