Jibao He

Super Crystal Structures of Octahedral c-In2O3 Nanocrystals

The three-dimensional self-assembly of a nanocrystal superlattice, i.e., a super crystal, has attracted increasing attention. The small building blocks for assemblies are usually spherical nanocrystals. Recent progress indicates that it is possible to achieve a super crystal using cubic nanocrystals. We further analyze and describe two-dimensional and some three-dimensional assemblies of uniform cubic-phase In2O3 nanocrystals with an octahedral shape. In this article, we demonstrate our amazing observations on these kinds of super crystals (or superlattices) as a model system, report their scale in at least tens of microns, and show other interesting features such as steps, terraces, kinks, and vacancies which are similar to those from a single crystal. Based on electron microscopy observations, three types of well-defined octahedral nanocrystal packed structures in such super crystal systems are also identified. The investigation of octahedral super crystal systems provides an alternate direction in research that may extend the interest of superlattice study to a broad spectrum by enriching and varying the shape of elemental building blocks. This may potentially result in new concepts and more challenging applications such as soft X-ray photonics.

Simple cubic super crystals containing PbTe nanocubes and their core-shell building blocks.

We report a preparation of high-quality cubic PbTe nanocrystals and their assembly into both square-array, two-dimensional patterns and three-dimensional simple cubic super crystals. The influence of oleylamine in the nanocrystal synthesis and core-shell formation through an anion-exchange mechanism was also studied. The simple cubic super crystals together with two-dimensional assembly patterns containing PbTe nanocubes and their core-shell building blocks were examined using TEM, SEM, AFM, XRD, SAXS, and FTIR. Such super crystals consisting of cubic structural building blocks may allow engineering of more complex materials from which novel properties may emerge.

Nonaqueous Synthesis and Photoluminescence of ITO Nanoparticles

SnO(2) has successfully been doped into octahedral In(2)O(3) nanoparticles using a high-temperature nonaqueous reaction. The resultant ITO nanoparticles exhibit a particle/crystal decrease in size, sphericity in morphology, and enhancement in photoluminescence.

Room temperature tunneling magnetoresistance of electron beam deposited (Co50Fe50)x(Al2O3)1−x cermet granular films

A series of (Co50Fe50)x-(Al2O3)1−x cermet granular thin films deposited on glass substrates by dual electron beam evaporation was studied for their structural, magnetotransport, and magnetic properties. Upon varying the magnetic volume fraction, x, from 0.07 to 0.52 the percolation threshold (xc) was determined from resistivity measurements to be ∼0.17. This value agrees well with the theoretical prediction for a three-dimensional system of spherical particles. Values of the isotropic tunneling magnetoresistance (TMR) as high as 10% at room temperature were found for films with x<0.16. The relationship between magnetotransport (maximum TMR) and the granular film topology (the percolation threshold) is discussed.

Synthesis and magnetic properties of CoPt–poly(methylmethacrylate) nanostructured composite material

We have prepared nanometer-sized CoPt particles dispersed in a poly(methyl methacrylate) (PMMA) matrix, as a novel nanostructured magnetic plastic, through a soft chemical processing route. In this work, CoPt nanoparticles were successfully synthesized from a solution phase reduction system in the presence of capping ligands and stabilizing agents at high temperature. The CoPt nanoparticles were annealed at 400u200a°C for 3 h, and were subsequently re-dispersed in methylmethacrylate (monomer). The polymerization was induced by a UV source and the hardness of final product was adjusted by varying the amount of monomeric cross-link agent. Annealed bare CoPt nanoparticles as a “core” material and CoPt–PMMA composite material were characterized by using energy dispersive spectroscopy, transmission electron microscopy, and x-ray diffraction, indicating that we are able to prepare CoPt nanoparticles with <10 nm in diameter (after annealing) by employing this high temperature colloidal processing method. Magnetic in...

Self-assembly of FePt nanoparticles into nanorings

The application of nanoparticles as quantum dots in nanoelectronics demands their arrangement in ordered arrays. Shape controlled self-assembly is a challenge due to the difficulties of obtaining proper self-assembling parameters, such as solvent concentration, organic ligands, and nanoparticle size. In this article, hard magnetic FePt nanoparticles were synthesized using a combination approach of reduction and thermal decomposition. The nanoparticles are about 4.5 nm and appeared as truncated octahedral enclosed by the {100} and {111} crystal facets of fcc structure. The nanoparticles are of hexagonal close packing and orient randomly in the self-assembly nanoarrays. By diluting the solution for large-area self-assembly, monolayer, submonolayer, and multilayer nanorings of FePt nanoparticles were formed. The nanoring formation is determined by hydrodynamics, surface effects, and interaction between the FePt nanoparticles and substrates.

Magnetic Properties of Fe-Doped Rutile

Ball-milling method was applied to dissolve Fe into titanium dioxide (TiO2). X-ray diffraction indicated the starting anatase changed to a rutile-type structure with oxygen deficiency after ball milling. Transmission electron microscopy and X-ray absorption experiments were conducted to examine the possible existence of magnetic impurities in the ball-milled powders after they were leached in HCl solutions. Temperature dependence of the resistivity shows semiconducting behavior and the magnetic hysteresis loops at 5 and 300 K exhibit ferromagnetic characteristics. Fe-doped TiO2 films were also prepared by pulsed laser deposition. The magnetic properties of the films are discussed.

Synthesis of one-dimensional magnetic Co nanoparticles in a novel solution system.

Magnetic Co nanoparticles with different morphologies were synthesized in a novel solution system using a UV irradiation technique. By adjusting the compositions in the solution, long nanowires with different aspect ratios as well as spherical nanoparticles with controllable particle size could be obtained.

Convenient arc-electrodeposition technique to synthesize CdS nanotubes at room temperature

Over the past few years, shape control of nanomaterials has raised significant concerns in the fabrication of onedimensional (1D) nanomaterials such as nanowires, nanotubes and interesting nanobelts [1]. These 1D nanostructures are ideal systems for investigation of the relationship between the properties (e.g. electrical transport, optical and magnetic behaviors) and dimensionality [2]. For example, considerable progress has been made in the synthesis of 1D semiconductor nanostructured materials due to their unique properties [3]. Especially, much more efforts have been focused on the fabrication of nanotubes. A particularly significant breakthrough in the preparation of MX2 (M: Mo or W; X: S or Se) nanotubes was made by Tenne and co-workers [4]. Later, various approaches to other nanotubes such as BN [5], vanadium oxide [6], InS [7] and metal Bi [8] have also been reported. Recently we explored a novel convenient arcelectrodeposition technique to prepare shapecontrolled metal nanorods [9], nanorods or nanotubes of metal oxides and hydroxides [10]. The so-called arcelectrodeposition technique is based on the momentary contact of two metallic electrodes on an electrolyte aqueous solution, forming instantaneous circulation between two electrodes and the arc discharge sparks at the point ends of the electrodes. The arc discharge of the electrodes releases great exothermic heat, leading to dissolution of the metallic electrodes in a form of metallic clusters into the aqueous solution. The produced metallic clusters either aggregate into metal nanowires or are oxidized into the corresponding oxides and further grow into nanorods or nanotubes. Herein we extend the arc-electrodepostion technique to prepare CdS nanotubes at room temperature. The basic experimental setup and procedure for the preparation of the CdS nanotube by the arcelectrodepostion technique at room temperature are similar to those in our previous reports [9, 10]. In the present work, the mixture of Na2S and KCl aqueous solution was used as electrolyte solution. Two highpurity metallic Cd filaments of 1 mm in diameter were employed as electrodes with the applied alternating current (AC) voltage of 100 V. In the arc-electrodeposition process, the colorless transparent electrolyte aqueous solution turned into yellow gradually, indicating the formation of CdS nanoparticles. The produced solution was allowed to stand for 24 h. The final product was collected by centrifugation, followed by washing using distilled water and ethanol several times. The phase identification of as-prepared product was conducted at room temperature using an X-ray diffractometer (Cu Kα, Philips X’pert system). A transmission electron microscope (Jeol 2010) was employed to observe particle morphology. Fig. 1 shows the XRD trace of as-prepared CdS nanoparticles using this technique, in which two Cd metallic wires of 1 mm in diameter were employed as electrodes and an aqueous solution containing 0.1 M Na2S and 0.1 M KCl as electrolyte medium. In this XRD pattern, all the detectable peaks are indexed as those from CdS according to the standard card (JCPDSICDD 10-0454). The morphology of the as-prepared CdS was examined by TEM observation. The typical image is shown in Fig. 2a. It can be seen that the CdS nanoparticle obtained using this arc-electrodeposition technique under the conditions mentioned above exhibits a tubular structure in nanoscale. The length of the nanotubes ranges from 50 nm to 80 nm, and the outer diameter is around 10–15 nm with the inner that of 3–8 nm. A magnified TEM image, as shown in Fig. 2b, further reveals this structure. The formation mechanism of the CdS nanotubes produced by the present arc-electrodeposition technique was proposed as follows:

Morphology control of the produced Ag nanoparticles by soft-template technique.

The morphology of the produced Ag nanoparticle is controlled successfully by UV irradiating the reaction solution of AgAc/ethyl alcohol/1-octadeconal/1-dodecanethiol. With use of a novel solution such as soft template, Ag nanorods with different sizes and different ratios of length to diameter can be obtained by adjusting the concentrations of the solution compositions.