The Future is Flat—Two-Dimensional Nanomaterials
The bulk properties of materials often change dramatically with nanoscale ingredients. Composites made from particles of nano-size ceramics or metals smaller than 100 nanometers can suddenly become much stronger than predicted by existing materials-science models. For example, metals with a so-called grain size of around 10 nanometers are as much as seven times harder and tougher than their ordinary counterparts with grain sizes in the hundreds of nanometers. The causes of these drastic changes stem from the weird world of quantum physics. The bulk properties of any material are merely the average of all the quantum forces affecting all the atoms. As you make things smaller and smaller, you eventually reach a point where the averaging no longer works. The properties of materials can be different at the nanoscale for two main reasons: first, nanomaterials have a relatively larger surface area when compared to the same mass of material produced in a larger form. This can make materials more chemically reactive (in some cases materials that are inert in their larger form are reactive when produced in their nanoscale form), and affect their strength or electrical properties. Second, quantum effects can begin to dominate the behavior of matter at the nanoscale—particularly at the lower end—affecting the optical, electrical and magnetic behavior of materials. Materials can be produced that are nanoscale in one dimension (for example, very thin surface coatings), in two dimensions (for example, nanowires and nanotubes) or in all three dimensions (for example, nanoparticles such as quantum dots). Nanomaterials fall into two categories: the nanoscale version of bulk materials (titanium, gold, ceramics...) that exhibit new properties and allow new functionalities. And secondly, entirely new material structures that were discovered or synthesized over the past 30 years. These new materials include carbon nanotubes, fullerenes, quantum dots, and a new class of single-atomic-layer materials such as graphene. In this chapter we will not look at “conventional” nanomaterials but at two new classes of novel materials with exciting properties and promising applications such as invisibility cloaks: two-dimensional materials and metamaterials. Today, all these materials are being synthesized in laboratories and researchers are beginning to find ways to integrate them into devices and make them practical enough to find their way into industrial manufacturing processes.