Bismuth telluride is a well-studied topological insulator. Its physical properties have been shown to change at highly reduced thicknesses, when its conducting surface states are exposed and isolated. These thin samples are obtained through either epitaxy or mechanical exfoliation.
Epitaxial growth methods such as molecular beam epitaxy and metal organic chemical vapor deposition are common methods of obtaining thin  samples. The stoichiometry of samples obtained through such techniques can vary greatly between experiments, so Raman spectroscopy is often used to determine relative purity. However, thin  samples are resistant to Raman spectroscopy due to their low melting point and poor heat dispersion.
The crystalline structure of  allows for mechanical exfoliation of thin samples by cleaving along the trigonal axis. This process is significantly lower in yield than epitaxial growth, but produces samples without defects or impurities. Similar to extracting graphene from bulk graphite samples, this is done by applying and removing adhesive tape from successively thinner samples. This procedure has been used to obtain  flakes with a thickness of 1 nm. However, this process can leave significant amounts of adhesive residue on a standard Si/SiO substrate, which in turn obscure atomic force microscopy measurements and inhibit the placement of contacts on the substrate for purposes of testing. Common cleaning techniques such as oxygen plasma, boiling acetone and isopropyl alcohol are ineffective in removing residue.