Single-Molecule Rotational Switch on a Dangling Bond Dimer Bearing

Single-Molecule Rotational Switch on a Dangling Bond Dimer Bearing Szymon Godlewski,*,† Hiroyo Kawai,*,‡ Marek Kolmer,† Rafał Zuzak,† Antonio M. Echavarren,§ Christian Joachim,∥ Marek Szymonski,† and Mark Saeys⊥ †

Centre for Nanometer-Scale Science and Advanced Materials, NANOSAM, Faculty of Physics, Astronomy and Applied Computer Science, Jagiellonian University, Łojasiewicza 11, PL 30-348 Krakow, Poland ‡ Institute of Materials Research and Engineering, 2 Fusionopolis Way, Innovis, #08-03, Singapore 138634 § Institute of Chemical Research of Catalonia (ICIQ), Av. Països Catalans 16, 43007 Tarragona, Spain ∥ Nanosciences Group & MANA Satellite, CEMES-CNRS, 29 rue Jeanne Marvig, F-31055 Toulouse, France & International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan ⊥ Laboratory for Chemical Technology, Ghent University, Technologiepark 914, 9052 Ghent, Belgium S Supporting Information *

ABSTRACT: One of the key challenges in the construction of atomic-scale circuits and molecular machines is to design molecular rotors and switches by controlling the linear or rotational movement of a molecule while preserving its intrinsic electronic properties. Here, we demonstrate both the continuous rotational switching and the controlled step-by-step single switching of a trinaphthylene molecule adsorbed on a dangling bond dimer created on a hydrogen-passivated Ge(001):H surface. The molecular switch is on-surface assembled when the covalent bonds between the molecule and the dangling bond dimer are controllably broken, and the molecule is attached to the dimer by long-range van der Waals interactions. In this configuration, the molecule retains its intrinsic electronic properties, as confirmed by combined scanning tunneling microscopy/spectroscopy (STM/STS) measurements, density functional theory calculations, and advanced STM image calculations. Continuous switching of the molecule is initiated by vibronic excitations when the electrons are tunneling through the lowest unoccupied molecular orbital state of the molecule. The switching path is a combination of a sliding and rotation motion over the dangling bond dimer pivot. By carefully selecting the STM conditions, control over discrete single switching events is also achieved. Combined with the ability to create dangling bond dimers with atomic precision, the controlled rotational molecular switch is expected to be a crucial building block for more complex surface atomic-scale devices. KEYWORDS: hydrogenated semiconductor surface, organic molecule, single-molecule devices, molecular rotor, molecular switch, scanning tunneling microscope, single-molecule manipulation, surface dangling bonds rotation and tautomerization, either activated thermally,19,20 by light,21,22 or by inelastic tunneling electrons,23,24 have been reported on metal surfaces. The controlled manipulation, rotation, and switching of molecules on semiconducting and insulating surfaces25−28 did not yet reach the level of maturity reported on metals. On the industrially important silicon surface, however, a number of experiments have been reported,29−33 including local STMinduced switching between different configurations,34,35 tipinduced hopping,36 molecule−surface bond breaking,37,38

T

he design of electronic devices based on the intrinsic electronic properties of individual molecules is one of the ultimate goals for nanotechnology.1 A crucial yet challenging element in any molecular-scale device is the ability to controllably switch between two states, for example, by controlling the linear or rotational movement of a molecule between two different configurations. Over the past two decades, the development of scanning probe microscopy has facilitated the controlled tip-induced positioning of individual atoms and molecules.2−14 This development has reached unprecedented levels of precision on metal surfaces12−15 and has allowed the atom-by-atom or molecule-by-molecule construction of complex nanostructures.16 Scanning tunneling microscopy (STM)-induced switching of molecules is also quite well-established on metal surfaces,2−10,17,18 and single-molecule © 2016 American Chemical Society

Received: May 31, 2016 Accepted: August 9, 2016 Published: August 9, 2016 8499

DOI: 10.1021/acsnano.6b03590 ACS Nano 2016, 10, 8499−8507

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ACS Nano binding state conversion,39 nonlocal long-range molecular migration,40 and mechanically activated switching of a singlemolecule junction.41 In the construction of prototypical singlemolecule devices, the application of thin insulating films42 or of passivated semiconductors43 as platforms for molecular devices to avoid strong interaction of the molecule with the substrate has been reported recently. These substrates have the important advantage that the molecules can be electronically decoupled from the underlying bulk states and hence retain their intrinsic electronic properties.6,42 A particularly promising technique to decouple molecular from substrate electronic states is the use of hydrogen-passivated semiconductor surfaces.43−47 In addition, the tip-induced desorption of hydrogen atoms from the Ge(001):H and Si(001):H surfaces allows atomically precise patterning of surface dangling bonds (DBs) on these substrates.48−58 Such surface DBs can serve both as van der Waals46 and as strong covalent anchoring sites for individual molecules and also enable control over singlemolecule conductance due to defect charging.59 Furthermore, it was recently shown that the STM tip-induced conversion from the covalent state to the van der Waals configuration of planar aromatic molecules on surface DB dimers is feasible,47 hoping for the fabrication of single-molecule switches. In general, however, controlled manipulation of molecules on passivated surfaces is rarely described. Recently, the lateral manipulation of a trinaphthylene on a Ge(001):H surface in van der Waals manipulation mode46 was presented. Dujardin et al. reported the manipulation of molecular molds,60 and Hersam et al. described rotating phthalocyanines, however, with no control over the molecule movement.61 Controlled lateral manipulation of individual molecules on insulating films initiated by vibronic excitations was demonstrated by Swart et al.62 However, until now, controlled rotational manipulation and switching on a passivated surface have not been achieved. Here, we demonstrate the fabrication and controlled operation of the first molecular rotational switch on a hydrogen-passivated semiconductor surface. It is shown that a lone DB pair can act as the atomic-scale pivot point for a planar rotating molecular switch, which can be operated controllably between two equivalent surface configurations on Ge(001):H. This molecular switch is prepared by STM-tip-induced breaking of the covalent bonds between a planar aromatic molecule and the DB dimer. We demonstrate that the device could be operated in two modes, either continuous or discrete. Continuous rotational switching is induced by vibronic excitations triggered by inelastic tunneling electrons. Control over individual switching movements is achieved by a suitable positioning of the STM tip and application of the appropriate bias voltage within the tunneling junction. Finally, it is shown that the van der Waals interaction between the DB dimer and the molecule is sufficient to stabilize the molecule at the pivot, even if frequent DB dimer flipping is initiated by holes injected from the STM tip.

Figure 1. Breaking of the covalent bonds between the trinaphthylene molecule and the DB dimer. (a) Molecule is attached covalently to the DB dimer (white circle). (b) Same molecule after breaking the covalent bonds (white circle). The molecule adsorbed on a single DB (yellow circle) is used as a reference for the position of the molecule. STM scanning parameters: 2 pA and −2.0 V.

We have recently shown that the covalent bonds between the trinaphthylene molecule and the DB dimer can be broken by applying an STM pulse at around +3.0 V,47 a voltage corresponding to the energy of the lowest unoccupied molecular orbital (LUMO) of the molecule.43 After the STM pulse, the molecule rotates 90° but remains pinned to the same DB dimer as marked by white dashed circles in Figure 1. In the new configuration, the adsorbed molecule is no longer covalently attached to the DB dimer but rather held by longrange van der Waals forces to a buckled DB dimer (for details, see Godlewski et al.47). In this geometry, the molecule retains its intrinsic electronic properties as will be demonstrated below. Molecule Rotation. An intriguing phenomenon is observed when a positive bias voltage is applied with the STM tip directly positioned above the molecule on the DB dimer. For a voltage above +2.5 V, the tunneling current is found to switch continuously between two levels (Figure 2a). In this experiment, the movement of the molecule causes switching of the current value. Indeed, filled-state images corresponding to the two current levels show that the molecule switches back and forth between two mirror surface configurations (Figure 2b). This suggests that the molecule is rotating and the DB dimer acts as the pivot for this rotation. Occasionally, as marked by the red I(t) trace in Figure 2a, the molecule escapes from the DB dimer and can be found near the dimer on the hydrogenated Ge(001):H surface. The STM appearance of the molecule in the latter configuration (Figure 2b, bottom) closely resembles previously reported images of the molecule placed intentionally on a fully hydrogenated Ge(001):H

RESULTS AND DISCUSSION Fabrication of the Molecular Switch. Trinaphthylene molecules evaporated on a Ge(001):H surface kept at room temperature (RT) move freely across the surface until they are immobilized by surface defects. The majority of the molecules attaches covalently to surface DB dimers, and they can be identified by their characteristic STM constant current images presented in Figure 1.39 8500


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functional63−65 to account for the van der Waals-type interaction between the molecule and the DB dimer (see Supporting Information, section 1). The calculations show that the initial potential barrier is steeper for the 180° rotation path than for the sliding−rotation−sliding path. For example, initial rotation of the molecule by 20° is 0.13 eV uphill, whereas initial sliding of the molecule by 2 Å is only 0.04 eV uphill, which may indicate the preference for the combination of sliding and 60° rotation over the 180° rotation on the DB dimer. However, the calculations do not show a large difference in the overall barrier height for the two paths (Supporting Information, section 1). As we demonstrate below, the switching is initiated by vibronic excitations (Figure 2 and discussion below), and therefore, a ground-state DFT calculation for the switching motion path is not expected to capture the detailed dynamics of the switching event, which involves excited electronic states, in particular, its LUMO component. Molecular Electronic Properties. To elucidate how the switching of the molecule is triggered, we have analyzed the electronic properties of the molecule attached noncovalently to the DB dimer. The dI/dV scanning tunneling spectroscopy (STS) data are presented in Figure 4a. The blue curve shows the spectrum acquired within a narrow voltage range and for low tunneling currents. With these settings, DB dimer oscillations at negative voltage are avoided and the resonance originating from the buckled DB dimer underneath the molecule can be captured. The spectrum clearly shows two dI/dV peaks at around −1.1 V and +0.85 V, which are attributed to the π and π* states of the DB dimer. These resonances are recorded within the same voltage range as for the bare DB dimer.48,50,66 Slight differences in the position of the resonances can be attributed to small differences in the buckling angle when the trinaphthylene molecule is adsorbed on the DB dimer. The presence of the DB dimer resonances again confirms that there are no covalent bonds between the molecule and the DB dimer and that the DB dimer underneath the molecule is buckled. Furthermore, experimental observation of DB dimer flipping underneath the molecule supports such assignment (see Supporting Information, section 2). To capture the spectrum associated with the molecule, the tip height was increased (green curve, Figure 4a). The resonance at around +3.0 V is similar to the resonance obtained for the molecule on a fully hydrogenated Ge(001):H surface (red curve). In both cases, the resonance is attributed to the LUMO of the molecule. For positive bias voltages, it is worth noting that the rapid DB dimer oscillations do not introduce telegraph noise into the measurements50 because the high frequency of the oscillations goes beyond the time resolution of the apparatus.50,66 Therefore, for positive voltages, the dI/dV spectra were recorded with the tip placed over the DB dimer as indicated in Figure 4b. This, however, does not hold for negative voltages, and the DB dimer oscillations result in a noisy dI/dV spectrum (see Figure 5e). Therefore, for negative voltages, the dI/dV spectrum was recorded with the STM tip positioned over one of the legs of the molecule, away from the DB dimer, as marked by the pink circle in Figure 4b. The corresponding dI/ dV curve shows a resonance at around −2.4 V. This is within the same voltage range as for the molecule on the fully hydrogenated Ge(001):H surface (red curve). In both cases, the resonance is attributed to the highest occupied molecule orbital (HOMO) of the molecule. The similarity between the resonance for the molecule on the DB dimer and on the

Figure 2. (a) Tunneling current vs time trace, I(t), at +2.7 V for the STM tip positioned above the trinaphthylene molecule on the DB dimer. Three different current levels correspond to three different configurations of the molecule adsorbed on or near the DB dimer. Experimentally measured (b) and calculated (c) filled-state STM images are shown for the configurations corresponding with the three current levels. (d) Atomic structures corresponding to the three calculated images. The dashed lines indicate the dimer row in which the DB dimer is located. The black cross in panel (b) shows the lateral tip position during manipulation. Experimental STM images: 2 pA and −2.0 V. Calculated images: 2 pA and −1.3 V.

surface.43,47 Subtle differences with STM images obtained on a fully hydrogenated surface result from the slightly different position of the molecule relative to the characteristic dimer rows,43 which is likely caused by the presence and influence of the DB dimer. The calculated STM images (Figure 2c) are in good agreement with the experimental STM images, confirming the positions of the molecule above the DB dimer. The current versus time trace for the escaping molecule (red trace) provides an indication of the path followed by the molecule on the surface as it switches between the two mirror geometries. Analysis of several escape events shows that the molecule never rotates during its escape. This observation suggests that the switching path may in fact be a combination of sliding and 60° rotation rather than a 180° rotation on the DB dimer. Both motions are schematically illustrated in Figure 3a,b. To distinguish both paths, their energy profiles were calculated using density functional theory (DFT) with the vdW-DF

Figure 3. Illustration of the (a) sliding−rotation−sliding path and (b) 180° rotation path for the switching of the molecule on the DB dimer pivot point. The yellow dashed line indicates the dimer row in which the DB dimer is located; blue and red arrows mark the switching direction in (a) and (b), respectively, and small black arrows indicate the escape of the molecule from the DB dimer site into the nearby position. 8501


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Figure 4. (a) Experimental dI/dV and (c) calculated T(E) spectra obtained for a trinaphthylene molecule adsorbed on a fully hydrogenated Ge(001):H surface (red curves) and on a DB dimer (blue and magenta curves). The experimental dI/dV spectrum with the tip above the DB dimer was measured for two different tip heights. A decreased tip height (blue curve) was used to capture the resonances associated with the DB states, while a larger tip height was used to obtain the resonance associated with the LUMO of the molecule (green curve). For negative voltages, the dI/dV spectrum (magenta curve) was obtained with the tip positioned over the leg of the molecule because the spectrum is affected by DB dimer oscillations. Experimental (b) and calculated (d) STM images of the molecule adsorbed on a DB dimer (see Figure 2d for the atomic structure). The tip positions at which the spectra were obtained are labeled by a blue cross and green and magenta circles, corresponding to the blue, green, and magenta curves in the spectra. Experimental STM image: 2 pA and −2.0 V. Calculated STM image: 2 pA and −1.3 V. Scan area: 1.67 nm × 1.67 nm for both.

Figure 5. Experimental and calculated STM images of trinaphthylene adsorbed on a DB dimer at (a,b) low and (c,d) high biases. The calculated STM images are a superposition of the image for the “up” and for the “down” geometry (see Supporting Information, section 3, for details). (e) I−V curve obtained with the tip above the DB dimer, as indicated in (a) by a black cross. The current fluctuations caused by DB dimer oscillations are apparent. Experimental STM images: 2 pA, −1.0 V (low bias) and −2.7 V (high bias). Calculated images: 2 pA, −0.8 V (low bias) and −2.0 V (high bias). Scan area 1.67 nm × 1.67 nm for all images.

the molecule on the surface as described in more detail by Godlewski et al.46 The nature of the filled-state dI/dV resonance was confirmed by experimental and calculated STM images acquired at different voltages. The image recorded within the gap of the molecule, at a voltage of −1.0 V and close to the DB dimer resonance, is shown in Figure 5a. The image is clearly dominated by the DB dimer. For voltages exceeding the position of the dI/dV resonance associated with the HOMO of the molecule, the contribution from the HOMO states becomes apparent in both the experimental and the calculated images, as shown by the intramolecular contrast in Figure 5c,d (for details of image calculations, see Supporting Information, section 3). The noisy nature of the dI/dV data collected with the tip placed above the DB dimer is illustrated in Figure 5e. Again, it is clear that the DB dimer is oscillating for negative voltages, even while exceeding the voltage where the HOMO

Ge(001):H surface further supports the weak electronic interaction between the molecule and the DB dimer and shows that the electronic properties of the molecule are nearly unperturbed by the van der Waals interaction with the DB dimer. The T(E) spectra calculated for the molecule on the DB dimer and on the passivated Ge(001):H surface (Figure 4c) support the assignments in the experimental spectra. The differences between the calculated and experimental positions of the resonances can be attributed to several factors, that is, the well-known underestimation of HOMO−LUMO gaps by DFT,67 the tip-induced band bending,51,68 and screening of 8502


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molecule tends to escape from the DB dimer rather than switch, which hinders determination of the switching rate versus tunneling current dependence. Control over the switching event is clearly delicate. The fact that continuous switching is triggered for voltages above +2.5 V, which coincides with the appearance of the LUMO resonance of the molecule as shown in Figure 6a, strongly suggests that the rotation is triggered by vibronic excitations, similarly to the manipulation events described on insulating films by Swart et al.62 Controlling Single Switching Events. In addition to the continuous rotational switching initiated at voltages corresponding to the LUMO resonance, it is also possible to induce discrete, single switching events. This is achieved when the tip is placed slightly off-center above the DB dimer and over the outer part of the bright lobe corresponding to the DB dimer, as indicated by the black cross in Figure 7a. Next, the feedback

resonance of the molecule is captured. It is important to note that, despite the rapid oscillations of the DB dimer, the molecule remains attached to the DB dimer and does not move or rotate for negative voltages. Indeed, the rotation is only observed for positive voltages (Figure 2). Vibronic Excitations. The dependence of the rotation rate on the applied bias voltage displayed in Figure 6a is obtained

Figure 7. (a−c) STM images illustrating the single switching event achieved with an STM tip positioned slightly off-center above the DB dimer, as indicated by the black cross in (a) (2 pA and −2.0 V; scan area 1.67 nm × 1.67 nm). (d) Typical I−V curve acquired during a single switching event. The switching event is recorded as a sudden drop in the tunneling current at approximately +1.3 V. Figure 6. (a) Dependence of the rotation rate of the molecule on the bias voltage for a tunneling current of 2 pA. The blue line shows the STS dI/dV data recorded for the molecule on the DB dimer. (b) I(t) telegraph noise recorded at +2.6 V over the switching molecule (black trace) and on a Ge(001):H surface (pink). (c) Experimental STM image of the molecule adsorbed on a DB dimer (2 pA and −2.0 V; scan area 1.67 nm × 1.67 nm). The tip position during the molecule rotation is indicated by the black cross.

loop is switched off with a fixed STM tip position, and the voltage is increased from −2.0 to +1.5 V. The single switching event is normally recorded as a sudden drop in the tunneling current intensity (see Figure 7d) at bias values far below the threshold for continuous rotation, which rules out vibronic excitations. This means that a single switching event is triggered differently than continuous switching. Single switching events depend on the lateral position of the tip and could be initiated only if the tip is placed over the outer part of the molecule, offcenter above the DB dimer. This suggests that the field between the tip apex and the surface causes the switching event. Indeed, manipulation experiments on fully hydrogenated Ge(001):H show that a nearby molecule tends to move toward the tip when empty states are probed.43,47 The off-center location of the STM tip in a single switching event hence induces in-plane

from the recorded telegraph noise signals (Figure 6b). Rotation starts when the voltage exceeds +2.5 V, and the rate grows quickly with the bias. In fact, for voltages exceeding +2.8 V, the molecule often escapes rather than rotates during the experiments. Also the tunneling current needs to be kept small to prevent the molecule from escaping. Typically, tunneling currents of 1−2 pA are used. Even at 50 pA, the 8503


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Figure 8. Tunneling current vs time trace, I(t), at −1.0 V for an STM tip positioned above the DB dimer for a low (a) and a high (b) tunneling current. The position of the tip during acquisition of the I(t) data is shown schematically on the left. (c) Experimental STM image of a DB dimer (−2.0 V, 2 pA). (d,e) Corresponding tunneling current vs time trace, I(t), at −1.0 V for an STM tip positioned above a trinaphthylene molecule adsorbed on a DB dimer. The position of the tip during acquisition of I(t) data is shown schematically on the left. (f) Experimental STM image of the adsorbed molecule (−2.0 V and 2 pA). The tunneling current exhibits telegraph noise behavior and switches between two values as the DB dimer (bare or underneath the molecule) switches from one configuration to the other. The two buckling configurations and the tip position in the experiment are illustrated in the left column. (g) Dimer switching rate (SR) as a function of the tunneling current for a bare DB dimer and for the DB dimer underneath a trinaphthylene (Y) molecule. Both the rates of switching from “down” to “up” (DU) and from “up” to “down” (UD) configurations are shown. (h) Atomic structure of the molecule adsorbed on a DB dimer. The position of a DB dimer underneath the molecule is indicated.

rotational sliding of the molecule toward the tip, following the slide−rotation−slide switching path illustrated in Figure 3a. Note that the position of the STM tip remains fixed during a single switching event; that is, the tip is not approached toward the molecule. This rules out that other interactions, like van der Waals attraction between the molecule and the tip, cause the single switching event. DB Dimer Flipping Underneath the Molecule. In the ground state, the DB dimers on Si(001):H and Ge(001):H are buckled by about 20°. Injection of holes or electrons from an STM tip positioned above the DB dimer induces DB dimer flipping between two equivalent geometries, as illustrated by the current versus time trace, I(t), in Figure 8a.49,50,66 Placing the STM tip over one side of the DB dimer removes the equivalence of the geometries. As illustrated in Figure 8, in the “up−down” switching event, the Ge atom below the STM tip moves down from the high position to the low position of the buckled DB dimer. The rate of “up−down” switching grows almost linearly with the tunneling current, Figure 8g, whereas the “down−up” switching rate is proportional to the IN, with N reaching approximately 1.4. Note that the switching rates in both directions are of the same order of magnitude for a given tunneling current. The difference in the N value may originate from the strongly nonuniform charge distribution of the buckled DB dimer. The top Ge atom is negatively charged, whereas the bottom Ge atom is positive. Electron extraction

therefore might proceed more effectively when the tip is placed over the top Ge atom, hence promoting “up−down” flipping. In addition, the electric field generated within the tunneling junction may also influence the switching behavior, leading to further differences between “up−down” and “down−up” flipping. When the trinaphthylene molecule is attached noncovalently to the DB dimer, the dimer underneath the molecule is buckled, as well, and dimer flipping is stimulated when holes are injected from the STM tip.47 However, both geometries are now no longer equivalent, even without the STM tip (Figure 8). As reported in detail by Godlewski et al.,47 analysis of the I(t) traces together with DFT calculations indicates that the geometry in which the Ge atom located closer to the center of the molecule is positioned higher (“up” geometry) is more stable than the “down” geometry (Figure 8 and Supporting Information, sections 2 and 3). We note that for the DB dimer located underneath the molecule, the switching rate at a given voltage increases with the tunneling current, similarly to the case of a bare DB dimer (Figure 8g). However, with the trinaphthylene molecules, the value of N is larger than that for bare DB dimer flipping. We found that for “down−up” switching N reaches approximately 1.2 (0.9 for the bare DB dimer), whereas for the “up−down” processes N equals 2.0 (1.4 for the bare DB dimer). Since the molecule vibration manifold has a vibronic state density increasing nonlinearly as a function 8504


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Package.70−73 The surface is modeled as a 4 × 4 supercell of a fivelayer Ge slab terminated by H atoms at the top and bottom surfaces. The geometry of the trinaphthylene molecule adsorbed on the Ge(001):H surface is optimized using a γ-centered (2 × 2 × 1) k-point grid and a cutoff energy of 400 eV. The surface Green function matching method and an extended Hückel molecular orbital (EHMO) Hamiltonian are used to calculate the STM images and T(E) spectra of the optimized structures,74 where the parameters in the EHMO Hamiltonian are fitted to accurate DFT band structures.43,48 Unlike the more common Tersoff−Hamann approach, where the direct interaction of the tip with surface is not considered,75 our STM model takes into account all the electronic couplings between the tip, the molecule, the Ge(001):H surface, as well as the bulk Ge, as described by Kolmer et al.48

of the excitation energy, a more than linear growth of the switching rate with the tunneling current is expected. For a similar tunneling current, the “up−down” switching rate is 2 orders of magnitude larger than the “down−up” switching rate, as expected from difference in stability for the two geometries. It should be noted that the molecule attached to the DB dimer is completely stable during filled-state imaging and not affected by the frequent switching of the DB dimer underneath the molecule. The vibrational excitations do not seem to force the molecule to escape, and only at higher voltages or currents the molecule eventually tends to be detached from the DB dimer.

CONCLUSIONS We have shown that a planar polyaromatic trinaphthylene molecule attached to a surface DB dimer by van der Waals interactions can function as a planar molecular rotational switch on a DB dimer pivot point. This surface molecular switch is fabricated when the covalent bonds between the molecule and the surface DB dimer are deliberately broken with the STM at liquid helium (4.5 K) temperature. The ultimate control over the discrete, single switching event is obtained when a positive voltage pulse from a carefully positioned STM tip activates the molecule motion. Further, the continuous switching of the molecule is initiated when the applied bias voltage approaches the resonance corresponding to the LUMO of the molecule. This indicates that continuous operation is induced by vibronic excitations involving the excited states of the molecule. On the basis of combined theoretical and experimental studies, we have identified that the molecule follows a sliding−rotation−sliding path to switch between the two equivalent geometries. The described system constitutes the first planar molecular rotational switch constructed on a passivated semiconductor surface and is expected to be a key building block in the fabrication of atomic-scale circuits. We demonstrate that the delicate balance in the molecule−DB dimer interactions makes it possible to use the DB dimer both as an anchoring site and as a pivot point for prototypical molecular switches. The experiment shows that the set of molecular switches could be created initially in the “locked” position, where all molecules are covalently attached to surface DB dimers, and subsequently selectively unlocked to the switching van der Waals configuration by performing a deliberate bond breaking using the STM tip. Finally, we demonstrate that stabilization of the molecule by van der Waals interaction with the DB dimer is sufficient to survive frequent oscillations of the DB dimer pivot point underneath the molecule.

ASSOCIATED CONTENT S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsnano.6b03590. Additional I(t) traces measured for flipping dangling bond dimer and switching molecules; ground-state potential energy profiles for the molecule switching path; and additional STM image calculations for a trinaphthylene molecule adsorbed on a DB dimer (PDF)

AUTHOR INFORMATION Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. Notes

The authors declare no competing financial interest.

ACKNOWLEDGMENTS This research was supported by the National Science Centre, Poland (2014/15/D/ST3/02975). A.M.E. acknowledges the MINECO (Grant No. CTQ2013-42106-P). H.K. acknowledges the A*STAR Computational Resource Centre (A*CRC) for the computational resources and support. M.K. acknowledges financial support received from the Foundation for Polish Science (FNP). C.J. acknowledges the MANA NEXT financial support during this work. The experimental part of the research was carried out with equipment purchased with financial support from the European Regional Development Fund in the framework of the Polish Innovation Economy Operational Program (Contract No. POIG.02.01.00-12-023/08). REFERENCES

METHODS

(1) Lörtscher, E. Wiring Molecules into Circuits. Nat. Nanotechnol. 2013, 8, 381−384. (2) Eigler, D. M.; Schweizer, E. K. Positioning Single Atoms with a Scanning Tunnelling Microscope. Nature 1990, 344, 524−526. (3) Eigler, D. M.; Lutz, C. P.; Rudge, W. E. An Atomic Switch Realized with the Scanning Tunnelling Microscope. Nature 1991, 352, 600−603. (4) Crommie, M. F.; Lutz, C. P.; Eigler, D. M. Confinement of Electrons to Quantum Corrals on a Metal Surface. Science 1993, 262, 218−220. (5) Hla, S.-W.; Bartels, L.; Meyer, G.; Rieder, K.-H. Inducing All Steps of a Chemical Reaction with the Scanning Tunneling Microscope Tip: Towards Single Molecule Engineering. Phys. Rev. Lett. 2000, 85, 2777. (6) Liljeroth, P.; Swart, I.; Paavilainen, I.; Repp, J.; Meyer, G. SingleMolecule Synthesis and Characterization of Metal-Ligand Complexes by Low-Temperature STM. Nano Lett. 2010, 10, 2475−2479.

Experimental Details. The experiments are performed in a multichamber ultrahigh vacuum system equipped with a lowtemperature STM manufactured by Omicron Nanotechnology GmbH. STM imaging and planar manipulation are performed at liquid helium temperature using electrochemically etched tungsten tips as probes. Germanium samples are prepared by a standard procedure of argon ion bombardment and thermal annealing at 770 °C. Hydrogen passivation is performed with a home-built hydrogen cracker to provide a flux of hydrogen atoms to the surface.48 The trinaphthylene molecules are thermally evaporated from a powder placed inside a Knudsen cell. The temperature of the cell is maintained at approximately 180 °C. STM images are processed using SPIP and WsxM software.69 Calculation Scheme. The structures of trinaphthylene adsorbed on a Ge(001):H surface are modeled using DFT with the vdW-DF functional63−65 as implemented in the Vienna Ab initio Simulation 8505


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(28) Nacci, C.; Erwin, S. C.; Kanisawa, K.; Foelsch, S. Controlled Switching within an Organic Molecule Deliberately Pinned to a Semiconductor Surface. ACS Nano 2012, 6, 4190−4195. (29) Preuss, M.; Miotto, R.; Bechstedt, F.; Rada, T.; Richardson, N. V.; Schmidt, W. G. Structure, Energetics, and Vibrational Spectra of Perylene Adsorbed on Si(001): First-Principles Calculations Compared with STM and HREELS. Phys. Rev. B: Condens. Matter Mater. Phys. 2006, 74, 115402. (30) Rada, T.; Chen, Q.; Richardson, N. STM Study of Large Organic Molecules Adsorption on Si(100)-2 × 1. Phys. Status Solidi B 2004, 241, 2353−2357. (31) Rada, T.; Chen, Q.; Richardson, N. V. Scanning Tunnelling Microscopy of Tetracene on Si(100)-2 × 1. J. Phys.: Condens. Matter 2003, 15, S2749−S2756. (32) Lopinski, G. P.; Wayner, D. D. M.; Wolkow, R. A. Self-Directed Growth of Molecular Nanostructures on Silicon. Nature 2000, 406, 48−51. (33) Wolkow, R. A. Controlled Molecular Adsorption on Silicon: Lying a Foundation for Molecular Devices. Annu. Rev. Phys. Chem. 1999, 50, 413−441. (34) Mayne, A. J.; Lastapis, M.; Baffou, G.; Soukiassian, L.; Comtet, G.; Hellner, L.; Dujardin, G. Chemisorbed Bistable Molecule: Biphenyl on Si(100)-2 × 1. Phys. Rev. B: Condens. Matter Mater. Phys. 2004, 69, 045409. (35) Pitters, J. L.; Wolkow, R. A. Detailed Studies of Molecular Conductance Using Atomic Resolution Scanning Tunneling Microscopy. Nano Lett. 2006, 6, 390−397. (36) Labidi, H.; Sonnet, P.; Riedel, D. Electronic Control of the TipInduced Hopping of an Hexaphenyl-Benzene Molecule Physisorbed on a Bare Si(100) Surface at 9 K. J. Phys. Chem. C 2013, 117, 13663− 13675. (37) Patitsas, S. N.; Lopinski, G. P.; Hulko, O.; Moffatt, D. J.; Wolkow, R. A. Current-Induced Organic Molecule−Silicon Bond Breaking: Consequences for Molecular Devices. Surf. Sci. 2000, 457, L425−L431. (38) Pitters, J. L.; Piva, P. G.; Tong, X.; Wolkow, R. A. Reversible Passivation of Silicon Dangling Bonds with the Stable Radical TEMPO. Nano Lett. 2003, 3, 1431−1435. (39) Lopinski, G. P.; Moffatt, D. J.; Wolkow, R. A. Benzene/Si(100): Metastable Chemisorption and Binding State Conversion. Chem. Phys. Lett. 1998, 282, 305−312. (40) Harikumar, K. R.; Polanyi, J. C.; Zabet-Khosousi, A.; Czekala, P.; Lin, H.; Hofer, W. A. Directed Long-Range Molecular Migration Energized by Surface Reaction. Nat. Chem. 2011, 3, 400−408. (41) Nakamura, M.; Yoshida, S.; Katayama, Y.; Taninaka, A.; Mera, Y.; Okada, S.; Takeuchi, O.; Shigekawa, H. Mechanically Activated Switching of Si-Based Single-Molecule Junction as Imaged with ThreeDimensional Dynamic Probe. Nat. Commun. 2015, 6, 8465. (42) Repp, J.; Meyer, G.; Stojkovic, S. M.; Gourdon, A.; Joachim, C. Molecules on Insulating Films: Scanning-Tunneling Microscopy Imaging of Individual Molecular Orbitals. Phys. Rev. Lett. 2005, 94, 026803. (43) Godlewski, S.; Kolmer, M.; Kawai, H.; Such, B.; Zuzak, R.; Saeys, M.; de Mendoza, P.; Echavarren, A. M.; Joachim, C.; Szymonski, M. Contacting a Conjugated Molecule with a Surface Dangling Bond Dimer on a Hydrogenated Ge(001) Surface Allows Imaging of the Hidden Ground Electronic State. ACS Nano 2013, 7, 10105−10111. (44) Bellec, A.; Ample, F.; Riedel, D.; Dujardin, G.; Joachim, C. Imaging Molecular Orbitals by Scanning Tunneling Microscopy on a Passivated Semiconductor. Nano Lett. 2009, 9, 144−147. (45) Gruyters, M.; Pingel, T.; Gopakumar, T. G.; Néel, N.; Schütt, Ch.; Köhler, F.; Herges, R.; Berndt, R. J. Electronic Ground-State and Orbital Ordering of Iron Phthalocyanine on H/Si(111) Unraveled by Spatially Resolved Tunneling Spectroscopy. J. Phys. Chem. C 2012, 116, 20882−20886. (46) Godlewski, S.; Kolmer, M.; Engelund, M.; Kawai, H.; Zuzak, R.; Garcia-Lekue, A.; Saeys, M.; Echavarren, A. M.; Joachim, C.; SanchezPortal, D.; Szymonski, M. Interaction of a Conjugated Polyaromatic Molecule with a Single Dangling Bond Quantum Dot on a

(7) Stroscio, J. A.; Eigler, D. M. Atomic and Molecular Manipulation with the Scanning Tunneling Microscope. Science 1991, 254, 1319− 1326. (8) Gimzewski, J. K.; Joachim, C. Nanoscale Science of Single Molecules Using Local Probes. Science 1999, 283, 1683−1688. (9) Soe, W.-H.; Manzano, C.; Renaud, N.; de Mendoza, P.; De Sarkar, A.; Ample, F.; Hliwa, M.; Echavarren, A. M.; Chandrasekhar, N.; Joachim, C. Manipulating Molecular Quantum States with Classical Metal Atom Inputs: Demonstration of a Single Molecule NOR Logic Gate. ACS Nano 2011, 5, 1436−1440. (10) Lafferentz, L.; Ample, F.; Yu, H.; Hecht, S.; Joachim, C.; Grill, L. Conductance of a Single Conjugated Polymer as a Continuous Function of Its Length. Science 2009, 323, 1193−1197. (11) Uhlmann, C.; Swart, I.; Repp, J. Controlling the Orbital Sequence in Individual Cu-Phthalocyanine Molecules. Nano Lett. 2013, 13, 777−780. (12) Hla, S. − W. Atom-by-Atom Assembly. Rep. Prog. Phys. 2014, 77, 056502. (13) Kudernac, T.; Ruangsupapichat, N.; Parschau, M.; Maciá, B.; Katsonis, N.; Harutyunyan, S. R.; Ernst, K. − H.; Feringa, B. L. Electrically Driven Directional Motion of a Four-Wheeled Molecule on a Metal Surface. Nature 2011, 479, 208−211. (14) Manzano, C.; Soe, W.-H.; Wong, H. S.; Ample, F.; Gourdon, A.; Chandrasekhar, N.; Joachim, C. Step-by-Step Rotation of a MoleculeGear Mounted on an Atomic-Scale Axis. Nat. Mater. 2009, 8, 576− 579. (15) Swart, I.; Gross, L.; Liljeroth, P. Single-Molecule Chemistry and Physics Explored by Low-Temperature Scanning Probe Microscopy. Chem. Commun. 2011, 47, 9011−9023. (16) Loth, S.; Baumann, S.; Lutz, C. P.; Eigler, D. M.; Heinrich, A. J. Bistability in Atomic-Scale Antiferromagnets. Science 2012, 335, 196− 199. (17) Schendel, V.; Borca, B.; Pentegov, I.; Michnowicz, T.; Kraft, U.; Klauk, H.; Wahl, P.; Schlickum, U.; Kern, K. Remotely Controlled Isomer Selective Molecular Switching. Nano Lett. 2016, 16, 93−97. (18) Ladenthin, J. N.; Grill, L.; Gawinkowski, S.; Liu, S.; Waluk, J.; Kumagai, T. Hot Carrier-Induced Tautomerization within a Single Porphycene Molecule on Cu(111). ACS Nano 2015, 9, 7287−7295. (19) Gimzewski, K.; Joachim, C.; Schlittler, R. R.; Langlais, V.; Tang, H.; Johannsen, I. Rotation of a Single Molecule within a Supramolecular Bearing. Science 1998, 281, 531−533. (20) Shirai, Y.; Osgood, A. J.; Zhao, Y.; Kelly, K. F.; Tour, J. M. Directional Control in Thermally Driven Single-Molecule Nanocars. Nano Lett. 2005, 5, 2330−2334. (21) van Delden, R. A.; ter Wiel, M. K. J.; Pollard, M. M.; Vicario, J.; Koumura, N.; Feringa, B. L. Unidirectional Molecular Motor on a Gold Surface. Nature 2005, 437, 1337−1340. (22) Böckmann, H.; Liu, S.; Mielke, J.; Gawinkowski, S.; Waluk, J.; Grill, L.; Wolf, M.; Kumagai, T. Direct Observation of Photo-Induced Tautomerization in Single Molecules at a Metal Surface. Nano Lett. 2016, 16, 1034−1041. (23) Tierney, H. L.; Murphy, C. J.; Jewell, A. D.; Baber, A. E.; Iski, E. V.; Khodaverdian, H. Y.; McGuire, A. F.; Klebanov, N.; Sykes, E. C. H. Experimental Demonstration of a Single-Molecule Electric Motor. Nat. Nanotechnol. 2011, 6, 625−629. (24) Perera, U. G. E.; Ample, F.; Kersell, H.; Zhang, Y.; Vives, G.; Echeverria, J.; Grisolia, M.; Rapenne, G.; Joachim, C.; Hla, S.-W. Controlled Clockwise and Anticlockwise Rotational Switching of a Molecular Motor. Nat. Nanotechnol. 2013, 8, 46−51. (25) Custance, O.; Perez, R.; Morita, S. Atomic Force Microscopy as a Tool for Atom Manipulation. Nat. Nanotechnol. 2009, 4, 803−810. (26) Sugimoto, Y.; Abe, M.; Hirayama, S.; Oyabu, N.; Custance, O.; Morita, S. Atom Inlays Performed at Room Temperature Using Atomic Force Microscopy. Nat. Mater. 2005, 4, 156−159. (27) Keeling, D.; Humphry, M.; Fawcett, R.; Beton, P.; Hobbs, C.; Kantorovich, L. Bond Breaking Coupled with Translation in Rolling of Covalently Bound Molecules. Phys. Rev. Lett. 2005, 94, 146104. 8506


Article

ACS Nano Hydrogenated Semiconductor. Phys. Chem. Chem. Phys. 2016, 18, 3854−3861. (47) Godlewski, S.; Kawai, H.; Engelund, M.; Kolmer, M.; Zuzak, R.; Garcia-Lekue, A.; Novell-Leruth, G.; Echavarren, A. M.; SanchezPortal, D.; Joachim, C.; Saeys, M. Diels-Alder Attachment of a Planar Organic Molecule to a Dangling Bond Dimer on a Hydrogenated Semiconductor Surface. Phys. Chem. Chem. Phys. 2016, 18, 16757− 16765. (48) Kolmer, M.; Godlewski, S.; Kawai, H.; Such, B.; Krok, F.; Saeys, M.; Joachim, C.; Szymonski, M. Electronic Properties of STMConstructed Dangling-Bond Dimer Lines on a Ge(001)-(2 × 1):H Surface. Phys. Rev. B: Condens. Matter Mater. Phys. 2012, 86, 125307. (49) Kolmer, M.; Godlewski, S.; Zuzak, R.; Wojtaszek, M.; Rauer, C.; Thuaire, A.; Hartmann, J.-M.; Moriceau, H.; Joachim, C.; Szymonski, M. Atomic Scale Fabrication of Dangling Bond Structures on Hydrogen Passivated Si(001) Wafers Processed and Nanopackaged in a Clean Room Environment. Appl. Surf. Sci. 2014, 288, 83−89. (50) Godlewski, S.; Kolmer, M.; Lis, J.; Zuzak, R.; Such, B.; Gren, W.; Kantorovich, L.; Szymonski, M. Dynamical Behavior of a Dangling Bond Dimer on a Hydrogenated Semiconductor: Ge(001):H. Phys. Rev. B: Condens. Matter Mater. Phys. 2015, 92, 115403. (51) Taucer, M.; Livadaru, L.; Piva, P. G.; Achal, R.; Labidi, H.; Pitters, J. L.; Wolkow, R. A. Single-Electron Dynamics of an Atomic Silicon Quantum Dot on the H−Si(100)−(2 × 1) Surface. Phys. Rev. Lett. 2014, 112, 256801. (52) Bellec, A.; Chaput, L.; Dujardin, G.; Riedel, D.; Stauffer, L.; Sonnet, P. Reversible Charge Storage in a Single Silicon Atom. Phys. Rev. B: Condens. Matter Mater. Phys. 2013, 88, 241406Rgo. (53) Haider, M. B.; Pitters, J. L.; DiLabio, G. A.; Livadaru, L.; Mutus, J. Y.; Wolkow, R. A. Controlled Coupling and Occupation of Silicon Atomic Quantum Dots at Room Temperature. Phys. Rev. Lett. 2009, 102, 046805. (54) Labidi, H.; Taucer, M.; Rashidi, M.; Koleini, M.; Livadaru, L.; Pitters, J.; Cloutier, M.; Salomons, M.; Wolkow, R. A. Scanning Tunneling Spectroscopy Reveal a Silicon Dangling Bond Charge Transition. New J. Phys. 2015, 17, 073023. (55) Fuechsle, M.; Mahapatra, S.; Zwanenburg, F. A.; Friesen, M.; Eriksson, M. A.; Simmons, M. Y. Spectroscopy of Few-Electron SingleCrystal Silicon Quantum Dots. Nat. Nanotechnol. 2010, 5, 502−505. (56) Weber, B.; Mahapatra, S.; Ryu, H.; Lee, S.; Fuhrer, A.; Reusch, T. C. G.; Thompson, D. L.; Lee, W. C. T.; Klimeck, G.; Hollenberg, L. C. L.; Simmons, M. Y. Ohm’s Law Survives to the Atomic Scale. Science 2012, 335, 64−67. (57) Schofield, S. R.; Studer, P.; Hirjibehedin, C. F.; Curson, N. J.; Aeppli, G.; Bowler, D. R. Quantum Engineering at the Silicon Surface Using Dangling Bonds. Nat. Commun. 2013, 4, 1649. (58) Kolmer, M.; Zuzak, R.; Dridi, G.; Godlewski, S.; Joachim, C.; Szymonski, M. Realization of a Quantum Hamiltonian Boolean Logic Gate on the Si(001):H surface. Nanoscale 2015, 7, 12325−12330. (59) Piva, P. G.; DiLabio, G. A.; Pitters, J. L.; Zikovsky, J.; Rezeq, M.; Dogel, S.; Hofer, W. A.; Wolkow, R. A. Field Regulation of SingleMolecule Conductivity by a Charged Surface Atom. Nature 2005, 435, 658−661. (60) Mayne, A. J.; Soukiassian, L.; Commaux, N.; Comtet, G.; Dujardin, G. Molecular Molds. Appl. Phys. Lett. 2004, 85, 5379. (61) Hersam, M. C.; Guisinger, N. P.; Lyding, J. W. Silicon-Based Molecular Nanotechnology. Nanotechnology 2000, 11, 70−76. (62) Swart, I.; Sonnleitner, T.; Niedenfuehr, J.; Repp, J. Controlled Lateral Manipulation of Molecules on Insulating Films by STM. Nano Lett. 2012, 12, 1070−1074. (63) Dion, M.; Rydberg, H.; Schröder, E.; Langreth, D. C.; Lundqvist, B. I. Van der Waals Density Functional for General Geometries. Phys. Rev. Lett. 2004, 92, 246401. (64) Román-Pérez, G.; Soler, J. M. Efficient Implementation of a van der Waals Density Functional: Application to Double-Wall Carbon Nanotubes. Phys. Rev. Lett. 2009, 103, 096102. (65) Klimeš, J.; Bowler, D. R.; Michaelides, A. Van der Waals Density Functionals Applied to Solids. Phys. Rev. B: Condens. Matter Mater. Phys. 2011, 83, 195131.

(66) Engelund, M.; Godlewski, S.; Kolmer, M.; Zuzak, R.; Such, B.; Frederiksen, T.; Szymonski, M.; Sánchez-Portal, D. The Butterfly - A Well-Defined Constant-Current Topography Pattern On Si(001):H and Ge(001):H Resulting From Current-Induced Defect Fluctuation. Phys. Chem. Chem. Phys. 2016, 18, 19309−19317. (67) Koch, W.; Holthausen, M. C. A Chemist’s Guide to Density Functional Theory, 2nd ed.; Wiley-VCH: Weinheim, Germany, 2001. (68) Feenstra, R. M. Electrostatic Potential for a Hyperbolic Probe Tip near a Semiconductor. J. Vac. Sci. Technol., B: Microelectron. Process. Phenom. 2003, 21, 2080. (69) Horcas, I.; Fernandez, R.; Gomez-Rodriguez, J. M.; Colchero, J.; Gomez-Herrero, J.; Baro, A. M. WSXM: A Software for Scanning Probe Microscopy and a Tool for Nanotechnology. Rev. Sci. Instrum. 2007, 78, 013705. (70) Kresse, G.; Hafner, J. Ab Initio Molecular Dynamics for Liquid Metals. Phys. Rev. B: Condens. Matter Mater. Phys. 1993, 47, 558. (71) Kresse, G.; Hafner, J. Ab Initio Molecular-Dynamics Simulation of the Liquid-Metal−Amorphous-Semiconductor Transition in Germanium. Phys. Rev. B: Condens. Matter Mater. Phys. 1994, 49, 14251. (72) Kresse, G.; Furthmüller, J. Efficient Iterative Schemes for Ab Initio Total-Energy Calculations Using a Plane-Wave Basis Set. Phys. Rev. B: Condens. Matter Mater. Phys. 1996, 54, 11169. (73) Kresse, G.; Furthmüller, J. Efficiency of Ab-Initio Total Energy Calculations for Metals and Semiconductors Using a Plane-Wave Basis Set. Comput. Mater. Sci. 1996, 6, 15−50. (74) Cerda, J.; Van Hove, M. S.; Sautet, P.; Salmeron, M. Efficient Method for the Simulation of STM Images. I. Generalized GreenFunction Formalism. Phys. Rev. B: Condens. Matter Mater. Phys. 1997, 56, 15885. (75) Tersoff, J.; Hamann, D. R. Theory and Application for the Scanning Tunneling Microscope. Phys. Rev. Lett. 1983, 50, 1998.

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