Beam charging

Changes in the composition of a specimen over the analyzed depth can be caused by beam heating or by beam charging of the specimen. Beam heating can lead to selective vaporization of some elements or diffrisional redistribution of the elements. If the surflice charges up to some potential, then electric-field enhanced diffusion can selectively redistribute certain elements. Beam-heating effects usually... 

Figure 5. FAB SIMS Spectra of Polyethylene Showing Thermal Damage with e Beam Charge Neutralization...

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. 

Figures 7a, b, and c show the SIMS spectra of known polymers PTFE, FEP, and PVF2. Briggs and Wootton (13) report that radiation from electron beam charge neutralization...

The energy of the 7) state can also be determined for soluble conjugated polymers by the technique of T-T energy transfer (Monkman et al., 2001). When the solvent in a polymer solution is ionised with an intense, pulsed electron beam, charge recombination gives rise to excited solvent molecules in... 

Zimek Z. (1978) A single-pulse toroidal coil beam-charge monitor. RadiatPhys Chem 11 179-181. 

Vojnovic B. (1985) A sensitive single-pulse beam charge monitor for use with charged particle accelerators. Radiat Phys Chem 24 517-522. 

Fig. 23 TSC measurements of corona charged i-PP films containing different concentrations of additive 4 (top) and TSC measurements of electron-beam-charged i-PP films with different concentrations of additive 4 (bottom) [41]. Published by permission of IOP Publishing Ltd...

An electron beam is focused on the surface of the mosaic of p-type semiconductors and, by proper electronic control, scans the vidicon tube target. The electron beam charges each p-type cell to a negative potential. A positive voltage is applied to the silicon n-type base to create a depletion zone. Each diode thus acts as a capacitor, storing electrical energy. 

Electron microscopy is one example of electron beam analysis of polsrmers and PMC. Beam charging effects occur in most polymers and PMC (99), imless when coated with a thin conductive layer (carbon, gold, or platinum). Environmental scanning electron microscopes (ESEM) do not require such coatings (100). Size and shape of the test object and possible electron beam heating effects then decide whether the method is NDT... 

Use the scatter raster type, which is the one designed to be used for insulating samples each pixel point is located as far from the previous and next pixel so as to spread the primary beam charge homogeneously. 

Use of a negative polarity primary ion beam, i.e. 0 . This method, commonly used in the Earth Sciences, is effective, in that, the primary beam introduces negative charge onto the samples surface and in the area being sputtered. This complements electron beam charge neutralization... 

Figure 3 Minimum detectable limit oftrace elements in a carbon matrix as a function of atomic number and proton energy. The calculation assumes a beam charge of 1 xC and curves are presented for K and L lines. Reproduced with permission of Wiley from Johansson SAE, Campbell JL and Malmqvist KG (1995) Particle-Induced X-ray Emission Spectrometry. New York Wiley.

In spite of the relative complexity of interpreting the spectra, RBS with alpha particles is widely used for materials analysis for characterizing thin film structures or depth profiles of impurities or dopants. RBS with protons can be used simultaneously with PIXE to help to determine the bulk matrix composition and also the incident beam charge. 

N= number of projectile atoms, number of photons g = terminal charge Q = total beam charge ... 

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