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The occurrence of oxygen-driven metal-insulator-transition (MIT) in SrNbO3 (SNO) thin films epitaxially grown on (110)-oriented DyScO3 has been reported. SNO films are fabricated by the pulsed laser deposition technique at different partial O-2 pressure to vary the oxygen content and their structural, optical, and transport properties are probed. SNO unit cell has been found to shrink vertically as the oxygen content increases but keeping the epitaxial matching with the substrate. The results of Fourier-transform infra-red spectroscopy show that highly oxygenated SNO samples (i.e., grown at high oxygen pressure) show distinct optical conductivity behavior with respect to oxygen deficient films, hence demonstrating the insulating character of the formers with respect to those fabricated with lower pressure conditions. Tailoring the optical absorption and conductivity of strontium niobate epitaxial films across the MIT will favor novel applications of this material.

Hybridization of electronic states and orbital symmetry in transition metal oxides are generally considered key ingredients in the description of both their electronic and magnetic properties. In the prototypical case of ${\mathrm{La}}_{0.65}{\mathrm{Sr}}_{0.35}{\mathrm{MnO}}_{3}$ (LSMO), a landmark system for spintronics applications, a description based solely on Mn $3d$ and O $2p$ electronic states is reductive. We thus analyzed elemental and orbital distributions in the LSMO valence band through a comparison between density functional theory calculations and experimental photoelectron spectra in a photon energy range from soft to hard x rays. We reveal a number of hidden contributions, arising specifically from La $5p$, Mn $4s$, and O $2s$ orbitals, considered negligible in previous analyses; our results demonstrate that all these contributions are significant for a correct description of the valence band of LSMO and of transition metal oxides in general.

Methylammonium lead tribromide (MAPbBr3) perovskite single crystals demonstrate to be excellent direct X-ray and gamma-ray detectors with outstanding sensitivity and low limit of detection. Despite this, thorough studies on the photophysical effects of exposure to high doses of ionizing radiation on this material are still lacking. In this work, we present our findings regarding the effects of controlled X-ray irradiation on the optoelectronic properties of MAPbBr3 single crystals. Irradiation is carried out in air with an imaging X-ray tube, simulating real-life application in a medical facility. By means of surface photovoltage spectroscopy, we find that X-ray exposure quenches free excitons in the material and introduces new bound excitonic species. Despite this drastic effect, the crystals recover after 1 week of storage in dark and low humidity conditions. By means of X-ray photoelectron spectroscopy, we find that the origin of the new bound excitonic species is the formation of bromine vacancies, leading to local changes in the dielectric response of the material. The recovery effect is attributed to vacancy filling by atmospheric oxygen and water.

In situ atomic force microscopy (AFM) allowed us to investigate the evolution at the early stages of the growth of organic thin films. An ultrahigh-vacuum atomic force microscope, integrated with a Knudsen effusion cell for the sublimation of ?-sexithiophene (6T), continuously scans the same region during the deposition of sublimed molecules on native silicon oxide as a function of the substrate temperature. Noncontact AFM images acquired sequentially provide snapshots of the time evolution of the film morphology that is monitored up to the deposition of five monolayers. At all substrate temperatures, a Stranski-Krastanov growth mode of organic films is observed: the first two monolayers grow layer-by-layer (two-dimensional?2D), then films evolve into islands (three-dimensional?3D). Despite the apparent similarity, we find an anomalous dynamic scaling characterized by the abrupt change of the growth exponent ? vs substrate temperature. This novel transition, induced by the substrate temperature, is ascribed to the morphological transition from ziggurat islands to large terraces. The analysis of the evolution of the root-mean-square (RMS) roughness based on the distributed growth model underlines the role of down-hill mass transport for the growth of the first two monolayers, transport that is progressively hindered for the next monolayers.

We have probed the structural and magnetic properties of a ferromagnetic/organic interface constituted by a polycrystalline Co layer deposited on a fullerene thin film through resonant soft X-ray reflectivity measurements. The fitting analysis of the reflectivity indicates the formation of a sharp interface with limited intermixing and a null remanent magnetization in a & x007E;1 nm thick region of the Co film at the interface with C60. This information contributes to elucidate the role of organic & x2013;inorganic interfaces in the charge and spin transport inside organic spintronic devices.

We report the study of anatase TiO2(001)-oriented thin films grown by pulsed laser deposition on LaAlO3(001). A combination of in situ and ex situ methods has been used to address both the origin of the Ti(3+)-localized states and their relationship with the structural and electronic properties on the surface and the subsurface. Localized in-gap states are analyzed using resonant X-ray photoelectron spectroscopy and are related to the Ti(3+) electronic configuration, homogeneously distributed over the entire film thickness. We find that an increase in the oxygen pressure corresponds to an increase in Ti(3+) only in a well-defined range of deposition pressure; outside this range, Ti(3+) and the strength of the in-gap states are reduced.

Cobalt ferrite nanoparticles have been attracting considerable interest in the recent years because of the large number of potential applications, including magnetic storage, magnetic fluid hyperthermia and as contrast agents for magnetic resonance imaging. Physical properties of this class of materials depend critically on a number of parameters, including crystallinity, stoichiometry and cation distribution. In this work we have performed a Resonant Inelastic soft X-ray Scattering (RIXS) study on a series of 5 nm cobalt-doped maghemite nanoparticles to obtain direct quantitative information on cation distribution as a function of cobalt doping. We found that the distribution of divalent cobalt is stable in the investigated doping range and slightly different from that of bulk, stoichiometric cobalt ferrite. These results confirm that cobalt doping can be used to finely tune the magnetic properties of nanostructured ferrites without modifying their structural integrity.

The longstanding problem of interpretation of satellite structures in core-level photoemission spectra of metallic systems with a low density of conduction electrons is addressed using the specific example of Sb-doped SnO2. Comparison of ab initio many-body calculations with experimental hard x-ray photoemission spectra of the Sn 4d states shows that strong satellites are produced by coupling of the Sn core hole to the plasma oscillations of the free electrons introduced by doping. Within the same theoretical framework, spectral changes of the valence band spectra are also related to dynamical screening effects. These results demonstrate that, for the interpretation of electron correlation features in the core-level photoelectron spectra of such narrow-band materials, going beyond the homogeneous electron gas electron-plasmon coupling model is essential.

Vertical cross-bar devices based on manganite and cobalt injecting electrodes and metal-quinoline molecular transport layer are known to manifest both magnetoresistance and electrical bistability. The two effects are strongly interwoven, inspiring new device applications such as electrical control of the magnetoresistance and magnetic modulation of bistability. To investigate the full device functionality, we first identify the mechanism responsible for electrical switching by associating the electrical conductivity and the impedance behavior with chemical states of buried layers obtained by in operando photoelectron spectroscopy. These measurements revealed that a significant fraction of oxygen ions migrates under voltage polarity, resulting in a modification of the electronic properties of the organic material and of the oxidation of interfacial layer with ferromagnetic contacts. Variable oxygen doping of the organic molecule represents the key element for correlating bistability and magnetoresistance and our measurements provide the first experimental evidence in favor of the impurity band model describing the spin transport in organic semiconductors in similar devices.

The understanding of spin injection and transport in organic spintronic devices is still incomplete, with some experiments showing magnetoresistance and others not detecting it. We have investigated the transport properties of a large number of tris-(8-hydroxyquinoline)aluminum-based organic spintronic devices with an electrical resistance greater than 5 MΩ that did not show magnetoresistance. Their transport properties could be described satisfactorily by known models for organic semiconductors. At high voltages (>2 V), the results followed the model of space charge limited current with a Poole-Frenkel mobility. At low voltages (∼0.1 V), that are those at which the spin valve behavior is usually observed, the charge transport was modelled by nearest neighbor hopping in intra-gap impurity levels, with a charge carrier density ofn0 = (1.44 ± 0.21) × 1015 cm−3at room temperature. Such a low carrier density can explain why no magnetoresistance was observed.

We report the study of anatase TiO

In multiphase/multilayer solid electrolytes, the composition, reactivity, and structure of interfaces between materials and phases play a fundamental role for fast ion-conduction. Here, the properties of buried interfaces in prototypical fast ion-conducting LaF3/SrF2 epitaxial multilayers are investigated. Photoelectron spectroscopy--both with soft-X and high-energy photons--is applied to separate composition and reactivity of buried interfaces with respect to the outermost surface. X-ray reflectivity, high-energy electron diffraction, X-ray diffraction, atomic force and transmission electron microscopies are used to study morphology, layer crystallinity, epitaxy relations, and buried interface structure. It is found that while the alternated layers present good crystallinity and high lattice matching, with formation of almost ideal sharp interfaces, buried interfaces show a sizeable reduction of the energy barrier for F vacancy formation with respect to bare materials. A density higher by a factor of six of fluorine vacancies is observed at buried interfaces in multilayers with respect to the bare materials. This is correlated to the formation of space charge regions, favoring ion conduction. The formation of F depleted La fluoride regions at interfaces is also promoted by annealing. This is associated to the increase of ion conductivity in annealed heterostructures reported in literature.

Journal of electron spectroscopy and related phenomena 190(Part B), 228 - 234 (2013). doi:10.1016/j.elspec.2013.01.002, Designing, understanding and controlling the properties of engineered and functional materials, based on oxides and buried interfaces, is one of the most flourishing research fields and one of the major challenges faced by contemporary solid state science and technology. Often, a reliable spectroscopic analysis of such systems is hindered by surface effects, as structural distortion, stoichiometry changes, strong reactivity to external agent and major atomic and/or electronic reconstruction to name but a few. Hard X-Ray PhotoEmission Spectroscopy (HAXPES) is a powerful technique to overcome such limitations, allowing to monitor truly bulk sensitive properties. We report selected HAXPES results for manganese-based oxides, both in films and crystal forms, and for buried metal–organic interfaces, with the aim of highlighting some of the important features such technique brings in the analysis of electronic properties of the solids., Published by Elsevier, New York, NY [u.a.]

TiO2 is commonly used as the active switching layer in resistive random access memory. The electrical characteristics of these devices are directly related to the fundamental conditions inside the TiO2 layer and at the interfaces between it and the surrounding electrodes. However, it is complex to disentangle the effects of film “bulk” properties and interface phenomena. The present work uses hard X-ray photoemission spectroscopy (HAXPES) at different excitation energies to distinguish between these regimes. Changes are found to affect the entire thin film, but the most dramatic effects are confined to an interface. These changes are connected to oxygen ions moving and redistributing within the film. Based on the HAXPES results, post-deposition annealing of the TiO2 thin film was investigated as an optimisation pathway in order to reach an ideal compromise between device resistivity and lifetime. The structural and chemical changes upon annealing are investigated using X-ray absorption spectroscopy and are further supported by a range of bulk and surface sensitive characterisation methods. In summary, it is shown that the management of oxygen content and interface quality is intrinsically important to device behavior and that careful annealing procedures are a powerful device optimisation technique.

Photoelectron spectroscopy is one of the most powerful tool to unravel the electronic structure of strongly correlated materials also thanks to the extremely large dynamic range in energy, coupled to high energy resolution that this form of spectroscopy covers. The kinetic energy range typically used for photoelectron experiments corresponds often to a strong surface sensitivity, and this turns out to be a disadvantage for the study of transition metal oxides, systems where structural and electronic reconstruction, different oxidation state, and electronic correlation may significantly vary at the surface. We report here selected Hard X-ray PhotoElectron Spectroscopy (HAXPES) results from transition metal oxides, and from buried interfaces, where we highlight some of the important features that such bulk sensitive technique brings in the analysis of electronic properties of the solids.

The influence of the transition metals on the molecular orientation and molecule-substrate interaction has been investigated by angular dependent NEXAFS spectroscopy for the recently synthesised dialkynyl bridged complexes M-2-DEBP (Cl(PBu3)(2)M-C equivalent to C-C6H4[4 C6H4-C equivalent to CM(PBu3)(2)Cl, M = Pt, Pd; DEBP = diethynyl-biphenyl, i.e. C equivalent to C-C6H4-C6H4-C equivalent to C-). Thin films of both samples have been deposited on Au/Si(111), and the angular dependent analysis of the main pi* feature deriving by the superimposition of the resonances due to benzene and acetylene carbon orbitals showed a polarisation effect for Pd-2-DEBP only. A tendency to a preferential molecular orientation at nearly 50 degrees to the surface was calculated. Furthermore, for Pd2-DEBP, the two pi* resonances already assigned to benzene and acetylene carbon atoms showed different angular effects; a likely explanation for this behaviour bear in mind the interaction between sp and sp 2 carbons of the organic DEBP moieties with Pd centres of neighbouring macromolecules, giving rise to interchain interactions then leading to an enhancement of the already assessed self-assembling properties.

We present a spectroscopic study of the structure of two peptides deposited on Au and TiO2: – PeptA, (EAK16-RGD) bringing the adhesive RGD sequence linked to EAK16; – PeptB, having RGD linked to a “scrambled” sequence of the EAK16 peptide. Previously reported NEXAFS investigations on thin films of the self-assembling peptide EAK16 deposited on Au and TiO2, revealed molecular order and orientation for both substrates. IR spectra show a β-sheet conformation for PeptA and a random structure for PeptB. Angular-dependent NEXAFS measurements reveal an ordered structure with preferential molecular orientation only for PeptA. XPS analysis indicates that PeptA is adsorbed on TiO2 in a larger amount than PeptB.

Magnetic properties of epitaxial Fe films on MnPt/Fe(1 0 0) were measured using X-ray magnetic circular dichroism (XMCD) and Mott electron spin polarimetry (SP). Surface sensitive secondary electron spin polarization images revealed the magnetization orientation of the Fe overlayers with respect to that of the substrate Fe crystal that was measured with bulk-sensitive XMCD. The magnetic domains of the Fe overlayer are influenced by the substrate magnetic domain structure, giving a clear evidence of the magnetic interaction between the Fe overlayer and the substrate Fe through the antiferromagnetic MnPt film. (C) 2007 Elsevier B.V. All rights reserved.

Epitaxial cobalt films on CaF2(110) buffer layers on Si(001) were grown by molecular beam epitaxy. It is found that Co grows in a face-centered cubic lattice forming nanodimensional islands. The islands tend to align along the parallel grooves which characterize the self-patterned CaF2(110) surface grown on Si(001). Photoemission was used to probe the uniformity of the film and the occurrence of chemical reactions with the substrate. X-ray magnetic circular dichroism at the Co L-2.3 edges was used to access the magnetic properties of the films. The thick Co film presents an in-plane easy magnetization axis along the directions of the grooves of the CaF2(110) surface. (c) 2006 Elsevier B.V. All rights reserved.

We studied the adsorption and oxidation of NO adlayers on Pt(1 1 1) prepared from different NO precursors in an electrochemical cell in situ by surface X-ray diffraction and ex situ by X-ray photoemission spectroscopy. We found that NO adsorbs molecularly, independent of the preparation method. There is no relaxation of the outermost Pt atomic layer induced by the presence of adsorbed NO. We observe a surface structure of the Pt(1 1 1) very similar to the clean surface prepared under ultra-high vacuum conditions. A surface mediated oxidation process of the NO towards NO 2 is initiated at a potential of around 0.95 V vs. normal hydrogen electrode. The in situ measurements of crystal truncation rods show that this process is accompanied by a significant roughening of the surface.

Advanced functional materials 27(45), 1702282 (2017). doi:10.1002/adfm.201702282, Published by Wiley-VCH, Weinheim

The electronic structure of IrO2 has been investigated using hard x-ray photoelectron spectroscopy and density-functional theory. Excellent agreement is observed between theory and experiment. We show that the electronic structure of IrO2 involves crystal field splitting of the iridium 5d orbitals in a distorted octahedral field. The behavior of IrO2 closely follows the theoretical predictions of Goodenough for conductive rutile-structured oxides [J. B. Goodenough, J. Solid State Chem. 3, 490 (1971)]. Strong satellites associated with the core lines are ascribed to final state screening effects. A simple plasmon model for the satellites applicable to many other metallic oxides appears to be not valid for IrO2.

We discuss the application of resonant inelastic X-ray scattering to the study of magnetic systems in the soft X-ray range. To this end we distinguish two broad areas. In the first the layout of the experiment is such that the absorption magnetic circular dichroism (MCD) is not zero. In the second the magnetisation is perpendicular to the incident helical beam so that the absorption MCD is zero. In the first area we summarise published results on Fe-Co alloys and we present new data on Mn impurities in Ni together with calculations. In the second area we summarise published results on Ni in Ni-ferrite with final 3s shell excitation and we present new results on Co-metal and Co in Co-ferrite measured with a new approach. This is based on the incident energy dependence of the integral of the Raman spectrum in inner shell excitation (integrated resonant Raman scattering). The potentialities and the limitations of the above methods are critically presented.

The crystallization of two organic molecules, tetrahexil-sexithiophene (H4T6) and dibenzotetrathiafulvalene (DBTTF), into nano-sized cavities has been investigated by means of in situ grazing incidence X-ray diffraction measurements, during the solvent evaporation. Thanks to these real time experiments, the phase content has been determined from the onset of the first crystalline molecular assembly to the stable system. The correlation between the size of the nano-cavities and crystallization mechanism, in the complex systems Proposed, has been established. The obtained results shows that the nano-confinement can induce organic molecules, for which polymorphs coexistence is otherwise difficult to avoid, to selectively crystallize in a single phase. The proposed system can be applied to a wide range of organic molecules and can be advantageously exploited in different application fields including organic semiconductor devices.

We present experimental results on resonant Raman scattering in Te, La, and Gd with ${M}_{5}$ and ${M}_{4}$ excitation. The spectra show clearly the importance of the final-state interaction between the configuration having one $4p$ hole and that having two $4d$ holes. The weight of the spectral region at higher transferred energies is very much dependent on Z and it is higher at low Z. Moreover, the sensitivity to the change of the excitation energy is quite different in the three cases, while the energy extension of the spectra is not very different in the three cases (typically 50\char21{}55 eV with ${M}_{5}$ excitation). We show how these findings can be rationalized in a simple and expressive way by considering the interplay between all energy scales characteristic of the process. These are the multiplet splitting, the spin orbit, the strength of the configuration interaction, and the energy separation between the two configurations.

We present results on inelastic photon scattering in NiO and CoO in the L 3 threshold region ending with a final 3s hole i.e. 2p 6 3d n →2p 5 3d n +1 →2p 6 3d n +1 3s 1 . The spectra show the presence of Raman features dispersing with the incident photon energy and of a strong feature at constant outgoing photon energy. In CoO the results show that this constant energy feature is present only when the core excitation is 2–3 eV above the core absorption thresholds. This supports a simple model based on the energy loss due to the creation of electron hole pairs across the gap. This mechanism can convert the intermediate excited state into a state of lower energy decaying with the emission at constant photon energy. The implications of these results are briefly discussed.

We studied the Co/Fe bi- and multilayer growth on Fe single crystal using the primary-beam diffraction modulated electron emission (PDMEE) technique. This approach enables a chemical selected structural characterization of both surface and buried layers and interfaces to be performed. Co growth on the Fe(001) surface was studied in the 3–70 ML coverage range. The transition from the initial epitaxial bcc phase of the Co film to the stable hcp phase was found to occur rather abruptly at 25–30 ML coverage, a value larger than previously reported in the literature. Subsequent Fe deposition on the Co hcp film recovers the bcc structure in the sandwiched Co layer. However, removal of the Fe epilayer by mild sputtering results again in an hcp Co film.

Memristors are one of the most promising candidates for future information and communications technology (ICT) architectures. Two experimental proofs of concept are presented based on the intermixing of spintronic and memristive effects into a single device, a magnetically enhanced memristor (MEM). By exploiting the interaction between the memristance and the giant magnetoresistance (GMR), a universal implication (IMP) logic gate based on a single MEM device is realized.

We have investigated the role of the electroforming process in the establishment of resistive switching behaviour for Pt/Ti/Pr0.5Ca0.5MnO3/SrRuO3 layered heterostructures (Pt/Ti/PCMO/SRO) acting as non-volatile Resistance Random Access Memories (RRAMs). Electron spectroscopy measurements demonstrate that the higher resistance state resulting from electroforming of as-prepared devices is strictly correlated with the oxidation of the top electrode Ti layer through field-induced electromigration of oxygen ions. Conversely, PCMO exhibits oxygen depletion and downward change of the chemical potential for both resistive states. Impedance spectroscopy analysis, supported by the detailed knowledge of these effects, provides an accurate model description of the device resistive behaviour. The main contributions to the change of resistance from the as-prepared (low resistance) to the electroformed (high resistance) states are respectively due to reduced PCMO at the boundary with the Ti electrode and to the formation of an anisotropic np junction between the Ti and the PCMO layers.

We investigated the effects of scattering-interference of primary electrons on the secondary electron emission intensity fron ordered surfaces and interfaces. Because of the focusing-defocusing of the primary wave along atomic chains, maxima in the electron yield occur when the exciting beam is aligned with low index axes. Therefore the electron intensity distributions as a function of the angle of incidence of the primary beam can be interpreted as projected images of real space, local atomic arrangement. The process can be modelled in a single scattering cluster (SSC) approximation. Potential of primary-beam diffraction modulated electron emission (PDMEE) technique for surface and subsurface structural characterization is shown, for Co epitaxy on Fe(001).

Self-Assembly Monolayers (SAMs) are considered a promising route for solving technolog-ical hindrances (such as bias-stress, contact resistance, charge trapping) affecting the elec-trical performances of the Organic Field-Effect Transistors (OFETs). Here we use an OFETbased on pentacene thin film to investigate the charge transport across conjugated SAMsat the Au/pentacene interface. We synthesized a homolog series of p -conjugated mole-cules, termed Tn-C8-SH, consisting of a n-unit oligothienyl Tn (n =1...4) bound to anoctane-1-thiol (C8-SH) chain that self-assembles on the Au electrodes. The multi-paramet-ric response of such devices yields an exponential behavior of the field-effect mobility ( l ),current density (J), and total resistivity (R), due to the SAM at the charge injection interface(i.e. Au-SAM-pentacene). The surface treatment of the OFETs induces a clear stabilization ofdifferent parameters, like sub-threshold slope and threshold voltage, thanks to standard-ized steps in the fabrication process. 2012 Elsevier B.V. All rights reserved.

International audience; We investigated the electronic properties of MnAs nano-clusters embedded in GaAs by bulk sensitive photoemission spectroscopy and cross-sectional scanning tunneling microscopy/spectroscopy. We report experimental evidences that the clusters are metallic MnAs, in close resemblance to MnAs thin films, and display a sharp interface with the surrounding GaAs. These results are supported by the comparison with GaMnAs and MnAs film in the same experimental condition. Furthermore, we observe a clear Coulomb blockade effect, as due to confinement and their nanometric size. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4704778]

Spin-based electronics in topological insulators (TIs) is favored by the long spin coherence1,2 and consequently fault-tolerant information storage. Magnetically doped TIs are ferromagnetic up to 13 K,3 well below any practical operating condition. Here we demonstrate that the long range ferromagnetism at ambient temperature can be induced in Bi2-xMnxTe3 by the magnetic proximity effect through deposited Fe overlayer. This result opens a new path to interface-controlled ferromagnetism in TI-based spintronic devices., Comment: accepted in Nano Letters

We report x-ray photoemission spectroscopy results on (Ga,Mn)As films as a function of both temperature and Mn doping. Analysis of Mn 2p core level spectra reveals the presence of a distinct electronic screening channel in the bulk, hitherto undetected in more surface sensitive analysis. Comparison with model calculations identifies the character of the Mn 3d electronic states and clarifies the role, and the difference between surface and bulk, of hybridization in mediating the ferromagnetic coupling in (Ga,Mn)As.

We present a home-built high-vacuum system for performing organic semiconductor thin-film growth and its electrical characterization during deposition (real-time) or after deposition (in situ). Since the environment conditions remain unchanged during the deposition and electrical characterization process, a direct correlation between growth mode and electrical properties of thin film can be obtained. Deposition rate and substrate temperature can be systematically set in the range 0.1-10 ML/min and RT-150 degrees C, respectively. The sample-holder configuration allows the simultaneous electrical monitoring of up to five organic thin-film transistors (OTFTs). The OTFTs parameters such as charge carrier mobility mu, threshold voltage V(TH), and the on-off ratio I(on)/I(off) are studied as a function of the semiconductor thickness, with a submonolayer accuracy. Design, operation, and performance of the setup are detailed. As an example, the in situ and real-time electrical characterization of pentacene TFTs is reported. (C) 2011 American Institute of Physics. [doi:10.1063/1.3534007]

We investigate how multiscale morphology of functional thin films affects the in vitro behavior of human neural astrocytoma 1321N1 cells. Pentacene thin film morphology is precisely controlled by means of the film thickness, Theta (here expressed in monolayers (ML)). Fluorescence and atomic force microscopy allow us to correlate the shape, adhesion, and proliferation of cells to the morphological properties of pentacene films controlled by saturated roughness, sigma, correlation length, xi, and fractal dimension, d(f). At early incubation times, cell adhesion exhibits a transition from higher to lower values at Theta approximately 10 ML. This is explained using a model of conformal adhesion of the cell membrane onto the growing pentacene islands. From the model fitting of the data, we show that the cell explores the surface with a deformation of the membrane whose minimum curvature radius is 90 (+/- 45) nm. The transition in the adhesion at approximately 10 ML arises from the saturation of xi accompanied by the monotonic increase of sigma, which leads to a progressive decrease of the pentacene local radius of curvature and hence to the surface area accessible to the cell. Cell proliferation is also enhanced for Theta10 ML, and the optimum morphology parameter ranges for cell deployment and growth are sigmaor= 6 nm, xi500 nm, and d(f)2.45. The characteristic time of cell proliferation is tau approximately 10 +/- 2 h.

We present an ex situ, nondestructive chemical characterization of deeply buried organic-inorganic interfaces using hard x-ray photoelectron spectroscopy. Co/Alq3 and Co/AlOx/Alq3 interfaces were studied in order to determine the role of a thin (1-2 nm) AlOx interdiffusion barrier in organic spin valves. Interfacial Alq3, 15 nm below the surface, exhibits strong sensitivity to the electronic structure of the interfacial region and to the presence of the AlOx. In addition to reducing Co-Alq3 interdiffusion, we find that the barrier prevents charge donation from the Co to the interfacial Alq3, thus preventing the formation of Alq3 anions within the interface region.

We report on efficient spin polarized injection and transport in long (102 nm) channels of Alq(3) organic semiconductor. We employ vertical spin valve devices with a direct interface between the bottom manganite electrode and Alq3, while the top-electrode geometry consists of an insulating tunnel barrier placed between the "soft" organic semiconductor and the top Co electrode. This solution reduces the ubiquitous problem of the so-called ill-defined layer caused by metal penetration, which extends into the organic layer up to distances of about 50-100 nm and prevents the realization of devices with well-defined geometry. For our devices the thickness is defined with an accuracy of about 2.5 nm, which is near the Alq3 molecular size. We demonstrate efficient spin injection at both interfaces in devices with 100- and 200-nm-thick channels. We solve one of the most controversial problems of organic spintronics: the temperature limitations for spin transport in Alq(3)-based devices. We clarify this issue by achieving room-temperature spin valve operation through the improvement of spin injection properties of both ferromagnetic/Alq(3) interfaces. In addition, we discuss the nature of the inverse sign of the spin valve effect in such devices proposing a mechanism for spin transport.

The organic semiconductor dibenzotetrathiafulvalene (DB-TTF) presents, at ambient conditions, four polymorphic modifications. In addition to the already known monoclinic structure (a) with Z ¼ 2, we have resolved by single crystal X-ray diffraction (XRD) a second crystal structure (b), also monoclinic but with Z ¼ 4. Two other polymorphic modifications (g and d) have been found by means of lattice phonon confocal Raman microscopy and XRD. In this paper we present a series of growth experiments, from vapour or from solution, in films and in the bulk phase, describing the variety of transformations which occur among the different phases and their mixing, also at a micrometric scale. Quasi harmonic lattice dynamics calculations satisfactorily reproduce the structures of the a and the b polymorphs and help the phonon assignment of polarized Raman spectra in single crystals.

The crystallization of an organic semiconductor, viz., tetrahexil-sexithiophene (H4T6) molecules, confined into nanosized cavities of a self-organized polystyrene beads template, has been investigated by means of in situ grazing incidence X-ray diffraction measurements, during the solvent evaporation. Thanks to these real time experiments, the phase content and the crystalline domain orientation of H4T6 have been determined, from the onset of the first crystalline molecular assembly to the stable system. The correlation between the bead size dependent crystallization mechanism in this complex system and the enhanced transistor performance has been established. These results, which can be extended to a wide range of organic materials, are useful for developing an attractive sustainable process for fabrication of organic devices with enhanced performance.

We report high structural order in thin films of the organic semiconductor perfluoro-pentacene (PFP), which is a candidate material for n-type applications, deposited by vacuum sublimation on oxidized silicon wafers. Bragg reflections up to high order in both specular and grazing incidence geometries and a mosaicity of less than 0.01° demonstrate the well defined structure. The thin film entirely consists of crystallites with a structure close to the bulk phase without any contamination with a second phase. Real-time X-ray measurements show that PFP grows in a Stranski–Krastanov growth mode with the first monolayer wetting the substrate before 3d-growth sets in during growth of the second monolayer. Implications for its use are discussed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We investigated the growth of Fe nanostructured films on c(2 × 2)-N/Cu(1 0 0) surface with Fe K-edge X-ray absorption fine structure (XAFS) in the near edge and in the extended energy region. The high photon flux of the incident X-rays allowed us to perform multishell analysis of the XAFS oscillations for Fe coverage ΘFe < 1 ML. This data analysis yields a detailed investigation of the atom geometry and some insights in the film morphology. At ΘN < 0.5 ML (N saturation coverage) there is absence of contribution to XAFS from N atoms. First shell analysis of linearly polarized XAFS gives Fe–Fe (or Fe–Cu) bond length values varying between R1 = 2.526 ± 0.006 A at the highest Fe coverage (3 ML ) and R1 = 2.58 ± 0.01 A at ΘFe = 0.5 ML, ΘN = 0.3 ML, with incidence angle Θ = 35°. These values are different from the case of bcc Fe (R = 2.48 A), and compatible with fcc Fe (R1 = 2.52 A) and fcc Cu (R1 = 2.55 A). At the Fe lowest coverage (ΘFe = 0.5 ML) the dependence of R1 on the incidence angle indicates expansion of the outmost layer. Near edge spectra and multishell analysis can be well reproduced by fcc geometry with high degree of static disorder. At N saturation pre-coverage (ΘN = 0.5 ML) the XAFS analysis has to keep into account the Fe–N bonding. The results suggest two different adsorption sites: one with Fe in a fcc hollow site, surrounded by other metal atoms as nearest neighbours, and one resulting from an exchange with a Cu atom underneath the N layer.

X-ray magnetic linear and circular dichroism at the Mn ${L}_{2,3}$ edges are used to determine the magnetic properties of epitaxial MnPt films on Fe(100). The good agreement between experimental linear dichroism and multiplet calculations reveals that the Mn spins are aligned in plane but perpendicularly to the underlying in-plane Fe spins. The absence of magnetic circular dichroism rules out the presence of uncompensated Mn spins at the interface.