We have developed the floating catalyst chemical vapor deposition (FCCVD) synthesis of single walled carbon nanotubes (SWCNTs) using C₂H₄ hydrocarbon as a carbon source and iron nanoparticles as the catalyst in an environmentally friendly and economical process. For the first time, ethylene was used as the only carbon source in FCCVD with N₂ as the main carrier gas. No sulphur and less than 15% H₂ in a N₂ carrier gas were used. By varying the ferrocene concentration, the diameter of the SWCNTs was tuned in the range of 1.3–1.5 nm with the optimized control of ferrocene concentration. The process produced SWCNTs with an average length of 13 μm and with a low level of bundling, that is a high proportion (28%) of individual tubes. The electron diffraction (ED) pattern indicated a random chirality distribution of the tubes between armchair and zigzag structures. The ED analysis also revealed that 35–38% of tubes are metallic. As a result of having long SWCNTs with a low level of bundling and a high fraction of metallic tubes, we produced a highly conductive transparent film with a sheet resistance of 51 Ohm per sq. for 90% transmission at 550 nm after HNO₃ treatment, this being one of the lowest sheet resistance values reported for SWCNT thin films.

Great effort has been applied to scientific research on the controllable synthesis of carbon nanotubes (CNTs) with high semiconducting selectivity or high areal density toward the macroscale applications of high-performance carbon-based electronics. However, the key issue of compatibility between these two requirements for CNTs remains a challenge, blocking the expected performance boost of CNT devices. We report an in situ acoustic-assisted assembly of high-density monochromatic CNT tangles (m-CNT-Ts), consisting of one self-entangled CNT with a length of up to 100 mm and consistent chirality. On the basis of a minimum consumed energy model with a Strouhal number of approximately 0.3, the scale could be controlled within the range of 1 × 10⁴ to 3 × 10⁴ μm² or even a larger range. Transistors fabricated with one m-CNT-T showed an on/off ratio of 10³ to 10⁶ with 4-mA on-state current, which is also the highest on-state current recorded so far for single CNT–based transistors. This acoustic-assisted assembly of chiral-consistent m-CNT-Ts will provide new opportunities for the fabrication of high-performance electronics based on perfect CNTs with high purity and high density.

Although single‐wall carbon nanotubes (SWCNTs) exhibit various colors in suspension, directly synthesized SWCNT films usually appear black. Recently, a unique one‐step method for directly fabricating green and brown films has been developed. Such remarkable progress, however, has brought up several new questions. The coloration mechanism, potentially achievable colors, and color controllability of SWCNTs are unknown. Here, a quantitative model is reported that can predict the specific colors of SWCNT films and unambiguously identify the coloration mechanism. Using this model, colors of 466 different SWCNT species are calculated, which reveals a broad spectrum of potentially achievable colors of SWCNTs. The calculated colors are in excellent agreement with existing experimental data. Furthermore, the theory predicts the existence of many brilliantly colored SWCNT films, which are experimentally expected. This study shows that SWCNTs as a form of pure carbon, can display a full spectrum of vivid colors, which is expected to complement the general understanding of carbon materials.