Carbon is a very versatile element. It has long been identified by its allotropes of graphite and diamond, but more recent research has let us in on a number of tricks up its sleeve. Most popular are the carbon nanotube and Buckminsterfullerene (bucky ball), and even these can come in sub categories of single wall, multiwall, various chiralties, C60 vs. C 120 and so on. Where does it end? Perhaps with the beginning of other options.
There’s no doubting that carbon allotropes will maintain their popularity and that there is yet to be a climax in the interesting properties they possess (or are expected to). All that attention, however, has overshadowed other options from the periodic table. That is where phosphorus is now turning heads.
Black phosphorus can provide atomic sheets, and like graphene, has a hexagonal atomic structure. There is a big difference between the two when it comes to electronic properties. Graphene, a single sheet of graphite, acts quite differently. It behaves as a semi-metal and has no band gap.
Phosphorene is a semiconductor and has a natural band gap. That means it can exhibit conductive or insulative properties. This versatility is the foundation for silicon-based electronics and a prerequisite for use as a "switch" in advanced computing.
Researchers in the US and China have successfully isolated 2 or 3 atomic layers, though not yet isolating a single phosphorene layer. The process for extraction is similar to graphene isolation where an adhesive layer is used to “peel” off atoms (called mechanical exfoliation).
Phosphorene shows promise as an elemental replacement for molybdenum disulfide which has been worked with for years. There are other “enes” as well. For instance, single-layer silicon (silicene), germanium (germanene) and tin (stanene) have also been investigated. All of these materials still face varying obstacles to commercialization, but work to manufacture and understand them continues.
Graphene is by no means obsolete for many reasons, but one reason is that progress has been made on its use in switching needed for transistor applications. The researchers exploited a property of graphene called negative differential resistance to modify the charge transfer. Under specific conditions, when charge is applied the voltage of the circuit is reduced.
Although graphene is still a very young and promising material, the need for diversity in materials is evident. Phosphorene has native properties that graphene lacks which make it a promising transistor material, but both materials, as well as other competitors, need more work.
Image courtesy of RSC News