Oxygen Vacancies and Surface Wettability: Key Factors in Activating and Enhancing the Solar Photocatalytic Activity of ZnO Tetrapods

This paper reports on the high photocatalytic activity of ZnO tetrapods (ZnO-Ts) using visible/solar light and hydrodynamic water flow. It was shown that surface oxygen defects are a key factor in the photocatalytic activity of the ZnO-Ts. The ability to control the surface wettability of the ZnO-Ts and the associated concentration of surface defects was demonstrated. It was demonstrated that the photocatalytic activity during the MB decomposition process under direct and simulated sunlight is essentially identical. This presents excellent prospects for utilizing the material in solar photocatalysis.

A Brief Review of Bone Cell Function and Importance

This review focuses on understanding the macroscopic and microscopic characteristics of bone tissue and reviews current knowledge of its physiology. It explores how these features intricately collaborate to maintain the balance between osteoblast-mediated bone formation and osteoclast-mediated bone resorption, which plays a pivotal role in shaping not only our physical framework but also overall health. In this work, a comprehensive exploration of microscopic and macroscopic features of bone tissue is presented.

Loading of Silver (I) Ion in L-Cysteine-Functionalized Silica Gel Material for Aquatic Purification

The L-cysteine-functionalized silica (SG-Cys-Na+) matrix was effectively loaded with silver (I) ions using the batch sorption technique. Optimal Ag(I) loading into SG-Cys-Na+ reached 98% at pHi = 6, 80 rpm, 1 mg L-1, and a temperature of 55 °C. The Langmuir isotherm was found to be suitable for Ag(I) binding onto SG-Cys-Na+ active sites, forming a homogeneous monolayer (R2 = 0.999), as confirmed by FTIR spectroscopy. XRD analysis indicated matrix stability and the absence of Ag2O and Ag(0) phases, observed from diffraction peaks. The pseudo-second-order model (R2 > 0.999) suggested chemisorption-controlled adsorption, involving chemical bonding between silver ions and SG-Cys-Na+ surface. Thermodynamic parameters were calculated, indicating higher initial concentrations leading to increased equilibrium constants, negative ΔG values, positive ΔS values, and negative ΔH. This study aimed to explore silver ion saturation on silica surfaces and the underlying association mechanisms. The capability to capture and load silver (I) ions onto functionalized silica gel materials holds promise for environmental and water purification applications.

Exploring the Piezoelectric Properties of Bismuth Ferrite Thin Films Using Piezoelectric Force Microscopy: A Case Study

Over recent decades, the scientific community has managed to make great progress in the theoretical investigation and practical characterization of bismuth ferrite thin films. However, there is still much work to be completed in the field of magnetic property analysis. Under a normal operational temperature, the ferroelectric properties of bismuth ferrite could overcome the magnetic properties due to the robustness of ferroelectric alignment. Therefore, investigation of the ferroelectric domain structure is crucial for functionality of any potential devices. This paper reports deposition and analyzation of bismuth ferrite thin films by Piezoresponse Force Microscopy (PFM) and XPS methods, aiming to provide a characterization of deposited thin films. In this paper, thin films of 100 nm thick bismuth ferrite material were prepared by pulsed laser deposition on multilayer substrates Pt/Ti(TiO₂)/Si. Our main purpose for the PFM investigation in this paper is to determine which magnetic pattern will be observed on Pt/Ti/Si and Pt/TiO₂/Si multilayer substrates under certain deposition parameters by utilizing the PLD method and using samples of a deposited thickness of 100 nm. It was also important to determine how strong the measured piezoelectric response will be, considering parameters mentioned previously. By establishing a clear understanding of how prepared thin films react on various biases, we have provided a foundation for future research involving the formation of piezoelectric grains, thickness-dependent domain wall formations, and the effect of the substrate topology on the magnetic properties of bismuth ferrite films.

Multiferroic/Polymer Flexible Structures Obtained by Atomic Layer Deposition

The paper considers how a film of bismuth ferrite BiFeO₃ (BFO) is formed on a polymeric flexible polyimide substrate at low temperature ALD (250 °C). Two samples of BFO/Polyimide with different thicknesses (42 nm, 77 nm) were studied. As the thickness increases, a crystalline BFO phase with magnetic and electrical properties inherent to a multiferroic is observed. An increase in the film thickness promotes clustering. The competition between the magnetic and electrical subsystems creates an anomalous behavior of the magnetization at a temperature of 200 K. This property is probably related to the multiferroic/polymer interface. This paper explores the prerequisites for the low-temperature growth of BFO films on organic materials as promising structural components for flexible and quantum electronics.

Piezo-, photo- and piezophotocatalytic activity of electrospun fibrous PVDF/CTAB membrane

A composite material based on polyvinylidene fluoride (PVDF) nanofibers modified with cetyltrimethylammonium bromide (CTAB) was synthesized by coaxial electrospinning. The morphology and structure of the material were studied by SEM, FTIR spectroscopy, X-ray diffraction analysis, XPS, and the piezo-photo- and piezo-photocatalytic activity during the decomposition of the organic dye Methylene blue (MB) was studied. It is shown that the addition of CTAB promotes additional polarization of the PVDF structure due to ion-dipole interaction. It has been shown for the first time that the addition of CTAB promotes the photosensitivity of the wide-gap dielectric polymer PVDF (the band gap is more than 6 eV). It was demonstrated that the photocatalytic decomposition efficiency was 91% in 60 minutes. The material exhibits piezocatalytic activity – 73% in 60 minutes. Experiments on trapping active oxidizing forms have established that OH hydroxyl radicals play the main role in the photocatalytic process.

Characterization and Evaluation of Engineered Coating Techniques for Different Cutting Tools-Review

Coatings are now frequently used on cutting tool inserts in the metal production sector due to their better wear resistance and heat barrier effect. Protective hard coatings with a thickness of a few micrometers are created on cutting tools using physical or chemical vapor deposition (PVD, CVD) to increase their application performance. Different coating materials are utilized for a wide range of cutting applications, generally in bi-or multilayer stacks, and typically belong to the material classes of nitrides, carbides, carbonitrides, borides, boronitrides, or oxides. The current study examines typical hard coatings deposited by PVD and CVD in the corresponding material classes. The present state of research is reviewed, and pioneering work on this subject as well as recent results leading to the construction of complete "synthesis-structure-property-application performance" correlations of the different coatings are examined. When compared to uncoated tools, tool coatings prevent direct contact between the workpiece and the tool substrate, altering cutting temperature and machining performance. The purpose of this paper is to examine the effect of cutting-zone temperatures on multilayer coating characteristics during the metal-cutting process. Simplified summary and comparisons of various coating types on cutting tools based on distinct deposition procedures. Furthermore, existing and prospective issues for the hard coating community are discussed.

Corrosion resistance and surface microstructure of Mg3 N2 /SS thin films by plasma focus instrument

Utilizing a plasma focus (PF) instrument, magnesium nitride (Mg₃ N₂ ) thin films were synthesized on stainless steel substrates. Twenty five optimum focus shots at 8 cm distance from the anode tip were used to deposit the films at different angular positions regarded to the anode axis. Scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray diffraction (XRD) analyses were performed to assess the surface morphology and structural characteristics of Mg₃ N₂ films. Based on AFM images, these films were studied to understand the effect of angular position variation on their surfaces through morphological and fractal parameters. By increasing the angle, we verify that the grain size decreased from 130(0) nm to 75(5) nm and also the mean quadratic surface roughness of the films reduced in its average values from (28.97 ± 3.24) nm to (23.10 ± 1.34) nm. Power spectrum density analysis indicated that films become more self-affine at larger angles. Furthermore, the corrosion behavior of the films was investigated through a potentiodynamic polarization test in H₂ SO₄ solution. It was found that the ion energy and flux, varying with the angular positions from the anode tip, directly affected the nanostructured roughness and surface morphology of the samples. The electrochemical studies of films show that the uncoated sample presented the lowest corrosion resistance. The highest corrosion resistance was obtained for the sample deposited with 25 optimum shots and at 0° angular position reaching a reduction in the corrosion current density of almost 800 times compared to the pure stainless steel-304 substrate. HIGHLIGHTS: Mg₃ N₂ /SS films have been deposited at different angles by plasma focus (PF) instruments. The effect of angular position on the surface microtexture, morphological parameters, and corrosion features of the films was studied. The RBS measurement and X-ray diffraction are utilized to identify the crystalline phases and thickness of films.

Multiferroic behavior of the functionalized surface of a flexible substrate by deposition of Bi2 O3 and Fe2 O3

Thin films of bismuth and iron oxides were obtained by atomic layer deposition (ALD) on the surface of a flexible substrate poly(4,4'-oxydiphenylene-pyromellitimide) (Kapton) at a temperature of 250°C. The layer thickness was 50 nm. The samples were examined by secondary-ion mass spectrometry, and uniform distribution of elements in the film layer was observed. Surface morphology, electrical polarization, and mechanical properties were investigated by atomic force microscope, piezoelectric force microscopy, and force modulation microscopy. The values of current in the near-surface layer varied in the range of ±80 pA when a potential of 5 V was applied. Chemical analysis was performed by X-ray photoelectron spectroscopy, where the formation of Bi₂ O₃ and Fe₂ O₃ phases, as well as intermediate phases in the Bi-Fe-O system, was observed. Magnetic measurements were carried out by a vibrating sample magnetometer that showed a ferromagnetic response. The low-temperature method of functionalization of the Kapton surface with bismuth and iron oxides will make it possible to adapt the Bi-Fe-O system to flexible electronics.

Comprehensive Characterization of PVDF Nanofibers at Macro- and Nanolevel

This study is focused on the characterization and investigation of polyvinylidene fluoride (PVDF) nanofibers from the point of view of macro- and nanometer level. The fibers were produced using electrostatic spinning process in air. Two types of fibers were produced since the collector speed (300 rpm and 2000 rpm) differed as the only one processing parameter. Differences in fiber's properties were studied by scanning electron microscopy (SEM) with cross-sections observation utilizing focused ion beam (FIB). The phase composition was determined by Fourier-transform infrared spectroscopy (FTIR) and Raman spectroscopy. The crystallinity was determined by differential scanning calorimetry (DSC), and chemical analysis of fiber's surfaces and bonding states were studied using X-ray photoelectron spectroscopy (XPS). Other methods, such as atomic force microscopy (AFM) and piezoelectric force microscopy (PFM), were employed to describe morphology and piezoelectric response of single fiber, respectively. Moreover, the wetting behavior (hydrophobicity or hydrophilicity) was also studied. It was found that collector speed significantly affects fibers alignment and wettability (directionally ordered fibers produced at 2000 rpm almost super-hydrophobic in comparison with disordered fibers spun at 300 rpm with hydrophilic behavior) as properties at macrolevel. However, it was confirmed that these differences at the macrolevel are closely connected and originate from nanolevel attributes. The study of single individual fibers revealed some protrusions on the fiber's surface, and fibers spun at 300 rpm had a core-shell design, while fibers spun at 2000 rpm were hollow.

Triboelectric Response of Electrospun Stratified PVDF and PA Structures

Utilizing the triboelectric effect of the fibrous structure, a very low cost and straightforward sensor or an energy harvester can be obtained. A device of this kind can be flexible and, moreover, it can exhibit a better output performance than a device based on the piezoelectric effect. This study is concerned with comparing the properties of triboelectric devices prepared from polyvinylidene fluoride (PVDF) fibers, polyamide 6 (PA) fibers, and fibrous structures consisting of a combination of these two materials. Four types of fibrous structures were prepared, and then their potential for use in triboelectric devices was tested. Namely, individual fibrous mats of (i) PVDF and (ii) PA fibers, and their combination-(iii) PVDF and PA fibers intertwined together. Finally, the fourth kind was (iv), a stratified three-layer structure, where the middle layer from PVDF and PA intertwined fibers was covered by PVDF fibrous layer on one side and by PA fibrous layer on the opposite side. Dielectric properties were examined and the triboelectric response was investigated in a simple triboelectric nanogenerator (TENG) of individual or combined (i-iv) fibrous structures. The highest triboelectric output voltage was observed for the stratified three-layer structure (the structure of iv type) consisting of PVDF and PA individual and intertwined fibrous layers. This TENG generated 3.5 V at peak of amplitude at 6 Hz of excitation frequency and was most sensitive at the excitation signal. The second highest triboelectric response was observed for the individual PVDF fibrous mat, generating 2.8 V at peak at the same excitation frequency. The uniqueness of this work lies in the dielectric and triboelectric evaluation of the fibrous structures, where the materials PA and PVDF were electrospun simultaneously with two needles and thus created a fibrous composite. The structures showed a more effective triboelectric response compared to the fibrous structure electrospun by one needle.

Structure Tuning and Electrical Properties of Mixed PVDF and Nylon Nanofibers

The paper specifies the electrostatic spinning process of specific polymeric materials, such as polyvinylidene fluoride (PVDF), polyamide-6 (PA6, Nylon-6) and their combination PVDF/PA6. By combining nanofibers from two different materials during the spinning process, new structures with different mechanical, chemical, and physical properties can be created. The materials and their combinations were subjected to several measurements: scanning electron microscopy (SEM) to capture topography; contact angle of the liquid wettability on the sample surface to observe hydrophobicity and hydrophilicity; crystallization events were determined by differential scanning calorimetry (DSC); X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and Fourier-transform infrared spectroscopy (FT-IR) to describe properties and their changes at the chemical level. Furthermore, for the electrical properties of the sample, the dielectric characteristics and the piezoelectric coefficient were measured. The advantage of the addition of co-polymers was to control the properties of PVDF samples and understand the reasons for the changed functionality. The innovation point of this work is the complex analysis of PVDF modification caused by mixing with nylon PA6. Here we emphasize that the application of nylon during the spin influences the properties and structure (polarization, crystallization) of PVDF.

Surface Analyses of PVDF/NMP/[EMIM][TFSI] Solid Polymer Electrolyte

Thermal treatment conditions of solid polymer polymer electrolyte (SPE) were studied with respect to their impact on the surface morphology, phase composition and chemical composition of an imidazolium ionic-liquid-based SPE, namely PVDF/NMP/[EMIM][TFSI] electrolyte. These investigations were done using scanning electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry as well as X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy. A thoroughly mixed blend of polymer matrix, ionic liquid and solvent was deposited on a ceramic substrate and was kept at a certain temperature for a specific time in order to achieve varying crystallinity. The morphology of all the electrolytes consists of spherulites whose average diameter increases with solvent evaporation rate. Raman mapping shows that these spherulites have a semicrystalline structure and the area between them is an amorphous region. Analysis of FTIR spectra as well as Raman spectroscopy showed that the β-phase becomes dominant over other phases, while DSC technique indicated decrease of crystallinity as the solvent evaporation rate increases. XPS and ToF-SIMS indicated that the chemical composition of the surface of the SPE samples with the highest solvent evaporation rate approaches the composition of the ionic liquid.

PVDF Fibers Modification by Nitrate Salts Doping

The method of inclusion of various additives into a polymer depends highly on the material in question and the desired effect. In the case of this paper, nitride salts were introduced into polyvinylidene fluoride fibers prepared by electrospinning. The resulting changes in the structural, chemical and electrical properties of the samples were observed and compared using SEM-EDX, DSC, XPS, FTIR, Raman spectroscopy and electrical measurements. The observed results displayed a grouping of parameters by electronegativity and possibly the molecular mass of the additive salts. We virtually demonstrated elimination of the presence of the γ-phase by addition of Mg(NO₃)₂, Ca(NO₃)₂, and Zn(NO₃)₂ salts. The trend of electrical properties to follow the electronegativity of the nitrate salt cation is demonstrated. The performed measurements of nitrate salt inclusions into PVDF offer a new insight into effects of previously unstudied structures of PVDF composites, opening new potential possibilities of crystalline phase control of the composite and use in further research and component design.

Characterization of GaAs Solar Cells under Supercontinuum Long-Time Illumination

This work is dedicated to the description of the degradation of GaAs solar cells under continuous laser irradiation. Constant and strong exposure of the solar cell was performed over two months. Time-dependent electrical characteristics are presented. The structure of the solar cells was studied at the first and last stages of degradation test. The data from Raman spectroscopy, reflectometry, and secondary ion mass spectrometry confirm displacement of titanium and aluminum atoms. X-ray photoelectron spectroscopy showed a slight redistribution of oxygen bonds in the anti-corrosion coating.

Piezoelectric Current Generator Based on Bismuth Ferrite Nanoparticles

Bismuth ferrite nanoparticles with an average particle diameter of 45 nm and spatial symmetry R3c were obtained by combustion of organic nitrate precursors. BiFeO₃-silicone nanocomposites with various concentrations of nanoparticles were obtained by mixing with a solution of M10 silicone. Models of piezoelectric generators were made by applying nanocomposites on a glass substrate and using aluminum foil as contacts. The thickness of the layers was about 230 μm. There was a proportional relationship between the different concentrations of nanoparticles and the detected potential. The output voltages were 0.028, 0.055, and 0.17 V with mass loads of 10, 30, and 50 mass%, respectively.

Characterization of Polyvinylidene Fluoride (PVDF) Electrospun Fibers Doped by Carbon Flakes

Polyvinylidene fluoride (PVDF) is a modern polymer material used in a wide variety of ways. Thanks to its excellent resistance to chemical or thermal degradation and low reactivity, it finds use in biology, chemistry, and electronics as well. By enriching the polymer with an easily accessible and cheap variant of graphite, it is possible to affect the ratio of crystalline phases. A correlation between the ratios of crystalline phases and different properties, like dielectric constant as well as piezo- and triboelectric properties, has been found, but the relationship between them is highly complex. These changes have been observed by a number of methods from structural, chemical and electrical points of view. Results of these methods have been documented to create a basis for further research and experimentation on the usability of this combined material in more complex structures and devices.

Atomic Layer Deposition of Mixed-Layered Aurivillius Phase on TiO2 Nanotubes: Synthesis, Characterization and Photoelectrocatalytic Properties

For the first time, one-dimensional phase-modulated structures consisting of two different layered Aurivillius phases with alternating five and six perovskite-like layers were obtained by atomic layer deposition (ALD) on the surface of TiO2 nanotubes (Nt). It was shown that the use of vertically oriented TiO2 Nt as the substrate and the ALD technology of a two-layer Bi2O3-FeOx sandwich-structure make it possible to obtain a layered structure due to self-organization during annealing. A detailed study by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that the coating is conformal. Raman spectroscopic analysis indicated the structure of the layered Aurivillius phases. Transient photocurrent responses under Ultraviolet-Visible (UV-Vis) light irradiation show that the ALD coating benefits the efficiency of photon excitation of electrons. The results of the photoelectrocatalytic experiments (PEC) with methyl orange degradation as a model demonstrate the significant potential of the synthesized structure as a photocatalyst. Photoluminescent measurement showed a decrease in the probability of recombination of photogenerated electron-hole pairs for ALD-coated TiO2 Nt, which demonstrates the high potential of these structures for use in photocatalytic and photoelectrochemical applications.

Surface Modification and Enhancement of Ferromagnetism in BiFeO3 Nanofilms Deposited on HOPG

BiFeO3 (BFO) films on highly oriented pyrolytic graphite (HOPG) substrate were obtained by the atomic layer deposition (ALD) method. The oxidation of HOPG leads to the formation of bubble regions creating defective regions with active centers. Chemisorption occurs at these active sites in ALD. Additionally, carbon interacts with ozone and releases carbon oxides (CO, CO2). Further annealing during the in situ XPS process up to a temperature of 923 K showed a redox reaction and the formation of oxygen vacancies (Vo) in the BFO crystal lattice. Bubble delamination creates flakes of BiFeO3-x/rGO heterostructures. Magnetic measurements (M-H) showed ferromagnetism (FM) at room temperature Ms ~ 120 emu/cm3. The contribution to magnetization is influenced by the factor of charge redistribution on Vo causing the distortion of the lattice as well as by the superstructure formed at the boundary of two phases, which causes strong hybridization due to the superexchange interaction of the BFO film with the FM sublattice of the interface region. The development of a method for obtaining multiferroic structures with high FM values (at room temperature) is promising for magnetically controlled applications.

Field Emission Properties of Polymer Graphite Tips Prepared by Membrane Electrochemical Etching

This paper investigates field emission behavior from the surface of a tip that was prepared from polymer graphite nanocomposites subjected to electrochemical etching. The essence of the tip preparation is to create a membrane of etchant over an electrode metal ring. The graphite rod acts here as an anode and immerses into the membrane filled with alkali etchant. After the etching process, the tip is cleaned and analyzed by Raman spectroscopy, investigating the chemical composition of the tip. The topography information is obtained using the Scanning Electron Microscopy and by Field Emission Microscopy. The evaluation and characterization of field emission behavior is performed at ultra-high vacuum conditions using the Field Emission Microscopy where both the field electron emission pattern projected on the screen and current–voltage characteristics are recorded. The latter is an essential tool that is used both for the imaging of the tip surfaces by electrons that are emitted toward the screen, as well as a tool for measuring current–voltage characteristics that are the input to test field emission orthodoxy.

Polymer Graphite Pencil Lead as a Cheap Alternative for Classic Conductive SPM Probes

This paper presents polymer graphite (PG) as a novel material for the scanning tunneling microscopy (STM) probe. Conductive PG is a relatively modern nanocomposite material used for micro-pencil refills containing a polymer-based binding agent and graphite flakes. Its high conductivity and immunity against surface contamination, with a low price, make it seem like a highly suitable material for electrode manufacturing in general. For the tip production, three methods were developed and are further described in the paper. For the production, three commercially available polymer graphite rods were used. Each has been discussed in terms of performance within the tunneling microscope and within other potential applications.

Scanning electron microscopy and energy-dispersive X-ray spectroscopy analysis of electrochemically etched graphite tips created from pencil lead

Modern day pencil lead is a material of many possibilities. Manufacture process is fast, easy, and well established, yet the full potential of its use still remains to be uncovered. Graphite content ratio to binding clays determines basic properties of the lead like its toughness and color, but more interesting qualities like conductivity and reactivity as well. Properly employed electrochemical etching with a bubble membrane creates sharp and smooth graphite tips, which can be, given enough graphite content, used as probes in several measurement techniques. Observing and adjusting the tip creation process and the results for use in further research are the objectives of this paper.

Multifractal Characterization of Butterfly Wings Scales

A lot of insect families have physical structures created by evolution for coloration. These structures are a source of ideas for new bio-inspired materials. The aim of this study was to quantitatively characterize the micromorphology of butterfly wings scales using atomic force microscopy and multifractal analysis. Two types of butterflies, Euploea mulciber ("striped blue crow") and Morpho didius ("giant blue morpho"), were studied. The three-dimensional (3D) surface texture of the butterfly wings scales was investigated focusing on two areas: where the perceived colors strongly depend on and where they do not depend on the viewing angle. The results highlight a correlation between the surface coloration and 3D surface microtexture of butterfly wings scales.

Influence of scanning rate on quality of AFM image: Study of surface statistical metrics

The purpose of this work is to study the dependence of AFM-data reliability on scanning rate. The three-dimensional (3D) surface topography of the samples with different micro-motifs is investigated. The analysis of surface metrics for estimation of artifacts from inappropriate scanning rate is presented. Fractal analysis was done by cube counting method and evaluation of statistical metrics was carrying out on the basis of AFM-data. Combination of quantitate parameters is also presented in graphs for every measurement. The results indicate that the sensitivity to scanning rate growths with fractal dimension of the sample. This approach allows describing the distortion of the images against scanning rate and could be applied for dependences on the other measurement parameters. The article explains the relevance and comparison of fractal and statistical surface parameters for characterization of data distortion caused by inappropriate choice of scanning rate.