Structural transitions and relaxation processes during the epitaxial growth of ultrathin CaF2 films on Si(111)
Name
Deiter-2010-Structural transitio.pdf
Size
338.87 KB
Format
Adobe PDF
Checksum (MD5)
64b558c898c1c86cb7b5db019d708624
Author(s)
Deiter, Carsten
Bierkandt, Markus
Klust, Andreas
Kumpf, Christian
Su, Yixi
Bunk, Oliver
Feidenhans’l, Robert
Wollschlager, Joachim
Date Issued
August 2010
Journal
Physical Review B
Publisher
American Physical Society
Citation
Deiter, Carsten et al. “Structural Transitions and Relaxation Processes During the Epitaxial Growth of Ultrathin CaF2 Films on Si(111).” Physical Review B 82.8 (2010) : 085449. © 2010 The American Physical Society
Version
Final published version
Abstract
The structure and morphology of ultrathin lattice matched CaF2 films of very few monolayers thickness, which were deposited on Si(111) substrates by molecular-beam epitaxy, have been studied in situ by synchrotron based grazing incidence x-ray diffraction. Even for the thinnest investigated film of three monolayers thickness, the in-plane structure of the CaF2 film is determined by a lateral separation in two domains: a pseudomorphic phase assuming the lateral lattice constant of the Si(111) substrate and a completely relaxed phase. Analysis of the crystal truncation rods verifies that both phases adopt the entire homogeneous CaF2 film thickness. Therefore, we propose that atomic steps of the substrate bypass the nucleation barrier for the formation of (Shockley partial) dislocations so that the film starts to relax below the classical critical film thickness. While the relaxed phase assumes also the CaF2 bulk lattice constant for the vertical direction, the vertical lattice constant of the pseudomorphic phase increases due to the compressive lateral strain at the interface. This vertical expansion of the pseudomorphic phase, however, is larger than expected from the elastic constants of the CaF2 bulk. The fraction of the pseudomorphic CaF2 phase decreases with increasing film thickness. The interface between the pseudomorphic CaF2 phase and the Si(111) substrate is characterized by Ca on T4 sites, a smaller distance between the Si(111) substrate and the CaF interface layer and an expanded layer distance between CaF interface layer and the completely stoichiometric CaF2 film.
MIT Department
Massachusetts Institute of Technology. Department of Chemistry
Terms of Use
Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use.
Persistent DSpace Link
DOI of Published Version
https://doi.org/10.1103/PhysRevB.82.085449
