US scientists have studied spin Hall and Klein tunnelling effects during oxidation of graphene and few-layer graphene. Previous studies had suggested that the reductive properties of graphene change depending on the external magnetic field, with explosive redox reactions between graphene and strong oxidants accelerating following temperature reduction from 22 to 16 °C.
A typical way to oxidise graphene to oxide is to use a mixture of sulfuric acid, NaNO3 and KMnO4 (Hummers method). The Na+ and K+ ions of KMnO4 /NaNO3 have until now been assumed not to influence the redox reactions involved. This work shows that changing the cations has a big effect: replacing Na+ and K+ with Mg2+ and Ca2+, the team observed faster, more electronically delocalised complete oxidation to CO2 at temperatures between 16 and 21 °C. With Na+ and K+, they saw faster, more electronically localised oxidation to CO at temperatures >22 °C. These observations are attributed to the spin Hall effect (SHE) for the Na+ and K+ ions and Klein tunnelling effect for the Mg2+ and Ca2+ ions.
The observations will be very helpful in aiding understanding of the correlation between the structure and the properties of layered materials, such as graphene and boron nitride. The observed SHE gives an explanation of recently reported tunnelling of graphene electrons through boron nitride.
Read the full details of this fascinating PCCP article today:
Nuclear spin Hall and Klein tunneling effects during oxidation with electric and magnetic field inductions in graphene
Reginald B. Little, Felicia McClary, Bria Rice, Corine Jackman and James W. Mitchell