Fundamental sputtering studies: Nonresonant ionization of sputtered neutrals

Because of the practical importance of sputtering, numerous theories and computer simulations are used for predicting many aspects of the sputtering process. Unfortunately, many of the calculated sputtering results are untested by experiment. Until recently, most sputtering experiments required either very high ion fluences or the detection of only minor constituents of the sputtered flux, i.e., ions. These techniques may miss the subtleties involved in the sputtering process. High-detection-efficiency mass spectrometry, coupled with the laser ionization of neutral atoms, allows the detection of the major sputtered species with very low incident ion fluences. The depth-of-origin of sputtered atoms is one example of an important but poorly understood aspect of the sputtering process. By following the sputtering yield of a substrate atom with various coverages of an adsorbed overlayer, the depth of origin of sputtered atoms has been determined. Our results indicate that two-thirds of the sputtered flux originates in the topmost atomic layer. The ion-dose dependence of sputtering yields has long been assumed to be quite minor for low- to-moderate primary ion fluences. We have observed a two-fold decrease in the sputtering yield of the Ru(0001) surface for very low primary ion fluences. Data analysis results in a cross section for damage of 2.7 {plus minus} 1.0 {times} 10{sup {minus}15}cm{sup 2}. 40 refs., 3 figs., 2 tabs

Femtosecond laser postionization of sputtered and laser desorbed atoms

This paper examines the photoionization efficiency of a femtosecond laser ionization source on several atomic species. Use of femtosecond laser ionization pulses to photoionize the desorbing flux from a sample surface is examined. Example of mass spectra produced is given using 248 nm pulse on sputtered Au. Al and Mo have widely different ionization potentials and show that 248 nm pulses are more efficient at photoionization than longer wavelengths; this is enhanced for Mo with high ionization potential. It is concluded that efficient photoionization occurs for atoms with ionization potentials low enough for two-photon ionization to occur

Velocity and electronic state distributions of sputtered Fe atoms by laser-induced fluorescence spectroscopy

Velocity distributions and relative populations in the fine-structure levels of the a/sup 5/D/sub J/ ground state of Fe atoms, produced by sputtering with 3 keV argon ions, have been investigated by Doppler shifted laser induced fluorescence. The laser system employs a single-mode, scanning ring dye laser, amplified by a sequence of three excimer-pumped flowing-dye cells. Frequency doubling in a KD*P crystal was used to produce high energy (> .5 mJ) pulses of narrowband tunable UV output near 300 nm. Laser power influence on effective velocity bandwidth was investigated. Favorable light-collection geometry minimized distortion of the velocity spectra from apparatus-averaging effects. In impurity flux diagnostic applications in fusion devices, substantial spatial averaging may occur. In the latter case, the narrow velocity bandwidth (70 m/s, transform limit) of the present laser system is particularly useful

Chemical processing of liquid lithium fusion reactor blankets

A 50-gallon-capacity lithium loop constructed mostly from 304L stainless steel has been operated for over 6000 hours at temperatures in the range from 360 to 480/sup 0/C. This facility, the Lithium Processing Test Loop (LPTL), is being used to develop processing and monitoring technology for liquid lithium fusion reactor blankets. Results of tests of a molten-salt extraction method for removing impurities from liquid lithium have yielded remarkably good distribution coefficients for several of the more common nonmetallic elements found in lithium systems. In particular, the equilibrium volumetric distribution coefficients, D/sub v/ (concentration per unit volume of impurity in salt/concentration per unit volume of impurity in lithium), for hydrogen, deuterium, nitrogen and carbon are approx. 3, approx. 4, > 10, approx. 2, respectively. Other studies conducted with a smaller loop system, the Lithium Mini-Test Loop (LMTL), have shown that zirconium getter-trapping can be effectively used to remove selected impurities from flowing lithium

Laser-based secondary neutral mass spectroscopy: Useful yield and sensitivity

A variety of problems exist in order to optimally apply resonance ionization spectroscopy (RIS) to the detection of sputtered neutral atoms, however. Several of these problems and their solutions are examined in this paper. First, the possible useful yields obtainable and the dependence of useful yield on various laser parameters for this type of sputtered neutral mass spectrometer (SNMS) are considered. Second, the choice of a mass spectrometer and its effect on the instrumental useful yield is explored in light of the unique ionization region for laser based SNMS. Finally a brief description of noise sources and their effect on the instrumental sensitivity is discussed. 33 refs., 12 figs

Selectivity, specificity and sensitivity in the photoionization of sputtered species

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155736/1/Gruen_et_al_1991_Selectivity_specificity.pd

Resonance ionization mass spectrometry of sputtered osmium and rhenium atoms

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155703/1/Blum_et_al_1990_Resonance_ionization.pd

Secondary neutral mass spectrometry using three-colour resonance ionization: osmium detection at the p.p.b. level and iron detection in silicon at the < 200 p.p.t. level

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155725/1/Pellin_et_al_1990_Secondary_neutral.pd