5 research outputs found
Ice Nanoribbons Confined in Uniaxially Distorted Carbon Nanotubes
Water confined inside
nanopores exhibits unusual static and dynamic
properties that depend on the pore size, pore topology, and hydrophobicity
and roughness of the pore walls. The properties also depend on the
geometrical shape of the pore cross sections. Here, we investigated
water inside distorted single-wall carbon nanotubes (SWCNTs) by means
of classical molecular dynamics calculations, over a temperature range
of 100–350 K. SWCNTs, which provide ideal one-dimensional cylindrical
pores with atomically smooth nonpolar walls, were uniaxially compressed
in a direction perpendicular to the SWCNT axes with a deformation
ratio γ up to 60%, where γ represents the ratio of deformation
amount to the initial SWCNT diameter <i>D</i>. With increasing
γ in an SWCNT with <i>D</i> = 1.24 nm, a hexagonal
ice nanotube was converted to the liquid state with high water mobility
down to 200 K and then to a new form of ice, ice nanoribbon, consisting
of four ferroelectric water chains. In an SWCNT with <i>D</i> = 1.51 nm, on the other hand, the water was converted to an ice
nanoribbon with five ferroelectric water chains from the liquid state.
It was demonstrated that the application of uniaxial pressure is a
useful technique to control water properties, such as dielectricity,
mobilities, and structures
Tuning of the Thermoelectric Properties of One-Dimensional Material Networks by Electric Double Layer Techniques Using Ionic Liquids
We report across-bandgap p-type and
n-type control over the Seebeck
coefficients of semiconducting single-wall carbon nanotube networks
through an electric double layer transistor setup using an ionic liquid
as the electrolyte. All-around gating characteristics by electric
double layer formation upon the surface of the nanotubes enabled the
tuning of the Seebeck coefficient of the nanotube networks by the
shift in gate voltage, which opened the path to Fermi-level-controlled
three-dimensional thermoelectric devices composed of one-dimensional
nanomaterials
Single Chirality Extraction of Single-Wall Carbon Nanotubes for the Encapsulation of Organic Molecules
The hollow inner spaces of single-wall carbon nanotubes
(SWCNTs)
can confine various types of molecules. Many remarkable phenomena
have been observed inside SWCNTs while encapsulating organic molecules
(peapods). However, a mixed electronic structure state of the surrounding
SWCNTs has impeded a detailed understanding of the physical/chemical
properties of peapods and their device applications. We present a
single-chirality purification method for SWCNTs that can encapsulate
organic molecules. A single-chiral state of (11,10) SWCNTs with a
diameter of 1.44 nm, which is large enough for molecular encapsulation,
was obtained after a two-step purification method: metal-semiconductor
sorting and cesium-chloride sorting. The encapsulation of C<sub>60</sub> to the (11,10) SWCNTs was also succeeded, promising a route toward
single-chirality peapod devices
Selective Formation of Zigzag Edges in Graphene Cracks
We report the thermally induced unconventional cracking of graphene to generate zigzag edges. This crystallography-selective cracking was observed for as-grown graphene films immediately following the cooling process subsequent to chemical vapor deposition (CVD) on Cu foil. Results from Raman spectroscopy show that the crack-derived edges have smoother zigzag edges than the chemically formed grain edges of CVD graphene. Using these cracks as nanogaps, we were also able to demonstrate the carrier tuning of graphene through the electric field effect. Statistical analysis of visual observations indicated that the crack formation results from uniaxial tension imparted by the Cu substrates together with the stress concentration at notches in the polycrystalline graphene films. On the basis of simulation results using a simplified thermal shrinkage model, we propose that the cooling-induced tension is derived from the transient lattice expansion of narrow Cu grains imparted by the thermal shrinkage of adjacent Cu grains
Growth and Optical Properties of High-Quality Monolayer WS<sub>2</sub> on Graphite
Atomic-layer transition metal dichalcogenides (TMDCs) have attracted appreciable interest due to their tunable band gap, spin-valley physics, and potential device applications. However, the quality of TMDC samples available still poses serious problems, such as inhomogeneous lattice strain, charge doping, and structural defects. Here, we report on the growth of high-quality, monolayer WS<sub>2</sub> onto exfoliated graphite by high-temperature chemical vapor deposition (CVD). Monolayer-grown WS<sub>2</sub> single crystals present a uniform, single excitonic photoluminescence peak with a Lorentzian profile and a very small full-width at half-maximum of 21 meV at room temperature and 8 meV at 79 K. Furthermore, in these samples, no additional peaks are observed for charged and/or bound excitons, even at low temperature. These optical responses are completely different from the results of previously reported TMDCs obtained by mechanical exfoliation and CVD. Our findings indicate that the combination of high-temperature CVD with a cleaved graphite surface is an ideal condition for the growth of high-quality TMDCs, and such samples will be essential for revealing intrinsic physical properties and for future applications