用可见激光在聚(氨酯-酰亚胺)表面制备周期性亚微米结构

由于含有偶氮苯染料侧基,聚(氨酯-酰亚胺)(PUI)对532nm的光具有较强的吸收.采用该波长的可见偏振脉冲激光(Nd∶YAG激光器的倍频输出),在PUI薄膜表面制备了激光诱导周期性表面微结构(LIPSS).研究了染料引入方式以及染料侧基含量对微结构形成过程的影响,讨论了入射角、激光脉冲数、激光脉宽等激光辐射条件对LIPSS形成过程以及对微结构形貌和周期性的影响.     

Assessment and formation mechanism of laser-induced periodic surface structures on polymer spin-coated films in real and reciprocal space

In this work we evaluate the potential of grazing incidence X-ray scattering techniques in the investigation of laser-induced periodic surface structures (LIPSSs) in a series of strongly absorbing model spin-coated polymer films which are amorphous, such as poly(ethylene terephthalate), poly(trimethylene terephthalate), and poly(carbonate bisphenol A), and in a weaker absorbing polymer, such as semicrystalline poly(vinylidene fluoride), over a narrow range of fluences. Irradiation was performed with pulses of 6 ns at 266 nm, and LIPSSs with period lengths similar to the laser wavelength and parallel to the laser polarization direction are formed by devitrification of the film surface at temperatures above the characteristic glass transition temperature of the polymers. No crystallization of the surface is induced by laser irradiation, and crystallinity of the material prevents LIPSS formation. The structural information obtained by both atomic force microscopy and grazing incidence small-angle X-ray scattering (GISAXS) correlates satisfactorily. Comparison of experimental and simulated GISAXS patterns suggests that LIPSSs can be well described considering a quasi-one-dimensional paracrystalline lattice and that irradiation parameters have an influence on the order of such a lattice.     

Material removal and chemical and structural changes induced by irradiation of polymer surfaces with KrF-excimer laser radiation

Holes in polypropylene (PP) and polymethylmethacrylate (PMMA) plates, 0.5 mm in thickness were drilled by irradiation with up to 3000 pulses of KrF-excimer laser radiation (λ = 248 nm) at fluences per pulse ? in the range 0.1–10 J/cm², conditions which yield a laser-induced plasma/vapor plume. The process was analyzed experimentally in terms of material removal rate, optical emission of the laser-induced plasma, hole geometry, debris production at the hole edge, and chemical changes in the polymer induced by the laser irradiation. Additionally, the process was simulated using a model based on degradation of the polymer induced by optical absorption and heating, leading to gas-phase products. Such characteristics as the material removal rate as a function of fluence, the nature of the gas phase products and the deposition of debris were calculated.     

Impact of Pre-Patterned Structures on Features of Laser-Induced Periodic Surface Structures

The efficiency of light coupling to surface plasmon polariton (SPP) represents a very important issue in plasmonics and laser fabrication of topographies in various solids. To illustrate the role of pre-patterned surfaces and impact of laser polarisation in the excitation of electromagnetic modes and periodic pattern formation, Nickel surfaces are irradiated with femtosecond laser pulses of polarisation perpendicular or parallel to the orientation of the pre-pattern ridges. Experimental results indicate that for polarisation parallel to the ridges, laser induced periodic surface structures (LIPSS) are formed perpendicularly to the pre-pattern with a frequency that is independent of the distance between the ridges and periodicities close to the wavelength of the excited SPP. By contrast, for polarisation perpendicular to the pre-pattern, the periodicities of the LIPSS are closely correlated to the distance between the ridges for pre-pattern distance larger than the laser wavelength. The experimental observations are interpreted through a multi-scale physical model in which the impact of the interference of the electromagnetic modes is revealed.     

Effect of alcohols on the initial growth of multibubble sonoluminescence

The effect of alcohols on the initial growth of the multibubble sonoluminescence (MBSL) intensity in aqueous solutions has been investigated. With increasing concentrations of the alcohols, the number of pulses required to grow the MBSL intensity to a steady state (N(crit)) increases (relative to that of water) initially to a maximum for all the alcohols used in this study, followed by a decrease for methanol and ethanol. The cause of the initial increase in N(crit) is attributed to the inhibition of bubble coalescence in the system. This inhibition in bubble coalescence results in a population of bubbles with a smaller size range and thus a larger number of pulses is required to grow the bubbles to their sonoluminescing size range. It is suggested that the decrease in the N(crit) at higher alcohol concentrations may be caused by an increase in the bubble growth by rectified diffusion.     

Incubation Effect of Pre-Irradiation on Bubble Formation and Ablation in Laser Ablation in Liquids

Pulsed laser ablation in liquids (PLAL) is a multi-scale process, which is widely studied either in batch ablation with prolonged target irradiation as well as mechanistic investigations, in a defined (single-shot) process. However, fundamental studies on defined pulse series are rare. We have investigated the effect of a developing rough morphology of the target surface on the PLAL process with nanosecond pulses and, partially, picosecond pulses. At low fluence the cavitation bubble growth as well as the ablation yield depend on the irradiation history of the target. The bubble size increases with repeated irradiation on one spot for the first 2–30 pulses as well as with the applied dose. This is discussed within the framework of incubation effects. Incubation is found to be important, resulting in a bubble volume increase by a factor of six or more between pristine and corrugated targets. The target surface, changing from smooth to corrugated, induces a more efficient localization of laser energy at the solid-liquid interface. This is accompanied by a suppressed reflectivity and more efficient coupling of energy into the laser-induced plasma. Thus, the cavitation bubble size increases as well as ablation being enhanced. At high fluence, such incubation is masked by the rapid development of surface damage within the first shots, which eventually would lead to a reduction of bubble sizes.     

The effect of vacuum-ultraviolet laser wavelengths on the surface treatment of polyolefinic polymers

The laser-induced modification of the surface morphology of poly(propylene) fibers and films was investigated. It is known that strongly absorbing fibers such as poly(ethylene terephthalate) and polyamide obtain characteristic surface morphologies after treatment with 193 or 248 nm laser irradiation. Polyolefinic material cannot be modified directly (i.e., without doping) by irradiation with these wavelengths. Therefore experiments were carried out using a 157 nm F₂-laser. After irradiation in a vacuum chamber at fluences in excess of 50 mJ/cm² poly(propylene) also reveals the well-known surface morphology. Compared with aromatic polymers a rather high number of pulses is needed to generate the effect. © 1993 John Wiley & Sons, Inc.     

Bimodal Size Distribution of Gold Nanoparticles under Picosecond Laser Pulses

The evolution of size distributions of gold nanoparticles under pulsed laser irradiation (Nd:YAG, lambda = 355 nm, pulse width 30 ps) was carefully observed by transmission electron microscopy. Interestingly, the initial monomodal size distribution of gold nanoparticles turned into a bimodal one, with two peaks in the number of particles, one at 6 nm and the other at 16-24 nm. The sizes for small particles depended very little on the irradiated laser energy. This change is attributed to laser-induced size reduction of the initial gold nanoparticles followed by the formation of small particles. In our analysis, we extracted a characteristic value for the size-reduction rate per one pulse and revealed that laser-induced size reduction of gold nanoparticles occurred even below the boiling point. When laser energy is insufficient for the boiling of particles, formation of gold vapor around liquid gold drops is thought to cause the phenomenon. With enough laser energy for the boiling, the formation of gold vapor around and inside liquid gold drops is responsible for the phenomenon. We also observed particles with gold strings after one pulse irradiation with a laser energy of 43 mJ cm(-2) pulse(-1), which is sufficient energy for the boiling. It is considered that such particles with gold strings are formed by the projection of gaseous gold from liquid gold drops with some volume of liquid gold around the bubble. On the basis of comparison with previous work, picosecond laser pulses are thought to be the most efficient way to cause laser-induced size reduction of gold nanoparticles.     

Ablation thresholds and morphological changes of poly-l-lactic acid for pulse durations in the femtosecond-to-picosecond regime

Biodegradable polymers such as poly-l -lactic acid (PLLA) are essential tools for a wide range of medical applications because of their mechanical robustness and bio-affinity. Laser processing is commonly used to construct various structures from biodegradable polymers. However, in general, polymers deteriorate rapidly owing to laser-induced heating effects. In this study, we investigate the optimum irradiation conditions for PLLA processing, using an ultrafast laser and finely controlling the pulse duration over the femtosecond-to-picosecond range. We report on the morphological characteristics of the craters generated by single-shot and multiple-shot laser irradiation under pulse duration control. Our results show that crater morphology and damage threshold in the single-shot regime depend on pulse duration and that the degree of crater unevenness is insensitive to pulse duration in the multishot regime.     

Analysis of laser-induced breakdown images measuring the sizes of mixed aquatic nanoparticles

Sizes of aquatic colloidal nanoparticles are determined by utilizing the laser-induced breakdown detection technique. Specifically, the number of breakdown events is measured as a function of area in laser-induced plasma images, generated from a mixture of two different size nanoparticles in aqueous solution, by minimizing the energy of the incident laser irradiation to generate the plasma. We find that the accuracy of measuring the sizes of nanoparticles in mixtures is greatly improved when selecting the plasma images produced only within one-half of the Rayleigh range of the focused Gaussian beam where the irradiation is most uniformly distributed.     

Optical emission studies of plasma induced by single and double femtosecond laser pulses

Double-pulse femtosecond laser ablation has been shown to lead to significant increase of the intensity and reproducibility of the optical emission signal compared to single-pulse ablation particularly when an appropriate interpulse delay is selected, that is typically in the range of 50–1000 ps. This effect can be especially advantageous in the context of femtosecond laser-induced breakdown spectroscopy analysis of materials. A detailed comparative study of collinear double- over single-pulse femtosecond laser-induced breakdown spectroscopy has been carried out, based on measurements of emission lifetime, temperature and electronic density of plasmas, produced during laser ablation of brass with 450 fs laser pulses at 248 nm. The results obtained show a distinct increase of plasma temperature and electronic density as well as a longer decay time in the double-pulse case. The plasma temperature increase is in agreement with the observed dependence of the emission intensity enhancement on the upper energy level of the corresponding spectral line. Namely, intensity enhancement of emission lines originating from higher lying levels is more profound compared to that of lines arising from lower energy levels. Finally, a substantial decrease of the plasma threshold fluence was observed in the double-pulse arrangement; this enables sensitive analysis with minimal damage on the sample surface.     

Effects of substrate surfaces in matrix‐assisted laser desorption/ionization mass spectrometry

For matrix‐assisted laser desorption/ionization (MALDI) mass spectra, undesirable ion contamination can occur due to the direct laser excitation of substrate materials (i.e., laser desorption/ionization (LDI)) if the samples do not completely cover the substrate surfaces. In this study, comparison is made of LDI processes on substrates of indium and silver, which easily emit their own ions upon laser irradiation, and conventional materials, stainless steel and gold. A simultaneous decrease of ion intensities with the number of laser pulses is observed as a common feature. By the application of an indium substrate to the MALDI mass spectrometry of alkali salts and alkylammonium salts mixed with matrices, 2,5‐dihydroxybenzoic acid (DHB) or N‐(4‐methoxybenzylidene)‐4‐butylaniline (MBBA), the mixing of LDI processes can be detected by the presence of indium ions in the mass spectra. This method has also been found to be useful for investigating the intrinsic properties of the MALDI matrices: DHB samples show an increase in the abundance of fragment ions of matrix molecules and cesium ions with the number of laser pulses irradiating the same sample spot; MBBA samples reveal a decrease in the level of background noise with an increase in the thickness of the sample layer. Copyright © 2009 John Wiley & Sons, Ltd.     

The use of intense femtosecond laser pulses for the fragmentation of chitosan

The use of ultrashort laser pulses for the fragmentation of chitosan was investigated. Femtosecond Ti-saphire laser pulses were focused into a flask containing 1.0% chitosan in 0.1 M acetic acid. The effects of the pulse energy (between 0.1 and 0.82 mJ) and the focal length on the laser-induced fragmentation were followed by viscometry and size exclusion chromatography. The chemical structure and degree of acetylation of chitosan and its fragments were studied using elemental analysis, IR and ¹H NMR spectroscopy. The experimental results showed that (i) Ti-saphire laser irradiation induced chain scission in the chitosan macromolecules, (ii) the chemical structure, including the degree of acetylation, did not change significantly upon laser irradiation, (iii) the number of chain scission dependence on laser energy suggests that fragmentation was a two-photon process, and (iv) at constant pulse energy, the molecular weight dropped to a minimum as a function of the focal length (between 45 and 330 mm), indicating that the efficiency of fragmentation was very sensitive to the geometry of the laser beam.     

Surface properties of polymers treated with F2 laser

Selected polymers (polyethylene‐PE, polypropylene‐PP, polytetrafluoroethylene‐PTFE, polystyrene‐PS and polyethylenterephthalate‐PET) were irradiated with the linearly polarized light of a pulsed 157 nm F₂ laser. The irradiation results in degradation of polymers and ablation of polymer surfaces. Contact angle, measured by goniometry, was studied as a function of the number of laser pulses. The volume of the ablated polymer layer was determined by gravimetry. Changes in surface morphology and roughness were observed using atomic force microscopy. Surface chemistry of the samples was investigated by electrokinetic analysis and by XPS. While PET and PE exhibit small ablation, the ablation of PS and PTFE is more significant, and the most pronounced ablation is observed on PP. Contact angle of all polymers, with the only exception of PP, is a decreasing function of the number of laser pulses up to 2000 pulses. Laser irradiation leads to a refinement of the polymer surface morphology and a decrease of their surface roughness. Electrokinetic analysis and PS show changes in the surface chemistry of polymers after the laser treatment. Copyright © 2011 John Wiley & Sons, Ltd.     

有机纳米材料在肿瘤光热治疗中的应用

光热治疗是利用在近红外具有较强光吸收的材料将光能转化为热能从而杀死癌细胞,与传统的化疗、放疗相比具有副作用小、治疗特异性好的优点。近年来各种不同的纳米材料被用于肿瘤光热治疗,并在动物肿瘤模型实验中取得了令人鼓舞的治疗效果。本文重点介绍几种典型的有机纳米材料在光热治疗中的应用,并讨论这一新兴领域的发展趋势。     

Irradiation of Amelanotic Melanoma Cells with 532 nm High Peak Power Pulsed Laser Radiation in the Presence of the Photothermal Sensitizer Cu(II)-Hematoporphyrin: A New Approach to Cell Photoinactivation

Cu(II)-hematoporphyrin (CuHp) was efficiently accumulated by B78H1 amelanotic melanoma cells upon incubation with porphyrin concentrations up to 52 microM. When the cells incubated for 18 h with 13 microM CuHp were irradiated with 532 nm light from a Q-switched Nd: YAG laser operated in a pulsed mode (10 ns pulses, 10 Hz) a significant decrease in cell survival was observed. The cell photoinactivation was not the consequence of a photodynamic process, as CuHp gave no detectable triplet signal upon laser flash photolysis excitation and no decrease in cell survival was observed upon continuous wave irradiation. Thus, it is likely that CuHp sensitization takes place by photothermal pathways. The efficiency of the photoprocess was modulated by different parameters; thus, while varying the amount of added CuHp in the 3.25-26 microM range had little effect, pulse energies larger than 50 mJ and irradiation times of at least 120 s were necessary to induce a cell inactivation of about 50%. The porphyrin-cell incubation time prior to irradiation had a major influence on cell survival, suggesting that the nature of the CuHp microenvironment can control the efficiency of photothermal sensitization.     

用原子力显微镜研究甲基丙烯酸缩水甘油酯在高密度聚乙烯表面的紫外接枝

利用AFM研究了紫外光引发甲基丙烯酸缩水甘油酯(GMA)在高密度聚乙烯(HDPE)表面接枝初期生成的接枝物的微结构, 对HDPE表面接枝反应的引发速率进行了初步研究. 紫外照射30 s后在HDPE表面形成一些接枝物微粒, 随着照射时间的增加, 微粒越来越多, 其体积也越来越大. 分析结果表明, 每一个接枝物微粒即为一个高度枝化甚至超级枝化的接枝聚合物链. 在30~45 s之间, 接枝密度随照射时间延长几乎呈线性增长; 在45 s后, 接枝密度的增长速度减慢. 在30~45 s之间的引发速度约为6.5 Unit/(μm2·s).     

Synthesis method-dependent photothermal effects of colloidal solutions of platinum nanoparticles used in photothermal anticancer therapy

One of the most common anticancer therapies is photothermal therapy (PTT). The effectiveness of PTT depends on the photosensitizer being a molecule which is toxic for the cancer cells after electromagnetic wave irradiation. Therefore, a simulation of PTT was performed in this work on two colon cancer cells (SW480 and SW620) using platinum nanoparticles (Pt NPs). Interestingly, in the literature the dependence between the synthesis method and the photothermal properties of Pt NPs was not discussed. Consequently, in this paper, we evaluated the photothermal properties of Pt NPs synthesized by two different methods: polyol (PtI NPs) and green chemistry (PtII NPs). Scanning transmission electron microscopy revealed that the size of both Pt NPs obtained was 2 nm, the NPs were not agglomerated, and that the PtII NPs were distributed on green tea supports. The selected area electron diffraction and X-ray diffraction analysis confirmed the crystallinity of both types of Pt NPs. Fourier-transform infrared (FTIR) spectrum of the PtII NPs showed interactions between the NPs and stretching modes for C=O groups from flavonoids and polyphenols. Therefore, these chemical compounds could be responsible for reducing Pt⁴⁺ ions to Pt⁰. Moreover, the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay showed that the PtII NPs exhibited 10% and 20% better cytotoxicity effect on SW480 and SW620 cells, than PtI NPs. The viability of cancer cells decreased when Pt NPs were used in PTT. The highest percentage of dead cells (82%) was observed for PtII NPs and 650-nm laser irradiation. FTIR and Raman spectroscopy showed structural changes induced by both Pt NPs and laser irradiation of cells in the range corresponding to levels of DNA, phospholipids, proteins, and lipids. Moreover, the calculated photothermal conversion efficiency showed that the value of this parameter is around 35%, regardless of the synthesis method and used wavelengths.     

Dynamic effects of a pre-ablation spark in the orthogonal dual-pulse laser induced breakdown spectroscopy

We have observed dynamic effects of a pre-ablation spark on the signal intensity in the orthogonal dual-pulse laser-induced breakdown spectroscopy. We applied pre-ablation and ablation laser pulses with significantly reduced energy for an aluminum metal in open air. Under this experimental condition, the well-known signal enhancement through the increase in ablated mass was negligible. The Al I and II emissions were investigated by both top-view and spatially-resolved side-view collection modes. In this low laser power regime, dynamic effects of a pre-ablation spark on the signal intensity were clearly revealed. The principal factor of signal enhancement is the increase in temperature. Without the mass removal enhancement, effective rarefaction leads to decrease in the Al I emission intensity and simultaneous increase in the Al II emission intensity. This is attributed to the role of Saha equilibrium. Selective prolongation of emission lifetime only for the enclosed part of the analyte plasma in the rarefied region and other fluid-dynamic effects of a pre-ablation spark have been visualized by wavelength-selected time-space correlation maps of plasma emissions.     

Kinetics and mechanism of the NCN + NO2 reaction studied by experiment and theory

The rate constant for the NCN + NO 2 reaction has been measured by a laser photolysis/laser-induced fluorescence technique in the temperature range of 260-296 K at pressures between 100 and 500 Torr with He and N 2 as buffer gases. The NCN radical was produced from the photolysis of NCN 3 at 193 nm and monitored by laser-induced fluorescence with a dye laser at 329.01 nm. The rate constant was found to increase with pressure but decrease with temperature, indicating that the reaction occurs via a long-lived intermediate stabilized by collisions with buffer gas. The reaction mechanism and rate constant are also theoretically predicted for the temperature range of 200-2000 K and the He and N 2 pressure range of 10 (-4) Torr to 1000 atm based on dual-channel Rice-Ramsperger-Kassel-Marcus (RRKM) theory with the potential energy surface evaluated at the G2M//B3LYP/6-311+G(d) level. In the low-temperature range (<700 K), the most favorable reaction is the barrierless association channel that leads to the intermediate complex (NCN-NO 2). At high temperature, the direct O-abstraction reaction with a barrier of 9.8 kcal/mol becomes the dominant channel. The rate constant calculated by RRKM theory agrees reasonably well with experimental data.