Stephen Erickson, Brigham Young University
Physical Sciences
“The spherical protein ferritin has often been used to fabricate nanoparticles of various shapes and compositions with its walls. Ferritin occurs naturally with a ferrihydrite (FeOOH) mineral core, but it has also been used to synthesize nanoparticles of several other semiconductors. While the methods for creating these nanoparticles within ferritin are well established, the characterization of such nanoparticles is not. Previous studies on native ferrihydrite core ferritin disagree on the band gap, giving values anywhere from 1.1-3.5 eV, depending on the method. We have used absorption spectroscopy to measure these band gaps with an unprecedented accuracy of up to .01 eV. This method also allowed us to determine that ferrihydrite nanoparticles are indirect gap semiconductors. By employing this method on particles of various sizes, we have shown the effects of quantum confinement, resulting in variations in the band gap. We also provided the first ever direct evidence that ferritin works to crystalize its core with time, an effect that has long been theorized but never observed. By characterizing the effect of size and time on nanoparticle band gap, we have shown the potential for selectively tuning that gap. This opens up a world of possible applications in light harvesting and photo detectors. By controlling the band gap, we will be able to select which wavelengths of light are absorbed, allowing for full spectrum photovoltaic cells and wavelength specific optical detectors. Future studies will focus on nanoparticles of other metal hydroxides and various anion replacements to further expand our tunable range of band gaps.