Search

The production of $D^{\ast + }$ , D 0, D + , D s + and $\Lambda_c^ + $ charm hadrons and their antiparticles in e p scattering at HERA was measured with the ZEUS detector using an integrated luminosity of $79 \rm {pb}^{-1}$ . The measurement has been performed in the photoproduction regime with the exchanged-photon virtuality $Q^2 < 1 \rm {GeV}^2$ and for photon-proton centre-of-mass energies in the range $130 < W < 300 \rm {GeV}$ . The charm hadrons were reconstructed in the range of transverse momentum $p_T(D,\Lambda_c) > 3.8 \rm {GeV}$ and pseudorapidity $\vert\eta(D,\Lambda_c)\vert < 1.6$ . The production cross sections were used to determine the ratio of neutral and charged D-meson production rates, $\smash{R_{u/d}}$ , the strangeness-suppression factor, $\gamma_s$ , and the fraction of charged D mesons produced in a vector state, $\smash{P^d_{\rm v}}$ . The measured $\smash{R_{u/d}}$ and $\smash{\gamma_s}$ values agree with those obtained in deep inelastic scattering and in e + e - annihilations. The measured $\smash{P^d_{\rm v}}$ value is smaller than, but consistent with, the previous measurements. The fractions of c quarks hadronising as a particular charm hadron, $f(c \rightarrow D, \Lambda_c)$ , were derived in the given kinematic range. The measured open-charm fragmentation fractions are consistent with previous results, although the measured $f(c\rightarrow D^{* + })$ is smaller and $f(c\rightarrow \Lambda_c^ + )$ is larger than those obtained in e + e - annihilations. These results generally support the hypothesis that fragmentation proceeds independently of the hard sub-process. [ABSTRACT FROM AUTHOR]

Highly dispersed cobalt atoms were deposited on porous alumina particles using atomic layer deposition (ALD) with a CoCp2/H2 chemistry at approximately 7 wt%. H2 did not completely reduce the cyclopentadienyl organic ligands bound to deposited Co atoms at ALD reaction conditions. A sharp decline in Co deposited per cycle for two or more ALD cycles indicates that much of the Al2O3 surface is sterically blocked from further CoCp2 deposition after the first CoCp2 exposure. Temperature programmed reduction confirmed that the adsorbed precursor organic ligands persist after H2 exposures during ALD and temperatures as high as 500 °C are required to fully reduce the organic ligands to CH4. High resolution, element sensitive imaging showed that Co atoms were dispersed on the Al2O3 surface and could deposit in previously unobserved multiple growth morphologies, specifically layers that were continuous over several angstroms or discrete nanoparticles. Density functional theory calculations were used to examine Co atom adsorption, show the altered haptic binding of cracked Cp ligands, and to calculate the thermodynamics of Cp ligand decomposition. The lateral steric hindrance between organic ligands bound to deposited Co atoms, Cp ligand decomposition mechanism, and local Al2O3 surface termination all likely determine the observed Co growth morphology during initial ALD cycles. [ABSTRACT FROM AUTHOR]