In order to explore the e®ect of hierarchical porous carbon on the performances of Li-S batteries, we synthesized three kinds of micro-/meso-/macroporous carbon materials with di®erent pore properties by facile hard-template method. Di®erent from the majority of reports on porous carbon ensuing large speci¯c surface area (SSA) and total pore volume, it was found that in the case of identically high sulfur content, the pore size distribution substantially in°uences the performances of Li-S batteries rather than the SSA and total pore volume. Furthermore, in the assembly of micro-/meso-/macropores, the micropore volume ratio to the total pore volume is dominant to the capabilities of batteries. Among the samples, the porous carbon carbonized with the precursor of sucrose at 950 C presents the highest initial discharge speci¯c capacity of 1327 mAh/g and retention of 630 mAh/g over 100 cycles at 0.2C rate along with the best rate capability. This sample possesses the largest micropore volume ratio of 47.54% but a medium SSA of 1217 m 2 /g and inferior total pore volume of 0.54 cm 3 /g. The abundant micropores e®ectively improve the conductivity of dispersed sulfur particles, inhibit the loss of sulfur series and enable the cathode to exhibit superior electrochemical performances.
The epitaxial growth of Cu on Si(111) substrate at room temperature was achieved using the Partially Ionized Beam (PIB) deposition technique in a conventional (10−4 Pa) vacuum without prior in situ cleaning of the substrate or post-annealing of the film. The beam contained ≍2% of Cu self-ions, and a bias of 0 to 4.2 kV was applied to the substrate during deposition. X-ray diffraction studies showed the existence of a twin structure in the epitaxial Cu layer deposited at 1 kV. A mechanism of epitaxial growth of Cu(111) on Si(111) substrate via an η″—Cu3Si intermediate phase is proposed. Based on the crystal structure of η″—Cu3Si, it is demonstrated that the geometrical lattice matching concept provides a simple picture of lattice continuity at the interface in this epitaxial system.
Vapor-deposited films prepared under low adatom mobility conditions commonly exhibit columnar structures. We present the scanning electron microscopy study of Cu films with a thickness around 3.7 μm deposited on rough Al2O3 ceramic substrates and smooth SiO2 substrates. The Cu films were deposited using the partially ionized beam deposition technique under the same deposition conditions. The films deposited on the rough substrates have a typical columnar structure while those deposited on the smooth substrates are noncolumnar. The complete difference in physical structures is due to the difference in the substrate surface roughness. The results indicate that in any structure zone model for the physical structure of the film the substrate surface roughness is an important parameter and cannot be neglected. It is reasoned that the adatom surface diffusion length, which is determined by the deposition conditions, serves as a critical measure for the length scale of surface roughness. At the initial stage of the film growth, the columnar structure develops only for the roughness with a length scale longer than adatom surface diffusion length.
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