Improved Crystallinity of Graphene Grown on Cu/Ni (111) through Sequential Mobile Hot-Wire Heat Treatment.

Over the past few years, many efforts have been devoted to growing single-crystal graphene due to its great potential in future applications. However, a number of issues remain for single-crystal graphene growth, such as control of nanoscale defects and the substrate-dependent nonuniformity of graphene quality. In this work, we demonstrate a possible route toward single-crystal graphene by combining aligned nucleation of graphene nanograins on Cu/Ni (111) and sequential heat treatment over pregrown graphene grains. By use of a mobile hot-wire CVD system, prealigned grains were stitched into one continuous film with up to ∼97% single-crystal domains, compared to graphene grown on polycrystalline Cu, which was predominantly high-angle tilt boundary (HATB) domains. The single-crystal-like graphene showed remarkably high thermal conductivity and carrier mobility of ∼1349 W/mK at 350 K and ∼33 600 (38 400) cm2 V-1 s-1 for electrons (holes), respectively, which indicates that the crystallinity is high due to suppression of HATB domains.

A half millimeter thick coplanar flexible battery with wireless recharging capability.

Most of the existing flexible lithium ion batteries (LIBs) adopt the conventional cofacial cell configuration where anode, separator, and cathode are sequentially stacked and so have difficulty in the integration with emerging thin LIB applications, such as smart cards and medical patches. In order to overcome this shortcoming, herein, we report a coplanar cell structure in which anodes and cathodes are interdigitatedly positioned on the same plane. The coplanar electrode design brings advantages of enhanced bending tolerance and capability of increasing the cell voltage by in series-connection of multiple single-cells in addition to its suitability for the thickness reduction. On the basis of these structural benefits, we develop a coplanar flexible LIB that delivers 7.4 V with an entire cell thickness below 0.5 mm while preserving stable electrochemical performance throughout 5000 (un)bending cycles (bending radius = 5 mm). Also, even the pouch case serves as barriers between anodes and cathodes to prevent Li dendrite growth and short-circuit formation while saving the thickness. Furthermore, for convenient practical use wireless charging via inductive electromagnetic energy transfer and solar cell integration is demonstrated.

Electrochemical flow-based solution-solid growth of the Cu2O nanorod array: potential application to lithium ion batteries.

The catalyzed solution-liquid-solid (SLS) growth has been well developed to synthesize semiconductor nanowires with controlled diameters. The SLS growth occurs in the longitudinal direction of nanowires, due to the directional anisotropy driven by the metal catalysts where chemical precursors are introduced. In the present study, we report a selective, template-free, and environmentally-friendly electrochemical flow-based solution-solid (electrochemical flow-SS) growth of the Cu2O nanorod array. The anisotropy for directional growth without any catalysts is generated by the electrical field in a flowing electrolyte of ultra-dilute CuSO4. The filamentary anisotropy originates from electric field enhancement on pyramidal nanocrystals in the electrolyte of low ionic conductivity (13 µS cm(-1)). The Cu2O and Cu nanorods are able to be selectively synthesized by controlling the electrolyte pH and oxygen dissolution into the electrolyte. The synthesized Cu2O nanorod array shows excellent electrochemical properties as an anode material for lithium-ion batteries; the specific capacities increase from 323 to 1206 mA h g(-1) during 500 cycles. The capacity enhancement is due to the phase transformation from Cu2O to CuO, nano-restructuring of nanorods into fragmented nanoparticles, and the progressive generation of an electroactive polymeric gel-like layer on the surface of the nanoparticles. The electrochemical flow-SS growth of Cu2O nanorods is expected to contribute to further development of other functional nanorods.

High figure-of-merit for ZnO nanostructures by interfacing lowly-oxidized graphene quantum dots.

Thermoelectric technology has potential for converting waste heat into electricity. Although traditional thermoelectric materials exhibit extremely high thermoelectric performances, their scarcity and toxicity limit their applications. Zinc oxide (ZnO) emerges as a promising alternative owing to its high thermal stability and relatively high Seebeck coefficient, while also being earth-abundant and nontoxic. However, its high thermal conductivity (>40 W m-1K-1) remains a challenge. In this study, we use a multi-step strategy to achieve a significantly high dimensionless figure-of-merit (zT) value of approximately 0.486 at 580 K (estimated value) by interfacing graphene quantum dots with 3D nanostructured ZnO. Here, we show the fabrication of graphene quantum dots interfaced 3D ZnO, yielding the highest zT value ever reported for ZnO counterparts; specifically, our experimental results indicate that the fabricated 3D GQD@ZnO exhibited a significantly low thermal conductivity of 0.785 W m-1K-1 (estimated value) and a remarkably high Seebeck coefficient of - 556 µV K-1 at 580 K.

Asymmetric magnetoconductance and magneto-Coulomb effect in a carbon nanotube single electron transistor.

We report single step-like asymmetric magnetoconductance from a double-walled carbon nanotube single electron transistor contacted by ferromagnetic cobalt electrodes. The device conductance changed significantly when the direction of the applied magnetic field was reversed, but did not show the spin-valve-type double extrema feature near the coercive field of the electrodes. The magnetoconductance also showed quasi-periodic sign-reversing oscillations with respect to the applied bias. The bias-dependent oscillation of the magnetoconductance was compared with the quantum dot stability diagram for the device. As a result, it was confirmed that the asymmetric magnetoconductance was caused by the magneto-Coulomb effect.

Corrosion behavior of silver-coated conductive yarn.

The corrosion mechanism and kinetics of the silver-coated conductive yarn (SCCY) used for wearable electronics were investigated under a NaCl solution, a main component of sweat. The corrosion occurs according to the mechanism in which silver reacts with chlorine ions to partly form sliver chloride on the surface of the SCCY and then the local silver chloride is detached into the electrolyte, leading to the electrical disconnect of the silver coating. Thus, the electrical conductance of the SCCY goes to zero after 2.7 h. The radial part-coating of gold, which is continuously electrodeposited in the longitudinal direction on the SCCY but is partly electrodeposited in the radial direction, extends the electrical conducting lifetime up to 192 h, despite the corrosion rate increasing from 129 to 196 mpy (mils per year). Results show that the gold partly-coating on the SCCY provides a current path for electrical conduction along the longitudinal direction until all the silver underneath the gold coating is detached from the SCCY strands, which creates the electrical disconnect. Based on the corrosion behavior, i.e., local oxidation and detachment of silver from the SCCY, the gold part-coating is more cost effective than the gold full-coating electrodeposited on the entire surface for electrically conducting SCCY.

Intramuscular fat formation in fetuses and the effect of increased protein intake during pregnancy in Hanwoo cattle.

Understanding adipocyte development in fetus during bovine pregnancy is important for strengthening fattening technology. Additionally, nutritional level of dams during pregnancy has the potential to improve offspring growth and fat development. The purpose of this study is to evaluate the intramuscular adipocyte development and expression level of related genes in bovine fetus, and the effect of increased crude protein (CP) intake during pregnancy on the growth performance and carcass characteristics of male offspring. Eighty six pregnant Hanwoo cows (average body weight, 551.5 ± 51.3 kg, age 5.29 ± 0.61 y) were used. Fetuses were collected at 90, 180 and 270 d of gestation from 18 pregnant Hanwoo cows. The remaining 68 pregnant cows were randomly assigned to 2 feeding groups. The control (CON) group was provided the standard protein diet (n = 34), and treatment (TRT) group was provided a diet with a 5% increase in CP intake (n = 34). Male offspring were divided into two groups according to protein treatment of the pregnant cows: CON male offspring (CON-O) and TRT male offspring (TRT-O). Intramuscular adipocytes were found in the fetal skeletal muscle after 180 days of gestation. Male calf's birth weight increased in the TRT group compared to that in the CON group (p < 0.002). The final body weight (p < 0.003) and average daily gain (p < 0.019) of male offspring were significantly higher in TRT-O than in CON-O. The feed conversion ratio was also improved by 10.5% in TRT-O compared to that in CON-O (p < 0.026). Carcass weight was significantly higher in the TRT-O group than that in the CON-O group (p < 0.003), and back fat was thicker in the TRT-O group (p = 0.07). The gross receipts and net income were higher in TRT-O than in CON-O (p < 0.04). Thus, fetal intramuscular fat can be formed from the mid-gestation period, and increased CP intake during pregnancy can increase net income by improving the growth and carcass weight of male offspring rather than intramuscular fat.

Isolation, screening and identification of Swine gut microbiota with ochratoxin a biodegradation ability.

The potential for ochratoxin A (OTA) degradation by swine intestinal microbiota was assessed in the current study. Intestinal content that was collected aseptically from swine was spiked with 100 ppb OTA and incubated for 6 and 12 h at 39°C. An OTA assay was conducted using the incubated samples, and it was found that 20% of the OTA toxin was detoxified, indicating the presence of microbes capable of OTA degradation. Twenty-eight bacterial species were isolated anaerobically in M 98-5 media and 45 bacterial species were isolated using nutrient broth aerobically. Screening results showed that one anaerobic bacterial isolate, named MM11, detoxified more than 75% of OTA in liquid media. Furthermore, 1.0 ppm OTA was degraded completely after 24 h incubation on a solid 'corn' substrate. The bacterium was identified by 16S rDNA sequencing as having 97% sequence similarity with Eubacterium biforme. The isolation of an OTA-degrading bacterium from the swine natural flora is of great importance for OTA biodegradation and may be a valuable potential source for OTA-degradation enzymes in industrial applications.

In situ Fenton remediation for diesel contaminated clayey zone assisted by thermal plasma blasting: Synergism and cost estimation.

Thermal plasma blasting technology has been widely applied for rock cracking. Though, the application for environmental remediation has yet to be reported. Since the delivery of remediation agents into diesel contaminated clayey zones are exceptionally challenging, herein, this study explores the effect of pilot-scale thermal plasma blasting for soil fracturing and concurrently dispersing the Fenton reagent into the diesel contaminated silty soils. Six times plasma blasting with sole H2O2 at 20 kV had the highest degradation of diesel (>97%) with an equilibrium time of 3 h, and the final diesel concentration was below the South Korean regulated health standard (500 mg kg-1). This study highlights plasma blasting able to deliver H2O2 instantaneously and homogeneously into contaminated zone while promoting Fenton reaction synergism (fsyn: 2.04) between H2O2 and ≡Fe surface for effective remediation. Furthermore, the remediation cost (USD 4 metric ton-1) is much lower than most reported in situ technologies.

Comparative Study of Thermoelectric Properties of Sb2Si2Te6 and Bi2Si2Te6.

Charge carrier transport and corresponding thermoelectric properties are often affected by several parameters, necessitating a thorough comparative study for a profound understanding of the detailed conduction mechanism. Here, as a model system, we compare the electronic transport properties of two layered semiconductors, Sb2Si2Te6 and Bi2Si2Te6. Both materials have similar grain sizes and morphologies, yet their conduction characteristics are significantly different. We found that phase boundary scattering can be one of the main factors for Bi2Si2Te6 to experience significant charge carrier scattering, whereas Sb2Si2Te6 is relatively unaffected by the phenomenon. Furthermore, extensive point defect scattering in Sb2Si2Te6 significantly reduces its lattice thermal conductivity and results in high zT values across a broad temperature range. These findings provide novel insights into electron transport within these materials and should lead to strategies for further improving their thermoelectric performance.

Active doping of B in silicon nanostructures and development of a Si quantum dot solar cell.

Active doping of B was observed in nanometer silicon layers confined in SiO(2) layers by secondary ion mass spectrometry (SIMS) depth profiling analysis and confirmed by Hall effect measurements. The uniformly distributed boron atoms in the B-doped silicon layers of [SiO(2) (8 nm)/B-doped Si(10 nm)](5) films turned out to be segregated into the Si/SiO(2) interfaces and the Si bulk, forming a distinct bimodal distribution by annealing at high temperature. B atoms in the Si layers were found to preferentially substitute inactive three-fold Si atoms in the grain boundaries and then substitute the four-fold Si atoms to achieve electrically active doping. As a result, active doping of B is initiated at high doping concentrations above 1.1 × 10(20) atoms cm( - 3) and high active doping of 3 × 10(20) atoms cm( - 3) could be achieved. The active doping in ultra-thin Si layers was implemented for silicon quantum dots (QDs) to realize a Si QD solar cell. A high energy-conversion efficiency of 13.4% was realized from a p-type Si QD solar cell with B concentration of 4 × 10(20) atoms cm( - 3).

Biological synthesis of platinum nanoparticles using Diopyros kaki leaf extract.

The leaf extract of Diopyros kaki was used as a reducing agent in the ecofriendly extracellular synthesis of platinum nanoparticles from an aqueous H(2)PtCl(6).6H(2)O solution. A greater than 90% conversion of platinum ions to nanoparticles was achieved with a reaction temperature of 95 degrees C and a leaf broth concentration of >10%. A variety of methods was used to characterize the platinum nanoparticles synthesized: inductively coupled plasma spectrometry, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy (FTIR). The average particle size ranged from 2 to 12 nm depending on the reaction temperature and concentrations of the leaf broth and PtCl(6) (2-). FTIR analysis suggests that platinum nanoparticle synthesis using Diopyros kaki is not an enzyme-mediated process. This is the first report of platinum nanoparticle synthesis using a plant extract.

Tunable in-plane thermal conductivity of a single PEDOT:PSS nanotube.

Understanding the mechanism of thermal energy transport in a single nanotube (NT) is essential for successfully engineering nanostructured conducting polymers to apply to thermoelectrics or flexible electronic devices. We report the characterization of the in-plane thermal energy transport in a single poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) NT via direct measurement of the in-plane thermal conductivity (κ). We also demonstrate that the in-plane κ of PEDOT:PSS NT can be tuned within the range of 0.19 to 1.92 W·m-1·K-1 merely by changing the solvent used to treat the NTs in the post-fabrication stage. The in-plane thermal energy transport in a pristine NT, with its low in-plane κ, is primarily due to phonons; in a sulfuric acid-treated NT however, significant electronic contributions lead to a high in-plane κ. The present study will contribute to understanding the mechanism of thermal energy transport in highly disordered structures, such as conducting polymers, and to designing highly efficient polymer-based devices in which in-plane κ plays a pivotal role in determining the energy conversion efficiency.

Rapid biological synthesis of silver nanoparticles using plant leaf extracts.

Five plant leaf extracts (Pine, Persimmon, Ginkgo, Magnolia and Platanus) were used and compared for their extracellular synthesis of metallic silver nanoparticles. Stable silver nanoparticles were formed by treating aqueous solution of AgNO(3) with the plant leaf extracts as reducing agent of Ag(+) to Ag(0). UV-visible spectroscopy was used to monitor the quantitative formation of silver nanoparticles. Magnolia leaf broth was the best reducing agent in terms of synthesis rate and conversion to silver nanoparticles. Only 11 min was required for more than 90% conversion at the reaction temperature of 95 degrees C using Magnolia leaf broth. The synthesized silver nanoparticles were characterized with inductively coupled plasma spectrometry (ICP), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and particle analyzer. The average particle size ranged from 15 to 500 nm. The particle size could be controlled by changing the reaction temperature, leaf broth concentration and AgNO(3) concentration. This environmentally friendly method of biological silver nanoparticles production provides rates of synthesis faster or comparable to those of chemical methods and can potentially be used in various human contacting areas such as cosmetics, foods and medical applications.

Template-Free Electrochemical Growth of Ni-Decorated ZnO Nanorod Array: Application to an Anode of Lithium Ion Battery.

ZnO nanorods (NRs) decorated with Ni nanoparticles were synthesized using a template-free electrochemical deposition in an ultra-dilute aqueous electrolyte and a subsequent galvanic reaction. The electrochemical properties of the ZnO NRs as an anode material for rechargeable Li-ion batteries were evaluated for different binder morphologies (film and close-packed spherical particles) of polyvinylidene fluoride (PVDF). Results showed that the close-packed spherical PVDF simultaneously improved electrochemical capacity and cyclability because the free-volume between the spherical PVDF helped to accommodate the volume change in the anode caused by the Li ions discharge and charge processes. Furthermore, the Ni nanoparticles decorated on the surface of ZnO NRs enhanced the electrical conductivity of the ZnO NR anode, which enabled faster electronic and ionic transport at the interface between the electrolyte and the electrode, resulting in improved electrochemical capacity. The free-volume formed by the close-packed spherical PVDF, and the decoration of metal nanoparticles are expected to provide insight on the simultaneous improvement of electrochemical capacity and cyclability in other metal oxide anode nanostructures.

Composition change-driven texturing and doping in solution-processed SnSe thermoelectric thin films.

The discovery of SnSe single crystals with record high thermoelectric efficiency along the b-axis has led to the search for ways to synthesize polycrystalline SnSe with similar efficiencies. However, due to weak texturing and difficulties in doping, such high thermoelectric efficiencies have not been realized in polycrystals or thin films. Here, we show that highly textured and hole doped SnSe thin films with thermoelectric power factors at the single crystal level can be prepared by solution process. Purification step in the synthetic process produced a SnSe-based chalcogenidometallate precursor, which decomposes to form the SnSe2 phase. We show that the strong textures of the thin films in the b-c plane originate from the transition of two dimensional SnSe2 to SnSe. This composition change-driven transition offers wide control over composition and doping of the thin films. Our optimum SnSe thin films exhibit a thermoelectric power factor of 4.27 µW cm-1 K-2.

Thickness-dependent and anisotropic thermal conductivity of black phosphorus nanosheets.

Thickness effects on thermal conductivities of black phosphorus nanosheets, which are anisotropic in the zigzag and armchair planar directions, are experimentally and theoretically investigated in the thickness range of 13 to 48 nm. The thermal conductivities decrease with the thickness, decreasing from 13 to 8 W m-1 K-1 in the zigzag direction and from 10 to 6 W m-1 K-1 in the armchair direction at 300 K, respectively. The anisotropic thermal conductivities, regardless of the thickness, might result from the anisotropic phonon velocity arising from the hinge-like structure. The surface-driven suppression of the thermal conductivities at a nanometer scale is remarkable for a wide temperature range of 100 to 300 K due to phonon-boundary scattering, while the thermal conductivity becomes less dependent on the thickness at higher temperatures above 300 K, owing to the dominant phonon-phonon scattering.

Anomalous thermoelectricity of pure ZnO from 3D continuous ultrathin nanoshell structures.

ZnO is a potential thermoelectric material because of its non-toxicity, high thermal stability, and relatively high Seebeck coefficient (S) of metal oxides. However, the extremely low figure of merit (zT), which comes from a high thermal conductivity (κ) over 40 W m-1 K-1, limits the thermoelectric application of ZnO. In particular, below 500 K, ZnO exhibits a nearly negligible zT (<10-3), unless a dopant is incorporated into the crystal structure. Here, we propose a new strategy for achieving a reduced κ and a correspondingly increased zT of pure ZnO over a wide temperature range from 333 K to 723 K by forming an ∼72 nm thick, 3D continuous ultrathin nanoshell structure. The suppressed κ of the 3D ZnO film is ∼3.6 W m-1 K-1 at 333 K, which is ∼38 times lower than that of the blanket ZnO film (3.2 µm thick), which was set as a reference. The experimental zT of the 3D ZnO film is ∼0.017 at 333 K, which is the highest value among pure ZnO reported to date and is estimated to increase by ∼0.072 at 693 K according to the Debye-Callaway approach. Large-area (∼1 in2) fabrication of the 3D ZnO film with high structural uniformity allows the realization of an integrated thermoelectric device, which generates ∼60 mV at a temperature difference of 40 K along the in-plane direction.

Low-Cost Black Phosphorus Nanofillers for Improved Thermoelectric Performance in PEDOT:PSS Composite Films.

In recent years, two-dimensional black phosphorus (BP) has seen a surge of research because of its unique optical, electronic, and chemical properties. BP has also received interest as a potential thermoelectric material because of its high Seebeck coefficient and excellent charge mobility, but further development is limited by the high cost and poor scalability of traditional BP synthesis techniques. In this work, high-quality BP is synthesized using a low-cost method and utilized in a PEDOT:PSS film to create the first ever BP composite thermoelectric material. The thermoelectric properties are found to be greatly enhanced after the BP addition, with the power factor of the film, with 2 wt % BP (36.2 µW m-1 K-2) representing a 109% improvement over the pure PEDOT:PSS film (17.3 µW m-1 K-2). A simultaneous increase of mobility and decrease of the carrier concentration is found to occur with the increasing BP wt %, which allows for both Seebeck coefficient and electrical conductivity to be increased. These results show the potential of this low-cost BP for use in energy devices.

Thermoelectric Properties of Hot-Pressed Bi-Doped n-Type Polycrystalline SnSe.

ᅟ: We report on the successful preparation of Bi-doped n-type polycrystalline SnSe by hot-press method. We observed anisotropic transport properties due to the (h00) preferred orientation of grains along the pressing direction. The electrical conductivity perpendicular to the pressing direction is higher than that parallel to the pressing direction, 12.85 and 6.46 S cm-1 at 773 K for SnSe:Bi 8% sample, respectively, while thermal conductivity perpendicular to the pressing direction is higher than that parallel to the pressing direction, 0.81 and 0.60 W m-1 K-1 at 773 K for SnSe:Bi 8% sample, respectively. We observed a bipolar conducting mechanism in our samples leading to n- to p-type transition, whose transition temperature increases with Bi concentration. Our work addressed a possibility to dope polycrystalline SnSe by a hot-pressing process, which may be applied to module applications. HIGHLIGHTS: 1. We have successfully achieved Bi-doped n-type polycrystalline SnSe by the hot-press method. 2. We observed anisotropic transport properties due to the [h00] preferred orientation of grains along pressing direction. 3. We observed a bipolar conducting mechanism in our samples leading to n- to p-type transition.