Journal of Nano Research Vols. 18-19

Abstract: Mechanical performance of nanocomposites is strongly dependent on the interaction properties between the matrix and the reinforcement. Therefore, the aim of this work is to investigate the carbon nanotube – polymer interaction in nanocomposites. With the ever-increasing power of computers, and enormous advantage of parallel computing techniques, molecular dynamics is the favourite technique to simulate various atomic and molecular systems for this application. In order to simulate nanocomposites using molecular dynamics techniques, a stepwise approach was followed. First, a single-walled carbon nanotube was modelled as the reinforcing material. The validity of the model was examined by applying simple tension boundary conditions and comparing the results with the literature. Next, PMMA chains, with different geometries and molecular weights, were modelled employing the chemical potentials extracted from the literature. The last step included the modelling of the nanotubes surrounded by the matrix material and the investigation of the energy minimization for the system. Based on the results, the non-covalent interaction energy between a single-walled carbon nanotube and the PMMA matrix was obtained.

Abstract: Nano/microstructures of zinc oxide (ZnO) were grown by the laser assisted flow deposition (LAFD) method. This new process has proved to be very efficient, allowing high yield ZnO deposits at high-rate applicable to large-scale substrates. Laser local heating promotes fast ZnO decomposition and recombination under a self-catalytic vapour–liquid-solid mechanism for the nucleation and growth. Three types of ZnO morphologies were obtained according to the temperature/oxygen availability inside the growth chamber. The morphology can also be controlled adding rare-earth elements to the initial composition. Particularly, tetrapod morphology was obtained by europium oxide addition to the precursors. The structural and microstructural characterizations confirm the good crystallinity of the wurtzite structure. The photoluminescence spectroscopy revealed high optical quality of the as-grown ZnO. Specifically, the free exciton recombination and a strong near band edge recombination due to donor bound exciton transitions can be clearly recognized, although deep level emission in the green spectral region is present.

Abstract: In the present study, the pursued purposes were: (i) monitoring the electrical properties of silicon-on-insulator nanowires (SOI NWs), (ii) determination of surface treatments suitable for obtaining reproducible states on the surface of SOI NWs after their long-term storage, and (iii) identification of surface treatments suitable for regenerating the NW surface after protein (bovine serum albumin molecules) detection. It is shown that, during storage, with the passage of time a negative effective charge was accumulated on the surface of n-SOI NWs up to surface density Q_eff = (2-4)х10¹² cm^-2, while the interface states at the NW/SiO₂ interface underwent relatively slow depassivation. Treatments in H₂O₂ with subsequent treatments in HF can be used for removing organic contaminations from the NW surface and for regenerating the initial working state of SOI NWs after protein detection.

Abstract: In this study, arsenic sulphide A_s4S₄ nanoparticles have been prepared, by high-energy wet milling, in the presence of sodium dodecylsulphate, which acts a surfactant. Solid state properties of the nanoparticles were characterised by XRD, Raman scattering, specific surface area and particle size distribution. Changes in surface areas of the particles, in the 0.2 - 5.4 m² g-¹ range, and nanosize distributions, in the 100 - 250 nm range, characterise the surface and morphological properties of nanorealgar. Raman scattering revealed various species in the milled sample that indicate a disproportionate reaction (3A_s4S₄ → 4A_s2S₃ + 4As) occurring as a consequence of milling. Anticancer effects, of the milled species, were confirmed for the human multiple myeloma U266 and OPM1 cell lines. Dissolution experiments in simulated gastric fluid show a possibility for the application of the realgar nanoparticles as an oral dose in future arsenic drug cancer treatments.

Abstract: Carbon nanotubes are grown by catalytic chemical vapour deposition over components of electronic devices. Samples are analyzed by thermogravimetry, scanning and transmission electron microscopy and X-ray photoelectron spectroscopy. The carbon materials deposited on the microchips present the morphology of multiwall carbon nanotubes and grow vertically aligned on the substrates. The preparation procedure parameters are changed to control sizes and height of the grown multiwall carbon nanotubes. The selectivity to incorporate, or not, carbon nanotubes depends on the chemical composition of the substrate. While carbon nanotubes are efficiently grown on Au surfaces, this reaction does not occur on Pt surfaces. These results correlate with a heterogeneous nucleation of iron catalyst particles on the substrate surface. The resulting composite materials can find numerous technological applications.

Abstract: Urbanism and communities centralization enlarges atmospheric pollution that affects both human beings as well as their constructed buildings. Different scientific and technological studies are being conducted, both in academic and construction industry, aiming the development of new construction materials with properties that can decrease visual pollution of cities, reducing also the number of cleanings required. The present research work aims the study and the production of self-cleaning ceramic surfaces in an economical and viable way without changing aesthetical aspect of material substrates used. The use of TiO₂ nanoparticles (TiO₂-NNPs) represents an attractive way to generate self-cleaning surfaces, therefore promoting the degradation of pollutant agents and reducing cleaning maintenance costs. In order to impart self-cleaning properties to ceramic surfaces, TiO₂-NNPs based layers were deposited on different ceramic material substrates using the dip-coating method. The Photocatalytic activity (degradation of pollutants adsorbed on the surface) of the TiO₂-NNPs based layers was characterized via the decomposition rate of an aqueous solution of Methylene blue (MB) under UV light irradiation. Colourless layers were successfully produced onto gray and white ceramic substrates using this sol-gel technique, without changing their aesthetical appearance. It was observed that the best photocatalytic activity was exhibited by the most porous ceramic substrate (gray); nevertheless, all the TiO₂-NNPs coated ceramic surfaces showed good photocatalytic efficiency.

Abstract: Nanocomposite thin films composed of a TiO₂ matrix doped with noble metals nanoparticles (MNPS), Au and Ag, were deposited on Si (100) and glass substrates by dc magnetron sputtering. The samples were annealed in a protective atmosphere at temperatures ranging from 200 to 700 °C. The main goal of this work is to characterize and compare the Surface Plasmon Resonance (SPR) behaviour in both systems. The studies have been focused on the growth of the nanoclusters and on their role on the optical properties of the films. Size, shape and distribution of the nanoclusters embedded on the titanium oxide dielectric matrix are reported as key factors on the SPR behaviour in both systems (Au:TiO₂ and Ag:TiO₂). The MNPs grew due to diffusion mechanisms, which were led by the annealing treatments, even at the highest annealing temperatures. Evidences of the correlation between the nanocomposite film structural changes and the evolution of the optical properties due to the SPR activity are reported. The SPR phenomenon manifests itself as a wide band on the visible range on the absorption spectra, and it is confirmed by an important change on the surface colour tones of the samples.

Abstract: In this work photoluminescence together with photocatalytic activity of nanocrystalline TiO₂ thin films doped with different amount of Tb are described. Thin films were manufactured by high energy reactive magnetron sputtering process. Structural investigation has shown that all as-deposited films had rutile structure. Doping of the matrix resulted in decrease of the average crystallite sizes from 8.7 nm to 6.6 nm for undoped and doped films, respectively. This testifies about densification of the matrix structure by Tb-doping. Photoluminescence measurements of TiO₂:Tb films have revealed light emission in wide spectral range (from 350 up to 700 nm) with a strong green luminescence at 545 nm. In order to explain Tb³⁺ luminescence phenomenon in TiO₂-rutile matrix possible energy transfer mechanisms are discussed. The photocatalytic activity of nanocrystalline films was determined based on phenol decomposition during UV-light irradiation. Results showed that all manufactured films were photocatalytically active and their activity was growing with increase of terbium amount. The highest decomposition rate was observed for the TiO2 thin films with Tb amount of 2.6 at. %.

Abstract: In this work results of hardness investigations of nanocrystalline TiO₂ thin films are presented. Thin films were prepared by low pressure hot target reactive sputtering (LPHTRS) and high energy reactive magnetron sputtering (HERMS). In both processes a metallic Ti target was sputtered under low pressure of oxygen working gas. After deposition by LPHTRS TiO2 thin films with anatase structure were obtained and after additional post-process annealing at 1070 K, these films recrystallized into the rutile structure. Annealing also resulted in an increase of average crystallite size from 33 nm (for anatase) to 74 nm (for rutile). The HERMS process is a modification of the LPHTRS process with the addition of an increased amplitude of unipolar voltage pulses, powering the magnetron. This effectively increases the total energy of the depositing particles at the substrate and allows dense, nanocrystalline (8.7 nm crystallites in size) TiO₂ thin film with the rutile structure to be formed directly. The hardness of the films was determined by nanoindentation. The results showed that the nanocrystalline TiO2-rutile thin film as-deposited using HERMS had high hardness (14.3 GPa), while the TiO2-anatase films as-deposited by LPHTRS, were 4-times lower (3.5 GPa). For LPHTRS films recrystallized by additional annealing, the change in thin film structure from anatase to rutile resulted in an increase of film hardness from 3.5 GPa to only 7.9 GPa. The HERMS process can therefore produce the TiO₂ rutile structure directly, with hardness that is 2 times greater than rutile films produced by LPHTRS with additional annealing step.

Abstract: Chromium nitride and silicon doped chromium nitride thin films have been deposited by r.f. reactive magnetron sputtering. The effect of processing parameters on the properties of chromium nitride films and the correspondent influence of the addition of silicon on the chromium nitride matrix in the films structure and mechanical properties have been investigated. The characterization of the coatings was performed by X-ray diffraction (XRD), and nano-indentation experiments. These studies allow analyzing the crystalline phases, crystal orientation/texture, crystallite size, mechanical properties and the relations between the characteristics of the films. The increase of the nitrogen partial pressure in the working atmosphere produces changes from a body-centered cubic (bcc) Cr structure, to hexagonal Cr₂N to face-centered cubic (fcc) CrN structure, with CrN (111) preferred orientation. For the films with a dominant Cr2N phase the hardness has a relative maximum (42 GPa). The highest hardness was measured for a coating with dominant CrN phase (45 GPa) with a crystallite size around 18 nm. The addition of Si, in the films with CrN dominant phase, maintains the CrN (111) preferred orientation and produced variable changes in films hardness, depending on deposition conditions.