Here we outlines some principles for cleaving. These notes are specifically for oxides, which are often relatively hard to cleave. These notes do not apply to Van der Waals materials, which should usually be cleaved rather differently with tape.
- How well samples cleave depends a lot on their crystal symmetry. If the samples are hard to cleave, one can improve the chances of success by cutting or choosing a sample that is taller than it is wide by a factor of three or so. If you do cut a sample, consider making several samples at once to improve one’s odds of obtaining at least one good sample. In choosing the mounting note that you will want to be able to firmly hold the sample, for example via screwing the holder into a block of metal or putting the holder in a vice. Consider whether to label the sample holders at this point, so that they can be identified. If the sample is hard to cleave, and a lot narrower than it is wide, it might be worth making the lateral size smaller, especially if the sample has more than one terrace. This is only appropriate for relatively robust samples.
- Coat the holder and the back of the sample with torr seal glue. Aim that the glue surrounds the bottom of the sample at little, but that it is below halfway up the side of the sample.
- Stick down the sample onto the holder and press it with, for example, a cotton bud to ensure it is firmly seated. If you will cleave in vaccuum, this is the best time to perform a final check of the crystallographic alignment of the sample before it is cleaved. Make sure that the alignment is referenced to either a clear facet on the sample or a clear line drawn on the holder. You might want to quickly cure the glue a little so that the sample is held in place – it is unnecessary to fully cure the glue to full hardness at this point. Aluminum metal are popular choices for making the post.
- Prepare a post with a cross section of similar size to the top of the sample. Put torr seal on the top of the sample and on the post. Fix the post in place. Try to use enough glue to fully bind all of the top of the sample to the post, while avoiding putting so much glue that it attaches to the glue used for the bottom of the sample.
- Fully cure the epoxy. When doing the curing, it is worth also curing any left-over mixed epoxy, so that you can check the glue is fully hard before you cleave.
- If possible, make a notch halfway up the side of the sample that helps nucleate a single plane of cleavage.
- Knock the post off the top of the sample. Note that it is important to apply a short sharp tap and not a continuous push. Firstly, find a way to firmly hold the sample holder. Then either directly hit the post or rest something against the post and hit that. Be sure to catch the post and inspect both the sample and the post. This can be informative in terms of how successful the cleave was.