Energetic ion beam

Near Surface Analysis with Energetic Ion Beams... 

The field of materials analysis by energetic ion beams has begun to mature in the last decade after arising within the nuclear physics community. The basic method, Rutherford back-scattering, has been the subject of a text (1 ), and the field has also engendered a useful handbook (2). Publications are scattered throughout the literature with much of the output in articles relating to the properties of materials. In these the ion beam analysis may form only a part of the work. New developments in technique and applications continue and have been the subject of a series of international conferences (see for example (3) for the latest of these). 

First, because of the large energy difference, this method is completely insensitive to chemical binding effects. While other conventional surface analysis techniques which are sensitive to the chemical state are unquestionably frequently required, it is also true that methods thus dependent on the chemical state may suffer from difficulties in calibration, particularly in transition regions where an element is found in more than one chemical state. Energetic ion beam analysis, on the other hand, offers an absolute technique independent of these effects. As such, this technique and other conventional techniques (e.g. Auger, ESCA etc.) may often prove to be complementary, each supplying information not available by the other techniques. 

Third, the requirement of accelerating an ion to the MeV range of energies must necessarily entail a larger size, more expensive and often more complex acceleration apparatus. Thus, the technique of energetic ion beam analysis grew in the... 

The use of elastic backscattering, which is the primary technique for energetic ion beam analysis, is the normal method of choice when it will produce satisfactory results. Some other ion beam techniques which may be useful in supplementing backscattering in specific cases will be discussed later in this paper. 

Because all phases of the interaction of the incident energetic ion beam with materials, including kinematics and cross section of the elastic collision and the energy losses by means of inelastic interaction with the electrons are readily calculable, the analysis lends itself to computer simluation. One of the first such programs, developed at IBM (4), is used at NRL, while other programs have also been developed at a number of other laboratories. 

It has been shown that energetic ion beams may be utilized to "nondesthuctively" determine the profile of composition vs. depth in a wide variety of near surface situations. The major difficulties and limitations of the method have been delineated with descriptions of alternative methods applicable in difficult cases. The advantages of using these techniques as complementary to other surface analysis methods has also been pointed out. 

Ion scattering spectrometry and secondary ion mass spectrometry are the best-known types of ion-beam-induced analyses applicable to catalysis. Other ion-beam techniques have not enjoyed wide use, probably because accelerators are required to produce sufficiently energetic ion beams. 

Endothermic charge transfer. Also called energetic ion beam electron transfer. 

Sectors require precisely collimated mono-energetic ion beams, which places additional requirements on the ion source and ion optics. Given a mono-energetic beam, the equation for a mass spectrometer with a sector of radius R and with ions accelerated to a kinetic energy V is ... 

Energetic ion beam irradiation is an efficient tool for introducing defect states in solid materials. This ion beam modifies materials through electronic excitation followed by the slowing down of SHIs in the material. Consequently, it is an important technique for controlled modifications of structural, optical, and magnetic properties of semiconductors. So the impact of ion beam irradiation on solid materials, particularly semiconductors, has been discussed. 

As NRA has grown from accelerator-based nuclear physics and expanded after the invention of solid-state detectors (the surface barrier Si detector for the detection of particles and Ge(Li) detectors for the detection of y rays), its instrumentation is very much similar to those used in particle and y-ray nuclear spectroscopy. The PIXE method also started to use an existing instrumentation, the Si(Li) X-ray detectors, nearly a decade later. Consequently, this review will refer to the previous O Sects. 33.1 and O 33.2 on PIXE and RBS concerning the acceleration and the formation of energetic ion beams, the internal and external sample chambers, scanning particle microprobe facilities, particle detection, and data acquisition. It will only deal with the characteristic features of the detection of ions and y rays produced in nuclear reactions. Neutrons are also produced in these reactions, but in practice they are rarely used for NRA. Because of space limitations, that technique (Bird and Williams 1989) will not be discussed. 

The principle of operation of secondary ion mass spectrometry (SIMS) devices was described in Chapter 1 an energetic ion beam (primary beam) impinges on the sample causing secondary ions and neutrals to be desorbed from the surface and enter a mass spectrometer where these ions are analyzed. A schematic of a SIMS device is shown in Figure 5.2 (Betti 2005). This device includes two ion sources (Duoplasmatron and cesium), a sample chamber with a transfer rod. 

Classical sputtering experiments with a mono-energetic ion beam in high vacuum show that the sputtering yield first increases with the mass of the incident ions and the pressure, but then decreases. For polycrystals, it is maximum at incident angle 30°. For single crystals, it is maximum in the direction perpendicular to a densely packed plane. 

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