Disturbed Array Formation of Electrochemically Grown Self-Organised Nanostructures
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NTRODUCTION
The increasing miniaturisation of components and storage media in micro-electronics forces the existing processing techniques to their limits. Recent progress in the production of nanostructures
opens new possibilities in
a technological
application area governed
by
quantum-effects I. The small characteristic dimensions of the individual components leads to special quantum effects which determine electrical and magnetic properties. Besides simple individual quantum structures (dots, lines and heterojunctions), research is now primarily focused on the development of very sophisticated ordered quantum arrays for application as new mass storage media and micro-electronic components 2. The traditional production methods like e-beam lithography show their limitations under these extreme conditions: (1) long processing times due to the strictly serial patterning by writing each pixel individually, (2) presence of process induced defects due to the high energy e-beams and reactive etching, (3) decreased spatial accuracy when these methods are used to write large areas. Additionally, the equipment needed for these procedures is very sophisticated and expensive, especially taking into account parallel e-beam writers when high throughput speeds are aimed for. Especially in the production of large repetitive arrays of simple nanostructures the existing ebeam techniques will be replaced by a cheaper electrochemical process. Billions of simple structures can be formed in a parallel way using electrochemical selforganising procedures 3'4 , yielding large regular arrays of nanodots at the appropriate electrochemical cell conditions. This allows a fast and cheap alternative electrochemical production of large (up to cm scale) regular arrays of electrical or magnetic dot or line structures. Potential applications of such structures are in the field of high density magnetic storage media or microelectronic components. With a lateral period of the self-organised array 331 Mat. Res. Soc. Symp. Proc. Vol. 517 © 1998 Materials Research Society
of 200 nm this kind of patterning could yield a storage density of 30 Gbyte/cm2 in the absence of magnetic interactions between neighbouring magnetic nanodots. The self-organised electrochemical array formation is mainly governed by the metal/electrolyte couple, cell potential and processing time. The system tends to a stable regime of regular surface arrays of nanostructures THEORY OF EXPERIMENT Samples of l.0xl.0 cm 2 were prepared from bulk Al with a purity of 99.99%. Sample surfaces were ground to 7 pm, polished using diamond to a 1 pm finish and subsequently degreased. The polishing procedure was performed just prior to electrochemical etching. The electrolyte consisted of ethanol, butylcellusolve and water, for details see ref. 3. The electrochemical etching set-up consists of a vertical tubular cell with the sample mounted
at the bottom and a tubular Pt counter electrode at 3 cm distance. The electrolyte was injected in the cell just prior to applying the cell potential
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