Three dimensional X-ray Bragg ptychography of an extended semiconductor heterostructure

Abstract : Ptychography is a coherent diffraction imaging technique which aims in retrieving the lost phase from intensity-only far-field measurements. The versatility of the approach has proved an important asset for 3D mapping of different physical quantities, like the electron density of micrometer-sized specimens with resolution in the 10 - 100nm range. In this work, we explored the possibility to push further the current limits of 3D Bragg ptychography, by addressing the case of an extended InP/InGaAs nanostructured thin film, bonded on a silicon wafer. The experiment was performed at the ID13 beamline at ESRF, with a monochromatic beam focused down to 100nm. 2D intensity patterns were acquired at several incidence angles in the vicinity of the InP (004) Bragg peak, stacking up a three dimensional dataset. Numerical analysis of the given problem was performed beforehand in order to optimize the inversion strategy and study the possibility of introducing additional physical constraints through regularization approaches. Inversions of the dataset were done using a ptychographical gradient-based optimization phase retrieval algorithm. The developed strategy was applied on the experimental data which led to the retrieval of a complex-valued 3D image. The result exhibits the high crystallinity quality of the sample with the expected values of thickness and lattice mismatch, nevertheless, small local lattice tilts have been observed - in the order of 0.02°- and confirmed by numerical modeling. This result demonstrates the high sensitivity of the technique, as well as its exciting perspectives for imaging complex organic and inorganic nanostructured materials.
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Anastasios I. Pateras. Three dimensional X-ray Bragg ptychography of an extended semiconductor heterostructure. Materials Science [cond-mat.mtrl-sci]. Aix-Marseille Université; Karlsruhe Institut für Technologie (KIT), 2015. English. ⟨tel-02187453⟩

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