The monolayer formation time or monolayer time is the length of time required, on average, for a surface to be covered by an adsorbate, such as oxygen sticking to fresh aluminum. If the adsorbate has a unity sticking coefficient, so that every molecule which reaches the surface sticks to it without re-evaporating, then the monolayer time is very roughly:
where t is the time and P is the pressure. It takes about 1 second for a surface to be covered at a pressure of 300 µPa (2×10 Torr).