Determination of the vacancy migration energy of aluminum by NMR

Monovacancy diffusion is a thermally activated process characterized by an activation energy E(,d). The diffusion of atoms requires the formation and migration of vacancies. The concentration of vacancies n/N is given by n/N (DBLTURN) exp(-E(,f)/kT). It can be shown that the activation energy E(,d) is the sum of the energy to form a vacancy E(,f) and the energy required for an atomic jump E(,m): E(,d) = E(,f) + E(,m). Furthermore, the atomic jump rate (omega)(,j) can be shown to be thermally activated and given by (omega)(,j) (DBLTURN) (nu)(,o)(n/N)exp(-E(,m)/kT) ((nu)(,o) is the attempt frequency).;NMR offers many techniques to measure the activation energy, E(,d). However, there are no NMR techniques available for the determination of the migration energy. This thesis presents an NMR experiment for the measurement of the migration energy. It is a simple NMR experiment performed on a sample prepared with a nonequilibrium concentration of vacancies. By preparing the sample such that the vacancy concentration does not change with temperature, the jump rate has only one thermally activated term. Thus, the jump rate now has an activation energy equal to the migration energy E(,m).;This experiment was performed on pure aluminum metal. The migration energy was found to be .69 ev (+OR-) 20% (the accepted value is .67 ev); however, we do not consider this an accurate determination. We do consider the experiment successful and promising. The activation energy of self diffusion was also determined; its value is 1.33 ev

¹H MAS NMR Study of Cysteine-Coated Gold Nanoparticles

¹H MAS NMR experiments were performed on gold nanoparticles coated with l-cysteine. The experiments show that l-cysteine molecules are zwitterions and support a structural model of cysteine forming two layers. The inner layer is composed of cysteine molecules chemisorbed to the gold surface via the sulfur atom. The outer layer interacts with the chemisorbed layer. The ¹H NMR suggests that the cysteine in the outer layer exhibits large amplitude motion about specific carbon–carbon bonds