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The misfit layer compounds with a general formula (MX)1+ delta TX2 (with M=Sn, Pb, Bi or rare earth metal; X=S, Se; T=Ti, V, Cr, Nb, Ta and 0.05< delta <0.25) have a stacking of MX double layers with a NaCl-type structure alternated by TX2 sandwiches. The unit cell axes in the plane of the layers of both subsystems are equal in the b direction but are incommensurate in the a direction. To understand the stability of this remarkable and ordered stacking of the two different layers, charge transfer from the MX subsystem to the TX2 subsystem has been suggested. In this study misfit layer compounds with Sn, Pb and Bi as the M element have been investigated with X-ray photoelectron spectroscopy. The information obtained from the core levels shows that for the Sn and Pb containing compounds the Pb and Sn atoms are divalent, and no significant charge transfer takes place between the layers. The spectra of the Bi misfit layer compound indicate a valency close to three for Bi. The stability of the misfit layer compounds is attributed to the presence of covalent interlayer bonds.

Two-dimensional quantum well states in ultrathin metal films generally exhibit a dispersion relation of s-p-derived states that can be described through an effective mass of the corresponding bulk band. By contrast, the effective masses in Pb quantum well states on Si͑111͒, measured through angle-resolved photoemission, are up to an order of magnitude larger than those from the bulk states or predicted by slab calculations, while similar anomalies are not observed in the related In/ Si͑111͒ system. We interpret these data in terms of an enhanced electron localization, and use them to interpret recent scanning tunneling microscopy results.

The growth of Pb on Si(111)7ϫ7 has been studied with photoelectron spectroscopy. At low temperature ͑110 K͒, Pb grows in a quasi layer-by-layer mode that allows for the direct observation of discrete quantum well states. The quantum well states are analyzed in terms of the Bohr-Sommerfeld phase quantization model using a phenomenological phaseshift function and reduced quantum numbers. Fermi-level crossings occur when the film thickness Ndϭn(F /2), where d is the atomic layer spacing and F the bulk Fermi wavelength (N,n are integers͒. The photoemission intensity from the quantum well states shows a strong modulation with photon energy which can be interpreted on the basis of the matrix elements for direct transitions in bulk Pb͑111͒. The in-plane effective mass of the quantum well states is greatly enhanced in the vicinity of the substrate band edge. The present results provide important elements for understanding the growth morphology of Pb films in recent STM studies.