Directional and angular locking in the driven motion of Au islands on ${\mathrm{MoS}}_{2}$

Directional and angular locking in the driven motion of Au islands on ${MoS}_{2}$

Felix Trillitzsch, Roberto Guerra, Arkadiusz Janas, Nicola Manini, Franciszek Krok, and Enrico Gnecco

Phys. Rev. B 98, 165417 – Published 12 October 2018

Abstract

We have performed AFM nanomanipulation experiments on triangular Au islands (with typical linear size of 25–80 nm) previously grown on a ${MoS}_{2}$ surface. These islands are found to move along preferential directions, independently of the angle of attack of the scanning probe. A comparison between molecular-dynamics simulations and atomically resolved STM images prove that these directions correspond to the zigzag alignments of the Mo and S atoms on the substrate. This is related to the observed systematic orientation of the islands, which is in turn a consequence of a sharp energy minimum as a function of each island's angular orientation. This directional-locked motion is entirely different from nanomanipulation involving disordered contact interfaces, where the direction of motion is determined by the island geometry and the scan pattern, and roto-translational motion is observed in arbitrary directions. Besides shedding light on the fundamental mechanisms of friction in the considered class of materials, our results could find important applications in the controlled positioning of metal nanoislands as electrodes for molecular electronics.

Received 17 January 2018
Revised 10 September 2018

DOI:https://doi.org/10.1103/PhysRevB.98.165417

Physics Subject Headings (PhySH)

Friction

Nanoclusters

Atomic force microscopy

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Felix Trillitzsch

Otto Schott Institute of Materials Research (OSIM), Friedrich Schiller University Jena, Löbdergraben 32, 07743 Jena, Germany

Roberto Guerra

Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria 16, 20133 Milano, Italy and Center for Complexity and Biosystems, University of Milan, 20133 Milan, Italy

Arkadiusz Janas

Marian Smoluchowski Institute of Physics, Jagiellonian University, Lojasiewicza 11, 30-348 Krakow, Poland

Nicola Manini

Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria 16, 20133 Milano, Italy

Franciszek Krok

Marian Smoluchowski Institute of Physics, Jagiellonian University, Lojasiewicza 11, 30-348 Krakow, Poland

Enrico Gnecco

Otto Schott Institute of Materials Research (OSIM), Friedrich Schiller University Jena, Löbdergraben 32, 07742 Jena, Germany

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Vol. 98, Iss. 16 — 15 October 2018

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Images

Figure 1
(a) SEM, (b) AFM, and (c) STM images of different areas of the Au/ ${MoS}_{2}$ sample in the region chosen for the nanomanipulation experiment. Scan parameters for STM: bias voltage $V_{bias} = 1$ V and tunneling current $I = 100$ pA. (d), (e) Atomically resolved STM images of a Au island and the ${MoS}_{2}$ substrate ( $V_{bias} = 2.5$ V, $I = 400$ pA in both cases). Note the orientation of the armchair and zigzag directions of the substrate. Simultaneous imaging of islands and substrate with comparable resolution was not possible since the islands started moving while the tip was climbing up them already with $I = 150$ pA, which explains the slightly different distortions due to thermal drift. To avoid misunderstanding, one should also note that the STM detects only half of the hexagonal vertices in Fig. 3.
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Figure 2
(a) QI-mode AFM topography of a sample region enclosing a square area (inside the dashed gray line) where previous manipulation took place. (b) Adhesion image recorded during manipulation of Au islands on ${MoS}_{2}$ using a pyramidal tip with the turnable stage rotated by an angle $α = 25^{\circ}$ . In this case, the AFM tip was scanned along a series of parallel lines separated by a distance $b = 2$ nm. Switching between imaging and manipulation is simply achieved by increasing the maximum normal force from 1 nN to 1.5 nN.
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Figure 3
(a) Preferential sliding direction of the Au islands manipulated in tapping mode as a function of the scan direction, as defined by the angles $θ$ and $α$ in (b). The filled and empty circles correspond to the values of $θ$ obtained as described in the text. Red segments highlight the locking directions. (b) Schematics of the manipulation experiment. The Au islands are approached by the tip with a certain angle $α$ , and they move with a generally different angle $θ$ . Both angles are referred to the armchair direction of the ${MoS}_{2}$ substrate. Note that, in a “scan-hit-move” sequence, the tapping tip hits the corner region of the island, and pushes it in a rather unpredictable direction identified by an angle $γ$ , with $60^{\circ} < γ < 120^{\circ}$ (in green).
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Figure 4
(a) The simulated pathways of the island COM on the ${MoS}_{2}$ surface for several applied force directions $γ$ , overlapped to the computed PES map (in grayscale); inset: the initial configuration of the island. (b) Island orientation $β$ as a function of the COM distance from the starting point, during the corresponding motions reported in panel (a). (c) Red circles: as a function of the island orientation angle $β$ on ${MoS}_{2}$ , the simulated total energy, $E_{tot}$ including Au-Au and Au- ${MoS}_{2}$ interaction energies; blue squares: the sole Au- ${MoS}_{2}$ interaction energy contribution, $E_{int}$ .
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Physical Review B

covering condensed matter and materials physics

Directional and angular locking in the driven motion of Au islands on ${MoS}_{2}$

Felix Trillitzsch, Roberto Guerra, Arkadiusz Janas, Nicola Manini, Franciszek Krok, and Enrico Gnecco

Phys. Rev. B 98, 165417 – Published 12 October 2018

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Physical Review B

covering condensed matter and materials physics

Directional and angular locking in the driven motion of Au islands on MoS2

Felix Trillitzsch, Roberto Guerra, Arkadiusz Janas, Nicola Manini, Franciszek Krok, and Enrico Gnecco

Phys. Rev. B 98, 165417 – Published 12 October 2018

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Directional and angular locking in the driven motion of Au islands on ${MoS}_{2}$