2D Monoelements. Группа авторов

Figure 2.5 (a) Schematic diagram of the synthesis process of antimonene by the vdWE method. (b) Optical microscope images of few-layer antimonene polygons with various shapes. The scale bar is 5 μm. (c) HRTEM image of a typical antimonene polygon. Inset: selected area electron diffraction (SAED) pattern along the [001] axis. The scale bar is 2 nm. (d) Raman spectra of antimonene polygons with different thicknesses. (e) Scanning electron microscopy (SEM) image of 10-nm thick antimonene on an as-grown graphene substrate. (f) Atomic models of the epitaxial alignments between Sb (0001) and graphene in three morphs of Sb. (a–d) Reproduced with permission [25]. Copyright 2016, Nature Publishing Group. (e, f) Reproduced with permission [26]. Copyright 2018, American Chemical Society.

In particular, there are no dangling bonds in 2D materials, thus the 2D materials can also be employed as the substrates to grow antimonene. Sun et al. grew a series of antimonene (Sb) with various morphs on two types of single-crystalline graphene substrates by the vdWE method [26]. One of the substrates was the as-grown graphene on Cu (111)/c-sapphire via chemical vapor deposition (CVD), and another was the transferred graphene on SiO₂/Si. On the as-grown graphene, triangle Sb islands (up-pointing and down-pointing triangles) were grown in Volmer-Weber (VW) modes with height of ~17.5 ± 0.7 nm, while Sb sheets were grown in Frank-van der Merve (FM) modes with height of ~4.5 ± 0.7 nm (Figure 2.5e). The growth of Sb sheets was probably caused by the remote epitaxy between Sb and underlying Cu. The epitaxial alignments between Sb (0001) and graphene were different in various morphs of Sb, i.e., Sb [1i00]∥graphene [10] and [10i0]∥graphene [10] for up-pointing and down-pointing Sb islands, [2ii0]∥graphene [10] for Sb sheets (Figure 2.5f). In contrast, only VW growth of Sb islands was found on the transferred graphene due to the absence of Cu. In addition, high-quality Sb thin films were also grown on both substrates, and these two films showed no significant difference. The epitaxial alignment in Sb thin films was the same as that in Sb islands. In another work, β-antimonene was also grown on WSe₂ substrate to form the Sb/WSe₂ heterostructure through van der Waals interactions [27].

      The earliest MBE growth of antimonene was reported by T. Lei et al. in 2016 [28]. In this work, bilayer antimonene was grown smoothly on 3D topologically insulated Bi₂Te₃ (111) and Sb₂Te₃ (111) substrates with small lattice mismatch. The clear low-energy electron diffraction (LEED) pattern indicated the 1 × 1 periodicity of the antimonene/Sb₂Te₃ (111) surface, showing that high-quality epitaxial antimonene was formed. The surface states of MBE grown antimonene were probed by angle-resolved photoemission spectroscopy (ARPES), and it showed similar electronic structures on the surfaces of two substrates, but the bands of antimonene on Bi₂Te₃ (111) surface were flatter than on Sb₂Te₃ (111) surface due to the larger lattice constants of Bi₂Te₃ (111) substrate. The interfacial strain and charge transfer induced a change in band dispersions. This work is a milestone in this kind of study, which is critical for the understanding of the electrical structure of antimonene.

Subsequently, monolayer-to-multilayer antimonene were successfully grown on 2D substrates by the MBE method, such as PdTe₂, MoS₂, WTe₂, and graphene [29–32]. Wu et al. grew large-area monolayer antimonene on a freshly cleaved PdTe₂ substrate in an ultrahigh vacuum (UHV) MBE chamber (2 × 10⁻¹⁰ mbar), and the schematic of growth process was shown in Figure 2.6a [29]. 2D PdTe₂ was chosen as a suitable substrate in the growth of antimonene, because of its small mismatch of crystal periodicity with free-standing antimonene and chemically stable surface. From the topological scanning tunneling microscopy (STM) image shown in Figure 2.6b, it is observed that an atomically smooth antimonene film was obtained with no obvious defects or domain boundaries. According to the LEED pattern in the inset of Figure 2.6b, this film is a well-ordered single crystalline with a commensurate (1 × 1) lattice periodicity. The height of this film is about 2.8 Å, which is consistent with that of a monolayer antimonene (Figure 2.6c). Figure 2.6d shows an atomic-resolution STM image of antimonene, it is clearly seen that this epitaxial film has a buckled honeycomb lattice with a periodicity of 4.13 ± 0.02 Å. It is noted that monolayer antimonene grown on PdTe₂ was chemically inert to the air. This work first unveils the atomic-scale morphology of epitaxial monolayer β-antimonene.