No description available.

No description available.

Complete understanding of the physics underlying the changes in viscoelasticity, relaxation time, and phase transitions that mesoscopic fluid-like systems undergo at solid-liquid interfaces or under confinement remains one of the major challenges in condensed matter physics. Moreover, studies of confined mesoscopic fluid films are relevant to technological areas like adhesion, wetting processes and nanotribology. This thesis addresses the interaction between two sliding solids interfaces separated by a nanometer sized gap, with emphasis on the role of the mesoscopic fluid film trapped between them. For this purpose we integrated two acoustic techniques, recently introduced by our group, into a sub-nanometer precision and thermal drift corrected scanning probe microscope (SPM): the shear-force/acoustic near-field Microscope (SANM) and the whispering gallery acoustic sensing (WGAS). The SANM monitors the sound waves originating in the probe-layer interaction while the motion of the probe is monitored by the WGAS. Additionally, we decouple the interaction forces by using frequency modulation and measure the local tunneling current to help establish the location of the substrate. Our results show a strong correlation between the elastic component of the probe's interaction and the SANM amplitude, as well as between the phase lag response of the fluid relative to the probe's excitation (represented by the SANM phase) and the onset of the probe-sample contact region. Frequency modulation SANM-WGAS brings a new acoustic sensing mechanism to the challenging characterization of fluid-like physical systems at the nanometer scale.

<p>The work presented in this thesis concernes two sorts of nanostructures: energetic-ion-impact-induced surface tracks and gas-deposited WO₃ nanoparticles. Our aims to characterise these nanostuctures and understand the physical principles behind their formation are of general interests for basic science as well as of the field of nanotechnology.</p><p>AFM studies of irradiated organic surfaces showed that individual ion impacts generate craters, most often accompanied by raised plastically deformed regions. Crater sizes were measured as a function of ion stopping power and incidence angle on various surfaces. Observed crater volumes were converted into estimates of total sputtering yields, which in turn were correlated with data from collector experiments. The observations were compared to predictions of theoretical sputtering models. The observed plastic deformations above grazing-incidence-ion penetration paths agree with predictions of the pressure pulse model. However, closer to the ion track, evaporative sputtering can occur.</p><p>AFM images of gas-deposited WO₃ nanoparticle-films indicated the formation of agglomerates. The size distribution of the agglomerates was measured to be log-normal, <i>i.e.</i> similar to the size distribution of the gas-phase nanoparticles forming the deposit. By simulations we could relatively well reproduce this observation. The agglomerates exhibited high thermal stability below 250°C when considering their size, implying that these porous films can be useful in applications involving elevated temperatures in the 250°C range. The appearance of the nanoparticles in the tapping-mode AFM images was sensitive to the free amplitude of the oscillating tip. We could show by model calculations that the high adhesion between the tip and the sample could account for some of these observations.</p>

The work presented in this thesis concernes two sorts of nanostructures: energetic-ion-impact-induced surface tracks and gas-deposited WO3 nanoparticles. Our aims to characterise these nanostuctures and understand the physical principles behind their formation are of general interests for basic science as well as of the field of nanotechnology. AFM studies of irradiated organic surfaces showed that individual ion impacts generate craters, most often accompanied by raised plastically deformed regions. Crater sizes were measured as a function of ion stopping power and incidence angle on various surfaces. Observed crater volumes were converted into estimates of total sputtering yields, which in turn were correlated with data from collector experiments. The observations were compared to predictions of theoretical sputtering models. The observed plastic deformations above grazing-incidence-ion penetration paths agree with predictions of the pressure pulse model. However, closer to the ion track, evaporative sputtering can occur. AFM images of gas-deposited WO3 nanoparticle-films indicated the formation of agglomerates. The size distribution of the agglomerates was measured to be log-normal, i.e. similar to the size distribution of the gas-phase nanoparticles forming the deposit. By simulations we could relatively well reproduce this observation. The agglomerates exhibited high thermal stability below 250°C when considering their size, implying that these porous films can be useful in applications involving elevated temperatures in the 250°C range. The appearance of the nanoparticles in the tapping-mode AFM images was sensitive to the free amplitude of the oscillating tip. We could show by model calculations that the high adhesion between the tip and the sample could account for some of these observations.

Combined atomic force microscopy-scanning electrochemical microscopy (AFM-SECM) is capable of providing simultaneous topographical and electrochemical imaging at sample surfaces. Integration of amperometric biosensors at tip-integrated electrodes recessed from the apex of the AFM tip further enhances the versatility of such bifunctional probes. Of particular interest to this work was the detection of adenosine triphosphate (ATP) at a cellular level, since ATP is involved in many biologically relevant processes. There are challenges concerning the integration of biosensors into bifunctional AFM-SECM probes. This thesis focuses on addressing and advancing several of these limitations. Thin insulation layers are important for AFM-SECM based applications to enhance AFM and SECM performance. Plasma-polymerized fluorocarbon membranes are introduced as novel thin film insulation materials for AFM-SECM probes. Insulation layers with a thickness of < 300 nm were found to exhibit excellent insulating properties and satisfying temporal stability for successful application in AFM-SECM experiments. Furthermore new approaches for increasing the electrode area in conventionally focused ion beam (FIB) fabricated AFM-SECM probes were implemented, since enhancement of the current response in conjunction with biosensing experiments is required. Ion beam induced deposition (IBID) was used to generate platinum carbon (PtC) deposits at AFM-SECM probes, thereby successfully increasing the tip-integrated electrode area. PtC composites were thoroughly characterized in terms of their physical and electrochemical properties. Since a high carbon fraction in the PtC composite was inhibiting the charge transfer kinetics at the electrode surface for certain analytes, several pre-treatment strategies were investigated including annealing, UV/ozone treatment, and FIB milling. FIB milling proved to be the most promising procedure improving charge transfer properties at the electrode along with fabrication compatibility at AFM-SECM probes. The last part of this thesis aimed at providing fundamental studies on AFM-SECM application at live epithelial cell monolayers. AFM was used in different imaging modes to characterize the topography of epithelial cells. ATP detection at epithelial cells was achieved with amperometric biosensors combined with non-invasive SECM. Biosensors were further miniaturized at batch-fabricated AFM-SECM probes enabling laterally-resolved detection of ATP at epithelial cells. Additionally, PtC composite materials were evaluated for applicability as transducer platforms for enzymatic biosensors.

This dissertation focuses on quantitative subsurface and mechanical properties imaging potential of AFM probes. Extensive modeling of AFM probes are presented for thorough understanding of capabilities and limitations of current techniques, these models are verified by various experiments, and different methods are developed by utilizing force-sensing integrated read-out active tip (FIRAT), which is an active AFM probe with broad bandwidth. For quantitative subsurface imaging, a 3-D FEA model of AFM tip-sample contact is developed and this model can simulate AFM tip scan on nanoscale-sized buried structures. FIRAT probe, which is active and broadband, is utilized for interaction forces imaging during intermittent contact mode and mechanical characterization capability of this probe is investigated. It is shown that probe dynamics, stiffness, stiffness ambiguity, assumed contact mechanics, and noise are important parameters for the accuracy of mechanical properties imaging. An active tip control mechanism is introduced to limit contact forces during intermittent contact mode. In addition to these, a combined ultrasonic AFM and interaction forces imaging method is developed and modeled to solve the reduced elasticity measurement sensitivity on composite materials. This method is capable of imaging a broader range of elasticity on combination samples such as metal nanoparticles in polymers at nanoscale.

Scanning probe microscopes (SPMs) are the highest resolution imaging instruments available today and are among the most important tools in nanoscience. Conventional SPMs suffer from several drawbacks owing to their large and bulky construction and to the use of piezoelectric materials. Large scanners have low resonant frequencies that limit their achievable imaging bandwidth and render them susceptible to disturbance from ambient vibrations. Array approaches have been used to alleviate the bandwidth bottleneck; however as arrays are scaled upwards, the scanning speed must decline to accommodate larger payloads. In addition, the long mechanical path from the tip to the sample contributes thermal drift. Furthermore, intrinsic properties of piezoelectric materials result in creep and hysteresis, which contribute to image distortion. The tip-sample interaction signals are often measured with optical configurations that require large free-space paths, are cumbersome to align, and add to the high cost of state-of-the-art SPM systems. These shortcomings have stifled the widespread adoption of SPMs by the nanometrology community. Tiny, inexpensive, fast, stable and independent SPMs that do not incur bandwidth penalties upon array scaling would therefore be most welcome. The present research demonstrates, for the first time, that all of the mechanical and electrical components that are required for the SPM to capture an image can be scaled and integrated onto a single CMOS chip. Principles of microsystem design are applied to produce single-chip instruments that acquire images of underlying samples on their own, without the need for off-chip scanners or sensors. Furthermore, it is shown that the instruments enjoy a multitude of performance benefits that stem from CMOS-MEMS integration and volumetric scaling of scanners by a factor of 1 million. This dissertation details the design, fabrication and imaging results of the first single-chip contact-mode AFMs, with integrated piezoresistive strain sensing cantilevers and scanning in three degrees-of-freedom (DOFs). Static AFMs and quasi-static AFMs are both reported. This work also includes the development, fabrication and imaging results of the first single-chip dynamic AFMs, with integrated flexural resonant cantilevers and 3 DOF scanning. Single-chip Amplitude Modulation AFMs (AM-AFMs) and Frequency Modulation AFMs (FM-AFMs) are both shown to be capable of imaging samples without the need for any off-chip sensors or actuators. A method to increase the quality factor (Q-factor) of flexural resonators is introduced. The method relies on an internal energy pumping mechanism that is based on the interplay between electrical, mechanical, and thermal effects. To the best of the author???s knowledge, the devices that are designed to harness these effects possess the highest electromechanical Qs reported for flexural resonators operating in air; electrically measured Q is enhanced from ~50 to ~50,000 in one exemplary device. A physical explanation for the underlying mechanism is proposed. The design, fabrication, imaging, and tip-based lithographic patterning with the first single-chip Scanning Thermal Microscopes (SThMs) are also presented. In addition to 3 DOF scanning, these devices possess integrated, thermally isolated temperature sensors to detect heat transfer in the tip-sample region. Imaging is reported with thermocouple-based devices and patterning is reported with resistive heater/sensors. An ???isothermal electrothermal scanner??? is designed and fabricated, and a method to operate it is detailed. The mechanism, based on electrothermal actuation, maintains a constant temperature in a central location while positioning a payload over a range of >35??m, thereby suppressing the deleterious thermal crosstalk effects that have thus far plagued thermally actuated devices with integrated sensors. In the thesis, models are developed to guide the design of single-chip SPMs and to provide an interpretation of experimental results. The modelling efforts include lumped element model development for each component of single-chip SPMs in the electrical, thermal and mechanical domains. In addition, noise models are developed for various components of the instruments, including temperature-based position sensors, piezoresistive cantilevers, and digitally controlled positioning devices.

No description available.

Nanostructuring functional materials can lead to a variety of enhanced intrinsic material properties. In particular, nanowires (NWs) have large surface-to-volume ratio and large aspect ratio (length / diameter), which makes them sensitive to low-amplitude vibrations and have increased flexibility compared to the bulk form of the material. In this thesis, piezoelectric, ferroelectric, ferromagnetic and magnetoelectric (ME) NWs have been explored in the context of vibrational energy harvesting and magnetic energy harvesting and sensing; because of their increased piezoelectric coefficients and ME coupling compared to bulk. Low-temperature, solution-processable and hence scalable fabrication techniques have been used throughout this work. Electrochemical deposition or electrodeposition (ED) in conjunction with nanoporous templates i.e. template-assisted electrodeposition (TAED) have been used to grow piezoelectric zinc oxide (ZnO) and ferromagnetic nickel (Ni) NWs and three template-wetting based techniques have been used to grow ferroelectric poly(vinylidene fluoride trifluoroethylene) (P(VDF-TrFE)) NWs and nanotubes (NTs). Both techniques have been optimised and subsequently combined to synthesise core-shell or (1-1) Ni - P(VDF-TrFE) composite NWs. The structural and crystalline properties of each type of nanostructure has been studied using a variety of techniques including: scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD) and transmission electron microscopy (TEM) and all of the NWs have been shown to be polycrystalline. The energy harvesting performance of vertically aligned ZnO NW arrays embedded in flexible, polycarbonate (PC) templates when incorporated into a flexible nanocomposite nanogenerator (NG), has been tested via periodic impacting and flexing of the NG at different frequencies. The voltage ($V$), current ($I$) and power were recorded during testing and measured across a range of external load resistances. The aligned nature of the embedded NWs ensures good piezoelectric performance across the entire device under impacting, while the PC template ensures mechanical stability and longevity of the device, confirmed by good fatigue performance over 24 hours of continuous testing, which is rarely studied in this field. The power density ($P_\mathrm{d}$) was found to be 151 mW m$^{-3}$ for low-amplitude (0.68 mm) and low-frequency (5 Hz) impacting, resulting in energy conversion efficiencies ($\chi$) and device efficiencies ($\chi$') of $\approx$ 4.2 \% and $\approx$ 3.76 x 10$^{-3}$ \% respectively. The nanoscale or surface piezoelectric charge coefficient ($d_{33}$) was measured to be $\approx$ 12.5 pm V$^{-1}$ on an individual ZnO NW, using a combination of Kelvin probe force microscopy (KPFM) and non--destructive piezoresponse force microscopy (ND-PFM). Both nanoscale and bulk ME measurements have been performed on Ni - P(VDF-TrFE) ME composite (1-1) NWs, nanocomposite (1-3) films and (2-2) laminates. The latter two structures have been fabricated using TAED and ED for the Ni NW and film respectively, in combination with drop-casting and spin-coating for the P(VDF-TrFE) films. The scanning probe microscopy (SPM) measurements used here include atomic force microscopy (AFM), KPFM, magnetic force microscopy (MFM) and piezoresponse force microscopy (PFM) and it has been found that the ME coupling in the (1-1) composites NWs is enhanced compared to the other structures, confirmed by approximating the converse ME coupling coefficient ($\alpha^\mathrm{C}$) of each composite. Additionally, vibrating sample magnetometry (VSM) has been used to confirm the ferromagnetic nature of the Ni phases in the composite structures. ME composite devices based on (2-2) and (1-3) composite materials and have been fabricated and preliminary bulk ME measurements of the ME coupling coefficient ($\alpha^\mathrm{E}$) plus energy harvesting measurements have also been performed as a proof of concept that the nanoscale ME coupling translates to the bulk, to some extent.