V. G. Il’ves

Production of ZnO and Zn-ZnO nanopowders using evaporation by a pulsed electron beam in low-pressure gas

This paper describes a method for the production of ZnO and Zn-ZnO nanopowders (NPs) using the evaporation of a target by a pulsed electron beam in a low-pressure gas and condensation on a cold crystallizer. Crystalline and amorphous NPs of pure ZnO and a Zn-ZnO mixture have been synthesized. These powders have a specific surface of up to 40 m2/g and are produced at a rate as high as 5 g/hour. It has been found that the pressure and the composition of gases (air, oxygen, and argon) in the evaporation chamber of the installation influenced the composition and the morphology of the powders. The effect that the target composition has on the production rate and characteristics of the powders has been studied. All the synthesized powders possessed marked magnetic properties.

Properties of the Amorphous-Nanocrystalline Gd 2 O 3 Powder Prepared by Pulsed Electron Beam Evaporation

An amorphous-nanocrystalline Gd2O3 powder with a specific surface area of 155 m2/g has been prepared using pulsed electron beam evaporation in vacuum. The nanopowder consists of 20- to 500-nm agglomerates formed by crystalline nanoparticles (3–12 nm in diameter) connected by amorphous-nanocrystalline strands. At room temperature, the Gd2O3 nanopowder exhibits a paramagnetic behavior. The phase transformations occurring in the powder have been investigated using differential scanning calorimetry and thermogravimetry (40–1400°C). The amorphous phase of the nanopowder is thermally stable up to a temperature of 1080°C. It has been found that the amorphous phase has an inhibitory effect on the temperature of the polymorphic transformation from the cubic phase into the monoclinic phase. It has been revealed that, compared with the microcrystalline powder, the Gd2O3 nanopowder is characterized by a complete quenching of photoluminescence.

Magnetic properties of oxide nanopowders obtained by pulsed electron beam evaporation

The magnetic properties of oxide nanopowders obtained by pulsed electron beam evaporation of targets in a low-pressure gas phase have been studied. Using this method, we obtained Zn-ZnO and ZnO nanopowders with the specific magnetization amounting to 2.8 × 10−2 and 2 G cm3/g, respectively. Significant room-temperature ferromagnetism has been observed for the fist time in a nanopowder of yttria-stabilized zirconia, where the specific magnetization reached ∼6.7 × 10−2 G cm3/g.

Effect of Iron Doping on the Properties of Nanopowders and Coatings on the Basis of Al 2 O 3 Produced by Pulsed Electron Beam Evaporation

Multiphase nanopowders (NPs) and amorphous/amorphous-nanocrystalline coatings (A-NC) have been prepared by the evaporation of ceramic targets of Al2O3-Fe2O3 (0.1, 3, 5 Fe2O3 mass %) by a pulsed electron beam in vacuum. The specific surface area of NP Al2O3-Fe2O3 reached 277 m2/g. The α and γ phases Al2O3 and other nonidentified phases have been found in the composition of NP Al2O3-Fe2O3. All coatings contained an insignificant fraction of the crystalline γ phase. No secondary phases on the basis of iron have been revealed. According to transmission electron microscopy, the fine fraction of NP Al2O3-Fe2O3 consists of amorphous nanoparticles of an irregular and quasispherical shape no more than 10 nm in size which form agglomerates reaching 1.5 μm. A large fraction of NPs consists of crystal spherical nanoparticles with preferential sizes of about 10–20 nm. All NP Al2O3-Fe2O3 showed ferromagnetic behavior at room temperature. The maximum magnetic response has been established in NPs with a minimum iron content (1.1 mass %). The pulsed cathode luminescence spectra of coatings and NP Al2O3-Fe2O3 have been presented by a wide band in the wavelength range of 300–900 nm regardless of their phase composition. Phase transformations into NP AL2O3-1.1% Fe and coatings from undoped Al2O3 heated to 1400°C occur according to the following scheme: amorphous phase → γ → δ → θ → α, regardless of their initial phase composition. The threshold of thermal stability of the Γ phase in NPs and the coating of undoped Al2O3 does not exceed 830°C. For the first time, the increased thermo and optically stimulated luminescent response comparable with the response of the leading TLD-500K thermoluminescent dosimeter has been reached in A-NC coatings of undoped Al2O3.

Investigation of properties of ZnO-Zn-Cu nanopowders obtained by pulsed electron evaporation

ZnO-Zn and ZnO-Zn-Cu nanopowders with a high specific surface (up to 68 m2/g) is obtained by pulsed electron evaporation. The characteristics of nanopowders (NPs) are investigated by X-ray phase analysis (RPA), high-resolution transmission electron microscopy (HR TEM), electron diffraction analysis, differential scanning calorimetry (DSC), thermogravimetric (TG) analysis, inductively coupled plasma (ICP) method, and pulsed cathodoluminescence (PCL). For the first time, ferromagnetism at room temperature is found in ZnO-Zn-Cu nanopowders. The powder magnetism is connected with defects and magnetic Cu2+ ions in amorphous interlayers at interfaces between ZnO nanocrystallites. The connection of magnetic properties of nanopowders with the lattice constant of the fine-crystalline fraction of ZnO is shown.

Production and studies of properties of nanopowders on the basis of CeO2

Nanopowders (NPds) of pure CeO2 of a specific surface area up to 210 m2/g and those doped with copper, carbon, and iron (≤1 wt % of dopant) of a specific surface area in the range 130–160 m2/g have been produced by evaporation with a pulsed electron beam. According to the X-ray phase analysis data, no secondary phases (aside from the cubic CeO2 phase) were found in the produced NPds. All the powders contained fine- and coarse-crystalline fractions differing in the size of their coherent scattering region (CSR) and in their amorphous component. The degree of crystallinity of the powders was not above 22%. The powders have a fractal structure and consist of agglomerates of sizes from dozens to hundreds of nanometers formed by crystalline nanoparticles (NPts) 3–5 nm in size with a very narrow particle size distribution. NPds have a high structural defectiveness degree, which was reflected in their magnetic properties. The room ferromagnetism was established in NPds of pure CeO2 − x and those doped with nonmagnetic elements (carbon and copper): here the ferromagnetic state in the CeO2-C system was established for the first time, whereas the magnetic moment on the carbon atom was 35-fold lower than the theoretical estimation. The ferromagnetic contribution to CeO2 NPd increases with a decrease in the NPt size and reaches 0.1 emu/g in CeO2-Fe NPd (xFe = 0.54 wt %). It has been established that there is no direct dependence between magnetization and the content of iron ions in the CeO2-Fe-based NPds.

Influence of Fe-Doping on the Structural and Magnetic Properties of ZnO Nanopowders, Produced by the Method of Pulsed Electron Beam Evaporation

The nanopowders (NPs) ZnO-Zn-Fe and ZnO-Fe with the various concentrations of Fe () ( mass.%) were prepared by the pulsed electron beam evaporation method. The influence of doping Fe on structural and magnetic properties of NPs was investigated. X-ray diffraction showed that powders contain fine-crystalline and coarse-crystalline ZnO fractions with wurtzite structure and an amorphous component. Secondary phases were not found. The magnetic measurements made at room temperature, using the vibration magnetometer and Faraday’s scales, showed ferromagnetic behavior for all powders. Magnetization growth of NPs ZnO-Zn and ZnO-Zn-Fe was detected after their short-term annealing on air at temperatures of 300–500°C. The growth of magnetization is connected with the increase in the concentration of the phase ZnO with a defective structure as the result of oxidation nanoparticles (NPles) of Zn. The scanning transmission electron microscopy (STEM) showed a lack of Fe clusters and uniform distribution of atoms dopant in the initial powder ZnO-Zn-Fe. A lack of logical correlation between magnetization and concentration of a magnetic dopant of Fe in powders is shown.

Properties of an amorphous silicon dioxide nanopowder prepared by pulsed electron beam evaporation

An amorphous SiO2 nanopowder with a specific surface area of 154 m2/g has been prepared using pulsed electron beam evaporation of a target from a pyrogenic amorphous Aerosil 90 nanopowder (90 m2/g). It has been found that SiO2 nanoparticles exhibit improved magnetic, thermal, and optical properties as compared to the properties of particles of the Aerosil 90 nanopowder. Possible factors responsible for the appearance of ferromagnetism at room temperature in the amorphous SiO2 nanopowder formed upon electron beam evaporation have been discussed. The photoluminescence and cathodoluminescence properties of the SiO2 nanopowder have been investigated.

Luminescent and Dosimetric Properties of Thin Nanostructured Layers of Aluminum Oxide Obtained Using Evaporation of a Target by a Pulsed Electron Beam

Results of a study of optically and thermally stimulated luminescence (OSL and TL) of thin nanostructured aluminum oxide coatings obtained with evaporation of the target by a pulsed electron beam and deposited on quartz glass, Al, steel, Cu, Ta, and graphite wafers are presented. It follows from data of X-ray phase analysis that the obtained Al2O3 layers have an amorphous nanocrystal structure with different contents of the γ phase depending on the geometry of the wafer location on evaporation and annealing temperature of the samples. It is established that the material of the wafer and the ratio of the amorphous and γ phase in Al2O3 layers affect the yields of OSL and TL. Annealing at up to 970 K results in an increase of γ-phase concentration and OSL and TL responses. It was found that the yields of OSL and TL for the most emission-effective coating samples are comparable with those for the detectors on the basis of anion-defective corundum. The dose-dependence for β radiation, which was linear in the range 20–5000 mGy, was investigated.

Effect of iron doping on the structural and magnetic properties of ZnO nanoparticles prepared by pulsed electron beam evaporation

Nanocrystalline ZnO, ZnO-Zn, and ZnO-Zn-Fe powders with a specific surface area up to 45 m2/g and a low Fe concentration (no more than 0.619 wt %) have been prepared using pulsed electron beam evaporation. The crystal structure, morphology, and size of the nanoparticles have been determined using X-ray powder diffraction, transmission electron microscopy, and scanning electron microscopy. It has been found that the magnetization of the ZnO-Zn and ZnO-Zn-Fe nanopowders increases after annealing in an oxidizing atmosphere. An elemental mapping with energy-dispersive X-ray analysis has revealed the absence of Fe clusters in the ZnO-Zn-Fe sample. A thermal analysis has demonstrated that dopants of Fe in ZnO increase the temperature of complete oxidation of Zn nanoparticles to 600°C, which creates favorable conditions for an increase in the density of structural defects upon oxidation of Zn to ZnO. The absence of clusters and secondary magnetic Fe phases in pure and doped ZnO-based nanopowders indicates the intrinsic nature of ferromagnetism at room temperature in nanopowders prepared by pulsed electron beam evaporation.