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

采用离子微束辐照技术，研究了微纳米辐照对二氧化硅玻璃三维结构的影响。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二氧化硅玻璃的空间分布。在TIARA（JAERI Takasaki, Japan）的设备上，采用1.7 mev H^+、15-MeV O^<4+>或18-MeV Si^<5+>辐照高纯度硅玻璃，其影响达到1.0×10^<17>离子/cm^2。辐照效应包括缺陷形成、结构变化和压实，其空间分布可以通过微拉曼/PL和原子力显微镜来绘制。在二氧化硅玻璃中，我们观察到与致密化和悬空键缺陷相关的小环结构的形成以及离子的轨迹。原子力显微镜观察到的表面变形表明二氧化硅玻璃内部致密化了0.4%。H^+微束辐照在30 μm深度处表现为折射率变化。另一方面，O^<4+>和Si^<5+>等重离子辐照引起的辐射效应限制在距离表面小于10 μm的深度，且分布相对均匀。利用显微双束干涉仪对H^+微束辐照到1×10^<17>离子/cm^2时，折射率变化高达6×10^<-3>。我们还讨论了这些结果对微束辐照效应在光学元件制造中的应用的技术意义。

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.