Maricarmen Grisolia’s research while affiliated with Centre for Materials Elaboration and Structural Studies and other places

A supramolecular nanostructure composed of four 4 acetylbiphenyl molecules and self-assembled on Au (111) was loaded with single Au adatoms and studied by scanning tunneling microscopy at low temperature. By applying voltage pulses to the supramolecular structure, the loaded Au atoms can be rotated and translated in a controlled manner. The manipulation of the gold adatoms is driven neither by mechanical interaction nor by direct electronic excitation. At the electronic resonance and driven by the tunneling current intensity, the supramolecular nanostructure performs a minute work of about 8 × 10(-21) J, while transporting the single Au atom from one adsorption site to the next. Using the measured average excitation time necessary to induce the movement, we determine the mechanical motive power of the device yielding about 3 × 10(-21) W.

Surface-supported molecular motors are nanomechanical devices of particular interest in terms of future nanoscale applications. However, the molecular motors realized so far consist of covalently bonded groups that cannot be reconfigured without undergoing a chemical reaction. Here we demonstrate that a platinum-porphyrin-based supramolecularly assembled dimer supported on a Au(111) surface can be rotated with high directionality using the tunneling current of a scanning tunneling microscope (STM). Rotational direction of this molecular motor is determined solely by the surface chirality of the dimer, and most importantly, the chirality can be inverted in situ through a process involving an intradimer rearrangement. Our result opens the way for the construction of complex molecular machines on a surface to mimic at a smaller scale versatile biological supramolecular motors.

A new disc-shaped highly symmetric C54H20 nanographene fragment, tetrabenzocircumpyrene, has been synthesized and characterized by scanning tunnelling microscopy, demonstrating the potential of this technique for identifying highly insoluble graphenic molecules.

a b s t r a c t Single gold adatoms were manipulated on a Au(1 1 1) surface with the tip of a scanning tunnelling microscope to contact selected peripheral p bonds of a single Coronene molecule. Tunnelling electron spectroscopy and differential conductance mapping of the Au–Coronene complexes show how Coron-ene's electronic ground state is shifted down in energy as the function of the number of interacting Au atoms, demonstrating that a Coronene molecule can function like a single molecule counter. The number of interacting atoms can be counted by simply following the linear energy downshift of Coronene's ground state. Ó 2013 Elsevier B.V. All rights reserved.

The design of molecular systems as functional elements for use in next-generation electronic sensors and devices often relies on the addition of functional groups acting as spacers to modify adsorbate-substrate interactions. While advantageous in many regards, these spacer groups have the secondary effect of amplifying internal conformational effects of the parent molecule. Here we investigate one such molecule-2,5,8,11,14,17-hexa-tert-butyl-decacyclene (HBDC, C60H66) deposited on Cu(100) at monolayer and sub-monolayer coverages using an ultra-high vacuum (UHV) scanning tunneling microscope (STM). By combining sub-molecular resolution imaging with computational methods, we describe a variety of properties related to the effects of adding tert-buytl spacers to a decacyclene core including: molecular conformation, structure and chiral separation of the molecular adlayer, strong intermolecular interactions, and a meta-stable pinned conformation of the molecule brought on by deformation under high bias conditions which enables examination of its diffusive 2D molecular gas at room temperature. Collectively, these observations provide direct insight into the effect of adding spacers to a flexible molecular core such as decacyclene as relates to both intermolecular and adsorbate-substrate interfaces.

The design of artificial molecular machines often takes inspiration from macroscopic machines. However, the parallels between the two systems are often only superficial, because most molecular machines are governed by quantum processes. Previously, rotary molecular motors powered by light and chemical energy have been developed. In electrically driven motors, tunnelling electrons from the tip of a scanning tunnelling microscope have been used to drive the rotation of a simple rotor in a single direction and to move a four-wheeled molecule across a surface. Here, we show that a stand-alone molecular motor adsorbed on a gold surface can be made to rotate in a clockwise or anticlockwise direction by selective inelastic electron tunnelling through different subunits of the motor. Our motor is composed of a tripodal stator for vertical positioning, a five-arm rotor for controlled rotations, and a ruthenium atomic ball bearing connecting the static and rotational parts. The directional rotation arises from sawtooth-like rotational potentials, which are solely determined by the internal molecular structure and are independent of the surface adsorption site.

For the development of nanoscale devices, the manipulation of single atoms and molecules by scanning tunneling microscopy is a well established experimental technique. However, for the construction of larger and higher order structures, it is important to move not only one adsorbate, but several at the same time. Additionally, a major issue in standard manipulation experiments is the strong mechanical interaction of the tip apex and the adsorbate, which can damage the system under investigation. Here, we present a purely electronic excitation method for the controlled movement of a weakly interacting assembly of a few molecules. By applying voltage pulses, this supramolecular nanostructure is moved in a controlled manner without losing its collective integrity. Depending on the polarity and location of the applied voltage, the movement can be driven in predefined directions. Our gentle purely electronic approach for the controlled manipulation of nanostructures opens new ways to construct molecular devices.

Electronic states of a molecule are usually analyzed via their decomposition in linear superposition of multielectronic Slater determinants built up from monoelectronics molecular orbitals. It is generally believed that a scanning tunneling microscope (STM) is able to map those molecular orbitals. Using a low-temperature ultrahigh vacuum (LT-UHV) STM, the dI/dV conductance maps of large single hexabenzocoronene (HBC) monomer, dimer, trimer, and tetramer molecules were recorded. We demonstrate that the attribution of a tunnel electronic resonance to a peculiar π molecular orbital of the molecule (or σ intermonomer chemical bond) in the STM junction is inappropriate. With an STM weak-measurement-like procedure, a dI/dV resonance results from the conductance contribution of many molecular states whose superposition makes it difficult to reconstruct an apparent molecular orbital electron probability density map.

We present Density Functional Theory (DFT) investigations in the General Gradient Approximation (GGA) of the structural and electronic properties of the Ag2V4O11 (SVO) compound. We carried out a detailed study of the different structures of SVO proposed in the literature, by comparing the results obtained using DFT and the DFT+U approach. We found that two of the proposed structures are equally probable, the third one being unstable. We have obtained detailed information concerning the structural and electronic properties of SVO, including previously non-existent information on one of the SVO structures, considered hypothetical yet probable in the light of experimental facts from analogous compounds. From the analysis of the electronic density of states and of the Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) states, we propose that, during the earlier stage of the reaction of lithium insertion and de-insertion in Li/SVO primary batteries, the reduction of V5+ takes place before that of Ag. In addition, our results allow to predict that only one kind of vanadium atom would be firstly reduced.