IVC17 / ICSS13 and ICN+T 2007

Insulating properties of ultrathin KCl layers on Cu(100)
Nommiste, Ergo¹; Kikas, Arvo¹; Kisand, Vambola¹; Kooser, Kuno¹; Kaambre, Tanel¹; Ruus, Rein¹; Kukk, Edwin²; Valden, Mika²; Hirsimaki, Mika²; Jussila, Petri²; Lampimaki, Markus²; Aksela, Helena²; Aksela, Seppo² ¹Estonia; ²Finland

Recent progress in nanosciences has stimulated the interest in ultrathin insulating films of a few monolayer thickness and their production process with the prospect to use these films as insulators in microelectronic industry.
We present here an experimental study of potassium chloride as an adsorbate on the Cu(100) surface with thickness ranging from partly formed monolayer to thick film with the properties of bulk polycrystalline KCl. The resonant excitations near the potassium 2p edge have been created by monochromatized synchrotron radiation. Our study focuses on the substrate-induced effects in the creation and decay of K+ 2p core excitations in KCl films. For this purpose we investigated the photoexcitation and the Auger decay of K+ 2p core excited states of thin films with various thicknesses. The experiments were carried out at beamline D1011 of MAX-II storage ring (Lund, Sweden). The beamline was equipped with a modified SX-700 plane grating monochromator and Scienta SES-200 electron energy analyzer.
Photoabsorption spectra show the onset of crystal field splitting already at KCl coverages below one monolayer. It has been suggested that when increasing layer thickness, the photoabsorption spectra reflect the increase of absorption at bulk sites with Oh symmetry and a decrease at interface and surface sites with C4v symmetry. Photoelectron spectra show in case of submonolayer films one peak, corresponding to the single KCl monolayer at copper surface. In thicker films three structures are seen, corresponding to the atoms at copper-KCl interface, in bulk KCl and at KCl surface. The analysis of Auger decay spectra taken at the photoabsorption resonances shows that the most important differences between the K+ L23M23M23 resonant Auger spectra of solid and thin layers can be explained by the delocalization of the excited K+ 3d electron from the photoabsorption site into the copper substrate. In case of thin films K+ 3d level is strongly hybridized with states of copper substrate, which makes possible very fast delocalization (faster than core hole decay) of the excited electron.

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