Water Window Ptychographic Imaging with Characterized Coherent X-rays

We report on a ptychographical coherent diffractive imaging experiment in the water window with focused soft X-rays at $500~\mathrm{eV}$. An X-ray beam with high degree of coherence was selected for ptychography at the P04 beamline of the PETRA III synchrotron radiation source. We measured the beam coherence with the newly developed non-redundant array method. A pinhole $2.6~\mathrm{\mu m}$ in size selected the coherent part of the beam and was used for ptychographic measurements of a lithographically manufactured test sample and fossil diatom. The achieved resolution was $53~\mathrm{nm}$ for the test sample and only limited by the size of the detector. The diatom was imaged at a resolution better than $90~\mathrm{nm}$.Comment: 22 pages. 7 figure

In situ\textit{In situ} hydride breathing during the template-assisted electrodeposition of Pd nanowires

We investigated the structural evolution of electrochemically fabricated Pd nanowires $\textit{in situ}$ by means of grazing-incidence transmission small- and wide-angle x-ray scattering (GTSAXS and GTWAXS), x-ray fluorescence (XRF) and 2-dimensional surface optical reflectance (2D-SOR). This shows how electrodeposition and the hydrogen evolution reaction (HER) compete and interact during Pd electrodepositon. During the bottom-up growth of the nanowires, we show that $\beta$-phase Pd hydride is formed. Suspending the electrodeposition then leads to a phase transition from $\beta$- to $\alpha$-phase Pd hydride. Additionally, we find that grain coalescence later hinders the incorporation of hydrogen in the Pd unit cell. GTSAXS and 2D-SOR provide complementary information on the volume fraction of the pores occupied by Pd, while XRF was used to monitor the amount of Pd electrodeposited.Comment: 17 pages, 11 figures, 4 appendice

Characterization of nanowires by coherent x-ray diffractive imaging and ptychography

Imaging techniques are of paramount importance for our understanding of the universe. From galaxies and stars explored by huge telescopes down to micro and nanostructures studied by microscopes, imaging systems provide invaluable scientific information. When an object under investigation has a size of about 100 nanometers, x-rays become a perfect probe for non-destructive imaging. The manufacturing process of image forming lenses for x-rays becomes much more complicated comparing to optical ones. Therefore, ”lensless” techniques which rely on the coherent properties of radiation were developed. With third generation of synchrotron sources highly coherent and intense x-ray beams became widely accessible. They are used in new imaging methods such as coherent x-ray diffractive imaging (CXDI) and x-ray ptychography. Modern nanotechnology opens a wide spectrum of possible applications in different branches of physics, chemistry, biology and engineering. At the nanoscale, matter has different physical and chemical properties compared to the macroscale bulk material. Thecontinuing trend of miniaturization of functional components in semiconductor industry brings new challenges both in growth and characterization methods. This Thesis is focusedon application of coherent diffractive imaging methods to reveal the structure of single semiconductor nanowires (NWs). They have been attracting significant attention for a couple of decades due to their efficient strain relaxation properties. And since the strain plays a significant role in NW performance the projects carried out in this work are oriented on Bragg CXDI approaches. Three distinct projects were carried out during my research activity at DESY research center of the Helmholtz Association. Experimental work was performed at P06 and P10 beamlines at PETRA III synchrotron. The first part of this Thesis extends the application of the three-dimensional (3D) Bragg CXDI to strain field mapping in a single InP NW with a diameter of 100 nm. The measurement employed a nanofocused beam, which is characterized by transmission x-ray ptychography. It is shown that the separation of the object and probe functions is possible in the direct space after a 3D reconstruction. The influence of a catalyst particle at the tip of the NW on the strain distribution in InP part of the NW is revealed. The second part of the manuscript is dedicated to the development and application of two-dimensional x-ray Bragg ptychography (2D XBP) to studies of single NWs. This approach providesa larger field of view on the sample and the reliability of reconstruction results improves, due to the advantages of ptychography. The limitations of the technique are discussed bytheoretical analysis and finite element method modeling (FEM). Successful experimental implementation is demonstrated on a single InGaN/GaN core-shell NW. The third part isdevoted to 3D Bragg CXDI of strain evolution in a single GaNNWwith respect to applied voltage bias. A complicated tilting and defect formation process in the NW was revealedfrom the evolution of the Bragg peak. This study gives an insight into piezoelectrical properties of the sample, which dramatically influence electron-hole pair recombinationand may decrease the efficiency of optoelectronic devices based on GaN NWs

Unraveling the Spatial Distribution of Catalytic Non-Cubic Au Phases in a Bipyramidal Microcrystallite by X-ray Diffraction Microscopy

Tuning of crystal structures and shapes of submicrometer-sized noble metals have revealed fascinating catalytic, optical, electrical, and magnetic properties that enable developments of environmentally friendly and durable nanotechnological applications. Several attempts have been made to stabilize Au, knowing its extraordinary stability in its conventional face-centered cubic (fcc) lattice, into different lattices, particularly to develop Au-based catalysis for industry. Here, we report the results from scanning X-ray diffraction microscopy (SXDM) measurements on an ambient-stable penta-twinned bipyramidal Au microcrystallite (about 1.36 μm in length and 230 nm in diameter) stabilized in noncubic lattice, exhibiting catalytic properties. With more than 82% of the crystal volume, the majority crystallite structure is identified as body-centered orthorhombic (bco), while the remainder is the standard fcc. A careful analysis of the diffraction maps reveals that the tips are made up of fcc, while the body contains mainly bco with very high strain. The reported structural imaging technique of representative single crystallite will be useful to investigate the growth mechanism of similar multiphase nano- and micrometer-sized crystals

Theoretical analysis of the strain mapping in a single core-shell nanowire by x-ray Bragg ptychography

X-ray Bragg ptychography (XBP) is an experimental technique for high-resolution strain mapping in a single nano- and mesoscopic crystalline structures. In this work we discuss the conditions that allow direct interpretation of the ptychographic reconstructions in terms of the strain distribution obtained from the two dimensional (2D) XBP. Simulations of the 2D XBP experiments under realistic experimental conditions are performed with a model of InGaN/GaN core-shell nanowire with low (1%) and high (30%) Indium concentrations in the shell. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Probing Dynamics in Colloidal Crystals with Pump-Probe Experiments at LCLS : Methodology and Analysis

We present results of the studies of dynamics in colloidal crystals performed by pump-probe experiments using an X-ray free-electron laser (XFEL). Colloidal crystals were pumped with an infrared laser at a wavelength of 800 nm with varying power and probed by XFEL pulses at an energy of 8 keV with a time delay up to 1000 ps. The positions of the Bragg peaks, and their radial and azimuthal widths were analyzed as a function of the time delay. The spectral analysis of the data did not reveal significant enhancement of frequencies expected in this experiment. This allowed us to conclude that the amplitude of vibrational modes excited in colloidal crystals was less than the systematic error caused by the noise level.publishe