http://nanoscaleworld.bruker-axs.com/nanoscaleworld/forums/p/851/2127.aspx#2127
Probe-Sample Interaction at Conductive AFM
Re: TUNA on oxides?
By Dmitry Sokolov in SPM Digest
I would just add my 20 cents to the answer from Stefan.
Tip shape can be changed any time under following factors:
- initial shape, how sharp the tip is
- combination material/coating of the probe
- bias voltage (1V can already be high enough to modify a coating of a sharp probe)
- load on the probe (matter of rigidity of the probe)
- scanning mode for imaging and measurements
- roughness of the surface
- hardness of the surface
- length scanned before the (next) measurement
The tip conductivity can also be changed with time (Diamond Tip Ageing AFM) or during the measurement itself due to the development of the oxide layer, for example.
The probe however can be calibrated on a known sample(s) with the electric and viscoelastic characteristics close to the required. Combined STS - QNM on a hard and electrically and chemically stable conductive surface like doped diamond film at a required for measurements bias voltage should theoretically indicate the conditions for stable and reproducible measurements. A series of STS plots taken at 3-5 points across your presumably uniform sample will show variations caused by the tip-sample gap change (caused not necessarily by the tip shape change) within one run and between the measurement runs at different locations. Comparison of the data variations achieved with the stable tip and the accuracy required will characterize the applicability of the method for your experiment.
Sample modification at electrical measurements is a separate story however. I hope that is not the case in your studies.
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