12 research outputs found
Interactions and Reactions of Transition Metal Clusters with the Interior of Single-Walled Carbon Nanotubes Imaged at the Atomic Scale
Clusters of transition metals, W, Re, and Os, upon encapsulation
within a single-walled carbon nanotube (SWNT) exhibit marked differences
in their affinity and reactivity with the SWNT, as revealed by low-voltage
aberration-corrected high-resolution transmission electron microscopy
(AC-HRTEM). Activated by an 80 keV electron beam, W reacts only weakly
with the SWNT, Re creates localized defects on the sidewall, and Os
reacts readily causing extensive defect formation and constriction
of the SWNT sidewall followed by total rupture of the tubular structure.
AC-HRTEM imaging at the atomic level of structural transformations
caused by metal–carbon bonding of π- and σ-character
demonstrates what a crucial role these types of bonds have in governing
the interactions between the transition metal clusters and the SWNT.
The observed order of reactivity W < Re < Os is independent
of the metal cluster size, shape, or orientation, and is related to
the metal to nanotube bonding energy and the amount of electronic
density transferred between metal and SWNT, both of which increase
along the triad W, Re, Os, as predicted by first-principles density
functional theory calculations. By selecting the appropriate energy
of the electron beam, the metal–nanotube interactions can be
controlled (activated or precluded). At an electron energy as low
as 20 keV, no visible transformations in the nanotube in the vicinity
of Os-clusters are observed
Interactions and Reactions of Transition Metal Clusters with the Interior of Single-Walled Carbon Nanotubes Imaged at the Atomic Scale
Clusters of transition metals, W, Re, and Os, upon encapsulation
within a single-walled carbon nanotube (SWNT) exhibit marked differences
in their affinity and reactivity with the SWNT, as revealed by low-voltage
aberration-corrected high-resolution transmission electron microscopy
(AC-HRTEM). Activated by an 80 keV electron beam, W reacts only weakly
with the SWNT, Re creates localized defects on the sidewall, and Os
reacts readily causing extensive defect formation and constriction
of the SWNT sidewall followed by total rupture of the tubular structure.
AC-HRTEM imaging at the atomic level of structural transformations
caused by metal–carbon bonding of π- and σ-character
demonstrates what a crucial role these types of bonds have in governing
the interactions between the transition metal clusters and the SWNT.
The observed order of reactivity W < Re < Os is independent
of the metal cluster size, shape, or orientation, and is related to
the metal to nanotube bonding energy and the amount of electronic
density transferred between metal and SWNT, both of which increase
along the triad W, Re, Os, as predicted by first-principles density
functional theory calculations. By selecting the appropriate energy
of the electron beam, the metal–nanotube interactions can be
controlled (activated or precluded). At an electron energy as low
as 20 keV, no visible transformations in the nanotube in the vicinity
of Os-clusters are observed
Interactions and Reactions of Transition Metal Clusters with the Interior of Single-Walled Carbon Nanotubes Imaged at the Atomic Scale
Clusters of transition metals, W, Re, and Os, upon encapsulation
within a single-walled carbon nanotube (SWNT) exhibit marked differences
in their affinity and reactivity with the SWNT, as revealed by low-voltage
aberration-corrected high-resolution transmission electron microscopy
(AC-HRTEM). Activated by an 80 keV electron beam, W reacts only weakly
with the SWNT, Re creates localized defects on the sidewall, and Os
reacts readily causing extensive defect formation and constriction
of the SWNT sidewall followed by total rupture of the tubular structure.
AC-HRTEM imaging at the atomic level of structural transformations
caused by metal–carbon bonding of π- and σ-character
demonstrates what a crucial role these types of bonds have in governing
the interactions between the transition metal clusters and the SWNT.
The observed order of reactivity W < Re < Os is independent
of the metal cluster size, shape, or orientation, and is related to
the metal to nanotube bonding energy and the amount of electronic
density transferred between metal and SWNT, both of which increase
along the triad W, Re, Os, as predicted by first-principles density
functional theory calculations. By selecting the appropriate energy
of the electron beam, the metal–nanotube interactions can be
controlled (activated or precluded). At an electron energy as low
as 20 keV, no visible transformations in the nanotube in the vicinity
of Os-clusters are observed
Interactions and Reactions of Transition Metal Clusters with the Interior of Single-Walled Carbon Nanotubes Imaged at the Atomic Scale
Clusters of transition metals, W, Re, and Os, upon encapsulation
within a single-walled carbon nanotube (SWNT) exhibit marked differences
in their affinity and reactivity with the SWNT, as revealed by low-voltage
aberration-corrected high-resolution transmission electron microscopy
(AC-HRTEM). Activated by an 80 keV electron beam, W reacts only weakly
with the SWNT, Re creates localized defects on the sidewall, and Os
reacts readily causing extensive defect formation and constriction
of the SWNT sidewall followed by total rupture of the tubular structure.
AC-HRTEM imaging at the atomic level of structural transformations
caused by metal–carbon bonding of π- and σ-character
demonstrates what a crucial role these types of bonds have in governing
the interactions between the transition metal clusters and the SWNT.
The observed order of reactivity W < Re < Os is independent
of the metal cluster size, shape, or orientation, and is related to
the metal to nanotube bonding energy and the amount of electronic
density transferred between metal and SWNT, both of which increase
along the triad W, Re, Os, as predicted by first-principles density
functional theory calculations. By selecting the appropriate energy
of the electron beam, the metal–nanotube interactions can be
controlled (activated or precluded). At an electron energy as low
as 20 keV, no visible transformations in the nanotube in the vicinity
of Os-clusters are observed
Interactions and Reactions of Transition Metal Clusters with the Interior of Single-Walled Carbon Nanotubes Imaged at the Atomic Scale
Clusters of transition metals, W, Re, and Os, upon encapsulation
within a single-walled carbon nanotube (SWNT) exhibit marked differences
in their affinity and reactivity with the SWNT, as revealed by low-voltage
aberration-corrected high-resolution transmission electron microscopy
(AC-HRTEM). Activated by an 80 keV electron beam, W reacts only weakly
with the SWNT, Re creates localized defects on the sidewall, and Os
reacts readily causing extensive defect formation and constriction
of the SWNT sidewall followed by total rupture of the tubular structure.
AC-HRTEM imaging at the atomic level of structural transformations
caused by metal–carbon bonding of π- and σ-character
demonstrates what a crucial role these types of bonds have in governing
the interactions between the transition metal clusters and the SWNT.
The observed order of reactivity W < Re < Os is independent
of the metal cluster size, shape, or orientation, and is related to
the metal to nanotube bonding energy and the amount of electronic
density transferred between metal and SWNT, both of which increase
along the triad W, Re, Os, as predicted by first-principles density
functional theory calculations. By selecting the appropriate energy
of the electron beam, the metal–nanotube interactions can be
controlled (activated or precluded). At an electron energy as low
as 20 keV, no visible transformations in the nanotube in the vicinity
of Os-clusters are observed
Interactions and Reactions of Transition Metal Clusters with the Interior of Single-Walled Carbon Nanotubes Imaged at the Atomic Scale
Clusters of transition metals, W, Re, and Os, upon encapsulation
within a single-walled carbon nanotube (SWNT) exhibit marked differences
in their affinity and reactivity with the SWNT, as revealed by low-voltage
aberration-corrected high-resolution transmission electron microscopy
(AC-HRTEM). Activated by an 80 keV electron beam, W reacts only weakly
with the SWNT, Re creates localized defects on the sidewall, and Os
reacts readily causing extensive defect formation and constriction
of the SWNT sidewall followed by total rupture of the tubular structure.
AC-HRTEM imaging at the atomic level of structural transformations
caused by metal–carbon bonding of π- and σ-character
demonstrates what a crucial role these types of bonds have in governing
the interactions between the transition metal clusters and the SWNT.
The observed order of reactivity W < Re < Os is independent
of the metal cluster size, shape, or orientation, and is related to
the metal to nanotube bonding energy and the amount of electronic
density transferred between metal and SWNT, both of which increase
along the triad W, Re, Os, as predicted by first-principles density
functional theory calculations. By selecting the appropriate energy
of the electron beam, the metal–nanotube interactions can be
controlled (activated or precluded). At an electron energy as low
as 20 keV, no visible transformations in the nanotube in the vicinity
of Os-clusters are observed
Size, Structure, and Helical Twist of Graphene Nanoribbons Controlled by Confinement in Carbon Nanotubes
Carbon nanotubes (CNTs) act as efficient nanoreactors, templating the assembly of sulfur-terminated graphene nanoribbons (S-GNRs) with different sizes, structures, and conformations. Spontaneous formation of nanoribbons from small sulfur-containing molecules is efficiently triggered by heat treatment or by an 80 keV electron beam. S-GNRs form readily in CNTs with internal diameters between 1 and 2 nm. Outside of this optimum range, nanotubes narrower than 1 nm do not have sufficient space to accommodate the 2D structure of S-GNRs, while nanotubes wider than 2 nm do not provide efficient confinement for unidirectional S-GNR growth, thus neither can support nanoribbon formation. Theoretical calculations show that the thermodynamic stability of nanoribbons is dependent on the S-GNR edge structure and, to a lesser extent, the width of the nanoribbon. For nanoribbons of similar widths, the polythiaperipolycene-type edges of zigzag S-GNRs are more stable than the polythiophene-type edges of armchair S-GNRs. Both the edge structure and the width define the electronic properties of S-GNRs which can vary widely from metallic to semiconductor to insulator. The encapsulated S-GNRs exhibit diverse dynamic behavior, including rotation, translation, and helical twisting inside the nanotube, which offers a mechanism for control of the electronic properties of the graphene nanoribbon <i>via</i> confinement at the nanoscale
Size, Structure, and Helical Twist of Graphene Nanoribbons Controlled by Confinement in Carbon Nanotubes
Carbon nanotubes (CNTs) act as efficient nanoreactors, templating the assembly of sulfur-terminated graphene nanoribbons (S-GNRs) with different sizes, structures, and conformations. Spontaneous formation of nanoribbons from small sulfur-containing molecules is efficiently triggered by heat treatment or by an 80 keV electron beam. S-GNRs form readily in CNTs with internal diameters between 1 and 2 nm. Outside of this optimum range, nanotubes narrower than 1 nm do not have sufficient space to accommodate the 2D structure of S-GNRs, while nanotubes wider than 2 nm do not provide efficient confinement for unidirectional S-GNR growth, thus neither can support nanoribbon formation. Theoretical calculations show that the thermodynamic stability of nanoribbons is dependent on the S-GNR edge structure and, to a lesser extent, the width of the nanoribbon. For nanoribbons of similar widths, the polythiaperipolycene-type edges of zigzag S-GNRs are more stable than the polythiophene-type edges of armchair S-GNRs. Both the edge structure and the width define the electronic properties of S-GNRs which can vary widely from metallic to semiconductor to insulator. The encapsulated S-GNRs exhibit diverse dynamic behavior, including rotation, translation, and helical twisting inside the nanotube, which offers a mechanism for control of the electronic properties of the graphene nanoribbon <i>via</i> confinement at the nanoscale
Formation of Nickel Clusters Wrapped in Carbon Cages: Toward New Endohedral Metallofullerene Synthesis
Despite
the high potential of endohedral metallofullerenes (EMFs) for application
in biology, medicine and molecular electronics, and recent efforts
in EMF synthesis, the variety of EMFs accessible by conventional synthetic
methods remains limited and does not include, for example, EMFs of
late transition metals. We propose a method in which EMF formation
is initiated by electron irradiation in aberration-corrected high-resolution
transmission electron spectroscopy (AC-HRTEM) of a metal cluster surrounded
by amorphous carbon inside a carbon nanotube serving as a nanoreactor
and apply this method for synthesis of nickel EMFs. The use of AC-HRTEM
makes it possible not only to synthesize new, previously unattainable
nanoobjects but also to study in situ the mechanism of structural
transformations. Molecular dynamics simulations using the state-of-the-art
approach for modeling the effect of electron irradiation are performed
to rationalize the experimental observations and to link the observed
processes with conditions of bulk EMF synthesis
Origin of Aging of a P2-Na<i><sub>x</sub></i>Mn<sub>3/4</sub>Ni<sub>1/4</sub>O<sub>2</sub> Cathode Active Material for Sodium-Ion Batteries
Sodium-ion batteries
(SIB) are currently being developed
and commercialized
as a promising new technology for cost-effective and powerful electrical
energy storage. In this study, we investigate the origin of capacity
fading in P2-type layered sodium cathode materials for SIBs using
a micron-sized single-crystalline P2-NaxMn3/4Ni1/4O2 model cathode active
material. Using various electrochemical techniques, we identify the
following aging effects upon cycling: (i) a state of charge (SOC)-independent
increase in polarization, (ii) a SOC-dependent increase in polarization
at high voltage, and (iii) a loss of active material due to electronic
disconnection after prolonged cycling. With high-resolution transmission
electron microscopy (HRTEM) and energy-dispersive X-ray (EDX) spectroscopy,
we identify surface densification, resulting in 5–10 nm thick
surface layers on cycled cathode active materials as the origin for
SOC-independent increase of polarization. The corresponding oxygen
loss is in accordance with gas evolution in differential electrochemical
mass spectrometry (DEMS) measurements. Furthermore, with scanning
electron microscopy (SEM) electrode cross sections, we identify (partly)
reversible cracking at a high SOC as the cause for increased polarization
depending on SOC. Operando X-ray diffraction (XRD) identifies significant
anisotropic volume change, which suggests mechanical stress as the
cause for cracking at a high SOC and loss of active material after
prolonged cycling. We believe that the herein provided understanding
on the aging of this highly attractive class of cathode active materials
for SIBs will enable the development of future powerful and stable
layered oxide cathode materials for SIBs