Dependence of Optical Emission Spectra on Argon Gas Pressure during Modulated Pulsed Power Magnetron Sputtering (MPPMS)

Modulated pulsed power magnetron sputtering (MPPMS) of titanium was investigated as a function of argon gas pressure using optical emission spectroscopy (OES). Delays in discharge and the formation of comb-like discharge current waveforms due to splitting and pulsing were observed with a decrease in pressure. This observation corresponds to the evolution from MPPMS condition to deep-oscillation-magnetron-sputtering (DOMS)-like condition by changing discharge gas pressure. The optical emission intensities of the ionic species (Ar+ and Ti+) increased as the comb-like current waveforms were formed with decreasing Ar pressure. This behavior showed a marked contrast to that of the neutral species (Ar and Ti). The Ar pressure dependence of OES was revealed to be due to the plasma build-up stage, which is the initial generation process of plasma discharge in pulsed dc magnetron sputtering, from the temporal profile for the atomic-line intensities of the optically emitting species in MPPMS and DOMS-like plasmas

Delayed Discharge Bridging Two Sputtering Modes from Modulated Pulsed Power Magnetron Sputtering (MPPMS) to Deep Oscillation Magnetron Sputtering (DOMS)

Delayed discharges due to electrical breakdown are observed in modulated pulsed pow er magnetron sputtering (MPPMS) plasma of titanium. The delayed discharge, which is remarkable with decreasing argon gas pressure, transforms the discharge current waveform from a standard modulated pulsed discharge current waveform to a comb-like discharge current waveform consisting of several pulses with high power. In addition, the delay times, consisting of statistical times and formative times in the delayed MPPMS discharges, are experimentally measured with the help of Laue plot analysis. The pressure dependence of delay times observed indicates that the delayed discharge behavior matches the breakdown characteristics well. In the present study, the delayed discharge dynamics of the comb-like discharge current waveform, which can be the origin of deep oscillation magnetron sputtering, are investigated based on measurement of the delay times and the characteristics of discharge current waveforms

Correlation between Electronic Shell Structure and Inertness of Cu_<i>n</i>⁺ toward O₂ Adsorption at <i>n</i> = 15, 21, 41, and 49

The inertness of metal clusters in air is important for their application to novel materials and catalysts. The adsorption reactivity of copper clusters with O₂ has been discussed in connection with the electronic structure of clusters because of its importance in electron transfer from the cluster to O₂. Mass spectrometry was used to observe the reaction of Cu_<i>n</i>⁺ + O₂ (<i>n</i> = 13–60) in the gas phase. For O₂ adsorption on Cu_<i>n</i>⁺, the relative rate constants of the <i>n</i> = 15, 21, 41, and 49 clusters were clearly lower than those with other <i>n</i>. Theoretical calculations indicated that the inertness of Cu₁₅⁺ with 14 valence electrons was related to the large HOMO–LUMO gap predicted for the oblate Cu₁₅⁺ structure. The Clemenger–Nilsson model was used to predict that the electronic subshell of oblate Cu₄₉⁺ with 48 electrons was closed. This electronic shell closing of Cu₄₉⁺ corresponds to the inertness for O₂ adsorption