Christian David - Academia.edu (original) (raw)

Papers by Christian David

Optics Letters, 2011

We fabricate computer generated holograms for the generation of phase singularities at extreme ul... more We fabricate computer generated holograms for the generation of phase singularities at extreme ultraviolet (EUV) wavelengths using electron beam lithography and demonstrate their ability to generate optical vortices in the nonzero diffraction orders. To this end, we observe the characteristic intensity distribution of the vortex beam and verify the helical phase structure interferometrically. The presented method forms the basis for further studies on singular light fields in the EUV frequency range, i.e., in EUV interference lithography. Since the method is purely achromatic, it may also find applications in various fields of x ray optics.

Journal of Molecular Structure: THEOCHEM, 1982

The recent report of Swepston et al. [l] of high quality ab initio quantum mechanical computation... more The recent report of Swepston et al. [l] of high quality ab initio quantum mechanical computations on clusters of LiF molecules prompted these computations on LiF clusters based on the polarization model for water and its ionic dissociation products [ 21. A polarization model for solid LiF would allow simulation of this solid and of the solution process wherein a crystal of LiF in a sample of water is allowed (presumably under molecular dynamic conditions) to dissolve. These computations are possible due to the fact that the polarization model has been excited to fluoride in its interactions with protons [3] and with water [4] and to the Li+ cation [ 51 in its interactions with water. Further, the Li-F system has been calibrated against the results of Brumer and Karplus [6] in the context of the polarization model. In another report based on the same calibration, the process of bringing an Li+ cation (tetrahydrated) into collision with a F-anion (also tetrahydrated) has been explored [ 71. Here, an investigation of the minimum energy structures found by the polarization model for (LiF), clusters, for n = 2, 3,4, and 8, is reported. In these computations, there is no K(r) or L(r) function for Li'. The polarization energy of the monomer of LiF,-185.0 kcal mol-', has been adjusted to fit the Brummer and Karplus value. Table 1 shows the values of the energies which have been achieved for various (LiF),. As can be seen, within reason all the structures generated are non-polar. There is no doubt that our results mimic in several ways the results of the ab initio computations. The LiF bond length in the cyclic trimer is reproduced almost perfectly (1.58 vs. 1.687 A from the ab initio work). On the other hand, the energy difference on dimerizing LiF, relative to two isolated molecules, is reported as-76.1 kcal mol-', while we obtain only-41.5 kcal mol-'. Furthermore, the quantum mechanical calculations obtain 1.71 K for r(LiF) while we obtain 1.58A in the dimer. On trimerizing, the relative error is even worse, with the ab initio calculations reporting-150.8 kcal mol-', while we obtain only-89.7 kcal mol-'. Our cyclic quadrimer relaxes from the embryonic NaCl starting structure to the planar, cyclic zero dipole moment structure. In packing two such cyclic quadrimers in parallel planes, two structures emerged. The first

The invention relates to an arrangement and method for the projective and / or tomographic phase ... more The invention relates to an arrangement and method for the projective and / or tomographic phase contrast imaging with X-rays, wherein one or more phase grating (G1) is arranged in the beam path in such a way / are that during one revolution of the at least one X-ray source (B), the examination subject (P) with different spatial orientations of the grating lines relative to the examination object (P) is scanned, so that from the two scans with differently oriented phase gratings (G1) can be each x-ray beam of the full refraction and thus the complete Phasenschubgradient determined by the phase shift of an examination subject (P) projection as or to show in tomographic representation.

A focus-detector arrangement of an X-ray apparatus is disclosed for generating projective or tomo... more A focus-detector arrangement of an X-ray apparatus is disclosed for generating projective or tomographic phase contrast recordings of an observed region of a subject. In at least one embodiment, the arrangement includes a radiation source which emits a coherent or quasi-coherent X-radiation and irradiates the subject, a phase grating which is arranged behind the subject in the beam path of the radiation source and generates an interference pattern of the X-radiation in a predetermined energy range, and an analysis-detector system which detects at least the interference pattern generated by the phase grating in respect of its phase shift with position resolution. Further, the beam path of the X-radiation used diverges in at least one plane between the focus and the detector

Micritic limestones exhibit large variation of (1) sedimentary texture from mudstone to packstone... more Micritic limestones exhibit large variation of (1) sedimentary texture from mudstone to packstone, (2) facies composition and (3) petrophysical properties (porosity, acoustic velocity). Those heterogeneities imply a complex distribution of fluid flow properties and a complex petrophysical signature. In the Eastern Paris Basin, Late Jurassic micritic carbonate deposits constitute a main aquifer located directly above the Callovian-Oxfordian clay-rich formation studied by the French National Radioactive Waste Management Agency (Andra) as a potential host rock for a deep geological disposal of high level radioactive wastes. A precise understanding of the factors controlling the petrophysical properties within carbonate aquifers is thus essential for rock-typing studies and fluid flow modelling. The first objective of this study is to better characterize the vertical distribution of both petrographical characteristics (texture, facies and composition) and petrophysical properties (poros...

SPIE Proceedings, 2011

A new imaging setup, aimed to perform differential X-ray phase contrast (DPC) imaging with a Talb... more A new imaging setup, aimed to perform differential X-ray phase contrast (DPC) imaging with a Talbot interferometer on a microfocus X-ray tube, is demonstrated. The main features compared to recently proposed setups are an extremely short source to detector distance, high spatial resolution and a large field of view. The setup is designed for an immediate integration into a industrial micro CT scanner. In this paper, technical challenges of a compact setup, namely the critical source coherence and divergence, are discussed. A theoretical analysis using wave optics based computer simulations is performed to estimate the DPC signal visibility and the size of the field of view for a given setup geometry. The maximization of the signal visibility as a function of the inter-grating distance yields the optimal grating parameters. Imaging results using the optimized grating parameters are presented. The reduction of the field of view, being a consequence of the high beam divergence, was solved by fabricating new, cylindrically bent diffraction gratings. The fabrication process of these gratings required a change of the currently used wafer materials and an adaption of the manufacturing techniques. The implementation of the new setup represents a major step forward for the industrial application of the DPC technique.

We report how an interferometic method can produce quantitative x-ray and neutron phase contrast ... more We report how an interferometic method can produce quantitative x-ray and neutron phase contrast images. The interferometer is based on diffraction gratings fabricated using microlithography techniques. Separate phase and absorption images are recorded simultaneously (1). By taking data sets under many viewing angles, a tomographic reconstruction of both the real part and the imaginary part of the objects complex refractive index distribution can be obtained. In the x-ray case, the method can be used to enhance the contrast in medical radiography and it has the potential to reduce the applied radiation dose. As opposed to existing techniques, the method requires only little coherence and can be scaled up to fields of view of many centimetres (see Fig. 1). Its application is therefore not limited to be used at synchrotron light sources, but it can be used with standard x-ray tube sources (2). This opens up a wide range of applications in medical imaging and non destructive testing. I...

SPIE Proceedings, 2001

Cellular micro-irradiation is now seen as a potent method for understanding how radiations intera... more Cellular micro-irradiation is now seen as a potent method for understanding how radiations interact with living cells and tissues. The strength of this technique lies in its ability to deliver precise doses of radiation to selected individual cells in vitro, or to pre-selected targets ...

Advances in X-Ray Optics, 2001

ABSTRACT

$Research paper thumbnail of Kinoform diffractive lenses for efficient nano-focusing of hard X-rays$

Optics express, Jan 14, 2014

A nano-focusing module based on two linear Fresnel zone plates is presented. The zone plates are ... more A nano-focusing module based on two linear Fresnel zone plates is presented. The zone plates are designed to generate a kinoform phase profile in tilted geometry, thus overcoming the efficiency limitations of binary diffractive structures. Adjustment of the tilt angle enables tuning of the setup for optimal efficiency over a wide range of photon energies, ranging from 5 to 20 keV. Diffraction efficiency of more than 50% was measured for the full module at 8 keV photon energy. A diffraction limited spot size of 100 nm was verified by ptychographic reconstruction for a lens module with a large entrance aperture of 440 μm × 400 μm.

$Research paper thumbnail of High resolution double-sided diffractive optics for hard X-ray microscopy$

Optics Express, 2015

The fabrication of high aspect ratio metallic nanostructures is crucial for the production of eff... more The fabrication of high aspect ratio metallic nanostructures is crucial for the production of efficient diffractive X-ray optics in the hard X-ray range. We present a novel method to increase their structure height via the double-sided patterning of the support membrane. In transmission, the two Fresnel zone plates on the two sides of the substrate will act as a single zone plate with added structure height. The presented double-sided zone plates with 30 nm smallest zone width offer up to 9.9% focusing efficiency at 9 keV, that results in a factor of two improvement over their previously demonstrated single-sided counterparts. The increase in efficiency paves the way to speed up X-ray microscopy measurements and allows the more efficient utilization of the flux in full-field X-ray microscopy.

Este documento analiza los determinantes que afectan la decisión de invertir por parte de una fir... more Este documento analiza los determinantes que afectan la decisión de invertir por parte de una firma, y en qué grado hacerlo, por lo que se examinan las principales teorías microeconómicas de la inversión, sin dejar de lado los aspectos macroeconómicos que afectan esta decisión. Con la intención de contrastar empíricamente estas teorías, se estimó un modelo de datos panel, con

Ultramicroscopy, 2009

Further progress in the spatial resolution of X-ray microscopes is currently impaired by fundamen... more Further progress in the spatial resolution of X-ray microscopes is currently impaired by fundamental limitations in the production of X-ray diffractive lenses. Here, we demonstrate how advanced thin film technologies can be applied to boost the fabrication and characterization of ultrahigh resolution X-ray optics. Specifically, Fresnel zone plates were fabricated by combining electron-beam lithography with atomic layer deposition and focused ion beam induced deposition. They were tested in a scanning transmission X-ray microscope at 1.2 keV photon energy using line pair structures of a sample prepared by metal organic vapor phase epitaxy. For the first time in X-ray microscopy, features below 10nm in width were resolved.

$Research paper thumbnail of High-Resolution Scanning X-ray Diffraction Microscopy$

Science, 2008

Coherent diffractive imaging (CDI) and scanning transmission x-ray microscopy (STXM) are two popu... more Coherent diffractive imaging (CDI) and scanning transmission x-ray microscopy (STXM) are two popular microscopy techniques that have evolved quite independently. CDI promises to reach resolutions below 10 nanometers, but the reconstruction procedures put stringent requirements on data quality and sample preparation. In contrast, STXM features straightforward data analysis, but its resolution is limited by the spot size on the specimen. We demonstrate a ptychographic imaging method that bridges the gap between CDI and STXM by measuring complete diffraction patterns at each point of a STXM scan. The high penetration power of x-rays in combination with the high spatial resolution will allow investigation of a wide range of complex mesoscopic life and material science specimens, such as embedded semiconductor devices or cellular networks.

Review of Scientific Instruments, 2011

X-ray phase-contrast radiography and tomography enable to increase contrast for weakly absorbing ... more X-ray phase-contrast radiography and tomography enable to increase contrast for weakly absorbing materials. Recently, x-ray grating interferometers were developed that extend the possibility of phase-contrast imaging from highly brilliant radiation sources like third-generation synchrotron sources to non-coherent conventional x-ray tube sources. Here, we present the first installation of a three grating x-ray interferometer at a low-coherence wiggler source at the beamline W2 (HARWI II) operated by the Helmholtz-Zentrum Geesthacht at the second-generation synchrotron storage ring DORIS (DESY, Hamburg, Germany). Using this type of the wiggler insertion device with a millimeter-sized source allows monochromatic phase-contrast imaging of centimeter sized objects with high photon flux. Thus, biological and materials-science imaging applications can highly profit from this imaging modality. The specially designed grating interferometer currently works in the photon energy range from 22 t...

Nature Protocols, 2006

Microcontact printing (lCP) of proteins has been successfully used for patterning surfaces in var... more Microcontact printing (lCP) of proteins has been successfully used for patterning surfaces in various contexts. Here we describe a simple 'lift-off' method to print precise patterns of axon guidance molecules, which are used as substrate for growing chick retinal ganglion cell (RGC) axons. Briefly, the etched pattern of a silicon master is transferred to a protein-coated silicone cuboid (made from polydimethylsiloxane, PDMS), which is then used as a stamp on a glass coverslip. RGC explants are placed adjacent to the pattern and cultured overnight. Fluorescent labeling of the printed proteins allows the quantitative analysis of the interaction of axons and growth cones with single protein dots and of the overall outgrowth and guidance rate in variously designed patterns. Patterned substrates can be produced in 3-4 h and are stable for up to one week at 4 1C; the entire protocol can be completed in 3 d.

Nature Communications, 2012

The high photon flux and femtosecond pulse duration of hard X-ray free-electron lasers have spurr... more The high photon flux and femtosecond pulse duration of hard X-ray free-electron lasers have spurred a large variety of novel and fascinating experiments in physical, chemical and biological sciences. many of these experiments depend fundamentally on a clean, welldefined wavefront. Here we explore the wavefront properties of hard X-ray free-electron laser radiation by means of a grating interferometer, from which we obtain shot-to-shot wavefront information with an excellent angular sensitivity on the order of ten nanoradian. The wavefront distortions introduced by optical elements are observed in-situ and under operational conditions. The source-point position and fluctuations are measured with unprecedented accuracy in longitudinal and lateral direction, both during nominal operation and as the X-ray free-electron laser is driven into saturation.

Nanotechnology, 2011

Extreme ultraviolet (EUV) lithography is currently considered as the leading technology for high-... more Extreme ultraviolet (EUV) lithography is currently considered as the leading technology for high-volume manufacturing below sub-20 nm feature sizes. In parallel, EUV interference lithography based on interference transmission gratings has emerged as a powerful tool for industrial and academic research. In this paper, we demonstrate nanopatterning with sub-10 nm resolution using this technique. Highly efficient and optimized molybdenum gratings result in resolved line/space patterns down to 8 nm half-pitch and show modulation down to 6 nm half-pitch. These results show the performance of optical nanopatterning in the sub-10 nm range and currently mark the record for photon-based lithography. Moreover, an efficient phase mask completely suppressing the zeroth-order diffraction and providing 50 nm line/space patterns over large areas is evaluated. Such efficient phase masks pave the way towards table-top EUV interference lithography systems.

Journal of Synchrotron Radiation, 2007

A new type of diffractive X-ray optical elements is reported, which have been used as beam-shapin... more A new type of diffractive X-ray optical elements is reported, which have been used as beam-shaping condenser lenses in full-field transmission X-ray microscopes. These devices produce a square-shaped flat-top illumination on the sample matched to the field of view. The size of the illumination can easily be designed depending on the geometry and requirements of the specific experimental station. Gold and silicon beam-shapers have been fabricated and tested in full-field microscopes in the hard and soft X-ray regimes, respectively.

Journal of Synchrotron Radiation, 2005

It is demonstrated that X-ray beam positions can be extracted from twodimensional profiles with s... more It is demonstrated that X-ray beam positions can be extracted from twodimensional profiles with sub-pixel resolution. Beam-position measurements utilizing a self-designed low-cost two-dimensional detector have been performed at two synchrotron radiation beamlines of the Swiss Light Source. The effective detector pixel size was 4.8 mm and the resolution achieved for the beam position was about 5 nm. At a data rate of 25 frames per second, periodic variations of the beam position could be detected with a frequency resolution below 0.1 Hz. This allowed, for example, the influence of a turbo-pump in the X-ray optics hutch on the beam position to be quantified, and even minute variations related to the electron beam in the storage ring could be detected.