Atomic force microscopic observation of step movements on NaCl(001) and NaF(001) with the help of adsorbed water

Shindo, Hitoshi; Ohashi, M.; Tateishi, Osamu; Seo, Akihiro

doi:10.1039/a606256c

Cited by 60 publications

(56 citation statements)

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“…However, as information averaged over the whole surface of the sample is obtained, a detailed molecular scale picture is missing from this work. Much more detailed information has been obtained using atomic force microscopy (AFM), scanning force microscopy (SFM), or scana) Electronic mail: angelos.michaelides@ucl.ac.uk ning polarization force microscopy (SPFM) 5,6 techniques in experiments of Dai at al., 7 Shindo et al, [8][9][10] and others. [11][12][13][14][15] The measurements revealed slow step movements and rounding of sharp kinks at humidities below ∼40% and a faster step movement when the humidity is increased above ∼40%.…”

Section: Introductionmentioning

confidence: 99%

Understanding the role of ions and water molecules in the NaCl dissolution process

Klimeš

Bowler

Michaelides

2013

The Journal of Chemical Physics

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A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu The Journal of Chemical Physics 132, 154104 (2010) The dissolution of NaCl in water is one of the most common everyday processes, yet it remains poorly understood at the molecular level. Here we report the results of an extensive density functional theory study in which the initial stages of NaCl dissolution have been examined at low water coverages. Our specific approach is to study how the energetic cost of moving an ion or a pair of ions to a less coordinated site at the surface of various NaCl crystals varies with the number of water molecules adsorbed on the surface. This "microsolvation" approach allows us to study the dependence of the defect energies on the number of water molecules in the cluster and thus to establish when and where dissolution becomes favorable. Moreover, this approach allows us to understand the roles of the individual ions and water molecules in the dissolution process. Consistent with previous work we identify a clear preference for dissolution of Cl ions over Na ions. However, the detailed information obtained here leads to the conclusion that the process is governed by the higher affinity of the water molecules to Na ions than to Cl ions. The Cl ions are released first as this exposes more Na ions at the surface creating favorable adsorption sites for water. We discuss how this mechanism is likely to be effective for other alkali halides.

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Section: Introductionmentioning

confidence: 99%

Understanding the role of ions and water molecules in the NaCl dissolution process

Klimeš

Bowler

Michaelides

2013

The Journal of Chemical Physics

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“…But more interesting, though not yet understood, was the re-deposition of crystal material in the area over which the tip-substrate meniscus was scanned in the absence of drying. This re-deposition was attributed to continuous evaporation of the meniscus [29,34,35], or even to differences in the water chemical potential in ultrathin water layers compared to bulk (i.e., within the meniscus) [13]. Although the physical mechanism that underlies this phenomenon still remains in question, here we use it to create 3D nanoscale structures and to study the kinetics of changes in surface shape when these overgrowths are allowed to relax away in order to minimize curvature and thus surface free energy.…”

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confidence: 99%

Solvent-mediated repair and patterning of surfaces by AFM

Elhadj¹,

Chernov

Yoreo³

2008

Nanotechnology

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A tip-based approach to shaping surfaces of soluble materials with nanometer-scale control is reported.The proposed method can be used, for example, to eliminate defects and inhomogeneities in surface shape, repair mechanical or laser-induced damage to surfaces, or perform 3D lithography on the length scale of an AFM tip. The phenomenon that enables smoothing and repair of surfaces is based on the transport of material from regions of high-to low-curvature within the solution meniscus formed in a solvent-containing atmosphere between the surface in question and an AFM tip scanned over the surface. Using in situ AFM measurements of the kinetics of surface remodeling on KDP (KH 2 PO 4 ) crystals in humid air, we show that redistribution of solute material during relaxation of grooves and mounds is driven by a reduction in surface free energy as described by the Gibbs-Thomson law. We find that the perturbation from a flat interface evolves according to the diffusion equation where the effective diffusivity is determined by the product of the surface stiffness and the step kinetic coefficient.We also show that, surprisingly, if the tip is instead scanned over or kept stationary above an atomically flat area of the surface, a convex structure is formed with a diameter that is controlled by the dimensions of the meniscus, indicating that the presence of the tip and meniscus reduces the substrate chemical 2 potential beneath that of the free surface. This allows one to create nanometer-scale 3D structures of arbitrary shape without the removal of substrate material or the use of extrinsic masks or chemical compounds. Potential applications of these tip-based phenomena are discussed.

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“…In the latter case, a difference from the air/solid interface is noticed when the step H passes the dislocation. In the case of NaCl(001) in air, reconnection of the steps occurs immediately [14]; one-half of the catching-up step combines with the step originating at a dislocation and they proceed together, leaving the other half trapped at the dislocation. In the present case, however, the whole step H became trapped and formed a step of mixed heights; partly monatomic and partly diatomic (not shown in Fig.…”

Section: Resultsmentioning

confidence: 98%

“…Since NaCl surfaces cleaved in air are not entirely flat, step motions are observed depending on the local curvature even in the saturated solution. In this case, the transport of ions will occur mainly by two-dimensional motions of ad-ions on the surface.The results are compared with our previous results on the step motions on NaCl and NaF faces in humid air, where adsorbed water transports the ions [13,14]. …”

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confidence: 91%

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In-situ AFM observation of crystal growth of NaCl in an aqueous solution

Shindo

Ohashi

1998

Applied Physics A: Materials Science & Processing

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The step motions on the NaCl(001) surface in a saturated aqueous solution were studied using atomic force microscopy. The transport of salts from the higher to the lower terraces were observed in situ. Monatomic steps proceed very quickly on flat terraces as long as the salt supply is sufficient.Step advancement, however, is retarded at intersections, at right angles, of the electrically neutral steps along the axes of the crystal. As a result, the steps are segmented into arcs connecting such corners. After several steps become bunched together, monatomic steps grow out at the bottom. At a more inclined part, the surface is completely covered by arcs of monatomic steps that are bunched at the corners. The development of such shapes is explained by a simple model considering the coordination of first, second and third neighbour ions at various adsorption sites. The step bunching is explained without assuming any adsorption of impurity from the solution. Monatomic steps were observed to grow out at neutral parts near the corners. These observed processes must be the main features in the crystal growth of NaCl in solutions.Atomic force microscopy (AFM) is a powerful tool for studying the atomic processes involved in the growth and dissolution of crystal faces in liquids. Most such works, however, have been carried out on sparingly soluble crystals such as. This is understandable since the processes for more soluble crystals are too fast to be followed at atomic levels. However, the processes can be considerably slowed by using nearly saturated solutions [9].In this work, we have observed step motions on the NaCl(001) surface in a saturated aqueous solution. Since NaCl surfaces cleaved in air are not entirely flat, step motions are observed depending on the local curvature even in the saturated solution. In this case, the transport of ions will occur mainly by two-dimensional motions of ad-ions on the surface.The results are compared with our previous results on the step motions on NaCl and NaF faces in humid air, where adsorbed water transports the ions [13,14]. ExperimentalA natural rock salt crystal was cleaved in air by hitting a knife edge placed along an axis of the crystal. The crystal obtained was typically of dimensions 5 mm × 3 mm × 1 mm, which was quickly placed in a liquid cell designed for the NanoScope III AFM of Digital Instruments.After obtaining topographic images of the cleaved surface in air, a saturated aqueous solution of NaCl was introduced into the cell from a container having an excess of NaCl powder. The temperature difference between the reservoir and the cell, if any, would not have much effect since the solubility of NaCl in water is not highly temperature dependent. The degree of supersaturation of the solution calculated from the grain size (about 0.3 mm) and the surface energy estimated for the (001) face (212 erg cm −2 [15]) was about 5 × 10 −5 [16]. However, since the flow of the solution was stopped during the AFM experiment in order to stabilize the observation, the degree of super...

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Atomic force microscopic observation of step movements on NaCl(001) and NaF(001) with the help of adsorbed water

Cited by 60 publications

References 6 publications

Understanding the role of ions and water molecules in the NaCl dissolution process

Understanding the role of ions and water molecules in the NaCl dissolution process

Solvent-mediated repair and patterning of surfaces by AFM

In-situ AFM observation of crystal growth of NaCl in an aqueous solution

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