Hi, I am trying to obtain large area graphene (>100um) by mechanical exfoliation, and I seem to be unable to do so because of graphene sheets tearing in wedge-shaped features.
Does anyone know how to prevent this and obtain large area graphene by the tape method?
I have used the method known in this ACS Nano paper:
Huang, Yuan, et al. "Reliable exfoliation of large-area high-quality flakes of graphene and other two-dimensional materials." ACS nano 9.11 (2015): 10612-10620.
I have used Highly Oriented Pyrolytic Graphite (HOPG ZYA) bought from HQGraphene, and the substrate I am exfoliating on is SiO2(300nm)/Si. The tape I used was the blue Nitto tape ( I have tried the white Scotch tape, with the same wedge results).
Prior to exfoliation, the SiO2/Si substrate was sonicated and O2 plasma treated. After placing the tape with graphite flakes on the substrate, the substrate was placed on a hot plate of 100'C for 2 min.
(this step is known to produce larger area graphene)
I have tried at least 200 times, and still was unable to produce graphene flakes larger than 20um. The paper above introduces cases of at least 100um and even up to 500um size. I suspect this is because of the wedge shaped tearing that occurs as in the picture below.
Does anyone known how to prevent such tearing?
to prevent wedges in mechanically exfoliated graphene
you have to check the temperature parameter
You may get different HOPG. I noticed that HOPG from different suppliers could be very different even from the same DAY grade. My suggestion is to buy different HOPG to try.
No answer here but fantastic images, they look like the icy flames of hell!
Foued Zouai Thank you, I have tried three different temperatures (80'C, 100'C, 130'C) till now, but with no discernible difference in quality. The wedge shapes still appear.
Xuhua Wang Thanks, maybe it is a problem of the quality of the original HOPG single crystal. Do you have any recommendations of any supplier that I could use, other than HQGraphene?
Also, does anyone have any experience regarding the speed of exfoliating the tape from the substrate? I have tried both slow (30min/1cm with motor) and fast (by hand) but cannot seem to find which is better.
Here is the supplier we used to use. Please see the following
http://www.ntmdt-tips.com/products/group/hopg
I have, frustratingly, had very similar results to what you are showing when I have worked with HOPG (Momentive performance ZYA grade, very expensive) for graphene exfoliation.
Unless you are attached to HOPG, I would suggest taking a look at some other types of graphite crystals. Here is what I have found that works well for me:
For my work, NGS Naturagraphit brand natural graphite has yielded the largest area yields of graphene (as well as some very high mobility samples when encapsulated in hexagonal boron nitride). Using oxygen plasma treatment and scotch "magic" tape I have seen areas of monolayer graphene up to about 0.5 mm across. Other tapes seem to work decently, too. While these areas are not quite as large as what was seen in the ACS Nano paper from Huang at all, they were plenty large enough for my work.
As an aside, I have noticed that heating the sample on the hotplate has not been required for yields of large area graphene (or other 2D materials, for that matter). It does increase the yield slightly, but I have found that when trying to pick hot-exfoliated graphene up (with h-BN) off SiO2, it has been exceptionally difficult compared to samples which have not been heat treated. What has helped my yield of large area graphene is to press the tape quite hard to the substrate with my thumb prior to peeling.
Hopefully this helps!
- Badges
- Science topic
- Similar topics
- Chemistry
- Nanotechnology
- Nano