With a lateral bisnaphtho-extended chemical structure, finite 7-13 carbon atom wide armchair graphene nanoribbons (7-13-aGNRs) were on-surface synthesized. For all lengths up to N = 7 monomer units, low-temperature ultrahigh vacuum scanning tunneling spectroscopy and spatial dI/dV maps were recorded at each captured tunneling resonance. The degeneracy of the two central electronic end states (ESs) occurs in a slowly decaying regime with N converging toward zero for N = 6 long 7-13-aGNR (12 bonded anthracenes), while it is N = 2 (4 bonded anthracenes) for seven carbon atoms wide armchair GNRs (7-aGNRs). The two end dI/dV conductance maxima of ESs are also shifted away from strictly two ends of the 7-13-aGNR compared to the 7-aGNR. Using the quantum topology graph filiation between finite length polyacetylene and 7-13-aGNRs wires, we show that this slow decay of 7-13-aGNR ESs is coming from the property of the topological Hückel band matrix that expels the ESs into its eigenvalue spectrum gaps to keep harmony in the core spectrum.

Using low temperature scanning tunneling microscopy (STM), spectroscopy (STS), and precise $dI/dV$ mapping in combination with density-functional theory-parametrized semiempirical calculations, we report and discuss the origin of tunneling electronic excitations that occur along a seven-carbon-atom-wide armchair graphene nanoribbon (7-aGNR) physisorbed on Ag(111) as compared to a reference on Au(111) surface. On both surfaces, on-surface synthesized 7-aGNRs of variable lengths are selectively chosen for performing the STM and STS ($dI/dV$) excitation mapping along a truly isolated molecule. For exactly the same 7-aGNR molecule length, the difference in work functions between Ag(111) and Au(111) generates different edge states electronic configuration that result in a curved molecular conformation on Ag(111) and a strictly flat one on Au(111). At the interface between the 7-aGNR and Ag(111), this curved conformation produces an additional set of quantum-box-like tunneling resonances that partially mix with the intrinsic 7-aGNR tunneling excitations.

Abstract The controlled surface annealing by steps of 50°C of graphene nanoribbon (GNR) precursors on Au(111) is characterized, during the GNR on-surface synthesis, using low-temperature ultrahigh vacuum scanning tunneling microscopy and dI/dV spectroscopy. The initial monomer coverage is increased up to 3 monolayers (MLs) and annealed at every 50°C. After the first annealing step, the monomers self-organize into 2 ML islands and, then, the Ullmann coupling reaction takes place in both 1st and 2nd MLs. An optimal initial monomer coverage of ~ 1.5 ML is necessary for reaching a final GNR length distribution up to 50 nm and a low surface coverage of 0.4 ML required for single GNR molecule experiments.

Scanning tunneling microscopy (STM) enables the bottom-up fabrication of tailored spin systems on a surface that are engineered with atomic precision. When combining STM with electron spin resonance (ESR), these single atomic and molecular spins can be controlled quantum-coherently and utilized as electron-spin qubits. Here we demonstrate universal quantum control of such a spin qubit on a surface by employing coherent control along two distinct directions, achieved with two consecutive radio-frequency (RF) pulses with a well-defined phase difference. We first show transformations of each Cartesian component of a Bloch vector on the quantization axis, followed by ESR-STM detection. Then we demonstrate the ability to generate an arbitrary superposition state of a single spin qubit by using two-axis control schemes, in which experimental data show excellent agreement with simulations. Finally, we present an implementation of two-axis control in dynamical decoupling. Our work extends the scope of STM-based pulsed ESR, highlighting the potential of this technique for quantum gate operations of electron-spin qubits on a surface.

Low electronic gap graphene nanoribbons (GNRs) are used for the fabrication of nanomaterial-based devices and, when isolated, for mono-molecular electronics experiences, for which a well-controlled length is crucial. Here, an on-surface chemistry protocol is monitored for producing long and well-isolated GNR molecular wires on an Au(111) surface. The two-step Ullmann coupling reaction is sequenced in temperature from 100 °C to 350 °C by steps of 50 °C, returning at room temperature between each step and remaining in ultrahigh vacuum conditions. After the first annealing step at 100 °C, the monomers self-organize into 2-monolayered nano-islands. Next, the Ullmann coupling reaction takes place in both 1st and 2nd layers of those nano-islands. The nano-island lateral size and shape are controlling the final GNR lengths. Respecting the above on-surface chemistry protocol, an optimal initial monomer coverage of ~1.5 monolayer produces isolated GNRs with a final length distribution reaching up to 50 nm and a low surface coverage of ~0.4 monolayer suitable for single molecule experiments.

A planar molecular Pascaline mechanical calculator design is presented based on existing molecule gears which have 6 teeth consisting each of a tert-butyl group at the end of a shaft consisting of a phenyl group. The central phenyl-core is mounted on a single copper ad-atom which is the physical rotation axle on the superconducting Pb(111) surface. In order to construct such a planar molecular calculator, it is essential to realize two key mechanisms: the gearing that is in our design the molecular interlock across a monoatomic step edge and the carry function. Experimental results using the atom/molecule manipulation capability of one low temperature scanning tunneling microscope (LT-STM) of a unique LT-UHV 4-STM instruments demonstrate the feasibility of the above two mechanisms. Experiments with 2.2 nm in diameter large molecule gears are also presented with the same tert-butyl end tooth. They confirm that mutual tert-butyl groups of molecule gears on a terrace with the different heights of the monoatomic step on Pb(111) interlock and gear across the step edge, even if it is imperfect. In addition, experiments using a carry molecule gear containing one shaft with one phenyl group extended also confirmed that the carry mechanism works on the same Pb(111) terrace.

A specifically designed aza-starphene molecule is presented where contacting one, two, and/or three single Al adatoms allows this molecule to function as a "3-inputs & 2-outputs" digital full adder on a Au(111) surface. Sequentially positioning single Al adatoms with atomic precision to interact with aza-starphene, inputs one classical digit per Al, which is converted to quantum information by the molecule. The intramolecular logical calculations do not require a solid-state digital full adder cascade-like architecture. The measured Boolean truth table results in part from the quantum level repulsion effect and in part from a nonlinear magnetic effect also intrinsic to the aza-starphene molecule with its contacted Al adatoms.

Starting from a long aza-starphene neutral and nonmagnetic organic molecule, a single-molecule magnet is on-surface constructed using up to 3 light nonmagnetic aluminum (Al) atoms. Seldom observed in solution with transition-metal atoms and going from 1 to 3 Al coordinated atoms, the doublet-singlet-doublet transition is easily on-surface accessible using the scanning tunneling microscope single-atom and single-molecule manipulations on a gold(111) surface. With 3 coordinated Al atoms, the lateral vibration modes of the Al3-aza-starphene molecule magnet are largely frozen. Using the Kondo states, this opens the observation of the in-phase Al vertical atom vibrations and out-of-phase central phenyl vibrations.

A tetrabenzo[a,c,j.h]phenazine molecule is functionning like a "2 input - 1 output" XOR Boolean logic gate using the quantum level repulsion effect of the Quantum Hamiltonian Computing approach. The logical inputs are performed using one aluminum atom per input. The logical output is measured by the dI/dV tunnelling spectrum at +1.1 V low bias voltage. On an Au(1 1 1) surface, each Al atom is manipulated in and out of the molecule by scanning tunnelling microscope molecular manipulations. This single molecule XOR gate functions without the need of cascading OR, AND and NAND gates inside its molecular structure.

A molecule-gear rotating without a lateral jittering effect is constructed using a single copper adatom as a physical axle on a lead superconducting surface. The molecule-gear has a diameter of 1.2 nm with 6 tert-butyl-teeth. It is mounted on this Cu axle using the atom/molecule manipulation capability of a low temperature scanning tunneling microscope (LT-STM). Transmission of rotational motions between 2 molecule-gears, whose axles have to be exactly 1.9 nm separated, is functioning when this train of molecule-gears is completed with a molecule-handle. To manipulate the molecule-handle laterally, the first molecule-gear of the train directly entangled with the molecule-handle is step by step rotated around its Cu adatom axle. It drives the second molecule-gear mechanically engaged with the first gear to rotate like along a train of macroscopic solid-state gears. Such rotation transmission is one of the most basic function for the future construction of a complex molecular machinery.

A train of molecule gears consisting of PF3 molecules was studied using semi-empirical ASED+ method to explore the mechanism of rotational transmission along this train. It was observed that a unidirectional rotational transmission occurs between only the first two PF3 molecules for a PF3 molecule train up to six molecule-gears, the four PF3 molecules at the end of the train being used to rigidify the rotation axle of the first two PF3. This demonstrates that in a train of molecule-gears, the rotation of each molecule is resulting from a collective action of many degrees of freedom per molecule. This collective motion is rather fragile against many others possible minimum energy trajectories which can develop on the multidimensional ground state potential energy surface of a molecule-gear train to respond to the increase of the potential energy required to rotate the first molecule-gear of the train.

On a Pb(111) surface in its superconducting state, the construction of a train of two and three hexa-tert-butylbiphenylbenzene molecule-gears (HB-BPB) is presented using a single Cu ad-atom rotation axle per molecule-gear for the two first ones. The new presented HB-BPB gears have been designed and synthesized with very long biphenyl teeth to minimize the number of Cu rotation axles for a long train construction when engaged at larger interaxle distances. It leads to a strong mechanical entanglement between the gears and renders a transmission of rotation along the train difficult. To minimize this classical entanglement, a practical solution is presented by using a native Pb(111) surface monoatomic step and by positioning each molecule-gear of the train at different monoatomic step heights on the supporting surface. This allows the construction of functioning long molecule-gear trains.

On a Pb(111) superconducting surface, low temperature dI/dV tunnelling spectra are recorded between two scanning tunnelling microscopes (STM) metallic tips with the Pb(111) sample metallic support non-grounded. The tunnelling current intensity I passing between the 2 tips through the sample is controlled by changing one or both STM vacuum tunnelling junction resistances. The chemical potential of this floating Pb(111) surface depends on the normalized ratio between those two quantum resistances. When ungrounded, the Pb(111) sample chemical potential balances between those of the 2 STM tips while tuning their respective tip end atomic apex to Pb(111) surface distances with a picometer precision without any physical contact between the STM tips and the surface.

The Kondo effect results from the interactions of the conduction electrons in a metal bulk with localized magnetic impurities. While adsorbed atop a metallic surface, the on-surface nanoscale version of this effect is observed when a single magnetic atom or a single magnetic molecule (SMM) is interacting with the conduction electrons. SMMs are commonly organometallic complexes incorporating transition-metal atoms in different oxidation states. We demonstrate how a single nonmagnetic neutral tetrabenzo[a,c,j,h]phenazine molecule can be on-surface-coordinated with exactly two aluminum metal atoms (between Al(I) and Al(II) oxidation state on the Au(111) surface) by low-temperature scanning tunneling microscope (LT-STM) single-atom manipulation. It results in a Kondo measurable localized molecular magnetic moment. This opens a new way to design SMM complexes without the need for heavy transition-metal atoms and complex ligands to stabilize the molecular coordination sphere.

Two molecule-gears, 1.2 nm in diameter with six teeth, are mounted each on a single copper adatom separated exactly by 1.9 nm on a lead surface using a low-temperature scanning tunneling microscope (LT-STM). A functioning train of two molecule-gears is constructed complete with a molecule-handle. Not mounted on a Cu adatom axle, this ancillary molecule-gear is mechanically engaged with the first molecule-gear of the train to stabilize its step-by-step rotation. Centered on its Cu adatom axle, the rotation of the first gear of the train step by step rotates the second similar to a train of macroscopic gears. From the handle to the first and to this second molecule-gear, the exact positioning of the two Cu adatom axles on the lead surface ensures that the molecular teeth-to-teeth mechanics is fully reversible.

•A long trianthracene molecule is used for logical operations with single metal atom contact inputs.•Energy difference of the ground state before and after an atom contact is large enough for the molecule NOR logic gate functioning.

With a central curved chassis, a four-wheeled molecule-vehicle was deposited on a Au(111) surface and imaged at low temperature using a scanning tunneling microscope. The curved conformation of the chassis and the consequent moderate interactions of the four wheels with the surface were observed. The dI/dV constant current maps of the tunneling electronic resonances close to the Au(111) Fermi level were recorded to identify the potential energy entry port on the molecular skeleton to trigger and control the driving of the molecule. A lateral pushing mode of molecular manipulation and the consequent recording of the manipulation signals confirm how the wheels can step-by-step rotate while passing over the Au(111) surface native herringbone reconstructions. Switching a phenyl holding a wheel to the chassis was not observed for triggering a lateral molecular motion inelastically and without any mechanic push by the tip apex. This points out the necessity to encode the sequence of the required wheels action on the profile of the potential energy surface of the excited states to be able to drive a molecule-vehicle.

The surface diffusion of individual molecules is of paramount importance in self-assembly processes and catalytic processes. However, the fundamental understanding of molecule diffusion peculiarities considering conformations and adsorption sites remain poorly known at the atomic scale. Here, we probe the 4'-(4-tolyl)-2,2':6',2″-terpyridine adsorbed on the Au(111) herringbone structure combining scanning tunneling microscopy and atomic force microscopy. Molecules are controllably translated by electrons excitations over the reconstruction, except at elbows acting as pinning centers. Experimental data supported by theoretical calculations show the formation of coordination bonds between the molecule and Au atoms of the surface. Using force spectroscopy, we quantify local variation of the surface potential and the lateral force required to move the molecule. We found an elevation of the diffusion barrier at elbows of the reconstruction of ∼100 meV compared to the rest of the surface.

The molecular conformation of a bisbinaphthyldurene (BBD) molecule is manipulated using a low-temperature ultrahigh-vacuum scanning tunneling microscope (LT-UHV STM) on an Au(111) surface. BBD has two binaphthyl groups at both ends connected to a central durene leading to anti/syn/flat conformers. In solution, dynamic nuclear magnetic resonance indicated the fast interexchange between the anti and syn conformers as confirmed by density functional theory calculations. After deposition in a submonolayer on an Au(111) surface, only the syn conformers were observed forming small islands of self-assembled syn dimers. The syn dimers can be separated into syn monomers by STM molecular manipulations. A flat conformer can also be prepared by using a peculiar mechanical unfolding of a syn monomer by STM manipulations. The experimental STM dI/dV and theoretical elastic scattering quantum chemistry maps of the low-lying tunneling resonances confirmed the flat conformer BBD molecule STM production. The key BBD electronic states for a step-by-step STM inelastic excitation lateral motion on the Au(111) are presented requiring no mechanical interactions between the STM tip apex and the BBD. On the BBD molecular board, selected STM tip apex positions for this inelastic tunneling excitation enable the flat BBD to move controllably on Au(111) by a step of 0.29 nm per bias voltage ramp.

A new disc-shaped highly symmetric C54H20 nanographene fragment, tetrabenzocircumpyrene, has been synthesized and characterized by scanning tunnelling microscopy, demonstrating the potential of this technique for identifying highly insoluble graphenic molecules.