National Institute Of Materials Physics - Romania

Due to the emergence of antibiotic-resistant pathogens, the need to find new, efficient antimicrobial agents is rapidly increasing. Therefore, in this study, we report the development of new biocomposites based on zinc-doped hydroxyapatite/chitosan enriched with essential oil of Artemisia dracunculus L. with good antimicrobial activity. Techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX) and Fourier transform infrared spectroscopy (FTIR) were used in order to evaluate their physico-chemical properties. Our studies revealed that biocomposite materials with nanometric dimension and homogeneous composition could be obtained through an economic and cost-effective synthesis method. The biological assays demonstrated that ZnHA (zinc-doped hydroxyapatite), ZnHACh (zinc-doped hydroxyapatite/chitosan) and ZnHAChT (zinc-doped hydroxyapatite/chitosan enriched with essential oil of Artemisia dracunculus L.) did not exhibit a toxic effect on the cell viability and proliferation of the primary osteoblast culture (hFOB 1.19). Moreover, the cytotoxic assay also highlighted that the cell morphology of the hFOB 1.19 was not altered in the presence of ZnHA, ZnHACh or ZnHAChT. Furthermore, the in vitro antimicrobial studies emphasized that the samples exhibited strong antimicrobial properties against Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 25923 and Candida albicans ATCC 10231 microbial strains. These results are encouraging for the following development of new composite materials with enhanced biological properties that could promote the osteogenic process of bone healing and also exhibit good antimicrobial properties.

The diffusion of iodide defects has been considered the most important degradation mechanism of methylammonium lead iodide (MAPI) in solar cells. The present study demonstrates the importance of the pressure inside this material on the dynamics of iodide defects, using molecular dynamics simulations. It is known that the diffusion coefficient of an iodide vacancy is an order of magnitude higher than that of interstitial iodide. We show that this difference systematically increases with increased tensile strain and that both diffusion coefficients tend to zero when a compressive strain is applied. This result suggests that compression of the MAPI can be a good solution to reduce its degradation rate. Besides, the statistical aspect of deriving the diffusion coefficient from the mean squared displacement (MSD) is discussed in terms of the initial conditions (positions and velocities) of the atoms and the simulation time, considering different seeds of the pseudorandom number generator used in the simulations performed with the LAMMPS software.

Active and stable materials that utilize solar radiation for promoting different reactions are critical for emerging technologies. Two of the most common polymeric carbon nitrides were prepared by the thermal polycondensation of melamine. The scope of this work is to investigate possible structural degradation before and after photoelectrochemical testing. The materials were characterized using synchrotron radiation and lab-based techniques, and subsequently degraded photoelectrochemically, followed by post-mortem analysis. Post-mortem investigations reveal: (1) carbon atoms bonded to three nitrogen atoms change into carbon atoms bonded to two nitrogen atoms and (2) the presence of methylene terminals in post-mortem materials. The study concludes that polymeric carbon nitrides are susceptible to photoelectrochemical degradation via ring opening.

In the view of the advantages of using P, N, Si and graphene oxide (GO) for the development of flame retardants materials, a multi-structure synergistic composite was synthesized by grafting a novel nitrogen-containing polyhedral oligomeric silsesquioxane (HAK) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) on the surface of GO nanosheet. In the first step, 2-hydroxyethyl acrylate was selectively reacted, and then, HAK was synthetized by the condensation of the aza-Michael addition product with 3-(methacryloyloxy)propyltrimethoxysilane. Finally, the GO obtained by an innovative variant of Marcano-Tour improved exfoliation method was functionalized, first with DOPO, and then with HAK. The structural, morphological and surface properties of GO and GO-DOPO-HAK were investigated by means of XRD, TEM-EDX, FT-IR, Raman, zeta potential and XPS techniques, and it was evidenced the functionalization of GO with DOPO, and then with HAK. The performed microscale combustion calorimetry (MCC) and TG measurements indicated a great potential of the GO-DOPO-HAK as flame retardant material as the obtained residual weight for this sample was found to be the highest one compared to the other investigated samples. MCC analyses further revealed a major decrease in heat release capacity (HRC) and a significant increase in char yield, results that confirm the great potential of GO-DOPO-HAK as flame retardancy material. [GRAPHICS] .

Novel biomaterials with promising bone regeneration potential, derived from rich, renewable, and cheap sources, are reported. Thus, thin films were synthesized from marine-derived (i.e., from fish bones and seashells) hydroxyapatite (MdHA) by pulsed laser deposition (PLD) technique. Besides the physical-chemical and mechanical investigations, the deposited thin films were also evaluated in vitro using dedicated cytocompatibility and antimicrobial assays. The morphological examination of MdHA films revealed the fabrication of rough surfaces, which were shown to favor good cell adhesion, and furthermore could foster the in-situ anchorage of implants. The strong hydrophilic behavior of the thin films was evidenced by contact angle (CA) measurements, with values in the range of 15-18 degrees. The inferred bonding strength adherence values were superior (i.e., similar to 49 MPa) to the threshold established by ISO regulation for high-load implant coatings. After immersion in biological fluids, the growth of an apatite-based layer was noted, which indicated the good mineralization capacity of the MdHA films. All PLD films exhibited low cytotoxicity on osteoblast, fibroblast, and epithelial cells. Moreover, a persistent protective effect against bacterial and fungal colonization (i.e., 1- to 3-log reduction of E. coli, E. faecalis, and C. albicans growth) was demonstrated after 48 h of incubation, with respect to the Ti control. The good cytocompatibility and effective antimicrobial activity, along with the reduced fabrication costs from sustainable sources (available in large quantities), should, therefore, recommend the MdHA materials proposed herein as innovative and viable solutions for the development of novel coatings for metallic dental implants.

Sub-stochiometric nickel oxide (NiOx) films were investigated as a hole selective contact option in silicon (Si) heterojunction solar cells. Numerical simulations were carried out to evaluate the impacts of the NiOx electronic properties variations and the NiOx/Si interface defect density (D-it) on device performance. Simulation data suggest that the best performance is achievable for wide bandgaps (E-g) and corresponding high valence band edge (E-VB) positions in the NiOx films. Overall, in simulations, the performance remains practically unchanged for the nickel vacancy concentrations [V-Ni] = 10(17)-10(21 )cm(-3), assuming high E-VB and low D-it. The experimental data measured using NiOx films prepared by radio-frequency magnetron sputtering reveal that the increase in [V-Ni] lifts the conductivity, concurrently decreasing E-g and E-VB. As a result, we concluded that the performance of the fabricated sputtered NiOx/Si heterojunction solar cell is limited by high D-it as well as narrow E-g and low E-VB.

Sodium hexatitanate (Na2Ti6O13) nanoparticles have been synthesized by the hydrothermal method with microwave and conven-tional heating, after which their photocatalytic properties toward an azo dye pollutant degradation have been investigated. Insights into the dynamics and reactivity of the species involved in the photocatalytic mechanism of the (Na2Ti6O13) samples were precisely investigated, for the first time, by X-band electron paramagnetic resonance (EPR) spectroscopy under different experimental conditions. X-ray diffraction structural analysis revealed that all samples crystallized in a monoclinic C2/m structure, with different short-range structural order according to the employed heating, as indicated by Raman. Field-emission scanning electron microscopy and transmission electron microscopy results revealed the formation of rod-and fiber-like nanoparticles with different diameters and lengths. EPR measurements indicated the presence of different Ti3+ point defects and F centers in the samples. X-ray photoelectron spectroscopy analysis proved the presence of oxygen-related defects, but no Ti3+ was detected on the surface. Spin trapping experiments monitored the generation of hydroxyl (OH center dot) radicals over UV-irradiation time. Various parameters contribute to the photocatalytic activity of the samples; however, the type of defect and particle morphology appeared as key factors for enhanced efficiency. Our study provides significant information about paramagnetic defects in Na2Ti6O13 materials and their role in photocatalysis to design other Ti-based photocatalysts.

Nonmagnetic chiral crystals are a new class of systems hosting Kramers-Weyl Fermions, arising from the combination of structural chirality, spin- orbit coupling (SOC), and time-reversal symmetry. These materials exhibit nontrivial Fermi surfaces with SOC-induced Chern gaps over a wide energy range, leading to exotic transport and optical properties. In this study, we investigate the electronic structure and transport properties of CdAs2, a newly reported chiral material. We use synchrotron-based angle-resolved photoelectron spectroscopy (ARPES) and density functional theory (DFT) to determine the Fermiology of the (110)-terminated CdAs2 crystal. Our results, together with complementary magnetotransport measurements, suggest that CdAs2 is a promising candidate for novel topological properties protected by the structural chirality of the system. Our work sheds light on the details of the Fermi surface and topology for this chiral quantum material, providing useful information for engineering novel spintronic and optical devices based on quantized chiral charges, negative longitudinal magnetoresistance, and nontrivial Chern numbers.

The development of new thin-film cathodes triggered a recent research interest in energy storage applications. Over the past years, vanadium oxides have been extensively explored as promising electrodes for batteries owing to their rich valence states and remarkable electrochemical properties. Herein, we report on the synthe-sis of undoped and Sn doped V2O3 thin-films on graphene (G)/Al foil by pulsed laser deposition followed by rapid thermal annealing in N2 at low temperature (similar to 430 degrees C). The obtaining V2O3 phase on graphene/Al foil (G/Al) has been confirmed by X-ray diffraction and Raman and X-ray photoelectron spectroscopy analyses. The synthesized vanadium oxide films were tested as cathodes in coin cells. The electrochemical properties have been systematically investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge discharge (GCD) measurements. A superior electrochemical performance was observed for the V2O3 on G/Al structures, with an initial capacity of around 300 mAh g-1, with respect to the bare G/Al electrode. The use of the Sn-doped (5 mol%) V2O3 thin-films improved slightly the initial capac-ity up to a value of ca. 311 mAh g-1. Both V2O3/G/Al and Sn-doped V2O3/G/Al exhibited excellent cycling performances after 40 cycles with a capacity maintenance at a C-rate C/20 of 317 mAh g-1. Long-term cycling test (up to 200 cycles) showed that the Sn doping could be an excellent strategy to improve the stability of the electrodes, which yielded a capacity loss of only 0.128% per cycle. Possible mechanisms are presented and dis-cussed. This work could serve as point of reference for future developments in the field of batteries employing vanadium oxide-based thin-films deposited by physical vapor deposition techniques.

Transparent conductive electrodes (TCE) obtained by the electrospinning method and gold covered were used as cathodes in the organic light-emitting diodes (OLEDs) to create double side-emission. The electro-active nanofibers of poly(methyl methacrylate) (PMMA) with diameters in the range of several hundreds of nanometers, were prepared through the electrospinning method. The nanofibers were coated with gold by sputtering deposition, maintaining optimal transparency and conductivity to increase the electroluminescence on both electrodes. Optical, structural, and electrical measurements of the as-prepared transparent electrodes have shown good transparency and higher electrical conductivity. In this study, two types of OLEDs consisting of indium tin oxide (ITO)/ poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT-PSS)/ Ir(III) complex (8-hydroxyquinolinat bis(2-phenylpyridyl) iridium-IrQ(ppy)(2) 20 wt% embedded in N, N '-Dicarbazolyl-4,4 '-biphenyl (CBP) sandwich structure and either gold-covered PMMA electrospun nanoweb (OLED with electrospun cathode) were fabricated together with a similar structure containing thin film gold cathodes (OLED with thin film cathode). The luminance-current-voltage characteristics, the capacitance-voltage, and the electroluminescence properties of these OLEDs were investigated.