Yichi_Wang

Insulating SrTiO₃ (STO) can host 2D electron systems (2DESs) on its surfaces, caused by oxygen defects. This study shows that the STO surface exhibits phase separation once the 2DES is formed and relates this inhomogeneity to recently reported magnetic order at STO surfaces and interfaces. The results open pathways to exploit oxygen defects for engineering the electronic and magnetic properties of oxides.

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.

The chemistry and the structure of solid-liquid interface in partially molten particles of an Al-Si alloy during high temperature phase transformation were investigated at nanoscale using (Scanning) Transmission Electron Microscopy. The images display intensity bands along the interface which could be due to enrichment of Cu at the interface. The concentration profiles across the interface display element-specific variation in the chemical widths.

Reliable quantification of 3D results obtained by X-ray energy-dispersive spectroscopy (XEDS) tomography is currently hampered by the presence of shadowing effects and poor spatial resolution. Here, a method is presented which overcomes these problems by synergistically combining quantified XEDS data and high angle annular dark field–scanning transmission electron microscopy tomography. As a proof of principle, the approach is applied to characterize a complex Au/Ag nanorattle obtained through a galvanic replacement reaction. However, the technique that is proposed here is widely applicable to a broad range of nanostructures.

A new method to quantify X-ray energy dispersive spectroscopy (XEDS) data in 3D is presented. The synergistic combination of XEDS quantification and Scanning Transmission Electron Microscopy (STEM) tomography enables to overcome the “shadowing” problem and obtain a chemically quantified 3D reconstruction. The technique is used to determine the distribution of elements in a complex Au/Ag nanorattle.

Electron tomography is a key technique that enables the visualization of an object in three dimensions with a resolution of about a nanometre. High-quality 3D reconstruction is possible thanks to the latest compressed sensing algorithms and/or better alignment and preprocessing of the 2D projections. Rigid alignment of 2D projections is routine in electron tomography. However, it cannot correct misalignments induced by (i) deformations of the sample due to radiation damage or (ii) drifting of the sample during the acquisition of an image in scanning transmission electron microscope mode. In both cases, those misalignments can give rise to artefacts in the reconstruction. We propose a simple-to-implement non-rigid alignment technique to correct those artefacts. This technique is particularly suited for needle-shaped samples in materials science. It is initiated by a rigid alignment of the projections and it is then followed by several rigid alignments of different parts of the projections. Piecewise linear deformations are applied to each projection to force them to simultaneously satisfy the rigid alignments of the different parts. The efficiency of this technique is demonstrated on three samples, an intermetallic sample with deformation misalignments due to a high electron dose typical to spectroscopic electron tomography, a porous silicon sample with an extremely thin end particularly sensitive to electron beam and another porous silicon sample that was drifting during image acquisitions.

Electron tomography is a key technique that enables the visualization of an object in 3 dimensions with a resolution of about a nanometer. Multiple 2D images are acquired using a transmission electron microscope while rotating the sample. Then reconstruction algorithms are used to reconstruct the object in 3D. 2D images need to be aligned before 3D reconstruction. Alignment is usually done shifting the 2D images, but misalignments can also be induced by deformations of the sample during the image acquisitions. Those misalignments cannot be corrected by simple shifting, and yet they can give rise to artefacts in the reconstruction. We propose a simple-to-implement non-rigid alignment technique that can distort images to correct the deformations of the sample. This technique is initiated by shift corrections of complete images. It is then followed by several shift corrections of different parts of the images. Piecewise linear deformations are applied to each images to force them to simultaneously satisfy the shift corrections of the different parts. The efficiency of this technique is demonstrated on two samples, an intermetallic sample with deformation misalignments due to a long acquisition time and a sensitive porous silicon sample.