Research Exchange

Nicholas Farr's Report:

I am a PhD student at the University of Sheffield and my research is centred around using Secondary Electron Hyperspectral Imaging (SEHI) as a novel characterisation technique to better understand biomaterials. In March 2020, I visited Gareth Hughes at the David Cockayne Centre for Electron Microscopy, Department of Materials, University of Oxford.

The purpose of this visit was to provide and test Sheffields Secondary Electron Hyperspectral Imaging (SEHI) scripts (developed for Sheffield Helios Dualbeam) at Oxford in their plasma Helios FIB with the aim to assess the nature and severity of Xe+ ion damage. SEHI was successfully transferred to Oxford PlasmaFIB and this collaboration resulted in the submission of a joint abstract for EMC2020

Eduardo Serralta's Report:

I’m a PhD student at the Helmholtz-Zentrum Dresden-Rossendorf and the Technische Universität Dresden. I study the implementation and applications of transmission imaging modes in the helium ion microscope.

In February 2020, I visited Luxembourg Institute of Science and Technology (LIST) to use the npSCOPE prototype, which is a modified helium ion microscope that combines secondary ion mass spectrometry (SIMS), scanning transmission helium ion microscopy (STHIM) and cryomicroscopy. This prototype was developed in collaboration between LIST, HZDR, and other project partners.

During my stay, I installed and tested a new detector that my colleagues and I had developed for imaging in transmission mode. To study different contrast mechanisms that might be observable in this imaging mode, like mass-thickness, channelling, and diffraction, I imaged several samples with a variety of material properties with this detector.

One exciting application of this technique and the npSCOPE prototype, in particular, is identifying buried particles in biological materials. Since the standard secondary electron signal image is only surface sensitive, embedded particles will not exhibit any contrast. However, using the STHIM detector, we can detect the buried particles, and later we can complement the analysis with SIMS.

We plan to show the results of this visit at the HeFIB conference in Knoxville, USA. Currently, we are preparing an article describing the npSCOPE prototype and its capabilities and another paper about the new detector for STHIM.

Laura Wheatcroft's Report:

I travelled to the HZDR to use their Helium Ion Microscope (HIM) and Secondary Ion Mass Spectrometry (SIMS) equipment to analyse surface layers on high voltage Li-ion battery materials. High voltage Li-ion battery cathodes undergo a number of degradation mechanisms during cycling. One of these mechanisms is the formation of nano-metre thick surface films from the degradation of the electrolyte at high potentials which can contain Li.

HIM has very high surface sensitivity for imaging and SIMS is one of the few techniques which can detect Li. The combination of HIM and SIMS offers the unique opportunity to analyse the microstructure and chemically characterise the surface layers.

The work was performed in collaboration with Dr Nico Klingner and Dr Gregor Hlawacek, HZDR, and Johnson Matthey.

Read more about Laura's research on Sheffield NanoLAB website.

Tudor Scheul's Report:

I am a PhD student at the University of Southampton, in the School of Electronics and Computer Science. I am working with Dr Stuart Boden on high-efficiency silicon photovoltaics with a special interest in optical losses and various texturing technologies that reduce top surface reflectance and help couple more sunlight into the substrate to maximize the power output of the silicon solar cell.

I have spent most of my time as a PhD student developing, improving, and studying the opto-electronic properties of ‘black silicon’, which is nanostructured silicon that supresses reflections to below 3% and appears visually black.

I am using a cheap and fast wet-etching method called Metal-Assisted Chemical Etching to fabricate these nanostructures, resulting in a heterogeneous array of vertical nanowires of uniform height (usually about 1 μm). The diameters of the nanowires are in the range 20-100 nm, which is less than 1/1000 the width of a human hair! The nanowire array is coated with a 17 nm thick layer of aluminium oxide to improve the electrical properties of the material to try to ensure the extra light absorbed is translated into a gain in electrical power output in a solar cell. At this scale, morphological characterisation of the structures is very challenging but is important to figure out how to optimise the optical and electrical response.

For this purpose, I have visited the London Centre for Nanotechnology (LCN), UCL, three times during the past year to use their Carl Zeiss NanoFab helium/neon ion microscope. The advanced capabilities of this tool enable higher resolution and higher quality images, as well as larger depth of field when compared to standard scanning electron microscopes, making it advantageous for clearly imaging structures at the nanoscale at various stage tilts and magnifications. Moreover, the more aggressive neon ion beam can be used to mill through silicon and consequently cut through these nanowires to gain a better view of their cross-sectional morphology.

I was able to use this technique to study the conformity of the aluminium oxide depositions, even in the deep and narrow trenches between the nanopillars, which allowed me to assess the thickness and uniformity of the coating directly from the images.

I presented my results at the prestigious SiliconPV conference (held 8-11^th April 2019 in Leuven, Belgium) and my paper entitled “Characterisation of atomic layer deposited alumina thin films on black silicon textures using helium ion microscopy” was published in the conference proceedings (DOI: 10.1063/1.5123858). The work was also presented at the PicoFIB annual workshop in London in February 2019.

In addition to specific training for the tool (a six-hour-session), I have been inducted into the LCN cleanroom and I have undertaken health and safety training for the laboratories and the building itself, which is crucial when working with hazardous substances and equipment. I would like to thank all the staff at LCN, especially Dr Suguo Huo, who was very kind and helpful with the experimental work, as well as the PicoFIB network for funding this work.