Enhanced two consecutive samples based de-modulation technique for atomic force microscopy application

This article investigates robust amplitude detectors suitable for atomic force microscopy (AFM) while discussing better alternatives. An AFM instrument’s measurement unit is responsible for providing the amplitude information obtained from the tip of a cantilever beam to identify the surface smoothness of a test material. Therefore, two efficient approaches are suggested to leverage Lyapunov’s theory while adhering to better noise suppression and DC-offset rejection capabilities. Nevertheless, an enhanced two samples-based Lyapunov’s demodulation approach is proposed to detect the amplitude information rapidly. Consequently, the modifications applied to the conventional method help reduce the tuning efforts and structural complications. The proposed solution remains structurally simpler and useful for high- and low-frequency probes. Furthermore, the extensive design guidelines for all techniques and the simulation results are presented. Different amplitude signals are synthetically generated from several rough pseudo-test surfaces for early verification and sent to a real-time digital controller to judge the proposal’s efficacy

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