Atomic force microscopy improved resolution employing large scanning speeds: Effects of the double relaxation time

Abstract

The minimum scanning speed of atomic force microscopes for improved atomic resolution has been measured in liquid media, and shown to be equal to 100 nm/s for mica immersed in water corresponding to the time spent scanning the distance between two neighbor ions (∼0.52 nm) of ∼5 ms. The scanning velocity dependence of the force acting on the tip in the double-layer region (∼135 nm) when it approaches the surface was also measured. The stationary component of this force, for scanning speeds up to 30 μm/s, was identified as the exchange of the liquid media with ε≈80 by the tip with ε≈6. As the tip approaches the surface and as well as when the tip images atomic features, this repulsive force shows a relaxation time of a few milliseconds, corresponding to the shielding of the surface charge by the solution, i.e., the double-layer relaxation time. Scanning surfaces at speeds higher than the ratio of the atomic features distance and this relaxation time results in a variable repulsive force acting on the tip, as a function the scanning speed, which might be used to improve the atomic imaging resolution.

Imaging of soft structures: Dependence of contrast in atomic force microscopy images on the force applied by the tip

“…The atomic force microscope ͑AFM͒ obtains topographical information from the shortrange repulsion resulting from the overlap of electronic shells between the tip and sample. 8 However, the presence of long-range interactions such as the double layer electrostatic force [9][10][11][12][13] when scanning soft samples in liquid media leads to a very different imaging scenario. The purpose of this article is to report on forces acting on the tip when imaging soft samples, as surfactant layers, in liquid media and to determine their effects on the AFM image contrast.…”

Chiral Asymmetric Structures in Aspartic Acid and Valine Crystals Assessed by Atomic Force Microscopy

“…The AFM was operated in lateral force mode with all feedback loops open, and there was no scanning velocity limitation by the time constant of the piezoelectric translator and feedback circuits. 16 All images showing a periodic atomic structure were processed as follows: initially, the images were horizontally autoleveled with a first-order polynomial. Then images acquired directly from the electric signal associated with the tip movement were fast Fourier transformed and filtered by selecting bright spots in the FFT spectrum.…”

“…The AFM was operated in lateral force mode with all feedback loops open, and there was no scanning velocity limitation by the time constant of the piezoelectric translator and feedback circuits . All images showing a periodic atomic structure were processed as follows: initially, the images were horizontally autoleveled with a first-order polynomial.…”

Dielectric exchange: The key repulsive or attractive transient forces between atomic force microscope tips and charged surfaces

“…In a recent article 16 we reported that the double-layer relaxation time measurements and the value determined for mica in water is around ϳ5 ms, which corresponds to an approach velocity Ͼ20 m/s ͑in water͒ in order to obtain a transient charge distribution. Since both the tip and the substrate are insulators and consequently have very long charge relaxation times, charges in the solution partially neutralize the new charge arrangement in the tip/electrolyte/ substrate interaction region and the time constant involved in the process is the double-layer charge relaxation time.…”