National Institute Of Materials Physics - Romania

The time evolution of a quantum dot exciton in Coulomb interaction with wetting layer carriers is treated using an approach similar to the independent boson model. The role of the polaronic unitary transform is played by the scattering matrix, for which a diagrammatic, linked cluster expansion is available Similarities and differences to the independent boson model are discussed. A numerical example is presented.

We propose a concept of hybrid nanoelectronic-magnetic device made of magnetic Fe-C core-shell nanoparticles deposited onto prepatterned Si (111) substrate with basic circuitry made of metallic conductive lines. The synthesis of magnetic material and the creation of nanoelectronic prepatterned interdigitated die are reported and to prove the effectiveness in devices, their magnetotransport properties are investigated. Magnetic Fe/FeC nanoparticles, 11 nm diameter, with a core-shell structure have been prepared by laser pyrolysis. Two different layouts of prepatterned interdigitated die, have been conceived using e-beam lithography, with various geometries. A range of microscopy techniques, transmission electron, scanning and optical, were employed for morphological characterization of the as-obtained structures. Magnetic and magnetotransport characterization using SQUID magnetometry has been performed onto both the core-shell nanoparticles and onto the hybrid device obtained by depositing centrifugated and dispersed core-shell nanoparticles from liquid carrier solutions. From magnetotransport measurements, it has been revealed that the hybrid device made of Fe/FeC nanosized materials on prepatterned interdigitated die exhibit a large giant magnetoresistive (GMR) effect of about 8% at 300 K. This result is promising in view of the use of such devices as arrays of nanosensors and in spintronic applications.

Hybrid organic-inorganic thin films based on zinc phthalocyanine (ZnPc) and ZnO nanoparticles were deposited by Matrix Assisted Pulsed Laser Evaporation (MAPLE). Synthesized by a simple wet chemical precipitation method, the ZnO nanoparticles were featured by a hexagonal wurtzite structure, a band-gap value of similar to 3.3 eV and emission bands typical for this semiconductor. The hybrid films containing ZnPc and various amounts of ZnO nanoparticles were evaluated from morphological, compositional, structural, optical and electrical point of view. No chemical decomposition of the organic compound was observed in the FTIR spectra of the deposited layers. The transmittance and photoluminescence spectra recorded on hybrid films disclose the optical signature of both organic (ZnPc) and inorganic (ZnO) components. The electrical measurements carried out under illumination emphasized the importance of the quantity of the inorganic component on the performance parameters of the structures prepared with the hybrid films. Our study provides new insight in the MAPLE deposition of the organic-inorganic hybrid films with potential applications in the photovoltaic cells area.

We show that a simple ethanol (EtOH) refluxing treatment at mild temperature (120 degrees C) allows producing blue-colored and reduced titanium dioxide (TiO2-x) exhibiting improved visible-light (VIS) photocatalytic properties. The treatment causes an increase in the density of Ti(III) species and the appearance of two optical absorption features: a broad absorption band-responsible for the blue coloration- extending from the green region (similar to 2.3 eV) up to the near-infrared and a subgap absorption tail close to the band gap energy. The experimental results combined with a computation of the density of states via hybrid Hartree-Fock density functional support the hypothesis that the EtOH reflux treatment leads to formation of surface and subsurface oxygen (O) vacancies. We also show that the excitation-resolved photoluminescence technique allows a high-contrast detection of a subgap optical excitation band peaked at about 430 nm (similar to 2.9 eV), associated with anatase photoluminescence, whose intensity increases after the EtOH reflux treatment. This result gives a very direct support to the debated hypothesis identifying O vacancy states as the energy levels involved in the radiative transition of anatase TiO2. Improved photocatalytic degradation by the processed TiO2 under VIS illumination is demonstrated, and the possible mechanism involved in the formation of surface O vacancies is discussed. The method outlines a very simple, low-cost, and fast procedure to target the formation of O vacancies in the TiO2 surface region.

The emerging field of electronics based on ferro-functional materials relies on driving effectively and predictably a ferroelectric system between different polarization states through bias applied to metallic contacts. This requires detailed understanding of the growth mechanisms and electronic properties of the interface, including ferroelectric and material - dependent band alignment and Schottky barrier heights. Whether the major contribution at the interface band alignment comes from the work function difference or from the ferroelectric state is still under debate. Here, using X-ray photoemsion and ab-initio calculations, we derive the complex microscopic picture of metal/ferroelectric interface formation, including growth mechanism, valence alteration, ferroelectric-dependent electrostatic potential and thickness - dependent compensation mechanisms of ferroelectricity, starting from the ultrathin growth of Cu up to 100 angstrom on BaTiO3. One establishes the evolution of the band bending and of the build-in potential from the initial probed thickness of the ferroelectric in the range of 3 lambda (lambda - the inelastic mean free path) while gradually approaching the contact region with the metal at higher thickness of the top layer. We find that the well-defined orientation of the ferroelectric polarization lead to a band bending at the interface, which add at the bending expected from the work function difference of the two joining materials.

Memristors characterized by non-volatile memory resistance switching are promising candidates for building brain inspired computing architectures. However, existing memristive devices are still far from the energy efficiency of petaflops per joule exhibited by biological neural networks. Therefore, to achieve the goal of ultra-low power operation, it is necessary to develop new materials for the active layer in memristors. Here, we show highly energy efficient memristive devices built from liquid-exfoliated 2D WS2 and MoS2 nanosheets, enriched in monolayers using a cascade centrifugation method. Lateral devices with electrochemically inert electrodes were built using the drop casting method. The devices show non-volatile resistive switching with a remarkable low energy consumption. This work contributes to the realization of energy efficient and high performance neuromorphic computing applications. (c) 2020 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

Aminopropyl-silica nanoparticles S0 were obtained and further functionalized with eight halogen-reactive organic compounds 1-8, leading to the S1-S8 hybrid organic-inorganic materials, with spherical morphology and having a 50-200 nm size, as showed TEM analysis. These were further characterized by IR and DLS. Biological assays were performed using five microbial strains, belonging to species frequently encountered in the aetiology of human infections (Enterococcus faecalis, Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia toll and Candida albicans). The obtained materials exhibited promising antimicrobial properties, being active against planktonic, but particularly on biofilm-embedded cells. Among the tested hybrid nanomaterials, S6 seemed to exhibit the most promising antimicrobial profile.

Graphene oxide has been synthesized, additionally derivatized with chloroacetic acid for increase the number of available carboxylic groups and further functionalized with crown-ether moieties. The thus obtained material was characterized by IR, thermal analysis, SEM, Raman, and XPS. Tests on adsorption of several metal cations showed that cooper and iron are more retained than potassium.

Iridium thin films are grown by direct-current plasma magnetron sputtering, on MgO single-crystal substrates with various surface orientations, i.e. (100), (111), and (110). The surface morphology, the crystalline properties of the films, and the substrate-thin-film interface are investigated by atomic force microscopy, X-ray diffraction (XRD), focused ion beam scanning electron microscopy, and high-resolution transmission electron microscopy, respectively. The results reveal that hetero-epitaxial thin films with different crystallographic orientation and notable atomic scale smooth surface are obtained. From the XRD analysis, the following epitaxial relations are obtained: (1) (100)(Ir)||(100)(MgO) out-of-plane and [001](Ir)||[001](MgO) in-plane for Ir grown on MgO(100), (2) (110)(Ir)||(110)(MgO) out-of-plane and [1-10](Ir)||[1-10](MgO) in-plane for Ir grown on MgO(110), and (3) (111)(Ir)||(111)(MgO) out-of-plane and two variants for in-plane orientation [1-10](Ir)||[1-10](MgO) and [1-10](Ir)||[10-1](MgO), respectively, for Ir grown on MgO(111). Because of the large misfit strain (9.7%), the thin films are found to grow in a strain-relaxed state with the formation of geometrical misfit dislocations with a similar to 2.8-nm spacing, whereas thermal strain is stored upon cooling down from the growth temperature (600 degrees C). The best structural characteristics are obtained for the (111)-oriented films with a mosaicity of 0.3 degrees and vanishingly small lattice distortions. The (100)- and (110)-oriented films exhibit mosaicities of similar to 1.2 degrees and lattice distortions of similar to 1% which can be explained by the larger surface energy of these planes as compared to (111).

This work reports the use of electrospun conductive gold covered polycaprolactone fibers for the quantification of dissolved O-2. The morphologies of the electrospun fibers obtained at a static and a dynamic drum collector were investigated by scanning electron microscopy. The reduction process of O-2 at negative potentials is analyzed by cyclic voltammetry and electrochemical impedance spectroscopy (EIS) in sodium phosphate buffer (NaPB) pH 7.0 and in cellular media pH 7.4. The electrochemical sensing performance of Au/PCL towards O-2 quantification in NaPB and cellular media is compared by using three electrochemical techniques: cyclic and linear sweep voltammetry and EIS. Measurements are done in a two electrode configuration, using a silver wire as reference, to show the applicability of the method for O-2 quantification in cellular culture media.