Synthesis, morphologies and Raman-scattering spectra of crystalline stannic oxide nanowires

SnO₂ nanowires were synthesized using a direct gas reaction route and were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), selected-area electron diffraction (SAED), high-resolution transmission electron microscopy (HRTEM) and Raman-scattering spectroscopy. XRD, SEM, SAED and HRTEM indicated that the products were tetragonal SnO₂ nanowires with diameters of 10–50 nm. The nanowires were single crystal and solid inside. Dendritic nanowires were observed for the first time. Three vibrational modes were observed in the Raman spectra of the samples. Received: 7 January 2002 / Accepted: 11 April 2002 / Published online: 19 July 2002     

金刚石镶嵌非晶碳膜表面形貌对场致电子发射的影响

用微波等离子体化学气相沉积设备，在经过不同研磨预处理的金属钼衬底上沉积出了表面形貌有较大差异的金刚石镶嵌非晶碳膜，分别用扫描电子显微镜（ＳＥＭ）、金相显微镜和Ｘ射线衍射谱（ＸＲＤ）以及Ｒａｍａｎ光谱对样品进行了分析测试．研究了各样品的场致电子发射特性，结果发现薄膜表面由大量镶嵌有金刚石小晶粒的非晶碳球组成，在我们的实验范围内，薄膜表面非晶碳球尺寸越小，场致电子发射效果越好     

Synthesis of ZnS nanorods by annealing precursor ZnS nanoparticles in NaCl flux

ZnS nanorods were fabricated by annealing precursor ZnS nanoparticles, which were prepared by one-step, solid-state reaction of ZnCl₂ and Na₂S through grinding by hand at ambient temperature, in NaCl flux. The as-prepared ZnS nanorods have diameters of 40-80 nm, and lengths up to several micrometers. The structural features and chemical composition of the nanorods were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), high-resolution transmission electron microscopy (HRTEM), and Raman spectra.     

Nanostructure of thin silicon films by combining HRTEM, XRD and Raman spectroscopy measurements and the implication to the optical properties

A series of thin silicon films with different degrees of crystallinity were prepared by decomposition of silane gas highly diluted with hydrogen, in radiofrequency glow discharge. The crystallite size, shape, and the portion of crystalline phase were investigated by high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), Raman spectroscopy (RS), and X-ray powder diffraction (XRD). The absorption coefficient (α) was calculated from the measurement of UV-vis-transmittance. By using RS, the volume fractions of the crystalline phase were estimated from the ratio of the integrated intensities of transversal optical (TO)-related crystalline and amorphous bands. These results were in excellent agreement with the mean crystallite sizes measured in HRTEM images and crystallite sizes refined from XRD measurements. The red shift of absorption, appearing as a result of the increase of the crystal fraction, depends on the size and distribution of nanocrystals.     

Structural, optical and Raman studies of template-free solvothermally synthesized ZnSe/ZnSe:Ce nanoparticles

The present work reports a general, single step and easy solvothermal method to synthesize well crystallized and pure phase Ce³⁺ doped ZnSe nanocrystals for the first time in a unified system. The products were well characterized by powder X-ray diffraction (XRD), UV-vis spectroscopy (UV-vis), photoluminescence spectroscopy (PL), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), energy dispersive X-ray diffraction (EDAX) and Raman spectroscopy. The products were found to show significant finite size effect as characterized by broadened XRD peaks, blue-shifts of the interband optical absorption edge and the asymmetric broadening of Raman spectra. The emission intensity of Ce³⁺ ion doped ZnSe was found to be considerably increased with respect to the pure one. The observed lineshape of LO modes indicates broadening that is due to the nanosized effect. The structure and properties were correlated and detailed growth mechanism is also discussed.     

Fabrication of bamboo-shaped GaN nanorods

Bamboo-shaped GaN nanorods were formed through a simple sublimation method. They were characterized by means of X-ray powder diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and selected-area electron diffraction (SAED). The TEM image showed that the nanorods were bamboo-like. XRD, HRTEM and SAED patterns indicated that the nanorods were single-crystal wurtzite GaN. Received: 8 January 2001 / Accepted: 28 April 2001 / Published online: 20 December 2001     

Nanoporous AlN particles production from a solid-state metathesis reaction

This paper reports that nanoporous AlN particles are synthesized from solid-state metathesis reactions using AlCl₃ and Mg₃N₂ as reactants. The samples are characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction, high-resolution transmission electron microscopy (HRTEM), ultraviolet--visible (UV--vis) absorption spectroscopy and Raman spectroscopy. The results show that samples with walls 10 nm in thickness and pores between 10 nm and 100 nm in diameter were produced successfully from these reactions, and their band gap and vibration modes agree with those of AlN bulk crystal.     

Synthesis and characterization of GaP nanochains with a twin-modulated quasi-periodic structure

GaP nanochains have been synthesized by hydrogen-assisted thermal evaporation, and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL), and Raman spectroscopy. GaP nanochains possess a (111) twin crystal plane-modulated quasi-periodic structure, that gives a strong green photoluminescence at 618 nm. While the Raman spectrum of the nanochains is similar to that of the GaP crystal, the intensity of the longitudinal optical (LO) peak is stronger than that of the transverse optical (TO) peak, which is supposedly related to the nanochain microstructures.     

Microstructure and microhardness analysis of the hexagonal oxides formed on the surface of the AISI 304 stainless steel after Nd:YAG pulsed laser surface melting

The laser surface melting (LSM) technique was adopted to modify the surface layer microstructure of the AISI 304 stainless steel in this paper. The results showed that the hexagonal morphologies have been successfully fabricated on the surface after LSM. These hexagons had side lengths of about 0.5-1 μm and were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), field emission scanning electron microscope (FESEM) and high resolution transmission electron microscope (HRTEM). It was proved by the XRD that the stainless steel surface mainly consisted of γ-Fe, Cr₂O₃, Fe₂O₃ and some manganese oxides. The FESEM micrographs showed that the hexagonal oxides were regular hexagons in geometry. The HRTEM micrographs also indicated the presence of the hexagons on the surface of the stainless steel. The spacing values were calculated from the HRTEM micrograph and the SAED pattern, and the hexagonal oxide phases determined by these spacing values were consistent with those verified by the XRD. After LSM, the microhardness of the stainless steel was significantly improved.     

The effect of Fe and Ni catalysts on the growth of multiwalled carbon nanotubes using chemical vapor deposition

The effect of Fe and Ni catalysts on the synthesis of carbon nanotubes (CNTs) using atmospheric pressure chemical vapor deposition (APCVD) was investigated. Field emission scanning electron microscopy (FESEM) analysis suggests that the samples grow through a tip growth mechanism. High-resolution transmission electron microscopy (HRTEM) measurements show multiwalled carbon nanotubes (MWCNTs) with bamboo structure for Ni catalyst while iron filled straight tubes were obtained with the Fe catalyst. The X-ray diffraction (XRD) pattern indicates that nanotubes are graphitic in nature and there is no trace of carbide phases in both the cases. Low frequency Raman analysis of the bamboo-like and filled CNTs confirms the presence of radial breathing modes (RBM). The degree of graphitization of CNTs synthesized from Fe catalyst is higher than that from Ni catalyst as demonstrated by the high frequency Raman analysis. Simple models for the growth of bamboo-like and tubular catalyst filled nanotubes are proposed.     

Synthesis of aligned gallium nitride nanowire quasi-arrays

Self-aligned GaN nanowire quasi-arrays were synthesized on MgO crystal through a simple gas reaction method. They were characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray (EDX) spectroscopy and high-resolution transmission electron microscopy (HRTEM). FE-SEMimages showed that the product consisted of quasi-arrays of nanowires. XRD, EDX and HRTEM indicated that the nanowires were wurtzite GaN single crystals. Received: 19 June 2000 / Accepted: 21 June 2000 / Published online: 9 August 2000     

Effect of Pt and Fe catalysts in the transformation of carbon black into carbon nanotubes

In this research carbon nanotubes and carbon nano onion-like structures were synthesized from carbon black using metal catalysts at 400 °C and 700 °C. Platinum and iron-group metals were used as catalysts for the transformation of CB into graphitized nanocarbon and the effect of both metals was compared. The synthesized products were characterized using X-ray diffraction (XRD), transmission electron microscope (TEM), high resolution transmission electron microscope (HRTEM) and Raman spectroscopy. The characterization shows that this process is very efficient in the synthesis of high quality graphitized products from amorphous carbon black, even though the process temperature was relatively low in comparison with previous studies. Distinguished graphitic walls of the newly formed carbon nanostructures were clearly visible in the HRTEM images. Possible growth difference related to the type of catalyst used is briefly explained with the basis of electron vacancies in d-orbitals of metals.     

Preparation and characterization of Ag nanoparticle-embedded polymer electrospun nanofibers

Poly (vinyl alcohol) (PVA) and poly (vinyl pyrrolidone) (PVP) nanofibers embedding Ag nanoparticles (5–18 nm) have been prepared successfully by electrospinning at room temperature. Scanning electron microscope (SEM), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Fourier transform IR spectra (FTIR), and Raman scattering were used to characterize the structure and properties of Ag nanoparticle-embedded PVA and PVP nanofibers before and after heat treatment at different temperature. The antibacterial activity of Ag nanoparticle-embedded PVP nanofibers after heat treatment was also tested, which indicated that the biological activity of yeast cells was effectively inhibited by these Ag nanoparticle-embedded PVP nanofibers.     

Growth and field emission properties of globe-like diamond microcrystalline-aggregate

The globe-like diamond microcrystalline-aggregates were fabricated by microwave plasma chemical vapor deposition (MPCVD) method. The ceramic with a Ti mental layer was used as substrate. The fabricated diamond was evaluated by Raman scattering spectroscopy, X-ray diffraction spectrum (XRD), and scanning electron microscope (SEM). The field emission properties were tested by using a diode structure in a vacuum. A phosphor-coated indium tin oxide (ITO) anode was used for observing and characterizing the field emission. It was found that the globe-like diamond microcrystalline-aggregates exhibited good electron emission properties. The turn-on field was only 0.55 V/μm, and emission current density as high as 11 mA/cm² was obtained under an applied field of 2.9 V/μm for the first operation. The growth mechanism and field emission properties of the globe-like diamond microcrystalline-aggregates are discussed relating to microstructure and electrical conductivity.     

Decorating graphene sheets with Pt nanoparticles using sodium citrate as reductant

In this paper, we proposed a novel and green approach for the synthesis of graphene nanosheets (GNS) and Pt nanoparticles-graphene nanosheets (Pt/GNS) hybrid materials, employing graphene oxide (GO) as precursor and sodium citrate as environmentally friendly reducing and stabilizing agent. The microstructures of GO and Pt/GNS were characterized by high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), Raman spectroscopy, atomic force microscopy (AFM), X-ray diffraction (XRD) and electrochemical measurements. The results confirmed that the uniform size distribution of Pt nanoparticles on the surface of GNS without agglomerates could be easily obtained via using sodium citrate as reductant, moreover the Pt/GNS hybrids exhibited high electrochemical activity.     

磁头抛光液用金刚石超微粉研究

利用原子吸收光谱（AAS）、电感耦合等离子体质谱（ICP-MS）、粉晶X射线衍射（XRD）、激光拉曼光谱（RAMAN）、透射电子显微镜（TEM）等手段对磁头抛光液用金刚石超微粉进行了研究。AAS和ICP-MS测试结果显示,静压触媒法合成的金刚石超微粉中主要含有硅的氧化物和铁、镍、铝等一些金属杂质;XRD图谱中除了金刚石尖锐的特征峰以外,在2θ=35.6°, 39.4°, 59.7°处还观察到SiO₂的特征衍射峰,表明金刚石超微粉结晶程度高、硬度大,但其中含有一定量的硅氧化物物相;在RAMAN图谱中除了金刚石的特征谱外在1 592 cm-1处可观察到宽化了的石墨的特征谱;从TEM照片可以观察到微粉粒度分布在0.1～0.5 μm之间,但是颗粒锋利棱角的存在有利于提高抛光效率。金刚石超微粉的高硬度、强的耐磨性、高的抛光效率使其适于作为磁头抛光液磨料使用。但是,杂质的存在影响抛光效率、缩短抛光液寿命;宽的粒度分布降低了抛光的精度。因此,使用前必须对金刚石超微粉进行提纯、分级处理;使得金刚石超微粉的纯度达到99.9％以上、有害杂质SiO₂的含量不超过0.01%,并且使超微粉的平均粒径为100 nm且大于200 nm的颗粒在总的颗粒中小于2%。     

Efficient field emission from coiled carbon nano/microfiber on copper substrate by dc-PECVD

Crystalline coiled carbon nano/micro fibers in thin film form have been synthesized via direct current plasma enhanced chemical vapor deposition (PECVD) on copper substrates with acetylene as a carbon precursor at 10 mbar pressure and 750 °C substrate temperature. The as-prepared samples were characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). XRD pattern as well as selected area electron diffraction (SAED) pattern showed that the samples were crystalline in nature. SEM and HRTEM studies showed that as synthesized coiled carbon fibers are having average diameter ∼100 nm and are several micrometers in length. The as-prepared samples showed moderately good electron field emission properties with a turn-on field as low as 1.96 V/μm for an inter-electrode distance 220 μm. The variation of field emission properties with inter-electrode distance has been studied in detail. The field emission properties of the coiled carbon fibrous thin films are compared with that of crystalline multiwalled carbon nanotubes and other carbon nanostructures.     

GROWTH MODEL OF TEXTURED DIAMOND (111) FILM IN CH4/O2/H2 ATMOSPHERE

Partially oriented and highly textured diamond films on Si( 111 ) substrates were achieved by hot-filament chemical vapor deposition(HFCVD). High nucleation density greater than 5×10⁸cm^-2 was realiged in 3 min by near-surface glow discharge. The os-grown films were characterized by scanning electron microscopy(SEM), X-ray diffraction(XRD) and Raman spectroscopy. It was found that by adding a small amount of oxygen to the mixture of CH₄/H₂, the appearance of facet(111) was well controlled, and the secondary nucleation on the facet(111) was suppressed greatly. Growth feature of homoepitaxy on diamond (111) surface was demonstrated to be in Stranski-Krastanov model by SEM.     

Growth mechanism and photoluminescence of the SnO2 nanotwists on thin film and the SnO2 short nanowires on nanorods

SnO2 nanotwists on thin film and SnO2 short nanowires on nanorods have been grown on single silicon substrates by using Au-Ag alloying catalyst assisted carbothermal evaporation of SnO2 and active carbon powders.The morphology and the structure of the prepared nanostructures are determined on the basis of field-emission scanning electron microscopy(FESEM),transmission electron microscopy(TEM),selected area electronic diffraction(SAED),high-resolution transmission electron microscopy(HRTEM),x-ray diffraction(XRD),Raman and photoluminescence(PL) spectra analysis.The new peaks at 356,450,and 489 nm in the measured PL spectra of two kinds of SnO2 nanostructures are observed,implying that more luminescence centres exist in these SnO2 nanostructures due to nanocrystals and defects.The growth mechanism of these nanostructures belongs to the vapour-liquid-solid(VLS) mechanism.     

Porous ZnO nanobelts: synthesis,mechanism, and morphological evolutions

Porous ZnO nanobelts with rough surface and poly-crystalline nature have been developed from a facile wet chemical method. The as-prepared products were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), cold field emission scanning electron microscopy (CFE-SEM), and energy dispersive analysis of X-rays (EDAX). The ZnO nanobelts were synthesized with usually 5 to 6 nm in thickness, 10 to 40 nm in width, and about several micrometers in length. A PVP promoted self-assembly mechanism is believed to be responsible for the morphology shaping process of the ZnO nanostructures. This first wet chemical synthesis of such hierarchical structures without any hard templates implies a simple and inexpensive way to prepare transition metal superstructures on a large scale for modern chemical synthesis. Optical characterization by a confocal laser Raman were also carried out to explore their optical properties; the PL and Raman results showed both good agreement with the characters of our samples and potential for future applications such as sensors and other modern technologies.