Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session D31: Novel Properties in Nanomaterials |
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Sponsoring Units: DCMP Chair: Guangyu Chai, University of Central Florida Room: Colorado Convention Center 401 |
Monday, March 5, 2007 2:30PM - 2:42PM |
D31.00001: In Situ Measurement of Noise and Resistance Reductions During the High Temperature Anneal of Single-Walled Carbon Nanotubes Alexander Kane, Brett Goldsmith, Philip Collins The use of high temperature treatments is increasingly common in the post-processing of lithographically-fabricated carbon nanotube electronic devices. Empirically, high temperature treatments decrease both the resistance and noise of as-fabricated devices through undetermined mechanisms. This work investigates the most effective processing temperatures by measuring devices in situ in a UHV environment. The measurements focus on metallic nanotubes contacted by Ti or Pd electrodes. The results clearly differentiate between the resistive effects of adsorbates and of non-ohmic nanotube-metal contacts, since the two are eliminated at different temperatures and with different degrees of reversibility. The two mechanisms also affect device noise and fluctuations differently, with the net effect that noise decreases are more than proportional to resistance decreases. [Preview Abstract] |
Monday, March 5, 2007 2:42PM - 2:54PM |
D31.00002: Characterization and Reduction of 1/f Noise in Carbon Nanotube Devices Yu-Ming Lin, Phaedon Avouris 1/f noise is a ubiquitous fluctuation in semiconductors and metals. Unlike other types of fluctuations such as the thermal noise and the shot noise, 1/f noise increases with decreasing device dimension and is highly dependent on the material quality and interface properties. Therefore, the noise characteristics in nanoscaled devices are usually dominated by the 1/f-type fluctuations. Here we perform a systematic study on the 1/f noise of carbon nanotube devices consisting of individual single-wall carbon nanotubes. We have examined the impact of the contact and the substrate to the 1/f noise in carbon nanotube devices in order to reduce the 1/f noise level. By eliminating the charge traps associated with oxide substrates, we found that the 1/f noise in carbon nanotube devices can be lowered by up to two orders of magnitude. These results reveal important factors contributing to the 1/f noise source in carbon nanotube devices, and are of great importance for applications based on carbon nanotubes. [Preview Abstract] |
Monday, March 5, 2007 2:54PM - 3:06PM |
D31.00003: Tunneling spectroscopy in carbon nanotubes Yung-Fu Chen, Gassem Al-Zoubi, Norman Birge, Nadya Mason Carbon nanotubes are one-dimensional metallic or semiconducting wires that serve as good model systems to study Luttinger liquids, in which electron-electron interaction are essential to electronic transport. Luttinger behavior has previously been measured via transport through the ends of nanotubes. We have fabricated novel nanotube devices with three-terminal configurations---two normal contacts at the ends and one non-invasive superconducting tunnel probe in the middle. This configuration is well-suited to tunnel spectroscopy studies of bias-dependence, non-equilibrium effects, and carrier interactions in nanotubes. We present results on low-temperature tunneling measurements performed using this configuration. [Preview Abstract] |
Monday, March 5, 2007 3:06PM - 3:18PM |
D31.00004: ABSTRACT WITHDRAWN |
Monday, March 5, 2007 3:18PM - 3:30PM |
D31.00005: Experimental and Theoretical studies on Synthesis of Massively Aligned Single-Walled Carbon Nanotubes and Transistor Applications. Koungmin Ryu, Chongwu Zhou Synthesis of highly aligned single-walled carbon nanotubes with controlled diameters is an important step towards manufacturable ultra dense carbon nanotube integrated circuits. We have successfully demonstrated the synthesis of highly aligned carbon nanotube arrays on a-plane sapphire and miscut quartz substrates. Our calculation of the Lennard-Jones potential clearly reveals that a nanotube would lie normal to the c-axis of a-plane sapphire for minimized potential energy, consistent with our experimental observation. In addition, we have developed a patterned growth method to control both the orientation and position of the aligned nanotubes. This was achieved by using photolithography to deposit catalyst at desired locations on sapphire or quartz, followed by CVD growth of the aligned nanotubes. Furthermore, based on aligned nanotubes array, we have fabricated transistors combined with Pd source/drain contact and HfO2 high-k dielectric material. The transistors show on/off ratios up to 1000000 and subthreshold swings down to around 150 mV/decade. Our aligned Nanotube growth work paves the way for a better understanding of the aligned synthesis and could eventually lead to the growth of aligned nanotubes with controlled diameters and even chiralities. Moreover, transistors approach based on massively aligned Nanotube arrays may work as a platform for explorations of nanotube integrated circuits. [Preview Abstract] |
Monday, March 5, 2007 3:30PM - 3:42PM |
D31.00006: Extreme Thermal Stability of Carbon Nanotubes Gavi Begtrup, Keith G. Ray, Brian M. Kessler, Thomas D. Yuzvinsky, Henry Garcia, Alex Zettl The versatility of carbon-carbon bonding creates a wealth of extraordinary physical properties. Of the two common allotropes of carbon, diamond (sp-3 bonded) exhibits record thermal conductivity but is meta-stable and transitions to graphite at elevated temperatures. Graphite (sp-2) is electrically conducting but sublimes at temperatures as low as 2400K. Carbon nanotubes (also sp-2) capitalize on the extraordinary strength of the sp-2 hybridized carbon-carbon bond and exhibit high electrical and thermal conductivities as well as tremendous mechanical strength. Here we report a new technique to measure the thermal properties of nanosystems. We apply this technique to determine the extreme high temperature stability and thermal conductivity of multiwalled carbon nanotubes. [Preview Abstract] |
Monday, March 5, 2007 3:42PM - 3:54PM |
D31.00007: High Current All-Semiconductor Carbon Nanotube Electronics Guangyu Zhang, Pengfei Qi, Xinran Wang, Yuerui Lu, Xiaolin Li, Ryan Tu, Sarunya Bangsaruntip, David Mann, Li Zhang, Hongjie Dai Existence of both metallic and semiconducting carbon nanotubes in as-grown materials has hindered the development of nanotube electronics. A gas-phase plasma hydrocarbonation reaction is shown here to selectively etch and gasify metallic nanotubes, retain semiconducting nanotubes in near-pristine forms without covalent modification, and narrow down diameter distribution of the semiconductors. 100{\%} of purely semiconducting nanotubes are obtained and connected in parallel for high-current transistors without shorts by metallic species. The `dry' chemical approach is scalable and compatible with existing semiconductor processing technology for future integrated circuits. [Preview Abstract] |
Monday, March 5, 2007 3:54PM - 4:06PM |
D31.00008: Chemoresistance of carbon nanotube circuits incorporating electrochemically-decorated defects Vaikunth Khalap, Alexander Kane, Phillip Collins The chemical functionalization of single-walled carbon nanotubes (SWNTs) is of broad interest, since it allows SWNT properties to be widely tailored. We specifically investigate SWNT devices with single point functionalizations. Standard fabrication techniques are supplemented by an electrochemical point-oxidation process that creates insulating defects into otherwise pristine SWNTs. Selective electrochemistry subsequently deposits metal onto the insulating site(s) and restores the device conductivity. Furthermore, the resulting circuits inherit the chemical sensitivity of the metal deposits. For example, nickel deposits produce an air-sensitive reconnection which readiy oxidizes in air back to an open circuit. Palladium deposits are air stable but highly sensitive to hydrogen gas. The interaction of Pd with point defects appears to entirely reproduce the reported characteristics of SWNT-based hydrogen sensors. [Preview Abstract] |
Monday, March 5, 2007 4:06PM - 4:18PM |
D31.00009: Electron channeling through an individual multiwall carbon nanotube Guangyu Chai, Helge Heinrich, Lee Chow, Thomas Schenkel The hollow structure of the carbon nanotube (CNT) provides a significant chance to use it for the channeling of charged particles and associated channeling radiation. However, the nano size of the CNTs make them difficult to be precisely controlled the position and the orientation. We successfully prepared a monolithic multiwall CNT with a graphitic shield by chemical vapor deposition technique. The graphitic shield provides a handle which allows the manipulation of the supported CNTs. A single CNT collimator is fabricated with focused ion beam technique. The electron channeling through the single CNT collimator is demonstrated for the first time. [Preview Abstract] |
Monday, March 5, 2007 4:18PM - 4:30PM |
D31.00010: Test for superconductivity in individual end-bonded MWNTs Y. Sun, S. Chen, J.Y. Huang, Z.F. Ren, J.I. Oh, M.J. Naughton, M. Vaziri Takesue {\it{et al.}} [1] recently reported 12K superconductivity in templated arrays of $\sim 10^4$ ``end-bonded" multi-walled carbon nanotubes (MWNTs). They attributed the occurrence of superconductivity to intershell (interlayer) effects within each MWNT. We have tested this by preparing and measuring {\it{individual}} end-bonded MWNTs, which were grown by arc-discharge without catalyst. High resolution TEM showed they had typical outer (inner) diameters of 10 - 15 nm (1-2 nm), with no visible defects, values verified by AFM and electrical measurements. We also verified by TEM that, as grown, the nanotube ends were closed. We then used a novel nanolithographic approach to facilitate end-bonding ({\it{i.e.}} contacting all layers), which was subsequently verified in $I-V$ tests. Four-probe resistivity was measured for several such individual end-bonded MWNTs, to 1.4 K, including the use of current densities smaller than those used in Ref. 1. No evidence for superconductivity was found. \newline \newline [1] I. Takesue \textit{et al.}, Phys. Rev. Lett. $\bf{96}$, 057001 (2006) [Preview Abstract] |
Monday, March 5, 2007 4:30PM - 4:42PM |
D31.00011: Electron-phonon scattering in suspended carbon nanotubes Vikram Deshpande, Adam Bushmaker, Steve Cronin, Marc Bockrath We perform variable temperature transport measurements of individual suspended single-walled carbon nanotubes varying in length from 0.5um to 3um. To interpret our data, we use a model for electronic scattering that incorporates twiston phonons as well as radial breathing mode (RBM) phonons. We estimate the electron-phonon coupling for these phonons and find that it is in qualitative agreement with theory. At low temperatures, the RBM phonons can also be observed at finite bias voltage corresponding to characteristic RBM phonon energies. At higher bias, the mean free path is strongly reduced to $\sim $30 nm, suggesting the production of a non-equilibrium population of RBM phonons analogous to the non-equilibrium optical and zone-boundary phonon population observed previously to limit transport in substrate-supported and suspended nanotube devices [1-3]. Finally, we are also conducting simultaneous Raman spectroscopy and electrical measurements on our devices to study the signatures of electron-phonon scattering in Raman data. We will report our latest findings in this regard. 1. Z Yao et al, Phys Rev Lett 84, 2941 (2000) 2. E Pop et al, Phys Rev Lett 95, 155505 (2005) 3. M Lazzeri et al, Phys Rev Lett, 95, 236802 (2005) [Preview Abstract] |
Monday, March 5, 2007 4:42PM - 4:54PM |
D31.00012: Ge/Si nanowire mesoscopic Josephson junctions Jie Xiang, Andy Vidan, Michael Tinkham, Robert M. Westervelt, Charles M. Lieber Superconductor-normal conductor-superconductor (S-N-S) Josephson junctions have displayed rich macroscopic quantum phenomena. A novel mesoscopic regime emerges when the width of the normal conductor shrinks to become comparable to carrier Fermi wavelength and its normal conductance becomes quantized in multiples of 2e2/h due to quantum confinement. We have previously demonstrated transport through individual 1D subbands in the hole gas formed in Ge/Si core/shell nanowire (NW) heterostructures. Here we present a study of the interplay between quasi-1D transport and proximity-induced superconductivity using Ge/Si NWs contacted by superconducting leads. Transport measurements on S-NW-S devices reveal high order resonant multiple Andreev reflections, indicating that the NW channel is smooth and that transport is highly coherent. By using a top gate to modulate carrier density in the NW, the critical supercurrent Ic can be tuned from zero to $>$ 100 nA. Significantly, we found that Ic exhibits step-wise increases as a function of gate voltage, corresponding to transport through discrete 1D subbands due to radial carrier confinement. The implications of these results and possible applications of S-NW-S devices will be discussed. [Preview Abstract] |
Monday, March 5, 2007 4:54PM - 5:06PM |
D31.00013: One-dimensional electron behavior in semiconducting carbon nanotubes studied using random telegraph signal David Tobias, A. Tselev, P. Barbara, C.J. Lobb, M.S. Fuhrer We have analyzed the random telegraph signal (RTS) from a semiconducting carbon nanotube in a field effect transistor geometry. We interpret the RTS as due to a single electronic charge tunneling between the nanotube and a nearby defect. We study the tunneling rate of electrons between the nanotube and defect as a function of defect energy, controlled by gate bias, and temperature. An analysis of the tunneling rates allows us to determine an effective temperature for the electron system inside the nanotube as a function of drain bias. The change in the tunneling rates versus the energy of the defect is inconsistent with Fermi liquid theory, providing evidence for the non-Fermi liquid ground state of the one-dimensional semiconducting carbon nanotube. [Preview Abstract] |
Monday, March 5, 2007 5:06PM - 5:18PM |
D31.00014: Torsional Electromechanics of Carbon Nanotubes Ernesto Joselevich, Tzahi Cohen-Karni, Lior Segev, Onit Srur-Lavi, Sidney R. Cohen Carbon nanotubes are known to be distinctly metallic or semiconducting depending on their diameter and chirality. Here we show that continuously varying the chirality by mechanical torsion can induce conductance oscillations, which can be attributed to metal-semiconductor periodic transitions. The phenomenon is observed in multi-walled carbon nanotubes, where both the torque and the current are shown to be carried predominantly by the outermost wall. The oscillation period with torsion is consistent with the theoretical shifting of the corners of the first Brillouin zone of graphene across different subbands allowed in the nanotube. Beyond a critical torsion, the conductance irreversibly drops due to torsional failure, allowing us to determine the torsional strength of carbon nanotubes. Our experiments indicate that carbon nanotubes could be used as self-sensing torsional springs for nanoelectromechanical systems (NEMS). [1] E. Joselevich, Twisting nanotubes: From torsion to chirality, \textit{ChemPhysChem} \textbf{2006}, $7$, 1405. [2] T. Cohen-Karni, L. Segev, O. Srur-Lavi, S. R. Cohen, E. Joselevich, Torsional electromechanical quantum oscillations in carbon nanotubes, \textit{Nature Nanotechnology}, \textbf{2006}, $1$, 36. [Preview Abstract] |
Monday, March 5, 2007 5:18PM - 5:30PM |
D31.00015: Effects of Torsional Strain in Single Wall Carbon Nanotubes Hyungbin Son, Xiaojie Duan, Yingying Zhang, Georgii Samsonidze, Mildred Dresselhaus, Jing Kong, Jin Zhang Since it was predicted that the electronic properties of single wall carbon nanotubes (SWNTs) can be tuned drastically by strain, strain in SWNTs was intensively studied. Particularly, the effects of uniaxial strain on electronic and vibrational properties of SWNTs have been reported in several experimental works. However, little experimental work has been reported on other types of strain such as torsional strain. Our previous work has reported that we can induce torsional strain in SWNTs using AFM manipulation and that torsional strain has distinctive signature in various vibrational modes. In this work, we further investigate the effect of torsional strain on the vibrational modes of SWNTs in detail: frequency shift on different symmetry modes, mode splitting due to symmetry breaking, and changes in electron-phonon matrix elements. [Preview Abstract] |
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