اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدConformal oxide coating of Carbon Nanotubes
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The International Roadmap for Ferroelectric Memories requires three-dimensional integration of high-dielectric materials onto metal interconnects or bottom electrodes by 2010. We report the first integration of high-dielectric oxide films onto carbon nanotube electrodes with an aim of ultra-high integration density of FeRAMs (Tb/in2).
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ultiwalled carbon nanotubes, prepared by both electric arc discharge and chemical vapor deposition methods, show a strong visible light emission in photoluminescence experiments. All the samples employed in the experiments exhibit nearly same super-l
inear intensity dependence of the emission bands on the excitation intensity, and negligible temperature dependence of the central position and the line shapes of the emission bands. Based upon theoretical analysis of the electronic band structures and optical transition, it is suggested that besides the electronic transitions across the fundamental gap, the transitions between pi and sigma conduction bands are the major source of the light emissions. A two-step transition mechanism is proposed.
We use ab initio total-energy calculations to predict the existence of polarons in semiconducting carbon nanotubes (CNTs). We find that the CNTs band edge energies vary linearly and the elastic energy increases quadratically with both radial and with
axial distortions, leading to the spontaneous formation of polarons. Using a continuum model parametrized by the ab initio calculations, we estimate electron and hole polaron lengths, energies and effective masses and analyze their complex dependence on CNT geometry. Implications of polaron effects on recently observed electro- and opto-mechanical behavior of CNTs are discussed.
Light emission from carbon nanotubes is expected to be dominated by excitonic recombination. Here we calculate the properties of excitons in nanotubes embedded in a dielectric, for a wide range of tube radii and dielectric environments. We find that
simple scaling relationships give a good description of the binding energy, exciton size, and oscillator strength.
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We perform ab initio calculations of charged graphene and single-wall carbon nanotubes (CNTs). A wealth of electromechanical behaviors is obtained: (1) Both nanotubes and graphene expand upon electron injection. (2) Upon hole injection, metallic nano
tubes and graphene display a non-monotonic behavior: Upon increasing hole densities, the lattice constant initially contracts, reaches a minimum, and then starts to expand. The hole densities at minimum lattice constants are 0.3 |e|/atom for graphene and between 0.1 and 0.3 |e|/atom for the metallic nanotubes studied. (3)Semiconducting CNTs with small diameters (d <~ 20 A) always expand upon hole injection; (4) Semiconducting CNTs with large diameters (d >~ 20 A) display a behavior intermediate between those of metallic and large-gap CNTs. (5) The strain versus extra charge displays a linear plus power-law behavior, with characteristic exponents for graphene, metallic, and semiconducting CNTs. All these features are physically understood within a simple tight-binding total-energy model.
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