Tour of the Laboratories
Dr Frank Dillon kindly let us have a look at his laboratory and talked to us about nanotubes and his work with them.
He joined the Nanomaterials Group in the Department of Materials, Oxford University in July 2008. He is a member of the Royal Society of Chemistry and of the British Carbon Group.
The addition of carbon nanotubes to ceramic or glass matrices has the potential to provide composites with novel properties but composites with a uniform dispersion of undamaged nanotubes have proved difficult to make. Dr Dillon’s work in Oxford has involved the production of nanotubes using aerosol assisted CVD which can be used to produce large quantities of clean nanotubes. These nanotubes were then coated with ceramic precursors and were characterised by XRD, HRSEM, Raman, HRTEM and TGA and their mechanical strength and thermal conductivity were also measured. Recent work has concentrated on the formation of transition metal based nanoparticles (NiP, CoO and Fe3O4) as catalysts for carbon nanototube growth. Also, he has worked to find a correlation between the magnetic properties and the synthesis parameters of iron-filled carbon nanotubes. This should enable one to optimise and tune the magnetic properties according to a specific application. He is also working on novel, fast and facile methods for the controlled synthesis of tungsten disulphide and other chalcogenide nanomaterials.
Chemical vapour deposition (CVD) is a chemical process used to produce high-purity, high-performance solid materials. The process is often used in the semiconductor industry to produce thin films. In typical CVD, the wafer (substrate) is exposed to one or more volatile precursors, which react and/or decompose on the substrate surface to produce the desired deposit. Frequently, volatile by-products are also produced, which are removed by gas flow through the reaction chamber.
Microfabrication processes widely use CVD to deposit materials in various forms, including: monocrystalline, polycrystalline, amorphous, and epitaxial. These materials include: silicon, carbon fiber, carbon nanofibers, fluorocarbons, filaments, carbon nanotubes, SiO2, silicon-germanium, tungsten, silicon carbide, silicon nitride, silicon oxynitride, titanium nitride, and various high-k dielectrics. CVD is also used to produce synthetic diamonds.
XRD stands for X-ray diffraction. X-ray crystallography is a tool used for identifying the atomic and molecular structure of a crystal, in which the crystalline atoms cause a beam of incident X-rays to diffract into many specific directions. By measuring the angles and intensities of these diffracted beams, a crystallographer can produce a three-dimensional picture of the density of electrons within the crystal. From this electron density, the mean positions of the atoms in the crystal can be determined, as well as their chemical bonds, their disorder and various other information.
HRSEM stands for high resolution scanning electron microscopy.
Raman spectroscopy is a spectroscopic technique used to observe vibrational, rotational, and other low-frequency modes in a system. It relies on inelastic scattering, or Raman scattering, of monochromatic light, usually from a laser in the visible, near infrared, or near ultraviolet range. The laser light interacts with molecular vibrations, phonons or other excitations in the system, resulting in the energy of the laser photons being shifted up or down. The shift in energy gives information about the vibrational modes in the system. Infrared spectroscopy yields similar, but complementary, information.
HRTEM stands for high resolution transmission electron microscopy
Thermogravimetric analysis or thermal gravimetric analysis (TGA) is a method of thermal analysis in which changes in physical and chemical properties of materials are measured as a function of increasing temperature (with constant heating rate), or as a function of time (with constant temperature and/or constant mass loss). TGA can provide information about physical phenomena, such as second-order phase transitions, including vaporization, sublimation, absorption, adsorption, and desorption. Likewise, TGA can provide information about chemical phenomena including chemisorptions, desolvation (especially dehydration), decomposition, and solid-gas reactions (e.g., oxidation or reduction).
Models of carbon allotropes
A bottle of carbon nantotubes
Information posters (sorry they are a bit blurred)
Dr Dillon explaining some of his work
Next stop the electron microscopes – transmission electron microscope
The above and following images are of a transmission electron microscope.
The sample holder
In the above picture the electron source of the TEM is at the top, where the lensing system (4,7 and 8) focuses the beam on the specimen and then projects it onto the viewing screen (10). The beam control is on the right (13 and 14)
Scanning electron microscopes
The sample holder
The next stop on our tour was to the Institute of Advanced Technology
Assia Kasdi, a DPhil student in Prof. Andrew Watt’s group, was on hand to show us around.
The objective of the group is to develop new materials and devices to generate energy or reduce consumption using colloid chemistry and vacuum deposition techniques. They are focused on a strong in-house connection between materials production and device realisation.
Ms Kasdi is working on metal nanowires.
Silver nanowire thin films are of interest due to the expense, high demand and limited supply of indium used in the industry standard transparent conductor tin doped indium oxide. The group has developed a thick coat metal nanowire composites with very high nanowire aspect ratios which form low density highly interconnected nanowire networks with low sheet resistances and good optical transparency. This work is the subject of a patent application and they have used them in their standard colloidal quantum dot device architecture with success. Current work is focused on replacing silver with a cheaper ternary alloy, developing printing methods and examining the use of electrochemical precursor sources to create flow type reaction systems for large volume production.
Ms Kasadi showing us some examples of her group’s work
In the image below Ms Kasadi is demonstrating the electrical properties of her nano samples.
Other areas of research
The above left image shows colloidal quantum dots and the above right image shows colloidal quantum dots irradiated with UV light. Different sized quantum dots emit different colour light due to quantum confinement.
A quantum dot is a nanocrystal made of semiconductor materials that are small enough to exhibit quantum mechanical properties. It ranges between 2 to 10 nanometers in diameter, which is equivalent to 50 atoms.
Quantum Dot Photovoltaics The power conversion efficiency of solution processed colloidal quantum dot (CQD) solar cells has increased from less than 1 to over 8% in the last 6 years. This topic has been the largest area of growth for the research group. Notable recent results include disentangling the nature of charge transport, designing novel device architectures, improving the electronic properties of thin films using core/shell nanoparticles and producing heavy metal free quantum dots.
Light Emitting Quantum Dots The group is exploring the synthesis of light emitting quantum dots for displays and lighting. The project aims to utilise the synthesis techniques developed to produce ternary and quaternary alloy and core/shell nanocrystals which are both heavy-metal and indium free. They are developing new materials and performing the initial device fabrication and hand over materials for large area deposition.