We describe a simple process for the fabrication of ultrathin, transparent, optically homogeneous, electrically conducting films of pure single-walled carbon nanotubes and the transfer of those films to various substrates. For equivalent sheet resistance, the films exhibit optical transmittance comparable to that of commercial indium tin oxide in the visible spectrum, but far superior transmittance in the technologically relevant 2- to 5-micrometer infrared spectral band. These characteristics indicate broad applicability of the films for electrical coupling in photonic devices. In an example application, the films are used to construct an electric field-activated optical modulator, which constitutes an optical analog to the nanotube-based field effect transistor.
Rechargeable Li-ion batteries are currently being explored for high-power applications such as electric vehicles. However, in order to deploy Li-ion batteries in next-generation vehicles, it is essential to develop electrodes made from durable, nontoxic, and inexpensive materials with a high charge/discharge rate and a high reversible capacity. Transition metal oxides such as Fe
We exploit the low density of electronic states in single wall carbon nanotubes to demonstrate active, electronic modulation of their Fermi level offset relative to n-type silicon in a nanotube-Si (metal-semiconductor) Schottky junction solar cell. Electronic modulation of the Fermi level offset, the junction interface dipole and a field developed across the depletion layer modifies the built-in potential in the device and its power generation characteristics. As produced (before modulation) devices exhibit ∼8.5% power conversion efficiency (PCE). With active modulation the PCE is continuously and reversibly changed from 4 to 11%.
Using atomic layer deposition of Al 2 O 3 coating, improved high-voltage cycling stability has been demonstrated for the layered nickel-manganese-cobalt pseudo-ternary oxide, LiNi 0.4 Mn 0.4 Co 0.2 O 2 . To understand the effect of the Al 2 O 3 coating, electrochemical impedance spectroscopy, operando synchrotron-based X-ray diffraction, and operando X-ray absorption near edge fine structure spectroscopy have been utilized to characterize the structure and chemistry evolution of the LiNi 0.4 Mn 0.4 Co 0.2 O 2 cathode during cycling. Using this combination of techniques, we show that the Al 2 O 3 coating successfully mitigates the strong side reactions of the active material with the electrolyte at higher voltages (> 4.4 V), without restricting the uptake and release of Li ions. The impact of the Al 2 O 3 coating is also revealed at beginning of lithium deintercalation, with an observed delay in the evolution of oxidation and coordination environment for the Co and Mn ions in the coated electrode due to protection of the surface. This protection prevents the competing side reactions of the electrolyte with the highly active Ni oxide sites, promoting charge compensation via the oxidation of Ni and enabling high-voltage cycling stability.
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