Thermomechanical Sensitivity of Microcantilevers in the Mid-Infrared Spectral Region

Abstract

This article reports the thermomechanical sensitivity of bimaterial cantilevers over a mid-infrared (IR) spectral range (5–10 μm) that is critical both for chemical analyses via vibrational spectroscopy and for direct thermal detection in the 300–700 K range. A physics-based model of cantilever bending was developed by including heat transfer to and within the cantilever, temperature-dependent cantilever bending, and cantilever and optical system IR characteristics. Detailed measurements of the optical system IR characteristics were used as inputs to the model, including Fourier transform infrared (FT-IR) spectral characterization of cantilever absorbance as well as characterization of the light source and monochromator. Mechanical bending sensitivity and noise were modeled and measured for six commercially available microcantilevers, which consist of either an aluminum film on a silicon cantilever or a gold film on a silicon nitride cantilever. The spectral sensitivity of each cantilever was measured by recording cantilever deflection when illuminated with IR light from a monochromator. Predictions of cantilever bending sensitivity and noise compare very well with measurements over the entire spectral range with no fitting parameters or normalization. The results are used to rank the cantilevers for their potential use in IR measurements.

Keywords:

• bimaterial
• microcantilevers
• infrared
• thermomechanical
• photothermal
• FT-IR microscopy
• monochromator
• modeling

Notes

This work was supported by the Air Force Office of Scientific Research MURI FA9550–08–1–0407 and a Grainger Emerging Technology award.