Laser-induced Forward Transfer Process Research Articles

Alternate deposition and remelting microdroplets via single laser for printing low-defect and high-performance metal micropillars

Laser-induced forward transfer (LIFT) has emerged as a versatile technique for printing high-resolution metal microstructures. However, a common drawback of this method is the inadequate coalescence of the deposited metal microdroplets, which results in inferior electrical and mechanical properties. This paper proposes a novel approach for fabricating high-performance metal micropillars using a single-pulsed laser to alternately deposit and remelt metal microdroplets. Specifically, an ultraviolet nanosecond laser was used to induce the deposition of copper microdroplets, forming a patterned powder bed with high resolution. Subsequently, a laser pulse train was applied to fuse the patterned powder bed. The results showed that voids and microdroplet delamination were eliminated in the printed copper micropillars, whose yield strength and elastic modulus increased threefold, approaching 63% of those of the bulk metal. The remelting behavior of the deposited microdroplets was elucidated by modelling and analysing the thermal accumulation effects of a laser pulse train. A remelting map was proposed, including the non-melting, remelting, and vaporizing regimes. According to the depth of melt pool, the evolutions of morphology and microstructure in the depositing and remelting process were elucidated. Hence, this study advances the LIFT process for fabricating high-performance metal microstructures.

Lithography‐free fabrication of a local contact interlayer for Si‐based tandem solar cells

AbstractCurrently, the Si solar cell market share is dominated by PERC solar cells. Although the efficiency of PERC solar cells has been steadily increasing, it is expected to reach the practical efficiency limit in the near future. The thin film/PERC Si tandem cell technique can be one of the solutions to overcome the single‐cell efficiency limit. In this study, we developed a novel interlayer fabrication technology for the diffused junction Si solar cells of the PERC and Al BSF cell architectures. We combined laser contact opening (LCO) and laser‐induced forward transfer (LIFT) processes to fabricate local contact opening with low contact resistance while maintaining the high passivation performance of the Si bottom cell. The dielectric‐passivated emitter of the Si solar cell was ablated locally by the LCO process, and subsequently, the Ti nanoparticles were transferred selectively by the LIFT process to the opened emitter region followed by transparent conducting oxide deposition. Laser process parameters were carefully optimized to fabricate low‐loss interlayers. We applied the developed interlayer fabrication technology to the Si bottom cells of Al BSF and PERC cells. Finally, we demonstrated successfully the perovskite/PERC Si tandem cell with an interlayer developed in this study. The developed interlayer fabrication technology does not include a photolithography step and vacuum deposition processes for buffer metals; thus, we expect it may be more compatible with the mass production of thin film/diffused junction Si tandem solar cells.

Laser-Induced Printing of Next Generation Silicon-Graphite Anodes for the Development of Advanced Lithium-Ion Batteries

The expansion of renewable causing a rising demand for affordable and improved energy storage systems. Lithium-ion batteries (LIB) are one of the most promising technologies for this achievement, with further improvements to be made in terms of new materials and an advanced electrode architecture. As a new generation electrode material to be included in LIB, silicon is in the focus of the today’s investigations. Silicon offers one order of magnitude higher theoretical specific capacity (3579 mAh/g) compared to the state-of-the-art material graphite (372 mAh/g). However, during lithiation of silicon a volume expansion of up to 300 % takes place. Due to the huge volume expansion tremendous mechanical degradation of the anode occurs, resulting in a drop in capacity and a shorten lifetime.Laser induced forward transfer (LIFT) is applied in this study as printing technology to develop enhanced silicon-graphite electrode compositions and electrode architectures. LIFT was performed using a pulsed nanosecond UV-laser with a maximum power of 10 W and repetitions rate of up to 30 kHz. For the LIFT process of anodes, polyacrylic acid (PAA) is used as binder, in contrast to the polyvinylidene fluoride (PVDF) binder commonly used for LIFT assisted printing of electrodes. PAA is a more appropriate binder for silicon-containing anodes than PVDF. In addition, also a customized architecture using subtractive and additive laser process techniques is introduced for an increase in lifetime of batteries containing silicon-based electrodes. For this purpose, graphite electrodes were structured with an ultrashort pulse laser with pattern widths of 100 µm. Subsequently, silicon rich slurry was printed into the patterns to increase the areal capacity. The as-prepared electrodes have spatially separated graphite and silicon regions. The respective electrodes were electrochemically cycled in half-cells and charged at different C-rates up to 5C to investigate their lithiation capability. After the rate capability analysis, the cells were cycled at C/2 to investigate the long-term degradation. The cells with the printed electrodes were cycled for more than 450 cycles with a capacity fade of 5 %. At their end-of-life, the cells were analyzed post-mortem. Finally, full-cells were assembled with cathodes containing NMC 622 as the active cathode material. Subsequently to the cell priming a lifetime analysis was performed at a C-rate of C/2 and cycle stability as well as lithium loss during cycling were evaluated.

Laser-induced forward transfer (LIFT) based bioprinting of the collagen I with retina photoreceptor cells

This study focuses on the 3D bioprinting of retina photoreceptor cells using a laser-induced forward transfer (LIFT) based bioprinting system. Bioprinting has a great potential to mimic and regenerate the human organoid system, and the LIFT technique has emerged as an efficient method for high-resolution micropatterning and microfabrication of biomaterials and cells due to its capability of creating precise, controlled microdroplets. In this study, the parameters for an effective femtosecond laser-based LIFT process for 3D bioprinting of collagen biomaterial were studied. Different concentrations of collagen I solutions were tested and 0.75 mg/ml to 1 mg/ml collagen Ⅰ was identified as the right concentration that can be transferred through the LIFT system. Then, retinal cone cells were mixed with collagen I and Dulbecco's Modified Eagle's Medium (DMEM) and printed drop-by-drop lines. Some important laser parameters such as pulse energy and pulse pick divider were experimented with to form a successful, smooth, high-resolution deposition. The cell viability in the bioink and printed droplet was measured at different time horizons. A general full factorial design of the experiment was used to analyze and observe the relationship between the droplet quality and the LIFT process parameters. Using 15 µJ and 16 µJ pulse energy, the cell-laden bioink was printed successfully. This research study will help to print other retinal neuron cells with collagen Ⅰ in the LIFT system and show the way of constructing layer-by-layer different cell lines that will help to fabricate the retina ultimately.

Experimental investigation of various energy-absorbing layer materials and sodium alginate viscosities on the jet formation in laser-induced-forward-transfer (LIFT) bioprinting

Laser-induced-forward-transfer (LIFT) bioprinting technology has been viewed as a regenerative medicine technology because of its high printing quality and good cell viability. To stabilize the jet to achieve high-quality printing, an energy-absorbing layer (EAL) can be introduced. In this study, three materials (graphene, gelatin, and gold) were utilized as the EAL. The effect of each EAL on the jet generation process was investigated. Besides, the effect of graphene EAL thickness was addressed for various experimental conditions. The jet generation process using sodium alginate solutions with different concentrations (1 and 2 wt. %) was also discussed to investigate the effect of viscosity. The time sequence images of the formed jets utilizing three EALs showed that both graphene EAL and gelatin EAL can promote the formation of jet flow. For the gold EAL, no jet flow was observed. This study provides experimental verifications that the interaction between laser and EAL materials can result in different jets due to various dominant interaction mechanisms. For example, strong absorption in the infrared range for the graphene EAL, strong scattering loss for the gelatin EAL, and strong absorption in the ultraviolet range but weak absorption in the infrared for the gold EAL. We also observed the holes left on the EAL after the printing was completed. The thermal effect is dominant to create regular and round shape holes for the graphene EAL, but it changes to the mechanical effect for the gold EAL because of the existence of irregular and unorganized holes. In addition, we identified the existence of an input laser energy threshold value for a certain thickness graphene EAL. More laser energy is required to break down thicker graphene EALs, which will result in a higher initial jet velocity. Furthermore, we explored the effect of sodium alginate (SA) solution's viscosity on the generated jet. We found that a high-viscosity SA solution can result in a low initial jet velocity, a short jet, and small droplets on the receiving substrate. The findings from this study help determine the mechanisms of EAL–laser interaction with different EAL materials in the LIFT process. This work aims to facilitate the development of new EAL and bioink to achieve stable jet formation and high printing quality in future LIFT bioprinting.

Liquid crystal doped photopolymer micro-droplets printed by a simple and clean laser-induced forward transfer process.

We print a tunable photopolymer (photopolymer dispersed liquid crystal -PDLC), using the laser-induced direct transfer technique without absorber layer, which was a challenge for this technique given the low absorption and high viscosity of PDLC, and which had not been achieved so far to our knowledge. This makes the LIFT printing process faster and cleaner and achieves a high-quality printed droplet (aspheric profile and low roughness). A femtosecond laser was needed to reach sufficiently peak energies to induce nonlinear absorption and eject the polymer onto a substrate. Only a narrow energy window allows the material to be ejected without spattering.

Hybrid structural electronics fabrication by combined SLA and metal printing

A method is described where 3D electronic devices are fabricated using a hybrid printing approach which combines several steps: Top illumination stereolithography; laser induced forward transfer (LIFT) printing of conductive materials; placement of active and passive components and their electrical interconnection by a non-contact, metal LIFT process. By applying this approach, free-form 3D functional electronic structures could be manufactured by a single hybrid tool. The adhesion of LIFT printed metal droplets onto various organic substrates of interest for device fabrication was investigated. The results suggest two possible approaches for improved adhesion by either printing at elevated surface temperature or surface roughening by laser pre-treatment. The resulting track resistivities were found to be in the range of ×5–10 higher than bulk copper resistivity. We present several exemplary printed devices with different complexities and functionalities as demonstrators of the proposed hybrid technology.

Laser transfer for circulating tumor cell isolation in liquid biopsy.

75Cancer research has found in the recent years a formidable ally in liquid biopsy, a noninvasive technique that allows the study of circulating tumor cells (CTCs) and biomolecules involved in the dynamics of cancer spread like cell-free nucleid acids or tumor-derived extracellular vesicles. However, single-cell isolation of CTCs with high viability for further genetic, phenotypic, and morphological characterization remains a challenge. We present a new approach for single CTC isolation in enriched blood samples using a liquid laser transfer (LLT) process, adapted from standard laser direct write techniques. In order to completely preserve the cells from direct laser irradiation, we used an ultraviolet laser to produce a blister-actuated laser-induced forward transfer process (BA-LIFT). Using a plasma-treated polyimide layer for blister generation, we completely shield the sample from the incident laser beam. The optical transparency of the polyimide allows direct cell targeting using a simplified optical setup, in which the laser irradiation module, standard imaging, and fluorescence imaging share a common optical path. Peripheral blood mononuclear cells (PBMCs) were identified by fluorescent markers, while target cancer cells remained unstained. As a proof of concept, we were able to isolate single MDA-MB-231 cancer cells using this negative selection process. Unstained target cells were isolated and culture while their DNA was sent for single-cell sequencing (SCS). Our approach appears to be an effective approach to isolate single CTCs, preserving cell characteristics in terms of cell viability and potential for further SCS.

레이저 유도 전사를 이용한 유연기판의 액체금속 미세 패터닝

We have developed a direct conductive patterning method with micro-scale line widths using the laser-induced-forward transfer (LIFT) and liquid metal. As this method does not need post-thermal processing, there is no thermal damage even on heat-sensitive polymer substrates by low-power laser irradiation on the dynamic release layer (DRL). Unlike other liquid metal patterning processes, this procedure can easily achieve fine line widths of a few tens of micrometers corresponding to laser spot size. The solid-state UV pulse laser with 266 nm wavelength and 20 ns pulse duration was used to transfer Eutectic Gallium Indium (EGaIn) liquid metal and the results for the single and multi-pulse laser irradiation were investigated to determine the effective process conditions. The applicability of flexible circuit fabrication and selective circuit repair was successfully tested on Polyimide (PI) substrate. After the LIFT process, the electrical properties of liquid metal on the pattern were measured to be approximately 5~8 x 10SUP-3/SUP Ω/m of resistance.

Ordered Porous Electrodes Obtained Using LIFT for Electrochemical Applications.

Numerous synthetic techniques for the fabrication of porous metal electrodes were developed in recent decades. A very promising and facile route is the 3D printing of structures, which can be designed directly on the computer first. However, the current techniques allow structures to be printed with a resolution down to 20 µm, which is still quite rough regarding tuning the pore distribution and diameter of electrode materials for potential applications. For the first time, a laser-induced forward transfer (LIFT) process was used to 3D print metal voxels on a solid surface, resulting in a porous electrocatalytically active gold (Au) electrode film. Porous Au electrodes produced using LIFT showed an increase in the electrochemically active surface area (SA) by a factor of four compared with a sputtered dense Au film when characterized using cyclic voltammetry (CV) in Ar-saturated 0.1 M KOH. Therefore, the LIFT process can be considered very promising for the printing of ordered porous electrodes with high surface areas for electrochemical applications.

Laser-Induced Forward Transferred Optical Scattering Nanosilica for Transparent Displays.

Laser printing has become a promising alternative for large-scale fabrication of functional devices. Here, laser-induced forward transfer (LIFT) of nanosilica was successfully achieved using a lower-cost nanosecond laser with a center wavelength of 1064 nm. To enhance the light absorption of silica, a small amount of graphene oxide (GO) was added to the fumed silica. Investigations were conducted to give an insight into the role of GO in the LIFT process. Pattern deposition was achieved with a minimum line width of 221 μm. The scattering can be tuned from ~2.5% to ~17.5% by changing the laser fluence. The patternable transparent display based on laser transferred nanosilica (LTNS) film was also demonstrated, showing its capability to deliver information on multiple levels. This LIFT based technique promotes fast, flexible, and low-cost manufacturing of scattering-based translucent screens or patterns for transparent displays.

Separated nano jetting and micro jetting regimes by double-pulse irradiation of a metal film: towards multiscale printing.

The Double-Pulse (DP) version of the Laser-Induced Forward Transfer (LIFT) technique holds great potential to improve the resolution and flexibility of printing applications. In this study, we investigate the transfer of copper. A long laser pulse is first applied to melt thin copper films deposited on a transparent substrate, followed by an ultrashort laser pulse to initiate the transfer of the liquid material towards a receiver substrate. Time-resolved imaging experiments reveal that ejections from nanodrops to liquid jets with controllable diameters, from few micrometers down to the nanometers scale can be obtained with the control parameters of DP-LIFT. Comparing simulation and experiments we discuss how the ejection characteristics are governed by various factors including the shape, diameter and temperature of the melted pool created with the first long pulse. While the formation of microjets is due to the dynamical deformation of the melted film, as for the conventional LIFT process applied with liquid donors, the results indicate a different and distinct process for the formation of nanojets. We extrapolate from the observations a feature caused by the interaction of the shockwave, generated by the femtosecond laser irradiation, with the deformed surface of the pool. Ultimately, we establish the range of irradiation parameters leading to the observation of single separated microjets and nanojets. The latter are accompanied by nano printing demonstrations. Considering all accessible regimes together, a unique technological perspective is the possibility to achieve multi-scale printing from the same donor.

Transfer characteristics for laser-induced forward transfer of stainless steel particle

Additive manufacturing (AM) holds great development potential in several applications. In particular, the fabrication of metal parts has been rapidly developing as an industry recently. In such applications, a powder feeder with low material loss is required to ensure effective material usage. Thus, the manufacturing process using laser-induced forward transfer (LIFT) is attractive as a candidate for advances in powder feeder technology. We show that stainless steel particle with diameters of 26 to 53 μm can be transferred via the particle LIFT process; the transfer of particles started at a peak fluence of ∼0.05 J cm − 2 (26- and 36-μm diameters) and ∼0.15 J cm − 2 (53-μm diameter), and the particles were fully transferred (i.e., the probability of transfer reaches unity) at a peak fluence of 0.2 (26 μm), 0.4 (39 μm), and 0.5 J cm − 2 (53 μm). The initial velocity, v0, at which the particle leaves the substrate increased proportionally with the increase in peak fluence. When the point of irradiation of the laser beam was displaced from the contact point of the particle on the substrate, the particle was transferred with a transfer angle (i.e., not vertically). These results demonstrate the possibility of transferring metal particles via the LIFT process. To use this technology for AM, the laser power should be adjusted to control the transfer angle of the particle.

Laser-Induced Forward Transfer of Silver Nanoparticles for a Black Metal Absorber

Plasmonic nanostructures emerged as an appealing approach for black metal absorbers (BMAs) to provide significant light absorption. We present the simple and rapid fabrication of BMAs using laser-induced forward transfer of silver nanoparticles (AgNPs). Randomly distributed plasmon silver nanostructures at a multiscale were produced simultaneously during laser transfer, providing significant light absorption and antireflection features. The laser-transferred BMAs exhibit excellent absorption capacity of a value over 96% and a minimum reflection of 0.38%. A high scanning speed of 10 m/s was used that can complete the laser-induced forward transfer (LIFT) process within 2 s for a 1 cm2 area. The nearfield light confinement is discussed in terms of the morphology of the obtained nanostructures. Photothermal conversion with macroscale temperature rising was demonstrated for the LIFT process is an effective method for the industrial production of BMAs with excellent absorption capacity.

Liquid Crystal Doped Photopolymer Microlenses Printed by a Simpler and Cleaner Laser-Induced Forward Transfer Process

Liquid Crystal Doped Photopolymer Microlenses Printed by a Simpler and Cleaner Laser-Induced Forward Transfer Process

Parametric investigation on Laser-Induced Forward Transfer of ZnO nanostructure on flexible PET sheet for optoelectronic application

ZnO nanostructures gained much attention for the micro/nano devices fabrication, but it is facing challenges in the deposition on the flexible substrate for optoelectronics applications. In the present work, Laser-Induced Forward Transfer (LIFT) was deployed for the deposition of the ZnO nanostructures on the flexible polyethylene terephthalate (PET) sheet using Indium Tin Oxide (ITO) sacrificial layer. The process window was developed for the laser parameters in COMSOL Multiphysics simulation for estimating the temperature distribution. Three different laser wavelengths (355 nm, 532 nm, and 1064 nm) and laser fluence ranging from 100 to 550 mJ/cm2 were used in the numerical simulation. Subsequent to the numerical simulation, the LIFT process was deployed at three different laser fluence (100, 250, and 550 mJ/cm2) with 355 nm wavelength for the transfer of ZnO nanorods. SEM images reveal that the higher fluence (550 mJ/cm2) melts the donor materials and degrades the quality of deposition. During the experiments, the time-resolved imaging measured the velocity of the deposited materials and observed that the velocity of 960 m/s, 200 m/s, and 90 m/s is achieved at a laser fluence of 550, 250 and 100 mJ/cm2, respectively. The XRD analysis and PL analysis show better structural and optical properties of deposited ZnO nanostructures as compared to previously published work available in the literature.

3D printing of liquid metal EGaIn through laser induced forward transfer: A proof-of-concept study

In this work, we introduce Laser Induced Forward Transfer (LIFT) of Liquid Metal (LM) alloys, specifically Eutectic Gallium-Indium (EGaIn). LIFT for LM provides a fairly simple manufacturing method with better control and modularity for patterning LMs compared to existing methods such as imprinting, and extrusion. LIFT is a direct-write printing method which is used for a wide range of applications, such as, laser printing of electronic materials, biomolecules, and cells. Our preliminary results demonstrate great potential of LIFT process for LM deposition and patterning, and can help achieve finer and scalable features with high throughput.

Laser induced forward transfer of brittle Cu3Sn thin film

Abstract Cu3Sn intermetallic compound as an interconnecting material has great prospect in power electronic device applications due to its high melting temperature. However, the intermetallic compound is essentially brittle, and hard to be transferred. In this study, Cu3Sn thin films have been successfully transferred by means of laser-induced forward transfer (LIFT) process with millisecond pulse length. The morphology of LIFT-processed Cu3Sn thin film was investigated by optical microscopy and Atomic Force Microscopy (AFM). The optimized transfer process parameters were 0.3 ms laser irradiation, 8001100 W laser power and 14 mm defocusing amount. Under the optimized conditions, the deposition pattern of Cu3Sn thin films were complete and uniform. The transfer mechanism was that the solid Cu3Sn films have been pushed and transferred by the gasified part Cu3Sn near the interface of the donor substrate during the LIFT process.

Concurrent Formation of Metallic Glass During Laser Forward Transfer 3D Printing

AbstractIn recent years, bulk metallic glasses (BMGs) have drawn much research attention and are shown to be of industrial interest due to their superior mechanical properties and resistance to corrosion. In spite of the interest in harnessing MG for microelectromechanical systems devices, there are limitations in manufacturing such micrometer‐scale structures. A novel approach for the fabrication of 3D MG structures using laser‐induced forward transfer (LIFT) is demonstrated. Inherent tremendous cooling rates associated with the metal LIFT process (≈1010 k s−1) make the formation of a variety of BMGs accessible, including also various binary compositions. In this work, it is demonstrated that LIFT printing of ZrPd‐based metallic glass microstructures can also be performed under ambient conditions. X‐ray diffraction analysis of the printed structures reveals > 95% of amorphous metal phase. Taking advantage of the properties of BMG, high quality printing of high aspect ratio BMG pillars, and microbridges are demonstrated. It is also shown how a composite, amorphous‐crystalline metal structure with a required configuration can be fabricated using multimaterial LIFT printing. The inherent high resolution of the method combined with the noncontact and multimaterial printing capacity makes LIFT a valuable additive manufacturing technique to produce metallic glass‐based devices.

The Jet formation in Ring-shape Laser Induced forward transfer

In this study, ring-shape laser spot was used to induce a ring-shape cavitation aiming to improve the separation accuracy in the laser induced forward transfer (LIFT) process. The roles of laser pulse energy and the size of the ring-shape laser spot on jet formation in LIFT process were theoretically analyzed with ring-shape bubble collapse model established by Lattice Boltzmann Method. The results show that the geometrical symmetry of the ring-shape cavitation blocks the interaction between the inner and outer liquids, leading to higher separation accuracy. The simulation results show that under a specific ratio of internal and external diameter of the ring-shape laser spot, a secondary produced vortex velocity flow can further promote the accuracy of the transferring.