Nanodiode based on a multiwall CN(x)/carbon nanotube intramolecular junction

Towards 3D self-assembled rolled multiwall carbon nanotube structures by spontaneous peel off

Controlling the 3D assembly of individual nanomaterials can be a challenging task. However, it opens up opportunities for the production of increasingly complex nanostructures. Unusual rolled multiwall carbon nanotube structures are synthesized here by simply inducing a change of precursor composition during the growth of multiwall carbon nanotube forests. The multiwall carbon nanotube structures are comprised of nitrogen-doped and undoped sections, and are obtained via a detailed peel off and roll mechanism. These results open new doors for the development of increasingly complex nanostructures.

Tiny nano-scale junction built on B/N doped single carbon nanotube

The characteristic sizes of carbon nanotube (CNT)-based devices are constantly being reduced. However, this continuing miniaturization is still facing many problems and requires innovative ideas and structures. By regular doping of boron and nitrogen atoms in a semiconducting single-wall carbon nanotube (SWCNT), we have constructed a nano-scale junction with rectifying characteristics. The I-V curve of our junction resembles the I-V curve of an ideal diode with a p-n junction. This junction channel is about 0.6 nm wide and 3.4 nm long, and the footprint is 5.1 nm long. Under a 0.5 V bias, the junction has a leakage current of -8.8 × 10^-3 μA, a rectifying ratio I_on/I_off of 0.716 × 10³, and a current density of 10.52 mA μm^-1. Our study also shows how different dopant distributions influence the I-V curve. Such a regular nano-scale doping method is effective and important, compared with the traditional random doping method.

The formation and stability of junctions in single-wall carbon nanotubes

The structure and stability of molecular junctions, which connect two single-wall carbon nanotubes (SWCNTs) of different diameters and chiral angles, (n ₁, m ₁)-(n ₂, m ₂), are systematically investigated by density functional tight binding calculations. More than 100 junctions, which connect well-aligned SWCNTs, were constructed and calculated. For a highly stable junction between two chiral (n ₁, m ₁) and (n ₂, m ₂) SWCNTs with opposite handedness, the number of pentagon-heptagon (5/7) pairs required to build the junction can be denoted as ∣∣n ₂ - n ₁∣ - ∣m ₂ - m ₁∣∣+min{∣n ₂ - n ₁∣, ∣m ₂ - m ₁∣} with (n ₂, m ₂) rotating π/3 angle or not. While for a junction connected by two zigzag, armchair or two chiral SWCNTs with the same handedness, the number of 5/7 pairs is equal to ∣n ₁ - n ₂∣ + ∣m ₁ - m ₂∣. Similar to the formation energies of grain boundaries in graphene, the curve of the formation energies vs. chiral angle difference present an 'M' shape indicating the preference of ∼30 degree junctions. Moreover, the formation energies of the zigzag-type and armchair-type junctions with zero misorientation angles are largely sensitive to the diameter difference of two sub-SWCNTs.

Electronic and transport properties of a molecular junction with asymmetric contacts

Asymmetric molecular junctions have been shown experimentally to exhibit a dual-conductance transport property with a pulse-like current-voltage characteristic, by Reed and co-workers. Using a recently developed first-principles integrated piecewise thermal equilibrium current calculation method and a gold-benzene-1-olate-4-thiolate-gold model molecular junction, this unusual transport property has been reproduced. Analysis of the electrostatics and the electronic structure reveals that the high-current state results from subtle bias induced charge transfer at the electrode-molecule contacts that raises molecular orbital energies and enhances the current-contributing molecular density of states and the probabilities of resonance tunneling of conduction electrons from one electrode to another.

Gate voltage dependent characteristics of p-n diodes and bipolar transistors based on multiwall CN(x)/carbon nanotube intramolecular junctions

The electrical transport characteristics of multiwall CN(x)/carbon nanotube intramolecular junctions were studied. The junctions could be used as diodes. We found that the rectification resulted from p-n junctions, not from metal-semiconductor junctions. The gate effect was very weak when the diodes were reverse biased. At forward bias, however, some of the p-n diodes could be n-type transistors. Experimental results supported the opinion that the gate voltage dependent property is derived from the Schottky barrier between the CN(x) part and the electrode. Using p-n diodes, a bipolar transistor with nanoscale components was built, whose behavior was very similar to that of a conventional planar bipolar transistor.

The synthesis and fabrication of one-dimensional nanoscale heterojunctions

There are a variety of methods for synthesizing or fabricating one-dimensional (1D) nanostructures containing heterojunctions between different materials. Here we review recent developments in the synthesis and fabrication of heterojunctions formed between different materials within the same 1D nanostructure or between different 1D nanostructures composed of different materials. Structures containing 1D nanoscale heterojunctions exhibit interesting chemistry as well as size, shape, and material-dependent properties that are unique when compared to single-component materials. This leads to new or enhanced properties or multifunctionality useful for a variety of applications in electronics, photonics, catalysis, and sensing, for example. This review separates the methods into vapor-phase synthesis, solution-phase synthesis, template-based synthesis, and other approaches, such as lithography, electrospinning, and assembly. These methods are used to form a variety of heterojunctions, including segmented, core/shell, branched, or crossed, from different combinations of semiconductor, metal, carbon, and polymeric materials.