A Study on the Effect of Ambient Air Plasma Treatment on the Properties of Methylammonium Lead Halide Perovskite Films

Organic-inorganic halide perovskite materials are considered excellent active layers in the fabrication of highly efficient and low-cost photovoltaic devices. This contribution demonstrates that rapid and low-temperature air-plasma treatment of mixed organic-inorganic halide perovskite film is a promising technique, controlling its opto-electrical surface properties by changing the ratio of organic-to-inorganic components. Plasma treatment of perovskite films was performed with high power-density (25 kW/m2 and 100 W/cm3) diffuse coplanar surface barrier discharge (DCSBD) at 70 °C in ambient air. The results show that short plasma treatment time (1 s, 2 s, and 5 s) led to a relatively enlargement of grain size, however, longer plasma treatment time (10 s and 20 s) led to an etching of the surface. The band-gap energy of the perovskite films was related to the duration of plasma treatment; short periods (≤5 s) led to a widening of the band gap from ~1.66 to 1.73 eV, while longer exposure (>5 s) led to a narrowing of the band gap to approx. 1.63 eV and fast degradation of the film due to etching. Surface analysis demonstrated that the film became homogeneous, with highly oriented crystals, after short plasma treatment; however, prolonging the plasma treatment led to morphological disorders and partial etching of the surface. The plasma treatment approach presented herein addresses important challenges in current perovskite solar cells: tuning the optoelectronic properties and manufacturing homogeneous perovskite films

Large-area roll-to-roll atmospheric plasma treatment of nanocellulose transparent paper

Abstract Cellulose, as the most abundant polymer in the world, and recently nanocellulose, have emerged as sustainable, biodegradable and recyclable substrates for flexible and printed electronics in applications that require rapid roll-to-roll manufacturing. However, the wetting and printability of any material surface are linked to its surface energy. These may be modified by cleaning and activation of the surface, i.e. removal, formation or alteration of the adventitious or functional chemical groups on it. Recently, novel surface treatment techniques compatible with roll-to-roll manufacturing have attracted considerable attention on the part of researchers. In this contribution, we present atmospheric-pressure plasma generated by diffuse coplanar surface barrier discharge (DCSBD) for the surface treatment of nanocellulose transparent paper. The effect of ambient-air, low-temperature plasma on the surface of nanocellulose was investigated. Water contact angle measurements revealed increased hydrophilicity of the surface after short plasma treatment. X-ray photoelectron spectroscopy was utilized for chemical analysis of the surface of the nanocellulose. Plasma treatment led to a decrease in carbon concentration and a corresponding increase in oxygen concentration. Analysis of carbon peaks in the spectra revealed decreased C–C bonds and the formation of oxygen polar groups. The formation of polar groups was directly related to the increased hydrophilicity. Scanning electron microscopy was used to observe the morphological effects of plasma treatment on the nanocellulose surface. No damage to the nanocellulose fibres was observed after plasma treatment, which confirms that low-temperature plasma is suitable for large-area roll-to-roll treatment of nanocellulose

Conductive silver films on paper prepared by atmospheric pressure argon plasma conversion of silver nitrate

Abstract We present a novel approach for deposition of metallic silver films from silver nitrate (AgNO₃) ink. The conversion of AgNO₃ is induced by argon plasma of the diffuse coplanar surface barrier discharge (DCSBD) generated at atmospheric pressure. The macroscopically homogeneous and diffuse plasma of high power density allows fast reduction of AgNO₃ into conductive metallic silver within two minutes. The process is carried out at temperatures below 70 °C and without the need for a complex vacuum chamber and is therefore highly suitable for deposition onto temperature-sensitive materials. In our study we used paper prepared from nanocellulose fibres, which offers mechanical flexibility, translucency and recyclability while having lower surface roughness and enhanced mechanical properties and thermal stability compared to regular paper. As a figure of merit, the resistivity of prepared films was measured. The X-ray photoelectron spectroscopy was used to study the conversion of AgNO₃ into metallic silver. Scanning electron microscopy revealed the morphology of the surface of the films giving insight on the nucleation and the growth process. The silver films prepared according to our methodology are an attractive possibility for applications in sensing devices or as conductive lines and other features in flexible electronics

High-performance perovskite solar cells using the graphene quantum dot-modified SnO2/ZnO photoelectrode

WOS:000708176800011Regardless of the excellent improvement in the assembling of perovskite solar cells (PSCs), the photon harvesting performance of these devices is inadequate through the disproportionate recombination of generated charge carriers. The improvement of the charge carrier mobility can significantly reduce the recombination and help the perovskite devices reach the theoretical power conversion efficiency (PCE). The modification of charge selective contacts is one of the most effective approaches for reducing the carrier recombination. Herein, we introduce a facile and effective doping engineering approach based on graphene quantum dots (GQDs) for the modification of the SnO2/ZnO bilayer electron transport layer (ETL). A comparative study of perovskite films deposited on SnO2/ZnO layers with altered concentrations of GQDs was employed to significantly enhance the opto-electronic properties. The integration of GQDs into the ETL indicates a potential for improving the charge carrier transporting in PSCs. Overall, the PSC using the 4% GQD-modified ETL yields a PCE of 19.81% with a striking open-circuit voltage (V-OC) of 1.17 V. Besides, 4% GQD-modified ETL-based devices enhance the long-term ambient and thermal stability

Electrochemical and in vitro biological behaviors of a Ti-Mo-Fe alloy specifically designed for stent applications

There is a deep interest in developing new Ni-free Ti-based alloys to replace 316 L stainless steel and Co-Cr alloys for endovascular stent application, mainly because the release of Ni can generate toxicity and allergenicity. Interactions of Ti alloy biomaterials with bone cells and tissues have been widely investigated and reported, while interactions with vascular cells and tissues, such as endothelial cells (ECs) and smooth muscle cells (SMCs), are scarce. Therefore, this study focused on the relationship among the surface finishing features, corrosion behavior and in vitro biological performances regarding human ECs, SMCs and blood of a newly developed Ti-8Mo-2Fe (TMF) alloy, specifically designed for balloon-expandable stent applications. The alloy performances were compared to those of 316 L and pure Ti, prepared with the same surface finishing techniques, which are mechanical polishing and electropolishing. Surface properties were investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), contact angle (CA) and x-ray photoelectron spectroscopy (XPS). The corrosion behavior was assessed with potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) tests in phosphate buffered saline (PBS) solution. No significant differences were observed regarding the corrosion rate measured with PDP analyses, which was of the order of 2 × 10−4 mm/y for all the studied materials. Moreover, similarly to pure Ti, TMF exhibited an advantage over 316 L for biomedical applications, namely remarkable resistance to pitting corrosion up to high potentials. The results evidenced a good cytocompatibility and hemocompatibility, making this group of alloy a potential candidate for cardiovascular implants. In fact, both ECs and SMCs proliferated on TMF surfaces showing a 7-day viability similar to that of pure Ti. Regarding hemocompatibility, TMF did not cause hemolysis, and blood coagulation was delayed on its surface in comparison to pure Ti. When compared to 316 L, TMF showed similar hemocompatibility

Characterization of a Magnesium Fluoride Conversion Coating on Mg-2Y-1Mn-1Zn Screws for Biomedical Applications

MgF2-coated screws made of a Mg-2Y-1Mn-1Zn alloy, called NOVAMag® fixation screws (biotrics bioimplants AG), were tested in vitro for potential applications as biodegradable implants, and showed a controlled corrosion rate compared to non-coated screws. While previous studies regarding coated Mg-alloys have been carried out on flat sample surfaces, the present work focused on functional materials and final biomedical products. The substrates under study had a complex 3D geometry and a nearly cylindrical-shaped shaft. The corrosion rate of the samples was investigated using an electrochemical setup, especially adjusted to evaluate these types of samples, and thus, helped to improve an already patented coating process. A MgF2/MgO coating in the µm-range was characterized for the first time using complementary techniques. The coated screws revealed a smoother surface than the non-coated ones. Although the cross-section analysis revealed some fissures in the coating structure, the electrochemical studies using Hanks’ salt solution demonstrated the effective role of MgF2 in retarding the alloy degradation during the initial stages of corrosion up to 24 h. The values of polarization resistance (Rp) of the coated samples extrapolated from the Nyquist plots were significantly higher than those of the non-coated samples, and impedance increased significantly over time. After 1200 s exposure, the Rp values were 1323 ± 144 Ω.cm2 for the coated samples and 1036 ± 198 Ω.cm2 for the non-coated samples, thus confirming a significant decrease in the degradation rate due to the MgF2 layer. The corrosion rates varied from 0.49 mm/y, at the beginning of the experiment, to 0.26 mm/y after 1200 s, and decreased further to 0.01 mm/y after 24 h. These results demonstrated the effectiveness of the applied MgF2 film in slowing down the corrosion of the bulk material, allowing the magnesium-alloy screws to be competitive as dental and orthopedic solutions for the biodegradable implants market

Study on the mechanical properties of magnetron sputtered W-based degradable radiopaque coatings for tiny biodegradable metallic endovascular implants

Bioresorbable metals constitutes a new class of biomaterials, and raised increasing interest over the last decade to fabricate tiny endovascular metallic implants. However, the lack of visibility especially when tiny bioresorbable implants are implanted is a major concern in clinics, affecting their implantation and limiting their clinical follow-up. Among the radiopaque elements, tungsten (W) is a promising candidate to be used as a radiopaque resorbable agent due to its high radiopacity and high corrosion rate. Therefore, this research aimed to produce a W-based radiopaque coatings providing mechanical properties close to Fe–Mn–C alloys. The mechanical mismatch between the substrate and the coating was also investigated and optimized. A magnetron sputtering was used to deposit Fe–Mn–C–W coatings (A and B) with 38 and 79 at. % of W, respectively, and at different deposition temperatures, i.e. 25, 300 and 600 °C. TEM and XRD analyses evidenced that coatings A, ∼38 at.% of W, at all deposition temperature, exhibited an amorphous structure. The amorphous structure of coating A was composed of a matrix of Fe with tiny α-W nanocrystals embedded, while coating B (W: 73–79 at. %) displayed the presence of a pyramidal-like β-W phase, observed only at low deposition temperature (25 °C). The presence of this β-W phase significantly increased the coating roughness, and increased its corrosion rate. Mechanical properties, assessed by nanoindentation tests, confirmed that samples containing β-W exhibited higher elastic modulus and hardness when compared to other samples. X-ray studies by CT scanning demonstrated that 1 μm of coatings A and B deposited at high temperature could increase significantly the radiopacity of the samples by 109% and 62%, respectively. On the basis of all these results, the coating A deposited at 600 °C appears to be the most promising coating for X-ray enhancement as well as providing the mechanical properties matching those of Fe–Mn alloy