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X-ray photoelectron spectroscopy (XPS) has become one of the most widely used surface analysis techniques, and XPS instrumentation has become more user friendly, making the technique available to a large number of researchers. The number of experts in the field, however, has not increased, and XPS data are often misinterpreted in the literature. This paper is intended to provide an introduction to XPS for prospective or novice users. We present the basic principles of the technique including (1) the photoelectric effect, (2) how electrons interact with matter and escape from a surface and how this determines the surface sensitivity of the technique, and (3) how the chemical environment around an element affects the binding energy of its electrons. A description of the instrumentation helps a novice user understand how data are acquired, and information is included on sample preparation and mounting. The important parameters for data acquisition are noted to help guide users starting to acquire data. Interpretation of data on both a qualitative and quantitative level is discussed, and additional sections provide information on more advanced techniques such as angle resolved XPS, small area analysis, near ambient pressure XPS, valence XPS, and ultraviolet photoelectron spectroscopy.

The performance of superconducting radio-frequency (SRF) cavities made of bulk Nb at high fields (peak surface magnetic field greater than about 90 mT) is characterized by exponentially increasing rf losses (high-field Q slope), in the absence of field emission, which are often mitigated by low-temperature (100-140 C, 12-48 h) baking. In this contribution, recent experimental results and phenomenological models to explain this effect will be briefly reviewed. New experimental results on the high-field Q slope will be presented for cavities that had been heat treated in a vacuum furnace at high temperature without subsequent chemical etching. These studies are aimed at understanding the role of hydrogen on the highfield Q slope and at the passivation of the Nb surface during heat treatment. Improvement of the cavity performances, particularly of the cavities' quality factor, have been obtained following the hightemperature heat treatments, while secondary ion mass spectroscopy surface analysis measurements on Nb samples treated with the cavities revealed significantly lower hydrogen concentration than for samples that followed standard cavity treatments.

Large-grain Nb has become a viable alternative to fine-grain Nb for the fabrication of superconducting radio-frequency cavities. In this contribution we report the results from a heat treatment study of a large-grain 1.5 GHz single-cell cavity made of "medium purity" Nb. The baseline surface preparation prior to heat treatment consisted of standard buffered chemical polishing. The heat treatment in the range 800 -1400 • C was done in a newly designed vacuum induction furnace. Q0 values of the order of 2 × 10 10 at 2.0 K and peak surface magnetic field (Bp) of 90 mT were achieved reproducibly. A Q0-value of (5 ± 1) × 10 10 at 2.0 K and Bp = 90 mT was obtained after heat treatment at 1400 • C. This is the highest value ever reported at this temperature, frequency and field. Samples heat treated with the cavity at 1400 • C were analyzed by secondary ion mass spectrometry, secondary electron microscopy, energy dispersive X-ray, point contact tunneling and X-ray diffraction and revealed a complex surface composition which includes titanium oxide, increased carbon and nitrogen content but reduced hydrogen concentration compared to a non heat-treated sample.

Particles of Zn powder have been studied to show that high-quality scanning electron microscope (SEM) and transmission electron microscope (TEM) specimens can be rapidly produced from a sitespecific region on a chosen particle by the focused ion beam (FIB) lift-out technique. A TEM specimen approximately 20-m long by 5-m wide was milled to electron transparency, extracted from the bulk particle, and micromanipulated onto a carbon coated copper mesh TEM grid. Using the FIB lift-out method, we were able to prepare a site-specific TEM specimen from a difficult material in under 3 hours. The TEM analysis of the lift-out specimen revealed a large amount of thin area free from characteristic signs of damage that may be observed as a result of conventional argon ion milling. The overall microstructure of the specimen prepared by the FIB lift-out method was consistent with samples prepared by conventional metallographic methods. A grain size of ϳ10 to 20 m was observed in all specimens by both TEM and SEM analysis. Light optical microscopy revealed the presence of internal voids in ϳ10 to 20 pct of all particles. The SEM analysis showed the voids to extend over ϳ70 pct of the particle volume in some cases.

Commercially available focused ion beam (FIB) workstations with spatial resolution of 5-7 nm can prepare specimens with excellent lateral resolution. This capability has been utilized extensively by the semiconductor industry to obtain materials characterization from continually smaller areas. The FIB has been adopted generally as a preparation tool for scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The ability to prepare site-specific specimens that can be removed from the bulk of a sample provides enhanced SEM and TEM analyses and new approaches for other analytical tools. Dedicated scanning transmission electron microscopy (STEM) can provide images through samples several micrometers thick. Auger electron spectroscopy (AES) can analyze with improved ability to identify a small particle. Secondary ion mass spectrometry (SIMS) can provide trace analysis at high mass resolution. Automatic operation of FIB workstations permits the creation of multiple lift-out samples without the presence of an operator.

Recently, Nb superconducting radio frequency cavities vacuum heat treated between 300 and 400 °C for a few hours have exhibited very high quality factors (∼5 × 1010 at 2.0 K). Secondary ion mass spectrometry measurements of O, N, and C show that this enhancement in RF surface conductivity is primarily associated with interstitial O alloying via dissolution and diffusion of the native oxide. We use a theory of oxide decomposition and O diffusion to quantify previously unknown parameters crucial in modeling this process. RF measurements of a vacuum heat-treated Nb superconducting radio frequency cavity confirm the minimized surface resistance (higher Q0) previously expected only from 800 °C diffusive alloying with N.