498 research outputs found
Elastomeric carbon nanotube circuits for local strain sensing
We use elastomeric polydimethylsiloxane substrates to strain single-walled
carbon nanotubes and modulate their electronic properties, with the aim of
developing flexible materials that can sense local strain. We demonstrate
micron-scale nanotube devices that can be cycled repeatedly through strains as
high as 20% while providing reproducible local strain transduction by via the
device resistance. We also compress individual nanotubes, and find they undergo
an undulatory distortion with a characteristic spatial period of 100-200 nm.
The observed period can be understood by the mechanical properties of nanotubes
and the substrate in conjunction with continuum elasticity theory. These could
potentially be used to create superlattices within individual nanotubes,
enabling novel devices and applications
Plastic deformations in mechanically strained single-walled carbon nanotubes
Antiferromagnetic manipulation was used to controllably stretch individual metallic single-walled carbon nanotubes (SWNT's). We have found that SWNT's can sustain elongations as great as 30% without breaking. Scanned gate microscopy and transport measurements were used to probe the effects of the mechanical strain on the SWNT electronic properties, which revealed a strain-induced increase in intra-tube electronic scattering above a threshold strain of ~5–10 %. These findings are consistent with theoretical calculations predicting the onset of plastic deformation and defect formation in carbon nanotubes
Scanning Tunneling Spectroscopic Studies of the Effects of Dielectrics and Metallic Substrates on the Local Electronic Characteristics of Graphene
Atomically resolved imaging and spectroscopic characteristics of
graphene grown by chemical vapor deposition (CVD) on copper
foils are investigated and compared with those of mechanical
exfoliated graphene on SiO_2. For exfoliated graphene, the local
spectral deviations from ideal behavior may be attributed to strain
induced by the SiO_2 substrate. For CVD grown graphene, the
lattice structure appears strongly distorted by the underlying
copper, with regions in direct contact with copper showing nearly
square lattices whereas suspended regions from thermal relaxation
exhibiting nearly honeycomb or hexagonal lattice structures. The
electronic density of states (DOS) correlates closely with the
atomic arrangements of carbon, showing excess zero-bias
tunneling conductance and nearly energy-independent DOS for
strongly distorted graphene, in contrast to the linearly dispersive
DOS for suspended graphene. These results suggest that graphene
can interact strongly with both metallic and dielectric materials in
close proximity, leading to non-negligible modifications to the
electronic properties
Localization, Coulomb interactions and electrical heating in single-wall carbon nanotubes/polymer composites
Low field and high field transport properties of carbon nanotubes/polymer
composites are investigated for different tube fractions. Above the percolation
threshold f_c=0.33%, transport is due to hopping of localized charge carriers
with a localization length xi=10-30 nm. Coulomb interactions associated with a
soft gap Delta_CG=2.5 meV are present at low temperature close to f_c. We argue
that it originates from the Coulomb charging energy effect which is partly
screened by adjacent bundles. The high field conductivity is described within
an electrical heating scheme. All the results suggest that using composites
close to the percolation threshold may be a way to access intrinsic properties
of the nanotubes by experiments at a macroscopic scale.Comment: 4 pages, 5 figures, Submitted to Phys. Rev.
Disorder, pseudospins, and backscattering in carbon nanotubes
We address the effects of disorder on the conducting properties of metal and
semiconducting carbon nanotubes. Experimentally, the mean free path is found to
be much larger in metallic tubes than in doped semiconducting tubes. We show
that this result can be understood theoretically if the disorder potential is
long-ranged. The effects of a pseudospin index that describes the internal
sublattice structure of the states lead to a suppression of scattering in
metallic tubes, but not in semiconducting tubes. This conclusion is supported
by tight-binding calculations.Comment: four page
Electric Switching of the Charge-Density-Wave and Normal Metallic Phases in Tantalum Disulfide Thin-Film Devices
We report on switching among three charge-density-wave phases - commensurate,
nearly commensurate, incommensurate - and the high-temperature normal metallic
phase in thin-film 1T-TaS2 devices induced by application of an in-plane
electric field. The electric switching among all phases has been achieved over
a wide temperature range, from 77 K to 400 K. The low-frequency electronic
noise spectroscopy has been used as an effective tool for monitoring the
transitions, particularly the switching from the incommensurate
charge-density-wave phase to the normal metal phase. The noise spectral density
exhibits sharp increases at the phase transition points, which correspond to
the step-like changes in resistivity. Assignment of the phases is consistent
with low-field resistivity measurements over the temperature range from 77 K to
600 K. Analysis of the experimental data and calculations of heat dissipation
suggest that Joule heating plays a dominant role in the electric-field induced
transitions in the tested 1T-TaS2 devices on Si/SiO2 substrates. The
possibility of electrical switching among four different phases of 1T-TaS2 is a
promising step toward nanoscale device applications. The results also
demonstrate the potential of noise spectroscopy for investigating and
identifying phase transitions in materials.Comment: 32 pages, 7 figure
Evidence for Strain-Induced Local Conductance Modulations in Single-Layer Graphene on SiO_2
Graphene has emerged as an electronic material that is promising for device applications and for studying two-dimensional electron gases with relativistic dispersion near two Dirac points. Nonetheless, deviations from Dirac-like spectroscopy have been widely reported with varying interpretations. Here we show evidence for strain-induced spatial modulations in the local conductance of single-layer graphene on SiO_2 substrates from scanning tunneling microscopic (STM) studies. We find that strained graphene exhibits parabolic, U-shaped conductance vs bias voltage spectra rather than the V-shaped spectra expected for Dirac fermions, whereas V-shaped spectra are recovered in regions of relaxed graphene. Strain maps derived from the STM studies further reveal direct correlation with the local tunneling conductance. These results are attributed to a strain-induced frequency increase in the out-of-plane phonon mode that mediates the low-energy inelastic charge tunneling into graphene
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