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2022 Vol. 4, No. 1

Fundamentals of atomic and close-to-atomic scale manufacturing: a review
Jian Gao, Xichun Luo, Fengzhou Fang, Jining Sun
2022, 4(1) doi: 10.1088/2631-7990/ac3bb2

Atomic and close-to-atomic scale manufacturing (ACSM) represents techniques for manufacturing high-end products in various fields, including future-generation computing, communication, energy, and medical devices and materials. In this paper, the theoretical boundary between ACSM and classical manufacturing is identified after a thorough discussion of quantum mechanics and their effects on manufacturing. The physical origins of atomic interactions and energy beams-matter interactions are revealed from the point view of quantum mechanics. The mechanisms that dominate several key ACSM processes are introduced, and a current numerical study on these processes is reviewed. A comparison of current ACSM processes is performed in terms of dominant interactions, representative processes, resolution and modelling methods. Future fundamental research is proposed for establishing new approaches for modelling ACSM, material selection or preparation and control of manufacturing tools and environments. This paper is by no means comprehensive but provides a starting point for further systematic investigation of ACSM fundamentals to support and accelerate its industrial scale implementation in the near future.

Modulation of the thermal transport of micro-structured materials from 3D printing
Qiangsheng Sun, Zhixiang Xue, Yang Chen, Ruding Xia, Jianmei Wang, Shen Xu, Jun Zhang, Yanan Yue
2022, 4(1) doi: 10.1088/2631-7990/ac38b9

It is desirable to fabricate materials with adjustable physical properties that can be used in different industrial applications. Since the property of a material is highly dependent on its inner structure, the understanding of structure-property correlation is critical to the design of engineering materials. 3D printing appears as a mature method to effectively produce micro-structured materials. In this work, we created different stainless-steel microstructures by adjusting the speed of 3D printing and studied the relationship between thermal property and printing speed. Our microstructure study demonstrates that highly porous structures appear at higher speeds, and there is a nearly linear relationship between porosity and printing speed. The thermal conductivity of samples fabricated by different printing speeds is characterized. Then, the correlation between porosity, thermal conductivity, and scanning speed is established. Based on this correlation, the thermal conductivity of a sample can be predicted from its printing speed. We fabricated a new sample at a different speed, and the thermal conductivity measurement agrees well with the value predicted from the correlation. To explore thermal transport physics, the effects of pore structure and temperature on the thermal performance of the printed block are also studied. Our work demonstrates that the combination of the 3D printing technique and the printing speed control can regulate the thermophysical properties of materials.

Underwater gas self-transportation along femtosecond laser-written open superhydrophobic surface microchannels (<100 μm) for bubble/gas manipulation

Jiale Yong, Qing Yang, Jinglan Huo, Xun Hou, Feng Chen
2022, 4(1) doi: 10.1088/2631-7990/ac466f

Underwater transportation of bubbles and gases has essential applications in manipulating and using gas, but achieving this function at the microscopic level remains a significant challenge. Here, we report a strategy to self-transport gas in water along a laser-induced open superhydrophobic microchannel with a width less than 100 μm. The femtosecond laser can directly write superhydrophobic and underwater superaerophilic microgrooves on the polytetrafluoroethylene (PTFE) surfaces. In water, the single laser-induced microgroove and water medium generate a hollow microchannel. When the microchannel connects two superhydrophobic regions in water, the gas spontaneously travels from the small region to the large area along this hollow microchannel. Gas self-transportation can be extended to laser-drilled microholes through a thin PTFE sheet, which can even achieve anti-buoyancy unidirectional penetration. The gas can overcome the bubble's buoyance and spontaneously travel downward. The Laplace pressure difference drives the processes of spontaneous gas transportation and unidirectional bubble passage. We believe the property of gas self-transportation in the femtosecond laser-structured open superhydrophobic and underwater superaerophilic microgrooves/microholes has significant potential applications related to manipulating underwater gas.

Localized electrodeposition micro additive manufacturing of pure copper microstructures
Wanfei Ren, Jinkai Xu, Zhongxu Lian, Xiaoqing Sun, Zhenming Xu, Huadong Yu
2022, 4(1) doi: 10.1088/2631-7990/ac3963

The fabrication of pure copper microstructures with submicron resolution has found a host of applications, such as 5G communications and highly sensitive detection. The tiny and complex features of these structures can enhance device performance during high-frequency operation. However, manufacturing pure copper microstructures remain challenging. In this paper, we present localized electrochemical deposition micro additive manufacturing (LECD-µAM). This method combines localized electrochemical deposition (LECD) and closed-loop control of atomic force servo technology, which can effectively print helical springs and hollow tubes. We further demonstrate an overall model based on pulsed microfluidics from a hollow cantilever LECD process and closed-loop control of an atomic force servo. The printing state of the micro-helical springs can be assessed by simultaneously detecting the Z-axis displacement and the deflection of the atomic force probe cantilever. The results showed that it took 361 s to print a helical spring with a wire length of 320.11 µm at a deposition rate of 0.887 µm s-1, which can be changed on the fly by simply tuning the extrusion pressure and the applied voltage. Moreover, the in situ nanoindenter was used to measure the compressive mechanical properties of the helical spring. The shear modulus of the helical spring material was about 60.8 GPa, much higher than that of bulk copper (∼44.2 GPa). Additionally, the microscopic morphology and chemical composition of the spring were characterized. These results delineate a new way of fabricating terahertz transmitter components and micro-helical antennas with LECD-µAM technology.

Irregular LIPSS produced on metals by single linearly polarized femtosecond laser
Dongshi Zhang, Ruijie Liu, Zhuguo Li
2022, 4(1) doi: 10.1088/2631-7990/ac376c

Currently, supra-wavelength periodic surface structures (SWPSS) are only achievable on silica dielectrics and silicon by femtosecond (fs) laser ablation, while triangular and rhombic laser induced periodic surface structures (LIPSS) are achievable by circularly polarized or linear cross-polarized femtosecond laser. This is the first work to demonstrate the possibility of generating SWPSS on Sn and triangular and rhombic LIPSS on W, Mo, Ta, and Nb using a single linearly polarized femtosecond laser. We discovered, for the first time, SWPSS patches with each possessing its own orientation, which are completely independent of the light polarization direction, thus, breaking the traditional rules. Increasing the laser power enlarges SWPSS periods from 4-6 µm to 15-25 µm. We report a maximal period of 25 µm, which is the largest period ever reported for SWPSS, ∼10 and ∼4 times the maximal periods (2.4 µm/6.5 µm) of SWPSS ever achieved by fs and ns laser ablation, respectively. The formation of triangular and rhombic LIPSS does not depend on the laser (power) or processing (scan interval and scan methodology) parameters but strongly depends on the material composition and is unachievable on other metals, such as Sn, Al, Ti, Zn, and Zr. This paper proposes and discusses possible mechanisms for molten droplet generation/spread/solidification, Marangoni convection flow for SWPSS formation, and linear-to-circular polarization transition for triangular and rhombic LIPSS formation. Reflectance and iridescence of as-prepared SWPSS and LIPSS are characterized. It was found that besides insufficient ablation on W, the iridescence density of Ta-, Mo-, Nb-LIPSS follows the sequence of melting temperatures:Ta > Mo > Nb, which indicates that the melting temperature of metals may affect the regularity of LIPSS. This work may inspire significant interest in further enriching the diversity of LIPSS and SWPSS.

Enhanced ablation efficiency for silicon by femtosecond laser microprocessing with GHz bursts in MHz bursts(BiBurst)
Francesc Caballero-Lucas, Kotaro Obata, Koji Sugioka
2022, 4(1) doi: 10.1088/2631-7990/ac466e

Ultrashort laser pulses confine material processing to the laser-irradiated area by suppressing heat diffusion, resulting in precise ablation in diverse materials. However, challenges occur when high speed material removal and higher ablation efficiencies are required. Ultrafast burst mode laser ablation has been proposed as a successful method to overcome these limitations. Following this approach, we studied the influence of combining GHz bursts in MHz bursts, known as BiBurst mode, on ablation efficiency of silicon. BiBurst mode used in this study consists of multiple bursts happening at a repetition rate of 64 MHz, each of which contains multiple pulses with a repetition rate of 5 GHz. The obtained results show differences between BiBurst mode and conventional single pulse mode laser ablation, with a remarkable increase in ablation efficiency for the BiBurst mode, which under optimal conditions can ablate a volume 4.5 times larger than the single pulse mode ablation while delivering the same total energy in the process.

Understanding the Rayleigh instability in humping phenomenon during laser powder bed fusion process
Wenxuan Zhang, Wenyuan Hou, Luc Deike, Craig Arnold
2022, 4(1) doi: 10.1088/2631-7990/ac466d

The periodic undulation of a molten track's height profile in laser-based powder bed fusion of metals (PBF-LB/M) is a commonly observed phenomena that can cause defects and building failure during the manufacturing process. However a quantitative analysis of such instabilities has not been fully established and so here we used Rayleigh-Plateau theory to determine the stability of a single molten track in PBF-LB/M and tested it with various processing conditions by changing laser power and beam shape. The analysis discovered that normalized enthalpy, which relates to energy input density, determines whether a molten track is initially unstable and if so, the growth rate for the instability. Additionally, whether the growth rate ultimately yields significant undulation depends on the melt duration, estimated by dwell time in our experiment.

Reshapeable, rehealable and recyclable sensor fabricated by direct ink writing of conductive composites based on covalent adaptable network polymers
Xu He, Yuchen Lin, Yuchen Ding, Arif M Abdullah, Zepeng Lei, Yubo Han, Xiaojuan Shi, Wei Zhang, Kai Yu
2022, 4(1) doi: 10.1088/2631-7990/ac37f2

Covalent adaptable network (CAN) polymers doped with conductive nanoparticles are an ideal candidate to create reshapeable, rehealable, and fully recyclable electronics. On the other hand, 3D printing as a deterministic manufacturing method has a significant potential to fabricate electronics with low cost and high design freedom. In this paper, we incorporate a conductive composite consisting of polyimine CAN and multi-wall carbon nanotubes into direct-ink-writing 3D printing to create polymeric sensors with outstanding reshaping, repairing, and recycling capabilities. The developed printable ink exhibits good printability, conductivity, and recyclability. The conductivity of printed polyimine composites is investigated at different temperatures and deformation strain levels. Their shape-reforming and Joule heating-induced interfacial welding effects are demonstrated and characterized. Finally, a temperature sensor is 3D printed with defined patterns of conductive pathways, which can be easily mounted onto 3D surfaces, repaired after damage, and recycled using solvents. The sensing capability of printed sensors is maintained after the repairing and recycling. Overall, the 3D printed reshapeable, rehealable, and recyclable sensors possess complex geometry and extend service life, which assist in the development of polymer-based electronics toward broad and sustainable applications.

3D printed ultra-fast photothermal responsive shape memory hydrogel for microrobots
Ziheng Zhan, Lei Chen, Huigao Duan, Yiqin Chen, Min He, Zhaolong Wang
2022, 4(1) doi: 10.1088/2631-7990/ac376b

Hydrogels with stimuli-responsive capabilities are gaining more and more attention nowadays with prospective applications in biomedical engineering, bioelectronics, microrobot, etc. We develop a photothermal responsive hydrogel based on N-isopropylacrylamide that achieved a fast and reversible deformation manipulated only by near-infrared (NIR) light. The hydrogel was fabricated by the projection micro stereolithography based 3D printing technique, which can rapidly prototype complex 3D structures. Furthermore, with the variation of the grayscale while manufacturing the hydrogel, the deformation of the hydrogel structure can be freely tuned within a few seconds by losing and absorbing water through adjusting the intensity and the irradiation direction of the NIR light, showing a potential application in ultra-fast object grabbing and transportation. The present study provides a new method for designing ultrafast photothermal responsive hydrogel based microrobot working in water.

Nanosecond laser shock detonation of nanodiamonds: from laser-matter interaction to graphite-to-diamond phase transition
Xing Zhang, Haofan Sun, Bo Mao, Rui Dai, Houlong Zhuang, Yiliang Liao, Qiong Nian
2022, 4(1) doi: 10.1088/2631-7990/ac37f1

Nanodiamonds (NDs) have been widely explored for applications in drug delivery, optical bioimaging, sensors, quantum computing, and others. Room-temperature nanomanufacturing of NDs in open air using confined laser shock detonation (CLSD) emerges as a novel manufacturing strategy for ND fabrication. However, the fundamental process mechanism remains unclear. This work investigates the underlying mechanisms responsible for nanomanufacturing of NDs during CLSD with a focus on the laser-matter interaction, the role of the confining effect, and the graphite-to-diamond transition. Specifically, a first-principles model is integrated with a molecular dynamics simulation to describe the laser-induced thermo-hydrodynamic phenomena and the graphite-to-diamond phase transition during CLSD. The simulation results elucidate the confining effect in determining the material's responses to laser irradiation in terms of the temporal and spatial evolutions of temperature, pressure, electron number density, and particle velocity. The integrated model demonstrates the capability of predicting the laser energy threshold for ND synthesis and the efficiency of ND nucleation under varying processing parameters. This research will provide significant insights into CLSD and advance this nanomanufacturing strategy for the fabrication of NDs and other high-temperature-high-pressure synthesized nanomaterials towards extensive applications.

Wideband mid-infrared thermal emitter based on stacked nanocavity metasurfaces
Tun Cao, Meng Lian, Kuan Liu, Xianchao Lou, Yaoming Guo, Dongming Guo
2022, 4(1) doi: 10.1088/2631-7990/ac3bb1

Efficient thermal radiation in the mid-infrared (M-IR) region is of supreme importance for many applications including thermal imaging and sensing, thermal infrared light sources, infrared spectroscopy, emissivity coatings, and camouflage. The ability to control light makes metasurfaces an attractive platform for infrared applications. Recently, different metamaterials have been proposed to achieve high thermal radiation. To date, broadening the radiation bandwidth of a metasurface emitter (meta-emitter) has become a key goal to enable extensive applications. We experimentally demonstrate a broadband M-IR thermal emitter using stacked nanocavity metasurface consisting of two pairs of circular-shaped dielectric (Si3N4)-metal (Au) stacks. A high thermal radiation can be obtained by engineering the geometry of nanocavity metasurfaces. Such a meta-emitter provides wideband and broad angular absorptance of both p- and s-polarized light, offering a wideband thermal radiation with an average emissivity of more than 80% in the M-IR atmospheric window of 8-14 µm. The experimental illustration together with the theoretical framework establishes a basis for designing broadband thermal emitters, which, as anticipated, will initiate a promising avenue to M-IR sources.