Current and Recent Research Projects
Development of an Electron State Depletion Microscope (w/ Dr. Sergio Mendes)
High-resolution imaging is extremely important for electronic materials characterization, particularly in the present era of nanoscale material synthesis and device fabrication. The goal of this proposal is to develop a far-field sub-diffraction resolution optical microscope able to detect material variations, defect states, disorder, and impurities, in three dimensions without damaging the material under test. The microscope will utilize a high resolution imaging scheme developed for fluorescence microscopy, but using charge displacement rather than photoluminescence to generate a detectable signal. The electrical imaging capabilities of the 3D sub-diffraction microscope will be used by researchers at the University of Louisville to study nanowire composition for photovoltaic applications, spatial variations in midgap states in oxidized and hydrogenated graphene, and composition variations in organic and inorganic solar cells. The ability to study material variations and defect states in three dimensions, non-destructively, and on the nanometer scale is unprecedented, and will give researchers the opportunity to correlate material properties with device operation in nanoscale systems.
Intracellular Delivery Of Semiconductor Quantum Dots (w/ Dr. P. Sethu and Dr. R. Keynton)
One of the most important applications of nanomaterials in medicine is undoubtedly in drug delivery and imaging. Traditional drug delivery methods utilize plasmids, cationic polymers and lipids, and viruses which have underlying disadvantages such as degradation and require complex conjugation techniques. Quantum dots (QDs) are nanometer sized semiconductor crystals typically between 2nm to 6nm in diameter. Quantum dots have several advantages over traditional fluorescent molecules (organic dyes) such as high resistance to photo bleaching and emission wavelength that can be tuned depending on the core diameter and composition. As a result of their unique size dependent optical and electronic properties, they have found use in many biomedical applications as imaging agents and drug delivery carriers
Unlocking the efficiency of next-generation solar cells with Capacitive Photocurrent Spectroscopy
Progress on next generation solar cells manufactured from organic materials is hindered by a lack of knowledge of a critical step in the photo-conversion process, namely excitonic charge dissociation. Here, we present a new technique "Capacitive Photocurrent Spectroscopy" or CPS, that is uniquely able to probe exciton dissociation efficiency and thereby unlock the potential of organic solar cells. The technique has been demonstrated in our laboratory to be sensitive to photo-generated charge only when it is physically separated across an organic heterojunction or organic / contact interface. In this way, it is possible to distinguish between charge that remains fixed, and charge that dissociates (and can contribute to the photocurrent). The charge dissociation efficiency can be measured in isolation from slow charge diffusion processes and multiple interface effects that complicate standard photocurrent measurements. By varying interface conditions and interface potential, bound and free charge carriers can be distinguished, and excitonic binding energies can be determined.
Energy Harvesting for Battery Free Sensing
Mechanical vibrations occur all around us in the workplace and home, but are often overlooked as a possible source of energy. In this project, we will extract energy from environmental vibrations to power a battery-free monitoring system. Our proprietary energy harvesting module is able to obtain usable energy even from very low level mechanical vibrations existing in standard settings. The harvested energy will be used to power a storage container environmental monitoring system, or "smart container", able to track internal parameters such as temperature, humidity, or vibration level in addition to detecting the presence of radiation, chemical contaminants, or reactive products within the container. The information will be transmitted to a data logger outside of the container without exposing the contents to the external environment. Monitoring will continue as the container is transported between different locations, or while in storage for extended periods of time. The smart container can be used for the storage of materials sensitive to air, temperature, or humidity fluctuations, or for hazardous materials (such as radioactive waste) that require storage for long periods of time. The smart container can also be used for inventory control (information on the contents and its history is transmitted), or as part of a theft deterrent system.