Topological crystalline insulators (TCIs) are new materials with metallic surface states protected by crystal symmetry. The properties of molecular beam epitaxy grown SnTe TCI on SrTiO3(001) are investigated using scanning tunneling microscopy (STM), noncontact atomic force microscopy, low‐energy and reflection high‐energy electron diffraction, X‐ray diffraction, Auger electron spectroscopy, and density functional theory. Initially, SnTe (111) and (001) surfaces are observed; however, the (001) surface dominates with increasing film thickness. The films grow island‐by‐island with the [011] direction of SnTe (001) islands rotated up to 7.5° from SrTiO3[010]. Microscopy reveals that this growth mechanism induces defects on different length scales and dimensions that affect the electronic properties, including point defects (0D); step edges (1D); grain boundaries between islands rotated up to several degrees; edge‐dislocation arrays (2D out‐of‐plane) that serve as periodic nucleation sites for pit growth (2D in‐plane); and screw dislocations (3D). These features cause variations in the surface electronic structure that appear in STM images as standing wave patterns and a nonuniform background superimposed on atomic features. The results indicate that both the growth process and the scanning probe tip can be used to induce symmetry breaking defects that may disrupt the topological states in a controlled way.
The properties of artificially grown thin films are strongly affected by surface processes during growth. Coherent X-rays provide an approach to better understand such processes and fluctuations far from equilibrium. Here we report results for vacuum deposition of C60on a graphene-coated surface investigated with X-ray Photon Correlation Spectroscopy in surface-sensitive conditions. Step-flow is observed through measurement of the step-edge velocity in the late stages of growth after crystalline mounds have formed. We show that the step-edge velocity is coupled to the terrace length, and that there is a variation in the velocity from larger step spacing at the center of crystalline mounds to closely-spaced, more slowly propagating steps at their edges. The results extend theories of surface growth, since the behavior is consistent with surface evolution driven by processes that include surface diffusion, the motion of step-edges, and attachment at step edges with significant step-edge barriers.
more » « less- Award ID(s):
- 1709380
- PAR ID:
- 10153405
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 10
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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