lifeProcessor provides program control and program sensing of the cantilever base and tip at micro time slices throughout the entire advance/single touch/magnetic withdraw cycle at every pixel. It executes on a DSP computer on an installed card.
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Each 5 µsec the DSP issues a command to the piezo that drives the cantilever base.
- 200 commands are given during the advance part of the cycle.
- 100 or more commands occur during the unbinding of the tip and withdrawal.
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The intelligence in the DSP senses and controls the significant aspects of the cantilever at all times with resulting distinctive capabilities:
The DSP also communicates with the host PC and handles a mass of housekeeping details.
lifeView is a large, Windows-based operator program designed for intuitive ease of use. The main menu is the gateway to all operating functions via extensive dropdown menus. It accesses AFM properties such as scanner calibration and cantilever force constant.
Multiple parameters open to digital control by the lifeScan design can be specified, including the compressive force at detection, and the force applied in the magnetic pull-off.
The main lifeView screen displays any number of performance monitoring data and imaging data.
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The data visible in this screen include:
ADeviation from set point
BForce curves
CDetect/differential height
DTopography/Height
EAdhesion
FCompliance
GUncorrected Z
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ADeviation from set point. The blue curve in (A) displays for an entire scan line the deviation of the contact step from the set point---it shows quantitatively the failure to track a smooth surface exactly.
BForce curves for all pixels are recorded and can be replayed. A force curve is displayed during the approach/contact/withdrawal for any chosen pixel of each scan line.
The dotted red line indicates the selected detect force, the dotted horizontal green line the selected break off force. The file size of each 256x256 scan with all scanning data accessible is 25 mB.
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CDetect/differential height. This plot is an assembly of the blue curves in (A), one for each scan line and with the ordinate in (A) replaced by brightness in the display. As in the blue curve, it shows the difference of the step at contact from the set point at 120 steps.
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DTopography/height. This is the integral of the differential height in (C). It is measured in steps from a fixed starting height above the molecule and is easily converted to nm because the step distance is accurately measured in terms of specimen piezo displacement in nm.
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EAdhesion force This plots the number of steps in the ramp of increasing magnetic force at which the tip breaks free. It is known absolutely, i.e., in picoNewtons.
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FCompliance The compliance or compressibility plot is only semi-quantitative but is frequently interesting. It is based on the amount of cantilever deflection that occurs for the 10 steps before the contact threshold is passed.
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GUncorrected Z In the topography map (D), the plotted Z has a smooth straight-line fit subtracted from every scan line, so that the average Z of each line is zero. In (G), the raw data are displayed, which is useful for understanding and correcting mechanically any large tilts in the specimen.
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Data display and analysis features are available from mouse action (e.g., distance, area, compare) and extensive drop down menus. The latter include a variety of palettes and color display options, histogram and line fits, plane fits, smoothing and averaging, Fourier transforms, and correlation maps.
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