The movement of individual atoms through liquid has been captured in camera for the first time.
Using a sandwich of materials so thin they are effectively two-dimensional, the scientists trapped and watched platinum atoms “swim” along a surface under different pressures.
The results will help us better understand how the presence of liquid alters the behavior of a solid with which it is in contact, which, in turn, has implications that could lead to the development of new substances and materials.
“Given the widespread industrial and scientific importance of this behavior, it is truly surprising how much we still have to learn about the fundamentals of how atoms behave on surfaces in contact with liquids,” explained materials scientist Sarah Haigh of the University of Manchester in the UK. .
“One of the reasons for the lack of information is the absence of techniques capable of producing experimental data for solid-liquid interfaces.”
When a solid and a liquid are in contact with each other, the behaviors of both materials change where they meet. These interactions are important for understanding a wide range of processes and applications, such as the transport of materials within our own bodies or the movement of ions within batteries.
As the researchers point out, it is extremely difficult to see the world at the atomic scale. Transmission electron microscopy (TEM), which uses an electron beam to generate an image, is one of the few techniques available.
However, obtaining reliable data on the behavior of atoms in this way has been difficult. Previous work on graphene liquid cells has shown promise but yielded inconsistent results. In addition, TEM typically requires a high vacuum environment to operate. This is a problem since many materials do not behave in the same way under different pressure conditions.
Fortunately, a form of TEM has been developed to work in both liquid and gaseous environments, which is what the team used for their research.
The next step was to create a special set of microscope “slides” to hold the atoms. Graphene is the ideal material for these experiments, because it is two-dimensional, strong, inert and impermeable. Building on previous work, the team developed a double-graphene liquid cell capable of working with existing TEM technology.
This cell was filled with a precisely controlled saltwater solution containing platinum atoms, which the team observed moving on a solid molybdenum disulfide surface.
The images revealed some fascinating insights. For example, atoms move faster in liquid than out of it, and choose different places on the solid surface to rest.
In addition, the results inside and outside a vacuum chamber were different, suggesting that variations in the pressure of the environment can influence the behavior of the atoms. Also, the results of experiments obtained in vacuum chambers will not necessarily be indicative of this behavior in the real world.
“In our work we show that studying atomic behavior in a vacuum instead of using our liquid cells gives misleading information,” said materials engineer Nick Clark from the University of Manchester.
“This is a milestone and just the beginning: we are already looking to use this technique to support the development of materials for sustainable chemical processing, needed to achieve the world’s net zero ambitions.”
The material the team studied is relevant to green hydrogen production, but both their techniques and the results they obtained have much broader implications, the researchers said.
The paper has been published in Nature.