Sonochemical synthesis of SnS and SnS2 quantum dots from aqueous solutions, and their photo- and sonocatalytic activity.

Our study reports the ultrasound-assisted synthesis of SnS and SnS2 in the form of nanoparticles using aqueous solutions of respective tin chloride and thioacetamide varying sonication time. The presence of both compounds is confirmed by powder X-ray diffraction, energy-dispersive X-ray spectroscopy, as well as Raman and FT-IR spectroscopic techniques. The existence of nanoparticles is proven by powder X-ray diffraction investigation and by high resolution transmission electron microscopy observations. The size of nanocrystallites are in the range of 3-8 nm and 30 50 nm for SnS, and 1.5-10 nm for SnS2. X-ray photoelectron spectroscopy measurements, used to investigate the chemical state of tin and sulphur atoms on the surface of nanoparticles, reveal that they are typically covered with tin on the same oxidation degree as respective bulk compound. Values of optical bandgaps of synthesized nanoparticles, according to the Tauc method, were 2.31, 1.47 and 1.05 eV for SnS (60, 90 and 120 min long synthesis, respectively), and 2.81, 2.78 and 2.70 eV for SnS2 (60, 90 and 120 min long synthesis, respectively). Obtained nanoparticles were utilized as photo- and sonocatalysts in the process of degradation of model azo-dye molecules by UV-C light or ultrasound. Quantum dots of SnS2 obtained under sonication lasting 120 min were the best photocatalyst (66.9 % color removal), while quantum dots of SnS obtained under similar sonication time were the best sonocatalyst (85.2 % color removal).

Atomic Layer Deposition of HfO2 Films Using TDMAH and Water or Ammonia Water.

Atomic layer deposition of HfO2 from TDMAH and water or ammonia water at different temperatures below 400 °C is studied. Growth per cycle (GPC) has been recorded in the range of 1.2-1.6 Å. At low temperatures (≤100 °C), the films grew faster and are structurally more disordered, amorphous and/or polycrystalline with crystal sizes up to 29 nm, compared to the films grown at higher temperatures. At high temperatures of 240 °C, the films are better crystallized with crystal sizes of 38-40 nm but grew slower. GPC, dielectric constant, and crystalline structure are improved by depositing at temperatures above 300 °C. The dielectric constant value and the roughness of the films have been determined for monoclinic HfO2, a mixture of orthorhombic and monoclinic, as well as for amorphous HfO2. Moreover, the present study shows that the increase in the dielectric constant of the films can be achieved by using ammonia water as an oxygen precursor in the ALD growth. The detailed investigations of the relationship between HfO2 properties and growth parameters presented here have not been reported so far, and the possibilities of fine-tuning and controlling the structure and performance of these layers are still being sought.

Structural Quality and Magnetotransport Properties of Epitaxial Layers of the (Ga,Mn)(Bi,As) Dilute Magnetic Semiconductor.

Structural analysis of epitaxial layers of the (Ga,Mn)(Bi,As) quaternary dilute magnetic semiconductor (DMS), together with investigations of their magnetotransport properties, has been thoroughly performed. The obtained results are compared with those for the reference (Ga,Mn)As layers, grown under similar conditions, with the aim to reveal an impact of Bi incorporation on the properties of this DMS material. Incorporation of Bi into GaAs strongly enhances the spin-orbit coupling strength in this semiconductor, and the same has been expected for the (Ga,Mn)(Bi,As) alloy. In turn, importantly for specific spintronic applications, strong spin-orbit coupling in ferromagnetic systems opens a possibility of directly controlling the direction of magnetization by the electric current. Our investigations, performed with high-resolution X-ray diffractometry and transmission electron microscopy, demonstrate that the (Ga,Mn)(Bi,As) layers of high structural quality and smooth interfaces can be grown by means of the low-temperature molecular-beam epitaxy method, despite a large difference between the sizes of Bi and As atoms. Depending on the applied buffer layer, the DMS layers can be grown under either compressive or tensile misfit strain, which influences their magnetic properties. It is shown that even small 1% Bi content in the layers strongly affects their magnetoelectric properties, such as the coercive field and anisotropic magnetoresistance.

Eugenia umbelliflora mediated reduction of silver nanoparticles incorporated into O-carboxymethylchitosan/y-Fe2O3: Synthesis, antimicrobial activity and toxicity.

The purpose of this study was to synthesize a new magnetic material with antimicrobial properties, incorporated into a biopolymer and containing silver nanoparticles (Ag NP) prepared extract of Eugenia umbelliflora as a reducing agent. Silver nanoparticles incorporated into magnetic nanocomposite O-carboxymethylchitosan/y-Fe2O3/Ag0 (CMAgE) composite were synthesized using an extract of E. umbelliflora. The antimicrobial activity of the pathogenic microorganism is reported here. The synthesized nanoparticles were also characterized, and quantified by Ag analysis. The minimum inhibitory concentrations (MIC) of CMAgE against Staphylococcus aureus, Escherichia coli, and Candida albicans were 16.5, 1000 and 500 µg/mL, respectively. The results show that these materials have significant synergistic effect on each other. The potential phytotoxic effect of the nanocomposites was evaluated using Cucumis sativus seeds. The positive values for seedling elongation inhibition (SEI) show that CMAgE and methanol extract of Eugenia umbelliflora (Eug) cause growth inhibition at a concentration of 1000 mg/L. The germination index (GI) values of 40% and 80% at 1000 mg/L, for CMAgE and Eug, respectively, showed inhibition of germination. CMAgE and Eug showed cytotoxic effects against Artemia salina nauplii, with LC50 values of 72.5 µL/mL and < 5.0 µL/mL respectively, after 48 h.

Hole Trapping Process and Highly Sensitive Ratiometric Thermometry over a Wide Temperature Range in Pr3+-Doped Na2La2Ti3O10 Layered Perovskite Microcrystals.

We demonstrate a potential optical thermometric material, Pr3+-doped triple-layered perovskite Na2La2Ti3O10 microcrystals, which promises a remarkable performance in temperature sensing over a wide temperature range (125-533 K), with a maximum relative sensitivity of 2.43% K-1 at 423 K. Both temperature and high-pressure dependent photoluminescence measurements were performed for this compound. It turns out that the Pr3+-Ti4+ intervalence charge transfer state is the primary cause for the very efficient thermometric characteristics in the 296-533 K range. In the 125-300 K range, 3P1 and 3P0 levels of Pr3+ can be exploited as thermally coupled energy levels for temperature sensing with high sensitivity at and below room temperature. A significant enhancement of the Pr3+ ions' luminescence observed in the 4.5-300 K range is ascribed to an efficient, thermally activated energy transfer process from the host to Pr3+ ions. Carrier recombination on Pr3+ related hole traps was proposed in the studied system. The thermoluminescence properties are investigated, and possible mechanisms for the interpretation of the experimental results are discussed as well. This work may provide a perspective approach to design a high-performance, self-calibrated optical thermometer operating over a wide temperature range.

Synthesis of Ag@Fe2O3 nanocomposite based on O-carboxymethylchitosan with antimicrobial activity.

In this paper, nano-hybrid particles of Ag@Fe2O3 based on O-carboxymethylchitosan were successfully synthesized using different reducing agents (NaBH4, sucrose) and without reducing agent. The smallest silver nanoparticles were those prepared without reducing agent (∼5±3nm). The average size of silver particles prepared with NaBH4 is around 5-15nm, and for samples prepared with sucrose, the average particle size is 10-25nm. The magnetization curves are roughly reversible, indicating that γ-Fe2O3 nanoparticles transit to a superparamagnetic state. Nanocomposites subjected to antimicrobial tests showed great antimicrobial activity against gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli) bacteria, and good activity against the yeast Candida albicans and resistant strains of Staphylococcus aureus. The antibacterial behavior as a function of time was investigated in microbial growth kinetics, and the best nanocomposite was the one without reducing agent, which completely inhibited microbial growth for 48h.

Role of heat accumulation in the multi-shot damage of silicon irradiated with femtosecond XUV pulses at a 1 MHz repetition rate.

The role played by heat accumulation in multi-shot damage of silicon was studied. Bulk silicon samples were exposed to intense XUV monochromatic radiation of a 13.5 nm wavelength in a series of 400 femtosecond pulses, repeated with a 1 MHz rate (pulse trains) at the FLASH facility in Hamburg. The observed surface morphological and structural modifications are formed as a result of sample surface melting. Modifications are threshold dependent on the mean fluence of the incident pulse train, with all threshold values in the range of approximately 36-40 mJ/cm2. Experimental data is supported by a theoretical model described by the heat diffusion equation. The threshold for reaching the melting temperature (45 mJ/cm2) and liquid state (54 mJ/cm2), estimated from this model, is in accordance with experimental values within measurement error. The model indicates a significant role of heat accumulation in surface modification processes.

Facile synthesis of core/shell ZnO/ZnS nanofibers by electrospinning and gas-phase sulfidation for biosensor applications.

This study describes a new method of passivating ZnO nanofiber-based devices with a ZnS layer. This one-step process was carried out in H2S gas at room temperature, and resulted in the formation of core/shell ZnO/ZnS nanofibers. This study presents the structural, optical and electrical properties of ZnO/ZnS nanofibers formed by a 2 nm ZnS sphalerite crystal shell covering a 5 nm ZnO wurtzite crystal core. The passivation process prevented free carriers from capture by oxygen molecules and significantly reduced the impact of O2 on nanostructure conductivity. The conductivity of the nanofibers was increased by three orders of magnitude after the sulfidation, the photoresponse time was reduced from 1500 s to 30 s, and the cathodoluminescence intensity increased with the sulfidation time thanks to the removal of ZnO surface defects by passivation. The ZnO/ZnS nanofibers were stable in water for over 30 days, and in phosphate buffers of acidic, neutral and alkaline pH for over 3 days. The by-products of the passivation process did not affect the conductivity of the devices. The potential of ZnO/ZnS nanofibers for protein biosensing is demonstrated using biotin and streptavidin as a model system. The presented ZnS shell preparation method can facilitate the construction of future sensors and protects the ZnO surface from dissolving in a biological environment.

A magnetic nanogel based on O-carboxymethylchitosan for antitumor drug delivery: synthesis, characterization and in vitro drug release.

This paper studied the synthesis, characterization and use of the magnetic chitosan nanogel for carrying meleimidic compounds. The hydrogel polymer was prepared using O-carboxymethylchitosan, which was crosslinked with epichlorohydrin for subsequent incorporation of iron oxide magnetic nanoparticles. The characterization revealed that the magnetic material comprises about 10% of the hydrogel. This material is comprised of magnetite and maghemite and exhibits ferro-ferrimagnetic behavior. The average particle size is 4.2 nm. There was high incorporation efficiency of maleimides in the magnetic nanogel. The release was of sustained character and there was a greater release when an external magnetic field was applied. The mathematical model that best explained the process of drug release by the magnetic hydrogel was that of Peppas-Sahlin. The magnetic nanogel proved to be an excellent candidate for use in drug-delivery systems.

Formation of two-dimensionally confined superparamagnetic (Mn, Ga)As nanocrystals in high-temperature annealed (Ga, Mn)As/GaAs superlattices.

The annealing-induced formation of (Mn, Ga)As nanocrystals in (Ga, Mn)As/GaAs superlattices was studied by x-ray diffraction, transmission electron microscopy and magnetometry. The superlattice structures with 50 Å thick (Ga, Mn)As layers separated by 25, 50 and 100 Å thick GaAs spacers were grown by molecular beam epitaxy at low temperature (250 °C), and then annealed at high temperatures of 400, 560 and 630 °C. The high-temperature annealing causes decomposition to a (Ga, Mn)As ternary alloy and the formation of (Mn, Ga)As nanocrystals inside the GaAs matrix. The nanocrystals are confined in the planes that were formerly occupied by (Ga, Mn)As layers for the up to 560 °C annealing and diffuse throughout the GaAs spacer layers at 630 °C annealing. The two-dimensionally confined nanocrystals exhibit a superparamagnetic behavior which becomes high-temperature ferromagnetism (~350 K) upon diffusion.

Adsorption of Remazol Red 198 onto magnetic N-lauryl chitosan particles: equilibrium, kinetics, reuse and factorial design.

PURPOSE: The discharge of colored effluents from industries is an important environmental issue and it is indispensable to remove the dyes before the water gets back to the rivers. The magnetic adsorbents present the advantage of being easily separated from the aqueous system after adsorption by positioning an external magnetic field. METHODS: Magnetic N-lauryl chitosan (L-Cht/γ-Fe(2)O(3)) particles were prepared and characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, transmission electron microscopy, and vibrating sample magnetometry. Remazol Red 198 (RR198) was used as a reactive dye model for adsorption on L-Cht/γ-Fe(2)O(3). The adsorption isotherms were performed at 25°C, 35°C, 45°C, and 55°C and the process was optimized using a 2(3) factorial design (analyzed factors: pH, ionic strength, and temperature). The desorption and regeneration studies were performed in a three times cycle. RESULTS: The characterization of the material indicated that the magnetic particles were introduced into the polymeric matrix. The pseudo-second order was the best model for explaining the kinetics and the Langmuir-Freundlich was the best-fitted isotherm model. At room temperature, the maximum adsorption capacity was 267 mg g(-1). The material can be reused, but with a decrease in the amount of adsorbed dye. CONCLUSIONS: L-Cht/γ-Fe(2)O(3) is a promising material to remove RR198 and probably other similar reactive dyes from aqueous effluents.

Synthesis, characterization and in vitro drug release of magnetic N-benzyl-O-carboxymethylchitosan nanoparticles loaded with indomethacin.

Magnetic N-benzyl-O-carboxymethylchitosan nanoparticles were synthesized through incorporation and in situ methods and characterized by Fourier transform infrared spectroscopy, X-ray diffraction, differential scanning calorimetry, and magnetization measurements. Indomethacin was incorporated into the nanoparticles via the solvent evaporation method. The indomethacin-loaded magnetic nanoparticles were characterized by the same techniques, and also by transmission electron microscopy. The nanoparticles containing the polymer showed a drug loading efficiency of between 60.8% and 74.8%, and the magnetic properties were not significantly affected by incorporation of the drug. The in vitro drug release study was carried out in simulated body fluid, pH 7.4 at 37°C. The profiles showed an initial fast release, which became slower as time progressed. The percentage of drug released after 5 h was between 60% and 90%, and the best fitting mathematical model for drug release was the Korsmeyer-Peppas model, indicating a Fickian diffusion mechanism.

Zn(1-x)MnxTe diluted magnetic semiconductor nanowires grown by molecular beam epitaxy.

It is shown that the growth of II-VI diluted magnetic semiconductor nanowires is possible by the catalytically enhanced molecular beam epitaxy (MBE). Zn(1-x)MnxTe NWs with manganese content up to x=0.60 were produced by this method. X-ray diffraction, Raman spectroscopy, and temperature dependent photoluminescence measurements confirm the incorporation of Mn(2+) ions in the cation substitutional sites of the ZnTe matrix of the NWs.

GaAs:Mn nanowires grown by molecular beam epitaxy of (Ga,Mn)as at MnAs segregation conditions.

GaAs:Mn nanowires were obtained on GaAs(001) and GaAs(111)B substrates by molecular beam epitaxial growth of (Ga,Mn)As at conditions leading to MnAs phase separation. Their density is proportional to the density of catalyzing MnAs nanoislands, which can be controlled by the Mn flux and/or the substrate temperature. After deposition corresponding to a 200 nm thick (Ga,Mn)As layer the nanowires are around 700 nm long. Their shapes are tapered, with typical diameters around 30 nm at the base and 7 nm at the tip. The wires grow along the 111 direction, i.e., along the surface normal on GaAs(111)B and inclined on GaAs(001). In the latter case they tend to form branches. Being rooted in the ferromagnetic semiconductor (Ga,Mn)As, the nanowires combine one-dimensional properties with the magnetic properties of (Ga,Mn)As and provide natural, self-assembled structures for nanospintronics.