Workshop on "X-ray Science with Coherent Radiation"

Focusing X-ray Beams to Nanometer Dimensions

C. Bergemann^1,*, H. Keymeulen², and J.F. van der Veen<sup>2

1</sup>Laboratorium für Festkörperphysik, ETH-Hönggerberg, CH-8093 Zürich, Switzerland

²Paul Scherrer Institut, CH-5232 Villigen, and ETH-Zürich, Switzerland
We address the question: what is the smallest spot size to which an X-ray beam can be focused? We show that confinement of the beam within a narrowly tapered waveguide leads to a theoretical minimum beam size on the order of 10 nm (FWHM), the exact value depending only on the electron density of the confining material. This limit appears to apply to all X-ray focusing devices. Mode mixing and interference can help to achieve this spot size without the need for ultra-small apertures.
^*Present address: Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 OHE, UK.

Magnetic Speckles from Nanostructures
K. Chesnel, M. Belakhosky, G. van der Laan, G. Beutier, A. Marty, F. Livet

ALS, LBNL

1 Cyclotron road, MS 7R0100, Berkeley, CA 94709

Ph: 510-495-2830; Fax: [phone]; [e-mail]

The recent development of Resonant Magnetic Scattering (XRMS) in the soft X-ray range provides increasing opportunities to study magnetic order and reversal processes in nanostructures. Indeed, besides the chemical selectivity and the polarization sensitivity, this technique gives the possibility to penetrate thin layer in depth and study the magnetic ordering at the nanoscopic scale. Moreover, the use of coherent light and 2D detection provides remarkable speckle patterns that are related to the local magnetic topology. Magnetic speckles have been recorded in a reflection geometry on two types of systems with perpendicular magnetic anisotropy: thin epitaxied FePd films with striped magnetic domains [1] and etched lines grating covered by Co/Pt multilayer [2]. The resulted images from FePd layers exhibit magnetic speckles with a strong intensity contrast, evidencing the high coherence of the incident light [3]. This coherence degree, close to 90%, results from the excellent beam quality and the use of a pinhole placed very close to the sample, thus opening possibilities to perform real space reconstruction. In case of CoPt lines, the scattering pattern presents a serial of sharp peaks related to the grating periodicity. In some specific demagnetized state, remarkable magnetic satellites appear in between the structural peaks, evidencing a tendency to antiferromagnetic order [2]. This scattering pattern is significantly modified when a magnetic field is applied on the system, perpendicularly to its surface. By following the signal variations through the whole magnetization loop, starting from the demagnetized point, one can observe antiferromagnetic satellites disappearing at the saturated state, then a wider magnetic signal appearing at the coercive point. This magnetic signal evolution gives information about the ordering and switching processes. In conclusion, these coherent XRMS

results performed with in situ magnetic field show rich possibilities to study local magnetic behavior in nanostructures and open the door to dynamic studies.

Poster Abstracts
[1] H.A. Durr and al., Science 284, 2166 (1999)

[2] K.Chesnel and al., Phys. Rev. B 66, 024435 (2002)

[3] K.Chesnel end al., Phys. Rev. B 66, 172404 (2002)

Single-Element Elliptical Hard X-Ray Micro-Optics
K. Evans-Lutterodt

Brookhaven National Laboratory

Using micro-fabrication techniques, we have manufactured two optics; a single element kinoform lens in single-crystal silicon with an elliptical profile for 12.4 keV (1Å) x-rays, and a Fresnel prism. By choosing to fabricate an optic optimized at a fixed wavelength, absorption in the optic can be significantly reduced by removing 2π phase-shifting regions, while maintaining phase coherence across the optic. This permits short focal length devices to be fabricated with small radii of curvatures, allowing one to obtain a high demagnification of a finite synchrotron electron source size. We present our first results from experiments at the National Synchrotron Light Source X13B beamline.
Research carried out at the National Synchrotron Light Source under DOE Contract No. DE-AC02-98CH10886.

A fast CCD camera for x-ray photon correlation spectroscopy and

time-resolved x-ray scattering and imaging
Peter Falus, Matthew A. Borthwick

Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139

Simon G. J. Mochrie

Departments of Physics and Applied Physics, Yale University, New Haven, CT 06520
It was widely recognized at the beamline proposal stage that one of the most exciting scientific opportunities o®ered by coherent X-ray sources is the possibility of carrying out x-ray photon correlation spectroscopy (XPCS) experiments. As increasingly challenging experiments are attempted and the demand for synchrotron beam time grows, in order to collect the most meaningful data most e±ciently, it is also essential to optimize the beam line optics, and the x-ray detection scheme. However, in contrast to the intensive e®ort to increase source brilliance and improve beam line optics, with a few notable exceptions, the development of x-ray detectors has often seemed a relatively neglected area. The purpose of this poster is to describe a new, inexpensive, fast, charge-coupled device (CCD)-based, x-ray area detector – the SMD1M60 – which we have implemented in the context of a research e®ort at beam line 8-ID at the Advanced Photon Source to carry out x-ray photon correlation spectroscopy (XPCS) experiments. The key feature of the SMD1M60 detector for XPCS experiments is that it permits us to continuously acquire images at full-frame data rates of up to 60 Hz and one-sixteenth-frame data rates of up to 500 Hz. While very fast the detector is photon counting, suppressing any detector noise. Thus, it is straightforward to acquire data with a time resolution of as little as 2 ms, and data from a considerably larger solid angle can

Poster Abstracts
be collected if a time resolution of 17 ms is acceptable. The much greater data rate possible with the SMD1M60 permits a 100 fold increase in the XPCS Signal to Noise Ratio in cases where sub-second time steps are called for. In addition, the SMD1M60 is based on an inexpensive, commercially-available CCD camera. It is also lightweight and conveniently transportable to the synchrotron. Beyond XPCS, because of the superior data rates possible, we expect that this detector may find application in time-resolved x-ray scattering experiments of all sorts, especially where the scattering is weak and diffuse. In addition, we have found it capable of collecting superior small angle x-ray scattering (SAXS) data.