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Below are resources to better understand the tools of surface analysis and materials characterization, when to use a particular tool and why one tool may be more appropriate for a specific type of analysis. New content is regularly being added. If you have any questions or suggestions, please feel free to contact me.

Analytical Techniques

A wide array of analytical techniques are available for use in surface analyses and material characterization. Often, analytical chemists refer to these using their acronyms. Many of the more commonly used techniques are listed below. Click on an active button to learn more about that respective technique. Those techniques with darker buttons contain detailed information.

AES

GCMS

ICP-OES

TEM/STEM

XRD

TOF-SIMS

XRF

SIMS

TXRF

VPD-ICPMS

XPS

Information Depth Importance

One too often forgotten consideration when choosing an analytical technique is information depth. Information depth is important as the composition of a sample can vary dramatically with depth. Not only can the surface composition differ significantly from that of the bulk, but it rarely consists of a pure material. Factors contributing to this difference include:

Contamination
Corrosion
Oxidation
Degradation products from tribology, heat, light, chemical reaction
Migration of bulk impurities or additives to the surface
Surface Engineered Coatings

In some cases the surface is intentionally different from the bulk (e.g. Engineered Surface Coating) while in many others it is not (e.g. Contamination). Analysis of a sample by a Surface Analysis Technique (e.g. AES, TOF-SIMS, XPS) will provide compositional information of the surface/near surface region. Such an analysis is desirable if one is interested in determining what is actually on the surface. However, if one is interested in the sample bulk, then the surface analysis technique will likely provide a poor representation of the bulk composition. A Bulk Analysis Technique (e.g. SEM-EDS, XRF, ICP-MS etc…) will be preferred. Conversely, if one wants to know the surface composition, using a more bulk analysis technique, will provide little, if any, information of the surface. This is because the percentage of signal originating from the sample surface will be extremely small relative to that of the bulk. The surface signal will be insufficient for detection.

While bulk analysis is desirable for many applications such as determining the identity of an alloy or a polymer, other times the surface composition is important. Knowing surface composition is important because the surface can affect properties such as:

Adhesion
Wettability
Appearance of Stains/Discolorations
Corrosion Resistance
Ability for films to laminate to their surface
Biocompatibility
Wear
Antistatic Properties

A wide variety of materials are commonly found on surfaces including:

Reaction Products
Processing Contaminants
Cleaning Residues (e.g. Surfactants/Detergents)
Compounds that migrate and enrich at surfaces (e.g. Anti-Oxidants)
Mold Release Agents
Environmental Contaminants
Packaging Contaminants
Contaminants from Handling
Engineered Coatings
Treatment (e.g. Plasma and Chemical) Products
Wear Products

Schematic of Surface and Various Film Definitions

Figure 1: Comparison of Surface and various Film definitions (not too scale).

While some samples primarily consist of a bulk component and a surface/near surface region, others have films intentionally (and sometimes unintentionally) present. Films can be of a wide variety of thicknesses and they can be broken down into a few general categories including Ultra-Thin (~1-10nm), Thin (~10nm-5um) and Thick (~5-20um) as shown in Figure 1. The thickness ranges shown are somewhat arbitrary as slight variations to the thicknesses reported in the Figure are found in literature.

Nevertheless, the Figure provides a basic guide to the thickness of films commonly applied to materials. In cases where films are present, techniques are needed that can reveal how the composition varies with depth. This can be done with a variety of profiling techniques (e.g. SIMS, TOF-SIMS, AES, XPS, GDMS, LA-ICP-MS), cross-sectional analyses (e.g. SEM, TEM) or with non-destructive techniques (e.g. RBS, XRF) for the analysis of Ultra-Thin to Thin Films.

Quick Guide For Choosing Analytical Techniques

How do you determine.....

1. Surface Elemental Composition: AES, TOF-SIMS, XPS

2. Surface Organic Composition: TOF-SIMS, XPS (limited information)

3. Bulk Elemental Composition: GDMS, ICP-MS, ICP-OES, LA-ICP-MS, SEM-EDS, XRF

4. Bulk Organic Composition: FTIR, Raman, GCMS (after dissolution), LCMS (after dissolution), NMR (after dissolution)

5. Elemental Composition Versus Depth: AES, XPS, SIMS, TOF-SIMS (non-quantitative), SEM-EDS Cross-Section, TEM-EDS Cross-Section

6. Organic Composition Versus Depth: TOF-SIMS (non-quantitative), Raman Cross-Section (thicker films)

7. Inorganic Composition: Raman, XPS (Surface), XRD

8. H Content within Films/Samples: RBS (Films), IGA (Bulk)

9. Surface Morphology: AFM, OP, SEM

10. Surface Roughness: AFM, OP, SEM (more involved)

11. Film Thickness: SEM Cross-Section, TEM Cross-Section, XRR, RBS

12. Film Composition: AES, XPS, SIMS, TOF-SIMS (non-quantitative), SEM-EDS Cross-Section, TEM-EDS Cross-Section

13. Film Density: RBS, XRR

14. Percent Crystallinity: XRD

15. Trace Impurities within Films: SIMS, GDMS

16. Elemental Mapping/Imaging of Surfaces: TOF-SIMS, AES, XPS

17. Elemental Mapping/Imaging of Thick Films and Bulk: SEM-EDS, XRF, LA-ICP-MS

18. Alloy of a Sample: ICP-MS, GDMS, XRF

Disclaimer: Techniques listed are the more common methods of solving the respective analytical problem. However, in most instances other techniques can be used and may be a better approach for a particular analysis.