{"id":768,"date":"2015-07-07T13:43:00","date_gmt":"2015-07-07T04:43:00","guid":{"rendered":"https:\/\/www.ulvac-phi.com\/surface-analysis\/topics\/hxps-1\/"},"modified":"2026-07-13T13:02:18","modified_gmt":"2026-07-13T04:02:18","slug":"hxps-1","status":"publish","type":"topics","link":"https:\/\/www.ulvac-phi.com\/en\/surface-analysis\/topics\/hxps-1\/","title":{"rendered":"What is Hard X-ray Photoelectron Spectroscopy"},"content":{"rendered":"\n

Background<\/h2>\n\n

Photoelectron spectroscopy was reported by Kai M. Siegbahn in the 1950s. At that time, he reported the photoelectron spectrum of Cu 1s using Mo K\u03b1 radiation\u00b9\u207e. Subsequently, there were reports of hard X-ray photoelectron spectroscopy in the 1970s\u00b2\u207e, but due to technical challenges such as insufficient intensity of the hard X-ray excitation source and inadequate photoelectron collection capability of the analyzer, the technique did not reach a practically viable level as an analytical method. As a result, photoelectron spectroscopy was put into practical use using soft X-rays such as Al K\u03b1 and Mg K\u03b1 radiation, as well as ultraviolet light sources such as helium discharge lamps, and continues to be widely used today as a powerful analytical technique.<\/p>\n\n

With the advent of the 21st century, the emergence of third-generation synchrotron radiation facilities represented by SPring-8 made it possible to utilize hard X-rays with dramatically increased intensity. At the same time, improvements in the voltage tolerance and sensitivity of analyzers resolved the aforementioned technical challenges. As a result, the number of reports on hard X-ray photoelectron spectroscopy\u00b3\u207e\u2074\u207e\u2075\u207e increased rapidly.<\/p>\n\n

Reports on hard X-ray photoelectron spectroscopy continue to increase to this day, attracting attention as a relatively new analytical technique.<\/p>\n

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Aerial view of the SPring-8 facility<\/figcaption><\/figure>\n<\/div>\n

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Principles of hard X-ray photoelectron spectroscopy<\/h2>\n\n

The basic principle of hard X-ray photoelectron spectroscopy is the same as conventional <\/a>XPS<\/a>: exciting the sample surface with excitation light and measuring the kinetic energy of the emitted photoelectrons. While the photon energy of monochromatic Al K\u03b1 radiation, most commonly used in conventional <\/a><\/p>\n\n

Hard X-ray photoelectron spectroscopy is written as “Hard X-ray Photoelectron Spectroscopy” and is abbreviated as HX-PES or HAXPES. To distinguish it from this, photoelectron spectroscopy using soft X-rays such as Al K\u03b1 and Mg K\u03b1 radiation as excitation sources is sometimes referred to as “Soft X-ray Photoelectron Spectroscopy” (abbreviated as SX-PES).<\/p>\n\n

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Features of hard X-ray photoelectron spectroscopy<\/h2>\n\n

Information from deep core levels<\/h3>\n\n

Since hard X-rays have high incident energy, they can excite photoelectrons from deeper core levels than soft X-rays. For example, in the case of Si, soft X-rays can only excite up to the 2s orbital, whereas hard X-rays can excite up to the 1s orbital. Figure 1 shows examples of photoelectron excitation using Al K\u03b1 (h\u03bd = 1486.6 eV) and Cr K\u03b1 (h\u03bd = 5414.8 eV) radiation.<\/p>\n\n

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