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Visualizing Chemistry: The Progress and Promise of Advanced Chemical Imaging
insights into geological and weather modifications, and to help correlate data returned by parallel instruments on board the spacecraft.
WHAT IS CHEMICAL IMAGING?
While chemical imaging means many things to many people, concisely it is the spatial (and temporal) identification and characterization of the molecular chemical composition, structure, and dynamics of any given sample. Today’s technologies and demands on imaging are growing well beyond traditional “photographic” imaging as exemplified by medical X-ray applications. To address issues such as the next generation of microelectronics technologies, disease detection and treatment, chemical manufacturing, and advanced materials development, the ability to perform spatially resolved measurements of chemical structure, function, and dynamics is vital. For example, the location and identification of atoms and molecules in the heterostructures within a state-of-the-art microprocessor are crucial to developing faster and more reliable computing architectures. Imaging the dynamic chemical processes involved in the catalytic production of chemicals is essential to improving chemical manufacturing. Imaging and tracking molecular biochemical processes is central to the development of new ways to detect and treat diseases.
Modern spectroscopic techniques rely on the interaction of light or other radiation with a sample of interest. The resulting spectra from these techniques provide vast amounts of information about molecular interactions and structures that occur in chemical processes. Even the best spectra, however, are limited in their ability to reveal the exact characteristics of a chemical reaction definitively. Most common spectroscopic methods require significant samples; for example, nuclear magnetic resonance (NMR) spectroscopy usually requires on the order of a milligram or more. While NMR is not as sensitive as many of the other techniques, in general spectra acquired using standard spectroscopic methods are the result of the accumulation of data from millions (or billions) of individual molecules. In other words, most common spectroscopic techniques provide only an approximation of what occurs between individual units in a single chemical reaction.
Chemical imaging takes advantage of a number of spectroscopic techniques (which will be discussed in depth in Chapter 3). These techniques provide the needed information about the molecular composition, structure, and dynamics of a given sample in space and time. Unlike traditional spectroscopy, however, it is now possible in certain implementations of chemical imaging to obtain images on the molecular scale, where interactions between the smallest units of structure are revealed. These advances greatly enhance the fundamental understanding of chemical interactions. As shown in Figures 1.1A and 1.1B, imaging techniques cover a wide range of time scales and penetration depths for samples of varying lateral dimension.