Peter Lievens

In the search for new magnetic materials, few atom metal clusters are of great interest because they can posses greatly enhanced magnetic moments with respect to bulk moments per atom. This is particularly the case for bimetallic transition metal clusters. Here, we report on the magnetism of ConRhm (n = 10–45 and m = 0–3) neutral clusters studied in molecular beam experiments using a combination of Stern–Gerlach magnetic deflection and mass spectrometry. Large dopant-induced and size-dependent increases in the total magnetic moment of the clusters were found, of up to 10% per added rhodium atom in the n = 15–30 size range. Density functional theory calculations indicate significant induced local spin magnetic moments on the rhodium atoms but fail to predict systematic enhancement of the spin magnetic moments on the cobalt atoms. The observed large enhancement of magnetic moments suggests an important role of orbital contributions.

Gold nanoparticles are renowned for intense localized surface plasmon resonances, featuring intense linear light extinction and low threshold saturable absorption, yet the reverse saturable absorption (RSA) in gold nanoparticles is typically limited to small clusters. Here, we show that alloying gold with iron or cobalt enables RSA at sizes readily achieved by standard nanoparticle synthesis methods. The size-dependent (5–34 nm) nonlinear optical response of colloidal bimetallic Au–Fe and Au–Co nanoalloys synthesized by laser ablation in liquid are investigated with open-aperture z-scan measurements at 532 nm and compared with monometallic Au nanoparticles. While pure Au exhibits no RSA, Au–Fe and Au–Co nanoalloys display RSA at larger sizes with remarkable nonlinear absorption cross sections up to 1012 GM. This behavior is attributed to alloy-induced transitions involving virtually bound states near the Fermi energy, providing a practical route to engineer nonlinear optical responses.

Efficient preparation, isolation, and soft-landing deposition of stable clusters with atomic precision are important for developing new catalysts. However, small metal clusters are often highly susceptible to oxidation and prone to structural deformation on supports, which poses substantial challenges to experimental catalysis and theoretical calculations. In this study, we prepared pure Ag_n⁺ and Cu_n⁺ clusters and screened out superatomic clusters Ag₉⁺ and Cu₉⁺ by gas-phase reactions of sufficient collisions. We then deposited the two clusters onto different substrates using soft landing techniques. Characterization by X-ray photoelectron spectroscopy verified successful deposition and revealed that these superatomic clusters preserve unoxidized states at exposure to air, highlighting their unique stability rooted in superatomic eight-electron shell closure. We tested the catalysis of Ag₉⁺ and Cu₉⁺ clusters for acetylene hydrogenation and related hydrogen-deuterium exchange reactions. The results revealed that the Cu₉⁺ clusters on TiO₂ exhibit superior catalytic activity, which is associated with the enhanced cluster-support interactions and favorable H₂ activation behavior. This study validates the applicability of superatom clusters for designing new catalysts, with enhanced stability and tailorable active sites.

By using XEOL–XAFS, we show that the intense broadband white-light emission of Ag/S-zeolites originate from a combination of distinct oxygen-coordinated Ag ₃ O, Ag ₄ O ₂ , and Ag ₆ O ₄ nanoclusters stabilized within their sodalite cages by SO ₄ ²⁻ anions.

Infrared multiple-photon dissociation (IR-MPD) spectroscopy is used to investigate the vibrational spectra of a series of Ar-tagged Nb/Al clusters, AlNbn+, n = 5−9. In the smaller cluster size regime (n...

Anodization induced nanostructuring of copper surfaces facilitates CO ₂ electroreduction to C ₂₊ products.

The relationship between the atomic-level structure and the photoelectrochemical water splitting reaction of Au _x Cu _{1− x} nanoalloys on titania nanotubes photoanodes was investigated.

High-pressure studies of catalyst quantities down to a few hundred nanograms, particularly well-defined catalysts prepared using physical methods in ultra-high vacuum on planar supports can potentially bridge the surface science and applied catalysis approaches to catalyst development. However, the chemical reactors required for such investigations are lacking. We present the novel design and evaluation of a 50 µL rectangular microchannel reactor capable of testing small quantities of catalyst at pressures up to 40 bar and temperatures up to 250°C. To evaluate the microreactor's performance, Pd0.25Zn0.75Ox nanoclusters soft-landed on SiO2-coated mica sheets using the cluster beam deposition technique, were tested for the reverse water-gas shift reaction through a series of kinetic experiments. Experimental results, combined with computational fluid dynamics and mass transport analysis, demonstrate that the proposed microreactor setup allows for testing minute quantities of catalysts with high sensitivity at industrially relevant temperatures and pressures. Although not restricted to a particular catalyst preparation method, the setup is an excellent platform for conducting catalytic tests on composition-controlled, mass-selected, gas-phase nanoparticles deposited on planar substrates, facilitating the development of reliable structure-activity relationships and enabling a more rational design of catalysts.

Infra-red multi-photon dissociation (IR-MPD) spectroscopy has been used to characterise the family of Re/Si clusters, [ReSi _3–9 ] ⁺ . DFT is used to assign the spectra and also as a basis for a comparison with the lighter group 7 analogues, [MnSi _n ] ⁺ .