Thickness Dependency of Battery Anode Properties in Multilayer Graphene.

With the development of practical thin-film batteries, multilayer graphene (MLG) is being actively investigated as an anode material. Therefore, research on determining a technique to fabricate thick MLG on arbitrary substrates at low temperatures is essential. In this study, we formed an MLG with controlled thickness at low temperatures using a layer exchange (LE) technique and evaluated its anode properties. The LE technique enabled the formation of a uniform MLG with a wide range of thicknesses (25-500 nm) on Ta foil. The charge/discharge characterization using coin-type cells revealed that the total capacity, which corresponded to Li intercalation into the MLG interlayer, increased with increasing MLG thickness. In contrast, cross-sectional transmission electron microscopy showed a metal oxide formed at the MLG/Ta interface during annealing, which had small Li capacity. MLG with sufficient thickness (500 nm) exhibited an excellent Coulombic efficiency and capacity retention compared to bulk graphite formed at high temperatures. These results have led to the development of inexpensive and reliable rechargeable thin-film batteries.

High Thermoelectric Performance in Polycrystalline GeSiSn Ternary Alloy Thin Films.

Group IV materials are promising candidates for highly reliable and human-friendly thin-film thermoelectric generators, used for micro-energy harvesting. In this study, we investigated the synthesis and thermoelectric applications of a Ge-based ternary alloy thin film, Ge1-x-ySixSny. The solid-phase crystallization of the highly densified amorphous precursors allowed the formation of high-quality polycrystalline Ge1-x-ySixSny layers on an insulating substrate. The small compositions of Si and Sn in Ge1-x-ySixSny (x < 0.15 and y < 0.05) lowered the thermal conductivity (3.1 W m-1 K-1) owing to the alloy scattering of phonons, while maintaining a high carrier mobility (approximately 200 cm2 V-1 s-1). The solid-phase diffusion of Ga and P allowed us to control the carrier concentration to the order of 1019 cm-3 for holes and 1018 cm-3 for electrons. For both p- and n-type Ge1-x-ySixSny, the power factor peaked at x = 0.06 and y = 0.02, reaching 1160 µW m-1 K-2 for p-type and 2040 µW m-1 K-2 for n-type. The resulting dimensionless figure of merits (0.12 for p-type and 0.20 for n-type) are higher than those of most environmentally friendly thermoelectric thin films. These results indicate that group IV alloys are promising candidates for high-performance, reliable thin-film thermoelectric generators.

Novel Dyadic Amorphous-Crystalline Nano-Titania Hybrids for Sacrifiers-Stored Photocatalysis.

Sacrifiers-promoted photocatalysis is a useful way to achieve high efficiency photoreduction and photocatalytic hydrogen production for photocatalysts of weak reductive power such as TiO2. Herein we report a new method to fabricate a unique dyadic hybrid consisting of closely compacted crystalline (anatase) and titanium glycerolate (TiG)-derived organic group-retained amorphous nanoparticles to validate adsorption-stored sacrifiers-promoted photocatalysis instead of using sacrifiers in bulk solution. It was found that ascorbic acid (AA)-modified TiG prepared at a small fraction of glycerol, characterized by peculiar cocoon/open nanocontainer-type morphologies, varieties of oxygen containing groups, and remarkably high specific surface area, is suitable for precursing such hybrids. AA can change crystallization processes and particle morphologies by terminating chain linkages in TiG structure, which increases porosity and brings about visible light responsive photocatalysis for the dyadic hybrid. Benefiting from good adsorption affinity to organic sacrifiers, the sacrifier-prestored hybrid can catalyze significantly enhanced photoreduction with good reproducibility toward dye molecules via the synergy of sacrifier enrichment and photocatalysis. AA modified TiG also exhibits good self-reducibility enabling pre-loading of highly dispersed and localized platinum nanoparticles, and the resulted dyadic hybrid facilitates photocatalytic hydrogen production of extremely higher turn-off frequency and better impurities interference-resistivity compared to the P25-based commercial catalyst.

Impact of Amorphous-C/Ni Multilayers on Ni-Induced Layer Exchange for Multilayer Graphene on Insulators.

Layer exchange growth of amorphous carbon (a-C) is a unique technique for fabricating high-quality multilayer graphene (MLG) on insulators at low temperatures. We investigated the effects of the a-C/Ni multilayer structure on the quality of MLG formed by Ni-induced layer exchange. The crystal quality and electrical conductivity of MLG improved dramatically as the number of a-C/Ni multilayers increased. A 600 °C-annealed sample in which 15 layers of 4-nm-thick a-C and 0.5-nm-thick Ni were laminated recorded an electrical conductivity of 1430 S/cm. This value is close to that of highly oriented pyrolytic graphite synthesized at approximately 3000 °C. This improvement is likely related to the bond weakening in a-C due to the screening effect of Ni. We expect that these results will contribute to low-temperature synthesis of MLG using a solid-phase reaction with metals.

Laser-assisted biomineralization on human dentin for tooth surface functionalization.

A technique for tooth surface modification with biocompatible calcium phosphate (CaP) has huge potential in dental applications. Recently, we achieved a facile and area-specific CaP coating on artificial materials by a laser-assisted biomimetic process (LAB process), which consists of pulsed laser irradiation in a supersaturated CaP solution. In this study, we induced the rapid biomineralization on the surface of human dentin by using the LAB process. A human dentin substrate was immersed in a supersaturated CaP solution, then its surface was irradiated with weak pulsed laser light for 30 min (LAB process). Ultrastructural analyses revealed that the pristine substrate had a demineralized collagenous layer on its surface due to the previous EDTA surface cleaning. After the LAB process, this collagenous layer disappeared and was replaced with a submicron-thick hydroxyapatite layer. We believe that the laser irradiation induced pseudo-biomineralization through the laser ablation of the collagenous layer, followed by CaP nucleation and growth at the dentin-liquid interface. The mineralized layer on the dentin substrate consisted of needle-like hydroxyapatite nanocrystals, whose c-axes were weakly oriented along the direction perpendicular to the substrate surface. This LAB process would offer a new tool enabling tooth surface modification and functionalization through the in situ pseudo-biomineralization.

Low-Temperature (400 °C) Synthesis of Multilayer Graphene by Metal-Assisted Sputtering Deposition.

Low-temperature synthesis of multilayer graphene (MLG) is essential for combining advanced electronic devices with carbon materials. We investigated the vapor-phase synthesis of MLG by sputtering deposition of C atoms on metal-coated insulators. Ni, Co, and Fe catalysts, which have high C solid solubility, enabled us to form MLG at 400 °C. The domain size and surface coverage of MLG were determined by the supplied amount of C atoms and the thickness of the metal layer associated with the solid solution amount of C. An average domain size of 2.5 µm and surface coverage of approximately 50% were obtained for a 1 µm thick Ni layer. Transmission electron microscopy demonstrated the high crystalline quality of the MLG layer despite the low processing temperature. Therefore, this simple sputtering technique has great potential for integrating graphene-based devices on various platforms.

High-Electrical-Conductivity Multilayer Graphene Formed by Layer Exchange with Controlled Thickness and Interlayer.

The layer exchange technique enables high-quality multilayer graphene (MLG) on arbitrary substrates, which is a key to combining advanced electronic devices with carbon materials. We synthesize uniform MLG layers of various thicknesses, t, ranging from 5 nm to 200 nm using Ni-induced layer exchange at 800 °C. Raman and transmission electron microscopy studies show the crystal quality of MLG is relatively low for t ≤ 20 nm and dramatically improves for t ≥ 50 nm when we prepare a diffusion controlling Al2O3 interlayer between the C and Ni layers. Hall effect measurements reveal the carrier mobility for t = 50 nm is 550 cm2/Vs, which is the highest Hall mobility in MLG directly formed on an insulator. The electrical conductivity (2700 S/cm) also exceeds a highly oriented pyrolytic graphite synthesized at 3000 °C or higher. Synthesis technology of MLG with a wide range of thicknesses will enable exploration of extensive device applications of carbon materials.

Metal Catalysts for Layer-Exchange Growth of Multilayer Graphene.

Metal-induced layer-exchange growth of amorphous carbon (a-C) is a unique technique for fabricating high-quality, uniform multilayer graphene (MLG) directly on an insulating material. Here, we investigated the effect of transition-metal species on the interaction between metals and a-C in the temperature range of 600-1000 °C. As a result, metals were classified into four groups: (1) layer exchange (Co, Ni, Cr, Mn, Fe, Ru, Ir, and Pt), (2) carbonization (Ti, Mo, and W), (3) local MLG formation (Pd), and (4) no graphitization (Cu, Ag, and Au). Some layer-exchange metals allowed for low-temperature MLG synthesis at 600 °C, whereas others allowed for high-quality MLG with a Raman G/D peak ratio of up to 8.3. Based on the periodic table, we constructed metal selection guidelines for growing MLG on an insulator, opening the door for applications that combine advanced electronic devices with carbon materials.

A carbonaceous two-dimensional lattice with FeN4 units.

A metal-containing carbonaceous two-dimensional lattice was formed on a graphene plane by sublimation, deposition, and pyrolysis of Fe phthalocyanine (Pc). The formation and growth of the FePc-derived π-conjugated planar system were reflected by its orientation conversion from the perpendicular to horizontal mode and by the N K-edge X-ray absorption near-edge structure.

Structure and solvents effects on the optical properties of sugar-derived carbon nanodots.

Carbon nanodots are a new and intriguing class of fluorescent carbon nanomaterials and are considered a promising low cost, nontoxic alternative to traditional inorganic quantum dots in applications such as bioimaging, solar cells, photocatalysis, sensors and others. Despite the abundant available literature, a clear formation mechanism for carbon nanodots prepared hydrothermally from biomass precursors along with the origins of the light emission are still under debate. In this paper, we investigate the relationships between the chemical structure and optical properties of carbon nanodots prepared by the hydrothermal treatment of glucose. Our major finding is that the widely reported excitation-dependent emission originates from solvents used to suspend the as-prepared carbon nanodots, while emission from dry samples shows no excitation-dependence. Another important highlight is that the hydrothermal conversion of biomass-derivatives under subcritical conditions leads to a heterogeneous mixture of amorphous-like nanoparticles, carbon onion-type and crystalline carbons composed of at least three different phases. The potential chemical reaction pathways involved in the formation of these hydrothermal carbon products along with a comprehensive structural and optical characterization of these systems is also provided.

Synthesis and characteristics of graphene oxide-derived carbon nanosheet-Pd nanosized particle composites.

Carbon nanosheet (CNS)-Pd nanosized particle (NP) composites were synthesized by using graphite oxide (GO) and bis(ethylenediamine)palladium(II) (Pd(en)(2)(2+)) as the precursors, and their structure and adsorption properties were examined. It was found that the Pd(en)(2)(2+) complex ions can be intercalated into GO layers highly efficiently to form a layered structure containing a large amount of Pd (approximately 12 wt %). By the subsequent chemical reduction, Pd NPs (2-6 nm in size) are well dispersed between CNS to form a CNS-Pd NP composite and serve as spacers to increase the porosity of the composite. Hydrogen adsorption results demonstrate that both Pd NPs and CNS play important roles in hydrogen adsorption, particularly at a lower temperature and for CNS with deficient sites, which bring about a H(2) adsorption greater than those on other Pd-loaded nanocarbon materials reported so far. The unique composite nanostructure having large contents of Pd NPs (20-25 wt %) stabilized by CNSs is hopeful to be applied to the fields of H(2)-related catalysis, sensing, and so forth.

Enhanced hydrogen adsorptivity of single-wall carbon nanotube bundles by one-step c60-pillaring method.

Single-wall carbon nanotube (SWCNT) bundles were pillared by fullerene (C60) by the cosonication of C60 and SWCNT in toluene to utilize the interstitial pores for hydrogen storage. C60-pillared SWCNTs were confirmed by the shift in the X-ray diffraction peak and the expanded hexagonal and distorted tetragonal bundles revealed by high-resolution transmission electron microscopy. The H2 adsorptivity of the C60-pillared SWCNT bundles was twice that of the original SWCNT bundles, indicating a design route for SWCNT hydrogen storage.

A 12-year-old boy with acute gastroenteritis caused by Edwardsiella tarda O4:H4.

A 12-year-old boy was brought to the hospital with a 3-week history of watery diarrhea mixed with mucus and colicky abdominal pain. Stool culture identified Edwardsiella tarda O4: H4, and no other pathogenic bacteria were detected. Acute gastroenteritis caused by Edwardsiella tarda O4: H4 was diagnosed. This bacterium was shown to be sensitive to ampicillin hydrate. When this antibiotic was administered, the condition of the patient improved within a week. The patient had a history of eating raw shrimp and fish while traveling with his parents.

Lamellar carbon nanosheets function as templates for two-dimensional deposition of tubular titanate.

A novel composite composed of tubular titanate-two dimensionally deposited carbon nanosheets was prepared with carbon nanosheets as templates through intercalation and hydrothermal treatment; this nanotube-based composite and its calcined products exhibit both excellent adsorptivity and high photocatalytic activity toward organic molecules.