- Researchers discovered a method to change the electrical conductivity of graphene using hydrostatic pressure.
- The study gives us in-depth knowledge about the properties of the band gap in graphene.
Consisting of a thin layer of carbon atoms locked in a hexagonal lattice, Graphene exhibits several unusual properties. It efficiently conducts electricity and heat, and has interesting light absorption abilities. It is nearly transparent and strongest material ever tested.
Graphene can be combined with other elements to create different materials with superior properties. Since its discovery (in 2004), scientists all over the world have been constantly studying graphene to learn more about its characteristics and possible applications.
Recently, a research team at the Columbia University came up with a method to manipulate graphene’s electrical conductivity using pressure. This brings graphene one step closer to being a feasible semiconductor for electrical applications.
Graphene is a good conductor of electricity. In fact, it’s too efficient that scientists do not know how to effectively halt the flow of current. For the first time, scientists were able to increase the band gap of graphene by compressing the two-dimensional material. Moreover, if this technique is applied to other intriguing 2D materials, it could result in new rising phenomena, like superconductivity, magnetism, and more.
Graphene is an atomic-scale
The special alignment of carbon atoms in graphene enables electrons to flow at extremely fast speed without scattering, preserving a lot of energy usually lost in other conducting materials.
So far, no one has disabled this electron-transmission through graphene without changing its qualities.
Compressing Graphene Structure
The main objective of this research is to find a way to preserve all favorable qualities of graphene while forming a band gap (energy difference between the bottom of the conduction band and the top of the valence band).
To do this, they sandwiched the graphene between Boron Nitrate (BN) layer – a thin insulator and chemically stable compound. The 2 layers were rotationally aligned.
This setup effectively modified the graphene’s electronic structure, forming a band gap. Because of this band gap, graphene started acting like a semiconductor. However, the band gap isn’t big enough to be used in transistor instruments at room temperature.
Compressing Boron-Nitrate-graphene layers | Image credit: Columbia University
To improve it, they compressed the Boron-Nitrate-graphene layers. Somehow, this pressure significantly expanded the band gap size, efficiently blocking the electron flow through the graphene.
The band gap expanded, as they further squeezed and applied pressure. Still, it isn’t large enough to be used in electrical equipment like transistors at room temperature.
More specifically, raising pressure generates a super-linear increase in the band gap along with an expansion in the capacitive gate coupling to the active channel by as much as 25%.
Reference: Nature | doi:10.1038/s41586-018-0107-1 | Columbia University
The study gives us in-depth knowledge of the properties of the band gap in graphene – why it exists in the first place, and what exactly it takes to alter it. The study also suggests how it could be targeted in the future. Graphene would have tons of applications if we figure out a way to make it behave as a transistor.
Now, scientists can test (in their own labs) what changes occur in different stacks of atomic-thin materials by applying various hydrostatic pressures with controlled rotational orders.
According to the authors, properties of combinations of stacked atomic-thin materials change (become stronger) as they are squeezed. Take any 2D structure and compress them, and the strength of the final effect is configurable.