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The VariGATR™ is a single reflection ATR accessory designed for analyzing monolayers and adsorbed species on semiconductor and metallic substrates.
The VariGATR™ integrates the theoretical conditions that provide the highest sensitivity to these extremely thin films¹ ² ³ in a convenient horizontal ATR sampler. The VariGATR™ features a Ge ATR crystal for use from 5000 to 650 cm-1. Its incident angle can be varied from 60º to 65º, making it possible to optimize the angle for any given spectrometer and sample. Its specially integrated Slip-Clutch pressure applicator optimizes contact between the sample and the relatively small active portion of the crystal. For greater sensitivity, a polarizer can be added to the VariGATR™ and, for more precise measurements of the force applied to the sample by the pressure applicator, a force sensor with digital read-out is available.
Figure 1. ATR Spectrum of an Organic Monolayer on Silicon, Measured at a 65º Incident Angle
Figure 2. ATR Spectrum of an Organic Monolayer on Gold, Measured at a 65º Incident Angle.
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Figure 3. ATR Spectrum of a Thin Film on Si, Measured at Incident Angles of 60º (red) and 65º (blue).
Figures 1 and 2 demonstrate the high sensitivity of the VariGATR™ to monolayers. Figure 1 is a spectrum of an organic monolayer on a polished silicon surface. Figure 2 shows the spectrum of a monolayer on a gold-coated glass substrate. Figure 3 shows spectra of a thin film on Si for two different angles. For this particular film, the lower angle was closer to the experimental critical angle and hence provided stronger band intensities.
For sampling versatility, the VariGATR™ can also be used to analyze liquids, powders, pastes, and other solids. It is especially useful for samples with intense spectral bands. Such samples might otherwise exhibit too high absorbance or band distortions.
¹ M. Milosevic and S. L. Berets, 'ATR of Monolayers on Si and Neat Powders by Single Reflection ATR,' PittCon 2002 invited paper.
² M. Milosevic, S. L. Berets, and Y. Fadeev, 'Single Reflection Attenuated Total Reflection of Organic Monolayers on Silicon', Appl. Spectros., 57 (6), 4724 (2003).
³ Milan Milosevic, Violet Milosevic, and S. L. Berets, 'Grazing Angle Attenuated Total Reflection Spectroscopy: Fields at the Interface and Source of the Enhancement', Appl. Spectros, 61(5), 530 (2007).
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