(Invited) Growth of Germanene, Stanene, Plumbene, and Their Lateral Heterostructure
Authors: Yuhara Junji 
Published: December 2024

The synthesis and characterization of post-graphene materials have been intensively studied with the aim of utilizing novel two-dimensional (2D) properties. Most studies adopted molecular beam epitaxy as a synthesis method of 2D materials grown on clean crystalline surfaces. In my talk, I will talk on the epitaxial growth of (1) germanene, (2) stanene, lateral heterostructure, and (3) plumbene by segregation and deposition methods[1–11].

(1) Germanene on Ag(111) thin film by segregation
[1]

On annealing the specimen of Ag(111) thin film grown on Ge(111)the Ge atoms segregate on the surface and germanene has been epitaxially formed on the surface. Low-energy electron diffraction clearly shows incommensurate “(1.3×1.3)”±30° spots, corresponding to a lattice constant of 0.39 nm, in perfect accord with close-up scanning tunneling microscopy (STM) images, which clearly reveal an internal honeycomb arrangement with corresponding parameter and low buckling within 0.01 nm. From the STM images, two types of protrusions, named hexagon and line, form a (7√7×7√7) ±19.1° supercell with respect to Ag(111) with a super large periodicity of 5.35 nm.

(2) Stanene on Ag2Sn surface alloy by deposition
[2]

The lattice parameters of Ag2Sn surface alloy and free-standing stanene are close to each other. The Ag(111) easily react with Sn atoms on annealing, while the Ag2Sn surface alloy is chemically inert against the Sn atoms. Thus, the Ag2Sn surface alloy is physically and chemically ideal surface for epitaxial growth of stanene. We have successfully prepared large area planar stanene on Ag2Sn surface alloy by Sn deposition.

(3) Plumbene on Pd1-xPbx(111) alloy surface by deposition and segregation
[3]

The bulk Pb-Pd system exists in fcc solid solution with a Pb concentration up to 10 %. The Pb atoms deposited dissolve into the Pd crystal and segregate on the surface on annealing. Through this process, plumbene is epitaxially grown on Pd1-xPbx(111) surface. The surface also exhibits a unique morphology in the STM images resembling the famous Weaire-Phelan bubble structure of the Olympic “WaterCube” in Beijing.

(4) Germanene and stanene lateral heterostructure
[5]

We use a unique combination of atomic segregation epitaxy (ASE) and molecular beam epitaxy (MBE) for the in-situ continuous fabrication of nearly atomically precise lateral multi-junction heterostructures, respectively consisting of atom-thin germanene and stanene on a Ag(111) thin film. The STM observations down to 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; remarkably, 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 directly derived from atomic-scale STM images, while scanning tunneling spectroscopy reveals key features of the electronic structure at the heterojunction[1,2,5]. Our innovative approach of ASE and MBE growths combined in synergy offers great flexibility for the realization of unprecedented lateral 2D heterostructures.

References

[1] J. Yuhara et al, ACS Nano 12, 11632 (2018).
[2] J. Yuhara et al, 2D Materials 5, 025002 (2018).
[3] J. Yuhara et al, Adv. Mater. 31, 1901017 (2019).
[4] J. Yuhara and G. Le Lay, Jpn. J. Appl. Phys. 59, SN0801 (2020).
[5] T. Ogikubo et al, Adv. Mater. Inter. 7, 1902132 (2020).
[6] W. Pang et al, Appl. Surf. Sci. 517, 146224 (2020).
[7] J. Yuhara et al, Appl. Surf. Sci. 550, 149236 (2021).
[8] J. Yuhara et al, Phys. Rev. Mater. 5, 053403 (2021).
[9] J. Yuhara et al, 2D Mater. 8, 045039 (2021).
[10] S. Mizuno et al, Appl. Phys. Express 14, 125501 (2021).
[11] J. Yuhara et al, Surf. Sci., 738, 122382 (2023).

Figure 1 STM images of germanene on Ag(111), stanene on Ag2Sn surface alloy on Ag(111), plumbene on Pd1-xPbx(111) and the lateral heterostructure on Ag(111) and plumbene

Figure 1