SPring-8, the large synchrotron radiation facility

（Note1）Silver halide
A halide of silver. Silver halide undergoes a chemical reaction when exposed to high-energy radiation, such as X-rays, resulting in the formation of metallic silver. Silver halide is used in photographic films. In this study, thin film samples were prepared from silver bromide (AgBr) and silver chloride (AgCl) by vacuum vapor deposition.

（Note2）Changes in lattice structure of metallic silver
Crystal lattices consist of a regular arrangement of atoms and molecules. The lattice structure may change due to photoreactions. These changes seem to occur because metallic silver atoms aggregate to form new nanograins in silver halide grains and the lattice structure of the newly formed metallic silver grains is unstable.

（Note3）Diffracted X-ray blinking (DXB)
A molecular dynamics measurement technique using monochromatic X-rays. This is the only measurement technique to enable the operando measurement (a measurement method wherein devices under operation are directly monitored) of quantum beams at the single-molecule level. Conventionally, target protein molecules were chemically labeled with gold nanocrystals with size on the order of 10 nm to obtain information on the molecular fluctuations and rotational motion associated with the motion of nanocrystals. Because DXB uses monochromatic X-rays, the diffraction spots reflecting the internal motion of single molecules are detected only in a certain wavelength range that satisfies the diffraction conditions. If the motion of single molecules is rapid, the diffraction spots moving in and out of the wavelength range fluctuate rapidly in the time trajectory of the diffraction intensity, reflecting the motion of single molecules. On the other hand, the diffraction spots fluctuate slowly if the motion of single molecules is slow. The molecular motion is evaluated by time-series analysis of the changes in the diffraction intensity reflecting this molecular motion. DXB was originally proposed by a research group led by Sasaki et al. in 2018 as a technique to measure the dynamics in single protein molecules. By this technique, the internal motion of single protein molecules can be captured not only at large synchrotron radiation facilities but also using laboratory-level X-ray source devices. In this study, DXB was applied for the first time in the world to measure the dynamics of polycrystalline materials associated with the expression of their functions.

（Note4）AIST-UTokyo Advanced Operando-Measurement Technology Open Innovation Laboratory (AIST-UTokyo OIL)
The center of research of the National Institute of Advanced Industrial Science and Technology (AIST) and the University of Tokyo, which was established at the Kashiwa Campus of the University of Tokyo on 1 June 2016. The seeds of technology developed by the two institutes are combined to enhance objective basic research, which will contribute to the construction of a network or “bridge” between industry, academia, and government. Research and development aimed at the industrialization and practical application of biofunctional materials, new materials, and innovative devices utilizing advanced operando-measurement technology are also carried out at AIST-UTokyo OIL.

（Note5）Large synchrotron radiation facility SPring-8 and BL39XU
SPring-8 is a facility that generates the world’s highest-performance synchrotron radiation. It is located in Harima Science Garden City in Hyogo prefecture and is owned by RIKEN. JASRI is responsible for supporting users. The name SPring-8 is derived from Super Photon ring-8 GeV. Synchrotron radiation is a narrow, powerful beam of electromagnetic radiation generated when electron beams, accelerated to nearly the speed of light, are forced to travel in a curved path by an electromagnet. Studies conducted at SPring-8 using synchrotron radiation include those on nanotechnology, biotechnology, and industrial applications. X-ray beams focused to a diameter of 100 nm (a ten-thousandth of a millimeter) are available at beamline BL39XU where the experiments were performed. The stable availability of high-brilliance X-ray microbeams significantly contributed to the analyses of the microcrystal in this study.

（Note6）Single-pixel autocorrelation function (sp-ACF)
A time-series analysis technique that measures the degree of consistency (correlation) between the obtained time-series data and the time-shifted version of their signals. sp-ACF was developed in this study and its effectiveness was demonstrated. When sp-ACF is used with DXB, the autocorrelation analysis is performed for each pixel in X-ray diffraction images. The decay constants are obtained from the calculated sp-ACF curves. The motion is evaluated from the distribution of the obtained decay constants. A statistical test is performed to clearly define the differences in mobility.

Fig. 1
(a) DXB setup at BL39XU in SPring-8. (b) Concept of molecular dynamics analysis by sp-ACF. Approximately 2,000 time-resolved X-ray diffraction images are taken at high speed. The properties of single grains and lattice dynamics can be quantitatively evaluated by performing sp-ACF on the changes in the intensity of target X-ray diffraction images. The research group originally developed this analytical technique.

Fig. 2 Examples of X-ray diffraction images of silver halide and silver formed by X-ray irradiation.
(a) Movements of diffraction spots caused by tilting and rotational motion of crystal grains.
(b) Changes in lattice structure of formed metallic silver.
(c) Atomic force microscopy (AFM) images of the surface of non-annealed and annealed silver halide. The increase in the crystal grain size of silver halide by annealing is observed.
(d) Results of sp-ACF of the time trajectory of X-ray diffraction intensity in Ag(111). The distribution of ACF decay constants is significantly different between the non-annealed and annealed silver halide, indicating that their dynamic properties are completely different. P < 0.001 in the figure is the significance probability.