Stability and Reliability of an Electrical Device Employing Highly Crystalline Single-Walled Carbon Nanotubes as a Field Emitter

Carbon nanomaterial is drawing keen interest from researchers as well as materials scientists. Carbon nanotubes (CNTs)—and their nanoscale needle shape—offering chemical stability, thermal conductivity, and mechanical strength exhibit unique properties as a quasi-one-dimensional material. Among the expected applications, field emission electron sources appear the most promising industrially and are approaching practical utilization. However, efforts to construct a field emission (FE) cathode with single-walled carbon nanotubes (SWCNTs) have so far only helped average out a non-homogeneous electron emitter plane with large FE current fluctuations and a short emission life-time because they failed to realize a stable emission current owing to crystal defects of the carbon network in CNTs. The utilization of CNTs to obtain an effective cathode, one with a stable emission and low FE current fluctuation, relies on the ability to disperse CNTs uniformly in liquid media. In particular, highly crystalline SWCNTs hold promise to obtain good stability and reliability. The author successfully manufactured highly crystalline SWCNTs-based FE lighting elements that exhibit stable electron emission, a long emission life-time, and low power consumption for electron emitters. This FE device employing highly crystalline SWCNTs has the potential for conserving energy through low power consumption in our habitats

Conductive Effect of Increased Crystallinity of Single-Walled Carbon Nanotubes as Field Emitter

Carbon nanotubes (CNTs) exhibit chemical stability, thermal conductivity, mechanical strength, and unique properties as a quasi-one-dimensional material with nanoscale needle shape. Field-emission (FE) electron sources appear to be the most promising industrial application for CNTs, and their deployment is approaching practical utilization. So far, efforts to construct an FE cathode with single-walled carbon nanotubes (SWCNTs) have only managed to average out the large FE current fluctuations in a nonhomogeneous electron emitter plane and the short emission lifetime because the crystal defects in the carbon network in CNTs prevent the realization of a stable emission current. The utilization of CNTs to obtain an effective electronic device, one with stable emission and low FE current fluctuations, relies on the high crystallization of CNTs, a task that can be fulfilled by using highly crystalline SWCNTs (hc-SWCNTs). The author could succeed in developing a model of the flow of electrons through the inside of the hc-SWCNTs and SWCNTs with crystal defects to the outside using the fluctuations of the tunneling current. Therefore, we expect that the hc-SWCNTs are used as field emitters with stable emission and low power consumption for saving energy

Excitons in soliton and bipolaron lattice states of doped Peierls systems

Exciton effects on soliton and bipolaron lattice states are investigated using an electron-lattice Peierls model with long-range Coulomb interactions. The Hartree-Fock (HF) approximation and the single-excitation configuration-interaction (single-CI) method are used to obtain optical absorption spectra. We discuss the following properties: (1) The attraction between the excited electron and the remaining hole makes the excitation energy smaller when the correlations are taken into account by the single-CI. The oscillator strengths of the lower excited states become relatively larger than in the HF calculations. (2) We look at variations of relative oscillator strengths of two or three kinds of excitons described by the single-CI. While the excess-electron concentration is small, the ratio of the oscillator strengths of the exciton with the lowest energy, which is calculated against the total electronic excitation oscillator strengths, increases almost linearly. The oscillator strengths accumulate at this exciton as the concentration increases.Comment: See http://www.etl.go.jp/People/harigaya/ 1) The pointers which link to physics related WWW sites - especially in Japan - are summarized in the "WWW for Physics" section: http://www.etl.go.jp/People/harigaya/PHYS_WWW.html 2) The obtained PHYS-FAQ documents (related to the fj.sci.physics - fj means 'from Japan' -) and several useful pointers are listed in the "Physics Forum" section: http://www.etl.go.jp/People/harigaya/PHYS_FAQ.htm

Selection of Optimum Binder for Silicon Powder Anode in Lithium-Ion Batteries Based on the Impact of Its Molecular Structure on Charge–Discharge Behavior

The high-capacity and optimal cycle characteristics of the silicon powder anode render it essential in lithium-ion batteries. The authors attempted to obtain a composite material by coating individual silicon particles of µm-order diameter with conductive carbon additive and resin to serve as a binder of an anode in a lithium-ion battery and thus improve its charge–discharge characteristics. Structural strain and hardness due to stress on the binder resin were alleviated by the adhesion between silicon or copper foil as a collector and the binder resin, preventing the systematic deterioration of the anode composite matrix immersed in electrolyte compositions including Li salt and fluoride. Moreover, the binder resin itself was confirmed to play a role of active material with occlusion and release of Li-ion. Furthermore, charge–discharge characteristics of the silicon powder anode active material strongly depend on the type of binder resin used; therefore, the binder resin used as composite material in rechargeable batteries should be carefully selected. Some resins for binding silicon particles were investigated for their mechanical and electrochemical properties, and a carbonized polyimide obtained a good charge–discharge cyclic property in a lithium-ion battery