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Flexible conductive composites based on ultra-high molecular weight polyethylene (UHMWPE) filled with multi-walled carbon nanotubes (CNTs) modified by perfluoropolyethers (PFPEs) were produced. The bonding of PFPE chains, added in 1:1 and 2:1 weight ratios, on CNTs influences the dispersion of nanotubes in the UHMWPE matrix due to the non-polar nature of the polymer, facilitating the formation of nanofillers-rich conductive pathways and improving composites’ electrical conductivity (two to five orders of magnitude more) in comparison to UHMWPE-based nanocomposites obtained with pristine CNTs. Electrochemical atomic force microscopy (EC-AFM) was used to evaluate the morphological changes during cyclic voltammetry (CV). The decrease of the overpotential for hydrogen oxidation peaks in samples containing PFPE-functionalized CNTs and hydrogen production (approximately −1.0 V vs. SHE) suggests that these samples could find application in fuel cell technology as well as in hydrogen storage devices. Carbon black-containing composites were prepared for comparative study with CNTs containing nanocomposites.

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)

Nano-sensor materials, especially if they target biological purposes, require fine control and tuning of the properties at the molecular scale when intramolecular properties have to be exploited, for example, in optical sensors. By means of optical spectroscopies (namely, spectrophotometry, spectrofluorimetry, and surface differential reflectivity), we demonstrate that thin films of porphycene show a spectacular chromatic change when exposed to acid vapors (specifically to hydrochloric acid). After exposure, the original optical properties of the porphycene films are recovered within a few seconds and without any thermal annealing. In addition, since clear spectroscopic signatures are observed both in absorption and in reflectivity, the parent porphycene is shown to be suitable even for deposition of films onto opaque substrates. These findings are of significant interest in view of potential engineering of the molecules and implementation in devices.

Porous crystalline Ni-doped TiO2 films were produced using DC plasma electrolytic oxidation in refrigerated H2SO4 aqueous solutions containing NiSO4. The crystalline phase structure consisted of a mixture of anatase and rutile, ranging from ~30 to ~80 wt % rutile. The oxide films obtained at low NiSO4 concentration showed the highest photocurrent values under monochromatic irradiation in the UV-vis range, outperforming pure TiO2. By increasing NiSO4 concentration above a threshold value, the photoelectrochemical activity of the films decreased below that of undoped TiO2. Similar results were obtained using cyclic voltammetry upon polychromatic UV-vis irradiation. Glow discharge optical emission spectrometry (GD-OES) analysis evidenced a sulfur signal peaking at the TiO2/Ti interface. XPS spectra revealed that oxidized Ni2+, S4+ and S6+ ions were included in the oxide films. In agreement with photocurrent measurements, photoluminescence (PL) spectra confirmed that less intense PL emission, i.e., a lower electron-hole recombination rate, was observed for Ni-doped samples, though overdoping was detrimental.

Intercalation mechanisms and diffusion or segregation phenomena in graphitic materials play a crucial role in different applied science fields. The investigation of such phenomena is usually accomplished through depth profiling experiments. Ar-GCIBs (Argon- Gas Cluster Ion Beams) are commonly adopted for in-depth concentration profiling of organic or soft materials; on the other hand, cesium ions are in general more suitable for the sputtering of inorganics. During such experiments, the beam-target interaction could alter chemistry and structure of the material. In this work, we define the optimal conditions in terms of both sputtering ion source and energy to preserve the crystal features. HOPG was used as a model system to compare morphological, physical, and chemical effects induced by different Arn+ clusters, and ultra-low energy Cs+ beam during ToF-SIMS (Time of Flight Secondary Ion Mass Spectrometry) depth profiling experiments. We demonstrated, through in-situ AFM (Atomic Force Microscopy) analysis, that the monoatomic Cs+ beam alters to a lower extent the HOPG structure. On the contrary, Ar-GCIBs strongly modify the graphite surface basal plane and underlying layers. However, HOPG crystals treated with the cesium monoatomic source undergo a chemistry modification leading to the formation of graphite oxide (GOx) together with the presence of hydrogen, and cesium adducts.

An innovative and versatile set-up for in situ and real time measures in an electrochemical cell is described. An original coupling between micro-Raman spectroscopy and atomic force microscopy enables one to collect data on opaque electrodes. This system allows for the correlation of topographic images with chemical maps during the charge exchange occurring in oxidation/reduction processes. The proposed set-up plays a crucial role when reactions, both reversible and non-reversible, are studied step by step during electrochemical reactions and/or when local chemical analysis is required.

Metal-oxide nanostructures play a fundamental role in a large number of technological applications, ranging from chemical sensors to data storage devices. As the size of the devices shrinks down to the nanoscale, it is mandatory to obtain sharp and good quality interfaces. Here, it is shown that a two-dimensional material, namely, graphene, can be exploited as an ideal buffer layer to tailor the properties of the interface between a metallic substrate and an ultrathin oxide. This is proven at the interface between an ultrathin film of the magnetoelectric antiferromagnetic oxide Cr2O3 and a Ni(111) single crystal substrate. The chemical composition of the samples has been studied by means of X-ray photoemission spectroscopy, showing that the insertion of graphene, which remains buried at the interface, is able to prevent the oxidation of the substrate. This protective action leads to an ordered and layer-by-layer growth, as revealed by scanning tunneling microscopy data. The structural analysis performed by low-energy electron diffraction indicates that the oxide layer grown on graphene experiences a significant compressive strain, which strongly influences the surface electronic structure observed by scanning tunneling spectroscopy.

It is generally accepted that anion intercalation occurs when HOPG is kept at high electrochemical potentials in oxidant electrolytes, such as perchloric and sulfuric acids. The graphite surface undergoes a detriment, made also evident by the swelling of the uppermost layers (blisters formation) caused by gas evolution in standard electrochemical conditions (namely, by cycling the HOPG voltage at speeds up to 25 mV/s). Surface swelling is therefore considered as being indicative of anion intercalation. Recently, suppression of blister formation when the potential is swept at larger speeds (such as 600 mV/s) has been observed, raising the question as to whether this phenomenon might be able to suppress anion intercalation. In this work, by combining atomic force microscopy and X-ray photoemission spectroscopy, we unequivocally show that the HOPG electrode undergoes similar chemical modifications, regardless of the chosen electrochemical conditions and consequently of the morphological evolution at the surface.

Thin organic films are widely used in sensors, solar cells, and optical devices due to their intense absorption in the visible/near-infrared (IR) region. Shifting, quenching, or reshaping of some spectral features can be achieved by chemical functionalization of the molecules, whereas an anisotropic fingerprint due to preferential molecular alignment can be induced via a proper design and/or preparation of the substrate. Recently, we investigated the optical response of thin films of porphycene to acidification. With respect to the well-known and closely related tetraphenyl porphyrin, porphycene has the clear advantage of being optically active in the full visible range, and this makes visible by naked eye the immediate change of the film from brilliant blue-turquoise to green when exposed to HCl vapors. In this work, by exploiting a homemade reflectance anisotropy spectroscopy (RAS) apparatus, we explore possible optical anisotropies in the visible spectral range of porphycene films and relate them to the film morphology analyzed by atomic force microscopy (AFM).

In this paper we focus on the structural, electronic, and magnetic properties of Ni tetra-phenyl-porphyrins (NiTPP) grown on top of Fe(001)–p(1 × 1)O. Ordered thin films of metal TPP molecules are potentially interesting for organic electronic and spintronic applications, especially when they are coupled to a ferromagnetic substrate. Unfortunately, porphyrin layers deposited on top of ferromagnetic substrates do not generally show long-range order. In this work, we provide evidence of an ordered disposition of the organic film above the iron surface and we prove that the thin layer of iron oxide decouples the molecules from the substrate, thus preserving the molecular electronic features, especially the HOMO-LUMO gap, even when just a few organic layers are deposited. The effect of the exposure to molecular oxygen is also investigated and an increased robustness against oxidation with respect to the bare substrate is detected. Finally, we present our results for the magnetic analysis performed by spin resolved spectroscopy, finding a null magnetic coupling between the molecules and the substrate.

Silicate nanoparticles occur in various astrophysical environments where they experience substantial processing due to events such as grain-grain collisions and irradiation. However, the structure and chemical evolution together with the origin of these grains are still poorly understood and intensively debated. For this purpose, we performed liquid-phase nanosecond pulsed laser ablation on olivine single crystals to (i) simulate space weathering in a water environment (e.g., hydrous or volatile-rich bodies) and (ii) study the chemical and structural evolution of both the target surface and the ablated material. In particular, optical spectroscopy analyses have been performed on the ablated material and correlated with high-resolution transmission electron microscopy and diffraction, whereas compositional variations of the ablated target surface were determined by X-ray photoelectron spectroscopy. Our results show that the target material is enriched in Fe and depleted in Mg after the ablation process, with the water environment triggering the oxidation of Fe2+ into Fe3+ in a region confined at the solid-liquid interface and thus promoting the formation of magnetite on the sample surface. On the other hand, in the ablated material we find olivine crystalline fragments with shock features together with Mg-rich crystalline nanoparticles. Notably, no metallic iron nanoparticles have been detected in the ablated material. Our simulation of space weathering in the water environment revealed structural and chemical changes which are expected to give rise to distinctive features in the reflectance spectra when compared to those from airless bodies of the inner solar system.

Carbonate dissolution processes are key in many environmental areas as well as in the industrial sector. In subsurface environments, a detailed knowledge of mineral dissolution/precipitation kinetic rate laws is a critical component in the context of, e.g., aquifer contamination assessment, geologic carbon sequestration, toxic waste disposal, or hydraulic fracturing of hydrocarbon reservoirs. The recent employment of advanced measurement instruments such as Atomic Force Microscopy (AFM) and Vertical Scanning Interferometry (VSI) enables direct observations of the mechanisms occurring on the mineral surface during the reaction, providing evidence that the dissolution process is strongly affected by several sources of variability at the local (i.e., micro-scale) mineral-fluid interface. In this context result, marked spatial heterogeneities in the dissolution rate are documented. Therefore, a change of perspective towards a quantification based on a stochastic approach is of primary importance. We propose to employ geostatistical tools to characterize the spatial heterogeneity of dissolution rate maps obtained from in-situ and real-time AFM imaging. We collect datasets of the surface topography of a millimeter-scale calcite sample subject to dissolution, from which we evaluate reaction rate maps. Our work is aimed at (1) characterizing the statistical behavior of topography and dissolution rate data and their spatial increments; (2) identifying an appropriate interpretive model for such statistics; and (3) evaluating quantitatively, through observed trends of model parameters, the temporal evolution of the spatial heterogeneity of reaction kinetics.

A detailed stratigraphic investigation of the intercalation mechanism when graphite electrodes are immersed inside diluted perchloric (HClO4) and sulfuric (H2SO4) electrolytes is obtained by comparing results when graphite crystals are simply immersed in the same acid solutions. By combining time-of-flight secondary ion mass spectrometry (ToF-SIMS) and in-situ atomic force microscopy (AFM), we provide a picture of the chemical species involved in the intercalation reaction. The depth intensity profile of the ion signals along the electrode crystal clearly shows a more complex mechanism for the intercalation process, where the local morphology of the basal plane plays a crucial role. Solvated anions are mostly located within the first tens of nanometers of graphite, but electrolytes also diffuse inside the buried layers for hundreds of nanometers, the latter process is also aided by the presence of mesoscopic crystal defects. Residual material from the electrolyte solution was found localized in well-defined circular spots, which represent preferential interaction areas. Interestingly, blister-like micro-structures similar to those observed on the highly oriented pyrolytic graphite (HOPG) surface were found in the buried layers, confirming the equivalence of the chemical condition on the graphite surface and in the underneath layers.

Abstract The evolution of the surface topography of a calcite crystal subject to dissolution is documented through in situ real-time imaging obtained via atomic force microscopy (AFM). The dissolution process takes place by exposing the crystal surface to deionized water. AFM data allow detection of nucleation and expansion of mono- and multilayer rhombic etch pits and are employed to estimate the spreading rate of these structures. Spatially heterogeneous distributions of local dissolution rate are evaluated from the difference between topographic measurements taken at prescribed time intervals. We rest on a stochastic framework of analysis viewing the dissolution rate as a generalized sub-Gaussian (GSG) spatially correlated random process. Our analysis yields: (i) a quantitative assessment of the temporal evolution of the statistics of the dissolution rates as well as their spatial increments; (ii) a characterization of the degree of spatial correlation of dissolution rates and of the way this is linked to the various mechanisms involved in the dissolution process and highlighted through the experimental evidences. Our results indicate that the parameters driving the statistics of the GSG distribution and the spreading rate of the multilayer pits display a similar trend in time, thus suggesting that the evolution of these structures imprints the statistical features of local dissolution rates. Article Highlights We investigate dynamics of dissolution patterns on a calcite crystal in contact with deionized water via AFM imaging Temporal behavior of parameters of our statistical model is consistent with surface pattern evolution A nested model for the spatial correlation of rates embeds multiple mechanisms driving dissolution rate.

Silicate nanoparticles, otherwise referred to as very small grains (VSGs) [1], occur in various astrophysical environments. These grains experience substantial processing (e.g., amorphization) during their lifetime in the diffuse interstellar medium due to events such as grain-grain collisions and irradiation [2]. Moreover, several studies have pointed out that the main building blocks of these silicates are O, Si, Fe, Mg, Al and Ca, all elements that are among the principal constituents of the Earth’s surface [3], thus leading to the name “astronomical silicates”. However, the structure and chemical evolution together with the origin of these grains are still poorly understood and intensively debated [4,5]. The aim of this study is the simulation of space weathering processes on olivine single crystals by liquid phase pulsed laser ablation (LP-PLA). The study of the resulting structure of both the target and the ablated material together with their chemical evolution has been carried out by a multiple technique characterization. In particular, spectroscopy and dynamic light scattering measurements, analyses of the electrostatic properties and reactivity to acids and bases on the obtained colloidal solutions of the ablated nanoproducts have been performed and coupled with high-resolution transmission electron microscopy (HR-TEM). Selected olivine target crystals (Fo87) from the São Miguel island (Azores) were analyzed by Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray spectroscopy (EDX). LP-PLA experiments were performed with a Nd:YAG laser focused via a singlet lens onto the surface of the target, which was fixed at the bottom of a polystyrene box filled with 4 ml of deionized water (type 1) to immerge it completely. Laser pulses of 5 ns and 100 mJ simulate the timeframe and energy exchange occurring during grain-grain interstellar collisions [6] and they generate a plasma plume at the crystal/liquid interface. The rapid cooling induced by the confining liquid layer brings about the condensation of the chemical vapor it contains with production of a colloidal solution of nanoparticles. These solutions were analyzed by dynamic light scattering techniques and optical absorption spectroscopy in the range from 200 nm to 1100 nm (6.20 eV - 1.13 eV). Absorption measurements on the colloidal solutions have been compared against reference colloidal solutions dispersed in deionized water (i.e. mesoporous silica [SiO2] nanoparticles, brucite [Mg(OH)2] nanoparticles, aluminum hydroxide [Al(OH)3] nanoparticles, chrysotile [Mg3Si2O5(OH)4] nanotubes, and synthetic forsterite [Mg2SiO4] nanoparticles). Moreover, additional absorption analyses have been carried out as a function of the addition of known aliquots of sulfuric acid and sodium hydroxide solutions. TEM/EDS analyses were then performed on the ablated nanoparticles deposited via electrophoresis on C-coated Cu grids and compositional variations of the ablated target were determined by X-ray photo-emission spectroscopy analyses. The size distribution of LP-PLA synthesized nanoparticles is typically multimodal due to aggregation phenomena. Aggregation is consistent with the measured ζ-potential, which is negative with a relatively low absolute value, within the range 30-50 mV. Nonetheless, a recurrent mode is centered at about 2 nm (hydrodynamic diameter) and it is consistent with the measured size distribution obtained by transmission electron microscopy analysis (average nanoparticles diameter around 3-5 nm). Optical absorption measurements on the ejected material show a main band around 215 nm. This feature is very similar to the “B2 band” reported in several studies on silica glass [7] and ascribed to oxygen vacancies, but its nature is still far to be fully understood. We also found that this feature at 215 nm is very common among both Si and Mg compounds (e.g., Si-oxide, Mg-hydroxide, chrysotile). Moreover, additional absorption bands in the range 240-350nm are observed suggesting the formation of new space weathering products as result of the ablation process. Therefore, these results suggest that substantial chemical processing might be expected during space weathering of “typical” interstellar grains into VSGs. Moreover, coupling these experimental results with remote sensing datasets will provide fundamental information about the origin and evolution of these silicate grains. Acknowledgments: M.M is supported by the SIMP PhD thesis award. References: [1] Witt A. N. (2000) Journal of Geophysical Research: Space Physics, 105(A5), 10299-10302. [2] Carrez P. et al. (2002) Meteoritics & Planetary Science, 37, 1599-1614. [3] Henning T. (2010) Annual Review of Astronomy and Astrophysics, 48, 21-46. [4] Draine B. T. (2003) Annual Review of Astronomy and Astrophysics, 41, 241-289. [5] Escatllar A. M. et al. (2019) ACS Earth and Space Chemistry, 3, 2390-2403. [6] Loeffler M. J. et al. (2016) Meteoritics & Planetary Science, 51, 261-275. [7] Skuja L. N. et al. (1984), Solid State Communications, 50, 1069-1072.

Semiconductors interfaced with heavy elements possessing a strong atomic spin–orbit coupling are important building blocks for the development of new spintronic devices. Here, we present a microscopic and spin-resolved spectroscopic investigation of ultrathin Bi films grown onto a Ge(111) substrate. At monolayer coverage, a Bi wetting layer is formed, characterized by a semiconducting behavior and a ( 3 × 3 ) R 30 ° superstructure. The wetting layer supports the subsequent growth of Bi islands with a pseudo-cubic structure similar to that of Bi(110), showing a well-defined orientation with respect to the substrate high-symmetry directions. We performed photoemission and spin-resolved inverse photoemission experiments at off-normal electron emission and incidence, respectively, along the substrate Γ ¯ K ¯ direction. Inverse photoemission, in particular, highlights the presence of a spin-polarized empty Bi state, not reported so far, due to the strong spin–orbit effects characteristic of the Bi surface and thin layers. Finally, scanning tunneling spectroscopy is employed to link the observed spectroscopic features to either the wetting layer or the Bi islands.

We have recently discussed how organic nanocrystal dissolution appears in different morphologies and the role of the solution pH in the crystal detriment process. We also highlighted the role of the local molecular chemistry in porphyrin nanocrystals having comparable structures: in water‐based acid solutions, protonation of free‐base porphyrin molecules is the driving force for crystal dissolution, whereas metal (ZnII) porphyrin nanocrystals remain unperturbed. However, all porphyrin types, having an electron rich π‐structure, can be electrochemically oxidized. In this scenario, a key question is: does electrochemistry represent a viable strategy to drive the dissolution of both free‐base and metal porphyrin nanocrystals? In this work, by exploiting electrochemical atomic force microscopy (EC‐AFM), we monitor in situ and in real time the dissolution of both free‐base and metal porphyrin nanocrystals, as soon as molecules reach the oxidation potential, showing different regimes according to the applied EC potential., Free‐base porphyrin (P) nanocrystals can be dissolved in acid electrolytes only when the second porphyrin oxidation is reached. Indeed, molecules only show a surface‐pit enhancement after the first oxidation. In addition, metal‐Ps, which are stable when immersed in acids, can be dissolved if their oxidation electrochemical potential is applied. These occurrences prove that molecule oxidation is the driving mechanism of crystal dissolution.

Abstract Surface differential reflectivity (SDR) and reflectance anisotropy spectroscopy (RAS) [sometimes known as reflectance difference spectroscopy] are two well-known optical spectroscopies used in the investigation of surfaces and interfaces. Their adaptability on different experimental conditions (vacuum, controlled atmosphere and liquid environment) allows for the investigation not only of surface states and/or ultra-thin films but also of more complex interfaces. In these circumstances, the analysis of the sample with both techniques is decisive in view of obtaining a correct picture of the sample optical properties. In this work, we show a microelectronic hardware solution useful to control both a SDR and a RAS apparatus. We describe an electronic architecture that can be easily replicated, and we applied it to a representative sample where the interpretation of the optical properties requires an analysis by both SDR and RAS. Graphic abstract

Carbon forms (graphite, pyrolytic graphite, highly oriented pyrolytic graphite (HOPG), glassy carbon, carbon foam, graphene, buckypaper, etc) are a wide class of materials largely used in technology and energy storage. The huge request of carbon compounds with reliable and tunable physical and chemical properties is tackled by contriving new production protocols and/or compound functionalizations. To achieve these goals, new samples must be tested in a trial-and-error strategy with techniques that provide information in terms of both specimen quality and properties. In this work, we prove that electrochemical scanning probe techniques allow testing the performances of carbon compounds when are used as an electrode inside an electrochemical cell. Comparing the results with a reference sample (namely, HOPG) gives an insight on defects in the specimen structure, performances, and possible applications of the new samples. In this study, we concentrate on traditional carbon forms already employed in many fields versus new recently-developed specimens, in view of possible applications to the field of energy storage.

We give evidence of the formation of an ordered array of tetra-phenyl porphyrins (TPP) when these molecules are deposited on top of oxygen-passivated Fe(001), namely the Fe(001)-p(1 × 1)O surface. We also prove that they are magnetically coupled with the substrate. The ordered molecular packing, together with the magnetic coupling, are fundamental conditions for application in organic spintronic devices. The system is studied by means of spin-resolved photoemission spectroscopies and scanning tunneling microscopy.

The intercalation of graphite by electrochemical methods is an efficient strategy to produce massive graphene flakes. In fact, when graphite is biased inside an acidic solution, anions enter inside the stratified structure of the electrode and reduce the layer-to-layer interaction. Consequently, a gentle sonication is sufficient to disperse the graphene flakes inside the electrolyte. In view of an optimisation of the production protocol, a detailed analysis of the intercalation mechanism at the molecular length scale is mandatory. In the last 30 years, electrochemical (EC) scanning probe microscopies (e.g. EC-STM and in situ AFM) have been widely exploited in this research topic. In fact, these techniques have the possibility of combining the EC characterisation (e.g. cyclic-voltammetry, CV) with mechanical characterisation (e.g. adhesion and friction) and topography acquisition with high (molecular) lateral resolution. In this work, we investigate the tribological properties of the basal surface of graphite before and after the anion intercalation. By comparing the results acquired after the extraction of the graphite electrode from the EC cell with those collected inside the EC cell during the CV by an in situ AFM, we show how some features deriving from anisotropic friction can be exploited to unveil the very early stage of graphite exfoliation.

The use of organic molecules in hybrid devices (i.e., heterogeneous junctions) requires a fine tuning of their electronic properties in view of, on the one hand, matching the energy levels of the electrodes and, on the other hand, exploit their potentialities as photosensitive elements.

Ultra-thin organic films must be screened when deposited onto freshly prepared metal surfaces in view of preserving the molecular physical-chemical properties. A current promising strategy prescribes the oxidation of the substrate and, when possible, the creation of a single oxide layer. This strategy was successfully exploited with metal-tetra-phenyl porphyrins (M-TPP) on Fe(0 0 1)-p(1 × 1)O. Here, our study is extended to the oxidized Cu(1 1 0)-(2 × 1)O. Having free coordination sites, the Co-TPP is perturbed when deposited onto the freshly prepared copper surface and the HOMO-LUMO levels quenched, as reported in the literature. Here, we prove that the oxide copper surface reduces the molecule-substrate interaction and photoemission spectroscopy is able to reveal the characteristic electronic features of the molecules.