ABSTRACT
The following lists a brief summary of some major developments in ERD techniques over the years:
◾ In 1976, the idea of ERD was first introduced by L’Ecuyer et al. to analyze light elements in a thin target (LiF or LiOH) with 25-40 MeV 35Cl ions. [L’Ecuyer et al. 1976]
◾ In 1979, Doyle and Peercy first proposed using a conventional RBS beam (MeV 4He ions) to analyze H-depth profiles distributed in Si3N4 layers. [Doyle and Peeray, 1979]
◾ In 1983, the time-of-flight (TOF) particle detection method was first applied to ERD by Groleau, Gujrathi, and Martin (TOF-ERD), where both 30 MeV 35Cl+ and 4 MeV 4He+ ions were used to investigate a Mylar film. [Groleau et al. 1983]
◾ In 1984, Ross and co-workers first presented an inexpensive and novel method of profiling hydrogen isotopes in beryllium where a 350 keV 4He+ beam and crossed electrical and magnetic fields (ExB filter) were used for particle detection (ExB-ERD). [Ross et al. 1984]
◾ In 1990, Tirira, Trocellier, and Frontier first described the analytical capabilities of ERD in transmission geometry using 1.8-3 MeV 4He+ ions in which an analyzing depth of 6 μm and a depth resolution of 35 nm at the target surface were obtained. [Tirira et al. 1990]
◾ In 1990, Hofsass and co-workers first introduced depth profiling of light elements using elastic recoil coincidence spectroscopy (ERCS) based on simultaneous measurement of scattered and recoiled particle energies. [Hofsass et al. 1990]
◾ In 1994, ΔE-E solid-state telescopes were first developed in ERD by Arnoldbik, de Laat, and Habraken to discriminate hydrogen isotopes. [Arnoldbik et al. 1994]
◾ In 1996, a dedicated ERD book was published by Tirira, Serruys, and Trocellier to give an excellent review of various elastic recoil detection techniques and their applications in various fields. [Tirira et al. 1996]
◾ In 2005, channeling ERD under a conventional range foil configuration was introduced by Shao and colleagues to study lattice location of hydrogen in silicon. [Shao et al. 2005]
ERD kinematics is identical to that of RBS. Figure 6.1 shows a schematic diagram of an elastic recoil process. ERD involves measurement of the number and energy distribution of target atoms forward-recoiled by the incident heavier ions. From the physics point of view, ERD deals with a two-body elastic collision process in a central force field (Coulomb repulsion), an identical process where RBS occurs. Based on the conservation of energy and momentum equations in
Chapter 2, one can obtain the recoil kinematic factor at a recoil angle of ϕ as described in Equation (6.1):
(6.1)
= =
+ φK E
E 4 M M
(M M ) cosR 2
where M1 and M2 are the masses of the incident ion and recoil target atom. It is important to realize that at the same time, the forward scattering of M1 from M2 is possible at the same angle ϕ that is governed by the forward scattering kinematic factor:
(6.2)
=
φ ± − φ +
K (M / M ) cos [1 (M / M ) sin ] 1 (M / M )S
In RBS, where M1 < M2, the sign of the radical term in Equation (6.2) is
always positive for all possible angles. However, in ERD, where M1 > M2, the only way to satisfy the positive sign for the radical term is for the elastically scattered projectiles to be limited within a cone of half-angle ϕmax that is defined by:
(6.3)
φ = arcsin M Mmax
1 For example, to observe scattered 4He events from 1H, 2H (D), or 3H (T)
target atoms, the maximum detector angle will be limited to ϕmax = 14.47°, 30°,
FIGURE 6.1 Schematic representation of an elastic collision between a projectile of M1, atomic number Z1, and energy E0 and a target of mass M2 (atomic number Z2), which is at rest before the collision. After the collision, the target mass is recoiled forward at an angle ϕ and an energy E2 and the projectile is scattered at an angle of θ with an energy E1. The scattering and recoil angles in the center of the mass frame are designated as θc and ϕc, respectively.
