4 research outputs found
Local Conformational Switching of Supramolecular Networks at the Solid/Liquid Interface
We use the electric field in a scanning tunneling microscope to manipulate the transition between open and close packed 2D supramolecular networks of neutral molecules in nonpolar media. We found that while the magnitude of the applied field is not decisive, it is the sign of the polarization that needs to be maintained to select one particular polymorph. Moreover, the switching is independent of the solvent used and fully reversible. We propose that the orientation of the surface dipole determined by the electric field might favor different conformation-depended charge transfer mechanisms of the adsorbates to the surface, inducing open (closed) structures for negative (positive) potentials. Our results show the use of local fields to select the polymorphic outcome of supramolecular assemblies at the solid/liquid interface. The effect has potential to locally control the capture and release of analytes in hostâguest systems and the 2D morphology in multicomponent layers
Comparative Study of the Adsorption of Thiols and Selenols on Au(111) and Au(100)
The effect of the
Au crystalline plane on the adsorption of different
thiols and selenols is studied via reductive desorption (RD) and X-ray
photoelectron spectroscopy (XPS) measurements. Self-assembled monolayers
(SAMs) using aliphatic (ATs) and aromatic thiols (ArTs) on both Au(111)
and Au(100) were prepared. The electrochemical stability of these
SAMs on both surfaces is evaluated by comparing the position of the
RD peaks. The longer the AT chain the more stable the SAM on Au(100)
when compared to Au(111). By means of XPS measurements, we determine
that the binding energy (BE) of the S 2p signal corresponding to the
S atoms at the thiol/Au interface, commonly assigned at 162.0 eV,
shifts 0.2 eV from Au(111) to Au(100) for SAMs prepared using thiols
with the C* (C atom bonded to S) in sp<sup>3</sup> hybridization,
such as ATs. However, when the thiol presents the C* with an sp<sup>2</sup> hybridization, such as in the case of ArTs, the BE remains
at 162.0 eV regardless of the surface plane. Selenol-based SAMs were
characterized comparatively on both Au(100) and Au(111). Our results
show that selenol SAMs become even more electrochemically stable on
Au(100) with respect to Au(111) than the analogue sulfur-based SAM.
According to our results, we suggest that the electronic distribution
around the AuâS/Se bond could be responsible for the different
structural arrangements reported in the literature (gold adatoms,
etc.), which should be dependent on the crystalline face (AuÂ(<i>hkl</i>)âS) and the chemical nature of the environment
of the adsorbates (sp<sup>3</sup>-C* vs sp<sup>2</sup>-C* and AuâSR
vs AuâSeR)
Rational Design of 2D Supramolecular Networks Switchable by External Electric Fields
The reversible formation
of hydrogen bonds is a ubiquitous mechanism
for controlling molecular assembly in biological systems. However,
achieving predictable reversibility in artificial two-dimensional
(2D) materials remains a significant challenge. Here, we use an external
electric field (EEF) at the solid/liquid interface to trigger the
switching of H-bond-linked 2D networks using a scanning tunneling
microscope. Assisted by density functional theory and molecular dynamics
simulations, we systematically vary the molecule-to-molecule interactions,
i.e., the hydrogen-bonding strength, as well as the molecule-to-substrate
interactions to analyze the EEF switching effect. By tuning the building
blockâs hydrogen-bonding ability (carboxylic acids vs aldehydes)
and substrate nature and charge (graphite, graphene/Cu, graphene/SiO2), we induce or freeze the switching properties and control
the final polymorphic output in the 2D network. Our results indicate
that the switching ability is not inherent to any particular building
block but instead relies on a synergistic combination of the relative
adsorbate/adsorbate and absorbate/substrate energetic contributions
under surface polarization. Furthermore, we describe the dynamics
of the switching mechanism based on the rotation of carboxylic groups
and proton exchange, which generate the polarizable species that are
influenced by the EEF. This work provides insights into the design
and control of reversible molecular assembly in 2D materials, with
potential applications in a wide range of fields, including sensors
and electronics
Rational Design of 2D Supramolecular Networks Switchable by External Electric Fields
The reversible formation
of hydrogen bonds is a ubiquitous mechanism
for controlling molecular assembly in biological systems. However,
achieving predictable reversibility in artificial two-dimensional
(2D) materials remains a significant challenge. Here, we use an external
electric field (EEF) at the solid/liquid interface to trigger the
switching of H-bond-linked 2D networks using a scanning tunneling
microscope. Assisted by density functional theory and molecular dynamics
simulations, we systematically vary the molecule-to-molecule interactions,
i.e., the hydrogen-bonding strength, as well as the molecule-to-substrate
interactions to analyze the EEF switching effect. By tuning the building
blockâs hydrogen-bonding ability (carboxylic acids vs aldehydes)
and substrate nature and charge (graphite, graphene/Cu, graphene/SiO2), we induce or freeze the switching properties and control
the final polymorphic output in the 2D network. Our results indicate
that the switching ability is not inherent to any particular building
block but instead relies on a synergistic combination of the relative
adsorbate/adsorbate and absorbate/substrate energetic contributions
under surface polarization. Furthermore, we describe the dynamics
of the switching mechanism based on the rotation of carboxylic groups
and proton exchange, which generate the polarizable species that are
influenced by the EEF. This work provides insights into the design
and control of reversible molecular assembly in 2D materials, with
potential applications in a wide range of fields, including sensors
and electronics