X‐Ray Photoelectron Spectroscopy in Analysis of SurfacesUpdate based on the original article by Steffen Oswald,Encyclopedia of Analytical Chemistry, © 2000, John Wiley & Sons, Ltd.

Abstract

X‐ray photoelectron spectroscopy (XPS) is an analytical technique that uses photoelectrons excited by X‐ray radiation (usually Mg Kα or Al Kα) for the characterization of surfaces to a depth of 2–5 nm. Elemental identification and information on chemical bonding are derived from the measured electron energy and energy shifts, respectively. The use of ultrahigh vacuum (UHV) during analysis requires special sample handling. Depth profiling is possible using ion sputtering. In contrast to the most popular surface analytical technique, Auger electron spectroscopy (AES), nonconducting material can be investigated, weak material damage occurs, and the chemical shifts are easier to interpret. However, the lateral resolution of the complementary AES technique (typically down to 20 nm) is much better than for XPS (50 µm for standard equipment, down to lower than 3 µm for dedicated instruments). The detection limit (of about 0.1 at%) is not as low as for mass spectroscopic techniques, but the quantification from XPS peak area measurements is more reliable, even disclaiming standard sample measurements. This article briefly discusses the principles of the technique, sample requirements, and the typical measuring strategy. Possible information sources (elements, chemical bonding, depth and lateral distributions) are described and their quantification principles are summarized. The main part deals with typical applications relating to several material classes (metals, semiconductors, insulators, and polymers) to give an impression of the capabilities of the method over a wide range of research and technological problems. A comparison with further complementary analytical techniques is given as a summary. Technological developments in electronics, nanotechnology, polymers, biotechnology, and medicine are all concerned with surface‐related phenomena, suggesting sustained interest in XPS in the foreseeable future.

Graphite Electrodes Immersed in Nonaqueous Li+ Electrolytes Studied with a Combined Ultrahigh Vacuum–Electrochemistry Approach

“…In terms of the pristine sample, XPS in Figure a–c shows a pronounced asymmetric C 1s peak at 284.4 eV, while the valence spectrum shows a broad series of features with a notable peak at 18.0 eV. These observations are consistent with the presence of sp 2 hybridized carbon. − Aside from the C 1s features, no other features are present in the wide spectrum, while the negligible O 1s spectrum (Figure S2a) indicates that the pristine surface is clean and without functional groups. In line with XPS are the STM images in Figure d (larger-scale images in Figure S2d), which show that the pristine HOPG contains atomically flat terraces that are hundreds of nanometers in size, while the step heights are close to the expected 0.335 nm .…”

Suppression of Hydrophobic Recovery in Photo-Initiated Chemical Vapor Deposition

“…Upon the closer investigation of the Fe content in the films, we noticed similar behavior to that of O. Fe peaks appeared at 710.9 and 726 eV, corresponding to Fe2p 3/2 and Fe2p 1/2 , respectively [52]. Furthermore, the couplings of the Fe peaks situated from 710.8-711 eV and O1s peaks at 529.8 were indicative of the formation of Fe oxides such as α-Fe 2 O 3 or γ-Fe 2 O 3 [53,54]. Similarly, Fe peaks at binding energy of 711.5 eV coupled with two distinct O peaks at 529.9 and 531.6 eV were associated with the formation of FeOOH [53,54].…”

“…Furthermore, the couplings of the Fe peaks situated from 710.8-711 eV and O1s peaks at 529.8 were indicative of the formation of Fe oxides such as α-Fe 2 O 3 or γ-Fe 2 O 3 [53,54]. Similarly, Fe peaks at binding energy of 711.5 eV coupled with two distinct O peaks at 529.9 and 531.6 eV were associated with the formation of FeOOH [53,54]. Overall, Fe seemed to be present under its different oxidation states in the films.…”

One-Pot Synthesis of Gel Glass Embedded with Luminescent Silicon Nanoparticles

“…For detailed composition and elemental analysis of the prepared sample, XPS measurements were performed. Six major peaks at 100.1, 152.3, 284.8, 398, 530, and 1070 eV, corresponding to Si 2p, Si 2s, C 1s, N 1s, O 1s and Na 1s, are observed in the full-range XPS image shown in Figure a. − Each of these peaks are resolved and deconvoluted using multiple Gaussian peaks ( R 2 between the experimental and fitted data >0.99, for all cases), as shown in Figure b–f. The details of the deconvoluted XPS peak positions and their assignments are listed in Table S1 (Supporting Information).…”