Laure Bourgeois

High-resolution scanning transmission electron microscopy images of nanoparticles embedded in a crystalline matrix can be easily misinterpreted, leading to proposed crystal structures that are incorrect and phases that do not exist, or ”Phantom Phases”. This is illustrated here through the case of low-dimensional precipitates buried in an aluminium matrix, as commonly observed in high-strength aluminium alloys. Guidelines for testing proposed structural models and avoiding such pitfalls are provided, incorporating the use of electron diffraction and simulations. Other benefits of this approach are also presented, such as identifying deeply buried particles and accurately mapping nanostructures.

A three-term equation for phenomenological absorption of electron beams in materials is derived for use in quantitative transmission electron microscopy simulations. This is motivated by differential quantitative convergent-beam electron diffraction (QCBED) using CBED patterns that have not been electron-optically energy filtered. As a starting point, this three-parameter function reproduces inelastic scattering factors generated by the ubiquitous ATOM subroutine of Bird & King [Acta Cryst. (1990), A46, 202–208] to within a few per cent, spanning elements Z = 1 to 98, Debye–Waller parameters from B = 0.05 Ų to B = 2.0 Ų, scattering angles from s = 0 Å⁻¹ to s = 6.0 Å⁻¹ and electron energies from E ₀ = 1 keV to E ₀ = 1 MeV. As such, it is applicable to zero-energy-loss electron-optically filtered pattern matching for which the Bird and King ATOM subroutine was designed. Crucially, the coefficients of the three terms in the present equation can be refined to produce inelastic scattering factors with differing local and non-local contributions, which are better suited to unfiltered differential QCBED pattern matching.

Microalloying elements are commonly added to high-strength aluminium alloys to promote the formation of strengthening precipitate phases and therefore enhance alloy strength. Classic examples include Sn, Cd and In at the 100 ppm level [ 1], which significantly accelerate the nucleation of the strengthening phase θ′ in Al-Cu alloys, thereby improving the precipitation hardening response. More dramatic is the effect of Ag additions to Al-Cu-Mg and Al-Cu-Li alloys, where new phases (Ω and T ₁) form in high number densities, leading to ultra-high-strength alloys typically used in the aerospace industry. In all these cases, the microalloying additions either segregate at the precipitate-matrix interfaces or precipitate first as a well-defined crystalline phase before acting as heterogeneous nucleation sites [ 1]. An unusual case is that of Au additions to Al-Cu, where the precipitation hardening response is enhanced and accelerated through Au dissolving inside the strengthening precipitate phase θ′ [ 2]. This observation leads to two questions which this work aimed to address: What is the atomic-scale mechanism by which Au promotes the formation of the θ′ phase? Can other elements behave in this way? Answering these questions would be useful not only for improving one’s fundamental understanding of phase transformations and offering another avenue for the design of high-strength alloys, but also for providing a potential way of immobilizing contaminants. This work employed a combination of aberration-corrected scanning transmission electron microscopy, density functional theory (DFT) simulations and classical nucleation theory (CNT) calculations. The microscopy was performed on a FEI Titan ³ FEGTEM and a Thermo Fisher Scientific Spectra-φ FEGTEM, both double-aberration corrected and operated at an accelerating voltage of 300 kV in scanning transmission electron microscopy (STEM) mode.

This work presents observations of symmetry breakages in the intensity distributions of near-zone-axis convergent-beam electron diffraction (CBED) patterns that can only be explained by the symmetry of the specimen and not the symmetry of the unit cell describing the atomic structure of the material. The specimen is an aluminium–copper–tin alloy containing voids many tens of nanometres in size within continuous single crystals of the aluminium host matrix. Several CBED patterns where the incident beam enters and exits parallel void facets without the incident beam being perpendicular to these facets are examined. The symmetries in their intensity distributions are explained by the specimen morphology alone using a geometric argument based on the multislice theory. This work shows that it is possible to deduce nanoscale morphological information about the specimen in the direction of the electron beam – the elusive third dimension in transmission electron microscopy – from the inspection of CBED patterns.

Despite the clinical benefits that chemotherapeutics has had on the treatment of breast cancer, drug resistance remains one of the main obstacles to curative cancer therapy. Nanomedicines allow therapeutics to be more targeted and effective, resulting in enhanced treatment success, reduced side effects, and the possibility of minimising drug resistance by the co-delivery of therapeutic agents. Porous silicon nanoparticles (pSiNPs) have been established as efficient vectors for drug delivery. Their high surface area makes them an ideal carrier for the administration of multiple therapeutics, providing the means to apply multiple attacks to the tumour. Moreover, immobilising targeting ligands on the pSiNP surface helps direct them selectively to cancer cells, thereby reducing harm to normal tissues. Here, we engineered breast cancer-targeted pSiNPs co-loaded with an anticancer drug and gold nanoclusters (AuNCs). AuNCs have the capacity to induce hyperthermia when exposed to a radiofrequency field. Using monolayer and 3D cell cultures, we demonstrate that the cell-killing efficacy of combined hyperthermia and chemotherapy via targeted pSiNPs is 1.5-fold higher than applying monotherapy and 3.5-fold higher compared to using a nontargeted system with combined therapeutics. The results not only demonstrate targeted pSiNPs as a successful nanocarrier for combination therapy but also confirm it as a versatile platform with the potential to be used for personalised medicine.