Binary digits can be encoded in the positions of Au nanoparticles lying on a square grid with nodes d apart. The presence of a particle at a node signifies a “1”, and its absence a “0”. The top part of the figure shows the three characters “LMR” in ASCII code, one character per row. In this example, the particles have 15 nm diameters and are located on a grid with d ~ 100 nm. This corresponds to a density of 10 gigabits per square cm, which is two orders of magnitude better than standard compact disks (CDs).
To read this “nanoCD” we use a single line scan with an AFM in non-contact mode. The bottom part of the figure shows the signal obtained by reading the “M” in the second row. Note the very high signal to noise ratio. It is clear that we could pack the particles tighter, use smaller particles, and so on, and therefore we could easily get another order of magnitude increase in the density. Because reading is done in non-contact mode, the tips and patterns should last a long time. The CD is editable by nanoparticle manipulation, by the techniques developed in our lab.
We normally scan at speeds ~ 2um/s, with a single tip. This would correspond to a very slow reading speed. However, scanning speeds on the order of 3 mm/s or higher have been reported by others, and tip arrays are under development at various labs. If we assume a scanning speed of 2 mm/s and one million tips, the reading speed is ~ 20 Gb/s, which is some 4 orders of magnitude faster than standard CD speeds. Of course, much work needs to be done before this nanoCD becomes (hopefully) a practical storage technology.
Reference: C. Baur, A. Bugacov, B. E. Koel, A. Madhukar, N. Montoya, T. R. Ramachandran, A. A. G. Requicha, R. Resch and P. Will, “Nanoparticle manipulation by mechanical pushing: underlying phenomena and real-time monitoring“, Nanotechnology, Vol. 9, No. 4, pp. 360- 364, December 1998. (PDF version)
