Formation of quasi-ordered structures on the surface of strontium titanate in a plasma field

The X-ray diffraction and X-ray spectroscopic properties of strontium titanate single crystals and their surface exposed to plasma have been investigated. Both undoped SrTiO₃ crystals and crystals containing impurity ions of the iron or lanthanum groups have been analyzed. Data on the plasma-induced formation of ordered crystallites on the sample surface were obtained by electron and atomic force microscopy. The crystallites are from 10^?7 to 10^?9 m in size and their hypothetical orientation [321] is independent of the sample orientation and irradiation dose.     

Cobalt-containing silicon oxycarbide glasses derived from poly[methyl(phenyl)]siloxane and cobalt phthalate

Cobalt-containing silicon oxycarbides have been produced by curing and pyrolysis of polymethyl(phenyl)siloxane resin Lukosil 901 and Co-phthalate blends. The structure of the Si(Co)OC glasses was studied by electron microscopy, back-scattered electron imaging (BSE), Raman and infrared spectroscopies. The cobalt incorporated into SiOC structure increases the polymerization degree of the glass phase. It seems that the free carbon phase is closing into the SiO(Co)C network. This idea also supports the results of combustibility studies – prepared glasses are characterized by excellent oxidation resistance at high temperatures.     

电子辐照对VO2薄膜热致相变过程中光学性能的影响

利用能量为1.7MeV,注量分别为10^13-10^15/cm^2,的电子束辐照二氧化钒薄膜,对辐照及未辐照样品进行了UV－VIS,XPS参数测试,并测量900nm处光透射性能随温度的变化,发现电子辐照导致了VO2薄中的V离子价态由V^4向V^5 转变,薄膜热致相变前后的光透射比随注量增加变化较小,只在注量为10^14/cm^2时光透射比减小得较明显,相变温度点及热滞回线宽度随注量增加出现显著变化,并对有关的结果进行了讨论。     

Study of the structural features of ε-Co nanoparticles synthesized by cobalt carbonyl decomposition in the presence of surfactant

Cobalt nanoparticles (3–7 nm in size) obtained by cobalt carbonyl decomposition in 1,2-dichlorobenzene in the presence of surfactants (trioctylphosphine oxide and oleic acid) have been studied by a complex of structural methods: small-angle X-ray scattering, electron diffraction, and transmission electron microscopy. The nanoparticles synthesized are found to consist of the cubic ε-Со phase; their crystal structure is described within the sp. gr. P4₁32, a = 6.097 Å. Using small-angle X-ray scattering, the size and shape of nanoparticles have been determined directly in the liquid dispersion. Most of the particles have a spherical shape; their average size is ≈3.5 ± 0.5 nm, which agrees with the electron microscopy data. Possible factors causing the ε-phase formation during synthesis of metallic Co nanoparticles are discussed.

     

Inclusion of carbon nanotubes in a TiO2 sol-gel matrix

We report here the successful inclusion of carbon nanotubes (CNs) into a TiO₂ matrix prepared by a sol-gel method. The presence of CNs in the sol-gel matrix and the structure of the film were analyzed principally by transmission electron microscopy. Complementary information about the behavior of embedded carbon nanotubes versus heat treatment and ion irradiation were obtained by X-ray photoelectron spectroscopy. The elaboration of an inorganic matrix containing embedded carbon nanotubes leads to a new nanocomposite. The possible applications of this nanocomposite are discussed.     

Structural and physical properties of cobalt nanocluster composite glasses

Composite systems with metallic nanoparticles embedded in dielectrics present peculiar physical properties which are attractive in several application fields. In the case of transition elements, the magnetic properties of the metal clusters embedded in a dielectric matrix mainly depend on the particle size and structure. In this work, silica films containing cobalt atoms were synthesized by RF magnetron co-sputtering deposition technique, with cobalt concentration of a few atomic percent. X-ray diffraction and transmission electron microscopy showed the presence of hcp cobalt nanoclusters in the as-deposited sample with the highest cobalt concentration. After deposition, thermal treatments were performed to promote cobalt compounds or nanoparticle formation. The thermal treatments were able to change the oxidation state of cobalt atoms, as well as the structure of metallic cobalt nanoclusters (from hcp to fcc), their final size depending on both the preparation parameters and the subsequent annealing atmospheres.     

Effect of high-energy electron irradiation in an electron microscope column on fluorides of alkaline earth elements (CaF2, SrF2, and BaF2)

The effect of high-energy (150 eV) electron irradiation in an electron microscope column on crystals of fluorides of alkaline earth elements CaF₂, SrF₂, and BaF₂ is studied. During structural investigations by electron diffraction and electron microscopy, the electron irradiation causes chemical changes in MF₂ crystals such as the desorption of fluorine and the accumulation of oxygen in the irradiated area with the formation of oxide MO. The fluorine desorption rate increases significantly when the electron-beam density exceeds the threshold value of ∼2 × 10³ pA/cm²). In BaF₂ samples, the transformation of BaO into Ba(OH)₂ was observed when irradiation stopped. The renewal of irradiation is accompanied by the inverse transformation of Ba(OH)₂ into BaO. In the initial stage of irradiation of all MF₂ compounds, the oxide phase is in the single-crystal state with a lattice highly matched with the MF₂ matrix. When the irradiation dose is increased, the oxide phase passes to the polycrystalline phase. Gaseous products of MF₂ destruction (in the form of bubbles several nanometers in diameter) form a rectangular array with a period of ∼20 nm in the sample.     

Micro-Raman studies on 50 keV electron irradiated silicate glass

A potassium–lime-silicate glass was irradiated with a 50 keV electron beam. The impact of irradiation conditions on the glass structure (beam diameter, current, and irradiation time) was studied by Micro-Raman spectroscopy. For irradiation time less than the incubation time (around 360 s), structural evolutions are attributed to a glass densification. Irradiations longer than the incubation period led to a precipitation of supposed calcium enriched phase and formation of a more depolymerized silicate phase. A non-homogeneous irradiated glass structure was observed with the existence of an area (along the electron beam border) composed by a mixture of a concentrated Ca phase diluted into the amorphous silicate phase.     

Synthesis and properties of Fe/Ni nanotubes

Fe/Ni nanotubes were formed in pores of polyethylenterephtalate-based template matrices by electrochemical deposition. The inner diameter, wall height, and thickness of the nanostructures, as well as the elemental and phase compositions, can be controlled by varying the deposition conditions. The volume deposition rate constants have been determined for each potential difference, due to which the nanostructure growth could be controlled. An X-ray diffraction analysis of the samples obtained at a potential difference of 1-1.6 V has revealed their composition to correspond to the substitutional solid solution, with an iron atom replaced by a nickel atom and dominance of the bcc a-Fe phase. The samples obtained at a potential difference of 1.8–2 V contain the bcc a-Fe phase and fcc Ni phase; the fcc phase dominates in the sample obtained at a potential difference of 2 V, which can be related to the high Ni content in nanotubes.     

电子辐照对MgAl2O4尖晶石光学性质的影响

本文利用1.7 MeV电子辐照MgAl2O4尖晶石后,通过吸收谱测量表明,被电子辐照的尖晶石可产生大量的F型色心缺陷, 而且电子的辐照剂量明显地影响尖晶石的光谱特性.随着电子辐照剂量增加, F型色心缺陷的浓度增大;椭偏光谱分析得到的光学常数谱随电子辐照剂量的变化而改变.我们对上述现象进行了合理的分析.     

Structure and conditions for the formation of fullerite crystallites in Sn-C<Subscript>60</Subscript> films

The structure of tin-fullerite films with different thicknesses of the Sn coating layer (50, 100, 200, 300, 450, and 700 nm) and the conditions for the formation and growth of fullerite crystallites on the tin surface during sample exposure in air have been investigated. The methods of X-ray diffraction; scanning electron, transmission electron, and atomic force microscopy; and X-ray microanalysis were used to reveal changes in the structure and phase composition of the tin-fullerite films. Fullerite crystallites in the form of plates and bolts grown under internal stress have been found on the surface of tin films with thicknesses of 50, 100, and 200 nm. The incubation period of crystallite formation is established to be 12–22 months, depending on the thickness of the tin layer.     

Observation of the growth of carbon nanotubes prepared at low temperature

Lack of information during the growth of carbon nanotubes has hindered efforts to understand the growth mechanism of these unique nanoscale structures. Here, we report that Multi‐walled carbon nanotubes with bamboo‐shaped structure may be synthesized by solvothermal method at 300°C using benzene as carbon source and Zn as catalyst. We have obtained direct experimental information on the growth under Transmission electron microscopy. It has been shown that all the compartments of bamboo‐like tube successively joined leading to the formation of regularly segmented nanobamboos. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of Magnetic Field and γ Irradiation on the Properties of Tl‐2212 Superconducting Tape

The critical temperature and critical current of Tl‐2212 superconducting sample in the form of a tape have been studied near T_c under magnetic field and gamma irradiation. T_c decreases from 109 to 94 K with increase of magnetic field up to 300 mT. In 77‐109 K range, J_c decreases rapidly in low fields up to around 50 mT followed by a very slow decrease in J_c up to 300 mT. T_c of the sample did not change up to 100 MR γ dose and then started to decrease from 109 to 102 K with increase of g dose up to 800 MR, most of the change taking place in high doses. The critical currents of the sample decreased steadily with γ irradiation up to 600 MR after which no further change was noticed.     

利用基板法在V型热解火焰中合成碳纳米管的实验研究

利用V型热解火焰合成碳纳米管是一项新的技术和方法,实验中采用304不锈钢片作为取样基板,将硝酸镍溶液均匀涂敷在取样基板上作为催化剂,利用扫描电镜和透射电镜对碳纳米管进行形态和结构表征。实验中得到了典型形态及特殊形态的碳纳米管,催化剂颗粒的直径在为5~8 nm之间。实验结果表明,取样时间为10 min,温度约为1150 K时最有利于产生碳纳米管。最后分析讨论了特殊形态的碳纳米管的结构及可能的形成机理。     

XPS and nuclear analysis of compositional changes occurring in glass on electron beam irradiation

X-ray photoelectron spectrometry and nuclear microanalysis have been utilized to study the compositional changes occurring in a commercial soda-lime-silica glass after electron beam irradiation. Samples were irradiated with electron energies between 2.5 and 4.5 keV and current densities of 1.2 and 4.0 μA/cm².After electron bombardment a reduction in the Na and O surface concentration appears. Na has been observed to migrate towards the inside of the sample. It accumulates at depths comparable to the maximum electron ranges. The accumulation rate has been observed to depend on the beam power.For a beam energy of 4.5 keV the amount of Na accumulated at depth is nearly twice its surface depletion, supporting the hypothesis that the irradiation influences the glass composition at depths greater than the maximum electron ranges.     

Investigation of structural defects in polycrystalline silicon by electron microscopy

Thermostability of polycrystalline films and their structure changes have been investigated in dependence on the fast electron irradiation. It was shown that the type of the radiation defects depends on the irradiation. temperature. The temperature of the recrystallization process is shown to decrease from 1300°C in the case without irradiation down to 1000°C in the case of recrystallization when irradiating.     

Complementary study of the internal porous silicon layers formed under high-dose implantation of helium ions

The surface layers of Si(001) substrates subjected to plasma-immersion implantation of helium ions with an energy of 2–5 keV and a dose of 5 × 10¹⁷ cm^–2 have been investigated using high-resolution X-ray reflectivity, Rutherford backscattering, and transmission electron microscopy. The electron density depth profile in the surface layer formed by helium ions is obtained, and its elemental and phase compositions are determined. This layer is found to have a complex structure and consist of an upper amorphous sublayer and a layer with a porosity of 30–35% beneath. It is shown that the porous layer has the sharpest boundaries at a lower energy of implantable ions.     

Magnetic whiskers of p-aminobenzoic acid and their use for preparation of filled and microchannel silicone rubbers

A thin cobalt layer has been formed on the surface of p-aminobenzoic acid whiskers by chemical vapor deposition (CVD). The metallized crystals have been oriented in liquid polydimethylsiloxane rubber by applying a dc magnetic field. After vulcanization, the filler has been removed by processing in an alcohol solution of trifluoroacetic acid. The cobalt deposition on the surface of the organic compound and the properties of metallized whiskers are investigated by optical microscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM).     

混合碱媒介法制备磁性铁酸钴纳米粉体

采用混合碱媒介法制备铁酸钴磁性纳米粉体,探索了制备工艺,利用X射线衍射仪、透射电镜、振动样品磁强计对样品的结构和磁性能进行了研究.结果表明:以硝酸盐或醋酸盐为原料用混合碱法可制得粒度均匀、粒径范围在10～50 nm的铁酸钴纳米粉,所制备的样品具有粒径小、粒度均匀、分散性较好的特点,中等饱和磁化强度、高矫顽力,是性能优良的磁性材料.     

Electron microscopy of carbon nanotubes

High-resolution electron microscopy was used to study multiwall carbon nanotubes obtained by the arc-discharge technique and double-and single-wall nanotubes produced by the arc-discharge catalytic synthesis. The structure of conical layer nanotubes obtained by the CVD technique is characterized in detail. It is established that heat treatment of nanotubes gives rise to their structural changes. The structure of nanotubes obtained by carbon evaporation in the N₂-Ar atmosphere under high pressure is determined. A new type of nano-and microtubes with surface-modulated walls is revealed. Possible applications of carbon nanotubes are reviewed.