MS-1-P-2165 Diffusion effects investigations of self-organized Gold nanostructures on Ge(001) surface by Electron Microscopy

The self-organized gold nanostructures on Ge(001) surface are currently of special interest due to their applications for mono-molecular electronic devices [1,2]. The understanding of electrical as well as physical properties of the system is of great importance.
The Ge(001) substrate samples were cleaned to achieve atomically flat terraces by low energetic ions bombardment and by annealing. Next, 6 ML of Au was deposited by the Molecular Beam Epitaxy in room temperature. Later, the sample was post-annealed to temperature from 473 K to 770 K. The gold self-organizes to create island structures on Ge surface as depicted in Figure 1.
The morphology of Au/Ge(001) samples was measured for different post-annealing temperatures with SEM FEI Quanta 3D FEG. The island surface density and their sizes were measured providing the information on surface diffusion effects. The autocorrelation analysis shows that there exists preferred island orientation along crystallographic directions on the substrate surface.
Cross sections from the Au/Ge(001) samples were prepared using FIB technique for transmission electron microscopy measurements conducted with TEM FEI Tecnai Osiris 200 kV equipped with Super-X EDX detector. The TEM measurements show that some island are submerged in germanium substrate. The chemical composition of the islands was mapped by the STEM/EDS measurements. This uncovered core/shell structure of the islands, with germanium shell on top. The crystalline nature was first studied by Selected Area Electron Diffraction (SAED) diffraction and Dark Field imaging. Later, detailed investigations were performed by Nano Beam Diffraction (NBD) measurements in STEM micro-Probe. This showed differences in crystalline structure of the islands.
The electron microscopy gives the possibility to fully study the creation dynamics and to completely characterize the fabricated nanostructures. Surface diffusion effects are investigated by the SEM as well as effects of diffusion processes into the bulk Ge crystal are measured by the TEM cross sections. This gives the unique scientific possibilities to fully investigate the evolution of the self-organized systems. The results and used experimental techniques will be discussed.

[1] C. Joachim et. al., Nature 408, 2000
[2] M. Wojtaszek et. al., Advances in Atom and Single Molecule Machines, Vol.1, 2012