The exchange bias of epitaxially grown CoO/Fe/Ag(001) was investigated using Xray Magnetic Circular Dichroism (XMCD) and X-ray Magnetic Linear Dichroism (XMLD) techniques. A direct XMLD measurement on the CoO layer during the Fe magnetization reversal shows that the CoO compensated spins are rotatable at thinner thickness and frozen at larger thickness. By a quantitative determination of the rotatable and frozen CoO spins as a function of the CoO film thickness, we find the remarkable result that the exchange bias is well established before frozen spins are detectable in the CoO film. We further show that the rotatable and frozen CoO spins are uniformly distributed in the CoO film.

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Organic/inorganic semiconductor heterojunctions are being explored in hybrid solar cells that take advantage of unique properties of both material systems. A key question concerns the mechanism of charge separation across the localized/delocalized semiconductor interface. Here we probe photoinduced charge transfer at a model interface between copper phthalocyanine (CuPc) and gallium arsenide (GaAs) by tracking the electric field on the femtosecond time scale using timeresolved second harmonic generation. For above bandgap excitation of GaAs, we resolve distinction channels of charge separation on 10 2 fs time scales: charge carrier separation in GaAs due to the delocalized space charge field and hole injection from photoexcited GaAs to localized CuPc molecular orbitals. At sufficiently high excitation density (>10 17 /cm 3 ), charge separation by the space charge field leads to band flattening, which accelerates resonant hole transfer from GaAs to CuPc. We discuss implications of these findings to the design of organic/inorganic hybrid solar cells.