87 research outputs found
Imaging and Dynamics of Light Atoms and Molecules on Graphene
Observing the individual building blocks of matter is one of the primary
goals of microscopy. The invention of the scanning tunneling microscope [1]
revolutionized experimental surface science in that atomic-scale features on a
solid-state surface could finally be readily imaged. However, scanning
tunneling microscopy has limited applicability due to restrictions, for
example, in sample conductivity, cleanliness, and data aquisition rate. An
older microscopy technique, that of transmission electron microscopy (TEM) [2,
3] has benefited tremendously in recent years from subtle instrumentation
advances, and individual heavy (high atomic number) atoms can now be detected
by TEM [4 - 7] even when embedded within a semiconductor material [8, 9].
However, detecting an individual low atomic number atom, for example carbon or
even hydrogen, is still extremely challenging, if not impossible, via
conventional TEM due to the very low contrast of light elements [2, 3, 10 -
12]. Here we demonstrate a means to observe, by conventional transmision
electron microscopy, even the smallest atoms and molecules: On a clean
single-layer graphene membrane, adsorbates such as atomic hydrogen and carbon
can be seen as if they were suspended in free space. We directly image such
individual adatoms, along with carbon chains and vacancies, and investigate
their dynamics in real time. These techniques open a way to reveal dynamics of
more complex chemical reactions or identify the atomic-scale structure of
unknown adsorbates. In addition, the study of atomic scale defects in graphene
may provide insights for nanoelectronic applications of this interesting
material.Comment: 9 pages manuscript and figures, 9 pages supplementary informatio
N-type graphene induced by dissociative H-2 adsorption at room temperature
Studies of the interaction between hydrogen and graphene have been increasingly required due to the indispensable modulation of the electronic structure of graphene for device applications and the possibility of using graphene as a hydrogen storage material. Here, we report on the behaviour of molecular hydrogen on graphene using the gate voltage-dependent resistance of single-, bi-, and multi-layer graphene sheets as a function of H-2 gas pressure up to 24 bar from 300 K to 345 K. Upon H-2 exposure, the charge neutrality point shifts toward the negative gate voltage region, indicating n-type doping, and distinct Raman signature changes, increases in the interlayer distance of multi-layer graphene, and a decrease in the d-spacing occur, as determined by TEM. These results demonstrate the occurrence of dissociative H-2 adsorption due to the existence of vacancy defects on graphene.open12
Visualizing chemical states and defects induced magnetism of graphene oxide by spatially-resolved-X-ray microscopy and spectroscopy
[[abstract]]This investigation studies the various magnetic behaviors of graphene oxide (GO) and reduced
graphene oxides (rGOs) and elucidates the relationship between the chemical states that involve
defects therein and their magnetic behaviors in GO sheets. Magnetic hysteresis loop reveals that the
GO is ferromagnetic whereas photo-thermal moderately reduced graphene oxide (M-rGO) and heavily
reduced graphene oxide (H-rGO) gradually become paramagnetic behavior at room temperature.
Scanning transmission X-ray microscopy and corresponding X-ray absorption near-edge structure
spectroscopy were utilized to investigate thoroughly the variation of the C 2p(π*) states that are
bound with oxygen-containing and hydroxyl groups, as well as the C 2p(σ*)-derived states in flat
and wrinkle regions to clarify the relationship between the spatially-resolved chemical states and
the magnetism of GO, M-rGO and H-rGO. The results of X-ray magnetic circular dichroism further
support the finding that C 2p(σ*)-derived states are the main origin of the magnetism of GO. Based
on experimental results and first-principles calculations, the variation in magnetic behavior from GO
to M-rGO and to H-rGO is interpreted, and the origin of ferromagnetism is identified as the C 2p(σ*)-
derived states that involve defects/vacancies rather than the C 2p(π*) states that are bound with
oxygen-containing and hydroxyl groups on GO sheets.[[notice]]補正完
Edge-Functionalization of Pyrene as a Miniature Graphene via Friedel–Crafts Acylation Reaction in Poly(Phosphoric Acid)
The feasibility of edge-functionalization of graphite was tested via the model reaction between pyrene and 4-(2,4,6-trimethylphenyloxy)benzamide (TMPBA) in poly(phosphoric acid) (PPA)/phosphorous pentoxide (P2O5) medium. The functionalization was confirmed by various characterization techniques. On the basis of the model study, the reaction condition could be extended to the edge-functionalization of graphite with TMPBA. Preliminary results showed that the resultant TMPBA-grafted graphite (graphite-g-TMPBA) was found to be readily dispersible in N-methyl-2-pyrrolidone (NMP) and can be used as a precursor for edge-functionalized graphene (EFG)
Electronic Structures of Porous Nanocarbons
We use large scale ab-initio calculations to describe electronic structures
of graphene, graphene nanoribbons, and carbon nanotubes periodically perforated
with nanopores. We disclose common features of these systems and develop a
unified picture that permits us to analytically predict and systematically
characterize metal-semiconductor transitions in nanocarbons with superlattices
of nanopores of different sizes and types. These novel materials with highly
tunable band structures have numerous potential applications in electronics,
light detection, and molecular sensing.Comment: 7 pages, 8 figure
Oxidation behavior of graphene-coated copper at intrinsic graphene defects of different origins
The development of ultrathin barrier films is vital to the advanced semiconductor industry. Graphene appears to hold promise as a protective coating; however, the polycrystalline and defective nature of engineered graphene hinders its practical applications. Here, we investigate the oxidation behavior of graphene-coated Cu foils at intrinsic graphene defects of different origins. Macro-scale information regarding the spatial distribution and oxidation resistance of various graphene defects is readily obtained using optical and electron microscopies after the hot-plate annealing. The controlled oxidation experiments reveal that the degree of structural deficiency is strongly dependent on the origins of the structural defects, the crystallographic orientations of the underlying Cu grains, the growth conditions of graphene, and the kinetics of the graphene growth. The obtained experimental and theoretical results show that oxygen radicals, decomposed from water molecules in ambient air, are effectively inverted at Stone-Wales defects into the graphene/Cu interface with the assistance of facilitators
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