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In-Situ Observation of Crystal Growth: in the past and in the future
Graduate school of Scienece, Tohoku University, Sendai 980-8578, Japan
It was during the banquet of ICCG-4 (1974) in Tokyo when I met Professor Frank. I was a master course student who attended international conference for the first time. I knew his name for spiral growth theory. I wanted to have his signature on a small square wooden cup for Japanese rice wine. The organizer at the banquet presented the cup to us. Although I was very much hesitated to ask him, he kindly wrote his signature on my wooden cup. I still keep this cup in my office for the memory of my start of crystal growth study, so that it was my biggest honor to receive the award that bears the name of Frank.
In the lecture, I want to discuss why in-situ observation of crystal growth from solution phase was necessary in those days, followed by the recent development together with the applications and then possible future of in-situ observation.
Ichiro Sunagawa was my first professor who introduced me to the world of crystal growth by showing beautiful spiral patterns on various minerals that were grown mainly from vapor phases. It was a shock for me not only because of the beautiful spiral patterns but also because of the ability of optical phase-contrast microscopy, which could reveal mono-molecular growth steps with the height of a few Angstrom.
He often showed me a work of Bennema in the Netherlands who had been investigating the growth mechanism of aqueous solution grown crystals by measuring the growth rate vs supersaturation. His thesis was to verify the applicability of spiral growth theory to aqueous solution grown crystals. Professor Sunagawa then invited Professor Bennema to Tohoku University, where we had a good time for discussion on crystal growth. After he came back to the Netherlands, he invited me to his laboratory in 1977-1979.
I leaned from Sunagawa to observe crystal surface by phase-sensitive optical microscopy to understand the growth history of the crystal. However the surface pattern, which could be observed, were already “dead”. While, in the lab of Bennema, I learned how to measure extremely slow growth rate of crystals by measuring the weight increase or the size increase and how to apply crystal growth theories to real crystal growth. However I was not satisfied with their methods because of two reasons: it takes several weeks to finish a measurement of growth rate vs supersaturation, and we could not see, during experiment, the crystal surfaces that should posses the information about the growth mechanism.
In order to overcome these difficulties, I started to couple the surface observation method with the crystal growth rate measurement by developing various optical in-situ observation methods for crystal growth.
These in-situ observation methods have been applied to crystal growth not only to investigate crystal growth mechanisms for fundamental sciences but also to crystal growth in earth and in astronomical environments for the understand of nature and the history. These new and successful studies could be achieved thanks to the efforts of my colleagues, students and companies.
The topics for Frank Prize Award Lecture will be selected from the following categories:
1. Development of High Resolution Optical In-Situ Observation Methods and the Application to Fundamental Crystal Growth Studies
Before 1980s, if one wants to investigate growth mechanism from solution, the measure the growth rate vs supersaturation by weighing method developed by Bennema was the only way. However, it took more than a few weeks to complete all of the measurements and the analysis on growth mechanism was indirect. We developed in-situ observation method directly to observe mono-molecular spiral steps on crystal faces by advanced optical microscopies during crystal growth in well-controlled conditions (1983). This made us possible also to understand the effect of defects and flows in crystals on the growth of kinetics of inorganic crystals (1988) and of proteins (1989).
The in-situ surface observation was later coupled with interferometer to visualize the concentration/temperature fields over the surface together with the observation of monomolecular growth steps, to study the effect of flow and the inhomogeneity of concentration around the crystals (1988). The high temperature in-situ observation method was applied to study the natural crystallization from magma, LiNibO3 and GaAs from the melt phase.
Ultra-high resolution interferometry (Real-Time Phase-Shift Interferometry, RPSI) for crystal growth studies was developed in 1994. This interferometer showed two-order of magnitude higher resolution than conventional interferometry and thus pioneered some new research fields, in which crystal growth/dissolution rate is extremely slow like in earth sciences, in environmental sciences or in carbon sequestration. The interferometry has further been developed to posesse the capability of 3D observation (2010) and ultra-high speed (10,000 frame/s) for the study of mass and heat transfer in nucleation process as well (unpublished).
2. Utilization in Other Fields:
(1) Application to Space Experiments
Numerous growth experiments have been conducted under microgravity in space shuttles, rockets and so on. However the method to study the growth mechanism of crystals was a simple way as follows: to grow crystal in space followed by the transport of these materials to the ground for the characterization on the ground. We did not like this indirect way of studies and for the first time successfully used interferometer for in-situ studies of crystal growth mechanism under microgravity (1991). The in-situ method was later applied in NASA and ESA projects for mainly to the studies of protein crystal growth mechanism using space shuttles.
Everybody believed that growth rate of protein crystals under microgravity would be smaller than that in gravity because buoyancy driven convection and flows could be suppressed in space. However the growth rate of protein crystals measred in a Russian satellite in 2007 and in the International Space Sation in 2011 by in-situ method was sometimes larger than that in gravity.
Simultaneously with this velocity increase in microgravity, appearance of the sharp corner of the elementary step was observed even in impure soluiotns. That sharpning was identified as impurity controlled. These two findings (the velocity measurements and morphology change) suggest that lack of convection allows self- purification of the growing crystal via absorbing impurities from the surrounding mother liquor. That may be solution of the long standing problem on why protein crystals sometimes grow more perfect in microgravity.
(2) Application to environmental sciences and engineers
Application of in-situ observation to natural slow phenomena was started to measure the solubility and reaction kinetics of insoluble minerals (1991). The ultra-slow growth rate of giant gypsum crystals, ~11 m long in Mexico was measured with collaboration of Garcia Ruiz et al. (2012) to be 10-5nm/s (<1μm/year) by newly developed white beam phase-shift interferometry (PSI). This was the champion data of the slowest crystal growth rate which has been mesed so far.
The PSI had practically been applied to nuclear waste studies in Japan (1993). The waste will be stored in the glass state with surrounding barrier of clay minerals under the ground for 100,000 years but reacts with ground water. However, so far there is not suitable method to measure the dissolution rate of the clay minerals exactly. The meased growth rate is the order of 10-5 nm/s.
The in-situ observation was also useful to the study of “Carbon Sequestration” or “CCS” in which how the dissolved CO2 in water could be sealed and trapped in the cap rocks is the key.
(3) Crystallization 4.6 billion years ago: rapid crystallization in space
Combination of in-situ observation of crystal growth with experience under microgravity made a new progress in space sciences (1998, 2006). Chondrules are silicate spheres with a few mm size formed from melt droplets 4.6 billion years ago in the primitive solar system. These spheres are often found in meteorites and regarded as the result of very slow cooling and growth rate in many years time. However, levitating these melt droplets experimentally showed that the crystallization of the melts has to be finished in a few seconds at the supercooling of several hundreds K or more in the hypercooling regime (2010).
(4) Structures of the solution at the crystal surface
Recently, we have successfully used newly developed frequency-modulate AFM (FM-AFM) with atomic resolution to reveal atomic configuration of the crystal surface during crystal growth from solution (2012). Since this FM-AFM is very sensitive, we also succeeded to visualize the hydrated structures in-situ at the crystal surface and even at the step front. Notwithstanding that the growth rate of solution grown crystals is controlled by the dehydration process, we know litte about the hydrated structure at the surface and steps.
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Presentation: Plenary Lecture at 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17, Plenary Session, by Katsuo Tsukamoto
See On-line Journal of 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17
Submitted: 2013-07-03 21:27 Revised: 2013-07-15 21:24