Surface and morphological features of laser-irradiated silicon under vacuum, nitrogen and ethanol
Surface and morphological features of laser-irradiated silicon under vacuum, nitrogen and ethanol
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DOI：
10.1016/j.apsusc.2015.10.008
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发表时间：
2015-12
影响因子：
6.7
通讯作者：
Asma Hayat;S. Bashir;M. Akram;K. Mahmood;M. Iqbal
中科院分区：
文献类型：
--
作者：
Asma Hayat;S. Bashir;M. Akram;K. Mahmood;M. Iqbal
研究了在真空、氮气（100 Torr）和乙醇三种不同环境下激光诱导硅（Si）表面和结构的改性。用1000脉冲KrF准分子激光（λ = 248 nm，τ = 18 ns，重复频率= 30 Hz），在2.8 J/cm 2和4 J/cm 2两种不同能量密度下相互作用，在薄膜表面形成了各种形貌，如激光诱导周期性表面结构（LIPSS）、尖峰、柱状、锥形和裂纹等。用扫描电子显微镜（SEM）观察了表面形貌。而利用拉曼光谱研究了辐照靶的结构修饰。SEM分析表明，在真空条件下，在2.8 J/cm 2的低激光能量密度下辐照硅的中心烧蚀区域，微尺度柱和尖峰的分布不均匀。而在边界处可以看到锥形、凹坑、空腔和波纹状特征。在4 J/cm ~ 2的能量密度下，观察到了周期性结构和微柱。在氮气环境中烧蚀的情况下，在较低的注量下，观察到熔化、飞溅、自组织颗粒结构和裂纹沿着并伴有再沉积。氮中的这种类型的小尺度结构归因于氮等离子体的限制和屏蔽效应。而在较高注量下烧蚀，则形成多层烧蚀坑。在乙醇中烧蚀的情况下，观察到显着不同的表面形貌的Si。结果表明，孔隙沿着分布，孔隙规模小，再沉积少。这些结果表明，辐照Si的表面生长和形态特征强烈依赖于激光能量密度以及环境条件。表面形态的差异可归因于冷却、约束和屏蔽效应以及等离子体温度、密度和环境介质压力的差异，其对应于靶表面的不同能量沉积。拉曼光谱表明，在所有三种环境中的烧蚀的情况下，没有新的频带被识别。然而，观察到一个显着的拉曼位移，这是由于激光诱导的应力。
Laser-induced surface and structural modification of silicon (Si) has been investigated under three different environments of vacuum, nitrogen (100 Torr) and ethanol. The interaction of 1000 pulses of KrF (λ≈ 248 nm,τ≈ 18 ns, repetition rate ≈ 30 Hz) Excimer laser at two different fluences of 2.8 J/cm2and 4 J/cm2resulted in formation of various kinds of features such as laser induced periodic surface structures (LIPSS), spikes, columns, cones and cracks. Surface morphology has been observed by Scanning Electron Microscope (SEM). Whereas, structural modification of irradiated targets is explored by Raman spectroscopy. SEM analysis exhibits a non-uniform distribution of micro-scale pillars and spikes at the central ablated regime of silicon irradiated at low laser fluence of 2.8 J/cm2under vacuum. Whereas cones, pits, cavities and ripples like features are seen at the boundaries. At higher fluence of 4 J/cm2, laser induced periodic structures as well as micro-columns are observed. In the case of ablation in nitrogen environment, melting, splashing, self-organized granular structures and cracks along with redeposition are observed at lower fluence. Such types of small scaled structures in nitrogen are attributed to confinement and shielding effects of nitrogen plasma. Whereas, a crater with multiple ablative layers is formed in the case of ablation at higher fluence. Significantly different surface morphology of Si is observed in the case of ablation in ethanol. It reveals the formation of cavities along with small scale pores and less redeposition. These results reveal that the growth of surface and morphological features of irradiated Si are strongly dependent upon the laser fluence as well as environmental conditions. The difference in surface morphology is attributable to cooling, confinement and shielding effects as well as difference in plasma temperature, density and pressure of environmental media that corresponds to different energy deposition to the target surface. Raman spectroscopy shows that no new bands are identified in case of ablation in all three environments. However, a significant Raman shift is observed which is attributed to laser-induced stresses.