arXiv subjects

Yuanjia Liu

Publications and source records attributed to Yuanjia Liu.

6 recordsLinked to original sources

arXiv2026

Substrate-dependent electrical transport in individual single-walled carbon nanotubes grown across SiO$_2$ and hexagonal boron nitride

The electronic transport properties of carbon nanotubes (CNTs) are strongly affected by their surrounding environment, making the underlying substrate a critical factor for device performance. Here, we demonstrate enhanced carrier transport of individual single-walled CNTs on hexagonal boron nitride (hBN) by directly comparing CNT channels on SiO$_2$ and hBN within the same nanotube. This within-tube comparison removes tube-to-tube variability in chirality, diameter, and defect density, allowing the intrinsic substrate effect to be evaluated more reliably. The CNTs were synthesized using gas flow-directed growth, which yields long, well-aligned CNTs without transfer processes, allowing a single nanotube to extend across different substrate regions. Multichannel field-effect transistors fabricated along an individual CNT exhibit clear ambipolar characteristics. CNT channels on hBN consistently exhibit higher field-effect mobility than those on SiO$_2$. In contrast, temperature-dependent transport near the charge neutrality point exhibits thermally activated behavior with similar activation energies (15-20 meV) on both substrates, indicating that the intrinsic small bandgap of CNTs is largely unaffected by the substrate. These results provide direct evidence that hBN enhances low-field carrier transport in CNTs and establish a foundation for the fabrication of high-performance electronics based on hBN-supported CNTs.

cond-mat.mtrl-sci↗

arXiv2026

Multi-strategy Improved Northern Goshawk Optimization for WSN Coverage Enhancement

To enhance the coverage rate of Wireless Sensor Networks (WSNs), this paper proposes an advanced optimization strategy based on a multi-strategy integrated Northern Goshawk Optimization (NGO) algorithm. Specifically, multivariate chaotic mapping is first employed to improve the randomness and uniformity of the initial population. To further bolster population diversity and prevent the algorithm from stagnating in local optima, a bidirectional population evolutionary dynamics strategy is incorporated following the pursuit-and-evasion phase, thereby facilitating the attainment of the global optimal solution. Extensive simulations were conducted to evaluate the performance of the proposed multi-strategy NGO in WSN coverage. Experimental results demonstrate that the proposed algorithm significantly outperforms existing benchmarks in terms of both coverage enhancement and node connectivity.

cs.NE↗

arXiv2025

Crossover between kite growth and vibrational bridging in pillar-assisted controlled formation of carbon nanotube networks

Pillar-assisted growth is a technique in which short carbon nanotubes (CNTs) form suspended networks by growing across closely spaced microfabricated pillars. During growth, the CNT tips exhibit vibrations that allow them to bridge the neighboring pillars. To improve the complexity and controllability of the CNT networks, we introduce a kite-growth mechanism in which CNTs are elongated and aligned by gas flow during growth, enabling a longer bridging distance compared to vibrational bridging. By integrating theoretical modeling, simulations, and experimental synthesis, we found that CNT tip vibrations dominate bridging at short lengths, whereas gas flow increasingly influences alignment as CNTs grow longer. This results in a crossover behavior governed by gas flow and pillar arrangement. We also developed a bridging model based on geometric constraints to quantify the bridging behavior based on pillar spacing and angular accessibility. The statistical analysis of the resulting network structures demonstrates that the pillar arrangement significantly influences the connection types, with kite growth enabling more diverse network topologies. These findings provide design principles for tuning the density and structural complexity of suspended CNT networks, offering promising applications in nanoscale electrical interconnect wiring and three-dimensional circuit architectures.

cond-mat.mtrl-sci↗

arXiv2025

Efficient defect healing of single-walled cabron nanotubes through $ \mathrm{C}_{2}\mathrm{H}_{2} $-assisted multiple-cycle treatment with air exposure

Defects in single-walled carbon nanotubes (SWCNTs) degrade their mechanical,electrical, and thermal properties, limiting their potential applications. To realize the diverse applications of SWCNTs, it is essential to enhance their crystallinity through effective defect healing. However, traditional thermal treatments typically require temperatures above 1800°C, which can alter the nanotube structure. Previously, defect healing of SWCNTs was achieved at a relatively low temperature of 1100°C, using C$_{2}$H$_{2}$ assistance, but the efficiency was limited. In this study, we developed a C$_{2}$H$_{2}$-assisted multiple-cycle process at an even lower temperature of 1000°C combined with air exposure, achieving highly efficient defect healing while preserving the nanotube structure. The combination of multiple-cycle treatment and air exposure between cycles was found to promote defect activation, suppress the formation of amorphous carbon, and enhance the effectiveness of defect healing. Additionally, we successfully healed commercially available bulk-scale SWCNTs (super-growth SWCNTs), noting that their healing behavior differed from lab-grown SWCNTs with smaller diameters synthesized from nanodiamond. The efficient and structure-preserved healing process developed in this study broadens the potential applications of high-quality SWCNTs, including flexible electronics, high-performance composites, and energy storage devices.

cond-mat.mtrl-sci↗

arXiv2023

Gas flow-directed growth of aligned carbon nanotubes from nonmetallic seeds

Kite growth is a process that utilizes laminar gas flow in chemical vapor deposition to grow long, well-aligned carbon nanotubes (CNTs) for electronic application. This process uses metal nanoparticles (NPs) as catalytic seeds for CNT growth. However, these NPs remain as impurities in the grown CNT. In this study, nanodiamonds (NDs) with negligible catalytic activity were utilized as nonmetallic seeds instead of metal catalysts because they are stable at high temperatures and facilitate the growth of low-defect CNTs without residual metal impurities. Results demonstrate the successful growth of over 100-$μ$m-long CNTs by carefully controlling the growth conditions. Importantly, we developed an analysis method that utilizes secondary electron (SE) yield to distinguish whether or not CNTs grown from metal impurities. The absence of metallic NPs at the CNT tips was revealed by the SE yield mapping, whereas the presence of some kind of NPs at the same locations was confirmed by atomic force microscopy (AFM). These results suggest that most of the aligned CNTs were grown from nonmetallic seeds, most likely ND-derived NPs, via the tip-growth mode. Structural characterizations revealed the high crystallinity of CNTs, with relatively small diameters. This study presents the first successful use of nonmetallic seeds for kite growth and provides a convincing alternative for starting materials to prepare long, aligned CNTs without metal impurities. The findings of this study pave the way for more convenient fabrication of aligned CNT-based devices, potentially simplifying the production process by avoiding the need for the removal of metal impurities.

cond-mat.mtrl-sci↗

arXiv2023

Combination effect of growth enhancers and carbon sources on synthesis of single-walled carbon nanotubes from solid carbon growth seeds

In the synthesis of highly crystalline single-walled carbon nanotubes (SWCNTs), high growth temperatures are preferred, while the formation of impurity amorphous carbon (a-C) causes the termination of SWCNT growth and degrades its properties. To remove this by-product, H2O and CO2 have been employed in metal-catalyzed SWCNT growth systems because of their oxidizing ability. Recently, nonmetallic nanoparticles have become one of the growth seed candidates because of their high melting points and fewer metal impurities. In this study, by using nanodiamond-derived carbon nanoparticles as the solid growth seeds, we investigated the effect of CO2 and H2O on high-temperature SWCNT growth with two types of carbon-source supplies: C2H2 and C2H4. In this growth system, H2O showed oxidizing ability to etch a-C with either carbon sources. CO2 exhibited a similar a-C formation-preventing role in C2H4-supplied growth and achieved higher-purity SWCNTs with higher concentration of C2H4 than the case of H2O. However, in contrast to the other combinations, CO2 injection in the C2H2-supplied growth significantly enhanced the formation of a-C rather than the removal of it while the yield of SWCNTs was also increased, indicating the occurrence of the dehydration reaction between CO2 and C2H2. The present findings will lead to efficient growth of high-quality SWCNTs from nonmetallic growth seeds with the use of growth enhancers.

cond-mat.mtrl-sci↗