Unambiguous Interpretation of Atomically Resolved Force Microscopy Images of an Insulator

Foster, Adam S.; Barth, Clemens; Shluger, AL; Reichling, Michael

doi:10.1103/physrevlett.86.2373

Cited by 155 publications

(121 citation statements)

References 12 publications

(18 reference statements)

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“…This finding agrees well with experimental atomic force microscopy (AFM) studies in ultra high vacuum conditions of vacuum-cleaved slabs [70]. Furthermore, the (111) CaF 2 termination has been used as a model system to investigate the imaging mechanism of AFM measurements by comparing theory and experiment [71,72]. AFM images reveal a hexagonal arrangement of the topmost F anions with a regular spacing between them.…”

Section: Surface Reconstructions a (100) Caf 2 Reconstructionssupporting

confidence: 76%

Surface reconstruction of fluorites in vacuum and aqueous environment

Fisicaro

Sicher

Amsler

et al. 2017

Phys. Rev. Materials

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Surfaces and interfaces of bulk materials with liquids are of importance for a wide range of chemical processes.In this work, we systematically explore reconstructions on the (100) surface of calcium fluoride (CaF 2 ) and other fluorites (MF 2 ), M = {Sr,Cd,Ba} by sampling the configurational space with the minima hopping structure prediction method in conjunction with density functional theory calculations. We find a large variety of structures that are energetically very close to each other and are connected by very low barriers, resulting in a high mobility of the topmost surface anions. This high density of configurational states makes the CaF 2 (100) surface a very dynamic system. The majority of the surface reconstructions found in CaF 2 are also present in SrF 2 , CdF 2 , and BaF 2 . Furthermore, we investigate in detail the influence of these reconstructions on the crystal growth of CaF 2 in solvents by modeling the fluorite-water interface and its wetting properties. We perform a global structural search both by explicitly including water molecules and by employing a recently developed soft-sphere solvation model to simulate an implicit aqueous environment. The implicit approach correctly reproduces both our findings with the explicit-water model and the experimentally reported contact angles for the partial-hydrophobic (111) and hydrophilic (100) surfaces. Our simulations show that the high anion mobility and the low coordination of the (100) surface atoms strongly favors the adsorption of water molecules over the (111) surface. The aqueous environment makes terminations with low-coordination surface atoms more stable, promoting (100) growth instead of the (111).

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Section: Surface Reconstructions a (100) Caf 2 Reconstructionssupporting

confidence: 76%

Surface reconstruction of fluorites in vacuum and aqueous environment

Fisicaro

Sicher

Amsler

et al. 2017

Phys. Rev. Materials

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“…A large number of high-quality atomically resolved experimental images have been produced with a blunt tip, and some of them are reported by and Foster, Barth, et al (2001). Therefore theoretical images, as well, have been calculated using a macroscopic tip of radius 675 nm and an applied bias of 0.03 V. Real tips were unsputtered, covered by oxide, and likely to be contaminated by surface material.…”

Section: B Simulating Scanningmentioning

confidence: 99%

“…Extensive SPM modeling suggests that only the shortrange chemical forces are responsible for atomic resolution (Livshits and Shluger, 1997b;Foster, Barth, et al, 2001;Hofer, Fisher, Wolkow, and Grü tter, 2001), whereas the macroscopic forces can be treated as a background attractive force. This background force is important in reproducing experimentally observed frequency changes in an SFM, but is independent of the identity of the atom under the tip and does not play a role in atomic displacements.…”

Section: Tip-surface Interactionmentioning

confidence: 99%

Theories of scanning probe microscopes at the atomic scale

2003

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Significant progress has been made both in experimentation and in theoretical modeling of scanning probe microscopy. The theoretical models used to analyze and interpret experimental scanning probe microscope (SPM) images and spectroscopic data now provide information not only about the surface, but also the probe tip and physical changes occurring during the scanning process. The aim of this review is to discuss and compare the present status of computational modeling of two of the most popular SPM methods-scanning tunneling microscopy and scanning force microscopy-in conjunction with their applications to studies of surface structure and properties with atomic resolution. In the context of these atomic-scale applications, for the scanning force microscope (SFM), this review focuses primarily on recent noncontact SFM (NC-SFM) results. After a brief introduction to the experimental techniques and the main factors determining image formation, the authors consider the theoretical models developed for the scanning tunneling microscope (STM) and the SFM. Both techniques are treated from the same general perspective of a sharp tip interacting with the surface-the only difference being that the control parameter in the STM is the tunneling current and in the SFM it is the force. The existing methods for calculating STM and SFM images are described and illustrated using numerous examples, primarily from the authors' own simulations, but also from the literature. Theoretical and practical aspects of the techniques applied in STM and SFM modeling are compared. Finally, the authors discuss modeling as it relates to SPM applications in studying surface properties, such as adsorption, point defects, spin manipulation, and phonon excitation. CONTENTS

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“…The method should prove valuable in determining the chemical forces in atomic force microscopy (AFM). Thus far, a perturbation method to treat these forces, which are at the bottom of atomic resolution [24,25], has proved elusive. As shown here, these forces can be calculated from the overlap of the wave functions of the decoupled systems and a single point of the energy curve of the coupled system.…”

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confidence: 99%

Signature of a Chemical Bond in the Conductance between Two Metal Surfaces

Hofer

Fisher

2003

Phys. Rev. Lett.

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Conductance in monatomic metal contacts is quantized; it increases in discrete steps of one conductance quantum 2e 2 =h. By contrast, in a vacuum barrier between two metal surfaces we find that conductance increases linearly and continuously with the interaction energy between individual atoms. This behavior shows unambiguously that current flow between single atoms is a measure for their chemical interaction. In the controlled environment of a scanning tunneling microscope it should allow us to study the formation of covalent bonds up to the point where these atoms finally jump into contact. DOI: 10.1103/PhysRevLett.91.036803 PACS numbers: 73.40.Gk, 71.15.Mb, 73.23.Hk Because of their importance for technical applications the conductance properties of metals have been widely researched. In metal break junctions at close to zero temperature the conductance of single atomic contacts has been measured with great accuracy, and it was generally found that conductance increases in discrete steps of one conductance quantum 2e 2 =h [1][2][3][4][5]. The rupture of a bond probes into material properties from the starting point of material stability. Quite the opposite is true for the operation of scanning probe microscopes. There, the interaction between two separate surfaces is generally kept at such a low level that the small changes in the forces between the surfaces or in the number of electrons tunneling through the vacuum barrier can be used as an indication of the surface topographic and electronic properties. The intermediate range between these two methods continues to be problematic. In particular, the role of chemical interactions in scanning probes, even though widely researched [6 -13], is still not well understood. Part of the problem is the theoretical representation of the situation in different frameworks: perturbation methods are generally limited to high distances, they can incorporate chemical interactions only from the outset [13][14][15]. Scattering methods, while electronically accurate, cannot treat atomic interactions and their shift of position at low distances [16]. Nonequilibrium methods are in principle reliable, but they cannot simulate actual probe scans due to their innate restrictions of the symmetry of the combined system [17,18].Here, we propose a new method, which incorporates chemical interactions in a natural way. The method is based on extensive ab initio calculations of coupled systems. These calculations, including chemical interactions from the outset, establish that the suggested perturbation method is in general sufficient to reach the highest level of experimental accuracy.A system, composed of a conducting surface and an equally conducting probe, will be completely decoupled if the distance between the surface atoms and the foremost atom of the probe (apex atom) is substantially greater than 1 nm. Then the electron states of surface and probe are orthogonal: every productwill be zero. If the two systems are brought into closer contact, with a distance of about 0.5-0.6 nm,...

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Unambiguous Interpretation of Atomically Resolved Force Microscopy Images of an Insulator

Cited by 155 publications

References 12 publications

Surface reconstruction of fluorites in vacuum and aqueous environment

Surface reconstruction of fluorites in vacuum and aqueous environment

Theories of scanning probe microscopes at the atomic scale

Signature of a Chemical Bond in the Conductance between Two Metal Surfaces

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