Surface Sciences

High performance Low Energy Ion Scattering (LEIS)

Quantitative top atomic layer characterisation

The Qtac is a high sensitivity low energy Ion Scattering (LEIS) instrument. It is extremely surface sensitive, providing quantitative elemental characterization of the top atomic layer.

This instrument has been developed to include small spot analysis, surface imaging, and both static and dynamic depth profiling.

Its unique surface sensitivity makes the Qtac the perfect tool to study surface processes. The Qtac provides valuable information in many production and research areas on materials such as catalysts, semiconductors, metals, polymers, and fuel cells.

Key features are

•  Quantitative, elemental characterization of the top atomic layer

•  Spectroscopy, imaging and depth profiling capabilities

•  Time-of-flight mass filtering for improved sensitivity

•  Analysis of rough and non-conductive materials


Energy Analyser

The unique Qtac energy analyzer design is based on the advanced Calipso technology. At the optimum scattering angle, the analyzer has an acceptance over the full azimuth while maintaining a well defined scattering angle.

This, together with parallel energy detection, simultaneously provides high sensitivity and high mass resolution. The possibility of using heavier noble gas ions, which is usually not possible with conventional ion scattering spectrometers, is essential for unambiguous identification of all elements.

The dedicated analyzer design allows for non-destructive, reproducible and quantitative analysis of the top atomic layer.


1.  Noble Gas Ion Gun
2.  Pulsing System
3.  Position Sensitive Detector
4.  Energy Analyser
5.  Focussing Optics
6.  Sample


Time-of-Flight Mass Filter

In conventional LEIS, secondary ions, generated by the impact of the noble gas ions, lead to a high background for low scattering energies.

This background reduces dynamic range and detection limits, in particular for light elements.

The Qtac is equipped with a time-of-flight detection system, which separates the scattered noble gas ions from this background. This unique feature significantly improves the elemental detection limits and the dynamic range of the instrument.

LEIS spectrum of a technical polymer without time-of-flight mass filtering



LEIS spectrum of the same sample with time-of-flight mass filtering showing significantly improved detection limits



Vacuum System

The state-of-the-art Qtac100 vacuum system guarantees high uptime and low maintenance costs. The vacuum system is fully computer controlled and interlock protected.

The ION-TOF buffer technology supersedes continuously running forepumps. It is built with magnetic bearing turbomolecular pumps and an oil-free forepump.

The stand-alone version of the Qtac is equipped with a dual stage sample introduction system. This includes the intermediate vacuum chamber between the loadlock and the main chamber.

The intermediate UHV chamber is ideally suited for sample preparation and can be equipped with various devices, such as an atomic oxygen/hydrogen source for sample cleaning.

Benefits are:

1.  Minimised maintenance (high uptime and low service costs)

2.  Oil-free vacuum

3.  Low noise level



Qtac Bolt-on Module

Many materials preparation, surface treatment, and thin layer deposition techniques benefit from on-line quality control and in situ analysis. For coverage and layer thickness measurements, the Qtac makes an ideal addition.

The Qtac is available as a bolt-on system, to be integrated into laboratory instruments or industrial tools. ALD and MBE depostion systems are typical examples.


Home-built UHV system with Qtac bolt-on module



LEIS Dual Beam Depth Profiling

The Qtac can be equipped with a high current ion optical column fitted with an Ar electron impact gas ion source. This ion gun is used for ultra-low energy sputtering in combination with LEIS analysis. In this dual beam depth profiling mode high resolution chemical depth profiles are obtained.

In contrast to SIMS, there is no need to use reactive sputter species, which would lead to changes in sputter rate and ionisation yield close to the surface. The Qtac100 provides easy quantification even in the first few nanometres of the profile.

The example shows a LEIS sputter profile through a CrNi multilayer system. The LEIS analysis was done with a 5 keV Ne analysis beam. For sputtering, a 500 eV Ar beam was used. The plot on the right shows the "liniarity" of the "correspondeing" correlation plot over the full concentration range very nicely.


LEIS depth profile through a CrNi multilayer