Resolving the Evolution of Atomic Layer-Deposited Thin-Film Growth by Continuous In Situ X-Ray Absorption Spectroscopy

• Published in: Chemistry of materials 2021-02, Vol.33 (5)
• Main Authors: Qu, Xiaohui, Yan, Danhua, Li, Ruoshui, Cen, Jiajie, Zhou, Chenyu, Zhang, Wenrui, Lu, Deyu, Attenkofer, Klaus, Stacchiola, Dario J., Hybertsen, Mark S., Stavitski, Eli, Liu, Mingzhao
• Format: Article
• Language: English
• Subjects: atomic layer deposition; MATERIALS SCIENCE; oxides; precursors; thickness; x-ray absorption near edge spectroscopy
• ISSN: 0897-4756; 1520-5002

In situ synchrotron X-ray absorption near-edge structure characterization of thin-film titania growth by atomic layer deposition (ALD) over ZnO nanowires reveals persistent low-coordinated Ti motifs leading to a new picture of ALD growth. Through the design of growth and measurement cycles, Ti K-edge spectral data are continuously recorded so as to characterize the film evolution as a function of ALD cycle number and the surface changes within the time scale of the ALD cycle. A unified set of analysis tools is developed to interpret the time-series of spectral data. A prenucleation stage of growth, a transition region, and then a steady-state growth stage are observed with distinguishable features. Multivariate curve resolution analysis, that is physically constrained, demonstrates two specific spectral components with associated, time-dependent concentrations. The bulk-film component tracks the stages of growth. The surface and interface components, present throughout the stages of growth, reveal a significant coverage of relatively isolated or loosely networked tetrahedrally coordinated Ti atomic motifs. Lastly, spectral signatures for the intra-cycle growth kinetics are reconstructed at a time resolution of ~1 s and demonstrate that the transient Ti motifs on the growing surface stabilize within a few seconds of the Ti precursor pulse.