| Blomqvist, M., Bongiorno, G., Podesta, A., Serin, V., Abrasonis, G., Kreissig, U., Moller, W., Coronel, E., Wachtmeister, S., Csillag, S., Cassina, V., Piseri, P., and Milani, P. |
| Structural and tribological properties of cluster-assembled CNx films. |
| Applied Physics A-Materials Science & Processing v.87, n.4, pp.767-772. (2007). |
| Abstract: We report the structural and tribological characterization of nanostructured CNx thin films produced by the deposition of a supersonic carbon cluster beam assisted by nitrogen ion bombardment. The influence of the deposition parameters on the chemical composition and structure of the films has been systematically studied by X-ray photoelectron spectroscopy, elastic recoil detection analysis, transmission electron microscopy and atomic force microscopy. Depending on the deposition parameters, the films show a structure ranging from amorphous to disordered graphitic with interlinked planes. Nitrogen content depends on the nitrogen ion kinetic energy. The films have a very low density with a high surface roughness. Friction measurements at the nanoscale show a correlation between nitrogen content and mechanical properties of the system |
| Internal Reference: [ID: 2503]
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|
| Bogana, M., Ravagnan, L., Casari, C. S., Zivelonghi, A., Baserga, A., Bassi, A. L., Bottani, C. E., Vinati, S., Salis, E., Piseri, P., Barborini, E., Colombo, L., and Milani, P. |
| Leaving the fullerene road: presence and stability of sp chains in sp(2) carbon clusters and cluster-assembled solids. |
| New Journal of Physics v.7, n.81, (2005). |
| Abstract: We report an experimental and theoretical investigation of the growth and structure of large carbon clusters produced in a supersonic expansion by a pulsed microplasma source. The absence of a significant thermal annealing during the cluster growth causes the formation of disordered structures, where sp(2) and sp hybridizations coexist for particles larger than similar to 90 atoms. Among the various structures, we recognize sp2 closed networks encaging sp chains. This 'nutshell' configuration can prevent the fragmentation of sp species upon deposition of the clusters, thus allowing the formation of nanostructured films containing carbynoid species, as shown by Raman spectroscopy. Atomistic simulations confirm that the observed Raman spectra are the signature of the sp/sp(2) hybridization typical of isolated clusters and surviving in the film and they provide information about the structure of the sp chains. Endohedral sp chains in sp(2) cages represent a novel way in which carbon nanostructures may be organized with potentially interesting functional properties |
| Internal Reference: [ID: 2499]
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|
| Bongiorno, G., Podesta, A., Ravagnan, L., Piseri, P., Milani, P., Lenardi, C., Miglio, S., Bruzzi, M., and Ducati, C. |
| Electronic properties and applications of cluster-assembled carbon films. |
| Journal of Materials Science-Materials in Electronics v.17, n.6, pp.427-441. (2006). |
| Abstract: Nanostructured carbon thin films can be grown by deposition of cluster beams produced in supersonic expansions. By using a pulsed microplasma cluster source and by exploiting aerodynamic focusing effects typical of supersonic expansions, the structure and the properties of the films can be controlled by varying the cluster mass distribution prior to deposition. Nanocomposite films can be produced by co-depositing carbon clusters and metallic nanoparticles. The films have been characterized by various spectroscopic techniques and tested in view of applications for field emission, supercapacitors, gas sensing. The possibility of patterning cluster-assembled carbon films by shadow masking or by ultraviolet photon irradiation suggests interesting perspective for the integration of nanostructured carbon films on microfabricated devices and for the production of components for an all-carbon electronics |
| Internal Reference: [ID: 2504]
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|
| Casari, C. S., Li Bassi, A., Bottani, C. E., Lenardi, C., Ravagnan, L., Siviero, F., Barborini, E., Piseri, P., and Milani, P. |
| Nanoscale and mesoscale properties of nanostructured carbon films. |
| Fullerenes Nanotubes and Carbon Nanostructures v.13, pp.199-210. (2005). |
| Abstract: A multi-scale investigation of nanostructured carbon films has been performed by means of inelastic light scattering (Raman and Brillouin scattering). Carbon films with different nano- and mesostructure have been deposited from supersonic cluster beams in a low energy deposition regime by exploiting aerodynamic focusing effects. Acoustic phonon propagation in the porous amorphous structure, where disorder acts as a damping factor, is investigated by Brillouin scattering. Depending on the nano- and meso-structure, acoustic phonons can either propagate along the medium, which acts as an elastic continuum at the meso-scale (i.e., hundreds of nm), or turn to overdamped oscillations localized by the structural disorder. Nevertheless, we show that it is always possible to measure the elastic constants of thin and porous films, when other techniques (e.g., nano-indentation) become critical. At the nano-scale, Raman scattering measurements show the typical structure of an amorphous carbon, where the structural disorder is affected by the primeval cluster mass distribution. The synthesis of cluster-assembled carbon films and the in situ Raman characterization in a UHV system allowed to observe the presence of a relevant fraction of sp(1)-hybridized carbon chains (also known as carbynoid structures) embedded in the sp(2) amorphous network |
| Internal Reference: [ID: 2500]
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|
| Cheng, H. P. and Landman, U. |
| Controlled Deposition, Soft Landing, and Glass-Formation in Nanocluster-Surface Collisions. |
| Science v.260, n.5112, pp.1304-1307. (1993). |
| Abstract: Molecular dynamics simulations have been used to investigate the dynamics and redistribution of energy during the impact of a nanocrystal with adsorbed liquid films. Although impact of a 32-molecule NaCl cluster on a solid surface at 3 kilometers per second leads to melting, disordering, fragmentation, and rebounding, the same size cluster colliding with a liquid neon film transfers its energy efficiently to the liquid for a controlled soft landing. Impact on a higher density film (argon) leads to rapid attenuation of the cluster velocity, accompanied by fast heating. Subsequent disordering, melting, and fast cooling by evaporation of argon quench the cluster to a glassy state. These results suggest a method for the controlled growth of nanophase materials |
| Internal Reference: [ID: 2512]
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|
| Cleveland, C. L. and Landman, U. |
| Dynamics of Cluster-Surface Collisions. |
| Science v.257, n.5068, pp.355-361. (1992). |
| Abstract: The structure, energetics, and dynamics of shock conditions generated in a nano-cluster upon impact on a crystalline surface are investigated with molecular-dynamics simulations for a 561-atom argon cluster incident with a velocity of 3 kilometers per second onto a sodium chloride surface. The "piling-up" shock phenomenon occurring upon impact, coupled with cascades of energy and momentum transfer processes and inertial confinement of material in the interior of the cluster, creates a transient medium lasting for about a picosecond and characterized by extreme local density, pressure, and kinetic temperature. The nano-shock conditions and impulsive nature of interactions in the newly formed compressed nonequilibrium environment open avenues for studying chemical reactivity and dynamics catalyzed via cluster impact |
| Internal Reference: [ID: 2516]
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|
| D'Urso, L., Scalisi, A. A., Altamore, C., and Compagnini, G. |
| Formation, evolution, and degradation of nanostructured covalent thin films deposited by low-energy cluster beam deposition. |
| Journal of Materials Research v.21, n.7, pp.1638-1644. (2006). |
| Abstract: Low-energy cluster beam deposition (LECBD) is considered an intriguing technique for obtaining thin layers with well-defined structures at the nano- and mesoscale levels, allowing novel optical, electronic, and magnetic properties. The produced layers are highly porous and extremely reactive due to the high surface to volume ratio and must be characterized with in situ techniques to study their original composition and their evolution once exposed to reactive gases. In this work, we present a general overview and some results on the formation, evolution, and deposition of silicon and carbon cluster beams produced using a laser vaporization source |
| Internal Reference: [ID: 2515]
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|
| Donadio, D., Colombo, L., Milani, P., and Benedek, G. |
| Growth of nanostructured carbon films by cluster assembly. |
| Physical Review Letters v.83, n.4, pp.776-779. (1999). |
| Abstract: The structural properties of nanostructured films obtained by deposition of supersonic beams of carbon clusters are investigated by classical molecular dynamics simulations and compared to experiments. Simulations are shown to predict how the structural properties of the deposited him depend on the actual growth protocol. In particular, it is shown that the assembly of small linear clusters can lead to the formation of random schwarzite structures |
| Internal Reference: [ID: 2241]
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|
| Donadio, D., Colombo, L., and Benedek, G. |
| Elastic moduli of nanostructured carbon films. |
| Physical Review B: Condensed Matter v.70, n.19, pp.195419-195419-4. (2004). |
| Abstract: We have computed the elastic constants of nanostructured carbon films as obtained from classical molecular dynamics simulations of a cluster beam deposition process. The calculations show that the elastic constants of the deposited films are related to the average size of the clusters by a power law. This allows us to extrapolate the present theoretical data to the scale of the experimental results obtained by Brillouin scattering. |
| Internal Reference: [ID: 1804]
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|
| Du, A. J., Pan, Z. Y., Ho, Y. K., Huang, Z., and Zhang, Z. X. |
| Memory effect in the deposition of C-20 fullerenes on a diamond surface. |
| Physical Review B v.66, n.3, pp.035405 (2002). |
| Abstract: In this paper, the deposition of C-20 fullerenes on a diamond (001)-(2x1) surface and the fabrication of C-20 thin film at 100 K were investigated by a molecular dynamics (MD) simulation using the many-body Brenner bond order potential. First, we found that the collision dynamic of a single C-20 fullerene on a diamond surface was strongly dependent on its impact energy. Within the energy range 10-45 eV, the C-20 fullerene chemisorbed on the surface retained its free cage structure. This is consistent with the experimental observation, where it was called the memory effect in "C-20-type" films [P. Melion , Int. J. Mod. B 9, 339 (1995); P. Milani , Cluster Beam Synthesis of Nanostructured Materials (Springer, Berlin, 1999)]. Next, more than one hundred C-20 (10-25 eV) were deposited one after the other onto the surface. The initial growth stage of C-20 thin film was observed to be in the three-dimensional island mode. The randomly deposited C-20 fullerenes stacked on diamond surface and acted as building blocks forming a polymerlike structure. The assembled film was also highly porous due to cluster-cluster interaction. The bond angle distribution and the neighbor-atom-number distribution of the film presented a well-defined local order, which is of sp(3) hybridization character, the same as that of a free C-20 cage. These simulation results are again in good agreement with the experimental observation. Finally, the deposited C-20 film showed high stability even when the temperature was raised up to 1500 K |
| Internal Reference: [ID: 2506]
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|
| Dunlop, A., Jaskierowicz, G., Ossi, P. M., and la-Negra, S. |
| Transformation of graphite into nanodiamond following extreme electronic excitations. |
| Physical Review B: Condensed Matter v.76, n.15, pp.155403-155414. (2007). |
| Abstract: Graphite targets have been irradiated at 90 K and 300 K with 850 MeV and 6 GeV lead ions and with 20–30 MeV fullerene cluster ions in a large range of fluences. Damage creation was studied both by transmission electron microscopy and Raman spectroscopy. The very strong energy density deposited in electronic processes generates a highly excited region around the projectile path. The relaxation of the deposited energy via hydrodynamic expansion and shock-wave propagation leads to the formation of small defective graphitic domains and of nanocrystalline diamond particles. |
| Internal Reference: [ID: 2301]
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|
| Gross, A., Kornweitz, H., Raz, T., and Levine, R. D. |
| Driving high threshold chemical reactions during the compression interlude in cluster surface impact. |
| Chemical Physics Letters v.354, n.5-6, pp.395-402. (2002). |
| Abstract: Molecular-dynamics simulations of a cluster impacting a hard surface show that, initially, the cluster is rapidly compressed and translationally heated. During this short but distinct stage, the cluster is a suitable medium for chemistry: the number of layers of the cluster is not changing; the constituents of the cluster can collide several times and both bimolecular and collisionally driven unimolecular reactions can occur. Hypersonic velocities of impact are needed for a considerable temperature rise. Following compression, the cluster fragments by expanding into a hemispheroidal plume. For supersonic impact. the cluster expands nearer to the surface forming an oblate, omelet-like, hemispheroid. (C) 2002 Elsevier Science B.V. All rights reserved |
| Internal Reference: [ID: 2522]
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|
| Gross, A. and Levine, R. D. |
| Evanescent high pressure during hypersonic cluster-surface impact characterized by the virial theorem. |
| Journal of Chemical Physics v.123, n.19, pp.194307 (2005). |
| Abstract: Matter under extreme conditions can be generated by a collision of a hypersonic cluster with a surface. The ultra-high-pressure interlude lasts only briefly from the impact until the cluster shatters. We discuss the theoretical characterization of the pressure using the virial theorem and develop a constrained molecular-dynamics procedure to compute it. The simulations show that for rare-gas clusters the pressures reach the megabar range. The contribution to the pressure from momentum transfer is comparable in magnitude and is of the same sign as that ("the internal pressure") due to repulsive interatomic forces. The scaling of the pressure with the reduced mechanical variables is derived and validated with reference to the simulations |
| Internal Reference: [ID: 2524]
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|
| Gross, A. and Levine, R. D. |
| Mechanical simulation of the pressure and the relaxation to thermal equilibrium of a hot and dense rare gas cluster. |
| Journal of Physical Chemistry B v.110, n.47, pp.24070-24076. (2006). |
| Abstract: A cold atomic cluster can be very rapidly heated and compressed by a hypersonic impact at a hard surface. The impact can be simulated by computing a classical trajectory for the motion of the atoms. By suddenly confining the hot and dense cluster within a rigid container, it is possible to monitor the time evolution of the force acting on the faces of the container. It is found that the pressure computed this way very rapidly decays to a time-independent value. After a somewhat longer time, this value reproduces the value for the pressure computed as the sum of the kinetic and internal pressures. This agreement is expected for a system in equilibrium. These observations support the conclusion that there is a fast relaxation to thermal equilibrium in these essentially hard-sphere systems. The deviation from equilibrium is primarily due to the propagation of shock waves within the cluster. The equilibrium pressure can reach up to the megabar range |
| Internal Reference: [ID: 2521]
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|
| Henley, S. J., Silva, S. R. P., and Carey, J. D. |
| Surface morphology and evolution of amorphous carbon thin films. |
| Diamond and Related Materials v.16, n.10, pp.1777-1781. (2007). |
| Abstract: The surface morphology of disordered carbon films grown by nanosecond pulsed laser ablation of graphite is reviewed. It is shown that the presence of a background gas can have a profound effect on the plume of material ejected during ablation. At low pressures smooth films are produced but at higher pressures rough films with an evolution from a nodular morphology to a large area cluster-assembled morphology occurs. The surface morphology changes with increasing background pressure as a result of collisions, which reduce the kinetic energy of the ejected material and allow for cluster formation within the plume. It is shown that the energy of some of the carbon ablated species in vacuum can exceed 100 eV The nature of the species present in the plume is discussed in terms of electron-ion recombination and impact ionisation/excitation. The cluster-assembled films are shown to be useful as a scaffold for supporting metal namoparticles to produce substrates for surface enhanced Raman spectroscopy. (c) 2007 Elsevier B.V. All rights reserved |
| Internal Reference: [ID: 2509]
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|
| Hu, Y. H. and Sinnott, S. B. |
| A molecular dynamics study of thin-film formation via molecular cluster beam deposition: effect of incident species. |
| Surface Science v.526, n.3, pp.230-242. (2003). |
| Abstract: Molecular dynamics simulations are used to study thin-film nucleation and growth through the deposition of molecular cluster beams on diamond surfaces. A reactive, empirical bond-order hydrocarbon potential is used to calculate the forces on the atoms. Beams of ethylene (C2H4) molecular clusters, adamantane (C10H16) molecules, and fullerene (C-20) molecules are deposited on hydrogen terminated diamond (1 1 1) surfaces at room temperature. These three beams are chosen because. of the different chemical bonding in the incident particles-van der Waals interactions in the case of the ethylene molecular clusters, pure spa bonds in the case of the adamantane molecules, and covalent sp(2) bonds with distorted p-orbitals in the case of the fullerene molecules. All three beams are deposited on the surface along either the [(1) over bar(1) over bar 2] direction or the [(1) over bar 1 0] direction at incident angles of 0, 15, 45 and 60 from the surface normal. Two deposition energies are considered: a total energy of 400 eV/cluster or molecule and a total energy where the momentum normal to the surface is equivalent to an energy of 400 eV/cluster or molecule: The C-20 is found to be the most efficient species at producing an amorphous thin film while the molecular cluster beam of ethylene is the least efficient. Despite the differences in the chemical bonding in the three incident species, the structures of the resultant thin films are predicted to be similar at these energies. (C) 2002 Elsevier Science B.V. All rights reserved |
| Internal Reference: [ID: 2505]
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|
| Kitagawa, T., Miyauchi, K., Toyoda, N., Tsubakino, H., and Yamada, I. |
| Optimum incident angle of ar cluster ion beam for superhard carbon film deposition. |
| Japanese Journal of Applied Physics Part 1-Regular Papers Short Notes & Review Papers v.43, n.6B, pp.3955-3958. (2004). |
| Abstract: Diamond-like carbon (DLC) films with super hardness (>50GPa) were deposited using Ar cluster ion beams at various oblique incident angles irradiated towards substrates on which C-60 was simultaneously deposited. When the incident angles of Ar cluster ions were from 0degrees to 20degrees, the DLC films had a super hardness of approximately 50 GPa, the hardness three times higher than that of conventional DLC films. Furthermore, the films had a flat surface and a low sp(2) content, which was estimated with a near edge X-ray absorption fine structure (NEXAFS). However, in the range of angles above 40degrees, the carbon films had a lower hardness, a rougher surface, and a higher sp(2) content. Therefore, the incident angles of the Ar cluster ions for obtaining super hardness ranged from 0degrees to 20degrees |
| Internal Reference: [ID: 2513]
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|
| Makarov, G. N. |
| Extreme processes in clusters impacting on a solid surface. |
| Physics-Uspekhi v.49, n.2, pp.117-166. (2006). |
| Abstract: A large high-energy cluster impacting on a solid surface (the number of particles in a cluster N >= 10(2) - 10(6), the collision energy per particle E-col >= 10 - 10(3) eV) forms for a short time (<= 50-500 fs) a medium characterized by extremely high temperature (>= 10(4) - 10(5) K), density (up to 4 to 5 times the solid state value), and pressure (>= 1 - 10 Mbar). As this takes place, the cluster heating rate reaches the value >= 10(15)-10(16) K s(-1). In these extreme conditions, physical and chemical processes that are impossible in thermal equilibrium can occur both in the cluster itself and the collision zone. In this paper, extreme processes induced in clusters as a result of their strong excitation at collisions with a solid surface are reviewed, including ionization, light and charged-particle emission, fragmentation, breaking and making of chemical bonds, microshock wave generation, nuclear fusion, and surface bombardment. Conditions for these processes to proceed are examined and models to describe them discussed. It is shown that the characteristics of the processes depend significantly on the velocity, size, and composition of the cluster, as well as the material and temperature of the surface. Cluster excitation by an impact with a surface and that by a superhigh-power ultra-short laser pulse are compared and practical applications of the above processes are discussed |
| Internal Reference: [ID: 2517]
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|
| Melinon, P., Prevel, B., Dupuis, V., Perez, A., Champagnon, B., Guyot, Y., Boudeulle, M., Pellarin, M., Dugourd, P., and Broyer, M. |
| New phases of amorphous carbon and silicon films obtained by low energy cluster beam deposition. |
| Materials Science and Engineering A-Structural Materials Properties Microstructure and Processing v.217, pp.69-73. (1996). |
| Abstract: Since the last two decades, the physics of free clusters and assembled materials obtained from cluster deposition have opened a large field of potential applications [1]. Molecular dynamics simulations of the thin film growth by low energy cluster beam deposition (LECBD) show that impact energy (i.e. the initial free cluster energy) is the main characteristic parameter [2]. In the LECBD technique, the impact energy is low enough to have a ''soft landing'' process. Thus, the film grows by ballistic deposition of the free clusters ii no rearrangement into clusters or coalescence between abutting supported clusters occurs. In the case of metallic clusters, small particles down to 2 nm diameter coalesce and the memory effect is destroyed [3] whereas covalent clusters present several features allowing the memory effect. Firstly, the covalent bond is highly oriented. Two abutting supported clusters can merge only if their own dangling bonds are in close direction. Secondly, the bond energy is high enough to avoid a large reconstruction because the break between two bonds cost appreciable energy. Thirdly, the equilibrium shape of the clusters present a large proportion of five-fold rings (see for example C-60 having an I-h symmetry). Since the five-fold axis is not compatible with the translation symmetry, the film growth presents a large void component as in pure ballistic deposition. To study the specific properties of these new materials, we have deposited carbon and silicon clusters produced in a laser vaporization source. The properties of the films are studied using several techniques (Raman spectroscopy, XPS, EXAFS, etc.) |
| Internal Reference: [ID: 2511]
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|
| Nordlund, K., Jarvi, T. T., Meinander, K., and Samela, J. |
| Cluster ion-solid interactions from meV to MeV energies. |
| Applied Physics A-Materials Science & Processing v.91, n.4, pp.561-566. (2008). |
| Abstract: The nature of cluster ion-surface interactions changes dramatically with the kinetic energy and mass of the incoming cluster species. In this article we review some recent work on the nature of cluster-surface interactions spanning an energy range from a few tens of meV/atom to several MeV/cluster and cluster sizes in the range of 1-300000 atoms/cluster. We describe five possible distinct outcomes of a single cluster impact event: (i) deposition into a non-epitaxial configuration, (ii) deposition into an epitaxial configuration, (iii) crater formation by liquid flow, (iv) crater formation by hydrostatic pressure, (v) implantation |
| Internal Reference: [ID: 2498]
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|
| Paillard, V., Melinon, P., Dupuis, V., Perez, J. P., Perez, A., and Champagnon, B. |
| Diamondlike carbon films obtained by low energy cluster beam deposition: Evidence of a memory effect of the properties of free carbon clusters. |
| Physical Review Letters v.71, n.25, pp.4170 (1993). |
| Abstract: Free carbon clusters with various selected sizes (C20,C60,C900) have been deposited on different substrates to obtain continuous thin films (thickness ?100 nm). The characterization of nanostructures and electronic structures of the films have been performed using various complementary techniques (atomic force microscopy, transmission electron microscopy, electron energy loss spectroscopy, Raman spectroscopy, Fourier transform infrared spectroscopy). A memory effect of the free carbon cluster properties permits the synthesis of amorphous diamond or graphite films depending on the deposited incident species (C20 or C900, respectively). |
| Internal Reference: [ID: 2520]
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|
| Pan, Z. Y., Man, Z. Y., Ho, Y. K., Xie, J., and Yue, Y. |
| Energy dependence of C-60-graphite surface collisions. |
| Journal of Applied Physics v.83, n.9, pp.4963-4967. (1998). |
| Abstract: The resilience of C-60 fullerene with graphite (0001) surfaces has been investigated by means of molecular dynamics simulations with empirical model potentials. The initial energy of C-60 ranges from 30 to 300 eV. It is shown that when the impact energy is above 60 eV, the rebounding energy of C-60 is nearly independent of the impact energy. The scattering is highly inelastic and the internal excitation energy of the scattered molecule increases with the incident energy. These results are consistent with experiment. Furthermore, the simulations provide insight into the microscopic aspects of the scattering. The rebounding processes at different energies are found to exhibit similar dynamic behavior and the molecular center-of-mass motion can be regarded as moving in a quadratic harmonic potential. All of these results support a schematic picture to describe nonreactive C-60-surface collisions. (C) 1998 American Institute of Physics |
| Internal Reference: [ID: 2510]
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|
| Peng, D. L., Yamada, H., Sumiyama, K., Uchida, T., and Hihara, T. |
| Formation and characterization of high-density Fe cluster-assembled films with soft magnetic behaviors. |
| European Physical Journal D v.34, n.1-3, pp.173-176. (2005). |
| Abstract: High-density, magnetically soft Fe cluster-assembled films were obtained at room temperature by an energetic cluster deposition. Size-monodispersed Fe clusters with the mean cluster size d = 9, 13 and 16 nm were produced using a plasma-gas-condensation technique. Ionized clusters in cluster beam were accelerated electrically and deposited onto the substrate together with neutral clusters from the same cluster source. The morphology, microstructure and magnetic properties of the cluster-assembled films have been studied by an atomic force microscopy, scanning electron microscopy, transmission electron microscopy, and superconducting quantum interference device magnetometer. By increasing the impact energy of the ionized clusters up to 0.6 eV/atom, the Fe cluster-assembled film has a packing fraction of 0.86 +/- 0.03, and reveals a soft magnetic behavior. In addition, it is found that oxidization of the cluster-assembled films is remarkably suppressed with the increase in the density of the films |
| Internal Reference: [ID: 2508]
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|
| Pukha, V. E., Stetsenko, A. N., Dub, S. N., and Lee, J. K. |
| Nanocrystalline diamond thin films deposited from C-60 monoenergetic fullerene ion beam. |
| Journal of Nanoscience and Nanotechnology v.7, n.4-5, pp.1370-1376. (2007). |
| Abstract: Carbon films 250 divided by 500 nm in thickness deposited on Si wafers from mass-selected flow of accelerated C-60 ions with energies of 5.0 +/- 0.1 keV at temperatures of 300 K and 673 K are characterized by TEM and nanoinclentation. On the TEM images of the films deposited at 673 K, nanocrystalline graphite with the typical grain size of similar to 6 nm is observed. The films deposited at 300 K are transparent in visible light. TEM study of these films has revealed structural elements with lattice spacing close to that of diamond and the grain size of about 4 nm. Nanohardness and elastic modulus of the films prepared at a substrate temperature of 300 K were 23.1 +/- 0.2 GPa and 200 +/- 1 GPa, respectively. Possible mechanisms of the carbon films structure formation are suggested in the framework of a hydrodynamic shock wave model |
| Internal Reference: [ID: 2518]
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|
| Raz, T. and Levine, R. D. |
| Fast translational thermalization of extreme disequilibrium induced by cluster impact. |
| Chemical Physics v.213, n.1-3, pp.263-275. (1996). |
| Abstract: Impact heating of cold molecular clusters moving at high velocities dissipates extreme amounts of energy (often more than several eV per atom) in very short times. Molecular dynamics simulations of larger rare gas clusters show that this excess energy is thermalized in 100 fs or less, depending on cluster size and impact velocity. Dissipation is also extensive for smaller clusters but these shatter before being fully thermalized. A simple analytical hard sphere model that recovers this behavior is discussed. The model attributes the ultrafast relaxation to the random orientation of the interatomic distance before the collision, A perfectly ordered army of atoms is indeed found not to relax. Such an array also allows for a dispersion-free propagation of a shock front. The route to equilibrium is therefore the efficient mixing in phase space caused by the velocity components after the collision having a random part. The implications for the maximum entropy description of cluster impact induced chemistry, for the production of electronically excited and ionic species and for electron emission are discussed |
| Internal Reference: [ID: 2523]
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|
| Song, F., Zhou, F., Bu, H., Wang, X., He, L., Han, M., Wan, J., Zhou, J., and Wang, G. |
| Films with discrete nano-DLC-particles as the field emission cascade. |
| Journal of Physics D-Applied Physics v.41, n.4, pp.042001 (2008). |
| Abstract: Films with discrete diamond-like-carbon (DLC) nanoparticles were prepared by the deposition of the carbon nanoparticle beam. Their morphologies were imaged by scanning electron microscopy and atomic force microscopy (AFM). The nanoparticles were found to be distributed on the silicon (100) substrate discretely. Hemispherical shapes of the nanoparticles were demonstrated by the AFM line profile. Electron energy loss spectra were measured and an sp(3) ratio as high as 86% was found. Field-induced electron emission of the as-prepared cascade (nanoDLC/Si) was tested and a current density of 1 mA cm(-2) was achieved at 10.2 V mu m(-1) |
| Internal Reference: [ID: 2501]
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|
| Webb, R. and Chatzipanagiotou, A. |
| The computer simulation of cluster induced desorption of molecules. |
| Nuclear Instruments & Methods in Physics Research Section B-Beam Interactions with Materials and Atoms v.242, n.1-2, pp.413-416. (2006). |
| Abstract: Molecular dynamics computer simulation has been used to investigate the desorption phenomenon that takes place when an energetic molecule or cluster impacts a solid surface. The use of clusters and molecules in secondary ion mass spectrometry (SIMS) is growing as it is becoming evident that the yield of ionised particles is high by comparison with the more conventional single ion sputtering beam. It has also been noticed that there is a much higher desorption of intact molecular ions ejected from the surface. Computer simulations have demonstrated why this should happen. The cluster impact stimulates correlated motion in the surface of the target which encourages the gentle lift off of large molecular species from the target surface. The technique is finding particular uses in allowing SIMS techniques to be used on large organic molecules. What is less known at this point is the efficiency of the cluster beam in lifting off such molecules and the potential for the cluster to break the molecule if it hits it directly. The work presented here shows some early results from a systematic study of the desorption mechanism from a set of simulations of impact points close to and far from an adsorbed molecule. As expected the closer to the adsorbed molecule the cluster impacts the higher the probability for desorption. If the cluster impacts the adsorbed molecule it damages it as expected. However, there is a region such that the cluster does not strike the adsorbed molecule but within which the adsorbed molecule does not get desorbed, but remains intact and still bound substantially to the surface. At first sight this seems to be surprising, but the simulations show that in this region the surface of the target becomes substantially damaged and the broken surface bonds provide a strong capture site for the adsorbed molecule, bonding it more securely to the surface and "pulling" towards the impact site. An energetic particle exchange mechanism is shown in which a sputtered surface particle exchanges with an adsorbate atom in a dynamic collisional process. Descriptions of these processes and the behaviour of the size of this zone are given as a function of the initial cluster energy. (c) 2005 Elsevier B.V. All rights reserved |
| Internal Reference: [ID: 2507]
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| Wegner, K., Piseri, P., Tafreshi, H. V., and Milani, P. |
| Cluster beam deposition: a tool for nanoscale science and technology. |
| Journal of Physics D-Applied Physics v.39, n.22, pp.R439-R459. (2006). |
| Abstract: Gas phase nanoparticle production, manipulation and deposition is of primary importance for the synthesis of nanostructured materials and for the development of industrial processes based on nanotechnology. In this review we present and discuss this approach, introducing cluster sources, nanoparticle formation and growth mechanisms and the use of aerodynamic focusing methods that are coupled with supersonic expansions to obtain high intensity cluster beams with a control on nanoparticle mass and spatial distribution. The implication of this technique for the synthesis of nanostructured materials is also presented and applications are highlighted |
| Internal Reference: [ID: 2502]
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| Yasumatsu, H. and Kondow, T. |
| Reactive scattering of clusters and cluster ions from solid surfaces. |
| Reports on Progress in Physics v.66, n.10, pp.1783-1832. (2003). |
| Abstract: Specific chemical reactions take place in a cluster when it impinges on a solid surface. These intracluster processes ranging from vibrational excitation to atomic rearrangements are called 'cluster-impact' processes, the features of which change specifically with the collision energy and the cluster size. The specificity of the cluster-impact processes arises from impulsive energy transmission to specific modes of the cluster followed by rapid energy redistribution among other degrees of freedom, including those of the surface. In this review, citing several representative collision systems (cluster + surface), we explain the features of a cluster-impact process by dividing the collision energy into several energy ranges, in each of which a characteristic feature is manifested; high vibrational excitation of fullerenes in the lowest energy range, mechanical bond splitting of I-2(-) and a four-centre reaction between N-2 and O-2 in a higher energy range, etc |
| Internal Reference: [ID: 2519]
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| Zhong, Z. R., Wang, X. W., and Feng, X. H. |
| Effects of pressure and temperature on sp(3) fraction in diamondlike carbon materials. |
| Journal of Materials Research v.22, n.10, pp.2770-2775. (2007). |
| Abstract: In this work, formation of diamond coating is studied using large-scale molecular dynamics (MD) simulation. The diamond coating is studied to explore how and to what extent the temperature and pressure affects the deposition structure. To analyze the coating results, the radial distribution function and the fraction of diamond (spa bonds) is calculated. It is found that the spa fraction in the deposition structure increases with the temperature and pressure. When the pressure becomes large enough (10 GPa), the effect of the pressure on the coating structure is quite small and the sp(3) fraction tends to be constant |
| Internal Reference: [ID: 2514]
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