SURFACE LAYERS CHARACTERIZATION METHODS BASIC AND TUTORIALS

Numerous surface analytical techniques that can be used for the characterization of surface layers are commercially available (Buckley, 1981; Bhushan, 1996).

The metallurgical properties (grain structure) of the deformed layer can be determined by sectioning the surface and examining the cross section by a high magnification optical microscope or a scanning electron microscope (SEM).

Microcrystalline structure and dislocation density can be studied by preparing thin samples (a few hundred nm thick) of the cross section and examining them with a transmission electron microscope (TEM). The crystalline structure of a surface layer can also be studied by X-ray, high-energy or low-energy electron diffraction techniques.

An elemental analysis of a surface layer can be performed by an X-ray energy dispersive analyzer (X-REDA) available with most SEMs, an Auger electron spectroscope (AES), an electron probe microanalyzer (EPMA), an ion scattering spectrometer (ISS), a Rutherford backscattering spectrometer (RBS), or by X-ray fluorescence (XRF). The chemical analysis can be performed using X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS).

The thickness of the layers can be measured by depth-profiling a surface, while simultaneously conducting surface analysis. The thickness and severity of deformed layer can be measured by measuring residual stresses in the surface.

The chemical analysis of adsorbed organic layers can be conducted by using surface analytical tools, such as mass spectrometry, Fourier transform infrared spectroscopy (FTIR), Raman scattering, nuclear magnetic resonance (NMR) and XPS. The most commonly used techniques for the measurement of organic layer (including lubricant) thickness are depth profiling using XPS and ellipsometry.