Ultra-thin AlAs films on GaAs (001) investigated by high-resolution electron-energy-loss spectroscopy

High-resolution electron-energy-loss spectroscopy has been applied to AlAs ultra-thin films grown by molecular beam epitaxy on GaAs (001). Below 12 AlAs monolayers, the loss intensities deviate from the prediction of the long-wavelength dielectric properties of AlAs and GaAs. Microscopic lattice-dynamics calculations of the surface dielectric response of AlAsGaAs slabs have been performed. A better qualitative agreement with the experimental results is obtained when some cation intermixing is assumed to take place at the interface between the two media.