排序方式: 共有24条查询结果,搜索用时 15 毫秒
21.
22.
Z. Liu D. J. Styers-Barnett A. A. Puretzky C. M. Rouleau D. Yuan I. N. Ivanov K. Xiao J. Liu D. B. Geohegan 《Applied Physics A: Materials Science & Processing》2008,93(4):987-993
The nucleation and rapid growth of single-wall carbon nanotubes (SWNTs) were explored by pulsed-laser assisted chemical vapor
deposition (PLA-CVD). A special high-power, Nd:YAG laser system with tunable pulse width (>0.5 ms) was implemented to rapidly
heat (>3×104°C/s) metal catalyst-covered substrates to different growth temperatures for very brief (sub-second) and controlled time periods
as measured by in situ optical pyrometry. Utilizing growth directly on transmission electron microscopy grids, exclusively
SWNTs were found to grow under rapid heating conditions, with a minimum nucleation time of >0.1 s. By measuring the length
of nanotubes grown by single laser pulses, extremely fast growth rates (up to 100 microns/s) were found to result from the
rapid heating and cooling induced by the laser treatment. Subsequent laser pulses were found not to incrementally continue
the growth of these nanotubes, but instead activate previously inactive catalyst nanoparticles to grow new nanotubes. Localized
growth of nanotubes with variable density was demonstrated through this process and was applied for the reliable direct-write
synthesis of SWNTs onto pre-patterned, catalyst-covered metal electrodes for the synthesis of SWNT field-effect transistors. 相似文献
23.
Calcium as the superior coating metal in functionalization of carbon fullerenes for high-capacity hydrogen storage 总被引:1,自引:0,他引:1
We explore theoretically the feasibility of functionalizing carbon nanostructures for hydrogen storage, focusing on the coating of C60 fullerenes with light alkaline-earth metals. Our first-principles density functional theory studies show that both Ca and Sr can bind strongly to the C60 surface, and highly prefer monolayer coating, thereby explaining existing experimental observations. The strong binding is attributed to an intriguing charge transfer mechanism involving the empty d levels of the metal elements. The charge redistribution, in turn, gives rise to electric fields surrounding the coated fullerenes, which can now function as ideal molecular hydrogen attractors. With a hydrogen uptake of >8.4 wt % on Ca32C60, Ca is superior to all the recently suggested metal coating elements. 相似文献
24.
Xiao K Yoon M Rondinone AJ Payzant EA Geohegan DB 《Journal of the American Chemical Society》2012,134(35):14353-14361
The deterministic growth of oriented crystalline organic nanowires (CONs) from the vapor-solid chemical reaction (VSCR) between small-molecule reactants and metal nanoparticles has been demonstrated in several studies to date; however, the growth mechanism has not yet been conclusively understood. Here, the VSCR growth of M-TCNQF(4) (where M is Cu- or Ag-) nanowires is investigated both experimentally and theoretically with time-resolved, in situ X-ray diffraction (XRD) and first-principles atomistic calculations, respectively, to understand how metals (M) direct the assembly of small molecules into CONs, and what determines the selectivity of a metal for an organic vapor reactant in the growth process. Analysis of the real-time growth kinetics data using a modified Avrami model indicates that the formation of CONs from VSCR follows a one-dimensional ion diffusion-controlled tip growth mechanism wherein metal ions diffuse from a metal film through the nanowire to its tip where they react with small molecules to continue growth. The experimental data and theoretical calculations indicate that the selectivity of different metals to induce nanowire growth depends strongly upon effective charge transfer between the organic molecules and the metal. Specifically, the experimental finding that Cu ions can exchange and replace Ag ions in Ag-TCNQF(4) to form Cu-TCNQF(4) nanowires is explained by the significantly stronger chemical bond between Cu and TCNQF(4) molecules than for Ag, due to the strong electronic contribution of Cu d-orbitals near the Fermi level. Understanding how to control the VSCR growth process may enable the synthesis of novel organic nanowires with axial or coaxial p/n junctions for organic nanoelectronics and solar energy harvesting. 相似文献