Characterisation

Contact Prof. Rik Brydson, Professor of Nanoscale Materials Characterisation

(i) High Spatial Resolution Imaging and Microanalysis

The macroscopic properties of many advanced materials and their relationship to processing parameters are often determined by microstructural features at the scale of nanometres, such as the structure and chemistry of second phases, grain boundaries, defects and surfaces. Leeds Electron Microscopy and Spectroscopy (http://www.materials.leeds.ac.uk/lemas website) (LEMAS) Centre is an integral part of materials research at Leeds and coordinates the characterization of engineering materials at this level. Microanalytical techniques employed may be divided into three main groups:

(i) Transmission Electron Microscopy and Spectroscopy - facilities in LEMAS include two 200 keV transmission electron microscopes (TEMs): a new FEI CM200 Supertwin field emission TEM plus energy dispersive X-ray (EDX) system and Gatan Imaging Filter (GIF) as well as a FEI CM20 LaB6 TEM plus EDX system. The former provides a high resolution imaging (2 Angstrom) capability combined with the ability to perform chemical analysis using EELS and EDX at a spatial resolution of 1 nm and energy filtered TEM (EFTEM) for mapping elemental distributions and bonding states. Both microscopes have in-situ heating/cooling capabilities and an ex-situ environmental cell for reaction studies. Dr Brydson is also a principal investigator in the £4.2 million Daresbury SuperSTEM project which will provide a sub-Angstrom probe for atomic resolution imaging and EELS.

(ii) Scanning Electron Microscopy - facilities in LEMAS include a new high resolution field emission SEM (LEO) plus EDX, a new environmental SEM (FEI) for in-situ studies, an electron microprobe (Cameca) for quantitative elemental analysis and three Conventional SEMs (CamScan) all fitted with EDX facilities and additionally a Cathodoluminescence detector and electron backscattered diffraction (EBSD) facilities for orientation imaging.

(iii) Surface Analysis - facilities in LEMAS include a VG EscaLab Mk 1 for Ultraviolet/X-ray Photoelectron spectroscopy (UPS/XPS), Auger electron Spectroscopy (AES) and Secondary Ion Mass Spectrometry (SIMS) of surface and sub-surface composition and chemistry. These are enhanced by integral ex-situ reaction cell facilities. Additional facilities include a Topometrix Atomic Force Microscope (AFM) for both dry and wet surface imaging and a microDTA facility for thermal imaging of surfaces.

These facilities are supported by extensive image analysis software (Kontron and Gatan Digital Micrograph) and specimen preparation facilities (Gatan, South Bay, Fischione).

Facilities have been extensively funded by HEFCE, EPSRC, Industry and the University.

Besides providing extensive expertise in the characterization of powders, glasses, ceramics, metals and alloys, polymers, catalysts, thin films, nanostructures and some limited biological specimens using the range of complementary techniques listed above, the LEMAS centre conducts fundamental research in the following areas:

(i) Extraction of localized chemistries and electronic structures from nanostructured solids, grain boundaries and defects using high spatial resolution EELS in the TEM.

(ii) High spatial resolution elemental and chemical state mapping using EFTEM.

(iii) Determination of pore size distributions in microporous solids and elucidation of atomistic structures using High Resolution Electron Microscopy (HREM) and associated image simulation.

Key Researchers:
Rik Brydson, Andy Brown, Andrew Scott, Eric Condliffe and Geoff Lloyd (Earth Sciences), John Harrington, Tony Nichells, Howard Daniels, Clair Calvert, Steve McBride, Fiona Loughran, Claudia Menini, Mohammed Ramzan, Manoch Naksata, George Lovely, Zabeada Aslam, Sarah Pan, Jon Earl, Ahmed Hussein.

Collaborators:
Max-Planck Institutes (Stuttgart and Berlin), CNRS Toulouse, NNTU Trondheim Norway, Lehigh University USA, University of Jena, Germany, University of Sheffield, University of Liverpool University of Cambridge, University of Oxford, University of Huddersfield, University of Surrey, University of Birmingham, ICI, Shell, BP.

Recent Project Areas funded by EPSRC and Industry:

• TEM/SEM of mechanically alloyed Ti-alloys.
• TEM/SEM/Surface analysis of stabilized zirconias.
• Synthesis/TEM/SEM of sintered chromia ceramics.
• TEM/SEM of vitreous chinas.
• EELS of minerals.
• EELS of graphitisation processes.
• TEM of liquid phase sintered alumina grain boundaries.
• TEM/SEM of metal/ceramic and carbon/ceramic composites.
• TEM/SEM/Surface Analysis of novel carbon alloys, fibres and tapes.
• TEM/SEM/Surface Analysis/Impedance Spectroscopy of ceramic gas sensors.
• TEM/SEM/Surface analysis of ferroelectric thin film devices
• TEM of environmental catalysts.
• TEM/SEM of ferrous alloys.
• TEM/SEM/Surface Analysis of biomaterial coatings

Three Key Publications:

• Microstructure and chemistry of intergranular glassy films in liquid phase sintered alumina. J. Am. Ceram. Soc. 81, 396-379 (1998).
• Growth of highly ordered carbon filaments during the catalytic hydrochlorination of chlorobenzene at 553 K, J. Phys. Chem B 104, 4281- 4284 (2000).
• Experimental and Theoretical Evidence for the Magic Angle in Transmission Electron Energy Loss Spectroscopy, Ultramicroscopy 96, 523, 2003.
• Synthesis of a New Boron Carbonitride with a B4C-Like Structure from the Thermolysis of N-Alkylated Borazines, Chem Comm. 7, 718-719 (2002).

(ii) Quantum Mechanical Modelling of Electronic Structures

Fundamentally all chemical and structural properties of solids are dependent on the electronic structure formed when the electronic energy levels of isolated atoms interact to form the energy bands associated the array of atoms found in either a crystalline or amorphous material. With increases in computing power, previously intractable problems involved with ab-initio calculations of solids such as the treatment large complex unit cell materials, doped materials, amorphous materials, surfaces, defects and homophase and heterophase interfaces between materials are now possible. Derived quantities include total energies, relaxed structures and both occupied and unoccupied densities of electronic states which may be directly compared with the results of microstructural characterisation studies using high spatial resolution imaging (HREM) and spectroscopic techniques (PEELS and UPS).

Electronic modelling techniques may be divided into three main groups:

(i) All electron band structure modelling using full linearized augmented plane wave (FLAPW) codes.

(ii) Pseudopotential band structure codes (CASTEP)

(iii) Multiple Scattering Green's Function methods (FEFF8 and ICXANES)

Key Researchers:

Rik Brydson, Andrew Scott, Andy Brown, Charlotte Dennis.

Collaborators:

Max-Planck Institutes Stuttgart, CNRS Toulouse, CNRS Paris, NNTU Trondheim Norway, University of Illinois at Chicago USA, University of Jena, Germany, University of Sheffield, University of Liverpool University of Cambridge, University of Oxford.

Recent Project Areas funded by EPSRC:

• Improved modelling of ELNES for Materials Characterization.
• Modelling of the ELNES of Interfaces and Defects using Multiple Scattering Calculations.
• Mechanisms of hydrothermal degradation in yttria-stabilized zirconias.

Three Key Publications:

• Band Structure of TiB2: Orientation dependent ELNES and the effect of the core hole at the B K-edge. Phys. Rev. B 59, 5361 (1999).
• Electron energy loss spectroscopic studies of copper/alumina interfaces grown by MBE. Phil. Mag A. 78, 439-465 (1998).
• A theoretical investigation of the ELNES of transition metal carbides for the extraction of structural and bonding information. Phys. Rev B 63, 245105 (2001).
• Electron Energy Loss Near Edge Structure - a tool for the inevstigation of electronic structure on the nanometre scale. J. Microscopy 203, 135-175 (2001).
  
• Electron Energy Loss Spectroscopy, Bios Publishers, Oxford. September 2001.