David Waldman, Ph.D., CUMIRP Director
David Waldman, Ph.D., CUMIRP Director
X rays - discovered by W.C. Rontgen in 1895 - have become established as an invaluable probe of the structure of matter. Progress in understanding the interaction between x rays and matter and of exploiting X rays experimentally has been increasing steadily since its discovery. In more recent times this has lead to unraveling the structure and morphology of compounds of increasing complexity like self-assembling molecular systems, including functional units of bio-organisms like DNA and proteins. MRSEC has funded within the Department of Polymer Science and Engineering an X-Ray Facility with several modern instruments for x-ray scattering (small, intermediate and wide angles), powder x-ray diffraction, and x-ray reflectivity studies of thin films.
SAXSLAB GANESHA 300XL http://saxslab.com/ganesha/
X-ray Scattering facility was substantially upgraded in late 2014 with the next-generation SAXSLAB GANESHA 300XL instrument, which
makes extensive use of synchrotron type tried and trusted motorization, neutron-type experimental approaches, as well as the latest
technology in networked instrument control and data analysis. The customized SAXSLAB Ganesha 300XL includes capability of interactively performing SAXS, MAXS, WAXS, GISAXS and Reflectometry on both isotropic and oriented samples, and is fully automated and remotely controllable, representing a true leap in x-ray scattering instrument user-friendliness and functionality.
The cooled hybrid pixel Dectris Pilatus 300K 2D CMOS photon counting detector (size 83.8 x 106.5 x mm2) is situated inside a large continuous vacuum chamber, where it can be controlled to adjust the distance between sample and detector. This allows for access to an unprecedented q-range, spanning both the very low q-range for extreme SAXS to standard WAXS range (q = 2E-3 Å-1 to ~4Å-1). The 3-axis motorized Dectris Pilatus detector, with 172 micron resolution and associated beam stop, delivers an unprecedented combination of low-noise, high dynamic range (very high maximum pixel count rate at 2 million counts per second per pixel), high spatial resolution, high detection efficiency at 8 keV, and extremely high resistance to radiation damage and deterioration.
The SAXSLAB GANESHA 300XL features a large spacious sample area allowing for a variety of sample environments and specialized measurement techniques, including a high performance thermal stage (Linkam -190 C to 300 C, for GISAXS, Sandwich Cells and Capillaries) for temperature control of solid, gel and liquid samples, including solution scattering in refillable capillaries at temperatures from -30 to 120°C, a motion controller with optically encoded automated motorized positioning of the sample stage and of selected samples inside its large continuous vacuum chamber, motorized control of multiple interchangeable beam stops in front of the detector, motorized pinholes with automated positioning and alignment for changing between different pinhole configurations and optimizing intensity in the beam, and a cooled Xenocs Genix 3D (Cu) 2nd Generation Microfocus X-ray Source with SAXS optic, with motorized x-ray filtering and insertable Pin-diode detector for recording beam intensity and transmission.
PANalytical X'Pert XRD http://www.panalytical.com/XPert3-MRD-XL.htm?product=Reflectivity
A Cu x-ray tube with a line source (focal spot 12x0.04 mm2) provides the CuKa line used at 0.1542 nm. No separation of Ka1 and Ka2.
In rest the power is left at 40kV x 20 mA; in operation it is set to 45 kV x 40 mA.
The scattering plane is vertical and the sample remains horizontal.
- Divergence slit 1/32°, limiting the height of the beam to h=75 mm. The width is about 20 mm.
- Cu 0.1 mm attenuator (factor 87.7) to reduce the direct beam (about 108 cps) to the maximum allowed at the detector (about 106 cps).
- Parabolic graded multilayer system (Göbel mirror) converting the divergent beam into an almost parallel beam (divergence ≤ 50 mdeg).
- Mask of 20/10/4/2 mm (usually taken as 10 mm) restricting the width of the beam at the sample position to 24/14/8/6 mm.
- Sample on Z-Tilt-Phi stage (centered). The angle between the incident beam and the sample surface is ω; 2Θ is the angle between the diffracted and the incident beam. Rotation angle φ is about the sample normal and Ψ is the tilt angle of the sample surface.
- Parallel-plate collimator (fixed to detector unit), restricting the residual divergence of the received beam in the vertical scattering plane.
- Soller slit: set of parallel plates that restrict the received beam (perpendicular to the scattering plane where the beam is divergent) to angles to ≤ 0.04 rad = 2.3°.
- Pre-detector slit 0.09 mm. Collimator slit defining the acceptance of the detector.
- Xe filled proportional counter with 8x26 mm2 rectangular window. For Cu radiation, the efficiency is 93%.
Types of Scan:
- Relative scans are over an angular range around the current instrumentation position.
- Scans can be made by changing either of the two relative goniometer axes (sample rotation ω, detector rotation 2Θ.
- The gonio scan is used for reflectivity; it moves both angles together with 2Θ at twice the value of ω at all times ( ω = Θ.
- For calibration and quick surveys, manual scans are used. These are just gonio-, ω-, or 2Θ scans.