The knowledge of atomic and molecular structure is fundamental in physics, chemistry and biology. Therefore, it is not surprising that even today, scientists try to find new techniques for structural investigations. Lately a new method, atomic-resolution X-ray holography has emerged. It is based on the same principles as traditional holography with light: a coherent wave (called the reference wave) illuminates the object and the detector surface. The intensity modulation caused by the interference between the reference wave and the wave scattered by the object (called the object wave) is recorded. This interference pattern contains both the phase and the magnitude information of the object wave. Therefore the original wavefront can be reconstructed, giving the 3-D spatial arrangement of the objects.

In hard X-ray holography, the special feature which allows atomic-resolution is that the sources or the detectors of the hologram-forming waves are located within the sample: they are the individual atoms [1,2]. Based on the experience gained in the first two demonstration experiments [2,3], a setup was developed for synchrotron holographic studies. This work was done at ID32, ID18 and ID22 beamlines. Since there was no place in the world where this type of measurement were routinely done, even the different phases of the developments were significant scientific achievements. During this developmental phase several holograms were taken. Here, the holographic imaging of Co atoms in a CoO sample is shown as an example of what holography can give us. The quality of the data allowed the extension of the hologram to the full solid angle, using the measured symmetries. The extended hologram at 13.86 keV is shown in Figure 122.

In the reconstruction process the Helmholtz-Kirchhoff integral-transformation was used to obtain the 3-D real space image of the first two shells of Co atoms (Figure 123). It should be pointed out here that the resolution of this imaging is isotropic, and its value (0.5 Å) reached the diffraction limit. In contrast to previous measurements, the measuring time of a full data set took only a few hours. Further developments, i.e. the use of direct undulator radiation will reduce it to the minute range. This and other developments in the experimental technique and in the evaluation methods gives us hope that this novel method will be a useful tool for structural studies in the near future.

[1] A. Szöke, in Short Wavelength Coherent Radiation: Generation and Applications, AIP Conference Proc. No 147 ed D T Attwood and J Boker (New York: AIP), 361 (1986).
[2] T. Gog et al., Phys. Rev. Lett., 76, 3132, (1996).
[3] M. Tegze, G. Faigel, Nature, 380, 49, (1996).

Principal Publication and Authors
M Tegze (a), G. Faigel (a), S. Marchesini (b), M. Belakhovsky (b), A.I. Chumakov (c), Phys. Rev. Lett., 82, 4847, (1999).

(a) Research Institute for Solid State Physics and Optics, Budapest (Hungary)
(b) DRFMC-SP2M, CEA Grenoble (France)
(c) ESRF