National Institute Of Materials Physics - Romania

In this work, we investigated the influence of reduced graphene oxide (RGO) on the electrical performances of ZnO/Ag multilayer transparent conductive electrodes. RGO flakes were successfully laser transferred by matrix assisted pulsed laser evaporation (MAPLE) using frozen targets obtained from suspensions of commercially chemically RGO powder dispersed in dimethyl sulfoxide (DMSO). The main deposition parameters such as RGO concentration, laser fluence, number of the laser pulses and deposition pressure were varied to identify the optimal morphological and optical characteristics. The laser transfer conditions for the RGO structures with the best transmittance were further employed in preparation of RGO/Ag/ZnO multilayer transparent conductive electrodes (MTCE). Thus, the MAPLE deposited RGO structures were covered with metal (Ag) by vacuum thermal evaporation (VTE) and subsequently with metal oxide (ZnO) by radio frequency magnetron sputtering (RF-MS). In comparison to the optical and electrical properties of a ZnO/Ag/ZnO reference structure, the results emphasize that the RGO/Ag/ZnO are featured by a similar transmittance (similar to 82-85 %) and improved sheet resistance (similar to 10.6 Omega/square, meaning up to 2-fold smaller).

Magnesium-doped hydroxyapatite/chitosan composite coatings produced by the radio-frequency magnetron sputtering technique were exposed to 5 MeV electron beams of 8 and 30 Gy radiation doses in a linear electron accelerator. The surfaces of unirradiated layers are smooth, while the irradiated ones exhibit nano-structures with sizes that increase from 60 nm at a 8 Gy dose to 200 nm at a 30 Gy dose. Young's modulus and the stiffness of the layers decrease from 58.9 GPa and 10 mu N/nm to 5 GPa and 2.2 mu N/nm, respectively, when the radiation doses are increased from 0 to 30 Gy. These data suggest the diminishing of the contribution of the chitosan to the elasticity of the magnesium-doped hydroxyapatite/chitosan composite layers after electron beam irradiation. The biological capabilities of the coatings were assessed before and after their immersion in RPMI-1640 cell culture medium for 7 and 14 days, respectively, and further cultured with a MG63 cell line (ATCC CRL1427) in Dulbecco's Modified Eagle Medium supplemented with fetal bovine serum, penicillin-streptomycin, and L-glutamine. Thus, 1 mu m spherical structures were developed on the surfaces of the layers exposed to a 30 Gy radiation dose and immersed for 14 days in the RPMI-1640 biological medium. The molecular structures of all the RPMI-1640 immersed samples were modified by the growth of a carbonated hydroxyapatite layer characterized by a B-type substitution, as Fourier Transform Infrared Spectroscopy revealed. The biological assay proved the increased biocompatibility of the layers kept in RPMI-1640 medium and enhanced MG63 cell attachment and proliferation. Atomic force microscopy analysis indicated the elongated fibroblastic cell morphology of MG63 cells with minor alteration at 30 Gy irradiation doses as a result of layer biocompatibility modifications.

In the last decade, it has been observed that the field of biomaterials has gained the attention of the researchers. This study presents the physicochemical and biological properties of coatings based on chromium-doped hydroxyapatite (CrHAp) and chromium-doped hydroxyapatite enriched with amoxicillin (CrHApAx). The coatings were obtained for the first time using the dip coating technique, beginning from dense suspensions of CrHAp and CrHApAx. The obtained layers were then analyzed by various methods in order to have a comprehensive overview of their physicochemical properties. Stability studies performed using ultrasound measurements showed that the CrHAp suspension has very good stability (S = 6.8610-6 s-1) compared to double-distilled water. The CrHApAx suspension (S = 0.00025 s-1) shows good but weaker stability compared to that of the CrHAp suspension. Following XRD studies, a single hydroxyapatite-specific phase was observed in the CrHAp sample, while in the case of the CrHApAx sample, an amoxicillin-specific peak was also observed. The AFM results showed that the CrHAp coatings had a surface topography of a homogenous and uniform layer, with no significant cracks and fissures, while the CrHApAx coatings exhibited a surface morphology of homogenous layers formed of particles conglomerates. The biocompatibility of CrHAp and CrHApAx coatings was assessed using the MG63 cell line. The cytotoxicity of the coatings was evaluated by measuring cell viability with the aid of an MTT assay after 24, 48, and 72 h of incubation with the CrHAp and CrHApAx coatings. The results demonstrated that both CrHAp and CrHApAx coatings exhibited good biocompatibility for all the tested time intervals. The in vitro antibacterial activity of the coatings was also assessed against Pseudomonas aeruginosa 27853 ATCC (P. aeruginosa) bacterial cells. The potential of P. aeruginosa bacterial cells to adhere and develop on the surfaces of CrHAp and CrHApAx coatings was also investigated using AFM analysis. The findings of the biological assays suggest that CrHAp and CrHApAx coatings could be considered as promising candidates for biomedical applications, including the development of novel antimicrobial materials.

In this work, we report for the first time the development and complex characterization of new bioceramics based on hydroxyapatite (HAp, Ca10(PO4)6(OH)2). On the other hand, the lyophilization process was used for the first time in this research. The samples were obtained by a modified coprecipitation method and were dried by lyophilization (lyophilized hydroxyapatite (HApLF) and lyophilized zinc-doped hydroxyapatite (5ZnHApLF)). Valuable information about the HApLF and 5ZnHApLF stability was obtained through nondestructive ultrasound measurements. The X-ray diffraction (XRD) studies revealed the phase and the effects of the incorporation of Zn ions into the HAp structure. The chemical composition of the samples was evaluated by energy dispersive X-ray analysis (EDS) and X-ray photoelectron spectroscopy (XPS). Information about the functional groups present in the HApLF and 5ZnHApLF was obtained using Fourier Transform Infrared Spectroscopy (FTIR) studies. The morphology of HApLF and 5ZnHApLF pellets was observed by scanning electron microscopy (SEM). The surface topography of HApLF and 5ZnHApLF pellets was studied with the aid of atomic force microscopy (AFM). Details regarding the roughness of the samples were also obtained using AFM topographies and SEM images. A complementary study was also carried out on a larger analysis surface using a Scanning Acoustic Microscope (SAM). The SAM was used for the first time to analyze the surface of HAp and 5ZnHAp pellets. The biological properties of the HApLF and 5ZnHApLF pellets was investigated with the aid of MG63 and human gingival fibroblasts (HGF-1) cell lines. The results of the cell viability assay highlighted that both the HApLF and 5ZnHApLF pellets exhibited good biological activity. Moreover, SEM and AFM studies were conducted in order to emphasize the development of MG63 and HGF-1 cells on the pellet's surface. Both SEM and AFM images depicted that the pellets' surface favored the cell attachment and development of MG63 and HGF-1 cells. Furthermore, the antimicrobial properties of the HApLF and 5ZnHApLF were evaluated against Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 25923, and Candida albicans ATCC 10231. The results of the antimicrobial assays highlighted that the 5ZnHApLF exhibited a strong antimicrobial activity against the tested microbial strains. The results of the biological assays suggested that the samples show great potential for being used in the development of novel materials for biomedical applications.

When used as the active layers-either as a light absorber in photovoltaic devices or as an electroluminescent material in light-emitting devices-lead-free perovskites significantly impact the performance of optoelectronic devices. This study focuses on antimony-based perovskites, which are promising for lighting applications. These types of perovskites enable the formation of self-trapped excitons (STEs) with higher dissociation energy than lead-based perovskites, which generate excitons with lower dissociation energy. The (CH3NH3)3Sb2I9 crystals are synthesized using two methods, resulting in distinct spatial configurations - dimer and dimer/layered mixtures, each exhibiting unique structural and spectroscopic properties, as revealed by comprehensive multi-parametric complementary analyses. Their emissive properties underscore the efficiency of the STE photoluminescence, driven by electron-phonon interactions and influenced by Sb-Sb distances in (CH3NH3)3Sb2I9 powder, whether dispersed in polymethyl-methacrylate or solution. The phase transition from monoclinic to hexagonal (dimer) and trigonal (layered) structures enabled the tuning of the optical properties in direct correlation with the structural and electrical features. The photoluminescence behavior of the STEs, analyzed in conjunction with the Raman spectroscopy, elucidates the dynamic process of the electron-phonon coupling effects in the dimer (face-capping Sb-I octahedra) and layered (corner-sharing Sb-I octahedra) crystallographic structures.

In this paper, we present the development of magnesium-doped hydroxyapatite in chitosan matrix (MHA_Ch) powder by an adapted coprecipitation method. The MHA_Ch powder was then deposited as thin layers by radio frequency magnetron sputtering. The MHA_Ch layers were exposed to various irradiation doses and immersed in Dulbecco's Modified Eagle's Medium (DMEM) for various time intervals. We report, for the first time, the effects of DMEM on irradiated layers of magnesium-doped hydroxyapatite in a chitosan matrix. The surface morphology of the layers before and after irradiation and immersion in DMEM was evaluated by SEM, AFM, and MM studies. Additionally, data about the functional groups present in the layers and the changes induced by exposure of the layers to irradiation and DMEM were obtained by FTIR studies. In vitro biological assays were conducted using an MG63 cell line (ATCC CRL1427). Our results suggest that the magnesium-doped hydroxyapatite in chitosan matrix layers may be suitable candidates for applications in the biomedical domain.

Herein we present a comparative study among different spray-coated nanometric mesoporous electron transporting layers (ETLs) in perovskite solar cells (PSC), namely m-TiO2, 2 , m-SnO2 2 and m-SnO2 2 quantum dots (mSnO2QDs). 2 QDs). The solutions used for deposition were prepared from commercial pastes and colloidal suspensions for m-TiO2 2 and m-SnO2. 2 . For m-SnO2QDs 2 QDs in-house QDs solutions were prepared. The formamidiniummethylamonium-potassium (FAMA@10 K) has been used as light absorber material in the fabricated PSCs. The structural, compositional and morphological studies, correlated with the photovoltaic performance of PSCs, indicate that the m-SnO2 2 QDs layer is the best candidate among the three investigated mesoporous ETLs. Compared with the suspensions used for the other two ETLs, the in-house prepared SnO2 2 QDs solution presents smaller agglomerates of nanoparticles and results in the formation of a thinner, more uniform and compact mesoporous ETL. The FAMA@10 K perovskite deposited on m-SnO2 2 QDs ETL presents a lower roughness, better uniformity and a higher amount of PbI2. 2 . Our work unveils that the SnO2 2 QDs solution can be easily produced in laboratory and when is deposited as mesoporous scaffold in a PSC with FAMA@10 K perovskite, the power conversion efficiency increases up to 14.90 %, being with up to 27 % larger than in the PSCs with m-TiO2 2 and mSnO2 2 ETLs prepared from commercial solutions. By modeling the J-V dynamic hysteresis with more than 90 % match between the calculated and experimental J-V data, for all three types of mesoporous ETLs, the relevant parameters that explain the hysteresis magnitude and account for ionic-induced recombination processes in PSCs were determined.

Laser thin layer deposition technologies were applied to develop organic heterostructures on flexible transparent conductive electrode (TCE). Flexible substrates such as flexible glass (FG), polyethersulfone (PES), amorphous polyethylene terephthalate (PET-A) and biaxially-oriented polyethylene terephthalate (PET-B) were employed to assess the influence of the substrate type on the optical and electrical characteristics of the organic devices. For comparison reason, the organic heterostructures were fabricated on rigid glass substrate and commercially available indium tin oxide (ITO)-coated PET. Hence, flexible and rigid glass substrates were coated with ITO film by pulsed laser deposition (PLD) at low fluence, subsequently a blend layer based on zinc phthalocyanine (ZnPc) and N, N '-bis-(1-dodecyl)perylene-3,4,9,10 tetracarboxylic diimide (AMC14) being deposited by matrix assisted pulsed laser evaporation (MAPLE) on the TCE film. The investigations evidenced that the roughness and the substrate type can strongly influence the properties of the ITO layer deposited by PLD as well as the optical and electrical characteristics of the organic heterostructures based on the blend layer deposited by MAPLE. Thus, the lowest roughness (0.8 nm) and the best Hall mobility (41.9 cm2/V center dot s) were achieved for ITO coatings deposited on flexible glass substrate. Also, the highest current density value (9.3 x 10- 4 A/cm2 at 0.5 V) was reached for the organic heterostructures fabricated on this type of flexible substrate.

Hydroxyapatite (HAp), resembling human bone tissue, is a promising biomaterial for dental and hip prosthetics. Incorporating fluorine ions enhances HAp properties, particularly in dental restoration. This new study examines the physicochemical and biological properties of fluorine substituted hydroxyapatite (FHAp) coatings. Structural and morphological properties of the coatings were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The elemental composition of the FHAp coatings was studied using energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy. Fourier Transform Infrared spectroscopy (FTIR) investigations were also conducted. The typical peaks identified in XRD patterns of the FHAp were associated with pure hydroxyapatite with hexagonal structure. The general XPS spectrum of FHAp coatings shows peaks corresponding to the constituent elements of stoichiometric HAp as well as the presence of F that was used as a substituent. Consequently, the FTIR studies results underlined the presence of hydroxyapatite in the FHAp coatings. The SEM images reveal the presence of a uniform and continuous layer of particle conglomerates evenly distributed across the FHAp surface. Valuable information about the FHAp coating's wettability, adhesion and coating thickness were also obtained. Also, the AFM images suggest the absence of the significant irregularities from the surface of the FHAp coatings. Investigations of FHAp coatings reveal promising outcomes for cell viability and proliferation. Detailed analysis of FHAp's 3D surface characteristics and roughness, following ISO 25178-2:2012 standards, highlights their favorable biocompatibility, supporting MG63 cell proliferation. The surface roughness parameters of FHAp coatings were found to vary, with Sa values spanning from 0.029 +/- 0.004 mu m to 0.778 +/- 0.007 mu m, while Sq ranged from 0.035 +/- 0.005 mu m to 0.907 +/- 0.011 mu m. Furthermore, FHAp exhibits skewness (Ssk) from -0.048 +/- 0.006 to 0.195 +/- 0.009, kurtosis (Sku) from -0.600 +/- 0.011 to -1.050 +/- 0.021, and fractal dimension from 2.14 +/- 0.01 to 2.19 +/- 0.01, indicating consistent surface complexity and favorable properties. The Minkowski Functionals mirror the morphological observations from AFM images, emphasizing their dynamic influence on the samples' surfaces.

In this work, three methods for the synthesis of composites based on poly(ortho-toluidine) (POT) and WS2 are reported: (a) the solid-state interaction (SSI) of POT with WS2 nanoparticles (NPs); (b) the in situ chemical polymerization (ICP) of ortho-toluidine (OT); and (c) the electrochemical polymerization (ECP) of OT. The preparation of WS2 sheets was performed by the ball milling of the WS2 NPs followed by ultrasonication in the solvent N,N'-dimethyl formamide. During the synthesis of the POT/WS2 composites by SSI and ICP, an additional exfoliation of the WS2 NPs was reported. In this work, we demonstrated the following: (a) the ICP method leads to POT/WS2 composites, which contain repeating units of POT in the leucoemeraldine salt (LS) state, while (b) the ECP method leads to POT/WS2 composites, which contain repeating units of POT in the emeraldine salt (ES) state. Capacitances equal to 123.5, 465.76, and 751.6 mF cm-2 in the cases of POT-ES/WS2 composites, synthesized by SSI, ICP, and ECP, respectively, were reported.