A versatile,fast pumping ultraviolet photoelectron spectrometer for the study of transient and unstable species

A high resolution ultraviolet photoelectron spectrometer specifically designed to study transient and unstable species is described. Its capabilities are enhanced by the novel pumping system for the analyzer, thus removing the necessity of a large vacuum chamber, and giving close access to the ionization chamber. Additional fast pumping for the ionization chamber and versatile sampling systems are also incorporated. Spectra are presented to show the general performance and the potential of the spectrometer for studying unusual chemical systems. In particular, the design features permit studies of discharge reactions, pyrolyses, atom-molecule reactions, highly reactive molecules and variable temperature work.     

A UV photoelectron spectrometer featuring rapid analysis

An improved sensitivity electron spectrometer for use in UV photoelectron spectrometry has been developed for rapid analysis. High sensitivity is achieved by the use of a focal-plane position-sensitive multidetector consisting of a linear array of photosensitive diodes (a CCD imaging device) allowing parallel detection and rapid data-acquisition. In the measurement of the He (I) 58.4 nm photoelectron spectrum of Ar, the gain in acquisition time is estimated to be by a factor of ～12.     

A three-element cylindrical electrostatic lens for a photoelectron spectrometer

The properties of a three-element electrostatic lens for use in photoelectron spectroscope is reported. The lens, which keeps a constant focal position over a wide range of photoelectron kinetic energies, is coupled to a high resolution hemispherical electrostatic analyzer. Maximum utilization of the electron optics is described.     

A variable angle photoelectron spectrometer using a position-sensitive detector

A variable angle photoelectron spectrometer utilizing a position-sensitive multidetector is described. Photoelectron spectra of N₂ obtained using a synchrotron radiation source are presented. The data are acquired using a new technique in which the photoelectron yield is obtained as a function of both wavelength and photoelectron energy, and this gives detailed information on autoionization processes.     

A traceable quantification procedure for a multi-mode X-ray photoelectron spectrometer

A modification to the quantification procedure used by a multi-mode X-ray photoelectron spectrometer (XPS) instrument is described which enables transfer of quantification between instruments, and which is referenced to a verified source. The procedure takes account of the intensity/energy response function of the instrument, which is appended to the data file, eliminating ambiguities in intensity calibration at a later date, and allowing background subtraction techniques based on electron scattering to be used on corrected spectra. A strategy is proposed to minimise inaccuracies arising from surface contamination and low signal intensity. Use of the procedure is illustrated by comparing quantification using different data processing software.     

Auger signals obtained with a photoelectron spectrometer

If the initial ionization energy of a system emitting an Auger electron needs an energy somewhat below the mono-energetic photons used in a photoelectr     

Electrical characteristics of an X-ray photoelectron spectrometer

Current-voltage characteristics have been measured for an AEI ES200B X-ray photoelectron spectrometer with both conducting and insulating samples. With the conducting sample, the flux of secondary electrons falling on the specimen and probe amounts to approximately 20 percent of the photoelectron flux, over a wide range of irradiation conditions. The results for the insulating sample, taken in conjunction with subsidiary data from charging shifts, indicate that the secondary flux incident on the specimen alone exceeds 99 percent of the photoelectron flux.     

Classical ultraviolet photoelectron spectroscopy of polymers

Although X-ray photoelectron spectroscopy of polymers was well established by Clark and coworkers in the 1970s, ultraviolet photoelectron spectroscopy of polymer films, was developed later. Previous to the 1970s, the first attempts to use ultraviolet light on polymer films took the form of appearance potential (valence band edge) measurements. Only some years later could the full valence band region of thin polymer films, including insulating polymers, semiconducting polymers and electrically conducting polymers. The development of what might be termed “classical ultraviolet photoelectron spectroscopy” of polymer films may be loosely based upon a variety of issues, including adapting thin polymer film technology to ultra high vacuum studies, the widespread use of helium resonance lamps for studies of solid surfaces, the combined advent of practical and sufficient theoretical–computational methods. The advent of, and the use of, easily available synchrotron radiation for multi-photon spectroscopies, nominally in the area of the near UV, is not included in the term “classical”. At the same time, electrically conducting polymers were discovered, leading to applications of the corresponding semiconducting polymers, which added technologically driven emphasis to this development of ultraviolet photoelectron spectroscopy for polymer materials. This paper traces a limited number of highlights in the evolution of ultraviolet photoelectron spectroscopy of polymers, from the 1970s through to 2008. Also, since this issue is dedicated to Prof. Kazuhiko Seki, who has been a friend and competitor for over two decades, the author relies on some of Prof. Seki's earlier research, unpublished, on who-did-what-first. Prof. Seki's own contributions to the field, however, are discussed in other articles in this issue.     

Adsorption studies by ultraviolet photoelectron spectroscopy

The application of ultraviolet photoelectron spectroscopy (UPS) for adsorption studies is illustrated using three examples. The observation of difference curves for various gases adsorbed on the same substrate allows those features due to the substrate or the adsorbate to be distinguished. The observation of the coverage dependence of UPS difference spectra allows one to relate the observed features to results from other techniques, as shown for oxygen adsorbed on the (100) face of tungsten. Finally, the measurement of difference spectra of the same species adsorbed on different faces of the same crystal gives information on the substate-adsorbate bonding as illustrated for the case of hydrogen on the (100) and (110) faces of tungsten.     

Investigating ultraviolet photoelectron spectroscopy of ice

Photoelectron energy distribution curves (EDCs) from ice excited by HeI (21.2 eV) and NeI (16.8 eV) radiation are presented. The strict connection between valence density of states and EDCs forces to rule out the previous suggestion by Shibaguchi et al. that conduction band density of states is of paramount importance in determining the EDCs excited by ultraviolet light. The results also allow a discussion of band calculations published till now; the need for a theoretical investigation on photoemission from ice is put forward.     

Repeatable intensity calibration of an X-ray photoelectron spectrometer

Ten years ago, NPL developed an infrastructure for calibrating the intensity response functions of electron spectrometers for Auger electron and for X-ray photoelectron spectroscopies. Two software systems were developed: one for Auger electron spectrometers or for Auger electron and X-ray photoelectron spectrometers combined, and one for X-ray photoelectron spectrometers on their own; the latter being applied if no suitable electron gun is available. The system for Auger electron and X-ray photoelectron spectrometers combined has been used regularly to calibrate the Metrology Spectrometer II at NPL and experience shows that this gives an instrumental intensity consistency of 0.4% over 10 years. Evaluations have not previously been reported at this level. The system for Auger electron and X-ray photoelectron spectrometers combined is used here in preference to the system solely for X-ray photoelectron spectrometers since it is more robust to the sample condition and can be used over a wider energy range. These issues, and how observed variations in the instrument intensity response may arise, are explained.