Dmitry Anatolyevich Tsukanov

Effect of C60 layer on the growth mode and conductance of Au and Ag films on Si(111)3-Au and Si(111)3-Ag surfaces

The surface morphology and electrical conductance of C60-precoated Si(111)3-Au and Si(111)3-Ag surfaces have been monitored in the course of Au and Ag depositions. In both cases, the deposited metal atoms penetrate through the fullerene layers. However, the similarity in the growth mode does not result in similar dependencies of conductance versus deposited metal dose. Deposition of Au onto the C60-precoated Si(111)3-Au surface leads to a monotonic gradual increase in conductance starting from ∼0.4 ML Au coverage. Deposition of Ag onto the C60-precoated Si(111)3-Ag surface results in a nonmonotone peak-like dependence with a maximum at ∼0.5 ML of Ag. Both dependencies can be explained in terms of the acceptor-type behavior of the fullerenes, which trap the electrons donated by Au or Ag atoms. The difference between the two dependencies is a consequence of the difference in conduction mechanisms at the original surfaces, namely, the main conductance channel in Si(111)3-Au is the space-charge layer, while i...

Effect of Na adsorption on the structural and electronic properties of Si(111)

Adsorption of ∼0.1 ML of Na onto the Si(111)√3 × √3-Au surface held at 300 °C has been found to induce pronounced changes in its structural and electronic properties. Domain wall networks, characteristic of the pristine surface, are removed completely, leading to the formation of a highly ordered homogeneous surface. The original atomic arrangement of the Si(111)√3 × √3-Au is preserved and Na atoms occupy T4 adsorption sites at the centers of surface Si trimers. Upon Na adsorption, a pronounced metallic S1 surface-state band develops. It is characterized by a large spin splitting (momentum splitting at the Fermi level Δk∥ = 0.027 A(-1) and consequent energy splitting ΔEF = 110 meV), large electron filling (on the order of 0.5 electrons per √3 × √3 unit cell) and small effective electron mass of (0.028 ± 0.006)me. The natural consequence of the latter properties is a high surface conductivity of the Si(111)√3 × √3-(Au, Na) surface.

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Electrical conductance of sodium-doped C60 ultra-thin layers (1–6 monolayers) grown on the Na-adsorbed Si(111)√3 × √3-Au surface has been studied in situ by four-point probe technique, combined with low-energy electron diffraction observations. Evidence of conductance channel formation through the C60 ultrathin layer is demonstrated as a result of Na dosing of 3 and 6 monolayers thick C60 layers. The observed changes in surface conductivity can be attributed to the formation of fulleride-like NaC60 and Na2C60 compound layers.

-Au surface

Changes in electrical conductance of the Bi/Si (111) reconstructed surfaces and Bi {012} or Bi (001) ultra-thin films have been studied after sodium deposition at room temperature. It was observed that deposition of sodium onto Si (111)-β-3×3-Bi surface results in increasing of surface conductivity up to 0.3 monolayers (ML) of adsorbed sodium atoms. These conductance changes were explained by developing of the metallic surface states in the band gap as revealed by angle resolved photoemission spectroscopy spectra. Moreover, it was shown that sodium adsorption onto Bi {012} and Bi (001) thin films leads to drastic changes in its surface conductivity including a peak of maximum electrical conductance at 0.5 monolayers of adsorbed sodium.

Electrical conductivity of reconstructed Si(111) surface with sodium-doped C60 layers

Electrical conductivity of surface phases on silicon have been studied in ultrahigh vacuum at room temperature by four-point probe method. It has been shown that surface conductance of silicon substrate strongly depends on crystal and electronic structure of surface phases, surface morphology and density of atoms involved in surface phases formation. The atom adsorption, structural and morphological transformation lead to changing of long-order structure of surface phases and consequently in decreasing of electrical conductivity. It is shown that surface phases as new ultrathin 2D material presents additional conducting channel on silicon substrate and is believed to be promising in microelectronics technology.