{"id":117,"date":"2023-10-24T07:33:28","date_gmt":"2023-10-24T07:33:28","guid":{"rendered":"https:\/\/flats.c2n.universite-paris-saclay.fr\/?page_id=117"},"modified":"2026-09-09T13:45:04","modified_gmt":"2026-09-09T13:45:04","slug":"stacking-twisting","status":"publish","type":"page","link":"https:\/\/twistronics.c2n.universite-paris-saclay.fr\/?page_id=117","title":{"rendered":"Stacking"},"content":{"rendered":"\n

Before starting to stack your 2D materials you should think in what type of stack you want to do and what are the more appropriated methods to do so. Here are some examples:<\/p>\n\n\n\n

Stacking to a fragile substrate (e.g., TEM grid):<\/mark><\/strong> For this you migth want to use the membrane transfer. This one consist in exfoliating in a polymer and releasing this as a membrane to later deposit it the target substrate. You can find all the details in this article<\/a> and its supplementary.<\/p>\n\n\n\n

Stamping:<\/mark><\/strong> This is the so called dry technique and consists in using a 2D material to pick up sucesive 2D materials. One of the first publications to explain the technique is here<\/a>. The animation below is very self-explanatory of the process.<\/p>\n\n\n

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Illustration of the principle of stacking 2D materials process. Courtesy of Cory Dean (Columbia University).<\/strong><\/figcaption><\/figure>\n<\/div>\n\n\n

The process consist in picking up the different 2D materials one at the time using a combination of polymers (e.g.<\/em>, PPC or PC on top of PDMS) or a SiN membrane (see here). After picking up all the different 2D materials the polymer is melted on top and the stack deposited on the substrate of your preference.<\/p>\n\n\n\n

The hot pick up technique<\/mark> (under construction)<\/strong>:<\/p>\n\n\n\n

Bubble squeezing: <\/mark><\/strong>After picking up all the layers you might realize that some bubbles are formed in your stack. This are formed of tape residues, water and\/or air. To clean up your stack you can squeeze the bubbles mechanically at higher temperatures. The techniques to do this (either with PC or PPC) are described in the following article<\/a>. As you can see in the pictures bellow the technique is very effective to get ride of bubbles<\/p>\n\n\n\n

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Stack on PPC slide before bubbles squeezing<\/strong><\/figcaption><\/figure>\n<\/div>\n\n\n\n
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Squeezing process in progress<\/strong><\/figcaption><\/figure>\n<\/div>\n<\/div>\n\n\n\n

PDMS stamping:<\/mark><\/strong> As you could see all along this post we have mentioned two main polymers PC and PPC that are deposited on top of PDMS, these are the most used ones in for the stacking. However, there are other polymers also used for this, in the following table we summarize them and give you their main use and temeprature range to be used.<\/p>\n\n\n\n

Polymer<\/strong><\/td>Temperature <\/strong>
pick-up<\/strong><\/td>		Temperature release<\/strong><\/td>Cleaning<\/strong><\/td><\/tr>
PPC
Ploy(propylene carbonate)<\/td>		40 o<\/sup>C<\/td>80 o<\/sup>C \u2013 120 o<\/sup>C<\/td>Annealing in vacuum
at 360 o<\/sup>C<\/td><\/tr>
PC
Polycarbonate<\/td>		90 o<\/sup>C<\/td>185 o<\/sup>C<\/td>Chloroform<\/td><\/tr>
PET
Poly(ethylene terephthalate)<\/td>		60 o<\/sup>C<\/td>130 o<\/sup>C<\/td><\/td><\/tr>
PVC
Poly(vinyl choride)<\/td>		70 o<\/sup>C<\/td>130 o<\/sup>C<\/td><\/td><\/tr>
PCL
Poly(caproalactone)<\/td>		30 o<\/sup>C<\/td>60 o<\/sup>C<\/td><\/td><\/tr><\/tbody><\/table>
Table of polymers to transfer 2D materials in a PDMS stamp<\/strong><\/figcaption><\/figure>\n\n\n\n

Cutting 2D materials<\/strong><\/h2>\n\n\n\n

Now that you have the basic notions of stacking you can start preparing twisting heterostructures. For twisted graphene structures the most widely used technique is the tear and stack technique detailed here<\/a>. However, the tear part of this technique has been proven to give many problems of breaking the layers. A clear improvement in reproducibility has come with the implementation of different techniques to cut graphene before starting the stacking. Here we list few of them:<\/p>\n\n\n\n