Abstract
Laser-induced forward transfer is a promising method for 3D printing of various materials, including metals. The ejection mechanism is complex and depends strongly on the experimental parameters, such as laser fluence and donor layer thickness. However, the process can be categorized by the physical condition of the ejected material, i.e., the donor layer is transferred in liquid phase or the material is transferred as a ‘pellet’ in solid phase. Currently, solid-phase transfer faces several problems. Large shearing forces, occurring at the pellet perimeter during transfer, limit the similarity between the desired pellet shape and the deposited pellet shape. Furthermore, the deposited pellet may be surrounded by debris particles formed by undesired transferred donor material. This work introduces a novel approach for laser-induced forward transfer of variable shaped solid-phase pellets. A liquid-crystal spatial light modulator (SLM) is used to apply grayscale intensity modulation to an incident laser beam to shape the intensity profile. Optimized beams consist of a high fluence perimeter around an interior characterized by a lower fluence level. These beams are used successfully to transfer solid-phase pellets out of a 100-nm Au donor layer using a single laser pulse. The flexibility of the SLM allows a variable desired pellet shape. The shapes of the resulting deposited pellets show a high degree of similarity to the desired shapes. Debris-free deposited pellets are achieved by pre-machining the donor layer, prior to the transfer, using a double-pulse process.
Highlights
IntroductionLaser-induced forward transfer (commonly abbreviated to LIFT) is a direct-write technique that allows the selective transfer of many materials on a micrometer scale [1,2,3,4,5], including liquids [6] and living cells [7, 8]
Laser-induced forward transfer is a direct-write technique that allows the selective transfer of many materials on a micrometer scale [1,2,3,4,5], including liquids [6] and living cells [7, 8]
The process can be categorized by the physical condition of the ejected material, i.e., the donor layer is transferred in liquid phase or the material is transferred as a ‘pellet’ in solid phase
Summary
Laser-induced forward transfer (commonly abbreviated to LIFT) is a direct-write technique that allows the selective transfer of many materials on a micrometer scale [1,2,3,4,5], including liquids [6] and living cells [7, 8]. In the LIFT process, a thin film serves as a donor material that is to be transferred, which is referred to as the donor layer, see Fig. 1 A pulsed laser is focused on the carrier–donor interface to induce the necessary energy to transfer the donor material onto a receiving substrate, referred to as the receiver. The latter is separated from the donor with a typical gap size in the order of 0–100 lm. The a b part of the donor layer that is transferred in solid phase is usually referred to as a ‘pellet.’
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