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

Abstract

organic ligands act as bridges between the metal centers to form infinite 1D, 2D, or 3D structures. These materials are often referred to as coordination polymer (CP) [1] or metal-organic framework (MOF) [2] materials; the latter term is used when the metal-organic material is crystalline and highly porous. [3] The research field of CP-and MOF-type materials has grown tremendously over the last two decades. The structural and chemical diversity of these materials has served as a continuous source of scientific excitement; the same diversity has also triggered huge technological interest as these materials possess enormous potential to be tailored for a wide variety of applications ranging from gas capture, storage, and separation to sensing, catalysis, optics, electronics, and energy storage. [4][5][6][7] Most of the targeted application breakthroughs of metal-organics require that these materials can be produced as highquality thin films and coatings, which can be integrated with the other components in the actual device configuration. The possibility to deposit such thin films in an industry-feasible manner on the substrate types needed, would be a major step forward in the field. [8] Traditionally, solvent-based processes such as liquid-phase epitaxy, Langmuir-Blodgett, layer-by-layer, and electrochemical deposition techniques have been used for metal-organic thin films. [9][10][11] These are, however, incompatible with the requirements set by the possible integration of the materials in microelectronics. This is due to corrosion and contamination risks, and the problems in patterning and precise deposition on high-aspect-ratio features. Hence, it is vital to develop solventfree thin-film deposition routes for the metal-organic material family. In the optimal case, these deposition methods should allow conformal coatings on large-area and high-aspect-ratio substrates.The currently strongly emerging ALD/MLD technique is uniquely suited to address the challenge in a scientifically elegant yet industrially feasible way. This technique is derived from the two parent gas-phase thin-film techniques: ALD for inorganic materials (mostly binary metal oxides, sulfides, and nitrides), [12][13][14] and its counterpart MLD for purely organic thin films (e.g., polyimides and polyamides). [15] In both cases, the attractive film growth characteristics are derived from the unique way of separating the different precursor gas pulses. Currently, ALD is the standard thin-film technology in many 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...

Transition Metal Dichalcogenide TiS2 Prepared by Hybrid Atomic Layer Deposition/Molecular Layer Deposition: Atomic-Level Insights with In Situ Synchrotron X-ray Studies and Molecular Surface Chemistry

“…Such possibility can be accessed by combining the use of organic precursors during the ALD process (such as alcohols, ROH�R being a generic organic fragment�rather than H 2 O as an oxygen source). The presence of the organic chemical residues prevents the crystallization during the growth of the hybrid inorganic−organic thin film (metalcones in the examples just mentioned 13,19 ) at low temperatures. A subsequent treatment (typically annealing, which induces the loss of most of the organic fragment) leads to the crystallization of the mineral phase.…”

“…Such possibility can be accessed by combining the use of organic precursors during the ALD process (such as alcohols, ROHR being a generic organic fragmentrather than H 2 O as an oxygen source). The presence of the organic chemical residues prevents the crystallization during the growth of the hybrid inorganic–organic thin film (metalcones in the examples just mentioned , ) at low temperatures. A subsequent treatment (typically annealing, which induces the loss of most of the organic fragment) leads to the crystallization of the mineral phase. , For instance, the combination of such an organic precursor-based ALD approachwhich is called herein atomic layer deposition/molecular layer deposition (ALD/MLD)and the post-annealing step allowed to control the porosity of Al 2 O 3 thin films, as well as the crystallinity, composition, and electrochemical properties of SnO/SnO 2 , TiO 2 , and V 2 O 5 .…”

Solution Atomic Layer Deposition of Smooth, Continuous, Crystalline Metal–Organic Framework Thin Films

“…Hybrid (metal–organic) materials have been accessed by gas-phase ALD as the so-called “molecular layer deposition” (MLD) generalization; however, the range of compounds accessible in MLD is quite narrow. − This is related to the limited choice of molecular precursors that possess sufficient thermal stability and volatility. , ZIF-8 MOF has been obtained from a conversion of ALD-grown ZnO . Success in the direct growth of MOFs by ALD has remained limited. − In the literature, it is reported that the crystallinity is obtained upon post-deposition processing, either with a thermal annealing step or an extended aging at room temperature. Gas-phase deposition methods usually compete with the limited thermal stability of MOFs.…”

“… 26 Success in the direct growth of MOFs by ALD has remained limited. 27 − 30 In the literature, it is reported that the crystallinity is obtained upon post-deposition processing, either with a thermal annealing step or an extended aging at room temperature. Gas-phase deposition methods usually compete with the limited thermal stability of MOFs.…”

Low-temperature ALD/MLD growth of alucone and zincone thin films from non-pyrophoric precursors

“…[1][2][3] Molecular layer deposition (MLD) is based on the same principles as ALD but for purely organic polymers, while the combination of the two techniques, ALD/MLD, provides an attractive route for the fabrication of intriguing metal-organic thin films for a variety of emerging application fields. [4][5][6][7][8] While the inorganic component in these hybrid materials typically forms the basis for the desired electrical, optical, magnetic or catalytic functionality, the organic component could bring e.g. mechanical flexibility, 5,9,10 additional structural/chemical tunability [11][12][13][14][15] or even unforeseen bio-or lightbased actions [16][17][18][19] for the hybrid material.…”