The electronic structure of Mn in amorphous Si (a-MnxSi1−x) is studied by x-ray absorption spectroscopy at the Mn L3,2 edges for x=0.005−0.18. Except for the x=0.005 sample, which shows a slight signature of Mn2+ atomic multiplets associated with a local Mn moment, all samples have broad and featureless L3,2 absorption peaks, corresponding to an itinerant state for all 3d electrons. The broad x-ray absorption spectra exclude the possibility of a localized 3d moment and explain the unexpectedly quenched Mn moment in this magnetically doped amorphous semiconductor. Such a fully delocalized d state of Mn dopant in Si has not been previously suggested.

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Ultrathin two-dimensional gold films have been grown on an amorphous Ge underlayer by quench condensation at low temperature, followed by adsorption of magnetic Gd atoms and nonmagnetic Y atoms. The resulting electrical transport as a function of temperature and composition has been investigated in situ. Gold films of different sheet resistances ͑R ᮀ ͒ have been used for the Gd and Y adsorption platform. The temperature and thickness dependence of the conductance G ͑G =1/ R ᮀ ͒ indicates that the Au films cross from a strongly localized regime, where conductivity is through hopping and where electron correlation effects are expected to be strong, to a weakly localized regime. The system is shown to be sensitive to different added electronic states, in that adding Gd or Y increases G, but much less than adding the same amount of Au for all initial G values. No difference is observed ͑down to 5 K͒ between added Gd and Y, showing that there is no effect of the Gd magnetic moments on electrical transport. The absence of magnetic localization and dominance of adding electronic states over added electronic potential disorder in this quench-condensed ultrathin system is discussed and attributed to the intrinsically high electronic concentration of Au.