NCMN Central Facility for X-Ray Structural Characterization / Crystallography
The NCMN X-Ray Characterization Facility is dedicated to materials identification and characterization through non-destructive, X-Ray Diffraction (XRD) technique. The following equipment is utilized: (1) Bruker-AXS D8 Discover High-Resolution Diffractometer; (2) Rigaku D-Max/B Horizontal Q/2Q X-Ray Diffractometer (with normal and small angle goniometer).
Powder X-Ray Diffraction
High Resolution X-Ray Diffraction
Bruker-AXS D8 Discover High-Resolution Diffractometer
This recently acquired system is a state-of-the-art machine including HI-STAR area detector, centric 1/4-circle Eulerian cradle, domed hot stage, hi-flux in-plane hardware, laser/video sample-alignment system, Göbel mirror, V-groove Ge crystal monochromator, fine tilt stage, and dual-beam path analyzer module. The system can be configured for grazing-incidence in-plane XRD, grazing-incidence XRD, x-ray reflectivity, high-temperature XRD, high-resolution XRD (rocking curves, reciprocal space maps), texture (pole figures), residual stress, and microdiffraction and capillary diffraction.
Rigaku D/Max-B Diffractometer
X-Rays are produced by a 2 kW, copper target, sealed tubeor diffracted beam then converges (is “focused”) into a diffracted beam monochromator which removes all radiation except the Cu Ka wavelength (about 1.544 Å) which then enters a scintillation counter. The sample and detector are rotated with respect to the incident beam at angles q and 2q, respectively. A typical XRD scan consists of a plot of detector angle (2q) vs. diffracted intensity. These diffractograms can be printed out or saved to disk in application-friendly ASCII format. Analysis can be carried out in the facility on any of 3 PCs equipped with qualitative and quantitative XRD software and access to the latest ICDD powder diffraction file database.
Most powder, thin-film, and bulk samples are acceptable. The sample holders can accommodate samples up to 30 x 30 x 10 cm in size (sometimes larger) with the 30 x 30 cm surface tangent to the diffracting circle. The amount of material needed for a diffraction pattern depends on the diffracting power of the sample and the type of analysis desired. For example, phase identification of a well crystallized powder, with small (< 40 mm) particle size, may only require 1 mg. or less.
Rigaku X-Ray Diffraction Laue Camera System
This instrument consists of a 2 kW, copper target X-Ray tube, a Polaroid XR-7 camera system, a manual goniometer with three rotational axes, and a movable platform. The camera uses film that is sensitive to x-radiation. The Laue x-ray diffraction method requires a continuous (white) spectrum of X-Ray which is what you get from an unfiltered, unmonochromatized X-Ray tube. The single crystal sample is fixed in position throughout the X-ray exposure with respect to the incident beam and the camera. Using this configuration, we obtain diffraction peaks (show as white spots on film) from many sets of crystal planes simultaneously because, although the geometry and d-spacing are different for each set of diffracting planes, there is a wavelength of radiation present for which the Bragg law is satisfied. The relative location of these spots on the film can be used to determine crystal structure and orientation. The system can be set up to allow transmission (sample between incident radiation and film) or back-reflection (film between sample and incident radiation Laue patterns)
The NCMN Central Facility for X-Ray Structural Characterization / Crystallography has been established to bring on-site small molecule crystal structure determination and analysis to UNL. Services provided include unit cell determinations, complete structure determinations, and collection of single crystal data for users to solve and refine themselves. A Bruker AXS SMART APEX instrument equipped with an Oxford Cryosystems 700 series Cryostream is used to collect the single crystal data. A Meiji stereo zoom microscope with polarizer attachment is used to select single crystal samples. A special fitting for the Meiji microscope allows a digital camera to photograph the crystals.
The facility holds licenses for the Bruker AXS software, including SMART, SAINT, SADABS, SHELXTL and XSHELL, as well as ATOMS and the Cambridge Structural Database (CSD). There are also many freeware crystallography programs which are maintained on the facility computers, such as PLATON and ORTEP. There are one Mac and 3 PC’s available in the facility for collecting data and performing structure determinations. The specialist is available daily for consultation and can provide advice on crystallization techniques or problems. The Bruker AXS SMART APEX CCD X-ray Diffractometer is equipped with a 4K Apex CCD detector, a Mo sealed-tube X-ray source, and MonoCap collimator, and an Oxford Cryosystems 700 Series Cryostream Cooler. The data collection temperature ranges from 80 to 400 K. The standard operating temperature is 120 K for materials that do not undergo phase transitions. Users are encouraged to communicate their preference for data collection temperature.
Data collection and structure determinations are performed on a first-come, first-serve basis. If you are preparing a highly unstable and possibly fleeting material, make arrangements ahead of time with the specialist. When a structure is considered final and complete, a CD will be written containing all pertinent data and distributed to the user who submitted the crystal. If users develop a later need for different pictures or new analysis of interactions, they should see the specialist with the archived CD in hand. A folder will be saved on your archive CD called FINAL. All pertinent files (.cif, .res, tables, ortep, etc.) will be saved in this folder.
You are responsible for safekeeping your own released data.
If you need to meet with the specialist, please visit the facility for questions and information.
Dr. Shah Valloppilly, Specialist
The Bruker AXS SMART APEX CCD X-ray Diffractometer.