Pulsed Ultraviolet Laser Irradiation Research Articles

Characterization of graphene oxide by pulsed UV nanosecond laser irradiation for flexible electrodes

This article focused on the fabrication of a thin film of rGO through pulsed Ultraviolet nanosecond laser irradiation. With the influence of laser power energy, the thickness of the fabricated thin film decreased, the contents of Carbon increased, Oxygen contents decreased, electrical resistance decreased, and a normalized specific surface area increased. When the thin film of GO was exposed to laser-irradiation, leads to the reduction of oxygen and the restoration of sp2 hybridization, resulting in a material with reduced electrical resistance and improved specific surface area. As a result, at 125 mW of laser power energy and 200 mm/s scanning speed of pulsed UV nanosecond laser, the contents of Carbon increased up to 81.6%, Oxygen contents decreased to 11.3%, and normalized specific surface area of 0.97 m2/g with good electrical conductivity was obtained. Therefore, its good electrical properties offer prospects for fabricating flexible electrodes and the practical application of pulsed laser-irradiated rGO substrate films for flexible electronics applications.

Review of Research Progress on Damage Characteristics of Fused Silica Optics under Ultraviolet Pulsed Laser Irradiation

Review of Research Progress on Damage Characteristics of Fused Silica Optics under Ultraviolet Pulsed Laser Irradiation

Ultrathin Highly Flexible Featherweight Ceramic Temperature Sensor Arrays.

We fabricated highly flexible Sr- and Ni-doped perovskite SmMnO3 thermistor film sensor arrays on an ultrathin (5 μm thick) and lightweight (21 mg) polyimide sheet for healthcare monitoring devices. The Ag nanowire and nanoparticle-impregnated carbon microcone array, which was prepared by precisely controlled surface laser carbonization of polyimide, showed sufficiently low resistance as a bottom electrode and good stability against sharp bending angles. The dot-shaped (diameter: 900 μm) perovskite thermistor film with a thickness of 900 nm was crystallized by pulsed ultraviolet laser irradiation of a precursor film printed with perovskite nanoparticle dispersion ink, and the film functioned well as the thermistor with a thermistor constant of 2820 K. The thermistor sensor sheet exhibited rapid responses to temperature variation and high stability in the temperature cycle tests over 1000 cycles between room temperature and 80 °C. The bending durability for a bending angle of 60° with a small bending radius (500 μm) was also high. During the bending test over 1000 cycles, the monitoring temperature variation was suppressed only within 0.1 °C. This ultrathin sensor array sheet can be mounted on surfaces with shape variations, and we used the sensor for real-time monitoring in healthcare to detect precise temperature variations on the human skin during physical exercise.

Programmed Ultrafast Scan Welding of Cu Nanowire Networks with a Pulsed Ultraviolet Laser Beam for Transparent Conductive Electrodes and Flexible Circuits.

Metal nanowires (NWs) have shown superior advances for the next-generation transparent conducting (TC) materials. Most concerns were focused on uniform conductive films; however, fabrication of a programmed circuit is still lacking. Here, we demonstrate a programmable ultrafast welding method by pulsed laser beam scanning under ambient conditions to achieve a Cu NW pattern-free TC circuit as well as various size films. High-aspect ratio Cu NWs (> 3000) are synthesized through an oleylamine-mediated solution system. Pulsed ultraviolet laser irradiation together with a programmed moving station is set up for the welding of Cu NW networks. Finite element simulations reveal that the transient heating by efficient absorption of UV light (∼ 250 nm) could remove the organic residues on the surface and realize local welding of interlaced NW junctions. With only 10 ms pulsed irradiation, high optoelectronic performance (33 ohm/sq. at 87% transmittance at 550 nm) and excellent stability of the Cu NW TC film have been achieved. The line-by-line and selected route scanning modes could rapidly make large area TC films and directly write flexible circuits. Moreover, completely transparent micron-size UV and blue LED chips are fabricated and successfully lit with bright emission. This method opens up a future way of circuit and device fabrication by direct one-step laser writing.

Electrospray Photochemical Oxidation of Proteins.

Photooxidation of peptides and proteins by pulsed ultraviolet laser irradiation of an electrospray in the ion source of a mass spectrometer was demonstrated. A 193-nm excimer laser at 1.5-mJ pulse energy was focused with a cylindrical lens at the exit of a nanoelectrospray capillary and ions were sampled into a quadrupole time-of-flight mass spectrometer. A solution containing a peptide or protein and hydrogen peroxide was infused into the spray at a flow rate of 1μL/min using a syringe pump. The laser creates OH radicals directly in the spray which modify biomolecules within the spray droplet. These results indicate that photochemical oxidation of proteins can be initiated directly within electrospray droplets and detected by mass spectrometry.

High stability and luminescence efficiency in donor-acceptor neutral radicals not following the Aufbau principle.

With their unusual electronic structures, organic radical molecules display luminescence properties potentially relevant to lighting applications; yet, their luminescence quantum yield and stability lag behind those of other organic emitters. Here, we designed donor-acceptor neutral radicals based on an electron-poor perchlorotriphenylmethyl or tris(2,4,6-trichlorophenyl)methyl radical moiety combined with different electron-rich groups. Experimental and quantum-chemical studies demonstrate that the molecules do not follow the Aufbau principle: the singly occupied molecular orbital is found to lie below the highest (doubly) occupied molecular orbital. These donor-acceptor radicals have a strong emission yield (up to 54%) and high photostability, with estimated half-lives reaching up to several months under pulsed ultraviolet laser irradiation. Organic light-emitting diodes based on such a radical emitter show deep-red/near-infrared emission with a maximal external quantum efficiency of 5.3%. Our results provide a simple molecular-design strategy for stable, highly luminescent radicals with non-Aufbau electronic structures.

Synthesis of graphene-based photocatalysts for water splitting by laser-induced doping with ionic liquids

The synthesis of metal-free graphene-based photocatalysts has received great attention recently due to their expected contributions to the development of solar-based hydrogen generation via water-splitting in a low cost and ecological manner. In this work, a new method for the generation of nitrogen-doped graphene-based powder employing an alternative solution to commonly used toxic and hazardous organic solvents is presented. The procedure involves ultraviolet pulsed laser irradiation of graphene oxide (GO) flakes dispersed in 1-butyl-3-methylimidazolium [bmim]-based ionic liquids using both chloride and acetate anions. The structural and compositional analysis using transmission electron microscopy, X-ray photoelectron and infrared spectroscopy indicate that the irradiated GO becomes partially reduced and doped with graphitic, pyrrolic and pyridinic nitrogen species. Interestingly, the relative content of the nitrogen functionalities is controlled by the anion in the ionic liquid and its concentration, with the obtained graphene-based powders showing higher photocatalytic activity than GO. Furthermore, a remarkable synergistic effect is observed for GO-[bmim]-acetate powder (acting as co-catalyst) in combination with anatase TiO2 nanoparticles. The presented method opens new research avenues for the cost-effective mass production of graphene-based photocatalysts for water splitting applications.

Modification of reactively sputtered NiOxthin films by pulsed UV laser irradiation

This work reports on the effect of ultraviolet (UV) laser irradiation on the structural, electrical, and optical properties of nickel oxide (NiOx) thin films, deposited by reactive sputtering of nickel in an oxygen containing atmosphere. It was found that the conduction type can be changed from p-type to n-type and the resistivity decreased as the number of laser pulses is increased and then increases again. The as-deposited films are polycrystalline, while laser irradiation renders the films amorphous. The observed transition from O-rich NiOx as-deposited films to Ni-rich laser-irradiated NiOx can be significant to electrochromic, resistive switching, and other applications. The band gap of the as-deposited and the laser irradiated NiOx films was obtained from spectroscopic ellipsometry measurements and was found to slightly increase upon laser irradiation. It is also observed that the surface roughness increases slightly. Aging effects or instabilities in the structure and composition of the films are also observed under normal conditions.

Growth of ferroelectric Ba0.8Sr0.2TiO3 epitaxial films by ultraviolet pulsed laser irradiation of chemical solution derived precursor layers

Highly crystalline epitaxial Ba0.8Sr0.2TiO3 (BST) thin-films are grown on (001)-oriented LaNiO3-buffered LaAlO3 substrates by pulsed laser irradiation of solution derived barium-zirconium-titanium precursor layers using a UV Nd:YAG laser source at atmospheric conditions. The structural analyses of the obtained films, studied by X-ray diffractometry and transmission electron microscopy, demonstrate that laser processing allows the growth of tens of nm-thick BST epitaxial films with crystalline structure similar to that of films obtained through conventional thermal annealing methods. However, the fast pulsed nature of the laser employed leads to crystallization kinetic evolution orders of magnitude faster than in thermal treatments. The combination of specific photothermal and photochemical mechanisms is the main responsible for the ultrafast epitaxial laser-induced crystallization. Piezoresponse microscopy measurements demonstrate equivalent ferroelectric behavior in laser and thermally annealed films, being the piezoelectric constant ∼25 pm V−1.

Maskless laser processing of graphene

Graphene on a SiO2/Si substrate was removed by ultraviolet pulsed laser irradiation. Threshold laser power density to remove graphene depended on the graphene thickness. The mechanism is discussed using kinetic energy of thermal expansion of the substrate surface. Utilizing the thickness dependence, thickness (or layer-number) selective process for graphene is demonstrated. Maskless patterning of graphene using laser irradiation in the air is also demonstrated.

ChemInform Abstract: UV‐Assisted Nucleation and Growth of Oxide Films from Chemical Solutions

AbstractReview: 50 refs.

Design of process diagnostics for excimer laser irradiation of oxide thin films

The authors have developed an in situ excimer laser irradiation system that can monitor the temperature field of oxide thin films through thermal radiation produced upon a pulsed ultraviolet laser irradiation. Thermal emission signals from a Si single crystal obtained using with this system agreed well with a numerical simulation result, validating the time constant of the measurement system. The time-dependent transient temperature profile of tin-doped indium oxide thin films, which was converted from thermal emission signals, clearly showed a recalescence behavior in its cooling curve. The transmittance data of the laser-irradiated indium oxide thin films suggested that the transmittance monitoring at near-infrared and ultraviolet–visible regions could be useful in monitoring the dopant levels and laser processing conditions, respectively.

Ultraviolet pulsed laser irradiation of multi-walled carbon nanotubes in nitrogen atmosphere

Laser irradiation of randomly oriented multi-walled carbon nanotube (MWCNT) networks has been carried out using a pulsed Nd:YAG UV laser in nitrogen gas environment. The evolution of the MWCNT morphology and structure as a function of laser fluence and number of accumulated laser pulses has been studied using electron microscopies and Raman spectroscopy. The observed changes are discussed and correlated with thermal simulations. The obtained results indicate that laser irradiation induces very fast, high temperature thermal cycles in MWCNTs which produce the formation of different nanocarbon forms, such as nanodiamonds. Premelting processes have been observed in localized sites by irradiation at low number of laser pulses and low fluence values. The accumulation of laser pulses and the increase in the fluence cause the full melting and amorphization of MWCNTs. The observed structural changes differ from that of conventional high temperature annealing treatments of MWCNTs.

UV-assisted nucleation and growth of oxide films from chemical solutions

The fabrication of thin oxide films at low temperatures using simple processes has been a significant challenge associated with expanding the potential applications of these materials. Recent developments have demonstrated that the photo-assisted chemical solution deposition (PACSD) process offers a promising means of solving these difficulties, allowing high volume, on-demand production of variable sample sizes using an advantageous wet process. A better understanding of the crystal growth phenomena associated with this process, however, is required to enable various oxide thin films to be prepared using this new concept. Under pulsed ultraviolet (UV) laser irradiation, crystal growth has been confirmed to proceed by near-instantaneous photothermal heating and photochemical effects at the reaction interface. Vacuum UV lamp irradiation is also a useful means of generating oxide nuclei, since it results in effective chemical bond cleavage and simultaneously produces reactive oxidant (O3/O((1)D)) species. In this review, the nucleation and growth mechanisms which occur during the PACSD process are introduced and discussed and we examine the future possible applications of this process.

White light emission from polystyrene under pulsed ultra violet laser irradiation

This paper reports for the first time the luminescent property of polystyrene (PS), produced by pulsed ultra violet laser irradiation. We have discovered that, in air, ultra-violet (UV) irradiated PS nanospheres emit bright white light with the dominant peak at 510 nm, while in vacuum they emit in the near-blue region. From the comparison of PS nanospheres irradiated in vacuum and air, we suggest that the white luminescence is due to the formation of carbonyl groups on the surface of PS by photochemical oxidation. Our results potentially offer a new route and strategy for white light sources.

A universal value of effective annealing time for rapid oxide nucleation and growth under pulsed ultraviolet laser irradiation

The effective annealing times (t(eff)) for nucleating various oxides from an amorphous matrix under nanosecond pulsed laser irradiation have been determined. The oxides, which had perovskite, bixbyite, anatase, and pyrochlore structures, showed similar t(eff) values for crystal nucleation of around 60 ns. This indicates that the effective annealing time is a good universal value for evaluating pulsed laser-induced oxide nucleation. Time-resolved resistance measurements of tin-doped In2O3 thin films under pulsed laser irradiation showed that crystal nucleation and rapid growth proceeded spontaneously with an instantaneous temperature rise.

Picosecond Photovoltaic Response in Tilted Lanthanum Doped Manganite Films

Anisotropic picosecond photovoltaic responses were observed in lanthanum doped manganiteLaxCa1-xMnO3(x=0.67and 0.4) thin films, which were deposited on miscut LaSrAlO4substrates under ultraviolet pulsed laser irradiation without external bias. The 10%–90% rise time and the full width at half maximum of La0.67Ca0.33MnO3were 470 and 585 ps, respectively, and those of La0.4Ca0.6MnO3were 220 and 515 ps. The photovoltage sensitivities of La0.67Ca0.33MnO3and La0.4Ca0.6MnO3, which are sensitive to the concentrations of lanthanum of the samples, are 0.28 V/mJ and 3.47 V/mJ, respectively. The photosensitivity in the films deposited on MgO is higher than that in those deposited on LaSrAlO4substrates, for it has a big lattice mismatch. These results should open a route for the application of lanthanum doped manganite as an ultrafast photodetector material.

Voltage tunable photodetecting properties of La0.4Ca0.6MnO3 films grown on miscut LaSrAlO4 substrates

We report the voltage tunable photodetecting properties of a La0.4Ca0.6MnO3 film grown on miscut LaSrAlO4 (001) substrates under ultraviolet pulsed laser irradiation at ambient temperature. The photovoltage and photocurrent peak sensitivities can be tuned in the range of 0.295–0.786 V/mJ and 0.172–0.314 A/mJ, respectively, when the applied bias is changed from −20 to +20 V, indicating that the vicinal manganite film can be used as an electric tunable ultraviolet photodetector. A possible mechanism based on the high resolution transmission electron microscopy is introduced to explain the experiment results.

Laser transfer processing for the integration of thin and thick film ferroelectrics

Laser transfer processing (LTP) offers the potential to overcome the problems of integrating ferroelectric thin and thick film materials with polymers and other technologically useful substrate materials that cannot sustain the high process temperatures, 600–1,000 °C, required for normal film deposition. The LTP technique involves the fabrication of a ceramic film on a high-temperature substrate material such as sapphire, and subsequent release by application of pulsed ultra-violet laser radiation. Here, the LTP technique is reviewed in the context of ferroelectric thin and thick films, and current developments are presented. Micro- and nanostructural features of the films before and after transfer to a second substrate are revealed using scanning and transmission electron microscopy. The consequences of laser-generated structural changes on ferroelectric properties are illustrated, and measures to mitigate the effects of an amorphous damage-layer are discussed.

Ultrafast photovoltaic effects in miscut Nb-doped SrTiO3 single crystals

Picosecond photovoltaic effect in miscut Nb-doped SrTiO3 single crystal has been observed under ultraviolet pulsed laser irradiation at ambient temperature without an applied bias. The 10%–90% rise time and the full width at half maximum are 828 and 670 ps, respectively, which is faster than that of exact cut Nb-doped SrTiO3 single crystal. A model based on terrace structure is put forward to explain the observation.