MICROCANTILEVER-BASED FORCE SENSING, CONTROL AND IMAGING

This dissertation presents a distributed-parameters base modeling framework for microcantilever (MC)-based force sensing and control with applications to nanomanipulation and imaging. Due to the widespread applications of MCs in nanoscale force sensing or atomic force microscopy with nano-Newton to pico-Newton force measurement requirements, precise modeling of the involved MCs is essential. Along this line, a distributed-parameters modeling framework is proposed which is followed by a modified robust controller with perturbation estimation to target the problem of delay in nanoscale imaging and manipulation. It is shown that the proposed nonlinear model-based controller can stabilize such nanomanipulation process in a very short time compared to available conventional methods. Such modeling and control development could pave the pathway towards MC-based manipulation and positioning. The first application of the MC-based (a piezoresistive MC) force sensors in this dissertation includes MC-based mass sensing with applications to biological species detection. MC-based sensing has recently attracted extensive interest in many chemical and biological applications due to its sensitivity, extreme applicability and low cost. By measuring the stiffness of MCs experimentally, the effect of adsorption of target molecules can be quantified. To measure MC\u27s stiffness, an in-house nanoscale force sensing setup is designed and fabricated which utilizes a piezoresistive MC to measure the force acting on the MC\u27s tip with nano-Newton resolution. In the second application, the proposed MC-based force sensor is utilized to achieve a fast-scan laser-free Atomic Force Microscopy (AFM). Tracking control of piezoelectric actuators in various applications including scanning probe microscopes is limited by sudden step discontinuities within time-varying continuous trajectories. For this, a switching control strategy is proposed for effective tracking of such discontinuous trajectories. A new spiral path planning is also proposed here which improves scanning rate of the AFM. Implementation of the proposed modeling and controller in a laser-free AFM setup yields high quality image of surfaces with stepped topographies at frequencies up to 30 Hz. As the last application of the MC-based force sensors, a nanomanipulator named here MM3A® is utilized for nanomanipulation purposes. The area of control and manipulation at the nanoscale has recently received widespread attention in different technologies such as fabricating electronic chipsets, testing and assembly of MEMS and NEMS, micro-injection and manipulation of chromosomes and genes. To overcome the lack of position sensor on this particular manipulator, a fused vision force feedback robust controller is proposed. The effects of utilization of the image and force feedbacks are individually discussed and analyzed for use in the developed fused vision force feedback control framework in order to achieve ultra precise positioning and optimal performance

AFM-Based Mechanical Nanomanipulation

Advances in several research areas increase the need for more sophisticated fabrication techniques and better performing materials. Tackling this problem from a bottom-up perspective is currently an active field of research. The bottom-up fabrication procedure offers sub-nanometer accurate manipulation. At this time, candidates to achieve nanomanipulation include chemical (self-assembly), biotechnology methods (DNA-based), or using controllable physical forces (e.g. electrokinetic forces, mechanical forces). In this thesis, new methods and techniques for mechanical nanomanipulation using probe force interaction are developed. The considered probes are commonly used in Atomic Force Microscopes (AFMs) for high resolution imaging. AFM-based mechanical nanomanipulation will enable arranging nanoscale entities such as nanotubes and molecules in a precise and controlled manner to assemble and produce novel devices and systems at the nanoscale. The novelty of this research stems from the development of new modeling of the physics and mechanics of the tip interaction with nanoscale entities, coupled with the development of new smart cantilevers with multiple degrees of freedom. The gained knowledge from the conducted simulations and analysis is expected to enable true precision and repeatability of nanomanipulation tasks which is not feasible with existing methods and technologies

Sub-Micron Nano-Composite CoC Hall Sensors by Focused Electron-Beam Induced Deposition for Microbead Detection

In order to track single superparamagnetic microbeads serving as markers in biomolecular assays, high-sensitivity, sub-micron magnetic sensors which can be integrated onto Lab-on-a-chip platforms are needed. This thesis studies the realization and characterization of such magnetic sensors using Focused Electron Beam Induced Deposition (FEBID) of Cobalt in a High Vacuum (HV) Scanning Electron Microscope (SEM). In FEBID, a finely focused electron beam is used to selectively irradiate a surface where functional precursor molecules are adsorbed. Electron-impact dissociation of the adsorbates lead to non-volatile fragments being deposited at the point of irradiation, while volatile fragments desorb and are pumped away. We have investigated FEBID of Dicobalt octacarbonyl [Co2(CO)8]. The deposit consists of a nanocomposite CoC material, where Co nanocrystals 2-3 nm in size are embedded in a carbonaceous matrix. This material exhibits a scattering enhanced Extraordinary Hall Effect (EHE) which allows for high magnetic sensitivities. Combined with the inherent nanometric resolution of the deposition process, this makes this nanocomposite CoC material the material of choice for the deposition of small (sub-micron), high-sensitivity magnetic sensors. However, the magnetic field resolution is found to be highly dependent on the exact composition of the deposition process. We report for the first time the controlled tuning of the composition of deposits from Co2(CO)8 using the electron beam pulse time as the process parameter. We explain the tunability in terms of co-deposition of chamber background hydrocarbons. A novel, general model describing the electron-induced deposition in terms of surface adsorbate densities in the presence of two adsorbate species is presented. The analytical model allows to describe the conditions for a broad tunable composition window for any two-adsorbate system. The model is applied to the two-adsorbate system consisting of Co2(CO)8 and HV chamber background hydrocarbons and we show that it allows for a quantitative description of the compositional variations. The CoC nanocomposite material is studied and characterized using a Langevin fit of the Hall signal. We show that this approach yields insight into the nanocrystal mean size, providing a nanocharacterization method of the material. A linear dependency between the electrical resistivity and the Hall resistivity at saturation is found. Empirically, the material is found to exhibit an optimum in terms of magnetic field resolution at around 65 at.% Co, corresponding to a trade-off between magnetic field sensitivity and electrical resistivity. Finally, we demonstrate single superparamagnetic bead detection using a sub-micron, CoC Hall sensor. Using a novel nanomanipulation setup providing a magnetic coil integrated into a SEM, we show the bead tracking capacities of these sensors

How to Characterize Cylindrical Magnetic Nanowires

Cylindrical magnetic nanowires made through the help of nanoporous alumina templates are being fabricated and characterized since the beginning of 2000. They are still actively investigated nowadays, mainly due to their various promising applications, ranging from high-density magnetic recording to high-frequency devices, passing by sensors, and biomedical applications. They also represent suitable systems in order to study the dimensionality effects on a given material. With time, the development in fabrication techniques allowed to increase the obtained nanowire complexity (controlled crystallinity, modulated composition and/or geometry, range of materials, etc.), while the improvements in nanomanipulation permitted to fabricate system based either on arrays or on single nanowires. On the other side, their increased complexity requires specific physical characterization methods, due to their particular features such as high anisotropy, small magnetic volume, dipolar interaction field between them, and interesting electronic properties. The aim of this chapter was to offer an ample overview of the magnetic, electric, and physical characterization techniques that are suitable for cylindrical magnetic nanowire investigation, of what is the specific care that one needs to take into account and which information will be extracted, with typical and varied examples

Opto-Mechanical Manipulation Of Molecules And Chemical Reactions

We developed optical methods to manipulate molecules in a microfluidic environment. Optical tweezers can manipulate micro-spheres in solutions with the gradient force but are not practical for spheres smaller than 500 nm in diameter. Nanotweezers use the evanescent field out of waveguides, slot-waveguides, plasmonic resonances, and photonic crystal resonators. They were able to manipulate objects down to 40 nm. Proteins and many biomolecules are of sizes on the order of a few nanometers, a priori out of reach of these techniques. During my PhD, I developed nanophotonic and nano-optic systems aimed at applying electromagnetic potential wells to bias the motion of molecules against Brownian motion and eventually demonstrated that chemical reaction pathways could also be altered. I showed that photonic crystal resonators are a toolbox for nanoscale assembly enabling trapping, transport, and orientation of nano-objects. I also investigated the heat arising in optofluidic photonic crystals and found it to be higher than previously thought, up to 57 K for 10 mW of power input, which makes such devices incompatible with biological single molecule experiments. I then used electromagnetic fields shaped by waveguides-carbon nanotubes hybrids to trap immunoglobulin of mass down to 160 kDa. Last, I developed the optical manipulation of chemical reactions. I showed that electromagnetic gradient force can transport molecules across reaction barriers along a reaction coordinate demonstrating it experimentally by guiding the adsorption of immunoglobulin proteins onto carbon nanotubes. These techniques are part of a wider evolution that is changing the way we interact with molecules. Although originally dismissed for studying single molecules because of the diffraction limit, nano-optics and nanophotonics are becoming the center of this revolution

Nanomanipulation and in-situ electrical characterisation of nanowires

Nanotechnology is a diverse area of research that involves the creation of new materials and tools that are able to manipulate and make contact to objects at the nanoscale. One current area of research is into carbon nanotubes, which exhibit unique electrical properties. It is hoped that one-day these nanotubes will be utilised in a variety of applications including use as interconnects in electronic devices. As these new structures have been discovered and microelectronic circuits have decreased in size and increased in complexity, the need for new techniques, capable of fabricating and characterising structures with nanometre precision at specific locations has also increased. One such technique, which is attracting considerable attention, is electron beam induced deposition, because it is a direct-write or maskless procedure with a simple manufacturing process that can be used with a wide variety of materials. However, in order for it to be accepted as a mainstream technique it is necessary to first achieve a high degree of understanding and control of the process.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Nanotribology of metallic glasses in corrosive environments

Metallic glasses (MGs) are promising materials for micromechanical systems, where miniaturized components involving mechanical contact require control of friction. Nanotribological experiments on MGs in corrosive aqueous solutions are carried out using atomic force microscopy (AFM), focusing on the role of surface oxide films formed during corrosion. A new method is developed to study in situ the structure of surface oxide films. The surface oxide film has a bilayer structure as revealed by repeated scanning with the AFM tip. The dependence of friction on electrochemical potential reveals the growth mechanism of the oxide film. Friction and adhesion after different immersion times in different solutions allow to compare the physicochemical processes of surface dissolution at the interfaces of the two layers of surface films and elucidate their influence on friction. An irregular atomic-scale stick-slip friction is observed and attributed to the amorphous nature of corroded surfaces. Finally, we show three different friction processes occurring at increasing normal loads: removal of the dissolution layer at low-load regime; stress-assisted tribo-oxidation in intermediate-load regime; and tribochemical wear in high-load regime. The chemical sensitivity of nanotribology studies demonstrates a novel route to explore fundamental mechanisms of corrosion at the microscopic scale.Metallische Gläser (MG) sind vielversprechende Materialien für mikromechanische Systeme, in denen der mechanische Kontakt eine Kontrolle über Reibung erfordert. Mit Hilfe der Rasterkraftmikroskopie (AFM) wurden nanotribologische Experimente auf MG in korrosiven wässrigen Lösungen durchgeführt, wobei die Rolle von Oxidfilmen im Fokus stand. Eine neuartige Methode für die in situ-Untersuchung der Struktur der Oberflächenoxidfilme wurde entwickelt. Der Oberflächenoxidfilm weist eine zweilagige Struktur auf, die durch wiederholtes Rastern mit der AFM-Spitze nachgewiesen wurde. Die Abhängigkeit der Reibung vom elektrochemischen Potential zeigt die Wachstumsmechanismen der Oxidfilme an. Reibung und Adhäsion nach verschieden langer Immersion erlauben den Vergleich der physikochemischen Prozesse der Oberflächenauflösung an der Grenzfläche der beiden Lagen. Es wurde eine unregelmäßige stick-slip Reibung auf atomarer Skala beobachtet und auf die amorphe Natur der korrodierten Oberflächen zurückgeführt. Schließlich beschreiben wir drei verschiedene Reibungsprozesse, die mit zunehmender Normalkraft auftreten: die Abtragung der abgeschiedenen Lage bei niedrigen Auflagekräften, eine durch mechanische Spannung unterstützte Tribo-Oxidation bei mittleren Kräften sowie tribochemischen Verschleiß bei hohen Kräften. Die chemische Empfindlichkeit der nanotribologischen Studien zeigt eine neue Möglichkeit auf, grundsätzliche Mechanismen der Korrosion auf der mikroskopischen Skala zu erforschen