Electron transport in ultra-thin films and ballistic electron emission microscopy

Abstract : We have developed a calculation scheme for the elastic electron current in ultra-thin epitaxial heterostructures. Our model uses a Keldysh's non-equilibrium Green's function formalism and a layer-by-layer construction of the epitaxial film. Such an approach is appropriate to describe the current in a ballistic electron emission microscope (BEEM) where the metal base layer is ultra-thin and generalizes a previous one based on a decimation technique appropriated for thick slabs. This formalism allows a full quantum mechanical description of the transmission across the epitaxial heterostructure interface, including multiple scattering via the Dyson equation, which is deemed a crucial ingredient to describe interfaces of ultra-thin layers properly in the future. We introduce a theoretical formulation needed for ultra-thin layers and we compare with results obtained for thick Au(1 1 1) metal layers. An interesting effect takes place for a width of about ten layers: a BEEM current can propagate via the center of the reciprocal space ($\overline{\Gamma}$ ) along the Au(1 1 1) direction. We associate this current to a coherent interference finite-width effect that cannot be found using a decimation technique. Finally, we have tested the validity of the handy semiclassical formalism to describe the BEEM current.
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Yann Claveau, Sergio Di Matteo, P L Andres, F Flores. Electron transport in ultra-thin films and ballistic electron emission microscopy. Journal of Physics: Condensed Matter, IOP Publishing, 2017, 29 (11), pp.115001. ⟨10.1088/1361-648X/aa575e⟩. ⟨hal-01484634⟩

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