With support from the Chemical Measurement and Imaging Program in the Division of Chemistry, Professor Baldelli at the University of Houston and Professor Kelly at Rice University are developing a new type of microscope that is able to see molecules on surfaces faster and with higher sensitivity than regular microscopes. With cameras, pictures can be taken that show colors to help identify objects; for example, grass is green and sky is blue. However, to look at molecules, more specific information is needed about the "colors" that molecules absorb. For many molecules, this absorption occurs in the infrared region of light. To look at these infrared colors, traditional cameras are not very good so methods that can obtain pictures without cameras are necessary. Professor Baldelli and Professor Kelly are developing a new type of microscope to figure out the surface image of surface molecules. The results of this new microscope are useful to all researchers interested in surfaces related to biomaterials, energy, and environmental topics. For example, it can be used to study the distribution of lipid molecules on cell membranes that controls proteins moving in and out of cells, which in turn regulate cell growth and signaling. It can also be used to look at chemical dopants on a thin film that accelerate the oxygen reduction reaction in fuel cells, an important step in efficient energy conversion. The research project also presents a valuable opportunity to learn and experience collaborative multidisciplinary research -- a current emphasis of science and engineering education. The topics and research project have many components to encourage undergraduate and high school students into the research, including instrument building, data analysis and interpretation, and research presentations. This later point is an important aspect since it builds much confidence in the younger students and scientist.
Professors Baldelli and Kelly are developing a new state-of-the-art surface spectroscopic imaging microscope to study the molecular, spatial, and temporal evolution of patterns and chemical heterogeneity present in many fundamental and technologically important systems. This new CS-SFG (compressive sensing-sum frequency generation vibrational spectroscopy) imaging technique utilizes a digital mirror device (DMD). The DMD is the heart of the DLP projector and flat screen displays. It is a 2-D array of mirrors that reflects the SFG image onto a detector. Using computer control and a random pattern generator, the signal intensity changes depending on which mirrors are reflecting toward the detector. Each pattern results from 50% of the randomly chosen mirrors being turned on for each measurement. After many such measurements, the image is reconstructed based on the signal and the known mirror pattern. CS allows for efficient image acquisition where only a few percent of the total information is necessary to faithfully reconstruct the surface features. Two configurations broad-band and narrow-band IR are set up to evaluate the effect on the image reconstruction. In addition the detection system incorporates heterodyne detection to extract phase information forth monolayer signal. This new capability allows for alternate imaging schemes and orientation analysis. The effect of compression algorithms and quantitative analysis ultimately aid in the interpretation of heterogeneous monolayer films on surfaces. The CS-SFG microscope will be a significant improvement over current approaches that either use probe areas on the order of a millimeter or acquire the full hyperspectral data cube but at considerable expense in sample throughput. Once demonstrated, Professors Baldelli and Kelly are to employ this microscope to investigate the molecular-level static and dynamic details of chemical patterns (such as lipid domains) formed under the control condition of lithography and the transfer of films to solid substrates via the Langmuir-Blodgett technique. The research project provides both graduate students and local high school students with highly interdisciplinary training in chemistry, physics, engineering, and computer science.
