Development of an Infrared Spectrometer/Scanning Probe Microscope for Materials Characterization at High Spatial Resolution

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The goal of this project is to construct a powerful new research instrument for determining the composition of materials at sub-micron spatial resolution. The key feature of the new instrument will be the use of a scanning probe microscope (SPM) to detect the absorption by materials of infrared radiation from a Fourier-transform infrared (FTIR) spectrometer. Ultimately, the spatial resolution of this instrument is expected to approach 50 nm. This spatial resolution is at least two orders of magnitude better than that of infrared microscopes that are limited by diffraction effects to a spatial resolution that is approximately equal to the wavelength of infrared radiation (~ 2.5 - 25 mm). Since an SPM will be used as an infrared "detector," the best features of FTIR and SPM systems will be integrated into a single powerful instrument that can provide information about variations in the surface composition, topography, and properties of materials at high spatial resolution. Two general approaches will be employed. In one, the SPM will be used to measure the thermal expansion that occurs when a sample absorbs infrared radiation. Signals from the SPM will be routed to the external input of the FTIR where functions such as signal averaging and Fourier-transformation will be performed to yield the infrared spectrum of the sample. The FTIR spectrometer will be operated in a step-scan mode and the infrared radiation will be modulated at a frequency of about 100 kHz to limit the thermal diffusion length and enhance the spatial resolution of the instrument. The second approach will be similar except that the SPM will be equipped with a miniature resistance thermometer that will be used to measure the increase in temperature of a sample when it is illuminated with infrared radiation. This new research instrument will be used extensively in research concerned with gradients that occur in composition, structure, and properties of materials near interfaces in adhesive joints and composite materials and in research concerned with phase separation in elastomers having a bimodal distribution of long and short chains. A novel aspect of the research plan is to make the FTIR/SPM available to remote users over the Internet.