Biomedical Engineering Reference
In-Depth Information
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FIGURE 1.5
Examples of stents coated with diamond-like carbon using plasma-enhanced CVD 5 .
1.3.2 Bottom-Up Approach
The bottom-up approach involves making nanostructures and devices by arranging atom by atom.
The scanning tunnelling microscope (STM) has been used to build nanosized atomic features such
as the letters IBM written using xenon atoms on nickel [5] ( Figure 1.6 ). While this is beautiful and
exciting it remains that the experiment was carried out under carefully controlled conditions, i.e.,
liquid helium cooling, high vacuum, and it took something like 24 h to get the letters right. Also the
atoms are not bonded to the surface just adsorbed and a small change in temperature or pressure will
dislodge them. Since this demonstration, significant advances have been made in nanomanufacturing.
The discovery of the STM's ability to image variations in the density distribution of surface state
electrons created in the artists a compulsion to have complete control of not only the atomic land-
scape, but also the electronic landscape [6] . Here they have positioned 48 iron atoms into a circular
ring in order to “corral” some surface state electrons and force them into “quantum” states of the cir-
cular structure ( Figure 1.7 ). The ripples in the ring of atoms are the density distribution of a particular
set of quantum states of the corral. The artists were delighted to discover that they could predict what
5 Dr T. Okpalugo, University of Paisley (2007) Private communication.
 
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