For the sake of clarity, structures are referred to by their initial configuration, rather than their fully relaxed configuration. Furthermore the monolayer to which metal atoms are adsorbed will be denoted by the chalcogen species as a prefix in the label, e.g. S-Neighbour-X is a Neighbouring (vide infra) configuration starting at site X on WS 2 . This allows for easy reference to the SI, which contains images for all final structures. It should be noted that due to the significant amount of adatom migration which often occurs during relaxation, the starting structure name may not describe the fully relaxed configuration. Nonetheless, this approach allows for a consistent description of copper-TMD adsorption structures. It is also important to note that different starting configurations may relax to the same final configuration, resulting in identical relaxed configurations being referred to by different initial labels.