Fast spiral-scan atomic force microscopy

In this paper, we describe a new scanning technique for fast atomic force microscopy. In this method, the sample is scanned in a spiral pattern instead of the well established raster pattern. A spiral scan can be produced by applying single frequency cosine and sine signals with slowly varying amplitudes to the x -axis and y -axis of an atomic force microscope (AFM) scanner respectively. The use of the single tone input signals allows the scanner to move at high speeds without exciting the mechanical resonance of the device and with relatively small control efforts. Experimental results obtained by implementing this technique on a commercial AFM indicate that high-quality images can be generated at scan frequencies well beyond the raster scans

High-speed spiral imaging technique for an atomic force microscope using a linear quadratic Gaussian controller

This paper demonstrates a high-speed spiral imaging technique for an atomic force microscope (AFM). As an alternative to traditional raster scanning, an approach of gradient pulsing using a spiral line is implemented and spirals are generated by applying single-frequency cosine and sine waves of slowly varying amplitudes to the X and Y-axes of the AFM's piezoelectric tube scanner (PTS). Due to these single-frequency sinusoidal input signals, the scanning process can be faster than that of conventional raster scanning. A linear quadratic Gaussian controller is designed to track the reference sinusoid and a vibration compensator is combined to damp the resonant mode of the PTS. An internal model of the reference sinusoidal signal is included in the plant model and an integrator for the system error is introduced in the proposed control scheme. As a result, the phase error between the input and output sinusoids from the X and Y-PTSs is reduced. The spirals produced have particularly narrow-band frequency measures which change slowly over time, thereby making it possible for the scanner to achieve improved tracking and continuous high-speed scanning rather than being restricted to the back and forth motion of raster scanning. As part of the post-processing of the experimental data, a fifth-order Butterworth filter is used to filter noises in the signals emanating from the position sensors and a Gaussian image filter is used to filter the images. A comparison of images scanned using the proposed controller (spiral) and the AFM PI controller (raster) shows improvement in the scanning rate using the proposed method

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

Development of a XYZ scanner for home-made atomic force microscope based on FPAA control

Atomic force microscopy (AFM) is one of the useful tools in the fields of nanoscale measurement and manipulation. High speed scanning is one of the crucial requirements for live cell imaging and soft matter characterization. The scanning speed is limited by the bandwidth of the AFM’s detection and actuation components. Generally, the bandwidth of a traditional scanner is too low to conduct the live cell imaging. This paper presents a simple and integrated compact home-made AFM for high speed imaging. To improve the bandwidth of the scanner, a parallel kinematics mechanism driven by piezoelectric actuators (PZTs) is proposed for the fast positioning in the X, Y and Z directions. The mechanical design optimization, modeling and analysis, and experimental testing have been conducted to validate the performance of the proposed scanner. A number of experimental results showed that the developed scanner has the capability for broad bandwidth with low coupling errors in the actuation directions. A hybrid control strategy including feedforward and feedback loops has been designed to significantly improve the dynamic tracking performance of the scanner and a field programmable analog array (FPAA) system is utilized to implement the control algorithm for excellent and stable tracking capability. Further, a number of high speed measurements have been conducted to verify the performance of the developed AFM

Design and application of a data driven controller using the small-gain constraint for positioning control of a nano-positioner

In this paper, the design of a data driven controller using a small-gain theorem approach for improving the positioning accuracy of a piezoelectric tube scanner (PTS) is demonstrated. Open-loop frequency responses of both the X-PTS and Y-PTS are measured using a band-limited sweep sine signal and are used as primary data for this control design. The frequency response of the controllers is synthesized by the application of the small-gain theorem constraints over the entire frequency range for both the axes. The experimental implementation of this feedback data driven controller provides significant vibration reduction, with 19 dB and 15 dB damping at the resonance frequencies of the X and Y-axes of the PTS, respectively. A comparison between the open-loop and closed-loop tracking performance for triangular signals shows significant improvement up to the scanning frequency of 150 Hz. Moreover, the design of this data driven controller is less complex than conventional controller design methods as it does not need a system model.This work was supported by the Australian Research Council under grant DP160101121

Precision engineering center. 1988 Annual report, Volume VI

To reverse the downward trend in the balance of trade, American companies must concentrate on increasing research into new products, boosting productivity, and improving manufacturing processes. The Precision Engineering Center at North Carolina State University is a multidisciplinary research and graduate education program dedicated to providing the new technology necessary to respond to this challenge. One extremely demanding manufacturing area is the fabrication and assembly of optical systems. These systems are at the heart of such consumer products as cameras, lenses, copy machines, laser bar-code scanners, VCRs, and compact audio discs - products that the Japanese and other East Asian countries are building dominance. A second critical area is the fabrication of VLSI and ULSI circuits. The tolerances required to produce the next generation of components for such systems have created the need for new approaches - approaches that could either make or break America`s competitive position. This report contains individual reports on research projects grouped into three broad areas: measurement and actuation; real-time control; precision fabrication. Separate abstracts for these articles have been indexed into the energy database

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

Mechanical compression of coiled carbon nanotubes

Carbon nanotubes are molecular-scale tubes of graphitic carbon that possess many unique properties. They have high tensile strength and elastic modulus, are thermally and electrically conductive, and can be structurally modified using well established carbon chemistries. There is global interest in taking advantage of their unique combination of properties and using these interesting materials as components in nanoscale devices and composite materials. The goal of this research was the correlation of the mechanical properties of coiled carbon nanotubes with their chemical structure. Individual nanocoils, grown by chemical vapor deposition, were attached to scanning probe tip using the arc discharge method. Using a scanning probe microscope the nanocoils are repeatedly brought into and out of contact with a chemically-modified substrate. Precise control over the length (or area) of contact with the substrate is achievable through simultaneous monitoring the cantilever deflection resonance, and correlating these with scanner movement. The mechanical response of nanocoils depended upon the extent of their compression. Nonlinear response of the nanocoil was observed consistent with compression, buckling, and slip-stick motion of the nanocoil. The chemical structure of the nanocoil and its orientation on the tip was determined using scanning and transmission electron microscopy. The mechanical stiffness of eighteen different nanocoils was determined in three ways. In the first, the spring constant of each nanocoil was computed from the slope of the linear response region of the force-distance curve. The assumptions upon which this calculation is based are: 1) under compression, the cantilever-nanocoil system can be modeled as two-springs in series, and 2) the nanocoil behaves as an ideal spring as the load from the cantilever is applied. Nanocoil spring constants determined in this fashion ranged from 6.5x10-3 to 5.16 TPa for the CCNTs understudy. In the second, the spring constant of the nanocoil was computed from measuring the critical force required to buckle the nanocoil. The critical force method measured the force at the point where the nanocoil-cantilever system diverges from a linear region in the force curve. Nanocoil spring constants determined in this fashion ranged from 1.3x10-5 to 10.4 TPa for the CCNTs understudy. In the third, the spring constant of each nanocoil was computed from the thermal resonance of the cantilever-nanocoil system. Prior to contact of the nanocoil with the substrate, the effective spring constant of the system is essentially that of the cantilever. At the point of contact and prior to buckling or slip-stick motion, the effective spring constant of the system is modeled as two springs in parallel. Nanocoil spring constants determined in this fashion ranged from 2.7x10-3 to 0.03 TPa for the CCNTs understudy. Using the thermal resonance of the cantilever system a trend was observed relating nanocoil structure to the calculated modulus. Hollow, tube-like nanostructures had a higher measured modulus than solid or fibrous structures by several orders of magnitude. One can conclude that the structure of carbon nanocoils can be determined from using their mechanical properties. This correlation should significantly contribute to the knowledge of the scientific and engineering community. It will enable the integration of carbon nanocoils in microelectromechanical (MEMS) or nanoelectromechanical systems (NEMS) as resonators, vibration dampers, or any other application in which springs are used within complex devices.Ph.D.Committee Chair: Lawrence Bottomley; Committee Member: Aldo Ferri; Committee Member: E. Kent Barefield; Committee Member: Levent Degertekin; Committee Member: Robert Whetten; Committee Member: Satish Kumar; Committee Member: Zhong Lin Wan