Abstract
The temperature-dependent energetics of self-assembled Au nanowires on Ge(001) surfaces is studied with the help of density-functional theory (DFT) calculations: By calculating the surface phonon modes within harmonic approximation the surface vibrational free energy is obtained to complement the zero-temperature DFT total energies. We consider several previously suggested structural models for a Au coverage between 0.75 and 1.75 monolayer and investigate a temperature range between 0 and 900 K. The stability of the investigated surface models is found to depend clearly on temperature. We find that the extended Ge bridge dimer model previously predicted to be most stable for a large range of preparation conditions is less prominent in the phase diagrams for finite temperatures. On the other hand, a model derived previously from the giant missing row structure with a higher Au coverage gets stabilized by temperature. These findings explain, at least partially, the discrepancies between experimental data and previous theoretical investigations neglecting temperature effects.
Published Version
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