- FT-IR Spectrometers
The group is equipped with different Fourier-Transformed Infrared (FT-IR) spectrometers. The principle of FT-IR spectroscopy is based on the Michelson interferometer. Measurements between ~10 cm^-1 and 50000 cm^-1 are possible with suitable detectors and light sources.
The actual setups are :
- Bruker 113 (Temperature from 7K to 400K, UHV cryostat, High stability setup)
- Bruker 70v + Microscope
- Bruker 66 + Pressure setup
- Bruker 70V + 7T Magnet
- Time-Domain Spectrometer
For very low frequencies (1-100 cm-1, 0.03-3 THz, 0.12-12 meV) a Time-Domain Spectrometer (TDS) is available. TDS works by the excitation of a source by ultrafast femtosecond laser pulses. This excitation induces a current in the source which in turn emits terahertz radiation. The emitted pulse is collected in the detector that is triggered by the femtosecond laser pulse. By changing the delay between the THz and laser pulse on the detector it is possible to record the time variation of the electrical field of the THz pulse. Therefore the fourier transform of the signal embed both the frequency dependant amplitude and phase of the field.
A 4T (1.6T) superconducting magnet is available for reflective (transmission) measurements.
Ellipsometry has two advantages with respect to “classical” spectroscopic techniques. It is self-normalizing, meaning that no reference measurement has to be done and it provides directly both the real and imaginary parts of the dielectric function.
- Raman Spectrometer
Raman scattering is the inelastic scattering of photons by the lattice vibrations or other excitations in the system. The sample is illuminated with a laser beam through an optical microscope. Light from the illuminated spot is collected and only the dispersed light is sent to the detector.