Publications

We demonstrate the anisotropic features of the A(1g), B-2g and A(2g) vibrational Raman modes of phosphorene by performing for the first time a comparison of two orthogonal polarized Raman scattering studies in edge and top view measuring configurations. Despite the orthogonality between the vibration modes of A(1g) and A(2g), they exhibit intense and very weak Raman intensities under light polarized along and transverse to the armchair edge, respectively, while the B-2g mode is virtually non-existent. The B-2g mode significantly appears only in the top view configuration. The studies performed under different intensities of excited light in the top view configuration are detailed for the sample rotated at 0 degrees, 40 degrees, 80 degrees and 130 degrees about the incident laser beam. The studies reveal a quadratic opposite behavior of the A(2g) and B-2g modes and an unusual angle dependence of the A(1g) vibrational mode. An unexpected behavior of the A(2g) Raman mode at higher intensities, which still persists for the A(1g) mode, is shown. The anomalous behavior of the A(1g) mode from the edge and top view and the A(2g) mode in the top view configuration is explained in terms of the layer stacking structures of phosphorene.

The leakage current for a thin film metal-ferroelectric-metal device was modelled using an electron tunnelling approach. The potential energy through the device was obtained from an electrostatic argument and a balance equation was imposed for the incoming and outgoing currents. Using the obtained leakage current, experimental data was fitted in order to obtain qualitative values for the model parameters. Good agreement between the obtained dielectric constant and numerical calculations performed in the literature.

This study presents a novel method for the oxidative polymerization of thiophene (T) by employing cadmium selenide (CdSe) quantum dots and CdSe-graphene oxide (GO) as activators of the polymerization system. The polymerization initiation mechanism is based on the difference between the HOMO-LUMO energy levels of the components, which permits the formation of a donor-acceptor exchange. Thus, T should act both as acceptor and donor for a component with suitable HOMO-LUMO energy levels. We have investigated the polymerization reaction evolution as well as the molecular weights of the obtained polymers. The resulting materials containing PT, CdSe quantum dots and GO have been characterized by FTIR, UV-vis, fluorescence, HRTEM, conductivity and AFM analyses.

In this work, the charge storage properties of trilayers with Ge nanocrystals (NCs) embedded in HfO2 matrix prepared by using two approaches for obtaining the intermediate layer with Ge NCs as nodes are investigated. Trilayer structures with tunnel and control oxides of HfO2, but with different intermediate layers of Ge and Ge-HfO2, respectively, were deposited by magnetron sputtering. Ge nanostructuring was achieved by subsequent rapid thermal annealing. Charge storage behaviour was studied by measurements of capacitance-voltage characteristics on MOS-like capacitors based on the annealed trilayers. The MOS samples with intermediate layer obtained by depositing a continuous Ge layer show hysteresis with memory windows up to similar to 1.3 V, while the ones with co-deposited Ge and HfO2 as intermediate layer present higher memory windows, similar to 1.8 V. In both cases, the memory windows are independent on the frequency demonstrating that the memory effect is due to storing the charge only inside Ge NCs. These show that the approach based on co-deposition of a Ge-HfO2 intermediate layer is more effective for charge storage with direct application in memory devices.

Wettability properties of thin TiO2 amorphous layers obtained by sputtering or sol-gel onto polyester textile materials were investigated. Contact angle (CA) measurements by the sessile drop method were used to evaluate these properties. Comparison was performed with coated samples of related poly(lactic acid) material. The samples coated by sol gel have CAs a few degrees higher than those coated by sputtering. Wetting properties were conversely changed under alternate darkness/illumination conditions. Photoinduced hydrophilicity was observed even for these amorphous coating particles, being higher for sputtered samples than for sol gel ones.

A two-dimensional array of a large number of identical densely-packed indium-oxide nano-columns was prepared by pulsed laser deposition. The structure closely mimics tubular structure of the under-cap layer of tubular mushrooms. The growth was initiated by a dense array of gold or silver nanodots. The resulting structure forms a transparent semiconducting layer whose resistance is highly sensitive to composition of gases in atmosphere. A simple device based on the array of nano-columns is able to accurately monitor gas balance in an open or closed-space environment. The simplicity of the device, its compactness and a well-established process of deposition would allow incorporating it in various equipment of general or personal use. The application of the sensor could range from health monitoring during the exhale to the check of the car exhaust or gas content in homes, offices, workplaces or in the dangerous and threatening environment.

Bioactive materials play an increasingly important role in the biomaterials industry, and are extensively used in a range of applications, including biodegradable metallic implants. We report on Bioactive Glasses (BG) films deposition by pulsed laser techniques onto biodegradable substrates. The BG coatings were obtained using a KrF* excimer laser source (lambda= 248 nm, t(FWHM) <= 25 ns). Their thickness has been determined by Profilometry measurements, whilst their morphology has been analysed by Scanning Electron Microscopy (SEM). The obtained coatings fairly preserved the targets composition and structure, as revealed by Energy Dispersive X-Ray Spectroscopy, Grazing Incidence X-Ray Diffraction, and Fourier Transform Infra-Red Spectroscopy analyses.

One of the simplest routes to prepare polycrystalline Zn(OH)(2) is by coprecipitation, with zinc nitrate as a cation source. However, the addition of even minute amounts of manganese nitrate to the precursors used to prepare pure Zn(OH)(2) results in Mn2+ doped nanostructured ZnO. The comparison with other Mn2+ doped metal hydroxides prepared by the same coprecipitation method, involving metal nitrates precursors, shows that this behavior is unique, pertaining only to Zn(OH)(2). A systematic study of the samples prepared without and with variable amounts of Mn2+ ions, in the 1 to 5000 ppm nominal concentrations range showed that the re-routing of the reaction takes place even for the lowest nominal dopant concentration of 1 ppm. According to X-ray diffraction, transmission electron microscopy and Fourier transform infrared spectroscopy investigations, both crystallite size and morphology of the resulting nanostructured ZnO samples varied with the Mn2+ nominal concentration. Moreover, quantitative electron paramagnetic resonance investigations showed that the incorporation rate of the Mn2+ ions at different sites in the nanostructured ZnO depended on the nominal Mn2+ concentration. The results are discussed in terms of the coordination properties of the Mn2+ and Zn2+ ions and the nature of the reaction precursors.

An alternative and simple coprecipitation method was developed to obtain carbon nanotube-hydroxyapatite (CNTs:HAp) based nanocomposites. The incorporation of CNTs (in a concentration of 5% and 10% of total weight of the nanocomposite) and their impact on both structural and biological properties were studied by using a set of standard complementary biological, microscopic, and spectroscopic techniques. The characteristic peaks of carbon structure in CNTs were not observed in the CNTs-HAp composites by X-ray diffraction analysis. Moreover, FTIR and Raman spectroscopies confirmed the presence of HAp as the main phase of the synthesized CNTs: HAp nanocomposites. The addition of CNTs considerably affected the nanocomposite morphology by increasing the average crystallite size from 18.7 nm (for raw HAp) to 28.6 nm (for CNTs:HAp-10), confirming their proper incorporation. The biocompatibility evaluation of CNTs:HAp-5 and CNTs:HAp-10 nanocomposites included the assessment of several parameters, such as cell viability, antioxidant response, and lipid peroxidation, on human G-292 osteoblast cell line. Our findings revealed good biocompatibility properties for CNTs: HAp nanocomposites prepared by the coprecipitation method supporting their potential uses in orthopedics and prosthetics.