Spectroscopic electric-field-induced second harmonic generation on a Si(111)-SiO2-C r metal-oxide-silicon structure shows a bias-independent " interface" resonance at 3.25 eV and a ''bulk'' resonance at 3.43 eV which is strongly bias dependent. The symmetry forbidden bulk dipole contribution becomes observable, and even dominating, due to the bias-induced band-bending that breaks the bulk inversion symmetry. The origin of these resonances is discussed, as well as the prospects for using second harmonic generation as a probe of metal-oxide-silicon characteristics.

No abstract

No abstract

No abstract

4We have measured the polar nonlinear magneto-optical Kerr rotation and the total generated second harmonic intensity from a perpendicularly magnetized Co(0001)/Au(lll) thin film (6 ML) versus the thickness of a Au overlayer. For both experiments we find a clear oscillation with a period of about 13,5 ML. This behavior can be interpreted as arising from quantum-well states (QWSs) in the Au overlayer, though interestingly, the observed period is twice the expected one. Especially for the reflected intensity this oscillation is very pronounced: the intensity changes by a factor of 10 when the Au overlayer thickness changes from 7 to 13 ML. These strong effects make this nonlinear technique very suitable for the study of these QW oscillations. © 1.996 American Institute of Physics. [S0021 -8979(96) 19808-5] Since the discovery that magnetic films separated by a nonmagnetic spacer layer could be coupled antiferromagnetically,1 and the subsequent discovery that this coupling could oscillate between ferromagnetic and antiferromagnetic,2 there have been intense efforts to under stand these phenonema. It was shown that in ultrathin films, due to the electronic potential discontinuities experienced by electronic states at interfaces, the perpendicular component of the wave vector can become quantized, giving rise to reso nances in the density of states. Those quantum-well states (QWSs) may act as the mediator for this magnetic coupling.3 Magneto-optical Kerr effect (MOKE) and direct-and inverse photo emission experiments have shown direct evidence of such QWSs in thin noble metal films on magnetic substrates (Fe and Co),4"'6 and in a bcc Fe(100) layer on Au(100).7,8 More recently, oscillations of the Kerr angle with changes of overlayer film thickness have been observed for a Au/Co/Au system.9 These results showed the existence of quantum size effects in the thin Au overlayer and also gave an indication of possible interface contributions.Due to the fact that optical second harmonic generation (SHG) is known to be surface sensitive on an atomic scale, it seems that SHG studies might be particularly suitable for improving our knowledge of the electrodynamics of ultrathin metallic films. Though the absolute nonlinear signals are small, the nonlinear magneto-optical effects can be large: compared to the linear Kerr angle, enhancements up to a factor of 1000 have been observed.10 Wierenga et al.n were the first to report about the possibilities of this nonlinear optical technique for detecting QW oscillations. They have found very strong oscillations in the magnetization-induced SHG signal for the Cu/Co/Cu system as a function of the thickness of the Cu overlayer, which are probably related to QWSs in these films.11 These strong effects are directly re lated to the extreme interface localization of the nonlinear response.In this paper we report the unambiguous observation of QWSs in a A u (lll) overlayer on Co(0001). The oscillations are found in both the polar nonlinear MOKE as well as in the total generated second harmo...