Hybrid nanomaterials through molecular and atomic layer deposition: Top down, bottom up, and in-between approaches to new materials

The ability to produce or alter materials to obtain drastically different or improved properties has been the driving goal of materials science since its inception. Combining multiple elements, compounds, or materials while maintaining the beneficial aspects of each constituent is a complex problem often involving highly interdisciplinary research. Hybrid materials, i.e. materials that incorporate organic and inorganic parts, have become popular in a variety of fields. Though not entirely new, the modern embodiment of hybrid materials has led to a large variety of new materials and techniques to produce them. One of the most recent being combination of atomic layer deposition (ALD), which produces inorganic materials, and molecular layer deposition (MLD), which produces organic materials. Furthermore, a variation on these techniques, commonly referred to as infiltration, has allowed for the modification of a variety of natural and synthetic polymers with surprising results related to their bulk mechanical properties. In this review three approaches are taken. First, hybrid materials through bottom-up combinations of ALD and MLD are reviewed, focusing on the process and properties of the resulting materials. Second, the modification of biomaterials through coating is discussed, and finally the relatively new concept of vapor phase infiltration is considered as a new and unique method to produce hybrid materials from a top down perspective.