Cleavage and brittle fracture in GaAs: Indication of lattice dynamic instability on the nanometer scale

Atomic configurations of cleaved GaAs (110) surfaces are analysed to check existing models of cleavage and step formation in solids. Morphologies of $1\;\mu{\rm m}^2$ were investigated in UHV at 300 K with a Scanning Tunneling Microscope and compared to Monte Carlo simulations. The analysis supports the view that the processes involved in fracture are far from thermal equilibrium. Two characteristic length scales are found in the morphologies. Mean terrace widths of 10 nm and large-scale fluctuations of 100 nm both point to non-linear lattice dynamic instabilities which occur during crack propagation.