Three macromolecular crystallography (MX) beamlines at the HelmholtzZentrum Berlin (HZB) are available for the regional, national and international structural biology user community. The state-of-the-art synchrotron beamlines for MX BL14.1, BL14.2 and BL14.3 are located within the low-section of the BESSY II electron storage ring. All beamlines are fed from a superconducting 7 T wavelength-shifter insertion device. BL14.1 and BL14.2 are energy tunable in the range 5-16 keV, while BL14.3 is a fixed-energy side station operated at 13.8 keV. All three beamlines are equipped with CCD detectors. BL14.1 and BL14.2 are in regular user operation providing about 200 beam days per year and about 600 user shifts to approximately 50 research groups across Europe. BL14.3 has initially been used as a test facility and was brought into regular user mode operation during the year 2010. BL14.1 has recently been upgraded with a microdiffractometer including a mini-goniometer and an automated sample changer. Additional user facilities include office space adjacent to the beamlines, a sample preparation laboratory, a biology laboratory (safety level 1) and highend computing resources. In this article the instrumentation of the beamlines is described, and a summary of the experimental possibilities of the beamlines and the provided ancillary equipment for the user community is given.

We report on a formalism for the calculation of diffusely scattered x-ray intensity from spatially inhomogeneous strain fields in Ge rich islands and in the surrounding Si matrix of SiGe/Si multilayers. The data analysis is based on a theory considering the two-dimensional statistical distribution of the dot positions, which allows a common formalism for both coplanar and grazing incidence scattering geometries. The strain fields were simulated based on the approach of the elastic Green function, taking the influence of the elastic strain relaxation at the sample surface into account. From these simulations the degree of relaxation of the islands was obtained, which compared very well with experimental data derived from x-ray reciprocal space maps. ͓S0163-1829͑98͒02736-2͔

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Vapor-deposited nanocrystalline titanium layers have been irradiated at room temperature with 350-MeV-Au ions up to 4x10;{15} Au/cm;{2}. Bombardment-induced texture changes were determined at the BESSY synchrotron light source. During off-normal irradiation, the nanocrystals undergo grain alignment and rotation up to approximately 90 degrees at the highest ion fluence. At the same time, the whole layer exhibits shear flow very similar to that observed previously in amorphous materials. Below 1x10;{15} Au/cm;{2}, a reversal of the ion incidence angle leads to a back rotation of the grains. These effects are absent or immeasurably small in coarse-grained titanium but have also been found in nanocrystalline TiN and NiO. The observations can be modeled by assuming that grain boundaries behave during ion bombardment like amorphous matter or by assuming a generation of disclination dipoles moving along grain boundaries.

We report on the exchange biasing of self-assembled ferromagnetic GeMn nanocolumns by GeMnoxide caps. The x-ray absorption spectroscopy analysis of this surface oxide shows a multiplet fine structure that is typical of the Mn 2+ valence state in MnO. A magnetization hysteresis shift |H E |~100 Oe and a coercivity enhancement ΔH c~7 0 Oe have been obtained upon cooling (300-5K) in a magnetic field as low as 0.25 T. This exchange bias is attributed to the interface coupling between the ferromagnetic nanocolumns and the antiferromagnetic MnO-like caps. The effect enhancement is achieved by depositing a MnO layer on the GeMn nanocolumns.

The ferromagnetic phase transition in a MnAs film on GaAs͑111͒, where the MnAs unit cell is epitaxially fixed in its hexagonal plane, proceeds under conditions qualitatively different from the transition in bulk MnAs crystals or in MnAs films on GaAs͑001͒. We present experimental evidence for the coexistence between ferromagnetic and paramagnetic phases in a temperature interval of 10°C. Temperature dependencies of the phase fractions and the in-plane lattice parameters obtained by grazing incidence x-ray diffraction are compared with magnetization measurements.

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