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Changes in the Photoluminescence of Monolayer and Bilayer Molybdenum Disulfide during Laser Irradiation
摘要： Various postsynthesis processes for transition metal dichalcogenides have been attempted to control the layer number and defect concentration, on which electrical and optical properties strongly depend. In this work, we monitored changes in the photoluminescence (PL) of molybdenum disulfide (MoS2) until laser irradiation generated defects on the sample flake and completely etched it away. Higher laser power was required to etch bilayer MoS2 compared to monolayer MoS2. When the laser power was 270 μW with a full width at half-maximum of 1.8 μm on bilayer MoS2, the change in PL intensity over time showed a double maximum during laser irradiation due to a layer-by-layer etching of the flake. When the laser power was increased to 405 μW, however, both layers of bilayer MoS2 were etched all at once, which resulted in a single maximum in the change of PL intensity over time, as in the case of monolayer MoS2. The dependence of the etching pattern for bilayer MoS2 on laser power was also reflected in position changes of both exciton and trion PL peaks. The subtle changes in the PL spectra of MoS2 as a result of laser irradiation found here are discussed in terms of PL quantum efficiency, conversion between trions and excitons, mean interatomic spacing, and the screening of Coulomb interaction.
关键词： photoluminescence,defects,etching,laser irradiation,molybdenum disulfide
更新于2025-09-23 15:19:57
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Effect of Laser Irradiation on Reversibility and Drug Release of Light-Activatable Drug-Encapsulated Liposomes
摘要： Although several studies have demonstrated repetitive drug release using light-activatable liposomes, inconsistent drug release at each activation limits widespread usage. Here, we report reversible plasmonic material-coated encapsulated liposomes for proportional controlled delivery of methotrexate (MTX), which is a common drug for cancer and autoimmune diseases, using repetitive laser irradiation. Our results suggest a proportional increase in total drug release after repetitive laser irradiation. We hypothesize that the drug is released via “melted” lipid bilayers when the plasmonic materials on the liposome surface are heated by laser irradiation followed by reversible formation of the liposome. To evaluate our hypothesis, the number density of liposomes after laser irradiation was measured using single-particle (liposome) collision experiments at an ultramicroelectrode. Collisional frequency data suggest that the number density of liposomes remains unaltered even after 60 s of laser irradiation at 1.1 and 1.8 W, indicating that the liposome structure is reversible. The results were further compared with gold nanorod-coated nanodroplets where drug is released via irreversible phase transition. In contrast to what was observed with the liposome particles, the number density of the nanodroplets decreased with increasing laser irradiation duration. The structure reversibility of our liposome particles may be responsible for repetitive drug release with laser heating. We also studied the temperature rise in the lipid bilayer by incorporating polymerized 10,12-pentacosadiynoic acid (PCDA) in the lipid composition. The red shift in the UV?vis spectrum due to the structural change in PCDA lipids after laser irradiation indicates a rise in temperature above 75 °C, which is also above the chain-melting temperature of the main lipid used in the liposomes. All these results indicate that drug is released from the light-activatable liposomes due to reversible nanostructural alteration in the lipid bilayer by plasmonic resonance heating. The liposomes have potential to be a drug carrier for dose-controlled repetitive drug delivery.
关键词： drug release,reversible nanostructural alteration,light-activatable liposomes,plasmonic materials,laser irradiation,methotrexate
更新于2025-09-23 15:19:57
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Microstructure and laser irradiation characteristics of TiC-free and TiC-doped tungsten-based coatings prepared by supersonic atmospheric plasma spraying
摘要： Tungsten-based coatings without TiC addition (TiC-free) and with 1.5 wt% TiC addition (TiC-doped) were fabricated by supersonic atmospheric plasma spraying (SAPS) technique, respectively. The as-sprayed coatings were then irradiated by laser. The results showed that the as-sprayed coatings were mainly composed of lamellar structure. TiC phase located mainly at lamellar gaps of the as-sprayed TiC-doped coating with a morphology of strip filled the gaps. The as-sprayed TiC-doped coating exhibited dense structure, lower porosity, reduced oxygen content and higher thermal conductivity as compared with the as-sprayed TiC-free coating. The as-irradiated coatings could be divided into remelted zone, un-remelted zone and/or mixing zone. Cracks were more easily formed in the as-irradiated TiC-free coating than in the as-irradiated TiC-doped coating. The stripped TiC phase in the as-sprayed TiC-doped coating changed into quasi-spherical/spherical ones in the remelted zone of the irradiated coating and distributed along the tungsten grain boundaries. The averaged tungsten grain size in the remelted zone of the as-irradiated TiC-doped coating was about 5.4 μm and that of the as-irradiated TiC-free coating was about 14.8 μm. There were about 96 wt% α(W) and about 4 wt% γ(W) existed in the remelted zone near the surface of the as-irradiated TiC-free coating. Only α(W) could be received in the remelted zone far from the surface of the as-irradiated TiC-free coating and the remelted zone of the as-irradiated TiC-doped coating. There were no obvious diffraction peaks for γ(W) could be indexed from the XRD patterns for the as-irradiated TiC-doped coating. The ability of the as-sprayed TiC-doped coating to resist laser irradiation was greater than the as-sprayed TiC-free coating, mainly attributing to the higher thermal conductivity of the as-sprayed TiC-doped coating and the refinement effect of TiC particles in the as-irradiated TiC-doped coating.
关键词： TiC-doped,Microstructure,Tungsten-based coating,Irradiation characteristic,Laser irradiation,Supersonic atmospheric plasma spraying
更新于2025-09-19 17:15:36
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Control of the photoluminescence properties of Nd:YAG crystals by laser irradiation
摘要： This paper presents luminescence properties of Nd:YAG crystal defects including oxygen vacancy, O-hole center, F and F+ centers. The Nd:YAG crystal defects have photoluminescence emission peaks in the ~ 350-500 nm range of UV-Vis spectral region. The results show that laser irradiation can control photoluminescence properties of the Nd:YAG crystal samples. Our results can be very important in solid state laser and surface engineering.
关键词： solid state laser,laser irradiation,crystal defects,photoluminescence,Nd:YAG
更新于2025-09-19 17:13:59
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Dynamic behavior modeling of laser-induced damage initiated by surface defects on KDP crystals under nanosecond laser irradiation
摘要： the issue of laser-induced damage of transparent dielectric optics has severely limited the development of high-power laser systems. exploring the transient dynamic behaviors of laser damage on KDp surface by developing multi-physics coupling dynamics model is an important way to reveal the mechanism of nanosecond laser damage. In this work, KDP crystals are taken as an example to explore the mechanism of laser-induced surface damage. Based on the theories of electromagnetic field, heat conduction and fluid dynamics, a multi-physics coupling dynamics model is established for describing the evolution of nanosecond damage processes. The dynamics of laser energy transmission, thermal field distribution and damage morphology during nanosecond laser irradiation are simulated with this model. it is found that the enhancement of light intensity caused by surface defect plays an important role in the initial energy deposition and damage initiation of the laser irradiation area. The evolution of temperature field and crater morphology during subsequent laser irradiation is helpful to understand the laser damage process. The feasibility of this model is verified by the morphology information of typical defect-induced laser damage. this work provides further insights in explaining the laser-induced damage by surface defects on KDp crystals. the model can be also applied to investigate the laser damage mechanisms of other transparent dielectric optics.
关键词： laser-induced damage,multi-physics coupling model,nanosecond laser irradiation,KDP crystals,surface defects
更新于2025-09-19 17:13:59
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[IEEE 2019 SBFoton International Optics and Photonics Conference (SBFoton IOPC) - Sao Paulo, Brazil (2019.10.7-2019.10.9)] 2019 SBFoton International Optics and Photonics Conference (SBFoton IOPC) - Evaluation of the Adhesive Strength in Dentin after Irradiation with Ti:Sapphire Ultrashort Laser Pulses
摘要： This study was done to evaluate whether the irradiation of dentine with ultrashort laser pulses prior to adhesive procedures contributes to increase the adhesive resistance to microtraction essays. Twenty-four human teeth (third molars) were used, divided into 4 groups (n=6): standard adhesive procedures with etch-rinse adhesive were used in the control group, and in the experimental groups, the dentin was irradiated by 25 fs pulses prior to the adhesive procedures, with varying fluences. One tooth from each group was used to evaluate its surface roughness. After 24h, the teeth were sectioned with perpendicular cuts, producing toothpicks that were submitted to the microtraction test. The results showed that the groups irradiated with fluences under 4 J/cm2 presented similar results among themselves, comparable to the control group, while the group irradiated with 8 J/cm2 showed lower adhesive strength. We propose that the adhesive strength and surface roughness reduction resulting from the fluence increase is probably related to the shielding arising from an electron plasma formation during the ablation, decreasing the material removal efficiency. Nevertheless, the lower energy densities did not affect the adhesiveness, maintaining values similar to the control.
关键词： dentin,femtoseconds laser pulses,microtensile bond strength,adhesion,Ti:Sapphire laser irradiation
更新于2025-09-19 17:13:59
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Laser irradiation for controlling size of TiO2-Zeolite nanocomposite in removal of 2,4-dichlorophenoxyacetic acid herbicide
摘要： This study has focused on the synthesis of TiO2-Zeolite nanocomposite through a sol-gel approach. The decrease in the size of the nanocomposite considers as a primary parameter to improve the photocatalytic activity. In this regards fabricated samples exposed to laser irradiation (532 nm) at four different time intervals in order to investigate the size variation of nanocomposite. FTIR, UV-Vis, XRD, DLS, SEM and EDX analysis were applied to characterize and determine the size of the products. Optimized nanocomposite sample, in term of the particle size, used for photodegradation of 2, 4-D herbicide from aqueous solution. Photodegradation carried out under UV- irradiation (12 W) and Xe lamp irradiation (200 W). Obtained results showed that laser irradiation time has a substantial effect on controlling the size of nanocomposite. Results from the photocatalyst study indicated that the elimination of 2, 4-D under the Xe lamp irradiation was higher compared to the UV-irradiation. Also, the ?nal synthesized nanocomposite exhibited higher catalytic activity for photodegradation of 2,4-D compared to pure Zeolite and pure anatase TiO2 samples. The reusability of TiO2-Zeolite nanocomposite was studied in four successive cycles to evaluate the removal of 2,4-D under UV- irradiation.
关键词： photocatalyst,laser irradiation,zeolite,nanocomposite,TiO2,2, 4-D
更新于2025-09-19 17:13:59
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Laser Surface Hardening of Gun Metal Alloys
摘要： The effect of laser irradiation with different numbers of laser shots on the microstructure, the surface, and the hardness of gun metal alloy was studied by a KrF pulsed excimer laser system, X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and Vickers hardness test. The influence of 100–500 laser shots was irradiated on the surface hardness profile and on the microstructure of gunmetal alloy. XRD results showed the maximum 2θ shift, the maximum full width of half maximum FWHM, the maximum dislocation density, and the minimum crystallite size for the sample irradiated with 300 laser shots. The hardness was measured in three different regions at the laser irradiated spot, and it was found that maximum hardness was present at the heat affected zone for all samples. The hardness value of the un-irradiated sample of gun metal was 180, and the value increased up to 237 by raising the number of laser shots up to 300. The peak value of surface hardness of the laser treated sample was 32% higher than the un-irradiated sample. The Raman shift of the un-exposed sample was 605 cm?1 and shifted to a higher value of wave number at 635 cm?1 at 300 laser shots. The hardness value was decreased by further increasing the number of laser shots up to 500. The samples irradiated with 400 and 500 laser shots exhibited smaller hardness and dislocation defect density, which was assigned to possible annealing caused by irradiation.
关键词： hardness,heat affected zones,laser irradiation,gun metal
更新于2025-09-19 17:13:59
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Anti-cancer effect of gallic acid in presence of low level laser irradiation: ROS production and induction of apoptosis and ferroptosis
摘要： Background: There are different treatments for breast cancer and melanoma that mostly have some side effects. One of the therapeutic strategies is the use of natural components. Phenol components are a class of antioxidants in plants that have many biological functions like anticancer effects. Gallic acid (GA) is a natural polyhydroxy phenolic compound and commonly found in various foods. In the present study, GA effects alone and in combination with low-level laser irradiation on human dermal fibroblast cell line (HDF), human non-tumorigenic breast epithelial cell line (MCF10A), breast cancer cell line (MDA-MB-231) and melanoma cancer cell line (A375) was under the investigation. Methods: The normal and cancerous cell lines were exposed to 660 nm low-level laser with 3 J/cm2 for 90 s. Then, the cells were treated with different concentrations of GA for 24 h. In another study, the cell lines firstly were treated with GA and then exposed to low-level laser irradiation. The effects of GA and low-level laser on cell survival and apoptosis were examined using MTT assay, light microscopy, ROS production assay, fluorescence microscopy (AO/EB double staining) and flow cytometry. Results: The results showed that pre-treatment with low-level laser and then GA reduced the survival of breast cancer cells and melanoma more than the first treatment with GA and then low-level laser irradiation. Our findings showed that ROS production in cells treated with both low-level laser and GA was more than the cells treated with GA alone. The apoptosis and ferroptosis assays confirmed the MTT results which combination treatment with low-level laser and then GA increase the cell death probably via apoptosis and ferroptosis cell death mechanisms compared to GA alone. Conclusions: This study suggests that low-level laser irradiation alone is not able to cause death in human normal and cancerous cells. Preirradiation followed by GA treatment did not change the cell viability in human normal significantly but reduces the cell survival of cancer cells more than GA alone.
关键词： Breast cancer,Apoptosis,Low level laser irradiation,Ferroptosis,Melanoma cancer,Gallic acid
更新于2025-09-19 17:13:59
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Laser Irradiation and Temperature Annealing of CuOa??Cu2O Complex Thin Films
摘要： CuO–Cu2O complex thin films were synthesised on glass and p-type Si substrates through the dip-coating method. A precursor solution was prepared by dissolving CuCl2·6H2O powder in methanol. The films were deposited through the dip-coating method and dried at 430?K. One group of samples was irradiated with a green laser (λ = 540?nm, 10?W), and another group of samples was annealed at 530?K or 630?K. Fourier-transform infrared spectroscopy confirmed the presence of the functional groups of CuO and Cu2O. X-ray diffraction and ultraviolet–visible spectroscopy were used to investigate the structural and optical properties of the films. The effects of laser irradiation and annealing temperature on the films were discussed. Results indicated that the deposited CuO–Cu2O complex films were resistive, and Au enabled Ohmic contact.
关键词： Thin films,Cu2O,Laser irradiation,CuO,Annealing
更新于2025-09-19 17:13:59