Cryogenic X-Ray Photoelectron Spectroscopy

X-ray Photoelectron Spectroscopy (XPS) is a surface sensitive technique (top 10-15 nm) with sensitivity down to single atomic layer. XPS provides unique information about elemental composition and on the chemical and electronic state of the element in the material. One of the basic requirements for the successful XPS analysis is high vacuum atmosphere (1·10^-9-1·10^-10 torr) iside the instrument, therefore XPS samples are usually nonvolatile solids or powders.

For some research goals, it is essential that not only the composition, but also the morphology of the sample preserved during the measurements. This is particularly important in the studies of the biological objects and natural products, where the sample is kept in its “natural atmosphere” (ambient pressure or aqueous solution). High vacuum requirements make practically impossible analysis of this kind of samples by XPS.

However, if the morphology of the sample can be preserved by freezing, and the sample kept frozen during the measurements, its treatment becomes similar to the nonvolatile solid samples and it can be easily analyzed by XPS.

In addition to the basic functions of standard XPS, our instrument is equipped with the cooling assemblies located in the loading and measuring compartments of the instrument. Sample (liquid or high volatile solid) is freezing during the loading to the XPS machine, using the fast freezing procedure^1-2, and remains frozen up to its removal from the instrument.

In this work we present several examples where cryogenic XPS was successfully used for the qualitative and quantitative analysis of the biological samples and for the study of the kinetics of chemical reactions.

1. Burger K. et al., Nucl. Chem. Lett., 1974, 10, 171-177.
2. Shchukarev A., Interf. Anal., 2006, 38, 682-685.