Thermal stability of atomic-order nitrided Si(100), Si(0.6)Ge(0.4)(100) and Ge(100) formed in NH(3) gas environment at 400 degrees C and structural change of the nitrided surface were investigated. It was found that N atom amount on Ge(100) tends to decrease at higher heat-treatment temperatures above 400 degrees C. Especially with H(2) heat treatment, the N atom amount on Ge(100) becomes below detection limit for X-ray photoelectron spectroscopy measurement. On the other hand, it was confirmed that the N atom amount on Si (100) and Si(0.6)Ge(0.4)(100) is almost independent of heat-treatment conditions in the temperature range of 400-700 degrees C. From the change of chemically shifted components in Si 2p and Ge 3d spectra for Si(0.6)Ge(0.4)(100), it is suggested that N atoms bound to Ge atoms tend to be transferred to Si atoms at higher heat-treatment temperatures above 400 degrees C. (c) 2008 Elsevier B.V. All rights reserved.