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

Abstract

Construction of inverse oxide/metal model catalyst with specific chemical composition and interfacial structure is essential for clarifying their structure−performance relationship. This work describes the structural evolution of Mn−Au surface alloy and two-dimensional manganese oxide (MnO x ) islands on Au(111) surface under different treatment conditions. By employing near-ambient pressure scanning tunneling microscopy and Xray photoelectron spectroscopy, we can obtain four different MnO x structures. Among them, double-layer square lattice Mn 3 O 4 (001) and monolayer parallelogram-shaped Mn 3 O 4 are prepared by postannealing Mn−Au surface alloy in "oxygen-poor" and "oxygenrich" regimes, respectively. Annealing the monolayer parallelogram-shaped Mn 3 O 4 in vacuum to 700 K produces a double-layer structure consisting of Mn 3 O 4 top layer and MnO(111) bottom layer, while double-layer MnO(111) is formed after annealing in vacuum to 800 K. Our study lays the foundation for exploring the catalytic properties of inverse manganese oxide/metal model catalysts.

Direct observation of accelerating hydrogen spillover via surface-lattice-confinement effect

“…The atomic structure (Fig. 1e) is almost the same as that of Mn 3 O 4 / Au(111) surface prepared in "oxygen rich" regime 21 , where the bright features are arranged in a zigzag-like pattern with a spacing of ∼3.0 Å.…”

Scanning Tunneling Microscopy of Mno X Ultrathin Films on Au(111)

“…A variety of stoichiometries and structures exist for MnO x (1 < x < 2), among which Mn 3 O 4 (hausmannite, with a spinel structure) is of particular research interest because of the mixed valence states of Mn (3+ and 2+) and the possibility of a variety of surface terminations. Mn 3 O 4 growth has been studied on a range of crystalline substrates, each with a varying degree of influence on the terminations and atomic structures of Mn 3 O 4 via the mechanisms of epitaxy and associated strain, e.g., SrTiO 3 (001) [7][8][9], SrTiO 3 (111) [9,10], Si(001) [11,12], Ag(001) [13][14][15], Pd(001) [16], Cu(111) [14,17,18], and Au(111) [14,[19][20][21]. The atomic and crystalline structures of the Mn 3 O 4 films were investigated using X-ray diffraction (XRD) [7,8,10,12,21], reflection high energy electron diffraction (RHEED) [8], transmission electron microscopy (TEM) [12], atomic force microscopy (AFM) [7,10], scanning tunneling microscopy (STM) [15,17,19,20], scanning transmission electron microscopy (STEM) [17], and low-energy electron diffraction (LEED) [13][14][15][17][18][19].…”

Spatially Separated Active Sites Enable Selective CO Oxidation Reaction on Oxide Catalyst

“…The construction of Mn 3 O 4 (001) islands on Au(111) can be referred to the previously reported two-step method . Square lattice spinel Mn 3 O 4 (001) was prepared by postannealing 0.7 monolayer (ML) Mn/Au(111) in 2 × 10 –8 mbar O 2 and at 500 K, followed by annealing in 1 × 10 –7 mbar O 2 at 500 K. A typical scanning tunneling microscopy (STM) image of Mn 3 O 4 (001) islands grown on Au(111) with 3.7 Å apparent height is depicted in Figure A.…”

“…Square lattice spinel Mn 3 O 4 (001) was prepared by postannealing 0.7 monolayer (ML) Mn/Au(111) in 2 × 10 –8 mbar O 2 and at 500 K, followed by annealing in 1 × 10 –7 mbar O 2 at 500 K. A typical scanning tunneling microscopy (STM) image of Mn 3 O 4 (001) islands grown on Au(111) with 3.7 Å apparent height is depicted in Figure A. A multilayer structure may be formed here because the Mn 3 O 4 (001) islands are much higher than the single-layer Mn 3 O 4 islands on Au(111) . STM images in Mn and O modes (Figure B,C) indicate that the island surface is terminated by mixed Mn and O.…”

“…The construction of Mn 3 O 4 (001) islands on Au(111) can be referred to the previously reported two-step method. 17 1B, the spacing between Mn rows ([21̅ 1̅ ] direction) is 5.7 Å, while that along Mn rows ([011̅ ] direction) is 2.9 Å. Between neighboring Mn rows, two adjacent Mn atoms (indicated by dark cyan balls) stand in alignment with the Mn atoms in rows (indicated by light pink balls), resulting in a (√2 × √2)R45°reconstruction.…”