Charge-Transfer Complexes: Halogen-Doped Anthracene as a Case of Study.

Charge transfer (CT) crystals exhibit unique electronic and magnetic properties with interesting applications. We present a rational and easy guide which allows to foresee the effective charge transfer co-crystal production and that is based on the comparison of the frontier molecular orbital (MO) energies of a donor and acceptor couple. For the sake of comparison, theoretical calculations have been carried out by using the cheap and fast PM6 semiempirical Hamiltonian and pure HF/cc-pVTZ level of the theory. The results are then compared with experimental results obtained both by chemical (bromine and iodine were used as the acceptor) and electrochemical doping (exploiting an original experimental set-up by this laboratory: the electrochemical transistor). Infra-red vibrational experimental results and theoretically calculated spectra are compared to assess both the effective donor-acceptor (D/A) charge-transfer and transport mechanism (giant IRAV polaron signature). XPS spectra have been collected (carbon (1 s) and iodine (3d5/2)) signals, yielding further evidence of the effective formation of the CT anthracene:iodine complex.

Thermally activated delayed fluorescence (TADF) organic molecules for efficient X-ray scintillation and imaging.

X-ray detection, which plays an important role in medical and industrial fields, usually relies on inorganic scintillators to convert X-rays to visible photons; although several high-quantum-yield fluorescent molecules have been tested as scintillators, they are generally less efficient. High-energy radiation can ionize molecules and create secondary electrons and ions. As a result, a high fraction of triplet states is generated, which act as scintillation loss channels. Here we found that X-ray-induced triplet excitons can be exploited for emission through very rapid, thermally activated up-conversion. We report scintillators based on three thermally activated delayed fluorescence molecules with different emission bands, which showed significantly higher efficiency than conventional anthracene-based scintillators. X-ray imaging with 16.6 line pairs mm-1 resolution was also demonstrated. These results highlight the importance of efficient and prompt harvesting of triplet excitons for efficient X-ray scintillation and radiation detection.

Growth Dynamics of Ultrathin Films of Benzo[1,2-b:4,5-b']dithiophene Derivatives on Au(111): A Photoelectron Spectroscopy Investigation.

Ultrathin films of a stereoisomeric mixture of benzo[1,2-b:4,5-b']dithiophene derivatives were grown by thermal evaporation in vacuum on Au(111), and they were studied in situ by photoelectron spectroscopy. X-ray photons from a non-monochromatic Mg Kα conventional X-ray source and UV photons from a He I discharge lamp equipped with a linear polarizer were used. He I photoemission results were compared with density functional theory (DFT) calculations: density of states (DOS) and 3D molecular orbital density distribution. Au 4f, C 1s, O 1s, and S 2p core-level components suggest a surface rearrangement as a function of film nominal thickness, with the variation of the molecular orientation, from flat-laying at the initial deposition to tilted toward the surface normal at coverages exceeding 2 nm. Eventually, the DFT results were exploited in assigning of the valence band experimental structures. Moreover, polarization-dependent photoemission confirmed the tilted arrangement of the molecules, starting at 2 nm. A variation of the work function of 1.4 eV with respect to the clean substrate was measured, together with a valence band offset of 1.3 eV between the organic layer and gold.

Spin-dependent electrochemistry and electrochemical enantioselective recognition with chiral methylated bis(ethylenedithio)-tetrathiafulvalenes.

Enantio-discrimination and spin-dependent electrochemistry (SDE), as a manifestation of the chirality-induced spin selectivity (CISS) effect, are important phenomena that can be probed by "chiral" electrochemistry. Here, we prepared chiralized surfaces of gold and nickel, to serve as working electrodes, through effective chemisorption of enantiopure dimethyl-bis(ethylenedithio)-tetrathiafulvalene (DM-BEDT-TTF) 1, tetramethyl-bis(ethylenedithio)-tetrathiafulvalene (TM-BEDT-TTF) 2, and their capped silver nanoparticle (AgNPs) aggregate by simple incubation of the metallic substrates. The effective chemisorption was checked by means of ultrahigh vacuum x-ray photoelectron spectroscopy (XPS) and by electro-desorption experiments, i.e., cyclic voltammetry (CV) scans showing a first electro-desorption peak at about -1.0 V. The Au|1 and Au|2 chiral electrodes were successfully used in CV experiments exploiting chiral redox probes. Finally, the hybrid interfaces Ni|enantiopure 1 or 2|AgNPs served as working electrodes in SDE experiments. In particular, the hybrid chiral interfaces Ni|(R)-2|AgNPs and Ni|(S)-2|AgNPs exhibited a significant spin-filtering ability, as a manifestation of the CISS effect, with average spin polarization values of 15%.

Structure Model and Toxicity of the Product of Biodissolution of Chrysotile Asbestos in the Lungs.

Asbestos is a commercial term indicating six natural silicates with asbestiform crystal habit. Of these, five are double-chain silicates (amphibole) and one is a layer silicate (serpentine asbestos or chrysotile). Although all species are classified as human carcinogens, their degree of toxicity is still a matter of debate. Amphibole asbestos species are biopersistent in the human lungs and exert their chronic toxic action for decades, whereas chrysotile is not biopersistent and transforms into an amorphous silica structure prone to chemical/physical clearance when exposed to the acidic environment created by the alveolar macrophages. There is evidence in the literature of the toxicity of chrysotile, but its limited biopersistence is thought to explain the difference in toxicity with respect to amphibole asbestos. To date, no comprehensive model describing the toxic action of chrysotile in the lungs is available, as the structure and toxic action of the product formed by the biodissolution of chrysotile are unknown. This work is aimed at fulfilling this gap and explaining the toxic action in terms of structural, chemical, and physical properties. We show that chrysotile's fibrous structure induces cellular damage, mainly through physical interactions. Based on our previous work and novel findings, we propose the following toxicity model: inhaled chrysotile fibers exert their toxicity in the alveolar space by physical and biochemical action. The fibers are soon leached by the intracellular acid environment into a product with residual toxicity, and the dissolution process liberates toxic metals in the intracellular and extracellular environment.

Characterization and assessment of the potential toxicity/pathogenicity of fibrous glaucophane.

In California, the metamorphic blueschist occurrences within the Franciscan Complex are commonly composed of glaucophane, which can be found with a fibrous habit. Fibrous glaucophane's potential toxicity/pathogenicity has never been determined and it has not been considered by the International Agency for Research on Cancer (IARC) as a potential carcinogen to date. Notwithstanding, outcrops hosting fibrous glaucophane are being excavated today in California for building/construction purposes (see for example the Calaveras Dam Replacement Project - CDRP). Dust generated by these excavation activities may expose workforces and the general population to this potential natural hazard. In this work, the potential toxicity/pathogenicity of fibrous glaucophane has been determined using the fibre potential toxicity index (FPTI). This model has been applied to a representative glaucophane-rich sample collected at San Anselmo, Marin County (CA, USA), characterized using a suite of experimental techniques to determine morphometric, crystal-chemical parameters, surface reactivity, biodurability and related parameters. With respect to the asbestos minerals, the FPTI of fibrous glaucophane is remarkably higher than that of chrysotile, and comparable to that of tremolite, thus supporting the application of the precautionary approach when excavating fibrous glaucophane-rich blueschist rocks. Because fibrous glaucophane can be considered a potential health hazard, just like amphibole asbestos, it should be taken into consideration in the standard procedures for the identification and assessment of minerals fibres in soil and air samples.

Electronic structure of CuTPP and CuTPP(F) complexes: a combined experimental and theoretical study II.

The unoccupied electronic structure of thick films of tetraphenylporphyrin and tetrakis(pentafluorophenyl)porphyrin Cu(ii) complexes (hereafter, CuTPP and CuTPP(F)) deposited on Au(111) has been studied by combining the outcomes of near-edge X-ray absorption fine structure (NEXAFS) spectroscopy with those of spin-unrestricted time-dependent density functional (TD-DFT) calculations carried out either within the scalar relativistic zeroth order regular approximation (ZORA) framework (C, N and F K-edges) or by using the Tamm-Dancoff approximation coupled to ZORA and including spin-orbit effects (Cu L2,3-edges). Similarly to the modelling of NEXAFS outcomes pertaining to other Cu(ii) complexes, the agreement between theory and experiment is more than satisfactory, thus confirming the open-shell TD-DFT to be a useful tool to look into NEXAFS results pertinent to Cu(ii) compounds. The combined effect of metalation and phenyl (Ph) fluorine decoration is found to favour an extensive mixing between (Ph)σ* and pristine porphyrin macrocyle (pmc) (pmc)π* virtual levels. The lowest lying excitation in the C and N K-edge spectra of both CuTPP and CuTPP(F) is associated with a ligand-to-metal-charge-transfer transition, unambiguously revealed in the (CuTPP)N K-edge spectral pattern. Moreover, the comparison with literature data pertaining to the modelling of the (Cu(II))L2,3 features in the phthalocyanine-Cu(ii) (CuPc) complex provided further insights into how metal-to-ligand-charge-transfer transitions associated with excitations from 2p(Cu(II)) AOs to low-lying, ligand-based π* MOs may contribute to the Cu(ii) L2,3-edge intensity and thus weaken its believed relationship with the Cu(ii)-ligand symmetry-restricted covalency. Despite the coordinative pocket of CuTPP/CuTPP(F) mirroring CuPc, the ligand-field strength exerted by the phthalocyanine ligand on the Cu(ii) centre is experimentally found and theoretically confirmed to be slightly stronger than that experienced by Cu in CuTPP and CuTPP(F). On the whole, the obtained results complement those published in the near past by the same group on the occupied and empty states of the H2TPP and H2TPP(F) free ligands as well as on the occupied states of both CuTPP and CuTPP(F), thus providing the final piece to get a thorough description of electronic perturbations associated with the metalation and the Ph halogen decoration of H2TPP.

New one-step thiol functionalization procedure for Ni by self-assembled monolayers.

This article reports on a facile and fast strategy for the self-assembled monolayer (SAM) functionalization of nickel surfaces, employing cyclic voltammetry (CV) cycling of a suitable tailored solution containing the species to be adsorbed. Results are presented for ultrathin films formed on Ni by 1-hexadecanethiol (C16), L-cysteine (L-cys), and the poly{methyl (2R)-3-(2,2'-bithiophen-4-ylsulfanyl)-2-[(tert-butoxycarbonyl)amino]propanoate} (PCT-L) thiophene-based chiral polymer. The effective formation of high-quality ultrathin organic films on the nickel was verified both electrochemically and by exploiting typical surface characterization techniques such as contact angle, ellipsometry, atomic force microscopy (AFM), polarization modulation-infrared reflection-absorption spectroscopy (PM-IRRAS), and X-ray photoelectron spectroscopy (XPS).

XAS of tetrakis(phenyl)- and tetrakis(pentafluorophenyl)-porphyrin: an experimental and theoretical study.

The unoccupied electronic structure of tetrakis(phenyl)- and tetrakis(pentafluorophenyl)-porphyrin thick films deposited on SiO2/Si(100) native oxide surfaces has been thoroughly studied by combining the outcomes of near-edge X-ray absorption fine structure spectroscopy at the C, N, and F K-edges with those of scalar relativistic zeroth order regular approximation time-dependent density functional theory calculations carried out on isolated molecules. Both experimental and theoretical results concur to stress the electronic inertness of pristine porphyrin macrocycle based 1s(C)→π* and 1s(N)→π* transitions whose excitation energies are substantially unaffected upon fluorination. The obtained results complement those published by the same group about the occupied states of both molecules, thus providing the missing tile to get a thorough description of the halide decoration effects on the electronic structure of the tetrakis(phenyl)-porphyrin.

On sulfur core level binding energies in thiol self-assembly and alternative adsorption sites: An experimental and theoretical study.

Characteristic core level binding energies (CLBEs) are regularly used to infer the modes of molecular adsorption: orientation, organization, and dissociation processes. Here, we focus on a largely debated situation regarding CLBEs in the case of chalcogen atom bearing molecules. For a thiol, this concerns the case when the CLBE of a thiolate sulfur at an adsorption site can be interpreted alternatively as due to atomic adsorption of a S atom, resulting from dissociation. Results of an investigation of the characteristics of thiol self-assembled monolayers (SAMs) obtained by vacuum evaporative adsorption are presented along with core level binding energy calculations. Thiol ended SAMs of 1,4-benzenedimethanethiol (BDMT) obtained by evaporation on Au display an unconventional CLBE structure at about 161.25 eV, which is close to a known CLBE of a S atom on Au. Adsorption and CLBE calculations for sulfur atoms and BDMT molecules are reported and allow delineating trends as a function of chemisorption on hollow, bridge, and atop sites and including the presence of adatoms. These calculations suggest that the 161.25 eV peak is due to an alternative adsorption site, which could be associated to an atop configuration. Therefore, this may be an alternative interpretation, different from the one involving the adsorption of atomic sulfur resulting from the dissociation process of the S-C bond. Calculated differences in S(2p) CLBEs for free BDMT molecules, SH group sulfur on top of the SAM, and disulfide are also reported to clarify possible errors in assignments.

Electrochemical fabrication of surface chemical gradients in thiol self-assembled monolayers with tailored work-functions.

The studies on surface chemical gradients are constantly gaining interest both for fundamental studies and for technological implications in materials science, nanofluidics, dewetting, and biological systems. Here we report on a new approach that is very simple and very efficient, to fabricate surface chemical gradients of alkanethiols, which combines electrochemical desorption/partial readsorption, with the withdrawal of the surface from the solution. The gradient is then stabilized by adding a complementary thiol terminated with a hydroxyl group with a chain length comparable to desorbed thiols. This procedure allows us to fabricate a chemical gradient of the wetting properties and the substrate work-function along a few centimeters with a gradient slope higher than 5°/cm. Samples were characterized by cyclic voltammetry during desorption, static contact angle, XPS analysis, and Kelvin probe. Computer simulations based on the Dissipative Particle Dynamics methods were carried out considering a water droplet on a mixed SAM surface. The results help to rationalize the composition of the chemical gradient at different position on the Au surface.

Studies of the interface of conducting polymers with inorganic surfaces.

Many of the properties of multi-material systems and relevant devices depend on the interfaces between the different components. This review focuses on characterization of the interfaces between intrinsically conducting polymers and inorganic materials consisting of metals and metal oxides. These materials are chosen because of their importance in several analytical applications. Although use of conducting polymers and metals or metal oxides in analytical systems, specifically in sensing, is well established, the number of novel materials used for analytical purposes is continuously increasing. This further increases the possible number of effective combinations of different materials within multicomponent systems. As a consequence, innovative characterization techniques have become as important as more conventional techniques. On the other hand, sophisticated characterisation techniques are increasingly widespread and, consequently, also readily accessible. This critical review is not an exhaustive discussion of all possible analytical techniques suitable for characterization of interfaces. It is, instead, limited to an overview of the most effective, relatively widespread techniques, emphasising their most significant recent advances. Critical analysis of the individual techniques is complemented by a few selected examples.

Comparative study of in-vitro autofluorescence of normal versus non-melanoma-skin-cancer cells at different excitation wavelengths.

In this experimental study the autofluorescence of squamous carcinoma cells, stimulated by 6 different excitation wavelengths in the range 280-533 nm, has been compared with the autofluorescence of normal control keratinocytes. Skin cells were cultivated in vitro, to isolate their characteristic autofluorescence form the more complex one that would be originated by the complete skin tissue. Autofluorescence spectra in the visible range were complemented by absorption measurements. It was observed that the control cells showed characteristic emission (and absorption) structures due to typical endogenous chromophores [FAD and NAD(P)H, lipo-pigments, porphyrins], that were severely dumped in pathological cells. The autofluorescence spectra were then elaborated by multivariate analysis: after a first exploratory data analysis by means of Principal Component Analysis, the whole dataset was used to develop classification models using partial least squares-discriminant analysis, to differentiate between normal and pathological cells. This permitted us to identify the most suitable fluorescence spectral interval, in the 550-670 nm range, to discriminate between normal and pathological behavior, independently on the excitation wavelength.

First-Principles Estimation of Core Level Shifts for Hf, Ta, W, and Re.

A simple first-principles approach is used to estimate the core level shifts observed in X-ray photoelectron spectroscopy for the 4f electrons of Hf, Ta, W, and Re; these elements were selected because their 4f levels are relatively close to the Fermi energy. The approach is first tested by modeling the surface core level shifts of low-index surfaces of the four elemental metals, followed by its application to the well-studied material TaSe2 in the commensurate charge density wave (CDW) phase, where agreement with experimental data is found to be good, showing that this approach can yield insights into modifications of the CDW. Finally, unterminated surface core level shifts in the hypothetical MXene Ta3C2 are modeled, and the potential of XPS for the investigation of the surface termination of MXenes is demonstrated.

Surface Optimization of Commercial Porous Ti Substrates by EPD of Titanium Nitride.

In this work, the infiltration of TiN powders by electrophoretic deposition (EPD) in aqueous media was considered as alternative method to reduce the size craters and the roughness of commercial porous Ti substrates. Ti substrates can be used as suitable supports for the deposition of dense hydrogen separation TiNx-based membranes by physical vapor deposition (PVD) techniques. The influence of various EPD deposition parameters on surface morphology and roughness of TiN-infiltrated substrates were investigated in order to optimize their surface properties. The results suggest that a multi-step EPD procedure is an effective technique for reducing substrate surface defects of commercial porous Ti substrates which could then be successfully used as proper supports for the deposition of dense and defect-free TiNx layers, also aligning the thermal mismatch between the active layer and the porous substrate.

UPS, XPS, and NEXAFS study of self-assembly of standing 1,4-benzenedimethanethiol SAMs on gold.

We report a study of the self-assembly of 1,4-benzenedimethanethiol monolayers on gold formed in n-hexane solution held at 60 °C for 30 min and in dark conditions. The valence band characteristics, the thickness of the layer, and the orientation of the molecules were analyzed at a synchrotron using high resolution photoelectron spectroscopy and near edge X-ray adsorption spectroscopy. These measurements unambiguously attest the formation of a single layer with molecules arranged in the upright position and presenting a free -SH group at the outer interface. Near edge X-ray absorption fine structure (NEXAFS) measurements suggest that the molecular axis is oriented at 24° with respect to the surface normal. In addition, valence band features could be successfully associated to specific molecular orbital contributions thanks to the comparison with theoretically calculated density of states projected on the different molecular units.

Production Strategies of TiNx Coatings via Reactive High Power Impulse Magnetron Sputtering for Selective H2 Separation.

This scientific work aims to optimize the preparation of titanium nitride coatings for selective H2 separation using the Reactive High Power Impulse Magnetron Sputtering technology (RHiPIMS). Currently, nitride-based thin films are considered promising membranes for hydrogen. The first series of TiNx/Si test samples were developed while changing the reactive gas percentage (N2%) during the process. Obtained coatings were extensively characterized in terms of morphology, composition, and microstructure. A 500 nm thick, dense TiNx coating was then deposited on a porous alumina substrate and widely investigated. Moreover, the as-prepared TiNx films were heat-treated in an atmosphere containing hydrogen in order to prove their chemical and structural stability; which revealed to be promising. This study highlighted how the RHiPIMS method permits fine control of the grown layer's stoichiometry and microstructure. Moreover, it pointed out the need for a protective layer to prevent surface oxidation of the nitride membrane by air and the necessity to deepen the study of TiNx/alumina interface in order to improve film/substrate adhesion.

Ag/MgO Nanoparticles via Gas Aggregation Nanocluster Source for Perovskite Solar Cell Engineering.

Nanocluster aggregation sources based on magnetron-sputtering represent precise and versatile means to deposit a controlled quantity of metal nanoparticles at selected interfaces. In this work, we exploit this methodology to produce Ag/MgO nanoparticles (NPs) and deposit them on a glass/FTO/TiO2 substrate, which constitutes the mesoscopic front electrode of a monolithic perovskite-based solar cell (PSC). Herein, the Ag NP growth through magnetron sputtering and gas aggregation, subsequently covered with MgO ultrathin layers, is fully characterized in terms of structural and morphological properties while thermal stability and endurance against air-induced oxidation are demonstrated in accordance with PSC manufacturing processes. Finally, once the NP coverage is optimized, the Ag/MgO engineered PSCs demonstrate an overall increase of 5% in terms of device power conversion efficiencies (up to 17.8%).

Wavy graphene sheets from electrochemical sewing of corannulene.

The presence of non-hexagonal rings in the honeycomb carbon arrangement of graphene produces rippled graphene layers with valuable chemical and physical properties. In principle, a bottom-up approach to introducing distortion from planarity of a graphene sheet can be achieved by careful insertion of curved polyaromatic hydrocarbons during the growth of the lattice. Corannulene, the archetype of such non-planar polyaromatic hydrocarbons, can act as an ideal wrinkling motif in 2D carbon nanostructures. Herein we report an electrochemical bottom-up method to obtain egg-box shaped nanographene structures through a polycondensation of corannulene that produces a new conducting layered material. Characterization of this new polymeric material by electrochemistry, spectroscopy, electron microscopy (SEM and TEM), scanning probe microscopy, and laser desorption-ionization time of flight mass spectrometry provides strong evidence that the anodic polymerization of corannulene, combined with electrochemically induced oxidative cyclodehydrogenations (Scholl reactions), leads to polycorannulene with a wavy graphene-like structure.