Non-contact friction between nanostructures

TL;DR

This paper investigates non-contact van der Waals friction between nanostructures, revealing significant differences based on motion direction and surface conditions, with implications for nanotechnology applications.

Contribution

It provides a detailed theoretical analysis of van der Waals friction in different configurations, including effects of adsorbates and surface plasmons, and compares results with experimental data.

Findings

Friction differs greatly between normal and parallel motion.

Adsorbates and surface plasmons can enhance friction by orders of magnitude.

Resonant photon tunneling dominates friction when surface modes are supported.

Abstract

We calculate the van der Waals friction between two semi-infinite solids in normal relative motion and find a drastic difference in comparison with the parallel relative motion. The case of the good conductors is investigated in details both within the local optic approximation, and using a non-local optic dielectric approach. We show that the friction may increase by many order of magnitude when the surfaces are covered by adsorbates, or can support low-frequency surface plasmons. In this case the friction is determined by resonant photon tunneling between adsorbate vibrational modes, or surface plasmon modes. The theory is compared to atomic force microscope experimental data.