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Tip selection for PFT-QNM

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Chunzeng Li posted on Tue, Mar 2 2010 3:21 PM

Is there a rule of thumb in tip selection for PFT-QNM (peakforce tapping and quantitative nanomechanical measurements) toward reliable mechanical property measurements?

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For general purpose imaging we recommend ScanAsyst-AIR probes because their low spring constants and sharp tips provide the best high-resolution imaging on soft samples without damaging tips or samples. To enable quantitative modulus mapping, some deformation of the sample is necessary. For stiffer samples, a ScanAsyst-AIR probe will not be able to sufficiently deform the sample to ensure accurate results. In this case it is necessary to switch to a stiffer probe such as a TAP150A, TESP, or DNISP. If the modulus of the sample is approximately known, it is possible to select a probe that matches the sample (see attached chart). If not, Veeco recommends starting with a TAP150A probe and checking the deformation data channel. For accurate measurements, at least 2nm of deformation is required, but the tip should not cause permanent damage to the sample. If there is a lot of deformation, resolution may suffer. For best results, the (calibrated) ratio of deformation to deflection should be between 3 and 30.

A simple method for probe selection is to use ScanAsyst to optimize the scan parameters for the height image. If the sample is damaged after optimization, the probe is probably too stiff. If the sample deformation is less than 2nm, disable setpoint control and manually double the setpoint. If the deformation is still less than 2nm, the probe probably is too soft.

For inhomogeneous samples, try to use probes that can cover the range of all of the sample’s components. If that is not possible, different probes will be needed to measure different components of the material accurately.

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