Technology Description: |
The FT-IR laboratory at UiO MiNaLab is equipped with a state-of-the-art Bruker IFS 125HR Fourier Transform spectrometer that measures IR light transmitted through a material. 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 with range of 4 – 1 000 cm-1. Mid-infrared (MIR): water-cooled Globar source with range of 40 – 13 000 cm-1. Near-infrared (NIR) / visible (VIS): Tungsten lamp with range of 1 000 – 25 000 cm-1. |
Beam Splitters: |
Multilayer Mylar: range of 30 – 650 cm-1. KBr: range of 450 – 4 800 cm-1. CaF2: range of 1 850 – 14 000 cm-1. Quartz(II): range of 9500 – 25 000 cm-1. |
Detectors: |
DLaTGS (room temperature cooled): one for the MIR / NIR (370 -12 000 cm-1) and on for the FIR (10 – 700 cm-1). Mercury cadmium telluride (MCT) (Liquid nitrogen cooled): 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.* |
Technical Description: |
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. |