Impact of sample storage type on adventitious carbon and native oxide growth: X-ray photoelectron spectroscopy study

Highlights

• We test the effects of common sample storage environment on XPS spectra.

• Samples are thin films of transition metals (TMs), TM nitrides, and TM diborides.

• Keeping samples in sealed polyethylene bags with direct surface contact is the worst option.

• Locked polypropylene wafer carriers or polyethylene boxes are recommended.

• Results provide guidance for all studies where in-situ cleaning is not applicable.

Abstract

The type and degree of contamination on surfaces intended for X-ray photoelectron spectroscopy (XPS) studies is considered decisive for meaningful and reliable analysis as in many cases in-situ cleaning methods are not applicable or otherwise undesired. We report on the effects of sample storage environment on predominantly carbon- and oxygen-containing species accumulating on the surfaces of fourteen types of thin film samples spanning group IVB-VIB transition metals (TMs), TM nitrides, and TM diborides. All specimens were deposited by magnetron sputtering and stored for six months in different common sample storage environments such as openly on a shelf in the office or XPS lab, or within a polypropylene wafer carrier, polystyrene box, cellulose/polyester wipers or sealed polyethylene bag. Self-consistent modelling of C 1s, O 1s, B 1s, N 1s, and metal core level spectra allowed to identify the types and quantities of surface contaminants, metal oxidation states, and thicknesses of native oxides, as well as to address influence from storage ambient type and volume, direct sample contact to other surfaces, or material release from containers. The results reveal significant differences between the various storage types and, hence, provide guidance for all sorts of studies including even those that employ Ar⁺ ion etch prior to analyses, as also in such cases the amount and type of surface contaminants may impact the outcome.