National Institute Of Materials Physics - Romania

The corrosion protection property of three Brij-type surfactants, namely, Brij 35, Brij 56 and Brij 58P, was considered on OLC 45 carbon steel in a 0.5 M H2SO4 medium. The efficacy for these organic compounds was examined using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) methods, scanning electron microscopy (SEM) procedures, and Fourier transform infrared (FT-IR) spectroscopy. We hypothesized that these surfactants hinder the corrosion for OLC 45 samples through a protecting mechanism owing to the adsorption of organic molecules that form an inhibitive film or through the formation of complex oxides. These surfactants exhibited an appreciable protective effect against OLC 45 corrosion, operating as mixed inhibitors, as could be demonstrated by their influence on the electrochemical characteristics of the metallic substrates. The adsorption of surfactants over the substrates zone conformed to the representation of the Langmuir isotherm. The effect of temperature on the electrochemical comportment of the OLC 45 specimens in H2SO4 without and with Brij at 800 ppm was examined in the temperature interval of 293 to 333 K. The negative estimate of thermodynamic attributed as Gibbs free energy of adsorption presented the spontaneity of the adsorption activity. The investigation with FT-IR and SEM established the adsorption of Brij and the constitution of the corrosive components on the OLC 45 surface. Electrochemical determinations of these surfactants indicated its anticorrosion inhibition performance and the highest inhibition of 96% was reached when the Brij 35 concentration was at 800 or 1000 ppm, while for Brij 56 and Brij 58P, the highest inhibition was obtained when their concentrations were 500, 800, or 1000 ppm.

In the quest for advanced materials suitable for next-generation electronic and optoelectronic applications, tungsten disulfide (WS2) ultrathin films have emerged as promising candidates due to their unique properties. However, obtaining WS2 directly on the desired substrate, eliminating the need for transfer, which produces additional defects, poses many challenges. This paper aims to explore the synthesis of WS2 ultrathin films via physical vapor deposition (PVD) followed by sulfurization in a confined space, addressing the challenge of film formation for practical applications. Precursor layers of tungsten and WS2 were deposited by RF magnetron sputtering. Subsequent sulfurization treatments were conducted in a small, closed, graphite box to produce WS2 films. The physical and chemical properties of these precursor and sulfurized layers were thoroughly characterized using techniques such as X-ray reflectometry (XRR), X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The findings reveal notable distinctions in film thickness, structural orientation, and chemical composition, attributable to the different precursor used. Particularly, the sulfurized layers from the tungsten precursor exhibited a preferred orientation of WS2 crystallites with their (00L) planes parallel to the substrate surface, along with a deviation from parallelism in a small angular range. This study highlights the necessity of precise control over deposition and sulfurization parameters to tailor the properties of WS2 films for specific technological applications.

Selective growth of 2D MoS2 layers on patterned substrates is highly desired for easy fabrication of devices. Selectively grown 2D MoS2 on Mo patterned substrates for the formation of intimate metallic contact was obtained by a Mo-CVD method in which MoO2 from an oxidized Mo pattern and S powder are the growth precursors. Mo films were deposited by magnetron sputtering on SiO2(300 nm)/c-Si substrates and patterned by photolithography techniques for obtaining Mo strips and finger contact structures, with the gap between the strips and finger varied from 5 to 20 mu m. The filling of the gap by selectively grown atomically thin MoS2 plates of 1-2 monolayers (MLs) was demonstrated by scanning electron microscopy and atomic force microscopy imaging. Field effect devices for the characterization of the photosensitivity of selectively grown MoS2 have been fabricated from finger contact structures. The dark current is drastically reduced from 10(-9) to 10(-13)-10(-14) A by varying the gate voltage from +7 to -7 V, showing the n-type semiconductor behavior of the selectively grown 2D MoS2. High photosensitivity of 10(5) (%) was obtained for 4.5 x 10(-4) mW/cm(2) at 650 nm wavelength illumination. The spectral responsivity reaches values of 15-25 A/W at 600 nm wavelength and shows an energy onset of 1.72-1.77 eV corresponding to about 2 ML MoS2. The carrier-trapping effect responsible for the slow part of the device response can be caused by structural defects and also by adsorbed molecules like in gas sensors.

Bioactive glasses (BGs) are known for their selective ability to (i) form a mechanically strong interfacial bond with hard (bone) or soft tissues (gingivae or cartilages) (i.e., silica-, silica-phosphate-, phosphate-, boratephosphate-, or silica-phosphate-borate-based BGs); or (ii) serve as reservoirs for fast-release of therapeutic (osteogenic, angiogenic, anticarcinogenic, or antimicrobial) ions (i.e., phosphate-based BGs and mesoporous BGs). The strength of the bone bond yielded by the osteoproductive-capable BGs is generally equivalent to, or higher than the bone strength. The resorbability of phosphate-based BG is dependent on the content of network formers and cross-linkers. All BGs elicit excellent biochemical compatibility. However, their fracture toughness is typically less than and the elastic modulus is greater than those of bone, indicating that most BGs have suboptimal biomechanical compatibility when used in load-bearing applications. One promising approach to overcome this problem is the development of BGs in coating form, applied to the surface of load-bearing endosseous implants. This work critically assesses BG thin-layers fabricated by the radio-frequency magnetron sputtering method, an industry-ready large-scale physical vapour deposition technology. It is demonstrated that, despite the relative lack of attention paid to this technology, it enables the development of unique BG coatings with efficacious therapeutic capabilities. Here, we present an overview of the most relevant developments achieved thus far, along with the remarkable advantages, drawbacks to overcome, and future perspectives with the intention of highlighting the vast possibilities of this specific field of research.

Synapses play a vital role in information processing, learning, and memory formation in the brain. By emulating the behavior of biological synapses, electronic synaptic devices hold the promise of enabling high-performance, energy-efficient, and scalable neuromorphic computing. Ferroelectric memristive devices integrate the characteristics of both ferroelectric and memristive materials and present a far-reaching potential as artificial synapses. Here, it is reported on a new ferroelectric device on silicon, a field-effect memristor, consisting of an epitaxial ultrathin ferroelectric Hf(0.5)Z(r0.5)O(2) film sandwiched between an epitaxial highly doped oxide semiconductor SrTiO3-delta and a top metal. Upon a low voltage of less than 2 V, the field-effect modulation in the semiconductor enables to access multiple states. The device works in a large time domain ranging from milliseconds down to tens of nanoseconds. By gradually switching the polarization by identical pulses, the ferroelectric diode devices can dynamically adjust the synaptic strength to mimic short- and long-term memory plasticity. Ionic contributions due to redox processes in the oxide semiconductor beneficially influence the device operation and retention.

Dense samples of MgB2, with a relative density of 98.3-99.1 %, were prepared by ex-situ spark plasma sintering using a raw powder supplied by Alfa Aesar. Samples were added with Ge-based organometallics (repagermanium/RGe, propagermaniu/PGe, linear Ge-based organometallic/GeSP, and Na-doped octamer/8THGP-Na) for the starting composition (MgB2)(Ge-based organometallics)0.0014. Except for the 8THGP-Na, they have a similar chemical composition in respect to Ge and C, while the crystal structure differs. Below 20 K, all studied additions increased the critical current density, Jc, and the irreversibility field, Hirr. Samples added with GeSP and 8THGPNa have marginal differences regarding superconducting characteristics. The best Jc and Hirr are obtained for the sample added with RGe. This sample has the highest amount of carbon in the crystal lattice of MgB2. Results point out that there is a complex influence of the additive on carbon behaviour. Although in general it is accepted that a higher amount of carbon produces higher Jc and Hirr, a comparison with the literature indicates that C-rich raw MgB2 powders (e.g. the C-enhanced MgB2 nanopowder produced by Pavezyum) are not suitable to promote strong superconductivity enhancement in the samples added with indicated organometallics, and the origin, states, and evolution of carbon should to be carefully assessed.

The effect of the annealing temperature on 1% nitrogen-doped WO3 materials was studied, which were then used as electrode materials for high-performance supercapacitor (SC) devices. The supercapacitive performance of the proposed materials was strongly influenced by the doping element and the annealing temperature by directly changing the defect structure of the host material. The 1% N-doped WO3 materials annealed at different temperatures were thoroughly characterized through various characterization techniques, including electron paramagnetic resonance and photoluminescence spectroscopy, giving insight into the effect of N-doping on the defect structure and optical properties of WO3. When the WO3:N materials were used as electrode material in symmetric SCs, the doping element and the annealing temperature improved the electrochemical performance. No booster materials (such as carbon black) were used in the symmetric SC designs, showing increased specific capacitance (102 F/g) and energy density (14.6 W h/kg) values.

Undoped and Sm3+doped 45P2O5-45Na2O-2Al2O3-8BaO glasses were synthesized by the melt-quenching technique. The glass structure and luminescence properties were investigated by using Raman spectroscopy, scanning electron microscopy (SEM), spectroscopic ellipsometry, Judd-Ofelt theory and photoluminescence. Electron microscopy showed the homogeneity of samples. Raman spectroscopy revealed that the overall struc-ture of the glass was unaffected by the doping of Sm3+ and ellipsometry was used to measure the optical constants. Judd-Ofelt (JO) analysis was performed on the absorption bands of Sm3+ (4f5) and the three phenomenological parameters (omega 2, omega 4, and omega 6) were computed and then used to determine radiative properties such as the radiative transition probability (Ar), the fluorescent branching ratio (beta r), the stimulated emission cross-section (sigma e) and the radiative lifetime (tau rad). Photoluminescence (PL) spectrum showed the typical four transitions of Sm3+ at wavelengths of 564, 600, 645 and 703 nm corresponding to 4G5/2 -> 6H5/2, 6H7/2, 6H9/2 and 6H11/2, respectively. The spectroscopic quality factors omega 4/omega 6, the predicted lifetime (tau rad) calculated using the JO method and the experimentally lifetime (tau exp) for the 4G5/2level were calculated and discussed. The glass color purity is as high as 98%, which makes it a potential candidate for laser emission.

In this work, electrochemical deposition techniques (galvanostatic and potentiostatic) were used to obtain coatings of a new composite polymer, 3-methylpyrrole-sodium dodecyl sulfate/poly 2-methythiophene (P3MPY-SDS/P2MT), on cobalt-based alloy samples for anti-corrosion safety. The use of sodium dodecyl sulfate as a dopant ion in electrosynthesis can have a relevant effect on the anticorrosive property of the composite polymer layer by blocking the entry of corrosive ions. The cobalt alloy specimen had an important impact on the electrochemical performance of the composite coating and this together with the presence of the polymeric layer was achieved by simultaneously constitution of a complex oxides film and polymeric layers. The polymeric coatings were analyzed using scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, and cyclic voltammetry (CV) methods. The corrosion protection of the P3MPY-SDS/P2MT-covered cobalt-based alloy was explored using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization procedures in a 1 M HCl solution. The corrosion speed of the P3MPY-SDS/P2MT-covered cobalt-based alloy was observed to be similar to 10 times less than an uncovered specimen, and the effectiveness of the composite layers of this coating is greater than 91%. This superior efficaciousness was obtained by the electropolymerization of P3MPY-SDS/P2MT at current densities of 1 mA/cm(2) and 0.5 mA/cm(2), applied potentials of 0.9 V and 1.0 V, and a molar ratio of 5:1. Corrosion test results indicate that the P3MPY-SDS/P2MT coatings provide a good result: protection against the corrosion of a cobalt-based alloy in aggressive solutions.

In this paper, graphene was obtained on a copper substrate using the CVD method, and then it was transferred to various substrates such as glass and SiO2/Si patterned with metallic interdigitated electrodes. The graphene thus obtained was characterized using Raman spectroscopy, scanning electron microscopy (SEM), current-voltage measurements, and electrochemical methods, in order to be used for sensing applications.