Pervasive orientational and directional locking at geometrically heterogeneous sliding interfaces

TL;DR

This paper investigates how crystalline clusters with various lattice structures lock in orientation and direction when sliding across different regular substrates, revealing complex relationships influenced by surface symmetries and moiré patterns.

Contribution

The study generalizes the understanding of orientational and directional locking to arbitrary lattice and substrate symmetries, supported by experiments, simulations, and a new formalism.

Findings

Locking features occur for arbitrary lattice and substrate combinations.

Locking orientations and directions are correlated via moiré patterns.

The formalism describes complex locking relations for diverse symmetries.

Abstract

Understanding the drift motion and dynamical locking of crystalline clusters on patterned substrates is important for the diffusion and manipulation of nano- and micro-scale objects on surfaces. In a previous work, we studied the orientational and directional locking of colloidal two-dimensional clusters with triangular structure driven across a triangular substrate lattice. Here we show with experiments and simulations that such locking features arise for clusters with arbitrary lattice structure sliding across arbitrary regular substrates. Similar to triangular-triangular contacts, orientational and directional locking are strongly correlated via the real- and reciprocal-space moir\'e patterns of the contacting surfaces. Due to the different symmetries of the surfaces in contact, however the relation between the locking orientation and the locking direction becomes more complicated compared to interfaces composed of identical lattice symmetries. We provide a generalized formalism which describes the relation between the locking orientation and locking direction with arbitrary lattice symmetries.