Energy Shifts of the C 1s Lines from Adventitious Hydrocarbons on Gold Surfaces

In X-ray photoelectron spectroscopy (XPS), the correction of XPS spectra shifted due to surface charging is very important for chemical state determination. Although the C 1s line from the adventitious hydrocarbon has been widely used as a reference for the charge correction, this method has some problems. For example, there is a possibility that the C 1s peak energy of the adventitious hydrocarbon shifts depending on the experimental conditions and the XPS instruments. Therefore, we executed a round-robin test in which we measured the C 1s lines of adventitious hydrocarbon on gold plate and gold-coated substrates, and we verified whether the binding energy of the C 1s peak of the adventitious hydrocarbon correlated with the concentration of carbon using the same sample with the same energy correction method. We revealed the following results: (1) The binding energy of C 1s line from naturally grown adventitious hydrocarbon on gold plate was almost constant at 284.69±0.12 eV within the range of atomic concentration ratio of C/(C+Au)=0.52-0.78. (2) The C 1s binding energy of the hydrocarbon on gold-coated Ni42Fe58 alloy shifted higher with increasing the amount of hydrocarbon within the range of atomic concentration ratio of C/(C+Au)=0.41-0.67. (3) The C 1s binding energy of the hydrocarbon on gold-coated glass was 284.8 to 285.4 eV which is higher than other type samples without reproducibility. (4) When take off angle changed, the C 1s binding energy shift was maintained within 0.2 eV although the concentration of carbon apparently changed. (5) The C 1s binding energy shifted higher immediately after Ar+ sputter cleaning, and after few hours it shifted lower toward a binding energy of amorphous carbon, and then it shifted higher again with increasing carbon.