Bottom-up approaches exploiting on-surface synthesis reactions allow atomic-scale precision in the fabrication of graphene nanoribbons (GNRs); this is essential for their technological applications since their unique electronic and optical properties are largely controlled by the specific edge structure. By means of a combined experimental-theoretical investigation of some prototype GNRs, we show here that high-resolution electron energy-loss spectroscopy (HREELS) can be successfully employed to fingerprint the details of the GNR edge structure. In particular, we demonstrate how the features of HREEL vibrational spectra - mainly dictated by edge CH out-of-plane modes - are unambiguously related to the GNR edge structure. Moreover, we single out those modes which are localized at the GNR termini and show how their relative intensity can be related to the average GNR length.

In this work, we investigated the effect of Au-intercalation on the magnetic coupling between a sub-monolayer of Co-Tetraphenylporphyrin molecules and a graphene-covered Ni(111) single crystal. Using x-ray absorption spectroscopy and x-ray magnetic circular dichroism, the element-specific magnetization and its field dependence were probed. Cobalt strongly couples antiferromagnetically to the nickel substrate, also through the graphene layer. The intercalation of graphene with gold leads to a complete removal of this coupling.

Lanthanides (Ln) bis-phthalocyanine (Pc), the so-called LnPc(2) double decker, are a promising class of molecules with a well-defined magnetic anisotropy. In this work, we investigate the magnetic properties of LnPc(2) molecules UHV-deposited on a graphene/Ni(111) substrate and how they modify when an Au layer is intercalated between Ni and graphene. X-ray absorption spectroscopy (XAS), and linear and magnetic circular dichroism (XLD and XMCD) were used to characterize the systems and probe the magnetic coupling between LnPc(2) molecules and the Ni substrate through graphene, both gold-intercalated and not. Two types of LnPc(2) molecules (Ln = Tb, Er) with a different magnetic anisotropy (easy-axis for Tb, easy-plane for Er) were considered. XMCD shows an antiferromagnetic coupling between Ln and Ni(111) even in the presence of the graphene interlayer. Au intercalation causes the vanishing of the interaction between Tb and Ni(111). In contrast, in the case of ErPc2, we found that the gold intercalation does not perturb the magnetic coupling. These results, combined with the magnetic anisotropy of the systems, suggest the possible importance of the magnetic dipolar field contribution for determining the magnetic behaviour.

Electrospray deposition (ESD) in ambient conditions has been used to deposit graphene nanoribbons (GNRs) dispersed in liquid phase on different types of substrates, including ones suitable for electrical transport. The deposition process was controlled and optimized by using Raman spectroscopy, Scanning Probe Microscopies and Scanning Electron Microscopy. When deposited on graphitic electrodes, GNRs were used as semi-conducting channel in three terminal devices showing gate tunability of the electrical current. These results suggest that ESD technique can be used as an effective tool to deposit chemically synthesized GNRs onto substrates of interest for technological applications.

Learning the art of exploiting the interplay between different units at the atomic scale is a fundamental step in the realization of functional nano-architectures and interfaces. In this context, understanding and controlling the magnetic coupling between molecular centers and their environment is still a challenging task. Here we present a combined experimental-theoretical work on the prototypical case of the bis(phthalocyaninato)-lanthanide(III) (LnPc(2)) molecular nanomagnets magnetically coupled to a Ni substrate. By means of X-ray magnetic circular dichroism we show how the coupling strength can be tuned by changing the Ln ion. The microscopic parameters of the system are determined by ab-initio calculations and then used in a spin Hamiltonian approach to interpret the experimental data. By this combined approach we identify the features of the spin communication channel: the spin path is first realized by the mediation of the external (5d) electrons of the Ln ion, keeping the characteristic features of the inner 4 f orbitals unaffected, then through the organic ligand, acting as a bridge to the external world.

We investigate the electronic and magnetic properties of TbPc2 single ion magnets adsorbed on a graphene/Ni(111) substrate, by density functional theory (DFT), ab initio complete active space self-consistent field calculations, and X-ray magnetic circular dichroism (XMCD) experiments. Despite the presence of the graphene decoupling layer, a sizable antiferromagnetic coupling between Tb and Ni is observed in the XMCD experiments. The molecule-surface interaction is rationalized by the DFT analysis and is found to follow a relay-like communication pathway, where the radical spin on the organic Pc ligands mediates the interaction between Tb ion and Ni substrate spins. A model Hamiltonian which explicitly takes into account the presence of the spin radical is then developed, and the different magnetic interactions at play are assessed by first-principle calculations and by comparing the calculated magnetization curves with XMCD data. The relay-like mechanism is at the heart of the process through which the spin information contained in the Tb ion is sensed and exploited in carbon-based molecular spintronics devices.

Friction characteristics of graphene deposited on different substrates have been studied by atomic force microscopy (AFM). In particular, we compared mechanically exfoliated graphene transferred over Si/SiO2 with respect to monolayer (ML) graphene grown in our laboratory by low temperature chemical vapor deposition on Ni(111) single crystal. Friction force measurements by AFM have been carried out as function of load under different environment conditions, namely vacuum (10−5 Torr), nitrogen and air. The typical decrease of friction force with increasing number of layers has been observed on graphene over Si/SiO2 in all environment including vacuum. Continuum mechanical approximation has been used to analyze the friction versus load curves of ML graphene on Ni(111). Analysis shows that Derjaguin–Mueller–Toporov model is in good agreement with our experimental data indicating that overall behavior of the interface graphene–Ni(111) is relatively rigid respect to out of plane deformations. This result is consistent with the structural characteristics of the interface since graphene grows in registry with Ni(111) surface with covalent bonding character. Finally, the shear strength and the work of adhesion of the two systems with respect to AFM tip in vacuum have been compared. The result of this procedure indicates that shear strength and work of adhesion measured on graphene–Si/SiO2 interface are always greater than those on graphene–Ni(111) interface.

Future applications of molecular units in quantum information technologies require a fine control at the single molecule level. This includes the choice of each functional element, the intramolecular interaction and the robustness of molecules when dispersed on a substrate. Keeping these goals in mind, we designed and synthesized a heterometallic phthalocyaninato-complex including two different lanthanides in each moiety, namely [PcDyPcTbPc*] (Pc being phthalocyanines; and Pc* being 2,3,9,10,16,17,23,24-octahexyl-substituted phthalocyanines). Full magnetic characterization was performed down to the mK temperature range on bulk microcrystals by means of AC susceptibility, DC magnetization (including microSQUID) and specific heat measurements. A weak, yet sizeable, interaction between the two lanthanides is clearly detected by different techniques, altering the magnetic behavior of the single lanthanide as observed in the parent [LnPc(2)] complexes. Isolated [PcDyPcTbPc*] molecules dispersed on HOPG and the Au surface by liquid phase deposition are proven to maintain their main chemical and magnetic features by combined XPS, XAS and XMCD analysis and to lie with one Pc ligand flat to the surface. Opening of a small but sizable hysteresis loop at 1.8 K is directly observed on both Tb and Dy sites proving the retention of magnetization at the single molecule level.

The interface spin coupling mechanism is studied in a hybrid structure made of Fe phthalocyanine molecules sublimed in ultrahigh vacuum on graphene grown on the magnetic substrate Ni(111). By using synchrotron X-ray magnetic circular dichroism, the field-dependent magnetization of the isolated Fe Pc molecules and of the Ni substrate has been measured at low temperature (8 K). Along with density functional theory calculations, the role of the graphene interlayer in transmitting the magnetic coupling is addressed. Both experiments and theory show a ferromagnetic coupling between the molecules and the substrate which is weakened by the insertion of graphene. DFT calculations indicate that the key role is played by the pi orbitals of graphene, which hybridize with the underlying magnetic Ni, giving rise to a sizable spin polarized continuum at the molecular interface. The resulting overlap with the Fe orbitals favors a direct coupling of ferromagnetic nature, as evidenced by our spin density distribution plots.

The electronic properties of a prototype system suitable for dye-sensitized solar cell applications are investigated both experimentally and theoretically by means of electron spectroscopies (high-resolution electron energy loss spectroscopy, HREELS, and ultraviolet and X-ray photoemission spectroscopies, UPS and XPS) and first-principles density functional theory (DFT)-based calculations. The comparison of HREELS and UPS data with the DFT results allows the microscopic description of electronic structure modifications upon interface formation, and provides a quantitative evaluation of the ionization energy and electron affinity changes induced by functionalization: these variations can be associated to the electric dipole of the functional species and, thus, to the formation of an interface dipole layer.

Proving the preservation of functionality at the molecular scale is still a major challenge, both for the choice of suitable derivatives and protocols and for the employed experimental tools and methods. By using a combined scanning probe (AFM and STM) and spectroscopic methodology (XPS, XAS and XMCD), it is shown that Gd 4 M 8 derivatives (with M = Zn 2+ , Ni 2+ ) are robust molecular units which preserve their electronic, magnetic, and thermodynamic properties when deposited on a metallic surface. Namely, entropy variation Δ S = [ S (6 T) – S (0 T)] exceeding 8 R (20 J kg −1 K −1 ) at 4 K in isolated Gd 4 Ni 8 molecules dispersed on Au(111) surface is measured and a viable route to exploit large magnetocaloric effect at single molecule level is shown.

Hybrid organic-inorganic [2]- and [3]rotaxanes have been synthesised, and their ability to bind to Au surfaces studied; the length of the tethering group is found to control how the supramolecular assembly binds to the surface and we find that [2]rotaxanes show improved stability over previous studies of simple inorganic rings.

The spin and orbital configuration of magnetic metal phthalocyanines (MPcs) deposited on metallic substrates are strongly influenced by the rehybridization of the molecular states with the underlying metal. FePc, CoPc, and CuPc isolated molecules are archetypal systems to investigate the interrelationship between magnetic moments and orbital symmetry after deposition on a metallic substrate. MPcs form long-range ordered chains self-assembled along the reconstructed channels of the Au(110) surface. X-ray magnetic circular dichroism from the L-2,L-3 absorption edges of Fe, Co, and Cu shows that the orbital and spin configuration are strongly modified upon adsorption on the Au(110) surface if the orbitals responsible of the magnetic moment are involved in the interaction process. The magnetic moment for a single layer of molecular chains is completely quenched for the CoPc molecules, fully preserved for the CuPc and reduced for the FePc ones. The modified magnetic configuration is confined to the very interface layer, i.e., to the MPc molecules bound to the metal substrate up to the compact packing of the single layer. The different response can be rationalized in terms of the symmetry/orientation of the metal-ion d states interacting with the substrate states, as indicated by density functional theory calculations in agreement with experimental findings. DOI: 10.1103/PhysRevB.87.165407

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

A sub-monolayer distribution of isolated molecular Fe14 (bta)6 nanomagnets is deposited intact on a Au(111) surface and investigated by X-ray magnetic circular dichroism spectroscopy. The entropy variation with respect to the applied magnetic field is extracted from the magnetization curves and evidences high magnetocaloric values at the single molecule level.

The magnetic and electronic properties of single-molecule magnets are studied by X-ray absorption spectroscopy and X-ray magnetic circular dichroism. We study the magnetic coupling of ultrathin Co and Ni films that are epitaxially grown onto a Cu(100) substrate, to an in situ deposited submonolayer of TbPc2 molecules. Because of the element specificity of the X-ray absorption spectroscopy we are able to individually determine the field dependence of the magnetization of the Tb ions and the Ni or Co film. On both substrates the TbPc2 molecules couple antiferromagnetically to the ferromagnetic films, which is possibly due to a superexchange interaction via the phthalocyanine ligand that contacts the magnetic surface.

The problem of the experimental and theoretical determination of magnetic anisotropy in isolated molecular spin clusters is addressed here. To this end, the case of molecular Cr 7 Ni rings sublimated in ultrahigh vacuum conditions and assembled in an ordered fashion on Au(111) surface is addressed and investigated using X‐ray magnetic dichroism (XMCD) and theoretical calculations. Fixing the experimental conditions at a temperature T = 8 K and a magnetic field of 5 T, the angular‐dependence of the dichroic signal reveals an easy‐axis anisotropy for the Ni magnetization along the direction perpendicular to the ring while the magnetization of the whole Cr 7 Ni molecule is preferentially aligned within the ring plane. These features are well reproduced by spin Hamiltonian simulations, which reflect the character of the S = 3/2 first excited multiplet, dominating at T = 8 K and 5 T. Density functional theory (DFT) calculations show that local spin orbit interactions determine an easy axis anisotropy at the Ni site while the Cr magnetic moment turns out to be more isotropic. This is the first direct observation of the interplay between the single ion and the overall magnetic anisotropy in complex (polynuclear) molecular systems.

Structural, electronic, and magnetic properties of [Mn12O12(bet)(16)(EtOH)(4)](PF6)(14)center dot 4CH(3)CN center dot H2O (in short Mn(12)bet, bet = betaine = N+(CH3)(3)-CH2-COO-) single-molecule magnets (SMMs) deposited on previously functionalized gold surfaces have been investigated. Self-assembled monolayers (SAMs) either of sodium mercaptoethanesulfonate (MES) or mercaptopropionic acid (MPA) are used as functionalization to avoid the direct interaction between the Mn(12)bet molecules and the Au surface with the aim of preserving the main functional properties of the molecules. Scanning tunneling microscopy (STM) and X-ray photoemission spectroscopy (XPS) analysis show deposited Mn(12)bet SMMs well-isolated from each other and uniformly distributed on both MES SAMs. X-ray absorption spectroscopy (XAS) studies show that the oxidation state of the mixed-valence Mn(12)bet core is largely reduced to Mn+ when molecules are deposited on MES-SAM, whereas in the case of MPA-SAM the relative weights of Mn2+, Mn3+, and Mn4+ in the Mn(12)bet core are preserved. Despite the substantial retaining of their electronic properties, the magnetization of Mn(12)bet molecules deposited on MPA-SAM measured by X-ray magnetic circular dichroism (XMCD) is perturbed with respect to the pristine molecules.

We investigate the low-temperature magnetic and entanglement properties of a series of molecular Cr2nCu2 heterometallic spin rings (with n = 4,5,6). These are cyclic spin systems, consisting of two Cu2+ (s = 1/2) ions, coupled by two antiferromagnetic segments of n Cr3+ (s = 3/2) ions. Thermodynamic measurements (magnetization, susceptibility, and specific heat) allow us to determine the total spin of the ground state and to estimate the spin-Hamiltonian parameters related to magnetic anisotropy. X-ray spectroscopies (XAS and XMCD) are used to probe the local magnetization of the Cr and Cu ions, and provide results that are consistent with the bulk magnetization data. We finally investigate the relation between heterometallicity and entanglement in these prototypical spin systems. In particular, we focus on the spatial modulation of entanglement induced by the Cu defect spins and on the long-distance entanglement between them induced by the two Cr chains.