A composite structure consisting of a thick chemical vapour deposition (CVD
) polycrystalline diamond layer grown on an aluminium substrate, covered wi
th a thin gold cap layer has been studied using positron beam and other tec
hniques. The diamond layer has a strong [110] texture and also contains sma
ll fractions of aluminium carbide and graphitic phases. Positron beam analy
sis reveals two states, corresponding to a highly defective thin gold layer
and an homogeneous diamond layer with large, essentially defect free, crys
tallites. (C) 1999 Elsevier Science B.V. All rights reserved.