Atomic underlayer formation during the reaction of Ti{0001} with nitrogen

Changes in the {0001} surface of Ti during exposure to nitrogen gas are monitored by low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES). Evidence is provided for the formation of a Ti{0001}1 × 1-N phase followed by a Ti{001} 3 × 3-30°-N structure. A LEED intensity analysis of the Ti{0001}1 × 1-N phase reveals that the N atoms penetrate into the octahedral interstitial holes underneath the first layer of Ti atoms. This is the first ordered monoatomic underlayer found in the earliest stages of any solid-gas interaction. The surface structure bears close resemblance to that of {111} planes in bulk TiN. We find a Ti-N bond length of 2.095 Å to be compared with the value of 2.120 A in bulk TiN. The analysis of the Ti{0001}1 × 1-N structure indicates that Ti{0001} 3 × 3-30°-N is not a low-coverage phase. The importance of recognizing the existence of 1 × 1 phases prior to the formation of superstructures is emphasized, and some procedures for extracting the information from experimental observations are discussed. © 1976.