Study on the three-dimensional structures in silica glass induced by micro- and nano-scale irradiation effects using focused ion beam

利用离子微束辐照石英玻璃，研究了微纳米尺度辐照效应在石英玻璃中诱导的三维结构。利用微PL/拉曼光谱和原子力显微镜（AFM）研究了离子微束辐照石英玻璃的空间分布。在TIARA（日本JAERI高崎）的装置上，利用微束线，用1.7 MeV H^+、15 MeV O^&lt;4+&gt;或18 MeV Si^&lt;5+&gt;辐照高纯石英玻璃，辐照剂量高达1.0×10^<17>ions/cm ^2。辐照效应包括缺陷的形成、结构的变化和致密化，其空间分布可以通过显微拉曼/光致发光和原子力显微镜来绘制。我们观察到形成的小环结构与致密化和悬空键缺陷沿着与轨道的离子在石英玻璃。AFM观察到的表面变形表明石英玻璃的内部致密化0.4%。H^+微束辐照在30 μm深度范围内表现出折射率变化形式的辐射效应。而O^&lt;4+&gt;和Si^&lt;5+&gt;等重离子辐照产生的辐射效应仅限于距表面小于10 μm的深度，且分布相对均匀。使用显微双光束干涉仪对折射率变化的评估表明，<-3>当H^+微束照射到1×10^<17>ions/cm ^2的能量密度时，折射率变化高达6×10^。我们还讨论了这些结果的应用微束辐照效应的光学元件的制造的技术影响。

We studied three dimensional structures in silica glass induced by micro- and nano-scale irradiation effects by means of ion microbeam irradiation. Spatial distribution of irradiation effects by ion microbeam on silica glass was investigated by micro-PL/Raman spectroscopy and atomic force microscopy(AFM). High-purity silica glass was irradiated by 1.7-MeV H^+, 15-MeV O^<4+>, or 18-MeV Si^<5+> up to fluences of 1.0×10^<17> ions/cm^2 using microbeam lines at the facility of TIARA(JAERI Takasaki, Japan). The irradiation effects include defect formation, structural changes, and compaction, whose spatial distribution can be mapped out by micro-Raman/PL and AFM. We observed the formation of small ring structures associated with densification and dangling bond defects along with the tracks of ions in silica glass. Surface deformation observed by AFM suggests the internal densification of silica glass by 0.4 %. The H^+ microbeam irradiation shows radiation effects up to depth of 30 μm in the form of refractive index change. On the other hand, the heavy ion irradiations such as O^<4+> and Si^<5+> induce radiation effects limited to the depth of less than 10 μm from the surface with relatively homogeneous distribution. Evaluation of the refractive index change using a microscopic two-beam interferometer shows the change as high as 6×10^<-3> for H^+ microbeam irradiation to the fluence of 1×10^<17> ions/cm^2. We also discuss technological implications of these results on the applications of microbeam irradiation effects to the fabrication of optical elements.