A Modified Positive Velocity and Position Feedback scheme with delay compensation for improved nanopositioning performance

Acknowledgments This paper was sponsored by the Spanish FPU12/00984 Program (Ministerio de Educacion, Cultura y Deporte). It was also sponsored by the Spanish Government Research Program with the Project DPI2012-37062-CO2-01 (Ministerio de Economia y Competitividad) and by the European Social Fund.Peer reviewedPostprin

Improvement of accuracy and speed of a commercial AFM using Positive Position Feedback control

The atomic force microscope (AFM) is a device capable of generating topographic images of sample surfaces with extremely high resolutions down to the atomic level. It is also being used in applications that involve manipulation of matter at a nanoscale. Early AFMs were operated in open loop. As a result, they were susceptible to piezoelectric creep, thermal drift, hysteresis nonlinearity and scan-induced vibration. These effects tend to distort the generated image. The distortions are often minimized by limiting the scanning speed and range of the AFMs. Recently a new generation of AFMs has emerged that utilizes position sensors to measure displacements of the scanner in three dimensions. These AFMs are equipped with feedback loops that work to minimize the adverse effects of hysteresis, piezoelectric creep and thermal drift on the obtained image using standard PI controllers. These feedback controllers are often not designed to deal with the highly resonant nature of an AFM's scanner, nor with the cross-coupling between various axes. In this paper we illustrate the drastic improvement in accuracy and imaging speed that can be obtained by proper design of a feedback controller. Such controllers can be incorporated into most modern AFMs with minimal effort since they can be implemented in software with the existing hardware

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

A monolithic MEMS position sensor for closed-loop high-speed atomic force microscopy

The accuracy and repeatability of atomic force microscopy (AFM) imaging significantly depend on the accuracy of the piezoactuator. However, nonlinear properties of piezoactuators can distort the image, necessitating sensor-based closed-loop actuators to achieve high accuracy AFM imaging. The advent of high-speed AFM has made the requirements on the position sensors in such a system even more stringent, requiring higher bandwidths and lower sensor mass than traditional sensors can provide. In this paper, we demonstrate a way for high-speed, high-precision closed-loop AFM nanopositioning using a novel, miniaturized micro-electro-mechanical system position sensor in conjunction with a simple PID controller. The sensor was developed to respond to the need for small, lightweight, high-bandwidth, long-range and sub-nm-resolution position measurements in high-speed AFM applications. We demonstrate the use of this sensor for closed-loop operation of conventional as well as high-speed AFM operation to provide distortion-free images. The presented implementation of this closed-loop approach allows for positioning precision down to 2.1 Å, reduces the integral nonlinearity to below 0.2%, and allows for accurate closed loop imaging at line rates up to 300 Hz

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

High-bandwidth nanopositioning via active control of system resonance

Acknowledgements This work was supported in part by the National Natural Science Foundation of China (Grant Nos. U2013211 and 51975375), the Open Foundation of the State Key Laboratory of Fluid Power and Mechatronic Systems, China (Grant No. GZKF-202003), and the Binks Trust Visiting Research Fellowship (2018), University of Aberdeen, UK, awarded to Dr. Sumeet S. Aphale.Peer reviewedPublisher PD

Studying biological membranes with extended range high-speed atomic force microscopy

High-speed atomic force microscopy has proven to be a valuable tool for the study of biomolecular systems at the nanoscale. Expanding its application to larger biological specimens such as membranes or cells has, however, proven difficult, often requiring fundamental changes in the AFM instrument. Here we show a way to utilize conventional AFM instrumentation with minor alterations to perform high-speed AFM imaging with a large scan range. Using a two-actuator design with adapted control systems, a 130 x 130 x 5 mu m scanner with nearly 100 kHz open-loop small-signal Z-bandwidth is implemented. This allows for high-speed imaging of biologically relevant samples as well as high-speed measurements of nanomechanical surface properties. We demonstrate the system performance by real-time imaging of the effect of charged polymer nanoparticles on the integrity of lipid membranes at high imaging speeds and peak force tapping measurements at 32 kHz peak force rate

Nanopositionnement 3D à base de mesure à courant tunnel et piezo-actionnement

The objective of this thesis was to elaborate high performance control strategies and their real-time validation on a tunneling current-based 3D nanopositioning system developed in GIPSA-lab. The thesis lies in the domain of micro-/nano mechatronic systems (MEMS) focused on applications of fast and precise positioning and scanning tunneling microscopy (STM). More precisely, the aim is to position the metallic tunneling tip (like in STM) over the metallic surface using piezoelectric actuators in X, Y and Z directions and actuated micro-cantilever (like in Atomic Force Microscope AFM), electrostatically driven in Z direction, with high precision, over possibly high bandwidth. However, the presence of different adverse effects appearing at such small scale (e.g. measurement noise, nonlinearities of different nature, cross-couplings, vibrations) strongly affect the overall performance of the 3D system. Therefore a high performance control is needed. To that end, a novel 3D model of the system has been developed and appropriate control methods for such a system have been elaborated. First the focus is on horizontal X and Y directions. The nonlinear hysteresis and creep effects exhibited by piezoelectric actuators have been compensated and a comparison between different compensation methods is provided. Modern SISO and MIMO robust control methods are next used to reduce high frequency effects of piezo vibration and cross-couplings between X and Y axes. Next, the horizontal motion is combined with the vertical one (Z axis) with tunneling current and micro-cantilever control. Illustrative experimental results for 3D nanopositioning of tunneling tip, as well as simulation results for surface topography reconstruction and multi-mode cantilever positioning, are finally given.L'objectif de la thèse est l'élaboration de lois de commande de haute performance et leur validation en temps réel sur une plateforme expérimentale 3D de nano-positionnement à base de courant à effet tunnel, développée au laboratoire GIPSA-lab. Elle s'inscrit donc dans le cadre des systèmes micro-/nano-mécatronique (MEMS), et de la commande. Plus précisément, le principal enjeu considéré est de positionner la pointe métallique à effet tunnel (comme en microscopie à effet tunnel STM) contre la surface métallique en utilisant des actionneurs piézoélectriques en X, Y et Z et un micro-levier (comme en microscopie à force atomique AFM) actionné électrostatiquement en Z avec une grande précision et une bande passante élevée. Cependant, la présence de différents effets indésirables apparaissant à cette petite échelle (comme le bruit de mesure, des non-linéarités de natures différentes, les couplages, les vibrations) affectent fortement la performance globale du système 3D. En conséquence, une commande de haute performance est nécessaire. Pour cela, un nouveau modèle 3D du système a été développé et des méthodes de contrôle appropriées pour un tel système ont été élaborées. Tout d'abord l'accent est mis sur de positionnement selon les axes X et Y. Les effets d'hystérésis et de fluage non linéaires présents dans les actionneurs piézoélectriques ont été compensés et une comparaison entre les différentes méthodes de compensation est effectuée. Des techniques modernes de commande robuste SISO et MIMO sont ensuite utilisées pour réduire les effets des vibrations piézoélectriques et des couplages entre les axes X et Y. Le mouvement horizontal est alors combiné avec le mouvement vertical (Axe Z) et une commande du courant tunnel et du micro-levier. Des résultats expérimentaux illustrent le nano positionnement 3D de la pointe, et des résultats de simulation pour la reconstruction de la topographie de la surface ainsi que le positionnement du micro-levier à base d'un modèle multi-modes