Atomic and molecular layer deposition for surface modification

Atomic and molecular layer deposition (ALD and MLD, respectively) techniques are examples of self-assembly based on repeated cycles of self-limiting gas-solid reactions. The precursors are pulsed into a reactor alternately, separated by inert gas pulses. During a single cycle, only one molecular layer is deposited on the surface, enabling tailored film composition in principle down to molecular resolution on ideal surfaces. These cycles are repeated until a layer with a specific thickness is achieved. Few materials are, however, ideal. During the early film growth precursors adsorb onto the surface and absorb into the near-surface regions depending both on the substrate and the deposition parameters. These precursors can react with the substrate affecting e.g. mechanical, barrier and surface properties. The deposited material starts then to form clusters leading to nonuniform early film growth. The purpose of this presentation is to demonstrate that thin and non-uniform layers can be used to tailor the surface characteristics of different substrates. For example, print quality (ink spreading and penetration) of inkjet printing on polymer films can be adjusted with metal oxide. Secondly, this can be used to control water penetration into porous nonwovens. Third example demonstrates how adhesion of extrusion coated biopolymer to inorganic oxides can be improved with a novel hybrid layer based on lactic acid. As the amount of material to be deposited is small, this will help to increase the speed in ALD/MLD processes designed for moving webs.