Prof Andrew Horn - research
Vibrational Spectroscopy of thin films and interfaces. The study of interfaces between bulk (sold or liquid) materials and gases presents a difficult challenge to the experimentalist. The quantity of material in a monolayer adsorbed on a surface is of the order of 10^14 molecules per cm2 - many interfaces of interest have much less than this. I am particularly interested in the development of vibrational spectroscopic methods to interrogate interfaces of metals, oxides and functional materials. Current studies utilise attentuated total internal reflection infrared (ATR-IR) spectroscopy and, with colleagues in the Photon Science Institute, I am involved in the development of ultrafast vibrational sum-frequency spectroscopy (VSFS) for for a variety of applications in materials chemistry and catalysis.
Simultaneous mechanistic and kinetic studies of heterogeneous atmospheric chemistry on aerosol surfaces. Aerosol particles influence climate directly by scattering and absorption of light and indirectly through their role as cloud condensation nuclei and reaction substrates. In collaboration with colleagues in the Centre for Atmospheric Science, spectroscopic studies of organic and mixed organic/inorganic aerosols are performed in a custom-built aerosol flow tube (AFT) reactor fitted with an IR probe supported by on- and off-line analysis using mass spectrometry (ESI and CIMS) and chromatography (GC/MS and LC/MS). Our studies are aimed at the development of new experiments to follow the kinetics and mechanisms of aerosol chemistry alongside measurements of their evolving physical properties, both to inform atmospheric models and to develop a detailed physical understanding of the nature of the relevant transformations.
Transformations of thin films and interfaces. A thin film flow-tube apparatus with a surface sensitive IR probe based upon attenuated total internal reflection (ATR) is used to follow surface reactions from the analysis of vibrational spectra during variation of parameters such as relative humidity, temperature and reactive gas partial pressure. To date, this apparatus has been used to follow reactions on ices, atmospherically relevant salts and soot. An in vacuo version of the apparatus has also been constructed and used to follow the reactions of sulfuric and nitric acid (and their salts and hydrates), which are found in many parts of the atmosphere. Similar studies of the oxidation and photochemical conversion of organic electronic candidates are also being performed using ATR-IR.