Synthesis of Si-C nanostructures by laser ablation of silicon target in n-heptane vapor

Controllable synthesis of Si-C nanostructures was realized in a laser ablation system by adopting solid silicon target and n-heptane vapor as starting materials. Ultrafine SiC nanocrystals and graphite-coated SiC nanocrystals were synthesized with the laser frequency of 1 Hz and 20 Hz, respectively. According to the real-time observation on the plasma evolvement, we proposed a formation mechanism of Si-C nanostructure related to vapor-phase reaction. Our method can be extended to other material systems for diverse novel nanostructures.     

Colloid‐Interface‐Assisted Laser Irradiation of Nanocrystals Superlattices to be Scalable Plasmonic Superstructures with Novel Activities

High‐efficient charge and energy transfer between nanocrystals (NCs) in a bottom‐up assembly are hard to achieve, resulting in an obstacle in application. Instead of the ligands exchange strategies, the advantage of a continuous laser is taken with optimal wavelength and power to irradiate the film‐scale NCs superlattices at solid–liquid interfaces. Owing to the Au‐based NCs' surface plasmon resonance (SPR) effect, the gentle laser irradiation leads the Au NCs or Au@CdS core/shell NCs to attach each other with controlled pattern at the interfaces between solid NCs phase and liquid ethanol/ethylene glycol. A continuous wave 532 nm laser (6.68–13.37 W cm^?2), to control Au‐based superlattices, is used to form the monolayer with uniformly reduced interparticle distance followed by welded superstructures. Considering the size effect to Au NCs' melting, when decreasing the Au NCs size to ≈5 nm, stronger welding nanostructures are obtained with diverse unprecedented shapes which cannot be achieved by normal colloidal synthesis. With the help of facile scale‐up and formation at solid–liquid interfaces, and a good connection of crystalline between NCs, the obtained plasmonic superstructured films that could be facilely transferred onto different substrates exhibit broad SPR absorption in the visible and near‐infrared regime, enhanced electric conductivities, and wide applications as surface enhanced Raman scattering (SERS)‐active substrates.     

External field-assisted laser ablation in liquid: An efficient strategy for nanocrystal synthesis and nanostructure assembly

Laser ablation in liquid (LAL) has received considerable attention over the last decade, and is gradually becoming an irreplaceable technique to synthesize nanocrystals and fabricate functional nanostructures because it can offer effective solutions to some challenges in the field of nanotechnology. The goal of this review is to offer a comprehensive summary of recent developments of LAL in nanocrystal synthesis and nanostructure fabrication. First, we will introduce the fundamental processes of microsecond, nanosecond, and femtosecond LAL, and how the active species act differently in plasma, cavitation bubbles, and droplets in the different LAL processes. Second, a variety of LAL-based techniques for nanomaterials synthesis and processing are presented, such as electric-, magnetic-, and temperature-field LAL, as well as electrochemically assisted LAL, pulsed laser deposition in liquid, and laser writing of nanopatterns in liquid. Third, new progress in LAL-generated nanomaterials is described. Fourth, we emphasize five applications of LAL-generated nanomaterials that have emerged recently in the fields of optics, magnetism, environment, energy, and biomedicine. Finally, we consider the core advantages of LAL, the limitations of LAL and corresponding solutions, and the future directions in this promising research area.     

Femtosecond Photon‐Mediated Plasma Enhances Photosynthesis of Plasmonic Nanostructures and Their SERS Applications

Laser ablation in liquid has proven to be a universal and green method to synthesize nanocrystals and fabricate functional nanostructures. This study demonstrates the superiority of femtosecond laser‐mediated plasma in enhancing photoredox of metal cations for controllable fabrication of plasmonic nanostructures in liquid. Through employing upstream high energetic plasma during laser‐induced microexplosions, single/three‐electron photoreduction of metallic cations can readily occur without chemical reductants or capping agents. Experimental evidences demonstrate that this process exhibits higher photon utilization efficiency in yield of colloidal metal nanoparticles than direct irradiation of metallic precursors. Photogenerated hydrated electrons derived from strong ionization of silicon and water are responsible for this enhanced consequences. Furthermore, these metallic nanoparticles are accessible to self‐assemble into nanoplates for silver and nanospheres for gold, favored by surface‐tension gradients between laser irradiated and unirradiated regions. These metallic nanostructures exhibit excellent surface‐enhanced Raman spectroscopy performance in trace detection of Rhodamine 6G (R6G), 4‐mercaptobenzoic acid (4‐MBA), and mercapto‐5‐nitrobenzimidazole molecules with high sensitivity (down to 10^?12 mol L^?1, 30 × 10^?15 m for R6G), good reproducibility (relative standard deviation < 7%), and good dual‐analyte detection ability with mixture ratios of R6G to 4‐MBA ranging from 20 to 0.025. The conceptual importance of this plasma‐enhanced‐photochemical process may provide exciting opportunities in photochemical reactions, plasmofluidics, and material synthesis.     

Dynamics of Laser Ablation in Superfluid $$^4\hbox {He}$$

Pulsed laser ablation of metal targets immersed in superfluid \(^4\hbox {He}\) is visualized by time-resolved shadowgraph photography and the products are analyzed by post-experiment atomic force microscopy (AFM) measurements. The expansion dynamics of the gaseous ablation half-bubble on the target surface appears underdamped and follows the predicted behavior for the thermally induced bubble growth mechanism. An inherent instability of the ablation bubble appears near its maximum radius and no tightly focused cavity collapse or rebound events are observed. During the ablation bubble retreat phase, the presence of sharp edges in the target introduces flow patterns that lead to the creation of large classical vortex rings. Furthermore, on the nanometer scale, AFM data reveal that the metal nanoparticles created by laser ablation are trapped in spherical vortex tangles and quantized vortex rings present in the non-equilibrium liquid.     

Fabrication of particle free epitaxal AlN thin films by reactive PLD combined with an electron beam and a rotating crucible

An AlN epitaxial film without projections or spiral growth features was successfully fabricated on a (0 0 0 1) sapphire substrate by reactive laser ablation of a liquid Al target in NH₃ using a 248 nm laser. The liquid Al target was prepared with an electron beam in a rotating crucible. The surface of the rotating liquid Al target was always smooth. Spiral growth features were greatly suppressed. AlN films have a surface roughness less than 0.3 nm. The X-ray rocking curve's narrowest FWHM was 180 arcsec, which is nearly identical to that recently reported in films grown by MOCVD or reactive MBE.     

Growth of Niobium Thin Films on Si Substrates by Pulsed Nd:YAG Laser Deposition

The growth of Nb thin films on Si(100) substrates by pulsed Nd:YAG laser deposition(PLD) under different laser fluences(4-15 J/cm~2) was reported.The influence of laser fluence on ablation rate and deposition rate was discussed.X-ray diffraction(XRD) investigations of the deposited films showed an amorphous structure.The droplet density on the film surface observed by scanning electron microscopy(SEM) analyses was extremely low.It was experimentally proved that the droplets on the film surface originated from liquid phase on the target surface.Profilometric measurements of the deposited Nb films revealed a substantial asymmetry in the film thickness related to the plume deflection effect.The measured electrical resistivity of the Nb film was higher than that of high purity Nb bulk.The present investigations of ablation and deposition process of Nb thin films are related to its potential application in superconducting radio-frequency(SRF) cavities.     

The features of the synthesis of ZnO nanostructures by laser ablation of zinc in water-surfactant solutions

The data of experimental investigation of optical properties of colloidal solution, its composition and morphology of the dispersed phase, resulting from laser ablation of zinc in aqueous solutions of surfactants—sodium dodecyl sulfate (SDS) and dioctil sodium sulfosuccinate (AOT) are presented. It is shown that an optical absorption spectra of the colloids, X-ray spectra and AFM (atomic force microscopy) images solid phase of colloids can trace the dynamics of synthesis ZnO nanostructures from zinc nanoclusters in the size of nanometers to fractal aggregates (FA) up to hundreds of nanometers. Determinants of this process are the average power and duration of irradiation, the frequency of the laser pulses, the colloid aging time, the type and concentration of surfactant in the solution. At the selecting of appropriate regimes of the process, along with zinc oxide other nanoproducts-hydrozincite and organic-inorganic layered composite [(β)-Zn(OH)₂ + SDS] are obtained.     

Formation of Au nanostructures through an alumina mask by laser-assisted deposition

We report a new method to produce ordered arrays of metal nanostructures on substrates. The method employs a through-hole nanoporous alumina membrane as a mask that is attached onto the substrate, silicon in this study. The material of deposition, Au in this study, was provided by pulsed laser ablation of a target gold. At an early stage of the deposition, a significant portion of Au penetrated the alumina through-holes and formed an ordered nanodot array on the silicon surface. At the later stage, the through-hole deposition was blocked by the growth of Au film on the top surface of the alumina, so that the heights of the Au nanodots were limited to about 10 nm under current experimental conditions. Subsequent attempts to clean up the top surface of the alumina with a lower power laser illumination resulted in the formation of new nanostructures around the alumina pores, nanospheres, or nanorings, depending on the fluence of the laser and the duration of the cleanup. We will discuss the underlying mechanism of the formation of these nanostructures.     

一维碳化硅纳米材料的研究进展

介绍了具有一维纳米结构的碳化硅(SiC)如SiC纳米棒、纳米线、纳米管、纳米带的制备方法,着重介绍了碳纳米管模板生长法、碳还原法、激光烧蚀法、电弧放电法、流动催化剂法和热解有机前驱体法以及它们的生长机理,并对这几种方法的优缺点进行了分析,指出了目前研究一维纳米SiC中存在的问题和未来发展方向.     

脉冲激光诱导液—固界面反应制备金刚石纳米晶

采用液体水中激光熔蚀固体石墨靶的方法，制成晶形较好的六方金刚石相和立方金刚石，还观察到一种柱状纳米金刚石晶体。     

Synthesis, assembly, and characterization of Si nanocrystals and Si nanocrystal-carbon nanotube hybrid structures

Silicon nanocrystals of a few nanometers in size are of great interest for optoelectronic applications. Here we present a mini-arc plasma method to produce silicon nanocrystals at atmospheric pressure directly from solid silicon precursors. The product silicon nanocrystals are then assembled onto the external surface of carbon nanotubes (CNTs) to form hybrid nanostructures. The absorption properties of both the silicon nanocrystals and the Si-CNT hybrid structures have been characterized. Quantum size effects have been observed for as-produced silicon nanocrystals. The resulting silicon nanocrystals and hybrid nanostructures are promising for optoelectronic applications.     

Optical properties of petal-like aggregated nanocrystalline zinc oxide synthesized by laser ablation

The results of the investigations carried out on the third-order nonlinearity in zinc oxide (ZnO) nanocrystals (NCs) by Z-scan technique are included in this paper. ZnO NCs show negative nonlinearity and good nonlinear absorption behavior at 532 nm. The third-order optical susceptibility χ(3) increases with enlargement of NCs due to the size dependent enhancement of exciton oscillator strength.The synthesis of ZnO NCs was performed by laser ablation from a high-purity metallic target of Zn in distilled water medium. For the ablation process, a high frequency pulsed Nd:YAG laser was employed operating at 532 nm with 100 ns pulse duration. UV–vis absorption spectroscopy illustrated the enhancement of the size of ZnO NCs upon increasing the laser pulse energy applied in ablation process. Accordingly the corresponding optical band gap (E_g) decrease by increasing the size of NCs. X-ray diffraction (XRD) associated with transmission electron microscopy (TEM) was utilized to characterize the crystalline phase and also for determining the ZnO NCs morphology.     

Solvent-dependent evolution of cyclic penta-twinned rhodium icosahedral nanocrystals and their enhanced catalytic properties

Cyclic penta-twinned noble metal nanocrystals exhibit promising properties due to their unique geometric and electronic structures. However, the controlled synthesis of cyclic penta-twinned nanostructures, especially of noble metals with a high cohesive energy (e.g., Rh), is very difficult, and the corresponding growth mechanism is not fully understood. Herein, we report a facile one-pot hydrothermal approach for the synthesis of cyclic penta-twinned Rh icosahedral nanocrystals. It was found that apart from regulating the surface free energy by changing the concentration or category of the capping agents, the solvent might influence the adsorption ability of the surfactant on the Rh crystal surface, which results in a change in the surface free energy and thus allows the formation of Rh cyclic penta-twinned nanostructures. In addition, due to their unique electronic and geometric structures, the Rh icosahedral nanocrystals exhibit superior catalytic activity and stability for the electrooxidation of ethanol as compared to single-crystal Rh tetrahedral nanocrystals and commercial Rh black.

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Controlled Synthesis of Kinked Ultrathin ZnS Nanorods/Nanowires Triggered by Chloride Ions: A Case Study

Colloidal synthesis of kinked ultrathin ZnS nanorods/nanowires with mixed phases using tiny Ag₂S nanocrystals as catalysts is reported. It is found that chloride ions can induce the controlled morphology transition from straight to kinking. The synthetic parameters modulating the growth of kinked ZnS nanorods/nanowires are systematically investigated. Chloride ions introduced in the reaction can generate more proportion of wurtzite phase by slowing the nucleation and growth rates during the growth of one‐dimensional (1D) ZnS nanorods/nanowires. The formation of kinked morphology is responsible for the increased domains of mixed stacking and twinning in single 1D nanostructures. The present recipe on controlled synthesis of 1D kinked nanorods/nanowires provides a model of crystal growth control, and these unique 1D nanostructures may also offer new opportunities to fabricate nanodevices with special functions.     

Facile preparation of TiO2 nanostructures by direct annealing of the Ti foil

TiO₂ nanostructures have been fabricated by direct annealing of the Ti foil with Pd catalyst. The Pd catalysts play an important role in reducing sintering temperature for the synthesis of TiO₂ nanostructures. The morphologies can be varied between the nanowires (NWs) and nanobelts (NBs) by adjusting the amount of Pd and annealing temperature. It shows that the vapor liquid solid and vapor solid may be the most suitable mechanism for the TiO₂ nanostructure growth. Experimental results suggest that this method is an effective, simple and inexpensive route for the preparation of TiO₂ nanostructures with high quality and high yield.     

Thermophysical property measurement at high temperatures by laser-produced plasmas

Excitation by a high-power laser pulse of a material surface generates a sequence of plasma, fluid flow, and acoustic events. These are well separated in time, and their detection and analysis can lead to determination of material properties of the condensed phase target. We have developed a new methodology for real-time determination of molten metal composition by time-resolved spectroscopy of laser-produced plasmas (LPP). If the laser pulse is shaped in such a way that the movement of the bulk surface due to evaporation is kept in pace with the thermal diffusion front advancing into the interior of the target, the LPP plume becomes representative of the bulk in elemental composition. In addition, the mass loss due to LPP ablation is very well correlated with the thermal diffusivity of the target matter. For several elemental solid specimens, we show that the product of the ablation thickness and heat of formation is proportional to the thermal diffusivity per unit molecular weight. Such measurements can be extended to molten metal specimens if the mass loss by ablation, density, heat of formation, and molecular weight can be determined simultaneously. The results from the solid specimen study and the progress with a levitation-assisted molten metal experiment are presented.Paper presented at the Third Workshop on Subsecond Thermophysics, September 17–18, 1992, Graz, Austria.     

Precise, controlled laser delivery with evanescent optical waves

Precise laser surgery is possible with laser pulses at wavelengths that are strongly absorbed at the surface of tissue. However, pulses at these wavelengths (far UV, far infrared) are not compatible with fiber-optic transmission, making endoscopic surgical procedures inside the body difficult. We use evanescent optical waves to demonstrate an alternative for confining energy near the tissue surface. Precise, superficial tissue ablation is achieved with evanescent waves generated at a sapphire-tissue interface by a free-electron laser, where the ablation depth may be varied. A new class of precise, controlled laser surgical tools may be achieved in this novel approach for use in endoscopic procedures. Electromagnetic theory governing evanescent-wave tissue ablation is presented.     

Mn-doped ZnO nanocrystals embedded in Al2O3: structural and electrical properties

We report on the structural and electrical properties of Mn-doped ZnO/Al(2)O(3) nanostructures produced by the pulsed laser deposition technique. Grazing incidence small angle x-ray scattering (GISAXS) and Rutherford backscattering spectrometry revealed the multilayered structure in as-deposited samples. Annealing of the nanostructures was shown to promote the formation of nanocrystals embedded in the Al(2)O(3) matrix, as was evidenced by GISAXS and high resolution transmission microscopy. Particle-induced x-ray emission analysis showed a doping of 8 at.% Mn in ZnO. Grazing incidence x-ray diffraction and Raman spectroscopy demonstrated that the nanocrystals have the pure wurtzite ZnMnO crystalline phase. Resonant Raman scattering displayed an increase of intensity of the 1LO mode as well as broadening of the 2LO mode related to the size effect. Capacitance-voltage measurements showed carrier retention with a voltage shift higher than those reported for similar systems.