Photonic sintering via flash white light combined with deep UV and NIR for SrTiO3 thin film vibration touch panel applications.

An ultra-high speed photonic sintering method consisting of flash white light (FWL) combined with near infrared (NIR) and deep UV light irradiations was developed to fabricate a SrTiO3 (STO) thin film for application in electro-vibration touch panels. The STO thin film was sintered on PEN by FWL irradiation at room temperature under ambient conditions, which is a dramatically simple and ultrahigh speed fabrication process compared to the conventional high temperature (600 °C-900 °C) thermal sintering process. The effects of the FWL irradiation conditions (energy density, pulse numbers, and pulse duration) on the dielectric constant of the sintered STO thin films were evaluated. Furthermore, the effects of NIR and deep UV irradiation during the FWL sintering process were also investigated.

Highly conductive copper nano/microparticles ink via flash light sintering for printed electronics.

In this study, the size effect of copper particles on the flash light sintering of copper (Cu) ink was investigated using Cu nanoparticles (20-50 nm diameter) and microparticles (2 µm diameter). Also, the mixed Cu nano-/micro-inks were fabricated, and the synergetic effects between the Cu nano-ink and micro-ink on flash light sintering were assessed. The ratio of nanoparticles to microparticles in Cu ink and the several flash light irradiation conditions (irradiation energy density, pulse number, on-time, and off-time) were optimized to obtain high conductivity of Cu films. In order to precisely monitor the milliseconds-long flash light sintering process, in situ monitoring of electrical resistance and temperature changes of Cu films was conducted during the flash light irradiation using a real-time Wheatstone bridge electrical circuit, thermocouple-based circuit, and a high-rate data acquisition system. Also, several microscopic and spectroscopic characterization techniques such as scanning electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy were used to characterize the flash light sintered Cu nano-/micro-films. In addition, the sheet resistance of Cu film was measured using a four-point probe method. This work revealed that the optimal ratio of nanoparticles to microparticles is 50:50 wt%, and the optimally fabricated and flash light sintered Cu nano-/micro-ink films have the lowest resistivity (80 µΩ cm) among nano-ink, micro-ink, or nano-micro mixed films.

In situ monitoring of a flash light sintering process using silver nano-ink for producing flexible electronics.

In this work, a flash light sintering process using silver nano-inks is investigated. A silver nano-ink pattern was printed on a flexible PET (polyethylene terephthalate) substrate using a gravure-offset printing system. The printed silver nano-ink was sintered at room temperature and under ambient conditions using a flash of light from a xenon lamp using an in-house flash light sintering system. In order to monitor the light sintering process, a Wheatstone bridge electrical circuit was devised and changes in the voltage difference of the silver nano-ink were recorded during the sintering process using an oscilloscope. The sheet resistance changes during the sintering process were monitored using the in situ monitoring system devised, under various light conditions (e.g. light energy, on-time and off-time duration, and pulse numbers). The microstructure of the sintered silver film and the interface between the silver film and the PET substrate were observed using a scanning electron microscope, a focused ion beam and an optical microscope. The electrical sheet resistances of the sintered silver films were measured using a four-point probe method. Using the in situ monitoring system devised, the flash light sintering mechanism was studied for each type of light pulse (e.g. evaporation of organic binder followed by the forming of a neck-like junction and its growth, etc).The optimal flash light sintering condition is suggested on the basis of the in situ monitoring results. The optimized flash light sintering process produces a silver film with a lower sheet resistance (0.95 Ω/sq) compared with that of the thermally sintered silver film (2.03 Ω/sq) without damaging the PET substrate or allowing interfacial delamination between the silver film and the PET substrate.

Flexible Sensor Film Based on Rod-Shaped SWCNT-Polypyrrole Nanocomposite for Acetone Gas Detection.

A nanocomposite rod-shaped structure with a single-walled carbon nanotube (SWCNT) embedded in polypyrrole (PPy) doped with nonafluorobutanesulfonic acid (C4F), SWCNT/C4F-PPy, was synthesized using emulsion polymerization. The hybrid ink was then directly coated on a polyimide film interdigitated with the Cu/Ni/Au electrodes via a screen-printing technique to create a flexible film sensor. The sensor film showed a response of 1.72% at 25 °C/atmospheric pressure when acetone gas of 5 ppm was injected, which corresponds to almost 95% compared to the Si wafer-based array interdigitated with the Au electrode. Additionally, C4F was used as a hydrophobic dopant of PPy to improve the stability of humidity and to produce a highly sensitive film-type gas sensor that provides stable detection even in humid conditions.

In situ monitoring of flash-light sintering of copper nanoparticle ink for printed electronics.

In this work, a flash-light sintering process for Cu nanoinks was studied. In order to precisely monitor the milliseconds flash-light sintering process, a real-time Wheatstone bridge electrical circuit and a high-rate data acquisition system were used. The effects of several flash-light irradiation conditions (irradiation energy, pulse number, on-time, and off-time) and the effects of the amount of poly(N-vinylpyrrolidone) in the Cu nanoink on the flash-light sintering process were investigated. The microstructures of the sintered Cu films were analyzed by scanning electron microscopy. To investigate the oxidation or reduction of the oxide-covered copper nanoparticles, a crystal phase analysis using x-ray diffraction was performed. In addition, the sheet resistance of Cu film was measured using a four-point probe method. From this study, it was found that the flash-light sintered Cu nanoink films have a conductivity of 72 Ωm/sq without any damage to the polyimide substrate. Similar nanoinks are expected to be widely used in printed and flexible electronics products in the near future.

Shape-Tuned Junction Resistivity and Self-Damping Dynamics in Intense Pulsed Light Sintering of Silver Nanostructure Films.

Concurrently reducing processing temperature, electrical resistance, and material cost with scalable fabrication capabilities is critical for conductive elements of flexible and planar electronics. Intense pulsed light sintering (IPL) of mixed dissimilar-shape conductive nanostructures may achieve this goal. However, this potential is hindered by knowledge gaps on how dissimilarity in nanostructure shape affects interparticle neck growth kinetics in general and the self-damping coupling between neck growth and optical absorption in IPL. We study these phenomena for IPL of mixed Ag nanowires (NWs, 40 nm diameter, 100-200 µm length) and nanospheres (NSs, 40 nm diameter), both experimentally and by linking molecular dynamics simulations with optical modeling. An optimal 50:50 mixing ratio lowers resistivity (5.59 µΩ·cm) and peak temperatures (250-150 °C) relative to pure NS films and reduces material costs relative to pure NW films with similar resistivity, in 2.5 s of IPL. The drop in peak temperatures in consecutive optical pulses reduces with greater NW content. Sintering-induced dislocation generation drives higher neck growth at NW-NS and NW-NW interfaces and anisotropic neck growth at NW-NS interfaces. This indicates that when NWs are introduced into NS films, along with lesser number of interfacial contact points, an inherent reduction in sintering-induced junction resistivity plays a major role in reducing film resistivity. The self-damping coupling and optical absorption, which drive temperature evolution in IPL, are tunable by nanostructure shape. The introduction of NWs into a NS ensemble reduces the dependence of optical absorption on neck growth. We discuss how these insights elucidate a set of physical phenomena that can guide the choice of dissimilar shaped nanostructures to concurrently reduce resistivity and temperatures in IPL and other sintering processes.

Ultra-High-Speed Intense Pulsed-Light Irradiation Technique for High-Performance Zinc Oxynitride Thin-Film Transistors.

In this study, we investigated the effects of intense pulsed light (IPL) on the electrical performance properties of zinc oxynitride (ZnON) thin films and thin-film transistors (TFTs) with different irradiation energies. Using the IPL process on the oxide/oxynitride semiconductors has various advantages, such as an ultrashort process time (∼100 ms) and high electrical performance without any additional thermal processes. As the irradiation energy of IPL increased from 30 to 50 J/cm2, the carrier concentration of ZnON thin films decreased from 5.07 × 1019 to 9.96 × 1016 cm-3 and the electrical performance of TFTs changed significantly, which is optimized at an energy of 40 J/cm2 (field effect mobility of 48.4 cm2 V-1 s-1). The properties of TFTs, such as mobility, subthreshold swing, and hysteresis, and the stability of the device under negative bias degraded as the irradiation energy increased. This degradation contributed to the change in nitrogen-related bonding states, such as nonstoichiometric Zn xN y and N-N bonding, rather than that of oxygen-related bonding states and the atomic composition of ZnON thin films. Optimization of the IPL process in our results makes it possible to produce high-performance ZnON TFTs very fast without any additional thermal treatment, which indicates that highly productive TFT fabrication can be achieved via this process.

Selective Wavelength Plasmonic Flash Light Welding of Silver Nanowires for Transparent Electrodes with High Conductivity.

In this work, silver nanowires (AgNWs) printed on a polyethylene terephthalate substrate using a bar coater were welded via selective wavelength plasmonic flash light irradiation. To achieve high electrical conductivity and transparent characteristics, the wavelength of the flash white light was selectively chosen and irradiated by using high-pass, low-pass, and band-pass filters. The flash white light irradiation conditions such as on-time, off-time, and number of pulses were also optimized. The wavelength range (400-500 nm) corresponding to the plasmonic wavelength of the AgNW could efficiently weld the AgNW films and enhance its conductivity. To carry out in-depth study of the welding phenomena with respect to wavelength, a multiphysics COMSOL simulation was conducted. The welded AgNW films under selective plasmonic flash light welding conditions showed the lowest sheet resistance (51.275 Ω/sq) and noteworthy transmittance (95.3%). Finally, the AgNW film, which was welded by selective wavelength plasmonic flash light with optical filters, was successfully used to make a large area transparent heat film and dye-sensitized solar cells showing superior performances.

Rapid Pulsed Light Sintering of Silver Nanowires on Woven Polyester for personal thermal management with enhanced performance, durability and cost-effectiveness.

Fabric-based personal heating patches have small geometric profiles and can be attached to selected areas of garments for personal thermal management to enable significant energy savings in built environments. Scalable fabrication of such patches with high thermal performance at low applied voltage, high durability and low materials cost is critical to the widespread implementation of these energy savings. This work investigates a scalable Intense Pulsed Light (IPL) sintering process for fabricating silver nanowire on woven polyester heating patches. Just 300 microseconds of IPL sintering results in 30% lesser electrical resistance, 70% higher thermal performance, greater durability (under bending up to 2 mm radius of curvature, washing, humidity and high temperature), with only 50% the added nanowire mass compared to state-of-the-art. Computational modeling combining electromagnetic and thermal simulations is performed to uncover the nanoscale temperature gradients during IPL sintering, and the underlying reason for greater durability of the nanowire-fabric after sintering. This large-area, high speed, and ambient-condition IPL sintering process represents an attractive strategy for scalably fabricating personal heating fabric-patches with greater thermal performance, higher durability and reduced costs.

Efficiency enhancement in dye-sensitized solar cells using the shape/size-dependent plasmonic nanocomposite photoanodes incorporating silver nanoplates.

In this work, we describe the efficiency enhancement in dye-sensitized solar cells (DSSCs) by using TiO2/silver nanoplate plasmonic nanocomposite photoanodes. The nanocomposite photoanodes with tunable plasmonic properties assembled from shape/size-selected silver (Ag) nanoplates were applied to enhance the light absorption for high-performance DSSCs. It was found that the localized surface plasmon resonance can be tuned over a range from 500 to 1000 nm, which is strongly dependent on the shape and size of Ag nanoplates and the refractive index of the surrounding dielectric. The effects of the size and shape of Ag nanoplates on the surface plasmonic resonance and the efficiency of DSSCs were evaluated experimentally. Furthermore, a three-dimensional finite element method was employed to investigate the localized surface plasmon resonance (LSPR) for the shape and size effect of Ag nanoplates.

All-photonic drying and sintering process via flash white light combined with deep-UV and near-infrared irradiation for highly conductive copper nano-ink.

We developed an ultra-high speed photonic sintering method involving flash white light (FWL) combined with near infrared (NIR) and deep UV light irradiation to produce highly conductive copper nano-ink film. Flash white light irradiation energy and the power of NIR/deep UV were optimized to obtain high conductivity Cu films. Several microscopic and spectroscopic characterization techniques such as scanning electron microscopy (SEM), a x-ray diffraction (XRD), and Fourier-transform infrared (FT-IR) spectroscopy were employed to characterize the Cu nano-films. Optimally sintered Cu nano-ink films produced using a deep UV-assisted flash white light sintering technique had the lowest resistivity (7.62 µΩ·cm), which was only 4.5-fold higher than that of bulk Cu film (1.68 µΩ•cm).

Ultra-High Speed Fabrication of TiO2 Photoanode by Flash Light for Dye-Sensitized Solar Cell.

In this work, a new way to fabricate nanoporous TiO2 photoanode by flash light is demonstrated. TiO2 nanoparticles are sintered on FTO glass by flash light irradiation at room temperature in ambient condition, which is dramatically simple, ultrahigh speed and one-shot large area fabrication process compared to a conventional high temperature (120 °C) thermal sintering process. The effect of the flash light conditions (flash light energy, pulse numbers and pulse duration) on the nanostructures of sintered TiO2 layer, was studied and discussed using several microscopic and spectroscopic characterization techniques such as SEM, FT-IR, XRD and XPS. The sintered TiO2 photoanodes by flash light were used in DSSC and its performance were compared with that of DSSC fabricated by conventional thermal sintering process. It was found that a flash light sintered TiO2 photoanode has efficiency which is similar to that of the thermal sintered photoanode. It is expected that the newly developed flash light sintering technique of TiO2 nanoparticles would be a strong alternative to realize the room temperature and in-situ sintering of photoanode fabrication for outdoor solar cell fabrication.

Copper Nanoparticle/Multiwalled Carbon Nanotube Composite Films with High Electrical Conductivity and Fatigue Resistance Fabricated via Flash Light Sintering.

In this work, multiwalled carbon nanotubes (MWNTs) were employed to improve the conductivity and fatigue resistance of flash light sintered copper nanoparticle (NP) ink films. The effect of CNT weight fraction on the flash light sintering and the fatigue characteristics of Cu NP/CNT composite films were investigated. The effect of carbon nanotube length was also studied with regard to enhancing the conductivity and fatigue resistance of flash light sintered Cu NP/CNT composite films. The flash light irradiation energy was optimized to obtain high conductivity Cu NP/CNT composite films. Cu NP/CNT composite films fabricated via optimized flash light irradiation had the lowest resistivity (7.86 µΩ·cm), which was only 4.6 times higher than that of bulk Cu films (1.68 µΩ·cm). It was also demonstrated that Cu NP/CNT composite films had better durability and environmental stability than those of Cu NPs only.