Fourier-Transform Infrared Spectroscopy
We actually have 3 chambers incorporating IR spectroscopy, including our UHV-STM chamber and a new instrument that has a fully evacuated interferometer and mirror boxes (designed and constructed by Prof. Stephen Simpson of Oxford). Here we detail our primary instrument with its focus on Fourier-transform infrared (FTIR) spectroscopy for measuring surface vibrations. Vibrational spectroscopy is carried out using a Mattson Galaxy 6020 FTIR (0.25 cm-1 resolution) spectrometer for infrared studies of samples over a large pressure range of 10-9 torr to atmospheric pressure, using an ultrahigh vacuum (UHV) compatible and isolable reaction cell The FTIR spectrometer has an option for sending the excitation output through an external path to a sample, which in our experiments is in a reaction chamber coupled to the UHV chamber, and to an external detector. The optics were constructed to enable both reflection (FT-IRAS or FT-RAIRS) and transmission (FT-ITAS) modes of operation. The reflection mode is applicable for primarily metal and non-transparent substrates. The transmission mode can be used for substrates transparent to infrared radiation, including insulators such as LiF and MgO, and thin films of molecular solids deposited on these substrates. Either mode provides for high resolution vibrational spectroscopy of molecules with very high sensitivity, sufficient to probe surfaces and adsorbates at monolayer concentrations. The transmission mode can also be used to gain information about the orientation of infrared-absorbing molecules through the use of polarized infrared radiation.
An important feature of our system is the high pressure reaction/pretreatment cell incorporating a sample holder and transfer system which was designed to move the sample between the FTIR analysis region and the UHV chamber. This analysis chamber incorporates equipment for other surface analysis techniques, including AES, rear-view LEED, and TPD.