Quasiperiodic Pb monolayer on the fivefoldi-Al-Pd-Mnsurface: Structure and electronic properties

Abstract

Lead is one of few elements that adopts a pseudomorphic structure when deposited on quasicrystalline substrates. We present a structural model of quasiperiodic Pb overlayers formed on the fivefold surface of an icosahedral Al-Pd-Mn quasicrystal at two different coverages close to saturation. The skeleton of the Pb monolayer is formed by a network of "starfish" ͑SF͒ clusters formed at the initial stages of Pb deposition, as studied in detail in our previous work ͓Ledieu et al., Phys. Rev. B 79, 165430 ͑2009͔͒. The atomic structure of the Pb monolayers can be represented as a decorated pentagonal Penrose P1 tiling. The structural models reproduce also the quasiperiodic superstructure of the layers observed in experimental scanning tunneling microscopy ͑STM͒ images which is described by the -scaled P1 tiling ͑ is the golden mean͒. The atomic structure underlying the observed -scaled "white flower" motifs and the origin of irregular bright spots in STM images are discussed. The bright spots appear in the centers of the SF clusters centered at substrate sites occupied by Al atoms. The calculated electronic structure shows that the minimum in the density of states ͑pseudogap͒ at the Fermi level which is characteristic for the Al-Pd-Mn quasicrystals appears also in the local density of states of the adsorbed Pb monolayer. However, our analysis demonstrates that the formation of this pseudogap is not due to the quasiperiodic arrangement of the Pb atoms but to the strong hybridization of their orbitals with the substrate.

Thin Film Growth on Quasicrystalline Surfaces

“…To further support this conclusion, the electronic properties have been calculated for both periodic and aperiodic unsupported Pb monolayers (triangular and square lattices). It follows that the periodic structures exhibit also a deep pseudo‐gap at E F , while only a shallow minimum is obtained for the unsupported quasiperiodic Pb monolayer 17…”

“…The reduction in the electronic density of states (pseudo‐gap) at the Fermi level (E F ) measured on the clean Al‐Pd‐Mn quasicrystal surface is preserved and even larger on this Pb monolayer. First attributed to the quasiperiodic ordering of the structure, the ab initio calculations have demonstrated that the hybridization of the Pb p states with the substrate was responsible for the presence of this pseudo‐gap 17. To further support this conclusion, the electronic properties have been calculated for both periodic and aperiodic unsupported Pb monolayers (triangular and square lattices).…”

“…Ab initio DFT methods have proved to be a powerful tool for studying structural properties of quasiperiodic thin films17, 20 and clean surfaces 21. They are indispensable also for investigation of fundamental properties of quasicrystals as a character of the electronic spectrum,22 magnetic,23 or catalytic properties 24…”

Crystalline and quasicrystalline allotropes of Pb formed on the fivefold surface of icosahedral Ag-In-Yb

“…The sticking coefficient of an adatom on a surface vanishes to zero if the binding energy of the adatom to the surface is negligible or if there is inefficient dissipation of kinetic energy of the adatom to the surface through phonon excitation. 47 It was speculated that the latter case is responsible for the vanishing sticking coefficient of Pb atoms on the Al-based quasicrystals. The Pb layer on the Al-based quasicrystals was highly dense (0.09 atoms/Å 2 ), 47 compared to the Pb layer on i-Ag-In-Yb (0.004-0.007 atoms/Å 2 ), 26 one order of magnitude less).…”

“…47 It was speculated that the latter case is responsible for the vanishing sticking coefficient of Pb atoms on the Al-based quasicrystals. The Pb layer on the Al-based quasicrystals was highly dense (0.09 atoms/Å 2 ), 47 compared to the Pb layer on i-Ag-In-Yb (0.004-0.007 atoms/Å 2 ), 26 one order of magnitude less). The sparse layer on i-Ag-In-Yb should be less rigid, and therefore should exhibit a broader phonon spectrum and be more efficient at absorbing kinetic energy.…”