making mica-peeled gold samples

[Jason Haaheim]

Preparation of mica peeled gold samples

Required supplies:
EPO-TEK 377 High Temperature Epoxy
150ºC Oven for curing the samples
Gold Mica substrates from Molecular Imaging, small (1.4 cm x 1.1 cm)
0.5 oz coverslips 12 mm #1
Diamond scribe
Kimwipes
Small plastic pipet tip for dispensing epoxy
Piranha (3 parts H2SO4 : 1 part H2O2)
Ethanol for rinsing
DI water for rinsing
Clean tweezers for handling

1) Lay down a cushion of kimwipes several layers thick, and break glass slides in half using the diamond scribe and tweezers. One particular method which works well involves placing tweezers at the center of the glass slide and then initiating a crack at the edge of the slide with a diamond scribe while pushing down with the tweezers.
2) Piranha clean the glass slide halves for 15 minutes. Piranha consists of 3 parts sulfuric acid and one part hydrogen peroxide; add the H2O2 first and then the H2SO4. Hydrogen peroxide should be stored in a cool place so that it retains its effectiveness. After cleaning, dispose of piranha solution in proper container.
3) During the piranha clean, mix up the epoxy, parts A and B, adding 500 ml of each part and mixing well. Set the oven to 150ºC, setting number 5.
4) Rinse slides thoroughly with DI water, 5 X per side, flipping over.
5) Rinse slides thoroughly with ethanol, 5 X per side, flipping over.
6) Remove slides to clean kimwipe and let air dry.
7) Remove gold from storage tubes and inspect, flipping the scribed side down. The backside of each of the samples is scribed.
Picking up a small amount of the epoxy with the eppendorf tip, draw a line of epoxy on the mica peeled gold, as seen in the diagram below. Choosing a clean slide half circle, place on top of the epoxy, allowing the epoxy to naturally spread out underneath the slide. There should be no need to press down on the slide, as the line of glue should be enough to wet the entire gold/slide interface.
Repeat this process with the second slide half and place in a clean Petri dish.
9) Anneal in 150ºC oven for 2 hours, and no longer. Remove and let cool to room temperature.
10) To use, peel the glass side off the time mica and flip over to expose the atomically flat, fresh gold surface. Samples can be stored unpeeled in air for several months and still remain very good.

[Jason Haaheim]

Relevant question regarding mica-peeled gold:

...my questions for your are: in the mica-peeled gold process, does the gold peel 100% completely from the mica surface (that is, all the gold that is covered by epoxy and the glass support)? I assumed that it does based on the little bit of information I found from your papers and Nanoink's website. Also, in order for the separation process to work, does the mica need to be the absolute best freshly cleaved surface possible, or can lower grade micas be used (or maybe the cleaving process is not done perfectly)?

Also, do you think other types of epoxies or adhesives, besides the one listed by you (one requiring a thermal cure at 150 degrees C), would also work for the peeling process, or is the light temperature cure actually needed for good gold peeling?

The short answer is yes: the gold completely peels from the mica …(when done carefully and correctly). The caveat mainly has to do with what kind of backing material you use for the peeling (e.g. glass coverslip), and which kind and how much epoxy you use. Yes – fresh-cleaved mica surface is best, highest grade you can get.

In terms of the epoxy, I’ve had poor luck any time I’ve deviated from the listed epoxy or cure temp. There may be others out there, but I haven’t had the time or patience to wade through them all!

Bottom line: it will take you a while to get the feel of this just right. The cleaning has to be immaculate, and if there’s just a little too much (or too little) epoxy, the results are pretty poor. But when you get it just right the substrates are incomparable.