In order to further develop integrated quantum-functional devices it has become indispensable in recent years to ingeniously utilize selective surface reactions of neutral free radicals for the device processing. The problem encountered in the experimental study of a chemical reaction between a neutral free radical and a well-characterized material surface is how to sufficiently supply a steady-flux refined beam of neutral free radicals (RBNR), that is to say, purified beam of momentum-controlled neutral free radicals onto the surface. In order to overcome the difficulty we have proposed several experimental production approaches¹⁾, one of which is the method of photo-deionization of negative ion beams (PDINIB). When we apply RBNR to thin film growth, a steady-flux beam obtained using a CW laser is more useful than a pulsed beam. However, the power of available CW lasers is generally much weaker than the peak power of pulsed lasers. Thus, development of a multiple-pass photo-deionizer (MPDI) to enhance the photo-neutralization efficiency has been a key point to realize a practical steady-flux PDINIB apparatus. The rate of neutral free radical production by our trial PDINIB apparatus is estimated in Ref.2 based on measurement of decrease in the negative-ion beam current (DNIC).
In the present study, we could improve the S/N ratio and the spatial resolution of the DNIC measurement system 40 times and 7 times, respectively. This improved monitoring system was used for measurements of the spatial profile of the neutral-beam flux under various conditions of the neutral-beam production. At the meeting, we discuss the beam-profile controllability of the trial PDINIB apparatus based on the experimental results.
This work is supported by the Ministry of Education, Science, Sports and Culture, Japan.
1) K. Hayashi et al., J. Vac. Sci. Technol. A 20 (3), 991 (2002).
2) K. Hayashi et al., Nucl. Instrum. Methods Phys. Res. B 206C, 403 (2003).

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