Growth and characterization of antimony nanostructures on inert layer-material substrates

With the aid of sophisticated growth techniques, a wide variety of nanostructured materials have become fabricated with high control over their size, dimensionality and lattice type. By large, the physical properties of such nanomaterials are quite different from their normal bulk counterparts, therefore providing a plethora of applications in various solid state devices. Antimony (Sb) based nanostructures have drawn special attention recently. Bulk Sb crystallizes in the rhombohedral structure with its ground state being semi-metallic in nature. Material properties in reduced dimensions are strongly modified due to quantum confinement and surface effects in general. Furthermore, nanostructural Sb could become topological insulators because the non-trivial bulk band order supporting topologically protected surface states. Thus, in requisite is the choice of synthesizing techniques capable of controlled growth. In this limelight, this chapter is devoted to understanding the self-assembly mechanism of Sb nanostructures from initial nucleation stage to final texture transformation. To nullify the influence of substrates on the Sb nanomaterials grown, we use inert layer-material substrates such as highlyoriented pyrolytic graphite (HOPG) and molybdenum disulphide (MoS2). These growth systems serve as models for the self-assembly of nearly free-standing nanostructures. Furthermore, the surface properties of these inert substrates are quite similar to their single- and few-atomic-layer counterparts. These ultrathin materials have drawn tremendous interests for applications in two-dimensional (2D) electronic devices. Nanostructure growth on HOPG and MoS2 therefore also serve as models for understanding contact and interface formations on those 2D electronic materials. The growth of Sb nanostructures on HOPG and MoS2 in ultra-high vacuum is monitored via in situ scanning tunneling microscopy (STM). 3D islands, 2D thin films and 1D nanorods of Sb are obtained on these substrates with different flux and temperatures. The formations of different types of Sb nanostructures are explained in terms of diffusion and dissociation of Sb4 clusters generated from a thermal evaporator. The lattice parameters of these 3D and 2D Sb structures on HOPG are close to the bulk values. The Sb nanorods often form bundles with 90° intersection. Atomic resolution STM images revealed a simple cubic lattice structure in the 90° elbow area of Sb nanorods whereas rhombohedral Sb(110) lattice was obtained away from the intersection, indicating an allotropic modification at nanoscale. In addition, the pre-deposited Sb on graphite shows remarkable effect on the nucleation and growth of Ge and Al nanostructures. A significant increase in the Ge cluster island density and pinning of Al islands on HOPG terraces have been observed in the presence of Sb. These observations offer material design strategies via altering the dimensionality and size with possible extension to mass production of electronic, thermoelectric, magnetic and spintronic nano-devices.