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Mechanistic Insight into Solution-Based Atomic Layer Deposition of CuSCN Provided by In Situ and Ex Situ Methods

Solution-based atomic layer deposition (sALD) processes enable the preparation of thin films on nanostructured surfaces while controlling the film thickness down to a monolayer and preserving the homogeneity of the film. In sALD, a similar operation principle as in gas-phase ALD is used, however, with a broader range of accessible materials and without requiring expensive vacuum equipment. In this work, a sALD process was developed to prepare CuSCN on a Si substrate using the precursors CuOAc and LiSCN. The film growth was studied by ex situ atomic force microscopy (AFM), analyzed by a neural network (NN) approach, ellipsometry, and a newly developed in situ infrared (IR) spectroscopy experiment in combination with density functional theory (DFT). In the self-limiting sALD process, CuSCN grows on top of an initially formed two-dimensional (2D) layer as three-dimensional spherical nanoparticles with an average size of ∼25 nm and a narrow particle size distribution. With increasing cycle number, the particle density increases and larger particles form via Ostwald ripening and coalescence. The film grows preferentially in the β-CuSCN phase. Additionally, a small fraction of the α-CuSCN phase and defect sites form.

solution atomic layer deposition ; liquid phase ; in situ IR spectroscopy ; atomic force microscopy ; copper thiocyanate ; neural network ; density functional theory ; liquid atomic layer deposition

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsami.2c16943. In situ IR spectra between 3000 and 1100 cm–1 of the growth of CuSCN by sALD; comparison of AFM images of the growth of CuSCN by sALD with the corresponding blind experiments; ν(SCN) band position of ν-CuSCN during 23 cycles of the sALD process; detailed measurement procedure and proposed reaction mechanism for deposition of CuSCN; description of home-build in situ sALD flow cell; and proof of self-limitation of the deposition process (PDF)