The Coherent X-Ray Scattering and Imaging Group

Our group is working in the field of Coherent X-ray Scattering and Coherent X-ray Diffractive Imaging (CXDI). The method is based on the following principle: if an object of finite size is coherently illuminated and its diffraction pattern is sufficiently sampled then it can be uniquely inverted (R. H. T. Bates, 1982) to obtain an image of this object. As no lenses are required in this imaging technique (therefore also known as lensless microscopy) it allows us, at least in principle, to overcome the resolution limits of conventional microscopy techniques and to obtain diffraction-limited images of a sample using phase retrieval techniques (R.W. Gerchberg&W.O. Saxton, 1972; J. R. Fienup, 1982; V. Elser, 2003). This idea was originally proposed by D. Sayer (1952) and has been developed by different groups around the world.

Figure 1a

Figure 1b

Fig. 1 (a) Truncated pyramid with a square base of 200 nm size. (b) Corresponding three-dimensional distribution of intensity in reciprocal space (from I. Vartanyants et al., Phys. Rev. B 77, 115317 (2008)).

In our group we are interested in the development (computational modeling) and the application of CXDI methods for imaging nano-systems (including nano-islands and quantum dots) and biological samples. As we require sources of coherent radiation, we use 3rd generation synchrotron sources including the European Synchrotron Radiation Facility (ESRF), the Swiss Light Source (SLS), or the first XUV Free Electron Laser (FLASH) at DESY in Hamburg.

Present members of the group:

Dr. Ivan Vartaniants (Senior Scientist)
Dr. Ruslan Kurta (PostDoc)
Dmitry Dzhigaev (PhD student)
Anatoly Shabalin (PhD student)
Oleg Gorobtsov (PhD student)
Ivan Zaluzhny (PhD student)
Max Rose (PhD student)

Former members of the group:

Roman Dronyak
Ulf Lorenz (now PostDoc, University of Potsdam)
Dr. Adrian Mancuso (now PostDoc, XFEL)
Dr. Olexander Yefanov (now PostDoc, CFEL)
Johannes Gulden (now, FH-Stralsund)
Andrei Singer (now PostDOc, UCSD)
Alexei Zozulya (now PostDoc, EMBL, Hamburg)
Andreas Schropp (now PostDoc, TU Dresden)

Recent publications:

1. G.J. Williams, M.A. Pfeifer, I.A. Vartanyants, and I.K. Robinson
''Effectiveness of iterative algorithms in recovering phase in the presence of noise'' Acta Cryst. A63, 36-42 (2007).

2. I. A. Vartanyants, D. Grigoriev, A. V. Zozulya,
"Coherent x-ray imaging of individual islands in GISAXS geometry", Proceedings of the 9th International Conference on Surface X-ray and Neutron Scattering, Taipei, Taiwan (2006) Thin Solid Films 515, 5546–5552 (2007).

3. R. Harder, M.A. Pfeifer, G.J. Williams, I.A. Vartanyants, and I.K. Robinson, ''Orientation variation of surface strain'', Phys. Rev. B 76, 115425 (2007).

4. I. A. Vartanyants, I. K. Robinson, I. McNulty, C. David, P.Wochner, and Th. Tschentscher,
''Coherent X-ray scattering and lensless imaging at the European XFEL Facility'', J. Synchrotron Rad. 14, 453–470 (2007).

5. I.A. Vartanyants, A.V. Zozulya, K. Mundboth, O. M. Yefanov, M.-I. Richard, E. Wintersberger, J. Stangl, A. Diaz, C. Mocuta, T.H. Metzger, G. Bauer, T. Boeck, M. Schmidbauer,
''Crystal Truncation Planes Revealed by 3D Reconstruction of Reciprocal Space'', Phys. Rev. B 77, 115317/1-9 (2008).

6. C. Mocuta, J. Stangl, K. Mundboth, T.H. Metzger, G. Bauer, I. Vartanyants, M. Schmidbauer, T. Boeck,
''Beyond the ensemble average: X-ray microdiffraction analysis of single SiGe islands'', Phys. Rev. B 77, 245425 (2008).

7. A.V. Zozulya, O. M. Yefanov, I.A. Vartanyants, K. Mundboth, C. Mocuta, T.H. Metzger, J. Stangl, G. Bauer, T. Boeck, M. Schmidbauer,
''Imaging of nanoislands in coherent grazing-incidence small-angle x-rays scattering experiments'', Phys. Rev. B Rapid Communications (2008) (in print).