Ph. Avouris

Single- and multi-wall carbon nanotube field-effect transistors

We fabricated field-effect transistors based on individual single- and multi-wall carbon nanotubes and analyzed their performance. Transport through the nanotubes is dominated by holes and, at room temperature, it appears to be diffusive rather than ballistic. By varying the gate voltage, we successfully modulated the conductance of a single-wall device by more than 5 orders of magnitude. Multi-wall nanotubes show typically no gate effect, but structural deformations—in our case a collapsed tube—can make them operate as field-effect transistors.

Photodetectors based on graphene, other two-dimensional materials and hybrid systems

Graphene and other two-dimensional materials, such as transition metal dichalcogenides, have rapidly established themselves as intriguing building blocks for optoelectronic applications, with a strong focus on various photodetection platforms. The versatility of these material systems enables their application in areas including ultrafast and ultrasensitive detection of light in the ultraviolet, visible, infrared and terahertz frequency ranges. These detectors can be integrated with other photonic components based on the same material, as well as with silicon photonic and electronic technologies. Here, we provide an overview and evaluation of state-of-the-art photodetectors based on graphene, other two-dimensional materials, and hybrid systems based on the combination of different two-dimensional crystals or of two-dimensional crystals and other (nano)materials, such as plasmonic nanoparticles, semiconductors, quantum dots, or their integration with (silicon) waveguides.

Vertical scaling of carbon nanotube field-effect transistors using top gate electrodes

We have fabricated single-wall carbon nanotube field-effect transistors (CNFETs) in a conventional metal–oxide–semiconductor field-effect transistor (MOSFET) structure, with gate electrodes above the conduction channel separated from the channel by a thin dielectric. These top gate devices exhibit excellent electrical characteristics, including steep subthreshold slope and high transconductance, at gate voltages close to 1 V—a significant improvement relative to previously reported CNFETs which used the substrate as a gate and a thicker gate dielectric. Our measured device performance also compares very well to state-of-the-art silicon devices. These results are observed for both p- and n-type devices, and they suggest that CNFETs may be competitive with Si MOSFETs for future nanoelectronic applications.

Controlling doping and carrier injection in carbon nanotube transistors

Carbon nanotube field-effect transistors (CNTFETs) fabricated out of as-grown nanotubes are unipolar p-type devices. Two methods for their conversion from p- to n-type devices are presented. The first method involves conventional doping with an electron donor, while the second consists of annealing the contacts in vacuum to remove adsorbed oxygen. A comparison of these methods shows fundamental differences in the mechanism of the transformation. The key finding is that the main effect of oxygen adsorption is not to dope the bulk of the tube, but to modify the barriers at the metal–semiconductor contacts. The oxygen concentration and the level of doping of the nanotube are therefore complementary in controlling the CNTFET characteristics. Finally, a method of controlling individually the contact barriers by local heating is demonstrated.

Atomic scale desorption through electronic and vibrational excitation mechanisms

The scanning tunneling microscope has been used to desorb hydrogen from hydrogen-terminated silicon (100) surfaces. As a result of control of the dose of incident electrons, a countable number of desorption sites can be created and the yield and cross section are thereby obtained. Two distinct desorption mechanisms are observed: (i) direct electronic excitation of the Si-H bond by field-emitted electrons and (ii) an atomic resolution mechanism that involves multiple-vibrational excitation by tunneling electrons at low applied voltages. This vibrational heating effect offers significant potential for controlling surface reactions involving adsorbed individual atoms and molecules.

Electroluminescence in Single Layer MoS2

We detect electroluminescence in single layer molybdenum disulfide (MoS2) field-effect transistors built on transparent glass substrates. By comparing the absorption, photoluminescence, and electroluminescence of the same MoS2 layer, we find that they all involve the same excited state at 1.8 eV. The electroluminescence has pronounced threshold behavior and is localized at the contacts. The results show that single layer MoS2, a direct band gap semiconductor, could be promising for novel optoelectronic devices, such as two-dimensional light detectors and emitters.

Role of contacts in graphene transistors: A scanning photocurrent study

A near-field scanning optical microscope is used to locally induce photocurrent in a graphene transistor with high spatial resolution. By analyzing the spatially resolved photoresponse, we find that in the

Carbon nanotubes : nanomechanics, manipulation, and electronic devices

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Electronic excitations of benzene, pyridine, and pyrazine adsorbed on Ag(111)

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Intertube coupling in ropes of single-wall carbon nanotubes

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