We have investigated the growth of Pt on Ge(110) using scanning tunneling microscopy and spectroscopy. The deposition of several monolayers of Pt on Ge(110) followed by annealing at 1100 K results in the formation of three-dimensional metallic Pt-Ge nanocrystals. The outermost layer of these crystals exhibits a honeycomb structure. The honeycomb structure is composed of two hexagonal sub-lattices that are displaced vertically by 0.2 Å with respect to each other. The nearest-neighbor distance of the atoms in the honeycomb lattice is 2.50.1 Å, i.e. very close to the predicted nearest-neighbor distance in germanene (2.4 Å). Scanning tunneling spectroscopy reveals that the atomic layer underneath the honeycomb layer is more metallic than the honeycomb layer itself. These observations are in line with a model recently proposed for metal di-(silicides/)germanides: a hexagonal crystal with metal layers separated by semiconductor layers with a honeycomb lattice. Based on our observations we propose that the outermost layer of the Ge2Pt nanocrystal is a germanene layer. Keywords: germanene, platinum, germaniumIn 2004 Novoselov and Geim [1] ignited a revolution in materials science by preparing graphene, i.e. a single layer of sp 2 hybrizided carbon atoms. The unique electronic structure of this archetype 2D material has led to a large number of exciting physical discoveries [2][3][4]. Shortly after this discovery it has been suggested that two-dimensional sheets of other group IV elements, such as Si [5,6] and Ge [6], might exhibit similar properties as graphene. Already in 1994 Takeda and Shiraishi [7] performed quantum mechanical ab initio calculations on planar silicon and germanium structures that have the graphite structure. They pointed out that the lowest energy configuration was obtained if the two atoms of the honeycomb are slightly displaced with respect to each other in a direction normal to the planar structure. Their calculations also revealed that these buckled Si and Ge structures exhibited semimetallic properties. Unfortunately, they did not pay any attention to the exact k-dependence of the energy dispersion relations in the vicinity of the Fermi level. More than a decade later Guzmán-Verri and Lew Yan Voon [5] showed, using tight binding calculations, that a 2D silicon sheet with the graphite structure has Dirac cones. Hence the electrons in these 2D 2 silicon sheets behave as massless Dirac fermions. The Si and Ge analogues of graphene are referred to as silicene and germanene, respectively. First-principles calculations by Cahangirov et al. [6] revealed that a single sheet of germanium atoms with a honeycomb structure is also stable. The free-standing Ge honeycomb lattice is not fully planar, but buckled. The two hexagonal sub-lattices of the honeycomb lattice are displaced vertically by 0.64 Å, which is slightly larger than the buckling in silicene (0.44 Å). The buckling results into a weaker  bonding and the perpendicular pz orbital hybridizes with the in-plane orbitals.Similar to graphene...

A model has been developed to account for the dependence of melting temperature on the size of nanosolids (nanoparticles, nanowires and nanofilms). In this model the effect of particle size and shape, lattice and surface packing factor, and the coordination number of the lattice and of the surface crystalline planes are considered. A general equation is proposed, having nonlinear form as a function of the reciprocal of nanosolid size. This model is consistent with reported experimental data for nanoparticles of In and Au, nanowires of Pb and In, and nanofilms of In.

The dependency of the surface-to-volume coordination number upon particle size has been obtained by an analytical function based upon our previous work, and a model for melting temperature as a function of size is presented. This expression for the melting temperature is a nonlinear relation in terms of the reciprocal of size. Also, the geometrical characteristics of nanoclusters have been applied to our general equation for the melting temperature of nanoparticles. It was found that the results of considering the geometrical characteristics of nanoclusters are in good agreement with the melting temperature achieved by the derived analytical function. Finally, this model has been compared with other theoretical models as well as the available experimental data. The predictions are consistent with the experimental data.

We have used low-energy electron microscopy and scanning tunneling microscopy to visualize the dynamics of the formation of one-dimensional Au-induced nanowires on a Ge(001) substrate. At low temperature, the growth of nanowire domains is limited by the diffusion of Au. A wetting-dewetting transition occurs at a temperature of 665 K that transforms nanowire domains into three-dimensional Au clusters. Dewetting occurs at temperatures above 665 K and is fully reversible during repetitive heating and cooling cycles. The decay and growth rates of the nanowire domains below 665 K show intriguing dynamics, caused by the complex diffusion of gold. It correlates directly with the diffracted intensity of a reconstruction along the top of the nanowires, indicating a temperature-dependent potential landscape for the thermally activated diffusion of Au atoms across nanowire domains.