KrF Laser Research Articles

Superhydrophobic-antibacterial polycarbonate fabrication using excimer laser treatment

In this paper, effect of the excimer laser irradiation on bacterial adhesion of the polycarbonate films was investigated. For this purpose, the surface roughness and wettability as two important factors are examined following laser treatment. The samples were irradiated by a KrF laser with the wavelength of 248 nanometers and pulse duration of about 25 ns. Scanning electron spectroscopy was used for investigating the changes in surface morphology. Finally, the results show that excimer laser irradiation with a proper irradiation parameters improve the antibacterial properties of polycarbonate surface.

Investigation of irradiation parameters on fluid flow in microchannels fabricated on polymethyl methacrylate by a KrF laser

Due to the increasing importance of microfluidic chips in medical, nuclear, and chemical industries, we focused on improving various parameters in manufacturing their components, most importantly microchannels. Channels with a length of several hundred microns are constructed based on two crucial factors: substrates and the procedure. Numerous substrates can be employed, amongst which PMMA polymer has been chosen due to its transparency, flexibility, and cheapness with respect to glass. As for the procedure, laser ablation is commonly used for manufacturing microchannels. Nanosecond KrF laser is used to advantage from not only its high absorption of polymeric material in ultra-violet wavelengths but also its higher accessibility and cost-effectiveness. In this paper, irradiation parameters are optimized including the scanning speed of the laser, laser fluence, and repetition rate of the laser pulse in the fabrication of microchannels on PMMA polymer. The fluidic properties of the fabricated channels such as hydraulic diameter, Reynolds number, and the regime of water flow are also investigated. Results confirm the domination of the laminar regime for water flow in these microchannels.

Absorption spectra and mechanical properties of C : F nanocoatings deposited from laser plasma onto leucosapphire surface

It is experimentally shown that during laser annealing of micron layers of fluorocarbon oil by high-power KrF laser radiation pulses, C : F nanocoatings with a thickness of up to ∼100 nm can be synthesised on a leucosapphire surface. The absorption spectra of these coatings, measured in the 0.19 – 6 μm range, virtually coincided with the absorption spectra of fluorographene in the quantum energy range of 5 ± 1 eV. The nanohardness and elasticity modulus of the C : F nanocoatings are found to be 7 and 250 GPa, respectively, which is close to the characteristics of fluorographene.

A comparative study on the adhesive bonding strength of unidirectional, 4-Harness Satin weaved and plain weaved carbon fibre reinforced polymer after KrF excimer laser pre-treatment

Several types of carbon fibre reinforced polymers (CFRP) are available based on the appearance of the carbon fibre laminates. In this study, three distinct types of CFRPs, namely, unidirectional (UD CFRP), 4-Harness Satin weaved (4HSW CFRP) and plain weaved (PW CFRP) were selected to compare the bonding strength performance of specific CFRP/CFRP adhesive joints after KrF laser pre-treatment. KrF excimer laser with top hat beam profile was utilized. This treatment increased the Sq and Sdr values significantly for all three CFRP types. KrF laser affected the matrix polymer C-N bonds and converted the tertiary and secondary aliphatic amines to secondary and primary amines, respectively, after de-polymerization. Single lap shear stress (SLSS) test revealed that the average adhesive bonding strength achieved respectively for UD CFRP, 4HSW CFRP and PW CFRP after KrF laser pre-treatment were 32.80, 23.97 and 35.21 MPa which were 104.34%, 47.24% and 39.72% higher than their pristine counterparts. Repeatability of the SLSS results were more for weaved pattern CFRPs. Adhesive failure reduced drastically and presence of cohesive failure, thin layer cohesive failure and fibre tear failure were prevalent in SLSS for all considered CFRPs. Comparison of all results showed that the best performance was obtained for PW CFRP.

Discharge KrF Laser with a High Specific Energy of Radiation

Discharge KrF Laser with a High Specific Energy of Radiation

KrF Laser and Plasma Exposure of PDMS-Carbon Composite and Its Antibacterial Properties.

A polydimethylsiloxane (PDMS) composite with multi-walled carbon nanotubes was successfully prepared. Composite foils were treated with both plasma and excimer laser, and changes in their physicochemical properties were determined in detail. Mainly changes in surface chemistry, wettability, and morphology were determined. The plasma treatment of PDMS complemented with subsequent heating led to the formation of a unique wrinkle-like pattern. The impact of different laser treatment conditions on the composite surface was determined. The morphology was determined by AFM and LCM techniques, while chemical changes and chemical surface mapping were studied with the EDS/EDX method. Selected activated polymer composites were used for the evaluation of antibacterial activity using Gram-positive (Staphylococcus epidermidis) and Gram-negative (Escherichia coli) bacteria. The antibacterial effect was achieved against S. epidermidis on pristine PDMS treated with 500 mJ of laser energy and PDMS-C nanocomposite treated with a lower laser fluence of 250 mJ. Silver deposition of PDMS foil increases significantly its antibacterial properties against E. coli, which is further enhanced by the carbon predeposition or high-energy laser treatment.

Immobilization of Glucose Oxidase on pH-Responsive Polyimide-Polyacrylic Acid Smart Membranes Fabricated Using 248 nm KrF Excimer Laser for Drug Delivery

The permeability of polyimide–polyacrylic acid (PI-PAAc) pH-responsive membrane fabricated using a 248 nm KrF laser was investigated. These membranes were further immobilized with glucose oxidase enzyme, which led to the successful development of a glucose-responsive membrane. The base PI membranes were developed using a simple photolithographic technique. Further grafting of PAAc inside the pores was carried out using the same laser wavelength. The effect of various solution parameters and laser parameters were studied and discussed in detail in our previous work. A variety of grafting yields were obtained by changing laser exposure time. Glucose Oxidase (GOD) enzyme was then immobilized on the membrane using a carbodiimide-based amidation method. The polyacrylic acid grafted inside the pores shows pH-responsive gating. The immobilized GOD molecules show glucose sensitivity and convert the glucose into gluconic acid. The experiment results show that these membranes can detect the amount of glucose and release the corresponding solute amount.

Photoexfoliation Synthesis of 2D Materials

Quantum two-dimensional (2D) materials discovered in the early 21st century have outsmarted existing nanomaterials in various frontiers of applications. Among the preparation of 2D materials, molecular beam epitaxy, atomic layer deposition, and chemical vapor deposition are nonscalable costly methods, whereas sonochemical and Hummer’s exfoliation methods provide functionalized sheets. Conversely, ultrafast liquid-phase laser processing promises quick delivery of defect-free 2D quantum materials. We report photoexfoliation synthesis of atomic graphene layers, boron nitride (BN), and molybdenum disulfide (MoS2) by the intense KrF laser irradiation into aqueous dispersions of parent material powders in DMF taken in quartz beakers. The number of atomic layers and the lateral size of the sheets gradually decrease with an increase in the laser irradiation duration. Also, the laser fluence becomes the critical control parameter of the lateral size and the number of layers. The average lateral size shrinks from ∼400 nm at 1.5 J/cm2 to 20–30 nm at 4 J/cm2, which accompanies a surge in the ratio of sheets with fewer layers. We correlate the laser processing parameters with the sample size and analyze the molecule-atom-scale interactions. Simulation and DFT calculations suggest the mild out-of-plane thermal expansion of atomic layers followed by solvent intercalation stretches interlayer distance to ∼6.68 Å and thereby lowers the activation energy of exfoliation. The optimum photon fluence at the solvent-assisted condition reduces the activation barrier, enabling us to synthesize 2D crystals in the solution phase. Photoexfoliation synthesis of pure crystals of 2D materials can be promising for next-generation electronic devices.

Электроразрядный KrF-лазер с высокой удельной энергией излучения

Results of experimental and numerical studies of an electric-discharge KrF laser with a specific pump power of 3.5 and 7 MW/cm3 are presented; in this case, lasing was obtained with a specific radiation pulse energy of ~ 6 and 9.5 J/l, with an internal energy efficiency of ~ 4%. Time dependences of the formation of charged and excited particles in a dense excimer plasma with an electron concentration of ne ~ 1016 cm-3 are shown. Conditions for the effective operation of the laser are proposed, which will make it possible to ensure a further increase in the specific radiation energy by more than two times while maintaining the high internal efficiency of the laser relative to the energy deposited into the discharge.

Electrical Properties Engineering of Sputtered Indium Gallium Zinc Oxide Semiconductor Thin Films

The influence of deposition conditions and laser annealing on the electrical properties of indium gallium zinc oxide (IGZO) semiconducting thin films was investigated. 50 nm thick IGZO films were deposited by radio frequency (RF) magnetron sputtering at room temperature and subsequently laser annealed in ambient conditions to enhance the IGZO electrical properties. Excimer laser annealing (ELA) was conducted by Krypton fluoride (KrF) excimer laser (λ= 248 nm) with single pulse over a range of fluences up to 175 mJ/cm2. The electrical properties of IGZO films were studied by four point probe (4PP) and Hall Effect measurements. Results demonstrated that the applied deposition conditions control the IGZO films metallic composition, which is found to be directly linked to IGZO films electrical properties. The as-deposited IGZO films were highly resistive with sheet resistance > 5 MΩ/sq and therefore 4PP and Hall Effect measurements could not be performed on the as-deposited films. Upon ELA, however, the sheet resistance is noticeably reduced to about 500 ± 10 % Ω/sq. Also, IGZO films demonstrated Hall mobility of 14 cm2/Vs and electron density of 3×1019/cm3 subsequent to ELA at 100 mJ/cm2. The reported findings present ELA as an efficient technique to engineer the electrical properties of sputter-deposited IGZO films. Therefore, a combination of room temperature deposition, via RF magnetron sputtering, and laser annealing could be used as a fabrication route of IGZO films for active layers of transparent thin film transistors (TTFTs) and applicable to flexible electronics which require low substrate temperature.

Direct-Drive Oscillation of KrF Excimer Laser Using Pulsed Power Generator Based on LTD

The excimer laser is a laser characterized by high output and high gain oscillation in the ultraviolet region. Utilizing these features, excimer lasers are currently in practical use as light sources for semiconductor lithography. We are aiming to improve the oscillation efficiency and to extend the lifetime of excimer lasers. In this article, we have evaluated the oscillation efficiency by directly driving the krypton fluoride (KrF) excimer laser using a pulsed power generator based on a linear transformer driver (LTD), which is one of the new pulsed power generation methods. As a result, we have demonstrated, for the first time, the direct pumping of KrF excimer laser using LTDs. However, although it is confirmed that the oscillation efficiency was improved by about 15% on the low-input level, it is observed that the laser output is significantly reduced on the high-input level, compared with the traditional method. It is concluded that the circuit and the pumping waveform need further optimization.

A STUDY ON THE RELATION BETWEEN MORPHOLOGICAL AND CHEMICAL CHANGES AND WETTABILITY MODIFICATION OF POLYETHERSULFONE SURFACE AFTER IRRADIATION WITH A PULSED KrF LASER

Laser irradiation is used for surface modification of polymers aiming to improve their properties for different applications. The wettability of a polymeric surface can significantly affect its performance for biological applications. In this paper, the interaction of high-energy KrF laser photons in the two above- and below-threshold regimes with polyethersulfone polymer is studied. The role of morphological and chemical changes of the irradiated polymer and their correlation in the modification of the wetting property of this polymer is investigated. The obtained results show that the morphological parameter of surface roughness is the dominant mechanism in the below-threshold regime, while in the above-threshold region, the competition between this parameter and the carbonization amount of the surface determines the final hydrophilic response.

Acaricidal efficacy of ultraviolet-C irradiation of Tetranychus urticae adults and eggs using a pulsed krypton fluoride excimer laser

BackgroundPulsed ultraviolet (UV)-C light sources, such as excimer lasers, are used in emerging non-thermal food-decontamination methods and also have high potential for use in a wide range of microbial decontamination applications. The acaricidal effect of an experimental UV-C irradiation device was assessed using female adults and eggs of a model organism, the two-spotted spider mite Tetranychus urticae.MethodsUV-C light was generated by a pulsed krypton fluoride excimer laser operating at 248-nm emission wavelength. The pulse energy and pulse repetition rate were 5 mJ and up to 100 Hz, respectively. The distance from the light source to the target was 150 mm; the target surface area was 2.16 cm2. The exposure time for the mites and fresh eggs varied from 1 to 4 min at 5–300 mW, which corresponded to UV doses of 5–80 kJ/m2. Post-irradiation acaricidal effects (mite mortality) were assessed immediately and also measured at 24 h. The effects of UV-C irradiation on the hatchability of eggs were observed daily for up to 12 days post-irradiation.ResultsThe mortality of mites at 5 and 40 kJ/m2 was 26% and 92%, respectively. Mite mortality reached 98% at 80 kJ/m2. The effect of exposure duration on mortality was minimal. The effect of irradiation on egg hatchability was even more significant than that on adult mite mortality, i.e. about 100% egg mortality at an accumulated dose of as little as 5 kJ/m2 for each exposure time.ConclusionsA high rate of mite mortality and lethal egg damage were observed after less than 1 min of exposure to 5 mJ UV-C pulsed irradiation at 60 Hz. Pending further developments (such as beam steering, beam shaping and miniaturisation) and feasibility studies (such as testing with mites in real-life situations), the reported results and characteristics of the UV-C generator (modulation of energy output and adaptability to varying spot sizes) open up the use of this technology for a vast field of acaricidal applications that require long-range radiation.Graphical

Deep Penetration of UV Radiation into PMMA and Electron Acceleration in Long Plasma Channels Produced by 100 ns KrF Laser Pulses

Long (~1 mm), narrow (30−40 μm in diameter) corrugated capillary-like channels were produced in the axially symmetric 2D interaction regime of 100 ns KrF laser pulses with polymethylmethacrylate (PMMA) at intensities of up to 5 × 1012 W/cm2. The channels extended from the top of a deep (~1 mm) conical ablative crater and terminated in a 0.5 mm size crown-like pattern. The modeling experiments with preliminary drilled capillaries in PMMA targets and Monte Carlo simulations evidenced that the crown origin might be caused by high-energy (0.1–0.25 MeV) electrons, which are much higher than the electron temperature of the plasma corona ~100 eV. This indicates the presence of an unusual direct electron acceleration regime. Firstly, fast electrons are generated due to laser plasma instabilities favored by a long-length interaction of a narrow-band radiation with plasma in the crater. Then, the electrons are accelerated by an axial component of the electrical field in a plasma-filled corrugated capillary waveguide enhanced by radiation self-focusing and specular reflection at the radial plasma gradient, while channel ripples serve the slowing down of the electromagnetic wave in the phase with electrons.

Optical Bend Sensor Based on Eccentrically Micro-Structured Multimode Polymer Optical Fibers

We report on a novel bend sensor with high flexibility and elasticity based on Bragg grating structures in polymer optical fibers to detect bending for the measurement of movement. The concept is very simple and relies on the inscription of eccentrical Bragg gratings into multimode graded-index polymer optical fibers via contact exposure with a krypton fluoride excimer laser in the ultraviolet region and an optimized phase mask. Depending on the fiber deformation, the lattice constant of the inscribed Bragg grating is strained or compressed due to its position relative to the fiber core. This in turn results in a specific shift of the Bragg wavelength of up to $1.3\text{ nm}$ to the red or blue wavelength region, respectively, which is sufficiently large to be reliably detected. Therefore, as proof of principle, deformation along one axis can be observed with a single Bragg grating with a maximum sensitivity of up to $65\text{ pm/m}^{-1}$ . Moreover, multiple Bragg gratings inscribed into the same polymer optical fiber at different positions around the fiber axis allow to determine the shape deformation of the fiber relative to a reference frame with similar accuracy. Consequently, this technology could form the basis for new applications in the areas of medical diagnostics, robotics or augmented reality, which are lacking affordable sensor systems to date.

Bimetallic Nanowires on Laser-Patterned PEN as Promising Biomaterials

As inflammation frequently occurs after the implantation of a medical device, biocompatible, antibacterial materials must be used. Polymer–metal nanocomposites are promising materials. Here we prepared enhanced polyethylene naphthalate (PEN) using surface modification techniques and investigated its suitability for biomedical applications. The PEN was modified by a KrF laser forming periodic ripple patterns with specific surface characteristics. Next, Au/Ag nanowires were deposited onto the patterned PEN using vacuum evaporation. Atomic force microscopy confirmed that the surface morphology of the modified PEN changed accordingly with the incidence angle of the laser beam. Energy-dispersive X-ray spectroscopy showed that the distribution of the selected metals was dependent on the evaporation technique. Our bimetallic nanowires appear to be promising antibacterial agents due to the presence of antibacterial noble metals. The antibacterial effect of the prepared Au/Ag nanowires against E. coli and S. epidermidis was demonstrated using 24 h incubation with a drop plate test. Moreover, a WST-1 cytotoxicity test that was performed to determine the toxicity of the nanowires showed that the materials could be considered non-toxic. Collectively, these results suggest that prepared Au/Ag nanostructures are effective, biocompatible surface coatings for use in medical devices.

Pathways control in modification of solid surfaces induced by temporarily separated femtosecond laser pulses

Reaction control by laser light is a unique method of the reaction dynamics mastery in the molecular chemistry. We provide evidence of phase control processing with femtosecond lasers in macroscopic solids. Rutile TiO2 monocrystals with (001) and (100) surface orientations were irradiated with repetitive pulses of femtosecond KrF laser of variable fluences and a temporal delay between two superimposed linearly polarized beams. The appearance of three types of surface morphology was thoroughly analyzed: low-spatial frequency laser-induced periodic surface structures (LSFL), grooves and unusual featureless flat area (FFA). The interaction of light with the excited surface led to the onset or suppression of the subwavelength LSFL, depending on whether the temporal delay between laser beams is larger or smaller than the critical value of ~6 ps. By contrast, the suprawavelength grooves and FFA appeared at longer temporal delays. A strong decrease of the grooves onset energy was observed on the (001) oriented crystal after the delay of ~8 ps; the decrease of onset energy was also observed on the (100) oriented crystal, where FFA appeared instead of grooves. The critical delay is discussed in framework of a phenomenological model describing the energy evolution of excited transient states along the “reaction” coordinate.

Shock front behavior during pulsed laser ablation of graphite

Pulsed laser ablation of pyrolytic graphite with a 4-J / cm2 KrF laser in backgrounds of air, argon, nitrogen, and helium at pressures up to 10 Torr was performed to study the plume dynamics. Optical emission imaging with a 2-ns gated intensified charged-coupled device camera was used to determine shock front positions and plume trajectories for characterization by free expansion, Sedov–Taylor (ST) blast, and drag models. The plume expands with initial Mach numbers of M = 55, decreasing to M ∼ 20 as the emission becomes too weak to detect. The plumes begin with a planar shock front and thickness of a few mean free paths, but evolve to higher dimensionality, n, depending on pressure and mass of the background gas. The ST energy released in the sudden ablation is typically 33% the laser pulse energy. Blast energy and plume dimensionality are correlated with stopping distances, which are typically greater than 103 mean free paths. Upper bounds for the mass ablated (1 to 2 μg / pulse) and hole depth (∼88 to 183 nm) are inferred from the shock kinetic energy relative to laser pulse energy. The inferred hole depth ranges from 0.32 to 0.67 percent of the thermal diffusion length as the pressure increases from 1 to 10 Torr for these conditions where the fluence is just above twice the ablation threshold.

Effect of KrF Laser Irradiation on the Morphology and Microstructure of Amorphous PZT Thin Films Grown by RF Magnetron Sputtering

Effect of KrF Laser Irradiation on the Morphology and Microstructure of Amorphous PZT Thin Films Grown by RF Magnetron Sputtering

A comparative study of KrF laser ablation of aluminum and alumina in oxygen ambiance

This paper is dedicated to a comparative study of aluminum and alumina plasmas, induced under the same conditions of laser fluence and oxygen gas pressure in the range of 0.02 to 5 mbar. In this comparative analysis, measurements of ablated mass versus laser fluence and optical emission spectroscopy diagnostic of the plasmas are studied. The results from ablated mass measurements reveal the existence of two regimes of ablation according to a laser fluence threshold for phase explosion mechanism. This laser fluence threshold was found different for Al and Al2O3. A difference in the amount of ablated mass/pulse is also observed and is assigned to the optical (reflectivity and absorption) and thermodynamical properties (evaporation temperature) of the targets. Below a certain laser fluence threshold, thermal and non-thermal processes are involved. Above this laser fluence threshold, the mechanism of ablation is assigned to phase explosion. For plasma diagnostic by optical emission spectroscopy, two species were followed; the neutral Al (396.15 nm) for its persistence in time and distance and the AlO (the band head emission at 484.21 nm) molecule that is probably the precursor in alumina thin films formation. The spectra revealed a disparity in the intensity emission of neutral Al and AlO molecules, which were, related to the target's properties. The origin of AlO molecules recorded in aluminum and alumina plasma under oxygen ambiance is discussed. Their translational temperature for neutral Al, molecular vibrational temperature, and free linear velocities, are also compared.