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Carbon Nanotube Tips for MAC Mode AFM Measurements in Liquids
This publication discusses the use of carbon nanotube (CNT) tips in Magnetic AC (MAC) Mode for Atomic Force Microscopy (AFM) in liquid environments, highlighting their potential for high-resolution imaging of both hard and soft materials. CNT tips offer advantages over conventional silicon or silicon nitride tips due to their sharp geometry, mechanical resilience, and resistance to wear. They enable imaging of high-aspect-ratio features and consistent tip performance without rapid degradation.
The study demonstrates the application of CNT tips in MAC Mode, which reduces liquid disturbances by directly driving the cantilever with a magnetic field. Experiments include imaging vapor-deposited gold films and plasmid DNA molecules on mica, achieving resolutions of 5–8 nm. While CNT tips avoid multi-tip artifacts and maintain stability, challenges remain in securing nanotubes to tips in liquid environments.
This work establishes CNT tips as a robust solution for nanoscale imaging, with further improvements anticipated through advanced attachment methods.
How to Choose your MAC Lever
This publication provides guidance on selecting MAC Levers for Magnetic AC (MAC) Mode in Atomic Force Microscopy (AFM), particularly for imaging delicate samples such as soft polymers and biological materials. MAC Mode enhances AC imaging by oscillating the AFM probe at its inherent resonance frequency, reducing noise and eliminating artifacts like the “forest of peaks” observed in traditional AAC Mode.
MAC Levers are specialized AFM probes coated with a paramagnetic film, enabling precise oscillation control via an external magnetic field. Five types of MAC Levers—Types I, II, V, VI, and VII—are tailored for specific applications. Type I is versatile for air or liquid imaging, Type II suits stiffer samples, while Types V, VI, and VII are optimized for soft samples like DNA or proteins in aqueous environments.
This versatility and precision make MAC Levers ideal for studying nanoscale properties of delicate materials, with minimized imaging forces and enhanced resolution, even in complex environments.
Using Non-Contact AFM to Image Liquid Topographies
This publication highlights the use of non-contact atomic force microscopy (NCAM-AFM) for imaging liquid topographies with high resolution, avoiding perturbations such as capillary wetting or deformation of liquid surfaces. Using the Agilent 5500 AFM system with MAC Mode, the study demonstrates the capability of dynamic amplitude modulation to maintain non-invasive imaging conditions.
In NCAM-AFM, a cantilever oscillates at a fixed frequency above its resonance, with interactions between the tip and sample surface controlled by maintaining a reduced amplitude (Asp). This technique enables mapping of liquid surfaces by leveraging van der Waals forces to adjust cantilever height without direct contact. Fine adjustments in amplitude and drive frequency improve lateral and vertical resolution while minimizing artifacts.
The publication provides guidelines to optimize NCAM-AFM performance, such as selecting high-spring constant cantilevers, reducing drive amplitudes, and employing slower scan rates. These refinements enhance image quality and ensure stable interactions for sensitive liquid topography studies.
MAC Mode Atomic Force Microscope for Precision Interfacial Force Measurements
This publication explores the use of Magnetic AC Mode (MAC Mode) Atomic Force Microscopy (AFM) for precise interfacial force measurements. MAC Mode overcomes challenges in fluid-based tapping AFM by directly oscillating the cantilever via a magnetic field, ensuring stable operation and superior signal-to-noise ratios.
The study investigates molecular layering of octamethylcyclotetrasiloxane (OMCTS) and mesitylene on graphite. Using force spectra, seven molecular layers were detected for OMCTS with an interlayer spacing of 8.2 ± 0.3 Å, consistent with its molecular dimensions. Similarly, mesitylene formed layers with a spacing of 4.5 ± 0.2 Å, indicating a flat orientation relative to the graphite surface.
Young’s modulus at the centers of molecular layers was determined, showing an exponential decay with increasing layers. This method demonstrates sub-angstrom vertical resolution, enabling detailed analysis of interfacial structures. The findings highlight MAC Mode AFM’s potential for studying surface interactions and molecular arrangements at liquid-solid interfaces.
Manipulation of Gold Nanoparticles
in Liquids Using MAC Mode Atomic Force Microscopy
This publication explores the use of Magnetic AC Mode (MAC Mode) Atomic Force Microscopy (AFM) for precise manipulation of gold nanoparticles in aqueous environments. Unlike traditional approaches, MAC Mode’s oscillating cantilever minimizes sample interference, enabling controlled nanomanipulation.
The study demonstrates nanomanipulation by depositing 15 nm gold colloidal particles on a mica substrate coated with poly-L-lysine. Using custom Probe Control Software (PCS), the AFM tip pushed individual particles to predefined positions. The feedback-off mode allowed the tip to overcome adhesive forces between particles and the substrate, as observed through real-time line scans.
This technique successfully repositioned particles within a 500 × 500 nm scan area underwater. The results highlight the potential of AFM for constructing nanoscale structures and manipulating objects in liquid environments, with implications for biomedical and nanoengineering applications. Future integration with automated tools and multitip arrays could establish AFM as a programmable nanorobotic platform for high-throughput tasks.
Adsorption of Poly(2-vinylpyridine) Wormlike Polyelectrolyte Brushes on Mica Studied in situ with MAC Mode® AFM
This publication investigates the adsorption of poly(2-vinylpyridine) (PVP) polyelectrolyte brushes onto mica substrates using Magnetic AC Mode (MAC Mode) Atomic Force Microscopy (AFM). Cylindrical PVP brushes, synthesized with controlled side-chain grafting density and converted to polyelectrolytes via quaternization, exhibit stiff, wormlike conformations in aqueous environments. The study explores the influence of environmental factors such as ionic strength, pH, and polymer concentration on adsorption behavior.
MAC Mode AFM enables high-resolution imaging in liquid environments by directly oscillating the cantilever via a magnetic field, minimizing surface deformation. Individual PVP molecules adsorbed on mica were visualized as single rods, with electrostatic interactions influencing their alignment and aggregation. The study also demonstrates that adding NaCl significantly increases surface coverage due to ion diffusion enhancing electrostatic interactions.
This work highlights MAC Mode AFM’s capabilities for in situ monitoring of molecular adsorption, providing insights into nanoscale polymer behavior and thin-film formation processes.
Probing the Three-Dimensional Structure of Soft Organized Surfactants at the Solid-Liquid Interface via Atomic Force Microscopy
This publication examines the three-dimensional structure of dodecyltrimethylammonium bromide (DTAB) surfactant aggregates adsorbed on mica in aqueous solutions using Atomic Force Microscopy (AFM). The study compares contact mode and Magnetic AC Mode (MAC Mode) AFM to investigate the surfactant organization at the solid-liquid interface.
In contact mode, using double-layer electrostatic interaction forces, the observed heights of DTAB aggregates were significantly lower than expected due to compression, measuring 1.8 Å at moderate forces and 5.6 Å at minimal forces. However, MAC Mode, with its low-force imaging capability, revealed DTAB aggregate heights exceeding 2 nm, approximating half the theoretical height of 4–5 nm. These findings indicate reduced sample deformation and enhanced imaging resolution in MAC Mode.
This study demonstrates the effectiveness of MAC Mode for capturing more accurate three-dimensional topographies of soft surfactants, providing valuable insights into adsorption mechanisms and the structural organization of self-assembled systems at interfaces.