Abstract
In this paper, the indirect monitoring of plasma-induced defect formation within fused silica via plasma emission spectroscopy is presented. It is shown that low-pressure plasma treatment with hydrogen as process gas leads to a decrease in UV transmission of fused silica. This decrease can be directly attributed to oxygen vacancy-related defects and the presence of hydrogen within the silicon dioxide glass network. By the analysis of the plasma composition, it was observed that the amount of oxygen within the plasma increases with increasing treatment duration. Hence, oxygen was continuously released from glass network in the course of the plasma treatment. It was further observed that this release is strongly dependent on the applied plasma power where the lowest process efficiency occurs at the highest plasma power. It is shown that an increase in plasma power leads to a remarkable increase in light emission from the working gas, hydrogen. This observation indicates that the higher the degree of excitation and ionisation of the plasma, the lower the efficiency of plasma-induced formation of oxygen deficiency-related defects. This finding is of mentionable relevance for a better understanding of plasma-induced surface modification and coating processes.
Highlights
IntroductionIn contrast to the above-mentioned disturbing and unwanted effects, an oxygen deficiency-related increase in absorption is of certain interest for laser structuring of optical glasses and fused silica [6,7,8]
The understanding of oxygen deficiency centres (ODC), hydrogen centres and other oxygen deficiency-related defects such as E′-centres in glasses has gained in importance due to the growing number of optical and opto-electrical devices and systems used
The matrix model (MM) was suggested by Hinds et al assuming silicon suboxide to be given by clusters of Si embedded in a matrix of SiO2 or clusters of SiO2 embedded in a matrix of Si, respectively [17]
Summary
In contrast to the above-mentioned disturbing and unwanted effects, an oxygen deficiency-related increase in absorption is of certain interest for laser structuring of optical glasses and fused silica [6,7,8]. The random mixture model (RMM) as introduced by Temkin describes silicon suboxide as a mixed phase made up of clearly separated and homogeneous clusters of silicon (Si) and S iO2 [16]. The interface cluster mixture model (ICMM) was presented by Hohl et al and represents a combination of both the RBM and the RMM According to this model, homogeneous Si and S iO2 clusters are embedded into (and separated by) a boundary layer consisting of silicon suboxide and silicon monoxide [18]
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