激光诱导玻璃内部金纳米颗粒的析出及光谱

使用钛宝石飞秒激光引发和热处理相结合，实现了在含有金离子的硅酸盐玻璃内部，有空间选择性地析出金纳米颗粒。对吸收光谱的研究表明，随着热处理温度的升高，吸收峰强度增大且红移；随着激光功率密度的增大，金纳米颗粒也增大。在特定的激光和热处理条件作用下，可以在玻璃内部有空间选择性的使金离子还原后聚集，形成金纳米颗粒，具有量子尺寸效应。改变激光功率和热处理温度可以控制所析出的金属纳米粒子的尺寸，从而实现多色显示，飞秒激光诱导金纳米颗粒具有稳定性，颜色具有持久性。     

Nanocomposite ZnO/Au formation by pulsed laser irradiation

The ZnO/Au nanocomposite formation involves synthesis of Au and ZnO colloidal solutions by 532 nm pulse laser ablation of metal targets in deionized water followed by laser irradiation of the mixed colloidal solution. The transmission electron microscope (TEM) and high-resolution transmission electron microscope (HRTEM) images show evolution of spherical particles into ZnO/Au nanonetworks with irradiation time. The formation mechanism of the nanonetwork can be explained on the basis of near resonance absorption of 532 nm irradiation by gold nanoparticles which can cause selective melting and fusion of gold nanoparticles to form network. The ZnO/Au nanocomposites show blue shift in the ZnO exciton absorption and red shift in the Au plasmon resonance absorption due to interfacial charge transfer.     

Laser-Assisted Formation of Elongated Au Nanoparticles and Subsequent Dynamics of Their Morphology under Pulsed Irradiation in Water

The processes of laser-assisted formation of elongated Au nanoparticles and their subsequent agglomeration and fragmentation have been experimentally investigated. Elongated gold nanoparticles were formed by laser ablation of a solid target in water. IR radiation of ytterbium-doped fiber laser with a pulse width of 200 ns and a pulse energy of 0.5 to 1 mJ was used to this end. The extinction spectra and transmission electron microscopy images indicate the formation of elongated gold nanoparticles. The interaction of laser radiation with aqueous colloids of elongated nanoparticles in dependence of the pulse energy and exposure time has been analyzed. Possible processes of laser-assisted formation of elongated Au nanoparticles and their subsequent transition from agglomeration to fragmentation of gold nanoparticles, induced by laser irradiation are discussed.     

One-step synthesis of silica-coated magnetite nanoparticles by electrooxidation of iron in sodium silicate solution

In the present study, solid-solution gold?Cplatinum (Au?CPt) nanoparticles with controllable compositions were fabricated by high-intensity femtosecond laser irradiation of an aqueous solution of gold and platinum ions without any chemicals and complicated processes. Transmittance electron microscopy revealed that the single nanometer-sized particles were fabricated by femtosecond laser irradiation of mixed aqueous solutions of gold and platinum ions. The crystalline structure of nanoparticles was characterized by electron and X-ray diffractions. Contrary to the bulk Au?CPt binary systems, which commonly contain a pair of diffraction peaks between pure gold and platinum peaks because of its large miscibility gap in phase diagram, or mixture of Au and Pt, the diffraction peaks of Au?CPt nanoparticles fabricated in the experiment showed a characteristic of the fcc-type lattice. Moreover, the diffraction patterns shifted monotonically from the peak position of pure gold to that of pure platinum as the fractions of platinum ions in the solution were increased. These observations strongly imply that the Au?CPt nanoparticles were solid solution with intended compositions. This technique is not only simple and environmentally friendly, but also applicable to other binary and ternary systems.     

Spatially selective modification of optical and magneto-optical properties in Fe- and Au-doped glasses irradiated with femtosecond-laser

The optical property and the magneto-optical response were space-selectively modified in transparent Fe³⁺- and Au³⁺-doped glasses by using infrared femtosecond- (fs-) laser irradiation and subsequent annealing. This irradiation process induces the precipitation of not only magnetic spinel-type Fe-oxide nanoparticles but also Au nanoparticles inside the glasses, which shows localized surface plasmon resonance absorption at the wavelengths larger than 500 nm. As the annealing time and the temperature increases, the position of the LSPR peaks exhibits red shifts, which is due to the growth of Au nanoparticles. Faraday rotation angles as a function of wavelength were measured, and the difference spectra exhibit distinct positive peaks, indicating that the coupling between the LSPR due to the Au nanoparticles and the diamagnetism of the matrix glass is effective. To decrease the coupling with the diamagnetic glass, a two-step annealing process (at 450 °C for 90 min and at 550 °C for 30 min) was carried out after irradiation with fs-laser. The preliminary annealing at the lower temperature contributes to the precipitation of ferrimagnetic magnetite nanoparticles. Au nanoparticles were subsequently grown by annealing at 550 °C. In this case, effective coupling between the LSPR and ferrimagnetic nanoparticles has significantly suppressed the intensity of the positive peak in the Faraday spectra compared with the single annealing process.     

Rapid synthesize of gold nanoparticles by microwave irradiation method and its application as an optical limiting material

We present rapid synthesis of gold nanoparticles by microwave irradiation method. Sample with average particle size 7.7 nm is obtained from TEM. Linear and nonlinear optical studies of the prepared samples are discussed. Reverse saturable absorption (RSA) at longitudinal surface plasmon resonance (SPR) in gold nanoparticles (Au NPs) have been observed using Z-scan and transient absorption techniques with 532 nm laser pulses. Such RSA behavior makes Au NPs an ideal candidate for optical limiting applications.     

Au cluster growth on ZnO thin films by pulsed laser deposition

Nanostructures formed by Au nanoparticles on ZnO thin film surface are of interest for applications which include medical implants, gas-sensors, and catalytic systems. A frequency tripled Nd:YAG laser (λ = 355 nm, τ_FWHM ∼ 10 ns) was used for the successive irradiation of the Zn and Au targets. The ZnO films were synthesized in 20 Pa oxygen pressure while the subsequent Au coverage was grown in vacuum. The obtained structures surface morphology, crystalline quality, and chemical composition depth profile were investigated by acoustic (dynamic) mode atomic force microscopy, X-ray diffraction, and wavelength dispersive X-ray spectroscopy. The surface is characterized by a granular morphology, with average grain diameters of a few tens of nanometers. The surface roughness decreases with the increase of the number of laser pulses applied for the irradiation of the Au target. The Au coverage reveals a predominant (1 1 1) texture, whereas the underlying ZnO films are c-axis oriented. A linear dependence was established between the thickness of the Au coverage and the number of laser pulses applied for the irradiation of the Au target.     

Optical properties of structurally modified glasses doped with gold ions

We report on the optical properties of a structurally modified silicate glass doped with Au ions. The area in the vicinity of the focal point of an 800-nm femtosecond laser in a glass sample became gray as a result of the formation of color centers after laser irradiation and turned red because of precipitation of Au nanoparticles after further annealing at 550 degrees C for 30 min. When the glass was excited by UV light at 365 nm, yellowish-white and orange-yellow emissions were observed in the laser-irradiated and the Au-nanoparticle-precipitated area, respectively. An optical Kerr shutter experiment showed that the Au nanoparticle-precipitated glass had an ultrafast nonlinear optical response, and the third-order nonlinear susceptibility was estimated to be approximately 10(-11) esu.     

金膜表面等离激元诱导邻巯基苯甲酸脱羧反应的表面增强拉曼光谱研究

贵金属纳米结构表面等离激元共振（SPR）因其广泛的用途而备受关注,它不仅可以催化某些特殊的表面反应,同时还能产生表面增强拉曼散射效应（SERS）,极大增强分子的表面拉曼信号,因此两者结合后可在纳米结构表面采用SERS光谱跟踪SPR催化反应。目前此类研究主要集中在氮氮（N═N）偶联,因此亟待拓展SPR反应种类及提高催化活性和效率。采用SERS光谱研究邻巯基苯甲酸（OMBA）分子在金纳米粒子单层膜（Au MLF）表面的脱羧行为。通过气液界面组装法制备“热点”分布均匀的金纳米粒子单层膜,以此作为基底,探讨了溶液pH值、激光功率及激光照射时长对该基底表面脱羧反应的影响。研究结果表明,吸附在Au MLF表面的OMBA分子在表面等离激元驱动下碱性和中性介质中发生脱羧基反应,生成苯硫酚（TP）,且碱性中反应活性大于中性溶液。在酸性介质中几乎不发生脱羧反应。较强的激光功率,脱羧反应的活性越高;产物SERS强度的增加与激光照射时间成线性关系,时间延长可提高脱羧反应的产率。这为拓展SPR驱动的光催化反应及深入理解其反应机理提供了实验依据。     

Enhanced photoluminescence from gallium arsenide semiconductor coated with Au nanoparticles

We demonstrate a method for improving photoluminescence of gallium arsenide semiconductor by simply coating a thin layer of Au nanoparticles on its surface. Further focused ion beam bombardment at the sputter-coated Au film was conducted to control the size, the distribution, and the morphology of the Au nanoparticles via the changes of the focused ion-beam irradiation conditions. Photoluminescence of GaAs coated with the Au nanoparticles with average size of 5 nm in diameter is enhanced to about threefold relative to that of pure GaAs. Numerical calculations were conducted based on finite-different time-domain method. Results indicated that the enhancement is mainly attributed to the contribution of local surface plasmon resonance of Au nanoparticles.     

A novel method of nanocrystal fabrication based on laser ablation in liquid environment

Metal nanoparticles can be prepared by a novel technique that consists of the laser ablation of a solid target immersed in a water solution of a metal salt. Silicon was chosen as the most adequate target to synthesize silver and gold nanoparticles from a water solution of either AgNO₃ or HAuCl₄. The influence of both the silver nitrate concentrations and the irradiation time of the Si target on the optical properties of the Au and Ag nanoparticles have been investigated. The crystalline nature of the metal nanoparticles has been determined by X-ray diffraction (XRD). Average size and particle size distribution have been measured by means of TEM. The absorbance spectra show the characteristic band of the surface resonant plasmon of silver and gold nanoparticles.     

Influence of the deposition parameters on the properties of SnS2 films prepared by PECVD method combined with solid sources

We report a simple and rapid biological approach to synthesize water-soluble and highly roughened “meatball”-like Au nanoparticles using green tea extract under microwave irradiation. The synthesized Au meatball-like nanoparticles possess excellent monodispersity and uniform size (250 nm in diameter). Raman measurements show that these tea-generated meatball-like gold nanostructures with high active surface areas exhibit a high enhancement of surface-enhanced Raman scattering. In addition, the Au meatball-like nanoparticles demonstrate good biocompatibility and remarkable in vitro stability at the biological temperature. Meanwhile, the factors that influence the Au meatball-like nanoparticles morphology are investigated, and the mechanisms behind the nonspherical shape evolution are discussed.     

Magnetic properties of bimetallic Au/Co nanoparticles prepared by thermal laser treatment

The irradiation of metallic films by a nanosecond pulsed laser leads to a self-assembly of nanoparticle arrays. This method has been used to prepare bimetallic Au/Co nanoparticles on a SiO₂ substrate. The microstructure and morphology of the bimetallic nanoparticles have been investigated using scanning electron microscopy and transmission electron microscopy. It has been shown that the bimetallic nanoparticles have a hemispherical shape with a single-crystal structure and an average size of ~50 nm. The magnetic properties of these nanoparticles have been examined using a vibrating-sample magnetometer in the transverse and longitudinal directions. It has been found that the direction of the magnetization of the bimetallic nanoparticles lies in the plane of the substrate, and the coercive forces in the transverse and longitudinal directions differ by 25%. The use of the vibrating-sample magnetometer method makes it possible to investigate the differences in the magnetic saturations and the coercive forces of an array of bimetallic nanoparticles on a large surface area. The performed investigations have demonstrated that the anisotropic nanomagnetic materials with the desired magnetic orientation can be easily and quickly prepared by means of thermal laser treatment.     

Stabilization of Au nanoparticles prepared by laser ablation in chloroform with free-base porphyrin molecules

Laser ablation (LA) of a Au foil immersed in chloroform and/or in diluted 5,10,15,20-tetrakis-4-pyridylporphine (TPyP) chloroform solutions was carried out using 1064 nm nanosecond laser pulses. The products were characterized by UV-visible-NIR optical extinction and IR absorption measurements, Raman spectroscopy and transmission electron microscopy (TEM). They were found to be strongly influenced by the convergence of the incident laser beam and delivered energy per pulse. Our results show that with highly focused laser beam chloroform underwent photochemical reactions and no nanoparticles with observable surface plasmon extinction (SPE) band were formed whereas at particular focusing conditions Au nanoparticles with the SPE band typical for Au organosols were created. Au organosols in pure chloroform showed a limited stability, the SPE band disappeared in a few hours after the preparation. When a small amount of TPyP was present in the course of LA both the efficiency of Au nanoparticles formation and the stability of the resulting organosols were improved. A possible mechanism of LA of the Au target in chloroform and in diluted TPyP chloroform solutions is discussed.     

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.     

Control of plasmon resonance of gold nanoparticles via excimer laser irradiation

A significant shift of the surface plasmon resonance absorption spectrum of gold nanoparticles was obtained by the oxidation of the nanoparticle surface via pulsed excimer laser irradiation. The high UV-light absorption of gold nanoparticles chemically produced by citrate reduction led to the important surface oxidation up to 26%. As a result of laser irradiation, the gold/gold oxide core-shell nanoparticles with little variation of the nanoparticle size were produced. After only 5 min of laser irradiation, a 12-nm blue shift in surface plasmon resonance was obtained. The possible mechanisms governing the modification in surface plasmon resonance by laser irradiation of gold nanoparticles were discussed.     

Laser induced synthesis of nanoparticles in liquids

The review of results on nanoparticles formation is presented under laser ablation of Ag, Au, and Cu-containing solid targets in liquid environments (H₂O, C₂H₅OH, C₂H₄Cl₂, etc.). X-ray diffractometry (XRD), UV-vis optical transmission spectrometry, and high resolution transmission electron microscopy (HRTEM) characterize the nanoparticles. The morphology of nanoparticles is studied as the function of both laser fluence and nature of the liquid. The possibility to control the shape of nanoparticles by ablation of an Au target by an interference pattern of two laser beams is demonstrated. Formation of alloyed Au-Ag and Ag-Cu nanoparticles is reported under laser exposure of a mixture of individual nanoparticles. The effect of internal segregation of brass nanoparticles is discussed due to their small lateral dimensions. The factors are discussed that determine the distribution function of particles size under laser ablation. The influence of laser parameters as well as the nature on the liquid on the properties of nanoparticles is elucidated.     

Excimer laser ablation of gold-loaded inverse polystyrene-block-poly (2-vinylpyridine) micelles

Diblock-copolymers (PS(1700)-b-P2VP(450) or PS(1350)-b-P2VP(400)) forming spherical micelles, can be loaded with a Au-salt and deposited on top of various substrates. Such polymer films have been exposed to a pulsed ArF excimer laser in order to remove the polymer matrix and, in parallel, to chemically reduce the salt into metallic Au nanodots. To analyze this process in detail, it was subdivided into three steps: (a) laser ablation of thick and thin diblock-copolymer films; (b) laser irradiation of Au-salt loaded diblock-copolymer films; and (c) laser irradiation of arrays of metallic Au nanodots. In (a) it was found that a complete removal of the polymer by laser ablation is only possible in air under ambient conditions while identical laser irradiations under vacuum result in a residual layer of approximately 14 nm. Substep (b) revealed a nucleation process of the resulting metallic Au within the micellar core leading to clusters of small Au dots. Furthermore, this substep provided evidence for an asymmetric interplay between the macroscopic temperature of a polymer film during laser treatment and the energy density per laser pulse. In (c) it could be demonstrated that metallic Au nanodots on mica are stable against laser irradiation under conditions leading to a polymer removal. Received: 7 August 2000 / Accepted: 2 November 2000 / Published online: 3 April 2001     

Synthesis of composite gold/tin-oxide nanoparticles by nano-soldering

Composite Au–SnO₂ nanoparticles (NPs) are synthesized by nano-soldering of pure Au and SnO₂ NPs. The multi-step process involves synthesis of pure Au and SnO₂ NPs separately by nanosecond pulse laser ablation of pure gold and pure tin targets in deionized water and post-ablation laser heating of mixed solution of Au colloidal and SnO₂ colloidal to form nanocomposite. Transmission Electron Microscopy (TEM) and High-Resolution Transmission Electron Microscopy (HRTEM) were used to study the effect of laser irradiation time on morphology of the composite Au–SnO₂ NPs. The spherical particles of 4 nm mean size were obtained for 5 min of post-laser heating. Increased mean size and elongated particles were observed on further laser heating. UV–vis spectra of Au–SnO₂ nanocomposites show red shift in the plasmon resonance absorption peak and line shape broadening with respect to pure Au NPs. The negative binding energy shift of Au 4f_7/2 peak observed in X-ray Photoelectron Spectra (XPS) indicates charge transfer in the nano-soldered Au–SnO₂ between gold and tin oxide and formation of soldered nanocomposite.     

利用激光烧蚀法制备表面等离子体可调谐的金核银壳层纳米颗粒胶体

利用激光烧蚀方法在水中制备了金核银壳层纳米颗粒胶体,发现这种复合胶体的等离子体振动吸收峰频率会随着激光烧蚀时间的不同而发生改变。利用等离子杂化理论定性解释了共振吸收峰可调谐的物理机制.