73 research outputs found
Orbital and spin magnetic moments of transforming 1D iron inside metallic and semiconducting carbon nanotubes
The orbital and spin magnetic properties of iron inside transforming metallic
and semiconducting 1D carbon nanotube hybrids are studied by means of local
x-ray magnetic circular dichroism (XMCD) and bulk superconducting quantum
interference device (SQUID) measurements. Nanotube hybrids are initially
ferrocene filled single-walled carbon nanotubes (SWCNT) of different
metallicities. After a high temperature nanochemical reaction ferrocene
molecules react with each other to form iron nano clusters. We show that the
ferrocenes molecular orbitals interact differently with the SWCNT of different
metallicities without significant XMCD response. This XMCD at various
temperatures and magnetic fields reveals that the orbital and/or spin magnetic
moments of the encapsulated iron are altered drastically as the transformation
to 1D Fe nanoclusters takes place. The orbital and spin magnetic moments are
both found to be larger in filled semiconducting nanotubes than in the metallic
sample. This could mean that the magnetic polarizations of the encapsulated
material is dependent on the metallicity of the tubes. From a comparison
between the iron 3d magnetic moments and the bulk magnetism measured by SQUID,
we conclude that the delocalized magnetisms dictate the magnetic properties of
these 1D hybrid nanostructures
Unified Quantification of Quantum Defects in Small-Diameter Single-Walled Carbon Nanotubes by Raman Spectroscopy
The covalent functionalization of single-walled carbon nanotubes (SWCNTs)
with luminescent quantum defects enables their application as near-infrared
single-photon sources, as optical sensors, and for in-vivo tissue imaging.
Tuning the emission wavelength and defect density are crucial for these
applications. While the former can be controlled by different synthetic
protocols and is easily measured, defect densities are still determined as
relative rather than absolute values, limiting the comparability between
different nanotube batches and chiralities. Here, we present an absolute and
unified quantification metric for the defect density in SWCNT samples based on
Raman spectroscopy. It is applicable to a range of small-diameter nanotubes and
for arbitrary laser wavelengths. We observe a clear inverse correlation of the
D/G ratio increase with nanotube diameter, indicating that curvature
effects contribute significantly to the defect-activation of Raman modes.
Correlation of intermediate frequency modes with defect densities further
corroborates their activation by defects and provides additional quantitative
metrics for the characterization of functionalized SWCNTs
Reversible changes in the electronic structure of carbon nanotube-hybrids upon NO2 exposure under ambient conditions
Single-walled carbon nanotubes have enormous potential for gas sensing. This study shows that cluster filling is a key to high sensitivity and it opens the possibility for a very high desorption at ambient temperature
Disentangling Vacancy Oxidation on Metallicity-Sorted Carbon Nanotubes
Pristine single-walled carbon nanotubes (SWCNTs) are rather inert to O
and N, which for low doses chemisorb only on defect sites or vacancies of
the SWCNTs at the ppm level. However, very low doping has a major effect on the
electronic properties and conductivity of the SWCNTs. Already at low O
doses (80 L), the X-ray photoelectron spectroscopy (XPS) O 1s signal becomes
saturated, indicating nearly all the SWCNT's vacancies have been oxidized. As a
result, probing vacancy oxidation on SWCNTs via XPS yields spectra with rather
low signal-to-noise ratios, even for metallicity-sorted SWCNTs. We show that,
even under these conditions, the first principles density functional theory
calculated Kohn-Sham O 1s binding energies may be used to assign the XPS O 1s
spectra for oxidized vacancies on SWCNTs into its individual components. This
allows one to determine the specific functional groups or bonding environments
measured. We find the XPS O 1s signal is mostly due to three O-containing
functional groups on SWCNT vacancies: epoxy (CO), carbonyl
(CCO), and ketene (CCO), as ordered by abundance. Upon
oxidation of nearly all the SWCNT's vacancies, the central peak's intensity for
the metallic SWCNT sample is 60\% greater than for the semiconducting SWCNT
sample. This suggests a greater abundance of O-containing defect structures on
the metallic SWCNT sample. For both metallic and semiconducting SWCNTs, we find
O does not contribute to the measured XPS O~1s spectra
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