An individual suspended graphene sheet was connected to a scanning tunneling microscopy probe inside a transmission electron
microscope, and Joule heated to high temperatures. At high temperatures and under electron beam irradiation, the few-layer
graphene sheets were removed layer-by-layer in the viewing area until a monolayer graphene was formed. The layer-by-layer
peeling was initiated at vacancies in individual graphene layers. The vacancies expanded to form nanometer-sized holes, which
then grew along the perimeter and propagated to both the top and bottom layers of a bilayer graphene joined by a bilayer edge.
The layer-by-layer peeling was induced by atom sublimation caused by Joule heating and facilitated by atom displacement caused
by high-energy electron irradiation, and may be harnessed to control the layer thickness of graphene for device applications.
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We show by molecular dynamics simulations that configuration-sensitive molecular spectroscopy can be realized on optimally
doped graphene sheets vibrated by an oscillatory electric field. High selectivity of the spectroscopy is achieved by maximizing
Coulombic binding between the detected molecule and a specific nest, formed for this molecule on the graphene sheet by substituting
selected carbon atoms with boron and nitrogen dopants. One can detect binding of different isomers to the nest from the frequency
shifts of selected vibrational modes of the combined system. As an illustrative example, we simulate detection of hexanitrostilbene
enantiomers in chiral nests formed on graphene.
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We present molecular dynamics simulation evidence for a freezing transition from liquid silicon to quasi-two-dimensional (quasi-2D)
bilayer silicon in a slit nanopore. This new quasi-2D polymorph of silicon exhibits a bilayer hexagonal structure in which
the covalent coordination number of every silicon atom is four. Quantum molecular dynamics simulations show that the stand-alone
bilayer silicon (without the confinement) is still stable at 400 K. Electronic band-structure calculations suggest that the
bilayer hexagonal silicon is a quasi-2D semimetal, similar to a graphene monolayer, but with an indirect zero band gap.
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We have studied the elastic deformation of freely suspended atomically thin sheets of muscovite mica, a widely used electrical insulator in its bulk form. Using an atomic force microscope, we carried out bending test experiments to determine the Young’s modulus and the initial pre-tension of mica nanosheets with thicknesses ranging from 14 layers down to just one bilayer. We found that their Young’s modulus is high (190 GPa), in agreement with the bulk value, which indicates that the exfoliation procedure employed to fabricate these nanolayers does not introduce a noticeable amount of defects. Additionally, ultrathin mica shows low pre-strain and can withstand reversible deformations up to tens of nanometers without breaking. The low pre-tension and high Young’s modulus and breaking force found in these ultrathin mica layers demonstrates their prospective use as a complement for graphene in applications requiring flexible insulating materials or as reinforcement in nanocomposites. 相似文献
An in situ chemical synthesis approach has been employed to prepare an Ag-chemically converted graphene (CCG) nanocomposite. The reduction
of graphene oxide sheets was accompanied by generation of Ag nanoparticles. The structure and composition of the nanocomposites
were confirmed by means of transmission electron microscopy (TEM), atomic force microscopy (AFM) and X-ray diffraction. TEM
and AFM results suggest a homogeneous distribution of Ag nanoparticles (5–10 nm in size) on CCG sheets. The intensities of
the Raman signals of CCG in such nanocomposites are greatly increased by the attached silver nanoparticles, i.e., there is
surface-enhanced Raman scattering activity. In addition, it was found that the antibacterial activity of free Ag nanoparticles
is retained in the nanocomposites, which suggests they can be used as graphene-based biomaterials.
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The controlled etching of graphite and graphene by catalytic hydrogenation is potentially a key engineering route for the
fabrication of graphene nanoribbons with atomic precision. The hydrogenation mechanism, though, remains poorly understood.
In this study we exploit the benefits of aberration-corrected high-resolution transmission electron microscopy to gain insight
to the hydrogenation reaction. The etch tracks are found to be commensurate with the graphite lattice. Catalyst particles
at the head of an etch channel are shown to be faceted and the angles between facets are multiples of 30°. Thus, the angles
between facets are also commensurate with the graphite lattice. In addition, the results of a post-annealing step suggest
that all catalyst particles—even if they are not involved in etching—are actively forming methane during the hydrogenation
reaction. Furthermore, the data point against carbon dissolution being a key mechanism during the hydrogenation process.
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We report a facile approach to synthesize narrow and long graphene nanoribbons (GNRs) by sonochemically cutting chemically
derived graphene sheets (GSs). The yield of GNRs can reach ∼5 wt% of the starting GSs. The resulting GNRs are several micrometers
in length, with ∼75% being single-layer, and ∼40% being narrower than 20 nm in width. A chemical tailoring mechanism involving
oxygen-unzipping of GSs under sonochemical conditions is proposed on the basis of experimental observations and previously
reported theoretical calculations; it is suggested that the formation and distribution of line faults on graphite oxide and
GSs play crucial roles in the formation of GNRs. These results open up the possibilities of the large-scale synthesis and
various technological applications of GNRs.
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We report synthesis windows for growth of millimeter-long ZnTe nanoribbons and ZnSe nanowires using vapor transport. By tuning
the local conditions at the growth substrate, high aspect ratio nanostructures can be synthesized. A Cu-ion immersion doping
method was applied, producing strongly p-type conduction in ZnTe and ionic conduction in ZnSe. These extreme aspect ratio
wide-bandgap semiconductors have great potential for high density nanostructured optoelectronic circuits.
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We have demonstrated a facile and efficient strategy for the fabrication of soluble reduced graphene oxide sheets (RGO) and
the preparation of titanium oxide (TiO2) nanoparticle-RGO composites using a modified one-step hydrothermal method. It was found that graphene oxide could be easily
reduced under solvothermal conditions with ascorbic acid as reductant, with concomitant growth of TiO2 particles on the RGO surface. The TiO2-RGO composite has been thoroughly characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction,
X-ray photoelectron spectroscopy, and thermogravimetric analysis. Microscopy techniques (scanning electron microscopy, atomic
force microscopy, and transmission electron microscopy) have been employed to probe the morphological characteristics as well
as to investigate the exfoliation of RGO sheets. The TiO2-RGO composite exhibited excellent photocatalysis of hydrogen evolution.
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We demonstrate the role of catalysts in the surface growth of single-walled carbon nanotubes (SWNTs) by reviewing recent progress
in the surface synthesis of SWNTs. Three effects of catalysts on surface synthesis are studied: type of catalyst, the relationship
between the size of catalyst particles and carbon feeding rates, and interactions between catalysts and substrates. Understanding
of the role of catalysts will contribute to our ability to control the synthesis of SWNTs on various substrates and facilitate
the fabrication of nanotube-based devices.
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We demonstrate the feasibility of using a carbon nanotube to nanopump molecules. Molecular dynamics simulations show that
the transport and ejection of a C20 molecule via a single-walled carbon nanotube (SWNT) can be achieved by a sustained mechanical actuation driven by two oscillating
tips. The optimal condition for nanopumping is found when the tip oscillation frequency and magnitude correlate to form quasi
steady-state mechanical wave propagation in the SWNT, so that the energy transfer process is optimal leading to maximal molecular
translational motion and minimal rotational motion. Our finding provides a potentially useful mechanism for using an SWNT
as a vehicle to deliver large drug molecules.
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The central goal of synthetic chemistry of colloidal nanocrystals at present is to discover functional materials. Such functional
materials should help mankind to meet the tough challenges brought by the rapid depletion of natural resources and the significant
increase of population with higher and higher living standards. With this thought in mind, this essay discusses the basic
guidelines for developing this new branch of synthetic chemistry, including rational synthetic strategies, functional performance,
and green chemistry principles.
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We report the synthesis of high magnetic moment CoFe nanoparticles via the diffusion of Co and Fe in core/shell structured
Co/Fe nanoparticles. In an organic solution, Co nanoparticles were coated with a layer of Fe to form a Co/Fe core/shell structure.
Further raising the solution temperature led to inter-diffusion of Co and Fe and formation of CoFe alloy nanoparticles. These
nanoparticles have high saturation magnetization of up to 192 emu/g CoFe and can be further stabilized by thermal annealing
at 600 °C.
Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.
These two authors made an equal contribution to the work. 相似文献
Facile dry decoration of graphene oxide sheets with aerosol Ag nanocrystals synthesized from an arc plasma source has been
demonstrated using an electrostatic force directed assembly technique at room temperature. The Ag nanocrystal-graphene oxide
hybrid structure was characterized by transmission electron microscopy (TEM) and selected area diffraction. The ripening of
Ag nanocrystals on a graphene oxide sheet was studied by consecutive TEM imaging of the same region on a sample after heating
in Ar at elevated temperatures of 100 °C, 200 °C, and 300 °C. The average size of Ag nanocrystals increased and the number
density decreased after the annealing process. In particular, migration and coalescence of Ag nanocrystals were observed at
a temperature as low as 100 °C, suggesting a van der Waals interaction between the Ag nanocrystal and the graphene oxide sheet.
The availability of affordable graphene-nanocrystal structures and their fundamental properties will open up new opportunities
for nanoscience and nanotechnology and accelerate their applications.
This article is published with open access at Springerlink.com 相似文献
The thermoelectric properties of individual solution-phase synthesized p-type PbSe nanowires have been examined. The nanowires
showed near degenerately doped charge carrier concentrations. Compared to the bulk, the PbSe nanowires exhibited a similar
Seebeck coefficient and a significant reduction in thermal conductivity in the temperature range 20 K to 300 K. Thermal annealing
of the PbSe nanowires allowed their thermoelectric properties to be controllably tuned by increasing their carrier concentration
or hole mobility. After optimal annealing, single PbSe nanowires exhibited a thermoelectric figure of merit (ZT) of 0.12 at
room temperature.
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Reliable ohmic contacts were established in order to study the strain sensitivity of nanowires and nanobelts. Significant
conductance increases of up to 113% were observed on bending individual ZnO nanowires or CdS nanobelts. This bending strain-induced
conductance enhancement was confirmed by a variety of bending measurements, such as using different manipulating tips (silicon,
glass or tungsten) to bend the nanowires or nanobelts, and is explained by bending-induced effective tensile strain based
on the principle of the piezoresistance effect.
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We analyze the chemical bonding in graphene using a fragmental approach, the adaptive natural density partitioning method,
electron sharing indices, and nucleus-independent chemical shift indices. We prove that graphene is aromatic, but its aromaticity
is different from the aromaticity in benzene, coronene, or circumcoronene. Aromaticity in graphene is local with two π-electrons
delocalized over every hexagon ring. We believe that the chemical bonding picture developed for graphene will be helpful for
understanding chemical bonding in defects such as point defects, single-, double-, and multiple vacancies, carbon adatoms,
foreign adatoms, substitutional impurities, and new materials that are derivatives of graphene.
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Graphene has many unique properties that make it an ideal material for fundamental studies as well as for potential applications.
Here we review recent results on the Raman spectroscopy and imaging of graphene. We show that Raman spectroscopy and imaging
can be used as a quick and unambiguous method to determine the number of graphene layers. The strong Raman signal of single
layer graphene compared to graphite is explained by an interference enhancement model. We have also studied the effect of
substrates, the top layer deposition, the annealing process, as well as folding (stacking order) on the physical and electronic
properties of graphene. Finally, Raman spectroscopy of epitaxial graphene grown on a SiC substrate is presented and strong
compressive strain on epitaxial graphene is observed. The results presented here are highly relevant to the application of
graphene in nano-electronic devices and help in developing a better understanding of the physical and electronic properties
of graphene.
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Finite-sized graphene sheets, such as graphene nanoislands (GNIs), are promising candidates for practical applications in graphene-based nanoelectronics. GNIs with well-defined zigzag edges are predicted to have spin-polarized edge-states similar to those of zigzag-edged graphene nanoribbons, which can achieve graphene spintronics. However, it has been reported that GNIs on metal substrates have no edge states because of interactions with the substrate.We used a combination of scanning tunneling microscopy, spectroscopy, and density functional theory calculations to demonstrate that the edge states of GNIs on an Ir substrate can be recovered by intercalating a layer of Si atoms between the GNIs and the substrate. We also found that the edge states gradually shift to the Fermi level with increasing island size. This work provides a method to investigate spin-polarized edge states in high-quality graphene nanostructures on a metal substrate.
We report graphene films composed mostly of one or two layers of graphene grown by controlled carbon precipitation on the
surface of polycrystalline Ni thin films during atmospheric chemical vapor deposition (CVD). Controlling both the methane
concentration during CVD and the substrate cooling rate during graphene growth can significantly improve the thickness uniformity.
As a result, one- or two- layer graphene regions occupy up to 87% of the film area. Single layer coverage accounts for 5%–11%
of the overall film. These regions expand across multiple grain boundaries of the underlying polycrystalline Ni film. The
number density of sites with multilayer graphene/graphite (>2 layers) is reduced as the cooling rate decreases. These films
can also be transferred to other substrates and their sizes are only limited by the sizes of the Ni film and the CVD chamber.
Here, we demonstrate the formation of films as large as 1 in2. These findings represent an important step towards the fabrication of large-scale high-quality graphene samples.
Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users. 相似文献