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All-boron analogues of aromatic hydrocarbons: B17− and B18− J. Chem. Phys. 134, 224304 (2011) On the simulation of photoelectron spectra complicated by conical intersections: Higher-order effects and hot bands in the photoelectron spectrum of triazolide (CH)2N3− J. Chem. Phys. 134, 184314 (2011) Time-resolved photoelectron spectroscopy of coupled electron-nuclear motion J. Chem. Phys. 134, 184307 (2011) Photoelectron angular distributions from autoionizing 4s14p66p1 states in atomic krypton probed with femtosecond time resolution A Q-switched Nd:YAG ͑yttrium aluminum garnet͒ laser ͑1064 nm wavelength͒ with a 9 ns pulse width, 1-900 mJ pulse energy, and 0.5 mm 2 target spot, is employed to irradiate tantalum targets in vacuum. The irradiation produces a strong etching of the metal and forms a plasma in front of the target. The plasma contains neutrals and ions with a high charge state and a wide energy distribution. Time-of-flight measurements are presented for the ionic production. A cylindrical electrostatic ion analyzer permits to measure the yield and the charge state of the emitted ions and to extrapolate the ion energy distribution as a function of the laser fluence in the range 10-100 J/cm 2 . The measurements indicate that at high laser fluence the tantalum charge state may reach 8ϩ and the maximum ion energy about 6 keV. The ion energy distribution is presented as a function of the charge state. It follows approximately a ''shifted Maxwellian distribution.'' A better theoretical approach has been further developed considering the Coulomb interactions occurring inside the plasma, which produce ion acceleration at velocities comparable with thermal ones, according to the so-called ''shifted Maxwellian-Coulombian distribution.''

The present work analyzes possible increases in resistance to wear of nickel-titanium endodontic instruments that have undergone a process of ionic implantation. ProFile .04 taper #25 instruments were subjected to ionic implantation with bands of nitrogen ions of 250 KeV, currents in the order of 10 microA/cm2, and doses of 2 x 10(17) ions/ cm2. The instruments were used to make preparations in acrylic endodontic training blocks. Scanning electron microscopic investigations showed that after 60 s of work inside the endodontic training blocks nonionic implanted control instruments showed small modifications in their blades, and their tips showed the first signs of wear. After 240 s the control instruments showed consistent signs of wear and frequent changes to their surfaces. After 240 s of use the ionic-implanted instruments did not present any significant changes in the micromorphology of their surfaces. The implanted instruments did not manifest the typical signs of wear and did not show the surface changes that quickly affect the working life of untreated endodontic instruments manufactured from nickel-titanium.

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The charge production from laser-generated plasmas generates not isotropically ion acceleration in vacuum and with mean kinetic energy proportional to the ion charge state. The ion velocity depends on many factors of which the most important are the plasma temperature, the adiabatic gas expansion in vacuum and the Coulomb acceleration. The ion energy distributions of the emitted ions from the plasma can be well explained by the Coulomb-Boltzmann-Shifted function, with a cut-off limitation at high energy for a wide range of laser intensities. It can be applied for intensities of 10 10 W/cm 2 , when plasma is produced only in the backward direction from thick targets (backward plasma acceleration regime), as well as at intensities of the order of 10 19 W/cm 2 , when plasma is produced in the forward direction from thin targets in target-normal sheath acceleration regime. It loses of validity in radiation pressure acceleration regime, at which ions are emitted near mono-energetically. ARTICLE HISTORY

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