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In the melanin synthesis process, oxidative reactions play an essential role, and it is a good strategy to inhibit melanin production by reducing oxidative stress. Fullerene and its derivatives, or the complexes, were considered as strong free-radical scavengers, and we further applied multilayered sp2 nanocarbons to discover melanin synthesis inhibitory mechanisms. In the present study, we used novel nanomaterials, such as multiwalled carbon nanotubes (MWCNTs), short-type MWCNTs, graphene oxide nanoribbons (GONRs), and short-type GONRs, as anti-oxidative agents to regulate melanin production. The results showed that GONRs had better anti-oxidative capabilities in intracellular and extracellular oxidative stress analysis platforms than others. We proposed that GONRs have oxygen-containing functional groups. In the 2',7'-dichlorodihydrofluorescein diacetate assay, we found out GONR could chelate metal ions to scavenge reactive oxygen species. In the molecular insight view, we observed that these nanomaterials downregulated the melanin synthesis by decreasing microphthalmia-associated transcription factor-related gene expressions, and there were similar consequences in protein expressions. To sum up, GONRs is a potential agent as a novel antioxidant and skin-whitening cosmetology material.

We propose a function-field analog of Pisot's d-th root conjecture on linear recurrences, and prove it under some “non-triviality” assumption. Besides a recent result of Pasten-Wang on Buchi's d-th power problem, our main tool, which is also developed in this paper, is a function-field analog of a GCD estimate in a recent work of Levin and Levin-Wang. As an easy corollary of such a GCD estimate, we also obtain an asymptotic result.

We give a natural sufficient condition which ensures the finiteness of the number of integral points on a projective space omitting finitely many hyperplanes defined over a one-dimensional function field of positive characteristic. In this setting, when the number of hyperplanes is 2 n + 2 , where n is the dimension of the ambient projective space, we use this natural condition to explain and sharpen an earlier result of the second named author, which provides a concrete condition on the coefficients of the linear forms producing hyperplanes such that the above finiteness property is satisfied.

In this work, we demonstrate multi-bandgap photodetectors with an inherently lattice-matched structure by the natural stacking of graphene oxide nanoribbons. The stacked multilayer graphene oxide nanoribbons are produced by unzipping multi-walled carbon nanotubes. A correlation study between image inspection and photoelectrical characterization of stacked graphene oxide nanoribbon devices is performed in specific chips. Transmission electron microscopy images reveal the presence of a multilayer graphene oxide nanoribbon with gradually increasing widths, suggesting that multilayer graphene oxide nanoribbons with decreasing bandgaps could innately act as low-pass photon energy filters and serve to increase the spectral absorption window in these photodetectors. Photoelectrical measurements show visible-light spectrum absorption, which suggests that the various energy bandgaps of the multi-layer graphene oxide nanoribbons contribute toward the increased bandwidth in photon absorption. Furthermore, photo-responsivities on the order of 10 A/W with a stable photo-switching behavior as well as fast response times are observed. The response times range from 2 ms in the membrane devices down to a few hundred of μs in the suspended devices due to elimination of the substrate effect. Based upon this correlation study, we believe that this stacked multilayer graphene oxide nanoribbon structure with gradually varying widths is a promising candidate towards the development of novel high performance photodetectors and optoelectronics.

Chemical vapor deposition (CVD) graphene is reported to effectively prevent the penetration of outer factors and insulate the underneath metals, hence achieving an anticorrosion purpose. However, there is little knowledge about their characteristics and corresponding corrosion properties, especially for those prepared under different parameters at low temperatures. Using electron cyclotron resonance chemical vapor deposition (ECR-CVD), we can successfully prepare graphene nanostructures on copper (Cu) at temperatures lower than 600 &deg, C. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, and potentiodynamic polarization measurements were used to characterize these samples. In simulated seawater, i.e., 3.5 wt.% sodium chloride (NaCl) solution, the corrosion current density of one graphene-coated Cu fabricated at 400 &deg, C can be 1.16 &times, 10&minus, 5 A/cm2, which is one order of magnitude lower than that of pure Cu. Moreover, the existence of tall graphene nanowalls was found not to be beneficial to the protection as a consequence of their layered orientation. These correlations among the morphology, structure, and corrosion properties of graphene nanostructures were investigated in this study. Therefore, the enhanced corrosion resistance in selected cases suggests that the low-temperature CVD graphene under appropriate conditions would be able to protect metal substrates against corrosion.

In this study, the growth of graphene by chemical vapor deposition (CVD) on SUS304 stainless steel and on a catalyzing Ni/SUS304 double-layered structure was investigated. The results indicated that a thin and multilayered graphene film can be continuously grown across the metal grain boundaries of the Ni/SUS304 stainless steel and significantly enhance its corrosion resistance. A 3.5 wt% saline polarization test demonstrated that the corrosion currents in graphene-covered SUS304 were improved fivefold relative to the corrosion currents in non-graphene-covered SUS304. In addition to enhancing the corrosion resistance of stainless steel, a graphene coating also ameliorates another shortcoming of stainless steel in a corrosive environment: the formation of a passive oxidation layer on the stainless steel surface that decreases conductivity. After a corrosion test, the graphene-covered stainless steel continued to exhibit not only an excellent low interfacial contact resistance (ICR) of 36 mΩ cm2 but also outstanding drainage characteristics. The above results suggest that an extremely thin, lightweight protective coating of graphene on stainless steel can act as the next-generation bipolar plates of fuel cells.

We demonstrate the microwave-assisted synthesis of short graphene oxide nanoribbons (GONRs) through unzipping cut multiwalled carbon nanotubes (MWCNTs). Transmission electron microscopy and dynamic light scattering spectroscopy were used to examine the length, size, and morphology, i. e. unzipping level, of our various products. The nanotube core and nanoribbon shell can be observed from short GONRs via a modified unzipping recipe. Then the short GONRs were adopted to modify the glassy carbon electrode for the electrochemical detection of ascorbic acid (AA), uric acid (UA), and dopamine (DA). Compared to other nanomaterials, cyclic voltammograms of short GONRs show higher anodic oxidation currents for AA, UA, and DA. The detection limits of three analytes are 26, 98, and 24 nM, respectively, in amperometric current-time measurements. Especially, the sensitivity for DA is improved to be 40.86 μA μM(-1) cm(-2). The improved detection signals are due to the increased active sites of the open ends of short GONRs. Moreover, the width side of short GONRs could be more active than their length side. All above-mentioned results reveal that the short GONRs can provide a novel platform for electrochemically biomarker detection of Parkinson's disease.

We generalize a result by Stoll on the Brauer–Manin–Scharaschkin obstruction for zero-dimensional subvarieties of abelian varieties to almost split semi-abelian varieties. As consequences, we give an essentially different proof of a partial result on some exponential local–global principle over number fields, originally established by Bartolome, Bilu, and Luca, and generalize it to any global field; we also extend our consideration of this obstruction to a broader situation which has some dynamical interpretation, and improve a result by Hsia and Silverman.

In this study, the size-selected platinum (Pt) nanoparticles are loaded on sulfonated graphene with polyvinyl alcohol (PVA) as the conductive polymer for fuel-cell applications. Methanol oxidation reactions and reliability of various catalysts based on carbon black, graphene, and sulfonated graphene catalyst supports are compared under alkaline conditions. When PVA is used as the conductive polymer in place of Nafion, both the electrochemical active surface area (ECSA) and the methanol oxidation property were superior, irrespective of the catalyst and support. On the other hand, the catalyst with Pt on sulfonated graphene (Pt/sG) outperforms those on other supports. For methanol oxidation, the catalyst decay occurs with a decay of only 9.06% for Pt/sG. It is suggested that the sulfonate functional group on graphene not only improves catalytic activity but can also enhance catalyst reliability.

We report here a nonenzymatic glucose sensor based on a CuO/graphene-modified screen-printed carbon electrode (CuOG-SPCE) integrated with flow-injection analysis (FIA). The highly active CuOG-SPCE with well-dispersed CuO nanoparticles on graphene surfaces performed excellent electrocatalytic oxidation of glucose. Under optimal FIA conditions, the proposed biosensor can be employed in the quantification of glucose with the linear range from 0.122 μM to 0.5 mM, the desirable sensitivity up to 2367 μA mM−1 cm−2 and the ultralow detection limit of 34.3 nM (S/N=3) simultaneously. Good repeatability of 1.92% (n=30) and less effects of common interfering species including ascorbic acid, uric acid, dopamine, fructose, lactose and sucrose were also demonstrated. The CuO-SPCE with highly sensitive, selective and stable consecutive monitoring (t=1 h) of glucose is promising for the development of an advanced nonenzymatic glucose sensor device. Keywords: Graphene, Nanoparticle, Screen-printed carbon electrode, Nonenzymatic glucose sensor, Flow-injection analysis

Significance Four types of carbons (activated carbon, Maxsorb superactivated carbon, mesoporous templated carbon CMK-3, and graphene) were investigated as selective sorbents for adsorption of thiophene from its solution in n-octane. Graphene showed clearly the highest sulfur capacity. The relative sulfur capacities correlated well with the relative heats of adsorption. The carbene-type zigzag edge sites and the carbyne-type armchair edge sites on graphene are among the possible sites for strong interactions with thiophene.

In this study, a graphene/Pt-modified glassy carbon (GC) electrode was created to simultaneously characterize ascorbic acid (AA), dopamine (DA), and uric acid (UA) levels via cyclic voltammetry (CV) and differential pulse voltammetry (DPV). During the preparation of the nanocomposite, size-selected Pt nanoparticles with a mean diameter of 1.7 nm were self-assembled onto the graphene surface. In the simultaneous detection of the three aforementioned analytes using CV, the electrochemical potential differences among the three detected peaks were 185 mV (AA to DA), 144 mV (DA to UA), and 329 mV (AA and UA), respectively. In comparison to the CV results of bare GC and graphene-modified GC electrodes, the large electrochemical potential difference that is achieved via the use of the graphene/Pt nanocomposites is essential to the distinguishing of these three analytes. An optimized adsorption of size-selected Pt colloidal nanoparticles onto the graphene surface results in a graphene/Pt nanocomposite that can provide a good platform for the routine analysis of AA, DA, and UA.

In this study, carbon nanotubes (CNTs) were fabricated using an arc-discharge method assisted with samarium-cobalt (Sm-Co) chloride as a catalyst. The optimal fabrication condition was determined through a series of experiments on various ambient conditions. Observations were completed using scanning electron microscopy (SEM), Raman spectroscopy, and tunneling electron microscopy (TEM); the main products we observed are well-structured multi-walled carbon nanotubes. By identifying the radial breathing modes (RBMs) of the Raman spectra with a TEM micrograph, we also observed a small number of single-walled carbon nanotubes. With the assistance of the Sm-Co chloride catalyst, the RBMs of the Raman spectra were measured in the ambient pressure of 760 torr. The TEM observations revealed that our nanotubes have good graphitic structures and almost no bamboo defects, which agrees with their Raman measurements with a high IG/ID ratio (~88). A perfect graphitic flat cap was found to be attached at the end of the nanotube. Simulation shows that by incorporating 5 carbon pentagons, it is possible to construct a flat capped carbon nanotube. The results of our experiment offer a unique approach to growing high quality CNTs. Such a flat capped structure may useful for further advanced application in nano-electronics and nano-optics.

Active carbons were prepared by polymer blend with various chemical concentrations and carbonization conditions. The resultant porosity and electrochemical properties were studied by nitrogen adsorption–desorption isotherm and cyclic voltammetry techniques, and compared with those of commercial carbon black, Vulcan XC-72R. The polymer-derived active carbons exhibit a mesoporous structure, large surface area, low capacitance, and high electrochemical activity, thus are suitable for catalyst support. By ion-exchange method with appropriate functionalization treatments (three different ways were conducted in this paper) on these carbon supports, we have achieved a uniform dispersion of ultra-fine Pt nanoparticles (~ 2 nm) with a total loading amount up to 10 wt.% and an exchange efficiency of 60%, much higher than the values of Vulcan XC-72R.

Significant enhancement in supercapacitor performance has been achieved via a new RuO2 nanocomposite materials prepared by direct ruthenium sputtering on arrayed multi-walled carbon nanotubes supported by Ti-buffered Si wafer. XPS, HRTEM and SAED analyses reveal that as-prepared nanoparticles have a crystalline Ru metal core with RuO2 oxide coating. The nanocomposites convert to RuO2–CNx NTs with subsequent electrochemical cycling. At present, well-dispersed and strongly adhered RuO2 NPs have been densely populated on CNx NTs to obtain the overall specific capacitance (1380 F/g-RuO2), charging–discharging rate (up to 600 mV/s) and operation stability (5000 cycles). Thus, RuO2–CNx NTs nanocomposites would make a promising candidate for use in next-generation high efficiency miniaturized supercapacitors directly fabricated on Si substrate. Keywords: Supercapacitors, Direct growth, Well-aligned carbon nanotubes, RuO2 nanoparticles, Arrayed nanocomposites

The electrochemical detection of hydrogen peroxide (H2O2) has attracted much attention recently. Meanwhile, the size of nanoparticles which significantly influences electrocatalytic activity is crucial for electrocatalysts. Hence, we prepared five different size-selected Pt/graphene-modified glassy carbon (GC) electrodes to characterize H2O2level via electrochemical measurements. During the preparation of the nanocomposites, size-selected Pt nanoparticles (NPs) with the mean diameter of 1.3, 1.7, 2.9, and 4.3 nm were assembled onto the graphene surfaces. The electrochemical measurement results are size-dependent for Pt NPs when sensing H2O2. When all cyclic voltammogram results from various electrodes are compared, the Pt-1.7 nm/G-modified GC electrode has the highest reduction current, the best detection limit, and the best sensitivity.

High-quality single crystal indium nitride nanorods were grown on Si substrates by catalytic chemical vapor deposition. Both Raman and high resolution transmission electron microscopic analyses suggested that even a minute amount of oxygen, from the residual oxygen in the growth environment and/or native oxide on the Si, would effectively help the growth of InN nanorods. The In2O3 formed on Au nanoparticles helped dissolve nitrogen as a catalyst with the subsequent growth of InN nanorods. Variations in the apparent color and photoluminescence (PL) spectra of the InN nanorods were observed. For the optically brown InN nanorods that exhibited diameters in the range of 30–50 nm, the PL study showed a peak at 1.9 eV, the possible origins of which are discussed. In contrast, for the optically black InN nanorods that exhibited diameters in the range of 50–100 nm, the PL peak at approximately 0.766 eV measured at 20 K was attributed to band edge emission.

Polycrystalline PbTiO 3 thin films have been prepared on Si substrates with ultra-thin SiO 2 and Al 2 O 3 buffer layers by chemical solution deposition, respectively. Although capacitance–voltage characteristics show hysteresis loops in both cases, the memory window of PbTiO 3 /Al 2 O 3 stacked dielectric is 3.3 V larger than that on SiO 2 . In addition, well-behaved capacitance–voltage characteristics are only obtained in PbTiO 3 /Al 2 O 3 and the PbTiO 3 films on Al 2 O 3 have the dielectric constant of 116 larger than 42 of PbTiO 3 films on SiO 2 . The leakage current density of PbTiO 3 /Al 2 O 3 dielectric is 1.3×10 −7 A cm −2 at −2.5 V, which is low enough for deep sub-μm application.

Diamond-like carbon coatings have been deposited by a pulse biased arc ion plating. In order to improve their adherence to metal substrate, two systems of graded transition layers, namely Ti/TiN/TiC and Ti/TiCN/TIC, have been applied. The structure and composition of the diamond-like carbon/transition composite coatings were studied by scanning electron microscopy, Raman spectroscopy and energy dispersive X-ray spectroscopy. The total thickness of the coatings was within a range of 1.0-2.0 mum. Such multi-layer coatings showed excellent properties including high hardness, low friction coefficient and long wear-resistant lifetime. Diamond like carbon coatings as well as their wear tracks developed by sliding steel balls have been investigated by scanning electron microscopy. The results of the analysis, particularly that of the tribological study showed that the wear resistance and film-to-substrate adherence of diamond like carbon coatings with stainless steel surface were dramatically improved by using a graded transition layer and pulse biased arc ion plating. (C) 2001 Elsevier Science B.V. All rights reserved.

A novel core–shell heterostructure with multi-walled carbon nanotubes (MWCNTs) as the core and graphene oxide nanoribbons (GONRs) as the shell (MWCNT@GONR) is investigated for the first time as anode material for Na-ion batteries (NIBs) in this study. The MWCNT@GONR material with carboxylic acid groups has been synthesized through unzipping of MWCNTs by a microwave-assisted process. The influence of the amount of carboxylic acid groups on the electrochemistry of MWCNT@GONR is investigated in this work by applying thermal treatment at different temperatures. In this MWCNT@GONR core-shell structure, the MWCNTs between flat GONR sheets prevent the restacking problem of graphene and enable penetration of the electrolyte. MWCNTs provide high electronic conductivity and direct electron transfer path while GONRs provide high surface area and defect sites (carboxylic acid groups, COOH-) that can adsorb more Na ions on the surface thereby increasing capacity. MWCNT@GONR provides high capacity (317 mA h g−1) at a current density of 50 mA h g−1 in the second cycle. A full cell using MWCNT@GONR as anode and P2-NaxMnO2 as cathode is fabricated and it exhibits a high energy density of 99 Wh kg−1 which successfully demonstrates that MWCNT@GONR is a promising anode material for NIB applications.

For a semi-abelian variety over a global function field which is isogenous to an isotrivial one, we show that on the product of local points of a subvariety satisfying a minor condition, the topological closure of a finitely generated subgroup of %the group of its global points cuts out exactly the global points of the subvariety lying in this subgroup. As a corollary, on every non-isotrivial super-singular curve of genus two over a global function field, we conclude that the Brauer-Manin condition cuts out exactly the set of its rational points.

We explain that decomposition methods, in particular, SMO-type algorithms, are not suitable for linear SVMs with more data than attributes. To remedy this difficulty, we consider a recent result by S.S. Keerthi and C.-J. Lin (see http://www.csie.ntu.edu.tw//spl sim/cjlin/papers/limit.ps.gz, 2002) that for an SVM which is not linearly separable, after C is large enough, the dual solutions are at similar faces. Motivated by this property, we show that alpha seeding is extremely useful for solving a sequence of linear SVMs. It largely reduces the number of decomposition iterations to the point that solving many linear SVMs requires less time than the original decomposition method for one single SVM. We also conduct comparisons with other methods which are efficient for linear SVMs, and demonstrate the effectiveness of the proposed approach for helping the model selection.

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One-dimensional electrodes consisting of N-doped carbon nanotubes and ternary PtRuNi metal catalysts deposited via a vacuum deposition are made. Material analysis shows that high density nanoparticles that are well dispersed on the nanotube surface are deposited. The average catalyst particle size is between 3 and 4.5 nm depending on the sputtering conditions. The methanol oxidation current of the ternary PtRuNi catalysts increases up to a factor of 2.6 as compared to the binary PtRu catalyst. Our studies shed light on the advanced control of nanotube-supported electrocatalysts under a low loading via the vacuum deposition techniques and can contribute to the controlled synthesis and understanding of fuel-cell catalysts.

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The effects of a Ti buffer layer on structural and electrochemical properties of arrayed nitrogen-containing carbon nanotubes (CNx NTs) directly grown on Si substrates have been investigated. Cyclic voltammograms using Fe(CN)(6)(3-)/Fe(CN)(6)(4-) as redox couple were measured to study the electrochemical activities of CNx NTs. The highest peak current density was achieved at an optimal Ti thickness of 20 nm owing to the good conductivity of TiSi2 and high number density of NTs. Therefore, we have demonstrated the direct growth of aligned NTs on Ti- buffered Si with improved electrochemical activity that is believed to be suitable for advanced microsystem applications. (c) 2006 The Electrochemical Society.

On-chip growth of vertically aligned nitrogen-containing carbon nanotube (CNx NT) arrays was demonstrated. The nanotubes were grown by microwave plasma-enhanced chemical-vapor deposition on different types of silicon substrates (n, p, n(+),p(+)) using a few nanometer thick Fe layer as a catalyst and a Ti buffer layer. The effects of the Ti thickness on the electrochemical (EC) characteristics of the CN, NT arrays were studied. It was found that for a Ti thickness of 20 rim, while vertically aligned CNx NTs were produced on all Si substrates, an almost ideal Nerstian behavior was observed only on highly conductive n(+) and p(+) substrates. As the Ti buffer thickness increased to 200 nm, good electrical contacts were established at the bottom end of the CNx NTs and fast electron kinetics were then attainable on all kinds of Si substrates. Nevertheless, the use of thick buffer layers inhibited directional growth. Oxidation treatment of the catalyst Fe layer prior to nanotube growth proved efficient for achieving directional CNx NT formation. Pretreatment of the Ti buffer layer at a temperature of 800 degrees C, leading to the formation of TiSi2, was appropriate for achieving simultaneously enhanced current density and fast electron kinetics comparable to those of CNx NTs on bulk Ti electrodes. The Si-based micro-EC platform established in this work has superior current collection efficiency and is amenable for fundamental EC studies and energy applications. (c) 2006 American Vacuum Society.