Multiple Functionality in Nanotube Transistors

Calculations of quantum transport in a carbon nanotube transistor show that such a device offers unique functionality. It can operate as a ballistic field-effect transistor, with excellent characteristics even when scaled to 10 nm dimensions. At larger gate voltages, channel inversion leads to resonant tunneling through an electrostatically defined nanoscale quantum dot. Thus the transistor becomes a gated resonant tunelling device, with negative differential resistance at a tunable threshold. For the dimensions considered here, the device operates in the Coulomb blockade regime, even at room temperature.Comment: To appear in Phys. Rev. Let

Negative differential resistance in nanotube devices

Carbon nanotube junctions are predicted to exhibit negative differential resistance, with very high peak-to-valley current ratios even at room temperature. We treat both nanotube p-n junctions and undoped metal-nanotube-metal junctions, calculating quantum transport through the self-consistent potential within a tight-binding approximation. The undoped junctions in particular may be suitable for device integration.Comment: 4 pages, 4 figures, to appear in Physical Review Letter

Properties of short channel ballistic carbon nanotube transistors with ohmic contacts

We present self-consistent, non-equilibrium Green's function calculations of the characteristics of short channel carbon nanotube transistors, focusing on the regime of ballistic transport with ohmic contacts. We first establish that the band lineup at the contacts is renormalized by charge transfer, leading to Schottky contacts for small diameter nanotubes and ohmic contacts for large diameter nanotubes, in agreement with recent experiments. For short channel ohmic contact devices, source-drain tunneling and drain-induced barrier lowering significantly impact the current-voltage characteristics. Furthermore, the ON state conductance shows a temperature dependence, even in the absence of phonon scattering or Schottky barriers. This last result also agrees with recently reported experimental measurements.Comment: Nanotechnology, in pres

Theory of enhancement of thermoelectric properties of materials with nanoinclusions

Based on the concept of band bending at metal/semiconductor interfaces as an energy filter for electrons, we present a theory for the enhancement of the thermoelectric properties of semiconductor materials with metallic nanoinclusions. We show that the Seebeck coefficient can be significantly increased due to a strongly energy-dependent electronic scattering time. By including phonon scattering, we find that the enhancement of ZT due to electron scattering is important for high doping, while at low doping it is primarily due to a decrease in the phonon thermal conductivity

Poole-Frenkel Effect and Phonon-Assisted Tunneling in GaAs Nanowires

We present electronic transport measurements of GaAs nanowires grown by catalyst-free metal-organic chemical vapor deposition. Despite the nanowires being doped with a relatively high concentration of substitutional impurities, we find them inordinately resistive. By measuring sufficiently high aspect-ratio nanowires individually in situ, we decouple the role of the contacts and show that this semi-insulating electrical behavior is the result of trap-mediated carrier transport. We observe Poole-Frenkel transport that crosses over to phonon-assisted tunneling at higher fields, with a tunneling time found to depend predominantly on fundamental physical constants as predicted by theory. By using in situ electron beam irradiation of individual nanowires we probe the nanowire electronic transport when free carriers are made available, thus revealing the nature of the contacts

Theme Analysis of Flora Nwapa’s Never Again: A Systemic Functional Approach

This paper deals with theme analysis of Flora Nwapa’s Never Again. The theory that underpins this study is systemic functional linguistics, which is one of the approaches proposed by scholars such as M.A.K Halliday, S. Eggins, J. R. Martin, R. Fowler, J. D. Benson to mention but a very few, for the study of language and its function(s). In this system, the study of language involves three functional labels: experiential, interpersonal and textual meanings. This study aims at describing and analysing linguistic features which connote textual meaning in Never Again so as to have a deep understanding of the novel and provide a new interpretation of it. It also aims at uncovering the deep messages conveyed through the novel. Both quantitative and qualitative methods have been used in this study. Thus, two extracts have been selected from Never Again and systemic functional linguistic theories have been applied to each of them for the purpose of exploring how language is used to organise itself. The study of the internal organisation and communicative nature of the selected Texts has enabled the researchers to come up with valuable findings. Indeed, through Mood adjuncts that conflate interpersonal themes, participants in Text 1 have expressed particular attitudes and judgments about the limited power of women and the roles of women and children during war whereas those in Text 2 have expressed a high degree of certainty and inclination. This study enables the researchers to provide a deeper understanding of Never Again by contending that the deep messages conveyed through the novel are the Nigerian civil war and the roles of women and children in our societies especially during war time. Keywords: Metafunctions, register variables, systemic functional linguistics, theme patterns