High viscosity environments: an unexpected route to obtain true atomic resolution with atomic force microscopy

Abstract

Atomic force microscopy (AFM) is widely used in liquid environments, where true atomic resolution at the solid-liquid interface can now be routinely achieved. It is generally expected that AFM operation in more viscous environments results in an increased noise contribution from the thermal motion of the cantilever, thereby reducing the signal-to-noise ratio (SNR). Thus, viscous fluids such as ionic and organic liquids have been generally avoided for highresolution AFM studies despite their relevance to, e.g. energy applications. Here, we investigate the thermal noise limitations of dynamic AFM operation in both low and high viscosity environments theoretically, deriving expressions for the amplitude, phase and frequency noise resulting from the thermal motion of the cantilever, thereby defining the performance limits of amplitude modulation (AM), phase modulation (PM) and frequency modulation (FM) AFM. We show that the assumption of a reduced SNR in viscous environments is not inherent to the technique and demonstrate that SNR values comparable to ultra-high vacuum systems can be obtained in high viscosity environments under certain conditions. Finally, we have obtained true atomic resolution images of highly ordered pyrolytic graphite and mica surfaces, thus revealing the potential of high-resolution imaging in high viscosity environments.High viscosity environments: an unexpected route to obtain true atomic resolution with atomic force microscopy 2

Simultaneous Deconvolution of In‐Plane and Out‐of‐Plane Forces of HOPG at the Atomic Scale under Ambient Conditions by Multifrequency Atomic Force Microscopy

“…Also, because graphene devices are exposed to environmental influences, measurements in air under ambient conditions are more relevant than those under ultrahigh vacuum (UHV). While imaging graphitic surfaces at the atomic scale has become a standard procedure using atomic force microscopy (AFM) under UHV, [ 7 ] at low temperatures [ 8–11 ] or in a liquid environment [ 12 ] it remains a challenging task to obtain comparable high resolution in air under ambient conditions.…”

Exploring site-specific chemical interactions at surfaces: a case study on highly ordered pyrolytic graphite

“…From the respective data in figure 2, we see that the contrast reversal in the TO-AFM images (figures 2(a), (c)) is complemented by a more complex behavior in the corresponding current signals (figures 2(b), (d)). For the analysis, let us start by noting that the appearance of figure 2(c) matches the most commonly observed contrast for the NC-AFM imaging of graphite, which has been well understood [16,19,35,44,[56][57][58][59][60]. Therefore, we can make an unambiguous assignment of the various lattice sites in figure 2(c), with the hillocks reflecting the positions of the hollow sites while the A-and B-atoms are located at minima (cross-section below figure 2(c)).…”

Robust high-resolution imaging and quantitative force measurement with tuned-oscillator atomic force microscopy

“…While resolving lattice periodicity in contact mode [4,5] and atomic resolution imaging by scanning tunneling microscopy [40] have always been considered 'easy', the low surface interactions of this van der Waals material have made atomic resolution imaging with NC-AFM challenging. Often, specialized equipment (such as low temperature microscopes [36,[41][42][43]) or unconventional approaches (such as imaging at higher eigenmodes [44], using torsional resonances [45], or by imaging in high-viscosity liquids [46]) have been used to achieve atomic resolution. We were able to image graphite at room temperature in vacuum at both the large-(figure 3(a)) and atomic-scales (figure 3(b)).…”