Digital printing of 3D metal micro-structures by laser induced forward transfer under ambient conditions is reviewed. Recent progress has allowed drop on demand transfer of molten, femto-liter, metal droplets with a high jetting directionality. Such small volume droplets solidify instantly, on a nanosecond time scale, as they touch the substrate. This fast solidification limits their lateral spreading and allows the fabrication of high aspect ratio and complex 3D metal structures. Several examples of micron-scale resolution metal objects printed using this method are presented and discussed.
© 2016 Optical Society of America
3 February 2016: A correction was made to the author affiliations.
There are currently several methods for the manufacturing of 3D micro-structures [1,2]. MEMS devices are manufactured using well known silicon fabrication processes. For the fabrication of 3D metal structures laser based processes play a major role, such as in selective laser sintering (SLS) [3–6] although their resolution is limited and require special atmospheric conditions (i.e. vacuum conditions or inert atmosphere). There has been recently an important surge of 3D printing technology where polymers serve as the principal structural material , however these methods have inherent limitations when it comes to forming micron-scale, multi-metal structures, or when mixing of metals and dielectrics is required. The advent of digital printing  can support multi-material printing however it is still typically limited to low viscosity inks. Moreover, an intensive optimization effort is often required to obtain appropriate formulations for quality jetting [8–10]. Inkjet printing of functional materials is a most active field in recent years [11–16] and a significant development effort is invested in developing jettable, low viscosity (typically <~50cP) “metal inks” which contain metal nano-particles (NP) as electronic functional materials.
There are several well-known limitations associated with current functional printing methods. For one there is still a limited number only of suitable metal inks, typically based on noble metal NPs (e.g. Ag, Au) showing reasonable stability. Also, resolution and pattern geometry (line height, for example) are typically limited as they are dictated by the ink wetting properties and the rather large droplet volume (~>pL). Finally, there is the sintering step, a thermal post-treatment step, which is almost always unavoidable in order to transform the metal particles into a conductive metal track. This thermal step often limits the type of substrates one can print on without compromising the sintered line conductivity.
The laser induced forward transfer technique (LIFT)  has the advantage of being able to solve, under certain conditions, most of the problems mentioned above which relate to digital printing. First, note that instead of the three process steps of conventional metal pattern forming, namely metal deposition step, pattern formation (phororesist deposition, exposure, development and etching) and finally metal growth - all these steps are essentially replaced by one printing step only. Moreover, unlike the case with metal inks and pastes, there is no post-treatment needed to render the printed track conductive. The method can allow high speed jetting, it is nt complex in terms of material preparation and allows for high resolutions pattern formation. In principle, almost every material that can be deposited on a transparent substrate could be LIFT printed. The LIFT process is schematically described in Fig. 1. It involves the transfer from a thin material layer which is coated on a transparent substrate, this is usually denoted as the ‘donor’ to the receiver, see Fig. 1(a). The donor is placed in front of the receiver substrate in a close proximity (a few ten of micrometers). Jetting of a material part follows local heating by a focused laser pulse which is absorbed at the interface between the material layer and the transparent substrate. Local heating provides the conditions to transfer part of the material (Fig. 1(c) and Fig. 1(d)). LIFT printing of a large variety of materials has been reported to date, metals [18–24], semiconductors , dielectrics  and organics [27–30]. Moreover, since the printed volume depends on the laser spot size one can tune the printing conditions so as to obtain a droplet volume as low as a few femto-liters only.
LIFT printing of 3D micro-structures was first proposed by A. Pique . In their technique the printed materials shape is identical to the laser pulse spatial shape which defines the printable pattern. B. Chichkov first demonstrated LIFT printed 3D micro-structures in the transfer regime of sub-micron droplets . This method allows to print 2D and 3D micro-structures with high lateral resolution. In this work we concentrate on the utilization of LIFT for 3D printing applications. In sections 1.1, 1.2 and 1.3 we introduce the LIFT method development. It is followed by an experimental session that describe the methodology we used to print 3D micro-objects. Then we show a few examples of LIFT printed 3D structures where each example emphasises a particular capability of such printing method: high lateral resolution, high aspect ratio, non-contact printing mask-less, digital printing and finally printing under normal atmospheric conditions, avoiding the need for a special environment.
1.1 LIFT printing of shaped deposit
LIFT was first proposed  as a method to transfer a shaped deposit (SD) of material (Fig. 1) using nano-second laser pulses. The term of SD indicated that the size and the shape of the transferred material typically follow the laser beam size and profile. The LIFT mechanism in this case involves material transfer driven by an explosive ablation at the material/substrate interface when the donor reaches boiling temperatures. Numerical simulations [33,34] support this hypothesis. However, this specific transfer mechanism suffers from a few rather important drawbacks. First, the gap between the donor and the receiver should be kept small (<20µm) otherwise the printing quality deteriorates. Secondly, LIFT of SD also lacks in terms of the material choice. For example since the effectiveness of this process depends on the optical absorption and mechanical properties of the transferred materials, transfer of organic or biological materials is often impractical as they get deteriorated . One approach to resolve this issue is to inserting an active, intermediate layer between the print material and the donor substrate [36–44] (Fig. 2). Here the transfer material is no more exposed to the laser pulse directly and direct damage can be avoided. The intermediate layer can be a thermal, absorptive layer, which serves to transfer the laser energy as heat to the print material  or as blister actuated  or alternately serve as a dynamic release layer (DRL), typically involving an exothermic reaction which contributes thrust to the transfer process [38–44]. With such intermediate layers, thermal sensitive materials, i.e. bio-materials, polymers, and also non-absorptive, transparent materials (for example oxide layers) could be transferred. Recently this method served the transfer of organic light emitting diodes for display applications [39,43,44]. The DRL material should be compatible with the donor material so as to avoid residual contamination of the deposited material. A special polymer was recently designed, triazene polymer (TP), to serve as DRL which fully dissociates upon UV irradiation into gaseous fragments [39,40]. TP decomposes exothermally upon irradiation and thus provides extra thrust for material transfer.
Another variant is ‘laser decal transfer’  which deals with the transfer of high viscosity (typically > 100,000cP) pastes, e.g. silver NPs pastes. Here one takes advantage of shear thinning to prevent the breakup of the donor layer during transfer. The pattern of the transferred SD follows closely the laser pulse spatial profile. Laser decal transfer can generate high quality patterns with well-defined edges and avoid debris and satellites. Decal transfer served to demonstrate at an early stage the printing of simple 3D microstructure. While micron-scale SDs from a rather large range of materials can be printed by Decal transfer, the method allow printing continuous patterns by using an adequate annealing step . Moreover, since a small jetting gap is typically required (10’s of microns) to maintain accuracy and integrity of the material its adoption in high throughput manufacturing might be be limited.
1.2 LIFT of fluids
LIFT was initially developed for deposition of metal patterns but soon extended to various inorganic materials. In 2004  it was demonstrated that LIFT could be used to transfer pastes and liquids. The method was first applied to bio-materials. The donor layer was prepared using standard liquid coating methods, spin coating or roller coating. The printing principle (Fig. 3) consists of a fast evaporation of the solvent (Fig. 3(a)), bubble formation, and vapor expansion to the point where the pressure of the bubble equals the ambient pressure followed by droplet separation and liquid jet retraction. Two main jetting mechanisms were reported: close to the threshold a filament jet is formed (Fig. 3(b)) which is shorter than the gap distance, then the liquid jet retracts along with a single droplet which separates towards the substrate (Fig. 3(c)). A second mechanism takes place at a higher laser pulse energy giving rise to long jet filament which extends and eventually gets in contact with the substrate. Then the jet splits with one part deposited and the rest recoils back.
The jetting dynamics and bubble formation can be roughly approximated by Rayleigh-Plasset equation [47–49] describing the bubble radius evolution which mainly depends on the liquid kinematic viscosity and surface tension. When the bubble reaches it maximum diameter, it starts to collapse under the external pressure and a jet forms according the dimensionless standoff distance Γ [50,51]. The standoff distance depends on the laser pulse energy, the optical absorption of the liquid and the material viscosity. The printing regime limits are set by Γth and Γmax. When Γ < Γth there is no droplet ejection, if on the other hand Γ > Γmax we get at the regime where the bubble bursts at the free surface and sputtering of a sub-micron droplets jet takes place. The printing regime is therefore limited to Γth <Γ < Γmax.
Transfer printing of various fluids (also highly viscous) has probably been the most successful contribution of LIFT printing so far. LIFT printing served for the transfer of proteins and cells [51–53], several researchers [54–59] have employed LIFT to print silver NP inks with the aim of reducing droplet’s volume to below ~200fL, much smaller than possibly obtainable by inkjet typically. Figure 4(a) depicts LIFT printed droplets of NP pastes (InkTec, Type PA010), the layer was prepared with bar coating to provide uniform layer of 15µm on a soda lime slide. Using the setup describe in the experimental section it obtain (in our lab) droplet with diameter <20 µm (laser pulse energy = 1.18µJ). Figure 4(b) shows the role of the ink surface tension in dictating the printing morphology [60,61]. Ring shaped metal inks can be printed when using high surface tension inks, e.g. glycerol based inks (Fig. 4(b)). The integrity of the droplet is conserved while the ring shaped form on the substrate is controlled by surface tension. The ring geometry itself can be varied by changing laser pulse energy (Fig. 4(b)). Such patterns could be useful for the production of transparent conductive films as overlapped droplets form connected, conducting arrays.
1.3 LIFT of metal micro-droplet
The great success of LIFT of fluid droplets encouraged researchers in the field to also look for ways to transfer droplets of molten solids. If successful, this might resolve the problems associated with SD transfer (section 1.1). In 2005 [62,63] LIFT transfer of micro-droplets of aluminum was shown. This followed with reports describing jetting of sub-micron metal droplets [64–67] using femto-second laser pulses, and also in the backward configuration . The governing mechanism in all these cases involved generation of a molten metal pool in a very thin (<~200nm) metal donor layer. The entire layer melts within the laser pulse duration and droplet formation and jetting derives from this transient melt pool which is under a high thermally induced pressure at the substrate-liquid interface [66,67]. The molten metal droplet which thus form from the molten layer have a limited directionality and jetting accurracy is limited. To maintain print quality the donor should be brought into close proximity with the receiver, up to a few tens of microns typically [62–68].
Recently [69–71] we have shown how stable jetting of metal droplets can be achieved while maintaining a relatively large donor-receivergap, >200µm. This was made possible due primarily to a different jetting mechanism which is effective when using sub-nano-second pulses and relatively thick metal donor layers (thickness > 300nm). We have termed this new stable regime “Thermal Induced Nozzle” (TIN-LIFT). It involves the formation of a nozzle-like structure which, unlike the cases described above, provides high directionality to the emerging molten metal droplets. With sub-nano-second pulses one can melt a 300nm thick layer all the way to the free surface within the pulse duration. However, for thicker layers, >300nm, the thermal diffusion length within the pulse duration is smaller than the layer thickness. For the molten metal front to reach the free surface by heat diffusion one has to increase the pulse energy to allow for the excess thermal energy which is needed for the metal melt front to continue to propagate after the pulse has ceased. The molten material front will indeed reach the free surface by thermal diffusion however at the same time a solid wall forms around the central melt region forming an effective aperture . The solidified, circularly symmetric aperture (‘nozzle’) which forms provides the high directionality to the molten metal droplet as it travels towards the receiversubstrate.
A special case of interest for LIFT printing is Aluminum. It is considered an excellent candidate for metallization of semiconductor surfaces and preferred over copper which tends to reduce excitons life time. Despite its importance there is yet no direct-write method available for printing aluminum tracks or micro-structures. One reason for this is the extremely high reactivity of aluminum in the micro/nano scale. The TIN-LIFT regime was shown to be effectively used for printing high resolution aluminum micro-structures on sensitive substrates such as plastic and paper. The droplet velocity and the incubation time for aluminum micro-droplets formation, in the TIN-LIFT regime have been determined  from the transient electrical signal which arises when the droplet lands on a sitable electrical test pattern. This method is capable of measuring the extremely fast dynamics of LIFTed droplets and has been exploited to the study of small volume droplets with supersonic velocities . The electrical properties of aluminum structures printed by laser forward transfer of molten, femto-litter droplets in air were also determined . Morphological analysis show that the resulting printed material is actually an aluminum/aluminum-oxide nano-composite. By controlling the printing conditions, and thereby the droplet volume and its jetting velocity and duration, it is possible to tune the electrical resistivity to a large extent. The material resistivity depends on the degree of oxidation which takes place during jetting and on the formation of electrical contact points as molten droplets impact the substrate. Evidence for these processes is provided by FIB cross-sections of such printed structures.
Recent results in LIFT printing of metal structures suggests that we are approaching an important milestone for functional, micron-scale, 3D printing [31,32,70,71,74,75]. It amounts to finally achieving high printing uniformity and high droplet positional accuracy while jetting from a rather large donor to receiver distance (a gap of few 100’s of microns is essential for realistic printing conditions of 3D objects) in ambient conditions [71,74]. Also, it was showed  how in a rather simple manner, using a couple of metals having a slight compositional difference, it is possible to print complex 3D structures (also free standing parts) with one of the metals serving as sacrificial material. It relies on the fact that one of the metals couple is made slightly more anodic which makes it an ideal sacrificial material as it can easily be removed afterwards in a galvanic bath. The close similarity in material properties (mechanical and thermal) of the more anodic material with the base material, makes them an ideal couple (structural/sacrificial metal couple) for 3D buildup of complex structures. We have also described recently a new method, Laser Induced Self Alloying (LISAT), by which LIFT printing of alloys, or more generally of composite materials, is carried out in a rather simple way starting from a pure metals, multi-layer donor structure. As a specific example we demonstrate self-alloying of copper and silver. This is a case of interest which we have used for the generation of free standing, 3D micron-scale structures.
The laser source is a passive Q-switch laser with wavelength of 532 nm and is based on the second harmonic of a Nd:YAG (Teem Photonics, model Power Chip). This laser has a pulse width of 400ps with maximal pulse energy of 30µJ. For power control of the laser an Acousto-optics-modulator (AOM) (Gooch&Housego, model AOMO-3080) is used. The scanning of the laser’s spot is done with a fast scanning mirror where a relay optics arrangement keeps the chief central ray of the beam on the same position at the entrance of the objective, independently of the incidence angle. This configuration permits monitoring of the process using the same objective for imaging purpose. The AOM switching (On/Off) is synchronized with the scanning mirror assuring control of the printing position on the donor. A zoom-beam-expander serves for tuning the spot size (four sigma) from d = 4µm to 32µm using an x10 objective.
The receiver holder has a hole to permit process monitoring using a bottom microscope. This holder is placed on an XYZ motorized stage for accurate translation. This configuration provides in situ monitoring of the printing results and supports the search for best working window. The donor and the receiver holders are both controlled by XYZ motorized stage. A high resolution (1µm) distance meter measures the relative distance to the receiver and by calibration of the donor distance to the receiver with accurate mechanical shims, we can also determine the exact gap between the donor and the receiver. Both holders are connected to tilt plates to permit alignment of the donor and the receiver to possess high parallelism. This mechanical setup allows us to achieve gap tuning from 5µm up to 1mm with a resolution of 1µm. The setup sketch described in the supplementary information of the reference .
2.2 Printing algorithm
LIFT jetting of a single metal droplet forms an opening in the metal donor layer which is surrounded by an extended heat-affected zone (HAZ) (Fig. 5). The diameter of the HAZ (DHAZ) determines the minimal distance to the next jetting spot. The size of the opening and HAZ range reflects the transient thermo-mechanical processes involved in droplet formation and jetting. The HAZ is therefore taken into consideration in the printing recipe in order to maintain high print quality and also to optimize the utilization of the printable metal layer. In the current case, where sub-nano-second pulses and thin metal donors are used, a step size on the order of the laser spot size suffices to avoid HAZ related effects on neighboring spots. Specifically, for a 22µm spot we have found the minimal step to be DHAZ = 30µm.
The fabrication of the metal structure requires jetting of overlapped metal droplets (Fig. 6). The printing recipe consists of dividing the pattern into N square cells of area DHAZ2 each. With the donor held at a fixed position, we first print one droplet per each cell, then we proceeded to jet droplets at a fixed distance dx = dy = DHAZ/Kcell where Kcell is an integer in the case of an equal distribution along the rows and columns (see Fig. 6(a) and Fig. 6(c) where each single colored dot represented a droplet). There is a total of Kcell2 droplets per unit cell and this defines a single layer whose thickness is determined by droplet volume and by the overlap. To build up thick structures the same recipe can be repeated over and over again. An example of the printing method is shown in Fig. 6. The pattern shape to be printed is shown in Fig. 6(a), then various print densities can be employed where the density is set by the droplets overlap defined by Kcell. Figure 6(c)-6(e) describes different print recipes with various Kcell values. Each dot indicates a single laser pulse position, which is also the printed droplet nominal position. The dots color indicates donor position. After an entire set of droplets has been printed from the static donor (all indicated with the same color), the donor is translated to a new position and the arrya of droplets is printed again (indicated now with a different color). The complete the printing plan amounts to Kcell2 steps of donor movements (this amounts to Kcell2 different colors in the drawing).
2.3 Three dimensional printing
In order to print 3D objects we follow the general principles which are being used for 3D printing of polymeric materials. The process starts with the part design using a computer aided design (CAD) software tool. We have used an STL format which consists of “2D” slices of the 3D structure serving for layer by layer deposition of the print material until the final 3D part is achieved. In principle printing each layer amounts to 2D printing as shown in Fig. 6. Figure 7 depicts another example, that of a printed cone like structure. Following a CAD design step an STL file is generated with equal slice thicknesses (see Fig. 7(b)). The print plan consists of 19 slices (each layer is denoted by a specific color - Fig. 7(b)). The print outcome is shown in Fig. 7(c)-7(f) and in Visualization 1. The topography was measured by 3D white light interferometer microscope (Bruker, 3Dcontour). The radius of cone base is 250µm and the cone height is 60 µm. We should note that the thinnest slice possible in LIFT printing is determined by both the single droplet thickness and by the degree of droplets overlap. When LIFT printing copper (or copper alloy) structures a typical minimal layer thickness is on the order of ~3.5µm. The printed layer thickness can be controlled to some extent by tuning print parameters, e.g. by modifying the droplet overlap print plan. We note that a Z-resolution on the order of ~3μm is far better than what can be obtained by other 3D metal printing methods (e.g., by selective laser sintering of metal powders). The main drawback of the method is the roughness with stanrdard deviation of <2µm .
3. Few examples of specific 3D structures
LIFT printing of metal and non-metal complex 3D structures is expected to serve a rather large number of applications in diverse fields, for example, printed micro-electrode arrays for neural research [76,77], photonic devices [78,79], biomedical  and micro-mechanical devices [81,82], micro-batteries [83,84] and more. In what follows we will present several 2D and 3D printed metallic structures to exemplify LIFT printing potential. For examples 3.1, 3.2, 3.4 and 3.5 we used donor coated with a layer of 500nm of copper and laser pulse fluence of 0.8 J/cm2. For example 3.3 we used donor coated with a layer of 500nm of gold and laser pulse fluence of 0.95J/cm2.
3.1 An array of high aspect ratio metal pillars
In Fig. 8 an array of LIFT printed high aspect ratio copper pillars is depicted. Each pillar is made up from 200 copper droplets accurately piled up one on top of the other. Pillars were chosen to demonstrate of the inherent accuracy of TIN-LIFT. Metal pillars of a few micron diameter and an exceptionally large aspect ratio (AR>>10) could find their use many applications. We should also note that in principle each single pillar in the array can have its own special geometry, a specific height, width and inclination . Also, one can fine tune the physical characteristics of the pillars by locally changing the type of metal which is being printed (or alloy composition). Such a versatility in fabrication is very unique when considering current micron-scale fabrication methods (e.g. lithography + electroplating).
3.2 High surface area, interdigitated microstructures
Printed metallic micro-structures with a high surface area should be useful for e.g. micro-batteries and plasma cell displays as well as for sensing applications. Figure 9 depicts a printed micron-scale, interdigitated (ID), metal structure. The deposited digits are 25µm wide and 170µm thick. Such a high aspect ratio of the printed lines is easily made possible with TIN-LIFT. The surface roughness (see Fig. 9(c)) and bulk porosity can be controlled to a large extent by choosing a suitable print recipe.
Such micro-structures can also serve for the fabrication of plasma based illumination cells. In Fig. 10, we connected the ID metal structure to a high voltage source using two metal micro-probes and monitored the resulting effect under an optical microscope. When a high voltage (300V, 1kHz, 10% duty cycle) was applied, we observed a continuous, high brightness, blue light emission (Fig. 10(b), Visualization 2). It is clear that other, more suitable metals will be needed for efficient and long term operation of such plasma micro-cells. Nevertheless, the point we want to make is that printing ID metal structures of a high-aspect ratio, can find its use in different applications given the advantage provided by direct digital printing.
3.3 Conformal, laser micro-cladding of 3D parts
Local laser cladding of mechanical parts is of considerable industrial interest as demonstrated by OPTOMEC’s LENS technique . LENS involves metal powder injection via a nozzle towards the part surface where it is locally laser melted to provide surface cladding. The TIN-LIFT method can be used for a similar target however on a much finer scale and in normal atmospheric conditions. Relying on the high directionally of the jetting process and fine (~micron scale) droplets, it allows to coat micron-scale features on complex geometries. More generally, local plating at the micron-scale is currently a multi-step process involving several lithographic and plating steps. The TIN-LIFT coating process involves a single step only. We show below (Fig. 11) an example of how a gold layer is being deposited by TIN-LIFT on a Nitinol shape-memory metal part.
3.4 Printing of 3D micro-mechanical metal parts
Another potential application is printing of 3D micro-mechanical metal parts. Figure 12 shows TIN-LIFT printing a ‘micro-gear’ type of structure made of a copper-silver alloy. The donor is a bi-layer of copper and silver with a thickness ratio which yields a print structure with a composition of Cu98%/Ag2% . The printed gear-like structure is 400µm wide and the finest metal feature resolution is 20µm. Printing on an appropriate sacrificial material (a dissolvable polymer, or a selectively etchable metal) which can then be selectively removed is a reasonable and adequate post-process which will allow gear functionality.
3.5 Printed interconnects
Providing electrical interconnects via through holes is a well known challenge currently addressed typically by a few step process involving lithography, electroplating and etching. Direct deposition of metal droplets into the via hole in order to form the interconnect line should be a most welcome alternative. TIN-LIFT with its high jetting directionality makes it possible to deposit contacts also into 100’sμm deep holes. Figure 13 exemplifies micron scale, direct metal printing for electrical interconnects in a flexible foil. To demonstrate the printing capabilities we have printed our company logo through a 300µm wide blind via in an epoxy laminate which is 150µm thick. The logo which was directly printed on the bottom copper pad has its finest features on the order of 10µm. The jetting took place from a distance of 300µm with no noticeable loss of resolution. With such high print resolution and distance jetting one can appreciate the potential of TIN-LIFT in providing metal interconnects also for smaller diameter via holes, potentially <100μm.
Digital jetting of femto-liter, molten metal droplets is made possible with LIFT. However, this method was impaired so far by the requirement to keep the distance (gap) between the donor and the receiver substrate very small. To obtain reasonable droplet positional accuracy typically required a gap on the order of 30μm or less. This made it quite impractical for adoption in industrial manufacturing, and kept it within the realm of research laboratories .
We have demonstrated [69–71] how this limitation could be alleviated using sub-nano-second laser pulses and thicker donor layers which gives highly directional droplet jetting due to a self-induced nozzle (TIN) formation effect. We termed this printing regime TIN-LIFT and have shown how it allows accurate and stable jetting of femto-droplets from various metal donors and alloys while keeping a large gap, in excess of 300μm.
Digital printing of molten metal droplets has a clear advantage over other printing methods due to the rapid solidification upon droplet landing which overcomes wetting related printing issues such as spilling, spreading or fragmentation. For example it is specifically beneficial for the printing of ultra-high aspect ratio structures and can also serve to locally tune the printed material density by controlling the porosity. The examples which we have presented of TIN-LIFT printed 3D metal structures exemplify its potential benefits to a wide range of applications. The LIFT printing technology seems to approach an important milestone. What makes this happen is the high printing uniformity and positional accuracy while still jetting from a large donor to receiver distance. In many cases this can still be done in an ambient atmosphere without imparing the print properties.
Printing of metals will play a major role in the 3D technology, as most contemporary 3D printing methods rely on polymeric materials which lack the electrical, thermal and mechanical properties required for functional device manufacturing. On the other hand, metal printers based on selective sintering of powders, lack the multi-material dimension and the resolution which our method provides. Digital LIFT printing of complex, 3D, multi-material, functional structures can realize the vision of a micron-scale additive manufacturing technology.
There is much work to be done to further improve and expand the capabilities of this printing method. While there is already a rather large number of LIFT printed metals (the simple fabrication of metal donor has encouraged testing of different metals), there is certainly a need to increase the material palette to include a larger span of pure metals and alloys. Demonstration of novel digital materials printed by LIFT, either composite materials, graded structures or meta-materials can further promote its acceptance and encourage further development also towards printed fubctional micro-devices. There is still much research work to be done in order to better understand and control the physical and morphological properties of the printed materials.
This project has received funding from the OCS (Office of Chief Scientist) of Israel; Project No. 51697, “Micrometer scale, 3D Functional Printing”.
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