Boosting memory capacity with Prussian Blue
Prussian blue has been prized by artists since the 18th century. Today, scientists are taking a keen interest in this pigment by studying what happens when some of its iron atoms are replaced by cobalt atoms. This research was carried out on the infrared beamline AILES in 2011.
Autumn 2024: a look back at this research
In 2011, the AILES beamline of the SOLEIL synchrotron hosts chemist Anne Bleuzen, who delves into Prussian blue, a pigment highly valued by painters since the 18th century. It is a compound of iron and cyanide, and when slightly modified, for example, by replacing some iron atoms with cobalt atoms, it acquires properties that have become the focus of extensive research worldwide. These new compounds open up a vast field of research, known as "Prussian blue analogues" or "PBA."
PBAs can indeed take on two distinct states, each associated with a different color—blue and brown. These two states can be "activated" by a stimulus, whether it be light, temperature, or pressure. So, we now have tiny objects with two states that can be controlled—does that remind you of anything? It’s precisely the basis of a binary coding system. Each state can be interpreted as a 0 or a 1. Based on this, it could become possible to create extremely small computer memories.
But to achieve this, many obstacles must be overcome, and Anne Bleuzen sets out to tackle each one, relying every time on the versatile tool that is the synchrotron.
First, she needs to control the transition from one state to the other, "from 0 to 1," and vice versa. Normally, this switching requires very low temperatures, around -200°C, which is highly impractical for creating computer devices. In 2012, with the help of the combination of X-rays from the ODE beamline and infrared rays from the SMIS beamline, Anne succeeded in achieving this transition at room temperature—a significant breakthrough!
Next, it is necessary to create nanomaterials from PBAs that could become the building blocks for new electronic components. In 2018, on the SAMBA beamline at SOLEIL, Anne received confirmation that she had successfully synthesized these valuable nanocrystals. They are indeed "photo-switchable": they can transition between states under the influence of light.
Another way to activate PBAs is by using pressure. In 2012, on ODE and SMIS, Anne applied external pressure to slightly distort the material, enabling the transition at room temperature. In 2022, she turned her attention to another kind of pressure, not physical but chemical. PBAs contain interstitial cations that exert stress on the main structure. Once again on the ODE beamline, she conducted analyses and gained a better understanding of how these cations interact with the cyanide-cobalt-iron complex.
Finally, to envision the creation of electronic components one day, it is necessary to manufacture tiny structures that resemble the elements of circuits. Two experiments conducted by Anne, in 2010 and 2017, laid the groundwork for this. She managed to "grow" nanocrystals in the form of pillars, starting from molecules in solution.
Anne Bleuzen’s ideas continue to evolve in the PBA galaxy. Moreover, Prussian blue analogues are generating real excitement in fields such as electric batteries, catalysis, and even radioactive decontamination.
Related publications
(1) Cafun, J.D., Lejeune, J., Baudelet, F., Dumas, P., Itié, J.P., Bleuzen, A. "Room-Temperature Photoinduced Electron Transfer in a Prussian Blue Analogue under Hydrostatic Pressure" Angewandte Chemie International Edition, 51(36): 9146-9148 (2012).
(2) Bordage, A., Moulin, R., Fonda, E., Fornasieri, G., Riviere, E., Bleuzen, A. "Evidence of the core-shell structure of (photo)magnetic CoFe Prussian blue analog nanoparticles and peculiar behavior of the surface species." Journal of the American Chemical Society, 140(32): 10332–10343 (2018).
(3) V. Trannoy, M. Faustini, David Grosso, F. Brisset, P. Beaunier, E. Rivière , M. Putero, A. Bleuzen. "Spatially controlled positioning of coordination polymer nanoparticles onto heterogeneous nanostructured surfaces." Nanoscale, 9 (16): 5234-5243 (2017).
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AUDIO TRANSCRIPTION OF THE VIDEO
VOICE-OVER
Prussian blue – composed of iron and cyanide – has been prized by artists since the 18th century. Today, scientists are taking a keen interest in this pigment by studying what happens when some of its iron atoms are replaced by cobalt atoms.
And for good reason, this new compound is able to change colour by switching from one state to another in a stable manner. The two colours and states make it possible to memorize binary information and store computerised data in binary form using the digits “0” and “1”.
Anne Bleuzen - lecturer and chemist (Paris 11 University - CNRS)
There are two very closely related energy states in these compounds, and it is possible to cause the compound to switch from one state to another by applying an external stimulus, such as light, temperature or pressure. Here, for example, the violet ground state is the “0” state; if we subject it to an external stimulus such as light, for example, we can cause it to switch to the “1” state and the colour changes to brown.
VOICE-OVER
With the help of these Prussian Blue derivatives, chemists hope to be able to store information on the scale of a few atoms and thus substantially reduce the size of hard drives.
The downside, however, is that the change of state occurs at very low temperatures with Prussian blue: at around -200°C. But in order to use this compound to make miniature hard drives someday, the switching must be operative at room temperature.
To try to solve this problem, Anne Bleuzen’s team is performing measurements on SOLEIL synchrotron’s AILES beamline, an infrared radiation beamline that can reveal the structure of Prussian blue.
Pascale Roy - manager of the AILES beamline (Synchrotron)
We have two components and the position of the atoms, and we also have the restoring force between the various atoms. The far-infrared will not only provide information on the position of the atoms, but also on the force that binds the different atoms together.
VOICE-OVER
Prussian blue derivatives are composed of iron, cobalt and cyanide. They also contain cations – Sodium, in this case – that make the overall structure more or less rigid and switching more or less easy.
Anne Bleuzen:
The cobalt iron cyanide linkages comprise strong chemical bonds and the alkali cations disrupt these chemical bonds.
We are interested in the interaction of this cation with the structure and the cobalt iron cyanide linkages.
VOICE-OVER
This knowledge at the atomic scale is an essential step towards finding the right mix of cations so that someday memory drives weighing just a few grams can be manufactured for laptops, mobile phones and MP3 players. It will take a few more years, however, to find manufacturing processes for these extremely small structures.