A Fully Tunable Single-Walled Carbon Nanotube Diode

We demonstrate a fully tunable diode structure utilizing a fully suspended single-walled carbon nanotube (SWNT). The diode's turn-on voltage under forward bias can be continuously tuned up to 4.3 V by controlling gate voltages, which is ~6 times the nanotube bandgap energy. Furthermore, the same device design can be configured into a backward diode by tuning the band-to-band tunneling current with gate voltages. A nanotube backward diode is demonstrated for the first time with nonlinearity exceeding the ideal diode. These results suggest that a tunable nanotube diode can be a unique building block for developing next generation programmable nanoelectronic logic and integrated circuits.Comment: 14 pages, 4 figure

Theoretical and Experimental Studies of Schottky Diodes That Use Aligned Arrays of Single Walled Carbon Nanotubes

We present theoretical and experimental studies of Schottky diodes that use aligned arrays of single walled carbon nanotubes. A simple physical model, taking into account the basic physics of current rectification, can adequately describe the single-tube and array devices. We show that for as grown array diodes, the rectification ratio, defined by the maximum-to-minimum-current-ratio, is low due to the presence of m-SWNT shunts. These tubes can be eliminated in a single voltage sweep resulting in a high rectification array device. Further analysis also shows that the channel resistance, and not the intrinsic nanotube diode properties, limits the rectification in devices with channel length up to ten micrometer.Comment: Nano Research, 2010, accepte

Large-Area, Highly Sensitive SERS Substrates with Silver Nanowire Thin Films Coated by Microliter-Scale Solution Process

A microliter-scale solution process was used to fabricate large-area, uniform films of silver nanowires (AgNWs). These thin films with cross-AgNWs were deposited onto Au substrates by dragging the meniscus of a microliter drop of a coating solution trapped between two plates. The hot spot density was tuned by controlling simple experimental parameters, which changed the optical properties of the resulting films. The cross-AgNW films on the Au surface served as excellent substrates for surface-enhanced Raman spectroscopy, with substantial electromagnetic field enhancement and good reproducibility

Quantitative Determination of the Raman Enhancement of Ag₃₀(CO)₂₅ and Ag₅₀(CO)₄₀ Matrix Isolated in Solid Carbon Monoxide

Size-selected Ag clusters in the range Ag₃–Ag₅₀ were prepared by sputtering a silver substrate, mass-selecting Ag cation clusters using a Wien filter, neutralizing and matrix-isolating them at cryogenic temperatures in solid CO. The Raman spectra of the resulting silver-cluster carbonyls were recorded using excitation wavelengths in the range 457.9 to 514.5 nm. For Ag₃₀ and Ag₅₀, the “adsorbed” carbon monoxide (which we estimated to number ∼25 and ∼40, respectively) gave rise to broad Raman bands centered at ∼2110 cm^–1. Because both the metal cluster and the CO density were measured quantitatively, a good estimate was computed for the increase in the Raman scattering cross-section per CO molecule adsorbed on the silver particle. For Ag₅₀ and 457.9 nm laser excitation, an enhancement of ∼1850 was measured, which dropped to ∼1350 at 514.5 nm excitation. For Ag₃₀ (and 457.9 nm excitation) the enhancement was ∼530. The enhancements of Ag₃, Ag₅, and Ag₉ were too low to measure accurately (i.e., <10). Extrapolating the enhancements obtained with blue and green wavelengths to the “plasmonic” band center, which for an Ag₅₀ cluster is expected to be at ∼370 nm, and assuming the excitation band to be a Lorentzian with a fwhh of 0.8 eV, the maximum Raman enhancement per CO ligand in Ag₅₀CO₄₀ was estimated to be ∼12000, in good agreement with computed results using a time-dependent density functional quantum calculation, carried out on a Ag₂₀ cluster complex by Jensen et al. (Jensen et al. Size-Dependence of the Enhanced Raman Scattering of Pyridine Adsorbed on Ag_<i>n</i> (<i>n</i> = 2–8, 20) Clusters. <i>J. Phys. Chem. C</i> <b>2007</b>, <i>111</i>, 4756–4764)

Sample preparation protocols for realization of reproducible characterization of single-wall carbon nanotubes

Harmonized sample pre-treatment is an essential first step in ensuring quality of measurements as regards repeatability, inter-laboratory reproducibility and commutability. The development of standard preparation methods for single-wall carbon nanotube (SWCNT) samples is therefore essential to progress in their investigation and eventual commercialization. Here, descriptions of sample preparation and pre-treatment for the physicochemical characterization of SWCNTs are provided. Analytical methods of these protocols include: scanning electron microscopy (SEM; dry, wet), transmission electron microscopy (TEM; dry, wet), atomic force microscopy (AFM), inductively-coupled plasma mass spectrometry (ICP-MS), neutron activation analysis (NAA), Raman spectroscopy (dry, wet), UV-Vis-NIR absorption and photoluminescence spectroscopy, manometric isothermal gas adsorption and thermogravimetric analysis (TGA). Although sample preparation refers to these specific methods, application to other methods for measurement and characterization of SWCNTs can be envisioned.Le pr\ue9traitement harmonis\ue9 de l?\ue9chantillon est une premi\ue8re \ue9tape essentielle pour garantir la qualit\ue9 des mesures en termes de fid\ue9lit\ue9, de reproductibilit\ue9 interlaboratoire et de commutabilit\ue9. Le d\ue9veloppement de m\ue9thodes de pr\ue9paration standard pour des \ue9chantillons de nanotube de carbone \ue0 simple paroi (NTCSP) est par cons\ue9quent essentiel au progr\ue8s de leur investigation et \ue0 leur \ue9ventuelle commercialisation. Nous fournissons ici les descriptions de la pr\ue9paration et du pr\ue9traitement des \ue9chantillons aux fins de la caract\ue9risation physico-chimique des NTCSP. Les m\ue9thodes analytiques de ces protocoles comprennent les suivantes : microscopie \ue9lectronique \ue0 balayage (sec, humide); microscopie \ue9lectronique \ue0 transmission (sec, humide); microscopie \ue0 force atomique; spectrom\ue9trie de masse avec plasma induit par haute fr\ue9quence; analyse par activation neutronique; spectrom\ue9trie Raman (sec, humide); spectrophotom\ue9trie d?absorption atomique et photoluminescente UV-visible-dans le proche infrarouge; et analyse isotherme par technique manom\ue9trique d?adsorption de gaz et de thermogravim\ue9trie. Bien que la pr\ue9paration de l?\ue9chantillon renvoie \ue0 ces m\ue9thodes pr\ue9cises, on peut envisager une application \ue0 d?autres m\ue9thodes aux fins de la mesure et de la caract\ue9risation physicochimique des NTCSP.Peer reviewed: YesNRC publication: Ye