Angular Linearity and Resolution on Theta Probe

Significance of the topic

Angle‐resolved X‐ray photoelectron spectroscopy (ARXPS) is a powerful technique for probing the chemical composition of material surfaces and thin films. Accurate angular measurements are essential for depth profiling and quantitative surface analysis, affecting applications in catalysis, corrosion, semiconductor manufacture and thin‐film quality control.

Objectives and study overview

This study evaluates the angular linearity and resolution of the Thermo Scientific Theta Probe when operated in its angle‐resolving mode. The goal is to confirm that the instrument’s angular response follows the expected cosine distribution and to quantify its ability to discriminate small angular changes using a calibration ladder.

Methodology

A smooth silver sample was illuminated by a 500 eV electron beam from a flood gun. Elastically scattered electrons were collected by the Theta Probe’s two‐dimensional detector, which records kinetic energy in one axis and emission angle across 96 discrete channels in the other. Initial measurements determined the angular intensity profile without obstruction, then repeated with a precision calibration ladder placed against the lens.

Instrumentation

• Thermo Scientific Theta Probe in angle‐resolving XPS mode
• Two‐dimensional detector recording angular channels versus electron kinetic energy
• 500 eV flood‐gun electron source
• Calibration ladder defining seven equal angular bands over a 60° range

Main results and discussion

Unobstructed measurements matched the theoretical cos θ dependence of emitted electron intensity, confirming correct angular response. With the calibration ladder in place, four transmission bands and three blocked regions were observed, each spanning 8.57°. Plotting the measured 50 % transmission angles against the ladder geometry showed excellent linearity across the full range. Angular resolution, defined by the 20 %–80 % signal transition at each step, was consistently below 1.6°, with a mean of < 1.3°. This indicates that the instrument optics, rather than the detector channel width (60°/96≈0.625°), limit resolution.

Practical benefits and applications

• Reliable angular calibration ensures accurate depth profiling in ARXPS analyses.
• High angular resolution (< 1.3°) enables fine surface layer discrimination.
• No sample tilting reduces alignment errors and streamlines data acquisition.

Future trends and potential applications

Advances in electron optics and detector technology may further enhance angular resolution and dynamic range. Integrating automated calibration routines and extending accessible angular spans could broaden ARXPS utility in fields such as in situ reaction monitoring, advanced thin‐film characterization, and real‐time industrial process control.

Conclusion

The Thermo Scientific Theta Probe demonstrates excellent angular linearity and sub–1.3° resolution in angle‐resolved mode, validating its performance for precise ARXPS measurements. Its unique simultaneous angle collection without sample tilting enhances efficiency and measurement reliability.

Reference

• Thermo Fisher Scientific, Application Note 31004: Angular Linearity and Resolution on Theta Probe.
• Thermo Fisher Scientific, Technical Document AN31014.