Fabrication of periodic nickel silicide nanodot arrays using nanosphere lithography

The interfacial reactions of the 2D-ordered nickel metal nanodots that were prepared by polystyrene nanosphere lithography (NSL) on Si substrates after different heat treatments have been investigated. Epitaxial NiSi₂ nanodot arrays were found to form at a temperature as low as 350 °C. The results indicated that the growth of epitaxial NiSi₂ is more favorable for the Ni metal dot array samples. The sizes of these epitaxial NiSi₂ nanodots in samples annealed at 350–800 °C are in the range of 84–110 nm. The shape of the epitaxial NiSi₂ nanodot was found to be pyramidal. Furthermore, for the samples annealed at 900 °C, amorphous SiO_x nanowires were found to grow on individual nickel silicide nanoparticles. The diameters of these nanowires are in the range of 15–20 nm. As the size of metal nanodot can be adjusted by tuning the diameter of the polystyrene (PS) spheres, the NSL technique promises to be an effective patterning method without complex lithography.     

Dependence of photovoltaic performance of solvothermally prepared CdS/CdTe solar cells on morphology and thickness of window and absorber layers

In the present work a new strategy for straightforward fabrication of CdS/CdTe solar cells, containing CdS nanowires and nanoparticles as a window layer and CdTe nanoparticles and microparticles as an absorber layer, are reported. CdS and CdTe nanostructures were synthesized by solvothermal method. X-ray diffraction analysis revealed that highly pure and crystallized CdS nanowires and nanoparticles with hexagonal structure and CdTe nanoparticles with cubic structure were obtained. Atomic force microscope and field emission scanning electron microscope images showed that CdS nanowires with length of several μm and average diameter of 35 nm, CdS nanoparticles with average particle size of 32 nm and CdTe nanoparticles with average particle size of 43 nm, were uniformly coated on the substrate by the homemade formulated pastes. Based on ultraviolet–visible absorption spectra, the band gap energies of CdS nanowires, CdS nanoparticles and CdTe nanoparticles were calculated 2.80, 2.65 and 1.64 eV, respectively. It was found that, the photovoltaic performance of the solar cells depends on thickness of CdTe and CdS films, reaching a maximum at a specific value of 6 μm and 225 nm, respectively. For such cell made of CdS nanowires and CdTe nanoparticles the V_OC, J_SC, fill factor and power conversion efficiency were calculated 0.62 V, 6.82 mA/cm², 59.7 and 2.53 %, respectively. Moreover, photovoltaic characteristics of the solar cells were dependent on CdTe and CdS morphologies. CdS/CdTe solar cell made of CdTe and CdS nanoparticles had the highest cell efficiency (i.e., 2.73 %) amongst all fabricated solar cells. The presented strategy would open up new concept for fabrication of low-cost CdS/CdTe solar cells due to employment of a simple chemical route rather than the vapor phase methods.     

Synthesis and characterization of amorphous silicon oxide nanowires embedded with Ni nanoparticles

The growth of silicon oxide nanowires (SiOxNWs) was obtained by thermal process of nickel (Ni) nanoparticles (NPs) deposited on silicon (Si) wafer in mixed gases of nitrogen (N₂) and hydrogen (H₂). TEM analysis showed that SiOxNWs had diameters ranging from 100 to 200 nm with lengths extending up to a few μm and their structure was amorphous. SiOxNWs were grown by the reaction between Ni NPs and Si wafer and Ni NPs acted as catalysts. Ni silicides (NixSi) were also formed inside the wafer by Ni diffusion into Si wafer.     

OWL-Based Nanomasks for Preparing Graphene Ribbons with Sub-10 nm Gaps

We report a simple and highly efficient method for creating graphene nanostructures with gaps that can be controlled on the sub-10 nm length scale by utilizing etch masks comprised of electrochemically synthesized multisegmented metal nanowires. This method involves depositing striped nanowires with Au and Ni segments on a graphene-coated substrate, chemically etching the Ni segments, and using a reactive ion etch to remove the graphene not protected by the remaining Au segments. Graphene nanoribbons with gaps as small as 6 nm are fabricated and characterized with atomic force microscopy, scanning electron microscopy, and Raman spectroscopy. The high level of control afforded by electrochemical synthesis of the nanowires allows us to specify the dimensions of the nanoribbon, as well as the number, location, and size of nanogaps within the nanoribbon. In addition, the generality of this technique is demonstrated by creating silicon nanostructures with nanogaps.     

NH4Cl-assisted low temperature synthesis of anatase TiO2 nanostructures from Ti powder

A simple, low temperature and low cost method, which was based on heating the mixture of Ti and NH₄Cl powders in air at 300 °C, has been developed for the controlled synthesis of anatase TiO₂ nanostructures including irregular nanoparticle aggregates, curved nanowires built up by the oriented attachment of nanoparticles, and nanoplates constructed with nanoparticles. The characterization results from X-ray diffraction and Raman spectra indicated that the as-obtained products were anatase TiO₂. Field emission scanning electron microscope images revealed that the products obtained for 3, 10 and 16 h comprised, in turn, irregular nanoparticle aggregates (8-55 nm), curved nanowires built up by the oriented attachment of nanoparticles (~ 9 nm), and nanoplates constructed with nanoparticles (~ 8 nm).     

Synthesis,characterization and growth mechanism of ZnO nanowires on NiCl<Subscript>2</Subscript>-coated Si substrates

Well-crystallized ZnO nanowires have been successfully synthesized on NiCl₂-coated Si substrates via a carbon thermal reduction deposition process. The pre-deposited Ni nanoparticles by dipping the substrates into NiCl₂ solution can promote the formation of ZnO nuclei. The as-synthesized nanowires were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectrum. The results demonstrate that the as-fabricated nanowires with about 60 nm in diameter and several tens of micrometers in length are preferentially arranged along [0001] direction with (0002) as the dominate surface. Room temperature PL spectrum illustrates that the ZnO nanowires exist a UV emission peak and a green emission peak, and the peak centers locate at 387 and 510 nm. Finally, the growth mechanism of the nanowires is briefly discussed.     

Synthesis and structural features of Ni–Al nanoparticles by hydrogen plasma–metal reaction

Eight kinds of Ni–Al nanoparticles have been prepared by hydrogen plasma–metal reaction. The morphology, crystal structure and chemical composition of the nanoparticles obtained in this study were investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD) and induction-coupled plasma (ICP) spectroscopy. The particle size was determined by TEM and BET gas adsorption. It was found that all the nanoparticles have spherical shapes, with average particle size in the range of 14∼62 nm. The crystal structures of Ni–Al nanoparticles vary with the composition of master alloys. Pure Al₃Ni₂ (D5₁₃), NiAl (B2) and Ni₃Al (L1₂) structures were successfully produced with 55.0, 58.3 and 72.6 at.% Ni in bulk, respectively. The analysis result about the phase equilibrium based on the crystal structures of nanoparticles is not consistent with those based on the equilibrium phase diagram.     

Mass-synthesized anatase titania nanocrystals with tunable size and shape via sol-gel in organic solvents with adsorbing ligands

High-quality anatase titania (TiO₂) nanoparticles, nanowires, and nanorods have been mass-synthesized by the modified sol-gel method in the saturated fatty alcohol, acid, and amine systems with adsorbing ligands, respectively. These obtained quasi-spherical TiO₂ nanoparticles showed the mean size of 16.5 nm with a narrow size-distribution. These resulting TiO₂ nanowires had the uniform diameter of 3.8 nm with the length range of 80-180 nm, and TiO₂ nanorods had the uniform diameter of 7.5 nm with the length range of 40-70 nm, respectively. We demonstrated that the shapes, sizes and morphology of these anatase TiO₂ nanocrystals could be controlled systematically by adjusting certain reaction parameters, such as the kind of organic solvents, the alkyl length of organic solvents, and the reaction time. It has been found that the shape of the products was primarily determined by the kind of organic solvents. However, their sizes, size-distributions, and morphology could be controlled by adjusting the alkyl length of organic solvents and the reaction time. Based on the analysis of all experiment results, we have investigated the growth mechanism of these TiO₂ nanocrystals with the different shape. Meanwhile, this synthetic method can be extended further for the preparation of other oxides nanocrystals.     

Formation and photoluminescence properties of amorphous silicon oxide nanowires

The silicon oxide nanowires (SiOxNWs) were grown by the thermal process of nickel (Ni) nanoparticles (NPs) deposited on silicon (Si) wafers in mixed gasses of nitrogen (N₂) and hydrogen (H₂) at temperatures of 900, 1000, and 1100 °C. Each NW was about 20–100 nm in diameter embedding with Ni NPs inside, and its structure was amorphous. The ratio of Si and oxygen (O) was 1:2.18. Blue emission spectrum was observed at the wavelength of 450 nm and the peak intensity increased with the increasing process temperature.     

Fabrication and magnetic property of α-Fe2O3 nanoparticles/TiO2 nanowires hybrid structure

α-Fe₂O₃ nanoparticles/TiO₂ nanowires hybrid structure is fabricated by two-step hydrothermal treatment. TiO₂ nanowires are prepared by heating of titanate nanowires, which are obtained by hydrothermal treatment of TiO₂ powder and further repeated HCl treatment. α-Fe₂O₃ nanoparticles are deposited on the surface of TiO₂ nanowires by hydrothermal treatment in Fe(NO₃)₃ solution. The HRTEM images confirm the junctions between α-Fe₂O₃ nanoparticles and TiO₂ nanowires. The formation of hybrid structures has significant influence on the magnetic properties of α-Fe₂O₃. The Morin transition temperature of α-Fe₂O₃ nanoparticles/TiO₂ nanowires hybrid structure is 190 K, which is determined by the sharp peak in the differential ZFC curve. Whereas there is no observable Morin transition for the corresponding isolated α-Fe₂O₃ nanoparticles with similar average particles size of ca. 20 nm.     

Synthesis of Ni nanoparticles by hydrolysis of Mg<Subscript>2</Subscript>Ni

A simple, new method utilizing the hydrolysis of Mg₂Ni has been successfully developed for the synthesis of Ni nanoparticles. The possible growth mechanisms of Ni nanoparticles are discussed. Compared with conventional preparation methods for Ni nanoparticles, this method has the potential to inexpensively produce Ni nanoparticles on a large scale. In addition, the principle of the method could be applied to the synthesis of other transition metal nanoparticles such as Co, Cu, Ag, Au, Pt, and Pd.     

Microwave-assisted synthesis of Ag nanophases and their optical properties

By microwave-assisted method, silver nanophases were produced with size and morphology control. Silver nanoparticles of controlled size from 10 to 80 nm were obtained. Particle size was controlled by varying reaction conditions, including metal source concentration and molecular weight of protecting agent (PVP). Silver nanowires were produced by releasing the metal source gradually from AgFn(1-n)(n = 1-6) with PVP as the morphology directing agent. UV-Vis spectra showed that Ag nanoparticles have absorption bands around 400 nm and the UV-Vis absorptions slightly blue shifted with decreasing particle size.     

Synthesis of CoNi nanowires by heterogeneous nucleation in polyol

CoNi nanorwires/nanorods, depending on the loading of Ni, were prepared by heterogeneous nucleation in polyol. CoNi nanowires with the length up to 1000 nm and the diameter of about 10 nm were obtained when the loading of Ni was no more than 30%, whereas nanorods with the length of about 500 nm and the diameter of 20 nm were produced with further increasing the loading of Ni. It was revealed that the nanowires might be a core-shell structure where the core was formed by the fast reduction of Co²⁺ and the shell was constructed by the combined reduction of Co²⁺ and Ni²⁺. When used for hydrogenolysis of glycerol, the CoNi nanowires showed significantly enhanced glycerol conversion and propanediol selectivity as compared to the pure Co nanowires.     

Probing cellular traction forces with magnetic nanowires and microfabricated force sensor arrays

In this paper, the use of magnetic nanowires for the study of cellular response to force is demonstrated. High-aspect ratio Ni rods with diameter 300?nm and lengths up to 20?μm were bound to or internalized by pulmonary artery smooth muscle cells (SMCs) cultured on arrays of flexible micropost force sensors. Forces and torques were applied to the cells by driving the nanowires with AC magnetic fields in the frequency range 0.1-10?Hz, and the changes in cellular contractile forces were recorded with the microposts. These local stimulations yield global force reinforcement of the cells' traction forces, but this contractile reinforcement can be effectively suppressed upon addition of a calcium channel blocker, ruthenium red, suggesting the role of calcium channels in the mechanical response. The responsiveness of the SMCs to actuation depends on the frequency of the applied stimulation. These results show that the combination of magnetic nanoparticles and micropatterned, flexible substrates can provide new approaches to the study of cellular mechanotransduction.     

Preparation and properties of NiFe2O4 nanowires

Polycrystalline NiFe₂O₄ nanowires have been synthesized by PEG assisted co-precipitation method. The formation mechanism of the nanowires proposed is by means of the orientational aggregation of individual nanoparticles. X-ray diffraction, high resolution scanning electron microscopy, transmission electron microscopy, microRaman and vibrating sample magnetometry studies were carried out. The results show that NiFe₂O₄ nanowires were in polycrystalline form with diameter of 58 nm. The synthesized nanowires show room temperature ferromagnetic property with high coercivity. This method is expected to be useful for large scale synthesis of NiFe₂O₄ nanowires for the application of magnetic recording.     

水热合成法制备La0.7Sr0.3FeO3纳米线的合成机理研究

在表面活性剂CTAB水溶液中添加硝酸盐溶液,并滴加氨水,采用水热合成法在180℃的温度下反应9h,制备了La0.7Sr0.3FeO3前驱体,在700℃下煅烧6h后得到La0.7Sr0.3FeO3纳米颗粒组装的纳米线。利用SEM、TEM和XRD对其形貌、尺寸和结构等进行了表征。制备的La0.7Sr0.3FeO3纳米线是由约为20nm的纳米颗粒组装而成的,纳米线的最大长径比达100以上。通过改变水热合成时间和前驱体的煅烧温度等实验条件,对La0.7Sr0.3FeO3纳米线的物相转化和生长机理进行了分析。表面活性剂CTAB作为生长控制剂和颗粒凝聚载体,能够控制材料沿着轴向生长,形成纳米线。     

Synthesis of nanocrystalline materials through reverse micelles: A versatile methodology for synthesis of complex metal oxides

We have been successful in obtaining monophasic nanosized oxides with varying chemical compositions using the reverse micellar method. Here we describe our methodology to obtain important metal oxides like ceria, zirconia and zinc oxide. The oxalate of cerium, zirconium and zinc were synthesized using the reverse micellar route. While nanorods of zinc oxalate with dimension, 120 nm in diameter and 600 nm in length, could be obtained, whereas spherical particles of size, 4–6 nm, were obtained for cerium oxalate. These precursors were heated to form their respective oxides. Mixture of nanorods and nanoparticles of cerium oxide was obtained. ZrO₂ nanoparticles of 3–4 nm size were obtained by the thermal decomposition of zirconium oxalate precursor. ZnO nanoparticles (55 nm) were obtained by the decomposition of zinc oxalate nanorods. Photoluminescence (PL) studies at 20 K shows the presence of three peaks corresponding to free excitonic emission, free to bound and donor-acceptor transitions. We also synthesized nanoparticles corresponding to Ba_1−x Pb _x ZrO₃ using the reverse micellar route. The dielectric constant and loss were stable with frequency and temperature for the solid solution.     

Ultimate bending strength of Si nanowires

Test platforms for the ideal strength of materials are provided by almost defect-free nanostructures (nanowires, nanotubes, nanoparticles, for example). In this work, the ultimate bending strengths of Si nanowires with radii in the 20-60 nm range were investigated by using a new bending protocol. Nanowires simply held by adhesion on flat substrates were bent through sequential atomic force microscopy manipulations. The bending states prior to failure were analyzed in great detail to measure the bending dynamics and the ultimate fracture strength of the investigated nanowires. An increase in the fracture strengths from 12 to 18 GPa was observed as the radius of nanowires was decreased from 60 to 20 nm. The large values of the fracture strength of these nanowires, although comparable with the ideal strength of Si, are explained in terms of the surface morphology of the nanowires.     

Synthesis and characterization of C3N4 nanowires and pseudocubic C3N4 polycrystalline nanoparticles

C₃N₄ nanowires and pseudocubic C₃N₄ polycrystalline nanoparticles have been synthesized by the reaction between C₃N₃Cl₃ and NaN₃ with Zn powder as catalyst. The process was carried out using a constant-pressure benzene thermal method at 40 MPa and 220 °C. The prepared nanowires have a diameter range of 3-6 nm and length range of 100-200 nm, while the diameters of the nanoparticles range from 10 nm to 40 nm. The as-prepared samples were characterized by X-ray powder diffraction (XRD), Fourier transform spectroscopy (FTIR), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS).     

A comprehensive study of structural and magnetic properties of sputter deposited nickel–silica thin films

The present work reports the formation of Ni nanoparticles inside the SiO₂ matrix and deals with the influence of Ni concentration on structural and magnetic properties of Ni–SiO₂ nanocomposite thin films. The films with varying Ni concentration (20–55 at% measured by Rutherford back scattering spectroscopy) were deposited using DC/RF magnetron co-sputtering. TEM and XRD analysis reveal the formation of FCC Ni nanoparticles in all the samples. The particle size varies from 3 to 10 nm as a function of Ni concentration. The surface roughness of the films is also found to increase with increase in nickel concentration. Magnetic measurements show that the Ni nanoparticles behave as superparamagnets when their size is ≤6 nm, in spite of their large volume fractions. The results show that the magnetic properties of the nanoparticles can be controlled by their size and Ni concentration in the samples.