Continuous Growth of Germanene and Stanene Lateral Heterostructures

Abstract

of a band gap in its electronic structure is difficult, these novel 2D materials are expected to possess sizeable band gaps, making them typically suitable for electronic applications. Furthermore, theory predicts that they are robust topological insulators, even up to about room temperature (RT) and above for germanene and stanene.In experiment, these artificial 2D materials were firstly realized in situ by molecular beam epitaxy (MBE) for silicene in 2012, [1,2] germanene in 2014, [3] stanene in 2015, [4] and finally plumbene in 2019. [5] One of the next targets is the growth of in-plane heterostructures because abrupt lateral interfaces promise controlled heterojunction functionalities. Lateral heterostructures of graphene and hexagonal boron nitride (h-BN) were grown on Cu(110) in 2014. [6] First-principles calculations on the electronic properties of graphene quantum dots embedded in monolayer h-BN sheets typically indicate that the h-BN band gap shrinks upon increasing the diameter of the graphene dots. [7] Besides lateral graphene/h-BN heterostructures, fabrication of several in-plane heterostructures of transition metal dichalcogenides has also been reported. [8] Very recently, vertical heterostructures have been prepared by boron intercalation underneath Group 14 elemental post-graphene materials receive much attention because of their outstanding properties, typically, as robust 2D topological insulators. Their heterostructures are a main target in view of disruptive applications. Here, the realization of striking in-plane lateral heterostructures between germanene and stanene are shown, which are sustainable 2D Ge-and Snbased graphene analogs, but with a strong intrinsic spin-orbit coupling. A unique combination of atomic segregation epitaxy (ASE) and molecular beam epitaxy (MBE) for the in situ continuous fabrication of nearly atomically precise lateral multijunction heterostructures, respectively, consisting of atom-thin germanene and stanene on a Ag(111) thin film is used. Scanning tunneling microscopy (STM) observations at atomic scale and low-energy electron diffraction testify that germanene and stanene sheets without intermixing are prepared simultaneously on the same terraces at wide scale: tin and germanium atoms neither exchange their sites nor adsorb on the germanene and stanene sheets. The atomic structure of the boundary between germanene and stanene is derived from STM images, while scanning tunneling spectroscopy reveals key electronic features at the heterojunction. This innovative synergetic approach of ASE and MBE growths offers great flexibility for the realization of unprecedented lateral 2D heterostructures.

Preparation Engineering of Two-Dimensional Heterostructures via Bottom-Up Growth for Device Applications

“…(d) STM image of germanene/stanene LHSs. Reproduced with permission from ref . Copyright 2020 Wiley-VCH.…”

“…With these merits, HS direct growth under UHV conditions is a marvelous choice for some in situ or quasi- in situ characterizations, such as STM characterization. Ogikubo et al designed a preparation solution by comprehensively using both atomic segregation epitaxy and MBE under UHV conditions to form stanene/germanene LHSs (Figure d) . The growth procedure under ultrahigh vacuum conditions is at variance with both solution synthesis and CVD/PVD methods due to the UHV condition without other gas flow and solution atmospheres.…”

“…Ogikubo et al designed a preparation solution by comprehensively using both atomic segregation epitaxy and MBE under UHV conditions to form stanene/germanene LHSs (Figure 2d). 21 The growth procedure under ultrahigh vacuum conditions is at variance with both solution synthesis and CVD/PVD methods due to the UHV condition without other gas flow and solution atmospheres. In the UHV sample preparation path, as previously mentioned borophene/PTCDA HSs grown by Liu and colleagues, the characterization without removing the UHV condition ensured the observation of HSs in a relatively small region (Figure 2e).…”

Elemental 2D Materials: Solution‐Processed Synthesis and Applications in Electrochemical Ammonia Production

“…[45] Germanane exhibits many interesting and appealing properties including a direct bandgap of 1.59 eV, [100] high carrier mobility of >10 4 cm 2 V −1 s −1 , [101] high thermal stability of up to 75 °C in ambient conditions, [45] low effective mass, [102] and the operation of both electron and hole transport regimes with an on/off current ratio of up to 10 5 (10 4 ). [103] While both Ge [104][105][106] and GeH [107,108] have been widely synthesized via the epitaxial growth method, a limited number of studies on their exfoliation by liquid-phase protocols have been reported. To the best of our knowledge, Goldberger and his colleagues were the first to report the preparation of a hydrogenterminated germanium via the topochemical deintercalation of CaGe 2 .…”

Fundamental Properties of Transition-Metals-Adsorbed Germanene: A DFT Study

“…Although germanene has not been found in nature, it can be synthesized by a few methods, such as molecular beam epitaxial (MBE) [16] and topological deintercalation [17].…”