The interaction of UHV cleaved InSe crystals with Na deposited at room
temperature has been investigated using X-ray and soft X-ray photoemi
ssion. An insertion reaction is observed leading to an intercalation c
ompound Na(x)InSe for small Na concentrations (x less-than-or-equal-to
0.1). A chemical reaction occurs with x > 0.1 generating Na2Se and me
tallic In. The comparison of the XPS and the SXPS experiments clearly
indicates the bulk character of this decomposition reaction.