Question about imaging a biconcave sample and using the force scripting interface in Dimension Icon

nhung posted on Sat, Dec 3 2011 3:32 PM

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Hi,

I am using Veeco Dimension Icon. My sample is made of PLGA, and has a biconcave shape similar to red blood cell. The maximum diameter is about 30 microns, and the height is about 3 microns. I want to get a good image of the sample and then using point and shoot to get the force curve at specific locations.  I have tried two modes: QNM, and Tapping mode. However, I met some difficulties in getting good images and force curves.

1) With Imaging:

Using QNM and Scan-Asyst in Air probe, when the scan size is increased (30-50 micron), the error message "tip crash" pops up and asks for withdraw and re-alignment of the laser. I also tried to turn Scan Asyst off when imaging large area in QNM, however, that error still occurs.  

Using tapping mode (using Scan-Asyst in Air probe, I can't engage, so I changed to Tap 150 A). I can get the image of the large area, however, I was not sucessful to get the biconcave shape. Most of the images can only capture one part of the sample, the rest of the image is the substrate.  I tried to use "off set" to center at the sample, but some times the voltage drop off to the extreme cases (extended, or retracted - Red- Yellow) or sometimes the sample is moved. 

When an image is scanned, can I change the set point to to control the voltatge so that it doesn't turn red or yellow? Does it affect the image quality?

How can I get the sample at the center of my image? When I engage should I place the engagement point at the substrate or the sample?

Some of my images have the whole samples, but the top of the sample appear to be flat, or one side of the sample is flattened out. And it also depends on how I process the image (using flaten or plane fit 1,2 or 3 order). So, What should I do to capture the biconcave shape?

When I use the offline analysis, what order of flatten or plane fit should I use? Do I need to use both or just flatten is enough? For flatten, should I flatten the whole image or the image with the sample is excluded?  

2) Force curve:

a) Calibration:

To get the force curve, I calibrate using the hard sample (Sapphire in the QNM kit) to get the deflection sensitivity and then use thermal tune.

However, in the force curve, the approach and retract paths do not really coincide. I turned on Z-closed loop, using deflection set point 0.2V-2V, start mode: calibrate, end mode: retracted, scan size: 500 nm.

 And in the thermal tune, I choose the range 1-100 kHz, or 5-2000 kHz, but the curve I get is very weird. I only get a vertical line with the horizontal noisy base line, but not a parabolic shape like what it should be (I use QNM with scan Asyst in air, and when I calibrate, it works well and gives me k=0.4-0.6), but I don't know why do I get this weird shape when using tapping mode and Tap 150 probe. thus, the spring constant is very large (>200) which is unreasonable.

Do you have any advice or experience with it? Can the Thermal tune curve be the weird shape that I obtained?

b) I also want to perform the creep, and relaxation test to get viscoelastic infomation. I know that I need to use the scripting/ strip chart. And from one disscussion on this forum, it seems that the QNM does not have the ability to perform the creep or relaxation test, thus I go to Tapping mode, and Contact mode. But I could not figure out how to access the scripting interface in Dimension Icon. The expanded mode (the red puzzle) only gives the surface delay, retracted delay, but there is no way to get a scripting interface where I can input my data such as how long I can delay the ramping, set point (similar to creep and relaxation test). (I tried to use surface delay/retracted delay, but was not sucessful to get the creep/relaxation test) 

Thus, could you please let me know how to access the scripting interface to perform those tests on Dimension Icon?

Sorry for a long message with a lot of questions, but I have tried to repeat my experiment many times, and read the manuals, the threads on the website but still could not figure them out. I would really appreciate any suggestion, or comments so that I can get good imaging, calibration, and force scripting for relaxation and creep tests. In case emailing is more convenient: my email is:  "nhungng at umich.edu"

Thank you!!