Press Releases – Graduate School of Science, University of Tokyo, Faculty of Science

date01/24/2024 #Press statements

–Development of ultrafast sample flow-type X-ray diffraction method—

Shinichi Okoshi (Professor, Department of Chemistry)

Yuko Tokoro (Professor, Department of Mathematics and Materials, University of Tsukuba)

Eric Collet (Professor, University of Rennes)

Key points of presentation

• Since the optical phase transition in optical memory materials is irreversible, tracking structural changes has been difficult. Using a newly developed sample flow-type ultrafast X-ray diffraction method, we have developed a technique that enables ultrafast observation with a temporal resolution of 35 picoseconds.
• Using this method, we performed a demonstration experiment on Prussian blue for rubidium, manganese, cobalt, and iron and demonstrated that structural changes after light irradiation can be measured very quickly and with high precision.
• Optical phase transition at room temperature is a phenomenon used in memories, optical devices, etc., and this measurement method is expected to be useful.

Development of an ultrafast sample flow-type X-ray diffraction method

Presentation summary

The optical phase transition of optical recording materials at room temperature is an irreversible phenomenon caused by a single shot of laser light irradiation, which makes it impossible to perform integrated measurements and makes it difficult to observe changes in phase transition over time.

This time Professor Shinichi Okoshi from the Graduate School of Science, University of Tokyo (Director of DYNACOM, CNRS International Cooperative Research Institute, France)^{(Note 1)}), Professor Yuko Tokoro from the Department of Mathematics and Materials at the University of Tsukuba (simultaneously working at CNRS DYNACOM), and Professor Eric Collet from the University of Rennes, France (Deputy Director of CNRS DYNACOM) are collaborating in a research team that has developed a new method for monitoring changes in crystal structure using diffraction Ultrafast Time-resolved ultrafast X-rays. This method has been used at the European Synchrotron Radiation Facility (ESRF) beamline to produce Prussian blue (Rb) rubidium, manganese, cobalt, and iron compounds._0.94(from_0.94a company_0.06)[Fe(CN)₆]_0.98)^{(Note 2)}We succeeded in observing the change in the crystal structure of the optical phase transition in… The use of the newly developed sample flow-type ultrafast X-ray diffraction is expected to enhance research on the temporal dynamics of irreversible phenomena such as optical writing and optical scanning.

Display content

Optical phase transition is a phenomenon in which light switches between two states, which is an important phenomenon that forms the operating principle of optical devices, memories, actuators, etc. In practice, optical phase transition occurs at room temperature, and the temperature range over which two states can be switched is wide, i.e. Temperature hysteresis as phase transition materials.^{(Note 3)}It is important that the area is spacious.

Understanding the fundamental physical mechanisms that drive optical phase transitions is important for materials development. However, until now, it has been difficult to observe the phase transition process at room temperature because the optical phase transition within temperature hysteresis occurs instantaneously when laser light is irradiated even once. Therefore, the research team developed ultrafast and temporal X-ray diffraction using a sample flow system. As an illustrative example, the compound of rubidium, manganese, cobalt, and Prussian blue iron (Rb_0.94(from_0.94a company_0.06)[Fe(CN)₆]_0.98) were measured at room temperature.

Prussian blue shows newly synthesized rubidium, manganese, cobalt and iron blue with a charge transfer type phase transition. Mn on the temperature rise side^secondly-NC-Fe^Thirdfrom^Third-NC-Fe^secondlyIt showed a phase transition to a charged state called the low temperature (LT) phase. Figure 1 shows this situation. During cooling, the phase transition from the HT phase to the LT phase occurs at -20 °C (253 K), and when the temperature rises, the phase transition from the LT phase to the HT phase occurs at +55 °C (328 K). The hysteresis temperature range was up to 75 K, covering room temperature. In this material, the phase transition from the LT phase to the HT phase can be induced at room temperature by irradiating laser light. As shown in Figure 1a, a color change occurs as the laser beam is irradiated, and a high-temperature phase is created.

Figure 1: Schematic of the optical phase transition in rubidium, manganese, cobalt, and Prussian blue iron and ultrafast X-ray diffraction using a sample flow system.
(a) Image of a Prussian blue thin film of rubidium, manganese, cobalt, and iron irradiated with laser light at room temperature. LT stage (Mn^Third-NC-Fe^secondly) and HT phase (Mn^secondly-NC-Fe^Third) The color change appears between Starting from the LT phase, the laser is excited (120 W/cm3).²Spot size 0.2 mm², 3 seconds of irradiation) leads to an optical phase transition, and a color change is observed at the position of the laser spot (spot at the end of the green arrow). (b) Temperature hysteresis between LT and HT phases in magnetic susceptibility × temperature versus temperature. The inset is a schematic diagram of the electronic configuration of the LT and HT phases. (c) Time-resolved ultrafast X-ray diffraction using a sample flow system. Microcrystals of rubidium, manganese, cobalt and Prussian blue iron (about 1 micrometer in size) dispersed in solution are distributed through a liquid jet. The crystal is transformed from the LT phase (blue) to the HT phase (red) by irradiating laser light within a temperature hysteresis, and changes in the crystal structure are examined by irradiation with an X-ray beam with a time delay (Δt). The dispersion in the tank is cycled through a cooling device (230 K, below the transition temperature) to re-crystallize it to the primary LT phase before a new laser beam is applied at room temperature.

In this paper, we develop a time-resolved ultrafast X-ray diffraction method using a sample flow system at the European Synchrotron Radiation Facility (ESRF). This method studies changes in crystal structure during optical phase transitions by irradiating dispersed crystals in solution with light and performing ultrafast time-resolved X-ray diffraction measurements. The important point is that by flowing and circulating dispersed crystals in a solvent, crystals that have undergone a phase transition due to light irradiation can be reformatted back to their original crystalline structure through a coolant, and thus the number of measurements can be accumulated infinitely. This makes it possible to obtain ultra-fast and detailed information about changes in crystal structure even during temperature hysteresis. The time resolution of time-resolved ultrafast X-ray diffraction is 35 picoseconds.

Using this method, we performed a demonstration experiment on the optical phase transition in Prussian blue for rubidium, manganese, cobalt, and iron. As a result, we found that the optical phase transition from the LT phase to the HT phase occurs at laser light intensity above the threshold (Figure 2). We also found that the energy barrier between the LT and HT phases plays the following two important roles within the temperature hysteresis (Figure 3). First, in order to destabilize the crystal structure of the LT phase and cause the transition to occur during the optical phase transition, the critical volume is required to expand, and this increases the laser light intensity during the phase transition. threshold. Second, this volumetric expansion stabilizes the photo-induced HT phase and allows it to be maintained for a long time.

Time-resolved ultrafast X-ray diffraction using sample flow systems holds great promise for measurements of optically driven devices, memories, or actuators that exhibit room temperature switching. It is expected that this method will be used to investigate the dynamics of irreversible phenomena in various optically functional materials.

Figure 2: Intensity dependence of laser light in time-resolved ultrafast X-ray diffraction
This shows how the X-ray diffraction pattern changes with time when a Prussian blue crystal of rubidium, manganese, cobalt and iron in the LT phase is irradiated with laser light. t = 0 represents the irradiation time of laser light. Light irradiation was performed at room temperature and at three different light intensities: low intensity (15 mJ cm^-2 ), medium density (36 mJ cm^-2), high strength (115 mJ cm^-2)) executed.

Figure 3: The optical phase transition mechanism is observed this time
(a) When irradiated with low-intensity laser light within temperature hysteresis.The number above is the Landau potentialgAnd the iron breedtheThe figure below shows a diagram of how the crystal changes. When the upper LT phase is irradiated with a weak laser beam, the ferroelastic strain shift does not become significant due to small volume expansion, and the photoexcited tetramer (PT phase) returns to its original LT phase. (b) When high-intensity laser light is irradiated within a temperature hysteresis. Large volumetric expansion ∆Fifthoccurs within 100 ps, ​​destabilizing the tetragonal crystal structure and transforming the cubic phase (the = 0). The photogenerated cubic phase (PIC) is preserved due to the energy barrier and becomes the HT phase at equilibrium. (c) Time course plot when laser light intensity is low and high.

Paper information

Journal title	Nature Communications
Paper title	Ultrafast, continuous phase transition at room temperature monitored by powder diffraction flow
author	Marius Hervé, Gaël Brévault, Elzbieta Trzope, Shintaro Akagi, Yves Watier, Serhan Zardan, Evgenia Chaban, Ricardo Ge. Torres Ramirez, Celine Mariette, Alex Folt, Marco Cammarata, Matteo Levantino, Hiroko Tokoro*, Shin-ichi Okushi*, Eric Collet*
DOI number	10.1038/s41467-023-44440-3

Research grants

This work was carried out with support from the Grant-in-Aid for Scientific Research “Fundamentals A (Project Number: 20H00369)” and the JST “Emergency Support Project (Project Number: JPMJFR213Q)” by the International Collaborative Research Institute CNRS of France IRL DYNACOM.

Glossary of terms

Note 1 France CNRS International Institute for Cooperative Research DYNACOM (Dynamic Control of Materials)
An international organization studying the fast-time dynamics of optical phase transition phenomena, initiated in 2022 by the French National Center for Scientific Research (CNRS), the University of Tokyo, and the University of Rennes. We conduct research in cooperation with the European Synchrotron Radiation Facility and the Swiss Free X-ray Laser Facility.↑

Note 2 Rubidium-manganese-cobalt-iron complex Prussian blue (Rb_0.94(from_0.94a company_0.06)[Fe(CN)₆]_0.98)
Rubidium, manganese and iron Prussian blue (RbMn) is the base material of this material.[Fe(CN)₆]) is a compound that was first reported by Okoshi et al in 2002.[S. Ohkoshi, et al., J. Phys. Chem.B, 106, 2423 (2002)]. The material used in this study is a material in which part of the manganese (Mn) is replaced by cobalt (Co).↑

Note 3 Temperature deceleration
In a phase change material, when a phase transition occurs by changing temperature, the temperature at which the phase transition occurs during the cooling process and the heating process may be different. The temperature difference at this time is called temperature hysteresis.↑