Structural and chemical evolution of Au-silica core-shell nanoparticles during 20 keV helium ion irradiation: a comparison between experiment and simulation.

Au-silica core-shell nanoparticles have been irradiated with 20 keV He+ ions up to a maximum fluence of 4.7 × 1017 ions/cm2. The nanoscale structural and crystallographic evolution induced by He+ ion irradiation was followed at various stages using Transmission Electron Microscopy (TEM). During irradiation satellite Au clusters are formed around the main Au core, which remained crystalline even after the maximum He+ ion fluence. The spherical silica shell deformed into a hemisphere due to He+ ion irradiation. Three dimensional Monte-Carlo simulations, based on the binary collision approximation, have been performed on stacked infinite layers and an individual particle. The stacked layers results show that the He+ beam interacts with most of the nanoparticle and Au migrates in the direction of beam incidence agreeing with experimental findings. The individual particle results match the experiment in terms of the volume which is sputtered away however additional mechanisms, not included in the simulations, are present in the experiment during the satellite formation and silica shell deformation. These results show the ability for 20 keV He+ ions to be used for the modification of nanostructures. Furthermore, these results contribute to a quantitative understanding of the dynamic evolution of materials observed using microscopy techniques based on He+ ions.

An in situ correlative STEM-EDS and HRTEM based nanoscale chemical characterization of solid-liquid interfaces in an aluminium alloy.

The chemistry and the structure of solid-liquid interface in an Al-Si based alloy during high temperature phase transformation were characterized at nanoscale using scanning Transmission Electron Microscopy-EDS and HRTEM. Such studies were until recently limited by large sample drift associated with conventional heating holders. This study was made possible thanks to the modern low-drift MEMS-chip based localized heating technology. The results reveal that (i) the structural interface between solid (111) oriented Si phase and the liquid phase (i.e. decay of crystalline order) coexisting at 600°C is 3.2 nm wide (ii) the STEM-EDS chemical maps show inhomogeneous distribution of the elements with the solid phase being rich in Si and the liquid phase rich in Al (iii) the HRTEM and the HAADF images display respectively dark and bright intensity bands along the interface which could be due to apparent enrichment of Cu at the interface region resulting in enhanced amplitude-contrast (darker band in HRTEM) and Z-contrast (bright band in HAADF) and (iv) intriguingly, the concentration profiles within (i.e. compositional width) and across the solid-liquid interface display element-specific complex and asymmetric variation in the chemical widths.

High-resolution high-sensitivity elemental imaging by secondary ion mass spectrometry: from traditional 2D and 3D imaging to correlative microscopy.

Secondary ion mass spectrometry (SIMS) constitutes an extremely sensitive technique for imaging surfaces in 2D and 3D. Apart from its excellent sensitivity and high lateral resolution (50 nm on state-of-the-art SIMS instruments), advantages of SIMS include high dynamic range and the ability to differentiate between isotopes. This paper first reviews the underlying principles of SIMS as well as the performance and applications of 2D and 3D SIMS elemental imaging. The prospects for further improving the capabilities of SIMS imaging are discussed. The lateral resolution in SIMS imaging when using the microprobe mode is limited by (i) the ion probe size, which is dependent on the brightness of the primary ion source, the quality of the optics of the primary ion column and the electric fields in the near sample region used to extract secondary ions; (ii) the sensitivity of the analysis as a reasonable secondary ion signal, which must be detected from very tiny voxel sizes and thus from a very limited number of sputtered atoms; and (iii) the physical dimensions of the collision cascade determining the origin of the sputtered ions with respect to the impact site of the incident primary ion probe. One interesting prospect is the use of SIMS-based correlative microscopy. In this approach SIMS is combined with various high-resolution microscopy techniques, so that elemental/chemical information at the highest sensitivity can be obtained with SIMS, while excellent spatial resolution is provided by overlaying the SIMS images with high-resolution images obtained by these microscopy techniques. Examples of this approach are given by presenting in situ combinations of SIMS with transmission electron microscopy (TEM), helium ion microscopy (HIM) and scanning probe microscopy (SPM).