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

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

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

Modeling and control of undesirable dynamics in atomic force microscopes

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2002.Includes bibliographical references (leaves 156-165).The phenomenal resolution and versatility of the atomic force microscope (AFM), has made it a widely-used instrument in nanotechnology. In this thesis, a detailed model of AFM dynamics has been developed. It includes a new model for the piezoelectric scanner coupled longitudinal and lateral dynamics, creep, and hysteresis. Models for probe-sample interactions and cantilever dynamics were also included. The models were used to improve the dynamic response and hence image quality of contact-mode AFM. An extensive parametric study has been performed to experimentally analyze in-contact dynamics. Nonlinear variations in the frequency response were observed, in addition to changes in the pole-zero structure. The choice of scan parameters was found to have a major impact on image quality and feedback performance. Further, compensation for scanner creep was experimentally tested yielding a reduction in creep by a factor of 3 to 4 from the uncompensated system. Moreover, fundamental performance limitations in the AFM feedback system were identified. These limitations resulted in a severe bound on the maximum achievable feedback bandwidth, as well as a fundamental trade-off between step response overshoot and response time. A careful analysis has revealed that a PID controller has no real advantage over an integral controller.(cont.) Therefore, a procedure for automatically selecting key scan parameters and controller gain was developed and experimentally tested for I-control. This approach, in contrast to the commonly used trial and error method, can substantially improve image quality and fidelity. In addition, a robust adaptive output controller (RAOC), was designed to guarantee global boundedness and asymptotic regulation in the presence and absence of disturbances, respectively. Simulations have shown that a substantial reduction in contact force can be achieved with the RAOC, in comparison with a well-tuned I-controller, yet with no increase in the maximum scan speed. Furthermore, a new method was developed to allow calibrating the scanner's vertical displacement up to its full range, in addition to characterizing scanner hysteresis. This work has identified and addressed crucial problems and proposed practical solutions to factors limiting the dynamic performance of the AFM.by Osamah M. El Rifai.Ph.D

Design and control of a 6-degree-of-freedom precision positioning system

This paper presents the design and test of a6-degree-of-freedom (DOF) precision positioning system, which is assembledby two different 3-DOF precision positioning stages each driven by three piezoelectric actuators (PEAs). Based on the precision PEAs and flexure hinge mechanisms, high precision motion is obtained.The design methodology and kinematic characteristics of the6-DOF positioning system areinvestigated. According to an effective kinematic model, the transformation matrices are obtained, which is used to predict the relationship between the output displacement from the system arrangement and the amountof PEAsexpansion. In addition, the static and dynamic characteristics of the 6-DOF system have been evaluated by finite element method (FEM) simulation andexperiments. The design structure provides a high dynamic bandwidth withthe first naturalfrequency of 586.3 Hz.Decoupling control is proposed to solve the existing coupling motion of the 6-DOF system. Meanwhile, in order to compensate for the hysteresis of PEAs, the inverse Bouc-Wen model was applied as a feedforward hysteresis compensator in the feedforward/feedback hybrid control method. Finally, extensive experiments were performed to verify the tracking performance of the developed mechanism

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

A new scanning method for fast atomic force microscopy

In recent years, the atomic force microscope (AFM) has become an important tool in nanotechnology research. It was first conceived to generate 3-D images of conducting as well as nonconducting surfaces with a high degree of accuracy. Presently, it is also being used in applications that involve manipulation of material surfaces at a nanoscale. In this paper, we describe a new scanning method for fast atomic force microscopy. In this technique, the sample is scanned in a spiral pattern instead of the well-established raster pattern. A constant angular velocity 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 AFM nanopositioner, respectively. The use of single-frequency input signals allows the scanner to move at high speeds without exciting the mechanical resonance of the device. Alternatively, the frequency of the sinusoidal set points can be varied to maintain a constant linear velocity (CLV) while a spiral trajectory is being traced. Thus, producing a CLV spiral. These scan methods can be incorporated into most modern AFMs with minimal effort since they can be implemented in software using the existing hardware. Experimental results obtained by implementing the method on a commercial AFM indicate that high-quality images can be generated at scan frequencies well beyond the raster scans

Development of a high resolution position sensor for atomic force microscopy

Tese de mestrado integrado, Engenharia Física , 2022, Universidade de Lisboa, Faculdade de CiênciasThis work aims to develop a position sensor with nanometric resolution and its implementation in a scanner that performs displacements in a three-dimensional space, responsible for the tip-sample scanning in an atomic force microscope (AFM). The work will be developed in the laboratory of “Atomic Force Microscopy and related techniques” (AFMaRT) under the guidance of professors Mario S Rodrigues and Miguel V Vitorino. ´ All AFMs use piezoelectric elements to perform displacements in 3 dimensions with high spatial resolution. Consequently, the observables of the instrument are the voltages applied to the various piezoelectric elements, later converted to displacement of the sample/tip, after calibrating the scanner movement. Due to hysteresis and creep characteristics of piezoelectric elements this conversion is only approximated and is insufficient for some applications that require greater precision in the knowledge of the sample position relative to the probe. After a previous study of the state of the art, it was decided to develop position sensors using lasers and quadrant photodetectors. Laser-photodetector systems are mainly sensitive to angular variations. To take advantage of this fact, the idea is to focus 3 lasers on 3 reflecting cylinders solidary with the sample. The angles of the surfaces on which the 3 beams lasers are incident, depend on the position of the cylinders with respect to fixed lasers in an inertial reference frame. This system was mounted on a prototype of AFM already existing in the laboratory, requiring the development/adaptation of the existing scanner to facilitate integration of the sensors, which included redrawing the scanner and the sample’s holder. During this work, it was necessary to dimension the optical system, design ways of coupling to the scanner, design electronic circuits that allow reading sensors and characterize and calibrate the sensors