Feb 28, 2014
Atomic chisel chips away at graphene
Researchers at Harvard University, FEI Corporation and the Lawrence Berkeley National Lab in US together with colleagues at Graphenea Ltd in Spain have invented a new atomic “chisel” made from a single silicon atom that can be used to sculpt and create ultraclean nanostructures in graphene. The tool, which overcomes Richard Smalley’s “fat finger” problem, could be used to fashion clean edges in the carbon material, fabricate a host of nanostructures for use in future molecular electronics devices and make nanopores for DNA sequencing applications.
“A conventional chisel produces a wedge so that the kinetic energy from a hammer helps to chip off a piece of material, such as wood, for example,” explained team members Elton Santos and Wei Li Wang of Harvard. “An atomic chisel, like the silicon atom in our experiments, which is controlled by a high-energy beam in a transmission electron microscope, produces a ‘catalytic wedge’. Here, the kinetic energy from the electron beam helps to selectively chip off carbon atoms from the graphene lattice one by one so we obtain nice clean holes or edges in the carbon material.”
The Harvard team, led by Efthimios Kaxiras and Robert Westervelt, says that it is able to observe the chiselling process in real time in the microscope. The silicon atom remains intact throughout the entire procedure.
“To the best of our knowledge, this is the first report that a catalysis process (albeit with a non-conventional catalyst, silicon) has been observed in real time and at the single-atomic level,” Wang ,who carried out the experiment at the Berkeley National Lab, told nanotechweb.org.
Ultimately small, precise fabrication tool
Kaxiras and colleagues have already used their technique to fabricate different-sized graphene molecular pores and clean graphene edges. “Our atomic chisel is an ultimately small, precise fabrication tool (compared with focused electron beams themselves or energetic ions, for example) that can remove individual atoms from a material,” said Santos. “The tool overcomes the ‘fat finger’ problem – coined by Smalley when he referred to the fundamental limitations of top-down nanofabrication, where precisely selecting and manipulating single atoms is just not feasible.”
The technique could be used to fashion a host of nanostructures for making molecular electronics devices from graphene and other layered materials. Molecular devices promise to be smaller, faster and more easily tunable than conventional transistors and logic gates. Examples of other nanostructures that could be made include precisely sculpted nanojunctions for conductance measurements, nanoribbons and nanoflakes, which should be useful as the quantum elements in computing logic devices.
The researchers say that they are now busy looking into making chisels from other single atoms apart from silicon. “We would also like to be able to better control the chiselling process using external driving forces, such as electrical current, mechanical stress and perhaps even temperature gradients,” said Wang and Santos.
The current work is detailed in Nano Letters doi: 10.1021/nl403327u.
About the author
Belle Dumé is contributing editor at nanotechweb.org