Germanene termination of Ge₂Pt crystals on Ge(110)

Abstract

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...

Two-dimensional Dirac signature of germanene

“…Line scans taken across and along the step edge are depicted in Figures 3B and 3C, respectively. The monatomic step height is 0.56 nm and agrees well with observations by Bampoulis et al [12]. A line scan taken along the step edge reveals a 4a periodicity, where a=0.43 nm is the lattice constant of germanene.…”

“…A few monolayers of Pt were deposited on a Ge(110) substrate at room temperature and subsequently the substrate was annealed at a temperature of about 1100 K for 10 seconds. In a previous paper [12] we have described that at temperatures higher than 1000 K eutectic Pt0.22Ge0.78 droplets are formed on the Ge(110) substrates. Upon cooling down, the eutectic droplets undergo spinodal decomposition into a pure Ge phase and a Ge2Pt phase The Ge phase segregates to the surface, whereas the Ge2Pt remains at the interior of the solidified droplets.…”

Structural and Electronic Properties of Germanene onMoS2

“…In the past few years various groups have successfully synthesized silicene [7][8][9] and germanene [10][11][12][13] on a variety of substrates. To date germanene has only been grown on metallic substrates, such as Pt(111) [10], Au(111) [11], Ge 2 Pt [12,14] and Al(111) [13], which might hinder a proper decoupling of the key electronic states of germanene near the Fermi level from the underlying substrate.…”

A nitride-based epitaxial surface layer formed by ammonia treatment of silicene-terminated ZrB2

“…Currently, the growth on insulating substrates is one of the largest challenges faced by research on 2D semiconductors, in particular, for silicene [1][2][3] and germanene, [4][5][6] as these materials have so far only been synthesized on metal substrates. Silicene and germanene are single-atom thick layers of Si or Ge atoms, respectively, in a buckled honeycomb lattice.…”