Growth of silicated films at the solid/liquid interface

Studies of the initial stages of growth of silicated films at the silicon/liquid interface have been performed with neutron reflectometry. The use of special cells allows this first direct observation of film growth by reflectometry that is not at the air/solution interface, removing complications due to drying. The induction period is reduced in time compared with the air/water interface case and the appearance of diffraction peaks is not dependent on whether the silicon surface is initially hydrophilic or hydrophobic. However the structures initially formed at the interface are different. The hydrophilic interface initially has a layer of spherical or rodlike micelles of the cationic surfactant adsorbed. At the hydrophobic interface hemispheres are initially adsorbed. These structures remain almost unchanged during the induction period, contrasting with the multilayer which develops at the air/solution interface prior to growth. The results suggest that the induction period and bulk film growth depend on bulk solution properties and not interfacial conditions. We also observe similar adsorption of the cationic surfactants at the hydrophilic and hydrophobic silicon interfaces with a pH well below the isoelectric point of silicon oxide for similar surfactant solutions when the silicate source is omitted.