Grazing angle Ge ATR spectroscopy is extremely sensitive to monolayers and thin films on high refractive index substrates such as Si. As with any ATR method, the sensitivity increases as the critical angle is approached, as demonstrated herein.
Monolayers and other thin coatings on Si and other high refractive index substrates are of key importance in materials science, bioscience, synthetic organic, and semiconductor research. These films are often close to the FTIR detection limit so methods that improve sensitivity are vital. Traditionally, these samples were examined by transmission or grazing angle specular reflectance spectroscopy. Grazing angle Ge-ATR has recently gained wider use because of its higher sensitivity. Grazing angle Ge-ATR measurements have typically been recorded at 65°, an angle sufficiently above the critical angle for the Si-Ge interface, 58.7°.
This note explores the increased sensitivity gained by optimizing the incident angle and also discusses the potential spectral anomalies if the nominal critical angle of a given sample is exceeded.Experimental
Results and Discussion
In conclusion, it is clear that selecting the incident angle to approach the critical angle does increase sensitivity. However, for ease of interpretation, the incident angle should be optimized for greatest sensitivity without significant dispersion effects.
Harrick Scientific Products, Inc.