Surface Analysis refers to sophisticated techniques that provide the tools necessary to explore the surface and subsurface chemistry of materials or components. Physical and chemical analysis of the materials surface is vital for understanding how they interact with the process environment or at the interface between two different materials in contact. Surface analytical techniques provide the tools to explore the surface and subsurface chemistry of solid materials.

X-ray Photoelectron Spectroscopy (XPS)

X-ray Photoelectron Spectroscopy (XPS or ESCA), is an analytical technique that depends upon the measurement of the energies of photoelectrons that are emitted from atoms when they are irradiated by soft X-ray photons (1 - 2 keV). When used to study solids, XPS has a number of powerful attributes, including a high (and variable) range of sensitivities to structures on the outermost surface of the solid, an ability to identify such structures chemically, a reasonable capacity for elemental quantification, as well as the ability to determine structure thickness. As a method for characterizing surface composition, there is no single other technique that can compare with XPS, in terms of the wealth of useful information, reliability of the data, and ease of interpretation. In addition to the above, an XPS imaging mode has emerged that was hardly even anticipated 10 years ago. Since its introduction in 1970, the technique has produced an extraordinary amount of useful information, both for academic and industrial scientists. These developments have had strong influences on our views of surface chemistry, physics, and engineering.

Advancements in spectrometer technology have resulted in major improvements in spectral resolution and counting efficiency over the past 20 years. This has dramatically improved the level of confidence in spectral positions, and the ability to carry out analyses in numbers that have much better statistical significance. The exploitation of the imaging developments is likely the most exciting prospect, because, historically, little research has been done using highly-resolved XPS images. The recognition of co-localization of different species (elemental or chemical) will be one of the most powerful elements shaping XPS in the future.

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Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS)

ToF-SIMS is a surface analytical technique that uses an ion beam to remove small numbers of atoms from the outermost atomic layer of a surface. A short pulse of primary ions strikes the surface, and the secondary ions produced in the sputtering process are extracted from the sample surface into a time-of-flight mass spectrometer. These secondary ions are dispersed in time according to their velocities (which are proportional to their mass/charge ratio m/z). Discrete packets of ions of differing mass are detected as a function of time at the end of the flight tube. ToF-SIMS is capable of detecting ions over a large mass range of 0 - 10000 atomic mass units at a mass resolution of 10000. The technique is capable of generating an image of lateral distributions of these secondary ions at spatial resolutions of better than 0.15 microns. Pulsed operation of the primary beam allows insulating surfaces to be completely neutralized between pulses using a low energy electron beam.

Advantages of ToF-SIMS

The ToF-SIMS technique is frequently compared with other major surface techniques such as XPS or AES. ToF-SIMS provides the following advantages over these other methods:

ToF-SIMS produces secondary electron (SE) images down to a 50 nm lateral resolution, and back-scattered ion (BSI) images, and SIMS images with lateral resolution down to 100 nm for elements, or 0.5 µm for big molecules.

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Scanning Auger Microscopy (SAM)

In Scanning Auger Microscopy (SAM), bomardment of a high energy (3 - 10 KeV) primary electron beam on the sample results in the emission of secondary, backscattered and Auger electrons that can be detected and analyzed. The secondary and the backscattered electrons are used for imaging purposes similar to that in a scanning electron microscope (SEM). The Auger electrons are emitted at discrete energies that are characteristic of the elements present on the sample surface. All elements in the periodic table, except hydrogen and helium, can be detected, and the depth of analysis is in the range of 2 - 5 nm. As the electron beams can be focused to a very small probe size, SAM has excellent spatial resolution (0.1 µm).

Using present instrumentation, microanalysis of a volume 100 x 100 x 2 nm can be obtained. This is 100 million times smaller than the analytical volume excited in SEM/EDX analysis. This spatial resolution combined with surface sensitivity is important for the analysis of very small phases in metallurgical/corrosion studies and in many integrated circuit applications.

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Atomic Force Microscopy (AFM)

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