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Young Investigator Group Nanoscale Solid-Liquid Interfaces

FTIR spectro/microscopy

FTIR_MXene - enlarged view

Operando FTIR monitoring of proton intercalation in Ti3C2Tx MXenes. Adapted from Lounasvuori et al, Nature Communications, 2023, 14 (1), 1322.

FTIR Spectroscopy

Fourier transform infrared spectroscopy (FTIR) is a well-established technique that benefits from lab-based setups, ease of use and relatively short acquisition times. FTIR is well suited for studying water since O-H bonds absorb strongly in the mid-infrared. In our group, we are particularly interested in probing the aqueous microenvironment at the interfaces of layered 2D materials, such as MXenes, during electrochemical cycling. With FTIR, we aim to characterise the hydrogen-bonding state of water that co-intercalates in the interlayer spaces of MXene as a function of cation and potential.

We have several FTIR spectrometers serving different purposes:

- a Bruker Alpha spectrometer for routine measurements of solid and liquid samples. The spectrometer is operated in the attenuated total reflection (ATR) mode and comes equipped with a diamond ATR accessory. The beam path is purged with dry air to minimise interference from atmospheric moisture and CO2.

- a Bruker Vertex 70v spectrometer for in-situ measurements. The spectrometer can be operated under vacuum to eliminate atmospheric interference, which is especially important when probing the vibrational modes of water molecules and hydroxyl groups. Several sample environments are available, including temperature control with range −190 to +250 °C (liquid cell down to −70 °C), humidity control, and electrochemical control. Fast data acquisition (up to 90 spectra/second) is made possible by a liquid-nitrogen cooled detector and rapid-scan capability. Measurement possibilities include: sample wheels for KBr pellets; transmission cell with gas and liquid feedthroughs; diamond ATR unit; home-made optical unit accommodating microstructured Si ATR crystals; spectroelectrochemical cells compatible with both diamond and Si optical units.

- a Bruker IFS 125HR spectrometer for high-resolution measurements. The spectrometer is operated under vacuum for best signal-to-noise ratio. Cryostats are available.

·       Spectrometer and sample compartment are in vacuum

·       High resolution of up to 0.001 cm−1 from 5cm−1 to 10000 cm−1

·       Temperature range from 5 to 300 K

·       Reflectance and transmission measurements

FTIR Microscopy

A Bruker Hyperion 3000 FTIR microscope equipped with various objectives serves for transmission and reflection mapping measurements of solid samples in the NIR to MIR spectral ranges with lateral resolutions in the 160 µm range. A temperature stage and microfluidic equipment is available. A photovoltaic mercury cadmium telluride detector is used to ensure maximum linearity of the detected signals.

Our group are also frequent users of the infrared beamline IRIS at BESSY II. A recent upgrade to this beamline saw the installation of a scattering-type scanning near field optical microscope (s-SNOM). By using broadband synchrotron light and an AFM probe that acts as an antenna, this technique enables FTIR measurements with a spatial resolution down to 10 nm, depending on the tip apex radius. We have already performed first measurements of individual MXene particles at this endstation, with further measurements planned.