Quantum-well states and resonances in thin single-crystal layers of noble metals on W(110) substrates

This paper reports on the first experimental observation of quantum-well states and sp-type resonances in thin single-crystal gold, silver, and copper layers formed on single-crystal W(110) surfaces, which result from spatial localization of Bloch-type electronic wave functions in a quantum well with potential barriers at the vacuum/metal and metal/W(110) interfaces. The quantization of the valence-band electronic structure in Au/W(110), Ag/W(110), and Cu/W(110) systems was studied experimentally using angle-resolved photoelectron spectroscopy.     

Atomic force microscopy of the nanostructure of metals and alloys subjected to mechanical and thermal stresses

Low-carbon structural steels are an extremely important material used widely in all industries, e.g., in the manufacture of industrial pipelines and equipment operating at elevated temperatures and pressures, in contact with chemically aggressive environments. In this work, we study nanoscale changes in the substructure of structural steels that result from operational wearing out.     

Electronic structure of gold nanoclusters on oxidized Ni(755) surface

The electronic energy structure of gold nanoclusters grown on oxidized single-crystal stepped surface Ni(755) is studied. It is shown that oxidation of the stepped Ni(755) surface results in the formation of a well-ordered continuous structure O(2 × 2) similar to that grown on a flat Ni(111) single-crystal surface. Evaporation of gold on such a surface leads to the formation of gold nanoclusters of a size determined by the size of the terraces on the Ni(755) surface. A comparison of the photoelectron spectra of the Au 4f _{5/2, 7/2} core levels in clusters grown on clean and oxidized Ni(755) surfaces reveals that the spectra obtained for a gold cluster system on an oxidized Ni(755) surface contain not only the spectral components characteristic of metallic gold but also additional components of Au^+δ. It is assumed that additional components for gold clusters on the oxidized Ni(755) surface originate from partial oxidation of gold atoms with the participation of defects inherent in the stepped relief of the nickel substrate.     

High-resolution Russian–German beamline at BESSY

The superior performance of the high-resolution Russian–German bending-magnet beamline at BESSY is demonstrated by measuring photon flux and photoionization spectra in the spectral region of the 2,-1₃ resonance of doubly-excited He as well as at the 1s absorption thresholds of gas-phase N₂, O₂, and Ne. It is shown that even after 6 years of successful operation, the beamline remains to provide a solid basis for a further development of the Russian–German scientific cooperation in the field of applications of synchrotron radiation.     

Spectra of quantum states in thin metal films and their modification: Al/W(110) system

The modification of spectra of quantum well states of sp-type in thin Al films on the W(110) surface was experimentally investigated by angular-resolved photoelectron spectroscopy both during deposition and in dependence of the detection angle. Quantum well states are observed for the partially filled band of valence states in the range of binding energies from 4.4 eV to the Fermi level. An Al film with a thickness of 11 monolayers exhibits a jump of the dispersion relations of quantum well states in the local W(110) band gap in the ΓS direction and splitting of these relations due to the effect of substrate electronic structure on the formed spectrum of quantum states and their possible spin polarization.     

Silicon interaction with the (0001) surface of La and Gd layers

A study is reported on a system consisting of a Si layer on the surface of rare-earth metals (REMs), which is the reverse of a rare-earth metal on silicon, the system of current widespread interest. Interaction of silicon with the (0001) surface of trivalent La and Gd single-crystal layers grown on a W(110) surface is studied by Auger spectroscopy combined with layer-by-layer argon-ion etching of the system and photoelectron spectroscopy. It is found that silicon interacts with the La(0001) and Gd(0001) surfaces even at room temperature with the formation of silicide, but no mutual mixing of the silicon and substrate atoms occurs. When the Si/La(0001) and Si/Gd(0001) systems are heated at 400°C, silicon does not diffuse into the bulk of the metal substrate or to the REM/W(110) interface.     

Carbon phases on nickel surfaces

The conditions of the formation of different carbon surface phases on nickel substrates by the example of a planar Ni( 110) surface and a stepped Ni(771 ) surface similar in structure were determined. The structure of the phases was investigated by means of scanning tunneling microscopy (STM), and the influence of carbon on the structure of the nickel surface was demonstrated. The process of graphene synthesis by propylene cracking is described. A method for forming graphene islands on nickel is proposed. A variety of phase transitions between the carbon surface phases (e.g., surface carbide, graphene, and graphene islands) and the reasons for their irreversibility are discussed. The relation between the structures of the surface carbide phases and the crystal structures of the initial surfaces for two different substrates is shown.     

Interaction of thin silicon layers with the (0001) surface of rare-earth metals

The electronic and crystalline structures of the systems formed upon deposition of silicon layers onto the Gd(0001) and Dy(0001) surfaces of single-crystal films annealed subsequently at T=450–500°C have been studied by low-energy electron diffraction (LEED) and also by the Auger electron and angle-resolved photoelectron spectroscopy of the valence band and the Si(2p) core level. It is shown that the systems thus produced can be described as starting single-crystal films of Gd and Dy, with 3D islands of the silicides of these metals on the surface of the corresponding metalfillms.     

Formation and lithium doping of graphene on the surface of cobalt silicide

The intercalation of silicon under graphene on the Co(0001) surface, which is accompanied by the formation of a silicon solid solution in cobalt and by the formation of a surface crystalline Co₂Si phase, has been investigated using photoelectron spectroscopy. It has been shown that the formation of cobalt silicide leads to a substantial weakening of the hybridization of electronic states of graphene and cobalt and to the recovery of the Dirac spectrum of electronic states of graphene near the Fermi level. This has made it possible to investigate the electron doping of graphene on the cobalt silicide substrate upon deposition of lithium on its surface. It has been found that doping with lithium leads to a significant charge transfer onto graphene, and the electron concentration reaches 3.1 × 10¹⁴ cm^?2. Moreover, the specific form of the Fermi surface creates favorable conditions for the enhancement of the electron-phonon coupling. As a result, the formed system can be considered as a candidate for the creation of superconductivity in single-layer graphene.