Nuclear Instruments and Methods in Physics Research B 85 (1994) 508-515 North-Holland NONI zyxwvutsrqpo B Beam Interactions with Materials 8 Atoms Perturbed angular distribution studies in natural, synthetic CVD and HPHT diamond S.H. Connell a, E. Sideras-Haddad a, K. Bharuth-Ram b, C.G. Smallman a, J.P.F. Sellschop a, M.G. Bossenger a a zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Schonland Research Centre, for Nuclear Sciences, University of the W itwatersrand, PO W T.9 2050, Johannesburg, South Africa b Physics Dept, University of Durban- W estville, Durban, 4000 South Africa The time differential perturbed angular distribution (TDPAD) technique as applied to semi-conductors and insulators has a unique place among the other analytical methods involving ion beams. It provides an opportunity to study molecular complex-like systems involving the radioactive probe, and also in-situ hot atom chemistry. Both of these aspects are important in understanding dopant-impurity dynamics, particularly in the context of ion-implantation. The very recent advances in the synthetic growth and the defect engineering of diamond have ensured it will be no exception. “F TDPAD data for various natural and synthetic diamonds, as well as for some polymer systems, is reviewed in this context, and confirm that “F TDPAD could become an extremely sensitive probe of the important but elusive impurity, hydrogen. 1. Introduction In time differential perturbed angular distribution (TDPAD) studies using 19F as a probe, one observes the precession of the 19F nuclear spin (for the 197 keV excited state) about the local electric field gradient (efg) at the site where the implanted radioactive probe ion has stopped. The local efg at the excited 19F is determined predominantly (in non-metal systems) by the chemistry of the molecule-like system in which the probe ion becomes involved at its residence site. Since the chemical bonds are formed in the environment of a crystal lattice, rather than in an isolated molecule, the chemistry is modified from that of the free molecule. The chemical environment and the residence site of the molecular complex can be determined by reproduc- ing the experimentally measured efg parameters with a theoretical calculation based on a particular formula- tion of the local lattice-molecule configuration. To first order, the Townes-Dailey model [l] for bond efg’s in isolated molecules reproduces the efg principal component V, as measured in TDPAD by the quadrupole coupling frequency vq. In this way, the Erlangen group has extensively cataloged by measure- ment and theory a variety of 19F containing bonds [2] in a “perioditi table” of 19F bond efg’s. This may be regarded as a starting point for a molecular complex spectroscopy using TDPAD. The inclusion of the effects of the lattice environ- ment in the theory is done by means of cluster calcula- tions. These calculations, appropriately performed, have proved surprisingly accurate in the case of defect characterisations in the macromolecule diamond. (For a recent review see ref. [3]). The propensity of the 19F probe to form molecule-like complexes in the lattice makes it an ideal tool to study impurity-lattice and impurity-impurity interactions. TDPAD with 19F has a natural time window during recoil implantation due to the excitation of the (aligned) 197 keV state and the 127 ns mean lifetime of this state. This means that the 19F senses the local efg’s starting from the thermalisation time (10 ps) to the gamma decay of the excited state (about four mean lifetimes). The effective time window including experi- mental limitations is therefore 3-500 ns starting imme- diately on implantation. This property of 19F TDPAD is what makes it unique to study in situ hot atom chemistry arising from the energy transferred to the lattice during the implantation cascade. The system under investigation is diamond. The physical, chemical and mechanical properties of dia- mond have always marked it as one of the most appro- priate materials from which to fabricate modern coat- ings, structures and electronic devices. However, the scarcity of natural diamonds, the difficulties in engi- neering the material, and the complexity of the native defects have until recently discouraged its “high-tech” exploitation. In particular, advances in synthetic growth under thermodynamically metastable conditions have increased the potential of coating and layer fabrication under controlled, reproducible conditions [5,6]. These TDPAD measurements aim to study impurity and defect interactions. Data for three established types of natural diamonds (Ia, IIa, IIb), for synthetic 0168-583X/94/$07.00 0 1994 - Elsevier Science B.V. All rights reserved SSDI 0168-583X(93)E0697-F