National Institute Of Materials Physics - Romania

Amorphous metal chalcogenides have good switching properties for resistive memories, but have low thermal stability. In this work, the response to rapid thermal stress, as high as 550 degrees C, of amorphous Cu-GeSe, Ag-GeSe, Cu-GeTe, Ag-GeTe thin films, is investigated. Metal-GeTe films, which are amorphous up to 280 degrees C, are the most stable. Metal-GeSe films start to crystallize at 190 degrees C and a Cu1.59Se phase, with 20.5% Cu vacancies and a structure similar to the c-Cu2-xSe superionic conductor, is formed. This might boost the performance of memory devices. Silver atoms migration is facilitated in Ag-GeSe by poor crystallization (below 5%, at all temperatures). Difussion of Ag is enhanced in Ag-GeTe, due to the crystallization of the cubic (Ag2Te)(4)-GeTe2 (Ag8GeTe6) phase, which has Ag+ vacancies. In Cu-GeTe, the formation of stoichiometric polycrystalline Cu0.67Ge0.33 Te might hinder diffusion. An unusual anisotropic behaviour (increase in thickness, simultaneously with contraction of surface) is observed at 100 degrees C in Cu-GeSe and Cu-GeTe thin films, which suggests the orientation of the amorphous clusters package along a preferential direction.

Continuing growth in global energy consumption and the growing concerns regarding climate change and environmental pollution are the strongest drivers of renewable energy deployment. Solar energy is the most abundant and cleanest renewable energy source available. Nowadays, photovoltaic technologies can be regarded as viable pathways to provide sustainable energy generation, the achievement attained in designing nanomaterials with tunable properties and the progress made in the production processes having a major impact in their development. Solar cells involving hybrid nanocomposite layers have, lately, received extensive research attention due to the possibility to combine the advantages derived from the properties of both components: flexibility and processability from the organic part and stability and optoelectronics features from the inorganic part. Thus, this review provides a synopsis on hybrid solar cells developed in the last decade which involve composite layers deposited by spin-coating, the most used deposition method, and matrix-assisted pulsed laser evaporation, a relatively new deposition technique. The overview is focused on the hybrid nanocomposite films that can use conducting polymers and metal phthalocyanines as p-type materials, fullerene derivatives and non-fullerene compounds as n-type materials, and semiconductor nanostructures based on metal oxide, chalcogenides, and silicon. A survey regarding the influence of various factors on the hybrid solar cell efficiency is given in order to identify new strategies for enhancing the device performance in the upcoming years.

In this paper we report the results of a photoelectrochemical study performed on photoanodes based on hematite nanowire arrays and films prepared on fluoride-doped tin oxide coated glass (FTO) and FTO/TiO2 substrates, respectively by hydrothermal and spray pyrolysis methods. The hematite nanowires grown on FTO/TiO2 substrate are more stable mechanically, longer (1 ?m) and their density on substrate is higher. Hematite film obtained on FTO substrate has a thickness of 92 nm covering uniformly the substrate. X-ray photoelectron spectroscopy measurements showed that hematite samples synthesized on FTO/TiO2 substrate have lower content of oxygen vacancies. The photoelectrochemical performances of the prepared photoanodes are in close connection with the presence or absence of the TiO2 underlayer, with oxygen vacancies content and with their morphological characteristics. Electrochemical impedace spectroscopy was used to investigate the charge transfer kinetics at electrode/electrolyte interface and Mott-Schottky analysis was performed to estimate the flatband potential and the carrier density. TiO2 underlayer led to the formation of defects on the samples surface which induced a positive shift of the flatband potentials compared to that of the bare hematite film. The results showed that the best density photocurrent was obtained with a photoanode of hematite nanowires grown on FTO/TiO2 substrate.

Environmentally-friendly bio-organic materials have become the centre of recent developments in organic electronics, while a suitable interfacial modification is a prerequisite for future applications. In the context of researches on low cost and biodegradable resource for optoelectronics applications, the influence of a 2D nanostructured transparent conductive electrode on the morphological, structural, optical and electrical properties of nucleobases (adenine, guanine, cytosine, thymine and uracil) thin films obtained by thermal evaporation was analysed. The 2D array of nanostructures has been developed in a polymeric layer on glass substrate using a high throughput and low cost technique, UV-Nanoimprint Lithography. The indium tin oxide electrode was grown on both nanostructured and flat substrate and the properties of the heterostructures built on these two types of electrodes were analysed by comparison. We report that the organic-electrode interface modification by nano-patterning affects both the optical (transmission and emission) properties by multiple reflections on the walls of nanostructures and the electrical properties by the effect on the organic/electrode contact area and charge carrier pathway through electrodes. These results encourage the potential application of the nucleobases thin films deposited on nanostructured conductive electrode in green optoelectronic devices.

The purpose of this review is to provide an overview of the available gypsum based composite including various phase change materials employed to increase the thermal energy storage capacity of building materials. A wide range of materials such as n-alkane, saturated fatty acid, fatty acid esters etc are used as phase change materials. Adding carbonaceous material (carbon nanofibers, activated nanocarbon, graphite nanosheets etc.) to augment some properties is also a common practice. In addition, there are presented the methods of obtaining the nano/macro-composites together with some thermal characteristics of the newly prepared materials.

The azathioprine (AZA) electrochemical adsorption onto the screen-printed carbon electrodes (SPCE) modified with the reduced graphene oxide (RGO) sheets in the absence and in the presence of polyaniline-emeraldine salt (PANI-ES) is reported in this work. Using cyclic voltammetry(CV), in the case of the SPCE modified with the RGO sheets non-functionalized and functionalized with PANI-ES, respectively, an irreversible process at the electrode/electrolyte interface is highlighted to take place. In the case of the SPCE modified with the non-functionalized RGO sheets(SPCE-RGO), the oxidation-reduction processes induce an up-shift of the AZA Raman lines from 856 and 1011 cm(-1) to 863 and 1020 cm(-1), respectively. These variations indicate an AZA adsorption onto the surface of the SPCE modified with the RGO sheets that takes place throughtthe imidazole and pyrimidine cycles of mercaptopurine, when the generation of the pi-pi(*) bonds between the mercaptopurine structure and hexagonal carbon cycles of RGO occurs. The electrochemical functionalization of the RGO sheets with PANI-ES is proved bythe appearance of the Raman lines at 1165, 1332-1371, 1496 and 1585 and 1616 cm(-1). The oxidation-reduction processes induced at the interface of the SPCE modified with PANI-ES functionalized RGO sheets and the electrolyte consisting into a phosphate buffer (PB) and AZA lead to thegeneration of new positive charges onto the PANI macromolecular chain and the adsorption of the drug on the working electrode surface that takes place via the pi-pi(*) bonds established between the benzene/quinoide rings of PANI and the imidazole/ purine cyclesof AZA. These results indicate that the SPCE modified with the PANI-ES functionalized RGO sheets shows potential applications in the field of sensors for AZA detection.

Looking for multifunctional materials, an assessment of the performances both as fire retardant and generator of electrically conductive surfaces for a three component mixture of graphene oxide, phosphoric acid and melamine applied on wood chipboard was performed. A simple approach was used to investigate the intumescent char formation and quantify the loss mass during vertical burning tests, in which the prepared samples were exposed for a certain time interval to a flame generated by an ethanol lamp in ambient conditions. Moreover, mass loss evolution and structural changes that occur during the burning process were more comprehensive investigated by differential thermal and thermogravimetric (DTA/TGA) techniques. By comparing the performances between the wood chipboard samples without any coverage and those covered with one or multiple component mixture, an increase of protection against the fire action was noticed when the three component mixture was used. Also, an improvement of the electrical properties was observed, after flame exposure of the samples covered with multiple layers (i.e., two and three), when the three component mixture was used. Morphological and structural investigations by microscopy (optical and electronic-SEMEDX), X-ray diffraction (XRD) and spectral (Raman, FTIR) methods are described. An assessment of market potential is also discussed.

Chemical polymerization of o-phenylenediamine (OPD) in the presence of poly(ethylene oxide), double-wall carbon nanotubes (DWNTs) and ferric chloride is carried out in order to obtain composites based on the poly(o-phenylenediamine)-poly(ethylene oxide) (POPD-PEO) fibres covered and interconnected with DWNTs. Vibrational and photoluminescence properties of these composite materials as well as their morphologies are shown by infrared (IR) spectroscopy, Raman scattering, photoluminescence (PL) and scanning electron microscopy (SEM). An adsorption of DWNTs onto the POPD rods surface in the absence and in the presence of. PEO is highlighted by SEM. The vibrational changes reported by Raman scattering and IR spectroscopy prove a covalent functionalization of DWNTs with the macromolecular compound POPD which is doped with FeCl4- T ions. New hydrogen bonds are generated between POPD covalently functionalized DWNTs and hydroxyl groups of PEO according to IR spectroscopic studies. The two macromolecular compounds, POPD and POPD-PEO, show a complex emission band with maxima at 572 and 566 nm, having a shoulder at 667 nm. A significant change in the profile of the PL bands of POPD and POPD-PEO is induced in the DWNTs presence. We show that DWNTs induce (i) a diminution in the POPD PL band intensity peaked between 525-600 nm simultaneous with the increase in the intensity of the PL band situated in the 600-800 nm spectral range and (ii) an enhancement process of the emission band localized in the 475-800 nm spectral range in the case of POPD-PEO.

In this work, the electrochemical polymerization of pyrrole in the presence of H3PMo12O40 onto the screen-printed carbon electrodes (SPCE) modified with double-walled carbon nanotubes (DWNTs) is reported. The influence of the pyrrole and H3PMo12O40 concentration as well as a scan rate used to recording of cyclic voltammograms that describe the electrochemical synthesis of polypyrrole (PPY) onto the DWNTs surface is assessed. Using scanning electron microscopy (SEM) we demonstrate that the electrosynthesis of PPY doped with H3PMo12O40 heteropolyanions (PPY-PMo12) results in the generation of a globular morphology. Considering the variations induced of DWNTs in the IR and Raman spectra of PPY doped with H3PMo12O40 heteropolyanions, a functionalization process of carbon nanotubes with macromolecular compound is invoked. According to SEM investigations, DWNTs allow the realization of connections between the globular structures of the macromolecular compound. The changes induced of folic acid (FA) during the oxidation-reduction processes at the interface of the DWNTs functionalized with PPY doped with H3PMo12O40 heteropolyanions (SPCE-DWNT/PPY-PMo12) with electrolyte solution are reported.