The Weird WorldofNanoscale Gold/////////////Where appropriate, examples of the rather different and curiousproperties of
gold at the nanoscale are used to illustrate the points covered. Thatis the nano-scale. Why the excitement?Matter behaves rather differently at the nanoscale. For example, in thecase of metallic elements, the thickness of most passivating oxide layers is ofthe order of at least several micrometers. It also has the advantage of beingthe least susceptible of all metals to oxidation. The cost of the tiny amountsof gold used in existing or anticipated nanotech products is completely swampedby the overall added value of the product. These new properties and phenomenaare one of the things that the practitioners of this young field ofnanotechnologyseek to exploit.Why does the structure of gold change at the nanoscale?The crystal structure of the elements in the bulk state is largely determinedby their electronic configurations, and the element will adopt the packingarrangement that minimizes its free energy. This is the size range to which thecatalytic activity of gold is normally attributed. The melting point of goldnano-particles isdepressed from that of the bulk material. The magnitude ofbulk magnetic properties changes as the
dimensions of the materials approachthe nanoscale, and the magnetic moment per atom rises sharply. But at
thenanoscale, the physical dimensions of the objects have begun to approachthose of quantum quantities such as the density distribution function ofelectrons. Objects or structures that have at least one important dimension in therange 0.5 to perhaps 50nm may be considered to be in the nanoscale domain. The field ofnanotechnology is attracting keen interest at present. The excitement ismotivated by the observation that control of matter at the nanoscale holds thepromise of, amongst others, faster computing, better medicines, and more usefulmaterials. Where appropriate, examples of the rather different andcurious properties of gold at thenanoscale are used to illustrate the points covered.