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Despite its simple structure and low degree of electronic correlation, SrTiO_{3} (STO) features collective phenomena linked to charge transport and, ultimately, superconductivity, that are not yet fully explained. Thus, a better insight into the nature of the quasiparticles shaping the electronic and conduction properties of STO is needed. We studied the low-energy excitations of bulk STO and of the LaAlO_{3}/SrTiO_{3} two-dimensional electron gas (2DEG) by Ti L_{3} edge resonant inelastic x-ray scattering. In all samples, we find the hallmark of polarons in the form of intense dd+phonon excitations, and a decrease of the LO3-mode electron-phonon coupling when going from insulating to highly conducting STO single crystals and heterostructures. Both results are attributed to the dynamic screening of the large polaron self-induced polarization, showing that the low-temperature physics of STO and STO-based 2DEGs is dominated by large polaron quasiparticles.

In this work, a method of obtaining graphene layers from natural source specifically from rice husk was developed. A rice husk (RH) was used as a raw material, and potassium hydroxide was used as activation agent. The graphene layers were obtained after four successive stages: pre-carbonization, desilication in 1M NaOH solution, chemical activation and exfoliation of the carbonized rice husk (CRH). The obtained samples were studied using Raman spectroscopy, TEM and SEM; the Raman peaks evidenced the presence of graphene multilayers in the sample. A detailed observation of Raman spectroscopy showed that the obtained samples with ratio of 1/4 and 1/5 (RH/KOH) consisted of graphene layers with a high content of amorphous component. The yield of the product was ~ 3% by weight. This study can provide a new way to the large-scale synthesis of low-cost single and multi-layered graphene using rice husk or other renewable resources.

The recent development of eumelanin pigment-based blends integrating “classical” organic conducting materials is expanding the scope of eumelanin in bioelectronics. Beyond the achievement of high conductivity level, another major goal lays in the knowledge and feasible control of structure/properties relationship. We systematically investigated different hybrid materials prepared by in situ polymerization of the eumelanin precursor 5,6-dihydroxyindole (DHI) in presence of various amounts of graphene-like layers. Spectroscopic studies performed by solid state nuclear magnetic resonance (ss-NMR), x-ray photoemission, and absorption spectroscopies gave a strong indication of the direct impact that the integration of graphene-like layers into the nascent polymerized DHI-based eumelanin has on the structural organization of the pigment itself, while infrared, and photoemission spectroscopies indicated the occurrence of negligible changes as concerns the chemical units. A tighter packing of the constituent units could represent a strong factor responsible for the observed improved electrical conductivity of the hybrid materials, and could be possible exploited as a tool for electrical conductivity tuning.

The discovery of 2D conductivity at the LaAlO3/SrTiO3 interface has been linking, for over a decade, two of the major current research fields in materials science: correlated transition-metal-oxide systems and low-dimensional systems. Notably, despite the 2D nature of the interfacial electron gas, the samples are 3D objects with thickness in the mm range. This prevented researchers so far from adopting strategies that are only viable for fully 2D materials, or from effectively exploiting degrees of freedom related to strain, strain gradient and curvature. Here a method based on pure strain engineering for obtaining freestanding LaAlO3/SrTiO3 membranes with micrometer lateral dimensions is demonstrated. Detailed transmission electron microscopy investigations show that the membranes are fully epitaxial and that their curvature results in a huge strain gradient, each layer showing a mixed compressive/tensile strain state. Electronic devices are fabricated by realizing ad hoc circuits for individual micro-membranes transferred on silicon chips. The samples exhibit metallic conductivity and electrostatic field effect like 2D-electron systems in bulk heterostructures. The results open a new path for adding oxide functionalities into semiconductor electronics, potentially allowing for ultra-low voltage gating of a superconducting transistors, micromechanical control of the 2D electron gas mediated by ferroelectricity and flexoelectricity, and on-chip straintronics.

This article reports a new way to prepare expanded graphite using a thermal method. Natural graphite was added to crystalline hydrate of metals with mechanical stirring at room temperature, taken in the number of 20-80% of the mass of mix. This was then placed in muffle furnace. All process of activation takes from 10 to 20 minutes. X-ray diffraction patterns were used to analyze the structure and confirm that expanded graphite had indeed been prepared. A scanning electron microscope was utilized to observe the morphologies of the expandable graphite and expanded graphite.

Metal-organic framework (MOF) incorporating conductive graphene-like layers were synthesized and characterized. The selected MOF, HKUST-1, combines high surface area, water stability, simple preparation and low costs. Graphene-like layers incorporated into the MOF structure were obtained by a two-step oxidation/reduction wet treatment of a high surface carbon black. MOF composites were produced at different carbonaceous layers content. It was shown, through a wide characterization of the samples, that the composites preserve the main features of the parent MOF, additional exhibiting a tunable electrical conductivity. © 2014 Elsevier B.V. All rights reserved.

Reduction of strongly oxidized carbon black by hydrazine hydrate yields water-insoluble graphene-like sheets that undergo to self-assembling in thin film on surfaces after drying. The height of a drop-casted graphene-like film was determined by atomic force microscopy (AFM) to be around 20 nm, corresponding to approximately 25 graphene-like layers. The oxidized carbon black and the corresponding reduced form were carefully characterized.

Organic (bio)electronics appears to be the first target for competitive exploitation in the materials science of eumelanins, black insoluble photoprotective human biopolymers. Nonetheless, the low conductivity of these pigments is limiting the implementation of eumelanin-based devices. Here we present a novel organic/organic hybrid material (EUGL) by integration of conductive graphene-like (GL) layers within the EUmelanin pigment (EU). GL layers were obtained by a two-step oxidation/reduction of carbon black. The stability of GL layers over a wide pH range and the self-assembling tendency place this material in a leading position for the fabrication of hybrid materials in aqueous media. EUGL was obtained by inducing the polymerization of eumelanin precursors (5,6-dihydroxyindole, DHI and 5,6-dihydroxyindole-2 carboxylic acid, DHICA) in aqueous media containing GL layers. The new material featured promising biocompatibility and an increased conductivity with respect to eumelanin by four orders of magnitude.

Neutron irradiation was performed on MgB2 thin films grown by hybrid physical chemical vapor deposition. Samples irradiated with different neutron fluences, having different critical temperatures, were studied by scanning tunneling spectroscopy in order to investigate the effect of the introduced disorder on the superconducting and spectroscopic properties. A monotonic increase of the pi gap with increasing disorder was found. (c) 2007 Elsevier B.V. All rights reserved.