Calibration and Nonlinearity Compensation for Force Application in AFM based Nanomanipulation

Abstract — Both the extent and accuracy of force application in atomic force microscope (AFM) nanomanipulation are significantly limited by the nonlinearity of the commonly used optical lever with a nonlinear position-sensitive detector (PSD). In order to compensate the nonlinearity of the optical lever, a nonlinear calibration method is presented. This method applies the nonlinear curve fit to a full-range position-voltage response of the photodiode, obtaining a continuous function of its voltagerelated sensitivity. Thus, Interaction forces can be defined as integrals of this sensitivity function between any two responses of photodiode voltage outputs, instead of rough transformation with a single conversion factor. The lateral position-voltage response of the photodiode, a universally acknowledged puzzle, was directly characterized by an accurately calibrated force sensor composed of a tippless piezoresistive force sensor, regardless of any knowledge of the cantilevers and laser measuring system. Experiments using a rectangular cantilever (normal force constant 0.24 N/m) demonstrated that the proposed nonlinear calibration method restrained the sensitivity error of normal position-voltage responses to 3.6 % and extended the force application range. Index Terms — Atomic force microscope, nanomanipulation, force calibration, nonlinearity compensation. I

A Modified Preisach Model for Hysteresis in Piezoelectric Actuators

Piezoelectric actuators (PEAs) exhibit hystérésis nonlinearity in open-loop operation, which may lead to undesirable inaccuracy and limit system performance. Classical Preisach model is widely used for portraying hysteresis but it requires a large number of first-order reversal curves to ensure the model accuracy. All the curves may not be obtained due to limitations of experimental conditions, and the detachment between the major and minor loops is not taken into account. This paper aims to propose a modified Preisach model that demands relatively few measurements and that describes the detachment. The modified model is implemented by adding a damper in parallel with the classical Preisach model. The parameter of the damper is adjusted to an appropriate value so that the measured and predicted hysteresis loops are in good agreement. Experimental results prove that the proposed modified Preisach model can characterize hysteresis more accurately than the classical model

Hybrid Electronic Materials: Characterization and Thin-film Deposition

Hybrid Electronic Materials (HEMs), as defined for this dissertation, are combinations of organic and inorganic materials as may be used to fabricate active device components in “beyond the transistor” electronics. However, the use of organics is often limited by issues such as thermal stability, compatibility with traditional (semiconductor) materials, and current processing technology. Thus, we began our exploration of HEMs with a “new” class of materials called GUMBOS (Group of Uniform Materials Based on Organic Salts) as derived from ionic liquids. For this first segment of our work, we investigated selected species of GUMBOS and nanoGUMBOS via their current-voltage characteristics, electronic sensing capabilities, and amenability to thin-film formation using the technique of electrospraying. For the next segment, and primarily thin-film portion of this research, we elected to include the now more “traditional” material of carbon nanotubes (CNTs). Although reasonably well-characterized, CNTs still offer a significant challenge in terms of thin-film deposition, particularly upon non-conductive substrates. Electrophoretic deposition (EPD) is a solution-based technique that we have previously researched for the deposition of CNT thin-films onto metal and semiconductor substrates. However, EPD is limited by its need for conductive electrodes. We eliminate the latter through an electrospray-assisted form of EPD which accomplishes the two fold task of successfully depositing CNT thin-films onto non-conductive material while increasing the utility of EPD as it applies to HEMs. We also characterized the effect of our electrospray-assisted EPD technique upon CNT film thickness, quality, and morphology. Our investigation concludes with the prototype development of a new method of electrospraying based upon Faraday waves. In conjunction with characterization and thin-film deposition, this prototype demonstrates a means by which to scale HEMs to feasible commercial utilization

Miniaturised magnetic bead actuator-based atomic force microscope for single-molecule measurements

Single molecular techniques have been providing researchers powerful tools to reveal the mechanisms of bioprocesses by investigating the behaviours and properties of individual molecules. It’s also an essential way to study the functional differences and accesses the parameters of individual molecules. Atomic force microscopy (AFM) is one of the most popular technologies to probe into individual molecules and has provided insights into structure, kinetics and dynamics of many molecules. However, the conventional AFM use cantilever-based sensors and piezo-based actuators which are relatively large in dimension and prone to drift and noise. This thesis focuses on the development of a customised AFM for single molecule force spectroscopy experiments which is capable of both magnetic and piezo actuation. The magnetic actuation method unitises miniaturise magnetic beads as actuators reduces the actuator size significantly and performs experiment in non-contact way, thus reduces the impact of noise and drift. The resolution of the setup is verified experimentally and comparable to commercial AFM in single molecule force spectroscopy applications. Single molecule force spectroscopy experiments using both varying loading rates and force clamp methods have been performed using biotin-streptavidin and heparin-FGF2 molecule pairs. The energy landscapes of their bonds have been studied

Propuesta y Evaluación de Algoritmos para la Corrección de Errores en Sensores Táctiles

Los sensores táctiles suelen ser matrices de unidades detectoras denominadas tácteles, utilizados habitualmente en robótica para proporcionar capacidades de percepción en aplicaciones que requieren de contacto físico con objetos. Así, es posible determinar su forma, tamaño, textura o dureza permitiendo a los robots interactuar de forma autónoma y con seguridad en un entorno que puede mostrar condiciones cambiantes. Sin embargo, la necesidad de cubrir grandes áreas de contacto de manera flexible y con bajo coste, lleva a utilizar sensores que presentan errores de histéresis, no linealidad, deriva o dispersión. Esto provoca una escasa presencia efectiva de estos sensores en las plataformas robóticas existentes en la actualidad. En esta tesis, en primer lugar, se estudia el efecto de estos errores sobre la información de control derivada de las imágenes táctiles obtenidas como respuesta de un sensor al contacto con un objeto, y que se utiliza en tareas de manipulación robótica. Se realiza el estudio sobre dos sensores táctiles piezo-resistivos, uno flexible de bajo coste y propenso a errores, y otro comercial con menores limitaciones. En segundo lugar, a nivel de táctel, se exploran y proponen algoritmos de corrección de las no linealidades de histéresis complejas mostradas por el sensor de bajo coste, que permitan obtener medidas precisas y fiables de la presión ejercida sobre su superficie. Se analizan tres métodos utilizados por otro tipo de sensores y actuadores: el modelo generalizado de Prandtl-Ishlinskii, un modelo modificado del método clásico de Prandtl-Ishlinskii y un modelo basado en polinomios que aproximan las curvas externas de los bucles de histéresis. Además, como aportación principal de esta tesis, se propone un nuevo algoritmo de modelado denominado ELAM. Este método se basa en la determinación por algoritmos de aproximación de unos puntos intermedios en las curvas y la aplicación de distintas estrategias de mapeo lineal de las curvas externas a las internas del bucle de histéresis medido experimentalmente. El análisis de las medidas y pruebas realizadas, muestra que los errores a nivel de matriz tienen una influencia sobre los parámetros de control similar a otras fuentes admitidas como la dispersión y la resolución limitada. La información extraída del contacto del objeto con un sensor de bajo coste es suficientemente buena en términos de distribución espacial y orientación como para ser utilizada en aplicaciones robóticas, pero no lo es sobre la fuerza de contacto, por lo que en aplicaciones que necesiten una alta precisión en la medida de la presión ejercida, será necesario compensar los errores del sensor. En este sentido, se demuestra que el método ELAM propuesto en esta tesis, consigue un modelo con un ajuste mucho más preciso a los datos experimentales que los otros métodos evaluados. Además, se trata de un método flexible, simple de implementar en dispositivos como FPGAs para aplicaciones en tiempo real, con pocos parámetros de control, apropiado para ciclos de histéresis complejos de otros tipos de sensores o actuadores y que permite corregir los errores de histéresis, no linealidad y dispersión en la respuesta de los sensores táctiles