Imaging with XPS

Tatyana Bendikov, Chemical Research Support, Weizmann Institute of Scince, Rehovot, Israel
Rivka Maoz, Materials and Interfaces, Weizmann Institute of Science, Rehovot, Israel
Jacob Sagiv, Materials and Interfaces, Weizmann Institute of Science, Rehovot, Israel

X-ray Photoelectron Spectroscopy (XPS), as a surface sensitive technique with the sensitivity down to single atomic layer, provides unique information about elemental composition and chemical and electronic states of elements in the material. For some research goals, however, this knowledge is not sufficient as it does not provide the entire information required for a comprehensive characterization of the investigated system. In addition to the basic functions of standard XPS, our instrument is equipped with advanced capabilities such as XPS imaging, which is particularly valuable in the analysis of patterned or inhomogeneous specimens.

In line with the Hemispherical Analyzer, that is required to obtain electron energy spectra and can be used for imaging in the scanning (low resolution and relatively slow) mode, our XPS instrument is equipped with an additional Spherical Mirror Analyzer especially suitable for imaging applications. Together with a Delay Line Detector, this analyzer allows fast acquisition of high resolution (3-5 μm) images in the parallel mode (Parallel Imaging) from areas up to 800×800 square micrometers. Following image acquisition, specific areas can thus be chosen and small spot XP spectra acquired at sites of particular interest. This information is useful in the characterization of patterned surfaces or inhomogeneous samples with surface features between several to hundreds of micrometers. The sensitivity and resolution of parallel imaging is sufficient for the analysis of different functionalities in thin film samples down to single monolayers.

As a test system for the investigation of patterned surfaces we used silicon wafers coated with a self-assembled monolayer of n-octadecyltrichlorosilane (OTS) on top of which a patterned silver film was deposited consisting of 20-30 μm wide silver squares spaced 20-30 μm apart. The XPS images of such Ag/OTS/Si patterns offer direct evidence for the lateral distribution of their Ag, C, O and Si constituent elements.