Observation of a thermally activated gearing effect between two hexa-tert-butyl-decacyclene (HBDC) molecule-gears is reported using the Au(111) surface to constrain lateral diffusion of the molecules at 77 K. An on-purpose selected small 2D HBDC nano-island is first destabilized using the tip of a scanning tunneling microscope (STM) in a soft-pulling mode of molecular manipulation. It follows a long sequence of thermally activated spontaneous molecular reconfigurations, leading up to a molecular gearing effect. Using coupled Langevin equations, a simulation of this thermal process is proposed to determine the conditions for this thermally activated gearing effect.

We present the analytical, exact, explicit, and assumption free formulas for the evolution operators corresponding to four instances of time-dependent Hamiltonians relevant to quantum spin batteries including two stochastic cases. We demonstrate how to recover and go beyond existing expansions and approximations directly from the exact solutions giving, for example, an explicit exact formula for Floquet Hamiltonians at all orders. The exact solutions are obtained through a completely novel combination of three mathematical techniques, the ⋆-algebra, path-sums and Omega calculus, which we briefly overview. These are widely applicable to other non-autonomous differential systems.

A microfabrication process for UHV-compatible bimaterial microcantilevers (BMCs) based on ultrapure muscovite mica substrate is presented. The fabricated BMCs are coated with atomically flat Au(111) surfaces exhibiting monoatomic terraces wider than 100 nm. With a BMC of dimension 800 & micro;m & times; 200 & micro;m & times; 15 & micro;m, a deflection sensitivity of 0.1 pm nW-1 is achieved at 77 K in UHV under optical heating. This sensitivity is quantified us ing tunneling current-distance (I-Delta z) measurements acquired with a scanning tunneling microscope, in which thermally induced bending of the cantilever results in measurable variations of Delta z with a resolution of similar to 3 pm. BMCs combining high thermal sensitivity with atomically clean Au(111) enable nanoscale calorimetry with high sensitivity while providing an atomically well-defined platform for molecular surface science.

This study presents three different types of molecular switches studied on an Au(111) surface. For each case, the switching is induced via tip-based manipulations through inelastic tunnelling electrons. However, the mechanism responsible for the switching is different in each molecule. The first molecule is a well-known dipolar switch, wherein the chemical reaction required to switch between the two conformers is usually thermally activated. We show how a unidirectional switching event can be triggered through voltage pulses. The second molecule demonstrates that tuning intermolecular reactions can change its planarity, switching from a non-planar to planar geometry. The third molecule is a reversible switch that can be transformed from one conformation to another by causing an intramolecular change. We find that this is possible by addressing high-energy excited states through tip electrons.

A generalization of the double sample holder (DSH) concept is presented for an ultra-high vacuum (UHV) low-temperature (LT) multi-probe scanning tunneling microscope (STM). In UHV, the DSH is carrying, side-by-side, a reference metal sample [Au(111) single crystal for STM tip apex preparation] and an ancillary stand-alone small sample holder (for samples originating from a clean room) that can be mounted in situ in/out of the DSH plate. STM tip navigation on both sample surfaces is performed using a UHV scanning electron microscope positioned above the STM stage. For demonstration, clean room nanofabricated graphene nano-gears (diameter down to 25 nm) on a sapphire sample are characterized using STM. The STM tip apices are cleaned on the atomically precise and UHV cleaned Au(111) reference sample surface. Using our new DSH plate and in situ STM tip apex re-preparation on the reference metallic sample, we demonstrate how a clean room originating sample can be imaged at the atomic resolution using our LT-UHV 4-STM.

This study investigates the unidirectional rotation of single moleculerotors, crucial for nanoscale work. We compared two DMBI-based molecule-rotors on an Au(111) surface, exploring their one-way rotation induced by tunneling electrons and thermally-induced random rotation rates. By optimizing the parameters of temperature and tunneling current, we identified a narrow voltage range that enhances unidirectional rotation without inelastic tunneling effects. By the quantum mixing of the ground and excited states occurring at each tunneling electron transfer event through the molecule-rotor, the thermal energy can be projected in part on the excited states of the molecule-rotor to enhance the one-way rotation effect in a bias voltage range where inelastic tunneling effects are nearly absent.

A direct focused He+ beam direct machining is presented to fabricate solid-state nano-disk at the surface of a graphene multilayer micro-flake deposited on an Au/Ti/sapphire surface. At irradiation doses larger than 5.0 x 1017 ions cm-2 and with a beam size well below 1 nm, graphene disks down to 20 nm in diameter have been machined with for nano-disk down to 50 nm in diameter, a central hole for preparing the positioning of a rotation axle. The local heat generated by this irradiation is inducing a partial graphene amorphization and deformation, leading to a complete graphene nano-disk vaporization at doses larger than 5 x 1018 ions cm-2. A dry transfer printing technique followed by a graphene surface cleaning was used to transfer the nano-disks from its initial surface to a fresh and clean surface. Tapping mode atomic force micrograph have been recorded to follow the vaporization as a function of the He+ dose to confirm the graphene solid-state nano-disk fabrication limit to about 20 nm with this process.

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.

Depending on its adsorption conformation on the Au(111) surface, a zwitterionic single-molecule machine works in two different ways under bias voltage pulses. It is a unidirectional rotor while anchored on the surface. It is a fast-drivable molecule-vehicle (nanocar) while physisorbed. By tuning the surface coverage, the conformation of the molecule can be selected to be either rotor or nanocar. The inelastic tunneling excitation producing the movement is investigated in the same experimental conditions for both the unidirectional rotation of the rotor and the directed movement of the nanocar.

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.

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.

Abstract With an average diameter of ≈2 nm, on‐surface synthesized amino‐ferrocene nanoclusters are chemisorbed onto a graphene oxide nanosheet, where their Fe ions are in an S = 5/2 high‐spin state. In this two‐dimensional (2D) nanomaterial, the molecular spins in a given nanocluster are weakly magnetic dipole interacting. It generates spin correlations and slow dynamics accessible by magnetic susceptibility and Mössbauer spectroscopy at a temperature where the magnetic anisotropy is negligible. Magnetic simulations show that minimizing their magnetic dipole energies produces spatially entangled structures of the spin orientations under thermal fluctuations at T ≲ 15 K and that the structures behave like a spin liquid. The competition between the formation of the structures and their thermal destruction generates slow dynamics. The ability to create emergent functionalities from dense stacks of weakly interacting magnetic molecules in a 2 nm space paves the way for new designs of an ultra‐compact building block and a functional component in 2D spintronic and neuromorphic devices.

Exploring the limits of the microscopic reversibilityprinciple,we investigated the interplay between thermal and electron tunnelingexcitations for the unidirectional rotation of a molecule-rotor onthe Au(111) surface. We identified a range of moderate voltages andtemperatures where heating the surface enhances the unidirectionalrotational rate of a chemisorbed DMNI-P rotor. At higher voltage,inelastic tunneling effects dominate, while at higher temperature,the process becomes stochastic. At each electron transfer event duringtunneling, the quantum mixing of ground and excited electronic statesbrings part of the surface thermal energy in the excited electronicstates of the molecule-rotor. Thermal energy contributes thereforeto the semiclassical unidirectional rotation without contradictingthe microscopic reversibility principle.

The direct focused helium ion beam milling of solid-state nanogears down to 25 nm in diameter is presented. Sapphire is the supporting surface to release the heat created by this milling process. For this free of resist process, the He+ dosing was first calibrated to limit the lateral fusion in the deposited nanomaterial during the sculpturing of the teeth. 25 nm in diameter solid-state nanogears were fabricated in a 20 nm in thickness Au nanomaterial, in a graphene multilayer and in a monolayer having a van der Waals thickness compatible with a single molecule-gears for transmission of rotation. Optimizing again the He+ dosing for a transmission electron microscope grid, free standing graphene monolayer nanogears were also sculptured down to 40 nm in diameter.

On Cu(111) surface and in interaction with a single hexa-tert-butylphenylbenzene molecule-gear, the rotation of a graphene nanodisk was studied using the large-scale atomic/molecular massively parallel simulator molecular dynamics simulator. To ensure a transmission of rotation to the molecule-gear, the graphene nanodisk is functionalized on its circumference bytert-butylphenyl chemical groups. The rotational motion can be categorized underdriving, driving and overdriving regimes calculating the locking coefficient of this mechanical machinery as a function of external torque applied to the nanodisk. The rotational friction with the surface of both the phononic and electronic contributions is investigated. For small size graphene nanodisks, the phononic friction is the main contribution. Electronic friction dominates for the larger disks putting constrains on the experimental way of achieving the transfer of rotation from a graphene nanodisk to a single molecule-gear.

From their early prototypes to their most recent versions, the history of on-surface molecule-vehicles is briefly presented. An emphasis on their mechanical properties upon different manipulation modes induced by the STM tip, namely constant current, constant height, STM voltage pulse and dipolar mode are discussed. In addition, the chemical structure/mechanical property relationship of those nano-vehicles is described with a highlight on the first edition of the Nanocar Race. Finally, perspectives of the field are given with the introduction of molecular motors in the design of nano-vehicles thus leading to the first prototypes of motorized molecular vehicles on a surface for the technomimetic approach.

In a bridge configuration, a single graphene nanoribbon (GNR) is positioned with a picometer precision over a trench in between two monoatomic steps on an Au(111) surface. This GNR molecular wire adopts a deformed conformation towards the down terrace in between the two contact step edges. Using differential conductance dI/dV mapping from a low-temperature scanning tunneling microscope, it is demonstrated how the electronic delocalization along GNR is cut at each contact by its down curvature. It points out the need to bring conductive nanocontacts backside of the support for preserving the front side GNR planar conformation.

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.

In coordination chemistry, knowledge on the oxidation state of the central metal is a significant basis for the design and synthesis of novel complexes. We examined the mechanism of on-surface coordination bonding to d-block metals by investigating the coordination of the newly designed and synthesized 4(3,3-dimethyl-2,3-dihydro-1H-indol-1-yl)benzonitrile (IBN) ligand with Au adatoms on a Au(111) surface. The formation of mono-, di-, tri-, and tetra-IBN complexes of gold [Au- (IBN)(n) (n = 1, 2, 3, and 4)] and metal-free hydrogen-bonded IBN complexes on the Au surface was examined by scanning tunneling microscopy. The nature of the coordinated Au adatom was clarified by density functional theory calculations. The 5d(z)(2) pseudospheroidal orbital of the Au adatom is the predominant contributor to the Au-N coordination bond, and the Au(111) surface maintains a zero oxidation state of the Au adatom for coordination numbers n = 1, 2, 3, and 4. This on-surface control of the oxidation state of the Au adatom explains the different coordination numbers that were observed when Au adatoms coordinate to IBN molecules, together with an absence of variability in the electronic structures of the Au complexes as a function of their coordination number.