National Institute Of Materials Physics - Romania

A study on clay mineral polymer nanocomposites (CPN), namely polyaniline/montmorillonite-cetyltrimethylammonium bromide (PANI/Mt-CTAB), poly o-anisidine/montmorillonite-cetyltrimethylammonium bromide (poly(o-ANIS)/Mt-CTAB) and poly o-anisidine-co-aniline/montmorillonite-cetyltrimethylammonium bromide (poly(o-ANIS-co-ANI)/Mt-CTAB), synthesized by oxidative chemical polymerization method is presented. The nanocomposites have been characterized by Fourier transform infrared spectroscopy, UV-vis spectroscopy, and cyclic voltammetry, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, cyclic voltammetry and thermogravimetry and differential scanning calorimetry analysis. By UV-vis measurements different electronic transitions for the CPNs were pointed out. The voltammograms indicate that the synthetized materials are electroactive. The FTIR analysis reveals the characteristic bands of the polymers and of the Mt-CTAB. The shift of the bands to higher/lower wavenumbers demonstrate the interaction between the pristine polymers macromolecular chains and the montmorillonite (Mt). The intercalation of the polymers inside the mineral clay was confirmed by the increased interlayer distance connected with the position of the 011 diffraction plane of the Mt., and the intercalation and exfoliation states were highlighted in the scanning and transmission electron microscopy images. The obtained results are encouraging in respect with the purpose to use them in the field of photovoltaic applications.

Thin nanostructured films are the state-of-the-art materials for detection of very low limits of toxic gases. The work presents a comparison between the properties of WO3 thin films obtained by two different deposition techniques: Advanced Gas Deposition (AGD) and DC Reactive Sputtering. Films have been characterized by XRD, SEM and XPS. WO3-based sensors have selective sensitivity in H2S detection at operating temperature of 200 degrees C and relative humidity specific to field applications. The potential interferences with CO2, SO2 and NH3 are negligible, highlighting the application potential of WO3.

Dense samples (94-96%) with starting composition (MgB2)(0.99)(X-acac)(0.01) (X-acac denotes Ga or In acetylacetonate) were obtained by spark plasma sintering. The resulting material is a superconducting composite, where carbon substitutes for boron in the crystal structure of MgB2. Added samples show enhanced critical current density at high magnetic fields and this is reflected in high values of irreversibility field (H-irr) at temperatures below 25 K when compared to a pristine sample. More efficient is In-acac addition and it promotes a H-irr of similar to 12.4T (100 A/cm(2) criterion) at 5 K. Carbon substitution for boron in the crystal structure of MgB2 has a strong influence on the pinning force and its related parameters and promotes in the added samples a grain boundary pinning mechanism as the dominant one, whereas the pristine sample with a low amount of carbon shows a major mechanism of point pinning type. However, our analysis indicates on the synergetic effects of the carbon substituting for boron and of the microstructural details on pinning and critical current density. The result strongly emphasizes the significantly different behavior of the additive during processing of the MgB2 samples, although thermal analysis experiments on both additives show very similar decomposition patterns. (C) 2020 The Authors. Published by Elsevier B.V.

The 1600 nm-extended SWIR photoresponse of SiGe/TiO2 multilayers with Ge-rich SiGe nanocrystals (NCs) is demonstrated. The SiGe NCs based multilayers are obtained by magnetron sputtering deposition of TiO2/ 6x(Ge/SiGe/Ge/TiO2) layers on heated p-Si substrate followed by rapid thermal annealing (RTA). Grazing incidence X-ray diffraction and Raman spectroscopy evidence the formation of cubic Ge-rich SiGe NCs and anatase TiO2. ITO/Ge-rich SiGe NCs based multilayer /p-Si heterostructure diodes, fabricated by depositing top ITO and bottom Al contacts, show n-p behavior. Photocurrent-voltage characteristics measured at 100 K under integral light illumination of reverse biased diode present a photocurrent higher with up to 2 orders of magnitude than the dark current. Spectral photocurrent increases with bias voltage increase and presents a bandgap-related cutoff wavelength of similar to 1600 nm due to the high Ge content of SiGe NCs.

Novel lanthanidomesogens based on lanthanide nitrates carrying three 4-pyridone ligands having two alkoxy chains at the periphery were synthesized and their structure was assigned based on IR spectroscopy and elemental analysis. Their thermal stability was evaluated by TG analysis confirming that the decomposition starts at very high temperatures around 300 degrees C. The liquid crystalline properties were investigated by using a combination of techniques: polarized optical microscopy (POM) and differential scanning calorimetry (DSC) and, for selected compounds, by variable-temperature powder X-ray diffraction. The new liquid crystal display a hexagonal columnar phase (Col(h)) between 63 degrees C and 242 degrees C, depending on the length of the alkyl chain Dielectric spectroscopy on a wide frequency range was used to evaluate the dipolar relaxation processes. The emission properties of a mixture of E7 doped with a selected europium complex filled in a planar cell were investigated on changing the applied voltage, ranging from 0V up to 15V.

Behavior of some wool fabrics as such or functionalized with semiconductor nanoparticles against the photodegradation of Rhodamine B was investigated. The wool samples were commercially purchased, they were chosen to differ by the chemical nature of the yarns, by the size of the 2D texture elements and by the applied pretreatment. The samples were routinely characterized both in the original form and in the form coated with the oxide particles as well to consider the structure, the surface morphology and their changes due to dye deposition. Several techniques were routinely applied: optical microscopy, XRD, SEM, TGA, UV-Vis spectroscopy and FTIR-ATR. Data have shown that TiO2 layer has either an amorphous structure or is highly dispersed. Drops of Rhodamine B solution were deposited by sessile drop method. We have obtained optical images of the wet/colored spot during the radial wicking, collected with a usual camera. Image comparison was made by direct visualisation. The optical images of the spot on fabrics were taken immediately after the dye was applied, after the fabric was dried and afterwards, after the system illumination by UV-vis light as function of the time. The obtained final spots speak about the dye photodegradation in the studied cases.

Pb0.98Bi0.02Zr0.5Fe0.1Nb0.09Ti0.31O3 (PBiZFNT) powder obtained by a solid state reaction technique was uniaxial pressed and sintered at 1200 degrees C in order to fabricate dense thin disk ceramics with different thickness (200 mu up to 600 mu m). The pyroelectric response was influenced by the thickness of the ceramics. The thin ceramic disks of 250 mu m thickness show better pyroelectric signal (approximate to 35 mV) which recommend them for potential use in laser energy meters.

Nanostructured hematite prepared via anodic deposition has been studied as photoanode in neutral and alkaline electrolytes. The morphology of the nanostructures was characterized by SEM, XRD analysis was performed to verify the phase of the films, absorption coefficient and band gap were determined from spectrophotometric measurements and the atomic concentration of Sn in hematite film was estimated from XPS measurements. EIS measurements and photocurrent responses showed the different behavior of hematite photoanode in alkaline and neutral electrolytes. The alkaline medium favors the chemisorption of the water molecules on hematite photoanode, contributing to the diminishing of the charge transfer resistance.

The objective of this study is to investigate the methods to create durable self-cleaning textiles by coating fabrics with TiO2-(1%)Fe-N-graphene (2%). To improve the adherence of the nanoparticles, the polyester/cotton woven fabrics were pre-treated with polyacrylic acid (PA), carboxymethylcellulose (CMC) and polyethylene polyamine resin (EZF). The pre-treated materials were immersed in a doped TiO2 for 30 minutes at 40 degrees C and dried at 125 degrees C. The finished fabrics were stained with methylene blue dye and exposed to visible light. The SEM images show the presence of particles on polymers layers firmly attached on the material surface. The treatments determine the decrease of the exothermic peak (452.48 degrees C), characteristic of the cellulose decomposition, demonstrating an increase of the thermal conductivity of the materials. The doped TiO2-graphene induces a double degradation of methylene blue in comparison with untreated material and the materials treated with CMC, polyacrylic acid and cationic polymer. The effect is maintained after washing.