Particle scattering layers

Knowing the composition of a layer, it is possible to establish a depth scale for the distribution of an element or to measure the layer thickness from the energy of the scattered particles. This depends on the energy loss of the projectile on its inward and outward paths, as described in Sect. 3.5.1. The energy difference, AE, for a particle scattered at the surface and a particle scattered at a depth x is given by ... 

For an ensemble of uncorrelated ID particles (cylinders, layers) with a Gaussian96 particle thickness distribution the ID scattering intensity is [197]... 

Basic information needed to understand the physical and chemical properties of solid surfaces and thin solid films include the atomic structures and the compositional variations across the surface and interface layers. The atomic structures can be studied with microscopies and with surface sensitive diffraction and particle scattering techniques. Compositions of surfaces and thin films can be studied with the atom-probe FIM. In general, however, compositional analyses are mostly done with surface sensitive macroscopic techniques, such as auger electron... 

As the charge and mass of the a-particles are known (they are He++ ions, for which M = E 2e) and their velocities can be determined from deflection experiments, the formula can be used to find the nuclear charge Z. For this we need only know the number of scattering atoms per unit volume and count the number of a-particles in the presence and absence of the scattering layer. For example, accurate experiments by Chadwiclv gave the following values for Z ... 

LEIS is a typical surface specific method, which detects particles scattered only from the uppermost surface layer of the soHd. The scattering of low energy ions of inert gases from the surface of a sample is measured. At low energies (< 5 keV) the ions are neutralised, if they penetrate below the top two or three monolayers, so only a few monolayers of the solid participate in the ion scattering process. In this way LEIS differs from RBS, in which the neutrahsation processes are negligible. 

The optical measmements of diffuse reflectance are dependent on the composition of the system. Several theoretical models have been proposed for diffuse reflectance, which are based on the radiative transfer theory, and all models consider that the incident hght is scattered by particles within the medium. The most widely used theory in photometric sensors is the Kubelka-Munk theory, in which it is assumed that the scattering layer is infinitively thick, which may, in practice, be the case with the chemical transducers utilized in photometric sensors. The absolute value of the reflectance R is related to the absorption coefficient K and the scattering coefficient S by the equation... 

It is possible to deconvoluate the spectrum of the particles scattered by a thick target composed of several layers of elements and to determine their nature and their thickness. 

Figure 2.22 shows the energy spectrum of a-particles scattered from a double layer of hafnium and yttrium on a thick silicon substrate while Fig. 2.23 shows the RBS spectrum of a sample containing Si and Au in the C-substrate as function of atomic masses present in their successive layers and from surface atoms of a thin layer. 

Fig. 7.2 Illustration of the spectroelectrochemical characterisation of a laboratory scale DSSC with a nanocrystalline Ti02 film sensitised with the RuN3 dye, measured under simulated AM 1.5G solar irradiation (100 mW cm ) electrolyte composition methoxyproprionitrile with 0.6 M propylmethylimidazolium iodide, 0.1 M Lil, 0.1 M tert butylpyridine, and 0.1 M iodine or guanidium thiocyanate 5 pm thick Ti02 film (9 nm particles) and scattering layer, a J-V curve, b IPCE spectrum (Courtesy of Patricia Jesus, Coimbra Chemistry Centre). In an optimised RuN3 DSSC the /sc reaches a value 20 mV and the maximum incident photon to current efficiency reaches 85 % [25]...

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