The invention is from the field of additive manufacturing. Specifically, the invention is from the field of laser printing. More specifically the invention is from the field of laser printing of metals, metal oxides and metal composites.
Publications and other reference materials referred to herein are numerically referenced in the following text and respectively grouped in the appended Bibliography, which immediately precedes the claims.
While 2D and 3D printing of polymeric materials is prevalent, metals are indispensable for structural support, heat dissipation and electrical conductivity. Extensive research to allow additive manufacturing (AM) of metals has resulted in a range of techniques, the most established of them are selective laser melting (SLM) and electron beam melting (EBM). However, these methods are not suitable for the microscale regime because they are limited by the size of the metal particles used and heat dissipation to minimum line width of tens of microns.
Several attempts have been made in the last few years by commercial companies to develop metal printing technologies for the sub cubic millimeter range for micro-electronic applications. Some of these attempts utilize inkjet methods for doing so. To date, none of them have produced a product that can work in a production environment in the field and none of them are aiming at producing parts in the size range of several microns to several dozen microns; because their droplets are 10's of microns in diameter.
It is therefore a purpose of the present invention to provide a laser printing method capable of producing very fine (˜1 μm feature size) single metal or multiple metals structures.
It is another purpose of the present invention to provide a laser printing method capable of producing single metal, multiple metals, metal oxides or alloys structures having good and homogenous structure with very fine surface roughness.
It is another purpose of the present invention to provide a laser printing method for providing improved finished material properties by combining nano-diamonds, nano-carbon particles, and similar nanoparticles with single metal or multiple metals structures.
Further purposes and advantages of this invention will appear as the description proceeds.
Presented in this application is a novel method for two-dimensional with controlled height and three-dimensional photo-thermal printing of metals, metal oxides, alloys, and metal composites to produce objects having predetermined shapes. The method comprises:
In embodiments of the method the laser is modulated using one of: a mechanical shutter, an optical chopper, and a device for controlling power delivered to the laser.
In embodiments of the method the metal ion solution comprises ions of at least one metal from the following families: transition metals, Alkali metals, Alkaline earth metals, post-transition metals, metalloids and lanthanides. In embodiments of the method the metals can be: copper, iron, platinum, aluminum, gold, silicon, tin and silver.
In embodiments of the method the metal ion solution comprises an aprotic polar solvent that could prevent oxidation of the formed metal structures such as: alkyl carbonates, esters, cyclic ethers, lactones, aliphatic ethers, amides, nitriles and sulfoxides.
In embodiments of the method the metal ion solution is provided on the substrate and previously deposited structure by one of:
In embodiments of the method, when the metal ion solution is provided by immersing the substrate in a bath containing the solution, the metal ion solution is added to the bath as the deposited metal structure grows in order to maintain the top of the printed object a threshold distance below a surface of the metal ion solution.
The method can be carried out using the following printing methods:
In embodiments of the method the substrate is not moved and the system comprises an optical system configured to move the focus of the modulated laser light in the X-Y-Z directions to continuously form new microbubbles on the previously deposited structure and directly attach reduced metal ions to the previously deposited structure as metal, metal oxide, alloy, or metal composite until the predetermined shape of the object has been produced.
In embodiments of the method nanoparticles are added to the metal ion solution and incorporated into the printed structure by being deposited together with the metal ions.
In embodiments of the method two or more metallic ions are present in the solution thus forming a structure composed of more than one metal, metal oxide and/or an alloy. In these embodiments the printed object can have a two-dimensional shape.
All the above and other characteristics and advantages of the invention will be further understood through the following illustrative and non-limitative description of embodiments thereof, with reference to the appended drawings.
The present invention uses inexpensive continuous wave (CW) lasers to promote directed thermal decomposition of metal ion solutions, leading to formation of 2D with controlled height and 3D metallic microstructures with a feature size of ˜1 micro-meter. The method allows incorporation of various nanoparticles (NPs) in the metallic microstructures, thus forming metal composites with superb mechanical, thermal and magnetic properties. Moreover, this method can be used for printing various metal combinations and fast vector printing that form more homogenous structures when compared to layer by layer printing. Because the materials used are solutions of metal ions, they are abundant, cheap and reusable. In embodiments of the invention, two or more metallic ions are present in the solution thus forming a structure composed of more than one metal and/or an alloy.
In the 2D laser-induced microbubble technique (LIMBT), a laser beam is focused on a dispersion of NPs. As the particles absorb the light and their temperature rises, vapor pressure from the surrounding medium increases until, eventually, a microbubble is formed. Then, two types of convective flow occur: natural and Gibbs-Marangoni convection. Natural convection is a result of a temperature gradient between the top and bottom of the microbubble. As the hotter medium has lower density, it flows upwards. The Gibbs-Marangoni convection results from a surface-tension gradient within the dispersion. As the bottom of the microbubble has a lower surface tension than its upper part, the dispersion flows to the upper part of the microbubble. To compensate for these convections that stream the dispersion upwards, there is also flow toward the bottom of the microbubble. If the focal point is near the substrate, particles carried by the dispersion will be pinned to the bubble/substrate contact area.
If the focused beam is moved relative to the sample, migration of the microbubble and deposition of fresh material at the bubble/substrate contact area takes place. LIMBT has two main limitations: inconsistency in continuousness, and a minimum linewidth of ˜4 μm [Ref 2,3]. So far, continuous patterns have only been reported for soft oxometalates [Ref 3], while most studies show images that demonstrate non-continuous patterns [Ref 2] or do not address this issue.
The inventors of the present invention have previously found [Ref 1] that by modulating the laser beam (with mechanical or electrical means) to control the formation and destruction of the microbubble, continuous material deposition can be achieved from preformed nanoparticles. They have named this method modulated-LIMBT.
In modulated-LIMBT, when the laser is turned on, the laser energy is transferred to the microbubble, resulting in the expansion of the microbubble [Ref 3] and material deposition [Ref 4,5]. Once the laser is turned off, the microbubble rapidly collapses [Ref 3]. The inventors hypothesize that if the microbubble totally collapses, once the laser is turned on again, a new microbubble is formed at a new location which is determined by the stage movement. Depending on the modulation parameters (higher frequencies and/or lower duty cycles), the microbubble may shrink rather than totally collapse. In this case, the microbubble edges are detached from the deposited material and, once the laser is turned on, the microbubble follows the focus of the laser due to the Marangoni convection flow [Ref 3]. Either way, the pinning of the microbubble is avoided and better control over its size is achieved. An extended quantitative analysis of the dependence between modulation frequency and duty cycle with width and height of material deposition has also been carried out [Ref 1]. Comparison of
In the present invention the inventors show that in a similar way 2D and 3D printing of metals, oxides and alloys can be achieved without using preformed nanoparticles. When a laser is focused on a metal ion solution near a substrate, photo-thermal decomposition may occur. The metal ions are reduced and can directly attach to a previously deposited metal structure or form nanoparticles (NPs). These NPs will then move with the convection flows around the microbubble (that is also formed due to the exerted heat) and be deposited by pinning to its base. It is noted that the convection flows of the microbubble also serve to flow additional metal ions, and thus contribute to forming a steady and controllable deposition. As discussed above for 2D formations from preformed nanoparticles, a key element for receiving continuous features with high resolution in 2D and 3D from an ion solution is laser modulation. Without laser modulation, deposition can be uncontrollable. One can 2D or 3D print only very small elements (a few micrometers{circumflex over ( )}3) very slowly without modulation, before large bubbles appear that rip the forming structure.
There are several configurations that could be used to carry out 2D and 3D photo-thermal laser printing of metals and metal composites, but for clarity and simplicity only the system schematically shown in
The laser system 16 consists of a CW laser system attached to a microscope. Modulation of the CW laser is performed by mechanical means (mechanical shutter or an optical chopper) or electrical means (controlling the power delivered to the laser diode). The inventors have found that for the same parameters, all the types of modulation devices give similar results, but each instrument has a limited range of parameters. An objective lens system 14 (comprised of one or more lenses) focuses the laser light on the sample 12. In the work carried out various objective lenses (×10, ×20, ×40, ×50, ×60, ×100) have been employed. The microscope stage is computer-controlled and the experiments were recorded using a CMOS camera 18. The camera 18 and illumination source 20 are for research purposes only and can be omitted.
The metal ion solution can comprise ions of at least one any type of metal from the families: transition metals, Alkali metals, Alkaline earth metals, post-transition metals, metalloids and lanthanides.
The metal ion solutions can be deposited as droplets for printing small parts using a syringe (with surface tension holding them in place) or alternatively, the solution can be deposited in a bath with size varying according to the size of the required part. While using a bath for printing, solution droplets are added (by a syringe or tubes) whenever the printed object has reached below a threshold distance (that varies depending on solution concentration, ion type, laser intensity etc.) from the upper part of the solution. The structure being printed is always immersed in solution.
SEM images of an example of preliminary results for 3D iron oxide printing obtained by the inventors are presented in
These preliminary results were obtained using manual control over X/Y/Z axes (using a joystick connected to the controller, hence the diversity in thickness). Nonetheless, it is impressive to see that long (the inventors didn't try more than ˜300 μm) freestanding columns are formed, standing on a base that is just ˜1 μm in diameter.
There are two general methods for 2D with controlled height and 3D printing: layer by layer (LBL) printing and vector printing. The LBL method is the most common method for 3D printing. It requires separating the 3D image into multiple 2D layers and then printing each layer sequentially. Vector printing is the direct printing of 2D with controlled height and 3D lines that together form the 2D with controlled height or 3D shape. Such a method that combines direct ink writing with a focused laser that locally anneals printed metallic features “on-the-fly” was recently developed by the group of Jennifer Lewis from Harvard [Ref 6]. 3D pens also use the same concept.
One of the unique abilities of the present photo-thermal method is that both LBL and vector printing can be used. The advantage of vector printing over LBL printing is that it is faster and can form hanging structures without support.
It is pointed out that both three-dimensional and two-dimensional shape can be produced by depositing only one layer. The modulation parameters (frequency and duty cycle) for a set of stage velocities and laser powers could be varied to allow additional control over deposition characteristics such as height, width, continuity and density.
It is also noteworthy to point out that the structures obtained in the preliminary results described in the preceding paragraphs were created by vector printing. Vector printing combined with metal sintering also leads to a very smooth outer-layer.
Most of the ion solutions, e.g. copper, iron, platinum, aluminum, and gold, used by the inventors to date are very stable and have not shown degradation even after a few months. The exception is solutions of silver (that are known for their instability), which when exposed to light shows degradation in the form of a deposit. The sensitive ions are stored covered to prevent exposure to light.
The preliminary results carried out by the inventors to date strongly indicate that the feature size (defined as the X & Y dimension upon a short laser illumination without moving the stage) is controllable by adjusting laser power, modulation parameters and the focusing objective and can vary from 1 μm to 500 μm (see for example the “legs” in
Furthermore, advantage can be taken of the convection flows around the microbubble to incorporate nanoparticles that are added to the metal ion solution. Conceptually, any kind of nanoparticle could be added with controlled amounts by changing the ratio between the metal ions and nanoparticles. The nanoparticles could therefore be used to improve the properties of the metal.
It is important to distinguish between the photo-thermal (PT) method described herein and the previously reported laser-induced photo-reduction (PR) method [Ref 7,8] also known as two/multi photo reduction. While the laser-induced PR method has some common features with the present method, the PT method has several advantages since: The PR process requires expensive (>100K$) femto-second lasers to allow a multi-photon process, while the PT process can work with low intensity, continuous wave inexpensive lasers (potentially <10$).
A printer (3D and 2D) incorporating the photo-thermal method described herein could be used for the following applications:
Microelectronics:
Microelectromechanical systems (MEMS):
Medicinal devices:
Although embodiments of the invention have been described by way of illustration, it will be understood that the invention may be carried out with many variations, modifications, and adaptations, without exceeding the scope of the claims.
Filing Document | Filing Date | Country | Kind |
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PCT/IL2020/051118 | 10/27/2020 | WO |
Number | Date | Country | |
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62927707 | Oct 2019 | US |