SCANNING-TUNNELING-MICROSCOPY STUDY OF FACETING ON HIGH-STEP-DENSITY TAC SURFACES

We have studied the morphologies of the TaC(310), (210), and (110) sur faces using scanning tunneling microscopy. Heating the crystals to hig h temperatures activates a faceting of these surfaces into a hill-and- valley structure consisting of enlarged (100) terraces and (010) step walls. Step-separation distributions obtained from these surfaces can be well fit by sharp Gaussians and are much narrower than predicted fo r the noninteracting terrace-step-kink model, indicating a strong repu lsive interaction exists between steps on the faceted surfaces. This f aceting is suggested to be driven by a decrease in the total step repu lsive energy through a reduction of the total number of step pairs.