Mesoscopic self-ordering in oxygen doped Ce films adsorbed on Mo(112)

• Published in: Surface science 2021-03, Vol.705, p.121766, Article 121766
• Main Authors: Afanasieva, T.V., Fedorus, A.G., Goriachko, A.M., Naumovets, A.G., Neporozhnii, I.M., Rumiantsev, D.V.
• Format: Article
• Language: English
• Subjects: Annealing; Cerium adsorption; Contact potentials; Density functional theory; Domains; LEED; Low energy electron diffraction; Molybdenum; Nanostructures; Oxygen; Room temperature; Self-ordering; Substrates; Surface structure; Work function
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/j.susc.2020.121766

•A set of ordered structures are found in submonolayer Ce/Mo(112) films doped by O.•Self-ordering of the p(2 × 1) Ce/Mo(112) film into wide periodic stripes is detected.•Mesoscopic self-ordering in the adlayer is activated by annealing at T > 1200 K.Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), contact potential difference (CPD) measurements and density functional theory (DFT) calculations have been used to study submonolayer adsorption of Ce on the molybdenum (112) surface. Oxygen impurities ranging from 1 to 25 atomic % within different Ce deposits were detected by AES in our work. Depositing various amounts of Ce (below and above a single monolayer) on Mo(112) at room temperature produced only a highly defective adlayer with a p(2  ×  1) structure, which is specific of coverage θ = 0.5. However, the DFT simulations of a pure Ce/Mo(112) system clearly pointed to a c(2  ×  2) adlayer structure as energetically preferable at θ = 0.5. This discrepancy has been attributed to the presence of oxygen in the Ce deposit, which substantially affects the properties of the Ce-Mo(112) system. Annealing the samples at temperatures Ta ≤ 1450 K improved the degree of ordering in the p(2  ×  1) adlayer, but also led to significant surface structure changes. In particular, incommensurate c(8  ×  4) and c(1.44  ×  2) structures were found at coverages of 0.63 and 0.7, respectively. In a broad coverage range of θ = 0.1−0.45, annealing at Ta ≥ 1200 K gave rise to complex LEED patterns which correspond to p(2  ×  1) and (n  ×  1) structures, with n ≥ 24 being coverage dependent. This has been ascribed to the formation of p(2  ×  1) striped Ce domains arranged with a mesoscopic 1D periodicity amounting to dozens of substrate lattice spacings along the [111̅] direction (about 65 Ǻ at n =24). The self-organization of such domains is discussed in terms of strain-induced and electrostatic (contact potential) driving forces. [Display omitted]