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  • 1
    Electronic Resource
    Electronic Resource
    Path-integral Monte Carlo studies of para-hydrogen clusters (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 3590-3599 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Path-integral Monte Carlo calculations have been used to study para-hydrogen clusters, (p-H2)N, with N=13, 19, 33, and 34. Particular attention has been given to the low temperature structures and their evolution with increasing temperature. The structures of these quantum clusters have a clear relationship to their classical counterparts. In particular, the core of the N=19, 33, and 34 clusters is bipyramidal, in constrast to that of the N=13 cluster, which is icosahedral. At T∼2 K, these clusters exhibit a large propensity for exchanging particles, even without explicitly including exchange permutations (Bose statistics). This behavior has its origin in the large zero-point motion of the very weakly bound small p-H2 clusters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462994
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  • 2
    Electronic Resource
    Electronic Resource
    Excited-state dynamics of rare-gas clusters (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 4273-4288 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper we explore the dynamic implications of energy exchange in electronically vibrationally excited states of mixed rare-gas clusters. The classical molecular dynamics method was applied for the study of vibrational energy flow from electronically excited atomic Xe(3P1) states in Xe*Ar12 and Xe*Ar54, and the consequences of Xe@B|2 (3Σu) excimer formation in Xe*2 Ar11 and Xe@B|2 Ar53 clusters. We have established the occurrence of an ultrafast vibrational energy flow (∼300 fs) from local Rydberg atomic and excimer excitations into the cluster, which is accompanied by large configurational dilation around the excited state, due to short-range repulsive interactions. Size effects on cluster dynamics were elucidated, being manifested by vibrational predissociation in small clusters and by vibrational relaxation and vibrational energy redistribution in large clusters. A gradual transition from reactive molecular type relaxation in small clusters to nonreactive condensed-matter type relaxation in large clusters was documented. Qualitative and quantitative differences between relaxation of excited species initially located in the interior or on the surface of the cluster were established, being exhibited in the details of the vibrational energy flow. In the case of bulk Xe*2 Ar53, excessive local heating is manifested in cluster melting, which results in mass transport of the excimer to the cluster surface. The many facets of the dynamics of electronically excited mixed rare-gas clusters are amenable to experimental interrogations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453786
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  • 3
    Electronic Resource
    Electronic Resource
    Path-integral Monte Carlo study of a lithium impurity in para-hydrogen: Clusters and the bulk liquid (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 8997-9012 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Simulation studies using the path-integral formulation of quantum statistical mechanics are reported for single atomic lithium impurities in bulk liquid para-hydrogen and in clusters, Li(p-H2)n, with n=12, 13, 32, 33, and 34. Over the range of temperatures studied in the clusters (T=2.5–6.0 K), the lithium impurity is found to reside outside or at the surface of the clusters. Nevertheless, perturbations of the structure are observed in comparison to neat para-hydrogen clusters. The solvation energy of the lithium in the bulk liquid and subcritical gas (T=14–25 K) is found to be slightly positive. In both the clusters and the liquid, the inhomogeneously broadened dipole spectrum of the lithium atom was calculated using the radial fast Fourier transform Lanczos method. In the clusters, the spectra exhibit a main absorption band near the unperturbed atomic Li value and a second, asymmetric band shifted to the blue. The latter can be identified as the p orbital oriented radially towards the cluster, while the main band is composed of two p orbitals oriented parallel to the cluster surface. The spectrum in the liquid, while broader, has a more symmetric line shape. The ionization spectrum of the lithium atom in the clusters was also obtained. These spectra have finite width and a band center that progressively red shifts from the atomic value as the number of para-hydrogen molecules increases. The predicted trends should be amenable to testing using molecular beam experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465568
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  • 4
    Electronic Resource
    Electronic Resource
    Nature of lithium trapping sites in the quantum solids para-hydrogen and ortho-deuterium (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 9013-9020 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Quantum mechanical studies of a lithium impurity in solid para-hydrogen and ortho-deuterium have been performed using the path integral formulation of statistical mechanics. Since an isolated lithium atom is much larger than the host molecules, trapping sites consisting of from one to six vacancies have been investigated. Interestingly, all of the sites are comparable in energy. This is due to the large compressibility of para-hydrogen and ortho-deuterium solids, which permits the lattice to relax to comfortably accommodate the impurity. The inhomogeneously broadened dipole spectrum of the lithium impurity in the various sites was calculated using the radial fast Fourier transform Lanczos method and compared to experiments by Fajardo [J. Chem. Phys. 98, 110 (1993)]. Based on the present calculations, lithium atoms appear to occupy preferentially a three-vacancy trapping site in para-hydrogen while in ortho-deuterium a four-vacancy trapping site seems to be favored. Complementary variational Einstein model calculations predict that the four-vacancy trapping site is favorable in both para-hydrogen and in ortho-deuterium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465569
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  • 5
    Electronic Resource
    Electronic Resource
    Tensors with icosahedral symmetry that are invariant under a certain wreath product (1987)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 28 (1987), S. 2323-2324 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: Faithful icosahedral symmetry exists only for tensors of rank higher than 5. The most relevant tensor of this type is the one for third-order elastic constants C(3)ijklmn defined by the series expansion Tij=C(2)ijklεkl+ 1/2 C(3)ijklmnεklεmn +⋅⋅⋅ of the stress tensor T in terms of the deformation tensor ε. A basis for those tensors in (R3)⊗6 that are invariant under a certain action of both the icosahedral group S2×A5 and the wreath product S2∼S3 of the symmetric groups S2 and S3 are evaluated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.527831
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  • 6
    Electronic Resource
    Electronic Resource
    Nanowear/nanomechanical testing and the role of stress in sputtered CNx overcoats : The 41st annual conference on magnetism and magnetic materials (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 5393-5395 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: a:C–Nx films were deposited on Si(111) wafers at ambient temperatures by reactive magnetron sputtering of C in a mixed Ar/N2 discharge. The hardness (H) and elastic modulus (E) were assessed via nanoindentation using a Berkovich diamond indenter. The nitrogenated films exhibited increased hardness and elastic moduli values compared to the amorphous carbonated films, i.e., 25 and 240 GPa to 16 and 160 GPa, respectively. A sphere-on-flat (magnetic tape) wear tester was used to assess wear scar volume losses as a function of wear time. All films were in a state of compression (intrinsic and thermal stress). The bonding, composition, and structure of the films for all the deposition conditions were assessed by micro-Raman spectroscopy, energy dispersive x-ray spectroscopy (EDX), and x-ray diffraction (XRD), respectively, and subsequently correlated to overall film properties.© 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.365562
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  • 7
    Electronic Resource
    Electronic Resource
    Adhesion assessment of silicon carbide, carbon, and carbon nitride ultrathin overcoats by nanoscratch techniques : The 41st annual conference on magnetism and magnetic materials (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 5396-5398 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This paper presents experimental results for adhesion assessment of 20 nm ultrathin SiC, amorphous carbon and carbon nitride films deposited on silicon (111) substrates by sputtering. In the experiment, the ultrathin overcoats were scratched by a face-forward Berkovich diamond indenter with a continuous depth sensing nanoscratch system. Experimental results indicate that the nanoscratch system has very good sensitivity for detecting ultrathin overcoat cracking, delamination, and brittle fracture caused by scratching. A well-defined critical load for each film was determined by the nanoscratch techniques. The highest critical load (800 μN) is found for the CN film and the lowest (500 μN) is for SiC. Scanning electron microscopy (SEM) investigations to the surface damage of the samples reveal that the SiC overcoat was damaged more severely than other films due to its brittle fracture. The adhesion properties of the three films tested in this work are best in carbon nitride, followed by amorphous carbon and then silicon carbide. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364551
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  • 8
    Electronic Resource
    Electronic Resource
    Structural and tribological characterization of protective amorphous diamond-like carbon and amorphous CNx overcoats for next generation hard disks (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 3142-3154 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Further insight into processing-structure-property relationships have been carried out for existing and candidate carbon-based protective overcoats used in the magnetic recording industry. Specifically, 5 nm thick amorphous diamond-like carbon (a:C) and nitrogenated diamond-like carbon (a:CNx) overcoats were deposited by low deposition rate sputtering onto a thin film disk consisting of either CoCrPt/CrV/NiP/AlMg or CoCrPt/CrV/glass. The wear durability and frictional behavior of these hard disks were ascertained using a recently developed depth sensing reciprocating nanoscratch test. It was determined that the CN0.14/CoCrPt/CrV/glass disk exhibited the most wear resistance, least amount of plastic deformation, and lowest kinetic friction coefficient after the last wear event. Core level x-ray photoelectron spectroscopy (XPS) results of sputter cleaned overcoats indicated that nitrogen up to 14 at. % incorporated into the amorphous network resulted in these improvements near the overcoat/magnetic layer interface, since there was an increase in the number of N-sp3 C bonded sites in a predominantly N-sp2 C bonded matrix. However, nonsputter cleaned overcoats exhibited a more graphitic pyridine-like (nondoping configuration) structure near the surface as evidenced by the increase in C(Double Bond)N versus C–N bonds and the valence band XPS determined appearance of the 2p-π band near the Fermi level (EF). Therefore, XPS sputter cleaning revealed a gradient in the chemical nature of the overcoats through the thickness. In addition, micro-Raman spectroscopy established that a further increase of nitrogen (≥18 at. %) weakened the overcoat structure due to the formation of terminated sites in the amorphous carbon network, since nitrogen failed to connect the sp2 domains within the network. This, in conjunction with an increase in the intensity of the 2p-π band from the valence band XPS spectra and the increase in the G-band position and ID/IG ratio from the Raman spectra, confirmed the increase in the size and number of sp2 bonds in the CN0.18 overcoat. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369654
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  • 9
    Electronic Resource
    Electronic Resource
    Improved method for the precise determination of the compressibility factor from refractive index measurements (1986)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 26-32 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We show that the absolute determination of the refractive index when combined with an expansion technique for obtaining the higher-order coefficients of the Lorentz–Lorenz expansion leads to precise values of density. The compressibility factor of methane calculated with the first three coefficients of the Lorentz–Lorenz expansion is comparable to the best PVT values. The optical method for the determination of the compressibility factor is shown to be not only precise, but also has the ability to produce numerous experimental points in a short time as compared to other methods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139112
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  • 10
    Electronic Resource
    Electronic Resource
    Nanostructured magnetic networks (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 2758-2760 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nanostructured contiguous networks of Fe well suited to fundamental studies of the effects of confinement are described. The Fe networks are prepared by sputter deposition onto the surface of nanochannel alumina. One of the most obvious consequences of confining the magnetic material to a nanostructured network is a dramatic enhancement in the coercivity when compared to a continuous Fe film of the same thickness. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117666
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