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Single-atom manipulation mechanisms during a quantum corral construction
Abstract
We describe a complete picture of how single Ag atoms move on the various potential energy landscapes of an Ag(111) surface during a quantum corral construction by using a scanning tunneling microscope (STM) tip at 6 K. The threshold tunneling resistance and tip-height to move the Ag atom across the surface are experimentally measured as 210±19 kΩ and 1.3±0.2 Å. The experimental atom manipulation signals reveal remarkably detailed atom movement behaviors dependent on the surface crystallographic orientation and offer atomic-level tribology information.
... Following Eigler and Schweiter's work, many manipulations of individual atoms on a surface such as atomic corrals of Fe or Co on Cu (111) have been performed [15]. In 2016, researchers at Delft University of Technology in the Netherlands developed a new method under ultrahigh vacuum for atom manipulation using an STM [16]. ...
... Furthermore, by adding some charge carriers to this insulating state, a superconducting state is obtained that can be electrically controlled. It is now known that by superimposing two sheets of graphene and rotating one around the other, the periodic alignment and misalignment of the atoms creates a moiré 15 pattern that results in a grid of low and high energy sites throughout the material. As a consequence, the behavior of electrons in the material is strongly modified thus inducing new electronic properties in the material. ...
... Thus, topological insulators are materials that are insulators in their bulk but are perfect conductors at their boundaries. 15 A moiré pattern is an interference pattern obtained by superimposing similar but slightly offset or rotated stencils with respect to each other. 16 The quantum Hall system is considered to be the first topological insulator known to physicists. ...
This work is focused on reviewing the theoretical vision of the physicist Richard Feynman about nanoscience and nanotechnology, giving continuity to his ideas in the proper context of physics laws that has led nanoscience and nanotechnology to become robust and active sciences. Some implications of nanotechnology as a general-purpose foundational technology for all economic areas are discussed. Some aspects related to interactions between the fields of mathematics, high-energy physics and condensed matter physics that have allowed the remarkable development of new quantum material platforms for nanoelectronics are also analyzed.
... T he lateral force needed to move a molecule on a surface is important for understanding dynamics as well as related tribological phenomena at the atomic and molecular scales. With the advancement of surface science techniques, such as atomic force microscopy (AFM) 1−9 and scanning tunneling microscopy (STM), 10,11 it has become possible to gain deeper insight into the lateral forces and corresponding tribological phenomena of the atoms, molecules, and nanoscale systems on surfaces. Although a myriad of studies have been conducted to elucidate the friction at the nano-and atomic scale, 12−17 many tribological phenomena are yet to be understood. ...
... On this surface, an equal magnitude of lateral force is expected to move an adsorbate along six equivalent directions formed by the surface close-packed atomic rows. 11 This is the case for lateral movement of individual atoms simply due to the surface symmetry and the zero-dimensional nature of the adsorbed atom ( Figure 1a). But for a one-dimensional (1D) adsorbate, moving it along six equivalent close-packed atomic rows involves two directions; one is parallel to its long axis (parallel direction), and the other is 60°with respect to its long axis (sideways direction). ...
... Consequently, averaged manipulation curves provide a smaller force angle (ϕ) in moving 6P along the sideways direction than it does for the parallel direction (Figure 3g and Supporting Information). 34 Note that the aperiodicity in the manipulation curves (Figure 3c,f) is caused by a slight deviation (∼1 to 3°) of the manipulation paths from the exact [110] surface direction 11 inducing flipping of the π-rings (Supporting Information). Only single surface-atom site hopping signals are counted for the force measurement and aperiodic manipulation signals are discarded in force analysis. ...
Using a q+ atomic force microscopy at low temperature, a sexiphenyl molecule is slid across an atomically flat Ag(111) surface along the direction parallel to its molecular axis and sideways to the axis. Despite identical contact area and underlying surface geometry, the lateral force required to move the molecule in the direction parallel to its molecular axis is found to be about half of that required to move it sideways. The origin of the lateral force anisotropy observed here is traced to the one-dimensional shape of the molecule, which is further confirmed by molecular dynamics simulations. We also demonstrate that scanning tunneling microscopy can be used to determine the comparative lateral force qualitatively. The observed one-dimensional lateral force anisotropy may have important implications in atomic scale frictional phenomena on materials surfaces.
... The first example of lateral manipulation of atoms on a surface was performed by D. Eigler and E. Schweitzer, who used the STM tip to arrange 35 Xe atoms on Ni(110) at 4 K to spell out 'IBM' [3] (see figure 2.6). The quantum corral [28] and other 2D quantum systems [13,131,132] followed shortly after (see Section 2.4 for more detail). The mechanism of manipulation in these cases involved bringing the tip from the imaging height (∼ 0.8 − 1.0 nm) to a closer distance (∼ 0.3 − 0.5 nm) above the adsorbate in order to induce a strong enough force between the tip and the adsorbate to overcome the surface diffusion barrier. ...
... The procedure is then repeated for a range of tip-sample biases. Finally, the threshold resistance is estimated from the gradient of a plot of the threshold current against tip-sample bias voltage [131]. The magnitude of the diffusion barrier determines the character of the manipulation process -via van der Waals attraction [27,31,131,132] or repulsion [133][134][135], or by the formation of a chemical bond between the adsorbate and the tip [27,136,137]. ...
... Finally, the threshold resistance is estimated from the gradient of a plot of the threshold current against tip-sample bias voltage [131]. The magnitude of the diffusion barrier determines the character of the manipulation process -via van der Waals attraction [27,31,131,132] or repulsion [133][134][135], or by the formation of a chemical bond between the adsorbate and the tip [27,136,137]. ...
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.
... Arranging adatoms with atomic precision requires tuning tipadatom interactions to overcome energetic barriers for vertical or lateral adsorbate motion. These interactions are carefully controlled via the tip position, bias, and tunneling conductance set in the manipulation process [24][25][26] . These values are not known a priori and must be established separately for each new adatom/surface and tip apex combination. ...
... The agent's performance improves along the training process as reflected in the reward, error, success rate, and episode length, as shown in Fig. 2a, b. The agent minimizes manipulation error and achieves 100 % success rate over 100 episodes after~2000 training episodes or equivalently 6000 manipulations, which is comparable to the amount of manipulations carried out in previous large-scale atomassembly experiments 21,25 . In addition, the agent continues to learn to manipulate the adatom efficiently with more training, as shown by the decreasing mean episode length. ...
Atomic-scale manipulation in scanning tunneling microscopy has enabled the creation of quantum states of matter based on artificial structures and extreme miniaturization of computational circuitry based on individual atoms. The ability to autonomously arrange atomic structures with precision will enable the scaling up of nanoscale fabrication and expand the range of artificial structures hosting exotic quantum states. However, the a priori unknown manipulation parameters, the possibility of spontaneous tip apex changes, and the difficulty of modeling tip-atom interactions make it challenging to select manipulation parameters that can achieve atomic precision throughout extended operations. Here we use deep reinforcement learning (DRL) to control the real-world atom manipulation process. Several state-of-the-art reinforcement learning (RL) techniques are used jointly to boost data efficiency. The DRL agent learns to manipulate Ag adatoms on Ag(111) surfaces with optimal precision and is integrated with path planning algorithms to complete an autonomous atomic assembly system. The results demonstrate that state-of-the-art DRL can offer effective solutions to real-world challenges in nanofabrication and powerful approaches to increasingly complex scientific experiments at the atomic scale.
... Apart from these applications, the STM tip was also used to manipulate individual molecules along the surface. The precise control of the interaction between tip and adsorbate enables one to move atoms [11][12][13] or molecules [14][15][16] to the desired position on the surface without rupturing the atom (molecule)-surface bond. This is called lateral manipulation. ...
... The tunnel current during the translation of the tip shows characteristic saw-tooth shape (Fig. S1), where individual jumps are associated with the hopping of the molecule from site to site. This is different from previous, related manipulations [11][12][13][14][15][16] in that the tip is in contact with the molecule during the lateral manipulation and thus the molecule is dragged while it is on the tip. ...
Electronic conduction through molecular junctions depends critically on the electronic state at the anchor site, suggesting that local reactions on the electrodes may play an important role in determining the transport properties. However, single-molecule junctions have never been studied with the chemical states of the electrodes controlled down to the atomic scale. Here, we study the effect of surface adsorbates on the molecular junction conductance by using a scanning tunneling microscope (STM) combined with density functional theory (DFT) and nonequilibrium Green's function (NEGF) calculations. By vertical control of a STM tip over a phenoxy (PhO) molecule on Cu(110), we can lift and release the molecule against the tip, and thus reproducibly control a molecular junction. Using this model system, we investigate how the conductance changes as the molecule is brought to the vicinity of oxygen atoms or a hydroxyl group chemisorbed on the surface. This proximity effect of surface adsorbates on the molecular conductance is simulated by DFT-NEGF calculations.
... These experiments are, however, difficult to interpret in terms of friction since straightforward force information cannot be extracted from the STM data; thus friction forces. This aspect of 'sliding dynamics' was first discussed in [70,71]. In these works, the high level of control of the manipulation procedure allowed the investigation of atom displacement along different crystalline directions (figures 5(c) and (d)) [71] and characteristic behavior in the current channel while displacing single atoms was observed (figure 5(e)). ...
... This aspect of 'sliding dynamics' was first discussed in [70,71]. In these works, the high level of control of the manipulation procedure allowed the investigation of atom displacement along different crystalline directions (figures 5(c) and (d)) [71] and characteristic behavior in the current channel while displacing single atoms was observed (figure 5(e)). A novel STM imaging mode, the 'atom manipulation image', was even introduced by Stroscio et al [70,72] consisting of scanning (at constant-current) the surface with a single atom trapped between tip and sample. ...
Friction forces, which arise when two bodies that are in contact are moved with respect to one another, are ubiquitous phenomena. Although various measurement tools have been developed to study these phenomena at all length scales, such investigations are highly challenging when tackling the scale of single molecules in motion on a surface. This work reviews the recent advances in single-molecule manipulation experiments performed at low temperature with the aim of understanding the fundamental frictional response of single molecules. Following the advent of 'nanotribology' in the field based on the atomic force microscopy technique, we will show the technical requirements to direct those studies at the single-molecule level. We will also discuss the experimental prerequisites needed to obtain and interpret the phenomena, such as the implementation of single-molecule manipulation techniques, the processing of the experimental data or their comparison with appropriate numerical models. Finally, we will report examples of the controlled vertical and lateral manipulation of long polymeric chains, graphene nanoribbons or single porphyrin molecules that systematically reveal friction-like characteristics while sliding over atomically clean surfaces.
... 27 By recording the tunnel current during the manipulation, that is to say with respect to a lateral coordinate of the tip, one gets curves showing specific signatures according to the manipulation mode. [28][29][30] An example of such a manipulation is reported in Fig. 9. ...
... However, it is generally reported that the manipulation of single atoms or small molecules along close packed directions induces tip height modulations in accordance with atomic surface periodicities. [28][29][30][31][32][33] In contrast, the complex and large structure of Ad 6 HBC implies sophisticated displacement mechanisms which significantly differ from single atom manipulations. 34 Moreover, the manipulation signatures are difficult to interpret according to the initial position of the tip above or in front of the molecule. ...
Large molecules made of a central hexabenzocoronene plateau surrounded by six adamantyl groups have been investigated by low temperature scanning tunneling microscopy and scanning tunneling spectroscopy coupled with image calculations and molecular mechanics. The structure of large self-assembled domains reveals that the intermolecular interactions between adamantyl peripheral groups dominate film growth. At very low coverage, the molecules can present a certain instability for negative bias voltages which induces a partial rotation. Manipulations of single objects using the STM tip are used to create small clusters of two or three molecules. The formed structures can be obtained and manipulated provided that the flexible adamantyl moieties of neighbouring molecules are brought in close contact promoting a robust mechanical anchoring.
... For a direct comparison with the experiment, we assign absolute heights to the tunneling parameters used in Fig. 1(f) following Ref. [44]. For instance, at a tunneling resistance of 1GΩ that corresponds to a tip-surface distance of 5ðAE1Þ Å [44], the difference in calculated apparent height is 0.37 Å which is comparable with the measured value of 0.30 Å [ Fig. 1(f)]. ...
... [44]. For instance, at a tunneling resistance of 1GΩ that corresponds to a tip-surface distance of 5ðAE1Þ Å [44], the difference in calculated apparent height is 0.37 Å which is comparable with the measured value of 0.30 Å [ Fig. 1(f)]. Based on this agreement, we can conclude that the TMA II complex has the structure illustrated in Fig. 2(c); i.e., a Co atom bridges the TMA molecule to the gold surface. ...
We report on in situ chemical reactions between an organic trimesic acid (TMA) ligand and a Co atom center. By varying the substrate temperature, we are able to explore the Co–TMA interactions and create novel magnetic complexes that preserve the chemical structure of the ligands. Using scanning tunneling microscopy and spectroscopy combined with density functional theory calculations, we elucidate the structure and the properties of the newly synthesized complex at atomic or molecular size level. Hybridization between the atomic orbitals of the Co and the π orbitals of the ligand results in a delocalized spin distribution onto the TMA. The here demonstrated possibility to conveniently magnetize such versatile molecules opens up new potential applications for TMAs in molecular spintronics.
... When manipulating laterally, the adatom is either pulled (pushed) across the surface due to an attractive (repulsive) tip-adsorbate interaction. [17,18] The adatom remains on the surface; the diffusion barrier to lateral motion is overcome by the tip-adsorbate interaction. This mode is typically used on metallic substrates, where the potential landscape is rather flat. ...
The tip of the scanning tunneling microscope can be used to position atoms and molecules on surfaces with atomic scale precision. Here, we report the controlled vertical and lateral manipulation of single Cs atoms on the InAs(111)A surface. The Cs adatom adsorbs on the In-vacancy site of the InAs(111)A—(2x2) surface reconstruction. Lateral manipulation is possible in all directions over the surface, not just along high-symmetry directions. Both pushing and pulling modes were observed in the height profile of the tip. We assembled two artificial structures, demonstrating the reliability of the manipulation procedures. Structures remained intact to a temperature of at least 44 K.
... The agent minimizes manipulation error and achieves 100 % success rate over 100 episodes after approximately 2000 training episodes or equivalently 6000 manipulations, which is comparable to the amount of manipulations carried out in previous large-scale atom-assembly experiments. 6,24 In addition, the agent continues to learn to manipulate the adatom efficiently with more training, as shown by the decreasing mean episode length. Major tip changes (marked by arrows in Fig. 2(a,b)) lead to clear yet limited deterioration in the agent's performance, which recovers within a few hundreds more training episodes. ...
Atomic-scale manipulation in scanning tunneling microscopy has enabled the creation of quantum states of matter based on artificial structures and extreme miniaturization of computational circuitry based on individual atoms. The ability to autonomously arrange atomic structures with precision will enable the scaling up of nanoscale fabrication and expand the range of artificial structures hosting exotic quantum states. However, the a priori unknown manipulation parameters, the possibility of spontaneous tip apex changes, and the difficulty of modeling tip-atom interactions make it challenging to select manipulation parameters that can achieve atomic precision throughout extended operations. Here we use deep reinforcement learning (DRL) to control the real-world atom manipulation process. Several state-of-the-art reinforcement learning techniques are used jointly to boost data efficiency. The reinforcement learning agent learns to manipulate Ag adatoms on Ag(111) surfaces with optimal precision and is integrated with path planning algorithms to complete an autonomous atomic assembly system. These results demonstrate that state-of-the-art deep reinforcement learning can offer effective solutions to real-world challenges in nanofabrication and powerful approaches to increasingly complex scientific experiments at the atomic scale.
... A recent experimental realization of the kagome lattice (and the one that inspires this work) is in the framework of artificially designed electronic lattices [21]. This technique has its origin in the manipulation of adatoms on metallic surfaces [23]. The idea is to confine the surface state of the metal, which behaves as a two-dimensional electron gas (2DEG), by means of a user-defined potential that patterns an antilattice. ...
We study the non-trivial phase of the two-dimensional breathing kagome lattice, displaying both edge and corner modes. The corner localized modes of a two-dimensional flake were initially identified as a signature of a higher-order topological phase but later shown to be trivial for perturbations that were thought to protect them. Using various theoretical and simulation techniques, we confirm that it does not display higher-order topology the corner modes are of trivial nature. Nevertheless, they might be protected. First, we show a set of perturbations within a tight-binding model that can move the corner modes away from zero energy, also repeat some perturbations that were used to show that the modes are trivial. In addition, we analyze the protection of the corner modes in more detail and find that only perturbations respecting the sublattice or generalized chiral and crystalline symmetries, and the lattice connectivity, pin the corner modes to zero energy robustly. A destructive interference model corroborates the results. Finally, we analyze a muffin-tin model for the bulk breathing kagome lattice. Using topological and symmetry markers, such as Wilson loops and Topological Quantum Chemistry, we identify the two breathing phases as adiabatically disconnected different obstructed atomic limits.
... A recent experimental realization of the kagome lattice (and the one that inspires this work) is in the framework of artificially designed electronic lattices [21]. This technique has its origin in the manipulation of adatoms on metallic surfaces [23]. The idea is to confine the surface state of the metal, which behaves as a two-dimensional electron gas (2DEG), by means of a user-defined potential that patterns an anti-lattice. ...
We study the non-trivial phase of the two-dimensional breathing kagome lattice, displaying both edge and corner modes. The corner localized modes of a two-dimensional flake were initially identified as a signature of a higher-order topological phase. However, using various theoretical and simulation techniques, we show that it does not display higher-order topology: the corner modes are of trivial nature. Nevertheless, they might be protected. First, we develop a set of perturbations within a tight-binding model that can move the corner modes away from zero energy. We then show that only perturbations respecting the sublattice or generalized chiral and crystalline symmetries, and the lattice connectivity, pin the corner modes to zero energy robustly. A destructive interference model corroborates the results. Finally, we develop a muffin-tin model for the bulk breathing kagome lattice. Using topological and symmetry markers, such as Wilson loops and Topological Quantum Chemistry, we identify the two breathing phases as adiabatically disconnected different obstructed atomic limits.
... To confirm this assumption, we laterally manipulated single Fe adatoms with the STM tip [66,67] to intentionally form dimers and trimers and measure their apparent STM heights. To do so, the STM tip was positioned above a single Fe atom. ...
Topological superconductivity emerging in one- or two-dimensional hybrid materials is predicted as a key ingredient for quantum computing. However, not only the design of complex heterostructures is primordial for future applications but also the characterization of their electronic and structural properties at the atomic scale using the most advanced scanning probe microscopy techniques with functionalized tips. We report on the topographic signatures observed by scanning tunneling microscopy (STM) of carbon monoxide (CO) molecules, iron (Fe) atoms and sodium chloride (NaCl) islands deposited on superconducting Pb(111). For the CO adsorption a comparison with the Pb(110) substrate is demonstrated. We show a general propensity of these adsorbates to diffuse at low temperature under gentle scanning conditions. Our findings provide new insights into high-resolution probe microscopy imaging with terminated tips, decoupling atoms and molecules by NaCl islands or tip-induced lateral manipulation of iron atoms on top of the prototypical Pb(111) superconducting surface.
... In this case, the STM tunneling junction resistance was below 50 MΩ in an STM "pushing" manipulation mode. 13 Figure 1a−c presents a series of STM images resulting from the step-by-step construction of Al x −HATA complexes with up to x = 3 Al adatoms. During a single HATA STM tip molecular manipulation and reaching its first Al adatom, the HATA molecule systematically found a surface minimal potential energy location where this Al goes always in between two HATA anthracene molecular branches and in between the 2 nitrogens of the adjoining pyrazine molecular groups. ...
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.
... As a result, science is currently in close integration with many branches of technology and human activity, and its applied significance is growing. Scientific research has now reached such a level that the individual atoms or molecules manipulating mechanisms [3][4][5] fall under observation, and sometimes the impact on materials reaches the level of single electrons [6,7], bosons [8,9], fermions [10,11], photons [12,13] or other elementary particles. ...
The paper presents an analytical review of theoretical methods for modeling functional nanostructures. The main evolutionary changes in the approaches of quantum-mechanical modeling are described. The foundations of the first-principal theory are considered, including the stationery and time-dependent Schrödinger equations, wave functions, the form of writing energy operators, and the principles of solving equations. The idea and specifics of describing the motion and interaction of nuclei and electrons in the framework of the theory of the electron density functional are presented. Common approximations and approaches in the methods of quantum mechanics are presented, including the Born–Oppenheimer approximation, the Hartree–Fock approximation, the Thomas–Fermi theory, the Hohenberg–Kohn theorems, and the Kohn–Sham formalism. Various options for describing the exchange–correlation energy in the theory of the electron density functional are considered, such as the local density approximation, generalized and meta-generalized gradient approximations, and hybridization of the generalized gradient method. The development of methods of quantum mechanics to quantum molecular dynamics or the dynamics of Car–Parrinello is shown. The basic idea of combining classical molecular modeling with calculations of the electronic structure, which is reflected in the potentials of the embedded atom, is described.
... Lateral displacements can be attained with pulling, pushing and sliding, named due to the similarity to classical concepts [53]. Prominent examples of structures obtained via lateral manipulation include the letters IBM written with Xe atoms [70], a rewritable atomic memory made with vacancies [71] and the quantum corral [72], [73] (Fig. 2.3). ...
... The typical STM configuration is shown in Figure 33. The tip-sample interaction is sensitive to l proximity location of STM-top and surface, which allows for the manipulation of single atoms or molecules one by one [80][81][82][83]. It thus allows the measurement of physical/chemical properties of atoms/molecules, which are elusive to other experimental measurements and provides access at the atomic level [84][85][86]. ...
Human beings have witnessed unprecedented developments since the 1760s using precision tools and manufacturing methods that have led to ever-increasing precision, from millimeter to micrometer, to single nanometer, and to atomic levels. The modes of manufacturing have also advanced from craft-based manufacturing in the Stone, Bronze, and Iron Ages to precision-controllable manufacturing using automatic machinery. In the past 30 years, since the invention of the scanning tunneling microscope, humans have become capable of manipulating single atoms, laying the groundwork for the coming era of atomic and close-to-atomic scale manufacturing (ACSM). Close-to-atomic scale manufacturing includes all necessary steps to convert raw materials, components, or parts into products designed to meet the user's specifications. The processes involved in ACSM are not only atomically precise but also remove, add, or transform work material at the atomic and close-to-atomic scales. This review discusses the history of the development of ACSM and the current state-of-the-art processes to achieve atomically precise and/or atomic-scale manufacturing. Existing and future applications of ACSM in quantum computing, molecular circuitry, and the life and material sciences are also described. To further develop ACSM, it is critical to understand the underlying mechanisms of atomic-scale and atomically precise manufacturing; develop functional devices, materials, and processes for ACSM; and promote high throughput manufacturing.
... These forces can be tailored by the distance and the applied voltage. The actual tunnelling current is often negligble in view of the acting forces; 152 it is only employed as a feedback loop to keep the distance constant. Usually, less force is needed to move an atom along a surface than to extract it from the surface. ...
Nano device prototyping (NDP) is essential for realizing and assessing ideas as well as theories in the form of nano devices, before they can be made available in or as commercial products. In this review, application results patterned similarly to those in the semiconductor industry (for cell phone, computer processors, or memory) will be presented. For NDP, some requirements are different: thus, other technologies are employed. Currently, in NDP, for many applications direct write Gaussian vector scan electron beam lithography (EBL) is used to define the required features in organic resists on this scale. We will take a look at many application results carried out by EBL, self-organized 3D epitaxy, atomic probe microscopy (scanning tunneling microscope/atomic force microscope), and in more detail ion beam techniques. For ion beam techniques, there is a special focus on those based upon liquid metal (alloy) ion sources, as recent developments have significantly increased their applicability for NDP.
... La procédure indiquée par la suite est dérivée d'une méthode détaillée en [36]. Dans notre cas, nous avons suivi les étapes [90] : ...
La construction de circuits électroniques de section atomique est l'un des grands défis de la nanoélectronique ultime. Pour construire un circuit électronique atomique, il faut d'abord mettre au point l'instrument de construction puis choisir la surface-support stabilisant ce circuit. Sur la surface d'Au(111) préparée en ultra vide, nous avons mis en œuvre et stabilisé le tout premier LT-UHV-4 STM. Ce microscope à 4 pointes STM balayant en même temps et indépendamment une même surface a été construit pour le CEMES par la société ScientaOmicron. Sur l'Au(111), nous avons reproduit tous les résultats expérimentaux obtenus sur les meilleurs LT-UHV-STM à une pointe comme la précision en rugosité de 2 pm, les caractéristiques I-V sans moyenne sur un seul atome pendant plusieurs dizaines de minutes et la manipulation atomique suivant les modes de tiré, glissé et poussé d'un seul atome d'or sur la surface. Une fois cette optimisation réalisée, nous avons appliqué notre LT-UHV-4 STM à la surface de Si(100):H, support probable des futurs circuits atomiques électroniques. Le choix de ce support est discuté en détail avant l'enregistrement et l'analyse des images STM. Les échantillons utilisés proviennent, soit du procédé semi-industriel pleine-plaque de silicium mis au point au CEA-LETI, soit de leur préparation in situ se déroulant directement dans la chambre de préparation du LT-UHV-4 STM. Nous avons pris soin de bien interpréter les images STM de la surface Si(100):H afin par exemple de déterminer la position de chaque atome d'hydrogène. La lithographie atomique par STM a été exploitée, par pointe, sur le LT-UHV-4 STM, en mode manipulation verticale atome-par-atome et mode balayage plus rapide mais rendant l'écriture atomique moins précise. Nous avons construit nos propres fils atomiques puis des plots de contact atomiques, petits carrés de Si(100)H dépassivés de quelques nm de côté. Les courants de fuite à 2 pointes et à l'échelle atomique ont ainsi pu être mesurés sur la surface de Si(100):H entre deux de ces plots. Pour préparer les contacts atomiques à au moins 2 pointes sur un fil atomique ou sur des plots de contact nanométrique, nous avons étudié en détail les différents types de contact pointe STM-liaison pendante unique montrant la difficulté d'atteindre un quantum de conductance au contact, de par un effet de courbure de bandes. Il est donc difficile sans une mesure de force complémentaire de déterminer en partant du contact tunnel les différentes étapes du contact mécanique, électronique au contact chimique. Nos résultats ouvrent la voie à la caractérisation des circuits électroniques construits atome par atome et à l'échelle atomique à la surface d'un semi-conducteur.
... However, not only has it been possible to analyze the behavior of these adsorbates on substrates, but new artificially created structures could be constructed such as corrals or nanowires consisting of a few atoms/molecules up to micrometer length in size [24][25][26][27][28]. With that approach, macroscopic phenomena, such as Snell's law or standing waves patterns, could be verified as occurring on the surface of nanostructured materials as well [29][30][31][32][33]. ...
The present study provides an experimental and computational insight into amino acid adsorption on a graphite substrate. We investigated two aromatic amino acids, histidine and tyrosine, and their behavior on highly-ordered pyrolytic graphite (HOPG). The study was carried out under ambient conditions, in a 1-octanol solution and at room temperature. We found that both amino acids form well-ordered molecular films on graphite, as opposed to dimer rows found for another amino acid (methionine). Scanning Tunneling Microscopy reveals intermolecular spacings and angular orientations of the individual molecules in the well-ordered molecular layer. Both amino acids arrange themselves into a chevron pattern governed by inter-molecular attractive forces. The configuration consists of adjacent rows of parallel molecules, however, individual molecules in neighboring rows are angled with respect to each other. Additional computational chemistry methods using a Molecular Mechanics approach and the AMBER ff03 force field are employed in support of the experimental findings. These calculations provide suggested molecular geometries and estimated adsorption energies and inter-molecular binding energies for molecules on a graphene sheet.
... Parallel nanoprobes are used as a way to overcome this constraint, boosting its productivity [11][12][13][14]. Atomic force microscope (AFM), scanning tunneling microscope (STM), and scanning near-field optical microscope (SNOM) are among the apparatus which can be modified and used in SPL techniques [15][16][17][18][19]. Patterning with atomic resolution of about 1Å has been predicted by AFM [1]. ...
... Parallel nanoprobes are used as a way to overcome this constraint, boosting its productivity [11][12][13][14]. Atomic force microscope (AFM), scanning tunneling microscope (STM), and scanning near-field optical microscope (SNOM) are among the apparatus which can be modified and used in SPL techniques [15][16][17][18][19]. Patterning with atomic resolution of about 1Å has been predicted by AFM [1]. ...
Line nanopatterns are produced on the positive photoresist by scanning near-field optical microscope (SNOM). A laser diode with a wavelength of 450 nm and a power of 250 mW as the light source and an aluminum coated nanoprobe with a 70 nm aperture at the tip apex have been employed. A neutral density filter has been used to control the exposure power of the photoresist. It is found that the changes induced by light in the photoresist can be detected by
in situ
shear force microscopy (ShFM), before the development of the photoresist. Scanning electron microscope (SEM) images of the developed photoresist have been used to optimize the scanning speed and the power required for exposure, in order to minimize the final line width. It is shown that nanometric lines with a minimum width of 33 nm can be achieved with a scanning speed of 75
µ
m/s and a laser power of 113 mW. It is also revealed that the overexposure of the photoresist by continuous wave laser generated heat can be prevented by means of proper photoresist selection. In addition, the effects of multiple exposures of nanopatterns on their width and depth are investigated.
... le concurrently adjusting vertically the tip-substrate height to keep the tunneling current constant. In a successful STM atom/molecule manipulation, the most important parameter is the tunneling resistance, which can be adjusted by changing the tip-molecule distance or by directly increasing or decreasing the tunneling current or the bias voltage.[4] The tunneling resistance is reduced to bring the tip very close to the atom or molecule to be manipulated, so close that the tunneling junction is forming a potential energy trap strong enough for an atom or molecule to stay moving along the tip tracking its lateral displacement. Therefore this mode is ideal for manipulating over a long ...
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.
... [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] Recent developments in nanoscience make it possible to fabricate structures and investigate their unique properties down to the atomic level. To date, two main approaches have been used: atomic manipulation through scanning tunneling microscopy (STM) [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] and self-assembly growth. [2,3,9,10,[31][32][33][34][35][36][37][38][39][40] Atomic manipulation is an advantage in building structures in arbitrary geometry, while self-assembly can provide large-scale wellordered structures spontaneously and more economically. ...
Recent advances in the study of magnetic atomic structures on noble metal surfaces are reviewed. These include one-dimensional strings, two-dimensional hexagonal superlattices, and novel structures stabilized by quantum guiding. The combined techniques of low-temperature scanning tunneling microscopy, kinetic Monte Carlo simulations, and ab initio calculations reveal that surface-state-mediated adatom-step and adatom—adatom interactions are the driving forces for self-assembly of these structures. The formation conditions are further discussed by comparing various experimental systems and the kinetic Monte Carlo simulations. Using scanning tunneling spectroscopy and tight-binding calculations together, we reveal that the spectra of these well-ordered structures have characteristic peaks induced by electronic scattering processes of the atoms within the local environment. Moreover, it is demonstrated that quantum confinement by means of nano-size corrals has significant influence on adatom diffusion and self-assembly, leading to a quantum-guided self-assembly.
... However, not only has it been possible to analyze the behavior of these adsorbates on substrates, but new artificially created structures could be constructed such as corrals or nanowires consisting of a few atoms/molecules up to micrometer length in size [24][25][26][27][28]. With that approach, macroscopic phenomena, such as Snell's law or standing waves patterns, could be verified as occurring on the surface of nanostructured materials as well [29][30][31][32][33]. ...
Poster presentation of initial research efforts.
The common ways to activate a chemical reaction are by heat, electric current, or light. However, mechanochemistry, where the chemical reaction is activated by applied mechanical force, is less common and only poorly understood at the atomic scale. Here we report a tip-induced activation of chemical reaction of carbon monoxide to dioxide on oxidized rutile TiO2 (110) surface. The activation is studied by atomic force microscopy, Kelvin probe force microscopy under ultrahigh-vacuum and liquid nitrogen temperature conditions, and density functional theory (DFT) modeling. The reaction is inferred from hysteretic behavior of frequency shift signal further supported by vector force mapping of vertical and lateral forces needed to trigger the chemical reaction with torque motion of carbon monoxide towards an oxygen adatom. The reaction is found to proceed stochastically at very small tip-sample distances. Furthermore, the local contact potential difference reveals the atomic-scale charge redistribution in the reactants required to unlock the reaction. Our results open up new insights into the mechanochemistry on metal oxide surfaces at the atomic scale.
The quantum mirage effect is a fascinating phenomenon in fundamental physics. Landmark experiments on quantum mirages reveal atomic-scale transport of information with potential to remotely probe atoms or molecules with minimal perturbation. Previous experimental investigations are Kondo-effect based; the quantum mirages appear only near the Fermi energy. This strongly limits the exploration of the mechanism and potential application. Here we demonstrate a Kondo-free quantum mirage that operates in a wide energy range beyond Fermi energy. Together with an analytical model, our systematic investigations identify that the quantum mirage is the result of quantum interference of the onsite electronic states with those scattered by the adatom at the focus of elliptical quantum corrals, where two kinds of scattering paths are of critical importance. Moreover, we also demonstrate the manipulation of quantum mirages with pseudo basic logic operations, such as NOT, FANOUT and OR gates. The quantum mirage effect is a fascinating phenomenon but in general the underlying mechanism is unclear. Here, by building elliptical quantum corrals of adatoms on a metal surface, the authors establish the mechanism of Kondo-free mirages and utilize it to build atomic-scale logic gates.
A new way to control individual molecules and monoatomic chains is devised by preparing a human-machine augmented system in which the operator and the machine are connected by a real-time simulation. Here, a 3D motion control system is integrated with an ultra-high vacuum (UHV) low-temperature scanning tunnelling microscope (STM). Moreover, we coupled a real-time molecular dynamics (MD) simulation to the motion control system that provides a continuous visual feedback to the operator during atomic manipulation. This allows the operator to become a part of the experiment and to make any adaptable tip trajectory that could be useful for atomic manipulation in three dimensions. The strength of this system is demonstrated by preparing and lifting a monoatomic chain of gold atoms from a Au(111) surface in a well-controlled manner. We have demonstrated the existence of Fabry-Pérot-type electronic oscillations in such a monoatomic chain of gold atoms and determined its phase, which was difficult to ascertain previously. We also show here a new geometric procedure to infer the adatom positions and therefore information about the substrate atoms, which are not easily visible on clean metallic surfaces such as gold. This method enables a new controlled atom manipulation technique, which we will refer to as point contact pushing (PCP) technique.
Scanning probe instruments in conjunction with a very low temperature environment have revolutionized the ability of building, functionalizing, and analysing two dimensional interfaces in the last twenty years. In addition, the availability of fast, reliable, and increasingly sophisticated methods to simulate the structure and dynamics of these interfaces allow us to capture even very small effects at the atomic and molecular level. In this review we shall focus largely on metal surfaces and organic molecular compounds and show that building systems from the bottom up and controlling the physical properties of such systems is no longer within the realm of the desirable, but has become day to day reality in our best laboratories.
We demonstrate cascade manipulation between magic number gold-Fullerene hybrid clusters by channelling thermal energy into a specific reaction pathway with a trigger from the tip of a scanning tunnelling microscope (STM). The (C60)m-Aun clusters, formed via self-assembly on the Au(111) surface, consist of n Au atoms and m C60 molecules; the three smallest stable clusters are (C60)7-Au19, (C60)10-Au35, and (C60)12-Au49. The manipulation cascade was initiated by driving the STM tip into the cluster followed by tip retraction. Temporary, partial fragmentation of the cluster was followed by reorganization. Self-selection of the correct numbers of Au atoms and C60 molecules led to the formation of the next magic number cluster. This cascade manipulation is efficient and facile with an extremely high selectivity. It offers a way to perform on-surface tailoring of atomic and molecular clusters by harnessing thermal energy which is known as the principal enemy of the quest to achieve ultimate structural control with the STM.
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 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 centres. Experimental data supported by theoretical calculations show there the formation of coordination bonds between the molecule and Au atoms of the surface. Using force spectroscopy, we quantify an increase of the lateral force for displacing the molecule of ∼ 280 pN corresponding to an elevation of the diffusion barrier of ∼ 100 meV compared to the rest of the surface.
The authors demonstrate lateral manipulation of individual Si adatoms on the Si(111) (7×3)-Pb surface at ∼125 K using the tip of a scanning tunneling microscope (STM). At this sample temperature, Si adatoms are not mobile. However, a Si adatom could be moved along, or across, the surface trimer row through a vertical movement of the tip toward the surface at certain positions near the Si adatom. The repulsive interaction between the tip and the Si adatom pushed the adatom toward a neighboring adsorption site. Through this manipulation, the authors also moved a Si adatom to meet another Si adatom. When a Si dimer was formed, it diffused rapidly on the Pb-covered surface until it was trapped by a defect site. This work demonstrates the potential to use atomic manipulation methods to reveal the surface dynamic processes that cannot be observed with scanning tunneling microscopy alone. In addition, the manipulation revealed the true atomic positions of Si adatoms on the surface, which solves a common problem that STM images may not reflect the real positions of adsorbed atoms.
Atomic force microscopy
(AFM) has demonstrated its capabilities as a nanotechnology tool. These capabilities include imaging/characterizing individual atoms on various surfaces and manipulating atoms and molecules. Here, we report how atom manipulation works on a well-known semiconducting surface, Si(111)-(7 × 7)
. To quantify the stochastic behavior of atom manipulation at room temperature (RT), atom hopping probabilities with various tip
–surface distances are derived. The different hopping processes of Si adatoms have different tendencies in the probability plots. More remarkably, the ability of atom manipulation strongly depends on the AFM tip used. Tips
can be characterized by their interaction force with surface Si adatoms. Force spectroscopic measurements combined with atom manipulation clarified that the ability to manipulate atoms is correlated with maximum attractive chemical bonding force with surface Si adatoms. Knowing the degree of chemical reactivity on the tip apex
used for manipulation is key to enhancing the efficiency of the manipulation process occurring on semiconductor surfaces.
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 photolithographic processes use a mask to fabricate nanostructures, but the direct-writing nanolithography processes avoid the masks to build nanoscale patterns. Electron beams, ion beams, laser beams, and probes are used to write on the surface of samples. These beams or probes have a narrow radius, which can write a pattern pixel by pixel. This chapter discusses two major technologies within the scanning probe microscopy (SPM) family: scanning tunneling microscopy (STM) and atomic force microscopy (AFM). AFM was developed from STM, and the attractive or repulsive forces between the tip and the sample are used in the measurement instead of the tunneling current in STM. Electron beam (e-beam) lithography (EBL) uses software to design the pattern and control the movement and blocking of the electron beams. By utilizing gas-assisted etching, the scanned area is simultaneously exposed to reactive gas molecules, which can significantly enhance the etching rate of e-beam and ion beam lithography.
The performances of the new ScientaOmicron LT-UHV 4-STM microscope have been certified by a series of state-of-art STM experiments on an Au(1 1 1) surface at 4.3 K. During the STM operation of the 4 STM scanners (independently or in parallel with an inter tip apex front to front distance down to a few tens of nanometers), a ΔZ stability of about 2 pm per STM was demonstrated. With this LT-UHV 4-STM stability, single Au atom manipulation experiments were performed on Au(1 1 1) by recording the pulling, sliding and pushing manipulation signals per scanner. Jump to contact experiments lead to perfectly linear low voltage I-V characteristics on a contacted single Au ad-atom with no need of averaging successive I-V's. Our results show how this new instrument is exactly 4 times a very precise single tip LT-UHV-STM. Two tips surface conductance measurements were performed on Au(1 1 1) using a lock-in technique in a floating sample mode of operation to capture the Au(1 1 1) surface states via two STM tips dI/dV characteristics.
We present evidence that subsurface carbon nanoparticles in {\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\delta{}} can be manipulated with nanometer precision using a scanning tunneling microscope. High-resolution images indicate that most of the carbon particles remain subsurface after transport observable as a local increase in height as the particle pushes up on the surface. Tunneling spectra in the vicinity of these protrusions exhibit semiconducting characteristics with a band gap of approximately 1.8 eV, indicating that the incorporation of carbon locally alters the electronic properties near the surface.
Using a low-temperature scanning tunneling microscope, atom manipulations were performed on Cu(111) surface. We succeeded in manipulating single Cu atoms which were deposited on the Cu substrate at low temperature, and arranging them in an intended pattern. Besides the brightly contrasted Cu adatom, we also successfully moved single dark spots, presumably an adsorbed molecule of carbon monoxide, by using the same manipulation technique.
Based on the micro-fabrication techniques combining with biochemistry and biophysics, we can get function structures with feature sizes close to the biomacromolecule scale, which promotes the applications of micropatterning in many research fields such as drug screening and discovery, tissue engineering and disease diagnosis. This review summarizes the development of micropatterning techniques in biomedical field and analyzes the advantages, limitations and application scopes of each micropatterning approach including photolithography, soft lithography, stencil-assisted patterning, scanning-probe lithography, jet patterning and laser guided patterning. Photolithography usually includes several steps such as exposure, development, lift-off and so on. Although it has the advantages of high accuracy, high efficiency and accurate alignment system, it depends on super-clean labs and lift-off processes, which means high cost and unsatisfied bio-compatibility. Soft lithography and stencil-assisted patterning methods avoid exposure and lift-off steps by using elastomeric stamps, which can enhance the bio-compatibility and reduce the cost. However, these two methods have deficiencies in alignment accuracy. Different from above methods, scanning-probe lithography is a kind of direct-writing technique, which sacrifices the advantage of high efficiency to improve its accuracy. Jet patterning is developed from industry with the advantages of low complexity and cost. However, its low accuracy of 10 μm scale is the limitation. Two novel laser based micropatterning techniques are also discussed. Although laser-induced transfer method solves the problem of jet patterning technique in the patterning thickness control, the low accuracy is still a problem. Optical tweezers technique offers a substitution for the scanning-probe lithography, although it has a long way to go in terms of liquor environment limitation and efficiency. It is indicated that current micropatterning methods already have the ability to make micro devices featured from nanometer scale to millimeter scale on a variety of surface materials different in geometry, stiffness and so on. The resolution and accuracy, the patterning scale and the processing condition are the bases for choosing micropatterning methods. The development of micropatterning techniques provides a rapid, real time, and accurate study tool in biological mechanism, drug action and biochemical reaction research. Micropatterning methods can enhance the sensitivity, the automation degree and the integration scale biosensors, which will further improve the efficiency of drug screening and diseases diagnosis. Also by micropatterning techniques, we can control the cells action easily, accurately and concurrently, which is helpful to shorten the development cycle. The main trends of micropatterning research are the further physicochemical analyses of the particles on nano-scale based on biochemistry and biophysics, the further enhancement of its bio-compatibility and material adaptability, as well as the development of in vivo microenvironment simulations suitable for micropatterning chips.
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.
Transport properties of gold atomic-chains and nanofilms under surface modulation are studied by performing self-consistent first-principle calculations. Quantum conducting channels of gold atomic-chains with absorbing atoms can be partly transparent or even blocked for certain injecting energies. Conductances of gold nanofilms with ridges show great dependence on their structures. We demonstrate that the transport properties of gold atomic-chains and nanofilms can be engineered through surface modulation, which may be helpful for designing low-dimensional nanodevices.
Abstract: The successful conjunction of the ultimate spatial resolution capability of the scanning tunneling microscope (STM) with the sensitivity to the spin of the tunneling electrons
has opened the door to investigations of magnetism at the nanoscale where the fundamental
interactions responsible for magnetic order can be studied. Spin-polarized (SP) STM allows
insight into a fascinating world with surprisingly rich magnetic phenomena. Ferromagnetic
structures with magnetic domains are found at nanometer length scales, or 2D antiferromagnetically ordered monolayers (MLs) where the magnetization is reversed from one atom to the next. Such collinearly ordered states may be modified by the Dzyaloshinsky–Moriya
(DM) interaction which can induce a small canting angle between neighboring atomic
moments, thus giving rise to novel non-collinear spin spiral ground states. DM interaction is
a result of electron scattering in a crystal environment with broken inversion symmetry. Spin
spirals were observed in a variety of systems, like ultrathin Fe films, or MLs of Mn atoms on
the (110) and (001) faces of a W crystal. Using a magnetically sensitive probe tip, individual
Co atoms were assembled to form chains on top of a spin spiral. The magnetization orientation
of each individual atom can be manipulated by repositioning it along the spin spiral.
Keywords: magnetic properties; scanning tunneling microscopy (STM); nanostructures; thin
films; transition metals.
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.
An ultrahigh vacuum low-temperature scanning tunneling microscope operated at 7 K is used to assemble Cu adatom chains on a Cu(111) surface by atom manipulation. Cu atoms within the close-packed chain reside on nearest-neighbor fcc hollow sites (Cu–Cu spacing 2.55 Å) along the in-plane directions. Spectroscopic measurements of the differential tunneling conductance dI/dV reveal that the monatomic Cu chain exhibits unoccupied one-dimensional (1D) quantum well states trapped in the pseudogap of the -projected Cu bulk bands. These chain-localized states are described by a 1D energy band centered 3.2 eV above the Fermi level (total band width 3.6 eV) and derive from spz hybrid atomic orbitals associated with the single Cu/Cu(111) adatom. Pentacene molecules (C22H14) deposited on Cu(111) by thermal evaporation adopt a planar adsorption geometry with their long molecular axis aligned with the in-plane directions. The organic molecule can be laterally manipulated along different high-symmetry directions of the substrate via attractive tip/molecule interactions. Lateral manipulation is also capable to attach single pentacene molecules to the ends of assembled Cu chains with atomic-level precision. We find (i) an enhanced adsorptive binding of the attached molecule characterized by spatial overlap between its carbon framework and the outermost chain atoms, (ii) persistence of the chain-localized states for the molecule-chain hybrid structure, and (iii) a clear correspondence between the number of Cu chain atoms involved in the spatial overlap and the observed energetic upward shift of the chain-localized quantum levels.
Previously, the authors reported direct evidence of channel saturation
and conductance quantization in atomic-sized gold constrictions through
mechanical perturbation studies, and also showed that peaks in
conductance histograms are insufficient in evaluating their mechanical
stability [Armstrong , Phys. Rev.
BPRBMDO1098-012110.1103/PhysRevB.82.195416 82, 195416 (2010)]. In the
present study, gold constrictions spanning the range from quantum to
semiclassical (Sharvin) conductance regimes are mechanically probed with
picolevel resolution in applied force and deformation, along with
simultaneous measurements of conductance. While reconfiguration from one
constriction size to another is known to occur by apparently random
discrete atomic displacements, results reveal a remarkable
simplicity—the magnitude of discrete atomic displacements is
limited to a small set of values that correspond to elementary slip
distances in gold rather than Au-Au interatomic distance. Combined with
measurements of the spring constant of constrictions, results reveal two
fundamental crossovers in deformation modes with increasing contact
diameter—first, from homogeneous shear to defect-mediated
deformation at a diameter that is in close agreement with previous
predictions [Sørensen , Phys. Rev.
BPRBMDO1098-012110.1103/PhysRevB.57.3283 57, 3283 (1998)]; and second,
the discovery of another crossover marking surface- to volume-dominated
deformation. A remarkable modulus enhancement is observed when the size
of the constrictions approaches the Fermi wavelength of the electrons,
and in the limit of a single-atom constriction it is at least two times
that for bulk gold. Results provide atomistic insight into the stability
of these constrictions and an evolutionary trace of deformation modes,
beginning with a single-atom contact.
In this thesis, we present our findings on two major topics, both of
which are studies of molecules on metal surfaces by scanning tunneling
microscopy (STM). The first topic is on adsorption of a model amine
compound, 1,4-benzenediamine (BDA), on the reconstructed Au(111)
surface, chosen for its potential application as a molecular electronic
device. The molecules were deposited in the gas phase onto the substrate
in the vacuum chamber. Five different patterns of BDA molecules on the
surface at different coverages, and the preferred adsorption sites of
BDA molecules on reconstructed Au(111) surface, were observed. In
addition, BDA molecules were susceptible to tip-induced movement,
suggesting that BDA molecules on metal surfaces can be a potential
candidate in STM molecular manipulations. We also studied graphene
nanoislands on Co(0001) in the hope of understanding interaction of
expitaxially grown graphene and metal substrates. This topic can shed a
light on the potential application of graphene as an electronic device,
especially in spintronics. The graphene nanoislands were formed by
annealing contorted hexabenzocoronene (HBC) on the Co(0001) surface. In
our experiments, we have determined atop registry of graphene atoms with
respect to the underlying Co surface. We also investigated the
low-energy electronic structures of graphene nanoislands by scanning
tunneling spectroscopy. The result was compared with a first-principle
calculation using density functional theory (DFT) which suggested strong
coupling between graphene pi-bands and cobalt d-electrons. We also
observed that the islands exhibit zigzag edges, which exhibits unique
electronic structures compared with the center areas of the islands.
Using a cryogenic scanning tunneling microscope, the dynamics of lateral
translations of a single silver atom adsorbed on Ag(111) were
investigated with a time resolution of 10 ns. Elevated tunneling
currents passed through the tip close to the adsorbed atom induce sudden
adsorption site changes, which are reflected by two-level fluctuations
of the tunneling conductance. The voltage dependence of the fluctuation
rate reveals different local heating of the adsorbed atom in different
positions relative to the tip.
Using molecular statistics simulations based on the embedded atom method potential, we investigate the reliability of the lateral manipulation of single Pt adatom on Pt(111) surface with a single-atom tip for different tip heights (tip-surface distance) and tip orientations. In the higher tip-height range, tip orientation has little influence on the reliability of the manipulation, and there is an optimal manipulation reliability in this range. In the lower tip-height range the reliability is sensitive to the tip orientation, suggesting that we can obtain a better manipulation reliability with a proper tip orientation. These results can also be extended to the lateral manipulation of Pd adatom on Pd(111) surface.
Detailed tip height measurements during manipulation of single atoms, molecules, and dimers on a Cu(211) surface reveal different manipulation modes depending on tunneling parameters. Both attractive (Cu, Pb, Pb dimers) and repulsive manipulation (CO) are identified. Using attractive forces, discontinuous hopping of Cu and Pb atoms from one adsorption site to the next can be induced (``pulling''). Pb dimers can be pulled with repeated single, double, and triple hops. Pb atoms can also be ``slid'' continuously. The occurrence of different movement patterns is shown to be a sensitive probe for surface defects.
We report on the numerical implementation of a virtual scanning tunneling microscope which calculates imaging and manipulation modes and reproduces a feedback loop signal (FLS). Calculating the FLS during a manipulation serves as a direct diagnostic of the mechanics of the adsorbate under the tip apex because pulling, sliding, or pushing modes have their own FLS signatures independently of the manipulated species. As an example, the different FLS are provided for the case of a Xe atom manipulated in the constant current mode.
Since the realization that the tips of scanning probe microscopes can interact with atoms at surfaces, there has been much interest in the possibility of building or modifying nanostructures or molecules directly from single atoms. Individual large molecules can be positioned on surfaces, and atoms can be transferred controllably between the sample and probe tip. The most complex structures are produced at cryogenic temperatures by sliding atoms across a surface to chosen sites. But there are problems in manipulating atoms laterally at higher temperatures--atoms that are sufficiently well bound to a surface to be stable at higher temperatures require a stronger tip interaction to be moved. This situation differs significantly from the idealized weakly interacting tips of scanning tunnelling or atomic force microscopes. Here we demonstrate that precise positioning of atoms on a copper surface is possible at room temperature. The triggering mechanism for the atomic motion unexpectedly depends on the tunnelling current density, rather than the electric field or proximity of tip and surface.
The semiconductor industry has seen a remarkable miniaturization trend, driven by many scientific and technological innovations. But if this trend is to continue, and provide ever faster and cheaper computers, the size of microelectronic circuit components will soon need to reach the scale of atoms or molecules--a goal that will require conceptually new device structures. The idea that a few molecules, or even a single molecule, could be embedded between electrodes and perform the basic functions of digital electronics--rectification, amplification and storage--was first put forward in the mid-1970s. The concept is now realized for individual components, but the economic fabrication of complete circuits at the molecular level remains challenging because of the difficulty of connecting molecules to one another. A possible solution to this problem is 'mono-molecular' electronics, in which a single molecule will integrate the elementary functions and interconnections required for computation.
The elastic electronic channels through a single hydrogen atom adsorbed on a Ge(111)-c(2 x 8) surface have been investigated by scanning tunneling microscopy and I(V) spectroscopy, whereas inelastic channels have been probed by the vertical and horizontal manipulation of individual hydrogen atoms. The substrate temperature, over the range 30-300 K, has proven to be a powerful parameter to freeze specific electronic channels, offering the possible control of elastic and inelastic channels through a single atom. This opens up very interesting perspectives for controlling the operation of nanodevices.
We show that carbon nanotube transistors operate as unconventional "Schottky barrier transistors," in which transistor action occurs primarily by varying the contact resistance rather than the channel conductance. Transistor characteristics are calculated for both idealized and realistic geometries, and scaling behavior is demonstrated. Our results explain a variety of experimental observations, including the quite different effects of doping and adsorbed gases. The electrode geometry is shown to be crucial for good device performance.
The rapid progress in molecular manipulation with a scanning tunneling microscope (STM) tip opens up entirely new opportunities in nanoscience and technology. With these advances , the ultimate chemical reaction steps such as dissociation, diffusion, adsorption, re-adsorption and bond formation processes become possible to be performed by using the STM tip at the single molecule level with an atomic scale precision. By using a variety of manipulation techniques in a systematic and step-by-step manner, a complete chemical reaction sequence has been induced with the STM tip leading to the synthesis of molecules on an individual basis. In this paper, various STM manipulation techniques useful in the single molecule engineering process are reviewed, and their impact on the future of nanoscience and technology is discussed.
From total energy calculations we show that for certain tip-adatom separations the activation barrier for the adatom to move towards the tip disappears and the adatom experiences an attractive force in the direction of the tip. For a Cu adatom at a (100) microfaceted step on Cu(111) this happens at a lateral separation of about one lattice constant, in agreement with recent experimental findings. Simultaneously, the activation barrier in the direction away from the tip increases significantly. The details of the changes in the potential energy surface induced by the tip are found to depend on the characteristics of the tip apex and its height above the adatom. {copyright} {ital 1999} {ital The American Physical Society}
We report on a fast simulation method to investigate the movement of an atom induced by the tip during lateral manipulation with a scanning tunneling microscope. The simulation is based on a model assuming the atom moving in the combined potential of tip and surface. The pathway of the tip is subdivided in small steps, and the atomic position for each step is calculated by an iterative algorithm searching for the closest energetic minimum. The method is demonstrated for manipulation on the (1 1 1) surface of an fcc metal. Our model calculations predict which energetic minima of the surface are attained by the atom during manipulation. The details of the modelled manipulation curves allow a precise description of the atomic pathway in dependence on manipulation direction and positioning of the tip relative to the atom. Furthermore, the simulation predicts a transition from the so-called pulling to sliding manipulation mode upon reducing tip–surface distance, well in agreement with general experimental observations. To test our algorithm we present experimental results for the manipulation of iodine on Cu(1 1 1) along the direction and compare them to simulated manipulation curves. The comparison allows for a complete understanding of all details in atomic movements during manipulation along a complicated path.
The curling of a graphitic sheet to form carbon nanotubes produces a class of materials that seem to have extraordinary electrical and mechanical properties. In particular, the high elastic modulus of the graphite sheets means that the nanotubes might be stiffer and stronger than any other known material, with beneficial consequences for their application in composite bulk materials and as individual elements of nanometre-scale devices and sensors. The mechanical properties are predicted to be sensitive to details of their structure and to the presence of defects, which means that measurements on individual nanotubes are essential to establish these properties. Here we show that multiwalled carbon nanotubes can be bent repeatedly through large angles using the tip of an atomic force microscope, without undergoing catastrophic failure. We observe a range of responses to this high-strain deformation, which together suggest that nanotubes are remarkably flexible and resilient.
The influence of the tip in a scanning tunneling microscope on the atomic motion of Ag on Ag(110) is investigated at T = 50 and 295 K. At T = 50 K the tip can move single Ag atoms preferentially along [ 11¯0] via an attractive interaction. At T = 295 K, the tip can displace monatomic steps over distances as large as several hundred Å. The structures thus created decay on a time scale of minutes. In contrast to prevailing assumptions significant tip-induced disturbances of the equilibrium shape of steps are observed even at sub-nA tunneling currents.
Experiments on individual molecules using scanning probe microscopies have demonstrated an exciting diversity of physical, chemical, mechanical, and electronic phenomena. They have permitted deeper insight into the quantum electronics of molecular systems and have provided unique information on their conformational and mechanical properties. Concomitant developments in experimentation and theory have allowed a diverse range of molecules to be studied, varying in complexity from simple diatomics to biomolecular systems. At the level of an individual molecule, the interplays of mechanical and electronical behavior and chemical properties manifest themselves in an unusually clear manner. In revealing the crucial role of thermal, stochastic, and quantum-tunneling processes, they suggest that dynamics is inescapable and may play a decisive role in the evolution of nanotechnology.
Image projection relies on classical wave mechanics and the use of natural or engineered structures such as lenses or resonant cavities. Well-known examples include the bending of light to create mirages in the atmosphere, and the focusing of sound by whispering galleries. However, the observation of analogous phenomena in condensed matter systems is a more recent development, facilitated by advances in nanofabrication. Here we report the projection of the electronic structure surrounding a magnetic Co atom to a remote location on the surface of a Cu crystal; electron partial waves scattered from the real Co atom are coherently refocused to form a spectral image or 'quantum mirage'. The focusing device is an elliptical quantum corral, assembled on the Cu surface. The corral acts as a quantum mechanical resonator, while the two-dimensional Cu surface-state electrons form the projection medium. When placed on the surface, Co atoms display a distinctive spectroscopic signature, known as the many-particle Kondo resonance, which arises from their magnetic moment. By positioning a Co atom at one focus of the ellipse, we detect a strong Kondo signature not only at the atom, but also at the empty focus. This behaviour contrasts with the usual spatially-decreasing response of an electron gas to a localized perturbation.
All elementary steps of a chemical reaction have been successfully induced on individual molecules with a scanning tunneling microscope (STM) in a controlled step-by-step manner utilizing a variety of manipulation techniques. The reaction steps involve the separation of iodine from iodobenzene by using tunneling electrons, bringing together two resultant phenyls mechanically by lateral manipulation and, finally, their chemical association to form a biphenyl molecule mediated by excitation with tunneling electrons. The procedures presented here constitute an important step towards the assembly of individual molecules out of simple building blocks in situ on the atomic scale.
By means of atomic manipulation, 51 Ag atoms have been precisely positioned to form a triangle with a base length of 245 A on a Ag(111) substrate. The scattering of the surface electrons at these adatoms results in a complex interference pattern. Spectroscopic data and dI/dV maps taken inside the triangle have been quantitatively evaluated by multiple scattering calculations of the wave pattern. Adjustment of the scattering parameters to the data yields the properties of the scatterers and the electron lifetimes. The experimental results for the electron lifetimes deviate from a (E-E(F))(-2) dependence and reflect the electronic band structure at the surface as well as the local influence of the triangle.
A method for confining electrons to artificial structures at the nanometer lengthscale is presented. Surface state electrons on a copper(111) surface were confined to closed structures (corrals) defined by barriers built from iron adatoms. The barriers were assembled by individually positioning iron adatoms with the tip of a 4-kelvin scanning tunneling microscope (STM). A circular corral of radius 71.3 A was constructed in this way out of 48 iron adatoms. Tunneling spectroscopy performed inside of the corral revealed a series of discrete resonances, providing evidence for size quantization. STM images show that the corral's interior local density of states is dominated by the eigenstate density expected for an electron trapped in a round two-dimensional box.