Anatoly Shabalin

Structural Evolution of Colloidal Crystal Films in the Process of Melting Revealed by Bragg Peak Analysis

In situ X-ray diffraction studies of structural evolution of colloidal crystal films formed by polystyrene spherical particles upon incremental heating are reported. The Bragg peak parameters, such as peak position, integrated intensity, and radial and azimuthal widths were analyzed as a function of temperature. A quantitative study of colloidal crystal lattice distortions and mosaic spread as a function of temperature was carried out using Williamson-Hall plots based on mosaic block model. The temperature dependence of the diameter of polystyrene particles was obtained from the analysis of Bragg peaks, and the form factor contribution extracted from the diffraction patterns. Four stages of structural evolution in a colloidal crystal upon heating were identified. Based on this analysis, a model of the heating and melting process in the colloidal crystal film is suggested.

Water window ptychographic imaging with characterized coherent X-rays.

Water window ptychographic coherent diffractive imaging was demonstrated at the P04 beamline of PETRA III synchrotron radiation source. The beam coherence was characterized with the non-redundant array method.

Strain mapping in an InGaN/GaN nanowire using a nano-focused x-ray beam

Strained InGaN/GaN core-shell nanowires (NWs) are promising candidates for solid state lighting applications due to their superior properties compared to planar films. NW based devices consist of multiple functional layers, which sum up to many hundred nanometers in thickness, that can uniquely be accessed in a non-destructive fashion by hard X-rays. Here, we present a detailed nanoscale strain mapping performed on a single, 400 nm thick and 2 μm long core-shell InGaN/GaN nanowire with an x-ray beam focused down to 100 nm. We observe an inhomogeneous strain distribution caused by the asymmetric strain relaxation in the shell. One side of the InGaN shell was fully strained, whereas the other side and the top part were relaxed. Additionally, tilt and strain gradients were determined at the interface with the substrate.

Characterization of spatial coherence of synchrotron radiation with non-redundant arrays of apertures.

A method to characterize the spatial coherence of soft X-ray radiation from a single diffraction pattern is presented. The technique is based on scattering from non-redundant arrays (NRAs) of slits and records the degree of spatial coherence at several relative separations from 1 to 15 µm, simultaneously. Using NRAs the spatial coherence of the X-ray beam at the XUV X-ray beamline P04 of the PETRA III synchrotron storage ring was measured as a function of different beam parameters. To verify the results obtained with the NRAs, additional Youngs double-pinhole experiments were conducted and showed good agreement.

Bragg coherent x-ray diffractive imaging of a single indium phosphide nanowire

Three-dimensional (3D) Bragg coherent x-ray diffractive imaging (CXDI) with a nanofocused beam was applied to quantitatively map the internal strain field of a single indium phosphide nanowire. The quantitative values of the strain were obtained by pre-characterization of the beam profile with transmission ptychography on a test sample. Our measurements revealed the 3D strain distribution in a region of 150 nm below the catalyst Au particle. We observed a slight gradient of the strain in the range of 0.6% along the [111] growth direction of the nanowire. We also determined the spatial resolution in our measurements to be about 10 nm in the direction perpendicular to the facets of the nanowire. The CXDI measurements were compared with the finite element method simulations and show a good agreement with our experimental results. The proposed approach can become an effective tool for in operando studies of the nanowires. (Less)

Double hexagonal close-packed structure revealed in a single colloidal crystal grain by Bragg rod analysis

A coherent X-ray diffraction study of a single colloidal crystal grain composed of silica spheres is reported. The diffraction data contain Bragg peaks and additional features in the form of Bragg rods, which are related to the stacking of the hexagonally close-packed layers. The profile of the Bragg rod shows distinct intensity modulations which, under the specific experimental conditions used here, are directly related to the stacking sequence of the layers. Using a model for the scattered intensity along the Bragg rod for an exact stacking sequence of a finite number of hexagonally close-packed layers, it is found that a double hexagonal close-packed stacking sequence is present in the colloidal crystal grain. This analysis method opens up ways to obtain crucial structural information from finite-sized crystalline samples by employing advanced third-generation X-ray sources.

X-ray Bragg Ptychography on a Single InGaN/GaN Core–Shell Nanowire

The future of solid-state lighting can be potentially driven by applications of InGaN/GaN core-shell nanowires. These heterostructures provide the possibility for fine-tuning of functional properties by controlling a strain state between mismatched layers. We present a nondestructive study of a single 400 nm-thick InGaN/GaN core-shell nanowire using two-dimensional (2D) X-ray Bragg ptychography (XBP) with a nanofocused X-ray beam. The XBP reconstruction enabled the determination of a detailed three-dimensional (3D) distribution of the strain in the particular nanowire using a model based on finite element method. We observed the strain induced by the lattice mismatch between the GaN core and InGaN shell to be in the range from -0.1% to 0.15% for an In concentration of 30%. The maximum value of the strain component normal to the facets was concentrated at the transition region between the main part of the nanowire and the GaN tip. In addition, a variation in misfit strain relaxation between the axial growth and in-plane directions was revealed.

Revealing Three-Dimensional Structure of an Individual Colloidal Crystal Grain by Coherent X-Ray Diffractive Imaging

We present results of a coherent x-ray diffractive imaging experiment performed on a single colloidal crystal grain. The full three-dimensional (3D) reciprocal space map measured by an azimuthal rotational scan contained several orders of Bragg reflections together with the coherent interference signal between them. Applying the iterative phase retrieval approach, the 3D structure of the crystal grain was reconstructed and positions of individual colloidal particles were resolved. As a result, an exact stacking sequence of hexagonal close-packed layers including planar and linear defects were identified.

In situ X-ray crystallographic study of the structural evolution of colloidal crystals upon heating

The results of a real-time X-ray crystallographic study of the melting transition of polystyrene colloidal crystals during heating are presented.

Ptychographical imaging of the phase vortices in the x-ray beam formed by nanofocusing lenses

We present the ptychographical reconstruction of the x-ray beam formed by nanofocusing lenses (NFLs) containing a number of phase singularities (vortices) in the vicinity of the focal plane. As a test object Siemens star pattern was used with the finest features of 50 nm for ptychographical measurements. The extended ptychographical iterative engine (ePIE) algorithm was applied to retrieve both complex illumination and object functions from the set of diffraction patterns. The reconstruction revealed the focus size of 91.4±1.1 nm in horizontal and 70±0.3 nm in vertical direction at full width at half maximum (FWHM). The complex probe function was propagated along the optical axis of the beam revealing the evolution of the phase singularities.