Counter-scanning
Encyclopedia
Counter-scanning is a scanning method that allows correcting raster distortions caused by drift of the probe of scanning microscope
relative to the measured surface. During counter-scanning two surface scans, viz., direct scan and counter scan are obtained (see Fig. 1). The counter scan starts in the point where the direct scan ends. This point is called the coincidence point (CP). With the counter scan, the probe movement along the raster line and the probe movement from one raster line to the other raster line are carried out along the directions that are opposite to the movements in the direct scan. The obtained pair of images is called counter-scanned images
(CSIs).
When the raster distortions are linear, i. e., when the drift velocity is constant, to correct drift, it is sufficient to measure coordinates of only one common feature in the direct and the counter scans. In case of nonlinear distortion, when the drift velocity varies during the scan, the number of common features on CSIs whose coordinates need to be measured increases in proportion to the degree of the nonlinearity.
Typically, the drift of the microscope probe relative to the measured surface consists of two components: one is associated with creep
of the scanner
piezoceramics, the other is caused by a thermal deformation of the instrument due to change in temperature. The first component is nonlinear (it can be approximated by logarithm
), the second component can be considered as linear in most practical applications.
The use of the counter-scanning method allows, even in the case of a strong drift leading to errors in tens of percents, measuring the surface topography with error of few tenths of a percent.
Fig. 1. Counter-scanning with (a) an idle line (shown by the dotted line), (b) no idle line. Digits 1…4 designate the numbers of the images obtained. 1, 3 are direct images, 2, 4 are counter images corresponding to the direct ones. CP is a coincidence point of the counter-scanned image pair. The raster presented conditionally consists of four lines.
Scanning probe microscopy
Scanning Probe Microscopy is a branch of microscopy that forms images of surfaces using a physical probe that scans the specimen. An image of the surface is obtained by mechanically moving the probe in a raster scan of the specimen, line by line, and recording the probe-surface interaction as a...
relative to the measured surface. During counter-scanning two surface scans, viz., direct scan and counter scan are obtained (see Fig. 1). The counter scan starts in the point where the direct scan ends. This point is called the coincidence point (CP). With the counter scan, the probe movement along the raster line and the probe movement from one raster line to the other raster line are carried out along the directions that are opposite to the movements in the direct scan. The obtained pair of images is called counter-scanned images
Counter-scanned images
Counter-scanned images are a pair of images obtained during counter-scanning. During the counter-scanning it is possible to obtain one or two pairs of CSIs . Each pair consists of a direct image and the image counter to it...
(CSIs).
When the raster distortions are linear, i. e., when the drift velocity is constant, to correct drift, it is sufficient to measure coordinates of only one common feature in the direct and the counter scans. In case of nonlinear distortion, when the drift velocity varies during the scan, the number of common features on CSIs whose coordinates need to be measured increases in proportion to the degree of the nonlinearity.
Typically, the drift of the microscope probe relative to the measured surface consists of two components: one is associated with creep
Creep
Creep may refer to:* CREEP, the Committee for the Re-Election of the President, associated with the Watergate scandal of U.S. president Nixon's administration....
of the scanner
Scanner
Scanner may refer to:* WikiScanner, a tool that provides a searchable database of anonymous Wikipedia edits* A personality type described by self-help author Barbara Sher-Technology:* Scanner , for searching for and receiving radio broadcasts...
piezoceramics, the other is caused by a thermal deformation of the instrument due to change in temperature. The first component is nonlinear (it can be approximated by logarithm
Logarithm
The logarithm of a number is the exponent by which another fixed value, the base, has to be raised to produce that number. For example, the logarithm of 1000 to base 10 is 3, because 1000 is 10 to the power 3: More generally, if x = by, then y is the logarithm of x to base b, and is written...
), the second component can be considered as linear in most practical applications.
The use of the counter-scanning method allows, even in the case of a strong drift leading to errors in tens of percents, measuring the surface topography with error of few tenths of a percent.
Fig. 1. Counter-scanning with (a) an idle line (shown by the dotted line), (b) no idle line. Digits 1…4 designate the numbers of the images obtained. 1, 3 are direct images, 2, 4 are counter images corresponding to the direct ones. CP is a coincidence point of the counter-scanned image pair. The raster presented conditionally consists of four lines.
External links
- Drift elimination based on counter-scanned images, Research section, Lapshin's Personal Page on SPM & Nanotechnology
- Counter-scanning, Dictionary of Nanotechnological Terms, Russian Corporation of Nanotechnologies