Macroscopic and mesoscopic surface diffusion from a deposit formed by a Stranski-Krastanov type of growth: Pb on Cu(100) at above one layer coverage

Abstract : Under ultrahigh-vacuum conditions, we have studied the diffusion from Pb deposits on Cu(100), at above one-layer coverage, in the 250–625 K temperature range. The growth mode is Stranski-Krastanov, and the deposits consist of thick three-dimensional Pb islands which form above a dense Pb single layer. This latter layer has a two-domain structure which “melts” around TM=520 K. In the 475–625 K temperature range, we have measured the spread of the deposits in the mm range, using in situ Rutherford backscattering analysis. To study diffusion at lower temperature, on a smaller scale, the Pb layer between the islands has been removed by sputtering around 150 K. We have then studied, in the 250–380 K temperature range, the kinetics of its reformation by using in situ Auger spectroscopy. In these experiments the Pb diffusion is followed over distances of the order of the spacing between Pb islands, i.e., about 1 μm. Our measurements demonstrate that the diffusing species is a Pb adatom moving above the dense Pb layer, leading to its spread with a quasiconstant Pb concentration, the adatom source being the Pb islands. We have analyzed our results via numerical integration of a diffusion equation with a concentration-dependent diffusion coefficient, using the finite-difference method. This analysis provides the activation energy ET governing the process. ET is the sum of two characteristic energies ES and Ed. ES is the formation energy of Pb adatoms from the islands, and Ed the activation energy for the motion of these adatoms on the Pb layer. Ed is markedly higher below TM than above, indicating that when the Pb layer is structured, the diffusion is probably limited by the crossing of domain boundaries.
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Submitted on : Thursday, April 21, 2005 - 10:27:26 AM
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Geoffroy Prévot, C. Cohen, J.-M. Guigner, Didier Schmaus. Macroscopic and mesoscopic surface diffusion from a deposit formed by a Stranski-Krastanov type of growth: Pb on Cu(100) at above one layer coverage. Physical Review B : Condensed matter and materials physics, American Physical Society, 2000, 61, pp.10393-10403. ⟨10.1103/PhysRevB.61.10393⟩. ⟨hal-00004774⟩

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