The structure of sodium intercalated 1T and 2H polytypes of TaS2: a photoemission and SEXAFS study

Na deposited 1T and 2H polytypes of TaS 2 have been investigated by means of surface extended X-ray absorption fine-structure (SEXAFS) and photoemission studies. The photoemission spectra show that at room temperature Na mainly intercalates for both polytypes with no reactive component. The intercalated sodium atoms are positioned in the van der Waals gap in a sixfold coordinated site due to the SEXAFS analysis. The Na-S nearest neighbour distances are 2.95 ± 0.05 A for 1T and 2.85 ± 0.05 A for 2H polytype corresponding to an increase of the gap width by 1.5 ± 0.06 and 1.3 ± 0.06 A, respectively. With increasing amount of deposited Na, a fraction of sodium atoms remains on the surface. The adsorbed Na atoms occupy a threefold hollow site on the surface with a Na-S bond length of 2.91 ± 0.05 A for 1T and 2.80 ± 0.05 A for 2H polytype.