Abstract
We present an extensive atomic resolution frequency modulation dynamic force microscopy study of ultrathin aluminium oxide on a single crystalline NiAl(110) surface. One-dimensional surface defects produced by domain boundaries have been resolved. Images are presented for reflection domain boundaries (RDBs), four different types of antiphase domain boundaries, a nucleation-related translation domain boundary and also domain boundary junctions. New structures and aspects of the boundaries and their network are revealed and merged into a comprehensive picture of the defect arrangements. The alumina film also covers the substrate completely at the boundaries and their junctions and follows the structural building principles found in its unit cell. This encompasses square and rectangular groups of surface oxygen sites. The observed structural elements can be related to the electronic signature of the boundaries and therefore to the electronic defects associated with the boundaries. A coincidence site lattice predicted for the RDBs is in good agreement with experimental data. With Σ = 19 it can be considered to be of low-sigma type, which frequently coincides with special boundary properties. Images of asymmetric RDBs show points of good contact alternating with regions of nearly amorphous disorder in the oxygen sublattice.
Highlights
We present an extensive atomic resolution frequency modulation dynamic force microscopy study of ultrathin aluminium oxide on a single crystalline NiAl(110) surface
We present a comprehensive atomic resolution dynamic force microscopy study of several new as well as known surface structures of the defect network
At the node the sum of all Burgers vectors has to be zero to satisfy Frank’s node condition, if lattice strain is to be prevented. This is facilitated by the decomposition of each junction into two triple junctions which are connected by a well-defined segment of antiphase domain boundaries (APDBs) III delivering the required Burgers vector bIII
Summary
All data have been recorded in ultrahigh vacuum (UHV) at cryogenic temperature (5 K). The microscope is equipped with a quartz tuning fork sensor which comprises a Pt/Ir wire attached with electrically insulating epoxy adhesive to one quartz prong as a tip. For FM-DFM, the microscope is operated in the frequency modulation mode at a small constant oscillation amplitude AOSC of 3.8 Å. Sensor parameters are the unperturbed resonance frequency f0= kHz, spring constant k ∼ 000 N m−1 and quality factor Q ∼ 25 000 of the tuning fork. Due to slight thermal drift, the unit cells had to be straightened out. The deviation of the unit cell measures in the model from those experimentally determined by low-energy electron diffraction (LEED) is considered small. Exposure to molecular oxygen in the 10−6 mbar range at 550 K and subsequent annealing in vacuum at about 1100 K, each for ∼10 min, produces the ordered oxide film. If present and not desired, may be closed by repeating the oxidation procedure [32, 33]
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