Laser-induced forward transfer of high viscosity graphene inks

The potential to deposit minute amounts of material from a donor to an acceptor substrate at precise locations makes laser-induced forward transfer (LIFT) a frequently used tool within different research fields, such as materials science and biotechnology. While many different types of LIFT exist, each specialized LIFT application is based on a different underlying transfer mechanism, which affects the to-be-transferred materials in different ways. Thus, a characterization of these mechanisms is necessary to understand their limitations. The most common investigative methods are high-speed imaging and numerical modeling. However, neither of these can, to date, quantify the material deposition. Here, analytical solutions are derived for the contact-based material deposition by LIFT, which are based on a previously observed equilibrium state. Moreover, an analytical solution for the previously unrecognized ejection-based material deposition is proposed, which is detectable by introducing a distance between the donor and acceptor substrates. This secondary mechanism is particularly relevant in large scale production, since each deposition from a donor substrate potentially induces a local distance between the donor and acceptor substrates.

The development of rapid prototyping techniques for the fabrication of microelectronic structures has seen rapid growth over the past decade. In particular, laser-induced forward transfer (LIFT) is a non-lithographic direct-write technique that offers the advantages of high speed / throughput, high resolution, materials versatility, and substrate compatibility. Because of the high degree of control over size and shape of printed material, the development of a wide range of microelectronic components, including interconnects, antennas, and sensors, has become possible using LIFT. In this paper, we explore the use of LIFT to print various 3D microstructures including high aspect ratio micro pillars using high viscosity Ag nanopastes. In addition, we demonstrate the fabrication of interconnects via LIFT on RF switches that, after printing and subsequent curing, perform similarly to an analogous wire-bonded device.

Single-step printing of high-resolution, high-aspect ratio silver lines through laser-induced forward transfer

High-speed video (100 000 fps) is used to examine the behavior of silver nanoparticle suspensions ejected from a donor substrate during laser-induced forward transfer (LIFT) as a function of viscosity, donor film thickness, and voxel area. Both high-speed video and inspection of the post-transferred material indicate dramatic changes in the behavior of the fluid as the viscosity of the nano-suspensions increases from that of inks (∼0.01 Pa·s) to pastes (>100 Pa·s). Over a specific range of viscosities (90–150 Pa·s) and laser fluences (35–65 mJ/cm2), the ejected voxels precisely reproduce the size and shape of the laser spot. This LIFT regime is known as laser decal transfer or LDT. Analysis of the high-speed video indicates that the speeds of the voxels released by the LDT process do not exceed 1 m/s. Such transfer speeds are at least an order of magnitude lower than those associated with other LIFT processes, thus minimizing voxel deformation during flight and upon impact with the receiving substrate. Variation in the threshold fluence for initiating the LDT process is measured as a function of donor film thickness and transfer spot size. Overall, the congruent nature of the silver nanopaste voxels deposited by LDT is unique among non-contact digital printing techniques given its control of the voxel's size and shape, thus allowing partial parallelization of the direct-write process.

Laser-induced forward transfer (LIFT) and selective laser sintering (SLS) are two distinct laser processes that can be applied to metal nanoparticle (NP) ink for the fabrication of a conductive layer on various substrates. A pulsed laser and a continuous-wave (CW) laser are utilized respectively in the conventional LIFT and SLS processes; however, in this study, CW laser-induced transfer of the metal NP is proposed to achieve simultaneous sintering and transfer of the metal NP to a wide range of polymer substrates. At the optimum laser parameters, it was shown that a high-quality uniform metal conductor was created on the acceptor substrate while the metal NP was sharply detached from the donor substrate, and we anticipate that such an asymmetric transfer phenomenon is related to the difference in the adhesion strengths. The resultant metal electrode exhibits a low resistivity that is comparable to its bulk counterpart, together with strong adhesion to the target polymer substrate. The versatility of the proposed process in terms of the target substrate and applicable metal NPs brightens its prospects as a facile manufacturing scheme for flexible electronics.

Temporal distance, social distance and probabilistic distance are three basic dimensions of psychological distance. It has been proved that different kinds of psychological distance have similar effects on cognitive representations of events. In general, distant events are represented as high-level construals, whereas near events are represented as low-level construals. As events become more distant, the high-level construals become more influential in shaping preference whereas the low-level construals become less influential(Liberman, Trope, Stephan, 2007; Liberman, Trope, 2008; Trope, Liberman, 2010).This study investigates the effects of temporal, social and probabilistic distance on intertemporal choice and risky choice. We hypothesize that different kinds of distance have similar effects on intertemporal and risky choice, based on the assumptions that these three kinds of distance share the same nature as psychological distance, and that intertemporal choice and risky choice have common processes of option representation and weighting. When psychological distance increases, money magnitude as high-level construal becomes more influential while time and probability as low-level construals become less influential(Sagristano, Trope, Liberman, 2002; Trope Liberman, 2003). Therefore, participants in distant conditions would choose delayed and risky alternatives with larger monetary value.Experiment 1 investigated the effect of temporal distance on intertemporal and risky choices. Participants were told that they would participate in a visual experiment, but before that they needed to make an intertemporal choice as their rewards between "$50 immediately" and "$90 in 3 months"(experiment 1a), or between " $ 50 for sure" and " $ 200 with the probability of 20%"(experiment 1b). In near condition, the experiment would be conducted soon, and in distant condition the experiment would be conducted in 6 months.Experiment 2 investigated the effect of social distance. In near condition, participants would make choice for themselves, and in distant condition, for other people. Experiment 3 investigated the effect of probabilistic distance. In near condition, participants were told that they would participate in the experiment with 90%probability, and in distant condition, with 10% probability. The options of intertemporal choice and risky choice are similar to experiment 1. The results show that no matter what kind of distance was involved, there were more participants in distant condition who chose delayed or risky alternatives than those who did in near condition,which confirms the hypotheses.The similar effects of temporal, social and probabilistic distance on intertemporal and risky choices suggest that intermporal and risky choices share common psychological process, and these three kinds of distance are homogeneous psychological distance.

Conductive graphene inks have attracted extensive research interests for printed electronics due to the excellent electrical and mechanical properties of graphene. While the traditional organic solvents used for graphene inks will result in high environmental cost, environmentally friendly solvents are required for conductive graphene inks. In this work, we demonstrate a highly conductive aqueous graphene ink printed on a paper substrate using screen printing technique. The well-tuned rheological properties of the graphene ink enable the printed lines to achieve a high resolution as fine as 45 µm in width. After being dried at 70 °C and roller compressed, the printed graphene lines present a high conductivity, up to 4.23 × 104 S m−1 at 3 µm thickness. It also shows an excellent bending stability during the roller compression process, which is compatible for large-scale manufacturing. Combining with inkjet-printed graphene oxide as the sensing layer, the graphene lines are exploited as the electrodes for a fully printed humidity sensor on the paper substrate. Such a low drying temperature, high printing resolution and low-cost printing method offers an example that two-dimensional materials are cooperatively utilized for fully printed flexible electronic devices.

Recently, health-related misinformation has plagued social media. We investigate the behavior of misinformation sharing on Twitter. We argue that misinformation sharing is likely to be influenced by the distance to the health crisis as afforded by Twitter. This article investigates three types of distances, namely social (personal relations), spatial (geometric), and temporal (time gap). We address three research questions in the context of Zika virus: first, how does social, spatial, and temporal distances affect the threat appeal of a misinformation message? Second, how does social, spatial, and temporal distances influence misinformation sharing? Third, how does the effect of social, spatial, and temporal distances on misinformation sharing varies based on the influence afforded by Twitter? The results indicate the negative effect of social and temporal distances on threat appeal, and the negative effect of spatial distance on misinformation sharing. The results also indicate the negative effect of temporal distance on misinformation sharing for more influential Tweeters and the negative effect of social and spatial distance on misinformation sharing for less influential Tweeters.

Experiments of laser-induced forward transfer (LIFT) have been performed using ultrashort laser pulses (800nm, 100fs). 40nm of Cr thin film have been transferred on glass and Silicon acceptor substrates in different conditions. The analysis of the deposits was carried out by optical and electronic scanning microscopy. An optimisation of the process has been carried out and a good resolution of the patterns was obtained. The dynamics of the plume has been monitored with a gated ICCD camera and the images analysis gave us indications on the transfer of the material.

We experimentally demonstrated a laser-based approach for the maskless printing of solder paste with a predefined size and position. In this work, a 532 nm laser marking system is used to induce the formation of a solder paste bridge between the donor and acceptor substrate. After the donor is removed vertically, the bridge will rupture and a high aspect ratio voxel can be obtained on the acceptor substrate. The width and height of transferred voxels can be controlled by modifying the laser fluence. In order to find out the specific conditions for the solder paste bridge formation, we carried out transfer experiments at different gap distances and found out a bridge formation threshold. Solder paste bridges can be produced only when the gap distance is smaller than the threshold. Furthermore, the threshold can be affected by the film thickness and spot size. In this condition, a solder paste array with an average size of 100 µm and a pitch of 200 µm has been successfully transferred. Compared to conventional printing methods, the method proposed in this paper can effectively improve the transfer accuracy and reduce the production cost.

Graphene inks for printed flexible electronics: Graphene dispersions, ink formulations, printing techniques and applications

Aqueous graphene inks were obtained by liquid-phase exfoliation of graphite and bonded to biodegradable polymers. Consequently, green and eco-friendly graphene inks are proposed that are free of VOCs and harmful organic compounds. Three graphene inks indicated as GGe, GTr, and GTw were prepared with corresponding optimized biopolymer concentrations of 0.1 mg.mL <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> of gelatin, 1 mg.mL <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> triton X-100, and 1.5 mg.mL <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> tween-20. The flake diameter distribution for the graphene inks ranged from 100 nm to 800 nm as measured by dynamic light scattering (DLS). GTr is made of smaller flake diameters followed by GTw and GGe has the largest flakes. Graphene films were printed using aerosol jet technique with a 500 nm thickness and their sheet resistance (sR) was of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$2.6\ \mathrm{k}\Omega/\square$</tex> for GTr, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$5\ \mathrm{k}\Omega/\square$</tex> for GTw, and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$14\ \mathrm{k}\Omega/\square$</tex> for GGe. The low sheet resistance for GTr was assigned to better ink wettability and adhesion on top PET substrates. These electrical resistances are suitable for the fabrication of green chemiresistive flexible sensors.

Electronic printing is an interdisciplinary technology of traditional printing technology and microelectronics manu- facturing. The development of electronic printing has mostly benefited from the progress of nanomaterials research. Graphene, a novel two-dimensional carbon nanomaterial, has shown excellent electrical, thermal, optical properties in flexible electrical devices. Graphene with traditional metals or polymer materials together could act as the main conductive components in conductive ink. Printing of graphene ink represents a cost-effective deposition technique to obtain patterned conductive graphene films, and further assemble them into functional electrical devices. Therefore, electronic printing based on graphene conductive ink is one of the recent research hotspots. In this paper, we review recent developments and advances in research of graphene conductive ink. This review begins with an introduction of different preparation strategies for graphene conductive inks. For printing, the three major pathways for producing graphene sheets are oxidation-reduction, solvent exfoliation and electrochemical expansion of graphite. Different preparation strategies for conductive inks are classified into three major methods: Graphene inks stabilized by surfactants or functional groups, and graphene-based composite conductive ink. The detailed review of graphene conductive ink preparation is discussed with specific examples. Preparation of graphene conductive inks of high concentrations, stability and printing adaptability is the key issue in electronic printing. Subsequently, an introduction of common printing methods and principles is given. Five printing methods are discussed in this review, including inkjet printing, gravure printing, transfer printing, direct writing and three- dimensional (3D) printing. Printing is kind of additive manufacturing, by depositing graphene onto substrates of various materials, sizes, flexibility and roughness for conductive pattern. Different printing techniques have unique requirements of ink rheological properties. The inkjet printing is becoming the most common technique employed in both academic research and industrial application. The realization of rapid, accurate, simple and controllable printing has important influence on the application of graphene conductive ink. Finally, applications of printed graphene conductive ink in flexible functional devices, including basic electrical circuits, energy storage devices and mechanical/chemical sensing devices, are envisioned. Basic electrical circuits, like flexible conductive patterns, field-effect transistors and radio-frequency circuits, play an important role in the fabrication of wearable devices. Printing also offers a cheap, scalable method of fabricating energy storage devices, including supercapacitor and lithium battery. The unique structure of graphene makes possible the fabrication of different kinds of sensors, including strain, temperature, chemical, electrochemical, photo-electricity sensors and biosensors. An outlook of potential future trends in printing graphene conductive ink research and technology is followed. In summary, printing graphene conductive ink has made many significant advances in a wide range of applications. However, the industrial-level application is still limited, and the preparation and application of graphene conductive ink still need further study. A number of key issues should be solved, including stability of graphene ink, electronic conductivity of printed circuit, limited printing resolution, etc. Overall, electronic printing technology based on graphene conductive ink is not meant as a replacement for microelectronic manufacturing engineering, but instead provides an opportunity to produce large-area flexible electronic devices at low cost. Electronic printing of graphene conductive ink will result in a diverse range of novel applications in many fields, and it calls for more research in the future.

Purpose The purpose of this study was to examine the effects of temporal and spatial distance and types of advertising messages on sport consumer’s attitudes toward and advertising and purchase intentions, based on the construal level theory. Methods Toward this end, 253 usable data were conducted using frequency analysis, exploratory factor analysis, reliability analysis, correlation analysis, MANOVA, and ANOVA with SPSS 24.0. Results and Conclusion The study obtained the conclusion that when using different types of messages, the consumer’s attitudes and purchase intentions are influenced by temporal distance, by spatial distance, and by the interaction between both factors.

The adhesive bond strength of composite structures is predominantly governed by the surface characteristics of the bonding interface. In this study, picosecond laser was employed to modify the surface properties of carbon fiber reinforced polymer (CFRP) composites. A comprehensive investigation was conducted to analyze the effects of different laser processing parameters on the surface morphology, roughness, and wettability of CFRP substrates. The mechanical performance of the adhesive joints was systematically evaluated through single lap shear (SLS) and double cantilever beam (DCB) tests, while the underlying mechanisms governing the relationship between interfacial properties and fracture toughness were thoroughly examined. The results show that laser surface treatment significantly enhances the surface roughness and wettability of CFRP substrates, thereby promoting mechanical interlocking at the adhesive-substrate interface. Compared to untreated specimens, optimally laser-treated joints exhibited remarkable improvements in mechanical performance, with a 227% increase in bond strength and a 234% enhancement in fracture energy. Furthermore, the laser treatment process induces the formation of micro-voids during joint fabrication, which subsequently leads to localized debonding and fiber bridging phenomena during fracture propagation. These mechanisms collectively contribute to the improved fracture resistance observed in laser-treated adhesive joints.