Deposition Of Ink Research Articles

Time-Resolved Nanostructural Analysis of Thin-Film Formation Process from Nafion Solution by Synchrotron X-Ray Scattering

Perfluorosulfonate ionomers such as Nafion consist of a polytetrafluoroethylene backbone having pendant side chains terminating with sulfonic acid groups. These materials have attracted much attention as proton-conducting materials in polymer electrolyte membrane fuel cells (PEMFCs), due to their excellent chemical stability and high proton conductivity. The catalyst layer is fabricated by deposition of catalyst ink containing catalyst, ionomer, and solvents. In the catalyst layers, ionomer provided an ultra-thin film, coating the catalyst and the catalyst support surfaces. These ultra-thin films have a significant influence on the electrochemical activity and transport phenomena that determine the whole cell performances. Recently, precise structural analyses of ionomer in the solutions and solid-state thin films have been reported. To the best of our knowledge, however, the dynamics of ionomer thin-film formation process remain unclear.Herein, time-resolved measurements of grazing-incidence small- and wide-angle X-ray scattering (GISAXS/GIWAXS) utilizing synchrotron radiation at BL45XU/SPring-8 were carried out to observe the nanostructural evolution of thin film during solidification processes (i.e., spin-coating) from the Nafion solution. GISAXS and GIWAXS are synchrotron-based X-ray techniques that have been used extensively to provide nanostructural insight of polymeric thin films. In the present study, effects of solvent evaporation and centrifugal force on the structural formation behaviors of Nafion were observed for water/1-propranol (NPA) solution of Nafion (3.5 wt% Nafion in water/NPA (1/1 in volume ratio)). The wavelength of the X-ray beam was 0.1 nm, and camera length was 270 mm and 2503 mm for GIWAXS and GISAXS measurements, respectively. The scattering intensity at a certain scattering vector q was measured as a function of time after deposition of Nafion solution on the rotated Si substrate (2000 rpm). The 2D-scattering image was acquired using a photon counting detector (PILATUS3X 2M, DECTRIS Ltd.). In the first stage from t = 0 to 20 s, the 2D GIWAXS profile showed strong solvent peak and crystalline peak arising from the packing of the Nafion backbone (q z ~ 11.7 nm-1, d-spacing is defined as 2π/qz , d ~ 0.5 nm) quickly appeared. After 180 s, the solvent peak disappeared, and only the crystalline peak was observed. This supports that fine crystallites were contained in Nafion solution. The 2D GISAXS profile, on the other hand, significantly changed with time. Selected GISAXS patterns during thin-film formation process are shown in Fig. 1. In the first stage (from t = 0 to 110 s), an interaction peak was observed at q > 0.1 nm-1, the position of which is related to the main first neighbor distance D between the scatter structures in Nafion solution, and the peak position shifted towards larger q values with time. This indicates that solvent evaporation decreases the distance between the scatter structures in Nafion solution. At the second stage (from t = 110 to 135 s), the new peak of q z ~ 1.9 nm-1 (d ~ 3.3 nm) corresponding to so-called ionomer peak appeared. At the third stage (form t = 135 to 180 s), the interaction peak disappeared, and only the peak of qz ~ 1.9 nm-1 was observed, indicating that the ordered structure were fixed in solid-state thin film after the solvent evaporation. This work clearly indicates that second-scale nanostructural evolution of Nafion during the film forming process can be traced by utilizing synchrotron GISAXS/GIWAXS measurements. Further investigations on the effects of process parameters during film forming with a film applicator on nanostructural formation behaviors of Nafion are now in progress.This presentation is based on results obtained from the PEMFC Research and Development Program for “Highly‐Coupled Analysis of Phenomena in MEA and its Constituents and Evaluation of Cell Performance” commissioned by the New Energy and Industrial Technology Development Organization (NEDO). The synchrotron radiation experiments were performed at BL45XU in SPring-8 with the approval of JASRI (Proposal No.2015B1105). Figure 1

Brush-painting and photonical sintering of copper and silver inks on cotton fabric to form antennas for wearable ultra-high-frequency radio-frequency identification tags

Additive deposition of inks with metallic inclusions provides compelling means to embed electronics into clothing in a seamless way. We present a simple single-step brush-painting method for depositing copper and silver inks directly on ordinary cotton fabric and discuss the optimization of the photonical sintering of both materials. For the first time, we demonstrate the deposition and sintering of copper oxide ink on fabric achieving high electrical conductivity suitable for radio-frequency electronics. The results from wireless testing confirmed that the radio-frequency identification tags based on the copper and silver ink antennas were readable from 6 and 10 m, respectively.

ChemInform Abstract: Surface Control of a Photoresponsive Self‐Assembled Monolayer and Selective Deposition of Ag Nanoparticulate Ink

AbstractA highly hydrophobic self‐assembled monolayer (SAM) with high photosensitivity to soft UV (λ = 365 nm) is formed on thermally surface‐oxidized silicon wafers by a silane coupling agent bearing a 2‐nitrobenzyl carbamate moiety.

Template Synthesis of Nanostructured Polymeric Membranes by Inkjet Printing.

The fabrication of functional nanomaterials with complex structures has been serving great scientific and practical interests, but current fabrication and patterning methods are generally costly and laborious. Here, we introduce a versatile, reliable, and rapid method for fabricating nanostructured polymeric materials. The novel method is based on a combination of inkjet printing and template synthesis, and its utility and advantages in the fabrication of polymeric nanomaterials is demonstrated through three examples: the generation of polymeric nanotubes, nanowires, and thin films. Layer-by-layer-assembled nanotubes can be synthesized in a polycarbonate track-etched (PCTE) membrane by printing poly(allylamine hydrochloride) and poly(styrenesulfonate) sequentially. This sequential deposition of polyelectrolyte ink enables control over the surface charge within the nanotubes. By a simple change of the printing conditions, polymeric nanotubes or nanowires were prepared by printing poly(vinyl alcohol) in a PCTE template. In this case, the high-throughput nature of the method enables functional nanomaterials to be generated in under 3 min. Furthermore, we demonstrate that inkjet printing paired with template synthesis can be used to generate patterns comprised of chemically distinct nanomaterials. Thin polymeric films of layer-by-layer-assembled poly(allylamine hydrochloride) and poly(styrenesulfonate) are printed on a PCTE membrane. Track-etched membranes covered with the deposited thin films reject ions and can potentially be utilized as nanofiltration membranes. When the fabrication of these different classes of nanostructured materials is demonstrated, the advantages of pairing template synthesis with inkjet printing, which include fast and reliable deposition, judicious use of the deposited materials, and the ability to design chemically patterned surfaces, are highlighted.

Fabrication of Crack-Free Barium Titanate Thin Film with High Dielectric Constant Using Sub-Micrometric Scale Layer-by-Layer E-Jet Deposition.

Dense and crack-free barium titanate (BaTiO3, BTO) thin films with a thickness of less than 4 μm were prepared by using sub-micrometric scale, layer-by-layer electrohydrodynamic jet (E-jet) deposition of the suspension ink which is composed of BTO nanopowder and BTO sol. Impacts of the jet height and line-to-line pitch of the deposition on the micro-structure of BTO thin films were investigated. Results show that crack-free BTO thin films can be prepared with 4 mm jet height and 300 μm line-to-line pitch in this work. Dielectric constant of the prepared BTO thin film was recorded as high as 2940 at 1 kHz at room temperature. Meanwhile, low dissipation factor of the BTO thin film of about 8.6% at 1 kHz was also obtained. The layer-by-layer E-jet deposition technique developed in this work has been proved to be a cost-effective, flexible and easy to control approach for the preparation of high-quality solid thin film.

Surface Control of a Photoresponsive Self-Assembled Monolayer and Selective Deposition of Ag Nanoparticulate Ink

Abstract A highly hydrophobic self-assembled monolayer (SAM) with high photosensitivity to soft UV (λ = 365 nm) was formed on thermally surface-oxidized silicon wafers by a silane coupling agent bearing a 2-nitrobenzyl carbamate moiety. Very smooth SAM was obtained by the use of 1,3-bis(trifluoromethyl)benzene as a solvent. Photopatterning of the SAM was carried out by irradiation with soft UV at 2 J cm−2 (80 s) in acetone under a photomask. Selective deposition of Ag nanoparticulate ink by spin coating on the resulting patterned surface afforded a well-defined 10 µm line and space pattern. Subsequent photodeprotection to generate amino groups enabled the space regions to be selectively modified with fluorescent dye bearing a succinimidyl ester moiety.

Printing of silver conductive lines through laser-induced forward transfer

The generation of conductive lines from liquid inks through laser-induced forward transfer (LIFT) is achieved by printing a sequence of overlapping droplets. This procedure, however, is not free from drawbacks: the formation of continuous lines is often accompanied with undesired scalloping or bulging. In this work we present an innovative method consisting in the deposition of conductive ink through LIFT inside fluidic guides produced by laser ablation. The aim of the approach is that the guides confine the liquid within them so that the most common defects can be prevented. The production of guides through laser ablation followed by LIFT of ink inside them has proved that it is possible to find conditions in which the total confinement of liquid within the guides is achieved with good uniformity all along the line. This proves the feasibility of the proposed approach for printing continuous lines free from scalloping and bulging with excellent definition.

CMOS integration of inkjet-printed graphene for humidity sensing.

We report on the integration of inkjet-printed graphene with a CMOS micro-electro-mechanical-system (MEMS) microhotplate for humidity sensing. The graphene ink is produced via ultrasonic assisted liquid phase exfoliation in isopropyl alcohol (IPA) using polyvinyl pyrrolidone (PVP) polymer as the stabilizer. We formulate inks with different graphene concentrations, which are then deposited through inkjet printing over predefined interdigitated gold electrodes on a CMOS microhotplate. The graphene flakes form a percolating network to render the resultant graphene-PVP thin film conductive, which varies in presence of humidity due to swelling of the hygroscopic PVP host. When the sensors are exposed to relative humidity ranging from 10–80%, we observe significant changes in resistance with increasing sensitivity from the amount of graphene in the inks. Our sensors show excellent repeatability and stability, over a period of several weeks. The location specific deposition of functional graphene ink onto a low cost CMOS platform has the potential for high volume, economic manufacturing and application as a new generation of miniature, low power humidity sensors for the internet of things.

Spray and inkjet fabrication of Cu2ZnSnS4 thin films using nanoparticles derived from a continuous-flow microwave-assisted synthesis

Patterning of kesterite (Cu2ZnSnS4 or CZTS) thin films by the inkjet printing technique has been demonstrated for the first time. For the ink formulation, CZTS nanoparticles were obtained in large quantities using a continuous-flow synthesis based on microwave-assisted heating of a mixture of mercaptoacetic acid, sodium sulfide, tin chloride, copper and zinc acetates dissolved in water. For the further formulation of a stable nanoparticle ink with rheological and wetting properties suitable for inkjet pattering on Mo/SLG substrates, a mixture of methyl-ethyl-ketone (MEK) and dodecanthiol (DDT) with the volume ratio MEK:DDT=9:1 was used as a solvent. It has been shown that the same ink can be successfully used for the preparation of thin films by spray-coating technique. Deposition of the nanoparticle ink by both methods followed by annealing at 540°C in a sulfur-containing atmosphere allowed obtaining crystalline thin films of kesterite with the desired (copper poor and zinc rich) chemical composition. The process developed in the present study is promising for a low-cost non-vacuum production of thin films of CZTS which is expected to serve as a substitute for the solar absorber materials based on rare and toxic elements.

Photocatalytic and Antimicrobial Activity of Printed Hybrid Titania/Silica Layers.

Stable mixed dispersion of TiO2 and SiO2 was developed and hybrid TiO2/SiO2 layers were fabricated by the direct inkjet patterning technique. The prepared layers were tested for photoinduced hydrophilicity and their photocatalytic activity was tested using stearic acid and dichloroindophenol as model compounds. The antimicrobial activity of prepared layers was tested and evaluated by the traditional plate counting method according to ISO 27447:2009, using Escherichia coli CCM 3988. Material printing proved to be well suited for the deposition of this complex nanoparticulate ink and samples with variable thickness were conveniently fabricated. Printed layers are able to change their surface properties from hydrophobic to superhydrophilic and also decompose the model contaminants rapidly.

Roll-to-roll compatible flexible polymer solar cells incorporating a water-based solution-processable silver back electrode with low annealing temperature

The solution-based deposition of the metal back electrode in inverted polymer solar cells (PSCs) using roll-to-roll (R2R) compatible processing technologies is considered one of the crucial issues towards the upscaling of PSC technology, as it may allow the full exploitation of the high through-put and prospective low-costs envisaged by the R2R fabrication approach. In this work, a water-based solution-processable silver ink formulation with low annealing temperature was developed to be used as precursor for the fabrication of the metallic back-electrode in flexible inverted PSC devices fabricated by means of R2R-compatible printing techniques. In order to investigate the effect of the deposition of such reactive silver ink on the underlying PSC layers, different back-electrode architectures were investigated and thoroughly characterized. In addition, the influence of the thickness of the hole-transporting poly(ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) buffer layer on the functional performance of the PSC devices was also investigated and an optimized combination of back-electrode architecture and PEDOT:PSS thickness was found, that also allowed to obtain semi-transparent PSC devices. The results of this study demonstrate the possibility to employ R2R-compatible processing techniques for the deposition of the metallic back-electrode in flexible inverted PSCs from a solution-processable water-based reactive silver ink formulation characterized by low-annealing temperature, and provide useful insights into the key role played by the hole-transporting buffer layer in the realization of fully functional flexible PSC devices.

Graphene-Based Flexible Circuit on Cotton Fabric Using Wax Patterning Method

With recent development in the field of wearable devices for biomedical applications, various studies have been conducted on the fabrication of electrically conductive circuit on flexible substrate materials such as paper or textile. In this project, we propose the fabrication of electrically conductive circuit on cotton fabric using simple wax patterning method. Using this method, hydrophilic and hydrophobic regions were patterned on the fabric and graphene-poly (3,4-ethylenedioxythiophene): poly (styrenesulfonic acid) (graphene-PEDOT:PSS) ink was deposited on the hydrophilic region using pipetting method. Conductive lines with higher conductance were fabricated by multiple deposition of the conductive ink and electronic components were successfully attached on the fabric to develop a simple fully functional flexible circuit.

30.2: Invited Paper: Advancements in Inkjet Printing for OLED Mass Production

AbstractContinuous improvements in inkjet printing of organic light emitting diode (OLED) displays have resulted in a number of recent demonstrations of uniform, mura‐free TV‐sized panels. These improvements combined with steady progress in solution OLED material performance, have allowed inkjet to become a realistic near term enabler of cost‐effective mass production of large size OLED TVs. However, for inkjet to make the transition from R&D to mass production, a number of equipment challenges must be overcome, including achieving low particle contamination, maintaining the optimal process environment while preserving serviceability, and providing consistent, uniform, mura‐free results with a wide process window. In this paper, the methodology (with respect to algorithms and process control) used in Kateeva's YIELDjet platform are described that lead to the uniform deposition of ink across an OLED display using inkjet printing, resulting in a highly uniform OLED emission with a wide process window.

Properties of Polylactide Inks for Solvent-Cast Printing of Three-Dimensional Freeform Microstructures

Solvent-cast printing is a highly versatile microfabrication technique that can be used to construct various geometries such as filaments, towers, scaffolds, and freeform circular spirals by the robotic deposition of a polymer solution ink onto a moving stage. In this work, we have performed a comprehensive characterization of the solvent-cast printing process using polylactide (PLA) solutions by analyzing the flow behavior of the solutions, the solvent evaporation kinetics, and the effect of process-related parameters on the crystallization of the extruded filaments. Rotational rheometry at low to moderate shear rates showed a nearly Newtonian behavior of the PLA solutions, while capillary flow analysis based on process-related data indicated shear thinning at high shear rates. Solvent vaporization tests suggested that the internal diffusion of the solvent through the filaments controlled the solvent removal of the extrudates. Different kinds of three-dimensional (3D) structures including a layer-by-layer tower, nine-layer scaffold, and freeform spiral were fabricated, and a processing map was given to show the proper ranges of process-related parameters (i.e., polymer content, applied pressure, nozzle diameter, and robot velocity) for the different geometries. The results of differential scanning calorimetry revealed that slow solvent evaporation could increase the ability of PLA to complete its crystallization process during the filament drying stage. The method developed here offers a new perspective for manufacturing complex structures from polymer solutions and provides guidelines to optimize the various parameters for 3D geometry fabrication.

Effect of Solids Loading on Resonant Mixed Al‐Bi2O3 Nanothermite Powders

AbstractSensitive nanoenergetic powders, such as nanothermites, have traditionally been processed by ultrasonic mixing of very low solids loaded suspensions in organic solvents, which has restricted their use and application due to high solvent content and associated handling issues. In this work, we report on the performance and mixing quality of nanothermite mixtures prepared in a LabRAM resonant mixer at high solids loadings as compared to ultrasonic mixing. Specifically, the aluminum‐bismuth(III) oxide (Al/Bi2O3) system processed in the polar solvent N,N‐dimethylformamide (DMF) was investigated. It was found that the performance and overall quality of mixing was strongly correlated to the volumetric solids loading during processing; increasing volumetric solids loading decreases separation of particles, leading to more particle interaction and more intimate mixing. The measured performance of this system processed at 30 vol‐% was similar to traditionally ultrasonicated mixtures. Increasing the solids loading above 30 vol‐% yielded diminishing returns in performance and may introduce additional safety concerns since dry powders are very sensitive to electrostatic discharge. This mixing approach uses significantly less solvent than traditional ultrasonic mixing, results in a higher density final material, and is amenable to scaling. In addition, solvent wetted nanothermite mixed at 30 vol‐% solids loading can be mixed and deposited from a single applicator and was observed to be over five orders of magnitude less sensitive to electrostatic discharge than dry powders. This relative insensitivity enables the safe deposition of high density nanothermite ink onto devices.

Enhanced Redifferentiation of Chondrocytes on Microperiodic Silk/Gelatin Scaffolds: Toward Tailor-Made Tissue Engineering

Direct-write assembly allows rapid fabrication of complex three-dimensional (3D) architectures, such as scaffolds simulating anatomical shapes, avoiding the need for expensive lithographic masks. However, proper selection of polymeric ink composition and tailor-made viscoelastic properties are critically important for smooth deposition of ink and shape retention. Deposition of only silk solution leads to frequent clogging due to shear-induced β-sheet crystallization, whereas optimized viscoelastic property of silk-gelatin blends facilitate the flow of these blends through microcapillary nozzles of varying diameter. This study demonstrates that induction of controlled changes in scaffold surface chemistry, by optimizing silk-gelatin ratio, can govern cell proliferation and maintenance of chondrocyte morphology. Microperiodic silk-gelatin scaffolds can influence postexpansion redifferentiation of goat chondrocytes by enhancing Sox-9 gene expression, aggregation, and driving cartilage matrix production, as evidenced by upregulation of collagen type II and aggrecan expression. The strategy for optimizing redifferentiation of chondrocytes can offer valuable consideration in scaffold-based cartilage repair strategies.

On-chip microlasers for biomolecular detection via highly localized deposition of a multifunctional phospholipid ink

We report on a novel approach to realize on-chip microlasers, by applying highly localized and material-saving surface functionalization of passive photonic whispering gallery mode microresonators. We apply dip-pen nanolithography on a true three-dimensional structure. We coat solely the light-guiding circumference of pre-fabricated poly(methyl methacrylate) resonators with a multifunctional molecular ink. The functionalization is performed in one single fabrication step and simultaneously provides optical gain as well as molecular binding selectivity. This allows for a direct and flexible realization of on-chip microlasers, which can be utilized as biosensors in optofluidic lab-on-a-chip applications. In a proof-of-concept we show how this highly localized molecule deposition suffices for low-threshold lasing in air and water, and demonstrate the capability of the ink-lasers as biosensors in a biotin-streptavidin binding experiment.

Non-vacuum processed CuInSe2 thin films fabricated with a hybrid ink

CuInSe2 (CIS) thin films were formed on a Mo-coated soda lime glass with a newly formulated hybrid ink composed of binary Cu2−xSe nanoparticles and an In precursor solution. The thin films were fabricated by the spin coating method and a subsequent selenization process, and the compositional and structural properties of the CIS thin films were characterized. Deposition of a hybrid ink provides the unique advantage of producing centers composed of pure material-based nanoparticles that can promote stress-relief and crack-deflection. Additionally, hybrid inks offer efficient binding with nanoparticles by using precursor solutions without other organic binders. Binary Cu2−xSe nanoparticles were synthesized by a low-temperature colloidal process, and an In precursor solution was prepared by using a non-toxic chelating agent for dispersing the In component stably. The band gap of the CIS thin film was measured to be 1.14eV by the external quantum efficiency (EQE) technique, and the best conversion efficiency of the fabricated device was determined to be 4.19%.

Electrical circuits from capillary flow driven evaporation deposition of carbon nanotube ink in non-porous V-grooves

Low cost pliable electronics portend the advancement of novel inexpensive microfluidic electrochemical devices. In the direct printing approach, the manner of deposition of conductive material from a liquid suspension to ensure electrical continuity is crucial. We describe here an approach in which V-groove networks that make up the path of circuitry are first scribed on non-porous inexpensive surfaces. Liquid drops of carbon nanotube ink are then placed on the surface adjacent to the V-grooves to enable wicking to produce the electrical circuit. This method essentially bypasses the need for inkjet printing. We investigate the basic efficacy of the conductive networks developed using this approach and demonstrate its use in generating electrically driven liquid flow of particles in a simple open capillary channel.

Fabrication of an inkjet-printed seed pattern with silver nanoparticulate ink on a textured silicon solar cell wafer

In this study, the possibility of using inkjet printing in the fabrication of a conductive seed pattern on a textured silicon solar wafer is investigated. Firstly, solar cell wafers were coated with a hydrophobic solution. It was found that the surface texture of a solar cell wafer causes a slight increase in the contact angle of silver nanoparticulate ink by 7.5° due to a weak Cassie–Baxter wetting state. After selective laser ablation of the hydrophobic coating and the SiN x layer in preparation for the surface energy-patterned finger electrode regions, silver nanoparticulate ink was deposited with a piezo drop-on-demand inkjet print head. Because the threshold laser fluence for the ablation of the hydrophobic coating is lower than that for the SiN x layer, the effective width of a surface energy-patterned finger electrode region with the Gaussian laser beam profile was found to be wider than the actual width of the SiN x -ablated region. Although this initially results in a widened deposition of silver nanoparticulate ink, the subsequent drying of silver nanoparticulate ink is found to cause a reduction of line width of around 6% to 14%. Therefore, the final line width of the seed pattern is the outcome of two opposing phenomena. The physical and electrical characteristics of the seed pattern are as narrow as 58.5 ± 1.2 µm, as thick as 1.81 µm on average and as conductive as 2.72 µΩ cm.