Development of microcantilever mid-infrared detectors and sources and their application in infrared spectroscopy.

摘要

Mid-infrared (mid-IR) light is an electromagnetic radiation with the wavelengths of 3 -- 30 mum. This spectral range includes the dominant wavelengths of the thermal radiation emitted by objects at or near room temperature, and vibrational and rotational resonance frequencies of many molecules. The detection and generation of mid-IR light, thus, have been extensively studied for the applications in thermal and chemical sensing. However, the mid-IR light detection with a high resolution at room temperature has been a difficult task, since the thermal noise is significant in the traditional detection methods. In addition, there have been few mid-IR light sources available for microscopic and rapid experiments.;This study presents the development of microcantilever mid-IR detectors and sources. First, this research investigates the dynamic thermomechanical response of bimaterial cantilevers to periodic heating by an IR laser. A model relates incident IR radiation, heat transfer, temperature distribution in the cantilever, and thermal expansion mismatch to find the cantilever displacement. Silicon nitride-aluminum bimaterial cantilevers are designed, fabricated, and tested for validating the developed model. The custom-fabricated cantilevers show 9X or 190X improvements in IR detection sensitivity compared to commercial cantilevers.;To improve the sensitivity of silicon based bimaterial cantilever IR detectors, this research introduces the integration of black silicon nanocone arrays into commercially available silicon-aluminum cantilevers. The black silicon consists of nanometer-scale silicon cones. Compared to a cantilever with smooth single crystal silicon, the cantilever with black silicon has about 2X increased responsivity at the wavelengths of 5 -- 9 mum. Developed model also provides further insights into the influence of the nanocone height on the IR absorbance and responsivity of the cantilever.;Next, this study introduces the integration of one-dimensional high-contrast grating into silicon-aluminum bimaterial cantilevers which enhances the amplitude and bandwidth of the IR absorbance as well as the responsivity. With the integrated grating, the silicon layer acts as a grating coupler and waveguide, while the aluminum layer acts as an IR absorber. At the wavelengths of 3 -- 11 mum, the cantilevers with high-contrast grating show about 2X larger bandwidth for the IR absorbance > 0.2 and an order of magnitude larger responsivity as compared to a commercial silicon-aluminum cantilever.;Bimaterial cantilever with a sharp tip can perform standard atomic force microscope (AFM) imaging and also detect IR light. This study reports nanotopography and IR microspectroscopy measurements performed using a bimaterial cantilever in the same AFM system. This system uses micrometer scale engineered skin and three-dimensional cell culture samples for the demonstration.;Finally, this research investigates the IR emission of two silicon cantilevers with integrated solid-state heaters over the 2500 -- 3000 cm-1 spectral range. A model calculates the spectral power emitted by the cantilever based on the Planck function, dielectric function of the doped silicon at elevated temperatures, and cantilever spectral emissivity. Measurements of the cantilever spectral power compare well with predictions. The cantilevers provide radiative powers on the order of 1 -- 100 microW at the temperature near 1000 K.