In this study, Cu-coated Al_2O_3 composite powders were synthesized by using electroless plating method. The influence of the plating bath composition and ceramic powder concentration on the Cu plating was characterized by scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction techniques. The results showed that the electroless bath composition plays an important role for the structure of nano core-shell Al_2O_3/Cu composite powders. The content of copper in the composite powders could be effectively controlled by adjusting the content of copper sulfate and formaldehyde in the plating solution. Furthermore, the pretreatment of the Al_2O_3 powders is also a key factor to form a uniform shell copper layer coating on Al_2O_3 particles.
The Ni₂₅Ti₅₀Cu₂₅ shape memory alloy exhibits one-step martensitic transformation. Transformation occurs between the B2 parent phase and the B19 orthorhombic martensite. The course of the martensitic transformation was in situ studied in the alloy with use of electron backscatter diffraction. During heating, reverse martensitic transformation occurs from the B19 orthorhombic martensite to the B2 parent phase. On cooling, from the parent phase the B19 martensite is formed. Obtained results proved that the B19 martensitic plates forms the variants indexed as 1, 3, and 5. Thermal cycling does not change the crystallographic correlation between the parent phase and the martensite. However, after cycling, different rearrangement of the martensitic plates can be received. In consequence, characteristic temperatures of the martensitic transformation are shifted.
We have studied the effect of leaching treatments on the surface microstructure and chemical composition on the two different twofold surfaces, (10000) and (101̅00), and the tenfold surface (00001) of a decagonal (d-) Al-Ni-Co quasicrystal. A sample exposing the three surfaces was leached with NaOH solution and then studied using atomic force microscopy and scanning electron microscopy combined with energy dispersive X-ray analysis. The leaching treatment preferentially removes the Al present in the crystal surface leaving a mixture of transition metal and their associated oxides. The high symmetry, tenfold axis was found to be less resistant to leaching than either of the twofold axes, providing further information regarding the effect of crystallographic direction on leaching kinetic.
Cadmium selenide (CdSe) thin films on glass substrates were prepared by physical vapour deposition under vacuum using the electron beam evaporated technique for different substrate temperatures: room temperature, 100, 200, 300°C, respectively. X-ray diffraction analysis indicates that the films are polycrystalline, having hexagonal (wurtzite) structure irrespective of their substrate temperature. All the films show most preferred orientation along (0 0 2) plane parallel to the substrates. The microstructural parameters such as particle size, stress, strain and dislocation density were calculated. The grain size of deposited CdSe films is small and is within the range of 18 to 42 nm. The optical absorption spectra of electrom beam deposited CdSe films were studied in the wavelength region of 250-2500 nm. The energy gap (E_{g}) values (allowed direct transitions), calculated from the absorption spectra, ranged between 1.77 and 1.92 eV. The surface morphological quality of electron beam evaporated CdSe films were analyzed by scanning electron microscopy and atomic force microscopy.
The paper describes the materials with a developed surface fabricated on the basis of electrodeposited copper icosahedral small particles and coatings made of such particles. Increasing the specific surface area of the electrolytic metal is achieved by special heat and/or chemical treatments. Changes in the structure and morphology of icosahedral small particles are analyzed with scanning electron microscopy and X-ray diffraction. The specific surface area of the material is determined with low-temperature gas adsorption technique. Annealing of icosahedral small particles and coatings leads to the formation of the porous structure and a "forest" of whiskers on their surface. Chemical etching of icosahedral small particles corrodes the inside material and provides the formation of hollow particles. Possible applications for obtained materials with a developed surface are offered.
Ion beam assisted deposition of alloying metals (Zn, Cd, Zr, Cr) onto pure aluminum and aluminum alloy substrates from the plasma of a pulsed arc discharge for the purpose of materials corrosion stability was carried out. The Rutherford backscattering spectrometry, electron backscatter diffraction, scanning electron microscopy, and electron probe microanalysis methods were applied to investigate composition and microstructure of the prepared layers. It was found that the obtained layers are characterized by amorphous atomic structure and contain the atoms of deposited metal, substrate material components, as well as impurities of oxygen and carbon; their thickness was measured to be ≈ 30-100 nm.
This paper investigates the effect of different electrolytes containing silicate and phosphate by two-step oxidation using the micro-arc oxidation technique. The growth effect, surface roughness, and element distributions of the micro-arc oxidation coatings were characterized. The composition of coating was characterized using X-ray diffraction and energy dispersive spectrum, and the morphology was examined using scanning electron microscope. The surface characterizations results show that the coating growth forms are different in Si and P electrolytes while the coated samples were almost composed of γ-Al₂O₃.
Rapidly quenched bilayers consisting of Fe-Si-B and Co-Si-B layers have been prepared by planar flow casting from a single crucible with two nozzles. Temperature dependences of electrical resistivity, dilatation and magnetization have been investigated in the amorphous state and during crystallization of both layers. Preliminary studies of the structure of the layers and of the interlayer have been performed by X-ray diffraction, cross-sectional electron microscopy and microanalysis. From the results it seems evident that the process of connection of the two layers during preparation takes place by solidification with only a small extent of mutual interdiffusion of component atoms localized to a narrow well-defined interface, leading to mechanically solid connection between the two layers. The effect of combined presence of two different soft magnetic alloys on the overall magnetic properties is discussed with respect to potential applications of such materials.
The atomic force microscopy in ultrahigh vacuum and at low temperature demonstrated its excellent capability to reach atomic resolution. Nevertheless in the case of biological samples high resolution has been achieved only in very few cases. We demonstrated here the importance of the appropriate choice of probes and substrates in order to image DNA at low temperature with high resolution. We investigated properties of three types of cantilevers and they were studied by scanning electron microscopy as a function of temperature. A large bending of cantilevers, which were coated from both sides, was observed at low temperatures. Therefore uncoated cantilevers are strongly recommended for low temperature applications. Different methods for immobilization of DNA on the substrate are examined at low temperatures. First images of linear DNA on graphite at 82 K under ultrahigh vacuum conditions are presented.
The aim of the present work is to compare two methods of synthesis of nanocrystallline zinc oxide doped with iron oxide. The synthesis was carried out using microwave asssisted hydrothermal synthesis and traditional wet chemistry method followed by calcination. The phase composition of the samples was determined using X-ray diffraction measurements. Depending on the chemical composition of the samples, hexagonal ZnO, and/or cubic ZnFe_{2}O_{4} were identified. The morphology of the received materials was characterized using scanning electron microscopy. Two different structures of agglomerates were observed: a hexagonal structure (corresponding to zinc oxide) and spherical (corresponding to spinel phase). The effect of the iron oxide concentration on specific surface area and density of the samples was determined.
X-ray diffraction, scanning electron microscopy and hardness measurements were applied as experimental methods to investigate the structure and properties of the crystalline-amorphous Al-based composites prepared by mechanical alloying and subsequent high pressure high temperature compaction of the powders. It was possible to obtain bulk, fully dense crystalline-amorphous composites and the applied compaction technique allowed preservation of amorphous structure in the composite. Addition of amorphous Al_{60}Nb_{40} phase to AA6061 alloy resulted in significant increase of hardness of the composite (120 HV), comparing to pure Al alloy compacted at the same conditions (75 HV).
We prepared Pt₃Ni and PtNi₃ nanoparticles of various sizes on conductive and atomically smooth highly oriented pyrolytic graphite surfaces using potentiostatic electrodeposition. We can control the size of electrodeposited nanoparticles and their density on the surface by changing the deposition time. The morphology of nanoparticles was determined by scanning electron microscopy. PtNi₃ particles have spherical shape, while Pt₃Ni particles have more irregular shape. Composition of particles was confirmed by energy dispersive spectroscopy. We have measured magnetic properties of both systems with 100 s preparation time, superparamagnetic behavior was observed in PtNi₃ nanoparticles with blocking temperature T_{B}=225 K.
In this work we evaluate structural and optical properties of ZnO nanoparticles grown by wet chemistry method. Light emission properties of these nanoparticles are studied with cathodoluminescence and micro-photoluminescence. Even at the room temperature excitonic emission is well resolved, due to high exciton binding energy of ZnO. Decay kinetics of photoluminescence emissions and efficiency of inter-nanoparticles energy migration is evaluated from maps of in-plane variations of photoluminescence decay times measured in microphotoluminescence setup.
The effect of modification of montmorillonite (with 3-aminopropyltrimethoxysilane or hexadecyltrimethylammonium chloride) on the mechanical properties of the composites based on HDPE Hostalen ACP 5831 with the modified montmorillonite as filler, was studied. The structures of the fillers and nanocomposites were characterised by the scanning electron microscopy and X-ray diffraction study. The effect of the filler modification on the mechanical parameters of the nanocomposites and their structure was assessed on the basis of determination of the mechanical resistance, elongation at maximum tearing stress, bending strength, deformation at the maximum force and elasticity modulus on bending (three-point bending strength).
Piezomagnetic materials in composition Ni_{0.284}Zn_{0.549}Cu_{0.183}Fe_{1.984}O₄ were prepared by mixed oxide method at 1100°C. Powder X-ray diffraction studies confirm the crystalline nature of the synthesized Ni_{0.284}Zn_{0.549}Cu_{0.183}Fe_{1.984}O₄ piezomagnetic material. The crystallite size is calculated to be 19.332 μ m using the Debye-Scherrer formula. The surface morphology and particle size of the samples has been studied by scanning electron microscopy. The thermal stability and decomposition behaviour of Ni_{0.284}Zn_{0.549}Cu_{0.183}Fe_{1.984}O₄ piezomagnetic material have been studied by thermogravimetric analysis at a heating rate of 15°C/min. The effective activation energy of the prepared composite was calculated using single heating rate methods: Broido's and Coats-Redfern methods. Dielectric properties of Ni_{0.284}Zn_{0.549}Cu_{0.183}Fe_{1.984}O₄ piezomagnetic material have been studied in a wide range of frequencies and temperatures. The magnetic behavior of Ni_{0.284} Zn_{0.549} Cu_{0.183} Fe_{1.984}O₄ piezomagnetic material at room temperature has been confirmed by vibrational sample magnetometer studies.
We describe the realization and characterization of a distributed Bragg reflectors and InAs quantum dots grown by molecular beam epitaxy. The distributed Bragg reflectors are based on a stack of eight or twenty pairs of GaAs and AlAs layers with a stopband centered at about E_0=1.24 eV (λ_0=1000 nm). The whole structures exhibit a reflectivity coefficient above 90%. The growth rate was monitored in situ by measurement of the oscillations of the thermal emission intensity. The investigations conducted on the InAs quantum dots grown on GaAs show photoluminescence around E=1.25 eV (λ=990 nm). The combination of these two elements results in the realization of a microcavity containing InAs quantum dots and surrounded by 20 pairs of distributed Bragg reflectors.
This work presents porous silicon technology, adapted to improve the characteristics of monocrystalline silicon solar cell. This is achieved by taking advantage of properties provided by porous silicon technology in production of diverse structures in the material. We produce a porous silicon derivative, which is mostly hidden in the emitter of solar cell. Research of the initial and modified solar cells was made by measuring current-voltage characteristics under illumination of a 5000 K xenon lamp. Spectrally resolved studies of current-voltage characteristics were carried out using radiation of halogen lamps and diffraction grating monochromator. Studies revealed that the manufacturing of buried porous silicon structure improves solar cell performance by increasing the fill factor of the modified solar cell current-voltage characteristics, maximum output power and efficiency, when compared to unmodified ones. Spectral studies revealed that the above-mentioned improvement differs for various sections of light spectrum. Largest relative enhancement of solar cell current was observed at the wavelengths of Δ λ = 450-550 nm. We consider the cumulative result of several effects resulting in solar cell efficiency enhancement. Most of them were the influence of porosity on effective optical path length and better anti-reflecting properties of multiple porous structures.
We study CdTe:Cr single crystals grown by the physical vapor transport method from pre-synthesized (Cd,Cr)Te alloys with 5 at.% of chromium nominal content. Macrodefects in the form of (111)-oriented thin platelets of dopant-related second phases were detected by scanning electron microscopy patterning of the chemically treated surfaces of the crystals. Magnetic properties of the crystals were investigated by ferromagnetic resonance using X-band Bruker spectrometer (9.43 GHz). Their ferromagnetic resonance spectra show several broad lines, which position depends on the orientation of the sample in relation to the external magnetic field in spectrometer. The angular dependences of ferromagnetic resonance spectra are interpreted in the frame of shape anisotropy of ferromagnetic resonance of the planar defects embedded in a weak magnetic CdTe matrix.
In the work tests of the influence of the technological conditions on the basic applied properties of the Pb(Fe_{0.5}Nb_{0.5})O_3 ceramics were carried out. The Pb(Fe_{0.5}Nb_{0.5})O_3 specimens were obtained by a two-stage method of synthesizing (the niobite method), a technique of the powder mixture calcinations, changing a temperature range of the iron-niobate (FeNbO_{4}), whereas compacting was conducted by free sintering.
Ag-ZnO composite thin films were prepared on glass substrates by chemical bath deposition at lower temperature. The samples were characterized by X-ray diffraction, scanning electron microscopy, photoluminescence and the optical transmission spectra. The morphology analysis showed that Ag nanoparticles were not deposited on the ZnO nanorods surface but on the glass substrate. The influence of the reaction time on the size and density of Ag nanoparticles was studied, the results showed that the reaction time played an important role in determining of the optical characteristics. There were two obvious photoluminescence peaks located at about 395 nm and 471 nm, respectively. The blue emission centered at 471 nm can be ascribed to the electron transition from Zn_{i} to V_{Zn}.
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