Evolution of the phase-structure state during annealing of Fe-ZrN films grown by magnetron sputtering

The evolution of the phase-structure state of Fe-ZrN films grown by RF magnetron sputtering and annealed at T = 200–650°C has been studied by transmission electron microscopy, high-resolution electron microscopy, and X-ray diffraction analysis. It has been found that the initial state of the film contains 1- to 5-nm crystallites of α-Fe-based solid solution supersaturated with nitrogen. The number of such crystallites increases, the concentration of nitrogen in them decreases and 2- to 10-nm nanocrystallites of ZrN and Fe2N nitride phases appear after annealing. The formation of zirconium nitride at the first stage (200–500°C) is associated with a decrease in the degree of supersaturation of the α-Fe lattice with nitrogen. At a higher annealing temperature (650°C), a decrease in the nitrogen concentration in the lattices of both the bcc Fe and zirconium nitride phase leads to the formation of iron nitride crystallites.     

Disordered bcc γ-phase to δ-phase transformation in Zr-rich U-Zr alloy

The transformation mechanism of hexagonal delta phase from the disordered bcc gamma phase has not been reported before in the Zr-rich U–Zr alloy system. With the help of X-ray diffraction, transmission electron microscopy (TEM) and high-resolution TEM analyses it was shown that the gamma to delta conversion takes place by the lattice collapse mechanism of omega transformation. It was also ascertained that a higher aging temperature or time promotes the growth of all four variants of the delta phase within a parent gamma grain. In addition, ab initio electronic structure calculations showed that the bcc to hexagonal transformation, involving partial ordering of the parent bcc phase followed by (111) plane collapse, is energetically favorable.     

Evolution of structure, microstructure and hyperfine properties of nanocrystalline Fe50Co50 powders prepared by mechanical alloying

Nanostructured Fe₅₀Co₅₀ powders were prepared by mechanical alloying of Fe and Co elements in a vario-planetary high-energy ball mill. The structural properties, morphology changes and local iron environment variations were investigated as a function of milling time (in the 0-200 h range) by means of X-ray diffraction, scanning electron microscopy (SEM), energy dispersive X-ray analysis and ⁵⁷Fe Mössbauer spectroscopy. The complete formation of bcc Fe₅₀Co₅₀ solid solution is observed after 100 h milling. As the milling time increases from 0 to 200 h, the lattice parameter decreases from 0.28655 nm for pure Fe to 0.28523 nm, the grain size decreases from 150 to 14 nm, while the meal level of strain increases from 0.0069% to 1.36%. The powder particle morphology at different stages of formation was observed by SEM. The parameters derived from the Mössbauer spectra confirm the beginning of the formation of Fe₅₀Co₅₀ phase at 43 h of milling. After 200 h of milling the average hyperfine magnetic field of 35 T suggests that a disordered bcc Fe-Co solid solution is formed.     

Probe Mössbauer spectroscopy of the grain boundaries of a Mo-O nanocrystalline system obtained by mechanical alloying

The localization of Fe atoms in the process of mechanical alloying of a Mo powder composite with 8 at % O at boundaries of the bcc Mo grains has been investigated by Mössbauer spectroscopy on impurity ⁵⁷Fe isotope atoms (1 at %), X-ray diffraction, and Auger spectrometry. The process begins with the formation of a nanostructure (～10 nm) in bcc Mo and ends with the formation of a bcc supersaturated solid solution with O atoms at interstitial positions and Fe atoms at substitutional positions. The presence of oxygen in the boundaries of bcc Mo grains leads to an extraordinarily large isomer shift (2 mm/s with respect to α-Fe) for the grainboundary component in the Mössbauer spectrum. This circumstance makes it possible to consider ⁵⁷Fe-O complexes as new probes for studying grain boundaries of powder nanocrystalline materials. As a result, the following three structural components have been identified in the mechanically activated system: a grain boundary and distorted near-boundary regions with the common name interface and a grain with the perfect (defect-free) structure. For powder nanocrystalline (～10 nm) materials subjected to intense mechanical treatment in a planetary ball mill, the widths of the unrelaxed grain boundary and interface average over the entire volume of particles have been experimentally estimated as 0.2 and 1 nm, respectively.     

Structural, microstructural and hyperfine properties of nanocrystalline iron particles

Nanocrystalline Fe particles were successfully prepared by the mechanical milling process using a high-energy planetary ball mill. The physical properties of the samples were investigated as a function of the milling time, t (in the 0-54 h range) by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and Mössbauer spectroscopy. After 54 h of milling, the lattice parameter increases from 0.28620 (3) nm for the starting Fe powder to 0.28667 (3) nm, the grain size decreases from 110 to 13 nm, while the strain increases from 0.09% to 0.7%. The powder particle morphology was observed by SEM at different stages of milling. For t less than 24 h, the Mössbauer spectra are characterized by one sextet corresponding to the crystalline bcc Fe phase, while for t greater than 24 h, the iron particles exhibit a two-component Mössbauer spectrum due to the presence of two phases: the crystallites bcc Fe phase and the grain-boundary region. The appearance and the increase in intensity of the second sextet with t may indicate that the interfacial region effect increases with milling time due to the grain size reduction and a probable disordered state of the grain boundaries.     

Hydrothermal synthesis of CeF<Subscript>3</Subscript> nanocrystals and characterization

CeF₃ nanocrystals with plate-like and perforated morphologies were successfully synthesized via a facile hydrothermal route. The nanocrystals of CeF₃@silica can dispersed in aqueous solution were also prepared. The effects of fluoride sources on the morphology and microstructure of the nanocrystals were investigated by means of transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and powder X-ray diffraction (XRD). Results indicate that the morphology of the rare earth compound nanocrystals can be well tuned by selecting proper fluoride sources. The ultraviolet (UV) absorption peak of the CeF₃ nanocrystals is slightly blue shifted along with the decrease of size. And the photoluminescence (PL) intensity of the CeF₃ nanocrystals is closely related to size and microstructure as well.     

Studies of structure and morphology of sputter-deposited stainless steel–nitrogen films

Stainless steel films doped with nitrogen were deposited on heated and unheated (100) silicon substrates by radio-frequency magnetron sputtering of an austenitic stainless steel target in argon and nitrogen gas mixtures, containing a range of nitrogen compositions. The evolution of phases, morphologies and grain structures in the resultant films was studied by X-ray diffraction and field emission scanning electron microscopy. It was found that, with increasing nitrogen composition in the gas mixture, the crystalline structure of the films deposited on the heated substrates changed from bcc ferrite (α), to nitrogen-stabilized fcc austenite (γ), then to distorted expanded austenite phase (γ_N) with nitrogen supersaturation, and finally to the newly discovered fcc ‘MN’ phase with ideal cubic symmetry and further enlarged lattice. On the unheated substrates, the phase-evolution trend was found to be different for % N₂ above 10. For the 25% N₂ film, amorphous phase formed along with the crystalline austenite and ferrite phases, while the percentage of amorphous content decreased when % N₂ was increased to 50. This different trend was understood to be due to the role of increase in % N₂ in decreasing the energy loss of sputtered species through collisions. The dependence of crystalline phase formation on the energy of sputtered species is less severe on the heated substrates. Although all the films deposited experienced three-dimensional fibrous growths, they exhibited different surface morphology and grain structure. There exists a correlation between film morphology and phase constituents, while grain size was influenced by the nucleation density and the energy and mobility of adatoms that are reduced due to nitrogen incorporation. PACS 68.55.-a; 81.15.Cd     

Crystal structure and morphology of the NdSr 2 RuCu 2 O y compound

We report the preparation and the structural and morphological characterization of the perovskite compound NdSr₂RuCu₂O_y. The crystal structure of this material has been determined by a combined high-resolution electron microscopy, selected area electron diffraction and high-resolution X-ray powder diffraction study. The morphology of the samples has been monitored by a scanning electron microscope equipped with an energy dispersive spectrometer attachment by which the microanalysis of the crystallites has been also performed. Finally, dc magnetic susceptibility measurements show that this compound behaves like an enhanced paramagnetic metal with evidence of neither magnetic order and neither superconducting one. Received 15 November 2001     

Aging of supersaturated Al-Cu-Co decagonal phase

Aging of the supersaturated Al₆₈Cu₁₁Co₂₁ decagonal phase was studied by transmission and scanning electron microscopy. Changes in the twofold [12100] electron diffraction patterns are reported. The decagonal phase aged at 700–800°C exhibited a reduction of the intensities of the quasiperiodic odd-n reflections and the appearance of extra-reflections along quasiperiodic directions.     

Ti-B-C-N纳米复合薄膜结构及力学性能研究

利用反应磁控溅射方法在单晶硅和高速钢(W18Cr4V)基片上制备出不同C含量Ti-B-C-N纳米复合薄膜. 使用X射线衍射和高分辨透射电子显微镜研究了Ti-B-C-N纳米复合薄膜的组织和微观结构,用纳米压痕仪测试了它们的硬度和弹性模量. 结果表明,利用往真空室通入C₂H₂气体的方法制备得到的Ti-B-C-N纳米复合薄膜中,在所研究成分范围内只发现TiN基的纳米晶. 当C₂H₂流量较小时,C元素的加入可以促进Ti-B-C 关键词： Ti-B-C-N薄膜 磁控溅射 微观结构 力学性能     

X-ray diffraction line-profile analysis of hexagonal ϵ -iron nitride compound layers: composition–and stress–depth profiles

Two hexagonal ε-Fe₃N_{1+ x} layers grown on α-Fe substrates by nitriding in NH₃/H₂ gas atmospheres were investigated by high-resolution X-ray powder diffraction using synchrotron radiation employing systematic tilting of the diffraction vector with respect to the specimen surface. Considering all recorded reflections simultaneously, the complicated diffraction profiles obtained were analyzed using a model incorporating hkl-dependent (anisotropic) and tilt angle (ψ)-dependent diffraction-line broadening and diffraction-line shifting. The diffraction-line broadening is mainly ascribed to the nitrogen concentration–depth profile within the layers causing depth-dependent strain-free lattice parameters, whereas the line shifts are predominantly caused by the stress–depth profile originating from the concentration-dependence of the coefficients of thermal expansion of the ε phase, with stress parallel to the surface, which is of tensile nature at the surface and of compressive nature at the ε/γ′ interface. This stress gradient additionally leads to a ψ dependence of the line broadening. Fitting of the microstructure and diffraction model led to determination of microstructure parameters, which can be related to the different sets of treatment conditions applied for the ε-iron nitride layer growth.     

Synthesis and optical properties of tetragonal KTa0.6Nb0.4O3 nanoparticles

Tetragonal phase KTa_0.6Nb_0.4O₃ (KTN) nanoparticles have been prepared by hydrothermal method. The obtained particles were characterized by X-ray powder diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy and UV-vis absorption spectrum techniques. A systematic change in crystal structure from cubic to tetragonal is observed with the increase of reaction temperature and KOH concentration. Room temperature UV-vis absorption spectrums of KTN particles show that the band gap changes from 3.24 to 3.34 eV with grain size diminished, which reveals the existence of blue-shift phenomenon of absorption bands.     

Electron-microscopy studies of NaAlH4 with TiF3 additive: hydrogen-cycling effects

NaAlH₄ is a promising candidate material for hydrogen storage. Ti additives are effective in reducing the reaction temperatures and improving kinetics. In this work, the microstructure of NaAlH₄ with 2% TiF₃ has been studied in different conditions using a combination of transmission electron microscopy and scanning electron microscopy, both with energy-dispersive spectroscopic X-ray analysis. The effect of the additive on particle and grain size was examined after the initial ball-milling process and after 15 cycles. The additive has an uneven distribution in the sample after ball milling. Selected-area diffraction and high-resolution imaging confirmed the presence of TiF₃. This phase accounts for most of the Ti in the material at this stage and showed limited mixing with the alanate. The grain size within particles for TiF₃ is larger than for the alanate particles. Diffraction from the latter was dominated by metallic aluminium. After cycling, the TiF₃ has decomposed and energy-dispersive spectroscopic X-ray analysis maps showed some combination of Ti with the alanate phase. There is no significant change in the measurable grain size of the Al-containing alanate particles between the ball-milled and the 15-cycled samples, but more cycles result in agglomeration of the material. PACS 61.14.-x; 68.37.LP; 68.37.Hk     

Synthesis, morphologies and Raman-scattering spectra of crystalline stannic oxide nanowires

SnO₂ nanowires were synthesized using a direct gas reaction route and were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), selected-area electron diffraction (SAED), high-resolution transmission electron microscopy (HRTEM) and Raman-scattering spectroscopy. XRD, SEM, SAED and HRTEM indicated that the products were tetragonal SnO₂ nanowires with diameters of 10–50 nm. The nanowires were single crystal and solid inside. Dendritic nanowires were observed for the first time. Three vibrational modes were observed in the Raman spectra of the samples. Received: 7 January 2002 / Accepted: 11 April 2002 / Published online: 19 July 2002     

Microstructure and mechanical properties of reactive magnetron sputtered Ti-B-C-N nanocomposite coatings

Ti-B-C-N nanocomposite coatings with different C contents were deposited on Si (1 0 0) and high speed steel (W18Cr4V) substrates by closed-field unbalanced reactive magnetron sputtering in the mixture of argon, nitrogen and acetylene gases. These films were subsequently characterized ex situ in terms of their microstructures by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM), their nanohardness/elastic modulus and facture toughness by nano-indention and Vickers indentation methods, and their surface morphology using atomic force microscopy (AFM). The results indicated that, in the studied composition range, the deposited Ti-B-C-N coatings exhibit nanocomposite based on TiN nanocrystallites. When the C₂H₂ flow rate is small, incorporation of small amount of C promoted crystallization of Ti-B-C-N nanocomposite coatings, which resulted in increase of nano-grain size and mechanical properties of coatings. A maximum grain size of about 8 nm was found at a C₂H₂ flux rate of 1 sccm. However, the hardness, elastic modulus and fracture toughness values were not consistent with the grain size. They got to their maximum of 35.7 GPa, 363.1 GPa and 2.46 MPa m^1/2, respectively, at a C₂H₂ flow rate of 2 sccm (corresponding to about 6 nm in nano-grain size). Further increase of C content dramatically decreased not only grain size but also the mechanical properties of coatings. The presently deposited Ti-B-C-N coatings had a smooth surface. The roughness value was consistent with that of grain size.     

Sonochemical preparation of antimony subiodide

The substantiated isolation of the antimony subiodide (Sb₃I) is presented for the first time. It has been prepared using elemental Sb and I in ethanol under ultrasonic irradiation at 323 K. Its composition was characterized using X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray analysis (EDAX). The scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) investigations exhibit that the samples are made up of large quantity of nanoparticles with diameters smaller than 20 nm and single crystalline in nature. The interplanar spacings in Sb₃I that have been determined using powder X-ray diffraction (XRD), selected area electron diffraction (SAED) and HRTEM are very similar. Surprisingly, the registered XRD patterns are identical to the one reported earlier for Sb₄O₅I₂.     

Using of sonochemically prepared components for vapor phase growing of SbI3·3S8

The using of sonochemically prepared components for growth of SbI₃·3S₈ single crystals from the vapor phase is presented for the first time. The good optical quality of the obtained crystals is important because this material is valuable for optoelectronics due to its non-linear optical properties. The products were characterized by using techniques such as X-ray crystallography, powder X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, high-resolution transmission electron microscopy, selected area electron diffraction, optical diffuse reflection spectroscopy and optical transmittance spectroscopy. The direct and indirect forbidden energy gaps of SbI₃·3S₈ illuminated with plane polarized light with electric field parallel and perpendicular to the c-axis of the crystal have been determined. The second harmonic generation of light in the grown crystals was observed.     

辉光放电等离子体辅助XeCl准分子激光溅射沉积碳氮薄膜

利用直流辉光放电等离子体辅助的脉冲激光沉积技术在Si衬底上生长了碳氮薄膜.通过扫描电子显微镜、X射线衍射、X射线光电子能谱、俄歇电子能谱等多种手段,对薄膜的形貌、成分、晶体结构、价键状态等特性进行了分析和确定.结果表明,沉积薄膜为含有非晶SiN和晶态氮化碳颗粒结构,晶态成分呈多晶态,主要为α-C₃N₄相、β-C₃N₄相,晶粒大小为40—60nm.碳氮之间主要以C-N非极性共价键形式相结合. 关键词： 脉冲激光沉积 直流辉光放电 碳氮薄膜     

Characterization of magnetic iron oxide nanoparticles

Magnetic nanoparticles have promising applications in many areas, for example optics, electronics, biology, medicine, etc. The main goal of this study is to synthezise and characterize ε-Fe₂O₃ magnetic nanoparticles embedded in amorphous SiO₂ matrix. The Mössbauer spectroscopy analysis of the samples was complemented by the study of X-ray powder diffraction and high-resolution transmission electron microscopy.     

溅射制备的Co/V多层膜微观结构特征与铁磁共振研究

研究了用射频磁控溅射方法制备的［Co(1.5nm)/V(d_V)］₂₀(0.5nm≤d_V≤4nm)多层膜的结构和磁性.用X射线衍射、透射电子显微镜、高分辨率透射电子显微镜等手段对其结构的分析,表明它们层状周期结构良好,沿膜的生长方向具有fcc Co(111)和bcc V(110)织构,且是由小的柱状晶粒构成的多晶薄膜.界面一定程度的合金化,使其成为成分调制周期结构,也是它们的一个结构特征.由其铁磁共振谱计算得到较小的g因子和4πM_{e 关键词：}