Effects of Catalyst Pretreatment on Carbon Nanotube Synthesis from Methane Using Thin Stainless-Steel Foil as Catalyst by Chemical Vapor Deposition Method

Synthesis of carbon nanotubes (CNTs) was carried out using methane as a carbon source via the chemical vapor deposition (CVD) method. A thin stainless-steel foil was used as catalyst for CNT growth. Our results revealed that pretreatment step of the stainless-steel foil as a catalyst plays an important role in CNT formation. In our experiments, a catalyst pretreatment temperature of 850 °C or 950 °C was found to facilitate the creation of Fe- and Cr-rich particles are active sites on the foil surface, leading to CNT formation. It is noted that the size of metallic particles after pretreatment is closely related to the diameter of the synthesized CNTs. It is interesting that a shorter catalyst pretreatment brings the growth of semiconducting typed CNTs while a longer pretreatment creates metallic CNTs. This finding might lead to a process for improving the quality of CNTs grown on steel foil as catalyst.

CNTFETs

In recent years, carbon nanotube (CNT) emerged as one of the promising materials that shows various advantages over silicon material (e.g., aggressive channel length scaling due to absence of mobility degradation, variable bandgap with single material, ultra-thin body device that is possible due to smaller diameter [1-3nm], and compatibility of CNT with high-k materials resulting in high ION). Moreover, CNTs show both metallic and semiconducting properties; hence, by using metallic CNTs, interconnects can be realized to fabricate a circuit purely consisting of CNTs. This chapter will provide introduction to carbon nanotubes field effect transistor (CNTFETs) starting from material properties of carbon nanotubes and followed by how it can be used as semiconductor channel in field effect transistor (MOSFET) to form CNTFET. The different types of CNTFETs will be discussed based on the type of CNT used along with their advantages and disadvantages.

Rate-selected growth of ultrapure semiconducting carbon nanotube arrays

Carbon nanotubes (CNTs) are promising candidates for smart electronic devices. However, it is challenging to mediate their bandgap or chirality from a vapor-liquid-solid growth process. Here, we demonstrate rate-selected semiconducting CNT arrays based on interlocking between the atomic assembly rate and bandgap of CNTs. Rate analysis confirms the Schulz-Flory distribution which leads to various decay rates as length increases in metallic and semiconducting CNTs. Quantitatively, a nearly ten-fold faster decay rate of metallic CNTs leads to a spontaneous purification of the predicted 99.9999% semiconducting CNTs at a length of 154 mm, and the longest CNT can be 650 mm through an optimized reactor. Transistors fabricated on them deliver a high current of 14 μA μm−1 with on/off ratio around 108 and mobility over 4000 cm2 V−1 s−1. Our rate-selected strategy offers more freedom to control the CNT purity in-situ and offers a robust methodology to synthesize perfectly assembled nanotubes over a long scale.

Dynamic Conductivity and Two-Dimensional Plasmons in Lateral CNT Networks

We study theoretically the carrier transport and the plasmonic phenomena in the gated structures with dense lateral carbon nanotube (CNT) networks (CNT “felt”) placed between the highly-conducting slot line electrodes. The CNT networks under consideration consist of a mixture of semiconducting and metallic CNTs. We find the dispersion relations for the two-dimensional plasmons, associated with the collective self-consisted motion of electrons in the individual CNTs, propagating along the electrodes as functions of the net electron density (gate voltage), relative fraction of the semiconducting and metallic CNTs, and the spacing between the electrodes. In a wide range of parameters, the characteristic plasmonic frequencies can fall in the terahertz (THz) range. The structures with lateral CNT networks can used in different THz devices.

A Metallic CNT Tolerant Design Methodology for Carbon Nanotube-Based Programmable Gate Arrays

Carbon nanotube field effect transistor (CNFET) is one of the promising technologies as a replacement for current CMOS technology due to its excellent electronic properties. CNFETs can be fabricated in regular structures, making them ideal for creating the repetitive architectures found in field programmable gate arrays (FPGAs). However, CNFETs face some fabrication challenges. The unwanted metallic carbon nanotubes (CNTs) are one of the major challenges in using CNFET technology for FPGAs. In this paper, we take the advantage of FPGAs programmability allowing reconfiguration around the metallic CNTs to tolerate this defect. We demonstrate a multi-stage solution to the metallic CNT problem in CNFET-based FPGAs that does not require any metallic nanotube removal of any kind. The proposed methodology consists of four consecutive stages in logic mapping process: (i) reordering of input variables, (ii) inputs complementing, (iii) adding inputs redundancy to basic logic element (BLE) and (iv) BLE lookup table (LUT) splitting. A fault simulation tool is designed to work closely with VPR, an academic FPGA CAD tool, to provide the investigation of metallic CNTs effects on CNFET-based FPGAs. Experimental results show that the proposed method can successfully map all logical nets at a cost of [Formula: see text] area overhead if the fraction of metallic CNTs is reduced to 30%.

Advances of Study on the Developments and Applications of Carbon Nanotubes

Many electronic applications of carbon nanotubes crucially rely on techniques of selectively producing either semiconducting or metallic CNTs, preferably of certain chirality. Several methods of separating semiconducting and metallic CNTs are known, but most of them are not yet suitable for large-scale technological processes. The most efficient method relies on density-gradient ultracentrifugation, which separates surfactant-wrapped nanotubes by the minute difference in their density. This density difference often translates into difference in the nanotube diameter and (semi) conducting properties. Another method of separation uses a sequence of freezing, thawing, and compression of SWNTs embedded in agarose gel.

Modulation of Carbon Nanotube Metal Contacts in Gaseous Hydrogen Environment

Carbon nanotubes (CNTs), contacted by electrodeposited Pd0.59Ni0.41 alloys, are characterised using electrical measurements and Raman spectroscopy. The high workfunctions of Nickel and Palladium form an ohmic contact with the CNT valence band, but the contact properties change on Hydrogen exposure due to a reduction in the PdNi workfunction and the realignment of the PdNi Fermi level with the CNT band structure. A PdNi contacted semiconducting CNT exhibited significantly lower currents after Hydrogen exposure while a metallic CNT exhibited a small current increase. The semiconducting and metallic natures of the CNTs are confirmed by their Raman spectra. This study demonstrates a technique for modulating the PdNi-CNT contact and differentiating between semiconducting and metallic CNTs via contact modulation. It also provides experimental evidence of the theoretical allocation of features in the CNT Raman spectra.