Instability and transformation kinetics of the reconstructions in carburized W(1 1 0)

We investigate the instability and transformation kinetics of the carbon-induced surface reconstructions on W(1 1 0) by the low temperature scanning tunneling microscopy. R(15×3) reconstruction, a moiré pattern of W₂C(0 0 0 1) bi-layer on W(1 1 0), is the most carbon-rich reconstruction on the carburized W(1 1 0), which gradually transforms to the most carbon-poor R(15×12) reconstruction by repeated annealing at around 2070 K. In between, various reconstructions, albeit not globally ordered, develop. Notable is that all the observed reconstructions are invariably composed of only two kinds of building blocks, namely A-block and B-block. A-block is the surface unit cell of the R(15×3) reconstruction. During the transformation, the virtually carbon free B-block is created at the cost of two neighboring A-blocks by the annealing. The robustness of the block structure allows us to perform a coarse-grained kinetic Monte Carlo simulation of the transformation in terms of the creation and diffusion of B-blocks on the R(15×3) lattice that is initially entirely tiled by A-blocks. We find that the transformation kinetics is governed by both the anisotropic creation and diffusion of B-block that are attributed to the instability of A-block driven by the anisotropic compressive stress in it.