Using Piezo Flexure Stages in AFM Experiments for Correcting Orthogonality

Table of Contents

Introduction
Measuring Orthogonality Error
nPoint DSP Controller

Introduction

nPoint offers an easy way for rectifying the orthogonality error of XY scanners for the most challenging scanning applications.

OEM customers mainly require this capability in applications such as Atomic Force Microscopy (AFM). Prior to applying such corrections, an external technique for measuring the orthogonality error is needed.

So as to exhibit this capability, the AFM application is used as an example while an nPoint XY scanner is used as the AFM scanner. It must be kept in mind that orthogonality correction capabilities may be available in certain AFM software. In this case, no external capabilities were employed.

Measuring Orthogonality Error

Orthogonality error can be measured by obtaining an image of a calibration grid. The image below shows a 50 µm scan of a 10 µm calibration grid. Although the scanner has outstanding orthogonality, it can still be used to demonstrate that the orthogonality behavior can be easily altered via nPoint GUI.

Measuring Orthogonality Error

Figure 1. 50 x 50 µm scan using an nPoint XY scanner without orthogonality correction.

Using the nPoint application GUI, users can enter the number of degrees they want to alter the orthogonality by. The interface is very simple and is shown in the image below. Either axis (X or Y; Ch1 or Ch2) can be chosen by the user to “sheer” by a specific amount. Future versions will include the rotation capability.

Sheer correction GUI

Figure 2. Sheer correction GUI. The user can pick either Ch1 or Ch2 and apply a certain “sheer” which will change the angle of one axis with respect to the other.

The same grid was employed and a 4° sheer (Figure 3a) and a 9° sheer (Figure 3b) were applied. This is seen in the following images.

AFM images of a calibration grid

Figure 3a. AFM images of a calibration grid after a 4° sheer has been applied using the nPoint GUI.

AFM images of a calibration grid

Figure 3b. AFM images of a calibration grid after a 9° sheer has been applied using the nPoint GUI.

nPoint DSP Controller

The orthogonality correction explained above is just one example of what would normally be known as a co-ordinate transformation function. This sort of function can be used to sheer one axis with respect to the other (as illustrated), to rotate the coordinate system by a specific angle, to map three Z actuators into a tilt, tip and Z movement combination or three planar actuators into an X, Y, theta configuration.

In order to achieve such co-ordinate transformations, the nPoint DSP controller does not treat each sensor circuit and piezo driver as part of a single physical axis, but rather it executes a linear mapping using many channels. In order to work the individual physical axes, the output of the control loop is changed back into the real world system.

nPoint | Nanopositioning and Motion Control

This information has been sourced, reviewed and adapted from materials provided by nPoint | Nanopositioning and Motion Control.

For more information on this source, please visit nPoint | Nanopositioning and Motion Control.

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