The reduced dimensionality of thin transition metal dihalide films on single-crystal surfaces unlocks a diverse range of magnetic and electronic properties. However, achieving stoichiometric monolayer islands requires precise control over the growth conditions. In this study, we employ scanning probe microscopy to investigate the growth of MnI2 on Ag(111) via single-crucible evaporation. The catalytic properties of the Ag(111) surface facilitate MnI2 dehalogenation, leading to the formation of a reconstructed iodine adlayer that acts as a buffer layer for the growth of truncated hexagonal MnI2 islands. These islands exhibit alternating edge lengths and distinct Kelvin potentials, as revealed by Kelvin probe force microscopy. Density functional theory (DFT) calculations support the experimentally observed island heights and lattice parameters and provide insights into the formation energies of both pristine and reconstructed edges. The asymmetry in edge lengths is attributed to differences in edge formation energies, driven by the position (up or down) of edge iodine atoms, as confirmed by DFT. This structural difference accounts for the observed variation in the Kelvin potential between the two types of island edge terminations.

Graphene nanoribbons show exciting electronic properties related to the exotic nature of the charge carriers and to local confinement as well as atomic-scale structural details. The local work function provides evidence for such structural, electronic, and chemical variations at surfaces. Kelvin prove force microscopy can be used to measure the local contact potential difference (LCPD) between a probe tip and a surface, related to the work function. Here we use this technique to map the LCPD of graphene nanoribbons grown on a Au(111) substrate. The LCPD data shows charge transfer between the graphene nanoribbons and the gold substrate. Our results are corroborated with density functional theory calculations, which verify that the maps reflect the doping of the nanoribbons. Our results help to understand the relation between atomic structure and electronic properties both in high-resolution images and in the distance dependence of the LCPD.

Using scanning tunneling microscopy and spectroscopy we demonstrate a revival of magnetism in 7-armchair nanoribbon by unpassivated atoms at the termini. Namely, a pair of intense Kondo resonances emerges at the peripheries of zigzag terminus revealing the many-body screening effects of local magnetic moments. Although Kondo resonance originates from a missing local orbital, it extends to a distance of 2.5 nm along the edge of the ribbon. The results are complemented by density functional theory calculations which suggest a possible coupling between Kondo states despite screening effects of substrate electrons. These findings indicate a possibility to restore intrinsic magnetic ordering in graphene nanoribbon without major structural modifications.

C60is a model system to study molecule-surface interactions and phase transitions due to its high symmetry and strong covalentπbonding within the molecule versus weak van-der-Waals coupling between neighboring molecules. In the solid, at room temperature, the molecule rotates and behaves as a sphere. However, the pentagonal and hexagonal atomic arrangement imposes deviations from the spherical symmetry that become important at low temperatures. The orientation of the C60can be viewed to represent classic spins. For geometrical reasons the preferred orientation of neighboring C60cannot be satisfied for all of the neighboring molecules, making C60a model for disordered spin systems with frustration. We study several molecular layers of C60islands on highly oriented pyrolytic graphite using scanning tunneling microscopy at liquid nitrogen temperatures. By imaging several layers we obtain a limited access to the three-dimensional rotational structure of the molecules in an island. We find one rotationally disordered layer between two partially rotationally ordered layers with hexagonal patterns. This exotic pattern shows an example of the local distribution of order and disorder in geometrically frustrated systems. Scanning tunneling spectroscopy data confirms the weak interactions of neighboring molecules.

Graphene nanoribbons show exciting electronic properties related to the exotic nature of the charge carriers and to local confinement as well as atomic-scale structural details. The local work function provides evidence for such structural, electronic and chemical variations at surfaces. Kelvin prove force microscopy (KPFM) can be used to measure the local contact potential difference (LCPD) between a probe tip and a surface, related to the work function. Here we use this technique to map the LCPD of graphene nanoribbons grown on a Au(111) substrate. The LCPD data shows charge transfer between the graphene nanoribbons and the gold substrate. Our results are corroborated with density functional theory calculations which verify that the maps reflect from the doping of nanoribbons. Our results help to understand the relation between atomic structures and electronic properties.

We have investigated the self-assembly of the graphene nanoribbon molecular precursor 10,10'-dibromo-9,9'-bianthryl (DBBA) on Au(111) with frequency modulation scanning force microscopy (FM-SFM) at room temperature combined with ab initio calculations. For low molecular coverages, the molecules aggregate along the substrate herringbone reconstruction main directions while remaining mobile. At intermediate coverage, two phases coexist, zigzag stripes of monomer chains and decorated herringbones. For high coverage, the molecules assemble in a dimer-striped phase. The adsorption behaviour of DBBA molecules and their interactions are discussed and compared with the results from ab initio calculations.

In crystal growth, surfactants are additive molecules used in dilute amount or as dense, permeable layers to control surface morphologies. We investigate the properties of a strikingly different surfactant: a 2D and covalent layer with close atomic packing, graphene. Using in situ, real-time electron microscopy, scanning tunneling microscopy, kinetic Monte Carlo simulations, and continuum mechanics calculations, we reveal why metallic atomic layers can grow in a 2D manner below an impermeable graphene membrane. Upon metal growth, graphene dynamically opens nanochannels called wrinkles, facilitating mass transport while at the same time storing and releasing elastic energy via lattice distortions. Graphene thus behaves as a mechanically active, deformable surfactant. The wrinkle-driven mass transport of the metallic layer intercalated between graphene and the substrate is observed for two graphene-based systems, characterized by different physicochemical interactions, between graphene and the substrate and between the intercalated material and graphene. The deformable surfactant character of graphene that we unveil should then apply to a broad variety of species, opening new avenues for using graphene as a 2D surfactant forcing the growth of flat films, nanostructures, and unconventional crystalline phases.

Using low-energy electron microscopy, we image in real time the intercalation of a cobalt monolayer between graphene and the (111) surface of iridium. Our measurements reveal that the edges of a graphene flake represent an energy barrier to intercalation. Based on a simple description of the growth kinetics, we estimate this energy barrier and find small, but substantial, local variations. These local variations suggest a possible influence of the graphene orientation with respect to its substrate and of the graphene edge termination on the energy value of the barrier height. Besides, our measurements show that intercalated cobalt is energetically more favorable than cobalt on bare iridium, indicating a surfactant role of graphene.

The use of graphene in electronic devices requires a band gap, which can be achieved by creating nanostructures such as graphene nanoribbons. A wide variety of atomically precise graphene nanoribbons can be prepared through on-surface synthesis, bringing the concept of graphene nanoribbon electronics closer to reality. For future applications it is beneficial to integrate contacts and more functionality directly into single ribbons by using heterostructures. Here, we use the on-surface synthesis approach to fabricate a metal-semiconductor junction and a tunnel barrier in a single graphene nanoribbon consisting of 5- and 7-atom wide segments. We characterize the atomic scale geometry and electronic structure by combined atomic force microscopy, scanning tunneling microscopy, and conductance measurements complemented by density functional theory and transport calculations. These junctions are relevant for developing contacts in all-graphene nanoribbon devices and creating diodes and transistors, and act as a first step toward complete electronic devices built into a single graphene nanoribbon.

We measure uniaxial strain fields in the vicinity of edges and wrinkles in graphene prepared by chemical vapor deposition (CVD), by combining microscopy techniques and local vibrational characterization. These strain fields have magnitudes of several tenths of a percent and extend across micrometer distances. The nonlinear shear-lag model remarkably captures these strain fields in terms of the graphene-substrate interaction and provides a complete understanding of strain-relieving wrinkles in graphene for any level of graphene-substrate coherency.

Single layer graphene is grown on 10 nm-thick Ir(111) thin films grown on sapphire substrates. These samples have high structural...

Graphene nanoribbons (GNRs)—narrow stripes of graphene—have emerged as promising building blocks for nanoelectronic devices. Recent advances in bottom-up synthesis have allowed production of atomically well-defined armchair GNRs with different widths and doping. While all experimentally studied GNRs have exhibited wide bandgaps, theory predicts that every third armchair GNR (widths of N =3 m +2, where m is an integer) should be nearly metallic with a very small bandgap. Here, we synthesize the narrowest possible GNR belonging to this family (five carbon atoms wide, N =5). We study the evolution of the electronic bandgap and orbital structure of GNR segments as a function of their length using low-temperature scanning tunnelling microscopy and density-functional theory calculations. Already GNRs with lengths of 5 nm reach almost metallic behaviour with ∼100 meV bandgap. Finally, we show that defects (kinks) in the GNRs do not strongly modify their electronic structure.

We report the coexistence of charge puddles and topographic ripples in graphene decoupled from the Ir(111) substrate it was grown on. We show the topographic and the charge disorder to be locally correlated as a result of the intercalation of molecular species. From the analysis of quasiparticle scattering interferences, we find a linear dispersion relation, demonstrating that graphene on a metal can recover its intrinsic electronic properties. The measured Fermi velocity v(F) = 0.9 +/- 0.04x10(6) m/s is lower than in graphene on dielectric substrates, pointing to a strong screening of electron-electron interactions in graphene by the nearby metallic substrate.

Using low-energy electron microscopy, we study Co intercalation under graphene grown on Ir(111). Depending on the rotational domain of graphene on which it is deposited, Co is found intercalated at different locations. While intercalated Co is observed preferentially at the substrate step edges below certain rotational domains, it is mostly found close to wrinkles below other domains. These results indicate that curved regions (near substrate atomic steps and wrinkles) of the graphene sheet facilitate Co intercalation and suggest that the strength of the graphene/Ir interaction determines which pathway is energetically more favorable.

By limiting the carbon segregation at the copper surface defects, a pulsed chemical vapor deposition method for single layer graphene growth is shown to inhibit the formation of few-layer regions, leading to a fully single-layered graphene homogeneous at the centimeter scale. Graphene field-effect devices obtained after transfer of pulsed grown graphene on oxidized silicon exhibit mobilities above 5000 cm^2.V^-1.s^-1.

The intercalation of an oxide barrier between graphene and its metallic substrate for chem- ical vapor deposition is a contamination-free alternative to the transfer of graphene to dielectric supports, usually needed for the realization of electronic devices. Low-cost pro- cesses, especially at atmospheric pressure, are desirable but whether they are achievable remains an open question. Combining complementary microscopic analysis, providing structural, electronic, vibrational, and chemical information, we demonstrate the spontaneous reactive intercalation of 1.5 nm-thick oxide ribbons between graphene and an iridium substrate, at atmospheric pressure and room temperature. We discover that oxygen-containing molecules needed for forming the ribbons are supplied through the graphene wrinkles, which act as tunnels for the efficient diffusion of molecules entering their free end. The intercalated oxide ribbons are found to modify the graphene-support interaction, leading to the formation of quasi-free-standing high quality graphene whose charge density is modulated in few 10-100 nm-wide ribbons by a few 10^12 cm-2, where the inelastic optical response is changed, due to a softening of vibrational modes - red-shifts of Raman G and 2D bands by 6 and 10 cm-1, respectively.

Le graphene epitaxie sur des substrats metalliques est un modele prometteur pour le developpement de nouveaux systemes hybrides, dans lesquelles les effets d'interface peuvent etre exploites pour concevoir de nouvelles proprietes. L'insertion d'especes entre le graphene et son substrat, une operation connues sous le nom d'-«intercalation», est une approche tres puissante a cet egard. Avec l'aide des outils de la physique des surfaces, nous avons etudie trois systemes graphene/metal, dont deux sont des systemes hybrides intercales, et l'autre est un candidat pour un tel systeme : (i) le graphene/Ir(111) intercale avec un oxyde ultra-mince, (ii) graphene/Ir(111) intercale avec des couches sub-atomiques du cobalt et (iii) de graphene sur Re(0001). Nous avons montre que certains defauts, en particulier les ridules (delamination du graphene de son substrat) et d'autres regions courbees du graphene, jouent un role crucial, non anticipe, dans le processus d'intercalation. Nous avons egalement observe que l'intercalation se deroule d'une maniere nettement differente sous ultravide et a pression atmospherique. Dans le premier systeme, des especes contenant de l'oxygene entrent a l'extremite ouverte des ridules et diffusent au long de ces ridules pour former des nano-rubans d'oxyde. Ces rubans modifient le dopage electronique du graphene, ce qui se traduit egalement par des changements substantiels dans la reponse optique inelastique (Raman) du graphene. Dans le second systeme, l'efficacite de l'intercalation est apparue dependante de l'interaction graphene-metal, laquelle varie entre les domaines de graphene orientes differemment sur_(111). Dans ce systeme, les sites d'entree pour les especes intercalees, des regions courbees dans le graphene, ont pu etre identifies grâce a l'observation in_operando (en cours de croissance) du processus. Enfin, la croissance de graphene dans un troisieme systeme (graphene/Re(0001)), a ete etudiee afin de permettre le developpement de futurs systemes graphene/Re hybrides supraconducteurs. Dans ce systeme, nous avons propose deux voies de croissance, l'une etant base sur un processus de croissance en surface d'un monocristal massif de Re(0001), l'autre reposant sur la segregation en surface, activee thermiquement, du carbone dissout a haute temperature dans des films minces de Re sur saphir.

At vanishing charge carrier density, graphene on a dielectric substrate exhibits spatial doping inhomogeneities forming electron-hole puddles. Understanding and controlling the latter is of crucial importance for unraveling many of graphene's fundamental properties at the Dirac point, where the linear valence and conduction bands meet. Charged impurities trapped in the dielectric substrate as well as the local graphene curvature have been pointed to as the puddles' origin. Here we show by scanning tunneling microscopy/spectroscopy the coexistence and correlation of charge puddles and topographic ripples in graphene decoupled from a metallic Ir substrate. The perfect screening of charged impurities by the metallic substrate reveals charge puddles directly induced by the local graphene-substrate distance and the ensuing charge transfer. Furthermore, the analysis of Dirac fermion interferences shows that electron-electron interactions are also strongly screened. Our findings therefore demonstrate that graphene on Ir provides a new platform to study the non-interacting limit for massless Dirac electrons in graphene.