STM-theory: Image potential, chemistry and surface relaxation

Blanco, José M.; Flóres, F.; Pérez, Rúben

doi:10.1016/j.progsurf.2006.07.004

Cited by 139 publications

(120 citation statements)

References 80 publications

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“…60,105,106 When two metal surfaces are brought in front of each other, the image potential has to be corrected by the inclusion of the multiple image term V mi (z) accounting for the cross terms in the screening interactions: 105,106 V mi ðzÞ ¼ 1 4…”

Section: Electron Tunnelingmentioning

confidence: 99%

A classical treatment of optical tunneling in plasmonic gaps: extending the quantum corrected model to practical situations

et al. 2015

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(2015). A classical treatment of optical tunneling in plasmonic gaps: extending the quantum corrected model to practical situations. Faraday Discussions, 178, The optical response of plasmonic nanogaps is challenging to address when the separation between the two nanoparticles forming the gap is reduced to a few nanometers or even subnanometer distances. We have compared results of the plasmon response within different levels of approximation, and identified a classical local regime, a nonlocal regime and a quantum regime of interaction. For separations of a fewÅngstroms, in the quantum regime, optical tunneling can occur, strongly modifying the optics of the nanogap. We have considered a classical effective model, so called Quantum Corrected Model (QCM), that has been introduced to correctly describe the main features of optical transport in plasmonic nanogaps. The basics of this model are explained in detail, and its implementation is extended to include nonlocal effects and address practical situations involving different materials and temperatures of operation.

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Section: Electron Tunnelingmentioning

confidence: 99%

A classical treatment of optical tunneling in plasmonic gaps: extending the quantum corrected model to practical situations

et al. 2015

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“…39 A set of 60 tips consisting of a pyramid of 35 metal atoms and a C 60 molecule attached to the apex in various geometries has been used 40 as a probe over both candidates. The calculated images were carefully compared to the experimental images with varying contrast.…”

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confidence: 99%

van der Waals interactions mediating the cohesion of fullerenes on graphene

et al. 2012

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Fullerenes on single-layer epitaxial graphene are a model system to study very faint interactions at a molecular level. By a variable temperature scanning tunneling microscope we have been able to study ordered fullerene layers at 40 K, exclusively bound by van der Waals interactions. The experimentally determined adsorption geometry of the molecules is computationally confirmed only if van der Waals interactions are included in the calculation formalism. The relative orientation of fullerenes in their close-packed arrangement is found to be the crucial factor for determining the total energy. Observation of collective movements of fullerene islands points out the weak coupling to the substrate and the important role of the van der Waals cohesion forces within. Mechanical stability, friction, or adhesion are among the physical properties that strongly depend on van der Waals (vdW) interactions. This is also true for the nanoscale. The nucleation and growth of molecular surface structures involve dynamic processes such as diffusion, molecular rotations, or conformational changes, which rely also on vdW intermolecular interactions. 1,2 Moreover, self-assembly and adsorption studies focus on determining the preferred adsorption site and configuration, the adsorbate-adsorbate interaction, and the distance between the adsorbate and substrate (e.g., Ref. 3).There is an increasing interest in the role of vdW interactions of organic molecules on graphite and other surfaces. 4,5 Generally, long-distance forces as vdW are not described by the most widely used functionals of the density-functional theory (DFT). Thus, in many of the works performed until now they are simply not included. However, when planar systems of carbon-based materials are in question, they require a different approach to the interplay between intermolecular (lateral) and adsorbate-substrate (vertical) interactions in determining the properties of ordered molecular structures. To evidence the important role of the vdW interactions in adsorption processes we have chosen a system of a very weakly interacting substrate and adsorbate, single-layer graphene (SLG) 6 and fullerenes (C 60 ). 7 The fact that both materials consist exclusively of carbon atoms arranged in an atomically thin planar mesh without H or any other atoms inside the atomic structure that could lead to long-range H-bond interactions makes this system a good prototype for a demonstration of the effect of these forces at a molecular level.Thus, we consider the C 60 on SLG grown on 6H-SiC(0001) 8-10 as a model system to test the strength of the vdW forces and mutual interactions that occur between neutral inert nanostructures. C 60 adsorbed on surfaces generally tend to form hexagonal close-packed arrangements 11 in order to optimize their lateral interactions. In very recent studies of C 60 molecules deposited on SLG epitaxially grown on metal, 12,13 it has been shown that the interaction between the molecules and the substrate, and consequently the molecular arrangement, is ruled by the m...

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“…The tip was gradually approached towards the Si adatom by 0.25 Å , and the atomic structure was relaxed at each step until the forces acting on free atoms were below 1 meV= # A. The tunneling conductance was calculated within a Green's function formalism [34], as implemented in the FIREBALL code [35]. The geometry of the system for the electron transport was taken from the VASP calculations.…”

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confidence: 99%

Quantum Degeneracy in Atomic Point Contacts Revealed by Chemical Force and Conductance

et al. 2013

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Quantum degeneracy is an important concept in quantum mechanics with large implications to many processes in condensed matter. Here, we show the consequences of electron energy level degeneracy on the conductance and the chemical force between two bodies at the atomic scale. We propose a novel way in which a scanning probe microscope can detect the presence of degenerate states in atomic-sized contacts even at room temperature. The tunneling conductance G and chemical binding force F between two bodies both tend to decay exponentially with distance in a certain distance range, usually maintaining direct proportionality G / F. However, we show that a square relation G / F 2 arises as a consequence of quantum degeneracy between the interacting frontier states of the scanning tip and a surface atom. We demonstrate this phenomenon on the Sið111Þ-ð7 Â 7Þ surface reconstruction where the Si adatom possesses a strongly localized dangling-bond state at the Fermi level. The invention of scanning probe microscopy (SPM), almost three decades ago, boosted research of matter at the nanoscale. Nowadays, SPM techniques are routinely used not only for imaging with unprecedented atomic resolution [1,2] or single atom manipulation [3] but also for an advanced characterization on an atomic scale [4][5][6][7][8][9]. What is more, SPM provides direct access to the nanoscale where the quantum phenomena tend to emerge. Many of them have been the subject of intensive SPM studies [10,11]. Nevertheless, quantum degeneracy, one of the basic concepts of quantum mechanics, has received little attention so far. The quantum degeneracy is defined as the presence of two or more quantum states localized at the same energy level. Among others, the degeneracy plays an important role in the low temperature charge transport phenomena at the nanoscale, such as the Kondo effect modulated by mechanical action [12], resonant tunneling [13], or Coulomb blockade [14]. Recent progress in scanning probe instrumentation has allowed the combination of atomic force microscopy (AFM) and scanning tunneling microscopy (STM) [15] where both tunneling current and force are collected simultaneously. This approach opens new possibilities not only in the characterization at the atomic scale but also to understand the fundamental relation between the chemical force and the conductance in a well-defined atomic contact [see Fig. 1(a)]. In this Letter, we demonstrate that the quantum degeneracy of frontier electronic states of two interacting bodies forming an atomic point contact can be explored by precise AFM/STM experiments, even at room temperature, through an intimate relation between the chemical force and the conductance.The understanding of the mechanical and transport properties at the atomic scale is of importance not only in fundamental physics but also for practical applications in nanotechnology. An atomic scale junction forms when two objects (e.g., scanning probe and sample) are brought near to mechanical contact with a subnanometer distance control. In a f...

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STM-theory: Image potential, chemistry and surface relaxation

Cited by 139 publications

References 80 publications

A classical treatment of optical tunneling in plasmonic gaps: extending the quantum corrected model to practical situations

A classical treatment of optical tunneling in plasmonic gaps: extending the quantum corrected model to practical situations

van der Waals interactions mediating the cohesion of fullerenes on graphene

Quantum Degeneracy in Atomic Point Contacts Revealed by Chemical Force and Conductance

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