Negative hydrogen ion densities and drift velocities in a multicusp ion source

Abstract

We have determined densities of negative hydrogen ions in a discharge by a laser detachment technique. We measured the electron density, the electron temperature, and the positive ion density using a Langmuir probe. We also performed extraction measurements. Combination of H− density measurements and extraction measurements yields information about the H− drift velocity. It was found that the velocity scaled with the square root of the electron temperature. All measurements were done as a function of discharge voltage, discharge current, and gas pressure. The densities are compatible with a semiquantitative model in which H− is produced by dissociative attachment of plasma electrons to vibrationally excited molecules and destroyed by wall collisions at very low pressure and collisions with H atoms, positive ions and/or hot thermal electrons at higher pressure.

Efficient production of negative hydrogen ions in RF plasma by using a self-biased grid electrode

“…This − is as the same level as the density obtained by using DC discharge with magnetic filter at 4 kW [2]. This result suggests that much higher density − plasma can be produced if parmanent magnets are employed [11].…”

“…When electrons distribute apploximately like Maxwelian, the average electron energy is expressed by the electron temperature e . Therefore, the control of e is of crucial importance for finding the best conditions of the chemical reactions necesary for the material processing [1][2][3][4]. In general, however, it is difficult to control e in weakly-ionized discharge plasmas, although several methods have been reported for the e control [1][2][3][4][5][6][7][8][9].…”

“…One side of the probe is used as a collector of the probe current, and the other surface is covered with Torr Seal which is a sealant made of low vapor pressure resin. Therefore, the surface area of the probe is equal to 0.07 cm 2 . The values of the dc probe current p and voltage p collected through Source Meter-2400 manufactured by Keithley Instruments are stored on a personal computer, and at the same time, a probe characteristic curve is drawn automatically on a display of the computer using the software that we have created using Microsoft Visual C++.…”

Sticking, adsorption, and absorption of atomic H on Cu(110)

“…The yield of the ion sources used to produce some beams depends on the concentration of atomic H in the source, which in turn is determined by the reflection and absorption properties of the wall [2]. Eenshuistra et al [2] reported recently that the measured densities in a multicusp ion source could only be modeled by assuming a H recombination coefficient of ~ 10% on the walls. This is surprisingly small in view of the strong H metal chemisorption bond [3].…”

“…A detailed calculation would require an accurate knowledge of the two-dimensional energy surface going beyond our present simplified analysis. A rough estimate, however, indicates immediately that one can easily obtain energy transfers from normal to parallel energy comparable to phonons: For a corrugation da/a one obtains parallel momentum transfers of the order of Sp/p~2Sa/a and energy transfers of 8E/(E+D) ~4(Sa/a) 2 .…”