Model-based Control of the Scanning Tunneling Microscope: Enabling New Modes of Imaging, Spectroscopy, and Lithography

The invention of scanning tunneling microscope (STM) dates back to the work of Binnig and Rohrer in the early 1980s, whose seminal contribution was rewarded by the 1986 Nobel Prize in Physics for the design of the scanning tunneling microscope. Forty years later, the STM remains the best existing tool for studying electronic, chemical, and physical properties of conducting and semiconducting surfaces with atomic precision. It has opened entirely new fields of research, enabling scientists to gain invaluable insight into properties and structure of matter at the atomic scale. Recent breakthroughs in STM-based automated hydrogen depassivation lithography (HDL) on silicon have resulted in the STM being considered a viable tool for fabrication of error-free silicon-based quantum-electronic devices. Despite the STM's unique ability to interrogate and manipulate matter with atomic precision, it remains a challenging tool to use. It turns out that many issues can be traced back to the STM's feedback control system, which has remained essentially unchanged since its invention about 40 years ago. This article explains the role of feedback control system of the STM and reviews some of the recent progress made possible in imaging, spectroscopy, and lithography by making appropriate changes to the STM's feedback control loop. We believe that the full potential of the STM is yet to be realized, and the key to new innovations will be the application of advanced model-based control and estimation techniques to this system

Precise tip positioning of a flexible manipulator using resonant control

A single-link flexible manipulator is fabricated to represent a typical flexible robotic arm. This flexible manipulator is modeled as an SIMO system with the motor torque as the input and the hub angle and the tip position as the outputs. The two transfer functions are identified using a frequency-domain system identification method, and the resonant modes are determined. A feedback loop around the hub angle response with a resonant controller is designed to damp the resonant modes. A high-gain integral controller is also implemented to achieve zero steady-state error in the tip position response. Experiments are performed to demonstrate the effectiveness of the proposed control scheme

Two sensor based H-infinity control of a piezoelectric tube scanner

The performance of a feedback-controlled piezoelectric tube scanner is limited by its inherent nonlinear properties such as hysteresis and creep, its mechanical resonance modes and its displacement sensor bandwidth and associated noise properties. Capacitive sensors have emerged as the displacement sensor of choice in piezoelectric tube scanners. Resolution of a capacitive sensor is largely determined by its bandwidth and noise density which is typically in the order of 20 pm/root Hz for a +/-100 micrometer range. Consequently, to achieve sub-nanometer resolution, the sensors bandwidth needs to be made small. Achieving satisfactory tracking performance using a low-bandwidth displacement sensor is a challenging task. To improve the bandwidth, the piezoelectric strain voltage induced in the electrode opposite to the actuating electrode is used as a secondary measurement. A two-sensor-based H-infinity controller is designed and implemented on a prototype piezoelectric tube nanopositioning system. The tube is driven by a charge amplifier to reduce the hysteresis. Experimental results demonstrate a significant increase in the tracking bandwidth due to the use of the additional sensor

Precise tip positioning of a flexible manipulator using resonant control

A single-link flexible manipulator is fabricated to represent a typical flexible robotic arm. This flexible manipulator is modeled as a SIMO system with the motor-torque as the input and the hub angle and the tip position as the outputs. The two transfer functions are identified using a frequency-domain system identification method. A feedback loop around the hub angle response with a resonant controller is designed to damp the resonant modes. A high gain integral controller is also designed to achieve zero steady-state error in the tip position response. Experiments are performed to demonstrate the effectiveness of the proposed control scheme

Negative Imaginary Control Using Hybrid Integrator-Gain Systems: Application to MEMS Nanopositioner

In this paper, we propose a new approach to address the control problem for negative imaginary (NI) systems by using hybrid integrator-gain systems (HIGS). We investigate the single HIGS of its original form and its two variations, including a multi-HIGS and the serial cascade of two HIGS. A single HIGS is shown to be a nonlinear negative imaginary system, and so is the multi-HIGS and the cascade of two HIGS. We show that these three types of HIGS can be used as controllers to asymptotically stabilize linear NI systems. The results of this paper are then illustrated in a real-world experiment where a 2-DOF microelectromechanical system nanopositioner is stabilized by a multi-HIGS.Comment: 13 pages, 9 figures. Accepted for publication as a Full Paper in the IEEE Transactions on Control Systems Technology (TCST

A survey of recent innovations in vibration damping and control using shunted piezoelectric transducers

Research on shunted piezoelectric transducers, performed mainly over the past decade, has generated new opportunities for control of vibration and damping in flexible structures. This is made possible by the strong electromechanical coupling associated with modern piezoelectric transducers. In vibration control applications, a piezoelectric transducer is bonded to, or embedded in a base structure. As the structure deforms, the piezoelectric element strains and converts a portion of the structural vibration energy into electrical energy. By shunting the piezoelectric transducer to an electrical impedance, a part of the induced electrical energy can be dissipated. Hence, the impedance acts as a means of extracting mechanical energy from the base structure. This paper reviews recent research related to the use of shunted piezoelectric elements for vibration damping and control. In particular, the paper presents an overview of the literature on piezoelectric shunt damping and discusses recent observations on the feedback nature of piezoelectric shunt damping systems