Driving chemical interactions at graphene-germanium van der Waals interfaces via thermal annealing

Abstract

Despite its extraordinary charge carrier mobility, the lack of an electronic bandgap in graphene limits its utilization in electronic devices. To overcome this issue, researchers have attempted to chemically modify the pristine graphene lattice in order to engineer its electronic bandstructure. While significant progress has been achieved, aggressive chemistries are often employed which are difficult to pattern and control. In an effort to overcome this issue, here we utilize the well-defined van der Waals interface between crystalline Ge(110) and epitaxial graphene to template covalent chemistry. In particular, by annealing atomically pristine graphene-germanium interfaces synthesized by chemical vapor deposition under ultra-high vacuum conditions, chemical bonding is driven between the germanium surface and the graphene lattice. The resulting bonds act as charge scattering centers that are identified by scanning tunneling microscopy. The generation of atomic-scale defects is independently confirmed by Raman spectroscopy, revealing significant densities within the graphene lattice. The resulting chemically modified graphene has the potential to impact next-generation nanoelectronic applications.

Epitaxial graphene/Ge interfaces: a minireview

“…As was found, the CVD graphene growth on Ge(110) leads to the disordered structure of the Ge surface quenched by graphene ( Fig. 2(g), left) 57,68,69 . This can be compared to the coexisting c(8 × 10) and (16 × 2) reconstructions characteristic for pristine Ge(110).…”

“…Annealing of the as-grown gr/Ge(110) at 700 • C in UHV drives the formation of the (6 × 2)-Ge(110) reconstruction, which is stabilized by the graphene layer and which was not previously reported for this Ge surface ( Fig. 2(g), right) 57,[69][70][71] . As shown by STM and surface x-ray diffraction (SXRD), the interfaced Ge layer reorganizes in clusters, which are ordered along the 112 direction of bulk Ge.…”

Driving with temperature the synthesis of graphene on Ge(110)

“…The former structure has been attributed to the (6x2) reconstruction of Ge(110) below the graphene. This reconstruction has not been observed for bare Ge(110), its being peculiar to the graphene/Ge system [33][34][35]45]. Instead, the origin of structural motif in Fig.…”

CVD graphene/Ge interface: morphological and electronic characterization of ripples

“…Nevertheless, there are several works about other atomically flat orientations such as (110) and (111) that arise as models to future applications as these surface orientations are expected to facilitate the high electron and hole mobility for n- and p- field effect transistors (FETs), respectively 17,18,25 . In the last few years, the study of the graphene/Ge interface was focused on the surface reconstruction of germanium 18,26 , the interaction between graphene and germanium substrate 27 , the effect of doping of the substrate on graphene growth 28 , and graphene as a protective layer of germanium substrate 29 . However, a more complete investigation that also considers the role of crystallographic orientation and the morphology of graphene is still needed.…”