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Figure 1. The Seagull™ Variable Angle Reflection Attachment.
Variable angle reflection spectroscopy is becoming increasingly important. Certain samples such as powders, opaque substances, films on opaque substrates, and films on liquids are tedious or practically impossible to analyze with conventional transmission spectroscopic equipment. The analysis of such samples with reflection spectroscopy, however, is straightforward.
The Seagull™ is shown in Figure 1. Three mirrors (M1, M2, and M3) direct the beam to an ellipsoid (E1) that focuses the FT-IR beam onto the sample. The sample reflects the light onto a second ellipsoid (E2). Ellipsoid E2 reflects the beam from mirrors M4, M5, and M6 onto the detector of the spectrometer. Mirrors M3 and M4 are coupled to rotate together, in mirror image fashion. This directs the beam to and from different portions of the ellipsoids, changing the incident angle of the beam on the sample. This configuration automatically preserves the optical alignment for any selected angle of incidence.
The Seagull™ is ideal for examining surface and optical coatings, for measuring optical constants, and for liquid or electrochemical analysis with the appropriate cells. Sampling accessories are available for convenient sampling of a variety of types of samples. For ATR studies, the Seagull can be equipped with our ATR Kit. This kit includes a ZnSe hemispherical ATR crystal mounted in a holder that slides into the Seagull in place of the specular reflectance holder. The holder has a built-in pressure applicator. The kit also includes a compatible pressure plate.
For specular reflectance of liquids, the trough liquid cell provides an open reservoir to contain the sample. The trough readily mounts onto the standard specular reflectance holder.
For heated studies, a sample stage is available that can be operated up to 150°C. This stage can be used to support samples for either ATR or specular reflectance measurements.
For ATR studies of liquids, a flow-through liquid cell is offered. This cell is equipped with two luer ports and seals against the ATR crystal with an o-ring. The cell can be used for both flow-through measurements and for applications requiring a sealed liquid cell. A temperature-controlled liquid version of the cell is also available for examining liquids from room temperature to 150°C.
For ATR measurements of powders, a convenient powder holder (SEA-PSH) is available. This holder provides a spring-loaded removable cup that minimizes spillage of the sample while optimizing contact with the ATR crystal.
For studying oriented polymers and determining ordering in systems with molecules on inorganic surfaces, our Ming-Sung™ ATR Rotator is available. This rotator is a specially designed crystal holder that permits a 0° to 90° rotation of the sample without dismounting the sample. It is compatible with the hemispheres that can be purchased separately or with the ATR Kit.
In addition, a model of the Seagull™ with independently variable angles of incidence and collection is available on special order.
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Figure 2. External Reflectance of 0.05 µm SiO2 on Aluminum (p-polarization).
Figure 3. Internal Reflectance of a 2.5 µm Mylar Film on a Silicon Substrate.
The versatility of the Seagull™ makes it a powerful tool for the analysis of a number of different sample types using a variety of reflection techniques. Representative spectra are shown in Figures 2 through 5.
Figure 4. Diffuse Reflectance of Kaolinite Diluted in KBr at a 15° Angle of Incidence.
Figure 5. ATR spectrum of 10 µm silica powder, recorded at a 45° angle of incidence using the powder sample holder.
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