Effect of annealing on the morphology evolution and densification of LiMn2O4 film from chitosan-containing solution

Dense LiMn₂O₄ films deposited on a Pt-coated silicon substrate were obtained by annealing the deposited Li–Mn–O-chitosan films under a two-stage heat-treatment procedure. It was demonstrated that the heat-treatment at 300 °C plays an important role in the subsequent densification of LiMn₂O₄ films. This is attributed to the formation and rearrangement of the nano-sized LiMn₂O₄ crystallites. The surface morphology of the calcined Li–Mn–O-chitosan films was highly related to the annealing temperature. Ridge-like bumps formed on the surface of the films after being heated at 200 °C for 1 h. With calcination at 400 °C or higher, the surface morphology turned into a wrinkle-like microstructure. This morphology transformation is ascribed to the flowing characteristics of the Li–Mn–O-chitosan films during heat-treatment and subsequent thermal decomposition of the precursor at higher temperatures. Moreover, the electrochemical tests showed that the 700 °C-annealed LiMn₂O₄ film possesses the highest discharge capacity of 56.3 μA h/(cm² μm) and best capacity retention of 90.7% after 50 charge/discharge cycles of all annealed films.     

Alloys Preparation of Ag Particles/Islands on Si Wafer by RF Magnetron Sputtering

In order to investigate the morphology change of Ag nano-particles/island film with the sputtering time and annealing temperature,Ag nano-particles/island films were sputtered on the silicon wafers by radio-frequency(RF)magnetron sputtering.Ag nano-particles/islands films were sputtered on Si wafer with different time.After sputtering,the samples with Ag nano-particles/islands films were annealed at 100,200 and 400 o C for 1 h,respectively.Raman spectrum was employed to examine the phase stability of Ag particles/island film after annealed at 400 o C for 1h.The result showed that the Raman spectrum peak of Ag particles/island film with annealed at 400 o C was similar to that of pure Ag.Scanning electron microscope(SEM)was used to test the microstructures and morphology of the films with different condition.To further study the morphology change,atomic force microscope(AFM)was used to test surface morphology of the Ag particles/islands films.The SEM and AFM results showed that the morphology of Ag nano-particles/island films were different with the increasing sputtering time.Ag particles went through a dramatic change on the Si wafer surface,when sputtering time changed from 3 to 60 s,Ag particles diffused and agglomerated with the annealing temperature increasing.     

Microwave-assisted synthesis of CaMoO4 nano-powders by a citrate complex method and its photoluminescence property

Nano-sized CaMoO₄ powders, which have scheelite type structure, were successfully synthesized at low temperatures by a modified citrate complex method using microwave irradiation. The citrate complex precursors were heat-treated at temperatures from 300 to 700 °C for 3 h. Crystallizations of the CaMoO₄ nano-sized powders were detected at 400 °C, and entirely completed at a temperature of 500 °C. Almost nano-powders of CaMoO₄ heat-treated between 400 and 600 °C showed primarily spherical and homogeneous morphology. The average crystalline sizes of CaMoO₄ were 12–27 nm at temperatures of 400–700 °C, showing an ordinary tendency to increase with the temperatures. The CaMoO₄ powders prepared at 600 °C showed the strongest photoluminescence intensity.     

Grain growth and precipitation in an annealed cold-rolled Ni50.2Ti49.8 alloy

In this paper we present a transmission electron microscopic study on the effect of annealing on the microstructure of a cold-rolled Ni_50.2Ti_49.8 ribbon. Transmission electron microscopy of the as-received sample shows the presence of alternating amorphous and crystalline bands. The crystalline bands have widths of the order of a few microns and contain amorphous nanopockets and B2 nanograins, the latter at around 20 nm diameter and preferentially oriented with their normal along the 111 direction and perpendicular to the strip surface. As-received samples were annealed for 30 min at different temperatures up to 800 °C. Crystallization starts in the amorphous bands at around 350 °C and finally ends up with the coarsening of the grains in the entire sample. Annealing of the samples at 450 °C entirely transforms the amorphous bands into crystalline bands. At 800 °C the grain size increases to 30–50 μm with a formation of a tweed kind of morphology inside the grains when observed at room temperature. Diffraction patterns from such grains reveal the presence of diffuse intensity around 1/3110^* indicating the formation of the R-phase. NiTi₂ precipitates form at 450 °C while annealing at 600 °C and higher yields Ni₃Ti₂ precipitates. For samples annealed at 500 °C for a longer time, Ni₄Ti₃ precipitates have been observed along with the austenite to martensite transformation in the grains.     

Spray Pyrolysis Deposition of ZnO Thin Films from Zinc Chloride Precursor Solution at Different Substrate Temperatures

ZnO films were prepared at different substrate temperatures through spraying pyrolysis deposition of zinc chloride precursor onto glass substrate. Substrate temperature affects surface morphology of films and therefore their optical and electrical properties. All films are polycrystalline with Wurtzite crystal structure and preferentially grow along c-axis direction. Formation of ZnO rods start at about 500 °C. The diameter and length of rods deposited at 500 °C are350–500 and 550–700 nm, respectively. By increasing substrate temperature, film becomes more coverage and diameter of the rods reduces to 250–300 nm but their length increases to 1,000–1,200 nm, respectively. Optical transmission in visible region decreases with increasing substrate temperature. An ultraviolet emission and two visible emissions at 2.82 and2.37 eV are observed for photoluminescence spectra at room temperature. The resistivity of ZnO films increases with increasing substrate temperature due to surface morphology.     

Le système binaire Pd---Si

The Pd---Si phase diagram has been revised in details (178 alloys) on carefully annealed specimens by microprobe analysis, X-rays diffraction and DTA. The Pd₂Si intermetallic phase (m.p. 1404 °C) is confirmed to be stoichiometric with the C22-structure, but within the ranges of composition 33.3–33.9 and 34.5 at.% Si it diversifies in three very similar crystalline structures formed peritectically at 1053–1083 and 1072 ± 2 °C respectively. PdSi only exists in a very short range of temperature (888–908 °C melting congruently), whereas Pd₅Si (m.p. 856 °C) disappears below 811 °C, likewise producing four very narrow and similar phases at 16 at.% Si (below 811 °C), 17.7 (below 795 °C), 18.2 at.% Si (between 819 and 764 °C) and 21.0 at.% Si (between 792 and 753 °C), all these phases being formed by peritectoïd transformations. The only Pd₃Si-phase (congruent m.p. 1074 °C) remains stable at low temperature.

Résumé

L'étude très détaillée du diagramme de phase Pd---Si (178 alliages) révèle que la phase intermétallique Pd₂Si (Fus. 1404 °C) est stoechiométrique avec une structure C22. Cependant, elle se diversifie en trois structures cristallines ordonnées étroites, qui se forment péritectiquement à 1053–1083 et 1072 ± 2 °C, dans un domaine restreint de composition 33,3–33,9 et 34,5 at.% Si respectivement. Le composé PdSi (Fus. congruente 908 °C) existe dans un très faible domaine de température (888–908 °C). Pd₅Si (Fus. 856 °C) disparaît au-dessous de 811 °C en donnant naissance à quatre phases très proches et très similaires à 16 at.% Si (au-dessous de 811 °C), 17,7 (au-dessous de 795 °C), 18,2 at.% Si (Pd₉Si₂) (entre 819 et 764 °C) et 21,0 at.% Si (entre 792 et 753 °C), toutes ces phases sont issues de transformations péritectoïdes. Seule la phase Pd₃Si se maintient sans autre modification à basse température (Fus. congruente 1074 °C).     

Observations on the growth of Al–Ni–Co decagonal thin films by atomic force microscopy and transmission electron microscopy

Thin films of Al–Ni–Co alloy were produced by vacuum deposition technique using a substrate material of amorphous carbon thin-foil. Attempts were made to obtain a homogeneous decagonal quasicrystalline film, where the preparation technique was based on the direct evaporation of pre-alloyed ingot of Al₇₂Ni₁₅Co₁₃ onto the heated substrates. In order to explore early stages of the decagonal film growth, the Al–Ni–Co films with different thicknesses ranging from 2 nm to 30 nm were deposited on either substrates heated at 500 °C or non-heated substrates. The film samples so obtained were examined mainly by atomic force microscopy in combination with transmission electron diffraction and imaging techniques. On the basis of these observations, deposition conditions necessary for the growth of decagonal phase in the resulting films as well as the growth mechanism of the decagonal film will be discussed.     

Growth of highly oriented Pt(100) thin films on a MgO(100) seed layer deposited on Si(100) substrates by rf magnetron sputtering

The growth of highly oriented Pt(100) thin films on Si(100) substrates deposited by rf magnetron sputtering was studied using a MgO(100) seed layer. The effects of the sputtering parameters on the growth of the MgO(100) seed layer were investigated in order to obtain the deposition condition which gives the best crystalline quality of (100) oriented MgO thin films. A highly crystallized MgO(100) film was obtained at a substrate temperature of 425°C, a rf power of 4.4W/cm² and a pressure of 12.5 mTorr. The crystalline quality of the MgO film was greatly decreased when the Si substrate was oxidized. The degree of (100) preferred orientation of the Pt film deposited on a MgO(100)//Si(100) substrate was found to be sensitive to the thickness of the MgO(100) seed layer, which is explained by the thickness dependence of the crystalline quality and the surface roughness of the MgO seed layer. A highly oriented Pt(100) film, for which the I₂₀₀/(_I200+I₁₁₁) ratio was about 0.8, was obtained at 550°C on a 50 nm thick MgO seed layer.     

Nucleation of 3C–SiC on 6H–SiC from a liquid phase

The aim of this work is to elucidate the mechanism involved in the 3C–SiC formation during growth by a vapor–liquid–solid mechanism on 6H–SiC substrate. Polytype selection is shown to occur at the first stage of the experiments, before propane injection into the reactor. The contact of the seed with a Si–Ge melt during the initial heating ramp causes the formation of 3C–SiC islands on the seed surface, probably below 1200 °C. The proposed mechanism first involves a partial dissolution of the seed in a Ge-rich liquid which becomes C-supersaturated. Then the Si content of the liquid rapidly increases, which provokes the precipitation of the dissolved carbon in the form of 3C–SiC islands. When growth starts upon propane injection, these islands enlarge and coalesce to form a continuous 3C–SiC layer. If the growth temperature is too high (1550 °C), the initial 3C–SiC islands are dissolved and homoepitaxial layers are obtained.     

Effects of the solution temperature and the pH on the electrochemical properties of the surface oxide films formed on Alloy 600

The surface oxide films on Alloy 600 have been investigated as a function of the solution temperature and the pH by using a cyclic voltammetry, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and a depth profiling by Auger electron spectroscopy (AES). H₃BO₃, Na₂SO₄ and NaOH aqueous solutions with temperatures in the range of 30–300 °C were used as the test solutions. As the solution temperature of the 0.5 M H₃BO₃ increased, the thickness of the passive film increased but the resistance of the passive film was diminished, which is coincident with a solution temperature dependency of the passive current in the potentiodynamic curve. The inner oxide film on Alloy 600 was distinguishable from the Cr-rich outer oxide film above 100 °C. From the Mott–Schottky relation, the oxide formed in 0.5 M H₃BO₃ at 300 °C showed a p-type semiconductor property, accompanied by a Cr-rich oxide film throughout the whole oxide film unlike the n-type oxide films up to 250 °C. The oxide resistance of the passive film decreased in the order of 0.5 M H₃BO₃, 0.1 M NaOH and 0.5 M Na₂SO₄, which is consistent with the pH dependency of the passive current. Ni-rich oxide films of a p-type were formed in the 0.5 M Na₂SO₄ or 0.1 M NaOH.     

Charge trapping and ac-electrical conduction in nanocrystalline erbium manganate film on Si substrate

Thin film of nanocrystalline ErMnO₃ was prepared by thermal annealing of Er–Mn oxide film deposited on p-Si(1 0 0) substrates. The X-ray fluorescence (XRF) and X-ray diffraction (XRD) technique were used to investigate the structure of the prepared Er–Mn oxide films. XRD study shows that films pre-annealed at 400 °C have amorphous structure and they were crystallised forming ErMnO₃ compound under pre-annealing at 800 °C or more. Moreover, in the prepared Er–Mn oxide films, Er oxide or Mn oxide cannot be crystallised each alone, but instead they interact chemically with each other forming ErMnO₃ compound. A comprehensive study on electrical properties was carried on. The ac-conductance and capacitance as a function of gate voltage, frequency, and temperature were studied on samples made in form of metal/oxide film/Si MOS devices. The fixed charge and interface state densities were determined and their variation with annealing process was studied and explained. It was found that the “correlated barrier hopping” CBH model controls the frequency dependence of the ac-conductivity, while Kramers–Kronig (KK) relations explain the frequency dependence of the relative permittivity. The parameters of CBH model were determined showing that the ac-conduction is realised by bipolaron hopping mechanism. dc conduction properties were also studied through the voltage and temperature dependence of the leakage dc-current density. The obtained dc-data follow a space charge limited current (SCLC) mechanism.     

Structural transformation of carbon nanotubes to silicon carbide nanorods or microcrystals by the reaction with different silicon sources in rf induced CVD reactor

Silicon carbide (SiC) nanorods and microcrystals were synthesized through a two-step reaction scheme. Carbon nanotubes (CNTs) were first grown over metal catalyst-loaded Si(1 0 0) wafer surface by thermal decomposition of C₂H₂. The grown CNTs were then reacted with a gas mixture of SiH₄ and C₃H₈ or tetramethylsilane (TMS) to form β-SiC nanostructures. The growth of SiC nanorods was observed when CNTs were reacted with SiH₄ and C₃H₈, whereas SiC microcrystals were formed when reacting the CNTs with TMS. However, the SiC nanostructures were not grown without CNTs. The diameter of the nanorods was around six times larger than that of the mother nanotubes. The nanorods were crystalline β-SiC with the diameter of 300–400 nm and grew along (1 1 1) direction. The structural transformation of CNTs to SiC nanorods or to microcrystals during the reaction was discussed in this paper.     

Correlation between dielectric properties and strain in Pb0.5 Sr0.5TiO3 thin films prepared by using the sol–gel method

Pb_0.5Sr_0.5TiO₃ (PST) thin films were fabricated by the alkoxide-based sol–gel process using spin-coating method on Pt/Ti/SiO₂/Si substrate. The PST films annealed from 500 °C to 650 °C for 1 h show a perovskite phase and dense microstructure with a smooth surface. The grain size and dielectric constant of PST films increase with the increase in annealing temperature, which reduces the SiO₂ equivalent thickness of the PST film. The crystallinity or internal strain in the PST thin films analyzed from the diffraction-peak widths correlates well with the decrease in the dielectric losses. The dielectric constants and dielectric loss (%) of the PST films annealed at 650 °C (t_eq=0.89 nm) were 549 and 0.21%, respectively.     

Formation of BN films on carbon fibers by dip-coating

Turbostratic boron nitride (BN) films (amorphous with some microcrystallinity) were successfully deposited onto carbon fibers and graphite substrates by dip-coating in methanolic boric acid and urea solutions, followed by nitriding in an ammonia flow at 1000 °C. BN coatings exhibited an orange-peel or pebble-like structure. Surface morphology results indicated that the sizes of the grain-like particles increased with the concentration of the dipping solution. The thickness of the BN film exhibited parabolic relationships with the viscosity of the dipping solution and the withdrawal speed. With the homogeneous surface, the thickness of the BN film increased with the concentration of the reactant in the solution. However, stripping and cracking at the surface have been observed while the reactant concentration was higher than 0.9 M. The yield of BN increased with the nitriding temperature. The increasing trend was slowed down at 800 °C and attained a maximum at 1000 °C.     

Fabrication of carbon-coated cobalt nanoparticles by the catalytic method

A mass of carbon-coated cobalt nanoparticles were successfully synthesized by chemical vapor deposition of methane over Co/Al catalyst at 650 °C. The phases found in the as-prepared carbon-coated nanoparticles were fcc-Co. The diameter of these nanoparticles with 2–10 nm carbon coating shell was in the range of 5–80 nm. However, it is well-known that the Co nanoparticles are suitable for carbon nanotube synthesis, such as Co/Al₂O₃ and Co/SiO₂ catalysts. Here, we speculated that the formation mechanism of carbon-coated cobalt nanoparticles might due to that the formation of carbon nanotubes was inhibited by the catalyst supporter of Al. Compared with Al₂O₃ and SiO₂, Al possesses very low melting point (660 °C), very high diffusion coefficient and thermal conductivity, thus the isotropic precipitation of carbon species on the surface of cobalt particles took place, favoring the formation of carbon-coated Co nanoparticles.     

Synthesis and thermal stability of nano-crystalline vanadium disilicide

Nano-crystalline vanadium disilicide was successfully synthesized using vanadium tetrachloride and silicon as starting materials via reduction–silication route at 650 °C in the molten salt solution of magnesium chloride and sodium chloride in an autoclave. X-ray powder diffraction patterns indicated that the product was hexagonal VSi₂ (a=4.572 Å, c=6.372 Å). Transmission electron microscopy images showed that the particle size of the product was in the range of 40–60 nm in diameter. There was a strong absorption peak at 271 nm in the UV-Vis absorption spectra. The oxidation of nano-crystalline VSi₂ began to proceed at the temperature of 400 °C in air. But the product had high thermal oxidation stability below 1000 °C. It can be used as an antioxidation coating material.     

Ni-Cr-Ti protective coating

Ni-Cr-Ti protective films were prepared by a plasma beam sputter deposition process at 250 °C. Ni-Cr-Ti thin films (50 nm) have been used to study the microstructure by transmission electron microscopy and the grain growth during heating in the heating stage of an electron microscope and after baking in an oxygen flow in an oven. Energy-dispersive spectroscopy analysis in the transmission electron microscope was used to study compositional variations in the films. Ni-Cr-Ti films 300 nm thick deposited on polished hot-worked tool steel (AISI H11) substrates have been studied by Auger electron spectroscopy and depth profiling before and after heat treatment in oxygen in an oven at temperatures from 600 to 800 °C. Basic microstructural, morphological, compositional and mechanical properties have been studied on Ni-Cr-Ti protective coatings 3 μm thick. Oxidation and electrochemical properties have also been studied.     

Crystallization and microstructural evolution of cordierite-based thick film dielectrics

Microstructural evolution of glass–ceramic dielectric thick films based on a nonstoichiometric cordierite, 2.4MgO·2Al₂O₃·5SiO₂, containing B₂O₃, P₂O₅, and PbO were investigated in conjunction with nucleation and crystal growth. The cordierite thick films were deposited by screen printing on a 96% alumina substrate, and then fired in the temperature range of 850–950°C in a N₂ atmosphere. Surface microstructure characteristics of the thick films depended on PbO content. Heterogeneous nucleation originated predominantly from the interface between the densified thick film and the alumina substrate. The added PbO segregated to the remaining glass during crystallization, and the relative concentration of Pb in the glass was proven to increase with rising temperature. Most of the remaining glass protruded from the film surface at the final temperature of 950°C. Penetration of the alumina substrate by the remaining glass was also observed. The influences of temperature and PbO on the microstructural evolution including nucleation and growth will be discussed with possible explanations for the observed results.     

Growth behavior of cubic boron nitride (cBN) phase in B-C-N film deposited on Si substrate with non-uniform ion flux

B-C-N film with a ～450 nm thickness was prepared on a (100) oriented silicon wafer (4 cm × 4 cm) by unbalanced magnetron sputtering of a B₄C target with a unipolar pulsed DC substrate bias. At a substrate bias of ?250 V, a cubic boron nitride (cBN) phase appeared in the B-C-N film when the nitrogen content was over 6.7 vol% in Ar-N₂ reactive gases. For the B-C-N film deposited on unipolar pulsed DC biased Si substrate with Ar-16.7%N₂ reactive gas, the content and formation behavior of the cBN phase along with the film thickness were critically dependent on the substrate position due to the difference in ion flux. In contrast to the circular central region of a substrate 2.5 cm in diameter, where cBN was nucleated and grown on hexagonal boron nitride (hBN) in a layered manner, the cBN phase was co-grown with the hBN phase and was surrounded by hBN at the circumference region of the circle. Only hBN was observed at the outer region of the circle. The microstructure of B-C-N film in which cBN is surrounded by hBN is believed to be effective in reducing residual stress developed by the nucleation of a cBN phase.     

金刚石膜/硅复合基片的制备工艺研究

通过等离子体喷射法硅衬底制备金刚石的试验,研究了硅片规格、硅片前期预处理、金刚石膜沉积以及后期热处理等对制备复合基片性质和裂纹产生的影响,对各个工序进行优化和改进,确定了制备金刚石膜/硅复合基片最佳的工艺流程.实验结果表明:在硅基片制备的金刚石膜厚度大于20 μm,抛光后金刚石膜表面粗糙度Ra达到5.2 nm,剩余金刚...