DEVELOPMENT OF A VERSATILE HIGH SPEED NANOMETER LEVEL SCANNING MULTI-PROBE MICROSCOPE

The motivation for development of a multi-probe scanning microscope, presented in this dissertation, is to provide a versatile measurement tool mainly targeted for biological studies, especially on the mechanical and structural properties of an intracellular system. This instrument provides a real-time, three-dimensional (3D) scanning capability. It is capable of operating on feedback from multiple probes, and has an interface for confocal photo-detection of fluorescence-based and single molecule imaging sensitivity. The instrument platform is called a Scanning Multi-Probe Microscope (SMPM) and enables 45 microm by 45 microm by 10 microm navigation of specimen with simultaneous optical and mechanical probing with each probe location being adjustable for collocation or for probing with known probe separations. The 3D positioning stage where the specimen locates was designed to have nanometer resolution and repeatability at 10 Hz scan speed with either open loop or closed loop operating modes. The fine motion of the stage is comprises three orthogonal flexures driven by piezoelectric actuators via a lever linkage. The flexures design is able to scan in larger range especially in z axis and serial connection of the stages helps to minimize the coupling between x, y and z axes. Closed-loop control was realized by the capacitance gauges attached to a rectangular block mounted to the underside of the fine stage upon which the specimen is mounted. The stage's performance was studied theoretically and verified by experimental test. In a step response test and using a simple proportional and integral (PI) controller, standard deviations of 1.9 nm 1.8 nm and 0.41 nm in the x, y and z axes were observed after settling times of 5 ms and 20 ms for the x and y axes. Scanning and imaging of biological specimen and artifact grating are presented to demonstrate the system operation. For faster, short range scanning, novel ultra-fast fiber scanning system was integrated into the xyz fine stage to achieve a super precision dual scanning system. The initial design enables nanometer positioning resolution and runs at 100 Hz scan speed. Both scanning systems are capable of characterization using dimensional metrology tools. Additionally, because the high-bandwidth, ultra-fast scanning system operates through a novel optical attenuating lever, it is physically separate from the longer range scanner and thereby does not introduce additional positioning noise. The dual scanner provides a fine scanning mechanism at relatively low speed and large imaging area using the xyz stage, and focus on a smaller area of interested in a high speed by the ultra-fast scanner easily. Such functionality is beneficial for researchers to study intracellular dynamic motion which requires high speed imaging. Finally, two high end displacement sensor systems, a knife edge sensor and fiber interferometer, were demonstrated as sensing solutions for potential feedback tools to boost the precision and resolution performance of the SMPM

A scanning tunneling microscope control system with potentiometric capability

Includes bibliographical references.This report starts by describing the background research and work that had already been done on the UCT scanning tunneling microscope (STM). This system is being developed in the Department of Electrical Engineering at UCT. It goes on to describe the continuation of the research work that was done for this dissertation on the STM at UCT. The work was originally started by Dr. Tapson for his PhD (1994). and continued by the author for his MTech degree in ) 997 and 1998. The work was temporary discontinued from May 2000 till August 2002 to enable the author to work as a contract engineer at the Institute of Physics in Basel, Switzerland to learn more about the construction of probe microscopes. The new work evolved around the need to implement scanning tunneling potentiometry (STP) capability in the new STM. This capability should give the end-user the capability of looking at the sub-surface structure of any material on a sub-micron scale. The basic STP function must be implemented in two dimensions in the plane of the specimen. The STM tip is then used as a highly localized voltmeter to sense what the potential distribution is at that point on the surface. The potential information that is obtained is then used to plot two images of the potential distribution over the surface in the X and Y directions. The topographic information is obtained in the usual way from the STM scan. This method gives three collocated imagesas the result and a better understanding of the surface structure is obtained in this way. The penetration depth of the potential scan can be varied by adjusting the frequency of the applied AC signal in the X and Y directions. This use of the skin effect should allow the end user to obtain slices of the surface at various penetration levels of the specimen. These slices will give a picture of what happens from the surface up to a certain penetration depth. The interpretation of these images could be very difficult because the skin effect does not stop at a defined penetration depth. Only the 3 dB point is defined, which means that sub surface structures below the 3 dB point will also have an influence on the obtained image. During the course of the research new hardware and scanning software was implemented to enable the error-free acquisition of new data. This entailed splitting the existing XY controller into three separate parts namely a Communications interface, and two STP measurement boards. This was suggested as one of the conclusions of the MTech thesis results. The PC software stayed the same but for a change in the array size, that holds theacquired data. This was again changed after the work experience in Basel and is explained in chapter 6

Improvement in the Imaging Performance of Atomic Force Microscopy: A Survey

Nanotechnology is the branch of science which deals with the manipulation of matters at an extremely high resolution down to the atomic level. In recent years, atomic force microscopy (AFM) has proven to be extremely versatile as an investigative tool in this field. The imaging performance of AFMs is hindered by: 1) the complex behavior of piezo materials, such as vibrations due to the lightly damped low-frequency resonant modes, inherent hysteresis, and creep nonlinearities; 2) the cross-coupling effect caused by the piezoelectric tube scanner (PTS); 3) the limited bandwidth of the probe; 4) the limitations of the conventional raster scanning method using a triangular reference signal; 5) the limited bandwidth of the proportional-integral controllers used in AFMs; 6) the offset, noise, and limited sensitivity of position sensors and photodetectors; and 7) the limited sampling rate of the AFM's measurement unit. Due to these limitations, an AFM has a high spatial but low temporal resolution, i.e., its imaging is slow, e.g., an image frame of a living cell takes up to 120 s, which means that rapid biological processes that occur in seconds cannot be studied using commercially available AFMs. There is a need to perform fast scans using an AFM with nanoscale accuracy. This paper presents a survey of the literature, presents an overview of a few emerging innovative solutions in AFM imaging, and proposes future research directions.This work was supported in part by the Australian Research Council (ARC) under Grant FL11010002 and Grant DP160101121 and the UNSW Canberra under a Rector's Visiting Fellowshi

Systems approach based solution to fundamental limitations in unraveling spatial and temporal regimes in nano-interrogation and nano-positioning

A design scheme that achieves an optimal tip-sample force regulation with an ideal topography image reconstruction is presented. It addresses the problem of obtaining accurate sample profiles when scanning at high bandwidth while maintaining a constant cantilever-tip sample force in atomic force microscopes. It is shown that the proposed scheme provides a faithful replica of the sample at all relevant scanning speeds limited only by the inaccuracy in the model for the atomic force microscope. This provides an improvement over existing designs where the sample profile reconstruction is typically bandwidth limited. The experimental results corroborate the theoretical development.;Conventional imaging signals such as the amplitude signal and the vertical piezoactuation signal cannot identify the areas of probe loss, where dynamic atomic force microscopy based image where the cantilever fails to be an effective probe of the sample. A real-time methodology is developed to determine regions of probe loss. It is experimentally demonstrated that probe-loss affected portion of the image can be unambiguously identified by a real-time signal called reliability index. Reliability index, apart from indicating the probe-loss affected regions, can be used to minimize probe-loss affected regions of the image, thus aiding high speed AFM applications.;A new immobilization technique for quantitative imaging and topographic characterization of living yeast cells in solid media using Atomic force microscope (AFM) is presented. Unlike previous techniques, proposed technique allows almost complete cell surface to be exposed to environment and studied using AFM. Apart from the new immobilization protocol, in this report, for the first time, high resolution height imaging of live yeast cell surface in intermittent contact mode is presented. High resolution imaging and significant improvement in operational stability facilitated investigation of growth patterns and evolution of surface morphology in quantitative terms. Growth rate of mother cell and budding cell showed distinct patterns over the imaging time

Modeling and Control of MEMS-based Multi-layered Prestressed Piezoelectric Cantilever Beam

Piezoelectric materials are the preferred smart materials for sensing and actuation in the form of micro and nano-engineering structures like beams and plates. Cantilever beams play a significant role as key components in atomic force microscopy and bio and chemical sensors. Adding an active layer such as lead zirconate titanate (PZT) thin-film to form smart cantilever beams with sensing and actuation capabilities is highly desirable to facilitate miniaturization, enhance performance and functionali- ties such as enabling on-chip high-speed parallel AFM. During the micro-fabrication process, residual stresses develop in the different layers of the cantilever beam, causes initial deflection. The residual stress in the different layers of the cantilever beam and the application of voltage to the PZT thin-film affects their dynamics. This the- sis investigates the dynamic behaviour and develops a control technique and a novel charge readout circuit to improve the performance of a micro-fabricated multi-layer prestressed piezoelectric cantilever beam as an actuator and a deflection sensor. Firstly, the fabrication process of a unimorph PZT cantilever beam is explained. A low thermal budget Ultra-high vacuum e-beam evaporated polysilicon thin-film (UHVEEpoly) process is used for the fabrication of multi-layered PZT cantilever beam in d31 mode. The sharp peaks at resonant frequencies in the frequency response of the PZT cantilever beam show very little damping and a large settling time of the cantilever beam. Secondly, the dynamic behaviour of the prestressed PZT cantilever beam is in- vestigated subjected to change in driving voltage. Experimental investigations show a shift in resonant frequencies of a PZT cantilever beam. However, there is no reported mathematical model that predicts the shift in resonance frequencies of a multi-layered prestressed piezoelectric cantilever beam subjected to a change in driving voltage. This work developed a mathematical model with experimental val- idation to estimate the shift in resonance frequencies of such cantilever beams with the change in the driving voltage. A very good agreement between the model predic- tions and experimental measurements for the frequency response of the cantilever beam at different driving voltages has been obtained. A novel linear formulation has been developed to predict the shift in resonance frequencies of the PZT can- i tilever beam for a wide range of driving voltages. The formulation shows that the shift in resonance frequencies of a multi-layered prestressed piezoelectric cantilever beam per unit of applied voltage is dependent on geometric parameters and material properties. Thirdly, a robust resonant controller has been designed and implemented to re- duce the settling time of a highly vibrating PZT cantilever beam. The controller design is based on a mixed negative-imaginary, passivity, and a small-gain approach. The motivation to design a resonant controller using the above-mentioned analyti- cal framework is its bandpass nature and the use of velocity feedback, as the charge collected from a vibrating PZT cantilever beam gives the velocity information of the beam. The proposed controller design results in finite gain stability for a pos- itive feedback interconnection between two stable linear systems with a large gain and phase margin. Experimental results demonstrate that the designed resonant controller is able to effectively damp the first resonant mode of a cantilever, signifi- cantly reducing settling time from 528 ms to 32 ms. The robustness of the designed resonant controller is tested against changes in the cantilever beam dynamics due to residual stress variation and or stress variation due to driving voltage. Finally, to facilitate the miniaturization of on-chip sensors and parallel high- speed AFM, a single layer of a PZT thin-film in a cantilever beam is used as a deflection sensor and an actuator instead of bulky optical deflection sensors. A novel charge readout circuit is designed for deflection sensing by capturing the electrical charge generated due to the vibration of the PZT beam. The signal-to-noise ratio and sensitivity analysis of the readout circuit shows similar results compared to the commercially available optical deflection sensors. Our work highlights very important aspects in the dynamic behaviour and perfor- mance of a multi-layered prestressed piezoelectric cantilever beam. The agreement between the proposed theoretical formulation and experimental investigations in modeling, control design, and a novel readout circuit will provide the platform for further the development and miniaturization of microcantilever-based technologies, including on-chip parallel HS-AFM

Advances in High-Speed Atomic Force Microscopy

High-speed atomic force microscopy (HS-AFM) is a scanning probe technique capable of recording processes at the nanometre scale in real time. By sequentially increasing the speed of individual microscope components, images of surfaces can be recorded at up to several images per second. We present a HS-AFM platform composed of custom¿built measurement head, controller and software, scanners and amplifiers that is shared with the community in an open¿hardware fashion. A new scanner design combined with an advanced control system is shown. The simple addition of a secondary actuator to widely available tube scanners increases the scan speed by over an order of magnitude while allowing for a 130 ¿m × 130 ¿m wide field of view, which is not possible with traditional high¿speed scanner designs. Controllers beyond standard proportional-integral controllers are capable of significantly increasing imaging speed by anticipating resonances. Such filters are cumbersome to design with conventional methods. It is shown how convex optimization can be used to design optimal controllers with guaranteed stability for atomic force microscopy in an automated fashion. By integrating two lasers into the small spot¿size optics of an AFM readout head we are able to use the first laser for detecting the deflection of the smallest, and thus fastest currently available high¿speed cantilevers, while using the second for photo¿thermal actuation. Using this instrument, we demonstrate multi¿frequency atomic force microscopy (MF-AFM) at previously not accessible frequencies of more than 20 MHz. By employing the driving laser not for resonant excitation as is usual in dynamic AFM, a new imaging mode, photothermal off-resonance tapping (PORT) is presented. By repeatedly thermally bending the cantilever below it¿s resonant frequency, the surface is probed at a rapid rate. The resulting force is extracted from the deflection of the cantilever in time¿ domain at real time and used for feedback and image generation. The dynamic and static force contributions in both PORT and state of the art high-speed amplitude modulation atomic force microscopy (AM-AFM) are measured and analyzed in detail. It is shown that by decoupling the driving frequency from the resonant frequency the dynamic tip¿sample impact forces can be drastically reduced when compared to resonance based AFM modes. SAS-6 is a centriolar scaffolding protein with a crucial role in the duplication of centrioles, which are the main microtubule organizing organelle of eukaryotic cells. Defects in centriole duplication are associated with cancer and microencephaly. To understand these defects, is therefore important to understand the kinetics of SAS-6. In¿vitro, SAS-6 polymerizes into rings of between eight and ten monomers. Using the new PORT mode we are able to study the dynamic assembly of SAS-6. It is shown how SAS-6 rings can not only assemble by canonical one-by-one addition, but can form as a fusion of larger, already assembled fragments. Finally, it is shown how PORT can be used to observe fast processes of and on living cells. The adhesion and detachment of thrombocyte cells is studied. Membrane disruptive effects are shown on gram¿negative as well as gram¿positive bacteria

High-speed atomic force microscopy for nano-visualization of dynamic biomolecular processes

金沢大学理工研究域数物科学系The atomic force microscope (AFM) has a unique capability of allowing the high-resolution imaging of biological samples on substratum surfaces in physiological solutions. Recent technological progress of AFM in biological research has resulted in remarkable improvements in both the imaging rate and the tip force acting on the sample. These improvements have enabled the direct visualization of dynamic structural changes and dynamic interactions occurring in individual biological macromolecules, which is currently not possible with other techniques. Therefore, high-speed AFM is expected to have a revolutionary impact on biological sciences. In addition, the recently achieved atomic-resolution in liquids will further expand the usefulness of AFM in biological research. In this article, we first describe the various capabilities required of AFM in biological sciences, which is followed by a detailed description of various devices and techniques developed for high-speed AFM and atomic-resolution in-liquid AFM. We then describe various imaging studies performed using our cutting-edge microscopes and their current capabilities as well as their limitations, and conclude by discussing the future prospects of AFM as an imaging tool in biological research. © 2008 Elsevier Ltd. All rights reserved

Transient force atomic force microscopy: systems approaches to emerging applications

In existing dynamic mode operation of Atomic Force Microscopes (AFMs) steady-state signals like amplitude and phase are used for detection and imaging of material. Due to the high quality factor of the cantilever probe the corresponding methods are inherently slow. In this dissertation, a novel methodology for fast interrogation of material that exploits the transient part of the cantilever motion is developed. This method effectively addresses the perceived fundamental limitation on bandwidth due to high quality factors. It is particularly suited for the detection of small time scale tip-sample interactions. Analysis and experiments show that the method results in significant increase in bandwidth and resolution as compared to the steady-state-based methods;In atomic force microscopy, bandwidth or resolution can be affected by active quality factor (Q) control. However, in existing methods the trade off between resolution and bandwidth remains inherent. Observer based Q control method provides greater flexibility in managing the tradeoff between resolution and bandwidth during imaging. It also facilitates theoretical analysis lacking in existing methods;In this dissertation we develop a method for exact constructive controllability of quantum-mechanical systems. The method has three steps, first a path from the initial state to the final state is determined and intermediate points chosen such that any two consecutive points are close, next small sinusoidal control signals are used to drive the system between the points, and finally quantum measurement technique is used to exactly achieve the desired state. The methodology is demonstrated for the control of spin-half particles in a Stern-Gerlach setting;In this dissertation, a novel closed-loop real-time scheduling algorithm is developed based on dynamic estimation of execution time of tasks based on both deadline miss ratio and task rejection ratio in the system. This approach is highly preferable for firm/soft real-time systems since it provides a firm performance guarantee in terms of high guarantee ratio. Proportional-integral controller and H-infinity controller are designed for closed loop scheduling. Simulation studies showed that closed-loop dynamic scheduling offers a better performance over the openloop scheduling under all the practical conditions

Advances in self-sensing techniques for atomic force microscopy

Atomic force microscope (AFM) is a tool that allows micro and nano scale imaging of samples ranging from solid state physics to biology. AFM uses mechanical forces to sense the sample and recreate a topography image with high spatial resolution. The biggest disadvantage of the standard AFMs is their scanning speed, as it typically takes up to several tens of minutes to capture an image. A lot of research was conducted to increase AFM scanning speed, which resulted in the development of high-speed AFMs (HS-AFMs), that can obtain an image in matter of seconds. Such increase in scanning speed enabled the study of various processes, ranging from functional mechanisms of proteins to cellular biology dynamics. Increasing the speed further, towards several tens of images per second would highly benefit many applications, from both material and life sciences. The imaging speed of an AFM is limited by the speed of its components. While scanners and electronic systems are constantly being improved, there exists a certain hold-up in the development of cantilevers and deflection sensing techniques. The mechanical bandwidth of the cantilever can be increased by decreasing its size. While it is possible to fabricate sub-micron sized cantilevers it becomes very challenging to sense their deflection. Standard AFMs rely on the optical beam deflection (OBD) readout, which can sense cantilevers down to 2 µm in width. Novel sensing techniques are needed to increase AFM imaging speed further. Strain-sensing techniques are particularly interesting as they offer many advantages over OBD readout, like the ability to sense sub-micron sized cantilevers. We investigated nanogranular tunneling resistors (NTRs) as strain-sensors for cantilever deflection sensing. With NTR ability to be deposited on various substrates and in arbitrary geometries, with lateral dimensions down to tens of nm and having reasonably high gauge factors, they are an interesting candidate for cantilever deflection sensing. We applied NTRs in AFM imaging for the first time, showing that their sensitivity is well suited for imaging of both solid state and biological samples. We also demonstrated that NTRs can be used for sensing of 500 nm wide cantilevers. We performed a study of doped Si piezoresistive strain sensors and of an unexploited potential which can be reached with the miniaturization of the cantilever dimensions. We demonstrated both theoretically and experimentally that by decreasing the size of the piezoresistive cantilevers, one can reach the AFM imaging noise performance equal or better than the noise performance of the OBD readout. We showed that piezoresistive cantilevers are very well suited for nm and Å scale imaging of both solid state and biological samples in air. In addition, we performed a research on an advancement of the AFM feedback controller. Most AFMs use digital signal processor (DSP) based feedback controllers. Digital implementation of the controller has some disadvantages, as it necessitates data converters which introduce additional delays in the feedback loop. We developed a fast digitally controlled analog proportional-integral-derivative (PID) controller. We successfully used this PID controller in AFM imaging, realizing several hundreds of Hz line rates. While the analog implementation of the controller provided large amplification and frequency bandwidth, digital control provided precise control of the system and reproducibility of parameter values

Modeling and Control of Piezoactive Micro and Nano Systems

Piezoelectrically-driven (piezoactive) systems such as nanopositioning platforms, scanning probe microscopes, and nanomechanical cantilever probes are advantageous devices enabling molecular-level imaging, manipulation, and characterization in disciplines ranging from materials science to physics and biology. Such emerging applications require precise modeling, control and manipulation of objects, components and subsystems ranging in sizes from few nanometers to micrometers. This dissertation presents a comprehensive modeling and control framework for piezoactive micro and nano systems utilized in various applications. The development of a precise memory-based hysteresis model for feedforward tracking as well as a Lyapunov-based robust-adaptive controller for feedback tracking control of nanopositioning stages are presented first. Although hysteresis is the most degrading factor in feedforward control, it can be effectively compensated through a robust feedback control design. Moreover, an adaptive controller can enhance the performance of closed-loop system that suffers from parametric uncertainties at high-frequency operations. Comparisons with the widely-used PID controller demonstrate the effectiveness of the proposed controller in tracking of high-frequency trajectories. The proposed controller is then implemented in a laser-free Atomic Force Microscopy (AFM) setup for high-speed and low-cost imaging of surfaces with micrometer and nanometer scale variations. It is demonstrated that the developed AFM is able to produce high-quality images at scanning frequencies up to 30 Hz, where a PID controller is unable to present acceptable results. To improve the control performance of piezoactive nanopositioning stages in tracking of time-varying trajectories with frequent stepped discontinuities, which is a common problem in SPM systems, a supervisory switching controller is designed and integrated with the proposed robust adaptive controller. The controller switches between two control modes, one mode tuned for stepped trajectory tracking and the other one tuned for continuous trajectory tracking. Switching conditions and compatibility conditions of the control inputs in switching instances are derived and analyzed. Experimental implementation of the proposed switching controller indicates significant improvements of control performance in tracking of time-varying discontinuous trajectories for which single-mode controllers yield undesirable results. Distributed-parameters modeling and control of rod-type solid-state actuators are then studied to enable accurate tracking control of piezoactive positioning systems in a wide frequency range including several resonant frequencies of system. Using the extended Hamilton\u27s principle, system partial differential equation of motion and its boundary conditions are derived. Standard vibration analysis techniques are utilized to formulate the truncated finite-mode state-space representation of the system. A new state-space controller is then proposed for asymptotic output tracking control of system. Integration of an optimal state-observer and a Lyapunov-based robust controller are presented and discussed to improve the practicability of the proposed framework. Simulation results demonstrate that distributed-parameters modeling and control is inevitable if ultra-high bandwidth tracking is desired. The last part of the dissertation, discusses new developments in modeling and system identification of piezoelectrically-driven Active Probes as advantageous nanomechanical cantilevers in various applications including tapping mode AFM and biomass sensors. Due to the discontinuous cross-section of Active Probes, a general framework is developed and presented for multiple-mode vibration analysis of system. Application in the precise pico-gram scale mass detection is then presented using frequency-shift method. This approach can benefit the characterization of DNA solutions or other biological species for medical applications