The CAREM (Microscopy Research and Teaching Support Unit) at the University of Liège has just acquired a cutting-edge instrument that enables engraving and imaging on a nanometric scale (one-millionth of a millimetre). Thanks to this atomic force microscope, it is possible to obtain an image of the topography of the surface or to draw patterns of a few nanometres by engraving the same surface.
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Emile Fourneau, a researcher in the Experimental Physics of Nanostructured Materials (EPNM) laboratory (CESAM Research Unit / Faculty of Science), took up the challenge of reproducing the University of Liège logo on a microscopic structure ... a hair! And not only did he succeed, but he could have engraved thousands more. In the end, the design was no bigger than a red blood cell," explains the researcher. The width of the lines in this design is comparable to the size of a virus, while the depth of the engraving is around 30 nm, or the equivalent of around 300 atoms". With writing dimensions reduced to a millionth of a millimetre, the instrument could inscribe up to 30,000 names on a small piece of hair, provided there was enough time to complete the task since it takes about as long to engrave a word as it does to write it by hand.
The instrument, used in the laboratories of the ULiège nanofabrication platform managed by Prof Alejandro Silhanek and Prof Ngoc Duy Nguyen in the Physics Department, is an atomic force microscope, an advanced instrument that enables engraving and imaging on a nanometric scale (10-9 m). “It's a stylus with a tip of no more than ten nanometres, whose movement in the three directions of space - height, width and depth - is controlled with nanometric resolution," explains Alejandro Silhanek, director of the EPNM laboratory. Depending on the type of tip and the force applied to the surface of the sample, it is possible to obtain an image of the topography of the surface - similar to the way a finger reads text in Braille - or to engrave patterns of a few nanometres by scratching the same surface".
Unlike other lithography techniques such as electron beam lithography, which ULiège researchers also use, atomic force microscopy lithography is highly versatile. It works at ambient pressure and temperature, in air or immersed in a liquid, can be applied to almost any surface (curved or flat, conductive or insulating, etc.) and requires no prior sample preparation. "As part of our research projects, this nano-stylus allows us to correct or modify quantum or magnonic electronic nano-circuits in situ, regardless of the materials used in their manufacture," adds Alejandro Silhanek. Regarding the instrument's imaging capabilities, the choice of a particular tip (magnetised, conductive, etc.) also enables us to image the magnetic and electrical domains, differentiate the phases of a material or measure variations in the doping of a semiconductor". A list that is far from exhaustive.
Professor Silhanek's research group is active in many areas of low-dimensional physics, including superconducting and magnetic materials, metamaterials and quantum sensors. The laboratory's main experimental assets are an electron-beam nanofabrication platform, a versatile deposition system and facilities for magneto-optical imaging and electrical transport measurements at low temperatures. Current topics of interest include fluctuations in superconductors at the nanoscale, controlled electromigration, manipulation of magnetic flux quanta and thermomagnetic instabilities in superconductors.
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