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SEM image (top) showing the nucleation of large dendritic structures following electrodeposition of Au on HOPG for long periods. AFM image (bottom) shows a localization, or pinning, of Au nanoparticles on the upper terraces of setp edges surrounding pits in thermally-etched HOPG.

INL is studying the fundamental growth mechanisms of nanostructures to increase our understanding of alloy formation at the nanoscale and investigate potential to tailor deposition for nanoengineering structures.

Electrodeposition and controlled growth of nanostructures is a cutting-edge area mating the field of electrochemistry with material science. There are many questions that arise when considering growth of nanoscale structures. First, do nanoscale intermetallic compounds grow in the same way that they do macroscopically, e.g. are the equilibrium structures (crystallographic phases) similar to those characterized in macroscopic intermetallic systems? Second, can nanostructures be synthesized in such a way that the rules of quantum mechanics be exploited to either determine shape or some desired physical property or characteristic? Third, how does electrochemical control differ from other methods of intermetallic compound synthesis, e.g. reactive sputtering or physical vapor deposition?

In collaboration with Henry White’s Group at the University of Utah, we have begun examining some of these questions. The deposition and stripping of Au from HOPG has been studied to better understand the unusual electrodeposition process of metals on graphite. In these studies, three distinct particle size distributions, from nanometer to micron sizes, were observed as a function of the electrodeposition process (see figure above). Using the atomic force microscope (AFM) we observed that the nanoscale particles preferentially decorate the top plane of step edges although deposits are also located on terraces, likely at defect (vacancy) sites (see bottom panel of Figure above). The stripping of the defects has shown a very unusual behavior, as complete stripping of the deposits is never observed, even for long stripping times at overpotential situations.

A nanoscience proposal has been submitted to the DOE-Basic Energy Science (BES) Nanoscale Initiative for possible expansion of this research to investigate the controlled synthesis of ‘nanoalloys.’ The goal is to increase our understanding of alloy formation on the nanoscale and look into tailoring deposition for nanoengineering structures.

Apparati: For more information about these instruments, see the capabilities page.

• Molecular Imaging PicoSPM
• Digital Instruments Multimode Nanoscope IIIa
• Cypress Systems EI-400 Bipotentiostat
• FEI Environmental Scanning Electron Microscope (ESEM)

Peer-Reviewed Publications:

C.J. Boxley, H.S. White, T.E. Lister, P.J. Pinhero, “Electrochemical Deposition and Reoxidation of Au at Highly Orented Pyrolytic Graphite. Stabilization of Au Nanoparticles on the Upper Plane of Step Edges,” J. Physical Chemistry B 107, 451 (2003).