The technique is used primarily for chemical identification of molecules from IR-active vibrations of their atomic constituents. Absolute quantification is possible when used in combination with certain techniques, e.g., secondary ion mass spectrometry.
FT-IR can also be used to investigate absorption arising from impurities (electronic or vibrational) and provides a contact-free probe for free-charge carriers. Notably, the IFS 125HR can achieve a spectral resolution of up to 0.0063 cm-1, which is necessary for resolving closely spaced ro-vibrational lines in gas phase spectroscopy.
The use of pre-aligned optical components, a permanently-aligned interferometer, and various sources, beam splitters, and detectors provides access to a wide spectral range: from the mid-IR (600 cm-1 = 16.7 µm = 74.3 meV) up to the visible (12 000 cm-1 = 833 nm = 1488 meV). Absorption originating from residual CO2 and H2O vapor in the instrument is suppressed by operating the spectrometer under vacuum (base pressure of < 0.02 hPa) or by purging the instrument with dry N2 gas.
The spectrometer is equipped with a Janis PTSHI-950-5 low vibration, pulse tube cryostat, which permits temperature-dependent measurements from room temperature down to 5.0 K with a typical stability of ± 0.01 K. The cryostat is equipped with ZnSe windows that complement the spectral range provided by the available sources, beam splitters, and detectors.
Sources
- Far-infrared (FIR) (water-cooled Hg lamp)
- Mid-infrared (MIR) (water-cooled globar source)
- Near-infrared (NIR)/visible (VIS) (tungsten lamp)
Beam splitters
- Multilayer Mylar (30 – 650 cm-1)
- KBr (450 – 4 800 cm-1)
- CaF2 (1 850 – 14 000 cm-1)
- Quartz(II) (9 500 – 25 000 cm-1)
Detectors
- DLaTGS (room temperature cooled) – one for the MIR/NIR (370 – 12 000 cm-1) and one for the FIR (10 – 700 cm-1)
- Mercury cadmium telluride (MCT) (liquid nitrogen cooled) – one mid-band (600 – 12 000 cm-1) and one broad-band (420 – 12 000 cm-1)
- Indium antimonide (InSb) (liquid nitrogen cooled) – 1 850 – 12 000 cm-1
- Indium gallium arsenide (InGaAs) (room temperature cooled) – high gain unit, 5 800 – 12 800 cm-1
- Silicon (Si) photodiode (room temperature cooled) – 9 000 – 25 000 cm-1
Note: the usable spectral range is determined by the exact combination of source, beam splitter, and detector used during the measurement. The IFS 125HR at UiO has an upper limit of ~17 000 – 18 000 cm-1 due to the use of gold mirrors.
Instrument Features
- Complete software control – Bruker’s OPUS software allows selection of the IR source, apertures, optical filters, sample channels, and detectors without breaking the instrument’s vacuum.
- Dry N2 purging – significantly reduces the amount of time required to vent and re-evacuate the instrument when swapping beam splitters.
- Advanced optics – easily incorporate additional optical elements, such as polarizers or cut-off filters, into the beam path.
- External illumination – sapphire windows mounted perpendicular to the IR beam path allows one to check the effect of external illumination on a material; e.g., the effect of above-bandgap illumination on charge carriers.
- Specialized sample holders – various holders available to accommodate crystalline samples of different sizes (5 × 5 or 10 × 10 mm2 preferred). Each holder can accommodate typically 6–8 samples, reducing the time required to exchange samples.
- Temperature-dependent measurements – sample cooling/heating in He exchange gas between 5 and 295 K using a LakeShore Model 335 temperature controller.
- Automatic data acquisition – custom-written LabVIEW code issues joint commands to the spectrometer, temperature controller, and sample positioner, allowing automated measurements of, e.g., multiple samples at pre-defined temperatures.
- Sample Limitations – Currently, samples are limited to bulk single crystal samples or thin films deposited on IR transparent substrates. Measurements of powders or liquids are not possible with our setup. Measurements of gas-phase samples should be discussed in more detail between the user and the lab responsible.
Prices
The FT-IR is available for rent with or without an operator. Prices are in Norwegian kroner (NOK) excl. VAT. All prices are subject to change.
| User Category | Price without operator/hour | Price with operator/hour |
|---|---|---|
| Academia | 500 NOK | 1250 NOK |
| Start-up | 625 NOK | 1725 NOK |
| Industry | 750 NOK | 1850 NOK |
The reduced fees for start-up companies are available for the first 24 months after start-up. Training costs are currently covered by NorFab.
Contact
- Simon Phillip Cooil, Lab Manager
- Eirini Zacharaki, Research Infrastructure Coordinator and FT-IR Lab Responsible