Starting from the late 1980s, scanning probe microscopy has progressively diffused in Italy until today. In this paper, we provide a brief account of the main historical events and a current picture of the distribution of the active groups. A survey was prepared by LimeSurvey, made of six sections asking for personal and institutional data, human resources, equipment available, fields of interest, research projects, educational/dissemination activities, and two relevant publications in the last six years. It turns out that the Italian community includes more than seventy groups and two companies. It is widely diffused, although mostly concentrated near large academic and research institutions, often in locations where prominent Italian researchers have operated. This community is active in many scientific fields and can produce research of high international quality. It shows a wide competence, as proven by the list of research works published in journals ranked within the top 20% class. The diffusion of SPM microscopes in industry is still sporadic, possibly due to extensive collaborations between the research institutions and industries themselves. The authors hope that this work might be useful to the community and beyond, and that it might stimulate the formation of a more structured network.

The Pd cyclometallated complex [(5-bromo-2-phenylpyridine)Pd(?-Cl)]2 is deposited on Ag(110) at room temperature by sublimation in ultra-high vacuum. The thermal evolution of the system is followed by scanning tunnelling microscopy and X-ray photoemission spectroscopy, while the initial and final configurations are validated by ab-initio calculations. We observe the surface induced dissociation of the molecule and the occurrence of a cross coupling reaction between the two organic fragments, leading to the surface assisted synthesis of diphenyl-bipyridine molecules. Such a process, occurring with low probability at RT, is thermally activated and competes with desorption. At variance with most cross-coupling reactions at surfaces reported in literature, in this case the reactants come from the dissociation of the same compound so that only one precursor is employed, leading to a simplified preparation protocol. The Br and Cl atoms dissociated from the molecule bind to the surface and promote an extended surface reconstruction upon annealing, which was not observed previously upon deposition of halogenated aromatic compounds.

In this article, we analyze the electronic structure modifications of triphenylamine (TPA), a well-known electron donor molecule widely used in photovoltaics and optoelectronics, upon deposition on Au(111) at a monolayer coverage. A detailed study was carried out by synchrotron radiation-based photoelectron spectroscopy, near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, scanning tunneling microscopy (STM), and ab initio calculations. We detect a new feature in the pre-edge energy region of the N K-edge NEXAFS spectrum that extends over 3 eV, which we assign to transitions involving new electronic states. According to our calculations, upon adsorption, a number of new unoccupied electronic states fill the energy region between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the free TPA molecule and give rise to the new feature in the pre-edge region of the NEXAFS spectrum. This finding highlights the occurrence of a considerable modification of the electronic structure of TPA. The appearance of new states in the HOMO-LUMO gap of TPA when adsorbed on Au(111) has crucial implications for the design of molecular nanoelectronic devices based on similar donor systems.

Dirac semimetals are classified into different phases based on the types of Dirac fermions. Tuning the transition among different types of Dirac fermions in one system remains a challenge. Recently, KMgBi was predicted to be located at a critical state in which various types of Dirac fermions can be induced owing to the existence of a flatband. Here, we carried out systematic studies on the electronic structure of KMgBi single crystals by combining angle-resolve photoemission spectroscopy and scanning tunneling microscopy/spectroscopy. The flatband was clearly observed near the Fermi level. We also revealed a small bandgap of similar to 20 meV between the flatband and the conduction band. These results demonstrate the critical states of KMgBi that transition among various types of Dirac fermions can be tuned in one system.

Quantum materials are central for the development of novel functional systems that are often based on interface specific phenomena. Fabricating controlled interfaces between quantum materials requires adopting a flexible growth technique capable to synthesize different materials within a single-run deposition process with high control of structure, stoichiometry, and termination. Among the various available thin film growth technologies, pulsed laser deposition (PLD) allows controlling the growth of diverse materials at the level of single atomic layers. In PLD the atomic species are supplied through an ablation process of a stoichiometric target either in form of polycrystalline powders or of a single crystal. No carrier gases are needed in the deposition process. The ablation process is compatible with a wide range of background pressure. We present results of thin-film growth by PLD obtained by using an Nd:YAG infrared pulsed laser source operating at its first harmonics. With respect to the traditional PLD systems-based on excimer KrF UV-lasers-optimal conditions for the growth of thin films and heterostructures are reached at large target-To-substrate distance. Merits and limitations of this approach for growing oxide and non-oxide thin films are discussed. The merits of an Nd:YAG laser to grow very high-quality thin films suggest the possibility of implementing compact in-situ setups e.g. integrated with analytical instrumentation under ultra-high vacuum conditions.

In this work we present a detailed surface science characterization of L-arginine adsorption on the Cu(1 1 0) surface in a submonolayer regime. Arginine (ARG) is one of the main components of the tripeptide RGD (arginine-glycine-aspartic acid) commonly used as a linker/binder when engineering biomedical devices such as integrin receptors. We replaced the traditional Knusden cell sublimation method to obtain molecular films by dosing arginine directly from an aqueous solution through an electrospray ionization device (ESI). X-ray Photoelectron Spectroscopy (XPS) evidenced the co-existence of different adsorbed molecular species. In addition, Scanning Tunneling Microscopy (STM) data show that the arginine molecules form short and well-separated lines, constituted of dimers of molecules on the surface. Density Functional Theory (DFT) calculations helped clarifying these experimental findings, bringing strong evidences that ARG molecules adsorb in an ionic and a neutral form, with varied binding modes between N atoms and Cu atoms from the surface. These different N[sbnd]Cu bonds lead to the establishment of intermolecular H-bonds, responsible for the dimerization process.

Nanographenes (NGs) have gained increasing attention due to their immense potential as tailor-made organic materials for nanoelectronics and spintronics. They exhibit a rich spectrum of physicochemical properties that can be tuned by controlling the size or the edge structure or by introducing structural defects in the honeycomb lattice. Here, we report the design and on-surface synthesis of NGs containing several odd-membered polycycles induced by a thermal procedure on Au(111). Our scanning tunneling microscopy, noncontact atomic force microscopy, and scanning tunneling spectroscopy measurements, complemented by computational investigations, describe the formation of two nonbenzenoid NGs (2A,B) containing four embedded azulene units in the polycyclic framework, via on-surface oxidative ring-closure reactions. Interestingly, we observe surface-catalyzed skeletal ring rearrangement reactions in the NGs, which lead to the formation of additional heptagonal rings as well as pentalene and as-indacene units in 2A,B, respectively. 2A,B on Au(111) both exhibit narrow experimental frontier electronic gaps of 0.96 and 0.85 eV, respectively, and Fermi level pinning of their HOMOs together with considerable electron transfer to the substrate. Ab initio calculations estimate moderate open-shell biradical characters for the NGs in the gas phase.

Fully conjugated ladder polymers (CLP) possess unique optical and electronic properties and are considered promising materials for applications in (opto)electronic devices. Poly(indenoindene) is a CLP consisting of an alternating array of five- and six-membered rings, which has remained elusive so far. Here, we report an on-surface synthesis of oligo(indenoindene) on Au(111). Its structure and a low electronic band gap have been elucidated by low-temperature scanning tunneling microscopy and spectroscopy and noncontact atomic force microscopy, complemented by density functional theory calculations. Achieving defectfree segments of oligo(indenoindene) offers exclusive insight into this CLP and provides the basis to further synthetic approaches.

Relazione sui risultati dell'attività di ricerca svolta dal 15/01/2020 al 05/02/2020

Motorized molecules where an external stimulus leads to controlled motion can perform work on the atomic scale. In Feringa-type motors, controlled motion is initiated by ultraviolet light that triggers a sequence of isomerization and helical inversion steps leading to the unidirectional rotation of the motor. Studying motor molecules on solid surfaces is advantageous because molecules can be studied in real space with scanning probe microscopy, surface features act as a spatial reference, and motion can be activated by pulses from the scanning probe tip. However, commonly used metal substrates have drawbacks, notably the quenching of excited molecular states by surface conduction electrons. An alternate approach is to deposit molecular motors on semiconducting substrates, thereby removing a potential path for quenching. Here we present results on the adsorption configurations and demonstrate the motion of unidirectional Feringa molecular motors adsorbed on the wide band gap semiconductor rutile TiO2(110).

An operando investigation of graphene growth on (100) grains of polycrystalline nickel (Ni) surfaces was performed by means of variable-temperature scanning tunneling microscopy complemented by density functional theory simulations. A clear description of the atomistic mechanisms ruling the graphene expansion process at the stepped regions of the substrate is provided, showing that different routes can be followed, depending on the height of the steps to be crossed. When a growing graphene flake reaches a monoatomic step, it extends jointly with the underlying Ni layer; for higher Ni edges, a different process, involving step retraction and graphene landing, becomes active. At step bunches, the latter mechanism leads to a peculiar 'staircase formation' behavior, where terraces of equal width form under the overgrowing graphene, driven by a balance in the energy cost between C-Ni bond formation and stress accumulation in the carbon layer. Our results represent a step towards bridging the material gap in searching new strategies and methods for the optimization of chemical vapor deposition graphene production on polycrystalline metal surfaces. (C) 2020 Elsevier Ltd. All rights reserved.

Metal-tetraphenyl-porphyrin (M-TPP) molecules typically self-assemble forming square-like superlattices, as dictated by their shape. The dependence of the adsorption properties on the central atom is systematically studied for Co-, Ni-, and Zn-TPP adsorbed on oxygen passivated Fe(001), namely the Fe(001)-p(1 x 1)O surface. It is found by low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) that despite the weak molecule-substrate interaction, preserving many features of quasi-free molecules, the self-assembled structure switches from the (5 x 5)R37 degrees superlattice of Co-TPP and Ni-TPP to the plain (5 x 5) of Zn-TPP. Ab initio calculations based on density functional theory (DFT) are used to investigate the adsorption properties of the different molecules and the possible overlayers formed. Adsorption energies, structures, and electronic properties are reported, discussing the bonding mechanisms and the magnetic character. Only moderate energy differences are found, suggesting that subtle effects may steer the selection of the structure among overlayers with similar properties although differing substantially as for the LEED and STM experimental results.

Many studies have shown the potential of using flame-formed CNPs for several advanced technologies including: fluorescent nanoparticles, active material for new solar cells generation or as supercapacitor material; (in addition to the classical carbon black uses); Flame-formed CNPs can have different features: particles size, morphology, degree of carbonization, optical properties; In this poster we report some results achieved, in our lab, and in collaboration with other groups, by scanning probe microscopies on CNPs.

Hydrogenation of nitrogen (N) doped GaAs allows for reversible tuning of the band gap and the creation of site controlled quantum dots through the manipulation of N-nH complexes, N-nH complexes, wherein a nitrogen atom is surrounded by n hydrogen (H) atoms. Here we employ cross-sectional scanning tunneling microscopy (X-STM) to study these complexes in the GaAs (110) surface at the atomic scale. In addition to that we performed density functional theory (DFT) calculations to determine the atomic properties of the N-nH complexes. We argue that at or near the (110) GaAs surface two H atoms from N-nH complexes dissociate as an H2 molecule. We observe multiple features related to the hydrogenation process, of which a subset is classified as N-1H complexes. These N-1H related features show an apparent reduction of the local density of states (LDOS), characteristic to N atoms in the GaAs (110) surface with an additional apparent localized enhancement of the LDOS located in one of three crystal directions. N-nH features can be manipulated with the STM tip. Showing in one case a switching behavior between two mirror-symmetric states and in another case a removal of the localized enhancement of the LDOS. The disappearance of the bright contrast is most likely a signature of the removal of an H atom from the N-nH complex.

Iron phthalocyanines (FePc) adsorbed onto a Ag(110) substrate self-assemble into different monolayer phases going from rectangular to different oblique phases, with increasing molecular density. We have investigated the oxygen uptake capability of the different phases and their associated magneto-structural changes. Our study combines scanning tunneling microscopy and spectroscopy (STM/STS), X-ray magnetic circular dichroism (XMCD), and density functional theory (DFT) calculations. STM measurements reveal that the oxygenation reaction of the FePc/Ag(110) generally involves a displacement and a rotation of the molecules, which affects the electronic state of the Fe centers. The oxygen intercalation between FePc and the substrate is greatly obstructed by the steric hindrance in the high-density phases, to the point that a fraction of oblique phase molecules cannot change their position after oxidizing. Depending on the oxidation state and adsoption geometry, the STS spectra show clear differences in the Fe local density of states, which are mirrored in the XAS and XMCD experiments. Particularly, XMCD spectra of the oxidized phases reflect the distribution of FePc species (nonoxygenated, oxygenated-rotated, and oxygenated-unrotated) in the different cases. Sum rule analysis yields the effective spin (m(s)(eff)) and orbital (m(L)) magnetic moments of Fe in the different FePc species. Upon oxygenation, the magnetic moment of FePc molecules increases about an order of magnitude, reaching m(TOT) similar to 2.2 mu(B) per Fe atom.

There is a great interest in the scientific community to perform calorimetry on samples having mass in the nanogram range. A detailed knowledge of the energy (heat) exchange in the fast growing family of micro- and nano-systems could provide valuable information about the chemistry and physics at the nano-scale. The possibility to have an atomically flat thermal probe represents an added value, because it provides the unique opportunity to perform Scanning Probe Microscopy (SPM) together with calorimetry. Here we report the fabrication, characterization, and calibration of atomically flat, single-crystalline gold film thermometers on mica substrate. Gold re-crystallization has been obtained, and successively the thermometer surface has been studied by Low Energy Electron Diffraction (LEED) and Scanning Tunneling Microscopy (STM). The thermometer calibration demonstrates a heat exchange coefficient of W/K and a performance about 10 times better than previous sensors based on Si substrates. The experimental setup allows the simultaneous investigation of heat exchange and surface physics on the same sample.

Ni nanoclusters up to 30 angstrom in diameter are grown by Ni deposition on ultrathin MgO/Ag(100) films at different temperatures and characterized by combining low-temperature scanning tunneling microscopy with photo-emission and vibrational spectroscopies. At 200 K, both small NixOyD aggregates and 2D Ni nanoparticles of average size close to 12 angstrom form. The latter have a metallic nature and efficiently catalyze CO dissociation at 200 K. When Ni is deposited at 300 K, only larger 3D Ni clusters are observed.

Graphene (Gr) is known to be an excellent barrier preventing atoms and molecules to diffuse through it. This is due to the carbon atom arrangement in a two-dimensional (2D) honeycomb structure with a very small lattice parameter forming an electron cloud that prevents atoms and molecules crossing. Nonetheless at high annealing temperatures, intercalation of atoms through graphene occurs, opening the path for formation of vertical heterojunctions constituted of two-dimensional layers. In this paper, we report on the ability of silicon atoms to penetrate the graphene network, fully epitaxially grown on a Ni(111) surface, even at room temperature. Our scanning tunneling microscopy (STM) experiments show that the presence of defects like vacancies and dislocations in the graphene lattice favor the Si atoms intercalation, forming two-dimensional, flat and disordered islands below the Gr layer. Ab-initio molecular dynamics calculations confirm that Gr defects are necessary for Si intercalation at room temperature and show that: i) a hypothetical intercalated silicene layer cannot be stable for more than 8 ps and ii) the corresponding Si atoms completely lose their in-plane order, resulting in a random planar distribution, and form strong covalent bonds with Ni atoms.

The regular packing of atoms, molecules and nanoparticles provides the basis for the understanding of structural order within condensed phases of matter. Typically the constituent particles are considered to be rigid with a fixed shape. Here we show, through a combined experimental and numerical study of the adsorption of cyclic porphyrin polymers, nanorings, on a graphite surface, that flexible molecules can exhibit a rich and complex packing behaviour. Depending on the number of porphyrin sub-units within the nanoring we observe either a highly ordered hexagonal phase or frustrated packing driven by directional interactions which for some arrangements is combined with the internal deformation of the cyclic polymer. Frustration and deformation occur in arrays of polymers with ten sub-units since close packing and co-alignment of neighbouring groups cannot be simultaneously realised for nanorings with this internal symmetry.

In this work, the optoelectronic properties of flame-formed carbon particles at the initial stages of formation and growth was investigated. To this aim, Scanning Tunneling Spectroscopy technique was implemented and applied for the first time to characterize soot particles. Two classes of particles, that can be defined as incipient soot and primary soot particles, have been selectively collected on the basis of their size distribution. Scanning Tunneling Spectroscopy measurements was performed to evaluate the energy band gap and the density of states of flameformed soot nanoparticles and to compare them to those of reference materials, namely coronene and HOPG. The results obtained showed that Scanning Tunneling Spectroscopy is a powerful tool to investigate the optoelectronic properties of nanomaterials, with possible application in combustion science and technology as well as in material science field.