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Experimental Techniques
The majority of beamtime currently used is for spectromicroscopy experiments either in transmission or reflection mode, with mapping possibilities using the XY-stage of the microscope. There is also an available MTEC 300 detector for Photoacoustic Spectroscopy (PAS), with an additional micro-PAS detector currently being constructed for use with the IR microscope.
The Mid IR beamline has several accessories for the Bruker Hyperion microscope that allow for additional experimental techniques beyond simple transmission and reflection measurments. The figures below show some of the ones currently available, with brief descriptions of their purpose.
Figure 1: Attenuated Total Reflection (ATR) is one of the most used experimental techniques in traditional FTIR spectrometry. The Hyperion microscope on the beamline has the ability to attach an ATR objective with a Germanium internal reflection element (“prism”). This technique is suitable for measuring surface properties of samples as the penetration depth of the IR light is about 1 μm. The benefit of this technique is that sample preparation is very easy, as the sample is placed in direct contact with the internal reflection element. This allows for samples to be measured that are not easily made into mulls, or KBr disks.
Figure 2: Grazing Incidence Reflection (GIR) is used to measure atomically thin layers on surfaces. It works when the layer thickness is less than the wavelength of the incoming radiation. GIR is suited for when other traditional sample preparation techniques are not possible. It has been used for measuring self-assembled monolayers (SAMs) on metal surfaces, and other organic molecules absorbed on the surfaces of various metal and semiconducting substrates.
Figure 3: The available Hinds Photoelastic Modulator is suited for doing measurements on samples that exhibit differential absorption between s- and p-polarized light.
Figure 4: A liquid flow cell that allows for the solution to flow continuously during measurements.
Figure 5: A liquid sample cell has been designed that can be used with the microscope for transmission measurements that allows for highly accurate temperature control. The cell can operate from -10 °C to 100 °C, with ramping and cooling capabilities for time-resolved temperature dependent studies.
Figure 6: An Instec HCS601 sample holder for operation between -190 °C to 600 °C, with ramping and cooling capabilities for time-resolved temperature dependent studies.