Backscattering

Under ideal conditions (e.g., point sources producing spherical waves and no multiple reflections) a rectified backscattered signal represents line integrals of the ultrasonic reflectivity over concentric arcs centered at the transducer position. To reconstruct the reflection tomo-... 

By plotting InCp po) against x the damping coefficient a is the gradient of the resulting straight line. To separate the elements oq and Ota in a it is possible to measure the backscattering acoustic wave pressure Ps. 

LEED Low-energy electron diffraction [62, 75, 105] Elastic backscattering of electrons (10-200 eV) Surface structure... 

ISS Ion scattering spectroscopy [153, 154] Inelastic backscattering of ions (-1 keV ion beam) Surface composition... 

EXAFS Extended x-ray absorption fine structure [177, 178] Variation of x-ray absorption as a function of x-ray energy beyond an absorption edge the probability is affected by backscattering of the emitted electron from adjacent atoms Number and interatomic distance of surface atoms... 

Figure Al.7.12 shows the scattered electron kinetic energy distribution produced when a monoenergetic electron beam is incident on an A1 surface. Some of the electrons are elastically backscattered with essentially...

Chu W-K, Mayer J W and Nicolet M-A 1978 Backscattering Spectrometry (New York Academic)... 

Raman microscopy is more developed than its IR counterpart. There are several reasons for this. First, the diffraction limit for focusing a visible beam is about 10 times smaller than an IR beam. Second, Raman spectroscopy can be done in a backscattering geometry, whereas IR is best done in transmission. A microscope is most easily adapted to a backscattermg geometry, but it is possible to do it in transmission. 

Figure Bl.23.3. Schematic illustrations of backscattering with shadowing and direct recoiling with shadowing and blocking.

As a increases, a critical value " i-.iiiis reached each time the th layer of target atoms moves out of the shadow cone allowing for large-angle backscattering (BS) or small-/i collisions as shown in figure Bl.23.3. If the BS intensity 1, is monitored as a fimction of a, steep rises [36] witli well defined maxima are observed when the... 

Heiland W and Taglauer E 1977 The backscattering of low energy ions and surface structure Surf. Sc/. 68 96-107... 

Taglauer E 1997 Low-energy Ion scattering and Rutherford backscattering Surface Analysis The Principal Techniques ed J C VIckerman (Chichester Wiley) pp 215-66... 

B1.24 Rutherford backscattering, resonance scattering, PIXE and forward (recoil) scattering... 

Rutherford backscattering spectrometry is the measurement of the energies of ions scattered back from the surface and the outer microns (1 micron = 1 pm) of a sample. Typically, helium ions with energies around 2 MeV are used and the sample is a metal coated silicon wafer that has been ion implanted with about a... 

By inserting a semiconductor x-ray detector into the analysis chamber, one can measure particle induced x-rays. The cross section for particle induced x-ray emission (PIXE) is much greater than that for Rutherford backscattering and PIXE is a fast and convenient method for measuring the identity of atomic species within... 

This overview covers the major teclnhques used in materials analysis with MeV ion beams Rutherford backscattering, chaimelling, resonance scattering, forward recoil scattering, PIXE and microbeams. We have not covered nuclear reaction analysis (NRA), because it applies to special incident-ion-target-atom combinations and is a topic of its own [1, 2]. 

The discussion of Rutherford backscattering spectrometry starts with an overview of the experimental target chamber, proceeds to the particle kinematics that detennine mass identification and depth resolution, and then provides an example of the analysis of a silicide. 

Figure Bl.24.1. Schematic diagram of the target chamber and detectors used in ion beam analysis. The backscattering detector is mounted close to the incident beam and the forward scattering detector is mounted so that, when the target is tilted, hydrogen recoils can be detected at angles of about 30° from the beam direction. The x-ray detector faces the sample and receives x-rays emitted from the sample.

Figure Bl.24.5. Backscattering spectrum of a thin Ni film (950 A) with near monolayers ( 30 x 10 at cm of An on the front and back surfaces of the Ni film. The signals from the front and back layers of An are shown and are separated in energy from each other by nearly the same energy width as the Ni signal.

The essentially non-destmetive nature of Rutherford backscattering spectrometry, combmed with the its ability to provide botli compositional and depth mfomiation, makes it an ideal analysis tool to study thm-film, solid-state reactions. In particular, the non-destmetive nature allows one to perfomi in situ RBS, thereby characterizing both the composition and thickness of fomied layers, without damaging the sample. Since only about two minutes of irradiation is needed to acquire a Rutherford backscattering spectmm, this may be done continuously to provide a real-time analysis of the reaction [6]. 

Figure Bl.24.7. A tliree-dimensional plot of backscattering signal versus time for a Pt film deposited onto Si...

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