Differential interference contrast X-ray microscopy with twin zone plates at ESRF beamline ID21 T. Wilhein, B. Kaulich, E. Di Fabrizio, F. Romanato, M. Altissimo, J. Susini, B. Fayard, U. Neuhäusler, S. Cabrini and F. Polack J. Phys. IV France, 104 (2003) 535-541 DOI: 10.1051/jp4:20030139