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Transparent conductive films composed of CuS were formed by wet deposition on PET at room temperature followed by annealing at 100 °C for 1 hour. The resistance of the films was tuned by doping with In3+. A decrease of over an order of magnitude of the sheet resistance was obtained, from 1721 Ω sq−1 for undoped CuS film to 109 Ω sq−1 for In3+ doped. Transparency of the conducting films could be tuned by an appropriate selection of reaction time and In3+ concentration. It was found that films containing 10 mol% of In3+ ions after a reaction duration of 24 hours have a sheet resistance of ∼270 Ω sq−1 and a transparency of ∼80%. The fabricated films are characterized by excellent adhesion to the PET substrate and are shown to be suitable for use as transparent conducting electrodes (TCE) in flexible electroluminescent (EL) devices. [ABSTRACT FROM AUTHOR]

In order to develop a prediction model for resistivity evolution during isothermal sintering, a commercial silver nanoparticle ink was characterized for its metal content, particle size and behavior upon heating. Electrical properties, mass loss behavior, grain size development and material densification were studied for thermal sintering at 175 °C. The correlation between mass loss, height loss of the resulting sintered structures, grain size and electrical resistivity was investigated to gain further understanding of the silver nanoparticle sintering process. The results of thermal sintering were used to calibrate a discrete element sintering model that provides microstructural properties with which the resistivity development at 150 and 200 °C was successfully predicted. The model was validated by experimental data obtained at these temperatures. A variation of particle size and particle size distribution in the simulations furthermore illustrate their influence on final resistivity showing that using small particles with a broad distribution are preferable for reducing the final resistivity of the inkjet-printed pattern. [ABSTRACT FROM AUTHOR]

Silver-coated copper microparticles combine the oxidation resistance of silver with the low cost of copper. They are interesting components for printed conductive structures. We studied whether printed films of such particles can be printed and sintered at low temperatures in air to create highly conductive films and whether it is possible to recover the particles from them for recycling. Pastes containing 1.5 μm to 5 μm spheres and 3 μm flakes with L -ascorbic acid were prepared, screen-printed, and treated at temperatures of 110 °C to 300 °C in air. The bulk resistance of films treated below 160 °C were two orders of magnitude higher than that of bulk copper, ρCu, and limited by particle–particle contact resistances. They were reduced by treating the prints at 160 °C to 250 °C, leading to bulk film resistances down to 41ρCu. We demonstrate that the high mobility of silver enables the formation of necks that bridge the copper cores and reduce resistivity in this temperature window. The sintered prints retained their conductivity for at least 6 months. Treatments at higher temperatures in air were detrimental: resistances increased above 250 °C. These temperatures led to dewetting of the silver coating and fast copper oxidation, resulting in a continuously increasing resistance. In a final study, we demonstrated that films treated below 200 °C can be recycled by recovering the metal powder from the printed conductors and that the powder can be printed again. [ABSTRACT FROM AUTHOR]

Graphene composite conductive inks are promising for the scalable production of printable electronics, and multifunctional coatings, owing to their cost-effectiveness, high conductivity, and remarkable flexibility. However, the restacking of graphene (Gr) sheets and agglomeration of carbon black (CB) significantly reduce the conductivity of aqueous graphene composite inks, limiting the exploration of high-performance devices. Herein, a highly conductive and dispersed graphene composite ink, based on a composite system of two- and zero-dimensional carbon materials was developed by a scalable sand-milling method. Carboxymethyl cellulose (CMC) can effectively address the aggregation issues of Gr and CB through steric hindrance. Functionalized Gr and CB can synergistically form an interpenetrating conductive network structure. The synthesis of a highly dispersed Gr/CB composite was facilitated by an in situ exfoliation process, which resulted in a high electrical conductivity of 2.12 × 104 S m−1 (i.e., a sheet resistance of 2.16 Ω sq−1). A screen-printed Gr/CB @ thermoplastic polyurethane fabric based on the Gr/CB composite ink exhibited an excellent electrical conductivity (7.08 Ω sq−1). The resulting composite fabric demonstrated promising potential for application in low-voltage driven wearable heaters and ultra-sensitive flexible strain sensors, while being waterproof, stable, and comfortable, suggesting significant potential for use in flexible wearable electronics. [ABSTRACT FROM AUTHOR]

Particle-free metal–organic-decomposition inks, especially amine-coordinated copper formate compounds, can be employed as highly conductive binder precursors to replace the commonly used polymer adhesives. Herein, we used the copper formate complex (Cuf-C) as the conductive binder precursor instead of organic binders and dispersants to prepare a series of composite inks. The lowest voltage solid block resistance of the graphene composite conductive ink was 7.34 Ω per sq per mil. In addition, we applied the pyrolysis products of Cuf-C to the cathode of lithium-ion batteries as conductive binder. Compared with the traditional poly(vinylidene fluoride) binder, the battery with the Cuf-C binder displayed lower charge transfer resistance and interface impedance at the cathode/electrolyte interface, as well as lower polarization and better electrochemical kinetics. We also observed the positive effect of the Cuf-C binder on the cathode in finite element simulation. [ABSTRACT FROM AUTHOR]

In this study, high-quality conductive electrodes were fabricated by improving the sintering efficiency and packing density of Cu sub-microparticle (sub-μP) electrodes through IPL sintering with redox reaction-induced nano-welding. This process includes both pre-oxidation and photothermal chemical reduction. The pre-oxidation in the Cu sub-μP electrodes can easily be triggered (within a few seconds) via a hot air treatment (500 °C). The oxidized Cu sub-μP electrodes are reduced and sintered simultaneously through a photothermal chemical reaction during the IPL sintering process. Cu nanoparticles, which are newly formed in the photothermal chemical reduction process, play an important role as interconnection materials between Cu sub-μPs during the IPL sintering process. The effect of exposure time and temperature in the hot air treatment on the oxidation properties of Cu sub-μPs are investigated systematically using noncontact spectroscopic temperature-sensing techniques and X-ray diffraction analysis. After IPL sintering, the conductive Cu sub-μP electrodes showed highly sintered morphologies, which resulted in extremely low electric resistivity (8.34 μΩ cm) under optimal conditions. [ABSTRACT FROM AUTHOR]

Wearable electronics with optical modulation in the visible and infrared range attract great interest due to promising diverse applications in displays, camouflage, visual sensation, and thermal management. Among different optical modulation approaches, electrochromic (EC) technology, with high controllability, abundant colour species, and low energy consumption, can realize reversible visible and infrared modulation through electrochemical redox reactions of the EC materials under a low voltage. As a result, the wearable flexible EC devices have made significant progress in mechanical flexibility, device structure, and optical modulation range. In this Review, we systematically introduce and discuss the recent advances in wearable EC devices with optical modulation from the visible to infrared range. The structure features for planar and fibre EC devices are first introduced. The bendable, stretchable, and EC fibre devices are then discussed based on the choice of materials and structural design. The progress of EC devices with infrared modulation is summarized according to material classification. At last, their potential applications are demonstrated in wearable displays, camouflage, energy storage, visual sensation, and thermal comfort, which may promote the wide application of wearable electronics. [ABSTRACT FROM AUTHOR]

The advancement of printed flexible electronics technology endows RFID tags with a simple fabrication process and innovative features such as flexibility, stretchability, and wearability. Flexible RFID tags based on printed flexible electronics technology are attracting considerable research interest. There are two main factors to consider when employing flexible printed electronics technology to create a flexible RFID tag antenna. One is the antenna structure design and the selection of conductive and flexible substrate materials, and the other is the fabrication of antenna prototypes and performance assessment that can satisfy specific demands. Both bring significant challenges to the materials, printing process, structural design and performance tuning of the antenna. Currently, most research is focused on the design and structure optimization of flexible RFID antennas, with just a few exceptions in inkjet printing based flexible electronics technology. Flexible antennas and printed flexible electronics technologies are yet to be efficiently combined, and systematic research and mutual development in terms of material selection, antenna design and simulation, prototype fabrication and measurement are yet to be achieved. Therefore, there is a strong need to do the research work in this field. This paper summarizes the current advances in flexible printed RFID antennas, with particular attention to antenna design, material selection, fabrication technologies, and applications. The challenges in each aspect are also explored. Further research should concentrate on the development of innovative materials with improved electrical properties and good surface functionality, the optimization of the fabrication processes, and the intelligent structural design of RFID antennas for multifunction operation. This paper is expected to provide guidance and new ideas for the development of flexible RFID tag antennas. [ABSTRACT FROM AUTHOR]

Photonic sintering of Cu-particle-based printed patterns using intense pulsed light (IPL) is a promising route to the large-scale fabrication of printed electronics for commercial applications. Despite the significant advantages of photonic sintering, which include the process being ultrafast, extremely low-cost, and eco-friendly, realizing a high-conductivity Cu-printed electrode remains a major challenge. In particular, low light absorption caused by the low surface plasmon density of Cu particles is the origin of insufficient temperature increase even after IPL irradiation. In this study, hierarchical nanostructured (HN) Cu microparticles (Cu μPs) with improved light absorption ability and lower surface melting point were prepared for the fabrication of high-conductivity Cu electrodes by using IPL sintering. HN-Cu μPs of uniform size were synthesized using a wet chemical hydrothermal method, with Cu(II) nitrate trihydrate, ethylenediamine (EDA), and Cu μPs as the precursor, structure-directing agent, and template, respectively. The morphology of the hierarchical nanostructures could be readily tuned by varying the synthesis time and the amounts of the precursor and EDA. On the basis of ultraviolet-visible spectroscopy, X-ray diffraction, and temperature measurements, the enhanced light absorption in the visible wavelength range was ascribed to the increase in the surface plasmon density of the hierarchical Cu nanostructures. After photonic sintering, the HN-Cu μP-based printed patterns showed highly dense Cu morphologies, which resulted in an extremely low electrical resistivity of 16 μΩ cm for IPL with an energy density of 7 J cm−2. [ABSTRACT FROM AUTHOR]

Flexible electronics have attracted great attention with the enhanced flexibility of electronic devices, which could be used as flexible sensors, flexible batteries, electronic skin, soft robots, and so on. They play a crucial role in realizing human-machine interactions and developing wearable devices. The stable flexible conductive structure (FCS) with bending, folding, and stretching is necessary for these flexible electronics. As a type of solution processing method, printing techniques have been widely used in fabricating FCSs by printing conductive inks on flexible surfaces. The printable conductive materials are critical for fabricating FCSs by the printing techniques. In this review, the printing techniques for fabricating FCSs are described with inkjet printing, extrusion printing, screen printing, gravure printing, and micro-contact printing. Moreover, the printable conductive materials for fabricating FCSs are presented, including organic conductive materials, inorganic conductive materials, and metallic materials. Meanwhile, the synergistic effects for fabricating FCSs are discussed among printing techniques, printable conductive materials, and flexible substrates. Finally, the remaining challenges and prospects are proposed for fabricating FCSs, which would provide a valuable reference for constructing flexible electronics. [ABSTRACT FROM AUTHOR]

In this paper, we show that the surface morphology of silver (Ag) structures prepared by plasma conversion of particle-free inks can be controlled by solvent evaporation effcts. A series of three ethylene-glycol-based solvents were used to systematically vary the vapor pressure of the ink. Following inkjet printing, films were converted by exposure to a low-pressure, low-temperature radio-frequency (RF) plasma. Scanning electron microscopy (SEM) and profilometry of the Ag films showed that the surface roughness and porosity depend on the vapor pressure of the ink solvent, with each increasing with decreasing vapor pressure. As a result of changes to the porosity, electrical resistivity increased as the solvent vapor pressure decreased. To demonstrate the utility of a printing technique for rough and porous metal films, we fabricated Ag-based hydrogen peroxide (H2O2) sensors using inks comprised of the three ethylene-glycol-based solvents. The sensitivity of these sensors was found to increase with the surface roughness and porosity, which in turn, was related to the vapor pressure of the solvent. [ABSTRACT FROM AUTHOR]

In this study, we investigated facile "dragging mode" electrohydrodynamic (EHD) jet printing of a polymer-wrapped semiconducting single-walled carbon nanotube (s-SWCNT) ink, for fabrication of NO gas-sensing field-effect transistors (FETs). The "dragging mode" provides a favorable environment for reliable printing and interconnection between the s-SWCNTs. Printing parameters such as supply voltages, printing speeds, and the number of prints were manipulated to find an optimal printing condition and obtain high-performance FETs. Under optimal conditions, the polymer-wrapped s-SWCNT-based FETs exhibited an average field-effect mobility of 2.939 cm2 (V−1 s−1), a threshold voltage of 2.21 V, an on/off ratio of ∼103, and a subthreshold swing of 0.968 V dec−1. Additionally, we demonstrated the application of FETs as NO sensors with high sensitivity and selectivity. The FET-type NO gas sensor exhibits a dynamic sensing range of 500 ppb–30 ppm and clear selectivity among various analyte gases including ethanol, ammonia, and acetone. Therefore, the "dragging mode" EHD jet printing introduced in this study simplifies patterning processes and is a potential reproducible method for the fabrication of next-generation gas sensors. [ABSTRACT FROM AUTHOR]

The advances in the nanotechnology and materials chemistry research has revolutionized the field of stretchable, flexible, and wearable electronics for next-generation applications. Specifically, the exploration and progress of MXene have made a remarkable breakthrough in modern materials chemistry research to fabricate and design high-performance wearable electronics. MXene has been extensively studied to design flexible and wearable devices by integrating them with highly flexible conducting polymers to improve their performance and impart new functionalities. This review summarizes the recent advances of MXene integrated conducting polymers (MXCP) to design composite structures for wearable electronics. Synthesis of MXene and strategies to fabricate MXCP composites are highlighted along with their mechanical and electrical properties. Different applications of MXCP in energy storage, electromagnetic shielding, personal thermal management, sensors and bioelectronics are discussed. The review also suggests the routes towards exploring the vast potential of MXCP composites for wearable electronic applications. [ABSTRACT FROM AUTHOR]

The fabrication of electronics on the basis of biofriendly materials aims to counterbalance the negative trends conveyed by the short life-cycle of electronics. Furthermore, these materials open the possibility to develop optoelectronic technologies which will be in contact with the human body. In this work, we present an electrochromic display fabricated by resource- and energy-efficient digital printing techniques. The biodegradation of the device is certified under the ISO 14855 standard. The display comprises of a poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) electrochromic layer, a gelatin-based electrolyte and Au electrodes deposited on a cellulose di-acetate substrate. We investigate the impact of various naturally sourced ionic species on the ionic conductivity of the electrolyte and the figures of merit of the display. The printed devices show an electrochromic contrast of 32 ± 4% and switching times of 3.0 ± 1.4 s, comparable to the spincoated reference devices. The utilization of inkjet printing enables the fabrication of different device designs with individually addressable pixels. The display can be worn innocuously on the skin without loss of performance thanks to the self-adhesion properties of the gelatin hydrogel. The present work highlights the use of industrial relevant technology for the fabrication of truly ecofriendly optoelectronic systems. [ABSTRACT FROM AUTHOR]

The strong light confinement and near field enhancement by metallic scatters enabled the development of a large family of plasmonic-based technologies, including broadly used gold metasurfaces. Despite progress, the engineering of non-precious metal plasmonic devices remains challenging, due to the limited chemical stability of most nanostructured metals. Here, we report the preparation of earth-abundant plasmonic metasurfaces by the engineering of copper-graphene nano-resonators, and their use as localized surface plasmon resonance (LSPR) sensors. We achieve the large-scale self-assembly of Cu nanocrystals, featuring a protective graphene film, by one-step reduction of CuO nanoparticle networks in a hydrocarbon-containing atmosphere. Microscopic and spectroscopic investigations reveal that coalescence and reduction of the CuO nanoparticles during graphene growth result in the formation of graphene-encapsulated metallic Cu nano-islands (NIs). These Cu–graphene metasurfaces can detect down to 1% concentrations of toluene gas at room temperature, displaying a reproducible and rapid LSPR shift of 0.2 nm. Finite-difference time-domain (FDTD) simulation and structural characterization reveal that the graphene layer significantly improves the Cu crystals' long-term stability, leading to a prolonged LSPR performance over periods of three months. These insights provide promising directions for the development of earth-abundant plasmonic materials with applications ranging from biosensing to photo-catalysis and other optoelectronic devices. [ABSTRACT FROM AUTHOR]

The ability to add functionality to flexible substrates through additive approaches using electronic and optical materials for wearable or conformal applications has become increasingly important in recent years. In this paper, the development of several germanium based semiconductor inks is detailed, their printing and post-processing using photonic annealing is demonstrated, and their electro-optic performance is characterized. A range of inks were developed, namely a pristine germanium nanoparticle ink, a nickel doped germanium nanoparticle ink, and a hybrid silver nanoparticle/germanium nanoparticle ink. Aerosol jet printing was performed on both rigid substrates and a common flexible polyimide substrate (KaptonTM). Photonic sintering was used on all three printed inks to improve their optoelectronic properties and coalesce the individual particles into a continuous film. Optical and structural characterization of the printed films was performed before and after photonic sintering to investigate morphological changes in the film. Finally, the applicability of these inks in flexible optoelectronic applications was demonstrated by measuring the photo-excited conductivity changes as well as the flexibility of the printed films. [ABSTRACT FROM AUTHOR]

The emerging human–machine interfacing applications have driven the developments of soft electronic devices that can seamlessly bridge electronics and tissues. Despite impressive progress, mismatches between current bioelectronic devices and biological tissues in both mechanical properties and charge transportation still exist, which could cause severe pain and damage to tissues. Herein, we present an ultra-stretchable all-hydrogel device with custom-designed microchannel patterns perfused with ionic liquids. Hydrophobic ionic liquids (ILs) are sufficiently conductive and remain stably separated from aqueous surroundings both in air and underwater, representing a perfect soft conductor for stretchable electronics. The potential of such designer IL-perfused all-hydrogel devices is demonstrated as soft conductors for triggering light-emitting diodes and as soft sensors for skin-conformed sensing under large stretches. We envision that such soft ionic devices may be useful for stimulating neurons and muscles in vivo with reduced immune responses. [ABSTRACT FROM AUTHOR]

Copper nanowire (Cu NW)-based functional electrodes are one of the most important components in next-generation flexible and wearable electronics due to their superior electrical conductivity and remarkable mechanical flexibility. In the past decades, researchers have focused on the study of Cu NWs and have achieved many innovative results from synthesis to applications. Importantly, Cu NWs have immeasurable potential for extensive practical applications, especially in the field of electronic devices, due to their significantly lower price compared to other metal NWs. This review article emphasizes the recent progress of Cu NWs in electronic applications, including flexible transparent electrodes for optical devices, current collectors for lithium-ion batteries, and stretchable electrodes for wearable devices. Furthermore, various technical issues and personal perspectives are discussed that will help the researchers to solve some of the difficulties faced in the future. Finally, we put forward a brief outlook of Cu NWs in the above-mentioned electronics to promote better exploration and development of research for practical applications. [ABSTRACT FROM AUTHOR]

Stretchable electronics are becoming an important branch in the field of electronics, with a rapidly growing number of studies on highly deformable circuits that can handle large tensile strains without losing electronic functionality. However, as the field continues to advance, a variety of manufacturing approaches must be explored so that these circuits can be produced in a rapid, precise, repeatable, inexpensive, and high-volume manner. Even in cases where methods from conventional printed circuit board (PCB) manufacturing are used, these techniques must be significantly modified in order to process the soft materials and fluids that are unique to stretchable electronic architectures. Digital printing methods such as Inkjet printing, 3D printing and laser ablation are especially attractive since they can be automated and eliminate the need for a stencil, mask or clean-room lithography. This article reviews recent advances in digital fabrication of stretchable circuits using either additive techniques, that allow direct printing of certain materials with a determined shape, or subtractive methods, in which the desired pattern is obtained by selectively removing parts of a greater film. For most of the materials used in stretchable electronics, these fabrication methods can be simple to implement, low cost, scalable over large areas, compatible with a broad variety of materials and have a size resolution that is comparable to conventional PCB manufacturing. [ABSTRACT FROM AUTHOR]

Inkjet printing is recognised as an efficient method for direct deposition of functional materials on flexible substrates in predesigned patterns owing to simple processing, low cost and higher adaptability for large scale fabrication of electronic devices, sensors, light emitting diodes, etc. Inks used in inkjet printing mostly consist of organic polymers, metal nanoparticles and carbon materials such as graphene and carbon nanotubes. For effectiveness of the printing process, the fluid dynamic parameters such as viscosity and surface tension, as well as dimensionless quantities such as the Weber number, Reynolds number, and Ohnesorge number, must be within a suitable limit. More frequently, this process suffers due to the formation of a coffee ring during the post printing process, which affects the morphology as well as electrical conductivity of the printed pattern. In this review, we have summarized the various aspects of inks such as fluid dynamical parameters of inks, mechanism of the coffee ring formation, different types of ink preparation strategies and their applications in sensors, thin film transistors, and energy storage devices. [ABSTRACT FROM AUTHOR]

The strong spin–orbital coupling in the two-dimensional semiconducting materials i.e. MoS2 sheets, originated from the d orbitals of Mo atoms, splits their valence band at the K and K′ valleys of the Brillouin zone into two levels. Ultra-high-resolution absorption, photoluminescence (PL), and Raman measurements conducted for an individual MoS2 sheet functionalized with polymer on the top of silver nanoparticle arrays suggested that the plasmon–exciton interaction and photothermal mechanisms are not supported. A direct correlation between the strength of the electromagnetic plasmon field of the silver nanoparticle arrays, calculated by finite time domain difference technique, and the energy difference between A and B absorption and PL peaks is observed. This suggested that the electromagnetic field of the plasmonic nanoparticles altered the spin–orbital coupling in the MoS2 thus changed the ground state splitting. Silver nanoparticle arrays such as nanotetrahedron (AgNT) and nanocube (AgNC) are used. AgNT 2D arrays with different sizes were prepared on glass substrates by the overgrowth of silver hemispheres, while AgNC 2D arrays were prepared by the overgrowth of silver monolayers. [ABSTRACT FROM AUTHOR]

Smart windows are defined by their ability to regulate incoming solar radiation in order to reduce the energy consumption of buildings by modulating the heat intake. Vanadium dioxide (VO2) is one of the most promising potential candidates for smart window materials due to its ability to reversibly transit from monoclinic VO2 (M) to rutile VO2 (R) at near room temperature. As a result of this transition, the infrared radiation (IR) transparent VO2 (M) abruptly becomes IR opaque, effectively regulating the heat intake by solar radiation. Despite their promising potential, VO2-based smart windows have various significant intrinsic limitations: a high transition temperature (τC) of 68 °C; low luminous transmission (Tlum) of around 40% and low solar modulation (ΔTsol) of less than 25%. Currently, various methods have been used to fabricate VO2 thin films in an attempt to improve their intrinsic properties. One of those methods is physical vapour deposition (PVD). In this paper, various PVD techniques, such as pulsed laser deposition (PLD), evaporation decomposition (ED) and sputtering, are examined with respect to their conditions for VO2 fabrication, film quality and the strategies for film improvements. Lastly, some challenges and opportunities for further studies into VO2-based smart windows are discussed. [ABSTRACT FROM AUTHOR]

Electrochromic devices (ECDs) have attracted considerable attention due to their high coloration efficiency and low power consumption. However, the development of flexible ECDs is still at a rudimentary stage due to the poor chemical stability of flexible electrodes, which prevents the fabrication of widely used WO3 electrochromic (EC) materials via traditional techniques. Herein, uniform and lamellar porous WO3 films were successfully prepared on a flexible Ag nanofiber (Ag NF) network film via a pulsed electrochemical deposition method. The sandwich structure with configuration WO3/Ag NFs/WO3 (W/Ag NFs/W) could not only protect the Ag networks from oxidation and corrosion in the oxidizing electrolyte, but also promote the electrodeposition of WO3 films in the gaps among the Ag networks. The obtained porous WO3 film is beneficial for electrolyte infiltration and alleviates mechanical stress. An 89.7% optical modulation with excellent cycling stability was achieved when the hybrid electrode was utilized as the EC film. Moreover, we demonstrated the practical suitability of our hybrid films in all-solid-state ECDs by fabricating EC sunglasses and a smart window. [ABSTRACT FROM AUTHOR]

Large-scale industrialization of flexible printed electronics will thrive on advanced functional conductive pastes with excellent properties such as high electrical conductivity and mechanical stability. Herein, we develop an effective method to simultaneously decrease the electrical resistivity and improve the mechanical stability of silver-resin-based conductors by adding a small amount of nanostructured polyaniline (PANI). PANI nanomaterials for improving the properties of conductive composites were synthesized by a facile and repeatable chemical oxidative polymerization method and characterized. Significant improvements in electrical performance were observed. For example, for the 60 wt% silver-filled flexible conductors, the addition of 0.5 wt% PANIs reduces their electrical resistivity to one-thirtieth (from 1253.1 × 10−5Ω cm to 37.1 × 10−5Ω cm). After adding 0.5 wt% PANIs, the bending stability (ΔR/R0) was also greatly improved from 92% to 2.3% (about 1/40th). Meanwhile, elastic conductors showed a much better performance in resistance stability and fatigue life (5 times longer than before) during stretching cycles after the addition of PANIs. A bendable printed circuit and a printed tensile resistive sensor were fabricated using the above PANIs to enhance conductive composites, which proved their potential applications in flexible printed circuits, stretchable pressure sensors, and e-skin or other fields. [ABSTRACT FROM AUTHOR]

Transparent conducting electrodes (TCEs) have played a pivotal role in driving the continuous development of optoelectronics technologies, which include organic optoelectronic applications. In recent years, there has been huge interest in designing innovative TCEs to replace the conventional indium tin oxide (ITO) electrodes, which suffer from complex fabrication issues and are incompatible with flexible, wearable electronic devices. In this regard, TCEs based on metal meshes are considered to be the best candidates because of their inherently high electrical conductivity, optical transparency, mechanical robustness and, more importantly, cost-competitiveness. In this review, we describe the technology developments of metal mesh-based transparent conductors and their applications in organic optoelectronic devices, including organic and perovskite solar cells, organic light emitting diodes, supercapacitors, electrochromic devices etc. Specifically, we discuss the fundamental features, optoelectronic properties, fabrication techniques and device applications of metal mesh TCEs. We also highlight the important criteria for evaluating the performance of metal mesh electrodes and propose some new research directions in this emerging field. [ABSTRACT FROM AUTHOR]

Copper hydroxide possesses a much higher copper content and lower price than other copper salts, however it decomposes to cupric oxide and water upon heating, restricting it as a self-reducible copper precursor. In this study, a novel self-reducible copper hydroxide complex with amino–alcohol is successfully developed. Copper hydroxide was converted to a self-reducible complex with 3-dimethylamino-1,2-propanediol (DMAPD), in which the copper ions could be reduced to elementary copper at suitable temperatures. Moreover, the addition of a small amount of formic acid can catalyze the self-reduction of the complex to copper completely. In particular, the self-reduction temperature could be reduced to about 130 °C and the sintered films exhibited good electrical conductivity. A possible cyclic reduction mechanism showing the catalytic effect of formic acid was proposed. This low temperature sintering self-reducible complex makes copper hydroxide a new potential copper source for the fabrication of conductive copper films. [ABSTRACT FROM AUTHOR]

We report a novel cost-effective digital fabrication method for the production of high resolution electrodes of 1 μm-grade width on multiple planes connected at an angle using an affordable light source. This was achieved by the laser filament growth sintering of nanoseed/organometallic hybrid precursors, which were reformulated from a low-cost, particle-free, ionic organometallic solution. Growth sintering of the hybrid precursor, which creates solid electrodes through the sequential thermo-chemical interactions of nucleation, clustering, thermal growth, and aggregation, improves the conductivity and resolution of the electrodes via bottom-up thermal crystallization and stable chemical transition processes. The laser filament with a Bessel profile, which was modulated from a conventional low-cost laser with a Gaussian profile, localizes the growth sintering interaction within a transversely elongated focusing area close to the diffraction limit, unlike the very narrow focusing area in typical laser optics. As a result, this method enabled the fabrication of an ultra-transparent conductor with a transmittance of more than 97% in the visible spectrum. The electrodes were completely invisible to the naked eye, even when viewed at close range. A transparent micro-heater for humidity-free smart glasses was successfully fabricated to demonstrate the potential of one-step manufacturing of functional wearable devices. [ABSTRACT FROM AUTHOR]

Thermochromic systems are promising candidates for energy-saving smart window applications. However, these passively responsive optical materials are subject to limitations such as a lack of active optical control, poor solar modulation (ΔTsol) ability, and rather inconvenient switching-temperature tunability. Herein, we present a simply processed hybrid thermochromic soft-matter material sandwiched between two transparent graphene sheets, where the intermediate material possesses a phase-separated polymer framework containing liquid-crystalline micro-domains with sematic A (SmA) to chiral nematic (N*) phase change behavior and tungsten doped vanadium dioxide (W–VO2) nanocrystals (NCs). This hybrid organic/inorganic thermochromic system not only features high mechanical strength, excellent flexibility and large-area processibility, but also possesses a dual-active/passive optical modulation mode, controllable visible and near infrared light transmittance, a tunable switching-temperature and a high ΔTsol of 40.9%. This work not only enriches the family of thermochromic materials, embracing broad practical applications in buildings and automobiles, but also gives new insights into the next generation of smart window technologies. [ABSTRACT FROM AUTHOR]

Recently, nanoporous gold nanoparticles have attracted great interest due to their optical and catalytic properties. However, most reports on their fabrication are based on the dealloying method. Here, we report a new fabrication technique for hollow nanoporous gold nanoshells (NPGNSs) with high structural tunability by sintering chemically synthesized gold nanoparticles (AuNPs) on the surface of polymer colloid particles. Size reduction of the colloid template by plasma etching induces contact of the AuNPs on the colloid surface. Elimination of the capping layers of AuNPs by plasma etching facilitates sintering of the contacted AuNPs. Complete removal of the colloid template after AuNP sintering results in hollow NPGNSs. A combination of AuNPs and polymer colloid templates of different sizes can change the structure and optical properties of hollow NPGNSs. Furthermore, AuNPs of different shapes, such as gold nanorods with a high aspect ratio and spherical AuNPs, can be used to make hollow NPGNSs, which gives more flexibility in tuning their structures. Our proposed fabrication technique based on shrinkage of templates and sintering of nanoparticles can be a new platform to prepare hollow nanoporous metal structures having nanoscale overall sizes with high structural tunability. [ABSTRACT FROM AUTHOR]

A novel generation of flexible opto-electronic smart applications is now emerging, incorporating photovoltaic and sensing devices driven by the desire to extend and integrate such technologies into a broad range of low cost and disposable consumer products of our everyday life and as a tool to bring together the digital and physical worlds. Several flexible polymeric materials are now under investigation to be used as mechanical supports for such applications. Among them, cellulose, the most abundant organic polymer on the Earth, commonly used in the form of paper, has attracted much research interest due to the advantages of being recyclable, flexible, lightweight, biocompatible and extremely low-cost, when compared to other materials. Cellulose substrates can be found in many forms, from the traditional micro-cellulose paper used for writing, printing and food/beverage packaging (e.g. liquid packaging cardboard), to the nano-cellulose paper which has distinct structural, optical, thermal and mechanical properties that can be tailored to its end use. The present article reviews the state-of-the-art related to the integration and optimization of photonic structures and light harvesting technologies on paper-based platforms, for applications such as Surface Enhanced Raman Scattering (SERS), supporting remarkable 107 signal enhancement, and photovoltaic solar cells reaching ∼5% efficiency, for power supply in standalone applications. Such paper-supported technologies are now possible due to innovative coatings that functionalize the paper surfaces, together with advanced light management solutions (e.g. wave-optical light trapping structures and NIR-to-visible up-converters). These breakthroughs open the way for an innovative class of disposable opto-electronic products that can find widespread use and bring important added value to existing commercial products. By making these devices ubiquitous, flexible and conformable to any object or surface, will also allow them to become part of the core of the Internet of Things (IoT) revolution, which demands systems’ mobility and self-powering functionalities to satisfy the requirements of comfort and healthcare of the users. [ABSTRACT FROM AUTHOR]

Inorganic printed electronics is now recognized as an area of tremendous commercial, potential and technical progress. Many research groups are actively involved worldwide in developing metal nanoparticle inks and precursors for printing inorganic/organic materials using different printing techniques. This review article focuses on inkjet printed metal structures and their applications. It comprises ink formulation, optimal droplet formation as well as adhesion of the printed patterns at the underlying substrate and post-treatment like sintering to be considered in the initial ink design. Besides some examples demonstrating aspects on ink formulation via patterning solid surfaces such as glass and silicon oxide, special emphasis will be placed on compatibility for usage in plastic and paper electronics. Printing of nanoparticles of copper, silver, gold etc. will be discussed and will be compared to printing of a variety of metal–organic precursor inks. Finally, a brief account on exemplary applications using the printed inorganic nanoparticles/materials is provided. [ABSTRACT FROM AUTHOR]

Due to the increased power density of electronic devices, the heat originated from the core components increases the working temperature of the devices, enormously degrading their reliability and shortening their lifespan. So, effective heat dissipation from high-power electronic devices has become an urgent and complex problem. Herein, we report epoxy-based composites with an enhanced thermal conductivity by using reduced graphene oxide encapsulated copper sphere (Cu@rGO) hybrids as fillers. The Cu@rGO hybrid exhibits a 3D structure with high oxidation resistance. The obtained polymer composites exhibit a high thermal conductivity (7 W m−1 K−1), as the loading of the Cu@rGO hybrids is 80 wt%, which is 2.6 times higher than that of the polymer composites filled with only Cu spheres. The high thermal conductivity might be attributed to the synergistic effects between spherical Cu and rGO nano-sheets, which enhanced the oxidation resistance of copper and increased the thermal transfer path, along with the reduced interfacial thermal resistance between Cu and epoxy resins. In addition, the Cu@rGO/epoxy composites reveal a decreased thermal expansion coefficient (CTE), an increased glass transition temperature (Tg), and an enhanced shear strength. This unique 3D core–shell Cu@rGO structure and its epoxy composites with high thermal conductivity and dimensional stability could be suitable as excellent thermal interface materials in advanced electronic packaging techniques. [ABSTRACT FROM AUTHOR]

Flexible transparent conducting electrodes (TCEs) are promising for use in electrochromic devices (ECDs), owing to their flexibility to operate in nonplanar configuration. The successful introduction of indium tin oxide (ITO)-coated glass into rigid and planar display devices made ITO on a transparent polymer film an attractive option for flexible devices. However, the flexible characteristic of the ITO film is compromised by its higher surface resistance compared to that of ITO glass. Here, we report printing silver grid on ITO film using an electrohydrodynamic (EHD) jet method, varying the grid pitch. This mask-free method to introduce silver grids onto ITO was used for ECD fabrication. The results showed improvements in colour quality and response time that are attributed to the enhanced conductivity of the silver grid ITO film under low-voltage (1.0 V) operation. Our approach can be used to improve soft ECDs by improving the performance of flexible TCEs. [ABSTRACT FROM AUTHOR]

A water-based environmentally friendly electrically conducting ink composed of cellulose nanocrystals (CNC) and polyaniline (PANI) was prepared. PANI was synthesized by the emulsion polymerization approach using dodecylbenzenesulfonic acid (DBSA) as the dopant to induce spherical nanoparticulate formation. Glycerol was used to adjust the viscosity of the ink. The CNC–PANI ink was characterized by transmission electron microscopy, UV-visible spectroscopy and viscosity measurements. The ink was successfully printed on multilayer curtain coated paper by the flexographical printing method. The printed layers were characterized by optical and atomic force microscopy techniques and cyclic voltammetry. A stable nanoparticulate CNC–PANI ink with an electrical conductivity of the printed films between 30 and 60 S cm−1 was obtained which was more than an order of magnitude higher than for the corresponding film without CNC. [ABSTRACT FROM AUTHOR]

Inkjet printing of graphene inks is considered to be very promising for wearable e-textile applications as benefits of both inkjet printing and extra-ordinary electronic, optical and mechanical properties of graphene can be exploited. However, the common problem associated with inkjet printing of conductive inks on textiles is the difficulty to print a continuous conductive path on a rough and porous textile surface. Here we report inkjet printing of an organic nanoparticle based surface pre-treatment onto textiles to enable all inkjet-printed graphene e-textiles for the first time. The functionalized organic nanoparticles present a hydrophobic breathable coating on textiles. Subsequent inkjet printing of a continuous conductive electrical path onto the pre-treated coating reduced the sheet resistance of graphene-based printed e-textiles by three orders of magnitude from 1.09 × 106Ω sq−1 to 2.14 × 103Ω sq−1 compared with untreated textiles. We present several examples of how this finding opens up opportunities for real world applications of printed, low cost and environmentally friendly graphene wearable e-textiles. [ABSTRACT FROM AUTHOR]

A facile aqueous-based seed-mediated chemical reduction method is developed for the synthesis of copper nanoparticles. The nanoparticles are utilized to fabricate a flexible chemical sensor. The seed particles are spherical in shape with a mean diameter of 4.5 nm. Seed mediated growth is carried-out on the seed particles using l-ascorbic acid as a reducing and a capping agent in an aqueous solution. The seed mediated growth yields pure copper nanoparticles with a bimodal size distribution with mean diameters of 3.6 and 64.6 nm. The structural characterization, using X-ray diffraction (XRD) and UV-Visible spectroscopy (UV-Vis), reveals that the synthesized particles are oxidation free and exhibit a monotonic surface plasmon resonance (SPR) peak at 572 nm. The formulated nanoparticulate ink is printed on a flexible polyethylene terephthalate (PET) substrate and sintered with an intense pulse light (IPL) technique under ambient conditions resulting in an oxidation-free copper film within a milli-second time scale. The sheet resistance of the sintered film reaches 0.16 Ω□−1 yielding a film resistivity of 9.6 × 10−5Ω cm. The as-synthesized particles are further employed to print interdigitated electrode patterns on a PET substrate using a syringe dispensing system. A chemical sensor is fabricated on the interdigitated electrodes using a novel graphite and polyethylene glycol (PEG) composite film. The chemical sensor exhibits an excellent response with up to 300 times change in the initial resistance when exposed to different concentrations of ethanol vapors, which demonstrates the potential of utilizing the copper nanoparticles developed in this study for flexible printed electronics applications. [ABSTRACT FROM AUTHOR]

Correction for ‘Inkjet printed paper based frequency selective surfaces and skin mounted RFID tags: the interrelation between silver nanoparticle ink, paper substrate and low temperature sintering technique' by Veronica Sanchez-Romaguera et al., J. Mater. Chem. C, 2015, DOI: 10.1039/c4tc02693d. [ABSTRACT FROM AUTHOR]

Electrochromic materials could modulate the optical transmittance reversibly by the application of electric potential and the increase in the surface area for fast ionic diffusion is an efficient way to improve their electrochromism. In this work, WO3 based nanomaterials with a size as small as 5 nm were synthesized via a facile wet bath method that leads to Ti doping of WO3 based on the heterovalency of W(vi) and Ti(iv). Ti doping improved the WO3 electrochromism effectiveness in transmittance contrast and coloration efficiency due to the reduced crystallite size and therefore an increase in the surface area, the Ti doping also enhanced the cycling stability benefiting from the stable Ti–O bonding. However, the coloring/bleaching kinetics were deteriorated due to the reduced proton diffusion coefficient after the Ti ion substitution into the WO3 lattice. A high coloration efficiency of 106.6 cm2 C−1 and a good optical contrast of ∼67.6% can be obtained for the optimized Ti-doped WO3 at a wavelength of 633 nm. [ABSTRACT FROM AUTHOR]

Recently, intense pulsed light (IPL), also referred to as flash lamp annealing, has gained interest among materials scientists as a highly effective photonic technology for structural reformation and/or chemical modification of various nanomaterials. Split-second exposure of IPL on advanced materials of various compositions, including ceramics, metals, and carbon, and various structures, including nanoparticles, nanowires, and thin films, resulted in dramatic changes in the morphologies and chemical functional groups of the materials. Compared to conventional thermal heating and established photonic technologies such as lasers, IPL technologies have considerable advantages, such as facile equipment set-up, surface-selective treatment, large treatment area, short process times ranging from milliseconds to a few seconds, and roll-to-roll process compatibility. In this review, recent advances in the structural development and/or chemical modifications of various nanomaterials by IPL irradiation will be highlighted. [ABSTRACT FROM AUTHOR]

Herein, a reversible electrochemical mirror (REM) device was electrochemically tuned to achieve dual transmittance and reflectance modulations in a single device. Conventional REM devices reversibly switch between transparent and mirror states. However, it is a significant challenge to maintain the mirror state of the REM devices due to the diffusion of anions into the metal film at the open-circuit state. In this study, we report a Cu-based REM device that offers reversible switching between transparent, blue, and mirror states via a judicious selection of electrolyte and controllable electrodeposition. The blue state can be obtained through the formation of copper(i) chloride (CuCl) when copper(ii) chloride (CuCl2) undergoes electrochemical reduction. Moreover, the polymer host PVA (polyvinyl alcohol) plays an important role in reducing the surface roughness of the electrodeposited mirror film, improving film uniformity, and maintaining the mirror state of the device during the voltage-off state. [ABSTRACT FROM AUTHOR]

In recent years, wearable electronics have experienced tremendous development due to their promising applications in fields such as portable, flexible/stretchable human-interactive sensors, displays, and energy devices. To effectively fabricate wearable electronics, a high-efficient, cost-saving, and eco-friendly manufacture technology is required. Inkjet printing, which rapidly, precisely, and reproducibly deposits a broad variety of functional materials in a non-impact, addictive patterning, and maskless approach, serves as an effective tool for the fabrication of wearable electronics. In this review, the recent advances in inks, strategies, and the applications of inkjet-printed wearable electronics are summarized. Based on uniform and high-resolution patterns, well-compatible functional inks can be deposited to fabricate flexible/stretchable and durable wearable electronics. Perspectives on the remaining challenges and future developments are also proposed. [ABSTRACT FROM AUTHOR]

A route to cheap and disposable sensors for the chemical sensing market, with potential applications including monitoring of food spoilage, is reported herein. The sensor is the result of the direct integration of a stimuli-responsive material, poly(dimethylsiloxane) (PDMS), with an electronic component. The printing and sintering of colloidal silver ink solutions onto PDMS was optimized to allow the printing of conductive silver feed loops, which are the active sensing component in antennas for passive (battery-free) Radio Frequency Identification (RFID) tags. The response of these devices is related to the degree of swelling of the PDMS, which, in turn, has been shown to be correlated to the Hansen solubility parameters and the vapour pressures of the corresponding volatile organic compounds (VOCs). When exposed to solvent vapour the printed feed loop fractures, increasing resistance and ultimately breaking conductivity, leading to a change in the transmitted power and read range of the wireless device. Remarkably upon removal from the vapour, the fractured feed loops reassemble and become conductive again, making them switchable and “multi-use”. This work paves the way to a fully inkjet printed RFID substrate for vapour detection. [ABSTRACT FROM AUTHOR]

Submicron Cu particle ink was developed to successfully achieve highly reliable and highly conductive Cu patterns on low-cost, transparent, and flexible substrates by an optimized two-step sintering process involving low temperature heat-welding and subsequent flash light sinter-reinforcement. The Cu ink contains a special additive of the Cu–amino complex made from copper(ii) formate and 2-amino-2-methyl-1-propanol solvent. Low temperature heat-welding promotes the decomposition of the Cu–amino complex into fresh metallic Cu particles, which as nano-welders can in situ weld those big submicron Cu particles. The subsequent flash light sintering further reinforces the connection between big Cu particles with the assistance of these active nano-welders and strengthens the adhesion between sintered Cu patterns and polymer substrates due to the local soft-effect. The achieved resistivities of sintered Cu patterns on polyethylene terephthalate (PET), polyethylene naphthalate (PEN) and polyimide (PI) substrates are 26.5 μΩ cm, 15.9 μΩ cm and 7.2 μΩ cm at a low welding temperature of 140 °C for 10 min and subsequent flash light energies of 1080 mJ cm−2, 1273 mJ cm−2 and 2073 mJ cm−2, respectively, at which the same electrical properties cannot be obtained from either pure nano-Cu or submicron Cu particle ink as reported in previous research studies. Moreover, bending fatigue and oxidation-resistance tests indicate that the sintered Cu patterns have superior mechanical and environmental stability. Finally, flexible and foldable LED circuits and flexible dipole antennas were successfully fabricated to demonstrate the applicability of the sintered Cu patterns for printed electronic devices. It should be noted that this method opens a new way for making highly reliable and highly conductive Cu patterns on low-cost, transparent, and flexible substrates with big Cu particles instead of nanoparticles under a suitable sintering process, which may largely decrease the cost and enhance the application of Cu inks for flexible electronic devices. [ABSTRACT FROM AUTHOR]

A method for producing Cu films with low resistivity, based on low temperature sintering, is demonstrated. The Cu inks for preparing conductive Cu films consisted of Cu particles that were coated with a decomposable polymer (poly(propylenecarbonate), PPC) as well as a self-reducible copper formate/1-amino-2-propanol (CuF–IPA) complex as an additive. The sintering temperature used in this study was as low as 100 °C. Following sintering at a temperature of 100 °C, the lowest reported resistivity (8.8 × 10−7Ω m) was achieved through the use of Cu-based metal–organic decomposition (MOD) inks. This was due to the dual promotional effects of the aminolysis of PPC with IPA and the pyrolysis of the CuF–IPA complex. [ABSTRACT FROM AUTHOR]

A critical requirement for highly conductive metallic printing circuits is to obtain consecutive and high-resolution printed patterns. However, the aggregation or assembly of metallic nanocrystals in solution is usually random, which perplexes the consecutiveness and resolution of the printed circuits. In this study, we prepared consecutive nano-resolution circuits by gas/liquid interfacial manipulation. Consecutive gas/liquid interfaces were achieved by electrostatic inducing of a cationic metal ink using anionic surfactant onto the gas/liquid interface to form continuous patterns. Gas/liquid interfacial morphology was manipulated by gas/liquid/solid three phase contact line (TCL); Through controlling TCL sliding on different surfaces, submicron or nano-resolution circuits were fabricated, which showed excellent conductivity. This facile strategy showed significant potential for use in wearable electronics and high-resolution electronic circuits. [ABSTRACT FROM AUTHOR]

Copper (Cu) based conductive inks have been widely studied with the objective of achieving highly conductive and low-cost electrodes for various electrical devices. However, the unstable oxidation properties of Cu inks make them difficult to be applied for a wide range of practical applications. The oxidation properties induce high resistivity in the electrode fabrication, and storage problem of ink. Herein, we introduce a novel self-reducible Cu ion complex ink (Cu-ink), composed by formate, alkanolamine groups and poly alcohols, for the air sinterable, low-cost, environmentally friendly fabrication of Cu conductive electrodes. The air sinterable properties of this novel Cu-ink are induced by the self-reducing activity of the Cu-ink ligand decomposition and the reduction-assistance properties of the polyol solvents. In particular, among various polyol solvents, glycerol was found to be the most suitable reduction assistant-material because of its relatively abundant hydroxyl groups, good evaporation properties, and environmentally friendly solvents. Through investigation of the Cu-ink sintering temperature and glycerol contents, we obtained the Cu electrode films with a low resistivity of 17 μΩ cm at 350 °C under air sintering conditions. Furthermore, various practical characteristics such as excellent storage stability (of up to 4 weeks), enhanced adhesion properties, and flexible retention characteristics for up to 2000 bending times (R/R0 ＜ 1.2, bending radius 20 mm) were also demonstrated for Cu electrode films. [ABSTRACT FROM AUTHOR]

Low-temperature and self-reducible copper inks composed of copper–amino complexes and proper submicron copper seeds are successfully developed, which can increase the copper load of inks to achieve high performance thick and dense conductive patterns. During the heat treatment, the preset copper seeds provide heterogeneous nucleation sites for metallic copper generated from the decomposition of self-reducible copper–amino complexes. These fresh copper nuclei homogeneously attach to the copper seeds to activate their surface, which contributes to the connection and neck-growth between these submicron copper seeds to achieve high conductive copper patterns. The effects of the size of copper seeds and the ratio of the amount of copper–amino complexes to seeds on the electrical resistivity and morphology of sintered copper patterns are clarified, and the functions of the heat treatment temperature and holding time are investigated. The results show that the sintered copper pattern with a high metal load of 36.8%, prepared by heat treatment at a low temperature of 140 °C for only 15 min under nitrogen atmosphere, achieves a low resistivity of 11.3 μΩ cm. Furthermore, the sintered patterns maintain a high-qualitative surface morphology and favorable thickness, and also exhibit a strong adhesion to polymer substrates which will be advantageous for the fabrication of wearable devices. [ABSTRACT FROM AUTHOR]

VO2 has garnered much attention in recent years as a promising candidate for thermochromic window applications due to rising awareness about energy conservation. However, the trade-off between improving the luminous transmittance (Tlum) and solar modulation ability (ΔTsol) limits the commercialization of VO2-based smart windows. Four major nanostructuring approaches were implemented to enhance both Tlum and ΔTsol, namely nanocomposites, nanoporous films, biomimetic moth-eye structures and anti-reflection coating (ARC) multilayers. This work demonstrates a novel approach that fabricates periodic, micro-patterned structures of VO2 using a facile screen printing method. The micro-patterned structure is able to favorably transmit visible light without sacrificing high near-infrared modulation, and the patterned film shows improved Tlum (67% vs. 60%) and ΔTsol (8.8% vs. 6.9%) compared with continuous films. By varying the thickness, periodicity and solid concentration, this approach can give a ΔTsol of 14.9% combined with a Tlum of 43.3%, which is comparable, if not superior to, some of the best reported results found using other approaches. [ABSTRACT FROM AUTHOR]