Site:University of Oxford
Department of Materials
Oxford OX1 3PH, United Kingdom
Date Visited: 16 October 1997
WTEC: R.W. Siegel (report author), C. Koch
The full day of 16 October from 9:30 to 15:30 was spent at the University of Oxford visiting the Head of the Department of Materials, Prof. Brian Cantor, and various other members of the Department. It was a very interesting visit, with much to hear about in the area of nanostructure science and technology at this prestigious university. An additional one-hour visit at the end of the day was made to a group of faculty from the Departments of Chemistry and Inorganic Chemistry, and the Physical and Theoretical Chemistry Laboratories. Although brief, the visit was quite effective, since it was held in a very informative roundtable format well organized by Prof. Malcolm L.H. Green and Prof. Paul Madden.
According to an initial overview of the University of Oxford and its Department of Materials presented by Prof. Cantor, the Department currently consists of about 330 people in total, with 20 academic staff and about 30 support staff, 80 research fellows and visitors, 80 postgraduate students, and the remainder undergraduate students. The Department's current annual research budget of ~£S 3 million, comes two-thirds from government and one-third from industry, with about 50% of this focused in nanoscale research activities. The research in general is quite broad-based and includes processing, characterization, and modeling activities in all classes of materials: metals, ceramics, polymers, semiconductors, and composites (see references list). The Department also houses the Materials Modelling Laboratory (Prof. David Pettifor, Director) as well as the Oxford Centre for Advanced Materials and Composites (Dr. Brian Derby, Director). In the important area of nanostructure characterization, the very impressive electron microscopy facilities here are particularly noteworthy, owing in part to the tradition left by Professor Sir Peter Hirsch, as are those in atom-probe field-ion microscopy. A series of visits with individual department staff ensued.
Dr. Patrick Grant reviewed the department's ongoing work in nanocrystalline sprayed coatings. This work utilizes a variety of spray processing methods including the Ospray process, electric-arc spraying, plasma spraying, and ink-jet spraying. He described some examples in more detail. For example, plasma spraying of titanium along with 100 µm diameter SiC fibers yielded multilayered structures with a matrix having a nanoscale substructure, owing to the rather stochastic process of oxide contamination. Work was planned to soon begin on spraying 600 nm diameter Al2O3 particles and 200 nm diameter SiC feedstock, as the research moved more toward the true nanoscale regime.
Dr. Amanda Petford-Long then described her work on nanolayered magnetic thin films. The primary focus of the work is on magnetic recording materials at the nanoscale. A significant collaboration is ongoing between Dr. Petford-Long at Oxford, Prof. Ami Berkowitz at UCSD, and Hewlett-Packard, Palo Alto, who together are funding three post-doctoral researchers in electron microscopy, band-structure modeling, etc., mainly on spin-valve materials. These are made by spraying multilayered films, such as NiFe/Cu/Co/NiFe/MnNi. Additional funding comes from small companies in the UK and the Science Research Council. Also described were unique capabilities for mapping local magnetization in devices using Lorentz transmission electron microscopy. They are also working on nanocomposite optical films, such as Bi nanoclusters in an amorphous Ge matrix, made by pulsed laser ablation techniques.
Dr. Kenya A.Q. O'Reilly then described her work on the nucleation of nanocrystalline secondary phases and the heterogeneous nucleation of droplets on matrix surfaces studied by TEM in various alloy systems. Melt spinning is used to produce composites of low and high melting point materials. The method is apparently limited to about 20 nm diameter particles, for example with Pb in Al. Melting (freezing) is observed via differential scanning calorimetry (DSC) at different cooling rates to examine kinetics. Studies of Al/Al3Zr sponsored by ALCAN have shown that small particles melt first and then interface regions. The excellent electron microscopy facilities in the Materials Department (consisting of ~ 14 instruments, presently) are used in this work. A new high-resolution FEG-TEM will be added in a few months to upgrade further these facilities.
Next, Dr. Alfred Cerezo and Dr. Paul J. Warren reviewed some of their current work involved with investigations of nanocrystalline and amorphous materials, mainly alloys, using atom-probe field-ion microscopy and high-resolution TEM. The position-sensitive atom-probe (PoSAP) field-ion microscope was pioneered in this group and represents the ultimate in combined structural and chemical nanoscale analysis, since it has atom-by-atom sensitivity. The instrumentation, through a technology transfer arrangement with the University, has been commercialized by Kindbrisk, Ltd., in Oxfordshire. A variety of phase decomposition studies are being carried out in order to develop an understanding of the mechanisms and effects of different such processes in nanocrystalline materials, including Al-based (high strength), Fe-based (soft magnetic), and Zr-based (high strength) alloys. Pulse electroplated Ni-Fe alloys have also been investigated because of their interesting increased hardness and improved magnetic properties.
Dr. Steve Roberts discussed the ongoing research in the Department on nanocrystalline ceramics and ceramic-matrix composites, the latter with Dr. Brian Derby. Most of this work is being carried out on the Al2O3/SiC system containing ~ 5% SiC particles, similar to the materials studied by Prof. Koichi Niihara in Osaka. The work is funded by BRITE/EURAM and the Engineering and Physical Sciences Research Council (UK) with some in-kind support from UK industry. Using 30-40 nm SiC particles well dispersed (intra- or inter-granularly) in 3-4 µm grain size Al2O3 yields a factor of 2 increase in strength (cf. the factor of 4 increase found by Niihara's group at Osaka), but a similar fracture toughness and 2-3 times greater wear resistance compared with conventional Al2O3. This material is found to be effective as a grinding medium, and good interactions with industry in the UK and abroad have resulted.
Dr. John L. Hutchison then discussed his work on supported metal catalysts and also on in situ high-resolution electron microscopy (HREM) observations of filling carbon nanotubes (multiwalled tubes now, but starting on single-walled tubes) with metals via reduction in the microscope. Dr. Hutchison is the director of the HREM facility, which has an environmental cell that has 0.25 nm resolution up to 20 mbar pressure and 500°C. He is also working on WS2 and other related fullerene-like sulfides and selenides in collaboration with a group at the Weizmann Institute. These are found to give excellent lubricity in oil suspensions, since they apparently roll and don't slide.
The WTEC team's next visit on a very busy and interesting day was with Prof. Peter J. Dobson, Department of Engineering Science, who described the wide range of activities in nanoparticles and nanocomposites in his Department, much of it done in collaboration with colleagues in the Departments of Materials and Chemistry. They create a variety of nanoparticles via several methods, including colloidal, aerosol, gel/aerosol, sputtering, gas evaporation, and electrochemical routes. These nanoparticles (e.g., CdS, CdSe, ZnS, Ag/ZnO, etc.) are generally dispersed in a matrix to make a "high technology" paint or coating with a specific functionality. For example, semiconductor quantum dots with narrow size distributions for use as light emitters are being dispersed in a glassy or polymeric matrix to develop new display technology. Surface capping of the nanoparticles is also being investigated in order to optimize and control their dispersion and properties.
Finally, the last hour of the visit was spent with a group of eight faculty from the Departments of Chemistry and Inorganic Chemistry and the Physical and Theoretical Chemistry Laboratories in an informative roundtable format that was well organized and briskly guided by Prof. Malcolm L.H. Green, Department Head, and Prof. Paul Madden. First, Dr. R.K. Thomas spoke of neutron scattering studies of interfaces, for example the surfactant layer at an aqueous/silica surface. The interaction appears to be independent of silica particle size down to 5 nm, the smallest size looked at. Next, Dr. C.D. Bain described nonlinear optical studies related to tribology, work on crystal growth, and dissolution, as well as confined molecules trapped between glass ("lens") surfaces. Dr. F. Marken then discussed his work on electrocatalysis using small particles, emulsions in aqueous media. Ab initio molecular dynamics simulations of Na clusters in zeolite Y were then described by Prof. Madden in terms of what the Na cluster looks like in the super cage after the sodalite cages are filled. Grain boundary migration in Na with symmetric tilt boundaries was also being simulated and could be followed for tens of picoseconds at two-thirds TM using a simpler molecular dynamics (MD) approach than Car-Parrinello with Kohn-Sham for materials, such as Na, with spherically symmetric bonding. Prof. H.A.O. Hill then presented his work on nanoelectrodes for sensor applications in which a different enzyme could be placed on each nanoelectrode. Profs. Dobson and Hill and others are now using carbon nanotubes with redox proteins in a tube of 3 nm radius for such sensors. Results of a new project on nanostructured polymers was then described by Prof. R.G. Denning in which one-, two-, and three-dimensional nanostructures were being created using optical interference methods. It is planned to fill the ordered voids created in these polymers with TiO2 or other high refractive index materials. Prof. M.L.H. Green then spoke of his elegant results with filled carbon nanotubes opened by reduction with Nd2O3, FeBiO3, or MoO3, for example. Dr. D. O'Hare ended this session with a discussion of mesoporous silicates used for nanochemistry with organometallic catalysts. The general issue was then raised about funding for nanoscale science in the UK and, while EPSRC has an initiative in microstructure materials, it was felt that the monies were small and insufficient, with money for people and equipment easier to obtain than actual research support. It was perceived that even EPSRC is now being focussed toward "wealth creation" and the situation appears that it is not going to be getting better.
At the end of this long and interesting day, it was very clear that the time allowed could not possibly do justice to all of the excellent work being done on nanostructure science and technology at Oxford, and that an hour with the Chemistry Department could really at best only whet one's appetite.
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_____. 1997. Pressureless sintering and elastic constants of Al2O3-SiC "nanocomposites." J. of the European Ceramic Society 17:565-573.
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_____. 1994b. Supercritical drying of barium titanate alcogels. In Proc., Int. Symp. on Applications of Ferroelectrics.
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_____. 1997b. Lorentz transmission electron microscopy on NiFe/Cu/Co/NiFe/MnNi active spin valve elements. Appl. Phys. Lett. 71(14)(6 Oct.):2032-2034.
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_____. 1994b. Fabrication of PbS nanoparticles embedded in a polymer film by a gas-aerosol reactive electrostatic deposition technique. Advanced Materials 6(10):772-775.
_____. 1994. Uniform GaAs quantum dots in a polymer matrix. Appl. Phys. Lett. 65:189-91
Salata, O.V., P.J. Dobson, S. Sabesan, P.J. Hull, and J.L. Hutchison. 1996. Preparation of nanoparticulate CdS films suitable for opto-electronic device applications. Thin Solid Films 288:235-238.
Sloan, J., J. Cook, M.L.H. Green, J.L. Hutchison, and R. Tenne. 1997. Crystallization inside fullerene related structures. J. Mater. Chem. 7:1089-1095.
Sloan, J., J. Cook, J.R. Heesom, M.L.H. Green, and J.L. Hutchison. 1997. The encapsulation and in situ rearrangement of polycrystalline SnO inside carbon nanotubes. J. of Crystal Growth 173:81-87.
Wakefield, G., P.J. Dobson, Y.Y. Foo, A. Lonl, A. Simons, and J.L. Hutchison. 1997. The fabrication and characterization of nickel oxide films and their application as contacts to polymer/porous silicon electroluminescent devices. Semicond. Sci. Technol. 12:1304-1309.