33 research outputs found
Silver Makes Better Electrical Contacts to Thiol-Terminated Silanes than Gold
We report that the single-molecule junction conductance of thiol-terminated silanes with Ag electrodes are higher than the conductance of those formed with Au electrodes. These results are in contrast to the trends in the metal work function Phi(Ag)< Phi(Au). As such, a better alignment of the Au Fermi level to the molecular orbital of silane that mediates charge transport would be expected. This conductance trend is reversed when we replace the thiols with amines, highlighting the impact of metal-S covalent and metal-NH2 dative bonds in controlling the molecular conductance. Density functional theory calculations elucidate the crucial role of the chemical linkers in determining the level alignment when molecules are attached to different metal contacts. We also demonstrate that conductance of thiol-terminated silanes with Pt electrodes is lower than the ones formed with Au and Ag electrodes, again in contrast to the trends in the metal work-functions
In Situ Formation of N鈥慔eterocyclic Carbene-Bound Single-Molecule Junctions
Self-assembled
monolayers (SAMs) formed using N-heterocyclic carbenes
(NHCs) have recently emerged as thermally and chemically ultrastable
alternatives to those formed from thiols. The rich chemistry and strong
蟽-donating ability of NHCs offer unique prospects for applications
in nanoelectronics, sensing, and electrochemistry. Although stable
in SAMs, free carbenes are notoriously reactive, making their electronic
characterization challenging. Here we report the first investigation
of electron transport across single NHC-bound molecules using the
scanning tunneling microscope-based break junction (STM-BJ) technique.
We develop a series of air-stable metal NHC complexes that can be
electrochemically reduced in situ to form NHC鈥揺lectrode contacts,
enabling reliable single-molecule conductance measurements of NHCs
under ambient conditions. Using this approach, we show that the conductance
of an NHC depends on the identity of the single metal atom to which
it is coordinated in the junction. Our observations are supported
by density functional theory (DFT) calculations, which also firmly
establish the contributions of the NHC linker to the junction transport
characteristics. Our work demonstrates a powerful method to probe
electron transfer across NHC鈥揺lectrode interfaces; more generally,
it opens the door to the exploitation of surface-bound NHCs in constructing
novel, functionalized electrodes and/or nanoelectronic devices
In Situ Formation of N鈥慔eterocyclic Carbene-Bound Single-Molecule Junctions
Self-assembled
monolayers (SAMs) formed using N-heterocyclic carbenes
(NHCs) have recently emerged as thermally and chemically ultrastable
alternatives to those formed from thiols. The rich chemistry and strong
蟽-donating ability of NHCs offer unique prospects for applications
in nanoelectronics, sensing, and electrochemistry. Although stable
in SAMs, free carbenes are notoriously reactive, making their electronic
characterization challenging. Here we report the first investigation
of electron transport across single NHC-bound molecules using the
scanning tunneling microscope-based break junction (STM-BJ) technique.
We develop a series of air-stable metal NHC complexes that can be
electrochemically reduced in situ to form NHC鈥揺lectrode contacts,
enabling reliable single-molecule conductance measurements of NHCs
under ambient conditions. Using this approach, we show that the conductance
of an NHC depends on the identity of the single metal atom to which
it is coordinated in the junction. Our observations are supported
by density functional theory (DFT) calculations, which also firmly
establish the contributions of the NHC linker to the junction transport
characteristics. Our work demonstrates a powerful method to probe
electron transfer across NHC鈥揺lectrode interfaces; more generally,
it opens the door to the exploitation of surface-bound NHCs in constructing
novel, functionalized electrodes and/or nanoelectronic devices
In Situ Formation of N鈥慔eterocyclic Carbene-Bound Single-Molecule Junctions
Self-assembled
monolayers (SAMs) formed using N-heterocyclic carbenes
(NHCs) have recently emerged as thermally and chemically ultrastable
alternatives to those formed from thiols. The rich chemistry and strong
蟽-donating ability of NHCs offer unique prospects for applications
in nanoelectronics, sensing, and electrochemistry. Although stable
in SAMs, free carbenes are notoriously reactive, making their electronic
characterization challenging. Here we report the first investigation
of electron transport across single NHC-bound molecules using the
scanning tunneling microscope-based break junction (STM-BJ) technique.
We develop a series of air-stable metal NHC complexes that can be
electrochemically reduced in situ to form NHC鈥揺lectrode contacts,
enabling reliable single-molecule conductance measurements of NHCs
under ambient conditions. Using this approach, we show that the conductance
of an NHC depends on the identity of the single metal atom to which
it is coordinated in the junction. Our observations are supported
by density functional theory (DFT) calculations, which also firmly
establish the contributions of the NHC linker to the junction transport
characteristics. Our work demonstrates a powerful method to probe
electron transfer across NHC鈥揺lectrode interfaces; more generally,
it opens the door to the exploitation of surface-bound NHCs in constructing
novel, functionalized electrodes and/or nanoelectronic devices
In Situ Formation of N鈥慔eterocyclic Carbene-Bound Single-Molecule Junctions
Self-assembled
monolayers (SAMs) formed using N-heterocyclic carbenes
(NHCs) have recently emerged as thermally and chemically ultrastable
alternatives to those formed from thiols. The rich chemistry and strong
蟽-donating ability of NHCs offer unique prospects for applications
in nanoelectronics, sensing, and electrochemistry. Although stable
in SAMs, free carbenes are notoriously reactive, making their electronic
characterization challenging. Here we report the first investigation
of electron transport across single NHC-bound molecules using the
scanning tunneling microscope-based break junction (STM-BJ) technique.
We develop a series of air-stable metal NHC complexes that can be
electrochemically reduced in situ to form NHC鈥揺lectrode contacts,
enabling reliable single-molecule conductance measurements of NHCs
under ambient conditions. Using this approach, we show that the conductance
of an NHC depends on the identity of the single metal atom to which
it is coordinated in the junction. Our observations are supported
by density functional theory (DFT) calculations, which also firmly
establish the contributions of the NHC linker to the junction transport
characteristics. Our work demonstrates a powerful method to probe
electron transfer across NHC鈥揺lectrode interfaces; more generally,
it opens the door to the exploitation of surface-bound NHCs in constructing
novel, functionalized electrodes and/or nanoelectronic devices
In Situ Formation of N鈥慔eterocyclic Carbene-Bound Single-Molecule Junctions
Self-assembled
monolayers (SAMs) formed using N-heterocyclic carbenes
(NHCs) have recently emerged as thermally and chemically ultrastable
alternatives to those formed from thiols. The rich chemistry and strong
蟽-donating ability of NHCs offer unique prospects for applications
in nanoelectronics, sensing, and electrochemistry. Although stable
in SAMs, free carbenes are notoriously reactive, making their electronic
characterization challenging. Here we report the first investigation
of electron transport across single NHC-bound molecules using the
scanning tunneling microscope-based break junction (STM-BJ) technique.
We develop a series of air-stable metal NHC complexes that can be
electrochemically reduced in situ to form NHC鈥揺lectrode contacts,
enabling reliable single-molecule conductance measurements of NHCs
under ambient conditions. Using this approach, we show that the conductance
of an NHC depends on the identity of the single metal atom to which
it is coordinated in the junction. Our observations are supported
by density functional theory (DFT) calculations, which also firmly
establish the contributions of the NHC linker to the junction transport
characteristics. Our work demonstrates a powerful method to probe
electron transfer across NHC鈥揺lectrode interfaces; more generally,
it opens the door to the exploitation of surface-bound NHCs in constructing
novel, functionalized electrodes and/or nanoelectronic devices