Cuncheng Li

A Facile Polyol Route to Uniform Gold Octahedra with Tailorable Size and Their Optical Properties

A straightforward and effective polyol route for the controllable synthesis of high-quality gold (Au) octahedra with uniform size is presented in an ethylene glycol solution. Large-scale Au octahedra with the size ranging from tens to hundreds of nanometers were selectively synthesized in high-yield. The surfaces of octahedral Au nanocrystals are smooth and correspond to {111} planes. Formation of Au nanooctahedra was attributed to the preferential adsorption of cationic surfactant poly(diallyldimethylammonium) chloride (PDDA) molecules on the {111} planes of Au nuclei that inhibited the growth rate along the <111> direction. The reduction rate of gold ions in the synthesis process can be rationally manipulated by acidic and basic solutions. This provides a facile and effective route to harvest Au octahedra with different dimensions. The synthetic strategy has the advantage of one-pot and requires no seeds, no foreign metal ions, and no pretreatment of the precursor, so that this is a practical method for controllable synthesis of Au octahedra. Size-dependent optical properties of Au octahedra were numerically and experimentally analyzed. The analysis shows that Au octahedra with sharp edges possess attractive optical properties, promising their applications to surface-enhancement spectroscopy, chemical or biological sensing, and the fabrication of nanodevices.

Two-dimensional hierarchical porous silica film and its tunable superhydrophobicity

Base do na monolayer polystyrene (PS) colloidal crystal, large-scale two-dimensional (2D) hierarchical porous silica (orderly arranged macropores and disordered mesopores in its skeleton) with a high specific surface area was fabricated by the sol–gel technique. Such material has demonstrated superhydrophilicity with a water contact angle (CA) of 5 ◦ and superhydrophobicity with a water CA of 154 ◦ after surface modification with fluoroalkylsilane. More interestingly, the water CA can be increased to 165 ◦ using a heat-deformed PS template, which suggests that the superhydrophobicity can be controlled by the template with different heat-deformed extents. Such silica films have applications in fields of adsorbent, catalytic, chromatographic support, microseparator and microfluid devices. (Some figures in this article are in colour only in the electronic version)

Controllable Polyol Synthesis of Uniform Palladium Icosahedra: Effect of Twinned Structure on Deformation of Crystalline Lattices†

Palladium plays a key role in technologies used for hydrogen storage, hydrogen purification, water treatment, and fuel cells. Palladium is also widely used as the primary catalyst for low-temperature reduction of automobile pollutants, organic reactions, hydrogenation, and petroleum cracking. These numerous applications result in palladium drawing considerable interest. Most applications of palladium are related to its remarkable hydrogen-adsorption capacity. A recent study indicated that icosahedral palladium nanoparticles (Pd NPs) can absorb a larger quantity of hydrogen than their cuboctahedral analogues. Moreover, the catalytic activity of a metal NP is commonly enhanced by surface atoms located on the corners and edges. Accordingly, icosahedral Pd NPs, with a high density of twins and corners on their surfaces, are expected to be the most active catalysts, and this has led to an explosion of interest in their synthesis. Much effort has been devoted to synthesizing various metal NPs with specific shapes in aqueous or nonhydrolytic media. Among these strategies, the polyol process is a convenient, versatile, and low-cost route for the synthesis of metal NPs. In recent years, this technique has been further modified through the introduction of polymers, foreign ions, and seeds, as well as careful regulation of reaction temperature, to yield metal NPs with well-defined sizes and geometric shapes. 8,12, 13] Initial nucleation is known to be one of the determining factors for the shape of final products. The metal nuclei can adopt single-crystal, singly twinned, or multiply twinned structures. Compared with gold, multiply twinned Pd nuclei are highly susceptible to oxidation under the reaction conditions. Multiply twinned Pd NPs are depleted in favor of stable single-crystalline NPs during the growth process. Consequently, the shape of the final Pd products of a solution-phase synthesis is restricted to spherical NPs, single-crystalline plates, bars, rods, cubes, and cuboctahedra owing to highly oxidative etching, poorer protection of the twinned structures, and fast reduction and growth rate. 16] In comparison, under slow reaction conditions, nucleation of metal atoms and growth of nuclei can be kinetically controlled through polymers or foreign ions. The icosahedral structure is favored over both decahedral and cuboctahedral structures for Pd at small sizes (number of Pd atoms N< 309). Therefore, it is possible to selectively synthesize high-quality Pd icosahedra by carefully manipulating the growth process of icosahedral seeds generated by slow reactions. Thus, Pd icosahedra were synthesized in 80% yield by a water-based synthetic strategy. To the best of our knowledge, it remains a challenge to control the synthesis of uniform Pd icosahedra in high yield. Here we present a facile and effective polyol route for controllable synthesis of icosahedral Pd NPs with uniform size in ethylene glycol (EG) solution. A high yield of icosahedral Pd NPs was obtained in a one-pot reaction. Furthermore, the dimensions of the icosahedral NPs can be readily tailored from 15 to 42 nm by tuning the experimental parameters. A unique powder X-ray diffraction (PXRD) pattern of Pd owing to the multiply twinned structure was observed for the first time for Pd icosahedra. The as-synthesized Pd icosahedra are stable in air for months. Compared with spherical Pd NPs, Pd icosahedra can maintain their high catalytic activity even after several cycles. For a typical synthesis of Pd icosahedra, an EG solution containing a given amount of sodium chloride (NaCl), polyvinylpyrrolidone (PVP, Mw = 360 000), and sodium tetrachloropalladate (Na2PdCl4) was vigorously stirred and heated in air at an appropriate temperature (see the Supporting Information). Transmission electron microscopy (TEM) images demonstrate that the Pd NPs synthesized in an EG solution containing 5 mm Na2PdCl4, 10 mm NaCl, and 200 mm PVP have a hexagonal projection with a size of 31 2 nm (Figure 1a and b). Energy-dispersive X-ray spectroscopy (EDS, Figure S1, Supporting Information) and field-emission scanning electron microscopy (FESEM, Figure 1c) analyses showed that these Pd NPs consist of only Pd and have an icosahedral shape. Figure 1 d shows a high-resolution TEM [*] Dr. C. Li , R. Sato, Dr. M. Kanehara, Prof. T. Teranishi Department of Chemistry Graduate School of Pure and Applied Sciences University of Tsukuba Tennodai 1-1-1, Tsukuba, Ibaraki 305-8571 (Japan) Fax: (+ 81)29-853-4011 E-mail: teranisi@chem.tsukuba.ac.jp Homepage: http://www.chem.tsukuba.ac.jp/teranisi/index_E.html

Black Gold: Plasmonic Colloidosomes with Broadband Absorption Self-Assembled from Monodispersed Gold Nanospheres by Using a Reverse Emulsion System†

A facile approach for the fabrication of novel black plasmonic colloidosomes assembled from Au nanospheres is developed by an emulsion-templating strategy. This self-assembly process is based on a new reverse water-in-1-butanol emulsion system, in which the water emulsion droplets can dissolve into 1-butanol (oil) phase at an appropriate rate. These Au colloidosomes possess hexagonal close-packed multilayer shells and show a low reflectivity and intense broadband absorption owing to the strong interparticle plasmonic coupling, which is further investigated by a finite-difference time-domain method. This method is universal and is suitable for self-assembly of different noble-metal nanoparticles into different colloidosomes. These colloidosomes have important applications in photothermal therapy, biosensors, and drug delivery.

Fully indium-free flexible Ag nanowires/ZnO:F composite transparent conductive electrodes with high haze

Solution-processed metal nanowires (NWs) and Earth-abundant doped ZnO have been proposed to replace the most widely used indium tin oxide (ITO) transparent and conductive electrode. Generally, there is a dilemma, the trade-off between optical transparency and conductivity for these materials taken alone makes them difficult to compete with commercial ITO. In this work, a modified polyol synthesis method was adopted to grow single-crystal silver nanowire with controlled length by adding AgNO3 solution in advance and using high molecular weight polyvinylpyrrolidone (PVP). Ag nanowires ink was then spin coated onto flexible PET substrate to form Ag NW mesh, which shows impressive transparent and conductive (TC) property with sheet resistance of 23 Ω sq−1 and transmittance of 90.4% at a wavelength of 550 nm. A post fluorine-doped ZnO (FZO) layer was then deposited by pulsed laser deposition method to improve the TC, stability and mechanical property. High-quality Ag NW/FZO composite electrode was finally acquired at room temperature after optimizing the Ag NW length, concentration in suspension, and FZO layer thickness, with transmittance of 83% at wavelength of 550 nm, sheet resistance of 17 Ω sq−1, and high haze of 36.5%. Perovskite solar cells incorporating such Ag NW/FZO composite electrode exhibited a better cell performance compared to the similar FTO-based perovskite solar cells.

Strong terahertz pulse generation by chirped laser pulses in tenuous gases

Mechanism of terahertz (THz) pulse generation in gases irradiated by ultrashort laser pulses is investigated theoretically. Quasi-static transverse currents produced by laser field ionization of gases and the longitudinal modulation in formed plasmas are responsible for the THz emission at the electron plasma frequency, as demonstrated by particle-in-cell simulations including field ionization. The THz field amplitude scales linearly with the laser amplitude, which, however, holds only when the latter is at a moderate level. To overcome this limitation, we propose a scheme using chirped laser pulses irradiating on tenuous gas or plasma targets, which can generate THz pulses with amplitude 10-100 times larger than that from the well-known two-color laser scheme, enabling one to obtain THz field up to 10MV/cm with incident laser at approximately 10(16)W/cm(2).

Morphology-controlled 2D ordered arrays by heating-induced deformation of 2D colloidal monolayer

We develop a strategy to fabricate morphology-controlled two dimensional (2D) ordered arrays by solution-dipping sintered colloidal monolayer template. By heating colloid monolayer templates for different times, the morphology of ordered arrays can be controlled effectively, which is valuable to investigate the morphology-dependent optical, magnetic, electrochemical, catalytic properties of arrays. With increase of the heating time for templates, 2D ordered arrays with different morphologies can be fabricated in turn, such as, spherical pore array, honeycomb-shaped nanowall array, nanopillar array and regular network. Two kinds of morphology-controlled 2D periodic arrays, ferric oxide and silica, have been fabricated successfully by this way. This route is universal for synthesis of other compounds’ ordered arrays with controlled morphology. This strategy has expanded the applications of the colloidal monolayers as templates to prepare ordered nanostructured functional arrays.

Strong terahertz radiation from relativistic laser interaction with solid density plasmas

We report a plasma-based strong THz source generated in intense laser-solid interactions at relativistic intensities > 10(18) W/cm(2). Energies up to 50 mu J/sr per THz pulse is observed when the laser pulses are incident onto a copper foil at 67.5 degrees. The temporal properties of the THz radiation are measured by a single shot, electro-optic sampling method with a chirped laser pulse. The THz radiation is attributed to the self-organized transient fast electron currents formed along the target surface. Such a source allows potential applications in THz nonlinear physics and provides a diagnostic of transient currents generated in intense laser-solid interactions

Effect of oxygen content on the dielectric and ferroelectric properties of laser-deposited BaTiO3 thin films

BaTiO3 thin films were epitaxially grown on SrTiO3 (001) and LaNiO3/SrTiO3 substrates by pulsed laser deposition under different oxygen pressures. The oxygen content in the BaTiO3 films was determined using modified Rutherford backscattering. The structural characteristics of the films were analysed by x-ray diffraction θ/2θ scan, scan, and symmetric and asymmetric ω scans. The dielectric and ferroelectric properties of the films were measured by an impedance analyser and by a Sawyer-Tower circuit, respectively. It was found that the atomic ratio of O/Ba and Ti/Ba in the BaTiO3 films increases with oxygen pressure. The films fabricated in the intermediate oxygen pressure range of 2 to 10 Pa show the c-axis oriented tetragonal structure with a stoichiometry close to the ideal value. These films exhibit a relatively large dielectric constant, small dielectric loss and good ferroelectricity with a symmetric hysteresis loop. For growth at low oxygen pressure i.e. 0.1 Pa, the film with tetragonal c-axis orientation shows significant degradation in its dielectric properties. For a higher deposition oxygen pressure of 20 Pa, the film has tetragonal a-axis orientation and shows no ferroelectricity but has the largest dielectric constant.

In situ x-ray diffraction study of the thermal expansion of silver nanoparticles in ambient air and vacuum

The thermal expansion behavior of silver nanoparticles in ambient air and vacuum was studied by in situ x-ray diffraction (XRD) measurement of the particles dispersed within mesoporous silica in the temperature range of 25–700 °C. It has been shown that thermal expansion coefficient of Ag nanoparticles in vacuum is about 0.6×10−5∕°C, only near one fourth that of bulk silver (2.2×10−5∕°C). However, the coefficient in air is about 1.7×10−5∕°C, about 3 times as high as that in vacuum and close to the value of bulk Ag. These were explained in terms of Ag particles’ surface energy, oxygen surface adsorption, and dissolution into lattice. This study is of importance in architectonics of future nanodevices.