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Mechanics with Molecules

Periodic Reporting for period 2 - MEMO (Mechanics with Molecules)

Reporting period: 2018-10-01 to 2020-03-31

The main objective of the MEMO project is to construct and test single molecule-machines on a surface and one at a time, controlling the rotation and the work delivered by a single molecule-motor directly at the atomic scale. The molecule motors and gears designed and tested by MEMO will be further adapted to applications requiring collective and synchronous motion.
"During the first reporting period, the MEMO project has reached the following main results:

WP1 aims at the design, chemical synthesis, deposition and assembly of molecule-gears of increasing diameters. In this context, different strategies have been tested to provide a rotation axle to molecule-gears, and various molecule-gears have been designed and synthesized accordingly. We succeeded in producing single Cu atom axles on Pb(111) and mounting hexa(aryl)benzene molecule-gears on top of these single atoms in view of rotation experiments. In parallel, we investigated the chemical anchoring of molecules by direct chemisorption of ether functional groups, or by thermally- or voltage pulse-induced on-surface reactions. We also explored an alternative strategy to include the metallic rotation axle within a metallo-organic complex pre-assembled by chemical synthesis in solution. A ruthenium complex featuring a supporting tris(indazolyl)borate ligand was thus prepared and its synthetic route was optimized. Various molecule-gears with a small core, such as a benzene or cyclopentadiene ring, or a large polyaromatic core, such as hexabenzocoronene, were synthesized in order to test the compatibility of such cores with the atomic scale rotation axles. Short teeth based on single para-phenylene units were first targeted, but molecule-gears with longer teeth were also prepared. Finally, we investigated a variety of methods (choice of fuel, solvent, temperature) to control the rate of rotation of a known chemically-fueled [2]catenane rotor in view of AFM studies in solution.

In WP2, we have investigated (experimentally and theoretically) a first example of molecular motor, a o-MeO-DMBI molecule, that will be useful in the next MEMO phase to drive the rotation of molecule-gears. By applying voltage pulses with the STM tip we proved that the molecule reproducibly rotates step by step around its anchoring point. Driven by inelastic tunneling electrons, the molecule can controllably rotate, stepwise and unidirectional, either clockwise or counterclockwise depending on their enantiomeric form. A molecular motor, suitable for force spectroscopy measurements in solution has been synthesized. We have derivatized the structure of the motor synthesized and described in WP1 to extend one arm of the rotating subunit with a long chain. The synthesis of a linear ratchet mimicking half rotation of the motor envisaged, is also in progress. We have also progressed in the theory of molecule-motor motive power. The dynamics of a windmill molecule on a gold surface was characterized as induced by electrons. The partial energy barriers were evaluated and the windmill superstructure was unravelled.

The aim of WP3 is to transmit motion between molecules, which has been studied in the first year by different approaches. First, by linking molecule-gears, one of them being adsorbed on a single metal atom. If the second ""handle"" molecule is then manipulated by an STM tip, a rotation of the entire molecule-gear dimer is achieved. Second, four molecular switches were combined in a tetrahedral shape. The upwards pointing switch can be reversibly and very efficiently isomerized between an extended and a shorter configuration, which is the basis to transmit motion in a next step to molecules that are adsorbed on top. In addition, the transmission of motion between planar molecules has been studied by different groups in theoretical simulations.

MEMO has defined five technology Nodes for the roadmap of miniaturizing a mechanical calculator: Node 1: between 10 mm and 1 mm, Node 2: between 1 mm and 10 m, Node 3: between 10 m and 100 nm, Node 4: between 100 nm and 10 nm and Node 5: the molecular scale. During year 1, Node 1 was assessed by machine tools, 3D printers and laser cutting leading to a 5 stages mechanical calculator metallic gears with a diameter of 2 mm and two levels of mechanics per stage. Node 2 was demonstrated using scanning optical lithography with the construction of a two-stages mechanical calculator with 50 m in diameter gears and only 1 level of mechanics per stage. Node 3 was started in anticipation to explore the new He+ lithography technique. 80 nm gears with 10 asymmetric teeth have been fabricated first on SiO2 and then on an 8 m thick graphite layer deposited on the SiO2 surface to master the friction effect of the gears around their axle.

MEMO organized the first Academy-Industry day to favour exchanges and synergy with the industry, which took place on the 31 August 2018 at the QF Hotel in Dresden, Neumarkt 1. The list of participants comprised representatives from clock industry, a German SME working in Nano-indentation, the Fraunhofer Institutes in Dresden, as well as the director of the Arithmeum Museum in Bonn, Germany, who is an expert on the historical development of mechanical calculating machines."
In the first reporting period, we started to organize Nanocar Race II. An international organizing committee was nominated, with members from MEMO and outside MEMO to cover all the possible interested continents. In February 2018, a first call for preregistration was published. At the end of June 2018, MEMO had received 13 official pre-registration forms, which have been accepted by the organizing committee. The teams have now time until January 2019 to complete, if needed, the pre-registration. Then, each team will have two years to improve its molecular design and to train on its own LT-UHV single tip STM on Au(111).
1st version of a planar mechanical calculator inspired by the machine of G. Auch (printed in 3D)