Structural characterization and magnetic properties of superparamagnetic zinc ferrite nanoparticles synthesized by the coprecipitation method

Single phase zinc ferrite (ZnFe₂O₄) nanoparticles have been prepared by the coprecipitation method without any subsequent calcination. The effects of precipitation temperature in the range 20–80 °C on the structural and the magnetic properties of zinc ferrite nanoparticles were investigated. The crystallite size, microstructure and magnetic properties of the prepared nanoparticles were studied using X-ray diffraction (XRD), Fourier transmission infrared spectrum, transmission electron microscope (TEM), energy dispersive X-ray spectrometer and vibrating sample magnetometer. The XRD results showed that the coprecipitated nanoparticles were single phase zinc ferrite with mixture of normal and inverse spinel structures. Furthermore, ZnFe₂O₄ nanoparticles have the crystallite size in the range 5–10 nm, as confirmed by TEM. The magnetic measurements exhibited that the zinc ferrite nanoparticles synthesized at 40 °C were superparamagnetic with the maximum magnetization of 7.3 emu/g at 10 kOe.     

Influence of acid catalysts on the structural and magnetic properties of nanocrystalline barium ferrite prepared by sol–gel method

BaFe₁₂O₁₉ powders with nanocrystalline size were prepared by sol–gel techniques. Nitric, hydrochloric, acetic and stearic acid were used to improve the magnetic properties. Amorphous gels were formed with Fe/Ba molar ratio of 10.5. Then powders were obtained by subsequent heat treatment at 800–1000 °C for 1 h. Barium ferrite powder was also synthesized by solid state reaction at 1210 °C. X-ray diffraction, scanning electron microscopy and transmission electron microscopy (TEM) experiments were conducted to evaluate structural properties of the samples. The value of the effective magnetic susceptibility was measured. The results show that the magnetoplumbite structure was formed in all of the powders. The TEM observation showed that the minimum particle size (20 nm) was produced with the stearic acid catalyst. The highest value of the effective magnetic susceptibility was achieved also using stearic acid.     

Self filling of Ni nanoparticles in amorphous AlN nanotubes and its field emission property

Unique aluminum nitride amorphous nanotubes filled with Ni nanoparticles have been successfully synthesized through the reaction of NH₃ over Ni-Al thin film at 1000 °C, which is similar to the extended vapor-liquid-solid technique. The X-ray diffraction and high-resolution transmission electron microscopic results are in good agreement with the amorphous nature of AlN nanotubes and crystallinity of Ni nanoparticles. The AlN nanotubes were having average diameter 35 nm and length ∼4 μm, whereas the Ni nanoparticles were having 5 nm in diameter. The unique structure showed excellent field emission property and high electrical conductivity ∼0.43 kmho/m at room temperature. The mechanism of good field emission property has been explained in detail.     

埃洛石纳米管负载Ni纳米粒子的研究

以天然纳米管埃洛石为载体,以Sn-Pd胶体溶液作为活化剂,利用化学镀法在埃洛石的内表面镀金属Ni。利用XRD、TEM对合成的产物进行分析表征,表明在埃洛石纳米管的内腔沉积了颗粒连续、尺寸大小约为10nm的Ni粒子,而HRTEM分析表明Ni微粒为纳米晶体。良好分散性能的镍-埃洛石纳米复合材料将会在高效催化剂、润滑剂、传感器,高密度磁记录材料等领域有潜在的应用前景。     

Synthesis by sol–gel process,structural and optical properties of nanoparticles of zinc oxide doped vanadium

We report the elaboration of vanadium-doped ZnO nanoparticles prepared by a sol–gel processing technique. In our approach, the water for hydrolysis was slowly released by esterification reaction followed by a supercritical drying in ethyl alcohol. Vanadium doping concentration of 10 at.% has been investigated. After treatment in air at different temperatures, the obtained nanopowder was characterised by various techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and photoluminescence (PL). Analysis by scanning electron microscopy at high resolution shows that the grain size increases with increasing temperature. Thus, in the case of thermal treatment at 500 °C in air, the powder with an average particle size of 25 nm shows a strong luminescence band in the visible range. The intensity and energy position of the obtained PL band depends on the temperature measurement increase. The mechanism of this emission band is discussed.     

The influence of annealing temperature on the structure,morphologies and optical properties of ZnO nanoparticles

ZnO nanoparticles (NPs) have been successfully synthesized by the simple solution method at low temperature. The effects of annealing temperature on the structure and optical properties of ZnO NPs were investigated in detail by X-ray diffraction, transmission electron microscopy (TEM), ultraviolet–visible (UV–vis) spectroscopy and photoluminescence (PL) measurements. As the annealing temperature was increased above 180 ^°C the particles morphology evolved from spherical to hexagonal shape, indicating that the average particle size increased from 11 nm to 87 nm. The UV-vis and PL spectra showed a red-shift from 3.62 to 3.33 eV when the annealing temperature was increased.     

Temperature and substrate dependence of structure and growth mechanism of carbon nanofiber

The carbon nanofibers were grown on Ni/Si and Ni/Ti/Si substrates in 1 atm CH₄ atmosphere at 640 °C and 700 °C by thermal chemical vapor deposition method. The carbon nanofibers were characterized by field emission scanning electron microscopy, transmission electron microscopy, and Raman spectrometry for morphology, microstructure, and crystallinity. The electron emission property of carbon nanofibers was also investigated by current-voltage (I-V) measurement. The results showed that the solid amorphous carbon nanofibers could be grown on Ni/Si substrate at 640 °C through tip growth mechanism, the carbon nanotubes could be grown on Ni/Si substrate at 700 °C through tip growth mechanism, and the carbon nanotubes could be grown on Ni/Ti/Si substrate at 700 °C through root growth mechanism.     

Green synthesis and characterization of gold nanoparticles using extract of anti-tumor potent Crocus sativus

In the present study, we have explored anti-tumor potent Crocus sativus (saffron) as a reducing agent for one pot size controlled green synthesis of gold nanoparticles (AuNps) at ambient conditions. The nanoparticles were characterized using UV–vis, scanning electron microscope (SEM), high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and FTIR analysis. The prepared AuNPs showed surface Plasmon resonance centered at 549 nm with average particle size of 15±5 nm. Stable, spherical and triangular crystalline AuNPs with well-defined dimensions were synthesized using anti-tumor potent Crocus sativus (saffron). Crystalline nature of the nanoparticles is confirmed from the HR-TEM, SAED and SEM images, and XRD patterns. From the FTIR spectra it is found that the biomolecules are responsible for capping in gold nanoparticles.     

Effect of Ni, Pd and Ni-Pd nano-islands on morphology and structure of multi-wall carbon nanotubes

In this research, the effect of Ni, Pd and Ni-Pd catalysts have studied on morphology and structure of synthesized multi-wall carbon nanotubes (MWCNTs). Initially, thin films of Ni (with two thicknesses of 10 and 20 nm), Pd/Ni (5/10 nm) and Pd (10 nm) were deposited as catalysts on SiO₂ (60 nm)/Si(1 0 0) substrates, using dc magnetron sputtering technique. The deposited films were annealed at 900 °C in ammonia environment for 45 min, in order to obtain nano-structured catalyst on the surface. Using scanning electron microscopy (SEM), the average size of Ni nano-islands (synthesized by the 10 and 20 nm Ni films), Pd and Ni-Pd nano-islands were measured about 55, 110, 45 and 50 nm, respectively. According to X-ray photoelectron spectroscopy analysis (XPS), the ratio of Ni/Pd on the surface was about 3 for the bilayer sample. The CNTs were synthesized on the nano-island catalysts at 940 °C in CH₄ ambient using a thermal chemical vapor deposition method. The results revealed that average diameter of the CNTs were about 70, 110, 120 nm for Ni, Ni-Pd and Pd catalysts, respectively. Raman spectra of the MWCNTs showed that intensity ratio of two main peaks located in the range of 1550-1600 and 1250-1450 cm⁻¹ (as a quality factor for the CNTs) for Ni, Pd and Ni-Pd catalysts were 1.42, 0.91 and 0.85, respectively. Therefore, based on our data analysis, although addition of Pd to Ni catalyst caused a considerable reduction in the quality of the grown MWCNTs as compared to the pure Ni catalyst, but it resulted in an enhancement in the methane decomposition rate. For the pure Pd catalyst samples, both a slow methane decomposition rate as compared with Ni-Pd catalyst samples and a poor quality of CNTs were observed as compared with the Ni catalyst, under similar experimental conditions.     

Synthesis and characterization of CdS nanoparticles in the presence of oleic acid as solvent and stabilizer

Oleic acid (OA)-capped CdS nanoparticles (NPs) have been successfully synthesized via the direct reaction of Cd(CH₂COO)₂·2H₂O with S powder in OA solvent at 230 °C under nitrogen flow, which was a kind of clean and air-stable solvent. The morphologies and structures of the as-synthesized CdS NPs are examined by transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), X-ray diffractometer (XRD), and Fourier transform infrared (FTIR) spectroscopy, and the typical Ostwald ripening growth mechanism is concluded. Moreover, the collected ultraviolet–visible (UV–vis) absorption spectroscopy and photoluminescence (PL) spectroscopy demonstrate good optical properties of CdS NPs.     

Preparation and characterization of Co–Pt bimetallic magnetic nanoparticles

CoPt₃ nanoparticles are synthesized by a two-stage route using NaBH₄ as a reductant. The nanoparticles are characterized by thermogravimetry (TG) and differential thermal analysis (DTA), Fourier transform infrared (FT-IR), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Structural and spectroscopic studies show that the nanoparticles adopt a face-centered-cubic (FCC) crystalline structure with an average particle size of 2.6 nm. SQUID studies reveal that as-synthesized nanoparticles are superparamagnetic at room temperature and ferromagnetic at 1.85 K with coercivity of 980 Oe. Annealing of the samples at 500 °C causes an increase of particle size and a decrease of coercivity.     

New aspects on pulsed laser deposition of aligned carbon nanotubes

We have grown carbon nanotubes (CNT) by pulsed laser deposition (PLD) at 1000 °C in Ar atmosphere. A Nd/YAG laser was used for irradiation of a graphite target containing Ni and Co rods. High-resolution scanning electron microscopy (HRSEM) and transmission electron microscopy (TEM) images showed that “closed” carbon nanotubes were grown between clusters of metallic particles, so that the individual nanotubes were arranged in parallel to each other forming a shape of “Rope-Bridge”. The nanotubes structure was analyzed by high-resolution transmission electron microscopy (HRTEM) and their type was found to be of MWNT, containing about five SWNT. Total diameter was 5-20 nm and their length was about 1 μm. High homogeneous distribution carbon nanotubes were grown and different structures were observed such as well-aligned carbon nanotubes, bamboo-like and Y-junction carbon nanotubes.     

Synthesis of coprecipitated strontium hexaferrite nanoparticles in the presence of polyvinyl alcohol

Strontium hexaferrite (SrFe₁₂O₁₉) nanoparticles were synthesized by the chemical coprecipitation method and using polyvinyl alcohol (PVA) as a protective agent. The synthesized samples were characterized by differential thermal analysis, X-ray diffraction, scanning and transmission electron microscopy, particle size analyzer, sedimentation test and vibrating sample magnetometer. In the presence of PVA, the single-phase SrFe₁₂O₁₉ nanoparticles were obtained at low temperature of 650 °C. The average particle size of SrFe₁₂O₁₉ precursor was 15 nm, which increased to 61 nm after calcination at 650 °C. The magnetic measurements indicated that PVA decreased coercivity from 4711 to 3216 Oe with particle size reduction. The results showed that PVA as a protective agent could be effective in decreasing the particle size, calcination temperature and coercivity of SrFe₁₂O₁₉ nanoparticles.     

Synthesis,structure, and magnetic properties of iron and nickel nanoparticles encapsulated into carbon

Nanocomposites based on iron and nickel particles encapsulated into carbon (Fe@C and Ni@C), with an average size of the metal core in the range from 5 to 20 nm and a carbon shell thickness of approximately 2 nm, have been prepared by the gas-phase synthesis method in a mixture of argon and butane. It has been found using X-ray diffraction, transmission electron microscopy, and Mössbauer spectroscopy that iron nanocomposites prepared in butane, apart from the carbon shell, contain the following phases: iron carbide (cementite), α-Fe, and γ-Fe. The phase composition of the Fe@C nanocomposite correlates with the magnetization of approximately 100 emu/g at room temperature. The replacement of butane by methane as a carbon source leads to another state of nanoparticles: no carbon coating is formed, and upon subsequent contact with air, the Fe₃O₄ oxide shell is formed on the surface of nanoparticles. Nickel-based nanocomposites prepared in butane, apart from pure nickel in the metal core, contain the supersaturated metastable solid solution Ni(C) and carbon coating. The Ni(C) solid solution can decompose both during the synthesis and upon the subsequent annealing. The completeness and degree of decomposition depend on the synthesis regime and the size of nickel nanoparticles: the smaller is the size of nanoparticles, the higher is the degree of decomposition into pure nickel and carbon. The magnetization of the Ni@C nanocomposites is determined by several contributions, for example, the contribution of the magnetic solid solution Ni(C) and the contribution of the nonmagnetic carbon coating; moreover, some contribution to the magnetization can be caused by the superparamagnetic behavior of nanoparticles.     

Preparation and Faraday rotation of Bi-YIG/PMMA nanocomposite

Bismuth-substituted yttrium iron garnet (Bi-YIG) nanoparticles (NPs) were prepared by coprecipitation and subsequent heating treatment. Thermal gravity-differential thermal analysis was performed to investigate the thermal behavior of the Bi-YIG precursors and to decide the best annealing temperature. Phase formation of garnet NPs was investigated by X-ray powder diffraction. The size of Bi-YIG NPs was investigated by transmission electron microscopy, and the magnetic properties of Bi-YIG NPs were measured using a vibrating sample magnetometer. The results show that the temperature needed for the transformation of Bi-YIG from the amorphous phase to the garnet phase decreases with increasing Bi content, and Bi-YIG NPs with sizes of 28–78 nm are obtained after heating treatment at 650–1000 °C. The saturation magnetization of Bi-YIG NPs increases as the Bi content increases. Moreover, the Faraday rotation of polymethyl methacrylate (PMMA) slices doped with Bi-YIG NPs was investigated. The results indicate that the angle of Faraday rotation increases with increasing Bi content in PMMA composites, and the maximum value of the figure of merit is 1.46°, which is comparable to the value of a sputtered film. The Bi-YIG NPs-doped PMMA slices are new promising materials for magneto-optical devices.     

Phase transition and magnetic properties of Mg-doped hexagonal close-packed Ni nanoparticles

Mg-doped Ni nanoparticles with the hexagonal close-packed (hcp) and face-centered cubic (fcc) structure have been synthesized by sol-gel method sintered at different temperatures in argon atmosphere. The sintering temperature played an important role in the control of the crystalline phase and the particle size. The pure hcp Mg-doped Ni nanoparticles with average particle size of 6.0 nm were obtained at 320 °C. The results indicated that the transition from the hcp to the fcc phase occurred in the temperature range between 320 °C and 450 °C. Moreover, the VSM results showed that the hcp Mg-doped Ni nanoparticles had unique ferromagnetic and superparamagnetic behavior. The unsaturation even at 5000 Oe is one of the superparamagnetic characteristics due to the small particle size. From the ZFC and FC curves, the blocking temperature T_B of the hcp sample (6.0 nm) was estimated to be 10 K. The blocking temperature was related to the size of the magnetic particles and the magnetocrystalline anisotropy constant. By theoretical calculation, the deduced particle size was 6.59 nm for hcp Mg-doped Ni nanoparticles which was in agreement with the results of XRD and TEM.     

Study on effects of substrate temperature on growth and structure of alignment carbon nanotubes in plasma-enhanced hot filament chemical vapor deposition system

Alignment carbon nanotubes (ACNTs) were synthesized on silicon substrate coated with Ni catalyst film and Ta buffer layer by plasma-enhanced hot filament chemical vapor deposition using CH₄, NH₃, and H₂ as the reaction gas, and they were investigated by scanning electron microscopy and transmission electron microscopy. It is found that the diameter of the bamboo-structured ACNTs is increased from 62 to 177 nm when the substrate temperature was changed from 626 to 756 °C. Their growth rate is enhanced by the substrate temperature in a range of 626-683 °C and it is reversely reduced with the substrate temperature after the substrate temperature is over 683 °C. Beginning with wetting phenomenon, the effects of the substrate temperature on the structure and growth rate of the ACNTs are analyzed.     

Optoelectronic characterization of Au/Ni/n-AlGaN photodiodes after annealing at different temperatures

The optoelectronic characteristics of Ni/Au Schottky photodiodes based on Al_0.35Ga_0.65N were investigated. The transmission of the Ni (50 Å)/Au (50 Å) layer was determined by evaporating it on a quartz substrate. As evaporated, the transmission coefficient in the 200–350 nm wavelength range was found to be 43 to 48%. Annealing at temperatures of up to 400 °C did not influence the transmission coefficient. After annealing at 500 °C, the transmission coefficient increased from 50 to 68% over the 200–350 nm range. The reverse bias current was optimised in terms of annealing temperature and was found to be as low as 1.94×10⁻¹³ A after annealing at 400 °C for a 0.6 mm diameter contact. The Schottky barrier heights increased with annealing temperature reaching as high as 1.46 and 1.89 eV for I–V and C–V measurements, respectively. The quantum efficiency was measured to be 20.5% and the responsivity reached its peak of 0.046 A/W at 275 nm. The cut-off wavelength was 292 nm.     

Preparation and structure of carbon encapsulated copper nanoparticles

Carbon-encapsulated copper nanoparticles were synthesized by a modified arc plasma method using methane as carbon source. The particles were characterized in detail by transmission electron microscope, high-resolution transmission electron microscopy, selected-area electron diffraction, X-ray diffraction, thermogravimetric and differential scanning calorimetry. The encapsulated copper nanoparticles were about 30 nm in diameter with 3–5 nm graphitic carbon shells. The outside graphitic carbon layers effectively prevented unwanted oxidation of the copper inside. The effect of the ratio of He/CH₄ on the morphologies and the formation of the carbon shell were investigated.     

Structural and spectroscopic studies of thin film of silver nanoparticles

We report the deposition of thin film of silver (Ag) nanoparticles by wet chemical method. The as-synthesized Ag nanoparticles have been characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray energy dispersive spectroscopy (EDS), field emission transmission electron microscopy (FETEM) and high-resolution TEM (HRTEM), UV-vis spectroscopy and thermogravimetric-differential thermal analysis (TG-DTA) respectively. FESEM image indicates that the silver film prepared on the quartz substrate is smooth and dense. XRD pattern reveals the face-centered cubic (fcc) structure of silver nanoparticles. EDS spectrum indicates that samples are nearly stoichiometric. From TEM analysis, it is found that the size of high purity Ag nanoparticles is ranging from 10 to 20 nm with slight agglomeration. Absorption in UV-vis region by these nanoparticles is characterized by the features reported in the literature, namely, a possible Plasmon peak at ∼403 nm. Optical absorbance spectra analysis reveals that the Ag film has an indirect band structure with bandgap energy 3.88 eV. TGA/DTA studies revealed that a considerable weight loss occurs between 175 and 275 °C; and the reaction is exothermic.