Ultrathin Molybdenum Polyoxometalate−Polyelectrolyte Multilayer Films

Ultrathin multilayer films of a novel molybdenum(VI) polyoxometalate cluster ((NH 4 ) 21 [H 3 Mo 57 V 6 (NO) 6 O 183 (H 2 O) 18 ]) (Mo 57 ) and poly(allylamine hydrochloride) (PAH) have been prepared by the consecutive stepwise adsorption of Mo 57 and PAH from dilute aqueous solution. The Mo 57 /PAH multilayer films have been characterized by optical spectroscopy and small-angle X-ray reflectivity (XR) methods. UV−vis measurements reveal regular film growth with each Mo 57 adsorption. The average Mo 57 surface density was found to be (1.4 ± 0.4) × 10 13 clusters per cm 2, corresponding to an average surface coverage of 56 ± 12%. XR experiments confirm uniform film growth, with the film thickness increasing with each Mo 57 adsorption step. The average thickness for the Mo 57 /PAH layer pair was determined to be 0.8 ± 0.1 nm. The Mo 57 density in the film can be readily controlled by varying the polyelectrolyte interlayer separation between each Mo 57 layer, and the total film thickness can be controlled by altering the number of adsorption cycles.