Browsing by Author "Grill, Leonhard"

Now showing 1 - 5 of 5
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    Autonomous Single-Molecule Manipulation Based on Reinforcement Learning
    (American Chemical Society, 2023) Ramsauer, Bernhard; Simpson, Grant J.; Cartus, Johannes J.; Jeindl, Andreas; García-López, Victor; Tour, James M.; Grill, Leonhard; Hofmann, Oliver T.; Smalley-Curl Institute; NanoCarbon Center
    Building nanostructures one-by-one requires precise control of single molecules over many manipulation steps. The ideal scenario for machine learning algorithms is complex, repetitive, and time-consuming. Here, we show a reinforcement learning algorithm that learns how to control a single dipolar molecule in the electric field of a scanning tunneling microscope. Using about 2250 iterations to train, the algorithm learned to manipulate the molecule toward specific positions on the surface. Simultaneously, it generates physical insights into the movement as well as orientation of the molecule, based on the position where the electric field is applied relative to the molecule. This reveals that molecular movement is strongly inhibited in some directions, and the torque is not symmetric around the dipole moment.
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    Chirality-Specific Unidirectional Rotation of Molecular Motors on Cu(111)
    (American Chemical Society, 2023) Schied, Monika; Prezzi, Deborah; Liu, Dongdong; Kowarik, Stefan; Jacobson, Peter A.; Corni, Stefano; Tour, James M.; Grill, Leonhard; Smalley Institute for Nanoscale Science and Technology; Welch Institute for Advanced Materials; NanoCarbon Laboratory
    Molecular motors have chemical properties that enable unidirectional motion, thus breaking microscopic reversibility. They are well studied in solution, but much less is known regarding their behavior on solid surfaces. Here, single motor molecules adsorbed on a Cu(111) surface are excited by voltages pulses from an STM tip, which leads to their rotation around a fixed pivot point. Comparison with calculations shows that this axis results from a chemical bond of a sulfur atom in the chemical structure and a metal atom of the surface. While statistics show approximately equal rotations in both directions, clockwise and anticlockwise, a detailed study reveals that these motions are enantiomer-specific. Hence, the rotation direction of each individual molecule depends on its chirality, which can be determined from STM images. At first glance, these dynamics could be assigned to the activation of the motor molecule, but our results show that this is unlikely as the molecule remains in the same conformation after rotation. Additionally, a control molecule, although it lacks unidirectional rotation in solution, also shows unidirectional rotation for each enantiomer. Hence, it seems that the unidirectional rotation is not specifically related to the motor property of the molecule. The calculated energy barriers for motion show that the propeller-like motor activity requires higher energy than the simple rotation of the molecule as a rigid object, which is therefore preferred.
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    Directing and Understanding the Translation of a Single Molecule Dipole
    (Amerian Chemical Society, 2023) Simpson, Grant J.; García-López, Víctor; Boese, A. Daniel; Tour, James M.; Grill, Leonhard; Smalley-Curl Institute; NanoCarbon Center
    Understanding the directed motion of a single molecule on surfaces is not only important in the well-established field of heterogeneous catalysis but also for the design of artificial nanoarchitectures and molecular machines. Here, we report how the tip of a scanning tunneling microscope (STM) can be used to control the translation direction of a single polar molecule. Through the interaction of the molecular dipole with the electric field of the STM junction, it was found that both translations and rotations of the molecule occur. By considering the location of the tip with respect to the axis of the dipole moment, we can deduce the order in which rotation and translation take place. While the molecule–tip interaction dominates, computational results suggest that the translation is influenced by the surface direction along which the motion takes place.
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    How to control single-molecule rotation
    (Springer Nature, 2019) Simpson, Grant J.; García-López, Víctor; Daniel Boese, A.; Tour, James M.; Grill, Leonhard
    The orientation of molecules is crucial in many chemical processes. Here, we report how single dipolar molecules can be oriented with maximum precision using the electric field of a scanning tunneling microscope. Rotation is found to occur around a fixed pivot point that is caused by the specific interaction of an oxygen atom in the molecule with the Ag(111) surface. Both directions of rotation are realized at will with 100% directionality. Consequently, the internal dipole moment of an individual molecule can be spatially mapped via its behavior in an applied electric field. The importance of the oxygen-surface interaction is demonstrated by the addition of a silver atom between a single molecule and the surface and the consequent loss of the pivot point.
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    Inverted Conformation Stability of a Motor Molecule on a Metal Surface
    (American Chemical Society, 2022) Schied, Monika; Prezzi, Deborah; Liu, Dongdong; Jacobson, Peter; Corni, Stefano; Tour, James M.; Grill, Leonhard; Smalley Institute for Nanoscale Science and Technology; Welch Institute for Advanced Materials
    Molecular motors have been intensely studied in solution, but less commonly on solid surfaces that offer fixed points of reference for their motion and allow high-resolution single-molecule imaging by scanning probe microscopy. Surface adsorption of molecules can also alter the potential energy surface and consequently preferred intramolecular conformations, but it is unknown how this affects motor molecules. Here, we show how the different conformations of motor molecules are modified by surface adsorption using a combination of scanning tunneling microscopy and density functional theory. These results demonstrate how the contact of a motor molecule with a solid can affect the energetics of the molecular conformations.