| AVS 64th International Symposium & Exhibition | |
| Surface Science Division | Wednesday Sessions |
| Session SS-WeM |
| Session: | Deposition and Growth at Surfaces |
| Presenter: | Shen Hu, The University of Texas at Austin |
| Authors: | S. Hu, The University of Texas at Austin A. Posadas, The University of Texas at Austin A. Demkov, The University of Texas at Austin J.G. Ekerdt, The University of Texas at Austin |
| Correspondent: | Click to Email |
The growth SrTiO3, SrZrO3 and BaTiO3 perovskites on Ge (001) has been achieved by atomic layer deposition (ALD). We find that the initial dosing of the barium- or strontium-bis(triisopropylcyclopentadienyl) precursors on a clean Ge (001) surface forms the same Zintl template as 0.5-monolayer (ML) of Ba on Ge (001) when deposited by molecular beam epitaxy (MBE).1 The procedure to produce a Zintl template is shown in Figure 1. The Zintl templates formed by both ALD and MBE display the same X-ray photoelectron binding energy shifts for Ba 3d, Sr 3d and Ge 3d and both surfaces result in symmetric Ge surface dimers. The surface core level shifts indicate charge transfer from the alkaline earth metal to the Ge surface. In-situ reflective high energy electron diffraction images demonstrate the same 2×1-reconstructed surface after using both molecular and atomic Ba sources. High-angle annular-dark-field scanning transmission electron microscopy further confirms all ALD-grown BaTiO3, SrZrO3, SrHfO3 and SrHf0.55Ti0.45O3 on Ge have the similar Zintl template interface structure as MBE-grown BaTiO3 on Ge. Carbon, likely in the form of dissociated ligands, binds to the Ge (001) surface during precursor dosing and some of this carbon contaminates the interface after growth.
Herein we report the role of a Zintl template formed from 0.5-ML of elemental Ba in minimizing surface carbon contamination and facilitating crystal growth. SrZrO3 films are grown using ALD on the templated-surface at 225 °C using strontium-bis(triisopropylcyclopentadienyl), tetrakis(dimethylamido) zirconium (IV) and H2O. The ALD chamber surfaces cannot be purged perfectly and previously-dissociated ligand products will adsorb on a clean Ge surface as shown in Figure 2 before any precursor dosing; the red line indicates that around 1 ML equivalent carbon adsorbs on the surface. An MBE-formed Zintl template blocks carbon adsorption (Figure 2). Examination of carbon levels in 2-nm and 10-nm SrZrO3 films grown on bare Ge indicates the presence of carbon in the 2-nm films suggesting this initial carbon adsorption remains at the interface. Carbon levels in 2-nm and 10-nm SrZrO3 films grown on 0.5-ML Ba Zintl layers cannot be detected in 2-nm and 10-nm SrZrO3 films, confirming that the Zintl layer protects the surface from carbon contamination. In-situ XPS analysis also shows the MBE-grown Zintl template is relatively unreactive with H2O; H2O reacts with adsorbed Sr and Zr precursors. The growth mechanism will be discussed during the presentation.
(Figure 1 and Figure 2 are shown in supplemental document)
1S. Hu et al., J. Chem. Phys. 146, 052817 (2016).