Germanene Epitaxial Growth by Segregation through Ag(111) Thin Films on Ge(111)

Abstract

Large-scale two-dimensional sheets of graphene-like germanium, namely, germanene, have been epitaxially prepared on Ag(111) thin films grown on Ge(111), using a segregation method, differing from molecular beam epitaxy used in previous reports. From the scanning tunneling microscopy (STM) images, the surface is completely covered with an atom-thin layer showing a highly ordered long-range superstructure in wide scale. Two types of protrusions, named hexagon and line, form a (7√7 × 7√7)R19.1° supercell with respect to Ag(111), with a very large periodicity of 5.35 nm. Auger electron spectroscopy and high-resolution synchrotron radiation photoemission spectroscopy demonstrate that Ge atoms are segregated on the Ag(111) surface as an overlayer. Low-energy electron diffraction clearly shows incommensurate “(1.35 × 1.35)”R30° spots, corresponding to a lattice constant of 0.39 nm, in perfect accord with close-up STM images, which clearly reveal an internal honeycomb arrangement with corresponding parameter and low buckling within 0.01 nm. As this 0.39 nm value is in good agreement with the theoretical lattice constant of free-standing germanene, conclusively, the segregated Ge atoms with trivalent bonding in honeycomb configuration form a characteristic two-dimensional germanene-like structure.

A perspective on conventional high-temperature superconductors at high pressure: Methods and materials

“…Moreover, the possibility to induce surface metallic states in insulators by means of an intense electric field and turn two dimensional materials into superconductors [525] have opened a new avenue of research. The successful synthesis of a plethora of two-dimensional systems over the last years such as transition metal dichalcogenides [526], layered transition metal oxides [527,528], hexagonal-boron nitride [529], topological insulators [530], 2D-cuprates [531], ferromagnetic 2D systems [532], phosphorene [533], bismuthene [534], silicene, germanene [535,536] and borophene [537] have fuelled the field opening the possibility to investigate doping and induced superconductivity in a large array of different systems.…”

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“…[3] Emerging two-dimensional (2D) monoelemental materials (Xenes) with planar topology have provided more possibilities for the development of novel and robust PTAs (for example,graphene and black phosphorus (BP)). [4] Germanene is ar ecently developed 2D monoelemental material [5] that shows unique advantages over the prototypical 2D Xenes,such as graphene and BP. [4] Germanene is ar ecently developed 2D monoelemental material [5] that shows unique advantages over the prototypical 2D Xenes,such as graphene and BP.…”

“…[4] Due to their unique properties,including broad absorption, ultrahigh surface-to-volume ratio,t ractable synthesis,e ase of modification, potentially simple metabolism and degradation mechanisms,t heir applications as all-aspect-satisfactory PTAs are promising. [4] Germanene is ar ecently developed 2D monoelemental material [5] that shows unique advantages over the prototypical 2D Xenes,such as graphene and BP. [5b,6] Thewide absorption range of germanium from ultraviolet to NIR region [7] indicates that the synthesized 2D germanene may have ag reat chance to be ar obust PTA.…”

Graphene's Latest Cousin: Plumbene Epitaxial Growth on a “Nano WaterCube”

“…After the pioneering growth of silicene on Ag(111) in 2012, the next, down the column, group 14 monoelemental 2D honeycomb lattices were at the focus. Soon, germanene (2014) and stanene (2015), as well as silicene again, have been realized on diverse surfaces . Moreover, group 13 and 15 analogs such as borophene, phosphorene, antimonene, and bismuthene, have been also synthesized …”

“…Just recently, our group has demonstrated that a Ag‐Sn surface alloy, instead of a pure Ag(111) template, is involved in the formation of stanene, using such an MBE method . Otherwise, a segregation process is, in a sense, an ideal method to create 2D materials since it is possible to prepare them at relatively high temperatures, resulting in the energetically most stable phases, as in the case of germanene growth . The Ge segregation stems from the temperature dependence of the Ge solubility in the silver‐rich range.…”