Synthesis of nanoparticles and suspensions by pulsed laser ablation of microparticles in liquid

Recent studies demonstrated that the process to produce metal and oxide nanoparticles by laser ablation of consolidated microparticles is a convenient and energy-efficient way to prepare nanoparticles. In this work, the novel process is applied to nanoparticle synthesis in the liquid environment and the results are compared with those by the gas-phase process. Metal and oxide nanoparticles are synthesized by pulsed laser ablation of the compacted metal microparticles using a Q-switched Nd:YAG laser in water. It is shown that the process is effective for preparing nanoparticle suspensions having relatively uniform size distributions. While the laser fluence and the degree of compaction strongly influence the size of the produced nanoparticle in air, the sedimentation time is shown to be the most critical factor to determine the mean size of the suspended particles.     

Generation and characterization of Nd-Fe-B-C nanoparticles by pulsed Nd:YAG laser ablation in liquid

We have generated Nd-Fe-B-C nanoparticles by Nd:YAG (1064 nm) laser irradiation in distilled water. Exposure times were 1, 5, and 10 min. Characterization of such nanoparticles in terms of their size distribution, shape, and chemical composition was carried out by transmission electron microscopy, energy-dispersive X-rays, and Fourier transform infrared spectroscopy. To investigate the nanoparticle stability, the size distribution of nanoparticles was measured two weeks after the nanoparticle generation, using dynamic light scattering. Investigations with the help of the atomic force microscope and magnetic force microscope showed other aspects of the generated nanoparticles.     

Generation of phosphor nanoparticles for temperature sensing by laser ablation in liquid

Nano-size phosphor particles of Y_2.97Ce_0.03(Al_1?x Gd _x )₅O₁₂ were fabricated by ablating commercial micron-size powders in deionized water. We show that these colloidal phosphor nanoparticles suspended in deionized water can be used as a liquid sensor for all-optical, non-contact measurements of temperature with nanosecond time resolution. The nanophosphors can be used as temperature-sensing reporters in many applications where real-time measurements of temperature are necessary to understand physical processes, such as the mechanisms of temperature–time profiles in laser ablation.     

Synthesis of ZnO2 nanoparticles by laser ablation in liquid and their annealing transformation into ZnO nanoparticles

A pulsed laser emitting UV radiations generated by the third harmonic of Nd:YAG was applied for the synthesis of nano-structured ZnO₂ and ZnO. For the synthesis of nanoparticles of ZnO₂, a high-purity metallic plate of Zn target was fixed at the bottom of a glass cell, in the presence of deionized water mixed with oxidizing agent H₂O₂, under repeated laser irradiation. The optical properties, size and the morphology of the synthesized ZnO₂ and ZnO by laser ablation was influenced strongly by post-annealing conditions which is not previously reported. By annealing ZnO₂ at 200 °C for 8 h, the product (ZnO₂) synthesized primarily was converted completely to ZnO. By variation of the annealing temperatures from 200 to 600 °C, the grain size of ZnO changes from 5 to 19 nm with a change in lattice parameters, the band gap and some other optical properties of nano-ZnO.     

Investigation of nanoparticle generation during femtosecond laser ablation of metals

The production of nanoparticles via femtosecond laser ablation of gold and copper is investigated experimentally involving measurements of the ablated mass, plasma diagnostics, and analysis of the nanoparticle size distribution. The targets were irradiated under vacuum with a spot of uniform energy distribution. Only a few laser pulses were applied to each irradiation site to make sure that the plume expansion dynamics were not altered by the depth of the laser-produced crater. Under these conditions, the size distribution of nanoparticles does not exhibit a maximum and the particle abundance monotonously decreases with size. Furthermore, the results indicate that two populations of nanoparticles exist within the plume: small clusters that are more abundant in the fast frontal plume component and larger particles that are located mostly at the back. It is shown that the ablation efficiency is strongly related to the presence of nanoparticles in the plume.     

Synthesis and characterization of zinc oxide nanoparticles by laser ablation of zinc in liquid

We report formation of colloidal suspension of zinc oxide nanoparticles by pulsed laser ablation of a zinc metal target at room temperature in different liquid environment. We have used photoluminescence, atomic force microscopy and X-ray diffraction to characterize the nanoparticles. The sample ablated in deionized water showed the photoluminescence peak at 384 nm (3.23 eV), whereas peaks at 370 nm (3.35 eV) were observed for sample prepared in isopropanol. The use of water and isopropanol as a solvent yielded spherical nanoparticles of 14-20 nm while in acetone we found two types of particles, one spherical nanoparticles with sizes around 100 nm and another platelet-like structure of 1 μm in diameter and 40 nm in width. The absorption peak of samples prepared in deionized water and isopropanol are seen to be substantially blue shifted relative to that of the bulk zinc oxide due to the strong confinement effect. The technique offers an alternative for preparing the nanoparticles of active metal.     

Ultra fine carbon nitride nanocrystals synthesized by laser ablation in liquid solution

Crystalline carbon nitride nanopowders and nanorods have been successfully synthesized at room temperature and pressure using the novel technique of pulsed laser ablation of a graphite target in liquid ammonia solution. High-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and Fourier transform infrared spectroscopy (FTIR) were used to systematically study the morphology, nanostructure and chemical bonding. The experimental composition and structure of the nanoparticles are consistent with the theoretical calculations for α-C₃N₄. After 2 h ablation the particles had a size distribution ∼8–12 nm, whereas after 5 h ablation the particles had grown into nanorod-like structures with a crystalline C₃N₄ tip. A formation mechanism for these nanorods is proposed whereby nanoparticles are first synthesized via rapid formation of an embryonic particle, followed by a slow growth, eventually leading to a one-dimensional nanorod structure.     

两种纤维增强复合材料与连续激光耦合规律

 利用双积分球-光电管系统,开展了不同厚度的芳纶纤维/环氧、碳纤维/环氧复合材料在不同强度（低于烧蚀阈值）的1.319 mm连续激光辐照下的能量耦合规律研究。结果表明：芳纶纤维/环氧复合材料的反射率、能量耦合率随材料厚度增加而增大,透射率随材料厚度增加而减小;在材料厚度一定时,反射率、透射率随激光强度增加而增大,能量耦合率随激光强度增加而减小;体吸收系数随材料厚度的增加而减小,激光强度的变化对其没有影响。碳纤维/环氧复合材料的反射率随激光强度增加而增大,能量耦合率随激光强度的增加而减小,材料厚度对反射率和能量耦合率的影响不大。     

Ag nanoparticles obtained by pulsed laser ablation in water: surface properties and SERS activity

We studied the surface properties and reactivity of silver nanoparticles obtained by picosecond or nanosecond pulsed laser ablation in water and with 1064‐nm wavelength. Ultraviolet–visible spectroscopy results and subsequent modelling by Mie theory indicated the presence of an oxide layer on the nanoparticle surface, which favours the colloidal stability, but reduces the interaction with the environment. The oxide layer is also responsible for the reduced surface enhanced Raman spectroscopy (SERS) activity of these colloids with respect to those obtained by chemical reduction. However, SERS activation can be efficiently obtained by addition of chloride ions to the colloids, leading to SERS enhancement factors that are comparable with those of the chemically prepared counterparts. Copyright © 2015 John Wiley & Sons, Ltd.     

Particle diagnostics of a ZnO laser ablation plume for nanostructured material deposition

We report results on the pulsed laser deposition of ZnO obtained with the help of a new apparatus that includes in situ reflectron time-of-flight mass spectrometry, with a view to progress the understanding of the role of clusters in the laser deposition of nanostructured materials. Experiments were carried out using a Nd-YAG laser at its fundamental frequency and frequency tripled, with a fluence on target of ∼7.7 J/cm², in vacuum (10⁻⁴ Pa) or oxygen (1 Pa) atmospheres. The results show that under certain conditions there is preferential clusterisation of the material into certain mass numbers and finally that there exists a correlation between cluster presence in the plume and the deposition of nanostructures.     

The effect of liquid environment on size and aggregation of gold nanoparticles prepared by pulsed laser ablation

The effects of liquid environment on nucleation, growth and aggregation of gold nanoparticles were studied. Gold nanoparticles were prepared by pulsed laser ablation in deionised water with various concentrations of ethanol and also in pure ethanol. UV/visible extinction and TEM observations were employed for characterization of optical properties and particle sizes respectively. Preparation in water results in smaller size, shorter wavelength of maximum extinction and stable solution with an average size of 6 nm. Nanoparticles in solution with low concentration ethanol up to 20 vol% are very similar to those prepared in water. In the mixture of deionised water and 40 up to 80 vol% ethanol, wavelength of maximum extinction shows a red shift and mean size of nanoparticles was increased to 8.2 nm. Meanwhile, in this case, nanoparticles cross-linked each other and formed string type structures. In ethanol, TEM experiments show a mean size of 18 nm and strong aggregation of nanoparticles. The data were discussed qualitatively by considering effects of polarity of surrounding molecules on growth mechanism and aggregation. This study provided a technique to control size, cross-linking and aggregation of gold nanoparticles via changing the nature of liquid carrier medium.     

光伏型碲镉汞探测器在波段内连续激光辐照下的两种不同过饱和现象的产生机理

利用连续波段内激光对两批光伏型碲镉汞探测器进行了激光辐照实验, 发现了两种不同的过饱和现象. 实验表明, 光伏型碲镉汞探测器在强光辐照下都会出现开路电压随光强增强而减小的过饱和现象, 明晰了PV型探测器在强光辐照下的一般规律性现象和由探测器个体差异导致的特殊现象. 从等效电路模型出发, 剖析了两种过饱和现象的发生条件, 建立了数值计算的理论模型, 对两种过饱和现象进行了数值模拟, 计算结果与实验结果符合得较好. 研究表明, 光伏型碲镉汞探测器在波段内强光辐照下引起的过饱和现象有两种产生机理, 一种是热效应引起的暗电流增大机理; 另一种是探测器材料中缺陷引起的漏电流增大机理. 关键词： 波段内连续激光 光伏型碲镉汞探测器 过饱和现象     

Silicon nanoparticles formation by means of laser ablation in liquid media

The possibility to produce silicon nanoparticles by the method of the pulse laser ablation of monocrystaline silicon targets in the water, glycerol and liquid nitrogen have been shown. Studies by the atomic-force microscopy and Raman scattering methods revealed the nanoparticles have a crystalline structure and their mean size depends on the buffer liquid composition.     

Generation of titanium-oxide nanoparticles in liquid using a high-power, high-brightness continuous-wave fiber laser

Previous studies on laser-assisted nanomaterial formation in liquids have focused on using pulsed laser ablation of metals. We report, for the first time to our knowledge, the fabrication of nanoparticles via high-power high-brightness continuous-wave fiber laser ablation of titanium in liquids. Analysis revealed the generation of spherical nanoparticles of titanium-oxide ranging mainly between 5 nm and 60 nm in diameter. A mechanism of formation for crystallized nanoparticles, based on the self-organized pulsations of the evaporated metal, is proposed. This may account for the observed substantial efficiency gain owing to the high average power and brightness of the source. PACS 42.62.-b; 81.07.-b; 52.50.-b; 47.20.-k; 45.55.-t     

树脂基复合材料在连续激光作用下的损伤

 采用热压工艺制备了碳纤维布和高硅氧纤维布增强的环氧树脂和酚醛树脂基复合材料,研究了不同功率密度连续激光辐照下,复合材料的破坏形式及其组织结构与力学性能的变化。结果表明：当激光辐照功率密度大于0.1 kW/cm²后,树脂基体产生燃烧,碳纤维没有明显的损伤,而玻璃纤维布开始熔融,复合材料的拉伸性能降低30%~40%;当功率密度达到1 kW/cm²以后,除基体燃烧外,碳纤维复合材料产生明显的鼓泡分层,表层碳纤维有少量破断,而高硅氧纤维产生明显的熔融烧损,复合材料的拉伸性能降低80%以上。采用有限元计算方法,对碳纤维增强环氧树脂复合材料在连续激光辐照下的温度场进行了研究,计算结果与实验中复合材料的损伤行为相吻合。     

Two-step synthesis and characterization of ZnO nanoparticles

A novel two-step procedure has been employed for the synthesis of ZnO nanoparticles: (1) mechanochemical synthesis of ZnC₂O₄2H₂O nanoparticles by grinding a mixture of zinc acetate and oxalic acid in an agate mortar at 27 °C and (2) thermal decomposition of ZnC₂O₄2H₂O nanoparticles at 400 °C to form ZnO nanoparticles. XRD and FESEM characterize the final product as highly crystalline ZnO with wurtzite structure and crystallite sizes in the range 5–20 nm. FTIR and EPR are used to identify molecular species during thermal decomposition and impurity/defect status of the ZnO powder respectively.     

Gold nanoparticles produced by laser ablation in water and in graphene oxide suspension

The comparison between two different approaches based on the use of the laser ablation in medium to synthetise gold nanoparticles is presented and discussed. Deionised water as well as a graphene oxide (GO) suspension in deionised water have been employed as solution to produce gold nanoparticles by laser ablation. In the former case, the nanoparticles assembly has been stabilised by using surfactants, but in the latter case to avoid undesired effects the use of chemicals was not necessary and Au reduced graphene oxide (Au-rGO) nanocomposites have been obtained. The structure, size and composition of the gold nanoparticles and of the Au–rGO nanocomposites have been monitored by UV–Vis–NIR absorption spectroscopy and Raman spectroscopy, the transmission and scanning electron microscopies and the X-ray energy-dispersive spectroscopy. The presented methodology of Au rGO nanocomposites preparation could represent a green alternative on the production of metallic nanoparticles in biocompatible environment.     

ZnO films grown by laser ablation with and without oxygen CVD

In the present work we have studied the properties of zinc oxide (ZnO) thin films grown by laser ablation of ZnO targets under different substrate temperature and background oxygen conditions. The ZnO layers were deposited with a Pulsed Laser Deposition (PLD) system on pre-nitrided (0001) sapphire (Al₂O₃), using the base line of a Nd:YAG laser at 1064 nm. The films were characterized by different structural and optical methods, including X-ray diffraction (XRD), scanning electron microscopy (SEM), optical transmission spectroscopy, and steady-state photoluminescence (PL). XRD analysis with rocking curves and θ–2θ scans indicates preferential growth along the c-axis direction with a full width at half maximum (FWHM) smaller than 1.5. Low-temperature photoluminescence (PL) showed strong excitonic emission near 3.36 eV between 9 and 65 K.     

Fabrication of gold nanoparticles in water by laser ablation technique and their characterization

A colloidal solution of gold nanoparticles in deionized nanopure water was produced by laser ablation technique without the use of any chemical/surfactant. Spectral characterization and morphological studies of these nanoparticles were carried out by UV-Vis Spectroscopy and Scanning Electron Microscopy, respectively. A number of variables of the ablating laser pulse have been used to control the size of the fabricated nanoparticles. Excellent correlation between ablating laser pulse parameter and optical and morphological parameters of the gold colloids were obtained. The peak of the extinction spectra shows a monotonic blue shift for laser fluence of 410 J/cm² and above. Below this the extinction peak remains fairly constant in wavelength. Blue shifts of the extinction spectra were also observed with increasing re-ablation time of previously ablated gold colloids. Possible explanations of all these observations are discussed.     

Synthesis and characterization of titania-based monodisperse fluorescent europium nanoparticles for biolabeling

Inorganic-organic hybrid titania-based nanoparticles covalently bound to a fluorescent Eu³⁺ chelate of 4,4′-bis(1′′,1′′,1′′,2′′,2′′,3′′,3′′-heptafluoro-4′′,6′′-hexanedion-6′′-yl)chlorosulfo-o-terphenyl (BHHCT-Eu³⁺) were synthesized by a sol-gel technique. A conjugate of BHHCT with 3-[2-(2-aminoethylamino) ethylamino]propyl-trimethoxysilane (APTS) was used as a precursor for the nanoparticle preparation and monodisperse nanoparticles consisting of titania network and silica sub-network covalently bound to the Eu³⁺ chelate were prepared by the copolymerization of APTS-BHHCT conjugate, titanium tetraisopropoxide (TTIP) and free APTS in EuCl₃ water-alcohol solution. The effects of reaction conditions on size and fluorescence lifetime of the nanoparticles were investigated. The characterizations by transmission electron microscopy and fluorometric methods indicate that the nanoparticles are near spherical and strongly fluorescent having a fluorescence quantum yield of 11.6% and a long fluorescence lifetime of ∼0.4 ms. The direct-introduced amino groups on the nanoparticle's surface by using free APTS in nanoparticle preparation facilitated the biolabeling process of the nanoparticles. The nanoparticle-labeled streptavidin (SA) was prepared and used in a sandwich-type time-resolved fluoroimmunoassay (TR-FIA) of human prostate-specific antigen (PSA) by using a 96-well microtiter plate as the solid phase carrier. The method gives a detection limit of 66 pg/ml for the PSA assay.