Like several related surface analysis techniques, Electron Spectroscopy for Chemical Analysis (ESCA) provides information about the composition of surfaces by probing the interaction of the samples with various types of radiation. In ESCA, a beam of energetic X-rays irradiates the surface, while detectors measure the energies of the electrons ejected by the high-energy X-ray photons. An alternative name for ESCA is X-ray photoelectron spectroscopy, or XPS.

Photons typically do not penetrate very far into the sample; consequently, the information derived from the electrons comes from the top few nanometers of the surface layers. These electrons have been knocked out of inner electron shells of the atoms making up these surface layers. The discrimination of the electron energy analyzers in ESCA is sufficient to determine the identity of the elements making up the surface as well as the chemical state of the atoms. This allows the instrument to provide more than just an atomic composition; it also provides information about the molecular composition and surface chemistry.

ESCA is generally complementary to other surface analysis modes, such as Auger spectroscopy, electron microscopy or secondary ion mass spectrometry. Most of these techniques, like ESCA, require vacuum conditions in order to operate. To efficiently examine a sample with multiple analysis tools, multiple techniques are commonly installed on the same ultra-high vacuum system. The addition of an ion beam to sputter away the surface material can enable depth-profiling analyses using ESCA. ESCA can also be used to examine the same surface before and after some particular treatment regimen.

Because ESCA penetrates only a few nanometers into the surface layers, it is invaluable for the study of thin films, coatings and surface chemistry. Areas of application for the technique include semiconductor devices, polymers, catalysts, adhesives and even biomaterials, as the technique does not require a conducting sample. Another important application for ESCA is surface imaging, which is carried out by rastering the beam spot over the surface. For imaging applications, the spot size of the beam is typically the critical parameter for image quality.

Thermo Fisher Scientific recently eclipsed Ulvac-PHI as the leading vendor, following the release of two notable products. In 2007, Thermo introduced the K-Alpha XPS system, which offers a simplified design that provides excellent ease of use for a technique that is very demanding on the operator. Last year, Thermo introduced the Escalab 250Xi (see IBO 12/31/09), a more function-rich surface analysis tool with multiple analysis modes (ESCA, SIMS, REELS) available on the base model, which can be expanded to include Auger, electron microscopy and other methods. Other vendors, like Shimadzu and JEOL, have also introduced newer hemispherical analyzers for their systems. The market for ESCA systems was roughly $54 million in 2009.

ESCA at a Glance:

Leading Suppliers

• Thermo Fisher Scientific

• Ulvac-PHI

• Shimadzu

Largest Markets

• Semiconductors

• Thin Films

• Academia

Instrument Cost

• $325,000–$800,000