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Hi everyone, I'm new to SPM and new to this forum. I am looking at measuring the surface roughness of single fibres with diameters ranging from about 13 to 20 microns. I'm looking at measuring the roughness over a 5 micron area, but due to the curvature of the fibre I need to flat the area first. In the manual, the instructions say to flatten then do a planefit. I get different roughness results when I use a 3 order flattening or 3 order planefit. However when I flatten first, any subsequent planefits do not change the result. When I planefit first, then flatten, I get the same result as just flattening. So should I ignore planefitting and just flatten?
Linda
Linda.Hillbrick@csiro.au
Dear Linda,
I suspect the main reason for what you are seeing is that Veeco software generally applies a planefit to your files when they are saved by the acquisition software. Thus, planefitting after wards does nothing. YOu can actually turn this off in the Nanoscope acquisition module, but in most cases, it does not do any harm having it turned on. Now, in your particualr case, you are looking at samples which will be curved by default (fibres). So, a "curved" fitting (or flattening) is ideal. I suspect that 2nd order polynomial fitting (called "flatten" in the nanoscope analysis module), would be best for you, but you might find 3rd order better. In anycase, the most important thing is thatfor roughness, you must always appy the same protocaol before measurement of roughness parameters. As you noticed, you get different values depending on how the data is treated beforehand.
THere is a section discussing this in my book "atomic force microscopy", which you can see details of at :http://afmhelp.com. Some relevent things are in chapters 4 and 5, but look particulalry at seciton 7.1.1, which shows how differnet measurement parameters and processing treatments affect surface roughness. But given that you probablywant to see effects on surface roughness of various treatments to curved fibre surfaces, the main thing is to find a treament that makes the images look more or less flat, and stick to it for comparative analysis.
good luck,
Pete.
Hi Linda, For your application and in general, it is important to get a good understanding of what the Flatten and Planefilt routines do to the data and how this will effect your results. They are different routines, but as you have experienced there is some similarity between the effect on the image. Flatten modifies the image by adjusting each line scan in the image to the same average height. This is what a 0th order flatten performs on the image. A 1st order flatten will also remove tilt from each line scan. A 2nd order will remove curvature, and a 3rd order will remove S-shape curvature from each line. Another thing to consider about flattening is that it will flatten the information in the Y direction.
This is different from a Planefit which works on the entire image. A 1st order Planefit will apply a best fit plane to the image and use this to remove tilt in X and/or Y. A 2nd order removes curvature, and a 3 order removes S-shaped curvature from the entire image. As Peter just mentioned, you can have the software automatically conduct a 1st order Planefit upon saving the data by having the parameters "Offline Planefit" set to "Full" for that image channel. If you do not want a Planefit to occur upon saving the data, you can set it to "Offset" or "None". For your sample, I am not sure if this matters since you will need to conduct a flatten and/or Planefit on the saved data anyway.
So, in your example below, if you are first applying a 3rd order Flatten to an image, then you have already removed the curvature from the line scans in the image that you would also be removing from the image with a 3rd order Planefit. So, I am not surprised if you are not seeing any or much affect from applying the Planefit after the Flatten. You would really choose the best routine for what you are trying to measure, and stay consistent in your are conducting comparisons. Usually for roughness comparisons, I will run a flatten (maybe 0th or 1st order for flat samples), but it really depends on the samples structure and what you are measuring.
For your samples, you have fibers with curvature and you want to remove the curvature to measure the microroughness of the fibers. I would first consider how you are going to process the data before scanning. For instance, if you scan with the fast scan direction (horizontal line scans) perpendicular to the axis of the fiber, then will have the fiber curvature in the X direction of the image, and you will need to conduct a 2nd (or maybe 3rd) order flatten to remove the fiber curvature before measuring roughness. If you scan with the fast scan direction parallel to the axis of the fiber, then the flatten routine will remove the curvatures of the fiber (in the Y direction), and you can either use a 0th or 1st order flatten.
I hope this helps, and I am happy to discuss this with your further if you would like.
Thanks,John
Hi Again.
Yes, I think John made an important point there -scanning with the fast axis (usually the horizontal axis of the image in the software) parallel to the fibre axis, can actually remove/lessen many problems.
For example, as mentioned, it will simplify processing, and lead to "removal" of effects due to different fiber radii (assuming you want to remove these differences). It should also allow you to scan more quickly since the feedback has less to do.
regards,