In this award, funded by the Chemical Measurement and Imaging Program of the Division of Chemistry, Professor Tianquan Lian of Emory University and his postdoctoral, graduate and undergraduate student researchers will be supported to investigate the feasibility of imaging charge transfer dynamics in nanomaterials using specially modified atomic force microscopy (AFM) tips. Prof. Lian and his research group will attach quantum dots to the AFM tips and will measure the photoinduced charge transfer between the modified tip and the probed surface. The goal of this research is to develop a better understanding of the photophysical process taking place at the boundaries in nanomaterials used in solar energy conversion.
Atomic force microscopy methods use contact between a nanometer-scale probe and a surface to measure the changes in morphology of the probed surface. The probe is able to measure differences in the physical properties (e.g. hardness, softness) of the underlying surface at the nanometer (or smaller) length scale. Prof. Lian and his group are attempting to build an AFM probe that will be able to do what the AFM does, except by measuring differences in the rate of photoinduced charge transfer between the modified probe tip and the underlying surface. The goal is to develop the ability to measure the photophysical/electrical properties of nanoscale materials with the same resolution that can be obtained with AFM methods. The students working on this project will gain useful experience in developing cutting-edge analytical spectroscopy tools that will be useful for evaluating and characterizing technologically useful materials. As part of this work, Prof. Lian will continue his exemplary efforts at encouraging students from underrepresented groups to pursue careers in the sciences.
Meeting the clean energy needs for human activities is one of the most important scientific challenges in the 21st century. Solar energy conversion is one of the most promising approaches for meeting this challenge. Many potential solar-to-electricity and solar-to-fuel conversion devices use nanostructured composite materials. The dynamics of photo-induced interfacial charge separation and recombination play essential roles in determining the efficiencies of these devices. Detailed characterization of these processes are often challenging due to the lack of spectroscopic techniques with both high time and spatial resolutions. As a result of this NSF supported project, Prof. Tianquan Lian and his team at Emory University has developed a new imaging technique for studying charge transfer properties of solar energy conversion materials. This technique is based on a novel integration of high spatial-resolution atomic force microscopy (AFM) and confocal time-resolved fluorescence microscopy. Using single quantum dot modified AFM tips, Prof. Lian demonstrated that electron transfer dynamics between a quantum dot (attached on the tip) and a TiO2 nanocrystal can be spatially and temporally resolved. This one-year NSF grant has lead to three papers in high impact journals (ACS nano, J. Phys. Chem. Lett., Nano Lett.). Prof Lian has given 16 invited talks between September 1, 2012 to August 31, 2013 at meetings and in different universities. This grant also leads to the training of one postdoctoral fellow, one PhD student, two undergraduate students from Emory, one undergraduate student from Georgia Perimeter College (a two year college in Atlanta) and a high school student. Both the technical capability and human resources developed by this NSF grant will have important impact on the advancement of solar energy conversion technology.
