Unimolecular Logic Gate with Classical Input by Single Gold Atoms

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Unimolecular Logic Gate with Classical Input by Single Gold Atoms Dmitry Skidin, Omid Faizy, Justus Krüger, Frank Eisenhut, Andrej Jancarik, Khanh-Hung Nguyen, Gianaurelio Cuniberti, André Gourdon, Francesca Moresco, and Christian Joachim ACS Nano, Just Accepted Manuscript • DOI: 10.1021/acsnano.7b06650 • Publication Date (Web): 21 Dec 2017 Downloaded from http://pubs.acs.org on December 21, 2017

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Unimolecular Logic Gate with Classical Input by Single Gold Atoms Dmitry Skidin,1 Omid Faizy,2,3,# Justus Krüger,1 Frank Eisenhut,1 Andrej Jancarik,2 Khanh-Hung Nguyen,2 Gianaurelio Cuniberti,1,4 Andre Gourdon,2 Francesca Moresco,*,1 Christian Joachim2 1

Institute for Materials Science, Max Bergmann Center of Biomaterials, and Center for

Advancing Electronics Dresden, TU Dresden, 01069 Dresden, Germany 2

GNS & MANA Satellite, CEMES, CNRS, 29 rue J. Marvig, 31055 Toulouse Cedex, France

3

Laboratoire de Physique Théorique, IRSAMC, Université de Toulouse, CNRS, UPS, France

4

Dresden Center for Computational Materials Science (DCMS), TU Dresden, 01069 Dresden,

Germany

*Corresponding author: [email protected] KEYWORDS: scanning tunneling microscopy (STM), molecular logic gate, quantum Hamiltonian computing (QHC), asymmetric starphene, on-surface synthesis

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Abstract By a combination of solution and on-surface chemistry, we synthesized an asymmetric starphene molecule with two long anthracenyl input branches and a short naphthyl output branch on the Au(111) surface. Starting from this molecule, we could demonstrate the working principle of a single molecule NAND logic gate by selectively contacting single gold atoms by atomic manipulation to the longer branches of the molecule. The logical input “1” (“0”) is defined by the interaction (non-interaction) of a gold atom with one of the input branches. The output is measured by scanning tunneling spectroscopy following the shift in energy of the electronic tunneling resonances at the end of the short branch of the molecule.


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For applications in molecular electronics, molecular Boolean logic gates can be designed based on classical, semi-classical or quantum architectures (with or without qubits).1 The classical architecture relies on the wiring of molecular rectifiers, switches, or transistors by means of long metallic nanowires. This strategy is about to be abandoned due to the absence of molecular transistors showing a large power gain.2 In a semi-classical approach, on the other hand, the active molecular elements are connected by the chemical groups of short molecular wires.2 However, the tunneling current passing through a molecular wire decays exponentially by increasing its length.3 This can become a serious problem for designing a large unimolecular electronic circuit. Therefore, to develop a single molecule Boolean logic gate, quantum architectures must be exploited. Standard quantum computing design, however, has the inconvenience that the qubits embedded in the molecular structure must be separated from each other to avoid inter-qubit through-bond electron transfer.4 This spatial separation certainly slows down the calculation speed and is not leading to the ultimate miniaturization of a logic gate. To overcome these problems, we have recently proposed the quantum Hamiltonian computing (QHC) approach1 where the intrinsic electronic time-dependent quantum response of a single molecule is used without the need of structuring the molecule logic gate in qubits.5 The working principle is based on quantum level repulsion effects complemented with time-dependent electronic quantum interference effects.6 Following this approach, we recently modelled a universal QHC logic gate with a calculating block composed only of three quantum states.7 By using two symmetric inputs and one output, the six Boolean logic gates (NOR, AND, OR, NAND, XOR, NXOR) can be obtained. Based on these theoretical considerations, a first logic gate was designed, formed by a symmetric shortbranch conjugated starphene molecule. The experimental realization demonstrated by scanning


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tunneling microscopy (STM) and spectroscopy (STS) the operation as a NOR gate.8 In that case however, the other predicted five Boolean logic gates (AND, OR, NAND, XOR, NXOR) were not experimentally accessible because the energy position of the corresponding electronic resonances (output signals) lies outside the range of bias voltages needed for stable STM and STS operations. To design logic gates other than NOR, we therefore propose here to elongate part of the QHC graph corresponding to the input branches, while keeping the output branch unchanged. The resulting molecule is an asymmetric NAND QHC starphene (starphene 1 in Scheme 1) with one benzene ring more per input branch as compared to the symmetric NOR starphene. The synthesis of this asymmetric starphene molecule was only possible by taking advantage of on-surface reaction of molecular precursors adsorbed on the Au(111) surface, by means of intramolecular cyclodehydrogenation starting from a 2,3-di(anthracen-2-yl) naphthalene. In this paper, we present the on-surface synthesis of the asymmetric starphene molecule, and we demonstrate the experimental implementation of the NAND logic gate by combining the STM manipulation of single gold atoms with high precision dI/dV spectroscopy. Finally, we describe the theoretical background of the QHC architecture concept and its application to the NAND quantum graph, showing that this approach is able to provide a general description of quantum logic gates, well beyond the few examples experimentally available.

RESULTS AND DISCUSSION

On-surface synthesis of an asymmetric starphene


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On-surface chemistry is a powerful technique for the fabrication of a large variety of molecular architectures, which are difficult to sublimate without breaking the initial molecular structure, or could not be synthesized by conventional solution chemistry.9-11 The asymmetric starphene 1 (Scheme 1) belongs to this category of compounds. Its preparation is presented in Scheme 1 below. Since this target polyaromatic hydrocarbon molecule is expected to be highly insoluble due to its size, rigidity and planarity, the synthesis has been carried out in two steps. The first step is a double Suzuki coupling in solution of 2,3-dibromonaphthalene with 2-(anthracen-2-yl)4,4,5,5-tetramethyl-1,3,2-dioxaborolane to give 2,3-di(anthracen-2-yl) naphthalene which is soluble enough for purification and characterization. In a second step, this latter molecule was sublimated under vacuum conditions onto an Au(111) surface to perform an intramolecular cyclodehydrogenation. This reaction can potentially lead to three final compounds (1-3) on the Au(111) surface depending on the molecular conformation.

Scheme 1. Chemical synthesis of an asymmetric starphene. Top: the mechanism of the reaction to produce a molecular precursor for on-surface reaction. Bottom: possible products of thermally activated on-surface reaction.


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After a thermal sublimation of the precursor molecules (Scheme 1) on the surface kept at room temperature, the precursors show two main different conformations in the STM images, as presented in Figure 1a,b. Both structures are non-flat, and a part of the molecule is protruding higher above the surface: one of the branches (Figure 1a) or its central part (Figure 1b). In order to trigger the surface chemical reaction and to obtain fully-conjugated asymmetric starphene molecules, we have annealed the sample at 433 K. It is known that organic molecules can undergo thermally-induced intramolecular dehydrogenation and subsequently form additional CC bonds on the metallic substrates.12-14 After this first annealing step performed at 433 K, only a small portion of the molecules have reacted (yield 17%). The complete cyclodehydrogenation and C-C bonds formation for all the precursors was achieved by annealing the surface at 477 K (see Supporting Information for details). As shown in Scheme 1, three conformational isomers can be predicted for the reaction products. Due to the flexibility of the bonds between the anthracenyl and naphthyl units, the branches of the precursors can rotate prior to deposition on the surface. However, most of the reaction products appear as isomers of type 1 with a characteristic Y shape, the desired result for further experiments on logic gate functioning. Only around 8% of the molecules reacted into isomer 2, while we never observed isomer 3, which would require the rotation of both anthracenyl branches. Since only isomer 1 is of importance for our experiments and is constituting the vast majority of the reaction products, all following discussion concentrates solely on this type. After annealing, the molecules appear flat and symmetric along the naphthyl branch axis (Figure 1c). The successful flattening of the molecule is supported by comparing the line scans over the initial and final species (Figure 1e) taken along the same path. The observed topography is also in a good accordance with STM images of symmetric trinaphthylene8 and decastarphene molecules.15


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Figure 1. On-surface reaction to produce a fully-conjugated asymmetric starphene molecule. (a) and (b) STM images of two types of the molecules as they appear after deposition. (c) STM image of the reaction product. Imaging parameters: I = 100 pA, V = 0.5 V, 3 nm x 3 nm. (d) Molecular structure of the precursor molecule. (e) Line scan comparison of the precursor and the product molecules taken on the dashed lines of (a) (black) and (c) (red), respectively. (f) Molecular structure of the product molecule.

We have characterized the electronic structure of an isolated asymmetric starphene molecule on Au(111) recording dI/dV spectroscopy and differential conductance maps at energies of the observed tunneling resonance as presented in Figure 2 (for the other maps, see Supporting Information). Each resonance position was determined in the middle of the corresponding lobe. It is worth noting that the resonances of naphthyl and anthracenyl branches are separated and localized at the positions of the respective branches. The maps of the frontier filled and empty molecular electronic resonances preserve the characteristic shape typical for acene molecules adsorbed on the Au(111) surface.16-17


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Figure 2. Electronic characterization of an asymmetric starphene. (a) STM image (3 nm x 3 nm) of a single molecule with red and blue crosses marking the tip positions during STS probing of the anthracenyl and naphthyl branches, respectively. Imaging parameters: I = 100 pA, V = 0.5 V. (b) and (c) Differential conductance maps recorded at -1.15 V and 1.75 V showing mainly the HOMO and LUMO content of those two resonances, respectively. (d) dI/dV spectra taken at anthracenyl (red) and naphthyl (blue) branches show resonances at 1.15 V, -1.7 V, 1.75 V, 2.06 V, 2.5 V. Spectrum of a bare Au surface (black) is presented for reference.

Demonstration of the NAND functioning To investigate the logic gate functioning of the asymmetric starphene molecule through its interactions with single Au atoms, we have first produced isolated Au atoms on the surface by a gentle indentation of the STM tip on a clean spot of the Au(111) surface.8, 18 Afterwards, we have controllably and laterally manipulated these Au atoms one after the other to a specific input


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branch of an asymmetric starphene. Similarly, an asymmetric starphene molecule can be manipulated on Au(111) towards the Au atoms using higher STM junction tunneling resistance. However, for a better controllability and reproducibility, we choose to manipulate only the Au atoms. In some cases, Au atoms can also diffuse directly toward the molecule after the tip indentation, thus leading to an Au-starphene complex without the need for more STM tip lateral manipulation (see Supporting Information). When a molecule and an Au atom are brought together, they form a weak coordination complex, which remains stable at STM bias voltages varying from -2 to +2 V. When the bias voltage exceeds this range, one or two input Au atoms can slip out from their positions. The tunneling spectrum measured while the two input branches are free of Au atoms (the (0,0) logical input configuration) will serve in the following as a reference output spectrum (See Figure 2). Starting from the configuration presented in Figure 3a, we have successively manipulated the Au atoms one after the other to reach the anthracenyl branches of an asymmetric starphene. We have measured a dI/dV spectrum at the naphthyl output branch after each manipulation step. Then, we have studied the shift of the resonance positions as a function of the logical input configuration resulting from the number of Au atoms in interaction with the molecule. In the following discussion, we concentrate mostly on the negative bias voltage side, corresponding to the ground and occupied molecular resonances. These resonances appear sharper in STS spectroscopy and are therefore easier to analyze. On the positive voltage bias side, an empty state electronic resonance can be measured on the naphthyl branch at around 2.5 V. However, it is difficult to experimentally follow this resonance as a function of the logical input configuration without breaking the corresponding Au-molecule complex structure. Nevertheless, it is worth mentioning that in general the same trends apply for the positive bias voltage side.


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As can be seen in Figure 3b, after the manipulation of a single Au atom to interact with only one of the two anthracenyl branches, there is essentially no shift of the ground state resonant energy of the Au-molecule complex. An apparent very small shift of no more than 15 meV is sometimes observed and seems to be due to the limited energy resolution of STS. It is eliminated when averaging the results of many dI/dV spectra in this voltage range. However, after the manipulation of a second Au atom to contact the remaining anthracenyl input branch, the shift of the ground state resonance is significant reaching about 100 meV. Contrary to the case of a symmetric starphene molecule, the input of two single Au atoms is required to produce an observable shift of the ground state STS resonance. For a symmetric starphene NOR QHC gate, a logical output “1” was defined as the ground state STS resonance with no single Au atoms in contact.8 By keeping the same reference here, only the (1,1) logical input configuration is able to push the ground state resonance down in energy and away from its reference position shown in Figure 3, thus producing a logical output “0”. As logical input configurations (0,1) and (1,0) lead to a non-measurable ground state energy shift, the asymmetric starphene is functioning like a NAND gate. Its truth table is shown in the inset of Figure 3g. Note that other logical output reference energies are possible. For example, by choosing the logical output “0” for the ground state energy position of a starphene free of Au atoms, we can obtain OR (symmetric starphene)8 and AND (asymmetric starphene) logic gates.


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Figure 3. Manipulation of the molecular states through the Au atom inputs to demonstrate NAND logic gate functionality. (a) STM image of an asymmetric starphene with two Au atoms nearby. (b) and (c) STM images of an asymmetric starphene with one and two Au atoms under anthracenyl branches, respectively. (d-f) dI/dV maps of an asymmetric starphene with 0, 1 and 2 Au atom inputs taken at the resonance energies. (g) dI/dV spectra for all the three cases show a significant shift in energy only when two inputs are applied. The black curve corresponds to the case of an unperturbed molecule, red – one Au atom input, blue – two inputs. All STM images: 4 nm x 4 nm; I = 50 pA, V = 0.5 V. In the inset, the truth table as well as a shift diagram of a NAND logic gate are shown.


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The absolute value of the shift is rather small, but is unambiguously detected and provides a clear proof of concept of the NAND logic gate implementation. A stronger interaction between the molecule and an input atom would largely perturb the electronic structure of the whole molecule, and no Boolean function would result. The changes in the positions of molecular resonances as a result of interaction with metal atoms have been observed before and supported theoretically.19 However, special molecular design is required to cause the shifts, which comply with a Boolean truth table. In the following, we discuss the design principles and the concept of QHC graph, which explains the connection between the observed behavior and the molecular structure of an asymmetric starphene. Theoretical background: an asymmetric QHC graph To design Boolean logic gates, the QHC approach uses a combination of quantum repulsion and time-dependent destructive interference effects.6 A set of quantum states called the calculating states is brought into electronic interactions with input states responsible (when coupled) for the energy shifts of well-determined eigenstates of this calculating block. With two logical inputs and a single logical output, the proper functioning of a QHC gate is measured by adding a reading block composed of two states |ϕa> and |ϕb> at eigenenergy E to the “calculating states + two input states” quantum system. The role of |ϕa> and |ϕb> is to detect when at least one eigenstate of the calculating block is resonating with these two states to encode a logical output “1”. Preparing the reading block in a non-stationary state with one electron localized exclusively on |ϕa> (or |ϕb>) results in Heisenberg-Rabi time-dependent quantum oscillations through the calculating block. The secular frequency of these oscillations is encoding the logical output of the QHC logic gate. A very fast oscillation is encoding a logical output “1”, while a very slow


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one a logical output “0”. This frequency can be measured experimentally because its square is proportional to the intensity of the tunneling current passing through the calculating block states when the two pointer states |ϕa> and |ϕb> are interacting electronically with two metallic nanopads, for example, the tip of an STM and a metallic surface.8

Figure 4. Comparison of the QHC graphs (top) and the corresponding molecular structures (bottom) for QHC NOR and NAND gates. (a) The universal QHC graph with its central calculating block consisting of three quantum states at energy e0 and the corresponding starphene molecule.8 (b) The extended asymmetric QHC graph and the asymmetric starphene molecule studied in this paper. The |ϕa> and |ϕb> quantum states of the surface and the tip, respectively, constitute the reading block, while the e1 and e2 input states correspond to the single Au atom logical inputs. Positions of the Au atoms inputs and the tip during dI/dV measurements are indicated on the molecular structure.

The three-states calculating block at energy e0 presented in the Figure 4a is universal and the corresponding structural parameters have already been determined for the NOR, AND, OR, NAND, XOR, NXOR symmetric Boolean logic gates with two inputs and one output.7 The passage from a formal QHC graph to a conjugated molecular structure is done by building a simple topological Hückel Hamiltonian5 to determine the minimum number and position of


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phenyl rings along the QHC gate molecular skeleton. This first step provides the reference energy E of the reading block for capturing some of the six Boolean logic gates mentioned above. Based on the chemical structure, a comprehensive calculation of the molecular electronic structure completes the design of QHC logic gates accessible in the STM bias voltage range. Following the QHC graph from Figure 4a, only the NOR gate was implemented using the symmetric starphene molecule.8 To obtain other logic functions, different QHC calculating blocks must be designed. For the NAND, we have constructed an asymmetric calculating block where two input branches are longer than the output branch (Figure 4b) to suppress the repulsion effect due to the (0,1) and (1,0) inputs in the QHC graph leading to a NOR. The logical answer delivered by this QHC graph can be calculated in the same way as in the case of the three-states calculating block. Starting from the known universal three-states calculating block Hamiltonian,6 the extended QHC 9 x 9 H(α,β) Hamiltonian including a 2 x 2 reading block at energy E is given by:

0 0 , = 0 0 0 0 0

Reading block

0

0 0 0 0 0 0

0 0 0 0

0 0 0 0 0 0 0

0 0 0 0 0 0

0 0 0 0 0

0 0 0 0 0

0 0 0 0 0 0

0 0 0 0 0 0 0

Calculating block

(1)

To simplify the determination of the structural parameters for the NAND gate, we fix E = 0 for the reading block. In this case, the Boolean truth table delivered by (1) is simply obtained by calculating the determinant of the 7 x 7 calculating block matrix7 leading to:


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, = 3 2 2 2 3 4 4 5 2

(2)

The logical answer is obtained from (2) by selecting e1 = e2 = e = 0 eV and e0 = -k. This leads to ∆(α,β) = 4k3 α2β2 with ∆(0,0) = ∆(0,1) = ∆ (1,0) = 0 and ∆(1,1) = 4k3, where k is the structural parameter determining the margin between the logical outputs “1” and “0”. We obtain in this way the logical response of a NAND gate since for each ∆(α,β) zero value, one eigenstate of the 7 x 7 calculating block is resonating with |ϕa> and |ϕb>, where E = 0 eV to simplify the analytical demonstration. Considering, for example, the Figure 4b quantum graph in the nonstationary initial state |ϕa> and solving the time-dependent Schrödinger equation with the generator of the evolution given by (1), we obtain the time-dependent population of the |ϕb> target state presented in Figure 5.

Figure 5. The time-dependent population P(t) of state |ϕb> after preparing the Figure 4b quantum graph in the non-stationary state |ϕa> and by selecting k = 1.0 eV, e1 = e2 = 0.0 eV and e0= -1.0 eV with ε = 0.05 eV for the weak coupling between |ϕa>, |ϕb> and the calculating block. For consistency, the inputs α and β are taking the normalized values 0.0 eV or 1.0 eV. Corresponding to a NAND gate, P(t) is fast-oscillating for (0,0), (0,1) and (1,0) and is showing a very slow oscillation for (1,1), practically not visible on the corresponding P(t) curve.


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Notice that compared to the universal three-states QHC graph from Figure 4a,6 the modified graph (Figure 4b) can also lead to the NOR, XOR and AND when e ≠ 0 and e0 ≠ 0. In this case, the structural parameter k needs to be tuned again with, for example, =

!√ #

for the NOR,

e = - 8/(3k) with k = -e0 for the XOR and e = - 2/(3k) with k = - e0 for the AND. The corresponding logical answer output can be easily obtained by solving the time-dependent Schrödinger equation, similarly to the NAND time response presented in Figure 5. However, with the 7 x 7 calculating block in (1), only the NAND gate is working with structural energies close to the reference reading block energy, which is an important point for the experimental implementation. As already mentioned, in the case of the universal 5 x 5 calculating block of Figure 4a, only the NOR gate was obtained in the STM-measurable range.6

CONCLUSION In conclusion, we implemented a unimolecular NAND logic gate by extending the π molecular system of a symmetric starphene molecule in accordance with the QHC graph design. The transition from the QHC graph to the molecular chemical structure is done by using a simple topological Hückel model. The realization of an asymmetric starphene molecule operating as a NAND logic gate is possible due to a combination of solution and on-surface synthesis, STM atomic and molecular manipulation, and high-resolution STS measurements. Out of the possible reaction products, STM allows to select the ones with a desired symmetry and electronic structure. The interaction of single Au atoms with the longer input branches of this asymmetric starphene leads to the shift of the ground state energy and to realization of a NAND logic gate, as


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predicted by the QHC design. The described approach is not limited to the specific case of the asymmetric starphene molecule and facilitates the development of an atomic-scale technology based on the quantum-mechanical properties of single molecules and atomic structures. METHODS The experiments were carried out with a custom-built low-temperature (T = 5 K) STM under ultra-high vacuum conditions (base pressure < 10-10 mbar). Single-crystal gold substrate was cleaned by repeated cycles of sputtering with Ar ions and annealing at 723 K. Asymmetric starphene precursor molecules were sublimated from a Knudsen cell at a temperature 500 K onto Au(111) surface kept at room temperature. After sublimation, the sample was cooled down to cryogenic temperature and transferred to the STM without breaking the vacuum. For manipulation of single Au atoms, tunneling resistance between 0.2 and 1 MΩ was used. Scanning tunneling spectroscopy measurements were performed using lock-in technique with bias modulation amplitude 40 mV at a frequency 707 Hz. AUTHOR INFORMATION Corresponding Authors E-mail: [email protected] Present Address #

Present address: School of Nano Science, Institute for Research in Fundamental Sciences

(IPM), Tehran 19395-5531, Iran

ASSOCIATED CONTENT


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The authors declare no competing financial interests.

Supporting Information. Details about synthesis, additional STM data. This material is available free of charge on the ACS Publications website at http://pubs.acs.org.

ACKNOWLEDGMENT This work was funded by the ICT-FET European Union Integrated Project PAMS (Agreement No. 610446). Support by the German Excellence Initiative via the Cluster of Excellence EXC1056 ‘‘Center for Advancing Electronics Dresden’’ (cfaed), the International Helmholtz Research School “Nanonet” and MANA-NIMS is gratefully acknowledged. A. Jancarik thanks the Experientia Foundation for support. This work was supported in part by the ANR-11-IDEX-0002-02 Program Investissements d'Avenir, COMPMOL project ref. ANR-10-LABX-0037-NEXT


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REFERENCES 1. Joachim, C.; Renaud, N.; Hliwa, M. The Different Designs of Molecule Logic Gates. Adv. Mater. 2012, 24, 312-317. 2. Joachim, C.; Gimzewski, J. K.; Aviram, A. Electronics Using Hybrid-Molecular and Mono-Molecular Devices. Nature 2000, 408, 541-548. 3. 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, 11931197. 4. Hliwa, M.; Bonvoisin, J.; Joachim, C. A Controlled Quantum SWAP Logic Gate in a 4Center Metal Complex. In Architecture and Design of Molecule Logic Gates and Atom Circuits: Proceedings of the 2nd Atmol European Workshop; Lorente, N.; Joachim, C., Eds.; Springer Berlin Heidelberg: Berlin, Heidelberg, 2013; pp 237-247. 5. Renaud, N.; Hliwa, M.; Joachim, C. Quantum Design Rules for Single Molecule Logic Gates. Phys. Chem. Chem. Phys. 2011, 13, 14404-14416. 6. Soe, W. H.; Manzano, C.; De Sarkar, A.; Ample, F.; Chandrasekhar, N.; Renaud, N.; de Mendoza, P.; Echavarren, A. M.; Hliwa, M.; Joachim, C. Demonstration of a NOR Logic Gate Using a Single Molecule and Two Surface Gold Atoms to Encode the Logical Input. Phys. Rev. B 2011, 83. 7. Dridi, G.; Julien, R.; Hliwa, M.; Joachim, C. The Mathematics of a Quantum Hamiltonian Computing Half Adder Boolean Logic Gate. Nanotechnology 2015, 26. 8. 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, 1436-40. 9. Franc, G.; Gourdon, A. Covalent Networks through On-Surface Chemistry in Ultra-High Vacuum: State-of-the-Art and Recent Developments. Phys. Chem. Chem. Phys. 2011, 13, 1428314292. 10. Mendez, J.; Lopez, M. F.; Martin-Gago, J. A. On-Surface Synthesis of Cyclic Organic Molecules. Chem. Soc. Rev. 2011, 40, 4578-4590. 11. Lindner, R.; Kühnle, A. On-Surface Reactions. ChemPhysChem 2015, 16, 1582-1592. 12. Cai, J. M.; Ruffieux, P.; Jaafar, R.; Bieri, M.; Braun, T.; Blankenburg, S.; Muoth, M.; Seitsonen, A. P.; Saleh, M.; Feng, X. L.; Müllen, K.; Fasel, R. Atomically Precise Bottom-Up Fabrication of Graphene Nanoribbons. Nature 2010, 466, 470-473. 13. Treier, M.; Pignedoli, C. A.; Laino, T.; Rieger, R.; Mullen, K.; Passerone, D.; Fasel, R. Surface-Assisted Cyclodehydrogenation Provides a Synthetic Route Towards Easily Processable and Chemically Tailored Nanographenes. Nat. Chem. 2011, 3, 61-67. 14. Wiengarten, A.; Lloyd, J. A.; Seufert, K.; Reichert, J.; Auwärter, W.; Han, R. Y.; Duncan, D. A.; Allegretti, F.; Fischer, S.; Oh, S. C.; Saglam, O.; Jiang, L.; Vijayaraghavan, S.; Ecija, D.; Papageorgiou, A. C.; Barth, J. V. Surface-Assisted Cyclodehydrogenation; Break the Symmetry, Enhance the Selectivity. Chem.-Eur. J. 2015, 21, 12285-12290. 15. Guillermet, O.; Gauthier, S.; Joachim, C.; De Mendoza, P.; Lauterbach, T.; Echavarren, A. M. STM and AFM High Resolution Intramolecular Imaging of a Single Decastarphene Molecule. Chem. Phys. Lett. 2011, 511, 482-485. 16. Soe, W. H.; Manzano, C.; De Sarkar, A.; Chandrasekhar, N.; Joachim, C. Direct Observation of Molecular Orbitals of Pentacene Physisorbed on Au(111) by Scanning Tunneling Microscope. Phys. Rev. Lett. 2009, 102.


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17. Krüger, J.; Eisenhut, F.; Alonso, J. M.; Lehmann, T.; Guitian, E.; Perez, D.; Skidin, D.; Gamaleja, F.; Ryndyk, D. A.; Joachim, C.; Pena, D.; Moresco, F.; Cuniberti, G. Imaging the Electronic Structure of On-Surface Generated Hexacene. Chem. Commun. 2017, 53, 1583-1586. 18. Ohmann, R.; Meyer, J.; Nickel, A.; Echeverria, J.; Grisolia, M.; Joachim, C.; Moresco, F.; Cuniberti, G. Supramolecular Rotor and Translator at Work: On-Surface Movement of Single Atoms. ACS Nano 2015, 9, 8394-8400. 19. Manzano, C.; Soe, W. H.; Hliwa, M.; Grisolia, M.; Wong, H. S.; Joachim, C. Manipulation of a Single Molecule Ground State by Means of Gold Atom Contacts. Chem. Phys. Lett. 2013, 587, 35-39.


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Unimolecular Logic Gate with Classical Input by Single Gold Atoms

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