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# University of Trieste, CNR, Elettra and Technical University of Munich team maps room-temperature nanocluster fragmentation on magnetite
- URL: https://research-pop.com/university-of-trieste-cnr-elettra-and-technical-university-of-munich-team-maps-room-temperature-nanocluster-fragmentation-on-magnetite/
- Published: 2026-09-19T20:43:03.000Z
- Updated: 2026-09-19T21:15:17.000Z
- Author: ResearchPOP
- Tags: Materials Science, Chemistry

![](https://storage.ghost.io/c/7c/5e/7c5e0911-739b-4a35-94eb-3e810bf78ba7/content/images/2026/09/Screenshot-2026-09-19-at-22.37.20.png)

**Source**: [https://doi.org/10.1021/jacs.6c15419](https://doi.org/10.1021/jacs.6c15419?ref=research-pop.com)

## At a glance

Metal clusters are often expected to remain as compact units when they land on an oxide surface, especially at room temperature. A team from the University of Trieste, the Italian National Research Council, Elettra Sincrotrone Trieste and the Technical University of Munich shows that this expectation does not hold for several early transition metals on reconstructed magnetite.

The researchers deposited size-selected tungsten, molybdenum and tantalum clusters on Fe₃O₄(001) at 300 K. High-resolution X-ray photoelectron spectroscopy, scanning tunnelling microscopy and density-functional-theory calculations indicate that the clusters can fragment spontaneously after adsorption, without an initial heating step or reactive gas treatment. The surface reconstruction and its subsurface cation vacancies help stabilize separated metal atoms through strong metal–oxygen bonding.

Exposure to O₂ advances the process for clusters that are not already fully separated. Across the three metals, the authors report a fragmentation tendency of Ta > W > Mo. Their energetic comparison places calculated adsorption energies of 13.9 eV for Ta, 11.2 eV for W and 8.4 eV for Mo beside metal–metal bond energies of 4.0, 5.0 and 4.5 eV, respectively. The study uses this balance to explain why apparently similar clusters follow different paths on the same oxide surface.

## Background

The behavior of a supported metal cluster depends on more than its elemental identity and number of atoms. The atomic arrangement of the support can determine where the cluster lands, how strongly each atom binds and whether the original metal–metal framework survives. Magnetite provides a useful surface for studying these effects because its Fe₃O₄(001) face adopts a well-defined reconstruction.

The reconstructed surface is commonly described through a subsurface cation-vacancy model. In this structure, the distribution of iron cations beneath the top oxygen layer creates chemically distinct adsorption environments. Low-energy electron diffraction identifies the characteristic (√2 × √2)R45° periodicity, while scanning tunnelling microscopy resolves zigzag rows associated with surface iron and distinguishes wide and narrow regions between them. Small patches with a locally unreconstructed arrangement can also occur.

These structural differences give incoming metal atoms and clusters more than one possible environment. Strong bonds may form between the deposited metal and surface oxygen, while the cation vacancies beneath the surface provide space for the adsorbate to relax into new geometries. The question is then whether the support merely holds an intact cluster or actively reorganizes it.

To follow that process, the authors combine real-space imaging with element-specific spectroscopy and calculations. Scanning tunnelling microscopy shows where deposited species appear on the surface. High-resolution X-ray photoelectron spectra distinguish metal atoms in different local coordination environments. Stochastic structural searches and density-functional-theory calculations then connect those measurements with candidate atomic arrangements and their energies.

## Research question

What happens when size-selected W, Mo and Ta clusters reach reconstructed Fe₃O₄(001) at room temperature? Do they retain their metal–metal connectivity, or does the surface pull them into separated atoms with new metal–oxygen coordination?

The study also examines how the subsurface cation-vacancy reconstruction changes this outcome, whether O₂ exposure drives the process further and why the three early transition metals show different fragmentation tendencies.

## Inside the study

The researchers first establish the structure of the magnetite surface before cluster deposition. Low-energy electron diffraction confirms the (√2 × √2)R45° reconstruction, with a reported Pendry reliability factor of 0.16 for the structural analysis. Scanning tunnelling microscopy shows the expected zigzag iron rows, together with wide and narrow adsorption regions and occasional locally unreconstructed defects. This surface map provides the setting for interpreting the deposited clusters.

![](https://storage.ghost.io/c/7c/5e/7c5e0911-739b-4a35-94eb-3e810bf78ba7/content/images/2026/09/Screenshot-2026-09-19-at-22.37.31.png)

Tungsten offers the most detailed view of the fragmentation process. After deposition, scanning tunnelling microscopy shows features about 2 Å high positioned between the iron rows. Their location is consistent with adsorption in the reconstructed surface regions rather than simple accumulation on top of the rows.

The W 4f spectra change systematically with cluster size. W₁ and W₃ are dominated by higher-binding-energy components associated with strongly oxygen-coordinated tungsten. Lower-binding-energy contributions become more visible as the deposited cluster grows, showing that larger clusters contain a wider range of local environments. Even for W₁₃ and W₂₅, however, the spectra do not develop the signature expected for metallic tungsten. The result points away from an intact metallic nanoparticle and toward extensive interaction with the oxide.

![](https://storage.ghost.io/c/7c/5e/7c5e0911-739b-4a35-94eb-3e810bf78ba7/content/images/2026/09/Screenshot-2026-09-19-at-22.37.48.png)

The team then exposes the tungsten-covered surfaces to O₂, reaching a total dose of 436 L. Oxygen does not introduce a completely new family of W 4f components. Instead, it redistributes intensity among states already present. W₁ and W₃ change little, consistent with small species that are already strongly coordinated to the surface. W₅ and larger clusters respond more clearly. The W₅ spectrum approaches saturation after about 20 L, while W₂₅ continues changing to about 50 L.

The integrated tungsten signal also increases for several cluster sizes after oxygen exposure. The reported changes are 7.8% for W₇, 8.3% for W₁₃ and 22.5% for W₂₅. The authors relate this growth to the conversion of three-dimensional cluster environments into more exposed, separated tungsten species that contribute more strongly to photoemission. In this account, O₂ continues an atomization process initiated by adsorption on magnetite.

![](https://storage.ghost.io/c/7c/5e/7c5e0911-739b-4a35-94eb-3e810bf78ba7/content/images/2026/09/Screenshot-2026-09-19-at-22.37.59.png)

The calculations show how the reconstructed support can drive that change. For W₃ and W₅ on reconstructed Fe₃O₄(001), the optimized W–W separations extend by more than 1 Å relative to bulk tungsten distances. Surface oxygen atoms pull the tungsten atoms outward, increasing W–O coordination while weakening the original cluster geometry. The subsurface cation vacancies allow the adsorbed atoms to relax into positions that stabilize this separation.

The contrast with an unreconstructed surface is important. In the corresponding calculation, W₅ remains more compact and retains W–W coordination numbers of about two to three. The result identifies the reconstruction as an active part of the fragmentation process rather than a passive geometric detail.

![](https://storage.ghost.io/c/7c/5e/7c5e0911-739b-4a35-94eb-3e810bf78ba7/content/images/2026/09/Screenshot-2026-09-19-at-22.38.20.png)

Calculated W 4f binding energies provide a second connection between structure and experiment. For separated W₁-, W₃- and W₅-derived structures on reconstructed magnetite, the calculated values span 34.87–36.02 eV. Higher oxygen coordination shifts the signal toward higher binding energy. A lower-binding-energy state can arise from W₅ retained on a locally unreconstructed region. By comparison, models based only on intact W₅ or W₁₃ clusters do not reproduce the dominant high-binding-energy spectral response as closely as structures containing separated tungsten atoms.

Molybdenum and tantalum extend the comparison beyond tungsten. Neither series develops a clear metallic core-level component after room-temperature deposition. Ta₂₅ is dominated by high-oxidation-state contributions, indicating extensive interaction between tantalum and the oxide. After O₂ exposure, the Ta⁴⁺ contribution increases, while a Mo⁴⁺ component disappears from the Mo₅ and Mo₁₃ spectra.

![](https://storage.ghost.io/c/7c/5e/7c5e0911-739b-4a35-94eb-3e810bf78ba7/content/images/2026/09/Screenshot-2026-09-19-at-22.38.34.png)

The signal-area changes reveal different responses to oxygen. The molybdenum series changes by 0% for Mo₁, 20% for Mo₅ and 4% for Mo₁₃. The tantalum signals change by no more than 1.5%, which the authors interpret as evidence that tantalum clusters have already fragmented extensively during their initial adsorption and leave less scope for additional O₂-driven atomization.

To explain the order Ta > W > Mo, the authors compare the energy gained by binding an isolated metal atom to magnetite with the energy holding the metal atoms together. The calculated adsorption energies are 8.4 eV for Mo, 11.2 eV for W and 13.9 eV for Ta. The corresponding metal–metal bond energies are 4.5, 5.0 and 4.0 eV. Tantalum combines the strongest surface binding with the weakest metal–metal bond in this set, favoring separation. Molybdenum gains less energy from adsorption while retaining comparatively strong metal–metal bonding, making fragmentation less extensive. Tungsten lies between those cases.

![](https://storage.ghost.io/c/7c/5e/7c5e0911-739b-4a35-94eb-3e810bf78ba7/content/images/2026/09/Screenshot-2026-09-19-at-22.38.44.png)

Taken together, the measurements and calculations describe a sequence that begins as soon as the size-selected clusters reach reconstructed magnetite. Metal–oxygen bonds form, the reconstructed lattice and its cation vacancies accommodate separated atoms, and the original cluster framework expands or breaks apart. Subsequent O₂ exposure can move partially fragmented clusters further along the same path.

## Takeaways and outlook

The study shows that reconstructed Fe₃O₄(001) can actively reshape early-transition-metal clusters at room temperature. For W, Mo and Ta, adsorption is not simply the attachment of an intact cluster to a support. Strong metal–oxygen bonding competes with metal–metal bonding, while the subsurface cation-vacancy structure provides an environment that stabilizes the separated atoms.

The comparison among three metals makes that picture more specific. Tantalum fragments most readily, tungsten occupies an intermediate position and molybdenum retains more resistance to separation. O₂ exposure reveals how much further each deposited cluster population can move toward atomization. Small or already separated species change little, while larger and less completely fragmented clusters respond more strongly.

This working-state view is relevant to the design of supported metal materials. Cluster size alone does not fully specify the structure present after deposition. The reconstruction of the oxide, local surface defects, oxygen exposure and the balance between metal–surface and metal–metal bonding can determine whether a nominal cluster survives or becomes a collection of individually coordinated atoms.

## About the researchers

Gabriele Coltrioli and Deborah Perco are affiliated with the University of Trieste, and Luca Sementa is affiliated with the Institute for Chemical-Physical Processes of the Italian National Research Council. The three are marked as equal contributors.

Marco Bianchi, Paolo Lacovig, Silvano Lizzit and Aras Kartouzian are affiliated with Elettra Sincrotrone Trieste. Andrea Berti and Mikhail Bandurist are affiliated with the University of Trieste. Ueli Heiz is affiliated with the Technical University of Munich, and Alessandro Fortunelli is affiliated with the Institute of Chemistry of Organometallic Compounds of the Italian National Research Council.

Alessandro Baraldi, affiliated with the University of Trieste and Elettra Sincrotrone Trieste, is the corresponding author.

## Original research

Gabriele Coltrioli; Deborah Perco; Luca Sementa; Marco Bianchi; Andrea Berti; Mikhail Bandurist; Paolo Lacovig; Silvano Lizzit; Aras Kartouzian; Ueli Heiz; Alessandro Fortunelli; Alessandro Baraldi. “Room-Temperature Adsorption on Magnetite Induces Spontaneous Fragmentation of Early Transition-Metal Size-Selected Nanoclusters.” *Journal of the American Chemical Society*, published online 18 September 2026\. DOI: [10.1021/jacs.6c15419](https://doi.org/10.1021/jacs.6c15419?ref=research-pop.com). Open access. 

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## Research POP Notes

This article reflects the independent interpretation of the Research POP team and does not represent the views of the authors, their institutions or the journal. If you identify any inaccuracies or have concerns regarding the content, figures or attribution, please contact us at [team.researchpop@gmail.com](mailto:team.researchpop@gmail.com). We will review the matter promptly and make corrections or remove the relevant material where appropriate.