Yuki Kuwahara

Robust and Soft Elastomeric Electronics Tolerant to Our Daily Lives

Clothes represent a unique textile, as they simultaneously provide robustness against our daily activities and comfort (i.e., softness). For electronic devices to be fully integrated into clothes, the devices themselves must be as robust and soft as the clothes themselves. However, to date, no electronic device has ever possessed these properties, because all contain components fabricated from brittle materials, such as metals. Here, we demonstrate robust and soft elastomeric devices where every component possesses elastomeric characteristics with two types of single-walled carbon nanotubes added to provide the necessary electronic properties. Our elastomeric field effect transistors could tolerate every punishment our clothes experience, such as being stretched (elasticity: ∼ 110%), bent, compressed (>4.0 MPa, by a car and heels), impacted (>6.26 kg m/s, by a hammer), and laundered. Our electronic device provides a novel design principle for electronics and wide range applications even in research fields where devices cannot be used.

Wall-Number Selectivity in Single/Double-Wall Carbon Nanotube Production by Enhanced Direct Injection Pyrolytic Synthesis

The effect of methane (CH4) gas as a secondary carbon source in addition to liquid feedstock, on the number of walls and the diameter of carbon nanotubes (CNTs) produced by floating-catalyst CVD under different conditions has been investigated in this study. Transmission electron microscopy reveals that the products mainly contain single-wall (SW) and double-wall (DW) CNTs with the relative abundance of DWCNTs being 9.2–50.7%, which increases linearly with increasing CH4 gas flow rate. In contrast, the distributions of the tube diameters of SW- and DWCNTs are almost constant and are much less dependent on the CH4 gas flow rate. These results suggest that the carbon generated from the pyrolysis of CH4 mainly contributes to the formation of additional walls during the CNT growth in the present CVD system.

Quantitative analysis of isolated single-wall carbon nanotubes with their molar absorbance coefficients

The molar absorbance coefficients of metallic, semiconducting, and (6,5) chirality enriched single-wall carbon nanotubes were evaluated by a spray technique combined with atomic force microscopy. Single-wall carbon nanotubes with isolated and a single predominant electronic type were obtained by using the density-gradient ultracentrifugation technique. In the visible region, all coefficients had similar values around 2-5 × 109/mLmol-1 cm-1, independent of their diameter distribution and the electronic types of single-wall carbon nanotubes, and the eS22/eM11 and eS11/eM11 were estimated to be 1.0 and 4.0, respectively. The coefficient strongly depends on the length of single-wall carbon nanotubes, independent of their electronic types and chirality.

Low variability with high performance in thin-film transistors of semiconducting carbon nanotubes achieved by shortening tube lengths

Extremely low variability with excellent device performances in a SWCNT-TFT array has been demonstrated in SWCNT-TFTs fabricated by using a semiconducting ink of short SWCNTs with an average length of 340 nm; the field-effect mobility of 3.9 ± 0.45 cm2 V−1 s−1, on/off ratio from 105 to 106, and hysteresis of ≈0.5 V. AFM observations revealed that the nonionic surfactant, Brij 700, adopted for dispersing SWCNTs during their extraction, causes the significant and homogeneous shortening of SWCNTs compared with sodium cholate, which is frequently used for the dispersion of SWCNTs as an ionic surfactant. Thus, it has been concluded that the shortening of SWCNTs in the dispersing process using the Brij 700 surfactant contributes to the observed uniformity of performance among the devices.

Thin-film transistors using DNA-wrapped semiconducting single-wall carbon nanotubes with selected chiralities

Selected semiconducting chiralities, , , and , of DNA-wrapped single-wall carbon nanotubes (DNA-SWCNTs) were used for thin-film transistors (TFTs). Chirality separation was carried out by ion exchange chromatography (IEX) with the ssDNA of the (TAT)4 sequence. An on/off ratio of 3.8 × 106 with a carrier mobility of 11 cm2/(Vs) was successfully achieved in the fabricated SWCNT-TFTs. The comparison between the on/off ratios obtained before (101–102) and after IEX (104–107) indicated that the IEX separation process sufficiently improves the performance of SWCNT-TFTs because of the reducing metallic SWCNT pathways in the TFT channel.

Effects of Tube Diameter and Length on Transparent Conductivity of Single-Walled Carbon Nanotube Network Films

The effects of single-walled carbon nanotube (SWCNT) structures on the transparent conductivity of their network films have been investigated. SWCNTs with different average tube diameters of 1.3 nm, 1.7 nm, and 2.0 nm were processed at the same conditions. Then unit structure characterization was performed by determining the tube diameter, length, bundle thickness, and so on, before the fabrication of SWCNT network films by the filtration and transfer method using the dispersions. The result of the transparent conductivity measurements clearly showed better performance with a decrease in the tube diameter: that is, narrower SWCNTs form narrow bundles, and their dense network results in an increase in the total length of conduction pathways in the SWCNT network films with high transparency. Furthermore, the figure of merit and the percolation exponent for the transparent conductivity obtained by using the data fitting of the percolation model were also discussed in terms of the tube diameter and length.