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  • 1
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    Sputtering of silicon membranes with nanoscale thickness (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-06-28
    Description: A theoretical study of forward and backward sputtering produced by the impact of single 20 keV Ar ions on freestanding amorphous Si membranes is carried out. We use three techniques: Monte Carlo (MC) and molecular dynamics (MD) simulations, as well as analytical theory based on the Sigmund model of sputtering. We find that the analytical model provides a fair description of the simulation results if the film thickness d exceeds about 10%–30% of the mean depth of energy deposition a . In this regime, backward sputtering is nearly independent of the membrane thickness and forward sputtering shows a maximum for thicknesses d ≈ a . The dependence of forward sputtering on the ion's incidence angle shows a qualitative change as a function of d : while for d ≲ a , the forward sputter yield has a maximum at oblique incidence angles, the maximum occurs at normal incidence for d ≳ a . As the membrane thickness is reduced below 0.1– 0.3 a , the theory's predictions increasingly deviate from the MC results. For example, the predicted forward sputter yield approaches a finite value but the MC result tends to zero. This behavior is interpreted in terms of energy deposition and sputtering efficiency. Near-perfect agreement is observed between the sputter yields calculated by MD and MC simulations even for the thinnest membranes studied ( d  = 5 Å).
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 2
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    Erratum: “H2—AgCl: A spectroscopic study of a dihydrogen complex” [J. Chem. Phys. 141, 114306 (2014)] (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-07-09
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
    Published by American Institute of Physics (AIP)
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  • 3
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    H2—AgCl: A spectroscopic study of a dihydrogen complex (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-09-20
    Description: H 2 —AgCl has been observed on a Fourier transform microwave spectrometer equipped with laser ablation source and determined to be a dihydrogen complex. Transitions up to J = 3–2 have been measured and analyzed for four isotopologues of the complex containing ortho and para H 2 . The ortho and para spin states have been included in one fit, a deviation from the typical H 2 complex. Rotational constants B and C , centrifugal distortion constants Δ J and Δ JK , nuclear electric quadrupole coupling constants χ aa , χ bb , and χ cc for 35 Cl and 37 Cl have been fit for both spin states while nuclear spin-nuclear spin constants D aa , D bb , and D cc , and nuclear spin-rotation constant C aa have been reported for the ortho spin state. Quantum chemical calculations predict a strong bonding interaction and the strength of the complex has been related to reported χ aa and Δ J values amongst a host of comparable species, including the AgCl monomer itself. Bond lengths have been determined for Ag—Cl, Ag—H 2 center-of-mass, and H—H and are reported.
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
    Published by American Institute of Physics (AIP)
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  • 4
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    Crater production by energetic nanoparticle impact on Au nanofoams (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-03-17
    Description: Impact of energetic nanoparticles on solids produces craters on the surface. We use molecular dynamics simulations to compare crater production on a compact Au solid with that in a porous (foam) target. Our results show a complex picture: (i) At low impact velocities, the nanoparticles produce permanent craters in the foam while they cannot penetrate the compact target. (ii) With increasing velocity and/or projectile mass, the crater depth in the foam target increases less strongly than for the compact target. The plasticity-affected zone in the foam target is of similar size as in the compact target. Our results are relevant for the use of porous structures as shields against nanoparticle impact.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 5
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    Influence of phase transition on shock-induced spallation in nanocrystalline iron (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-11-13
    Description: Intense shock waves may lead to spallation of the sample. Recent experiments show differences of shock spallation in iron depending on whether the samples underwent the pressure-induced bcc-hcp phase transformation or not. In this study, we perform molecular dynamics simulations of shock-induced spallation in polycrystalline iron. Our results show that the phase transformation decreases the probability of multiple spallation and crack formation. In agreement with experiments, the phase transformation changes the surface morphology showing smoother spallation surfaces.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 6
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    Morphological changes in polycrystalline Fe after compression and release (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-02-26
    Description: Despite a number of large-scale molecular dynamics simulations of shock compressed iron, the morphological properties of simulated recovered samples are still unexplored. Key questions remain open in this area, including the role of dislocation motion and deformation twinning in shear stress release. In this study, we present simulations of homogeneous uniaxial compression and recovery of large polycrystalline iron samples. Our results reveal significant recovery of the body-centered cubic grains with some deformation twinning driven by shear stress, in agreement with experimental results by Wang et al. [Sci. Rep. 3 , 1086 (2013)]. The twin fraction agrees reasonably well with a semi-analytical model which assumes a critical shear stress for twinning. On reloading, twins disappear and the material reaches a very low strength value.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 7
    Electronic Resource
    Electronic Resource
    Effect of gas-phase collisions in pulsed-laser desorption: A three-dimensional Monte Carlo simulation study (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 8544-8551 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The gas flow of particles laser desorbed from an elemental target into a vacuum is studied by Monte Carlo simulation. Pulsed desorption off a finite area is modeled; this is possible by using a three-dimensional simulation algorithm. We monitor the temporal evolution of the desorption cloud and global features of the flow, such as the number of collisions occurring in the gas, and the fraction of particles backscattered to the surface. The angle and energy distribution of the desorbed particles is investigated as a function of the number of monolayers desorbed, and the laser spot width. Our results show the formation of a desorption jet, in which fast particles are focused towards the jet axis, while slow particles leave the jet at oblique angles. Many features of the particle flux may be fitted by so-called elliptical distributions. However, these represent the velocity distribution of particles at oblique angles only poorly. Finally, we demonstrate the differences which exist between our three-dimensional simulation and previous, one-dimensional treatments. These studies are of fundamental interest for the characteristics of thin films deposited from the desorbed material.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353384
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  • 8
    Electronic Resource
    Electronic Resource
    Molecular-dynamics simulations of bulk and surface damage production in low-energy Cu→Cu bombardment (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 5410-5418 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Molecular-dynamics simulations are employed to study in detail the effects of low-energy (≤100 eV) bombardment of a Cu (001) surface by Cu atoms. By following the simulation up to 4 ps in real time, the end configuration of defects in the target can be observed. We present results on the vacancy and interstitial distribution in the target, the spontaneous defect recombination, the number of surface vacancies and adatoms produced, and the mixing of target atoms induced by the bombardment. Furthermore, the fate of the projectile atom−backscattering and implantation−and the sputtering behavior are investigated. The relevance of the results on the modelling of ion-beam (assisted) deposition is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350563
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  • 9
    Electronic Resource
    Electronic Resource
    The rotational spectrum and structure of chlorine peroxide (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 6588-6597 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The products of the ClO self-reaction have been studied in a flowing chemical reactor using submillimeter wave spectroscopy. The complete spectrum between 415 to 435 GHz has been measured as well as selected transitions in the range 285 to 415 GHz. The major products have been identified as the ClO dimer (Cl2O2) and chlorine dioxide (OClO). The observed rotational b-type spectra of the most abundant isotopic species35 ClOO35Cl and 37ClOO35Cl have been analyzed. The observed nuclear spin statistics for the main species, the relative abundance of the lesser species, and the structure determination demonstrate unambigiously that the ClO dimer must possess identical chlorine atoms in a peroxide structure. The rotational constants as well as a complete set of quartic centrifugal distortion constants have been determined. Structural parameters for the vibronic ground state have been calculated: rOO=142.59(21) pm, rClO=170.44(4) pm, (angle)ClOO=110.07(1)° and dihedral angle=81.03(1)°. Rotational transitions in the first excited torsional state have been measured and analyzed for the isotopic species 35,35 and 35,37. An effective molecular structure for the first torsional excited state has been calculated. A torsional frequency has been derived from relative intensity measurements and the cis and the trans barrier heights estimated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457377
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  • 10
    Electronic Resource
    Electronic Resource
    Damage production in a-Si under low-energy self-atom bombardment (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 689-695 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using a molecular-dynamics simulation, we study the buildup of damage in an a-Si specimen bombarded by Si atoms with energies between 10 and 150 eV for fluences up to 1.4×1015 cm−2, i.e., an equivalent of 2 monolayer growth. The production rate of overcoordinated atoms increases with the bombarding energy; we analyze its fluence and bombarding-energy dependence in detail. The number of undercoordinated atoms decreases for low-energy bombardment due to the saturation of dangling bonds at the surface; for higher bombarding energies, it increases slightly, but shows only little dependence on bombarding energy. The depth distribution of the damage, of the induced stress, and of the atom relocation in the target demonstrate that bombardment modifies the target at considerably greater depths than the ion range. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1380408
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