Experimental setups for XPS measurements beyond the instrumental lateral resolution limit

TL;DR

This paper introduces two experimental setups that enable XPS measurements with lateral resolution beyond the instrument's beam size, allowing analysis of smaller sample features.

Contribution

The paper presents novel methods to overcome the lateral resolution limit in XPS by using differential charging and energy analyser acceptance volume techniques.

Findings

Differential charging method estimates surface composition of non-conductive areas.

Energy analyser acceptance volume method isolates signals from the illuminated sample.

Both methods enable sub-beam resolution in XPS measurements.

Abstract

The lateral resolution of an X-ray photoelectron spectroscopy instrument, which is equipped with a focused X-ray beam, is limited by the nominal X-ray beam diameter and the long tail intensity distri-bution of the X-ray beam. The long tail intensity distribution of the X-ray beam impedes to perform a measurement with good lateral resolution and low detection limits at the same time. Two experimental setups are described which allow examining sample structures that are smaller than the X-ray beam dimensions. The first method uses differential sample charging on partly non-conductive samples by low energy electron flooding. The spectra of the non-conductive sample areas are shifted towards lower binding energy. That way, the surface compositions of conductive and non-conductive sample areas are estimated independently. The second method utilizes the rather limited dimensions of the energy analyser acceptance volume. Here only the sample is placed inside the energy analyser acceptance volume. That way, signals from the illuminated sample contribute exclusively to the measured photoelectrons intensity, independent form the sample size.