Adhesion is a phenomenon that occurs when two surfaces come sufficiently close in contact. It can be observed in the nanoscale and is important in applications such as the head-disk interface in hard disks (HDI), or in micro-electro-mechanical systems (MEMS), where the involved structures are extremely tiny and their surfaces are relatively smooth. In cases where the roughness is large enough, adhesion is neglected. It is also neglected in cases where a liquid substance exists between the two surfaces, when capillary forces, which are much larger and more significant, are very likely to occur.
However, in the applications where it is needed, adhesion can be calculated using equations that were derived from physical principles (LJ potential). One, commonly used, set of equations for adhesion is known as the Improved DMT (IDMT) Adhesion Model. It has two components; one calculates the adhesive forcebefore contact occurs, while the other is used for cases whencontact has occurred. Other models are used, depending on the system parameters, such as the JKR and the Maugis-Dugdale models, which are both valid only for cases where contact has occurred. The DMT model considers that adhesion forces act only outside the contact area, while the JKR model, which is only valid where contact has occurred, considers that the adhesion forces only act within the contact area. An adhesion parameter is used to establish the appropriate adhesion model for each system.