Catalyst-free synthesis of sub-5 nm silicon nanowire arrays with massive lattice contraction and wide bandgap.

The need for miniaturized and high-performance devices has attracted enormous attention to the development of quantum silicon nanowires. However, the preparation of abundant quantities of silicon nanowires with the effective quantum-confined dimension remains challenging. Here, we prepare highly dense and vertically aligned sub-5 nm silicon nanowires with length/diameter aspect ratios greater than 10,000 by developing a catalyst-free chemical vapor etching process. We observe an unusual lattice reduction of up to 20% within ultra-narrow silicon nanowires and good oxidation stability in air compared to conventional silicon. Moreover, the material exhibits a direct optical bandgap of 4.16 eV and quasi-particle bandgap of 4.75 eV with the large exciton binding energy of 0.59 eV, indicating the significant phonon and electronic confinement. The results may provide an opportunity to investigate the chemistry and physics of highly confined silicon quantum nanostructures and may explore their potential uses in nanoelectronics, optoelectronics, and energy systems.

High Thermal Conductivity Enhancement of Polymer Composites with Vertically Aligned Silicon Carbide Sheet Scaffolds.

Owing to the growth of demand for highly integrated electronic devices, high heat dissipation of thermal management materials is essential. Epoxy composites have been prepared with vertically aligned (VA) three-dimensional (3D)-structured SiC sheet scaffolds. The required VA-SiC sheet scaffolds were prepared by a novel approach starting with a graphene oxide (GO) scaffold. The VA-GO scaffolds were reduced to VA-graphene scaffolds in an argon environment, and the latter were subsequently transformed into VA-SiC sheet scaffolds by a template-assisted chemical vapor deposition method. Epoxy resin was filled in the empty spaces of the 3D scaffold of SiC sheets to prepare the composite mass. The material so prepared shows anisotropic thermal property with ultrahigh through-plane conductivity of 14.32 W·m-1·K-1 at a SiC sheet content of 3.71 vol %. A thermal percolation is observed at 1.78 vol % SiC filler. The SiC sheet scaffold of covalently interconnected SiC nanoparticles plays a vital role in the formation of the thermal conductive network to significantly enhance the thermal conductivity of epoxy composites. The application of the VA-SiC/epoxy composite as an efficient thermal dissipating material has also been presented. The VA-SiC/epoxy composites have a strong potential for preparing heat-dissipating components in integrated microelectronics.

Cluster Hepaticojejunostomy Is a Useful Technique Enabling Secure Reconstruction of Severely Damaged Hilar Bile Ducts.

Secure reconstruction of multiple hepatic ducts severely damaged by tumor invasion or iatrogenic injury is very difficult. If percutaneous or endoscopic biliary stenting fails, one or more percutaneous transhepatic biliary drainage (PTBD) tubes must be maintained in place for the rest of the patient's life. To cope with such difficult situations, we present a surgical technique termed cluster hepaticojejunostomy (HJ), which can be coupled with palliative bile duct resection. The cluster HJ technique consisted of applying multiple internal biliary stents and a single wide porto-enterostomy to surrounding connective tissues. We present a preliminary study with six patients. Five perihilar cholangiocarcinoma patients undergoing palliative bile duct resection received this procedure. Follow-up PTBD tubogram and hepatobiliary scintigraphy were performed at 1-2 weeks after surgery, after which the PTBD tubes were removed. No patient showed surgical complications, and the 6-month patency rate of clustered HJ was 80%. Another patient with laparoscopic cholecystectomy-associated major bile duct injury showed no biliary complications in the 5-year period following this procedure. Based on the results of this study, the cluster HJ technique may be a useful surgical method enabling the secure reconstruction of severely damaged hilar bile ducts.

Thermally conductive polyamide 6/carbon filler composites based on a hybrid filler system.

We explored the use of a hybrid filler consisting of graphite nanoplatelets (GNPs) and single walled carbon nanotubes (SWCNTs) in a polyamide 6 (PA 6) matrix. The composites containing PA 6, powdered GNP, and SWCNT were melt-processed and the effect of filler content in the single filler and hybrid filler systems on the thermal conductivity of the composites was examined. The thermal diffusivities of the composites were measured by the standard laser flash method. Composites containing the hybrid filler system showed enhanced thermal conductivity with values as high as 8.8 W (m · K)-1, which is a 35-fold increase compared to the thermal conductivity of pure PA 6. Thermographic images of heat conduction and heat release behaviors were consistent with the thermal conductivity results, and showed rapid temperature jumps and drops, respectively, for the composites. A composite model based on the Lewis-Nielsen theory was developed to treat GNP and SWCNT as two separate types of fillers. Two approaches, the additive and multiplicative approaches, give rather good quantitative agreement between the predicted values of thermal conductivity and those measured experimentally.

Influence of the capping agents on synthesis of Bi2Te3 nanotubes by solution-phase reaction.

Bi2Te3 nanotubes were synthesized by first synthesizing Te nanorods and then alloying it with Bi(O) reduced from Bi3+ using solution-phase reaction. The alloying of Bi(0) and Te nanorods was enabled by the atomic diffusion on the interface between two metals. The morphology of Bi2Te3 crystals was greatly influenced depending on kind and concentration ratio of capping agents during solution-phase reaction. When only a trioctylphosphine oxide (TOPO) was used as a capping agent, the cylinder like Bi2Te3 nanotubes with diameters of 130-160 nm or larger were formed while the rod like Bi2Te3 nanobelts with diameters of 25-40 nm were formed when only poly vinyl pyrrolidone (PVP) was used. When the mixture of trioctylphosphine oxide and poly vinyl pyrrolidone was used, Bi2Te3 nanotubes with diameters of 30-80 nm were formed.

Bundling dynamics regulates the active mechanics and transport in carbon nanotube networks and their nanocomposites.

High-density carbon nanotube networks (CNNs) continue to attract interest as active elements in nanoelectronic devices, nanoelectromechanical systems (NEMS) and multifunctional nanocomposites. The interplay between the network nanostructure and its properties is crucial, yet current understanding remains limited to the passive response. Here, we employ a novel superstructure consisting of millimeter-long vertically aligned single walled carbon nanotubes (SWCNTs) sandwiched between polydimethylsiloxane (PDMS) layers to quantify the effect of two classes of mechanical stimuli, film densification and stretching, on the electronic and thermal transport across the network. The network deforms easily with an increase in the electrical and thermal conductivities, suggestive of a floppy yet highly reconfigurable network. Insight from atomistically informed coarse-grained simulations uncover an interplay between the extent of lateral assembly of the bundles, modulated by surface zipping/unzipping, and the elastic energy associated with the bent conformations of the nanotubes/bundles. During densification, the network becomes highly interconnected yet we observe a modest increase in bundling primarily due to the reduced spacing between the SWCNTs. The stretching, on the other hand, is characterized by an initial debundling regime as the strain accommodation occurs via unzipping of the branched interconnects, followed by rapid rebundling as the strain transfers to the increasingly aligned bundles. In both cases, the increase in the electrical and thermal conductivity is primarily due to the increase in bundle size; the changes in network connectivity have a minor effect on the transport. Our results have broad implications for filamentous networks of inorganic nanoassemblies composed of interacting tubes, wires and ribbons/belts.

Preparation of silver nanoparticles and antibiotic test of its polycarbonate films composite.

General synthetic methods for silver nanoparticles are reduction of metal salt in aqueous solution or alcoholic solution. However, the preparation of silver nanoparticles in organic solvent is rarely reported. The most common preparation methods for silver nanoparticles in organic solvent are based on transfer of nanoparticles from aqueous phase to organic phase by phase transfer agent. We describe an easy synthetic method to prepare dispersed silver nanoparticles (approximately 10 nm) by reduction of silver cation in organic solvent such as toluene using a reducing agent and a capping agent. The synthesized silver nanoparticles and polycarbonate were mixed and molded to prepare a new composite in methylene chloride. The composite was tested to investigate antifungal effect by coliform (Escherichia coil ATCC 25922). The antifungal effect of the composite reached high after 24 h (99.9999%). The composite and the silver nanoparticles have been characterized using X-ray diffraction (XRD), UV-vis spectroscopy, transmission electron microscopy (TEM), and inductively coupled plasma (ICP).