A NEW APPROACH TO X-RAY HOLOGRAPHY WITH ATOMIC RESOLUTION

M. Kopecký¹, J. Fábry¹, J. Kub¹, E. Busetto², and A. Lausi²

¹Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Prague 8, Czech Republic
²Sincrotrone Trieste, S. S. 14 – km 163.5 in Area Science Park, 34012 Basovizza – Trieste, Italy

One of promising tools for studies of samples with perturbed translational periodicity or even without it (like "bad" crystals, small clusters of atoms and molecules, or even single viruses, proteins etc.) is a method of x-ray fluorescence holography (XFH) with atomic resolution [1-3], which allows direct imaging of close neighbourhood of a selected atom. However, mostly demonstration holography experiments on known and very simple inorganic samples have been carried out so far because of practical difficulties [3] of this technique.

Therefore, we have proposed the method of x-ray diffuse scattering holography (XDSH) [4,5], which overcomes most problems inherent to XFH. Namely, we have shown that anomalous x-ray diffuse scattering pattern (Fig. 1) is, in fact, a hologram providing full information on local environment of an anomalous scatterer (Fig. 2). Compared to standard x-ray fluorescence holography, these holograms provide following crucial advantages: (i) The anomalous signal (and hologram) intensity of 1-10% with respect to the background can be achieved by choosing a suitable pair of energies close to the absorption edge. It means improvement by more than one order of magnitude compared to the signal of XFH. (ii) The problem of virtual atoms does not exist in the case of centrosymmetric structures. Virtual images of atoms in non-centrosymmetric structures can be removed by recording an additional diffuse scattering pattern using the reverse direction of the incident beam. (iii)  Measured holograms of crystalline samples are not overlapped by numerous Kossel lines. (iv) The experiment is very simple and fast. Diffuse scattering patterns can be collected on a large position-sensitive detector in short exposures.

[1] A. Szöke in Short Wavelength Coherent Radiation: Generation and Application, edited by Attwood, D. T. & Boker, J. (American Institute of Physics, New York, 1986). p. 361.

[2]  M. Tegze & G. Faigel, Nature, 380 (1996) 49.

[3]  G. Faigel & M. Tegze, Rep. Prog. Phys., 62 (1999) 355 and references therein.

[4]  M. Kopecký, J. Appl. Cryst., 37 (2004) 711.

[5]  M. Kopecký, J. Fábry, J. Kub, E. Busetto & A. Lausi, Appl. Phys. Lett. (submitted).

Fig. 1  The hologram obtained as a difference of diffuse scattering patterns recorded at energies of 15.060 keV and 15.120 keV.

Fig. 2  Holographic reconstruction of Rb and Cl atoms in the plane parallel to the (001) crystallographic plane at z = 0.