Development of a three-dimensional atomic force microscope for imaging solid-liquid interfaces
- Autores: Daniel Martín Jiménez
- Directores de la Tesis: Ricardo García García (dir. tes.)
- Lectura: En la Universidad Autónoma de Madrid ( España ) en 2017
- Idioma: español
- Tribunal Calificador de la Tesis: Rubén Pérez Pérez (presid.), Celia Polop Jordá (secret.), Carlos Pina (voc.), Enrique Chacón Fuertes (voc.), Kislon Voïtchovsky (voc.)
- Programa de doctorado: Programa Oficial de Doctorado en Física de la Materia Condensada y Nanotecnología
- Materias:
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- Resumen
A solid-liquid interface is formed by discrete entities (ions or molecules) that organize in the liquid close to a solid surface. Its detection has a high relevance since interfacial liquid layers are involved in a wide range of phenomena such as wetting, adhesion, surface electrochemistry, nanorheology, nanolithography, biomineralization, protein dynamics or protein folding and molecular recognition. Several experimental techniques, such as surface force apparatus or photon- and neutron-based techniques, provide accurate information about interfaces along the perpendicular direction of the solid surface; however, they are not able to detect the interfacial structure on the atomic position above the solid, lacking in the lateral resolution across the interfacial plane.
The atomic force microscope (AFM) is a versatile tool capable of obtaining topographical information of a sample (AFM imaging) and detecting forces perpendicular to the sample’s surface (force spectroscopy). The excitation of the AFM probe has provided the capability to work with dynamic observables, amplitude and phase, and to operate in amplitude modulation AFM (AM-AFM) or perform amplitude-phase curves. The standard motion of the probe can be modified to resolve solid-liquid interfaces with high resolution along the three spatial directions, x , y and z. This method, known as three-dimensional AFM (3D AFM) creates three-dimensional maps of the AM-AFM observables. By using small oscillation amplitudes around hundreds of picometers, the detection of liquid density organization at the interface in the three spatial directions is possible.
The thesis is divided in five chapters with a main goal, the development of a 3D AFM to imaging solid-liquid interfaces. The 3D AFM developed here has been tested and applied to study the mica-aqueous solution interface at different aqueous solution conditions. The results presented in this thesis extend the knowledge about the dynamic processes that take place on the mica surface. For the interpretation of the three-dimensional maps, force reconstruction methods for AM-AFM have been developed to provide the force interaction between the tip and the sample.
Chapter 1 is an introduction to AFM. It describes components, parameters and operational modes of the AFM. A solid-liquid interface is defined and the typical interfacial forces measured by AFM are presented.
Chapter 2 describes the modifications of the hardware of a commercial microscope for the development of a 3D AFM. Programs to control the three-dimensional motion of the AFM probe, to visualize the AFM observables in real time and to analyze the acquired data have been built.
In chapter 3, the 3D AFM has been used to study the connection between the adsorbed cations and hydration layer on the negatively charged muscovite mica surface. 3D AFM measurements in different solution conditions have been used to prove how the atomic interfacial structure depends on the number of adsorbed ions on the surface.
Chapter 4 describes how the process of epitaxial nucleation of alkali halide salts on mica is produced. Interfacial structures are measured in salt aqueous solution close to saturation. This chapter shows for the first time images of an organized interface structure of cations and anions mediated by water in the limit between liquid and solid phases.
In chapter 5, two new methods of force reconstruction from the dynamic AFM probe motion are developed. The first method reconstructs the force from an amplitude-phase curve. The second method obtains the time-varying force at a constant probe sample separation from the dynamic motion of the probe operating in AM-AFM. Both methods have been proved by simulations and experiments for different interaction forces.
