Step bunching on TaC(910) due to attractive step-step interactions

Using scanning tunneling microscopy, we study the step configuration on TaC(910) which is vicinal to the (100) plane, miscut 6.34{sup o} toward the [010] direction. After annealing at {approx}2100{sup o}C, the surface is dominated by double-height steps which are bunched between relatively long intervening (100) terraces. The step-separation distribution is very skewed and sharply peaked. Monte Carlo simulations show that a strong, medium-range, repulsive step interaction A/x{sup 2} must be combined with a weak, long-range, attractive interaction, -B/x{sup 1.0{+-}0.5} to fit the measured distribution. Possible physical origins for these interactions are discussed.