CONTROLLING THE SHORT-RANGE ORDER OF AMORPHOUS OXIDES BY NANOMETER SIZE

Amorphous materials, in contrast to crystalline ones, lack long-range order. Its order decays rapidly with the distance; yet, the local environment for a particular type of atom is quite similar - though not identical. These fine changes in the atomistic structure of the materials lead to new and very interesting phenomena which are unique for amorphous materials. Although many aspects of science and technology rely on amorphous materials, much less research is conducted about their structure than on their crystalline counterparts.¹

In nature there are many organisms that use crystallization via an amorphous phase in order to achieve controlled mineralization.² 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.³

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.⁴

It was shown lately in our group that indeed the short-range ordering changes as a function of size in amorphous aluminum-oxide. The results show 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.⁵

In this research we continue the study on how size affects the short-range order of different amorphous systems and correlate these changes to different properties. We believe that this amazing strategy if adopted for man-made materials could revolutionize many technological applications.

1. Drabold, D., Topics in the theory of amorphous materials. The European Physical Journal B-Condensed Matter and Complex Systems 2009, 68 (1), 1-21.
2. Addadi, L.; Raz, S.; Weiner, S., Taking advantage of disorder: amorphous calcium carbonate and its roles in biomineralization. Advanced Materials 2003, 15 (12), 959-970.
3. Gower, L. B., Biomimetic model systems for investigating the amorphous precursor pathway and its role in biomineralization. Chemical reviews 2008, 108 (11), 4551-4627.
4. George, S. M., Atomic layer deposition: an overview. Chemical reviews 2009, 110 (1), 111-131.
5. Bloch, L.; Kauffmann, Y.; Pokroy, B., Size Effect on the Short Range Order and the Crystallization of Nanosized Amorphous Alumina. Crystal Growth & Design 2014, 14 (8), 3983-3989.