Controller Design for Z Axis Movement of STM Using SPM Control Software
Neena Tom1, Rini Jones S. B2

1Neena Tom, Department of Applied Electronics and Instrumentation, Lourdes Matha College of Science and Technology, Kuttichal, Trivandrum (Kerala), India.
2Rini Jones S.B, Assoc. Prof., Department of Electronics and Communication, Lourdes Matha College of Science and Technology, Kuttichal, Trivandrum (Kerala), India.

Manuscript received on 15 June 2015 | Revised Manuscript received on 25 June 2015 | Manuscript Published on 30 June 2015 | PP: 134-138 | Volume-4 Issue-5, June 2015 | Retrieval Number: E4099064515/15©BEIESP
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Abstract: Scanning probe microscopy is a branch of microscopy that forms images of surfaces using a physical probe. This paper is devoted to the control system design for high performance scanning tunneling microscope (STM). The distance between tip and sample should be kept constant at every point of sample for better scanning results. Note that many samples have roughness, curvature and tilt that deviate from a flat plane .So it is necessary to move the probe in z-axis to maintain the height of probe from sample constant. But a sudden change in probe position can damage the probe. SPM feedback loops usually employ a proportional-integral (PI) controller to control the vertical movement of tip (z-direction). Our aim is to implement an accurate tuning algorithm that can find PI values that gradually change the position of the probe for higher safety and precision. Moreover, better sample topography image can be obtained after auto-tuning the control gains during different scanning speed. The square wave is given as input to the PI controller which represents the sudden change of surface that cause damage to the system, and the output should be triangular wave in nanometer range by proper tuning of PI controller. Triangular wave represents the tip being moved by the controller in z direction at the time represented by the square wave input.
Keywords: Scanning Tunneling Microscope, Feedback Loops, PI Controller, Tuning Algorithm.

Scope of the Article: Algorithm Engineering