E. V. Rut’kov

Interaction of silver atoms with iridium and with a two-dimensional graphite film on iridium: Adsorption, desorption, and dissolution

The initial stages in the interaction of silver with the (111)Ir surface and with a two-dimensional graphite film (2D GF) on (111)Ir were studied by high-resolution electron Auger spectroscopy in ultrahigh vacuum. The growth mechanisms of silver films and the desorption fluxes of Ag atoms were determined, and their desorption energies estimated. It was found that the Ag desorption fluxes from a 2D GF on Ir and from a thick silver film on the pure metal are similar and considerably (an order of magnitude) smaller than the sublimation fluxes from bulk silver at the same temperatures. The activation energy for desorption from a submonolayer film varies from 3.2 eV for coverage θ=1 to 3.7 eV at θ ∼ 0. It was shown that silver atoms do not penetrate into the substrate bulk throughout the temperature range covered (300–1800 K).

Carbon interaction with rhodium surface: Adsorption, dissolution, segregation, growth of graphene layers

Carbon interaction with rhodium (111) surface has been studied by Auger electron spectroscopy in ultrahigh vacuum within a broad temperature interval of 300-1800 K. It has been shown that the graphene monolayer remains stable on the metal surface within a relatively narrow temperature interval of ∼50 K below the carbonization point, and when heated above this point, graphene breaks up gradually by transferring first to the island state, and after that, to chemisorbed carbon “gas.“ As the temperature decreases, a stable multilayer graphite film forms.

Intercalation of nickel atoms under two-dimensional graphene film on (111)Ir

Abstract Intercalation of Ni atoms under a two-dimensional graphene film (2DGF) on (111)Ir was studied in ultra high vacuum using high resolution Auger spectroscopy. Ni atoms were shown to be intercalated effectively at 900 to 1500 K, and a polylayer nickel film was shown to grow under the 2DGF. A relationship between a proportion κ of Ni atoms intercalated under 2DGF and temperature was determined and it was shown that κ decreases from ∼30% at 900 K to ∼3% at 1500 K.

Role of edge atoms of graphene islands on metals in nucleation, growth, alkali metal intercalation

The effect of edge carbon atoms in graphene islands grown on a metal surface on the kinetics of nucleation, growth and dissolution of these islands, as well as of a multilayer graphite film, has been analyzed. It is shown that the part played by edge atoms should be taken into account in description of equilibrium processes taking place in multiphase carbon-metal systems as well. A common mechanism has been proposed for intercalation of graphene islands on metals by alkali metal atoms, and for temperature-induced escape of these atoms from under the layer.

Sequential Ta(100) carbonisation: from adsorption of single carbon atoms to bulk carbide production

Abstract Sequential stages of Ta carbonisation from the initial atomic adsorption to bulk carbide (BC) production throughout the sample have been studied by high temperature high resolution Auger spectroscopy in ultra-high vacuum. Two compounds – surface carbide (SC) Ta 5 C 2 and BC TaC – were found. The energy barrier heights for atomic carbon transport from the surface to the bulk were estimated to be E sl =2.1–2.3 eV and back E ls = E sl − ΔE ≈(1.2–1.6) eV and the activation energy of carbon bulk diffusion in Ta E dif ∼1.3 eV was refound. It is shown that SC can be treated as a thermodynamically ‘legal’ phase and should find its place in the equilibrium phase diagram.

Structural Properties of a Monolayer Graphite Film on the (111)Ir Surface

The structural properties of a monolayer graphite film prepared on the (111)Ir surface through thermal decomposition of benzene molecules were studied. The study was carried out in ultrahigh vacuum using scanning tunneling microscopy, which allowed observation of the atomic structure of the film. It is shown that, on extended smooth regions of the Ir surface, a continuous graphite film with a regular arrangement of carbon atoms in a planar hexagonal lattice is formed. The orientation of zigzag carbon atom chains coincides with the 〈110〉 direction on the Ir surface. Structural defects of the (5, 7) configuration were revealed in the film. A comparison of the topographies of the film and the (111)Ir surface shows that the graphite layer smoothly (without discontinuities) flows over subnanometer topographical features existing on the Ir surface and that the distance between the graphite film and the metal surface in this case can reach 1 nm.

Thermal destruction of two-dimensional graphite islands on refractory metals (Ir, Re, Ni, and Pt)

Thermal destruction of two-dimensional graphite films on Ni(111), Re(10-10), Ir(111), and Pt(111) substrates is studied. It is shown that the detachment of an edge carbon atom from an island is a limiting process stage for all the cases. The activation energy of this process varies from 2.5 eV for nickel to 4.5 eV for iridium. The variation of the activation energy is associated with the ability of the metal surface to form strong chemisorptive bonds with valence-active edges of graphite islands, which loosen C-C bonds in graphite.

Graphene-graphite phase transition at the surface of a carbonized metal

A phase transition leading to the transformation of a graphene layer into a multilayer graphite film at the surface of a carbonized metal has been experimentally studied on the atomic level under ultrahigh-vacuum conditions. It has been shown that this process is governed by dynamic equilibrium between edge atoms of graphene islands and a chemisorbed carbon phase, two-dimensional carbon “gas,” and is observed in the temperature range of 1000–1800 K. The features of the phase transition at the surfaces Ni(111), Rh(111), and Re(10-10) are similar, although the specific kinetic characteristics of the process depend on the properties of the substrate. It has been shown that change in the emissivity of the substrate after the formation of a multilayer graphite film increases the rate of the phase transition and leads to a temperature hysteresis.

Interaction of aluminum with iridium surface: Adsorption, desorption, dissolution, and formation of surface compounds

The interaction of aluminum with an iridium (111) surface was studied in ultrahigh vacuum by Auger electron spectroscopy over the broad temperature range 300–2000 K. At room temperature, layer-by-layer growth of an aluminum film was observed, with a monolayer forming in coherent relation to the substrate. Deposition at 1100–1300 K gives rise to the formation of surface aluminide Ir4Al with an adatom concentration NAl = (4.20 ± 0.15) × 1014 cm−2. It was shown that aluminum escapes out of the surface aluminide by thermal desorption in the 1300–1700-K temperature interval, with the desorption activation energy changing from ∼4.5 to ∼5.7 eV as the coverage decreases from the value corresponding to the surface aluminide (taken for unity) down to zero.

Carbon diffusion between the volume and surface of (100) molybdenum

The diffusion of carbon atoms between the volume and the surface of (100) molybdenum is directly studied at temperatures between 1400 and 2000 K (i.e., at process temperatures) for the first time. The balance of carbon atoms in the system is determined. The difference in the activation energies of carbon dissolution and precipitation, ΔE=Es1-E1s, is found for the case when the diffusion fluxes of dissolved and precipitated carbon atoms are in equilibrium. This difference defines the enrichment of the surface by carbon relative to the bulk. The experimentally found activation energy of carbon dissolution is Es1=3.9 eV. The activation energy of carbon precipitation is estimated at E1s=1.9 eV. The latter value is close to the energy of bulk diffusion of carbon in molybdenum.