Forums
Bruker Media
Community Media
Bruker AFM Probes
SPM Digest
Application Notes
NanoTheater
Website
中文
Brochures & Datasheets
Publications
Probes Catalog
Events
Manuals & Documentation
Presentations
Guide to AFM Modes
News
Journal Club
Webinars & Video
Nanovations
Other
I am new to electrical measurements on the AFM and have been recently used our TUNA module on oxides (10-100 Ang.) for investigating breakdown. I have two main questions for anyone who has experience with these measurements.
(1) I've started to come to the conclusion that I am only able to perform relative (non quantitative) comparisons between samples provided my tip and measurement conditions are the same. My biggest worries with these measurements is tip wear (I will soon get a tip check sample for checking the shape) and applied force. Any indication on how many samples one may typically measure and still make comparisons (I am using the SCM-PIC tip)? Also, is there a procedure for minimizing the force even with applying varying bias to minimize tip wear and do this reproducibly to still make sample-sample comparisons.
(2) What methods data collection work the best to move towards getting quantified results, i.e. most straightforward to get reliable data for extracting thickness, barrier magnitude, ...? Currently I compare scanned TUNA current images at a particular bias but have noticed these are not the same values obtained from IV curves -- even varying the voltage ramp for IV measurements (an offset due to cap.?) gives varied results.
Hi Jhurst,
One of the main variables in your measurements is the coating of your tip. That caoting will, unfortunately, also change over time thus changing the conductive properties of the tip. Using the tip check sample will unfortunately not help you understanding this issue any better. while the sample is great for checking out the tip shape and is heavily used in PeakForce QNM measurements, it might actually be counter productive in your case. If I would be you I would try eliminating the coating unknown entirely by switching to solid metal probes such as: http://www.brukerafmprobes.com/Product.aspx?ProductID=3773
Reducing your setpoint will of course minimize the loading on your tip.
Best, Stefan
I would just add my 20 cents to the answer from Stefan.
Tip shape can be changed any time under following factors:
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 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.
Cheers, Dmitry
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.
Dmitry,
The tip shape is not really the issue, if the question is why a given tip changes over time, as the coating is what makes that tips the Jhurst used conductive. The wear of that coating is the issue. Hence my suggestion to use solid metal probes. Then, of course one has to keep an eye on the tip shape, loading force, and current flow thorugh the probe.
Best,
Stefan
Hi Stefan,
Thank you for your comments. I am just putting the general consideration to the reproducibility of the measurements with conductive probes. In some of my experiments I was able to restore the metal layer on the tip by applying higher bias voltage for a couple of seconds. The probe after these experiments was absolutely warn out as seen under SEM. I came to the conclusion that time that the processes observed were of the dip-pen lithography kind but with the metal flux instead of ink. Assuming the metal flow under the bias voltage and knowing about the high electric field at the sharp tip from papers we may assume that even solid metal probes will be modified if made too sharp for the given voltage and probe-sample combination where the contact resistance can be one of the factors. Load to the probe is another factor that especially in combination with the voltage can modify both the tip and the sample and create more reliable contact.
This subject is probably good enough to be simulated and studied in details but probably simple metrological approaches will be sufficient in this case to ensure the reproducibility of the measurements but not modification of any kind of probe.
Cheers, Dmitry MIAWiki
Thanks for the tip suggestion and comments. I will give the solid metal tips a try since the SCM-PIC tips I've been using become non-conductive quickly. Would the DDESP tips survive longer under the biases needed for breakdown -- leading to better reproducibility?
Yes, the DDEPS tips will last longer, much longer indeed. The lever is, however, a bit stiffer and the tip in general is not as sharp. We use that lever when we do need to push a bit harder on a surface.
If you have access to a system that runs PeakForce Tuna I would give that a shot. Most of the tip wear issues are eliminated when using PeakForce Tapping and thus results will be more reproducible as the tip will stay unchanged. Maybe you can schedule a demo with us?
I would for sure try the solid metal tips. Please keep us posted on your results if you don't mind.