Cluster size effect on reactive sputtering by fluorine cluster impact using molecular dynamics simulation

Computer Simulation of Radiation Effects in SolidsThe mechanism of high-yield sputtering induced by reactive cluster impact was investigated using molecular dynamics (MD) simulations. Various sizes of fluorine clusters were radiated on clean silicon surface. At an incident energy of 1 eV/atom, F atom and F2 molecule are only adsorbed on the surface and sputtering of Si atom does not occur. However, fluorine cluster, which consists of more than several tens molecules causes sputtering. In this case, most of Si atoms are sputtered as fluorinated material such as SiFx. This effect is due to the fact that cluster impact induces high-density particle and energy deposition, which enhances both formation of precursors and desorption of etching products. The deposition of atoms and energy becomes denser as the incident cluster size increases, so that larger clusters have shown higher sputtering yield.Articl

Visualization of the non-steady state oblique detonation wave phenomena around hypersonic spherical projectile

We studied experimentally the shock waves and combustion waves generated by a hypersonic spherical projectile in an explosive mixture. An acetylene/oxygen mixture diluted with argon (2C2H2 + 5O2 + 7Ar) was used with various initial pressures (detonation cell sizes) to observe optically with a shadowgraph imaging system a shock-induced combustion (SIC), a stable oblique detonation wave (ODW), and a wave called a Straw Hat type consisting of a strong SIC and ODW. The criticality of stabilizing an ODW around a projectile is expressed by the ratio of the projectile diameter, d, to the cell size, λ, as d/λ = 3.63–4.84. Although the Straw Hat type wave in the vicinity of criticality is an unstable phenomena, it has been mainly observed by a single frame picture to date, so that it is difficult to discuss the time history of its wave structure. In this study, it was remarkable to directly carry out continuous optical observations using a high speed video camera which can continuously film 100 pictures with a 1 μs frame speed so as to allow an investigation of the sustaining mechanism of the unstable wave structure. Our results allowed the identification of an increase in unsteadiness in the relative distance between the projectile fronts and the transition points to an ODW as the time increased. They also showed local explosions in the SIC region near transition point transformed the ODW front upstream

Thrust Measurement of a Multicycle Partially Filled Pulse Detonation Rocket Engine

In the present research, we experimentally verified the partial-fill effect in a multicycle pulse detonation rocketengine. The intermittent thrust of a pulse detonation rocket engine was measured by using a spring-dampermechanism that smoothed this intermittent thrust in the time direction. The intermittent mass flow rates wereassessed by gas cylinder pressure or mass difference measurement. The maximum specific impulse was 305 9 s atan ethylene and oxygen propellant fill fraction of 0:130 0:004. When the fill fraction was greater than 0.130, thespecific impulse was increased as the partial-fill fraction was decreased. When the fill fraction was less than 0.130, thespecific impulse was sharply decreased as the partial-fill fraction was decreased. This decrease was due to diffusionbetween propellant and purge gases and the short length of the transition from deflagration to detonation. Themulticycle pulse detonation rocket engine had a partial-fill effect that may have been mainly due to the suctioned airand was consistent with the single-cycle partial-fill model of Endo et al

Propulsive Performance and Heating Environment of Rotating Detonation Engine with Various Nozzles

Geometric throats are commonly applied to rocket combustors to increase pressure and specific impulse. This paper presents the results from thrust measurements of an ethylene/gas-oxygen rotating detonation engine with various throat geometries in a vacuum chamber to simulate varied backpressure conditions in a range of 1.1–104 kPa. For the throatless case, the detonation channel area was regarded to be equivalent the throat area, and three throat-contraction ratios were tested: 1, 2.5, and 8. Results revealed that combustor pressure was approximately proportional to equivalent throat mass flux for all test cases. Specific impulse was measured for a wide range of pressure ratios, defined as the ratio of the combustor pressure to the backpressure in the vacuum chamber. The rotating detonation engine could achieve almost the same level of optimum specific impulse for each backpressure, whether or not flow was squeezed by a geometric throat. In addition, heat-flux measurements using heat-resistant material are summarized. Temporally and spatially averaged heat flux in the engine were roughly proportional to channel mass flux. Heat-resistant material wall compatibility with two injector shapes of doublet and triplet injection is also discussed

Immunohistochemical Analysis of Connexin43 Expression in Infertile Human Testes

Connexin43 (Cx43) is abundantly expressed in mammalian testes and implicated in the regulation of cell-to-cell interaction between germ cells and Sertoli cells, which is essential to the normal process of spermatogenesis. In the present study, we investigated the relation between Cx43 expression and the degree of spermatogenesis in infertile human testes. Immunohistochemical analysis of Cx43 was performed on testicular biopsies from 29 patients with azoospermia (n=23) and severe oligospermia (n=6), who gave informed consent to this experiment. The degree of testicular spermatogenesis was evaluated by Johnsen score. In the interstitium, immunostaining for Cx43 was localized to some focal parts of plasma membrane between neighboring Leydig cells. In seminiferous tubules with normal spermatogenesis, Cx43 expression was found between Sertoli cells and germ cells. However, Cx43 expression in maturation arrest was decreased and located mainly in the basal compartment of seminiferous tubules. Finally, there was a significant positive correlation between histological score of spermatogenesis and intensity of Cx43 (p=0.0294). These data suggest that the alteration of Cx43 expression may be involved in spermatogenic impairment, and that the communication between Sertoli cells and germ cells through Cx43 may be important for maturation of spermatogenesis

Molecular dynamics simulations of sequential cluster ion impacts

Proceedings of the Seventh International Conference on Computer Simulation of Radiation Effects in SolidsMolecular dynamics (MD) simulations of cluster and solid target collisions were performed in order to understand the relationship between surface deformation processes and cluster sizes. MD simulations of single impacts of clusters with various sizes showed that, when a cluster size is less than 10 000 atoms, a crater-like damage could be caused at 20 keV of total energy, while no damage was observed at Ar10 000 and Ar20 000 clusters. The surface morphology change was examined by MD of sequential irradiation of Ar clusters under various conditions. When the initial roughness of the surface was about 10 Å in r.m.s. and the total incident energy was 20 keV, the surface roughness was reduced with the impact of Ar13 333 or larger cluster. The MD results give information about the final value and decay speed of surface roughness, which are required to optimize the cluster ion irradiation condition for various nano-scale modification processes.Articl

Molecular dynamics study of the angular dependence of reactive cluster impacts

The Application of Accelerators in Research and Industry — Proceedings of the Eighteenth International Conference on the Application of Accelerators in Research and Industry (CAARI 2004)Articl

Molecular dynamics simulations of surface modification and damage formation by gas cluster ion impacts

Ion Beam Modification of Materials - Proceedings of the 14th International Conference on Ion Beam Modification of MaterialsDamage formation process by gas cluster impact was studied using molecular dynamics simulations. Ar gas clusters with various sizes (several tens to several thousand) and energies (several to several tens keV, totally) were irradiated on Si substrates. The relationship between mean damage depth, incident energy and cluster size was examined and the model and conditions to cause damage by cluster impact were discussed.Articl