Laser-induced forward transfer (LIFT) of water soluble polyvinyl alcohol (PVA) polymers for use as support material for 3D-printed structures

The additive microfabrication method of laser-induced forward transfer (LIFT) permits the creation of functional microstructures with feature sizes down to below a micrometre [1]. Compared to other additive manufacturing techniques, LIFT can be used to deposit a broad range of materials in a contactless fashion. LIFT features the possibility of building out of plane features, but is currently limited to 2D or 2½D structures [2–4]. That is because printing of 3D structures requires sophisticated printing strategies, such as mechanical support structures and post-processing, as the material to be printed is in the liquid phase. Therefore, we propose the use of water-soluble materials as a support (and sacrificial) material, which can be easily removed after printing, by submerging the printed structure in water, without exposing the sample to more aggressive solvents or sintering treatments. Here, we present studies on LIFT printing of polyvinyl alcohol (PVA) polymer thin films via a picosecond pulsed laser source. Glass carriers are coated with a solution of PVA (donor) and brought into proximity to a receiver substrate (glass, silicon) once dried. Focussing of a laser pulse with a beam radius of 2 µm at the interface of carrier and donor leads to the ejection of a small volume of PVA that is being deposited on a receiver substrate. The effect of laser pulse fluence , donor film thickness and receiver material on the morphology (shape and size) of the deposits are studied. Adhesion of the deposits on the receiver is verified via deposition on various receiver materials and via a tape test. The solubility of PVA after laser irradiation is confirmed via dissolution in de-ionised water. In our study, the feasibility of the concept of printing PVA with the help of LIFT is demonstrated. The transfer process maintains the ability of water solubility of the deposits allowing the use as support material in LIFT printing of complex 3D structures. Future studies will investigate the compatibility (i.e. adhesion) of PVA with relevant donor materials, such as metals and functional polymers. References: [1] A. Piqué and P. Serra (2018) Laser Printing of Functional Materials. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA. [2] R. C. Y. Auyeung, H. Kim, A. J. Birnbaum, M. Zalalutdinov, S. A. Mathews, and A. Piqué (2009) Laser decal transfer of freestanding microcantilevers and microbridges, Appl. Phys. A, vol. 97, no. 3, pp. 513–519. [3] C. W. Visser, R. Pohl, C. Sun, G.-W. Römer, B. Huis in ‘t Veld, and D. Lohse (2015) Toward 3D Printing of Pure Metals by Laser-Induced Forward Transfer, Adv. Mater., vol. 27, no. 27, pp. 4087–4092. [4] J. Luo et al. (2017) Printing Functional 3D Microdevices by Laser-Induced Forward Transfer, Small, vol. 13, no. 9, p. 1602553

Experimental investigation of the jet-on-jet physical phenomenon in laser-induced forward transfer (LIFT)

Understanding the physics behind the ejection dynamics in laser-induced forward transfer (LIFT) is of key importance in order to develop new printing techniques and overcome their limitations. In this work, a new jet-on-jet ejection phenomenon is presented and its physical origin is discussed. Time-resolved shadowgraphy imaging was employed to capture the ejection dynamics and is complemented with the photodiode intensity measurements in order to capture the light emitted by laser-induced plasma. A focus scan was conducted, which confirmed that the secondary jet is ejected due to laser-induced plasma generated at the center of the laser spot, where intensity is the highest. Five characteristic regions of the focus scan, with regards to laser fluence level and laser spot size, were distinguished. The study provides new insights in laser-induced jet dynamics and shows the possibility of overcoming the trade-off between the printing resolution and printing distance

Printing of complex free-standing microstructures via laser-induced forward transfer (LIFT) of pure metal thin films

A combined approach of laser-induced forward transfer (LIFT) and chemical etching of pure metal films is studied to fabricate complex, free-standing, 3-dimensional gold structures on the few micron scale. A picosecond pulsed laser source with 515 nm central wavelength is used to deposit metal droplets of copper and gold in a sequential fashion. After transfer, chemical etching in ferric chloride completely removes the mechanical Cu support leaving a final free-standing gold structure. Unprecedented feature sizes of smaller than 10 μm are achieved with surface roughness of 0.3 to 0.7 μm. Formation of interfacial mixing volumes between the two metals is not found confirming the viability of the approach

Data supporting journal publication 'Time-resolved imaging of flyer dynamics for femtosecond laser -induced backward transfer of solid polymer thin films'

We have studied the transfer regimes and dynamics of polymer flyers from laser-induced backward transfer (LIBT) via time-resolved shadowgraphy. Database contains images and schematics of the used setup to collect this data. Data collection: Time-resolved shadowgraphy with CCD camera between 18 April 2016 and 23 April 2016.</span

Single-pulse multiphoton polymerization of complex structures using a digital multimirror device

We present a rapid technique for the patterning of complex structures with ~2µm resolution via multiphoton polymerization, through use of a single ultrashort pulse in combination with the spatial intensity modulation possible from a digital multimirror device. Sub-micron resolution has been achieved through the use of ten consecutive pulses

Sub-diffraction limit laser ablation via multiple exposures using a digital micromirror device

SEM images of resulting machined patterns Matlab scripts used to enhance SEM images Data pertains to Applied Optics paper &quot;Sub-diffraction limit laser ablation via multiple exposures using a digital micromirror device&quot;</span