Organic and inorganic–organic thin film structures by molecular layer deposition: A review

Abstract

SummaryThe possibility to deposit purely organic and hybrid inorganic–organic materials in a way parallel to the state-of-the-art gas-phase deposition method of inorganic thin films, i.e., atomic layer deposition (ALD), is currently experiencing a strongly growing interest. Like ALD in case of the inorganics, the emerging molecular layer deposition (MLD) technique for organic constituents can be employed to fabricate high-quality thin films and coatings with thickness and composition control on the molecular scale, even on complex three-dimensional structures. Moreover, by combining the two techniques, ALD and MLD, fundamentally new types of inorganic–organic hybrid materials can be produced. In this review article, we first describe the basic concepts regarding the MLD and ALD/MLD processes, followed by a comprehensive review of the various precursors and precursor pairs so far employed in these processes. Finally, we discuss the first proof-of-concept experiments in which the newly developed MLD and ALD/MLD processes are exploited to fabricate novel multilayer and nanostructure architectures by combining different inorganic, organic and hybrid material layers into on-demand designed mixtures, superlattices and nanolaminates, and employing new innovative nanotemplates or post-deposition treatments to, e.g., selectively decompose parts of the structure. Such layer-engineered and/or nanostructured hybrid materials with exciting combinations of functional properties hold great promise for high-end technological applications.

Tunable optical properties of hybrid inorganic–organic [(TiO2)m(Ti–O–C6H4–O–)k]n superlattice thin films

“…Fabrication of the thin films was carried out in a Picosun R-100 ALD reactor using N2 as a carrier 15 gas for the precursors and as a purging gas. Borosilicate glass and silicon were used as substrates and the deposition temperature was set at 210 o C for all the depositions.…”

“…10,11 Molecular layer deposition can be used to fabricate thin films of organic polymers, such as polyamides and polyimides. 12,13 Most interestingly, use of metal precursors together with organic precursors enables hybrid inorganic-organic thin films to be fabricated with combined ALD/MLD processes, 14,15 where the organic precursors can be, e.g., organic alcohols 14,16 or carboxylic acids. 17,18 Such combined ALD/MLD processes also allow for fabrication of hybrid inorganic-organic materials in the form of nanolaminates [19][20][21] and superlattices [22][23][24] in an elegant manner.…”

Ultra-low thermal conductivity in TiO2:C superlattices

“…[14][15] An intriguing route for mixing inorganics and organics with highly dissimilar properties in a controlled manner is to employ atomic layer deposition (ALD) and molecular layer deposition (MLD) techniques in combination (ALD/MLD). 16 Besides simple homogeneous hybrid thin-film materials, such a combinatorial approach enables one to fabricate inorganicorganic superlattices with atomic/molecular monolayer precision via self-limiting surface reactions. [17][18][19] The selflimited film growth moreover allows for conformal coating of nanostructures, the key requirement for many future applications.…”

Molecular Layer Deposition from Dissolved Precursors

“…Of course, a number of studies have shown the successful deposition of organic or hybrid films by gALD, 13,14 but the so-called 'molecular layer deposition' has remained limited in scope due to the constraints that the small number of available volatile and reactive precursors represents. The difficulty becomes apparent if we consider a polyamide as an example (an important class since it includes biological as well as manufactured fibers such as silk, Nylon and Kevlar), Figure 1.…”

“…likely to react with two neighboring reactive sites on the solid surface, which results in a non-reactive surface for the subsequent ALD/MLD step, situation 1. 13,14 Circumventing this limitation is possible by exploiting the wealth of activation and protection/deprotection strategies and reagents optimized in organic synthesis and solid-state synthesis of biopolymers, see 3 and 4. 15 Since activating and protecting groups are typically large and bulky, and often charged, these strategies cannot be implemented in gALD/gMLD.…”