Molecule length-induced reentrant self-organization of alkanes in monolayers adsorbed on Au(111).

We report the observation by scanning tunneling microscopy of the reentrant self-organization of n-alkanes (C(n)H(2n+2)) in monolayers adsorbed on Au(111) induced by a variation of the chain length. In the investigated range of lengths ( 10</=n</=38 with even n values), the presence of self-assembled monolayers which consist of a close-packed arrangement of molecules lying flat on the surface is evidenced except for alkanes with 18</=n</=26. The unexpected transition between ordered and disordered phases is related to the mismatch between Au(111) lattice and the CH2-group period along the chain.