Ion beam bombardment

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... 

Study [1], it was reported that with increasing ion dose density from 10" to lO ions/cm, RMS roughness of the ion beam bombarded membrane increased from 21 to 204 nm without changing ionic conductivity of the membrane. 

In secondary ion mass spectrometry (SIMS), a primary ion beam bombards the surface and a mass spectrometer analyses the ions sputtered from the surface by the primary bombardment. This extremely sensitive technique provides both elemental and structural information. 

Saha et al. [109] have proposed an improved ion deposition methodology based on a dual ion-beam assisted deposition (dual IBAD) method. Dual IBAD combines physical vapor deposition (PVD) with ion-beam bombardment. The unique feature of dual IBAD is that the ion bombardment can impart substantial energy to the coating and coating/substrate interface, which could be employed to control film properties such as uniformity, density, and morphology. Using the dual lABD method, an ultralow, pure Ft-based catalyst layer (0.04-0.12 mg Ft/cm ) can be prepared on the surface of a GDL substrate, with film thicknesses in the range of 250-750 A. The main drawback is that the fuel cell performance of such a CL is much lower than that of conventional ink-based catalyst layers. Further improvement... 

The FAB matrix is essentially a nonvolatile liquid material, such as those illustrated in Scheme 1, that serves to constantly replenish the surface with new sample as the incident ion beam bombards the surface. The matrix also serves to minimize sample damage from the high-energy particle beam by absorbing most of the incident energy and is believed to facilitate the ionization process. The spectrum produced often includes matrix peaks along with some fragments and a peak for the protonated or cationized (i.e., M + Na+) molecular ion. 

The possibility of any chemical contribution from the ions can be eliminated in the case of silicon etching with ions simply by noting that there is not enough fluorine per ion to chemically remove even one silicon atom as SiF and in addition this ignores the problem of the carbon which also arrives at the surface. The observation mentioned earlier involving CF ion beam bombardment of silicon in which the silicon surface is soon obscured by a thin carbon layer emphasizes the fact that CFj" " ions alone will not etch Si chemically (by forming SiF ) at a significant rate. 

Ion implantation is often recommended as an efficient tool to enhance electrocatalysis either by disrupting the surface structure of the catalyst or by placing active atoms on an inactive (or less active) matrix. The latter possibility (which links this section with Section 3.3 devoted to adatoms) offers also a way to the use of extremely small amounts of active but expensive materials. In order to investigate the effect of surface damages, self-implantation or ion beam bombardment is the most appropriate approach. Implantation of Ni on Ni has led to a modest enhancement of the surface area, but not to electrocatalytic effects [279]. On the other hand, Pt bombarded with neutrons has shown an increase in the activity for hydrogen evolution [280]. However, it has been suggested that this is not related to the formation of surface defects, but rather to the effect of the radioactivity induced on the electrode and on the electrolyte. 

Polymer Surface Analysis. The major technique used for the surface analysis of polymers has been X-ray photoelectron spectroscopy (XPS or ESCA). However, this technique is often not adequate to determine the molecular structure of polymers. This has prompted many workers to explore the potential of SIMS for this work (11-16). Significant problems encountered with ion beam bombardment in conjunction with electron beam charge neutralization have been drift in the polymer surface potential and thermal damage from the combined effects of the electron and ion beams. These problems do not exist when utilizing FAB in conjunction with photoelectron charge neutralization. 

Although the effect of chemical bonding on energy dissipation in chemical systems is not included [54,55], the cylindrical thermal spike model takes into account the specific features of an ion-beam bombardment process such as energy loss and collision cascade. In particular, the individual ion bombardment will induce an initial energy deposited in a finite volume through collision cascades as illustrated in Figure 16.5. 

O He ion beam bombardment of solid Li He ion beam bombardment of liquid Li... 

Nelson [29] first observed this dramatic increase in the loss rate of material from metal surfaces at elevated temperature while subjected to ion beam bombardment. The increase in the loss rate began at a lower temperature than could be explained by the vapor pressure of the material, yet the enhanced loss term had the same characteristic dependence on temperature as that exhibited by surface evaporation. Subsequent measurements on a variety of materials, including W [30] and C [31,32] exhibited similar behavior. 

Type II films appear to be more reliably produced by certain co-sputtered materials, and by ion beam bombardment, and these are discussed in Section 10.7. 

Fig. 27.1 Raman shift of chitosan film modified by Kr+ ion beam bombardments in the wavenumber range of 800 2,000 cm with surface color changes of (a), (b), and (c) (on the right) of chitosan films modified by Kr+ ion beam bombardments at (0.1 1.0xl0 3 5.0x 10 ...

Gulla et al. have demonstrated superior performance and stabUily of carbonless thin layer electrodes made by a dual ion beam assisted deposition (IBAD) technique that combines physical vapor deposition (PVD) with ion beam bombardment [47]. They found that bilayered coatings on GDL with either a Co or a Cr iimer layer ( 50 nm thin) and a Pt outer layer ( 50 nm thin, and 0.08 mg Pt cm ) showed a more than 50% higher Pt mass activity at 900 mV than a Pt single layer. 

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