This individual investigator award supports a project that will use Nuclear Magnetic Resonance (NMR) techniques to investigate the behavior of hydrogen in three different materials: lanthanum and yttrium hydrides, fullerenes, and quasicrystals. Thin films of lanthanum and yttrium hydrides switch from a reflecting state at low hydrogen concentrations to a transparent state at high concentrations. This "switchable mirror" behavior is due to a metal-to-non-metal transition, but a detailed understanding of this transition is still lacking. NMR will be used to characterize the crucial structural and electronic phenomena underlying the optical transition. Carbon-based materials are attractive candidates for new hydrogen storage media, and recent attention has focused on the use of carbon nanotubes. Difficulties in nanotube sample preparation and analysis have hampered progress in measuring crucial properties, including the hydrogen transport rate. The rate of hydrogen transport in solid fullerene, as a first step towards understanding the more complicated nanotube materials, will be studied using NMR techniques. Quasicrystals are solids with aperiodic yet highly ordered structures and remarkable electronic properties. Calculations showing fine structure in the electronic density of states may explain these properties; however, the experimental evidence remains controversial. NMR relaxation measurements combined with control of the hydrogen content of a titanium-based quasicrystal will be used to test for the existence of the fine structure. All of this work will be carried out at a liberal arts college using undergraduate research assistants, who will gain valuable experience as they prepare for and pursue careers in physics and related fields. %%% Hydrogen is absorbed by a surprising array of solids, often yielding materials with significant technological importance. This individual investigator award will support a project at a predominately undergraduate institution that utilizes Nuclear Magnetic Resonance (NMR) to study the behavior of hydrogen in three different materials: solid C60, rare earth "switchable mirrors, " and titanium-based quasicrystals. NMR measurements of the motion of hydrogen in C60 will serve as the first step in understanding hydrogen motion in more complicated derivatives of C60, such as carbon nanotubes. Carbon nanotubes are attractive candidates for next generation hydrogen storage media, crucial for the development of clean-burning hydrogen as a viable fuel. "Switchable mirrors" are thin films that change from reflecting to transparent depending on the hydrogen content. NMR measurements of their structure and electronic properties will yield a better fundamental understanding of the switching phenomenon. This understanding will aid the development of useful devices, such as switches for optical fiber networks. Quasicrystals are solids with unusual atomic structures that have a number of novel electronic properties. NMR measurements of the electronic properties combined with careful control of the hydrogen content of a quasicrystal will be used to test some of the more controversial theoretical explanations of the unusual properties. All of this work will be carried out at a liberal arts college using undergraduate research assistants, who will gain valuable experience as they prepare for and pursue careers in physics and related fields. ***
