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Scanning Neutral Helium Microscopy: A novel tool for fast, nondestuctive characterisation of mechanical parameters for nanostructured coatings

Final Report Summary - NEMI (Scanning Neutral Helium Microscopy: A novel tool for fast, nondestuctive characterisation of mechanical parameters for nanostructured coatings)

The majority of failures in pattern replication processes are caused by wear of forming and forging master tools. Tribology is the science applied for lowering the wear by developing advanced (nanostructured) coatings. However, even these coatings are subject to wear that manifest itself as changes in the mechanical properties of the master tool in the form of fractures, roughness changes (adhesion) or deformation of the 3D shape. Hence a careful examination of the surface structure is essential for validating the functionality of a master tool. Ideally by applying a fast, reliable measurement, which determines the first wear before any faulty replication takes place. No such method exists at present for nanoscale structures: Scanning probe microscopy is generally slow and not suitable for the high aspect ratio structures often present in forming and forging tools. Scanning electron and helium ion microscopy offer alternatives. However both beams penetrate into the material, which limits the accuracy, the beam energy can cause surface damage and there may be image distortions due to charging effects.

The main aim of the NEMI project was to develop a new microscope instrument based on neutral helium atoms. This new technique, which we have labelled NEMI (short for NEutral Microscopy) is strictly surface sensitive with no penetration into the bulk (the atoms interact with the outermost electronic layer on the surface). The energy of the atoms is less than 0.1 eV, 4-6 order of magnitudes less than typical electron and helium ion energies. The big limitation in helium microscopy up till now has been that existing helium detectors have had a much too low detection rate (detecting at the best only a few out of 1.000.000 atoms). A major sub-aim of the project as an absolutely crucial requirement for a NEMI microscope was therefore to develop a better helium detector. Because this was deemed such high risk two partners: University of Cambridge (CAM) and SME partner MBScientific AB(MB) were working on this following different methods. In the end, both partners managed to make detectors with an efficiency of the order of 0.01 - four orders of magnitude better than existing state of the art detectors. Using the new detectors helium microscopy images were successfully obtained using two different types of helium microscopes: A focussed beam microscope at the University of Bergen (UiB) and a so called pinhole microscope at CAM. Images with resolutions on the micron scale were obtained. The CAM instrument was used to produce the first images of a polymer sample - a Nanoimprint sample from SME partner Nil Technology APS (NILT).

Further results includes: i) A 3D self calibration algorithm developed by the Royal Institute of Technology (KTH). This is a very versatile tool that can be used with a range of other microscopy instruments and production tools, and is receiving considerable interest from industry. ii) A first focussing mirror for helium atoms using graphene/Ru on laser polished fused silica parabolic lenses developed by University Autonoma de Madrid (UAM) and iii) breakthroughs in the production for SME partners NILT and Winther Mould Technology (KW), obtained through metrology investigations by the DanishNational l Metrology institute (DFM): KW can now produce 50% more samples before the mould needs to be changed and NILT is launching a new antireflection product. Finally iv) the third SME partner MB is planning to start a production of neutral helium microscopes.

A total of three patent applications, 14 papers accepted or published in peer reviewed journals and 9 papers in preparations have resulted from this project.