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Register a new userSelf-organized growth of Ag islands on Si(111)-(7x7) - optimization of a scanning tunneling microscopy experiment by means of kinetic Monte Carlo simulations
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P. Kocan
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A growth model and parameters obtained in our previous experimental (scanning tunneling microscopy, KMC) and theoretical (kinetic Monte Carlo simulations, KMC) studies of Ag/Si(111)-(7x7) heteroepitaxy were used to optimise growth conditions (temperature and deposition rate) for the most ordered self-organized growth of Ag island arrays on the (7x7) reconstructed surface. The conditions were estimated by means of KMC simulations using the preference in occupation of half unit cells (HUCs) of F-type as a criterion of island ordering. Morphology of experimentally prepared island structures was studied by STM. High degree of experimentally obtained island ordering is compared with the simulated data and results are discussed with respect to the model and parameters used at the KMC simulations.
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Cesium adsorption structures on Ag(111) were characterized in a low-temperature scanning tunneling microscopy experiment. At low coverages, atomic resolution of individual Cs atoms is occasionally suppressed in regions of an otherwise hexagonally ordered adsorbate film on terraces. Close to step edges Cs atoms appear as elongated protrusions along the step edge direction. At higher coverages, Cs superstructures with atomically resolved hexagonal lattices are observed. Kinetic Monte Carlo simulations model the observed adsorbate structures on a qualitative level.
This paper has been withdrawn by first author KM Seemann.
The reliability of kinetic Monte Carlo (KMC) simulations depends on accurate transition rates. The self-learning KMC method (Trushin et al 2005 Phys. Rev. B 72 115401) combines the accuracy of rates calculated from a realistic potential with the efficiency of a rate catalog, using a pattern recognition scheme. This work expands the original two-dimensional method to three dimensions. The concomitant huge increase in the number of rate calculations on the fly needed can be avoided by setting up an initial database, containing exact activation energies calculated for processes gathered from a simpler KMC model. To provide two representative examples, the model is applied to the diffusion of Ag monolayer islands on Ag(111), and the homoepitaxial growth of Ag on Ag(111) at low temperatures.
The Te-covered Si(111) surface has received recent interest as a template for the epitaxy of van der Waals (vdW) materials, e.g. Bi$_2$Te$_3$. Here, we report the formation of a Te buffer layer on Si(111)$-$(7$times$7) by low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). While deposition of several monolayer (ML) of Te on the Si(111)$-$(7$times$7) surface at room temperature results in an amorphous Te layer, increasing the substrate temperature to $770rm,K$ results in a weak (7$times$7) electron diffraction pattern. Scanning tunneling microscopy of this surface shows remaining corner holes from the Si(111)$-$(7$times$7) surface reconstruction and clusters in the faulted and unfaulted halves of the (7$times$7) unit cells. Increasing the substrate temperature further to $920rm,K$ leads to a Te/Si(111)$-(2sqrt3times2sqrt{3})rm R30^{circ}$ surface reconstruction. We find that this surface configuration has an atomically flat structure with threefold symmetry.
We demonstrate that it is possible to mechanically exfoliate graphene under ultra high vacuum conditions on the atomically well defined surface of single crystalline silicon. The flakes are several hundred nanometers in lateral size and their optical contrast is very faint in agreement with calculated data. Single layer graphene is investigated by Raman mapping. The G and 2D peaks are shifted and narrowed compared to undoped graphene. With spatially resolved Kelvin probe measurements we show that this is due to p-type doping with hole densities of n_h simeq 6x10^{12} cm^{-2}. The in vacuo preparation technique presented here should open up new possibilities to influence the properties of graphene by introducing adsorbates in a controlled way.
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