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The IRM beamline has a Bruker Vis/IR Grazing Angle Objective (GAO, 15×) for grazing incidence analyses. This objective is specifically designed to analyse thin layers or films <1 µm thick that are deposited onto non-IR absorbing, reflecting surfaces e.g. highly polished metal slides (Au or Al) or indium tin oxide (ITO) coated glass, for example. GAOs increase the optical path length of a sample by essentially skimming the beam across the surface using high angles of incidence. This objective uses an incident angle of ~84° and shows excellent sensitivity down to monolayer thicknesses, particularly when used with polarised light, and good spatial resolution. The Bruker design relies on transflectance from the sample surface, effectively increasing the sample path length to again assist sensitivity, and uses a polariser in the IR beam; p-polarised light is polarised perpendicular to the surface of the sample and shows enhanced IR absorption when large angles of incidence are used.   Examples of samples grazing angle experiments:
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Time resolved spectroscopy (TRS) using a FTIR spectrometer offers the advantage of being able to monitor rapidly changing chemical or physical properties of a system in high temporal resolution (up to 65 spectra/sec using a 160 kHz scan velocity @ 16 cm-1). It allows for the simultaneous observation of the progression and/or decay of various chemical species during an event. The rapid scan experiments can be initiated by an external trigger, such as a change in voltage, which can be programmed into the rapid-scan method editor in OPUS, making it ideal for the observation of kinetic chemical changed induced by an electrochemical potential event, to provide an example, More information on rapid scan FTIR spectroscopy can be found on the Bruker website. |