Formation of Iron Oxides by Surface Oxidation of Iron Plate

Oxidation of iron plates (α-phase) at high temperatures and in atmospheric conditions was monitored. The composition of oxidation products was analyzed with XRD, Raman and Mössbauer spectros-copies, whereas the morphologies of oxidation products were inspected by FE-SEM. The oxidation products formed at 300 and 400 °C consisted dominantly of magnetite and small fractions of hematite, whereas at 500 and 600 °C hematite was the dominant phase, as shown by XRD. In all these samples Raman spectra showed the presence of hematite in the outer oxidation layer. FE-SEM analysis showed the formation of nanowires at 500 °C and vertically grown hematite spikes against the lower oxidation layers at 600 °C. Oxidation products formed at 800 °C consisted of wüstite (Fe1–xO) as the dominant phase, nonstoichiometric magnetite (Fe3–xO4) and hematite (α-Fe2O3) in small fractions. The surface of these oxidation layers showed a hierarchical microstructure, as well as the hexagonal hematite rods vertically grown against the lower oxidation layers. The formation of the oxidation products can be considered a process which includes the oxidation of α-Fe to Fe1–xO and its transformation to Fe3–xO4 that further transforms to α-Fe2O3, probably via a short-lived γ-Fe2O3 (maghemite) phase. (doi: 10.5562/cca1943

The Effects of Three Remineralizing Agents on the Microhardness and Chemical Composition of Demineralized Enamel

This study aimed to determine the effects of three different varnish materials (containing casein phosphopeptide-amorphous calcium phosphate, nano- hydroxyapatite, and fluoride) on enamel. Thirty- three extracted human third molars were used for specimen preparation. These were demineralized using phosphoric acid. Three experimental groups (n = 11) were treated with 3M™ Clinpro™ White Varnish, MI Varnish®, and Megasonex® toothpaste, respectively, every twenty- four hours for fourteen days. Analysis of the microhardness of the specimens’ enamel surfaces was carried out via the Vickers method, and by scanning electron microscopy/energy dispersive X- ray spectroscopy (SEM/EDS). Analysis was performed at three stages: at baseline value, after demineralization, and after the period of remineralization. Data were subjected to Scheffe’s post hoc test. The mean microhardness values (HV0.1) obtained for the group of samples treated with MI Varnish® were higher compared with the other two groups (p = 0.001 for both comparisons), while the first and third groups did not differ significantly from each other (p = 0.97). SEM analysis showed uneven patterns and porosities on all samples tested. EDS results showed an increase in the mineral content of the examined samples, with the highest mineral content observed in the MI Varnish® group. It can be concluded that MI Varnish® use has a better remineralization effect on enamel than the other two materials

The Influence of Experimental Conditions on the Formation of ZnO Fibers by Electrospinning

The influence of experimental conditions on the formation of ZnO fibers by electrospinning has been investigated. The electrospinning of a viscous suspension containing polyvinylpyrrolidone and zinc acetate in C2H5OH/H2O produced very long fibers (several hundred μm). Upon calcination a thin deposit of precursor fibers at 400 or 500 °C for 1 h the fibers consisting of ZnO nanoparticles were obtained. On the other hand, ZnO fibers were not obtained upon heating a thick deposit of precursor fibers at 600 °C for 6 h. At all three heating temperatures (400, 500 or 600 °C) ZnO nanoparticles with a gradual increase in size were produced. The Raman spectrum of ZnO nanoparticles formed at 600 °C showed additional bands which were assigned to graphene oxide. It was suggested that in the thick deposit the organic com¬ponent did not burn out completely, i.e., the residual carbon (graphite) transformed into graphene oxide for the experimental conditions applied

Silicon Nanowires Substrates Fabrication for Ultra-Sensitive Surface Enhanced Raman Spectroscopy Sensors

The silicon based substrates for surface enhanced Raman spectroscopy (SERS) have been synthesized and tested. The silver-assisted electroless wet chemical etching method has been utilized for silicon nanowires production which has been proved as the promising SERS substrate. The morphology of the silicon nanowires coated with silver nanoparticles has been examined by scanning electron microscopy. The SERS measurements tested on rhodamine 6G molecules indicated the optimal silicon nanowire substrate production obtained for 5 M hydrofluoric acid and 30 mM silver nitrate etching solution. The results show SERS detection limit of 10–8 M rhodamine in aqueous solution. This work is licensed under a Creative Commons Attribution 4.0 International License

The New Ion-Selective Electrodes Developed for Ferric Cations Determination, Modified with Synthesized Al and Fe−Based Nanoparticles

The solid-state ion-selective electrodes presented here are based on the FePO4 :Ag2S:polytetrafluoroethylene (PTFE) = 1:1:2 with an addition of (0.25–1)% microwave-synthesized hematite (α-Fe2O3 ), magnetite (Fe3O4 ), boehmite [γ-AlO(OH)], and alumina (Al2O3 ) nanoparticles (NPs) in order to establish ideal membrane composition for iron(III) cations determination. Synthesized NPs are characterized with Fourier-Transform Infrared (FTIR) spectroscopy, Powder X-Ray Diffraction (PXRD), and Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDS). The iron oxides NPs, more specifically, magnetite and hematite, showed a more positive effect on the sensing properties than boehmite and alumina NPs. The hematite NPs had the most significant effect on the linear range for the determination of ferric cations. The membrane containing 0.25% hematite NPs showed a slope of −19.75 mV per decade in the linear range from 1.2·10−6 to 10−2 mol L−1 , with a correlation factor of 0.9925. The recoveries for the determination of ferric cations in standard solutions were 99.4, 106.7, 93.6, and 101.1% for different concentrations

Intense desert dust event in the northern Adriatic (March 2020); insights from the numerical model application and chemical characterization results.

The untypically extreme and sudden particulate matter outbreak set stage over Balkan region from 27 to 30 March 2020. The available observations at air quality stations in Croatia recorded the hourly PM10 concentrations up to 412 μgm-3. Meteorological analysis shows the PM10 concentrations increase was primarily affected by advection of mineral dust from the desert area east to the Caspian Sea. The anticyclone north of Croatia and cyclone over Anatolia formed a strong pressure gradient driving a transport from the east. The backward trajectories as well as satellite products indicated the dry Aral Sea as a major source of dust. A dust plume affected the PM10 increase observed in Croatia, starting at Osijek and easternmost air quality stations . Modeling study shows the vertical extension of a plume was up to ~2 km. However, the PM10 chemical (Pb, Cd, Cu, Zn, Fe, Mn, PAHs) and morphological (SEM analyses) composition at the site in the northeastern Adriatic revealed mainly the presence of the Saharan dust. Preceding the Asian dust advection, the Saharan dust transport towards Balkan driven by Sharav cyclone was observed in PM10 at several stations in the Adriatic and continental Croatia on 26 March 2020. Modeling results showed the Saharan dust transport was at levels below ~ 8 km. The mixing of the Asian and Saharan dust plumes over Balkan was favored by subsidence due to anticyclonic high pressure conditions, and it is the most likely explanation for the observed PMs chemical and morphological results

Low Temperature Deposition of SiNx Thin Films by the LPCVD Method

Thin silicon rich nitride (SiNx) films were deposited using the LPCVD (Low Pressure Chemical Vapor Deposition) method. Silane diluted in argon and ammonia were used as the reactant gasses, and the low temperature deposition at 570 °C was used. The films were deposited on silicon (111) substrates. Films with the different values of the nitrogen content were deposited by varying the ratio of the flows of ammonia and silane in the horizontal tube reactor. The films were characterized in terms on the surface quality (by scanning electron microscopy), in terms of the nitrogen content x by time of flight elastic recoil detection analysis and by Raman and FTIR spectroscopy. The thickness and dielectric constant were measured by ellipsometry. The films were found to have a very smooth, homogeneous surface with nitrogen content that vary from x = 0 to x = 1 in dependence on the deposition parameters. The intensity of the Si–N stretching peak has shown strong correlation with the film thickness measured by ellipsometry. The films showed a smooth surface layer and the value of dielectric constant easily controllable by the ratio of the flow of the gases in the reactor. (doi: 10.5562/cca1970

Enhanced near-infrared response of nano- and microstructured silicon/organic hybrid photodetectors

Heterojunctions between an organic semiconductor and silicon are an attractive route to extending the response of silicon photodiodes into the near infrared (NIR) range, up to 2000 nm. Silicon-based alternatives are of interest to replace expensive low band-gap materials, like InGaAs, in telecommunications and imaging applications. Herein, we report on the significant enhancement in NIR photodetector performance afforded by nano- and microstructuring of p-doped silicon (p-Si) prior to deposition of a layer of the organic semiconductor Tyrian Purple (TyP). We show how different silicon structuring techniques, namely, electrochemically grown porous Si, metal-assisted chemical etching, and finally micropyramids produced by anisotropic chemical etching (Si μP), are effective in increasing the NIR responsivity of p-Si/TyP heterojunction diodes. In all cases, the structured interfaces were found to give photodiodes with superior characteristics as compared with planar interface devices, providing up to 100-fold improvement in short-circuit photocurrent, corresponding with responsivity values of 1–5  mA/W in the range of 1.3–1.6 μm. Our measurements show this increased performance is neither correlated to optical effects, i.e., light trapping, nor simply to geometric surface area increase by micro- and nanostructuring. We conclude that the performance enhancement afforded by the structured p-Si/organic diodes is caused by a yet unresolved mechanism, possibly related to electric field enhancement near the sharp tips of the structured substrate. The observed responsivity of these devices places them closer to parity with other, well-established, Si-based NIR detection technologies