This paper presents an analysis of the field ion emission mechanism of tungsten–epoxy nanocomposite emitters and compares their performance with that of tungsten nano-field emitters. The emission mechanism is described using the theory of induced conductive channels. Tungsten emitters with a radius of 70 nm were fabricated using electrochemical polishing and coated with a 20 nm epoxy resin layer. Characterization of the emitters, both before and after coating, was performed using electron microscopy and energy-dispersive X-ray spectroscopy (EDS). The Tungsten nanocomposite emitter was tested using a field ion microscope (FIM) in the voltage range of 0–15 kV. The FIM analyses revealed differences in the emission ion density distributions between the uncoated and coated emitters. The uncoated tungsten tips exhibited the expected crystalline surface atomic distribution in the FIM images, whereas the coated emitters displayed randomly distributed emission spots, indicating the formation of induced conductive channels within the resin layer. The atom probe results are consistent with the FIM findings, suggesting that the formation of conductive channels is more likely to occur in areas where the resin surface is irregular and exhibits protrusions. These findings highlight the distinct emission mechanisms of both emitter types.

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.

Ultralow frequency (ULF) to low frequency (LF) electromagnetic radiation represents one of the most promising effects of brittle rock strain and microcracking that might be potentially helpful for short term earthquake forecasting. In this study the results of a six month monitoring campaign are presented from Obir Cave in the eastern Alps. Direct experimental observations of electromagnetic radiation have been made using a customised broadband data logger installed next to the Obir Fault - this seismogenic fault near the Periadriatic Lineament is known to be related to at least three large prehistoric earthquakes. On the basis of these measurements it has been possible to characterise a number of distinct signals: artificial constant narrowband signals at discrete frequencies; short serial broadband impulses; high energy broadband impulses; and low energy broadband impulses. The narrowband artificial signals were removed from the electromagnetic radiation time series analysis so that the natural signals were enhanced and could be compared more easily to meteorological parameters and rock strain indicators. Critically, the high energy broadband impulses show a strong correlation with lightning activity across much of central Europe and the eastern Mediterranean while the low energy broadband impulses appear to be associated with local rock strain in and around Obir Cave. Unfortunately, it seems certain that some of the essential strain related impulses are likely to have been overprinted by the larger lightning related impulses.

In this study a comparison of the topography of BiFeO3 (BFO) thin films deposited on tantalum pentoxide substrates of different thicknesses is provided. The Ta2O5 substrates had a roughness increasing with the film thickness. The relationship between substrates of different topography but the same composition with the quality of the growing bismuth ferrite film is estimated. For the first time the topography estimation of BFO on Ta2O5 is presented. The difference in temperature expansion coefficients leads to intensive evaporation of bismuth ferrite from the surface during annealing. XPS analysis is provided for asdeposited and annealed BFO layers.

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.

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.

This paper focuses on the research and development of a suitable method for creating a selective emitter for the visible and near-infrared region to be able to work optimally together with silicon photovoltaic cells in a thermophotovoltaic system. The aim was to develop a new method to create very fine structures beyond the conventional standard (nanostructures), which will increase the emissivity of the base material for it to match the needs of a selective emitter for the VIS and NIR region. Available methods were used to create the nanostructures, from which we eliminated all unsuitable methods; for the selected method, we established the optimal procedure and parameters for their creation. The development of the emitter nanostructures included the necessary substrate pretreatments, where great emphasis was placed on material purity and surface roughness. Tungsten was purposely chosen as the main material for the formation of the nanostructures; we verified the effect of the formed structure on the resulting emissivity. This work presents a new method for the formation of nanostructures, which are not commonly formed in such fineness; by this, it opens the way to new possibilities for achieving the desired selectivity of the thermophotovoltaic emitter.

The structure and properties of gallium arsenide photovoltaic cells were investigated using a wide range of analytical methods. Solar cells were exposed to intense gamma irradiation with a dose of 500 kGy. The radioactive isotope Cobalt-60 was used as the emitter. Fourier transform infrared spectroscopy (FTIR), ellipsometry, and spectrophotometry were used as optical measurement methods for observing the shift of permittivity, reflectance, and other surface investigation. Changes in thin-film composition were also analyzed by secondary-ion mass spectrometry (SIMS) by surface sputtering. Electrical characteristics were also observed. Minority carrier properties, junctions, or defects in semiconductor were investigated by scanning electron microscopy (SEM) with electron beam-induced current method (EBIC). Complementarily was proved diffusion of metals into thin layers of GaAs structure. This phenomenon affects the overall performance of the solar cell.

This work provides the benchmarking of two additive manufacturing (AM) technologies suitable for the fabrication of commercially pure titanium scaffolds for bone tissue engineering, i.e., selective laser melting (SLM) and robocasting. SLM is a powder bed fusion technique that is industrially used for the AM of titanium parts, whereas robocasting is an extrusion technique mainly studied for the fabrication of ceramic scaffolds that requires post-sintering for the consolidation. A novelty of this work is to combine robocasting with pressure-less spark plasma sintering (PL-SPS) for the fabrication and fast consolidation of titanium scaffolds. The results show that the metallurgical phenomena occurring in both techniques are different. Melting and fast solidification in SLM produced martensitic-like microstructure of titanium with low microporosity (6 %). In contrast, solid-state sintering in robocasting resulted in the equiaxed grain microstructure of alpha titanium phase with 13 % of microporosity. The mechanical performance of the scaffolds was determined by the microporosity of the rods rather than microstructure. Consequently, robocasting resulted in lower compressive yield strength and effective elastic modulus than SLM, which were in the range of human trabecular bone. Finally, both AM technologies produced cytocompatible scaffolds that showed evidence of in vitro osteogenic activity.

Tantalum pentoxide finds use in many electronic and optical applications, and in the recent years has been highly important for use in optics. Its sought-after properties include dielectric insulation and optical reflectivity. Its full potential seems not yet fully tapped and further research into the material brings ever more possibilities of use. To further the development of Tantalum pentoxide-based technologies, this paper explores the properties of thin film coating created by electron beam evaporation with plasma ion assisted deposition on a silicon substrate. Ion etching is a highly popular and precise method of surface alteration, as it allows for alteration on nanoscale and better control over optical properties of the resulting sample. In our paper, etching was used to increase the topographical variability of the surface, while not breaching the tantalum pentoxide coating. The sample is subjected to several different measurement methods: X-ray diffraction and ellipsometry were used to establish the quality and integrity of the material, and optical reflectometry, X-ray photoelectron spectroscopy and atomic force microscopy were used for characterization of argon etching results. Optical and morphological properties and their relationship before and after etching are observed and documented to improve the knowledge about the material and set a baseline for future development.

This work aims to clarify the application of electron beam-induced current (EBIC) method for the morphological analysis and detection of local defects and impurities in semiconductor structures such as solar cells. One of the advantages of this method is to observe a leakage path and microplasma sites with nanometer resolution. This technique allows to precisely locate the affected area and determine the type of defect that cannot be commonly characterized with sufficient accuracy. Simultaneously, a focused ion beam could be used to determine junction by milling of the samples at the area of interest. The evaluation results of experimental measurement using these techniques on photovoltaic cells illustrates the applicability and importance of the EBIC method.

We introduce an affordable and easy-to-implement method of determining the thickness of a mechanically damaged layer on the surface of a cadmium telluride single crystal after mechanical lapping. This method is based on This method is based on different usage of already known defect-revealing etchants: the side projection of the lapped surface. A comparison of developed etch pit patterns in the vicinity of the lapped side etched by the Everson solution, Nakagawa solution, Hähnert and Schenk solution, Saucedo solution, Inoue E-Ag II solution and FeCl3 is provided. The most commonly used defect-revealing etchants the Nakagawa and Everson solutions—did not show any trend of etch pit formation towards a mechanically damaged surface. On the other hand, the Saucedo, FeCl3 and E-Ag II etches were successful and achieved similar results. These etchants revealed three distinctive regions of sub-surface damage: (i) a severely polycrystalline 50 µm deep damaged region with micro cracks. This region was best revealed by the FeCl3 etch. (ii) A region of plastic deformations that is 180 µm deep. This region was best revealed by the E-Ag etch. (iii) A region free from mechanical damage. High-resolution X-ray diffraction (HRXRD) further confirmed the results obtained by chemical methods. Full-width at half maximum of the rocking curves decreased from the value of 1000 arcsec on the lapped surface to the value lower than 30 arcsec after the removal of 200 µm of the surface. From HRXRD analysis, the region (i) can be further divided into an approx. 10 µm thin nearly amorphous region, followed by a microcrystalline region. The region (ii) showed mosaic structure consisted of large crystallic blocks, with low angle misorientation from the main diffraction peak. The results showed that the thickness of the mechanically damaged layer is ten times higher than the size of the abrasive used.

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.

This research article presents results of silicon solar cell defects optoelectronic characterization based on several experimental methods. These microstructure defects have their origin mainly in the production process, but also can be caused by mechanical stress. However, some defect related spots emit light when the cell is reverse biased. Therefore, electroluminescence (EL) method is used for macroscopic localization and scanning near-field optical microscopy (SNOM) combined with photomultiplier tube in order to scan topography of defective area in microscale. Moreover, elemental analysis of the defects related spots provided by energy-dispersive X-ray spectroscopy (EDX) is presented as well. Besides that, focused ion beam (FIB) was used to isolate the defective spots by 2 µm wide and 2 µm deep barrier. Isolation pattern around the defect is avoiding leakage current flow through it. Since leakage current does not flow through defect, solar cell parameters in reverse conditions are improved.

This paper deals with problematics of energy harvesting and sensing using micro-fiber piezocomposite elements. During the past decade, piezocomposite materials have become an interest of many research activities and due to their favourable properties they have been utilized in wide spectrum of low power applications. Energy harvesting and non-destructive sensing is one of the areas that offers an interesting and challenging opportunity for the application of piezocomposite elements. However, because of the relatively complicated nature of a piezocomposite structure, it is necessary to integrate electronics for signal processing, control, and power management into the sensing or energy harvesting device. There are commercially available solutions in the form of integrated circuits that can be used for general applications of piezoelectric sensors and energy harvesters, they are, however, not optimized for specific piezoelectric materials and applications and do not allow using the elements up to their maximum potential. Therefore, it is necessary to design electronics with respect to the parameters of the element and a create a solution for a specific application. The aim of this paper is to formulate and measure key parameters and characteristics of a specific piezocomposite element and suggest a suitable way of signal processing and power management for sensing and energy harvesting applications.

The capability of using a linear kinetic energy harvester - A cantilever structured piezoelectric energy harvester - to harvest human motions in the real-life activities is investigated. The whole loop of the design, simulation, fabrication and test of the energy harvester is presented. With the smart wristband/watch sized energy harvester, a root mean square of the output power of 50 mu W is obtained from the real-life hand-arm motion in human's daily life. Such a power is enough to make some low power consumption sensors to be self powered. This paper provides a good and reliable comparison to those with nonlinear structures. It also helps the designers to consider whether to choose a nonlinear structure or not in a particular energy harvester based on different application scenarios. (C) 2018 Elsevier Ltd. All rights reserved.

The work focuses on the study of structure stability and electrical parameters of photovoltaic cells based on GaAs with Ge substrate. Solar cells of this type are used especially in adverse environments such as space applications, so their working parameters should be stable even under extreme operating conditions. Changes of electrical characteristics of the cells were recorded in the form of noise measurements for examination of distinctions in the pn-junction. Current-voltage characteristics under the light illumination and in the dark environment for comparison of the cells performance were also measured. Infrared camera showed the thermal irradiation of the stressed and damaged parts and support to localize the defected areas. Atomic force microscope (AFM) was applied for observation of changes in three-dimensional topography with high resolution. Scanning electron microscope (SEM) with energy-dispersive X-ray spectroscopy (EDS) showed morphology of the solar cells and provided the elemental analysis of the samples. Raman spectroscopy provided a structural fingerprint and helped to evaluate the influence of induced degradation methods. Variations of morphology and composition were compared, detected and well-observed. Furthermore, electrical measurements proved the solar cells to be stable under temperature stresses.

In cases when two concrete parts are cast against in different times are not connected by dowels, main contributors to the resistance are cohesion and friction. Shear resistance of the interface is highly dependent on surface treatment and its roughness. In this paper, besides the review of available methods of surface roughness determination, the optical profilometry will be introduced and described. Optical profilometry represents non-contact and non-destructive method for characterizing surface topography. Furthermore, results obtained by abovementioned method will be compared with Sand Patch Test, in order to determine its usability and limitations.

The aim of this research is to detect and localize microstructural defects by using an electrically excited light emission from a forward/reverse-bias stressed pn-junction in thin-film Cu(In, Ga)Se-2 solar cells with metal wrap through architecture. A different origin of the local light emission from intrinsic/extrinsic imperfections in these chalcopyrite-based solar cells can be distinguished by a spectrally-filtered electroluminescence mapping. After a light emission mapping and localization of the defects in a macro scale is performed a micro scale exploration of the solar cell surface by a scanning electron microscope which follows the particular defects obtained by an electroluminescence. In particular, these macroscopic/microscopic examinations are performed independently, then the searching of the corresponding defects in the micro scale is rather difficult due to a diffused light emission obtained from the macro scale localization. Some of the defects accompanied by a highly intense light emission very often lead to a strong local overheating. Therefore, the lock-in infrared thermography is also performed along with an electroluminescence mapping.

Low-frequency noise and I-V characteristics of reverse-biased thin-film chalcopyrite CIGS solar cell with a metal wrap through architecture were measured in order to evaluate the efficiency of edge deletion by a fine grinding and polishing. These electrical measurements were supplemented by a microscale exploration of the edges, electroluminescence mapping, and lock-in IR thermography. Research efforts are related to the local technological as well as purposely induced structure defects investigation.