Effect of Carbon Nanotube Aqueous Dispersion Quality on Mechanical Properties of Cement Composite

An effect of the quality of carbon nanotube (CNT) dispersions added to cement on paste mechanical properties has been studied. High-quality dispersions of few-walled CNT (FWCNTs) were produced in two steps. First, FWCNTs were functionalized in a mixture of nitric and sulfuric acids (70 wt.% and 96 wt.%, resp.) at 80 ∘C . Second, functionalized FWCNTs were washed out by acetone to remove carboxylated carbonaceous fragments (CCFs) formed during CNT oxidation. Mechanical test results showed 2-fold increase in the compressive strength of the cement paste prepared from the dispersion of acetone-washed functionalized FWCNTs, which is believed to occur due to the chemical interaction between cement matrix and functional groups (–COOH and –OH). Utilisation of unwashed FWCNTs led to a marginal improvement of mechanical properties of the cement pastes, whereas surfactant-treated functionalized FWCNT dispersions only worsened the mechanical properties.Peer reviewe

Carbon Nanotube/Nanofibers and Graphite Hybrids for Li-Ion Battery Application

To improve the electrical conductivity of negative electrodes of lithium ion batteries, we applied a direct CVD synthesis of carbon nanomaterials on the surface of graphite particles. To prepare a catalyst, two alternative approaches were utilized: colloidal nanoparticles (NPs) and metal (Ni and Co) nitrate salt precursors deposited on the graphite surface. Both colloidal and precursor systems allowed us to produce carbon nanofibers (CNFs) on the graphite surface with high coverage under the optimum CVD conditions. Electrical measurements revealed that the resistivity of the actual electrodes fabricated from CNFs coated graphite particles was about 40% lower compared to the original pristine graphite electrodes.Peer reviewe

Single-Walled Carbon Nanotube Network Field Effect Transistor as a Humidity Sensor

Single-walled carbon nanotube network field effect transistors were fabricated and studied as humidity sensors. Sensing responses were altered by changing the gate voltage. At the open channel state (negative gate voltage), humidity pulse resulted in the decrease of the source-drain current, and, vice versa, the increase in the source-drain current was observed at the positive gate voltage. This effect was explained by the electron-donating nature of water molecules. The operation speed and signal intensity was found to be dependent on the gate voltage polarity. The positive or negative change in current with humidity pulse at zero-gate voltage was found to depend on the previous state of the gate electrode (positive or negative voltage, respectively). Those characteristics were explained by the charge traps in the gate dielectric altering the effective gate voltage, which influenced the operation of field effect transistor.Peer reviewe

Freeze-Dried Carbon Nanotube Aerogels for High-Frequency Absorber Applications

A novel technique for millimeter wave absorber material embedded in a metal waveguide is proposed. The absorber material is a highly porous carbon nanotube (CNT) aerogel prepared by a freeze-drying technique. CNT aerogel structures are shown to be good absorbers with a low reflection coefficient, less than -12 dB at 95 GHz. The reflection coefficient of the novel absorber is 3-4 times lower than that of commercial absorbers with identical geometry. Samples prepared by freeze-drying at -25 degrees C demonstrate resonance behavior, while those prepared at liquid nitrogen temperature (-196 degrees C) exhibit a significant decrease in reflection coefficient, with no resonant behavior. CNT absorbers of identical volume based on wet-phase drying preparation show significantly worse performance than the CNT aerogel absorbers prepared by freeze-drying. Treatment of the freeze-dried CNT aerogel with n- and p-dopants (monoethanolamine and iodine vapors, respectively) shows remarkable improvement in the performance of the waveguide embedded absorbers, reducing the reflection coefficient by 2 dB across the band.QC 20180904</p

Millimeter Wave Beam Steering Based on Optically Controlled Carbon Nanotube Layers

In this paper, the dielectric constant changing of thin carbon nanotube layers under light illumination was used for phase shifter development in dielectric rod waveguides. This designed phase shifter was introduced to the dielectric rod waveguide dual-antenna array. The measurements of the beam steering at 90 GHz of the dielectric rod antenna array, covered with carbon nanotubes, were carried out.QC 20181119</p

Carbon Nanotube Layer Modeling for Computer Simulation of Optically Controlled Phase Shifters

We propose an approach for efficient modeling of thin carbon nanotube layers for full-wave device simulations without increasing the number of simulation mesh cells. A surface impedance, used in computer simulations, is calculated from the dielectric constant of the material. The dielectric constant is modeled by a Drude–Lorentz resonance, fitted to experimental results. The approach allowed to study the nanotube-induced losses and finite-size resonance effects in optically-controlled, dielectric rod waveguide-based phase shifters. The correctness of the model was verified both by the simulated and the measured S-parameters in the W-band.QC 20181211</p

Millimeter Wave Phase Shifter Based on Optically Controlled Carbon Nanotube Layers

Surfaces with tunable impedance are usually lossy at high frequencies, which limits the design of millimeter wave and Terahertz devices. This work experimentally demonstrates a phase shifter based on single-walled carbon nanotubes and dielectric rod waveguides in the 220–330 GHz frequency range. Thin carbon nanotube layers are used as a tunable impedance surface with the dielectric properties optically controlled by laser illumination.QC 20181119</p

Wavelength-dependent photoconductivity of single-walled carbon nanotube layers

A number of electronic devices such as phase shifters, polarizers, modulators, and power splitters are based on tunable materials. These materials often do not meet all the requirements namely low losses, fast response time, and technological compatibility. Novel nanomaterials, such as single-walled carbon nanotubes, are therefore widely studied to fill this technological gap. Here we show how the dielectric constant of single-walled carbon nanotube layers can be substantially modified by illuminating them due to unique light–matter interactions. We relate the optical excitation of the nanotube layers to the illumination wavelength and intensity, by resistance and capacitance measurements. The dielectric constant is modified under laser illumination due to the change of material polarization and free carrier generation, and is shown to not be temperature-related. The findings indicate that SWCNT layers are a prospective tunable optoelectronic material for both high and low frequency applications.QC 20190515</p

Freeze-Dried Carbon Nanotube Aerogels for High-Frequency Absorber Applications

A novel technique for millimeter wave absorber material embedded in a metal waveguide is proposed. The absorber material is a highly porous carbon nanotube (CNT) aerogel prepared by a freeze-drying technique. CNT aerogel structures are shown to be good absorbers with a low reflection coefficient, less than −12 dB at 95 GHz. The reflection coefficient of the novel absorber is 3–4 times lower than that of commercial absorbers with identical geometry. Samples prepared by freeze-drying at −25 °C demonstrate resonance behavior, while those prepared at liquid nitrogen temperature (−196 °C) exhibit a significant decrease in reflection coefficient, with no resonant behavior. CNT absorbers of identical volume based on wet-phase drying preparation show significantly worse performance than the CNT aerogel absorbers prepared by freeze-drying. Treatment of the freeze-dried CNT aerogel with <i>n</i>- and <i>p</i>-dopants (monoethanolamine and iodine vapors, respectively) shows remarkable improvement in the performance of the waveguide embedded absorbers, reducing the reflection coefficient by 2 dB across the band