Peak forces and lateral resolution in amplitude modulation force microscopy in liquid

This is an Open Access article under the terms of the Creative Commons Attribution License.The peak forces exerted on soft and rigid samples by a force microscope have been modeled by performing numerical simulations of the tip motion in liquid. The forces are obtained by using two contact mechanics models, Hertz and Tatara. We present a comparison between the numerical simulations and three analytical models for a wide variety of probe and operational parameters. In general, the forces derived from analytical expressions are not in good quantitative agreement with the simulations when the Young modulus and the set-point amplitude are varied. The only exception is the parametrized approximation that matches the results given by Hertz contact mechanics for soft materials and small free amplitudes. We also study the elastic deformation of the sample as a function of the imaging conditions for materials with a Young modulus between 25 MPa and 2 GPa. High lateral resolution images are predicted by using both small free amplitudes (less than 2 nm for soft materials) and high set-point amplitudes. © 2013 Guzman and Garcia.This work was funded by the Ministerio de Economía y Competitividad (Consolider Force-For-Future, CSD2010-00024, MAT2009-08650) and European Union Seventh Framework Programme [FP7/2007-2013] under grant agreement no. 280772, project iONE-FP7 and the Cost Action TD1002.Peer Reviewe

Modeling peak interaction forces of soft matter with dynamic AFM in liquid

total of 149 pages, Chapters 1 to 6 make a total of 128 pages.The atomic force microscope (AFM) is an instrument that has revolutionized the field of nanoscience and nanotechnology by enabling the characterization and manipulation of materials with nanometer (one billionth of a meter), molecular and atomic resolution. In the last 28 years a variety of experimental AFM techniques have been developed that go from contact to dynamic AFM modes or from working in air to liquid environments. A relevant research avenue within dynamic AFM modes is devoted to the generation of atomic and molecular resolution images of soft materials in liquid environments. Whereby different applications are envisioned into areas of medicine (nanomedicine) and advanced materials. The research presented here focus on two dynamic AFM methods: amplitude modulation AFM (AM-AFM) and Bimodal AM. This thesis describes the study of the peak interaction forces of soft materials under low-Q environments imaged with AM-AFM and Bimodal AM. The maximum interaction forces have been chosen because it rapidly enables tracking into the degree of invasiveness on the sample, its deformation and hence its resolution while imaging. This thesis proposes a theoretical modeling framework that can be divided in two closely related parts. The first part aims to refine the tip-sample interaction modeling for the description of elastic and viscoelastic phenomena of soft materials. The second part aims to obtain high-resolution imaging conditions from the numerical simulations of the dynamics of the cantilever-tip motion in liquid for an extensive range of dynamic AFM operational parameters and materials.Esta tesis doctoral aborda la descripción teórica de diversos modos dinámicos de la microscopia de fuerzas como son Amplitude Modulation AFM y Bimodal AM en líquidos. Uno de los objetivos es estimar la fuerza máxima ejercida sobre materiales blandos como polímeros o sistemas biológicos. La fuerza pico o máxima permite determinar el grado de invasividad de la técnica sobre una muestra, su deformación y por tanto la resolución espacial. El esquema de modelización se divide en dos partes. La primera parte tiene como objetivo la introducción de nuevos modelos de interacción entre la punta y la muestra para así describir fenómenos elásticos y viscoelásticos. La segunda parte se dedica a desarrollar las condiciones de trabajo del microscopio para obtener imágenes con alta resolución. Para ello se efectúan diversas simulaciones numéricas de la dinámica del sistema micropalanca-punta para una extensa variedad de parámetros operacionales y propiedades mecánicas de materiales.We thank the financial support from the Ministerio de Economia y Competitividad (Consolider Force-For-Future, CSD2010-00024, MAT2009-08650)Peer reviewe

Dynamic force microscopy simulator (dForce): A tool for planning and understanding tapping and bimodal AFM experiments

We present a simulation environment, dForce, which can be used for a better understanding of dynamic force microscopy experiments. The simulator presents the cantilever-tip dynamics for two dynamic AFM methods, tapping mode AFM and bimodal AFM. It can be applied for a wide variety of experimental situations in air or liquid. The code provides all the variables and parameters relevant in those modes, for example, the instantaneous deflection and tip-surface force, velocity, virial, dissipated energy, sample deformation and peak force as a function of time or distance. The simulator includes a variety of interactions and contact mechanics models to describe AFM experiments including: van der Waals, Hertz, DMT, JKR, bottom effect cone correction, linear viscoelastic forces or the standard linear solid viscoelastic model. We have compared two numerical integration methods to select the one that offers optimal accuracy and speed. The graphical user interface has been designed to facilitate the navigation of nonexperts in simulations. Finally, the accuracy of dForce has been tested against numerical simulations performed during the last 18 years.This work was funded by the European Research Council ERC-AdG-340177 (3DNanoMech) and the Spanish Ministry of Economy (MINECO) through grant CSD2010-00024.Peer reviewe