Optical Investigation of Nanoconfined Crystal Growth

Abstract:

Crystals growing in a confined space exert forces on their surroundings. This crystallization force causes deformation of solids and is therefore particularly relevant for the comprehension of geological processes such as replacement and weathering [1]. In addition, these forces are relevant for the understanding of damages in porous building materials caused by crystallization, which is of great economical importance and fundamental for methods that can help to preserve our cultural heritage [2,3].

However, the exact behavior of the growth and the dissolution process in close contact to an interface are still not known in detail. The crystallization, the dissolution and the transport of material is mediated by a nanoconfined water film.

We observe brittle NaClO₃ crystals growing against a glass surface by optical methods such as reflective interference contrast microscopy (RICM) [4]. In order to carefully control the supersaturation of the fluid close to the crystal interface, a temperature regulated microfluidic system is used (fig. A). The interference based precision of RICM enables to resolve distance variations down to the sub nanometer range without any unwanted disturbances by the measuring method. The combination of RICM with a sensitive camera allows us to observe phenomena such as periodic, wavelike growth of atomic layers. These waves are particularly obvious when observing the difference between two consecutive images (fig. B).

In contradiction to some theoretical results, which predict a smooth interface, some recent experiments have shown that the nanoconfined growth surfaces are rough. In combination with theoretical studies and Kinetic Monte Carlo simulations we aim at providing more realistic descriptions of surface energies and energy barriers which are able to explain the discrepancies between experiments and current theory.

References:

[1] Maliva, Diagenetic replacement controlled by force of crystallization, Geology, August (1988), v. 16

[2] G. W. Scherer, Cement and Concrete Research, 34 (2004) 1613

[3] Flatt, R. J. , Caruso, F., Sanchez, A. S. A. and Scherer, G. W., Nature Communications, 5 (2014) 4832

[4] Sekine, S., Okamoto, A.,Hayashi, American Mineralogist, 96 (2011) 101