Synthesis of two-dimensional gallium nitride via spin coating method: influences of nitridation temperatures

This paper reports the synthesis and characterization of gallium nitride (GaN) thin films deposited on p-type silicon (100) substrates by using low cost spin coating method under various nitridation temperatures. This work demonstrated that spin coating with the new prepared precursor solution can be used as a versatile method for the successfully growth of GaN thin films. Furthermore, the influence of varying nitridation temperatures on the structural, morphological, and optical properties of synthesized GaN thin films were studied in this work. The GaN thin films were characterized by X-ray diffraction, field-emission scanning electron microscopy, atomic force microscopy, photoluminescence and Raman spectroscopy. All the characteristics of the GaN thin films were effectively improved with the increasing of the nitridation temperatures from 750 to 950 °C and degraded at temperature of 1,050 °C. The measured results show that nitridation temperature plays an important role in improving the crystalline quality of the GaN thin films and the most efficient nitridation temperature was at 950 °C.     

Direct formation of thermally stabilized amorphous mesoporous Fe2O3/SiO2 nanocomposites by hydrolysis of aqueous iron III nitrate in sols of spherical silica particles

Nanocomposite materials containing 10% and 20% iron oxide/silica, Fe2O3/SiO2 (w/w), were prepared by direct hydrolysis of aqueous iron III nitrate solution in sols of freshly prepared spherical silica particles (St?ber particles) present in their mother liquors. This was followed by aging, drying, calcination up to 600 degrees C through two different ramp rates, and then isothermal calcinations at 600 degrees C for 3 h. The calcined and the uncalcined (dried at 120 degrees C) composites were characterized by thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, X-ray diffraction (XRD), N2 adsorption/desorption techniques, and scanning electron microscopy as required. XRD patterns of the calcined composites showed no line broadening at any d-spacing positions of iron oxide phases, thereby reflecting the amorphous nature of Fe2O3 in the composite. The calcined composites showed nitrogen adsorption isotherms characterizing type IV isotherms with high surface area. Moreover, surface area increased with the increasing of the iron oxide ratio and lowering of the calcination ramp rate. Results indicated that iron oxide particles were dispersed on the exterior of silica particles as isolated and/or aggregated nanoparticles. The formation of the title composite was discussed in terms of the hydrolysis and condensation mechanisms of the inorganic FeIII precursor in the silica sols. Thereby, fast nucleation and limited growth of hydrous iron oxide led to the formation of nanoparticles that spread interactively on the hydroxylated surface of spherical silica particles. Therefore, a nanostructured composite of amorphous nanoparticles of iron oxide (as a shell) spreading on the surface of silica particles (as a core) was formed. This morphology limited the aggregation of Fe2O3 nanoparticles, prevented silica particle coalescence at high temperatures, and enhanced thermal stability.     

Synthesis and Characterization of Hydrotalcite-like Compounds Containing V(3+) in the Layers and of Their Calcination Products

The synthesis and full characterization of a new hydrotalcite-like compound with the formula [Mg(0.71)V(0.29)(OH)(2)](CO(3))(0.145).0.72H(2)O and with V(3+) in the layers are described. The influence of hydrothermal treatment and drying rate on the crystallinity of the materials obtained is discussed. The evolution to mixed oxides upon calcination at different temperatures (448, 548, 773, 1023, and 1273 K) under different atmosphere environments (air or nitrogen) for 2 h has been studied. Characterization of the original layered materials and of the calcination products has been carried out by X-ray diffraction, thermal analysis, Fourier-transform infrared spectroscopy, BET specific surface area determination, temperature-programmed reduction, and transmission electron microscopy. X-ray absorption spectroscopies (XANES and EXAFS) have also been used to assess the local geometry of vanadium ions in the different compounds prepared. All experimental data agree with a well-crystallized hydrotalcite-like compound after thermal treatment, and also a minor effect of the drying rate on the crystallinity has been found. Thermal decomposition yields poorly crystalline layered compound at 448 K that undergoes transformation to mostly amorphous materials when calcined at 548-773 K, finally leading to a mixture of MgO and Mg(3)V(2)O(8), which has increasing crystallinity as the calcination temperature increases. XAS results indicate the presence of V(3+) ions in an octahedral coordination in the parent sample calcined at 448 K and tetrahedrally coordinated V(5+) species for samples calcined at higher temperatures, calcination giving rise to a better ordering of the second coordination sphere. Similar results were found when calcination was performed in nitrogen, although higher temperatures were needed to achieve the same result.     

Embedded atom model for liquid metals: Liquid iron

A method for calculating the embedded atom model potential suggested earlier for liquid Ga and Bi uses data on the structure and thermodynamic properties of metals close to their melting points. This method was applied to liquid iron at temperatures and pressures up to 5000 K and 360 GPa. Several iron models with the potential of the embedded atom model were constructed by the method of molecular dynamics at temperatures from 1820 to 5000 K and densities from 8.00 to 12.50 g/cm³. The thermodynamic, structural, diffusion, and viscosity properties of iron were calculated. The self-diffusion coefficients decreased almost linearly as the volume of the system became smaller. The conclusion is drawn that iron in the external region of the Earth’s core behaves as a liquid with self-diffusion coefficients of about ～10^-5 cm²/s and viscosity ～10^-3?10^-2 Pa s. At the boundary between the external and inner core regions, at densities of 11–12 g/cm³, iron has the properties of an amorphous phase and its self-diffusion coefficient becomes too low to be estimated by the method of molecular dynamics. Under the Earth’s inner core conditions, the embedded atom model of iron spontaneously crystallizes.     

程序升温反应法由纳米氧化铁制备纳米氮化铁

先以廉价的无机铁盐为主要原料,采用沉淀法和溶胶凝胶法制备纳米氧化铁粒子,由此得到粒径大小在10～20nm,20～40nm和40～60nm的氧化铁,在此基础上,以纳米氧化铁为前体,在氨气气氛下由程序升温反应法制备纳米氮化铁.研究发现,纳米氧化铁经程序升温反应氮化后,可以制备出纳米尺度的氮化铁.不同大小的氧化铁纳米粒子氮化后尺寸存在明显的差异,在一定范围内,小粒径的纳米氧化铁氮化后更容易长大;对于大小相近的γ相与α相纳米氧化铁粒子,γ氧化铁纳米粒子氮化后尺寸增大更为显著.制得的氮化铁的形貌与其氧化铁前体保持一致.     

Interactions of NO with iron deposited on alumina

The interaction of nitric oxide with single-crystal surfaces of alumina at temperatures of 298, 473, and 673 K, which had been covered by various amounts of iron, was studied using X-ray photoelectron spectroscopy. The iron was deposited onto Al₂O₃ in the Fe⁰ state. At low coverages, iron was partially oxidized due to its interaction with Al₂O₃. Scanning auger mapping analysis showed that the iron was randomly distributed on the Al₂O₃ surface. The amount of adsorbed NO increased with increasing iron coverage. However, at very high iron coverages, there was a decrease in adsorption. This indicated that the aluminum ions may have activated the NO adsorption on the iron atoms. For increasing temperature there was also an increase in adsorption for high iron coverages, but the adsorption decreased with increasing temperature for low iron coverages. Sticking probability calculations indicated that the adsorption was mobile and dissociative. Binding energy of the nitrogen peaks indicated that NO was adsorbed onto the Fe/Al₂O₃ surface as a nitride.     

Spin crossover studies in cationic complexes of iron by using Mössbauer spectroscopy

The spin transitions in two new cationic complexes of iron, i. e., iron bipyridine formate, [Fe/bipy/₃]/HCOO/₂. 5/HCOOH/ and iron bipyridine tetrafluoro borate, [Fe/bipy/₃]/BF₄/₂. 2H₂O have been studied by using Mössbauer spectroscopy. From quadrupole splitting values, at different temperatures, it has been established that both the complexes show the coexistence of both the high spin state and the low spin state at 300 K while complete transformation to low spin state occurs at 77 K. Both compounds were prepared by electrochemical technique.     

Fabrication of TiN nanorods by electrospinning and their electrochemical properties

TiN nanorods were synthesized using electrospinning technique followed by thermolysis in different atmospheres. A dimethyl formamide-ethanol solution of poly-(vinyl pyrrolidone) and Ti (IV)-isopropoxide was used as the electrospinning precursor solution and as-spun nanofibers were calcined at 500 °C in air to generate TiO₂ nanofibers. Subsequently, a conversion from TiO₂ nanofibers to TiN nanorods was employed by the nitridation treatment at 600∼1400 °C in ammonia atmosphere. A typical characteristic of the final products was that the pristine nanofibers were cut into nanorods. The conversion from TiO₂ to TiN was realized when the nitridation temperature was above 800 °C. As-prepared nanorods were composed of TiN nano-crystallites and the average crystallite size gradually increased with the increase of the nitridation temperature. Electrochemical properties of TiN nanorods showed strong dependence on the nitridation temperature. The maximum value of the specific capacitance was obtained from the TiN nanorods prepared at 800 °C.     

Grain sizes, surface areas, and porosities of vapor-deposited H2O ices used to simulate planetary icy surfaces

Mean grain sizes and specific surface areas (SSAs) of ice substrates formed by vapor deposition at low temperatures are of importance in simulating external surfaces of icy satellites in the solar system. Environmental scanning electron microscopy (ESEM) was used to obtain granule sizes and to observe the phase of ice granules prepared on borosilicate, silicon, and metallic plates. Ices prepared at a temperature lower than 140 K appear to be amorphous, and their granule sizes are typically submicrometer. At slightly warmer temperatures, near 180-200 K, ice films are composed of either hexagonal or cubic granules with sizes up to a few micrometers. When briefly annealed to even warmer temperatures, ice granule sizes approach approximately 10 microm. SSAs of ice substrates were determined from BET (Brunauer, Emmett, and Teller) analysis of gas adsorption isotherms in the temperature range from 83.5 to 261 K. SSAs decrease drastically from 102 m2/g at 83.5 K to 0.87 m2/g at 150 K and further decrease slowly to 0.22 m2/g at 261 K, suggesting that the transition from amorphous to crystalline forms occurs at approximately 150 K. The overall decrease in SSAs is primarily due to metamorphism and sintering. These results are comparable to recent field and laboratory measurements. Possible implications for theoretical models of icy satellites of outer planets using remote sensing techniques are also discussed.     

Ni-P非晶合金催化剂的制备、结构和性能

超细非晶态合金ＭＰ或ＭＢ(Ｍ=Ｎｉ,Ｃｏ,Ｆｅ)的高比表面和结构不规整性使其表现出催化加氢的高活性和选择性,有可能成为新型石油化工加氢催化剂[1-3].其制备主要有物理和化学两类方法[3-5].从提高催化活性角度,化学还原法是最为优越的方法.ＮｉＢ催化活性明显高于ＮｉＰ...     

Preparation of Fe3O4 thin film by the sol-gel method and its magnetic properties

Films consisting of magnetite particles were prepared by the sol-gel method using iron (III) nitrate dissolved in ethylene glycol and 2-methoxyethanol as a new precursor with the aim of decreasing the processing temperatures. Films were annealed under the mixture of hydrogen and nitrogen at various temperatures. Magnetite formation was found to be influenced both by temperature and atmosphere during firing and hydrogenation processes. Typical values of magnetization in saturation and coercive force of films were 440 mT and 196 kA/m, respectively.     

The effect of the starting material on the thermal decomposition of iron oxyhydroxides

The effect of the iron precursor on the thermal decomposition of iron oxyhydroxides was studied by DSC, DTA and TG in this work. Samples were prepared from iron nitrate, iron sulfate and iron chloride and the thermal curves obtained were analyzed by specific area measurements, X-ray diffraction and Mössbauer spectroscopy. It was found that the iron oxyhydroxide precursors affect the temperatures of the hematite formation as well as the textural properties of the final hematite producing particles with different diameters as following: iron sulfate (3.3 nm)相似文献   

Synthesis and characterization of two intensely colored tris(benzoylcyanoxime)iron(II) anionic complexes

Two intensely blue-colored complexes, P(C 6H 5) 4[Fe(BCO) 3] ( 1) and Na[Fe(BCO) 3] ( 2), where BCO (-) is the benzoylcyanoxime anion, have been prepared and characterized in solution and in the solid state. The crystal structure of 1 has been determined at several temperatures (100, 155, 225, and 293 K) and consists of layers of P(C 6H 5) 4 (+) cations and [Fe(BCO) 3] (-) anions. The latter exist as a pair of fac-Delta and Lambda enantiomers in a monoclinic unit cell in the P2(1)/ n space group. Iron(II) has a trigonal-prismatic N 3O 3 coordination environment with average Fe-N and Fe-O bond distances of 1.866 and 1.956 A, respectively, bonds that are unusually short and indicate a (1)A 1g low-spin ground state for iron(II). A sample of 1 prepared with iron-57 has been studied by Mossbauer spectroscopy between 4.2 and 430 K and found to be low-spin iron(II) in studied temperature range. The stepwise formation constants for 1 in aqueous solution at 296 K and pH of 7 are log beta 1 = 0.85 +/- 0.1, log beta 2 = 3.55 +/- 0.15, and log beta 3 = 6.36 +/- 0.15. Both 1 and 2 exhibit irreversible oxidation of iron(II) at approximately 1.0 V, indicating a significant degree of the ligand-to-iron charge transfer. Thus, 1 and 2 are rare examples of highly colored iron(II) anionic complexes that do not contain aromatic heterocyclic amine ligands, such as bipyridine or phenanthroline.     

Iron sulfide electrodeposits: effect of heat treatment on composition and structure

Iron sulfide thin films were prepared by pulsed electrolysis on titanium substrates from aqueous solutions containing sulfur and iron sulfate, at 333 K. Annealing of the electrodeposits was performed under nitrogen, at different temperatures ranging from 523 to 773 K. By using solid state characterization techniques (X-ray diffraction and scanning electron microscopy/energy dispersive spectroscopy), the influence of the annealing temperature on the morphological and structural properties of the electrodeposits has been investigated. For all the studied temperatures, more than one phase was always obtained. Received: 1 March 1999 / Accepted: 3 June 1999     

铁柱撑膨润土的微波合成及对甲基橙的光催化氧化降解作用

在微波作用下,由钙基膨润土和铁溶胶快速制备铁柱撑膨润土,分别用XRD、BET、SEM-EDS和TC-DSC测试技术表征了催化剂的组成和结构,结果表明,羟基铁阳离子进入膨润土层间取代Ca2+形成柱撑,膨润土孔结构基本不变,比表面积增加.考察了铁柱撑膨润土对光催化降解甲基橙反应的催化活性,确定了最佳降解反应条件为:体系pH=3,微波500W、80℃辐射10min制备的铁柱撑膨润土为催化剂,用量1.5g/L,H2O2浓度为7.345×10-3mol/L,甲基橙浓度100mg/L,紫外光照射60min,甲基橙的降解率可达98.1％.     

Photoresponse of p-type zinc-doped iron(III) oxide thin films

Stable zinc-doped iron(III) oxide thin films that exhibit p-type behavior were synthesized by spray pyrolytic deposition (SPD) on conducting indium-doped tin oxide-coated glass substrate. The highest photocurrent density of 1.1 mA/cm2 was observed at an illumination intensity of 40 mW/cm2 at -0.8 V vs Pt for zinc-doped p-Fe2O3 samples prepared at an optimum substrate temperature of 663 K using an optimum spray time of 70 s. A quantum efficiency of 21.1% at 325 nm was found for SPD samples prepared using a dopant concentration of 0.0088 M zinc nitrate hexahydrate. X-ray diffraction results showed structures of alpha-Fe2O3 and ZnFe2O4. A direct band gap energy of 2.2 eV was found from monochromatic photocurrent density data and agrees closely with the band gap obtained from UV-vis absorption. The X-ray photoelectron spectroscopy results also confirm the presence of zinc dopant (4.0 atomic %) in thin films of zinc-doped p-Fe2O3.     

Spherical iron/silica nanocomposites from core-shell particles

A simple procedure to coat silica spheres with smooth layers of iron compounds is reported. It is based on the forced hydrolysis (60-85 degrees C) of iron(III) acetylacetonate solutions containing the silica cores and sodium dodecylsulfate (SDS). The role that the iron(III) precursor and SDS play in the formation of uniform coatings is discussed. The thermal evolution of the composites up to the crystallization of the initially amorphous coating was also studied. Finally, the core-shell particles, as prepared, were thermally reduced under hydrogen atmosphere to produce magnetic composites whose magnetic properties were also evaluated as a function of the reduction temperature.     

焙烧温度对酯加氢制醇Cu-Al-Ba催化剂性能的影响(英文)

通过共沉淀法在不同焙烧温度下制备了新型无铬Cu-Al-Ba催化剂.测试了其在高压釜中将棕榈油甲酯加氢制备高碳醇的反应性能.结果表明催化剂的焙烧温度对催化性能有较大影响.在从150℃升至750℃的过程中,高碳醇的收率显示了三个阶段的变化,相应地,催化剂前驱体的热重(TG-DTG)曲线也显示了三个阶段的失重.X射线衍射(XRD)、X射线荧光(XRF),透射电镜-能谱分析-选区电子衍射(TEM-EDS-SAED)、N2物理吸附和程序升温还原(TPR)表征表明,催化剂是由一种孔雀石-勃石-碳酸钡前驱体制得的.在300或550℃焙烧后,催化剂组成为晶态的CuO、BaCO3和非晶态的Al2O3.其中,非晶态的Al2O3为CuO的高分散提供了大的比表面,杆状的BaCO3组分有利于提供微孔结构.在更高的焙烧温度750℃,新物相BaAl2O4的形成破坏了催化剂中的非晶态结构,导致其比表面积和孔容的急剧下降,并引起CuO物种的聚结.550℃焙烧的催化剂显示了最高的高碳醇收率,达到92.3%,这归因于其大的比表面积、大孔容和较高的CuO分散性.     

Comparison of electro-optical switching between polymer-stabilised cubic and amorphous blue phases

We prepared polymer-stabilised cubic and amorphous blue phase liquid crystals consisting of the same materials at different UV-curing temperatures using photopolymerisation. Then we investigated the effects of polymer stabilisation on their physical properties. The UV-curing temperature does not affect phase stabilisation of the polymer-stabilised amorphous BPIII (PS-BPIII). Temperatures of the PS-BPIII were found to be extended to more than 50 K. However, a critical temperature exists in the polymer stabilisation process for the PS-cubic BP. Although no substantial difference in response speed was found between the polymer-stabilised cubic and amorphous structures, larger hysteresis and higher residual birefringence were observed in the PS-cubic BP than in the PS-BPIII. Amorphous BPIII with an amorphous network of disclination lines has no critical temperature for the polymer stabilisation and realises a high-performance display.     

The nature of the product from the reaction of tetracyanoethylene with iron pentacarbonyl

The reaction of tetracyanoethylene with iron pentacarbonyl in mesitylene at 90° gave an insoluble product, Fe₂C₁₆H₁₂N₈O₇. The Mössbauer and IR spectra, the magnetic susceptibilities over the temperature range 95–298 K, and the thermal decomposition temperatures in a nitrogen atmosphere were measured. The solid is best described as an iron (III) ketoamine polymer with hydroxo bridges between iron atoms.