Ultrafast photocurrent measurement of the escape time of electrons and holes from carbon nanotube PN junction photodiodes

Ultrafast photocurrent measurements are performed on individual carbon nanotube PN junction photodiodes. The photocurrent response to sub-picosecond pulses separated by a variable time delay {\Delta}t shows strong photocurrent suppression when two pulses overlap ({\Delta}t = 0). The picosecond-scale decay time of photocurrent suppression scales inversely with the applied bias VSD, and is twice as long for photon energy above the second subband E22 as compared to lower energy. The observed photocurrent behavior is well described by an escape time model that accounts for carrier effective mass.Comment: 8 pages Main text, 4 Figure

Ultrafast photocurrent measurement of the escape time of electrons and holes from carbon nanotube PN junction photodiodes

Ultrafast photocurrent measurements are performed on individual carbon nanotube PN junction photodiodes. The photocurrent response to sub-picosecond pulses separated by a variable time delay {\Delta}t shows strong photocurrent suppression when two pulses overlap ({\Delta}t = 0). The picosecond-scale decay time of photocurrent suppression scales inversely with the applied bias VSD, and is twice as long for photon energy above the second subband E22 as compared to lower energy. The observed photocurrent behavior is well described by an escape time model that accounts for carrier effective mass.Comment: 8 pages Main text, 4 Figure

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

Plasmonic band gap structures for surface-enhanced Raman scattering

Cataloged from PDF version of article.Surface-enhanced Raman Scattering (SERS) of rhodamine 6G (R6G) adsorbed on biharmonic metallic grating structures was studied. Biharmonic metallic gratings include two different grating components, one acting as a coupler to excite surface plasmon polaritons (SPP), and the other forming a plasmonic band gap for the propagating SPPs. In the vicinity of the band edges, localized surface plasmons are formed. These localized plasmons strongly enhance the scattering efficiency of the Raman signal emitted on the metallic grating surfaces. It was shown that reproducible Raman scattering enhancement factors of over 105 can be achieved by fabricating biharmonic SERS templates using soft nano-imprint technique. We have shown that the SERS activities from these templates are tunable as a function of plasmonic resonance conditions. Similar enhancement factors were also measured for directional emission of photoluminescence. At the wavelengths of the plasmonic absorption peak, directional enhancement by a factor of 30 was deduced for photoluminescence measurements. (c) 2008 Optical Society of America

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

Raman studies of mass-selected metal clusters

grantor: University of TorontoSputtering a metal target under high vacuum conditions with 15 mA of 25 keV Ar+ ions produces cationic metal clusters, which are extracted and collimated into a beam using standard ion optics. A particular cluster nuclearity is selected from the beam by a Wein filter, co-deposited on an aluminum paddle with a matrix gas Ar+ or CO) at cryogenic temperatures, and neutralized. Once enough clusters accumulate, Raman spectra are excited by various lines of an Ar+ laser. The scattered light is dispersed onto a charge-coupled-device detector using a three-grating spectrometer. Strong bands at ~165 cm-1, assigned as "breathing" modes, dominate the Raman spectra of Ag5, Ag7, and Ag9 deposited in Ar. These bands fall close in frequency to that of small length scale vibrations in solid silver, indicating that the bonding between the atoms in these clusters already approximates that of bulk silver. Comparison of the Ag5 and Ag7 spectra with theoretically calculated ones reveals that the structure of Ag5 , is planar trapezoid and Ag7 is tricapped tetrahedron. The Raman spectra of Ag3 and Fe3 in an Ar matrix show these both to be dynamic Jahn-Teller molecules. All of the bands in the Ag3 spectrum are accounted for using a linear plus quadratic Jahn-Teller coupling model. The Fe3 spectrum cannot be fit using this model, probably due to the high spin state of the cluster ('S' = 4). A new derivation of the matrix elements for the linear plus quadratic Jahn-Teller coupling model, based on operator methods, is presented. Deposition of Ag9 Ag20, Ag35, and Ag 50 in CO and collection of the Raman spectra in the v(CO) region show that these clusters enhance the Raman scattering of CO by a factor of a few hundred with a strong dependence on cluster size. The results are interpreted as the maximum possible enhancement by the Chemical Mechanism of Surface Enhanced Raman Scattering.Ph.D

Helpless

Helpless is a creative thesis featuring a series of illustrations that metaphorically represent instances of abuse and trauma through the use of mythological and supernatural creatures