Since the discovery of graphene, two-dimensional (2D) atomic crystals characterized by strong in-plane covalent bonds and weak interlayer van der Waals forces have become one of the leading topics in condensed matter physics. In antimony triselenide (Sb₂Se₃), which is the subject of investigations published recently in Nanoscale, strong covalent bonds and weak van der Waals interaction are also well represented. The crystalline structure of this semiconductor is, however, quite unusual. Selenium and antimony atoms form covalently bound one-dimensional ribbons interacting weakly with each other by means of weak van der Waals forces. Antimony triselenide belongs, therefore, to the family of one-dimensional van der Waals semiconductors which is much less explored as compared to two-dimensional materials.

The researchers from the Institute of Physics PAS in collaboration with the Institute of Microelectronics and Photonics of the Lukasiewicz Research Network, the Institute of Photonics and Electronics of the Czech Academy of Sciences and the Faculty of Physics, University of Warsaw, have developed a procedure to obtain antimony triselenide by molecular beam epitaxy, a technique applied usually for the fabrication of thin films with superior purity for the applications in electronics and photonics. It is found that antimony triselenide forms spontaneously monocrystalline, one-dimensional nanostructures on the surface of standard GaAs substrates (Figure 1a). The length of these nanostructures is usually one order of magnitude larger than the other dimensions. Moreover, it is found that the orientation of the nanostripes, which are all lying flat on the surface, is defined by the crystal orientation of the substrate in a way that <011>_GaAs corresponds to  [010]_Se2Sb3 (Figure 1b-c). The elongated shape of the nano-stripes is directly related to the highly anisotropic crystalline structure of antimony triselenide.

After a sufficiently long growth, the nano-stripes begin to merge forming spontaneously networks of interconnected nanostructures (Figure 1). These well-ordered arrays of horizontal nanostripes aligned in directions defined by the orientation of the substrate may contribute significantly to the development of electronic circuits and networks composed of interconnected nanostructures leading to applications in the field of neuromorphic devices, gas sensors and polarization sensitive photodetectors.