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Trapping and moving metal atoms with a six-leg molecule
Abstract
Putting to work a molecule able to collect and carry adatoms in a controlled way on a surface is a solution for fabricating atomic structures atom by atom. Investigations have shown that the interaction of an organic molecule with the surface of a metal can induce surface reconstruction down to the atomic scale. In this way, well-defined nanostructures such as chains of adatoms, atomic trenches and metal-ligand compounds have been formed. Moreover, the progress in manipulation techniques induced by a scanning tunnelling microscope (STM) has opened up the possibility of studying artificially built molecular-metal atomic scale structures, and allowed the atom-by-atom doping of a single C(60) molecule by picking up K atoms. The present work goes a step further and combines STM manipulation techniques with the ability of a molecule to assemble an atomic nanostructure. We present a well-designed six-leg single hexa-t-butyl-hexaphenylbenzene (HB-HPB) molecule, which collects and carries up to six copper adatoms on a Cu(111) surface when manipulated with a STM tip. The 'HB-HPB-Cu atoms' complex can be further manipulated, bringing its Cu freight to a predetermined position on the surface where the metal atoms can finally be released.
... One of the most important applications of moving tiny objects on a surface, can be found in transport devices at the nanoscale [1]. In all such devices, one encounters the problem of interaction between the moving nanoparticles and the nanostructures under examination which is mainly due to the mass of the nanoparticles and the frictional forces [2][3][4][5][6]. ...
... In the nonlocal strain gradient theory, a new stress tensor is introduced: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t 5 (1) . Γ σ σ (1) where Γ is the total stress tensor, is the gradient operator,σ is the classical nonlocal stress tensor and (1) σ is a higher-order nonlocal stress tensor defined as: ...
... In the nonlocal strain gradient theory, a new stress tensor is introduced: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t 5 (1) . Γ σ σ (1) where Γ is the total stress tensor, is the gradient operator,σ is the classical nonlocal stress tensor and (1) σ is a higher-order nonlocal stress tensor defined as: ...
The size-dependent nonlinear vibration of Euler-Bernoulli nanobeams acted upon by moving harmonic loads travelling with variable velocities has been examined within the scope of the nonlocal strain gradient elasticity theory. Equations of motion have been derived by employing the extended Hamilton principle. For simply supported edges, the Galerkin discretizing method has been utilized to reduce the nonlinear partial differential equation of motion to a Duffing type equation. A multistage-linearization technique is employed to solve the Duffing equation approximately. The effects of the nonlocal and material length scale parameters, and the velocity, acceleration and the excitation frequency of the moving harmonic load on the nonlinear dynamic behavior of nanobeams are discussed in some detail.
... In this context, a number of studies describing the mesoscopic restructuring of metallic surfaces induced by chiral and prochiral organic molecules have been undertaken in the last decades [15][16][17]. In some cases, the local nanostructuring of the step edges and terraces occurred upon deposition of the achiral "Lander" molecules [18,19]. Reports of surface modification induced by adsorption of achiral planar MPc molecules in the literature are scarce [20][21][22]. ...
... The Cu(110) terrace reconstruction was instead achieved because of epitaxy and close lattice matching between the aromatic molecules and the underlying substrate [32]. Surface restructuring has also been observed when large non-planar Lander molecules are adsorbed on copper surfaces [18,19]. This class of molecules can trap and transport metal adatoms, leading to the formation of metal nanoclusters on the terraces or nanowires growing from the step edges. ...
The surface stability of coinage metals is paramount when they are used as electrode materials for functional electronic devices incorporating organic semiconductors. Here, adsorption of non-planar vanadyl phthalocyanine molecules on Cu(110) drastically restructures the metal surface at room temperature (RT) that is further enhanced upon moderate annealing. Scanning tunneling microscopy (STM) imaging demonstrates that the surface is restructured at step edges into sawtooth features which gradually replace the (110) terraces. The edges of modified steps are preferentially composed of chiral (1×6) kink sites decorated with VOPc molecules adsorbed in tilted configuration with oxygen atom pointing downwards. These results can have strong impact for optimization of organic device performance where these phthalocyanine molecules are integrated.
... A particular fascinating property of single Lander molecules adsorbed at step edges or to a lesser extent on terraces is their ability to induce reconstruction of the underlying metal substrate (see Fig. 6.1a,b) which is commonly referred to as the "molecular moulding" effect [155,156]. It was recently shown that four-and six-legged Lander molecules are capable of forming well-defined metallic nanostructures either spontaneously by trapping diffusive adatoms in the cavity underneath the aromatic board or deliberately by STM manipulation of the molecular mould [155,157]. The controlled self-assembly of Lander molecules on surfaces is therefore attractive for fabricating conductive metallic nanowires or nanoarrays which might be applied for nanoelectronic circuitry. ...
... The four bright lobes arranged in a rectangular manner (11.6 Å×6.7Å) are assigned to the tert-butyl groups due to a high electron tunnelling probability through the spacer legs into the metal substrate. The dimmer sub-protrusions in the centre can be attributed to the hexaphenyl benzene (HPB) core, similar to that observed earlier for HB-HPB molecule [157,163]. Strikingly, there is no signature of the two DAT groups in STM image. Notice that the evaporation of large and complex compounds involves a risk of thermal decomposition of the molecular building blocks if the intermolecular cohesive strength in the molecular source material exceeds the intramolecular binding energy. ...
Nanotechnology is one of key technologies that involve molecular self-assembly bottom-up approaches. Supramolecular 1D or 2D hydrogen-bonded organic systems are studied in detail in this thesis by means of scanning tunnelling microscopy under ultrahigh vacuum conditions. This work focuses on induction of homochirality at surfaces and self-organization of complementary hydrogen-bonded systems on insulating and metallic substrates. Peptide self-assembled structures have been realized and thoroughly investigated. This latter study is an attempt to clarify the assembly mechanisms of peptide fibrillization at the atomic scale.
... La première (figure 1.9-a) repose sur l'utilisation des forces attractives ou répulsive (en fonction de la polarisation de la jonction) qui s'établisse entre la pointe et l'adsorbat. Cette technique est sans doute celle qui a été le plus utilisée en particulier pour les molécules fonctionnalisées sur les surfaces métalliques [45,46]. Ensuite, il est possible aussi d'utiliser les électrons tunnel (figure 1.9-b) comme source très locale d'excitation [17,18]. ...
... Un benzène latéral servant de marqueur permet pour confirmer la rotation sur chaque topographie. Encore plus insolite, Gross et al [46] ont pu montrer que la molécule de HB-HPB pouvait englober plusieurs ad-atomes de cuivre sur la surface de Cu(111). [64]. ...
The objective of this thesis is to explore the control of electronically induced processes in various functionalized molecules adsorbed on the surface of silicon (100). In the context of molecular nanoscience, this work has been carried out using a scanning tunneling microscope operating at low temperature (9K). We used an approach combining statistical study and theoretical modelling in order to explore the physics of the various observed processes. This thesis begins with the study of the Hexaphenylbenzene (HPB) molecule for which the lateral phenyl rings enable the molecule-silicon surface electronic decoupling. Thanks to this effect, we could achieve a directive and reversible diffusion control of physisorbed HPB molecules along the SA silicon step edge through a process combining the joint actions of tunnel electrons and the local STM tip induced electrostatic field. These first results allowed considering the study of a couple of metaltetraphenyl porphyrin molecules adsorbed on the Si(100)-2x1 surface. Similarly to the HPB molecules, the two chosen metalloporphyrins: NiTPP and CuTPP, have lateral phenyl rings. Several adsorption conformations for these molecules were characterized and their response to electronic excitation has been studied. In the case of NiTPP, this led to the control of the reversible activation of an intra-molecular bistable despite the partial chemisorption of the molecule on the silicon surface. As for CuTPP molecule, our study revealed hysteresis behavior on the I(V) conduction curves associated with reversible conformation changes which represents the realization of a memory function. Following the study of each molecule apart, we performed the co-adsorption of the two molecules on the Si(100) surface to study molecular pairs. Various pairs of molecules have been studied. On one of them, we were able to activate an inter-molecular excitation transfer process by locally exciting one molecule and observing a conformation change of the second molecule of the pair. This result thus shows the electronic control of a bi-molecular device getting rid of substrate mediated electronic process. Finally, as a perspective, this thesis presents a novel technique allowing the controlled local hydrogenation of the Si(100) surface. This is achieved thanks to the passivation of the STM tip by molecular hydrogen at 9K. The tunnel electrons are then used to induce the intra-dimer dissociative adsorption of H2 molecules on the Si(100) surface. This technique could be considered for the passivation of Si(100) or to locally modify molecular circuits.
... Attempts to move atoms or molecules with the help of another molecule have been successful. However, they rely only on the mechanical interaction with the STM tip, 14,15 or the thermal noise coming from the surface is used to carry an attached molecule. 16 When the molecule carrying the load is moved mechanically following a direct interaction with the STM tip apex, 15 a deformation of its adsorption potential energy and of its conformation results and B contributes directly to the mechanically induced motion of the molecule and its load. ...
... However, they rely only on the mechanical interaction with the STM tip, 14,15 or the thermal noise coming from the surface is used to carry an attached molecule. 16 When the molecule carrying the load is moved mechanically following a direct interaction with the STM tip apex, 15 a deformation of its adsorption potential energy and of its conformation results and B contributes directly to the mechanically induced motion of the molecule and its load. ...
A supramolecular nanostructure composed of four 4 acetylbiphenyl molecules and self-assembled on Au (111) was loaded with single Au adatoms and studied by scanning tunneling microscopy at low temperature. By applying voltage pulses to the supramolecular structure, the loaded Au atoms can be rotated and translated in a controlled manner. The manipulation of the gold adatoms is driven neither by mechanical interaction nor by direct electronic excitation. At the electronic resonance and driven by the tunneling current intensity, the supramolecular nanostructure performs a minute work of about 8 × 10(-21) J, while transporting the single Au atom from one adsorption site to the next. Using the measured average excitation time necessary to induce the movement, we determine the mechanical motive power of the device yielding about 3 × 10(-21) W.
... This active domain has been widely studied [4][5][6]. For example, organic molecules have been adsorbed on a metallic surface where metal clusters have been created spontaneously by trapping diffusing adatoms by STM manipulation of the molecular mold [7,8]. These findings suggest that it is indeed possible to build extended metallic nanostructures, such as nanowires, for potential use in emerging molecular electronic circuitry, by utilizing the molding function of organized structures formed from large organic molecules. ...
The bottom-up fabrication of supramolecular and self-assembly on various substrates has become an extremely relevant goal to achieve prospects in the development of nanodevices for electronic circuitry or sensors. One of the branches of this field is the self-assembly of functional molecular components driven through non-covalent interactions on the surfaces, such as van der Waals (vdW) interactions, hydrogen bonding (HB), electrostatic interactions, etc., allowing the controlled design of nanostructures that can satisfy the requirements of nanoengineering concepts. In this context, non-covalent interactions present opportunities that have been previously explored in several molecular systems adsorbed on surfaces, primarily due to their highly directional nature which facilitates the formation of well-ordered structures. Herein, we review a series of research works by combining STM (scanning tunneling microscopy) with theoretical calculations, to reveal the processes used in the area of self-assembly driven by molecule Landers equipped with functional groups on the metallic surfaces. Combining these processes is necessary for researchers to advance the self-assembly of supramolecular architectures driven by multiple non-covalent interactions on solid surfaces.
... This can be a problem for nano-vehicles carrying a load because the load itself can be in this case also chemisorbed. In another context, the pacman molecule is a good example of a loadable molecule whose lateral diffusion barrier becomes so large that the molecule and its atoms cargo were not moving at all after loading more than five atoms [16]. On the contrary, other wheels like triptycenes present a large lateral diffusion barrier (mounted on a flat chassis [17]). ...
With a central curved chassis, a four wheels molecule-vehicle was deposited on an 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 a 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 potential energy surface of the excited states to be able to drive a molecule-vehicle.
... Investigating single Au III TPP molecules necessitates a well-designed experimental setup, including (i) ultra-high vacuum conditions to exclude obscure chemical reactions between molecules and ambient, (ii) low temperatures to reduce the effect of thermal excitations, (iii) an atomic-precision technique to access and characterize single molecules, (iv) an inert template to minimize molecule/substrate electronic coupling, and (v) isolated molecules to avoid molecule/molecule interactions. LT-STM meets requirements (i-iii) and therefore is established as unique tool for imaging, characterizing and manipulating single atoms [14,15] and molecules [16,17]. The requirements (iv-v) are met by chosing Au(111) as substrate surface. ...
Electron transfer in weakly coupled molecules typically occurs via a transient charging of the molecule by tunneling electrons. We report on the permanent electron injection into a single molecule in a controlled manner by employing low-temperature (LT) scanning tunneling microscopy (STM). Our model system is Au(III) 5,10,15,20-tetraphenylporphyrin (AuTPP) single molecules physisorbed on a single-crystal Au(111) surface. The results of our combined topographic STM images, tunnel conductance dI/dV spectra and two-dimensional spatial dI/dV mapping experiments support a switching of the molecular charge state of AuIIITPP on Au(111) induced by STM manipulation. We successfully realized STM tip-induced chemical reduction reactions in single AuTPP molecules, reducing AuIIITPP to AuIITPP, with the extra electron distributed either preferentially in a 5d state of the center gold ion or the aromatic (pi-conjugated) tetrapyrrole macrocycle of the porphyrin ligand. Details of the electron transfer process were identified and visualized with intra-molecular resolution by single-molecule tunneling spectroscopy and orbital mapping.
... It is conceivable to build up atomically controlled nano-objects with desired functions and performances by manipulating individual atoms and molecules with a scanning tunneling microscope (STM). Using this technique, it has been shown that organic molecules can be used to trap single adatoms on a surface, allowing one to control the electronic spectrum of a molecule by doping 1 or bond formation, 2 to trap and drive atoms, 3,4 or to confine a molecular motion to rotation during manipulation. 5 Particular attention has been given to the manipulation of macrocyclic molecules such as porphyrin 6 or phthalocyanine. ...
The ability to trap adatoms with an organic molecule on a surface has been used to obtain a range of molecular functionalities controlled by the choice of the molecular trapping site and local deprotonation. The tetraphenylporphyrin molecule used in this study contains three types of trapping site: two carbon rings (phenyl and pyrrole) and the center of a macrocycle. Catching a gold adatom on the carbon rings leads to an electronic doping of the molecule while trapping the adatom at the macrocycle center with single deprotonation leads to a molecular rotor and a second deprotonation leads to a molecular jumper. We call 'atom trapping chemistry' the control of the structure, electronic and dynamical properties of a molecule achieved by trapping metallic atoms with a molecule on a surface. In addition to the examples previously described, we show that more complex structures can be envisaged.
... It resulted in the easier H 2 split-off and C−C bond formation simultaneously. In another report presenting the radical applications of metal-inclusion abilities of HAB derivatives, Gross et al. 124 used an approach in which organic derivative was interacted with metal surface to intercalate atoms of the same metal. The hexa-tert-butylhexaphenylbenzene derivative 53 was designed and synthesized that was made to bind with a Cu(111) surface ( Figure 17) through metal−π interaction instead of cation−π interaction. ...
The easily rotatable peripheral aromatic rings around central benzene in hexaarylbenzene (HAB) derivatives create a very intriguing nonplanar, propeller-shaped geometry. Because of the very low susceptibility toward self-aggregation, HAB derivatives are much stronger candidates among various polyphenylenes/hetero-oligophenylenes when poor molecular cohesion and inefficient packing is required. However, the native properties of hexaphenylbenzene (HPB) can be varied by proper tailoring and substitution of the HAB core. The cohesion and packing in the structures of HAB aggregates induce effective structural variations so as to modify the fundamental features. Recently, HAB derivatives attracted a lot of research interest because of their significant role as liquid crystalline materials, organic light-emitting diodes, photochemical switches, redox materials, and molecular receptors. Herein, detailed attention is given to the pioneering work based on synthetic optimization of different HAB cores, elaborated study of their crystal engineering, various interesting applications of HAB derivatives, and future possibilities and capabilities of this still underexplored scaffold.
... the interaction between the aromatic core of HB-NBP molecule and the herringbone elbow is not strong enough, small lateral displacements of the molecule during its rotation happen easily. When the molecule is moved on the Au adatom it is never able to be concentric to the atom, it always stabilizes with the atom in the middle of two tertbutyl legs.[5] As an inevitable consequence, the molecules are rotated pinned on an off-centered axis. The potential corral is also able to confine the molecule but because it does not have a solid pinning center like an adatom the molecule rotates while swaying inside the corral. Besides, in this confining structure will complicate the construction of ...
The first experimental demonstration of a controllable rotating molecule gear is presented. A scanning tunneling microscope (STM) is used to construct, manipulate, and observe the rotation of the molecule gear. The appropriate combination of molecule design, molecule manipulation protocol, and surface atomic structure selection leads to the functioning of the molecule gear. Rotation of the molecule gear is done step-by-step and totally under control. The fabrication of solid-state SiO2 nanogears with diameters ranging from 30 nm up to 1 μm and their manipulation using an atomic force microscope tip on a graphite surface is also presented. Ranging in sizes from few tens of nanometers up to submicron diameters, they are going to enable the transmission of mechanical motion from functional mechanical molecule machineries to larger submicron or micron-sized devices through series of solid-state gears and mechanical components compatible with the semiconductor and electronics industry technology.
... The direct identification of intermolecular interactions and the delicate tailoring of structural motifs with molecular precision on solid surfaces have recently attracted considerable interest because of the prospect for artificial design of functional molecular nanostructures and nanodevices. Scanning tunneling microscopy (STM), especially under ultrahigh vacuum (UHV) conditions, has proven to be a powerful method for the precise manipulation of single molecules to trigger various single-molecule behaviors, such as translation, [1][2][3] rotation, [3][4][5][6][7][8][9] flipping, [10] cis-trans isomerization, [11][12][13] tautomerization, [14][15][16] dehydrogenation, [17][18][19] and dehalogenation. [20] Not limited to single molecules, STM manipulations have also been extended to larger molecular structural motifs with great progress in the following aspects: 1) moving clusters, [21] chains, [22][23][24][25] and patches; [26] 2) dissociating dimers, clusters, and complexes by breaking hydrogen bonds, [27] coordination bonds, [28][29][30] and carbon-metal bonds, [31] respectively; 3) constructing structural motifs by forming new bonds ranging from hydrogen bonds, [32] coordination bonds, [30,33] to robust covalent bonds; [20,34,35] and 4) probing different hierarchical interactions [36] and identifying hydrogen-bonding configurations [27] and covalent bonding sites. ...
Scanning tunneling microscopy (STM) manipulation techniques have proven to be a powerful method for advanced nanofabrication of artificial molecular architectures on surfaces. With increasing complexity of the studied systems, STM manipulations are then extended to more complicated structural motifs. Previously, the dissociation and construction of various motifs have been achieved, but only in a single direction. In this report, the controllable scission and seamless stitching of metal-organic clusters have been successfully achieved through STM manipulations. The system presented here includes two sorts of hierarchical interactions where coordination bonds hold the metal-organic elementary motifs while hydrogen bonds among elementary motifs are directly involved in bond breakage and re-formation. The key to making this reversible switching successful is the hydrogen bonding, which is comparatively facile to be broken for controllable scission, and, on the other hand, the directional characteristic of hydrogen bonding makes precise stitching feasible.
© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
... The site at which a molecule adsorbs onto a surface is known to influence its motion 8 , but the effect it has on the function of a single molecule has been reported only once (for changes in isomerization rates), but in that case the precise adsorption site was not known 5 . Moreover, atoms have been attached to molecules on a surface [9][10][11][12] and the molecular electronic structure modified by single atoms 13,14 . The influence of the local environment (as defects or other CO molecules) on the hopping of single CO molecules has been observed on a Cu(111) surface 15 , although so far only one study has investigated a chemical process in the vicinity of single atoms 16 . ...
Although the local environment of a molecule can play an important role in its chemistry, rarely has it been examined experimentally at the level of individual molecules. Here we report the precise control of intramolecular hydrogen-transfer (tautomerization) reactions in single molecules using scanning tunnelling microscopy. By placing, with atomic precision, a copper adatom close to a porphycene molecule, we found that the tautomerization rates could be tuned up and down in a controlled fashion, surprisingly also at rather large separations. Furthermore, we extended our study to molecular assemblies in which even the arrangement of the pyrrolic hydrogen atoms in the neighbouring molecule influences the tautomerization reaction in a given porphycene, with positive and negative cooperativity effects. Our results highlight the importance of controlling the environment of molecules with atomic precision and demonstrate the potential to regulate processes that occur in a single molecule.
... The so-called nanocars or nanovehicles (i.e., moving nanoparticles) could move several nanometers in size depending on the temperature [9]. By being able to move molecules on a surface, the molecules can also be used as a transport vehicle of several atoms; therefore, it is often called as nanotruck [13]. In all these applications, one somehow faces the problem of nanostructure–moving nanoparticle interaction, mostly because of the mass weights of the nanoparticles and the friction between the surfaces of the nanoparticle and the nanotube structure. ...
Dynamic analysis of nanotube structures under excitation of a moving nanoparticle is carried out using nonlocal continuum theory of Eringen. To this end, the nanotube structure is modeled by an equivalent continuum structure (ECS) according to the nonlocal Euler–Bernoulli, Timoshenko and higher order beam theories. The nondimen-sional equations of motion of the nonlocal beams acted upon by a moving nanoparticle are then established. Analytical solutions of the problem are presented for simply supported boundary conditions. The explicit expressions of the critical velocities of the nonlocal beams are derived. Furthermore, the capabilities of various nonlocal beam models in predicting the dynamic deflection of the ECS are examined through various numerical simulations. The role of the scale effect parameter, the slenderness ratio of the ECS and velocity of the moving nanoparticle on the time history of deflection as well as the dynamic amplitude factor of the nonlocal beams are scrutinized in some detail. The results show the importance of using nonlocal shear deformable beam theories, particularly for very stocky nanotube structures acted upon by a moving nanoparticle with low velocity.
Largish molecules on metal surfaces may act as not only the building blocks of 2D self-assemblies, but also as the template to reshape the metal surfaces. Here, we report the molecular adsorption-induced formation of the periodic nanostripe arrays of substrate atoms through long-range mass transport. When adsorbed on the close-packed Cd(0001) surface, the triphenyl bismuth (TPB) molecules form a 2D self-assembly with 4 × √13 reconstruction. Simultaneously, periodic nanostripe arrays of Cd atoms appear on the substrate terraces. High-resolution scanning tunneling microscopy (STM) images indicate that the Cd nanostrips are built from the parallel segments of Cd atomic chains with 2 × 2 reconstruction. In the mixed phase, the Cd atomic chains exhibit only high-order commensuration when situated between two molecular domains. The massive structural rearrangement of the Cd(0001) surface can be attributed to a strong molecule–substrate interaction.
It is a basic concept of physical chemistry that in thermal equilibrium every individual process is compensated by its reverse process, which is called microscopic reversibility. It is therefore a challenge to realize unidirectional motion of atoms and molecules. Here, various examples of unidirectional motion at surfaces are presented, which cover both rotation and translation of single molecules. Two ways to achieve unidirectionality are discussed. First, the presence of a local gradient that deforms the potential energy surface and leads to unidirectionality. This can be caused by the tip of a scanning tunneling microscope, which is also a very suitable instrument to follow the motion of individual molecules. Second, intrinsic unidirectionality of a molecule-surface system, which is of particular interest to be employed in molecular machines for useful work at the atomic scale.KeywordsUnidirectionalityMicroscopic reversibilitySurfacesMolecular motorsRotationTranslationScanning tunneling microscopy (STM)Single-molecule manipulationAdsorptionSingle-crystalsSurface-molecular-beamPotential energy surfaceMolecular machinesMechanics with molecules
The forced vibration behaviors are examined for nonlocal strain gradient nanobeams with surface effects subjected to a moving harmonic load travelling with a constant velocity in terms of three beam models namely, the Euler-Bernoulli, Timoshenko and modified Timoshenko beam models. The modification for nonlocal strain gradient Timoshenko nanobeams is exerted to the constitutive equations by exclusion of the nonlocality in the shear constitutive relation. Some analytical closed-form solutions for three nonlocal strain gradient beam models with simply supported boundary conditions are derived by using the Galerkin discretization method in conjunction with the Laplace transform method. The effects of the three beam models, the nonlocal and material length scale parameters, the velocity and excitation frequency of the moving harmonic load on the dynamic behaviors of nanobeams are discussed in some detail. Specifically, the critical velocities are examined in some detail. Numerical results have shown that the aforementioned parameters are very important factors for determining the dynamic behavior of the nanobeams accurately.
A reliable anchoring on the substrate is the fundamental prerequisite to investigate surface-bound molecular rotors. The choice of the anchor group is dependent on the used substrate, and the surface-molecule bond must be sufficiently strong to endure under electrical operation. Here, we give an overview of anchor groups suitable to immobilize molecules on gold and other coinage metals via chemisorption. Sulfur-, nitrogen- and oxygen-based anchors are reviewed, N-heterocyclic carbenes as well as selected examples of other carbon-based anchors are considered, and examples of anchor groups reported for surface-bound molecular rotors are given. Anchoring is discussed in terms of the surface-molecule binding mode, i.e. radical adsorption and lone pair interaction. Green’s ligand classification, Pearson’s hard/soft- acid/base (HSAB) principle as well as the concepts denticity and podality are considered. Emphasis is placed on chemical aspects, e.g. the need to protect and controllably deprotect reactive anchors such as thiols and acetylenes.
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.
Two molecule-gears, 1.2 nm in diameter with 6 teeth, are mounted each on a single copper ad-atom separated exactly by 1.9 nm on a lead surface using a low temperature scanning tunneling microscope (LT-STM). A functioning train of 2 molecule-gears is constructed completed with a molecule-handle. Not mounted on a Cu ad-atom 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 ad-atom 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 ad-atom axles on the lead surface ensures that the molecular teeth to teeth mechanics is fully reversible.
This thesis presents a detailed study of the physical processes underpinning manipulation of aromatic molecules with the scanning tunnelling microscope (STM) on Si(111)-7x7.We distinguish between two modes of manipulation: local and nonlocal.Nonlocal manipulation is when an electron injected from the STM tip induces amolecule some tens of nanometres distant from the original injection site to react,in this case desorb. We split this process into three steps: (i) electron injection, (ii)surface transport, and (iii) molecular manipulation. The first set of results presented in this thesis aim to gain comprehensive understanding of the transport process, step (ii). By drawing a comparison with laser two-photon photoemission experiments, we are able to show that the injected electrons are transported across the surface via a state localised at the silicon adatom backbonds. We also show that the temperature dependence of the length-scale of the nonlocal process obeys Einstein's electrical mobility equation, T^{0.5}. This, combined with a good t to the radial distribution data allows us to conclude that the observed nonlocal effect is the aftermath of diffusive hot electron transport across the surface. Furthermore, we observe a region of suppressed desorption close to the injection site, which behaves in a saw-tooth fashion as we increase the injection bias voltage. We show that each time the suppression region resets itself back to a minimum value, a new surface state appears as measured withscanning tunnelling spectroscopy (STS). We develop a theoretical model to link themagnitude of the supression region to the surface band structure, based on the coherent expansion of an electron wavepacket. By fitting the model to the experimental data we extract a coherent lifetime of 10 fs. We conclude that electron (and hole) transport is a two-step process: (1) ultrafast coherent inflation, followed by (2) incoherent diffusion.The second set of results presented here are aimed at understanding step (iii) ofthe nonlocal process, i.e. the molecular manipulation itself. To address this we perform extensive studies where we inject electrons (and holes) directly into a single target molecule on the surface and into the silicon adatoms themselves and look at the current and the voltage dependence of the manipulation rate. At low temperature, we compare directly the rate of desorption of toluene molecules to the rate of silicon adatom hopping. This, combined with a comparison of the voltage dependence of the manipulation rate with STS spectra acquired on top of a molecule and on top of a clean adatom, allows us to show that manipulation is in fact mediated by the underlying silicon surface. Injecting the tunnelling current into the molecule simply enhances this effect. Finally, the current dependence for hole injections into toluene molecules allows us to observe suppressed desorption rate at higher currents - the opposite effect of what is expected. By presenting the desorption rates as a function of tip height, we construct a simple model where we introduce a second decay channel for the excited state of the molecule: through the tip. This allows us to obtain an estimate of the tip-molecule separation during a `passive' scan of 0.4 A.In the context of all this, we discuss step (i), the injection process, and propose future experiments that will allow us to: gain better understanding of the injection process and measure the absolute reaction cross-section; extend the nonlocal manipulation to new surfaces, e.g. graphene, and employ this technique in order to observe relativistic quantum mechanics phenomena; and obtain quantitative information about some principal surface science properties on the nanoscale, like mobility.
Molecular flexure, and molecule-metal contact of para-sexiphenyl molecules on a Ag(111) surface are investigated by using low temperature scanning tunneling microscopy, and molecular manipulations. Atom trapping with sexiphenyl molecules is realized by laterally manipulating the molecules onto individual silver atoms and up to three silver atoms have been trapped. We also demonstrate breaking of a silver dimer into individual silver atoms by atom trapping. STM manipulation experiments show that the molecule-metal complexes formed by the atom trapping are mechanically stable. Moreover, Lateral manipulation of a single sexiphenyl across a Ag(111) atomic step highlights how the molecule moves across step-edges; the molecule can easily conform across the step and it recovers original configuration after the manipulation.
Using a combination of UHV-STM and molecular mechanics calculations, we investigate the surface self-assembly of a complex multi-component metal-molecule system with synergistic non- covalent interactions. Hydrogen bonding between three- dimensional...
This document is part of Subvolume A of Volume 45 'Physics of Solid Surfaces' of Landolt-Börnstein - Group III 'Condensed Matter'. It contains examples of chemical reactions on molecule level. Parent documents: SpringerMaterial s Volume III/ 45A General introduction to Volume III/ 45A
Functional molecules, especially with carboxyl groups are crucial in building supramolecular structures. It is great important to study the effect of the symmetry, number of carboxyl groups on the self-assembly behavior of corresponding molecules. A series of hexaphenylbenzene (HPB) derivatives (HPB-1,3,5-3A, HPB-1,2,4-3A and HPB-1,4-2A) substituted with different number of carboxyl groups at different position have been synthesized and their self-assembled structures were investigated at both 1-phenyloctane/HOPG and heptanoic acid/HOPG interfaces by using scanning tunneling microscopy (STM) technique. The self-assembled mechanisms of these HPB-based compounds were further studied with the help of density functional theory (DFT) calculations. The results indicate that symmetry and number of carboxyl groups as well as solvent play a significant role on the tuning self-assembled process resulting in various structures.
This article reviews the manipulation of single molecules by scanning tunneling microscopes, in particular, vertical manipulation, lateral manipulation, and inelastic electron tunneling manipulation. For a better understanding of these processes, we shortly review imaging by scanning tunneling microscopy as a prerequisite to detect the manipulated species and verify the result of the manipulation and scanning tunneling spectroscopy and inelastic electron tunneling spectroscopy, which is used to chemically identify the molecules before and after the manipulation that employs the tunneling current.
The dynamics at the interface between a close-packed porphyrin monolayer and Au(111) is investigated by time-dependent scanning tunneling microscopy, detecting the motion of single-interface adatoms in real space. Imaging sequences reveal predominant switching of the molecular appearance in adjacent molecules, pointing to a spatial correlation that is consistent with adatom diffusion from one molecule to the next. In some cases, the number of switching molecules is drastically increased, indicating collective switching events. In addition to the thermally induced motion of adatoms at the interface, also voltage pulses from the microscope tip can induce the process—revealing different yields in agreement with the model of adatom hopping.
Abstract : This work is directed towards the design and control of movements of nanomachines induced current in the tunnel system and for the rationalization and understanding of experience handling nano-objects and their molecular properties of Self-assembly and controlled nanostructuring of metal surfaces. In the first 2 chapters are outlined techniques and methods of quantum chemistry, mechanics and molecular electron transfer that we use in this work. The remaining 4 chapters are devoted to the study of adsorption properties and assembly of molecules, specially designed interest for nanoelectronics. Indeed, in Chapter 3, it is question of adsorbed molecule DAT (1,4-bis (4 - (2,4-diaminotriazine) phenyl) -2,3,5,6-tetrakis (4-tert -butyl-phenyl) benzene) on the surfaces Cu (110) and Au (111) under conditions of very low temperature under a vacuum ultra-advanced (UHV-LT: Low Temperature Ultra High Vacuum). The adsorption and self-assembly of DAT in 1D and 2D on the surface are governed by a complex process which we reveal the details. Next, in Chapter 4, we calculated the STM images, by the technique Electron Scattering Quantum Chemistry (ESQC) of the DAT molecule on the surface Cu (110) and Au (111), to confirm and explain the structures optimized by molecular mechanics using a comparison the STM images at atomic resolution and ESQC. Chapters 5 and 6 are respectively devoted to the study of adsorption properties and self-assembly of molecule-carboxylic di-imide (DCI) and a molecule derived PTCDI (perylene-3, 4,9, 10-tetracarboxylic di-imide) on the surface Au (111), we found that the Lander DCI adsorbed on the site top along the direction [11-2] of the surface Au (111). In the case of co-adsorption on Au (111), the challenge was to determine the adsorption sites. We found a stable energy system consists of one-dimensional molecular chains, these chains are oriented along the direction [11-2] of the surface Au (111) and are dominated by hydrogen bonds N-H---O intermolecular between functional groups carboxylic-di-imide (DCI) as the interaction between the molecule and the substrate contributes primarily to the alignment of the sequence of channels on the surface Au (111).
The expected limits of silicon-based microelectronics in the coming years, have promoted the development of alternative solutions. Among them, organic electronics, using pi-conjugated organic materials as the active part of components, sounds very attractive. Increases observed the past 20 years in the performances of organic devices, find for a great part their origin in a better structure of the active film and the understanding of the relationship between structure and electronic properties in these materials still appears as a keynote for organic electronics.
An STM structural study of self-assembled monolayers of either small molecules synthesised at the laboratory or polythiophenes was carried out in a first time to bring out self-assembly mechanisms. For the polymer monolayers, crystalline properties could be considerably improved with annealing of the sample. An organised second layer was observed for the first time on sample with higher coverage.
Finally the influence of local inter or intra-chain conformation on polymer electronic properties was investigated by two-dimensional scanning tunnelling spectroscopy. Although the electronic structure of the polymer seems unaffected by intra-chain defect such as folds, an increase of the bandgap was observed above isolated chains of the second layer. This is rather surprising as such chains are generally assumed to be pi-stacked on the first layer, which should cause a partial closure of the bandgap.
We investigate the modification of electronic properties of single cobalt phthalocyanine (CoPc) molecule by an extra Co atom co-adsorbed on Au (111) surface using scanning tunneling microscopy
(STM), joint with density functional theory
(DFT) calculations. By manipulating CoPc molecules using the STM tip to contact individually adsorbed Co atom, two types of relatively stable complexes can be formed, denoted as CoPc-Co(i) and CoPc-Co(ii). In CoPc-Co(i), the Co atom is at an intramolecular site close to aza-N atom of CoPc, which induces significant modifications of the electronic states of CoPc, such as energy shifts and splitting of nonlocal molecular orbitals. However, in CoPc-Co(ii) where the Co atom is underneath a benzene lobe of CoPc, it only slightly modifies the electronic states of CoPc, and mainly local characteristics of specific molecular orbitals are affected, even though CoPc-Co(ii) is more stable than CoPc-Co(i). Our DFT calculations give consistent results with the experiments, and related analyses based on the molecular orbital theory reveal mechanism behind the experimental observations.
Several methods were developed in the last decades to manipulate molecules using the tip of a scanning tunneling microscope (STM). In this chapter, experiments will be reviewed where the movement of model molecular machines is driven by the tip of a STM. By varying one of three main parameters, the chemical forces between tip and surface, the electric field, or the tunneling current, molecules can be exactly positioned on a metal surface and conformational changes in single molecules can be induced. For the development of larger and more complex machines, it is, however, important to move not only adsorbates one by one, but also structures composed by several molecules. Therefore, a purely electronic excitation method was recently developed for the controlled movement of weakly interacting assemblies of few molecules.
Hydrogen(H)-bond dynamics are involved in many elementary processes in chemistry and biology. Because of its fundamental importance, a variety of experimental and theoretical approaches have been employed to study the dynamics in gas, liquid, solid phases, and their interfaces. This review describes the recent progress of direct observation and control of H-bond dynamics in several model systems on a metal surface by using low-temperature scanning tunneling microscopy (STM). General aspects of H-bond dynamics and the experimental methods are briefly described in chapter 1 and 2. In the subsequent four chapters, I present direct observation of an H-bond exchange reaction within a single water dimer (chapter 3), a symmetric H bond (chapter 4) and H-atom relay reactions (chapter 5) within water–hydroxyl complexes, and an intramolecular H-atom transfer reaction (tautomerization) within a single porphycene molecule (chapter 6). These results provide novel microscopic insights into H-bond dynamics at the single-molecule level, and highlight significant impact on the process from quantum effects, namely tunneling and zero-point vibration, resulting from the small mass of H atom. Additionally, local environmental effect on H-bond dynamics is also examined by using atom/molecule manipulation with the STM.
C60 molecules were used to trap Co adatoms and clusters on a Au(111) surface using atomic/molecular manipulation with a scanning tunneling microscope. Two manipulation pathways (successive integration of single Co atoms in one molecule or direct integration of a Co cluster) were found to efficiently allow the formation of complexes mixing a C60 molecule with Co atoms. Scanning tunneling spectroscopy reveals the robustness of the π states of C60 that are preserved after Co trapping. Scanning tunneling microscopy images and density functional theory calculations reveal that dissociated Co clusters of up to 9 atoms can be formed at the molecule-substrate interface. These results open new perspectives in the interactions between metal adatoms and molecules, for applications in metal-organic devices.
This article reviews manipulation of single molecules by scanning tunnelling microscopes, in particular vertical manipulation, lateral manipulation, and inelastic electron tunnelling (IET) manipulation. For a better understanding of these processes, we shortly review imaging by scanning tunnelling microscopy – as a prerequisite to detect the manipulated species and to verify the result of the manipulation – as well as scanning tunnelling spectroscopy and IET spectroscopy which are used to chemically identify the molecules before and after the manipulation that employs the tunnelling current.
The co-adsorption of two molecular Landers equipped with functional groups capable of forming a complementary triple hydrogen-bonding motif is investigated with scanning tunneling microscopy and molecular mechanics calculations. Surprisingly, the anticipated complementary motif is not realised in 2-D terrace structures, but is observed in 1-D structures at step edges where molecular conformational flexibility is confined.
In a nonprotic solvent, a (H2O)2(COOH)3(L) supramolecular synthon was found to guide the formation of five new crystal structures together with HPB-3a (1,3,5-tris(4-carboxyphenyl)-2,4,6-tris(4-tert-butylphenyl)benzene). This synthon acted as a 3-connected trigonal planar node (L = acetone) in 1 [(HPB-3a)(H2O)2(acetone)3] or a 4-connected trigonal pyramidal node (L = pyridyl) in 2 [(HPB-3a)(bipy)0.5(H2O)2], 3 [(HPB-3a)(azopy)0.5(H2O)2], 4 [(HPB-3a)(bipy-ete)0.5(H2O)2], and 5 [(HPB-3a)(bipy-eta)0.5(H2O)2] (bipy = 4,4′-bipyridine, azopy = azopyridine, bipy-ete = trans-1,2-bis(4-pyridyl)ethene, bipy-eta = 1,2-bis(4-pyridyl)ethane). The formation of this synthon could be attributed to the C3-symmetry of planar HPB-3a molecules and the hydrophobic interactions between tert-butyl groups. 1 represents a continuously interdigitated 63-hcb layer structure. 2–5 are with the same topology and display amazing 2D homochiral bilayers, which were penetrated in parallel by two others (“above” and “below”) with the opposite chirality to form overall 3D racemic networks. However, the synthon was not as robust in the presence of protic solvents. In 6 [(HPB-3a)(MeOH)3], carboxyl groups interact directly with hydroxyl groups of methanol to form 1D hydrogen bonding chains. The structure is a 3-fold interpenetrated 49·66-acs network.
Atomic manipulation using a scanning tunneling microscope (STM) tip enables the construction of quantum structures on an atom-by-atom basis, as well as the investigation of the electronic and dynamical properties of individual atoms on a one-atom-at-a-time basis. An STM is not only an instrument that is used to 'see' individual atoms by means of imaging, but is also a tool that is used to 'touch' and 'take' the atoms, or to 'hear' their movements. Therefore, the STM can be considered as the 'eyes', 'hands' and 'ears' of the scientists, connecting our macroscopic world to the exciting atomic world. In this article, various STM atom manipulation schemes and their example applications are described. The future directions of atomic level assembly on surfaces using scanning probe tips are also discussed.
Analysis of signal fluctuations of a locally fixed probe, caused by molecules
diffusing under the probe, can be used to determine diffusion coefficients.
Theoretical treatments so far have been limited to point-like particles or to
molecules with circle-like shapes. Here we extend these treatments to molecules
with rectangle-like shapes, for which also rotational diffusion needs to be
taken into account. Focusing on the distribution of peak widths in the signal,
we show how translational as well as rotational diffusion coefficients can be
determined. We address also the question, how the distribution of interpeak
time intervals and autocorrelation function can be employed for determining
diffusion coefficients. Our approach is validated against kinetic Monte Carlo
simulations.
Coordination bonding between para-quarterphenyl-dicarbonitrile linkers and gadolinium on Ag(111) has been exploited to construct pentameric mononuclear supramolecules, consisting of a rare-earth center surrounded by five molecular linkers. By employing a scanning tunneling microscope tip, a manipulation protocol was developed to position the individual pentamers at the surface. In addition, the tip was used to extract and replace individual linkers yielding tetrameric, pentameric, nonameric and dodecameric metallosupramolecular arrangements. These results open new avenues towards advanced nanofabrication methods and rare-earth nanochemistry by combining the versatility of metal-ligand interactions and atomistic manipulation capabilities.
The electronic and structural properties of large molecules composed of a central hexa-phenylbenzene core surrounded by six adamantyl groups (Ad6HPB) adsorbed on Ag(111) have been investigated using low temperature scanning tunneling microscopy (STM), adsorption and image calculations. On large 2D domains, the molecular organization displays two lattices. In one of them, molecules are slightly nested as a result of their relative flexibility during packing. These compounds also exhibit contrast variations in terms of used bias voltage in the self-assembled domains as well as in single molecule observations. This is attributed to the peculiar electronic properties of Ad6HPB and to the role of peripheral groups.
The adsorption and self-assembly of Gd@C 82 molecules on Cu(100) surface have been investigated using scanning tunneling microscopy (STM). The metallofullerene molecules in the assemblies showed two characteristic apparent heights in the STM images. STM manipulation and spectroscopy was performed and revealed the formation of Cu adatom islands underneath the Gd@C 82 molecules. The monolayered Cu aggregates were resulted from the adatom-molecule complexation, which is supported by density functional theory (DFT) calculations that show charge transfer and electrostatic interactions between Gd@C 82 and adatoms. In addition, sub-molecularly resolved STM images demonstrated the structural and orientational ordering of Gd@C 82 assemblies upon thermal annealing. DFT calculations demonstrated that Gd atom located at the lower part of the carbon cage is a favored adsorption configuration for Gd@C 82 molecules adsorbed on Cu(100).
Single decastarphene molecules, adsorbed on Cu(111) and on a bilayer of NaCl/Cu(111) are imaged by a combination of low temperature scanning tunneling microscopy (STM) and dynamic atomic force microscopy in the non-contact mode (nc-AFM). This dual imaging technique provides the intramolecular electron density maps of the frontier molecular orbitals via the STM images and the atomic scale skeleton via its constant-height frequency shift nc-AFM images. Recording both images at the same time opens the way to exactly locate the valence states electronic density map of the imaged molecule on its atomic scale skeleton.
Scanning tunnelling microscope (STM) manipulation of single atoms and molecules has reached a level or maturity such that the electronic, optical, mechanical, magnetic, and chemical properties of individual nano-objects can now be investigated at the atomic scale. The synergy between STM manipulation and surface science on one side and chemical synthesis on the other, has been very fruitful in the design and experimentation on increasingly sophisticated functionalized nano-objects. Apart from this, while STM is the most versatile and powerful tool for working at the atomic scale, it has been now realized that it would be necessary to combine the STM with other techniques such as lasers, synchrotron radiation, atomic force microscopy (AFM), scanning electron microscopy (SEM), and lithography techniques, to extend its capabilities. As a result, a real new technology, atom-scale technology, is now emerging.
The in-situ metalation of monolayers of 2HTPP with Fe atoms on Ag(111) was studied with STM. This surface-confined coordination
reaction results in the formation of adsorbed FeTPP. It is demonstrated that metalation of 2HTPP is achieved either by depositing
iron atoms onto a monolayer of 2HTPP at RT, or, alternatively, by depositing 2HTPP onto a Ag(111) surface with pre-deposited
iron. The latter route requires elevated temperatures, indicating that this reaction includes at least one step with an activation
barrier.
A new class of nanovehicles incorporating trans-alkynyl(dppe)2ruthenium-based wheels is reported. A four-wheeled nanocar and a three-wheeled trimer were synthesized for future studies at the single molecule level.
This article focuses on the synthesis of a family of rotary molecular motors based on a penta-substituted cyclopentadienyl tris(indazolyl)borate ruthenium(II) complex. In order to demonstrate a movement of rotation in this family of molecular motors, dissymmetric derivatives with one ferrocene missing have also been synthesized. The molecules have been prepared with ester and thioether-functionalized tris(indazolyl)borate ligands in view of studying them as single molecules on various surfaces by STM or AFM techniques.
Two-dimensional positioning of intact individual molecules was achieved at room temperature by a controlled lateral “pushing”
action of the tip of a scanning tunneling microscope. To facilitate this process, four bulky hydrocarbon groups were attached
to a rigid molecule. These groups maintained sufficiently strong interactions with the surface to prevent thermally activated
diffusional motion, but nevertheless allowed controllable translation. Simulations demonstrated the crucial role of flexure
during the positioning process. These results outline the key role of molecular mechanics in the engineering of predefined
properties on a molecular scale.
The controlled formation of non-covalent bonds (H-bonding, metal–ligand interactions) is the key ingredient for the fabrication
of supramolecular architectures and nanostructures. Upon deposition of molecular building blocks at well-defined surfaces,
this issue can be directly addressed. Scanning tunneling microscopy observations are presented, which provide insight into
the interaction of functional groups on metal substrates at the molecular level. In particular, carboxylic acids were employed:
(4-[(pyrid-4-yl-ethynyl)]-benzoic acid (PEBA), 4-[trans-2-(pyrid-4-yl-vinyl)]-benzoic acid (PVBA) and trimesic acid (1,3,5-benzenetricarboxylic acid, TMA), which could be stabilized
in a flat geometry at the surface. By choosing the appropriate substrate material and symmetry, the sensitive balance of intermolecular
and molecule–substrate interactions can be tuned to obtain well-defined supramolecular architectures and nanostructures. The
head-to-tail hydrogen bonding of the related rod-like species PEBA and PVBA stabilizes molecular rows on Ag(111). The subtle
difference in the molecular geometries is reflected in the lateral ordering: While 2-D islanding is encountered with PEBA,
1-D nanogratings of supramolecular chiral H-bonded twin chains evolve for PVBA. The threefold symmetry of TMA in conjunction
with the self-complementarity of its exodentate groups accounts for the formation of H-bonded honeycomb networks on Cu(100)
at low temperatures. Metal–ligand interactions were probed with PVBA and TMA at Cu surfaces at ambient temperature. Deprotonation
of the carboxyl moiety takes place, which readily interacts with Cu adatoms evaporated from step edges. This leads to a head-to-head
pairing of PVBA on Cu(111) and cloverleaf-shaped Cu–TMA coordination compounds on Cu(001).
A low-temperature scanning tunneling microscopy (LT-STM) study of four slightly different hydrocarbons based on hexaphenylbenzene (HPB) and hexa-peri-hexabenzocoronene (HBC) on the Cu(111) surface at submonolayer coverage is presented. All molecules show a commensurate monolayer structure, with significant differences in structure and growth mode. We find that the long range order and the size of defect free domains increase when the intermolecular interaction becomes stronger with respect to the molecule-substrate interaction. Moreover, we can assign adsorption and self-ordering properties to the different chemical groups within the molecules.
The possibility of extending the lateral manipulation process performed with the tip of a scanning tunneling microscope at low temperature to large molecules is demonstrated. Single Cu-TBPP molecules deposited on a Cu substrate were manipulated by means of the interaction between the molecule and the tip. Due to the complicated structure of the molecules and to their high conductance, we have explored the possibilities of performing controlled lateral manipulation at constant height. On Cu(111) this method makes possible translation combined with rotation of the molecules on the surface.
The interaction of largish molecules with metal surfaces has been studied by combining the imaging and manipulation capabilities of the scanning tunneling microscope (STM). At the atomic scale, the STM results directly reveal that the adsorption of a largish organic molecule can induce a restructuring of a metal surface underneath. This restructuring anchors the molecules on the substrate and is the driving force for a self-assembly process of the molecules into characteristic molecular double rows.
The electronic connection of single molecules to nanoelectrodes on a surface is a basic, unsolved problem in the emerging
field of molecular nanoelectronics. By means of variable temperature scanning tunneling microscopy, we show that an organic
molecule (C90H98), known as the Lander, can cause the rearrangement of atoms on a Cu(110) surface. These molecules act as templates accommodating
metal atoms at the step edges of the copper substrate, forming metallic nanostructures (0.75 nanometers wide and 1.85 nanometers
long) that are adapted to the dimensions of the molecule.
A combined low-temperature scanning tunneling microscopy and density functional theory study on the binding and diffusion of copper monomers, dimers, and trimers adsorbed on Cu(111) is presented. Whereas atoms in trimers are found in fcc sites only, monomers as well as atoms in dimers can occupy the fcc as well as the metastable hcp site. In fact the dimer fcc-hcp configuration is only 1.3 meV less favorable with respect to the fcc-fcc configuration. This enables a confined intracell dimer motion, which at temperatures below 5 K is dominated by thermally assisted tunneling.
Ultrathin insulating NaCl films have been employed to decouple individual pentacene molecules electronically from the metallic substrate. This allows the inherent electronic structure of the free molecule to be preserved and studied by means of low-temperature scanning-tunneling microscopy. Thereby direct images of the unperturbed molecular orbitals of the individual pentacene molecules are obtained. Elastic scattering quantum chemistry calculations substantiate the experimental findings.
The syntheses of four hexabenzo[bc,ef,hi,kl,no,qr]coronene (HBC) derivatives have been carried out. Double Knoevenagel condensation of the benzil 5 with the ketone 6 gave the 2,3,4,5-tetrakis(4-tert-butylphenyl)cyclopenta-2,4-dien-1-one (7). Diels-Alder addition of 7 with di(4-tert-butylphenyl) acetylene, 4-[(4-tert-butylphenyl)ethynyl]-1,1'-biphenyl (9) or 1-tert-butyl-4-(phenylethynyl)benzene (11) gave the substituted hexaphenylbenzene 8, 10 and 12 which were cyclodehydrogenated to yield 1, 2 and 3, respectively. Similarly, condensation of 5 with dibenzylketone yielded the cyclopentadienone 13 which gave, by cycloaddition with di-(4-tert-butylphenyl)acetylene, the tetrasubstituted hexaphenylbenzene 14 which was cyclodehydrogenated to furnish 4.
SINCE its invention in the early 1980s by Binnig and Rohrer 1,2, the scanning tunnelling microscope (STM) has provided images of surfaces and adsorbed atoms and molecules with unprecedented resolution. The STM has also been used to modify surfaces, for example by locally pinning molecules to a surface3 and by transfer of an atom from the STM tip to the surface4. Here we report the use of the STM at low temperatures (4 K) to position individual xenon atoms on a single-crystal nickel surface with atomic precision. This capacity has allowed us to fabricate rudimentary structures of our own design, atom by atom. The processes we describe are in principle applicable to molecules also. In view of the device-like characteristics reported for single atoms on surfaces5,6, the possibilities for perhaps the ultimate in device miniaturization are evident.
We briefly survey our progress on manipulation of single atoms and small molecules and formation of prototypic nanostructures with our simple versatile temperature variable scanning tunneling microscope (STM). Lateral manipulation, i.e. sliding of species along the surface is demonstrated on the Cu(211) surface for carbon monoxide- and ethene-molecules, lead-atoms and lead-dimers. We show furthermore, that we can also manipulate substrate atoms and are even able to release native Cu-atoms from high coordinated substrate sites. Vertical manipulation, i.e. controlled transfer of species between tip and surface and vice versa is discussed for xenon atoms and propene molecules.
The design of a low‐temperature scanning tunneling microscope is described. The microscope can be operated in ultrahigh vacuum in the temperature range between 15 and 300 K. The main features are a scanner which is based on the Besocke ‘‘beetle’’ design principle combined with a spring suspension of the microscope and complete surrounding of the whole microscope by a 4 K radiation shield. The microscope can be extended to work as a force microscope using the optical lever detection technique for force measurement. It is demonstrated that this comparatively small and reliable setup is well suited to study the adsorption of single atoms and molecules at low temperatures. Moreover, examples of lateral and vertical manipulation of atoms and molecules are shown to demonstrate the performance of the system. © 1996 American Institute of Physics.
The large organic molecule C90H98, called Lander, has been investigated on the Cu(2 1 1) surface by low temperature scanning tunnelling microscopy (LT-STM). Different adsorption geometries, which differ in the internal conformation and the orientation of the molecule, are described. These adsorption conformations have been determined by elastic scattering quantum chemistry calculations (ESQC). For , adsorption at selected step edges is combined with an adsorbate induced restructuring. The reconstruction is revealed by lateral STM manipulation and could be imaged with atomic resolution. It has the form of a (3 1 1) facet. The restructured steps can be used as a guidance for lateral manipulation of large molecules.
Avoiding the Bardeen—Tersoff—Hamann approximation we present calculations of the scanning tunneling microscope (STM) image of benzene or Rh(111). The tunneling current between the tip and the substrate through the benzene is calculated from the generalized Landauer formula. The electronic structure of the complete system made of the tip, of the substrate and of the benzene adsorbate is obtained with its molecular orbitals from an extended Hückel molecular orbital calculation. Experimental and calculated images are in good agreement. This leads to a detailed analysis of the image using the molecular orbital approach in through-space and through-bond tunneling processes.
A new cooperative self-assembly process where molecules adsorbed on Au(110)-(1\ifmmode\times\else\texttimes\fi{}2) surfaces induce mass transport of Au surface atoms to form a (1\ifmmode\times\else\texttimes\fi{}5) interfacial reconstruction is presented. Scanning tunneling microscopy shows that the underlying Au atomic arrangement is modified, maximizing the number of molecules bonded to the Au ridges in a distorted (6\ifmmode\times\else\texttimes\fi{}5) hexagonal overlayer.
Artificial nanostructures, each composed of a copper(II) phthalocyanine (CuPc) molecule bonded to two gold atomic chains with
a controlled gap, were assembled on a NiAl(110) surface by manipulation of individual gold atoms and CuPc molecules with a
scanning tunneling microscope. The electronic densities of states of these hybrid structures were measured by spatially resolved
electronic spectroscopy and systematically tuned by varying the number of gold atoms in the chains one by one. The present
approach provides structural images and electronic characterization of the metal-molecule-metal junction, thereby elucidating
the nature of the contacts between the molecule and metal in this junction.
We report a quantitative study on the electronic interaction between a molecular wire and its atomic scale metallic contacting pad. A so-called "reactive Lander" molecule is manipulated using a low-temperature scanning tunneling microscope to form a planar one-end electronic contact. The increase of the STM contrast at the junction location is discussed by means of the electronic interaction between the contacting group of the molecular wire and the end atoms of the nanopad.
The prospect of manipulating matter on the atomic scale has fascinated scientists for decades. This fascination may be motivated by scientific and technological opportunities, or from a curiosity about the consequences of being able to place atoms in a particular location. Advances in scanning tunneling microscopy have made this prospect a reality; single atoms can be placed at selected positions and structures can be built to a particular design atom-by-atom. Atoms and molecules may be manipulated in a variety of ways by using the interactions present in the tunnel junction of a scanning tunneling microscope. Some of these recent developments and some of the possible uses of atomic and molecular manipulation as a tool for science are discussed.
We report a method for controllably attaching an arbitrary number of charge dopant atoms directly to a single, isolated molecule. Charge-donating K atoms adsorbed on a silver surface were reversibly attached to a C60 molecule by moving it over K atoms with a scanning tunneling microscope tip. Spectroscopic measurements reveal that each attached K atom donates a constant amount of charge (approximately 0.6 electron charge) to the C60 host, thereby enabling its molecular electronic structure to be precisely and reversibly tuned.
We report a novel atom extraction mechanism from the native substrate by
means of a scanning tunneling microscope tip-crash on a Ag(111) surface at 5 K.
Individual atoms are scattered on the surface when a silver coated tip is
dipped into the substrate at low tunneling biases. Quantitative analyses reveal
that the mechanical energy supplied by the tip-crash dominates the atom
extraction process. Application of this procedure is demonstrated by
constructing quantum structures using the extracted atoms on an atom-by-atom
basis.