Identification of non-thermal and thermal processes in femtosecond laser-ablated aluminum
Identification of non-thermal and thermal processes in femtosecond laser-ablated aluminum
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DOI：
10.1080/10420150.2013.784911
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发表时间：
2013-12-01
影响因子：
1
通讯作者：
Husinsky, Wolfgang
中科院分区：
文献类型：
--
作者：
Bashir, Shazia;Rafique, M. Shahid;Husinsky, Wolfgang
利用原子力显微镜（AFM）研究了飞秒激光在低、中和高能量密度下烧蚀铝（Al）的非热和热过程。为了这个目的，采用25 fs的钛：蓝宝石激光脉冲在800 nm的中心波长的Al的表面改性已被执行，以探索不同的纳米和微米尺度的功能，如小丘，凸起，孔隙，和火山口。这些不同种类的结构的形成机制进行了讨论的情况下，三个烧蚀制度。超快的电子和非热过程在较低的注量区占主导地位，而缓慢的热过程在较高的注量区占主导地位。因此，从消融阈值开始，选择了三种不同的注量方案：较低的注量制度（0.06-0.5Jcm ~（-2）真空条件下的单次辐照和0.25-2.5Jcm ~（-2）环境条件下的单次辐照），中等注量区（0.25-1.5Jcm（-2）多次照射）和高通量区2.5-3.5Jcm（-2）多次照射。对于较低的能量密度（温和消融）制度，在消融阈值附近，识别出典型地高度为几纳米且直径小于100 nm的单个局部纳米小丘的独特外观。这些纳米小丘状的功能可以被看作是一个非热的，电子诱导相变过程，由于局部能量沉积作为结果的库仑爆炸或场离子发射的表面光学整流。在一个中等的注量制度，略高于烧蚀阈值多脉冲照射产生凸块的形成，并归因于超快熔化（等离子体形成）。高能量密度制度的结果在更大的材料去除率与高度扰动和混乱的Al表面的外观较大的突起在激光能量密度远高于烧蚀阈值。这些不对称的形状，由于不均匀的成核，集群的形成，并在熔化后的金属表面的再固化是由于缓慢的热过程（ps时间尺度）。
Non-thermal and thermal processes due to femtosecond laser ablation of aluminum (Al) at low, moderate, and high-fluence regimes are identified by Atomic Force Microscope (AFM) surface topography investigations. For this purpose, surface modifications of Al by employing 25fs Ti: sapphire laser pulses at the central wavelength of 800nm have been performed to explore different nano- and microscale features such as hillocks, bumps, pores, and craters. The mechanism for the formation of these diverse kinds of structures is discussed in the scenario of three ablation regimes. Ultrafast electronic and non-thermal processes are dominant in the lower fluence regime, whereas slow thermal processes are dominant at the higher fluence regime. Therefore, by starting from the ablation threshold three different fluence regimes have been chosen: a lower fluence regime (0.06-0.5Jcm(-2) single-shot irradiation under ultrahigh vacuum condition and 0.25-2.5Jcm(-2) single-shot irradiation in ambient condition), a moderate-fluence regime (0.25-1.5Jcm(-2) multiple-shot irradiation), and a high-fluence regime 2.5-3.5Jcm(-2) multiple-shot irradiation. For the lower fluence (gentle ablation) regime, around the ablation threshold, the unique appearance of individual, localized Nano hillocks typically a few nanometers in height and less than 100nm in diameter are identified. These Nano hillock-like features can be regarded as a nonthermal, electronically induced phase transition process due to localized energy deposition as a result of Coulomb explosion or field ion emission by surface optical rectification. At a moderate-fluence regime, slightly higher than ablation threshold multiple-pulse irradiation produces bump-formation and is attributed to ultrafast melting (plasma formation). The high-fluence regime results in greater rates of material removal with highly disturbed and chaotic surface of Al with an appearance of larger protrusions at laser fluence well above the ablation threshold. These nonsymmetrical shapes due to inhomogeneous nucleation, cluster formation, and resolidification of a metallic surface after melting are attributable to slow thermal processes (ps time scale).