Bacteria could boost graphene semiconductivity

A team of researchers at the University of Illinois (UoI), Chicago, US, has found a way to open a ‘bandgap’ in graphene using a bacterium called Bacillus subtilis.

Since its discovery in 2004 graphene has developed numerous applications. Scientists, however, have long since imagined revolutionary, flexible, semi-transparent electronics as a primary function for graphene. Graphene, however, has always promised more than it has delivered in this area because, although an excellent conductor of electricity, other electronic properties in the so-called ‘wonder material’ leave much to be desired.

Electric current is not easily channelled in graphene but moves erratically across a sheet in all directions. It also lacks a bandgap – a property required to generate on/off states that transistors rely on. To open a bandgap within a material, it is necessary to disrupt the distribution of electrons.

One method is to introduce the atoms of other elements. For graphene, however, conductivity is weakened with this method. Another is the modification of the shape of atomic sheets by a process known as ‘wrinkling’. Existing methods of wrinkling, however, have no control over where the wrinkles are oriented.

UoI researchers have now introduced B. subtilis cells which, if dehydrated, shrink and shrivel, allowing them to be patterned on to graphene after vacuum heating them to 250°C.

B. subtilis cells form wrinkles about 33 nanometres apart; to create a significant bandgap they would have to be fewer than five nanometres apart. Lead researcher Dr Vikas Berry says this could be achieved by using other species with stronger cell walls or different sorts of cells.

Berry and his team are pushing graphene towards semiconductivity in an innovative way – a way that has once again turned to nature for inspiration.