Figure 1

(Color online) Experimental schematic phase stability diagram of the interfacial Mn oxides presented as a function of the oxygen pressure $P\left({\text{O}}_2\right)$ and of the oxygen chemical potential ${\mu }_{\text{O}}$ (Ref. 19). The nominal coverage of Mn on Pd(100) is $\sim 0.75$ ML.Reuse & Permissions

Figure 2

(Color online) HREELS phonon spectra of the four Mn oxide submonolayer phases discussed in this paper. From the top to the bottom: HEX-I, HEX-II, $c\left(4\times 2\right)$, and CHEV-I. The statistical uncertainty in the peak position is $\pm 0.5\text{meV}$.Reuse & Permissions

Figure 3

(Color online) Calculated loss peak spectra for the MnO(100) and MnO(111) unsupported thin oxide layers described in the text. The circle sketches provide a simplified view of the eigenvectors connected to the dipole active modes. Filled and empty circles refer to Mn and O atoms, respectively.Reuse & Permissions

Figure 4

(Color) (a) Top view of the geometrical model for the Pd(100)-supported $c\left(4\times 2\right){\text{-Mn}}_3{\text{O}}_4$ phase: red spheres: O atoms; light gray spheres: Mn atoms; green small spheres: Pd atoms underneath. Dashed lines delimit the 2D unit cell, the full line indicates the manganese lateral displacements, and circles highlight the position of the vacancies. (b) Experimental STM image of the $c\left(4\times 2\right){\text{-Mn}}_3{\text{O}}_4$ phase; sample bias $U=+0.5\text{V}$; tunneling current $I=0.2\text{nA}$. [(c) and (d)] High-resolution (c) simulated and (d) experimental STM images taken at sample bias $U=+1.0\text{V}$; tunneling current $I=0.25\text{nA}$. The theoretical image has been calculated considering tunneling into empty states between 0 and $+0.5\text{eV}$. Full lines indicate the 2D unit cell and the zigzag Mn chain. (e) Comparison between the measured HREELS phonon value (vertical bar) and PBE (dashed line) and HSE (full line) predicted dipole active modes for the $c\left(4\times 2\right){\text{-Mn}}_3{\text{O}}_4$ phase. The inset schematically depicts the atomic displacements giving rise to the calculated phonon peaks. Mn and O atoms are sketched as filled and empty circles, respectively. The dashed line circles indicate the vacancies.Reuse & Permissions

Figure 5

(Color online) (a) STM image showing the characteristic appearance of the chevrons structures and the local coexistence of the $c\left(4\times 2\right)$, CHEV-I, and CHEV-II phases ($140\text{Å}\times 100\text{Å}$; $U=+1.0\text{V}$; $I=0.2\text{nA}$). [(b) and (c)] Real lattice, reciprocal lattice, and experimental LEED pattern $\left(E=110\text{eV}\right)$ for the [panel (b)] $c\left(4\times 2\right)$ and [panel (c)] CHEV-I structures. The arrow in the top right panel shows how the periodicity of the CHEV-I structure can be obtained from the $c\left(4\times 2\right)$ periodicity by extending one of the two lattice vectors to a neighboring antiphase position.Reuse & Permissions

Figure 6

(Color) (a) Top view of the geometrical model for the Pd(100) supported CHEV-I ${\text{Mn}}_6{\text{O}}_7$ phase: red (dark gray) spheres: O atoms; light gray spheres: Mn atoms; green (gray) small spheres: Pd atoms underneath. Dashed lines delimit the 2D unit cell and circles highlight the position of the vacancies. (b) Experimental and simulated STM images of the CHEV-I phase; sample bias $U=+1.0\text{V}$; tunneling current $I=0.13\text{nA}$. The simulated STM image has been calculated considering tunneling into empty states between 0 and $+1.0\text{eV}$. Unit cells are indicated by full lines. (c) Comparison between the measured HREELS phonon value (vertical bar) and PBE (dashed line) and HSE (full line) predicted dipole active modes for the CHEV-I phase. The inset schematically depicts the atomic displacements giving rise to the calculated phonon peaks. Mn and O atoms are sketched as filled and empty circles, respectively. The dashed line circle denotes a vacancy.Reuse & Permissions

Figure 7

(Color online) (a) Real and (b) reciprocal lattice for a $\left(1\times 1\right)$ MnO(111)-like hexagonal structure on a Pd(100) surface. The lattice parameter of the overlayer is assumed to be the measured bulk value $a_{\text{MnO}}=3.14\text{Å}$, whereas $a_{\text{Pd}}=2.75\text{Å}$. In (a) only one of the two symmetry domains is reported for clarity. (c) SPA-LEED two-dimensional pattern measured at $E=90\text{eV}$, for the undistorted HEX-I phase. (d) LEED pattern of the distorted HEX-I phase, recorded at $E=96\text{eV}$. (e) Real and (f) reciprocal lattice associated with the distorted hexagonal MnO(111)-like phase. Only one symmetry domain is shown in (e) for clarity, for which the lattice parameter in the [011] direction of the distortion is $b_{{\text{MnO}}_x}=2.94\text{Å}$. In total, four symmetry domains contribute to the reciprocal lattice in (f): two are obtained from panel (e) with $a_{\text{MnO}}$ at either $+60°$ or $-60°$ from $b_{{\text{MnO}}_x}$, and the other two are obtained by rotating $a_{\text{MnO}}$ by $90°$ relative to the substrate mesh.Reuse & Permissions

Figure 8

(Color online) [(a) and (b)] Top view of geometrical models for unsupported (a) HEX-I MnO(111) and distorted (b) HEX-I MnO(111) phases: red (dark gray) spheres: O atoms; light gray spheres: Mn atoms. Dashed lines delimit the 2D unit cell. [(c)–(e)] [(c) and (d)] Experimental and (e) simulated STM images of HEX-I; experimental images: sample bias (c) $U=+0.5\text{V}$, (d) $+0.6\text{V}$; tunneling current (c) $I=0.13\text{nA}$, (d) 0.15 nA. The simulated STM image has been calculated considering tunneling into empty states between 0 and $+0.5\text{eV}$. (f) Comparison between the measured HREELS phonon value (vertical bar) and PBE (dashed line) and HSE (full line) predicted dipole active modes for the HEX-I phase. The inset schematically depicts the atomic displacements giving rise to the calculated phonon peaks. Mn and O atoms are sketched as filled and empty circles, respectively.Reuse & Permissions

Figure 9

(Color online) Thermodynamic DFT phase stability diagram of explored HEX-I models in equilibrium with an O particle reservoir controlling the chemical potential ${\mu }_{\text{O}}$. The top scale is converted into oxygen pressure.Reuse & Permissions

Figure 10

(Color online) Thermodynamic DFT phase stability diagram of explored HEX-II models in equilibrium with an O particle reservoir controlling the chemical potential ${\mu }_{\text{O}}$. The top scale is converted into oxygen pressure.Reuse & Permissions

Figure 11

(Color online) [(a) and (b)] Top view of the two most stable models for unsupported HEX-II, namely, (a) octopolarlike ${\text{Mn}}_5{\text{O}}_8$ and (b) ${\text{Mn}}_4{\text{O}}_7\text{−}\alpha$ phases: red (dark gray) spheres: O atoms; light gray spheres: Mn atoms. Dashed lines delimit the 2D unit cell, whereas triangles highlight the octopolar ${\text{Mn-O}}_3$ pyramids and the ${\text{O}}_3$ trimers of the $\alpha$ termination. (c) Experimental and simulated STM images of the hexagonal $\alpha$ HEX-II phase; sample bias $U=+0.75\text{V}$; tunneling current $I=0.1\text{nA}$. The simulated STM images have been calculated considering tunneling into empty states between 0 and $+0.75\text{eV}$. Unit cells are indicated by full lines. (d) Comparison between the measured HREELS phonon value (vertical bar) and PBE (dashed line) and HSE (full line) predicted dipole active modes for the $\alpha$ HEX-II phase. The inset schematically depicts the atomic displacements giving rise to the calculated phonon peaks. Mn and O atoms are sketched as filled and empty circles, respectively.Reuse & Permissions