Michael A. Greenwood
A promising new approach to traditional infrared emission spectroscopy has been developed by a team of researchers who maintain that their prototype allows for quicker time resolution, can be subjected to harsher environmental conditions and may be able to record spatially resolved emission spectra. Potential applications for the planar array IR emission spectroscopy technique include thin-film analysis, kinetic studies and real-time monitoring.
The investigators, who are based at the University of Delaware in Newark, combined a 2-D focal plane array IR camera with an IR monochromator to build a planar array spectrometer. Their instrument could record 700 cm–1 spectra across the 4000- to 950-cm–1 range with a low time resolution (∼17 ms). The spectrograph had a 300-μm slit, a reflection grating with 50 grooves per millimeter and a 256 × 256 mercury-cadmium-telluride focal plane array.
The planar array technique, tested on selected polymers, acquired emission spectra with a high signal-to-noise ratio at temperatures as low as 80 °C. Because it can be constructed with no moving parts, the device is not as vulnerable to extreme conditions as interferometers. It could, in principle, be reduced to the size of a shoe box.
The scientists, led by Christian Pellerin, now an assistant professor of polymer chemistry and IR spectroscopy at Université de Montréal, noted that the technique could become a viable alternative to Fourier transform IR spectroscopy. It would be particularly appropriate in cases where sensitivity, time and spatial resolution are essential.
Despite the promising results of the proof-of-principle experiments, several shortcomings of the method were identified. The researchers said that frequency precision was reduced and that the delicate relationship between spectral bandwidth and spectral resolution was compromised by the small size of the arrays. They said that they will continue to fine-tune their technique and will seek to apply it to online monitoring of processes using emission spectroscopy.
Analytical Chemistry, published online Jan. 5, 2007, doi: 10.1021/ac061799l.