Jih-Hsin Liu

Fabrication of metal alloy-deposited flexible MWCNT buckypaper for thermoelectric applications

We report the fabrication of a flexible network of multiwall carbon nanotubes (MWCNTs) known as buckypaper (BP) for thermoelectric (TE) applications. A thermal evaporation method was used to deposit TE metal alloys onto the BP. The TE properties were improved primarily by increasing the Seebeck coefficient values (50 and 75 µV/K) and the electrical conductivity by approximately 10 000 S/m. High-temperature resistivity studies were performed to confirmthe semiconductivity of buckypaper. Variations in resistivity were observed to be the result of the metal alloys coated on the BP surface. We also demonstrated that a substantial increase in the Seebeck coefficient values can be obtained by connecting 3 and 5 layers of metal-deposited BP in series, thereby enhancing the TE efficiency of MWCNT-based BP for application in thermoelectric devices.

Application of buckypaper for preserving cholesteric liquid crystal cells within a certain temperature range

Application of buckypaper to cholesteric liquid crystals (CLCs) is demonstrated. The buckypaper functions as a thin film resistant heater and a near-perfect absorber in this study. A planar CLC cell with buckypaper pasted onto one of its surfaces is used to develop a voltage-induced optical attenuator. The intensity of the reflection band of the CLC attenuator can decrease (increase) by the application (removal) of a single-pulse voltage, and the wavelength of the reflection band remains constant as the reflection intensity decreases (increases). The decrease in the reflection intensity is attributable to the cholesteric→isotropic phase transition of the LCs via heating of the buckypaper, and absorption by the black buckypaper. The increase in the reflectance results from the isotropic→cholesteric phase transition of the LCs through cooling of the environment. During cooling, the application of a low DC voltage to the buckypaper can keep the cell temperature constant because thermal equilibrium between the heating of the buckypaper and the cooling of the environment is established. Using this method, the blue phase of a CLC cell can stably exist for more than an hour at room temperature, without the need for a temperature stage, polymer materials or particular LCs.

Electrically controllable all-optical switches using dye-doped liquid crystal cells with buckypapers

This work fabricates an electrically controllable all-optical switch using a dye-doped liquid crystal (DDLC) cell on which is pasted a buckypaper. The buckypaper serves as a thin film resistant heater; it can maintain the temperature of the DDLC cell constant by environmental cooling. The threshold power of the DDLC cell, which is the input optical power at which the output optical power begins to fall, is controlled by applied voltages, and the switch-off power of the cell, which is the minimum input optical power at which the output optical power falls to zero, is also controlled by the applied voltages. Therefore, such a cell can be developed into optical limiting devices with adjustable threshold and switch-off powers for multi-purpose use.

Effect of swelling of a photoresist on electromagnetic resonance of terahertz metamaterials.

This work uses isopropyl alcohol (IPA) to develop a photoresist. IPA dissolves the photoresist that is not exposed to UV light, and swells the photoresist that is exposed to UV light. The swelling of the photoresist distorts the split-ring resonators (SRRs). The distorted SRRs have a larger loop length, smaller line width, and smaller split gap than undistorted SRRs. The change in the dimensions of the SRRs is caused by the extension of the SRR arms in their longitudinal directions. The resonance frequency of the distorted SRRs is smaller than that of the undistorted SRRs, and the resonance frequency decreases with the development time. The resonance frequency of the distorted SRRs depends on not only their dimensions, but also the bending of their arms. The distorted SRRs in this work have a frequency tuning range with a maximum width of 0.13 THz. The method that is proposed herein uses IPA to fabricate passively tunable terahertz metamaterials, which exhibit the advantages of high reliability, low cost, and ease of fabrication.

Plasma functionalization and effect of annealing on electrical properties of MWCNT buckypaper

We report the fabrication of flexible high conductive multi walled carbon nanotube buckypaper (BP) by the dispersion and filtration method. The work demonstrates the changes observed in the electrical resistivity by both plasma post-treatment and by high temperature thermal annealing. Here we also illustrate the resistivity changes occurred due to different gas atmosphere as Ar, N₂, O₂ and studied the difference in resistivity in vacuum and air. Our R_H data yields a carrier concentration of about ~10²⁸-10³⁰ m^-3 for plasma treated and annealed BP samples.

A study on the properties of photoconductivity and photo voltage of buckpaper

Based on the remarkable properties and the extraordinary performance in theory, carbon nanotube (CNT) has been attracted numerous of attention and research interest since it has been found from 1991. However, until now there are no mature applications in our daily life, because of its singularity properties (even in one single tube) and nano-scale size (hard to handle). In this study, the unique dispersion and filtration process were introduced to form a bulk material, so called buckypaper (BP), from few grams of CNTs. That causes the superior nature of CNTs could expand and homogenize from a nano scale to macro scale. And, make a great breakthrough for real application of CNTs.