Energy focussing

All crystal analyser spectrometers of the TOSCA type have two design features that improve their resolution. These are the use of time focussing and the Marx principle (also known as energy focussing). Incorporation of these features improves the resolution at high and low energy transfer respectively. 

Note that the Marx principle is more restrictive than time focussing in the latter all that is necessary is that the sample, analyser and detector planes are parallel, in the former the planes must not only be parallel but the sample and detector planes must also be co-planar. Time and energy focussing are so successfiil that all current and planned crystal analyser spectrometers employ it. The only exception is the forward scattering bank on TOSCA where limitations on space meant that the detectors were placed slightly downstream from the sample plane. In practice, the displacement is small enough that the resolution is essentially the same in both the forward and backscattering detector banks. 

Laser Beam Machining. A machining process in which material is removed by melting or vaporization with high energy focussed laser beams. Very precise localised heating is possible, by which means, for example, fine holes may be drilled in highly refractory materials. 

The extraction delay can produce energy focussing in a time-of-flight mass spectrometer. 

Energy focussing in a time-of-flight mass spectrometer that is accomplished by introducing a time delay between the formation of the ions and the application of the accelerating voltage pulse. 

Fig. 7.4. Crack stopping mechanism of a toughened adhesive, (a) Crack initiated due to overload, (b) Crack propagates and splits the glassy, load-bearing phase of the adhesive, (c) Crack stopped because the energy focussed at its tip is dissipated in the rubbery phase which distorts during redistribution and delocalisation of the destructive forces.

The low energy ions leaving the reaction chamber are re-accelerated for conventional mass analysis. Many of these instruments use a pair of quadrupole lenses (13) following re-acceleration to increase the intensity of secondary ions. Such a lens system is particularly well adapted to this application because of its large physical size and strong focussing properties. 

We shall concern ourselves here with the use of an X-ray probe as a surface analysis technique in X-ray photoelectron spectroscopy (XPS) also known as Electron Spectroscopy for Chemical Analysis (ESCA). High energy photons constitute the XPS probe, which are less damaging than an electron probe, therefore XPS is the favoured technique for the analysis of the surface chemistry of radiation sensitive materials. The X-ray probe has the disadvantage that, unlike an electron beam, it cannot be focussed to permit high spatial resolution imaging of the surface. 

A mass-energy filter may be included to remove contaminant ions, and multiply charged and clustered ions of the main beam species. Ions of the required mass and energy pass through the filter, while unwanted species are deflected out of the beam. Prior to final focussing, the beam is deflected through a few degrees, and any neutral particles will be undeviated and are therefore separated out. 

Si(Li) spectroscopy, with the capability of simultaneous quantitative analysis of 72 elements ranging from sodium through to uranium in solid, liquid, thin film and aerosol filter samples. The penetrating power of protons allows sampling of depths of several tens of microns, and the beam itself may be focussed, rastered or varied in energy. The use of a proton beam as an excitation source offers several advantages over other X-ray techniques, for example there is a higher rate of data accumulation across the entire spectrum which allows for faster analysis. 

A variable negative potential on the outer cylinder bends the Auger electrons of a particular kinetic energy E0 back through a second annular aperture on the inner cylinder they are then are focussed at an exit aperture on the analyser axis where they are collected by an electron multiplier. The energy of the transmitted electrons is proportional to the voltage on the outer cylinder (F), and simply scanning the... 

Figure 5.39. Illustrating the focussing and dispersive properties of a magnetic prism in an electron energy-loss spectrometer. In a serial spectrometer a slit at D is used to ensure that only electrons of a single energy loss enter the detector. In a parallel spectrometer, a position-sensitive detector is placed at D to collect electrons of all energies in parallel.

In SAM the electron beam can be focussed to provide a spatial resolution of < 12 nm, and areas as small as a few micrometers square can be scanned, providing compositional information on heterogeneous samples. For example, the energy resolution is sufficient to distinguish the spectrum of elemental silicon from that of silicon in the form of its oxide, so that a contaminated area on a semiconductor device could be identified by overlaying the Auger maps of the two forms of silicon obtained from such a specimen. 

In evaluating options for obtaining the energy needed to sustain world economic progress in the coming years, it is important to consider the full spectrum of risks to the environment and to human health that each option may create or reduce. This is particularly important in evaluating nuclear power, where often attention has been disproportionately focussed on the presumed dangers. 

Continuum models are being increasingly used to study protein-ligand recognition [115]. Most studies have considered series of similar ligands or protein mutants and focussed on binding free energy differences. This leads to partial cancelation of some troublesome contributions, especially rotational/translation/vibrational entropy... 

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