Article | Published:

Direct measurement of the propagation velocity of defects using coherent X-rays

Nature Physics volume 12, pages 794799 (2016) | Download Citation

Abstract

The properties of artificially grown thin films are often strongly affected by the dynamic relationships between surface growth processes and subsurface structure. Coherent mixing of X-ray signals promises to provide an approach to better understand such processes. Here, we demonstrate the continuously variable mixing of surface and bulk scattering signals during real-time studies of sputter deposition of a-Si and a-WSi2 films by controlling the X-ray penetration and escape depths in coherent grazing-incidence small-angle X-ray scattering. Under conditions where the X-ray signal comes from both the growth surface and the thin film bulk, oscillations in temporal correlations arise from coherent interference between scattering from stationary bulk features and from the advancing surface. We also observe evidence that elongated bulk features propagate upwards at the same velocity as the surface. Furthermore, a highly surface-sensitive mode is demonstrated that can access the surface dynamics independently of the subsurface structure.

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Acknowledgements

We thank R. Ziegler for beamline support. R.L.H. and J.G.U. were supported by the US Department of Energy (DOE) Office of Science, Office of Basic Energy Sciences (BES) under DE-FG02-07ER46380; C.W., K.F.L. and M.G.R. were supported by DOE BES grant DE-FG02-03ER46037. This research used resources of the Advanced Photon Source (APS), a US DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.

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Affiliations

  1. Department of Physics and Materials Science Program, University of Vermont, Burlington, Vermont 05405, USA

    • Jeffrey G. Ulbrandt
    •  & Randall L. Headrick
  2. Division of Materials Science and Engineering, Boston University, Boston, Massachusetts 02215, USA

    • Meliha G. Rainville
    • , Christa Wagenbach
    •  & Karl F. Ludwig Jr
  3. Advanced Photon Source, Argonne National Lab, Argonne, Illinois 60439, USA

    • Suresh Narayanan
    • , Alec R. Sandy
    •  & Hua Zhou
  4. Department of Physics, Boston University, Boston, Massachusetts 02215, USA

    • Karl F. Ludwig Jr

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Contributions

All authors participated in the experimental work at the APS. R.L.H., C.W. and M.G.R. were chiefly responsible for the subsequent processing and analysis of the data, with significant contributions from S.N.; R.L.H. and J.G.U. designed and constructed the growth chamber; R.L.H. and K.F.L. devised the new experimental methods and directed the project. All authors participated in preparing the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Randall L. Headrick.

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https://doi.org/10.1038/nphys3708

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