Francesca Moresco

The design of a nanoscale molecular barrow

The design of a monomolecular barrow 1.6 nm×1.5 nm in dimension made of a central board, two rear legs and two front wheels, is discussed. This barrow is guided and driven by the tip apex of an STM which manipulates it from the rear legs. The central board has been chosen in such a way that the rotation of the front wheels can be deduced from the surface tunnelling current intensity measured during a sequence of manipulations of the barrow. Our calculations show that in UHV and without friction, the front wheels of the barrow that we designed will not rotate. This led us to design a new barrow including two ratchet molecular groups to compensate for the absence of friction.

Low temperature manipulation of big molecules in constant height mode

The possibility of extending the lateral manipulation process performed with the tip of a scanning tunneling microscope at low temperature to large molecules is demonstrated. Single Cu–TBPP molecules deposited on a Cu substrate were manipulated by means of the interaction between the molecule and the tip. Due to the complicated structure of the molecules and to their high conductance, we have explored the possibilities of performing controlled lateral manipulation at constant height. On Cu(111) this method makes possible translation combined with rotation of the molecules on the surface.

Moving Nanostructures: Pulse-Induced Positioning of Supramolecular Assemblies

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 also 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.

Lander on Cu(2 1 1) – selective adsorption and surface restructuring by a molecular wire

The large organic molecule C90H98, called Lander, has been investigated on the Cu(2 1 1) surface by low temperature scanning tunnelling microscopy (LT-STM). Different adsorption geometries, which differ in the internal conformation and the orientation of the molecule, are described. These adsorption conformations have been determined by elastic scattering quantum chemistry calculations (ESQC). For T > 120 K, adsorption at selected step edges is combined with an adsorbate induced restructuring. The reconstruction is revealed by lateral STM manipulation and could be imaged with atomic resolution. It has the form of a (3 1 1) facet. The restructured steps can be used as a guidance for lateral manipulation of large molecules. 2003 Elsevier Science B.V. All rights reserved.

Controlled manipulation of atoms and small molecules with a low temperature scanning tunneling microscope

With the scanning tunneling microscope (STM) it became possible to perform controlled manipulations down to the scale of small molecules and single atoms, leading to the fascinating aspect of creating manmade structures on atomic scale. Here we present a short review of our work in the last five years on atomic scale manipulation investigations. Upon soft lateral manipulation of adsorbed species, in which only tip/particle forces are used, three different manipulation modes (pushing, pulling, sliding) can be discerned. We show that also manipulation of highly coordinated native substrate atoms is possible and demonstrate the application of these techniques as local analytic and synthetic chemistry tools with important consequences on surface structure research. Vertical manipulation of Xe and CO is presented, leading to improved imaging and even chemical contrast with deliberately functionalized tips. For the transfer of CO it is shown that beside tip voltage current effects play also an important role. This is also the case for the dissociation of molecules. With CO transferred deliberately to the tip we have also succeeded to perform vibrational spectroscopy on single molecules. Furthermore, first experiments aiming for the transfer of all manipulation modes to thin insulating films are described.

Tetracene Formation by On-Surface Reduction

We present the on-surface reduction of diepoxytetracenes to form genuine tetracene on Cu(111). The conversion is achieved by scanning tunneling microscopy (STM) tip-induced manipulation as well as thermal activation and is conclusively demonstrated by means of atomic force microscopy (AFM) with atomic resolution. We observe that the metallic surface plays an important role in the deoxygenation and for the planarization after bond cleavage.

Synthesis and STM Imaging of Symmetric and Dissymmetric Ethynyl‐Bridged Dimers of Boron–Subphthalocyanine Bowl‐Shaped Nanowheels

The futures wheel: A new class of wheels, based on subphthalocyanine fragments, for future incorporation in functional nanovehicles is reported (see figure). The syntheses of a symmetric wheel, a nitrogen-tagged wheel, and their ethynyl-bridged homodimers are presented. Theoretical calculations and STM imaging demonstrate the advantage of a bowl-shaped structure and the efficiency of the tag for STM imaging.

Decacene: On-Surface Generation

Acenes are intriguing molecules with unique electronic properties. The difficulties in their preparation owing to low stability under ambient conditions are apparent because successful syntheses of long unsubstituted acenes are still scarce, in spite of the great attention they have attracted. Only unsubstituted acenes up to heptacene have been isolated in bulk, with nonacene being the largest acene detected to date. Herein we use on-surface assisted reduction of tetraepoxy decacene precursors on Au(111) as the key step to generate unprecedented decacene which is visualized and its electronic resonances studied by scanning tunneling microscopy (STM) and spectroscopy (STS).

VIBRATIONAL SPECTROSCOPY OF CO/CU(211) WITH A CO TERMINATED TIP

Vibrational excitations of an isolated CO molecule adsorbed on a Cu(211) surface have been, for the first time, observed with a CO terminated scanning tunneling microscope tip. Both the frustrated translational and rotational modes were observed, and in agreement with the case of a metallic tip. The presence of a CO molecule on the tip, transferred by controlled vertical manipulation, strongly influences the frustrated translational mode of the CO molecule, while it does not affect the frustrated rotational mode. The present work demonstrates that scanning tunneling vibrational spectroscopy is also possible with a molecule at the end of the tip, opening new interesting fields of research and putting some more light on the still open question of inelastic tunneling and its selection rules.

STM manipulation of a subphthalocyanine double-wheel molecule on Au(111).

A new class of double-wheel molecules is manipulated on a Au(111) surface by the tip of a scanning tunneling microscope (STM) at low temperature. The double-wheel molecule consists of two subphthalocyanine wheels connected by a central rotation carbon axis. Each of the subphthalocyanine wheels has a nitrogen tag to monitor its intramolecular rolling during an STM manipulation sequence. The position of the tag can be followed by STM, allowing us to distinguish between the different lateral movements of the molecule on the surface when manipulated by the STM tip.