331 research outputs found
Long-Range Hydrophobic Attraction Between Graphene and Water/Oil Interfaces
Long-range hydrophobic attractions between mesoscopic surfaces in water play
an important role in many colloid and interface phenomena. Despite being
studied by several approaches, the origin of these forces has yet to be
adequately explained. While previous research has focused on solid/water/solid
and solid/water/air scenarios, we investigated a solid/water/liquid situation
to gain additional insight. We directly measured the long-range interactions
between a solid and a hydrophobic liquid separated by water using force
spectroscopy, where colloidal probes were coated with graphene oxide (GO) to
interact with immobilized heptane droplets in water. We detected attractions
with a range of ~0.5 {\mu}m that cannot be explained by standard
Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. When the GO was reduced to rGO
to become more hydrophobic, these forces increased in strength and ranged up to
1.2 {\mu}m. This suggests that the observed attractions result from long-range
hydrophobic forces. Based on our results, we propose air bubbles attached to
the colloidal probe and molecular rearrangement at the water/oil interface as
possible origins of the observed interactions. This knowledge will be useful to
understand and motivate the formation of emulsions using 2D materials and other
amphiphilic/hydrophobic particles
Cones, pringles, and grain boundary landscapes in graphene topology
A polycrystalline graphene consists of perfect domains tilted at angle
{\alpha} to each other and separated by the grain boundaries (GB). These nearly
one-dimensional regions consist in turn of elementary topological defects,
5-pentagons and 7-heptagons, often paired up into 5-7 dislocations. Energy
G({\alpha}) of GB computed for all range 0<={\alpha}<=Pi/3, shows a slightly
asymmetric behavior, reaching ~5 eV/nm in the middle, where the 5's and 7's
qualitatively reorganize in transition from nearly armchair to zigzag
interfaces. Analysis shows that 2-dimensional nature permits the off-plane
relaxation, unavailable in 3-dimensional materials, qualitatively reducing the
energy of defects on one hand while forming stable 3D-landsapes on the other.
Interestingly, while the GB display small off-plane elevation, the random
distributions of 5's and 7's create roughness which scales inversely with
defect concentration, h ~ n^(-1/2)Comment: 9 pages, 4 figure
Laser-induced etching of few-layer graphene synthesized by Rapid-Chemical Vapour Deposition on Cu thin films
The outstanding electrical and mechanical properties of graphene make it very
attractive for several applications, Nanoelectronics above all. However a
reproducible and non destructive way to produce high quality, large-scale area,
single layer graphene sheets is still lacking. Chemical Vapour Deposition of
graphene on Cu catalytic thin films represents a promising method to reach this
goal, because of the low temperatures (T < 900 Celsius degrees) involved during
the process and of the theoretically expected monolayer self-limiting growth.
On the contrary such self-limiting growth is not commonly observed in
experiments, thus making the development of techniques allowing for a better
control of graphene growth highly desirable. Here we report about the local
ablation effect, arising in Raman analysis, due to the heat transfer induced by
the laser incident beam onto the graphene sample.Comment: v1:9 pages, 8 figures, submitted to SpringerPlus; v2: 11 pages,
PDFLaTeX, 9 figures, revised peer-reviewed version resubmitted to
SpringerPlus; 1 figure added, figure 1 and 4 replaced,typos corrected,
"Results and discussion" section significantly extended to better explain
etching mechanism and features of Raman spectra, references adde
Mechanically Assisted Exfoliation and Functionalization of Thermally Converted Graphene Sheets
Published versio
Magnetic Properties of Single Transition-Metal Atom Absorbed Graphdiyne and Graphyne Sheet
The electronic and magnetic properties of single 3d transition-metal(TM) atom
(V, Cr, Mn, Fe, Co, and Ni) adsorbed graphdiyne (GDY) and graphyne (GY) are
systematically studied using first-principles calculations within the density
functional framework. We find that the adsorption of TM atom not only
efficiently modulates the electronic structures of GDY/GY system, but also
introduces excellent magnetic properties, such as half-metal and spin-select
half-semiconductor. Such modulation originates from the charge transfer between
TM adatom and the GDY/GY sheet as well as the electron redistribution of the TM
intra-atomic s, p, and d orbitals. Our results indicate that the TM adsorbed
GDY/GY are excellent candidates for spintronics.Comment: 8 pages, 7 figure
Probing the Thermal Deoxygenation of Graphene Oxide using High Resolution In Situ X-Ray based Spectroscopies
Despite the recent developments in Graphene Oxide due to its importance as a
host precursor of Graphene, the detailed electronic structure and its evolution
during the thermal reduction remain largely unknown, hindering its potential
applications. We show that a combination of high resolution in situ X-ray
photoemission and X-ray absorption spectroscopies offer a powerful approach to
monitor the deoxygenation process and comprehensively evaluate the electronic
structure of Graphene Oxide thin films at different stages of the thermal
reduction process. It is established that the edge plane carboxyl groups are
highly unstable, whereas carbonyl groups are more difficult to remove. The
results consistently support the formation of phenol groups through reaction of
basal plane epoxide groups with adjacent hydroxyl groups at moderate degrees of
thermal activation (~400 {\deg}C). The phenol groups are predominant over
carbonyl groups and survive even at a temperature of 1000 {\deg}C. For the
first time a drastic increase in the density of states (DOS) near the Fermi
level at 600 {\deg}C is observed, suggesting a progressive restoration of
aromatic structure in the thermally reduced graphene oxideComment: Pagona Papakonstantinou as Corresponding author, E-mail:
[email protected]
Computational studies for reduced graphene oxide in hydrogen-rich environment
We employ molecular dynamic simulations to study the reduction process of
graphene-oxide (GO) in a chemically active environment enriched with hydrogen.
We examine the concentration and pressure of hydrogen gas as a function of
temperature in which abstraction of oxygen is possible with minimum damage to
C-sp bonds hence preserving the integrity of the graphene sheet. Through
these studies we find chemical pathways that demonstrate beneficiary mechanisms
for the quality of graphene including formation of water as well as suppression
of carbonyl pair holes in favor of hydroxyl and epoxy formation facilitated by
hydrogen gas in the environment.Comment: 9 pages and 9 figures. Animations and movies are available at:
http://qmsimulatorgojpc.wordpress.com
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