Contrast mechanisms in neutral helium microscopy applied to organic electronics

The development of new electronic devices at the intersection between semiconductors and plastics is one of the most rapidly growing technological areas. Organic electronics offers enormous potential for the delivery of low cost electronic devices, such as solar cells, sensors and electronic circuitry. With the rapid development of these new devices, there is an urgent need for new characterization techniques tailored to the needs of organic electronics. In particular, the soft polymer materials used present severe challenges for conventional imaging techniques since they are extremely vulnerable to damage from the high energy probe beams found in electron, ion and X-ray microscopy. In addition, these materials are printed on rolls of insulating substrates; presenting further challenges for charged beam probes. Recent advances in scanning helium atom microscopy (SHeM) offer a promising new possibility for high resolution surface imaging of soft polymers. The atomic helium beam is neutral and has an energy (<100meV) too low to cause any surface damage. Thus, SHeM offers a non-destructive imaging technique that is chemically inert and equally suited to insulators, semiconductors, metals and delicate organic materials. However, SHeM is a novel technology and the image formation process is not fully understood. This timely research project exploits recent progress at the Universities of Bergen and Newcastle towards the development of SHeM imaging systems. The key goal was to characterise the contrast mechanisms of SHeM and to apply them to the imaging of organic electronic circuits and devices. Within this project, we managed to record first images of one of the most common polymer-fullerene material systems used in organic electronics. Indeed, aggregates formed by a combination of these two materials demonstrated the unique capability of SHeM, by revealing additional information from topographical contrast. This was followed by imaging organic electronic devices, more specifically Roll-to-Roll printed OPV`s (printed solar cells) at different stages of production. With these first images of all the different OPV production stages we were able to confirm that the SHeM offers a unique imaging tool for exactly these types of materials. Additionally, the project enabled us to add more scientific results to better understand the image formation in the SHeM. Amongst others this resulted in a publication in 2018 clearly defining topological resolution limitations on the SHeM in Newcastle. One major outcome of the project was a Nature`s Scientific Reports publication showing that SHeM is a promising tool for the field of taxonomy. By combining the SHeM technique with a stereophotogrammetry imaging approach we could show that these new instruments provide the means for comprehensive taxonomical data collection without any risk of sample damage resulting from high beam energies. Indeed, in cooperation with the Sea Life Sydney Aquarium, we were able to record the first ever neutral helium microscope images of shark skin. Additionally in collaboration with the Royal Botanic Gardens and Domain Trust, National Herbarium of New South Wales we could show that the SHeM technique is uniquely suited for imaging sensitive and historical samples. The paper we published on the shark skin images was also picked up by the Norwegian online newspaper forskning.no in their article called 'Derfor brukar vi helium for å sjå på dei ørsmå tennene på huda til ein hai' advertising our work also to the Norwegian public. In June 2019 UoN`s SHeM team together with the neutral helium imaging group of the Cavendish Laboratory at the University of Cambridge was awarded with presenting an exhibit called 'Seeing with Atoms' at the Royal Societies Summer Science Exhibition. This exhibit allowed us to present the SHeM technique to the broader public with a total audience of 12653 visitors including 11513 students, teachers, public and media as well as 1140 soirees. The work and results acquired during this NFR project was an important part of this exhibit. In addition work was started together with our nanostructering specialists here at UiB on fabricating a new type of aperture for a future UiB pinhole microscope. This new type of aperture will potentially allow us to reduce imaging times on the SHeM substantially. In a parallel effort to improve imaging quality and speed on all type of neutral helium microscopes we have started to develop a completely new type of neutral He-Detector here at UiB. Neutral He-Detectors are one of the bottlenecks in neutral helium microscopy. Current available Detectors do not have very high efficiencies and so far no 2D neutral He-Detectors are on the market or available from other research groups. During the final months of the project we have designed a test setup for this detector principle and assembled it here at UiB. First test measurements will be conducted within the end of 2019 and the beginning of 2020.

The main outcome is a thorough understanding of the image contrast in SHeM. This was achieved by a combined SHeM (Newcastle) and Helium atom scattering (Bergen) study of thin films and nanostructured surface. This work is crucial to the community to clearly determine the difference between scattering contrast and chemical -inelastic scattering contrast. During the project we also clarified how to distinguish between Supra-resolution (surface features big relative to beam diameter) and Sub-resolution contrast (surface roughness on the nanoscale). We were also able to expand the SHeM`s application areas to the field of Taxonomy. In collaboration with the Sea Life Sydney Aquarium and the National Herbarium of New South Wales, SHeM was established as a new, uniquely suited imaging tool for taxonomy and fragile historical samples. This work resulted in a nature scientific reports publication in 2019 which was later on picked up the Norwegian popular science online newspaper 'forskning.no'.

The development of new electronic devices at the intersection between semiconductors and plastics is one of the most rapidly growing technological areas. Organic electronics offers enormous potential for the delivery of low cost electronic devices, such as solar cells, sensors and electronic circuitry, via mass scale roll-to-roll printing technology. With the rapid development of these new printable materials and devices, there is an urgent need for the development of new characterization techniques that are tailored to the needs of organic electronics. In particular, the soft polymer materials used for organic electronic applications present severe challenges for conventional high resolution imaging techniques since they are extremely vulnerable to damage from the high energy probe beams found in electron, ion and X-ray microscopy. In addition, these materials are printed on rolls of insulating substrates (e.g.PET); presenting further challenges for charged beam probes. Recent advances in scanning helium atom microscopy (SHeM) offer a promising new possibility for high resolution surface imaging of soft polymers. The atomic helium beam is neutral and has an energy (<100meV) that is simply too low to cause any surface damage. Thus, SHeM offers a completely non-destructive imaging technique that is chemically inert and equally suited to insulators, semiconductors, metals and delicate organic materials. However, SHeM is a novel technology and the image formation process is not fully understood. This timely research project exploits recent progress at the Universities of Bergen and Newcastle towards the development of SHeM imaging systems. The key goal of this project is to characterise the contrast mechanisms of SHeM and to apply them to the imaging of organic electronic circuits and devices. This critically important project will deliver a unique imaging tool for imaging delicate soft materials at high resolution and with chemical contrast.