Pure beams of free radicals for studies of radical-surface chemistry

Free radicals, molecules with one or more unpaired electrons, are highly chemically reactive. This high reactivity means that free radicals exert a major influence on the chemistry of any environment in which they are formed, even though they are often not the most abundant species. For example, it is free radical chemistry that controls important atmospheric phenomena such as the ozone hole and the formation of photochemical smog.
The interactions of free radicals with surfaces are thought to be vitally important in controlling the chemistry of formation of thin-films from electrical discharges, so called plasma-assisted deposition. Such thin-films have enormous technological importance in fields such as integrated circuits and solar cells. However, the details of the interactions of the radicals with the surfaces in these film formation processes are not well understood. The major hurdle to investigating this surface chemistry of free radicals is that, currently, there is no general technique available to dose a surface with only the free radical of interest, for example CH. Current radical sources generate the radicals from a precursor gas (e.g. CH from C2H2) and the precursor gas molecules always outnumber the radicals. Thus if a surface was dosed from a conventional radical source, the precursor molecules would be the dominant species on the surface, making it almost impossible to study the interactions of the radical with the surface using standard surface science techniques.
In this application, we propose the development of a new source of free radicals which will generate "clean" beams of the radical species, uncontaminated by the precursor molecule. The source will work by generating negative ions (e.g. CH-), which can be mass selected to form a clean beam. The radicals are then generated from the negative ions by using a laser beam to knock off the electron. This photo-detachment of negative ions will yield a clean beam of the radical species of interest. Calculations given in the proposal show that a practical flux of free radicals can be generated by this methodology.
The clean beams of free radicals can then be used to dose the surface with the radical species, and the surface can be studied using the standard techniques of surface science to reveal the details of the radicals sticking and surface chemistry. We propose to develop the source and then use it to study the radical-surface interactions involved in three technologically important film deposition processes. The chemistry revealed by our investigations will dramatically improve our understanding of what is going on in these industrially relevant surface reactions and allow us to optimize and refine these deposition processes in the light of the chemistry that is occurring.

In addition to the academic beneficiaries identified above, we have identified three groups of beneficiaries of the proposed research programme:
1) Industrial companies with interests in plamsa deposition.
The central aspect of this research proposal is the development of a new source for generating clean beams of specific radical species, beams uncontaminated by any precursor molecules, and the use of that beam to probe the radical-surface chemistry involved in the, industrially important, field of thin-film deposition from plasmas.
After developing and commissioning the radical beam source, we will use the beam to investigate the radical-surface chemistry relevant to thin-film generation in three industrially important systems: a-C:H, SiCN and Al-ZnO. The consequent improvement in our fundamental understanding (as evidenced by our Project Partners) will stimulate scientifically-founded improvements in the industrial processes. Of particular interest will be our adventurous experiments to investigate new methodologies from growing ZnO:Al films. Our experiments should reveal which chemical species involving aluminium (e.g. AlO) interact most effectively with the surface to generate, for example, layers of the metal.
The above arguments are validated by our Project Partners. For example Ionbond write "... it is essential that we move to a coherent design strategy based on fundamental process and materials understanding, which the current proposal can help to provide. The technique described will allow access to the details of the surface chemistry of free radicals, which are thought to be the critical chemical species in plasma assisted coating processes. It will also provide data of value for rationalizing observed behaviour and predicting improvements in industrially relevant surface chemistry."
2) UK employers
This programme involves the recruitment and training of 2 research workers; specifically 1 PDRA and 1 PhD student. As detailed in the proposal, the career history of previous research workers trained by the applicants shows that they go on to contribute to all spheres of the UK economy. For example, Jon Gingell (UCL PhD, 2004) has gone on to set up "OpenSymmetry", now a leading consulting and integration firm, co-Directed by James Perry (UCL PhD 2005), that offers highly specialized services focused on delivering Sales Performance Management solutions to clients worldwide (http://www.opensymmetry.com).
The employability of our research workers shows the broad appeal of the fundamental and applied skills that these individuals assimilate when involved with projects such as that proposed in this application. Clearly, the problem solving abilities, coupled with numeracy and communications skills, which are developed by research in physical and materials chemistry are highly desirable for successful careers in a broad range of disciplines which contribute to the UK's economy.
3) The general public
The applicants have extensive experience with Public Engagement. The proposed research programme offers an exceptional opportunity for public outreach to demonstrate the key position of the physical sciences, and its interaction with Industry, in the UK's research portfolio. As detailed in the proposal, all of the investigators will add to their portfolio of public outreach by developing a range of presentations (depending on the audience: school children, adults ...) on the role of radicals in the environment (atmospheric and interstellar chemistry, plasmas ...) focusing on the goals of the proposed experiment. The presentations will reveal the fundamental synergy between basic science and industrially-relevant science, as illustrated by the radical beam. A key objective of this programme of outreach would be to develop a display, on radicals and radical surface chemistry, for the Royal Society Summer Science Exhibition.