Two-dimensional (2D) materials
One classification of nanomaterials is based on the number of dimensions of a material, which are outside the nanoscale (<100 nm) range.
Accordingly, in zero-dimensional (0D) nanomaterials all the dimensions are measured within the nanoscale (no dimension is larger than 100 nm). Most commonly, 0D nanomaterials are nanoparticles.
In one-dimensional nanomaterials (1D), one dimension is outside the nanoscale. This class includes nanotubes, nanorods, and nanowires.
In two-dimensional nanomaterials (2D), two dimensions are outside the nanoscale and one dimension is only a single or few atomic layers thick. This class exhibits plate-like shapes and includes graphene and other monolayer materials such as transition metal dichalcogenides, black phosphorous phosphorene), and diatomic hexagonal boron nitride.
Three-dimensional nanomaterials (3D) are materials that are not confined to the nanoscale in any dimension. This class can contain bulk powders, dispersions of nanoparticles, bundles of nanowires, and nanotubes as well as multi-nanolayers.
Classification of nanoscale dimensions. (Source: Tallinn University of Technology)
What makes 2D materials so interesting for researchers is their outstanding physical and chemical properties in contrast to their bulk counterparts.
Inspired by the unique optical and electronic properties of graphene, 2D layered materials – as well as their hybrids – have been intensively investigated in recent years, driven by their potential applications mostly for nanoelectronics.
The broad spectrum of atomic layered crystals includes transition metal dichalcogenides (TMDs), semiconducting dichalcogenides, monoatomic buckled crystals, such as black phosphorous (BP or phosphorene), and diatomic hexagonal boron nitride (h-BN).
This class of materials can be obtained by exfoliation of bulk materials to small scales, or by epitaxial growth and chemical vapor deposition (CVD) for large areas.
Such atomically thin, single- or few-layer crystals are featured with strong intralayer covalent bonding and weak interlayer van der Waals bonding, resulting in superior electrical, optical and mechanical properties.
By Michael Berger Michael Berger – Michael is author of two books by the Royal Society of Chemistry: Nano-Society: Pushing the Boundaries of Technology and Nanotechnology: The Future is Tiny. Copyright © Nanowerk