X-Ray Fluorescence (XRF) is a common technique for elemental analysis, and it can often be used with a minimum of sample preparation, making it suitable for a broad range of applications from inspection and QC to research. In XRF, a source of x-rays irradiates the sample. The x-rays are absorbed by some of the electrons in the sample and then ejected from the atom due to the increase in energy. When other electrons fill the gap in the electron structure, the quantum transition results in the emission of x-rays of a particular wavelength corresponding to each element. These are detected, and the strength of the fluorescence signal from each component reveals the relative concentration of each element in the sample.

The x-rays only penetrate the sample surface to a certain depth, so the technique is sensitive to surface composition. If the sample is heterogeneous, then bulk composition measurements might involve milling the sample to make it homogeneous. However, sometimes the analytical interest is precisely on the heterogeneous nature of the sample. It is in this situation that microspot XRF can be particularly advantageous.

In microspot XRF, the x-ray optics are designed so that the source focuses the x-rays into a small spot on the sample surface. Most instruments can produce a spot with a diameter of about a millimeter, and many have the option to focus it down more narrowly with a diameter of a few tens of microns. In this way, the x-ray spot can be aimed directly toward a point of interest on the sample, whether that is a component on a printed circuit board, or a particular mineral or inclusion in a geological sample.

Thus, the instrument can provide the elemental composition of just the target location. More sophisticated instruments can be programmed to analyze multiple spots along a linear scan to build up a fuller map of the composition across the sample. Another product differentiator is the atmospheric conditions of analysis; higher-end systems provide gas purges or vacuum systems to improve light-element performance.

Rather than determining composition, another specific application is the analysis of the thickness of surface layers that may be deposited on semiconductor materials, finished metals or other materials. In this case, if the sample composition is known, the detected x-ray information can be used to determine the thickness of one or more layers by gauging the intensity of the signal from each component of the layers.

Microspot XRF can be applied to just about any sample, but the strongest source of demand comes from the semiconductor and electronic industry. It can be used for thickness measurements of thin films, and other treatments of silicon wafers and additional materials. Completed circuit boards or other electronic devices can be examined for the composition of individual components, furthering compliance with regulations that cover the use of hazardous substances in these products. More broadly, the existence of hazardous substances can be tested across many consumer products from toys to clothing.

The metals and mining industry also has numerous applications for microspot XRF. Coating or plating thickness of finished metals is a common application, and many instruments are designed with libraries to quickly identify alloys. An interesting subset of these applications is the identification and grading of precious metals. More research-oriented applications also exist. Geological samples can be analyzed, with the focus on individual mineral grains within a complex sample. Other uses can be found in environmental testing, forensics, battery research, and art and archeology.

The market leader is Hitachi High-Technologies. The company has long been involved in this technology, but the April announcement of its acquisition of the Industrial Analysis business from Oxford Instruments (see IBO 4/30/17) has propelled Hitachi into the top position in the marketplace. AMETEK also has a strong presence in this market, with contributions from both its SPECTRO Analytical and EDAX businesses. SPECTRO recently released a precious metals version of its Midex product line, the Midex MID05.

Bruker is the third most significant vendor, and is one of the few to offer a specific instrument for the art and archeology market. This month, the firm expanded its microspot XRF product line with the acquisition of XGLab (see Executive Briefing). PANalytical (Spectris) also competes in this market, and in July released a new small spot version of its Epsilon 1 analyzer. In March, Shimadzu introduced a kit to allow small spot analysis on its EDX-7000 and EDX-8000 analyzers. Other market participants include Fischer, ISP, Quantum, Skyray, Thermo Fisher Scientific and Xenemetrix. The total market demand for microspot XRF was approximately $200 million in 2016.

Microspot XRF at a Glance:

Leading Suppliers:

• Hitachi High-Technologies
• AMETEK
• Bruker

Largest Markets:

• Semiconductors and Electronics
• Metals
• Geology

Instrument Cost:

• $20,000–$250,000