Pulsed Laser Irradiation In Liquid Research Articles

Dual‐laser pulse‐patterned α‐Co(OH)2/rGO heterointerface for accelerated water oxidation and surface phase‐transition via in‐situ Raman spectroscopy

AbstractThe dynamic surface reconstruction of electrodes is a legible sign to understand the deep phase‐transition mechanistic and electrocatalytic origin during the oxygen evolution reaction (OER). Herein, we report a dual‐laser pulse‐patterned heterointerface of α‐Co(OH)2 and reduced graphene oxide (rGO) nanosheets via pulsed laser irradiation in liquid (PLIL) to accelerate OER kinetics. α‐Co(OH)2 was formed from the OH− ions generated during the PLIL of GO at neutral pH. Co2+ modulation in tetrahedral coordination sites benefits as an electrophilic surface for water oxidation. Few d‐vacancies in Co2+ increase its affinity toward oxygen, lowering the energy barrier and generating many CoOOH and CoO2 active sites. rGO with an ordered π‐conjugated system aids the surface adsorption of OOH*, O*, and OH* during OER. α‐Co(OH)2 surface phase‐transition and OER mechanistic steps occurred via phase‐reconstruction to CoOOH and CoO2 reactive intermediates, uncovered using in situ electrochemical–Raman spectroscopy. Our findings in the dual‐laser pulse strategy and the surface reconstruction correlation in active OER catalysts pave the path for paramount in multiple energy technologies.image

Tribological analysis of ultra-high molecular weight polyethylene composites with boron carbide micro and nanoparticles

The goal of this study is to investigate the tribological and morphological changes obtained by addition of boron carbide (B4C) micro and nanoparticles into Ultra High Molecular Weight Polyethylene (UHMWPE/B4C). In this work, UHMWPE was reinforced with B4C micro, nano (powder) and nanoparticles prepared using pulsed laser irradiation in liquid by solvent mixing (SM). Subsequently, the mixtures were compression molded at 180 °C and 15 MPa for 15 min, then cooled for 5 min at different concentrations (0, 0.1, 0.3, and 0.5 wt%) to evaluate the thermal, mechanical, and tribological behavior of these composites. Studies on changes in the structural and morphological characteristics of the composite samples were carried out by means of Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The microhardness and scratch hardness of the composites were measured using a diamond indenter revealing nanoparticles outperformed micro-particles in both properties. In addition, the tribological behavior of the hot-pressed composite structures was analyzed via a scratch test machine using a normal load of 10 N and a ball-on-disk tribometer with a normal load of 30 N. As a result, the wear resistance of the composite revealed significant improvement up to a certain amount of particles. The coefficient of friction was also reduced. Worn surface analyses were done on the composite using the confocal and scanning electron microscopy (SEM), indicating various wear mechanisms such as delamination, micro-cutting, micro-plowing, and groove-formation. The composites showed low wear rates and were correlated with scratch hardness.

Moving beyond Ti2C3Tx MXene to Pt-Decorated TiO2@TiC Core-Shell via Pulsed Laser in Reshaping Modification for Accelerating Hydrogen Evolution Kinetics.

Phase engineering of nanocatalysts on specific facets is critical not only for enhancing catalytic activity but also for intensely understanding the impact of facet-based phase engineering on electrocatalytic reactions. In this study, we successfully reshaped a two-dimensional (2D) MXene (Ti3C2Tx) obtained by etching Ti3AlC2 MAX via a pulsed laser irradiation in liquid (PLIL) process. We produced a TiO2@TiC core-shell structure in spheres with sizes of 200-350 nm, and then ∼2 nm ultrasmall Pt NPs were decorated on the surface of the TiO2@TiC core-shell using the single-step PLIL method. These advances allow for a significant increase in electrocatalytic hydrogen evolution reaction (HER) activity under visible light illumination. The effect of optimal Pt loading on PLIL time was identified, and the resulting Pt/TiO2@TiC/Pt-5 min sample demonstrated outstanding electrochemical and photoelectrochemical performance. The photoelectrochemical HER activity over Pt/TiO2@TiC/Pt-5 min catalyst exhibits a low overpotential of 48 mV at 10 mA/cm2 and an ultralow Tafel slope of 54.03 mV/dec with excellent stability of over 50 h, which is hydrogen production activity even superior to that of the commercial Pt/C catalysts (55 mV, 62.45 mV/dec). This investigation not only serves as a potential for laser-dependent phase engineering but also provides a reliable strategy for the rational design and fabrication of highly effective nanocatalysts.

Ultraviolet to near infrared wavelength independent SnS-graphene hybrid thin film photodetector from nanocolloids

It is crucial and imperative to produce wavelength-independent photodetectors as most of the reported devices are limited by their operating wavelength region. We report graphene incorporated tin sulfide (SnS) hybrid thin films as photodetectors operational in the ultrabroadband range of wavelength using their nanocolloids. SnS nanocolloids obtained by Pulsed Laser Irradiation in Liquid (PLIL) performed by irradiating SnS powder using 532 nm laser output (Nd:YAG) is the first report on SnS by PLIL. Into this nanocolloid, graphene was ultrasonically dispersed. SnS-graphene hybrid films were deposited by spin-coating followed by annealing in vacuum. The morphological study of the films revealed graphene layers hybridized with spherical SnS nanoparticles. Raman analysis, X-ray diffraction and X-ray photoelectron spectroscopy results confirmed the phase, structure and chemical composition. A bandgap of 2.1–2.0 eV was obtained for the annealed SnS films and graphene addition helped in extending the absorption range over the entire UV–Vis-NIR reducing the bandgap values to 1.8–1.5 eV. The films showed high photoresponse independent of the different wavelengths of illumination. The hybrid photodetector exhibits a specific detectivity of 107 Jones and a responsivity of 10-5 AW−1. The SnS-graphene hybrid photodetectors, being wavelength-independent, are a promising candidate for optoelectronic applications.

Defects rich nanostructured black zinc oxide formed by nanosecond pulsed laser irradiation in liquid

Zinc oxide (ZnO) is a wide bandgap semiconductor for energy applications while the spectral absorption only in UV region limits the use as a visible light absorber. Here, visible light absorbing modified ZnO (black) is prepared by creating surface defects and vacancies using pulsed laser irradiation in liquid. The modified ZnO nanoparticles have spherical morphology and they are free from impurity phases. The optical bandgap of this modified material is narrowed by increased irradiation time with a morphological transformation to mostly nanospheres. XPS analysis confirmed the oxygen vacancies contribution and the valance band study showed a reduction in the band edge. With the results of Raman and photoluminescence spectra, the oxygen defects and vacancies were confirmed. Thin films were fabricated using these materials via doctor blade method and their photocatalytic studies showed enhanced activity in organic dye decay under visible light. Results of this study show a facile method for fabrication of defects rich metal oxide nanomaterials by pulsed laser irradiation in liquid.

(Invited) Facile Formation of Luminescent Colloidal Silicon Quantum Dots from Porous Silicon

Silicon quantum dot is nanometer sized single crystalline silicon particles. It shows exotic luminescence properties such as size tuneablilty of luminescence band and quasi-direct electron-hole recombination resulting in efficient visible luminescence at room temperature, due to quantum confinement effects. Because of its environmental friendliness and low cost, the silicon quantum dot is a promising material for future light-emitting applications. Recently, a free-standing form of silicon quantum dot dispersed in solution, i.e., colloidal silicon quantum dots are intensively investigated due to their potential usefulness in solution based light emitting technology. The luminescence properties and solution dispersibility in silicon quantum dots are known to depend on the surface properties such as the coverage of surface termination and the kinds of surface terminated species.Various formation techniques for colloidal silicon quantum dot have been proposed, such as wet-chemical synthesis, plasma synthesis and high-temperature thermal processing. Pulsed-laser irradiation in liquid is one of the simplest top-down method for the formation of colloidal silicon quantum dots. By irradiating bulk crystalline silicon target with a high power pulsed-laser beam in liquid, silicon quantum dots are easily formed due to the ablation of silicon crystal and resultant condensation effect of ablated silicon at the liquid interface. An additional merit of this process is the easiness of surface termination control; because the nanocrystal surface formed by laser ablation actively reacts with molecules consisting of solution, one can control the surface termination by changing the kinds of solution. However, the control of the formed quantum dot size is still a challenging work and the size distribution of the quantum dots prepared by this process is usually wide.To overcome these issues, we developed a novel top-down pulsed laser irradiation technique for the formation of colloidal silicon quantum dots. We used an interconnected wire-nanostructure assembly, i.e., porous silicon (PSi), as a target material for the laser irradiation process, on behalf of bulk crystalline silicon target. PSi has beneficial properties for laser irradiation target such as low thermal conductivity and large surface areas. Because of these properties, the pulsed-laser irradiation of PSi target in organic solution allows us to generate the silicon quantum dots with relatively high preparation yields, and with various emission bands by changing irradiation conditions and the porosity of PSi. Furthermore, in our developed process, the formed dots are brighter than the original PSi target due to the stable organic terminations.Recently, we further improved our developed facile formation process of luminescent colloidal silicon quantum dots via porous silicon target. In the improved process, we employed electrochemically prepared PSi flakes, which purely consists of porous layer. The PSi flakes show extremely low thermal conductivity and heat capacity due to their intrinsic geometrical feature. Thus, even a low temperature thermal treatment as well as pulsed laser irradiation to PSi flakes in organic solution are efficiently converted porous silicon layer to colloidal silicon quantum dots. Furthermore, we succeeded in preparing silicon quantum dots dispersed in a polar and non-polar solvent depending on the ligands terminated on the dot surface by using different solutions. The present facile formation process of silicon quantum dots from PSi allows us to develop future top-down and low-cost mass production of luminescent colloidal silicon quantum dots.

Laser-Generated Supranano Liquid Metal as Efficient Electron Mediator in Hybrid Perovskite Solar Cells.

Creating colloids of liquid metal with tailored dimensions has been of technical significance in nano-electronics while a challenge remains for generating supranano (<10nm) liquid metal to unravel the mystery of their unconventional functionalities. Present study pioneers the technology of pulsed laser irradiation in liquid from a solid target to liquid, and yields liquid ternary nano-alloys that are laborious to obtain via wet-chemistry synthesis. Herein, the significant role of the supranano liquid metal on mediating the electrons at the grain boundaries of perovskite films, which are of significance to influence the carriers recombination and hysteresis in perovskite solar cells, is revealed. Such embedding of supranano liquid metal in perovskite films leads to a cesium-based ternary perovskite solar cell with stabilized power output of 21.32% at maximum power point tracing. This study can pave a new way of synthesizing multinary supranano alloys for advanced optoelectronic applications.

Embedding of WO3 nanocrystals with rich oxygen-vacancies in solution processed perovskite film for improved photovoltaic performance

Seeking strategies of promoting the charge separation and transport of the photo-active layer has been always of significance for the development of high-performance optoelectronic devices. We herein demonstrate an effective way of decorating WO3 nanocrystals in perovskite films for boosted photogenerated carriers transport. The WO3 nanocrystals are generated by a simple technique of pulsed laser irradiation in liquid, then introduced into the perovskite film based on the anti-solvent approach. Such decoration is found helpful for the increase of the short-circuit current density (Jsc) of the device, which leads to the increase of the photoconversion efficiency (PCE) from 17.72% to 19.29%. The improved PCE is mainly due to the decoration of the WO3 at the grain boundaries of perovskite films that facilitates the charge transport between the adjacent grains, which is evidenced by the quenching of the film photoluminescence, shortened carrier lifetime, and increased carrier mobility. We thus believe our study provides an effective way of embedding ordinary metal oxides in perovskite films for enhanced optoelectronic performance.

A simple synthesis of ZnO:Co2O3 nanocomposites by pulsed laser irradiation in liquid

Nanocomposite materials are emerging in popularity due to their enhanced performance over the constituent materials. In this work, we report the fabrication of zinc oxide: cobalt oxide nanocomposites in a simple, fast and room temperature synthesis with good productivity. The nanocomposites synthesized were characterized by SEM, XPS and UV–Visible spectroscopy to analyze their morphology, composition, chemical states, optical absorption, band gap etc. The nanocolloids of the composite were drop casted to form thin films for photocatalytic studies. In SEM analysis, the morphological transformation of the material is observed where it transformed from agglomerated spherical particles to petals shaped and then to partially spherical forms due to pulsed laser irradiation. XPS analysis showed a gradual change in oxygen high resolution spectra in the samples with respect to the concentration difference of cobalt oxide. The optical studies show an enhanced absorption in visible region for the nanocomposite and the energy band gap reduced to 2.4 eV. All the thin films of nanocomposite showed photocatalytic decay of methylene blue dye under visible light irradiation. The results of this study support the effective use of laser irradiation in liquid to obtain nanocomposites of metal oxides for photocatalytic applications.

Generation of Size-Controlled Crystalline CeO2 Particles by Pulsed Laser Irradiation in Water

The defining characteristics of nanoparticles (NPs) include variation of properties as a function of size and shape, requiring their preparation with desirable dimensions and morphologies. Here, a unique approach based on pulsed laser irradiation in liquid (PLIL) was developed to reshape commercial CeO2 NPs suspended in water in an attempt to respond to these challenges. Guided by the results of Mie theory and the predictions of the heating–melting–evaporation model, the fourth harmonic of an Nd:YAG laser (266 nm, 10 Hz, ∼5 ns) was selected and used for lateral irradiation of colloidal CeO2 samples at particular laser fluences and number of laser pulses for producing size- and shape-specific crystalline NPs. Spectral and structural analyses of the NPs, prior to and following PLIL, revealed shape and crystal size alterations depending on the irradiation parameters, affecting melting, evaporation, and solidification of the particles. The change in size, shape, and agglomeration could be followed by the results of the analyses, where the first two could be also interpreted by the modeling results. This study demonstrates that controlled CeO2 crystal particles, from nano- to submicrometer diameters, could be generated by PLIL, shedding new light on the dynamics of the process.

Surface Engineering of MoS2 via Laser-Induced Exfoliation in Protic Solvents.

With excellent performance in the hydrogen evolution reaction (HER), molybdenum disulfide (MoS2 ) is considered a promising nonprecious candidate to substitute Pt-based catalysts. Herein, pulsed laser irradiation in liquid is used to realize one-step exfoliation of bulk 2H-MoS2 to ultrastable few-layer MoS2 nanosheets. Such prepared MoS2 nanosheets are rich in S vacancies and metallic 1T phase, which significantly contribute to the boosted catalytic HER activity. Protic solvents play a pivotal role in the production of S vacancies and 2H-to-1T phase transition under laser irradiation. MoS2 exfoliated in an optimal solvent of formic acid exhibits outstanding HER activity with an overpotential of 180 mV at 10 mA cm-2 and Tafel slope of 54 mV dec-1 .

Laser‐Generated Nanocrystals in Perovskite: Universal Embedding of Ligand‐Free and Sub‐10 nm Nanocrystals in Solution‐Processed Metal Halide Perovskite Films for Effectively Modulated Optoelectronic Performance

AbstractRegulating the chemical/physical features of solution processed metal halide perovskite films by integrating sub‐10 nm nanocrystals is a highly promising strategy to advance their outstanding optoelectronic performance. However, significant challenges remain for the universal embedding of the well‐defined nanocrystals in the film matrix. By generating nanocrystals in desired solvents via pulsed laser irradiation in liquid, the authors demonstrate the effective decoration of sub‐10 nm nanocrystals in perovskite films for enhanced optoelectronic performance. It is believed that this improved performance is due to the modification of the widely adopted “antisolvent” to a novel “anti‐colloidal‐solution” (ACS). Exemplified by a typical ACS; carbon dots in chlorobenzene, its encouraging superiority in regulating, not only the films morphology, but also the electronic structure, is demonstrated. This results in perovskite solar cells with a champion efficiency of 21.41% as well as a pronounced stability over 5000 h in relative humidity of 40%. The capability of nanocrystal embedding for boosted photovoltaic performance is further exploited by employing other laser generated ACSs. Such a strategy may open up a route to regulating hybrid perovskite film performance via nanocrystal embedding for photovoltaics or even beyond optoelectronic applications.

Synthesis and characterization of black TiO2 nanoparticles by pulsed laser irradiation in liquid

Modified TiO2 (black TiO2) nanoparticles (NPs) produced by different methods showed enhanced visible light absorption than ordinary white TiO2 NPs. Pulsed laser ablation in liquid (PLAL) is a promising technique for synthesizing nanostructures due to its simplicity, less usage of toxic reagents and absence of costly vacuum systems. In the present study, black TiO2 NPs synthesized by pulsed laser irradiation is examined for their structure, morphology and optical properties. Nanoparticles of modified TiO2 were prepared by pulsed laser ablation in liquid technique by irradiating white TiO2 powder in water using an Nd:YAG laser (532 nm, 10 ns, 10 Hz). Characterization of morphology of the nanoparticles by scanning electron microscopy (SEM) showed a change in morphology by laser irradiation for TiO2 nanoparticles. Crystalline structure was determined by X-ray diffraction (XRD) in which the major anatase phase in white TiO2 was changed to rutile during irradiation and for longer irradiation, rutile became the major phase. Most of the vibrational peaks for TiO2 were identified in Raman spectra. Ti 2p and O 1s binding energy analysis by X-ray photoelectron spectroscopy (XPS) for black TiO2 (90 min) showed changes of 0.5 eV and 0.7 eV respectively compared to the white TiO2 due to their change in chemical states. Optical absorption and band gap evaluation were done using the diffuse reflectance spectra measurements that showed enhanced absorption in the visible range for all the laser irradiated nanoparticles and a decrease in the bandgap from 2.98 eV of white TiO2 to 1.84 eV for black TiO2. Synthesis of black TiO2 at normal atmospheric conditions by irradiation of TiO2 in liquid using 532 nm laser output which is a very common Nd:YAG wavelength is reported for the first time.

Pulsed laser irradiation synthesis of lead selenide quantum dots from lead and selenium salts in various surfactants

HypothesisSemiconductor nanocrystals with response in the near-infrared region include lead chalcogenide quantum dots (QDs), and these materials show a strong quantum confinement effect due to their large Bohr radius compared with the group II–VI QDs. In the present study, a facile synthesis of lead selenide (PbSe) QDs using a pulsed laser irradiation in liquid (PLIL) is presented. ExperimentsPbSe QDs were produced using a pulsed Nd:YAG laser (532 nm, 10 Hz, 7 ns) irradiation of the Pb and Se mixed precursor solutions using the following three surfactants at various concentrations: cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), and polyvinylpyrrolidone (PVP). FindingsInterestingly, it was observed that the synthesis and particle size of PbSe QDs obtained via the PLIL technique were strongly influenced by the type and concentration of the surfactants and by the varying wavelength and power of the laser. A secondary irradiation of the prepared sample in PVP solution resulted in the formation of rock salt crystalline PbSe QDs that were approximately 6.83 nm in size.

Luminescence color control and quantum-efficiency enhancement of colloidal Si nanocrystals by pulsed laser irradiation in liquid.

We demonstrate the emission color change of white-emitting chlorine-terminated silicon nanocrystals (Cl:Si-ncs) to blue-emitting carbon-terminated silicon nanocrystals (C:Si-ncs), together with the enhancement of the luminescence quantum efficiency from 7% to 13%, by post-laser ablation in 1-octene. Such changes of the PL properties are caused by the size reduction of Si-nc and efficient surface passivation by hydrocarbons, resulting from a high reactivity of 1-octene in the laser-ablation and subsequent nanoparticle-formation processes. Furthermore, the second post-laser irradiation of the C:Si-ncs in trichloroethylene reversibly results in the formation of the Cl:Si-ncs. The preparation yield of C:Si-ncs via the post-laser ablation of Cl:Si-ncs is higher than that of C:Si-ncs directly prepared only by the laser ablation of PSi in 1-octene. This high preparation yield is due to the high laser-ablation efficiency in trichloroethylene compared with 1-octene, which is attributed to the low heat loss of the solvent in the laser-ablation process.

Tuning the Composition of Alloy Nanoparticles Through Laser Mixing: The Role of Surface Plasmon Resonance

In this work we report a technique for the preparation of AuxNi1–x alloy nanoparticles based on pulsed laser irradiation in liquid of Au and Ni@NiO colloidal mixtures. The structural and compositional characterization of the obtained materials, performed through X-ray diffraction and transmission electron microscopy coupled with energy dispersive X-ray spectroscopy, has shown a correlation between the final alloy composition and the different Au to Ni@NiO ratio in the irradiated mixture. With the support of theoretical calculations, we propose as possible mechanism for the formation of the alloy structures a temperature increase, enhanced by the strong absorption of gold surface plasmon resonance at resonant wavelength, and a subsequent melting of the structures. Optical characterization through UV–vis spectroscopy and magnetic characterization through SQUID magnetometry confirm a coexistence of the plasmonic and magnetic behaviors in the hybrid systems. In view of such results, AuxNi1–x alloy nanoparticl...

Bright and multicolor luminescent colloidal Si nanocrystals prepared by pulsed laser irradiation in liquid

We reported the preparation of bright and multicolor luminescent colloidal Si nanocrystal (Si-nc) by pulsed UV laser irradiation to porous Si (PSi) in an organic solvent. The different-luminescence-color (different-sized) colloidal Si-nc was produced by the pulsed laser-induced fragmentation of different-sized porous nanostructures. The colloidal Si-nc samples were found to have higher photoluminescence quantum efficiencies (20%–23%) than the PSi samples (1%–3%). The brighter emission of the colloidal Si-nc was attributed to an enhanced radiative band-to-band transition rate due to the presence of a surface organic layer formed by UV laser-induced hydrosilylation.

Micronization of red-emitting K2SiF6:Mn4+ phosphor by pulsed laser irradiation in liquid

We demonstrate a technique for the micronization of K2SiF6:Mn4+ phosphor particles by pulsed laser irradiation in liquid. Through nanosecond pulsed laser irradiation in liquid, the average diameter of the phosphor particles dramatically decreases from ∼110 to ∼2μm, and the extent of decrease depends on the wavelength of irradiated laser light. This is due to the wavelength dependence of phosphor absorbance. A bimodal size distribution peaked at ∼100nm and ∼2μm is also observed, indicating the coexistence of several different fragmentation mechanisms: shockwave, thermal-stress, and heating evaporation fragmentations. The micronized phosphor particles still exhibit red emission but show lower photoluminescence quantum efficiency (∼0.2) than that without micronization. This lower efficiency is caused by the increase in the nonradiative recombination channels, which is probably due to the formation of the internal and/or surface defects.