Ray Carter
Chemistry
Advanced BS University of Oklahoma, May 1996
Research Focus:
Interest in the synthesis of semiconductor nanoparticles has been generated by their unusual optical and electronic properties. These qualities arise from quantum confinement (QC) effects, which are defined as physical constraints on the exciton wave function. These observed properties, when seen in silicon nanoparticles, show great promise in the manufacture of light emitting diodes and quantum computing devices, such as molecular CPU's. Current means of characterizing these materials do not probe quantum confinement in relation to local chemical environment. NMR spectroscopy will be used to relate local chemical environment and QC.
My research focuses on the investigation of quantum confinement in Si nanocrystals. The QC effect can be viewed as raising the excited state energy levels of the nanocrystal, similar to the changes in the energy levels of a particle in a box. Using this analog, the edge of the three dimensional box, models the energy barrier found at the passivated surface of the particle. Synthetic techniques were developed to provide the smallest possible particle size distribution and most efficient production of Si-nanoparticles.
Internship or Partner Interaction:
A Silicon free NMR probe was constructed to provide zero background. Observed spectra display three distinct regions of chemical shift. Two of the three peaks have been assigned to an inner core crystal environment and an outer layer of Si-R terminations. The assignment of the third peak proves more problematic.
Solution NMR experiments were run to determine if the observed spectra were from nanoparticles or molecular species. Additional samples of nanoparticles with differing size distributions will be explored. The change in the chemical shift will be related to quantum confinement, which will ultimately be related to nanoparticle size. This change in the chemical shift will then be directly related to energy level changes from the original model of a particle in a box. Additional NMR experiments will be employed to determine the different spin relaxation characteristics of the nanomaterials leading to information on crystallinity of the sample.
Personal Statement:
The NEAT-IGERT program has provided me with a unique opportunity to pursue a degree outside the traditional roles of a Physical Chemist. The broad range of talents found in the program had allowed me to make connections outside my primary area of research. These connections have allowed be to look at research problems with more that one viewpoint.
