Structural Aspects of Nanometer Size Amorphous Materials

Amorphous materials, in contrast to crystalline ones, lack long-range order. Its order decays rapidly with the distance, so the local environment for a particular type of atom is similar but not identical. The fine changes in the atomistic structure of the materials lead to new phenomena, unique for amorphous materials.

In nature there are many organisms that use crystallization via an amorphous phase in order to achieve controlled mineralization. One of the main advantages of this method is that it enables the organism to exert control over the resulting polymorph which is not necessarily the thermodynamic stable one, by first controlling the short-range order in the amorphous phase. In nature, this control is achieved using different additives, such as: water molecules, Mg ions etc.

In this research we draw inspiration from nature and study the ability to control various structural aspects of amorphous materials via nanometer size effects. We chose atomic layer deposition (ALD) as our material deposition method, since it is a technique that can provide extremely precise, sub-nanometric, thickness control and can deposit conformal and pinhole-free amorphous films of various materials.

It was preliminarily shown in our group that indeed the short-range ordering changes as a function of nanometer size in amorphous aluminum-oxide. The results indicate that the surface of the amorphous alumina possesses a different short-range order than the average in its bulk, so the thinner the amorphous solid is, the more its short-range order resembles that near the surface.

Thus in this research we continue the study on how film thickness and various deposition parameters affect the short-range order and other physical properties. We believe that the ability to tune one property or another solely by size, according to a specific requirement, can open new possibilities for materials selections and applications, in science and technology.