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1.
This study demonstrates that hydrolysis should be carried out in a step manner in gel synthesis. The key to the increase in the amount of water added is the control of the hydrolysis rate of Ti(OC 4H 9) 4. The hydrolysis of Si(OC 2H 5) 4 can be carried out at about 75°C. The amount of added water (γ WI), which varied with TiO 2 content (in mol%), was about 64–88% of the total amount of added water. The hydrolysis reaction should be performed at room temperature while Ti(OC 4H 9) 4 is added. The total amount of added water (γ W) is related to the amount of solvent ( R). For example, if TiO 2 is 40mol%, γ W will vary from 3.2 to 8.0 when R varies from 0.8 to 2.0. The amount of added water was affected by the distribution of solvent in the metal alkoxides. The amount of added water can be increased when RSi(OC2H5)4 = 1, RTi(OC4H9)4 > 1. The rate of rise in temperature of the thermolysis of the dried gel should be less than 10°C per hour, and the heat treatment temperatyre is related to the TiO 2 content (in mol%). Gel glasses without devitrification can only be obtained by thermolysis at 600°C from the gel with no less than 20 mol% TiO 2. 相似文献
2.
Hydrogenated amorphous silicon (a-Si:H) thin films grown at 250°C on (1 0 0) crystalline substrate using plasma-enhanced chemical vapor deposition (PECVD) with SiH 4/H 2 gas flow ratio equal to 5/1 (sccm) are investigated by transmission electron microscopy. It is found that the thin film is totally amorphous when grown on a glass substrate. But when the substrate is changed to crystalline silicon, some crystalline grains are found embedded in the amorphous structure in certain regions even if the thickness of the film reaches 600 nm. It is suggested that the amorphous silicon film grown on a crystalline silicon substrate at a temperature of 250°C without heavy H 2 dilution is a mixed network of a small amount of crystalline silicon and the major portion of amorphous silicon. 相似文献
3.
High-quality ZnO thin films have been grown on a Si(1 0 0) substrate by plasma-enhanced chemical vapor deposition (PECVD) using a zinc organic source (Zn(C 2H 5) 2) and carbon dioxide (CO 2) gas mixtures at a temperature of 180°C. A strong free exciton emission with a weak defect-band emission in the visible region is observed. The characteristics of photoluminescence (PL) of ZnO, as well as the exciton absorption peak in the absorption spectra, are closely related to the gas flow rate ratio of Zn(C 2H 5) 2 to CO 2. Full-widths at half-maximum of the free exciton emission as narrow as 93.4 meV have been achieved. Based on the temperature dependence of the PL spectra from 83 to 383 K, the exciton binding energy and the transition energy of free excitons at 0 K were estimated to be 59.4 meV and 3.36 eV, respectively. 相似文献
4.
A precursor prepared from a methyltriethoxysilane ((CH 3)Si(OC 2H 5) 3, MTES)-B(OC 2H 5) 3-polyacrylonitrile (PAN) composition was used for the synthesis of boron-doped SiC by carbothermal reduction. Initially, MTES was hydrolyzed with HCl (MTES: H 2O: HCl = 1 : 1 : 0.01) for 1 h in a sealed vessel. The number-average molecular weight measurement and a NMR spectrum revealed that the species in the solution were mainly oligometric. With the addition of B(OC 2H 5) 3, no significant changes in the distribution of the Si containing species were detected. The mixing of the hydrolyzed solution with a PAN-dimethylsulfoxide solution led to a homogeneous solution. After the evaporation of the solvents and the subsequent heat treatment at 220° C, brown precursor powder was obtained. By the heat treatment at 1600° C in Ar, it was converted to boron-doped SiC powder. 相似文献
5.
Fluorine doped silica gels were synthesized by using the sol-gel processes of (A) SiF 4(g) and H 2O(1) and (B) the mixed solution of Si(OC 2H 5) 4, C 2H 5OH, H 2O and H 2SiF 6. By the former process we obtained a gel of relatively high fluorine content (8–12 at.%F), while we could synthesize the gel of 0–12 at.% F by adjusting the F/Si ratio of the starting solution mixtures by the latter process. The defluorination behavior and the structural change of these gels at high temperature were studied by heating-mass spectrometry, IR and ESR measurements. The results revealed the following: (1) defluorination by liberation of SiF4(g) was admitted from temperatures at about 400°C and was controlled by the diffusion of fluorine in the gel bulk. (2) The peak separation analysis for the IR band of 1300-900 cm−1, where the stretching vibrations of Si---O and Si---F appear, showed that the change of the band shape resulted from the increase or the decrease of the Si---F bonds and the change of the bond angle of Si---O---Si as well as the change of the force constant accompanied by fluorination or defluorination. (3) The defects of the Si E′ center were induced by X-ray irradiation depending on the degree of the defluorination, and were reduced by the heat treatment. However, with the heat treatment at temperatures higher than 1000°C, the E′ center increased again. The IR spectra suggest that this behavior might correspond to the gel-glass trasition. 相似文献
6.
Monolithic alumina gels were prepared by a novel non-hydrolytic sol-gel route based on the condensation reaction between aluminum alkoxides Al(OR) 3 and aluminum halides AlX 3, through the formation of alkyl halide RX(X = Br, Cl; R = iso-propyl, sec- or ter-butyl), around 100°C. Samples were then calcined and were found to be amorphous up to about 750°C; they kept a high specific surface area to about 900°C. This delayed crystallization is correlated with the large number of five-coordinate aluminum sites measured in dried gels by 27Al NMR spectroscopy. 相似文献
7.
Preparation of radial gradient refractive index ( r-GRIN) glass rods has been undertaken by a sol-gel process using metal alkoxides. Two binary systems, Si(OCH 3) 4---Ge(OC 2H 5) 4 and Si(OCH 3) 4−Ti(O− n-C 4H 9) 4 have been investigated. It has been shown that immersion of rod-shaped wet gels in neutral or acidic water gives rise to leaching of the dopants (germanium and titanium components). Since this leaching is controlled predominantly by diffusion, the dopants remaining in the gels are expected to form concentration gradients. Optical measurements of the glass rods obtained after drying and sintering of the leached gels have shown that the concentration gradients are retained in the glass rods and they give r-GRIN profiles. 相似文献
8.
Multi-domained heteroepitaxial rutile-phase TiO 2 (1 0 0)-oriented films were grown on Si (1 0 0) substrates by using a 30-nm-thick BaF 2 (1 1 1) buffer layer at the TiO 2–Si interface. The 50 nm TiO 2 films were grown by electron cyclotron resonance oxygen plasma-assisted electron beam evaporation of a titanium source, and the growth temperature was varied from 300 to 600 °C. At an optimal temperature of 500 °C, X-ray diffraction measurements show that rutile phase TiO 2 films are produced. Pole figure analysis indicates that the TiO 2 layer follows the symmetry of the BaF 2 surface mesh, and consists of six (1 0 0)-oriented domains separated by 30° in-plane rotations about the TiO 2 [1 0 0] axis. The in-plane alignment between the TiO 2 and BaF 2 films is oriented as [0 0 1] TiO 2 || BaF 2 or [0 0 1] TiO 2 || BaF 2 . Rocking curve and STM analyses suggest that the TiO 2 films are more finely grained than the BaF 2 film. STM imaging also reveals that the TiO 2 surface has morphological features consistent with the BaF 2 surface mesh symmetry. One of the optimally grown TiO 2 (1 0 0) films was used to template a CrO 2 (1 0 0) film which was grown via chemical vapor deposition. Point contact Andreev reflection measurements indicate that the CrO 2 film was approximately 70% spin polarized. 相似文献
9.
Homogeneous, crack-free, thin films of crystalline LiNbO 3 were synthesized above 250°C on Si(100) substrates by the dip-coating method using a double alkoxide solution. The coating solution, which was prepared by the controlled partial hydrolysis of the double alkoxide, gave stoichiometric LiNbO 3 crystalline films at temperatures as low as 250°C. The concentration of the alkoxide solution influenced both of thickness and quality of films. Crystallinity of thin film top-coated directly on the substrate affected the crystallization state of films coated on the film remarkably. Films crystallized on -Al 2O 3(0001) showed preferred orientation along the c-axis, while the preferred orientation could not be observed on Si(100) substrates. 相似文献
10.
Thin films of Tantalum nitride (TaN) were deposited from tetra-ethylamido-tantalum (Ta (NEt 2) 4) by low-pressure chemical vapor deposition. Good-quality step coverage is achieved below 400°C, because the deposition rate is determined by the reaction rates on the surface. The film resistivity increases, however, as the substrate temperature decreases. In order to obtain the low resistivity of films deposited at lower temperatures, we have increased the amount of injected H 2 gas during the deposition. The resistivity decreases by the increase in the H 2 gas flow rate, and it is shown that a large amount of H 2 gas injection during the deposition is an effective method for obtaining both low resistivity and high-quality step coverage. The residual carbon concentration in the film is measured to be >10%, on the other hand, the concentration of N less than 1%. The microstructural investigation using transmission electron microscopy (TEM) reveals that crystalline structure of the deposited film has an amorphous phase. 相似文献
11.
Titanium nitride (TiN) films were obtained by the atmospheric pressure chemical vapor deposition method of the TiCl 4–N 2–H 2 system with various flow rates of NH 3 at 600°C. The growth characteristics, morphology and microstructure of the TiN films deposited were analyzed by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Without NH 3 addition, no TiN was deposited at 600°C as shown in the X-ray diffraction curve. However, by adding NH 3 into the TiCl 4–N 2–H 2 system, the crystalline TiN was obtained. The growth rate of TiN films increased with the increase of the NH 3 flow rate. The lattice constant of TiN films decreased with the increase of the NH 3 flow rate. At a low NH 3 flow rate, the TiN (2 2 0) with the highest texture coefficient was found. At a high NH 3 flow rate, the texture coefficient of TiN (2 0 0) increased with the increase of the NH 3 flow rate. In morphology observation, thicker plate-like TiN was obtained when the NH 3 flow rate was increased. When the flow rate of NH 3 was 15 sccm, Moiré fringes were observed in the TiN film as determined by TEM analysis. The intrinsic strain was found in the TiN film as deposited with 60 sccm NH 3. 相似文献
12.
Thin films of crystalline lithium niobate (LN) grown on Si(1 0 0) and SiO 2 substrates by electron cyclotron resonance plasma sputtering exhibit distinct interfacial structures that strongly affect the orientation of respective films. Growth at 460–600 °C on the Si(1 0 0) surface produced columnar domains of LiNbO 3 with well-oriented c-axes, i.e., normal to the surface. When the SiO 2 substrate was similarly exposed to plasma at temperatures above 500 °C, however, increased diffusion of Li and Nb atoms into the SiO 2 film was seen and this led to an LN–SiO 2 alloy interface in which crystal-axis orientations were randomized. This problem was solved by solid-phase crystallization of the deposited film of amorphous LN; the degree of c-axis orientation was then immune to the choice of substrate material. 相似文献
13.
The growth kinetics of (SmY) 3(FeGa) 5O 12 garnets obtained by liquid phase epitaxy on Gd 3Ga 5O 12 substrates are discussed in the 920 to 980°C. range. The experiments have been carried out with the substrates in a horizontal plane and with unidirectional rotation ranging from 30 to 300 rotations per minute (rpm). A sharp increase in the growth velocity at temperatures higher than 960°C is interpreted on the basis of a diffusion-reaction theory. It is found that the diffusion constant increases steeper at higher temperatures and that the linear law of the growth rate as a function of the square root of the rotation rate holds to much higher rotation rates at these temperatures. The influence of the surface incorporation is too small to be detectable. The results are compared with published data concerning other compositions. 相似文献
14.
The single-crystalline β-wollastonite ( β-CaSiO 3) nanowires were prepared via a simple hydrothermal method, in the absence of any template or surfactant using cheap and simple inorganic salts as raw materials. Xonotlite [Ca 6(Si 6O 17)(OH) 2] nanowires were first obtained after hydrothermal treatment at a lower temperature of 200 °C for 24 h, and after being calcinated at 800 °C for 2 h, xonotlite nanowires completely transformed into β-wollastonite nanowires and the wire-like structure was preserved. The synthesized β-wollastonite nanowires had a diameter of 10–30 nm, and a length up to tens of micrometers, and the single-crystalline monoclinic parawollastonite structured β-wollastonite was identified by XRD with the space group of P2 1/a and cell constants of a=15.42 Å, b=7.325 Å, c=7.069 Å and β=95.38°. A possible growth mechanism of β-wollastonite nanowires was also proposed. The advantages of this method for the nanowire synthesis lie in the high yield, low temperature and mild reaction conditions, which will allow large-scale production at low cost. 相似文献
15.
Homoepitaxial silicon carbide (SiC) films were grown on 3.5° off-oriented (0 0 0 1) 6H–SiC by metal-organic chemical vapor deposition (MOCVD) using bis-trimethylsilylmethane (BTMSM, C 7H 20Si 2). A pronounced effect of the growth conditions such as source flow rate and growth temperature on the polytype formation and structural imperfection of the epilayer was observed. The growth behavior was explained by a step controlled epitaxy model. It was demonstrated by high-resolution X-ray diffractometry and transmission electron microscopy that high-quality 6H–SiC thin films were successfully grown at the optimized growth condition of substrate temperature 1440°C with the carrier gas flow rate of 10 sccm. 相似文献
16.
Silica gels doped with [Cu(C 5H 5N) 4] 2+ (C 5H 5N = Py), CuCl 2-HOCH 2CH 2OH and Cu(CH 3COO) 2-NH 2(CH 2) 3Si-(OC 2H 5) 3 (CH 3COO = OAc, C 2H 5 = Et) have been prepared and examined by X-ray diffraction, electron spin resonance, transmission electron microscopy (TEM), thermal gravimetric analysis and Fourier transform infrared spectroscopy. Different dopants have different interactions with the silica alcogels depending on the chemistry of the dopants: [Cu(Py) 4] 2+ forms chemical bonds with the hydroxyl oxygens on the surface of the silica matrix; in Cu(OAc) 2-NH 2(CH 2) 3Si(OEt) 3-doped alcogels, the siloamine enters into the sol-gel reaction and Cu(OAc) 2 coordinates to the -NH 2(CH 2) 3 ligand of the precursor. However, there is no evidence for bond formation between copper and the hydroxyl groups on the silica surface in the CuCl 2-HOCH 2CH 2OH-doped alcogels. The TEM images show a homogeneous and uniform distribution of copper particles on the reduced CuCl 2-HOCH 2CH 2OH- and Cu(OAc) 2-NH 2(CH 2) 3Si(OEt) 3-doped xerogel surface. The type of nitrogen adsorption isotherms of doped silica xerogels are unaffected by the dopant concentration. However, their surface areas do depend on the level of dopant. The microstructure of the silica matrix is primarily determined by the pH of the initial reactants, at least in the [Cu(Py) 4] 2+-doped case. 相似文献
17.
The MOCVD of AlN, GaN and InN thin films using the novel single source precursors (N 3) 2Ga[(CH 2) 3NMe 2] (1), (N 3)In[(CH 2) 3NMe 2] 2 (2), (N 3)Al[(CH 2) 3NMe 2] 2 (3) and (N 3)AlMe 2(H 2N tBu) (4) is reported. The compounds are non-pyrophoric. Compound 3 is air stable. No additional N-sources were used for the growth of the nitrides. We achieved epitaxial (AlN, GaN) or polycrystalline (InN) growth at least 200°C below the decomposition temperature of the respective nitride. Some aspects of the reactivity of the precursors with ammonia and the resulting influence on the deposition process were investigated. 相似文献
18.
A new method of direct synthesis nano-BaTiO 3 powders from solution was developed in this study. Dissolving Ba(OH) 2·8H 2O into water as base solution, nanocrystalline BaTiO 3 powders can be obtained by mixing ethanol solution of tetrabutyl titanate with hot base solution under normal pressure. When the temperature of the base solution was 60°C, we obtained crystalline powders with average particle size of about 25 nm. The activity of the powders can be held up because the calcination at high temperature is not necessary using this method. 相似文献
19.
The hydrolysis and condensation reactions of Si(OC 2H 5) 4 (TEOS) at 80°C in the TEOS---H 2O---C 2H 5OH---HCl solutions with H 2O/TEOS molar ratios ( r) from 1.0 to 2.0 were followed by gas chromatography (GC) and measurement of molecular weight (
) of the hydrolyzates, in order to explain the viscosity change of the solutions. It has been found that the siloxane oligomers with average polymerization degree ( n) from 2 to 7 are formed in the early stage of reaction and undergo condensation to form higher polymers. The n and the number of silanol groups of the oligomers are increased with increasing r. The fact that the solution viscosity increased once rapidly around the so-called gelation point followed by a sluggish increase with the increase of reaction time for an r of 1.7, while it increased rapidly without a break till gelation for an r of 2.0, was attributed to fewer silanol groups and higher steric hindrance as a result of more −OC 2H 5 groups remaining in the oligomers for an r of 1.7. 相似文献
20.
Ce substituted Bi 1−xCe xFeO 3 (BCFO) films with x=0–0.15 were deposited on indium tin oxide (ITO)/glass substrates by sol–gel process annealed at 500 °C. Rhombohedral phase was confirmed by XRD study and no impure phases were observed till x=0.15. Substantially enhanced ferroelectricity was observed at room temperature due to the substitution of Ce. In the films with x=0.05 and 0.10, the double remnant polarization are 75.5 and 57.7 μC/cm 2 at an applied field 860 kV/cm. Moreover, the breakdown field was enhanced in the films with Ce substitution. 相似文献
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