31 research outputs found
Site-Specific Substitutional Boron Doping of Semiconducting Armchair Graphene Nanoribbons.
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Heterostructures through Divergent Edge Reconstruction in Nitrogen-Doped Segmented Graphene Nanoribbons.
Atomically precise engineering of defined segments within individual graphene nanoribbons (GNRs) represents a key enabling technology for the development of advanced functional device architectures. Here, the bottom-up synthesis of chevron GNRs decorated with reactive functional groups derived from 9-methyl-9H-carbazole is reported. Scanning tunneling and non-contact atomic force microscopy reveal that a thermal activation of GNRs induces the rearrangement of the electron-rich carbazole into an electron-deficient phenanthridine. The selective chemical edge-reconstruction of carbazole-substituted chevron GNRs represents a practical strategy for the controlled fabrication of spatially defined GNR heterostructures from a single molecular precursor
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Heterostructures through Divergent Edge Reconstruction in Nitrogen-Doped Segmented Graphene Nanoribbons.
Atomically precise engineering of defined segments within individual graphene nanoribbons (GNRs) represents a key enabling technology for the development of advanced functional device architectures. Here, the bottom-up synthesis of chevron GNRs decorated with reactive functional groups derived from 9-methyl-9H-carbazole is reported. Scanning tunneling and non-contact atomic force microscopy reveal that a thermal activation of GNRs induces the rearrangement of the electron-rich carbazole into an electron-deficient phenanthridine. The selective chemical edge-reconstruction of carbazole-substituted chevron GNRs represents a practical strategy for the controlled fabrication of spatially defined GNR heterostructures from a single molecular precursor
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Initiator Control of Conjugated Polymer Topology in Ring-Opening Alkyne Metathesis Polymerization.
Molybdenum carbyne complexes [RC≡Mo(OC(CH3)(CF3)2)3] featuring a mesityl (R = Mes) or an ethyl (R = Et) substituent initiate the living ring-opening alkyne metathesis polymerization of the strained cyclic alkyne, 5,6,11,12-tetradehydrobenzo[a,e][8]annulene, to yield fully conjugated poly(o-phenylene ethynylene). The difference in the steric demand of the polymer end-group (Mes vs Et) transferred during the initiation step determines the topology of the resulting polymer chain. While [MesC≡Mo(OC(CH3)(CF3)2)3] exclusively yields linear poly(o-phenylene ethynylene), polymerization initiated by [EtC≡Mo(OC(CH3)(CF3)2)3] results in cyclic polymers ranging in size from n = 5 to 20 monomer units. Kinetic studies reveal that the propagating species emerging from [EtC≡Mo(OC(CH3)(CF3)2)3] undergoes a highly selective intramolecular backbiting into the butynyl end-group
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Initiator Control of Conjugated Polymer Topology in Ring-Opening Alkyne Metathesis Polymerization
Molybdenum
carbyne complexes [RCî—¼MoÂ(OCÂ(CH<sub>3</sub>)Â(CF<sub>3</sub>)<sub>2</sub>)<sub>3</sub>] featuring a mesityl (R
= Mes) or an ethyl (R = Et) substituent initiate the living ring-opening
alkyne metathesis polymerization of the strained cyclic alkyne, 5,6,11,12-tetradehydrobenzoÂ[<i>a</i>,<i>e</i>]Â[8]Âannulene, to yield fully conjugated
polyÂ(<i>o</i>-phenylene ethynylene). The difference in the
steric demand of the polymer end-group (Mes vs Et) transferred during
the initiation step determines the topology of the resulting polymer
chain. While [MesCî—¼MoÂ(OCÂ(CH<sub>3</sub>)Â(CF<sub>3</sub>)<sub>2</sub>)<sub>3</sub>] exclusively yields linear polyÂ(<i>o</i>-phenylene ethynylene), polymerization initiated by [EtCî—¼MoÂ(OCÂ(CH<sub>3</sub>)Â(CF<sub>3</sub>)<sub>2</sub>)<sub>3</sub>] results in cyclic
polymers ranging in size from <i>n</i> = 5 to 20 monomer
units. Kinetic studies reveal that the propagating species emerging
from [EtCî—¼MoÂ(OCÂ(CH<sub>3</sub>)Â(CF<sub>3</sub>)<sub>2</sub>)<sub>3</sub>] undergoes a highly selective intramolecular backbiting
into the butynyl end-group
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Initiator Control of Conjugated Polymer Topology in Ring-Opening Alkyne Metathesis Polymerization
Molybdenum
carbyne complexes [RCî—¼MoÂ(OCÂ(CH<sub>3</sub>)Â(CF<sub>3</sub>)<sub>2</sub>)<sub>3</sub>] featuring a mesityl (R
= Mes) or an ethyl (R = Et) substituent initiate the living ring-opening
alkyne metathesis polymerization of the strained cyclic alkyne, 5,6,11,12-tetradehydrobenzoÂ[<i>a</i>,<i>e</i>]Â[8]Âannulene, to yield fully conjugated
polyÂ(<i>o</i>-phenylene ethynylene). The difference in the
steric demand of the polymer end-group (Mes vs Et) transferred during
the initiation step determines the topology of the resulting polymer
chain. While [MesCî—¼MoÂ(OCÂ(CH<sub>3</sub>)Â(CF<sub>3</sub>)<sub>2</sub>)<sub>3</sub>] exclusively yields linear polyÂ(<i>o</i>-phenylene ethynylene), polymerization initiated by [EtCî—¼MoÂ(OCÂ(CH<sub>3</sub>)Â(CF<sub>3</sub>)<sub>2</sub>)<sub>3</sub>] results in cyclic
polymers ranging in size from <i>n</i> = 5 to 20 monomer
units. Kinetic studies reveal that the propagating species emerging
from [EtCî—¼MoÂ(OCÂ(CH<sub>3</sub>)Â(CF<sub>3</sub>)<sub>2</sub>)<sub>3</sub>] undergoes a highly selective intramolecular backbiting
into the butynyl end-group
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Synergistic Enhancement of Electrocatalytic CO<sub>2</sub> Reduction with Gold Nanoparticles Embedded in Functional Graphene Nanoribbon Composite Electrodes
Regulating the complex environment
accounting for the stability,
selectivity, and activity of catalytic metal nanoparticle interfaces
represents a challenge to heterogeneous catalyst design. Here we demonstrate
the intrinsic performance enhancement of a composite material composed
of gold nanoparticles (AuNPs) embedded in a bottom-up synthesized
graphene nanoribbon (GNR) matrix for the electrocatalytic reduction
of CO<sub>2</sub>. Electrochemical studies reveal that the structural
and electronic properties of the GNR composite matrix increase the
AuNP electrochemically active surface area (ECSA), lower the requisite
CO<sub>2</sub> reduction overpotential by hundreds of millivolts (catalytic
onset > −0.2 V versus reversible hydrogen electrode (RHE)),
increase the Faraday efficiency (>90%), markedly improve stability
(catalytic performance sustained over >24 h), and increase the
total
catalytic output (>100-fold improvement over traditional amorphous
carbon AuNP supports). The inherent structural and electronic tunability
of bottom-up synthesized GNR-AuNP composites affords an unrivaled
degree of control over the catalytic environment, providing a means
for such profound effects as shifting the rate-determining step in
the electrocatalytic reduction of CO<sub>2</sub> to CO, and thereby
altering the electrocatalytic mechanism at the nanoparticle surface
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Site-Specific Substitutional Boron Doping of Semiconducting Armchair Graphene Nanoribbons.
A fundamental requirement for the development of advanced electronic device architectures based on graphene nanoribbon (GNR) technology is the ability to modulate the band structure and charge carrier concentration by substituting specific carbon atoms in the hexagonal graphene lattice with p- or n-type dopant heteroatoms. Here we report the atomically precise introduction of group III dopant atoms into bottom-up fabricated semiconducting armchair GNRs (AGNRs). Trigonal-planar B atoms along the backbone of the GNR share an empty p-orbital with the extended π-band for dopant functionality. Scanning tunneling microscopy (STM) topography reveals a characteristic modulation of the local density of states along the backbone of the GNR that is superimposable with the expected position and concentration of dopant B atoms. First-principles calculations support the experimental findings and provide additional insight into the band structure of B-doped 7-AGNRs
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Site-Specific Substitutional Boron Doping of Semiconducting Armchair Graphene Nanoribbons
A fundamental
requirement for the development of advanced electronic
device architectures based on graphene nanoribbon (GNR) technology
is the ability to modulate the band structure and charge carrier concentration
by substituting specific carbon atoms in the hexagonal graphene lattice
with p- or n-type dopant heteroatoms. Here we report the atomically
precise introduction of group III dopant atoms into bottom-up fabricated
semiconducting armchair GNRs (AGNRs). Trigonal-planar B atoms along
the backbone of the GNR share an empty p-orbital with the extended
Ï€-band for dopant functionality. Scanning tunneling microscopy
(STM) topography reveals a characteristic modulation of the local
density of states along the backbone of the GNR that is superimposable
with the expected position and concentration of dopant B atoms. First-principles
calculations support the experimental findings and provide additional
insight into the band structure of B-doped 7-AGNRs