skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Adaptive AFM scan speed control for high aspect ratio fast structure tracking

Abstract

Improved imaging rates in Atomic Force Microscopes (AFM) are of high interest for disciplines such as life sciences and failure analysis of semiconductor wafers, where the sample topology shows high aspect ratios. Also, fast imaging is necessary to cover a large surface under investigation in reasonable times. Since AFMs are composed of mechanical components, they are associated with comparably low resonance frequencies that undermine the effort to increase the acquisition rates. In particular, high and steep structures are difficult to follow, which causes the cantilever to temporarily loose contact to or crash into the sample. Here, we report on a novel approach that does not affect the scanner dynamics, but adapts the lateral scanning speed of the scanner. The controller monitors the control error signal and, only when necessary, decreases the scan speed to allow the z-piezo more time to react to changes in the sample's topography. In this case, the overall imaging rate can be significantly increased, because a general scan speed trade-off decision is not needed and smooth areas are scanned fast. In contrast to methods trying to increase the z-piezo bandwidth, our method is a comparably simple approach that can be easily adapted to standard systems.

Authors:
; ;  [1]
  1. Department of Microelectronic and Nanoelectronic Systems, Faculty of Electrical Engineering and Information Technology Ilmenau University of Technology, Gustav-Kirchhoffstr. 1, 98684 Ilmenau (Germany)
Publication Date:
OSTI Identifier:
22306224
Resource Type:
Journal Article
Resource Relation:
Journal Name: Review of Scientific Instruments; Journal Volume: 85; Journal Issue: 10; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; ASPECT RATIO; ATOMIC FORCE MICROSCOPY; CONTROL; RESONANCE; SEMICONDUCTOR MATERIALS; SIGNALS; TOPOGRAPHY; TOPOLOGY

Citation Formats

Ahmad, Ahmad, Schuh, Andreas, and Rangelow, Ivo W. Adaptive AFM scan speed control for high aspect ratio fast structure tracking. United States: N. p., 2014. Web. doi:10.1063/1.4897141.
Ahmad, Ahmad, Schuh, Andreas, & Rangelow, Ivo W. Adaptive AFM scan speed control for high aspect ratio fast structure tracking. United States. doi:10.1063/1.4897141.
Ahmad, Ahmad, Schuh, Andreas, and Rangelow, Ivo W. 2014. "Adaptive AFM scan speed control for high aspect ratio fast structure tracking". United States. doi:10.1063/1.4897141.
@article{osti_22306224,
title = {Adaptive AFM scan speed control for high aspect ratio fast structure tracking},
author = {Ahmad, Ahmad and Schuh, Andreas and Rangelow, Ivo W.},
abstractNote = {Improved imaging rates in Atomic Force Microscopes (AFM) are of high interest for disciplines such as life sciences and failure analysis of semiconductor wafers, where the sample topology shows high aspect ratios. Also, fast imaging is necessary to cover a large surface under investigation in reasonable times. Since AFMs are composed of mechanical components, they are associated with comparably low resonance frequencies that undermine the effort to increase the acquisition rates. In particular, high and steep structures are difficult to follow, which causes the cantilever to temporarily loose contact to or crash into the sample. Here, we report on a novel approach that does not affect the scanner dynamics, but adapts the lateral scanning speed of the scanner. The controller monitors the control error signal and, only when necessary, decreases the scan speed to allow the z-piezo more time to react to changes in the sample's topography. In this case, the overall imaging rate can be significantly increased, because a general scan speed trade-off decision is not needed and smooth areas are scanned fast. In contrast to methods trying to increase the z-piezo bandwidth, our method is a comparably simple approach that can be easily adapted to standard systems.},
doi = {10.1063/1.4897141},
journal = {Review of Scientific Instruments},
number = 10,
volume = 85,
place = {United States},
year = 2014,
month =
}
  • In practice, diesel driven power-plants are either naturally aspirated, or meet their air requirements by turbo charging. The latter improves the running efficiency of the prime-mover, but introduces various non-linearities which can lead to oscillatory dynamic response. In this paper, an adaptive technique for fuel-flow control is introduced to mitigate the oscillatory effect. It is shown that modeling the engine dead-time effect as a fictitious frequency, and using this idea to estimate the dead-time, can lead to a very accurate predictor algorithm for prime-mover dynamics. Using this algorithm in an adaptive control scheme leads to virtually complete elimination of secondarymore » oscillations of speed, and smooth dynamic control, as compared to PI controllers.« less
  • This article introduces scan welding as a redesign of classical joining methods, employing automation technology to ensure the overall geometric, material and mechanical integrity of the joint. This is obtained by real-time control of the welding temperature field by a proper dynamic heat input distribution on the weld surface. This distribution is implemented in scan welding by a single torch, sweeping the joint surface by a controlled reciprocating motion, and power adjusted by feedback of infrared temperature measurements in-process. An off-line numerical simulation of the thermal field in scan welding is established, as well as a linearized multivariable model withmore » real-time parameter identification. An adaptive thermal control scheme is thus implemented and validated--both computationally and experimentally on a robotic plasma arc welding (PAW) station. The resulting thermal features related to the generated material structure and properties of the joint are finally analyzed in scan welding tests and simulations.« less
  • A high performance controller for dc brushless rotors is proposed in this paper. The controller is based on the theories of variable structure tracking. With the proposed method, the rotor position can trace any arbitrarily selected track with high degree of accuracy, and without overshooting or overstressing the hardware of the system. The control strategy is adaptive and very robust. External disturbances and variations in system parameters are adaptively compensated by the tracking controller. The proposed controller is suitable for such applications as robotic, actuation and manipulation where most of the present fixed parameters positional control methods are inadequate. Themore » proposed system is designed and implemented in the laboratory. Test results are presented and discussed in this paper.« less
  • A novel fabrication process produces high porosity polymer nanofilters with smooth, uniform, and straight pores with high aspect ratios. The process utilizes electron beam lithography and energetic neutral atom beam lithography and epitaxy techniques. The method has the potential to produce a new generation of high-precision, very-high-porosity, biocompatible filters with pore sizes down to 100 nm.