Abstract
The growth of Ag monolayers on Cu (001) was studied by periodic Density Functional Theory (DFT). Despite the limited solid solubility of Ag in Cu, the growth of a single Ag overlayer on Cu (001) was predicted as feasible. In contrast, the growth of consecutive Ag monolayers was found to be energetically forbidden. Inter-diffusion of Ag monolayers into Cu was raised as a possibility but it was dependent on the sequence in which the Ag monolayers were introduced into the Cu bulk. The Ag layers preferred to be kept neither too far apart nor too close to each other, the optimum spacing between two Ag monolayers determined to be that of two consecutive Cu layers. Ag diffusion mediated tensile stress in the Cu cell by causing an increase of the unit cell constant by as much as 22%. Interactions between the Ag and Cu species also involved a degree of covalency. In general, progression of a surface Ag monolayer into the Cu bulk involved charge depletion over the Ag species and a simultaneous charge concentration over neighboring Cu atoms; this mechanism was found to influence Cu up to a depth of four surface layers.
Highlights
Interface phenomena occurring between metallic monolayers become of interest in cases where end-product mechanical properties depend on structural discontinuity across the interface [1]
Formation energies normalized by the number of electrons and Fermi energy limits as calculated by Density Functional Theory (DFT) are listed in Table 1, both for relaxed and non relaxed cluster geometries
Spin unrestricted DFT calculations were performed with the periodic version of the Amsterdam density functional (ADF) program [35,36] within the realm of the generalized gradient approximation (GGA)
Summary
Interface phenomena occurring between metallic monolayers become of interest in cases where end-product mechanical properties depend on structural discontinuity across the interface [1]. The fundamental interest in the submicron range stems from the potential to access and manipulate electrical [7], magnetic, optical, thermal and mechanical properties such as conductance quantization [8], bandgap modification [9] and coulomb blockade [10]. All of these properties arise from confinement of charged carriers, in structures such as quantum wells, wires and dots and the successful manipulation of these properties stimulates promise for novel devices. This is because nm-sized devices dimensions exhibit improved characteristics compared to larger devices; typical examples of such improvements in the case of quantum dot lasers are lower threshold currents [11], augmented dynamic responses and enhanced emission line widths [12]
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