Publications (16)47.08 Total impact
- [Show abstract] [Hide abstract] ABSTRACT: We report a projection phase contrast microscopy experiment using hard x-ray pink beam undulator radiation focused by an adaptive mirror system to 100–200 nm spot size. This source is used to illuminate a lithographic test pattern with a well-controlled range of spatial frequencies. The oscillatory nature of the contrast transfer function with source-to-sample distance in this holographic imaging scheme is quantified and the validity of the weak phase object approximation is confirmed for the experimental conditions.
- [Show abstract] [Hide abstract] ABSTRACT: We have studied the propagation of hard x rays in a planar x-ray waveguide with a sub-20 nm guiding layer. To optimize the transmission and to minimize absorption losses, a novel waveguide design based on a two-component cladding was implemented. Optimized transmission is achieved by placing an appropriate interlayer between the cladding and the guiding core. The experimental results along with simulations of field propagation show that high transmission values can be obtained in waveguide optics at parameters relevant for x-ray imaging. These are small beam diameters below 20 nm and the relatively long guiding length necessary for efficient blocking of multi-keV photon energy beams.
- [Show abstract] [Hide abstract] ABSTRACT: The present work focuses on the question of localizing single object by hard x-ray phase contrast projection imaging. The authors present a setup where an x-ray channel waveguide defines a “quasi-point source” used to illuminate and image an object in a highly coherent cone beam. Knife edge fluorescence scans revealed a beam diameter of 75 nm at a distance of 30 μ m behind the guide. The recorded image corresponds to an in-line hologram of the object which can be reconstructed numerically. Object translations and associated shifts in the hologram allow for the 10 nm localization accuracy.
- [Show abstract] [Hide abstract] ABSTRACT: Two dimensionally confining x-ray channel waveguide structures are fabricated and used for the delivery of nanoscopic x-ray beams. The waveguides can be combined with a high gain Kirkpatrick-Baez-prefocusing mirror system yielding hard x-ray beams with a cross section down to 25 nm (full width at half maximum). The incoming synchrotron x-ray beam is coupled in from the front side of the waveguide. Here we address the general design of the x-ray optical devices and their fabrication by e-beam lithography methods. (c) 2007 American Institute of Physics.
- [Show abstract] [Hide abstract] ABSTRACT: We present an off-axis holography experiment based on the coherent cone beams emitted from a pair of x-ray waveguides. A magnified off-axis hologram is recorded, from which the phase of the optical transmission function of a sample is obtained by digital holographic reconstruction. A spatial resolution of about 100 nm has been achieved at 10.4 keV photon energy. Spatial resolution is determined by the cross-sectional dimensions of the waveguide and could approach a fundamental limit of about 10 nm in future experiments. In addition, we propose a new experimental setup that might overcome this limitation.
- [Show abstract] [Hide abstract] ABSTRACT: We study the propagation of X-rays in very narrow slits or waveguides. The onset of waveguiding effects is estimated analytically and quantified by finite-difference field calculations. A critical thickness is given below which waveguiding effects have to be taken into account. Finally, we consider the transmission of the smallest possible slits i.e. planar single-mode waveguides.
- [Show abstract] [Hide abstract] ABSTRACT: A numerical method for calculation of the electromagnetic field in two-dimensionally confined x-ray waveguides is presented. It is based on the parabolic wave equation, which is solved by means of a finite-difference scheme. The results are verified by a comparison to analytical theory, namely, Fresnel reflectivity and the weakly guiding optical fiber.
- [Show abstract] [Hide abstract] ABSTRACT: The far-field diffraction pattern of a front-coupled planar waveguide supporting two guided modes has been measured using a white X-ray beam. Interference of the guided modes leads to a characteristic variation of the far-field diffraction pattern for different photon energies. The experiment verifies the predicted properties of the guided modes, shows that these modes superpose coherently, and demonstrates that the electromagnetic field downstream of the waveguide is significantly different from that expected for a hypothetical small slit of the same size.
- [Show abstract] [Hide abstract] ABSTRACT: A two-dimensionally confining x-ray channel waveguide structure is combined with a high gain Kirkpatrick-Baez prefocusing mirror system yielding a hard x-ray beam with a cross section of 25 x 47 nm(2) (FWHM). Unlike the previously employed resonant beam coupling scheme, the incoming beam is coupled in from the front side of the waveguide and the waveguided beam is no longer accompanied by spurious reflected or transmitted beams. The field distribution in the waveguide channel has been calculated numerically. The calculated transmission and far-field intensity pattern are in good agreement with the experimental results.
- [Show abstract] [Hide abstract] ABSTRACT: The propagation of X-rays in one-dimensionally confined waveguides is analyzed by means of finite-difference calculations based on the parabolic wave equation. We compare the numerical results to an analytical approach and investigate the transmission and coherence properties of a waveguide depending on its length and the number of guided modes corresponding to the guiding layer thickness.
- [Show abstract] [Hide abstract] ABSTRACT: Metal/MgO multilayers (metal of Fe, Ni80Nb20, and Ti) with bilayer periods in the range 1.2-3.0 nm have been prepared by pulsed laser deposition and characterized by both hard and soft-x-ray reflectometry. The interface roughness is found to be < or = 0.5 nm in all the samples and is nearly independent of the total number of deposited bilayers. The interface roughness, however, depends on the absolute thickness of the individual layers and increases from approximately 0.3 nm for a 3.0-nm period to approximately 0.5 nm for a bilayer period of 1.2 nm. The multilayers are found to be highly stable up to temperatures as high as 550 degrees C. The hard-x-ray reflectivity of the multilayers decreases for T > 300 degrees C, whereas the layered structure is stable up to 550 degrees C. The reflectivity in the water window region of soft x rays, lambda = 3.374 nm, was found to be 0.4% at an angle of incidence of approximately 54 degrees for multilayers with 60 bilayers at a period of approximately 2.1 nm.
- [Show abstract] [Hide abstract] ABSTRACT: A hard x-ray beam of photon energy E=12.5 keV has been focused by a Kirkpatrick–Baez mirror system and coupled into the front side of a single-mode x-ray waveguide. The beam dimensions of 3.8×2.5 μm2 in the focus of the mirror system have thus been reduced in one direction to 32 nm, corresponding to the guiding layer thickness of the waveguide. At the same time the waveguide acts as a coherence filter and leads to a well-defined intensity distribution with steep tails in the near- and far-field regions. The total flux transmitted by the waveguide exceeded 108 photons/s while no significant contributions of radiation transmitted through the absorbing waveguide cladding have been observed.
- [Show abstract] [Hide abstract] ABSTRACT: Ceramic–metal (MgO combined with Fe, Ti and Ni80Nb20) and polymer–metal (polycarbonate combined with Ag and Pd) nanocomposite multilayers were deposited at room temperature by laser ablation (at 248nm). The multilayers were characterized by X-ray reflectometry, infrared spectroscopy and transmission electron microscopy. In the case of MgO/metal multilayers, well-layered structures are produced down to layer periodicities of 1.2nm, necessary for tunneling magnetoresistance devices and X-ray mirrors in the water window. The interface roughness in the case of polymer/metal multilayers is found to be a strong function of the metal layer thickness and also the nature of the metal.
- [Show abstract] [Hide abstract] ABSTRACT: Pulsed laser deposition (PLD) is for many reasons a versatile technique. Since with this method the energy source is located outside the chamber, the use of ultrahigh vacuum (UHV) as well as ambient gas is possible. Combined with a stoichiometry transfer between target and substrate this allows depositing all kinds of different materials, e.g., high-temperature superconductors, oxides, nitrides, carbides, semiconductors, metals and even polymers or fullerenes can be grown with high deposition rates. The pulsed nature of the PLD process even allows preparing complex polymer-metal compounds and multilayers. In UHV, implantation and intermixing effects originating in the deposition of energetic particles lead to the formation of metastable phases, for instance nanocrystalline highly supersaturated solid solutions and amorphous alloys. The preparation in inert gas atmosphere makes it even possible to tune the film properties (stress, texture, reflectivity, magnetic properties ...) by varying the kinetic energy of the deposited particles. All this makes PLD an alternative deposition technique for the growth of high-quality thin films.
Göttingen, Lower Saxony, Germany
- • Institute for X-Ray Physics
- • Institute of Material Physics