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1.
The Nd:YAG laser-induced breakdown of 20 μm glass microspheres was investigated using time-resolved optical shadow and Schlieren images. Time-resolved imaging showed the location of the initial breakdown and the shockwave motion over its first 400 μm of expansion. Measured shockwave velocities were in the range of 1–10 km/s and showed a linear dependency on laser fluence within 30 ns. 相似文献
2.
Nichols William T. Malyavanatham Gokul Henneke Dale E. O'Brien Daniel T. Becker Michael F. Keto John W. 《Journal of nanoparticle research》2002,4(5):423-432
Silver nanoparticles were produced by laser ablation of a continuously flowing aerosol of microparticles in nitrogen at varying laser fluences. Transmission electron micrographs were analyzed to determine the effect of laser fluence on the nanoparticle size distribution. These distributions exhibited bimodality with a large number of particles in a mode at small sizes (3–6-nm) and a second, less populated mode at larger sizes (11–16-nm). Both modes shifted to larger sizes with increasing laser fluence, with the small size mode shifting by 35% and the larger size mode by 25% over a fluence range of 0.3–4.2-J/cm2. Size histograms for each mode were found to be well represented by log-normal distributions. The distribution of mass displayed a striking shift from the large to the small size mode with increasing laser fluence. These results are discussed in terms of a model of nanoparticle formation from two distinct laser–solid interactions. Initially, laser vaporization of material from the surface leads to condensation of nanoparticles in the ambient gas. Material evaporation occurs until the plasma breakdown threshold of the microparticles is reached, generating a shock wave that propagates through the remaining material. Rapid condensation of the vapor in the low-pressure region occurs behind the traveling shock wave. Measurement of particle size distributions versus gas pressure in the ablation region, as well as, versus microparticle feedstock size confirmed the assignment of the larger size mode to surface-vaporization and the smaller size mode to shock-formed nanoparticles. 相似文献
3.
Marowsky G. Schäfer E. P. Keto J. W. Tittel F. K. 《Applied Physics A: Materials Science & Processing》1976,9(2):143-146
Fluorescence studies on electron-beam excited mixtures of POPOP dye vapor and various buffer gases are reported. Xenon has
been found to be a promising candidate as a buffer gas for efficient energy deposition of the electron-beam and energy transfer
to the POPOP dye vapor. These experiments may be an important step towards realization of an electrically excited dye vapor
laser.
Work supported in part by the National Aeronautics and Space Administration and the Energy Research and Development Administration. 相似文献
4.
Michael Gammage Hugo Celio Michael F. Becker John W. Keto Desiderio Kovar 《Journal of nanoparticle research》2017,19(8):276
Bare Ag nanoparticles (~10 nm) and Ag nanoparticles (1–20 nm) on the surfaces of larger TiOx nanoparticles were prepared by laser ablation of microparticle aerosols (LAMA). The behaviors of the nanoparticles during high temperature annealing were then studied with ex situ and in situ transmission electron microscopy. For the ex situ heating experiments, Ag and Ag-on-TiOx NPs were collected onto gold TEM grids and subjected to annealing treatments at 500 °C in argon, vacuum, and air. At this temperature, bare Ag NPs on carbon TEM supports coarsened rapidly in both air and argon atmospheres. In contrast, Ag-on-TiOx NPs that were heated to 500 °C in flowing argon or in a vacuum did not coarsen significantly and were remarkably stable. Ag-on-TiOx NPs that were heated to 500 °C in air, however, behaved quite differently. The TiOx crystallized upon heating and a significant loss of Ag were observed from the surfaces of the TiOx, likely due to sublimation. These results demonstrate that the surface defect structure and chemistry of the oxide support strongly influence the thermal stability of Ag NPs produced by LAMA. 相似文献
5.
Ekoko Bakambo Gracien Zhou Ruimin Li Jian Xin Li Hui Tondozi Keto 《Journal of Radioanalytical and Nuclear Chemistry》2004,262(3):751-754
Gamma-irradiation has been applied to synthesize the nanocomposite semiconductor constituted of zinc and cadmium sulfide Cd1-xZnxS ultra fine particles at room temperature by utilizing homogeneous release of S2– ions from the decomposition of sodium thiosulfate. The structure, morphology, size and optical properties of that compound have been studied by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and ultraviolet-visible spectrometer (UV-visible). The product obtained from irradiated solutions containing zinc ions, cadmium ions and the sulfur source has been characterized as a composite of (CdxZn1-x)S, with spherical morphology and with a diameter of average size of about 5.3 nm. The possible mechanism of formation of the composite is proposed.The financial support of Shanghai Science and Technology Foundation through No. 0252nm 095 is gratefully acknowledged.The authors would thank the staff of Shanghai Applied Radiation Institute of Shanghai University for their valuable contributions. 相似文献
6.
Thomas H Helal A Hoffmann K Kandadai N Keto J Andreasson J Iwan B Seibert M Timneanu N Hajdu J Adolph M Gorkhover T Rupp D Schorb S Möller T Doumy G DiMauro LF Hoener M Murphy B Berrah N Messerschmidt M Bozek J Bostedt C Ditmire T 《Physical review letters》2012,108(13):133401
Explosions of large Xe clusters ( ~ 11,000) irradiated by femtosecond pulses of 850 eV x-ray photons focused to an intensity of up to 10(17) W/cm(2) from the Linac Coherent Light Source were investigated experimentally. Measurements of ion charge-state distributions and energy spectra exhibit strong evidence for the formation of a Xe nanoplasma in the intense x-ray pulse. This x-ray produced Xe nanoplasma is accompanied by a three-body recombination and hydrodynamic expansion. These experimental results appear to be consistent with a model in which a spherically exploding nanoplasma is formed inside the Xe cluster and where the plasma temperature is determined by photoionization heating. 相似文献
7.
Ekoko Bakambo Gracien Zhou Ruimin Li Jian Xin Li Hui Tondozi Keto 《Journal of Radioanalytical and Nuclear Chemistry》2005,262(3):751-754
Gamma-irradiation has been applied to synthesize the nanocomposite semiconductor constituted of zinc and cadmium sulfide Cd1-xZnxS ultra fine particles at room temperature by utilizing homogeneous release of S2– ions from the decomposition of sodium thiosulfate. The structure, morphology, size and optical properties of that compound have been studied by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and ultraviolet-visible spectrometer (UV-visible). The product obtained from irradiated solutions containing zinc ions, cadmium ions and the sulfur source has been characterized as a composite of (CdxZn1-x)S, with spherical morphology and with a diameter of average size of about 5.3 nm. The possible mechanism of formation of the composite is proposed.The financial support of Shanghai Science and Technology Foundation through No. 0252nm 095 is gratefully acknowledged.The authors would thank the staff of Shanghai Applied Radiation Institute of Shanghai University for their valuable contributions. 相似文献
8.
G. Marowsky R. Cordray F. K. Tittel W. L. Wilson J. W. Keto 《Applied Physics A: Materials Science & Processing》1977,12(3):245-252
Excitation processes of selected dye vapor-rare gas mixtures pumped by an electron beam have been studied. These experiments
revealed the importance of effective collisional electron energy transfer pumping via a dense rare gas rather than a radiative
energy transfer from an excimer laser gas mixture to achieve population inversion in an organic dye vapor.
Work supported in part by the Energy Research and Development Adinistration, the Robert A. Welch Foundation and the National
Science Foundation. 相似文献
9.
Hon M. Chun Carlos E. Padilla Donovan N. Chin Masakatsu Watanabe Valeri I. Karlov Howard E. Alper Keto Soosaar Kim B. Blair Oren M. Becker Leo S. D. Caves Robert Nagle David N. Haney Barry L. Farmer 《Journal of computational chemistry》2000,21(3):159-184
A modeling approach that can significantly speed up the dynamics simulation of large molecular systems is presented herein. A multigranular modeling approach, whereby different parts of the molecule are modeled at different levels of detail, is enabled by substructuring. Substructuring the molecular system is accomplished by collecting groups of atoms into rigid or flexible bodies. Body flexibility is modeled by a truncated set of body‐based modes. This approach allows for the elimination of the high‐frequency harmonic motion while capturing the low‐frequency anharmonic motion of interest. This results in the use of larger integration step sizes, substantially reducing the computational time required for a given dynamic simulation. The method also includes the use of a multiple time scale (MTS) integration scheme. Speed increases of 5‐ to 30‐fold over atomistic simulations have been realized in various applications of the method. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 159–184, 2000 相似文献
10.
Nichols William T. Malyavanatham Gokul Henneke Dale E. Brock James R. Becker Michael F. Keto John W. Glicksman Howard D. 《Journal of nanoparticle research》2000,2(2):141-145
Silver nanoparticles were produced by laser ablation of a continuously flowing aerosol of microparticles entrained in argon, nitrogen and helium at a variety of gas pressures. Nanoparticles produced in this new, high-volume nanoparticle production technique are compared with our earlier experiments using laser ablation of static microparticles. Transmission electron micrographs of the samples show the nanoparticles to be spherical and highly non-agglomerated under all conditions tested. These micrographs were analyzed to determine the effect of carrier gas type and pressure on size distributions. We conclude that mean diameters can be controlled from 4 to 20 nm by the choice of gas type and pressure. The smallest nanoparticles were produced in helium, with mean sizes increasing with increasing molecular weight of the carrier gas. These results are discussed in terms of a model based on cooling via collisional interaction of the nanoparticles, produced in the laser exploded microparticle, with the ambient gas. 相似文献