All-electron local-density theory of alkali-metal bonding on transition-metal surfaces: Cs on W(001)

Growth and electronic structure of alkali-metal adlayers on icosahedralAl70.5Pd21Mn8.5

“…In fact, in many different metallic substrates, it has been reported that the physically appealing picture of charge transfer from the electropositive alkali metal to the metallic substrate does not hold. [15][16][17][18][20][21][22][23][24][25] Riffe et al showed that there is almost no shift between the clean and 1 ML alkali metal covered substrate core-level peak for W͑110͒. The authors argued that if the induced dipole moment is due to charge transfer, the shift would be higher for lower coverages.…”

“…Moreover, the linear decrease in BE also does not support the charge transfer model, but rather indicates a covalent nature of alkali metal bonding as suggested by different theoretical calculations. [16][17][18]23 To ascertain the nature of adlayer growth beyond 1 ML, we have plotted the area under the adlayer Na 1s and K 2p and the substrate Al 2p peaks as a function of the coverage ͑Fig. 5͒.…”

“…14 On the other hand, there is a large body of literature which suggests that there is almost no charge transfer from the alkali metal adsorbate to the metal substrate and the change in work function results from a dipole moment associated with the polarized adsorbate atom itself. [15][16][17][18] Different studies on metal substrates have shown that alkali metals grow as a dispersed phase or as condensed islands for the first monolayer ͑ML͒. 15,[19][20][21][22][23][24][25] In this paper, we report on the growth and electronic structure of alkali metal adlayers on the fivefold surface of an i-Al-Pd-Mn quasicrystal using x-ray photoelectron spectroscopy ͑XPS͒, since the core-level BE shift and line shape depend sensitively on the local surroundings and charge transfer.…”

Progress into Understanding of Alkali Metal Interaction with a Silicon Surface

“…However, even in its more recent approaches, the ionic bonding model was unable to explain the electronic properties of alkali metal adsorption on transition metal surfaces [13,14]. In this case, it is necessary to have theoretical methods taking into account the true electronic structure of the surface in particular the presence of highly localized electronic surface states [15]. From theoretical FLAPW ab initio calculations using the local density functional approach (LDF) [15,16] as well as from photoemission experiments using synchrotron radiation (XPS, UPS) and electron energy loss spectroscopies (ELS) [13,14,17], it was demonstrated that the nature of the bonding between alkali metal adsorbates and transition metal surfaces such as W(100), Mo(100), Ta(100), Mo(110) and W(110) was strong, polarized and covalent even at low coverages [17].…”

“…From theoretical FLAPW ab initio calculations using the local density functional approach (LDF) [15,16] as well as from photoemission experiments using synchrotron radiation (XPS, UPS) and electron energy loss spectroscopies (ELS) [13,14,17], it was demonstrated that the nature of the bonding between alkali metal adsorbates and transition metal surfaces such as W(100), Mo(100), Ta(100), Mo(110) and W(110) was strong, polarized and covalent even at low coverages [17]. This bonding was shown to be formed as a result of the hybridization between the alkali s valence electron and the substrate localized electronic d surface state [15,17]. The absence of significant charge transfer was also demonstrated by the lack of large shifts at the substrate and/or adsorbate core levels [17,18].…”