Korea Research Institute of Standards and Science

Significant enhancement in mechanical stiffness (10-200%) and fracture strength (approximately 50%) of graphene oxide paper, a novel paperlike material made from individual graphene oxide sheets, can be achieved upon modification with a small amount (less than 1 wt %) of Mg(2+) and Ca(2+). These results can be readily rationalized in terms of the chemical interactions between the functional groups of the graphene oxide sheets and the divalent metals ions. While oxygen functional groups on the basal planes of the sheets and the carboxylate groups on the edges can both bond to Mg(2+) and Ca(2+), the main contribution to mechanical enhancement of the paper comes from the latter.

ADVERTISEMENT RETURN TO ISSUEPREVReviewNEXTPorous Anodic Aluminum Oxide: Anodization and Templated Synthesis of Functional NanostructuresWoo Lee*†‡ and Sang-Joon Park†View Author Information† Korea Research Institute of Standards and Science (KRISS), Yuseong, 305-340 Daejeon, Korea‡ Department of Nano Science, University of Science and Technology (UST), Yuseong, 305-333 Daejeon, Korea*E-mail: [email protected]Cite this: Chem. Rev. 2014, 114, 15, 7487–7556Publication Date (Web):June 13, 2014Publication History Received2 January 2014Published online13 June 2014Published inissue 13 August 2014https://pubs.acs.org/doi/10.1021/cr500002zhttps://doi.org/10.1021/cr500002zreview-articleACS PublicationsCopyright © 2014 American Chemical SocietyRequest reuse permissionsArticle Views34157Altmetric-Citations1054LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Aluminum,Anodization,Electrolytes,Layers,Oxides Get e-Alerts

Field electron emission from vertically well-aligned zinc oxide (ZnO) nanowires, which were grown by the vapor deposition method at a low temperature of 550 °C, was investigated. The high-purity ZnO nanowires showed a single crystalline wurtzite structure. The turn-on voltage for the ZnO nanowires was found to be about 6.0 V/μm at current density of 0.1 μA/cm2. The emission current density from the ZnO nanowires reached 1 mA/cm2 at a bias field of 11.0 V/μm, which could give sufficient brightness as a field emitter in a flat panel display. Therefore, the well-aligned ZnO nanowires grown at such low temperature can promise the application of a glass-sealed flat panel display in a near future.

Nanotechnology has opened new and exhilarating opportunities for exploring glucose biosensing applications of the newly prepared nanostructured materials. Nanostructured metal-oxides have been extensively explored to develop biosensors with high sensitivity, fast response times, and stability for the determination of glucose by electrochemical oxidation. This article concentrates mainly on the development of different nanostructured metal-oxide [such as ZnO, Cu(I)/(II) oxides, MnO(2), TiO(2), CeO(2), SiO(2), ZrO(2,) and other metal-oxides] based glucose biosensors. Additionally, we devote our attention to the operating principles (i.e., potentiometric, amperometric, impedimetric and conductometric) of these nanostructured metal-oxide based glucose sensors. Finally, this review concludes with a personal prospective and some challenges of these nanoscaled sensors.

Graphene provides outstanding properties that can be integrated into various flexible and stretchable electronic devices in a conventional, scalable fashion. The mechanical, electrical, and optical properties of graphene make it an attractive candidate for applications in electronics, energy-harvesting devices, sensors, and other systems. Recent research progress on graphene-based flexible and stretchable electronics is reviewed here. The production and fabrication methods used for target device applications are first briefly discussed. Then, the various types of flexible and stretchable electronic devices that are enabled by graphene are discussed, including logic devices, energy-harvesting devices, sensors, and bioinspired devices. The results represent important steps in the development of graphene-based electronics that could find applications in the area of flexible and stretchable electronics.

According to quantum mechanics, a harmonic oscillator can never be completely at rest. Even in the ground state, its position will always have fluctuations, called the zero-point motion. Although the zero-point fluctuations are unavoidable, they can be manipulated. Using microwave frequency radiation pressure, we have manipulated the thermal fluctuations of a micrometer-scale mechanical resonator to produce a stationary quadrature-squeezed state with a minimum variance of 0.80 times that of the ground state. We also performed phase-sensitive, back-action evading measurements of a thermal state squeezed to 1.09 times the zero-point level. Our results are relevant to the quantum engineering of states of matter at large length scales, the study of decoherence of large quantum systems, and for the realization of ultrasensitive sensing of force and motion.

The modified embedded-atom method, a first nearest-neighbor semiempirical model for atomic potentials, can describe the physical properties of a wide range of elements and alloys with various lattice structures. However, the model is not quite successful for bcc metals in that it predicts the order among the size of low index surface energies incorrectly and that it generates a structure more stable than bcc for some bcc metals. In order to remove the problems, the formalism has been extended so that the second nearest neighbor interactions are taken into consideration. New parameters for Fe and comparisons between calculated and experimental physical properties of Fe are presented.

The second nearest-neighbor modified embedded atom method (MEAM) [Phys. Rev. B 62, 8564 (2000)], developed in order to solve problems of the original first nearest-neighbor MEAM on bcc metals, has now been applied to all bcc transition metals, Fe, Cr, Mo, W, V, Nb, and Ta. The potential parameters could be determined empirically by fitting to $(\ensuremath{\partial}B/\ensuremath{\partial}P),$ elastic constants, structural energy differences among bcc, fcc and hcp structures, vacancy-formation energy, and surface energy. Various physical properties of individual elements, including elastic constants, structural properties, point-defect properties, surface properties, and thermal properties were calculated and compared with experiments or high level calculations so that the reliability of the present empirical atomic-potential formalism can be evaluated. It is shown that the present potentials reasonably reproduce nonfitted properties of the bcc transition metals, as well as the fitted properties. The effect of the size of radial cutoff distance on the calculation and the compatibility with the original first nearest-neighbor MEAM that has been successful for fcc, hcp, and other structures are also discussed.

BACKGROUND: The electrochemical biosensor is one of the typical sensing devices based on transducing the biochemical events to electrical signals. In this type of sensor, an electrode is a key component that is employed as a solid support for immobilization of biomolecules and electron movement. Thanks to numerous nanomaterials that possess the large surface area, synergic effects are enabled by improving loading capacity and the mass transport of reactants for achieving high performance in terms of analytical sensitivity. MAIN BODY: We categorized the current electrochemical biosensors into two groups, carbon-based (carbon nanotubes and graphene) and non-carbon-based nanomaterials (metallic and silica nanoparticles, nanowire, and indium tin oxide, organic materials). The carbon allotropes can be employed as an electrode and supporting scaffolds due to their large active surface area as well as an effective electron transfer rate. We also discussed the non-carbon nanomaterials that are used as alternative supporting components of the electrode for improving the electrochemical properties of biosensors. CONCLUSION: Although several functional nanomaterials have provided the innovative solid substrate for high performances, developing on-site version of biosensor that meets enough sensitivity along with high reproducibility still remains a challenge. In particular, the matrix interference from real samples which seriously affects the biomolecular interaction still remains the most critical issues that need to be solved for practical aspect in the electrochemical biosensor.

Wearable strain sensors for human motion detection are being highlighted in various fields such as medical, entertainment and sports industry. In this paper, we propose a new type of stretchable strain sensor that can detect both tensile and compressive strains and can be fabricated by a very simple process. A silver nanoparticle (Ag NP) thin film patterned on the polydimethylsiloxane (PDMS) stamp by a single-step direct transfer process is used as the strain sensing material. The working principle is the change in the electrical resistance caused by the opening/closure of micro-cracks under mechanical deformation. The fabricated stretchable strain sensor shows highly sensitive and durable sensing performances in various tensile/compressive strains, long-term cyclic loading and relaxation tests. We demonstrate the applications of our stretchable strain sensors such as flexible pressure sensors and wearable human motion detection devices with high sensitivity, response speed and mechanical robustness.

There has been strong demand for novel nonvolatile memory technology for low-cost, large-area, and low-power flexible electronics applications. Resistive memories based on metal oxide thin films have been extensively studied for application as next-generation nonvolatile memory devices. However, although the metal oxide based resistive memories have several advantages, such as good scalability, low-power consumption, and fast switching speed, their application to large-area flexible substrates has been limited due to their material characteristics and necessity of a high-temperature fabrication process. As a promising nonvolatile memory technology for large-area flexible applications, we present a graphene oxide based memory that can be easily fabricated using a room temperature spin-casting method on flexible substrates and has reliable memory performance in terms of retention and endurance. The microscopic origin of the bipolar resistive switching behavior was elucidated and is attributed to rupture and formation of conducting filaments at the top amorphous interface layer formed between the graphene oxide film and the top Al metal electrode, via high-resolution transmission electron microscopy and in situ X-ray photoemission spectroscopy. This work provides an important step for developing understanding of the fundamental physics of bipolar resistive switching in graphene oxide films, for the application to future flexible electronics.

Monodisperse spherical Ni nanoparticles with diameters of 2 nm, 5 nm, and 7 nm were synthesized from the thermal decomposition of a Ni–oleylamine complex. Ni nanocrystal superlattices were generated via the controlled evaporation of solvent (see Figure). The nanoparticles were successfully used as catalysts for the Suzuki coupling reaction, and were readily oxidized to produce NiO nanoparticles.

Recently, the anomalous photovoltaic (PV) effect in BiFeO3 (BFO) thin films, which resulted in open circuit voltages (Voc) considerably larger than the band gap of the material, has generated a revival of the entire field of photoferroelectrics. Here, via temperature-dependent PV studies, we prove that the bulk photovoltaic (BPV) effect, which has been studied in the past for many non-centrosymmetric materials, is at the origin of the anomalous PV effect in BFO films. Moreover, we show that irrespective of the measurement geometry, Voc as high as 50 V can be achieved by controlling the conductivity of domain walls (DW). We also show that photoconductivity of the DW is markedly higher than in the bulk of BFO. The origin of the abnormal photovoltaic effect in bismuth ferrite thin films, which causes voltages larger than the band gap, is poorly understood. Bhatnagar et al.show that this effect can be attributed to a bulk photovoltaic effect and that it can be enhanced by controlling domain wall conductivity.

Chemically modified graphene (CMG) nanoplatelets have shown great promise in various applications due to their electrical properties and high surface area. Chemical doping is one of the most effective methods to tune the electronic properties of graphene materials. In this work, novel B-doped nanoplatelets (borane-reduced graphene oxide, B-rG-O) were produced on a large scale via the reduction of graphene oxide by a borane-tetrahydrofuran adduct under reflux, and their use for supercapacitor electrodes was studied. This is the first report on the production of B-doped graphene nanoplatelets from a solution process and on the use of B-doped graphene materials in supercapacitors. The B-rG-O had a high specific surface area of 466 m(2)/g and showed excellent supercapacitor performance including a high specific capacitance of 200 F/g in aqueous electrolyte as well as superior surface area-normalized capacitance to typical carbon-based supercapacitor materials and good stability after 4500 cycles. Two- and three-electrode cell measurements showed that energy storage in the B-rG-O supercapacitors was contributed by ion adsorption on the surface of the nanoplatelets in addition to electrochemical redox reactions.

We have developed a simple approach for the large-scale synthesis of water-soluble green carbon nanodots (G-dots) from many kinds of large food waste-derived sources. About 120 g of G-dots per 100 kg of food waste can be synthesized using our simple and environmentally friendly synthesis approach. The G-dots exhibit a high degree of solubility in water because of the abundant oxygen-containing functional groups around their surface. The narrow band of photoluminescence emission (400-470 nm) confirms that the size of the G-dots (∼4 nm) is small because of a similar quantum effects and emission traps on the surfaces. The G-dots have excellent photostability; their photoluminescence intensity decreases slowly (∼8%) under continuous excitation with a Xe lamp for 10 days. We carried out cell viability assay to assess the effect of cytotoxicity by introducing G-dots in cells such as Chinese hamster ovary cells (CHO-K1), mouse muscle cells (C2C12), and African green monkey kidney cells (COS-7), up to a concentration of 2 mg mL(-1) for 24 h. Due to their high photostability and low cytotoxicity, these G-dots are excellent probes for in vitro bioimaging. Moreover, the byproducts (not including G-dots) of G-dot synthesis from large food-waste derived sources promoted the growth and development of seedlings germinated on 3DW-supplemented gauze. Because of the combined advantages of green synthesis, high aqueous stability, high photostability, and low cytotoxicity, the G-dots show considerable promise in various areas, including biomedical imaging, solution state optoelectronics, and plant seed germination and/or growth.

Digital PCR (dPCR) has developed considerably since the publication of the Minimum Information for Publication of Digital PCR Experiments (dMIQE) guidelines in 2013, with advances in instrumentation, software, applications, and our understanding of its technological potential. Yet these developments also have associated challenges; data analysis steps, including threshold setting, can be difficult and preanalytical steps required to purify, concentrate, and modify nucleic acids can lead to measurement error. To assist independent corroboration of conclusions, comprehensive disclosure of all relevant experimental details is required. To support the community and reflect the growing use of dPCR, we present an update to dMIQE, dMIQE2020, including a simplified dMIQE table format to assist researchers in providing key experimental information and understanding of the associated experimental process. Adoption of dMIQE2020 by the scientific community will assist in standardizing experimental protocols, maximize efficient utilization of resources, and further enhance the impact of this powerful technology.

We report direct measurements of electrical transport through poly(dA)-poly(dT) and poly(dG)-poly(dC) DNA molecules containing identical base pairs. The observed experimental results suggest that electrical transport through DNA molecules occurs by polaron hopping. We have also investigated the effect of gate voltage on the current-voltage curve. It demonstrates the possibility of a DNA field-effect transistor operating at room temperature. Moreover, the gate-voltage dependent transport measurements show that poly(dA)-poly(dT) behaves as an n-type semiconductor, whereas poly(dG)-poly(dC) behaves as a p-type semiconductor.

We synthesized Ni/Pd core/shell nanoparticles from the consecutive thermal decomposition of metal-surfactant complexes. The nanoparticle catalyst was atom-economically applied for various Sonogashira coupling reactions.

Quantum-sized ZnS nanocrystals with quasi-spherical and rod shapes were synthesized by the aging reaction mixtures containing diethylzinc, sulfur, and amine. Uniform-sized ZnS nanorods with the average dimension of 5 nm x 21 nm, along with a small fraction of 5 nm-sized quasi-spherical nanocrystals, were synthesized by adding diethylzinc to a solution containing sulfur and hexadecylamine at 125 degrees C, followed by aging at 300 degrees C. Subsequent secondary aging of the nanocrystals in oleylamine at 60 degrees C for 24 h produced nearly pure nanorods. Structural characterizations showed that these nanorods had a cubic zinc blende structure, whereas the fabrication of nanorods with this structure has been known to be difficult to achieve via colloidal chemical synthetic routes. High-resolution TEM images and reaction studies demonstrated that these nanorods are formed from the oriented attachment of quasi-spherical nanocrystals. Monodisperse 5 nm-sized quasi-spherical ZnS nanocrystals were separately synthesized by adding diethylzinc to sulfur dissolved in a mixture of hexadecylamine and 1-octadecene at 45 degrees C, followed by aging at 300 degrees C. When oleic acid was substituted for hexadecylamine and all other procedures were unchanged, we obtained 10 nm-sized quasi-spherical ZnS nanocrystals, but with broad particle size distribution. These two different-sized quasi-spherical ZnS nanocrystals showed different proportions of zinc blende and wurtzite crystal structures. The UV absorption spectra and photoluminescence excitation spectra of the 5 nm ZnS quasi-spherical nanocrystals and of the nanorods showed a blue-shift from the bulk band-gap, thus showing a quantum confinement effect. The photoluminescence spectra of the ZnS nanorods and quasi-spherical nanocrystals showed a well-defined excitonic emission feature and size- and shape-dependent quantum confinement effects.

Abstract Recently SnSe, a layered chalcogenide material, has attracted a great deal of attention for its excellent p-type thermoelectric property showing a remarkable ZT value of 2.6 at 923 K. For thermoelectric device applications, it is necessary to have n-type materials with comparable ZT value. Here, we report that n-type SnSe single crystals were successfully synthesized by substituting Bi at Sn sites. In addition, it was found that the carrier concentration increases with Bi content, which has a great influence on the thermoelectric properties of n-type SnSe single crystals. Indeed, we achieved the maximum ZT value of 2.2 along b axis at 733 K in the most highly doped n-type SnSe with a carrier density of −2.1 × 10 19 cm −3 at 773 K.