共查询到20条相似文献,搜索用时 0 毫秒
1.
《Journal of Non》2004,337(1):42-47
Milling up to 800 h causes amorphous Co70.3Fe4.7Si10B15 alloy, prepared in the form of thin ribbon, to partially crystallize thus forming a powder material consisting of an amorphous phase and fcc-Co nanocrystals with an average grain size of about 10 nm. A gradual increase of the nanocrystalline fcc-Co fraction, produced by ball milling, was detected. Prolonged milling results in destabilization of the fcc-Co phase and oxidation of the powder material (presence of CoO phase after 1500 h of milling). The thermal stability studies of as-quenched and milled Co70.3Fe4.7Si10B15 alloy emphasized a two step crystallization behavior. During the first crystallization event, cobalt rich phases, i.e., fcc-Co and hcp-Co crystallize, whereas after the second crystallization event, Co2B and Co2Si are formed. 相似文献
2.
Tungsten powder (99.9% purity, 12 μm particle size) was milled in a hardened steel vial with six 440C stainless steel balls for 1–50 h. Because of the hardness of W, contamination and later alloying with Fe from abrasion of the stainless steel balls occurred. X-ray chemical analysis and weight-gain measurements of the milled powder indicated Fe contents varying from 3 at.% after 1 h to approximately 40 at.% after 50h milling. The powder pattern peaks of the nanocrystalline W were subjected to a Fourier analysis to determine the effective particle size and the microstrains within these particles. After 20 h milling, a particle size of 35 Å and microstrains of 0.5% were observed. The diffraction patterns from the W powder milled for 20 and 50 h were also analyzed in terms of the structure factor (interference function) and the atomic distribution function. The 20 h sample was predominantly nanocrystalline with a broad diffuse peak under the (110) and (211) reflections, while the 50 h sample was predominantly amorphous. After subtracting the remnant crystalline peaks, the position of the first peak in the reduced atomic distribution function, GI(r), was found to be 2.7 Å. 相似文献
3.
The effects of the annealing temperature on photoluminescence (PL) of non-stoichiometric silicon nitride (SiNx) thin films deposited by plasma enhanced chemical vapor deposition (PECVD) using ammonia and silane mixtures at 200 °C were investigated. The optical property and the chemical composition of the films annealed at different temperatures were investigated by PL spectroscopy and Fourier transform infrared absorption spectroscopy (FTIR), respectively. Based on the PL results and the analyses of the bonding configurations of the films, the light emission is attributed to the quantum confinement effect of the carriers inside silicon nanoparticles and radiative defect-related states. These results provide a better understanding of optical properties of silicon nanoparticles embedded in silicon nitride films and are useful for the application of nanosize silicon semiconductor material. 相似文献
4.
Motoshi Shibata Yoshiki Nitta Ken Fujita Masakazu Ichikawa 《Journal of Crystal Growth》2000,220(4):449-456
We have used in situ scanning tunneling microscopy (STM) to study the facet formation in the selective growth of pyramidal Si nanocrystals on Si(0 0 1) windows in ultrathin 0.3-nm-thick SiO2 films. Broad (0 0 1) surfaces developed as the top of the crystals, and {1, 1, (2n+1)} (n=1–6) facets formed the sidewalls. As growth continued, the slope angle of sidewall facets increased, and {1, 1, 9} and {1, 1, (2m+1)} (0 <m < 4) facets often came to coexist on the sidewalls. On well-oriented Si(0 0 1) surfaces, layer-by-layer growth in the [0 0 1] direction was dominant. On vicinal Si(0 0 1) surfaces, lateral step growth took place in the initial stage, and the layer-by-layer growth was suppressed until after a large (0 0 1) surface had formed as the top of the crystal. 相似文献
5.
W. Dewald C. Borschel D. Stichtenoth T. Niermann C. Ronning 《Journal of Crystal Growth》2010,312(10):1751-1754
Silicon nanowires have been grown in a horizontal tube furnace by disproportionation of silicon monoxide in combination with the vapor–liquid–solid mechanism. We present a phase diagram of the nanowire growth, indicating different morphologies for varying growth pressure and temperature. The morphology was characterized by scanning electron microscopy and detailed structural analysis was performed by transmission electron microscopy. A variety of morphologies is found and the optimum parameter range for the growth of straight and uniform nanowires consisting of crystalline silicon cores and amorphous SiO2 shells is identified and discussed. 相似文献
6.
We report about the formation of twinning-superlattice regions in Si epitaxial layers grown by molecular beam epitaxy on Si(1 1 1)()R30°-B surfaces. Twinning-superlattice regions were formed by periodical arrangement of 180° rotation twin boundaries along [1 1 1]-direction and are only separated by a few nanometers. The preparation method consists of repeating several growth, boron-deposition and annealing cycles on boron-predeposited undoped Si substrates. It is shown that the amount of subsurface boron and the growth mode influence the formation of twin boundaries. Only the nucleation of Si on the Si(1 1 1)()R30°-surface covered by at least ML boron results in the formation of 180° rotation twins. The size of superlattice regions is restricted by surface morphology. However, the presented technology should also be suitable to prepare a new type of semiconductor heterostructure based on Si polytypes. 相似文献
7.
N.H. Zhang X.L. Wang Y.P. Zeng H.L. Xiao J.X. Wang H.X. Liu J.M. Li 《Journal of Crystal Growth》2005,280(3-4):346-351
We describe the growth of GaN on Si(1 1 1) substrates with AlxGa1−xN/AlN buffer layer by ammonia gas source molecular beam epitaxy (NH3-GSMBE). The influence of the AlN and AlxGa1−xN buffer layer thickness and the Al composition on the crack density of GaN has been investigated. It is found that the optimum thickness is 120 and 250 nm for AlN and AlxGa1−xN layers, respectively. The optimum Al composition is between 0.3<x<0.6. 相似文献
8.
Haitao Wang Tian TianShancheng Yan Ningping HuangZhongdang Xiao 《Journal of Crystal Growth》2009,311(14):3787-3791
ZnSe nanoribbons have been successfully synthesized on a large scale by solvothermal treatment of Zn and Se powder in the mixture of hydrazine hydrate and diethanolamine at 140 °C for 24 h and subsequent annealing in Ar. The morphology of the final products strongly depended on the volume ratio of hydrazine hydrate and diethanolamine. Scanning electron microscopy (SEM) explorations indicated that the as-prepared ZnSe nanoribbons were mostly about 40 nm in thickness, 100 nm in width, and 50 μm in length. X-ray diffraction pattern (XRD) and transmission electron microscopy (TEM) investigations confirmed that resulting ZnSe nanoribbons are wurtzite structures and have a [0 0 1] growth direction. PL (photoluminescence) spectrum of the products exhibited a visible light emission. Based on these investigations, the products were expected to find wide applications in optoelectronic, field emission and catalytic fields. 相似文献
9.
Differential scanning calorimetry (DSC) studies were performed under nonisothermal conditions at various heating rates for glassy Se made by high-energy ball milling. Comparisons were made between the ball-milling technique and the melt-quenching and thin-film techniques. Well-defined endothermic and exothermic peaks were observed at the glass-transition temperature, Tg, and the onset temperature of crystallisation, Tc. The isoconversional method of Vyazovkin was used to determine the variation in the activation energy for crystallisation with temperature, Eα(T). The value of Eα(T) was dependent on the sample preparation method. The thermal stability of the Se glasses was evaluated by calculation of the temperature difference (Tc ? Tg) and the S-parameter. In addition, the glass-forming ability was estimated by the criteria of reduced glass-transition temperature, Trg, and the Hruby number, HR. The structures of the Se samples that resulted from the DSC analysis were identified using an X-ray diffractometer. The glasses formed using the thin film technique were the most stable. 相似文献
10.
Powder blend comprising Cu (25 wt.%) and 316-stainless steel (75 wt.%) has been subjected to ball milling upto 70 h followed by isothermal annealing at the temperature range of 350–750 °C for 1 h to investigate the evolution of microstructure and magnetic properties. The ball milling of the powder blends after 10 h has resulted in partitioning of the austenite stabilizing elements such as Ni from 316-stainless steel to elemental Cu leading to the transformation of the Bravais lattice of the Fe-rich phase from fcc (γ) to bcc (α). During further ball milling of the powder mixture upto 20 h, the α-Fe has dissolved completely in Cu, leading to the formation of partial amorphous phase after 70 h of milling. The amorphous phase of the alloy has been found to stable after annealing at 350 °C and super paramagnetic in nature. Annealing of the alloy at higher temperatures has resulted in precipitation of nanocrystalline bcc-Fe in the Cu evolving ferromagnetic properties. Annealing at 750 °C has resulted in collapse of the hysteresis loop due to the diminished exchange interaction as the result of grain coarsening of the α-Fe and Cu. 相似文献
11.
Jie Zhao Lizhong Hu Zhaoyang Wang Zhijun Wang Heqiu Zhang Yu Zhao Xiuping Liang 《Journal of Crystal Growth》2005,280(3-4):455-461
Epitaxial ZnO thin films have been grown on Si(1 1 1) substrates at temperatures between 550 and 700 °C with an oxygen pressure of 60 Pa by pulsed laser deposition (PLD). A ZnO thin film deposited at 500 °C in no-oxygen ambient was used as a buffer layer for the ZnO growth. In situ reflection high-energy electron diffraction (RHEED) observations show that ZnO thin films directly deposited on Si are of a polycrystalline structure, and the crystallinity is deteriorated with an increase of substrate temperature as reflected by the evolution of RHEED patterns from the mixture of spots and rings to single rings. In contrast, the ZnO films grown on a homo-buffer layer exhibit aligned spotty patterns indicating an epitaxial growth. Among the ZnO thin films with a buffer layer, the film grown at 650 °C shows the best structural quality and the strongest ultraviolet (UV) emission with a full-width at half-maximum (FWHM) of 86 meV. It is found that the ZnO film with a buffer layer has better crystallinity than the film without the buffer layer at the same substrate temperature, while the film without the buffer layer shows a more intense UV emission. Possible reasons and preventive methods are suggested to obtain highly optical quality films. 相似文献
12.
Li Ren Zhengguo Jin Shu Cai Jingxia Yang Zhanglian Hong 《Crystal Research and Technology》2012,47(4):461-466
Uniform near‐spherical SnS nanoparticles were prepared by a hydrazine hydrate‐assisted diethylene glycol solution synthesis based on the reaction of tin dichloride (SnCl2·2H2O) with thioacetamide (H3CCSNH2). The as‐prepared SnS nanoparticles were characterized by XRD, FETEM, EDS, XPS and UV‐vis‐NIR spectrophotometer. The results showed that the SnS nanoparticles had orthorhombic crystal structure, good stoichiometry and indirect bandgap of ∼1.1 eV. The nanoparticle size could be controlled by changing injection temperature. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
13.
Using sol-gel method, mesoporous and photoluminescent silica nanocomposites of soluble starch have been synthesized and characterized. Different ratios of H2O, TEOS and EtOH were used at fixed template (soluble starch) and catalyst (NH4OH) concentrations to obtain materials of different performances in terms of heavy metal binding from a solution which has been monitored using Cd(II) as representative divalent heavy metal ion. Optimum material was obtained when H2O, TEOS and EtOH were used in 14:1:2 ratio. This sample was not only an efficient metal ion adsorbent but also had an intense luminescence in ultra-violet region and potentially may be used in silicon-based UV-emitting devices. Metal binding by the material was further enhanced after calcination (at 800 °C in air) while its luminescence had a multipeak profile in UV-visible region. In a batch adsorption study, calcined hybrid composite (0.25 g/L) could remove 98.5% Cd(II) from 100 mg/L Cd(II) solution in 2 h. The chemical, structural and textural characteristics of the synthesized materials have been investigated using Fourier Transform Infrared Spectroscopy (FTIR), X-rays Diffraction (XRD), Thermal Analysis (TGA/DTA), Photoluminescence (PL), Brunauer-Emmett-Teller Analysis (BET) and Scanning Electron Microscopy (SEM). 相似文献
14.
Jason S. Overby Richard T. Woofter Arnold L. Rheingold Christopher D. Incarvito Roger D. Sommer 《Journal of chemical crystallography》2003,33(5-6):357-364
Three silyl-substituted fluorenes have been prepared by direct synthetic methods and structurally characterized by X-ray diffraction. The three silyl-substituted fluorenes studied were 9-trimethylsilylfluorene (1), 9-(tert-butyldimethyl)silylfluorene (2), and 2,7-di-tert-butyl-9-trimethylsilylfluorene (3). Complex 1 is orthorhombic, P212121, a = 6.2681(14) Å, b = 14.329(3) Å, c = 15.231(4) Å, Z = 4. Complex 2 is monoclinic, P21/c, a = 12.1953(10) Å, b = 6.9977(6) Å, c = 19.6536(17) Å, = 93.818(2), Z = 4. Complex 3 is monoclinic, P21/c, a = 11.9954(9) Å, b = 9.8978(7) Å, c = 18.5464(13) Å, = 92.456(2), Z = 4. The long carbon–silicon bonds effectively remove any significant intramolecular interactions as little distortion is exhibited around the sp
3-carbon atom and the fluorenyl backbone demonstrates near planarity. The bulky silicon substituents also prevent intermolecular interactions, as only a few close contacts less than 4.0 Å exist in all three solid state structures. 相似文献
15.
J. Dutkiewicz L. Lityska W. Maziarz K. Haberko W. Pyda A. Kanciruk 《Crystal Research and Technology》2009,44(10):1163-1169
Ball milling of 6061 aluminum alloy and nanocrystalline ZrO2 powder allowed to obtain homogeneous mixture of nanocrystalline aluminum solid solution of grain size near 50 nm and ZrO2 particles. The ZrO2 particles are partially transformed after milling from tetragonal to the monoclinic crystal structure. After hot pressing in vacuum at temperature of 380 °C bulk nanocomposites were obtained of porosity below 1% consisting of aluminum solid solution of the average grain size near 80 nm and nano‐size ZrO2 particles. Partial recrystallization occurred after hot pressing particularly near particles boundaries, where elongated recrystallized grains free from ZrO2 nanoparticles of thickness near 1 μm and length of a few μm were identified. Estimated fraction of recrystallized grains was below 10%. The compression strength approaching 1000 MPa was obtained in composites containing 20% ZrO2 nanoparticles, what is more than reported for ultra and nano‐grain 6XXX aluminum alloys. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
16.
Rapid synthesis of copper nanoparticles by sodium hypophosphite reduction in ethylene glycol under microwave irradiation 总被引:8,自引:0,他引:8
This paper presents a rapid method for preparation of copper metal nanoparticles by reducing CuSO4·5H2O with NaH2PO2·H2O in ethylene glycol under microwave irradiation. The influences of the reaction parameters, such as the concentrations of reducing agent and protective polymer time of microwave irradiation, on the size and agglomeration of copper nanoparticles were investigated by X-ray powder diffraction and transmission electron microscope. Well-dispersed copper nanoparticles with diameter of about 10 nm were obtained. The use of microwave irradiation accelerated the reaction rate and benefited the dispersion and the particle size distribution of the nanoparticles. 相似文献
17.
A simple method is presented for the one-pot synthesis of monodisperse MnO nanoparticles (NPs) using bulk MnO as the starting material. In the proposed approach, bulk MnO powder is dissolved in hot oleic acid to form manganese oleate (Mn(RCOO)2) and a decomposition process is then performed to obtain MnO NPs. The proposed method is environmentally friendly in that the only by-product is water, which can be easily distilled out. Conceptually, the synthesis method can be viewed as a controlled dissolution recrystallization process. It is shown that the size of the NPs can be controlled over the range of 6–32 nm via an appropriate specification of the precursor-to-oleic acid ratio and the reaction temperature (by the choice of an appropriate high b.p organic solvent). Finally, the size-dependent magnetic properties of three different monodisperse MnO NPs (7.7 nm, 19.4 nm and 31.7 nm) are studied. It is shown that the monodisperse MnO NPs exhibit a weak ferromagnetic behavior due to uncompensated surface spins at low temperatures. 相似文献
18.
《Journal of Crystal Growth》2006,286(2):487-493
The pure hexagonal phase YBO3:Tb3+ phosphors with good crystallinity and uniform size were prepared by hydrothermal reaction (HR). The particle size and morphology can be well controlled by adjusting the concentration of ammonium acetate and varying the reaction temperature and time. The phosphor prepared by HR emits an intense green light at 543 nm, which is stronger than that from crystals synthesized by solid-state reaction (SR). The influence of Tb3+-doping concentration on the crystallization and luminescent properties were investigated. The results showed that the samples exhibited a higher quenching concentration of Tb3+ in comparison with those prepared by the SR. The phenomena were also discussed. 相似文献
19.
《Journal of Non》2007,353(16-17):1606-1611
Mesostructured aluminosilicate nanoparticles with narrow grain size distribution have been hydrothermally prepared for the first time with assistance of binary surfactants and separate hydrolysis and assembly of inorganic precursors. Compared to the sample assembled at room temperature, condensation degree and aluminum stability were greatly improved using hydrothermal treatment. The formation of nanoparticles consists of two steps, that is, the hydrolysis of silica precursor via catalysis by an acidic aluminum salt, followed by facile assembly into mesostructured nanocomposites with cationic micelles by addition of condensation catalyst. Simultaneously, nonionic polyethylene glycol (PEG-4000) present in this process would surround the formed nanoparticles through hydrogen-bonding interactions, thereby tailoring the grain size distribution and preventing aggregation and growth of inter-nanoparticles during the hydrothermal treatment process. The microstructure and chemical compositions of these products were thoroughly characterized by XRD, SEM, TEM, N2 sorption and 27Al MAS NMR techniques. 相似文献
20.
AbstractMagnetic nanoparticles containing mesoporous carbon materials have been synthesized via an one-pot strategy associated with a direct carbonization process from resol, metal ion sources (Co(NO3)2·6H2O, Ni(NO3)2·6H2O) and triblock copolymer F127. The samples exhibited well-ordered 2-dimensional (2-D) hexagonal mesostructures with p6mm symmetry. The Brunauer-Emmet-Teller (BET) surface area and pore size 1.0wt%Co- and 1.0wt%Ni-FDU-15(700) with 1.0?wt% Co and 1.0?wt% Ni content were 700, 528 m2/g and 17.2, 36.4 Å, respectively, after carbonization at 700?°C. The saturation magnetization values of 1.0wt%Co- and 1.0wt%Ni-FDU-15(700) after carbonization at 700?°C were 1.3 and 1.0?emu/g, respectively. 相似文献