激光纹理化调控材料表面疏水性能研究进展

超疏水表面由于具有减阻、抗污、防水等独特性能,广泛应用于日常生活、军事、工业等场景,材料表面的微纳结构及化学成分对其超疏水性能有着重要影响。激光纹理化技术由于具有加工分辨率高、加工方式灵活、可加工材料多等优势,可用于制备疏水性能精确可控的表面微纳结构,在制造超疏水表面方面有着广阔的应用前景。首先,介绍了激光纹理化的作用机理,综述了常用的激光纹理化方式,如激光直接写入法、激光干涉图案化法及激光诱导周期性结构法等,并介绍了激光参数对微纳结构的影响。根据表面微纳结构的形貌、周期及尺寸特点对激光纹理化制备的表面分层微纳结构进行了总结归纳,包括覆盖随机纳米结构或激光诱导周期性结构的微沟槽、微网格、微柱及微峰,重点介绍了分层微纳结构的制备方式及微纳结构对疏水性的影响。总结了提高分层微纳结构表面疏水性的后处理方式,包括环境老化、表面化学改性及热处理等,并介绍了后处理方式调控疏水性的作用机理。最后,对采用激光纹理化技术制备超疏水表面的应用前景进行了展望。     

Advanced Design of Hierarchical Topographies in Metallic Surfaces by Combining Micro‐Coining and Laser Interference Patterning

A new process idea to create hierarchical surface structures is based on the combination of micro‐coining and laser interference patterning. Micro‐coining already proved to be a high precision cold bulk metal forging process which allows for the production of small surface structures in the range of 20–200 µm while fulfilling high requirements related to the geometrical accuracy of those structures. In addition to that, laser interference patterning utilizes interfering laser beams from a pulsed solid state Nd: YAG laser to generate precisely defined surface topographies with a long‐range order on the micron‐scale. For the first time, initial results of a process combination consisting of micro‐coining and laser interference metallurgy to induce hierarchical surface structures will be presented. The results highlight the advantages of the sequence micro‐coining prior to laser interference patterning due to smaller defects in contrast to the inverted process cycle. Additionally, process limitations such as shadowing which may result from steep flank angles of the coined structures and surface roughness effects are discussed by the use of finite element simulations within this research work.     

激光构筑槽棱与网格状结构超疏水耐腐蚀表面研究

采用激光加工方法在铝合金表面构筑了一种展现超疏水耐腐蚀特性的槽棱和网格状结构。采用扫描电子显微镜(SEM)、激光共聚焦显微镜(LSCM)、X射线衍射仪(XRD)、X射线能谱仪(EDS)、接触角测量仪和电化学工作站表征材料表面的特征和特性。结果表明:由激光烧蚀形成的槽棱和网格状结构均展现出槽、坑、鳞片和颗粒等复杂形貌和复合结构特征;线间距为200μm的网格状结构的疏水性最好,静态接触角达到154.9°,滚动角接近7°。通过Tafel曲线及其拟合结果分析表明,激光加工处理使两种结构表面均展现出更好的耐腐蚀性能,其中线间距为100μm的网格状结构的耐腐蚀性最好。     

基于准分子激光微加工的光热微驱动器(英文)

提出了基于光热(PT)微膨胀原理的新型光热微驱动技术.设计了一种能将纵向光热膨胀转化成横向偏转的微驱动器.以AutoCAD设计图为基础,采用KrF准分子激光微加工系统,在单层高密度聚乙烯(HDPE)上加工出长1 500μm、宽250μm、厚40μm的开关式光热微驱动器.从微驱动器的扫描电子显微镜(SEM)图可以看出,微驱动器形状与AutoCAD设计值符合良好.光热微驱动实验采用脉冲频率可调的半导体激光器(4 mW,650 nm)作为驱动源.实验结果表明,在一定的脉冲频率范围(如0～17 Hz)内,光热微驱动器具有良好的静态和动态特性,其横向偏转量最大可达11μm,足以实现微开关功能.这种光热微驱动器可由激光束直接控制,具有原理新颖、结构简洁、体积小、易于加工制作等特点,在微纳米技术领域和微光机电系统(MOEMS)中具有广阔的应用前景.     

Effects of Multi‐Scale Patterning on the Run‐In Behavior of Steel–Alumina Pairings under Lubricated Conditions

In nature, many examples of multi‐scale surfaces with outstanding tribological properties such as reduced friction and wear under dry friction and lubricated conditions can be found. To determine whether multi‐scale surfaces positively affect the frictional and wear performance, tests are performed on a ball‐on‐disk tribometer under lubricated conditions using an additive‐free poly‐alpha‐olefine oil under a contact pressure of around 1.29 GPa. For this purpose, stainless steel specimens (AISI 304) are modified by micro‐coining (hemispherical structures with a structural depth of either 50 or 95 μm) and subsequently by direct laser interference patterning (cross‐like pattern with 9 μm periodicity) to create a multi‐scale pattern. The comparison of different sample states (polished reference, laser‐patterned, micro‐coined, and multi‐scale) shows a clear influence of the fabrication technique. In terms of the multi‐scale structures, the structural depth of the coarser micro‐coining plays an important role. In case of lower coining depths (50 μm), the multi‐scale specimens show an increased coefficient of friction compared to the purely micro‐coined surfaces, whereas larger coining depths (95 μm) result in stable and lower friction values for the multi‐scale patterns.     

分级微纳结构氧化锌的制备及其光致发光

采用低温热蒸发法研制出新型的ZnO分级微纳结构,利用场发射扫描电子显微镜和X射线衍射仪对其形貌与结构进行了表征,结果表明,所制备的分级结构为纯六方纤锌矿结构,由主干直径为1-3μm的ZnO微米线和表面的宽度为1μm、厚度约为100nm的晶片组成。用气-固（VS）机制阐明了ZnO分级结构的生长机理。在室温下,用近场光学显微镜测量了ZnO分级结构的光致发光谱,结果显示,在380nm处存在很强的近带隙发光峰,而508nm左右的缺陷发光很弱。     

Toward Scalable Fabrication of Hierarchical Silica Capsules with Integrated Micro‐, Meso‐, and Macropores

Hierarchical porous structures are ubiquitous in biological organisms and inorganic systems. Although such structures have been replicated, designed, and fabricated, they are often inferior to naturally occurring analogues. Apart from the complexity and multiple functionalities developed by the biological systems, the controllable and scalable production of hierarchically porous structures and building blocks remains a technological challenge. Herein, a facile and scalable approach is developed to fabricate hierarchical hollow spheres with integrated micro‐, meso‐, and macropores ranging from 1 nm to 100 μm (spanning five orders of magnitude). (Macro)molecules, micro‐rods (which play a key role for the creation of robust capsules), and emulsion droplets have been successfully employed as multiple length scale templates, allowing the creation of hierarchical porous macrospheres. Thanks to their specific mechanical strength, these hierarchical porous spheres could be incorporated and assembled as higher level building blocks in various novel materials.     

Inelastic behavior of ceramics with hierarchical pore structure under compression

The compaction behavior is studied in Al₂O₃ ceramics with a pore space volume in the range from 35 to 60% and with the following three types of hierarchical pore structure: coarse porosity with a size of 80 to 100 μm, fine porosity with a size of 14 to 15 μm, and intermediate interblock porosity comprised of elongated (110–120 μm) porous microchannels formed as a result of zonal isolation during sintering. It is shown that the obtained hierarchical porous structure causes the formation of a hierarchical deformation structure in the volume of ceramics and leads to a decrease in the extent of destruction processes from the macroscopic scale in the case of unimodal ceramics to the microscale destruction comparable with the sizes of the blocks formed during sintering.     

Effect of selective laser melting on microstructure and properties of AZ91D alloy

Selective laser melting technology is used to manufacture porous and solid AZ91D alloys. The effects of laser power and hatch spacing on the density, blowholes, microstructure and mechanical properties of AZ91D alloy are studied. The laser power and hatch spacing play a significant role in the density and blowholes of AZ91D specimens. The grains size of specimens increases from 1 μm–2 μm to 8 μm–10 μm from the bottom to the top in single molten pool. Compared with grain size of die‐casting alloy (30 μm), that of selective laser melted gets refinement. There is no significant change in microstructure in the bottom, middle and top of specimens. The micro‐hardness of AZ91D alloy, reaching up to 115.3 HV 0.1, is superior to that of die‐casting alloy (56 HV 0.1). The compression properties of porous and solid specimens reach the degree of die‐casting solid magnesium alloy. AZ91D alloy shows the potential in the application of medical biodegradable materials.     

Efficient fabrication of carbon nanotube micro tip arrays by tailoring cross-stacked carbon nanotube sheets

Carbon nanotube (CNT) micro tip arrays with hairpin structures on patterned silicon wafers were efficiently fabricated by tailoring the cross-stacked CNT sheet with laser. A blade-like structure was formed at the laser-cut edges of the CNT sheet. CNT field emitters, pulled out from the end of the hairpin by an adhesive tape, can provide 150 μA intrinsic emission currents with low beam noise. The nice field emission is ascribed to the Joule-heating-induced desorption of the emitter surface by the hairpin structure, the high temperature annealing effect, and the surface morphology. The CNT emitters with hairpin structures will greatly promote the applications of CNTs in vacuum electronic devices and hold the promises to be used as the hot tips for thermochemical nanolithography. More CNT-based structures and devices can be fabricated on a large scale by this versatile method.     

Fabrication of micro pin fins on inclined V-shaped microchannel walls via laser micromilling

A laser-micromilling process was developed for fabricating micro pin fins on inclined V-shaped microchannel walls for enhanced microchannel heat sinks. A pulsed nanosecond fiber laser was utilized. The feasibility and mechanism of the formation of micro pin fins on inclined microchannel walls were investigated for a wide range of processing parameters. The effects of the laser output power, scanning speed, and line spacing on the surface morphologies and geometric sizes of the micro-pin fins were comprehensively examined, together with the material removal mechanisms. Micro pin fins with acute cone tips were readily formed on the V-shaped microchannel walls via the piling of recast layers and the downflow of re-solidified materials in the laser-ablation process. The pin-fin height exhibited an increasing trend when the scanning speed increased from 100 mm/s to 300 mm/s, and it decreased continuously when the line spacing increased from 5 μm to 20 μm. The optimal processing parameters for preparing micro pin fins on V-shaped microchannels were found to be a laser output power of 21 W, scanning speed of 100–300 mm/s, and line spacing of 2–5 μm. Moreover, the V-shaped microchannels with micro pin fins induced a 7%–538% boiling heat-transfer enhancement over their counterpart without micro pin fins.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-021-00382-x     

Hierarchical 3D SERS Substrates Fabricated by Integrating Photolithographic Microstructures and Self‐Assembly of Silver Nanoparticles

Most of the surface‐enhanced Raman scattering (SERS) substrates are 2D planar systems, which limits the SERS active area to a single Cartesian plane. Here, we fabricate 3D SERS substrates with the aim to break the traditional 2D SERS active area limitation, and to extend the SERS hotspots into the third dimension along the z‐axis. Our 3D SERS substrates are tailored with increased SERS hotspots in the z‐direction from tens of nanometers to tens of micrometers, increasing the hotspots in the z‐direction by at least an order of magnitude larger than the confocal volume (～1 μm) of most Raman spectrometers. Various hierarchical 3D SERS‐active microstructures are fabricated by combining 3D laser photolithography with Langmuir‐Blodgett nanoparticle assembly. 3D laser photolithography creates microstructured platforms required to extend the SERS‐active area into 3D, and the self‐assembly of Ag nanoparticles ensures homogeneous coating of SERS‐active Ag nanoparticles over the entire microstructured platforms. Large‐area 3D Raman imaging demonstrates that homogeneous signals can be collected throughout the entire 3D SERS substrates. We vary the morphology, height, and inclination angles of the 3D microstructures, where the inclination angle is found to exhibit strong influence on the SERS signals. We also demonstrate a potential application of this hierarchical 3D SERS substrate in information tagging, storage and encryption as SERS micro‐barcodes, where multiple micro‐barcodes can be created within a single set of microstructures.     

Formation of a system of microcraters on a titanium surface by femtosecond laser radiation under rapid cooling conditions

Results of structuring a titanium surface with femtosecond laser radiation are reported. Formation of an ordered system of microcraters with a diameter of about 2 μm and a step of about 3 μm is observed. The character of this process is determined by the laser-beam transverse structure. The possibility of fixing the structures formed is provided by rapid cooling (using liquid nitrogen) of the laser-irradiated region. The potential of this treatment mode for nanostructuring surfaces of materials is considered.     

微小孔尺寸形状的脱模与图像测量

将脱模方法与显微图像处理结合,实现了微小孔内部轮廓的尺寸形状测量.首先采用具有超弹性的乙烯基聚硅氧烷作为制模材料,通过脱模方法将微小孔内部轮廓复制为模型的外部轮廓.然后在显微镜上采集模型的放大图像,利用图像分割、边缘提取、直线检测等图像处理手段,测量出微小孔内部直径随深度的变化曲线.开发出用于测量微小孔尺寸形状的应用软件,利用该软件对脱模法的复制精度进行校验.对于孔口直径在145～155μm的微孔,所制模型在孔口处直径与原始孔口直径的平均绝对值误差为0.9μm.通过脱模方法制作三维型腔模型,得到脱模模型形貌与原始形貌的平均绝对值误差为0.37μm,均方根误差为0.51μm.所提方法融合微米量级的脱模精度和像素级的图像测量精度,可用于微小孔孔径、内部轮廓形状等的测量.     

电火花加工制备铜基微纳层次结构及其疏水性能

利用电火花成型加工技术制备铜基微纳层次结构疏水表面,该微纳层次结构主要由微纳孔洞、熔珠、重熔区和热应力裂纹等微观结构组成,考察了不同脉宽参数对微纳层次结构疏水性的影响。结果表明:随着脉宽的增大,微纳层次结构中微纳孔洞数量增加,各种微观结构的层次分布程度增强,增大“气垫”效应区域,可存储更多的空气在其表面,提高了微纳层次结构的疏水性。固-液界面所占面积分数(f sl)减小,水滴和表面孔洞中的“气垫”接触面积增大,使得微纳层次结构对水滴的物理吸附作用减弱。微纳层次结构接触角可增至(144.7±2.1)°,接触角滞后性范围为(8.46±3.3)°^14.10±1.2°。     

真空热压原位Al3Ti增强MgAl基复合材料合成机制

采用真空热压原位合成法制备Al₃Ti增强Mg-Al基复合材料。研究了烧结工艺对复合材料显微结构的影响。探讨了Al₃Ti的原位合成机制, 提出了Ti和Al的微观反应模型。采用XRD、 SEM等方法分析了复合材料的相组成及微观结构。结果表明, Mg-Al基复合材料组织致密, 原位合成增强相Al₃Ti颗粒在基体中均匀分布, 尺寸为0.5~2.0 μm, 与基体界面紧密结合, 同时存在少量残余的Ti和中间相Al-Ti。     

不同粒径微米/亚微米颗粒布朗运动的实验研究

利用显微粒子追踪测速系统(Micro-PTV)对四种不同粒径(2μm、1μm、0.71μm、0.52μm)的颗粒在纯水中的布朗运动进行了实验研究.使用波长为532nm的连续激光器、电子倍增CCD(EMCCD)相机以及放大倍率为63倍的显微物镜得到颗粒图像.对原始图像进行处理,借助于Video Spot Tracker软件获得相邻两帧图像中示踪颗粒的单步位移,在此基础上计算颗粒在纯水中的实验扩散系数,分别为0.191μm2/s,0.391μm2/s,0.579μm2/s及0.746μm2/s.将计算结果与采用Stokes-Einstein公式计算的无限大空间单个颗粒理论扩散系数进行了比对,偏差在10%以内,实验值略小.实验结果能够正确反映微米(μm)/亚微米颗粒布朗运动的特征.     

Random lasing in a dye-doped polymer thin film waveguide deposited on a Si surface microstructured by femtosecond laser ablation

Random laser action with ~8 nm of bandwidth from a special waveguide structure is reported. The waveguide structure is composed of a layer of rhodamine 6G-doped PMMA film and a silicon substrate with a microstructured surface induced by a femtosecond laser. The silicon substrate featured two-dimensional island-like microstructures with average sizes ranging from 0.8 μm to 3 μm and average heights at about 0.7 μm. A red-shift of laser peak positions and decrease of threshold were observed with decreasing size of silicon surface microstructures. The spectra at different probe directions were also measured, and the results reveal that the waveguide laser action is strongly confined within ±10° from the direction of the edge. The lasing modes emitted from the edge of the waveguide are found to be mainly transverse electric-polarized. Our experiments demonstrate a promising method to achieve waveguide random lasers.     

具有“荷叶效应”的硅基仿生表面的制备及其微摩擦性能

用扫描电子显微镜(scanning electron microscope,SEM)观测了荷叶表面的双微观结构,即特征尺度在10μm左右的微米乳突和直径为50～100 nm的纳米蜡质晶体.提出了制备具有"荷叶效应"的硅基仿生表面的两种方法,一是将表面制有特征尺度为100 nm左右纳米结构的硅片进行硅烷化疏水处理,仅制作了纳米结构,部分模拟了"荷叶效应;"另一种方法是将表面制有特征尺度为10μm左右微米结构的硅片进行烷基烯酮二聚体(AKD)化处理,该方法获得了具有双微观结构的仿生表面,比较完整地模拟了"荷叶效应."微摩擦性能测试结果表明光滑硅片微观摩擦系数为0.08～0.10,而具有120 nm～25μm微结构的硅片微观摩擦系数为0.04～0.07;具有特征尺度为200 nm线条阵列的粗糙区平均黏附力与光滑区平均黏附力之比为0.59.硅基仿生表面有利于降低摩擦系数和减小黏附,"荷叶效应"对于微机电系统(micro electro mechanical system,MEMS)防黏减摩具有一定的潜在应用价值.     

Sequential shrink photolithography for plastic microlens arrays

Endeavoring to push the boundaries of microfabrication with shrinkable polymers, we have developed a sequential shrink photolithography process. We demonstrate the utility of this approach by rapidly fabricating plastic microlens arrays. First, we create a mask out of the children's toy Shrinky Dinks by simply printing dots using a standard desktop printer. Upon retraction of this pre-stressed thermoplastic sheet, the dots shrink to a fraction of their original size, which we then lithographically transfer onto photoresist-coated commodity shrink wrap film. This shrink film reduces in area by 95% when briefly heated, creating smooth convex photoresist bumps down to 30 μm. Taken together, this sequential shrink process provides a complete process to create microlenses, with an almost 99% reduction in area from the original pattern size. Finally, with a lithography molding step, we emboss these bumps into optical grade plastics such as cyclic olefin copolymer for functional microlens arrays.