4. Bring your own or make your own

Once the surface has been prepared under ultra-high vacuum, the molecules or atoms must be transferred to it without polluting it, which means no direct contact with solvents. Until recently, adsorbates were transferred by sublimation of powders contained in an electrically heated crucible. However, this simple technique does not allow the deposition of large molecules with very low vapour pressures, nor of molecules that are too fragile due to thermal activation. This difficulty has led to the emergence of new solutions: firstly, transfer techniques and, secondly, by circumventing the problem, in situ synthesis of large molecules from small precursors that are easy to sublimate.