Imaging point defects in a liquid environment: A model AFM study

Abstract

Effects of the liquid on atomic force microscopy ͑AFM͒ imaging are examined for a model system consisting of a hexagonal flake of seven Lennard-Jones ͑LJ͒ atoms as a multiatom tip, a monolayer of LJ crystal containing a single point defect as a substrate, and three-site model water as the liquid. A previous simulation ͓Koutsos et al., Europhys. Lett. 26, 103 ͑1994͔͒ has shown that the true atomic resolution of a point defect cannot be achieved in vacuum by use of the multiatom tip. Here we examine the feasibility of such atomic resolution when both the tip and substrate are immersed in a liquid. The liquid-induced interaction between the tip and the substrate is evaluated in the framework of the integral equation theory of molecular fluids extended for the system consisting of an infinitely large crystal. It is found that the potential of mean force indeed manifests the point defect even when the tip and the substrate are a few Angstroms apart. This implies that in the liquid environment the point defect could be discerned in the constant-height mode of AFM measurement. For the constant-load mode of AFM, a characteristic potential can be used to determine the stable, metastable, and unstable vertical position ͑height͒ of the tip at any lateral position. The contour surface of the stable heights reveals periodic features of the underlying lattice of the substrate except in the vicinity of the defect, provided certain load is applied. ͓S0163-1829͑99͒10543-5͔

Role of water in atomic resolution AFM in solutions

“…[17][18][19] Other works have investigated the shorter ranged forces responsible for atomic or molecular resolution using several approaches. [19][20][21][22][23] This division is less artificial than it appears at first sight, as it is possible experimentally to separate the short and long range force interactions from approach curves made in spectroscopic mode, using the method of Sader. 7,24 This allows us to focus on short range forces that can lead to atomic resolution, whilst the longer range macroscopic interactions can be addressed separately.…”

Charged Barite−Aqueous Solution Interface: Surface Potential and Atomically Resolved Visualization

“…To understand the role of the tip in obtaining atomically resolved images, several models for the interaction between tips and ionic surfaces have been developed that account for distortions of both the tip and the surface. − These models have, in particular, used static atomistic simulation and quantum-chemical techniques. Giessibl and Binnig suggested that inductive polarization of the tip in the field of the sample ions provides the major contribution to the imaging mechanism in noncontact mode.…”

Theoretical Analyses of Cantilever Oscillation for Dynamic Atomic Force Microscopy in Liquids

“…[8][9][10] Recently, we are developing theoretical simulation methods for the dynamic AFM in liquids treating such fundamental problems properly. The aim of the present paper is to propose a numerical method for the analyses of the cantilever bending motion in liquids and clarify various dynamic features, particularly for the dynamic tapping mode cases.…”

“…For theoretical analyses of dynamic AFM in water, we must solve various difficult issues as the cantilever oscillation in the environment of liquid 6,7) as well as the tipsample interaction force mediated by many molecules composing the liquid. [8][9][10] Recently, we are developing theoretical simulation methods for the dynamic AFM in liquids treating such fundamental problems properly. The aim of the present paper is to propose a numerical method for the analyses of the cantilever bending motion in liquids and clarify various dynamic features, particularly for the dynamic tapping mode cases.…”