What Is Ion Scattering Spectroscopy (ISS)?
Ion Scattering Spectroscopy (ISS) – sometimes also called Low-Energy Ion Scattering (LEIS) or Low-Energy Ion Scattering Spectroscopy (LEISS) – is a method used to determine the composition of the outermost atomic layer of solid materials when sensitivity matters and precision is key. The ISS process bombards a material with a focused beam of low-energy ions – in the range of a few electron volts to a few kilo-electron (keV) range. Then, we measure the energy of ions scattered back from the surface to provide a highly accurate representation of elemental composition – electrical bombardment at the microscopic level and measurement of the scattering signal.
Complementary Integration
Exceptional Surface Sensitivity
Non-Destructive and Adaptable
Why Use ISS?
Ion Scattering Spectroscopy offers unparalleled sensitivity to the outermost atomic layer. While methods like XPS or EDS probe several surface atomic layers, ISS focuses exclusively on the very first nuclear layer. As a result, it delivers accurate surface composition information without interference from subsurface signals. When coatings are extremely thin, this level of precision is extremely important.
This exceptional surface specificity makes ISS very valuable in applications where surface chemistry impacts performance. In catalysis, for example, only the atoms at the immediate surface participate in chemical reactions, with atoms below the surface shielded from the interaction. Similarly, in semiconductor manufacturing, the chemical integrity of surface and interfacial layers plays a crucial role in device functionality and reliability.
Due to these capabilities, ISS analysis has found widespread adoption across various sectors where surface to surface interaction matters, including semiconductor fabrication, catalysis research, thin film development, corrosion studies, and advanced materials science. When operated in static mode, ISS is non-destructive, allowing for sequential measurements that monitor surface changes over time – think processes like annealing, chemical treatments, and other surface modifications. If you want to intentionally go deeper, however, you can operate ISS in the same spot for an extended period and strip away layers of material, enabling the creation of depth profiles of elements. We can tell you with extreme accuracy how many licks it takes to get to the center of this (very small) Tootsie Pop.
Surface Composition Precision
Wide Application Across Industries
Minimal Sample Preparation
How ISS Works
Ion Scattering Spectroscopy operates on the principle of binary collision physics — basically, we see what happens when we crash things into each other. The basic principle of ISS is that a beam of low-energy ions hits a sample surface, with some ions backscattering at different energies depending on the mass of surface atoms. The balls on our pool table are made of different material, and how they bounce when our cue ball strikes them can be measured, telling us what each is made of.
However, the extreme surface sensitivity of ISS is due to two factors: the low penetration depth of the low-energy ions and the high neutralization probability of ions that penetrate beyond the topmost layer. ISS is uniquely capable of analyzing accurate surface composition because only ions scattered from the outermost atomic layer contribute to the detected signal. In short, we tap each cue ball very lightly and measure each reaction very carefully to disrupt the table as little as possible.
Equipment Used for ISS
ThermoFisher Scientific Nexsa G2
- Ion beam of He/Ar/Ne.
- Energy range 500 to 2000eV.
- Internal reference of gold for primary energy calibration.
- Spot Size: 1 mm.
- Tilt option.
- Heating option.
Key Differentiators
At Covalent, we use the Nexsa G2 Surface Analysis System to conduct ISS measurements. This versatile instrument uniquely integrates ISS with X-ray Photoelectron Spectroscopy (XPS) and Ultraviolet Photoelectron Spectroscopy (UPS) within a single analysis chamber. This in situ capability allows for the sequential application of these surface-sensitive techniques on the same sample area without exposure to ambient air, generating a complementary dataset.
This type of approach is particularly critical for air-sensitive investigations, including research into catalytic properties, oxidation mechanisms, and temperature-dependent surface reactions, where maintaining surface integrity is imperative. In short, many surfaces react to ambient air and we can be sure that the results we observe are truly a result of the composition of your material, not your material exposed to the atmosphere.
Strengths
- Surface sensitivity: Exceptional sensitivity to the outermost atomic layers (typically top 1 to 2 monolayers).
- Elemental specificity: Capable of detecting all elements (except hydrogen and helium) based on their mass.
- Quantitative capability: Allows semi-quantitative to quantitative analysis of surface composition.
- Minimal sample preparation: Generally requires little to no special sample preparation.
Limitations
- Limited chemical state information: Does not provide direct insight into chemical bonding, states, or oxidation states.
- Can be destructive: Depth profiling involves sputtering, which is destructive to the sample.
- Complex interpretation: Data can require complex modeling or reference data for accurate interpretation.
- Surface contamination sensitivity: Very sensitive to adventitious carbon and other surface contaminants, which can obscure true surface composition.
Example Outputs
Sample Requirements
Covalent’s experts help make sure that the samples you’re providing are a good match for the analysis we’re performing. Sample requirements for ISS include:
- Solid phase.
- Must be stable under high vacuum.
- Maximum Thickness: 20 mm.
- Maximum Lateral Dimensions: 60 mm x 60 mm.
- For better quantification, the sample should be as smooth as possible.
ISS Applications by Industry
Catalysis Research
Surface composition directly determines catalytic performance. When you need to measure the efficiency and effectiveness of a catalyst that is intended to facilitate a chemical reaction, ISS testing helps researchers better understand catalyst surface composition before, after, and during reactions.
Thin Film Technology
ISS analyzes the composition of the outermost layer of thin films, crucial for applications like displays, solar cells, and protective coatings. This is one of the few methods to measure monolayer film and determine full/partial coverage of the surface.
Semiconductor
ISS analyzes wafer contamination, interfacial composition in multilayer devices, and surface modification processes.
Materials Science
ISS can monitor surface segregation, alloying behavior, and surface reactions.
Techniques That Complement ISS
ISS works well with other analytical techniques and provides comprehensive surface and near-surface characterization. Other techniques would be used when we need extra depth, sensitivity, or correlation of material identification with topographic or physical properties.
Why Choose Covalent for Your ISS Needs?
Covalent delivers high-sensitivity Ion Scattering Spectroscopy using advanced instrumentation and extensive expertise in surface analysis techniques. Our scientists provide rapid turnaround, customized methods, and actionable reporting, with the option to combine ISS with XPS, SIMS, and AFM for comprehensive surface characterization.