Near-ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) is a less traditional form of XPS that allows samples to be analyzed at relatively high pressures, i.e., greater than 2500 Pa. With NAP-XPS, a wide variety of unconventional materials can be analyzed, including moderately volatile liquids, biological samples, porous materials, and/or polymeric materials that outgas significantly. Charge compensation with NAP-XPS takes place simply through the residual/background gas in the chamber, which is ionized by the incident x-rays. High quality spectra—high resolution and good signal-to-noise ratios—are regularly obtained. This article is an introduction to a series of papers in Surface Science Spectra on the NAP-XPS characterization of a series of materials. The purpose of these articles is to introduce and demonstrate the versatility and usefulness of the technique.
X-ray photoelectron spectroscopy (XPS) has become the most widely used method for chemically analyzing surfaces. In XPS, photoelectrons are generated by irradiating a surface with x rays. As the importance and popularity of XPS have grown, it has drawn users without significant XPS experience, and incorrect and incomplete interpretations of XPS spectra regularly appear in the literature. This tutorial is designed as a tool to guide less experienced users in analyzing XPS survey spectra. Here, the authors examine a series of XPS survey spectra collected during the atomic layer deposition (ALD) of Al2O3 from trimethylaluminum and water precursors. Prior to this, brief explanations of XPS and ALD are presented. This tutorial is structured as a series of questions and answers that the interested reader may choose to engage in. The XPS spectra are scrutinized to extract information about the elements present in the film, the presence of contamination, and the nature of the film growth process. The questions and answers in this tutorial address important fundamental issues common to the interpretation of many XPS survey spectra in the context of ALD.
Although the fundamental, theoretical peak shape in X-ray photoelectron spectroscopy (XPS) is Lorentzian, some Gaussian character is observed in most XPS signals. Additional complexity in the form of asymmetry is also found in many XPS signals, which requires more advanced peak shapes than the traditional, symmetric Voigt and Gaussian-Lorentzian sum and product (pseudo-Voigt) functions. Here, we discuss the merits and disadvantages of four approaches that have been used to introduce asymmetry into XPS peak shapes: addition of a decaying exponential tail to a symmetric peak shape, the Doniach-Sunjic peak shape, the double-Lorentzian, DL, function, and
Near-ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) is a less traditional form of XPS that allows samples to be analyzed at relatively high pressures, i.e., greater than 2500 Pa. With NAP-XPS, XPS can analyze moderately volatile liquids, biological samples, porous materials, and/or polymeric materials that outgas significantly. In this submission, we show C 1s, O 1s, and survey NAP-XPS spectra from ethylene glycol, an organic solvent that could not be analyzed at near-ambient pressures by conventional approaches. An N 1s signal is present in the survey spectrum of the material.
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