Atomic Structure of Cr₂O₃/Ag(111) and Pd/Cr₂O₃/Ag(111) Surfaces: A Photoelectron Diffraction Investigation

Abstract

A detailed investigation concerning the atomic structure of Cr 2 O 3 and Pd/Cr 2 O 3 ultrathin films deposited on a Ag(111) single crystal is presented. The films were prepared by MBE (molecular beam epitaxy) and characterized in situ by LEED (low energy electron diffraction), XPS (X-ray photoelectron spectroscopy), and XPD (X-ray photoelectron diffraction). Evidences of rotated domains and an oxygen-terminated Cr 2 O 3 /Ag(111) surface were observed, along with significant contractions of the oxide's outermost interlayer distances. The deposition of Pd atoms on the Cr 2 O 3 surface formed a four-monolayer film, fcc packed and oriented in the [111] direction, which presented changes in monolayer spacing and lateral atomic distance compared to the expected values for bulk Pd. The observed surface structure may shed light on new physical properties such as the induced magnetic ordering in Pd atoms.

Boundary magnetization properties of epitaxialCr2−xAlxO3thin fi

“…Since the corundum structure has three-fold symmetry along the [0001] direction, the occurrence of the six-fold symmetry indicates that the films consist of twinned domains (marked by the stars in Fig. 5), which have been previously reported to occur during thermal annealing in pure Chromia [17,18,27]. The intensity of the twinned domain peaks decreases with the Al content, disappearing almost entirely for the x = 0.6 sample.…”

“…α-Cr 2 O 3 adopts the corundum crystal structure (space group R3 c), consisting of hexagonal close-packed layers of O atoms with two-thirds of the octahedral sites being occupied by Cr 3+ atoms. The oxygen atoms follow an hcp stacking, while the Chromium atoms exhibit an abcabc stacking sequence as found in fcc lattices [17]. A sketch of this structure is shown in Fig.1(a).…”

“…For all film compositions, the film thickness was fixed at 100 nm. In previous studies, it was shown that a combination of RT depositions with high temperature annealing is an effective method for the growth of epitaxial Cr 2 O 3 thin films [17,18,21,24,25]. Hereby, our as-grown samples were recrystallized via ex-situ thermal annealing in vacuum (pressure < 3 Pa) for 1h at 1000°C in an external furnace (Carbolite wire wound single zone tube furnace).…”

Evidencing the formation of Pt nano-islands on Cr2O3/Ag(111)

“…Research on NPs aiming at the enlightenment of their outermost layers, i.e., interlayer distances and packing, is essential for the improvement and development of advanced materials, for instance, more efficient and selective catalysts. [2][3][4][5][6][7] Nevertheless, it is a challenge to extract structural and electronic information straightforwardly via in situ experiments.…”

“…19 TMO supports may act to improve the NPs' catalytic performance, 20 although this factor is strongly linked to the catalyst synthesis route. 2,21,22 Particularly, Cr 2 O 3 is one example of TMO that is often used as a support for real catalysts in alkene dehydrogenation reactions, [23][24][25] or as a support for metallic NPs in model catalysts, 5,6 or investigated due to its magnetic properties when in the form of ultrathin films. 26,27 The Cr 2 O 3 crystalline structure is classified as belonging to the R3c space group.…”