Alkali displacements in intercalated 1T-TaSe2

Abstract

Abstract. Single crystals of lT-TaSe2 have been intercalated with different alkali metals by deposition in ultra-high vacuum onto in situ-cleaved (0001) surfaces. In a second step a different alkali metal, or C12, has been deposited on top. The interactions among the deposited species and the substrate have been investigated using soft x-ray photoelectron spectroscopy (SXPS). Li and Na appear to compete in the intercalation process. Li replaces Na, by pushing it deeper into the crystal. Cs on Li:TaSe2 does not intercalate, but stays on top, repelling intercalated Li + deeper inside. For Li on Cs:TaSe2 an exchange reaction takes place, and Cs is deintercalated. The same effect is induced by Na deposited on intercalated Cs. 1T--->2H phase transition for TaSe2 has been observed only for Li depos!tion. C12 deposition on Na intercalated substrate induced deintercalation of Na. The experimental results are discussed in relation to thermodynamic, electronic and electrostatic effects.

Origin of the Electrochemical Potential in Intercalation Electrodes: Experimental Estimation of the Electronic and Ionic Contributions for Na Intercalated into TiS2

“…Again in comparison to the Na adsorption experiments it can clearly be assigned to the intercalated Na. There is no decomposition of the substrate involved in the given charging-discharging range of about Na x TiS 2 , as is clear from the lack of decomposition products in the core level lines of Ti and S and the valence band spectra measured by UPS (a detailed analysis of the changes in electronic structure will be published elsewhere 41 ). The charge transfer associated with alkali intercalation leads to the filling of empty states in the conducting band, and consequently to a shift of the Fermi level, which implies a change for all binding energies.…”

“…This change is evaluated in Figure 5, where the shift of the binding energy of the Cl 2p core levels is compared with the variation of the work function. Also, the core level lines of the other elements show a BE shift, which, however, is smaller due to the superposition of different effects (for details see ref 41).…”

In-situ photoelectron spectroscopy study of a TiS2 thin film cathode in an operating Na intercalation electrochemical cell

“…It may be argued that this could be due to a reduced sticking coefficient of the evaporated metal to the substrate. But previous co-deposition experiments of different alkali species have shown that a prolonged deposition promotes the penetration of the intercalated alkali ions into deeper layers, instead of increasing their concentration [27][28][29]. To give more evidence for this effect and to obtain higher alkali concentration, we prepared TiS2 films in UHV in the present work and used those as a substrate.…”