Coherent X-ray spectroscopy reveals the persistence of island arrangements during layer-by-layer growth

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Understanding surface dynamics during epitaxial film growth is key to growing high-quality materials with controllable properties. X-ray photon correlation spectroscopy (XPCS) using coherent X-rays opens new opportunities for in situ observation of atomic-scale fluctuation dynamics during crystal growth. Here, we present XPCS measurements of two-dimensional island dynamics during homoepitaxial growth in the layer-by-layer mode. Analysis of the results using two-time correlations reveals a new phenomenon—a memory effect in the arrangement of islands formed on successive crystal layers. Simulations indicate that this persistence in the island arrangements arises from communication between islands on different layers via adatoms. With the worldwide advent of new coherent X-ray sources, the experimental and analysis methods pioneered here will enable broad application of XPCS to observe atomic-scale processes on surfaces.

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Fig. 1: Experimental schematic and diffuse scattering from islands.
Fig. 2: Measured two-time correlations.
Fig. 3: Simulated two-time correlations.
Fig. 4: Correlations of island positions.
Fig. 5: Persistence times of island arrangements.

Data availability

Raw X-ray data were generated at the Advanced Photon Source large-scale facility. The data that support the plots within this paper and other findings of this study are available from the corresponding authors on reasonable request.


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We thank M. Sutton for suggesting the smoothing method used in the speckle analysis, and D. Byelov of ASI and R. Woods of the APS Detector Pool for expert assistance with the area detector. Support was provided by the Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering (XPCS measurements and analysis) and Scientific User Facilities (KMC model development). Measurements were carried out at the Advanced Photon Source, a DOE Office of Science user facility operated by Argonne National Laboratory. Computing resources were provided on Blues and Fusion, high-performance computing clusters operated by the Laboratory Computing Resource Center at Argonne National Laboratory.

Author information

G.J., M.J.H., J.A.E, P.H.F., G.B.S., C.T., H.Z. and H.K. developed the pink beam XPCS set-up and carried out the measurements. D.X., P.Z., G.B.S. and C.T. developed and carried out the simulations. G.J. and G.B.S. analysed the results. All coauthors contributed to drafting and editing the manuscript.

Correspondence to Guangxu Ju or G. Brian Stephenson.

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