This observation is clearly seen for two different systems: (a) the friction of a nano-scale AFM tip sliding on a surface of graphene layers (which simulates AFM lateral force measurements) and (b) the friction between the graphene layers themselves. In case (a), it was shown that the friction decreases with increase of the number of layers [23] and [25], while in case (b) the friction was found to behave in the opposite way, achieving higher friction or stick-slip behavior once the number of layers increased to more than three[21] and [22].