Ion beam sources

Unlike traditional surface science techniques (e.g., XPS, AES, and SIMS), EXAFS experiments do not routinely require ultrahigh vacuum equipment or electron- and ion-beam sources. Ultrahigh vacuum treatments and particle bombardment may alter the properties of the material under investigation. This is particularly important for accurate valence state determinations of transition metal elements that are susceptible to electron- and ion-beam reactions. Nevertheless, it is always more convenient to conduct experiments in one s own laboratory than at a Synchrotron radiation focility, which is therefore a significant drawback to the EXAFS technique. These focilities seldom provide timely access to beam lines for experimentation of a proprietary nature, and the logistical problems can be overwhelming. 

As an electrolyte, Nafion 112 (Du Pont, Inc) membrane was pretreated using H2O2, H2SO4 and deionized water before ion beam bombardment. The prepared membranes with a size of 8 X 8 cm were mounted on a bombardment frame with a window size of 5 x 5 cm, equal to the active area of the test fuel cells, and dried up at 80 C for 2 hr. Then, the mounted membrane was brought in a vacuum chamber equipped with a hollow cathode ion beam source as described in the previous study [1]. Ion dose was measured using a Faraday cup. Ion density... 

Fig. 11.1. The scheme of the setup for composite film deposition by ion-beam sputtering of the compound target (1) substrate holder with heater (2) substrate (3) ion-beam source (4) shutter.

RF- and ion-beam assisted PLD PLD chamber equipped with RF or microwave plasma source or ion beam source to enhance the composition of particular film components such as N or O to grow in-plane aligned films on polycrystalline substrates, and to grow nanostructures [128]... 

Alternative dry etching techniques have recently been developed for the nitrides for low-damage applications. Photoassisted dry etching is set up analogously to CAIBE except that the ion beam source is replaced with an ultraviolet laser. Leonard and Bedair [25] reported on the photoassisted dry etching characteristics of GaN using HC1 gas and a 193 ran ArF excimer laser (1400 mJ/cm2) with the substrate... 

The application of ion beam analysis techniques to determine pore size and pore volume or density of thin silica gel layers was first described by Armitage and co-workers [114]. These techniques are non-destructive, sensitive and ideally suited for the analysis of thin porous films such as membrane layers (dense support is needed for backscattering). However, apart from a more recent report on ion-beam analysis of sol-gel films [115] using Rutherford backscattering and forward recoil spectrometry, ion beam techniques have not been developed further despite their potential for membrane characterisation. This is probably due to the limited availability of ion beam sources, such as charged particles accelerators. 

Because a defined start-stop signal is required for the measurement of time, an essential prerequisite in the TOP operation is that all ions enter the flight tube at exactly the same time. This arrangement would also avoid any artifact left behind from the previous ionization event. For this reason, TOP instruments are optimally combined with pulsed-mode ion sources such as Cf plasma desorption or MALDI. Alternatively, pulsing the accelerating potential can provide a pulsed ion beam from continuous ion beam sources (e.g., electron ionization, and electrospray ionization). 

In the last paragraph of this report some brief comments are made concerning the usefulness of resonant multiphoton ionization for the construction of an cold ion beam source and the diagnostic use of photo-ionization in collisional energy transfer studies /4/. 

High-quality films of TCOs have been fabricated by ion beam sputtering from oxide targets [173, 201] at deposition temperatures less than 100 °C. Fan [201] has used an argon-ion beam source with a typical value of current of 50 mA. 

The Bendix mass spectrometer must be considered a commercial success, since many of these instruments can still be found in industrial and academic laboratories throughout the United States. In later years, manufacture of these instruments was taken over by CVC Products (Rochester, NY), which continued to produce the model 2000 until a few years ago. An attractive feature of the Bendix instruments seems to have been the ease with which they could be modified for specific applications. In 1962, Lehrle et al. replaced the electron beam in the Bendix ion source with an ion beam source that could be used to generate either ions or neutrals with kinetic energies in the range of 0 to 2 keV. While used primarily for studies of gas-phase ion-molecule or neutral-molecule reactions, it was also further modified to enable sputtering of surfaces. Shortly after the introduction of chemical ionization by Field and Munson in 1966, Futrell et al. described a modified ion source for... 

The small spot capability is a direct result of the area over which these beams are produced (tip of a refractory metal needle) as this reduces spherical aberrations suffered by other ion beam sources. These sources also display a relative narrow energy spread ( 5 eV) which in turn has the effect of reducing chromatic aberrations (aberrations are discussed in Appendix A.7.1). 

Today, as the applications of molecular imaging experiments continue to expand, new variants of the experimental protocol promise further breakthroughs. For example, it is possible to improve the yield of molecular ions by using cluster ion beam sources rather than atomic ion sources [143,144]. Typically, a group of projectile atoms can more efficiently desorb labile molecules with less fragmentation than a single atomic ion [137]. 

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