Nanoscale Analysis of Frozen Water by Atom Probe Tomography Using Graphene Encapsulation and Cryo-Workflows: A Parametric Study

There has been an increasing interest in atom probe tomography (APT) to characterise hydrated and biological materials. A major benefit of APT compared to microscopy techniques more commonly used in biology is its combination of outstanding 3D spatial resolution (~0.2 nm) and mass sensitivity. APT has already been successfully used to characterise biological materials, revealing key structural information at the atomic scale, however there are many challenges inherent to the analysis of hydrated materials. New preparation protocols, often involving sample preparation and transfer at cryogenic temperature, enable APT analysis of hydrated materials and have the potential to enable 3D atomic scale characterisation of biological materials in the near-native hydrated state. In this study, APT specimens of pure water at the tips of tungsten needles were prepared at room temperature by graphene encapsulation. A parametric study was conducted where samples were transferred at either room temperature or cryo-temperature and analysed by APT by varying parameters such as the flight path and pulsing mode. The differences between the acquisition scenarios are presented along with recommendations for future studies

Analysis of water ice in nanoporous copper needles using cryo atom probe tomography

The application of atom probe tomography (APT) to frozen liquids is limited by difficulties in specimen preparation. Here, we report on the use of nanoporous Cu needles as a physical framework to hold water ice for investigation using APT. Nanoporous Cu needles are prepared by the electropolishing and dealloying of Cu-Mn matchstick precursors. Cryogenic scanning electron microscopy and focused-ion beam milling reveal a hierarchical, dendritic, highly-wettable microstructure. The atom probe mass spectrum is dominated by peaks of Cu+ and H(H2O)n+ up to n <= 3, and the reconstructed volume shows the protrusion of a Cu ligament into an ice-filled pore. The continuous Cu ligament network electrically connects the apex to the cryostage, leading to enhanced electric field at the apex and increased cooling, both of which simplify the mass spectrum compared to previous reports

A new volume scanner

Optical imaging through complex biological media remains a very challenging task due to the extremely high scattering experienced. A new design scanner is proposed and modelled which images scatter spatio-temporally. Modeling confirms the performance of the design. The inversion algorithm to reconstruct the scattering object remains as future work

Multiscale modification of aluminum alloys with deep cryogenic treatment for advanced properties

Deep cryogenic treatment (DCT) has arisen as a promising green technology to modify the properties of metallic materials. Here we present a substantial (55%) improvement to the wear resistance of an Al-Mg-Si alloy using DCT without any deterioration of other mechanical properties. This improvement is attributed to a slight hardness increase resulting from multiscale microstructural modifications. DCT modifies the morphology of dispersoids as well as the organization and morphology of β’’ precipitates that increase their fraction (25%) at the expense of β’ precipitates. These effects are related to the greater nanoscale mobility and segregation of the alloying elements (Mg, Si) following DCT, resulting from lattice defect recombination. This research provides a fundamental breakthrough in understanding the DCT effect on aluminum alloys, confirming DCT as a feasible CO2-free treatment step towards improvement of aluminum alloys