by Teik-Cheng LIM and Xianning XIE
s the names suggest, nanoscience and nanotechnology constitute the study and the application of objects with at least one of the dimensions smaller than 100 nanometres. A nanometre is a billionth of a metre or 1/80,000 the diameter of a human hair. Figure 1 gives an idea of its scale. At this level, objects are so small that they can no longer be assumed to be continuous media but rather to consist of discrete elements made up of atoms and molecules; that is, nanoscale objects and their behaviour/performance can best be understood from the molecular viewpoint.
Since early civilisation, mankind learnt that metals can be melted and recast into desired mould-determined shapes. At the dawn of this millennium, Anat Hatzor and Paul S Weiss from Pennsylvania State University developed the smallest-ever mould on the scale of a few molecules. The mould consists of parallel gold nanostructures on a silicate substrate developed using standard electron-beam lithography. By applying layers of organic molecules, the widths of the gold nanostructures widen, thereby narrowing the gaps between the strips of gold. These gaps work as the mould for casting thin wires 15-70nm wide. With a spacing of 10-40nm, these gaps allow numerous nanowires to be moulded at one time.
Most nanotubes, if not all, are made from carbon. Erman Bengu and Laurence D Marks recently developed nanotubes from two elements - boron and nitrogen. These boron nitride nanotubes (BNNTs) have higher tolerance to heat and are less likely to oxidise. To produce BNNT, they sprayed boron and energetic nitrogen atoms onto a heated tungsten surface in a vacuum so that the nanotubes grew as a kind of hair. The BNNT, according to Marks, has the potential for use in reducing friction on bearings in heavy machinery.