Introduction
Curve fitting in XPS data analysis is crucial to extract important chemical bonding information, however, this is the most difficult, ambiguous, and sometimes questionable step in XPS data analysis since a perfectly fitted curve can always be obtained by adjusting the fitting parameters. Three different ways were pointed out in a previous publication to eliminate the ambiguity caused by curve fitting, comparing the data to data from standard samples [2,3], monitoring the continuous surface modifications due to gradual increases in surface species under heating, cooling, or irradiation , and investigating the continuous surface modifications caused by slowly sputtering the surface . It is difficult to assign the chemical components or chemical bonds from binding energies (BEs) of photoelectrons of one element especially when samples were fabricated by different methods under various conditions in different laboratories. However, it was shown in this study that the assignment of N 1s photoelectrons to three different oxidation states of N + , N 2+ , and N 3+ in aluminum oxynitride films fabricated by different methods under various conditions in different laboratories can still be done by carefully comparing the XPS N 1s spectra to other previous publications.
In addition to published handbook of XPS [6], two web-based XPS data set indeed listed the possible oxidation states of elements by their various binding energies such as http://www.uksaf.org and http://srdata.nist.gov/xps/ which can be used to guide how to fit the XPS spectra; however, it is only the first step to assign the correct oxidation states of an element since too many available results for a single element were listed. A further step necessary to assign the oxidation states for an element is searching the literatures of related surfaces you are working on. Even many related publications of the same surfaces prepared by different methods under various conditions in different laboratories were found there are still lots of work to sort, to check, and to compare such that final assignment of oxidation states of a single element can be done. It is shown in this work how the correct oxidation states of N + , N 2+ , and N 3+ in aluminum oxynitride films were assigned and possible associated chemical forms, AlO 2 N, Al 2 O 5 N 2 , and AlO 3 N, were deduced through the processes mentioned above.
2. Experimental
Aluminum oxynitride films used in this work were deposited on B270 glass by ion-beam sputtering. The chamber was pumped down to a base pressure of 7 ร 10 ร6 Torr before deposition. The total pressure of nitrogen working gas fed into the ion source combined to various oxygen partial pressures during the deposition was kept at 2.0 ร 10 ร4 Torr. A pure Al slab (99.99% purity) was used as a sputtered target and mounted on a water-cooled copper