Historical Overview: the Origin of NDP

(Quoted from: Dietmar Fink, Neutron Depth Profiling, Berlin 1996 HMI-B 539, Pages 71-72)

In 1968, J. P. Biersack suggest that channeling and blocking effects should occur not only after nuclear reactions with charged particles in crystalline targets, but also after (n, p) and (n, a) reaction with thermal neutrons. This assumption was verified by the author (D. Fink) in his thesis. On July 1^st, the author performed the first successful blocking experiment with a LiF crystal and a plastic detector at the old research reactor BERI of the Hahn-Meitner-Institüt (HMI) Berlin, Germany. The experimental equipment was later moved to the reactor FMRB of the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig, Germany. Here, several more channeling and blocking experiments were performed on various lithium and boron containing systems.

Also, around 1971/1972, J. P. Biersack and the author (D. Fink) attempted the first depth profiling measurements after thermal neutron induced nuclear reactions. This technique, a prompt neutron activation analysis with subsequent proton or a-particle energy spectroscopy, became known later on as “NDP,” Neutron Depth Profiling*. Simultaneously, and independently from the German activities, J. F. Ziegler et al. applied this method in 1972 to the examination of boron in silicon for electronic applications as well as Bogancs et al. in Dubna. A little bit later (1974/1975), also R. Henkelmann and coworkers from Technische Universität München (TUM), Germany, applied this method for the determination of boron in silicon.

In 1975, our instruments were removed Braunschweig to the new Berlin reactor BER II at the HMI. In 1976, both the München and Berlin groups installed a common measuring chamber for depth profile analysis at the High Flux Reactor (HFR) of the Institute Max von Laue-Paul Langevin (ILL) Grenoble, France. In 1978 both groups additionally installed an upgraded channeling/blocking experiment at the same reactor. This close cooperation between both groups in the field of depth profile analysis and lattice position determination lasted till 1984. Thereafter, in 1985, and improved NDP vessel was installed at the ILL by the author (D. Fink), which operated until the reactor stop in 1991.

In the seventeens(sic) and eighties, similar NDP instruments were also installed by research groups in Czechoslovakia, the United States, and Japan. Meanwhile, the application of this technique do no longer cover only questions of basic physical understanding, but expand over a vast area, ranging from archaeometry via electronics and tribology up to fusion technology. Though in recent time, other competitive and very promising analysis techniques have been developed – e.g. the HERDA technique – new physical concepts already show up for NDP, and new detector developments are realized, which will increase the sensitivity of the NDP technique dramatically, so that a renaissance of the method is expected for the near future.

*The term "neutron depth profiling" (NDP) was first coined in the paper: “Neutron Depth Profiling at the National Bureau of Standards,” Downing, R.G., Fleming, R.F., Langland, J.K., and Vincent, D.H., Nuclear Instruments and Methods 218 (1983) 47-51