The effects of hydrogen plasma pretreatment on the formation of vertically aligned carbon nanotubes

The effects of H₂ plasma pretreatment on the growth of vertically aligned carbon nanotubes (CNTs) by varying the flow rate of the precursor gas mixture during microwave plasma chemical vapor deposition (MPCVD) have been investigated in this study. Gas mixture of H₂ and CH₄ with a ratio of 9:1 was used as the precursor for synthesizing CNTs on Ni-coated TiN/Si(1 0 0) substrates. The structure and composition of Ni catalyst nanoparticles were investigated by using scanning electron microscopy (SEM) and cross-sectional transmission electron microscopy (XTEM). Results indicated that, by manipulating the morphology and density of the Ni catalyst nanoparticles via changing the flow rate of the precursor gas mixture, the vertically aligned CNTs could be effectively controlled. The Raman results also indicated that the intensity ratio of the G and D bands (I_D/I_G) is decreased with increasing gas flow rate. TEM results suggest H₂ plasma pretreatment can effectively reduce the amorphous carbon and carbonaceous particles and, thus, is playing a crucial role in modifying the obtained CNTs structures.     

The electrical properties and phase transformation of PLZST 2/85/13/2 antiferroelectric thin films on different bottom electrode

Pb_0.97La_0.02(Zr_0.85Sn_0.13Ti_0.02)O₃ (PLZST 2/85/13/2) antiferroelectric thin films were deposited on Pt(111)/Ti/SiO₂/Si and LaNiO₃(LNO)/SiO₂/Si substrates through a modified sol-gel process. The phase structure and microstructure of PLZST 2/85/13/2 antiferroelectric thin films were analysed by x-ray diffraction (XRD), scanning electron microcopy (SEM) and field-emission SEM (FE-SEM). The antiferroelectric nature of the PLZST 2/85/13/2 thin films on two electrodes was demonstrated by the C-V (capacitance-voltage) and P-E (polarization-electric field) measurement. The maximum polarizations for PLZST 2/85/13/2 films on Pt and LNO electrodes were 42 and 18 μC/cm², respectively. The temperature dependence of the dielectric property of the PLZST 2/85/13/2 films was measured under different dc electric fields. Also, the phase transformation of the PLZST 2/85/13/2 films was studied in detail as a function of temperature and dc electric field.     

Growth and characterization of c-plane AlGaN on γ-LiAlO2

This study demonstrates a pure c-plane AlGaN epilayer grown on a γ-LiAlO₂ (1 0 0) (LAO) substrate with an AlN nucleation layer grown at a relatively low temperature (LT-AlN) by metal-organic chemical vapor deposition (MOCVD). The AlGaN film forms polycrystalline film with m- and c-plane when the nucleation layer grows at a temperature ranging from 660 to 680 °C. However, a pure c-plane AlGaN film with an Al content of approximately 20% can be obtained by increasing the LT-AlN nucleation layer growth temperature to 700 °C. This is because the nuclei density of AlN increases as the growth temperature increases, and a higher nuclei density of AlN deposited on LAO substrate helps prevent the deposition of m-plane AlGaN. Therefore, high-quality and crack-free AlGaN films can be obtained with a (0 0 0 2) ω-rocking curve FWHM of 547 arcsec and surface roughness of 0.79 nm (root-mean-square) using a 700-°C-grown LT-AlN nucleation layer.     

More spherical large fullerenes and multi-layer fullerene cages

According to the experimental investigation, the carbon nano-particles have spherical multi-layer structure (also called onion-like carbon structure). Theoretically, the optimum structures of these large fullerenes contain highly faceted shapes with icosahedral symmetry. This discrepancy in structure may be attributed to the formation mechanism. Thus, a method is devised to construct spherical large fullerenes (C₂₄₀, C₅₄₀, C₉₆₀, C₂₁₆₀, C₂₉₄₀, C₃₈₄₀, C₄₈₆₀) by using the triangular motif. The 5–7–5–7 shape defect is applied in this method for assembling the large spherical fullerenes which could transform the graphene sheet to a spherical motif via SW rearrangement. The geometry-optimized structures of large spherical fullerenes have been generated by molecular mechanics calculation. Then, the average radius and standard deviation of these large fullerenes were obtained to verify the spherical shape. The multi-layer fullerene with spherical shape was confirmed by the TEM observation. According to the structure analysis, the distance between two neighboring encapsulating carbons is about 3.5 Å, which approximately coincides with the distance between two layers of graphite. The van der Waals force per carbon atom and of multi-layer fullerene with the spherical shape generated by force field calculation, predict their relative stability.     

A theory for grain-size reduction in granular flows of spheres

Summary We derive a kinetic theory for homogeneous granular shear flows of identical spheres in which collisions between particles result in small fractures on their peripheries and, over time, effectively reduce their average diameter. In obtaining statistically averaged constitutive relations for the rates of energy dissipation and mass loss, we employ the integral expression derived by Jenkins and Savage [1983] for the collisional source of a particle property. However, in calculating the stress, we modify their expression for the collisional flux in order to ensure that the stress is symmetric when the particles interact through central forces. The constitutive relations are employed in the balance equations for mass, momentum, and energy in order to predict, for a fixed shear rate and particle number density, the manner in which the solid fraction, granular temperature, and induced stresses vary with time.

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Zusammenfassung Wir entwickeln eine kinetische Theorie für die homogene Scherströmung von identischen Kugeln, in welcher die Zusammenstösse der Teilchen kleine Risse in ihrer Oberfläche verursachen und sich dadurch ihr mittlerer Durchmesser mit der Zeit verringert. Um die statistisch gemittelten konstitutiven Beziehungen für die Energiedissipations- und Massenverlustraten zu erhalten, verwenden wir den von Jenkins und Savage [1983] hergeleiteten Integralausdruck für die von den Kollisionen verursachte Quellenstärke einer Teilchenzustandsgrösse. Bei der Berechnung der Spannung verwenden wir jedoch einen abgeänderten Ausdruck für den Fluss durch Kollision; dadurch wird sichergestellt, dass der Spannungstensor symmetrisch ist, wenn die Kontaktkraft zwischen den Teilchen normal zur Kontaktebene wirkt. Die konstitutiven Beziehungen werden in die Gleichungen für die Erhaltung von Masse, Impuls und Energie eingesetzt, um zu berechnen, wie sich der Festkörperanteil, die Granulartemperatur und die induzierten Spannungen als Funktion der Zeit verändern; der Geschwindigkeitsgradient und die Anzahl Teilchen pro Volumen sind dabei konstant.

     

Induction of differentiation of human leukemia cells by various combinations of cytokines and low-molecular-weight inducers

To explore agents for differentiation therapy of leukemias, various combinations of cytokines and low-molecular-weight inducers were examined for differentiation-inducing activity toward three kinds of human leukemia-derived cell lines. The strongest differentiation inducing activity on promyelocytic HL60 cells and histiocytic U937 cells was obtained by combining recombinant tumor necrosis factor (rTNF), interferon-gamma (IFN-gamma), retinoic acid (RA), and 1 alpha,25-dihydroxyvitamin D3 (1 alpha,25(OH)2D3). For myeloblastic ML1 cells, the combination of rTNF, IFN-gamma, and RA had the strongest differentiation-inducing activity.     

A lab-scale digital acoustic emission system for source location

Experimental Techniques - A PC-based, fully digital and lab-scale acoustic emission system for 3-D source location was set up. To get good results, a sampling rate higher than the Nyquist frequency...