National Institute Of Materials Physics - Romania

We present a simple two-dimensional model for a phase transition, then study its predictions, in particular the memory properties. The direct transformation is modeled by randomly placing small squares, "nuclei", on an initially empty surface. Then, the nuclei expand ("grow") up to finite final sizes which are randomly chosen in a given range, while keeping their square shape. An important issue is the "interaction" which forces some squares to remain at smaller sizes if the surrounding squares get in the way of their growth. Interestingly, this naturally leads to quasiequal total area covered by the squares of each size after a complete direct transformation. Next, it is shown that the system "remembers" incomplete ("arrested") reverse transformations taking place in reversed order of the squares sizes. The memory is "encrypted" in the distribution of the squares sizes after a next direct transformation and manifests as a significant imbalance between the areas covered by the "big" and "small" (relative to the arrest size) squares. We are able to also reproduce the so-called "hammer effect" and the memorizing of multiple arrest points. Our model is particularly relevant for the thermal memory effect in shape memory alloys, and we actually borrowed many features from existing thermodynamic models addressing this effect. However, here we eliminate the explicit thermodynamics and end up with a statistical geometry model, presumably easier to reproduce.

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 combination of low-temperature scanning tunnelling microscopy with a mass-selective electro-spray ion-beam deposition established the investigation of large biomolecules at nanometer and sub-nanometer scale. Due to complex architecture and conformational freedom, however, the chemical identification of building blocks of these biopolymers often relies on the presence of markers, extensive simulations, or is not possible at all. Here, we present a molecular probe-sensitisation approach addressing the identification of a specific amino acid within different peptides. A selective intermolecular interaction between the sensitiser attached at the tip-apex and the target amino acid on the surface induces an enhanced tunnelling conductance of one specific spectral feature, which can be mapped in spectroscopic imaging. Density functional theory calculations suggest a mechanism that relies on conformational changes of the sensitiser that are accompanied by local charge redistributions in the tunnelling junction, which, in turn, lower the tunnelling barrier at that specific part of the peptide. Chemical identification of the building blocks of biopolymers often considerably relies on the presence of markers, extensive simulations, or is not possible at all. Here, the authors report a molecular probe-sensitisation approach addressing the identification of a specific amino acid within different peptides.

A conductance zero that results from the destructive quantum interference of the electron states in quantum transport between two given sites of a molecular system persists or disappears depending on the location of an externally applied perturbation. The a priori knowledge of the perturbation site that destroys or preserves a zero is the basis of an algorithm that outlines the creation of logic gates having external perturbations as inputs and a given conductance as output. Using a graph of the possible conductance paths between the various sites, we showcase the several different scenarios that correspond to AND/OR/XOR logical functions for a given set of contacts. This setup is shown to be independent of the strength of the coupling to the leads and magnitude of the perturbation. We illustrate this approach in the case of bipartite and nonbipartite single carbon cycle molecules (fulvene and benzene) and double carbon cycle molecules (naphthalene and biphenyl).

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.

This study focused on investigating the optoelectronic properties of molybdenum trioxide (alpha-MoO3) thin films using the atomic layer deposition (ALD) technique through different cycle numbers and theoretical investigation. Initial band gap calculations using standard DFT with GGA-PBE resulted in a value of 1.19 eV, which deviated significantly from experimental measurements. The GGA + U method with Hubbard U corrections was applied for the first time to improve the accuracy. This refinement led to a more precise band gap value of 3.09 eV, closely matching previously reported experimental data. The electronic parameters of the alpha-MoO3 photodetector, such as ideality factor (n), barrier height (phi 0), and series resistance (Rs), were analyzed using the thermionic emission theory and confirmed by Cheung and Nord's methods. The results demonstrated that the sample deposited with 100 pulses exhibited higher photodetector performance under UV illumination, despite having a lower Rs.

Two hybrid materials, based on 7-amino-4-(trifluoromethyl)coumarin and 7-amino-4-methyl-coumarin that attach covalently to graphene oxide (GO) have been synthesized in two steps: i) increasing the number of carboxyl groups required for functionalization with aminocoumarin derivatives by derivatization of the hydroxyls groups with chloroacetic acid, transforming GO into GO-COOH material; ii) activation of carboxylic groups using the carbodiimide-promoted reaction. The obtained composites were characterized by numerous methods that highlighted their successful obtaining. The antimicrobial activity was evaluated on resistant Mycobacterium tuberculosis strains, as well as on ESKAPE pathogens ((Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.) in planktonic and biofilm growth states. The biocompatibility of the materials has been assayed using 3-(4, 5-dimethylthiazol-2-yl)2, 5-diphenyltetrazolium bromide assay as well as by measuring the level of nitric oxide/total reactive oxygen species and superoxide release in treated cells. The results have shown that materials exhibited improved inhibitory activity against resistant M. tuberculosis strains in comparison with GO, but also against planktonic and adherent strains. Also, the tested composites have been proved to be biocompatible on the MRC-5 fibroblast cells, demonstrating their promising potential to develop novel agents effective against multidrug resistant pathogens, including M. tuberculosis, as well as by the activation of a pro-inflammatory and of an oxidative response in the mammalian cells.

Flexible porous materials have gained a high interest due to their impact on the development of electrochemical point-ofcare devices for monitoring the state of health of individuals. Among the porous materials, paper and textiles are most commonly used due to their innate capillary action on fluids. In this article, attention is paid to the retention of analytes in paper and textile porous substrates, and possible procedures to overcome this effect are discussed. The patterning of hydrophilic and hydrophobic regions for sample flow manipulation, and the folding properties of the flexible substrates for 3D architectures capable of transfer of analytes, are considered in relation to current electrode materials and detection methodologies.

In the present study, sage-coated zinc-doped hydroxyapatite was incorporated into a dextran matrix (7ZnHAp-SD), and its physico-chemical and antimicrobial activities were investigated. A 7ZnHAp-SD nanocomposite suspension was obtained using the co-precipitation method. The stability of the nanocomposite suspension was evaluated using ultrasound measurements. The stability parameter calculated relative to double-distilled water as a reference fluid highlights the very good stability of the 7ZnHAp-SD suspension. X-ray diffraction (XRD) experiments were performed to evaluate the characteristic diffraction peak of the hydroxyapatite phase. Valuable information regarding the morphology and chemical composition of 7ZnHAp-SD was obtained via scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) studies. Fourier-transform infrared spectroscopy (FTIR) measurements were performed on the 7ZnHAp-SD suspensions in order to evaluate the functional groups present in the sample. Preliminary studies on the antimicrobial activity of 7ZnHAp-SD suspensions against the standard strains of Staphylococcus aureus 25923 ATCC, Enterococcus faecalis 29212 ATCC, Escherichia coli 25922 ATCC, and Pseudomonas aeruginosa 27853 ATCC were conducted. More than that, preliminary studies on the biocompatibility of 7ZnHAp-SD were conducted using human cervical adenocarcinoma (HeLa) cells, and their results emphasized that the 7ZnHAp-SD sample did not exhibit a toxic effect and did not induce any noticeable changes in the morphological characteristics of HeLa cells. These preliminary results showed that these nanoparticles could be possible candidates for biomedical/antimicrobial applications.

High density samples (92-94.5 %) of MgB2 were prepared by Spark Plasma Sintering (SPS). The on-off pulsed current patterns of SPS processing were 8-4, 12-2, 24-2, 99-1. Patterns with more on pulses favor formation of a higher amount of the secondary MgB4 phase through the decomposition of MgB2. They also promote enhancement of larger MgO crystallites without a strong increase in the amount of this phase. Densification rate and pressure in the SPS chamber show a similar behavior, but their amplitude varies and the temperatures defining different stages present some shifts. As-revealed differences induced by pulsed patterns impact superconducting properties in a complex manner. An attempt to assess correlations between the pattern and different superconducting parameters is presented.