Friday, September 6, 2013

AFM is a different animal...

Because the SEM technician who runs the microscopy lab at TU has been gone I have shifted focus primarily to imaging micelles on a plain silicon surface.  Although for as many papers of it I see it seems like this would be just a sit down at the AFM and get it done in a day or even a few days task, it has proven me wrong.  The main issue that I have run across is that working with micelles on the AFM requires a degree of art and a degree of science.  After speaking with someone this week who has worked with AFM for some time, although not on surfactants or micelles specifically, I came to realize that you really have to come to know each component that you're using personally.  I have tried three tips so far that did not show promise and have moved onto a new set of three which I am hoping will at least point me in the right direction.  I have also been in contact with Agilent and Nanosensors.com regarding these subjects and while they are helpful I have come to the conclusion that it will all come down to trial and error with tips and cleaning procedures.  It becomes pretty frustrating when I use the AFM for several hours in a day and come away with nothing other than "this wasn't a tip that will do the job" or "that cleaning procedure left too much on the surface".  However, there is always another procedure and another tip to try and with free samples from probe manufacturers I have plenty to work with.  Once I find "the tip", the plan is to purchase some and coat the backside of a couple with magnetic material which could (has been shown to) increase resolution by decreasing the motion of the solvent (in our case water) by the piezo.  A MAC mode nose cone will facilitate this by creating an oscillating magnetic field which will vibrate the tip alone without the piezo.  
Another problem which I am dealing with is that most AFM studies done on silicon use a cleaning procedure which leaves the surface hydrophilic, usually by washing in an RCA-1 cleaning solution.  For now I am just trying to achieve imaging micelles so I am following this procedure, but my work around in the end is to try a plasma cleaning step on the PMMA layered samples which should leave the exposed silicon in the trenches hydrophilic.  The time of the plasma will need to be short in order to prevent damage which could alter the roughness of the exposed surfaces.  This week I am trying the PPP-BSI-SPI, the PNP-TR-SPL and the SiNi AFM probes.  They are all soft cantilevers (less that .1 N/m and roughly 15 kHz).  The problem I have seen with these types of cantilevers so far is that the slightest environmental factor, whether it's air movement from closing the door to the room or sneezing too loudly, causes the cantilever to become erratic.  I have developed a few procedural additions which help to lessen their effect and will post on the efficacy of the new tips soon.