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文中总结了目前一些代表性的激光辅助三维金属微打印技术的基本原理、技术优势和主要应用。需要指出的是,尽管利用这些激光辅助金属微打印技术已在复杂三维微纳金属结构的制备方面取得了很多富有成效的进展,但如表1所示,上述技术无一例外都存在特定的适用条件和有待于进一步改善的技术不足。到目前为止,还未有一种技术能够同时将高分辨率、高纯度、大尺寸、金属通用性等制备要求完全结合起来,因此在制造三维金属结构时,大多根据具体需求进行考虑。
表 1 代表性的激光辅助三维金属微打印技术
Table 1. Representative techniques for laser-assisted 3D metal microprinting
Processing technique Feature size Speed Applicable metals Characteristics Laser-induced forward transfer (LIFT)[29-40] Several μm several tens of
micrometers per secondAg, Au,Al, Cu,Cr,Ge,Ni,Pd,
Pt,Sn,Ti,V,W,Zn, etc.Rapid manufacture of microstructures
with a precision down to submicron scale;
High surface roughness.Laser decal transfer (LDT)[41-45] Depended on
the voxel sizeDepended on the
voxel sizeAg, Au,Al, Cu,Cr,Ge,Ni,Pd,Pt,
Sn, Ti,V,W,Zn, etc.Rapid manufacture of voxels
with specific shapes.Femtosecond laser-induced photoreduction (FLIP)[46-57] 100 nm-3 μm several tens of
micrometers per secondAg,Au,Cu,Ni Direct fabrication of sub-micron metal
structures; High surface roughness.Laser micro-sintering (LMS)[58-69] >10 μm several tens of
centimeters per secondAl,Ag,Cu,Ni,T,
W,Mo,CrHigh density of metal microstructures;
High surface roughness.3D metalization of two-photon polymerization[70-80] $\gg $120 nm several tens of
centimeters per secondAg, Au, Cu, etc. Surface metallization for 3D structures. Laser-assisted electrophoretic deposition (LAED)[81-85] 500 nm-several μm several hundreds of
nanometers per secondAu Direct fabrication of metal microstructures;
High surface roughness.Glass-channel molding assisted 3D printing[105] 10-200 μm − Ag,Cu,Au,
Ni,Pd, etc.Low surface roughness;
Widely tunable feature size.当前大尺寸、高精度、高机械强度的金属微打印技术在微纳金属制备和增材制造领域都具有很大的技术挑战。常规的三维金属增材打印虽然可以实现很大的制造尺寸和很高的机械强度,但是打印的金属结构的精度很难达到几十微米以下,并且其表面粗糙度通常受限于增材制备过程的本征局限,使得这些技术在微尺度金属打印领域的应用受到限制。毫无疑问,研发具通用性的3D金属微打印技术还有很长的道路要走。令人欣慰的是,当前的各种金属微纳结构制造技术已经在无数的尝试中逐渐成熟。最令人兴奋的是,飞秒激光技术在金属微纳结构的制备和应用中存在巨大的潜力,随着工艺的优化和发展,实现对任意形状、粗糙度和分辨率可控的微纳米金属结构的三维打印技术指日可待。就微通道模具法而言,如果大尺寸、高精度微通道结构制造技术取得突破,由此延伸到大尺寸三维金属结构的高精度制备,从而可以降低三维复杂金属微结构的大尺寸制造难度。初步的研究进展已表明,通过在通道内部进行金属沉积的方法实现在微通道结构内的金属结构可控填充,进而可实现具有较高机械强度、高精度、低表面粗糙度的三维金属微打印。相信未来的3D金属微打印技术应该和传统微纳米金属制造业会相互结合、相互补偿,开创更加广阔的应用前景。
Laser assisted 3D metal microprinting (Invited)
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摘要: 当前微纳尺度的三维金属结构,由于其独特的物化性能和空间构型优势,在科学与工程领域的应用需求日益增多。由此应运而生的各种三维金属微尺度打印技术近年来相继被开发,并引起了广泛关注。在众多技术中,基于激光的三维微打印技术有着非接触加工、制造灵活性好等优势。文中综述了当前一些代表性的激光辅助三维金属微打印技术,总结了各种三维金属微打印的基本原理、技术优势及典型应用。针对高表面光滑度、高熔点、高电导率的三维金属微打印存在的挑战,介绍了超快激光制备玻璃微通道模具法辅助实现三维金属微制造的新技术。最后就三维金属微打印的未来方向和应用前景进行了探讨。Abstract: In recent years, the demand for fabrication of 3D metal micro/nanostructures has been rapidly increased in the fields of science and engineering due to their unique physical/chemical properties and flexible configurations. Therefore, various innovative techniques for 3D metal printing at the microscale have been developed, which have attracted intensive attentions. Among those techniques, laser-based assisted 3D metal microprinting exhibits superior performance in terms of its advantages of non-contact processing, flexible patterning capability, and so on. Some of current representative techniques for laser assisted 3D metal microprinting were firstly reviewed from basic principles, technical characteristics, to typical applications. To meet the challenges on fabrication of 3D metal microstructures with high smooth surfaces, high melting points and high conductivities, a glass-microchannel molding technique for assisting 3D metal microprinting was demonstrated. Finally, possible directions and potential applications of laser-assisted 3D metal printing were discussed.
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图 1 激光诱导前向转移。(a) LIFT原理示意图[30];(b) 铜金属液滴在低喷射速度(上)和高喷射速度(下)的情况下的沉积效果不同[31];(c) 热诱导喷嘴的示意图和SEM图[33];(d) 通过LIFT制造的金字母结构的SEM图,高度约32 μm[30];(e) 内层为金螺旋、外层为铜金属牺牲性支撑材料的结构,高度约48 μm[30];(f) 通过化学刻蚀去除支撑性材料后剩下的完整Au螺旋线的SEM图[30];(g) 铜金属沉积物横截面上的缝隙[33];(h) LDT原理示意图,通过光阑对激光束进行整形[41];(i) 使用方形截面激光束辐照银纳米颗粒溶剂制备出方形单体,同时移动基底实现方形单体的堆积[42];(j) 在不同温度下退火,单体的表面形态[43-45]
Figure 1. Laser-Induced Forward Transfer (LIFT). (a)Schematic of LIFT setup[30]; (b) Solidified copper droplets for low (top) and high (bottom) ejection speeds, showing a different impact and solidification behavior[31]; (c) Schematic and SEM image of the donor film after the formation of a thermally induced nozzle[33]; (d) SEM image of a Au structure fabricated via LIFT- the logo of the authors’ institution (UT)[30]; (e) Schematic and process of LIFT-printing a complex structure[30]; (f) SEM image of structures deposited via LIFT showing a Au helix[30]; (g) FIB cross-section of a copper structure fabricated with LIFT[33]; (h) Schematic of laser decal transfer (LDT) setup; the shape of the laser beam determines the shape of the transferred voxels[41]; (i) A stack of square voxels of silver paste fabricated by LDT[42]; (j) Surface structure of the transferred silver paste after various annealing steps[43-45]
图 2 飞秒激光诱导光还原。(a) FLIP原理示意图[46];(b) 沉积物的尺寸和激光功率、曝光时间的关系[49];(c) AgNO3溶液中添加香豆素440后,银沉积物的直径由3 μm减小到500 nm[48];(d) 未添加表面活性剂的AgNO3溶液中制备的三维银结构的SEM图[52];(e) 添加了表面活性剂的AgNO3溶液中制备的3D金属结构阵列[52];(f) 通过双光子还原制备的十四面体金属镍结构[56];(g) 一个典型支撑结构的SEM图,用于在热解过程中使零件与基体分离[56]
Figure 2. Femtosecond Laser-Induced Photoreduction (FLIP). (a) Principle of the FLIP[46]; (b) The dimension of silver-deposits is a function of the laser-power and the exposure time[49]; (c) SEM images of silver dots reduced from a AgNO3 solution without (top) and with (bottom) a photosensitizing dye[48]; (d) SEM image of 3D silver structures on glass substrates synthesized from a pure AgNO3 solution (without photosensitizing dye)[52]; (e) Surfactants were adopted as growth inhibitors of the metal particles to fabrication of 3D freestanding nanostructures[52]; (f) SEM image of supported 20 μm tetrakaidekahedron unit cell on a Si chip after pyrolysis[56]; (g) SEM image of a representative supporting structure used to decouple the part from the substrate during pyrolysis[56]
图 4 双光子聚合结构的3D金属化。(a) 实验装置图[75];(b) 磁性螺旋机械的制造过程[77- 78];(c) 磁性螺旋机械结构[77, 78];(d) 在聚合物SU-8表面涂覆镍金属层制成的多孔微龛[79- 80]
Figure 4. 3D metallization of two-photon polymerized (TPP) microstructures. (a) Schematic of the TPP fabrication system[75]; (b) Schematic for the fabrication of helical swimming micromachines[77-78]; (c) Photo of the helical swimming micromachines[77-78]; (d) A porous microniches as a transporter in 3D cell culture and targeted transportation[79-80]
图 5 激光辅助电泳沉积[83]。(a) 原理示意图;(b) 金纳米颗粒沉积的螺旋线圈的SEM图像;(c) 沉积物尺寸与激光强度的关系;(d) 宽度为500 nm的金线;(e) 沉积物的局部SEM图像
Figure 5. Laser-Assisted Electrophoretic Deposition (LAED)[83]. (a) Schematic of LAED principle: A nanoparticle solution is confined between a conductive substrate and a trans- parent flat cover electrode. Optical trapping of particles in the focal spot of a laser beam accumulates particles locally. The additional application of an electric potential across the solution results in electrophoretic deposition of the trapped nanoparticles; (b) SEM image of a gold coil fabricated by laser-assisted electrophoretic deposition; (c) The obtained feature size is a function of the laser intensity; (d) The focal spot is positioned on the of nanowires 500 nm in diameter; (e) FIB cross-section showing a porous microstructure
图 6 飞秒激光制备微通道模具辅助3D金属微打印[105]。 (a) 实验流程图;(b) 连续流化学镀示意图;(c) 通过连续流化学镀实现三维螺旋微通道结构的金属化
Figure 6. Glass-channel molding assisted 3D metal microprinting with femtosecond laser microfabrication[105]. (a) Schematic of the fabrication procedure for 3D metallic microstructures embedded in fused silica; (b) Schematic of the microfluidic electroless plating of a microchannel using a peristaltic pump; (c) Optical images of metallized 3D helical microchannels inside glass
图 7 飞秒激光制备微通道模具法制造的5 mm × 5 mm × 2 mm 3D金属支架结构[105]。(a) 制备流程示意图;(b) 数码照片图;(c)、(d) SEM图像
Figure 7. Fabrication of a 3D freestanding metal scaffold microstructure, which size is ~5 mm × 5 mm × 2 mm[105]. (a) Schematic of the fabrication procedure; (b) Photos of the metal scaffold microstructure self-supported in air; (c), (d) SEM images of the partial regions of the metallic microstructure
表 1 代表性的激光辅助三维金属微打印技术
Table 1. Representative techniques for laser-assisted 3D metal microprinting
Processing technique Feature size Speed Applicable metals Characteristics Laser-induced forward transfer (LIFT)[29-40] Several μm several tens of
micrometers per secondAg, Au,Al, Cu,Cr,Ge,Ni,Pd,
Pt,Sn,Ti,V,W,Zn, etc.Rapid manufacture of microstructures
with a precision down to submicron scale;
High surface roughness.Laser decal transfer (LDT)[41-45] Depended on
the voxel sizeDepended on the
voxel sizeAg, Au,Al, Cu,Cr,Ge,Ni,Pd,Pt,
Sn, Ti,V,W,Zn, etc.Rapid manufacture of voxels
with specific shapes.Femtosecond laser-induced photoreduction (FLIP)[46-57] 100 nm-3 μm several tens of
micrometers per secondAg,Au,Cu,Ni Direct fabrication of sub-micron metal
structures; High surface roughness.Laser micro-sintering (LMS)[58-69] >10 μm several tens of
centimeters per secondAl,Ag,Cu,Ni,T,
W,Mo,CrHigh density of metal microstructures;
High surface roughness.3D metalization of two-photon polymerization[70-80] $\gg $ 120 nmseveral tens of
centimeters per secondAg, Au, Cu, etc. Surface metallization for 3D structures. Laser-assisted electrophoretic deposition (LAED)[81-85] 500 nm-several μm several hundreds of
nanometers per secondAu Direct fabrication of metal microstructures;
High surface roughness.Glass-channel molding assisted 3D printing[105] 10-200 μm − Ag,Cu,Au,
Ni,Pd, etc.Low surface roughness;
Widely tunable feature size. -
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