Publications

Recently, spin asymmetry in O 2p related deep valence states was evidenced in SrTiO3(001) [Popescu et al., Phys. Scr. 99(10), 105925 (2024)]. In this work, we report the detection of a much higher (about four times) spin asymmetry in SrTiO3(011) by spin resolved photoelectron spectroscopy, with samples characterized also by core level x-ray photoelectron spectroscopy and low energy electron diffraction. The explanation of a so important spin asymmetry is related to the partial neutralization of O-2(4-) or SrTiO(4+) end layers. Missing electrons from O 2p states in the case of O-2 terminations enable robust atomic spins, according to Hund's rule. The parallel analysis of core level shifts for surface atoms and the amplitude of spin asymmetry suggests that 50% of the oxygens from the surface SrO layer of SrTiO3(001) have a 2p(5) configuration with an unpaired electron (the rest are in a 2p(6) configuration), while in the case of O-2 terminated SrTiO3(011), about 50% of surface oxygens have a 2p(5) configuration and 50% of surface oxygens are neutral (2p(4)), yielding a net charge per O-2 surface unit cell of (-1) instead of (-4). The magnetization is oriented along the rows formed by the (4 x 1) reconstruction in the 011 in-plane direction. (c) 2025 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license(https://creativecommons.org/licenses/by/4.0/).

We theoretically study the 2D Su-Schrieffer-Heeger model in the context of Floquet topological insulators (FTIs). FTIs are systems which undergo topological phase transitions, governed by Chern numbers, as a result of time reversal symmetry (TRS) breaking by a time periodic process. In our proposed model, the condition of TRS breaking is achieved by circularly polarized light irradiation. We analytically show that TRS breaking is forbidden in the absence of second order neighbors hopping. In the absence of light irradiation, we identify a symmetry-protected degeneracy and prove the appearance of a flat band along a specific direction in the momentum space. Furthermore, we employ a novel method to show that the four unit cell atoms, in the absence of irradiation, can be interpreted as conserved spin states. With the breaking of TRS via light irradiation, these spin states are no longer conserved, leading to the emergence of chiral edge states. We also show how the interplay between the TRS breaking and dimerization leads to some complex topological phase transitions. The validity of our findings is substantiated through Chern numbers, spectral properties, localization of chiral edge states and simulations of quantum Hall transport. Our model is suitable not only for condensed matter (materials), but also for cold gases trapped in optical lattices or topolectrical circuits.

Biodegradable templates are sought for targeted antibiotic administration/delivery in bone infections to avoid detrimental reactions during bone regeneration. We investigated two key-aspects in this direction: 1) the optimal antibiotic delineation, with thermal stability equivalent to the temperature involved for templates preparation and 2) the antibacterial templates development by a two-step homogenization process. The selected antibiotic - ampicillin (AMP) was mechanically and then thermally mixed with the prime materials: poly(lactic acid) (PLA) - the polymeric matrix, biogenic bovine bone-derived hydroxyapatite (HA, particles <40 mu m), and graphene nanoplatelets (GnP, micrometric range). For the first time, all materials were used in simultaneous modulated ratios for the synthesis of PLA/AMP (1-5 wt.%)/HA (0-30 wt.%)/GnP (0-3 wt.%) composites. The influence of the concomitant materials modulation was surveyed through several assays. The FTIR-ATR spectroscopy depicted a three-level model of overlapping structures asserting the solid molecular cross-linking between all materials, without structural alterations induced to any material (XRD analysis). The addition of AMP to the PLA matrix caused a slight particle conglomeration, alleviated through GnP addition. The microporous HA particles supported the adhesion to the PLA matrix and promoted the AMP particles' entrapment/attachment. Linked to the enhanced wettability of the composite materials, the phosphate buffered saline solution (PBS) degradation profiles revealed a pronounced burst during the first 14-28 days of incubation and a long-term, low-level process hereafter. Thus, the formation of pores and cavities were signalled along with the HA particles' fragmentation. The released AMP (percentage) pictured an ascending trendline during the 24 h of analysis, at all targeted ratios. The preservation of AMP features at 200 degrees C was endorsed by the strong antibacterial activity of composite materials against Staphylococcus aureus (S. Aureus) growth and the medium response against Escherichia coli (E. Coli) - the higher the drug release, the higher the inhibitory effect on bacteria evolution.

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 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 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.

A methodology for the quantitative estimation of the drug loading of iron oxide-based magnetic nanoparticles by corroborating magnetometry and M & ouml;ssbauer spectroscopy investigations is reported. The proposed methodology is exemplified in the case of two series of nanoparticles, namely Fe3O4 nanoparticles covered with citric acid molecules and further functionalized with doxorubicin, and Fe3O4 nanoparticles covered with L-Cysteine molecules and further functionalized with doxorubicin. The general idea of the proposed methodology is to probe the real magnetic structure of the magnetic core via low-temperature M & ouml;ssbauer spectroscopy for the correct estimation of the spontaneous magnetization of the magnetic core. It subsequently uses the ratio between the spontaneous magnetization of the covered nanoparticles and that of the magnetic core for the reliable and nondestructive evaluation of the nanoparticle loading by organic molecules. Although the methodology is exemplified in the case of magnetite-based nanoparticles, it can be successfully considered for a large class of medicine-loaded Fe-containing magnetic nanoparticles where 57Fe M & ouml;ssbauer spectroscopy can be applied.

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.

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.

The paper presents the features of the magnetization decay of proton-irradiated MgB2 bulk samples. Irradiation was performed with protons of energies between 8.6 and 15.07 MeV at different fluences. The creep activation energy is sensitive to the ratio between proton range and sample thickness. Experimental data show that the creep exponents are different from the theoretical predictions. When the proton range is shorter than the sample thickness (protons of 8.6 MeV), the thermomagnetic instabilities are strongly emphasized and affect the creep behavior.