Groundbreaking work by scientists from Switzerland, Finland and Germany has lead to a new world record in X-ray microscopy. For the first time ever, features below 10 nanometres (nm) in width were resolved.
Key to this new world record was doubling of the effective line density of FZP template (Fresnel Zone Plate, a key component of an X-ray microscope) by extremely conformal thin films created through the use of Atomic Layer Deposition (ALD). ALD work was carried out with a Picosun SUNALE R-150 reactor at the premises of the University of Helsinki's Laboratory of Inorganic Chemistry. One of the Finnish scientists, Dr Tero Pilvi, has since joined the staff of Picosun as Technical Sales Manager.
October issue of Ultramicroscopy Journal carries an article "Advanced thin film technology for ultrahigh resolution X-ray microscopy" by Joan Vila-Comanala, Jörg Raabe and Christian David from the Swiss Paul Scherrer Institute, the brand new holder of the X-ray microscopy spatial world record, Mikko Ritala and Tero Pilvi from the University of Helsinki, Konstantin Jefimovs from Eidgenössische Materialprufungs- und Forschungsanstalt (EMPA, Swiss Federal Laboratories for Materials Testing and Research) in Switzerland, Rainer H. Fink from Friedrich-Alexander Universität in Germany, Mathias Senoner from the German Bundesanstalt fur Materialforschung und -prufung (BAM, Federal Institute for Materials Research and Testing), and Andre Maassdorf from Ferdinand-Braun-Institut fur Höchstfrequenztechnik (Ferdinand-Braun Institute for High-Frequenzy Technology) in Germany.
The technology of X-ray microscopy was discovered some 100 years ago. It is a preferred technology for high-resolution imaging of biological and inorganic materials. X-ray microscopy can study materials at extreme nano-levels. Technology has, however, limited the useful ability to study features below 25 to 30 nm in width. For the past whole decade, the resolution of X-ray microscopy has been stagnated at this level. Some successful results have been reported at the 15 nm level, but these have not produced the required reproducibility to become really useful. The Swiss-Finnish-German group has finally solved the deadlock.
ALD is a thin film method which enables completely controlled growth of extremely conformal films through its signature self-limiting, sequential surface reactions. ALD produces complex layer structures with atomic level accuracy. ALD processes can be reproduced with stunning accuracy.
The group produced a modified FZP with structures based on the conformal deposition of high refractive index material by ALD onto the sidewalls of a pre-patterned template made from a low refractive index material. This new focusing structure achieves an unprecedented spatial resolution in X-ray microscopy. Line widths of down to 9 nm were successfully resolved.
X-ray microscopy serves biology, biomedicine and materials science. The resolution of X-ray microscopy is between that of the traditional optical microscope and the electron microscope. The main advantage of X-ray microscopy over electron microscopy is that it can view biological samples in their natural state. X-ray microscopy produces higher penetration power and can inspect much thicker samples than comparable methods can. X-ray microscopy is also capable of producing three-dimensional tomograms of individual cells of living organisms.