( ( Observations ( of ( ( ( ( the monolayers ) , ) and ) ( rough ( friction measurements ) ) ) ) ) ( ( were ( made ( with ( an ( atomic ( force microscope ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (NNS Observations)) (PP (IN of) (NP (NP (DT the) (NNS monolayers)) (, ,) (CC and) (NP (JJ rough) (NN friction) (NNS measurements))))) (VP (VBD were) (VP (VBN made) (PP (IN with) (NP (DT an) (JJ atomic) (NN force) (NN microscope))))) (. .)))
Observations of the monolayers, and rough friction measurements were made with an atomic force microscope.
(ROOT (S (NP (NN Friction) (NN force)) (VP (VBZ is) (VP (VBN caused) (PP (IN by) (NP (NP (JJ microscopic) (NNS bumps)) (, ,) (VP (VBZ lumps)) (, ,) (CC and) (NP (NP (NNS imperfections)) (VP (VBG colliding))))))) (. .)))