1,721,161 research outputs found
Robustness of attractors in tapping mode atomic force microscopy
Full text linkIn this work, we perform a comprehensive analysis of the robustness of attractors in tapping mode atomic force microscopy. The numerical model is based on cantilever dynamics driven in the Lennard–Jones potential. Pseudo-arc-length continuation and basins of attraction are utilized to obtain the frequency response and dynamical integrity of the attractors. The global bifurcation and response scenario maps for the system are developed by incorporating several local bifurcation loci in the excitation parameter space. Moreover, the map delineates various escape thresholds for different attractors present in the system. Our work unveils the properties of the cantilever oscillation in proximity to the sample surface, which is governed by the so-called in-contact attractor. The robustness of this attractor against operating parameters is quantified by means of integrity profiles. Our work provides a unique view into global dynamics in tapping mode atomic force microscopy and helps establishing an extended topological view of the system.Dynamics of Micro and Nano SystemsMicro and Nano Engineerin
Linear and non-linear vibrations of fluid-filled hollow microcantilevers interacting with small particles
No full textLinear and non-linear vibrations of a U-shaped hollow microcantilever beam filled with fluid and interacting with a small particle are investigated. The microfluidic device is assumed to be subjected to internal flowing fluid carrying a buoyant mass. The equations of motion are derived via extended Hamilton's principle and by using Euler-Bernoulli beam theory retaining geometric and inertial non-linearities. A reduced-order model is obtained applying Galerkin's method and solved by using a pseudo arc-length continuation and collocation scheme to perform bifurcation analysis and obtain frequency response curves. Direct time integration of the equations of motion has also been performed by using Adams-Moulton method to obtain time histories and analyze transient cantilever-particle interactions in depth. It is shown that exploiting near resonant non-linear behavior of the microcantilever could potentially yield enhanced sensor metrics. This is found to be due to the transitions that occur as a matter of particle movement near the saddle-node bifurcation points of the coupled system that lead to jumps between coexisting stable attractors.Accepted Author ManuscriptMicro and Nano Engineerin
Magnetic Self-Assembly with Unique Rotational Alignment
No full textThe majority of flexible electronics applications require integration of thin chips on low-cost polymer substrates, with a high volume manufacturing fashion. However, handling thin parts (below< 100?m) with contact-based micro-assembly techniques is challenging due to the strong adhesion forces at micro-scale. This situation slows down the traditional assembly methods, i.e. pick-and-place machines: In contact based placement, the chip is squeezed between the pick-and-place tool and the substrate and the force applied to release the chip, which should compensate the strong adhesion, might damage the delicate chip. This thesis focuses on developing a magnetic self-assembly method for high precision placement of parts with micro-scale thicknesses, i.e. ultra-thin chips (UTCs), without a direct mechanical contact. The chips are manipulated by the magnetic interactions between an externally applied magnetic field and nickel contact pads present on the chips. The method enables aligning the chips into a unique rotation by using shape matching between the asymmetric arrangement of nickel features on the chip and the gradient in the applied field.Precision and Microsystems EngineeringMechanical, Maritime and Materials Engineerin
Experimental Investigation of Adhesion and Friction Phenomena of Ultrananocrystalline Diamond (UNCD) and Aluminum Oxide in MEMS
No full textThis thesis aims to provide the latest progresses on the experimental investigation of friction and adhesion phenomena, occurring at the nanoscale in microelectromechanical systems (MEMS). I have studied and characterized the interaction between MEMS sidewalls in contact and sliding one onto another. Ultrananocrystalline diamond (UNCD) and aluminum oxide have been tested and utilized for the fabrication and integration process in MEMS micro-tribotesters. The results of this research are new in the field of nanotribology, and interesting for the development of micro-devices that can allow sliding surfaces in their operations.Micro and Nano EngineeringMechanical, Maritime and Materials Engineerin
Developing and Analysing sub-10 µm Fluidic Systems with Integrated Electrodes for Pumping and Sensing in Nanotechnology Applications
No full textIn this thesis, sub-10 µm fluidic systems with integrated electrodes for pumping and sensing in nanotechnology applications were developed and analyzed. This work contributes to the development of the scanning ion pipette (SIP), a tool to investigate surface changes on the nanometer scale induced by locally administering chemically or bio-active solutions. For this purpose, the already existing technology of a micropipette integrated into a scanning force microscope (SFM)-chip was enhanced by the use of electrodes for on-chip electrochemical sensing and electroosmotic (EO) pumping. The integration of an EO pump offered the possibility of storing, selecting and dispensing multiple different liquids with the SIP chip. For a high density and convenient electronic integration, an EO pump with a small footprint (less than 100 µm × 100 µm) and low actuation voltage (less than 10 V) had to be developed. The thesis starts with a detailed analysis of the microfabrication process to build the SIP’s network of capillaries, the freestanding cantilever and the tip. The fabrication was based on standard micromachining, from well established MEMS processes. The main innovation, previously developed by Hug et al., was to outline the capillaries of the fluidic system, the cantilever and the tip in one wafer, and fabricating the fluidic through wafer connections and the SIP chip outline in another wafer. By bonding the two wafers together, the former trenches were capped and by a subsequent high temperature oxidation, the hydrophilic silicon dioxide (SiO2) capillaries were formed. Afterwards, the buried fluidic system and the cantilever were released, providing optical access to the capillaries. Finally, the outlet hole was drilled next to the tip apex with a focussed ion beam. This SIP fabrication process was highly versatile with regards to the capillary geometry, allowing the design of a complex capillary geometry for a multifunctional microfluidic system. To obtain a first experience with these small capillary dimensions, the integration of an evaporation based micropump into the SIP was investigated. Its actuation did not require any electrodes and hence, it could be directly implemented into the SIP fabrication process, without any additional fabrications steps. The working principle of an evaporation based micropump is as follows: The hydrophilic capillaries of the SIP were spontaneously filled with a water based solution. Once the fluid reached the capillary outlet inside, it started evaporating. The capillary pressure kept the outlet of the capillaries wetted, and thereby, automatically replaced the evaporation loss by drawing additional water through the capillaries. This resulted in a unidirectional pump, which could be controlled by the temperature at the evaporation area. The evaporation induced flowrate was experimentally determined to range from 7 pl·s-1 at 23° C up to 53 pl·s-1 at 65° C depending exponentially on the temperature. A more advanced bidirectional EO pump with platinum (Pt) electrodes, based on a simplified fabrication process, resulting in comparable SIP capillary dimensions, was experimentally analyzed and modelled. The current-coupling between the Pt electrodes and the solution required a SIP specific on-chip design to ventilate the emerging electrolyzed gases. This was achieved by integrating the electrodes into a novel liquid-gas (LG) separator. The LG-separator separated the gas bubbles from the liquid and guided them away from the EO pump. Its operation principle is solely based on the LG-separator’s geometry of tapered sidewalls, taking advantage of the high capillary pressure occurring at the bubble’s liquid gas interfaces at this small scale. The LG-separator was experimentally analyzed and modelled. In the experimental analysis, the maximum backpressure of the LG-separator was determined to be 0.6 kPa. It was able to reliably separate and ventilate an emerging gas flow of 2 pl·s-1. For a deeper understanding, the development and the propagation of the bubble within the LG-separator was analytically described in three dimensions. The model and the derived design guidelines show that Pt electrodes, combined with the LG-separator, open an interesting new field for complex high density electrohydrodynamic and electrochemical microfluidic applications. A microfluidic system, containing two LG-separators sandwiching an EO pump, was also analyzed and modelled. The EO pump achieved a flow rate of 50 pl·s-1 at a low actuation voltage of 5 V. The developed corresponding model of the flows within the fluidic system was in good agreement with the measured values. According to the model, an EO pump with a high backpressure (3.6 kPa·V-1) enabling a high dispensing flowrate of 1.5 pl·V-1·s-1 (corresponding to a SIP immersed in water, outlet hole radius of 100 nm) can be built. The performance and integration of a second type of electrodes, based on silver/silver chloride (Ag/AgCl), into the SIP was investigated. These electrodes had the outstanding advantage that during electrode actuation the electrochemical reaction continued to transform Ag into AgCl and vice versa, rather than electrolyzing the liquid. Moreover, these electrodes could be integrated in a post SIP capillary fabrication step, circumventing electrode instability caused by the high temperature oxidation step to form the SiO2 of the capillary sidewalls. The general processflow to integrate the Ag/AgCl electrodes into the fabricated SIP capillary fabrication step was: The adhesion of the Ag electrode to the SiO2 capillary sidewall was improved by using an intermediate polymeric layer consisting of 3-mercaptopropylmethyldimethoxy silane (MPS). This silanization step turned out to be essential for reliably stable Ag electrodes in a capillary dimension of less than 10 µm, since the strong capillary force tended to delaminate the electrode. Crucial for a successful silanization was the use of a gas phase deposition on a dehydrated surface, to avoid the formation of polymeric MPS globuly. Electroless deposition provided a highly flexible and unique tool to deposit the electrodes in the closed SIP capillaries. The general idea was to fill a solution of Ag ions, as well as a reducing agent into the capillary. During the electrochemical reaction, the Ag electrodes started to grow on the capillary sidewall. The deposition of thick electrodes was required since during the electrode actuation, either Ag or AgCl was continuously consumed. This deposition of thick electrodes was especially challenging due to a minute available capillary volume, hence high concentrations within the electroless solution were used. The best electroless deposition process control was achieved with an improved Tollens solution and the reaction speed was controlled with the sodium citrate concentration (decrease) and the sodium hydroxide concentration (increase). Two different methods of electroless deposition were employed: First, a batch-like dip process of multiple electroless depositions, and second, a single electrode flow deposition process providing continuously fresh electroless solution. The electrode structuring was performed by controlling the capillary filling of the electroless solution within the fluidic system by microfluidic stopvalves. The stopvalve functionality was twofold, the solution was reliably stopped during the electroless deposition and afterwards the stopvalve was void free filled to ensure correct fluidic actuation of the final device. This should be done preferably without applying any external pressure. The switching from stopping to transmitting the solution was induced by a change in the solution’s surface tension. The stopvalve performance was modelled by improving the previously two dimensional model to three dimensions including, additionally, the design fabrication specific corner rounding and low capillary cross section’s aspect ratio. After the electroless deposition and structuring, the Ag electrode was further transformed into an Ag/AgCl electrode. Similarly to the electroless Ag deposition, the electrode transformation was performed with a flow of either sodium hypochloride or ferric(III) chloride. The transformation should be limited to 20% of the initial Ag layer thickness, due to stress related electrode delamination or cracking, originating in the density difference of Ag and AgCl. Interestingly, the electrochemical transformation process from Ag into AgCl could be described by the Deal-Grove model for the oxidation of silicon. The growth of AgCl depended nonlinearly on electrochemical reaction time. After an AgCl thickness of about 40 nm, the electrochemical reaction was dominated by the diffusion of the oxidizing species through an increasing layer of AgCl. Electrodes were deposited into three different capillaries: a) into the SIP capillary itself (cross section 2.2 µm × 3.7 µm), b) for larger availability and easier accessibility, into commercially available round capillaries (radius up to 520 µm), and c) a polymeric microfluidic system with rectangular capillaries (cross section 55 µm × 65 µm). Inside the SIP, the functionality of the microfluidic stopvalve was experimentally verified, a binary solution of 20% ethanol in water (contact angle 82°) was stopped and a binary solution of 40% ethanol in water (contact angle 58°) filled the stopvalve void free. In addition, a successful dip electroless deposition and stopvalve structuring of Ag electrodes was shown. Inside round capillaries, multiple electroless depositions revealed that each deposition increased the Ag layer thickness of 51 nm. The deposited Ag layer had a high specific conductivity of 6 × 107 S·m-1, indicating a high purity and density. The further transformation into Ag/AgCl provided electrodes to electrochemically measure different pH values. A linear pH sensitivity of 57.4 mV·pH-1 at 22.7° C with a good agreement of Nernstian behavior was reached. During these experiments, it turned out that the electroless Ag deposition was highly contamination sensitive which was strongly enhanced by the small capillary cross section. Therefore, the deposition into the polymeric fluidic system was performed with a flow of electroless solution instead of previously used multiple depositions. Despite the individual electrode deposition, the flow deposition had the advantage that the concentration could be kept constant throughout the capillary during the complete deposition time. This provided a better reaction control due to a lower concentration and in addition, it reduced the effect of the minute available capillary volume. The EO pump inside the polymeric fluidic system had an experimentally determined pump rate of 0.12 nl·s-1·V-1. First, experiments with the SIP for imaging and dispensing were performed. In order to get a first hand-on experience, a less delicate sample, in less challenging conditions, was chosen, then anticipated for the expected SIP imaging of a living cell. The imaging capabilities were illustrated by imaging in tapping mode a fixed and dried Escherichia Coli bacteria. The obtained images had a reasonable image quality and resolution. Moreover, no special skills in handling the SFM were required, since it did not perform differently with a mounted SIP than with a mounted standard commercially available SFM. In case of dispensing, with an externally applied pressure, the development of a bubble at the outlet hole of the tip was observed. With the currently used method of gluing the SIP to the SFM holder, no satisfying and reliable mounting was achieved. The main reasons of failure were leakage afflicted sealing between the SIP and the SFM holder, contamination of the SIP capillaries and finally breaking of the SIP cantilever during the complex and lengthy mounting procedure. This, again, shows the necessity of improving SIP techniques towards autonomous on-chip fluid handling.PMEMechanical, Maritime and Materials Engineerin
Mode Coupling in Dynamic Atomic Force Microscopy
Full text linkIncreasing the signal-to-noise ratio in dynamic atomic force microscopy plays a key role in nanomechanical mapping of materials with atomic resolution. In this work, we develop an experimental procedure for increasing the sensitivity of higher harmonics of an atomic-force-microscope cantilever without modifying the cantilever geometry but instead by utilizing dynamical mode coupling between its flexural modes of vibration. We perform experiments on different cantilevers and samples and observe that via nonlinear resonance frequency tuning we can obtain a frequency range where strong modal interactions lead to 7-fold and 16-fold increases in the sensitivity of the 6th and 17th harmonics while reducing sample indentation. We derive a numerical model that captures the observed physics and confirms that nonlinear mode coupling is the reason for the increase of the amplitude of higher harmonics during tip-sample interactions
Sub-micrometer accurate passive alignment of photonic chips - Submicrometer nauwkeurige passieve uitlijning van fotonische chips
No full textPrecision and Microsystems EngineeringMechanical, Maritime and Materials Engineerin
Development of Nanotools for Applications in (sub-)Femtofluidics and Graphene Technologies
No full textProperties of matter at the nano-scale may be very different from the ones observed at the macro-scale. The continuous variation of characteristics with diminishing size results in relevant changes in behavior. Similarly, these changes are caused by the rise of completely new phenomena (i.e. quantum confinement). Nanoscience can offer an unprecedented understanding about materials and nanotechnology can be used to exploit that understanding in order to generate devices that are likely to impact many fields. By using structure at nanoscale as a tunable physical parameter, we can greatly increase the range of performance of existing materials. Overall, nanoengineering could impact the production of virtually every object for all types of applications – from electronics to optical devices, advanced diagnostics, surgery, genetics, energy conservation and hydrogen separation. However, to achieve the intended applications we first have to understand how to manipulate diverse matter at such scale. This goal requires new knowledge and new approaches. Consequently, designed and controlled fabrication and integration of nanotools and nanodevices is likely to be revolutionary for science and technology. Currently, having the proper micro-instruments and nano-tools is the bottleneck for the full industrialization of the nanotechnology. Therefore, this thesis aims at developing new tools that would represent a step forward towards novel applications. In particular, our efforts were allocated to the design, fabrication and characterization of two different nanotools: the atomic force microscope-femtopipette and the MEMS-based in-plane tensile device. On one side, the femtopipette consists of a transparent hollow microfluidic cantilever with a nanometer scale aperture on the wall of the hollow tip. It is a multifunctional device that can weigh, image and locally dispense/aspirate liquids in the (sub)femtoliter regime. We envisage this tool will find applications to locally functionalize nanoscale devices, trafficking molecules across a living cell and micro/nano droplet arrays for diagnostics. Furthermore, we show that the femtopipette can be used to enable local dispensing and controlled synthesis of metallic nanoparticles, which could represent the pioneering results for eventual 3D nanomanufacturing. On the other side, theoretical calculations have predicted that extreme strains (>10%) in graphene would result in novel applications. However, before this work the highest reported strain reached 1.3%. Here, we demonstrate uniaxial strains >10% by pulling graphene using a MEMS-based in-plane tensile device. To prevent the graphene from slipping away during stretching, it was locally clamped with epoxy glue applied by the femtopipette. The results were analyzed using Raman spectroscopy and optical tracking. Furthermore, analysis proved the process to be reversible and nondestructive for the graphene.Precision and Microsystems EngineeringMechanical, Maritime and Materials Engineerin
Nonlinear dynamics for estimating the tip radius in atomic force microscopy
No full textThe accuracy of measurements in Amplitude Modulation Atomic Force Microscopy (AFM) is directly related to the geometry of the tip. The AFM tip is characterized by its radius of curvature, which could suffer from alterations due to repetitive mechanical contact with the surface. An estimation of the tip change would allow the user to assess the quality during imaging. In this work, we introduce a method for tip radius evaluation based on the nonlinear dynamic response of the AFM cantilever. A nonlinear fitting procedure is used to match several curves with softening nonlinearity in the noncontact regime. By performing measurements in this regime, we are able to maximize the influence of the tip radius on the AFM probe response, and this can be exploited to estimate with good accuracy the AFM tip radius.Micro and Nano EngineeringDynamics of Micro and Nano System
Product-internal assembly functions: A novel micro-assembly concept applied to optical interconnects
No full textIn this project, the technical feasibility of a novel assembly concept was explored, in which microsystem-based self-assembly functionality is added to an existing product. The case considered is the accurate alignment of an optical fibre relative to a telecommunication laser source. In the most demanding cases this requires alignment accuracies down to 0.1 µm to achieve adequate optical coupling. This is very difficult to achieve using conventional assembly, making the assembly cost up to 50 - 80% of the overall device cost. Project goal was to develop a chip for aligning and fixing the fibre using microsystem technology (MST), comprising lithography-based techniques from the integrated circuit domain for selectively depositing and removing material on wafers. Advantages of this technology are the high attainable accuracies and the potential of batch-wise fabrication. Two functionalities were developed: 2-D positioning and clamping. Positioning of the fibre is achieved by two oblique contact surfaces, which can each be moved by a thermal V-shaped silicon actuator. Fibre tip displacements in a diamond shaped positioning window of over 25 by 40 µm were demonstrated with positioning resolutions smaller than 0.1 µm. When the fibre position is correct, which is determined by measuring the coupled light, it is fixed by an internal mechanical clamping device. Powering down both clamp and positioning actuators showed a fibre shift of less than 0.1 µm, thus reaching the target value for the project. Initial vibration measurements showed no additional position shifts, thereby demonstrating the stability of the system.Mechanical Maritime and Materials Engineerin
- …
