The X-ray Analysis Facility of CMM is based on level two of the Chemistry building. It provides a range of X-ray techniques (XPS, XRD and SAXS) for studying chemical composition, nanometer-scale structure and crystalline phases in a range of materials.
POWDER X RAY DIFFRACTOMETER
X-ray Powder Diffraction (XRPD) uses X-rays to investigate and quantify the crystalline nature of materials. It is sensitive to the type of and relative position of atoms in a material as well as the length scale over which the crystalline order persists by probing length scales from approximately sub angstroms to a few nm and is sensitive to ordering over tens of nanometres. It can be used to: measure the crystalline content of materials; identify the crystalline phases present - including the quantification of mixtures in favourable samples; determine the lattice parameters of crystal phases and the length scales over which they persist (domain sizes). A similar technique can also be used to study preferential ordering and epitaxial growth of crystallites.
The samples for analysis are typically in the form of finely divided powders, but powder diffraction can also be obtained from surfaces, provided they are relatively flat, not too rough and the crystallites are isotopically averaged on the surface. The materials can be of a vast array of types, including inorganic, organic, polymers, metals or composites and the potential applications cover almost all research fields, e.g. metallurgy, pharmaceuticals, earth sciences, polymers and composites, microelectronics and nanotechnology. XRPD can also be applied to study the pseudo crystalline structure of mesoporous materials and colloidal crystals provided that the length scales are in the correct size regime.
CMM currently has two instruments for carrying out XRPD measurements:
· The Bruker D8 Advance MKII XRD is a versatile instrument and can measure in either divergent (Bragg-Brentano) or parallel-beam geometries. It has a 90 position magazine sample changer for high-throughput analysis, an energy discriminating 2D array detector to minimise fluorescent backgrounds (e.g. in Fe or Mn rich samples) and an automated knife edge to allow simultaneous measurements at low and high angles.
The instrument carries out the routine XRPD experiments and is run as in a service mode. That is, appropriately prepared samples are delivered by the clients after consultation with the instrument operator and the measurements are collected on behalf of the clients. Computers software and training are also available to clients to process data after its collection.
· The second instrument is the Rigaku Smartlab XRD (see below). Specialised XRPD experiments including those which need to be collected in capillaries in transmission geometery; insitu experiments requiring heating/cooling; or time resolved experiments are typically carried out on this instrument which is detailed below.
THIN FILM AND MICRO DIFFRACTION XRD
In addition to standard powder-averaged XRD it is possible to use X-ray diffraction to investigate the crystalline structure of films and non-isotropic samples. Examples of such investigations include the determination of the oThirientation of crystallites at surfaces (e.g. in epitaxial growth experiments), grazing-incidence diffraction measurements from thin films and studying superlattice structures.
X-ray reflectometery (XRR) can be used to study non-crystalline layers on substrate materials to probe the nano-scale structure perpendicular to a surface of the substrate.
Microdiffraction is a techniques which allows diffraction measurements to be carried out selectively on small areas. This method is essential for materials which are too small to be measured in a traditional X-ray diffraction beam or where mapping of the sample is required.
The Rigaku Smartlab is a highly versatile XRD instrument and which features a 9 kW Cu rotating anode source; a variety of collimation options including 2 and 4 bounce Ge-Monochromators for HRXRD and capillary optics for micro diffraction; a cryo-stream (capillary/transmission optics only) that allows XRPD measurements from ca. 90 K to 600 K; a 5 axis goniometer, a domed furnace (reflectance geometry) that allows XRPD measurements from ambient to 1100 °C; and a two-dimensional hybrid pixel array detector. It can be configured to carry out a wide range of experiments on a wide range of sample types including: XRR measurements, in-plane and out-of-plane GI diffraction, texture analysis, reciprocal space mapping, HRXRD, microdiffraction and 2D mapping of samples.
To determine if experiments and/or samples are suitable in this instrument it is recommended that you contact the facility manager.
Small-angle X-ray scattering (SAXS) is used to measures the elastic scattering from a material over an angular range of ca. 0.05 – 5°. These scattering profiles can be used to determine information about the sizes and shapes of, and the distance between, these structures. The ranges of sizes or distances that can be determined are typically on the order of a few to tens of nanometers (maximum for our instrument is around 50 nm) and the samples can be liquid or solid in nature.
Typical examples of the types of information that can be determined include measurements of: the size and shape of nanoparticles, polymers, proteins or micelles in solution; measurements of pore size and interpore spacing in mesoporous materials; characteristic length scales in partially ordered systems, e.g. block copolymers composites and gels; and interparticle interactions in colloidal dispersions. Hence SAXS has many applications in the fields of structural biology, chemistry, physics and engineering and sample types: e.g. polymers, pharmaceuticals, cosmetics, foods, catalysts, coal, membranes, and proteins.
The SAXS instrument within CMM is an Anton Paar SAXSess which is equipped with both CCD and image plate detection. The system uses a sealed X-ray tube and a Kratky camera (i.e. line collimation) which allows for the detection of dilute or weakly scattering systems. However in this geometry the systems must be isotropic in nature (i.e. not oriented). Currently we are able to measure a variety of sample types including liquid dispersions, films and finely ground powders over a range of temperature; ca. -20 – 100 °C, depending on the nature of the sample.
X-ray Photoelectron Spectroscopy (XPS), also known as ESCA - Electron Spectroscopy for Chemical Analysis, is a non-destructive technique which provides chemical analysis of the outermost 5 - 10nm of any vacuum compatible solid. The sample is illuminated with monochromatic X-rays which have sufficient photon energy to cause the photoemission of the core level electrons whose binding energies are characteristic of the elements present. The position and intensity of the peaks provide both chemical (e.g. oxidation state) and quantitative (> ~0.1 atom %) information for all elements except hydrogen. Underlying layers can be examined by the use of XPS in conjunction with argon-ion bombardment providing elemental depth information due to the destructive nature of the ion bombardment.
The X-ray analysis facility is equipped with a state of the art Kratos Axis Ultra photoelectron spectrometer which uses mono Al Kα (1486.6eV) x-rays with the following capabilities:
- Sample sizes up to 2cm in diameter and up to 10mm thick
- Load lock for fast sample interchange
- Precision auto stage for multiple unattended sample analysis
- Depth Profiling for multilayered thin film analysis
- Variable angle sample orientation- angular dependent XPS
- Sample heating (600C) and sample cooling (-150C)
- Elemental imaging (min 200 µm x 200 µm) on selected samples
- Small spot analysis (min 27µm) on selected samples
Casa XPS data processing software is available for use within the facility by all CMM members.