Synthesis of Vertical Carbon Nanotube Interconnect Structures Using CMOS-Compatible Catalysts

Synthesis of the vertically aligned carbon nanotubes (CNTs) using complementary metal-oxide-semiconductor (CMOS)-compatible methods is essential to integrate the CNT contact and interconnect to nanoscale devices and ultra-dense integrated nanoelectronics. However, the synthesis of high-density CNT array at low-temperature remains a challenging task. The advances in the low-temperature synthesis of high-density vertical CNT structures using CMOS-compatible methods are reviewed. Primarily, recent works on theoretical simulations and experimental characterizations of CNT growth emphasized the critical roles of catalyst design in reducing synthesis temperature and increasing CNT density. In particular, the approach of using multilayer catalyst film to generate the alloyed catalyst nanoparticle was found competent to improve the active catalyst nanoparticle formation and reduce the CNT growth temperature. With the multilayer catalyst, CNT arrays were directly grown on metals, oxides, and 2D materials. Moreover, the relations among the catalyst film thickness, CNT diameter, and wall number were surveyed, which provided potential strategies to control the tube density and the wall density of synthesized CNT array.

Similarity analysis of stacking sequences in a SiC nanowire pair grown from the same catalyst nanoparticle using Levenshtein distance

Stacking faults are easily formed in silicon carbide (SiC) crystals, and this is also the case for SiC nanowires. The stacking faults exercise influences on SiC’s properties, therefore it is important to understand their formation mechanism and to control their formation for applications of SiC and its nanowires. In this study, we propose a method for investigating stacking faults’ formation mechanism in nanowires and provide its proof of concept. Stacking sequences in a pair of SiC nanowires that were grown from the same metal catalyst nanoparticle were quantified as a pair of binary sequences, and Levenshtein distances between partial sequences extracted from the two sequences were measured to detect similarity between them, and the result was compared with that obtained using a surrogate data of one sequence. The similarity analysis using Levenshtein distances works as a probe for investigating possible influences of some phenomena in the catalyst nanoparticle on the formation of stacking faults. The analysis did not detect a correlation between the two sequences. Although a possibility that the formation of stacking faults in the nanowires were owing to some phenomena in the catalyst nanoparticle cannot be denied, the extrinsic cause in the catalyst nanoparticle was not detected through our analysis in this case.

Effect of magnetic field on the synthesis of carbon nanotubes using MPECVD

CNT production is limited by issues regarding CNT growth and morphology. Due to this, further studies on experimental factors regarding CNT production are needed to optimize CNT production in a commercial scale. This study focuses mainly on the determination of the effects of the presence of a magnetic field during CNT synthesis in a Microwave Enhanced Plasma Chemical Vapor Deposition (MPECVD) process using a Whirlpool AVM585 conventional microwave oven. The study also determined the effects of hydrogen catalyst plasma pretreatment on CNT growth. The experiment was based on a Taguchi orthogonal array design. The effects of the experimental factors such as magnetic field strength (0, 5, and 10 mT), catalyst pretreatment time (10, 15, and 20 min), hydrogen gas flow rate (25, 50, and 75 mL/min), and microwave power (451, 570, and 740 W) on the responses such as the catalyst nanoparticle Feret diameter, CNT diameter, tortuosity, weight, and purity were investigated. Among the design factors, application of magnetic field at 10 mT improved all the responses, most notably the CNT diameter and tortuosity being reduced by 60% and 48% compared to runs with no magnetic field, respectively. Under tortuosity, magnetic field was the design factor which had the greatest effect on decreasing the tortuosity of the CNTs at around 100 times the effect measured under other design factors. Catalyst plasma pretreatment was most optimal at the highest hydrogen flow rate and microwave power setting, under the influence of the highest magnetic field strength. The effects of the factors during catalyst plasma pretreatment also resulted to improved characteristics of the CNTs during the CNT synthesis. Overall, the findings suggest that the application of a magnetic field during catalyst plasma pretreatment and the subsequent CNT synthesis results to catalyst nanoparticles and CNTs with improved properties such as lower catalyst nanoparticle Feret diameter, CNT diameter, tortuosity and higher CNT yield and purity.