Study of indium-defect interactions in diamond using two-dimensional conversion-electron emission channelling

Channelling has, since its inception, proven to be a valuable tool in locat ing the geometric position of atoms in the crystal lattice. Allied with pow erful theoretical models, it can yield detailed information on the position s that these impurities occupy. In-111, a radioactive isotope with a conven iently shea half-life, is an often-used probe of heavy-atom doping of mater ials. Previous work has centred on the lattice location of In-111 implanted in type IIa diamond. Theoretical calculations on this 'pure' system have a lso recently been made. We have performed the first studies of In-111 impla nted into various carefully selected, defect-rich diamond systems and obtai ned fractions for the sites occupied. The defect systems investigated inclu de nitrogen in various configurations, boron, hydrogen and vacancies. The u se of two-dimensional conversion-electron emission channelling (CEEC) has e nabled the system to be studied in greater detail than with conventional on e-dimensional CEEC. Coupled with the acquisition of the CEEC spectra for al l the major channelling axes, this has yielded a comprehensive data set. Th e spectra are consistent with a pure substitutional fraction as well as ano ther fraction, approximately 0.45 Angstrom from the substitutional along a (111) direction. Previous measurements observed these two components togeth er as substitutional or 'near-substitutional'. The data have been compared to simulated CEEC spectra and earlier quantum chemical calculations. The pu re substitutional fraction is indicated to be in a defect-free configuratio n while the component displaced away from substitutional involves most prob ably the divacancy and another nearby defect. The results show no dependenc e on impurity type, even after annealing. If indium complexation with these defects does occur it is shown not to measurably affect the channelled spe ctra and thus the projected lattice location of the In-111 probe. The origi n of the random fraction measured in previous studies is proposed to be par tially due to In in different multi-vacancy complexes. Taken together, the data indicate the importance of vacancies (complexes) in the final configur ation for In after implantation in diamond.