31 research outputs found
Microstructure of ZnO Thin Films Deposited by High Power Impulse Magnetron Sputtering
High power impulse magnetron sputtering was used to deposit thin (~ 100 nm) zinc oxide (ZnO) films from a ceramic ZnO target onto substrates heated to 150 °C. The resulting films had strong crystallinity, highly aligned (002) texture and low surface roughness (root mean square roughness less than 10 nm), as determined by X-ray diffraction, transmission electron microscopy, scanning electron microscopy and atomic force spectroscopy measurements. Deposition pressure and target–substrate distance had the greatest effect on film microstructure. The degree of alignment in the films was strongly dependent on the gas pressure. Deposition at pressures less than 0.93 Pa resulted in a bimodal distribution of grain sizes. An initial growth layer with preferred orientations (101) and (002) parallel to the interface was observed at the film–substrate interface under all conditions examined here; the extent of that competitive region was dependent on growth conditions. Time-resolved current measurements of the target and ion energy distributions, determined using energy resolved mass spectrometry, were correlated to film microstructure in order to investigate the effect of plasma conditions on film nucleation and growth
Self-Assembly, Molecular Packing, and Electron Transport in n-Type Polymer Semiconductor Nanobelts
Improved Dehydrogenation Properties of Ti-Doped LiAlH<sub>4</sub>: Role of Ti Precursors
The dehydrogenation properties of LiAlH<sub>4</sub> doped
with
different Ti precursors (Ti, TiO<sub>2</sub>, and TiCl<sub>3</sub>) via ball milling are investigated. The results not only show significant
decreases in the decomposition temperatures (<i>T</i><sub>dec</sub>) and activation energies (<i>E</i><sub>A</sub>) of the first two dehydrogenation reaction steps of LiAlH<sub>4</sub> by doping with TiO<sub>2</sub> or TiCl<sub>3</sub>, but also reveal
how each Ti precursor affects the dehydrogenation process. Although
doping LiAlH<sub>4</sub> with TiCl<sub>3</sub> induced the largest
decrease in <i>T</i><sub>dec</sub> and <i>E</i><sub>A</sub>, TiO<sub>2</sub>-doped LiAlH<sub>4</sub> produced a
decrease in <i>T</i><sub>dec</sub> and <i>E</i><sub>A</sub> that is quite close to the TiCl<sub>3</sub>-doped sample
as well as superior short-term stability, suggesting that doping with
TiO<sub>2</sub> has certain advantages over doping with TiCl<sub>3</sub>. Further, the underlying mechanisms associated with the Ti precursors
during the dehydrogenation reaction of LiAlH<sub>4</sub> have been
studied using quasi in situ X-ray photoelectron spectroscopy. The
results reveal that the Ti<sup>4+</sup> and Ti<sup>3+</sup> reduction
processes and the segregation of Li cations to the surface of LiAlH<sub>4</sub> during ball milling play critical roles in the improved dehydrogenation
properties observed
Catalytic influence of Ni-based additives on the dehydrogenation properties of ball milled MgH 2
Heterogeneous nucleation of thermal storage material LiNO3·3H2O from stable lattice-matched nucleation catalysts
Effects of Titanium-Containing Additives on the Dehydrogenation Properties of LiAlH<sub>4</sub>: A Computational and Experimental Study
Metal hydrides are attractive materials for use in thermal
storage
systems to manage excessive transient heat loads and for hydrogen
storage applications. This paper presents a combined computational
and experimental investigation of the influence of Ti, TiO<sub>2</sub>, and TiCl<sub>3</sub> additives on the dehydrogenation properties
of milled LiAlH<sub>4</sub>. Density functional theory (DFT) is used
to predict the effect of Ti-containing additives on the electronic
structure of the region surrounding the additive after its adsorption
on the LiAlH<sub>4</sub> (010) surface. The electron distribution
and charge transfer within the LiAlH<sub>4</sub>/additive system is
evaluated. Electronic structure calculations predict covalent-like
bonding between the Ti atom of the adsorbate and surrounding H atoms.
The hydrogen (H) binding energy associated with the removal of the
first H from the modified LiAlH<sub>4</sub> surface is calculated
and compared with experimental dehydration activation energies. It
is seen that the weaker H binding corresponds to the larger amount
of charge transferred from the Ti atom to adjacent H atoms. A reduction
in charge transfer between the Al atom and surrounding H atoms is
also observed when compared to charge transfer in the unmodified LiAlH<sub>4</sub> surface. This reduction in charge transfer between Al–H
weakens the covalent bond within the [AlH<sub>4</sub>]<sup>−</sup> tetrahedron, which in turn reduces the dehydrogenation temperature
exhibited by LiAlH<sub>4</sub> when Ti-containing additives are used