Researchers develop a simple method to build stable, atom-thick metal layers using tiny defects in carbon, enabling efficient use of metals across technologies.
(Nanowerk Spotlight) Using metals in atom-sized fragments is one of the most effective ways to make chemical reactions faster and more efficient. In particular, metal clusters are tiny groupings of just a few atoms that sit on a surface where every atom can participate in a reaction. Unlike conventional metal particles, which may contain thousands of atoms with only the outer layer exposed, clusters allow all atoms to remain accessible. This makes them especially useful when working with rare or expensive metals such as platinum or palladium.
However, working at this scale presents a challenge. Metal atoms are highly mobile when dispersed across a surface. They tend to drift and combine, forming larger particles with internal atoms that are no longer accessible for reactions. To be effective, the cluster must stay flat and stable. It must remain as a single layer of atoms securely attached to the surface.
Scientists have attempted to solve this problem by modifying the surfaces onto which the metals are deposited. One strategy involves adding other elements, such as nitrogen or fluorine, into carbon materials to strengthen the bond between metal atoms and the surface. Another approach uses layered structures that physically confine the metal atoms. These methods can work in specific cases but are often difficult to scale and do not apply broadly to different metals.
A different idea involves using vacancies. These are defects on the surface where carbon atoms are missing, creating sites that can bond strongly with metal atoms. In theory, these vacancies could stabilize metal atoms more effectively than doping. In practice, they react quickly with air or solvents and lose their reactivity. This problem has prevented defect-based approaches from becoming a general method for forming stable, atomically thin metal clusters.
Using argon ions, they generate defects and deposit metal atoms in a controlled sequence, all within the same inert chamber. This prevents the defects from becoming chemically saturated and allows the formation of dense, stable metal clusters composed of just a single layer of atoms. The method works without doping or complex confinement and applies across a wide range of elements.
This approach produced single-layer clusters of platinum at a density of 4.3 atoms per square nanometer, which is the highest recorded value for undoped carbon supports. Almost all the platinum atoms, 98 percent, remained in a flat configuration rather than aggregating into larger particles.
The clusters formed through self-assembly, with individual metal atoms spontaneously anchoring to defect sites as they landed on the surface. The researchers confirmed this using high-resolution electron microscopy, which showed that the atoms stayed within a single atomic plane and avoided stacking into multiple layers.
Method for producing high-coverage single-layer metal clusters (SLMC) and 3D clusters for comparison. a) Schematic illustration of a pristine carbon support exposed to a flux of Pt atoms, resulting in the formation of 3D clusters at the native binding sites on the carbon surface. b) Argon ion irradiation of the carbon surface generates defect sites, which, upon exposure to Pt atoms, lead to the formation of high-coverage SLMC stabilized at the engineered defects. c) Pristine surface: AC-STEM cropped image and corresponding processed image showing a ≈87-atom 3D Pt cluster formed on a pristine carbon support. The line profile indicates stacking up to three atomic layers. d) Engineered binding sites: AC-STEM image and corresponding processed image showing a ≈76-atom SLMC formed on an argon-irradiated carbon surface. (Image: reprinted from DOI:10.1002/advs.202508034, CC BY) (click on image to enlarge)
To understand what controls this behavior, the team varied the amount of argon ion exposure during the surface preparation step. This allowed them to precisely control the number of defects in the carbon surface. On untreated carbon, platinum atoms were highly mobile and formed large clusters. As more defects were introduced, the atoms became increasingly anchored in place. At the highest defect concentrations tested, nearly every atom stayed isolated in a single-layer structure.
Simulations using molecular dynamics provided further insight. On a clean surface, platinum atoms experienced low binding energy and moved freely until they encountered each other. Their tendency to form bonds with other platinum atoms outweighed their attraction to the surface. In contrast, when vacancy defects were present, the binding energy between platinum and the defect was more than twice as strong. This caused the atoms to stop moving and remain fixed in place shortly after landing on the surface.
The researchers also examined how exposure to air affected the outcome. When the prepared surfaces were left in ambient conditions before metal deposition, even for a few minutes, the performance dropped sharply. After just five minutes of exposure, the fraction of platinum atoms forming single-layer clusters was cut in half. Longer exposures led to even greater losses. This confirmed that vacancies become chemically deactivated when exposed to oxygen, blocking metal atoms from binding to them later.
The strength of the method lies in its generality. The researchers applied the same process to 21 elements, including transition metals and one p-block metal. For each of these, they compared untreated surfaces to defect-rich ones. On pristine carbon, single-layer clusters were rare, with most metals forming conventional particles. On the defect-engineered surfaces, however, the single-layer cluster fraction ranged from 71 percent to 100 percent, depending on the element.
Calculations showed that the inherent surface bonding strength of different metals varies widely. Some, like tungsten and titanium, bind strongly to carbon. Others, like silver and gold, bind only weakly. Yet on the defect-rich surfaces, even the weak-binding metals remained dispersed as flat clusters. This suggests that once a critical defect density is reached, the specific identity of the metal becomes less important. The vacancy dominates the interaction and controls the metal’s behavior.
The method also supports combinations of metals. The team created materials that contained mixtures of nickel, palladium, and platinum, which differ in their bonding behavior. When deposited on untreated carbon, these mixtures formed irregular three-dimensional aggregates. On the defect-engineered surface, however, the metals formed well-dispersed, single-layer clusters. Spectroscopy confirmed that all three elements were present and evenly distributed, with no evidence of preferential aggregation.
These multimetallic clusters remained stable under a variety of conditions. They withstood heating to 200 degrees Celsius and maintained their structure after 16 months of air exposure. Electrochemical testing showed that platinum-based single-layer clusters continued to function under acidic conditions for at least ten hours without degradation.
By creating and preserving reactive defect sites under inert conditions, the researchers have demonstrated a practical and scalable method for fabricating atomically thin metal clusters. The technique does not rely on complex chemistries or element-specific interactions. Instead, it uses vacancy formation as a universal stabilizing mechanism, applicable to a wide range of metals and support surfaces.
This development has broad implications for fields that rely on efficient use of metals at the atomic scale. In catalysis, every atom counts, and this method ensures that each one remains active. In energy systems such as fuel cells, batteries, or carbon dioxide reduction, materials with high surface activity and long-term stability are essential. The ability to form stable, dense, single-layer clusters could improve performance while reducing material costs. With its combination of simplicity, control, and broad compatibility, this approach provides a clear foundation for next-generation atomic-scale materials.
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