Despite advances in single-atom doping, the controlled assembly of multi-atom defects in 2D materials remains difficult, limiting the ability to tailor their electronic, magnetic, or catalytic functionality. Here, we demonstrate that ultralow-energy (82 eV) implantation of mass-selected Mn2 cluster ions into monolayer graphene enables the formation of substitutional Mn dimers. Low-temperature scanning tunneling microscopy and spectroscopy, supported by density-functional theory calculations, reveal that these Mn–Mn pairs exhibit a characteristic four-lobe signature and distinct spectroscopic fingerprints. Molecular dynamics simulations show that Mn2 dimers fragment upon impact, displacing several carbon atoms and enabling recombination events that yield substitutional dimers. These results show that cluster-ion implantation can create multi-atom defects in 2D materials, extending ultralow-energy implantation beyond single-atom doping. This provides access to a broader range of defects relevant to spintronics, quantum technologies, and catalysis.

Strain is a key tuning parameter in solid-state systems, but most studies focus on strain fields extending over tens of nanometers or more. Here we investigate the extreme limit of ultra-localized strain in graphene, introduced through bond defects generated by ultralow-energy implantation of noble gas ions. Using molecular dynamics simulations, Raman spectroscopy, and scanning tunneling microscopy, we identify the formation and thermal stability of bond defects that locally stretch only a few C-C bonds without removing or substituting atoms. Tight-binding calculations reveal that such bond defects induce local charge trapping, leading to substantial Fermi-level shifts. Synchrotron-based angle-resolved photoemission spectroscopy directly confirms these predictions: even at modest defect densities (similar to 1012 cm-2), the graphene Fermi level shifts by up to 0.3 eV. This strong effect is remarkable given that it is achieved without altering graphene's composition, in contrast to conventional impurity doping or vacancy formation. Upon thermal annealing, the electronic structure recovers towards the pristine state, showing that these effects can be tuned and reversed. Our results establish bond defects as a new class of functional disorder in graphene, capable of strongly modifying its electronic properties solely by bond rearrangement.

Two-dimensional heterostructures combining sp-sp 2 hybridization-blending graphene with graphyne-based allotropes-offer substantial potential for enhancing the tunability of electronic and transport properties while providing significant structural flexibility, which are desirable characteristics for next-generation nanoscale electronics. Despite such potential, their experimental realization remains elusive, as synthesized carbon heterostructures are limited to doped, graphene-based systems exhibiting exclusively sp 2 hybridization. Here, the on-surface synthesis of covalently bonded sp-sp 2 lateral heterostructures between graphene nanoribbons and graphdiyne networks on Au(111) is demonstrated. Atomic-resolution scanning tunneling microscopy, combined with density functional theory, reveals the formation mechanism of the covalent interfacial bonds between nanoribbons and graphdiynes, also highlighting the key role of surface chemistry. Bromine atoms, deriving from the molecules dehalogenation and chemisorbed along the nanoribbon, inhibit junction formation, but bonding efficiency can be boosted up to 66% by controlled removal of these byproducts. Electronic structure and transport calculations show that the 2D heterostructure by itself is characterized by disentangled properties for the two subsystems, forming an atomically narrow junction, enabling voltage-tunable spatial current separation in two dimensions. These results define a viable strategy for engineering graphene-based sp-sp 2 heterostructures, paving the way for the design and synthesis of all-carbon nanoscale electronic architectures.

Graphdiynes are atomically thin carbon allotropes with mixed sp-sp2 hybridization, able to self-assemble into diverse 2D and 1D nanostructures, from atomic layers to nanoribbons and molecular wires, with tunable optoelectronic properties beyond those of graphene. Here, we investigate novel graphdiyne molecular wires obtained via Ullmann coupling of 1,4-bis(bromoethynyl)benzene molecules on Au(100) and Au(111) surfaces. Using scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED), we track the structural evolution of these systems under increasing annealing temperatures. Exploiting Raman spectroscopy, we perform the first-ever in situ monitoring of the thermally activated transition from organometallic to covalent organic wires (OMW-to-COW), resulting in the assignment of specific Raman features to both phases supported, by density functional theory calculations. We demonstrate that surface orientation affects the Ullmann coupling efficiency, resulting in a lower OMW-to-COW transition temperature on Au(100) than on Au(111). These findings provide new insights into the temperature-dependent structural dynamics of graphdiyne molecular wires, enabling the development of more efficient on-surface synthesis processes and the design of novel functional carbon nanostructures for new-generation optoelectronic devices.

Graphdiynes are emerging two-dimensional sp-sp^2 carbon materials with electronic structures complementing those of graphene, yet their on-surface synthesis is limited by the persistence of metalated intermediates or yields disordered covalent networks. Here, we report an iron-assisted route to covalent hydrogenated graphdiyne monolayers on Au(111) from 1,3,5-tris(bromoethynyl)benzene. Low-temperature scanning tunnelling microscopy, X-ray photoelectron spectroscopy and density functional theory show that Fe scavenges chemisorbed Br byproducts forming FeBr_2, in turn promoting the removal of Au adatoms from the organometallic network, thus enabling its metalated-to-covalent conversion under mild thermal treatment. Subsequent annealing removes FeBr_2 and yields covalent, ordered domains weakly coupled to the substrate. Scanning tunnelling spectroscopy, combined with density functional theory, reveals a semiconducting gap of about 1.6 eV associated with carbon p_z frontier orbitals. This Fe-mediated on-surface synthesis strategy provides a route to atomically precise, weakly substrate-coupled graphdiyne networks and offers a design principle for two-dimensional carbon semiconductors.

Using substitutional Mn in graphene/Cu(111) as a model point defect, we combine scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES) to test the predicted fingerprints of resonant scattering. As the Mn concentration increases to 0.44

Interfaces between molecular layers and ferromagnetic materials, named spinterfaces, have been widely studied on account of the intriguing magnetic phenomena associated with the spin-polarized hybrid interface states, and of possible innovative applications. This work starts exploring the opportunities given by coupling molecular layers and antiferromagnetic materials, focusing on the magnetoelectric antiferromagnetic insulator Cr2O3. Antiferromagnets are currently of great interest for the future development of spintronics and magnonics applications, since they are stable against external fields and they show dynamic behaviors at much higher frequencies, compared to ferromagnets. On the other hand, interacting with the magnetic structure of an antiferromagnet is more challenging. A possible approach is that of establishing an antiferromagnetic spinterface, in such a way that external stimuli acting on the molecular side can influence the substrate magnetic parameters. Self-assembled monolayers of FePc (iron phthalocyanine) are prepared on thin Cr2O3 films, and the morphological, structural, electronic, and magnetic properties of the resulting antiferromagnetic spinterface are experimentally and theoretically investigated. We observe flat-lying molecular layers that develop a long-range magnetic ordering of the magnetic moments associated with Fe ions. Our calculations support the conclusion that such ordering is established through the interaction at the interface between FePc and Cr2O3.

Interfaces between molecular layers and ferromagnetic materials, named spinterfaces, have been widely studied on account of the intriguing magnetic phenomena associated with the spin-polarized hybrid interface states, and of possible innovative applications. This work starts exploring the opportunities given by coupling molecular layers and antiferromagnetic materials, focusing on the magnetoelectric antiferromagnetic insulator Cr 2 O 3 . Antiferromagnets are currently of great interest for the future development of spintronics and magnonics applications, since they are stable against external fields and they show dynamic behaviors at much higher frequencies, compared to ferromagnets. On the other hand, interacting with the magnetic structure of an antiferromagnet is more challenging. A possible approach is that of establishing an , in such a way that external stimuli acting on the molecular side can influence the substrate magnetic parameters. Self-assembled monolayers of FePc (iron phthalocyanine) are prepared on thin Cr 2 O 3 films, and the morphological, structural, electronic, and magnetic properties of the resulting antiferromagnetic spinterface are experimentally and theoretically investigated. We observe flat-lying molecular layers that develop a long-range magnetic ordering of the magnetic moments associated with Fe ions. Our calculations support the conclusion that such ordering is established through the interaction at the interface between FePc and Cr 2 O 3 .

Interfaces between molecular layers and ferromagnetic materials, also called spinterfaces, are the test bed for the development of molecular spintronics, unveiling new effects and opportunities for novel potential applications. Among several combinations of materials that have shown intriguing behaviors, spinterfaces based on antiferromagnetic materials received much less consideration, despite the dramatic increase in attention recently drawn by the antiferromagnetic declination of spintronics. In this work, an antiferromagnetic spinterface based on the transition metal oxide NiO, a widely studied antiferromagnetic insulator with one of the highest critical temperatures, has been realized and characterized. As for the molecular counterpart, Co tetraphenyl porphyrin (CoTPP) is a very promising choice, being sublimable in vacuum and paramagnetic. CoTPP/NiO(001) spinterfaces are experimentally investigated with respect to their morphology, structure, electronic, and magnetic properties. Theoretical calculations have also been performed to circumstantiate and support the measurements. Although characterized by a relatively weak interface coupling, spin‐dependent hybridization is observed at the interface, which makes the CoTPP/NiO a perfect system for initiating the exploration of a molecular antiferromagnetic spintronics.

Graphdiyne-based carbon systems generate intriguing layered sp-sp$^2$ organometallic lattices, characterized by flexible acetylenic groups connecting planar carbon units through metal centers. At their thinnest limit, they can result in two-dimensional (2D) organometallic networks exhibiting unique quantum properties and even confining the surface states of the substrate, which is of great importance for fundamental studies. In this work, we present the on-surface synthesis of a highly crystalline 2D organometallic network grown on Ag(111). The electronic structure of this mixed honeycomb-kagome arrangement - investigated by angle-resolved photoemission spectroscopy and scanning tunneling spectroscopy - reveals a strong electronic conjugation within the network, leading to the formation of two intense electronic band-manifolds. In comparison to theoretical density functional theory calculations, we observe that these bands exhibit a well-defined orbital character that can be associated with distinct regions of the sp-sp$^2$ monomers. Moreover, we find that the halogen by-products resulting from the network formation locally affect the pore-confined states, causing a significant energy shift. This work contributes to the understanding of the growth and electronic structure of graphdiyne-like 2D networks, providing insights into the development of novel carbon materials beyond graphene with tailored properties.

Antiferromagnets are a class of magnetic materials of great interest in spintronic devices because of their stability and ultrafast dynamics. When interfaced with an organic molecular layer, antiferromagnetic (AF) films are expected to form a spinterface that can allow fine control of specific AF properties. In this paper, we investigate spinterface effects on CoO, an AF oxide. To access the magnetic state of the antiferromagnet, we couple it to a ferromagnetic Co film via an exchange bias (EB) effect. In this way, the formation of a spinterface is detected through changes induced on the CoO/Co EB system. We demonstrate that C60 and Gaq3 adsorption on CoO shifts its blocking temperature; in turn, an increase in both the EB fields and the coercivities is observed on the EB-coupled Co layer. Ab initio calculations for the CoO/C60 interface indicate that the molecular adsorption is responsible for a charge redistribution on the CoO layer that alters the occupation of the d orbitals of Co atoms and, to a smaller extent, the p orbitals of oxygen. As a result, the AF coupling between Co atoms in the CoO is enhanced. Considering the granular nature of CoO, a larger AF stability upon molecular adsorption is then associated with a larger number of AF grains that are stable upon reversal of the Co layer.

The organic molecules adsorbed on antiferromagnetic surfaces can produce interesting interface states, characterized by charge transfer mechanisms, hybridization of molecular-substrate orbitals, as well as magnetic couplings. Here, we apply an ab initio approach to study the adsorption of Fe phthalocyanine on stoichiometric Cr2O3(0001). The molecule binds via a bidentate configuration forming bonds between two opposite imide N atoms and two protruding Cr ones, making this preferred over the various possible adsorption structures. In addition to the local modifications at these sites, the electronic structure of the molecule is weakly influenced. The magnetic structure of the surface Cr atoms shows a moderate influence of molecule adsorption, not limited to the atoms in the close proximity of the molecule. Upon optical excitation at the onset, electron density moves toward the molecule, enhancing the ground state charge transfer. We investigate this movement of charge as a mechanism at the base of light-induced modifications of the magnetic structure at the interface.

The adsorption of organic molecules on antiferromagnetic surfaces forms interfaces with potential applications in organic spintronics devices. Molecules modify the dispersion of spin excitations in the substrate through charge transfer and crystal deformations, and offer the possibility to couple them to light excitations. Here, we follow an ab-initio approach to the study of the interface between the magnetic organo-metallic molecule Fe-phthalocyanine and the (001) surface of NiO. By applying Hubbard-corrected density-functional theory (DFT+U) calculations we determine the most stable adsorption configuration as that with the molecule lying flat with Fe above a surface O atom. We find a strong hybridization between Fe orbitals and surface ones, with the Fe spin coupled antiferromagnetically to subsurface Ni through the O atom. Moderate changes to the magnetic structure of the components and charge displacements are shown. Optical spectra show reduced absorption onsets and are investigated for the possibility of a coupling with the system spin properties.

Despite its broad potential applications, substitution of carbon by transition metal atoms in graphene has so far been explored only to a limited extent. We report the realization of substitutional Mn doping of graphene to a record high atomic concentration of 0.5%, which was achieved using ultralow-energy ion implantation. By correlating the experimental data with the results of ab initio Born-Oppenheimer molecular dynamics calculations, we infer that direct substitution is the dominant mechanism of impurity incorporation. Thermal annealing in ultrahigh vacuum provides efficient removal of surface contaminants and additional implantation-induced disorder, resulting in Mn-doped graphene that, aside from the substitutional Mn impurities, is essentially as clean and defect-free as the as-grown layer. We further show that the Dirac character of graphene is preserved upon substitutional Mn doping, even in this high concentration regime, making this system ideal for studying the interaction between Dirac conduction electrons and localized magnetic moments. More generally, these results show that ultralow energy ion implantation can be used for controlled functionalization of graphene with substitutional transition-metal atoms, of relevance for a wide range of applications, from magnetism and spintronics to single-atom catalysis.

The synthesis of silicene by direct growth on silver is characterized by the formation of multiple phases and domains, posing severe constraints on the spatial charge conduction towards a technological transfer of silicene to electronic transport devices. Here we engineer the silicene/silver interface by two schemes, namely, either through decoration by Sn atoms, forming an Ag2Sn surface alloy, or by buffering the interface with a stanene layer. Whereas in both cases Raman spectra confirm the typical features as expected from silicene, by electron diffraction we observe that a very well-ordered single-phase 4 × 4 monolayer silicene is stabilized by the decorated surface, while the buffered interface exhibits a sharp phase at all silicon coverages. Both interfaces also stabilize the ordered growth of a phase in the multilayer range, featuring a single rotational domain. Theoretical ab initio models are used to investigate low-buckled silicene phases (4 × 4 and a competing one) and various structures, supporting the experimental findings. This study provides new and promising technology routes to manipulate the silicene structure by controlled phase selection and single-crystal silicene growth on a wafer-scale.

Spin-electronic devices are poised to become part of mainstream microelectronic technology .Downsizing them, however, faces the intrinsic difficulty that as ferromagnets become smaller, it becomes more difficult to stabilize their magnetic moment. Antiferromagnets are much more stable, and thus research on antiferromagnetic spintronics has developed into a fast-growing field. Here, we provide proof of concept data that allows us to expand the area of antiferromagnetic spintronics to the hitherto elusive level of individual molecules. In contrast to all previous work on molecular spintronics, our detection scheme of the molecule's spin state does not rely on a magnetic moment. Instead, we use field-effect transistor devices constituting of an isolated, contacted single-wall carbon nanotube covalently bound to a limited number of molecular antiferromagnets incorporating four Mn(II) or Co(II) ions. Time-dependent quantum transport measurement along the functionalized nanotube show step-like transitions between several distinct current levels, which we attribute to transitions between different antiferromagnetic states of individual molecular complexes grafted on the nanotube. A statistical analysis of the switching events using factorial cumulants indicates that the cobalt complexes switch independently from each other, while a coherent superposition of the antiferromagnetic spin states of the molecules along the nanotube is observed for the manganese complexes. The long coherence time (several seconds at 100 mK) is made possible by the absence of spin and orbital momentum in the relevant states of the manganese complex, while the cobalt complex includes a significant orbital momentum contribution due to the pseudo-octahedral d$^7$ metal centers.

By using the Hubbard-corrected density functional theory (DFT+U), we investigate the surface of bulk transition metal monooxides, studying the interaction with adsorbed molecules with/without intrinsic magnetic character. For the paradigmatic case of pentacene/NiO(001), we see that interaction only moderately affects the surface ground state magnetization. Conversely, ultrathin magnetic layers appear controllable by the adsorption of an organic layer, as we see by our DFT investigation for the interface formed by a C-60 molecular layer on a two-dimensional Cr4O5 layer supported on Fe(001). There, the local hybridization between the electronic states of C60 and Cr4O5 is able to modify the magnetic coupling of the Cr atoms: molecules turn the ferromagnetic intra-layer coupling into an antiferromagnetic one; further patterning of the substrate spin polarization can be achieved by controlling the molecular adsorption site.

Network formed by sp-and sp2-hybridized carbon atoms with high degrees of π conjugation, namely graphynes and graphdiynes, are stimulating intense research effort for their potential use in nanoelectronics, catalysis and photo-conversion, due to their high-charge carrier mobility and tunable band gaps and band structures [1], [2], [3].

Stabilizing ordered assemblies of molecules represents the first step towards the construction of molecular devices featuring hybrid (organic-inorganic) interfaces where molecules can be easily functionalized in view of specific applications. Molecular layers of planar metal-tetraphenylporphyrins (MTPP) grown on an ultrathin iron oxide [namely Fe(001)-p(1 × 1)O] show indeed a high degree of structural order. The generality of such a picture is tested by exploiting non-planar porphyrins, such as vanadyl-TPP (VOTPP). These molecules feature a VO2+ ion in their center, with the O atom protruding out of the plane of the porphyrin ring. In this work, by employing diffraction, photoemission and X-ray absorption, we prove that non-planar VOTPP can nevertheless form a square and ordered superstructure, where porphyrin molecules lie flat with respect to the underlying substrate. Ab initio density functional theory simulations are used to elucidate the VO bond orientation with respect to the iron substrate.

Tailoring magnetic properties of antiferromagnetic coordination clusters by changing the inner core.