YAG Pulsed Laser Irradiation Research Articles

Laser-assisted synthesis of metallic composite nanostructures in aqueous solutions

The method of pulsed laser ablation in liquids (PLAL) is applied for synthesis of composite nanostructures on the basis of TiOx and ZnO combined with noble metals like Au, Pt and Pd. The metallic plate immersed in water is laser ablated by nanosecond Nd:YAG pulsed laser irradiation. Its fundamental wavelength and the fourth harmonic are used, respectively, to produce and to modify the morphology and structure of the nano-objects. The synthesis procedure consists of two consecutive steps: laser ablation of the selected metal targets followed by unfocused laser beam irradiation of the initial colloids of nanostructures. The phase composition, structural and the shape and size morphological features were assessed by analytical method – transmission electron microscopy (TEM) in its main modes – Bright Field TEM (BF TEM), High Resolution TEM (HRTEM) and Selected Area Electron Diffraction (SAED). Formation of bimetallic polycrystalline alloys and Pt/Ti(TixOy) and Pd/Ti(TixOy) core-shell nanoparticles was founded.

Preparation and application of novel thermo-sensitive molecularly imprinted polymer for selective extraction of omeprazole from pharmaceutical formulation and biological fluids

ABSTRACT Omeprazole selective molecularly imprinted polymer was synthesized by polymerization using 2-hydroxyethyl methacrylate as a monomer, N-vinylcaprolactam as a thermo-sensitive polymer, and N, N′-methylenebisacrylamide as cross-linker, respectively. This study aimed to develop a novel polymer as a nanoadsorbent for the extraction of omeprazole in biological and pharmaceutical samples. To achieve maximum extraction recovery of the drug, the Nd:YAG pulsed laser irradiation was used to convert adsorbent particles into smaller sizes using water solvent at different irradiation times. Properties of prepared thermo-sensitive molecularly imprinted polymer were characterized by different analyses. The optimal extraction conditions were thermo-sensitive molecularly imprinted polymer dosage of 0.01 g, a cross-linking agent of 0.15 g, contact time of 15 min, eluent of methanol, the temperature of 25°C, initial drug concentration of 20 mg L−1, and solution pH of 4. The sorption isotherms and selective recognition of thermo-sensitive molecularly imprinted polymer were investigated in detail. Sorption results fitted well into the linearized Langmuir equation. The selectivity experiment has shown that the sorption capacity and selectivity of thermo-sensitive molecularly imprinted polymer to omeprazole were higher than those of bicalutamide and prednisolone. A high-performance liquid chromatography-ultra-violet detector method was validated and utilized for analysis of drug extracted from biological and pharmaceutical samples. The method was linear in the range of 0.5–80 mg L−1 with a relative standard deviation value of 0.094 and a limit of detection and a limit of quantification of 0.9 and 30 µg L−1, respectively. The recovery of omeprazole drug ranged from 94.3%, 99.2%, and 98.1%, respectively, in human plasma, human urine, and pharmaceutical samples.

The influence of Nd: YAG pulsed laser treatment on the structure, morphology and hardness of e.max ceram dental material

The use of ceramics in dentistry is increasing day by day owing to their more aesthetic look, better mechanical properties, and easy-to-fit approach. The material used in the study is IPS e.max Ceram by Ivoclar Vivadent which has been widely adopted as the ceramic of choice by many dentists as it is ideally suitable for the veneering of more opaque substructures. The study aims to elucidate the result of Nd: YAG pulsed laser irradiation at different numbers of pulses on structure, surface morphology, and hardness of e.max Ceram dental material. XRD shows the amorphous nature of the material before the laser irradiation, whereas the crystallinity in the material is slightly induced after the exposure of e.max Ceram with 150 laser shots. The surface morphology and hardness degradation are attributed to the swelling potential of the material and induced increase of the residual micro-stresses during laser irradiation. This technique could provide more ease for bonding and de-bonding of orthodontic brackets and might be used as a chairside tool.

Evaluation of adhesion durability of Ni–P coating using repeated Laser Shock Adhesion Test

This study aims to evaluate the adhesion strength and durability of NiP coatings in a non-contact manner using the Laser Shock Adhesion Test (LaSAT). A hard coating of electroless NiP deposited on carbon steel substrate (SKD11) was prepared, and the effect of post heat treatment on adhesion was comprehensively investigated in this study. With the LaSAT, strong elastic waves induced by pulsed YAG laser irradiation applies tensile stress to the coating/substrate interface resulted in interfacial delamination. Computation of the elastic-wave propagation using finite element method (FEM) was carried out to estimate the interfacial tensile stress. In addition, the adhesion durability was investigated by repetitive pulsed-laser irradiation, and the relationship between adhesion strength and the number of laser irradiation cycles until delamination was obtained. Finally, the effects of heat treatment on the adhesion strength and durability of the NiP coating were discussed. Owing to the post-heat treatment, it is found that the hardness of coating, adhesion strength and durability were improved. Indentation test reveals that the coating hardness increases from 792 HV to 1163 HV. LaSAT quantitatively evaluated the adhesion strength with increasing from 84.4 MPa to 143.9 MPa. In addition, repetitive LaSAT reveals that adhesion durability improves twice or more. This result was verified using the tensile adhesion test and microscopic observations of the interface. Therefore, the present LaSAT is a quick measurement for the adhesion durability of hard coating, and it may shed some light on quality control of surface coatings.

Nd:YAG pulsed laser production of reduced-graphene oxide as hole transporting layer in polymer solar cells and the influences of solvent type

Abstract Graphene oxide (GO) was reduced using 532 nm Nd:YAG pulsed laser irradiation (unfocused, 10 Hz repetition rate, 0.3 J/cm2) in different solvents including water, ethanol and formic acid. The obtained reduced GOs (r-GOs) were employed as hole transporting layers (HTLs) in fabrication of polymer solar cells (PSCs). The changes in the chemical composition, phase purity, optical properties, level of defects, sheet resistance (Rsh), charge transfer resistance (Rct) and morphology of r-GOs were systematically investigated using Fourier transform infrared spectroscopy, x-ray diffraction, UV–Vis and Raman spectroscopy, four-point probe, electrochemical impedance spectroscopy and atomic force microscopy. Results revealed that laser reduction of GO in formic acid led to formation of r-GOs with superior physicochemical and electrochemical characteristics, implying higher hole scavenging ability of formic acid compared to water and ethanol. The r-GOs prepared in formic acid appeared to have the lowest Rsh, Rct and surface roughness. This was attributed to the higher elimination of oxygenated functional groups in formic acid, confirmed by results obtained from physicochemical characterization of the prepared samples. Comparing the photovoltaic parameters of PSCs prepared based on r-GOs as HTL revealed that the r-GO sample produced in formic acid can act as a better HTL in P3HT:PCBM-based PSCs. This cell exhibited the highest short circuit current density (10.15 mA) and power conversion efficiency (4.02%), which was about 22% higher than that achieved for the reference PSC prepared using PEDOT:PSS as HTL. Results suggest that pulsed laser production can be considered as a promising method to produce r-GOs possessing appropriate characteristics as HTL in PSCs.

Calcium phosphate coating on dental composite resins by a laser-assisted biomimetic process

ObjectivesDental composite resins with better biocompatibility and osteoconductivity have been sought in endodontic treatments. This study aimed to develop a technique to produce the osteoconductive resin surfaces through calcium phosphate (CaP) coating using a laser-assisted biomimetic (LAB) process. MethodsLight-cured, acrylic-based composite resins were used as substrates. The resin substrate was subjected to a LAB process comprising Nd:YAG pulsed laser irradiation in a supersaturated CaP solution. The LAB-processed substrate was immersed for 3 days in a simulated body fluid (SBF) for the preliminary osteoconductivity assessment. ResultsAfter irradiation for 30 min, the resin surfaces were partly coated with a newly formed CaP layer. The coating layer contained hydroxyapatite as the main crystalline phase and the coating coverage depended on the laser wavelength and the type of resin. The LAB-processed CaP-coated surface exhibited apatite-forming ability in SBF. ConclusionsLAB process is effective for CaP coating on light-cured dental composite resins and improving their osteoconductivity. Clinical significanceThe LAB process is a potential new tool to create a cementum-like osteoconductive surface on dental composite resins.

Model development and experimental validation for analyzing initial transients of irradiation of tissues during thermal therapy using short pulse lasers.

Short pulse lasers with pulse durations in the range of nanoseconds and shorter are effective in the targeted delivery of heat energy for precise tissue heating and ablation. This photothermal therapy is useful where the removal of cancerous tissue sections is required. The objective of this paper is to use finite element modeling to demonstrate the differences in the thermal response of skin tissue to short-pulse and continuous wave laser irradiation in the initial stages of the irradiation. Models have been developed to validate the temperature distribution and heat affected zone during laser irradiation of excised rat skin samples and live anesthetized mouse tissue. Excised rat skin samples and live anesthetized mice were subjected to Nd:YAG pulsed laser (1,064 nm, 500 ns) irradiation of varying powers. A thermal camera was used to measure the rise in surface temperature as a result of the laser irradiation. Histological analyses of the heat affected zone created in the tissue samples due to the temperature rise were performed. The thermal interaction of the laser with the tissue was quantified by measuring the thermal dose delivered by the laser. Finite element geometries of three-dimensional tissue sections for continuum and vascular models were developed using COMSOL Multiphysics. Blood flow was incorporated into the vascular model to mimic the presence of discrete blood vessels and contrasted with the continuum model without blood perfusion. The temperature rises predicted by the continuum and the vascular models agreed with the temperature rises observed at the surface of the excised rat tissue samples and live anesthetized mice due to laser irradiation respectively. The vascular model developed was able to predict the cooling produced by the blood vessels in the region where the vessels were present. The temperature rise in the continuum model due to pulsed laser irradiation was higher than that due to continuous wave (CW) laser irradiation in the initial stages of the irradiation. The temperature rise due to pulsed and CW laser irradiation converged as the time of irradiation increased. A similar trend was observed when comparing the thermal dose for pulsed and CW laser irradiation in the vascular model. Finite element models (continuum and vascular) were developed that can be used to predict temperature rise and quantify the thermal dose resulting from laser irradiation of excised rat skin samples and live anesthetized mouse tissue. The vascular model incorporating blood perfusion effects predicted temperature rise better in the live animal tissue. The models developed demonstrated that pulsed lasers caused greater temperature rise and delivered a greater thermal dose than CW lasers of equal average power, especially during the initial transients of irradiation. This analysis will be beneficial for thermal therapy applications where maximum delivery of thermal dose over a short period of time is important.

Pulsed laser irradiation-induced microstructures in the Mn ion implanted Si

We have examined microstructures induced by pulsed-laser-melting for the Mn ion implanted Si using transmission electron microscopy. Single crystalline Si(001) wafers were irradiated with 65keV and 120keV Mn ions to a fluence of 1.0×1016/cm2 at room temperature. The ion beam-induced amorphous layers in the as-implanted samples were melted and resolidified by pulsed YAG laser irradiation. After laser irradiation with appropriate laser fluence, the surface amorphous layers recrystallize into the single crystalline Si. The Mn concentration becomes higher in the near-surface region with increasing the number of laser shots. The migrated Mn atoms react with Si atoms and form the amorphous Mn–Si in the Si matrix.

Surface characteristics of aluminum 6061-T6 subjected to Nd:YAG pulsed-laser irradiation

The objective of this study was to investigate the surface characteristics of an aluminum 6061-T6 alloy subjected to Nd:YAG pulsed-laser irradiation. The test specimens were prepared by a mechanical polishing process using diamond paste and emery polishing paper to obtain different levels of initial surface roughness. After ten pulsed-laser shots, the surface morphology was observed via optical microscopy (OM) and scanning electron microscopy (SEM). Nano-indentation hardness testing was also conducted on the irradiated surface. The diameter of the melted zone increased with surface roughness because of the multiple reflection and absorption of the laser beam. The relative absorbance was measured as a function of the diameter of the melted zone with varied surface roughness.

반복적인 펄스레이저 조사에 의한 알루미늄 합금의 표면상태 변화분석

The objective of this study is to investigate the thermal behavior on material surface and the variation in the surface morphology of aluminum 6061 alloy by the Nd:YAG pulsed-laser irradiation. First, we predicted the surface temperature variation during pulsed-laser irradiation by using the two dimensional finite element analysis. When the pulsed-laser of 133 mJ energy and 5 ns pulse duration is irradiated on the surface of aluminum alloy, the material surface is thought to be melting because the surface temperature rises steadily up to about exceeding the melting point. Also, the experimental results show that the solidification microstructure has been developed clearly after surface melting. Second, the diameter of melted zone was analysed by finite element analysis and measured by OM(Optical Microscopy). It increased logarithmically with increase in the number of laser irradiation. In addition, AFM(Atomic Force Microscopy) measurement showed an increase in the average surface roughness during pulsed-laser irradiation.

UV laser-induced transport properties change in silver metaphosphate glass

Samples of AgPO 3 were prepared from analar oxides (BDH) using standard sintering ceramic technique. The effect of UV Nd:YAG pulsed laser irradiation with wavelength of 355 nm on the transport properties of the prepared glassy samples AgPO 3 was studied. The frequency and temperature dependences of the A.C. conductivity and dielectric properties were analyzed in the temperature range (300 K ≤ T ≤ 393 K) throughout a range of applied frequencies (0.1 kHz ≤ f ≤ 400 kHz). The activation energies were calculated at different temperatures for the unirradiated and irradiated samples. Comparison between the A.C. electrical conductivity, dielectric constant, and dielectric loss, for unirradiated and irradiated samples was performed. The bulk conductivity has been measured with complex impedance method. Cole–Cole diagram has been investigated to obtain the bulk activation energy which corresponds to D.C. conductivity. Results indicate the semiconducting like behavior. At low temperatures and frequencies, random diffusion of the ionic charge carriers via activated hopping gives rise to a frequency independent conductivity characterizing the D.C. conductivity. It was observed that the A.C. and D.C. activation energies have the same order of magnitude.

Microstructure and mechanical properties of stainless steel under Nd:YAG pulsed laser irradiation

Microstructure and mechanical properties of stainless steel under the Nd:YAG pulsed laser irradiation were investigated. X-ray diffraction was used to identify the phases in the laser treated layer, and the growth morphology was observed by field emission scanning electron microscope. The results showed that a homogeneous microstructure with fine grains (60–300 nm) can be attained under the applied laser energy densities (2˙175×103 to 3˙585×103 J cm–2) and after that, it was difficult to get further refinement. Mechanical properties including microhardness and sliding wear were evaluated. The results indicated that the laser surface treatment was beneficial to increase the microhardness and to decrease the sliding wear rate.

Formation of nano-crystalline and amorphous phases on the surface of stainless steel by Nd:YAG pulsed laser irradiation

Thin surface layers consisting of nano-crystalline and amorphous phases on the surface of stainless steel have been attained under the Nd:YAG pulsed laser irradiation. The phases and microstructures were investigated by X-ray diffraction (XRD) and high resolution transmission electron microscope (HRTEM). The phase compositions of the surface determined by XRD were α-Fe (ferrite) and γ-Fe (austenite) or only γ-Fe in the near surface region on the bases of the different laser power densities. The nano-crystalline grains with sizes of 4–100 nm could result from high cooling rate and crystallization in amorphous region by homogeneous and heterogeneous nucleation. The formation of the amorphous phase was attributed to the higher cooling rates.

Morphological and structural characterizations of different oxides formed on the stainless steel by Nd:YAG pulsed laser irradiation

The effects of laser surface irradiation on microstructure of AISI 304 stainless steel were investigated. The stainless steel surface was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). XRD patterns indicated that different oxides, such as chromium oxides and manganese oxides were fabricated successfully on the surface of the stainless steel by Nd:YAG pulsed laser irradiation. The effects of the growth conditions such as the laser power density on the morphologies of the different oxides have been investigated. From the FESEM, EDS (energy-dispersive spectrum) and TEM observations, the oxides with triangle-like, quadrangular and hexagonal morphologies have been fabricated successfully. The XPS was used to verify the formed oxides which had been detected by the XRD patterns. It was considered that laser power density had a critical role in the formation of different oxides.

Microstructure evolution on the surface of stainless steel by Nd:YAG pulsed laser irradiation

New structure phenomena with the grain sizes of 60 nm to 1 μm would be expected on the stainless steel surface by Nd:YAG pulsed laser irradiation. Nano-structures with various shapes and sizes were formed mainly during the solidification and most shapes of particles were diversiform according to different distances from the center of the spot. The morphologies were of equiaxed nano-particles and faceted hexagons. The surface re-solidification velocities have been estimated according to the numeral simulation of the thermal conditions. It was proved by the XRD that they were mainly consisted of γ-Fe and manganese oxides. The XPS results confirmed the EDS results that on the surface the alloy elemental composition in the outermost layer were rich in Mn and poor in Fe and in reverse in the center of the laser spot. Through observation of morphologies grown on the laser irradiated surfaces, direct evidence of growth mode transition from a continuous form to a lateral form was provided in one laser spot.

Arrays of periodic submicron conductive links in Si covered by SiO2 formed by polarized laser irradiation

Arrays of periodic submicron conductive links were fabricated in silicon covered by SiO2 when polarized frequency doubled Nd:YAG pulsed laser irradiation is focused on the gap between two highly doped regions. The principle of the process is based on the fact that the laser forms periodic melting in silicon, thus inducing preferential dopant diffusion and creating an array of fine conductive links between the highly doped regions. A scanning capacitance microscopy (SCM) was employed to detect these submicron structures and to measure their electrical properties. It was found that between two and seven submicron conductive links are observed in a focused spot size of 3 µm and their number depends only on the laser intensity ranging from 3.10 W to 3.75 W, while their average width (151–300 nm) and depth (108–147 nm) strongly depends on both the laser intensity and number of laser pulses. The resistances of these links are between 363–493 Ω and the effective average doping levels are from 1.5 × 1018 to 2.4 × 1019 cm−3.

Line patterning with large refractive index changes in the deep inside of glass by nanosecond pulsed YAG laser irradiation

Nanosecond (∼100 ns) pulsed (10 Hz) Nd:YAG laser operating at the wavelength ( λ) of 1064 nm with pulse energies of 0.16–1.24 mJ/cm 2 has irradiated 10Sm 2O 3·40BaO·50B 2O 3 glass. It is demonstrated for the first time that the structural modification resulting the large decease (∼3.5%) in the refractive index is induced by the irradiation of YAG laser with λ=1064 nm. The lines with refractive index changes are written in the deep inside of 100–1000 μm depths by scanning laser. The line width is 1–13 μm, depending on laser pulse energy and focused beam position. It is proposed that the samarium atom heat processing is a novel technique for inducing structural modification (refractive index change) in the deep interior of glass.

Morphological study of Sn–Se–Sb–Co amorphous thin film after Nd:YAG pulsed laser irradiation

Sn 29 Se 56 Sb 10 Co 5 amorphous thin films were prepared on the polymer substrates, and was irradiated at room temperature by Nd:YAG pulsed laser in air, with the wavelength of 532 nm, pulse width of 90 ns after equilibration. Irradiation-induced surface morphological modifications were characterized using Secco-etching aided scanning electron microscopy (SEM). Complementary information was obtained from X-ray diffraction (XRD) spectrum and energy dispersive X-ray spectrum (EDS). The experimental results demonstrated that the grain size distribution was closely related to the laser beam profile. As a function of laser fluence, the average grain size evolution was also studied, which may not be interpreted by the conventional crystallography theories, and was related to some threshold effects.

Morphological study of Sn–Se–Sb–Co amorphous thin film after Nd:YAG pulsed laser irradiation

Sn 29Se 56Sb 10Co 5 amorphous thin films were prepared on the polymer substrates, and was irradiated at room temperature by Nd:YAG pulsed laser in air, with the wavelength of 532 nm, pulse width of 90 ns after equilibration. Irradiation-induced surface morphological modifications were characterized using Secco-etching aided scanning electron microscopy (SEM). Complementary information was obtained from X-ray diffraction (XRD) spectrum and energy dispersive X-ray spectrum (EDS). The experimental results demonstrated that the grain size distribution was closely related to the laser beam profile. As a function of laser fluence, the average grain size evolution was also studied, which may not be interpreted by the conventional crystallography theories, and was related to some threshold effects.

Local surface modification of aluminum by laser irradiation

A novel method involving a combination of pulsed YAG laser irradiation and electrochemistry for chemical and physical modification of aluminum surface at a selected area is reviewed. Local metal deposition is carried out by successive steps of anodizing, laser irradiation, and electroplating (or electroless plating), and the fabrication of a prototype for printed circuit boards is attempted. Local organic film deposition with anodizing, laser irradiation, and electrophoretic deposition is introduced, and the formation of microtrenches and pores on aluminum surfaces with anodizing, laser irradiation, and electrochemical etching (or chemical etching) is also described. It is emphasized that the key technology in these procedures is to use aluminum as a target for the laser irradiation in solution, and that anodic oxide films on aluminum play an important role in the processes.