It was recalled that, when implanted into a material, the positive muon could mimic the proton in its chemical and elastic interactions. In the case of non-metals, it could pick up an electron to form muonium; which behaved as a light isotope of H. This could be observed with remarkable sensitivity by using electron spin resonance techniques (muon rotation, relaxation and resonance). On the other hand H, when present only as a trace impurity, could be difficult or impossible to detect by using conventional spectroscopic methods. It was noted that much of the structural information on isolated H defect centers in semiconductors had been provided by electron spin resonance studies of the muonium counterpart. Particularly important discoveries had been that of metastability and the bond-centered state. Current studies of fundamental and technological interest concerned the interplay of site and charge state, the trapping and de-trapping of carriers at deep-level centers, and the nature of interstitial diffusion. Extensions to the modelling of H passivation in doped material appeared to be promising.

S.F.J.Cox: Philosophical Transactions of the Royal Society A, 1995, 350[1693], 171-87