Electron Microscopy is an extremely versatile tool which allows the study of both morphology and material composition from virtually all areas of science and technology. The XRD instruments are used for studying the mineralogical composition of soils or sediments, but can also be used to investigate a very wide range of other materials.

Principal contacts for Mineralogy Analysis:

Electron Microscopy

The Electron Microscopy section has a Scanning Electron Microscope (SEM) fitted with an Energy Dispersive Spectrometer (EDS) for elemental analysis. High resolution Secondary Electron Imaging, Backscattered Electron Imaging, X-Ray microanalysis and X-Ray mapping are all possible. In addition, the SEM is equipped with a cryogenic stage allowing for the preservation of fluid phases in the samples, and analysis in situ if necessary.

A polarizing optical microscope fitted with a digital camera is also available for the analysis of thin sections of soil or rock.

Typical samples analysed by the Electron Microscopy Section include:

  • Biological (plants, fungi, bacteria, insects)
  • Geological (mineralogy, grain size, mineral relationships, porosity)
  • Fibres (glass, asbestos, natural, man made)
  • Powders and Dust.

Image of Secondary Electron Imaging
Secondary Electron Imaging

 A beam of electrons is scanned across the surface of the specimen; images are built up from low energy secondary electrons which reflect the topography of the sample. The benefits of SEM over conventional microscopy include very high resolution and greater depth of field at magnifications from x20 to x100,000.

Example image shows fungal hyphae of Telephora terrestris and a Nanhermannia sp. mite

Backscattered Electron Imaging

Image of Backscattered Electron Imaging

Backscattered electrons (BSE) provide an extremely useful signal for imaging in scanning electron microscopy as they respond to composition (atomic number or compositional contrast) and to local specimen surface inclination (topographic or shape contrast). BSE images obtained from flat polished surfaces reveal compositional changes due to variations in the average atomic number across the specimen.

Example image (right) shows a Dolomite-cemented sandstone.

X-ray Microanalysis

The electron beam is finely focused onto the specimen resulting in characteristic X-rays being produced from a microvolume (approximately 1µm3) of the sample. These X-rays are detected by an Energy Dispersive Spectrometer (EDS) and the results plotted as a spectrum.

Image from Secondary Electron Imaging

Each element has its own ‘fingerprint’ of peaks which allows both a qualitative and quantitative determination of the elements present in the selected region of the sample. EDS is an essential tool in geological applications combining elemental composition and morphology to identify minerals. It also has uses with biological specimens for example, localising elements such as calcium, potassium or phosphorus.

Example image (right) shows EDS spectrum of phosphorous-rich granules inside Telephora terrestris hyphae.

X-ray Mapping

Digital elemental distribution maps can be collected simultaneously with electron image acquisition thus giving a visual representation of the chemical distribution in the sample. X-ray mapping is performed using Position-tagged Spectrometry (PTS), a method whereby X-ray photons generated by the scanning electron beam are tagged with the position of their origin. From a PTS file, data can be extracted to form images, elemental maps and spectra. In PTS files a full spectrum is stored at each pixel, therefore additional elements can be mapped after the initial acquisition of the data.

Image of X-ray MappingIn this example (right) of sandstone the combination of various elemental maps allows to identify and visualise the distribution of minerals such as K-feldspar (silicon, aluminium, potassium), albite (silicon, aluminium, sodium) and dolomite (calcium, magnesium). The bright blue particles in the silicon map highlight quartz grains.

Instrumentation available

  • Carl Zeiss SIGMA VP Analytical Field Emission Scanning Electron Microscope
  • Image of the SEM

  • Bruker QUANTAX 400 Energy Dispersive X-ray Spectrometer with Xflash 5030 Silicon Drift Detector
  • Quorum Technologies PP2000T cryo-SEM preparation system
  • Leitz Polarizing microscope equipped with a Spot ‘Insight’ digital camera (Diagnostic Instruments, Inc.)

Contacts: Evelyne Delbos and Laura-Jane Strachan

X-ray Diffractometers

Image of the Siemens D5000

Our X-ray diffraction lab has two diffractometers, a Siemens D5000 and a Panalytical X-pert Pro, each with associated Bruker and Panalytical software along with the latest versions of the International Centre for Diffraction Data powder diffraction databases for phase identification.  The D5000 diffractometer is a theta/theta powder diffractometer. This means that the both the X-ray source and the X-ray detector move such that the sample remains horizontal.

The D5000 is equipped with a 40 position automatic sample changer and is fitted with a cobalt X-ray tube, filtered with a graphite monochromator.  It is sometimes advantageous to use cobalt radiation when examining samples to avoid the strong fluorescence that arises from the more common copper radiation when examining samples rich in Fe. The longer wavelength of cobalt radiation can also be useful if trying to measure or observe very low angle reflections that may arise from some mixed-layer clay minerals. The detector on the D5000 is a scintillation detector.

The Xpert Pro diffractometer has a variety of interchangeable stages and optics.  These include an Anton Par XRK 900 reaction chamber which is used for controlled humidity experiments and non-ambient diffraction at temperatures up to 900°C.  It also has a capillary stage that is used with an incident beam monochromator and is used for examining very small samples or samples which must be sealed form the atmosphere. 

The Xpert is fitted with a copper X-ray tube and uses an X-celerator position sensitive detector capable of very rapid data acquisition.  The XRD instruments are used for studying the mineralogical composition of soils or sediments, but can also be used to investigate a very wide range of other materials.

Surface area and porosity analyser

Photograph of the SA3100 Plus
Surface area and porosity are measured with a Coulter SA3100 Plus and associated software which has the ability to measure both adsorption and desorption isotherms. Essentially the SA3100 Plus automates the static volumetric method of gas adsorption measurement. Various different sample tube sizes are available to accept a variety of different sample types in powder or solid form.  Additionally, the lab is equipped with a Coulter SA-PREP six station auto outgasser for the simultaneous preparation of multiple samples. Surface area is a key parameter for understanding the behaviour of many materials and in our research we use it primarily to investigate soils and clay minerals.

Contacts for all instruments: Steve Hillier (Tel: +44 (0) 1224 395336), Ian Phillips (Tel: +44 (0) 1224 395356), Helen Pendlowski (Tel: +44 (0) 1224 395357).

Further information on some of the applications that these instruments are used for is also available on our consulting website Clays and Minerals.

The Institute also has an Infrared Section which you can read about on the chemical analysis page.