Can atomic force microscopy achieve atomic resolution in contact mode?

Atomic structure and surface defects at mineral-water interfaces probed by in situ atomic force microscopy

Atomic scale details of surface structure play a crucial role for solid-liquid interfaces. While macroscopic characterization techniques provide averaged information about bulk and interfaces, high resolution real space imaging reveals unique insights into the role of defects that are believed to dominate many aspects of surface chemistry and physics. Here, we use high resolution dynamic Atomic Force Microscopy (AFM) to visualize and characterize in ambient water the morphology and atomic scale structure of a variety of nanoparticles of common clay minerals adsorbed to flat solid surfaces. Atomically resolved images of the (001) basal planes are obtained on all materials investigated, namely gibbsite, kaolinite, illite, and Na-montmorillonite of both natural and synthetic origin. Next to regions of perfect crystallinity, we routinely observe extended regions of various types of defects on the surfaces, including vacancies of one or few atoms, vacancy islands, atomic steps, apparently disordered regions, as well as strongly adsorbed seemingly organic and inorganic species. While their exact nature is frequently difficult to identify, our observations clearly highlight the ubiquity of such defects and their relevance for the overall physical and chemical properties of clay nanoparticle-water interfaces.

How the atomic force microscope works?

This chapter aims at giving a quick but precise introduction of the atomic force microscope from the working principle point of view. It is intended to provide a useful starting point to those who first approach the instrument giving a general sketch of the working principles and technical implementations as well as last improvements. Subheading 1 is introductory: it gives an overview of what the instrument does and why it has been developed. Subheading 2 is focused on measurement ranges and on the comparison with scanning electron microscope (SEM) and transmission electron microscope (TEM) which have similar ranges and resolutions but different sample interactions and applications. Subheading 3 gives an overview of the working principles and the most diffused technical implementations on which most of the commercial microscopes rely, as we think it gives the useful base knowledge to understand possible applications, instrument capabilities, and results. In particular, technical improvements taking place over the past few years are highlighted. Despite of the simple and not very technical approach, it has a key importance in understanding concepts at the base of Chapter 3, which is, on the other side, useful for beginners and experienced users as well. Subheading 4 compares different instrument architectures and can, therefore, be useful for those who are going to choose an instrument having clear final applications. Latest solutions are once more highlighted. Subheading 5 gives an overview and some suggestions to start working, both in air and in liquid. Following the general philosophy of the book, it follows more an "how to do" concept than a general theoretical approach. Subheading 6 contains the future developments of the techniques.

Single crystal diamond tips for scanning probe microscopy

Single crystal diamond tips with perfect pyramidal geometry were obtained by a combination of chemical vapor deposition and selective oxidation of polycrystalline films. The parameters of the deposition process were chosen to provide growth of a textured film consisting of micrometer sized diamond crystallites embedded into nanodiamond ballas-like material. The heating of the film in an air environment was used for selective oxidation of the nanodiamond component. The films obtained contain free standing pyramidal single crystal diamond tips oriented by their apexes to the substrate surface. The tips were used for the fabrication of atomic force microscopy probes and their evaluation in comparison to common silicon probes.

Atomic-scale sharpening of silicon tips in noncontact atomic force microscopy

The atomic-scale stability of clean silicon tips used in noncontact atomic force microscopy (NC-AFM) is simulated by ab initio calculations based on density functional theory. The tip structures are modeled by silicon clusters with and termination. For the often assumed Si(111)-type tip we observe the sharpening of the initially blunt tip via short-range chemical forces during the first approach and retraction cycle. The structural changes corresponding to this intrinsic process are irreversible and lead to stable NC-AFM imaging conditions. In opposition to the picture used in literature, the Si(001)-type tip does not exhibit the so-called "two-dangling bond" feature as a bulklike termination suggests.