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Presents information on a study which investigated the dynamics of laser-induced vapor bubbles to understand the basic mechanism of cavitation erosion. Experimental setup; Details on the bubble dynamics of liquid microjet impact; Emission and effect of the acoustic transient; Conclusions.

Among the additive manufacturing techniques, laser-induced forward transfer addresses the challenges of printing thin films in solid phase or small volume droplets in liquid phase with very high resolution. This paper reviews the physics of this process and explores the pros and cons of this technology versus other digital printing technologies. The main field of applications are printed electronics, organic electronics and tissue engineering, and the most promising short terms ones concern digital laser printing of sensors and conductive tracks. Future directions and emerging areas of interest are discussed such as printing solid from a liquid phase and 3D digital nanomanufacturing. [ABSTRACT FROM AUTHOR]

Abstract: This paper deals with transfer induced by laser of thin layers of a conducting polymer, the poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), for applications in plastic electronics. This relatively simple technique of direct writing offers the ability to make surface micro-patterning by localized deposits of material. The study of the various mechanisms (ablation, transfer and deposit) has been carried out according to different conditions of irradiation: wavelength (from ultraviolet to infrared radiation), pulse duration (nanosecond and sub-nanosecond) and fluence. The morphology of the transferred patterns has been analyzed by optical microscopy and scanning electronic microscopy. Our objective is to understand the different mechanisms involved in the process in order to optimize it in terms of geometrical resolution while preserving the properties of the transferred material. [Copyright &y& Elsevier]

Highlights • A laser-induced forward transfer (LIFT) strategy combining quasi-continuous (QCW) and femtosecond (fs) lasers is successfully applied for high resolution printing from a 1 µm copper donor film. • Influences of copper film temperature, and especially diameter of the melted metal area, on the printing dynamics are revealed. • By simply adjusting the synchronization between the QCW and fs pulses, droplets with different shapes are printed. The reproducibility is demonstrated by printing two-dimensional arrays. • Double-pulse LIFT prints debris-free microstructures with controllable dimensions. Abstract Laser induced forward transfer process can be implemented in a double-pulse scheme where a solid thin film deposited on a transparent donor substrate is irradiated by two synchronized lasers. In a recently demonstrated methodology, a long pulse is first applied to melt the film and an appropriately delayed ultrashort laser pulse initiates material transfer in the liquid phase toward a receiver substrate. This provides a versatile method to print high-resolution (<2 µm) patterns with a long working distance (>40 µm). In this paper we focus on the study of the dynamical aspects associated with these printing performances. The temperature evolution of the thin copper film during irradiation with a quasi-continuous wave (QCW) pulse is calculated. By combining the calculations with time-resolved imaging experiments, we reveal the influence of the copper film temperature and molten metal diameter on the ejection dynamics. Characterization of the transferred materials shows that the delay between the two laser pulses is a control parameter for the shape and volume of the printed structures. This is finally exploited to demonstrate high-precision printing of different debris-free microstructures onto a Si receiver substrate set as far as 60 µm away from the donor film. [ABSTRACT FROM AUTHOR]

Highlights: [•] A silver-nanoparticles ink is transferred by laser using LIFT at high speed. [•] Multi-jet formation is investigated with a time-resolved imaging technique. [•] Laser pulses separated by 2μs and 25μm lead to stable jets. [•] Well-defined, 16μm droplets are printed at a rate of 500,000 droplets/s. [Copyright &y& Elsevier]

Abstract: Functional laser printed Organic Thin Film Transistors (OTFTs) have been achieved from multilayer substrates composed with semiconductor and electrodes. The p-type copper phthalocyanine (CuPc) was used to form the active layer. Different kinds of metallic materials were used for source and drain electrodes. Multilayer donor substrates were prepared by the successive depositions of materials by either thermal evaporation under vacuum or laser printing. The materials were transferred together in a single step onto a receiver substrate by laser pulses in the picosecond regime. The latter substrate formed the gate and the dielectric of the transistor. The results are compared with the step-by-step laser printing process, where electrodes and organic layer were successively printed from two different donor substrates. The multilayer laser printing reveals an improvement of the performances of the OTFT devices. [Copyright &y& Elsevier]

Abstract: The laser-induced forward transfer technique has been performed on thin layers of conducting organic materials for applications in plastic micro-electronics. This process is a promising alternative for fabrication of organic electronic components on flexible supports when usual techniques, such like ink-jet printing, cannot be considered. For example, when the organic material has no solubility properties or when complex architectures are needed. Experiments on the influence of pulse duration (nanosecond and picosecond) and wavelength on a large range of fluences have been proceeded using different lasers. An optimization of the process has been carried out by inserting a thin layer of absorbing metallic material between the substrate and the organic film. The advantage of this technique is to preserve organic layers from being damaged by thermal and photochemical effects during the interaction. The morphology and thickness of the deposit have been investigated by optical and scanning electronic microscopy. This experimental study is supplemented by electrical characterization of the deposits. [Copyright &y& Elsevier]

Organic thin-film transistors have been fabricated using laser-induced forward transfer as spatially resolved laser-printing method. Using this technique, source and drain electrodes were deposited from silver nanoparticle ink and the copper phthalocyanine (CuPc) was used to form the active layer. Both kinds of materials were transferred from a donor substrate onto a receiver substrate upon irradiation with laser pulses in the picosecond regime. The latter substrate formed the gate and the dielectric of the transistor. Electrical characterizations showed that the transistors are fully operative, showing well-defined linear and saturation regimes in the I-V curves. [ABSTRACT FROM AUTHOR]

We show that high-quality pentacene (P5) thin films of high crystallinity and low surface roughness can be produced by pulsed laser deposition (PLD) without inducing chemical degradation of the molecules. By using Raman spectroscopy and X-ray diffraction measurements, we also demonstrate that the deposition of P5 on Au layers result in highly disordered P5 thin films. While the P5 molecules arrange within the well-documented 1.54-nm thin-film phase on high-purity fused silica substrates, this ordering is indeed destroyed upon introducing an Au interlayer. This observation may be one explanation for the low electrical performances measured in P5-based organic thin film transistors (OTFTs) deposited by laser-induced forward transfer (LIFT). [ABSTRACT FROM AUTHOR]

Thin solid pixels made of Ag/PMMA stacks have been fabricated by laser-induced forward transfer (LIFT), to be tested as thin film microcapacitors in organic electronics applications. The square-shaped laser-printed pixels have a lateral size of ∼350 μm, and the thickness of the dielectric film was varied between 100 and 1500 nm. The pixels were deposited on electrode structures made by LIFT printing of silver nanoparticles ink and paste. Optimal printing conditions led to the fabrication of microcapacitors with typical capacitance in the pF range, tuned by changing the properties of the multilayered structure (e.g. pixel size and/or thickness of the dielectric). Their stability was also investigated over time. We discuss on the morphological and electrical properties of such laser-printed structures, with respect to the impact resistance of the polymer and its suitability for the LIFT process. [ABSTRACT FROM AUTHOR]

Carbon nanowalls (CNW) are two-dimensional interconnected graphitic nanostructures that have a few μm in length and height, reaching typical thicknesses of a few tens of nm. We present results on such layers synthesized in a low pressure argon plasma jet, injected with acetylene and hydrogen, on transparent substrates (quartz) heated at 600 °C, without catalyst. Thermogravimetric analysis reveals that the CNW are stable up to 420 °C in air, and Raman spectroscopy investigations highlight their graphene-like structure. Finally, using a pulsed Nd:YAG laser device (355 nm, 50 ps), we show that 2D-arrays of CNW (pixels and lines) can be printed by laser-induced forward transfer (LIFT), preserving their architecture and structure. Electrical measurements on 1 μm thick CNW demonstrate typical values in the range of 357.5–358.4 Ω for the samples grown on Au/Cr electrodes, and in the range of 450.1–474.7 Ω for the LIFT printed lines (under positive, negative, and neutral polarization; 1 kHz–5 MHz frequency range; 500 mV and 1 V, respectively). Their morphology is highlighted by means of optical and electronic microscopy. Such structures have potential applications as soft conductive lines, in sensor development and/or embedding purposes. [ABSTRACT FROM AUTHOR]

Following the standard Sonogashira cross-coupling conditions, the reaction between 1,4-diiodo-2,5-bis(octyloxy)benzene with 2.2 equiv. of 1-ethynylpyrene afforded a yellowish bis -pyrene derivative, namely 1,4-bis(octyloxy)-2,5-bis(ethynylpyrene)benzene , that exhibits typical fluorescence and semiconducting properties. Thermal analysis studies are discussed, with emphasis made on the oxidative decomposition and thermal effects. Further on, thin films have been grown by vacuum thermal evaporation, on silicon and quartz substrates. The temperature's influence on the thin film's morphology and electrical properties is investigated. Finally, top-contact thin film transistor configurations are presented and the influence of substrate temperature is discussed with respect to the semiconducting properties. [ABSTRACT FROM AUTHOR]

The use of laser-based processing is presented here for the transfer of azo-derivatives, for optoelectronics assembly applications. Laser-printing techniques are also adequate tools for rapid prototyping of diverse materials, since they avoid the usage of solutions, moulds, lithography masks, etc. Here, we present a study on the laser-induced forward transfer (LIFT) and printing of micrometric-sized pixels (350 μm × 350 μm), by using matrix-assisted pulsed laser evaporation (MAPLE) deposited thin film donors. Due to their particular optical properties, i.e. second harmonic generation, optical limiting and all-optical poling, and with applications in optoelectronics and sensor development, azo-dyes have been intensively studied in bulk or as thin films. The influence of a metallic dynamic release layer (DRL) during LIFT is investigated. [ABSTRACT FROM AUTHOR]

We present results on a newly synthesized bis -pyrene compound that, besides the typical fluorescence, also exhibits semiconducting properties. Thin films have been grown by vacuum thermal evaporation on oxidized silicon and on transparent quartz substrates. Micrometric-sized pixels have subsequently been printed by laser-induced forward transfer (LIFT), in air and at low pressure (90 mbar), by using a Nd:YAG laser source (355 nm, 50 ps pulse duration) to produce functional organic thin film transistors (o-TFTs). Top-contact (TC) configurations are emphasized, and the influence of the pressure and laser fluence during the LIFT procedure is discussed. [ABSTRACT FROM AUTHOR]

The printing of multilayered pixels using single picosecond laser pulses is investigated by using an improved laser-induced forward transfer (LIFT) technique. Micrometric low-k dielectric capacitors of hybrid organic polymer (parylene-C) and silver thin films have been transferred on laser-printed pads of annealed silver nanoparticles (AgNP) paste. This printing technique allows to design and print directly on virtually any substrate, in order to make the capacitors directly interface with other components, such as transducers or sensing devices, and which are further used for improving or complementing the characteristics of these devices. This study focuses on the use of the optimized LIFT technique using a double mask setup, i.e. smart beam shaping (SBS) in the picosecond laser pulse regime. The purpose is to optimize the energy repartition of the Gaussian beam on the thick multilayer donor by using a beam profile with increased intensity at the edges and low intensity in the center. This allows to keep the incoming irradiation fluence on the donor layer as low as possible in the centre area, and thus preventing the multilayer pixels from damage induced by laser irradiation. Electrical investigations of the SBS-LIFT printed micro-capacitors demonstrate that they are fully functional and stable over time, with capacities in the pF range. [ABSTRACT FROM AUTHOR]

Highlights: [•] We studied the laser-induced forward transfer of thin layers of semiconducting PQT-12. [•] PEDOT:PSS was laser-printed to act as conductor in the transistor configuration. [•] Optimization by reducing the background pressure and increasing the films thickness. [•] We fabricated polymeric thin-film transistors devices using the LIFT technique. [•] Transistor performances with mobilities up to 0.02cm2 V−1 s−1 were obtained. [ABSTRACT FROM AUTHOR]

Abstract: Organic thin-film transistor (OTFT) devices were achieved using the laser-induced forward transfer technique. As p-type organic semiconductor, distyryl-quaterthiophene (DS4T) was vacuum-deposited on a donor substrate and transferred with picosecond laser pulses on Si/SiO2-based receiver substrates to form an organic active layer. To avoid laser damage of the organic thin film, a UV-sensitive aryltriazene polymer as a sacrificial layer was used. The polymer layer, deposited on the donor substrate prior to the organic layer deposition, has high absorption at the laser wavelength and does not contaminate the printed pixels. The DS4T pixels printed on receiver substrates have well defined morphological properties as shown by atomic force microscopy and scanning electronic microscopy. OTFT devices were characterized in top- and bottom-contact configurations using thermally evaporated gold lines as source-drain electrodes. DS4T pixels printed as active layer for charge transport not only issue mobility values comparable to DS4T layers prepared by vacuum evaporation but also a relative electrical stability over time. [Copyright &y& Elsevier]

Abstract: Laser-induced forward transfer (LIFT) has been used to deposit pixels of an organic semiconductor, distyryl-quaterthiophenes (DS4T). The dynamics of the process have been investigated by shadowgraphic imaging for the nanosecond (ns) and picosecond (ps) regime on a time-scale from the laser iradiation to 1.5μs. The morphology of the deposit has been studied for different conditions. Intermediate sacrificial layer of gold or triazene polymer has been used to trap the incident radiation. Its role is to protect the layer to be transferred from direct irradiation and to provide a mechanical impulse strong enough to eject the material. [Copyright &y& Elsevier]