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飞秒激光诱导微纳结构调控材料润湿性能
其他题名Manipulation of wettability of materials by femtosecond laser induced micro-/nanostructures
泮怀海
学位类型博士
导师赵全忠
2016
学位授予单位中国科学院上海光学精密机械研究所
关键词飞秒激光 超疏水 超亲水 润湿特性 聚二甲基硅氧烷 菲涅耳透镜 阿妙脉冲 衍射级
摘要由于锁模技术和啁啾脉冲放大技术的发展,使脉冲激光宽度从纳秒(10-9秒),皮秒(10-12秒)阶段发展到了飞秒(10-15秒)阶段,利用这种飞秒脉冲激光在材料表面诱导微纳结构,进而改变材料表面的形貌特征,成为近年来一个重要的研究领域。这种具有极高峰值功率的飞秒脉冲激光可以通过显微物镜聚焦成具有微米尺度的焦斑,从而极大的提高激光的能流密度,例如,利用数值孔径为0.15的显微物镜,可以使光束直径为5.4mm、中心波长为800nm的近红外脉冲激光光束聚焦到直径为6.5μm的焦斑,其能流密度进而提高到大约五个数量级。首先,经过显微物镜聚焦的具有极强能流密度的飞秒脉冲激光能够在微米尺度上与固体材料实现非线性光学相互作用,突破光学衍射极限,诱导出各式各样的表面微纳结构,达到改变了材料表面形貌的目的。其次,由于飞秒脉冲激光的单个脉冲的持续时间极短,短于原子晶格振动的弛豫时间,尤其当飞秒脉冲激光在低重复频率的情况下与物质相互作用时,无法形成有效的热积累和热传递效应,此时电声耦合效应可以忽略不计,从而导致激光与材料作用区域周围的烧蚀效应微乎其微。 因此,具有极高峰值功率和极短脉冲持续时间的超短脉冲激光,可以应用于突破光学衍射极限的精细加工领域,实现微米尺度上的加工的精确控制,并避免作用区域边缘烧蚀现象的出现。其中,通过利用脉冲激光诱导材料表面微纳结构而改变表面形貌结构进而控制其润湿特性,成为超短脉冲激光微加工领域一个重要的研究方向。这种对材料表面润湿特性的微纳调控可以广泛应用于化学,生物学,医药研究中,例如,在微流体通道、生物芯片、芯片实验室、医学植入材料等方面有巨大的应用价值。 本论文的研究重点主要集中于利用脉冲宽度为120fs,重复频率为1kHz,中心波长为800nm的飞秒脉冲激光,通过0.15、0.3等不同数值孔径的显微物镜聚焦,在高分子材料,半导体材料等表面进行扫描直写,在微米尺度上制备具有不同润湿特性的表面材料。其中,研究材料包括聚二甲基硅氧烷、单晶硅、纯钛等材料表面,在其表面上实现了超疏水特性。 论文的第一章主要论述了超短脉冲激光技术的原理、发展历史、超短脉冲激光与物质相互作用的机理以及超短脉冲激光在微加工领域中的应用,尤其在利用超短脉冲激光改变材料表面润湿特性的研究现状,以及取得的成果。 论文的第二章主要介绍制备所采用的各种实验仪器,以及对材料表面润湿性的表征方法,包括:飞秒脉冲激光器的特性,实验装置的搭建,光学聚焦系统的校准,接触角测量仪对接触角的测量。另外,还着重介绍了材料表面润湿特性的原理,包括:理论模型、机理解释等知识。 第三章主要研究了利用飞秒脉冲激光直写技术制备调控聚二甲基硅氧烷表面的润湿特性,特别是其经过飞秒脉冲激光处理之后的超疏水特性,聚二甲基硅氧烷在不同的实验参数,例如,在激光单脉冲的能流密度、扫描速度以及扫描间隔的变化下,其表面润湿特性的改变,最终得到了不同润湿特性的表面材料,尤其实现了材料表面的超疏水特性。同时,利用拉曼光谱仪分析了激光作用前后的表面化学键成分,利用合理的理论模型解释了聚二甲基硅氧烷表面润湿性改变的原因。另外还研究了经过脉冲激光作用后的聚二甲基硅氧烷表面润湿特性的在最初的几个小时由超亲水到超疏水的变化过程。 第四章主要研究了利用飞秒脉冲激光转写技术在玻璃表面上制备具有不同润湿性能的表面。在激光转写过程中,利用聚二甲基硅氧烷作为靶材料,经过激光扫描直写,可以把聚二甲基硅氧烷靶材料通过激光扫描光压溅射到上面的基底材料的下表面,其中通过控制激光扫描速度、扫描间隔、和激光单脉冲的能流密度,实现了不同润湿性的玻璃表面材料。 第五章主要介绍了超疏水多孔硅表面材料的制备。在实验中,利用飞秒脉冲激光扫描单晶硅表面,在其表面得到不同的微米沟槽结构以及沟槽之中诱导出的纳米突起结构,然后把这种具有特殊微纳结构的表面硅材料放到一定配比浓度的混合酸中浸泡,最终得到具有超疏水特性的多孔硅表面。经过扫描电子显微镜和能量色散X射线分析仪分别测定了制备前后的硅表面的形貌变化和表面元素的分布图,观察发现在其表面形成的微纳尺度的蜂窝状的多孔硅结构。并利用接触角测量仪测试其表面与水滴的静态接触角来定量表征其超疏水特性。另外,还提出了合理的化学反应机制来解释这种蜂窝状多孔硅的形成,同时利用测到的扫描电子显微图和元素成分分析多孔硅超疏水特性的形成。 第六章,我们主要利用飞秒脉冲激光制备了超疏水特性的金属钛表面。通过激光扫描之后,钛片放在溶解了双面胶材质的丙酮溶液进行超声处理,然后通过测量其表面与水滴的静态接触角,发现其表面实现了不同的疏水特性甚至超疏水特性。同时,利用扫描电子显微镜观测了制备表面的形貌结构,并利用能量色散X射线分析仪对比了钛片制备前后的元素含量图以分析表面化学成分对其超疏水特性形成的影响。 此外,我们还在第七章介绍了利用菲涅尔透镜调控极紫外光波段的阿秒脉冲光的聚焦特性,其研究内容主要为:设计不同的菲涅尔透镜,并且利用新设计的菲涅尔透镜对阿秒光束,频率分布为高斯分布的阿秒脉冲平面光进行衍射、聚焦,以提高其在第一衍射级上的空间和时间分辨率,并同时提高其第一级衍射效率。首先,设计并模拟了不规则的阶梯状的菲涅尔透镜,并且经过数值模拟得到,利用这种不规则的菲涅尔透镜衍射阿秒脉冲光,得到了阿秒脉冲光在第一级衍射级对应的焦平面上纳米尺度的空间分辨率,同时也最大限度的保持了阿秒脉冲光在第一衍射级对应焦点处的阿秒尺度的时间分辨率,以及通过采用不同啁啾特性的阿秒脉冲光来提高其在第一衍射级所对应的焦点处的时间分辨率。另外,还设计了低色散的菲涅尔透镜,利用色散与菲涅尔透镜相反的透镜来补偿菲涅尔透镜产生的负色散,来降低菲涅尔透镜对一定带宽的阿秒脉冲光的色散,进而提高聚焦光束在第一衍射级上时间和空间分辨率。利用所设计的菲涅尔波带片可以应用于时间分辨的显微技术中,在未来可以探测微观尺度的电子超快动力学过程。
其他摘要The technology of mode locking and Chirped-pulse Amplification (CPA) makes the availability of laser pulse duration developing from ns (10-9 s), to ps (10-12 s) and even to fs (10-15 s). Intrinsically, owing to the ultrashort duration, these laser pulses, especially for femtosecond laser pulse, could reach to very high peak intensity for a low average power compared to the continous lasers or long pulse laser of the same average power. Such ultrashort laser pulses can be focused to a small spot via microscopic objective to further improve their laser fluence, e.g. using the microscopic objective with numerical aperture (NA) of 0.15; one can focus the laser beam with diameter of ~ 5.4 mm, to a small spot with diameter of ~ 6.5 mm, improving the laser fluence by ~ 5 orders of magnitude. Therefore, these ultrashort laser pulses with extreme high peak intensity as well as high laser fluence focused by microscopic objective have a great of potentials in laser processing on a variety of materials, for example, fabricating microfluidic channels inside glasses or inducing refractive index changed inside transparent material via multiple photons absorption or tunneling ionization on micro/nanoscales. Besides, owing to the pulse duration (i.e. femtosecond laser pulse) is shorter than that of vibration of lattice, when femtosecond laser interacts with materials, the thermal diffusion within sub-electron system can be ignored, realizing the ablation precisely on micro/nanoscales and damage-free at the edge of laser-processed region. Therefore, the ultrasort laser pulses are widely utilized as a sharp sword in micro manufacturing technology due to their ignorable thermal diffusion and high etching capability in combination with microscopic objectives when processing materials even for hard material like sapphire. Among others, one important application of great interest is that using ultroshort laser pulses to induce micro/nanostructures on material surfaces and then vary their surface morphologies, by which one could modify and further control the wettability of material surfaces on micro/nanoscales. These material surfaces with all kinds of wettability have a great of potentials in chemistry, biology and medicine science, e.g. in microfluidic channels, biochip, as well as lab on a chip. In this thesis, a regenerative amplified Ti: Sapphire laser at a central wavelength of 800 nm that emits a train of 120 fs mode-locked pulses at 1 kHz was used for light source. The laser beam emitted by this laser system is polarized horizontally to the optical table. The microscopic objectives with different NAs (e.g. 0.15 and 0.3) were used for focusing the pulsed laser beam to a small spot. Different materials such as semiconductor, metal, as well as polymer are processed by these laser pulses via microscopic objectives to induce micro/nanostructures on surfaces. We investigate the wettability of these laser-processed surfaces versus different parameters, for example, laser fluence, morphologies of surfaces (i.e. pitch between two adjacent scanning line by laser beam), finally realizing the superhydrophobicity or superhydrophilicity of surfaces. In the chapter 1, we mainly discussed the generation and mechanism of ultrashort pulsed laser, the interaction mechanism between ultrashort pulsed laser and materials, and also the applications of ultrashort pulsed laser in micromachining, especially in the field of using ultrashort pulsed laser to fabricate material surfaces aiming for different wettability. We also discussed about different model to explain the principle of surface wettability, i.e. Wenzel model and Cassie model. In chapter 2, we mainly introduced the experimental setup (i.e. the regenerative amplified Ti: Sapphire laser system) we used to fabricate material surfaces of different wettability in our work, all kinds of instruments we employed are to characterize the material surfaces and observe the wettability of material surfaces of different morphologies and chemical composition induced by femtosecond laser-irradiation. For example, using the contact angle measurement system (SL200B) to measure the contact angle between distilled water droplet and the material surfaces, employing the scanning electron microscope (SEM) to measure the material morphologies, and utilizing micro-Raman spectrometer (Renishaw inVia) to measure the micro-Raman spectra of material surface etc. In chapter 3, the focus is on the fabrication of polydimethylsiloxane (PDMS) surfaces with different wettability by using the femtosecond laser direct writing, especially on the realization of superhydrophobicity of PDMS surfaces. The wettability of PDMS surfaces via femtosecond laser direct writing was investigated versus different laser parameters, such as laser fluence, laser scanning speed, and laser scanning intervals between two adjacent scanning lines, realizing the surface superhydrophobicity at optimized parameters. SEM images of PDMS surfaces were measured to observe the morphological changes before and after laser processing, and the micro-Raman spectra is also measured to compare the surface chemical composition before and after laser processing. Furthermore, the immediate temporal evolution of wettability from superhydrophilic to from superhydrophobic of PDMS surfaces after laser processing in its initial few hours was also investigated. In chapter 4, the material surfaces of different wettability via laser-induced transfer forward were fabricated. The slide glass and cover glass were selected as membranes, and PDMS was employed as target materials that can be deposited on the membranes through pulsed laser deposition. And, a series of surfaces of different wettability on membranes were fabricated through tuning the laser parameters, such as laser fluence, scanning speed, scanning intervals between two adjacent scanning lines. In chapter 5, we mainly introduced the fabrication of superhydrophobic porous silicon using femtosecond laser processing followed by additional chemical etching. The single crystal silicon slice was proceed though femtosecond laser direct writing under air condition, and was immersed in mixed acid for chemical etching. Finally, the micro-honeycomb-like structures formed on the silicon surface, which exhibits the hydrophobicity or superhydrophobicity. Through tuning the laser parameter (i.e. laser fluence) and chemical etching time, we get a series of porous silicon surfaces with different hydrophobicity. The morphologies and chemical elements of porous silicon surfaces were measured using SEM and energy dispersion X-ray (EDX), respectively. It is shown that the porous structures formed on silicon surfaces play crucial role in enhancing the hydrophobicity of silicon surfaces. In chapter 6, the superhydrophobic titanium surfaces were fabricated using femtosecond laser, combining with ultrosinic cleaning with acetone. The water contact angle of laser-processed titanium surface is able to reach as high as 150°. In order to investigate the lifetime of superhydrophobic titanium surfaces, we also have measured its water contact angle after putting laser-processed titanium surfacces in air for more than two months, and found that it preserved its superhydrophobicity induced by femtosecond laser and ultrasonic cleaning with acetone. Furthermore, the SEM images and chemical element of laser-processed titanium surface were also obtained to analyse the effect of the morphology and chemical compositon on the wettability of laser-processed titanium surfaces. In chapter 7, we mainly discussed the focused property of attosecond pulse light in extreme ultraviolet (XUV) range diffracted by Fresnel zone plate (FZP). A single attosecond XUV pulse can be obtained from high harmonic generation using few-cycle infrared laser pulse (i.e. cosine-waveform). Different types of FZP were designed and the focused property of XUV attosecond pulse light was numerically simulated. We have proposed two new types of FZP that can focus the XUV attosecond pulsed to a small spot on nanometer in first focal plane. One is the partial multilevel zone plate (PMZP) that only outermost ten one-wave zone are designed, with other inner one-wave zones are blocked. Using PMZP, the spatiotemporal focusing of XUV attosecond pulse light to a nanometer-scale spot on focal place, as well as preserving the temporal attosecond structure of XUV pulse light at focus was achieved. Owing to the utilization of multilevel structures to FZP, PMZP is capable of compensating the reduced first-order diffraction efficiency due to the blocking of inner one-wave zones. Another design is to use the conventional lens of positive dispersion to compensate the negative dispersion produced by conventional amplitude zone plate. Therefore, achromatic FZP is the combination of conventional lens and FZP designed for low chromatic dispersion. The simulation shows that using achromatic FZP, one can focus the XUV attosecond pulse light to a nanometer-scale spot with decreasing chromatic dispersion along the optical axis. The simulation results also exhibits that one can get high spatial resolution of sub-100 namometer as well as conserve the temporal attosecond structure of focused XUV pulse light. These new concept of PMZP and achromatic FZP will be aiming at XUV imaging system, e.g. combining scanning transmission XUV microscopy or coherent diffractive imaging, with time-resolved microscope, to observe ultrafast sub-fs scale dynamics of electron on micro/nanosystem.
语种中文
文献类型学位论文
条目标识符http://ir.siom.ac.cn/handle/181231/15950
专题学位论文
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泮怀海. 飞秒激光诱导微纳结构调控材料润湿性能[D]. 中国科学院上海光学精密机械研究所,2016.
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