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Scanning tunneling microscopy (STM) of oxide surfaces and thin oxide films to determine atomic scale structure and defects relevant to catalytic processes and nanotechnology. Investigation of patterned oxide surfaces for use as templates for molecular ordering. Investigation of hydrogen-bonded self-assembled molecular networks. Development of a sensor for the detection of low concentrations of gas-phase analytes.

The surface structure of SrTiO3 reconstructions
Professor M.R. Castell
Ever increasing miniaturisation of integrated circuit technology continues to be a critical capability for the microelectronics industry in order to increase functionality and fuel market expansion. One of the major challenges identified by the International Technology Roadmap for Semiconductors (ITRS) is the introduction of new materials into the manufacturing process. The purpose of the project is to investigate the surface reconstructions of SrTiO3 (001), (011), and (111), and determine their influence on the growth of silicon and a variety of metals. Atomic resolution imaging through scanning tunnelling microscopy (STM) is the main research tool.

Growth and spectroscopy of metallic nanoislands
Professor M.R. Castell
Nanometre sized metal islands on oxide supports are used in diverse applications from catalytic materials to gas sensors. Interaction between the oxide support and the islands, the island shape, the temperature dependence of island ripening, and molecular interactions with the islands are all active areas of study. The atomic structures of the islands are imaged with scanning tunnelling microscopy, and a variety of spectroscopic techniques are used to measure their electronic structure.

Optical resonances of oxide nanostructures
S. Rahman, Professor M.R. Castell
Crystalline oxides such as SrTiO3 have vast potential as a material to be integrated in the next generation of microelectronic devices. It has recently been discovered in Oxford that certain surface treatments of SrTiO3 produce atomic scale nanostructures by subtly changing the ratio of Ti to Sr in the surface region. This project investigates the quantum confinement of electrons in these nanostructures, similar to the particle in a box problem in elementary quantum mechanics. Atomic resolution scanning tunnelling microscopy is used to determine the size and distribution of the nanostructures, and spectroscopy techniques will show the degree of quantum confinement.

Growth of ultra-thin oxide films
X. Hu, Dr C. Wu, Professor M.R. Castell
This project is concerned with growth of BaTiO3 films with atomic level precision using Ba and Ti as elemental sources and single crystal Au and SrTiO3 as substrates. The films are being characterised with scanning tunnelling microscopy, electron diffraction, and electron and optical spectroscopies. Molecular adsorption on the films is also being investigated.

Scanning tunneling microscopy of nucleobase pairs on sulfide surfaces
O.Y. Shvarova, Professor M.R. Castell, Professor D.G. Fraser*
We are using scanning tunneling microscopy to investigate the self-assembly of nucleobases and base pairs on inert metal and sulfide surfaces. (*Earth Sciences)

SrTiO3 supported catalysts for carbon nanotube growth
J. Sun, Professor N. Grobert and Professor M.R. Castell.
We are investigating the possibility of using the ceramic oxide SrTiO3 as metal nanoparticle catalyst support for the growth of carbon nanotubes.

Nanostructures on the SrTiO3 (001) surface
Professor M.R. Castell
Atomically resolved scanning tunnelling microscopy of the SrTiO3 (001) surface reveals that certain treatments give rise to many types of self assembled nanostructures. The one dimensional structures type consists of perfectly straight lines that run in <100> directions and have a minimum separation of 2.4 nm. The other structures are dots that on closest packing form 2.4 nm x 1.6 nm arrays. It is proposed that both structure types are formed through nano-crystalline growth of non-perovskite TiOx phases on the surface. Further structural characterization and spectroscopy on these surfaces is currently being carried out.

7 public active projects

Selected Recent Publications:

Controlled growth of Ni nanocrystals on SrTiO3 and their application in the catalytic synthesis of carbon nanotubes.

J. Sun, C. Wu, F. Silly, A.A. Koos, F. Dillon, N. Grobert and M.R. Castell.

Chemical Communications, 49, 3748 - 3750 (2013).

Formation mechanism for a hybrid supramolecular network involving cooperative interactions.

M. Mura, F. Silly, V. Burlakov, M.R. Castell, G.A.D. Briggs and L.N. Kantorovich.

Physical Review Letters, 108, 176103 (2012).

Surface and defect structure of oxide nanowires on SrTiO₃.

M.S.J. Marshall, A.E. Becerra-Toledo, L.D. Marks and M.R. Castell.

Physical Review Letters, 107, 086102 (2011).

A homologous series of structures on the surface of SrTiO₃ (110).

J.A. Enterkin, A.K. Subramanian, B.C. Russell, M.R. Castell, K.R. Poeppelmeier and L.D. Marks

Nature Materials, 9, 245 - 248 (2010).

Shape transitions of epitaxial islands during strained layer growth: anatase TiO₂ (001) on SrTiO₃ (001).

M.S.J. Marshall and M.R. Castell.

Physical Review Letters, 102, 146102 (2009).

Surface of sputtered and annealed polar SrTiO₃ (111): TiO_x - rich (n x n) reconstructions.

B.C. Russell and M.R. Castell.

Journal of Physical Chemistry C, 112, 6538 - 6545 (2008).

C₇₀ ordering on nanostructured SrTiO₃ (001).

D.S. Deak, K. Porfyrakis and M.R. Castell.

Chemical Communications, 2941 - 2943 (2007).

Template ordered open-grid arrays of paired endohedral fullerenes.

D.S. Deak, F. Silly, K. Porfyrakis and M.R. Castell.

Journal of the American Chemical Society, 128, 13976 - 13977 (2006).

Bimodal growth of Au on SrTiO₃ (001).

F. Silly and M.R. Castell.

Physical Review Letters, 96, 086104 (2006).

Selecting the shape of supported metal nanocrystals: Pd huts, hexagons, or pyramids on SrTiO₃ (001).

F. Silly and M.R. Castell.

Physical Review Letters, 94, 046103 (2005).

Martin Castell's full publication list can be accessed here

*/** Development of an ultra-sensitive molecular detector
Professor Martin Castell

A DPhil (PhD) studentship is available to develop a novel ultra-sensitive sensor for the detection of low concentrations of explosives. The sensor is based on a network of conducting polymers optimised for high sensitivity and functionalised for selectivity. The student will be involved in a broad range of interdisciplinary activities from sensor design to testing. This studentship is funded by the Defence Science and Technology Laboratory (Dstl) and will involve collaborative work with the Dstl Explosives Detection Group based near Sevenoaks in Kent. The student will have regular contact with Dstl scientists, and whilst the majority of the work will be undertaken in Oxford, some research may be undertaken in Dstl's laboratories.

Candidates are encouraged to apply as soon as possible and will be considered on a rolling basis until the position is filled. This is a 3.5 year studentship that is funded by Dstl. It will cover all University and College fees as well as carrying an annual stipend of £15,500. Only UK or EU students will be considered for this position.

Any questions concerning the project can be addressed to Professor Martin Castell (martin.castell@materials.ox.ac.uk). Some information on the Surface Nanoscience research group is available on the website: http://users.ox.ac.uk/~stm/. General enquiries on how to apply can be made by e-mail to graduate.studies@materials.ox.ac.uk. You must complete the standard Oxford University Application for Graduate Studies and further information and an electronic copy of the application form can be found at http://www.ox.ac.uk/admissions/postgraduate_courses/apply/index.html. Further information about Dstl can be found at www.dstl.gov.uk

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Tailored nanocrystal catalysts
Professor Martin Castell

Currently, industrial catalyst nanoparticles used for pollution control and chemical processing are randomly dispersed on their supports with a large variety of sizes and shapes. Within this multi-billion pound industry the main research driver is to find ways of increasing the catalytic efficiency of the precious metals used such as Pt, Pd, and Rh, or increasingly alloys of various metals. One method is to increase the surface to volume ratio of the particles, and much effort has been directed towards that goal. Another method, proposed here, is to recognise that the crystal facets of the catalyst particles all have different chemical properties. This means that highly efficient catalysts can be created by synthesising particles with particularly large fractions of highly active crystal facets. One of the central aims of this project is to develop new processing routes to allow large-scale manufacture of shape and size selected metal and oxide nanoparticles with high catalytic efficiency.

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Studies of metal nanocrystals on Strontium Titanate
Professor Martin Castell / A I Kirkland

It is possible to grow a variety of metal nanocrystals on clean single crystal strontium titanate surfaces. Such particles often adopt novel morphologies which can be controlled and which may provide novel catalysts and gas sensors. For example, silver nanocrystals with fivefold symmetry have been observed, and palladium crystals have been shown to change their shape depending on the detailed atomic structure of the substrate.  This project aims to characterize these materials with atomic resolution, using both scanning tunnelling microscopy (STM) and transmission electron microscopy (TEM) in an attempt to understand their growth and structure.

Also see homepages: Martin Castell Angus Kirkland

Electrical conductivity through 2D polymer networks
Professor Martin Castell

In this project the electrical transport properties of conducting polymer networks are investigated. The polymers are connected via metal nanoparticle nodes. The long term aim is to use these networks to act as highly sensitive gas sensors. 

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Atomic structure and secondary electron emission
Professor Martin Castell

The most popular method for image creation in the scanning electron microscope (SEM) is to use the secondary electron signal. Until recently it was assumed that secondary electrons are emitted isotropically i.e. with no particular preferred direction, but we now know that the atomic structure of the surface does in fact play a role. This DPhil project is concerned with correlating secondary electron emission using an ultra high vacuum SEM with atomic structure imaged in a scanning tunnelling microscope (STM). Both these techniques are located on the same world-leading instrument in Oxford. The powerful combination of signals will provide a hitherto unexplored path into some very fundamental aspects of nanoscale surface structure.

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Quantum confinement in oxide nanostructures
Professor Martin Castell

Crystalline oxides such as SrTiO3 have vast potential as a material to be integrated in the next generation of microelectronic devices. It has recently been discovered in Oxford that certain surface treatments of SrTiO3 produce atomic scale nanostructures by subtly changing the ratio of Ti to Sr in the surface region. The aim of this DPhil project is to investigate the quantum confinement of electrons in these nanostructures, similar to the particle in a box problem in elementary quantum mechanics. Atomic resolution scanning tunneling microscopy will be used to determine the size and distribution of the nanostructures, and spectroscopy techniques will show the degree of quantum confinement. For this research a new state of the art microscopy/spectroscopy facility is available.

Also see homepages: Martin Castell

Growth and spectroscopy of metallic nanocrystals and clusters
Professor Martin Castell

Nanometre sized metal islands on oxide supports are used in diverse applications from catalytic materials to gas sensors. Interaction between the oxide support and the islands, the island shape, the temperature dependence of island ripening, and molecular interactions with the islands are all active areas of study. In this DPhil project a variety of transition metal clusters on single crystal oxide supports will be investigated. The atomic structure of the nanocrystals will be imaged with scanning tunnelling microscopy, and their electronic structure will be probed using optical spectroscopies.

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Molecular alloy crystals
Professor Martin Castell

The surfaces of a variety of nanostructured oxides can be used to order molecules, such as fullerenes (e.g. C60, C70), into specific two dimensional patterns. This is called templated molecular ordering. In this DPhil project fullerenes of different sizes will be mixed together to give rise to molecular alloys. Specific concentrations and relative sizes of fullerenes are thought to form ordered systems. The structure of these molecular alloy crystals will be studied at atomic resolution with scanning tunnelling microscopy.

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Hydrogen-bonded chiral supramolecular networks
Professor Martin Castell

In this project molecular networks are synthesized through self-assembly on metal and oxide surfaces. Scanning tunnelling microscopy is used to investigate their ordering. In particular, methods will be studied that influence the chirality (handedness) of the molecular arrangements.

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Strained layer epitaxy of oxide on oxide islands
Professor Martin Castell

We have recently done some innovative work on anatase TiO2 and BaTiO3 epitaxy on SrTiO3 (001). The results of both these streams of work indicate that there is plenty of scope to expand these efforts into a coherent programme related to oxide strained epitaxy. The idea is to grow thin oxide layers on oxide substrates that have a slight lattice mismatch. The strain that builds up in the oxide layer will then affect its electronic properties such as the bandgap. There is a strong foundation of strain induced electronic structure engineering in semiconductors, and this project is to expand these ideas into oxides.

Also see homepages: Martin Castell

Also see a full listing of New projects available within the Department of Materials.