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Jürgen Härtwig

Jürgen Härtwig
Retired from European Synchrotron Radiation Facility

Dr. rer. nat. habil.

About

229
Publications
52,099
Reads
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3,704
Citations
Citations since 2016
8 Research Items
1200 Citations
2016201720182019202020212022050100150200
2016201720182019202020212022050100150200
2016201720182019202020212022050100150200
2016201720182019202020212022050100150200
Additional affiliations
August 2015 - July 2018
European Synchrotron Radiation Facility
Position
  • Professor Emeritus
April 2014 - April 2017
University of Johannesburg
Position
  • Professor
January 1993 - July 2015
European Synchrotron Radiation Facility
Position
  • Head of Department

Publications

Publications (229)
Presentation
Full-text available
X-ray diffraction topography - introduction - is a series of lectures for students and scientists starting to work or already working in the field of X-ray imaging, in particular the X-ray diffraction topography. It is used to detect and study macroscopic defects in single crystal of rater good quality or even to check their possible very high qual...
Article
Pure and Nd-doped Ca3Y2(BO3)4 and Ca3Gd2(BO3)4 orthoborate (space group Pnma) single crystals are considered for applications as materials for optoelectronics, in particular for ultrafast pulse lasers. In the present work, Czochralski-grown single crystals of such materials were studied. All of them were nearly free of defects such as impurity phas...
Article
Ytterbium doped calcium gadolinium aluminate (CaGdAlO4) crystals, which is a perspective material for femto-second lasers, have been studied by means of synchrotron and conventional X-ray diffraction topography. The investigation was performed with a series of samples cut out perpendicularly and parallel to the 〈100〉 growth axis from the initial an...
Article
Full-text available
Bragg diffraction imaging enables the quality of synthetic single-crystal diamond substrates and their overgrown, mostly doped, diamond layers to be characterized. This is very important for improving diamond-based devices produced for X-ray optics and power electronics applications. The usual first step for this characterization is white-beam X-ra...
Article
We report on the characterization of high quality sapphire single crystals suitable for high-resolution X-ray optics at high energy. Investigations using rocking curve imaging reveal the crystals to be of uniformly good quality at the level of 104 in lattice parameter variations, dd=d. However, investigations using backscattering rocking curve imag...
Presentation
Full-text available
Series of four (connected) lectures with some corrections and extensions with respect to earlier lectures
Presentation
Full-text available
Introduction into the dynamical theory of X-ray diffraction for perfect crystals
Conference Paper
Full-text available
In an introduction it will mentioned what is X-ray optics, its tasks, X-ray optical elements used at synchrotron and laboratory x-ray sources, the parameters they may control, and a bit related history. In the main part we shall discuss items like beam dimension, angular source size, elements like slits, windows, filters, multilayers or crystal tha...
Article
Full-text available
Heavily boron doped diamond epilayers with thicknesses ranging from 40 to less than 2 nm and buried between nominally undoped thicker layers have been grown in two different reactors. Two types of [100]-oriented single crystal diamond substrates were used after being characterized by X-ray white beam topography. The chemical composition and thickne...
Article
Full-text available
In order to correctly analyse high-resolution rocking curves of high-quality crystals, a special effort is needed to estimate the systematic contributions coming from the experimental setup. This article highlights the main areas that require special analytical treatment and presents results obtained using different approaches to the problem, as we...
Article
Full-text available
Sagittal focusing is a widely used geometry to horizontally focus X-rays in synchrotron beamlines. Usually, two types of devices are used: toroidal mirrors combined with flat X-ray monochromators or flat mirrors combined with sagittal focusing monochromators. The former option seems to be better since the stresses caused by the bending of the secon...
Article
Full-text available
The polarization purity of 6.457- and 12.914-keV x rays has been improved to the level of 2.4×10^{-10} and 5.7×10^{-10}. The polarizers are channel-cut silicon crystals using six 90° reflections. Their performance and possible applications are demonstrated in the measurement of the optical activity of a sucrose solution.
Article
Full-text available
Defects in the core of SrLaGaO4 single crystals, grown by the Czochralski method using a [001]-oriented seed, were studied by transmission X-ray diffraction projection topography. Topographs were taken with radiation from a laboratory source and with high-energy radiation available at the ESRF beamline ID19 in Grenoble. The contrast of the investig...
Article
Full-text available
The performance of a recently developed full-field X-ray micro-imaging system based on an in-line Bragg magnifier is reported. The system is composed of quasi-channel-cut crystals in combination with a Medipix single-photon-counting detector. A theoretical and experimental study of the imaging performance of the crystals-detector combination and a...
Data
Full-text available
X-ray diffraction topography is an imaging technique based on Bragg diffraction. The interpretation of the images often requires some results of the dynamical diffraction theory. For the simulation of defect images this theory is compulsory. X-ray diffraction topography provides a two dimensional intensity mapping of the beam(s) diffracted by a cry...
Article
Full-text available
White beam x-ray Laue microdiffraction allows fast mapping of crystal orientation and strain fields in polycrystals, with a submicron spatial resolution in two dimensions. In the well crystallized parts of the grains, the analysis of Laue spot positions provides the local deviatoric strain tensor. The hydrostatic part of the strain tensor may also...
Article
Full-text available
White beam x-ray Laue microdiffraction allows fast mapping of crystal orientation and strain fields in polycrystals, with a submicron spatial resolution in two dimensions. In the well crystallized parts of the grains, the analysis of Laue spot positions provides the local deviatoric strain tensor. The hydrostatic part of the strain tensor may also...
Article
High quality single-crystal synthetic diamond is the most suitable material for selected X-ray optical applications in the latest generation X-ray light sources. Excellent heat handling properties, as well as low absorption, coupled with high perfection in the crystal bulk and very good surface quality, are crucial for such applications. In recent...
Article
A method for obtaining a smooth, single crystal diamond surface is presented, whereby a sacrificial defective layer is created by implantation of a regular (4 nm roughness) Ib diamond plate. This was then graphitized by annealing before being selectively etched. We have used O(+) at 240 keV, the main process variables being the ion fluence (ranging...
Article
To be used for X-ray imaging, semiconductor materials must exhibit good and uniform electronic properties. Epitaxial layers are therefore better adapted than bulk materials which contain dislocations, precipitates and point defects in variable concentrations depending on the growth mode and the nature of the material. However, they have to be thick...
Article
Full-text available
Author(s) of this paper may load this reprint on their own web site or institutional repository provided that this cover page is retained. Republication of this article or its storage in electronic databases other than as specified above is not permitted without prior permission in writing from the IUCr. For further information see http://journals....
Article
Full-text available
The microstructure formed during the solidification step has a major influence on the properties of materials processed by major techniques (casting welding) In situ and real-time characterization by synchrotron X ray imaging is the method of choice to unveil the dynamical formation of the solidification microstructure in metallic alloys and thus p...
Article
Full-text available
Due to its outstanding thermal properties, diamond is an attractive alternative to silicon as a monochromator material for high intensity X‐ray beams. To date, however, the practical applications have been limited by the small size and relatively poor crystallographic quality of the crystals available. The ESRF Diamond Project Group has studied t...
Article
Full-text available
For nearly 20 years, the X-ray Optics Group of the ESRF has been playing a major role in the development of new X-ray optical systems, many of which are widely used at synchrotrons around the globe.
Article
We report on the measurement of the highest purity of polarization of X-rays to date. The measurements are performed by combining a brilliant undulator source with an X-ray polarimeter. The polarimeter is composed of a polarizer and an analyzer, each based on four reflections at channel-cut crystals with a Bragg angle very close to 45°. Experiments...
Article
Full-text available
The non-linear optical (NLO) crystals are very important for the development of all solid state lasers. Visible and UV solid state lasers are used for industrial or medical applications. The promising crystals in this fields are from the family of rare earth calcium oxyborates ReCa 4 O(BO 3) 3 (ReCOB), where Re = La 3+ , Gd 3+ , Sm 3+ , Y 3+ , Nd 3...
Article
Full-text available
The defect structure of gadolinium–calcium oxoborate single crystals highly doped with 22% Y, Gd 0.78 Y 0.22 Ca 4 O(BO 3) 3 , is studied using X-ray transmission topography both with the conventional source and synchrotron radiation. Straight dislocation diffraction contrasts, white or black, depending on absorption and on its changing while the di...
Data
Full-text available
Synthetic single-crystalline HPHT-diamond is in principle the best-suited material for Bragg diffracting X-ray optical elements. Already in the early days of the 3rd generation sources the utilisation of diamonds was discussed, tested and elements were realised. A real breakthrough in their application was not reached. The main reasons were, (and p...
Article
Full-text available
The trend in synchrotron radiation (x-rays) is towards higher brilliance. This may lead to a very high power density, of the order of hundreds of watts per square millimetre at the x-ray optical elements. These elements are, typically, windows, polarizers, filters and monochromators. The preferred material for Bragg diffracting optical elements at...
Article
Full-text available
We present an application of the Talbot effect [Talbot et al., Philos. Mag. 11, 196 (1836)] to measure the spatial coherence of a synchrotron beam, as well as the influence of optical elements on it. One advantage of using this effect is that regions of the beams down to 50 µm × 50 µm are still analysable (in our case). This spatial resolution allo...
Article
Samples cut out from different regions of SrLaGaO4 (SLG) single crystal grown along [001]-direction were studied with a number of X-ray diffraction topographic methods exploring both conventional and synchrotron X-ray sources. The synchrotron investigation included in particular white beam projection transmission topography at ultra short wavelengt...
Article
We present a new method based on femtosecond laser ablation for the fabrication of statically bent diamond crystals. Using this method, curvature radii of 1 m can easily be achieved, and the curvature obtained is very uniform. Since diamond is extremely tolerant to high radiation doses, partly due to its densely packed lattice, such bent crystals a...
Conference Paper
Full-text available
The purpose of this contribution is to study several phenomena influencing the formation of X-rays diffraction images of SAW propagating on crystals so to be able to use them to obtain further information about the SAW. We consider particularly new contrasts appearing in white beam section topographs made with low or large amplitude SAW. The first...
Article
Full-text available
A DuMond analysis of X-ray diffraction patterns has been carried out in the case of a combined σ–π polarization configuration, obtained using a setup with a double-crystal monochromator in reflection (Bragg) geometry and an analyser in transmission (Laue) geometry. The derived analytical expressions allow the characterization of the bending of the...
Article
The development of brilliant third-generation synchrotron X-ray sources, together with advances in X-ray optics and detectors, has provided timely efficient tools for in-depth understanding of physical phenomena in a broad spectrum of situations. Synchrotron X-ray radiography enables in situ and real-time observation of microstructure evolution, i....
Article
Full-text available
Alloy solidification was investigated in situ and real time by using a unique experimental setup developed at the European Synchrotron Radiation Facility (ESRF) combining both synchrotron X-ray radiography and topography. Although synchrotron X-ray radiography enables the investigation of the solid-liquid interface of metallic alloys, white-beam sy...
Conference Paper
Full-text available
There is currently interest in low strain HPHT diamond due to its expected application as various types of X-ray optical elements at Synchrotrons, where the X-ray intensity is becoming progressively too severe for the existing materials. The diamond crystals need to be synthesised with unprecedented lattice quality. In recent measurements at the ID...
Article
This special issue's cover shows a radiograph and a topograph recorded during Al–3.5 wt% Ni alloy solidification. On the radiograph (left), one can observe the development of a branching structure known as dendrite. The high quality of the dendrite in the early stage of the growth is confirmed by the equal-thickness fringes which are visible within...
Article
Full-text available
In this article, we present a review of observations during Al-3.5 wt pct Ni alloy solidi.cation experiments performed at the European Synchrotron Radiation Facility (ESRF) in Grenoble. These experiments provide direct access to dynamical phenomena during columnar growth (initial transient and breakdown of a planar solid-liquid interface), and for...
Article
Full-text available
One of the main challenges of quasicrystal science is to elucidate how the quasiperiodic order can extend so far, i.e. up to several centimetres according to the size of the single grains of various alloys routinely grown nowadays [M. Boudard, E. Bourgeat-Lami, M. de Boissieu, et al., Phil. Mag. Lett. 71 11 (1995); Y. Yokoyama, R. Note, A. Kimura,...
Article
Full-text available
The three-dimensional (3D) distribution of defects was investigated in several crystals by synchrotron radiation diffraction tomography. This experimental procedure combines white-beam synchrotron radiation section topography with electronic image recording and computer data processing. A scan involving many section topographs is performed with the...
Article
Full-text available
In solidification processing, the physical properties are primarily controlled by the microstructure built in the solid. Thus, materials engineering requires detailed understanding of microstructure formation dynamics. Using in situ and real-time synchrotron X-ray imaging at the European Synchrotron Radiation Facility, the solidification progress i...
Article
Full-text available
In situ X-ray imaging of the solidification progress can be carried out, nowadays, in front of the synchrotron sources, by combining X-ray radiography with X-ray topography. Thereby it is possible to obtain information directly, on the one hand on the shape and the velocity of the growing interface by means of X-ray radiography, and on the other ha...
Article
Full-text available
In order to better understand the long-range propagation of quasicrystalline order, as well as quasicrystal stability, it is important to know if defects are generated in the quasicrystal grains during their growth. Previously, we studied the degree of perfection of about ten icosahedral quasicrystal grains of various alloys (Al–Pd–Mn, Al–Cu–Fe, Zn...
Article
Full-text available
The solid microstructure built in the solid governs the properties of materials elaborated from the melt. In order to clarify the dynamical mechanisms controlling solidification processing, we use in situ and real-time synchrotron X-ray radiography at ESRF (European Synchrotron Radiation Facility) to analyze microstructure formation in thin aluminu...
Article
Full-text available
Recently, in some silicon carbide single crystals, some micropipes associated with screw dislocation have been observed by X-ray topography and the strain field around them produced images similar to those of screw dislocations with a very large Burgers vector, about 667 nm. The radius of the hole in the centre of the micropipe is less than 10 μm....
Article
Full-text available
Quasicrystal growth remains an unsolved problem in condensed matter. The dynamics of the process is studied by means of synchrotron live imaging all along the solidification of icosahedral AlPdMn quasicrystals. The lateral motion of ledges driving faceted growth at the solid-melt interface is conclusively shown. When the solidification rate is incr...
Article
In the present study homoepitaxial diamond films have been grown by microwave plasma chemical vapour deposition (MWPCVD) on (001)-oriented Ib HPHT substrates with off-axis angles of up to 11°. Freestanding films of several hundred microns thickness were produced by removal of the Ib substrate and of the polycrystalline rim. In high resolution X-ray...
Article
Full-text available
Quasicrystal growth remains an unsolved problem in condensed matter. The dynamics of the process is studied by means of synchrotron live imaging all along the solidification of icosahedral AlPdMn quasicrystals. The lateral motion of ledges driving faceted growth at the solid-melt interface is conclusively shown. When the solidification rate is incr...