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Nanometer scale holes and lines have been produced directly in calcium fluoride, aluminium oxide, and magnesium oxide by an intense beam of electrons. There is a threshold beam current density for drilling, and the variation of this with voltage has been studied. Observations using electron energy loss spectroscopy have confirmed that metallic aluminium is produced during the drilling of aluminium oxide. Aluminium oxide may be drilled when in contact with the aluminium substrate, which remains undrilled.

Repu le 6 juin 1990, acceptJ le 4 octobre 1990) Rksumk. Cet article aborde des questions fondamentales qui concement la germination et la propagation des dislocations dans les multicouches, et en particulier dans les semiconducteurs bpitaxibs. Nous considbrons le concept d'bpaisseur critique pour l'apparition des dislocations de dbsadaptation de rbseau dans les couches contraintes. Los rbsultats de topographie X et de microscopie blectronique qui sont prbsentbs montrent que le concept d'bpaisseur critique n'est pas aussi bien dbfini qu'on le supposait auparavant. Les considbrations thboriques sur les sources des dislocations de dbsadaptation, dans les couches bpitaxibes sur des substrats sans dislocations,

Stacking faults (and other planar defects) imaged under weak-beam conditions frequently exhibit marked changes in fringe contrast intensity on reversing the diffraction vector, and F811 et al. /1/ have suggested that most of the observed phenomena could be explained by means of a simple model in which the defects are considered to have finite thickness. The model is unlikely on two counts; no change should be observed for vacancy faults (the defects for which the phenomenbn first w a s reported), and the model would predict contrast changes of at least similar magnitude on tilting the defect while maintaining a constant 8. No such effect has been reported.Marked changes in the intensity of fault fringe contrast on reversing 8 in weak-beam were first reported by Chen and Thomas /2/ who considered that the effect resulted from the flattening of the Ewald sphere at high voltages (650 kV). They were investigating epitaxial growth defects in <111> silicon, which haveintrinsic character, and reported that the phenomenon depended upon the phase factor a ; being such that contrast was high in 3 (2 2)whenacwas negative, and considerably weaker when o ( was greater than zero. Although neither this empirical rule, nor the explanation, has been confirmed by later work, the phenomenon continues to be observed, and has never been satisfactorally explained. Salisbury and Loretto /3/ encountered contrast anomalies a t 100 kV in silicon, and Ferreira Lima and Howie /4/ found, in germanium, that for some reflections fringes which were strongly in contrast could become almost invisible on reversing 2. F811 et al. /1/ suggested that "a simple theory -1) P.O. Box 363, Birmingham B15 2TT, England.