Researchers build smileys from nanowires

New method developed for the production of silicon filaments

A smiley face made of silicon nanowires. © TU Vienna
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Using a new method, Viennese scientists are able to produce nanowires made of silicon faster and more effectively than before - a highly sought-after new structural element for electronic components. Growth Aid is not gold, as it was previously, but a focused ion beam that allows researchers to produce even tiny smileys.

To grow ultra-thin silicon wires - that is an important goal in materials science today. Nanometer-sized silicon wires have very specific chemical and physical properties, making them a highly attractive material for transistors, solar cells or special LEDs. However, such silicon wires are very difficult to manufacture.

Gold as a growth aid

Only about a hundred nanometers measure the silicon threads that promise new opportunities in electronics. Theoretically, these silicon crystals can be created by themselves: if a small crystal is surrounded by silicon-containing gas, it can bind individual atoms and grow layer by layer.

However, this takes much too long, so accelerating the now widespread "Vapor Liquid-Solid" the reaction with gold, which acts as a catalyst: "Tiny gold droplets on the nanowires can adsorb silicon atoms, and through the gold get to the nanowire, where the atoms then attach, "explains Alois Lugstein of the Institute of Solid State Electronics of the Technical University (TU) Vienna.

However, gold affects the electronic properties of the nanowires, thereby reducing their performance. Other manufacturing methods also bring about significant disadvantages: some work only at very high temperatures, others only in ultrahigh vacuum. display

Gallium ions: better than gold

The electrical engineers at the Vienna University of Technology have now found another way to grow the tiny silicon wires - and do without gold or extreme external conditions: With the help of a focused ion beam, gallium ions in a silicon crystal just below the surface implanted. Thereafter, the silicon is heated to 500 ° C, whereby the gallium ions migrate to the surface of the silicon crystal. Now the gallium ions play a very similar role as the gold droplets in the classic "Vapor-Liquid-Solid-Process".

Detail of the eye of the smiley. TU Vienna

In an atmosphere containing the silicon-containing gas silane, according to the scientists, the silicon is deposited on the crystal with the help of gallium ions. Extreme growth rates of several microns per minute can be achieved eine a fantastic growth rate for the nanoscale.

By means of targeted bombardment with gallium ions, this method can precisely determine where the nanostructures should grow and where not. The scientists proved this, among other things, by growing a smiley face out of nanodrugs.

(Technical University Vienna, 20.12.2011 - DLO)