Mesoporous CaF2 nanopowders with specific surface area up to 91.5 m2/g have been produced using by electron beam evaporation method in vacuum. The effect of nanosecond e-beam irradiation in air on magnetic and texture properties this nanopowders has been studied. The irradiation influence on the specific surface area and magnetization of CaF2 nanopowder has been discovered for the first time.
Mesoporous nanocrystalline CaF2 powder was obtained by pulsed electron beam evaporation (PEBE) in vacuum. The specific surface area (SSA) of the nanopowder (NP) of CaF2 reached 88.7 m2g. The effect of thermal annealing in air in the temperature range 200–900 oC on particle size, morphology, textural, thermal, magnetic, and luminescent properties of NP was studied. A strong deviation of the obtained nanoparticles from stoichiometry and a significant increase in SSA after annealing at 200 ° C was observed. The obtained CaF2 NP showed ferromagnetic (FM) behavior. The appearance of the FM response can be explained by the formation of structures and radiation defects. An analysis of the pulsed cathodoluminescence (PCL) curves and the magnetization of NP CaF2 allows us to draw conclusions about their relationship.
Nanophosphors in the amorphous state are first obtained via pulsed electron beam evaporation of targets made of polycrystalline phosphors with the compositions Ca_2M_8(SiO_4)_6O_2:Eu (M = Y and Gd) and Ca_2La_8(GeO_4)_6O_2:Eu with the structure of oxyapatite. Reduction of ions Eu^3+ → Eu^2+ in the electron beam is found. Modification of the Raman scattering (RS) spectra of the samples in the case of a decrease in the size of the particles from bulk to a nanosized state is found. The change in the forbidden band width E _ g of the samples in the case of transition from a bulk powder to an NP is considered. The spectral and luminescence characteristics of the samples in the polycrystalline and nanoamorphous states are studied. It is shown that, in the case of transition to nanosamples, the ligand field around Eu^2+ changes. This may be due to the violation of the translational symmetry in the NP. The bond between the 4 f and 5 d electrons weakens. Degeneracy of the ^2 e _ g level appears. Presumably, the reduction of ions Eu^3+ → Eu^2+ in the electron beam due to the breaking of the Si(Ge)–O bond in the process of evaporation of the samples and capture of the released electron by the Eu^3+ ions is found.
Импульсным электронным испарением в вакууме получены трехфазные (корунд + δ-фаза + аморфная фаза) аморфно-нанокристаллические порошки чистого и допированного углеродом Al 2 O 3 (x C = 1.07−6.6 wt.%). Размер гексагональных нанокристаллов корунда в нанопорошке Al 2 O 3 −C (x C = 1.07 wt.%) составлял около 5 nm. Граница растворимости углерода в решетке Al 2 O 3 находилась ниже 1.07 wt.% С. Установлена зависимость формы катодолюминесцентных спектров и фазового состава полученных нанопорошков Al 2 O 3 и Al 2 O 3 −C от материала испаряемой мишени. Обнаружено отсутствие R-линий от примесных ионов Cr
ВведениеСовременные исследования ферромагнетизма в низ-коразмерных структурах (тонких пленках, покрытиях, наночастицах (НЧ), нанопорошках (НП) и др.) чи-стых и допированных немагнитными элементами окис-лов показали ФМКТ c ясной петлей гистерезиса при температуре 390 K и удельной намагниченностью при 300 K около 3.5 · 10 −3 emu/g. Тонкие пленки оксида алюминия благодаря лучшей стабильности и высокой диэлектрической проницаемости широко используются в спинтронных приложениях и в будущем могут стать заменой традиционного полупроводника SiO 2 в устрой-ствах MOП (металл−оксид−полупроводник) и в других областях [19].Расчеты из первых принципов (ab initio) показали, что ферромагнетизм в Al 2 O 3 может быть индуцирован за счет допирования углеродом Al-и O-узлов решетки, в которых спиновые плотности локализуются в основном на С-допанте [20]. Допирование углеродом в узлах Al приводит к сужению запрещенной зоны и значительно изменяет потолок валентной зоны, хотя допирование С в узлах О действует на краях запрещенной полосы слабо.Однако
Using a method of pulsed electron beam evaporation in vacuum was produced the mesoporous multiphase amorphous and crystal nanopowder of Bi2O3 with a specific surface area up to 23 sq.m/g. Influence of thermal annealing of powder (200-300 0C) in air is investigated. The formation of droplets with a size of 2-5 nm was found on the surface of all large nanoparticles that make up the framework 3D nanopowder agglomerates due to extrusion of liquid bismuth from the volume during cooling.
Using a pulsed electron beam evaporation in vacuum a mesoporous nanopowder CaF2 with a specific surface area up to 60.5 m2/g were produced. The effect of annealing in different media on the evolution of magnetic and texture properties of CaF2 nanoparticles has been studied. For the first time, the effect of annealing medium on the specific surface area and magnetization of CaF2 nanopowders was discovered.
Polycrystalline phosphors with a Sr2Y8-x-yYbyTmxSi6O26 (x=0.005-0.5, y=0.2,0.3) total formula were synthesized. Nanoluminophor has been obtained from the Sr2Y7.695Yb0.3Tm0.005Si6O26 microcrystalline sample by the vacuum electron been evaporation, in the amorphous state, with the ~10.6 nm particle size. It is found, raman spectra undergoing modification by the transition from bulk- to nanosize state. Photoluminescene spectra micro- and nanophosphors are studied. Intensity of the blue emission, by the UV ligth excitation, grows in the x=0.005-0.02 region, with the x increasing. Upconversion photoluminescence (UPCL) spectra of the bulk phosphors and nanosample based on the Sr2Y7.695Yb0.3Tm0.005Si6O26 were measurd. At the pumping power around 70.8 mW, by the laser source with the λ=980 nm, thereshold population of the 3F3 level of Tm3+ ions exist. At a power higher 70.8 mW, a sharp increase of the luminescence intensityof the bulk- and nanophosphor occurs. For the 3H4->3H6 transition thereshold pumping power absent. This indicates that, pumping, during Yb->Tm energy transer, is a single photon process.
Mesoporous amorphous-crystalline nanopowders of BaF_2 with the specific surface area up to 34.8 m^2/g were obtained using evaporation by a pulsed electron beam in vacuum. Influence of the thermal annealing of the BaF_2 nanoparticles in air at the temperatures from 200 to 900°C on the size and morphology of the particles and changes in their magnetic and luminescent properties was studied. The paramagnetic response of the BaF_2 nanopowder was found to transform to the ferromagnetic response after annealing at 900°C. The appearance and transformation of the magnetic response in nanopowders made of BaF_2, which is diamagnetic as the bulk material, are ascribed to the appearance of radiation-induced and structural defects during the synthesis process by pulsed electron-beam evaporation.
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