High-intensity Pulsed Light Research Articles

Photon induced facile synthesis and growth of CuInS2 absorber thin film for photovoltaic applications

In this paper, we demonstrate the use of high intensity pulsed light technique for the synthesis of phase pure CuInS2 (CIS) thin film at room temperature. The intense pulse of light is used to induce sintering of binary sulfides CuS and In2S3 to produce CIS phase without any direct thermal treatment. Light energy equivalent to the 706mJ/cm2 is found to be the best energy to convert the CIS precursor film deposited at room temperature into CIS pure phase and well crystalline film. The CIS absorber film thus prepared is useful in making printed solar cell at room temperature on substrate with large area.

Facile fabrication of stretchable Ag nanowire/polyurethane electrodes using high intensity pulsed light

Silver nanowires (AgNWs) have emerged as a promising nanomaterial for next generation stretchable electronics. However, until now, the fabrication of AgNWbased components has been hampered by complex and time-consuming steps. Here, we introduce a facile, fast, and one-step methodology for the fabrication of highly conductive and stretchable AgNW/polyurethane (PU) composite electrodes based on a high-intensity pulsed light (HIPL) technique. HIPL simultaneously improved wire–wire junction conductivity and wire–substrate adhesion at room temperature and in air within 50 μs, omitting the complex transfer–curing–implanting process. Owing to the localized deformation of PU at interfaces with AgNWs, embedding of the nanowires was rapidly carried out without substantial substrate damage. The resulting electrode retained a low sheet resistance (high electrical conductivity) of <10 Ω/sq even under 100% strain, or after 1,000 continuous stretching–relaxation cycles, with a peak strain of 60%. The fabricated electrode has found immediate application as a sensor for motion detection. Furthermore, based on our electrode, a light emitting diode (LED) driven by integrated stretchable AgNW conductors has been fabricated. In conclusion, our present fabrication approach is fast, simple, scalable, and costefficient, making it a good candidate for a future roll-to-roll process.

Demonstration of the over dynamic range of MPPC by high intensity pulsed light illumination

Abstract The dynamic range of Multi-Pixel Photon Counter (MPPC) is considered to be limited by the total pixel number of MPPC, while it can be extended if the length of the pulsed incident light is larger than the width of the output avalanche pulse of MPPC, because single pixel could be triggered more than once. However, in this paper we demonstrated that the amplitude of the output signal of MPPC can reach several times larger than the equivalent amplitude of MPPC when all the pixels are fired, even if the length of the pulsed light is much smaller than the width of the output avalanche pulse of MPPC. The experimental phenomenon is described in detail. One possible explanation of this phenomenon is that the non-high electrical field region in the MPPC also has its own gain but smaller than the gain in the high electrical field region. The non-high electrical field region should be working in the linear mode like a linear mode avalanche photodiode (APD). The gain in the non-high electrical field region is of the order of 100 by estimation.

Fast fabrication of copper nanowire transparent electrodes by a high intensity pulsed light sintering technique in air.

Copper nanowire transparent electrodes have received increasing interest due to the low price and nearly equal electrical conductivity compared with other TEs based on silver nanowires and indium tin oxide (ITO). However, a post-treatment at high temperature in an inert atmosphere or a vacuum environment was necessary to improve the conductivity of Cu NW TEs due to the easy oxidation of copper in air atmosphere, which greatly cancelled out the low price advantage of Cu NWs. Here, a high intensity pulsed light technique was introduced to sinter and simultaneously deoxygenate these Cu NWs into a highly conductive network at room temperature in air. The strong light absorption capacity of Cu NWs enabled the welding of the nanowires at contact spots, as well as the removal of the thin layer of residual organic compounds, oxides and hydroxide of copper even in air. The Cu NW TE with a sheet resistance of 22.9 Ohm sq(-1) and a transparency of 81.8% at 550 nm has been successfully fabricated within only 6 milliseconds exposure treatment, which is superior to other films treated at high temperature in a hydrogen atmosphere. The HIPL process was simple, convenient and fast to fabricate easily oxidized Cu NW TEs in large scale in an air atmosphere, which will largely extend the application of cheap Cu NW TEs.

Using the Friedman method to study the thermal degradation kinetics of photonically cured electrically conductive adhesives

In this study, the electrically conductive adhesives were fabricated using vinyl ester resin and micro silver flakes, and then a high-intensity pulsed light was introduced to cure the adhesives under an ambient atmosphere at room temperature. The thermal degradation kinetics of photonically cured products was studied using the Friedman method and deduced by assuming a variable activation energy (E). The value of E spanned from 110 to 233 kJ mol−1, which first increased, then decreased, and finally increased again as the thermal degradation proceeded. The kinetic equation of thermal degradation was obtained as dα/dt = e26.62(1 − α)2.22 α 1.85e(−E(α)/RT) with E(α) = 961.73α 3 − 1453.9α 2 + 669.79α + 79.859, α ∈ (0, 1), where α was the fractional extent conversion at a given time (or given temperature). The overall order of reaction was 4.07 and >1, demonstrating that the thermal degradation was complex. With the Friedman method, a comprehensive and in-depth understanding of the thermal degradation kinetics of photonically cured electrically conductive adhesives has been achieved.

Photonic sintering of thin film prepared by dodecylamine capped CuInxGa1 − xSe2 nanoparticles for printed photovoltaics

In this paper, we report solution phase large scale synthesis of monodisperse phase pure CuInxGa1−xSe2 (CIGS) nanoparticles by using dodecylamine as solvent and dispersant. Various compositions of CIGS nanoparticles with different Ga content are synthesized by simply adding different amounts of Ga precursors. The band gap of CIGS nanoparticles can be tuned by changing Ga content. Effort is given to understand the formation pathway of CIGS phase so as to make the synthesis easier for the desired product. High intensity pulsed light technique, which provides extreme local heating, is used to sinter the thin film prepared using these nanoparticles on a Mo–glass surface. A uniformly conductive and dense CIGS film can be prepared by adjusting the energy of light and exposure time. The high intensity light irradiation of the CIGS film leads to diffusion of smaller CIGS nanoparticles to form a particle with larger grain size and thus enables sintering of particles without using high temperature processing.

Cu Salt Ink Formulation for Printed Electronics using Photonic Sintering

We formulate copper salt (copper formate/acetate/oleate) precursor inks for photonic sintering using high-intensity pulsed light (HIPL) based on the ink's light absorption ability. The inks can be developed through controllable crystal field splitting states (i.e., the ligand weights and their coordination around the metal centers). The inks' light absorption properties are extremely sensitive to the carbon chain lengths of the ligands, and the ink colors can drastically change. From the relationship between the ratios of C/Cu and the required sintering energies, it is possible to ascertain that the integral absorbance coefficients are strongly correlated with the photonic sintering behavior. These results suggest that the ink absorbance properties are the most important factors in photosintering. The wires formed by sintered copper formate complex ink via the HIPL method showed good electronic conduction, achieving a low resistivity of 5.6 × 10(-5) Ω cm. However, the resistivity of the wires increased with increasing contains carbon chain length of the inks, suggesting that large amounts of residual carbon have negative effects on both the wire's surface morphology and the electrical conductivity. We find in this study that high light absorptivity and low carbon inks would lead to a lower environmental load in future by reducing both energy usage and carbon oxide gas emissions.

High-intensity pulse light sintering of silver nanowire transparent films on polymer substrates: the effect of the thermal properties of substrates on the performance of silver films

Silver nanowire (AgNW) films with a random mesh structure have attracted considerable attention as high-performance flexible transparent electrodes that can replace the expensive and brittle ITO-sputtered films widely used in displays, touch screens, and solar cells. Methods such as heating, pressure treatment, and light treatment are usually used to obtain an optically transparent and electrically conductive film comparable to those of commercial ITO. However, the adhesion between the AgNW film and the substrate is so weak that other overcoatings or extra treatments are necessary. Here, a high-intensity pulsed light (HIPL) sintering technique was developed to rapidly and simply sinter the AgNW film and thus achieve strong adhesion and even high conductivity on these flexible polymer substrates which will be widely applied to the printing of electronic devices. The conductivity of the AgNW film closely depended on the thermal performance of substrates, and the adhesion was determined by the soft state of the substrate surface originating from the glass transition or melting of substrates with light intensity. The rapid sintering technique can be popularized to fabricate new devices on these polymer substrates by considering the thermal properties of the substrate to improve the performance of devices.

Inactivation of recalcitrant protozoan oocysts and bacterial endospores in drinking water using high-intensity pulsed UV light irradiation

This constitutes the first study to compare the use of high-intensity pulsed UV light (PUV) irradiation for the novel destruction of harmful protozoan (Cryptosporidium parvum Iowa isolate) oocysts and bacterial (Clostridium perfringens ATCC 13124 and Bacillus cereus ATCC 11178) endospores in artificially-spiked water where these organisms are resistant to conventional chlorination. Experimental results revealed that all three test organisms in their dormant recalcitrant state required extended levels of pulsing to achieve significant reductions in numbers compared to other similarly PUV-treated Escherichia coli ATCC 25922 that is a non-spore forming indicator of faecal pollution in water. 120 pulses at 900 V or 16.2 J per pulse (equivalent to a UV dose of 8.39 μJ cm−2) were required to achieve ca. 2 log C. perfringens spore numbers, whereas a similar level of PUV irradiation reduced both C. parvum oocysts and B. cereus endospores by ca. 5 log orders. A comparative ca. 5 log reduction of E. coli cell numbers was achieved after only 25 pulses at 900 V (equivalent to a UV dose of 1.74 μJ cm−2). A clear trend emerged where the order of resistance to PUV-irradiation observed was C. perfringens endospores &amp;gt; C. parvum oocysts, B. cereus endospores &amp;gt; E. coli cells. This study suggests disinfection kinetic data for the more resistant C. perfringens endospores can be used as a measure of estimating disinfection efficacy of PUV treatments for C. parvum oocysts in water, avoiding the need to use complex animal or cell culture infectivity models that are only available in specialised laboratories with highly trained technicians. This study will inform future studies exploring scale-up of PUV at waste-water treatment plants.

An energy-tunable positronium beam produced using the photodetachment of the positronium negative ion

We report here the production of an energy-tunable monoenergetic positronium beam using photodetachment of the positronium negative ion, a bound state of one positron and two electrons. The ions were produced efficiently by bombarding a Na-coated tungsten surface with a pulsed slow positron beam and accelerated using a static electric field. On irradiating the ions with a high intensity pulsed laser light, a positronium beam with a hitherto unrealized energy range of up to 1.9 keV has been produced in an ultra high vacuum environment.

Strongly adhesive and flexible transparent silver nanowire conductive films fabricated with a high-intensity pulsed light technique

Large-scale silver nanowire (AgNW) mesh films have received increasing attention as new transparent conductive films used in various printed devices. However, there are two crucial issues in implementing AgNWs that need to be addressed: (1) strong adhesion between AgNW film and substrate and (2) high conductivity with short treatment time for low-cost printed technology. Here, a high-intensity pulsed light (HIPL) sintering technique, which provides extreme heating locally in the AgNW film and at the interface between the film and polymer substrate, sinters the AgNW film to produce high conductivity with strong adhesion on the substrate. Importantly, light intensity, exposure time, and AgNW amount can be adjusted simply to form films that meet specific device needs. A flexible AgNW film with sheet resistance of 19 Ω sq−1 and transmittance of 83% at 550 nm is obtained with only one-step on a polyethylene terephthalate substrate with a light intensity of 1.14 J cm−2 under an exposure time of only 50 μs. The film can endure multiple peeling tests, which will play an important role in printed electronics.

Inkjet Printing and Sintering of Nano Copper Ink

An alternative low cost replacement for silver and gold conductive inks is of great interest to the printed electronics industry. Nano particle copper inks and silver coated nano copper inks are some of the alternative materials being tested for use, especially in applications where low temperature flexible substrates are favored. Although the inkjettability of nano copper ink influence on print quality has been reported, information regarding the relationship between ink film thickness and energy required for sintering by intensive pulse light is not yet understood. In this study, an inkjettable nano copper ink was printed on PET (PolyEthyleneTerepthalate) and glass and the samples were sintered using bursts of high intensity pulsed light. The amount of energy applied determined the degree of sintering among particles. The greater the number of sintered nanoparticles, the higher is the conductivity of the printed traces. A comparison of energy levels required for sintering on glass and PET in relationship to ink film thickness is reported and the thermal contribution of the substrate to the processing energy requirements of this ink is revealed.

Rapid flash annealing of thermally reactive copolymers in a roll-to-roll process for polymer solar cells

Light induced thermocleaving of a thermally reactive copolymer based on dithienylthiazolo[5,4-d]thiazole (DTZ) and silolodithiophene (SDT) in contact with the heat sensitive substrate the heat sensitive substrate polyethyleneterphthalate (PET) was effectively demonstrated with the use of high intensity pulsed light, delivered by a commercial photonic sintering system. Thermally labile ester groups are positioned on the DTZ unit of the copolymer that can be eliminated thermally for enhanced photochemical stability and advantages in terms of processing (solubility/insolubility switching). The photonic sintering system was successfully implemented in a full roll-to-roll process on flexible PET substrates and large-area polymer solar cell modules were prepared by solution processing of five layers under ambient conditions using the photonic sintering system for thermocleaving of the active layer. The PET foil did not show any deformation after exposure to the high intensity light only leaving the insoluble thermocleaved active layer. The active layer remained planar after light exposure thereby allowing the coating of supplementary material on top.

LED INDUCED CHLOROPHYLL FLUORESCENCE TRANSIENT IMAGER FOR MEASUREMENTS OF HEALTH AND STRESS STATUS OF WHOLE PLANTS

We have developed LED (light emitting diode) induced fluorescence transient imaging instrumentation to image the plant health/stress status by calculation of two images: Fv/Fm (variable fluorescence over saturation level of fluorescence) and the time response, tTR, of the fluorescence time curve. Within a short time interval (˜580 ms) multiple images (typically 20) are captured using the LEDs in the pulsed mode. For each pixel of the fluorescence image Fv/Fm and tTR are calculated and presented as images that correlate with the quantum yield of PSII photochemistry and the time response of this process, respectively. The advantage of the technology lies in the imaging of photosynthetic parameters within a short time interval, remotely and under light conditions. This was accomplished by the development of a high intensity pulsed LED light source (total 5 kW electrical power) and using the LEDs in the pulsed mode with a pulse width of 15 ms and time between sequential pulses of 14 ms. Using this instrumentation we investigated the effect of herbicide treatment, Sencor, on black nightshade (Solanum nigrum L.) plants. Effects of the herbicide on the first fluorescence images could be detected. At the saturation level of the fluorescence this effect disappeared. The effect of the herbicide was visualized on the Fv/Fm image and the time response tTR image. Healthy and herbicide treated parts of the plant yielded average values of Fv/Fm=0.81±0.03 and 0.06±0.02, respectively. Furthermore, the effect of drought stress was investigated on saintpaulia (Saintpaulia ionantha) plants. Under dark conditions no differences in the image of Fv/Fm and tTR could be detected between the control and the plant with drought stress. Under actinic light of 90 µmol m-2 s-1 differences were observed in images of (Fm’-F’)/Fm’ and tTR’. We conclude that for the first time images of a time response of the photosynthesis of leaves are presented. Furthermore, the proposed instrumentation can be used for high throughput screening, as a sensor in sorting machines and has potential greenhouse applications.

Light-assisted therapy in dermatology: The use of intense pulsed light (IPL)

Abstract Light is electromagnetic radiation and human beings encounter it on a number of levels. The versatility of the cutaneous biological effects allows the medical utilization of light to be used as a potential diagnostic and therapeutic tool. In almost all cases the light used is restricted to certain wavelengths and defined photophysical parameters. In terms of diagnostic purposes photo testing, Wood's light diagnostics and fluorescence diagnostics are frequently used tools. The therapeutic use of incoherent light can be divided in four main groups: (1) UV phototherapy, (2) photodynamic therapy (PDT), (3) treatment with light-emitting diodes (LEDs), and (4) treatment with intense pulsed light (IPL). Intense pulsed light (IPL) devices use flashlamps and bandpass filters to emit polychromatic, incoherent, high-intensity pulsed light of a determined wavelength spectrum, fluence, and pulse duration. Similar to lasers, the basic principle of IPL devices is the selective thermal damage of the target structure. This review summarizes the practical use of IPL devices and the current literature on IPL with regard to the treatment of unwanted hair growth, vascular lesions, pigmented lesions, acne vulgaris, and as a light source for PDT.

Intense pulsed light (IPL): A review

Intense pulsed light (IPL) devices use flashlamps and bandpass filters to emit polychromatic incoherent high-intensity pulsed light of determined wavelength spectrum, fluence, and pulse duration. Similar to lasers, the basic principle of IPL devices is a more or less selective thermal damage of the target. The combination of prescribed wavelengths, fluences, pulse durations, and pulse intervals facilitates the treatment of a wide spectrum of skin conditions. To summarize the physics of IPL, to provide guidance for the practical use of IPL devices, and to discuss the current literature on IPL in the treatment of unwanted hair growth, vascular lesions, pigmented lesions, acne vulgaris, and photodamaged skin and as a light source for PDT and skin rejuvenation. A systematic search of several electronic databases, including Medline and PubMed and the authors experience on intense pulsed light. Numerous trials show the effectiveness and compatibility of IPL devices. Most comparative trials attest IPLs similar effectiveness to lasers (level of evidence: 2b to 4, depending on the indication). However, large controlled and blinded comparative trials with an extended follow-up period are necessary.

Treatment of slices from carrot (Daucus carota) using high intensity white pulsed light

Experiments with washing of carrot slices using distilled water and 0.9% (w/w) NaCl in combination with varying number and pulses of high intensity white were carried out. Slices of carrot 3.5 cm in diameter and 2 mm thick were inoculated using diluted dispersions of yeasts (Saccharomyces cerevisiae) for varying time (0–240 min) and then the slices were treated with high intensity pulsed white light (one pulse = 0.7 J/cm2) using from none to 24 pulses. The major part of the yeast cells were killed using two pulses of light. The studies included washing of inoculated slices up to five times using salt 0.9% (w/w) NaCl and distilled water and inoculation at 22 °C for between 5 and 120 min. It was concluded that treatment of carrot slices with high intensity white light may reduce the load of yeast cells with up to 6 log cycles. Inoculation time at 22 °C had no effect on the maximum load of yeast cells.

Carbon nanotube synthesis in a flame using laser ablation for in situ catalyst generation

Laser ablation of either Ni or Fe is used to create nanoparticles within a reactive flame environment for catalysis of carbon nanotubes (CNTs). Ablation of Fe in a CO-enriched flame produces single-walled nanotubes, whereas, ablation of Ni in an acetylene-enriched flame produces carbon nanofibers. These results illustrate that the materials for catalyst particle formation and CNT, SWNT or nanofiber, inception and growth in the aerosol phase can be supplied from separate sources; a metal-carbon mixture produced by condensation is not necessary. Both particle formation and CNT inception can begin from molecular species in a laser-ablation approach within the complex chemical environment of a flame. Moreover, SWNTs and nanofibers can be synthesized within very short timescales, of the order of tens of milliseconds. Finally, high-intensity pulsed laser light can destroy CNTs through either vaporization or coalescence induced by melting.

Lichen removal from Chinese Spirit Path figures of marble

High-intensity pulsed light from a portable xenon flashlamp system was employed to remove lichen growth from Ming-dynasty statues located in the Seattle Art Museum sculpture garden. The ultraviolet and visible flashlamp radiation was found to decompose the lichens on the friable marble of the statues without damaging the stone. Thus, a non-chemical, non-mechanical, and non-abrasive divestment technique has been demonstrated for the conservation of artistic sculpture. The high efficiency and low cost of flashlamp systems makes this a cost-effective alternative to laser cleaning.

Presidential address: Venous disorders—Reflections of the past three decades

Presidential address: Venous disorders—Reflections of the past three decades