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Several Aspects of High Resolution Imaging in Atomic Force Microscopy
This publication explores high-resolution imaging in Atomic Force Microscopy (AFM), focusing on alkane layers on graphite and their molecular-scale visualization. AFM imaging reveals the lamellar structures of alkanes like C18H38 and C390H782, characterized by distinct periodicities such as the 0.25 nm molecular spacing and lamellae widths. These structures are influenced by the effective stiffness of lamellar cores and edges, providing insights into molecular organization.
The study compares AFM imaging to Scanning Tunneling Microscopy (STM), noting challenges in achieving similar atomic-scale resolution in AFM, especially for “dry” samples. Advanced techniques like amplitude modulation (AM) and frequency modulation (FM) modes are highlighted for their potential to improve resolution, especially under ambient or liquid conditions.
Despite progress, limitations in atomic-scale resolution and detection of individual molecular defects in AFM remain. The findings emphasize the need for instrumental improvements, sharper probes, and deeper theoretical understanding to enhance high-resolution imaging capabilities.
AFM High-resolution Imaging Molecular-level Understanding of n-Alkanes Self-Assembly onto Graphite
This publication demonstrates the capabilities of the Agilent 5600LS Atomic Force Microscope (AFM) in achieving molecular-level resolution, focusing on the self-assembly of n-C36H74 molecules on highly oriented pyrolytic graphite (HOPG). The study highlights AFM’s ability to directly visualize soft thin films with nanometer-scale details, emphasizing its relevance for understanding surface adsorption phenomena.
AFM imaging reveals that n-C36H74 molecules exhibit a striped morphology, aligned with long-range order and forming lamellar structures. The stripe width corresponds to the molecular length of fully extended n-C36H74, confirming a lying-down configuration. The images also capture domain boundaries, defect areas, and the influence of the substrate’s six-fold symmetry on molecular alignment.
These findings underscore AFM’s precision in resolving lateral dimensions below 5 nm, offering invaluable insights into the adsorption behavior and structural organization of long-chain molecules at solid-solution interfaces. This work exemplifies AFM’s role in advancing molecular-scale surface characterization.
Intrinsic Contact Noise: A Figure of Merit for Identifying High Resolution AFMs
This publication introduces the concept of Intrinsic Contact Noise (ICN) as a reliable metric for evaluating the performance of Atomic Force Microscopes (AFMs) in terms of imaging resolution and sensitivity. Unlike non-contact noise measurements, ICN directly reflects the noise experienced during tip-sample contact, making it a better indicator of an AFM’s capability to achieve atomic resolution.
ICN is measured by disabling raster-scanning, placing the tip in contact with the sample, and recording the detector signal without external noise influences. Experiments across four AFM configurations showed a strong correlation between lower ICN levels and better imaging resolution, while non-contact noise displayed no clear relationship to resolution. The study also highlights how mechanical vibrations intrinsic to the AFM frame and thermal noise contribute to ICN.
This work emphasizes the importance of ICN as a practical figure of merit, offering insights into optimizing AFM performance for high-resolution applications in diverse environments.