The ultrahigh carrier mobility and matchable work function of graphene have positioned this material as a leading candidate for the ideal contact material for carbon nanotubes (CNTs). Highly efficient carrier transport through CNT–graphene junctions is facilitated by covalently bonded contacts. This paper, therefore, proposes covalently bonded CNT–graphene junctions and investigates their characteristics theoretically. In these junctions, partially unzipped CNTs are longitudinally or radially bonded with graphene. By exploiting nonequilibrium Green's functions with density-functional theory, we examine ballistic electron transport (∼1.38 × 105 cm2/V s) and edge-dependent transport. Moreover, the contact properties of the junctions with adsorbed Cu atoms are investigated. Electron transfer from Cu to the junction turns the p-type Schottky contact into an n-type contact and decreases the Schottky barrier height from 0.2 to 0.08 eV. Furthermore, the junction resistance decreases by one to three orders of magnitude. The proposed design of Cu-decorated CNT–graphene junctions and first-principles calculations suggest an approach for low-power, high-performance CNT-based electronics.
Low-dimensional materials such as carbon nanotubes (CNTs) are promising candidates for gas sensing. Surface modification with specific molecules is considered an effective approach to enhance gas sensing. In this work, a kind of carbon hybrid is fabricated with phosphomolybdic acid (PMA) moleculedecorated single-walled CNTs (SWNTs) as a gas-sensing element and chemical vapor deposition-grown graphical graphene on prepatterned copper and nickel films as composite electrodes. According to the experimental results of NH 3 and NO 2 detection, the PMA-decorated carbon hybrids present much higher sensitivity, faster response, and lower power consumption than other previously reported oxide-modified CNT gas sensors. Responses of the DC resistance variation of approximately 23 or −21% to 5 ppm NH 3 or NO 2 are demonstrated at room temperature, with a power consumption of only hundreds of nanowatts (nWs). The enhanced gas sensitivity of the carbon hybrid is described by the first-principles calculation of the energy band and Schottky barrier in hybrid structures from the interface perspective. A significant change in Fermi level in SWNTs due to PMA decoration reduces the Schottky barrier at the SWNT/graphene interface and allows the hybrid to function at an appropriate status, which corresponds to a high response to the redox reaction between PMA and NO 2 or NH 3 molecules.
Carbon nanotube field-effect transistor (CNTFET) based circuit systems ha ve received extensive attention due to their energy-efficiency benefits. However, there is not yet a generally accepted compact SPICE model for CNTFETs compatible with existing electronics design automation platforms. In this paper, the Stanford top gate CNTFET model is optimized through the consideration of different doping levels in source/drain as well as the simplification of an equivalent capacitance network in the intrinsic channel. Based on this, compact models are built for both top gate and wrapped gate CNTFETs. Then the DC properties and the cut-off frequency of top gate and wrapped gate CNTFETs with 15 nm channel length, and their basic logic circuits based on our modelling, are simulated by HSPICE. In the circuit simulation, we add the influence of gate-to-gate capacitance. The influences of structural parameters such as the diameter, number of CNTs and their gap on the current-voltage property, transconductance, cut-off frequency, circuit delay and power consumption are studied. Through comparison with the simulation using the Stanford model, our modelling is more suitable for the design and development of CNTFET circuits. For given parameters, the top gate CNTFETs have a larger maximum cut-off frequency and the wrapped gate CNTFETs' saturate current is larger. Wrapped gate logic circuits have less delay but more dynamic power than top gate circuits. More CNTs in FETs with a bigger gap and shorter tube pitch lead to less circuit delay and more dynamic power.
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