Applied Surface Science (v.352, #C)

Preface by V. Craciun; F. Iacomi; C. Dubourdieu; F. Sánchez Barrera; M. Kompitsas (1).

Electrical transport in AZO nanorods by A. Yildiz; H. Cansizoglu; T. Karabacak (2-4).
Al-doped ZnO (AZO) nanorods (NRs) with different lengths were deposited by utilizing glancing angle deposition (GLAD) technique in a DC sputter system at room temperature. The structural and optical characteristics of the NRs were investigated by the X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV–vis–NIR spectroscopy measurements. A band gap of about 3.5 eV was observed for the NRs. A novel capping process utilizing varying deposition angles was used to introduce a blanket metal top contact for the electrical characterization of NRs. Current–voltage (IV) measurements were used to properly evaluate the approximate resistivity of a single NR. The electrical conduction was found to be governed by the thermally activated transport mechanism. Activation energy was determined as 0.14 eV from temperature dependent resistivity data.
Keywords: AZO nanorods; Glancing angle deposition (GLAD); Electrical properties; Activation energy;

Nanomechanical characterization of amorphous and nanocrystalline FeCuNbSiB thin films by Laura-Ioana Velicu; Maria Neagu; Lucian Costinescu; Vasile Tiron; Daniel Munteanu (5-9).
Mechanical properties (hardness and Young's modulus) of amorphous and nanocrystalline Fe73.5Cu1Nb3Si15.5B7 thin films (thicknesses from 1.4 μm to 2 μm) have been investigated using the depth-sensing nanoindentation technique. The amorphous films, having uniform and smooth surfaces, were deposited on glass, aluminum, silicon, and sapphire substrates using the high power impulse magnetron sputtering technique. The nanocrystalline state was achieved after isothermal treatments performed at temperatures between 463 °C and 475 °C. The mean value for the effective Young's modulus of the amorphous Fe73.5Cu1Nb3Si15.5B7 thin films is about 146 GPa, regardless of their thickness or the substrate's nature. Increasing the thickness of the films, the hardness value increases up to 1 GPa. After the thermal treatments performed at 475 °C (when the films’ structure consists of b.c.c. α-Fe(Si) grains with average size of 15 nm embedded in a residual amorphous matrix) the effective Young's modulus value decreases by about 13%, while hardness value increases by about 13% with respect to the as-deposited state.
Keywords: Amorphous materials; Hardness; High-power impulse magnetron sputtering; Nanocrystalline materials; Nanoindentation; Young's modulus;

Nickel oxide has been investigated for several potential applications, namely, ultraviolet detectors, electro chromic devices, displays, diodes for light emitting, transparent conductive electrode, and optoelectronic devices. These applications require an in depth analysis of nickel oxide prior to its exploration in aforementioned devices. Optical properties of materials were investigated by depositing thin film of nickel oxide on different substrates in order to understand if the choice of substrate can have effect on deducing various optical parameters and can lead to wrong conclusions. In view of this, we have investigated optical properties of nickel oxide deposited on different substrates (glass, transparent plastic, sapphire, potassium bromide, and calcium fluoride).
Keywords: Optical investigation; Substrate for nickel oxide; Bandgap of nickel oxide (NiO); Ideal substrate for NiO bandgap analysis;

Studies on optical properties of antimony doped SnO2 films by Sibel Gürakar; Tülay Serin; Necmi Serin (16-22).
Antimony doped tin oxide thin films were grown by spray method on microscope glass substrates. The antimony doping was varied from 0 to 4 at%. The structural properties of the films were investigated by X-ray diffraction method. The optical transmittances of thin films were measured with UV-Vis-NIR spectrometer in the 300–2000 nm wavelength range. A simple analysis according to Swanepoel's method was applied to derive the real and imaginary parts of the complex index of refraction plus film thickness. The dispersion of refractive index was investigated in terms of the single-oscillator Wemple and DiDomenico model and the important oscillating parameters such as the dispersion energy E d, the oscillation energy E o, the high frequency dielectric constant ɛ were determined. The analysis of the refractive index has been carried out to calculate the lattice dielectric constant ɛ L and the ratio of carrier concentration to the effective mass N/m*. The real and imaginary parts of the electronic dielectric constant and optical conductivity were analyzed. The optical band gap, E g values of the films were obtained from the spectral dependence of the absorption coefficient, using the Tauc relation.
Keywords: Sb doped SnO2; Thin films; Spray method; Structural properties; Optical properties;

Effect of annealing treatment on the structural and optical properties of AZO samples by P. Prepelita; V. Craciun; F. Garoi; A. Staicu (23-27).
AZO (2% Al doped ZnO) thin films, with thicknesses of 30 nm (AZO30), 50 nm (AZO50) and 400 nm (AZO400), deposited onto glass substrate by RF magnetron sputtering were subjected to annealing at a temperature of 700 K for a period of 90 min in air. As-deposited AZO30 and AZO50 samples were almost amorphous, with very small grains. After annealing, a crystallization process from amorphous to crystalline phase occurred. X-ray diffraction and scanning electron microscopy analyses showed a polycrystalline structure and a preferred orientation of the crystallites for the obtained thin films. Atomic force microscopy measurements indicated roughness values of 0.7 nm for AZO30, 1.4 nm for AZO50 and 18 nm for AZO400 annealed samples.Optical transmittance investigations of the layers in the 0.2–1.2 μm wavelength range showed a high transmission in the visible and near infrared range, as well as values between 3.36 and 3.45 eV for the optical bandgap. The present simple processing route is useful for device applications of transparent conductive oxides.
Keywords: Thin films; Polycrystalline; Surface morphology; AZO; Annealing; Bandgap;

Optical and mechanical properties of nanocrystalline ZrC thin films grown by pulsed laser deposition by D. Craciun; G. Socol; E. Lambers; E.J. McCumiskey; C.R. Taylor; C. Martin; N. Argibay; D.B. Tanner; V. Craciun (28-32).
Thin ZrC films (<500 nm) were grown on (100) Si substrates at a substrate temperature of 500 °C by the pulsed laser deposition (PLD) technique using a KrF excimer laser under different CH4 pressures. Glancing incidence X-ray diffraction showed that films were nanocrystalline, while X-ray reflectivity studies found out films were very dense and exhibited a smooth surface morphology. Optical spectroscopy data shows that the films have high reflectivity (>90%) in the infrared region, characteristic of metallic behavior. Nanoindentation results indicated that films deposited under lower CH4 pressures exhibited slightly higher nanohardness and Young modulus values than films deposited under higher pressures. Tribological characterization revealed that these films exhibited relatively high wear resistance and steady-state friction coefficients on the order of μ  = 0.4.
Keywords: ZrC; Hard coating; Pulsed laser deposition; Infrared optical properties;

Zinc telluride (ZnTe) thin films were sublimated on a glass substrate using closed space sublimation (CSS) technique. The influence of the substrate temperature on the physical properties is studied. The deposited films were immersed in AgNO3 solution with different concentrations, and then annealed in air. The structure and composition are studied using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). X-ray diffraction patterns of as-deposited ZnTe thin films exhibited polycrystalline behavior. The preferred orientation of (1 1 1) having cubic phase irrespective of the substrate temperature was observed. The XPS analysis confirmed the presence of Ag in the ZnTe thin films after doping by immersion in the AgNO3 solution of different concentrations.
Keywords: Close space sublimation method; ZnTe; Ag-doping; XRD; XPS;

The present work is investigating the photocatalytic activity of TiO2 thin films deposited by radiofrequency magnetron sputtering of a pure TiO2 target in Ar and Ar/H2O (pressure ratio 40/3) plasmas. Optical absorption, structure, surface morphology and chemical structure of the deposited films were comparatively studied. The films were amorphous and included a large amount of hydroxyl groups (about 5% of oxygen atoms were bounded to hydrogen) irrespective of the intentional content of water in the deposition chamber. Incorporation of hydroxyl groups in the film deposited in pure Ar plasma is explained as contamination of the working gas with water molecules desorbed by plasma from the deposition chamber walls. However, intentional input of water vapour into the discharge chamber decreased the deposition speed and roughness of the deposited films. The good photocatalytic activity of the deposited films could be attributed hydroxyl groups in their structures.
Keywords: Sputtering deposition; TiOx thin films; Photocatalytic activity; Hydroxyl groups;

Catalytical degradation of relevant pollutants from waters using magnetic nanocatalysts by C. Nadejde; M. Neamtu; R.J. Schneider; V.-D. Hodoroaba; G. Ababei; U. Panne (42-48).
The catalytic efficiency of two magnetically responsive nanocatalysts was evaluated for the degradation of Reactive Black 5 (RB5) and Reactive Yellow 84 (RY84) azo dyes using hydrogen peroxide as oxidant under very mild conditions (atmospheric pressure, room temperature). In order to obtain the nanocatalysts, the surface of magnetite (Fe3O4) nanoparticles, prepared by a co-precipitation method, was further modified with ferrous oxalate, a highly sensitive non-hazardous reducing agent. The sensitized nanomaterials were characterized by X-ray diffraction, scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy and vibrating sample magnetometry, and used in the catalytic wet hydrogen peroxide oxidation (CWHPO) of RB5 and RY84, in laboratory-scale experiments. The effect of important variables such as catalyst dosage, H2O2 concentration, and contact time was studied in the dye degradation kinetics. The results showed that it was possible to remove up to 99.7% dye in the presence of 20 mM H2O2 after 240 min of oxidation for a catalyst concentration of 10 g L−1 at 25 °C and initial pH value of 9.0. CWHPO of reactive dyes using sensitized magnetic nanocatalysts can be a suitable pre-treatment method for complete decolorization of effluents from textile dyeing and finishing processes, once the optimum operating conditions are established.
Keywords: Sensitized magnetic nanocatalysts; Chemical synthesis; Structural characterization; Catalytic wet peroxide oxidation; Reactive azo dye degradation;

Comparative structure analysis of magnetic fluids at interface with silicon by neutron reflectometry by M.V. Avdeev; V.I. Petrenko; I.V. Gapon; L.A. Bulavin; A.A. Vorobiev; О. Soltwedel; M. Balasoiu; L. Vekas; V. Zavisova; P. Kopcansky (49-53).
The adsorption of surfactant coated magnetic nanoparticles from highly stable magnetic fluids on crystalline functionalized silicon is studied by neutron reflectometry. Two types of magnetic fluids based on nanomagnetite dispersed and stabilized in non-polar organic solvent (deuterated benzene) and strongly polar solvent (heavy water) are considered. In both cases the interface shows the formation of just one well-defined adsorption layer of nanoparticles, which is insensitive to the effect of the external magnetic field. Still, the particle concentration in the benzene-based fluid is higher in the vicinity to the silicon surface as compared to the bulk distribution. Despite the presence of an aggregate fraction in the water-based system the width of the adsorption layer is consistent with the size of separated particles, thus showing the preferable adsorption of non-aggregated particles.
Keywords: Magnetic fluids; Ferrofluids; Neutron reflectometry; Nanoparticles adsorption; Structure of layer;

Magnetic behavior of Joule-heated magnetic core–shell nanowires with positive magnetostrictive core material by Ioan Dumitru; Iordana Astefanoaei; Dorin Cimpoesu; Alexandru Stancu (54-59).
Temperature field is an important parameter to be known and controlled in the magnetization process of the core–shell nanowires. The paper analyzes the temperature dependence of hysteretic process in a core–shell nanowire subjected to a dc Joule heating process. An electrical current that passes through the wire induces a temperature and a thermal stress field in the system. Spatial and temporal evolution of the temperature in system was analyzed using a model based on time-dependent heat conduction equation. The stresses determined by thermal gradients and different expansion characteristics of core and shell materials were computed. The temperature and stress depend on the size parameters of the system, dc Joule current and the initial temperature of the system. The magnetic behavior of the nanowire was analyzed using the Micromag application. The magnetic state of the core is influenced by the temperature field induced by a dc current applied to the system. For core materials with positive magnetostriction coefficient the coercive field increases at the increase of dc current intensity passed through the system.
Keywords: dc Joule heating; Magnetization process; Temperature field; Magnetoelastic energy;

The spin-crossover nanoparticles of different sizes and stochastic perturbations in external field taking into account the influence of the dimensionality of the lattice was studied. The analytical tools used for the investigation of spin-crossover system are based on an Ising-like model described using of the breathing crystal field concept. The changes of transition temperatures characterizing the systems’ bistable properties for 2D and 3D lattices, and their dependence on its size and fluctuations strength were obtained. The state diagrams with hysteretic and non-hysteretic behavior regions have also been determined.
Keywords: Spin-crossover; Ising model; Breathing crystal;

Nd–Fe–B films with good perpendicular magnetic anisotropy were obtained by using a Mo film with the thickness of about 40 nm as buffer layer. Large out-of-plane coercivity (H c⊥  = 1182 kA/m) and remanent ratio (remanent magnetization/saturation magnetization)  = 0.99 are obtained by the stratification of the Nd–Fe–B magnetic film in three NdFeB(180 nm)/Mo(5 nm) bilayer sequences using Mo as interlayer. Using a Ni film, with a thickness of about 8 nm, alongside with a Mo film of 40 nm as buffer layer improves the adhesion to substrate and keeps the anisotropic hard magnetic performances of the Nd–Fe–B films unchanged. By increasing the total thickness of the Nd–Fe–B magnetic layer from 540 nm to 1620 nm the coercivity measured at high fields increases from about 1350 kA/m for Nd–Fe–B film with 3 NdFeB(180 nm)/Mo(5 nm) sequences to about 1640 kA/m for Nd–Fe–B film with 9 NdFeB(180 nm)/Mo(5 nm) sequences which can be ascribed to a stronger pinning effect as a result of the increased number of NdFeB/Mo interfaces.
Keywords: Thin films; Hard magnetic properties; Layering; Out-of-plane anisotropy; Adhesion;

Photoelectron spectroscopy and spectro-microscopy of Pb(Zr,Ti)O3 (1 1 1) thin layers: Imaging ferroelectric domains with binding energy contrast by Marius A. Huşanu; Dana G. Popescu; Cristian A. Tache; Nicoleta G. Apostol; Alexei Barinov; Silvano Lizzit; Paolo Lacovig; Cristian M. Teodorescu (73-81).
The ability of photoelectron spectro-microscopy with sub-micrometer lateral resolution to identify ferroelectric domains by analysis of surface band bendings is demonstrated on lead zirco-titanate PZT(1 1 1) thin films grown by pulsed laser deposition. Conventional synchrotron radiation X-ray photoelectron spectroscopy allowed one to derive the surface composition of the sample and evidenced shifts toward higher binding energy when the sample is subject to intense soft X-ray beam. A basic model is developed which supposes that photogenerated carriers reduce the depolarization field, yielding a lower torque applied to the ferroelectric polarization. As a consequence, the out-of-plane component of the polarization increases. Domain migration during irradiation with soft X-ray is inferred from the relative amplitude of the components with different binding energy. When the flux density of soft X-ray is on the order of 1011 photons/(s μm2), metal Pb clusters are formed at the surface on areas with the out-of-plane component of the polarization pointing outwards only.
Keywords: Ferroelectrics; X-ray photoelectron spectroscopy; Photoelectron spectro-microscopy; Band bending; Depolarization; Metal segregation;

Excimer laser texturing of natural composite polymer surfaces for studying cell-to-substrate specific response by V. Dinca; P. Alloncle; P. Delaporte; V. Ion; L. Rusen; M. Filipescu; C. Mustaciosu; C. Luculescu; M. Dinescu (82-90).
Surface modifications of biocompatible materials are among the main factors used for enhancing and promoting specific cellular activities (e.g. spreading, adhesion, migration, and differentiation) for various types of medical applications such as implants, microfluidic devices, or tissue engineering scaffolds. In this work an excimer laser at 193 nm was used to fabricate chitosan–collagen roughness gradients. The roughness gradients were obtained in one step by applying single laser pulses and sample tilting. Fourier transform infrared spectroscopy measurements, atomic force microscopy (AFM), scanning electron microscopy (SEM), and spectro-ellipsometry (SE) were used for sample characterization. The goal is to determine the optimal morpho-chemical characteristics of these structures for in vitro tailoring of protein adsorption and cell behavior. The response induced by the roughness gradient onto various cell lines (i.e. L 929 fibroblasts, HEP G2 hepatocytes, OLN 93 oligodendrocytes, M63 osteoblasts) and bovine serum albumin (BSA) protein absorption was investigated.
Keywords: Roughness gradient; Excimer laser; Cell behavior;

Nanostructure of PDMS–TEOS–PrZr hybrids prepared by direct deposition of gamma radiation energy by Joana J.H. Lancastre; António N. Falcão; Fernanda M.A. Margaça; Luís M. Ferreira; Isabel M. Miranda Salvado; László Almásy; Maria H. Casimiro; Anikó Meiszterics (91-94).
Organic–inorganic materials have been the object of intense research due to their wide range of properties and therefore innumerous applications. We prepared organic–inorganic hybrid materials by direct energy deposition on a mixture of polydimethylsiloxane silanol terminated (33 wt% fixed content), tetraethylorthosilicate and a minor content of zirconium propoxide that varied from 1 to 5 wt% using gamma radiation from a Co-60 source. The samples, dried in air at room temperature, are bulk, flexible and transparent. Their nanostructure was investigated by small angle neutron scattering. It was found that the inorganic oxide network has fractal structure, which becomes denser as the zirconium propoxide content decreases. The results suggest that oxide nanosized regions grow from the OH terminal group of PDMS which are the condensation seeds. Their number and position remains unaltered with the variation of zirconium propoxide content that only affects their microstructure. A model is proposed for the nanostructure of the oxide network that develops in the irradiation processed hybrid materials.
Keywords: Hybrid materials; Gamma irradiation; Neutron scattering; PrZr effect; Microstructure;

Metal–polymer nanocomposites based on Ni nanoparticles and polythiophene obtained by electrochemical method by Petronela Pascariu; Anton Airinei; Mircea Grigoras; Loredana Vacareanu; Felicia Iacomi (95-102).
Polythiophene–nickel (PT–Ni) nanocomposites have been prepared by the electrochemical oxidative polymerization of thiophene in the presence of nickel nanoparticles. The metallic nickel nanoparticles were obtained by the chemical reduction of nickel chloride with hydrazine at 100–130 °C. Poly(N-vinylpyrrolidone) (PVP) was used as protective agent in the synthesis of nickel nanoparticles. Transmission electron microscopy data revealed the particle size to be in the range 6–20 nm. X-ray diffraction, scanning electron microscopy, thermal analysis, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were utilized to characterize the nanocomposites. XPS measurements for the PT–Ni nanocomposites showed that the nickel content varied between 0.43 and 1.3 at.% in the PT–Ni nanocomposites. The electrical conductivity of the composites increased from 4.5 × 10−3  Ω cm−1 to 1.25 × 10−2  Ω cm−1 as the amount of nickel was increased from 0.43% up to 1.3%, polythiophene–Ni nanocomposites exhibiting a good electrical conductivity response.
Keywords: Nickel nanoparticles; Chemical reduction; PT/Ni nanocomposites; Electrochemical synthesis;

Chitosan–gold nanoparticles (AuNPs) were prepared to investigate the behavior of such nanosystems at the interface with biological media. Microstructural characterization by Transmission Electron Microscopy, Atomic Force Microscopy, and Optical Microscopy was carried out in order to provide information regarding the morphology features and size distribution. In vivo studies showed no morphological changes within the brain tissue in rats after the administration of AuNPs. However, nanoparticles size distribution in the in vivo localized tissue areas indicated better dispersion than in the in vitro colloidal solution. Also the size of the AuNPs that reached the brain tissue seemed to decrease compared with their size in the colloidal solution.In order to understand the factors that contribute to the increase of AuNPs dispersion degree within the brain tissue, this study was focused on simulating the pH conditions from the hemato-encephalic medium. A theoretical model was also applied in order to correlate the intensity of the interaction between two AuNPs and their volume ratio to further explain the absence of the agglomerated AuNPs and their high degree of dispersion within the brain tissue.
Keywords: Chitosan–AuNPs; Brain; Surface plasmon; pH influence; Neighbors interaction;

Structural characterization of copolymer embedded magnetic nanoparticles by G.G. Nedelcu; A. Nastro; L. Filippelli; M. Cazacu; M. Iacob; C. Oliviero Rossi; A. Popa; D. Toloman; M. Dobromir; F. Iacomi (109-116).
Small magnetic nanoparticles (Fe3O4) were synthesized by co-precipitation and coated by emulsion polymerization with poly(methyl methacrylate-co-acrylic acid) (PMMA-co-AAc) to create surface functional groups that can attach drug molecules and other biomolecules. The coated and uncoated magnetite nanoparticles were stored for two years in normal closed ships and than characterized by Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, vibrating sample magnetometry, and electron paramagnetic resonance spectroscopy. The solid phase transformation of magnetite to maghemite, as well as an increase in particle size were evidenced for the uncoated nanoparticles. The coated nanoparticles preserved their magnetite structure and magnetic properties. The influences of monomers and surfactant layers on interactions between the magnetic nanoparticles evidenced that the thickness of the polymer has a significant effect on magnetic properties.
Keywords: Magnetic nanoparticles; Polymer coating; Ageing effect;

Study on iron oxide nanoparticles coated with glucose-derived polymers for biomedical applications by D.D. Herea; H. Chiriac; N. Lupu; M. Grigoras; G. Stoian; B.A. Stoica; T. Petreus (117-125).
Glucose-derived polymers were prepared along with magnetic nanoparticles by using one-step hydrothermal precipitation method at temperatures slightly below to the melting point of the monosaccharide. The cytotoxicity of the magnetic composites was tested against human cancer cells and showed them to be biocompatible. The polymer-coated magnetic nanoparticles could be used in specific biomedical applications such as magnetic hyperthermia or drug delivery by taking advantage from the intrinsic magnetic properties and/or the surface functional groups.This study reports an approach for a facile one-step synthesis of magnetic nanoparticles (MNPs) coated with glucose-derived polymers (GDP) through a mechanochemical hydrothermal process for biomedical applications. Polymer-coated magnetic nanoparticles (Fe2O3/Fe3O4), with sizes below 10 nm, exhibited superparamagnetic behavior, with a specific magnetization saturation value of about 40 emu/g, and a maximum specific absorption rate (SAR) of 30 W/g in AC magnetic fields. Depending on the intensity of the applied AC magnetic field, a temperature of 42 °C can be achieved in 4–17 min. The surface polymerized layer affords functional hydroxyl groups for binding to biomolecules containing carboxyl, thiol, or amino groups, thereby making the coated nanoparticles feasible for bio-conjugation. In vitro cytotoxicity evaluation pointed out that a relatively high concentration of polymer-coated magnetic nanoparticles (GDP-MNPs) did not induce severe cell alteration, suggesting a good biocompatibility.
Keywords: Glucose polymers; Magnetic nanoparticles; Cytotoxicity; Magnetic hyperthermia; Hydrothermal;

Study of surface phenomena in biomaterials: The influence of physical factors by Liliana Sachelarie; Mihaela Papusa Vasiliu; Catalina Ciobanu (126-128).
This study's purpose is pointing out the phenomenon that occurs at time of interaction between the tissue with implant. The materials used are Ti and its alloys. The oral tissue must be compatible with the materials used in surgical implant to human body. The bio-materials surface behavior is influenced by physical characteristics. The methods we use show a number of bio-compatibility aspects. The success of an implant in a hard tissue depends not only on the initial attachment and the osteogenic cells consecutive proliferation, but also on their capacity to create a new bone.
Keywords: Ti; Implant; Biocompatibility;

A new Fe–Mn–Si alloplastic biomaterial as bone grafting material: In vivo study by Mircea Fântânariu; Lucia Carmen Trincă; Carmen Solcan; Alina Trofin; Ştefan Strungaru; Eusebiu Viorel Şindilar; Gabriel Plăvan; Sergiu Stanciu (129-139).
Designing substrates having suitable mechanical properties and targeted degradation behavior is the key's development of bio-materials for medical application. In orthopedics, graft material may be used to fill bony defects or to promote bone formation in osseous defects created by trauma or surgical intervention. Incorporation of Si may increase the bioactivity of implant locally, both by enhancing interactions at the graft–host interface and by having a potential endocrine like effect on osteoblasts.A Fe–Mn–Si alloy was obtained as alloplastic graft materials for bone implants that need long recovery time period. The surface morphology of the resulted specimens was investigated using scanning electrons microscopy (VegaTescan LMH II, SE detector, 30 kV), X-ray diffractions (X’Pert equipment) or X-ray dispersive energy analyze (Bruker EDS equipment). This study objective was to evaluate in vivo the mechanisms of degradation and the effects of its implantation over the main metabolic organs. Biochemical, histological, plain X radiography and computed tomography investigations showed good compatibility of the subcutaneous implants in the rat organism. The implantation of the Fe–Mn–Si alloy, in critical size bone (tibiae) defect rat model, did not induced adverse biological reactions and provided temporary mechanical support to the affected bone area. The biodegradation products were hydroxides layers which adhered to the substrate surface. Fe–Mn–Si alloy assured the mechanical integrity in rat tibiae defects during bone regeneration.
Keywords: Fe–Mn–Si alloy; Implants; Degradation behavior; Biological activity; Subcutaneous; Tibiae; Rats;

In vivo degradation behavior and biological activity of some new Mg–Ca alloys with concentration's gradient of Si for bone grafts by Lucia Carmen Trincă; Mircea Fântânariu; Carmen Solcan; Alina Elena Trofin; Liviu Burtan; Dumitru Mihai Acatrinei; Sergiu Stanciu; Bogdan Istrate; Corneliu Munteanu (140-150).
Magnesium based alloys, especially Mg–Ca alloys, are biocompatible substrates with mechanical properties similar to those of bones. The biodegradable alloys of Mg–Ca provide sufficient mechanical strength in load carrying applications as opposed to biopolymers and also they avoid stress shielding and secondary surgery inherent with permanent metallic implant materials. The main issue facing a biodegradable Mg–Ca alloy is the fast degradation in the aggressive physiological environment of the body. The alloy's corrosion is proportional with the dissolution of the Mg in the body: the reaction with the water generates magnesium hydroxide and hydrogen. The accelerated corrosion will lead to early loss of the alloy's mechanical integrity. The degradation rate of an alloy can be improved mainly through tailoring the composition and by carrying out surface treatments. This research focuses on the ability to adjust degradation rate of Mg–Ca alloys by an original method and studies the biological activity of the resulted specimens. A new Mg–Ca alloy, with a Si gradient concentration from the surface to the interior of the material, was obtained. The surface morphology was investigated using scanning electron microscopy (VegaTescan LMH II, SE detector, 30 kV), X-ray diffraction (X’Pert equipment) and energy dispersive X-ray (Bruker EDS equipment). In vivo degradation behavior, biological compatibility and activity of Mg–Ca alloys with/without Si gradient concentration were studied with an implant model (subcutaneous and bony) in rats. The organism response to implants was characterized by using radiological (plain X-rays and computed tomography), biochemical and histological methods of investigation. The results sustained that Si gradient concentration can be used to control the rate of degradation of the Mg–Ca alloys for enhancing their biologic activity in order to facilitate bone tissue repair.
Keywords: Mg–Ca alloys; Si coating; Bone implant; Degradation; Biological activity; Rats;

Nanostructured composite layers for electromagnetic shielding in the GHz frequency range by M. Suchea; I.V. Tudose; G. Tzagkarakis; G. Kenanakis; M. Katharakis; E. Drakakis; E. Koudoumas (151-154).
We report on preliminary results regarding the applicability of nanostructured composite layers for electromagnetic shielding in the frequency range of 4–20 GHz. Various combinations of materials were employed including poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS), polyaniline, graphene nanoplatelets, carbon nanotubes, Cu nanoparticles and Poly(vinyl alcohol). As shown, paint-like nanocomposite layers consisting of graphene nanoplatelets, polyaniline PEDOT:PSS and Poly(vinyl alcohol) can offer quite effective electromagnetic shielding, similar or even better than that of commercial products, the response strongly depending on their thickness and resistivity.
Keywords: Paint-like nanocomposites; Graphene nanoplatelets; Electromagnetic shielding;

Influence of oxygen flow rate in CuO by T. Serin; S. Gurakar; Hakan Ot; Abdullah Yildiz; Necmi Serin (155-157).
The structural, optical and electrical properties of cupric oxide (CuO) films coated by DC magnetron sputtering method under different oxygen flow rate (0%, 35%, 70%) were examined. The electrical transport mechanism of the films was also investigated in a temperature range of 110–400 K. Electrical conductivity of the films mainly affected by oxygen flow rate since density of states (DOS) was critically dependent on the oxygen flow rate. Considering oxygen flow rate, a direct link between the DOS and electrical properties of the films was established.
Keywords: DC magnetron sputtering method; CuO; Oxygen flow rate;

Display OmittedCharge localization effects and transport properties in dendritic interfaces are investigated in the framework of a coherent scattering formalism. Due to the large surface area, tree shaped interfaces enhance the overall efficiency of bulk heterojunction photovoltaic applications. The charge localization effects are analyzed for different tree shapes, band offset potentials and in the context of varying the thickness of the tree branches. Two types of localization are pointed out – on the tree branches or inbetween. The transfer characteristics are influenced by the band offsets and the energy of the charged particles. A detailed statistical analysis shows the correlation between the average transmission function and the surface area of the dendritic interface. The current study provides a framework for the characterization and optimization of dendritic interfaces.
Keywords: Dendritic interface; Localization; Scattering; Transport;

In the present work, a TiC/TiB2 composite coating was produced onto a TC2 Ti alloy by laser cladding with Ti/TiC/TiB2 powders. The surface microstructure, phase components and compositions were characterized with methods of optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffractometry (XRD), and energy dispersive spectrometry (EDS). The cladding layer is consisted of Ti, TiC and TiB2. And the surface microhardness was measured. After laser cladding, a maximum hardness of 1100 HV is achieved in the laser cladding surface layer, which is more three times higher than that of the TC2 substrate (∼300 HV). Due to the formation of TiC and TiB2 intermetallic compounds in the alloyed region and grain refinement, the microhardness of coating is higher than TC2 Ti alloy. In this paper, the corrosion property of matrix material and treated samples were both measured in NaCl (3.5 wt%) aqueous solution. From the result we can see that the laser cladding specimens’ corrosion property is clearly becoming better than that of the substrate.
Keywords: Laser cladding; TC2 Ti alloy; TiB2; Microhardness; Corrosion resistance;

The influence of ZrO2/20%Y2O3 and Al2O3 deposited coatings to the behavior of an aluminum alloy subjected to mechanical shock by G.L. Pintilei; V.I. Crismaru; M. Abrudeanu; C. Munteanu; D. Luca; B. Istrate (169-177).
Aluminum alloys are used in the aerospace industry due to their good mechanical properties and their low density compared with the density of steels. Usually the parts made of aluminum alloys contribute to the structural frame of aircrafts and they must withstand static and variable mechanical loads and also mechanical loads applied in a very short time which determine different phenomenon's in the material behavior then static or fatigue loads. This paper analysis the resilience of a 2024 aluminum alloy subjected to shock loads and the way how a coating can improve its behavior. For improving the behavior two coatings were considered: Al2O3 with 99.5% purity and ZrO2/20%Y2O3. The coatings were deposited on the base material by plasma spraying. The samples with and without coating were subject to mechanical shock to determine the resilience of the materials and the cracks propagation was investigated using SEM analysis. To highlight the physical phenomenon's that appear in the samples during the mechanical shock, explicit finite element analysis were done using Ansys 14.5 software.
Keywords: Charpy test; Finite elements analyses; ZrO2/20%Y2O3; Al2O3; AA2024;

The behavior of ZrO2/20%Y2O3 and Al2O3 coatings deposited on aluminum alloys at high temperature regime by G.L. Pintilei; V.I. Crismaru; M. Abrudeanu; C. Munteanu; E.R. Baciu; B. Istrate; N. Basescu (178-183).
Aluminum alloy present numerous advantages like lightness, high specific strength and diversity which recommend them to a high number of applications from different fields. In extreme environments the protection of aluminum alloys is difficult and requires a high number of requirements like high temperature resistance, thermal fatigue resistance, corrosion fatigue resistance and galvanic corrosion resistance. To obtain these characteristics coatings can be applied to the surfaces so they can enhance the mechanical and chemical properties of the parts. In this paper two coatings were considered for deposition on an AA2024 aluminum alloy, ZrO2/20%Y2O3 and Al2O3. To obtain a better adherence of the coating to the base material an additional bond layer of NiCr is used. Both the coatings and bond layer were deposited by atmospheric plasma spraying on the samples. The samples were subjected to a temperature of 500 °C and after that slowly cooled to room temperature. The samples were analyzed by electron microscopy and X-ray diffraction to determine the morphological and phase changes that occurred during the temperature exposure. To determine the stress level in the parts due to thermal expansion a finite element analysis was performed in the same conditions as the tests.
Keywords: ZrO2/20%Y2O3; Al2O3; AA2024; Finite elements analyses;

Detection of copper ions from aqueous solutions using layered double hydroxides thin films deposited by PLD by A. Vlad; R. Birjega; A. Matei; C. Luculescu; A. Nedelcea; M. Dinescu; R. Zavoianu; O.D. Pavel (184-188).
Layered double hydroxides (LDHs) thin films with Mg–Al were deposited using pulsed laser deposition (PLD) technique. We studied the ability of our films to detect copper ions in aqueous solutions. Copper is known to be a common pollutant in water, originating from urban and industrial waste. Clay minerals, including layered double hydroxides (LDHs), can reduce the toxicity of such wastes by adsorbing copper. We report on the uptake of copper ions from aqueous solution on LDH thin films obtained via PLD.The obtained thin films were characterized using X-ray Diffraction, Atomic Force Microscopy, and Scanning Electron Microscopy with Energy Dispersive X-ray analysis. The results in this study indicate that LDHs thin films obtained by PLD have potential as an efficient adsorbent for removing copper from aqueous solution.
Keywords: LDH thin films; Pulsed laser deposition; Copper metals uptake;