Charge tranfer evidence by EELS in intercalated low dimensionnal compounds :correlation to tribological properties.
Vanina GOLABKAN 1, J.L. Mansot 1, Ph. Thomas 1, A .M. Marie 1, S. Golub 2, M. Danot 2, F. Boucher 2, K. Delbe 1, Ph. Moreau 1
e-mail: vanina.golabkan@univ-ag.fr
1 Groupe de Technologie des Surfaces et Interfaces (GTSI - EA 2432), Faculté des Sciences Exactes et Naturelles, Université des Antilles et de la Guyane, B.P. 250, 97 159 Pointe à Pitre Cedex, Guadeloupe (FWI)
2 Institut des Matériaux de Nantes Jean Rouxel, UMR CNRS 110, 2 rue de la Houssinière, 44072 NANTES Cédex 03.
Low dimensionnal compounds are subjected to intercalate lot of species (organic, mineral) in the van der Waals gap present in their structure. Depending on the electronegativity of the intercalant and the host structure, charge transfer can occur between the intercalant and the host structure modifying significantly the electronic structure and then the physical properties. Various effect can results from the charge transfer resulting in significant changes of electron energy loss spectra such as variation of energy position of the edges, modification of white line splitting. [1-2]
Three families of intercalated low dimensionnal compounds are mainly studied : MoS2, NbSe2 and TiS2. Charge transfers are evidenced either by ionization edge displacement or white line modifications (energy splitting, L3/L2 intensity ratio). Some band structure calculations (LMTO ASA) are done in order to explain the effects of charge transfer on the EEL spectra. In the case of TiS2 family a linear relationship is evidenced between energy splitting of the L3 white line and charge transfer. It allows us to estimate this last one. In the case of NbSe2 and MoS2 both energy position and L3/L2 intensity ratio are used. It allows us to classify the electron donor capabilities of the various intercalant types. Tribological results obtained on the studied compounds are then correlated to EELS results.
[1] R.D. Leapman, L.A. Grunes and P.L. Feyes, Phys. Rev B, n°26, p. 614 (1982)
[2] P. Leone, J.L. Mansot, J. Wéry, P. Euzen and P. Palvadeau, Microsc., Microa., Microstruc, 5 (1994) 79