Manganese Oxide Thin Films on Au(111): Growth Competition between MnO and Mn₃O₄

Abstract

The growth of manganese oxide on a Au(111) support has been examined over a wide range of preparation conditions and film thicknesses by means of scanning tunneling microscopy (STM), electron diffraction, and photoelectron spectroscopy. Two oxide polymorphs were found to coexist on the gold surface. Whereas MnO-type structures prevail at oxygenlean preparation conditions, annealing in oxygen gives Hausmannite Mn 3 O 4 as the dominant phase. Both polymorphs adopt square structures that only permit row-matched growth on the hexagonal gold, explaining the high tendency for oxide dewetting at elevated temperature. The manganese oxide films are thus polycrystalline and consist of a large number of submicrometer grains with different orientations and surface terminations. A variety of square and line patterns were identified on top of the oxide crystallites, all of them being compatible with either the primitive 5.8 × 5.8 Å 2 cell of Mn 3 O 4 (001) or an ordered MnO(100) vacancy structure. STM conductance spectroscopy provides insight into the electronic properties of the Mn−O islands and yields the approximate size of the band gap as well as the energy position of localized Mn 3d levels in the gap region. Our work illuminates the structural and electronic properties of manganese oxide films grown on Au(111) and therefore complements earlier studies performed on Pt(111), Pd(100), and Ag(100) supports.

Dynamic Structural Evolution of Mn–Au Alloy and MnOx Nanostructures on Au(111) under Different Atmospheres

“…Depending on the different preparation conditions, O–Mn–O trilayers, MnO(001), and MnO(111) can be prepared on Pt(111). A similar phenomenon was also observed on Rh(100). , Additionally, at higher oxygen partial pressure a transition from rock-salt MnO to spinel Mn 3 O 4 occurred. ,, …”

“…33,34 Additionally, at higher oxygen partial pressure a transition from rock-salt MnO to spinel Mn 3 O 4 occurred. 31,38,46 Although growth of MnO and Mn 3 O 4 nanoislands and thin films has been reported on many metal substrates, atomic structure and catalytic properties of these MnO x overlayers still need further investigation. Here, we first discuss the oxidation of the Mn−Au surface alloy using near-ambient pressure (NAP) scanning tunneling microscopy (STM).…”

“…Fundamental studies over MnO x nanoislands and thin films have been performed on many metal single crystal substrates, including Pd, − Ag, − Rh, − Cu, , Au, − and Pt. − It is well-known that the symmetry and lattice constant of the substrate surface are critical for epitaxial growth of oxide thin films. For instance, a square oxide overlayer can be obtained on a substrate surface with tetragonal symmetry, such as epitaxial rock salt MnO(001) on Ag(001) , and spinel Mn 3 O 4 (001) on Ag(001) .…”

Predominance of Subsurface and Bulk Oxygen Vacancies in Reduced Manganese Oxide

“…The coverage of the Mn oxide film could be controlled by the deposition time of Mn, and the film thickness was estimated to be ∼10 nm. 42 The XPS results of a freshly prepared film are shown in Figure S1. By fitting the Mn 2p peak, a pair of satellite peaks could be observed at 650.4 and 663.0 eV.…”

“…Mn was deposited on the clean Au(111) surface at room temperature in 1 × 10 –6 mbar O 2 ; then, the sample was heated to 673 K in 5 × 10 –6 mbar O 2 . The coverage of the Mn oxide film could be controlled by the deposition time of Mn, and the film thickness was estimated to be ∼10 nm . The XPS results of a freshly prepared film are shown in Figure S1.…”