Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session H28: Focus Session: Carbon Nanotubes and Related Materials: Devices I |
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Sponsoring Units: DMP Chair: Slava Rotkin, Lehigh University Room: C156 |
Tuesday, March 22, 2011 8:00AM - 8:12AM |
H28.00001: Individual SWCNT based ionic field effect transistor Pei Pang, Jin He, Jae Hyun Park, Predrag Krstic, Stuart Lindsay Here we report that the ionic current through a single-walled carbon nanotube (SWCNT) can be effectively gated by a perpendicular electrical field from a top gate electrode, working as ionic field effect transistor. Both our experiment and simulation confirms that the electroosmotic current (EOF) is the main component in the ionic current through the SWCNT and is responsible for the gating effect. We also studied the gating efficiency as a function of solution concentration and pH and demonstrated that the device can work effectively in the physiological relevant condition. This work opens the door to use CNT based nanofluidics for ion and molecule manipulation. [Preview Abstract] |
Tuesday, March 22, 2011 8:12AM - 8:24AM |
H28.00002: Chemically-Driven Two Level Fluctuations in Single-Walled Carbon Nanotubes (SWCNTs) with Defects Danny Wan, Steven R. Hunt, Brad L. Corso, Issa S. Moody, Gregory A. Weiss, Philip G. Collins When a SWCNT conductor contains a defect, its electronic fluctuations are sensitive indicators of the surrounding chemical environment and of the chemical state of the defect itself. We demonstrate this effect by fabricating single SWCNT devices and then engineering their defect condition through the method of electrochemical point-functionalization. By characterizing the same SWCNT before and after the introduction of a point defect, we clearly establish the defect's contribution to the overall device noise. Carboxylate defects are particularly interesting because they have a deprotonated state that is sensitive to pH, electrolyte, and electrochemical potential. Large amplitude, two level fluctuations are observed from carboxylate sites when probed under conditions near the dissociation constant pKa, and the occupation statistics can be reversibly tuned by either pH or potential. We interpret the fluctuation in terms of the controlled protonation and deprotonation of the defect site, and describe a simple electrostatic gating model that supports this conclusion. [Preview Abstract] |
Tuesday, March 22, 2011 8:24AM - 8:36AM |
H28.00003: Gas detection mechanism for single-walled carbon nanotube networks Anthony Boyd, Isha Dube, Georgy Fedorov, Makarand Paranjape, Paola Barbara We study field-effect transistors fabricated with carbon nanotube (CNT) networks to determine whether the gas sensing mechanism is due to molecules adsorbed on the nanotubes, or changes at the interface between the nanotubes and the contacts. Our previous work showed that in devices made with isolated CNT, the response to nitrogen dioxide was mainly due to the contact interfaces [1]. Here, we focus on CNT networks and use SU-8 layers patterned with e-beam lithography to passivate the contact interfaces, while leaving the network exposed. We look to investigate possible differences in sensing mechanism for devices made with isolated tubes versus networks. \\[4pt] [1] J. Zhang, A. Boyd, A. Tselev, M. Paranjape, and P. Barbara, \textit{Mechanism of NO}$_{2}$\textit{ detection in carbon nanotube field effect transistor chemical sensors}, Applied Physics Letters \textbf{88,} 123112-123115 (2006) [Preview Abstract] |
Tuesday, March 22, 2011 8:36AM - 8:48AM |
H28.00004: Effects of adsorbed gases on the conductance of individual carbon nanotubes David Cobden, Hao-Chun Lee, Erik Fredrickson, Richard Roy, Oscar Vilches We investigate the effects of adsorbed monolayers of Ar, Kr and other gases on individual suspended single-walled carbon nanotubes. The down-shifts of the vibrational resonances of a nanotube can be used to determine the monolayer density\footnote{Z. Wang et al, Science 327, 552 (2010)} while the electrical conductance is measured simultaneously, at temperatures as low as 4.3 K. In the case of Ar, by studying density isotherms in the range 38 to 65 K, we see behavior resembling that of the well known two-dimensional vapor, liquid and solid phases on exfoliated graphite, although the correspondence is not exact and is device dependent. In addition, we find that the conductance changes significantly and non-monotonically with the density, and there are indications that it is sensitive to ordering in the monolayer. [Preview Abstract] |
Tuesday, March 22, 2011 8:48AM - 9:00AM |
H28.00005: Anomalous Current-Voltage Characteristics in Suspended Carbon Nanotubes in Various Gas Environments Moh Amer, Adam Bushmaker, Steve Cronin Electrically-heated suspended, carbon nanotubes (CNTs) exhibiting
negative
differential conductance in the high bias regime experience a
sudden drop in
current (or ``kink'') in various gaseous environments. We study
the effect
of different gas molecules on these $I-V $characteristics while
simultaneously
monitoring the changes in the nanotube vibrational structure
under high bias
voltages using Raman spectroscopy. When the nanotube is
electrically biased
at the kink, the $G$ band Raman mode is observed to downshift, as
is typical of
electrically heated devices. However, the $G$ band frequency at
the kink ($\omega _G^{kink})$ lies in the narrow range between
1575 and 1579cm$^{-1}$
for all samples measured, regardless of gas environment. The
voltage at
which the kink occurs depends on the type of the gas environment
with the
following dependence:
$V_{kink}^{Ar} |
Tuesday, March 22, 2011 9:00AM - 9:12AM |
H28.00006: Heat Dissipation from Suspended Carbon Nanotubes to their Surrounding Gas Environment I. Kai Hsu, Michael T. Pettes, Mehmet Aykol, Li Shi, Stephen Cronin The assistance of gas molecules to dissipate heat in 5-$\mu $m-long, electrical heated suspended carbon nanotubes (CNTs) is observed by comparing the $G $band Raman phonon temperature profiles measured in different gas environments and in vacuum. The measurement results show that 50-60{\%} of the heat generated in the CNT is carried away by its surrounding gas molecules. By analyzing the temperature profiles investigated in different gases, the thermal boundary conductance (TBC) between the gas molecules and the CNT can also be extracted. We find the TBC to be higher in carbon dioxide than in nitrogen, argon and helium.\footnote{I Kai Hsu \textit{et al.} \textit{Journal of Applied Physics }\textbf{2010,} 108, (084307).} Moreover, we report another optical method to explore the heat spreading behavior on a longer suspended CNTs in air, in which one laser is used as a heat source while another laser is used as a local temperature probe. A fin-shape thermal transport model is applied to fit the exponentially decaying temperature profiles measured away from the heat source. These results yield a heat decay length and TBC for air to be around 6.5 $\mu $m and 3$\times $10$^{5}$ W/m$^{2 }$ \textbullet K, respectively. [Preview Abstract] |
Tuesday, March 22, 2011 9:12AM - 9:48AM |
H28.00007: Electroluminescence from a single nanotube-molecule-nanotube junction Invited Speaker: The reliable fabrication of metallic singlewall carbon nanotube (mSWNT) electrode pairs with sub-10 nm spacing allows us to contact organic molecules (M) via dielectrophoresis and to form mSWNT-M-mSWNT junctions. For this purpose we used specific designed molecules which have an appropriate length to bridge the SWNT electrode gap, and a sufficient polarizability to allow the molecule deposition between the SWNT electrodes via DC-dielectrophoresis. The molecules comprise a fluorescent chromophore subunit. During transport measurements several mSWNT-M-mSWNT junctions showed light emission at voltages $>$ 4 V. The electroluminescence spectrum from the junction is very similar to the photoluminescence signal of the molecules on HOPG-surfaces. This result together with control experiments indicates that light is emitted from the chromophore core of the mSWNT contacted molecule [1]. If time allows I will also report on a related work about phonon-assisted electroluminescence from biased metallic single wall carbon nanotubes (SWNT), multi wall carbon nanotube (MWNT) and few layer graphene (FLG) devices [2]. \\[4pt] [1] C.W. Marquardt, S. Grunder, A. Blaszczyk, S. Dehm, F. Hennrich, H. v. L\"{o}hneysen, M. Mayor, R. Krupke, Nature Nanotechnology 2010; DOI: 10.1038/NNANO.2010.230 \\[0pt] [2] S. Essig et al., Nano Letters 10, 1589 (2010) [Preview Abstract] |
Tuesday, March 22, 2011 9:48AM - 10:00AM |
H28.00008: Thermal Emission of Suspended Carbon Nanotube Zuwei Liu, Adam Bushmaker, Mehmet Aykol, Steve Cronin We study the thermal emission spectra of individual suspended carbon nanotube induced by electrical heating. Semiconducting and metallic devices exhibit different spectra, based on their distinctive bandstructures. These spectra are compared with the ideal blackbody emission spectrum. In the response region of our detector, i.e. visible to near infrared, the thermal emission spectra of semiconducting devices agree well with Planck's law, while the spectra of metallic devices show an additional peak around 1.65 eV. For semiconducting devices, the temperature of the nanotube was fitted to Planck's law, and was compared with the temperature fitted from the G band downshift as well as the Stokes:anti-Stokes intensity ratio. For devices showing thermal non-equilibrium, the electron temperature agrees well with G+ downshift, but deviates from G- downshift. Finally, for metallic devices, partially polarized IR emission was observed, and possible mechanisms are discussed. [Preview Abstract] |
Tuesday, March 22, 2011 10:00AM - 10:12AM |
H28.00009: Electric field dependence of photoluminescence from individual single-walled carbon nanotubes S. Yasukochi, T. Murai, T. Shimada, S. Chiashi, S. Maruyama, Y.K. Kato Using suspended single-walled carbon nanotubes, we investigate electric field effects on photoluminescence. Trenches are fabricated on SiO$_{2}$/Si substrates, and Pt is deposited for electrical contacts. Carbon nanotubes are grown by patterned chemical vapor deposition. These devices operate as back-gate field effect transistors, allowing application of electric fields on as-grown ultraclean nanotubes. Individual suspended carbon nanotubes are identified by taking photoluminescence images using a home-built laser-scanning confocal microscope. After determining the chirality by photoluminescence excitation spectra, we measure gate voltage dependence of photoluminescence. We observe quenching of photoluminescence intensity and shifts of emission wavelength as gate voltages are applied. [Preview Abstract] |
Tuesday, March 22, 2011 10:12AM - 10:24AM |
H28.00010: Simultaneous Rayleigh and Raman spectroscopy on suspended single-walled carbon nanotubes under electrostatic gating Yuhei Miyauchi, Zhengyi Zhang, Mitsuhide Takekoshi, Vikram Deshpande, St\'ephane Berciaud, Philip Kim, James Hone, Tony Heinz The optical properties of single-walled carbon nanotubes (SWNTs) under electrostatic gating are of great interest for fundamental understanding of one-dimensional physics and for their application as optoelectronics devices. Here, we report how the electronic transitions are modified by gating conditions through direct measurements of Rayleigh (elastic) light scattering from individual suspended SWNTs [1]. With increasing gate voltage, we observed both a broadening and shift of the excitonic resonances in the Rayleigh scattering spectra. The influence of carrier doping on the optical resonances and, as gauged through simultaneous Raman measurements, on vibrational transitions will be discussed.\\[4pt] [1] M. Y. Sfeir et al., Science 306, 1540 (2004). [Preview Abstract] |
Tuesday, March 22, 2011 10:24AM - 10:36AM |
H28.00011: Photoconductivity measurements of single-walled carbon nanotube field effect transistors T. Murai, S. Yasukochi, S. Moritsubo, T. Shimada, S. Chiashi, Y. Murakami, S. Maruyama, Y.K. Kato Photoconductivity measurements are performed on carbon nanotube field effect transistors. Carbon nanotubes are grown on SiO$_{2}$/Si substrate by patterned chemical vapor deposition using ethanol as carbon source. Next, electron beam lithography, metal deposition, and liftoff processes are performed to form source and drain electrodes. The Si substrate is used as a back-gate in these devices. Wavelength tunable Ti:sapphire laser is focused onto the sample with an objective lens, and the laser spot is scanned with a steering mirror. A lock-in amplifier is used to detect the photoconductivity signal of carbon nanotube field effect transistors. [Preview Abstract] |
Tuesday, March 22, 2011 10:36AM - 10:48AM |
H28.00012: Role of defects in optical phonon decay, softening and 1/f noise resonance in carbon nanotubes Moonsub Shim Scattering and relaxation of optical phonons are especially important processes in carbon nanotubes. Strong phonon softening near the Dirac point in metallic nanotubes occurs by coupling of carrier excitation to optical phonon transitions. Current saturation and negative differential conductance in the high bias regime in nanotube devices are attributed optical phonon absorption and emission. Cooling of hot carriers occurs mostly via optical phonons which eventually decay anharmonically into acoustic phonons. Whether intentional or unavoidable, defects will strongly influence these fundamentally important processes. In this talk, how defects affect optical phonon scattering will be discussed. In particular, defect-dependent optical phonon lifetime and resonant 1/f noise associated with phonon softening via the Kohn anomaly will be discussed. [Preview Abstract] |
Tuesday, March 22, 2011 10:48AM - 11:00AM |
H28.00013: Micro-scale ``air-gap'' circuitry with conducting carbon nanotube-copper composite Chandramouli Subramaniam, Takeo Yamada, Don N. Futaba, Kenji Hata The ability of water-assisted CVD to produce aligned close-packed single wall carbon nanotubes(CNT) with superior thermal and mechanical properties make them ideal materials for use in microelectronics. However, their poor electrical conductivity has been a major obstacle in realizing this. To overcome this, we report the synthesis of conducting CNT-copper composite (conductivity $\sigma $=10$^{5}$ Scm$^{-1})$ through a novel organic phase electrodeposition. The conductivity enhancement (10$^{3}$ times over CNT) is due to the high, uniform filling of Cu in the aligned CNT matrix. Micro-scale, three-dimensional lithographic engineering of CNT-Cu, involving fully suspended CNT-Cu beams, is achieved for microelectronic applications. Multi-tier CNT-Cu circuits are also fabricated, with the constituent lines separated by air (replaceable with vacuum). This ``vacuum-separation'' exists in the horizontal and vertical directions providing unique multi-tier ``air-gap'' circuits. This realization of dielectric-less, air-gap circuits with CNT-Cu is thought to be a breakthrough for developing faster and efficient microelectronic devices. [Preview Abstract] |
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