Low-temperature static friction of N2 monolayers on Pb(111)

Using a quartz crystal microbalance technique, we have measured the interfacial viscosity of nitrogen monolayers deposited on very homogeneous Pb(111) surfaces. At temperatures below 15 K, no dissipation is detected, suggesting that the N2 films are rigidly coupled to the oscillating electrode. By raising the temperature close to 20 K, we find sliding of the nitrogen film for coverages above about 0.5 nominal layers. The observed temperature dependence is in good qualitative agreement with recent calculations on the static friction of a nitrogen slab in contact with a crystalline Pb substrate.