Ionic Liquid-Mediated Route to Atomic Layer Deposition of Tin(II) Oxide via a C–C Bond Cleavage Ligand Modification Mechanism

Abstract

Atomic layer deposition (ALD) is a technologically important method to grow thin films with high conformality and excellent thickness control from vapor phase precursors. The development of new thermal ALD processes can be limited by precursor reactivity and stability: reaction temperature and precursor design are among the few variables available to achieve higher reactivity in gas-phase reactions, unlike in solution synthesis, where the use of solvent and/or a catalyst can promote a desired reaction. To bridge this synthesis gap between vapor-phase and solution-phase, we demonstrate the use of an ultrathin coating layer of a vapor phase-compatible solvent�an ionic liquid (IL)�on our growth substrate to perform ALD of SnO. Successful SnO deposition is achieved using tin acetylacetonate and water, a process that otherwise would require a stronger counter-reactant such as ozone. The presence of the layer of IL allows a solvent-mediated reaction mechanism to take place on the growth substrate surface. We report a growth per cycle of 0.67 Å/cycle at a deposition temperature of 100 °C in an IL comprising 1ethyl-3-methylimidazolium hydrogen sulfate. Characterization of the ALD films confirms the SnO film composition, and 1 H and 13 C NMR are used to probe the solvent-mediated ALD reaction, suggesting a solvent-mediated addition−elimination-type mechanism which breaks a C−C bond in acetylacetonate to form acetone and acetate. Density functional theory calculations show that the IL solvent is beneficial to the proposed solvent-mediated mechanism by lowering the C−C bond cleavage energetics of acetylacetonate compared to the vapor phase. A general class of ligand modification reactions for thermal ALD is thus introduced in this work.

The surface chemistry of the atomic layer deposition of metal thin films

“…Nevertheless, some novel ideas have been explored in this direction. In a notable recent example, a layer of an ionic liquid, 1-ethyl-3methylimidazolium hydrogen sulfate, was preadsorbed on the substrate (a silicon wafer) in order to facilitate the ALD of SnO films with tin(II)-acetylacetonate (Sn(acac) 2 ) using water instead of the more reactive ozone co-reactant [104]. The promotional effect of the ionic liquid in this case was ascribed to a lowering in the activation barrier for a C-C bond-scission step in a coordinated acac ligand to produce and release acetone and acetic acid.…”

A Scalable Synthesis of Ag Nanoporous Film As an Efficient SERS-Substrates for Sensitive Detection of Nanoplastics

“…40,41 For instance, DESs have been integrated with vapor phase deposition processes such as atomic layer deposition (ALD) to perform catalytic surface reactions. 42,43 We have also recently demonstrated the successful integration of DESs with the thermal evaporation process to prepare Ag−Au bimetallic nanoparticle films. 44 However, preparing nanoporous Ag over the DES surface using thermal evaporation is a challenging task.…”

“…Owing to their unique properties, DES has been widely used as a potential green solvent for many promising applications such as an electrolyte for metal ion batteries, in CO 2 capture, in biocatalysis, and in the synthesis of functional materials. , Moreover, DES exhibits extremely low vapor pressure in the range of 35.32 to 60.77 Pa below 343.15 K, and it withstands high vacuum pressure, which makes it ideal for vacuum deposition conditions. In addition, owing to their extended hydrogen bonding structure, DES has been used as a green medium for metallic nanoparticle synthesis and self-assembly of metal NPs over the DES surface. , For instance, DESs have been integrated with vapor phase deposition processes such as atomic layer deposition (ALD) to perform catalytic surface reactions. , We have also recently demonstrated the successful integration of DESs with the thermal evaporation process to prepare Ag–Au bimetallic nanoparticle films . However, preparing nanoporous Ag over the DES surface using thermal evaporation is a challenging task.…”

Photoinitiated chemical vapor deposition (piCVD) of composition tunable, ionically conductive hydrogels on diverse substrates

“…Using iCVD, the Gupta lab isolated a unique material that retained many of its ionic liquid capabilities, such as high conductivity, while also solidifying into a persistent gel material. Since this work, similar liquid templating techniques have also been shown to be useful in the production of metal-oxide layers [32] and previously-unachievable polymer structures [33,34]. While these ionic liquidbased gels are interesting, their cytotoxicity precludes their use in wearable/implantable electronics and their high cost limits their practicality for soft robotics applications.…”