How to obtain information from crystal surfaces: state-of- the-art techniques

In crystal growth from solution, the crystal surface and the environment immediately surrounding it form the frontline of the growth process. They contain essential information about how crystals actually grow. In this talk, I will present two examples.

(1) The first example involves advanced optical microscopy and frequency-modulation AFM (FM-AFM). These techniques can resolve not only the atomic positions on crystal surfaces in solution, but also the metastable hydration structures that appear just above growing or dissolving surfaces. Insights obtained from these observations have been applied to understanding crystallization in the early solar nebula, which I will briefly touch upon during the talk.

(2) The second example is a recent result from the Hayabusa-2 mission, which returned samples from an asteroid in our solar system. Using FM-AFM, we successfully observed spiral growth patterns on tiny crystals from the returned sample. From these patterns, we can infer the crystal’s growth rates and the solution activity that existed 4.6 billion years ago.

In crystal growth from solution, the crystal surface and the environment right next to it form the frontline of the growth process. They contain a great deal of information about how crystals actually grow. In this talk, I will introduce two examples: (1) one using modern optical microscopy, and using frequency-modulation AFM (FM-AFM). These techniques can resolve not only the positions of atoms on the crystal surface in solution, but also the metastable hydration structures just above growing or dissolving crystal surfaces. These understanding has been applied to the crystallization in relay solar nebula, which would be mentioned briefly during the talk. (2) Another example is a new result obtained from the returned sample by the Hayabusa-2 mission which returned from an asteroid in our solar system. In this study we successively observed spiral growth pattern on a small crystals by FM-AFM to get the information about the growth rate of the crystal and solution activity in 4.6 billion years ago.

Our goal is to visualize these interfacial processes in situ with atomic or molecular resolution. To do this, we have developed and used several diagnostic methods. For example, phase-sensitive optical phase-shift microscopy and interferometry allow us to directly observe surface growth at molecular level in real time. We have applied these methods to study a variety of crystals under extreme conditions—not only on Earth, but also inside the Earth and even in microgravity environments such as the International Space Station. By examining growth rates together with molecular-scale surface topography, we can better understand the fundamental mechanisms of crystal growth. More recently, FM-AFM, developed by Fukuma(1) and colleagues, has produced remarkable results. Because it can scan several frames per second with atomic resolution, it lets us visualize the dissolution of individual monomolecular steps as it happens. On calcite, Ca(CO3)2, crystal surfaces, we observed—for the first time— metastable dissolution layers that are only half the height of a minimal monolayer. These layers were identified as transient Ca(OH)2. Later work by Miyata and co-workers (2) showed that these layers are covered by hydration layers, which keep them attached to the surface for a short time before they disappear.

Zoom: https://dipc-org.zoom.us/j/98837185629

Youtube: https://youtube.com/live/ziezN86gV24