What Are Nanomaterials?
Nanomaterials are materials with a structure in the nanometer scale. The term “nano” originates from the Greek word "νᾶνος" for "dwarf". Nanomaterials exhibit mechanical, optical and electrical properties that differ distinctively from those of the corresponding bulk materials.
Although nanomaterials also occur naturally (e.g. the light-sensitive pigments inside plants enabling photosynthesis), the research area of nanomaterials focuses mainly on engineered nanomaterials.
Nanomaterials can be manufactured either via a top-down fabrication approach or a bottom-up approach.
While the top-down approach is using microfabrication techniques like photolithography to downscale the material, the bottom-up approach involves assembling atoms and molecules into the desired nanostructure.
Categorization of nanomaterials
Usually, nanomaterials are categorized according to their dimensions. This is based on the number of dimensions that are not confined in the nanometer scale (<100nm).
- Zero-dimensional (0D) nanomaterials: The most common 0D-nanomaterials are nanoparticles. These particles are fully confined to the nano-range in all of their dimensions.
- One-dimensional (1D) nanomaterials: 1D-nanomaterials have one dimension that is outside the nanometer scale and, therefore, have a needle-like-shape. Common examples include nanowires and nanotubes.
- Two-dimensional (2D) nanomaterials: 2D-nanomaterials have a plate-like shape since only one dimension is confined to the nanoscale. Nanocoatings and nanofilms are considered as two-dimensional nanomaterials. Besides, also graphene and the class of single-layer transition metal dichalcogenides (TMD) falls under this category.
- Three-dimensional (3D) nanomaterials: 3D-nanomaterials do not have any dimensional confinement in the nanoscale and are, thus, also referred to as bulk nanomaterials. However, they do feature a nanocrystalline structure or possess features at the nanoscale like for example dispersions of nanoparticles or nanostructured surfaces. Also, nanocomposites fall into this category.