Energy-dispersive X-ray micro Laue diffraction on a bent gold nanowire

Reconstruction of three-dimensional strain field in an asymmetrical curved core-shell hetero-nanowire

Crystal orientation and strain mapping of an individual curved and asymmetrical core-shell hetero-nanowire (NW) is performed based on transmission electron microscopy. It relies on a comprehensive analysis of scanning nanobeam electron diffraction data obtained for 1.3 nm electron probe size. The proposed approach also handles the problem of appearing twinning defects on diffraction patterns and allows for the investigation of materials with high defect densities. Based on the experimental maps and their comparison with finite element simulations, the entire core-shell geometry including full three-dimensional strain distribution within the curved core-shell NW are obtained. Our approach represents, therefore, a low-dose quasi-tomography of the strain field within a nanoobject using only a single zone axis diffraction experiment. Our approach is applicable also for electron beam-sensitive materials for which performing conventional tomography is a difficult task.

Using 2D integral breadth to study plastic relaxation in a quasi-lattice-matched HgCdTe/CdZnTe heterostructure

The newly defined and rotationally invariant 2D integral breadth correctly measures plastification-induced peak broadening during micro-Laue diffraction experiments, and allows for both critical thickness and plastic onset measurements. Applied to the quasi-lattice-matched HgCdTe/CdZnTe heterostructure and taking into account the critical thickness only, it showed that the plastic onset of the rigid substrate perfectly matches the elastic limit of the smooth layer: a striking demonstration of the propagation of threading dislocations.

Micro-Laue diffraction has been used to record cross-section profiles on a quasi-lattice-matched HgCdTe/CdZnTe heterostructure as a function of the stress induced by a flexion machine. The heterostructure may be decomposed into four different regions according to depth. Sufficiently far from the interface, the CdZnTe substrate is undisturbed by the HgCdTe layer, while the region situated 10 µm beneath the interface presents an in-plane lattice parameter adjustment to the +0.02% mismatched layer. The layer has a 2 µm critical thickness and, beyond, misfit dislocations induce a large peak broadening whose main direction changes with depth. The same occurs over the whole heterostructure once flexion-induced plastification has started. Consequently, the usual full width at half-maximum or integral breadth is no longer relevant, and only a newly defined and rotationally invariant 2D integral breadth correctly measures the plastification-induced peak broadening. Taking into account only the critical thickness region, a 15.1 ± 0.7 MPa tensile HgCdTe elastic limit was measured, slightly overestimated because of the initial compressive layer stress. It was observed that the plastic onset of the substrate perfectly matches the elastic limit of the layer, despite the fact that the substrate elastic limit is expected to be four times higher: a striking demonstration of the propagation of threading dislocations. The ‘plastification easiness’ is found to be 2.4 times smaller deep inside the substrate than in the layer critical thickness region, while in the substrate lattice adjustment region, the plastification easiness goes from the substrate to the layer value with a 22–25 MPa transition interval. This novel method using the 2D integral breadth allows for easy critical thickness measurement as well as precise plastic onset determination and plastification easiness assessment. It is a quite general method, since it may be applied to the vast class of epitaxial layers for which the critical thickness is larger than the micro-Laue beam size (currently 250 nm).

In situ transient Laue x-ray diffraction during high strain-rate tension

In situ transient synchrotron Laue x-ray diffraction based on high-energy and broadband x rays under high strain-rate tensile loading was developed at a superconducting wiggler beamline at the Beijing Synchrotron Radiation Facility. A split-Hopkinson tensile bar is utilized to realize this dynamic loading condition, while the transient Laue x-ray diffraction captures the transient internal structure of monocrystalline materials. Plastic deformation of a monocrystalline nickel specimen was investigated to prove the ability of this instrumentation in the characterization of a dynamic response of monocrystalline materials during a high strain-rate impact process with 5 µs time resolution.