National Institute Of Materials Physics - Romania

Rhombohedral phase HfxZr1-xO2 (HZO, x from 0 to 1) films are promising for achieving robust ferroelectric polarization without the need for an initial wake-up pre-cycling, as is normally the case for the more commonly studied orthorhombic phase. However, a large spontaneous polarization observed in rhombohedral films is not fully understood, and there are also large discrepancies between experimental and theoretical predictions. In this work, in rhombohedral ZrO2 thin films, we show that oxygen vacancies are not only a key factor for stabilizing the phase, but they are also a source of ferroelectric polarization in the films. This is shown experimentally through the investigation of the structural properties, chemical composition and the ferroelectric properties of the films before and after an annealing at moderate temperature (400 degrees C) in an oxygen environment to reduce the V-O concentration compared. The experimental work is supported by density functional theory (DFT) calculations which show that the rhombohedral phase is the most stable one in highly oxygen defective ZrO2 films. The DFT calculations also show that V-O contribute to the ferroelectric polarization. Our findings reveal the importance of V-O for stabilizing rhombohedral ZrO2 thin films with superior ferroelectric properties.

. The study on efflorescence in salts collected from Curtea de Arges cathedral's exterior wall during restorations aimed to characterize compounds and lithic material using SEM-EDX, XRD, Raman, FTIR. Radiocarbon measurements using AMS method and FTIR results demonstrate decarbonation/recarbonation at the compound-lithic interface but further research is required.

In this paper, short-wave infrared (SWIR) photosensing of GeSn-HfO2 films with small Si amount is studied in correlation with structure and composition of films. SiGeSnHfO2 films are deposited by magnetron sputtering and nanostructured by subsequent rapid thermal annealing. XRD and Raman spectroscopy investigations are carried out revealing the SiGeSn nanocrystallization in annealed films. Spectral responsivity shows enhanced sensitivity up to 2 mu m due to SiGeSn nanocrystals (NCs) and clusters with contribution from disorder.

This study examines the opto-electric characteristics of Ge:SiO2 composite films produced via magnetron sputtering at substrate temperatures of 300 degrees C, 400 degrees C, and 500 degrees C, with varying Ge concentrations. We employed x-ray diffraction, current-voltage measurements, and spectral photocurrent analysis to investigate the films structural, optical, and opto-electrical properties. Illumination of the samples resulted in a marked increase in current compared to dark conditions. Spectral photocurrent measurements revealed cutoff wavelengths of 1300 nm for films with 25:75 vol% Ge:SiO2 ratio, extending to 1320 nm for compositions with higher Ge content (60:40 vol%). These findings align with observations from I-V curve analyses. Our research highlights the potential of Ge:SiO2 composites for enhancing optoelectronic device performance. The results underscore the importance of continued investigation and innovative applications in this field to drive technological advancements.

This is the first report on an efficient, "environmentally friendly" chemical reduction method for the synthesis of aminated hyaluronic acid-based silver nanoparticles on the modified surface of titanium dioxide nanoparticles aimed for biological applications. Silver nanoparticles exhibit well-known physical-chemical and optical prop-erties appropriate for different biological applications. Modifying the nanoparticles leads to a change in their expected bioactivity. This represents an important topic for the current research. We have developed a novel aminated hyaluronic acid (HA-EDA)-based protocol to obtain silver nanoparticles, in which HA-EDA was used for the first time as a reducing and stabilizing agent. The effect of the size of silver nanoparticles on the titanium dioxide surface and the chemical composition of the obtained materials were investigated by TEM, XRD, XPS, ATR-FTIR, Raman spectroscopy, NMR and H2-TPR analyses. The antioxidant, in vitro biocompatibility, and antimicrobial activity of the fabricated composites have been evaluated. The results prove that the prepared materials exhibit antimicrobial, antioxidant, and anti-inflammatory activity, thus providing protection against infection and supporting tissue regeneration, these two key effects being of paramount importance for promoting wound healing.

Nanoscale Al-doped yttrium-iron garnets attract enhanced scientific and practical interest in the development of microwave devices due to their remarkable physical-chemical properties, which depend essentially on the method and conditions of synthesis. This work highlights the advantages of a specific two-stage synthesis of Y3AlFe4O12 garnet ferrite nanoparticles by the precipitation in aqueous solutions and deals with the detailed examinations of the precipitates obtained during this process. The results of the complex studies using high resolution transmission microscopy, dynamic light scattering and magnetic measurements have allowed assessing the features of the formation of crystalline structure. It is demonstrated that the sequence of the precipitation of components during the synthesis strongly affects the physical-chemical properties of the formed precipitate (filtration coefficient value, surface charge, micelle's structure) as well as the physical properties of nanoparticles obtained after their heat treatment at 800 degrees C (saturation magnetization, coercive force). Simultaneous precipitation of Fe(OH)3 and Al(OH)3 metal hydroxides, which form one of three crystallographic sub lattices of the garnet structure, at the first stage of the synthesis of ferrite-garnets is revealed to provide higher values of filtration coefficient of the formed precipitate and better technological and physical-chemical parameters of the fabricated garnet nanoparticles that makes this method highly advantageous for industrial application.

The effectiveness of mesoporous SnO2 nickel-decoration as a method for obtaining active electrode materials for bioethanol electrochemical oxidation and the way in which the embedment of a small amount of Black Pearls (BP) affects the electrocatalytic performances of Ni/SnO2 systems were investigated. XPS analysis reveals the presence of NiO, Ni(OH)(2) and Ni2O3 chemical species which favors the oxidation of bioethanol and improves the COx tolerance. Nickel deposition in a reducing environment does not affect the Sn chemistry and the mesoporosity but significantly increases S-BET. A slight amount of BP enhances the S-BET value and a induces a small contribution of larger pores appears. Tafel slopes of 80 mV decade(-1) were estimated for bioethanol oxidation at Ni/SnO2, which favorably compare to those reported in the literature. It was also found that BP incorporation leads to a decrease of the Tafel slope to 70 mV decade(-1), without deleteriously affecting the stability of the electrocatalyst during long-term polarization. EIS results suggested that this improvement might be the combined effect of a lower electrical resistance, a higher specific surface area and a certain contribution from larger pores, which could lead to a better access of the bioethanol species to the electrocatalyst surface.

Hydrothermally formed mesoporous SnO2 was used as a support for nickel chemical deposition and, after subsequent thermal treatment, a high specific surface area (36 m(2) g(-1)) Ni/SnO2 material was obtained. XPS analysis has shown that in the Sn 3d region the spectrum is similar to that of pristine SnO2, whereas Ni species are present on the surface as NiO, Ni2O3 and Ni(OH)(2). Mixing Ni/SnO2 with a small amount of Black Pearls (BP) leads to a significant enhancement of the resulting Ni/SnO2-BP composite activity for nitrite anodic oxidation, presumably due to the higher surface area (115 m(2) g(-1)), to better electrical conductivity and to a certain contribution of the BP to an increase in surface density of the active sites. Ni/SnO2-BP also outperforms pristine BP (in terms of Tafel slopes and electron-transfer rates), most likely due to the fact that the Ni(ii)/Ni(iii) couple can act as an electrocatalyst for nitrite oxidation. A voltammetric method is proposed for the determination of nitrite, over a concentration range of three orders of magnitude (0.05 to 20 mM), with good reproducibility, high stability and excellent sensitivity. The high upper limit of the dynamic range of the analytically useful response might provide a basis for the reliable quantification of nitrite in wastewater.

One of the new materials for next-generation thin film solar cells is Cu2ZnSnSe4 (CZTSe). However, achieving a single-phase CZTSe compound remains a challenge. This study describes the development of Cu2ZnSnSe4 thin films through the sequential deposition of stacked films of non-stoichiometric Cu2SnSe3 (CTSe) and ZnSe by magnetron sputtering. The structural, morphological, and electrical properties as well as the surface chemistry of the films were investigated and compared depending on the growth sequence of the thin films. By using Raman spectroscopy and grazing incidence X-ray diffraction, the tetragonal CZTSe structure was confirmed. Scanning electron microscopy and energy-dispersive spectroscopy measurements of the morphological and compositional properties indicated large grains and dense surfaces with an elemental composition close to the desired stoichiometry in SLG\SnSe2\Cu\ZnSe and SLG\SnSe2\Cu2Se\ZnSe stacks. To ascertain the surface chemistry and unique characteristics of the produced films, additional X-ray photoemission spectroscopy experiments were carried out. The optimal band gap values for the absorber layers were found using conventional spectroscopy, and they ranged from 0.88 to 1.47 eV. According to the electrical measurements, all the films were p-type and have high carrier concentrations between 1016 and 1020 cm-3. Our findings demonstrate that employing a sequential deposition approach and annealing in different atmospheres can yield CZTSe absorber layers with desirable properties, overcoming the challenge of non-stoichiometric CTSe precursors.

In this study, a sol-gel film based on lead sulfide (PbS) quantum dots incorporated into a host network was synthesized as a special nanostructured composite material with potential applications in temperature sensor systems. This work dealt with the optical, structural, and morphological properties of a representative PbS quantum dot (QD)-containing thin film belonging to the Al2O3-SiO2-P2O5 system. The film was prepared using the sol-gel method combined with the spin coating technique, starting from a precursor solution containing a suspension of PbS QDs in toluene with a narrow size distribution and coated on a glass substrate in a multilayer process, followed by annealing of each deposited layer. The size (approximately 10 nm) of the lead sulfide nanocrystallites was validated by XRD and by the quantum confinement effect based on the band gap value and by TEM results. The photoluminescence peak of 1505 nm was very close to that of the precursor PbS QD solution, which demonstrated that the synthesis route of the film preserved the optical emission characteristic of the PbS QDs. The photoluminescence of the lead sulfide QD-containing film in the near infrared domain demonstrates that this material is a promising candidate for future sensing applications in temperature monitoring.