Plasma reactivity in high-power impulse magnetron sputtering through oxygen kinetics

Abstract

The SuperCDMS experiment in the Soudan Underground Laboratory searches for dark matter with a 9-kg array of cryogenic germanium detectors. Symmetric sensors on opposite sides measure both charge and phonons from each particle interaction, providing excellent discrimination between electron and nuclear recoils, and between surface and interior events. Surface event rejection capabilities were tested with two 210 Pb sources producing ∼130 beta decays/hr. In ∼800 live hours, no events leaked into the 8-115 keV signal region, giving upper limit leakage fraction 1.7 × 10 −5 at 90% C.L., corresponding to < 0.6 surface event background in the future 200-kg SuperCDMS SNOLAB experiment.PACS numbers: 14.80. Ly, 95.35.+d, 95.30.Cq, 85.25.Oj, 29.40.Wk Weakly Interacting Massive Particles (WIMPs) are a generic class of candidates for the dark matter 1-3 which is responsible for the formation of structure in our universe 4 . These Big Bang relic particles are particularly interesting because their possible existence is motivated by arguments both from cosmology and from particle physics. Experiments are underway to detect WIMPs directly as they recoil off nuclei in terrestrial detectors 5 .The approach of the Cryogenic Dark Matter Search (CDMS) is to maximize the information on each particle interaction using technology with excellent signalto-noise and position information. These detectors with multiple readout channels have resulted in a series of robust experiments that have minimized unknown backgrounds. In addition to repeated improvements in sensitivity 6-11 , we have obtained constraints on annual modulation, inelastic dark matter interactions, axions, and electromagnetic interactions [12][13][14][15] .

An Overview on Time‐Resolved Optical Analysis of HiPIMS Discharge

“…Summarizing these remarks, we believe that the special attention should be played to the following points during the future HiPIMS discharge characterization work (the suggested diagnostics techniques are parenthesized in each case): Non‐intrusive analysis of propagation of the secondary electrons in the discharge, which can be obtained studying the electron temperature (line ratio methods), and excitation temperature (ROAS, OES). Further investigations of the particle transport phenomena, the quantitative estimations of the particle fluxes aiming at clarification of the angular distribution of the sputtered species in HiPIMS (space‐resolved film depositions, ROAS, DS‐LIF imaging). Study of the sputtered particles in terms of the velocity component perpendicular to target (), aiming at the analysis of the energetic ionized species (LIF imaging, DS‐LIF, Fabry‐Perot interferometry). Additional studies of ion propagation, namely the spatial symmetry of the ion velocity distribution, its connection to gyration of the charged particles and the discharge current instabilities (LIF imaging, DS‐LIF imaging), possibly involving heavier sputtered atoms (e.g., W ) in order to minimize the influence of collisions. Further characterization of the reactive HiPIMS processes. Time‐resolved density evolution of the main discharge species in reactive mode, including the dynamics of the energetic negative atomic O ions (O − ), as they may play crucial role in the discharge kinetics after acceleration by negative cathode potential (ROAS, DS‐LIF). Study of O metastables and ground state particles in R‐HiPIMS undertaken for different target materials may clarify the time‐resolved behavior of O met density observed by ROAS. The O ground state measurements by two‐photon absorption LIF technique in this case are highly demandable. Last, but not the least, the time‐ and space‐resolved modeling of a HiPIMS discharge, possibly using the numerous experimental results as the input data, should be mentioned. …”

Effect of pulsed off-times on the reactive HiPIMS preparation of zirconia thin films

“…This may be attributed to oxygen's greater reactivity with metals compared with nitrogen in reactive HiPIMS, resulting in more complex discharge activity and less control over the deposition process. Several studies have investegated the discharge current and deposition rate of the oxide preparation of titanium [18]- [19], aluminum [18], and tungsten [20]. Nevertheless, further research on metallic oxides as potential candidates for optical coating applications is required.…”

Ground state atomic oxygen in high-power impulse magnetron sputtering: a quantitative study

“…During the discharge afterglow the actinometry principle can still be applied to the nonradiative (metastable) upper states. Since in pulsed magnetron discharges the population of metastable states can be significant for both O [19] and Ar [17,37] atoms, the principles of emission actinometry can be transferred to the metastable levels. Since the number den sities of the corresponding metastable states are normally determined by atomic absorption spectroscopy [37,38], the proposed method can be called 'absorption actinometry'.…”

“…To date, apart from experimental and modeling studies on the O metastable atoms in RHiPIMS [19], there has been a significant lack of experimental data for the ground state O density. The main reason for this is the difficulty of meas uring the O ground state density directly by optical absorption spectroscopy, which is a straightforward nonintrusive tech nique used for this purpose [20].…”