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Toward a more scientific science

09/27/2018 - 12:59

Climb atop shoulders and wait for funerals. That, suggested Newton and then Planck, is how science advances (more or less). We've come far since then, but many notions about how people and practices, policies, and resources influence the course of science are still more rooted in traditions and intuitions than in evidence. We can and must do better, lest we resign ourselves to “intuition-based policy” when making decisions and investments aimed at driving scientific progress. Science invited experts to highlight key aspects of the scientific enterprise that are steadily yielding to empirical investigation—and to explain how Newton and Planck got it right (and Einstein got it wrong). —Brad Wible


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4 Water-evaporation-induced electricity with nanostructured carbon materials

01/30/2017 - 11:26

Water evaporation is a ubiquitous natural process that harvests thermal energy from the ambient environment. It has previously been utilized in a number of applications including the synthesis of nanostructures and the creation of energyharvesting
devices. Here, we show that water evaporation from the surface of a variety of nanostructured carbon materials can be used to generate electricity. We find that evaporation from centimetre-sized carbon black sheets can reliably generate
sustained voltages of up to 1 V under ambient conditions. The interaction between the water molecules and the carbon layers and moreover evaporation-induced water flow within the porous carbon sheets are thought to be key to the voltage
generation. This approach to electricity generation is related to the traditional streaming potential, which relies on driving ionic solutions through narrow gaps, and the recently reported method of moving ionic solutions across graphene surfaces, but as it exploits the natural process of evaporation and uses cheap carbon black it could offer advantages in the development of practical devices.

Hydroelectric generator from transparent flexible zinc oxide nanofilms

11/25/2016 - 11:06

Harvesting wave energy based on waving potential, a newly found electrokinetic effect, is attractive but limited mainly to monolayer graphene. Here we demonstrate that moving a transparent flexible ZnO nanofilm across the surface of ionic solutions can generate electricity. The generated electricity increases linearly with the
moving velocity with an open-circuit voltage up to tens of millivolt and a short-circuit current at the order of microampere. The harvested electricity can be efficiently scaled up through series and parallel connections. Theoretical simulations show that it is the proper electrical property that endows the ZnO nanofilm with the outstanding capacity in harvesting the wave energy.

Tunable electronic and magneticproperties of two-dimensionalmaterials and theirone-dimensional derivatives

03/15/2016 - 11:16

Low-dimensional materials exhibit many exceptional properties and functional-ities which can be efficiently tuned by externally applied force or fields. Here wereview the current status of research on tuning the electronic and magnetic prop-erties of low-dimensional carbon, boron nitride, metal-dichalcogenides, phos-phorene nanomaterials by applied engineering strain, external electric field andinteraction with substrates, etc, with particular focus on the progress of computa-tional methods and studies. We highlight the similarities and differences of theproperty modulation among one- and two-dimensional nanomaterials. Recent breakthroughs in experimental demonstration of the tunable functionalities intypical nanostructures are also presented. Finally, prospective and challenges forapplying the tunable properties into functional devices are discussed.

Large-Area, Periodic, Hexagonal Wrinkles on Nanocrystalline Graphitic Film

08/25/2015 - 15:28

Sinusoidal wrinkles develop in compressively stressed film as a means to release stored elastic energy. Here, a simple way to fabricate large-area, periodic, hexagonal wrinkled pattern on nanocrystalline graphitic films grown on c-plane sapphire (<50 nm thick) by the spontaneous delamination–buckling of the as-grown film during cooling is reported. According to the continuum mechanics calculation, strain-relief pattern adopting the hexagonal wrinkled pattern has a lower elastic energy than that of the telephone cord wrinkle at thickness regime below 50 nm. A high-fidelity transfer method is developed to transfer the hexagonal wrinkled films onto arbitrary substrates. Nanoindentation studies show that hexagonal wrinkle film engineered this way may act as shock absorber. The hexagonal wrinkled carbon film is able to selectively promote the differentiation of human mesenchymal stem cell toward the osteogenic lineage in the absence of osteogenic inducing medium.

Large Single-Crystal Hexagonal Boron Nitride Monolayer Domains with Controlled Morphology and Straight Merging Boundaries

06/15/2015 - 10:13

Hexagonal boron nitride monolayers with domain sizes up to 700 μm2 and geometry from triangle to hexagon are fabricated through a refined control over the precursor and morphology of the copper substrate. Hydrogen etching is shown to tailor the h-BN monolayers precisely along the grain boundaries, providing their morphology over micro­meter scale and a new avenue toward fabricating nanoribbons.

Low-voltage Driven Graphene Foam Thermoacoustic Speaker

06/14/2015 - 21:26

A low-voltage-driven thermoacoustic speaker is fabricated using graphene foams synthesized by a chemical vapor deposition method. When an audio signal is applied to the speaker, sound waves are produced due to the periodicity of air vibrations induced by Joule heating.

A low-voltage-driven thermoacoustic speaker is fabricated by W. Guo and co-workers using graphene foams synthesized by a chemical vapor deposition method. When an audio signal is applied to the speaker, sound waves are produced due to the periodicity of air vibrations induced by Joule heating. With the feasible tunability in structure and thermoacoustic performance, the graphene foam-based thermoacoustic speaker is shown to be promising for applications requiring flexible or ultrasonic acoustic devices

2D materials: Metallic when narrow

06/04/2014 - 13:22

Subnanometre metallic wires can be engineered from semiconducting sheets of transition-metal dichalcogenides by means of a focused electron beam.

Reducing the size of a crystal to the nanoscale can lead to a rearrangement of its atomic lattice and the creation of new material properties. Such rearrangements have been observed before in thin films and narrow wires fabricated from bulk materials of a single element1, 2. The use of materials made from more than one element has the potential to offer additional degrees of freedom because the composition of the crystals can also be modified3, and the atomic rearrangement of such structures has already been investigated using top-down methodologies such as electron-beam lithography4. Molybdenum sulphide ribbons with a width of around 0.35 nm have, for example, been fabricated by creating holes in a MoS2 sheet using electron irradiation in a transmission electron microscope (TEM)4. Writing in Nature Nanotechnology, Junhao Lin, Wu Zhou and colleagues now report the fabrication of subnanometre wires in MoS2 and other semiconducting transition-metal dichalcogenide sheets, and show that these nanowires are metallic5.

Bending Poisson Effect in Two-Dimensional Crystals

05/21/2014 - 13:35

As the Poisson effect formulates, lateral strains in a material can be caused by a uniaxial stress in the perpendicular direction, but no net lateral strain should be induced in a thin homogeneous elastic plate subjected to a pure bending load. Here, we demonstrated by ab initio simulations that significant exotic lateral strains can be induced by pure bending in two-dimensional crystals, in which the lateral components of chemical bonds can respond to bending curvature directly. The bending Poisson ratio, defined as the ratio of lateral strain to the curvature, is a function of curvature depending on chemical constitution, bonding structure, and atomic interaction of the crystal, and is anisotropic.

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Waving potential in graphene

05/06/2014 - 13:44

Nanoscale materials offer much promise in the pursuit of high-efficient energy conversion technology owing to their exceptional sensitivity to external stimulus. In particular, experiments have demonstrated that flowing water over carbon nanotubes can generate electric voltages. However, the reported flow-induced voltages are in wide discrepancy and the proposed mechanisms remain conflictive. Here we find that moving a liquid–gas boundary along a piece of graphene can induce a waving potential of up to 0.1 V. The potential is proportional to the moving velocity and the graphene length inserted into ionic solutions, but sharply decreases with increasing graphene layers and vanishes in other materials. This waving potential arises from charge transfer in graphene driven by a moving boundary of an electric double layer between graphene and ionic solutions. The results reveal a unique electrokinetic phenomenon and open prospects for functional sensors, such as tsunami monitors.

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