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To honour Finland's centenary celebration, a silicon structure, based on the official logo of the centennial, was created at Aalto University. Doctor of Nanotechnology Nikolai Chekurov created the structure in Micronova's cleanroom at Otaniemi in Espoo. His method combined focused ion beams with cryogenic deep reactive ion etching, where the target is first bombed with heavy ions and then etched with ICP-RIE, inductively coupled plasma reactive-ion etching.

This same method was used to create the world's tiniest Aalto vase, which has a capacity of just 0.1 femtolitres. This is not a standard technique, as it has been developed within Professor Ilkka Tittonen's Micro and Quantum Systems research group in several different doctoral dissertations.

'First, a thin layer of gallium ions are placed on the surface of a smooth silicon wafer in the shape of the desired shape, in this case the centennial logo. After this, the wafer is etched with gas, leaving the areas with the gallium as-is and etching away those areas without, thus revealing the shape. The longer the etching goes on, the taller the structure becomes,' Chekurov explains.

This method could have been used to make the centennial logo even smaller, but Chekurov and his colleagues wanted to create a nearly flawless and completely accurate replica of the original logo's design. The logo, which is only one-hundredth of a millimetre in size, is so tiny that it can barely be seen with an optical microscope. Marvelling its three-dimensional structure requires an electron microscope, as the logo's tiniest structures are under a micrometre, i.e. one-thousandth of a millimetre, in size.

'Naturally, this method has other practical applications as well. It can be used to create different microstructures that can be utilised in many ways, for example in photonics, measuring small amounts of liquids, or as mechanical microsensors,' notes Professor Tittonen. 

More information:

Professor Ilkka Tittonen
Aalto University
tel. +358 40 543 7564 
ilkka.tittonen@aalto.fi