High Speed Imaging while Heating and Cooling

Reply

Stephen Minne Posted: Fri, Oct 7 2011 3:32 PM

rated by 0 users

Dynamic heating and cooling AFM measurements can be challenging because the temperature changes can induce considerable drift both in position, and force control. Below is a video showing a high speed imaging dynamic experiment from 60 C to -2 C. Tip scanning greatly simplifies the temperature control, while low system drift makes possible the stability. PeakForce Tapping (rather than tapping), which “re-zeros” the force every interaction, enables the continuous imaging over the entire temperature range.

The sample is Poly(diethylsiloxane) (PDES). Siloxanes have broad application as greases, lubricants, elastomers and resins. PDES is a liquid crystal at Room Temperature. When heated, PDES transitions into a fully liquid state at it's isotropization temperature of ~ 60 C. Cooling back down, PDES undergoes two mesomorphic transitions:
Liquid -- Liquid Crystal (mesomorphic), Liquid Crystal -- Solid Crystal (~ -2 C).

AFM imaging can be used to study the film nano-morphology, and its changes
at each phase transition.

Enjoy,
Steve

Reply

dalia replied on Mon, Oct 10 2011 9:20 AM

rated by 0 users

Steve,

Neat video!  A couple of questions:

1) how did you prevent the tip from contaminating while you were heating nad imaging simultaneously?

2) how long did the whole experiment take?

3) how was sample affixed to the substrate (or maybe the film was spun coat or dip cast onto a substrate?)

Thanks!

Dalia

Reply

Stephen Minne replied on Wed, Oct 12 2011 3:55 PM

rated by 0 users

Hello Dalia, and glad you liked it. Regarding your questions:

1) How did you prevent the tip from contaminating while you were heating and imaging simultaneously?

No special precautions (ie tip coatings, heaters, etc) were taken in the instrumentation to prevent tip contamination, however a the experiment was conducted under a stream in N2 to prevent condensation during cooling. That said, in some cases because the sample is so sticky, the tip does become contaminated necessitating its change. In terms of imaging conditions, it’s important to use a large enough drive amplitude to make sure the tip always fully breaks free from the surface adhesion. Peak Force Tapping is useful here because, unlike Tapping, the pull-off force is inherently decoupled from the interaction force.

2) How long did the whole experiment take?

The video is 60 frames at 30s/frame, extracted from a 120 frame sequence, where 60 of the frames are “scan up” and 60 are “scan down”, for a total of 1hr. We often only use only frames in one direction in our videos so each pixel in each frame is separated by an equal amount of time. (If in the video, a frame down followed a frame up, the pixels at the top of the frame would have just been imaged in the frame-up, only to be immediately re-imaged in the frame down. Taking frames only in one direction, makes each pixel equally spaced in time by the twice the frame time.)

3) How was sample affixed to the substrate (or maybe the film was spun coat or dip cast onto a substrate?

PDES is a low molecular weight siloxane so it is pretty sticky (as you noted). The prep was done by simply smearing the PDES to the puck with a wooden stick - it’s sticky enough to adhere quite well. A melt cycle then makes it smooth enough to image. (This was done by Natalia who can give you details on the art if you wish.)

Best,

Steve