New epitaxial rules for two-dimensionally bonded materials grown on three-dimensionally bonded substrates

Electronic applications rely heavily on material interfaces for their optimum functionality. Materials that are used in conventional electronics are characterized by covalent bonding in three dimensions (3D). The interface formation mechanisms between 3D materials are therefore well studied and understood. In recent years it has become clear that materials that are characterized by covalent bonding in only two dimensions (2D) also have attractive properties for electronic devices. The bonding between individual layers in 2D materials occurs by van-der-Waals forces, which are weaker compared to the covalent bonding that occurs in 3D materials. In order to integrate 2D materials with conventional 3D materials, such as silicon, a detailed understanding of the mechanisms that determine the interface structure between 2D and 3D materials will be required. 2D materials include among others Sb2Te3, which is a well known thermoelectric, topological insulator and phase change material.

 

Figure 1: Angular dependence of the RHEED intensity for 1nm thick Sb2Te3 films grown on (a) Si(111)-(7x7) and (b) Si(111)-(√3x√3)R30°-Sb.

We shed some light on the mechanism that determines the interface structure between 2D and 3D materials by fabricating Sb2Te3 layers on top of Si(111) surfaces with different surface reconstructions using molecular beam epitaxy. X-ray diffraction and angular resolved reflection high energy electron diffraction (RHEED) studies revealed the presence of rotational domains in these films and, most importantly, that the rotation angles depend on the type of surface reconstruction. The latter aspect is visualized in the RHEED data shown in Fig. 1 by the fact that for growth on the Si(111)-(7x7) reconstruction (Fig. 1a) each bright feature is elongated and constituted by a merging of several dots, whereas for growth on the Si(111)-(√3x√3)R30°-Sb reconstruction (Fig. 1b) small spots constituted by a single dot are obtained. Moreover, by analyzing the rotation angles and the structure of the reconstructed surfaces we were able to show that the rotations are related to the location of the dangling bonds that are present on the surface.

This result implies that in contrast to classical epitaxy (3D/3D), during the deposition of 2D materials the surface reconstruction of the substrate is preserved, and a reordering of the surface bonds does not take place. On the other hand it also demonstrates that bonding continues to play a role during the epitaxy of 2D materials on top of 3D substrates. This makes such epitaxy (2D/3D) also distinct from van-der-Waals epitaxy (2D/2D) and thus special.

Publication

1 Autor J. E. Boschker , J. Momand , V. Bragaglia , R. N. Wang , K. Perumal , A. Giussani , B. J. Kooi , H. Riechert , R. Calarco
Titel

Surface Reconstruction-Induced Coincidence Lattice Formation Between Two-Dimensionally Bonded Materials and a Three-Dimensionally Bonded Substrate

Source Nano Lett. , 14 , 3534 ( 2014 )
DOI : 10.1021/nl5011492 | 2544 Cite : Bibtex RIS
J. E. Boschker, J. Momand, V. Bragaglia, R. N. Wang, K. Perumal, A. Giussani, B. J. Kooi, H. Riechert, and R. Calarco