Force Microscopy with Light-Atom Probes

Abstract

The charge distribution in atoms with closed electron shells is spherically symmetric, whereas atoms with partially filled shells can form covalent bonds with pointed lobes of increased charge density. Covalent bonding in the bulk can also affect surface atoms, leading to four tiny humps spaced by less than 100 picometers in the charge density of adatoms on a (001) tungsten surface. We imaged these charge distributions by means of atomic force microscopy with the use of a light-atom probe (a graphite atom), which directly measured high-order force derivatives of its interaction with a tungsten tip. This process revealed features with a lateral distance of only 77 picometers.

Atomic Row Doubling in the STM Images of Cu(014)-O Obtained with MnNi Tips

“…A more recent coupled tip-surface system analysis [7] also demonstrated that electron states with m Þ 0 should give significantly larger corrugations compared to the m 0 states, but the relative contributions of different orbitals can show strong dependence on the tip-surface distance. The effects of the tip electronic structure were recently observed in ultrahigh resolution atomic force microscopy experiments [8,9]. Similar effects may play a significant role in dynamic STM experiments on Si(111) where subatomic features could be explained by scattering of electrons into double dangling bonds of the silicon tip atoms [10].…”

Direct Imaging of Lipid-Ion Network Formation under Physiological Conditions by Frequency Modulation Atomic Force Microscopy

“…Although we cannot determine whether the front atom is oxygen or hydrogen, these atoms are comparable to or even smaller than the carbon atom used in Ref. [28], which may account for the high spatial resolution obtained in this experiment.…”

“…The distance between the apposing subunits is even smaller than the diameter of a single atom. In order to obtain such subatomic-scale contrast in FM-AFM, the tip-sample interaction force must be dominated by the short-range electrical interaction between the tip front atom (or surface atom) and charge distribution of the surface (or tip front atom) [19,28]. For example, Hembacher et al utilized a small atom (carbon atom of the graphite surface) as a probe to image the charge distribution of a tungsten atom at the end of the tip [28].…”

The Use of Scanning Probe Microscopy to Investigate Crystal-Fluid Interfaces

“…There is already some indication that aspects of these problems are coming reality with true in situ vacuum STM [15], video rate STM [57], atom tracking techniques, and true atomic resolution using non-contact AFM [58,59]. As always the trick is to combine dynamic growth with appropriate time and spatial sensitivity.…”