X-ray Degradation of Cu(OH)2

X-ray induced degradation of copper (II) species can complicate interpretation of results. One way to mitigate this issue is to perform the analysis of the Cu 2p (and Cu LMM Auger line) first and in as few scans as possible, then perform subsequent needed analysis afterward (e.g. other high resolution spectra, survey scans).  If the mechanism of reduction is due to thermal effects, as it appears to be for Cu(OH)2, cooling of the material can reduce the amount of degradation significantly. The charts below for copper (II) hydroxide samples analyzed by XPS at normal operating temperatures (top) and cooled to -100C (bottom) using the same X-ray source (15 kV, 14 mA, monochromatic Al K(alpha)) and charge neutralizer conditions (Kratos AXIS Ultra system) show that degradation is slowed significantly for the cooled sample.  Notably, degradation is minimal for the cooled sample for the initial window of analysis. 

X-ray induced degradation of Cu(OH)2 - normal operating temperatures.

X-ray induced degradation of Cu(OH)2 - sample cooled to -100C.

X-ray Degradation

It is important to remember that for certain samples the action of sample irradiation can change the sample chemistry - affecting the spectra obtained. This X-ray induced degradation is important to remember in the analysis of polymers and has been seen in the analysis of metal oxides. For polymers, keeping analysis time to a minimum can help negate this issue as can lowering the X-ray flux.

Metal oxides/hydroxides can also be susceptible to this effect. As local heating may play a role here one option to help mitigate this effect (in addition to minimizing analysis time or lowering the X-ray source flux) is to cool the samples using an in situ cooling stage (generally cooled using liquid nitrogen).  This has been shown to help in the analysis of copper and vanadium oxides [1].

Reference:
[1] M.C. Biesinger, L.W.M. Lau, A.R. Gerson, R.St.C. Smart, Resolving Surface Chemical States in XPS Analysis of First Row Transition Metals, Oxides and Hydroxides: Sc, Ti, V, Cu and Zn, Applied Surface Science, 257 (2010) 887-898.