Electrons at a strongly corrugated monolayer of h-BN lost their excited-state signal faster than electrons at a comparatively flat monolayer in a laboratory comparison of two metal interfaces. The result suggests that atomic-scale corrugation may be useful for tuning ultrafast interface dynamics, but the experiment does not show that corrugation alone accounts for the difference.
The researchers tracked image-potential-state (IPS) electrons—the states whose decay was measured—at monolayer h-BN on Ir(111) and Pt(111). The first and second IPS features, labelled n = 1 and n = 2, appeared at similar energies on both substrates even though their relaxation dynamics differed markedly.
The contrast began at the interface
Monolayer h-BN was fabricated on clean Pt(111) and Ir(111) substrates by chemical vapor deposition. Structural characterization reported a height variation of about 1.5 Å for h-BN/Ir(111), described as strongly corrugated, compared with about 0.5 Å for h-BN/Pt(111), described as comparatively flat.
That difference in shape was not matched by a clear difference in the occupied band pattern reported for the h-BN layer. Angle-resolved ultraviolet photoemission spectroscopy showed very similar overall h-BN π-band dispersion on the two substrates.
The chemical environments were also not identical. X-ray photoelectron spectroscopy found higher binding energies for the main boron 1s and nitrogen 1s components on h-BN/Ir(111) than on h-BN/Pt(111), a result the paper describes as consistent with stronger interaction between h-BN and the Ir substrate.
A difference visible within hundreds of femtoseconds
The key dynamic measurement was time-resolved two-photon photoemission, a pump-probe method that followed the IPS signal after excitation. Ultraviolet photons pumped the IPS electrons, and subsequent near-infrared photons probed them. The work used LEED, XPS, UPS and 2PPE under ultrahigh-vacuum conditions at room temperature.
The time traces showed a clear descriptive contrast. At approximately 200 femtoseconds, the n = 1 signal on h-BN/Ir(111) had fallen to about one-third of its value at approximately 100 femtoseconds. On h-BN/Pt(111), it was about one-half of the 100-femtosecond value. By approximately 300 femtoseconds, a Pt signal remained, while the Ir signal had disappeared.
Convolution fits to the traces estimated IPS lifetimes on Pt of 56 ± 23 femtoseconds for n = 1 and 75 ± 19 femtoseconds for n = 2. For Ir, the decay occurred within the experiment’s 185-femtosecond full-width-at-half-maximum system-response function, so the reported lifetime was at most 20 femtoseconds.
That instrument limit is important when reading the comparison. The Pt results are reported as lifetime estimates with stated uncertainties, whereas the Ir result is an upper bound rather than a resolved point estimate. The measurements therefore establish a strong difference in the observed decay, but they do not provide equally precise lifetimes for both interfaces.
The proposed mechanism remains a proposal
The authors propose that stronger corrugation enhances coupling between the IPS electron and the Ir(111) substrate. They present that corrugation-enhanced coupling as the most consistent explanation for the shorter reported Ir lifetime and as a possible way to tune ultrafast interface dynamics.
The comparison does not isolate corrugation from the other differences between the two systems. Changing from Ir(111) to Pt(111) also changes substrate chemistry, lattice mismatch, moiré registry, azimuthal disorder and the strength of the interfacial interaction.
The proposed change in IPS wavefunction overlap was inferred from comparative spectroscopy rather than measured directly in space. For that reason, the shorter Ir lifetime should be described as associated with the more corrugated interface, not as proof that corrugation alone controls the relaxation pathway.
The paper also does not report the number of independent sample preparations or replicate measurements. No inferential hypothesis tests or p values were reported, leaving the comparison descriptive rather than a statistical test of a general rule.
What the experiment leaves open
A stronger test would vary corrugation while keeping substrate chemistry and lattice mismatch approximately constant. Spatially resolved ultrafast measurements or calculations could then examine the proposed IPS-overlap pathway more directly, while additional metals, corrugation amplitudes and two-dimensional materials could show whether the relationship extends beyond these two interfaces.
For now, the evidence is limited to two monolayer h-BN/metal interface configurations measured under ultrahigh-vacuum conditions at room temperature. It informs IPS dynamics and related structural and electronic properties in these materials, but it does not establish downstream photochemical, catalytic, carrier-extraction or energy-dissipation effects.
Paper data and sources
Original title: Tuning of Photoexcited Electron Dynamics at Monolayer h-BN/Metal Interfaces by Corrugation
Authors: Masahiro Shibuta, Maximilian Schaal, Marco Gruenewald et al.
Journal/Repository: arXiv
Status: Preprint, not yet peer-reviewed
First online: 2026-08-20
DOI: Not available
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