In the 19th century, physicists discovered an unusual electrical phenomenon when ultraviolet light was shone upon metals. One of the mysterious aspects of this “photoelectric effect” was ultimately explained by Albert Einstein, and it was for this work that he received his Nobel Prize. He proposed that light was composed of quanta that carry energy proportional to the frequency. These light quanta are known as photons today.

Electron spectroscopy for chemical analysis (ESCA) is a surface science technique that is essentially an analytical application of the photoelectron effect. A narrow beam of X-rays is directed at a sample under ultra-high vacuum (UHV) conditions. An electron in the sample may absorb the energy from an individual X-ray photon and be ejected from the surface. Since electrons generally cannot travel very far through the sample, the ejected electrons come from the very uppermost surface layers. The electrons are collected by an energy detector, and the spectrum of energies provides information about the surface composition. By moving the X-ray spot, the instrument can build up a complete image. Since chemical bonding involves the electrons in the molecules of the sample, ESCA can distinguish not just the elements that make up the surface, but also the chemical composition. The possibility of chemical analysis makes ESCA stand out among other similar surface analysis tools, many of which can only provide elemental analysis or image maps of non-chemical parameters.

Most ESCA systems are also equipped with an ion gun, which can be used to remove the surface layer and expose a fresh surface for analysis. Repetition of this process allows ESCA to be used for depth profiling. Applications include measuring the thickness and identifying the composition of thin films deposited on substrates. These measurements are important for semiconductors and related materials, such as magnetic media, electronic components, solar cells and video display materials. The ability to perform chemical analysis also helps to expand the applications of ESCA outside of semiconductors and electronics. Polymers, catalysts and other surface chemistry applications are also quite common both in industry and academia. Life science applications are somewhat limited, usually due to the difficulties of exposing samples to the harsh UHV conditions.

Some of the major vendors of ESCA are broad-based instrument firms: Thermo Fisher Scientific, Shimadzu, JEOL and Oxford Instruments. The remaining significant vendor is Ulvac-PHI, which is narrowly focused on UHV surface analysis instrumentation, a market in which it is the leader. Smaller market participants are also from the world of surface analysis; while most of them offer complete systems, they are often more significant as vendors of sources, detectors and other components. Examples include Focus GmbH, Henniker Scientific, Riken Keiki, SPECS, VG Scienta and VSW.

ESCA at a Glance:

Leading Suppliers

• Thermo Fisher Scientific

• Ulvac-PHI

• Shimadzu

Largest Markets

• Semiconductors

• Thin Films

• Polymers

Instrument Cost

• $350,000–$850,000