Research Visit to Lawrence Berkeley Laboratory for Metal Oxide/Liquid Interfaces at the Advanced Light Source

There is currently a large research effort associated with alternative energy technologies. Light harvesting is one avenue that is being vigorously pursued, where the aim is to convert energy from the sun into either electrical power or to generate hydrogen as a portable fuel. Both routes require a catalyst to harvest the light, with titanium dioxide being a key model system. Near UV-light is absorbed in a process where electrons are promoted across the band gap of this semiconductor. The electrons and holes then travel to surfaces where they create electrical current and do some chemistry, such as reduce water to hydrogen. In the photovoltaic application, a dye at the surface of TiO2 also absorbs visible light, which leads to an increase in efficiency. The photovoltaics market is estimated to be worth US$600 billion by 2030, building from about US$20 billion in 2010. This is one reason why research on Energy, including solar is an EPSRC priority area.

Although the phenomenologies of light harvesting processes are well known, the details of the surface reactions are only now being revealed. What is known has been determined from experiments in the highly idealised conditions of ultra high vacuum. Experiments carried out in this project would examine the geometry of molecules related to dyes on the surface of TiO2, where the molecules are deposited from solution. The effect of the molecules on the electronic structure would also be monitored. These measurements are made possible by special instruments that employ synchrotron radiation to examine surfaces under liquid.

This project will impact on the public sector, commerce, other academics as well as the general public.

1. Public Sector
The project will serve to gain experience in the use of Resonant Inelastic X-ray Scattering (RIXS) and Ambient Pressure Photoemission (APPES) and NEXAFS (APNEXAFS). These are techniques that are currently being set up over a period of several years at the Diamond Light Source on the Harwell Science and Innovation campus, which is owned by the United Kingdom Atomic Energy Authority, the Science and Technology Facilities Council and the Health Protection Agency. The experience gained by PI and his group will be made available to the beamline scientists at Diamond through the extensive contacts of the PI.

2. Commercial Sector
Work carried out in this project is of close relevance to two projects in which the PI is currently engaged that involve commercial arrangements. One is through BioNano, a spin-off from the LCN that holds a contract with KAU on a water purification development project. The PI is a consultant on this project. The second is the recently funded European Union grant SMALL (Surfaces for Molecular recognition at the Atomic LeveL), which involves a swedish company European Nano Invest AB, a privately held nanotechnology investment company. The company are involved at a level where they provide guidance to the academic groups on development opportunities. This is enabled by regular meetings at the University sites, with an annual meeting of all the partners. Both projects will benefit from the new science that emerges in the ALS work.

3. Academic Sector
Potential users of the Inelastic X-ray Scattering (IXS) and Versatile Soft X-ray (VERSOX) beamlines at the Diamond Light Source will benefit from increased experience of the UK community in the use of Resonant X-ray Scattering (RIXS) and Ambient Pressure Photemission (APPES) and NEXAFS on a 3rd generation synchrotron radiation source. Theory groups doing total energy calculations of oxide surfaces in liquid environments will benefit since our results will provide a test of their methods. We have particularly strong links with the Michaelides group at UCL. This project will reveal details of the basic physics and chemistry associated with TiO2 light harvesting surfaces. It will inform the community working in photovoltaics about the bonding of dye molecules and it will inform the community working in photocatalysis about charge trapping centres and their effect on the surface chemistry. This will allow this community to design more efficient devices. It will also inform communities in related areas that work with metal oxide surfaces, such as in gas sensing and catalysis. Dissemination to the academic sector will employ the usual routes of presentations at conferences and publication in academic journals: the Nature group, PNAS and Physical Review Letters are some of the journals employed by the PI.

4. General Public
This project is attractive as a vehicle to engage with the public since it involves alternative energy development and it can be coupled to complementary work that involves process visualisation at the atomic level using scanning probe instruments. Our activities in this area will build on our previous experience with public engagement through a number of mechanisms. This will involve schools lectures as well as UCL lunch hour lectures, which are widely attended by the public. It will involve publicising our research wherever possible, on occasion to visiting politicians, writing articles for the popular scientific press, such as Nature. It will also involve a significant web presence making use of YouTube as well as web pages at the LCN site dedicated to this project.