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hi
Iam usind INNOVA ..when I am takindg contact mode force curves ,whatever is my sample my sensor response is not changing....I am getting similar sensor response for both hard and soft samples..
so please give me an advice how it would happen?
Hi Remya,
The slope of the force-distance curve will only change if your cantilever is actually stiff enough to indent the sample to some extend. Keep in mind that the force a cantilever can exert for a given z-movement is described by Hooke's law. So if you want to see a difference in complience of your sample by evaluating the slope of a force curve you have to choose a cantilever with an appropriate spring constant. This has nothing to do with your machine but rather with your choice of cantilevers.
On the Innova also take advantage of always using the "closed-loop z" option to eliminate z- hysteresis.
Stefan
Hello Remya,
A few things to consider. I am actually curious what you intend to measure on a memebrane. Membranes are usually homogenous so you would not expect any differences in the force curves. Besides that:
1. Make sure that your membrane is supported properly. If it is suspended then you might not indent it at all but just flex the whole piece.
2. Your measurement will depend on the thickness to an extend. I.e. if your memebrane is very thin you might actually push onto the substrate.
3. Make sure to carefully select the area you are attempting your indents. You want to avoid maming an indent in a pore of the mebrane. The "probe positioning (point and shoot)" feature should be used on your Innova.
4. Maybe a TAP150 is a good start. You may want to contact Bruker AFM Probes and ask them for a few samples of cantilevers with different spring constants. This way you can easily figure out which one(s) will give you success.
Good Luck
I am not sure what you are trying to achieve but steel has a Youngs modulus of around 100-200 GPa, Silicon is about in the same range depending on crystal orientation and so forth. So these are not accesible with a TESP tip at all. Our Nanoindention cantilevers are the stiffest ones we make at a k around 350 N/m equipped with a diamond tip but even then you obviously have a limit.
If you want to find out if you really make an indent I would suggest that you pick a rather soft sample and scan a smalla rea, maybe around 500nm - 1um. The make a few indents by executing force curves with various loadings. After that scan the area again and look for the indents. Measuring the indent will also give you additional useful information.
Best,
What exactly do you mean by "my force curves are not changing"? Do you get a force curve ? Are you wondering why the slope is the same? It would be helpful if you could post a screenshot here or alternatively you can email the screenshot to me and I can post it for you.
Stefan (stefan.kaemmer at bruker-nano dot com)
I think slope of the force distance curve should change according to the sample used....but in my machine either my sample is soft or hard it gives same slope....and I will send the screenshot today itself
Hi Stefan,
Thanks for your reply...Actually the sample i am using is a polymer membrane....so can you give me a rough idea that what should be the stiffness of cantilever i should use to get a better result.
Remya
Hi Stefan
I have used sapmles like PTFE, steel and silicon...the sensor response Im getting are 0.0475,0.0152,0.0151 respctively....and the standard modulus values for this samples are 0.5,200 and 112 respectively.....so can u tell me what shd be the sensor response i should get with these samples.....I just want to make sure that im getting correct values or not. the tip I have used is TESP (stiffness 42N/m)
Dear Stefan
Thank you very much for your comments and suggestions,we have great problems in getting useful results with INNOVA and any help you can give will be much appreciated.
We are trying to obtain a range of soft polymer samples.When we get then we will do some indentation works.In the meantime we indent to do the following.
1.Use a flat PTFE substrate of 5mm
2.we will use 3 cantilevers,OTR(Si3N4) of 0.15N/m ,DLCT of 5N/m and TESP of 42N/m stiffness.
3.We would use Z end(while taking force distance curves) of 300nm and set point voltage(load) of 2V and7V.
4.We will record the sensor response.
5.we will record the voltage(deflection) against piezo movement.
6.we will plot force separation curves
we will send you all the datas including the raw data and I shall be grateful for your comments and suggestions of wher to proceed
With regards
That sounds good. Once you email me I will also get in touch with the local applications center in your region to make sure they are up to date. I do have a comment on on of your statements:
" 3.We would use Z end(while taking force distance curves) of 300nm and set point voltage(load) of 2V and7V."
Please keep in mind that they is a difference between "setpoint volatge" and 'load". E.g. If you adjusted your mirror so that the detector signal is exactly 0V just before the tip touches the surface, then your setpoint voltage indeed becomes the loading voltages. If your detector signal is however +1V just before touching a setpoint voltage of +2V will only load the lever with 1V. The opposite is of course true for negative detector readings before touchdown. This is nothing to worrry about one just has to be aware of it!
" 6.we will plot force separation curves"
I think that the current analysis software does not allow to calculate separation plots from force curves coming from Innova. We are working on that. So plotting a regular force-distance curve will do OR you simply read in the data with external software for the time being and calculate it yourself.
From the 3 cantilevers you posted I think only the RTESP will actually be able to indent your sample sufficiently. Thry to find a smooth portion of your sample before you start indenting in order to actually see the indent made. I also suggest recording the sensor response of your cantilevers on a silicon or steel substrate before using the PTFE sample.
thanks for your reply....I have send the datas in your mail .kindly check...
I got your data, thank you. I emailed back with some questions.
Just a general comment that may be useful for a larger audience: In order to convert the cantilever deflection from [Volt] to [Newton] one has to do two things:
1. Measure the sensor respose. The sensor respoinse is [nm/Volt]. So by combining the deflection value with the sensor response one can convert the deflection now to a length. You perform that task by measuring the slope of a force curve on a sample that can not be indented, i.e. saphire (Often a piece silicon will do just fine). Once the slop is measured one can e.g. on an Innova or Dimension Edge click on the "calibrate" button in the force-curve menu and that sensior response is now used by the system.
2. One has to enter the spring cionstant of the cantilever. Depending on the stiffness of the lever various methods are possible to calibrate the lever. Juts as a try one can just use the nominal value but be aware that this can be way off.
The important thing is to measure the deflection sensitivity on a hard sample. Otherwise everything from there one will be wrong.
I have few more doubts...I have taken force curves on some soft polymer samples (polypropylene,nylon,gls epoxy etc).I have used TESP of 42N/m stiffness and i have got sensor response somwhat same for all the samples..nearly 0.03um/volt....when I calibrated my tip i got stiffness value around 5N/m...which is very less than expected....so can u give me an advice why i got such a small value?
I am not exactly sure what you are doing. There are a few steps to consider
1. The "sensor response' has to be calibrated on a "hard" surface that can not be indented by the cantilever/tip you are using. For your TESPs you may want to use a piece of sapphire or silicon. If you use a soft surface your values will not make sense.
2. If you get the same slope on different materials it means just that. It is a result that tells you that you very likely did not ident the sample significantly, hence the same slope. Did you try scanning the area looking for an indent? That would be useful thing to do.
3. What do you refer to when you say that you got a stiffness of around 5N/m? Did you try calibrating the spring constant of the cantilever?
4. I tried loading the data you send me into Nanoscope analysis but was not succesful. Mybe next time you can also send a "screen shot" by pressing Alt-PrtScreen and saving it in paint to have a look.
Thanks,
I have few more doubts.while taking force distance curve(we are taking it on bacteria) we used to keep the parameters Z start=-2.5um and varies the Z end value.We have taken f-s curves at different Zend values like 50nm,100nm,300nm,700nm. After that we have plotted force Vs indentation curves.Indentation is d1-d2
d1=sample movement
d2=cantilever movement
When my Zend value increases from 50 to 700nm my d1-d2 also increases...Can you tell me how this happens?Can you tell me the significance of Zstart and Zend while taking force -distance curves?How the piezo scanner is moving according to Zstart and Zend?