The alloying of Ag and Au has been investigated on the level of individual clusters by analyzing the light emission excited by electron injection from an STM tip. Different Ag-Au alloy and shell-core clusters have been prepared at room temperature on a thin Al 2 O 3 film on NiAl͑110͒ by simultaneous and successive deposition of both noble metals. For simultaneous deposition, one Mie-plasmon resonance has been detected with a wavelength position shifting from the pure Au to the Ag value with increasing Ag content. The results are in agreement with calculations based on Mie theory indicating a complete mixing of both materials. For successive deposition, two Mie resonances have been observed, attributed to plasmon excitations in the shell and core of the clusters. Comparing these results to model calculations, a considerable intermixing of the core and shell materials is concluded, which is especially strong in Au shell-Ag core clusters.
Light emission induced by inner-shell excitation of N 2 molecules has been investigated in the wavelength region 250р fluo р1000 nm. Synchrotron radiation from the SuperACO storage ring in Orsay ͑France͒ has been used for the photoexcitation and a high-resolution secondary monochromator (⌬ fluo ϭ0.2 nm) for the spectral analysis of the fluorescence light. Vibrationally resolved molecular N 2show clearly the coupling between the (1s→*) core excitation and the ionization of the (2 u ) valence electron. The main contribution to the fluorescence spectra stems from excited neutral and excited singly charged atoms produced by the dissociation of highly excited molecular states. The singly ionized N ϩ atoms are produced upon resonant (1s→*) excitation as well as upon excitation to the (1s Ϫ1 -*) continuum resonance. Fluorescence transitions of the type N ϩ 1s 2 2s 2 2p4 f →1s 2 2s 2 2p3d as well as 2p3d→2p3p and 2p3p→2p3s have been analyzed. The neutral N fragment is found nearly exclusively after excitation of the (1s Ϫ1 -*) resonance, and mainly radiative decay of the N 1s 2 2s 2 2p 2 3p excited states has been observed. The obtained experimental results represent additional and very detailed information on the final states of the molecular dissociation and provide a necessary basis for a theoretical treatment of the relaxation processes of inner-shell excited molecules.
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