Selective Laser Sintering of Nanoparticles

Selective laser sintering of nanoparticles has received much attention recently as it enables rapid fabrication of functional layers including metal conductors and metal‐oxide electrodes on heat‐sensitive polymer substrate in ambient conditions. Photothermal reactions induced by lasers rapidly increase the local temperature of the target nanoparticle in a highly selective manner, and subsequent sintering steps including melting and coalescence between nanoparticles occur to fabricate interconnected sintered films for various future applications. The mechanism of laser sintering, as well as possible target materials subject to laser sintering, together with experimental schemes developed to improve the process and potential applications, is briefly summarized in this chapter

Flexible and Stretchable Electronics

Flexible and stretchable electronics are receiving tremendous attention as future electronics due to their flexibility and light weight, especially as applications in wearable electronics. Flexible electronics are usually fabricated on heat sensitive flexible substrates such as plastic, fabric or even paper, while stretchable electronics are usually fabricated from an elastomeric substrate to survive large deformation in their practical application. Therefore, successful fabrication of flexible electronics needs low temperature processable novel materials and a particular processing development because traditional materials and processes are not compatible with flexible/stretchable electronics. Huge technical challenges and opportunities surround these dramatic changes from the perspective of new material design and processing, new fabrication techniques, large deformation mechanics, new application development and so on. Here, we invited talented researchers to join us in this new vital field that holds the potential to reshape our future life, by contributing their words of wisdom from their particular perspective

Fabrication and Applications of Flexible Transparent Electrodes Based on Silver Nanowires

There has been an explosion of interests in using flexible transparent electrodes for next-generation flexible electronics, such as touch panels, flexible lighting, flexible solar cells, and wearable sensors. Silver nanowires (AgNWs) are a promising material for flexible transparent electrodes due to high electrical conductivity, optical transparency and mechanical flexibility. Despite many efforts in this field, the optoelectronic performance of AgNW networks is still not sufficient to replace the present material, indium tin oxide (ITO), due to the high junction resistance. Also, the environmental stability and the mechanical properties need enhancement for future commercialization. Many studies have attempted to overcome such problems by tuning the AgNW synthesis and optimizing the film-forming process. In this chapter, we survey recent progresses of AgNWs in flexible electronics by describing both fabrication and applications of flexible transparent AgNW electrodes. The synthesis of AgNWs and the fabrication of AgNW electrodes will be demonstrated, and the performance enhanced by various methods to suit different applications will be also discussed. Finally, technical challenges and future trends are presented for the application of transparent electrodes in flexible electronics

Design and rapid prototyping of printed graphene electrochemical biosensors for sensitive monitoring of pesticide levels for agricultural use

While the use of pesticides (herbicides and insecticides) are critically important to meet the current and future food demands (increases crop yield by up to 40%), their overuse has shown long-term detrimental impacts on the environment from polluting watersheds used for drinking water to eutrophic “dead zones”. Current pesticide soil measurement methods (chromatography) are costly, require trained technicians, and take days to analyze; thus, farmers are taking an “over-application approach” which is pollution the environment and waterways. A disposable pesticide soil sensor would provide farmers the opportunity of precisely regulating the application of pesticides in an independent and economical fashion. Electrochemical biosensors provide the unique ability to quickly detect analytes with low-cost sensors; however, the detection limit and sensitivity of these biosensors are inadequate for current applications. This dissertation addresses this issue with the following focus in mind: 1) Increasing the enzymatic efficiency of organophosphate hydrolase by strategically functionalizing to nanomaterials [e.g., 17-fold increase in Vmax when functionalized to gold nanoparticles vs free enzyme]. 2) Develop a low-cost, rapid, and high-resolution manufacturing method to pattern solution-phase graphene [i.e., inkjet maskless lithography (IML), line resolution ~20 µm, sheet resistance ~ 0.7 kΩ/sq]. 3) Enhance the electroactive surface area by nano/microstructuring the graphene surface [3D petal-like graphene morphology] using laser annealing. 4) Increase the electrochemical surface area by incorporating macro and micro pores [2.2x with the inclusion of macropores] in the graphene surface. This work demonstrates the manufacturing of simple, low-cost electrochemical biosensors which suitable for rapid in-field detection of organophosphates. The fabricated graphene biosensors demonstrate high sensitivity, high linear sensing range, and ultra-low detection limits. Additionally, while this work is tailored towards a disposable pesticide sensor, the manufacturing techniques, sensor designs, and biosensor principle are a platform technology that could be amenable to other applications such as healthcare screening, drinking water monitoring, and even bioterror agent detection

Mechanical durability of screen-printed flexible silver traces for wearable devices

There is increased usage of flexible electronics recently in various applications such as wearable devices, flexible displays and sensors. Studies on the durability of conductive metal traces under cyclic mechanical loading is crucial since these conductors will be subjected to repeated bending. In this work, the mechanical and electrical behavior of silver printed conductors was tested using cyclic three-point bend test. The samples were flexible polymer thick film (PTF) silver (Ag) ink printed on a flexible polyethylene terephthalate (PET) substrate. The durability of this PTF Ag ink, which has a hyper-elastic binder and Ag flakes, was studied by performing cyclic bending tests. Four-point resistivity measurements and imaging of the sample both before and after bending were performed. A custom tester machine was used to apply strain to the circuit and measure the resistivity of the silver trace. The results of the bending test show that the silver trace does not undergo significant deformation and the change in resistance is less than 0.6% under both tensile and compressive tests. Fatigue tests were also performed by cyclic bending tests for three trials in which batches of 10,000 cycles were completed. The printed silver wire withstood 30,000 cycles of bend tests and produced only 2.64% change in resistance. This indicates that the printed wires are very durable even after 30,000 cycles of outer bending. Imaging was also conducted on these samples to study the effect of repeated bending on the morphology of the silver conductive trace. Although there was an increase in surface roughness before and after cyclic bending, there was no obvious deformation or delamination observed in the samples

Fabrication and Applications of Printed and Handwriting Electronics

The accelerating arrival of the Internet of Things (IoT) era creates a rapidly growing demand for printed electronic. As a low-cost and green substrate, cellulose paper has become the most attractive choice for the printing of sustainable and disposable electronics. However, manufacture of high quality circuits with high conductivity on cellulose paper remains a challenge due to the substrate’s high porosity and roughness. In this thesis, a method for facile fabrication of hybrid copper-fiber highly conductive features on low-cost cellulose paper with strong adhesion and enhanced bending durability is introduced. With three-dimensional electroless deposition (ELD) of copper, the as-fabricated circuits show ultra-low sheet resistance down to 0.00544 Ω/sq. Taking advantages of the porous structure of paper, together with the precise control of the inkjet droplets, highly conductive vertical interconnected accesses (VIAs) are fabricated for multilayered devices without physically drilling holes or depositing additional dielectric material. To further utilize the unique porous structure of cellulose paper, a scalable fabrication method for flexible, binder-free and all-solid-state supercapacitors is proposed based on the low-cost chemical engraving technique, to construct CuxO nanostructure in-situ on the three-dimensional metallized cellulose fiber structures. Benefitting from both the “2D Materials on 3D Structures” design and the binder-free nature of the fabricated electrodes, substantial improvements to electrical conductivity, aerial capacitance, and electrochemical performance of the resulting supercapacitors (SCs) are achieved, fulfilling the increasing demand of highly customized power systems in the IoT and wearable electronics industries. The above-mentioned work all use inkjet printing for materials deposition. However, as a solvent-based printing technique, inkjet printer has strict requirement of ink properties and suffer from inevitable nozzle clogging. To address these challenges, a fabrication method based on solvent-free laser printing technique is proposed, pushing the manufacture of printed electronics towards an environmentally benign and more cost-efficient manor. Lastly, a one-step react-on-demand (RoD) method for fabricating flexible circuits with ultra-low sheet resistance, enhanced safety and durability is proposed. With the special functionalized substrate, a real-time synthesize of the 3D metal-polymer (3DMP) conductive structure is triggered on demand. The as-fabricated silver traces show an ultralow sheet resistance down to 4 mΩ/sq

Laser-assisted processing of multilayer films for inexpensive and flexible biomedical microsystems

Flexible/stretchable electronics offer ideal properties for emerging health monitoring devices that can seamlessly integrate with the soft, curvilinear, and dynamic surfaces of the human body. The resulting capabilities have allowed novel devices for monitoring physiological parameters, improving surgical procedures, and human-machine interfaces. While the attractiveness of these devices are indubitable, their fabrication by conventional cleanroom techniques makes them expensive and incompatible with rapid large-scale (e.g., roll-to-roll) production. The purpose of this research is to develop inexpensive fabrication technologies using low-cost commercial films such as polyimide, paper, and metalized paper that can be utilized for developing various flexible/stretchable physical and chemical sensors for wearable and lab-on-chip applications. The demonstrated techniques focus on an array of laser assisted surfaces modification and micromachining strategies with the two commonly used CO2 and Nd: YAG laser systems. The first section of this dissertation demonstrates the use of localized pulsed CO2 laser irradiation to selectively convert thermoset polymer films (e.g., polyimide) into electrically conductive highly porous carbon micro/nanostructures.Thisprocessprovidesauniqueandfacileapproachfordirect writing of carbonized conductive patterns on flexible polyimide sheets in ambient conditions, eliminating complexities of current methods such as expensive CVD processes and complicated formulation/preparation of conductive carbon based inks used in ink jet printing. The highly porous laser carbonized layer can be transferred to stretchable elastomer or further functionalized with various chemical substances such as ionic solutions, nanoparticles, and chemically conductive polymers to create different mechanical and chemical sensors. The second section of this dissertation describes the use of laser ablation for selective removal of material from multilayer films such as ITO-coated PET, parchment paper, and metalized paper to create disposable diagnostic platforms and in-vitro models for lab-on-chip based studies. The ablated areas were analyzed using electrical, mechanical, and surface analysis tools to understand change in physical structure and chemical properties of the laser ablated films. As proof-of-concept demonstrations of these technologies, four different devices are presented here: mechanical, electrochemical, and environmental sensors along with an in-vitro cell culture platform. All four devices are designed, fabricated, and characterized to highlight the capability of commercial laser processing systems in the production of the next generation, low-cost and flexible biomedical devices

Wearable Supercapacitors, Performance, and Future Trends

The progress in portable technologies demands compactable energy harvesting and storage. In recent years, carbon-based lightweight and wearable supercapacitors are the new energy storage trends in the market. Moreover, the non-volatile nature, long durability, eco-friendliness, and electrostatic interaction mechanism of supercapacitors make it a better choice than traditional batteries. This chapter will focus on the progress of the wearable supercapacitor developments, the preferred material, design choices for energy storage, and their performance. We will be discussing the integrability of these supercapacitors with the next generation wearable technologies like sensors for health monitoring, biosensing and e-textiles. Besides, we will investigate the limitations and challenges involves in realizing those supercapacitor integrated technologies

Light-Material Interactions Using Laser and Flash Sources for Energy Conversion and Storage Applications.

This review provides a comprehensive overview of the progress in light-material interactions (LMIs), focusing on lasers and flash lights for energy conversion and storage applications. We discuss intricate LMI parameters such as light sources, interaction time, and fluence to elucidate their importance in material processing. In addition, this study covers various light-induced photothermal and photochemical processes ranging from melting, crystallization, and ablation to doping and synthesis, which are essential for developing energy materials and devices. Finally, we present extensive energy conversion and storage applications demonstrated by LMI technologies, including energy harvesters, sensors, capacitors, and batteries. Despite the several challenges associated with LMIs, such as complex mechanisms, and high-degrees of freedom, we believe that substantial contributions and potential for the commercialization of future energy systems can be achieved by advancing optical technologies through comprehensive academic research and multidisciplinary collaborations

Additive Manufacturing of Graphene for Identification and Sensing Applications

The huge growth of Internet of Things has been leading to a high demand in multipurpose radio frequency identification tags. The materials and manufacturing choices have subsequently become very essential for a lower cost and desired wireless performance. In addition, eco-friendly aspects are gaining more and more interest.This thesis investigates the possibilities of novel manufacturing methods for patterning graphene-based layer on versatile substrates. Graphene is a novel nanomaterial, which has gained a huge attraction due to extraordinary mechanical and electrical properties. In this work, graphene has been introduced as a promising candidate for environmentally-friendly and cost-effective wireless platforms.The focus of the research has been mostly on patterning and fabrication details. The used manufacturing methods are inkjet printing, doctor blade, and 3D direct writing. Additionally, required surface treatments and post treatments are investigated, which needed to be optimized according to ink and substrate materials properties. For instance, the inkjet printed graphene oxide needs annealing and a subsequent reduction process. This can be done using elevated temperature or under pulsed Xenon flashes. On the other hand, graphene inks require just one step curing process. This curing step can be carried out in a conventional oven or photonically by pulsed Xenon flashes.The results indicate that graphene inks have a great potential for fabricating antennas and RFID tags for sensing and identification applications. In this work, the graphene passive UHF RFID tags are manufactured and characterized. Then the wireless properties are evaluated which show acceptable read range values over the UHF band. In addition, the tags show excellent reliability at high humidity and harsh bending conditions. This indicates the great potential of graphene based tags in wireless identification and sensing platforms