Search

In this paper, we combine the atomic layer deposition synthesis method of inverse opal with the hydrothermal growth of nanorods. From 460 nm polystyrene nanospheres opal crystals were produced using vertical deposition on Si wafers. The opal templates were covered with ZnO by atomic layer deposition. High temperature annealing was used to remove the polystyrene nanospheres to obtain the inverse opal structure. For the hydrothermal growth of ZnO nanorods, two production routes were analysed: hydrothermal reaction before and after the removal of the template. The two paths produced two distinct structures, one with plate like formations and one with nanorods, respectively. Also, the sample modified by the hydrothermal growth after the annealing showed slight differences in optical properties compared to the regular inverse opal. Morphology, composition and structure of the samples were explored using SEM, EDX and XRD. Optical properties were investigated with reflectance UV–Vis spectroscopy. Thermal stability of the polystyrene opal was determined using TG.

In this study we investigated the material properties of ZnO thin film of ≈ 300 nm thickness, grown on glass and silicon substrates by using atomic layer deposition (ALD) technique. Structural characterization was carried out using incident X-ray diffraction pattern. The microstructural evolution was accompanied by the grain size measurement. A key element of this study was to prove that it is practically impossible to attribute the optical energy gap Eg and the refractive index n dependence to any typical thin film material because these parameters depend on the deposition condition and the program used for determination. Two different values (3.32 and 3.36 eV) for the optical energy gap Eg, and (2.29–2.27) for the refractive index, have been reported and analyzed for ZnO thin film due to the type of behavior of absorbance, transmittance and reflectance. The dielectric characteristics and the AC conductivity were also measured at temperature ranging from (303–413 K0 ) and at frequency range of (1 K Hz to 1 MH). The data of the AC conductivity was analyzed by the universal power law. It was found that the corelated barrier hopping model (CBH) model is the predominate conduction mechanism. This article contains recent advances in the modified ZnO metal oxide prepared by (ALD), for efficient approach for sensor device fabrication depending mainly on the estimated parameters.

In this article, the performance of brass electrode was investigated in a Zn-air (charcoal-based cathode) rechargeable battery. The construction of the battery was carried out with biodegradable materials, namely a cotton cloth diaphragm and carboxymethyl cellulose sodium salt (CMC-Na) viscosity modifier, while the battery skeleton was printed by 3D printing technology. The brass acted as a collector and a preferable surface for the metallic Zn deposition on the brass anode surface. The electrochemical behavior of the brass anode was investigated by cyclic voltammetry (CV). Cyclic performance tests were carried out, which showed stable cell operation even in the presence or absence of additives up to more than 100 cycles. Furthermore, high energy (Eeff) and Coulomb (Ceff) efficiencies, 80% (Eeff), 95% (Ceff), 75% (Eeff), and 95% (Ceff) were obtained, respectively. The Shepherd model was applied to describe the discharging processes of the Zn-air battery containing brass as anode in the presence of additive-free electrolyte or electrolyte with CMC-Na salt additive. It was found that the Shepherd equation described only approximately the resulting discharge curves. In order to attain a more precise mathematical description, stretched exponential function was implemented into the last term of the Shepherd equation. The need for such a correction shows the complexity of the electrochemical processes occurring in these systems. In addition, the surface of the brass anode was also investigated by scanning electron microscopy (SEM) and the composition of the brass alloys was determined by X-ray fluorescence spectroscopy (XRF). Importantly, the formation of dendritic deposition was successfully suppressed and a smooth and uniform surface was obtained after the cycling tests.

The analysis focused on how efficient management of the national data asset is supported by the Hungarian regulatory framework system concerning the use of public information, and whether public data constituting part of the national data asset can be deemed authentic and reliable to support the efforts for the digitalisation and artificial intelligence-based developments of the public sector. The analysis also referred to the audit experiences of the State Audit Office of Hungary (SAO), which emphasise the absence of authenticity and reliability of the audited data in several cases. The analysis shows why the availability of authentic and reliable data in terms of the national data asset has outstanding significance. In support of this assertion, it presents the different levels of data asset use, the role of using artificial intelligence in the public sector, and the significance, risks and challenges of the authenticity and reliability of public data, from both a data protection and a public finance aspect. Inaccuracy, unreliability of input data predestines the generation of incorrect result products (conclusion, decision), even if the appropriate algorithm is used, which could lead to direct financial loss, for both the citizens and the state. The authors of the analysis therefore suggest that a paradigm shift is necessary in the strategies targeting the efficient use of the public sector’s data, with the necessity to record the fundamental precondition that the national data asset must be based on reliable and authentic data.

Thin film properties are extremely sensitive to the film preparation conditions, thus our research is dedicated to establish the correlation between the deposition parameters and properties in Al2O3/ZnO bilayered and Al2O3/Al2O3-ZnO mixed oxide/ZnO trilayred thin film samples prepared by atomic layer deposition (ALD) technique with the same total thickness and the thickness ratio of the pure Al2O3 and ZnO layers. The extracted results from the X-ray diffraction suggested structural transformation as a function of the number of layers of pure and mixed Al2O3/ZnO. Analysis was performed to investigate the physical, optical and nonlinear optical properties. The dispersion parameters were investigated in the wavelength range of 280 – 2500 nm. The absorption coefficient, optical, electrical and thermal conductivities, furthermore penetration depth have also been determined. The absorption mechanism of the prepared samples obeys the rule of allowed indirect optical transitions. The value of the optical band gap was found to increase from 3.205 eV for bilayered to 3.229 eV for trilayered samples. The dispersion of the refractive index is described and discussed in terms of the single oscillator model proposed by Wemple – DiDomenico. Moreover, the phase velocity, electric susceptibility, reflectionloss, and dispersion of nonlinear parameters such as third order nonlinear optical susceptibility and nonlinear refractive index are presented. All the studied properties and determined parameters allowing us to indicate clearly the effect of the difference between Al2O3/ZnO bilayered and Al2O3/Al2O3-ZnO mixed oxide/ZnO trilayered thin films, and how the optical properties of thin films could be enhanced and improved by changing only the stacking of Al2O3 and ZnO layers. Overall, on the basis of these results several applications could be suggested for the layer samples obtained in this work.

This research presents strong photocatalytic activity for amorphous TiO1.7 prepared by atomic layer deposition to decompose the LBR (Levafix Brilliant Red) dye. LBR is an example of the pollutant dyes in the textile industrial wastewater. This activity has been enhanced significantly through decreasing the thickness from 40 to 8 nm. This behavior is explained by correlating the photocatalytic, optical, structural and photoluminescence properties. The thinner film has higher Urbach's energy (wider tail of localized states) and higher life time of the photo-generated charge carriers. This is attributed to increasing the non-lattice oxygen content which enhances the photocatalytic behavior of thinner films. Moreover, these ultra-thin films have ability to be recycled by the same efficiency indicating its promising application in the water purification from the organic dyes and pollutants.

Although Al2O3 is considered photocatalytically inactive, in this research, novel Al-rich Al2O3 ultra-thin films are employed for the first time as fast and active photocatalysts for water treatment from organic dyes. These films are prepared using plasma enhanced atomic layer deposition (ALD). Structure of the films is investigated using X-ray diffraction, X-ray photoelectron spectroscopy and high resolution scanning electron microscope showing amorphous structure. Films with different thicknesses (8–38 nm) are applied for photo-degradation of three dyes (Levafix Brilliant Red E−4BA, C.I. Reactive Orange 96 and Remazol Black 5) commonly used in the textile industry causing severe problems in the textile wastewater. As a further novelty, the thinner film (8 nm) is surprisingly about five times faster to decompose the dyes than the thicker film (38 nm). Enhancing the photocatalytic activity could be attributed to decreasing the energy gap from 4.75 to 4.3 eV with increasing the Al composition associated with decreasing the thickness. Also, existence of excess Oxygen vacancies in the amorphous Al2O3 provides the band gap with more defect levels which reduce recombination of the photo-generated charge carriers and increase their life time. Thus, they can reach surface of the film and participate in the photocatalysis process. This indicates the promising usage of Al-rich Al2O3 ultra-thin films in water treatment to save the time and cost significantly.

A nitrogen doped carbon aerogel was used as a substrate for the atomic layer deposition of TiO2 and ZnO layers in various thicknesses. The bare and composite products were analyzed using Raman spectroscopy, XRD, N2 adsorption, SEM-EDX, TEM, XPS, and ICP-OES and their photocatalytic activity was investigated in decomposing methyl orange dye under UV light irradiation. We investigated the effect of the different metal oxides and their thickness dependence on the photocatalytic activity.

The maximization of the number of exposed edges of layered MoS2-type transition metal dichalcogenides of general formula MX2 (M = Mo, W; X = S, Se) is difficult yet meaningful way to improve their electrochemical and electrocatalytic performance. In this work, an all-solid ball milling method for simultaneous introduction of defects and their hybridization through binding of ammonia borane (NH3BH3) to defect sites of MX2 is demonstrated. The milling conditions leads to partial separation and nanosizing of MX2 layers, simultaneously extensively introducing defects (cracks, vacancies, strains, voids etc.), while the detailed analysis revealed the functionalization of the material by binding of NH3BH3 to defect sites, which results in highly improved electrocatalytic performance of thus obtained composites with respect to MX2 for hydrogen evolution reaction. The mechanochemical approach thus enables preparation of MoS2-type materials with improved, highly tunable activity, potentially relevant for energy conversion and storage.

In this work core/shell composite polymer/TiO2 nanofibers and from those TiO2 nanotubes were prepared. First, poly(vinyl alcohol) (PVA) and poly(vinylpyrrolidone) (PVP) fibers were synthetized by electrospinning. They were covered with a 100 nm thick amorphous TiO2 layer by atomic layer deposition at 50 °C. Later the polymer core was removed by two different methods: dissolution and annealing. In the case of dissolution in water, the as-prepared TiO2 nanotubes remained amorphous, while when annealing was used to remove the polymers, the TiO2 crystallized in anatase form. Due to this, the properties of amorphous and crystalline TiO2 nanotubes with exactly the same structure and morphology could be compared. The samples were investigated by SEM-EDX, ATR-IR, UV-Vis, XRD and TG/DTA-MS. Finally, the photocatalytic properties of the TiO2 nanotubes were studied by decomposing methyl-orange dye under UV light. According to the results, crystalline anatase TiO2 nanotubes reached the photocatalytic performance of P25, while amorphous TiO2 nanotubes had observable photocatalytic activity.

Monolithic structured TiO2/aerogel composites were prepared from resorcinol-formaldehyde polymer aerogel (RFA) and its carbon aerogel (RFCA) derivative. A resorcinol-formaldehyde hydrogel was synthesized in a sol-gel reaction and transformed into polymer aerogel by supercritical drying. The RFA was converted to carbon aerogel by pyrolysis at 900 °C in dry N2. Amorphous and crystalline TiO2 layers were grown from TiCl4 and H2O precursors by atomic layer deposition (ALD) at 80 °C and 250 °C, respectively, on both RFA and RFCA. The substrates and the composites were studied by N2 adsorption, TG/DTA-MS, Raman, SEM-EDX and TEM techniques. Their photocatalytic activity was compared in the UV catalyzed decomposition reaction of methyl orange dye.

Coupling TiO2 nanofibers with other semiconductor metal oxides can effectively extend the light absorbability of TiO2 to the visible range of the electromagnetic spectrum. This study demonstrates the synthesis of TiO2–MoO3 composite nanofibers via electrospinning using Ti and Mo water-soluble precursors. Aqueous solutions of these precursors were added to a PVP solution in N–N dimethylformamide. The mixture was electrospun, followed by annealing in air at 600 °C obtaining oxide nanofibers. The fibers were characterized via thermogravimetry and differential thermal analysis, X-ray photoelectron spectroscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy, transmission electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, and Raman spectroscopy. The diameter of the TiO2–MoO3 fibers was between 90 and 110 nm after annealing, Furthermore, methylene blue dye was used to investigate the photocatalytic activity of the fibers in visible light. TiO2–MoO3 fibers showed the best photocalaytic activity with a rate constant of 0.0018 min−1 while pure TiO2 and MoO3 nanofibers had 0.0009 min−1 and 0.0008 min−1 respectively.

Interface induced diffusion had been identified in a thin film system damaged by electron bombardment. This new phenomenon was observed in Al2O3 (some nm thick)/Si substrate system, which was subjected to low energy (5 keV) electron bombardment producing defects in the Al2O3 layer. The defects produced partially relaxed. The rate of relaxation is, however, was different in the vicinity of the interface and in the "bulk" parts of the Al2O3 layer. This difference creates an oxygen concentration gradient and consequently oxygen diffusion, resulting in an altered layer which grows from the Al2O3/Si substrate interface. The relative rate of the diffusion and relaxation is strongly temperature dependent, resulting in various altered layer compositions, SiO2 (at room temperature), Al2O3 + AlOx + Si (at 500 °C), Al2O3 + Si (at 700 °C), as the temperature during irradiation varies. Utilizing this finding it is possible to produce area selective interface patterning.

Atomic layer deposition (ALD) on polymer substrates often requires a modification of the polymer surface properties. Plasma-enhanced ALD (PE-ALD) process is capable of establishing improved coating/substrate adhesion and layer properties by a plasma pre-treatment prior to the layer deposition. Low density polyethylene (LDPE) films were plasma treated using different gases (N2, O2, and N2+O2 mixture) for various exposure times. A novel method was proposed to reveal the chemical changes in the surface region of LDPE films with attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopy combined with multivariate analysis. The loading plots of principal component analysis (PCA) revealed the formation of polar functional groups on the surface of LDPE films, as a result of plasma pre-treatment. PCA was also able to explore the differences and similarities in the chemical modifications of LDPE originated from different plasma gas and exposure time.

Determining binary phase diagrams for nanoparticles proves to be a very difficult task regardless if it is tried either by computer simulations, theoretical considerations or experiments. In this work, using 3D Object Stochastic Kinetic Modelling Framework (3DO-SKMF) computer simulations, we reveal some of the reasons why this is the case. First of all, even the expressions “phase diagram” and “phase composition” are usually not well-defined. We show the two different types of phase diagrams that are rarely distinguished. For phase separating nanoparticles, one diagram shows the equilibrium phase compositions in two-phase state while the other represents if the system is in an alloyed or in a separated state. We calculate both diagrams for the case of binary Janus nanoparticles and show their dependences on size and average composition. The equilibrium compositions of the phases change with both the size and the average composition of the particle. This means that the use of 3D phase diagrams is unavoidable even if the size of the particle is fixed. The careful investigation of the simulation results reveals the essential role that the interfaces play in the behaviour of the system hence in the shape of the phase diagrams. We also point out that the methods used to determine the phase compositions in nanoparticles have a substantial influence on the details of both experimentally and theoretically constructed phase diagrams.

Interface induced diffusion had been identified in thin film system damaged by electron bombardment. This new phenomenon was observed in Al2O3 (some nm thick) / Si substrate system, which was subjected to low energy (5 keV) electron bombardment producing defects in the Al2O3 layer. The defects produced partially relaxed. The rate of relaxation is, however, different in the surrounding of the interface and in the "bulk" parts of the Al2O3 layer. This difference generates an oxygen concentration gradient and consequently oxygen diffusion, resulting in an altered layer which grows from the Al2O3 / Si substrate interface. The relative rate of the diffusion and relaxation is strongly temperature dependent, resulting in various altered layer compositions, SiO2 (at room temperature), Al2O3 + AlOx+Si (at 500o C), Si(at 700o C), as the temperature during irradiation varies. Utilizing this finding it is possible to make area selective interface patterning.

In this work, we report the development of a measurement chamber linked with a quadrupole mass spectrometer (QMS) for in situ investigation of the effect of thin film cracking on the gas permeation of coated flexible polymeric substrates. The chamber enables the establishment of a bulged state of the substrate/coating system, which causes the cracking of the coating layer. The increase in the gas permeation rate due to the presence of cracks can be monitored precisely using the QMS without movement or re-clamping of the samples between each measurement step. This method eliminates the probability of uncontrollable mechanical changes in the sample, and with the mass spectrometer, high sensitivity, reliability, and reproducibility of the experimental data become available.

Extending the absorption range of TiO2 nanofibers to visible light is a great improvement of the photocatalytic property of TiO2. In this study, TiO2/WO3/C/N nanofibers were prepared by electrospinning using precursors soluble in water then annealing in argon. Titanium(IV) bis(ammonium lactato)dihydroxide (TiBALDH) and ammonium metatungstate (AMT) were used as the precursor for TiO2 and WO3 respectively. Different volume ratios of the precursors were added to a solution of PVP before electrospinning. The fibers were studied by XPS, SEM-EDX, TEM, FTIR, XRD, Raman spectroscopy and UV–VIS diffuse reflectance spectroscopy (DRS). The photocatalytic degradation of methylene blue by the fibers in visible light was investigated. The fibers had anatase TiO2 and monoclinic WO3. Based on UV–VIS DRS and Kubelka-Munk function the fibers could absorb visible light. Moreover, 100% TiBALDH had an indirect band gap of 2.9 eV, and the band gap decreased with increase in AMT, i.e., for 0% TiBALDH, band gap was 2.4 eV. The fibers degraded methylene blue dye in visible light, and 90% TiBALDH had the highest photocatalytic activity, i.e., it degraded 40% of the dye after 240 min.

The influence of the 25-nm-thick Cr and V barrier layer on the diffusion and chemical composition formation in Ni/Cu bilayer films under annealing conditions was studied. Cu-Ni solid solution formation onset was found in both cases after annealing at 450°C, which led to constantan Cu 53 Ni 47 alloy formation at 550°C. Cr intense diffusion towards the outer surface followed by its oxidation and accompanied by porous defects formation through the whole film depth was revealed. The existence of slightly higher thermal stresses on V/substrate interface promoted faster Cu-Ni diffusion intermixing as compared to the Cr underlayer application.

For revealing internal atomic processes in bimetallic nanoparticles, individual hemispherical Ag-Cu alloy particles were grown by direct current (DC) magnetron sputtering. Phase separation of particles was found to be size- and composition-dependent. Particles smaller than 5 nm in diameter remained as a solid solution of the components for all tested compositions (15-80 at.% Ag). At 15 and 30 at.% Ag compositions phase separation was observed only for particles above 5 nm in diameter. Computer simulations by Stochastic Kinetic Mean Field model reproduced the size-dependence of the decomposition and the internal structure of two-phase particles. Theoretical explanation is given for the composition dependence of the phase separation tendency.

Penetration paths caused by nanoscopic defects in plasma-enhanced atomic layer deposited (PEALD) Al2O3 thin films could increase their transmission rate, mechanical limitations could impair their encapsulation utility. In contrast, this phenomenon could be beneficial in the case of polymer electrolyte fuel cells containing a proton exchange membrane, where water retention in the membrane is crucial for efficient transport of hydrated ions. Nanocracks in the deposited layer can act as nanovalves at low humidity levels and maintain the suitable level of hydration for the membrane. This paper presents the results of a unique, in situ oxide film cracking-gas permeation measurements on 25–100 nm Al2O3 coated low-density polyethylene. The developed measurement chamber enables the bulging of the substrate/coating system, which initiates the cracking of the coating. Under the same mechanical load, the permeability decreases exponentially with film thickness: quadrupling the film thickness reduced it by a tenth. Simulation-based empirical models on gas diffusion through defected barrier layers are summarized, and an analytical model is constructed instead. We have also carried out simulations to help understand the processes. The derived analytical equations perfectly describe the literature data, our simulations, and experimental results. The introduced technical setup, experimental and theoretical work may open further perspectives in understanding the behavior of barrier layers under mechanical loading.

Covering MFI-type zeolite crystals with Al2O3 by atomic layer deposition is shown to make the external zeolite crystal impermeable for guest molecules. By corresponding manipulations of the crystal certain faces can be opened for guest molecules. In this way, IR microimaging can be applied to record the evolution of transient intracrystalline concentration profiles along the crystals longitudinal extension. The introduced method of covering may provide the possibility of observing fluxes of reactant and product molecules within single zeolite crystals during catalytic reactions.

Nanoparticles are of considerable interest, owing to their size-dependent properties, different from those of bulk materials. For revealing internal atomic processes in them, individual nanoparticles of Cu-Ag alloys were grown by direct current (DC) magnetron sputtering. Phase-separation during growth in Cu-Ag particles was found to be size- and composition-dependent. Particles below 5 nm in diameter grow as a solid solution of the components for all compositions (15–80 at.% Ag). In the low Ag content range (15 and 30 at.% Ag) phase-separation occurs only for particles above 5 nm in diameter. The separation into Cu-rich and Ag-rich domains, when observed, takes place by spinodal decomposition for all particle sizes. In particles undergoing incomplete coalescence, phase-separation occurs even if the diameter of the colliding particles is below 5 nm. In the higher Ag content range (60–80 at.%), however, no phase-separation is observed until coalescence sets in. Lattice parameter measurements in alloy particles of 30 at.% Ag revealed that the miscibility gap in individual particles varies between 70 and 90 at.%. Calculation of the composition dependence of the critical length for spinodal decomposition provided quantitative explanation for the observed phenomena.

Vertically aligned carbon nanotubes (VACNTs or &ldquo, CNT forest&rdquo, ) were decorated with semiconductor particles (TiO2 and ZnO) by atomic layer deposition (ALD). Both the structure and morphology of the components were systematically studied using scanning (SEM) and high resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDX), Raman spectroscopy, and X-ray diffraction (XRD) methods. Characterization results revealed that the decoration was successful in the whole bulk of VACNTs. The effect of a follow-up heat treatment was also investigated and its effect on the structure was proved. It was attested that atomic layer deposition is a suitable technique for the fabrication of semiconductor/vertically aligned carbon nanotubes composites. Regarding their technological importance, we hope that semiconductor/CNT forest nanocomposites find potential application in the near future.

In this work, the photocatalytic properties of amorphous and crystalline TiO2 deposited on oxide and polymer nanoparticles by atomic layer deposition (ALD) were studied. Beside TiO2, as reference, both ALD grown amorphous Al2O3 and crystalline ZnO layers were also examined. When choosing the carrier, the priority was that it had no effect on the photocatalytic activity of TiO2; therefore the oxide layers were deposited on SiO2 and poly(methyl-methacrylate) (PMMA) nanoparticles. The amorphous SiO2 particles were synthetized by the Stöber method, while the PMMA particles were prepared by emulsion polymerization. Both the bare and core/shell composite nanoparticles were investigated by SEM-EDX, TEM, FT-IR, and XRD. Finally, the photocatalytic activity of PMMA, SiO2 and the core/shell nanoparticles was measured by the decomposition of methylene orange, monitored by UV-Vis spectroscopy. Based on the results, the SiO2 was uniformly coated with the deposited oxide films, while in the case of the PMMA a contiguous web-like polymer/TiO2 matrix was formed. During the photocatalytic reactions, the amorphous Al2O3 was not active, while the crystalline ZnO and TiO2 showed good photocatalytic activity. The amorphous TiO2 deposited by ALD on the SiO2 and PMMA nanoparticles had smaller, but a clearly detectable photocatalytic effect on the photodegradation of methylene orange.